Hydrodynamic bearing device and spindle motor using the same
A hydrodynamic bearing device being low in torque, low in power consumption, high in reliability and best suited for miniaturization and a spindle motor using the same. The hydrodynamic bearing device in accordance with the present invention, dynamic pressure generation grooves being provided on at least one of a shaft or a sleeve, and a lubricant being present in a clearance where the above-mentioned shaft and the above-mentioned sleeve are opposed to each other, is characterized in that the above-mentioned lubricant contains diesters obtained from a divalent alcohol having 4 to 8 carbon atoms and having no alkyl side chain at the β position and one or more kinds of saturated monovalent fatty acids having 9 to 13 carbon atoms.
1. 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.
2. The hydrodynamic bearing device according to claim 1 , wherein the radial clearance is 1.5 to 3 μm.
3. The hydrodynamic bearing device according to claim 1 , wherein the lubricant comprises no more than 1,000 inorganic foreign particles larger than a minimum dimension of the radial clearance.
4. The hydrodynamic bearing device according to claim 1 , wherein the lubricant further comprises at least one additive selected from the group consisting of a metal deactivator free of molecular sulfur and molecular chlorine and an oiliness improver.
5. The hydrodynamic bearing device according to claim 1 , wherein the sleeve comprises a material selected from the group consisting of copper alloy, iron alloy, stainless steel and a sintered material, and wherein at least a portion of a surface of the sleeve is reformed.
6. A spindle motor comprising the hydrodynamic bearing device according to claim 1 .