Fig. 3 shows a section at right angles to the crankshaftaxis; important technical data are listed in Table 1.

the New Beetle (sectional view)

Table 1: Technical Data of the 1.91 TDI New Beetle

Type: 4-Stroke DieselNo. of Cylinders: 4 In-LineDisplacement (cc): 1896Bore x Stroke (mm): 79.5 x 95.5Compression Ratio: 19.5Cylinder Distance (mm): 88Crankshaft Main BearingDiameter (mm): 54Crankshaft-end BearingDiameter (mm): 47.8Connecting Rod Length (mm:): 144Intake Valve Diameter (mm): 36Outlet Valve Diameter (mm): 31.5Induction: TurbochargedTurbocharger: VNT (Garret)Combustion System: Direct InjectionValve Configuration: OHCInjection Pump: Bosch VE VP 37

3

Plunger-Diameter:

Injector Nozzle:

10 mm (Manual ShiftVersion)11 mm (AutomaticVersion)5-Hole-Orifice-SeatNozzleHole HydrodynamicallyRounded

Performance-Data:

Max. Output (kW/rpm): 66/3750Max. Torque (Nm/rpm): 21 O/l 900Volumetric Efficiency (kW/!): 34.8Maximum Mean EffectivePressure (bar): 14Piston Speed at Rated EngineSpeed (m/s): 12.7

240

80

...

8,

c

\

I I I I *f--YI I I �e l I I�

--r --T--,-~*,---,---Tt-

- -& - - 1- - ..! - - -I- _ -I- - - L

*I I I I I ’ ‘.

* i I I I I

8 I

1 ;

&-T-+--’, - - -I- - -’’ :

r--r--

1000 1500 2000 2500 3000 3500 4000 4500

Engine Speed [rpm]

Fig. 4: Performance Data New Beetle 1.91 TDI MY’98

MODIFIED OIL CIRCUIT

One of the most significant changes made to theoil circuit is that the pressurised oil is controlled at theclean-oil end. This primarily results in a faster build-upof oil pressure which in turn has a positive influence onwear (shorter mixed friction time after cold starting).A further innovation is the introduction of a vertical oilfilter for simple maintenanc:e, as it is now quick and easyto replace. In the interests #of recycling, the filter is madeof fully incineratable material. Fig. 5 shows the modifiedoil circuit.

MODIFICATIONS FOR THE AMERICAN MARKET

The basic engine for use in Europe had to bemodified for the American market and further develop-ments incorporated to satisfy the conditions outlinedbelow:l The stringent emission limits applying to diesel

engines in Californial The mandatory fitting of an on-board diagnostic

system for diesel enginesl Special topographical and climatic usage conditionsl Driving style and habits different from those in

Europel Different fuels and lubricants with unfavourable

properties in some cases

FUEL INJECTION SYSTEM

The current lack of an effective means of exhausttreatment capable of diminishing both reducible andoxidizable pollutant levels lends particular significanceto pollutant prevention in diesel engines. The bestpossible mixture-formation quality and pinpointedcontrol of the combustion process are major factorsinfluencing compliance with stringent emission limits.

Fig. 5: Oil circuit

INJECTION PRESSURE AS A MEANS OFREDUCING EMISSIONS

The New Beetle features two different types offuel-injection equipment. In vehicles with manual shift,the Ll injection pump used in the 110 hp version of theTDI provides a plunger chamber pressure of 800 bar.Vehicles with automatic gearbox place particularlyexacting requirements on the fuel-injection equipment,as the mean effective pressure level is higher. This ledto the development of a higher-performance version ofthe injection pump. Enlarging the diameter of theinjection-pump plunger from 10 to 11 mm in conjunctionwith measures designed to provide greater strengthmade it possible to increase the pressure in the plungerchamber to 950 bar. The required quantity can thus beinjected in the limited time available using extremelysmall nozzle holes. A further approx. 20% reduction inparticulate emissions can be achieved.

The optimised design of the hydraulic com-ponents of the injection system permits an increase inpressure between plunger chamber and injector nozzle.

Fig. 6 shows the injection pressures at ratedpower in the plunger chamber and the nozzle pressuresboosted by the pressure surge.

1500

1250

= 1000.zy 750582 5000

250

0Pump Side Nozzle PressurePressure

---------Fig. 6: Comparison of plunger chamber and pressure

upstream of nozzle on New Beetle with manualshift (Ll pump) and automatic gearboxV-2 pump)

A problematic aspect of the operating principleis however that the pressure is governed by the quantityinjected and engine speed, with the result that themaximum injection pressure is reached at rated power.With the current design concept, the injection pressurelevels attained are such that acoustic problems wouldbe encountered if they were to be significantly increasedstill further. Fig. 7 shows the pressures at the injectornozzle along a load curve at 2000 rpm for the injectionpump used in the automatic gearbox version. As canbe seen, there is still plenty of potential in this range inparticular for reducing emissions by increasing injectionpressure. Future high-pressure injection systems willbring about improvements in this area.

y 1000ii2 8003z$ 6000)

-ii 400E.z 200c,

I I I I I I----_-----------___------I I I I I 1I I I I I 1 I Iz.-c.- 0

0 2 4 6 8 10 12 14 16mean effective pressure [bar]

Fig. 7: Injection pressure along a load curveat 2000 rpm

CALCULATION AND DESIGN DETAILS OFINJECTOR NOZZLES

The engine can only fully benefit from the goodperformance of the fuel-injection equipment if theassemblies downstream of the pressure source areprecisely coordinated. This can involve, for example,an increase in pressure between injection pump andinjector nozzle or specific optimisation of the flow ratein the holes as well. The aim of engine coordination asdiscussed in this paper is to achieve the highest possibleflow rate, thus avoiding unnecessary pressure loss andreducing cavitation. A particularly critical aspect of aninclined installation position such as the one involvedhere is the achievement of proper coordination of theindividual holes with their various angles to the nozzleaxis of symmetry.

For this fine coordination work, a three-dimen-sional FEM model was created to illustrate the innercontour of the injector nozzle (Fig. 8).

Fig. 8: 3D FEM model of inner contour of

5injector nozzle

The flow rate was first calculated for a situationin which the fuel flows directly out of the nozzle bodyinto a sharp-edged hole. It can be seen that the flowcharacteristics vary greatly from hole to hole (Fig. 9 a).The flow is at its least uniform in the hole where thedeflection angle is most pronounced, resulting inwidespread zones with a low flow velocity and thus alsoa reduced volumetric flow rate. This leads to an irregulardistribution of the quantities injected with the same inletpressures at all holes.

Fig. 10 a shows the flow velocity distributionperpendicular to the hole axis taking a nozzle hole withlarge deflection angle as an example.

As is clearly apparent from Fig. 9 b, rounding ofthe hole inlet produces a far more uniform flow. Theflow rate is enhanced and the danger of cavitationreduced. The flow profile in the cross section alsoreveals a greatly improved flow. A slight loss of velocityis only encountered on entering the hole.

Such optimised injector nozzles result in a farlower emission level and the injection pressuregenerated in the injection pump is converted into kineticenergy by the injector nozzle with a lower rate of loss.

a>

Fig. 9: Flow velocity in hoiiesa) With sharp-edged inletb) With flow optimised by roundingof the inlet edge

200 .0

MAGNITUDEMLOCIM

LOCAL MX-LOCAL MN=

MAGNITUDEvELoclM

LOCAL MX=LOCAL MN= 0.0

6

Fig. 10: Flow velocity profile in the holes at the followingpositions:# I ) Entry into hole,# II) 0.02 mm after entering hole,# Ill) 0.05 mm after entering hole,#IV) exit from hole

a) With sharp-edged inletb) With flow optimised by rounding of the inlet edge

Extensive utilisation of this method and parallelverification by way of experiment can achieve opti-misation of existing fuel-injection systems without theneed for major engine modification work.

TURBOCHARGER

As is already the case with the heavy-duty 110 hp TDIengine in Europe, use is made of an exhaust-driventurbocharger with variable turbine geometry. This latestturbocharger technology for mass production permitsrapid boost-pressure build-up at low engine speeds, lowexhaust back pressures in the part-load range andeffective pressure build-up at full load. For customersthis means rapid dynamic pressure build-up, smoothacceleration, low fuel consumption and virtually smoke-free acceleration.

270.0260 .0250 .0240 .0230 .0220 .0210.0

200 .0190.0180.0170.0160.0150.0140.0130.0120.0110.0

100.090 .0080.0070 .00

MAGNITUDEVELOCITY

M/SLOCAL MX= 294.7

LOCAL MN= 0.0

270.0260.0250.0240 .0230.0220 .0210.0

200 .0190.0180.0no.0160.0150.0140.0130.0120.0110.0

100.090 .0080.0070.00

MAGNITUDEVELOCITY

M/SLOCAL h4X= 297.7

LOCAL MN= 0.0

Fig. 11: VNT Turbocharger

7

EGR WITH EGR COOLING ECM - ELECTRONIC CONTROL MODULE

The pneumatic in a closed-loop-method con-trolled EGR-system wasI further improved by theapplication of EGR cooler. The result is a additional NO,-reduction by approx. 150/ due to lowering the peakcombustion temperature. Given sufficiently low NO,emissions, a certain scope is however also availablefor reducing particulate emissions by EGR or start ofinjection variation.

The engine management system used in the NewBeetle was derived from the familiar VW and Audisystems and has the following characteristic features:l 16/32 bit (extended instruction set) with Siemens

8OC167 processorl CAN bus for communication between engine,

gearbox, brake control and vehicle safety systemsl Internal fault detection systeml Integrated OBD II functionsl Drive by wire

Fig. 12: shows the entire OBD diesel systemblock diagram with all sensors and actuators, providingan outline of the principal functions executed by thecontrol unit.

1 R 1 actuatoiY -I

engine speed sensor fuel temperature control sleeve positionelectricshutOff

distributor pump VP37 /accelerator pedal sensorwith idle switchkickdownswitch

1.

coolanttemperature

intake airtemperaturevehicle speed

cruise controlactivatorbrakeclutch

1.air conditioning12v

u.pa==

ECM EDC 15voltage regulatorsatmospheric pressuresensorboost pressure sensor

sensor signalslogical signals

signals processing for:- fuel auantitvz tx&fi of injection control

- boost pressure control- cruise control- ext. torque request- glowing-limp home- adjustment

power stagessignal output

interfacesdiagnostics

engine speed informationglowing control lampMI1

Jl servicetester

Fig. 12: OBD Diesel System Block Diagram

8

ENGINE RESULTS 16

PERFORMANCE DATA 14

The full-load values of the TDI engine in the NewBeetle are identical to those achieved by VolkswagenTDI engines on the American market. The TDI enginedelivers a torque of 140 Nm at 1000 rpm and reachesits maximum of 210 Nm at 1900 rpm. Of particular noteare the low full-load smoke emissions and specific fuel-consumption values of less than 200 g/kWh.

The implementation of technical improvementsin the TDI made it possible to meet US and Californianemission requirements without any loss of performanceas compared to the European version.

15

10zi‘5; 5

0

-1---------I IT--

O-50 mph O-60 mph 40-60 mph

pi!iJ----- ____

:

--

Fig. 13: Performance Data New Beetle 1.91 TDI MY ‘98

LOW SPECIFIC FUEL CONSUMPTION IN MAP

An extremely high level of efficiency is howeveralso achieved at part load. With a specific consumptionof 197 g/kWh, the TDI is one of the most efficient enginesof its class. Particularly economical driving is possiblein the low part-load range which is frequently used inpractice. Only 350 g of diesel fuel is used per kilowatt-hour at an engine speed of 21000 rpm and a meaneffective pressure of 2 bar. (Fig. 14)

12

10‘;:2aia

6

1000 2000 3000Engine Speed [rpm]

4000

Fig. 14: Specific Fuel Consumption (BSFC) Map(New Beetle 1.91 TDI)

What does this mean in real terms? As Fig. 15shows, the most favourable consumption figures areobtained with the manual shift version (48 miles pergallon of diesel fuel in the highway test). Even greaterfuel economy can be achieved in practice with anappropriate driving style. The approximately 15% higherconsumption rate of the automatic version can beattributed to somewhat less favourable operating pointsand a poorer degree of efficiency of the automaticgearbox.

3z 1 0

0 /

--------_

- - - - - - - - -

- - - - - - - - -

El Citym Highway -

m Combined

Manual Shift Automatic

Fig. 15: Fuel Economy (New Beetle 1.91 TDI)

9

FUTURE COURSE OF DEWELOPMENT OFPASSENGER-VEHICLE DIESEL ENGINES

In order to be able to maintain a competitive edgein the field of passenger-car and light commercial-vehicle diesel engines, Volkswagen are intending tolaunch a new series of engines, the main feature ofwhich will be a newly developed fuel-injection system.Following on from the unit injector system primarily usedin commercial-vehicle engines, this will be the first high-pressure injection system with solenoid valve controlfor passenger vehicles with injection pressures of up to2000 bar. First of all a 3-cylinder TDI with 1.41displacement, 55 kW/75 hp and 195 Nm is to be offeredfor the compact class, with further DI engines to follow.

HIGH-PRESSURE WITH PILOT INJECTION

With the close cooperation of Bosch, a fuel-injection system has been developed with the followingmain features:l Direct actuation of the high-pressure plungers by the

camshaft, thus producing little dead space and highinjection pressures

l Solenoid-operated control valve, arranged perpen-dicular to the pump axis with a view to minimisingboth dead space and installation room required

l A hydraulic pilot injection system consisting ofretraction piston and needle damping

l A valve covered orifice nozzle with double needleguide

l Start-of-delivery control for each cylinder on the basisof detection and adjustment of the solenoid valveclosing time sensed from the energisation profile.

The fuel is supplied by way of gallery bores inthe cylinder head, with a patented mixing-tube systemensuring virtually identical fuel temperatures at all unitinjectors.

retraction piston

The unit injector elements are installed at a slightangle to the cylinder axis. The high-pressure plungersare actuated directly by the camshaft via a rocker arm.Particular importance was attached to the mechanicalstrength of the rocker arm, as the actuation force atrated power is more than 10 kN. Installation of the unitinjectors in the cylinder head permits a compact enginedesign, with encapsulation under the valve coverreducing noise levels. An internal cable strip providesthe control pulses for the unit injectors.

Fig. 17: Installation position of unit injector in cylinderhead

Pressure build-up starts during the downwardmovement of the pump plunger with energisation andsubsequent closure of the solenoid valve. On attainingthe nozzle opening pressure, the nozzle needle is lifted

and pilot injection commences.The stroke of the nozzle needleis restricted by a hydraulic stop,thus controlling the pilot quantityinjected. This is immediatelyfollowed by opening of theretraction piston, the deflectionof which causes the pressure tocollapse briefly and the needleto close again. The nozzlespring is further pre-tensionedon completion of deflection.Main injection commences onreaching the increased openingpressure. Deactivation of the so-lenoid valve initiates the end ofmain injection.

Fig. 16: Unit Injector Cross section

pump pressure

needle closed needleclosed Lift Lift closed

-0.05 mm -0.2 mm

Fig. 18: Injection profile

As compared to conventional fuel-injectionsystems, the rigid design and small dead-space volumepermit considerably higher injection pressures. It is nothowever possible to increase the pressure betweenpressure source and nozzle needle. Fig. 19 shows theclear increase in maximum injection pressures incomparison to the two versions of the distributor-typeinjection pump in the New Beetle.

2000 - -

I1750 - -5 1500 - - -t 1250 - - -2 - - -4

10002 750 - - -n r

- ‘--1-I---- --- -_ - -- -_ -- -_ ----I- -- -

--

--

--

.:.:.:.:.:.:.:$W:y:::::::::::::::::::::::::.ZZ$..:.:.:.x.:.:::::::;::::::::::::y:::::. . . . . . :: . . . ..EiE::::::::::::::::::::::::::::y~.~.:.:.~.~.:;gy*i:.:.:.:.:.:.:..:.:.:.:.:.:.::.:.:.:.:.:.::.:.:.:.:.:...“““i.:.;;:$:;:$:

~~. ..A! Z... :.

1

m Unit InjectorPl -Type

Pump Side Nozzle PressurePressure

Fig. 19: Maximum attainable injection pressures

Despite the fact that the operating principle issuch that injection pressure, quantity injected andengine speed are directly proportional, a high pressurelevel is reached at part load as well. The map shownhere illustrates the injection pressures of the 3-cylinderTDI engine with unit injector (Fig. 20).

18

16

6

i -

, -

2000 bar

1800 bar

1600 bar

1400 bar

7200 bar

7000 bar

1000 1500 2000 2500 3000 3500 4000Engine speed [rpml

Fig. 20: Injection pressure map

REQUIREMENTS FOR MODERN DIESEL FUELS

Increasing demands will be placed on the qualityof diesel fuel in future if the enormous potential offeredby the DI diesel engine is to be used to its full benefit inyears to come to cope with transport needs in thepassenger-vehicle sector.

The following is a list of certain important dieselfuel properties, indicating their direct and indirect effecton emissions.

Cetane number:A high cetane number ensures minimal ignition delay,enhancing comfort, reducing CO, HC, NO, andparticulate emissions and improving cold startingbehaviour.

Sulphur content:Sulphur compounds are an integral component of dieselparticles. Reducing the sulphur content decreases theparticulate mass emitted. The long-term aim is toachieve a sulphur content of 30 ppm in order to be ableto utilise future catalytic converter technology.

Improved lubricity:An HFRR value of c 400 pm guarantees the reliablelong-term functioning of modern fuel-lubricated high-pressure injection systems. Such systems provide a lowemission level by virtue of their good mixturepreparation.

Density:Again with a view to emissions, the density should bebetween 0.82 und 0.86 g/cm3.

11

Water content:Water in the fuel can be highly detrimental to thetribological systems in fuel-injection systems and causepremature wear. An excessively high water content canalso lead to corrosion in the event of long periods ofnon-use.

Winter resistance:A high level of winter resilstance is a prerequisite incertain regions to ensure the filtration capacity of thefuel even under unfavourable climatic conditions.

It is generally true to say that to a certain degree theemission and performance potential of the diesel engineis influenced by fuels and lubricants. By making use ofthis, a sustained improvement can be made to theemissions of existing vehicles without them all havingto be renewed, bringing an immediate benefit for theenvironment.

CONCLUSION

The passenger-vehiclle diesel engine will continueto play an important role iin satisfying transportationneeds in the future. It will retain its major significancenot least in view of its lower fuel consumption andassociated low level of CO, emissions. Further focalpoints of development work will be:

l Greater reduction in fuel consumptionl More improvements to emission qualityl Performance enhancementl Higher comfort standards

The introduction of new fuel-injection systems willbe an important step in this direction.

Involvement in developments on the Americanmarket enabled Volkswagen to gain the wealth of rele-vant expertise necessary to act quickly in supplying theGerman market with diesel-powered vehicles satisfyingthe stringent EU III D emission standards and qualifyingfor national tax relief. Field experience with an on-boarddiagnostic system will help to promote development ofsimilar systems for other markets in the future.

12

(1) Goergens, G.; Strauss, A.; Willmann, M.: Ein neuerTurbodieselmotor mit Direkteinspritzung und I,91Hubraum. In: MTZ 53 (1992) 3, S. 94-103

( 2 ) Bauder, R.; Dorsch, W.; Dotzauer, H.; Polzl, H. W.;Stable, H.: Audi-Turbodieselmotor mitDirekteinspritzung - leise und schadstoffarm nachMVEG II. In: MTZ 55 (1994) 6, S. 345-360

(3) Willmann, M.; Jelden, H.; Pohle, J.; Roost,G.; Kracke, A.: Der neuer 81 -kW-TDI-Motor vonVolkswagen. In: MTZ 56 (1995) 12, S. 722-727

(4) Willmann, M.: Pkw-Dieselmotoren. FachtagungHaus der Technik, Essen, 20./21.6.95

(5) N.N.: Die Zukunft heiOt Diesel. InformationBrochure, Volkswagen AG, Reserach andDevelopment

(6) Rhode, W. : Development Work On The 1.9-Liter81 kW Engine, SIA Presentation, 14.3.96

( 7 ) B. Georgi, S. Hunker-t, J. Liang, M. Willmann:Realizing Future Trends in Diesel Development,SAE 972686, 6.8.1997

(8) Neumann, K.-H., Neyer, D., Stehr, H.: Der neue3-Zylinder-Dieselmotor mit Hochdruckeinspritzungvon Volkswagen, Volkswagen AG, PrasentationWiener Motorensymposium, Vienna, 7.5.1998

(9) Schmidt, H.: Numerische Simulation der Dusen-innenstromung, Diplomarbeit, Volkswagen AGWolfsburg 1997

(lO)Willmann, M.; Ropke, S.; Hilbig, J.; Warnecke,D.; Gokesme, S.: Das neueTDI-Triebwerk vonVolkswagen. In: MTZ 57 (1996) 11

The authors wish to acknowledge the kind support ofthe following team members:

S. Ropke, H. Jelden, S. Koehn, S. Pingel, J. Pohle,Head of Diesel Development: R. DorenkampHead of Drive Unit Development: Dr. K.-H. Neumann.

Adaption of the 1.91 TDI in the New Beetle was jointlyrealised by the engineering staff of Volkswagen of Ame-rika, IAV lngenieurgesellschaft Auto und Verkehr GmbH,and Volke Entwicklungsring GmbH.

DEFINITIONS, ACRONYMS, .ABBREVIATIONS

MSA: Menge, Spritzbeginn, /!bgasruckfuhrung(injection quantity; timing)

EDC: Electronic Diesel Control

TDI: Turbo Diesel with Direct Injection

VNT Variable Nozzle Turbine

FEM: Finite Element Method

ECM: Electronic Control Module

OHC: Overhead Camshaft

NO,: Nitrogen Oxides

OBD: On-Board-Diagnostic

EGR: Exhaust Gas Recirculation

CAN: Control Area Network

NVH: Noise, Vibration, Harshness

HFRR: High Frequency Reciprocating Rack