Enhanced Thermal Management of Outer-Rotor Electric Motors Through Additively Manufactured Heat Exchangers With End-Winding Cooling

Effective cooling strategy is critical to achieve improved performance and efficiency in electric-drive vehicle motors. Among approaches, direct winding heat exchangers (DWHXs), positioned inside the motor component slots, have demonstrated superior potential for cooling compared to conventional methods such as forced convection air cooling and liquid jacket cooling. In this work, an in-slot heat exchanger (HEx) based on the DWHX concept is developed for an outer-rotor motor with a 100 kW peak and 55 kW continuous power output, and 50 kW/L power density. Initial work developed a baseline additively manufactured aluminum oxide heat exchanger to cool concentrated stator windings in an 18 -slot, 16 -pole outer-rotor motor; however, it lacked performance in cooling stator endwindings. A new design was envisioned to address this issue. The present study introduces a novel in-slot HEx design, which also incorporates a cooling solution for end-windings at both sides of the motor. The thermal performance of this new design is assessed and compared with the baseline concept. The results from the new design indicate an over 50% reduction in thermal resistance and more than 30% reduction in hot-spot temperature. The new design reduces end-winding temperature while maintaining improved thermal uniformity across the winding. The increase in pressure drop in the new design adds only 0.013 W to the pumping power. Furthermore, the results indicate that a potting material used as an interface material - with a thermal conductivity of 34 W/m . K - to attach these heat exchangers to motor components is found optimal to ensure effective thermal performance. The achieved performance is realized without altering critical electromagnetic parameters, facilitating seamless integration with the current motor design. These results underscore the potential of ceramic-based in-slot HExs in improving the thermal performance and efficiency of modern electric-drive vehicle motors, representing a substantial advancement in the development of high-power-density electric motors.