Hydraulic tensioner with improved pressure relief valve reactive to peak operating loads

摘要

A hydraulic tensioner (10) having in combination a pre-loaded biasing system (14) for a secondary piston (42) to reduce the operating loads in a drive chain or belt system (12) at or near the maximum limit of the prescribed range for the tensioner (10) and a pressure relief system (16) to quickly and temporarily relieve hydraulic pressure when the operating loads exceed the maximum limit of the prescribed range. The pressure relief system (16) is located at the juncture between a primary piston (32) and the secondary piston (42) and is opened when the secondary piston (42) is forced to move independently of and toward the primary piston (32) a predetermined stroke amount. Once the pressure relief system (16) is opened, hydraulic fluid is discharged from the chamber (40) to allow the tensioner (10) to temporarily release tension on the chain or belt system (12). When the operating loads reduce below the maximum limit, the secondary piston (42) moves to its normal operating range and the pressure relief system (16) closes to allow the tension to return to its normal operating state.