Low-cost electric powertrain aims at utility vehicles

Working on the ESKAM project, 11 researchers at the Fraunhofer Institute for Tool Machines and Forming Technology (IWU) have come up with an axle module and production process for electric commercial vehicles.

Motor, power electronics and transmission are integrated in a single compact casing. The casing can be incorporated into the target vehicle by means of a frame design, which also has been developed in this context.

The module offers numerous advantages. Besides high power density, it offers high torque that translates into good acceleration. While most motors for electric vehicles offer a rotation speed of 10,000rpm, or 15,000rpm at the utmost, the ESKAM motor can be driven up to 20,000rpm.

The project manager claims production cost savings up to 20 per cent compared to the conventional approach. For example, the integrated transmission consists of shafts and gearwheels. Usually such shafts are made either of tubes (expensive) or through deep hole drilling (complex, time-consuming, ineffective with regard to material). The IWU researchers instead established novel processes that make efficient use of time and material. They developed a processing technology, a combination of drilling and pressing which reduces material and labour cost by about 30 per cent; on top of that, it yields lightweight products.

In addition, the module is scalable—it can be manufactured in different sizes to fit small transporters and large buses or trucks equally. This feature is not possible with wheel hub drives.

At this opportunity, the Fraunhofer researchers discussed assets and drawbacks of wheel hub drives and their own approach. While wheel hub drives enable a higher steering angle and offer a more direct response to driver's actions, wheel hub drives are not suited for commercial vehicles, since they cannot exceed a rotation speed of much more than 2,000rpm. In addition, wheel hub drives are more expensive since they require a separated power electronics unit for each wheel while the ESKAM approach does it with one central power electronics unit per axle.

The next step will be integrating the axle into a demonstrator. By end of the year, they plan to install the axle module into a real-world car and test it.

-Christoph Hammerschmidt
  EE Times Europe