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.

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.

An auto tensioner is supported on one side surface of a cylinder block 4-(the outer surface of a front wall part) via a bracket. The auto tensioner includes: a tension pulley that is pressed against a belt; an arm that rotatably supports the tension pulley and is swingably supported to the bracket; and a hydraulic actuator that is supported by the arm and bracket to adjust the pressing force of the tension pulley to the belt using a predetermined position of the arm as a supporting point. The hydraulic actuator is disposed outside the water pump 8-on the front wall part of the cylinder block.

A hydraulic auto-tensioner for an engine accessory is provided where a sleeve fit-in hole is formed at an upper surface of a bottom portion of a cylinder accommodating a hydraulic oil, a lower end portion of a sleeve is press-fitted in the sleeve fit-in hole, and a lower end portion of a rod is slidably inserted in the sleeve to define a pressure chamber inside the sleeve. A lower end face of the sleeve is in abutment with a divided bottom surface of the sleeve fit-in hole to trap burrs produced when the lower end portion of the sleeve is press-fitted into the sleeve fit-in hole between the divided bottom surface of the sleeve fit-in hole and the lower end face of the sleeve, so that burrs are prevented from mixing into the hydraulic oil.

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.

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.

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.

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.

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.

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.