Patent ID: 8100792

Claim:
A hydraulic auto-tensioner, comprising: a high-pressure oil chamber pressed by a piston portion of a plunger in an interior of a cylinder; and a low-pressure oil chamber capable of communicating with the high-pressure oil chamber via a check valve, in which oil in the high-pressure oil chamber passes through a clearance between the cylinder and the piston portion and leaks into the low-pressure oil chamber from an end of the clearance near an end surface of the cylinder, wherein a recessed groove is provided in an inner peripheral surface of the cylinder by a conical surface extending from the end of the clearance to the end surface side of the cylinder and having a groove angle of 5 to 15 degrees relative to a length direction of the inner peripheral surface, a throttle portion projecting onto the piston portion side is provided further toward the end surface side of the cylinder than the groove in the inner peripheral surface of the cylinder, and a throttle gap which is larger than the clearance, is formed between the throttle portion and the piston portion.