Direct oil cooling of traction motors in hybrid drives

This paper presents comparisons of utilizing direct oil cooling approaches and conventional indirect cooling approaches for electrical motors which are mounted in HEVs or ZEVs. Both finite volume Computational Fluid Dynamic (CFD) model by FLUENT and finite element electromagnetic model by JMAG are applied to make the simulation accurate and comprehensive. Average temperature over the stator back, pressure drop between inlet and outlet and average heat transfer coefficient over the cooling duct are evaluated under identical flow rate, velocity and pressure drop for different cooling approaches. In addition, the influences on torque and power performances by the cooling ducts made in the housing or stator back are evaluated by JMAG model. The directly cooled motors show lower temperature rises at the stator back since the direct contact between coolant and stator back can avoid the unnecessary thermal contact resistances between the stator back and housing, meanwhile make the coolant more close to the heat sources, and thus improve the cooling efficiency.