Dynamic force measurement to assess NVH performance of electric motors

The electromagnetic (EM) force induced motor whine is a major noise source of hybrid and electric vehicles. Experimental quantification of dynamic EM force is highly desirable to assess the NVH performance of electric motors. However, it is difficult to measure EM forces directly on the stator teeth. This paper describes a new indirect method to measure the dynamic forces at stator mounting ear locations. First, high-precision tri-axial piezoelectric force ring sensors are selected and calibrated to measure dynamic forces under compressive mean loading. Next, special motor housings are designed and built to accommodate force sensors between the stator ears and the base mounting plate. Force sensors are then aligned with the stator circumferential directions to measure dynamic forces in radial, tangential and axial directions as a function of motor torque and speed. The new technology is successfully implemented for electric motors of GM's Spark and Bolt EVs. Measured dynamic forces correlate well with finite-element analytical results and show consistent trends with noise and vibration responses. This confirms the dynamic mounting force can be used as an effective and measurable indicator to optimize NVH designs for electric motors.