Analysis of cogging torque caused by manufacturing tolerances of surface-mounted permanent magnet synchronous motor for electric power steering

Abstract

The reduction of cogging torque is the most important design objective for electric power steering (EPS) motors, because the rotation characteristics of the motor are directly transmitted to a driver. Therefore, a variety of optimal design methods are applied to reduce the cogging torque for EPS motors. However, the measured cogging torques of fabricated models are significantly greater than the finite-element analysis (FEA) results, because the additional harmonic components (AHCs) of the cogging torque are generated by manufacturing tolerances. The cogging torque generated by manufacturing tolerances can be divided into two components, which are generated by stator and rotor tolerances. In this study, AHCs, which cause cogging torque, are analysed by FEA by applying various tolerances to the analysis model, and harmonic analysis is also conducted. The relation of AHC generated from the stator and rotor is analysed by a rotor swapping test. Consequently, this study can be helpful to analyse the components of the cogging torque generated by manufacturing processes.