Drives and Controls Magazine
Drive module ‘overcomes problems’ for commercial EVs
Published:  11 February, 2015

German researchers have developed an electric axle module for commercial vehicles that integrates a high-speed motor, gearbox and power electronics, and is claimed to be smaller, lighter and more cost-effective than most alternative technologies.

In a three-year project costing €8.9m, a group of 11 organisations, including the Fraunhofer Institute and the inverter developer Refu, have developed an integrated powertrain module that is designed for series production and could be scaled for applications ranging from small vans to large trucks. The module, which contains all of the components in a magnesium housing, can drive either the front or rear wheels – or both.

The Eskam (electric, scalable axle module) project, which has €5.1m of backing from the German government, has focused on developing a drive system specifically for commercial vehicles. Many previous attempts to develop such systems have failed at the prototype stage or have resulted in drivetrains that are too expensive ­– costing up to three times more than conventional drivetrains.

The Eskam researchers believe that the problem has been that the earlier systems were not designed for series production. They therefore focused on this aspect and believe that they have solved the problem by developing innovative techniques that, they say, could cut production costs by up to 20%.

For example, gearbox shafts are usually manufactured from costly cylinders or by deep-hole drilling. In both cases, material is wasted. By contrast, researchers at Fraunhofer’s Institute for Machine Tools and Forming Technology (IWU) are using methods that result in more efficient use of materials. For example, IWU has developed a technique, called spin extrusion, that also uses a block of material, but with a blank that is shorter than the finished shaft.

“To help visualise the process, think of pottery,” explains IWU project manager, Dr Hans Bräunlich. “The material is extruded during the shaping process – and pressed outward in a longitudinal direction. This allows us to use virtually all the material, cutting material costs by approximately 30% and reducing the overall weight of components.” The IWU researchers have made the technology suitable for series production.

The Eskam module can be used to drive a vehicle's front wheels (left) or rear wheels (right)

The gearbox’s toothed wheels are made using a different process. Instead of being milled, they are manufactured using a special forming process called gear-rolling, also developed at IWU. This method does not produce any metal chips, so no material is lost.

The axle module has a high power density and torque, resulting in rapid vehicle acceleration. It uses a motor that achieves speeds of 20,000 rpm, compared to 10,000–15,000 rpm typical for other EV motors. “When we started on the project three years ago, we were the only ones who could obtain such high speeds,” Bräunlich recalls. “Since then, others have been attempting similarly high speeds. But our head-start in accumulating development experience has given us a technological edge, which we intend to extend further.”