Method for triggering and controlling regenerative braking on an electric-assisted bicycle with a target speed

Abstract

The invention relates to a method for controlling the regenerative braking of an electrically assisted bicycle, comprising the following steps: detecting the end of mechanical braking; defining a target speed as a function of the bicycle's speed at the time the end of mechanical braking is detected; regulating the bicycle's regenerative braking according to this target speed. Figure for the abstract: 1

Description

Title of the invention: Method for triggering and controlling regenerative braking of an electrically assisted bicycle with a target speed. Technical field

[0001] The invention relates to electrically assisted bicycles and, more specifically, the process of triggering and controlling regenerative braking following the release of the mechanical brake. Background

[0002] Some electric bicycles offer regenerative braking systems to improve safety and energy efficiency. Several alternatives exist for engaging regenerative braking:

[0003] a. Regenerative braking with target torque by backpedaling. When a cyclist pedals backward, a constant target regenerative torque is applied. A time ramp can be applied to gradually reach this target torque from the initial torque at the beginning of backpedaling.

[0004] b. Regenerative braking with a target torque based on the pedal angle, after initiating backpedaling. The device may include a dead zone before a certain pedal angle, during which backpedaling braking is not activated. This dead zone allows the cyclist to adjust the pedal position without triggering the brake. Once the pedals reach the predefined angle, the method applies the target torque proportionally to the angle reached.

[0005] c. Brake with fixed regenerative power (P) activated via an interface such as a console. The target torque (C) varies according to the speed of the bicycle wheel (Q) according to the relationship C = P / Q.

[0006] None of these solutions existing to date is entirely satisfactory. Either they do not allow modulation, or they require complicated interaction, or they do not provide speed control, whereas this is desirable on descents for good user comfort. Summary of the invention

[0007] Method for controlling the regenerative braking of an electrically assisted bicycle, comprising the following steps: detecting the end of mechanical braking; defining a target speed as a function of the speed of the bicycle at the time of detection of the end of mechanical braking; regulating the regenerative braking of the bicycle as a function of this target speed.

[0008] The method can define the target speed as being equal to the measured speed or adjusted according to predefined criteria such as road conditions, battery charge level, and / or user preferences.

[0009] The method may include a step of using a proportional-integral-derivative (PID) controller to control the target speed of regenerative braking.

[0010] The method may include adding an additional term that is a function of at least one of the following: estimated friction forces, slope, wind speed, and road surface conditions, in order to improve the stability of the PID for regenerative braking.

[0011] The method may further include the following steps: recording the position of the pedals at the time of the end of mechanical braking for a later reference; modulating the target speed of regenerative braking in response to forward or backward pedaling, by monitoring the variation in angle of the pedals relative to the initial reference.

[0012] The method may further include a calculation of the target speed of the regenerative braking such that it varies linearly as a function of the angle of the pedals, and is bounded both by minimum and maximum target speeds, and by minimum and maximum total rotation angles relative to the initial reference.

[0013] The method may include an additional mechanism consisting of exiting regenerative braking mode as soon as the system detects human torque greater than a minimum threshold beyond which pedaling is considered active.

[0014] The method may further include an exit condition from the regenerative braking mode when the regenerative braking torque required to control the motor to reach the target speed is zero or transforms into a positive torque providing assistance.

[0015] The method may include an additional condition for exiting the regenerative braking mode when the target speed determined via the modulation of the target speed as a function of the pedal angle becomes zero.

[0016] The method can further allow a transition from a target speed control to a target torque control after the cyclist has initiated a backpedaling at a certain pedaling angle. Brief description of the figures

[0017] Embodiments will be described below, by way of non-limiting example, in relation to the accompanying figures, among which:

[0018] Fig. 1 represents a block diagram illustrating the interaction between the different physical components involved in an example of target speed regenerative braking implementation.

[0019] Fig. 2 represents an indicator of the presence or absence of mechanical braking.

[0020] Fig. 3 represents an example of the evolution of the bicycle's speed as well as the evolution of the target speed.

[0021] Fig. 4 represents the evolution of the pedal revolution counter set up during regenerative braking with target speed.

[0022] Fig. 5 represents an example of the evolution of the motor torque as well as the evolution of the human torque. Detailed description

[0023] None of the existing regenerative braking alternatives are suitable for the case of descents where the objective is to brake over a potentially long period of time while maintaining a speed low enough to maintain a level of comfort and remain safe.

[0024] Regenerative braking with target torque via backpedaling does not allow for modulation of the braking level and can be uncomfortable, or even dangerous, for prolonged use, such as downhill riding. The cyclist must maintain a backpedaling position, which can cause muscle strain and loss of control.

[0025] Regenerative braking with a target torque based on pedal angle, after initiating a backpedal stroke, is not suitable for downhill riding, because the torque affects the bicycle's acceleration, whereas what one typically wants to control is the bicycle's speed. Therefore, it is not possible to define an appropriate torque for varying downhill conditions.

[0026] The brake with fixed regenerative power, triggered using a dedicated interface, requires a console, which is undesirable on some bicycle models. Furthermore, finding the appropriate regenerative power can be difficult, as it must be adjusted according to the environment. For example, when going downhill, if the gradient varies, the fixed regenerative power may not be suitable, making braking ineffective or too abrupt.

[0027] A simple and intuitive method for triggering and controlling regenerative braking with a target speed on descents is proposed here. The method allows a transition from mechanical braking, potentially accompanied by initial regenerative braking with a torque setting, to purely regenerative braking with a target speed, without the need for a specific device such as a console and without requiring any unintuitive actions from the cyclist. For a good user experience and intuitive behavior, it is preferable that this type of regenerative braking not be active on flat ground, where the bicycle naturally slows down in the absence of driving force. The method should also offer the possibility of modulating the target speed according to changing environmental conditions. Finally, it is desirable that braking stability be improved by taking into account estimates of external forces.

[0028] The methods and functions referred to are implemented by programming the microcontroller of the bicycle motor control system. The method comprises three phases: triggering, control, and exiting the regeneration mode.

[0029] (i) Activation of regenerative braking mode with target speed by detection of the end of mechanical braking:

[0030] - A brake sensor can be used to detect the end of mechanical braking. If the sensor is omitted, the end-of-braking detection can be based on a balance of known driving and resistive forces. By observing whether these forces are consistent with the bicycle's acceleration, one can estimate the presence or absence of an additional braking force due to mechanical braking.

[0031] - A target speed for regenerative braking is defined. This may correspond at the speed of the bicycle at the time the end of mechanical braking is detected.

[0032] - The position of the pedals at the end of mechanical braking can be recorded for future reference. This is relevant in a later described variant which modulates the target speed based on the pedal angle.

[0033] (ii) Control of regenerative braking at target speed:

[0034] - The motor control by regenerative braking aims to maintain this target speed. One solution to do this is to use a proportional-integral-derivative (PID) controller to minimize the deviation from the target speed.

[0035] - Depending on an option, an additional parameter can be taken into account in the The control parameter, a function of at least one of the following: estimated friction forces, slope, wind speed, and road surface conditions, is used to improve control stability for regenerative braking. This parameter enhances the stability of the PID controller because a control system compensating for resistive forces could maintain a constant speed in the absence of a PID. Indeed, at constant speed, the propulsive forces are equal to the resistive forces. Therefore, by integrating all known terms corresponding to resistive forces, the stability of the PID is increased, as it only needs to compensate for deviations due to model errors.

[0036] - According to one variant, the target speed is modulated when the cyclist changes the angle The pedals. The pedal position is recorded as a reference when entering this control mode. Then, any variation in the pedal angle relative to this reference is measured, and a function adjusts the target speed accordingly. A maximum target speed limit can be applied.

[0037] (iii). Exiting regeneration mode:

[0038] - The regeneration mode is deactivated as soon as the system detects that the cyclist begins to pedal actively. One solution for this is to use a minimum threshold of human torque beyond which pedaling is considered active.

[0039] - When the regenerative torque required to maintain speed becomes If the current is zero or transforms into a positive torque providing assistance, the regenerative braking mode is also deactivated. Since the bicycle tends to slow down naturally on flat ground when there is no driving force, this mechanism automatically deactivates the motor control via regenerative braking with a target speed on flat ground.

[0040] - Regeneration mode is deactivated when the target speed becomes zero, in particular via the optional modulation of the target speed according to the angle of the pedals.

[0041] - If target speed modulation via the pedals is not used, it is possible to allow A transition from target speed control to target torque control occurs after the rider initiates backpedaling at a specific angle. One example implementation is to perform this transition after the rider has completed a half-turn of the pedals backward from the start of the target speed control. In this case, the target regenerative torque can be defined as the torque applied to maintain speed during target speed regenerative braking. The target torque for regenerative braking can then be modified in this new mode, as is the case with some conventional coaster-brake variations.

[0042] Figure 1 shows various components involved in an example implementation. A microcontroller 1 is programmed to perform the different functions enabling regenerative braking at the target speed: 11 represents the activation test of this braking, 12 the initialization phase, and 13 the control phase of this braking. The figure also shows the various sensors at 2, 3, and 4, as well as the motor at 6.

[0043] Figure 1 shows how the data from the brake sensor 2 determines whether or not to activate regenerative braking at the target speed. If mechanical braking is no longer active at the present moment, whereas it was active at the previous moment, the regenerative braking mode is activated.

[0044] During initialization, PO is recorded as the current position of the pedals and V0 as the current speed of the bicycle.

[0045] During the control phase, Ap = Pp - PO is calculated, namely a counter of pedal revolutions (positive or negative) since the start of the regenerative brake with target speed.

[0046] From this counter and the initial target speed V0, a ​​new target speed Vc is calculated. For this scenario, the target speed varies according to the formula Vc=V0+KAp, where K is a constant coefficient, for example K = 8 km / h per lap.

[0047] From this target speed Vc, a control setpoint is constructed which includes a PID regulator term based on the difference between the target speed Vc and the actual speed Vb.

[0048] The final control Cm applied to the motor may involve an additional parameter which corresponds to the forces necessary to compensate for the slope. Thus for a slope Pe in percent, we have a resistive torque Cp which can be approximated by Cp = Rmgsin(arctan(Pe / 100)), with R the radius of the drive wheel (here R = 0.26 m), m the mass of the bicycle plus cyclist (here m = 118 kg) and g = 9.81 N / kg the acceleration due to gravity.

[0049] The control may also involve a Cf term compensating for the various friction forces. Here, we consider a torque Cf = R (K0 + KLVb + K2Vb2) where R is the radius of the drive wheel, and K0, K1, and K2 are constants representing the static friction, rolling friction, and aerodynamic friction terms, respectively. For example, K0 = 4 Newtons, K1 = 1.0 m / s², and K2 = 0.179 kg / m. The static friction term K0 can be adjusted according to the road surface conditions. The aerodynamic friction term K2 can be adjusted according to the wind speed.

[0050] To illustrate an example of implementing the method, consider the scenario of a cyclist on a downhill slope using a bicycle equipped with the proposed system. The example describes a scenario for activating, controlling, and finally exiting regenerative braking with a target speed. The scenario includes the following steps:

[0051] (i) Downhill speed gain: at the beginning of the scenario, the cyclist is not pedaling and the The bike picks up speed downhill.

[0052] (ii) Activation of the mechanical brake: when the cyclist reaches a certain speed, they decide to brake by activating the mechanical brake. For this scenario, the detection of the mechanical brake can be considered to also be accompanied by regenerative braking via a torque command, without a target speed.

[0053] (iii) Initialization of regenerative braking with target speed: once the mechanical brake is released, regenerative braking with target speed is initialized with a target speed V0. In this variant, the cyclist can then modulate the target speed by pedaling forwards or backwards. For example, the target speed varies according to the formula Vc = V0 + K Ap, where Ap represents a counter of pedal revolutions (positive or negative) since the start of regenerative braking with target speed, and K is a constant coefficient, here K = 8 km / h per revolution.

[0054] (iv) Control by PID regulator: the control is carried out using a proportional-integral-derivative (PID) regulator based on the difference between the actual speed and the target speed, to which is added a term function of the slope and the speed f(Pe, Vb), corresponding to the motor force that would be necessary to add to compensate for the forces due to the slope and the friction forces.

[0055] (v) Exiting regenerative braking mode: the cyclist exits this braking mode regenerative with target speed by producing a torque on the pedals greater than a threshold torque where pedaling is considered active, here 10 Nm as an example.

[0056] Figure 2 shows the response of the brake sensor during the scenario. It can be seen that the cyclist activates the mechanical brake around t = 1 second and releases it shortly before t = 4 seconds.

[0057] Figure 3 shows the evolution of the bicycle's speed (solid lines) and the evolution of the target speed (dashed lines) during the scenario. The two vertical bars mark the beginning and end of regenerative braking at the target speed.

[0058] It is observed that the bicycle's speed increases as long as the mechanical brake is not active and then decreases when it is activated. When the brake is released, the regenerative braking with target speed is activated. A reference target speed V0 is then defined as being equal to the bicycle's current speed. This target speed then varies according to the pedal rotations performed by the cyclist. The target speed remains constant for a certain period, then increases just after t = 5 seconds, reaching a first plateau of target speed around t = 7 seconds. The target speed increases slightly again from t = 11 seconds, before decreasing to a fixed value around t = 14 seconds. During this time, the bicycle's speed follows the target speed, with a certain delay due in particular to the PID controller. Shortly before t = 15 seconds, the cyclist actively pedals, which switches the system out of the regenerative braking motor control mode.The bike's speed then increases again, as the regenerative braking is no longer active.

[0059] Figure 4 shows the evolution of the pedal revolution counter Ap calculated during regenerative braking with a target speed. The two vertical bars mark the beginning and end of regenerative braking with a target speed. At the start of this control mode, this counter is 0. It is then incremented or decremented according to the number of pedal revolutions performed by the cyclist. It can be seen that the evolution of the target speed described in Figure 3 closely follows the evolution of this pedal revolution counter.

[0060] Figure 5 represents the evolution of engine torque (solid lines) and human torque (dashed lines) during the scenario. The two vertical bars mark the beginning and end of regenerative braking at the target speed. The motor torque is initially zero as long as the cyclist does not brake. When the mechanical brake is activated, regenerative braking is added to the mechanical braking. The braking torque gradually increases to reach the target torque value of 40 Nm around t = 3 seconds. Note that between t = 1.75 seconds and t = 3 seconds, the motor torque does not increase linearly due to constraints on the maximum regenerative braking power at the speeds in question. Once braking with the target speed is active, the motor torque varies according to the PID controller and the slope to best control the target speed. Finally, this figure shows that the cyclist initiates active pedaling shortly before t = 15 seconds, generating torque on the pedals and thus deactivating regenerative braking. The motor torque then becomes positive in response to the cyclist's active pedaling.

Claims

Demands

1. Method for controlling the regenerative braking of an electrically assisted bicycle, comprising the following steps: detecting the end of mechanical braking; setting a target speed based on the measured speed of the bicycle at the time of detection of the end of mechanical braking; regulating the regenerative braking of the bicycle according to the target speed.

2. A method according to claim 1, wherein the target speed can be equal to the measured speed or adjusted according to predefined criteria such as road conditions, battery charge level, and / or user preferences.

3. Method according to claim 1, comprising the following step: using a proportional-integral-derivative (PID) controller to control the target speed of regenerative braking.

4. A method according to claim 3, comprising the following step: adding to the PID controller an additional term that is a function of at least one of the following: estimated friction forces, slope, wind speed, and road surface conditions.

5. Method according to claim 1, comprising the following steps: recording the position of the pedals at the end of mechanical braking; and modulating the target speed of regenerative braking in response to a variation in the position of the pedals relative to the recorded position.

6. A method according to claim 5, wherein the target speed of regenerative braking varies linearly as a function of the angle of the pedals relative to the recorded position, and is bounded by minimum and maximum target speeds.

7. Method according to claim 1, comprising the following step: exiting regenerative braking mode as soon as the system detects human torque greater than a minimum threshold beyond which pedaling is considered active.

8. Method according to claim 1, comprising the following step: exiting regenerative braking mode when the regenerative braking torque required to control the motor to reach the target speed is zero or transforms into a positive torque providing assistance.

9. A method according to claim 5, comprising the following step:

10. Exit regenerative braking mode when the target speed determined by the modulation based on the pedal angle becomes zero.

10. A method according to claim 1, comprising the following step: allowing a transition from a control having the target speed as its setpoint to a control having a target torque as its setpoint after the cyclist has initiated a backward pedaling at a certain pedaling angle.

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