Unlike HEVs, which combine conventional powertrains with electric traction, EVs tend to be limited to those types with sufficient space for mass energy storage, usually batteries, and possibly liquid hydrogen in the future. Space is not as constrained with EVs but it’s common to use forced cooling of the traction motor to increase the specific power density. This is important both from the vehicle dynamics perspective and economically, particularly with permanent magnet machines.
One of the most challenging aspects of EV traction motor design is to provide exceptionally efficient power delivery over the full operating range of the vehicle, unlike hybrid machines which usually assist the engine, or are used as the sole traction source over a very limited operating range.