Enhancement of cooling performance in traction motor of electric vehicle using direct slot cooling method

The torque of a traction motor for electric vehicles is directly proportional to the electric current applied to the motor winding. Since a power increment is directly linked with an increase in torque, traction motors with high electric current are needed to enhance the dynamic performance of electric vehicles. However, heat loss in the winding, which is proportional to the square of the applied electric current, may cause insulation breakdown in the winding or demagnetisation of permanent magnets in the rotor. In this study, we employed direct slot cooling (DSC) to directly cool motor windings, which are the main heat source in a motor, with cooling fluids. To evaluate the performance of DSC, we compared it with existing motor-cooling technologies, such as water-jacket, end-tip and channel cooling. The performances of the cooling methods were compared based on the change in the pumping power of the cooling fluid and the winding current density. Under two real road driving modes (urban dynamometer and highway driving modes), we compared the change in temperature with time in the traction motor of a compact car with the various cooling methods. The proposed DSC model showed good cooling performance; the winding maximum temperature did not exceed 90 °C in the highway driving mode, even when a high current density of 70 A/mm2 was momentarily applied.