Designing well-performing electric drivetrains requires a comprehensive understanding of the electro-mechanical interactions. The paper investigates the effect of unbalanced magnetic pull (UMP) due to rotor eccentricity in a typical automotive electric driveline with an integrated interior permanent magnet (IPM) machine and a two-stage gearbox. The investigation couples electromagnetic finite element analysis in Cobham Opera with electromechanical drivetrain simulation, including gears, shafts, bearings and housing in RomaxDESIGNER.
Gear force can deflect the rotor which causes UMP between the rotor and the stator. It is shown that UMP varies non-linearly with rotor offset and machine operating condition.
Harmonic analysis is performed on torque and radial rotor force to quantify the influence of rotor shaft deflections and hence rotor eccentricity on the frequency content of both torsional and radial electromagnetic excitations. The effect of such excitations on the system NVH response is shown. The presented methodology illustrates how a coupled electromagnetic-mechanical simulation can be used to understand how electromagnetic excitations can penetrate the mechanical system and manifest as structural vibrations of the housing and mounts, leading to airborne and structure borne noise.