New technology development has always been a key competitive factor in the automotive industry. There have been many advances in all areas of the vehicle, especially in the power train. Most advances replace an existing function with an improved function: fuel injectors deliver fuel in a more controlled and precise manner than carburetors, CVT transmissions offer infinitely variable speed ratio compared to the limited fixed ratios of step-shift transmissions, etc. When developing technologies, the performance specification starts with the capabilities of the previous system, and then is expanded to take advantage of the new features. It is these new features, sometime un-intended consequences, that can offer real breaks in development paths. One such new technology is the hybrid power train.
A hybrid power train is new technology power train with two power sources, typically an internal combustion engine and a battery (although other types exist). As a power train, it replaces a conventional power train, so its overall power and torque requirements start with specifications comparable to a conventional system. While the combined specification of the two power sources needs to match a conventional system, the individual specifications don't. It is this break that creates transformational opportunities for defining a vehicle power train. We can explore this opportunity with the characteristic equations of vehicle dynamics by characterizing vehicle loads as resistive or kinetic. From this we can specify a system whereby the primary power source is sized to the resistive loads and the secondary power source is sized to the kinetic loads. This approach results in a system with two power ratings: a transient power rating (for acceleration performance) and a sustained power rating (for maximum sustained speed). This allows a systematic approach to sizing components for a hybrid and provides a basis of comparison for competing technologies. It also hints at a future of high-performance vehicles where performance is not defined by the engine.