Multi-speed transmissions – manual or automatic – are only needed because of the inherent drawbacks of the internal combustion engine as a vehicle propulsion power source. There are other power sources which reduce or eliminate the needs for such transmissions, and these are likely to come into increasing prominence as the 21st century progresses, writes Jeff Daniels. (This article was extracted from just-auto’s exclusive report: ‘The global market for automotive transmissions: forecasts to 2010’.)
The most obvious example, and the one which is likely to have an overwhelming impact in the long run, is electric traction. Unlike the internal combustion engine, the electric traction motor has no need to continue running at a minimum self-sustaining (idling) speed when the vehicle comes to a stop – neglecting, for the sake of simpler argument, the various schemes which have been proposed and demonstrated involving the automatic stopping and restarting of IC engines in this case. Thus no vehicle with electric traction has any need for a clutch. Also, generally speaking, though to some extent depending on the design of the electric traction motor, maximum torque is available from zero speed and is either maintained, or gradually fall away as speed increases. Thus there is no need for a conventional gearbox with selectable gears either, simply a reduction gear which matches the motor characteristics to those of the vehicle – specifically, ensuring that the maximum safe speed of the motor corresponds with the desired maximum speed of the vehicle.
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It follows, therefore, that with electric traction, the need for transmissions as they have been so highly developed in over a century of IC engine propulsion will cease to exist. It is possible that some powertrain engineers will examine the possibility of incorporating gearing within electric traction, which might for example allow the use of a smaller and lighter traction motor, sacrificing initial acceleration but not, perhaps, maximum speed. However, most electric vehicles (EVs) so far demonstrated have been content with the single reduction-gear drive.
Vehicles with electric traction can be divided into two main classes, hybrid electric vehicles (HEVs) which retain an internal combustion engine as the prime power source but have an electric motor as the propulsion unit, and pure electric vehicles which derive their electric power from some other source. It is worth briefly considering both classes and the impact which they may have on the transmission market during this decade, to 2010.
Hybrid vehicles
Hybrid vehicles have again been generally divided into two classes, series and parallel hybrids. In the series hybrid, the internal combustion engine drives a generator whose output is taken to an electric motor, which in turn drives the wheels. Traction is therefore entirely electric and there is no requirement for a transmission as generally understood. In the parallel hybrid, the internal combustion engine has a direct drive to the wheels but may be assisted by an electric motor driving in parallel – hence the name. The many projects for vehicles with integral starter-generator-motors “sandwiched” between the engine and the transmission (in the manner of the Honda Insight, for example) are, therefore, parallel hybrids. Such vehicles still need a transmission, though the supporting torque of the electric motor may allow it to be slightly simplified, with fewer forward gears.
The distinction between series and parallel hybrids has been blurred since the appearance of the Toyota Prius, which has some of the characteristics of both types. For the purposes of this analysis, however, it should be noted that the Prius retains a transmission – in the form of a CVT.
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By GlobalDataElectric vehicles
Pure electric vehicles take their power from an on-board source – in effect, from a battery charged from an external source while parked (battery electric vehicle – BEV), or from a fuel cell (fuel cell electric vehicle – FCEV). The distinctions between the two are not relevant to this report. It suffices to note that both types necessarily use electric traction and have no need of a conventional transmission.
Electric traction effect on the transmission market
The BEV has been in low-volume use for many years and will continue thus. The drawbacks – including the high cost – of batteries precludes their widespread use for anything but specialised purposes in particular environments. Its overall effect on the transmissions market will continue to be negligible. The FCEV shows great promise for the future must most authorities agree that its need of further development and its present high cost mean that even by 2010, FCEVs will be numbered in thousands rather than tens of thousands (although by 2020, the picture could be very different). Again, therefore, the effect on the transmissions market to 2010 will be negligible.
The HEV, in the form of the Honda Insight, the Honda Civic IMA and the Toyota Prius, has already made some inroads into the passenger car market. However, all these models, and several more which are under development, are parallel (or quasi-parallel) hybrids and use conventional transmissions. Even if the vehicle market share of such cars increases, therefore, it will have no effect on the transmissions market. Series hybrid HEVs exist in very small numbers, mainly in Europe, in the form of BEVs to which a small motor-generator set has been added as a “range extender”. Such vehicles suffer the same drawbacks as pure BEVs (except for their extended range) and they are similarly likely to be confined to specialised uses in relatively small numbers.
Overall, therefore, there is no real likelihood of vehicles with electric traction claiming anything like enough of the market, prior to 2010, significantly to affect the size or shape of the transmissions market. The following decade is likely to be a different matter; it may, in fact, be much more difficult to make an accurate prediction for 2020 when looking forward from 2010. Much will depend on the pace at which fuel cell technology evolves.
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