Control method for a bicycle, control device and bicycle with the control device

Abstract

A control method is proposed for a bicycle (1) with a drive unit (2) for at least temporarily electrically driving a drive wheel (3) of the bicycle (1) to assist when pushing the bicycle (1), comprising the following steps: Detecting an actual slip value at the drive wheel (3) based on a deviation between a target value and an actual value with respect to the rotational state of the drive wheel (3); Controlling the electric machine (7) based on the actual slip value in the direction of a permissible slip value that is lower than the actual slip value.

Description

[0001] The present invention relates to a control method for a bicycle. In particular, the present invention relates to a control method for a bicycle designed as a pedelec, with which any slippage that may occur at a drive wheel of the bicycle can be reduced. Furthermore, the present invention relates to a control device configured to carry out the control method, and to a bicycle with such a control device.

[0002] The prior art disclosed in DE 10 2021 118 362 B3 describes a pedelec with an electric drive unit. This prior art includes a motor control unit and a slip detection unit. The slip value is determined, and the motor control unit adjusts its settings to reduce the slip.

[0003] DE 10 2021 203 172 A1 describes a method for controlling an electric bicycle and an electric bicycle itself. DE 10 2017 103 735 A1 describes a bicycle control device and a bicycle drive device. US 2019 / 0 291 815 A1 describes a friction drive system for a bicycle.

[0004] The task is to detect and reduce slippage of a drive wheel of a bicycle, and the independent claims solve this task.

[0005] The present invention relates, in one aspect, to a control method for a bicycle with a drive unit for at least temporarily electrically powering a drive wheel of the bicycle to assist when pushing the bicycle. The drive unit can, for example, be configured to provide a push assist function. For instance, the user can activate a push assist mode, which also activates the control method. Alternatively, the control method can also be activated when the push assist function is activated. The drive unit can additionally serve to provide at least temporary electrical assistance to a drive wheel of the bicycle powered by muscle force. The muscle force can be introduced into the drive unit via a crank mechanism and transmitted to an output element of the drive unit via a gear mechanism.For example, in a normal riding mode, the drive system can assist the rider by pedaling. The bicycle can, for instance, be designed as a pedelec. In this case, the drive system includes an electric motor to provide drive torque for electric assistance, whereby torque from the electric motor can be applied to the output element of the drive system. The torque can be transmitted to the output element, for example, via the transmission device. The electric motor can also be designed for recuperation.

[0006] The control procedure comprises the following steps: - Recording an actual slip value at the drive wheel based on a deviation between a target value and an actual value with respect to a rotational state of the drive wheel; and - Controlling the electric machine based on the actual slip value towards a permissible slip value that is lower than the actual slip value, whereby, for example, the drive torque and alternatively or additionally a drive speed of the electric machine are controlled, for example using a closed control loop. Furthermore, the control method includes the following step: At least temporary control of the electric machine, for example its drive torque or its drive speed, when detecting a predetermined difference between the actual slip value and the permissible slip value in order to reduce the difference between the actual slip value and the permissible slip value using a target value control.

[0007] The control method according to the aforementioned aspect is applicable, for example, to a bicycle in which the pushing force of a person pushing the bicycle can be combined with the drive power supplied by the electric motor. In normal operation, for example, muscle power introduced into the drive unit via the crank mechanism can be combined with the drive power supplied by the electric motor. The drive unit can have various configurations, as long as the concept underlying the invention can be realized. The bicycle to which the control method according to the aforementioned aspect is applicable can have a front wheel and a rear wheel. The front wheel can be a non-driven wheel, while the rear wheel can be the drive wheel.The drive unit can deliver a driving force via the output element, which can be transmitted to the drive wheel by suitable means. For example, the electric motor can be operatively connected to the drive wheel via a chain or a belt. The electric motor can also be designed as a hub motor. The bicycle can be operated solely by muscle power in a predetermined operating state, for example, when pushing and alternatively or additionally when riding. Furthermore, the drive unit can be operated in such a way that the driving force provided by the electric motor is based on predetermined parameters.The predetermined parameters can include the rotational speed of the crank mechanism, the speed of the bicycle relative to a surface, a target push assist force, a target push speed, and the rotational speed of at least one of the front and rear wheels. Further parameters can be considered for controlling the electric motor.

[0008] The drive system can be controlled in a predetermined operating state such that the speed of the electric machine is controlled. The speed of the electric machine, taking into account a predetermined gear ratio in the drive force curve between the electric machine and the drive wheel, can determine the speed of the drive wheel. The gear ratio in the drive force curve between the electric machine and the drive wheel can be variable. In this case, it is advantageous to determine the gear ratio and consider it in the control procedure. The speed of the electric machine, and thus the speed of the drive wheel, can be limited to a maximum speed in an operating state with electric assistance from the electric machine.This measure allows the bicycle's speed to be limited to a maximum speed when operating with electric assistance from the electric motor. This makes it possible, for example, to predefine a maximum pushing speed with motor assistance. A predetermined speed control method can be provided for the speed control of the electric motor. This speed control method can be implemented separately from the control method described here.

[0009] In this context, the actual slip value can refer to a value that reflects the slippage of the drive wheel relative to the surface on which the bicycle is traveling. The actual slip value is expressed as the difference between the peripheral speed of the drive wheel and the speed of the bicycle over the surface.

[0010] The permissible slip value can be determined in advance based on empirical investigations, according to the present aspect. The permissible slip value can be a fixed value. Alternatively, the permissible slip value can be variable and thus change depending on predetermined influencing factors. In particular, the permissible slip value can vary depending on the speed of the bicycle over the ground. The permissible slip value can be determined from the difference between the peripheral speed of the drive wheel and the speed of the bicycle over the ground and can represent a value that enables safe pushing. For example, on steep inclines and, alternatively or additionally, on wet roots, a push assist could otherwise lead to the drive wheel spinning. This could cause the drive wheel to slip sideways, and the user and the bicycle could lose their balance.Furthermore, users often lean on the bicycle for support while pushing, which means that a loss of traction can quickly lead to a fall. Additionally, a loss of traction can unexpectedly force the user to support the entire weight of the bicycle, which can be uncomfortable.

[0011] The actual slip value can alternatively be the time-dependent change in the difference between the circumferential speed of the drive wheel and the speed of the bicycle over the ground. Similarly, the permissible slip value can be a permissible time-dependent change in the circumferential speed of the drive wheel and the speed of the bicycle over the ground.

[0012] The actual slip value can be determined by comparing the bicycle's speed over the ground with the circumferential speed of the drive wheel, or their changes over time. The bicycle's speed can be determined using a speed sensor. Alternatively, the bicycle's speed over the ground can be determined by measuring the rotational speed, and thus the circumferential speed, of a non-driven wheel, particularly the front wheel.

[0013] When regulating the drive torque of the electric motor based on the actual slip value, a closed-loop control system can be used, as described above. This system continuously compares the actual slip value with the permissible slip value and adjusts the drive torque of the electric motor accordingly to reduce the difference between the two. If the peripheral speed of the drive wheel exceeds the speed of the bicycle over the ground, the drive torque of the electric motor is reduced by the closed-loop control system according to a predetermined curve. This predetermined curve can be a time-dependent profile. In this way, the tractive force acting between the drive wheel and the ground is reduced, thus decreasing the actual slip value.This allows for an anti-slip function even when using the push assist. This prevents or at least limits rear wheel spin. As soon as excessive wheel slip is detected, the torque or speed of the electric motor can be reduced to restore sufficient traction to the drive wheel and thus relieve the user when pushing the bicycle.

[0014] According to the present aspect, the drive torque of the electric machine can be controlled, at least temporarily, upon detection of a predetermined difference between the actual slip value and the permissible slip value, in order to reduce this difference. This involves target value control, in which the drive torque is set based on a predetermined target value. This target value can include an immediate reduction of the drive torque and, alternatively or additionally, a reduction in the speed of the electric machine upon detection of the predetermined difference between the actual slip value and the permissible slip value, so that the actual slip value approaches the permissible slip value.Furthermore, the predetermined setting can include a predetermined time profile based on the drive torque of the electric machine, which is present when the predetermined difference between the actual slip value and the permissible slip value is detected. The predetermined time profile can be designed as a ramp function. Furthermore, the predetermined time profile can represent a progressive or degressive function over time. With this control system, it can be provided that the drive torque of the electric machine is reduced to zero, based on the detection of a predetermined difference between the actual slip value and the permissible slip value, if the actual slip value does not reach the permissible slip value after a predetermined time.

[0015] The permissible slip value can be variable. It can also be set to zero or close to zero. Alternatively, the permissible slip value can be set to a value that allows the bicycle to be pushed safely, and this permissible slip value can be determined empirically.

[0016] In the aforementioned target value control, a reduction in the peripheral speed of the drive wheel is achieved by correspondingly controlling the drive torque of the electric motor. As described above, the inertia of moving masses, including rotating masses, can be taken into account in target value control. These masses are naturally subject to a certain degree of inertia. The inertia of the drive wheel can be considered in target value control to achieve a predetermined peripheral speed of the drive wheel over time by adjusting the drive torque of the electric motor. Similarly, the inertia of other moving elements, such as a drive chain and rotating components of the drive system, can be considered in target value control.

[0017] According to the aforementioned aspect, the control of the drive torque or drive speed of the electric machine using closed-loop control and the control of the drive torque of the electric machine using target value control can be performed simultaneously, at least temporarily. The adjustment of the drive torque of the electric machine using closed-loop control can be superimposed on the adjustment of the drive torque of the electric machine using target value control. Furthermore, a prioritization can be provided such that if a predetermined difference between the actual slip value and the permissible slip value is determined that exceeds a predefined threshold, the drive torque of the electric machine is controlled, at least temporarily, exclusively using target value control.The control of the electric machine's drive torque can be continued for a predetermined period using target value control. Furthermore, after the target value control has ended, the control of the electric machine's drive torque can be resumed using closed-loop control. Feedforward control can be incorporated into the control method. For example, a specific drive torque or drive torque differential can be set for the electric machine if the actual slip value exceeds a permissible slip value. This allows for a particularly rapid return to a state with a permissible slip.

[0018] In the control step, the drive torque of the electric machine is regulated. A PID controller is used for this control of the drive torque. The PID controller is particularly suitable for feedback control of the actual slip value, since overshooting of the electric machine can be prevented by appropriately setting the coefficients of the PID controller, and at the same time the actual slip value can be quickly reduced to the permissible slip value. The coefficients of the PID controller can be empirically determined and preset.

[0019] According to one embodiment, the control limit for the drive torque of the PID controller can be adjustable between a predetermined maximum value and zero. This control limit is a parameter used by the PID controller to adjust the drive torque based on the current drive torque of the electric machine. The predetermined maximum value of the control limit can be empirically determined. Alternatively, the predetermined maximum value can be variable and, in particular, set to the current drive torque. This allows the PID controller to gradually reduce the drive torque of the electric machine to zero, thus enabling the actual slip value to reach the permissible slip value.Furthermore, the controller's setpoint limit can be adjusted to zero, thus temporarily disabling the PID controller. This measure ensures that the drive torque of the electric machine is controlled exclusively using the target value control discussed above.

[0020] In one embodiment, a predetermined profile, including a ramp function, can be used to set the PID controller's setpoint limit. This embodiment achieves a smooth transition when the PID controller switches from a setpoint limit of zero to the predetermined maximum value, or vice versa. This improves the bicycle's operational safety by preventing excessive drive torque gradients.

[0021] According to one embodiment, a target speed and an actual speed of the drive wheel can be considered as the setpoint and actual values ​​with respect to the rotational state of the drive wheel. For considering slippage in a bicycle being pushed on a surface, the ratio between the peripheral speed of the drive wheel and the speed of the bicycle over the surface is useful. Furthermore, the rotational speeds of the drive wheel can be determined directly or indirectly and can readily be used for the control method.

[0022] According to one embodiment, a target rotational acceleration and an actual rotational acceleration of the drive wheel can be considered as the setpoint and actual values ​​with respect to the rotational state of the drive wheel. Changing the circumferential speed of the drive wheel is advantageous as an alternative or additional measure to considering the magnitude of the circumferential speed of the drive wheel, since a particularly fast response time of the control method can be achieved.

[0023] In one embodiment, the actual value of the drive wheel's rotational state can be derived from a speed signal of the electric motor of the drive unit. When applying this control method to a bicycle with a drive unit where the electric motor is coupled to the output element, which in turn is coupled to the drive wheel, the speed of the drive wheel can be determined by measuring the speed of the electric motor. For this purpose, it is particularly advantageous if the electric motor is coupled to the drive wheel with a predetermined gear ratio.Furthermore, it is possible to deduce the rotational speed of the drive wheel from the rotational speed of the electric machine if the gear ratio between the electric machine and the drive wheel is variable and, at the same time, the gear ratio between the electric machine and the drive wheel is known and can be provided for the implementation of the control method. This control method is particularly advantageous for a bicycle with a drive unit in which the electric machine is coupled to the output element on the output side or driven side. Similarly, it can be provided that the rotational acceleration of the drive wheel can be determined from the rotational acceleration of the electric machine. Alternatively, the actual value of the rotational state of the drive wheel can be determined by a sensor that detects the rotational speed of the drive wheel.

[0024] In one embodiment, the target value for the rotational state of the drive wheel can be derived from a directly or indirectly determined speed of the bicycle over the ground. The speed of the bicycle over the ground can be derived from the circumferential speed of the non-driven wheel. For this purpose, a wheel speed sensor can be provided on the non-driven wheel, the signal of which is available for further processing. Alternatively, a speed sensor can be provided that detects the speed of the bicycle and provides a corresponding signal for further processing.

[0025] In one embodiment, the speed of the electric motor can be controlled based on the operating conditions of the bicycle. In particular, for a bicycle that can be designed as a pedelec, the user's pushing force is determined, and the operation of the electric motor is controlled based on this force. Other operating conditions of the bicycle, including the bicycle's speed over the ground, input from the rider to control the speed of the electric motor, and the like, can be additionally or alternatively taken into account.

[0026] In one embodiment, the drive torque of the electric machine can be applied to the output element of the drive unit on the output side without passing through the transmission device. This control method is particularly applicable to a bicycle with a drive unit where the electric machine is coupled to the output element, and thus to the drive wheel, on the output side. In this way, the speed and torque of the electric machine can be regulated or controlled with simple means in such a way that any potential slippage at the drive wheel can be reliably counteracted.

[0027] In one embodiment, the method includes a step of controlling the bicycle's braking system based on the actual slip value, adjusting it towards the permissible slip value, which is lower than the actual slip value. For example, the bicycle may have an automatically actuated brake. The braking system may, for example, include an electric actuator for actuating a brake on the drive wheel. This could, for example, implement an ABS function. In the case of push assist, the braking system can be used to quickly decelerate a spinning drive wheel in order to regain sufficient traction.

[0028] According to another aspect, a control device for a bicycle drive system is provided, comprising input interfaces for receiving input signals and output interfaces for output signals, as well as a device for controlling an electric machine. The control device is configured to carry out the method with one or more of the features discussed above. The control device may be integrated into a higher-level control unit provided on the bicycle. Alternatively, the control device may be a separate unit that can be provided on the bicycle. Furthermore, the control device may be connected to an energy storage device that can be provided on the bicycle to supply electrical energy to the electric machine according to the control method and to bring about the predetermined operating state of the electric machine.The control device may include a speed sensor designed to detect the speed of the bicycle over the ground.

[0029] According to another aspect, a bicycle with a drive device for at least temporary electrical assistance of a drive wheel of the bicycle powered by muscle power has a control device which is explained in the preceding aspect.

[0030] The bicycle described above has one front wheel and one rear wheel. Alternatively, the bicycle can have more than two, in particular three, wheels, at least one of which can be designed as a drive wheel. Fig. Figure 1 shows a schematic view of a bicycle designed as a pedelec, to which the control method according to the embodiments is applicable; Fig. Figure 2 shows an exemplary drive unit, which is located in the Fig. 1 bicycle shown is intended for use and to which the control method according to the embodiments is applicable; Fig. Figure 3 shows a schematic diagram of the control procedure in one embodiment.

[0031] Fig. Figure 1 shows a schematic representation of a bicycle 1 to which embodiments of the control method are applicable. The in Fig. The bicycle shown is merely an example and serves to explain the functionality in connection with the control procedure.

[0032] The in Fig. Bicycle 1, as shown, has a frame (not described in detail) on which a front wheel 10 is mounted as a non-driven wheel and a rear wheel 3 as a drive wheel. Bicycle 1 also has other elements typical of a bicycle (not described in detail), such as a saddle, handlebars, a braking system, and other attachments, which will not be considered for the following explanation.

[0033] The in Fig. The bicycle shown is designed as a pedelec and therefore has a drive unit 2, which is mounted in the area of ​​the bottom bracket position of the frame of bicycle 1. For the operation of the drive unit 2, an energy storage device 9, designed as a rechargeable battery, is provided on the frame of bicycle 1, in the illustration on the down tube of the frame. Furthermore, the bicycle shown in Fig. The bicycle shown in Figure 1 has a control device 8 which is also mounted on the frame of the bicycle 1.

[0034] The rear wheel 3, designed as the drive wheel, is coupled to the drive unit 2 via a drive force transmission element in the form of a chain. The drive unit 2 also has a crank assembly 4, by means of which a rider of the bicycle 1 can apply muscle power to the drive unit 2 while riding. When pushing, the user, for example, pushes against the handlebars of the bicycle 1 to propel the bicycle 1 in front of them. The drive unit 2 also has an output element 6 in the form of a chainring or a gear, which is coupled to a sprocket of the rear wheel 3 via the chain. Rotation of the output element 6 is transmitted to the rear wheel 3 via the chain, so that the rear wheel 3 can be driven.

[0035] Fig. Figure 2 shows a detailed view of the drive unit 2. The drive unit 2 corresponds in design to the one described in Fig. 1. Drive unit mounted on bicycle 1. 2. As in Fig. As can be seen in Figure 2, the drive unit 2, housed in a casing, comprises an electric machine 7. The electric machine 7 can be operated with the electrical energy stored in the energy storage device 9. The operation of the electric machine 7 by the electrical energy stored in the energy storage device 9 is carried out by the control device 8. In this respect, the control device 8, the energy storage device 9, and the electric machine 7 are electrically and, if applicable, signal-wise coupled to each other.

[0036] The electric machine 7 serves to apply driving force to the output element 6 of the drive unit 2. In particular, the rotation of an output shaft of the electric machine 7 is transmitted to the output element 6 and subsequently to the drive wheel 3 with a defined transmission ratio. During normal operation, the electric machine 7 serves to electrically assist the muscle power introduced into the drive unit 2 by the crank 4. The muscle power introduced into the drive unit 2 via the crank 4 is transmitted to the output element 6 via a transmission device 5 provided in the drive unit 2. Thus, the drive unit 2 combines the driving force of the electric machine 7 and the muscle power introduced via the crank 4, and the combined driving force is transmitted to the rear wheel 3.In addition, a push-assist mode can be activated, in which the drive unit 2 assists the user when pushing the bicycle. In this mode, the electric motor 7 applies a driving force to the rear wheel 3, which assists the rider by driving the rear wheel 3 while pushing the bicycle 1. The control method used to prevent slippage will be explained below.

[0037] The in Fig. The schematically shown transmission device 5 is, in the present embodiment, designed as a continuously variable transmission with which the transmission ratio between the rotational speed of the crank mechanism 4 and the output element 6 can be continuously adjusted. In this context, a system configuration not shown in detail is used in which a second electric motor is coupled to the crank mechanism 4 for speed superposition. It should be noted that, in the present embodiment, the electric motor 7 is coupled on the output side, meaning that the rotation of the electric motor 7 is transmitted to the output element 6 without passing through the transmission device 5. Therefore, a predetermined relationship exists between the rotational speed of the electric motor 7 and the rotational speed of the rear wheel 3, at least in one operating condition in which the rear wheel 3 is driven.

[0038] The in Fig. The electric machine 7 shown in Figure 2 is operated by the control device 8 via corresponding electrical circuits. In particular, the speed of the electric machine 7 is controlled depending on the operating conditions of the bicycle 1. For example, the speed of the electric machine 7 is controlled depending on the speed of the crank mechanism 4 when the bicycle 1 is in operation, so that the assistance provided to the drive of the bicycle 1 by the electric machine 7 is in sync with the drive of the crank mechanism 4 by muscle power. Thus, when muscle power is applied to the crank mechanism 4, the drive of the pedelec is assisted by the electric machine 7. In contrast, when the push assist is activated, a fixed or user-variable drive torque is generated by the electric machine 7 to assist the user when pushing the bicycle 1.Alternatively, when the push assist is activated, the electric motor 7 is operated, for example, at a fixed or user-adjustable drive speed to assist the user in pushing the bicycle 1. A maximum pushing speed can also be taken into account. Furthermore, the strength of the push assist can be predefined based on detected values, such as the user's pushing force, provided the actual slip value is less than a permissible slip value.

[0039] The in Fig. The electric machine 7 shown in Figure 2 has a signal output from which the rotational speed of an output shaft of the electric machine 7 can be derived. This signal output is coupled to a signal input of the control device 8. This signal provides the control device 8 with information regarding the current rotational speed of the electric machine 7 at any given time. Furthermore, in the present embodiment, the drive unit 2 has a sensor, which is not relevant to the present control method, that detects the rotational speed of the crank mechanism 4 and provides a corresponding signal to the control device 8. Additionally, in the present embodiment, a speed sensor is provided that detects the rotational speed of the front wheel 10, which is designed as a non-driven wheel. This signal regarding the rotational speed of the front wheel 10 is also provided to the control device 8.Using this signal, the control device 8 can determine the speed of the bicycle 1 over the ground at any given time, provided that the front wheel 10 has a circumferential speed corresponding to the speed of the bicycle 1 over the ground. In a modified embodiment, a speed sensor is provided on the bicycle 1 to detect its speed. This could, for example, be an accelerometer or a GPS receiver.

[0040] The following describes an embodiment of the control method based on Fig. 3 described. Fig.Figure 3 shows a schematic flowchart illustrating the steps of the control procedure according to this embodiment. It should be noted that in a separate control system, not shown here, the speed of the bicycle 1 is controlled based on the rotational speed of the electric motor 7 with regard to the operating state.

[0041] With the push assist of bicycle 1 activated and an anti-slip control system in place, the drive torque of the electric motor 7 is continuously regulated or controlled, taking into account any potential slippage occurring at the rear wheel 3 of bicycle 1. For this purpose, in step S1, an actual slip value at the drive wheel 3 is first detected based on a deviation between a target value and an actual value with respect to the rotational state of the drive wheel 3. In the present embodiment, the control device 8 first determines the current speed of bicycle 1 based on the detected rotational speed of the front wheel 10.Provided that the circumferential speed of the front wheel 10 corresponds sufficiently accurately to the speed of the bicycle 1, the circumferential speed of the rear wheel 3 can then be evaluated to determine whether there is a deviation, taking into account the measured speed of the bicycle 1. As described above, the circumferential speed of the rear wheel 3 is determined by the control device 8 by determining the rotational speed of the electric motor 7.

[0042] The difference between the circumferential speed of the rear wheel 3 and the circumferential speed of the front wheel 10, which represents the speed of the bicycle 1 above the ground, allows us to determine whether slippage exists between the rear wheel 3 and the ground. In the present embodiment, a value is determined from the differences between the circumferential speed of the rear wheel 3 and the circumferential speed of the front wheel 10; this value is referred to as the slip value.

[0043] Since a certain amount of slip of the rear wheel 3 during pushing can be considered permissible, it is first checked whether the detected slip value is greater than the permissible slip value. If the detected slip value, namely the actual slip value, is greater than the permissible slip value, the difference between the actual slip value and the permissible slip value is determined in step S2. Based on this difference, the drive torque of the electric machine 7 is adjusted in step S2 using a PID control loop. In particular, in this embodiment, starting from the current drive torque of the electric machine specified by the control device 8, the PID control loop reduces the drive torque of the electric machine according to a predetermined curve, depending on the difference between the actual slip value and the permissible slip value.In the present embodiment, the parameters of the PID control loop are preset in such a way that overshoot of the control of the drive torque of the electric machine is avoided and at the same time the actual slip value can be reduced to or below the permissible slip value with a fast response.

[0044] Due to the control carried out in step S2 using a closed control loop, the slip state of the bicycle 1 can thus be reduced or eliminated on the basis of a targeted reduction of the drive torque of the electric machine 7.

[0045] In parallel with the control of the drive torque of the electric machine 7 based on step S2 using the closed-loop control system, in step S3 the drive torque of the electric machine is additionally adjusted using target value control in the form of feedforward control. For this purpose, in step S3 the actual slip value recorded in step S1 is first compared with the permissible slip value. If a predetermined difference between the actual slip value and the permissible slip value is detected, namely if the actual slip value is greater than the permissible slip value by a predetermined amount, the drive torque of the electric machine 7 is adjusted so that a reduced drive force is present at the rear wheel 3, and thus the actual slip value is reduced.For this purpose, a target value control is used, in which the reduction of the drive torque of the electric machine is carried out on the basis of the characteristics of the bicycle 1 to which the target value control is applied.

[0046] Thus, in step S3, after detecting a predetermined difference between the actual slip value and the permissible slip value, the drive torque of the electric machine is reduced from the current drive torque of the electric machine 7. In this embodiment, this reduction uses a time-dependent ramp with a negative slope. As soon as the predetermined difference between the actual slip value and the permissible slip value is no longer exceeded, the target value control is terminated, and the electric machine 7 is operated with the drive torque present at that time.

[0047] According to the basic concept of the control method in the present embodiment, the advantages of using a closed-loop control system in the form of a PID controller and target value control are combined. The use of a closed-loop control system offers a very precise adjustment of the actual slip value to the target slip value in the form of a predetermined additional slip value, although the PID control used is naturally subject to a certain delay in its response time. However, since, for example, when pushing the bicycle 1 on a slippery, steep surface, immediate intervention in the operation of the drive unit 2 is necessary to maintain driving safety and, for instance, prevent the rear wheel 3 from skidding and the corresponding consequences, the target value control implemented in step S3 is superimposed on the closed-loop control system via the control system implemented in step S2.As a result, the target value control used in step S3, with its correspondingly fast response time, can increase the safety of bicycle 1, especially on slippery surfaces, since the actual slip value can be reduced so significantly within fractions of a second that the risk of a fall can be largely prevented. Additionally, the precise control of the drive torque can be achieved through the closed-loop control system implemented in step S2, in order to regulate the drive torque of the electric motor 7 very accurately to the permissible slip value.

[0048] In a further embodiment, for controlling the drive torque of the electric machine 7 using target value control in the form of feedforward control, a permissible slip value is specified that is greater than the permissible slip value specified for controlling the drive torque based on closed-loop control. This measure ensures that the target value control is terminated when the permissible slip value specified for target value control is reached. In this case, the control of the drive torque of the electric machine is subsequently carried out using closed-loop control until the permissible slip value specified for closed-loop control is reached.Thus, in this embodiment, the target value control with its fast response is initially used as feedforward control, followed by closed-loop control, resulting in an overall advantageous control behavior. It should be noted that for this and other embodiments, the permissible slip value specified for closed-loop control can be set to zero. In this case, the slip at the rear wheel 3 can be significantly reduced.

[0049] In another embodiment, the control parameters of the PID controller are adjustable. In particular, in the present embodiment, the controller setpoint for the drive torque of the PID controller is set between a predetermined maximum value and zero. The controller setpoint is the value by which the PID controller modifies the currently applied drive torque of the electric machine 7. If the controller setpoint is set to zero, the function of the PID controller is disabled, and in the present embodiment, only the target value control provided in step S3 is used.If the controller setpoint is set to its maximum value, the PID controller can reduce the current drive torque of the electric machine 7 to zero, thus shutting off the support operation by the electric machine 7. The predetermined maximum value of the controller setpoint can be variably adjusted depending on the current drive torque of the electric machine 7.

[0050] In a further embodiment, a predetermined time profile is used when adjusting the controller setting limits between the predetermined maximum value and zero; in the present embodiment, this profile is provided as a ramp. This embodiment ensures that no abrupt change in the drive torque of the electric machine 7 occurs when changing the controller setting limits, which could result in an undesirable slip condition at the rear wheel 3. Reference sign 1 bicycle 2 Drive unit 3 Drive wheel (rear wheel) 4 Crank mechanism 5 Gearbox device 6 Starting element 7 electric machine 8 Control device 9 Energy storage device 10 non-driven wheel (front wheel) S1 Capture actual slip value S2 controls drive torque (closed control loop) S3 Controls Drive Torque (Target Value Control)

Claims

[1] Control method for a bicycle (1) with a drive unit (2) for at least temporarily electrically driving a drive wheel (3) of the bicycle (1) to assist when pushing the bicycle (1), wherein the drive unit (2) comprises an electric machine (7) for providing a drive torque for electric assistance, wherein a drive torque of the electric machine (7) can be applied to an output element (6) of the drive unit (2), comprising the following steps: - (S1) Recording an actual slip value at the drive wheel (3) based on a deviation between a target value and an actual value with respect to a rotational state of the drive wheel (3); - (S2) Control of the electric machine (7) on the basis of the actual slip value in the direction of an allowable slip value which is less than the actual slip value, characterized by that the procedure additionally includes the following step: - (S3) at least temporary control of the drive torque of the electric machine (7) upon detection of a predetermined difference between the actual slip value and the permissible slip value in order to reduce the difference between the actual slip value and the permissible slip value using a target value control, and that in step (S2) of the control the drive torque of the electric machine is controlled and a PID controller is used for controlling the drive torque. [2] Control method for a bicycle (1) according to claim 1, characterized by , that the (S2) control of the drive torque of the electric machine (7) is based on the actual slip value in the direction of the permissible slip value, which is lower than the actual slip value, using a closed control loop. [3] Control method for a bicycle (1) according to claim 1, characterized by, that a controller setpoint for the drive torque of the PID controller can be set within a range between a predetermined maximum value and 0. [4] Control method for a bicycle (1) according to claim 3, characterized by , that a predetermined profile including a ramp function is used to set the control limit of the PID controller. [5] Control method for a bicycle (1) according to any one of the preceding claims, characterized by , that a target speed and an actual speed of the drive wheel (3) are taken into account as the target value and actual value with regard to the rotational state of the drive wheel (3). [6] Control method for a bicycle (1) according to one of claims 1-5, characterized by , that a target rotational acceleration and an actual rotational acceleration of the drive wheel (3) are taken into account as the target value and actual value with regard to the rotational state of the drive wheel (3). [7] Control method for a bicycle (1) according to one of the preceding claims, characterized by , that the actual value regarding the rotational state of the drive wheel (3) is derived from a speed signal of the electric machine (7) of the drive device (2). [8] Control method for a bicycle (1) according to one of the preceding claims, characterized by , that the target value regarding the rotational state of the drive wheel (3) can be derived from a directly or indirectly determinable speed of the bicycle (1) over the ground. [9] Control method for a bicycle (1) according to any one of the preceding claims, characterized by , that the speed of the electric machine (7) is regulated on the basis of the operating conditions of the bicycle (1). [10] Control method for a bicycle (1) according to any one of the preceding claims, characterized by, that the drive torque of the electric machine (7) is applied on the output side to the output element (6) of the drive device (2) without passing through a gear device (5). [11] Control method for a bicycle (1) according to any one of the preceding claims, characterized by , that the procedure includes a step of controlling a braking system of the bicycle (1) on the basis of the actual slip value in the direction of the permissible slip value, which is lower than the actual slip value. [12] Control device (8) for a drive unit (2) for a bicycle (1) with input interfaces for receiving input signals and output interfaces for output signals and a device for controlling an electric machine (7), wherein the control device (8) is configured to carry out the method according to one of the preceding claims. [13] Bicycle (1) with a drive unit (2) for at least temporarily electrically driving a drive wheel (3) of the bicycle (1) when pushing the bicycle (1) and with a control device (8) according to claim 12.

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