Matching ICE and Electric Motor Specs and Performance

I'm not going too deed in motor specs or choices, but, if you have baiscally a 185 hp engine to move the car, the first approach is to use a motor with same power output. You should expect performance improvement if you do not use transmission. How much? depends. But basically, you may expect a power transmission efficiency of 85% in each pair of gears, and, if there's a differential with 90 degrees power transmission, efficiency could be as much as 75%.

You should then calculate the driveshaft speed at the to speed, and check it agains the motor speed. Maybe one pair of gears or some reduction device will be needed to match the available electric motor speed and torque.

Also the torque bands for the electric motors will be flatter so less gears are need if at all depending on the electric motor.

http://www.homepower.com/home/ Will get you tons of info.

Brad

AC motors are generally a good approach for traction motors in cars. However if you look at the thousands of EV that have been built by hobbyists, the vast, vast majority are powered by DC motors, and virtually all of those are series wound. Cost is the biggest reason. 100+peak hp AC traction motors and drives are horribly expensive. The Tesla motor and controller are $25,000, and that is about par for the course, because these Drives are very low production items: there just are consumers driving around in 100+ hp electric cars.

PML Flightlink produces wheel motors that are 160 hp each, but they make the Tesla motor seem cheap, by comparision. The Mini equipped with 4 of these (just what the market has been screaming for: a 640 hp mini) has a motor and controller cost that is equal to the cost of a nice house in many parts of the US.

Siemens makes some AC motors and controllers in this range, although they seem to be cutting back on models available. Smaller motors are available through Metric Mind, who specialize in more sophisticated conversion pieces, than the typical DC motors. It would be worth spending some time at their site.

The EValbum will give you loads of ideas: among other things you can search by motor type and manufacturer to see what others have done.

Take a look at the torque curves of PMDC, Brushless DC, Series DC, and AC induction motors. You'll see that the AC motor has the best potential for freeing you from a gearbox: it has very high torque at low speeds, and dimishing torque at higher speeds, (with most being roughly constant hp after some rpm). This means, that without a gearbox, they provide more or less the sort of performance that the Tesla has: very good acceleration up to 60 or so, and a relatively low top speed (which in the Tesla is now about 120, 30 mph slower than the Lotus on which it is loosely based.)

But definitely poke around the EValbum. DC series motors and controllers are pretty cheap, total efficiency is close to that of an AC motor, and there is loads of experience with them to draw upon. (They too have relatively high torque at low speeds, so it is not uncommon to use them without gearboxes, but thay can be made to perform better with multiple gears.) PM motors (including brushless) have a completel different torque curve (typically nearly linear vs amps) and they really almost demand a multispeed gearbox to take advantage of their characteristics. (The brusless motors are some of the most efficient and lightest, but also costly.)

As you seettle in on a motor type then you can calculate accelertion at discrete intervals, a process I can describe later, if you are interested. (The acceleration calculators availabe on the web, which simply ask for an hp and weight, don't get you partcularly close -- but are not incredibly far off, either.)