Abstract:
A tensioner comprising a base, a shaft connected to the base, an eccentric adjuster coaxially engaged with the shaft, an arm pivotally engaged with the shaft, a pulley journalled to the arm, a torsion spring engaged between the arm and the base, the arm comprising a first receiving portion and a second receiving portion disposed axially opposite from the first receiving portion, a first damping member disposed between the arm and the base, the first damping member frictionally engaged with the base and engaged with first receiving portion, a second damping member disposed between the arm and the eccentric adjuster having a member engaged with the second receiving portion, and a biasing member disposed between the first damping member and the arm for applying a normal force to the first damping member and to the second damping member.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a tensioner, and more particularly, a tensioner having a first damping member and a second damping member cooperatively connected to allow a relative axial movement and a compressive member disposed therebetween urging apart the first damping member and the second damping member. 
       BACKGROUND OF THE INVENTION 
       [0002]    The two most common methods synchronously driving rotating members such as cam shafts and balance shafts from a crankshaft are timing chains and belts. Timing chains require engine oil to operate. In comparison most timing belt applications require that no oil be present in the belt drive as the presence of oil can damage the belt and inhibit its intended purpose. Recent improvements in belts no long require that a belt be isolated from the engine oil environment. 
         [0003]    The recent improvement of belts to operate in oil, however poses other problems that need to be solved. One specific problem is properly tensioning the belt drive to keep the camshaft synchronized with the crankshaft. Should the camshaft or other synchronized driven crankshaft component loose synchronization with the crankshaft catastrophic engine damage can result. 
         [0004]    To transmit power through the belt from the rotating crankshaft one side of the belt is pulled around the crankshaft and is commonly referred to as the belt tight side by those skilled in the art. Conversely the other side is referred to as the belt slack side, since the belt is being “pushed” away from the crankshaft. It is important to provide tensioning to the slack side of the belt to prevent the belt from becoming unduly slack and thus causing a loss of synchronization between the crankshaft and the components rotated by the crankshaft. This loss of synchronization is commonly referred to as “tooth jump” or “ratcheting” by those skilled in the art. 
         [0005]    Compounding the problem of eliminating belt slack to prevent tooth jump or ratcheting is excessive tensioner arm motion or vibration induced by the engine&#39;s angular vibration. Excessive arm motion could not only lead to a tooth jump or ratcheting condition, but can also reduce the useful life of the tensioner and the belt as well. To minimize the amount of arm vibration friction damping is commonly used to prevent the tensioner from moving away from the belt. 
         [0006]    The presence of oil makes friction damping difficult to achieve. Application of a lubricant to two rubbing surfaces will allow relative motion between the two surfaces to occur more easily. 
         [0007]    Representative of the art is U.S. Pat. No. 7,951,030 which discloses a tensioner comprising a base, an arm pivotally engaged with the base, a pulley journalled to the arm, a torsion spring engaged between the arm and the base, the base comprising a cantilever leaf spring, a first friction disk operationally disposed between the cantilever leaf spring and the arm, the cantilever leaf spring biasing the first friction disk into frictional contact with the arm, the first friction disk rotationally fixed with respect to the base, a second friction disk rotationally fixed with respect to the base, a separator member disposed between the first friction disk and the second friction disk, the first friction disk and the second friction disk each having a wet coefficient of friction of approximately 0.12, and the separator member rotationally fixed with respect to the arm. 
         [0008]    What is needed is a tensioner having a first damping member and a second damping member cooperatively connected to allow a relative axial movement and a compressive member disposed therebetween urging apart the first damping member and the second damping member. The present invention meets this need. 
       SUMMARY OF THE INVENTION 
       [0009]    The primary aspect of the invention is to provide a tensioner having a first damping member and a second damping member cooperatively connected to allow a relative axial movement and a compressive member disposed therebetween urging apart the first damping member and the second damping member. 
         [0010]    Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
         [0011]    The invention comprises a tensioner comprising a base, a shaft connected to the base, an eccentric adjuster coaxially engaged with the shaft, an arm pivotally engaged with the shaft, a pulley journalled to the arm, a torsion spring engaged between the arm and the base, the arm comprising a first receiving portion and a second receiving portion disposed axially opposite from the first receiving portion, a first damping member disposed between the arm and the base, the first damping member frictionally engaged with the base and engaged with first receiving portion, a second damping member disposed between the arm and the eccentric adjuster having a member engaged with the second receiving portion, and a biasing member disposed between the first damping member and the arm for applying a normal force to the first damping member and to the second damping member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
           [0013]      FIG. 1  is a cross-sectional view of the tensioner. 
           [0014]      FIG. 2  is an exploded view of the tensioner. 
           [0015]      FIG. 2   b  is a side view of the wave spring. 
           [0016]      FIG. 3  is an exploded view of the tensioner. 
           [0017]      FIG. 4  is a cross-sectional view of an alternate embodiment. 
           [0018]      FIG. 5  is an exploded view of the alternate embodiment in  FIG. 4 . 
           [0019]      FIG. 6  is a chart illustrating the spring rate (k) as a function of spring height. 
           [0020]      FIG. 7  is a detail of the retainer and adjuster. 
           [0021]      FIG. 8  is a detail of the retainer on the adjuster. 
           [0022]      FIG. 9  is a detail of the assembled shaft and adjuster. 
           [0023]      FIG. 10  is a detail of the retainer in  FIG. 7 . 
           [0024]      FIG. 11  is a cross sectional view of the shaft. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]      FIG. 1  is a cross-sectional view of the tensioner. Tensioner  100  comprises a pulley  7  which engages a belt (not shown) to thereby provide a belt tension or load. Pulley  7  is journalled to arm  6  with a bearing  11 . Pulley is engaged with the bearing outer race. Bearing  11  comprises a ball bearing as shown, but could also comprise a needle bearing or other suitable bearing known in the art. 
         [0026]    Arm  6  is biased by torsion spring  3  thereby urging a pulley  7  into engagement with a belt which applies a tensile load to the belt. Torsion spring  3  is operationally disposed between base  1  and arm  6 . 
         [0027]    Arm  6  pivots about shaft  2 . Pivotal movement of arm  6  allows the tensioner to compensate for any changes in belt length as the belt stretches over time and as the drive length changes from thermal expansion. Arm  6  pivots about a low-friction bushing  10  about shaft  2 . Shaft  2  is press fit into base  1  and extends normally from base  1 . 
         [0028]    Eccentric adjuster  8  is also press fit to the end of shaft  2  opposite base  1 . Eccentric adjuster  8  is used to rotate the tensioner into proper engagement with the belt during installation. Eccentric refers to the center of hole  21  not being coaxial with a center of rotation of pulley  7  or of arm  6 . Eccentric adjuster  8  is used to properly load the belt with a predefined tension by compensating for all component and system tolerances. A tool (not shown) engages the adjuster at tool receiving portion  82 . Eccentric adjuster  8  is used only during belt installation. It is locked in place once the belt is installed by fully engaging a fastener inserted through a hole  21 ,  81  into a mounting surface. 
         [0029]    To minimize the amount of arm oscillation or movement during operation friction damping is used. Excessive arm motion induced by the engine vibration could cause the belt to jump a tooth or “ratchet”. Tooth jump or ratcheting of the belt causes a loss of synchronization between the driven and driving shaft(s) of the belt. 
         [0030]    Wave spring  5  is disposed between damping member  13  and arm  6 . Wave spring  5  imparts a normal force upon damping member  13 . Damping member  13  bears frictionally upon base  1 , thereby damping an oscillation of arm  6 . Damping member  13  is generally a toroid in shape, but may also be disk shaped. Torsion spring  3  is compressed between arm  6  and pad  12 . Pad  12  is mechanically engaged with base  1  wherein tangs  120  engage each side of a tab  41 . Being thus engaged pad  12  is constrained against rotation relative to base  1 . 
         [0031]      FIG. 2  is an exploded view of the tensioner. Damping member  13  creates friction damping between arm  6  and base  1 . Damping disk  9  is also used to create friction damping between arm  6  and eccentric adjuster  8 . Frictional surface engages eccentric adjuster  8 . Damping member  13  and damping disk  9  are disposed on axially opposite ends of arm  6 . 
         [0032]    Damping member  13  and damping disk  9  each move rotationally with arm  6 , while base  1  and eccentric adjuster  8  are fixed to the mounting surface, such as an engine (not shown). Pulley surface  71  may be flat, multi-ribbed or toothed to accommodate a suitable belt. 
         [0033]    An end  31  of spring  3  engages tab  41 , wherein tab  41  acts as a reaction point on base  1 . The other end  32  of spring  3  engages arm  6 . 
         [0034]    Rotation of arm  6  is limited by stops  63  coming into contact with a tab  41 . 
         [0035]      FIG. 2   b  is a side view of the wave spring. The wave spring comprises multiple coils  51 . Each coil comprises undulations wherein each coil comes into contact with an adjacent coil at a limited number of locations approximately 120° apart. This description is not intended to limit the coil design of the spring. Each spring may have more or fewer undulations per coil depending on design requirements. It may also comprise one or more coils. In an alternate embodiment the wave spring comprises only one coil with ends joined. 
         [0036]      FIG. 3  is an exploded view of the tensioner. Torque from arm  6  is transferred through keyway  61  to tab  130  thereby causing damping member  13  to move in locked unison with arm  6 . Keyway  61  is disposed at an axial end of arm  6 . Base  1  comprises tabs  41  (three are shown) which extend in a substantially axial direction. 
         [0037]    Torque from arm  6  is transferred through keyways  62 . Keyways  62  are disposed at an axial end of arm  6  opposite keyway  61 . Damping disk  9  comprises a tab  91  which extends in the axial direction. Tab  91  engages a keyway  62 . Rotation of arm  6  causes locked rotation of damping disk  9  through interaction of keyway  62  and tab  91 . 
         [0038]    Damping member  13  and damping disk  9  are loaded normally by compression of wave spring  5  thereby creating normal force friction. This arrangement compensates for wear and assembly tolerances. Wave spring  5  is captured between damping member  13  and arm  6  in a receiving portion  63 . Spring  5  rotates with arm  6  ensuring that relative motion only occurs between damping member  13  and base  1 , as well as only between damping disk  9  and eccentric adjuster  8 . 
         [0039]    Spring  5  is shown as a wave spring which is preferred due to its spring rate characteristic and area of surface contact.  FIG. 2   b  is a side view of the wave spring. In this embodiment spring  5  comprises multiple coils or volutes, each having a wave profile. This allows suitable control of the axial (or normal) force relative to the tolerances of the tensioner assembly. The force of the wave spring in combination with the compression of torsion spring  3 , and further in conjunction with the coefficient of friction of mating parts determines the damping level of the tensioner assembly. In alternate embodiments spring  5  may comprise a single coil wave spring. 
         [0040]    The coefficient of friction of the various mating parts is as follows: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Part 
                 CoF 
               
               
                   
                   
               
             
             
               
                   
                 Damping member 13 against base 1 
                 ≦0.4 
               
               
                   
                 Damping disk 9 against adjuster 8 
                 ≦0.4 
               
               
                   
                 Damping disk 18 against base 11 
                 ≦0.4 
               
               
                   
                 Damping disk 19 against arm 20 
                 ≦0.4 
               
               
                   
                   
               
             
          
         
       
     
         [0041]    Damping member  13  and damping disk  9  may comprise any known frictional material used in a tensioner damping application, including oil resistant metals and polymers. Alternate embodiments may produce sufficient axial force by use of the torsion spring  3  in compression without use of the wave spring.  FIG. 6  is a chart illustrating the spring rate (k) as a function of spring height. Total compression is indicated for each spring type, namely, spring washer, wave spring and compression or torsion spring. 
         [0042]      FIG. 4  is a cross-sectional view of an alternate embodiment.  FIG. 5  is an exploded view of the alternate embodiment in  FIG. 4 .  FIGS. 4 and 5  describe an alternate embodiment where a spring loads two damping disks,  18 ,  19 , that are fixed to rotate together thereby preventing the need to fix the damping disks to the arm  20  to be dampened. Damping disk  18  is in frictional contact with a static component, base  11 , and the damping disk  19  is in frictional contact with the moving member, arm  20 , to dampen the movement of the arm  20 . 
         [0043]    Eccentric adjuster  15  is an eccentric that is used to move the tensioner into proper engagement with the belt during installation. Eccentric refers to the center of hole  150  not being coaxial with a center of rotation of pulley  14  or of arm  12 . Eccentric adjuster  15  is used to load the belt with a predetermined tension. Eccentric adjuster  15  is used only during belt installation and is locked in place once the belt is installed by fully engaging a fastener (not shown) through a hole  150  with a mounting surface. The fastener may comprise a bolt or any other suitable fastener known in the art. 
         [0044]    Pulley  14  engages a belt to provide belt tension or load. Pulley  14  is journalled to arm  20  about a bearing  141 , Pulley  14  is engaged with the bearing outer race. Bearing  141  comprises a ball bearing as shown, but could also comprise a needle bearing or other suitable bearing known in the art. 
         [0045]    Arm  20  is biased by torsion spring  13  thereby urging pulley  14  into a belt (not shown). Pivotal movement of arm allows the tensioner to compensate for any changes in belt length as the belt stretches over time and as the drive length changes from thermal expansion or as engine load and therefor belt load changes. Arm  20  pivots about a low-friction bushing  16  on shaft  12 . Shaft  12  is fixed to base  1 . 
         [0046]    Motion of arm  20  is damped by frictional contact with damping disk  19 . Damping disk  19  is pressed into arm  20  by O-ring  17 . O-Ring  17  comprises an elastomeric material and is used as a compressible resilient member to apply a normal force to damping disk  19  and damping disk  18 . O-Ring  17  could be replaced by a wave spring, a compression spring, a Belleville spring, or other compressible resilient member having spring characteristics known in the art. Damping disk  18  is pressed by O-Ring  17  into base  11 . Base  11  is fixed to a mounting surface such as an engine (not shown). Frictional surface  193  engages arm  20 . Frictional surface  183  engages base  11 . Damping is created by the resistant torque created by the frictional force of the contact between damping disk  18  and base  11 , and damping disk  19  and arm  20 . 
         [0047]    Each tab  181  on damping disk  18  fits between two cooperating lug(s)  191  on damping disk  19 . This arrangement fixes damping disk  18  and damping disk  19  so there is no relative rotation between the two but allows movement between these two components in the axial direction. Movement in the axial direction allows O-Ring  17  to apply a preload force to both damping disks  18 ,  19  and to compensate for manufacturing tolerances and wear. A lip  182  on each tab  181  engages a cooperating rim  192  on damping disk  19  to limit the relative axial movement of the damping disks  18 ,  19  by locking them together. 
         [0048]    The assembly of damping disk  18  and damping disk  19  “floats” between the arm  20  and base  11 . Neither damping disk  18  nor damping disk  19  are rotationally fixed to base  11  or arm  20 . 
         [0049]    Retainer  21  holds the assembly together axially. Retainer  21  is fixed to eccentric adjuster  15  and engages shaft  12  to hold the assembly axially. 
         [0050]      FIG. 7  is a detail of the retainer and adjuster. Retainer  21  holds the assembly together when the tensioner is not mounted to an engine. Retainer  21  is attached to adjuster  15  by engagement of posts  151  and holes  211  and prongs  212 . The two posts  151  prevent retainer  21  from rotating and prongs  212  retain retainer  21  on posts  151 .  FIG. 10  is a detail of the retainer in  FIG. 7 . 
         [0051]      FIG. 8  is a detail of the retainer on the adjuster. The sub-assembly of retainer  21  and adjuster  15  is inserted into shaft  12 . Tabs  213  are resiliently bent inward during assembly to allow retainer  21  to pass through the bore of shaft  12 . Receiving portions  152  provide a space into which tabs  213  are bent. A circumferential groove  121  in shaft  12  allows tabs  213  to resiliently expand outward to lockingly engage shaft  12 .  FIG. 9  is a detail of the assembled shaft and adjuster. Relative axial movement of adjuster  15  and shaft  12  is restricted by interaction between the wall of groove  121  and the radially expanded tabs  213 .  FIG. 11  is a cross sectional view of the shaft. 
         [0052]    Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts and method without departing from the spirit and scope of the invention described herein.