Vehicles are designed to meet emissions, economy, and performance objectives under various conditions. These are usually defined by driving cycles (for emissions and fuel economy), and speeds and accelerations – sometimes on grades - (for performance), and are largely determined by the power train.
The classic solution – an internal combustion engine (ICE) driving via a gearbox – was evolved in the 1890s. Automatic transmissions first appeared in the 1940s, but almost all have hydrokinetic torque converters and epicyclic gear trains controlled by hydraulically-operated band brakes or clutches. These involve considerable power losses.
Possible power trains for super-low fuel consumption and emissions include: