Multiphysics Simulation of Electric Motor NVH Performance with Eccentricity

With the emphasis of electrification in automotive industry, tremendous efforts are made to develop electric motors with high efficiency and power density, and reduce noise, vibration and harshness (NVH). A multiphysics simulation workflow is used to predict the eccentricity-induced noise for GM’s Bolt EV motor. Both static and dynamic eccentricities are investigated along with axial tilt. Analysis results show that these eccentricities play a critical role in the NVH behavior of the motor assembly. Transient electromagnetic (EM) analysis is performed first by extruding 2D stator and rotor sections to form 3D EM models. Sector model is duplicated to form full 360-degree model. Stator is split into three rotated sections to characterize stator skew, and the skew between two sections of rotor and magnets are also modelled. Sinusoidal current is applied and lumped-sum forces on each stator tooth are computed. Next, full 3D structural model is constructed, and EM forces are applied as excitations for frequency domain analysis. Finally, surface velocities are computed for the motor fixture and used as boundary conditions in the harmonic acoustic analysis. DOE case studies are performed for baseline vs. multiple static and dynamic eccentricities including both offset and tilt. Analysis results show static eccentricity increases the winding and torque ripple orders, while dynamic eccentricity leads to significant increase in sidebands of dominant orders.