Bernd Cebulski
System Development E-Traction, IAV GmbH

Abstract

A highly efficient electric motor has been a key factor for high driving ranges of electric vehicles. The numerous parameters of rotor and stator geometry and the necessary calculation effort make it very difficult to do a full scale FEA-based optimization.
Hence some preliminary assumptions and investigations need to be done. These include manufacturing restrictions of the stator winding as well as selection of suitable rotor magnet arrangements.
Due to general limitations in rotor design according to short circuit current or open circuit voltage the degrees of freedom in rotor design are somewhat limited. Using pre-calculated maps from known and typical rotor magnet arrangements the calculation time for optimization can be greatly reduced.
In the past the different electric motor requirements that come from differences in power electronic demands or car limitations leaded to a great variety of rotor designs. Starting from simple parallel magnets to double V-shaped or the ‘dovetail’ structure there are plenty of possibilities to achieve the same power or torque. However, the cost for material and manufacturing can be quite different as well as the properties that are not directly connected to maximum torque density.