Symposium on International Automotive Technology 2007

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R. P. G. Heath and A. J. Child

Zeroshift, Milton Keynes, UK

Zeroshift Automated Manual Transmission (AMT)

SAE Paper No. 2007-26-061

Copyright © 2007 The Automotive Research Association of India, Pune, India

ABSTRACT

Zeroshift technology allows a manual transmission tochange gear in zero seconds. The Zeroshift AutomatedManual Transmission (AMT) is easy to manufacture andallows a cost effective alternative to the traditional torqueconverter based automatic transmission. Zeroshift offerspotential fuel economy improvements from drivelineefficiency and the best possible vehicle acceleration.Compared to an existing AMT, Zeroshift offers anuninterrupted torque path from the engine to vehiclewhich allows for a seamless gearshift. This seminalpaper provides an introduction to the technology togetherwith test data from a demonstrator vehicle.

INTRODUCTION

The world is dominated by two forms of transmission,the Manual Transmission (MT) and the AutomaticTransmission (AT). The MT has a single dry clutchoperated by the driver, whilst the AT uses wet clutchesthat are automatically controlled. There are pros and consin both transmissions.

The MT is the most efficient transmission available. Thislends itself to providing good fuel economy for thevehicles it is employed in. The efficiency of the MT isdependent on the load applied. Over a representativedrive cycle its efficiency can approach 97% [1]. The MTis very easy to manufacture having very few parts. Itis reliable and easy to maintain.

It’s main weakness is that it is less easy to drive thanan AT especially in congested traffic as it requires thedriver to operate the clutch for each gear shift. Gearshifts are sometimes not smooth which causesdiscomfort for passengers who will notice an interruptionof engine torque to the wheels when the transmissionis between gears. In severe situations, the interruption

of torque can cause dynamic instability of the vehicleresulting in loss of control.

The AT has many advantages which include ease ofdriving and very smooth shift quality. The choice of gearis determined by a Transmission Control Unit (TCU) andthis will ensure that the best gear is chosen for thevehicle road speed depending on whether the driverrequires fuel economy or performance. Drivers are willingto pay a premium for this type of transmission eventhough performance and fuel economy are inferior to theMT.

A reduced performance and fuel economy is apparentbecause of the lower efficiency of the transmission. Notonly are there parasitic losses for operation of thehydraulic pump, but large amounts of slip in the torqueconverter generates heat loss which warms thetransmission fluid rather than providing torque to thewheels. In recent years a lock up clutch bypasses thetorque converter for a large proportion of the journeywhich can improve the overall efficiency dramatically.The efficiency of an AT can be as high as 86% [1].

From a manufacturing point of view, the AT containsmany parts and is more difficult to service if it developsa fault. In addition, some countries like India have fewAT factories meaning that OEMs have to pay an importduty tax on each unit. This increases the purchase priceof vehicles equipped with an AT. This reduces thepenetration of a much desired transmission in a pricesensitive market.

If a transmission could have the benefits of both theMT and AT and the weaknesses of neither, this wouldintroduce a third option to segment the market. Byautomating the MT, a cheap and economic transmissionis created. Traditionally, the AMT has had good fueleconomy, inferior performance (compared to the MT) and

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bad shift quality. Zeroshift corrects these latter two issuesallowing simultaneously good fuel economy, performanceand shift quality. The combination of these has not beenseen in any other transmission, previously.

This paper is split into the following sections: Firstly, theconcept of Zeroshift is introduced. Secondly, the benefitsin terms of fuel economy, performance, shift quality andease of manufacture are illustrated. Finally, theconversion of a Ford Mustang demonstrator vehicle isdescribed.

ZEROSHIFT CONCEPT

The drive components that make up a Zeroshift hubassembly are very simple but very effective (Fig. 1). Thesystem consists of 2 drive elements mounted on acommon hub. Each element is double-faced where oneface can only drive in one direction and the oppositeface in the opposite. When paired back-to-back, theyboth provide either a direct-drive or a ramp facedepending on drive direction configuration.

result is a continual delivery of torque and unaffectedvehicle stability. The main benefits of Zeroshift are:

� fuel economy

� performance

� shift quality

� ease of manufacture

FUEL ECONOMY : The fuel economy of a vehicle is afunction of many components including its powertrain.The two main components of the powertrain thatdetermine fuel economy are the engine and transmission.It has been stated by more than one company that toreduce CO

2 it is twice as cost effective to develop the

transmission rather than the engine [2]. Havingdeveloped such technologies, the additional manufacturingcost of engine technology is more than twice that oftransmission technology for the same benefit in fueleconomy [3]. It is therefore beneficial both in terms ofdevelopment costs and manufacturing costs to first seeka fuel economy improvement via novel transmissions.

To date, the MT has shown better fuel economy ascompared to AT [4]. The only technology that hasdemonstrated better fuel economy than the MT is theAMT. This fuel economy improvement is not due to thein gear efficiency of the transmission as it is no moreefficient than the MT. But the gear shift schedule whichis more favourable for an AMT than a MT, gives betterfuel economy for AMT. In real driving with the AMT isin automated mode, an improvement in fuel economyover the MT can be achieved. It is unlikely that the driverwill always be in the correct gear for all situations. Athighway cruise, the AMT will be no better than the MT.It may be slightly worse if parasitic losses are presentto operate a hydraulic pump continuously.

Zeroshift is an AMT which has no significant parasiticlosses when in gear. A small amount of power isrequired during the gear shifting. There is no hydraulicactuation so there are no parasitic losses to operate ahydraulic pump. Both the gear actuation and clutchcontrol can be electrically operated from the standard12V vehicle electrical system.

If we compare the fuel economy of the manual,automatic, and simulated Zeroshift transmissionderivatives, Table- I shows that the Zeroshift is noworse than the manual and considerably better than theautomatic.

PERFORMANCE : Compared to a MT, the Zeroshiftconcept allows gear shifts to take place in zero seconds.This has an immediate performance benefit as thevehicle is never coasting in neutral. Every gearshift whichwould normally take a test driver at least 0.5 s to

Figure 1 : Two Zeroshift Hubs

When initiating a shift from the neutral position, one drivering is engaged with the dog faces on the gear and thesecond ring joins the first axially adjacent which providesdrive in the opposite direction to oppose engine overrunand, more importantly, eliminate perceivable backlash.This ring is unloaded and is the ring to make the nextshift and as such requires less shift force i.e. much lessthan synchroniser force.

The instantaneous shift is by definition a torquehand-over from one gear to another. This creates a torqueor energy spike in the driveline which is dissipatedthrough a combination of engine and transmissionmanagement, clutch control and system compliance. The

Symposium on International Automotive Technology 2007

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acceleration which will show the deceleration andacceleration experienced during a gear shift. It can beseen from Fig. 3 that during a standard upshift in a MTthere is a torque interrupt to the wheels. This is shownin the Fig. 3 by the reduction in longitudinal accelerationduring the shift. Subjectively, this is experienced by thevehicle’s occupants not only by observing the pitchingof the front of the vehicle but also by head nod. In itsmildest form, this is merely a discomfort to theoccupants. In its severest form, this can lead toinstability of the car, especially during cornering. The ATis less prone to this phenomenon as the torque variationduring a gear shift is less undulating.

On the above Indian Popular car, it is necessary toperform two gear shifts during a 0-100 km/h accelerationstarting in 1st gear and ending in 3rd gear. The Zeroshifttechnology enables the acceleration to be completed1 s quicker than a human. If we compare the acclerationof the manual, automatic, and simulated Zeroshifttransmission derivatives as given in Table- II and itshows that the Zeroshift is the clear winner.

Table- II : 0-100 km/h Acceleration Time

It can be seen from Fig. 4 that during a standard upshiftin a vehicle fitted with Zeroshift there is no torqueinterrupt to the wheels. This is shown in the Fig. 4 bythe consistently flat longitudinal acceleration during theshift. Subjectively, the shift is unobserved by thevehicle’s occupants as there is no pitching of the vehicleand stability is maintained.

Figure 3 : Manual Transmission with Torque Interrupt

Figure 4 : Zeroshift Transmission with no Torque In-terrupt

Table- I : Fuel Economy

complete is performed in 0 s with Zeroshift technologyas illustrated in Fig. 2.

Figure 2 : Zeroshift Compared to Manual Gear Shift

SHIFT QUALITY : Transmission shift quality is measuredin many ways, some objectively and others subjectively.The longitudinal acceleration of a vehicle which can bemeasured both objectively and subjectively. Objectively,a vehicle may be instrumented to measure longitudinal

EASE OF MANUFACTURE : The materials used for allcomponents are as per industry standard and require nounusual treatments. Manufacturing methods too arestandard including forging, sintering, stamping and castingwith defined final finishing. The comparative cost to which

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Zeroshift components replace standard components i.e.synchronisers is reduced purely on a lesser part count.The only additional cost is in shift actuation. This isconsistent with AMT but less than AT. Manufacturingplants have minimal line disruption when replacing justthe hub assemblies.

A Zeroshift hub assembly can be packaged within anexisting synchroniser envelope and in some instancesbe less – an inherent vehicle packaging advantage withever increasing engine torques and hence gear-widths.For the full vehicle torque range, independent fork controlis employed meaning 2 actuators per hub are neededbut with the shift forces being much less than that ofequivalent synchroniser the actuator sizes are muchsmaller than that of AMTs.

ZEROSHIFT CONVERSION

A Ford Mustang has been converted to demonstrate theZeroshift concept, Fig. 5. The existing Tremec T5transmission has been converted. The synchromesh hasbeen removed and replaced with Zeroshift hubs. Thehubs are independently actuated using solenoids.Solenoids can be employed because of the low force(much less than synchromesh) as it is the unloadedforks that are actuated.

To complement the conversion, a fly-by-wire clutchcontrol unit automatically regulates a speed differenceduring the shift event across the clutch, allowing theenergy spike to be monitored and conditioned to suit thedriving conditions.

CONCLUSION

The Zeroshift conversion of an existing manualtransmission has been demonstrated. This has thefollowing benefits:

� Automated gear shift

� Improved fuel economy compared with torqueconverter automatic transmission

� Improved acceleration performance compared withmanual transmission

� Improved shift quality compared with manualtransmission

� Easy to manufacture

REFERENCES

1. Kluger, M. and Long, D., “An Overview of CurrentAutomatic, Manual and Continuously VariableTransmission Efficiencies and Their Projected FutureImprovements”. SAE Paper No. 1999-01-1259

2. Transmission Suppliers Report, pp 4, 2006, SupplierBusiness

3 Toom, R., “Les Boites De Vitesses Automobiles”,CTI Seminar, 2006.

4. www.carfolio.com5. Autocar India, 2006

CONTACT

R. P. G. HeathE-mail: rayheath@zeroshift.com

Figure 5 : Zeroshift Demonstrator Vehicle