Abstract:
An engine tensioning system including a pair of pivoting arms used to simultaneously tension two separate strands of the same chain in an engine timing system. The tensioner system includes a lever. The lever has a pair of fixed pins attached to an end located between the two strands of chain. The arms extend outside separate strands of the chain and carry shoes positioned to contact an outside portion of the chain are pivotally mounted to the fixed pins. Rotation of the lever causes the fixed pins to move laterally with respect to the chain strands and cause the arms to draw inwardly. The inward movement of the arms draw the shoes into contact with the chain strands and impart tension to the separate strands of the chain simultaneously.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to tensioners used with chain drives in automotive timing and power transmission applications. In particular, the present invention is related to a chain tensioner system having a pair of arms. The arms are positioned outside opposite strands of chain in a power transmission system. The tensioner system causes the arms to travel inwardly towards a chain centerline which acts to simultaneously tension the two strands of a chain in an engine timing application. 
     Chain tensioning devices, such as hydraulic tensioners, are used as control devices for power transmission chains as the chain travels between a plurality of sprockets. In an automotive application, the tension of the chain can vary greatly due to the wide variation in the temperature and the linear expansion among the various parts of the engine. Moreover, wear to the chain components during prolonged use can produce a decrease in the tension of the chain. As a result, it is important to impart and maintain a certain degree of tension to the chain to prevent noise, slippage, or unmeshing of the chain with the sprocket teeth. It is especially important in the case of a chain-driven camshaft in an internal combustion engine to prevent the chain from slipping because the camshaft timing can be misaligned by several degrees, possibly rendering the engine inoperative or causing damage. 
     A hydraulic tensioner as used with a tensioner arm or shoe is shown in Simpson et al., U.S. Pat. No. 5,967,921, which is incorporated herein by reference. Hydraulic chain tensioners typically have a plunger slidably fitted into a chamber and biased outward by a spring to provide tension to the chain. A lever, arm or shoe is often used at the end of the plunger to assist in the tensioning of the chain. The hydraulic pressure from an external source, such as an oil pump or the like, flows into the chamber through passages formed in the housing. The plunger is moved outward against the arm by the combined efforts of the hydraulic pressure and the spring force. 
     When the plunger tends to move in a reverse direction (inward) into the housing, typically a check valve is provided to restrict the flow of fluid from the chamber. In such a fashion, the tensioner achieves a so-called no-return function, i.e., movements of the plunger are easy in one direction (outward) but difficult in the reverse direction. In addition, rack and ratchet mechanisms, which are well known in the art are employed to provide a mechanical no-return function. 
     One example of a chain tensioner which uses a hydraulic tensioner and a pivoted lever to tension a chain is described in Sato et al., U.S. Pat. No. 5,318,482. Sato et al. show a conventional hydraulic tensioner with a plunger pressing a pivoted lever against a chain to impart an appropriate tension to the chain. The tensioner and single shoe arm of Sato et al. has limitations, however, in the amount of chain slack it can take up during the life of the chain. In addition, the single shoe arm of Sato et al. has limitations in its ability to absorb and damp cyclic vibrations in the chain during operation. 
     Conventional prior art tensioners which tension only one strand of chain, i.e., a single length of chain between two sprockets, in an engine timing application with long center distances between the sprockets have a common weakness. During operation of the engine, wear on the various chain parts causes the chain to lengthen. Taking up the resulting slack on one side of an engine timing system and not the other can cause the timing of the camshaft to change relative to the crankshaft. In some engine timing chain applications, the large center distances cause both sides of the chain span between sprockets to slacken as the chain wears and extends in length. 
     To address the above problems the present invention includes an actuator, in the form of a conventional hydraulic tensioner in combination with a pivoting lever. The lever has a pair of fixed pins on opposite sides of a central pivot bore. The fixed pins each carry an arm with each arm carrying an attached shoe. In combination, the shoes contact and act on separate strands of a common chain. This provides potentially double the operating take-up for a given range of tensioner operation as compared to a conventional hydraulic tensioner acting upon a single arm with an end pivot that acts on one chain strand. 
     When the present invention is used to tension separate strands of a single chain, vibrations which occur in one strand of chain tend to be cancelled when the energy of those vibrations are transferred to or combined with those in another strand through the pivoting tensioner. Further, when taking up chain slack in an engine timing application, the present invention minimizes the chance for changes in the timing between the crankshaft and the camshaft as the chain wears and slackens on both sides of the chain span between the sprockets. 
     SUMMARY OF THE INVENTION 
     The present invention provides a chain tensioner system which includes an actuator which may be a conventional hydraulic tensioner, in conjunction with a pivoting lever. The lever carries a pair of pivoting arms. The arms extend outside of and contact both lengths or strands of the span of chain between a pair of sprockets. Actuation of the tensioner against the lever causes rotation of the lever which causes inward motion of the arms. The inward motion of the arms causes tension to be imparted to both strands of the chain simultaneously. 
     One example of the chain tensioner system of the present invention includes a hydraulic actuator as described above and a pivoting lever. Alternately, the actuator may be a mechanical tensioner or any suitable mechanism which is capable of providing sufficient force and travel to act on the lever to provide an adjustment in tension of the chain. The chain has two opposite strands, spans or lengths that are the portions extending between the sprockets. The strand between the sprockets where the chain leaves a driven sprocket and enters a driving sprocket is typically the tight strand or side and the strand between the sprockets where the chain leaves the driving sprocket and enters the driven sprocket is typically the slack strand or side of the chain. However, in systems with large center distances, both sides of the chain evidence some slack. 
     The lever includes a first end which is located between the chain strands. In the center of the first end of the lever is a pivot bore. The pivot bore is a hole with a cylindrical sleeve or bushing through which a pivot pin, shaft or bolt is inserted and about which the lever may rotate. The pivot pin is attached to an engine block or a mounting surface. The pivot bore and pivot pin are centered on a centerline extending between the two sprockets. 
     A pair of fixed pins are attached near the periphery of the first end of the lever. The fixed pins are located in near alignment with the chain centerline and equally spaced apart on opposite sides of the pivot bore. A pair of arms, each with an attached plastic shoe, are mounted to and allowed to rotate on each of the fixed pins. The arms extend outside the strands of the chain such that the shoes are positioned to contact an outside portion of the chain. A first arm and associated shoe extend outside the slack strand and a second arm and shoe extend outside the tight strand of chain. 
     A first fixed pin which is mounted to the lever in a position generally below the pivot bore carries the first arm. The first arm extends outside the slack strand of the chain (assuming a pair of sprockets with a wrapped chain traveling in a clockwise direction). A second fixed pin which is mounted to the lever in a position generally above the pivot bore carries the second arm. The second arm extends outside of the tight strand of the chain. 
     A second end of the lever extends a distance from the first end of the lever and extends outside the loop of the chain. The second end of the lever has at least one contact surface. It should be understood that the second end of the lever may be located in a number of equivalent positions. 
     In operation, actuation of the tensioner directs a force to the second end of the lever which causes rotation of the lever about the pivot pin. The fixed pins mounted on the first end of the lever pull the mounted arms in toward the chain centerline. For example, when the lever rotates in a counterclockwise direction, the first fixed pin and first arm are moved in a direction toward the chain centerline. Since the first arm is located outside the slack strand of the chain the inward travel of the first arm imparts an increased tension to the slack strand by displacing the slack chain strand path toward the chain centerline. Simultaneously, the second fixed pin and second arm are moved in a direction toward the chain centerline. Since the second arm is located outside the tight strand of the chain, the inward travel of the second arm imparts an increased tension to the tight strand by displacing the tight chain strand path toward the chain centerline. 
     Pivoting the lever about the pivot bore by applying a force to the contact surface causes the fixed pins to draw the arms and shoes inwardly into contact with the chain strands thereby causing the chain to be squeezed inwardly toward the centerline and tensioned on both tight and slack strands simultaneously. 
     In a second embodiment of the present invention, the pins mounted upon the lever are located different distances from the center of the pivot bore. In this manner, the fixed pin which is located closer to the center of the bore (the center of rotation) produces less take-up motion in the attached arm. This feature would be useful in the situation where less take-up is desired in the tight strand compared to the slack strand of a chain. 
    
    
     For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the preferred embodiment of the invention and to the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of the present invention. 
     FIG. 2 is a front view of the lever of the present invention. 
     FIG. 3 is a bottom view of the lever of FIG.  2 . 
     FIG. 4 is a front view of the arm of the present invention. 
     FIG. 5 is a side view of the arm of FIG.  4 . 
     FIG. 6 is a front view of the shoe of the present invention. 
     FIG. 7 is a side view of the shoe of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings, FIG. 1 shows a front view of a preferred embodiment of the present invention. In this figure, an engine timing system is represented generally by crankshaft sprocket  10  (the drive sprocket) and camshaft sprocket  12  (the driven sprocket). The path of a power transmission chain, i.e., a silent chain, roller chain or the like, is represented by broken chain line  14  wrapped around the drive sprocket  10  and the driven sprocket  12 . The path of a power transmission chain which has elongated due to wear is represented by broken chain line  15 . The tensioner system of the present invention is located between the tight and loose strands of the chain and between the two sprockets. 
     The tensioner system includes an actuator  16  which may be a hydraulic tensioner or the like. In the present illustration, the actuator  16  is represented by housing  18  and plunger  20 . The plunger is biased in an outward direction from the housing by spring  17 . The housing  18  is mounted to a fixed mount or engine block (not shown). The plunger extends outwardly from the housing. 
     The tensioner system includes a pivoting lever  30  which carries a pair of arms  60 ,  61  with attached shoes  70 ,  71 . The lever  30  has a first end  31  with a generally circular shape positioned between the opposite strands of the chain  14  and centered with respect to a centerline C extending between the center of the drive  10  and the driven sprocket  12 . The center of the first end  31  of the lever  30  has a pivot bore  32  formed therein. The pivot bore  32  is provided with a bushing  33 . The pivot bore  32  and bushing  33  are centered with respect to the centerline C. The first end  31  receives a fixed pivot pin  25  in the pivot bore  32  which allows the lever  30  to pivot about the pivot pin  25 . The pivot pin  25  may be fixed to a mounting surface or an engine block (not shown). 
     A second end  34  of the lever  30  extends to the outside of the chain  14 . The second end  34  has a contact surface  35  extending generally perpendicular to the lever  30 . The plunger  20  of the actuator  16  is positioned to act against the contact surface  35 . A combination of spring and fluid pressure causes the plunger  20  to extend from the housing  18  and causes the lever  30  to rotate about the pivot pin  25 , as shown in this illustration, in a counterclockwise direction D. 
     A pair of fixed pins  36 ,  37  are attached to the lever  30  near the periphery of the circular first end  31  on opposite sides with respect to the pivot bore  32 . A first fixed pin  36  is located below the pivot bore  32  and slightly to the left of the centerline C near the slack chain strand. A second fixed pin  37  is located above the pivot bore  32  and slightly to the right of the centerline C. The first and second pins are located equidistant from the center of the pivot bore. In this arrangement, movement of the lever  30  about the pivot pin  25  causes the fixed pins  36 ,  37  to move equally in a lateral direction, indicated in the direction M, substantially perpendicular with respect to the centerline C. 
     A first arm  60  is rotatably attached to the first fixed pin  36 . The first arm  60  extends outside the slack strand  14 A of the chain  14  and carries a shoe  70  with a wear face  72  positioned to contact the outside portion of the chain strand  14 A. A second arm  61  is rotatably attached to the second fixed pin  37 . The second arm  61  extends outside the tight strand  14 B of the chain  14  and carries a shoe  71  with a wear face  73  positioned to contact the outside portion of the chain strand  14 B. 
     In operation, the plunger  20  moves the second end  34  of the lever  30  (in direction D) about the pivot pin  25  causing a counterclockwise movement of the first end  31  of the lever  30 . In this manner, the fixed pins  36 ,  37  pull the arms  60 ,  61  and attached shoes  70 ,  71  laterally toward the chain centerline C and into contact with outside portions of the chain strands  14 A,  14 B. As the arms are pulled by the fixed pins into a position closer to the chain centerline C, the chain is essentially squeezed or tightened from both sides or along both spans, simultaneously and tension is imparted to the chain strands accordingly. 
     In this manner, the tensioner system of the present invention will potentially produce approximately double the take-up for a given range of tensioner operation as compared to a conventional hydraulic tensioner acting upon a single arm with an end pivot that acts on one chain strand. Additionally, vibration in a first strand of chain, whether it be the loose or tight strand is transferred and damped by action of the second strand of chain due to the coupling of the two arms through the lever. 
     FIG. 2 depicts the lever  30  of FIG. 1 in a front view. The first end  31  has a generally circular shape with a pivot bore  32  in the center. It should be understood that the first end of the lever may be a number of shapes. The pivot bore  32  has a bushing  33  disposed therein. Spaced equally apart and on opposite sides of the pivot bore near the periphery of the circular first end  31  are a first fixed pin  36  and a second fixed pin  37 . The lever  30  has a second end  34  with first contact surface  35 A and second contact surface  35 B, formed perpendicular to the lever, which enable the lever to be assembled into the tensioner system in a right facing or left facing orientation. In other words, the lever  30  may be used in a tensioner system with the second end  34  extending outside of either side of the chain and sprocket system. Alternately, the lever may be oriented along the chain centerline in a chain and sprocket system where the center-to-center distance between sprockets provides sufficient space for the lever. 
     FIG. 3 depicts a bottom view of the lever of FIG.  2 . In particular, the contact surface  35 B is a rectangular tab oriented perpendicular to the main body portion of the lever  30  at the second end  34  of the lever. The first fixed pin  36  is shown in alignment with the pivot bore  32  near the first end  31  of the lever  30 . 
     FIG. 4 depicts an arm  60  in a front view. The first and second arms ( 60 ,  61  as shown in FIG. 1) are identical in structure but oriented to operate on a strand of chain depending on the direction of chain travel. The arm  60  has an elongated bracket portion  60 A with a bore  80 . The bore  80  is slightly offset toward the leading end of the bracket portion  60 A of the arm  60 . More particularly, the bore  80  is offset toward the end of the arm  60  nearest the incoming chain. 
     The arm has a shoe attachment portion  60 B, also shown in FIG. 5, which is oriented perpendicular to the elongated bracket portion  60 A. The face attachment portion  60 B has a lengthwise gradual curve to generally match an associated span of chain and a plurality of rectangular openings  82 A,  82 B,  82 C to facilitate the attachment of a plastic shoe. 
     The shoe portion  70  of the tensioner system is shown in FIGS. 6 and 7. The shoe includes a plurality of clips  74 A,  74 B,  74 C formed on a back side of the shoe which insert through the rectangular openings in the shoe attachment portion of the arms. In particular, clip  74 A engages hole  82 A shown in FIG.  5 . Similarly, clip  74 B engages hole  82 B and clip  74 C engages hole  82 C. 
     Preferably, a clip is formed at each end of the shoe and another clip is formed in an intermediate portion of the shoe. Opposite the back side is a chain contacting wear face  72 A, preferably with a flat central face and raised edges  72 B,  72 C to form a channel over which the chain travels. 
     While several embodiments of the invention are illustrated, it will be understood that the invention is not limited to these embodiments. Those skilled in the art to which the invention pertains may make modifications and other embodiments employing the principles of this invention, particularly upon considering the foregoing teachings.