Patent ID: 8137224

Claim:
A tensioner for an endless transmission belt, comprising: a plunger body in which an installation hole is provided; a plunger movably provided in the installation hole to press the endless transmission belt; a plunger spring disposed between the plunger and the plunger body to push the plunger toward the endless transmission belt; a high-hydraulic-pressure chamber provided between the plunger and the plunger body and configured to store hydraulic oil supplied from an oil pump; an oil supply passage provided in the plunger body to supply the hydraulic oil from the oil pump to the high-hydraulic-pressure chamber; a check valve provided between the high-hydraulic-pressure chamber and the oil supply passage and configured to allow the hydraulic oil to be supplied from the oil pump to the high-hydraulic-pressure chamber, and wherein the check valve is configured to be closed when a pressure in the high-hydraulic-pressure chamber is higher than a pressure of the hydraulic oil supplied by the oil pump; a relief valve provided between the high-hydraulic-pressure chamber and the oil supply passage and configured to discharge the hydraulic oil in the high-hydraulic-pressure chamber to the oil supply passage when the pressure in the high-hydraulic-pressure chamber exceeds a first predetermined value; and a pressure retaining valve provided in the oil supply passage between the oil pump and the relief valve.