Browse Publications Technical Papers 2018-01-1504

Effects of Unbalanced Magnetic Pull on NVH performance of an electric drivetrain 2018-01-1504

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 internal permanent magnet (IPM) machine and a two-stage gearbox. The investigation couples electromagnetic finite element analysis with structural drivetrain simulation, including gears, shaft, bearings and housing. It is shown how gear force can make the rotor eccentric and trigger UMP between the rotor and the stator. The effects of rotor shaft deflections – due to mechanical forces from gears – on rotor eccentricity are shown. An analytical representation of UMP is introduced and electro-mechanical interactions are evaluated in various operating conditions. It is shown that while at no-load condition the relationship between UMP and eccentricity is essentially linear, for some load conditions it can be non-linear. 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, demonstrating that even for relatively low values of rotor eccentricity this can be significant. Moreover, as UMP can also affect the system natural frequencies, its influence on them is explained. UMP lies at the heart of several complex interactions between electromagnetic and structural performance. This paper will address some of these static and dynamic interactions, demonstrate their importance and provide computationally efficient methods to analyse them.


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