Abstract:
An apparatus and accompanying method are disclosed for a handgrip based gear-shifting mechanism used to manipulate the front and rear derailleur cables on a vehicle having a multi-sprocket gear system. The gear-shifter comprises a substantially hollow handgrip member that has first and second cam guide paths in the bore of its substantially cylindrical surface. First and second cam followers, preferably located inside the bore of the handgrip member, engage the first and second cam guide paths respectively. The first and second cam followers are coupled to the front and rear derailleur cables, such that a single rotation of the handgrip simultaneously adjusts the positions of the first and second cam followers and the front and rear derailleur cables.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to apparatus for actuating shifting mechanisms in devices having multi-sprocket variable-ratio power transmissions. The invention may be embodied in a bicycle gear changing mechanism.  
         BACKGROUND OF THE INVENTION  
         [0002]    A typical multi-speed bicycle has a chain drive, which connects a pedal-driven crank to a driven wheel. The chain drive may have several front sprockets (chain rings) of different pitch diameters and several rear sprockets of different pitch diameters. The front sprockets are connected to the crank and rotate with the pedals. The rear sprockets are coupled to the driven wheel of the bicycle. A chain couples one of the front sprockets to one of the rear sprockets. Different gear ratios can be selected by moving the chain so that it couples a selected front sprocket to a selected rear sprocket.  
           [0003]    Such bicycles typically have cable-actuated front and rear derailleurs. A cyclist can operate the front derailleur to move the chain to a selected one of the front sprockets. The cyclist can operate the rear derailleur to move the chain to a selected one of the rear sprockets.  
           [0004]    There are various handlebar mounted mechanisms, which a cyclist can use to operate the front and rear derailleurs to achieve a desired gear ratio. For example, some bicycles have a pivotable lever mounted on each side of the handle bar. One lever is connected to a cable that operates the front derailleur and the other is connected to a cable that operates the rear derailleur. A cyclist can select a desired gear ratio by pivoting the levers.  
           [0005]    The GRIP SHIFT™ shifting mechanism provides a pair of handle-bar mounted collars. One collar is mounted to a bicycle&#39;s right handlebar and the other to the bicycle&#39;s left handlebar. One of the collars is connected to a cable that operates the front derailleur. The other collar is connected to a cable that operates the rear derailleur. A cyclist can rotate the collars relative to the bicycle handlebar to select a desired gear ratio.  
           [0006]    Cirami, U.S. Pat. No. 4,201,095, describes a bicycle gear-shifter having a single lever that operates both front and rear derailleurs to yield a progressive and programmed series of gear ratios. The Cirami mechanism has two flat plane cams. Intermediate drive ratios are obtained in consecutive increments ordered from the lowest to the highest drive ratio positions of the lever. Cirami proposes a shift pattern that avoids gear ratios that result in cross chaining.  
           [0007]    Ross, U.S. Pat. No. 4,279,174, discloses another bicycle gear shifter which permits a cyclist to operate front and rear derailleurs by manipulating a single control. The Ross shifter requires two types of derailleurs: a spring-biased front derailleur and a “push-pull” rear derailleur. The Ross shifter is constructed to provide a progressive shift pattern. Ross describes a shift pattern in which four changes involve shifting or changing the position of both derailleurs simultaneously to provide a progressive series of gear ratios.  
           [0008]    Watarai, U.S. Pat. No. 5,577,969, discloses an electronic apparatus for controlling both the front and rear derailleurs of a bicycle. A cyclist can cause the apparatus to shift between gears by operating a lever.  
           [0009]    Brix, U.S. Pat. No. 1,114,400, describes a mechanism for adjusting the positions of rods, which control the spark control, throttle, muffler control and engine clutch of a motorcycle. Each control rod is independently adjusted. The Brix mechanism employs two cylindrical sleeves, which are coupled to, and located within, the motorcycle handgrip. Each sleeve is associated with one of the control rods and features a helical groove in its cylindrical surface. When the rider rotates the handgrip, one sleeve is rotated, while the other is prevented from rotating. A cam follower travels in the helical groove of the rotating sleeve, causing longitudinal movement of the associated control rod.  
           [0010]    Savard, U.S. Pat. No. 5, 970,816, describes a bicycle gear shifter, which provides a mechanism for controlling both front and rear derailleurs. The mechanism is operated by rotating one handgrip. A cylindrical barrel is attached to the inner end of the handgrip. The barrel has a track on each of its inner and outer faces. Cables from the front and rear derailleurs are each connected to a corresponding one of a pair of cam followers. The cam followers each slide in one of the tracks. When the barrel is rotated, the members move the derailleur cables to select different gear ratios. The cam followers and follower guides are located close to each other on the outside of the handlebar. This results in a large bulbous assembly on the inboard side of the separate rotatable handgrip. A separate detent mechanism holds the collar in a position corresponding to the selected gear ratio. Like Cirami, Ross, and others, the Savard mechanism may be constructed to provide an optimal shift pattern in which undesirable or redundant gear combinations are avoided. A mechanism like the Savard mechanism is marketed by EGS of France under the trademark SYNCHRO SHIFT™. The SYNCHRO SHIFT™ mechanism is undesirably bulky. Its size makes it incompatible with standard bicycle brake levers.  
           [0011]    Socard, U.S. Pat. No. 5,447,475 discloses two separate and quite different bicycle gear shifting mechanisms. The mechanisms provide an optimal shift pattern that avoids cross chaining. The mechanisms are actuated via a cable that links to a handle bar mounted shift mechanism which provides two levers; one for shifting up and the other for shifting down. The mechanisms include a cam which rotates 90 degrees for each shift.  
           [0012]    Wechsler, U.S. Pat. No. 4,530,678, discloses a bicycle gear shifting mechanism that uses a cylindrical cam with a cam follower to control a rear derailleur. The cam is integrated into the rear derailleur mechanism and has cam grooves cut into its exterior surface. A second rotary cam is used to control a front derailleur. The second cam is integrated into the front derailleur. There is a cable that mechanically connects the front and rear derailleurs so that as one moves, the other also moves. Wechsler&#39;s front derailleur cam is shaped to cause the front derailleur to alternate between a large and small chain ring with each consecutive shift.  
           [0013]    Patterson, U.S. Pat. No. 4,900,291 discloses a bicycle gear shifting mechanism which has a rotatable handgrip actuator cam that is coupled via a cable to a derailleur mechanism. Separate independent cams are provided for controlling front and rear derailleurs. A cam surface on an edge of each cam abuts against a fixed post. The cam surface has peaks and valleys and uses cable tension to index the shifter. As a cam is rotated the cam slides longitudinally. An end of the cable is attached to the cam.  
           [0014]    Ethington, U.S. Pat. No. 5,681,234, discloses an “Automatic Transmission Shifter For Velocipedes” that employs speed and force sensors as well as a programmable logic controller and two servo motors to automatically shift a bicycle transmission according to operating conditions. Ethington discloses a shift pattern that uses all gears in an ascending sequence. Many of the speed changes involve shifting both front and rear derailleurs simultaneously.  
           [0015]    Nier, U.S. Pat. No. 5,803,848, discloses a shifter system that employs a shift pattern that is identical to the one used by Socard and others. This system uses flat radial cams that are linked and rotatably mounted on a handle bar. Nier&#39;s system combines a cam which operates the front derailleur by way of a mechanical linkage and two other cams with nodes that actuate electric motors to either pull or release the rear derailleur by predetermined amounts. The use of these three cams in combination results in an optimal shift pattern.  
           [0016]    Lahat, U.S. Pat. No. 5,865,062, discloses several mechanisms that control both front and rear derailleurs to achieve an optimal shift pattern. These mechanisms show both single cylinders with two cam surfaces and several arrangements of dual cylinders with single cam surfaces. In all cases the cams and followers are located on the exterior of the handlebar. In some cases, the cam and follower assembly are mounted in a separate casing and are not rotatably mounted on the handlebar. In all cases, the mechanisms are “aimed at synchronously controlling both front and rear derailleurs to achieve a predetermined sequential combinations of front and rear gears.  
           [0017]    Despite the long history of bicycle development and the large variety of shifting mechanisms that have been proposed for bicycles, there remains a need for practical gear shifting mechanisms suitable for use in bicycles and other pedal-powered vehicles. There is a particular need for such mechanisms, which permit a user to select a desired gear ratio without needing to separately control two shifting mechanisms.  
         SUMMARY OF THE INVENTION  
         [0018]    This invention provides ratio selecting mechanisms and related methods. The ratio selecting mechanisms may be used in bicycles, and other pedal powered mechanisms. The ratio selecting mechanisms may also be used in other applications, wherein a gear ratio is selected by controlling two mechanisms.  
           [0019]    One aspect of the invention provides a gearshift mechanism. The mechanism comprises a rotatable handgrip member with first and second guide paths on an inner surface within its bore. First and second followers are configured to engage the first and second guide paths respectively and first and second cable anchors are coupled respectively to the first and second followers. Rotation of the handgrip member simultaneously adjusts the positions of the first and second cable anchors.  
           [0020]    The first and second followers may be on opposing sides of the bore.  
           [0021]    The first and second guide paths may comprise grooves on the surface of the handgrip member. One or more of the grooves may comprise a plurality of indentations on one of its sides and the indentations may be located at detent positions. The indentations may be conveniently provided in the groove that controls the operation of a front derailleur. In the alternative, the indentations may be provided in the groove that controls the operation of the rear derailleur or distributed between grooves which control the operations of front and rear derailleurs. In the further alternative, a separate detent mechanism may be provided to hold the handgrip member in positions corresponding to selected gear ratios.  
           [0022]    The handgrip member may be rotatably mounted on a hollow handlebar. The first and second followers may be coupled respectively to the first and second cable anchors by members that extend through a bore of the handlebar. With such an embodiment, the first and second followers may extend through longitudinally disposed slots in the handlebar. Each follower may comprise a head portion, which is wider than a corresponding one of the slots and a neck portion, which passes through the corresponding slot. The neck portions of the followers may be elongated relative to the head portions of the followers. Each of the slots may have an enlarged portion, through which the head portion of the corresponding follower can pass. The enlarged portion(s) are located outside of the normal range of motion of the followers.  
           [0023]    The handgrip member may also comprise one or more substantially cylindrical cam members. The inside walls of the cam members may bear the first and second guide paths. The cam members may be affixed within a bore of a substantially tubular outer handgrip member. The first and second guide paths may comprise grooves on the surfaces of the one or more cam members. The grooves may penetrate the walls of the one or more cam members.  
           [0024]    The cable anchors may project from the members through additional longitudinally disposed slots in the handlebar. The gearshift mechanism may comprise a bracket on each of the cable anchors, the bracket having a width greater than that of the corresponding additional slot.  
           [0025]    The gearshift mechanism may be used in combination with a transmission comprising: a plurality of front sprockets, a chain, a plurality of rear sprockets, a cable-actuated front derailleur capable of engaging the chain with a selected one of the front sprockets, a cable-actuated rear derailleur capable of engaging the chain with one of the plurality of rear sprockets, a first cable connecting the first cable anchor to the front derailleur, and a second cable connecting the second cable anchor to the rear derailleur.  
           [0026]    The handgrip member may be rotatably mounted on a handlebar and the first and second followers may be coupled respectively to the first and second cable anchors by members, which slide in longitudinally extending recesses in the handlebar.  
           [0027]    Another aspect of the present invention provides a gearshift mechanism comprising: a hollow handlebar, a member mounted for longitudinal movement within the handlebar, a cable anchor projecting from the member through a slot in a wall of the handlebar, and an actuating mechanism coupled to move the member longitudinally between a plurality of selected positions.  
           [0028]    Another aspect of the invention provides a bicycle, which comprises: a frame, a handlebar, a plurality of front sprockets mounted to the frame, a chain, a plurality of rear sprockets, a cable-actuated front derailleur capable of engaging the chain with a selected one of the front sprockets, a cable-actuated rear derailleur capable of engaging the chain with one of the plurality of rear sprockets, a first cable connected at its first end to the front derailleur, a second cable connected at its first end to the rear derailleur, and a gearshift mechanism. The gearshift mechanism comprises a handgrip member rotatably mounted on the handlebar. The handgrip member has first and second guide paths on a substantially cylindrical inner surface of its bore. A first follower engages the first guide path and is coupled to the first cable at its second end and a second follower engages the second guide path and is coupled to the second cable at its second end. Rotation of the handgrip member relative to the handlebar simultaneously adjusts the front and rear derailleurs.  
           [0029]    Another aspect of the invention provides for a method of controlling the positions of a first member and a second member along a longitudinal axis. The method involves locating the first and second members within a bore of a handgrip at first and second angular positions respectively about the longitudinal axis. The first and second members are made to respectively engage first and second guide paths on an inner surface of the handgrip. The method also involves rotating the handgrip about the longitudinal axis, while maintaining the first and second angular positions substantially fixed. In this manner, the positions of the first and second members along the longitudinal axis are independently determined by the shapes of the first and second guide paths.  
           [0030]    The method may also comprise adjusting positions of first and second cables, which may be coupled respectively to the first and second members.  
           [0031]    Other aspects and features of the invention and descriptions of specific embodiments of the invention are described below.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    In drawings, which depict non-limiting embodiments of the invention,  
         [0033]    [0033]FIG. 1 is an isometric view of a gear shifting mechanism according to one embodiment of the invention, which is mounted on a bicycle handlebar;  
         [0034]    [0034]FIG. 2 is a close-up view of the gear shifting mechanism of FIG. 1;  
         [0035]    [0035]FIG. 3 is a partially cut-away view of the gear shifting mechanism of FIG. 1;  
         [0036]    [0036]FIG. 4 is an exploded view of the gear shifting mechanism of FIG. 1;  
         [0037]    [0037]FIG. 5 is a plan view of the gear shifting mechanism of FIG. 1;  
         [0038]    [0038]FIG. 5A is a longitudinal cross-sectional view of the gear shifting mechanism of FIG. 1 in the plane  5 A- 5 A of FIG. 5;  
         [0039]    [0039]FIGS. 6A, 6B,  6 C and  6 D are transverse cross-sectional views of the gear shifting mechanism of FIG. 1 in the planes  6 A- 6 A,  6 B- 6 B and  6 C- 6 C and  6 D- 6 D respectively of FIG. 6;  
         [0040]    [0040]FIG. 7 is an isometric view of a cam cylinder of the gear shifting mechanism of FIG. 1;  
         [0041]    [0041]FIG. 8 is an isometric view of a portion of the handlebar of FIG. 1;  
         [0042]    [0042]FIGS. 8A and 8B are respectively enlarged views of the portions of FIG. 8 within areas  8 A and  8 B;  
         [0043]    [0043]FIG. 9 depicts is an enlarged isometric view of a portion of the handlebar of FIG. 1 with the cam follower removed;  
         [0044]    [0044]FIGS. 9A and 9B are respectively enlarged views of the portions of FIG. 9 within areas  9 A and  9 B;  
         [0045]    [0045]FIG. 10 is a graph of cable extension as a function of handgrip rotation angle for one embodiment of the gear shifting mechanism;  
         [0046]    [0046]FIG. 11 is a schematic diagram, which illustrates the operation of a gear shifting mechanism according to an embodiment of the invention;  
         [0047]    [0047]FIG. 12A is a view of guide paths in a shifter according to one embodiment of the invention and FIG. 12B is a magnified view of a portion of the guide paths of FIG. 12A;  
         [0048]    [0048]FIG. 13 is an elevational view of a shifter according to an alternative embodiment of the invention and FIGS. 13A-13D are cross sections through the gear shifting mechanism of FIG. 13; and,  
         [0049]    [0049]FIG. 14 is an elevational view of a shifter according to an alternative embodiment of the invention and FIGS. 14A-14D are cross sections through the gear shifting mechanism of FIG. 14. 
     
    
     DETAILED DESCRIPTION  
       [0050]    The following description describes embodiments of the invention which are useful for selecting gear ratios in a pedal-powered apparatus. In particular, the following description describes a bicycle having a cable-actuated front derailleur, capable of placing a drive chain onto a selected one of a plurality of front sprockets and a cable-actuated rear derailleur, capable of placing the drive chain onto a selected one of a plurality of rear sprockets. The invention is not limited to such embodiments however.  
         [0051]    In this description, a numeral followed by the letter “F” refers to an element that is associated with a front derailleur. The same numeral followed by the letter “R” is a reference to a corresponding element that is associated with the rear derailleur. The same numeral standing on its own refers generally to the elements associated with both the front and rear derailleurs.  
         [0052]    [0052]FIGS. 1 through 3 show a gear shifting mechanism  10  mounted on a bicycle handlebar  12 . Gear shifting mechanism  10  controls front and rear derailleurs (not shown) by way of cables  14 F and  14 R respectively. Mechanism  10  can be operated by rotating a handgrip  16 . As handgrip  16  is rotated in a first angular direction, mechanism  10  moves cables  14 F and  14 R in a coordinated manner, so as to select progressively increasing gear ratios. As handgrip  16  is rotated in a second angular direction opposite to the first angular direction, mechanism  10  moves cables  14 F and  14 R in a coordinated manner, so as to select progressively decreasing gear ratios.  
         [0053]    Handgrip  16  may be covered with a resilient material. The outside of handgrip  16  has a shape which can be comfortably gripped. For example, the outside of handgrip  16  may be cylindrical or generally cylindrical. Handgrip  16  preferably has a diameter, which does not exceed about 38 millimetres, so that it can be readily grasped by children and adult users with typical-sized hands. Handgrip  16  includes a cam cylinder  20 , which is coupled to rotate with handgrip  16  relative to handlebar  12 . Cam cylinder  20  may be integral with handgrip  16  or may comprise a separate part.  
         [0054]    Cam cylinder  20  has a bore  21 , which receives one end of handlebar  12 . An inner end  20 ′ of cam cylinder  20  bears against a surface which prevents cam cylinder  20  from sliding inwardly along handlebar  12 . A pair of guide paths  22  are defined in bore  21 . In the illustrated embodiment, guide paths  22 F and  22 R each comprise a groove.  
         [0055]    In the illustrated embodiment (see FIG. 4) a gasket  23  of a low friction plastic material such as Delrin™ is provided on the inboard end of cam  20 . Gasket  23  rotates with cam  20  and bears against the flat surface of housing  23 A which in turn bears against brake post  45  which is clamped to handlebar  12 . Gasket  23  prevents cam  20  and housing  23 A from wearing where they rub against one another and provides increased contact surface area with cam  20  and housing  23 A.  
         [0056]    The position of each cable  14  is controlled by one of a pair of members  24  (see FIG. 5A), each of which includes a follower  26 . Followers  26  each engage a corresponding one of guide paths  22 . Members  24  are at fixed circumferential locations relative to handlebar  12 , but are free to travel longitudinally. As handgrip  16  is rotated relative to handlebar  12 , followers  26  move members  24  longitudinally as indicated by arrows  27 F and  27 R. In the illustrated embodiment, followers  26  comprise pins, which project into the groove of the corresponding guide path  22 . Followers  26  are cylindrical and have diameters slightly less than the widths of the grooves into which they project. As best seen in FIG. 6C, the radially outermost ends of followers  26  may be curved to conform with the curves of the bases of guide paths  22 . This permits the area of contact between followers  26  and the surfaces of guide paths  22  to be increased.  
         [0057]    Each cable  14  is coupled to a corresponding one of members  24 . In the illustrated embodiment each member  24  has a cable anchor  28 , which receives one of cables  14 .  
         [0058]    Cables  14  are attached to cable anchors  28  by any suitable means for attaching the cables to the cable anchors. In the embodiment of FIGS. 8 and 9, each cable  14  passes through an aperture  29  in the corresponding cable anchor  28 . Cables  14  have enlarged portions  30  (see FIG. 4) that will not fit through apertures  29 . Other means could be used for attaching cables  14  to cable anchors  28 . For example, a cable  14  having an enlarged end portion could pass through a slot in a cable anchor or a mechanical clamp could be provided on the cable anchor for the purpose of holding the cable.  
         [0059]    Each cable  14  runs within a sheath  32 . The position of a cable  14  relative to its sheath  32  can be adjusted by way of an adjusting nut  34 , which adjustably engages a cable guide  35 . Cable guide  35  may be attached, for example by clamping, to handlebar  12 . In the illustrated embodiment, cable guide  35  is not affixed to handlebar  12 . Cable guide  35  is kept in position by cable  14  which is held in place by cam followers  22 . Allowing cable guide  35  to float somewhat permits mechanism  10  to be displaced so that it can absorb some impacts without suffering damage. Tension in cables  14  holds cable guide  35  snugly against brake post  45 . A cover  36  (see FIG. 2) may be provided to protect cable anchors  28  and keep dirt and other contaminants out of the mechanism.  
         [0060]    Members  24  are configured so that they do not interfere with one another as they move. This may be achieved by spacing members  24  apart in a circumferential direction. Members  24  may be opposed to one another, as illustrated, or may be more closely spaced around the circumference of handlebar  12 . For example, members  24  could be circumferentially spaced apart by 90 degrees or some other angle.  
         [0061]    As shown in FIG. 8, members  24  are located inside handlebar  12 . Followers  26  project outwardly through slots  33  in handlebar  12 . As shown in FIGS. 8A and 9A, each follower  26  may comprise a head portion  37 , which is wider than the corresponding slot  33 , and a neck portion  38 , which passes through the corresponding slot  33 . Neck portion  38  may be elongated relative to head portion  37  as shown in the illustrated embodiment. Slots  33  may have enlarged portions  33 ′ through which head portion  37  can pass. The illustrated configuration ensures that the followers  26  fully engage guide paths  22 . Enlarged portions  33 ′ are preferably located a small distance distal to the normal range of motion provided by guide paths  22  so that head portions  37  of followers  36  do not encounter enlarged portions  33 ′ during normal operation.  
         [0062]    Cable anchors  28  also project through slots  39  in handlebar  12 . In the illustrated embodiment, a bracket  40  is mounted to each of cable anchors  28 . Brackets  40  are configured to receive the enlarged ends  30  of cables  14 . Brackets  40  are wider than slots  39  and prevent cable anchors  28  from slipping radially inwardly through slots  39 . Brackets  40  hold cable anchors  28  in positions such that cables  14  are supported so that they do not rub excessively on surfaces within the bores of adjusting screws  34  and cable guides  35  as gear shifting mechanism  10  is operated. Since each cable  14  passes through a hole in bracket  40  as well as a hole in cable anchor  28 , the cable  14  holds its bracket  40  and cable anchor  28  together when the cable  14  is under tension. Therefore, follower members  24  are constrained to move in the longitudinal direction only. Brackets  40  are not essential to the operation of gear shifting mechanism  10 .  
         [0063]    Guide paths  22  follow trajectories, which move followers  26 , and consequently cables  14 , in a longitudinal direction as necessary to control front and rear derailleurs (or other shifting mechanisms), to switch through a sequence of gear ratios as handgrip  16  is turned through its range of motion. The longitudinal travel of a member  24  for a given rotation of handgrip  16  depends upon the helical slope (i.e. longitudinal displacement per unit of rotation) of guide path  22  in the region in question. If a particular angular region of a guide path  22  extends generally circumferentially, then rotation of handgrip  16  while a follower  26  is in that particular angular region causes little or no longitudinal motion of the corresponding member  24 . Conversely, if a follower  26  is in an angular region where the guide path  22  has a greater helical slope, rotation of handgrip  16  causes a greater longitudinal movement of the corresponding member  24 . Front and rear guide paths  22  are, in general, shaped differently from one another. Consequently, rotation of handgrip  16  through a range of angles can cause member  24 F to move through a different distance and/or move in a different direction from member  24 R.  
         [0064]    In the illustrated embodiments, guide paths  22  are shaped so that, when handgrip  16  is in any one of a plurality of discrete angular positions, cables  14  are positioned to provide a specific gear ratio corresponding to that angular position.  
         [0065]    Gear shifting mechanism  10  preferably includes a detent mechanism whereby, when handgrip  16  is in one of these discrete angular positions, there is some resistance to rotating handgrip  16  in either angular direction. In preferred embodiments, at least one of cables  14  is maintained under tension and a corresponding one of guide paths  20  has indentations  41  located along it. Indentations  41  are at places such that, when handgrip  16  is in one of the discrete angular positions, the follower  26  is engaged in one of the indentations. Indentations  41  are shaped so that follower  26  must be moved to pull on the corresponding cable if handgrip  16  is rotated in either angular direction. Cables  14  are maintained under tension by springs or other bias elements (not shown). The bias elements may be parts of the corresponding front and rear derailleurs or other shifting mechanisms operated by cables  14 . Currently available front and rear derailleurs typically include springs which serve as bias elements. A separate detent mechanism could be present within the mechanism of gear shifting device  10 . A separate detent mechanism is not required in the illustrated embodiment of the invention.  
         [0066]    Gear shifting device  10  can be made very compact. As shown in FIG. 2, gear shifting device  10  may be compact enough that it does not interfere with the use of a typical bicycle brake lever  44 . A post  45  which supports brake lever  44  may be integrated with gear shifting device  10  as shown in FIG. 3. Post  45  may be part of a standard brake clamp.  
         [0067]    A bicycle may have a large number of gear ratios which are available in theory. For example, a bicycle having 3 front sprockets and 8 rear sprockets has, in theory, 3×8=24 distinct gear ratios. With conventional shifters all possible gear ratios are typically available. In practice, not all combinations of a front sprocket and a rear sprocket are desirable for use. Many possible gear combinations provide gear ratios that are redundant and/or result in severe cross chaining conditions. It is desirable to avoid “cross-chaining”. Cross-chaining occurs, for example, where the chain is engaged on the largest front sprocket and the largest rear sprocket (or the smallest front sprocket and the smallest rear sprocket). Further, some different combinations of front and rear sprockets typically provide very similar gear ratios. For a given set of front and rear sprockets, there is typically a set of pairs of front and rear sprockets that provide an optimum shift pattern. For example, Table I shows gear ratios for a bicycle having three front sprockets respectively with 28, 38 and 48 teeth and eight rear sprockets, respectively with 11 , 13, 15, 17, 20, 23, 26, and 30 teeth.  
                                                   TABLE I                           GEAR RATIOS            TEETH (FRONT-REAR)   RATIO   INCLUDE   COMMENT                    28-30   0.93   Y   1 - Lowest gear       28-26   1.08   Y   2       28-23   1.22   Y   3       38-30   1.27   N   Cross chain       28-20   1.4   Y   4       38-26   1.46   N   Cross chain       48-30   1.6   N   Cross chain       38-23   1.65   Y   5       28-17   1.65   N   Cross chain       48-26   1.85   N   Cross chain       28-15   1.87   N   Cross chain       38-20   1.9   Y   6       48-23   2.09   N   Cross chain       28-13   2.15   N   Cross chain       38-17   2.24   Y   7       48-20   2.40   N   Cross chain       38-15   2.53   Y   8       28-11   2.55   N   Cross chain       48-17   2.82   Y   9       38-13   2.92   N   Cross chain       48-15   3.2   Y   10       38-11   3.45   N   Cross chain       48-13   3.69   Y   11       48-11   4.36   Y   12 - Highest gear                  
 
         [0068]    As shown in the “Include” column of Table I, one can achieve a sequence of front-rear sprocket pairs that represents a desirable shift pattern by eliminating front-rear sprocket pairs that have undesirable cross-chaining and front-rear sprocket pairs that provide gear ratios, which are similar to those of other front-rear sprocket pairs. The resulting optimized shift pattern has a reduced number of gear ratios. For example, the shift pattern of Table I includes 12 of the 24 possible front-rear sprocket pairs. Guide paths  22  may be shaped to provide an optimized shift pattern, such as that shown in Table I, in which continued rotation of handgrip  16  in one angular direction progressively operates cables  14  to select, in sequence, the pairs of sprockets included in the optimized shift pattern.  
         [0069]    [0069]FIG. 10 is a graph depicting the longitudinal displacement (×) of cables  14 F and  14 R for a given rotational angle (⊖) of handgrip  16 . FIG. 10 shows an optimal shift pattern for a 3×7 configuration in which 11 of 21 possible gear combinations are used. It can be seen from FIG. 10, that the discrete angular positions of handgrip  16  do not need to be equally angularly spaced-apart from one another. It can also be seen from FIG. 10 that guide paths  22  may extend around handgrip  16  by more than 360 degrees such that more than one full revolution of handgrip  16  is required to move through the full range provided by guide paths  22 .  
         [0070]    The torque required to turn handgrip  16  increases with the tension in cables  14  and with the displacement (×) through which cables  14  are pulled for a given angular rotation (⊖) of handgrip  16  (i.e. the helical slope of guide paths  22 ). Friction between components also affects the required torque. In general, a user must do more work between discrete angular positions for shifts in which both cables  14  are being pulled (e.g. shifts in which both front and rear derailleurs are moving the chain to a larger sprocket—an example of such a shift is the shift between the 8 th  and 9 th  gear ratios of the shift sequence shown in both Table I and FIG. 10, wherein the shift is from the 38-15 sprocket pair to the 48-17 sprocket pair). The torque that a user must apply to make such difficult shifts can be reduced by shaping guide paths  22 , so that hand grip  16  rotates through a larger rotation angle (⊖) when such difficult shifts are made than it does for shifts which require less mechanical work to accomplish. This shape for guide paths  22  is represented in FIG. 10 by a line having a lesser relative slope. Conversely, guide paths  22  can be shaped such that handgrip  16  rotates through a smaller angle when shifts that require less work are made. This variation in the rotational angle between discrete angular positions permits guide paths  22  to have a variety of helical slopes ranging from more gradual to less gradual depending on the amount of work required.  
         [0071]    In some embodiments of the invention, guide paths  22  are shaped such that followers  26  move by no more than 0.06 mm in a longitudinal direction per degree of rotation of handgrip  16  as they traverse the portions of guide paths  22  between adjacent discrete angular positions. In some embodiments followers move by not more than 0.03 mm per degree of rotation averaged over a shift.  
         [0072]    [0072]FIG. 11 illustrates one specific embodiment of the invention in which a front derailleur  60 F is controlled by cable  14 F and a rear derailleur  60 R is controlled by cable  14 R. A chain  61  can be engaged with a selected one of front sprockets FS- 1 , FS- 2 , and FS- 3  by placing front derailleur  60 F in a corresponding one of its positions FD- 1 , FD- 2 , and FD- 3 . Similarly, rear derailleur  60 R has a number of positions RD- 1  to RD- 7 , which place the chain on a corresponding one of rear sprockets RS- 1  to RS- 7 .  
         [0073]    The torque which a user must apply to rotate handgrip  16  can be further controlled by tailoring the shape of guide paths  22  in their portions which control shifts involving changes in the positions of both front and rear derailleurs. As shown in FIGS. 12A and 12B, guide paths  22  may be constructed so that only one derailleur is moved at a time in such shifts. Angular portion  65  corresponds to a shift in which guide path  22 F shifts front derailleur  60 F (see FIG. 11) and guide path  22 R shifts rear derailleur  60 R (see FIG. 11). As best seen in FIG. 12B, in a first part  66  of angular portion  65 , guide path  22 R angles so that rear derailleur  60 R is shifted while guide path  22 F has no slope so that front derailleur  60 F is not shifted. In a second part  67  of angular portion  65 , guide path  22 F angles so that front derailleur  60 F is shifted while guide path  22 R has no slope so that rear derailleur  60 R is not shifted.  
         [0074]    Some particular shifts involve changing the positions of both the front and rear derailleurs. For example, as shown in FIGS. 10 and 11, the shifts between the 4 th  and 5 th  gear ratios and the 8 th  and 9 th  gear ratios involve changing the positions of both front derailleur  60 F and rear derailleur  60 R. In some embodiments of the invention, such multi-derailleur shifts may involve moving one derailleur and then moving the other derailleur. For example, when switching from the 4 th  to 5 th  gear ratio, the guide paths  22 R and  22 F may be shaped, such that rear derailleur  60 R moves first, so that chain  61  moves from the 4 th  rear sprocket (RS- 4 ) to the larger 3 rd  rear sprocket (RS- 3 ), and thereafter front derailleur  60 F moves, so that chain  61  moves from the 1 st  front sprocket (FS- 1 ) to the larger 2 nd  front sprocket (FS- 2 ). The order of movement of front derailleur  60 F and rear derailleur  60 R will be reversed when shifting down from the 5 th  to the 4 th  gear ratio. Other multi-derailleur shifts may be implemented in a similar manner, such that one derailleur is moved prior to the other.  
         [0075]    It can be appreciated that the embodiments described above provide bicycle gear shifters, which may be made in a compact rugged units. One feature that helps to make mechanism  10  compact is that cable anchors  28  are located inboard with respect to brake post  45  while cam cylinder  20  and followers  26  are located out board with respect to brake post  45 . Cam follower members  24  move longitudinally within the normal bore of brake post  45 .  
         [0076]    While this invention has been described with reference to illustrative embodiments, the invention is not limited to the embodiments described herein. It will be apparent to those skilled in the art in the light of the foregoing disclosure that many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example:  
         [0077]    A shifting mechanism according to the invention may be adapted to control “push-pull” derailleurs;  
         [0078]    The invention may be applied to the selection of ratios in transmissions other than bicycle transmissions. The invention may be applied in pedal-powered vehicles such as pedal-powered tricycles, pedal cars, pedal-powered water craft and the like. The invention may be applied to selecting gear ratios in other apparatus, which include a handgrip and a suitable variable-ratio power transmission;  
         [0079]    Shifting mechanisms other than derailleurs may be controlled by the gear shifting mechanism. For example, a gear shifting mechanism according to the invention may be used to select a ratio in a transmission which includes a front or rear derailleur and a variable-ratio gear train internal to a hub of the driven wheel;  
         [0080]    With an additional guide path  22  and associated coupling to a third cable, a gear shifting mechanism according to the invention may be used to select a ratio in a transmission having three shifting mechanisms. For example, a transmission having front and rear derailleurs and an additional variable gear train internal to a hub of the driven wheel;  
         [0081]    While the gear shifting mechanism  10  is shown in the Figures as being associated with a right handgrip, a gear shifting mechanism according to the invention could be associated with a left handgrip or with a handgrip not mounted on a handlebar;  
         [0082]    The number of discrete angular positions for each of the gear selecting mechanisms may be varied (i.e. in the illustrated embodiments, the numbers of front and rear sprockets can be varied); and,  
         [0083]    The particular selection of gear ratios is not critical to the invention. The gear ratios used preferably provide an optimal shift pattern. Determining an optimal shift pattern for any derailleur system is a matter of simply arranging gear ratios in ascending order and selecting a sequence that minimizes cross chaining. This is not difficult for anyone skilled in the art and is an obvious starting point for any integrated shifter design.  
         [0084]    Instead of being located inside the bore of a handlebar, members  24  may slide in longitudinal grooves  70  on an exterior surface of a handlebar as shown, for example, in FIG. 13. As a further alternative, handlebar  12  may comprise flattened faces  70 A and members  24  may slide on the flattened faces as shown in FIG. 14.  
         [0085]    Instead of using cables  14  to control the operation of derailleurs, a gear shifter according to the invention may comprise hydraulic or pneumatic mechanisms which control the operation of gear shifting devices such as derailleurs in response to movements of followers  26 .  
         [0086]    Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.