| 摘要 |
An auto-tensioner includes a cylinder, and a sleeve having a bottom and fitted in the cylinder. Hydraulic oil is stored in the cylinder. A plunger is slidably inserted in the sleeve, thereby partitioning the interior of the housing into a pressure chamber and a reservoir chamber. The pressure chamber communicates with the reservoir chamber through an oil passage. A check valve is provided at the oil passage that permits only the flow of hydraulic oil from the reservoir chamber into the pressure chamber through the oil passage. The check valve includes a ceramic ball configured to move into contact with and separate from a seating surface formed on the end of the oil passage facing the pressure chamber, and a retainer for restricting the moving range of the ceramic material. The ceramic ball has a surface roughness Ra of not more than 0.01.
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