Noise reduction of an induction motor for a forklift

Abstract

This article presents the reduction of acoustic noise generated by electromagnetic forces in an induction motor. After summarizing the electromagnetic excitation forces due to the interaction between the stator-rotor slot permeance and the stator winding magnetornotive force, the effects of electromagnetic force on the noise and vibration of an induction motor are analysed. To identify experimentally the noise sources of the motor, the signal analyses for noise and vibration are performed by using waterfall plots of noise and vibration spectra. It is found that severe noise and vibration are caused by the electromagnetic force when the mode number of the excitation shape for a stator is low. Furthermore, it is verified that the motor noise is amplified if the excitation frequency of the electromagnetic force coincides with one of the natural frequencies of the stator. It is experimentally demonstrated that this severe noise can be considerably reduced by structure modifications. Finally, some design guidelines are suggested to develop an induction motor with a low level of noise.