>The diff will generate some windage losses whether you are turning or >not.
Oops, good point. >and losses from >meshing the gears. Being as they will be involute teeth, sliding is >pretty much a non issue. at least in a FWD application. You are going to have to explain that last bit. >gears, oil seal drag and the remainder of the bearing losses. AC motor >efficiency is not always 90% or greater. At high torque at low rpm, you >can be in the low 60s. How do you keep from doing that? Sure but the difference from going from an 11:1 (like the EV1) to something even lower is dubious at best, unless you are planning on spending a lot of time crawling around in parking lots. Ordinary cars only use first gear to get the car moving from a stop because ICEs don't handle zero RPM well. EVs excel at zero rpm torque so they don't really need 1st gear (or lower) unless they are going to spend a LOT of time going really slowly. >By changing the >ratio to increase shaft speed and reduce torque required at the same >time. You will spend less time in a inefficient area of operation this >way (quicker acceleration) and the losses will be less during this >event. Which you will repeat at every stoplight. And you really think that saving a few watt-hours per mile, of stop and go, is worth the hassle of shifting? > This more than makes up >for the losses of having another gear pair. I don't think so, I haven't seen any evidence that an EV with a granny gear will have that much better performance. >second best operation, and third best and so on. And finally, when the >motor, controller and batteries are all pooped, you can still make it up >the driveway. I think that is a good reason NOT to have it. If you are murdering your batteries by driving them until they are pooped it's even harder on them to wring out a few more watts by driving in a 'granny' gear. If you give people the option they WILL use it to the detriment of their batteries. >Another point or three: the car you keep referring to, the EV-1 does >have a single speed gearbox. It is unclear whether or not it has >electrical reconnection on the fly. Reconnection on the fly???? >The gearbox is double reduction, with all those extra parts. > Unless it sounds like it is in reverse all >the time, then the gears are helically cut. Not spur. Which I think you >would find *very* objectionable in an EV. I can't find the reference but I remember reading somewhere that it had spur cut gears. Perhaps I'm remembering wrong. >The EV-1 web site says 0-60 in 9.0 or less. I find 0-30 in 1.6 >difficult to believe. It would require an average acceleration of 27.5 >feet per second per second, or ~0.8G. If 80% of the mass of the car is Again my bad, I did a quick search and used the first number that popped up. Apparently someone in that review got their figures skewed. GM says less than 9 seconds (most sites state 8.4 seconds) and several sites state less than 3 seconds for 0-30 (I couldn't find it on GM's site). 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.
