Patent ID: 8876641

Claim:
A chain tensioner device comprising: a main arm pivotally supported by a first shaft, the main arm slidably contacting an endless chain to apply a tension to the endless chain, the endless chain being wound around a drive sprocket connected to a drive shaft and a driven sprocket connected to a driven shaft; a tensioner lifter comprising: a housing; a plunger slidably held by the housing; and a spring to press the plunger such that the plunger projects from the housing in order to generate a biasing force to press the main arm toward the endless chain; a sub-arm disposed between the main arm and the tensioner lifter, the sub-arm being pivotally supported by a second shaft about a rotational axis to transmit the biasing force applied by the plunger of the tensioner lifter to the main arm; and a moving direction of the plunger being substantially orthogonal to a direction of a tangent at a contact portion between an abutting portion of the plunger and a first abutting portion of the sub-arm when an elongation of the endless chain reaches a maximum elongation, wherein the tangent extends in a plane perpendicular to the rotational axis, wherein at least one of the abutting portion of the plunger and the first abutting portion of the sub-arm has an arc-shape as viewed in a direction parallel to the rotational axis, and wherein sub-arm has a second abutting portion configured to contact an abutting portion of the main arm, the second abutting portion of the sub-arm, which abuts the abutting portion of the main arm, having a flat surface.