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This paper aims to propose a new magnetic-geared motor (MGM) which can easily increase the gear ratio up to approximately several hundred. The operational principle is described, and the relationship between the maximum transmission torques of each layer of the differential harmonic magnetic gear is investigated using a mathematical model and finite element method (FEM).

The operational principle and maximum transmission torque are described using a mathematical model. The FEM is used to investigate the operational principle and torque characteristics.

As the proposed model can realize a larger gear ratio than the conventional model, the torque constant can be approximately 100 times as large as that of the conventional model.

The proposed and conventional models have the same shape stator, and it is not optimized.

The relationship between the maximum transmission torques of each layer is described, and this helps the design of a differential type MGM.

Early magnetic-geared motors have a high transmission torque density. However, the torque due to the coil is low because the permanent magnets in the stator become a large magnetic resistance when the current is applied to the coil. The purpose of this paper is to propose magnetic-geared motors which have a high transmission torque density and torque due to the coil. In addition, the proposed magnetic-geared motors are compared with past magnetic-geared motors and the effectiveness is verified by using finite element analysis.

A new magnetic-geared motor which has permanent magnets in the stator slot are proposed. The torque due to the coil increases by removing permanent magnets at the tip of the stator of past magnetic-geared motors. The permanent magnets placed in the stator slots are all magnetized to the outward direction and then the stator teeth are all magnetized to the inward direction. The maximum transmission torque and torque constant are compared.

The proposed magnetic-geared motor has a slightly smaller maximum transmission torque than the early magnetic-geared motors. However, the maximum transmission torque of the proposed magnetic-geared motor is high enough for practical uses. The torque due to the coils is higher than the early magnetic-geared motors.

The proposed magnetic-geared motor has originalities in its structure, especially in the permanent magnets in the stator slots.

The purpose of this paper is to propose a magnetic‐geared motor with permanent magnets only on the high‐speed rotor as a solution to the problems of magnetic gears. Magnetic gears have some advantages such as no mechanical loss and maintenance‐free operation that are not observed in conventional mechanical gears. Furthermore, they have inherent overload protection. A novel structure which the magnetic gear is integrated with the brushless motor (magnetic‐geared motor) was proposed by Atallah et al. This magnetic‐geared motor is based on the magnetic gear which consists of a high‐ and low‐speed rotor, and a stator. Although this magnetic‐geared motor has a high‐torque density, problems with manufacturing and cost exist because multi‐pole permanent magnets are mounted on the high‐speed rotor and stator.

A magnetic‐geared motor with permanent magnets only on the high‐speed rotor was proposed and its operational principle was described. The cogging torque characteristics were mathematically formulated and the authors ascertained that the cogging torque contains components of multiples of 60th order. In order to verify the order of the cogging torque, the 3‐D finite element method analysis was conducted and measurements on a prototype were carried out.

The 60th component and its multiples were observed in the computed and measured cogging torque waveform. However, the cogging torque characteristics, especially the order of the cogging torque on the low‐speed rotor, have not been clarified.

In the near future, cogging torque reduction methods will be proposed, and verified by conducting 3‐D FEM analyses and carrying out measurements on a prototype. Furthermore, the torque characteristics when an electrical current is applied to the coils and the eddy‐current loss characteristics will be verified.