To provide a combined dynamic pressure bearing capable of reducing the floating revolution number transferred to a dynamic pressure, while maintaining the dimension of the dynamic pressure bearing part small.
In this combined bearing structure, a magnet is mounted directly or indirectly to a position opposed to a sleeve 3 and a shaft 2 constituting a dynamic pressure bearing part. At this time, a magnet at a fixing member side is deviated from an axis center and a magnetic force caused by this is utilized for an axial bearing portion, and dynamic pressure caused by a relative rotation between the sleeve 3 and the shaft 2 is utilized at a radial portion. The amount of deviation of this magnet is set to 0.01-0.3 with respect to the average radius gap provided between both magnets 5, 6. The circularity of a slide portion cross section is 1.0×10-4 or lower, a difference of a heat expansion coefficients of both materials is 8×10-6/°C or less and an elastic modulus of a rotation side member is 2.5×104 kgf/mm2 or more. One or more positions where a radial gap is wide is preferably provided on a bearing portion for obtaining stable rotation.
OTSUKI MAKOTO
KOMURA OSAMU
