Patent ID: 7468012

Claim:
A ratchet tensioner comprising: a housing having a plunger-accommodating hole; a plunger slidable in the plunger-accommodating hole, and protruding therefrom in a protruding direction; a biasing spring urging the plunger in the protruding direction; a rack of ratchet teeth formed on the plunger and extending in said protruding direction; a pawl pivoted on the housing, and positioned to engage and disengage the rack, the pawl and the rack forming a ratchet mechanism having backlash, the ratchet mechanism allowing protruding movement of the plunger while limiting retracting movement of the plunger to a distance corresponding to the backlash of the ratchet mechanism; a pawl-biasing spring in compression between the housing and the pawl, the pawl-biasing spring urging the pawl into engagement with the rack, the pawl-biasing spring being disposed in a spring-accommodating hole in the housing; and a piston, disposed between the pawl-biasing spring and the pawl, a part of the piston being located within, and slidable in, the spring-accommodating hole, and a part of the piston, located outside the spring-accommodating hole, being in contact with the pawl; in which at least a part of the piston extending from the pawl toward the spring-accommodating hole has a maximum dimension less than the maximum dimension of the part of the piston slidable in the spring-accommodating hole, said dimensions being measured in directions perpendicular to the direction of piston movement.