Magnetic gears have advantages such as having low acoustic noise and being maintenance-free in comparison with widely-used mechanical gears. This paper deals with a magnetic planetary gear which has inner and outer surface permanent-magnet rotors, and has ferromagnetic-stator pole pieces arranged between both rotors. The magnetic planetary gear has higher transmission torque than other types of magnetic gears since all rotor magnets continuously contribute to generating torque. However, it has not been put into practical use yet. To achieve future practical use, this paper describes a method of improving the efficiency of magnetic planetary gears.

Permanent-magnet magnetic gears have various advantages such as having low acou stic noise and being maintenance-free in c omparison with c onventional mec hanical g ears. Var ious types of magnetic gears have been introduced in previous papers. Of th ese, planetary permanent-magnet magnet ic g ears h ave h igher tr ansmission torque than other types. We compared two types of planetary magnetic gears. The first utilized a surface permanent magnet (SPM), and the second used an interior permanent magnet (IPM). We compared the transmission torque and eddy-current loss that occurred in these magnets.

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A study is carried out based on the evaluation of IEC-standard. Two measurement results on N.O. magnetic steel sheets, one from S-SST (Stress load type single sheet tester developed in our research laboratory), another is from SST based on the IEC standard regulation, are compared and discussed. As a result of the measurements, both magnetization curves coincide mostly, but magnetic power loss determined by IEC method is larger than that achieved by S-SST. The differences between them may be caused by magnetic field strength evaluation for each measurement method, magnetizing current method for IEC-type-SST and H-coil method for S-SST. The effective magnetic path is regulated in IEC but actually this may be variable according to the type of magnetic sheet, the structure of the SST and of applied magnetic field strength. In order to discuss this point, a virtual magnetic path length is introduced by using the applied magnetic field strength.

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