Patent ID: 8568258

Claim:
A chain tensioner for use in an engine, comprising: a tensioner housing having a cylindrical plunger-accommodating hole having an inner peripheral surface and an opening at one end thereof; a plunger slidable in the plunger-accommodating hole and protruding therefrom through said opening, said plunger having an outer peripheral surface, and being movable in said plunger-accommodating hole both in a protruding direction and in a retracting direction opposite to said protruding direction; an annular circumferential groove formed in the inner peripheral surface of the plunger-accommodating hole adjacent said opening; a resilient ring retained in said annular circumferential groove and radially expansible and contractible therein between a radially contracted condition and a radially expanded condition; a plunger-biasing spring urging the plunger in a protruding direction; and a plurality of annular rack teeth formed on the outer peripheral surface and spaced from one another along said protruding direction; wherein the annular circumferential groove of the plunger-accommodating hole comprises a first ring-engaging wall facing in said retracting direction, and a second ring-engaging wall facing in said protruding direction; wherein each rack tooth of the plunger has a steeply sloping rear side facing in the said retracting direction and a gradually sloping front side facing in said protruding direction; wherein the resilient ring, when in its radially contracted condition can simultaneously engage a steeply sloping rear side of a rack tooth and a gradually sloping front side of an adjacent rack tooth; wherein the angle of inclination of the second ring-engaging wall surface is greater than the angle of inclination of the steeply sloping rear sides of the rack teeth, said angles of inclination being measured relative to the protruding direction of the plunger, whereby that the resilient ring can be prevented from crossing over a tip of a rack tooth when a design load in the retracting direction is applied to the plunger on engine start-up, but can cross over the tip of a rack tooth by expansion of the ring when a load greater than said design load is applied to the plunger in the retracting direction when chain tension becomes excessive; and wherein the gradually sloping front sides of the rack teeth have a convex curvature wherein the rate of increase in their diameters with respect to the retracting direction of the plunger decreases, proceeding along the retracting direction, whereby the protruding movement of the plunger becomes more nearly linear as the resilient ring is expanded by contact with a gradually sloping front side of a rack tooth.