Characterizing the Effect of Shrink Fitting of Stator Housings on Electric Vehicle Performance

High performance rotating electric machines are a necessity in the automotive sector. The characteristics of electric steel materials given in the datasheet used in electric machines do not account for the effect of stress due to the manufacturing process. It is possible to account for the effect of stress coming more precisely from stator housings after press and shrink fitting which degrades the loss properties of electrical steel. A process is developed, which includes the development of a test bench for characterizing the magnetic properties of electric steel when put under compressive stress. The proposed hardware setup is a novel test bench capable of achieving high compressive stress up to 60 MPa and for a maximum of 1 kHz fundamental frequency. A modified compressive stress dependent loss model for analyzing impact on the total power loss is proposed. Further, a coupled multiphysics finite element analysis including structural and magnetic analysis to evaluate the machine performance over the entire operating range and vehicle performance over relevant drive cycles for passenger electric vehicles. A 7% increase in total machine losses was found at an average in a WLTC class-3 drive cycle due to shrink and press fitting of the stator housing.