Patent ID: 7268453

Claim:
Axial magnetic bearing apparatus in which a rotary disc made of a magnetic material is fixedly attached to a rotating shaft, while a pair of electromagnetic stators in each of which a ring-like electromagnetic coil for generating magnetomotive force is inserted into a coil slot are fixed to casings respectively so as to be located on opposite sides of said rotary disc with suitable very small distances, and on the basis of an output signal of a displacement sensor for measuring axial displacement of said rotating shaft, magnetic attraction force is made to act between said rotary disc and each of said electromagnetic stators so as to bear said rotating shaft in a target position distant from said electromagnetic stators and in non-contact therewith, said axial magnetic bearing apparatus being characterized in that fan-shaped through holes for forming an air layer having large magneto-resistance are provided in a vicinity of an axial center of said rotary disc so as to extend from an outer circumferential portion of said rotary disc to said rotating shaft, while walls of rotary disc pieces located on axially opposite sides of said through holes are formed as solid walls having no through hole axially.