A hydraulic tensioning device, which is used in traction drives of internal combustion engines and which includes a piston (19) that is supplied with a hydraulic fluid, is provided. The piston is movably guided in a linear manner in a cylinder and is spring-loaded against a traction device. The hydraulic fluid can flow into a pressure chamber (17) via a non-return valve or out of the pressure chamber (17) via a pressure-relief valve (20), depending on an adjustment movement direction of the piston (19). For this purpose, the pressure-relief valve (20) is inserted in a central receiving area (16) of the piston (19) on the pressure-chamber side as a premountable valve group (21) and includes a pot-shaped valve housing (18) and into which a guide element (25) with a corresponding valve seat (29), a valve element designed as a valve plate (30), and a pressure spring (31) are integrated.

In an aspect, a tensioner includes a pulley, a main piston chamber, a reservoir, and first and second fluid passageways connecting the main piston chamber and reservoir, a main piston that is movable in the main piston chamber, a check valve, a control valve, and a movable reservoir member. The check valve prevents flow in one direction through the second passageway and permits flow in an opposing direction through the second passageway. The control valve is movable between to provide a first flow resistance, or a second flow resistance. The movable reservoir member is movable based on the amount of fluid in the reservoir in such a way as to change the volume of the reservoir, such that the reservoir, the main piston chamber and the first and second passageways together are included in a fluid circuit that is substantially free of any compressible fluids.

One or more radial holes in the body of the hydraulic tensioner are used to control outward hydraulic flow restriction from the hydraulic pressure chamber within the piston. The one or more holes can be arranged in different ways to allow the piston position to alter the outward oil flow of the tensioner.

A hydraulic auto-tensioner includes a sleeve; a rod vertically movable relative to the sleeve; a spring seat fixed to the portion of the rod protruding beyond the sleeve; a return spring configured to bias the spring seat upwardly; oil passages through which a pressure chamber communicate with a reservoir chamber; a check valve mounted to the oil passages; a tubular plunger vertically movably mounted between the outer periphery of the rod and the inner periphery of the sleeve; a first leakage gap defined between the inner periphery of the tubular plunger and the outer periphery of the rod; an upper stopper configured to restrict the upwardly movable range of the tubular plunger; and a pressure regulating spring disposed above the tubular plunger so as to surround the outer periphery of the rod.

To provide a chain tensioner and a relief valve unit that enable a reduction in the number of parts to be machined and the number of assembling steps, reduce the amount of oil flowing out to the outside, and prevent damage on a check valve, without having to increase the size of the chain tensioner. The chain tensioner includes a check valve unit that suppresses reverse flow of oil flowing into an oil pressure chamber, and a relief valve unit that releases the oil when the pressure inside the oil pressure chamber reaches or exceeds a predetermined high pressure. The check valve unit is disposed as a valve element of the relief valve unit, and the relief valve unit and the check valve unit are formed integral with each other.

Provided is a chain tensioner that can always provide a suitable reaction force and damping force to various tension fluctuations of the chain, has a simple structure, is easy to produce, and also enables a reduction in the production cost. The chain tensioner 100 has a plunger 120 inserted in a plunger bore 111, and biasing means 140 for biasing the plunger in a protruding direction of the plunger. A plurality of biasing means 140 are accommodated so as to freely expand and contract inside a high pressure chamber 101 and arranged in series along the protruding direction of the plunger 120, with a separator plate 130 interposed therebetween. The separator plate 130 has one or more oil passages that adjust oil flow.

An object of the present invention is to provide a tensioner capable of keeping the oil pressure in an oil pressure chamber stable in a favorable manner. Provided is a tensioner wherein a relief mechanism includes a partition part, a valve member at least partly positioned inside an internal relief hole such as to be able to approach and separate from an oil pressure chamber, a valve biasing unit, and an external relief hole. A movement restricting part that restricts movement of the valve member toward the oil pressure chamber is formed in the partition part. An oil passing groove is formed in at least one of an outer circumferential surface of the valve member and an inner circumferential surface of the internal relief hole, the outer circumferential surface and the inner circumferential surface facing each other.

To provide a simple-structured tensioner that can maintain good sliding properties of and hydraulic pressure for the plunger. The tensioner 10 includes a sleeve 30 inserted into a cylindrical body hole 21, a plunger 40 inserted in the sleeve 30 such as to be able to advance and retract along an axial direction of the sleeve 30, and biasing unit 60 for biasing the plunger 40 toward a front side. The sleeve 30 has, at a front end of a sleeve body 31 thereof, a flange part 33 extending radially outward.

A tensioner for tensioning a chain or belt 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 or belt tension as low as possible without sacrificing chain or belt control, significantly improving drive efficiency at new chain or belt conditions and conditions with dynamic loads.

Provided is a simple-structured tensioner that can ensure a smooth flow of oil while enabling a reduction in the production cost. A tensioner 10 includes a plunger 30 provided with a plunger through hole 32 extending from an outer circumferential surface to an inner circumferential surface of the plunger 30, and a tensioner body 20 provided with an oil supply hole 25 extending from an outer wall of the tensioner body 20 to the plunger bore 21. The oil supply hole 25 is formed in an elongated shape that extends along a protruding direction of the plunger.