Transfer Torque Performance Comparison in Coaxial Magnetic Gears with Different Flux-Modulator Shapes

Coaxial magnetic gears, which are capable of transferring torque without physical contact or a change in speed, have sufficient advantages, including high efficiency and reliability, allowing them to replace mechanical gears. Such the coaxial magnetic gears have therefore been receiving attention for various applications, including wind power generation and electric vehicles. However, when two rotors of a coaxial magnetic gear, which are attached using permanent magnets (PMs), rotate, a high transfer torque ripple is generated owing to the difference in magnetic resistance of the flux-modulator. In particular, the torque ripple of the inner rotor is relatively higher than that of the outer rotor. These torque ripples should be reduced as much as possible during the design process because they cause vibrations and noises in the machinery. Therefore, in this paper, various flux-modulator shapes are proposed to compare the transfer torque characteristics of a coaxial magnetic gear. The transfer torque characteristics resulting from the proposed shape were derived using nonlinear finite element analysis based on a 2-D numerical analysis.