Systems are provided for a belt tensioner. In one example, the belt tensioner comprises a fluid chamber divided into a first portion and a second portion via a dividing wall. An eccentric housing, which defines the fluid chamber, rotates relative to the dividing wall based on a spring force and a belt force.

A sealed tensioner includes a body having a high-pressure chamber; a low-pressure reservoir that is in fluid communication with the high-pressure chamber through a fluid conduit; a piston received by the body that moves axially to compress fluid in the high-pressure chamber; a seal positioned between the piston and the body that prevents passage of fluid from the high-pressure chamber between the piston and the body; and a check valve, regulating fluid flow between a low-pressure reservoir and the high-pressure chamber, including a stiffness control aperture.

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.

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.

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.

Provided is a tensioner which can ensure, with a simple structure, both the stability of the installation state of a check valve and the capacity of an oil storage chamber. A tensioner has a plunger, a housing, a check valve, and a coil spring. The plunger has a front-side plunger part having a pressing front end portion, and a rear-side plunger part disposed on the rear side of the front-side plunger part and having a valve movement restricting portion. The check valve is disposed on the rear side of the valve movement restricting portion. The coil spring is disposed so that one end thereof is in contact with a housing bottom portion and the other end thereof is in contact with the rear side of the check valve.

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 chain tensioner includes an oil supply passage for supplying hydraulic oil into a pressure chamber defined by a cylinder and a plunger, and a check valve provided at the end of the oil supply passage. A leak gap is defined between the sliding surfaces of the cylinder and the plunger. The plunger is biased by a return spring in the direction in which the plunger protrudes out of the cylinder. A plug is press-fitted in a cylindrical inner periphery of a through hole formed in the plunger to extend from a protruding end surface of the plunger to the pressure chamber to define an air vent passage. It is possible to change the hydraulic damper force simply by replacing the plug with another different type of plug to define a different air vent passage.

A hydraulic auto-tensioner includes a rod inserted in a cylinder having a bottom and containing hydraulic oil, and a hydraulic damper in the cylinder for damping the push-in force that tends to push the cylinder and the rod in the direction in which the rod is pushed into the cylinder. An oil seal including a dust lip on the inner periphery thereof seals an open end of the cylinder. A rose-shaped snap ring is formed integral with the oil seal.

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.