Wouldn't a Transmission Improve Efficiency?

by John
(Iowa)



I've noticed that most people are bolting their electric motors directly to their transmission. Why aren't they using a typical flywheel and torque converter setup between the motor and transmission? Wouldn't you be able to go faster with fewer horsepower if you could shift gears?

Hi, John -
The answer is in the difference in the torque curve between the internal combustion engine and the electric car motor. If you'd like to look at a good graph, check out p. 115 of Build Your Own Electric Vehicle.

With an internal combustion engine, most of the horsepower of the engine is needed to get you from 0-45 mph. A transmission helps it get there as efficiently as possible.

With an electric motor, like the series wound DC motor that is so popular in homebuilt electric car conversions, getting from 0-45 mph is what it does best.

Since an electric car's motor is controlled by a pot box and a controller, the real challenge is to avoid losses as much as possible.

At the present time, no transmission does a better job of minimizing losses than some sort of two-step arrangement; one gear for getting moving, one gear for the freeway.

All the best,
Lynne

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starstarstarstarstar 		CVT on electric isn't for what you'd think.
by: tlhonmey

The torque vs RPM curve on an electric motor is usually pretty close to flat, so you don't get the benefit you do with other types of engine where a CVT or IVT will let you run the engine in its "power band" all the time.

Now, since the simplicity of an electric motor means that the power consumption is dependent more on actual load than on RPM, you could use an appropriate CVT as an alternative to a controller. Just run the motor at full speed all the time and adjust the ratio to get the wheel speed you want. Twenty years ago this might actually have even been your best option efficiency-wise. A good quality modern controller board probably has efficiency at least as good as a CVT though, and likely quite a bit better, plus it has fewer moving parts to wear out, weighs less, and takes up less space.
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starstarstarstarstar 		Direct drive
by: Anonymous

How about removing transmission and drive shaft and mounting motor to differential using u joints
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starstarstarstarstar 		CVT transmissions
by: Anonymous

CVT transmissions are not generally suitable for EVs because they cannot handle the low range torque that well. I tried one about 5 yrs ago and could not get it to run for long before the belt would break. I thought at the time that the CVT would be the ideal trans for electric
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starstarstarstarstar 		Where is the most efficient place to put the motor and the two speed transmition?
by: Guardian Electronics

Where is the most efficient place to put the motor and the two speed transmission?

Can we put it on the back reel and keep the original gas engine?
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starstarstarstarstar 		CVT
by: Anonymous

Has anyone looked into using a CVT (continuously variable transmission)for an electric car? The motor can spin at it's most efficient or most powerful RPM as needed all the time.

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