Analytical and Experimental Studies of Electric Motor NVH Design Focusing on Torque Ripple and Radial Force

Electric motor whine is one of the main noise sources of hybrid and electric vehicles. This paper describes a comprehensive analytical and experimental investigation of permanent magnetic electric motor NVH designs focusing on the contribution from torque ripple (TR) and radial forces (RF). A design-of-experiment method is adopted to design and build candidate motors with (i) high TR and high RF; (ii) high TR and low RF; (iii) low TR and high RF and (iv) low TR and low RF. Four prototype motors are built and tested on motor fixtures to measure dynamic stator forces in radial, tangential and axial directions, track dominant motor orders, and estimate motor Operational Deflection Shapes (ODS). Finite-element based electromagnetic and NVH analyses are performed and correlated to test data. Both tests and analyses confirm reducing TR and RF improves motor NVH performance at dominant pole pass orders. More specifically, TR is most critical from low to mid frequency, where the stator torsional mode is dominant. On the other hand, RF plays an important role at higher frequency, where the stator breathing mode becomes most active. New learnings and validated analytical methods are implemented to improve NVH performance of GM’s next generation battery electric and hybrid electric vehicles.