You appear to be confusing torque and power. Granted a lower ratio will give you more starting torque, but with something like Victor's AC drive you would ALREADY be in a low ratio. You are effectively driving around in first gear ALL of the time so what excatly is the benifit you see from going to a lower gear? Going to a higher cruising gear gives you perhaps 2 to 3% higher efficiency, this will be MORE than overcome by the additional looses in a multispeed transmission.
As for the syncros, you do understand the concept of friction? Even with lubrication two rubbing surfaces WILL have friction. P.S. The EV1 has a single speed gearbox and does quite well from a stop. Seth wrote: >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) >>> >>> >>> >
