Patent ID: 7411762

Claim:
A fluid dynamic pressure bearing for a motor, comprising: a shaft; and a sleeve made of a porous material which is impregnated with a lubricating fluid, the sleeve and the shaft rotating relatively about a rotation central axis; wherein an upper radial dynamic pressure bearing and a lower radial dynamic pressure bearing are adjacently located around a location between said shaft and said sleeve, said upper and lower radial dynamic pressure bearings have a micro gap between said shaft and said sleeve, and said lubricating fluid is filled in said micro gap as a working fluid for inducing a dynamic pressure when said motor is rotating, wherein upper radial dynamic pressure-generating grooves are formed on an upper inner peripheral surface of said sleeve in said upper radial dynamic pressure bearing by plastic deformation, lower radial dynamic pressure-generating grooves are formed on a lower inner peripheral surface of said sleeve by plastic deformation, and said upper radial dynamic pressure-generating grooves are formed continuously to said lower radial dynamic pressure-generating grooves, and wherein an annular groove recessed radially inward is formed on an outer peripheral surface of said shaft at a place facing a borderline between said upper radial dynamic pressure-generating grooves and said lower radial dynamic pressure-generating grooves.