Patent ID: 8282520
Filing Date: 2012-10-09
Classification: F16H

Abstract:
1. In an engine having a timing drive comprising an endless timing chain, a chain tensioner arranged to maintain tension in said chain, the chain tensioner comprising: a tensioner housing having a cylindrical plunger-accommodating hole having an inner wall, an open end, and a bottom opposite from said open end; a cylindrical plunger slidable in the plunger-accommodating hole and protruding from said open end thereof; a plunger-biasing spring urging said plunger in a protruding direction; and a ratchet composed of a plurality of concave external grooves disposed around the outer periphery of the plunger, said external grooves being separated from one another by convex ridges, and a resilient ring within the tensioner housing for engaging surfaces of said grooves; an annular internal groove formed in the inner wall of the plunger-accommodating hole adjacent said open end thereof, at least a part of the resilient ring being disposed within the annular groove and said ring being expandable into the annular groove; wherein said annular internal groove has opposed first and second surfaces engageable by said resilient ring, the first of said internal groove surfaces being inclined at a first angle with respect to a plane perpendicular to said protruding direction and facing said bottom of the plunger-accommodating hole, and the second of said internal groove surfaces being inclined at a second angle with respect to a plane perpendicular to said protruding direction and facing the open end of the plunger-accommodating hole; wherein each said external groove on the plunger has opposed third and fourth surfaces engageable by said resilient ring, said third surfaces being inclined at a third angle with respect to a plane perpendicular to said protruding direction and facing the open end of the plunger-accommodating hole, and the said fourth surface being inclined at a fourth angle with respect to a plane perpendicular to said protruding direction and facing the bottom of the plunger-accommodating hole; wherein the difference between the first and third angles is different from the difference between the second and fourth angles; and wherein said fourth angle exceeds the second angle by a limited amount such that the resilient ring is prevented, by contact with said second and fourth surfaces, from expanding sufficiently to move from an external concave groove on the plunger and over a convex ridge of the plunger into a next external concave groove as a result of the force applied by said chain to the plunger during starting of the engine, but wherein said fourth angle exceeds the second angle by an amount sufficient that, when a predetermined force, greater than the maximum force exerted on said plunger during starting of the engine is exerted on the plunger during engine operation, the resilient ring is caused to expand, by contact with said second and fourth surfaces, into said annular internal groove so that said resilient ring passes from an external concave groove on the plunger, and over a convex ridge of the plunger into a next external concave groove, thereby allowing the plunger to move in said retracting direction, whereby the plunger is prevented from retracting on starting of the engine, but allowed to retract when tension in the chain becomes excessive during engine operation.