Investigation of Modulation Effect of Unsymmetric Structure on Vibration and Noise in Fractional-Slot Concentrated-Windings Permanent-Magnets In-Wheel Motors

Electromagnetic (EM) vibration and noise are a significant problem in fractional-slot concentrated-windings (FSCW) permanent-magnets (PM) in-wheel motors. Due to the structure of in-wheel motor is complicated, this paper aims to study the modulation effect induced by unsymmetric structure of an outer-rotor 72-slot/80-pole (72s/80p) in-wheel machine. Firstly, a 2-dimensional (2-D) EM FEA model is established to compute EM forces, and a 3-dimensional (3-D) structural FEA model of rotor assembly are built for modal analysis. Then, based on the Fourier-based vibration model, the spatial harmonics of EM forces and mode displacement are thoroughly studied. The bolts for securing cover and flange are found to have a modulation effect on the spatial harmonics of mode displacement. Further, the contributed acceleration level (ACL) is predicted to assess the modulation effect on vibration. Finally, sound pressure level (SPL) of the prototyped in-wheel machine is measured for validation.