Abstract

Coaxial magnetic gears (CMGs) have emerged as a promising alternative to conventional mechanical gear systems due to their contactless torque transmission, low maintenance requirements, and high reliability. However, under high-speed operation, conductivity-induced eddy current losses become dominant and significantly limit thermal performance. This study comparatively investigates the coupled electromagnetic and thermal behavior of two compact CMGs with identical torque capacity using M400-50A electrical steel and cobalt-based Hiperco 50A. Coupled electromagnetic–thermal finite element analyses are performed from 1000 to 12,000 rpm under worst-case natural convection conditions. The results demonstrate that the use of Hiperco 50A reduces core losses by up to 71% at high speeds and enables approximately 7.3% greater volumetric compactness owing to its higher saturation capability. Eddy-current-related losses remain the dominant loss mechanism at elevated speeds, causing inner-rotor permanent-magnet temperatures to exceed the allowable limits of NdFeB materials. Under natural convection, the outer permanent-magnet temperature remains below the critical threshold of 200 °C up to approximately 5800 rpm for the M400-50A design. With Hiperco 50A, this limit increases to approximately 6000 rpm under identical operating conditions, corresponding to an improvement of about 3%. These findings demonstrate the thermal benefits of high-saturation magnetic alloys; however, additional cooling strategies are required for operation at higher speeds.

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