Patent ID: 7427250

Claim:
A ring type hydraulic tensioner comprising: a housing having a plunger-accommodating hole having a cylindrical inner circumferential wall; a circular, cylindrical plunger, slidable along an axis in the plunger-accommodating hole and protruding therefrom; a plunger-biasing spring in an oil chamber formed by the plunger and the plunger-accommodating hole, said spring urging the plunger in the protruding direction; and a check valve unit permitting flow of oil into said high pressure oil chamber and blocking flow of oil out of said chamber; wherein the improvement comprises: an annular groove formed in the outer circumference of the plunger, said groove having a bottom facing, but spaced from, said cylindrical inner circumferential wall of the plunger-accommodating hole and axially spaced, opposed, end walls; and a resilient, radially expansible, split steel ring disposed in said annular groove, said ring having an outer diameter, when relaxed, greater than the diameter of said inner circumferential wall of the plunger-accommodating hole and being biased by its resilience so that it exerts a radial outward biasing force against said cylindrical inner circumferential wall of the plunger-accommodating hole; said ring being slidable, with sliding resistance, on said cylindrical inner circumferential wall of the plunger-accommodating hole, and fitting in said groove with a predetermined axial clearance in the groove width direction and a predetermined radial clearance between the ring and the bottom of the groove, in the groove depth direction, said ring being engageable by said end walls of the groove; said predetermined radial clearance existing along the entire axial length of the ring; said predetermined axial clearance allowing the plunger to protrude and retract within a predetermined range of movement with reference to the position of the ring; and the sliding resistance between the ring and the inner circumferential wall of the plunger-accommodating hole in the protruding and retracting directions when said ring is engaged respectively by said end walls of the groove being due solely to said biasing force, and imposing increased resistance to protruding and retracting movement of the plunger beyond said predetermined range.