Patent ID: 7427249

Claim:
A hydraulic tensioner comprising: a tensioner housing having a plunger-accommodating hole, said hole having an opening at one end and a bottom; 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; a plunger biasing spring, accommodated in said high pressure oil chamber, the plunger biasing spring urging the plunger in a protruding direction; a check valve unit at the bottom of said plunger-accommodating hole for allowing oil to flow into said high pressure oil chamber from an oil supply but blocking reverse flow of oil from said high pressure oil chamber; wherein said check valve unit comprises a check ball, a ball seat, a ball guide composed of synthetic resin, the ball guide having a flat end face facing the high pressure oil chamber, an end opposite from said flat end face and adjacent said ball seat, and an inner wall surrounding the check ball, and a disc-shaped retainer including at least one oil communicating hole, the disc-shaped retainer being attached to said ball guide and in facing contact with said flat end face of the ball guide; wherein the check ball is sealed in the ball guide, but freely movable therein, along an axis, toward and away from the ball seat, to allow oil to flow through the ball seat of the check valve unit, and through the guide and said at least one oil communicating hole, into the high pressure oil chamber but to block reverse flow of oil out of the high pressure oil chanter by seating of the check ball against the ball seat; wherein a plurality of oil communicating grooves is formed on said inner wall of the ball guide, said grooves extending through the ball guide from a location adjacent said ball seat to said end face, and providing an oil communication path past said check ball from the ball seat toward the high pressure oil chamber when the ball moves away from the ball seat, while the ball is prevented by said inner wall from violent movement within said ball guide; wherein the ball guide is fitted into the bottom of the plunger-accommodating hole; wherein the disc-shaped retainer and the ball seat are held in annular grooves formed in the ball guide; and wherein at least part of at least one oil communicating hole of the disc-shaped retainer is positioned so that it overlaps one of the at least one of said oil communicating grooves in the inner wall of the ball guide, whereby oil flowing through said at least one of the said oil communicating grooves can flow directly through said at least part of said at least one oil communicating hole of the disc-shaped retainer.