Improved hub motor design from Ford, Schaeffler advances EV design

April 16, 2013 // By Christoph Hammerschmidt
In tomorrow's city cars, electric wheel hub drives will be the solution of choice - they enable innovative, extremely flexible and versatile design solutions. Carmaker Ford and mechatronics company Schaeffler AG have developed such a drive and integrated it into a concept vehicle based on a Ford Fiesta.

The E-Wheel Drive, as they called their development, contains all functional elements associated with generating drive, deceleration, and safety. The electric motor, the power electronics along with the associated control unit, brake and cooling system are all integrated into the wheel hub. Unlike the normal Fiesta, the concept vehicle is equipped with rear wheel drive.

Fig. 1: Wheel hub drives offer remarkable design freedom. For full resolution click here .

Each motor in the test vehicle provides 40 kW of peak power or 33 kW of continuous output. The vehicle has an equivalent total engine power comparable to a vehicle with a conventional 110 hp / 90 hp engine. The liquid-cooled electric motor is currently available in its second design iteration and has reached beta status, offering torque of up to 700 Nm. In comparison to the first design version shown in 2010 in an Opel Corsa, this is an increase of 33% in power and 75% in torque. The motor is supplied from a high voltage battery of 360 to 420V. The wheel hub drive is relatively heavy: Compared to a normal wheel with brake and wheel bearing, the hub drive weighs 45 kg more; the total weight is 53 kg. The additional unsprung weight will necessitate changed suspension layout. The entire drive has a volume of 16 litres which makes it possible to integrate it into a standard 16-in. rim. While the current design version adds another 6 kg compared to its predecessor, the engineers were able to reduce the vehicle's total weight since the cooling system as well as the power electronics along with the control unit could be integrated into the wheel, which made complex wiring redundant.

The current vehicle serves as experimental platform. "Wheel hub drives can unfold their strengths only in new, innovative vehicle concepts", said Schaeffler executive manager Peter Gutzmer at the presentation of the vehicle during the congress of a car magazine.