A Weak Coupling Approach to Calculating the Effects of Electromechanical Interactions in an EV Drivetrain

Abstract

With the prevalent move of the automotive industry into electrification, the nature of vehicle powertrain NVH (Noise, Vibration and Harshness) has altered. Therefore, any previous approach to understanding and controlling NVH of the powertrain must now adapt to be applicable to the state of the art in powertrain design for electric vehicles. Electromagnetic excitation is a well-known source of noise in electrical machines and indeed, is likely be a dominant noise source in electric vehicles (EVs) as well as gear meshing excitation. The analysis of noise emission is one that requires a system level approach that accounts for the components that contribute to the noise production (electromagnetic and mechanical) and the resulting vibration transmission. A multifidelity, multiphysics electro-mechanical analysis approach is presented that enables scrutiny of noise producing mechanisms in the EV powertrain at the design stage. Here the authors present investigations into phenomena occurring in the air gap of the e-machine and the effect of these on vibration of the structure. Static eccentricity of the rotor with respect to the stator results in a static net force acting on the stator of the machine and additional spatial harmonics in the excitation spectrum. Whirling motion of the rotor creates an associated net whirling force and additional spatial and temporal harmonics in the excitation spectrum. Those excitation spectrums have been created and the vibration of the mechanical system as a result is analysed in each case. The authors have assessed the level of coupling between the mechanical and electrical systems required to successfully carryout these studies and a weak coupling approach is deemed suitable. The level and nature of machine housing vibration due to static and dynamic eccentricity is also detailed giving an overall assessment of the effect of eccentricity on NVH performance of a machine for an electrical vehicle application.