Tensioner for endless transmission belt and internal combustion engine having the tensioner

An internal combustion engine comprising:

• an endless transmission belt;
• and
• a tensioner configured to press the endless transmission belt and 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.