Patent ID: 7622837

Claim:
A hydrodynamic bearing device comprising: a sleeve having a bearing hole constituting a radial bearing; a shaft inserted to the bearing hole so as to be rotatable relative to the sleeve; a flange secured to the shaft and having a surface part facing one end surface of the sleeve proximate the bearing hole, wherein said facing surfaces of the flange and the sleeve are perpendicular to a central axis of the shaft to constitute a thrust bearing; and a lubricating fluid filled in the bearing hole and a gap between the end surface of the sleeve and the flange, wherein at least one of an inner surface of the bearing hole and an outer surface of the shaft has radial dynamic pressure generating grooves each having a herringbone shape formed therein so as to generate a radial dynamic fluid pressure having a distribution of a generally triangular shape such that the pressure of the lubricating fluid is maximized at bended portions of the herringbone shapes and gradually reduced toward both ends of the herringbone shapes of the grooves, and the flange has thrust dynamic pressure generating grooves each having a spiral shape formed in the surface thereof facing said one end surface of the sleeve so as to generate a thrust dynamic fluid pressure having a distribution of a generally trapezoidal shape such that the pressure of the lubricating fluid is high in a region defined by an inner periphery of the grooves and including a vicinity of an inner periphery of the flange and a shaft portion therein and that the pressure is gradually reduced toward an outer periphery of the grooves near an outer periphery of the flange, and wherein a dimension of the generally trapezoidal pressure distribution where the pressure is increased high by the thrust dynamic pressure generating grooves is equal to or larger than an axial dimension of the radial dynamic pressure generating grooves.