An electric car's motors are all about magnets. Magnets in the motors turn the wheels by switching rapidly between attracting and repelling forces to spin the hub.



But here's the problem: heat. Just like an internal combustion engine, the electric motor generates a lot of power-sapping heat. That's why electric motors often have two ratings: peak power and continuous power. The latter number is lower because heat saps power from the magnets during extended use. All conventional wheel-hub motors must confront this issue.

Across the pond, a team at Equipmake, a 28-person automotive engineering firm from Norfolk, England, is working on a better way around this efficiency impasse. Their new design for an electric motor arranges the magnets around the whole wheel hub by standing them on end, like the spokes of a wagon wheel. The APM 200, set to hit the market in 2020, can generate the same power for the same cost as conventional electric motors, but in a significantly smaller and lighter design that's easier to cool.

“It's been pretty well-known for a while,” Equipmake managing director Ian Foley says of the spoke motor design. “There just hasn't been a low-cost route to manufacture.”

Most of the motors in electric and hybrid cars arrange their magnets in a V-shape around the wheel hub. Because the magnets are stacked on one another, it's difficult to completely seal the laminations that envelop them. That means coolant can't flow directly over the magnets to cool them. So V-shape motor makers have had to use expensive, exotic types of rare earth magnets to mitigate the problems of heat buildup.

For example, neodymium is the most commonly used rare earth magnet. But for a V-shape motor to run at high temperatures, they must add the chemical dysprosium into the magnet, which drives up the cost.

In the spoke motor, by contrast, every magnet is mounted to a forged aluminum wheel hub, which means coolant can be piped through the hub and directly over its magnet “spokes.” Having coolant in contact with the magnets allows for more efficient cooling, and because the motor doesn't lose as much power due to heat buildup, it can use the cheapest grade of neodymium magnet without performance loss.

In addition, Foley says, the spoke motor has the advantage of packing more power into a lighter design. Half as big and 20 percent lighter than V-shape hub motors, a spoke motor would put out 25 percent more torque given the same size and type of magnets. That means engineers can afford to cheapen the magnets and scale down the design to meet a particular power target. Foley says:

“There was a paper published by General Electric in (2016), responding to a challenge by the U.S. Department of Energy, looking at power density for motors. and they came to the conclusion that a spoke motor was the best way to go… but that there are challenges to manufacture and cool it. The ideas they came up with weren't really practical for mass manufacture, and that's the bit we've solved.”

Equipmake is a cadre of automotive industry veterans, none more so than Foley. He developed active suspension for Lotus and then a paddle shift gearbox for Le Mans race cars in the 1990s. He was also the man behind Formula 1's KERS regenerative braking system for Williams-Toyota in 2009, and experience working on it led directly to Equipmake's spoke motor, by way of the electric car racing circuit Formula E.

“It started with a customer of ours who was interested in having a motor for Formula E,” Foley says. That would have been possible when the series was announced and initially proclaimed to be an open-competition series in which auto companies could build their own components. By its first season, though, the rules had changed to a more-open series in which teams could choose their engines. By the time first season began, it was a spec-racer format in which all competitors had to use the same electric motor developed by McLaren. Equipmake's customer saw their dreams of competing in Formula E's inaugural season fly out the window. Meanwhile, Foley's team had an unfinished motor on their hands.

Soon after, they caught wind that British sports car manufacturer Ariel (remember the Atom?) was designing a jet engine/hybrid electric supercar, the Hipercar, and Ariel needed a manufacturer to supply the electric wheel hub motors. Having proved the APM 200 concept for Formula E, it was a short hop fro Foley to adapt the spoke motor design for a road car. The Hipercar, coming in 2020, will pack four of Equipmake's APM 200 spoke motors, each generating 299 hp and 332 ft-lb. of torque. The same motor will also power a low-cost electric bus planned to begin service testing that year.

The hitch is that while it'll hit the market soon in the low-volume Hipercar, Equipmake's spoke motor is at least three years away from mass production, says Foley, and more like five. “Our expectation is that in two years time, we'll be starting at around 1,000 a year,” he says, “but that's on a manual (hand-made) manufacturing basis that requires two or three people.” Run with more people working a multiple-shift schedule, he says they're gearing up for 10,000 per year.

Designers of electric sports cars, in particular, want motors to be smaller and lighter in order to reduce unsprung wheel weight that bogs down handling and agility. Designers of all electric cars want motors to be lighter so that cars have less weight to push around and be more energy efficient. If the same motor can work as well for a low-cost all-electric bus as for a hybrid supercar, and if Equipmake can scale up production quickly enough to keep pace with the industry's electrification, the spoke motor of the future may be one of the few cases in which engine evolution actually means cheaper, simpler materials.

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