Axial Flux Motor Design Solutions for Loss Reduction, Cooling Enhancement, and Manufacturability Improvement

Axial flux topology motors have the advantages of high torque and power density. Their compact axial length offers design advantages to electric vehicle propulsion systems. However, three major challenges exist. First, motor efficiency needs to be competitive, as concentrated winding usually introduces more harmonics with high stator core loss and permanent magnet eddy current loss, especially at high-frequency condition. Second, thermal management of the stator and rotor is challenging due to the stator being sandwiched between the two rotors. Third, the segmented and trapezoidal-shaped stator core manufacture is difficult because it is formed by hundreds of laminations with varied sizes. To address the challenges, design solutions have been proposed and validated in this study through prototype design and optimization, simulation, and experimental evaluation. With the optimized PM partition and novel hybrid stator core design, the motor peak efficiency reaches 96.5%, while the stator manufacturing complexity can be significantly reduced. The cooling fin design at stator reduces core temperature by 15°C, and the direct air gap oil cooling keeps permanent magnet at low temperature with only 0.3 Nm drag torque above 500 rpm.