Patent ID: 8821326

Claim:
A ratchet-type tensioner, comprising: a housing; a plunger supported by the housing for movement in opposite advancing and setback directions in a plunger-receiving hole, the plunger having rack teeth provided thereon, and being arranged to advance with respect to the housing along the advancing direction for applying tension to a traveling transmission medium engaged with rotating members; a high pressure oil chamber formed by the plunger and tensioner housing; a ratchet mechanism capable of restricting the plunger from setting back due to a reaction force acting in a setback direction from the transmission medium; said ratchet mechanism comprising: a piston-receiving hole provided within the housing having a front end adjacent the plunger-receiving hole and a rear end remote from the plunger-receiving hole and having an outer circumferential surface; a piston slidable in the piston-receiving hole and movable in a sliding direction transverse to the advancing and setback directions; ratchet teeth on the piston engageable with the rack teeth of the plunger; a piston-biasing spring for biasing the piston in an engaging direction along the sliding direction so that the ratchet teeth engage with the rack teeth; a plug fitted in the rear end of the piston-receiving hole, the piston-biasing spring bearing against the plug; and a ratchet releasing mechanism for releasing engagement of the ratchet teeth with the rack teeth; said ratchet releasing mechanism comprising a tool engaging portion provided at the front end of the piston to abut and engage an end of a tool, and a tool inserting hole provided in the housing, through which the tool can be inserted and engaged with the tool engaging portion, thereby pushing the piston away from the plunger so that the ratchet teeth disengage the rack teeth.