Thrust magnetic bearing and turbo-compressor with same

A thrust magnetic bearing comprising:

• a stator having a coil;
• and
• a rotor,
• the stator including a main stator magnetic-pole surface, and an auxiliary stator magnetic-pole surface,
• the rotor including a main rotor magnetic-pole surface facing the min stator magnetic-pole surface, and an auxiliary rotor magnetic-pole surface facing the auxiliary stator magnetic-pole surface,
• when an electric current flows in the coil,
• an electromagnetic force in an axial direction is generated between the main stator magnetic-pole surface and the main rotor magnetic-pole surface, and
• an electromagnetic force in a radial direction is generated between the auxiliary stator magnetic-pole surface and the auxiliary rotor magnetic-pole surface, and
• when the rotor is displaced in the radial direction,
• a radial force that acts on the rotor between the auxiliary stator magnetic-pole surface and the auxiliary rotor magnetic-pole surface is increased in a direction of the displacement, and
• a radial force that acts on the rotor between the main stator magnetic-pole surface and the main rotor magnetic-pole surface is increased in a direction opposite to the direction of the displacement,
• the rotor having a circular cylindrical shape,
• one end surface of the circular cylindrical shaped rotor in the axial direction including a ring-shaped concave portion at a radial inner end portion and a portion at an outer side in the radial direction with respect to the ring-shaped concave portion forming the main rotor magnetic-pole surface, and
• the stator including a ring-shaped protruding portion, the ring-shaped protruding portion
• protruding toward the rotor in the axial direction,
• having a radial inner end that faces a radial inner end of the main rotor magnetic-pole surface in the axial direction,
• having a radial outer end that faces a radial outer end of the main rotor magnetic-pole surface in the axial direction, and
• having a protruding end surface that forms the main stator magnetic-pole surface.