Electric Motor Noise Reduction with Stator Mounted NVH Insert Ring

Electric motor noise mitigation is a challenge in electric vehicles (EVs) due to the lack of engine masking noise. The design of the electric motor mounting configuration to the motor housing has significant impacts on the radiated noise of the drive unit. The stator can be bolted or interference-fit with the housing. A bolted stator creates motor whine and vibration excited by the motor torque ripple at certain torsional resonance frequencies. A stator with interference fit configuration stiffens the motor housing and pushes resonances to a higher frequency range, where masking noise levels are higher at faster vehicle speeds. However, this comes with additional cost and manufacturing process and may impact motor efficiency due to high stress on stators. In this paper, a thin sheet metal NVH ring is developed as a tunable stiffness device between the stator and the motor housing. It is pre-compressed and provides additional torsional rigidity to mitigate torsional excitations. A CAE model is developed to model, analyze, and optimize the NVH ring for the bolted stator configuration. A system-level simulation method is utilized to characterize the interactions of the stator, the NVH ring, and the motor housing as well as the retention force variation of the insert ring due to thermal aspects. The optimized NVH ring provides increased torsional stiffness comparable to an interference fit configuration, which leads to reduced motor noise in the critical low frequency range.