Abstract:
A device and method of mechanically synchronizing the displacement requirements of a bicycle derailleur with the displacement created by an indexing gear shifter lever. The device includes a linkage element that is mounted to a bicycle between a gear shifter lever and a derailleur. The linkage element is mounted to the bicycle with a pivot hinge, wherein the linkage element is free to rotate about the pivot hinge. A cable from the gear shifter lever is attached to the linkage element at a first distance from the pivot hinge. A cable from the derailleur is attached to the linkage element at a second different distance from the pivot hinge. As the cable from the gear shifter is moved, the linkage element is rotated and that movement is transferred to the cable for the derailleur in a compensated manner.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the systems on bicycles used to shift between gears, wherein such systems include index-type gear shifter levers and derailleur assemblies that are interconnected by cables. More particularly, the present invention relates to devices that can adapt the use of a set of indexing gear shifter levers with dissimilar derailleur assemblies on a custom built bicycle. 
     2. Prior Art Statement 
     Many bicycles contain a drive mechanism that has multiple gears. By shifting the bicycle&#39;s chain between the gears, the mechanical advantage between the pedals and the rear wheel of the bicycle can be selectively altered. Traditionally, the mechanism used to shift the bicycle&#39;s chain between different gears contains three interconnected assemblies. These assemblies are the gear shifter levers, the derailleurs and the cables that extend between the gear shifter levers and the derailleurs. The gear shifter levers are the levers that are positioned on or near the handlebars of the bicycle. These levers are moved by the person riding the bicycle, thereby providing manual shifting control to rider. The derailleurs are the mechanism that guide the bicycle chain onto different gears and compensate for slack in the chain as the chain moves between gears of different diameters. The cables are the elements that interconnect the shifter levers and the derailleurs and transfer mechanical movement between the gear shifter levers and the derailleurs. The cable is a direct mechanical drive. Consequently, if a gear shifter lever is used to move a cable ⅝ th  of an inch, the cable transfers that ⅝ th  of an inch of movement directly to a derailleur. 
     Because cables directly interconnect the gear shifter levers and the derailleurs, the gear shifter levers and the derailleurs must be coordinated into matched sets. For example, if an indexing-type gear shifting lever is designed to shift gears for every ¼ inch of movement it causes in a cable, a derailleur must also be designed to shift gears for every ¼ inch of movement it receives from the cable. If the gear shifter levers and the derailleurs are not coordinated, movement of the gear shifter levers between gears will not correspond to the proper derailleur movement required to shift gears. The result is that the desired gear shifting will not occur or may only partially occur, thereby creating chain slippage or chain chatter between gears. 
     Many bicycling enthusiasts customize their bicycles. Often gear shifter levers of a first type are desired to be used with derailleurs of a second type. However, since the gear shifter levers and the derailleurs are not compatible, the two assemblies cannot be used together. In the prior art, devices have been designed that mechanically alter the movement of a cable between a gear shifter lever and a derailleur. Such prior art devices are exemplified by U.S. Pat. No. 5,447,475 to Socard, entitled Device And Process For synchronous Control Of Bicycle Derailleurs. However, such prior art devices are intended to convert the movement of one cable into two cables, or visa versa. Such prior art systems do not enable dissimilar gear shifter levers and derailleurs to be used. 
     A need therefore exists for a device and method that can enable dissimilar indexing shifting levers and derailleurs to be used on a custom bicycle. This need is met by the present invention as described and claimed below. 
     SUMMARY OF THE INVENTION 
     The present invention is a device and method of mechanically synchronizing the displacement requirements of bicycle derailleurs with the displacement created by index-type gear shifter levers. The device includes a linkage element that is mounted to a bicycle between the gear shifter levers and the derailleurs. The linkage element is mounted to the bicycle with a pivot hinge, wherein the linkage element is free to rotate about the pivot hinge. A cable from each gear shifter lever is attached to a linkage element at a first distance from the pivot hinge. A cable from each derailleur is attached to a linkage element at a second different distance from the pivot hinge. As the cable from one gear shifter is moved, a linkage element is rotated and that movement is transferred to the cable for one derailleur. However, since the cable for the derailleur and the cable for the gear shifter lever connect to the linkage element at different points, only a percentage of the gear shifter lever&#39;s movement is transferred to the derailleur through the cables. The result is that different gear shifter levers and derailleurs can be mechanically synchronized to work together on the same bicycle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the following description of an exemplary embodiment thereof, considered in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a side view of a bicycle containing two cable displacement compensation devices; 
     FIG. 2 is an enlarged view of a cable displacement compensation device; 
     FIG. 3 is an alternate embodiment of a cable displacement compensation device; and 
     FIG. 4 is another alternate embodiment of a cable displacement compensation device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the present invention cable displacement compensation device can be used in any cable control system, the cable displacement compensation device is particularly well suited to use on a bicycle. As such, the present invention cable displacement compensation device will be described in an application where it is applied to a bicycle, in order to set forth the best mode contemplated for the invention. 
     Referring to FIG. 1, a bicycle  10  is shown. The bicycle  10  has gear shifter levers  12 ,  13  positioned near the handlebars. It is these gear shifter levers  12 ,  13  that are manually moved by a person riding the bicycle  10  in order to selectively change the gear ratio of the bicycle  10 . Two derailleur assemblies  14 ,  16  are present on the bicycle  10 . The first derailleur assembly  14  is present over the chain wheel gears  18  that are affixed to the bicycle pedals  20 . It is the function of the first derailleur assembly  14  to move the bicycle chain  22  between the different chain wheels  18  that are present. The second derailleur assembly  16  is present near the freewheel gears  24  on the rear wheel  26  of the bicycle  10 . It is the function of the second derailleur assembly  16  to move the bicycle chain  22  between the different freewheel gears  24  that are present, while eliminating slack in the chain  22  as it moves between gears of differing diameters. The structures of such derailleur assemblies  14 ,  16  are well known in the prior art. 
     In the shown embodiment, the two derailleur assemblies  14 ,  16  are not designed to be used with the shifting levers  12 ,  13  present on that same bicycle  10 . The derailleur assemblies  14 ,  16  are designed to shift gears every time a cable displaces one of the derailleurs  14 ,  16  by a predetermined distance, e.g. {fraction (1/16)} th  of an inch. However, the gear shifter levers  12 ,  13  are designed differently and are intended to cause a gear to shift upon a second displacement of a cable, e.g. ⅜ inch. As such, the displacement created by the gear shifter levers  12 ,  13  to create a gear change does not match the displacement needed by the derailleurs  14 ,  16  to create that gear change. 
     On the bicycle, two gear shifter levers  12 ,  13  are present. One gear shifter lever  12  is intended to control the first derailleur assembly  14  and the other gear shifter lever  13  is intended to control the second derailleur assembly  16 . A cable  30 ,  32  extends from each of the shifting levers  12 ,  13 . However, the cables  30 ,  32  do not extend directly to the derailleur assemblies  14 ,  16 . Rather, the two cables  30 ,  32  extend to cable displacement compensation devices  40  that are disposed on the bicycle  10  between the shifter levers  12 ,  13  and the derailleurs  14 ,  16 . 
     Referring now to FIG. 2, it can be seen that a cable displacement compensation device  40  is comprised of a linkage element  42  that is connected to the frame of the bicycle  10  at a pivot joint  44 . The pivot joint  44  can be directly mated with the frame of the bicycle  10 . However, in the shown embodiment, the pivot joint  44  connects to a clamp  47  that can be selectively attached to the frame of the bicycle  10 . In this manner, the cable displacement compensation device  40  can be mounted to a bicycle  10  without having to drill a hole in the frame of the bicycle  10 . 
     The linkage element  42  is free to rotate about the pivot joint  44 . Two sets of holes are present on the linkage element  42 . One set of holes  46  is disposed upon the illustrated left edge of the linkage element  42 , while the second set of holes  48  is disposed upon the illustrated right edge of the linkage element  42 . Holes  46 ,  48  from the left edge set and the right edge set, respectively, are matched in pairs. Each pair of holes is a predetermined distance from the pivot joint  44 . It will be understood that as the linkage element  42  rotates about the pivot joint  44 , the movement along an arcuate path for each pair of holes differs. For any given rotational movement of the linkage element, the holes more distant from the pivot joint  44  will travel a further arcuate distance than will the holes closer to the pivot joint  44 . 
     Cable terminations  50  are provided. The cable terminations  50  are designed to engage the end of a cable and join that cable to one of the holes on the linkage element  42 . Using the cable termination  50 , a cable can be selectively attached to any of the holes  46 ,  48  present on the linkage element  42 . 
     The cable displacement compensation device  40  is placed on the bicycle  10  at some point in between the shift levers  12 ,  13  (FIG. 1) and the derailleurs  14 ,  16  (FIG.  1 ). Once a cable  52  from one of the derailleurs and a cable  32  from one of the gear shift levers are terminated with cable terminations  50 , they are attached to the linkage element  42  of the cable displacement compensation device  40  at different points. In the shown embodiment, the cable  32  from the gear shifter lever is connected to a hole closer to the pivot joint  44  than is the cable  52  from the derailleur. As the gear shifter lever (FIG. 1) is manually manipulated, the cable  32  from the gear shifter lever either pushes or pulls the linkage element  42 . This causes the linkage element  42  to rotate about the pivot joint  44 . As the linkage element  42  moves about the pivot joint  44 , the linkage element  42  either pulls or pushes the derailleur cable  52 , thereby displacing that cable  52 . Since the attachment point of the derailleur cable  52  is farther from the attachment point of the shifter cable  32 , the displacement of the derailleur cable  52  differs from that of the shifter cable  32 . If the shifter cable  32  is closer to the pivot joint  44  than is the derailleur cable  52 , the derailleur cable  52  will be displaced farther than the shifter cable  32  for any movement of the linkage element  42 . For example, if the shifter cable  32  is manually moved ⅛ th  of an inch by a bicycle rider, such a displacement can result in a {fraction (3/16)} th  of an inch displacement in the derailleur cable  52 . Alternatively, if the shifter cable  32  is farther from the pivot joint  44  than is the derailleur cable  52 , the derailleur cable  52  will be displaced less than the shifter cable  32  for any movement of the linkage element  42 . For example, if the shifter cable  32  is displaced {fraction (3/16)} th  of an inch by a bicycle rider, that displacement can result in a ⅛ th  inch displacement in the derailleur cable  52 . 
     The variation in displacement between the shifter cable  32  and the derailleur cable  52  can be selectively controlled by the placement of these cables in the holes in the lever linkage element  42 . The farther the attachment points are from each other, the larger the differences in displacement. Conversely, the closer the attachment points on the linkage element  42 , the less disparity in displacement will occur. 
     Thus, by using the cable displacement compensation device  40 , a gear shifter lever (FIG. 1) that is calibrated with one displacement to change gears can be used with derailleurs (FIG. 1) that are calibrated with a different displacement to change gears. 
     Referring to FIG. 3, an alternate embodiment of the cable displacement compensation device  60  is shown. In this embodiment, cable terminations  62  are directly coupled to a linkage element  64  at different points. As such, the raw ends of cables need not be terminated prior to attachment to the device. Furthermore, the cable terminations  62  on the linkage element  64  are not linearly aligned. This is illustrated to point out that the linkage element  64  can have any configuration and the cable connection points on the linkage element  64  can be created in any pattern. Provided, that the holes in the linkage element  64  are at varying distance from the pivot joint  66  around which the linkage element  64  rotates. 
     Also illustrated in FIG. 3 is a derailleur return spring compensator assembly  66 . Derailleurs typically have a return spring. The force applied by that return spring is designed to work in conjunction with a set of gear shifters. However, if a dissimilar set of gear shifters is used, the return spring in the derailleur may be strong enough to move the gear shifter out of gear. The derailleur return spring compensator assembly  66  is provided to stop this phenomenon from happening. 
     The derailleur return spring compensator assembly  66  is comprised of a spring element  68  and a base bracket  69 . The base bracket  69  is mounted to the frame of the bicycle a short distance from the cable adjustment compensator  60 . The spring element  68  is engaged with one of the cable terminations  62 . The spring element  68  biases the linkage element  64  toward the gear shifter. As such, the derailleur return spring compensator assembly  66  opposes any return spring that may be present within a particular derailleur assembly. In this manner, the return pull of a derailleur can be selectively corrected to match the needs of a particular gear shifter assembly. 
     Referring to FIG. 4, another alternate embodiment of the present invention cable displacement compensation device  70  is shown. This alternate embodiment is similar to the embodiment previously shown and described with reference to FIG.  2 . However, in the shown embodiment elongated slots  72 ,  74  are formed on either side of the linkage element  76 . Cable terminations  78 ,  80  are provided at the ends of the cables. The cable terminations  78 ,  80  can engage the elongated slots  72 ,  74  at any point along the length of those slots. As such, the position of the cable terminations  78 ,  80  are infinitely adjustable along the length of the slots  72 ,  74 . As such, the transfer in cable displacement created by the device  70  can be finely adjusted if particularly finicky derailleurs with indexing shifters are used. Returning to FIG. 1, it will be understood that to use the present invention, shifter levers  12 ,  13  and derailleurs  14 ,  16  are provided on a bicycle  10 . At least one cable displacement compensation  40  is then affixed to the frame of the bicycle  10  in between the shifter levers  12 ,  13  and the derailleurs  14 ,  16 . At least one cable from the gear shifter levers  12 ,  13  and at least one cable from the derailleurs  14 ,  16  are connected to the cable displacement compensation device  40 . The point of attachment of the cables synchronizes the needed displacements between each gear shifter lever  12 ,  13  and each derailleur  14 ,  16 . The proper positions can be done via trial and error or through the use of printed instructions for known brands of shifter levers and derailleurs. 
     It will be understood that the embodiments of the present invention device described and illustrated are merely exemplary and a person skilled in the art can make many variations to the shown embodiment. All such alternate embodiments and modifications are intended to be included within the scope of the present invention as defined below in the claims.