Magnetic gears can transmit torque without any mechanical contact. Hence, they have low vibration, no wear, and fatigue, which ensure maintenance-free operation. There are various types of magnetic gears. Among them, a planetary type magnetic gear, which consists of coaxial inner and outer rotors with surface-mounted permanent magnet and ferromagnetic stationary parts called pole-pieces, has recently attracted interest since it offers higher torque than other type magnetic gears. This paper presents a comprehensive investigation of the influence of geometry and position of the pole-pieces on torque characteristic based on finite element analysis and experiment. Surveyed parameters of the pole-pieces include lengths in the radial and axial directions and position in the radial direction. Finally, it is demonstrated that the maximum torque of the improved prototype magnetic gear is increased by 45% and the maximum efficiency achieves up to about 99%, which is equal to or more than a conventional planetary type mechanical gear.

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Magnetic gears offer several advantages against conventional mechanical gears such as easy maintenance, low vibration and acoustic noise, and high reliability. For the practical application of magnetic gears, experimental studies on gear characteristics that consider real manufacturing constraints should be performed. This paper presents the loss analysis, experimental tests, and performance improvement of a surface permanent magnet (SPM) magnetic gear. The torque characteristic and the efficiency of the SPM magnetic gear were calculated using finite element analysis (FEA). Experiments were performed on a trial magnetic gear. The FEA and experimental results demonstrated the improved efficiency of the trial gear. The maximum efficiency of the improved gear was over 96%.