Abstract:
A chain tensioner comprising a support member configured to support a stop bar for axial movement. A ratchet engages the support bar and is configured to permit axial movement of the stop bar in a first direction and prevent axial movement of the stop bar in a second, opposite direction. A shuttle assembly including a tensioning wheel is interconnected to the stop bar such that the shuttle assembly is axially moveable relative to the stop bar over a limited range of motion. A biasing member is configured to bias the shuttle assembly in the second direction.

Description:
BACKGROUND  
       [0001]     The present invention relates to a chain tensioner. More particularly, the present invention relates to a chain tensioner that automatically adjusts the slack in a drive chain as the chain stretches over its design life.  
         [0002]     In a drive chain system where power is transferred from one sprocket to another via a chain it is desired to maintain a specific range of slack in the chain in order to prevent excessive static loading of the sprocket support bearings via an overly tight adjustment, and to minimize noise and limit backlash in the chain system due to an overly loose adjustment. As the chain is operated over its life, wear takes place that has the effect of lengthening the chain, which causes the slack in the drive chain system to increase. If the amount of slack in the chain is not periodically checked and adjusted via a routine manual maintenance procedure, the drive chain system will become noisy and exhibit excessive backlash as a result of high slack. If the chain is adjusted improperly during the maintenance procedure, it can be set incorrectly, either too tight or too loose, resulting in the loading, noise and backlash conditions described above.  
       SUMMARY  
       [0003]     The present invention provides a chain tensioner comprising a support member configured to support a stop bar for axial movement. A ratchet engages the support bar and is configured to permit axial movement of the stop bar in a first direction and prevent axial movement of the stop bar in a second, opposite direction. A shuttle assembly including a tensioning wheel is interconnected to the stop bar such that the shuttle assembly is axially moveable relative to the stop bar over a limited range of motion. A biasing member is configured to bias the shuttle assembly in the second direction. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  is a front elevation view of a drive chain assembly incorporating a chain tensioner that is a first embodiment of the present invention.  
         [0005]      FIG. 2  is an isometric view, in partial section, of the chain tensioner of  FIG. 1 .  
         [0006]      FIGS. 3-7  are front elevation views, in partial section, of the adjustment assembly of the chain tensioner of  FIG. 1  illustrating operation of the adjustment assembly.  
         [0007]      FIG. 8  is an isometric view of a chain tensioner that is an alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0008]     The present invention will be described with reference to the accompanying drawing figures wherein like numbers represent like elements throughout. Certain terminology, for example, “top”, “bottom”, “right”, “left”, “front”, “frontward”, “forward”, “back”, “rear” and “rearward”, is used in the following description for relative descriptive clarity only and is not intended to be limiting.  
         [0009]     Referring to  FIG. 1 , an illustrative drive chain assembly  10  is shown. The drive chain assembly  10  includes a housing  12  in which a pair of sprockets  14  and  16  are positioned. A drive chain  18  is looped around the sprockets  14 ,  16  to transfer power from one of the sprockets to the other sprocket. To maintain a desired range of slack on the drive chain  18 , a chain tensioner  50  is positioned in the housing  12  with a tensioning wheel  110  in contact with the drive chain  18 .  
         [0010]     Referring to  FIGS. 2 and 3 , the chain tensioner  50  includes a support body  52  configured to be fixed in the housing  12 . In the current embodiment, the support body  52  has a plurality of ribs  54  configured to mate with a complementary set of ribs  32  in a retaining block  30  in the housing  12 . Other means of securing the chain tensioner  50  within the housing  12  may also be utilized. The support body  52  includes a bore  56  in which a stop bar  72  is received. The stop bar  72  is axially moveable within the bore  56 . The bore  56  may be provided with a shoulder (not shown) adjacent to the opening in to the bore  56  to limit the extent of axial movement.  
         [0011]     The support body  52  also includes a shoulder  58  spaced from the main portion of the body  52  to define a cavity  60  configured to receive an end of the ratchet  84 . The cavity  60  is configured such that the ratchet  84  can pivot therein over a limited range, but is generally prevented from axial movement. The ratchet  84  is a generally rectangular bar with a central bore  86  through which the stop bar  72  passes. The central bore  86  has a configuration that complements the geometry of the stop bar  72 . In the preferred embodiment, the stop bar  72  and central bore  86  both have a rectangular configuration with the central bore  86  having a close fit about the stop bar  72 .  
         [0012]     The opposite end of the stop bar  72  is connected to a tensioning wheel  110  via a shuttle assembly  90 . The shuttle assembly  90  includes a frame member  92  with a pair of legs  96  extending on opposed sides of the tensioning wheel  110 . An axle  112  extends through the tensioning wheel  110  and is supported by the legs  96  to support the tensioning wheel  110 . The frame member  92  has an opening  94  configured to receive the stop bar  72 . The stop bar  72  extends through the frame opening  94  in to a shuttle body  98  within the frame member  92 . The shuttle body  92  has a bore  99  configured to receive the stop bar  72 . A portion of the bore  99  has a larger diameter to define a stop ring travel area  100  within the shuttle body  98 . The stop bar  72  has a circumferential groove  78  configured to receive a stop ring  80 . The stop ring  80  has a diameter larger than the diameter of the stop bar  72  and is limited to travel within the travel area  100  defined between the frame member  92  and the shuttle body  98 . While a stop ring  80  provides the desired contact within the travel area, other stop members may be provided. For example, the stop bar  72  may be formed with an integral shoulder or opposed radial tabs. Alternatively, a stop pin may be positioned through and secured in a transverse hole through the stop bar. An adjuster spring  82  is positioned about the stop bar  72  and extends between the ratchet  84  and an outside surface of the frame member  92 .  
         [0013]     Having described the components of the preferred chain tensioner  50 , its operation will now be described with reference to  FIGS. 3 through 7 .  FIG. 3  illustrates an initial position of the chain tensioner  50 . The stop bar  72  is positioned radially outward a distance such that the tensioning wheel  110  provides the desired tension to the drive chain  18  and the stop ring  80  is positioned in the radially outward extent of the travel area  100 . The adjuster spring  82  maintains the desired tension on the shuttle frame  92  such that the tensioning wheel  110  applies the desired tension to the drive chain  18 . The stop bar  72  is prevented from traveling radially inward as the inward force causes the ratchet bore  86  edges to clutch the stop bar  72  with the inward force increasing the clamping load that the ratchet  84  exerts on the stop bar  72 , thereby locking it in place.  
         [0014]     Referring to  FIG. 4 , as the drive chain  18  wears and its length increases, the adjuster spring  82  exerts the desired tension force on the shuttle assembly frame member  72 . The shuttle frame member  92 , and thereby the tensioning wheel  110 , is free to move radially outward, as indicated by the arrow A, with the stop ring  80  moving within the travel area  100 . The adjuster spring  82  maintains the desired tension on the shuttle assembly  90  which in turn maintains the desired tension on the drive chain  18 .  
         [0015]     Referring to  FIG. 5 , eventually the shuttle assembly  90  moves radially outward a distance equal to the length of the travel area  100 . At this point, the shuttle frame member  92  contacts the stop ring  80 . The adjuster spring  82  force on the frame member  92  is transmitted to the stop ring  80  and thereby to the stop bar  72 . The adjuster spring  82  is therefore providing a radially outward force on the stop bar  72  as indicated by the arrow B in  FIG. 6 . The radially outward force on the stop bar  72  causes the ratchet  84  to rotate as indicated by arrow C. Rotation of the ratchet  84  removes the clamping force of the ratchet bore  86  on the stop bar  72 , thereby allowing the stop bar  72  to move radially outward due to the adjuster spring  82  force exerted thereon. The stop bar  72  moves radially outward until the stop ring  80  reaches the radially outer extent of the travel area  100  as illustrated in  FIG. 7 . Once the stop ring  80  reaches the radially outer extent, the force causes an inward force as indicated by arrow D, thereby causing the ratchet  84  to rotate back to the lock positioning with the stop bar  72  clamped within the ratchet bore  86 . The chain tensioner assembly  50  is again positioned as in the initial setup described with respect to  FIG. 3 . This adjustment process occurs continuously, requires no external power source, and eliminates the normal manual adjustment maintenance procedure.  
         [0016]     Referring to  FIG. 8 , a chain tensioner  150  that is an alternate embodiment of the present invention is shown. The chain tensioner  150  is similar to the previous embodiment and includes a shuttle assembly  90  connected to a stop bar  72 . The shuttle assembly  90  operates in the same manner as described with respect to the previous embodiment. In the present embodiment, the adjuster springs  182  are positioned on opposed sides of the stop bar  72  and provide the adjuster spring  182  force to shoulders  192  extending from the shuttle frame  92 . The support body is replaced by a support bracket  152  with a bore  156  configured to receive the stop bar  72 . The ratchet  184  includes a ratchet bore  186  through which the stop bar  72  passes. The ratchet  184  includes a ratchet spring  188  configured to bias the ratchet  184  to the lock positioning in which the stop bar  72  is clamped within the ratchet bore  186 . The adjuster spring  182  force is greater than the ratchet spring  188  such that once the shuttle assembly  90  reaches the extent of independent travel, the adjuster spring  182  force will cause the ratchet  184  to rotate to release the clamping force and allow the stop bar  72  to move radially outward.