What is it?
A prototype electric drivetrain under development by British electric motor specialist Equipmake.
While most traditional EV motors use radial flux motors, this application employs a less conventional axial flux motor. And unlike some conceptual EV drivetrains, the Equipmake design is destined for a real- world application, making its debut in British boutique sportscar manufacturer Ariel’s new ‘Hipercar’ in 2019.
How does it work?
While radial flux motors have proven their worth in EV powertrains, the axial flux motor has an inherently more compact design and the potential to provide more torque than a similarly sized radial design.
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There are also efficiency advantages offered by a shorter and single-dimension flux path – a fundamental force necessary for motor rotation.
At the heart of the system, Equipmake’s own APM200 axial motor provides 220kW and 450Nm with a maximum speed of 10,000rpm and sends power to either a single axle or both for four-wheel-drive traction. An epicyclic gearbox allows the output shaft to be connected directly to the wheel hub for a more compact and lightweight end product.
Power is provided by a 56kWh battery for emissions-free driving but if electricity reserves are low, a 35kW ‘micro-turbine’ gas turbine range-extender engine cuts in to generate electricity.
Why does it matter?
Put simply – power density. Equipmake claims its APM200 motor has a power to weight ratio of 7kW per kilogram – about the same as a mid-2000s V10 Formula 1 engine, which made about 700kW from 3.0 litres.
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The combination with a jet engine range-extender, which also has a high power density, maximises the overall system density figure. While large battery packs, radial flux motors and piston-engine hybrid powertrains are proving the feasibility of range-extended EVs, the Equipmake/Ariel approach scales down the size and weight of a long-range electric drivetrain without compromising power and performance.
That means the powertrain can be squeezed into a car that’s light and small enough to uphold Ariel’s reputation for bantamweight machines with supercar- destroying performance. If it’s successful, the Equipmake solution marks another significant milestone in the evolution of EVs that are fun and efficient.
Joining the club
Equipmake is not the only innovator to see the potential in axial flux motors and the segment is becoming increasingly populated.
Belgian motor developer Magnax is also pushing the boundaries and claims to have designed a motor with up to 15kW/kg.
The company’s innovative design is modular and scalable, allowing its motor/generator units to be used in a wide range of applications, from wind-turbine power generation to powering small electric vehicles, although the company is yet to reveal a working prototype as advanced as the Equipmake solution.