First, what rubbing surfaces in a syncromesh? Syncromesh is engaged or not, with a transition of sliding lasting perhaps a few hundred milliseconds.
Second, in a traction AC drive you are limited in how low you can gear. At 13:1, a likely first gear (VW golfs came with 12.7 to 14.5 for first gear depending on engine), the motor has to hit about 13,000 rpm for highyway speeds, assuming a 22.8" wheel, which is what is on my VW golf. I think Victor's AC motors spin to less than this, between 8 and 10,000. So at about 900 tire revolutions per mile, times 13.0:1, you get ~11,700 rpm at 60 mph. For first gear. If you geared it to hit the mechanical rev limit at 80mph, (so you don't blow the motor going down hills) and the motor rpm limit was 10,000 rpm, then at 900 tire revs per mile you get 10,000 /(80/60 *900) an 8.3:1 ratio. If you really want to spin to 8,000 rpm, then you get 8000/ (80/60*900) or 8000/1200 or about 6.7:1 ratio. 8.3: is roughly 2nd gear in a VW golf. 6.7 is halfway between 2nd and third. So now you need between 1.5 and 2X the tourque the ICE engine delivered to match the starting performance of the ICE. Plus you need 2X the RPM. And you need the torque beacause of all the batteries. All 24 or more. So you need a rotor that is small enough and light enough to go 10,000 rpm or more and will deliver at least 50% more torque than the ICE engine. And enough copper in the stator and motor leads to do this along with three phases of power silicon with high enough current rating to make the torque. Or you can shift a gear. All my texts say 98% efficiency for helically cut gears, 99% for spur cut. Which isn't that much for loss. If you picked up 2% by shuttling around on the efficiency map for the AC motor (which is very doable) then you could at least break even. And as a bonus, multispeed manual gearboxes are quite common, unlike single speed. I have driven about a dozen single speed AC traction powered EVs with no electrical reconnection. I haven't driven the EV1. Would I call them them an acceptable compromise? Most of them. But some weren't. Seth > > 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) > >>> > >>> > >>> > > -- vze3v25q@verizondotnet
