Performance judgment method for dynamic pressure bearing and dynamic pressure bearing

A method of judging performance of a dynamic pressure bearing that includes a shaft having a shank and a flange connected to one end of the shank, and a sleeve defining a flange housing space for housing the flange and a shank housing space for housing the shank and having a receiving surface for receiving the flange and an opposite surface opposed to the receiving surface through the flange housing space, the shank housing space communicating to the flange housing space and a dynamic pressure generation groove being formed in at least one of an inner peripheral surface of the sleeve facing the shank housing space and the shank, the method comprising the steps:

• measuring an axial clearance by subtracting an axial thickness of the flange from an axial dimension between the receiving surface and the opposite surface;
• measuring a floating amount that corresponds to an axial clearance between the flange and the receiving surface when lubricating oil is filled between the sleeve and the shaft and the shaft or the sleeve rotates at a predetermined speed in a state where the shaft is vertically disposed such that the flange is located below the shank;
• and
• calculating a ratio of the measured axial clearance to the measured floating amount and judging that leakage of lubricating oil and abnormal abrasion do not occur in the dynamic pressure bearing when the calculated ratio falls within the range from 0.45 to 0.70.

A dynamic pressure bearing comprising:

• a shaft that includes a shank and a flange connected to one end of the shank;
• a sleeve that defines a flange housing space for housing the flange and a shank housing space for housing the shank and has a receiving surface for receiving the flange and an opposite surface opposed to the receiving surface through the flange housing space, the shank housing space communicating to the flange housing space;
• and
• a dynamic pressure generation groove formed on at least one of an inner peripheral surface of the sleeve facing the shank housing space and the shank,
• wherein the condition 0.3≦b/a≦0.55 is satisfied,
• where “a” represents an axial clearance obtained by subtracting an axial thickness of the flange from an axial dimension between the receiving surface and the opposite surface, and “b” represents an axial clearance between the flange and the opposite surface in a state where lubricating oil is filled between the sleeve and the shaft, the shaft is vertically disposed such that the flange is located above the shank, and the shaft or the sleeve rotates at a predetermined speed.

A dynamic pressure bearing comprising:

• a shaft that includes a shank and a flange connected to one end of the shank;
• a sleeve that defines a flange housing space for housing the flange and a shank housing space for housing the shank and has a receiving surface for receiving the flange and an opposite surface opposed to the receiving surface through the flange housing space, the shank housing space communicating to the flange housing space;
• and
• a dynamic pressure generation groove formed on at least one of an inner peripheral surface of the sleeve facing the shank housing space and the shank,
• wherein the condition 0.45≦c/a≦0.70 is satisfied,
• where “a” represents an axial clearance obtained by subtracting an axial thickness of the flange from an axial dimension between the receiving surface and the opposite surface, and “c” represents an axial clearance between the flange and the receiving surface in a state where lubricating oil is filled between the sleeve and the shaft, the shaft is vertically disposed such that the flange is located below the shank, and the shaft or the sleeve rotates at a predetermined speed.