Abstract:
A motorcycle transmission shifter assembly including a cam drum having at least two pins extending therefrom, and a shift mechanism engageable with the pins. The shift mechanism includes a tooth that is operable to engage a first one of the pins to rotate the drum in a first direction and a stop that is operable to engage a second one of the pins to prevent over-rotation of the drum in the first direction. Preferably, the shift mechanism includes a shift pawl and a shift lever and the stop is mounted on either the shift pawl or the shift lever. Additionally, the shift mechanism can include a second stop mounted on the other of the shift pawl or the shift lever, the second stop being operable to engage a third one of the pins to prevent over-rotation of the drum in a second direction.

Description:
FIELD OF THE INVENTION 
     The invention relates to motorcycles, and more particularly to transmission shifters for motorcycles. 
     BACKGROUND OF THE INVENTION 
     Manual cam drum transmission shifters are well-known and commonly used for shifting between the gears of a motorcycle transmission. Typically, the transmission shifter assemblies include a cam drum that is mounted for rotation within the transmission and designed to move a series of gears. Rotation of the drum results in the shifting of the gears in the transmission. 
     The cam drum typically includes a plurality of equally spaced pins extending axially therefrom. The pins are engaged by a shift pawl that is pivotally connected to a shift lever. The shift pawl engages the pins to rotate the drum when the shift lever is actuated by the motorcycle operator. The shift pawl typically includes spaced-apart opposing teeth or claws. One tooth is operable to rotate the drum in a first or upshift direction, while the opposing tooth is operable to rotate the drum in a second or downshift direction. 
     During normal shifting, the shift pawl should rotate the drum by indexing through only one of the spaced-apart pins at a time. Sometimes, however, the rotational inertia of the drum during a shift will be great enough to cause the shift pawl to inadvertently index through two spaced-apart pins at once, thereby allowing over-rotation of the drum. Such over-rotation results in the transmission missing a shift, or skipping a gear, which can be hard on the engine. U.S. Pat. Nos. 3,421,384 and 4,455,884 disclose two transmission shifter assemblies having means for preventing the drum from over-rotating during shifting. 
     The prevention means utilized in U.S. Pat. No. 3,421,384 includes a cam plate fixed to the drum. The cam plate has concavities that correspond to the low speed, high speed and neutral shift positions. The concavities are separated by large projection portions. A swingable stopper is used to prevent over-rotation of the drum and to prevent rotation of the drum from the high speed position directly to the neutral position, thereby bypassing the low speed position. The swingable stopper has a roller that rides in the concavities of the cam plate to prevent the over-rotation or double shifting of the drum. 
     The prevention means utilized in U.S. Pat. No. 4,455,884 also includes a cam plate and a shift stopper similar to the one taught in the &#39;384 Patent, but further includes a lock mechanism that more positively prevents the shift drum from turning from the high speed shift position directly to the low speed shift position, thereby bypassing the medium shift position. When such an overshift is attempted, a lock piece engages an opening in the surface of the drum and prevents the transmission from shifting directly from the high speed position to the low speed position. When the shift pedal is released, the shift stopper biases the drum back to its high speed position. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved transmission shifter assembly with positive stop mechanisms to prevent overshifting in both the upshift and downshift directions. The improved shifter assembly has fewer parts, is more compact, is easier to assemble, is more robust, and is less expensive to manufacture than the assemblies disclosed in the prior art. The shifter assembly of the present invention eliminates the need for a separate cam plates, shift stoppers, or any other independent locking members by incorporating upshift and downshift stop mechanisms directly on the shift pawl and/or the shift lever. 
     More specifically, the invention provides a motorcycle transmission shifter assembly including a cam drum having at least two pins extending therefrom, and a shift mechanism engageable with the pins. The shift mechanism includes a tooth that is operable to engage a first one of the pins to rotate the drum in a first direction and a stop that is operable to engage a second one of the pins to prevent over-rotation of the drum in the first direction. 
     In a preferred aspect of the invention, the shift mechanism includes a shift pawl and a shift lever and the stop is mounted on either the shift pawl or the shift lever. In another preferred aspect of the invention, the shift mechanism includes a second stop mounted on the other of the shift pawl or the shift lever, the second stop being operable to engage a third pin to prevent over-rotation of the drum in a second direction. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a right side view of a motorcycle having a transmission embodying the invention. 
     FIG. 2 is a top view of the motorcycle transmission with the top of the housing removed. 
     FIG. 3 is a schematic view of a shifting linkage having a shifting mechanism operable to manually shift the transmission. 
     FIG. 4 is an exploded perspective view of the shifting mechanism embodying the invention. 
     FIG. 5 is an plan view of the shifting mechanism positioned in the home state. 
     FIG. 6 is a plan view of the shifting mechanism positioned in the upshift state. 
     FIG. 7 is a plan view of the shifting mechanism positioned in the upshift state during over-rotation of the cam drum. 
     FIG. 8 is a plan view of the shifting mechanism positioned in the downshift state. 
     FIG. 9 is a plan view of the shifting mechanism positioned in the downshift state during over-rotation of the cam drum. 
     Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a motorcycle  10  embodying the present invention. The motorcycle  10  includes a front wheel  14 , a rear wheel  18 , a frame  22  supported by the wheels  14  and  18 , an engine  26  supported by the frame  22 , a seat  30 , a tank  34 , and a transmission  38  that operates in conjunction with the engine  26 . 
     As seen in FIG. 2, the transmission  38  is a manually operated transmission that includes a housing  42  having a removable cover (not shown) for granting access to the transmission components. A cam drum  46  is mounted for rotation inside the housing  42 . Support shafts (not shown) extend axially from the ends of the cam drum  46  and support the cam drum  46  for rotation between respective bearing supports  54 . The cam drum  46  includes a plurality of cam grooves  58  that receive corresponding cam followers (not shown). As the cam drum  46  rotates, the cam followers are displaced by the grooves  58  to effect the shifting of gears  60  as is commonly understood. 
     The illustrated cam drum  46  also includes a plurality of equally spaced pins  62  that extend axially from one end of the cam drum  46 . As shown in FIG. 5, there are preferably five pins  62   a ,  62   b ,  62   c ,  62   d , and  62   e , respectively. The rotation of the cam drum  46  defines a pin path  64 . As best seen in FIG. 2, the distal ends of the pins  62  are preferably supported by a support disk  66  that is mounted on the support shaft on the same side of the cam drum  46  as the pins  62 . The support disk  66  provides added strength to the pins  62  by placing the pins  62  in double shear. Although preferred, the support disk  66  is not a necessary feature of the invention and the pins  62  could extend from the cam drum  46  in cantilevered fashion without any supporting structure at their distal ends. 
     FIG. 3 schematically illustrates a linkage  70  capable of rotating the cam drum  46  to shift the gears of the motorcycle  10 . The linkage  70  is shown for illustrative purposes only and other linkages can be used with the present invention. The linkage  70  includes a foot pedal member  74  which is supported for rocking movement by a suitable support member  78 . The driver of the motorcycle  10  can actuate the pedal member  74  by pressing downwardly on the front end portion  82  to rotate the pedal member  74  in the direction of arrow  86 . Alternatively, the driver can actuate the pedal member  74  by pressing upwardly on the front end portion  82  or downwardly on the rear end portion  90  to rotate the pedal member  74  in the direction of arrow  94 . 
     The rotation of pedal member  74  causes movement of the first linkage member  98  and the movement translates through the second and third linkage members  102  and  106 , respectively. The third linkage member  106  is mounted on one end of a shaft  110  and movement of the third linkage member  106  causes rotation of the shaft  110 . A shift mechanism  114  is mounted on the opposite end of the shaft  110  and moves in the directions indicated by arrow  118  depending upon the direction of rotation of the shaft  110 . 
     As best seen in FIG. 4, the shift mechanism  114  includes a shift lever  122 , a shift pawl  126 , a shift return spring  130 , and a pawl spring  134 . The shift lever  122  has first and second spaced-apart openings  138  and  142 , respectively. The first opening  138  receives the shaft  110 . The shaft  110  can be press-fit, shrink-fit, welded, or otherwise secured into the opening  138  such that the shift lever  122  rotates with rotation of the shaft  110 . The shift lever  122  further includes first and second engaging surfaces  146  and  150 , respectively, the purpose of which will be described below. Between the first and second engaging surfaces  146 ,  150  is an L-shaped portion  154 . 
     The shift return spring  130  has a coil portion  158  and first and second coil ends  162  and  166 , respectively. When the shift mechanism  114  is assembled, the shift lever  122  is mounted on the shaft  110  as described above and the coil portion  158  is supported on the shaft  110  adjacent the shift lever  122 . The first and second coil ends  162 ,  166  engage opposite edges of the L-shaped portion  154  and extend beyond the L-shaped portion  154 . The shift return spring  130  is operable to bias the shift lever  122  to a home state as shown in FIG.  5  and as will be described in more detail below. 
     The shift pawl  126  is coupled to the shift lever  122  with a pin  170 . The pin  170  extends through a first opening  174  in the shift pawl  126  and through the second opening  142  in the shift lever  122  to couple the shift pawl  126  and the shift lever  122  together and to permit pivotal movement of the shift pawl  126  with respect to the shift lever  122 . 
     The pawl spring  134  includes a coil portion  178  and first and second coil ends  182  and  186 , respectively. When the shift mechanism  114  is assembled, the coil portion  178  is supported on the pin  170  adjacent the shift lever  122 . The pawl spring  134  is retained on the pin  170  with a washer  190  and a snap ring  194 . The first coil end  182  engages the shift lever  122  while the second coil end  186  engages the shift pawl  126 . The pawl spring  134  biases the shift pawl  126  toward the shaft  110 . 
     The shift mechanism  114  is operable to shift the gears of the motorcycle  10  by rotating the cam drum  46  in response to driver input on the pedal member  74 . Specifically, the shift mechanism  114  includes an upshift tooth or jaw  198  and a downshift tooth or jaw  202 , both of which are formed on the shift pawl  126 . As seen in FIGS. 5-9, the upshift and downshift teeth  198  and  202  are capable of engaging the pins  62  to selectively rotate the cam drum  46 . In the preferred embodiment, the upshift and downshift teeth  198  and  202  are integrally formed with the shift pawl  126 . 
     The shift mechanism  114  of the present invention is also operable to prevent over-rotation of the cam drum  46  during a shift. Specifically, the shift mechanism  114  includes an upshift stop member  206  formed on the shift lever  122  and a downshift stop member  210  formed on the shift pawl  126 . The upshift stop member  206  is located adjacent the second opening  142  in the shift lever  122  and is adjacent the upshift tooth  198  when the shifting mechanism  114  is assembled. The upshift stop member  206  includes an engagement surface  214  capable of engaging a pin  62  to prevent further rotation of the cam drum  46  in the upshift direction (see FIG.  7 ). In the preferred embodiment, the upshift stop member is integral with the shift lever  122 . 
     The downshift stop member  210  is preferably adjacent the downshift tooth  202  and integral with the distal end of the shift pawl  126 . The downshift stop member  210  includes an engagement surface  218  that is capable of engaging a pin  62  to prevent further rotation of the cam drum  46  in the downshift direction (see FIG.  9 ). The upshift and downshift stop members  206  and  210  provide a simple, inexpensive, and robust way to prevent over-rotation of the cam drum  46  and will be described in greater detail below in the discussion of the shifting operation. 
     FIGS. 5-9 illustrate the shifting operation of the shifting mechanism  114 . FIG. 5 shows the shift mechanism  14  being positioned in its home state. The home state is illustrative of a point during operation of the motorcycle  10  when the driver is not shifting gears. In the home state, two pins  62  (pins  62   a  and  62   b  in FIG. 5) are positioned between the upshift and downshift teeth  198  and  202 . The first and second coil ends  162  and  166  of the shift return spring  130  straddle a lever stop  222  that extends from the housing  42 . 
     FIG. 6 illustrates the upshift state of the shift mechanism  114 . The upshift is initiated by the driver actuating the pedal member  74  as described above. As the shaft  110  rotates, the shift lever  122  moves in the direction of the arrow in FIG. 6 until the second engaging surface  150  engages the lever stop  222  to prevent further rotation of the shift lever  122 . This movement causes the shift pawl  126  to move such that the upshift tooth  198  engages pin  62   b  and causes rotation of the cam drum  46  through one pin position in the counter-clockwise direction as viewed in FIG.  6 . The rotation of the shift lever  122  causes the second coil end  166  to come out of engagement with the L-shaped portion  154  due to the engagement with the lever stop  222 . The increased separation between the coil ends  162 ,  166  generates a spring force that tends to bias the shift lever  122  back to its home state (see FIG.  5 ). 
     When the shift mechanism  114  returns to its home state, the side of the upshift tooth  198  closest to the shift lever  122  engages and slides over pin  62   c  without causing rotation of the cam drum  46 . The pawl spring  134  allows the shift pawl  126  to move slightly upwardly to allow passage of the upshift tooth  198  over the pin  62   c , but then biases the shift pawl  126  downwardly into the position illustrated in FIG.  5 . After the upshift is complete, the shift mechanism  114  returns to the home state shown in FIG. 5 with the pins  62   b  and  62   c  now positioned between the upshift and downshift teeth  198  and  202 . 
     As mentioned above, the shift mechanism  114  can prevent over-rotation of the cam drum  46  during an upshift. The tendency for the cam drum  46  to over-rotate usually occurs when the driver actuates the pedal member  74  with great force or in rapid succession. The inertia with which the cam drum  46  rotates after such actuation overcomes the biasing force of the shift spring  130  that tends to return the shift mechanism  114  to the home state. If such over-rotation is allowed to go unchecked, the cam drum  46  could rotate through two pin positions, thereby skipping a gear. 
     FIG. 7 illustrates the upshift stop member  206  operating to prevent over-rotation of the cam drum  46 . As the cam drum  46  over-rotates in the direction of the arrow in FIG. 7, the pin  62   b  comes out of engagement with the upshift tooth  198 . The upshift stop member  206  is positioned in the pin path  64  between the pins  62   c  and  62   d  such that when the cam drum  46  over-rotates, the pin  62   d  engages the engagement surface  214 . The engagement between the engagement surface  214  and the pin  62   d  prevents the cam drum  46  from rotating through an extra pin position in the upshift direction. Once rotation of the cam drum  46  is stopped, the shift spring  130  biases the shift mechanism  114  back to the home state. 
     FIG. 8 illustrates the downshift state of the shift mechanism  114 . Again, the downshift is initiated by the driver actuating the pedal member  74  as described above. As the shaft  110  rotates, the shift lever  122  moves in the direction of the arrow in FIG. 8 until the first engaging surface  146  engages the lever stop  222  to prevent further rotation of the shift lever  122 . This movement causes the shift pawl  126  to move such that the downshift tooth  202  engages pin  62   a  and causes rotation of the cam drum  46  through one pin position in the clockwise direction as viewed in FIG.  8 . The rotation of the shift lever  122  causes the first coil end  162  to come out of engagement with the L-shaped portion  154  due to the engagement with the lever stop  222 . The increased separation between the coil ends  162 ,  166  generates a spring force that tends to bias the shift lever  122  back to its home state (see FIG.  5 ). 
     When the shift mechanism  114  returns to its home state, the angled surface of the shift pawl  126  between the downshift tooth  202  and the engagement surface  218  engages and slides over pin  62   e  without causing rotation of the cam drum  46 . The pawl spring  134  allows the shift pawl  126  to move slightly upwardly to allow passage of the downshift tooth  202  over the pin  62   e , but then biases the shift pawl  126  downwardly into the position illustrated in FIG.  5 . After the downshift is complete, the shift mechanism  114  returns to the home state shown in FIG. 5 with the pins  62   e  and  62   a  now positioned between the upshift and downshift teeth  198  and  202 . 
     The shift mechanism  114  also prevents over-rotation of the cam drum  46  during a downshift. FIG. 9 illustrates the downshift stop member  210  operating to prevent over-rotation of the cam drum  46 . As the cam drum  46  over-rotates in the direction of the arrow in FIG. 9, the pin  62   a  comes out of engagement with the downshift tooth  202 . The downshift stop member  210  is positioned in the pin path  64  between the pins  62   e  and  62   a  such that when the cam drum  46  over-rotates, the pin  62   e  engages the engagement surface  218 . The engagement between the engagement surface  218  and the pin  62   e  prevents the cam drum  46  from rotating through an extra pin position in the downshift direction. Once rotation of the cam drum  46  is stopped, the shift spring  130  biases the shift mechanism  114  back to the home state. 
     It should be noted that other variations and configurations for the upshift and downshift teeth  198  and  202 , as well as for the upshift and downshift stop members  206  and  210  are contemplated by the present invention. For example, the upshift stop member  206  need not be located adjacent the second opening  142  as shown, but rather could be located in any other location on the shift lever  122  that would allow the upshift stop member  206  to prevent over-rotation of the cam drum  46 . More specifically, the upshift stop member  206  could extend from a position closer to the second engaging surface  150  of the shift lever  122 . Of course, changing the location of the upshift stop member  206  could (and would likely) entail changing the shape and size of the upshift stop member  206 . 
     In addition, while the upshift stop member  206  is illustrated as being integrally formed with the shift lever  122 , it is also possible to integrally form the upshift stop member  206  with the shift pawl  126 . Specifically, the upshift stop member  206  could be formed in the shift pawl  126  adjacent the first opening  174 . The configuration of such an upshift stop member  206  that is integrally formed on the shift pawl  126  could be substantially similar to the illustrated upshift stop member  206  or could have a different shape. 
     Likewise, it is possible to form the downshift stop member  210  integrally with the shift lever  122  instead of on the shift pawl  126  as illustrated. Specifically, the downshift stop member  210  could extend from an area of the shift lever  122  adjacent the first engaging surface  146 . 
     Various features of the invention are set forth in the following claims.