Second-stage testing by Schaeffler of its electric wheel-hub drive being developed together with Ford of Europe’s Research and Engineering Center at Aachen, Germany, has demonstrated significant weight saving, power and torque increases, and cold weather performance compared to the 2010 first-stage concept.
“The liquid cooling, power electronics, and controller can now be integrated into each wheel, which means that the complex wiring in the vehicle can be omitted,” noted Dr. Raphael Fischer, Director, Wheel Hub Drives Product Group, part of Schaeffler’s eMobility Systems Division.
The liquid-cooled hub drive (electric motor, power electronics, controller, brakes, cooling system) is positioned within each rear wheel. The combined drive/wheel unit weighs 53 kg (117 lb), approximately 45 kg (99 lb) more than a conventional wheel including bearings and brakes.
The Fiesta’s wheels are 16 in, and the design envelope is quoted at 16 L (976 in3).
The system is fitted to a development Ford Fiesta, now designated Fiesta E-Wheel Drive. Roger Graaf, Ford’s Project manager for the vehicle, stated that despite the higher wheel-sprung masses of the rear wheels compared to the conventional vehicle, testing had shown that the driving behavior of the E-Wheel in terms of comfort and safety had “remained at virtually the same level.” The E-Wheel has the added dynamic element of torque vectoring.
The hub system, now part of a research project listed by the German Federal Ministry of Economics and Technology, provides up to 40 kW (53.6 hp) per drive and a continuous output of 2 x 33 kW. Up to 700 N·m (949 lb·ft) is available. Voltage is 360-420 V. Compared to the first generation hub drive, the E-Wheel Drive Beta, as the second generation is known, has a power output increase of about 33% and 75% more torque.
Recent testing has been completed in northern Scandinavia in very low temperatures.
Although the project is based on a regular production car (the first generation was fitted to an Opel Corsa), wheel-hub drives have to be integrated into new vehicle concepts for their benefits to be fully demonstrated, stressed Prof. Peter Gutzmer, Member of Schaeffler’s Executive Board and Chief Technical Officer.
“Thanks to this highly integrated wheel-hub drive, we can re-think the city car without restrictions," Gutzmer said. "It will be a key factor in new vehicle concepts and automobile platforms in the future.”
He added that for electric cars used in urban environments where they may become obligatory forms of individual transport, the wheel-hub-drive solution made previously unheard-of space savings possible. “The vehicle platform provides maximum space for passengers, luggage, and for the battery, electronics, and communication systems," Gutzmer noted. "Vehicle manufacturers can use this as a basis for a range of different body designs.”