Improved hub motor design from Ford, Schaeffler advances EV design
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. "A highly integrated wheel hub drive makes it possible to completely rethink the concept of a city car. This drive is the key for novel concepts and vehicle platforms", he said.
Recently, Ford tested the vehicle under winter conditions in Scandinavia. A large part of these tests were driving dynamics assessments, and according to Ford, the results were surprisingly positive. "In terms of comfort and safety, the driving behaviour is almost at the same level as conventional vehicles, despite the large unsprung masses of the hub drive", said Roger Graaf, project manager at Ford Research & Advanced Engineering Europe. Since wheel hub drives enable torque vectoring – the selective distribution of the torque across the wheels – vehicles equipped this way display an unusual high driving dynamic. Another advantage of this kind of drive is that driving dynamics controls can be implemented directly into the drives. Thus, cars with wheel hub drive offer not only a very high manoeuvrability and active safety but also significant advantages in terms of space utilisation.
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