Mahle's Contact-Free Electric Motor
Mahle's Contact-Free Electric Motor
Image: Mahle

Automakers outside China are scrambling to develop electric motor designs that use no permanent magnets, partly because the magnets require rare earths, and mining rare earths causes pollution. It’s also partly because the mining is done in China, a formidable automotive competitor.

These alternative motors turn the rotor using electromagnetic force alone; we’ve covered more than one such motor recently. One problem: Designs that put copper windings in the rotor have to transmit electricity to a moving target, and the point of contact—the slip ring—is subject to wear and tear.

Today Mahle, a German auto parts company, unveiled a motor that’s free of both rare earths and of physical contact. Power is beamed into the rotor wirelessly, through induction, by a coil carrying alternating current. This induces a current in the receiving electrode, inside the rotor, which energizes the copper windings there to produce an electromagnetic field.

That means there’s practically nothing that can wear out. “There are no contacts to transmit electricity, no abrasion, no dust formation, no mechanical wear,” Martin Berger, Mahle’s head of research, said Wednesday, in an online press conference. “Also I have to say, if one must service a non-magnetized rotor, it’s not difficult to exchange the rotor.” 

It may seem strange to try to minimize wear and tear in electric motors, seeing as they are already famed for their simplicity and durability. Unlike internal-combustion engines, electric motors have practically no moving parts, and they are fairly easy to take apart and put back together. Perhaps Mahle’s engineers got the idea from their longstanding work in wireless charging technology. Maybe the contact-free rotor design provides advantages beyond mere durability. 

The rotor is supplied with energy via an alternating field, which is then converted into direct current for the electromagnetic coils.The rotor is supplied with energy via an alternating field, which is then converted into direct current for the electromagnetic coils.Image: Mahle

Berger says the new motor combines the best points of several motor designs, for instance by offering good efficiency at both low and high torque. Overall, the company asserts, the motor achieves at least 95 percent efficiency in typical EV use and tops 96 percent efficiency at many operating points. A release from Mahle says that no EV except for Formula E racing cars has done better.

The machine can easily be scaled up from use in subcompact cars up to small trucks, Berger says. However, it isn't ideal for ultracompact vehicles, such as e-bikes, or for large trucks that generally operate at a constant load.

“Very fast or heavy vehicles would need a transmission,” he adds. “But for the majority of application cases, passenger cars for example, one gear is enough.”

Mahle doesn’t say which companies are interested in the new motor, only that samples are already being delivered and that mass production is about two-and-a-half years away.

The Conversation (0)

Self-Driving Cars Work Better With Smart Roads

Intelligent infrastructure makes autonomous driving safer and less expensive

9 min read
A photograph shows a single car headed toward the viewer on the rightmost lane of a three-lane road that is bounded by grassy parkways, one side of which is planted with trees. In the foreground a black vertical pole is topped by a crossbeam bearing various instruments. 

This test unit, in a suburb of Shanghai, detects and tracks traffic merging from a side road onto a major road, using a camera, a lidar, a radar, a communication unit, and a computer.

Shaoshan Liu

Enormous efforts have been made in the past two decades to create a car that can use sensors and artificial intelligence to model its environment and plot a safe driving path. Yet even today the technology works well only in areas like campuses, which have limited roads to map and minimal traffic to master. It still can’t manage busy, unfamiliar, or unpredictable roads. For now, at least, there is only so much sensory power and intelligence that can go into a car.

To solve this problem, we must turn it around: We must put more of the smarts into the infrastructure—we must make the road smart.

Keep Reading ↓Show less