CEME Collaborator Julia Zhang – The Ohio State University

Typical hybrid-electric vehicle traction electric machines apply spraying cooling methods, which is effective for cooling the end-windings. However, the majority of the winding conductor parts are buried inside the slots, with a limited heat-transfer path to the sprayed coolant. Thermal analysis shows that the conductors inside the slots can be exposed to high temperatures, which will stress the winding insulation and eventually cause insulation degradation and possible machine failure. This research focuses on the integration of in-slot and end-winding cooling schemes to improve the performance of electric machine cooling systems.
We have developed a cooling scheme integrating end-winding and in-slot cooling systems as shown in Figures 4 and 5. In Figure 4, the yellow section is an end cap and the green structures are cooling channels inside the slots. Red bars represent the winding conductors. The cap and channels are adjoined to form one concealed cooling system covering all elements of the machine winding. The transparent blue element shows the coolant flowing around the end windings. Figure 5 shows the cross section of this machine stator with cooling channels in the slots. The yellow trapezoids are the cooling channel walls and the transparent blue areas represent the coolant. The coolant has direct contact with the heat source (machine windings inside the slots), thus improving cooling performance compared to end-winding spray cooling. We are evaluating the performance of this cooling design from both thermal and electromagnetic aspects via comparison with traditional cooling methods. The investigation of the manufacturability of this design is ongoing.

Cooling scheme for high power density electic machines

Figure 4. 3-D view of proposed electric machine cooling scheme

cooling channels for integration of end-winding and in-slot cooling system in high power density electric machines

Figure 5. Cross section of electric machine stator with cooling channels