In-wheel motors have been the future for electric cars—including fuel-cell cars and series hybrids—for decades.
Their benefits include simpler packaging and more interior or cargo space for the vehicle. They could help make vehicles lighter, and lower the center of mass. There are also potential efficiency gains, too, and traction and stability systems have the potential to become more precise in the way that they modulate power on a wheel-by-wheel basis.
Earlier this month, Nidec, the Japanese supplier of motors, generators, and related systems, revealed an updated, “fully integrated” motor system that is designed to fit within wheel hubs.
What makes the new system different is that it’s from an established supplier and an extension of its lighter and more compact E-Axle product line, due to launch this spring in China in the Aion S electric sedan, the debut model from a new sub-brand of the automaker GAC and a supposed rival to the Tesla Model 3.
Nidec says that it aims to mass-produce the wheel-hub motor design around 2023. The unit, it says, generates more than 100 kw (134 horsepower) while fitting inside a 20-inch wheel.
Nidec in-wheel motor
The reasons why in-wheel motors or hub motors haven’t jumped beyond concept cars and research-and-development projects revolve around one game-stopper: unsprung mass. Even in this new form, Nidec’s wheel-hub system weighs about 70 pounds. Having such a heavy motor system as part of the wheel-hub assembly would require radically different suspension tuning and likely require sophisticated dynamic damping systems that could negate any weight savings.
Opting for a motor at each wheel rather than one for each axle also potentially adds cost, and in-wheel motors are also more vulnerable to damage from curbs, potholes, ice, and road salt.
While we’ll almost certainly see more in-wheel motors in some special-interest vehicles like electric motorcycles this next decade, applications in passenger cars could be many years off yet. But with Nidec's announcement for 2023, just four years from now, it will be interesting to see if that prediction changes.