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 work machine having a belt tensioning system is described. A belt is engaged with an engine drive sheave and a driven sheave of a rotor having a plurality of cutting tools configured for reducing wood infeed material. An idler pulley is mounted to an idler arm that is hinged to the machine frame. An actuator is hinged to the idler arm and the frame. The actuator may be extended and retracted in order to press the idler pulley into stronger and weaker engagement with the belt in order to set the desired amount of tension in the belt. One or more sensors may be used to sense the amount of tension in the belt, and the one or more sensors may be in communication with a control system that controls the actuator to monitor and adjust the belt tension so that it is maintained within desired limits.

An object of the present invention is to provide a tensioner and a rocking lever that have simple configurations and that enable an increase in the volume of a space provided inside a plunger, the tensioner and the rocking lever being capable of preventing a stopper pin from being damaged or falling out. A plunger pin hole 121 is formed in a plunger 120 of a tensioner 100. In a tensioner body 110, a body pin hole 113 is formed in a tip protruding portion 112 provided so as to protrude from a side of an opening of the plunger housing hole 121. One of lips 154 provided on opposite sides, in a width direction, of the pressing surface 153 of a rocking lever 150 so as to protrude from the pressing surface 153, has a thinned portion 155 thinned in the width direction.

Provided is a tensioner which has a small total number of components and no risk of incorrect assembly, allows easy load change, is easy to assemble, and excellently stabilizes an oil pressure in a pressure oil chamber. The tensioner 100 includes a relief mechanism that relieves oil to the outside of a plunger 110 when the oil pressure in the pressure oil chamber formed between the plunger 110 and a plunger containing hole 121 in a housing 120 increases, relief holes 141 extending through the plunger 120 from the inside of a plunger inner space 111 to an outer circumferential side thereof, and a hole closing member 142 that is pressed into an opening of each of the relief holes 141 on the outer circumferential side.

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 hydraulic auto-tensioner is provided which 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.

A tensioner (10) for an endless loop power transmission member can induce a piston (12) operably engageable with an endless loop power transmission member, and a cylinder (14) guiding include a piston (12) for sliding coaxial movement in a direction of the endless loop power transmission member. The piston (12) and cylinder (14) defining an oil reservoir or pressure chamber (26) for receiving hydraulic fluid. A bearing (28) has bearing balls (30) located in a counter bore (32) coaxial with cylinder bore (34). The counter bore (32) has a steep taper (36) on which the bearing balls (30) ride. As the cylinder (14) moves in an extending direction, the bearing balls (30) move out of the counter bore (32) allowing free extending movement of the cylinder (14). As the cylinder (14) moves in a retracting direction, the bearing balls (30) are driven down into the steep taper (36) preventing the cylinder (14) from retracting.

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.

A hydraulic auto-tensioner includes a cylinder with a sleeve fitting hole, and a sleeve press-fitted therein. A rod has its bottom end slidable in the sleeve. A return spring is mounted between a spring seat at an upper portion of the rod and a bottom surface of the cylinder. An oil passage, with a check valve, is formed between the fitting surfaces of the sleeve fitting hole and the sleeve and communicates the pressure chamber with the reservoir chamber. The rod has a valve fitting hole open to its bottom surface, and an oil passage communicating the valve fitting hole with the reservoir chamber. A relief valve, mounted in the valve fitting hole, includes a valve seat with a valve hole having an orifice for restricting the flow rate of oil released from the pressure chamber into the reservoir chamber through the oil passage when the relief valve opens.

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.