Reducing Noise from Bus Drive Motor by Changing Frame Shape

This study identified the noise generation mechanism of a bus drive motor and proposed a design guideline for the motor frame to reduce this noise. By measuring the noise and vibration signals, it was found that the noise was amplified at a specific rotational speed, and a frequency analysis was performed to identify the cause. This analysis confirmed that the vibration of the housing and rear bracket generated by the electromagnetic force in the motor was related to the noise generation. Then, modal testing was performed to obtain the mode shapes and natural frequencies of the housing and rear bracket equal to the noise amplification frequencies. In the mode shapes of the housing, pumping and bending deformations of the lateral surface were observed, while radial asymmetric deformation appeared on the rear bracket. Therefore, ribs were added to the housing and rear bracket to suppress these deformations. Finally, the noise level of the improved motor was measured, which confirmed a reduction of up to 10.7 dB(A) compared to the original motor.