In theory at least, the disadvantages of the wheel hub drive are offset by a number of important advantages. The motors can thus be produced more cost-effectively than motors normally used in electric vehicles, which are either installed centrally in the bodywork or close to the axle. Even more important is the possibility of increasing the steering effect of the wheel hub drive by means of electronic torque vectoring of the individual motors, thus increasing the agility of the vehicle.
A third advantage is that with this type of drive, body designs can be realized with better space utilization than with conventional designs; experts call this a "skateboard configuration": Since the wheel hub concept does not require a central motor or transmission, this drive topology is low-maintenance and robust. Typical wear parts such as drive shafts are eliminated. The task of the SR4Wheel R&D project was to prove these theoretical advantages on a design close to series production.
At the heart of the Cologne researchers' concept are four rim motors which, together with associated power electronics, have been integrated into the space between the brake system and the rim of the standard wheels of a production vehicle. Each motor consists of a static part with 20 coils and a rotating part with 24 teeth. When a coil is energized, it attracts the nearest tooth of the rotor etc, thus generating the rotational movement of the wheel. The underlying physical principle is reluctance force, which minimizes the magnetic resistance between coil and rotor.