| 摘要 |
It is desired to improve the wear resistance of the valve seat of the check valve in a hydraulic tensioner. The hydraulic tensioner includes a cylinder having a hollow space filled with hydraulic oil. A plunger is slidably mounted in the cylinder. A pushrod is mounted in the hollow space so as to be axially movable together with the plunger with one end thereof protruding from the cylinder. A spring is mounted in the cylinder to bias the plunger and pushrod outwardly of the cylinder. The plunger is formed with a passage through which the pressure chamber and the reservoir chamber communicate with each other. The passage is formed with a valve seat. A check ball is arranged so as to be moved into and out of contact with the valve seat. The check ball is adapted to contact the valve seat when the pressure in the pressure chamber exceeds the pressure in the reservoir chamber, thereby closing the passage. The valve seat is formed of a steel for carburizing and has a surface carbon concentration of 0.55-0.75% to reduce deposition of carbides and to have a surface hardness at least equal to the check ball. This improves wear resistance of the valve seat and thus extends the life of the hydraulic tensioner.
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