Abstract:
An engine tensioning system including tensioner arms and a rotary actuating tensioner capable of driving multiple tensioner arms making multiple chain or belt contacts. The rotary actuating tensioner has connector pins fixed to a rotating surface to which tensioner arms are attached. Rotation of this surface is accomplished through a combination of springs and hydraulic pressure. When the surface rotates, the attached tensioner arms are driven laterally against the engine chain or belt, keeping it taut.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally, but not exclusively, to tensioners used with chain drives in automotive timing and power transmission applications. In particular, the present invention is related to a rotary actuating hydraulic tensioner which combines the benefits of typical hydraulic tensioners and the rotary motion of a torsion spring tensioner.  
         BACKGROUND OF THE INVENTION  
         [0002]    Chain tensioning devices are used to control power transmission chains as the chain travels between a set of sprockets. Such chains usually have at least two separate strands, spans or lengths extending between the drive sprocket, such as a crankshaft sprocket, and the driven sprocket, such as a cam sprocket. The strand between the sprockets where the chain leaves the driven sprocket and enters the drive sprocket is frequently is under tension as a result of the force imposed on the chain by the drive sprocket. The strand between the sprockets where the chain leaves the drive sprocket and enters the driven sprocket is frequently under reduced drive tension or slack due to the absence of driving force exerted on that strand. In systems with large center distances between the sprockets, both strands may evidence slack between the sprockets.  
           [0003]    As a consequence, it is essential to the proper operation of the chain and sprocket system that a proper degree of engagement between the chain members and the sprockets is maintained during operation of the system. One aspect of maintaining such engagement of chain and sprocket is maintaining a proper degree of tension in the chain strands. The loss of chain tension can cause undesirable vibration and noise in the chain strands. The loss of chain tension also increases the possibility of chain slippage or unmeshing from the teeth of the sprocket, reducing engine efficiency and, in some instances, causing system failures. For example, it is especially important to prevent the chain from slipping in the case of a chain-driven camshaft in an internal combustion engine because misalignment of camshaft timing by several degrees can render the engine inoperative or cause damage to the engine.  
           [0004]    The tension of the chain can vary due to wide variations in temperature and linear expansions among the various parts of an engine. Moreover, wear to the chain components during prolonged use also may produce a decrease in the chain tension. In addition, the intermittent stress placed on the chain devices in automotive applications due to variation in engine speed, engine load and other stress inducing occurrences can cause temporary and permanent chain tension.  
           [0005]    To maintain tension in such transmission systems, tensioner devices have been used to push a tensioner arm against the chain along a chain strand. Such transmission systems, typically press on the chain mechanically deflect the strand path imparting under the desired degree of tension on the chain. Current tensioner devices for performing this function, such as torsion spring tensioners, utilize the energy stored in a wound spring to drive the tensioner arm, such as shown in Ojima, U.S. Pat. No. 5,030,170. The small size of torsion spring tensioners makes them highly suitable in many situations. However, they often require an excessive spring load to effectively dampen chain vibrations and maintain a constant spring tension.  
           [0006]    Hydraulic tensioner devices typically have a plunger slidably fitted into a chamber and biased outward by a spring to provide tension to the chain. Hydraulic pressure from an external source, such as an oil pump or the like, flows into the chamber through a check valve and passages formed in the housing of the device. The plunger may move outward against the chain, directly against a tensioner arm principally by an internal spring or similar structure and the plunger position is maintained in large part by hydraulic pressure within the housing. Such a hydraulic tensioner as used with a tensioner arm or shoe is shown in Simpson et al., U.S. Pat. No. 5,967,921.  
           [0007]    Hydraulic tensioners frequently are preferred over torsion spring tensioners because they are much better at dampening chain movement and maintaining constant chain tension. For example, as a chain traverses its path, it may vibrate or “kick” causing the chain to push against the tensioner arm. The force of the kick is transferred to the tensioner device causing the hydraulic plunger to move in a reverse direction away from the chain. This reverse movement is resisted by the hydraulic fluid in the chamber, as flow of the fluid out of the chamber is restricted by the check valve assembly. In this fashion, the tensioner achieves a so-called no-return function, i.e., movements of the plunger are relatively easy in one direction (towards the chain) but difficult in the reverse direction. In addition, rack and ratchet assemblies also may be employed to provide a mechanical no-return function.  
           [0008]    In some applications, however, the size and bulk of hydraulic tensioners can present difficulties in mounting and operating such tensioners where the available space, is better suited for torsion spring tensioners. To overcome the difficulty created by the size of hydraulic tensioners, lever systems have been employed that allow the mounting of the hydraulic tensioner at a distance from the chain assembly. Through the lever system, the hydraulic tensioner imparts pressure on one or more strands of the chain assembly thereby maintaining chain tension.  
           [0009]    However, such lever mechanisms add to the complexity of the tensioner system and involve additional moving parts with a concomitant increase in maintenance expenses, problems and equipment failures. The use of such pivoted lever mechanisms may also diminish the ability of the hydraulic tensioners to dampen chain vibration. In addition, the mechanical limitations of the typical rod and piston design of hydraulic tensioners often limit the amount of slack which can be taken up by the tensioner during the life of the chain. One example of such a tensioner device is described in Sato et al., U.S. Pat. No. 5,318,482.  
         SUMMARY OF THE INVENTION  
         [0010]    The rotary actuating tensioner of the invention provides a hydraulically actuated tensioner of reduced size, but with performance capabilities exceeding torsion spring tensioners. The rotary actuating tensioner of the invention requires less spring force than traditional torsion spring tensioners, eliminating the need for expensive tensioner wear face materials, reducing chain noise and potentially increasing the overall life of the tensioner parts and the reliability of the engine systems using the rotary actuating tensioner.  
           [0011]    The rotary actuating tensioner is ideally suited for replacing hydraulic tensioner systems requiring levers with a more compact tensioner having similar or improved performance. The rotary actuating tensioners of the invention further may be installed at or near the pivot point of old tensioner arms to simplify the engine assembly, can reduce the space required for the tensioner, and can overcome the limitations inherent in tensioner configurations incorporating lever mechanisms.  
           [0012]    In an alternative aspect, control of multiple chain strands may be achieved with the rotary actuating tensioner. By incorporating multiple pin assemblies on the face of the rotary actuating tensioner to act as connection points, a single rotary actuating tensioner can drive multiple tensioner arms contacting multiple chain strands (or making multiple contacts with a single strand). This configuration is advantageous as significantly increases the potential operating take-up of chain slack for a given range of tensioner operation.  
           [0013]    By incorporating multiple contacts at different points, and opposing sides of a strand, the deviation of the chain from its original path also may be minimized to prevent potential interference of the mechanism with other engine components. Such a configuration also may minimize stress on the chain itself by limiting movement between the links as the chain traverses its path.  
           [0014]    The use of the multiple strand contacts, in addition, may be used to enhance the dampening of the chain&#39;s movement. Vibrations which occur in one strand of chain will tend to be reduced or canceled when the energy of those vibrations are transferred to or combined with those in another strand through the rotating tensioner. Further, by taking up chain slack of both strands 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/or slackens.  
           [0015]    In another aspect, the combination of multiple pin assemblies on a rotary surface provides the capability of imparting different degrees of movement in the tensioner arms attached to the pin assemblies. The degree of lateral movement imparted for a given rotational displacement is dependent upon the positioning of the pin assembly on the rotating surface. In other words, the degree of movement of the tensioner arm is a function of the radius formed between the pin assembly to which the tensioner arm is attached and the pivot point of the rotating surface. By varying the position of the pin assembly on the rotating surface, the degree of movement of tensioner arms can be altered for specific applications. For example, the tensioner arms of the invention may be positioned so they impart a different force to each chain strand for a given amount of rotation of the pin assemblies to compensate for differential strand tensions inherent in a system. In such a system, the separate chain strands may be placed under different degrees of tension depending upon whether the strand is being driven by a sprocket or is driving a sprocket.  
           [0016]    In one aspect, the rotary actuating tensioner provides two interacting housings. The first, typically the main housing, is fixed to a stationary surface, e.g., an automotive engine block. The first housing forms a base through which the second housing, a rotary housing, develops torque that is ultimately transferred to the chain system as a linear force. This torque may be transferred directly or via a system of cantilevers to remove any developing slack from the chain.  
           [0017]    The second, rotating housing sits within the main housing with a close and precisely controlled clearance between the housings. The two housings interact through a series of rigid wall sections which protrude from each housing into the cavity formed between the housings when the housings are joined. These protruding wall sections perform a variety of functions, such as an attachment point for tensioner springs that also are fixed to a wall section of the rotating housing. Thus, the rotation of one housing relative to the other will provide torsional resistance in the device and the spring recoil can be utilized to maintain chain tension.  
           [0018]    The protruding wall sections also create chambers capable of holding pressurized hydraulic fluid. By incorporating fluid conduits into the design, complete with a flow-control mechanism to prevent back flow, such as a check-valve, filling these chambers with a hydraulic fluid will produce a piston-like effect. When opposing chamber walls are formed by the wall sections from the respective housings, pumping a hydraulic fluid into the chamber expands its volume by pressing against the chamber walls, rotating one housing relative to the other. This rotational motion can be translated into a linear force and utilized to maintain chain tension by pins and tensioner arms mounted on the rotating housing.  
           [0019]    In another aspect, compressed springs are combined with the hydraulic fluid chambers to provide a tensioner with the tensioning capabilities of conventional hydraulic tensioner and the reduced size characteristics of torsion spring tensioners. In this aspect, when slack is present in an associated chain system, a reduction in resistance against the arms of the tensioner is transmitted to the rotary actuating tensioner. This reduction in resistance is countered by the internal spring mechanism of the system, which rotates rotary housing to impose force against the chain strands through tensioner arms, restoring the resistance. against the tensioner arms.  
           [0020]    As the springs restore resistance to the system, the volume of the high pressure chambers within the tensioner is concurrently increased as the first housing rotates relative to the second housing. This increase in volume in turn actuates a flow of hydraulic fluid into the chamber to provide resistance to “kickback” against the tensioner by one or more chain strands.  
           [0021]    In the rotating actuating tensioner of the invention, “kickback” forces from the chain are not countered solely by the spring mechanism, but by the hydraulic fluid filled the internal high pressure chambers. When a “kickback” occurs, the force imparted on the rotary tensioner acts to compress the hydraulic fluid and back flow out of the high pressure chamber holding the fluid is limited by a flow control mechanism (e.g., a check valve). The flow control dampens the force of the kickback on the system should the kickback force exceed typical loads, the hydraulic fluid is permitted to exit the tensioner between the first and second housings or through relief valves.  
           [0022]    For similar reasons, the rotary tensioner of the invention reduces the tensioner spring force necessary to restore and maintain the proper chain tension in the system by the use of the hydraulic chambers. Thus, the rotary actuation reduces the need for the tension overload typical of conventional torsion tensioners, and further reduces the need for expensive tensioner wear-face materials and chain operating noise.  
           [0023]    In another aspect, the rotary actuating tensioner of the invention permits the hydraulic fluid to lubricate the spring mechanism within the hydraulic fluid chamber, the fluid lubricates the spring mechanism, increasing its life and preventing corrosion. Similarly, a minimal clearance is required between the housings to allow them to rotate relative to each other, permitting the hydraulic fluid to seep into the movable joint between the housings, lubricating the entire mechanism.  
           [0024]    In yet another aspect, the rotary actuating tensioner incorporates tensioner arms through which the rotary tensioner contacts the chain and maintains tension in the chain system. The tensioner arms come in a variety of designs and is generally located adjacent to one of the strands of the chain. Typically they are formed from an elongated piece of metal, routinely steel, which possesses a flat surface upon which a wear material or “shoe” can be mounted.  
           [0025]    This aspect of the tensioner arm also incorporates at least one pivot joint through which the device communicates with the rotary actuating tensioner. Frequently the tensioner arm will possess a second pivot joint for attachment to a fixed mounting surface, such as an engine block. The pivot joints of the tensioner arm are formed by a hole with a cylindrical sleeve or bushing through which a pivot pin, shaft or bolt is inserted and about which the arm may rotate. The pivot pin also may be attached to an engine or mounting surface, a lever communicating with an actuating tensioner, or the tensioner device itself.  
           [0026]    In another aspect, the rotary actuating tensioner drives several alternative tensioner arm configurations. One alternative is to mount multiple tensioner arms on a single hub. The arms are arranged to contact multiple chain strands, make multiple contacts with a single strand, or a combination of the two. The hub itself is fastened to the rotary actuating tensioner located centrally between the sprockets and chain strands. Rotation of the rotary actuating tensioner simultaneously drives all of the tensioner arms attached to the hub.  
           [0027]    In another alternative aspect, a tensioner arm is mounted on a mounting pin centrally located between the sprockets and chain strands. The pin attachment forms a pivot joint and the hub assembly is driven by a lever attached to a rotary actuating tensioner mounted distally from the center line of the chain system.  
           [0028]    In yet another aspect, the rotary tensioner is mounted along a slack chain path and provides tension to two chain contacts on the slack chain without the use of any lever system. With the rotary tensioner mounted beneath the chain, dual tensioner arms can be secured directly to the rotary housing. These dual arms extend in opposite directions from each other, roughly parallel to the chain path.  
           [0029]    Each such arm has an attached shoe which contacts the chain. The shoe for one arm contacts the chain from the outside of the chain path and imparts tension by displacing the chain path toward the chain assembly center line. The shoe of the other arm contacts the chain on the inside of the chain path and imparts tension by deviating the chain path away from the centerline of the chain system. This orientation allows simple rotation of the rotary tensioner to maintain pressure on the chain at two points. Through the complementary placement of the chain contacts, chain path deviation is kept to a minimum.  
           [0030]    In yet another aspect, the rotary actuating tensioner is centrally located relative to both the sprockets and the chain strands traversing between them. A separate tensioner arm is attached to each of two connection points on the rotary housing through pivot joints. One arm extends toward a slack strand, bearing a shoe which contacts the strand on the side opposite the centerline. The other arm extends toward a tight strand and bears a shoe which contacts the tight strand on the side opposite the centerline. Rotation of the rotary housing pulls the tensioner arms inwards, thereby creating tension by displacing the chain strands toward the centerline of the chain system.  
           [0031]    In another aspect, a tensioner arm set parallel to the slack strand on the outside aspect of the chain assembly. One end of the arm is fixed to a stationary surface, such as an engine block, through a pivot joint. The other end of the arm is attached through a pivot joint to a lever. The lever in turn is attached through a pivot joint to a connecting pin of the rotary actuating tensioner. Through the lever and pivot joint mechanism, the rotary tensioner drives the shoe attached to the tensioner arm against the slack strand of the chain. This pressure deflects the slack strand toward the centerline of the chain system, thereby maintaining tension. The rotary tensioner may be mounted to either side of the arm assembly, as it is equally efficient “pushing” or “pulling” the tensioner arm against the chain. The rotary actuating tensioner also may be positioned such that the lever communicating between the tensioner and the tensioner arm is roughly perpendicular to the shoe face contacting the chain. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    [0032]FIG. 1 is a front view of one aspect of the tensioner system of the present invention.  
         [0033]    [0033]FIG. 2 is a side view of a tensioner arm from the system shown in FIG. 1.  
         [0034]    [0034]FIG. 3 is a second view of the tensioner arm shown in FIG. 2, rotated about 90°.  
         [0035]    [0035]FIG. 4 is a side view of a shoe assembly for the tensioner arm shown in FIG. 2.  
         [0036]    [0036]FIG. 5 is a second view of the shoe assembly for a tensioner arm shown in FIG. 4 rotated about 90°.  
         [0037]    [0037]FIG. 6 is a perspective view of the rotary actuating tensioner from the system shown in FIG. 1, with the tensioner arms removed.  
         [0038]    [0038]FIG. 7 is a partial top plan of the rotary actuating tensioner shown in FIG. 6.  
         [0039]    [0039]FIG. 8 is elevational view of the rotary actuating tensioner shown in FIG. 6.  
         [0040]    [0040]FIG. 9 is a sectional top view of the rotary actuating tensioner through the lines  9 - 9  shown in FIG. 8 indicating the rotary motion of the device and the fluid and air chambers of the tensioner.  
         [0041]    [0041]FIG. 10 is a sectional top plan view of rotary actuating tensioner shown in FIG. 6 indicating the fluid chambers having internal springs and the air chambers of the tensioner.  
         [0042]    [0042]FIG. 11 is a view of the rotary actuating tensioner through line  11 - 11  of FIG. 7 showing the hydraulic fluid inlet and check valve assembly.  
         [0043]    [0043]FIG. 12 is a front view of one aspect of the rotary tensioner system with dual tensioner arms directly attached to the rotary actuating tensioner, and contacting a single chain strand.  
         [0044]    [0044]FIG. 13 is a front view of another aspect of the rotary tensioner system with a single tensioner arm contacting a single chain strand.  
         [0045]    [0045]FIG. 14 is a front view of a prior art single arm torsion spring tensioner device. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0046]    As shown in FIG. 1, an engine timing system  10  is represented generally by crankshaft sprocket  12  (the drive sprocket) and camshaft sprocket  14  (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  16 ( a ) and the path of the chain where the chain has become elongated as shown by the broken lines  16 ( b ). One aspect of the rotary tensioner system of the present invention is shown with a rotary actuating tensioner  18  and two tensioner arms,  20  and  22 .  
         [0047]    In this aspect, the rotary actuating tensioner  18  is located between the strands of the chain  24 ( a ) and  24 ( b ) and between the two sprockets  12  and  14 . The rotary actuator  18  is generally centered with respect to the center line C extending between the center of the drive sprocket  12  and the driven sprocket  14 . The outer housing of the rotary actuating tensioner  18  possesses two mounting tabs  28  and  30  with mounting bores for attachment of the device to the engine block.  
         [0048]    As shown in FIGS. 1 and 6, secured within the tensioner housing  26  is a rotary body  32  which is rotatable around a central pivot point  34 . A first fixed pin  36  and a second fixed pin  38  are disposed near the periphery of the rotating body  32 , on opposite sides of the pivot point  34 . In this aspect, the first  36  and second  38  pins are located equidistant from the center of the pivot point  34 .  
         [0049]    The pins  36  and  38  may be disposed in other positions as may be needed for specific applications. As mentioned above, the pins  36  and  38 , for example, may be positioned at different distances from the pivot point  34 , or may be angularly offset, to impart different forces on the chain strands.  
         [0050]    In the arrangement of FIGS. 1 and 6, the rotation of the rotary body about the pivot point  34  causes the fixed pins  36  and  38  to move equally in a counter clockwise direction, at an angular relation with respect to the center line C. When the pins  36  and  38  are located at differing distances from the pivot point  34 , or are angularly offset, their relative movement with respect to the centerline C will differ and may be different for each pin relative to the other pin.  
         [0051]    As shown in the aspect of FIG. 1, the installed rotary actuator  18  is positioned so that the first fixed pin  36  is positioned below the pivot point  34  and slightly to the left of the centerline C near the chain strand  24 ( a ). The second fixed pin  38  is consequently positioned above the pivot point  34  and slightly to the right of the centerline C.  
         [0052]    The rotary actuating tensioner  18  also carries a first tensioner arm  20  and a second tension arm  22  with attached shoes  40  and  42 . The first arm  20  and second arm  22  are attached to the first fixed pin  36  and second fixed pin  38 , respectively, forming rotating joints between the arms and the fixed pins. The first arm  20  extends outside the strand  24 ( a ) of the chain and carries the shoe  40  with a wear face  44  positioned to contact the outside portion of the chain strand  24 ( a ). The second arm  22  extends outside the strand  24 ( b ) of the chain and carries the shoe  42  with a wear face  46  positioned to contact the outside portion of the chain strand  24 ( b ).  
         [0053]    In operation, when the rotating body  32  of the rotary actuating tensioner  18  moves counter clockwise (in this aspect), the fixed pins  36  and  38  pull the tensioner arms  20  and  22  and attached shoes  40  and  42  toward the chain centerline C and into contact with the outside portions of the chain strands  24 ( a ) and  24 ( b ). As the shoes  40  and  42  are positioned closer to the centerline C, the chain is squeezed or tightened from both sides along both strands  24 ( a ) and  24 ( b ), generally simultaneously. In this manner, this aspect of the tensioner system  10  will potentially provide twice the take up distance in a chain when compared to a conventional tensioner arm acting upon only one strand, for the same amount of relative actuator movement.  
         [0054]    Additionally, the configuration of this aspect of the rotary actuation  18  provides superior dampening of chain vibration by eliminating the need for the previously discussed independent lever mechanisms and by coupling the two tensioner arms  20  and  22  directly to the rotary actuating tensioner  18 . Thus, vibration in a first strand of chain, whether strand  24 ( a ) or  24 ( b ), is transferred and damped by the action of the second strand through the tensioner  18 .  
         [0055]    Referring to the figures to describe the two principle parts of the actuator  18  in greater detail, FIG. 2 depicts one aspect of a tensioner arm  20  in front view. The first and second arms ( 20  and  22  as shown in FIG. 1) are identical in structure but have a different orientation in operation, determined by the direction of chain travel. This aspect of the tensioner arm  20  has an elongated bracket portion  48  with a bore  50 . The bore  50  is slightly offset toward the leading end of the bracket portion  48  of the tensioner arm  20 . More particularly, the bore  50  is offset toward the end of the arm  20  nearest the incoming chain.  
         [0056]    In this aspect, the tensioner arm  20  has a shoe attachment portion  20 ( a ), also shown in FIG. 3, which is oriented perpendicular to the elongated bracket portion  48 . The shoe attachment portion  20 ( a ) has a lengthwise gradual curve to generally match an associated span of chain and a plurality of rectangular openings  20 ( b ) to facilitate the attachment of a shoe  40  to the arm  20 .  
         [0057]    One aspect of the shoe portion  40  of the tensioner system is shown in FIGS. 4 and 5 (the shoe  40  typically is substantially the same as the shoe  42 ). The shoe  40  includes a plurality of clips  40 ( a ) formed on a rear side of the shoe  40  which insert through the rectangular openings in the shoe attachment portion  20 ( a ) of the tensioner arms  20 . In particular, the clips  40 ( a ) engages holes  20 ( b ) shown in FIG. 3. Preferably, a clip  40 ( a ) is formed at each end of the shoe and another clip is formed in an intermediate portion of the shoe. Opposite the rear side of the shoe  40  is a chain contacting wear face  44 , preferably with a flat central face and raised edges  44 ( a ) to form a channel through which the chain travels.  
         [0058]    The aspect of the rotary actuating tensioner  18  shown in FIG. 1 is further illustrated in FIG. 6. The actuator housing  26  is comprised of a flat circular base  52  with a set of the above-mentioned mounting tabs  28  and  30  and a set of fastening tabs  54 . Atop this base sits the ring body  56  which also may have two sets of tabs,  58  (see FIG. 10), which are flush to the bottom edge of the ring body  56  and the second set, tabs  60 , which are flush to the upper edge of the ring body  56 . Tab  58  align with tabs  54  of base  52 . Each set of tabs has a bore  62  through which a fastening device such as a bolt or a rivet may be placed. The main body portion of this aspect is completed by the addition of the retainer ring  64 . The retainer ring  64  also has a set of tabs  66  which align with tabs  60  of the ring body  56 . Intercalated between these sets of tabs are bushings  68 . Thus, each assembly consists of a bushing and two aligned tabs, as well as a common bore  70  through which a fastening device such as a bolt or rivet may be passed.  
         [0059]    The rotary body  32  of the actuator is sized to fit closely within the ring body  56  forming a wholly or partially sealing engagement between the two body portions. The rotary body  32  also is sized to permit the rotational movement of the rotary body  32  within the ring body  56 . A bearing surface  72  is disposed between the retainer ring  64  and the rotary body  32  to facilitate the movement of the rotary body  32  within ring body  56 . Protruding upward from rotary body  32  are connector pins  36  and  38 . In the preferred embodiment, these pins  36  and  38  are jacketed with bushings or sleeves  74  made of a wearable or self-lubricating material, such as plastic.  
         [0060]    The retainer ring  64  secures the rotary body  32  within the ring body  56 . This also is shown in FIG. 7, where the retainer ring  64  is shown overhanging rotating body  32 . As indicated in FIG. 7 by the dashed lines, the outer diameter  76  of rotating body  32  is greater than the inner diameter  78  of retainer ring  64 . However, the inner diameter  78  of retainer ring  64  is not so small as to interfere with the symmetrically placed connector pins  36  and  38 .  
         [0061]    Within rotary actuating tensioner housing  36  are inner chambers and channels within and formed between the assembled ring body  56  and rotary body  32 . As shown in FIGS. 7 and 9, this aspect of the ring body  56  has two inner diameters, a first diameter defined by the wall sections  80  which is generally the same as the rotary body diameter  76 . The ring body further is provided with a second, smaller diameter indicated by the dashed lines  82 . The rotary body  32  similarly has a first diameter that is generally the same as the ring body diameter  82 , as well as the diameter  76  defined by the wall sections  86  extending from the rotary body  32 .  
         [0062]    As indicated in FIGS. 7 and 9, the ring body wall section  84  is sized and positioned to engage the rotary body  32  and in a generally sealing or partially sealing relation. The rotary body wall  86  sections similarly are sized and positioned to engage the ring body walls  80  in a generally sealing or partially sealing relation. The ring body wall sections  84  and rotating body sections  86  further are sized to provide hydraulic chambers  88  and open chambers  90 . The,hydraulic chambers  88  are served by hydraulic lines  92 . The open chambers  90  are provided with vents  94  through the ring body  56 . As shown in FIG. 9, it is readily appreciated that as the chambers  88  are filled with fluid, the rotating body  32  rotates in reducing the size of the open chambers  90 . Any air or other gases or fluids in the open chambers  90  are displaced through the vents  94 .  
         [0063]    The number of hydraulic chambers  88  will depend on the particular application, the hydraulic pressures required for the system, and the space permitted for the tensioner. The open chambers  90  also provide opportunities for substantial weight savings in the rotary body  32 . Such open chambers are not required, and the number, size and use of open chambers will depend on the specific application for the tensioner.  
         [0064]    Centrally located to the assembly is pivot pin  96 . In the aspect shown in the Figures, pivots pin  96  contains a channel  96 ( a ) for feeding hydraulic fluid into the rotary actuating tensioner  18 , through the hydraulic lines  92  which feed chambers  88 . In another aspect, the rotating body  32  can function without the pivot pin  96  where the hydraulic fluid is supplied to the high pressure chambers  88  through other conduit arrangements. Similarly, an alternative pivot elements also may be used depending on the application.  
         [0065]    The rotational movement of rotary body  32  allows the tensioner system  28  to take up slack in the transmission chain strands. This rotational movement is facilitated by a pair of coil springs  98  located in the hydraulic chambers  88 , as shown in FIG. 10. The springs  98  are orientated such that one end is seated on a rotary wall section  86  and the other end of the spring  98  is seated against a rotary body wall section  84  such that, in this aspect, the rotary body  32  is urged in a counterclockwise rotation (which also may be changed to a clockwise rotation by rearrangement of the springs and/or chambers). In operation, as force is exerted against the springs  98 , they are compressed and when slack forms in the transmission chain, the pressure against the tensioners arms  20  and  22  permit the springs  98  and hydraulic chamber  88  to expand to urge the arms  20  and  22  against the chain reducing the slack in the chain, by the rotational movement of the actuator  18 .  
         [0066]    The springs  98  serve a second function in that by expanding the hydraulic chambers  88  and they facilitate the filling of the chambers  88  with hydraulic fluid. To restrict the flow of hydraulic fluid out of the hydraulic chambers  88 , a check valve system is incorporated within the hydraulic system of the rotary actuating tensioner  18 , and specifically in the rotary pin  96  in this aspect. An example of such a check valve system  10  is shown in FIG. 11. In this aspect, hydraulic fluid may enter the pin  96  through channel  102 .  
         [0067]    A stop flow ball  104  (or similar member) is biased against the opening to the channel  102  by the valve spring  106  to effectively seal the opening to the channel  102  and prevent the flow of hydraulic fluid out of the tensioner  18 . When the hydraulic pressure within the tensioner  18  is reduced, for example by the rotation of the rotary body  32  and expansion of hydraulic chambers  88 , the stop flow ball  104  is easily displaced allowing hydraulic fluid to flow into the tensioner  18  through the previously mentioned channel  96 ( a ). As previously discussed, fluid entering through channel  102  may flow freely to chambers  88  via channels  96 ( a ) and lines  92 .  
         [0068]    The unimpeded communication between the hydraulic chambers  88 , the hydraulic channels  92  and the check valve  100  ensures that pressure alterations in the hydraulic chambers  88  are communicated throughout the device. The check valve  100  further prevents backflow of the hydraulic fluid from the tensioner  18 , and the reversal of the direction of the movement of the rotary body  32  is resisted by the trapped fluid, effectively preventing the reverse rotation of the tensioner  18 .  
         [0069]    Thus, the springs and the hydraulic system act synergistically in providing and maintaining chain tensions. The springs  98  cause the tensioner to rotate to take up the initial slack in the chain. This allows the hydraulic system to function at a relatively low pressure, sufficient to allow the free flow of fluid into the expanding chambers  88 . When vibrational forces from the chain work to cause pressure against rotary actuating tensioner  18 , the hydraulic fluid filled chambers  88  and check valve system  100  resists the movement of the rotary body  32 , rather than relying solely on the springs  88 . Consequently, the rotary actuating tensioner  18  does not require excessive spring load as found in the prior tensioners.  
         [0070]    By further promoting this movement of hydraulic fluid, the springs  98  allow the hydraulic system of the rotary actuating tensioner  18  to work at a lower pressure than would otherwise be needed if the hydraulic system were required to drive the rotary actuating tensioner  18 . The mounting of springs  98  in chambers  88  has the additional advantage of lubricating the springs  98  with hydraulic fluid, preventing corrosion and extending the working life of the rotary actuating tensioner  18 .  
         [0071]    In other aspects of the assembly, the springs may be located in the open chamber  90 , with a commensurate change in the dimensions, size, configuration and number of hydraulic chambers  88  and in hydraulic pressure used in the hydraulic chambers  88 . Other spring types, in addition, may be used in the system, such as suitably adapted torsion springs.  
         [0072]    The hydraulic aspect of the tensioner  18  is not a passive component of the present invention, as it permits the rotary body  32  to move in only one direction during operation. This unidirectional aspect is helpful in maintaining tension in the chain, maintaining the position of the chain strand, dampening chain vibration and prevent timing faults or other failures of the engine. As depicted in FIG. 10, this direction is counter clockwise M in the above-mentioned aspect of the tensioner system  18 . Its direction may be reversed in other applications.  
         [0073]    In one example, the actuating tensioner  18  may be used to replace a torsion spring rotary actuator for a power transmission chain system. In such systems, the prior, torsion spring actuators typically required torsion springs with a high spring force to impart the desired degree of position control of the chain. The rotary actuator  18 , in one aspect, may be provided with hydraulic chambers  88  with dimensions and clearances sufficient to provide suitable chain tension and control of the position of the chain strand when supplied with hydraulic fluid pressures typical of an engine oiling system. The hydraulic leakage in the tensioner is controlled sufficiently to react against high chain loads while not imparting high loads on the chain as would be required by a non-hydraulic, spring tensioner.  
         [0074]    It will be readily apparent to those skilled in the art that the above described aspect is but one possible application for the present rotating tensioner  18 . Other aspects, modifications and embodiments employing the principles of this invention, particularly upon considering the foregoing teachings, also may be used in other applications.  
         [0075]    For example, the design of the rotary tensioner  18  offers the ability to incorporate multiple connecting points for lever mechanisms driving chain contacts. As noted for the above aspect of the tensioner  18 , contacts on multiple chains are advantageous because the amount of movement required from the tensioner to take up any resulting slack in the system is minimized. Moreover, deviation of the chain from its original path as slack is taken up also is minimized to prevent potential interference of the mechanism with other engine components, and to minimize stress on the chain itself by limiting movement between the links as the chain traverses its path.  
         [0076]    Similar advantages can be achieved by designs which make multiple contacts with a single chain strand. The aspect of the tensioner shown in FIG. 12 illustrates such a design where an alternative aspect of the rotary tensioner  118  is mounted midway along and centered beneath the chain path to allow the tensioner  118  two chain contacts on a slack strand without the use of a lever system. In FIG. 12, an engine timing system is represented generally as described for FIG. 1, above. The path of the power transmission chain is represented generally by broken line  116 . The altered path of the chain due to wear is represented by broken lines  116 ( a ). With rotary tensioner  118  mounted beneath the strand S, dual tensioner arms  120  and  122  can be secured directly to the rotary body tensioner  118 .  
         [0077]    The dual arms  120  and  122  extend in opposite directions from each other, roughly parallel to strand S. Each arm consists of an elongated shoe mount  120 ( a ) and  122 ( a ) carrying an attached shoe  140  and  142  which contacts strand S. Shoe  140  of first arm  120  contacts strand S from inside chain path  116 , and shoe  142  of second arm  120  contacts strand S from outside chain path  116 . The tensioner arms  120  and  122  of this aspect may be interconnected and attached to rotary actuating tensioner  118  via connector pins  136  and  138 . This orientation allows simple rotation of rotary actuating tensioner  118  to maintain pressure on strand S at two points, minimizing chain path  116 ( a ) deviation and the amount of tensioner movement required to impart tension in chain  116 .  
         [0078]    In addition to supporting multiple chain contacts, the rotary actuating tensioner also can form part of another alternative tensioner systems. The aspect  210  shown in FIG. 13 illustrates an alternative, tensioner utilizing a pivoting arm. As in FIG. 12, an engine timing system is represented generally as described for FIG. 1. The path of the power transmission chain is represented generally by the triple line  216 . The altered path of the chain due to wear is represented by the broken line  216 ( a ). The tensioner system  210  of FIG. 13 is comprised of a rotary actuating tensioner  218 , a lever mechanism  222  and a single tensioner arm  220 . The rotary actuating tensioner  218  is as described above. The tensioner arm  220  is generally similar to the tensioner arm  20  described above for the aspect of the tensioner  18 . The arm  220  has an elongated bracket portion  220 ( b ) with a bore  250  set distally to one end. The bore  250  contains a bushing  252  and is fixed to a pin  254  located on the engine block such that the tensioner arm  220  lies in a generally parallel relation to the chain strand S. The arm  220  has a shoe attachment which is orientated perpendicular to the elongated bracket portion  220 ( b ). The arm shoe attachment portion  220 ( a ) has a lengthwise gradual cure to generally match the associated span of chain. The shoe attachment portion  220 ( a ) carries a shoe  240  composed of a wear face material which contacts the chain as described for the shoe  40  mentioned above.  
         [0079]    In this aspect, the rotary actuating tensioner  218  is located below the chain strands and the tensioner arm  220  and is mounted by tabs  230  and  232  to the engine block. The tensioner  218  communicates with the tensioner arm  220  via lever mechanism  222  which, in this aspect, is a rigid bar containing bore holes  222 ( a ) and  222 ( b ) at either end. The lever bore  222 ( a ) is sized to accept the pin  236  of the tensioner arm  218  to form a pivoting connection. The lever base  222 ( b ) similarly is sized to accept a pin  256  on the arm  220  to form a pivoting connection with the arm  220 . As a result, when the tensioner rotates, as discussed above, in the direction M the tensioner urges the lever  222  towards the arm  220  to press the shoe  240  into the chain strand to increase the chain tension and remove slack from the chain.  
         [0080]    While several embodiments of the invention have been illustrated, it will be understood that the invention is not limited to these embodiments.