Most electric vehicles (EVs) today rely on radial flux electric motors, but growing interest in an axial flux architecture could set the industry on an alternative path. By having the magnetic flux flow parallel to the motor’s rotational axis instead of radially from the centre outward as in a radial flux design, axial motors offer significant efficiency and performance improvements.
“Not all electric motors are the same,” says Simon Odling, Chief of New Technology Development at UK e-motor specialist YASA. “The radial motor is a perfectly good solution and the most convenient today, but ultimately it is not the best solution.”
The Oxford-based start-up emerged in 2009 as a pioneer of axial flux technology and was acquired by Mercedes-Benz in 2021. The name YASA stands for Yokeless and Segmented Armature—a reference to the unique design of its torus axial flux motor, which removes the usual stator yoke and splits it into segments. This allows for direct oil cooling and a very fast response time to heat. “The motor cooling is exceptional compared to a conventional radial machine design and eliminates the usual time constant, where you’re either waiting for the motor to cool down or getting the vehicle to a certain state before you can have full performance,” explains Odling.
In addition to continuously available power, the other main benefits include reduced weight and improved torque, power density, efficiency, and manufacturability. YASA claims its axial flux technology motors are up to four times more powerful than the market standard, as well as 50% smaller and lighter. “That means you can use a smaller battery and still enjoy the same range, and because the car is lighter, you can use smaller brakes and less associated systems for reduced overall mass,” Odling points out. “This compounding effect is really exciting.”
A true driver’s vehicle
YASA Founder and Chief Technology Officer Tim Woolmer believes axial motor technology could be “transformative” for the emerging EV industry. Company marketing materials describes it as a “step-change.” Odling is similarly optimistic, telling Automotive World: “Axial motors are the future of the automotive motors business, particularly for high-performance and lightweight vehicles.”
With the promise of higher power density and continuous torque delivery, YASA’s automotive applications have centred around high-performance supercars, including models from McLaren, Ferrari, Lamborghini and Swedish supercar maker Koenigsegg. Although the company operates as a whole-owned Mercedes-Benz subsidiary, it continues to supply other automakers.
Most of its projects so far have involved hybrid vehicles, and the first pure EV applications will launch on upcoming models in Mercedes’ AMG sportscar line. YASA’s axial motor was previewed in the Mercedes-Benz Vision One-Eleven concept car, unveiled in 2023 at the International Design Centre in Carlsbad, California. Speaking at the launch, Mercedes’ Chief Technology Officer Markus Schäfer described the YASA axial flux motor as “ideal for electric high-performance vehicles.”
“Mercedes regards this technology as the key to creating a true driver’s vehicle in the EV market,” Odling notes. Commenting at the time of the 2021 acquisition, then Mercedes-AMG Chief Executive and Head of the Top End Vehicle Group Philipp Schiemer asserted that the motor’s capabilities would allow it “to redefine the future of driving performance.”
Scaling
The acquisition by Mercedes-Benz provided YASA with security and funding for further e-motors innovation. “From a product development point of view, Mercedes talks about us as the speedboat and itself as the oil tanker,” Odling relates. “Being acquired by a big corporate is a change for any start-up business, but Mercedes has been pretty hands-off. That said, it remains very involved where we’re talking about work that goes towards vehicle launch.”
It current produces about 20,000-30,000 motors a year for non-Mercedes automakers and anticipates future programmes with those customers. Notably, Mercedes-Benz has underwritten work taking place in the non-Mercedes-Benz business, allowing YASA to improve throughput, volume, capacity, and quality to a degree it could never manage on its own. “We might have been able to make tens of thousands of motors a year, but AMG will ultimately need hundreds of thousands of motors a year for a Mercedes range,” he adds. “It’s very different going from lower volume hybrid sports and hyper car applications to next-generation fully battery electric AMG models in the future. When you are building to these volumes, you need more automation, faster machinery and better capacity, and Mercedes brings all of that.”
Down the line, the company anticipates expanding into more mass market segments. “With maturity comes opportunities for cost reduction, volume increases and applications in more vehicles for the wider market,” asserts Odling. “That’s always been our vision. It’s the right technology for far more than sports cars and sporting applications. This is highly efficient, lightweight and low-materials utilisation technology: all the right things for the future of the automotive industry.”
Future developments
But that’s not to say axial flux motor development is complete—far from it. YASA continues to innovate from different directions and has a ‘fail fast, learn fast’ mentality. “In engineering we are very driven to test and prove our concepts as quickly as we possibly can, because that’s the fastest way to advance the technology,” he claims. “We go through multiple laps of innovation and development, but it’s a case of monthly cycles rather than annual cycles. This is where we generate opportunities for big leaps forward in technology.”
One potential area for further development is near-wheel or in-wheel motors. This approach, favoured by YASA’s compatriot Protean, offers greater design freedom and potential weight savings. YASA is keen to explore the implications of this placement for its axial flux technology and recently secured a £21.2m (US$27.7m) grant from the UK’s Advanced Propulsion Centre. The funding will support research in collaboration with consortium partners Domin and Cranfield University. If successful, the partners believe it could transform the overall architecture and design of future EVs. “We are leveraging world-leading expertise and creating a new consortium that will move the needle on EV design and performance,” commented Woolmer.
The language that YASA and its management team employ is significant: “moving the needle”, “step-change”, “transformative”. There is growing realisation that e-motor design is pivotal to the wider success of electric transportation, and the technology is evolving rapidly. “It’s important to remember that we are at the beginning of EV innovation,” cautioned Woolmer in 2023. As the knowledge base builds and scale improves, e-motor developments could reset the bar for electric driving experiences.
