| 摘要 |
PROBLEM TO BE SOLVED: To improve a precision easily at a low cost and increase a mass productivity by setting at least one side of the surface area ratio of a bearing surface opening part including a dynamic pressure groove and the dynamic viscosity of a contained oil to a range in which a dynamic pressure oil film forming and circulation can be ensured. SOLUTION: A dynamic pressure groove 5 is provided on the bearing surface 17 of a bearing main body 1 and an oil is poured in/out to/from the bearing clearance between the opening part of the bearing surface 17 and the rotary shaft 2. In order to keep the circulation of oil properly, the surface area ratio A of the opening part of the bearing surface 17 including the dynamic pressure groove 5 is made to 2% or more, 20% or less and the dynamic viscosityηof an impregnated oil at 40 deg.C is made to 2 cSt or more and (3/5)A-1<=η<=(40/6)A+(20/3). Thereby, the efficiency at the assembly time is good and the surrounding contamination by the flowing away, scattering and evaporation of oil can be reduced at a low cost and an unstable vibration is restrained and a high rotation precision can be achieved and a favorable dynamic pressure oil film formation is maintained and the durability can be improved.
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