Ferrari and AMG opt for axial flux EV motors

SUPERCAR performance used to be predicated on the number and capacity of cylinders in an engine or forced induction. Now, as we transition to battery electric vehicles, there is increasing demand for “elegant” technology rather than the ability to burn large amounts of petrol quickly.

It leaves supercar manufacturers like Ferrari and Mercedes-AMG in a precarious position as to how they get electrified performance commensurate with their reputation such that they leave all the rest behind.

The horse may have already bolted in that regard, with a plethora of so called electric hyper-cars available or in production/under development. But they are prohibitively expensive and have constrained availability.

Ferrari and AMG have been looking for an electric edge sharp enough to satisfy “production” supercar customers and that means high-end electric motors. News has come to light that the two car-makers are eyeing axial flux electric motors to fulfil their requirements.

Axial flux motors have the capability to deliver extra power out of a battery pack when a driver pushes the accelerator in a performance car. It’s as simple as that. Said axial flux motors are much smaller than predominantly used radial motors yet pack a more powerful punch.

These high-end motors are considered to be crucial to brands like AMG and Ferrari as they race to electrify the high-performance vehicles that earn prestige and bumper profits.

According to a report in Automotive News Europe (ANE), all EVs offer the sensation of instant acceleration, from Nissan’s Leaf to Tesla’s Model S Plaid.

“In the combustion age, quicker times off the line and higher top speeds were achieved with more engine cylinders, but manufacturers will differentiate performance EVs by getting the most out of batteries with lighter and more efficient motors,” said the ANE report.

Markus Schaefer, Mercedes’s chief technology officer told ANE: “The forthcoming AMG electric vehicle platform gives a power-to-weight ratio that is really a record number, and much better than conventional motors.”

“It will make use of the small size of the motor.”

The ANE report explained how a conventional EV’s motor works thus: when a driver pushes the accelerator it pushes hundreds — and in some cases thousands — of amps of electric current to copper coils. When these coils are energised, they become electromagnets with attractive and repulsive forces. The magnetic force created by a stationary stator surrounding a rotating rotor produces the torque that turns the wheels of the vehicle.

On the other hand, in axial motors, rather than have a rotor spin inside a stator, disc-shaped rotors spin alongside a central stator. This leads the flow of current — the flux — to travel axially through the machine, rather than radially out from the centre.

Since the motor generates torque at a bigger diameter, less material is needed.

“England-based electric motor developer/manufacturer Yasa already supplies motors used in Ferrari’s SF90 and 296 GTB plug-in hybrids, and that unit uses a few mere kilograms of iron for its stators, reducing the mass of the machines by as much as 85 per cent,” says ANE.

Yasa’s motors are by Tim Woolmer, who focused on the technology for his electrical engineering PhD at the University of Oxford.

The motor design was planned to be used in Jaguar Land Rover vehicles specifically in the C-X75, a hybrid-electric two-seater with enough horsepower to rival the Porsche 918 Spyder, McLaren P1 and Ferrari LaFerrari.

But JLR couldn’t stump up the funds to continue with the program so Woolmer’s clever technology went into the Koenigsegg Regera hybrid hypercar and then to the Ferrari SF90.

Mercedes-Benz acquired Yasa in July last year for an undisclosed sum and stated that it will put its axial flux motors in AMG models scheduled to be launched in 2025.

The ANE report quoted Professor Woolmer: “If you look at the history of automotive generally, the auto companies have wanted to have the engine, their core technology, in-house.”

“The batteries, the motors, this is their core technology now. They recognise the importance of having long-term differentiation in these spaces, so they have to bring it in-house.”

The most important aspect of axial motors is form-factor potential, according to Malte Jaensch, professor of sustainable mobile drivetrains at the TUM School of Engineering and Design in Munich. Their smaller size could allow automakers to put one motor on each wheel, which is not feasible with radial motors, says ANE.

Putting a motor on each wheel — or at least one on each axle — could translate into hair-raising EV driving performance.

The innovation allows for torque vectoring that better controls how much power the motors send to each individual wheel for improved agility.

Yasa’s motors also could completely remove the need for a powertrain on the so-called skateboard underneath the middle of an EV, Woolmer said. That would open more space for engineers to package batteries, make more room for bigger front and rear boot spaces, or allow designers to experiment with new aerodynamic ideas.

The small size and light weight of axial motors will not just benefit high-performance cars. They are also finding a home in aerospace.

Yasa has offloaded its electric aviation division to a company called Evolito which supplied engines for a Rolls-Royce Holdings’s electric aircraft called the Spirit of Innovation, that uses three axial flux motors to drive its propeller. It can travel at 612 km/h v-max.

According to the ANE report, axial motors will not necessarily be the death knell of radial motors, which deliver higher top speeds. This led Ferrari to use two radial motors on the front axle of the SF90, along with an axial motor on the rear axle.

For the 296 GTB, handling was deemed more important, so only a lighter axial motor was used between the engine and transmission.