Patent ID: 7837390

Claim:
A hydrodynamic bearing, comprising: a sleeve having a bearing hole and an inner peripheral surface; a shaft having an outer peripheral surface, being disposed within the bearing hole of the sleeve so as to be rotatable relative to the sleeve, and being disposed so as to form a clearance between the sleeve and the shaft; and a radial bearing portion including a lubricant filling the clearance formed between the sleeve and the shaft, and radial hydrodynamic grooves formed on at least one of the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft, and which generates hydrodynamic pressures in a radial direction of the shaft by relative rotation between the sleeve and the shaft, the radial hydrodynamic grooves being formed so as to satisfy the following relational expression (1): L 2 <L 1/2 (1) wherein, L 1 is a length from a pressure peak generation position in a pressure distribution of the hydrodynamic pressure generated at the radial bearing portion in an axial direction of the shaft to an axial direction outer end portion which is an end portion of the radial bearing portion on an outer side in the axial direction, the length being a length of a hydrodynamic causing portion corresponding to a part which has an inclination with respect to the axial direction of the shaft, and L 2 is a length in the axis direction from a benchmark point where the end portion of the radial bearing portion on the outer side in the axial direction and a groove center line along a direction elongated from a predetermined radial hydrodynamic groove cross each other, to a relative rotational direction end portion on a backward side, which is an end portion of a radial hydrodynamic groove adjacent to the predetermined radial hydrodynamic groove on a forward side in the relative rotational direction, and which is on the backward side in the relative rotational direction, and wherein a groove angle of each radial hydrodynamic groove of the radial hydrodynamic grooves is modified in a portion between a pressure peak generation position in a pressure distribution of the hydrodynamic pressure generated at the radial bearing portion in an axial direction of the shaft and the end portion on the outer side in the axial direction, and a groove angle θ 1 of the radial hydrodynamic groove on the outer side in the axial direction is smaller than a groove angle θ 2 of the radial hydrodynamic groove on a hydrodynamic causing portion and adjacent the pressure peak generation position.