Patent ID: 7037229

Claim:
A hydraulic tensioner comprising: a cylinder having a hollow space to be filled with hydraulic oil; a plunger slidably mounted in said hollow space so as to partition said hollow space into a pressure chamber and a reservoir chamber, said plunger having a passage through which said pressure chamber and said reservoir chamber communicate with each other, said passage defining a valve seat formed of a steel for carburizing, said steel comprising a forgeable alloyed steel for a mechanical structure, said valve seat having a surface carbon concentration of from 0.55%–0.75% after heat treatment, and there being no deposition of carbides on the surface of said valve seat after the heat treatment; a pushrod mounted in said hollow space so as to be axially movable together with said plunger, said pushrod having one end thereof protruding from an end of said cylinder; a spring mounted in said hollow space so as to bias said plunger and said pushrod in a direction toward said end of said cylinder; and a check ball movable into and out of contact with said valve seat, said check ball being adapted to move into contact with said valve seat when pressure in said pressure chamber exceeds pressure in said reservoir chamber so as to close said passage.