Patent ID: 6866601

Claim:
A chain transmission comprising a chain arranged to transmit rotating motion from a driving sprocket to at least one driven sprocket, and a hydraulic tensioner arranged to apply tension to said chain, said tensioner comprising a housing having a plunger-receiving hole, a plunger disposed in said plunger-receiving hole and movable therein in a protruding and retracting direction, said plunger being spring-biased in the protruding direction, and arranged to apply tension to said chain, said plunger and said plunger-receiving hole together defining a high pressure oil chamber, a ratchet locking mechanism comprising a ratchet pawl pivotally supported on said housing and ratchet teeth provided on said plunger and engageable by said pawl, an oil supply opening for receiving oil fed under pressure from a source, an oil supply passage, a hydraulic valve mechanism in fluid communication, through said oil supply passage, with said oil supply opening, for allowing oil to flow into said high-pressure oil chamber but blocking backflow of oil from said high pressure oil chamber through said oil supply passage, wherein the improvement comprises an oil discharge passage, said oil discharge passage providing fluid communication from said oil supply passage to the exterior of said housing, whereby abnormally high tension in said chain, resulting from excessive pressure in said high pressure oil chamber when the supplied oil has a high viscosity, is avoided, and wherein said oil discharge passage is arranged to direct a spout of oil toward said chain.