Patent ID: 8277347

Claim:
A tensioner that imparts tension to a chain comprising: a piston having a plurality of engagement grooves on its outer circumferential surface; an expandable circlip member fitted around the engagement groove; and a housing comprising: a piston bore including an axial centerline and a guide groove, the piston bore receiving the piston slidably in the axial direction and having an opening end, the guide groove formed along the inner circumferential surface of the piston bore on the opening end side, the guide groove having a front side stop and a rear side stop that the circlip member is adapted to contact during travel of the piston, wherein the engagement groove of the piston is formed of a round seat portion that has a deepest portion of the engagement groove between a front side of the round seat portion and a rear side of the round seat portion and that the circlip member is adapted to seat, a piston-retraction restricting portion that is formed on the front side of the round seat portion, and a piston-protrusion permitting portion that is formed on the rear side of the round seat portion, wherein the piston-protrusion permitting portion is formed in such a manner as to permit protrusion of the piston when the circlip member contacts the front side stop of the guide groove during the protrusion of the piston and as to permit the piston-protrusion permitting portion to travel over the circlip member when the piston travels farther, and wherein the piston-retraction restricting portion is formed in such a manner as to permit a short travel of the circlip member in the forward direction along the rear side stop of the guide groove to allow extension of the circlip member and to restrict retraction of the piston when the circlip member contacts the rear side stop of the guide groove during retraction of the piston.