The Effect of Rotor Notches on Air Gap Heat Transfer Coefficient and Electromagnetic Performance in a Permanent Magnet Synchronous Motor for Traction Applications

<div class="section abstract"><div class="htmlview paragraph">This study investigates the impact of various notch geometries on the outer surface of the rotor of an interior permanent magnet synchronous motor intended for traction applications, focusing on improving both its thermal and electromagnetic performances. Traditional motor cooling methods, such as water jackets or oil spray/impingement, typically target the stator and/or end windings, neglecting rotor cooling. As a result, the dissipation of the heat from the rotor is dependent on the heat transfer across the air gap surrounding the rotor, despite air’s poor thermal conductivity, which causes it to act as an insulator. Rotor notches are used to limit the higher order harmonics from air gap flux density which results in decreased torque ripple, cogging torque, noise, and vibration of the machine. While the effect of rotor notches on electromagnetic performance is analyzed, their impact on the thermal management of the motor, particularly the heat transfer coefficient in the air gap, remains largely unexplored. Previous experimental and numerical works have predominantly focused on heat transfer in the air gap for a smooth stator and rotor or a slotted stator with a smooth rotor; there exists a lack of studies which have simultaneously examined the electromagnetic and thermal effects of a notched rotor on electric machines. This work utilizes computational fluid dynamics to model fluid and thermal behavior and finite element analysis to determine electromagnetic performance for different notch geometries. By investigating the notch geometry with a commercially available machine as a baseline, this study enhanced heat transfer in the air gap, improving rotor cooling, and yielded modest improvements in electromagnetic performance. This analysis provides valuable insights for developing advanced rotor designs that achieve excellent thermal and electromagnetic performance for high power density applications.</div></div>