Bicycle control and bicycle transmission system

Abstract

Bicycle control unit (110) designed for mounting on a bicycle (10) comprising a first transmission (52) having at least two gear stages (52X, 52Y) and capable of changing the ratio of the rotation of a wheel (14) to the rotation of a crank (38), a motor (56) assisting the muscle power supplied to the crank (38), and a second transmission (54) capable of transmitting rotational force from the motor (56) to a power transmission path extending from the crank (38) to the wheel (14) without changing the ratio of the rotation of the wheel (14) to the rotation of the crank (38), wherein the bicycle control unit (110) comprises a control unit (112) that controls the second transmission (54) according to a state of the bicycle (10) and a state of the first transmission (52) and a shift command for the first transmission (52).wherein the state of the bicycle (10) includes at least one of the torque generated by the muscle power and a rotational speed of the crank (38) or the motor (56), wherein the control unit (112) controls the second transmission (54) such that the gear ratio of the second transmission (54) increases when the operation of the first transmission (52) causes the rotational speed to exceed a predetermined first rotational speed, and wherein the control unit (112) predicts from the rotational speed and a state of the first transmission (52) and a shift command for the first transmission (52) whether the operation of the first transmission (52) will cause the rotational speed to change to a value exceeding the first rotational speed.

Description

The subject matter of the present disclosure relates to a bicycle control system and a bicycle transmission system. A well-known bicycle drive system includes a motor that assists muscle power. In addition to the motor, the bicycle drive system comprises a reduction gear and a power resultant component. Rotation is transmitted from the reduction gear and a crank to the power resultant component. JP 2 623 419 B2 describes an example of a conventional bicycle drive system. In a conventional bicycle drive system, the motor's speed is proportional to the crank's speed. The motor's output torque changes with its speed. Depending on the crank's speed, the motor's output torque may become insufficient, reducing the assistance provided or lowering the motor's drive efficiency. A gearshift control system for a bicycle, comprising a control unit for a gearshift device, is disclosed in the subsequently published document DE 20 2016 103 389 U1. The control unit controls the gearshift device based on the bicycle's riding condition and a range of predefined gear ratios. JP 2001 260 979 A describes a drive device on a bicycle in which a driving force at low speed and high torque is generated at a gear by selecting a high reduction ratio on a gear mechanism at startup, thereby reducing the load on a person pushing down the bicycle pedal. A low reduction ratio is selected for high-speed riding. A power control system for a motor in an electrically assisted bicycle is shown in JP H11 240 481 A. The power control is implemented according to the amount of work performed by a crankshaft driven by a pedal, and the rotation of the motor is transferred to a wheel drive shaft via a reduction mechanism to assist the rotation of the crankshaft. An example of a bicycle with an electrically assisted drive is disclosed in JP H11-227669A. The bicycle has an electric drive unit mounted on the frame, a motor control circuit for regulating the power supply to the motor, and a drive unit for the gear ratio adjustment mechanism. Using the motor drive circuit and the drive unit for the adjustment mechanism, the input power of the motor and the gear ratio of the reduction device are regulated according to the varying bicycle speed and pedaling force during riding, so that the efficiency of the motor is essentially maximized and the motor is always operated at maximum efficiency to prevent unnecessary consumption of battery power. Another example of a bicycle with an electric auxiliary drive is disclosed in DE 10 2009 045 447 A1. The bicycle comprises an electric motor, a battery for storing electrical energy which is connected to the electric motor, a crank mechanism with pedal cranks which are attached to a pedal crank shaft which is rotatably arranged about a crank axis, and a planetary gear for driving the bicycle both by the electric motor and by the muscle power of a rider. An example of an auxiliary drive device with a planetary gear for an electrically powered vehicle is disclosed in DE 198 19 705 A1. Two sensors are mounted on the bicycle's planetary carrier and rear wheel to measure the rotational speed of the manually driven pedals and the rear wheel. The signals representing the rotational speeds are processed and transmitted to a controller, which generates a control signal for auxiliary power based on these speeds. This signal is then amplified by a power amplifier to drive the motor. Thus, the energy required for the motor can be controlled depending on the rotational speed of the pedals. An example of a bicycle drive unit is disclosed in DE 10 2014 000 898 A1. In the bicycle drive unit, the crankshaft is rotatably arranged about a first axis of rotation. The torque combination mechanism is operatively coupled to the motor and the crankshaft. The torque combination mechanism has a gear assembly section configured to be operatively connected to a gear such that the gear rotates about a second axis of rotation of the gear in a first direction when the crankshaft rotates about the first axis of rotation in the first direction. The coupling mechanism is operatively arranged between the crankshaft and the gear. The coupling mechanism is configured to rotate the gear about the second direction of rotation in a second, opposite direction when the crankshaft rotates about the first axis of rotation in the second direction. The publication EP 3 023 327 A1 discloses an electric bicycle that can provide sufficient drive assistance with satisfactory gear changes, eliminates problems due to interference between a bracket or battery and a derailleur, and prevents a reduction in torque transmission efficiency. The electric bicycle includes a reduction mechanism comprising pairs of reduction gears and a selector clutch that engages with the reduction gears, combining human power and the auxiliary power, and shifting for the combined force of human power and the auxiliary power. Another example of a bicycle drive unit is disclosed in the subsequently published document DE 10 2016 105 242 A1. The bicycle drive unit comprises an auxiliary motor for providing support to a manual drive force applied by a crankshaft. The bicycle drive unit further comprises a housing in which the auxiliary motor and at least part of the crankshaft are mounted, and which is arranged around the crankshaft. The housing is designed such that, when the bicycle drive unit is attached to a bicycle frame, the minimum distance from the central axis of the crankshaft and the rear end face of the frame at the rear end of the housing is less than or equal to 50 mm and greater than the radius of the crankshaft. One objective of the present disclosure is to provide a bicycle control and bicycle transmission system that limits reductions in auxiliary power when the rotational speed of the crank changes. According to a first aspect of the present invention, a bicycle control system comprises the features of independent claim 1. According to a further aspect of the present invention, a bicycle controller can be mounted on a bicycle comprising a first gearbox having at least two gear stages and capable of changing the ratio of the wheel's rotation to the crank's rotation, a motor assisting the muscle power applied to the crank, and a second gearbox capable of transmitting torque from the motor to a power transmission path running from the crank to the wheel without altering the ratio of the wheel's rotation to the crank's rotation. The bicycle controller includes a control unit that controls the first gearbox and the second gearbox according to a state of the bicycle. Preferably, the state of the bicycle includes at least one of the torque generated by muscle power and a rotational speed of the crank or motor. Preferably, the control unit controls the second gearbox in such a way that the gear ratio of the second gearbox increases when the operation of the first gearbox causes the rotational speed to exceed a predetermined first rotational speed. Preferably, the control unit predicts, from the rotational speed and a state of the first transmission and a shift command for the first transmission, whether the operation of the first transmission will cause the rotational speed to change to a value that exceeds the first rotational speed or not. Preferably, the control unit controls the second gearbox in such a way that the gear ratio of the second gearbox increases when the rotational speed exceeds the first rotational speed, without the first gearbox being operated. Preferably, the control unit controls the second gearbox in such a way that the gear ratio of the second gearbox decreases when the operation of the first gearbox causes the rotational speed to be less than a predetermined second rotational speed. Preferably, the control unit predicts, from the rotational speed and a state of the first transmission and a shift command for the first transmission, whether the operation of the first transmission will cause the rotational speed to change to a value that is less than the second rotational speed or not. Preferably, the control unit controls the second gearbox in such a way that the gear ratio of the second gearbox decreases when the rotational speed becomes less than the second rotational speed, without the first gearbox being operated. Preferably, the first speed is higher than the second speed. Preferably, the control unit controls the second gearbox in such a way that the gear ratio of the second gearbox increases when the operation of the first gearbox causes the torque to be less than a predetermined first torque. Preferably, the control unit predicts, from the torque and a state of the first transmission and a shift command for the first transmission, whether the operation of the first transmission will cause the change in torque to a value that is smaller than the first torque or not. Preferably, the control unit controls the second gearbox in such a way that the gear ratio of the second gearbox decreases when the torque exceeds a predetermined second torque by operating the first gearbox. Preferably, the control unit predicts, from the torque and a state of the first transmission and a shift command for the first transmission, whether the operation of the first transmission will cause the change in torque to a value exceeding the second torque or not. Preferably, the control unit controls the first gearbox in such a way that the speed of the crank is kept within a predetermined range. Preferably, the control unit operates the first gearbox and the second gearbox in a predetermined sequence or operates the first gearbox and the second gearbox simultaneously. Preferably, the predetermined range has an upper limit that is higher than the first rotational speed, and the predetermined range has a lower limit that is lower than the second rotational speed. According to another aspect of the present invention, a bicycle transmission system comprises the bicycle control, the first transmission and the second transmission. Preferably, the bicycle transmission system further comprises a housing in which at least the second transmission is arranged. The housing rotatably supports a crankshaft. According to another aspect of the present invention, a bicycle transmission system comprises the features of claim 20 shown alongside. Preferably, the second gearbox transmits the rotational force from the motor to an upstream side of the first gearbox in the power transmission path. Preferably, the first transmission has at least one front transmission located near the crank and one rear transmission located near the axle of a rear wheel. Preferably, the bicycle transmission system also includes the bicycle control unit. The bicycle control and bicycle transmission system according to the present invention limit reductions in the auxiliary force when the rotational speed of the crank changes. Exemplary embodiments of the invention are described below with reference to the figures, wherein: Fig. 1 is a side view of a bicycle, which has a first embodiment of a bicycle transmission system; Fig. 2 is a block diagram of the first embodiment of the transmission system; Fig. 3 is a schematic representation of a bicycle power transmission path in the first embodiment; Fig. 4 is a cross-sectional view of a drive unit in the first embodiment; Fig. 5 is a flowchart of a first gear-shifting process in the first embodiment; Fig. 6 is a graphical representation showing the relationship between crank speed and torque; Figs. 7A to 7C are timing diagrams showing an example of the execution of a first gear-shifting process; Fig. 8 is a flowchart of a second gear-shifting process in the first embodiment; Fig.Fig. 9 is a flowchart of a third gear-shifting process in a second embodiment; Fig. 10 is a flowchart of a fourth gear-shifting process in the second embodiment; Fig. 11 is a flowchart of a fifth gear-shifting process in a third embodiment; Fig. 12 is a schematic representation of a bicycle power transmission path in a first modified example; Fig. 13 is a schematic representation of a bicycle power transmission path in a second modified example; Fig. 14 is a cross-sectional view of a drive unit in a third modified example; Fig. 15 is a schematic representation of a drive unit in a fourth modified example; Fig. 16 is a schematic representation of a second transmission in the fourth modified example; Fig. 17 is a schematic representation of a drive unit in a fifth modified example; Fig.Figure 18 is a schematic representation showing a second transmission in a first state in the fifth modified example; Figure 19 is a schematic representation showing the second transmission in a second state in the fifth modified example; Figure 20 is a schematic representation showing a second transmission in a first state in a sixth modified example; Figure 21 is a schematic representation showing a second transmission in a second state in the sixth modified example; and Figure 22 is a schematic representation showing the second transmission in a modified example of the sixth modified example. Now, with reference to Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 to Fig. 8, a first embodiment of a bicycle transmission system is described. Referring to Fig. 1, a transmission system 50 is mounted on a bicycle 10, which has a front wheel 12, a rear wheel 14, a body 16, a drive mechanism 18, and a battery unit 20. The rear wheel 14 serves as the wheel. The body 16 has a frame 22, a front fork 24 connected to the frame 22, and a handlebar 26A detachably attached to the front fork 24 by a handlebar stem 26. The front fork 24 is supported by the frame 22 and is connected to an axle 12A of a front wheel 12. The drive mechanism 18 comprises a crank linkage 28, two pedals 30, a rear sprocket 34 and a chain 36. The crank linkage 28 includes a crank 38 and a front sprocket 40. The crank 38 has a crankshaft 42, which is rotatably supported by the frame 22, and two crank arms 44. The crank arms 44 are connected to the crankshaft 42. The pedals 30 each have a pedal body 31 and a pedal shaft 32. The pedal shaft 32 is connected to a corresponding crank arm 44. The pedal body 31 is supported by the corresponding pedal shaft 32 in a manner that allows it to rotate about the pedal shaft 32. The front sprocket 40 is coupled to the crankshaft 42. The front sprocket 40 is coaxial with the crankshaft 42. The front sprocket 40 can be coupled to the crankshaft 42 in such a way that it is not rotatable with respect to the crankshaft 42. Alternatively, the front sprocket 40 can be coupled to the crankshaft 42 by means of a first coupling 62 (see Fig. 4) so ​​that when the crankshaft 42 rotates in the forward direction, the front sprocket 40 also rotates in the forward direction. The rear sprocket 34 is coupled to the rear wheel 14 so that it can rotate about an axle 14A of the rear wheel 14. The rear sprocket 34 is coupled to the rear wheel 14 by means of a second clutch (not shown). The second clutch is a freewheel clutch. The chain 36 is wound around the front sprocket 40 and the rear sprocket 34. When the crankshaft 42 is turned by muscle power applied to the pedals 30, the front sprocket 40, the chain 36, and the rear sprocket 34 turn the rear wheel 14. The battery unit 20 comprises a battery 46 and a battery holder 48, which is used for detachably connecting the battery to the frame 22. The battery 46 comprises one or more battery cells. The battery 46 is rechargeable and electrically connected to a motor 56 to supply the motor 56 with energy. Referring to Fig. 2, the transmission system 50 comprises a first transmission 52, a second transmission 54, and the motor 56. In one example, the transmission system 50 further comprises an operating unit 58 and a bicycle controller (hereinafter referred to as "the controller 110"). The motor 56, the second transmission 54, and the controller 110 form a drive unit 60. The controller 110 is designed to be installed in the bicycle 10, which comprises the motor 56, the first transmission 52, and the second transmission 54. Referring to Fig. 3, the first transmission 52 is located in a power transmission path RT that runs from the crank 38 to the rear wheel 14. The first transmission 52 has an internal wheel hub gear integrated into the hub of the rear wheel 14. The first transmission 52 changes the ratio of the rotation of the rear wheel 14 to the rotation of the crank 38. The first transmission 52 shown in Fig. 2 has a gear-shifting mechanism 52A and an actuator 52B. The gear-shifting mechanism 52A, for example, has a planetary gear mechanism. The first transmission 52 has at least two shift stages. The actuator 52B can be used to shift the connected gears of the gear-shifting mechanism 52A and to change the shift stage of the first transmission 52. This changes the gear ratio r1 of the bicycle.The gear ratio r1 of the bicycle 10 corresponds to the ratio of the rotational speed of the rear wheel 14 to the rotational speed of the crank 38, which are shown in Fig. 1. As shown in Fig. 3, the second gearbox 54 transmits torque from the motor 56 to the upstream side of the first gearbox 52 in the power transmission path RT, which runs from the crank 38 to the rear wheel 14. In each gear stage of the first gearbox 52, the second gearbox 54 can transmit the torque of the motor 56 to the power transmission path RT, which runs from the crank 38 to the rear wheel 14, without changing the ratio of the rotation of the rear wheel 14 to the rotation of the crank 38. The second gearbox 54 and the motor 56 are arranged in a housing 72 of the drive unit 60, which is shown in Fig. 4. The drive unit 60 serves to assist the muscle power supplied to the crankshaft 42. The drive unit 60 is detachably coupled to the frame 22 of the bicycle 10 (see Fig. 1). The drive unit 60 and the frame 22 can be connected to each other by, for example, screws. The control unit 58 shown in Fig. 2 is coupled to the handlebar 26A (see Fig. 1). The control unit 58 transmits signals to the control unit 110 for operating the first gearbox 52. When actuated by the rider, the control unit 58 transmits an upshift signal or a downshift signal to the control unit 110. The upshift signal increases the gear ratio r1 of the bicycle, and the downshift signal decreases the gear ratio r1 of the bicycle. As shown in Fig. 4, the drive unit 60 comprises a first planetary gear mechanism 64, the motor 56, and a force resultant component 70. The motor 56 comprises a first motor 66 and a second motor 68. An example of the first motor 66 is an electric motor. An example of the second motor 68 is also an electric motor. In an example, the drive unit 60 further comprises the crankshaft 42, the housing 72, a first reduction gear 74, a second reduction gear 76, a first freewheel clutch 78, and a second freewheel clutch 80. At least the first motor 66 serves to assist the muscle power supplied to the crank 38. The second motor 68 controls the rotation of a first gear body 90 of the first planetary gear mechanism 64 and the rotation of a second gear body 96 of a second planetary gear mechanism 74A in order to change the ratio of the rotational speed output by the second planetary gear mechanism 74A to the rotational speed supplied to the first planetary gear mechanism 64 from the first motor 66. The ratio of the rotational speed output by the second planetary gear mechanism 74A to the rotational speed supplied to the first planetary gear mechanism 64 is the gear ratio r2 of the second gear 54. The second gear 54 comprises the first planetary gear mechanism 64, the second planetary gear mechanism 74A, and the second motor 68. The crankshaft 42 is rotatably supported by the drive unit 60 and is mounted on it with respect to the drive unit 60. Both ends of the crankshaft 42 protrude from the housing 72. The first motor 66, the second gearbox 54, the first freewheel clutch 78, the second freewheel clutch 80, the first reduction gearbox 74, and the control unit 110 are arranged in the housing 72. The rotation of a first output body 88, which will be described later, is transmitted to the force resultant component 70. Furthermore, the rotation generated by muscle power is transmitted to the force resultant component 70, thereby redirecting the first planetary gear mechanism 64. The force resultant component 70 has a hollow shaft 82 and a gear wheel 84. The hollow shaft 82 is supported by the housing 72 in a manner that allows it to rotate with respect to the housing 72. The force resultant component 70 is rotatable about the axis of the crankshaft 42. The hollow shaft 82 has an end 82A that projects from the housing 72. The crankshaft 42 is inserted into the hollow shaft 82 such that both ends of the crankshaft 42 project from the housing 72. The crankshaft 42 is supported by the housing 72 with the hollow shaft 82. The gear wheel 84 is coupled to the hollow shaft 82 in a manner that is not rotatable with respect to the hollow shaft 82.The gear wheel 84 is coaxial with the hollow shaft 82. In another example, the gear wheel 84 is formed integrally with the hollow shaft 82 by machining the hollow shaft 82. The first clutch 62 is arranged between the outer circumference of the crankshaft 42 and the inner circumference of the force resultant component 70. The first clutch 62 is a freewheel clutch. When the crankshaft 42 is rotated in the forward direction, the first clutch 62 transmits the rotation from the crankshaft 42 to the force resultant component 70. When the crankshaft 42 is rotated in the reverse direction, the first clutch 62 engages with the crankshaft 42 and the force resultant component 70, thus interrupting the transmission of the rotation from the crankshaft 42 to the force resultant component 70. The front sprocket 40 is located outside and next to the housing 72. The front sprocket 40 is coupled to the drive unit 60 by a screw B. The screw B is attached to the force resultant component 70, so that the front sprocket 40 is fixed between the screw B and the force resultant component 70. When muscle power, which rotates the crankshaft 42 shown in Fig. 1 in the forward direction, is applied to the pedals 30, the crankshaft 42 rotates in the forward direction relative to the frame of the bicycle 10. In this case, the rotation of the crankshaft 42 is transmitted by the first clutch 62 and the force resultant component 70 to the front sprocket 40. When muscle power, which rotates the crankshaft 42 in the reverse direction, is applied to the pedals 30, the crankshaft 42 rotates in the reverse direction relative to the frame 22. In this case, the first clutch 62 serves to interrupt the transmission of the rotation of the crankshaft 42 to the force resultant component 70 and the front sprocket 40. As shown in Fig. 4, the first planetary gear mechanism 64 has a first drive body 86, the first output body 88 and the first gear body 90. The first drive body 86 has a sun gear 86A coupled to an output shaft 66B of the first motor 66. The sun gear 86A is arranged on the output shaft 66B and is integrally rotatable with the output shaft 66B. The first freewheel clutch 78 is arranged between the sun gear 86A and the output shaft 66B. When the crankshaft 42 is turned forward by muscle power, the first freewheel clutch 78 restricts the transmission of muscle power to the output shaft 66B of the second motor 68. The forward rotation of the crankshaft 42 is the direction of rotation of the crankshaft 42 that moves the bicycle 10 forward. Furthermore, the first freewheel clutch 78 is, for example, a roller locking clutch. If the rotational speed of the first drive body 86 is equal to the rotational speed of the output shaft 66B when the output shaft 66B rotates in a first direction, the first freewheel clutch 78 transmits the rotation of the output shaft 66B to the first drive body 86.If the rotational speed of the first drive body 86 is higher than the rotational speed of the output shaft 66B when the output shaft 66B is rotating in the first direction, the first freewheel clutch 78 engages with the output shaft 66B and the first drive body 86, thus interrupting the transmission of the rotation of the output shaft 66B to the first drive body 86. In this way, the first freewheel clutch 78 functions in such a way that the muscle power that rotates the crankshaft 42 in the forward direction does not rotate the output shaft 68B of the second motor 68. The first output body 88 has planet gears 88A which mesh with the first drive body 86, and a carrier 88B which rotatably supports the planet gears 88A. Preferably, the first planetary gear mechanism 64 has several planet gears 88A. The first gear body 90 transmits the rotation of the first drive body 86 to the first output body 88. The first gear body 90 has a ring gear 90A that meshes with the first output body 88. The ring gear 90A is centered around the sun gear 86A and is coaxial with it. The first gear body 90 is supported on the housing 72 by the second freewheel clutch 80. The second freewheel clutch 80 is, for example, a roller locking clutch. The second freewheel clutch 80 restricts the rotation of the first gear body 90 in a predetermined direction. More specifically, the first gear body 90 is rotatable in a first direction relative to the housing 72 and not rotatable in a second direction relative to the housing 72. The planet gears 88A are arranged between the sun gear 86A and the ring gear 90A. The planet gears 88A mesh with the sun gear 86A and the ring gear 90A. The carrier 88B rotatably supports each planet gear 88A by means of a planet pin 88C, which extends through the planet gear 88A in the axial direction. In another example, the planet pin 88C can be rotated integrally with the corresponding planet gear 88A and rotatably supported by the carrier 88B. The first reduction gear 74 reduces the rotational speed of the first output body 88 and transmits the rotation to the force resultant component 70. The first reduction gear 74 includes the second planetary gear mechanism 74A. The second planetary gear mechanism 74A is coaxial with the first planetary gear mechanism 64. The second planetary gear mechanism 74A is located next to the first planetary gear mechanism 64 in the axial direction of the first planetary gear mechanism 64. The second planetary gear mechanism 74A has a second drive body 92, a second output body 94 and the second gear body 96. The rotation of the first output body 88 is transmitted to the second drive body 92. The second drive body 92 has a sun gear 92A which is coupled to the first output body 88. The sun gear 92A is arranged on the outer circumferential section of the first output body 88 and rotates integrally with the first output body 88. Preferably, the number of teeth of the sun gear 92A of the second drive body 92 is equal to the number of teeth of the sun gear 92A of the first drive body 86. The second output body 94 has planet gears 94A which mesh with the second drive body 92, and a carrier 94B which rotatably supports the planet gears 94A. Preferably, the second planetary gear mechanism 94A has several planet gears 94A. The carrier 94B rotatably supports each planet gear 94A with a planet pin 94C which extends through the planet gear 94A in the axial direction. In another example, the planet pin 94C can be integrally rotated with the corresponding planet gear 94A and rotatably supported by the carrier 94B. Preferably, the number of teeth of each planet gear 94A of the second output body 94 is equal to the number of teeth of each planet gear 88A of the first output body 88. A gear wheel 94D is arranged on the outer circumferential section of the carrier 94B of the second output body 94. The gear wheel 94D is coaxial with the second output body 94. Furthermore, the gear wheel 94D engages with the gear wheel 84 on the outer circumferential section of the force resultant component 70. This allows the second output body 94 to transmit the rotation to the force resultant component 70. The gear wheel 94D and the gear wheel 84 form a reduction gear. Preferably, the rotational speed of the second output body 94 is reduced during transmission to the force resultant component 70. A further gear wheel can be arranged between gear wheel 94D and gear wheel 84 to transmit the rotation from the second output body 94 to the force resultant component 70. Alternatively, a ring component can be used to transmit the rotation from the second output body 94 to the force resultant component 70. An example of a ring component is a band that runs around the second output body 94 and the force resultant component 70.If the direction of rotation of the second output body 94 is the same as the direction of rotation of the force resultant component 70, because a gear wheel is arranged between the gear wheel 94D and the gear wheel 84, or because a ring component transmits the rotation from the second output body 94 to the force resultant component 70, the drive direction of the first motor 66 and the second motor 68, and the direction in which the first freewheel clutch 78 and the second freewheel clutch 80 are arranged, can be reversed. The force resultant component 70 combines the torque of the first motor 66 and the torque exerted on the crankshaft 42. The rotational speed of the first motor 66 is changed by the first planetary gear mechanism 64 and then transmitted to the force resultant component 70. The rotation generated by the crankshaft 42 is transmitted to the force resultant component 70 without changing its speed. The second gear body 96 serves to transmit the rotation of the second drive body 92 to the second output body 94. The second gear body 96 has a ring gear 96A that meshes with the second output body 94. Preferably, the number of teeth of the ring gear 96A of the second gear body 96 is equal to the number of teeth of the ring gear 90A of the first gear body 90. The first gear body 90 and the second gear body 96 are integrated within each other so that they rotate synchronously. Thus, the second gear body 96 is rotatable in the first direction relative to the housing 72 and non-rotatable in the second direction relative to the housing 72. The first gear body 90 and the second gear body 96 can be integrally formed together or be separate bodies that are coupled and integrated within each other. The first motor 66 is supported by the housing 72. The first motor 66 can rotate the first drive body 86. The first motor 66 has a main body 66A and an output shaft 66B. The main body 66A has a rotor and a stator (neither of which are shown). The output shaft 66B transmits the rotation of the rotor of the first motor 66 to the first drive body 86. The first motor 66 is coaxial with the first planetary gear mechanism 64. The first motor 66 and the first reduction gear 74 are located on opposite sides of the first planetary gear mechanism 64 in the axial direction of the first planetary gear mechanism 64. The second motor 68 can rotate the first gear body 90. The second motor 68 is supported by the housing 72. The second motor 68 has a main body 68A and an output shaft 68B. The main body 68A has a rotor and a stator (neither of which are shown). The second motor 68 is located on the radially outer side of the first motor 66. The axis of the second motor 68 is parallel to the axis of the first motor 66. A gear wheel 68C is arranged on the output shaft 68B of the second motor 68. The rotation generated by the second motor 68 is transmitted to the first gear body 90 by means of the second reduction gear 76. The gear wheel 68C can be connected to the output shaft 68B via a freewheel clutch in order to limit the transmission of the muscle power that turns the crankshaft 42 forward to the output shaft 68B of the second engine 68. The second reduction gear 76 reduces the rotational speed generated by the second motor 68 and transmits the rotation to the first gear body 90. The second reduction gear 76 has a gear wheel 68C on the output shaft 68B of the second motor 68, a carrier 98 having a gear wheel 98A, and a gear wheel 90B on the outer circumferential section of the first gear body 90. The gear wheel 98A is coaxial with the carrier 98 and rotates integrally with it. The carrier 98 is a shaft and is rotatably supported by the housing 72. The carrier 98 can be fixed to the housing 72 and rotatably supports the gear wheel 98A. The gear wheel 98A meshes with the gear wheel 90B. The gear wheel 90B is coaxial with the first gear body 90. The gear wheel 98A has more teeth than the gear wheel 68C. The gear wheel 90B has more teeth than the gear wheel 98A.Gear wheel 98A can be omitted from the second reduction gear 76, and gear wheel 68C can be engaged with gear wheel 90B. In this case, the drive direction of the second motor 68 is reversed. There is no limit to the number of gear wheels included in the second reduction gear 76. Referring to Fig. 2, the drive unit 60 further comprises a torque sensor 100 and a speed sensor 102. The torque sensor 100 is, for example, a strain gauge, a semiconductor strain gauge, or a magnetostrictive sensor. The torque sensor 100 is coupled to the hollow shaft 82 of the force resultant component 70. If a magnetostrictive sensor is used, a magnetostrictive element is coupled to the hollow shaft 82. The torque sensor 100 detects the torque exerted on the force resultant component 70. If the rotation of the crankshaft 42 is transmitted to the force resultant component 70, and the rotation generated by the first motor 66 and the rotation generated by the second motor 68 are not transmitted to the force resultant component 70, the torque sensor 100 sends a signal to the control unit 110 reflecting the muscle force supplied to the crankshaft 42. If the rotation of the crankshaft 42, the rotation generated by the first motor 66, and the rotation generated by the second motor 68 are transmitted to the force resultant component 70, the torque sensor 100 sends a signal to the control unit 110 reflecting the torque obtained by combining the muscle force supplied to the crankshaft 42 with the torque of the first motor 66 and the torque of the second motor 68, which was transmitted by means of the first planetary gear mechanism 64 and the first reduction gear 74. The speed sensor 102 includes a cadence sensor that detects the rotational speed of the crank 38. The cadence sensor detects, for example, a magnet located on the crank shaft 42. The cadence sensor can be a magnetic detection sensor such as a reed switch or a Hall effect sensor. The cadence sensor sends a signal to the controller 110 corresponding to the rotational speed of the crank shaft 42. The cadence sensor can also be configured to detect a magnet located on a crank arm 44. In this case, the cadence sensor sends a signal to the controller 110 corresponding to the rotational speed of the crank shaft 42. Furthermore, the speed sensor can include a speed sensor that detects the rotational speed of the front or rear wheel of the bicycle 10. The controller 110 calculates a crank rotation speed CA from the detection result of the speed sensor. The controller 110 comprises a control unit 112. Preferably, the controller 110 also comprises a memory 114. The memory 114 stores various control programs and information used for different control processes. The control unit 112 includes a computer that executes pre-set control programs. The computer can be, for example, a central processing unit (CPU) or a microprocessor unit (MPU). The control unit 112 controls the first motor 66 and the second motor 68. The control unit 112 regulates the rotation generated by the first motor 66 and the rotation generated by the second motor 68 according to the muscle force and the crank speed CA. The control unit 112 causes the first motor 66 to generate a rotation, thereby rotating the first drive body 86 in the first direction. When the first drive body 86 rotates in the first direction, the rotation, which moves the bicycle 10 forward, is transmitted to the power resultant component 70. If the first gear body 90 does not rotate relative to the housing 72, the rotational speed of the first drive body 86 is reduced and output by the first output body 88 to the second drive body 92. Thus, the gear ratio rX of the first planetary gear mechanism 64 is less than 1. The controller 110 causes the second motor 68 to generate a rotation, thereby rotating the first gear body 90 in the first direction. As the rotational speed of the first gear body 90 in the first direction increases, the gear ratio rX of the first planetary gear mechanism 64 increases. When the rotational speed of the first gear body 90 in the first direction equals the rotational speed of the first drive body 86, the gear ratio rX of the first planetary gear mechanism 64 is 1. More specifically, the controller 110 controls the rotational speed of the second motor 68, thereby continuously changing the gear ratio rX. The control of the second motor 68 allows the gear ratio rX to be changed from a value less than 1 to 1. The controller 110 controls the rotational speed of the second motor 68 in several steps and changes the gear ratio rX in several steps. Now the relationship of the transmission ratio rY of the second motor 68 and the first reduction gear 74 is described. If the second gear body 96 is not rotated relative to the housing 72, the rotational speed of the second drive body 92 is reduced and output by the first output body 88. Thus, the gear ratio rY of the second planetary gear mechanism 74A is less than 1. The gear ratio rY is the rotational speed of the second output body 94 relative to the rotational speed of the drive body 92. The controller 110 causes the second motor 68 to generate a rotation, thereby rotating the second gear body 96 in the first direction. As the rotational speed of the second gear body 96 in the first direction increases, the gear ratio rY of the second planetary gear mechanism 74A increases. When the rotational speed of the second gear body 96 in the first direction equals the rotational speed of the second drive body 92, the gear ratio rY of the second planetary gear mechanism 74A is "1". More specifically, the controller 110 controls the rotational speed of the second motor 68, thereby continuously changing the gear ratio rY. The controller of the second motor 68 allows the gear ratio rY to be changed from a value less than "1" to the value "1". The first gear body 90 and the second gear body 96 rotate integrally with each other. Thus, the gear ratio rX of the first planetary gear mechanism 64 and the gear ratio rY of the first reduction gear 74 are correlated. If the gear ratio rX of the first planetary gear mechanism 64 increases, the gear ratio rY of the first reduction gear 74 also increases. The gear ratio r2 of the second gear 54 is equal to the product of the gear ratio rX and the gear ratio rY. The control unit 112 switches between an automatic gear-shifting mode, in which the gear stage of the first transmission 52 is changed according to the crankshaft speed CA, and a manual gear-shifting mode, in which the gear stage of the first transmission 52 is changed exclusively by actuating the control unit 58. For example, a driver operates the control unit 58 (see Fig. 1) to switch the control unit 112 between an automatic gear-shifting mode and a manual gear-shifting mode. Preferably, in the automatic gear-shifting mode, the crankshaft speed CA is maintained within a predetermined range. In automatic gear-shift mode, the control unit 112 controls the first gear 52 according to the state of the bicycle 10. The state of the bicycle 10 includes the crank speed CA. The control unit 112 controls the first gear 52, thereby maintaining the crank speed CA within a predetermined range from less than or equal to an upper limit CAA to greater than or equal to a lower limit CAB. The control unit 112 controls the shift stage of the second gear 54 according to the crank speed CA and a predetermined first speed CAX. Furthermore, the control unit 112 controls the shift stage of the second gear 54 according to the crank speed CA and a predetermined second speed CAY. The upper limit CAA is higher than the first speed CAX. The lower limit CAB is less than the second speed CAY. The first speed CAX is higher than the second speed CAY. In automatic and manual gear-shift modes, the control unit 112 controls the second gear 54 according to a shift command for the first gear 52 and the state of the bicycle 10. In automatic gear-shift mode, the control unit 112 controls the second gear 54 according to the state of the first gear 52 and the state of the bicycle 10. The state of the first gear 52 includes the gear ratio r1 of the bicycle 10. Referring to Fig. 5, a first gear-shifting process, executed in automatic gear-shifting mode, is now described. This procedure is repeated in predetermined cycles when automatic gear-shifting mode is enabled. In step S11, the control unit 112 determines whether the crank speed CA has changed from a value higher than or equal to the lower limit CAB to a value lower than the lower limit CAB. If the crank speed CA has changed from a value equal to or higher than the lower limit CAB to a value lower than the lower limit CAB, the control unit 112 proceeds to step S12. In step S12, the control unit 112 determines whether the bicycle's gear ratio r1 is set to the minimum gear ratio r1. If it is determined that the bicycle's gear ratio r1 is not set to the minimum gear ratio r1, the control unit 112 proceeds to step S13. Here, the gear ratio r2 of the second gearbox 54 can be changed between two stages. In step S13, the control unit 112 determines whether the crank speed CA will exceed the first speed CAX by controlling the first gearbox 52 such that its gear ratio r1 decreases. The control unit 112 predicts, based on the state of the first gearbox 52 and the crank speed CA, whether the crank speed CA will change to a value exceeding the first speed CAX by operating the first gearbox 52. This determination is based on the current crank speed CA, the current gear ratio r1 of the bicycle, and the bicycle's gear ratio r1 after the gear change. The bicycle's gear ratio r1 is preset for each gear change and stored in memory 114.Thus, the crank speed CA can be predicted after the gear selection has been changed. Fig. 6 is a graphical representation showing the correlation between crank speed CA and muscle torque. It is generally known that increasing the crank speed CD reduces the muscle torque. If the operation of the first gearbox 52 causes the crank speed CA to exceed the predetermined first speed CAX, the control unit 112 operates the second gearbox 54 and the first gearbox 52 in a predetermined sequence. If the operation of the first gearbox 52 causes the crank speed CA to exceed the predetermined first speed CAX, the control unit 112, in step S14, first controls the second gearbox 54, thereby increasing the gear ratio r2 of the second gearbox 54. In step S14, the gear ratio r2 remains unchanged if the gear ratio r2 of the second gearbox 54 is set to that of the two stages with the higher gear ratio r2. In step S15, the control unit 112 controls the first gearbox 52, thereby increasing the gear ratio r1 of the bicycle. In step S15, the control unit 112 changes the gear stage of the first gearbox 52 by only one step.Upon completion of step S15, the control unit 112 terminates the current routine. If, in step S12, it is determined that the gear ratio r1 of the bicycle is set to the minimum gear ratio r1, the control unit 112 terminates the current routine. If in step S13 it is determined that the operation of the first gearbox 52 will not cause the crankshaft speed CA to exceed the first speed CAX, the control unit 112 proceeds to step S15. If, in step S11, it is determined that the crank speed CA has not changed from a value higher than or equal to the lower limit CAB to a value lower than the lower limit CAB, the control unit 112 proceeds to step S16. In step S16, the control unit 112 determines whether the crank speed CA has changed from a value lower than or equal to the upper limit CAA to a value higher than the upper limit CAA. If it is determined that the crank speed CA has changed from a value lower than or equal to the upper limit CAA to a value higher than the upper limit CAA, the control unit 112 proceeds to step S17. In step S17, the control unit 112 determines whether the bicycle's gear ratio r1 is set to the maximum gear ratio r1 or not.If it is determined that the gear ratio r1 of the bicycle is not set to the maximum gear ratio r1, the control unit 112 goes to step S18. In step S18, the control unit 112 determines whether the crank speed CA will be less than the second speed CAY by controlling the first gearbox 52 such that its gear ratio r1 increases. The control unit 112 predicts, based on the state of the first gearbox 52 and the crank speed CA, whether the crank speed CA will change to a value less than the second speed CAY by operating the first gearbox 52. This determination is based on the current crank speed CA, the current gear ratio r1 of the bicycle, and the gear ratio r1 of the bicycle after the gear change. If the operation of the first gearbox 52 causes the crank speed CA to become less than the predetermined second speed CAY, the control unit 112 operates the second gearbox 54 and the first gearbox 52 in a predetermined sequence. If the operation of the first gearbox 52 causes the crank speed CA to become less than the predetermined second speed CAY, the control unit 112, in step S19, controls the second gearbox 54 so that the gear ratio r2 of the second gearbox 54 decreases. In step S19, the gear ratio r2 remains unchanged if the gear ratio r2 of the second gearbox 54 is set to that of the two stages with the lower gear ratio r2. Then, in step S20, the control unit 112 controls the first gearbox 52 so that the gear ratio r1 of the bicycle increases. In step S20, the control unit 112 changes the gear stage of the first gearbox 52 by only one step.Upon completion of step S19, the control unit 112 terminates the current routine. If, in step S17, it is determined that the bicycle's gear ratio r1 is set to the maximum gear ratio r1, the control unit 112 terminates the current routine. If in step S18 it is determined that the operation of the first gearbox 52 will not cause the crankshaft speed CA to be less than the second speed CAY, the control unit 112 proceeds to step S20. If, in step S16, it is determined that the crank speed CA has not changed from a value less than or equal to the upper limit CAA to a value greater than the upper limit CAA, the control unit 112 terminates the current routine without changing the gear stages of the first gear 52 and the second gear 54. If the crank speed CA is within a predetermined range from the upper limit CAA or less to the lower limit CAB or higher, the control unit 112 does not perform any control to change the gear stage of the first gear 52 and the second gear 54 based on the state of the bicycle 10. An example of a first gear-change process, which is carried out by the control unit 112, is now described with reference to Figs. 7A to 7C. At time t11, the crankshaft speed CA changes from a value higher than or equal to the lower limit CAB to a value lower than the lower limit CAB. The solid lines in Figures 7A to 7C indicate a case in which, at time t11, the crankshaft speed CA is predicted to subsequently change to a speed exceeding the initial speed CAX when the control unit 112 controls the first gearbox 52, thus decreasing the gear ratio r1 of the first gearbox 52. In this case, the control unit 112 controls the second gearbox 54, increasing the gear ratio r2 of the second gearbox 54, and controls the first gearbox 52, decreasing the gear ratio r1 of the first gearbox 52. The double-dashed lines in Figures 7A to 7C indicate a case in which, at time t11, it is predicted that the crankshaft speed CA will not subsequently exceed the first speed CAX when the control unit 112 controls the first gearbox 52, thus reducing the gear ratio r1 of the first gearbox 52. In this case, the control unit 112 controls the first gearbox 52, reducing the gear ratio r1 of the first gearbox 52, without changing the gear ratio r2 of the second gearbox 54. At time t21, the crankshaft speed CA changes from a value less than or equal to the upper limit CAA to a value exceeding the upper limit. The solid lines in Figures 7A to 7C indicate a case in which, at time t21, it is predicted that the crankshaft speed CA will subsequently become less than the second speed CAY when the control unit 112 controls the first gearbox 52, thus increasing the gear ratio r1 of the first gearbox 52. In this case, the control unit 112 controls the second gearbox 54, thus decreasing the gear ratio r2 of the second gearbox 54, and controls the first gearbox 52, thus increasing the gear ratio r1 of the first gearbox 52. The double-dashed line in Fig. 7 indicates a case in which, at time t21, it is predicted that the crankshaft speed CA will subsequently not fall below the first speed CAX when the control unit 112 controls the first gearbox 52, thus reducing the gear ratio r1 of the first gearbox 52. In this case, the control unit 112 controls the first gearbox 52, increasing the gear ratio r1 of the first gearbox 52 without changing the gear ratio r2 of the second gearbox 54. A second gear-shifting process, which is executed in an automatic gear-shifting mode and a manual gear-shifting mode, is now described with reference to Fig. 8. The present method is executed in predetermined cycles as long as the transmission system 50 is supplied with energy. In step S21, the control unit 112 determines whether a downshift signal has been received from the operating unit 58. If a downshift signal has been received, the control unit 112 executes steps S12 to S15 of the first gear shift process and terminates the current routine. In the current routine, the control unit 112 uses the crankshaft speed CA and a shift command for the first transmission 52 to predict whether the operation of the first transmission 52 will change the crankshaft speed CA to a value exceeding the first speed CAX. If no downshift signal is received in step S21, the control unit 112 proceeds to step S22 and determines whether an upshift signal has been received. If an upshift signal has been received, the control unit 112 executes steps S17 to S20 of the first gear shift process and then terminates the current routine. In the current routine, the control unit 112 uses the crankshaft speed CA and a shift command for the first transmission 52 to predict whether the crankshaft speed CA will change to a value lower than the second speed CAY. If no upshift signal was received in step S21, the control unit 112 terminates the current routine without operating the first transmission 52 and the second transmission 54. The advantages of the transmission system 50 in the present embodiment will now be described. The second gearbox 54 of the gearbox system 50 can transmit torque from the motor 56 to the power transmission path running from the crank 38 to the rear wheel 14 without changing the ratio of the rotation of the rear wheel 14 to the rotation of the crank 38 in each gear stage of the first gearbox 52. This design allows the speed of the first motor 66 to be maintained within a predetermined range and limits reductions in auxiliary power that would occur if the crank speed CA changed. The control unit 112 controls the second gearbox 54 based on the crank speed CA and the state of the first gearbox 52 or a shift command for the first gearbox 52. This limits reductions in auxiliary power when a change in the shift stage of the first gearbox 52 changes the crank speed CA. If the operation of the first gearbox 52 causes the crankshaft speed CA to exceed the first speed CAX, the control unit 112 controls the second gearbox 54, thus increasing the gear ratio r2 of the second gearbox 54. More specifically, if it is predicted that the crankshaft speed CA will not be suitable for the gear ratio r2 of the second gearbox 54, the gear ratio r2 of the second gearbox 54 is changed in advance to a gear ratio r2 that is suitable for the crankshaft speed CA after the operation of the first gearbox 52. If the operation of the first gearbox 52 results in the crankshaft speed CA being lower than the second speed CAY, the control unit 112 controls the second gearbox 54, thus reducing the gear ratio r2 of the second gearbox 54. More specifically, if it is predicted that the crankshaft speed CA will not be suitable for the gear ratio r2 of the second gearbox 54, the gear ratio r2 of the second gearbox 54 is changed in advance to a gear ratio r2 that is suitable for the crankshaft speed CA after the operation of the first gearbox 52. The control unit 112 controls the first gearbox 52 in automatic gear-shift mode, so that the crank speed CA is maintained within the predetermined range from less than or equal to the upper limit CAA to greater than or equal to the lower limit. This limits changes in the crank speed CA when a rider is pedaling the bicycle and reduces the strain on the rider. The control unit 112 controls the speed of the second motor 68, so that the gear ratio r2 of the second gearbox 54 changes stepwise. This ensures that the gear ratio r2 of the second gearbox 54 is optimal for the crankshaft speed CA. A second embodiment of the transmission system 50 is now described with reference to Figures 2, 6, 9, and 10. The components, which are the same as the corresponding components of the first embodiment, have been designated with the same reference numerals. Such components are not described in detail. The control unit 112 shown in Fig. 2 performs a third gear-shifting process that changes the gear ratio r2 of the second transmission 54 based on the state of the bicycle 10. The state of the bicycle 10 includes the torque T generated by muscle power. The third gear-shifting process differs from the first gear-shifting process in that step S11 is replaced by step S41, step S13 is replaced by step S42, step S16 is replaced by step S43, and step S18 is replaced by step S44. The remaining steps are the same as in the first gear-shifting process and are not described in detail. Referring to Fig. 9, the third gear-shifting process, which is executed by the control unit 112, is now described. The process is executed in predetermined cycles as long as the automatic gear-shifting mode is active. In step S41, the control unit 112 determines whether the torque T generated by muscle power has changed from a value less than or equal to the upper limit TA to a value greater than the upper limit TA. If it is determined that the torque T has changed from a value less than or equal to the upper limit TA to a value greater than the upper limit TA, the control unit 112 proceeds to step S12. In step S12, if the control unit 112 determines that the gear ratio r1 of the bicycle is not set to the minimum gear ratio r1, the control unit 112 proceeds to step S42. In step S42, the control unit 112 determines whether the torque T will be less than a first torque TX when the first gearbox 52 is controlled to decrease its gear ratio r1. The control unit 112 predicts whether the torque T will change towards a value less than the first torque TX by operating the first gearbox 52. For example, the control unit 112 determines, based on the bicycle's gear ratio r1 in each gear and information relating to the correlation between the torque T and the crank speed CA (for example, the curve in Fig. 6), whether the torque T will change towards a value less than the first torque TX. The current crank speed CA is estimated from the current torque T.An estimated crank speed CA after a gear change is obtained from the estimated crank speed CA, the current gear ratio r1 of the bicycle, and the gear ratio r1 of the bicycle after the gear change. The torque T after the gear change can be estimated from the estimated crank speed CA after the gear change and the correlation between torque T and crank speed CA. The information relating to the correlation between torque T and crank speed CA is stored in memory 114, for example, as a numerical expression. The control unit 112 can estimate the crank speed CA without using the speed sensor 102 by measuring the torque T with the torque sensor 100. If the torque T becomes less than the first torque TX by operating the first gearbox 52, the control unit 112, in step S14, controls the second gearbox 54 such that the gear ratio r2 of the second gearbox 54 increases. The torque T even changes during a single crank rotation. Thus, the control unit 112 calculates, for example, the average torque of a single crank rotation or the average torque of several crank rotations and uses the average torque as the current torque. The control unit 112 operates the first gearbox 52 so that the torque T does not become less than the first torque TX and then proceeds to step S15. If step S41 determines that the torque T does not change from a value less than or equal to the upper limit TA to a value greater than the upper limit TA, the control unit 112 proceeds to step S43 and determines whether the torque T has changed from a value greater than or equal to the lower limit TB to a value less than the lower limit TB. If it is determined that the torque T has changed from a value greater than or equal to the lower limit TB to a value less than the lower limit TB, the control unit 112 proceeds to step S44. In step S44, the control unit 112 determines whether the torque T will exceed a second torque TY by controlling the first gearbox 52 such that its gear ratio r1 increases. Based on the state of the first gearbox 52 and the torque T, the control unit 112 predicts whether the torque T will change towards a value exceeding the second torque TY by operating the first gearbox 52. The determination of whether the torque T will change towards a value higher than the second torque TY is performed in the same way as in step S42. If the operation of the first gearbox 52 causes the torque T to exceed the second torque TY, the control unit 112 controls the second gearbox 54 in step S19 so that the gear ratio r2 of the second gearbox 54 decreases. If the torque T does not exceed the second torque TY in step S44 by operating the first gearbox 52, the control unit 112 proceeds to step S20. If in step S43 it is determined that the torque T has not changed from a value higher than or equal to the lower limit TB to a value lower than the lower limit TB, the control unit 112 terminates the current routine without changing the shift stages of the first transmission 52 and the second transmission 54. Referring to Fig. 10, a fourth gear-shifting process is now described, which is executed during both automatic and manual gear-shifting modes. The process is executed in predetermined cycles as long as the transmission system 50 is supplied with power. The fourth gear-shifting process differs from the third gear-shifting process in that step S41 is replaced by step S21 and step S43 is replaced by step S22. The remaining steps are the same as in the third gear-shifting process and are not described in detail. In step S21, the control unit 112 determines whether a downshift signal has been received from the operating unit 58. If a downshift signal has been received, the control unit 112 proceeds to step S42 of the third gear shift process. In the current routine, the control unit 112 predicts, based on the torque T and a shift command for the first transmission 52, whether the operation of the first transmission 52 will change the torque T to a value less than the first torque TX. If no downshift signal is received in step S21, the control unit 112 proceeds to step S22 and determines whether an upshift signal has been received. If an upshift signal has been received, the control unit 112 proceeds to step S44. In the current routine, the control unit 112 predicts, based on the torque T and the state of the first transmission 52, whether the torque T will change to a value exceeding the second torque TY. If no upshift signal was received in step S21, the control unit 112 terminates the current routine. The second embodiment of the transmission system 50 has, in addition to the advantages set out above which are described in relation to the first embodiment, the advantages described below. The control unit 112 controls the first gearbox 52 based on the torque T and the state of the first gearbox 52 or a shift command for the first gearbox 52. This limits reductions in the auxiliary power that would occur if a change in the shift stage of the first gearbox 52 changes the torque T. If the torque T becomes less than the predetermined first torque TX when the first gearbox 52 is operated, the second gearbox 54 is controlled such that the gear ratio r of the second gearbox 54 is increased. More specifically, if the control unit 112 predicts that the torque T will become unsuitable for the gear ratio r2 of the second gearbox 54, the gear ratio r2 of the second gearbox 54 can be changed in advance to a gear ratio r2 that is optimal for the torque T after the operation of the first gearbox 52. If the torque T exceeds the predetermined second torque when the first gearbox 52 is operated, the control unit 112 controls the second gearbox 54 such that the gear ratio r2 of the second gearbox 54 decreases. More specifically, if the control unit 112 predicts that the torque T will become unsuitable for the gear ratio r2 of the second gearbox 54, the gear ratio r2 of the second gearbox 54 can be changed in advance to a gear ratio r2 that is optimal for the torque T after the operation of the first gearbox 52. The control unit 112 controls the first gearbox 52 so that the torque T in automatic gear-shift mode is maintained within the predetermined range of less than or equal to the upper limit TA to greater than or equal to the lower limit TB. This limits changes in torque T when a rider is operating the bicycle and reduces the strain on the rider. A third embodiment of the transmission system 50 is now described with reference to Figures 2 and 11. The components, which are the same as the corresponding components of the first embodiment, have been designated with the same reference numerals. Such components are not described in detail. The control unit 112 shown in Fig. 2 performs a fifth gear-shifting process instead of, or in addition to, the second gear-shifting process, so that the gear ratio r2 of the second gearbox 54 changes based on the crankshaft speed CA. In the fifth gear-shifting process, the control unit 112 controls the second gearbox 54, so that the gear ratio r2 of the second gearbox 54 increases when the crankshaft speed CA exceeds the first speed CAX without the first gearbox 52 being operated. If the crankshaft speed CA becomes less than the second speed CAY without the first gearbox 52 being operated, the control unit 112 controls the second gearbox 54, so that the gear ratio r2 of the second gearbox 54 decreases. Referring to Fig. 11, the fifth gear-shifting process, executed by the control unit 112, will now be described. This process is executed in predetermined cycles as long as the transmission system 50 is supplied with energy. In step S31, the control unit 112 determines whether the crankshaft speed CA has exceeded the first speed CAX. If the crankshaft speed CA exceeds the first speed CAX, the control unit 112 proceeds to step S32 and controls the second gearbox 54, thus increasing the gear ratio r2 of the second gearbox 54. In step S32, if it is determined that the gear ratio r2 of the second gearbox 54 is the maximum gear ratio r2 that can be obtained by the second gearbox 54, the control unit 112 maintains the gear ratio r2. If, in step S31, it is determined that the crankshaft speed CA has not exceeded the first speed CAX, the control unit 112 proceeds to step S33 and determines whether the crankshaft speed CA has become less than the second speed CAY. If it is determined that the crankshaft speed CA has become less than the second speed CAY, the control unit 112 proceeds to step S34 and controls the second gearbox 54 so that the gear ratio r2 of the second gearbox 54 decreases. In step S34, if it is determined that the gear ratio r2 of the second gearbox 54 is the minimum gear ratio r2 that can be obtained by the second gearbox 54, the control unit 112 maintains the gear ratio r2. If, in step S33, it is determined that the crankshaft speed CA is greater than or equal to the second speed CAY, that is, the crankshaft speed CA is less than or equal to the first speed CAX and greater than or equal to the second speed CAY, the control unit 112 terminates the current routine without changing the gear ratio r2 of the second transmission 54. In the present embodiment, the advantages (1) and (2) of the first embodiment are obtained with the transmission system 50. The present invention is not limited to the foregoing embodiments, and various changes and modifications of its components can be made without departing from the scope of this disclosure. Furthermore, the components disclosed in the embodiments can be combined in any combination to embody this disclosure. For example, some of the components of all components disclosed in the embodiments can be omitted. Additionally, components in different embodiments can be combined in a suitable manner. In the first to third embodiments, the first transmission 52 can have a front derailleur located near the crank 38 instead of the internal wheel hub gear. In this case, the gear-shifting mechanism 52A has a front derailleur and several front chainrings. In the first and second gear-shifting processes of the first embodiment, the second gearbox 54 can be controlled according to the speed of the motor 56 instead of the crank speed CA. The speed of the motor 56 is the state of the bicycle 10. Preferably, the speed of the motor 56 is related to the speed of the first motor 66. In this case, if it is predicted in step S13 of the first and second gear-shifting processes that the speed of the motor 56 will exceed the first speed by operating the first gearbox 52, the second gearbox 54 is controlled such that the gear ratio r2 of the second gearbox 54 increases in step S14.Furthermore, if in step S18 of the first and second gear shift process it is predicted that the speed of the motor 56 will be less than the speed of the motor 56 by operating the first gearbox 52, the control unit 112 controls the second gearbox 54 in such a way that the gear ratio r2 of the second gearbox 54 decreases in step S19. In the first to fourth gear-shift processes of the first and second embodiments, step S14 can be executed after step S15. In such a case, after the first gearbox 52 has been controlled so that its gear ratio r1 decreases, the control unit 112 controls the second gearbox 54 so that its gear ratio r2 increases. Furthermore, steps S14 and S15 can be executed simultaneously. That is, the control unit 112 can operate the second gearbox 54 and the first gearbox 52 at the same time. To carry out such a process, if the control unit 112 produces negative results in steps S13 and S42, only step S15 is executed, and step S14 is not performed. In the first to fourth gear-shifting processes of the first and second embodiments, step S19 can be executed after step S20. In such a case, after the first gearbox 52 has been controlled so that its gear ratio r1 increases, the control unit 112 controls the second gearbox 54 so that its gear ratio r2 decreases. Furthermore, steps S19 and S20 can be executed simultaneously. That is, the control unit 112 can operate the second gearbox 54 and the first gearbox 52 at the same time. To carry out such a process, if the control unit 112 produces negative results in steps S18 and S44, only step S20 is executed, and step S19 is not performed. The design of the transmission system 50 can be modified in each of the above embodiments, for example as shown in Fig. 12. The first transmission 52 of the transmission system 50 in Fig. 12 has a front transmission located near the crank 38. The second transmission 54 transmits torque from the motor 56 to the downstream side of the front transmission in the power transmission path RT. In this case, the first transmission 52 can be arranged in the drive unit 60. Furthermore, the motor 56 and the second transmission 54 can be arranged in the hub of the rear wheel 14, and the first transmission 52 can have a front derailleur. The first gearbox 52 of each embodiment can have a rear derailleur instead of the internal wheel hub gearbox. In this case, the gear-shifting mechanism 52A has a rear derailleur and multiple sprockets. The transmission system 50 can, in any embodiment, for example, comprise first transmissions 52X and 52Y, as shown in Fig. 13. The first transmission 52X has the same structure as the first transmission 52 in the first to third embodiments, and the first transmission 52Y has the same structure as the first transmission 52 in the embodiment shown in Fig. 12. In this case, the control unit 112 can control the second transmission 54 based on the state of the first transmission 52X or a shift command for the first transmission 52X. Furthermore, the control unit 112 can control the second transmission 54 based on the state of the first transmission 52Y or a shift command for the first transmission 52Y. The planetary gear mechanisms 64 and 74A of each embodiment can be replaced by a planetary gear mechanism comprising a sun gear, planet gears, a carrier, and a ring gear. Furthermore, the gear wheels of each embodiment can be a spur gear or a helical gear. The design of the drive unit 60 in each embodiment can be modified, as shown, for example, in Fig. 14. Fig. 14 shows a drive unit 160 that differs from the drive unit 60 shown in Fig. 4 only in the design of the first gear body and the second gear body. The components in Fig. 14, which are the same as the corresponding components in Fig. 4, have been provided with the same reference numerals. Such components are not described in detail. The drive unit 160 is designed such that the first gear body 90 and the second gear body 96 are rotatable separately and relative to each other. The second freewheel clutch 80 is arranged between the first gear body 90 and the housing 72. The second gear body 96 is not rotatable relative to the housing 72.Thus, the first planetary gear mechanism 64 changes the rotational speed received by the first motor 66 according to the rotational speed of the second motor 68 and outputs the rotation to the first reduction gear 74. The second planetary gear mechanism 74A of the first reduction gear 74 constantly reduces the rotational speed supplied to the second drive body 92 at a fixed reduction ratio and outputs the rotation to the second output body 94. Therefore, the gear ratio rX of the first planetary gear mechanism 64 is variable, and the gear ratio rY of the second planetary gear mechanism 74A is a fixed value less than 1. The design of the drive unit 60 in each of the above embodiments can be modified, for example, as shown in Figures 15 and 16. Figure 15 shows a drive unit 260 that differs from the drive unit 60 shown in Figure 4 only with respect to the design of the second gearbox and the motor. Otherwise, the design of the drive unit 260 is the same as that of the drive unit 60. The drive unit 260 of Figure 15 has a motor 116 and a second gearbox 118. The motor 116 has the same design as the first motor 66. The second gearbox 118 has two stages. The second gearbox 118 has a first rotating element 120, a second rotating element 122, a third rotating element 124, and a fourth rotating element 126. The first rotating body 120 has a first rotating shaft 120A, a first gear wheel 120B and a second gear wheel 120C.The first gear wheel 120B and the second gear wheel 120C are rotatable around the first rotating shaft 120A. As shown in Fig. 16, the first gear wheel 120B engages with a gear wheel 116B, which is arranged on an output shaft 116A of the motor 116. A first freewheel clutch 128 couples the first gear wheel 120B and the second gear wheel 120C. The second rotating body 122 has a second rotating shaft 122A, a first gear 122B, and a second gear 122C. The first gear 122B and the second gear 122C are rotatable about the second rotating shaft 122A. The first gear 122B engages with the gear 116B, which is located on the output shaft 116A of the motor 116. A second freewheel clutch 130 couples the first gear 122B and the second rotating shaft 122A. The third rotating body 124 has a third rotating shaft 124A, a first gear 124B, and a second gear 124C. The first gear 124B and the second gear 124C are rotatable about the third rotating shaft 124A. The first gear wheel 124B and the second gear wheel 124C are coupled such that they rotate integrally with each other, or are integrally formed together. The first gear wheel 124B is in mesh with the second gear wheel 122C of the second rotating body 122. The fourth rotating body 126 has a fourth rotating shaft 126A, a first gear wheel 126B, and a second gear wheel 126C. The first gear wheel 126B and the second gear wheel 126C are rotatable about the fourth rotating shaft 126A. The first gear wheel 126B and the second gear wheel 126C are coupled such that they rotate integrally with each other, or are integrally formed together. The first gear wheel 126B engages with the second gear wheel 120C of the first rotating body 120 and the second gear wheel 124C of the third rotating body 124. The second gear wheel 126C engages with the gear wheel 84, which is formed by the outer circumference of the force resultant component 70 shown in Fig. 15. If the first freewheel clutch 128 receives the rotation of the first gear 120B of the first rotating body 120 in the first direction F1, the first freewheel clutch 128 rotates the second gear 120C in the first direction F1. If the first freewheel clutch 128 receives the rotation of the first gear 120B of the first rotating body 120 in the second direction F2, the first freewheel clutch 128 does not transmit the rotation to the second gear 120C. If the second freewheel clutch 130 receives the rotation of the first gear 122B of the second rotating body 122 in the second direction F2, the second freewheel clutch 130 rotates the second gear 122C in the second direction F2. If the second freewheel clutch 130 receives the rotation of the first gear wheel 122B of the second rotating body 122 in the first direction F1, the freewheel clutch 130 does not transmit the rotation to the second gear wheel 122C.Depending on the direction of rotation of the motor 116, the fourth rotating body 126 receives the rotation from the motor 116 via the first rotating body 120, as well as the rotation from the motor 116 via the second rotating body 122 and the third rotating body 124. The rotation of the motor 116 is transmitted via the first rotating body 120 to the fourth rotating body 126 with a transmission ratio that differs from the transmission ratio when the rotation of the motor 116 is transmitted via the second rotating body 122 and the third rotating body 124. In this way, the control unit 112 changes the transmission ratio of the second gearbox 118 by altering the transmission ratio of the second gearbox 118. The design of the drive unit 60 in each of the above embodiments can be modified, for example as shown in Figures 17, 18 to 19. Figure 17 shows a drive unit 360 that differs from the drive unit 260 shown in Figure 16 only with regard to the design of the second gearbox and the motor. Otherwise, the design of the drive unit 360 is the same as that of the drive unit 260. The drive unit 360 of Figure 17 has the motor 116 and a second gearbox 132. The second gearbox 132 has a planetary gear mechanism 134, a first freewheel clutch 136, a second freewheel clutch 138, a shift mechanism 140, and a rotating body 148. The planetary gear mechanism 134 shown in Fig. 18 comprises a sun gear 142, a ring gear 144, and a carrier 146. The sun gear 142 is arranged on the output shaft 116A of the motor 116 and rotates integrally with the output shaft 116A. The first freewheel clutch 136 is located between the carrier 146 and the housing 72, as shown in Fig. 17, so that the rotation of the carrier 146 relative to the housing 72 is limited in the first direction F1. The second freewheel clutch 138 is located between the ring gear 144 and the housing 72, as shown in Fig. 17, so that the rotation of the ring gear 144 relative to the housing 72 is limited in the second direction F2. The switching mechanism 140 switches the second freewheel clutch 138 between states that allow and restrict the rotation of the ring gear 144 in the second direction. The rotating body 148 comprises a rotating shaft 148A, a first gear 148B, a second gear 148C, and a third gear 148D. The first gear 148B, the second gear 148C, and the third gear 148D are rotatable about the rotating shaft 148A. The first gear 148B, the second gear 148C, and the third gear 148D are coupled such that they rotate integrally with one another or are integrally formed. The first gear 148B differs from the second gear 148C in the number of teeth. The first gear 148B meshes with a gear 146A, which is arranged on the outer circumferential section of the carrier 146. The second gear 148C meshes with a gear 144A, which is arranged on the outer circumferential section of the ring gear 144. The third gear wheel 148D engages with the gear wheel 84, which is formed on the outer circumference of the force resultant component 70. If the motor 116 generates a rotation in one direction and transmits the rotational force in the second direction F2 to the carrier 146, the second freewheel clutch 138 and the shifting mechanism 140 restrict the rotation of the ring gear 144 in the second direction F2. In this case, the rotation of the carrier 146 in the second direction F2 is transmitted to the outer circumferential section of the force resultant component 70 by means of the gear wheel 146A, the first gear wheel 148B and the third gear wheel 148D. If the motor 116 generates a rotation in the opposite direction and transmits the rotational force in the first direction to the carrier 146, the first freewheel clutch 136 restricts the rotation of the carrier 146 in the first direction. Furthermore, the second freewheel clutch 138 and the shifting mechanism 140 allow the rotation of the ring gear 144 in the second direction. In this case, the rotation of the ring gear 144 in the second direction is transmitted via the gear wheel 144A, the second gear wheel 148C, and the third gear wheel 148D to the gear wheel 84, which is arranged on the outer circumferential section of the force resultant component 70. The gear ratio of the rotation of the motor 116 is smaller when transmitted via the carrier 146 to the rotating body 148 than the gear ratio when transmitted via the ring gear 144 to the rotating body 148. Thus, the gear ratio of the second gearbox 132 can be changed by changing the direction of rotation of the motor 116. The design of the drive unit 60 in each of the above embodiments can be modified, for example, as shown in Figures 20 and 21. Figures 20 and 21 show a drive unit 460 that differs from the drive unit 260 shown in Figure 16 only with regard to the design of the second gearbox. Otherwise, the design of the drive unit 460 is the same as that of the drive unit 260. The drive unit 460 of Figure 20 has the motor 116 and a second gearbox 150. The second gearbox 150 has a first rotating element 152, a second rotating element 154, and a motion mechanism 156. The first rotating element 152 and the second rotating element 154 can transmit the rotation to the gear wheel 84 of the force resultant component 70. The first rotating body 152 has a rotating shaft 152A, a first gear wheel 152B, and a second gear wheel 152C. The first gear wheel 152B and the second gear wheel 152C are rotatable about the rotating shaft 152A. The first gear wheel 152B and the second gear wheel 152C are coupled such that they rotate integrally with each other, or are integrally formed. The second gear wheel 152C meshes with the gear wheel 84 of the force resultant component 70. The second rotating body 154 has a rotating shaft 154A, a first gear wheel 154B, and a second gear wheel 154C. The first gear wheel 154B and the second gear wheel 154C are rotatable about the rotating shaft 154A. The first gear wheel 154B and the second gear wheel 154C are coupled such that they rotate integrally with each other, or are integrally formed together. The second gear wheel 154C engages with the gear wheel 84 of the force resultant component 70. The motion mechanism 156 can move the motor 116 in a direction orthogonal to the motor 116's rotating shaft. The motion mechanism 156 switches the gear wheel 116B, which is arranged on the output shaft 116A of the motor 116, between an engagement state with the first gear wheel 152B of the first rotating body 152, as shown in Fig. 20, and an engagement state with the first gear wheel 154B of the second rotating body 154. The first gear wheel 152B of the first rotating body 152 differs from the first gear wheel 154B of the second rotating body 154 in the number of teeth, and / or the second gear wheel 152C of the first rotating body 152 differs from the second gear wheel 154C of the second rotating body 154 in the number of teeth. This changes the transmission ratio according to the path over which the power is transmitted.The control unit 112 moves the motor 116 so that the gear wheel 116B selectively engages with the first gear wheel 152B and the first gear wheel 154B, thus changing the gear ratio of the second gearbox 150. The drive unit 460 of Figs. 20 and 21 can be modified as shown in Fig. 22. Fig. 22 shows a drive unit 560 that differs from the drive unit 460 shown in Figs. 20 and 21 only with regard to the design of the second gearbox. Otherwise, the design of the drive unit 560 is the same as that of the drive unit 460. The motion mechanism 156 of a second gearbox 250 in Fig. 22 moves the second rotating body 154 in a direction orthogonal to the axis. The gear wheel 116B of the motor 116 is constantly engaged with the first gear wheel 152B of the first rotating body 152. The movement mechanism 156 switches the first gear wheel 154B of the second rotating body 154 between an engagement state with the gear wheel 116B of the motor 116 and an engagement released from the engagement with the gear wheel 116B of the motor 116.The second gear wheel 152C of the first rotating body 152, which engages with the gear wheel 84 of the force resultant component 70, is connected to the first gear wheel 152B via the freewheel clutch 158. The second gear wheel 152C of the first rotating body 152 differs from the first gear wheel 154B of the second rotating body 154 in the number of teeth. When the first gear wheel 154B of the second rotating body 154 engages with the gear wheel 116B of the motor 116, the rotation transmitted from the second rotating body 154 to the first rotating body 152 via the force resultant component 70 is faster than the rotation transmitted from the motor 116 to the first rotating body 152. In this situation, the freewheel clutch 158 serves to rotate the second gear wheel 152C of the first rotating body 152 and the first gear wheel 152B of the first rotating body 152.In this way, the control unit 112 moves the motor 116 so that the gear ratio of the second gearbox 150 is changed. The first freewheel clutch 78 can be omitted from the drive unit 60 in any of the above embodiments. In such a case, the sun gear 86A can be formed on the outer circumferential section of the output shaft 66B. Furthermore, the first freewheel clutch 78 can be located between the first output body 88 and the second drive body 92, between the second output body 94 and the gear wheel 94D, or between the force resultant component 70 and the gear wheel 84. As long as the first freewheel clutch 78 can restrict the transmission of muscle power to the output shaft 66B of the second motor 68 when the crankshaft 42 is rotated forward, the first freewheel clutch 78 can be located at any position in the drive path from the output shaft of the second motor 68 to the force resultant component 70. The crankshaft 42 can be omitted from the drive unit 60 in any of the above embodiments. In this case, the drive unit 60 includes the crankshaft 42 as a single element that configures the bicycle. In each of the above embodiments, a force resultant component can be configured from the crankshaft 42. In this case, the force resultant component 70 is omitted, and the rotation of the first reduction gear 74 is transmitted to the crankshaft 42. The first coupling 62 can be omitted from any of the above embodiments. In each of the above embodiments, the control unit 110 can be arranged outside the housing 72 on the frame 22 of the bicycle 10. REFERENCE MARK LIST 10 Bicycle 12 Front wheel 12A Axle 14 Rear wheel 14A Axle 16 Body 18 Drive mechanism 20 Battery unit 22 Frame 24 Front fork 26 Handlebar stem 26A Handlebar 28 Crank linkage 30 Pedal 31 Pedal body 32 Pedal shaft 34 Rear sprocket 36 Chain 38 Crank 40 Front sprocket 42 Crankshaft 44 Crank arms 46 Battery 48 Battery holder 50 Transmission system 52 First transmission 52A Shift mechanism 52B Actuator 52X First transmission 52Y First transmission 54 Second transmission 56 Motor 58 Control unit 60 Drive unit 62 First clutch 64 First planetary gear mechanism 66 First motor 66A Main body 66B Output shaft 68 Second motor 68A Main body 68B Output shaft 68C Gear wheel 70 Force resultant component 72 Housing 74 First reduction gear 74A Second planetary gear mechanism 76 Second reduction gear 78 First freewheel clutch 80 Second freewheel clutch 82 Hollow shaft 82A End 84 Gear wheel 86 First drive body 86A Sun gear 88 First output body 88APlanet gears 88B Carrier 88C Planet pin 90 First gear body 90A Ring gear 90B Gear wheel 92 Second input body 92A Sun gear 94 Second output body 94A Planet gears 94B Carrier 94C Planet pin 94D Gear wheel 96 Second gear body 96A Ring gear 98 Carrier 98A Gear wheel 100 Torque sensor 102 Speed ​​sensor 110 Bicycle control 112 Control unit 114 Memory 116 Motor 116A Output shaft 116B Gear wheel 118 Second gear 120 First rotating body 120A First rotating shaft 120B First gear wheel 120C Second gear wheel 122 Second rotating body 122A Second rotating shaft 122B First gear wheel 122C Second gear wheel 124 Third rotating body 124A Third rotating shaft 124B First gear wheel 124C second gear wheel 126 fourth rotating body 126A fourth rotating shaft 126B first gear wheel 126C second gear wheel 128 first freewheel clutch 130 second freewheel clutch 132 second gearbox 134 planetary gear mechanism 136 first freewheel clutch 138 second freewheel clutch 140Shifting mechanism 142 Sun gear 144 Ring gear 144A Gear wheel 146 Carrier 146A Gear wheel 148 Rotating body 148A Rotating shaft 148B First gear wheel 148C Second gear wheel 148D Third gear wheel 150 Second gear 152 First rotating body 152A Rotating shaft 152B First gear wheel 152C Second gear wheel 154 Second rotating body 154A Rotating shaft 154B First gear wheel 154C Second gear wheel 156 Motion mechanism 158 Freewheel clutch 160 Drive unit 250 Second gear 260 Drive unit 360 Drive unit 460 Drive unit 560 Drive unit S11 - S44 Process steps r1, r2, rX, rY Gear ratios t11 Time t21 Time B Screw CA Crank speed CAA Upper limit CAB Lower limit CAX First speed CAY, second speed F1, first direction F2, second direction RT, transmission path T, torque TA, upper limit TB, lower limit TX, first torque TY, second torque

Claims

Bicycle control unit (110) designed for mounting on a bicycle (10) comprising a first transmission (52) having at least two gear stages (52X, 52Y) and capable of changing the ratio of the rotation of a wheel (14) to the rotation of a crank (38), a motor (56) assisting the muscle power supplied to the crank (38), and a second transmission (54) capable of transmitting rotational force from the motor (56) to a power transmission path extending from the crank (38) to the wheel (14) without changing the ratio of the rotation of the wheel (14) to the rotation of the crank (38), wherein the bicycle control unit (110) comprises a control unit (112) that controls the second transmission (54) according to a state of the bicycle (10) and a state of the first transmission (52) and a shift command for the first transmission (52).wherein the state of the bicycle (10) includes at least one of the torque generated by the muscle power and a rotational speed of the crank (38) or the motor (56), wherein the control unit (112) controls the second transmission (54) such that the gear ratio of the second transmission (54) increases when the operation of the first transmission (52) causes the rotational speed to exceed a predetermined first rotational speed, and wherein the control unit (112) predicts from the rotational speed and a state of the first transmission (52) and a shift command for the first transmission (52) whether the operation of the first transmission (52) will cause the rotational speed to change to a value exceeding the first rotational speed. Bicycle control unit (110) that can be mounted on a bicycle (10) comprising a first gearbox (52) having at least two gear stages (52X, 52Y) and capable of changing the ratio of the rotation of a wheel (14) to the rotation of a crank (38), a motor (56) assisting the muscle power supplied to the crank (38), and a second gearbox (54) capable of transmitting rotational force from the motor (56) to a power transmission path extending from the crank (38) to the wheel (14) without changing the ratio of the rotation of the wheel (14) to the rotation of the crank (38), wherein the bicycle control unit (110) comprises a control unit (112) that controls the first gearbox (52) and the second gearbox (54) according to a state of the bicycle (10). Bicycle control (110) according to claim 2, wherein the state of the bicycle (10) comprises at least one of the torque generated by the muscle power and a rotational speed of the crank (38) or the motor (56). Bicycle control unit (110) according to claim 3, wherein the control unit (112) controls the second transmission (54) such that the gear ratio of the second transmission (54) increases when the operation of the first transmission (52) causes the rotational speed to exceed a predetermined first rotational speed. Bicycle control (110) according to claim 4, wherein the control unit (112) predicts from the rotational speed and a state of the first transmission (52) and a switching command for the first transmission (52) whether the operation of the first transmission (52) will cause the change in rotational speed to a value that exceeds the first rotational speed or not. Bicycle control (110) according to one of claims 1, 4 or 5, wherein the control unit (112) controls the second transmission (54) such that the gear ratio of the second transmission (54) increases when the rotational speed exceeds the first rotational speed without the first transmission (52) being operated. Bicycle control (110) according to one of claims 1, 3 to 6, wherein the control unit (112) controls the second transmission (54) such that the gear ratio of the second transmission (54) decreases when the operation of the first transmission (52) causes the rotational speed to be less than a predetermined second rotational speed. Bicycle control (110) according to claim 7, wherein the control unit (112) predicts from the rotational speed and a state of the first transmission (52) and a switching command for the first transmission (52) whether the operation of the first transmission (52) will cause the change in rotational speed to a value that is less than the second rotational speed or not. Bicycle control (110) according to claim 7 or 8, wherein the control unit (112) controls the second transmission (54) such that the gear ratio of the second transmission (54) decreases when the rotational speed becomes less than the second rotational speed, without the first transmission (52) being operated. Bicycle control (110) according to one of claims 7 to 9, which are directly or indirectly dependent on claim 4, wherein the first rotational speed is higher than the second rotational speed. Bicycle control unit (110) according to one of claims 1, 3 to 10, wherein the control unit (112) controls the second transmission (54) such that the gear ratio of the second transmission (54) increases when the operation of the first transmission (52) causes the torque to be less than a predetermined first torque. Bicycle control (110) according to claim 11, wherein the control unit (112) predicts from the torque and a state of the first transmission (52) and a switching command for the first transmission (52) whether the operation of the first transmission (52) will cause the change of the torque to a value that is less than the first torque or not. Bicycle control (110) according to one of claims 1, 3 to 12, wherein the control unit (112) controls the second transmission (54) such that the gear ratio of the second transmission (54) decreases when the torque exceeds a predetermined second torque by operating the first transmission (52). Bicycle control (110) according to claim 13, wherein the control unit (112) predicts from the torque and a state of the first transmission (52) and a switching command for the first transmission (52) whether the operation of the first transmission (52) will cause the change in torque to a value exceeding the second torque or not. Bicycle control (110) according to one of claims 3 to 14, which depend on claim 2, wherein the control unit (112) controls the first transmission (52) such that the rotational speed of the crank (38) is maintained within a predetermined range. Bicycle control unit (110) according to claim 1, wherein the control unit (112) operates the first transmission (52) and the second transmission (54) in a predetermined sequence or operates the first transmission (52) and the second transmission (54) simultaneously. Bicycle control (110) according to claim 15 or 16, which are directly or indirectly dependent on claim 10, wherein the predetermined range has an upper limit which is higher than the first rotational speed, and the predetermined range has a lower limit which is less than the second rotational speed. Bicycle transmission system comprising: the bicycle control (110) according to one of claims 1 to 17; the first transmission (52) and the second transmission (54). Bicycle transmission system according to claim 18, which further comprises a housing (72) in which at least the second transmission (54) is arranged, wherein the housing (72) rotatably supports a crankshaft. Bicycle transmission system comprising: a first transmission (52) configured to change the ratio of the rotation of a wheel (14) to the rotation of a crank (38) in a bicycle (10); and a second transmission (54) configured to have at least two gear stages and capable of transmitting rotational force from a motor (56) to a power transmission path extending from the crank (38) to the wheel (14) in any of the gear stages without changing the ratio of the rotation of the wheel (14) to the rotation of the crank (38), wherein the first transmission (52) has a front transmission located near the crank (38), and the second transmission (54) transmits the rotational force from the motor (56) to a downstream side of the front transmission in the power transmission path. Bicycle transmission system according to claim 20, wherein the second transmission (54) transmits the rotational force from the motor (56) to an upstream side of the first transmission (52) in the power transmission path. Bicycle transmission system according to claim 21, wherein the first transmission (52) comprises at least one of a front transmission located near the crank (38) and a rear transmission located near the axle (14A) of a rear wheel (14). Bicycle transmission system according to one of claims 20 to 22, further comprising the bicycle control (110) according to one of claims 1 to 17.

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