The design of rotor geometry in a permanent magnet traction motor for a hybrid bus

The paper addresses the electrical and mechanical design process of a traction motor for a hybrid bus application. In general, the design process of the electric motors requires intimate co-operation between different engineering disciplines. Often compromises are needed in order to satisfy both the electrical and mechanical performance specifications. From the mechanical point of view the stress values should be on reasonable level and safety factors should be taken into account. From the electrical point of view the torque level should be high while accelerating the traction motor and the losses of the machine should be small in order to be able to cool the machine and sustain high efficiency. In traction use the no-load iron losses will be loading the overall system all the time — also while driving direct with diesel engine. While selecting the best rotor design also the costs will be taken into account — one expensive part of the motor is the permanent magnet material. Therefore, the material price is estimated when selecting the rotor design.