Ford, Schaeffler demo advanced wheel hub drive
The E-Wheel Drive, as they called their development, contains all functional elements associated to generating thrust, deceleration, and safety. Electric motor, 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 vehicles is equipped with a rear wheel drive.
Fig. 1: Wheel hub drives offer remarkable design freedom. For full resolution click here.
Each motor in the test vehicle provides 40kW of peak power or 33 kW of continuous output. Thus, the vehicle disposes of a 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 a remarkable 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 % more power and 75% more torque. The motor is supplied from a high voltage battery with 360 to 420 volts. The wheel hub drive is relatively heavy: Compared to a normal wheel with brake and wheel bearing, the hub drive weighs 45 kilograms more; the total weight is 53 kilograms. The entire drive has a volume of 16 litres which makes it possible to integrate it into a standard 16" 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 been 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. "Under the aspect 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 utilization.
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