My experiences are somewhat different from Victor's. They are also somewhat different from the projected results I announced several months ago, and are somewhere between interesting and unexplicable.
[NOTE: All values below are approximate. Please don't plan your life around them.. they're just to give you the 'gesalt' of my experiments in this arena] I use 1st, 2nd, 3rd, and 4th. For highway cruising on level ground: 65 in 1st is not a option 65 in 2nd uses 10kW 65 in 3rd uses 9kW 65 in 4th uses 7.5-8kW I may have worn bearings in my transmission.. it is pretty noisy.. but still, these results are reliable - that is, they happen every time. OTOH, 0-60 remaining in 3rd is 12s, 0-60 going 1st, then 2nd is 9s. [times are approximate] so there is definately a acceleration advantage to using a multispeed transmission. I would say that at least for my transmission, one should not discount 'windage' loss as it is not negligable. For highway cruising with my gen-trailer, by the way, to demonstrate why I am doing a aero workover of it: 45 in 2nd uses 8kW 45 in 3rd uses 7.5kW 45 in 4th uses 7kW 50 in 2nd uses 12kW 50 in 3rd uses 11kW 50 in 4th uses 10kW 55 in 2nd uses 16kW 55 in 3rd uses 15kW 55 in 4th uses 14kW 65 2nd = 22kW 65 3rd = 20kW 65 4th = 18kW ----- Original Message ----- From: "Victor Tikhonov" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Tuesday, September 10, 2002 1:45 PM Subject: Re: AC drive trains (was Re: [EVDL]Re: Volume build proposed for high performing EVs) > "VanDerWal, Peter MSgt" wrote: > > > > > At any rate it's still pretty damn quick. I don't see where having a second > > gear with a ratio higher than 11:1 would help any, especially since, as you > > point out, the tires probably couldn't get any more torque to the road. If > > you spent a lot of time driving at 5mph it might improve your efficiency > > some, I guess. > > > > >It's my opinion that AC is only rarely flexible enough to do the job. > > >And for now I am keeping that opinion. I have never driven an EV-1. I > > >live in the northeast, so I probably never will. I sat in the Impact > > >once, but that didn't tell me much. > > > > I agree you are completely entitled to your own opinion. I'm just curious > > which AC powered vehicles you have driven that you've developed this opinion > > from? > > > > P.S. I'll grant you that the Siemens motors would need a ratio closer to > > 8.5:1 if you wanted a top speed of 80 mph; but I still don't think that an > > even higher ratio would help efficiency or torque much, certainly not enough > > to make it worth the extra hassle, weight, and complexity. And you could > > always solve that by deciding to have a top speed of 65-70mph, going faster > > than that is just a waste of energy anyway. > > > I have some expertise in this area and can chime in with some > hard data. > > Peter is right that switching gears within normal AC motor range > does not impact efficiency or it's very minimal. > But the ratios must be lower than 8.5:1 for "normal" > RPM range (3000-6000). > > Take my ACRX: > > 1st gear ratio is 3.25:1 > 2nd is 1.65:1 > 3rd is 1.033:1 > Final diff is 2.954:1 > > So total reduction on the second gear is only 4.87:1 and > on the third - 3.05:1. > > Now, I drive on the second gear all the time. > ACRX goes 65 mph at exactly 5000 RPM and consumes about 12 kW > to do that. I have a battery power monitor (part of inverter's > software) and can watch the power value as I drive. If I switch > to the third, the RPM becomes exactly 3000. Acceleration is not > as quick anymore because the torque at the wheels is lower > but the torque the motor puts out is the same at 3000 and > 5000 RPM (the case for my voltage). However, power consumption > is identical - still 12 kW because main contributor at that > speed is aero drag loss, not motor efficiency. The motor > current on the third is proportionally 1.7 times higher > than on the second so its losses may be few watts more, > but nothing compared to 12 kW overall. Switching to the first > gear in my case is not possible for highway use - the motor > would need to make 9800 rpm. It can do that, but there will > be little useable motor torque there - even multiplied by > 1st gear high ratio I suspect I will have less torque > at the wheels than on the second gear. Not to mention > the motor efficiency at near 10,000 rpm is lower - about 75% > (http://www.metricmind.com/line_art/efficiency.gif) > and the gear box will be very hot (more watts wasted to that). > > Victor >
