US Patent 7468012 Ratchet type tensioner

In a ratchet tensioner, a pawl, pivoted on a shaft in the tensioner housing, engages teeth on a plunger protruding from the housing to allow protruding movement of the plunger, while limiting retracting movement to a backlash distance. The pawl is biased into contact with the teeth on the plunger by a spring disposed in a hole in the housing and acting, through a piston slidable in the same hole, against a convexly curved surface of the pawl. The piston has a reduced portion in engagement with the pawl, which allows the pawl to be miniaturized without excessively reducing the radial dimensions of the portion of the pawl surrounding the pivot shaft.