Patent ID: 7947635

Claim:
A hydrodynamic bearing device for use in a magnetic disk apparatus, wherein the device comprises a shaft and a sleeve, dynamic pressure generation grooves are formed on at least one of the shaft or the sleeve, and a lubricant is present in a radial clearance formed between the shaft and the sleeve when the shaft and the sleeve are opposed to each other, wherein the radial clearance is 1 to 5 μm, and wherein the lubricant comprises at least: (A) esters obtained from 3-methyl-1,5-pentanediol, at least one saturated dibasic acid having 6 to 10 carbon atoms, and at least one straight-chain type saturated monovalent fatty acid having 7 to 10 carbon atoms, wherein a number of moles of the straight-chain type saturated monovalent fatty acid is greater than a number of moles of the saturated dibasic acid, and (B) an oxidation inhibitor free of molecular sulfur and molecular chlorine.