On Wed, 06 Feb 2008 14:56:50 +0100, scott wrote:

>> I still can't figure out why they don't make a car that's electric, but
>> has a small deisel generator in the boot...
>>
>> (You'd only need to run it when the battery gets low. You wouldn't
>> waste fuel sitting in traffic. Electric motors don't require a gearbox
>> or a differential, so you'd get continuous acceleration without gear
>> shifts...)
> 
> Actually you would need a gearbox for it to be useful.  Electric motors
> generate maximum torque at very slow speeds, the faster the motor goes
> the lower the torque.  This is exactly the wrong thing you need for a
> car, where the faster you go the more torque you need to overcome the
> speed squared air drag.  If you didn't use a gearbox you'd end up with a
> car capable of burning out the tyres at low speed, but that took 10
> minutes to accelerate from 60 to 70 mph.

Have a look at how the Prius' engine is designed.  It's very clever, and 
uses a continuous acceleration engine (yes, no shifting is done; I test 
drive one a few years ago, and it was smooth and there was sufficient 
power to get a pretty good start.  It wasn't a Ford Mustang, but I wasn't 
unhappy with the acceleration.)

Jim

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