Patent ID: 7241239

Claim:
An auto tensioner provided between a side of a stationary member and a side of a pulley, and applying a tensile force to a belt, comprising: a plunger corresponding to an upper side slidably insertable into a cylinder corresponding to a lower side via a seal member; a high pressure oil chamber sectioned by the cylinder and a leading end portion of the plunger formed within the cylinder; an oil reservoir chamber forming a gas chamber in an upper portion sectioned in a sealed manner in an outer periphery of the cylinder and the plunger; a first oil passage communicating the gas chamber with the high pressure oil chamber provided within the plunger; a second oil passage communicating the high pressure oil chamber with the oil reservoir chamber provided in the cylinder; the first oil passage is provided with a pressure side damping force generating means and a first check valve closing during expansion; a second check valve closing during compression is provided in the second oil passage; wherein the first oil passage is provided with a locking means operating in response to an external input signal and acting to close the first check valve.