Electric Traction Motor Spray Cooling—Empirical Model Development and Experimental Validation

The growing interest in electric vehicles leads to new developments of efficient electric traction motors with high power density. Since a large part of the losses in an electric motor can occur in the windings, it is important to cool the windings to reduce the temperature and protect the winding insulation from thermal aging. Oil spray cooling systems are becoming more and more relevant for cooling the windings. In this work, an approach for heat transfer modeling of electric traction motors (power classes #2–4 with 60–180 kW) with hairpin end windings (EWs) is developed and tested. The model is developed with a testing rig for different flat jet spray nozzle arrangements for a hairpin electric traction motor. The model approach showed a good agreement with the measured temperatures of the EWs in the testing rig. A transient thermal simulation of the testing rig confirms the good agreement. In a second step, the model approach is transferred to another electric traction motor with a different spray cooling system. The simulation results of the second electric traction motor also show good agreement with thermal quasi-static operating points and transient measurements at low and medium speed. At high speeds, the deviations increased. Possible causes for this behavior are discussed.