Automakers race to pack power into electric motors

Once seen as relatively simple commodity components that could power a forklift as well as a supercar, electric motors are increasingly becoming a differentiator, with a range of technologies for different applications. 

Tesla has touted the powertrain of its Model S Plaid, which uses three motors -- one in the front, two in the rear -- featuring carbon-sleeved rotors to achieve a maximum output of 1,020 hp, a top speed of 200 mph (322 kph) and a 0-60 mph time of 1.99 seconds. 

Mercedes-Benz, like Tesla, is promoting its in-house electric motors as a key selling point.

"The electric motor is not a commodity," Mercedes said last year at its EV strategy presentation. "It's a fast-developing technology where innovation and expertise will drive performance and differentiation."

Its AMG brand will use cutting-edge axial-flux motors, built in-house, in its coming AMG.ea EV architecture. "The era of the ultra high performance electric motor is here," said Markus Schäfer, board member responsible for R&D.

BMW -- with the word "motor" in its name -- sees electric motors as crucial to preserving its brand identity in the transition to electrification.

"Bayerische Motoren Werke (Bavarian Motor Works) always stood for the best drivetrains in the market," a spokesman told Automotive News Europe. "Our clear goal is to carry this over to the era of partially and fully electric drivetrains."

To that end, BMW has designated higher-performance versions of its new EVs with the "M" label, just as with combustion models. "The electric motor does make a significant difference for the customer experience," the spokesman said.

Automakers and experts say that future EV efficiency gains are just as likely to come from the motor and power electronics as they are from heavy, expensive batteries. A lighter, better-performing motor can lead to substantial weight savings.

And just as solid state is a potentially game-changing battery technology, automakers including Mercedes-Benz and Renault see a technology called axial flux as a big leap forward for electric motors.

But also like batteries, electric motors have their own raw materials issues. 

Up to 80 per cent of EV motors today use permanent magnets made of "rare earth" metals such as neodymium -- the vast majority of which are mined and processed by China. Their supply is tightly controlled, prices have been extremely volatile (more than doubling at one point in 2021) and extracting rare earths from ores produces toxic waste. 

Electric motors' use of rare earth elements including neodymium, praseodymium, dysprosium and terbium "raises concerns given the geographical concentration of raw material and processing in China, the lack of recycling pathways and high price fluctuations," the International Energy Agency said in a report last year. Each motor uses up to 1 kg of such elements, the IEA said.

The sourcing of electric motors has become a political issue, too, as Europe's automakers, suppliers and governments grapple with the potential loss of thousands of jobs in the internal combustion engine value chain. Motors use vastly fewer parts than a gasoline or diesel engine, endangering smaller suppliers as well as engine-factory jobs. 

Some automakers have brought electric motor production in-house; others continue to rely on Tier 1 suppliers; and joint ventures have found fans, notably at Stellantis.

All electric motors work on the same basic principle: Current delivered by a battery generates an electromagnetic field in a stator; the magnetic field turns a rotor that generates torque and traction at the wheels.

How that magnetic field is created and sustained, however, has become the main differentiator among primary-drive electric motors. Motor technologies are often divided into two main categories, synchronous and asynchronous (or induction), with variations within each one.

• Induction motors: With roots going back to the inventor Nikola Tesla, the induction motor uses direct AC current. (The Tesla brand logo is a cross-section of an induction rotor.) An electric-powered stator generates a rotating magnetic field, which "pulls" the rotor. Advantages: Robust, relatively inexpensive, no rare-earth metals, able to generate high speeds. Drawbacks: Less-efficient because of need to power the stator, less ability to draw back power through regenerative braking, potentially slower acceleration. Tesla's Model S and Model X used induction motors until recently; the twin-motor Model 3 still uses an induction motor in the front; also used in the Audi e-Tron.
• Synchronous motors: The rotor acts as an electromagnet and turns at the same speed as the magnetic field. Advantages: Better power density, low-speed starting and stopping. Drawbacks: Often need complex, costly thermal management systems; use of rare-earth metals in most synchronous motors. Synchronous motors with permanent magnets embedded in the rotor have become the dominant technology, with about 80 per cent market share compared with 17 per cent for induction motors, according to a recent study from IDTechX.

Other synchronous motors do not use rare earths, including Renault's and BMW's. These motors, known as electrically excited synchronous motors, represent a middle ground in terms of cost and efficiency. A wound rotor replaces the permanent magnets, and the rotor is excited by electric energy rather than a magnetic field. Key models with these motors include the Renault Zoe and Megane E-Tech Electric, and the BMW iX3, iX and i4.

Oliver Petschenyk, powertrain analyst at LMC Automotive, said permanent magnet motors were the dominant technology because of their high efficiency potential (ability to transfer energy into forward motion) -- up to 97 per cent; whereas induction motors topped out at about 90 per cent, with electrically excited synchronous motors in the middle (BMW says its new motors are 93 per cent efficient). 

"The efficiency benefits of permanent magnet motors make them far superior to induction motors," he said. Petschenyk estimated that 90 per cent of primary-drive electric motors now use permanent magnets, a figure supported by the IEA.

Lutz Stiegler, solution manager electric propulsion at Volvo Cars, said efficiency was the main reason cars such as the full-electric XC40 Recharge are using permanent magnet motors with rare earth metals.

"The reason why we have chosen this is the pure efficiency or torque or power density, and because of the best trade-off of power density, torque density and efficiency for these engines, most likely we will stick with this technology at least for the time being," he told Automotive News Europe.

Nonetheless, Stiegler said Volvo is closely monitoring its rare earth supply chain.

"When it comes to the environmental aspects and the human rights aspects, we are absolutely committed to the highest ethical standards and to really get our rare earths and neodymium magnets from sources where we can really trace them back," he said, citing blockchain technology as a way to track and trace them.

Even if the biggest EV makers including Volkswagen and Mercedes don't plan to switch from permanent magnets immediately, they say they are looking for ways to reduce their content.

"We have deliberately minimized the proportion of heavy rare earth metals in our e-drives through our design choices and continuously monitor the supply chain," VW told Automotive News Europe through a spokesman. "We are also investigating alternative concepts without rare earth metals."

Few components have more potential effects on jobs than electric motors. Overall, an electric vehicle can have 50 per cent fewer parts than a combustion vehicle, and require 30 per cent less labour. That difference is particularly acute for electric motors, which have few parts beyond rotors and stators. 

There will be many new jobs building batteries and electronics, but CLEPA, the European automotive suppliers' lobby group, says up to 500,000 jobs could be lost overall, especially at Tier 2 and Tier 3 suppliers that produce internal combustion engine components.

When EV adoption rates were miniscule, the majority of automakers outsourced engine production to Tier 1 suppliers, but that is changing, Petschenyk said. Just 35 per cent of electric motors are now built in-house, he said, but that will grow to 60 per cent by 2030, as automakers seek to retain jobs and gain control over the EV value chain.

"As internal combustion engine production is reduced, they will start using the same factory space to focus on electric motors," he said.

Renault Group has long made its own motors at its engine factory in Cleon, France. BMW builds motors at its Dingolfing, Germany, factory. VW plans to build up to 1.4 million electric motors for its MEB platform annually starting in 2023, at factories in Kassel, Germany (Europe and North America) and Tianjin, China.

Stellantis established a joint venture (as PSA Group) with the Japanese motor maker Nidec in 2017, with the first motors scheduled to roll off the line at the Tremery, France, factory at the end of this year. CEO Carlos Tavares has said Stellantis must "master its destiny" in the EV value chain to make up for lower margins. All told, he has said, in-house battery, inverter and motor production could save 10 per cent on the cost of the powertrain.

At Mercedes, "In-house electric motors are a key part of our strategy, with a clear focus in efficiency and cost," said Schäfer, the board of management menber.

Volvo is in a transition phase between "make" and "buy," Stiegler said. Its current generation of EVs, including the XC40 Recharge compact SUV and C40 compact sedan, are using motors from the Valeo-Siemens eAutomotive JV, but production is likely to be internalized in the future.

"The most important thing is to have the best available technology on the market in the cars as fast as possible," Stiegler said. "It's more a question of time to market for us." 

Volvo, though, will need many more motors to reach a goal of 50 per cent EV sales by 2025. In December 2020, Volvo committed to invest about US$83 million to build its own motors at its factory in Skovde, Sweden. The transition will start with assembly of motors for the next generation of Volvo EVs, which will start to debut this year, followed by full production "in mid-decade."

Even as Tesla and others push the limits of traditional electric motors, another technology, called axial flux, is making a bid for including in EVs. Also called "pancake motors," axial flux machines can produce greater torque density, use fewer materials and are lighter.

The main difference is that in an axial motor, the magnetic flux travels parallel to the motor rotation axis rather than perpendicularly, as in current designs (called "radial flux"). This gives axial flux motors a larger diameter, which can limit their placement in EV applications, but a shorter length.

But axial flux motors have a number of comparative advantages, proponents say: They generate more torque, because the magnets are further away from the central axis. They have fewer thermal management issues, and they use fewer materials, important from both a weight and cost standpoint.

Tim Woolmer, the founder of UK startup Yasa, an Oxford University spinoff, says that, in general, axial flux motors have 30 per cent greater torque density. Yasa's proprietary technology, he says, doubles that advantage.

Yasa's axial-flux motors made their debut in several plug-in hybrid supercars, including the Koenigsegg Rovera, and Ferrari's first plug-in hybrid, the SF90 Stradale. 

Mercedes, for one, is a believer in Woolmer's technology as a primary-drive unit. Last July parent company Daimler acquired a controlling stake in Yasa and in November announced it would build axial-flux motors at a repurposed combustion-engine factory in Berlin. 

The motors will be used in performance brand AMG's electric-only platform and potentially in future mass-market models.

Renault is moving on a smaller scale, taking a 21 per cent stake in Whylot, a French startup, aiming to have axial-flux technology in mass-market hybrids by 2025.

Woolmer, whose doctoral thesis work at Oxford formed the basis for Yasa, says EV motor technology is still in its relative infancy, with many more gains to be made even from radial flux motors. 

"The electric motor is no longer seen as a commodity -- I completely agree with that," he told Automotive News Europe. "There's a huge R&D race to make the motor, smaller and lighter, more efficient and low cost."