Except that the efficiency of most AC motor/controllers is relatively the same for a given power level regardless of RPM (at least over most of speed/torque combinations ) If you look at a three dimensional torque plot it's pretty much flat except at the extreems (very low/high power).
A multipeed transmission adds it's own losses over a single speed, especially if you want syncros. The additional transmission losses would more than likely exceed the gains from trying to keep the motor in it's "sweet spot". Over all the added complexity and weight is not worth the effort in an EV built from the ground up. Personally I think that if one is going to try building these things in volume, it would be simpler, cheap and lighter to have a custom built, single reduction transmission. Perhaps even contacting the folks who built the one for GM (assuming GM didn't build it themselves) Seth wrote: >Mike: > >A well thought out reply. I might point out one thing, which is that >although AC drives are very flexible and can often be used acceptably >with a fixed ratio drive, it can be possible to get a *further* >improvement in efficiency *and* performance with the addition of another >gear ratio or a reconnection of the motor on the fly. The idea is either >to keep the motor spinning where it is wound to be efficient (gear >change), or to change the connection of the motor to match the speed >range. Of the two, the gear change is the easiest for the average conversion. > >Seth (not Murray) > > >
