An orifice member is disposed in a plunger including a plunger hole that forms a hydraulic chamber in conjunction with a plunger housing hole in a housing. The orifice member includes a deformed fitting section deformed to fit on the inner circumferential surface of the plunger hole, a communication section that causes a surface in contact with the top surface on the front side of the plunger hole and a surface on the hydraulic chamber side to communicate, and an orifice groove that communicates with the communication section and an external relief hole provided in the plunger on the surface in contact with the top surface on the front side of the plunger hole to constitute an orifice.

A tensioner for tensioning a chain span which uses two pistons. The movement of the two pistons may be coupled together. The first piston provides damping to the chain span and a second piston provides variable, dominant and automatically adjusting spring force to the chain span. The tensioner automatically adjusts the mean tension force to keep the chain tension as low as possible without sacrificing chain control, significantly improving drive efficiency at new chain conditions and conditions with dynamic loads.

A hydraulic auto-tensioner includes a cylinder, a valve sleeve, a rod, a spring seat, and a plunger slidably fitted on the outer diameter surface of the rod. A first leakage gap is defined between the fitting surfaces of the plunger and the rod. A second leakage gap is defined between the fitting surfaces of the plunger and the valve sleeve such that the resistance to oil flowing in the second leakage gap is larger than the resistance to oil flowing in the first leakage gap. With the engine running normally, when the tension of the belt increases, and thus a pushing force is applied to the hydraulic auto-tensioner such that the cylinder and the spring seat are pushed toward each other, oil in a pressure chamber leaks through the first leakage gap into a reservoir chamber.

To provide a chain tensioner that can suppress oil leakage from a gap between a plunger bore and a plunger to achieve stable damping characteristics and that can avoid an increase in production cost, with a simple structure. The chain tensioner includes a packing member that is provided on an inner circumferential side of the plunger bore and that suppresses oil leakage from a cylindrical outer surface of the plunger. The plunger is provided with an oil leak passage that extends from an oil pressure chamber inside the plunger to the outside.

The present invention provides a chain tensioner that automatically adjusts flow path resistance inside an oil leak path with a simple configuration to make it possible to reduce a change in damping characteristics resulting from a change in oil temperature and reduce an increase in manufacturing cost. In the chain tensioner, a pressure oil chamber is provided with an oil leak path communicating with an outside of the chain tensioner, the oil leak path contains a movable piece which is movable with a temperature-dependent deformation member that deforms according to oil temperature, and the movable piece is formed into a shape that changes flow path resistance of the oil leak path according to a position to which the movable piece is moved.

In order to prevent noise, a ratchet clip and grooves for the ratchet clip to engage are added to the second piston, such that the second piston cannot hit the bottom of the second bore housing. The second piston is prevented from hitting the bottom of the second bore housing by the ratchet clip engaging the ratchet grooves on the outer circumference of the second piston.

Provided is a simple-structured tensioner that can reduce the processing and assembling workload. A tensioner 10 includes a plunger 20, a housing 30, a main spring 60, and a relief valve 40. The relief valve 40 includes a seat member 41, a valve member 42, and a relief spring 43. The plunger 20 includes an outward relief passage 23, and a bottom protrusion 22a protruding rearward integrally with and continuously from a plunger bottom 22. The relief spring 43 is disposed such that one end thereof is in contact with the valve member 42 while the other end is attached to the bottom protrusion 22a.

Check valve assembly for a tensioner with a U-shaped retainer defining a cavity and having at least one retainer opening and axially extending flanges; a moveable member received within the cavity; a check valve spring received within the cavity and between the moveable member and the retainer; a valve seat having axially extending flanges and defining a seat opening nesting within the cavity of the retainer, and a check valve vent washer. The check valve vent washer has an outer circumference with a plurality of spaced apart legs and openings; and an inner circumference in fluid communication with the outer circumference through the openings, the inner circumference has a concentric interior well connecting the plurality of openings to a vent reservoir, a central ring defining a central hole in communication with the internal reservoir, the central ring comprising a vent groove connecting the vent reservoir to the central hole.

A fixing tool of an auto-tensioner includes inwardly inclined engaging pieces inclined inwardly so as to be opposed to respective tapered surfaces of a spring seat and a cylinder of the auto-tensioner. The engaging pieces have concave surfaces that contact the tapered surfaces over a circumferentially extending area. This minimizes the deformation of the engaging pieces such that the diametrical distances therebetween increase due to contact with the tapered surfaces when sandwiching the spring seat and the cylinder with the engaging pieces from the axially opposite directions, thereby preventing the fixing tool from coming off.

To provide a tensioner and a relief valve unit that enable a reduction in the number of parts to be processed and the number of assembling steps, reduce the amount of oil flowing out to the outside, prevent damage to the check valve, and improve the oil recovery rate. The relief valve unit that releases oil when pressure inside an oil pressure chamber reaches or exceeds a predetermined high pressure includes a check valve unit that stops reverse flow of oil flowing into the oil pressure chamber as a valve element, the check valve unit being slidably inserted in the relief valve unit. The relief valve unit includes a unit pressing spring that presses the check valve unit toward a relief valve seat. The check valve unit includes an oil passage for allowing oil to flow between an inner side and an outer side of the check valve unit.