Patent ID: 7404776

Claim:
A hydraulic tensioner comprising: a tensioner housing having a plunger-accommodating hole, said hole having a cylindrical inner wall, an opening at one end and a bottom at an end opposite from said opening; a plunger slidable in said plunger-accommodating hole and protruding therefrom, said plunger being adapted to maintain tension in a flexible, traveling power transmission medium, said plunger and said housing together cooperating to define a high pressure oil chamber; an oil supply passage formed in the bottom of said plunger-accommodating hole; a plunger biasing spring, accommodated in said high pressure oil chamber, the plunger biasing spring urging the plunger in a protruding direction; and a check valve unit, disposed within said plunger-accommodating hole adjacent said oil supply passage, for allowing oil to flow into said high pressure oil chamber from said oil supply passage but blocking reverse flow of oil from said high pressure oil chamber; wherein said check valve unit comprises a check ball, a ball seat having an end surface facing said bottom of the plunger-accommodating hole, a ball guide including an inner wall surrounding the check ball with a clearance and an outer circumferential surface fitting said cylindrical wall of the plunger-accommodating hole, and a disc-shaped retainer sealing the check ball in the ball guide; wherein the check ball is movable in the ball guide toward and away from the ball seat, to allow oil to flow through the ball seat of the check valve unit into the high pressure oil chamber but to block reverse flow of oil out of the high pressure oil chamber by seating of the check ball against the ball seat; wherein ventilating grooves are formed on said outer circumferential surface of the ball guide and on said end surface of said ball seat, the ventilating grooves being in communication with one another and providing a path for the flow of air from said high pressure oil chamber to said oil supply passage; wherein the ball guide of the check valve unit is composed of a synthetic resin, and includes a circumferential tongue pressing against the inner wall of the plunger-accommodating hole, whereby the ball guide is press-fit in the plunger-accommodating hole adjacent the bottom of the plunger-accommodating hole, and wherein the circumferential tongue is interrupted by at least one ventilating groove formed on the outer circumferential surface of the ball guide; and wherein the ball guide has an inner portion defining said inner wall surrounding the check ball, and in which at least one arcuate slot is provided between said inner portion and the circumferential tongue, the arcuate slot allowing flexing of the tongue to press against the inner wall of the plunger-accommodating hole, and in which the tongue is connected to the inner portion of the ball guide at both ends of each said arcuate slot by a connecting element and in which each said ventilating groove formed on the outer circumferential surface of the ball guide is formed in one said connecting element.