Tensioner for an endless transmitting member

摘要

A tensioner for an endless transmitting member is provided to reliably prevent the loosening of an endless chain, while preventing the occurrence of an incorrect meshing of the endless chain with sprockets. A plunger holder is biased in an advancing direction by the action of a first spring supported in a housing, and a plunger, carried in the plunger holder, is biased in an advancing direction by the action of a second spring having a spring constant larger than that of the first spring. Only the movement of the plunger holder in the advancing direction is permitted by a ratchet mechanism mounted between the plunger holder and the housing. During operation of the engine, the advancing movement of the plunger holder is inhibited by the hydraulic pressure transmitted to a hydraulic pressure chamber, and the plunger is advanced and retracted in accordance with a variation in tension of the endless chain. When the engine is stopped, the ratchet mechanism is operated in accordance with the elongation of the endless chain due to wearing to advance the plunger holder one pitch at a time along with the plunger.