Lightweight British electric motors to power Mercedes-AMG’s 1,000bhp super-saloon

Unique British electric motors that slash size and weight and produce more power than rival machines are the heart of Mercedes-AMG’s new EV super-saloon – and Auto Express has the lowdown from their inventor.

Oxford graduate Tim Woolmer founded Yasa in 2009 to commercialise the axial flux electric motor he designed for his PhD. Almost a decade later, he clinched a deal for Yasa to supply Ferrari’s SF90 hybrid, and last week Auto Express toured the all-new £12million Oxfordshire factory also producing e-motors for Lamborghini and McLaren.

In a great British success story, Yasa motors provide the electric punch for hybrid supercars the Ferrari 296 GTB, Lamborghini Revuelto and Temarario and McLaren Artura. The new factory is scaling up to produce 25,000 motors a year.  

Another major breakthrough comes this summer when Yasa starts powering its first pure electric production car, the AMG GT 4-Door – although its motors will be produced in Berlin following Mercedes’ acquisition of Yasa in 2021.       

“The first cars we launch with Mercedes will be full EVs and we’re really excited,” chief technology officer (CTO) Woolmer exclusively told Auto Express. “I've been driven in one – it’s going to be fantastic.”

The AMG axial flux motors will be similar in design to the ones that power hybrid Lamborghini front axles. Woolmer’s big breakthrough was to shrink the motor’s stator (the stationary part generating a magnetic field around which the rotors spin), by repackaging a radial motor’s long, cylindrical copper windings into 18 stubby windings roughly the shape and size of orange segments.     

They’re arranged in a thin disc shape which gives a broad surface area for magnetic interaction and the space to fit a rotor on both sides of the stator, adding up to a dramatic boost in torque. 

“When we did the [initial] maths on the new design, it showed it would give you about three times the torque density and therefore power density, and its unique proposition is being one-third the size and weight of any other motor technology on the planet,” said the CTO. 

Each AMG motor can generate around 480bhp and 800Nm of torque – but it’s only 65mm long and weighs just 24kg. As with key rival the Porsche Taycan, Mercedes will be able to mix and match the motors to offer rear- and all-wheel drive, with a likely maximum of three motors packing well in excess of 1,000bhp.

Whereas the hybrid motors are limited by their adjoining engine’s speed, the AMG motors will be able to spin faster. “They’ve been scaled up to match the higher torque, power and speed required in an EV compared to a hybrid, and obviously higher voltage as well,” said Woolmer.

Yasa motors’ breakthrough design will also endow the AMG with a weight advantage, boosting range and agility. And future generations will go further, with reduced mass and an exponential improvement in harnessing regenerative braking energy to unlock smaller batteries yet longer-running high-performance EVs. 

“I think we’ve reached peak battery size,” said the CTO. “[Ultimately if] we can take hundreds of kilograms out of the mass of these vehicles, that starts to transform their behaviour. We’re really battling to get the weight of electric vehicles down: they’re fundamentally too heavy today.”

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