Patent ID: 7267626

Claim:
An auto tensioner for automatically maintaining a tensile force of a belt of a belt driving mechanism at a suitable level, comprising: a support member fixed to a mounting object in which the belt driving mechanism is provided; an arm having a boss portion on a base end portion thereof oscillatably supported with respect to the support member; a tension pulley rotatably engaged with the arm at a tip side thereof; a guide plate fixed to an axial tip portion of the support member to axially face the boss portion; a spring oscillatably energizing the arm around the support member in a certain direction and pressing the boss portion against the guide plate; a friction plate sandwiched between the boss portion of the arm and the guide plate and pressed against the boss portion and the guide plate by the spring to apply an oscillational resistance to the boss portion; and a vibration attenuating member provided in contact with an outer surface of the guide plate for controlling vibration of the guide plate caused by a stick-slip phenomenon during sliding contact between portions of the friction plate, the boss portion and the guide plate; wherein the vibration attenuating member has a structure of an inner member having a required elasticity and an outer member having less elasticity than the inner member and being laminated to the inner member, the inner member is located on a side in contact with the outer surface of the guide plate, and when the guide plate is vibrated to the extent that the guide plate is warped to consequently generate a sheer deformation between the guide plate and the outer member, an elasticity restoring force of the inner member nullifies the warping of the guide plate.