Abstract:
An electronic shift control apparatus is provided for a bicycle having a transmission with a plurality of speed stages. The apparatus comprises a shift unit that provides signals for shifting the transmission, a restriction selecting unit operated by a user to select a restricted speed stage, and a restricting unit operatively coupled to the shift unit and to the restriction selecting unit. The restricting unit prevents the shift unit from providing signals to shift the transmission to the restricted speed stage.

Description:
BACKGROUND OF INVENTION  
         [0001]    The present invention is directed to bicycles and, more particularly, to a shift control apparatus that selectively restricts one or more speed stages of a bicycle transmission.  
           [0002]    Some bicycles are equipped with shift control devices that automatically control the operation of front and rear transmissions (e.g., front and rear derailleurs that respectively cooperate with a plurality of front and rear sprockets) depending on bicycle velocity. An example of such a system is disclosed in JP 8-501,742. In that system, the bicycle chain may be engaged automatically with any combination of front and rear sprockets depending upon the velocity of the bicycle. The use of all sprocket combinations better accommodates more sensitive changes in riding conditions than is possible by operating the rear transmission alone and also avoids unnecessary shifting.  
           [0003]    While the ability to use all sprocket combinations allows the bicycle transmission to respond to more sensitive changes in riding condition, such fine response also may result in frequent shifting of the front and/or rear transmissions. Since in bicycles the operation of the front transmission results in a greater change of gear ratio than the operation of the rear transmission, operation of the front transmission exerts a greater shock on the rider&#39;s legs than operation of the rear transmission. Thus, frequent shifting by the front transmission to maintain the bicycle at a constant velocity runs the risk of imposing a considerable burden on the rider. On the other hand, frequent shifting by the front transmission to accommodate changing conditions when traveling uphill or on a rough road usually does not imposes a significant burden on the rider, and may even be beneficial. Thus, it may desirable to have the ability to control the operation of the front transmission to accommodate such different riding conditions. Of course, it also may be desirable to similarly control the operation of the rear transmission or both the front and rear transmissions to accommodate different riding conditions.  
         SUMMARY OF INVENTION  
         [0004]    The present invention is directed to various features of a bicycle transmission. In one embodiment, an electronic shift control apparatus is provided for a bicycle having a transmission with a plurality of speed stages. The apparatus comprises a shift unit that provides signals for shifting the transmission, a restriction selecting unit operated by a user to select a restricted speed stage, and a restricting unit operatively coupled to the shift unit and to the restriction selecting unit. The restricting unit prevents the shift unit from providing signals to shift the transmission to the restricted speed stage. Additional inventive features will become apparent from the description below, and such features alone or in combination with the above features may form the basis of further inventions as recited in the claims and their equivalents. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0005]    [0005]FIG. 1 is a side view of a particular embodiment of a bicycle;  
         [0006]    [0006]FIG. 2 is a more detailed view the handlebar assembly;  
         [0007]    [0007]FIGS. 3 and 4 are schematic block diagrams of a computer control device for components of the bicycle;  
         [0008]    [0008]FIG. 5 is an illustration of items displayed on the computer display;  
         [0009]    [0009]FIG. 6 is a flow chart of a particular embodiment of a main processing routine;  
         [0010]    [0010]FIG. 7 is a flow chart of a particular embodiment of a Restrict Front process;  
         [0011]    [0011]FIG. 8 is a flow chart of a particular embodiment of an Upshift 1 process;  
         [0012]    [0012]FIG. 9 is a flow chart of a particular embodiment of an Upshift 2 process;  
         [0013]    [0013]FIG. 10 is a flow chart of a particular embodiment of a Downshift 1 process;  
         [0014]    [0014]FIG. 11 is a flow chart of a particular embodiment of a Downshift 2 process;  
         [0015]    [0015]FIG. 12 is a flow chart of a particular embodiment of a manual shift process;  
         [0016]    [0016]FIG. 13 is a flow chart of a particular embodiment of a Downshift 3 process;  
         [0017]    [0017]FIG. 14 is a flow chart of a particular embodiment of an Upshift 3 process;  
         [0018]    [0018]FIG. 15 is a plurality of tables of particular embodiments of upshift threshold values; and  
         [0019]    [0019]FIG. 16 is a plurality of tables of particular embodiments of downshift threshold values. 
     
    
     DETAILED DESCRIPTION  
       [0020]    [0020]FIG. 1 is a side view of a particular embodiment of a bicycle  1 . Bicycle  1  comprises a frame body  2  constructed by welding together tubing having noncircular cross-sections. A front fork  3  is mounted to the front of frame body  2  for rotation around an inclined axis, and a handlebar assembly  4  is mounted to the top of front fork  3 . A saddle  18  is mounted to the upper middle part of frame body  2 , a drive mechanism  5  is mounted to the lower part of frame body  2 , a front wheel  6  is rotatably mounted to the bottom of front fork  3 , and a rear wheel  7  having a hub dynamo  10  is rotatably mounted to the rear of frame body  2 . Hub dynamo  10  houses an alternating current generator  19  (FIG. 3) for generating electricity through rotation of rear wheel  7 . A front transmission  8  including a front derailleur  26   f  is mounted to the lower middle part of frame body  2 , and a rear transmission  9  including a rear derailleur  26   r  is mounted to the rear of frame body  2 . A front suspension  13   f  is mounted to front fork  3 , and a rear suspension  13   r  is mounted between stationary and articulated portions of frame body  2 .  
         [0021]    As shown in FIG. 2, handlebar assembly  4  comprises a handle stem  12  mounted to the top of front fork  3  and a handlebar  15  mounted to the top of handle stem  12 . Brake lever assemblies  16  and grips  17  are mounted at the opposite ends of handlebar  15 . The right side brake lever assembly  16  includes a rear downshift switch  20   a  for manually downshifting rear derailleur  26   r  in single increments, a rear upshift switch  20   b  for manually upshifting rear derailleur  26   r  in single increments, and a mode switch  21   a  for switching between automatic and manual shift modes. The left side brake lever assembly  16  includes a front downshift switch  20   c  for manually downshifting front derailleur  26   f  in single increments, a front upshift switch  20   d  for manually upshifting front derailleur  26   f  in single increments, and a suspension control switch  21   b  for adjusting the stiffness of front suspension  13   f  and rear suspension  13   r . Special operation of switches  21   a  and/or  21   b  makes these switches function as a restriction selecting unit and causes the performance of a restriction procedure that restricts the operation of drive mechanism  5  in a manner described below.  
         [0022]    As shown in FIG. 1, drive mechanism  5  comprises a crank  27  rotatably mounted at the bottom bracket of frame body  2 , front and rear transmissions  8  and  9 , and a chain  29 . Front transmission  8  comprises, for example, three front sprockets F 1 -F 3  and front derailleur  26   f . Front sprockets F 1 -F 3  are mounted to crank  27 , and front derailleur  26   f  is mounted on frame body  2 . Rear transmission  9  comprises, for example, a multiple sprocket assembly  25  having eight rear sprockets R 1 -R 8  and rear derailleur  26   r . Multiple sprocket assembly  25  is mounted to rear wheel  7  and rear derailleur  26   r  is mounted at the back of frame body  2 . Crank  27  comprises a right crank arm  27   a  and a left crank arm  27   b , wherein front sprockets F 1 -F 3  are mounted to right crank arm  27   a . Chain  29  engages one of the front sprockets F 1 -F 3  and one of the rear sprockets R 1 -R 8 .  
         [0023]    Front sprockets F 1 -F 3  are arranged in the order of an increasing number of teeth, wherein front sprocket F 1  is the laterally innermost front sprocket having the least number of teeth, and front sprocket F 3  is the laterally outermost front sprocket having the most number of teeth. Rear sprockets R 1 -R 8  are arranged in the order of a decreasing number of teeth, wherein rear sprocket R 1  is the laterally innermost rear sprocket having the most number of teeth, and rear sprocket R 8  is the laterally outermost rear sprocket having the least number of teeth.  
         [0024]    A rotation sensor (not shown in FIG. 1) is provided for sensing the rotation of crank  27 . The presence or absence of rotation of crank  27  ordinarily is used in part to control the operation of front and rear transmissions  8  and  9 . For example, derailleurs cannot shift properly when crank  27  is stationary, so any requested operation of a derailleur may be delayed until crank  27  is rotating. A rotation sensor typically comprises a reed switch  23  (FIG. 3) mounted to frame body  2  and a magnet (not shown) mounted to one of the crank arms  27   a  and  27   b  so that reed switch  23  provides a pulse whenever the magnet passes by.  
         [0025]    A controller  11  (FIG. 3) is provided for controlling various components including the front and rear transmissions  8  and  9  and the front and rear suspensions  13   f  and  13   r . More specifically, controller  11  controls front and rear transmissions  8  and  9  in response to the operation of shift switches  20   a - 20   d  and mode switch  21   a , and it controls front and rear suspensions  13   f  and  13   r  in response to the operation of control switch  21   b . Controller  11  also automatically controls the operation of front and rear transmissions  8  and  9  in response to bicycle velocity.  
         [0026]    As shown in FIGS. 3 and 4, controller  11  comprises a first control unit  30 , a second control unit  31 , and a third control unit  32 . First control unit  30  may be mounted, for example, on the bottom bracket of frame body  2  in proximity to the rotation sensor and front derailleur  26   f , and it is connected to alternating current generator  19 . The electrical current generated by alternating current generator  19  powers first control unit  30 , and first control unit  30  uses the supplied electrical current to control the operation of front derailleur  26   f , rear derailleur  26   r  and rear suspension  13   r . First control unit  30  also supplies control signals (e.g., a velocity signal) superimposed on a relatively low current signal (e.g., pulse code modulated (PCM) signals) to second control unit  31  and third control unit  32 . Since first control unit  30  is disposed on the bottom bracket of frame body  2 , it is fairly close to alternating current generator  19 . As a result, a short power cable may be used to connect first control unit  30  to alternating current generator  19 , and the communication of power between the two may be carried out with high efficiency.  
         [0027]    First control unit  30  controls front transmission  8 , rear transmission  9  and rear suspension  13   r  in accordance with the operating mode set by mode switch  21   a . In this embodiment, in automatic mode, front transmission  8  and rear transmission  9  are controlled according to bicycle velocity, and rear suspension  13   r  may be set in one of two levels (e.g., hard or soft) depending on bicycle velocity. In manual mode, rear transmission  9  is controlled by the operation of shift switches  20   a  and  20   b , front transmission  8  is controlled by the operation of shift switches  20   c  and  20   d , and rear suspension  13   r  is controlled by the operation of control switch  21   b.    
         [0028]    First control unit  30  has a first control portion  35  that comprises a microcomputer including a CPU, memory, I/O interface, and the like. First control portion  35  also comprises a shift unit  35   a  and a restricting unit  35   b , which may comprise computer programs that operate in a manner discussed below. A number of modules are connected to first control portion  35 . Such modules include a waveform shaping circuit  36  for generating a velocity signal from pulses output from alternating current generator  19 ; a charging control circuit  33 ; a first power storage element  38   a ; a second power storage element  38   b ; the rotation sensor reed switch  23 ; a power supply and communications circuit  34  that switches on and off a relatively low current signal from second power storage element  38   b  to second control unit  31  and third control unit  32  and provides the composite power/control PCM signals mentioned above to second control unit  31  and third control unit  32 ; a power on/off switch  28  that switches on and off a relatively high current signal from first power storage element  38   a  to second control unit  31 ; a front motor driver (FMD)  39   f  for operating a front derailleur motor (FDM)  44   f  for front derailleur  26   f , a rear motor driver (RMD)  39   r  for operating a rear derailleur motor (RDM)  44   r  for rear derailleur  26   r , a front operating location sensor (FLS)  41   f  for front derailleur  26   f , a rear operating location sensor (RLS)  41   r  for rear derailleur  26   r , and a rear suspension driver (RSD)  43   r  for operating rear suspension  13   r.    
         [0029]    Second control unit  31  controls front suspension  13   f  in response to control signals sent by first control unit  30 . More specifically, in automatic mode the hardness of front suspension  13   f  is adjusted depending on bicycle velocity, whereas in manual mode the hardness of front suspension  13   f  is adjusted in response to the operation of control switch  21   b . Second control unit  31  also provides control information from switches  20   a - 20   d ,  21   a  and  21   b  to first control unit  30 . For that purpose, second control unit  31  includes a third power storage element  38   c , a front suspension driver (FSD)  43   f  for operating front suspension  13   f , a second control portion  45  such as a microcomputer, a first receiving circuit  46  for receiving composite power/control signals from power supply and communications circuit  34  in first control unit  30 , and a buffer  48 . As shown in FIG. 2, second control unit  31  is attached to handlebar  15  of handlebar assembly  4  by means of a bracket  50 .  
         [0030]    Third control unit  32  functions as a traditional cycle computer, and it is detachably installed on second control unit  31 . Third control unit  32  has a liquid crystal display (LCD)  56  that displays travel information such as bicycle velocity, cadence, distance traveled, shift position, suspension status, and other information. LCD  56  operates in response to control signals output by first control unit  30 . For that purpose, third control unit  32  also includes a fourth power storage element  38   d , a third control portion  55  such as a microcomputer, a voltage stabilizing circuit  57 , a backlight  58  for illuminating display  56 , a battery  59  such as a button cell, and a second receiving circuit  61  for receiving composite power/control signals from power supply and communications circuit  34  in first control unit  30 . With this arrangement, third control unit  32  can operate even when it is detached from second control unit  31 . This allows various initial settings, such as wheel diameter, to be set, as well as allowing data of various kinds such as travel distance, travel time, etc. to be stored.  
         [0031]    Returning to first control unit  30 , travel data of various kinds is stored in memory in first control portion  35 , as well as control data used to control front transmission  8 , rear transmission  9 , front suspension  13   f , rear suspension  13   r  and LCD  56 . As shown in FIGS. 15 and 16, such stored control data may include, for example, upshift threshold values U (F, R) (FIG. 15) and downshift threshold values D (F, R) (FIG. 16), for controlling the shifting of front transmission  8  and rear transmission  9  based the combination of bicycle velocity and the front and rear sprockets F 1 -F 3  and R 1 -R 8  engaged by chain  29 . In this embodiment, upshift threshold values U (F, R) and downshift threshold values D (F, R) are provided in nine tables labeled Table 4 to Table-4 to accommodate rider preference and riding conditions. For example, in FIG. 15, Table 0, the timing at which upshifting occurs with the chain  29  engaged on front sprocket F 2  and rear sprocket R 3  (U (F 2 , R 3 )) is 11.66. Downshift threshold values given in FIG. 16 are analogous.  
         [0032]    Second power storage element  38   b  is connected to first power storage element  38   a  through a diode  42 . Diode  42  causes electrical current to flow in one direction only from first power storage element  38   a  to second power storage element  38   b . In other words, diode  42  prevents reverse current flow from second power storage element  38   b  to first power storage element  38   a . In this embodiment, first power storage element  38   a  is employed mainly as a power supply for electrical components with high power consumption and high electrical capacity, such as drivers  39   f ,  39   r ,  43   f  and  43   r , whereas second power storage element  38   b  is employed as a power supply for electrical components having low power consumption and low electrical capacity, such as first control portion  35 , third control portion  55 , and LCD  56 . First and second power storage elements  38   a  and  38   b  may comprise high-capacity capacitors, such as electric double layer capacitors. These capacitors store direct current power output from alternating current generator  19  and rectified by charging control circuit  33 . Of course, instead of capacitors, first and second power storage elements  38   a  and  38   b  could comprise secondary cells, such as nickel-cadmium, lithium ion, or nickel hydrogen cells.  
         [0033]    Charging control circuit  33  comprises a rectifier circuit  37  and a charge on/off switch  40 . Rectifier circuit  37  rectifies current output from alternating current generator  19  to produce DC current, and charge on/off switch  40  switches on and off the current output by the rectifier circuit  37  in response to control signals from first control portion  35 . More specifically, first control portion  35  monitors the voltage of first power storage element  38   a . Below a predetermined voltage (e.g., 5.5V), first control portion  35  outputs a control signal for switching on the charge on/off switch  40 , thus allowing first power storage element  38   a  to charge. On the other hand, if the voltage of first power storage element  38   a  goes above a predetermined voltage (e.g., 7 V), first control portion  35  outputs a control signal for switching off the charge on/off switch  40 , thereby preventing excessive voltage from accumulating in first power storage element  38   a.    
         [0034]    Power on/off switch  28  is connected to first power storage element  38   a  and to first control portion  35 . Power is switched on to activate second control portion  45  and FSD  43   f  when it is necessary to adjust front suspension  13   f , but power is switched off otherwise. As a result, needless power consumption from first power storage element  38   a  can be avoided.  
         [0035]    Power supply and communications circuit  34  is connected to second storage element  38   b  and to first control portion  35 . As noted above, power supply and communications circuit  34  switches on and off a relatively low current signal from second power storage element  38   b  to second control unit  31  and third control unit  32  and provides composite power/control signals to second control unit  31  and third control unit  32 . Power supply and communications circuit  34  is controlled in response to information such as velocity, distance traveled, current transmission gear, automatic vs. manual modes, suspension hardness and the like.  
         [0036]    As shown in FIG. 4, first receiving circuit  46  in second control unit  31  is connected to power supply and communication circuit  34 . First receiving circuit  46  extracts the control signals from the composite power/control signals from power supply and communication circuit  34  and communicates the control signals to second control portion  45 . Third power storage element  38   c  also is connected to power supply and communications circuit  34 . Third power storage element  38   c  may comprise, for example, a relatively high capacity capacitor such as an electrolytic capacitor, and it is provided to smooth the electrical current from the composite power/control signals received from power supply and communications circuit  34 . Third power storage element  38   c  provides operating power to buffer  48  that functions to stabilize the analog voltage signals from shift switches  20   a - 20   db  and control switches  21   a  and  21   b.    
         [0037]    Second receiving circuit  61  and fourth power storage element  38   d  in third control unit  32  also are connected to power supply and communication circuit  34  (in parallel with first receiving circuit  46 ). Second receiving circuit  61  extracts the control signals from the composite power/control signals from power supply and communication circuit  34  and communicates the control signals to third control portion  55 . Fourth power storage element  38   d  may comprise an electrolytic capacitor that provides operating power directly to third control portion  55  and indirectly to backlight  58  through voltage stabilizing circuit  57 . Voltage stabilizing circuit  57  stabilizes the voltage from fourth power storage element  38   d  to avoid flickering of backlight  58  that otherwise may be caused by the pulsed control signals superimposed on the power signals from power supply and communications circuit  34 .  
         [0038]    [0038]FIG. 5 illustrates an embodiment of information that may be shown on a display screen  71  of LCD  56 . In this embodiment, display screen  71  comprises a main number display portion  72 , an auxiliary number display portion  73 , a description display portion  74 , a rear gear position display portion  75 , and a front gear position display portion  76 . Information such as bicycle velocity, time, etc. is displayed in numerical format in main number display portion  72  and auxiliary number display portion  73 . Description display portion  74  displays a description of the contents of main number display portion  72  and auxiliary number display portion  73 , as well as showing the transmission operating mode. For example, “VEL” indicates travel velocity, “DST” indicates distance traveled, “CLK” indicates current time, “TIM” indicates travel time, and “GEA” indicates current shift position of the front and rear transmissions, “AT” indicates automatic shift mode, “MT” indicates manual shift mode, and so on. The unit of velocity can be switched between “Km/h” and “Mile/h”, and the unit of distance can be switched between “Km” and “Mile.” 
         [0039]    The rear gear position display portion  75  shows the gear position of the rear transmission  9 , and it comprises a plurality of (e.g., nine) elliptical display symbols gradually decreasing in diameter from left to right to correspond with the size of the actual rear sprockets R 1 -R 8 . When initializing LCD  56 , the number of sprockets for rear transmission  9  can be set to match the actual number of sprockets installed on the bicycle. For example, when rear transmission  9  has eight sprockets, as in this embodiment, the number of rear sprockets is input to the cycle computer. Thereafter, eight elliptical display symbols are displayed from left to right in rear gear position display portion  75 , with the one remaining symbol at the right end not displayed. Similarly, the front gear position display portion  76  shows the gear position of the front transmission  8 , and it comprises a plurality of (e.g., three) elliptical display symbols gradually increasing in diameter from left to right to correspond with the size of the actual front sprockets F 1 -F 3 . When initializing LCD  56 , the number of sprockets for front transmission  8  can be set to match the actual number of sprockets installed on the bicycle. For example, when front transmission  8  has two sprockets, the number of front sprockets is input to the cycle computer. Thereafter, two elliptical display symbols are displayed from right to left in front gear position display portion  76 , with the one remaining symbol at the left end not displayed. As a result of this arrangement, the sprocket positions of front and rear transmissions  8  and  9  may be ascertained intuitively at a glance.  
         [0040]    In operation, the alternating current generator  19  of hub dynamo  10  generates electricity as the bicycle is pedaled, and this electricity is supplied to first control unit  30 , with power being stored by first and second power storage elements  38   a  and  38   b . Since alternating current generator  19  is disposed on rear wheel  7 , first and second power storage elements  38   a ,  38   b  can be charged simply by turning the pedals, with the bicycle remaining stationary, by lifting the rear wheel. Thus, it is a simple matter to at least partially charge first and second power storage elements  38   a ,  38   b  by turning the pedals to allow setting up of the electronically operated transmissions and the information displayed on LCD  56 .  
         [0041]    In automatic shift mode, derailleurs  26   f  and  26   r  and suspensions  13   f  and  13   r  are controlled according to a velocity signal generated by first control portion  35  from the shaped pulse output by waveform shaping circuit  36 . More specifically, a shift operation is performed when the bicycle velocity is greater or less than predetermined values, such as the values shown in FIGS. 12 and 13 discussed above. The rear derailleur  26   r  is given preference in ordinary shift operations. Also, when velocity goes above a predetermined value, the hardness of the suspensions  13   f  and  13   r  is increased.  
         [0042]    Control signals based on information such as velocity, distance, transmission gear, automatic vs. manual modes, suspension hardness, and the like, are generated by first control portion  35  and output to power supply communications circuit  34 . Power supply and communications circuit  34  superimposes the control signals on a power signal derived from second power storage element  38   b  to produce the appropriate PCM signals. The composite power/control signals are then communicated to second control portion  45  and third control portion  55 , where-upon the composite power/control signals are decoded.  
         [0043]    Second control portion  45  is powered by power signals received from power on/off switch  28  and outputs to RSD  43   f  signals for controlling front suspension  13   f  in response to the control signal portion of the composite power/control signals received from power supply and communications circuit  34 . The power signal portion of the composite power/control signals received from power supply and communications circuit  34  powers buffer amp  48 . When a control switch  21   a  or  21   b  or a shift switch  20   a - 20   d  is operated, a signal of different analog voltage is output to first control portion  35  via buffer amp  48 , and first control portion  35  generates the appropriate control signals for controlling one or more of derailleurs  26   f  and  26   r  or suspensions  13   f  and  13   r , or for changing the transmission operating mode.  
         [0044]    Third control portion  55  is powered by the power signal portion of the composite power/control signals received from power supply and communications circuit  34 . Third control portion  55  performs distance calculations and the like based on the control signal portion of the composite power/control signals received from power supply and communications circuit  34  and thereafter outputs to LCD  56  velocity and other kinds of information.  
         [0045]    When driving a motor-driven electrical component having large electrical capacity, such as derailleurs  26   f  and  26   r  or suspensions  13   f  and  13   r , there is a voltage drop in first power storage element  38   a . If first control portion  35 , third control portion  55  and LCD  56  were powered by first power storage element  38   a , the voltage drop could cause the microprocessors and other electronics to reset or cause some other problem. Since the power for these components in this embodiment is provided from second power storage element  38   b  connected to first power storage element  38   a  through diode  42 , the components are unaffected by voltage drops in first power storage element  38   a . While second control portion  45  is powered by first power storage element  38   a , it is normally off except when needed to control front suspension  13   f . Consequently, second control portion  45  is unaffected by voltage drops in first power storage element  38   a.    
         [0046]    More specific operations of first control unit  30  will now be described with reference to FIGS. 6-14. When rear wheel  7  turns, alternating current generator  19  supplies electrical power to first control unit  30 , and this power is stored in first power storage element  38   a  and second power storage element  38   b . The power stored in second power storage element  38   b  is supplied to first control portion  35 , and initialization of first control portion  35  is carried out in Step S 1  of FIG. 6. In this initialization process, the transmission operating mode may be set to automatic shift mode, for example. In Step S 2  it is determined whether or not front restricting mode has been requested, wherein one or more of front sprockets F 1 -F 3  will not be used for shift operations. This mode may be set by simultaneous operation of switches  21   a  and  21   b , for example. The same procedure may be used to cancel front restricting mode. If front restricting mode has been requested, then processing moves from Step S 2  to Step S 6 , and the Restrict Front process shown in FIG. 7 is performed in a Step S 6 . In any event, it is determined in Step S 3  whether or not the system is in automatic shift mode, and in Step S 4  it is determined whether or not the system is in manual shift mode. In Step S 5  it is determined whether or not any other mode has been requested. Such modes may be used for adjusting the hardness of front and rear suspensions  13   f  and  13   r , changing the information displayed on LCD  56 , setting shift threshold values, and so on.  
         [0047]    If it is determined in Step S 3  that the system is in automatic shift mode, then processing moves to Step S 7 . In Step S 7 , the current bicycle velocity V, calculated on the basis of signals output by alternating current generator  19  and shaped by waveform shaping circuit  36 , is acquired. Then, the current sprockets F, R engaged by front and rear transmissions  8  and  9  are acquired from the operating position sensors  41   f  and  41   r  associated with the derailleurs  26   f  and  26   r  in a Step S 8 . In this embodiment, variable F indicates the operating position of front derailleur  26   f  and can vary between 1 and 3. Variable R indicates the operating position of rear derailleur  26   r  and can vary between 1 and 8.  
         [0048]    In Step S 9  it is determined whether or not the bicycle velocity V is above an upshift threshold value U (F, R) for the current sprocket combination as shown in FIG. 15. In Step S 10  it is determined whether or not the bicycle velocity V is below a downshift threshold value D (F, R) for the current sprocket combination as shown in FIG. 16. In these steps, the pulse interval corresponding to velocity V output by waveform shaping circuit  36  is compared with the pulse interval corresponding to the relevant threshold value. Since the pulse intervals vary according to the bicycle velocity V, the decision whether or not the threshold value has been passed is made depending on whether the pulse interval corresponding to velocity V is shorter (velocity V is faster) or longer (velocity V is slower) than the pulse interval corresponding to the threshold value.  
         [0049]    If it is determined in Step S 9  that the bicycle velocity V exceeds the upshift threshold value U (F, R) for the current sprocket combination, processing moves to Step S 11 , and it is determined whether or not the bicycle velocity V is above an upshift threshold value U (F, R+1) established for the combination of front sprocket F and the smaller rear sprocket R+1 adjacent to the current rear sprocket. If so, then the bicycle is accelerating rapidly, and the Upshift 2 process shown in FIG. 9 is performed in Step S 13 , thus giving preference in shifting to front transmission  8 . If the bicycle velocity V is not above the upshift threshold value U (F, R+1), then the Upshift 1 process shown in FIG. 8 is performed in Step S 12 , thus giving preference in shifting to rear transmission  9 .  
         [0050]    If it is determined in Step S 10  that the bicycle velocity V is below the downshift threshold value D (F, R) for the current sprocket combination, then processing moves Step S 14 , and it is determined whether or not the bicycle velocity V is below a downshift threshold value D (F, R−1) established for the combination of front sprocket F with the larger rear sprocket R−1 adjacent to the current rear sprocket. If so, then the bicycle is decelerating rapidly, and the Downshift 2 process shown in FIG. 11 is performed in Step S 16  giving priority to shifting the front transmission  8 . If the bicycle velocity V is not below the downshift threshold value D (F, R−1), then the Downshift 1 process shown in FIG. 10 is performed in Step  13 , giving priority to shifting the rear transmission  9 . Thus, in the case of rapid acceleration or deceleration, i.e. a sudden change in bicycle velocity, shifting is performed giving priority to the front transmission  8  rather than the rear transmission  9  in order to produce a large change of gear ratio.  
         [0051]    If it is determined in Step S 4  that the system is in manual shift mode, then processing moves to Step S 17 , and the manual shift process shown in FIG. 12 is performed. If it is determined in Step S 5  that the system is in another mode, then processing moves to Step S 18 , and the selected other mode process is performed.  
         [0052]    [0052]FIG. 7 is a flow chart of a particular embodiment of the Restrict Front process. In Step S 21  of FIG. 7, it is determined whether or not a flag FS, which indicates that the system is in front restricting mode, is set. If so, then the request made in Step S 2  in FIG. 6 (from the simultaneous operation of switches  21   a  and  21   b ) actually was a request to cancel front restricting mode. Accordingly, flag FS is reset in Step S 23 , flags F 1 -F 3 , which indicate the previously restricted front sprockets, are reset in Step S 24  to enable use of all front sprockets F 1 -F 3 , and processing returns to the main routine.  
         [0053]    If it is determined in Step S 21  that flag FS is not set (the system is not currently in front restricting mode), then flag FS is set in Step S 22  to set the system into front restricting mode. Incidentally, when the rider makes a request to set the system in front restricting mode, the system could be programmed such that, for example, each time control switch  21   a  is pressed, the front gear position display portion  76  of LCD  56  sequentially flashes one of the elliptical display symbols, thus allowing one or more sprockets to be selected. The rider may select a front sprocket by allowing a particular elliptical display symbol to flash for a predetermined time interval, for example. It is then determined in Step S 25  whether or not the elliptical display symbol corresponding to front sprocket F 1  has been selected. If so, then flag F 1  is set in Step S 30 . Setting flag F 1  indicates that the use of the smallest-diameter front sprocket F 1  when shifting is disabled.  
         [0054]    In any event, it is then determined in Step S 26  whether or not the circular display symbol corresponding to front sprocket F 3  has been selected. If so, then flag F 3  is set in Step S 31 . Setting flag F 3  indicates that the use of the largest-diameter front sprocket F 3  when shifting is disabled.  
         [0055]    In any event, it is determined in Step S 27  whether or not flag F 1 , which prohibits the use of front sprocket F 1 , has been set previously. If so, then it is determined in Step S 32  whether or not front sprocket F 2  has been selected. If so, then flag F 2  is set in Step S 33 , in which case only front sprocket F 3  will be used when shifting. If not, then it is determined in Step S 34  whether or not front sprocket F 3  has been selected. If so, then flag F 3  is set in Step S 35 , in which case only front sprocket F 2  will be used when shifting.  
         [0056]    In any event, it is determined in Step S 28  whether or not flag F 3 , which prohibits the use of sprocket F 3 , has been set previously. If so, it is then determined in Step S 36  whether or not sprocket F 2  has been selected. If so, then flag F 2  is set in Step S 37 , in which case only front sprocket F 1  will be used when shifting.  
         [0057]    In any event, it is determined in Step S 29  whether or not the restriction selection procedure has been completed. This may be indicated when the rider operates switch  21   b , for example. If so, then processing returns to the main routine. Otherwise, processing returns to Step S 25 .  
         [0058]    [0058]FIG. 8 is a flow chart of a particular embodiment of the Upshift 1 process. Initially, a decision is made in Step S 40  whether or not crank  27  is turning. This decision is made because, with derailleur-based transmissions, shifting is not desirable unless crank  27  is turning. Whether or not crank  27  is turning may be ascertained by whether or not pulses are output from reed switch  23 . If crank  27  is not turning, then processing simply returns to the main routine. On the other hand, if it is determined in Step S 40  that crank  27  is turning, then it is determined in Step S 41  whether or not flag FS is set, thus indicating that the system is in front restricting mode. If not, then processing moves to step S 42 , and it is determined whether or not rear derailleur  26   r  is positioned at rear sprocket R 8 . If so, then no further upshifting of rear derailleur  26   r  is possible, so processing returns to the main routine. If not, then processing moves to Step S 43 , rear derailleur  26   r  upshifts by one sprocket, and processing returns to the main routine.  
         [0059]    If it is determined in Step S 41  that flag FS is set, then it is determined in Step S 44  whether or not flag F 1  is set, thus indicating that the use of front sprocket F 1  is prohibited. If so, then it is determined in Step S 49  whether or not front derailleur  26   f  is positioned at front sprocket F 1  (thus indicating a prohibited condition). If so, then processing moves to Step S 50 , front derailleur  26   f  upshifts to front sprocket F 2  to eliminate the prohibited condition, and processing returns to the main routine. On the other hand, if it is determined in Step S 49  that front derailleur  26   f  is not positioned front sprocket F 1 , then processing moves to Step S 42  to perform the remaining upshift routine described above.  
         [0060]    If it is determined in Step S 44  that flag F 1  is not set, then it is determined in Step S 45  whether or not flag F 2  is set, thus indicating that the use of front sprocket F 2  is prohibited. If so, then it is determined in Step S 47  whether or not front derailleur  26   f  is positioned at front sprocket F 2  (thus indicating a prohibited condition). If so, then processing moves to Step S 48 , front derailleur  26   f  upshifts to front sprocket F 3  to eliminate the prohibited condition, and processing returns to the main routine. On the other hand, if it is determined in Step S 47  that front derailleur  26   f  is not positioned at front sprocket F 2 , then processing moves to Step S 42  to perform the remaining upshift routine described above.  
         [0061]    If it is determined in Step S 45  that flag F 2  is not set, then it is presumed that flag F 3  is set, thus indicating that the use of front sprocket F 3  is prohibited. Accordingly, it is determined in Step S 46  whether or not front derailleur  26   f  is positioned at front sprocket F 3 . If so, then processing returns to the main routine, since further upshifting of front derailleur  26  to eliminate the prohibited condition is not possible. On the other hand, if it is determined in Step S 46  that front derailleur  26   f  is not positioned at front sprocket F 3 , then processing moves to Step S 42  to perform the remaining upshift routine described above.  
         [0062]    [0062]FIG. 9 is a flow chart of a particular embodiment of the Upshift 2 process. As a general rule, preferably front derailleur  26   f  is upshifted in this routine to accommodate rapid acceleration of the bicycle. It is first determined in Step S 60  whether or not crank  27  is turning. If not, then processing returns to the main routine. If so, then it is determined in Step S 61  whether or not flag FS is set, thus indicating that the system is in front restricting mode. If not, then it is determined in Step S 62  whether or not front derailleur  26   f  is positioned at front sprocket F 3 . If so, then no further upshifting of front derailleur  26   f  is possible, so processing returns to the main routine. If not, then processing moves to Step S 63 , front derailleur  26   f  upshifts by one sprocket, and processing returns to the main routine.  
         [0063]    If it is determined in Step S 61  that flag FS is set, then it is determined in step S 64  whether or not flag F 1  is set, thus indicating that the use of front sprocket F 1  is prohibited. If so, then it is determined in Step S 70  whether or not front derailleur  26   f  is positioned at front sprocket F 1  (thus indicating a prohibited condition). If so, then processing moves to Step S 71 , front derailleur  26   f  upshifts to front sprocket F 2  to eliminate the prohibited condition, and processing returns to the main routine. On the other hand, if it is determined in Step S 70  that front derailleur  26   f  is not positioned at front sprocket F 1 , then processing moves to Step S 62  to perform the remaining upshift routine described above.  
         [0064]    If it is determined in Step S 64  that flag F 1  is not set, then it is determined in a Step S 65  whether or not flag F 2  is set, thus indicating that the use of front sprocket F 2  is prohibited. If so, then processing moves to Step S 68 , front derailleur  26   f  upshifts to front sprocket F 3  (or remains positioned at front sprocket F 3  if it is already there) to avoid the prohibited condition, and processing returns to the main routine.  
         [0065]    If it is determined in Step S 65  that flag F 2  is not set, then it is presumed that flag F 3  is set, thus indicating that the use of front sprocket F 3  is prohibited. Accordingly, it is determined in Step S 66  whether or not front derailleur  26   f  is positioned at front sprocket F 1 . If not, then processing returns to the main routine, since further upshifting of front derailleur  26  is not possible without resulting in a prohibited condition. On the other hand, if it is determined in Step S 66  that front derailleur  26   f  is positioned at front sprocket F 1 , then processing moves to Step S 67 , front derailleur  26   f  upshifts to front sprocket F 2 , and processing returns to the main routine.  
         [0066]    [0066]FIG. 10 is a flow chart of a particular embodiment of the Downshift 1 process. As in the previous routines, a decision is made in Step S 80  whether or not crank  27  is turning. If crank  27  is not turning, then processing simply returns to the main routine. On the other hand, if it is determined in Step S 80  that crank  27  is turning, then it is determined in Step S 81  whether or not flag FS is set, thus indicating that the system is in front restricting mode. If not, then it is determined in Step S 82  whether or not rear derailleur  26   r  is positioned at rear sprocket R 1 . If so, then no further downshifting of rear derailleur  26   r  is possible, so processing returns to the main routine. If not, then processing moves to S 83 , rear derailleur  26   r  downshifts by one sprocket, and processing returns to the main routine.  
         [0067]    If it is determined in Step S 81  that flag FS is set, then it is determined in Step S 84  whether or not flag F 3  is set, thus indicating that the use of front sprocket F 3  is prohibited. If so, then it is determined in Step S 89  whether or not front derailleur  26   f  is positioned at front sprocket F 3  (thus indicating a prohibited condition). If so, then processing moves to Step S 90 , front derailleur  26   f  downshifts to front sprocket F 2  to eliminate the prohibited condition, and processing returns to the main routine. On the other hand, if it is determined in Step S 89  that front derailleur  26   f  is not positioned front sprocket F 3 , then processing moves to Step S 82  to perform the remaining downshift routine described above.  
         [0068]    If it is determined in Step S 84  that flag F 3  is not set, then it is determined in a Step S 85  whether or not flag F 2  is set, thus indicating that the use of front sprocket F 2  is prohibited. If so, then processing moves to Step S 87 , and it is determined whether or not front derailleur  26   f  is positioned at front sprocket F 2  (thus indicating a prohibited condition). If so, then processing moves to Step S 88 , front derailleur  26   f  downshifts to front sprocket F 1  to eliminate the prohibited condition, and processing returns to the main routine. On the other hand, if it is determined in Step S 87  that front derailleur  26   f  is not positioned at front sprocket F 2 , then processing moves to Step S 82  to perform the remaining downshift routine described above.  
         [0069]    If it is determined in Step S 85  that flag F 2  is not set, then it is presumed that flag F 1  is set, thus indicating that the use of front sprocket F 1  is prohibited. Accordingly, it is determined in Step S 86  whether or not front derailleur  26   f  is positioned at front sprocket F 1 . If so, then processing returns to the main routine, since further downshifting of front derailleur  26  to eliminate the prohibited condition is not possible. On the other hand, if it is determined in Step S 86  that front derailleur  26   f  is not positioned at front sprocket F 1 , then processing moves to Step S 82  to perform the remaining upshift routine described above.  
         [0070]    [0070]FIG. 11 is a flow chart of a particular embodiment of the Downshift 2 process. As a general rule, preferably front derailleur  26   f  is downshifted in this process to accommodate rapid deceleration of the bicycle. As in the previous routines, it is first determined in Step S 100  whether or not crank  27  is turning. If not, then processing returns to the main routine. If so, then it is determined in Step S 101  whether or not flag FS is set, thus indicating that the system is in front restricting mode. If not, then it is determined in Step S 102  whether or not front derailleur  26   f  is positioned at front sprocket F 1 . If so, then no further downshifting of front derailleur  26   f  is possible, so processing returns to the main routine. If not, then processing moves to S 103 , front derailleur  26   f  downshifts by one sprocket, and processing returns to the main routine.  
         [0071]    If it is determined in Step S 101  that flag FS is set, then it is determined in Step S 104  whether or not flag F 3  is set, thus indicating that the use of front sprocket F 3  is prohibited. If so, then it is determined in Step S 110  whether or not front derailleur  26   f  is positioned at front sprocket F 3  (thus indicating a prohibited condition). If so, then processing moves to Step S 111 , front derailleur  26   f  downshifts to front sprocket F 2  to eliminate the prohibited condition, and processing returns to the main routine. On the other hand, if it is determined in Step S 110  that front derailleur  26   f  is not positioned at front sprocket F 3 , then processing moves to Step S 102  to perform the remaining downshift routine described above.  
         [0072]    If it is determined in Step S 104  that flag F 3  is not set, then it is determined in Step S 105  whether or not flag F 2  is set, thus indicating that the use of front sprocket F 2  is prohibited. If so, then processing moves to Step S 108 , front derailleur  26   f  downshifts to front sprocket F 1  (or remains positioned at front sprocket F 1  if it is already there) to avoid the prohibited condition, and processing returns to the main routine.  
         [0073]    If it is determined in Step S 105  that flag F 2  is not set, then it is presumed that flag F 1  is set, thus indicating that the use of front sprocket F 1  is prohibited. Accordingly, it is determined in Step S 106  whether or not front derailleur  26   f  is positioned at front sprocket F 3 . If not, then processing returns to the main routine, since further downshifting of front derailleur  26   f  is not possible without resulting in a prohibited condition. On the other hand, if it is determined in Step S 106  that front derailleur  26   f  is positioned at front sprocket F 3 , then processing moves to Step S 107 , front derailleur  26   f  downshifts to front sprocket F 2 , and processing returns to the main routine.  
         [0074]    [0074]FIG. 12 is a flow chart of a particular embodiment of a manual shift process. As a general rule, when a shift switch  20   a  or  20   b  on the right side of handlebar  15  is operated in order to shift rear derailleur  26   r , only rear derailleur  26   r  upshifts or downshifts. Similarly, when a shift switch  20   c  or  20   d  on the left side of handlebar  15  is operated in order to shift front derailleur  26   f , only front derailleur  26   f  upshifts or downshifts.  
         [0075]    As shown in FIG. 12, it is first determined in Step S 121  whether or not downshift switch  20   a  has been operated. If so, then processing moves from Step S 121  to Step S 125 , and the Downshift 3 process shown in FIG. 13 is performed. In any event, it is then determined in Step S 122  whether or not upshift switch  20   b  has been operated. If so, then processing moves to Step S 126 , and the Upshift 3 process shown in FIG. 14 is performed. In any event, it is then determined in Step S 123  whether or not downshift switch  20   c  has been operated. If so, then processing moves to Step S 127 , and the Downshift 2 process shown in FIG. 11 is performed. In any event, it is then determined in Step S 124  whether or not upshift switch  20   d  has been operated. If so, then processing moves to Step S 128 , and the Upshift 2 process shown in FIG. 9 is performed.  
         [0076]    [0076]FIG. 13 is a flow chart of a particular embodiment of a Downshift 3 process. As in the previous routines, it is first determined in Step S 130  whether or not crank  27  is turning. If not, then processing returns to the manual shift process. If crank  27  is turning, then it is determined in Step S 131  whether or not rear derailleur  26   r  is positioned at rear sprocket R 1 . If so, then processing returns to the manual shift process, since no further downshifting of rear derailleur  26   f  is possible. If rear derailleur  26   r  is not positioned at rear sprocket R 1 , then rear derailleur  26   r  downshifts by one sprocket in a step S 132 , and processing returns to the manual shift process.  
         [0077]    [0077]FIG. 14 is a flow chart of a particular embodiment of an Upshift 3 process. As in the previous routines, it is first determined in Step S 135  whether or not crank  27  is turning. If not, then processing returns to the manual shift process. If crank  27  is turning, then it is determined in Step S 136  whether or not rear derailleur  26   r  is positioned at rear sprocket R 8 . If so, then processing returns to the manual shift process, since no further upshifting of rear derailleur  26   f  is possible. If rear derailleur  26   r  is not positioned at rear sprocket R 8 , then rear derailleur  26   r  upshifts by one sprocket in step S 137 , and processing returns to the manual shift process.  
         [0078]    It should be readily apparent from the above that, in this embodiment, it is possible for the cyclist to select the upshift and downshift speeds by selecting the appropriate tables shown in FIGS. 15 and 16. Also, the rider may use the front restricting mode, whether in manual or automatic mode, whenever it is desirable to limit the use of front transmission  8 . For example, the rider may use front restricting mode whenever traveling at a substantially constant rate over a relatively flat path, and then cancel front restricting mode when encountering hills or rough terrain to achieve the greatest flexibility in shifting.  
         [0079]    While the above is a description of various embodiments of inventive features, further modifications may be employed without departing from the spirit and scope of the present invention. For example, in the embodiment described hereinabove, front transmission  8  has three sprockets, but front transmission  8  may have any number of sprockets, with the processing routines modified accordingly. While the rider selected prohibited sprockets, it is possible that the system could be modified so that the rider selects allowed sprockets. Although bicycle velocity was used to determine when to shift front and rear transmissions  8  and  9 , crank rotation speed could be used as well. For example, crank RPM could be detected from the pulsed signals from reed switch  23 . In this case, downshifting could be performed if crank RPM is below a downshift threshold value (e.g., 45 RPM), and upshifting could be performed if crank RPM is above an upshift threshold value (e.g., 60 RPM).  
         [0080]    In the embodiment described above, bicycle velocity is derived from signals produced by alternating current generator  19 . However, bicycle velocity could be derived from signals produced by conventional velocity sensors comprising a reed switch and magnet that detect wheel rotation.  
         [0081]    While external gear shifting mechanisms were used in the described embodiment, the teachings herein could be used to control internal gear shifting mechanisms such as those disposed within a wheel hub.  
         [0082]    The size, shape, location or orientation of the various components may be changed as desired. Components that are shown directly connected or contacting each other may have intermediate structures disposed between them. The functions of one element may be performed by two, and vice versa. The structures and functions of one embodiment may be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature that is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the scope of the invention should not be limited by the specific structures disclosed or the apparent initial focus or emphasis on a particular structure or feature.