Patent Publication Number: US-2005126329-A1

Title: Shifter for a bicycle transmission

Description:
The present invention relates to bicycle shifters and more particularly to a bicycle shifter that includes a locking pawl that simultaneously engages a retaining contour and a releasing contour.  
      Bicycle shifters are used to pull and release a tensioned control cable connected to a gear change mechanism and to hold the desired gear ratio. These types of shifters are disclosed in the German patent applications DE 1 99 18 520 A1 and DE 1 033 063. These shifters generally include an actuator and a cable spool for pulling and releasing cable and a retaining device for holding the tensioned control cable in a particular position. The actuator rotates the cable spool, while the retaining device continuously holds the cable spool in a current shift position and thus counteracts the return force of the tensioned control cable.  
      DE 1 99 18 520 A1 discloses a shifter including a rotatable actuator nonrotatably connected to the cable spool having a locking pawl that engages retaining teeth on the housing and holds a current shift position or gear ratio. A releasing element on the actuator is provided to cancel the holding action of the locking pawl to release the control cable or shifting cable. Once the holding action of the locking pawl is cancelled, the cable spool rotates in a release direction, under the force of an additional spring element and the tension in the shifting cable, until the locking pawl once again engages a retaining tooth. To pull the shifting cable, the actuator is rotated in the opposite direction so that the cable spool and the locking pawl are rotated by a drive element. When the actuator is released, the locking pawl ratchets against the next retaining tooth and the cable spool may rotate slightly in the cable-release direction.  
      The shifter disclosed in DE 1 033 063 includes a cable spool having retaining teeth, and an actuator that always returns to its starting position after an operation. During a cable-pull operation, the actuator engages a stop on the cable spool causing the locking pawl to ratchet over the retaining teeth on the cable spool. After completion of the shifting operation, the actuator returns back to its starting position, while the locking pawl holds the current shift position by engaging the retaining teeth. The release operation is initiated by pivoting the actuator in the release direction. The locking pawl is moved by the actuator out of the retaining teeth, and after a defined pivoting motion, the locking pawl comes into contact against the next retaining tooth to hold the current shift position. The retaining teeth are located on different radii relative to the rotation point of the cable spool.  
      The shifters disclosed in the above-mentioned patent applications are functional but are sluggish, sensitive to tolerances and demanding in terms of manufacture and space requirements. Further, the shifters produce loud shifting noises. Therefore, there is a need for a shifter that is uncomplicated and has a single-axis configuration.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to provide a shifter having shifting components that can be economically manufactured and are both suitable for both lever shifters and twistshifters.  
      The present invention provides a shifter for a bicycle transmission. The shifter generally includes a housing, an actuator, a cable spool, a locking pawl and retaining and releasing elements. The housing is mounted to a handlebar. The actuator is operated by the rider to select a desired gear ratio. The actuator is connected to the housing via a mandrel. The cable spool includes a tab that rotatably connects the cable spool to the actuator. The releasing element is nonrotatably connected to the actuator and the retaining element is nonrotatably connected to the cable spool. The releasing element includes a releasing contour having a plurality of releasing teeth. The retaining element includes a retaining contour having a plurality of retaining teeth. The locking pawl holds the desired gear ratio. The locking pawl has first and second ends. The first end of the locking pawl is supported in the housing. The second end of the locking pawl simultaneously engages the retaining and releasing contours and may be biased toward the retaining element. In one embodiment of the present invention, the locking pawl is a spring supported by the housing near the cable guide for the control cable. This configuration minimizes the outer diameter of the housing which is especially favorable for twistshifters.  
      The retaining element may be a disk having a retaining contour on its periphery. Alternatively, the retaining element and the cable spool may form one part. The releasing element may also be a disk having a releasing contour on its periphery. Alternatively, the releasing element and the actuator may form one part. The elevations of the retaining contours form retaining teeth having retaining edges and the elevations of the releasing contour form releasing teeth having saw-tooth shapes. Each retaining tooth corresponds to a releasing tooth. The spacing between the retaining teeth corresponds to a gear ratio and the necessary control cable displacement for each gear change. The configuration of the releasing teeth, in particular the tooth flank facing in the releasing direction, provides a desired releasing profile that substantially influences shifting sensitivity. The releasing profile of the tooth flank of the releasing teeth can have a straight, convex, concave or any other type profile sufficient to move the locking pawl out of locked engagement with the retaining tooth. In addition to the simple and compact construction, the present invention provides an individual release travel and release force for each gear ratio because of the various shapes of the releasing teeth.  
      In one embodiment, the locking pawl is a spring supported by the housing near a control cable guide. The locking pawl may be biased toward the retaining and releasing elements to provide a rapid and reliable retaining function. A first end of the spring is supported by the housing and a second end of the spring is engageable with the retaining and releasing teeth. The contours of the retaining and releasing teeth have opposite facing profiles relative to each other. The retaining teeth have a steep retaining edge that functions as a stop for the locking pawl and the releasing teeth have a releasing profile. During the cable-release operation, the releasing element rotates relative to the retaining element causing the releasing profile of the releasing tooth to slide under the locking pawl and move it out of its locked state on the retaining tooth. A shifting sensitivity and releasing behavior dependent on gear ratio can be achieved by the association of the releasing teeth with the corresponding retaining teeth.  
      In another embodiment, a preload spring is arranged between the actuator and the cable spool to assist the release operation and to prevent any play between the actuator and the cable spool. The preload spring may be a compression spring received in a slot in one of the cable spool and the actuator. One end of the preload spring is braced against an end of the slot and another end of the preload spring is braced against a tab that extends from one of the actuator and cable spool. Another end of the slot also serves a stop for the tab that the preload spring acts on.  
      As the locking pawl is being pushed out of engagement with the retaining tooth by the releasing tooth during a release operation, the preload spring is being preloaded by the tab on the actuator because of the relative motion between the releasing element and the retaining element. As the locking pawl travels over the retaining tooth, the retaining element or the cable spool is then released and the preload spring once again presses the tab against the end of the slot. The preload spring provides a shifting force in the release direction that is built up before the locking pawl has ratcheted out. Depending on the spring preload and the spring characteristic curve, this shifting force influences the shifting behavior and shifting sensitivity of the shifter.  
      During the cable-pull operation, the rotational movement of the actuator or rotatable grip is transferred directly to the cable spool via at least one drive element extending from the actuator to the cable spool. The locking pawl slides over the retaining teeth and the corresponding releasing tooth. At the end of the cable-pull operation, the locking pawl ratchets into the next tooth gap of the retaining contour and braces itself once again against the corresponding retaining edge of the next retaining tooth. The cable spool or tensioned control cable thus travels a defined shifting distance. If the actuator is moved further, it is thus also possible to shift through several gears in succession with one actuation, the ratcheting of the locking pawl into place indicating that a new gear ratio has been reached.  
      The shifting operation in the cable-release direction can be effected either by way of two mutually independent actuators or with a single actuator. With two actuators, each actuator can be optimally designed in terms of ergonomics and shifting force. As a general rule, a longer lever arm or lever travel will be chosen for the cable-pull operation than for the release operation, which involves merely moving the locking pawl out of locked engagement with the retaining contour. The device having one actuator for the cable pull and release operations, on the other hand, is particularly suitable for a twistshifter that is rotatable in two directions.  
      The prevent invention allows its components, in particular the cable spool, retaining element, releasing element and the actuator, to be arranged around a central axis. This configuration permits a very compact design that is suitable for both lever shifters and twistshifters.  
      These and other features and advantages of the present invention will be more fully understood from the following description of certain embodiments of the invention, taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the drawings:  
       FIG. 1  is an exploded view of a shifter in accordance with one embodiment of the present invention;  
       FIG. 2  is an exploded view of the shifter showing, in particular, the control cable guide;  
       FIG. 3  is an exploded view of the shifting showing a preload spring in the actuator; and  
       FIGS. 4   a - 4   c  are front views of retaining and releasing elements of  FIGS. 1 and 2  showing various positions of the retaining and releasing elements during a release operation of the shifter. 
    
    
     DETAILED DESCRIPTION  
       FIGS. 1-4  illustrate a bicycle shifter in accordance with one embodiment of the present invention. The shifter generally includes a housing  1 , an actuator  7 , a retaining element  12 , a releasing element  13 , a locking pawl  16  and a cable spool  9 . Looking to  FIG. 1 , the housing  1  includes an integrated handlebar clamp  2 , a cable guide portion  3  for receiving a control cable (not shown) and a brake housing portion  5 . The actuator  7  is mounted over a mandrel  4  that includes two elastic retaining fingers  6  that snap into the housing  1 . The actuator  7  is rotatable in a cable-pull direction and a cable-release direction opposite the cable-pull direction. The actuator  7  includes at least one drive element  8  engageable with the cable spool  9  to transfer the shifting motion in the cable-pull direction to the cable spool. Alternatively, the drive element  8  may be located on the cable spool  9 . The retaining element  10  is nonrotatably connected to the cable spool  9  and includes a retaining contour  11  having a plurality of retaining teeth  12 . The releasing element  13  is nonrotatably connected to the actuator  7  and includes a releasing contour  14  having a plurality of releasing teeth  15 . The retaining and releasing elements  10 ,  13  are arranged relative to each other such that the releasing teeth  15  correspond to the retaining teeth  12 . The locking pawl  16  is supported by the housing  1 . A first end of the locking pawl  16 , in this embodiment a spring, is supported by an insert  18  received in the housing  1  and a second end of the locking pawl  16  simultaneously engages the retaining and releasing contours  11 ,  14 .  
      During a cable-pull operation, the locking pawl  16  slides over the retaining tooth  12  and the adjacent releasing tooth  15  and ratchets into the next tooth gap. The locking pawl  16  braces against a retaining edge  17  of the retaining to prevent the cable spool  9  from rotating back after the cable-pull operation. During a cable-release operation, the releasing element  13  is rotated with the actuator  7  in the release direction causing the releasing tooth  15  to move the locking pawl  16  over the retaining edge  17  of the retaining tooth  12 . As a result, the cable spool  9  and the retaining element  10  rotate under the tension force of the control cable, in the release direction, until the locking pawl  16  engages the next retaining edge  17 , terminating the release operation. The amount of releasing motion initiated by the control cable differs for each gear ratio because the control cable displacement for each gear ratio is different. Thus, a preload spring  19  that biases the cable spool  9  and the actuator  7  proves to be very advantageous here. The preload spring  19 , in this embodiment a compression spring, is arranged on the actuator  7  and has a first end braced against the actuator  7  and a second end biases a tab  20  on the cable spool against a stop  26  on the actuator  7 , see  FIG. 3 . This configuration eliminates any play between the actuator  7  and the cable spool  9 . The preload spring  19  is biased by the tab  20  during the release operation or during relative motion between the retaining and releasing elements  10 ,  13  and is not released until the releasing tooth  15  has moved the locking pawl  16  out of its current position over the retaining edge  17  of the retaining tooth  12 . As the preload spring  19  relaxes, the tab  20  is pushed back against the stop  26  of the actuator  7 , resulting in the cable spool  9  being accelerated in the release direction. The preload spring  19  ensures a rapid shifting motion, independent of the gear ratio, in the release direction.  
      The present invention provides a simple and space-saving configuration that is arranged about a central axis. This configuration is particularly suitable for twistshifters. The sophisticated and efficient arrangement of the retaining and releasing elements  10 ,  13  and the simultaneous engagement of the locking pawl  16  with the retaining and releasing contours  11 ,  14  are, however, also suitable for lever shifters. For example, the actuator  7  may be replaced with first and second actuating elements such as two levers, a cable-pull lever and a cable-release lever. The retaining element  10  is connected to or moved with the cable-pull lever and the cable-release lever is connected or moved with the releasing element  13 .  
      Looking to  FIG. 2 , the housing  1  is attached to the handlebar with handlebar clamp  2 . The brake housing portion  5  has holes for a brake lever pivot and a recess  21  for receiving the insert  18 . The insert  18  includes a receptacle  28  for the locking pawl  16  and a control cable guide. The rotationally movable parts of the shifter include the cable spool  9 , retaining element  10 , releasing element  13 , and the actuator  7 . These elements are mounted on the mandrel  4  that is secured to the housing  1  by the retaining fingers  6 . The tab  20  nonrotatably connects the retaining element  10  to the cable spool  9 . The cable spool  9  includes a cable groove  25  and a bore  23  for receiving an end of the control cable to secure the control cable to the cable spool  9 , see  FIG. 3 .  
      Looking to  FIG. 3 , the preload spring  19  is disposed in a slot  24  extending radially on the actuator  7 . In the assembled state, the tab  20  is received in the slot  24 . One end of the preload spring  19  is braced against the tab  20  and another end of the preload spring  19  is braced against one end of the slot  24 . Another end of the slot  24  is the stop  26  for the tab  20  that defines a relationship between the actuator  7  and the cable spool  9 . During a cable-pull operation, the cable spool  9  is rotated by the actuator  7  via the tab  20 . During a cable-release operation, the cable spool  9  is rotated only after the locking pawl  16  is disengaged. Disengagement of the locking pawl  16  is accomplished by relative motion between the retaining and releasing elements  10 ,  13 . This relative motion results from the relaxation of the preload spring  19 , or its preloading by the tab  20 . After disengagement of the locking pawl  16 , the preload spring  19  delivers this stored energy back to the cable spool  9 , thereby accelerating the cable spool and the release operation.  
       FIGS. 4   a - 4   c  show three positions of the retaining and releasing elements  10 ,  13  during the cable release operation. Looking to  FIG. 4   a , the retaining and releasing element  10 ,  13  are in a neutral position before a shifting operation begins. The locking pawl  16  has a width sufficient to simultaneously engage the retaining and releasing contour  11 ,  14  and engage the retaining edge  17  of the retaining teeth  12 . The releasing tooth  15  has, in the releasing direction, a releasing profile  27 , in this embodiment a saw-tooth shape, that slides under the locking pawl  16  and moves the locking pawl  16  over to the next retaining tooth  12  during a cable-release operation.  
       FIG. 4   b  shows the retaining and the releasing element  10 ,  13  during a cable-release operation. The releasing element  13  is rotated in the cable-release direction relative to the retaining element  10 . The releasing profile  27  of the releasing tooth  15  has already lifted the locking pawl  16 , against its spring tension, out of the neutral position to approximately the middle of the retaining edge  17  on the retaining tooth  12 .  
       FIG. 4   c  shows the releasing element in the release position. The locking pawl  16  has been displaced along the releasing profile  27  on the releasing tooth  15  and outward along the retaining edge  17  on the retaining tooth  12 . The locking action of the locking pawl  16  is thus cancelled. The retaining element  10  and the cable spool  9  are rotated by the tensioned control cable and the preload spring  19  in the cable release direction until the locking pawl  16  penetrates the next tooth gap and engages the retaining edge  17  of the next retaining tooth  12 . The spacing from one retaining edge  17  to the next need not always be the same; it corresponds to the control cable displacement needed for a gear change. Each retaining tooth to be shifted over has a corresponding releasing tooth associated with it. The contour of the releasing tooth, and their spacings from one another, can thus be coordinated with the respective gear ratio.  
      Shifting sensitivity is a factor that influences a decision to purchase or not to purchase a certain shifter. This shifting sensitivity is influenced by the coordination among the moving shifter components. This includes not only the coordination of the preload spring and the locking pawl spring, but also the profiles of the tooth flanks of the releasing teeth  15 , which in  FIGS. 4   a - 4   c  exhibit a saw-tooth shape. Concave and convex (or other) contours of this tooth flank may, of course, also prove advantageous in order to achieve a desired shifting sensitivity.  
      While this invention has been described by reference to a preferred embodiment, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.