Discussion of machine placement and integration on the thermal design of HEV IPM machines

State-of-the-art design methods for electric machines use published correlations of either power or torque with electromagnetic and current loading, available for different cooling approaches. However, the applicability of these correlations for electric machines used within HEVs, with their different degrees of integration into the overall system, is limited. Using an integrated starter-generator and an electric rear axle drive as example case applications, we study the influences of the thermal environment within the hybrid electric vehicle application, i.e., heat sinks and sources external to the machine, on the thermal design of the machines. We quantify these influences by scaling factors for the air gap shear stress of the machine.