Economical production of conically shaped concentrated windings using forming technology for use in wheel hub engines

In addition to the electromechanical properties, the design of the stator windings for electric drives depends strongly on the available installation space. In case of the wheel hub engine, the installation space is strongly limited by the rim diameter and the tyre width. Hence, stator windings for use in wheel hub engines should meet two requirements: On the one hand, the stator slot should be optimally filled with electrically conductive material so that a high torque can be guaranteed despite limited installation space. On the other hand, the end windings should be as compact as possible in order to ensure the greatest possible active length of the stator core. Conically shaped concentrated windings meet these requirements and are therefore suitable for use in wheel hub drives. In a cooperation between the Breuckmann company and the Institute of Metal Forming (IBF) of RWTH Aachen University, a multi-stage forming technology has been developed which enables the production of such a winding geometry. In this paper an automated multistage forming tool is described, which allows for an economical mass production of conically shaped concentrated windings. In addition, a 2D FE model is presented, which models the wire cross sectional development during forming. In this way, a suitable number and geometry of the forming stages could be designed prior to tool production and tool costs saved accordingly. Due to the high load on the primary insulation caused by the forming process, the effect of the forming process on the insulation layer thickness is investigated and alternative insulation processes after forming are described.