Electric wheels

Posted on December 7, 2007

7


So now I need to get my hands on some electric motors for my car.

As I said, I’d really like to install motorized wheels. I could do like the other 1.337 EV guys all over the world have done and use the traditional cylindrical motor and mechanical transmission, but I want nothing but the best for this project.

This idea is not new, it’s been around for a long time. I first saw it on the Mitsubishi MIEV’s “In-wheel motor”. Back in 2005 they built an “Evo 9” Lithium-ion battery rally car that was fully electric and had 4 wheel drive. And each wheel was a powerful 50kW motor. The great thing is, they didn’t even have to invent anything extremely forward thinking; they just adapted a permanent magnet synchronous motor (a.k.a. “DC brushless”) to a normal car wheel, and that was it.

miev-in-wheel.jpg

(This picture comes up in so many places, I have no idea whose copyright it is… I borrowed this one from www.autoblog.com)

My intention is to do exactly the same: fit an electric motor into the wheels.

My car has “normal” 15 inch wheel hubs, which is kind of tight compared with the ultra-large twenty-something inches of the MIEV. However, there is still a lot of useful volume available inside the rear wheels, because the rear brakes are of “drum” type. The front wheels have a lot less space, since the disk brake and caliper take over most of it. So, in order to make my life easier, I’m only concentrating on motorizing the rear wheels. The front ones will be left for another phase, if and when it comes to that.

So I did a little digging and e-mailed Japanese “Toyo Denki”, the manufacturer of the MIEV motors, in the hope that I could buy a pair of them. They never replied to me. I guess they have bigger plans (like the heavy transport industry) than to sell them to the public.

Why does it have to have permanent magnets? Because (as far as I know) it is impossible to have regenerative braking in a brushless motor without them. (This is not true. All electric motors work as generators, it’s just simpler and more energy-efficient to do it with magnets). And having no contact brushes is a big plus for zero-maintenance, lower cost, higher power density, lower weight, better thermal management, and overall reliability.

Another question that’s been on my mind (and other people’s) is: why not remove the brakes altogether? It would make it easy to include a motor, and we don’t actually need mechanical brakes once the electric system is working well… That is what another beautiful project has done: the QED Mini, sponsored by “PML flightlink” component manufacturers. They’ve built a monstrously powerful (>250HP) demonstration hybrid out of a BMW Mini, and it has no brakes except for a small set used for parking. That project is my strongest inspiration, because they have practically done everything right! 🙂 The vehicle is a Serial Hybrid, with 4 high-power and high-torque motorized wheels, and only a small 20HP on-board generator, environmentally friendly. Unfortunately, it is not for sale, and it will not be. It is a demo project created only to showcase their technology.

I e-mailed them, and what do you know, they actually replied! They gave me prices for their motors and their special 2-wheel and 4-wheel controllers. These where 9.000 GBP (13.300 EUR), 4.000 GBP (5.900 EUR), and 6.000 GBP (8.850 EUR), respectively. Since it would not be reasonable to spend 32.500 EUR (roughly the price of a Prius) in motors and controller to make a normal 2-wheel-drive car (apart from the batteries and the car itself), I think these prices where a funny and polite way of telling me to fuck off. Well, they’re British, and I can handle a joke. 🙂 If you read the news, you’ll see that they (and Volvo) also have bigger plans than selling to the public.

Of course, they have all the funding, know-how, and time resources that I don’t have. Plus, they don’t have to make a perfectly safe day-to-day vehicle, like I do. So, for the first generation, I think I’m going to stick with the mechanical brakes… 🙂

There is another international maker of motorized wheels: “TM4 Transport”, a division of “Hidro Québec Group”. I also e-mailed them, and they replied that they would only supply their motor-wheels to partners with the capacity of producing a high volume of vehicle units per year. I guess that rules me out.

In despair, I turned to the generic motor manufacturers, like Siemens or Phase, but I can’t locate any model that fits the bill. They’re either too small, too large, too weak, or too slow for this application. And I bet they’re all quite expensive, and impossible to buy as a member of the public.

My conclusion, at least over here in Europe, is that it’s impossible to go out and buy such an electric motor. Nobody wants to sell me a pair of them. If I ordered 1.000, maybe, but one or two…

So, unless you can tell me where to buy such a motor, I think I’ll have to just build it myself. It can’t be that hard, can it? After all, the electric motor is 170 years old, and the Chinese are presently the greatest manufacturers… 😉

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Posted in: Add-On-HEV, Motors