Mitigation of Cogging Torque in Coaxial Magnetic Gear by Rotors Skew-Shaping

The torque between an input and an output shaft can be transferred by magnetic gears without the need for physical contact. In certain instances, the design specifications of the entire system dictate that magnetic gears have an integer gear ratio. This leads to a higher cogging torque in the high-speed rotor (internal rotor), which results in vibration and acoustic noise. Creating an uneven air gap and skewing one of the three coaxial magnetic gear rotors are common ways to lower cogging torque. In this paper, in order to significantly reduce the cogging torque with an integer gear ratio, a coaxial magnetic gear with a skewed modulator is proposed. In addition, the proposed structure uses an internal rotor with a non-circular surface to create an unequal air gap. The proposed structure is optimized by a genetic optimization algorithm and Maxwell finite element software to simultaneously minimize the cogging torque and maximize the torque density. The results of comparing the proposed structure with the conventional spoke-type structure show a reduction of 88.3% and 5% in terms of the cogging torque and core losses, respectively.