A Feasibility Study of Oil Spray Cooling on the Stator Core Outer Surface of Electric Motors for Automotive Applications

The paper presents a feasibility study of oil spray cooling on the outer surface of a stator core for traction electric motor applications. Combined experiments and thermal simulations lead to the conclusion that oil spray cooling on stator laminations may be a more effective cooling approach than water jacket cooling. Tests are carried out on a single tooth segment as well as on a full stator. A unique data set of the Heat Transfer Coefficient (HTC) of oil on lamination stacks is presented, including the influence of spray angle and flow rate. Test results show that oil spray cooling on lamination outer surface can achieve a high HTC locally but lead to significant temperature variation around a stator. The results also identify optimal fluid flow rate, and recommendations on nozzle shape. Thermal simulation is carried out to compare oil spray cooling with water jacket cooling.