Hydraulic tensioner with two spring biased pistons and cushioned pull-back rack

摘要

A hydraulic rack-style tensioner includes two concentric pistons in the bore of a tensioner housing. The lower piston which occupies a generally lower position in the housing has conventional ratchet teeth on an outside surface. The ratchet teeth form a rack which are engaged by a pawl. An upper piston occupies a generally upper protruding position in the housing. A chamber is defined between the upper piston and the housing, or between the upper piston and lower piston. Pressurized fluid in the chamber between the upper and lower pistons act to cushion impact of the rack and pawl mechanism when high loads from an associated tensioner arm and chain cause the upper and the lower pistons to be forced back toward the tensioner housing.