Could this be the end of the transmission system as we know it? Two years ago, in Driveline News there was a report on Ford’s cooperation with Germany-based supplier Schaeffler on the eWheel – a self-contained wheel/tire unit housing an electric traction motor and all the necessary gearing, cooling and control systems. Now, presenting the results of the collaborative project to the CTI transmissions conference in Berlin, the two partners say the project has come a significant step closer.
The advantages for vehicle architecture are clear. There is no need for a separate engine or electric motor, no gearbox or driveshafts, nor even a separate braking system – all this is packaged within the eWheel. Further advantages include the freeing up of the space where the axle was between the wheels, and dynamics experts are excited about the potential for torque vectoring and trajectory control achieved by adjusting the output torque of one wheel in relation to the other. On the debit side, it is accepted that in terms of ride and handling refinement the eWheel will impose a higher unsprung weight, although Ford Germany chairman Bernhard Matthes insisted to his conference audience that there were gains in handling, too.
“The Fiesta prototype handles like a well set-up rear-wheel drive car, showing no understeer; it has a quick turn-in,” he said. “With no physical connection between the rear wheels, each one can operate independently to provide exactly the right amount of torque to keep the car pointing in the right direction at any given time.”
Matthes went on to explain that the torque vectoring between the two eWheel units – mounted on the rear axle on the Fiesta project demonstrator – were more effective than conventional brake-based ESP stability control systems.
Uwe Wagner, of Schaeffler, said that the current second-generation design was able to generate 40 kW peak power, as well as a maximum torque of 700 Nm. Its internal planetary gear ratio was set at 3.5:1, he said, and the company was currently working to develop a 24 kW version for city car applications.
Questioned on the weight issue associated with eWheels, Wagner admitted it would be a challenge to reduce the mass from the current level of over 50 kg. “This is our main task,” he said. “In the adapted [Fiesta] chassis, handling tests have found the driveability to be very good, and there is no difference compared with the standard car.”
Others expect eWheel cars will offer the potential for even greater agility, boosting their appeal as city vehicles. As to whether eWheel drive vehicles would become part of the mainstream Ford range, Matthes commented, “As for the when and how many, we are doing intensive research. There is a lot of interest, but we are still at the research stage and it is not yet part of our production plans.”
Other suppliers that have shown integrated eWheel systems include US-based start-up Protean, which has links with Mercedes-Benz tuner Brabus, and Michelin in France. The Michelin Active Wheel has been in development for more than a decade and incorporates steering and suspension, as well as the conventional traction and braking functions.