Yes. Except when you are talking about starting and stopping. Which EVs do a lot of. When do you want lots of torque the most? When you are trying not to roll backwards down the hill at the stop sign. Or trying to sort through an unprotected left hand turn. What is the motor speed? Very low. There are limits to how far you can really push the torque speed envelope. If you could have a low gear for those times and a high gear for cruising, the extra percent or three loss in gearbox efficiency would be made up for the times when your AC drive goes to 60% efficient and stays there longer in a higher gear. A single speed will have a higher efficiency cruising. A dual speed can have a higher trip efficiency.
And I would be curious to hear why syncromesh would result in lower efficiency. It has been a while since I had apart either a syncro or non-syncro transmission, but I can't immediately identify an additional source of drag with syncromesh versus face dogs. Both have all forward gears in mesh all the time, one just has cone clutches (syncros) to match speeds during engagement. Seth Peter VanDerWal wrote: > > 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) > > > > > > -- vze3v25q@verizondotnet
