Patent ID: 7118278

Claim:
A hydrodynamic bearing comprising: a shaft; a top plate fixed to the upper section of the shaft, the top plate having an ring-shaped portion extended in a lower direction, the ring-shaped portion having an inner peripheral face; a sleeve that rotates relative to the shaft about a rotation axis; a bottom plate fixed to the lower section of the sleeve; a bearing section including a minute gap formed between the upper end face of the sleeve and the lower end face of the top plate, a lubricating fluid retained in the minute gap and dynamic pressure generating grooves formed on at least one of the upper end face of the sleeve and the lower end face of the top plate, that induce dynamic pressure in the lubricating fluid when the shaft or the sleeve rotates relatively; and a capillary seal section adjoining the bearing section, having a radial gap between an outer peripheral face of the sleeve and the inner peripheral face of the ring-shaped portion; wherein the bearing section supports the shaft and the sleeve so as to rotate relative to the rotation axis, the lubricating fluid is continuously retained from the bearing section to the capillary seal section and forms a vapor-liquid interface within the capillary seal section, a radial separation of the inner peripheral face of the ring-shaped portion from the rotation axis at least widens the further along the rotation axis the radial separation is from the bearing section, and letting the minimum value of radial separation between the inner peripheral face of the ring-shaped portion and the rotation axis be R 1 , and the radial separation from the point in the vapor-liquid interface that is uppermost, in the direction toward the top plate and paralleling the rotation axis, be R 2 , then the minimum value R 1 and the radial-separation R 2 fulfill the relation R 1 >R 2 .