Dynamic pressure bearing and rotation machine employing same

A dynamic pressure bearing in which a shaft having a protruding tubular section for inserting into a toric thrust plate and a sleeve is fitted to an outer periphery of said shaft having said toric thrust plate fitted and fixed thereto so as to be rotatable relatively to the shaft, a clearance section for generating a thrust dynamic pressure by an axial inner face of said thrust plate and an opposite axial outer face of the protruding tubular section, a clearance section for generating a radial dynamic pressure by an inner peripheral face of the protruding tubular section of said sleeve and an opposite outer peripheral face of the shaft, and a magnetic fluid is retained and sealed in the clearance sections, wherein

• an annular cover made of a nonmagnetic material is formed on the sleeve outwardly from said thrust plate in an axial direction via a clearance section,
• a radially inward end of said annular cover serves as an opening,
• at least two clearance sections of the clearance section between said thrust plate and said annular cover and a clearance section between a position radially outward from said thrust plate and an opposite position radially inward from the sleeve are used as a reservoir for reserving the magnetic fluid,
• an end portion of the magnetic fluid is kept in the clearance section between said thrust plate and said annular cover, which forms said reservoir, and
• a magnetomotive force member positioned radially outward the end portion of the magnetic fluid and producing concentrated flux lines on magnetic fluid located radially outward from the end portion.