Batteries Aren’t the Only Obstacle to Clean Energy

Motors Matter, Too
by lawrence m. fisher

larry fisher, a former New York Times reporter, writes about business, technology and design.

Published May 13, 2022


Technology writers love breakthroughs. But technologies often don’t cooperate, advancing by steps rather than leaps. So it goes with electric motors.

Electric motors are, in fact, a very old technology. Benjamin Franklin experimented with a precursor, the electrostatic motor, in the 1740s, and Michael Faraday demonstrated the first electromagnetic motor in 1821. Industrial versions appeared about 10 years later, operating on direct current as supplied by batteries. Nikola Tesla invented the induction motor, which gave birth to alternating current motors, in 1874. A century and a half of incremental improvements followed.

Spruced up over the decades, the Tesla induction motor was good enough for most industrial applications and household appliances. But the rebirth of the electric vehicles a dozen years ago jumpstarted a new phase in motor development. And while media attention has rightly focused on the need for cheaper batteries that can store more energy in smaller packages, happily electric motors have been quietly improving in power output, weight and heat. These gains will contribute to a new generation of EVs with better performance, lower cost — and even green cred.

Lighter, Faster, Cheaper?

Five years ago, Spectrum, the journal of the Institute of Electrical and Electronics Engineers, ran an article headlined, “Shut Up About the Batteries: The Key to a Better Electric Car Is a Lighter Motor.” Interviewed recently, the author, Prof. Martin Doppelbauer of the Karlsruhe Institute of Technology said that he didn’t write the headline, and would have chosen less provocative words, but he’s not backing down.

Common industrial electric motors were already pretty efficient, turning about 80 percent of the energy they consume into power and torque, compared with as little as 30 percent for internal combustion engines in vehicles. But the motors being developed today spin ten times faster and weigh a tenth to one-hundredth as much, allowing them to achieve 95 percent efficiency. And engineers have 99 percent in their sights.

Doppelbauer and his students have eked out additional gains by combining multiple design principles in a single motor. Most EV motors use permanent magnets, which are affixed to the spinning rotor; the stationary housing, or stator, contains the coils through which electricity flows. This setup is quite efficient when the rotor is turning relatively slowly. But a few companies, notably BMW and Renault, use motors with the electric coils in the rotor, which work better at high speeds. The Karlsruhe motor finesses the trade-off by using both.

Add a few more bells and whistles and the result is a motor able to produce almost 6 percent more torque and attain 2 percent higher peak efficiency. On the road, this translates into an extra 4.4 percent driving range on a charge. What’s more, the extra range is close to a free lunch because the advanced design uses only a few additional parts, which cost less than the battery capacity they can replace. Early examples powered one team sponsored by Ka-Racing to victory in electric car racing, and a Karlsruhe motor is currently being tested by a major German auto company. “Had you asked me 20 years ago, I would not have thought this was possible,” says Doppelbauer.

Trickle Down Technology

It’s been said that Koenigsegg is best known for being largely unknown, and for making the most expensive cars on earth. The Swedish company makes $3 million hyper-cars with astronomical horsepower ratings and near-300 mph top speeds. So it was a surprise when the company recently announced a new type of electric motor to be used in a forthcoming gas-electric hybrid called the Gemera, its first four-seater.

Electric motors help boost the Gemera’s power and torque to 1,700 horsepower and 2,600 ft-lbs, truly astonishing numbers considering that Ferrari’s new hybrid, the 296 GTB, offers a “mere” 819 horsepower. Dragos-Mihai Postariu, who leads Koenigsegg’s electric motor design, concedes wryly that all this is in service of a “party trick — zero to 400 kmph (248.5 mph) in 15 seconds. “The motors are somewhat peculiar because you need nowhere near this kind of power in normal usage.”

While engineers are challenged to improve motors for electric vehicles, technology gains abound in more pedestrian applications like home appliances, and more lofty ones such as aerospace.

All EV motors in use today are radial flux designs, which are cylindrical in shape. But Koenigsegg’s Quark motor uses atrial flux, a low-profile design that suits applications where space is at a premium — like the space between the gasoline engine and the transmission in a hybrid. Radial flux motors, by the way, generate more power; axial flux motors more torque. (For a detailed explanation of the difference check out Charged, an EV magazine.)

Actually the Quark is a bit of a hybrid in itself, a “raxial flux” motor, if you will. Some “92-95 percent of its output is made by axial flux,” explains Postariu. But there is a small amount of axial flux in a radial flux design and vice-versa, which typically goes to waste.

Koenigsegg uses that leakage flux, much the way turbocharged internal combustion engines use the energy in exhaust gases to spin a turbo and make more power. “I have read quite a lot of articles speculating about what we’ve done and none of them are remotely right,” Postariu adds puckishly.

In a tiny package that weighs just 63 pounds, a Quark motor develops 335 hp and 443 lb-ft of torque — albeit just for 20 seconds after which output drops to 134 hp and 184 lb-ft of torque. But that’s not a problem for the Gemera, which boasts three Quarks along with a 600-hp internal combustion engine! Postariu says Koenigsegg is already in talks with more mainstream EV manufacturers about using its technology.

When might Quark-like motors trickle down to less exotic cars? Postariu says it could be before 2030. “The engineer in me would love to have somebody tell me we need to do this at the $100,000 price point. There is money to be made and things we can do much better than what’s on the road.”

Not Your Parents’ Vacuum Cleaner

While engineers are challenged to improve motors for electric vehicles, technology gains abound in more pedestrian applications like home appliances, and more lofty ones such as aerospace.

Much of the power gains over the past 20 years came from the advent of permanent magnets incorporating rare earth elements such as neodymium. “The problem is, the mining of these rare earths is pretty disastrous and nearly all the raw material comes from China,” points out Barrie Mecrow, professor of Electrical Power at Newcastle University.

Car makers thus face some pressure to avoid using rare earth magnets in new EV designs — primarily political pressure in the U.S. and environmental pressure in the EU. BMW has made environmental virtue a marketing priority, and uses no rare earth magnets in its new i4 EV.

EV motor efficiency has improved through spinning the rotor at higher speeds. “Old universal motors, like in a vacuum cleaner, weighed a pound,” Mecrow explains. “The motors in today’s vacuum cleaners might not weigh more than an ounce. I do a lot of work with Dyson; they’ve made their motors really tiny by making them go incredibly fast — over 100,000 revolutions per minute.”

Even the motors in production EVs spin at over 20,000 rpm with some reaching 30,000, compared with a max of 5,000 to 7,000 rpms for the crankshaft of most internal combustion engines. But super-speed motors are high-tech beasts. “You’ve got a lot of electronics driving the motors, big devices putting hundreds of thousands of amps into the motor,” says Mecrow. “If one of those devices fails, the software isn’t going to save you, so you need redundancy.”

That said, faster, lighter and more potent electric motors are beginning to find applications in powering aircraft, a few of which are nearing the market. Eviation, an Israeli startup, expects to launch the 11-seat Alice, the world’s first commercial all-electric passenger plane, within weeks. And it has already sold 12 to DHL, the German air courier giant. Meanwhile, a host of companies are developing electric “air-taxis,” including Airbus, Embraer and the California startup Wisk, which has received substantial funding from Boeing.

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The electric motor, suffice it to say, is a seemingly endless work in progress — a 19th century technology that is keeping up with the times. Good thing, too; without the newest versions, the transition to renewable energy would be slower and messier in a world that can ill-afford either.

main topic: Technology