Transverse flux motor with high specific torque and efficiency for a direct drive of an electric vehicle

摘要

The general requirements for drive systems of electric vehicles arc small volume and weight, low costs and maintenance and high efficiency. Direct drive systems meet these requirements, because the gearing, which increases volume, weight and costs of the complete system, is no longer needed. However, the required output torque of the motor increases.The transverse flux machine, which has a bigger torque both with respect to volume and weight compared to conventional machines, is able to produce the required higher output torque at high efficiency. Therefore, the transverse flux machine is well suited for direct drive systems.The first part of this paper presents the topology of the magnetic circuit and the mechanical construction of a new transverse flux motor concept. Two prototypes were built in our workshop and the improvements concerning efficiency and torque, which ledto the layout of the second prototype, will be explained. The second prototype is a permanent magnet excited three-phase design, for the use of conventional converters, with outside rotor, which enables the application as a wheel hub motor, andwater-cooled stator with three ring windings. The features of the second prototype are an easy assembly of both stator and rotor, an output torque over 400 Nm and an efficiency over 90% in a wide range of operation. The nominal speed is 540 rpm and themaximum speed reaches 1200 rpm. Detailed measurements of characteristic values will also be shown.In the second part of this paper alternative topologies of transverse flux machines are derived and a comparison of the calculated torque performances for three different topologies is made. A third prototype with the most promising design is underconstruction.