Abstract:
A closed loop chain tensioner system having a drive sprocket, one or more driven sprockets, a first mechanical tensioner located adjacent a slack strand and a second mechanical tensioner located adjacent a tight strand. Each tensioner is independently pivotally mounted to the engine block. The mounting point may be located at any point along the length of each tensioner. The tensioners are then linked to each other by a rigid, solid link. This solid link enables the tensioners to act in unison, thus providing damping across both strands of chain in response to engine torsional variations.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is related to an application filed simultaneously, entitled, “LONG MECHANICAL TENSIONER WITH A COMPLIANT BLADE SPRING”. The aforementioned application is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention pertains to the field of chain tensioners. More particularly, the invention pertains to a tensioner that has damping.  
         [0004]     2. Description of Related Art  
         [0005]     A tensioning device, is used as a control device for a power transmission chain, or similar power transmission devices, as the chain travels between a plurality of sprockets. In this device, 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 in the chain to prevent noise, slippage, or the unmeshing of teeth 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 jumping of teeth will throw off the camshaft timing, possibly causing damage or rendering the engine inoperative.  
         [0006]     However, in the harsh environment of an internal combustion engine, various factors can cause fluctuations in the chain tension. For instance, wide variations in temperature and thermal expansion coefficients among the various parts of the engine can cause the chain tension to vary between excessively high or low levels. During prolonged use, wear to the components of the power transmission system can cause a decrease in chain tension. In addition, camshaft and crankshaft induced torsional vibrations cause considerable variations in chain tensions. Reverse rotation of an engine, occurring for example during the stopping of the engine or in failed attempts at starting, can also cause fluctuations in chain tension. For these reasons, a mechanism is desired to remove excessive tensioning forces on the tight side of the chain and to ensure the necessary tension on the slack side of the chain.  
         [0007]     Blade tensioners are tensioners that are commonly used to control a chain or belt where load fluctuations are not so severe as to over flex the spring or springs. A ratchet with backlash is often added to tensioners to limit the effective backward or untensioned travel of a tensioning device.  
         [0008]      FIG. 1  shows a prior art chain driving system having a blade tensioner and a guide. A closed loop chain encircles driving sprocket  12  and driven sprocket  10 . Each sprocket  10 ,  12  accelerates and decelerates independently while maintaining forward motion. A fixed guide  14  is attached to a bracket  7  on the tight strand of the chain  8 . Opposite the guide  14  on the slack strand of the chain is a tensioner  16 , which is at least semi-rigidly fixed to the bracket  7  and biased towards the tight strand of the chain. Bolts  18  fasten the bracket containing the tensioner  16  and the guide  14  to the engine block (not shown).  
         [0009]     When the driving sprocket  12  accelerates or the driven sprocket  10  decelerates, an energy wave or high local load is created in the tight strand of the chain, which travels from the sprocket that changed in velocity toward the other sprocket. The chain  8  attempts to span the distance between the link of the chain in contact with the initiating sprocket to the other sprocket in the shortest possible distance, a straight line. The energy moves through the links on the free strand of the chain until it comes to the end of the guide  14 , which absorbs the energy. As a result of the constant absorption of the high local load, the ends of the guide  14  sustain significant wear. The energy wave would be present and show the same characteristics if it was to originate on the slack strand of the chain, although the wave energy may not occur at all depending on how well the tensioner keeps the slack out of the chain and how much damping the tensioner has.  
         [0010]     One solution to reduce the load that results in the prior art chain driving system is to add damping to the tensioner. One problem associated with adding the required damping to a tensioner is that if the tensioner is softened significantly, it may result in a loss of chain control, since tensioners are specifically designed to apply just enough force to provide adequate chain control. Other solutions are shown in U.S. Pat. Nos. 5,797,818, and 6,322,470, as well as US Publication Nos. 2002/0045503 and 2005/0085322.  
         [0011]     U.S. Pat. No. 5,797,818 discloses a chain assembly with reduced noise and vibration on the slack side of the chain that includes a blade shoe, a spring, and a resilient damping device. The shoe is pivotally mounted to the tensioner bracket. The spring is mounted to the shoe and biases the shoe towards the chain. The resilient damping device is mounted between the tensioner bracket and the spring to aid in controlling the vibration that occurs during valve events.  
         [0012]     U.S. Pat. No. 6,322,470 discloses a tensioner that includes a pair of pivoting arms used to simultaneously tension two separate strands of the same chain. A lever with fixed pins is located between the two strands. The arms extend outside the strands of the chain and carry shoes positioned to contact the outside portion of the chain which are pivotally mounted to the fixed pins. Rotation of the lever causes the fixed pins to move laterally and the arms draw inward and tension is imparted to the separate chain strands at the same time. In other words, a high load on one side of the chain tries to transfer to the other side of the chain but the load eventually evens out.  
         [0013]     US Publication No. 2002/0045503 discloses a chain tensioner that has a blade and spring assembly. The blade has a first end and a second end. The first end defines a hub. The hub is connected to the central portion of the blade shoe and a first end wall and defines a bore that receives a single pin that pivotably connects the blade to a mounting bracket.  
         [0014]      FIG. 2  shows the pivoting chain guide and tensioner assembly of US Publication No. 2005/0085322. It consists of a chain guide  124  and a tensioner each in contact with one of the two strands of a closed loop chain  108  in a dual sprocket chain system, the chain  108  being routed around a drive sprocket  112  and a driven sprocket  110 . The tensioner and chain guide are both connected to a bracket plate  122  which pivots about a single mounting point  120 .  
         [0015]     As shown in  FIG. 3 , a conventional chain tensioning system consists of two independently functional blade spring tensioners  306  and  306   a  that are located on each of the two strands of chain  300 . These separately functional tensioners each include a bracket body  307 ,  307   a,  which each contain chain guides  308  and  308   a.  Within each bracket body  307  and  307   a  are at least one blade spring, identified as  510  (see  FIG. 4 ) to urge chain guides  308  and  308   a  into forcible contact with the strands of chain  300  to which each mechanical spring tensioner  306  and  306   a  are adjacent. In this conventional system, each mechanical spring tensioner operates independently of the other. Each mechanical spring tensioner is securely mounted to the engine block, not shown, by securing means  312 , which may be, for example bolts or press fit pins. The only motion provided to adjust the tension between the slack and tight strand of chain  300  comes from the blade springs.  
       SUMMARY OF THE INVENTION  
       [0016]     The present invention comprises a power transmission system having a drive sprocket, one or more driven sprockets, a first mechanical tensioner located adjacent the slack strand and a second mechanical tensioner located adjacent the tight strand. Each mechanical tensioner may provide slack control by use of compliant blade springs.  
         [0017]     Each tensioner is pivotally secured to the engine block by separate mounting means. The tensioners are then linked to each other by a rigid, solid link which enables the tensioners to act in unison to control the backward and forward articulation of the chain between tight and slack conditions, thus providing damping across both strands of chain. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  shows a schematic of a prior art chain tensioner system having a securely mounted common bracket.  
         [0019]      FIG. 2  shows a schematic of a chain tensioner system having a single centrally mounted pivot point.  
         [0020]      FIG. 3  shows a schematic of independently functioning dual tensioners.  
         [0021]      FIG. 4  shows a cut away section of a conventional blade tensioner.  
         [0022]      FIG. 5  shows a chain guide for use in the tensioner of  FIG. 4 .  
         [0023]      FIG. 6  shows a front perspective view of the interconnected dual tensioner system of the present invention.  
         [0024]      FIG. 7  shows an isometric view of the dual tensioner system of the present invention with one of the mechanical blade spring tensioners removed to show the pivot mount and securing means for the rigid link.  
         [0025]      FIG. 8  shows a second embodiment of the present invention.  
         [0026]      FIG. 9  shows a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     The present invention, as shown in  FIGS. 6 and 7 , comprises a continuous chain loop drive system having a chain  500 , a drive sprocket  502 , one or more driven sprockets  504 ,  504   a  and a pair of mechanical tensioners  506 ,  506   a.  The mechanical tensioners each consist of a bracket body  507  and  507   a,  and respective chain guide elements  508  and  508   a  each having a chain sliding face  509 ,  509   a  ( FIG. 5 ). The chain sliding faces  509  and  509   a  are in slidable contact with the strand of chain  500  to which each mechanical tensioner is adjacent.  
         [0028]     Springs, generally identified as  510  ( FIG. 4 ), may provide the force needed to urge each of the chain guide elements  508  and  508   a  into forcible sliding contact with the chain  500 . Blade spring  510  is an elongated rectangle curled lengthwise in its free state. Within the preferred tensioner shown in  FIG. 4  the blade spring  510  exerts a force onto the underside of support member  505 , which is also an elongated rectangular structure that is made from any material that will enable it to provide spring tension. The primary force urging the chain guide elements  508  and  508   a  toward their respective strands of chain comes from blade spring  510 . The spring tension provided by the support member  505  need only be sufficient to transfer the force of the blade spring  510  substantially equally along the length of the chain guide elements  508  and  508   a.    
         [0029]     Each of the mechanical tensioners  506  and  506   a,  is secured to the engine block, not shown, by a single mounting means, such as a bolt, screw or press fit pivot pin, generally identified as  512  and  512   a,  respectively. In a first embodiment, as shown in  FIG. 6 , the mounting means provide a pivot point for its respective mechanical tensioner and is positioned at approximately the same corresponding location along the length of each mechanical tensioner. The mounting means  512  and  512   a  are shown as being located at a first end of each mechanical tensioner that is closest to the drive sprocket  502 . The mounting means may also be located at other points along the length of each mechanical tensioner  506 ,  506   a,  such as at any point along the length of each bracket body  507  and  507   a.  One alternate location for mounting means is shown in  FIG. 6  at  512   c  and  512   d.    
         [0030]     Positioned at the respective second ends of each of the bracket bodies  507  and  507   a,  as shown in  FIG. 6 , are pivot means  514  and  514   a,  respectively. Each pivot means  514  and  514   a  is secured to the second end of its respective bracket body  507  and  507   a  by locking means  515 ,  515   a,  respectively, or the like, or by a pin that is press fit into a hole in each bracket body  507  and  507   a.  One end of a solid rigid linking member  516  is attached to each pivot means  514  and  514   a,  thus coordinating the movements of the respective second ends of the mechanical tensioners  506  and  506   a.    
         [0031]      FIG. 7  shows an isometric view of the chain tensioner of  FIG. 6  with one of the mechanical tensioners  506  removed to show in more detail the mounting means  512  and the pivot means  514 .  
         [0032]     When the drive sprocket  502  or at least one of the driven sprockets  504 ,  504   a  decelerates, the strand of chain  500  (for purposes of this example, the tight strand) will attempt to span the distance between the link of the chain in contact with the initiating sprocket to the other sprocket in the shortest distance possible, namely, a straight line. The specific movement of the chain  500  is not shown. This energy wave or high local load will force the end of the respective mechanical tensioner, in this example  506 , at the pivot means  514  away from the chain  500 . The end of the mechanical tensioner secured by the mounting means  512  remains pivotally fixed to the engine.  
         [0033]     Concurrently, as the one strand is tightening, the opposite strand is becoming slack. However, due to the attachment of the linking member  516  to the opposite mechanical tensioner, in this case  506   a,  the linking member  516  will pull the end of mechanical tensioner  506   a  toward the slack strand of chain  500 , thus substantially tensioning the slack strand.  
         [0034]     The linking of the movements of the slack and tight strands provides for a degree of forgiveness in the cyclical tensioning and slackening of each of the strands of chain with respect to each other. By linking the relative movements of each of the strands, a damping effect occurs. The vibrations and torsional impulses experienced by one of the strands is substantially neutralized by linking this energy to the generally opposing energy impulse experienced by the opposite strand.  
         [0035]     As described hereinabove, the mounting means.  512  and  512   a  for each mechanical tensioner  506  and  506   a  may be located at the ends of both mechanical tensioners nearest to the drive sprocket  502 , for convenience, identified herein as their respective first ends. As further disclosed above, the mounting means may be located at any point along the length of each bracket body  507  and  507   a,  as dictated by design preferences. Many variables within the entire chain drive system may lead to different locations for, not only the mounting means  512 ,  512   a,  but also the pivot means  514 ,  514   a  and for linking member  516 .  
         [0036]     As shown in  FIG. 8 , different functional parameters and design requirements may necessitate locating the linking member  516  at a second end of each of the mechanical tensioners  506 ,  506   a  nearest the drive sprocket  502 . In this second embodiment, the first ends of each of the mechanical tensioners are securely mounted to the engine block, via mounting means  512  and  512   a  and are located adjacent to the drive sprockets, not shown.  
         [0037]     A third embodiment is shown in  FIG. 9 . In this embodiment, the first end  516   a  of the linking member  516  is pivotally secured to the end of the first tensioner  506   a  opposite the end of the first tensioner that is secured to the engine housing, not shown, by mounting means  512   a.  The second end  516   b  of the linking member  516  is pivotally secured at an approximate mid point along the length of second tensioner  506  by pivot means  514 .  
         [0038]     The blade spring  510  shown in  FIG. 4  is indicated as being of a much shorter length than chain guide  508 . It is within the contemplation of this invention, however, that other blade spring configurations may be used, such as those consisting of a blade spring substantially the entire length of chain guide  508 . Also, multiple short blade springs  510  may be located in series along the length of the bracket body  507 .  
         [0039]     Furthermore, the strength capabilities of each blade spring  510  in each of the mechanical tensioners  506  and  506   a,  may be the same or different. If a weaker spring is provided within the first tensioner (for example,  506 ), relative to the spring within the second tensioner ( 506   a ), all of the slack chain control is transferred to the second tensioner  506   a  by the linking member  516 . In this configuration, the first tensioner  506  acts as a guide having the capability to follow an uncontrolled chain  500  from its normal path, thus providing improved damping.  
         [0040]     In addition, the tensioners  506  and  506   a  may either be of the same length or of different lengths, as required by the design parameters of the power transmission chain system into which the tensioning device of the present invention is installed.  
         [0041]     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.