Patent ID: 7401979

Claim:
A fluid dynamic pressure bearing comprising: a fixed section; a rotary section rotating relative to the fixed section about a rotation axis; and a lubricating fluid held between the fixed section and the rotary section, wherein the rotary section includes a shaft and a thrust plate which extends radially outward from the shaft, the fixed section includes: a sleeve having a step portion and arranged to enclose the shaft and the thrust plate therein with a radial clearance and an axial clearance therebetween; and a counter plate closing a lower end portion of the sleeve, the thrust plate has at least one communication hole formed therein in a vicinity of an outer surface of the shaft, the communication hole penetrating the thrust plate, a radial distance between the shaft and an inner surface of a portion of the sleeve adjacent to the step portion becomes wider as the sleeve and the shaft move toward the thrust plate to form a wider flow path between the portion of the sleeve and the shaft, and a radially outermost portion of the portion of the sleeve defining the wider flow path with the shaft is located radially outside the communication hole.