| 摘要 |
PURPOSE:To enable high rigidity, low vibration and high reliability extending over the whole rotational frequency by exciting an electromagnet of a magnetic bearing to generate repulsive force or attraction force in the axial direction or in the direction of shaft diameter, in a rotational frequency region lacking dynamic pressure. CONSTITUTION:A permanent magnet 51 magnetized in the radial and axial directions is provided on a part of a shaft 1, and an electromagnet 6 is disposed on a housing 3 confronting with the magnet. At the time of stopping, low rotational frequency or high rotational frequency under the shortage of lubrication, the electromagnet 6 is excited to generate lines of magnetic force 8, thereby repulsing and attracting the permanent magnet 51 on the shaft to keep a gap in a pressure chamber 4 constant. On the other hand, in a rotational frequency region where dynamic pressure is sufficiently increased, the electromagnet 6 is low-excited or non-excited not to increase over-current loss at the magnetic bearing portions 5, 6.
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