Abstract:
A control device is provided for a bicycle having a transmission with a plurality of speed steps, wherein the control device includes a traveling condition signal receiver that receives traveling condition signals corresponding to a traveling condition value of the bicycle, a threshold value memory that stores a first threshold value of the traveling condition, and a processor that compares a plurality of the traveling condition values to the first threshold value and provides a first control signal for shifting the bicycle transmission when the plurality of traveling condition values pass the first threshold value. Additional inventive features will become apparent from the description below, and such features may be combined with the above features to provide additional benefits.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention is directed to bicycles and, more particularly, to various features of an apparatus for controlling a bicycle transmission.  
           [0002]    Bicycle transmissions usually comprise either internally mounted transmissions or externally mounted transmissions. Internally mounted transmissions usually are built into the hub of the rear wheel, and externally mounted transmissions usually have a derailleur for switching a chain among a plurality of sprockets. A shift control device mounted to the bicycle frame and connected to the transmission by a shift control cable usually controls both types of transmissions.  
           [0003]    The shift control device frequently comprises a shift lever mounted to the handlebars, and in many cases the shift lever is positioned close to the brake lever. The shifting operation is difficult when decelerating because it becomes necessary to operate the brake lever and the shift lever at the same time. For this reason, automatic shift control devices have been developed that automatically shifts gears (speed steps) in response to the bicycle&#39;s traveling conditions (e.g., wheel speed or crank revolutions).  
           [0004]    Conventionally, bicycle wheel speed has been detected using a magnet mounted on the bicycle wheel and a reed switch mounted to the bicycle frame. The reed switch produces one pulse per wheel revolution, and the wheel speed may be determined from the interval between detected pulses and the wheel diameter. The automatic shift control device sets an upshift threshold value and a downshift threshold value for each speed step. The bicycle transmission upshifts to the next higher speed step when the detected speed exceeds the upshift threshold value. If the detected wheel speed subsequently falls below the downshift value, then the bicycle transmission downshifts back to the original speed step. Sometimes the upshift threshold value for a particular speed step is set to a slightly higher value than the downshift threshold value of the next higher speed step to create a well known hysteresis effect that minimizes chatter from frequent gear shifting when the wheel speed hovers around the shift points.  
           [0005]    Chattering is prevented easily with the above technique when wheel speed is detected at relatively low frequencies such as one pulse per wheel revolution, since shift timing is controlled according to the different speeds set for upshifting and downshifting. But if, for example, attaching several magnets circumferentially around the bicycle wheel increases the wheel speed detection frequency per revolution, meaningless gear shifting may occur frequently. More specifically, if the bicycle speed drops even momentarily due to obstacles such as small bumps or stones on the road surface, the bicycle transmission would downshift against the rider&#39;s intent. Thereafter, when the bicycle speed returns to normal, the bicycle transmission would upshift back to the original gear. When such shifting actions occur repetitively, the pedal force required to maintain the desired speed changes frequently, thus causing the rider to pedal in an uncoordinated manner and reducing the stability of the ride.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is directed to features of an automatic bicycle transmission that contribute to a reduction of some undesirable characteristics of known bicycle transmissions. In one embodiment of the present invention, a control device is provided for a bicycle having a transmission with a plurality of speed steps, wherein the control device includes a traveling condition signal receiver that receives traveling condition signals corresponding to a traveling condition value of the bicycle, a threshold value memory that stores a first threshold value of the traveling condition, and a processor that compares a plurality of the traveling condition values to the first threshold value and provides a first control signal for shifting the bicycle transmission when the plurality of traveling condition values pass the first threshold value. Additional inventive features will become apparent from the description below, and such features may be combined with the above features to provide additional benefits.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a side view of a bicycle that includes an embodiment of an automatically controlled bicycle transmission;  
         [0008]    [0008]FIG. 2 is a detailed view of a particular embodiment of a handlebar mounted component of the bicycle transmission;  
         [0009]    [0009]FIG. 3 is a block diagram of a particular embodiment of a shift control device;  
         [0010]    [0010]FIG. 4 is a table showing a particular embodiment of upshift and downshift threshold values;  
         [0011]    [0011]FIG. 5 is a table showing a particular embodiment of relationships between threshold values and judgment timing;  
         [0012]    [0012]FIG. 6 is a flowchart of a particular embodiment of an algorithm for operating the bicycle transmission;  
         [0013]    [0013]FIG. 7 is a flowchart of a particular embodiment of an algorithm for automatically operating the bicycle transmission;  
         [0014]    [0014]FIG. 8 is a flowchart of a particular embodiment of an algorithm for manually operating the bicycle transmission;  
         [0015]    FIGS.  9 ( a ) and  9 ( b ) are graphs showing relationships between speed steps and wheel speed;  
         [0016]    [0016]FIG. 10 is a side view of a bicycle that includes an alternative embodiment of an automatically controlled bicycle transmission;  
         [0017]    [0017]FIG. 11 is a table showing a particular embodiment of upshift and downshift threshold values in this embodiment;  
         [0018]    [0018]FIG. 12 is a table showing another embodiment of upshift and downshift threshold values;  
         [0019]    [0019]FIG. 13 is a table showing a particular embodiment of relationships between threshold values and judgment timing;  
         [0020]    [0020]FIG. 14 is a flowchart of another algorithm for automatically operating the bicycle transmission;  
         [0021]    [0021]FIG. 15 is a flowchart of another algorithm for automatically operating the bicycle transmission; and  
         [0022]    [0022]FIG. 16 is a block diagram of another embodiment of a shift control device; 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0023]    [0023]FIG. 1 is a side view of a bicycle that includes a particular embodiment of an automatically controlled bicycle transmission. The bicycle comprises a frame  1  having a double-loop-shaped frame body  2 , a saddle  11 , a front fork  3 , a handlebar part  4 , a driving part  5 , a front wheel  6  in which is installed a generator hub  12 , a rear wheel  7  in which is installed an internal gear changing hub  10 , and front and rear brake devices  8  (only the front brake device is shown in the drawing). The handlebar part  4  has a handlebar stem  14 , which is fixed to an upper part of the front fork  3 , and a handlebar  15  fixed to the handlebar stem  14 . Brake levers  16  and grips  17  are installed on the two ends of the handlebar  15 . Brake levers  16  operate the brake devices  8 .  
         [0024]    A shift operation unit  9  is mounted on the right-side brake lever  16 . As shown in FIG. 2, the shift operation unit  9  has a control housing  20  formed integrally with the right-side (front-wheel) brake lever  16 , two control buttons  21  and  22  disposed next to each other to the left and right on the lower portion of the control housing  20 , a control dial  23  disposed above the control buttons  21  and  22 , and a liquid-crystal display component  24  disposed to the left of the control dial  23 .  
         [0025]    The control buttons  21  and  22  are triangular push buttons. The control button  21  on the left side is a button for performing shifts to a higher speed step from a lower speed step (upshifts), while the control button  22  on the right side is a button for performing shifts to a lower speed step from a higher speed step (downshifts). The control dial  23  is used for switching among two shifting modes and a parking mode (P), and it has three stationary positions: P, A, and M. The shifting modes comprise an automatic shift mode (A) and a manual shift mode (M). The parking mode (P) is for locking the internal gear changing hub  10  and controlling the rotation of the rear wheel  7 . The automatic shift mode (A) is for automatically shifting the internal gear changing hub  10  by means of a bicycle speed signal from the generator hub  12 . The manual shift mode (M) is for shifting the internal gear changing hub  10  through the operation of the control buttons  21  and  22 . The current riding speed is displayed on the liquid-crystal display component  24 , as is the current speed step selected at the time of the shift.  
         [0026]    A shift control unit  25  (FIG. 3) for controlling shifting operations is housed inside the control panel  20 . In general, the shift control unit  25  comprises a microcomputer consisting of a CPU, a RAM, a ROM, and an I/O interface. As shown in FIG. 3, the shift control unit  25  is connected to the generator hub  12 , to an actuation position sensor  26  such as a potentiometer that senses the actuation position of the internal gear changing hub  10 , to the control dial  23 , and to the control buttons  21  and  22 . The shift control unit  25  also is connected to a power supply  27  (for example, a battery), to a motor driver  28  for driving a variable-speed motor  29  that operates the internal gear changing hub  10 , to the liquid-crystal display component  24 , to a memory component  30 , and to other input/output components. The memory component  30  may be an EEPROM or another type of rewritable nonvolatile memory. Various types of data, such as passwords used during parking mode, tire diameter used for speed detection or the like, are stored in the memory component  30 . Also stored in memory component  30  are data expressing respective relations between each speed step and the shifting speeds during the automatic mode. The shift control unit  25  controls the motor  29  according to the various modes, and it also controls the display of the liquid-crystal display component  24 .  
         [0027]    The generator hub  12  is, for example, a 28-pole AC generator that generates an alternating current signal in response to wheel speed (i.e., 14 cycles per wheel revolution). The shift control unit  25  detects the bicycle speed S from the AC signals sent from generator hub  12 . Thus, wheel speed S can be detected 14 times per revolution, which results in much greater resolution that wheel speed detected using conventional magnets and reed switches. This permits real-time execution of shift control.  
         [0028]    The drive unit  5  comprises a gear crank  18  rotatably supported by the frame body  2 , a chain  19  driven by the crank  18 , and the internal gear changing hub  10 . The internal gear changing hub  10  is a three-speed hub having three speed step positions and a lock position, and it is switched by shift motor  29  to the three speed step positions and to the lock position, for a total of four positions. As noted above, the lock position restricts the revolution of internal gear changing hub  10 . In this embodiment, the gear ratios of internal gear changing hub  10  are 0.733, 1 and 1.360.  
         [0029]    [0029]FIG. 4 is a table showing a particular embodiment of upshift and downshift threshold values used when the bicycle is operating in automatic mode. In this embodiment, the downshift threshold value is divided into two thresholds, a first downshift threshold D 1  and a second downshift threshold D 2 . In general, when a downshift is to be performed at the first downshift threshold D 1 , the downshift is performed only when the traveling condition has initially passed the downshift threshold D 1 , and one or all of a plurality of subsequent detections of the traveling condition also have passed the downshift threshold D 1 . On the other hand, when the detected traveling condition passes the second downshift threshold D 2 , a downshift is performed immediately, regardless of any prior detected traveling condition. For example, if the thresholds are given in terms of bicycle speed as shown in FIG. 4, then the downshift is performed only when the bicycle speed has initially fallen below the downshift threshold D 1 , and one or all of a plurality of subsequently detected bicycle speeds also have fallen below the downshift threshold D 1 . When the detected bicycle speed falls below the second downshift threshold D 2 , a downshift is performed immediately, regardless of any prior detected speeds.  
         [0030]    In this embodiment, the upshift and downshift thresholds for each gear or speed step are derived using the crank rotation speed as a reference. For example, the upshift threshold U is set at a crank rotation speed of 65 rpm, whereas the first downshift threshold D 1  is set at a crank rotation speed of 42.5 rpm and the second downshift threshold D 2  is set at a crank rotation speed of 30 rpm. The upshift threshold for the first speed step U( 1 ) is 12 km/h, for example, and the upshift threshold for the second speed step U( 2 ) is 16.4 km/h, for example. For the third speed step, the first downshift threshold D 1 ( 3 ) is 14.6 km/h, for example, and the second downshift threshold D 2 ( 3 ) is 10.3 km/h, for example. For the second speed step, the first downshift threshold D 1 ( 2 ) is 10.7 km/h, for example, and the second downshift threshold D 2 ( 2 ) is 7.6 km/h, for example.  
         [0031]    An additional feature of this embodiment is that it may be desirable to determine whether or not the detected speed has fallen below the first threshold for a prescribed time period to further guard against spurious operation. For example, it could be ascertained whether or not the detected speed falls below the first downshift threshold D 1  for at least a period of one half of one rotation of the crank  18 . By making the judgment time longer than one half of one rotation of crank  18 , gear shift control can be performed with consideration of the pulses caused by the speed variations of the crank  18 . Thus, the pulses produced during one half of one rotation of the crank  18  have less of an effect on the shifting characteristics.  
         [0032]    The periods of the crank rotation speed used in the setting of the first downshift threshold D 1  in this embodiment, and the judgment times set in consideration thereof, are shown in FIG. 5. Here, in the case of the first downshift threshold D 1 , 42.5 rpm is set as the reference, and since the period is the reciprocal of the rotation speed, the period of one half of one rotation of the crank  18  is 0.71 seconds. In the case of the second downshift threshold D 2 , the period is 1 second. When the gear ratios of the first, second and third speeds of the internal gear changing hub  10  are set to 0.733, 1, and 1.360 respectively, and the numbers of teeth on a front sprocket (not shown) which is attached to the crank  18  and a rear sprocket (not shown) which is attached to the rear wheel  7  are set to 33 and 16 respectively, the speed increasing ratios of the crank rotation speed and the wheel rotation speed become 1.51, 2.06, and 2.81 in first speed, second speed and third speed respectively. Accordingly, since bicycle speed signals S are output from the generator hub  12  fourteen times per one rotation of the front wheel  6 , judgments as to whether or not a downshift will be performed according to the consecutive detection results of the bicycle speed S may be made 20 times when in third speed and 15 times when in second speed in order to exceed one half of one rotation of the crank  18 . Since the minimum judgment time must exceed the pulse period, and if the bicycle is traveling at a speed near the first downshift threshold D 1 , this minimum judgment time is 0.72 seconds in third speed and 0.74 seconds in second speed.  
         [0033]    The bicycle transmission is operated (including locking) using operating dial  23  and, in the case of the manual mode of operation, operating buttons  21  and  22 . FIGS.  6 - 8  are flowcharts showing a particular embodiment of an algorithm for the operation of shift control unit  25 . As shown in FIG. 6, when the power is turned on (start), initialization occurs in step S 1 . Here, various operating parameters may be set (e.g., that a 26-inch diameter wheel is installed on the bicycle), the current speed step VP is read and set (e.g., to the second speed VP=2) from position sensor  26 , and various flags are set. In step S 2 , a decision is made whether or not control dial  23  is set to the parking mode (P). In step S 3 , a decision is made whether or not control dial  23  is set to the automatic shift mode (A). In step S 4 , a decision is made whether or not control dial  23  is set to the manual shift mode (M). In step S 5 , a decision is made whether to select some other process, such as inputting tire diameter, for example.  
         [0034]    When the control dial  23  has been turned to the (P) position and set to the parking mode (P), then the process moves from step S 2  to step S 6 . In step S 6 , the parking process (P) is executed. In this process, various routines are executed by operating buttons  21 ,  22 . Such routines may include a password registration routine for registering a password that will clear the locked status of internal gear changing hub  10 , or a password input process for inputting and referencing the password for clearing the locked status, and so on. When the control dial  23  has been turned to the (A) position and set to the automatic shift mode (A), then the process moves from Step S 3  to step S 7  to execute the automatic shift process (A) shown in FIG. 7. If the control dial  23  is turned to the (M) position and set to the manual shift mode (M), then the process moves from step S 4  to step S 8  to execute the manual shift process (M) shown in FIG. 8. If other processes are selected, the process moves from step S 5  to step S 9 , and the selected process is executed.  
         [0035]    [0035]FIG. 7 is a flowchart of a particular embodiment of an algorithm for the automatic shift process (A) of step S 7 . In the automatic shift process of step S 7 , the operating position VP is set to the appropriate speed step which corresponds to the bicycle speed S. Initially, it is ascertained whether or not a determining flag DF is set or not (DF=1) in a step S 7 . This determining flag DF is set in a step S 25  described hereinbelow the first time the bicycle speed is detected to be below the first downshift threshold value D 1 , and it is used in order to determine whether or not a number of detection results corresponding to one half of one rotation of the crank  18  have elapsed at the time of a downshift in accordance with the first downshift threshold D 1 . If the determining flag DF is already set, processing moves to step S 12 , wherein a counting variable N showing the number of speed detections is increased by one. The count N also is used to determine whether or not a number of detection results corresponding to one half of one rotation of the crank  18  have elapsed at the time of a downshift in accordance with the first downshift threshold D 1 . If the determining flag DF is not set, then step S 12  is skipped.  
         [0036]    In step S 13 , the operating position VP of the operating position sensor  26  (indicating the current speed step) is acquired, and in step S 14 , the current bicycle speed S according to the speed signals from the generator hub  12  is acquired. In step S 15 , a judgment is made whether or not the current bicycle speed S exceeds the upshift threshold U (VP) for the current speed stepd step shown in FIG. 4. In step S 16 , a judgment is made whether or not the current bicycle speed S has fallen below the first downshift threshold D 1  (VP) shown in FIG. 4. If the detected bicycle speed S is higher than the first downshift threshold D 1  (VP) and lower than the upshift threshold U (VP), then processing moves from step S 16  to step S 17 , wherein the determining flag DF is reset in order to cancel any previous downshift judgment made from the first downshift threshold D 1  (VP), and processing returns to the main routine.  
         [0037]    If it was determined in step S 15  that the current bicycle speed S exceeds the upshift threshold U (VP) for the current speed step (e.g., if the bicycle speed S is faster than 16.4 km/h when in second gear (VP=2)), then processing moves to step S 18 . In step S 18 , the determining flag DF is reset in order to cancel any downshift judgment made from the first downshift threshold D 1  (VP). In step S 19 , a judgment is made whether or not the bicycle transmission is in third gear. When the bicycle transmission is in third gear, no further upshifts can be made, so the process moves to step S 16  without further upshift processing. Note that the upshift threshold in third speed is 255 km/h, a speed which is inconceivable under normal circumstances, and therefore this routine would not normally be performed in third gear. When the bicycle transmission is below third gear, then the process moves to step S 20 , wherein the operating position VP is incremented by one in order to shift up one speed step, after which processing moves to step S 16 . At approximately the same time, motor  29  is operated so that the internal gear shifting hub  10  shifts up one gear.  
         [0038]    If it is determined in step S 16  that the current bicycle speed S is below the first downshift threshold D 1  (VP) for the current speed step (e.g., if the bicycle speed S falls below 10.7 km/h when in second gear (VP=2)), then the process moves from step S 16  to step S 21 . In step S 21 , a judgment is made whether or not the current bicycle speed S has fallen below the second downshift threshold D 2  (VP) for the current speed step. In this embodiment, if the detected bicycle speed S falls below the second downshift threshold D 2  (VP), a downshift is performed immediately, regardless of any prior detection results. Thus, when the speed drops due to rider fatigue or an ascent of a steep slope, a downshift is performed quickly such that the load on the rider can be lightened. Hence, if it ascertained in step S 21  that the detected bicycle speed S falls below the second downshift threshold D 2  (VP), the process moves to step S 22 , and a judgment is made whether or not the bicycle transmission is in first gear. If the bicycle transmission is in first gear, then there is no lower gear, so no further downshift processing is performed and the process returns to the main routine. When the bicycle transmission is in second gear or above, the process moves to step S 23 , wherein the operating position VP is decreased by one in order to shift down one speed step, after which the process returns to the main routine. At approximately the same time, motor  29  is operated so that the internal gear changing hub  10  shifts down one gear.  
         [0039]    If it is determined in Step S 21  that the detected bicycle speed S is faster than the second downshift threshold D 2  (VP), then the process moves from step S 21  to step S 24 . In step S 24 , a judgment is made whether or not the determining flag DF is already set. This judgment is made to determine whether or not this is the first time that the bicycle speed is slower than the first downshift threshold D 1 (VP) and above the second downshift threshold. If the determining flag DF is not yet set (thus indicating that this time is the first such detection), then the determining flag is set in step S 25 , the counting variable N is set to 0 in Step  26 , and a maximum count number Nm is set to the number of judgments N (VP) for the current speed step as shown in FIG. 5. A judgment already has been made in step S 16 , so Nm is actually loaded with the number of judgments shown in FIG. 5 minus one, for example  19  in third gear and  14  in second gear.  
         [0040]    If it is determined that the determining flag DF is set (i.e., if the detected bicycle speed S already has been detected at least once to be lower than the first downshift threshold D 1 (VP) and faster than the second downshift threshold D 2 (VP)), then the process moves from step S 24  to step S 28 . In step S 28 , a judgment is made whether or not the count number N has reached the maximum count number Nm (i.e., whether or not the bicycle speed S has been detected to be slower than the first downshift threshold D 1  (VP) and higher than the second downshift threshold D 2  (VP) Nm number of times, which corresponds to one half of one rotation of the crank). If the count number N has not yet reached the maximum count number Nm, then the process returns to the main routine. If it is determined in step S 28  that the count number N has reached the maximum count number Nm, then the determining flag DF is reset in step S 29 , the maximum count number Nm is set to zero in step S 30 , and the process moves to step S 22 . As noted above, in Step S 22  a judgment is made whether or not the bicycle transmission is in first gear. If the bicycle transmission is in first gear, then there is no lower gear, so no further downshift processing is performed, and the process returns to the main routine. When the bicycle transmission is in second gear or above, processing moves to step S 23 , wherein the operating position VP is decreased by one in order to shift down one speed step, after which the process returns to the main routine. At approximately the same time, motor  29  is operated so that the internal gear changing hub  10  shifts down one gear.  
         [0041]    In conclusion, when the detected bicycle speed S has fallen below the first downshift threshold D 1  (VP), a downshift is not performed immediately, but rather downshifts are performed only when it is judged that one or all of a plurality of subsequently detected bicycle speeds S fall below the first downshift threshold D 1  (VP) and are above the second downshift threshold D 2  (VP). If it is judged that even only one of the detected bicycle speeds S has not fallen below the first downshift threshold D 1  (VP), a downshift is not performed, and the current speed step is maintained. As a result, spurious downshifting operations are reduced even when the traveling condition is detected frequently.  
         [0042]    [0042]FIG. 8 is a flowchart of a particular embodiment of an algorithm for manually operating the bicycle transmission (step S 8  in FIG. 6). In manual shift mode (M), gear shifts are performed one gear at a time by pressing operating buttons  21  and  22 . Initially, the operating position VP of the operating position sensor  26  is acquired in a step S 41 . In step S 42 , a judgment is made whether or not the operating button  21  has been pressed, and in step S 43  a judgment is made whether or not the operating button  22  has been pressed. If the operating button  21  has been pressed, then the process moves from step S 42  to step S 44 . In step S 44 , a judgment is made whether or not the bicycle transmission currently is in third gear. If not, then the process moves to step S 45 , wherein the operating position VP is incremented by one and the transmission is upshifted accordingly. Otherwise, this process is skipped. If the operating button  22  has been pressed, then the process moves from step S 43  to step S 46 . In step S 46 , a judgment is made whether or not the bicycle is in first gear. If not, then processing moves to step S 47 , wherein the operating position VP is decremented by one and the transmission is downshifted accordingly. Otherwise, this process is skipped.  
         [0043]    [0043]FIG. 9( a ) is a graph showing the relationships between speed steps and wheel speed for an automatic shifting device as described above, and FIG. 9( b ) is a graph showing the relationships between speed steps and wheel speed for a conventional automatic shifting device. In FIGS.  9 ( a ) and  9 ( b ), the vertical axis and the horizontal axis respectively show speed and time. In the automatic gear shift processing described above and shown in FIG. 9( a ), when, for example, the bicycle speed S falls below the first downshift threshold in third gear D 1  ( 3 ) (for example, 14.6 km/h), judgments are made in steps S 16 , S 24  and S 28  as to whether or not N ( 3 ) (e.g., 20) subsequent consecutive detection results have fallen below the first downshift threshold D 1  ( 3 ). In the case of FIG. 9( a ), the bicycle speed S does not fall below the first downshift threshold D 1  ( 3 ) in the region shown by shading, and hence a “No” judgment is made in step S 16  of FIG. 7. As a result, the downshift from the third speed step to the second speed step is cancelled, and no downshift is performed.  
         [0044]    After the bicycle speed S has exceeded the upshift threshold U ( 2 ) and once again fallen below the first downshift threshold D 1  ( 3 ), judgments are again made in steps S 16 , S 24  and S 28  whether or not N ( 3 ) subsequent consecutive detection results have fallen below the first downshift threshold D 1  ( 3 ). This time, all N ( 3 ) detection results have fallen below the first downshift threshold D ( 3 ), so when the N ( 3 ) detections are complete, a downshift from the third speed step to the second speed step is executed.  
         [0045]    In the conventional case, on the other hand, as is illustrated in FIG. 9( b ), when the bicycle speed S falls below the first downshift threshold D 1  ( 3 ), a downshift from the third speed step to the second speed step is performed immediately, and when the bicycle speed exceeds the upshift threshold U ( 2 ) (for example 16.4 km/h), an upshift back to the third speed step is performed immediately. Then, when the bicycle speed S again falls below the first downshift threshold D 1  ( 3 ), a downshift to the second speed step is performed immediately. As a result, frequent shifts that are against the will of the rider are performed.  
         [0046]    In the automatic control apparatus described above, whether or not downshifts are to be performed is decided by judging whether or not the bicycle speed S has fallen below the first downshift threshold D 1  (VP) over a number of judgment times N (VP) for each speed step at the time of downshift. Thus, even if speed signals are acquired frequently, unwanted downshifts can be prevented. As a result, smooth gear shift operations can be realized, and the sense of discomfort felt during a gear shift operation can be reduced. As an additional benefit, even when the first downshift threshold D 1  (VP) is exceeded, a downshift is not performed immediately, but rather the downshift threshold alters in accordance with the degree of speed reduction such that the actual downshift rate drops as the degree of speed reduction increases. Moreover, when the bicycle speed drops below the second downshift threshold D 2  (VP) which is lower than the first downshift threshold D 1  (VP), a gear shift is performed immediately without waiting for a plurality of detection results As a result, downshifts can be performed quickly when the speed has dropped due to rider fatigue, the ascent of a steep slope or the like. Thus, the load on the rider can be even further reduced.  
         [0047]    In the above embodiment, bicycle speed was used as the traveling condition. However, the crank rotation speed also may also be used. In such a case, as is illustrated in FIG. 10, the crank rotation speed may be detected by attaching a detection element  113  such as a magnet to the gear crank  18  of the bicycle, and attaching a crank rotation detector  112  comprising a reed switch, for example, which detects the rotation of the detection element  113 , to the frame body  2  of the bicycle. If desired, a large number of detection elements  113  and/or rotation detectors may be provided. As shown in FIG. 11, the upper limit and lower limit of the crank rotation speed may be set as thresholds in accordance with each speed step. In FIG. 11, the same value is set for each speed step, but these may be made to differ. In automatic gear shift mode, similarly to the operation shown in FIG. 7, control may be performed such that when the crank rotation speed falls below the first downshift threshold D 1  (VP) (step S 16 ) but does not fall below the second downshift threshold D 2  (VP) (step S 21 ), a judgment is made as to whether or not all of a plurality of consecutive subsequent detection results of the crank rotation speed fall below the first downshift threshold D 1  (VP). When all of the detection results fall below the first downshift threshold D 1  (VP), then a downshift is performed, whereas if even only one detection result does not fall below the first downshift threshold D 1  (VP), the downshift is cancelled.  
         [0048]    While the above is a description of embodiments of some inventive features, further inventive features may be employed without departing from the spirit and scope of the present invention. For example, the above embodiment used a three-speed internal gear changing hub  10  as an example of the gear shifting device. However, the number of speed steps and the form of the gear shifting device are not limited to these embodiments. For example, an external gear shift mechanism comprising a plurality of sprockets and a derailleur may be used as the gear shifting device. Also, the above embodiments employed a gear shifting device driven by a motor as an example. However, the gear shifting device may be driven by a solenoid; electric, hydraulic or pneumatic cylinders, and so on.  
         [0049]    In the above embodiments, a second downshift threshold D 2  (VP) is set such that when the bicycle speed S falls below the second downshift threshold D 2  (VP), a downshift is performed immediately. However, downshift control may be performed without the use of the second downshift threshold D 2  (VP).  
         [0050]    In the above embodiments, upshifts are performed immediately after the upshift threshold has been exceeded. However, upshifts may be performed in a similar manner to downshifts, requiring a predetermined number of judgments. In this case, first and second upshift thresholds U 1  (VP) and U 2  (VP) may be used, as well as a first upshift threshold U 1  (VP) alone. FIG. 12 shows an example of the respective thresholds in this case. As in the above embodiment, the upshift and downshift thresholds for each speed step are set with the crank rotation speed as the reference. The first and second upshift thresholds U 1  and U 2  are set at respective crank rotation speeds of 60 rpm and 75 rpm, whereas the first and second downshift thresholds D 1  and D 2  are set at respective crank rotation speeds of 42.5 rpm and 30 rpm. The first upshift threshold for the first speed step U 1  ( 1 ) is 11.1 km/h, for example, and the first upshift threshold for the second speed step U 1  ( 2 ) is 15.1 km/h, for example. The second upshift thresholds U 2  for the first and second speed steps are 13.9 km/h and 18.9 km/h respectively, whereas the downshift thresholds are the same as in FIG. 4.  
         [0051]    As in the above embodiments, an additional feature of this embodiment is that it may be desirable to determine whether or not the detected speed has exceeded the first upshift threshold for a prescribed time period to further guard against spurious operation. For example, it could be ascertained whether or not the detected speed exceeds the first upshift threshold U 1  for at least a period of one half of one rotation of the crank  18 . By making the judgment time longer than one half of one rotation of crank  18 , gear shift control can be performed with consideration of the pulses caused by the speed variations of the crank  18 . Thus, the pulses produced during one half of one rotation of the crank  18  have less of an effect on the shifting characteristics.  
         [0052]    The periods of the crank rotation speed used in the setting of the first upshift threshold U 1  in this embodiment, and the judgment times set in consideration thereof, are shown in FIG. 13. Here, the first upshift threshold U 1  is set with 60 rotations as a reference, and since the period is a reciprocal of the rotation speed, the period of half of one rotation of the crank  18  is 0.50 seconds. In the case of the second downshift threshold D 2 , the period is 0.40 seconds. If the gear ratios of the internal gear changing hub  10  and the number of teeth on the front and rear sprockets are set to be the same as in the above embodiment, the speed increasing ratios of the crank rotation speed and the wheel rotation speed become 1.51, 2.06, and 2.81 in first speed, second speed and third speed respectively, as noted previously. Accordingly, since speed signals S are output from the generator hub  12  fourteen times per one rotation of the front wheel  6 , judgments as to whether or not an upshift should be performed according to consecutive speed detection results are performed 11 times in first speed and 15 times in second speed in order to exceed a one half of one rotation of the crank  18 . Since the minimum judgment time must exceed the pulsation period, and if the bicycle is traveling at a speed near the first upshift threshold U 1 , this minimum judgment time is taken 0.52 seconds in first speed, and 0.52 seconds in second speed.  
         [0053]    [0053]FIG. 14 is a flowchart of a particular embodiment of an algorithm for automatically operating the bicycle transmission in this embodiment, which uses the first and second upshift thresholds U 1  (VP) and U 2  (VP) set in such a manner. In this embodiment, steps S 11  through S 30  are substantially identical to those in the embodiment shown in FIG. 7, and therefore explanation thereof has been omitted. Note that when it is judged in step S 11  that the determining flag DF for a downshift is not set, then the process moves to S 32 . In step S 32 , a judgment is made whether or not a determining flag UF for an upshift is set. This determining flag UF is a flag similar to the determining flag DF for a downshift, and this flag is set in step S 41  as discussed below. If the determining flag UF is already set, then a counting variable M displaying the number of speed detections for an upshift is increased by one in a step S 33 , and the processs moves to step S 13 . This determining flag UF and the counting variable M are used to determine the elapse of one half of one rotation of the crank  18  during an upshift in accordance with the first upshift threshold U 1 . If the determining flag UF is not set, then step S 33  is skipped and the process moves to step S 13 .  
         [0054]    In step S 17 , the determining flag UF is reset in addition to the determining flag DF. Additionally, if a judgment is made that the bicycle speed S detected in step S 16  has fallen below the first downshift threshold D 1  (VP), then the process moves to step S 31 , wherein the determining flag UF is reset in order to cancel any previous upshift judgment in accordance with the first upshift threshold U 1  (VP).  
         [0055]    If it is determined in step S 15  that the current bicycle speed S is above the first upshift threshold U 1  (VP) for the current speed step (e.g., if the bicycle speed S is above 15.1 km/h when in second gear (VP=2)), then the process moves from step S 15  to step S 35 , wherein the determining flag DF is reset to cancel any previously downshift judgment in accordance with the first downshift threshold D 1 (VP). In step S 36 , a judgment is made whether or not the current bicycle speed S has exceeded the second upshift threshold U 2  (VP) for the current speed step. In this embodiment, if the detected bicycle speed S exceeds the second upshift threshold U 2  (VP), an upshift is performed immediately, regardless of any prior detection results. Thus, when the speed increases dramatically, an upshift is performed quickly such that the load on the rider can be lightened. Hence, if it ascertained in step S 36  that the detected bicycle speed S exceeds the second upshift threshold U 2  (VP), the process moves to step S 37 , and a judgment is made whether or not the bicycle is in third gear. If the bicycle is in third gear, then no further upshift processing is performed, and the process returns to the main routine. When the bicycle transmission is in second gear or below, then the moves to step S 38  wherein the operating position VP is increased by one in order to shift up one speed step, after which the process returns to the main routine. At approximately the same time, motor  29  is operated so that the internal gear changing hub  10  shifts up one gear.  
         [0056]    If it is determined in Step S 36  that the detected bicycle speed S is slower than the second upshift threshold U 2  (VP), then the process moves from step S 36  to step S 40 . In step S 40 , a judgment is made whether or not the determining flag UF is already set. This judgment is made to determine whether or not this is the first time that the bicycle speed has been detected to be higher than the first upshift threshold U 1 (VP) and below the second upshift threshold. If the determining flag UF is not yet set (thus indicating that this is the first such detection), then the determining flag UF is set in step S 41 , the counting variable M is set to 0 in step S 42 , and the maximum count number Mm is set to the number of judgments M (VP) for the current speed step as shown in FIG. 13. A judgment already has been made in step S 15 , so Mm is actually loaded with the number of judgments shown in FIG. 13 minus one, for example  14  in second gear and  10  in first gear.  
         [0057]    If it is determined in step S 40  that the determining flag UF is set (i.e., if the detected bicycle speed S already has been detected at least once to be higher than the first upshift threshold U 1 (VP) and slower than the second upshift threshold U 2 (VP)), then the process moves from step S 40  to step S 44 . In step S 44 , a judgment is made whether or not the count number M has reached the maximum count number Mm (i.e., whether or not the bicycle speed S has been detected to be higher than the first upshift threshold U 1  (VP) and lower than the second upshift threshold U 2  (VP) Mm number of times, which corresponds to one half of one rotation of the crank). If the count number M has not yet reached the maximum count number Mm, then the process returns to the main routine. If it is determined in step S 44  that the count number M has reached the maximum count number Mm, then the determining flag UF is reset in step S 45 , the maximum count number Mm is set to zero in step S 46 , and the process moves to step S 37 . As noted above, in step S 37  a judgment is made whether or not the bicycle is in third gear. If the bicycle is in third gear, no further upshift processing is performed, and the process returns to the main routine. When the bicycle is in second gear or below, then the process moves to step S 38 , wherein the operating position VP is increased by one in order to shift up one speed step, after which the process returns to the main routine. At approximately the same time, motor  29  is operated so that the internal gear changing hub  10  shifts up one gear.  
         [0058]    In conclusion, when the detected bicycle speed S exceeds the first upshift threshold U 1  (VP), an upshift is not performed immediately, but rather upshifts are performed only when it is judged that one or all of a plurality of subsequently detected bicycle speeds S exceed the first upshift threshold U 1  (VP) and that the detected speed is below the second upshift threshold U 2  (VP). If it is judged that even only one of the prescribed plurality of detection results has not exceeded the first upshift threshold U 1  (VP), an upshift is not performed, and the current speed step is maintained. As a result, spurious upshifting operations are reduced even when the traveling condition is detected frequently.  
         [0059]    Upshifts to speed steps with a larger gear ratio also may be performed using only one upshift threshold such that when the detected bicycle speed S exceeds the upshift threshold U, an upshift is not performed immediately, but rather is performed only when all of the detection results over a predetermined period of time exceed the upshift threshold, and is not performed when the bicycle speed S does not exceed the upshift threshold even only once during the elapse of the predetermined period of time. FIG. 15 is a flowchart of an algorithm for automatically operating the bicycle transmission in this embodiment. In FIG. 15, the operations of steps S 11  through S 17  and the operations from step S 21  to step S 30  are the same as those in FIG. 7, and hence explanation thereof has been omitted.  
         [0060]    If a judgment is made in step S 15  that the current bicycle speed S exceeds the upshift threshold U (VP) for the current speed step (e.g., if the bicycle speed S becomes faster than 16.4 km/h when in second speed (VP=2) in FIG. 4), then the process moves from step S 15  to step S 51 , wherein the determining flag DF is reset in order to cancel any previous downshift judgment in accordance with the first downshift threshold D 1  (VP). In step S 52 , a judgment is made whether or not a predetermined period of time T 1  has elapsed since the judgment result in step S 15 . If not, then the process moves to step S 53 , and the bicycle speed S is acquired once more. In step S 54 , a judgment is made whether or not the re-acquired current bicycle speed S again exceeds the upshift threshold U (VP) of the current speed step. If the bicycle speed S does not exceed the upshift threshold U (VP), then the process moves to step S 16 . If the bicycle speed S again exceeds the upshift threshold U (VP), then the process returns to step S 52 , wherein another judgment is made whether or not the predetermined period of time T 1  from the judgment result in step S 15  has elapsed. When it is finally judged that the predetermined period of time T 1  has elapsed, then the process moves from step S 52  to step S 55 . In step S 55 , a judgment is made whether or not the bicycle is in third gear. If the bicycle is in third gear, then no further upshifts can be made, so the process moves to step S 16 . Note that the upshift threshold in third speed is 255 km/h, a speed which is inconceivable under normal circumstances, and therefore this routine would not normally be performed. When the bicycle transmission is in second gear or below, then the process moves to step S 58 , wherein the operating position VP is increased by one in order to shift up one speed step, after which the process returns to the main routine. At approximately the same time, motor  29  is operated so that the internal gear changing hub  10  shifts up one gear.  
         [0061]    Whether or not to perform an upshift is determined in this embodiment based on the judgment whether or not the upshift threshold U (VP) is exceeded during the elapse of the predetermined amount of time T 1  at the time of an upshift. Thus, once again upshifts which are against the will of the rider can be prevented even when speed signals are acquired frequently. As a result, smooth gear shift operations can be realized, and the sense of discomfort felt during a gear shift operation can be reduced.  
         [0062]    In the first embodiment, electric power from the power source  27  is used as the power source for motor  29  and the gear shift control section  25 . However, as is shown in FIG. 16, electric power supplied from the generator hub  12  also may be used as a power supply.  
         [0063]    The flowcharts showing implementation procedures, thresholds and so on in each of the aforementioned embodiments are nothing more than examples thereof, and other algorithms and other thresholds may be used as means for implementing the present invention.  
         [0064]    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 which 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 on a particular structure or feature.