Gasoline-engine management

Technical Instruction

M-MotronicEngine Management

Published by:© Robert Bosch GmbH, 2000Postfach 3002 20,D-70442 Stuttgart.Automotive Equipment Business Sector,Department for Automotive Services,Technical Publications (KH/PDI2).

Editor-in-Chief:Dipl.-Ing. (FH) Horst Bauer.

Editorial staff:Dipl.-Ing. (FH) Anton Beer,Ing. (grad.) Arne Cypra,Dipl.-Ing. Karl-Heinz Dietsche,Dipl.-Ing. (BA) Jürgen Crepin,Dipl.-Holzw. Folkhart Dinkler.

Authors:Dipl.-Ing. (FH) Ulrich Steinbrenner, Dipl.-Ing. (FH) Hans Barho, Dr.-Ing. Klaus Böttcher,Dipl.-Ing. (FH) Volker Gandert,Dipl.-Ing. Walter Gollin,Dipl.-Ing. Werner Häming,Dipl.-Ing. (FH) Klaus Joos,Dipl.-Ing. (FH) Manfred Mezger,Ing. (grad.) Bernd Peter,Dipl.-Ing. Ernst Wild.

Presentation:Dipl.-Ing. (FH) Ulrich Adler,Berthold Gauder, Leinfelden-Echterdingen.

Translation:Peter Girling.

Technical graphics:Bauer & Partner, Stuttgart.

Except where otherwise indicated, the above areemployees of the Robert Bosch GmbH, Stuttgart.

Reproduction, copying, or translation of this publi-cation, wholly or in part, only with our previous writ-ten permission and with source credit. Illustrations,descriptions, schematic drawings, and otherparticulars only serve to explain and illustrate thetext. They are not to be used as the basis for de-sign, installation or scope of delivery. We assumeno liability for agreement of the contents with locallaws and regulations. Robert Bosch is exempt fromliability, and reserves the right to make changes atany time.

Printed in Germany.Imprimé en Allemagne.

4th Edition, February 2000.English translation of the German edition dated: August 1999.

Combustion in the gasoline engineThe spark-ignition or Otto-cycle engine 2Gasoline-engine managementTechnical requirements 4Cylinder charge 5Mixture formation 7IgnitionFunction and requirements 10Inductive ignition systems 13Gasoline-injection systemsOverview 16M-Motronic engine managementM-Motronic: System overview 18Fuel system 20Operating-data acquisition 28Operating-data processing 38Operating conditions 42Integrated diagnosis 58Electronic control unit (ECU) 62Interfaces to other systems 64

M-Motronic Engine Management

Modern electronics are opening upnew perspectives in automotivedesign. The spark-ignition engine isbeing subjected to numerous, some-times mutually-antagonistic demands.It is now possible to satisfy thesedemands – including high specific out-put, modest fuel consumption and lowexhaust emissions – by using systemsproviding an optimal combination ofoperating characteristics.Separate mixture-formation and igni-tion systems deal with parts of theproblem: Jetronic controls fuel supplywhile the electronic ignition systemprovides optimal ignition control.Motronic combines the two systems. A computer controls the injection andignition systems with reference toshared optimization criteria.Digital data processing and micro-processors make it possible to trans-late extensive operating informationinto program-map-controlled injectionand ignition data.Installation of a Lambda oxygen sen-sor and integration of a Lambda con-trol unit in the CPU allow Motronic to meet tomorrow's emissions regu-lations today.

The spark-ignition or Otto-cycle engine

Operating conceptThe spark-ignition or Otto-cycle1)powerplant is an internal-combustion (IC)engine that relies on an externally-generated ignition spark to transform thechemical energy contained in fuel intokinetic energy. Today’s standard spark-ignition enginesemploy manifold injection for mixtureformation outside the combustionchamber. The mixture formation systemproduces an air/fuel mixture (based ongasoline or a gaseous fuel), which is then drawn into the engine by the suctiongenerated as the pistons descend. Thefuture will see increasing application ofsystems that inject the fuel directly into thecombustion chamber as an alternateconcept. As the piston rises, it compressesthe mixture in preparation for the timedignition process, in which externally-generated energy initiates combustion viathe spark plug. The heat released in the

combustion process pressurizes thecylinder, propelling the piston back down,exerting force against the crankshaft andperforming work. After each combustionstroke the spent gases are expelled fromthe cylinder in preparation for ingestion ofa fresh charge of air/fuel mixture. Theprimary design concept used to governthis gas transfer in powerplants forautomotive applications is the four-strokeprinciple, with two crankshaft revolutionsbeing required for each complete cycle.

The four-stroke principleThe four-stroke engine employs flow-control valves to govern gas transfer(charge control). These valves open andclose the intake and exhaust tractsleading to and from the cylinder:

1st stroke: Induction,2nd stroke: Compression and ignition,3rd stroke: Combustion and work,4th stroke: Exhaust.

Induction strokeIntake valve: open,Exhaust valve: closed,Piston travel: downward,Combustion: none.

The piston’s downward motion increasesthe cylinder’s effective volume to drawfresh air/fuel mixture through the passageexposed by the open intake valve.

Compression strokeIntake valve: closed,Exhaust valve: closed,Piston travel: upward,Combustion: initial ignition phase.

Combustion in the gasoline

engine

2

Combustion in the gasoline engine

Reciprocating piston-engine design concept

OT = TDC (Top Dead Center); UT = BDC (BottomDead Center), Vh Swept volume, VC Compressedvolume, s Piston stroke.

Fig. 1

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OT

UT

OT

UT

Vh

s

VC

1) After Nikolaus August Otto (1832–1891), whounveiled the first four-stroke gas-compression engineat the Paris World Exhibition in 1876.

As the piston travels upward it reducesthe cylinder’s effective volume tocompress the air/fuel mixture. Just beforethe piston reaches top dead center (TDC)the spark plug ignites the concentratedair/fuel mixture to initiate combustion.Stroke volume Vh

and compression volume VC

provide the basis for calculating thecompression ratioε = (Vh+VC)/VC.Compression ratios ε range from 7...13,depending upon specific engine design.Raising an IC engine’s compression ratioincreases its thermal efficiency, allowingmore efficient use of the fuel. As anexample, increasing the compression ratiofrom 6:1 to 8:1 enhances thermalefficiency by a factor of 12%. The latitudefor increasing compression ratio isrestricted by knock. This term refers touncontrolled mixture inflammation charac-terized by radical pressure peaks.Combustion knock leads to enginedamage. Suitable fuels and favorablecombustion-chamber configurations canbe applied to shift the knock threshold intohigher compression ranges.

Power strokeIntake valve: closed,Exhaust valve: closed,Piston travel: upward,Combustion: combustion/post-combus-tion phase.

The ignition spark at the spark plugignites the compressed air/fuel mixture,thus initiating combustion and theattendant temperature rise.This raises pressure levels within thecylinder to propel the piston downward.The piston, in turn, exerts force againstthe crankshaft to perform work; thisprocess is the source of the engine’spower.Power rises as a function of engine speedand torque (P = M⋅ω).A transmission incorporating variousconversion ratios is required to adapt thecombustion engine’s power and torquecurves to the demands of automotiveoperation under real-world conditions.

Exhaust strokeIntake valve: closed,Exhaust valve: open,Piston travel: upward,Combustion: none.

As the piston travels upward it forces thespent gases (exhaust) out through thepassage exposed by the open exhaustvalve. The entire cycle then recommenceswith a new intake stroke. The intake andexhaust valves are open simultaneouslyduring part of the cycle. This overlapexploits gas-flow and resonance patternsto promote cylinder charging andscavenging.

Otto cycle

3

Operating cycle of the 4-stroke spark-ignition engine

Fig. 2

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Stroke 1: Induction Stroke 2: Compression Stroke 3: Combustion Stroke 4: Exhaust

Technical requirements

Spark-ignition (SI)engine torque

The power P furnished by the spark-ignition engine is determined by theavailable net flywheel torque and theengine speed.The net flywheel torque consists of theforce generated in the combustionprocess minus frictional losses (internalfriction within the engine), the gas-exchange losses and the torque requiredto drive the engine ancillaries (Figure 1). The combustion force is generatedduring the power stroke and is defined bythe following factors:– The mass of the air available for

combustion once the intake valveshave closed,

– The mass of the simultaneouslyavailable fuel, and

– The point at which the ignition sparkinitiates combustion of the air/fuelmixture.

Primary engine-management functions

The engine-management system’s firstand foremost task is to regulate theengine’s torque generation by controllingall of those functions and factors in thevarious engine-management subsystemsthat determine how much torque isgenerated.

Cylinder-charge controlIn Bosch engine-management systemsfeaturing electronic throttle control (ETC),the “cylinder-charge control” subsystemdetermines the required induction-airmass and adjusts the throttle-valveopening accordingly. The driver exercisesdirect control over throttle-valve openingon conventional injection systems via thephysical link with the accelerator pedal.

Mixture formationThe “mixture formation” subsystem cal-culates the instantaneous mass fuelrequirement as the basis for determiningthe correct injection duration and optimalinjection timing.

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Gasoline-engine management

Driveline torque factors

1 Ancillary equipment(alternator,a/c compressor, etc.),

2 Engine,3 Clutch,4 Transmission.

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Fig. 1

Air mass (fresh induction charge)

Fuel mass

Ignition angle (firing point)Engine

Gas-transfer and frictionAncillaries

Clutch/converter losses and conversion ratiosTransmission losses and conversion ratios

Combustion output torque

Engineoutput torque

Flywheel torque

Drive force

– –– –– –Clutch Trans-

mission

1 1 2 3 4

Cylindercharge

5

IgnitionFinally, the “ignition” subsystem de-termines the crankshaft angle thatcorresponds to precisely the ideal instantfor the spark to ignite the mixture.

The purpose of this closed-loop controlsystem is to provide the torquedemanded by the driver while at thesame time satisfying strict criteria in theareas of– Exhaust emissions,– Fuel consumption,– Power,– Comfort and convenience, and– Safety.

Cylinder chargeElementsThe gas mixture found in the cylinderonce the intake valve closes is referred toas the cylinder charge, and consists ofthe inducted fresh air-fuel mixture alongwith residual gases.

Fresh gasThe fresh mixture drawn into the cylinderis a combination of fresh air and the fuelentrained with it. While most of the freshair enters through the throttle valve,supplementary fresh gas can also bedrawn in through the evaporative-

emissions control system (Figure 2). Theair entering through the throttle-valve andremaining in the cylinder after intake-valve closure is the decisive factordefining the amount of work transferredthrough the piston during combustion,and thus the prime determinant for theamount of torque generated by theengine. In consequence, modifications toenhance maximum engine power andtorque almost always entail increasingthe maximum possible cylinder charge.The theoretical maximum charge isdefined by the volumetric capacity.

Residual gasesThe portion of the charge consisting ofresidual gases is composed of– The exhaust-gas mass that is not

discharged while the exhaust valve isopen and thus remains in the cylinder,and

– The mass of recirculated exhaust gas(on systems with exhaust-gas recircu-lation, Figure 2).

The proportion of residual gas is de-termined by the gas-exchange process.Although the residual gas does notparticipate directly in combustion, it doesinfluence ignition patterns and the actualcombustion sequence. The effects of thisresidual-gas component may be thoroughlydesirable under part-throttle operation.Larger throttle-valve openings to com-pensate for reductions in fresh-gas filling

Cylinder charge in the spark-ignition engine

1 Air and fuel vapor,2 Purge valve

with variable aperture,3 Link to evaporative-emissions

control system,4 Exhaust gas,5 EGR valve with

variable aperture,6 Mass airflow (barometric pressure pU),7 Mass airflow

(intake-manifold pressure ps),8 Fresh air charge

(combustion-chamber pressure pB),9 Residual gas charge

(combustion-chamber pressure pB),10 Exhaust gas (back-pressure pA),11 Intake valve,12 Exhaust valve,α Throttle-valve angle.

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Fig. 2

1

6 7 108

2 3

54

11 12

9

α

are needed to meet higher torquedemand. These higher angles reduce theengine’s pumping losses, leading tolower fuel consumption. Precisely reg-ulated injection of residual gases canalso modify the combustion process toreduce emissions of nitrous oxides (NOx)and unburned hydrocarbons (HC).

Control elements

Throttle valveThe power produced by the spark-ignition engine is directly proportional tothe mass airflow entering it. Control ofengine output and the correspondingtorque at each engine speed is regulatedby governing the amount of air beinginducted via the throttle valve. Leavingthe throttle valve partially closed restrictsthe amount of air being drawn into theengine and reduces torque generation.The extent of this throttling effectdepends on the throttle valve’s positionand the size of the resulting aperture.The engine produces maximum powerwhen the throttle valve is fully open(WOT, or wide open throttle).Figure 3 illustrates the conceptualcorrelation between fresh-air chargedensity and engine speed as a functionof throttle-valve aperture.

Gas exchangeThe intake and exhaust valves open andclose at specific points to control thetransfer of fresh and residual gases. Theramps on the camshaft lobes determineboth the points and the rates at which thevalves open and close (valve timing) todefine the gas-exchange process, andwith it the amount of fresh gas availablefor combustion.Valve overlap defines the phase in whichthe intake and exhaust valves are opensimultaneously, and is the prime factor indetermining the amount of residual gasremaining in the cylinder. This process isknown as "internal" exhaust-gasrecirculation. The mass of residual gascan also be increased using "external"exhaust-gas recirculation, which relies

on a supplementary EGR valve linkingthe intake and exhaust manifolds. Theengine ingests a mixture of fresh air andexhaust gas when this valve is open.

Pressure chargingBecause maximum possible torque isproportional to fresh-air charge density, itis possible to raise power output bycompressing the air before it enters thecylinder.

Dynamic pressure chargingA supercharging (or boost) effect can beobtained by exploiting dynamics withinthe intake manifold. The actual degree ofboost will depend upon the manifold’sconfiguration as well as the engine’sinstantaneous operating point(essentially a function of the engine’sspeed, but also affected by load factor).The option of varying intake-manifoldgeometry while the vehicle is actuallybeing driven, makes it possible to employdynamic precharging to increase themaximum available charge mass througha wide operational range.

Mechanical superchargingFurther increases in air mass areavailable through the agency of

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Throttle-valve map for spark-ignition engine

Throttle valve at intermediate apertureU

MM

0543

-1E

Fig. 3

Fres

h ga

s ch

arge

RPMmin. max.

Throttle valve completely open

Throttle valve completely closed

Idle

Mixtureformation

7

mechanically driven compressors pow-ered by the engine’s crankshaft, with thetwo elements usually rotating at an in-variable relative ratio. Clutches are oftenused to control compressor activation.

Exhaust-gas turbochargersHere the energy employed to power thecompressor is extracted from the exhaustgas. This process uses the energy thatnaturally-aspirated engines cannotexploit directly owing to the inherentrestrictions imposed by the gas ex-pansion characteristics resulting from thecrankshaft concept. One disadvantage isthe higher back-pressure in the exhaustgas exiting the engine. This back-pressure stems from the force needed tomaintain compressor output.The exhaust turbine converts theexhaust-gas energy into mechanicalenergy, making it possible to employ animpeller to precompress the incomingfresh air. The turbocharger is thus acombination of the turbine in the exhaust-fas flow and the impeller that compressesthe intake air. Figure 4 illustrates the differences in thetorque curves of a naturally-aspiratedengine and a turbocharged engine.

Mixture formation

ParametersAir-fuel mixtureOperation of the spark-ignition engine iscontingent upon availability of a mixturewith a specific air/fuel (A/F) ratio. Thetheoretical ideal for complete combustionis a mass ratio of 14.7:1, referred to asthe stoichiometric ratio. In concrete termsthis translates into a mass relationship of14.7 kg of air to burn 1 kg of fuel, whilethe corresponding volumetric ratio isroughly 9,500 litres of air for completecombustion of 1 litre of fuel.

The air-fuel mixture is a major factor indetermining the spark-ignition engine’srate of specific fuel consumption.Genuine complete combustion andabsolutely minimal fuel consumptionwould be possible only with excess air,but here limits are imposed by suchconsiderations as mixture flammabilityand the time available for combustion.

The air-fuel mixture is also vital indetermining the efficiency of exhaust-gastreatment system. The current state-of-the-art features a 3-way catalyticconverter, a device which relies on astoichiometric A/F ratio to operate atmaximum efficiency and reduce un-desirable exhaust-gas components bymore than 98 %.

Current engines therefore operate with astoichiometric A/F ratio as soon as theengine’s operating status permits

Certain engine operating conditionsmake mixture adjustments to non-stoichiometric ratios essential. With acold engine for instance, where specificadjustments to the A/F ratio are required.As this implies, the mixture-formationsystem must be capable of responding toa range of variable requirements.

Torque curves for turbocharged and atmospheric-induction engines with equal power outputs

1 Engine with turbocharger,2 Atmospheric-induction engine.

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Fig. 4

1

2

14

12

34

11

Eng

ine

torq

ue M

d

Engine rpm nn

Excess-air factorThe designation l (lambda) has beenselected to identify the excess-air factor(or air ratio) used to quantify the spreadbetween the actual current mass A/F ratioand the theoretical optimum (14.7:1):λ = Ratio of induction air mass to airrequirement for stoichiometric com-bustion.λ = 1: The inducted air mass correspondsto the theoretical requirement.λ < 1: Indicates an air deficiency,producing a corresponding rich mixture.Maximum power is derived from λ =0.85...0.95.λ > 1: This range is characterized byexcess air and lean mixture, leading tolower fuel consumption and reducedpower. The potential maximum value for λ– called the “lean-burn limit (LML)” – isessentially defined by the design of theengine and of its mixture for-mation/induction system. Beyond thelean-burn limit the mixture ceases to beignitable and combustion miss sets in,accompanied by substantial degener-ation of operating smoothness.In engines featuring systems to inject fueldirectly into the chamber, these operatewith substantially higher excess-airfactors (extending to λ = 4) since com-bustion proceeds according to differentlaws.Spark-ignition engines with manifoldinjection produce maximum power at air

deficiencies of 5...15% (λ = 0.95...0.85),but maximum fuel economy comes in at10...20% excess air (λ = 1.1...1.2).Figures 1 and 2 illustrate the effect of theexcess-air factor on power, specific fuelconsumption and generation of toxicemissions. As can be seen, there is nosingle excess-air factor which cansimultaneously generate the mostfavorable levels for all three factors. Airfactors of λ = 0.9...1.1 produce“conditionally optimal” fuel economy with“conditionally optimal” power generationin actual practice.Once the engine warms to its normaloperating temperature, precise andconsistent maintenance of λ = 1 is vitalfor the 3-way catalytic treatment ofexhaust gases. Satisfying this re-quirement entails exact monitoring ofinduction-air mass and precise meteringof fuel mass.Optimal combustion from current en-gines equipped with manifold injectionrelies on formation of a homogenousmixture as well as precise metering of theinjected fuel quantity. This makeseffective atomization essential. Failure tosatisfy this requirement will foster theformation of large droplets of condensedfuel on the walls of the intake tract and inthe combustion chamber. These dropletswill fail to combust completely and theultimate result will be higher HCemissions.

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Effects of excess-air factor λ on power P andspecific fuel consumption be.

a Rich mixture (air deficiency),b Lean mixture (excess air).

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Fig. 1

Effect of excess-air factor λ on untreatedexhaust emissions

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Fig. 2

0.8 1.0 1.2

a b

P

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Pow

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Excess-air factor λ0.6 1.0 1.4

Rel

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HC

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OX

Excess-air factor λ0.8 1.2

COHC NOX

Mixtureformation

9

Adapting to specificoperating conditionsCertain operating states cause fuelrequirements to deviate substantially fromthe steady-state requirements of an enginewarmed to its normal temperature, thusnecessitating corrective adaptations in themixture-formation apparatus. The follow-ing descriptions apply to the conditionsfound in engines with manifold injection.

Cold startingDuring cold starts the relative quantity offuel in the inducted mixture decreases: themixture “goes lean.” This lean-mixturephenomenon stems from inadequateblending of air and fuel, low rates of fuelvaporization, and condensation on thewalls of the inlet tract, all of which arepromoted by low temperatures. To com-pensate for these negative factors, and tofacilitate cold starting, supplementary fuelmust be injected into the engine.

Post-start phaseFollowing low-temperature starts,supplementary fuel is required for a briefperiod, until the combustion chamberheats up and improves the internalmixture formation. This richer mixturealso increases torque to furnish asmoother transition to the desired idlespeed.

Warm-up phaseThe warm-up phase follows on the heelsof the starting and immediate post-startphases. At this point the engine stillrequires an enriched mixture to offset thefuel condensation on the intake-manifoldwalls. Lower temperatures are synony-mous with less efficient fuel proces-sing (owing to factors such as poor mix-ing of air and fuel and reduced fuel va-porization). This promotes fuel precip-itation within the intake manifold, with the formation of condensate fuel that willonly vaporize later, once temperatureshave increased. These factors make itnecessary to provide progressive mixtureenrichment in response to decreasingtemperatures.

Idle and part-loadIdle is defined as the operating status inwhich the torque generated by the engineis just sufficient to compensate for frictionlosses. The engine does not providepower to the flywheel at idle. Part-load (orpart-throttle) operation refers to therange of running conditions between idleand generation of maximum possibletorque. Today’s standard concepts relyexclusively on stoichiometric mixtures forthe operation of engines running at idleand part-throttle once they have warmedto their normal operating temperatures.

Full load (WOT)At WOT (wide-open throttle) supple-mentary enrichment may be required. AsFigure 1 indicates, this enrichmentfurnishes maximum torque and/or power.

Acceleration and decelerationThe fuel’s vaporization potential is stronglyaffected by pressure levels inside theintake manifold. Sudden variations inmanifold pressure of the kind encounteredin response to rapid changes in throttle-valve aperture cause fluctuations in thefuel layer on the walls of the intake tract.Spirited acceleration leads to highermanifold pressures. The fuel respondswith lower vaporization rates and the fuellayer within the manifold runners expands.A portion of the injected fuel is thus lost inwall condensation, and the engine goeslean for a brief period, until the fuel layerrestabilizes. In an analogous, but inverted,response pattern, sudden decelerationleads to rich mixtures. A temperature-sensitive correction function (transitioncompensation) adapts the mixture tomaintain optimal operational responseand ensure that the engine receives theconsistent air/fuel mixture needed forefficient catalytic-converter performance.

Trailing throttle (overrun)Fuel metering is interrupted during trailingthrottle. Although this expedient savesfuel on downhill stretches, its primarypurpose is to guard the catalytic converteragainst overheating stemming from poorand incomplete combustion (misfiring).

Ignition

FunctionThe function of the ignition system is toinitiate combustion in the compressedair/fuel mixture by igniting it at preciselythe right instant. In the spark-ignitionengine, this function is assumed by anelectric spark in the form of a short-duration discharge arc between thespark plug’s electrodes.Consistently reliable ignition is vital forefficient catalytic-converter operation.Ignition miss allows uncombusted gasesto enter the catalytic converter, leading toits damage or destruction from over-heating when these gases burn inside it.

Technical requirementsAn electrical arc with an energy content ofapproximately 0.2 mJ is required for eachsustainable ignition of a stoichiometricmixture, while up to 3 mJ may be neededfor richer or leaner mixtures. This energyis only a fraction of the total (ignition)energy contained in the ignition spark. Ifthe available ignition energy isinadequate, the mixture cannot ignitesince ignition fails to take place, and theresult is that the engine starts to misfire.This is why the system must supply levelsof ignition energy that are high enough toalways ensure reliable inflammation of theair/fuel mixture, even under the mostsevere conditions. A small ignitablemixture cloud passing by the arc isenough to initiate the process. Themixture cloud ignites and propagatescombustion through the remainingmixture in the cylinder. Efficient mixtureformation and easy access of the mixturecloud to the spark will improve ignitionresponse, as will extended sparkdurations and larger electrode gaps(longer arcs). The location and length ofthe spark are determined by the sparkplug’s design dimensions. Spark durationis governed by the design and con-figuration of the ignition system along withthe instantaneous ignition conditions.

Ignition timing

Ignition timing and its adjustmentApproximately two milliseconds elapsebetween the instant when the mixtureignites and its complete combustion.Assuming consistent mixture strength,this period will remain invariable. Thismeans that the ignition spark must arcearly enough to support generation ofoptimal combustion pressure under alloperating conditions.Standard practice defines ignition timingrelative to top dead center, or TDC on thecrankshaft. Advance angles are thenquantified in degrees before TDC, withthe corresponding figure being known asthe ignition (timing advance) angle.Moving the ignition point back towardTDC is referred to as “retarding” thetiming and displacing it forward toward anearlier ignition (firing) point is “advancing”it (Figure 1).Ignition timing must be selected so thatthe following criteria are complied with:– Maximum engine power,– Maximum fuel economy,– Prevention of engine knock, and– “Clean” exhaust gas.

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TDCZ

Position of crankshaft and piston at theignition (firing) point with advanced ignition

TDC Top Dead Center, BDC Bottom Dead Center,Z Ignition point.

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Fig. 1

It is impossible to fulfill all the abovedemands simultaneously, and a com-promise must be reachd from case tocase. The most favorable firing point at agiven torque depends upon a variety ofdifferent factors. These are in particular,engine speed, engine load, enginedesign, fuel, and the particular operatingconditions (e.g. starting, idle, WOT,overrun).Engine knock is due to the abruptcombustion of portions of the air-fuelmixture which have not yet been reachedby the advancing flame front triggered bythe ignition spark. In this case, the firingpoint is too far advanced. Combustionknock not only leads to increases incombustion-chamber temperature, whichin turn can cause pre-ignition, but also tomarked increases in pressure. Suchabrupt ignition events generate pressureoscillations which are superimposed onthe normal pressure characteristic (Fig. 2). Today, the high compressions employedin spark-ignition engines involve a fargreater risk of combustion knock thanwas the case with the compression ratioswhich were common in the past. Onedifferentiates between two different formsof “knock”:

– Acceleration knock at low enginespeeds and high load (clearly audibleas pinging), and

– High-speed knock at high enginespeeds and high load.

For the engine, high-speed knock is aparticularly critical factor, since the otherengine noises generated at such speedsmake it inaudible. This is why audibleknock is not a faithful index of preignitiontendency. At the same time, electronicmeans are available for precisedetection. Consistent knock causessevere engine damage (destruction ofcylinder-head gaskets, bearing damage,“holed” piston crowns) as well as spark-plug damage.Preignition tendency depends upon suchfactors as engine design (for instance:combustion chamber layout, homo-genous air-fuel mixture, efficient in-duction flow passages) and fuel quality.

Ignition timing and emissionsThe effects of the excess-air factor λ andignition timing on specific fuel consump-tion and exhaust emissions are dem-onstrated in Figures 3 and 4. Specific fuel consumption responds to leanermixtures with an initial dip before rising

Ignition

11

Combustion-chamber pressure curves for different firing points

1 Ignition Za with ideal advance,2 Ignition Zb advanced too far (knock),3 Ignition Zc too late.

Effect of excess-air factor λ and ignitiontiming αZ on fuel consumption

Fig. 2 Fig. 3

αz20o

30o

40o

50o

g/kWh

580

500

420

340

Spe

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con

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0.8 1.0 1.2 1.4Excess-air factor λ

660

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Before TDC After TDC

Com

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pres

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Ignition angle αZ

21

3

60

ZbZa Zc

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from λ = 1.1...1.2. Increases in the excess-air factor are accompanied by a corre-sponding increase in the optimal ignitionadvance angle, which is defined here asthe timing that will minimize specific fuelconsumption. The relationship betweenspecific fuel consumption and excess-airfactor (assuming optimal ignition timing)can be explained as follows: The airdeficiency encountered in the “fuel-rich”range leads to incomplete combustion,while substantial shifts toward the leanmisfire limit (LML) will start to causedelayed combustion and misfiring, ulti-mately leading to higher levels of specificfuel consumption. The optimal ignitionadvance angle increases at higher ex-cess-air ratios owing to the slower rate offlame-front propagation enountered inlean mixtures; the ignition timing must beadvanced to compensate for thesedelays.

HC emissions, which bottom out at λ = 1.1,display a similar response pattern. Theinitial rise within the lean range can beattributed to the flame being extinguisheddue to the cooling on the walls of thecombustion chamber. Extremely leanmixtures produce delayed combustionand failure to ignite, phenomena whichoccur with increasing frequency as thelean misfire limit is approached. Below λ =1.2, further ignition advance will lead tohigher HC emissions, but it will also shiftthe lean misfire limit to accomodatemixtures with even less fuel. This is why anincrease in ignition advance lowers thelevels of HC emissions in the lean rangebeyond λ = 1.25.Emissions of nitrous oxides (NOx) displaya completely different pattern by rising inresponse to higher oxygen (O2) con-centrations and maximum peak com-bustion temperatures. The result is thecharacteristic bell-shaped curve for NOx

emissions. These rise up to λ ≈ 1.05 inresponse to the accompanying increasesin O2 concentrations and peakcombustion temperatures. Then, beyondλ = 1.05, NOx generation displays asharp drop as the mixture continuesfurther into the lean range, owing to the

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Excess-air factor λ and ignition timing αZon exhaust emissions

g/kWh

16

12

8

4

0

HC

em

issi

ons

(FID

)N

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ons

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600

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em

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20

16

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4

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0.8 1.2 1.4

αz 50°

40°

30°

20°

0.8 1.0 1.2 1.4Excess-air factor λ

0.8 1.0 1.2 1.4Excess-air factor λ

αz50°40°

30°

20°

1.0Excess-air factor λ

αz

50°

40°30°

20°

Fig. 4

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rapid reduction in peak temperatures thataccompanies higher levels of mixturedilution. This response pattern alsoaccounts for the extreme sensitivity withwhich NOx emissions respond tochanges in ignition timing, escalatingsharply as advance is increased.Because a mixture of λ = 1 is needed toimplement emissions-control conceptsrelying on the 3-way catalytic converter,adjusting the ignition advance angle isthe only remaining option for optimizingemissions.

Inductive ignition systems

The spark-ignition engine’s inductive(coil) ignition system generates the high-tension voltage to provide the energythen employed to create an arc at thespark plug. While inductive ignitionsystems rely on coils to store ignitionenergy, an available alternative is storagein a condenser (R so-called high-voltagecapacitor-discharge ignition/CDI). Theinductive ignition circuit’s componentsare the driver (output amplifier) stage, thecoil and the spark plug

Ignition coil

FunctionThe ignition coil stores the requiredignition energy and generates the highvoltages required to produce an arc atthe firing point.

Design and functionIgnition-coil operation is based on aninductive concept. The coil consists oftwo magnetically coupled copper coils(primary and secondary windings). Theenergy stored in the primary winding’smagnetic field is transmitted to thesecondary side. Current and voltage aretransformed in accordance with the turnsratio of the primary and secondarywindings (Fig. 1).

Modern ignition coils feature an iron core,composed of individual metal platesinside a synthetic casing. Within thiscasing the primary winding is woundaround a bobbin mounted directly on thecore. These elements are concentricallyenclosed by the secondary winding,which is designed as a disc or chamberwinding for improved insulation resis-tance. For effective insulation of core andwindings, these elements are all en-closed in epoxy resin inside the casing.Specific design configurations areselected to reflect individual operationalrequirements.

Ignition driver stage

Assignment and functionIgnition driver stages featuring multi-stage power transistors switch the flow ofprimary current through the coil,replacing the contact-breaker pointsemployed in earlier systems.In addition, this ignition driver stage isalso responsible for limiting primarycurrent and primary voltage. The primaryvoltage is limited to prevent excessivelysteep increases of secondary voltage,

Ignition coils (schematic)

Rotating distribution: a Single-spark coil.Static distribution: b Single-spark coil, c Dual-spark coil.

Inductiveignition systems

13

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which could damage components withinthe high-tension circuit. Restrictions onprimary current hold the ignition system’senergy output to the specified level. The ignition system’s driver stage may beinternal (integrated within the ignitionECU) or external (mounted locally).

High-voltage generationThe ignition ECU switches on the ignitiondriver stage for the calculated dwellperiod. It is within this period that theprimary current within the coil climbs toits specified intensity.The energy for the ignition system isstored in the coil’s magnetic field anddefined by the levels of the coil’s primarycurrent and primary inductance. At the firing point the ignition driver stageinterrupts the current flow through theprimary winding to induce flux in themagnetic field and generate secondaryvoltage in the coil’s secondary winding.The ultimate level of secondary voltage(secondary voltage supply) dependsupon a number of factors. These includethe amount of energy stored in theignition system, the capacity of thewindings and the coil’s transformationratio as well as the secondary load factorand the restrictions on primary voltageimposed by the ignition system’s driverstage. The secondary voltage must alwaysexceed the level required to produce anarc at the spark plug (ignition-voltagerequirement), and the spark energy mustalways be high enough to reliably initiatecombustion in the mixture, even in theface of secondary arcing.When primary current is switched on, thisinduces an undesired voltage (switch-onvoltage) of roughly 1...2 kV in thesecondary winding whose polarityopposes that of the high voltage. It isessential that this is prevented fromgenerating an arc (switch-on arc) at thespark-plug.In systems with conventional rotatingvoltage distribution, this switch-on sparkis effectively suppressed by thedistributor’s spark gap. On distributorlessignition systems with non-rotating (static)

voltage distribution featuring dedicatedignition coils, a diode in the high-voltagecircuit performs this function.With distributorless (static) sparkdistribution and dual-spark coils, the higharcing voltage associated with two sparkplugs connected in series effectivelysuppresses the switch-on spark withoutany need for supplementary counter-measures.

Voltage distribution

High-tension voltage must be on hand atthe spark plug at the moment of ignition(firing point). This function is theresponsibility of the high-voltage distri-bution system.

Rotating voltage distributionSystems using a rotating voltage-distribution concept rely on a mechanicalignition distributor to relay the highvoltage from a single ignition coil to theindividual cylinders. This type of voltage-distribution has ceased to be relevant inthe current generation of engine-management systems.

Static voltage distributionDistributorless ignition (otherwise knownas static or electronic ignition) is availablein two different versions:

System equipped with single-sparkignition coilsEach cylinder is equipped with its ownignition coil and driver stage, which theengine-management ECU triggerssequentially in the defined firing order.Because internal voltage loss within adistributor is no longer a consideration,the coils can be extremely compact. Thepreferred installation location is directlyabove the spark plug. Static distributionwith single-spark ignition coils isuniversally suited for use with anynumber of cylinders. While there are noinherent restrictions on adjusting ignitionadvance (timing), these units do require asupplementary synchronization arrange-ment furnished by a camshaft sensor.

Gasoline-engine

management

14

System equipped with dual-sparkignition coilsEach set of two cylinders is supplied by asingle ignition driver stage and one coil,with each end of the latter’s secondarywinding being connected to a differentspark plug. The cylinders are paired sothat the compression stroke on one willcoincide with the exhaust stroke on theother.When the ignition fires an arc isgenerated at both spark plugssimultaneously. Because it is importantto ensure that the spark produced duringthe exhaust stroke will ignite neitherresidual nor fresh incoming gases, thissystem is characterized by restrictions onadjusting ignition advance (timing). Thissystem does not require a syn-chronization sensor at the camshaft.

Connectors and interference suppressors

High-voltage cablesThe high voltage from the ignition coilmust be able to reach the spark plugs.On coils not mounted in direct electricalcontact with the spark plugs this functionis performed by special high-voltagecables featuring outstanding high-voltage strength and synthetic insulation.Fitted with the appropriate terminals,these cables provide the electricalconnections between the high-voltagecomponents.Because every high-voltage lead re-presents a capacitive load for the ignitionsystem and reduces the available supplyof secondary voltage accordingly, cablesshould always be as short as possible.

Interference resistors, interferencesuppressionThe pulse-shaped, high-tension dis-charge that characterizes every arc at thespark plug also represents a source ofradio interference. The current peaksassociated with discharge are limited bysuppression resistors in the high-voltagecircuit. To hold radiation of interference

emanating from this circuit to a minimum,the suppression resistors should beinstalled as close as possible to theactual interference source.Resistors (capacitors) for interferencesuppression are generally installed in thespark-plug cable terminals, while rotatingdistributors also include rotor-mountedresistors. Spark plugs with integralsuppression resistors are also available.It is important to remember that higherlevels of resistance in the secondarycircuit are synonymous with cor-responding energy loss in the ignitioncircuit, and result in a reduction in theenergy available for firing the spark plug.Partial or comprehensive encapsulationof the ignition system can be im-plemented to obtain further reductions ininterference radiation.

Spark plug

The spark plug creates the electrical arcthat ignites the air-fuel mixture within thecombustion chamber. The spark plug is a ceramic-insulated,high-voltage conductor leading into thecombustion chamber. Once arcingvoltage is reached, electrical energyflows between the center and groundelectrodes to convert the remainder ofthe ignition-coil energy into a spark.

The level of the voltage required forignition depends upon a variety of factorsincluding electrode gap, electrodegeometry, combustion-chamber pres-sure, and the instantaneous A/F ratio atthe firing point.Spark-plug electrodes are subject towear in the course of normal engineoperation, and this wear leads toprogressively higher voltage require-ments. The ignition system must becapable of providing enough secondaryvoltage to ensure that adequate ignitionvoltage always remains available,regardless of the operating conditionsencountered in the intervals betweenspark-plug replacements.

Inductiveignition systems

15

Carburetors and gasoline-injection sys-tems are designed for a single purpose:To supply the engine with the optimal air-fuel mixture for any given operatingconditions. Gasoline injection systems,and electronic systems in particular, arebetter at maintaining air-fuel mixtureswithin precisely defined limits, whichtranslates into superior performance inthe areas of fuel economy, comfort andconvenience, and power. Increasinglystringent mandates governing exhaustemissions have led to a total eclipse of thecarburetor in favor of fuel injection.Although current systems rely almostexclusively on mixture formation outsidethe combustion chamber, concepts basedon internal mixture formation – with fuelbeing injected directly into the combustionchamber – were actually the foundationfor the first gasoline-injection systems. Asthese systems are superb instruments forachieving further reductions in fuelconsumption, they are now becoming anincreasingly significant factor.

Overview

Systems withexternal mixture formationThe salient characteristic of this type ofsystem is the fact that it forms the air-fuelmixture outside the combustion chamber,inside the intake manifold.

Multipoint fuel injectionMultipoint fuel injection forms the idealbasis for complying with the mixture-formation criteria described above. In thistype of system each cylinder has its owninjector discharging fuel into the areadirectly in front of the intake valve.

Representative examples are the variousversions of the KE and L-Jetronic systems(Figure 1).

Mechanical injection systemsThe K-Jetronic system operates byinjecting continually, without an exter-nal drive being necessary. Instead ofbeing determined by the injection valve,fuel mass is regulated by the fueldistributor.

Combined mechanical-electronicfuel injectionAlthough the K-Jetronic layout served asthe mechanical basis for the KE-Jetronicsystem, the latter employs expandeddata-monitoring functions for moreprecise adaptation of injected fuelquantity to specific engine operatingconditions.

Electronic injection systemsInjection systems featuring electroniccontrol rely on solenoid-operated injection

Multipoint fuel injection (MPI)

1 Fuel,2 Air,3 Throttle valve,4 Intake manifold,5 Injectors,6 Engine.

Gasoline-injection systems

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Gasoline-injectionsystems

16

valves for intermittent fuel discharge. Theactual injected fuel quantity is regulatedby controlling the injector's opening time(with the pressure-loss gradient throughthe valve being taken into account incalculations as a known quantity).Examples: L-Jetronic, LH-Jetronic, andMotronic as an integrated engine-manage-ment system.

Single-point fuel injectionSingle-point (throttle-body injection (TBI))fuel injection is the concept behind thiselectronically-controlled injection systemin which a centrally located solenoid-operated injection valve mountedupstream from the throttle valve spraysfuel intermittently into the manifold. Mono-Jetronic and Mono-Motronic are theBosch systems in this category (Figure 2).

Systems for internal mixture formationDirect-injection (DI) systems rely onsolenoid-operated injection valves to sprayfuel directly into the combustion chamber;the actual mixture-formation process takesplace within the cylinders, each of whichhas its own injector (Figure 3). Perfectatomization of the fuel emerging from theinjectors is vital for efficient combustion.Under normal operating conditions, DIengines draw in only air instead of the

combination of air and fuel common toconventional injection systems. This is oneof the new system's prime advantages: Itbanishes all potential for fuel condensationwithin the runners of the intake manifold.External mixture formation usuallyprovides a homogenous, stoichiometric air-fuel mixture throughout the entirecombustion chamber. In contrast, shiftingthe mixture-preparation process into thecombustion chamber provides for twodistinctive operating modes:With stratified-charge operation, only themixture directly adjacent to the spark plugneeds to be ignitable. The remainder of theair-fuel charge in the combustion chambercan consist solely of fresh and residualgases, without unburned fuel. This strategyfurnishes an extremely lean overall mixturefor idling and part-throttle operation, withcommensurate reductions in fuelconsumption.Homogenous operation reflects theconditions encountered in external mixtureformation by employing uniformconsistency for the entire air-fuel chargethroughout the combustion chamber.Under these conditions all of the fresh airwithin the chamber participates in thecombustion process. This operationalmode is employed for WOT operation.MED-Motronic is used for closed-loopcontrol of DI gasoline engines.

Overview

17

Throttle-body fuel injection (TBI)

1 Fuel,2 Air,3 Throttle valve,4 Intake manifold,5 Injector,6 Engine.

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Direct fuel injection (DI)

1 Fuel,2 Air,3 Throttle valve

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The M-Motronic systemSystem overview

M-Motronic combines all the electronicsystems for engine control in a singlecontrol unit (ECU) which, in turn, governsthe actuating systems used to control thespark-ignition engine. Engine-mountedmonitoring devices (sensors) gather therequired operating data and relay theinformation to input circuits for:– Ignition (on/off),– Camshaft position,– Vehicle speed,– Gear selection,– Transmission control,– Air conditioner, etc.Monitored analog data include:– Battery voltage,– Engine temperature,– Intake-air temperature,– Air quantity,– Throttle-valve angle,– Lambda oxygen sensor,– Knock sensor, etc.

as well as – Engine speed.

Input circuits located within the ECU con-vert these data for subsequent oper-ations in the microprocessor. The micro-processor, in turn, uses these data to de-termine the engine’s momentary operat-ing conditions; this information serves asthe basis for the ECU’s command sig-nals, which are amplified by power-output stages before being transmitted tothe final-control elements used to controlthe engine. This system combines fuelinjection, highest-quality mixture pre-paration and the correct ignition timing to provide mutual support over the entire

range of operating conditions encoun-tered in the spark-ignition engine.

M-Motronic versionsThe descriptions and illustrations on the following pages refer to a typical M-Motronic configuration (Figure 1).Other M-Motronic systems are availableto meet the special demands arising fromspecific national regulations as well asthe requirements of the individual auto-mobile manufacturers.

Basic functionsControl of the ignition and fuel-injectionprocesses is (independent of version) atthe core of the M-Motronic system.

Auxiliary functionsAdditional open and closed-loop controlfunctions – required in response to legis-lation aimed at reductions in exhaustemissions and fuel consumption – sup-plement the basic M-Motronic functionswhile making it possible to monitor allcomponents exercising an influence onthe composition of the exhaust gases.These include:– Idle-speed control,– Lambda oxygen control,– Control of the evaporative emissions

control system,– Knock control,– Exhaust-gas recirculation (EGR) for

reducing NOX emissions, and– Control of the secondary-air injection

to reduce HC emissions.The system can also be expanded tomeet special demands from automobilemanufacturers by including the following:– Open-loop turbocharger control as well

as control of variable-tract intake mani-folds for increased engine power output,

M-Motronic

18

M-Motronic engine management

– Camshaft control for achieving re-ductions in exhaust emissions and fuelconsumption as well as enhanced out-put, and

– Knock control along with engine andvehicle-speed governing functions, toprotect engine and vehicle.

The acquisition and processing of themeasured information is described in thechapters dealing with acquisition andprocessing of the operating data.

Vehicle managementM-Motronic supports the control units inother vehicle systems. It can, for in-stance, operate together with the auto-matic transmission’s control unit to pro-

vide reductions in torque during shifting,thereby lessening transmission wear. M-Motronic can also work together with the ABS control unit to provide tractioncontrol (TCS) for enhanced vehiclesafety.The schematic system illustration belowshows a maximal-configuration M-Motro-nic system. This type of system can beemployed to satisfy– The stringent emissions limits, and– The requirement for an integral, on-

board diagnosis (OBD) system for Cal-ifornia vehicles from 1993 onward.

The MotronicSystem

19

System diagram of M-Motronic M5 with integrated diagnostics (OBD)

1 Carbon canister, 10 Secondary-air valve, 19 Engine-speed sensor,2 Shutoff valve, 11 Air-mass meter, 20 Engine-temperature sensor,3 Canister-purge valve, 12 Control unit (ECU), 21 Lambda oxygen sensor,4 Fuel-pressure regulator, 13 Throttle-valve sensor, 22 Diagnosis interface,5 Injector, 14 Idle actuator, 23 Diagnosis lamp,6 Pressure actuator, 15 Air-temperature sensor, 24 Pressure differential sensor,7 Ignition coil, 16 EGR valve, 25 Electric fuel pump.8 Phase sensor, 17 Fuel filter,9 Secondary-air pump, 18 Knock sensor,

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Fuel system

Fuel supplyFuel-supply systemThe fuel-supply system must be capableof providing the engine with the requiredquantity of fuel under all operating con-ditions. An electric pump draws the fuel through a filter while extracting it from the tank for delivery to the fuel-distribution rail with its electromag-netic injectors. The injectors spray the fuel into the engine’s intake tract in precisely metered quantities. The ex-cess fuel flows through the pressure

regulator and back to the fuel tank (Figure 1).

The pressure regulator generally em-ploys the pressure within the intakemanifold as its reference. This charac-teristic pressure works in combinationwith the constant flow through the fuel rail(cooling effect) to prevent vapor bubblesfrom forming in the fuel. The resultingpressure differential at the injectorusually remains constant in the 300 kParange.Where necessary, the fuel-supply systemcan also be designed to incorporatepressure attenuators to reduce pulsationin the fuel line.

M-Motronic

20

Fuel supply system

1 Electric fuel pump (in-tank), 2 Fuel filter, 3 Fuel rail, 4 Injector, 5 Fuel-pressure regulator.

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Fuel system

21

Two-stage electric fuel pump (side-channel and internal-gear pump)

1 First stage (side-channel pump), 2 Main stage (internal-gear pump), 3 Motor armature, 4 Commutator, 5 Non-return valve, 6 Electrical connection.

Two-stage electric fuel pump (side-channel and peripheral pump)

1 Suction cover with supply connection, 2 Impeller, 3 First stage (side-channel pump), 4 Main stage (peripheral pump), 5 Pump housing, 6 Motor armature, 7 Non-return valve, 8 End cover with pressure connection.

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Electric fuel pump

FunctionThe electric fuel pump supplies a con-tinuous flow of fuel from the tank. It canbe installed either within the fuel tank it-self (“in-tank”) or at an external locationin the fuel line (“in-line”).The in-tank pumps currently in generaluse (Figures 2 and 3) are integrated with-in the fuel tank’s installation assemblyalong with the level sensor and a swirlplate to remove vapor bubbles from thefuel return line. When an in-line pump is used, hot delivery problems can be solved by using a supplementary in-tank

booster pump to supply fuel from the tankat low pressure. To ensure that the de-livery pressure in the system is main-tained at the required level, the maximumsupply capacity is always greater thanthe system’s theoretical maximum re-quirement. The fuel pump is activated by the engine-management ECU. A safety circuit inter-rupts fuel delivery when the engine is sta-tionary with the ignition on.

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DesignThe electric fuel pump consists of thefollowing elements:– Pump assembly,– Electric motor and end cover.

The electric motor and pump assemblyare located in a common housing, wherethey are immersed in circulating fuel.This arrangement provides effective cooling for the electric motor. Because no oxygen is present, it is impossible foran ignitable mixture to form; there is nodanger of an explosion. The end covercontains the electrical connections, thenon-return valve and the hydraulicconnection for the pressure side. Thenon-return valve maintains system pres-sure for a period of time after the unit is shut down to prevent vapor bubblesfrom forming. Interference-suppressiondevices can also be included in the end-cover assembly.

Design variationsVarious design principles are employedto satisfy individual system demands(Figure 4).

Positive-displacement pumpsRoller-cell (RZP) and internal-gearpumps (IZP) are both classified as posi-tive-displacement designs. Both types ofpump operate by using variable-sized,circulating chambers to expose a supplyorifice and draw in fuel as their volumeexpands. Once the maximum volume isreached, the supply orifice closes andthe discharge orifice opens. The fuel isnow forced out as the effective volume inthe chamber decreases. The chamberson the roller-cell pump are formed by rol-lers circulating in a rotor plate. A combi-nation of centrifugal force and fuel pres-sure forces them outward against the eccentric roller path. The eccentricity between rotor plate and roller path provides the constant increase anddecrease in chamber volume.

M-Motronic

22

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Principles of operation

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The internal-gear pump consists of an in-ternal drive gear that moves against thesurface of an eccentrically-mounted ringgear; the ring gear is equipped with onetooth more than the drive gear. As themutually-sealed tooth flanks turn, vari-able chambers are formed betweenthem. Roller-cell pumps can be used to obtain fuel pressures in excess of 650 kPa. Internal-gear pumps can supplyup to 400 kPa, a figure adequate for virtually all Motronic applications.

Hydrokinetic flow pumpsThe peripheral and side-channel pumpsare both classified as hydrokinetic flowpumps. In these pumps an impeller ac-celerates the fuel particles before dis-charging them into the tract where theygenerate pressure via pulse exchange.The peripheral pump differs from its side-channel counterpart in its larger numberof impeller blades and the shape of theimpellers, as well as in the positions ofthe side channels, which – unlike those ofthe side-channel unit – are located on thecircumference or periphery. Althoughperipheral pumps are only capable ofgenerating maximum fuel pressures inthe 400 kPa range, they do supply a con-tinuous, virtually pulseless flow of fuel.This makes them particularly attractivefor use in those vehicular applicationswhere limiting noise is a major priority.Side-channel pumps can only produce

pressures of up to 30 kPa. One impor-tant use for this type of unit is as abooster pump in systems with in-linemain pumps; another major application is as the primary stage in a two-stage in-tank pump of the kind installed invehicles susceptible to hot startingproblems and/or with single-point fuelinjection.

Fuel filterContaminants in the fuel can impair theoperation of both pressure regulator andinjectors. A filter is therefore installeddownstream from the electric fuel pump.This fuel filter contains a paper elementfeaturing a mean pore diameter of 10 µm.A backplate retains it in its housing. Thereplacement intervals are determined bythe filter’s volume and contaminationlevels in the fuel (Figure 5).

Fuel railThe fuel flows through the fuel rail whereit is evenly distributed to all injectors. Theinjectors are mounted on the fuel rail,which also usually includes a fuel-pres-sure regulator. A pressure attenuatormay also be present. The dimensions ofthe fuel rail are selected to inhibit the lo-cal fluctuations in fuel pressure that couldotherwise be triggered as the injectorsrun through their operating cycles. Thisprevents the injection quantities from re-acting to changes in load and enginespeed. Depending upon the particularvehicle type and its special requirements,the fuel rail can be made of steel, alumi-num or plastic. It may also include anintegral test valve, which can be used to bleed pressure for servicing as well as for test purposes.

Fuel-pressure regulatorInjection quantity should be determinedexclusively by injection duration. Thusthe difference between the fuel pressurein the distribution rail and the pressure inthe intake tract must remain constant. Ameans is thus required for adjusting thefuel pressure to reflect variations in theload-sensitive manifold pressure. Thefuel-presure regulator regulates the

Fuel system

23

Fuel filter

1 Paper element,2 Strainer,3 Support plate.

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amount of fuel returning to the tank tomaintain a constant pressure dropacross the injectors. The pressure regu-lator is generally positioned at the far endof the fuel rail to avoid impairing the flowwithin the rail. However, it can also bemounted in the fuel-return line.The fuel-pressure regulator is designedas a diaphragm-controlled overflow pres-sure regulator (Figure 6). A rubber-fiberdiaphragm divides the pressure regulatorinto two sections: fuel chamber and pres-sure chamber. The spring pressesagainst a valve holder integrated withinthe diaphragm. This force causes a flex-ibly mounted valve plate to push againsta valve seat. When the pressure exertedagainst the diaphragm by the fuel ex-ceeds that of the spring, the valve opensand allows fuel to flow directly back to thetank until the diaphragm assembly re-turns to a state of equilibrium, with equalpressure exerted on both of its sides. Apneumatic line is provided between thespring chamber and the intake manifolddownstream from the throttle valve,allowing the chamber to respond tochanges in manifold vacuum. Thus thepressures at the diaphragm correspondto those at the injectors. As a result, thepressure drop at the injectors remainsconstant, as it is determined solely by thespring force and surface area of the diaphragm.

Fuel-pressure attenuatorThe injectors’ operating cycles and theperiodic discharge of fuel that charac-terize the positive-displacement fuelpump both induce fluctuations in fuelpressure. Under unfavorable circum-stances, the mountings for the electricfuel pump, fuel lines and fuel rail cantransmit these vibrations to the vehicle’sbody. Noise from this source can be pre-vented using specially designed mount-ing elements and fuel-pressure attenua-tors. The layout of the fuel-pressureattenuator (Figure 7) is similar to that ofthe pressure regulator. In both cases aspring-loaded diaphragm separates thefuel from the air space. The spring forceis calculated to lift the diaphragm from its

seat as soon as the fuel reaches operat-ing pressure. This provides a variablefuel chamber which can accept fuel toease pressure peaks and then release itagain when pressure falls. The springchamber can be fitted with a manifold-vacuum line to stay within the optimumoperating range in the face of fluctuationsin the fuel’s absolute pressure. The pres-sure attenuator also shares the pressureregulator’s installation flexibility, as it canalso be mounted in the rail or in the fuel-return line.

M-Motronic

24

Fuel-pressure regulator

1 Intake-manifold connection, 2 Spring, 3 Valve holder, 4 Diaphragm, 5 Valve, 6 Fuel supply, 7 Fuel return.

Fuel-pressure attenuator

1 Spring, 2 Spring plate, 3 Diaphragm, 4 Fuel supply, 5 Fuel return.

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Fuel injection

Uncompromising demands for smoothrunning and low emissions in automobi-les have made it necessary to providethorough and precise mixture formationfor every single work cycle. The fuelmass must be injected in quantities thatare precisely metered to match theamount of intake air; in today’s appli-cations exact injection timing is acquiringincreasing significance. For this reason,every cylinder is assigned an electro-magnetic injector. The injector sprays thefuel – in precise quantities at a point intime determined by the ECU – directly to-ward the cylinder intake valve(s). Thus

condensation along the walls of the in-take tract of the kind that leads to de-viations from the desired Lambda valueis largely avoided. Because the engine’sintake manifold conducts only com-bustion air, its geometry can be opti-mized to meet the engine’s dynamic gas-flow requirements.

Electromagnetic injectorThe electromagnetic injector contains asolenoid armature mounted on a valveneedle (Figures 8 and 9), and travelsthrough precise motions within the valvebody. When the unit is at rest, a coilspring presses the valve needle againstthe seat to seal off the flow of fuel through

Fuel system

25

Injector (top-feed)

1 Filter strainer in fuel supply, 2 Electrical connection, 3 Solenoid winding, 4 Valve housing, 5 Armature, 6 Valve body, 7 Valve needle.

Injector (bottom-feed)

1 Electrical connection, 2 Filter screen in fuel supply, 3 Solenoid winding, 4 Valve housing, 5 Armature, 6 Valve body, 7 Valve needle.

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the outlet orifice and into the intake mani-fold. When the control transmits an ac-tivation current to the solenoid winding in the valve housing, the solenoid arma-ture rises between 60 and 100 µm, liftingthe valve needle in the process; the fuelcan now flow through the calibrated ori-fice. The response times lie between 1.5 ... 18 ms at a control frequency of3...125 Hz, depending upon the type ofinjection and the momentary enginespeed and load conditions.

Different injector designs are employedto meet varying requirements:

Top-feed injectorFuel enters the top-feed injector fromabove and flows through its vertical axis.This unit is installed in a specially-formedopening in the fuel rail. Sealing is pro-vided by an upper seal ring, while a clipholds the unit in place. The lower end,which also has a seal ring, extends intothe engine’s intake manifold (Figure 8).

Bottom-feed injectorThe “bottom-feed” injector is integratedwithin the fuel-rail assembly, where it isconstantly immersed in flowing fuel. Thefuel supply enters the unit from the side(“bottom-feed”). The fuel rail itself ismounted directly on the intake manifold.

M-Motronic

26

Injectors (bottom-feed) integrated in fuel rail

1 Fuel supply, 2 Injector, 3 Electrical connection, 4 Contact rail, 5 Pressure regulator, 6 Fuel return.

Metering layouts and fuel preparation

1 Ring-gap metering, 2 Single-orifice metering, 3 Multi-orifice metering, 4 Multi-orifice metering with dual-stream injector.

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The injector is retained in the fuel rail by either a clip, or a cover on the rail which can also house the electricalconnections. Two seal rings prevent thefuel from escaping. This type of modulardesign provides several advantages;these include good starting and drivingresponse with hot engines as well as lowinstallation height (Figures 9 and 10).

Mixture formationA variety of different fuel-metering ar-rangements are employed to satisfy thedemand for the effective fuel atomiz-ation necessary for ensuring maximumhomogeneity in the air-fuel mixture while simultaneously holding intake-

tract condensation to a minimum. Theinjector’s discharge orifice is speciallycalibrated to fulfill these requirements inthe respective applications (Figure 11).On units with ring-gap metering, a sec-tion of the valve needle (pintle) extendsthrough the valve body. The resulting ringgap forms the calibrated fuel-dischargeorifice. The lower end of the pintle fea-tures a machined breakaway edge wherethe fuel atomizes before emerging in a tapered pattern.On injectors with single-orifice metering,the pintle is replaced by a thin injection-orifice disk with a calibrated opening. Vir-tually none of the thin jet of fuel lands onthe walls of the intake tract. However, fuel atomization is limited. Injectorsfeaturing multi-orifice metering are fittedwith an injection-orifice disk of the kindused in the single-orifice units, the differ-ence being that the multi-orifice diskcontains numerous calibrated openings.These are arranged to provide a taperedspray pattern similar to that achieved with annular-orifice metering devices,and provide comparable fuel atomiz-ation. The orifices can also be designed to provide two or more spray patterns.This makes it possible to achieve opti-mum fuel distribution via separate in-jection into the individual inlet runners on multi-valve engines. Meanwhile, air-shrouded injectors can provide evenbetter mixture formation.Combustion air traveling at the speed ofsound is extracted from the intake mani-fold at a location upstream from thethrottle valve; it then proceeds through acalibrated opening located directly on theinjection-orifice disk. The interaction be-tween fuel and air molecules providesthorough atomization. To allow air to bedrawn in through the opening, a partialvacuum referred to atmospheric pres-sure is required in the intake manifold.The air-shrouded design is thus mosteffective during part-throttle operation(Figure 12).

Fuel system

27

Air-shrouded injector

1 Air supply, 2 Fuel supply.

1

2

Fig. 12

UM

K13

00Y

Operating-data acquisition

Engine load One of the most important variables usedfor determining injection quantity andignition advance angle is the engine’sload state (load monitoring).The various Motronic systems employthe following load sensors to monitorengine load:– Air-flow sensor,– Hot-wire air-mass meter,– Hot-film air-mass meter, – Intake manifold pressure sensor, and– Throttle-valve sensor.In the Motronic systems the throttle-valvesensor generally assumes the function ofa secondary load sensor, supplementingone of the primary load sensors listedabove. It is also employed as a primaryload sensor in some isolated cases.

Air-flow sensorThe air-flow sensor is located betweenthe air filter and the throttle valve, whereit monitors the volumetric flow rate [m3/h]of the air being drawn into the engine.The force of the air stream acts againstthe constant return force of a spring, andthe air flap’s deflection angle is moni-tored via potentiometer. The potentio-meter voltage is transmitted to the ECU

for comparison with the potentiometer’sinitial supply voltage. The resulting volt-age ratio serves as an index of the in-duction air’s volumetric flow rate. TheECU ensures accuracy by compensatingfor the effects of potentiometer aging and temperature when processing theresistance (Figure 1).In order to prevent pulsation in the intakeair stream from setting up oscillations inthe air-flow sensor flap, the system alsoincludes a counterflap and a “dampingvolume.” The air-flow sensor is equippedwith a temperature sensor. This transmitsa temperature-sensitive resistance valueto the control unit, allowing it to compen-sate for variations in air density arisingfrom changes in the temperature of theintake air.The air-flow sensor is still a component inmany of the M-Motronic and L-Jetronic sy-stems currently in production. The loadsensors described in the following sectionare preferably installed, and will replacethe flap-controlled air-flow sensor in futuresystems.

Air-mass metersThe hot-wire and hot-film air-mass meters are both “thermal” load sensors.They are installed between the air filterand the throttle valve, where they monitorthe mass flow [kg/h] of the air being drawn into the engine. The two metersoperate according to a common principle.

M-Motronic

28

1

����

�������������

4

6

5 3

2

αQL

Air-flow sensor in intake system

1 Throttle valve, 2 Air-flow sensor, 3 Intake air temperature signal to ECU, 4 ECU, 5 Air-flow sensor signal to ECU, 6 Air filter. QL Intake air quantity, α Deflection angle.

UM

K00

96-1

Y

Fig. 1

An electrically heated element is moun-ted in the intake-air stream, where it iscooled by the flow of incoming air. A con-trol circuit modulates the flow of heatingcurrent to maintain the temperature differential between the heated wire (orfilm) and the intake air at a constant level.The amount of heating current requiredto maintain the temperature thus pro-vides an index for the mass air flow. Thisconcept automatically compensates forvariations in air density, as this is one ofthe factors that determines the amount ofwarmth that the surrounding air absorbsfrom the heated element.

Hot-wire air-mass meterThe heated element on the hot-wire air-mass meter is a platinum wire only 70 µmin diameter. A temperature sensor is inte-grated within the hot-wire air-mass meterto provide compensation data for intake-air temperature. The main components inthe control circuit are a bridge circuit andan amplifier. The heated wire and the in-take-air temperature sensor both act astemperature-sensitive resistors within the bridge (Figures 2 through 4). Theheating current generates a voltage signal, proportional to the mass air flow,at a precision resistor. This is the signaltransmitted to the ECU.

Operating-data acquisition

29

Components of the heated-wire air-mass meter

1 Temperature sensor, 2 Sensor ring with hot wire,3 Precision resistor.QM Mass flow.

Bridge circuit in heated-wire air-mass meter

RH Hot wire, RK Compensation resistor,RM Measurement resistor, R1, R2 Adjustable resistors. UM Measurement voltage, QM Incomingair mass per unit of time.

Hot-wire air-mass meter

1 Hybrid circuit,2 Cover,3 Metal insert,4 Inner tube with hot wire,5 Housing,6 Screen,7 Retainer.

QM

1 2 3

R2 RM UM

R1

RK RH

QM

12

3

4

5

76

Fig. 2 Fig. 4

Fig. 3

UM

K03

11Y

UM

K13

02Y

UM

K00

87Y

To prevent the “drift” that could resultfrom contaminant deposits on the plati-num wire, the wire is heated up to “burn-off” temperature for one second after theengine is switched off. This processvaporizes and/or splits off the depositsand cleans the wire.

Hot-film air-mass meterThe heated element on the hot-film air-mass meter is a platinum film resistor(heater). It is located on a ceramic platetogether with the other elements in thebridge circuit. The temperature of theheater is monitored by a temperature-sensitive resistor (flow sensor) also in-cluded in the bridge.The separation of heater and flow sensorfacilitates design of the control circuitry.Saw cuts are employed to ensure ther-mal decoupling between the heatingelement and the intake-air temperaturesensor.The complete control circuitry is locatedon a single layer. The voltage at theheater provides the index for the mass

air flow. The hot-film air-mass meter’selectronic circuitry then converts the voltage to a level suitable for processingin the ECU (Figures 5 through 7).This device does not need a burn-off pro-cess to maintain its measuring precisionover an extended period. In recognitionof the fact that most deposits collect onthe sensor element’s leading edge, theessential thermal-transfer elements arelocated downstream on the ceramiclayer. The sensor element is also de-signed to ensure that deposits will not influence the flow pattern around thesensor.

Intake-manifold pressure sensorA pneumatic passage connects the in-take-manifold to this pressure sensor,which monitors the absolute pressure[kPa] within the intake manifold.The unit can be constructed as an in-stallation component for the ECU or as aremote sensor for mounting on or nearthe intake manifold. A hose connects theinstallation unit to the manifold.

M-Motronic

30

Hot-film air-mass meter

a Housing, b Hot-film sensor (installed in center of housing).1 Heat sink, 2 Intermediate component, 3 Power chip, 4 Hybrid circuit, 5 Sensor element.

Hot-film sensor element

1 Ceramic substrate, 2 Sawcut.RK Temperature-compensation sensor,R1 Bridge resistor, RH Heater resistor,RS Sensor resistor.

a

3

b

1

24

5

5

1

2

RK

R1

RH

RS

Fig. 5 Fig. 6

UM

K09

03Y

UM

K13

03Y

The sensor is divided into a pressure cellwith two sensor elements and a chamberfor the evaluation circuitry. Sensor el-ements and evaluation circuitry are located on a single ceramic layer (Figure 8).

The sensor element consists of a bell-shaped thick-layer diaphragm enclosinga reference volume with a specific inter-nal pressure. The diaphragm’s deflectionis determined by the pressure in the in-take manifold.A series of piezo-resistive resistor el-ements is arranged on the diagram; theconductivity of these elements varies inresponse to changes in mechanical ten-sion. These resistors are incorporated ina bridge circuit in such a manner that anydeflection at the diaphragm will lead to achange in the bridge balance. The bridgevoltage thus provides an indication of in-take-manifold pressure (Figure 9).

The evaluation circuit amplifies the bridge voltage, compensates for temper-ature effects and linearizes the pressureresponse curve. The output signal from the evaluation circuit is transmitted to the ECU.

Throttle-valve sensorThis sensor provides a secondary loadsignal based on the angle of the throttlevalve. The applications for this second-ary load signal include providing infor-mation for dynamic functions, load-rangerecognition (idle, full or part-throttle), andserving as a backup signal in the event of main-sensor failure.

The throttle-valve sensor is attached tothe throttle-valve assembly where it shares a common shaft with the throttlevalve. A potentiometer evaluates thethrottle valve’s deflection angle andtransmits a voltage ratio to the ECU via a resistance circuit (Figures 10 and 11).

Operating-data acquisition

31

Circuit of hot-film air-mass meter

RK Temperature-compensation sensor, RH Heater resistor, R1, R2, R3 Bridge resistors, UM Measurement voltage, IH Heater current,tL Air temperature, QM incoming air mass per unit of time.

Pressure sensor (for installation in ECU)

1 Pressure connection, 2 Pressure cell with sen-sor elements, 3 Sealing edge, 4 Evaluation cir-cuitry, 5 Thick-film hybrid.

Thick-film diaphragm in pressure sensor

1 Piezoresistive resistors, 2 Base diaphragm, 3 Reference pressure chamber, 4 Ceramic substrate.p Pressure.

UM

R1 RS

IHRK

tL

RH

Qm

R2 R3

2 3 4 51

p

1 3 42p

Fig. 8Fig. 7

Fig. 9

UA

E02

96Y

UM

K13

05-2

YU

MK

1304

-2Y

More exacting precision is required whenthe throttle-valve sensor is used as theprimary load sensor. This higher level ofprecision is obtained by using a throttle-valve sensor incorporating two poten-tiometers (two angle ranges) as well asimproved suspension. The control unit determines the mass ofthe intake air by monitoring throttle-valveangle and engine speed. Data fromtemperature sensors allows the unit torespond to variations in the air mass dueto temperature change.

Engine speed, crankshaftand camshaft positions

Engine speed and crankshaftpositionThe degree of piston travel within thecylinder is employed as a measuredvariable for determining the firing point.The pistons in all cylinders are connectedto the crankshaft via the connecting rods.A sensor at the crankshaft thus providesthe information on the locations of thepistons in the cylinders.The speed at which the crankshaftchanges its position is the engine speed,defined in the number of crankshaft rev-olutions per minute (rpm). This also re-presents another important Motronicinput variable for the Motronic unit, and iscalculated from the crankshaft positionsignal. Although the signal from thecrankshaft sensor basically indicatescrankshaft position, which is then con-verted to an engine-speed signal in theECU, the device has come to be knownas the engine-speed, or rpm sensor.

Generating the crankshaft position signalInstalled on the crankshaft is a ferromag-netic ring gear with a theoretical capacityof 60 teeth, whereby two teeth are miss-ing on the gear in question (tooth gap).An inductive speed sensor registers the58-tooth sequence. This sensor consistsof a permanent magnet and a soft-ironcore with a copper winding (Figure 12).

The magnetic flux field at the sensor responds as the teeth on the sensor gearpass by, generating AC voltage (Figure13). The amplitude of this AC voltagedecreases as the interval between sen-sor and sensor gear increases, and risesin response to higher engine speeds.Sufficient amplitude is already availableat a minimal engine speed (20 min-1).Pole and tooth geometry must be matched. The evaluation circuit in theECU converts the sinus voltage with itshighly varying amplitudes into square-wave voltage with a constant amplitude.

M-Motronic

32

Throttle-valve sensor

1 Throttle-valve shaft, 2 Resistor track 1, 3 Resistor track 2, 4 Wiper arm with wiper, 5 Electrical connection.

Throttle-valve sensor circuitry

UM Measurement voltage, R1, R2 Resistor tracks 1and 2, R3, R4, R5 adjustment resistors.1 Throttle valve.

5

42 31

UM

1

R1 R3

R5

R4R2

R6

Fig. 10

Fig. 11

UM

K13

06Y

UM

K13

07Y

Calculating the crankshaft positionThe flanks of the square-wave voltageare transmitted to the computer via aninterrupt input. A gap in the tooth patternis registered at those points where theflank interval is twice as large as in theprevious and subsequent periods. Thetooth gap corresponds to a specificcrankshaft position for cylinder no. 1. Thecomputer synchronizes the crankshaftposition according to this point in time. Itthen counts 3 degrees further for everysubsequent positive or negative toothflank. The ignition signals, however, mustbe transmitted in smaller stages. Theduration between two tooth flanks is thus further divided by four. The time unit

thus derived can be multiplied by two,three or four and added to a tooth flankfor the ignition advance angle (allowingsteps of 0.75 degrees).

Calculating segment duration and engine speed from the engine-speed sensor signalThe relatonship between the cylinders of the four-stroke engine is such that two crankshaft rotations (720 degrees)elapse between the start of each newcycle at cylinder no. 1. This interval is the mean ignition interval,and is referred to as the segment time Ts.When the interval is distributed equally,the result is:

Operating-data acquisition

33

Signal patterns for ignition, crankshaft and camshaft

a Ignition-coil secondary voltage, b Crankshaft rpm sensor signal,c Camshaft Hall-sensor signal.1 Close, 2 Ignition.

1 2

4

6

5

3

S

N

a

b

c

1

2

E A B C D

Interval Degrees Teeth

2 cylinders 360 60

3 cylinders 240 40

4 cylinders 180 30

5 cylinders 144 24

6 cylinders 120 20

8 cylinders 90 15

12 cylinders 60 10

UM

K13

08Y

Engine-speed sensor

1 Permanent magnet, 2 Housing, 3 Engine housing, 4 Soft-iron core, 5 Winding, 6 Ring gear with reference point (tooth gap).

UM

Z01

38-2

Y

Fig. 13

Fig. 12

Ignition, injection and the engine speedderived from the segment time are recal-culated for every new interval. The figurefor rotational speed describes the meancrankshaft rpm within the segment timeand is proportional to its reciprocal.

Camshaft positionThe camshaft controls the engine’s in-take and exhaust valves while operatingat half the rotating speed of the crank-shaft. When a piston travels to top deadcenter, the camshaft uses the settings ofthe intake and exhaust valves to de-termine whether the cylinder is in thecompression phase to be followed by ig-nition, or in the exhaust phase. This in-formation cannot be derived from thecrankshaft position.If the ignition is equipped with a high-volt-age distributor with a direct mechanicallink to the camshaft, the rotor will point tothe correct cylinder automatically: theECU does not require supplementary in-formation on the position of the camshaft.In contrast, Motronic systems featuringstationary voltage distribution and single-spark ignition coils require additional in-formation, as the ECU must be able todecide which ignition coil and spark plugare due to be triggered. To do so, it mustbe informed as to the camshaft’s pos-ition.The position of the camshaft must alsobe monitored in those systems whereseparate injection timing is used for eachindividual cylinder, as is the case withsequential injection (SEFI).

Hall-sensor signalCamshaft position is usually monitoredwith a Hall sensor. The monitoring deviceitself consists of a Hall element with asemiconductor wafer through which cur-rent flows. This element is controlled by atrigger wheel that turns together with thecamshaft. It consists of a ferromagneticmaterial and generates voltage at rightangles to the direction of the current as itpasses the Hall element (Figure 13).

Calculating camshaft positionAs the Hall voltage lies in the millivolt

range, it is processed within the sensorbefore being transmitted to the ECU inthe form of a switching signal. In thesimplest case, the computer responds totrigger-wheel gaps by checking to seewhether Hall voltage is present andwhether or not cylinder no. 1 is on itspower stroke.Special trigger-wheel designs make itpossible to use the camshaft signal as abackup for emergency operation in caseof crankshaft (engine-speed) sensor fail-ure. However, the resolution provided bythe camshaft signal is too imprecise toallow it to be employed as a permanentreplacement for the crankshaft speedsensor.

Mixture compositionExcess-air factor λThe lambda oxygen sensor monitors theexcess-air factor λ. Lambda defines thenumber for the mixture’s A/F ratio. Thecatalytic converter functions best at λ = 1.

Lambda oxygen sensorThe Lambda oxygen sensor’s outer elec-trode extends into the exhaust stream,while the inner electrode is exposed tothe surrounding air (Figure 14).

The essential constituent of the oxygensensor is a special-ceramic body fea-turing gas-permeable platinum elec-trodes on its surface. Sensor operation isbased on the ceramic material’s porosity,which allows oxygen in the air to diffuse(solid electrolyte). The ceramic materialbecomes conductive at higher tempera-tures. Voltage is generated at the elec-trodes when different oxygen levels arepresent on the respective sides. Astoichiometric air/fuel ratio of λ = 1 pro-duces a characteristic jump (jump func-tion) in the response curve (Figure 16).The oxygen sensor’s voltage and internalresistance are both sensitive to tempera-ture. Reliable control operation is pos-sible with exhaust-gas temperatures ex-ceeding 350°C (unheated sensor), or200°C (heated sensor).

M-Motronic

34

Heated Lambda oxygen sensorThe design of the heated Lambda oxy-gen sensor is largely the same as that ofthe unheated version (Figure 15). A cer-amic heater element warms the sensor’sactive ceramic layer from the inside, en-suring that its ceramic material remainshot enough for operation – even at lowexhaust-gas temperatures. The heatedsensor is protected by a tube with a re-stricted flow opening to prevent the sen-sor’s ceramics from being cooled by low-temperature exhaust gases.

The heated sensor reduces the waitingperiod between engine start and effective

closed-loop control. It also provides re-liable control with lower-temperatureexhaust gases (e.g., at idle). Heated sen-sors offer shorter reaction times for re-duced closed-loop response intervals.This type of sensor also offers greaterlatitude in selecting the installationposition.

Operating-data acquisition

35

Lambda oxygen sensor location in exhaustpipe

1 Special ceramic coat, 2 Electrodes, 3 Contact, 4 Housing contact, 5 Exhaust pipe, 6 Ceramic shield (porous), 7 Exhaust gas, 8 Air.

Lambda oxygen sensor voltage curve at 600°C operating temperature

a Rich mixture (air deficiency),b Lean mixture (excess air).

Heated Lambda oxygen sensor

1 Probe housing, 2 Ceramic shield tube, 3 Electrical connections, 4 Shield tube with slits, 5 Active ceramic sensor layer, 6 Contact, 7 Shield, 8 Heating element, 9 Clamp connections for heater element, 10 Disc spring.

4

3

U

2

1

6

5

87

0.9 1 1.1

1,000

800

600

400

200

Excess-air factor λ

Oxy

gen-

sens

or v

olta

ge U

s

mV

1.20.80

a b

1 2 3

4 5 6 7 8 9 10

Fig. 14 Fig. 16

UM

K16

84Y

UM

K02

79E

UM

K01

43Y

Fig. 15

Combustion knock

Under certain conditions combustion inthe spark-ignition engine can degenerateinto an abnormal process characterizedby a typical “knocking” or “pinging”sound. This phenomenon is an undesir-able combustion process known as“knocking”, which limits the engine’s out-put and specific efficiency levels. It oc-curs when fresh mixture preignites inspontaneous combustion before beingreached by the expanding flame front.Normally initiated combustion and thepiston’s compressive force lead to thepressure and temperature peaks thatproduce self-ignition in the end gas

(remaining unburned mixture). Flamevelocities in excess of 2,000 m/s can occur, as compared to speeds of roughly30 m/s for normal combustion. This ab-rupt combustion process produces sub-stantial local pressure increases in theend gas. The resulting pressure wavepropagates until stopped by impact withthe cylinder walls representing the outerextremity of the combustion chamber.Chronic preignition is accompanied bypressure waves and increased thermalstresses at the cylinder-head gasket,piston and in the vicinity of the valves. Allof these factors can lead to mechanicaldamage.

M-Motronic

36

Knock sensor

1 Seismic mass, 2 Cast mass, 3 Piezoelectric ceramic, 4 Contacts, 5 Electrical connection.

Knock-sensor signals

The knock sensor supplies a signal c corresponding to the pressure pattern a in the cylinder. The filtered pressure signal is shown in b.

“Listening” positions for the knock sensors

1 The knock sensor is located between the second and third cylinders. 2 If two knock sensorsare fitted, these are located between the first andsecond, and the third and fourth cylinders.

2

3

4

5

1 2 21

a

b

c

a

b

c

without knock with knock

Fig. 17 Fig. 19

Fig. 18

UM

Z01

99Y

UM

Z01

41Y

UM

Z01

21-2

E

The characteristic vibration patterns generated by combustion knock can bemonitored by knock sensors for con-version into electrical signals, which arethen transmitted to the Motronic ECU(Figures 17 and 18). Both the numberand positions of the knock sensors mustbe carefully selected. Reliable knock recognition must be guaranteed for allcylinders and under all engine operatingconditions, with special emphasis onhigh loads and engine speeds. As a general rule, 4-cylinder engines areequipped with one, 5 and 6-cylinder en-gines with two, and 8 and 12-cylinder en-gines with two or more knock sensors (Figure 19).

Engine and intake-airtemperaturesThe engine-temperature sensor incor-porates a temperature-sensitive resistorwhich extends into the coolant circuitwhose temperature it monitors. A sen-sor in the intake tract registers the intake-air temperature in the same fashion(Figure 20).The resistor is of the negative tempera-ture coefficient type (NTC, see Figure 21)and forms part of a voltage-divider circuitoperating with a 5 V supply. An analog-digital converter monitors the resistor’svoltage drop, which provides an index ofthe temperature. Compensation for thenon-linear relationship between voltageand temperature is provided by a tablestored in the computer’s memory; thetable matches each voltage reading witha corresponding temperature.

Battery voltage

The electromagnetic injector’s openingand closing times are affected by the bat-tery’s voltage. Should voltage fluctu-ations occur in the vehicle’s electricalsystem, the ECU will prevent responsedelays by adjusting the duration of the in-jection process. At low battery voltagesthe ignition circuit’s dwell times must beextended to provide the coil with the op-portunity to accumulate sufficient ignitionenergy.

Operating-data acquisition

37

Engine-temperature sensor

1 Electrical connection, 2 Housing, 3 NTC resistor.

Temperature-sensor response curve (NTC)

���������������������

��������������

������������������

������������

1 2 3

4

Temperature °C

Res

ista

nce

Fig. 20

Fig. 21

UM

K01

24-3

YU

MK

1309

E

Operating-data processing

Processing load signals

Monitored variablesThe ECU uses the signals for load andengine speed to calculate a load signalcorresponding to the air mass inductedinto the engine during each stroke. Thisload signal serves as the basis for calcu-lations of injection duration and for ad-dressing the programmed responsecurves for ignition advance angle (Figure 1).

Monitoring air massHot-wire or hot-film air-mass metersmeasure the air mass directly, producinga signal that is suitable for use as a para-

meter in load-signal calculations. Whenan air-flow meter is used, density cor-rection is also required before air massand load signal can be determined. In special cases monitoring errors due toheavy pulsation in the intake manifoldalso receive compensation in the form ofa pulsation correction.

Monitoring pressurePressure-monitoring systems (using apressure sensor to determine load) differfrom air-mass monitoring systems in thatno direct formulas are available for de-fining the relationship between intakepressure and the air-mass intake. TheECU therefore calculates the load signalwith the aid of corrections stored in a pro-gram map. Subsequent compensation is providedfor changes in temperature and residualgas relative to the initial state.

M-Motronic

38

Calculating injection timing

Basic injection timingfrom load signal

Injection timing for starting

Post-start andwarm-up correction

Operating-point-dependentinjection correction

Lambda controllercorrection withactive Lambda control

Overrun, engine orvehicle speed limiter

Transition compensation

Correction at switch-in

Battery voltagecorrection

Effective injection timing

yes

no

Injection switched off

Fig. 1

UM

K13

10E

Measuring throttle-valve angleWhen a throttle-valve sensor is used, theECU determines the load signal withreference to engine speed and throttle-valve angle. Compensation for variationsin air density are based on readings fortemperature and ambient pressure.

Calculating injection timingBase injection timingThe base injection timing is calculated di-rectly from the load signal and from theinjector constants, and defines the re-lationship between the duration of the activation signal and the flow quantity at the injector. This constant thus variesaccording to injector design. When theinjection duration is multiplied by the in-jector constant the result will be a fuelmass corresponding to a particular airmass for each stroke.

The base setting is selected for an ex-cess-air factor of λ = 1.This remains valid for as long as the pres-sure differential between fuel and intakemanifold stays constant. When it varies, aλ correction map compensates for this in-fluence on injection times.Meanwhile, a battery-voltage correctorcompensates for the effects that fluc-tuations in battery voltage have on theinjectors’ opening and closing times.

Effective injection timeThe effective injection time results whenthe correction factors are included in the calculations. The correction factorsare determined in corresponding specialfunctions and provide adjustment data for varying engine operating ranges andconditions. The correction factors areused both individually and in combi-nations according to applicable para-meters.

Operating-data processing

39

Comparison of injection types

a Simultaneous injection, b Group injection, c Sequential injection.

Firing order

Cyl. 1

Cyl. 3

Cyl. 4

Cyl. 2

Cyl. 1

Cyl. 3

Cyl. 4

Cyl. 2

Cyl. 1

Cyl. 3

Cyl. 4

Cyl. 2

Intake valveopen

Injection

Ignition

–360° 0° 360° 720° 1,080° CrankshaftCyl. 1 TDC

a

b

c

Fig. 2

UM

K13

11E

The process for calculating the injectiontime is illustrated in Figure 1. The indi-vidual operating ranges and conditionswill be explained in more detail in thefollowing chapters. Once cylinder filling drops below a cer-tain level, the mixture will cease to ignite.Restricting the injection time thus pre-vents the formation of unburned hydro-carbons in the exhaust gas.For starting, the injection time is calcu-lated separately using criteria inde-pendent of the calculated load signal.

Injection modeIn addition to the injection time, the in-jection mode is yet another importantparameter for fuel economy and exhaustemissions. The range of options dependsupon the type of injection system (Figure 2):– Simultaneous injection,– Group injection, or– Sequential injection.

Simultaneous injectionWith simultaneous injection, the injectionprocess is triggered twice per cycle at aspecific point in time at all injectors, thatis, once for each camshaft revolution, or once for every two crankshaft revo-lutions. The injection mode is static.

Group injectionGroup injection combines the injectors intwo groups, with each group being trig-gered once per cycle. The time intervalbetween the two triggering points isequal to one crankshaft rotation period.This arrangement makes it possible touse the engine operating point as the es-sential criterion in selecting the injectionmode while also preventing undesirablespray through the open intake valvesthroughout a wide range in the programmap.

Sequential injectionThis type of injection provides the highestdegree of design latitude. Here, the in-jection processes from the individualinjectors take place independently ofeach other at the same point in the cycle

referred to the respective cylinder. Thereare no restrictions on injection timing,which can be freely adapted to corre-spond with the optimization criteria.

ComparisonGroup and sequential injection require awider injector variation range (range ex-tending from the minimum quantity at idleto the maximum under full throttle) thansimultaneous injection.

Controlling dwell angleThe dwell angle varies the ignition coil’scurrent-flow period according to enginespeed and battery voltage. The dwellangle is selected to ensure availability ofthe required primary current at the end of the current flow time throughout thewidest possible range of operating con-ditions.The dwell angle is based on the ignitioncoil’s charge time, which, in turn, dep-ends upon battery voltage (Figure 3). Asupplementary dynamic reserve makes itpossible to supply the required currenteven during sudden shifts to high enginespeeds. The charge time is restricted in the upperrpm range to maintain an adequate arc-ing time at the spark plug.

M-Motronic

40

Primary current pattern at various system voltages

Specified

6 V 12 V 15 V

Prim

ary

curr

ent

Time t

A

Fig. 3

UM

Z01

37E

Controlling ignition advance angleA program map containing the basic ig-nition timing for various engine loads andspeeds is stored in the memory of the M-Motronic ECU. This ignition advanceangle is optimized for minimal fuel con-sumption and exhaust emissions.Data for engine and intake-air tempera-ture (monitored via sensors) provide thebasis for corrections to compensate fortemperature variations. The unit can sup-ply additional corrections and/or revert to other program maps to adapt to alloperating conditions. Thus the mutualeffects of torque, emissions, fuel con-

sumption, preignition tendency and driv-ability can all be taken into account. Spe-cial ignition-angle correction factors areactive during operation with secondaryair injection or exhaust-gas recirculation(EGR) as well as in dynamic vehicleoperation (e.g., when accelerating).The various operating ranges (idle, partthrottle, full throttle, start and warm-up) continue to be taken into account.Figure 4 shows a flow chart describingignition-angle processing.

Operating-data processing

41

Calculating ignition timing

Base ignition advance anglefrom load and rpm signal

Correction upontransmission adjustment

Temperature corrections

Post-start and warm-upcorrection

Overrun

Correction at switch-in

Ignition-advance limit

Ignition point

yes

no Correction before overrunfuel cutoff

Operating-point-dependentignition-angle correction

Ignition-angle correctionfor knock control

Ignition-anglecorrection at idle

Fig. 4

UM

Z02

73E

Operating conditions

StartSpecial calculations are employed todetermine the injection quantity for theduration of the starting procedure.In addition, special injection timing isused for the initial injection pulses. Theinjection quantity is augmented in ac-cordance with engine temperature to pro-mote formation of a fuel film on the wallsof the intake manifold, thereby compen-sating for the engine’s higher fuel re-quirements as it runs up to speed. Assoon as the engine starts to turn over, thequantity of supplementary fuel is reducedand then cancelled once the enginestarts to run.Ignition advance angle is also speciallyadjusted for starting. The adjustment oc-curs with reference to engine tempera-ture and engine speed.

Post-start phaseThe post-start phase is characterized by further reductions in the supplemen-tary injection quantity. The reductions are based on engine temperature andthe elapsed time since the end of thestarting process. The ignition advanceangle is also adjusted to correspond to the revised fuel quantities and

the different operating conditions.The post-start phase terminates with asmooth transition to the warm-up phase.

Warm-up phaseDifferent strategies can be employed forthe warm-up phase, depending upon en-gine and emissions-control design. Thedecisive criteria are drivability, emissionsand improved fuel economy. A leanwarm-up combined with retarded ignitiontiming raises the temperature of the ex-haust gas. Another way to obtain high ex-haust temperatures is to employ a richwarm-up mixture together with second-ary-air injection. Here air is injected intothe exhaust system downstream from theexhaust valves for a brief period after theengine starts. A secondary-air pump canprovide this additional air. When the tem-perature is high enough, this excess airsupports oxidation of HC and CO in theexhaust system while simultaneouslygenerating the desired high exhaust tem-peratures (Figure 1).Both of these measures help the catalyticconverter to begin effective operationsooner.The effects of the adjustments to ignitionangle and injection timing can be supple-mented by higher idle speeds. These areprovided by a specially designed air in-jection unit, and also result in shorterwarm-up times at the catalytic converter.

M-Motronic

42

Effect of secondary air on HC and CO

1 Without secondary air, 2 With secondary air.

0

100

200

300

400

500

600

0.7 0.9 1.10.6 0.8 1.0

ppm

0

2

4

6

8

10

12

%

0.6 0.7 0.8 0.9 1.0

HC

em

issi

ons

CO

em

issi

ons

1

2

1

2

Excess-air factor λ Excess-air factor λ1.20.5 0.5 1.1

Fig. 1

UM

K13

14E

Once the converter reaches operatingtemperature the injection is governed to λ = 1. This is accompanied by a corre-sponding adjustment in ignition angle.

Transition compensationAcceleration/decelerationA portion of the fuel sprayed into the in-take manifold does not reach the cylinderin time for the next combustion process.Instead, it forms a condensation layeralong the walls of the intake tract. The ac-tual quantity of fuel stored in this film in-creases radically in response to higherloads and extended injection times.A portion of the fuel injected when thethrottle valve opens is used for this film. Acorresponding amount of supplementaryfuel must thus be injected to compensateand prevent the mixture from leaning out.Because the additional fuel retained inthe wall film is released as the load factordrops, the injection time must be reducedby a corresponding amount during de-celeration.Figure 2 shows the resulting curve for in-jection times.

Overrun fuel cutoff/renewed fuel flowWhen the throttle closes, the injection isswitched off in the interests of reducedfuel consumption and lower exhaustemissions.

The injection stop is preceded by a re-duction in the ignition advance to at-tenuate torque jump during the transitionto trailing throttle.The injection starts again once a specificreactivation speed – located above idlespeed – is reached. Various activationspeeds are stored in the ECU. Thesevary according to different parameterssuch as engine temperature and rpm dy-namics, and are calculated to prevent ex-cessive drops in engine speed, regard-less of operating conditions.When the injection resumes, it sprays insupplementary fuel to rebuild the fuelwall layer. The ignition advance angle isalso adjusted to provide a smooth torqueincrease.

Closed-loop idle-speedcontrolIdleThe fuel consumption at idle is largelydetermined by the engine’s efficiencyand by the idle speed. A substantial pro-portion of the fuel consumed by vehiclesin heavy urban traffic is actually burned atidle. The idle speed should thus be aslow as possible. At the same time, theidle should never fall so far that roughrunning or stalling occur, even under ad-ditional loads such as electrical equip-ment, air conditioner, automatic trans-mission in gear, power steering, etc.

Operating conditions

43

Transition injection timing

1 Injection timing from load signal,2 Effective injection timing, 3 Additional fuel,4 Fuel reduction, 5 Throttle-valve angle αDK.

4

Inje

ctio

n du

ratio

n

Distance travelled

1

2 3

5

Fig. 2

UM

K13

15-2

E

Idle-speed controlThe idle-speed control must maintain abalance between torque generation andengine load in order to ensure a constantidle speed. The load on the idling engineis a combination of numerous elements,including internal friction within the en-gine’s crankshaft and valvetrain assem-blies as well as the ancillary drives (for in-stance, for the water pump). The idle-speed control compensates for thisinternal friction, which, in turn, changesover the life of the engine. These loadsare also extremely sensitive to tempera-ture variations.In addition to these internal sources offriction, there are also external factorssuch as the load from the air conditionerthat was mentioned above. The load fromthese external factors is subject to sub-stantial variations as ancillary devicesare switched on and off. Modern engineswith small flywheel weights and large-volume intake manifolds are especiallysensitive to these load fluctuations.

Input variablesIn addition to the signal from the engine-speed sensor, the idle-speed control cir-cuit also requires information on throttle-valve angle in order to recognize the idlestate (foot off accelerator pedal). Enginetemperature is also monitored to allowadvance compensation for the effects oftemperature. An air mass is specifiedwith reference to engine temperature andthe target idle-speed; this idle speed isthen corrected in closed-loop operation.Where present, the input signals from theair conditioner and automatic transmis-sion also facilitate the correction processand provide supplementary support forclosed-loop idle-speed control.

M-Motronic

44

Bypass actuator with hose connections

Fig. 3 Fig. 4

Manifold-mounted bypass actuator

UM

K13

17Y

UM

K13

16Y

Actuator adjustmentsPhysically, for idle-speed control thereare three possibilities for adjustment in-tervention:

Air controlThe proven control procedure is to regu-late air flow by means of a bypass aroundthe throttle valve, or to adjust the throttlevalve itself using either a variable throttlestop or a direct actuator unit as found in“Electronic Throttle Control (ETC).” On bypass actuators designed for hoseconnection, the bypass around thethrottle valve consists of air hoses and anactuator (Figure 3). More modern are by-pass actuators for direct installation; thistype of bypass-air regulation device isflange-mounted directly on the throttle-valve assembly.Figure 4: Example of a single-winding ro-tary actuator for direct installation.One disadvantage associated with by-pass actuators is that they add to thethrottle-valve’s own leakage air. Once theengine is well run-in, the combined airflowing through the throttle valve and the

bypass actuator could well exceed the airquantity that the engine needs at idle. Atthis point effective idle regulation is nolonger possible. This liability disappearswhen adjustments to the throttle valve it-self are employed to regulate the air flow.The idle throttle device uses an electricmotor and gear drive to vary the positionof the throttle valve’s idle stop (Figure 5).Delays in idle response are encounteredwhen adjustments to air flow are used insystems with large-volume intake mani-folds.

Adjustments to ignition advance angleThe second (and faster reacting) optionis to adjust the ignition advance angle.Systems with an rpm-sensitive ignitionadvance angle react to sinking enginespeeds by increasing the ignition ad-vance to provide a boost in torque.

Mixture compositionStrict emissions-control regulations anda limited range of practical possibilitiesrelegate the mixture-adjustment option tovirtual insignificance.

Operating conditions

45

Throttle-valve assembly with integral idle actuator

Fig. 5

UM

K13

18Y

Lambda closed-loop control

Post-treatment of exhaust gases in athree-way catalytic converter is an ef-fective means for reducing concen-trations of harmful exhaust emissions.The converter transforms the three pol-lutants CO, HC and NOX into H2O, CO2

and N2.

Control rangeThe range available for simultaneousconversion of all three of the above components is extremely narrow, and is termed the “lambda window” (λ =0.99 . . . 1). This means that closed-loopLambda control is essential.A Lambda oxygen sensor is installed inthe exhaust system upstream from thecatalytic converter, where it monitors theexhaust-gas oxygen content.Lean mixtures (λ > 1) produce a sensorvoltage of approx. 100mV, while a richmixture (λ < 1) generates approx. 800mV. At λ = 1 the sensor voltage jumpsabruptly from one level to the other(Figure 6). The ECU uses the signal from the air-mass meter and the monitored enginespeed to generate an injection signal. Atthe same time, it also produces a supple-mentary Lambda-control factor from theLambda-sensor signal for use in correc-ting the injection time.

OperationThe Lambda oxygen sensor must beoperational before the Lambda closed-loop control circuit can function. An auxiliary evaluation circuit monitors thisfactor on a continuing basis. A cold oxy-gen sensor or damaged circuitry (short oropen circuits) will generate implausiblevoltage signals which are rejected by theECU. The heated Lambda sensors usedin most systems are ready for operationafter only 30 seconds.Cold engines require a richer mixture (λ < 1) to idle smoothly. For this reasonthe Lambda closed-loop control circuitcan only be activated once a set tem-perature threshold has been passed.Once the lambda control is activated, the ECU uses a comparator to convertthe signal from the sensor into a binarysignal.The controller reacts to the transmittedsignal (λ > 1 = mixture too lean, or λ < 1= mixture too rich), by modifying the con-trol variables (with an initial jump fol-lowed by a ramp progression). The injec-tion time is adjusted (lengthened or shor-tened), and the control factor reacts tothe continuing data transfer by settlinginto a constant oscillation (Figure 7). Theduration of the oscillation periods is de-termined by the flow times of the gas,while the “ramp climb” maintains largelyconstant amplitudes within the load

M-Motronic

46

Fig. 6

Closed-loop control range for Lambda oxygensensor with emissions reduction

Without catalytic converterWith catalytic converter

Diagram of Lambda closed-loop control circuit

1 Air-mass meter, 2 Engine, 3a Lambda oxygensensor 1, 3b Lambda oxygen sensor 2 (as re-quired), 4 Catalytic converter, 5 Injectors, 6 ECU.US Oxygen-sensor voltage, UV Injector controlvoltage, VE Injected fuel quantity.

Air Exhaustgas

FuelVE

3a 3b

UV USa

1 2 4

5

6

USb

0.9 0.95 1.0 1.05 1.1Excess-air factor λ

Exh

aust

em

issi

ons,

sen

sor

volta

ge

NOx

NOx

λ-control range

HC

CO

CO

HCVoltage curveof λ sensor

Fig. 7

UM

K00

04-2

E

UM

K13

19-E

speed range despite variations in the travel time of the gas.

Lambda shiftThe optimum conversion range and thevoltage jump at the oxygen sensor do notcoincide precisely. An asymmetrical con-trol oscillation pattern can be used to shiftthe mixture into the optimal range (λ = 1).The asymmetry is obtained either by de-laying the switch in the control factor afterthe voltage jump (from lean to rich) at theoxygen sensor or by providing an asym-metrical jump. This is the case when thevoltage jump at the oxygen sensor duringthe transition from lean to rich is differentfrom that produced at the change fromrich to lean.

Adapting the pilot settings to theLambda closed-loop controlLambda closed-loop control corrects thesubsequent injection process on thebasis of the previous measurement at theoxygen sensor, whereby an unavoidabletime lag results from the gas travel times.For this reason, the approach to a newoperating point is accompanied by devi-ations from λ = 1 due to incorrect pilotcontrol, a condition alleviated once theclosed-loop control picks up the newcycle. Thus a special pilot control mecha-nism is needed to maintain compliancewith emissions limits. The pilot-control isdefined during adaptation to the engineand the Lambda response curve isstored in the ROM. However, revisionsmay become necessary due to the driftthat can occur during the life of the ve-hicle. Among the drift factors are varia-tions in the density and quality of the fuel.When the Lambda controller consistentlyrepeats the same corrections in a certainload and engine-speed range, the pilot-control adaption mechanism recognizesthis state. It corrects the pilot control forthis range and records the correction in aRAM memory chip (with an uninterruptedcurrent supply). The corrected pilot con-trol is thus ready to respond immediatelyat the next start, assuming duty until theLambda closed-loop control becomesoperative.

Power interruptions in the current to thepermanent memory are also recognized;the adaptation process then commencesagain with neutral default values provid-ing the initial basis for operation.

Dual-sensor Lambda closed-loopcontrolInstalling the Lambda oxygen sensordownstream of the catalytic converterprovides better protection against con-tamination from the exhaust gas (here,“downstream” = on the tailpipe side). Thistype of backup sensor can provide a sec-ond control signal to augment the onefrom the main sensor upstream of theconverter (here, “upstream” = on theengine side). The second signal is super-imposed on the first to provide stablemixture composition over an extendedperiod (Figure 7).The superimposed control modifies theasymmetry in the constant oscillationpattern that is associated with controlconcepts based on the oxygen sensormounted upstream from the converter;this compensates for the lambda shift. A Lambda closed-loop control strategybased solely on the downstream-mounted oxygen sensor would featureexcessive response delays due to thegas travel times.

Operating conditions

47

Evaporative-emissionscontrol systemsOrigins of fuel vaporsThe fuel in the fuel tank is heated by:– Heat radiation from outside sources,

and– The excess fuel from the system return

line which was heated during its pas-sage through the engine compartment.

The result is the HC emissions that areusually emitted from the fuel tank in theform of vapor.

Limiting HC emissionsEvaporative emissions are subject tolegal limits.Evaporative-emissions control systemsrestrict these emissions. These systemsare equipped with an activated charcoalfilter (the so-called carbon canister) located at the end of the fuel tank’s ventline. The activated charcoal in the can-ister binds the fuel vapors and allowsonly air to escape into the atmosphere,as well as serving as a pressure-release

device. In order to ensure that the char-coal can continually regenerate, an addi-tional line leads from the carbon canisterto the intake manifold. Vacuum is pro-duced in this line when the engine runs,causing a stream of atmospheric air toflow through the charcoal on its way tothe manifold. The fuel vapors stored inthe activated charcoal are entrained bythe air stream and conducted to the en-gine for combustion. A so-called can-ister-purge valve in the line to the intakemanifold meters the flow of this regener-ation or “cleansing” air (Figure 8).

Regeneration flowThe regeneration flow is an air-fuel mix-ture of necessarily indeterminate com-position, since fresh air as well as aircontaining substantial concentrations ofgasoline vapor can come from the carboncanister. The regeneration flow thus re-presents a major interference factor forthe Lambda control system. A regener-ation flow representing 1% of the intakeair and consisting solely of fresh air will

M-Motronic

48

Evaporative-emissions control system

1 Line from fuel tank to carbon canister, 2 Carbon canister, 3 Fresh air, 4 Canister-purge valve, 5 Line to intake manifold, 6 Throttle valve.

65

4

3

1

2

p

p

p

∆

u

s

∆p Difference between manifold pressureps and atmospheric pressure pu.

Fig. 8

UM

K06

72Y

lean out the intake mixture by 1%. A flowwith a substantial gasoline componentcan enrichen the mixture by something in the order of 30%, due to the effects on the A/F ratio λ of fuel vapor with astoichiometric factor of 14.7. In addition,the specific density of fuel vapor is twicethat of air.

Canister-purge valveThe canister-purge valve’s control mechanism must ensure adequate air-purging of the carbon canister whileholding Lambda deviations to a minimum(Figure 9).

ECU control operationsThe canister-purge valve closes at regu-lar intervals in order to allow the mixtureadaptation process to function withoutbeing interfered with by tank ventilation. The canister-purge valve opens in a“ramp-shaped” pattern. The ECU “mem-orizes” the resulting Lambda controldeviations as mixture corrections fromthe fuel-regeneration system. The

system is designed to operate with up to40% of the total fuel coming from the re-generation flow.With the Lambda control system inactive,only small regeneration quantities are ac-cepted, as there would be no controlmechanism capable of compensating forthe mixture deviations that would occur.The valve closes immediately in the over-run fuel cutoff mode to prevent unburnedgasoline vapors from entering the cata-lytic converter.

Knock controlElectronic control of the ignition timingallows extremely precise adjustments ofthe ignition-advance angle based on en-gine rpm, temperature and load factor.Nevertheless, a substantial safety marginto the knock limit must be maintained.This margin is necessary in order to en-sure that no cylinder will reach or gobeyond its preignition limit, even whensusceptibility is increased by risk factorssuch as engine tolerances, aging, en-vironmental conditions and fuel quality.The resulting engine design, with its fixedsafety margin, is characterized by lowercompression and reduced ignition ad-vance. The ultimate results are sacrificesin fuel economy and torque.These liabilities can be avoided by usinga knock sensor, whereby experience hasshown that the compression ratio can beraised with accompanying improvementsin both fuel economy and torque. Withthis device, it is no longer necessary toselect the default ignition advance anglewith the most knock-sensitive conditionsin mind. Instead, a best-case scenariocan be used (e.g., engine compression at lower tolerance limit, optimum fuelquality, cylinder with minimum preignitiontendency). This makes it possible tooperate each individual cylinder at thepreignition limit for optimum efficiency invirtually all operating ranges for the life of the vehicle.The essential prerequisite allowing thiskind of ignition-angle program is reliablerecognition of all preignition beyond aspecified intensity, extending to every

Operating conditions

49

Canister-purge valve

1 Hose connection, 2 Non-return valve, 3 Leaf spring, 4 Sealing element, 5 Solenoid armature, 6 Sealing seat, 7 Solenoid coil.

1

2

3

4

5

6

7

1

Fig. 9

UM

K07

08-1

Y

cylinder and throughout the engine’s en-tire operating range. The knock sensorsare solid-body sonic detectors installedat one or several suitable points on theengine. Here they detect the charac-teristic oscillation patterns that ac-company knock and transform them intoelectrical signals before transmittingthem to the Motronic ECU for processing.This ECU employs a special processingalgorithm to detect incipient preignition inany of the combustion cycles in the res-pective cylinders. When this condition isrecognized, the ignition advance angle isreduced by a programmed increment.When the knock danger subsides, theignition for the affected cylinder is thenslowly advanced back to the default set-ting. The knock recognition and knock-control algorithms are designed to pre-vent the kind of preignition that results inengine damage as well as audible knock(Fig. 10).

Adaptation Real-world engine operation results inthe individual cylinders having differentknock limits, and therefore different ig-nition points. In order to adapt the defaultvalues to reflect the respective knocklimits under varying operating conditions,individual ignition-retard increments arestored for each cylinder.The data are stored in the non-volatilememory programs in the permanentRAM for engine speed and load factor.This allows the engine to be operated atoptimum efficiency under all operatingconditions without any danger of audiblecombustion knock, even during abruptchanges in load and rpm. The engine can even be approved foroperation with fuels having a low anti-knock quality. Generally, the engine is ad-justed for use with premium-gradegasoline. Operation with regular-gradegasoline can also be approved.

Knock control on turbocharged enginesSystems combining boost pressure andknock control are especially effective onengines with exhaust-gas turbochargers.

The initial response to ignition knock is toreduce the timing advance angle. Furtheraction to reduce the pre-ignition ten-dency in the form of a reduction in boostpressure is initiated only once the ig-nition-retard limit – which varies ac-cording to the temperature of the exhaustgas – has been reached. This makes itpossible to maintain exhaust-gas tem-peratures within acceptable limits whileoperating the turbocharged engine at theknock limit for optimum efficiency.

Boost-pressure controlTurbocharger boostThe exhaust-gas turbocharger has pre-vailed in the face of competition fromother supercharging methods, such aspressure-wave and mechnical super-charging. Turbochargers make it pos-sible to achieve high torque and outputfrom small-displacement, high-efficiencypowerplants. Because a turbochargedengine can be smaller than its naturally-aspirated counterpart producing thesame amount of power, it boasts a higherpower-to-weight ratio.Automotive industry research has dem-onstrated that compared to a standardnaturally aspirated engine, a small-dis-placement turbocharged engine with el-ectronic boost control can provide impro-vements in fuel economy equal to thoseachieved with a prechamber diesel. The

M-Motronic

50

Closed-loop knock control

Control algorithm with active ignition interventionon 4-cylinder engine.K1. . . 3 Knock at cylinders 1 . . . 3 (no knock atcylinder 4)a Ignition retard, b Step width for advance, c Advance.

a b c

K1 K2 1 3 K1 K3

1

2

4

3

1 1 1 1 1 1Cyl.

αz

Igni

tion

adva

nce

angl

e

Cycles

Cyl.

Fig. 10

UM

Z00

20E

main components of the exhaust-gasturbocharger are the compressor and theexhaust-gas impeller mounted on theother side of the same shaft. The ex-haust-gas turbocharger transforms aportion of the energy in the exhaust gasinto the rotation energy used to power thecompressor. This, in turn, draws in freshair and compresses it before blowing itthrough the intercooler, throttle valve, in-take manifold and into the engine.

Actuators for exhaust-gas turbochargersPassenger-car engines must be capableof generating substantial torque at low

engine speeds. This is the reason whythe turbocharger housing is dimensionedto operate most efficiently with lowermass exhaust-gas flow rates (forexample, full load at n = 2,000 min–1). Toprevent the turbocharger from over-loading the engine at higher exhaust-gasmass flow rates, a bypass mechanism(waste gate) must be included in thehousing to divert a portion of the flowaround the turbine and into the down-stream exhaust system. The bypassvalve generally assumes the form of aflap in the turbine housing. Less commonis a disk valve installed parallel to theturbine in a separate housing. Variableturbine geometry has still not been usedfor spark-ignition engines, but could alsobe combined with boost-pressure control(Figure 11).

Boost-pressure (closed-loop) controlPneumatic-mechanical closed-loop con-trol systems use a turbocharger actuatordirectly exposed to the boost pressure atthe turbocharger outlet. This layout pro-vides only limited latitude for tailoring theprogression of the torque curve throughthe engine speed range. There is only afull-load limit. It is not possible to providecontrol compensation for tolerances atfull-load boost. At part load the closed by-pass valve reduces efficiency. Acceler-ation from low engine speeds can beaccompanied by delayed turbochargerreaction (turbo lag).These disadvantages can be avoidedwith electronic boost-pressure control(Fig. 11). The specific fuel consumptioncan be reduced in some part-throttleoperating ranges. The system operatesby opening the bypass valve, with thefollowing results:– Residual work on the part of the engine

and turbine output are reduced,– Pressure and temperature at the com-

pressor outlet are lowered, and– The pressure differential at the throttle

valve is lowered.

Operating conditions

51

Actuator for electronicboost-pressure control

1 Pulse valve,p2 Boost pressure,pD Pressure in diaphragm unit,TVM Triggering signal from ECU

to pulse valve,VT Flow volume through turbine,VWG Flow volume through waste gate.

1

pD

VWG

VT

TVM

p2

Fig. 11

UM

K13

20Y

A linear relationship between torquecurve and throttle-valve angle is also ob-tained, with improved sensitivity at theaccelerator pedal. In order to provide theimprovements listed above, the exhaust-gas turbocharger and the actuator mustbe perfectly adapted for use in the in-dividual engine. The affected elements inthe actuator are:– The electropneumatic pulse valve,– The effective diaphragm surface, stroke

and spring in the diaphragm unit, and– The diameter of the valve disk/flap at

the wastegate.

Depending upon the load sensor, the set-points stored in the M-Motronic ECU withelectronic boost-pressure control are forpressure, air quantity or air mass. Thesetpoints for various engine speeds andthrottle-valve angles are stored in a pro-gram map.

Actuators within the closed-loop controlcircuit adjust the monitored actual valueto coincide with the value prescribed forthe particular operating conditions. Thecalculated value is transmitted throughthe controller output in the form of a sig-nal (pulse-width modulated) to the pulsevalve. Within the actuator this signalmodifies the control pressure and thestroke to change the effective opening atthe bypass valve.

The temperature of the exhaust gasesbetween the turbocharged engine andthe turbine should never be allowed toexceed certain limits. This is why Boschonly uses boost-pressure control in con-junction with knock control. Knock controlis the only means of allowing the engineto run with the maximum potential ig-nition advance throughout its service life.Running the engine at the optimal ig-nition advance angle for the specificoperating conditions results in extremelylow exhaust-gas temperatures.

Additional adjustments to boost pressureand/or mixture can be used to lower thetemperature of the exhaust gas evenfurther.

Limiting engine and vehicle speedExtremely high engine speeds can leadto destruction of the engine (valve train,pistons). Engine-speed limiting preventsthe maximum approved engine speed(redline) from being exceeded.M-Motronic provides the option of re-stricting engine and vehicle speed byphasing out the injection.

When the maximum engine speed n0 (orthe maximum vehicle speed) is exceed-ed, the unit responds by suppressing theinjection signals. This limits the speed ofthe engine (or vehicle).

The injection resumes normal operationonce the speed falls below a narrow threshold.This process is repeated at rapid inter-vals within an engine-speed tolerancerange located around the prescribedmaximum.

A reduction in operating response andsmoothness calls the driver’s attention tothe engine speed and provides the mo-tivation for an appropriate response.Figure 12 illustrates the engine-speedcurve’s reaction to the engine-speed limi-tation.

M-Motronic

52

Limiting maximum engine speed n0by suppressing injection pulsesa Fuel-cutoff range.

min

s00

6,500

6,000

–1

Time

Eng

ine

spee

d

t

n

150 min–1

noa

Fig. 12

UM

K00

34E

Exhaust-gas recirculation(EGR)During valve overlap a certain amount ofresidual gas is returned from the com-bustion chamber to the intake manifold.This recirculated gas is then entrainedalong with the fresh air on the next intakestroke.The actual amount of recirculated gas is determined by the valve overlap, and is thus a fixed variable relative to the various points on the operating curve.The proportion of recirculated gas can beadjusted using either “external” exhaust-gas recirculation (EGR) with a M-Motro-nic-controlled exhaust-gas recirculationvalve (Fig. 13), or with variable camshafttiming.Up to a certain point, at least, larger amounts of recirculated gas can exercisea positive effect on energy conversionand thus on fuel consumption. An in-crease in recirculated gas also leads tolower combustion-chamber tempera-tures with corresponding reductions inthe NOx emission.At the same time, once a certain point is passed a higher residual-gas com-ponent will lead to incomplete com-bustion. The results here are higheremissions of unburned hydrocarbons,increased fuel consumption and roughidling (Figure 14).

Operating conditions

53

1 1

2

3

4

5

n

Effect of residual exhaust-gas recirculation onfuel consumption and emissions

1 Excess-air factor λ (residual exhaust-gascomponent RG = constant),2 Recirculated gas component RG (λ = constant).

ppm

ppm

0.9 1.0 1.1 1.2 1.3 1.4 1.5

0.16 0.36 0.56 0.76

Excess-air factor λ (RG=const.)

Recirculated exhaust-gascontent RG (λ=const.)

NO

X-e

mis

sion

HC

-em

issi

onS

peci

fic fu

el c

onsu

mpt

ion

g/kWh

1

2

1

2

12

Fig. 13Fig. 14

UM

K13

21E

Exhaust-gas recirculation (example).

1 Exhaust-gas recirculation (EGR),2 Electropneumatic converter,3 EGR valve,4 ECU, 5 Air-mass meter.n Engine speed.

UM

K09

13-2

Y

Camshaft timing

Camshaft timing can influence the spark-ignition engine in a variety of ways:– Higher torque and output, lower emis-

sions and fuel consumption,– Control of the mixture composition, and,– Graduated or infinitely-variable intake

and exhaust adjustment.

“Intake closes” timing plays a decisiverole in determining the amount of cylindercharge for a given engine speed. Whenthe intake valve closes early, maximumair will be inducted at low rpm, while lon-ger intake durations shift the maximumtoward higher engine speed ranges.

The phase in which the valves overlap (at“intake opens” and “exhaust closes”) de-termines the amount of internal residual-gas recirculation.

Longer “valve open” durations due to ad-vanced intake-valve timing will raise theproportion of recirculated gas, as they in-crease the mass of the gas returned tothe intake manifold for reinduction. Thisreduces the mass of fresh air beingdrawn in at a given throttle-valve open-ing; at any given load point the throttlevalve must open further to compensate.This “dethrottling” effect reduces the gas-exchange circuit to improve efficiencyand lower fuel consumption.The proportion of recirculated gas sinkswhen the intake cycle is shifted toward“retard.” This provides improvements infuel economy and operating smooth-ness.

Variable camshaft angleHydraulic or electric actuators turn thecamshaft by increments correspondingto specified engine speeds or operatingpoints (this system requires that at least one intake and one exhaust cam-shaft be located in the cylinder head).This varies the timing for “intake/exhaustopens” and/or “intake/exhaust closes”(Figure 15). As an example, if the actuators turn the intake camshaft to delay “intake

opens/closes” at idle or at high rpm, theresult will be a reduction in the proportionof recirculated gases at idle, or enhancedcylinder charging at higher enginespeeds.When the intake camshaft is turned to-ward earlier “intake opens/closes” at lowor moderate engine speeds or in certainload ranges, the result is a higher maxi-mum air charge to the cylinder.This would also lead to a larger propor-tion of recirculated gas in the part-throttle range, with corresponding ef-fects on fuel consumption and exhaustemissions.

M-Motronic

54

Intake camshaft rotation

1 Retarded, 2 Normal, 3 Advanced.

Variable camshaft timing

1 Standard, 2 Auxiliary lobes.

300° 360° 420° 480° 540° 600°TDC BDC

0

Str

oke

sIntake(adjustable)

Exhaust(fixed)

1

Crankshaft angle

2

3

Crankshaft angle

240° 360° 480° 600°BDC

0

Str

oke

s

Intake(adjustable)

Exhaust(adjustable

TDCBDC120°

1

1

22

Fig. 15

Fig. 16U

MM

0446

-2E

UM

M04

47-2

E

Camshaft lobe controlSystems with camshaft lobe controlmodify the valve timing by alternatelyactivating cam lobes with two differentshapes. The first lobe supplies optimumvalve timing and lift for intake and ex-haust valves during lower and mid-rangeoperation. A second cam lobe provideslonger valve-opening times and lift, andbecomes operational when the rockerarm to which it is connected is lockedonto the standard rocker arm in responseto engine speed (Figure 16).

An optimal but complicated process isinfinitely-variable valve timing and liftadjustment. This concept employs camlobes with 3-dimensional geometry andsliding camshafts to provide maximumlatitude in engine design (Figure 17).

Operating conditions

55

a b

Fig. 17

Infinitely-variable valve timing and lift adjustment

a minimum, b maximum lift.

UM

M04

48-1

Y

Variable-geometry intakemanifoldThe tandem objectives of engine designare maximum torque at low enginespeeds and high output at the ratedmaximum. The engine’s torque curve isproportional to the mass of the intake airas a function of engine speed.

One effective means of influencing torque is to provide the intake manifoldwith the appropriate geometrical con-figuration. The simplest method for pro-viding intake boost is to exploit the dynamics of the incoming air. To ensurebalanced distribution of the air-fuel mix-ture, intake manifolds for carburetor orsingle-point (Mono-Jetronic) injectionsystems need short intake runners withminimal variations in lengths.

The intake runners for multipoint systemstransport only air; the injectors dischargethe fuel. This arrangement offers a widerrange of options in intake-manifold de-

sign. The standard manifold for a multi-point injection system consists of indivi-dual curved runners and a plenum cham-ber with throttle valve.

General principles:– Short curved runners allow high maxi-

mum output accompanied by sacrifi-ces in torque at lower engine speeds;whereby long runners provide an in-verse response pattern.

– Large-volume plenum chambers canprovide resonance effects in certainengine-speed ranges, leading to im-proved cylinder filling. They are alsosubject to potential faults in dynamicresponse; these assume the form ofmixture variations under rapid loadchange.

Variable intake-manifold geometry canbe used to obtain an almost ideal torquecurve. Geometry can be changed for in-stance as a function of engine load, en-gine speed, and throttle-valve setting.Various changes are possible:

Variable-geometry intake systems

Switchable: a two-stage, b three-stage.A, B Cylinder groups; 1, 2 Flaps, engine speeddetermines opening time.

Resonance “supercharging”

a Configuration, b Curve of air input.1 Resonator runner, 2 Resonance chamber, 3 Cylinders, 4 With resonance boost,5 Normal intake manifold.

M-Motronic

56

1

2

3

a

Engine speed n

Cha

rge

dens

ity

λ a14

5

b

Engine

a A B

1

b A

B

21

1

Fig. 18 Fig. 19

UM

M04

53E

UM

M04

54Y

– Runner-length adjustment,– Change-over between runner lengths

or runner diameters,– In case of multiple runners, the selec-

tive cutoff of an individual runner foreach cylinder,

– Changeover between different ple-num-chamber volumes.

Intake oscillation boostEach cylinder has an individual, fixed-length intake runner, usually connectedto a plenum chamber. The energy bal-ance is defined by a process in which theinduction force from the piston is con-verted into kinetic energy in the gascolumn upstream from the intake valve.This kinetic energy then serves to com-press the fresh charge.

Resonance boostResonance boost systems use short run-ners to connect groups of cylinders withequal ignition intervals to resonancechambers. These, in turn, are connectedvia resonance tubes to the atmosphere

or a plenum chamber, allowing them toact as Helmholtz resonators (Figure 18).

Variable-geometry intake systemsBoth types of dynamic superchargingaugment the achievable cylinder charge,especially in the lower engine-speedrange.

Variable-response intake systems usedevices such as flaps to separate andconnect system areas assigned to vari-ous groups of cylinders (Figure 19).Variable-length intake runners operatewith the first resonance chamber at lowrpm. The length of the runner changes as engine speed increases, at whichpoint a second resonance chamberopens (Figure 20).Figure 21 shows the effects of variable in-take-runner geometry on the brake meaneffective pressure (bmep), which is usedas an index for cylinder charging.

Operating conditions

57

1

23

4

5

6 7

8

Infinitely-variable length intake system

1 Fixed housing,2 Rotating drum (air distributor),3 Drum air-supply opening,4 Air-supply opening for intake runners,5 Seal (e.g., leaf spring),6 Intake runners,7 Intake valve,8 Intake air stream.

min–12,000 4,000Engine speed n

7

8

9

10

11

Bra

ke m

ean

effe

ctiv

e pr

essu

re p

me

L1= 640mm, D1=36 mmL1= 950mm, D1=36 mm

L1= 330mm, D1= 40mm

12

bar

Brake mean effective pressure relative toengine speed at three lengths of the variable-geometry intake system

L1 Effective intake-runner length,D1 Intake-runner diameter.

Fig. 20 Fig. 21

UM

K09

10-1

Y

UM

K09

11E

Integrated diagnosis

Diagnostic procedureAn “on-board diagnosis (OBD) system” is standard equipment with M-Motronic.This integral diagnostic unit monitorsECU commands and system responses.It also checks the individual sensor sig-nals for plausibility. This test procedure is carried out constantly during normalvehicle operation.The ECU stores recognized errors to-gether with the operating conditions un-der which they occurred. When the ve-hicle is serviced, a tester can be used toread out and display the stored errorsthrough a standardized interface. The in-formation facilitates trouble-shooting forthe service personnel.In response to the demands of the Cali-fornia Air Resources Board, (CARB),diagnosis procedures extending far be-yond those in earlier tests have beendeveloped. All components whose failurecould cause a substantial increase inharmful emissions must be monitored.

Diagnosis areasAir-mass meterThe process for monitoring the air-massmeter provides an example of the M-Mo-tronic system’s self-diagnosis function.While the injection duration is being deter-mined on the basis of intake-air mass, asupplementary comparison injection timeis calculated from throttle-valve angle andengine speed. If the ECU discovers an ex-cessive variance between the two, its in-itial response is to store a record of the er-ror. As vehicle operation continues, plau-sibility checks determine which of thesensors is defective. The control unit doesnot store the corre-sponding error codeuntil it has unequivocally determinedwhich sensor is at fault.

Combustion missCombustion miss, as can result fromfactors such as worn spark plugs or faultyelectrical contacts, allows unburned mix-ture to enter the catalytic converter. Thismixture can destroy the converter, andrepresents an extra load on the environ-ment. Because even isolated combustionfailures result in higher emissions, thesystem must be able to recognize them.Figure 1 shows the effects of combustionmiss on emissions of hydrocarbons (HC),carbon monoxide (CO) and oxides ofnitrogen (NOX).Many potential methods of detectingcombustion miss were tested, and moni-toring the running response of thecrankshaft proved to be the most suit-able. Combustion miss is accompaniedby a shortfall in torque equal to the in-crement which would normally have been generated in the cycle where theerror occured. The result is a reduction inrotation speed. At high speeds and lowloads the interval from ignition to ignition(period duration) is extended by only0.2%. This means that the rotation mustbe monitored with extreme precision,while extensive computations are also re-quired to distinguish combustion missfrom other interference factors.

Catalytic converterYet another diagnostic function monitorsthe efficiency of the catalytic converter.For this purpose the Lambda oxygensensor upstream of the catalytic con-verter is supplemented by a seconddownstream oxygen sensor. A correctly-operating converter will store oxygen,thus attenuating the Lambda controloscillations. As the catalytic converterages, this response deteriorates untilfinally the signal pattern from the up-stream sensor approaches that receivedfrom the downstream sensor. A compari-son of the signals from the oxygen sen-sors thus provides the basis for deter-mining the catalytic converter’s con-dition. A warning lamp alerts the driver inthe event of a defect.

M-Motronic

58

Lambda oxygen sensorA stoichiometric air-fuel mixture must bemaintained if the catalytic converter is toperform to its full potential. This is takencare of by the signals from the Lambdaoxygen sensors. The fact that two oxy-gen sensors are fitted in each exhausttract makes it possible to use the sensordownstream from the converter to checkfor control variations in the upstream unit.A Lambda oxygen sensor that has beenexposed to excessive heat for a con-siderable period of time may react moreslowly to changes in the air-fuel mixture.This increases the period duration for the Lambda control’s two-state controller(Figure 2). A diagnosis function monitorsthis control frequency and informs thedriver of excessive delays in sensor re-sponse via warning lamp.The Lambda oxygen sensors’ heatingresistance is checked by measuring cur-rent and voltage. The M-Motronic ECUcontrols the heater resistance elementdirectly, with no relay in between, to allowthis test to be performed. The sensor sig-nal is subjected continuously to plausibi-lity checks, and the system responds toimplausible signals by denying access toother functions depending upon theLambda control. The appropriate errorcode is also stored in the fault memory.

Fuel supplyWhen the air-fuel mixture deviates fromstoichiometric for extended periods oftime, this condition is taken into accounttogether with the mixture adaptation. Ifthe deviations exceed specific pre-defined limits, this indicates that a fuel-system component or a fuel-meteringdevice has moved outside specificationtolerances. An example would be a faultypressure regulator or load sensor,whereby the error could also stem from a leak in the intake manifold or exhaustsystem.

Integrated diagnosis

59

Exhaust emissions relative to combustion-miss rate

Engine: 6-cylinder, 2.8 litreUS 94 emissions limitsHC = 0.25 g/mileCO = 3.40 g/mileNOx = 0.40 g/mile

Monitoring the Lambda oxygen sensor’s dyna-mic response pattern

a New sensor, b Aged Type II sensor,c Aged Type III sensor.

200

150

100

50

0 0 1 2

Miss rate

Exh

aust

em

issi

ons

(% o

f lim

it)

250

3 %

HC

CO

NOX

a

Sen

sor

volta

ge

b

c

Sen

sor

volta

ge

T = 3 s

T = 8 s

T = 11 s

0 10 20 30 40 s

Time

Sen

sor

volta

ge

Fig. 1Fig. 2

UM

K13

23E

UM

K13

22E

Secondary-air injectionThe secondary-air injection activatedafter cold starts must also be monitored,as its failure would also influence emis-sions. This can be done using the signalsfrom the Lambda oxygen sensors whenthe secondary-air injection is active, or itcan be activated and observed at idleusing a Lambda control test function.

Exhaust-gas recirculation (EGR)Various options are available for diag-nosing the exhaust-gas recirculationsystem, whereby two are in general use.With the first option, a sensor monitorsthe temperature increase at the locationwhere the hot exhaust gases return to the intake manifold while the EGR isoperating.

With the second procedure, the exhaust-gas recirculation valve (EGR valve) isopened all the way with the vehicle ontrailing throttle (overrun fuel cutoff). Theexhaust gases flowing into the intake ma-

nifold cause its internal pressure to rise.A pressure sensor measures and evalu-ates the increase in manifold pressure.

Tank systemEmissions emanating from the exhaustsystem are not the only source of en-vironmental concern; fuel vapors fromthe fuel tank are also a problem. In thenear term the legal requirements will belimited to a relatively simple check ofcanister-purge valve operation. A meansof recognizing leaks in the evaporative-emissions storage system will be re-quired at a later date. Figure 3 illustratesthe basic principle employed for thisdiagnosis. A cutoff valve closes off thestorage system.Then, preferably with the engine idling,the canister-purge valve is opened andthe intake-manifold pressure spreadsthrough the system. An in-tank pressuresensor monitors the pressure build-up todetermine whether leaks are present.

M-Motronic

60

Vacuum test to detect leaks in evaporative-emissions control system

1 Intake manifold, 2 Canister-purge valve, 3 Shutoff valve, 4 Fuel tank, 5 Pressure differential sensor, 6 Safety valve.

3

1

24

56

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Fig. 3

UM

K13

24Y

Other monitoring devicesThe main emphasis of the new statutesapplies to the engine-management sys-tem, but other systems (for instance,automatic transmission) are also moni-tored. These report any faults to theengine-management ECU, which thenassumes responsibility for triggering thediagnosis lamp. Greater system com-plexity and ever more stringent environ-mental regulations are making diagnosisincreasingly important.

Emergency running mode(limp-home)In the interval between the initial occur-rence of a fault and vehicle service, de-fault settings and emergency-runningfunctions assume responsibility for theignition and air-fuel mixture. This allowsthe vehicle to continue operating, albeitwith sacrifices in driving comfort. The

ECU responds to errors that have beenrecognized in an input circuit by replacingthe missing information or reverting to adefault value.When an output unit fails, specific backup measures corresponding to theindividual problem are implemented.Thus the ECU reacts to a defect in theignition circuit by switching off the fuelinjection at the affected cylinder in orderto prevent damage to the catalytic converter.

When the vehicle is serviced, the Boschengine tester can be used to read out anddisplay the faults and errors detectedduring operation (Figure 4).

Integrated diagnosis

61

Bosch engine tester

UW

T00

60Y

Fig. 4

ECU

FunctionThe ECU is the “computer and controlcenter” for the engine-management system. It employs stored functions andalgorithms (processing programs) to pro-cess the input signals transmitted by thesensors. These signals serve as thebasis for calculating the control signals tothe actuators (e.g., ignition coil, injectors)which it manages directly via power out-put stages (Figure 1).

Physical designThe ECU is a metal housing containing a printed-circuit board with electroniccomponentry. A multiple-terminal plug connector provides the link between ECU andsensors, actuators and power supply.Depending upon the specific ECU andthe number of system functions, the plug can be of 35-, 55- or 88-poledesign.

The amplifiers and power output com-ponents for direct actuator control are in-stalled on heat sinks in the ECU. Efficientheat transfer to the bodywork is neces-sary due to the the amount of heat thatthese components produce.

Environmental conditionsThe ECU must withstand temperatureextremes, moisture and mechanicalloads with absolutely no impairment ofoperation. Resistance to electromagneticinterference, and the ability to suppressradiation of high-frequency static, mustalso be of a high order.

The ECU must be capable of errorlesssignal processing within an operatingrange extending from – 30°C to +60°C, at battery voltages that range from 6 V(during starting) to 15 V.

Power supplyA voltage regulator provides the ECUwith the constant 5 V operating voltageneeded for the digital circuitry.

Signal inputsVarious processes are employed totransmit the input signals to the ECU.The signals are conducted through pro-tective circuits, while signal convertersand amplifiers may also be present. Themicroprocessor can process these sig-nals directly.

An analog/digital converter (A/D) withinthe microprocessor transforms analogsignals (for instance, information on in-take-air quantity, temperature of engineand intake air, battery voltage, Lambdaoxygen sensor) into digital form.The signal from the inductive sensor withinformation on engine speed and crank-shaft reference point is processed in aspecial circuit to suppress interferencepulses.

Signal processingThe input signals are processed by themicroprocessor within the ECU. In orderto function, this microprocessor must beequipped with a signal-processing pro-gram stored in a non-volatile memory(ROM or EPROM). This memory alsocontains the specific individual perform-ance curves and program maps used forengine control.Due to the large number of engine andvehicle variations, some ECU’s are equipped with a special version-codefeature. This allows the manufacturer orservice technician to feed supplementaryprogram data into the program mapsstored in the EPROM, making it possibleto provide the operating characteristicsdesired for the particular version. Othertypes of ECU are designed to allow com-plete data banks to be programmed intothe EPROM at the end of production(end-of-line programming). This reducesthe number of individual ECU configur-ations required by the manufacturer.A read/write memory component (RAM)is needed for storing calculated valuesand adaptation factors as well as anysystem errors that may be detected (diagnosis). This RAM requires an unin-terrupted power supply to function prop-erly. This memory chip will lose all

M-Motronic

62

data if the vehicle battery is discon-nected. The ECU must then recalculatethe adaptation factors after the battery isreconnected. To prevent this, some unitstherefore use an EEPROM instead of aRAM to store these required variables.

Transmitting the signalThe output stages triggered by the micro-processor supply sufficient power fordirect control of the actuators. Theseoutput stages are protected against shortcircuits to ground, irregularities in batteryvoltage and electrical overload that coulddestroy them.

At several output stages, the OBD diag-nosis function recognizes errors and re-acts by deactivating (where necessary)the defective output. The error entry isstored in the RAM. The service tech-nician can then read out the error using atester connected to the serial interface.Another protective circuit operates in-dependently of the ECU to switch off the

electric fuel pump when the engine-speed signal falls below a certain level.When some ECU’s are switched off at theignition/steering lock (Terminal 15, or “ig-nition off”), a holding circuit holds themain relay open until program processingcan be completed.

ECU

63

Motronic block diagram

Sensors

Switch inputs:

Ignition OFF/ONCamshaft position

Vehicle speed

Gear

Transmission interventionAir conditioner

Analog inputs:Battery voltage

Engine temperatureIntake-air temperatureAir quantity

Throttle-valve angleLambda sensor

Knock sensor

......

RPM signalData/Address bus

RAM EPROM

A/D

RAM ROM

Signal

conditioning

Computer Output

stages

Actuators

Injector

.

.

.

.

.

Ignition coilFuel-pump relay

Main relay

Canister-purge valve

Idle actuatorFault lamp

Diagnosis

Fig. 1

UM

K13

25E

Interfaces to othersystems

System overviewIncreased application of electronic con-trol systems in vehicles in areas such as– Transmission control,– Electronic throttle control (EMS,

E-Gas, drive-by-wire),– Electronic engine management

(Motronic),– Antilock braking system (ABS),– Traction control system (TCS),– On-board computer, etc.,has made it necessary to combine therespective ECU’s in networks. Data com-munications between control systemsreduce the number of sensors and allowbetter exploitation of the individualsystem potentials. The interfaces can be divided into twocategories:– Conventional interfaces, with binary

signals (switch inputs), pulse-duty fac-tors (pulse-width-modulated signals),

– Serial data transmission, e.g., Control-ler Area Network (CAN).

Conventional interfacesIn conventional automotive data-com-munications systems, each signal is as-signed to a single line. Binary signals canonly be transmitted as one of the twoconditions “1” or “0” (binary code), for instance, air-conditioning compressor“ON” or “OFF”.Pulse-duty factors (potentiometer) canbe employed to relay more detailed data,such as throttle-valve aperture.The increasing levels of data exchangebetween the various electronic compo-nents in the vehicle means that conven-tional interfaces are no longer capable ofproviding satisfactory performance. Thecomplexity of today’s wiring harnesses is already difficult to manage, while therequirements for data communicationsbetween ECU’s are on the rise (Figure 1).These problems can be solved by using

CAN (Controller Area Network), a bussystem (bus bar) specially designed forautomotive use.Provided that the ECU’s are equippedwith a serial CAN interface, CAN can be used to relay the signals from thesources listed above.

Serial data transmission (CAN)There are three basic applications forCAN in motor vehicles:– To connect ECU’s,– Bodywork and convenience electron-

ics (Multiplex),– Mobile communications.The following is limited to a description ofcommunications between ECU’s.

ECU networkingHere electronic systems such as M-Motronic, electronic transmission control,etc. are combined within a single net-work. Typical transmission times lie be-tween approx. 125 kBit/s and 1MBit/s.These times must be high enough tomaintain the required real-time response.One of the advantages that serial datatransmission enjoys over conventional in-terfaces (e.g., pulse-duty factor, switch-ing and analog signals) is the highspeeds achieved without high loads onthe central processing units (CPU’s) inECU’s.

M-Motronic

64

Conventional data communications

GS Transmission control, ETC Electronic throttlecontrol, ABS Antilock braking system, TCS Traction control system, MSR Engine-drag torque control.

GS Motronic

ETC ABS/TCS/MSR

Fig. 1

UM

K13

26E

Bus configurationCAN works on the “multiple master” prin-ciple. This concept combines severalequal-priority ECU’s in a linear bus struc-ture (Figure 2). The advantage of thisstructure is the fact that failure of onesubscriber will not affect access for theothers. The probability of total failure isthus much lower than with other logicalarrangements (such as loop or star struc-tures). With loop or star architecture, fail-ure in one of the subscribers or the cen-tral ECU will result in total system failure.

Content-keyed addressingThe CAN bus system addresses the dataaccording to content. Each message isassigned a permanent 11-bit identifier.This identifier indicates the contents ofthe message (e.g., engine speed). Eachstation processes only those data whoseidentifiers are stored in its acceptance list(acceptance check). This means thatCAN does not need station addresses totransmit data, and the junctions do notneed to administer system configuration.

Bus arbitrationEach station can begin transmitting itshighest priority message as soon as thebus is free. If several stations start trans-mitting simultaneously, the resulting bus-access conflict is resolved using a “wired-and” arbitration arrangement. This arrangement assigns first access to

the message with the highest priority,with no loss of either time or data bits.When a station loses the arbitration, itautomatically reverts to standby statusand repeats its transmission attempt assoon as the bus indicates that it is nolonger occupied.

Message formatA data frame of less than 130 bits inlength is created for transmissions to thebus. This ensures that the queue timeuntil the next – possibly extremely urgent– data transmission is held to a minimum.The data frames consist of seven con-secutive fields.

StandardizationThe International Standards Organis-ation (ISO) has recognized CAN as astandard for use in automotive applica-tions with data streams of over 125kBit/s, along with two additional protocolsfor data rates up to 125 kBit/s.

Interfaces

65

Linear bus structure

Station1

Station2

Station3

Station4

Fig. 2

UA

E02

83D

(4.0)

1 987 722 161

KH/PDI-02.00-En

The Program Order NumberGasoline-engine management

Emission Control (for Gasoline Engines) 1 987 722 102Gasoline Fuel-Injection System K-Jetronic 1 987 722 159Gasoline Fuel-Injection System KE-Jetronic 1 987 722 101Gasoline Fuel-Injection System L-Jetronic 1 987 722 160Gasoline Fuel-Injection System Mono-Jetronic 1 987 722 105Ignition 1 987 722 154Spark Plugs 1 987 722 155M-Motronic Engine Management 1 987 722 161ME-Motronic Engine Management 1 987 722 178Diesel-engine managementDiesel Fuel-Injection: An Overview 1 987 722 104Diesel Accumulator Fuel-Injection SystemCommon Rail CR 1 987 722 175Diesel Fuel-Injection SystemsUnit Injector System / Unit Pump System 1 987 722 179Radial-Piston Distributor Fuel-InjectionPumps Type VR 1 987 722 174Diesel Distributor Fuel-Injection Pumps VE 1 987 722 164Diesel In-Line Fuel-Injection Pumps PE 1 987 722 162Governors for Diesel In-Line Fuel-Injection Pumps 1 987 722 163Automotive electrics/Automotive electronicsAlternators 1 987 722 156Batteries 1 987 722 153Starting Systems 1 987 722 170Electrical Symbols and Circuit Diagrams 1 987 722 169Lighting Technology 1 987 722 176Safety, Comfort and Convenience Systems 1 987 722 150Driving and road-safety systemsCompressed-Air Systems for CommercialVehicles (1): Systems and Schematic Diagrams 1 987 722 165Compressed-Air Systems for CommercialVehicles (2): Equipment 1 987 722 166Brake Systems for Passenger Cars 1 987 722 103ESP Electronic Stability Program 1 987 722 177

Automotive electric/electronic systems

Safety, Comfort and

Convenience Systems

Technical Instruction

æ

Æ

Automotive Electric/Electronic Systems

Lighting Technology

Technical Instruction

æ

Æ

Vehicle safety systems for passenger cars

ESP Electronic Stability Program

Technical Instruction

æ

Æ

Engine management for diesel engines

Radial-Piston Distributor

Fuel-injection Pumps Type VR

Technical Instruction

æ

Æ

Electronic engine management for diesel engines

Diesel Acumulator Fuel-Injection

System Common Rail

Technical Instruction

æ

Æ

Engine management for spark-ignition engines

Emission Control

Technical Instruction

æ

Æ

Gasoline-engine managementME-Motronic

Engine Management

Technical Instruction

æ

ÆEngine management for spark-ignition engines

Spark Plugs

Technical Instruction

æ

Æ

Brake systems for passenger cars

Brake Systems

Technical Instruction

æ

Æ