Electrically assisted bicycle drive system, electrically assisted bicycle, and control method and program for electrically assisted bicycle

Abstract

To provide a drive system that is able to further improve riding comfort of an electric power assisted bicycle when changing a control mode.SOLUTION: When a change condition from a first mode to a second mode is satisfied, a control device 30 starts changing an assist ratio from a first assist ratio to a second assist ratio, at a change start position Ps between an angle position P1 obtained by adding 90 degrees to a crank angle position corresponding to a highest point P0 of a locus Lo of a pedal 2a and an angle position P2 obtained by adding 135 degrees to the crank angle position corresponding to the highest point P0. The control device 30 changes the assist ratio so that the assist ratio reaches the second assist ratio at a change end position Pe obtained by adding at least 45 degrees to the change start position Ps.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a drive system for an electrically assisted bicycle, an electrically assisted bicycle, and a control method and program for an electrically assisted bicycle. [Background technology]

[0002] Most electrically assisted bicycles have multiple control modes, such as a mode in which the assist torque output by the electric motor is relatively large and a mode in which the assist torque is relatively small. The following Patent Document 1 discloses the timing of mode change (timing of changing the assist ratio) in one pedal cycle. Specifically, it discloses that the assist ratio is changed when one of the pedals is in an angular position relatively close to the lowest point of its trajectory. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-137119 A Summary of the Invention [Problem to be solved by the invention]

[0004] As disclosed in the '1999 patent, if the assist ratio is changed when one pedal is near its lowest point, this can affect the comfort of the rider.

[0005] The present disclosure provides a drive system, an electrically assisted bicycle, and a control method and program for an electrically assisted bicycle that can further improve the riding comfort of the electrically assisted bicycle when changing control modes. [Means for solving the problem]

[0006] (1) The drive system of an electrically assisted bicycle proposed in this disclosure includes a sensor that detects the pedaling force acting on a pedal attached to a crankshaft, an electric motor that assists the pedaling of the pedal, and a control device that controls the electric motor based on an assist ratio corresponding to a control mode and the pedaling force detected by the sensor. The control device has, as the control modes, a first control mode in which the electric motor is controlled based on a first assist ratio, and a second control mode in which the electric motor is controlled based on a second assist ratio. When a change condition from the first mode to the second mode is satisfied, the control device starts changing the assist ratio from the first assist ratio to the second assist ratio at a change start position between an angular position of the crankshaft corresponding to the highest point of the pedal trajectory plus 90 degrees and an angular position of the crankshaft corresponding to the highest point plus 135 degrees. The control device changes the assist ratio so that the assist ratio reaches the second assist ratio at a change end position that is at least 45 degrees added to the change start position.

[0007] According to this drive system, the effect on ride comfort of a change in the assist ratio caused by a change in the control mode can be reduced.

[0008] (2) In the drive system of (1), the angle difference between the change start position and the change end position may be 135 degrees or less. This makes it possible to prevent an excessively long time from being required to change the assist ratio.

[0009] (3) In the drive system of (1) or (2), the angle difference between the change start position and the change end position may be 60 degrees or more. This makes it possible to more effectively suppress abrupt changes in assist torque.

[0010] (4) In the drive system of any one of (1) to (3), the change end position may be between an angular position obtained by adding 135 degrees to the highest point and an angular position obtained by adding 225 degrees to the highest point. When the crankshaft is in such an angular position, the pedaling force becomes weak. In other words, the change in the assist ratio is completed at the timing when the pedaling force becomes weak. Therefore, the change in the assist ratio becomes difficult for the rider to sense, and the riding comfort can be further improved.

[0011] (5) In the drive system of any one of (1) to (4), the change end position may be an angle position obtained by adding an angle of 270 degrees or less to the highest point. This makes it possible to prevent an excessive delay in starting running at the assist ratio in the changed control mode.

[0012] (6) In the drive system of any one of (1) to (5), the change end position may be an angle position obtained by adding an angle of 225 degrees or less to the highest point. This makes it possible to effectively prevent an excessive delay in starting running at the assist ratio in the changed control mode.

[0013] (7) In the drive system of (1) to (6), the control device may calculate the assist ratio so that the assist ratio gradually approaches the second assist ratio from the first assist ratio when the angular position of the crankshaft is between the change start position and the change end position.

[0014] (8) The drive system of (1) to (6) may include a sensor for detecting an amount of change in the angular position of the crankshaft. The control device may calculate the assist ratio based on an amount of change in the angular position of the crankshaft when the pedal is between the change start position and the change end position. This makes it easy to change the assist ratio between the change start position and the change end position.

[0015] (9) In the drive system of (1) to (8), the control device may calculate a rate of change of the assist ratio based on a difference between the first assist ratio and the second assist ratio and an angle difference between the change start position and the change end position. This makes it easy to complete the change of the assist ratio when the angle of the crankshaft reaches a predetermined change end position.

[0016] (10) The electrically assisted bicycle proposed in this disclosure has a drive system as described in (1) to (9) and a wheel to which the assist torque output by the electric motor is transmitted.

[0017] (12) A control method for an electrically assisted bicycle proposed in this disclosure controls an electric motor based on an assist ratio corresponding to a control mode and a pedaling force detected by a sensor, and has as the control modes a first control mode in which the electric motor is controlled based on a first assist ratio and a second control mode in which the electric motor is controlled based on a second assist ratio. When a change condition from the first mode to the second mode is satisfied, the control method starts changing the assist ratio from the first assist ratio to the second assist ratio at a change start position between an angular position of the crankshaft corresponding to the highest point of the pedal trajectory plus 90 degrees and an angular position of the crankshaft corresponding to the highest point plus 135 degrees. The control method changes the assist ratio so that the assist ratio reaches the second assist ratio at a change end position that is at least 45 degrees added to the change start position.

[0018] (13) A program proposed in the present disclosure causes a computer to function as a control device that controls an electric motor based on an assist ratio corresponding to a control mode and a pedaling force detected by a sensor, and has as the control modes a first control mode in which the electric motor is controlled based on a first assist ratio and a second control mode in which the electric motor is controlled based on a second assist ratio. When a change condition from the first mode to the second mode is satisfied, the program causes the computer to function as a means for starting a change of the assist ratio from the first assist ratio to the second assist ratio at a change start position between an angular position of the crankshaft corresponding to the highest point of the pedal trajectory plus 90 degrees and an angular position of the crankshaft corresponding to the highest point plus 135 degrees, and a means for changing the assist ratio so that the assist ratio reaches the second assist ratio at a change end position that is at least 45 degrees added to the change start position. [Brief description of the drawings]

[0019] [Figure 1] 1 is a side view showing an example of a vehicle proposed in the present disclosure. [Diagram 2] FIG. 1 is a block diagram showing the configuration of an electrically assisted bicycle. [Diagram 3] FIG. 2 is a block diagram showing functions of a control device. [Figure 4] 11A and 11B are diagrams for explaining a change start position and a change end position related to a change in the assist ratio. [Diagram 5] 4 is a time chart for explaining the processing executed by the peak pedal force detection unit and the start position detection unit. [Figure 6] FIG. 4 is a flowchart showing a process flow related to changing of a control mode executed by a control device. [Figure 7] FIG. 11 is a flow chart showing another example of processing related to changing of the control mode executed by the control device. [Figure 8] 6 is a time chart showing an example of a result of processing by the control device. [Figure 9]10 is a time chart showing another example of a result of processing by the control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The electrically power assisted bicycle proposed in this disclosure will be described below. FIG. 1 is a side view of an electrically power assisted bicycle 100, which is an example of an electrically power assisted bicycle proposed in this disclosure. FIG. 2 is a block diagram showing the configuration of the electrically power assisted bicycle 100. In FIG. 2, thick solid lines represent the transmission of power, and thin solid lines represent signals and currents. The electrically power assisted bicycle 100 has a drive system 10 for assisting the rider's pedaling force. The drive system 10 is made up of electrical components such as an electric motor 21, which will be described later, a control device 30, a motor drive device 39, and an operation input device 58. Below, the electrically power assisted bicycle 100 will be simply referred to as a bicycle.

[0021] [Electric assisted bicycle hardware] As shown in FIG. 1, a bicycle 100 has a crankshaft 2. A right pedal 2a and a left pedal 2a are attached to the right and left ends of the crankshaft 2 via crank arms, respectively. The crankshaft 2 is supported at the lower end of a seat tube 11. A saddle 18 is fixed to the upper end of the seat tube 11. At the front of the bicycle 100, a handlebar stem 8, a handlebar 7 fixed to the upper part of the handlebar stem 8, a front fork 19 fixed to the lower part of the handlebar stem 8, and a front wheel 9 supported by the lower end of the front fork 19 are provided. The handlebar stem 8 is supported by a head pipe 17a provided at the front end of a frame 17. The shape of the frame 17 is not limited to the example shown in FIG. 1 and may be modified as appropriate.

[0022] Bicycle 100 has a drive unit 20 (see FIG. 1). Drive unit 20 is made up of an electric motor 21 (see FIG. 2) that outputs assist torque to assist the rider in driving the rear wheel 6, and a reducer 25 (see FIG. 2). Electric motor 21 is driven by power supplied from a battery 22. Battery 22 may be disposed, for example, behind seat tube 11, and drive unit 20 may be disposed behind crankshaft 2. The positions of electric motor 21 and battery 22 are not limited to those in the example of bicycle 100, and may be changed as appropriate.

[0023] 2, the force applied to the crankshaft 2 through the pedal 2a is transmitted to the resultant force transmission mechanism 24 through the one-way clutch 23. The assist torque output from the electric motor 21 is transmitted to the resultant force transmission mechanism 24 through the reducer 25 and the one-way clutch 26.

[0024] The resultant force transmission mechanism 24 is composed of a shaft, a rotating member provided on the shaft, a chain 5 (see FIG. 1), etc., and combines the force applied to the crankshaft 2 and the torque output from the electric motor 21. In one example of the resultant force transmission mechanism 24, the two forces (torques) are combined by being input to a common shaft or a common rotating member. Both the force applied to the crankshaft 2 and the torque output from the electric motor 21 may be input to the chain 5 and combined. The power combined by the resultant force transmission mechanism 24 may be transmitted to the rear wheel 6 through a speed change mechanism 27 and a one-way clutch 28, as shown in FIG. 2. The speed change mechanism 27 is a mechanism that can change the speed by operating an operating member (e.g., a lever) provided on the handlebar 7, for example.

[0025] The bicycle 100 has a pedaling force sensor 41 (see FIG. 2) for detecting the pedaling force applied by the rider to the pedal 2a. The pedaling force sensor 41 may be, for example, a torque sensor that outputs a signal corresponding to the torque generated in the crankshaft 2. Hereinafter, the torque detected by the pedaling force sensor 41 will be simply referred to as the "pedaling force."

[0026] The bicycle 100 has a crank rotation sensor 45 that outputs a signal in response to changes in the angular position of the crankshaft 2. The crank rotation sensor 45 is a sensor that generates a pulse signal for each unit angular change (for example, each change of one degree) of the crankshaft 2. The control device 30 calculates the amount of change in the angular position of the crankshaft 2, the rotational speed of the crankshaft 2, and the like based on the signal from the crank rotation sensor 45. Note that a sensor capable of detecting the absolute angle (angular position) of the crankshaft 2 may be used as the crank rotation sensor 45.

[0027] The bicycle 100 has a motor rotation sensor (encoder) 42 that outputs a signal according to the rotation of the electric motor 21, and a wheel rotation sensor 43 that outputs a signal according to the rotation of the wheel. The control device 30 calculates the rotation speed of the electric motor 21 based on the output of the motor rotation sensor 42, and calculates the vehicle speed based on the output of the wheel rotation sensor 43. The wheel rotation sensor 43 may be attached to the front wheel 9 or the rear wheel 6.

[0028] 2, the bicycle 100 has an operation input device 58. The operation input device 58 includes operation members (e.g., buttons and levers) that can be operated by the rider, and inputs signals corresponding to the operation of these members to the control device 30. For example, the rider can select the control mode of the electric motor 21 through the operation input device 58. A touch sensor that detects the position of the rider's finger touching a display device (not shown) may be used as the operation input device 58.

[0029] [Control device] The control device 30 has one or more memories that store programs and maps related to the control of the electric motor 21, and one or more microprocessors that execute the programs. The control device 30 controls the electric motor 21 based on the output of the pedal force sensor 41.

[0030] [Multiple control modes] The control device 30 has a plurality of control modes with different assist ratios as the control mode for the electric motor 21. The control device 30 has, for example, three control modes (hereinafter, these modes are referred to as the "strong mode", the "standard mode", and the "eco mode", respectively). The number of control modes may be less than three or more than three.

[0031] The memory of the control device 30 may store one or more maps (hereinafter referred to as "assist ratio maps") that define the assist ratio. For example, the multiple assist ratio maps may correspond to multiple control modes, respectively. For example, if three control modes (strong mode, standard mode, and eco mode) are defined, the three assist ratios may be strong mode>standard mode>eco mode. The assist ratio may be set according to the vehicle speed, for example. When the bicycle 100 is traveling, the control device 30 may refer to the assist ratio map corresponding to the currently selected control mode and calculate the assist ratio corresponding to the vehicle speed calculated based on the output of the wheel rotation sensor 43.

[0032] An arithmetic expression may be used to calculate the assist ratio. In this case, the arithmetic expression may be provided for each of the multiple control modes and may define the relationship between the assist ratio and the vehicle speed. In another example of calculating the assist ratio, both the assist ratio map and the arithmetic expression may be used. For example, an assist ratio map that is commonly used in the multiple control modes may be defined. Then, for example, in the standard mode, a value obtained from the common assist ratio map may be used as the assist ratio as is, while in the eco mode or strong mode, a value obtained by correcting the value obtained from the common assist ratio map may be used as the assist ratio.

[0033] [Functions of the control device] 3 is a block diagram showing functions of the control device 30. The control device 30 has, as its functions, a control mode management unit 31, an assist ratio calculation unit 32, an assist torque calculation unit 33, and a peak pedaling force detection unit 34. These are realized by a microprocessor constituting the control device 30 executing a program stored in a memory.

[0034] [Control mode management section] The control mode management unit 31 changes the control mode in response to the driving conditions of the bicycle 100 and instructions from the rider. When the control mode is changed, the assist ratio map and calculation formula used to calculate the assist ratio are also changed.

[0035] The control mode management unit 31 determines whether a predefined control mode change condition is satisfied. When the change condition is satisfied, the control mode management unit 31 automatically changes the control mode regardless of the rider's operation. For example, the control mode management unit 31 determines whether the pedaling force calculated based on the output of the pedaling force sensor 41 satisfies the change condition.

[0036] For example, the control mode management unit 31 judges whether or not the peak pedal force exceeds a threshold value in a predetermined number of (one or more) depressing operations of the pedal 2a. The peak pedal force is the maximum pedal force in one depressing operation. When one or more peak pedal forces exceed the threshold value, the control mode management unit 31 changes the control mode to the up side. ("Changing to the up side" means changing to a control mode in which a higher assist ratio is calculated.) The control mode management unit 31 also judges whether or not the peak pedal force falls below a threshold value in a predetermined number of (one or more) depressing operations of the pedal 2a. When one or more peak pedal forces fall below the threshold value, the control mode management unit 31 changes the control mode to the down side. ("Changing to the down side" means changing to a control mode in which a lower assist ratio is calculated.) The peak pedal force is detected by processing by the peak pedal force detection unit 34, which will be described later.

[0037] The control mode management unit 31 may calculate an average of the pedaling force in a predetermined number of (one or more) depressing operations of the pedal 2a. If the average exceeds a threshold, the control mode management unit 31 may change the control mode to the up side, or if the average falls below the threshold, the control mode management unit 31 may change the control mode to the up side.

[0038] These thresholds may be set for each control mode related to the change. For example, different thresholds may be set for a change from the eco mode to the standard mode, a change from the standard mode to the strong mode, etc.

[0039] The bicycle 100 has an operation input device 58 (see FIG. 2). The rider can input a mode change command to the control device 30 through the operation input device 58. One of the conditions for changing the mode may be that such a mode change command is input from the operation input device 58 to the control device 30.

[0040] [Assist ratio calculation section] The assist ratio calculation unit 32 calculates the assist ratio corresponding to the vehicle speed detected by the wheel rotation sensor 43 by using an assist ratio map or a calculation formula corresponding to the currently selected control mode.

[0041] When the above-mentioned control mode change condition is satisfied, the assist ratio calculation unit 32 gradually changes the assist ratio from the assist ratio defined in the control mode before the change to the assist ratio defined in the control mode after the change. The assist ratio calculation unit 32 starts changing the assist ratio when the angular position of the crankshaft 2 reaches a predetermined position.

[0042] Hereinafter, the angular position of the crankshaft 2 will be referred to as the "crank angle position." The control mode before the change will be referred to as the "first control mode," and the assist ratio calculated by the first control mode will be referred to as the "first assist ratio." The control mode after the change will be referred to as the "second control mode," and the assist ratio calculated by the second control mode will be referred to as the "second assist ratio." The angular position at which the change in the assist ratio begins will be referred to as the "change start position," and the angular position at which the change in the assist ratio ends will be referred to as the "change end position."

[0043] FIG. 4 is a diagram for explaining the change start position and the change end position, and shows the trajectory Lo of the crankshaft 2 and the pedal 2a.

[0044] The change start position Ps is a position defined between an angular position P1 obtained by adding 90 degrees to an angular position corresponding to the highest point P0 of the trajectory Lo of the pedal 2a, and an angular position P2 obtained by adding 135 degrees to an angular position corresponding to the highest point P0. The change end position Pe is a position obtained by adding at least 45 degrees to the change start position Ps. The assist ratio calculation unit 32 starts changing the assist ratio when the crank angle position reaches the change start position Ps. The assist ratio calculation unit 32 gradually changes the assist ratio so that the assist ratio reaches the second assist ratio when the crank angle position reaches the change end position Pe.

[0045] According to such processing by the assist ratio calculation unit 32, the influence on the riding comfort of the change in the assist ratio caused by the change in the control mode can be reduced. In general, when the pedal 2a is at a position rotated 90 degrees from the highest point P0 (angle position P1 in FIG. 4), the pedal force is maximum. After passing this angle position P1, the pedal force gradually weakens. Therefore, a relatively weak pedal force is input to the pedal 2a between the above-mentioned change start position Ps and change end position Pe. In other words, the assist ratio changes in accordance with the period during which the pedal force weakens. Therefore, the change in the assist ratio becomes difficult for the rider to sense, and the riding comfort can be further improved.

[0046] This is particularly effective when changing the control mode to the up side. Between the change start position Ps and the change end position Pe described above, the pedal force acting on the pedal 2a gradually weakens, while the assist ratio gradually increases when changing the control mode to the up side. Therefore, the increase in the assist ratio can compensate for the decrease in assist torque or the decrease in acceleration of the bicycle 100 caused by the decrease in pedal force. As a result, the riding comfort can be further improved.

[0047] The angle difference Δθ (see FIG. 4) between the change start position Ps and the change end position Pe is preferably 60 degrees or more, which makes it possible to more effectively suppress abrupt changes in the assist torque caused by a change in the control mode.

[0048] The angle difference Δθ (see FIG. 4) between the change start position Ps and the change end position Pe may be 135 degrees or less. This can prevent the change of the assist ratio from the first assist ratio to the second assist ratio from taking an excessively long time. The angle difference Δθ may more preferably be 90 degrees or less. This can optimize the change speed of the assist ratio. The angle difference between the change start position Ps and the change end position Pe may be substantially 70 degrees.

[0049] The change end position Pe may be a position obtained by adding an angle of 360 degrees or less to the angle position corresponding to the highest point P0. This ensures that the change in the assist ratio ends before the pedal 2a reaches the highest point P0 again, thereby preventing a delay in starting to ride at the second assist ratio.

[0050] The change end position Pe may be an angle position obtained by adding an angle of 270 degrees or less to the highest point P0. This makes it possible to effectively prevent an excessive delay in starting running at the assist ratio in the changed control mode.

[0051] The change end position may be a position obtained by adding an angle of 225 degrees or less to the angle position corresponding to the highest point P0. This makes it possible to more effectively prevent a delay in starting to run at the second assist ratio.

[0052] The change end position Pe may be between an angular position P2 obtained by adding 135 degrees to the angular position corresponding to the highest point P0 and an angular position P4 obtained by adding 225 degrees to the angular position corresponding to the highest point P0. In other words, the change end position Pe may be close to an angular position P3 corresponding to the lowest point of the pedal 2a. When the pedal 2a is in such an angular position, the pedaling force becomes weak. In other words, the change in the assist ratio is completed at the timing when the pedaling force becomes weak. Therefore, the change in the assist ratio becomes difficult for the rider to sense, and the riding comfort can be further improved.

[0053] The gradual change of the assist ratio by the assist ratio calculation unit 32 may be executed only when the control mode is changed to the up side. When the control mode is changed to the down side, the above-mentioned process of the assist ratio calculation unit 32 does not need to be executed.

[0054] When the control mode is changed to the down side, the assist ratio may be changed immediately when the crank angle position reaches a predetermined position, which may be, for example, near the angular position P3 corresponding to the lowest point of the pedal 2a.

[0055] [Assist ratio calculation] The assist ratio calculation unit 32 calculates the assist ratio so that the assist ratio gradually approaches the second assist ratio from the first assist ratio when the crank angle position is between the change start position Ps and the change end position Pe. The assist ratio calculation unit 32 calculates the assist ratio based on, for example, the crank angle position. More specifically, the assist ratio calculation unit 32 calculates the assist ratio based on the crank angle position, the difference between the first assist ratio and the second assist ratio, and the angle difference Δθ between the change start position Ps and the change end position Pe.

[0056] The assist ratio calculation unit 32 calculates, for example, a change rate of the assist ratio based on the difference between the first assist ratio R1 and the second assist ratio R2 and the angle difference Δθ between the change start position Ps and the change end position Pe. The change rate is the amount of change in the assist ratio corresponding to a unit change (for example, 1 degree) in the angular position of the crankshaft 2. The change rate can be calculated, for example, by the following formula 1-1. r=(R2-R1) / Δθ (Formula 1-1) r: Rate of change in assist ratio R1: 1st assist ratio R2: 2nd assist ratio Δθ: angle difference between the change start position Ps and the change end position Pe

[0057] The assist ratio calculation unit 32 calculates the assist ratio based on the amount of change in the angular position of the crankshaft 2 from the change start position Ps (i.e., the difference between the change start position Ps and the current crank angle position) and the rate of change. The assist ratio calculation unit 32 calculates the assist ratio using, for example, the following formula 1-2. Rx=r×θ+R1 (Formula 1-2) Rx: Assist ratio at a position between the change start position Ps and the change end position Pe r: Rate of change in assist ratio θ: current angle position of the crankshaft 2 when the change start position Ps is 0 degrees (hereinafter, change progress angle)

[0058] The assist ratio calculation unit 32 calculates the crank angle position at a predetermined period based on the output of the crank rotation sensor 45. The assist ratio calculation unit 32 counts the "change elapsed angle θ" used in the equation 1-2 from the time when the crank angle position reaches the change start position Ps.

[0059] According to Equation 1-1 and Equation 1-2, as the changed elapsed angle θ approaches the angle difference Δθ, the assist ratio Rx gradually approaches the second assist ratio R2. Then, when the changed elapsed angle θ reaches the angle difference Δθ, that is, when the current crank angle position reaches a preset change end position Pe, the assist ratio Rx reaches the second assist ratio R2. In other words, the angle position at which the assist ratio Rx reaches the second assist ratio R2 can be fixed regardless of the assist ratios R1·R2.

[0060] The assist ratios R1·R2 may be assist ratios corresponding to the vehicle speed calculated immediately before the assist ratio change starts. That is, the assist ratio calculation unit 32 uses an assist ratio map or an arithmetic expression corresponding to the first control mode to calculate an assist ratio corresponding to the vehicle speed calculated immediately before the assist ratio change starts as a first assist ratio R1. Also, the assist ratio calculation unit 32 uses an assist ratio map or an arithmetic expression corresponding to the second control mode to calculate an assist ratio corresponding to the vehicle speed calculated immediately before the assist ratio change starts as a second assist ratio R2.

[0061] The processing of the assist ratio calculation unit 32 is not limited to the example using the formulas 1-1 and 1-2.

[0062] For example, the assist ratio calculation unit 32 may calculate the assist ratio based on the change elapsed angle θ of the crankshaft 2 and a preset change rate of the assist ratio (amount of change per unit change (e.g., 1 degree) of the crank angle position).

[0063] In this case, the rate of change of the assist ratio may be predefined so that the assist ratio reaches the second assist ratio before the crank angle position reaches the above-mentioned angular position P5 (the position obtained by adding 270 degrees to the highest point P0). Alternatively, the rate of change of the assist ratio may be predefined so that the change end position Pe ends up falling between the angular position P2 (see FIG. 4) and the angular position P4 (see FIG. 4).

[0064] As yet another example, the assist ratio calculation unit 32 may calculate the assist ratio based on the elapsed time since the start of changing the assist ratio (hereinafter, the changed elapsed time). For example, the assist ratio calculation unit 32 may calculate the assist ratio based on the changed elapsed time and the change speed of the assist ratio (the amount of change in the assist ratio per unit time).

[0065] In this case, the rate of change of the assist ratio may be preset so that the assist ratio reaches the second assist ratio before the crank angle position reaches the above-mentioned angular position P5 (the position obtained by adding 270 degrees to the highest point P0). Alternatively, the rate of change of the assist ratio may be preset so that the change end position Pe ends up falling between the angular position P2 (see FIG. 4) and the angular position P4 (see FIG. 4).

[0066] As yet another example, the assist ratio calculation unit 32 may calculate the change speed of the assist ratio based on the difference between the first assist ratio R1 and the second assist ratio R2 and the time required for the crank angle position to change from the change start position Ps to the change end position Pe. Then, the assist ratio calculation unit 32 may calculate the assist ratio based on the change elapsed time and the change speed.

[0067] [Start position determination section and peak pedal force detection section] The assist ratio calculation unit 32 includes a start position detection unit 32a. The start position detection unit 32a detects that the crank angle position has reached the change start position Ps. The start position detection unit 32a detects that the crank angle position has reached the change start position Ps based on, for example, the output of the pedal force sensor 41 and the output of the crank rotation sensor 45.

[0068] FIG. 5 is a time chart for explaining an example of processing performed by the start position detection unit 32a and the peak pedal force detection unit 34. The vertical axis in the figure is the pedal force detected based on the output of the pedal force sensor 41. As shown in the figure, the pedal force varies periodically. For example, at t1 when the peak pedal force Pk1 is obtained, one pedal 2a (for example, the right pedal 2a) is estimated to be in a horizontal position (angular position P1, see FIG. 4). At t2 when the pedal force becomes minimum, this one pedal 2a is estimated to be at the lowest point (angular position P3, see FIG. 4). At t3 when the next peak pedal force Pk2 is obtained, the other pedal 2a (for example, the left pedal 2a) is estimated to be in a horizontal position (angular position P1, see FIG. 4), and at t4 when the pedal force becomes minimum, this other pedal 2a is estimated to be at the lowest point (angular position P3, see FIG. 4).

[0069] The peak pedal force detection unit 34 searches for the maximum pedal force in "one stroke" (i.e., the peak pedal force). "One stroke" corresponds, for example, to the movement of each pedal 2a from its highest point P0 to its lowest point. In the above example, "one stroke" for the right pedal 2a corresponds to the period from t0 when the pedal force is minimal to t2 when the pedal force is the next minimal. Also, "one stroke" for the left pedal 2a corresponds to the period from t2 when the pedal force is minimal to t4 when the pedal force is the next minimal.

[0070] The peak pedaling force detection unit 34 detects the pedaling force at a sampling period that is sufficiently shorter than the time required for one pedal stroke, for example, based on the output of the pedaling force sensor 41. Candidates for peak pedaling forces are recorded in the memory. The peak pedaling force detection unit 34 compares the newly detected pedaling force with the candidates for peak pedaling forces recorded in the memory. If the newly detected pedaling force is larger than the candidates for peak pedaling forces recorded in the memory, the peak pedaling force detection unit 34 rewrites the candidates for peak pedaling forces recorded in the memory with the newly detected pedaling force. Conversely, if the newly detected pedaling force is smaller than the candidates for peak pedaling forces recorded in the memory, the peak pedaling force detection unit 34 maintains the candidates for peak pedaling forces recorded in the memory.

[0071] Then, if the pedaling force recorded in the memory is not changed while the crankshaft 2 rotates by a predetermined angle (periods t1 to t11 and t3 to t31 in FIG. 5), the peak pedaling force detection unit 34 determines the candidate recorded in the memory as the peak pedaling force. Hereinafter, this predetermined angle is referred to as the "peak determination angle" (see FIG. 5). The peak determination angle is, for example, 20 degrees, but may be an angle smaller than 20 degrees (for example, 10 degrees) or larger than 20 degrees (for example, 30 degrees).

[0072] The start position detection unit 32a determines the angle position at which the crankshaft 2 rotates a predetermined angle from the timing (time t1 in FIG. 5) when the peak pedal force is input to the pedal 2a as the change start position Ps. Hereinafter, this predetermined angle is referred to as the "start delay angle." This start delay angle may be the same as the peak determination angle (e.g., 20 degrees). In this case, it is determined that the change start position Ps has been reached at the same timing when the crank angle position reaches the peak determination angle and the peak pedal force is determined. In contrast, the start delay angle may be greater than the peak determination angle. For example, the change start detection unit 32a may determine the angle position at which the crankshaft 2 rotates a start delay angle (e.g., 30 degrees) greater than the peak determination angle from the timing (t1 in FIG. 5) when the peak pedal force is input to the pedal 2a as the change start position Ps.

[0073] The crank rotation sensor 45 may be a sensor that outputs a signal according to an absolute angle, rather than a sensor that generates a pulse signal for each unit angle change (for example, each change of 1 degree) of the crankshaft 2. In this case, the change start position Ps may be detected based on the output of the sensor. In this case, the peak pedal force does not need to be used in detecting the change start position Ps.

[0074] [Assist torque calculation section] The assist torque calculation unit 33 calculates the assist torque based on the assist ratio calculated by the assist ratio calculation unit 32 and the pedaling force detected by the pedaling force sensor 41. Specifically, the assist torque calculation unit 33 calculates the assist torque by multiplying the assist ratio by the pedaling force. The assist torque calculation unit 33 may calculate the assist torque by multiplying the average of the pedaling force in a predetermined number of times by the assist ratio. Here, the number of times of pedaling may be counted as one rowing from the uppermost point P0 to the lowermost point of each pedal 2a. In contrast to this, the assist torque calculation unit 33 may calculate the assist torque by multiplying the average of the pedaling force in a predetermined time by the assist ratio. As another example, the assist torque calculation unit 33 may multiply the current pedaling force by the assist ratio calculated by the assist ratio calculation unit 32 without using such an average, and calculate the result as the assist torque. The control device 30 outputs a command value corresponding to the assist torque to the motor drive device 39.

[0075] [Processing flow] An example of the processing executed by the control device 30 will now be described. Fig. 6 is a flow diagram showing the flow of processing related to changing the control mode, executed by the control device 30. The processing shown in Fig. 6 is repeatedly executed while the bicycle 100 is traveling.

[0076] First, the peak pedaling force detection unit 34 detects a peak pedaling force based on the output of the pedaling force sensor 41 (S101). As described with reference to FIG. 5, the peak pedaling force is the maximum pedaling force in one stroke. The control mode management unit 31 determines whether or not a control mode change condition is met (S102). For example, the control mode management unit 31 determines whether or not the peak pedaling force detected in S101 exceeds a threshold value.

[0077] If the control mode change condition is not satisfied ("No" in S102), the control device 30 ends this processing. If the control mode change condition is not satisfied in the determination of S102, the assist ratio calculation unit 32 and the assist torque calculation unit 33 execute a calculation process of the assist ratio and the assist torque in the current control mode. For example, the assist ratio calculation unit 32 calculates the assist ratio by using an assist ratio map or an arithmetic expression defined for the current control mode. The assist torque calculation unit 33 calculates the assist torque based on the calculated assist ratio and the pedaling force detected by the pedaling force sensor 41. The execution cycle of the calculation process of the assist ratio, etc. may be the same as or different from the execution cycle of the process shown in FIG. 6.

[0078] When the control mode change condition is met ("Yes" in S102), the control mode management unit 31 changes the control mode (S103). The control mode management unit 31 may record the changed control mode in the memory of the control device 30 as a newly selected control mode.

[0079] Next, the start position detection unit 32a judges whether or not the crank angle position has reached the change start position Ps (S104). For example, the start position detection unit 32a judges whether or not the crankshaft 2 has rotated by the start delay angle from the angular position at which the peak pedal force was input to the pedal 2a (the angular position at time t1 in FIG. 6). The start position detection unit 32a repeatedly executes the judgment process of S104 at a predetermined cycle until the crank angle position reaches the change start position Ps.

[0080] When the crank angle position reaches the change start position Ps ("Yes" in S104), the assist ratio calculation unit 32 calculates the rate of change of the assist ratio (S105). The rate of change can be calculated, for example, using the above-mentioned (Equation 1-1).

[0081] The assist ratio calculation unit 32 calculates the amount of change in the crank angle position from the change start position Ps, i.e., the difference between the change start position Ps and the current crank angle position (S106).Then, the assist ratio calculation unit 32 calculates an assist ratio according to the amount of change in the crank angle position calculated in S106 and the rate of change in the assist ratio calculated in S105 (S107).This calculation may use, for example, the above-mentioned (Equation 1-2).

[0082] The assist torque calculation unit 33 calculates the assist torque based on the calculated assist ratio and the pedaling force detected by the pedaling force sensor 41 (S108). As described above, in S108, the assist torque calculation unit 33 may use the average pedaling force for a predetermined number of strokes, the average pedaling force for a predetermined time, or a current pedaling force that is not an average. The control device 30 outputs a command value corresponding to the calculated assist torque to the motor drive device 39.

[0083] The assist ratio calculation unit 32 determines whether the crank angle position has reached the change end position Pe (S109). If the crank angle position has not yet reached the change end position Pe ("No" in S109), the control device 30 returns to S106 and executes the subsequent processes again. On the other hand, if the crank angle position has reached the change end position Pe ("Yes" in S109), the control device 30 ends this process.

[0084] The start position detection unit 32a determines the angular position at which the crankshaft 2 has rotated the start delay angle from the timing (t1 in FIG. 5) at which the peak pedaling force is input to the pedal 2a as the change start position Ps. As described above, this start delay angle may be the same as the peak determination angle. When such processing is performed, the crankshaft 2 has already reached the change start position Ps at the time the peak pedaling force is detected in S101, so the processing of S104 does not need to be performed. FIG. 7 is a flow diagram showing an example of the flow of processing executed by the control device 30 in such a case. The processing shown in FIG. 7 is repeatedly executed while the bicycle 100 is traveling.

[0085] The control device 30 (peak pedal force detection unit 34) detects the pedal force at a predetermined sampling period based on the output of the pedal force sensor 41, for example, and updates the peak pedal force candidate recorded in memory (S201). Specifically, the control device 30 compares the peak pedal force candidate recorded in memory with the newly detected pedal force. If the newly detected pedal force is larger than the candidate recorded in memory, the control device 30 rewrites the peak pedal force candidate recorded in memory to the newly detected pedal force. Conversely, if the newly detected pedal force is smaller than the peak pedal force candidate recorded in memory, the control device 30 maintains the peak pedal force candidate recorded in memory.

[0086] The control device 30 determines whether or not the crankshaft 2 has rotated a peak determination angle from the angle position at which the latest peak pedal force candidate recorded in the memory was detected (S202). As described above, the peak determination angle and the start delay angle are the same in the process described in Fig. 7. Therefore, the determination in S202 is, in other words, a determination of whether or not the crank angle position has reached the change start position Ps.

[0087] If the rotation of the crankshaft 2 has not yet reached the peak judgment angle ("No" in S202), the control device 30 returns to the process of S201. On the other hand, if the rotation of the crankshaft 2 has reached the peak judgment angle ("Yes" in S202), the control device 30 (peak pedal force detection unit 34) determines the latest candidate recorded in memory as the peak pedal force (S203). In this case, since the start delay angle and the peak judgment angle are the same, the crank angle position has reached the change start position Ps at the time the peak pedal force is determined.

[0088] The subsequent processing may be executed in the same manner as in the example of Fig. 6. That is, the control mode management unit 31 judges whether or not the control mode change condition is satisfied (S204). If the control mode change condition is not satisfied ("No" in S204), the control device 30 ends the current processing. Note that if the control mode change condition is not satisfied, the assist ratio calculation unit 32 and the assist torque calculation unit 33 execute the calculation processing of the assist ratio and the assist torque in the current control mode.

[0089] When the condition for changing the control mode is met ("Yes" in S204), the control mode management unit 31 changes the control mode (S205). The assist ratio calculation unit 32 calculates the rate of change of the assist ratio (S206). The rate of change can be calculated, for example, using the above-mentioned (Equation 1-1). The assist ratio calculation unit 32 then calculates the amount of change in the crank angle position from the change start position Ps, that is, the difference between the change start position Ps and the current crank angle position (S207). The assist ratio calculation unit 32 calculates an assist ratio according to the amount of change in the crank angle position calculated in S207 and the rate of change in the assist ratio calculated in S206 (S208). For example, the above-mentioned (Equation 1-2) can be used for this calculation.

[0090] The assist torque calculation unit 33 calculates the assist torque based on the calculated assist ratio and the pedaling force detected by the pedaling force sensor 41 (S209). The assist ratio calculation unit 32 determines whether the crank angle position has reached the change end position Pe (S210). If the crank angle position has not yet reached the change end position Pe ("No" in S210), the control device 30 returns to S207 and executes the subsequent processes again. On the other hand, if the crank angle position has reached the change end position Pe ("Yes" in S210), the control device 30 ends this process.

[0091] [Time chart] FIG. 8 is a time chart showing an example of the results of processing by the control device 30. FIG. 8(a) shows the change in pedal force. FIG. 8(b) shows the change in assist ratio. FIG. 8(c) shows the change in crank angle position. As shown in FIG. 8(a) and FIG. 8(c), the crank angle position where the pedal force is minimal is set to 0 degrees. FIG. 8(d) shows the change in assist torque. In FIG. 8, a case will be described where the control mode is changed to the up side.

[0092] At time t1, a peak pedal force exceeding a threshold value Th1 that defines the control mode change condition is input to the pedal 2a. As described above, the peak pedal force detection unit 34 compares the candidate peak pedal force detected in the past with the newly detected peak pedal force. If the newly detected peak pedal force is higher than the candidate peak pedal force, the candidate peak pedal force is rewritten to the newly detected peak pedal force. If the candidate peak pedal force does not change while the crankshaft 2 rotates a predetermined angle (peak determination angle, for example, 20 degrees), the candidate is determined as the peak pedal force. In the example shown in FIG. 8(a), the peak pedal force Pk1 is determined at time t2.

[0093] Furthermore, the control mode management unit 31 determines whether or not the peak pedal force Pk1 exceeds the threshold value Th1 at time t2. Since the peak pedal force Pk1 shown in FIG. 8(a) is higher than the threshold value Th1, the control mode management unit 31 changes the control mode to the up side (for example, from eco mode to standard mode). In the example shown in FIG. 8, the start delay angle is the same as the peak determination angle. Therefore, the crank angle position at time t2 is the change start position Ps. Therefore, from time t2, the assist ratio calculation unit 32 gradually increases the assist ratio from the first assist ratio (assist ratio in the control mode before the change) to the second assist ratio (assist ratio in the control mode after the change).

[0094] The start delay angle may be greater than the peak determination angle. In this case, the assist ratio calculation unit 32 increases the assist ratio from the first assist ratio to the second assist ratio with a delay from time t2.

[0095] At time t3, the crank angle position reaches the change end position Pe (FIG. 8(c)), and the assist ratio reaches the second assist ratio (FIG. 8(b)). In the period from the change start position Ps to the change end position Pe, the pedal force decreases as shown in FIG. 8(a), while the assist ratio increases as shown in FIG. 8(b). In FIG. 8(d), the assist torque is calculated by multiplying the current pedal force (not the average) by the assist ratio. Therefore, in the period up to time t2, the assist torque fluctuates according to the pedal force. However, in the period from time t2 to t3, the assist ratio gradually increases, so that the change in the assist torque can be reduced as shown in FIG. 8(d).

[0096] The dashed line L3 in Fig. 8(b) shows an example in which the assist ratio is fixed at the first assist ratio until time t3, and is then instantly increased to the second assist ratio at time t3 (for example, when the crank angle position is 180 degrees). In this case, as shown by the dashed line L4 in Fig. 8(d), the assist torque also decreases in accordance with the decrease in pedal force until time t3, and then increases suddenly in accordance with the instantaneous increase in the assist ratio at time t3. As shown by a comparison between the dashed lines L3 and L4, the processing by the control device 30 makes it possible to suppress a sudden change in the assist torque when the control mode change condition is satisfied.

[0097] Fig. 9 is a time chart showing another example of the results of processing by the control device 30. Fig. 9(a), (b), (c), and (d) show, like Fig. 8, changes in pedaling force, changes in assist ratio, changes in crank angle position, and changes in assist torque, respectively. Fig. 9(e) shows changes in acceleration in the front-rear direction of the bicycle 100. The acceleration of the bicycle 100 corresponds to the sum of the pedaling force shown in Fig. 9(a) and the assist torque shown in Fig. 9(d). In Fig. 9, like Fig. 8, a case will be described where the control mode is changed to the up side.

[0098] Unlike Fig. 8, Fig. 9 illustrates an example in which the assist torque is calculated based on the average pedaling force for a predetermined number of strokes (or the average pedaling force for a predetermined time) and the assist ratio. The changes in pedaling force and other parameters shown in Figs. 9(a), (b), and (c) are the same as those in Fig. 8, and therefore will not be described here.

[0099] In Fig. 9, the assist torque is calculated based on the average pedaling force and the assist ratio. Therefore, as shown in Fig. 9(d), in the period up to time t2, the assist torque does not change as much as the pedaling force shown in Fig. 9(a). Since the acceleration of the bicycle 100 corresponds to the sum of the pedaling force and the assist torque, as shown in Fig. 9(e), in the period up to time t2, the acceleration of the bicycle 100 changes according to the pedaling force.

[0100] As shown in FIG. 9(b), the assist ratio gradually increases from time t2. Because the average pedaling force does not change significantly, the assist torque also gradually increases along with the assist ratio during the period from time t2 to t3. Meanwhile, during this period (the angular range from change start position Ps to change end position Pe), as shown in FIG. 9(a), the pedaling force gradually decreases. Therefore, the decrease in pedaling force is compensated for by the increase in assist torque, and changes in the acceleration of bicycle 100 are suppressed. This can improve the riding comfort of bicycle 100 when changing control modes.

[0101] Note that dashed line L5 in Fig. 9(d) and dashed line L6 in Fig. 9(e) respectively show the assist torque and the acceleration of bicycle 100 when the assist ratio is constant up to time t3 and then changes from the first assist ratio to the second assist ratio at time t3, as shown by dashed line L3 in Fig. 9(b). In this case, there is no significant change in the average pedaling force during the period from time t2 to t3, and the assist ratio is constant, so there is no significant change in the assist torque, as shown by dashed line L5 in Fig. 9(d). Meanwhile, during this period, the pedaling force decreases (Fig. 9(a)), and the acceleration of bicycle 100 also decreases accordingly (dashed line L6 in Fig. 9(e)). As shown by dashed line L3 in FIG. 9(b), when the assist ratio changes from the first assist ratio to the second assist ratio at time t3, the assist torque rises sharply (dashed line L5 in FIG. 9(d)), and as a result, the acceleration of the bicycle 100 also rises sharply accordingly (dashed line L6 in FIG. 9(e)). This affects the ride comfort when the control mode is changed. According to the processing of the control device 30 proposed in this disclosure, such abrupt changes in acceleration are suppressed.

[0102] [summary] (1) The drive system 10 includes: A sensor that detects a pedaling force acting on a pedal 2a attached to the crankshaft 2; An electric motor 21 for assisting depression of the pedal 2a; The control device 30 controls the electric motor 21 based on the assist ratio according to the control mode and the pedaling force detected by the sensor. The control device 30 has, as control modes, a first control mode in which the electric motor 21 is controlled based on a first assist ratio, and a second control mode in which the electric motor 21 is controlled based on a second assist ratio. When a change condition from the first mode to the second mode is satisfied, the control device 30 starts changing the assist ratio from the first assist ratio to the second assist ratio at a change start position Ps between an angle position P1 obtained by adding 90 degrees to the crank angle position corresponding to the highest point P0 of the trajectory Lo of the pedal 2a, and an angle position P2 obtained by adding 135 degrees to the crank angle position corresponding to the highest point P0. The control device 30 changes the assist ratio so that the assist ratio reaches the second assist ratio at a change end position Pe obtained by adding at least 45 degrees to the change start position Ps.

[0103] According to this drive system 10, the assist ratio changes gradually, so that the effect on the ride comfort of the change in the assist ratio caused by the change in the control mode can be reduced. The pedaling force becomes weaker between the change start position Ps and the change end position Pe. In other words, the assist ratio changes according to the period in which the pedaling force becomes weaker. Therefore, the change in the assist ratio becomes less noticeable to the rider, and the ride comfort can be further improved.

[0104] (2) In the drive system 10 of (1), the angle difference Δθ between the change start position Ps and the change end position Pe may be 135 degrees or less. This makes it possible to prevent an excessively long time from being required to change the assist ratio.

[0105] (3) In the drive system 10 of (1) or (2), the angle difference Δθ between the change start position Ps and the change end position Pe may be 60 degrees or more. This makes it possible to more effectively suppress abrupt changes in the assist torque.

[0106] (4) In the drive system 10 of (1) to (3), the change end position Pe may be between an angular position P2 obtained by adding 135 degrees to the highest point P0 and an angular position P4 obtained by adding 225 degrees to the highest point P0. When the crankshaft 2 is in such an angular position, the pedaling force becomes weak. In other words, the change in the assist ratio is completed at the timing when the pedaling force becomes weak. Therefore, the change in the assist ratio becomes difficult for the rider to sense, and the riding comfort can be further improved.

[0107] (5) In the drive system 10 of (1) to (4), the change end position Pe may be an angle position obtained by adding an angle of 270 degrees or less to the highest point P0. This makes it possible to prevent an excessive delay in starting running at the assist ratio in the changed control mode.

[0108] (6) In the drive system 10 of (1) to (5), the change end position Pe may be an angle position obtained by adding an angle of 225 degrees or less to the highest point P0. This makes it possible to effectively prevent an excessive delay in starting running at the assist ratio (second assist ratio) in the changed control mode.

[0109] (7) In the drive system 10 of (1) to (6), the control device 30 may calculate the assist ratio so that when the crank angle position is between the change start position Ps and the change end position Pe, the assist ratio gradually approaches the second assist ratio from the first assist ratio.

[0110] (8) The drive system 10 of (1) to (6) may have a sensor 45 for detecting the amount of change in the crank angle position. The control device 30 may calculate the assist ratio based on the amount of change in the crank angle position when the pedal 2a is between the change start position Ps and the change end position Pe. This makes it easy to change the assist ratio between the change start position Ps and the change end position Pe.

[0111] (9) In the drive system 10 of (1) to (8), the control device 30 may calculate the rate of change of the assist ratio based on the difference between the first assist ratio and the second assist ratio and the angle difference Δθ between the change start position Ps and the change end position Pe. This makes it easy to complete the change of the assist ratio when the crank angle position reaches the predetermined change end position Pe.

[0112] (10) The power-assisted bicycle 100 proposed in this disclosure includes the drive system 10 described in (1) to (9) and wheels to which the assist torque output by the electric motor 21 is transmitted.

[0113] The drive system proposed in this disclosure is not limited to the above-mentioned example.

[0114] For example, the control device 30 calculates the rate of change of the assist ratio based on the difference between the first assist ratio and the second assist ratio and the angle difference Δθ between the change start position Ps and the change end position Pe. When the control mode change condition is satisfied, the assist ratio may be calculated based on this rate of change and the amount of change in the crank angle position from the position where the change of the assist ratio starts. This process may be applied to a drive system in which the assist ratio is changed within a range different from the range defined by the above-mentioned change start position Ps (between angular positions P1 and P2) and the change end position Pe. [Explanation of symbols]

[0115] 2: crankshaft, 2a: pedal, 5: chain, 6: rear wheel, 7: handle, 8: handle stem, 9: front wheel, 10: drive system, 11: seat tube, 17: frame, 17a: head pipe, 18: saddle, 19: front fork, 20: drive unit, 21: electric motor, 22: battery, 23: one-way clutch, 24: resultant force transmission mechanism, 25: reducer, 26: one-way clutch, 27: transmission mechanism, 28: one-way clutch, 30: control device, 31: control mode management unit, 32: assist ratio calculation unit, 32a: start position detection unit, 33: assist torque calculation unit, 34: peak pedal force detection unit, 39: motor drive device, 41: pedal force sensor, 42: motor rotation sensor, 43: wheel rotation sensor, 45: crank rotation sensor, 58: operation input device, 100: electrically assisted bicycle, P1, P2, P3, P4, P5: angular position, Ps: change start position, Pe: change end position, R1: first assist ratio, R2: second assist ratio.

Claims

1. A sensor that detects a pedal force acting on a pedal attached to a crankshaft; an electric motor for assisting depression of the pedal; a control device that controls the electric motor based on an assist ratio according to a control mode and the pedaling force detected by the sensor; having the control device has, as the control modes, a first control mode in which the electric motor is controlled based on a first assist ratio and a second control mode in which the electric motor is controlled based on a second assist ratio; The control device includes: when a change condition from the first control mode to the second control mode is satisfied, a change in the assist ratio from the first assist ratio to the second assist ratio is started at a change start position between an angular position of the crankshaft corresponding to a top point of the pedal trajectory plus 90 degrees and an angular position of the crankshaft corresponding to the top point plus 135 degrees; The assist ratio is changed so that the assist ratio reaches the second assist ratio at a change end position that is at least 45 degrees added to the change start position. Electrically assisted bicycle drive system.

2. The angle difference between the change start position and the change end position is 135 degrees or less.

2. A drive system for an electrically assisted bicycle according to claim 1.

3. The angle difference between the change start position and the change end position is 60 degrees or more.

2. A drive system for an electrically assisted bicycle according to claim 1.

4. The change end position is between an angle position obtained by adding 135 degrees to the uppermost point and an angle position obtained by adding 225 degrees to the uppermost point.

2. A drive system for an electrically assisted bicycle according to claim 1.

5. The change end position is an angle position obtained by adding an angle of 270 degrees or less to the uppermost point.

2. A drive system for an electrically assisted bicycle according to claim 1.

6. The change end position is an angle position obtained by adding an angle of 225 degrees or less to the uppermost point.

6. A drive system for an electrically assisted bicycle according to claim 5.

7. The control device calculates the assist ratio such that the assist ratio gradually approaches the second assist ratio from the first assist ratio when the angular position of the crankshaft is between the change start position and the change end position.

2. A drive system for an electrically assisted bicycle according to claim 1.

8. a sensor for detecting an amount of change in the angular position of the crankshaft; The control device calculates the assist ratio based on an amount of change in an angular position of the crankshaft when the pedal is between the change start position and the change end position.

2. A drive system for an electrically assisted bicycle according to claim 1.

9. The control device calculates a change rate of the assist ratio based on a difference between the first assist ratio and the second assist ratio and an angle difference between the change start position and the change end position.

9. A drive system for an electrically assisted bicycle according to claim 8.

10. A drive system as claimed in claim 1; a wheel to which the assist torque output by the electric motor is transmitted; An electrically assisted bicycle having the following features:

11. A control method for an electrically assisted bicycle, comprising: controlling an electric motor based on an assist ratio corresponding to a control mode and a pedaling force detected by a sensor; and having, as the control modes, a first control mode in which the electric motor is controlled based on a first assist ratio, and a second control mode in which the electric motor is controlled based on a second assist ratio, when a change condition from the first control mode to the second control mode is satisfied, a change in the assist ratio from the first assist ratio to the second assist ratio is started at a change start position between an angular position of the crankshaft corresponding to a top point of a pedal trajectory plus 90 degrees and an angular position of the crankshaft corresponding to the top point plus 135 degrees; The assist ratio is changed so that the assist ratio reaches the second assist ratio at a change end position that is at least 45 degrees added to the change start position. How to control an electric assist bicycle.

12. A program that causes a computer to function as a control device that controls an electric motor based on an assist ratio corresponding to a control mode and a pedaling force detected by a sensor, and has, as the control modes, a first control mode in which the electric motor is controlled based on a first assist ratio and a second control mode in which the electric motor is controlled based on a second assist ratio, a means for starting a change in the assist ratio from the first assist ratio to the second assist ratio at a change start position between an angular position of the crankshaft corresponding to the highest point of a pedal trajectory plus 90 degrees and an angular position of the crankshaft corresponding to the highest point plus 135 degrees when a change condition from the first control mode to the second control mode is satisfied; and a means for changing the assist ratio so that the assist ratio reaches the second assist ratio at a change end position which is at least 45 degrees added to the change start position; A program that makes a computer function as a

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