To reduce cogging while maintaining preferable magnetization of a compact permanent magnet.
If the thickness t of the permanent magnet is set within a range of the following expression (4) with D at and less than 20 mm, a preferable permanent magnet with reduced cogging can be obtained. The expression (4) is πD/(0.75PM-π)<t≤πD/(0.5PM-π), where D is an inner periphery of the permanent magnet, P is a pitch per pole, M is the number of phases of AC. An outer rotor type permanent magnet is described in this embodiment, however, the expression (4) is also applicable to an inner rotor type permanent magnet. Besides, this embodiment is preferably applicable to a compact permanent magnet of which the outer diameter is at and less than 20 mm. Moreover, Sm-Co (samarium-cobalt) series magnetic material is used as magnetic material in this embodiment.
KINOSHITA SHINJI
GOTO HIROMITSU
Hitoshi Nakano