Abstract:
A tensioner for a closed loop power transmission system for an internal combustion engine having a drive shaft terminating in a sprocket and at least one camshaft, each terminating in a sprocket, with a single continuous chain wrapping around all of the sprockets. The tensioner contains a pair of elongated tensioning arms, each one in slidable contact with one of the two strands of chain that traverses between the driving sprocket and the driven sprocket(s). Each tensioning arm contains a wear face that remains in constant slidable contact with the strand of chain to which it is adjacent. An adjusting arm connects one of the ends of the tensioning arms. The adjusting arm has a ratchet means that adjusts for the backlash in the system and takes up any slack in the chain.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention pertains to the field of chain tensioners. More particularly, the invention pertains to a tensioner for two strands of chain that contains a ratcheting device. 
         [0003]    2. Description of Related Art 
         [0004]    A tensioning device, such as a hydraulic tensioner, is used as a control device for a power transmission chain, or similar power transmission device, as the chain travels between a plurality of sprockets that are connected to the operating shafts of an internal combustion engine. In this system, the chain transmits power from a driving shaft to a driven shaft, so that part of the chain is slack and part of the chain is tight. Generally, it is important to impart and maintain a certain degree of tension on the chain to prevent noise, slippage, or the unmeshing of teeth as in the case of a toothed chain. Prevention of such slippage is particularly important in the case of a chain driven camshaft in an internal combustion engine because the jumping of teeth will throw off the camshaft timing, possibly causing damage to the engine or rendering it inoperative. 
         [0005]    However, in the harsh environment of the internal combustion engine, numerous factors cause fluctuations in the tension of any given portion of the chain. For instance, extreme temperature fluctuations and differences in the relative rates of thermal expansion coefficients among the various parts of the engine can cause the chain tension to vary between excessively high or very low levels. During prolonged use, wear to the components of the power transmission system can cause a steady decrease in chain tension. In addition, camshaft and crankshaft induced torsional vibrations cause considerable variations in chain tensions. For example, the reverse rotation of an engine, occurring during stopping of the engine or in failed attempts at starting the engine, can also cause significant fluctuations in chain tension. For these reasons, a mechanism is desired to remove excessive tensioning forces on the tight side of the chain while, at the same time, ensuring that adequate tension is applied to the slack side of the chain. 
         [0006]    Hydraulic tensioners are a common method of maintaining proper chain tension. In general, these mechanisms employ a lever arm that pushes against the chain on the slack side of the power transmission system. The lever arm pushes toward the chain, tightening the chain when the chain is slack, and it must remain relatively immoveable when the chain tightens. 
         [0007]    To achieve this, a hydraulic tensioner  1 , as shown in prior art  FIG. 1 , typically contains a rod or cylinder as a piston  2 , which is biased in the direction of the chain by a tensioner spring  3 . The piston  2  is housed within a cylindrical housing  5 , having an interior space which is open at the end facing the chain and closed at the other end. The interior space of the housing contains a pressure chamber  4  which is connected to a reservoir or exterior source of hydraulic fluid pressure via channels or ducts. The pressure chamber  4  is typically formed between the housing  5  and the piston  2 , and it expands or contracts when the piston  2  moves within the housing  5 . 
         [0008]    Typically, valves are employed to regulate the flow of fluid into and out of the pressure chamber. For instance, an inlet check valve such as a ball-check valve opens to permit fluid to flow into the pressure chamber  4  when the pressure inside the chamber has decreased as a result of the outward movement of the piston  2 . When the pressure in the pressure chamber is high, the inlet check valve closes, preventing fluid from exiting the pressure chamber. Closing the inlet check valve prevents the piston chamber from contracting, which in turn prevents the piston from retracting, thereby achieving a so-called “no-return” function. 
         [0009]    Many tensioners also employ a pressure relief mechanism that allows fluid to exit the pressure chamber when the pressure in the chamber is high, thus allowing the piston to retract in a regulated manner in response to rapid increases in chain tension. In some tensioners, the pressure relief mechanism is a spring biased check valve. The check valve opens when the pressure exceeds a certain pressure point. Some tensioners may employ a valve which performs both the inlet check function as well as the pressure relief function. 
         [0010]    Other mechanisms employ a restricted path through which fluid may exit the fluid chamber, such that the volume of flow exiting the fluid chamber is minimal unless the pressure in the fluid chamber is great. For instance, a restricted path may be provided through the clearance between the piston and bore, through a vent tube in the protruding end of the piston, or through a vent member between the fluid chamber and the fluid reservoir. 
         [0011]    A hydraulic tensioner used with a tensioner arm or shoe is shown in Simpson et al., U.S. Pat. No. 5,967,921, incorporated herein by reference. Hydraulic chain tensioners typically have a plunger slidably fitted into a chamber and biased by a spring to provide tension to a specific strand of 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 urged outward against the arm by the combined forces of the hydraulic pressure and the spring tension. 
         [0012]    When a force is applied to move the plunger in a reverse direction (retracting into the housing) away from the chain, typically a check valve will restrict the flow of fluid out of the chamber. In this way, the tensioner achieves the no-return function, i.e., movements of the plunger are easy in one direction (outward and away from the housing) but difficult in the reverse direction. 
         [0013]    Blade tensioners are commonly used to control a chain or belt where load fluctuations are not so severe as to overly stress the spring or springs. A ratchet with a backlash mechanism may be added to tensioners to limit the effective backward or untensioned travel of the tensioning device. 
         [0014]    Prior art  FIG. 2  shows a conventional blade tensioner. The blade tensioner  10  includes a blade shoe  11  having a curved chain sliding face and numerous blade springs  21 , preferably made of a seasoned metallic material to impart spring-like tension to the blade springs  21 . The blade springs  21  are arranged in layers on the opposite side of the blade shoe  11  from the chain sliding face, and exert a biasing force on the blade shoe  11 . The ends of each spring-shaped blade spring  21  are inserted in the indented portions  14  and  15 , which are formed in the distal portion  12  and proximal portion  13  of the blade shoe  11 , respectively. 
         [0015]    A bracket  17  is provided for mounting the blade tensioner  10  in an engine. Holes  18  and  19  are formed in the bracket  17 . Bolts or other secure mounting means are inserted into holes  18  and  19  for securing bracket  17  to the engine. A sliding face  16  is formed on the distal portion of the bracket  17  and slidably contacts the distal portion of the blade shoe  11 . A pin  20  secured on the bracket  17  supports the proximal portion  13  of the blade shoe  11  so that it may pivot with the changes in the position of the chain. 
         [0016]      FIG. 3  shows a chain tensioning device that has a pair of arms  202 ,  203  which are joined by a pivot  204 . The arms  202 ,  203  are urged apart so that arm  203  applies tensioning force to a chain (not shown) by means of a spring  206  loaded cam block  205 . To prevent collapse of arm  203  during load reversals of the chain, a catch disc  209  and rod  208  are arranged to prevent return movement of the spring loaded cam block  205 . 
         [0017]      FIG. 4  shows a tensioner that uses a ratchet device in a chain drive power transmission system. The power transmission system includes a drive shaft  302  having a sprocket  303  that uses a continuous loop chain  306  to drive the sprocket  305  of a driven shaft, such as a camshaft,  304 . The ratchet tensioner  301  contains a tensioner housing  307  having a hole  312  for receiving a plunger  308  and a ratchet pawl  317  pivotally mounted about shaft  316  to the tensioner housing  307  and biased by a ratchet spring  318 . The plunger  308  has teeth on one side of its outer perimeter to engage the ratchet pawl  317 . The plunger  308  is biased outward from the hole  312  toward contact with tension lever  310  by the introduction of pressurized fluid into the hollow section  313  and by the force of the plunger spring  314 . The tensioner lever  310  pivots on support shaft  309  and has a sliding face  311  that contacts and applies tension to the slack side of the timing chain  306 . The rearward movement of the plunger  308  back into the hole  312  is limited by the one way engagement of the ratchet pawl  317  with the teeth on the plunger. 
         [0018]    Prior art  FIGS. 5   a ,  5   b , and  5   c  show a tensioner  110  for a closed loop power transmission system of an internal combustion engine. The power transmission system includes a drive shaft terminating in a sprocket  102  and at least one camshaft, each in turn terminating in a sprocket  104 ,  104 ′, with a single continuous chain  100  wrapping around the sprockets. The tensioner  110  contains a pair of elongated tensioning arms  112 ,  112 ′, each one in slidable contact with one of the two strands of chain  100  that traverses between the driving sprocket  102  and the driven sprocket(s)  104 ,  104 ′. Each tensioning arm  112 .  112 ′ has a first end  107 ,  107 ′, a second end  109 ,  109 ′ and a mid point and may be pivotally mounted  106 ,  106 ′,  106   a ,  106   a ′ to the engine housing at either the first end  107 ,  107 ′, the mid point or at some location therebetween. Each tensioning arm  112 ,  112 ′ contains a wear face  105 ,  105 ′ to maintain slidable contact with the strand of chain with which it is operably engaged. 
         [0019]    The second end  109 ,  109 ′ of each tensioning arm  112 ,  112 ′ is pivotally connected to the other tensioning arm by an adjusting arm  130 . The adjusting arm  130  includes two pairs of rigid elongated straps  134 ,  134 ′,  136 ,  136 ′ that adjustably overlap with each other substantially in the middle of the length of the adjusting arm  130 . The overlapping ends  142 ,  142 ′ of the first pair of elongated straps  134 ,  134 ′ terminate in hook shapes to provide a seat for a first end of a lengthening coil spring  160 . The overlapping ends  150 ,  150 ′ of the second pair of elongated straps  136 ,  136 ′ also terminate in hook shapes that insert through slots  146 ,  146 ′ formed in each of the first pair of elongated straps  134 ,  134 ′. The hook shaped ends  150 ,  150 ′ of the second pair of straps  136 ,  136 ′ provide a seat for a second end of the lengthening coil spring  160 . Each strap of the first pair of elongated straps  134 ,  134 ′ contains a rack of teeth  172 ′ that operatively meshes with a rack of teeth  170  on each strap of the second pair of elongated straps  136 ,  136 ′. The lengthening coil spring  160  urges the overlap of both pair of elongated straps  134 ,  134 ′,  136 ,  136 ′ so that the adjusting arm  130  continues to shorten in response to increasing slack or wear conditions experienced by the chain  100 . The meshing teeth provide a “no-return” feature by engaging the teeth in only one direction. 
       SUMMARY OF THE INVENTION 
       [0020]    The present invention is a tensioner for a closed loop power transmission system of an internal combustion engine. The power transmission system includes a drive shaft terminating in a sprocket and at least one camshaft, each in turn terminating in a sprocket, with a single continuous chain wrapping around the sprockets. The tensioner contains a pair of elongated tensioning arms, each one in slidable contact with one of the two strands of chain that traverses between the driving sprocket and the driven sprocket(s). Each tensioning arm has a first end and a second end and the first end of the tensioning arms are pivotally attached to the engine. Each tensioning arm contains a wear face to maintain slidable contact with the strand of chain with which it is operably engaged. 
         [0021]    The second end of each tensioning arm is pivotally connected to the other tensioning arm by an adjusting arm. The adjusting arm includes two pairs of rigid elongated straps that adjustably overlap with each other substantially in the middle of the length of the adjusting arm. An anchoring base is present between the two rigid elongated straps. The overlapping ends of the first pair of elongated straps terminate in hook shapes and together with the anchoring base provide a seat for a first coil spring. The overlapping ends of the second pair of elongated straps also terminate in hook shapes that insert through slots formed in each of the first pair of elongated straps. The hook shaped ends of the second pair of straps together with the anchoring base provide a seat for a second coil spring. Each strap of the first pair of elongated straps contains a rack of teeth that operatively meshes with a rack of teeth on each strap of the second pair of elongated straps. The first and second coil spring urge the overlap of both pair of elongated straps so that the adjusting arm continues to shorten in response to increasing slack or wear conditions experienced by the chain. The meshing teeth provide a “no-return” feature by engaging the teeth in only one direction 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0022]      FIG. 1  shows a prior art hydraulic tensioner. 
           [0023]      FIG. 2  shows a prior art blade type tensioner. 
           [0024]      FIG. 3  shows an alternate prior art tensioner. 
           [0025]      FIG. 4  shows a prior art ratcheting tensioner. 
           [0026]      FIG. 5   a  shows a front elevational view of a prior art tensioner.  FIG. 5   b  shows an isometric view of the ratcheting device in the adjustment arm of the prior art tensioner of  FIG. 5   a .  FIG. 5   c  shows two straps segments of the prior art adjustment arm of the prior art tensioner of  FIG. 5   a.    
           [0027]      FIG. 6  shows an isometric view of the ratcheting tensioner of the present invention. 
           [0028]      FIG. 7  shows an isometric view of the ratcheting tensioner of the present invention without sprockets. 
           [0029]      FIG. 8  shows a top view of the ratcheting tensioner of the present invention. 
           [0030]      FIG. 9  shows a front view of the ratcheting tensioner of the present invention. 
           [0031]      FIG. 10  shows two straps having opposing ratchet teeth. 
           [0032]      FIG. 11  shows an exploded view of overlapping straps separated to show the ratchet teeth. 
           [0033]      FIG. 12  shows an isometric view of the two pairs of strap. 
           [0034]      FIG. 13  shows a top view of two pairs of straps. 
           [0035]      FIG. 14  shows an isometric view including springs. 
           [0036]      FIG. 15  shows a top view including springs. 
           [0037]      FIG. 16  shows an isometric view including the anchoring base, pins, snap rings, and back straps. 
           [0038]      FIG. 17  shows an isometric view including front straps. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    The tensioner  510  of the present invention is operatively engaged with a closed loop power transmission system of an internal combustion engine. The power transmission system contains a driving sprocket  102  and at least one driven sprocket  104 ,  104 ′. Power from the engine&#39;s drive shaft is transmitted from the driving sprocket  102  to the driven sprockets by means of a chain  100  or drive belt. Most commonly used with internal combustion engines are chain drives. Proper tension must be applied to the chain  100  at all times in order to prevent the jumping of the sprocket teeth by the chain during slackening of any portion of the chain during operation or as a result of increasing wear of the components over time. 
         [0040]    The tensioner  510  includes a tensioning arm  512  that is operatively engaged with the outer surface of one of the strands of chain between the driving sprocket  102  and one of the driven sprockets  104 . The second tensioning arm  512 ′ of tensioner  510  is operatively engaged with the outer surface of the other strand of chain between the driving sprocket  102  and a second driven sprocket  104 ′. It should be understood that the tensioner  510  of the present invention is also capable of being used in a closed loop power transmission system that has only one driving and one driven sprocket. 
         [0041]    Each tensioning arm  512 ,  512 ′, may be pivotally secured to the face of the engine housing (not shown) by pivot mounting means  506  at respective first ends  507  and  507 ′ of each tensioning arm  512  and  512 ′, as shown in  FIGS. 6 ,  7 , and  9 . The pivot mounting means  506  is present between the chain strands allows the tensioning arms  512  and  512 ′ to pivot in response to changes in the tension of the chain  100 . Alternative pivot mounting points may also be used. While both tensioner arms  512 ,  512 ′ are shown as being mounted to the same pivot point, multiple pivot points may be present and each arm may be mounted to different pivot points. 
         [0042]    Each tensioning arm  512  and  512 ′ contains an elongated rectangular shaped chain wear face  505  and  505 ′, respectively, that is semi-rigidly mounted along the length of each tensioning arm facing the strand of chain  100  with which it is operatively engaged. Each chain wear face  505  and  505 ′ terminates in hooked ends that wrap around the ends of the tensioning arm on which it is installed. Each chain wear face  505  or  505 ′ is the contact surface with the strand of chain with which its corresponding tensioning arm is engaged. 
         [0043]    Each chain wear face  505  and  505 ′ has a first end  505   a  and  505   a ′, respectively, and a second end  505   b  and  505   b ′, respectively. Each first end  505   a  and  505   a ′ is joined to its corresponding second end  505   b  and  505   b ′ by a middle portion that acts as the chain sliding face  505   c  and  505   c ′. This is best shown in  FIG. 7 . Each chain sliding face  505   c  and  505   c ′ is in sliding contact with a different strand of chain  100 . Each first end  505   a  and  505   a ′ and each second end  505   b  and  505   b ′ of its respective chain wear face  505  and  505 ′ are curved underneath and around towards the center of the corresponding wear face. Each chain wear face  505  and  505 ′ is longer than its corresponding tensioning arm  512  and  512 ′ such that each curved first end  505   a  and  505   a ′ receives the respective first end  507  and  507 ′ of the corresponding tensioning arm  512  and  512 ′ and each curved second end  505   b  and  505   b ′ receives the respective second end  509  and  509 ′ of the corresponding tensioning arm  512  and  512 ′, thereby loosely securing each chain wear face  505  and  505 ′ to its corresponding tensioning arm  512  and  512 ′. The chain wear faces  505  and  505 ′ are preferably made of a material that is semi-flexible at engine operating temperatures, in order to allow them to bow out to conform to the changing tension conditions of the chain  100 . Optionally, additional biasing means may be provided by one or more blade springs located between the tensioning arm  512 ,  512 ′ and the rear surface of each of the chain wear faces  505  and  505 ′. A gap clearance exists between each of the first ends  505   a  and  505   a ′ of the chain wears faces  505  and  505 ′ and the first ends  507  and  507 ′ of tensioning arms  512  and  512 ′. As well, a gap clearance exists between the second ends  505   b  and  505   b ′ of the chain wear faces  505  and  505 ′ and the second ends  509  and  509 ′ of tensioning arms  512  and  512 ′. 
         [0044]    The second ends  509  and  509 ′ of each of the respective tensioning arms  512  and  512 ′, are connected to an adjusting arm  530  as shown in  FIGS. 8 and 9 . Referring to  FIGS. 16 and 17 , the second end  509  of the tensioning arm  512  is secured to first ends  538  and  538 ′, respectively of a first pair of elongated straps  534  and  534 ′ by a pin  532 . The second end  509 ′ of tensioning arm  512 ′ is secured to first ends  540  and  540 ′, respectively, of a second pair of elongated straps  536 ,  536 ′, by pin  532 ′. Elongated straps  534 ,  534 ′,  536  and  536 ′ may be made of any rigid material, such as, for example, steel, aluminum, alloys thereof, or non-deformable synthetic resinous composite materials. 
         [0045]    Referring to  FIGS. 12 and 13 , the second ends  542  and  542 ′, of their respective first pair of elongated straps  534  and  534 ′ each terminate into a substantially 180° hook shape. The second ends  550  and  550 ′ of their respective second pair of elongated straps  536  and  536 ′ also each terminate into a substantially 180° hook shape. Second end  550  is slidably engaged through a longitudinal slot  546  in elongated strap  534  and second end  550 ′ is slidably engaged through a longitudinal slot  146 ′ in elongated strap  534 ′. 
         [0046]    Second ends  542  and  542 ′ and an anchoring base  580  securely mounted to the engine housing, present between the pairs of straps  534 ,  534 ′,  536 ,  536 ′ creates a seat to secure a first coil spring  560   a . The first end of the first coil spring  560   a  is secured to the second ends  542  and  542 ′ and the second end of the first coil spring is mounted to the anchoring base  580 . Second ends  550  and  550 ′ and anchoring base  580  securely mounted to the engine housing creates a seat to secure the second coil spring  560   b . The first end of the second coil spring  560   b  is secured to the second ends  550  and  550 ′. The second end of the second coil spring  560   b  is mounted to anchoring base  580 . 
         [0047]    The resting state of each of the coil springs  560   a ,  560   b  is longer than its length when installed in the adjusting arm  130  in order to provide a force to bias the respective second ends  542  and  542 ′ away from second ends  550  and  550 ′ and the anchoring base  580 . The elongating force of coil springs  560   a  and  560   b  urges the first pair of elongated straps  534  and  534 ′ to overlap with the second pair of elongated straps  536  and  536 ′, when required, in response to increasing slack or wear conditions exhibited by the chain  100 . 
         [0048]    Referring to  FIGS. 10 and 11 , various elements of the adjusting arm  530  are removed to better show certain features of ratcheting means  555 . Located on the inner surface  537  and in proximity to the second end  550  of elongated strap  536  is an inner rack of teeth  570 . Located on the outer surface  535 ′ (not shown) and in proximity to the second end  542 ′ of elongated strap  534 ′ is an outer rack of teeth  572 ′. Although not shown in these figures, the mirror image elongated strap  536 ′ also contains the same elements as does elongated strap  536 . Specifically, on the inner surface  537 ′ and in proximity to the second end  550 ′ of elongated strap  536 ′ is a rack of teeth  570 ′. The mirror image elongated strap  534  contains similar elements as are present on elongated strap  534 ′, that is, on the outer surface  535  (not shown) and in proximity to the second end  542  of elongated strap  534  is an outer rack of teeth  572 . When the adjusting arm  530  is fully assembled, the inner rack of teeth  570  of elongated strap  536  mesh with the outer rack of teeth  572  of elongated strap  534  and the inner rack of teeth  570 ′ of elongated strap  536 ′ mesh with the outer rack of teeth  572 ′ of elongated strap  534 ′. The teeth are designed to index in only one direction in response to the force of the coil spring  560  urging the second ends  542  and  542 ′ of the first pair of elongated straps  534  and  534 ′ away from the second ends  550  and  550 ′ of the second pair of elongated straps  536  and  536 ′ and the anchoring base  580 . Consequently, the distance between the tensioning arms  512  and  512 ′ will decrease in response to an increase in slack or excessive wear conditions exhibited by chain  100 . As the distance between the tensioning arms  512  and  512 ′ decreases, a relatively constant tensioning force on chain  100  is maintained. 
         [0049]    In order to insure that the inner racks of teeth  570  and  570 ′ remain securely engaged with their corresponding outer racks of teeth  572  and  572 ′, the coil spring seating surfaces of the second ends  550  and  550 ′ are angled toward the central axis of the adjusting arm  530 . Concurrently, the coil spring seating surfaces of the second ends  542  and  542 ′ are angled outward away from the central axis of the adjusting arm. When the compressed coil spring  560  is seated between second ends  542  and  542 ′ and second ends  550  and  550 ′, its natural tendency to return to its elongated resting state generates a force on both the angled portions of second ends  542  and  542 ′ and the angled portions of second ends  550  and  550 ′ to insure that the corresponding enmeshed racks of teeth do not jump out of engagement with each other until desired in response to changing chain tension conditions. 
         [0050]    The tensioning arms  512  and  512 ′ may only employ wear faces  505  or  505 ′ to provide tensioning in the direction of a slack or worn chain. In conjunction with the ratcheting means  555 , the minimal force applied by the wear faces alone may be sufficient enough to tension certain chain drive transmission systems. This embodiment may provide the desired tension for certain power transmission systems. However, other drive transmission systems may have different tension requirements. A blade spring may be added within a recess in the body of the tensioning arm  512  to provide additional force for urging the wear face  505  into forcible sliding contact with the chain  100 . Similar embodiments would include more than one blade spring, either stacked on top of one another in a single recess or placed in separate recesses along the length of the tensioning arm  512 . It should be understood that tensioning arm  512 ′ may also incorporate at least one blade spring, if desired. The design parameters of each specific chain drive system may necessitate a tensioner  510  in which both tensioning arms  512  and  512 ′ contain blade springs, or one in which only one of the tensioning arms would contain blade springs. Also, neither of the tensioning arms  512  and  512 ′ may contain a blade spring. 
         [0051]    Backlash is the backward or untensioned travel of a tensioning device. The combination of the amount of force provided by the wear faces  505  and  505 ′ and the indexing movement of the ratcheting means  555  of the invention controls the amount of backlash that occurs in the operation of a closed loop chain driven power transmission system. The gap created between the body of the tensioning arms  512  and  512 ′ and the under side of their respective wear faces  505  and  505 ′ is limited by the amount of gap clearance, previously discussed, between the ends of the wear faces  505  and  505 ′ and the corresponding ends of the tensioning arms  512  and  512 ′. The total amount of the combined gap from both tensioning arms defines the backlash in the power transmission system. Backlash determines the timing variation in the driven sprocket(s) and must be kept to a minimum. When slack in the chain cannot be absorbed because the maximum gap between the wear faces  505  and  505 ′ and their corresponding tensioning arms  512  and  512 ′ has been reached, the coil springs  560   a  and  560   b  of the ratchet means  555  provide the required force to index the meshed racks of teeth by at least one tooth and in only one direction. The indexing of the teeth increases the overlap between the pairs of elongated straps of the adjusting arm  530 , and biases the second ends  509  and  509 ′ of the corresponding tensioning arms  512  and  512 ′ toward each other. The reduced distance between the second ends of the tensioning arms  512  and  512 ′ reestablishes forceful contact of the wear faces  505  and  505 ′ with their respective strands of chain  100 . The unidirectional movement of the teeth prevents the adjusting arm  530  from returning to its previous elongated state which would result in an inability to tension the chain due to the loss of or a reduction in forceful contact between the wear faces  505  and  505 ′ and their corresponding strands of chain. 
         [0052]    Furthermore, the clocking of the driven sprocket  104 ,  104 ′ would be restricted over that of the prior art as the anchored base  580  restricts the system&#39;s freedom to sway about the pivoting ends  509 ,  509 ′ of the arms  512 ,  512 ′. 
         [0053]    Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.