Modeling and Analysis of Acoustic Noise in External Rotor In-Wheel Motor Considering Doppler Effect

In this paper, the characteristics of the electromagnetic noise radiated by an external rotor in-wheel motor (IWM) are investigated with the Doppler effect taken into consideration. First, Maxwell stress tensor method is employed to derive electromagnetic forces on the magnet surface. The effect of common current harmonics is also analyzed. Then, a structural model of the rotor is built and modal test is conducted to validate the model. Nodal forces, which are calculated by finite element method, are transferred from the electromagnetic mesh to the structural model for further vibration prediction. Finally, boundary element method is used to calculate the noise radiated by the rotor. In particular, the Doppler effect is considered. The calculated results are validated by the noise test. It is found that the end cap contributes more to the overall noise than the shell, and obvious sound directivity appears in the noise of the IWM. The noise measured perpendicular to the outer end cap is larger than that measured in other directions. In addition, the Doppler effect would induce additional side-frequency components around high-frequency peaks in the external rotor motor.