Abstract: A self-contained rotary hydraulic belt tensioner. The tensioner includes a housing mounted for eccentric rotation about a shaft and biased in a first angular direction to apply tension to a timing belt, and a hydraulic element within the housing which is operable to resist rotation of the housing in a direction opposite the first angular direction. The hydraulic element acts against a cam which is received within the housing, a rotary seal acting between the shaft and the housing being effective to contain the oil supply for the hydraulic element within the housing.

Abstract: An auto-tensioner for applying tension to a transmission belt by a tension pulley and for damping reaction force acting from the belt. The tension pulley is rotatably supported to a lever member rotatably supported to a fixed pulley. A movable pulley is provided on the lever member at a position offset with respect to an axis of the tension pulley. An endless belt is wound between a circular friction surface of the fixed pulley and a circular friction surface of the movable pulley. An initial tension applying spring forces to move the movable pulley outward, thereby applying initial tension to the belt. When the movable pulley is moved by reaction force acting on the tension pulley from the transmission belt, damping force according to the reaction force is generated by grip generated between the belt and respective pulleys owing to change of tension between both spans of the belt.

Abstract: A tension device for belts and chains with a tension arm (1) rotatably supported relative to a stationary machine element (6) and spring-loaded by means of a spring (12) against the traction means, on which tension arm, tension means, in particular a tension roller (2), are provided for bearing against the traction means, between the stationary machine element (6) and an element (7), disposed fixedly on the tension arm, are disposed in series a friction element (10) and a resiliently deformable spring element (11), and the resilient deformation of the spring element (11) is limited by the static friction acting between the element (7) fixedly disposed on the tension arm, and the stationary machine element (6) which avoids impermissibly high belt tensions and undesirably high tension arm excursions.

Abstract: An independently steerable idler pulley is operable by the means of a non-concentric adjustable inner sleeve bushing mounted interiorly of a radial ball bearing fitted within the ID of the pulley, with the sleeve bushing and bearing and pulley press fitted as an assembly for mounting on an idler shaft. The sleeve is movable in defining the angular alignment adjustment of the assembly with respect to the shaft upon which it is mounted. With the desired angular adjustment determined the sleeve is locked upon the shaft. Plural of such pulleys supported on a common shaft can be individually positioned.

Abstract: A vibration proofing system for an engine timing chain utilizes a tensioner on the slack side of the chain path, in which a ring-shaped, chain-engaging shoe is rotatably disposed on a circular frame mounted on the piston of a tensioner mechanism, and in which the shoe surrounds the frame and tensioner mechanism. Engine oil, which is used in the tensioner, is supplied from the tensioner to lubricate the rotatable chain-engaging shoe. On the tension side of the chain path, a guide includes fixed support, a first ring rotatable on the support, and a ring-shaped, chain-engaging shoe which is in off-centered relationship to the support and the inner diameter of which is larger than the outer diameter of the first ring. Engine oil is supplied through the support to lubricate the first ring.

Abstract: A rider propelled vehicle includes a frame having a hub portion. Each of two cranks has a crank shaft extending into the hub portion and mounted on the hub portion for rotation relative thereto independent of the other crank shaft. Both of the cranks can be rotated through a top dead center position and a bottom dead center position in which the force applied by the rider to the crank for propulsion of the vehicle is at a minimum. An output shaft extending from within the hub portion is operatively connected to a drive wheel of the vehicle for driving rotation of the drive wheel to propel the vehicle. The output shaft is mounted on the hub portion for rotation relative to the frame and the cranks. A torque transmission assembly interconnecting the output shaft with the crank shafts for transmitting torque from the crank shafts to the output shaft is contained within the frame.

Abstract: The object of this invention is to reduce the cost of an autotensioner for keeping constant the tension of a belt.A pulley 13 is mounted on the pulley support 6 eccentrically supported by the support shaft 3. A tension imparting member is provided which rocks the pulley support in a direction in which the pulley stretches a belt. The pulley support 6 has a cylindrical portion 8a which is concentrical with the support shaft. Damper 20 is provided between the cylindrical portion 8a and the support shaft 3 to impart a rocking resistance to the pulley support. The pulley support 6 has an eccentric ring 7 and a rocking shaft 8. The rocking shaft has at one end the cylindrical portion 8a and at the other end a cylindrical small-diameter portion 8b which is inserted in the eccentric ring. The pulley support 6 is comprised of two members which are simple in shape and easy to manufacture.

Abstract: A pivotal member 2a comprises a main member 19 having inner and outer peripheral faces formed axially symmetric, an auxiliary member 20 having an inner peripheral face 23 made eccentric with respect to an outer peripheral face 24, such that the main member 19 is pivotally supported on the outer peripheral face of a fixed shaft 1, and a tension pulley 5 supported so as to be freely rotatable, on the outer peripheral face of the auxiliary member 20, thereby simplifying manufacturing operations for a pivotal member 2a of an auto tensioner to reduce the manufactured cost.

Abstract: A spring bias tensioner of the eccentric type with a fixed cam ring and rotatable cam ring activated by a torsion spring wherein the cam rings generate an axially force to engage radial friction sliding surfaces to affect damping as a pivot arm of the tensioner is moved.

Abstract: A vibration proofing system for an engine timing chain utilizes a tensioner on the slack side of the chain path, in which a ring-shaped, chain-engaging shoe is rotatably disposed on a circular frame mounted on the piston of a tensioner mechanism, and in which the shoe surrounds the frame and tensioner mechanism. Engine oil, which is used in the tensioner, is supplied from the tensioner to lubricate the rotatable chain-engaging shoe.

Abstract: A chain drive is described in which the chain travel length remains constant, as well as the chain tension, in spite of changes in separation between the driving and driven sprockets. Eccentric idlers enable the chain to be initially tensioned by offsetting these eccentric idlers through a sufficient distance to establish the proper chain tension. An idler sprocket provides a pivot for the two arms that support the chain drive, thereby enabling the arms to form a "V" configuration as the linear separation of the driving and driven sprockets, mounted on opposite ends of their respective arms, is varied. The eccentric idlers wrap the chain around at least a portion of the idler sprocket's driven and driving sides.

Abstract: A variable speed drive mechanism (4) is disclosed for use in conjunction with multi-sided prismatic convertible sign elements (22). A drive gear (32) driven at constant speed causes a mounting gear (23) to rotate at an angular velocity both slower than the angular velocity of the drive gear (32) and at a varying angular velocity. An idler gear (38) guides a flexible tension supporting element (31) as it travels between an equalizer gear (35) and the drive gear (32). A series of the drive trains (21) may be mounted adjacent to each other so as to permit a plurality of prismatic sign elements (22, 47, 48) to create a convertible sign.

Abstract: An autotensioner having a fixed shaft, a pulley support pivotally supported on the fixed shaft, a pulley rotatably supported on the pulley support and a spring for biasing the pulley support in such a direction as to apply tension to a belt. The pulley support has a cylindrical portion arranged coaxially with the fixed shaft. The fixed shaft is formed with cam surfaces at such a position that wedge-shaped spaces are defined between the cam surfaces and the cylindrical portion. The wedge-shaped spaces narrow in a direction in which the pulley support pivots to slacken the belt. Friction members are each mounted in the respective wedge-shaped spaces. They have a shape substantially complementary to the shape of the wedge-shaped spaces. A spring member is also mounted in each wedge-shaped space to bias the friction members into the narrow area of each wedge-shaped space.

Abstract: An improved belt tensioning system 30 includes an improved tensioner 34 mounted on a fixed post 36. The improved tensioner 34 includes the body 37 having a bore 40 extending therethrough. Located in the bore 40 is an elastomeric material 42 having a Shore A durometer of between 30 and 50. Mounted within the bore 48 in the elastomeric material 42 is a bushing 44 that has a bore 46 therethrough sized to closely receive the post or shaft 36. The elastomeric material has damping characteristics capable of substantially eliminating resonant frequencies from the system. Location of the tensioner 34 on the fixed post or shaft 36 permits the appropriate tension to be applied in the system 30 and the driving auxiliary systems by the tensioner while avoiding the use of conventional belt tensioners 20 which may introduce vibrations or oscillations into the belt drive system.

Abstract: A tensioner includes a mechanism for presetting a biasing force for tensioning a belt or chain with a predetermined force. A locking and release mechanism maintains the tensioner in a locked or preset condition prior to installation and automatically releases the preset tensioning force during installation of the tensioner to a mounting surface.

Abstract: A tensioner of the eccentric type with a pivot-pin and pivot bushing disposed within the confines of an inside diameter of a bearing member attached to a stub shaft, the shaft having an axially oriented groove that receives the pivot bushing. A tensioner where the pivot bushing has a wall thickness sized to receive a load from the pivot-pin and where such thickness is greater than a radial dimension between the pivot-pin and a circumference for the stub shaft.

Abstract: A pre-adjustable, spring-loadable tensioner for belts or chains, in particular for a control gear of an internal combustion engine, comprising a tension roller (2) mounted on a tension roller support (3) of eccentric configuration which in turn is guided on an eccentric inner component which can be screwed onto a housing (20), the tensioner (1) further comprising a spring (12, 29) resiliently urging the tension roller support (3) against the housing (20), characterized in that the inner component comprises a flanged eccentric bush (5) which engages freely rotatable into a base plate (7) which is guided by a radial guide arm (9) on the housing (20).

Abstract: A high gain and high torsional stiffness servo axis drive system for machine tools is described as providing improved stability. This system includes a servo motor mounted on a base and connected to a C-Axis spindle drive arrangement via a toothed drive belt. A first by-damper is attached to the spindle drive pulley and tuned for damping torsional oscillations of the servo output shaft, belt, and spindle when the system is not fitted with a workpiece. An independent second damper is attached to the driving pulley of the servo motor and tuned for damping torsional oscillations of the entire servo drive system when the system is loaded with a workpiece. The resulting servo axis drive system features improved stiffness and can be adapted to a variety of predetermined loading conditions by convenient retuning of the second damper. At least the second damper is provided as a combination of a damper mass ring attached to the servo motor pulley by a plurality of viscoelastic damping elements.

Abstract: An autotensioner for a belt has a pulley support shaft secured to a base and an eccentric ring rotatably supported by the pulley support shaft with the center of its outer peripheral surface offset from the center of the pulley support shaft. A pulley is rotatably supported around the eccentric shaft through a rolling bearing. A spring for biasing the eccentric ring is provided to press the pulley against the belt. A damper for imparting resistance to rotation to the eccentric ring is provided to restrain the pivoting motion of the pulley. The resistance to rotation is imparted to the eccentric ring by the damper at the side of the rolling bearing opposite to the base.

Abstract: A chain-belt that extends between driving and driven members such as the leys of a continuous variable transmission wherein the chain-belt is formed of a plurality of interleaved sets of links. The links define a passageway and a plurality of load blocks are positioned in the passageway. Several members for reducing the noise produced by such a chain-belt are disclosed whereby certain of the load blocks in the chain-belt engage the pulleys at a different location to alter and reduce the pattern of noise produced by the chain-belt. The chain-belt also has links with a particular configuration that allows the links to have a short pitch length while still maintaining strength in the links.

Abstract: A tensioning device for drive belts includes a pin pivotable about an axis and having an eccentric surface on which a cam is pivotally mounted. A roller adapted to engage a belt is rotatably mounted on the cam. The cam pivots in reaction to forces on a spring acting between the cam and pin. The spring may be preloaded to a specific operating point by rotation of the pin. Markings or projections acting as stops facilitate adjustment of the preloading of the spring.

Abstract: A tensioner with a pulley rotatably mounted to a pivot arm that is biased with a compression spring. The pulley is generally tube-pan shaped and defines an annular space where the compression spring is located. A belt drive system of the automotive camshaft type that includes the tensioner for maintaining operative belt tension.

Abstract: In a pre-mounted tensioning device the fastening bolt is covered by the idler wheel. The fastening bolt is serviced through a recess provided in the wheel surface. A pre-mounted unit is created through the insertion of a fastening bolt whose head is pushed by spring elements against the wheel surface, thus preventing the idler wheel from turning and forcing the recess to coincide with the fastening bolt.

Abstract: Transmission tensioning pulley for flexible or articulated coupling, having a lever to compensate for thermal expansion and contraction, and regulated by a cam, characterized by the fact that under stable or transient conditions, the thermal expansions and contractions are compensated by the multiplier lever arm ratios and the length of the compensator bar.

Abstract: A belt tensioner comprising an intermediate annular member rotatably provided around a fixed member in the form of a solid cylinder and to be secured to a stationary portion, a movable eccentric member in the form of a solid cylinder and rotatably provided around the intermediate annular member eccentrically therewith, an idler in the form of a hollow cylinder and rotatably provided around the movable eccentric member for contact with a belt, and a spring provided between the stationary portion or the fixed member and the movable eccentric member for biasing the movable eccentric member in a direction to bring the idler into pressing contact with the belt. The intermediate annular member has a cylindrical or tapered first sliding surface in contact with the fixed member and a cylindrical or tapered second sliding surface in contact with the eccentric member.

Abstract: A tensioner comprising a first cylindrical member to be fixedly attached to a stationary portion, a movable eccentric member in the form of a cylinder and eccentrically rotatably provided around the first member, an idler in the form of a hollow cylinder and rotatably provided around the movable eccentric member for contact with a wrapping connector driving member, and a spring provided between the stationary portion and the movable eccentric member for biasing the eccentric member in a direction to press the idler into contact with the wrapping connector driving member. A one-way clutch is provided between the first member and the movable eccentric member.

Abstract: A drive mechanism and/or transmission for transmitting power or motion to an object includes an input driving member, an output driven member, and a rigid coupling member. By changing the arrangement of the driving and driven members and the shape of the rigid coupling member, the object can be either rotated continuously, rotated in a reciprocated motion, or translated.

Abstract: Apparatus for applying an optimum tensioning force to an endless belt or the like, including a first pivot axis, a belt engaging pulley eccentrically supported for rotation about a second axis displaced from the first pivot axis, a torsional biasing spring for urging the belt-engaging pulley into belt-tensioning engagement with the belt and for automatically maintaining the tension force applied to belt. The torsion spring is disposed about the first axis within the eccentric pulley, which includes further springs for releaseably gripping the pivot to adjustably limit the applied tensioning force in a first direction and in a second direction, whereby the tension in the belt is optimally maintained throughout the engine operating temperature cycle.

Abstract: A belt autotensioner for giving a desired tension to a belt. It includes a tension pulley pressed against the belt, an eccentric shaft extending through the tension pulley to rotatably support it and formed with a hole arranged eccentrically from the axis of the tension pulley, an actuator having a cylinder and a push rod silidably mounted in the cylinder and having its one end protruding from the cylinder and butting a projection fixed to the eccentric shaft, a bolt extending through the hole in the eccentric shaft and the cylinder of the actuator to pivotally support the eccentric shaft and a spring for biasing the eccentric shaft to pivot it in such a direction as to increase the tension of the belt. The spring may be a torsion coil spring mounted around the eccentric shaft with its one end fixed to the outer periphery of the eccentric shaft and the other end fixed to the cylinder of the actuator.

Abstract: An adapter assembly for the New Process Model 203 transfer case for four-wheel drive vehicles. The adapter assembly includes a first disc member mountable on the front surface of the forward wall of the principal housing. The first disc comprises a rearwardly extending bearing housing in the plane of the forward wall replacing the original forward bearing for the transfer shaft. A replacement bearing is mounted within the bearing housing on a new axis parallel to and displaced from the original axis of the transfer shaft, permitting continued usage of the chain after the chain would have to have been replaced according to prior practice.

Abstract: A transmission for connecting a propeller to an engine having a crankshaft. The transmission has an output shaft and a propeller shaft and a belt connecting the output shaft to the propeller shaft. The output shaft has a pulley connectable to the crankshaft of an engine and a pulley driven propeller shaft is supported on the frame by means of a flange having bolt holes supported in a circle having a center offset from the center of the output shaft so that the flange can be connected to the frame in any position and bolted in place. The bolts can be removed and the flange rotated to different bolt holes thereby swinging the center of the propeller shaft around the center of the bolt holes to tighten the belt. An improved coupling is provided for connecting the drive pulley to the engine.

Abstract: A pressing machine has a drive pulley secured to a press crank shaft, an intermediate shaft parallel to the press crank shaft and an input shaft of a material feeding device, the intermediate shaft being supported by a tension adjusting device which is rotatably supported by the crank shaft and the input shaft of the material feeding device, a first intermediate pulley which is secured to one end of the intermediate shaft and is drivingly connected to the drive pulley through a first endless torque transmission device, and a second intermediate pulley which is secured to the other end of the intermediate shaft and is drivingly connected to an input pulley secured to the input shaft of the material feeding device through a second endless torque transmission device.

Abstract: A tensioner comprising a solid cylindrical fixed member to be fixedly attached to a stationary portion, a movable eccentric member in the form of a solid cylinder and eccentrically rotatably provided around the fixed member, an idler in the form of a hollow cylinder and rotatably provided around the movable eccentric member for contact with a wrapping connector driving member, and a spring provided between the stationary portion and the movable eccentric member for biasing the eccentric member in a direction to press the idler into contact with the wrapping connector driving member. A high-viscosity oil is provided in a clearance between the outer periphery of the fixed member and the inner periphery of the movable eccentric member.

Abstract: A belt tensioner having a sleeve bearing pivotally mounting a pivoted structure on a fixed structure for spring pressed movement between first and second positions. The sleeve bearing is larger than and surrounds a ball bearing assembly rotatably mounting a pulley on the pivoted structure. The pulley has a cantilevered rim which axially overlaps and annularly surrounds the sleeve bearing. One of the structures and the sleeve bearing have slidably interengaging surfaces which are compressed together by the belt load force in the pivoted structure and the reactionary force acting in the fixed structure so as to provide a damping torque resistance to the pivotal movement of the pivoted structure which prevents movements resulting from dynamic changes in the belt load force within a range. The arrangement is such that independent vibrational forces instantaneously release the damping torque resistance to permit instantanteous movements otherwise prevented.

Abstract: A belt tensioner comprising a pivoted structure carrying a pulley for rotation about a rotational axis and mounted on a fixed structure for pivotal movement between an increased range of angular movement. The pulley is operatively positioned with respect to its rotational axis and the pivotal axis of the pivoted structure such that the lever arm to the pivotal axis through which the generally constant belt load force acts on the pivoted structure increases at a decreasing rate and then decreases at an increasing rate throughout the range of movement of the pulley between its first and second positions in a direction toward the second position. The spring assembly is operatively associated with the pivoted structure so as to apply a spring torque to the pivoted structure which increases at a decreasing rate and then decreases at an increasing rate throughout the range of movement of the pulley between its first and second positions in a direction toward said second position.

Abstract: An adjustable bottom bracket assembly for a bicycle comprises a body member and a wedge member, each having a circular cylindrical external surface in close fit with an internal circular cylindrical surface of a bottom bracket shell. The body and wedge members have abutting complementary planar wedge surfaces oriented obliquely to the axes of their cylindrical surfaces. A drive device, such as a screw, moves the body and wedge members axially to wedge them securely in an adjusted position in the bottom bracket shell.

Abstract: A belt tensioning device includes a resilient coupling which interconnects an idler pulley hub and a stationary mounting member. A ratchet and pawl mechanism interconnects the hub and the stationary mounting member to prevent the belt from overcoming the biasing force of the tensioning device during high belt loads. A resilient biasing element such as an elastomeric element is located between the ratchet and pawl mechanism and the stationary mounting member to allow limited movement of the idler pulley hub away from a belt in order to relieve belt tension such as caused during thermal expansion of an engine block.

Abstract: The application discloses a compensating mechanism for vehicles having two or more wheels with one of those driven wheels being pivotally mounted at the rear end of a swingarm. The compensating mechanism is comprised of a eccentric cam arrangement for the forward end of the swingarm to pivot on and a rocker arm with connecting members to interconnect the swingarm and the eccentric cam. A method of controlling the rotation of the eccentric cam with respect to the swingarm is also disclosed to allow the rear driven wheel to remain a fixed distance away from the engine driver sprocket as the swingarm moves with respect to the driver sprocket.

Abstract: A novel spring and dual pulley construction wherein the pulley includes a pair of co-axial grooves, one of the grooves having a constant diameter that accepts a powered cable acting in one direction, while the other groove has a varying radius of curvature that accepts a second cable connected to one end of the tension spring and with the other end of the spring fixedly mounted. This arrangement maintains a constant spring force on a member moving along a slide in a reciprocating fashion and having one side thereof connected to said powered cable for movement in one direction and the other side connected to the second cable for movement in the opposite direction activated by a constant spring force regardless of the extension of the spring.

Abstract: The invention realizes fluent drive without dead points by continuously cging the angle between the levers (13,14) of the pedals (1). The two pedal levers (13,14) are fixed to two separate shafts (15,16) with common axis (3). The driving shaft (18) is eccentric to this axis (3) and the mechanical connection between the driving shaft (18) and the shafts (15,16) of the pedal levers (13,14) is realized by eccentrics (19,20). With this construction the pedals move faster when coming upwards and slower when going downwards, so when the depressed pedal reaches its lowest point, the other one has already passed its highest point.

Abstract: An apparatus in which a tubular member mounted on a shaft moves linearly in response to rotation of the shaft. A cam is mounted on the shaft and in engagement with bearings mounted on the interior surface of the tubular member. As the shaft rotates, the cam moves in unison therewith to move the tubular member linearly. The linear movement of the tubular member moves a portion of a photoconductive belt between an operative position, adjacent a developer unit, and an inoperative position, spaced from the developer unit.

Abstract: A belt driving apparatus for a bicycle is disclosed wherein a driving gear has an outer gear over which is trained a toothed belt to impart rotational force to the bicycle rear wheel. An inner gear disposed within the outer gear includes teeth along its outer periphery meshing with teeth formed on the inner periphery of a crank gear disposed between the inner and outer gears. The crank gear is mounted on a crank shaft.

Abstract: A power transmission system utilizes a pair of pulleys in spaced parallel relation interconnected by a plurality of endless drive belts. Each pulley contains a plurality of eccentric drive lobes. The drive lobes have no teeth or means for increasing sliding friction between the lobes and each drive belt. Drive belts contain no apertures or joints and may be constructed of multiple wraps of any fiber or filament. A plurality of drive lobes spaced equally, about a 360-degree arc, link both shafts fully providing a smooth and even delivery of continuous turning force in either direction of rotation.

Abstract: A drive chain adjustment mechanism for a vehicle having two rear wheels includes a swing arm supported on a body frame for vertically pivotal movement, a pipe member fixed to the rear end thereof, and a holder member inserted into the pipe member, which has therethrough an eccentric bore for rotatably supporting a rear wheel axle driven by way of a drive chain. The holder member is provided on at least one end with a plurality of projections, which are recessed to receive a rod-like tool and thereby turn the holder member.

Abstract: A strip media tensioning system is set forth for imposing drag on a moving band such as a circulating endless belt for driving reel packs for delivery of magnetic tape therebetween. More particularly, an apparatus is set forth which includes a fixed shaft. A sleeve is journalled for rotation about the shaft, the endless belt engaging and rotating the sleeve. To create drag, a visco-elastic ring is positioned between the shaft and sleeve and is compressed against the sleeve creating drag by an eccentrically disposed roller device. The eccentricity of the roller device is adjustable for altering the drag on the circulating endless belt.

Abstract: A support housing for a tension roller formed as a one-piece deep drawn sheet metal cylindrical sleeve having a bottom end part which includes an eccentric bore therethrough, part of the bottom being axially displaced for increased stiffness and stability.

Abstract: A diametrical slot is provided in the bottom of the cup-shaped support of a tensioning roller assembly, for receiving a clamping bolt. A leaf spring is mounted in the bore and has a bending zone engaging the bolt, the leaf spring extending from on both sides of the bending zone to roll sections adapted to roll on and off the bore surface of the support so that, as tension is increased by the displacement of the bolt in the slot, a greater portion of the leaf spring rolls off of the bore surface of the support.

Abstract: A tension roller has a rolling bearing supported by a multipart support which is swivable about an eccentrically arranged mounting bolt. A rolling sleeve for a belt is arranged on the outer ring of the bearing. The support includes two side parts which abut the side surfaces of the bearing inner ring, thereby preventing axial movement. A central body is provided with respect to which the side parts are fixedly arranged. The central body is adapted to provide radial support for the bearing inner ring.

Abstract: A compact belt tensioning device includes a double acting pawl which selectively engages opposed sets of ratchet teeth formed on a stationary mounting. The tensioning device is adapted to be preset in a tensioned state to facilitate installation and repair procedures and may be easily activated by manually releasing the pawl.

Abstract: A belt tensioner having a sleeve bearing pivotally mounting a pivoted structure on a fixed structure for spring pressed movement between first and second positions. The sleeve bearing is larger than and surrounds a ball bearing assembly rotatably mounting a pulley on the pivoted structure. The pulley has a cantilevered rim which axially overlaps and annularly surrounds the sleeve bearing. One of the structures and the sleeve bearing have slidably interengaging surfaces which are compressed together by the belt load force in the pivoted structure and the reactionary force acting in the fixed structure so as to provide a damping torque resistance to the pivotal movement of the pivoted structure which prevents movements resulting from dynamic changes in the belt load force within a range. The arrangement is such that independent vibrational forces instantaneously release the damping torque resistance to permit instantaneous movements otherwise prevented.