When drivers of future Mercedes AMG models press the accelerator of their electric vehicles, they’ll get some extra battery inspiration from something that sounds straight out of Back to the Future.

No, not flux capacitors, but axial flux motors.

Mercedes-Benz AG and Ferrari NV turn to this type of electric motor to generate torque that would affect the headrest. Axial flow engines are much smaller than radial engines, which are mainly used, but still have more power.

High-end engines like these will be crucial for brands like AMG and Ferrari as they seek to electrify high-performance cars that earn prestige and big profits. All electric cars give the feeling of instant acceleration, from the Nissan Leaf to the Tesla Model S Plaid. While in the combustion era faster off-the-line times and higher top speeds were achieved with more engine cylinders, manufacturers will differentiate electric vehicle performance by getting the most out of batteries with lighter, more efficient engines. “The power-to-weight ratio is truly record-breaking and much better than conventional engines,” said Markus Schaefer, Mercedes’ chief technology officer, of the automaker’s upcoming AMG platform for electric vehicles. “It will use a small size motor.”

(Read also | Fast and furious. And faulty? More than 23,000 Ferrari units have been recalled)

With each press of the accelerator, electric car drivers push hundreds, and in some cases thousands, of amperes of electric current to the copper coils. When these coils are energized, they become electromagnets with attractive and repulsive forces. The magnetic force created by the stationary stator surrounding the rotating rotor creates a torque that turns the wheels of the vehicle.

In axial-flow motors, the rotor does not rotate inside the stator, and disc-shaped rotors rotate next to the central stator. This causes the flow of current – the flux – to move axially through the machine rather than radially from the center. Because the motor creates torque at a larger diameter, less material is required. Yasa, the Oxford-based maker of the engines used in Ferrari’s SF90 and 296 GTB plug-in hybrids, uses just a few kilograms of iron for its stators, reducing the machines’ weight by 85%.

Yasa motors are the brainchild of Tim Woolmer, whose work on them was the focus of his PhD in electrical engineering at Oxford University. Within a few years of his PhD, Jaguar Land Rover planned to use Yasa engines in the C-X75, a hybrid-electric two-seater with enough horsepower to rival the Porsche 918 Spyder, McLaren P1 and Ferrari LaFerrari. While JLR eventually scrapped the project due to financial constraints, Yasa engines found their way into the Koenigsegg Regera hybrid hypercar and then the Ferrari SF90.

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“If you look at the history of the auto industry as a whole, car companies wanted to have the engine, their core technology, in-house,” Woolmer said in an interview. – Batteries, engines, this is now their main technology. They recognize the importance of long-term differentiation in these spaces, so they need to bring that in.”

The most important aspect of axial motors is the form factor potential, according to Malte Jaensch, professor of sustainable mobile transmissions at the TUM School of Engineering and Design in Munich. Their smaller size can allow car manufacturers to put one engine on each wheel, which is not possible with radial engines.

Placing a motor on each wheel – or at least one on each axle – can make for stunning driving EVs. The innovation allows for torque vectoring, which better controls the power the engines send to each individual wheel for improved maneuverability. High-speed cornering can help AMG and Ferrari drivers overcome the lost roar of their eight-, 10- or 12-cylinder engines.

Yasa motors could also completely eliminate the need for a transmission on the so-called skateboard under the middle of the electric car, Vollmer said. This will open up more space for engineers to pack batteries, give more space to increase front and rear trunk space, or allow designers to experiment with new aerodynamic ideas.

The small size and light weight of axial engines will benefit not only high-performance vehicles. They also find a home in the aerospace sector, which led Yasa to launch the Evolito electric aviation division last year. The world’s fastest electric car, Rolls-Royce Plc’s electric plane called the Spirit of Innovation, uses three axial-flow engines to drive its propeller. The aircraft can travel at a speed of about 380 miles (612 kilometers) per hour, making it faster than the Spitfire fighter jet, which is powered by a Rolls-Royce V12 engine.

“The critical thing is their efficiency,” said Matteo Parr, head of Rolls-Royce’s Spirit of Innovation project. “It keeps the weight of the aircraft low.”

Axial motors will not necessarily be the death of radial motors, which provide a higher top speed. This led Ferrari to use two radial engines on the front axle of the SF90 along with an axial engine on the rear axle. For the 296 GTB, handling was deemed more important, so only a lighter shaft drive was used between the engine and transmission.

“It’s just a question of what kind of driving experience you want to create for your customers with a particular engine,” said Davide Ferraro, Ferrari’s Electric Motors Manager. – Different voices make pleasant notes.”

Date of first publication: 17 Aug 2022 12:40 IST


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