EV Motor Development Is on the Move

With EVs on the path to high-volume market penetration, automaker and supplier traction-motor production strategies come into focus.

Fifth-generation BMW “e-drive” electric-motor modules are designed and manufactured in-house. (BMW)

It’s happening – the transition to EVs is undeniably underway. Recent launches such as Ford’s Mustang Mach-E, versatile-body-style EVs from mainstream brands Hyundai and Kia and forthcoming electric pickups from Ford and GM are positioning EVs on the high-volume trajectory widely forecasted as inevitable. Scores of new EV models from all automakers are promised to launch by 2025. Vivid evidence of the sudden EV and electrification groundswell came in early February when the short list of candidates for the European Car of the Year award was announced: every one had a plug.

Cutway of BMW’s latest e-drive system, now in its fifth generation. (BMW)

Aside from batteries, the most significant component of the EV value and supply chain is the traction motor that – often integrated with an inverter and associated power electronics – is applied in single, dual, triple, or even at-each-wheel configurations to provide propulsion. Electric motors are vaunted for their comparative simplicity and efficiency. As such, the design hasn’t substantively varied in the past half-century. But as EV market penetration hits its stride, automakers, suppliers and specialist e-motor developers are flowing massive resources to motor design, manufacturing and deployment.

General Motors said its new family of traction motors is scalable for its full lineup of pending EVs and was designed for exceptional thermal control and efficiency. (GM)

Engineers and experts who spoke with SAE Media largely agree that two of the most crucial aspects of the transition from internal-combustion engines to electrified propulsion are how quickly it happens and whether automakers or suppliers will assume the development and manufacturing lead. Even if OEMs desire to emulate their tradition as the chief architects and builders of IC engines, the new paradigm of electrification may deliver different results. It is likely there will be markedly more traction motors designed and manufactured by suppliers than has ever been the case for IC engines.

“It seems there will be a mix of in-house, purchased, and in-house assembly with purchased components,” said Jeff Hemphill, chief technical officer at Schaeffler, in response to emailed questions from SAE media. “Our goal is to develop technical advantages that make us a preferred supplier,” he added. It’s a tack many Tier 1 suppliers are likely to take.

In-house or supplied

Premium-EV startup Lucid Motors lavished ingenuity from several engineering disciplines to derive thunderous performance and efficiency for its traction-motor design. (Lucid Motors)
Mercedes-Benz last year acquired Yasa, developer of power-dense and extremely thin axial-flux permanent-magnet motors, a design some believe may be advantageous in certain light-vehicle applications. (Mercedes-Benz)
Lucid Motors chief engineer Eric Bach. (Lucid Motors)

Currently, several global full-line automakers have indicated they intend to retain design and manufacture of traction motors as an in-house competency. General Motors plans to have some 1 million units of EV manufacturing capacity in North America by the end of 2025. Last fall GM revealed a “family” of electric motors – a pair of permanent-magnet (PM) synchronous units outputting 180 kW and 220 kW (241 hp and 295 hp) and an AC induction motor rated at 62 kW (83 hp) – designed to work as a system with the company’s Ultium lithium-ion batteries. GM has yet to provide specifics about manufacturing, but in January announced it is spending $154 million to upgrade and refit its components plant in Lockport, New York to produce motor stator modules. It is widely believed the company will produce most, if not all, of the new EV motor portfolio in North America.

Ford has not made any wide-ranging announcements about its electric-motor manufacturing strategy but has said the PM motors for Mustang Mach-E and the F-150 Lightning pickup coming in mid-2022 were developed in-house and are or will be built at the company’s Van Dyke transmission plant near Detroit. The company said the F-150 Lightning’s two traction motors – one per axle – will generate a combined 318 kW (426 hp) with the pickup’s standard-range battery pack and 420 kW (563 hp) with the extended-range battery. Torque in either configuration is 775 lb-ft (1051 Nm).

BMW, a brand with much to lose if the transition to electrification falls short of its storied propulsion-centric heritage, recently announced a half-billion-euro expansion of its Dingolfing, Germany, plant for its “e-drive” motor modules (traction motor, power electronics and transmission in a single housing). Production at the site and others in Germany will facilitate manufacturing of e-drive (now in its fifth generation) for upwards of 500,000 electrified vehicles in 2022. “We expect at least 50 percent of the vehicles we deliver to our customers worldwide to be electrified by 2030. To achieve this, we are relying on our extensive in-house drivetrain expertise,” said Michael Nikolaides, senior VP, Production Engines and E-Drives, BMW Group, in a release.

The “in-house advantage” might be most intense at startup Lucid Motors. In an interview with SAE media, chief engineer Eric Bach stressed that Lucid’s electric-drive module – a PM motor, inverter and gearbox the company dubs “impossibly compact,” is an entirely in-house effort. “We purchase components, obviously, like a casting, we purchase gears, we purchase bolts, we purchase copper wire, we purchase the lamination stacks, but they've all been designed and engineered in-house,” Bach asserted. “And we wind our copper in house. We do it really from single parts to the complete end-of-line-tested drive unit.”

Countering the current slant toward in-house design in manufacturing for traction motors is the opening that several suppliers see in e-axle design and manufacturing, supplying a motor-integral axle module to easily impart propulsion for an axle not typically powered in the standard vehicle configuration. Tier 1s including Bosch, ZF, Magna, GKN, Schaeffler, BorgWarner, and American Axle see e-axles as expanding business for many years, particularly for hybrids. E-axles also are considered a method to simply and cheaply impart AWD capability for typically front-drive vehicle architectures.

Design and materials in ‘flux’

As the light- and commercial-vehicle EV markets expand into volume, it seems certain that long-established PM motor designs will be the prevalent choice – particularly for high-volume or highly price-competitive vehicle segments. Such was the thinking for GM with its new three-motor lineup, said Patrick Curran, assistant chief engineer - drive units.

“When we designed the family of motors, we designed it such that in pretty much any combination, we can do anything in our fleet today. A lot of [vehicles] that we're not even talking about yet, we're going to be able to do with these. Think about how many engines and transmissions we have in the corporation,” he continued. “It's an embarrassingly large number. We're going to be able to do all that with three motor combinations. There are different gear ratios, so you can get different output torques. But that's how we can really fine-tune the performance for each of those.”

Schaeffler’s Hemphill confirmed that “Permanent-magnet synchronous [motors] have the momentum right now, with induction machines sometimes used on a second driven axle. This seems likely to continue but could be modified by market forces like magnet prices.”

Curran noted advancing technology will enable “conventional” permanent-magnet motors to do even more. “As technology advances, we'll probably be able to bump up (motor speeds). That's what we've seen in the industry over the years. We can play with those [gear] ratios. If your ratio goes up, you get more torque, your ratio goes down, you get more speed to the wheel. We can do a lot of things. As technology goes up, the speed is increasing.”

He said each of GM’s motors has a different maximum rpm, broadly connected to the mass of the unit. But developing motors capable of higher rpm typically enables more power output. “If you can go for more rpm, you basically can get more output from the motor,” Curran explained. “You have a constant torque phase, and then you get a constant power phase. That power phase comes in after you're through that constant torque speed. As the speed keeps going – obviously power is speed-based – you can get more and more power as you go along.”

Lucid already has won acclaim for its Air motors’ combination of monstrous power – ranging from 480 hp to 670 hp, depending on trim and battery-pack configuration – and industry-leading driving range. To get there, chief engineer Bach said the company’s engineering teams focused on efficiencies – chiefly windings and thermal management, but even gear-tooth design – for its highly power-dense yet ultra-compact PM motor. (The company claims the entire drive module can fit in an airline roller bag and weighs just 163 lb [74 kg]). The Air platform’s system architecture also operates at 900V, which also has a significant impact on power potential.

The Lucid drive motor has carefully calculated windings the company dubs “continuous-wave” because of the way in which the rectangular copper is precision laser-welded, rather than the typical “hairpin” copper windings pressed into slots. “The winding pattern has been developed in house to achieve a fundamentally efficient and torque-dense electromagnetic layout,” explained Bach. “The electromagnetic simulations, the flux simulations, the thermal simulations – that's all done in house. And then we've developed the winding not just to be great from a performance perspective, but so that it's really easy to manufacture.” Bach also claims the Lucid design uses “about half as much copper as the competition.”

He added that a clever augmentation to the motor’s powerful cooling of its windings comes easily – and at almost zero cost. As the stator stack’s laminated layers are stamped, the dies are indexed to punch a portion of the winding cooling channels into each layer. “We punch that entire lamination stack with the cooling channels included for free.”

As scrutiny mounts about electrification’s impact on scarce and expensive minerals, manufacturers and traction motor developers have long been at work to reduce the amount of rare-earth elements in motors, particularly their magnets. Toyota and Honda have for years worked to bring to mass production rare-earth-free drive motors. Development continues toward significant reductions in all motors that employ magnets.

“There are lots of reasons not to want to put a bunch of rare earth in there,” asserted GM’s Curran. “It's not just from where it comes from, but it's super expensive. You want to make sure you get as little as possible, and then eventually maybe you get out of it altogether. That's where the science is – how do you get the same efficiency and same torque with less and less, and ultimately zero rare earth?”

In October 2021, GM and GE Renewable Energy announced a non-binding Memorandum of Understanding (MoU) “to evaluate opportunities” to improve supplies of heavy and light rare-earth materials and magnets, copper and electrical steel used for manufacturing of electric vehicles and renewable energy equipment. The companies said the initial focus is on creating a North American and European-based supply chain for vertically integrated magnet manufacturing.

Lucid’s Bach said his company also is endeavoring to manage rare-earth consumption. “We are using neodymium magnets, obviously, because that's where you need to go. But we are using very, very little compared to the competition, again, for the power that we are pulling out.” He added Lucid is not using “heavy” rare earths infused into neodymium to impart extra heat-resistance characteristics crucial to consistent traction-motor performance.

Honda and Toyota also have for some time been developing drive motors without heavy rare-earth composition, substituting more abundant and lower cost rare earths that it believes can lead to magnets that retain exceptional heat resistance.

Hemphill said Schaeffler is studying design improvements such as improved cooling concepts to “reduce magnet content and/or cost.” The company also is developing new supply-chain partners to assure sustainable supply, as well as studying vertical integration to control costs. “At the moment,” he said, “it seems these measures and the developing market will be sufficient to stay with PM motors.”