| 摘要 |
A rotor unit includes a substantially circular plate shaped cover portion, a rotor hub including a lower cylinder portion, and a magnetic field generating member attached on the lower cylinder portion. An annular salient portion is provided on the lower surface of the cover portion 31. The annular salient portion lies radial inwards of the lower opening of the through-hole of the cover portion and protrudes downwards in the shape of a ring whose center coincides with the central axis. The magnetic field generating member includes a rotor magnet and a back iron covering the outer surface and upper surface of the rotor magnet. When the magnetic field generating member is mounted to the rotor hub, the upper portion of the back iron comes in contact with the annular salient portion, which determines the axial position of the magnetic field generating member.
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