A hydraulic tensioning device for a chain drive of an internal combustion engine, having a receptacle and having a tensioning piston which is guided in displaceable fashion in a cylindrical hollow space of the receptacle and which has a piston hollow space, wherein the piston hollow space together with the cylindrical hollow space of the receptacle forms a pressure chamber, and having a pressure relief valve unit arranged in the piston hollow space. The pressure relief valve unit is a preassembled structural unit and comprises a spring, a closing body and a valve seat and also a valve receptacle which surrounds the valve seat in a first subsection, wherein the valve receptacle forms an interference fit with the valve seat, and wherein the valve receptacle or the valve seat in a second subsection form an interference fit with the inner shell surface of the tensioning piston.

A tensioner that includes a mount, a pair of tensioner arms, and a spring. The mount defines a movement axis. Each tensioner arm assembly has a first tensioner arm, which is coupled to the mount for sliding movement about the movement axis, a tensioner pulley and a spring guide. The tensioner pulley and the spring guide are coupled to an associated tensioner arm for movement therewith. The spring is mounted on the spring guides and biases the tensioner arm assemblies about the movement axis in respective directions that urge the tensioner pulleys toward one another.

A tooth jump protection device is used to control chain slack and delay the torque at which chain jump occurs, thus increasing jump torque performance. The tooth jump protection device is preferably mounted to the transfer case.

A tensioner comprising a base defining a hole, the hole having a center C, the hole having a diameter sufficient to receive a driven pulley, a rotary arm engaged with the base by a retaining member connected to the base, the rotary arm rotatable about the center C, a pivot arm mounted to the rotary arm on a pivot, the pivot offset from center C, a first pulley journalled to the rotary arm, a second pulley journalled to the pivot arm, a torsion spring engaged between the rotary arm and the pivot arm for biasing the second pulley toward the first pulley, a damping member frictionally engaged between the base and the rotary arm, and the rotary arm defining a portion for receiving a first pulley fastener whereby a first pulley position is adjustable.

An orbital tensioner comprising an annular base, a ring journalled to the annular base on a ball bearing, said ring having a ring axis of rotation (A-A), a first pulley journalled to the ring, a first pulley axis of rotation (B-B) offset from the ring axis of rotation (A-A), a pivot arm pivotally mounted to the ring, a pivot arm pivot axis (C-C) offset from the ring axis of rotation (A-A), a second pulley journalled to the pivot arm, a torsion spring biasing the pivot arm in a first direction, the ball bearing having a first race and a second race, the ring fixed to the first race, the annular base fixed to the second race, and a damping mechanism frictionally disposed between the ring and the base.

An accessory drive system for an engine 1 includes: a drive shaft (a crankshaft 21); a driven shaft (an oil pump drive shaft 31); an endless transmission member (a drive chain 33); a first tensioner disposed on a slack side of the endless transmission member (a first hydraulic tensioner 41); and a second tensioner disposed on a tight side of the endless transmission member (a second hydraulic tensioner 43). The second tensioner has a damping function to damp pushing force applied to the second tensioner by the endless transmission member in a direction opposite to a biasing direction.

A tensioner comprising a carrier pivotably mountable to a mounting surface, an arm having a first pulley journalled thereto and a second pulley journalled thereto, the arm slidingly engaged with the carrier for a linear movement with respect to a carrier axis A-A, and a spring disposed between the carrier and the arm, the spring resisting an arm movement along carrier axis A-A.

The present invention provides a chain tensioner that, while being free from an increase in its size, reduces the number of processing parts and the number of assembling steps and reduces the outflow of oil to an outside. Inside a plunger, an inner sleeve including a check valve unit provided on a side of the inner sleeve facing a pressure oil chamber and a pressure regulating unit provided on an outer periphery of the inner sleeve is arranged. The inner sleeve has a cylinder part and a movement restricting part provided on the side of the inner sleeve facing the pressure oil chamber, and the pressure regulating unit has an annular relief valve slidably fitted onto an outer surface of the cylinder part and slidably contacting on an inner surface of the plunger and a relief spring urging the relief valve to a side of the movement restricting part.

A tensioner moves the flow restriction controlling the tensioner tuning to the nose of the piston through a hole ranging in cross sectional area from 0.01 mm.sup.2 to 1.1 mm.sup.2. It also eliminates a component from the design of the tensioner. The piston hole geometry is one or a plurality of holes.

A belt tensioner for a belt drive of a motor vehicle engine, comprising: a fixed part configured to be fixed with respect to the engine and provided with a pivot defining a rotation axis; an arm having a connection portion hinged to the pivot and rotatable about the rotation axis and an opposite portion rotatably supporting a pulley configured to cooperate with a belt of the drive; a main spring interposed between the fixed part and the arm to exert thrust on the arm such as to rotate said arm towards the belt; and at least one rolling bearing interposed between the arm and the pivot to support the arm and ensure the alignment thereof.