Method for controlling a drive motor of a bicycle, control device and bicycle

Abstract

The present invention relates to a method for controlling a drive motor of a bicycle. The drive motor is mechanically operatively connected to an output element of the bicycle by means of a freewheel. The method comprises at least the following steps: - Selecting (8) an operating mode for the powertrain; - determining (10) a variable target speed gradient for the drive motor; and - controlling (12) the drive motor as a function of the determined variable target speed gradient in order to approximate a motor speed (22) to a synchronous speed (20) of the freewheel. The invention also relates to a control device and a bicycle.

Description

Technical FieldThe present invention relates to a method for controlling a drive motor of a bicycle. The invention also relates to a control device and a bicycle.Prior ArtModern bicycles often have a drive motor to assist a user in propelling the bicycle. Bicycles designed as pedelecs are known, for example. In this case, support is provided only when the user pedals. On the other hand, when the user stops pedaling, the assistance by the driving motor is also stopped. In order that a mass inertia of the drive motor does not lead to an undesired driving of a pedal crankshaft, a rotation of a motor shaft and of the pedal crankshaft can be decoupled by a freewheel, for example.In order for the drive motor to be able to assist in driving the bicycle, the drive motor must be adapted with its rotational speed to a rotational speed of the pedal crankshaft. However, such tracking is difficult because users of bicycles frequently pedal unevenly and generally a pedaling speed frequently changes. For example, the rotational speed of the pedal crankshaft can vary greatly even within a single revolution.Therefore, if the drive motor tracks on the rotational speed of the pedal crankshaft in order to close the freewheel, undesirable effects can occur. If synchronization of the drive motor with the treading speed takes too long, the user may inquire about performance of the drive motor. In addition, driving purely with muscle power is then necessary, for example, for a large part of a starting process, which can make use of the bicycle more challenging in the case of physically impaired persons or heavy load wheels despite motorized support. If the drive motor is synchronized too quickly with the treading speed, sudden meshing can occur. This can cause loud noise and load components of a drive train of the bicycle excessively. In addition, a jerk that is perceptible to the user and thus possibly unpleasant can then occur.DE 10 2013 215 487 A1 describes a method for controlling an electric drive of a vehicle that can be operated with muscle power and / or engine power, and also a vehicle of this type.DE 10 2021 201 405 A1 describes a method for controlling an electric drive motor of an electrically drivable bicycle.JP 2022 161 319 A describes an electric assist drive bicycle and a method for controlling a motor of this assist drive.WO 2012 / 105 198 A1 describes a bicycle with an electric drive.JP 2017-226 296 A describes an electric assist vehicle and an electric assist control system.It is an object of the present invention to provide an improved control for a drive motor of a bicycle. This object is achieved by the subject matters of the independent claims.SUMMARY OF THE INVENTIONA first aspect relates to a method of controlling a drive motor of a bicycle. A bicycle can be designed, for example, as a mountain bike, city bike or cargo bike. A bicycle has, for example, two running wheels. The bicycle can be drivable by a user by means of a pedal crank shaft. The user may be, for example, a cyclist. A crank arm can be fixed to the pedal crank shaft in a rotationally fixed manner at each axial end. A pedal may be rotatably attached to each of the crank arms. The user can thus drive the bicycle, for example, by pedaling. The drive motor of the bicycle can be configured as an electric motor. The drive motor can be arranged, for example, in a bottom bracket region. The drive motor may have a motor shaft. The drive motor may be configured to assist the user in propelling the bicycle. The bicycle can be designed as a pedelec.The drive motor is mechanically operatively connectable to an output element of the bicycle by means of a freewheel. The output element can be designed, for example, as a pinion or impeller. A freewheel can be a clutch which can automatically change between a locked state and a released state depending on a relative rotational direction of two freewheel elements with respect to one another. The freewheel can be a clutch which transmits torque only in one direction of rotation and permits free running in another direction of rotation. In the release state, the two freewheel elements can rotate relative to one another. The two freewheel elements can thus be decoupled and, for example, no torque is transmitted via the freewheel. In the locked state, the two freewheel elements are connected to one another in a rotationally fixed manner. The two freewheel elements can be coupled in this way and, for example, a torque can be transmitted via the freewheel. Examples of a freewheel are a ratchet freewheel and a wrap spring clutch.The drive motor can be mechanically operatively connected to a pedal crankshaft, for example, by means of the freewheel. Via the pedal crankshaft, the drive motor can be mechanically operatively connected or operatively connected to the output element. The drive motor can be mechanically operatively connected directly to the output element, for example, by means of the freewheel. A mechanical operative connection can be a rotational coupling of two elements, optionally via further rotational elements, such as shafts and gearwheels. The pedal crankshaft can be mechanically operatively connected to the output element of the bicycle by means of a freewheel. This can be the same freewheel, which then connects both the drive motor and the pedal crankshaft to the output element. However, it can also be a further freewheel.The method comprises a step of selecting an operating mode for the drive motor. The operating mode can also be an operating mode for the drive train. The operating mode can be activated by the selection. The selection can be made, for example, by means of an operating element on the bicycle, such as a selector lever or a touchscreen. The selection can also be performed by an external operating device, for example a smartphone connected to a drive train of the bicycle or a smartwatch connected to the drive train. The connection for transmitting a selection can be effected, for example, wirelessly, for example via Bluetooth. The selected operating mode can be transmitted, for example, to a control device which controls the drive motor. The selected operating mode can likewise specify a motor control and also an assistance power during normal driving operation, for example when the freewheel is in its locked state. For example, one or more motor control characteristics may be selected by the operating mode. For example, in a first operating mode, the rider may be assisted more heavily in propelling the bicycle than in a second operating mode. For example, alternatively or additionally, different maximum travel speeds with motor assistance can also be predefined by the operating modes. For example, alternatively or additionally, different shifting characteristics for an automatically shifting gear shift of the bicycle can also be predefined by the operating modes. At least a first and a second operating mode can be selected.The method comprises a step of determining a variable target speed gradient for the drive motor depending on the selected operating mode. A speed gradient may be a rate of change of a speed. The rotational speed gradient of the drive motor may correspond to an acceleration by the drive motor. A setpoint rotational speed can be a desired rotational speed during operation of the drive motor. A setpoint rotational speed gradient can be a desired rotational speed gradient during operation of the drive motor. The desired speed gradient may be a desired acceleration by the drive motor before the freewheel engages and a torque is transmittable from the drive motor to the output element. A variable target speed gradient may be a target speed gradient that changes as it approaches a synchronous speed. During a meshing, at least two values can be determined for the variable setpoint rotational speed gradient. For example, a first value for the setpoint rotational speed gradient is determined for a first time period and a second value for the setpoint rotational speed gradient is determined for a second time period. Depending on the selected operating mode, these values for the variable setpoint rotational speed gradient may differ. For example, a first value for the target speed gradient is determined for the first time period and a second value for target speed gradient is determined for the second time period when the first operating mode is selected. For example, a third value for the target speed gradient is determined for the first time period and a fourth value for target speed gradient is determined for the second time period when the second operating mode is selected. The first value and the third value may be different, for example. The second value and the fourth value may be different, for example. For example, in the first operating mode, meshing can be performed more quickly or with higher values for the setpoint rotational speed gradient than in the second operating mode. As a result, a sport driving style can be better supported in the first operating mode, for example, and a comfortable and jerk-free support can be better achieved in the second operating mode. The operating mode can correspond, for example, to an assistance stage by the drive motor. For each operating mode, the respective values for the variable setpoint rotational speed gradient can be fixedly predefined or can be determined differently, for example, depending on other characteristic variables.The method comprises a step of controlling the drive motor in dependence on the determined variable target speed gradient in order to bring an engine speed close to a synchronous speed of the freewheel. For example, the drive motor is first controlled as a function of the first value of the setpoint rotational speed gradient and then as a function of the second value of the setpoint rotational speed gradient. The engine speed may be a speed of a motor shaft of the drive motor. The synchronous speed may be a required speed for both elements of the freewheel to rotate at the same angular speed. The synchronous rotational speed can correspond to a setpoint rotational speed of the drive motor at which the freewheel is locked in the current driving state. For example, the synchronous rotational speed can correspond to the current rotational speed of the pedal crankshaft taking into account a transmission ratio between the motor shaft and the freewheel. For example, an engine speed or an engine torque may be controlled depending on the determined target speed gradient. For example, a power supply of the drive motor can be adjusted accordingly by an inverter.Thus, for example, the drive motor is not given a fixed acceleration for engagement with the freewheel, but an acceleration can be determined as a function of an operating mode and can also change during engagement. In addition, the acceleration can be determined as a function of state variables. During the engagement, a constraint for the acceleration may change and the driver may modify the form of the determination by selecting the operating mode. As a result, a more comfortable and alternatively or additionally faster synchronization of the drive motor with the freewheel and alternatively or additionally of the pedal crankshaft can be achieved, which can also be adjusted as required by the driver. For example, first of all, the engine can be accelerated strongly in order to quickly adapt the engine speed. As a speed at which the freewheel engages and torque is transmitted from the drive motor to the output element is approached more, the acceleration can be reduced in order to avoid a jerklike engagement. Depending on, for example, a selected support stage, this acceleration can be modified. Overall, support by the drive motor can be provided as quickly as possible, while nevertheless strong impacts in a drive train of the bicycle can be avoided.The method is started, for example, when a user rotates the pedal crankshaft in the forward direction, for example by pedaling. Optionally, a minimum rotational speed must be reached by the pedal crankshaft and alternatively or additionally a minimum driving speed before the method is started.Optionally, an operating mode must be selected. Optionally, the method must be enabled by a user, for example by selecting and alternatively or additionally activating an assist mode. Respective support modes may correspond to operating modes. However, a predefined operating mode can also be automatically selected automatically when the bicycle or drive motor is switched on, for example a standard operating mode. This standard operating mode can be preset at the factory or can also be configurable by the user. The approach according to the control method can take place until the synchronous rotational speed is reached or shortly before it. Before or upon reaching the synchronous rotational speed, the method can be ended. Then, a classic follow-up control can be used for the control of the drive motor. An abort criterion for the method can be, for example, the synchronous rotational speed being reached or a threshold value which is below the synchronous rotational speed. This threshold value can, for example, have a fixed predetermined distance from the synchronous rotational speed. The distance of the threshold value from the synchronous rotational speed can also be predefined as a function of the synchronous rotational speed. For example, at 98% of the synchronous rotational speed, the method or the corresponding control of the drive motor can be ended. The method can also be ended if the setpoint gradient can no longer be maintained. This is the case, for example, when the freewheel engages or changes to its locked state. Accordingly, it can be recognized that the synchronous rotational speed has been reached by the engine rotational speed. Exceeding another threshold value by a motor torque or by an induced current may also indicate successful meshing, and the method may then be ended in response. Likewise, for example, successful engagement at the freewheel can also be detected by sensors and, in response, the control of the drive motor can be terminated according to the method.In a further embodiment of the method, it can be provided that the selected operating mode is an ECO mode. An ECO mode can be configured for a particularly high range or low energy consumption. For example, in the ECO mode, a very energy-saving acceleration to the synchronous rotational speed can also take place, as a result of which the drive train can also be saved. Alternatively, the selected mode of operation may be a race mode. A race mode may be configured for a particularly high motor assisted ground speed and alternatively or additionally a particularly high bicycle acceleration. For example, in the ECO mode, a very rapid acceleration to the synchronous rotational speed can also take place, as a result of which a driving power can be high. Alternatively, the selected mode of operation may be a hill-climbing mode. A hill-climbing mode can take account of the fact that different assistance can be expedient depending on the gradient. For example, in the hill-climbing mode, a rapid acceleration to the synchronous rotational speed can take place in the event of a sharp increase, in order to avoid an excessively large speed drop. In the case of flat terrain or a descending stretch, on the other hand, a slow acceleration to the synchronous speed can take place in order to conserve the drive train. Alternatively, the selected mode of operation may be a maximum assist mode. A maximum assist mode may be configured for particularly strong assist with the prime mover. Correspondingly, a rapid acceleration to the synchronous rotational speed can also be provided. Alternatively, the selected mode of operation may be a slide assist mode. In the sliding aid mode, for example, a freewheel is not engaged between the pedal crank shaft and a motor shaft, but rather a freewheel is engaged in a running wheel of the bicycle. This allows the user to be assisted in sliding the bicycle. In this case, too, a variable setpoint rotational speed gradient may be useful in order to conserve the drive train and to quickly engage it. For example, a different load capacity of the freewheel in a rear wheel of the bicycle than on the crankshaft can be taken into account for respective setpoint rotational speed gradients.It can be provided that at least between two of the operating modes described above can be selected. Only some or all of these operating modes may also be available. Further operating modes can also be selected, in which the method described here is not used to trace.In a further embodiment of the method, it can be provided that the determination of the variable setpoint rotational speed gradient is additionally carried out as a function of a comparison of the engine rotational speed with the synchronous rotational speed. A result of the comparison may be a difference. For example, in the case of a high difference between the synchronous rotational speed and the engine rotational speed, a high setpoint rotational speed gradient is determined. For example, the drive motor may initially accelerate strongly without a risk of jerking in. The tracking-in can thus be particularly fast. In the case of a high difference between the synchronous rotational speed and the engine rotational speed, a small setpoint rotational speed gradient is determined, for example. This makes it possible to approach the synchronous rotational speed with a low acceleration at the end of the meshing. As a result, a sudden meshing, as is often the case with an acceleration of the drive motor with a fixed rotational speed gradient, can be avoided.The method may include a step of determining the synchronous speed. For this purpose, for example, a carcass of the pedal crankshaft can be detected. The synchronous rotational speed can be determined as a function of the wheel speed and optionally a transmission ratio between the drive motor and the freewheel. The transmission ratio can be fixed or, for example, be predefined by a selected gear. The carcass may correspond to a tread frequency. The carcass may be a rotational speed of the pedal crankshaft with which it is driven by the driver.In a further embodiment of the method, it can be provided that the determination of the variable setpoint rotational speed gradient is additionally carried out as a function of at least one actuation of a crankshaft of the bicycle by a user. As a result, a driving behavior of the user can be taken into account when engaging the drive motor. For example, when the bicycle is being driven strongly by the user, the drive motor can accelerate at a greater speed gradient than when the bicycle is being driven weakly. As a result, a driver's wish can also be taken into account when synchronizing the drive motor. Thus, in the case of high driving dynamics, the support can be taken sufficiently quickly by the user. In this case, it can then also be accepted, for example, that a greater jerk occurs in the drive train.In the case of a more moderate driving style, on the other hand, driving comfort and protection of the components of the drive train can be prioritized more strongly.For example, the actuation of the pedal crankshaft can have one or more actuating parameters, such as a speed or rotational speed of the pedal crankshaft. These may also be derivatives or gradients of characteristic variables, such as a rotational speed gradient of the pedal crankshaft. As a result, an acceleration by the driver can also be taken into account and tracked in again more quickly. For example, it can also be ensured in this way that the variable setpoint rotational speed gradient for the drive motor is greater than a rotational speed gradient of the synchronous rotational speed. The rotational speed gradient of the synchronous rotational speed can correspond to the rotational speed gradient of the pedal crankshaft, for example taking into account respective transmission ratios between the pedal crankshaft and the freewheel and alternatively or additionally between the motor shaft and the freewheel. The actuation of the pedal crankshaft may correspond to a driver's wish and a desired driving style. The method can have a step of detecting the actuation, for example by means of a torque sensor and alternatively or additionally a rotational speed sensor.The determination of the variable setpoint rotational speed gradient can be effected as a function of the comparison of the engine rotational speed with the synchronous rotational speed and as a function of the actuation of the pedal crankshaft. A characteristic map for determining the setpoint rotational speed gradient can be obtained, in which two characteristic variables are taken into account. Depending on the selected operating mode, different characteristic maps can be provided.In a further embodiment of the method, it can be provided that the actuation has a pedaling torque introduced by the driver. The pedaling torque may be the only characteristic of the actuation that is taken into account for determining the variable target rotational speed gradient besides the operating mode. However, further characteristic variables, such as a pedaling speed gradient and alternatively or additionally a pedaling torque gradient, can also be taken into account. By taking into account the pedaling torque, a strength of the user's driving can be taken into account to quickly assist the driving motor with a high load on the driver. In the case of a high pedaling torque, for example, a higher setpoint rotational speed gradient is determined than in the case of a low pedaling torque. In addition, a drive torque provided by the drive motor can thus be adapted to a driver torque when the freewheel is engaged and the torque transmission then taking place to the output element. Thus, an incongruity between the assist torque and the drive torque after engagement has taken place can be avoided.In a further embodiment of the method, it can be provided that the control of the drive motor as a function of the variable setpoint rotational speed gradient comprises a comparison of an actual rotational speed gradient of the drive motor and the variable setpoint rotational speed gradient. As a result, a regulation for the setpoint rotational speed gradient can be provided. The drive motor can thus be controlled particularly precisely for following the variable setpoint rotational speed gradient. The method can have a step of determining an actual rotational speed gradient. The actual speed gradient may be a current speed gradient of the drive motor. The method can have a step of comparing the actual rotational speed gradient of the drive motor with the variable setpoint rotational speed gradient. A result of the comparison may be a difference. For example, the drive motor is controlled as a function of the difference between the actual rotational speed gradient of the drive motor and the variable setpoint rotational speed gradient. For example, an engine torque or an engine speed can thus be regulated as a function of the result of the comparison. For example, a motor current can then be correspondingly regulated and alternatively or additionally a required torque or a required rotational speed can be predefined for the motor. The determination of the actual rotational speed gradient can be effected by a sensor detection or else be derived from a control variable or state variable of the drive motor, such as, for example, a power supply of the drive motor.In a further embodiment of the method, it can be provided that the control of the drive motor as a function of the variable setpoint rotational speed gradient comprises a presetting of an engine torque as a function of the variable setpoint rotational speed gradient. This may be a pilot control for the drive motor. This presetting can be effected independently of a comparison of the actual rotational speed gradient of the drive motor and the variable setpoint rotational speed gradient. For example, the drive motor can be pilot controlled. For example, a setpoint torque can be predefined for the drive motor as a function of the present value of the variable setpoint rotational speed gradient. This specification can be made, for example, on the basis of a table. The specification can also correspond linearly to the setpoint rotational speed gradient, for example. The specification can be made independently of an actual rotational speed gradient. For example, the specification can correspond to a specific power supply of the drive motor. This allows particularly rapid control. In addition, a particularly fast approximation to the current value of the variable setpoint rotational speed gradient and alternatively or additionally to the synchronous rotational speed can thus be made possible. Depending on the load actually applied, for example due to an overloading, a rotational speed gradient actually achieved in this way can deviate from the specification.The pilot control and the regulation can also be combined. For example, a torque for the drive motor can be predefined as a function of the variable setpoint rotational speed gradient. For example, the torque or the rotational speed can linearly correspond to the variable setpoint rotational speed gradient. In addition, this torque can be combined with a further torque which is determined as a function of a comparison of the actual rotational speed gradient of the drive motor and the variable setpoint rotational speed gradient. For example, the further torque can be added to the torque of the pilot control, wherein the further torque can linearly correspond to the difference between the actual rotational speed gradient and the variable setpoint rotational speed gradient. Thus, firstly a very fast approach to the setpoint rotational speed gradient and alternatively or additionally to the synchronous rotational speed can take place and then a final meshing can take place very gently.The control of the drive motor can be a purely pilot control. The current determined value of the variable setpoint rotational speed gradient can correspond, for example, to a power supply or an engine torque with which the drive engine is controlled. For this purpose, a tabular relationship can be stored, for example. Such a control can be simple and robust. Alternatively or additionally, the control of the drive motor can have a speed gradient regulation. In this case, the current determined value of the variable setpoint rotational speed gradient is compared with a current actual rotational speed gradient. As a function thereof, the motor torque or the power supply of the drive motor is predetermined. The desired setpoint rotational speed gradient can thus be maintained precisely. In the combination with the pilot control, the desired setpoint rotational speed gradient can be reached particularly quickly by the drive motor. In a further variant, a derivative of the setpoint rotational speed gradient is also taken into account in the pilot control. For example, a rate of change of the variable target speed gradient is determined. The current determined value of the rate of change of the variable setpoint rotational speed gradient can correspond, for example, to a power supply or an engine torque with which the drive engine is controlled. The different variables for the power supply or the engine torque can be combined additively in the different variants, for example.For example, the following variants can be used for regulating and alternatively or additionally pilot controlling the drive motor in order to bring an engine speed close to a synchronous speed of the freewheel. A speed control, for example a PI control, can be provided, which operates as a function of a difference between the setpoint speed and the actual speed. Alternatively or additionally, a speed gradient control, for example a PI control, can be provided, which operates as a function of a difference between the setpoint speed gradient and the actual speed gradient. A speed gradient pilot control in combination with the speed gradient control can be provided. The rotational speed gradient pilot control can specify, for example, a minimum value for the setpoint rotational speed gradient. This minimum value can be predefined, for example, by a minimum current supply to the drive motor during the meshing process. For example, a value of the speed gradient control is added to this minimum value in order to control the drive motor. A pilot control for a gradient of the rotational speed gradient, i.e. for example a second derivative of the rotational speed, can be provided. The pilot control for the gradient of the rotational speed gradient can be provided in combination with the rotational speed gradient control. The pilot control for the gradient of the rotational speed gradient can also be provided in combination with the rotational speed gradient control and the rotational speed control.The speed gradient control without further controls and controls combined therewith can be implemented particularly easily. An exact desired rotational speed at a specific point in time may be difficult to determine, because this may result from a carcass and a current transmission ratio. Drivers usually run out of round. Due to the out-of-round stepping, there is a constantly changing carcass of the pedal crankshaft. If the setpoint rotational speed is calculated as a function of the pedal speed of the crankshaft, a continuously changing setpoint rotational speed is also obtained therewith. In the case of the speed gradient control, however, these changes have little or no influence. In addition, the gradient of the rotational speed gradient can physically correspond to a derivative of an engine torque. Frequently, interfaces of a motor torque controller of the drive motor do not have any setting of a specification for a change in the motor torque. In this respect, a modification of the engine control may be necessary for implementing a control or regulation of the gradient of the rotational speed gradient.A second aspect relates to a control device for a drive motor of a bicycle. The drive motor can be mechanically operatively connected to an output element of the bicycle by means of a freewheel. The control device may be configured to perform the method according to the first aspect. Respective further features, embodiments and advantages can be gathered from the descriptions of the first aspect. Conversely, features, embodiments and advantages of the second aspect also represent features, embodiments and advantages of the first aspect. The control device can have a microprocessor, for example. The control device can be formed as an inverter. The control device can be configured to receive a selected operating mode, to determine a variable setpoint rotational speed gradient for the drive motor and to control the drive motor as a function of the determined setpoint rotational speed gradient in order to approximate a rotational speed of the motor to a synchronous rotational speed of the freewheel. The control device may be configured to receive sensor signals from sensors of the bicycle. The control device may be configured to control a power supply of the drive motor.A further aspect relates to a drive train for a bicycle having a control device, a drive motor and an output element. The control device can be designed as a control device according to the second aspect. Respective further features, embodiments and advantages can be gathered from the descriptions of the second aspect. Conversely, features, embodiments and advantages of the further aspect also represent features, embodiments and advantages of the second aspect. The drive train can have a sensor device. The sensor device can be designed to detect state variables described above. For example, the sensor device may be designed to detect a rotational speed of the pedal crankshaft. For this purpose, the sensor device can have a rotational speed sensor.A third aspect relates to a bicycle. The bicycle includes a drive motor, an output member, and a freewheel. The drive motor is mechanically operatively connectable to the output element of the bicycle by means of the freewheel. In addition, the bicycle includes a control device. The control device can be designed as a control device according to the second aspect. Respective further features, embodiments and advantages can be gathered from the descriptions of the second aspect. Conversely, features, embodiments and advantages of the third aspect also represent features, embodiments and advantages of the second aspect. The control device can be designed to determine a variable setpoint rotational speed gradient for the drive motor as a function of a selected operating mode and to control the drive motor as a function of the determined variable setpoint rotational speed gradient in order to approximate a rotational speed of the motor to a synchronous rotational speed of the freewheel. The control device may receive the operating mode from, for example, an operating element of the bicycle, at which the operating mode is selectable by a user. The bicycle can also have the previously described drive train and alternatively or additionally the previously described sensor device.Brief Description of the FiguresFIG. 1 schematically illustrates a method of controlling a drive motor of a bicycle to approximate a motor speed to a synchronous speed of a freewheel. FIG. 2 is a graph illustrating a progression of the synchronous rotational speed and the engine rotational speed, wherein the engine is controlled by the method according to FIG. 1. FIG. 3 is a graph illustrating a drive torque by the user and an engine torque for the engine speed curve illustrated in FIG. 2. FIG. 4 illustrates in a diagram the state of the freewheel corresponding to the curve of the engine speed and the synchronous speed illustrated in FIG. 2.Detailed Description of EmbodimentsFIG. 1 illustrates a method of controlling a drive motor of a bicycle. The example described herein is based on torque control of the drive motor, and in other embodiments, the method is based on speed control. The drive motor is mechanically operatively connectable to an output element of the bicycle by means of a freewheel. At this freewheel, a driving force introduced by a cyclist on a pedal crank shaft of the bicycle is also transmitted to the output element. In one embodiment, a motor shaft of the drive motor can be operatively mechanically connected to the pedal crankshaft by means of the freewheel. A rotational speed of the drive motor must therefore be synchronized with a rotational speed of the pedal crankshaft for providing a motor-driven drive force and for assisting the cyclist with the drive motor. This is also referred to as meshing, as a result of which the freewheel then changes to its blocking state.The method comprises, as a first step 8, selecting an operating mode. In the embodiment described herein, an ECO mode and a race mode may be selected. The method comprises, as a second step 10, determining a variable setpoint rotational speed gradient for the drive motor. This step takes place when a rotational movement of the pedal crankshaft corresponding to a forward travel is detected and alternatively or additionally a selection of the operating mode has taken place. The determination of the variable setpoint rotational speed gradient takes place as a function of a comparison of the engine rotational speed with a synchronous rotational speed and as a function of the selected operating mode. The greater a difference of the engine speed from the synchronous speed, the greater the variable setpoint speed gradient is determined, wherein the control is more aggressive in the race mode than in the eco mode. Under otherwise equal conditions, the target speed gradient is higher in the race mode than in the eco mode. The synchronous rotational speed is the rotational speed which the motor shaft must have for meshing. The synchronous rotational speed results from the rotational speed of the pedal crankshaft multiplied by a current transmission ratio between the pedal crankshaft and the motor shaft. In the example shown, the determination of the variable setpoint rotational speed gradient takes place at discrete intervals. In other embodiments, the determination of the variable setpoint rotational speed gradient takes place continuously or at a frequency of a control device carrying out the determination. In a step 12, the drive motor is controlled as a function of the determined variable setpoint rotational speed gradient in order to bring a rotational speed of the motor closer to a synchronous rotational speed of the freewheel.In FIG. 2, the synchronous speed is plotted with a line 20 over time for a particular selected operating mode. Furthermore, the engine speed is plotted with a line 22 over time. A gradient of the line 22 or of the engine speed thus corresponds to the speed gradient of the drive engine. In a first region 30, the drive motor is stationary, since the rotational movement of the pedal crankshaft has not yet been detected. A first value of the variable setpoint rotational speed gradient is therefore determined to be zero in the first region 30. In a second range 32, a second value for the variable setpoint rotational speed gradient is determined and the drive motor is controlled accordingly. Due to the large difference between an actual rotational speed of the drive motor and the synchronous rotational speed, a high value is predefined for the setpoint rotational speed gradient for the drive motor, which can be seen on the basis of the strong gradient of the line 22 in the second region 32. The engine speed approaches the synchronous speed as quickly. At the end of the second range 32, a third value for the variable setpoint rotational speed gradient is determined in a third range 34 adjoining the second range 32. This third value of the variable setpoint rotational speed gradient is smaller, since a distance of the engine rotational speed from the synchronous rotational speed is now smaller. This can be seen on the basis of the mean gradient of the line 22 in the third region 34. Thus, a quick approach to the synchronous rotational speed can continue to take place, wherein a risk for a jerky engagement, for example due to a slowing of the pedaling by the cyclist, is low. At the end of the third range 34, a fourth value for the variable setpoint rotational speed gradient is determined in a fourth range 36 following the third range 34. This fourth value of the setpoint rotational speed gradient is once again smaller, since a distance of the engine rotational speed from the synchronous rotational speed is now even smaller. This can be seen on the basis of the small gradient of the line 22 in the fourth region 36. Thus, a gentle approach to the synchronous rotational speed can continue to be effected in order to reliably prevent a sudden meshing. Depending on the selected operating mode, the values are different.In a fifth range 38 adjoining the fourth range 36, the rotational speed at which the freewheel locks is reached by the drive motor. In the fifth range 38, the synchronous rotational speed is thus reached. In FIG. 4, a line 40 plots a state of the freewheel over time, wherein the freewheel is in its release state at a value 42 and in its blocking state at a value 44. In the first four regions 30, 32, 34, 36, the freewheel is in its release state. In the fifth region 38, the freewheel switches to its blocking state. The tracking thus effected is detected and the method according to FIG. 1 is ended. The drive motor is then controlled with a conventional follow-up control in order to maintain the synchronous rotational speed despite varying carcass of the pedal crankshaft, which can be seen in FIG. 2 by means of the wavy line 20.Alternatively or additionally to the determination of the variable target speed gradient as a function of the comparison of the engine speed with the synchronous speed, in another embodiment the variable target speed gradient is determined as a function of at least one actuation of a pedal crank shaft of the bicycle by a user in step 10, wherein the selected operating mode is also taken into account. In this case, as actuation, a pedaling torque of the cyclist, which is introduced at the pedal crankshaft, is detected. At a higher pedaling torque, a higher value is then specified for the setpoint rotational speed gradient than at a lower pedaling torque for the drive motor.FIG. 3 illustrates the torque control of the drive motor in step 10. a line 50 plots a torque requested by the cyclist over time, which results from the synchronous rotational speed and alternatively or additionally the pedaling torque. A line 52 plots a torque generated by the drive motor over time, which torque follows a torque specification for the drive motor at least in the first four regions 30, 32, 34, 36. In the first range 30, a torque of zero is predefined for the motor. In the second region 32, a highest torque is predefined, so that the drive motor can achieve the high setpoint rotational speed gradient in the second region 32 and thus a high acceleration. In the third range 34, an average torque is predefined so that the drive motor reaches the average setpoint rotational speed gradient in the third range 32 and thus an average acceleration. A low torque is predefined in the fourth region 36 so that the drive motor reaches the low setpoint rotational speed gradient in the fourth region 32 and thus a low acceleration. In the fifth region 38, there is a sudden increase in engine torque. This sudden increase is not caused by a high torque specification, but rather by the freewheel changing into its locked state. An acceleration of the drive motor then requires a substantially higher torque and also a holding of the synchronous rotational speed requires a higher torque, since the drive motor now drives the bicycle with it because of the closed freewheel. This sudden increase is detected and used to detect the change of the freewheel to the locked state and to end the control of the drive motor using the method according to FIG. 1.FIG. 3 also illustrates for the second region 32 that the torque specification for the drive motor is composed of two components. The control of the drive motor as a function of the variable setpoint rotational speed gradient comprises a comparison of an actual rotational speed gradient of the drive motor and the variable setpoint rotational speed gradient. The result of this comparison is a difference. Depending on this difference, a control value for the torque specification is calculated. This portion of the torque specification is illustrated in FIG. 3 with the region 54. By means of the regulation, the drive motor can be controlled particularly precisely in order to maintain the determined variable setpoint rotational speed gradient. The control of the drive motor as a function of the variable setpoint rotational speed gradient additionally comprises a presetting of a motor torque as a function of the variable setpoint rotational speed gradient. Depending on the variable setpoint rotational speed gradient, a pilot control value for the torque specification is calculated. In the example shown, the pilot portion linearly corresponds to the current value of the variable target speed gradient. In the case of a high setpoint rotational speed gradient, a high pilot control value is calculated accordingly, and in the case of a low setpoint rotational speed gradient, a low pilot control value is calculated. This portion of the torque specification is illustrated in FIG. 3 with the region 56. A total torque command is calculated as the sum of the pilot value and the control value. The variable setpoint rotational speed gradient can be reached particularly quickly by the drive motor by the pilot control value. By the combination of regulation and pilot control, the variable setpoint rotational speed gradient can be achieved particularly quickly by the drive motor and can then be maintained precisely. In another embodiment, the torque specification only has the control value. The drive motor is then only torque-controlled. In yet another embodiment, the torque specification only has the pilot control value. The drive motor is then only torque-controlled.Reference numerals denote reference numerals8 First step 10 Second step 12 Step 20 Line / synchronous rotational speed 22 Line / engine rotational speed 30 First region 32 Second region 34 Third region 36 Fourth region 38 Fifth region 40 Line / state of free-wheeling 42 Value / release state 44 Value / lock state 50 Line / requested torque 52 Line / generated engine torque 54 Proportion of control value torque specification 56 Proportion of pilot value torque specification

Claims

Method for controlling a drive motor of a bicycle, wherein the drive motor is mechanically operatively connectable to an output element of the bicycle by means of a freewheel, and wherein the method comprises at least the following steps: - selecting (8) an operating mode for the drive motor from at least a first operating mode and a second operating mode; - determining (10) a variable setpoint rotational speed gradient for the drive motor depending on the selected operating mode; and - controlling (12) the drive motor depending on the determined variable setpoint rotational speed gradient in order to bring a motor rotational speed (22) close to a synchronous rotational speed (20) of the freewheel.Method according to claim 1, characterized in that the selected operating mode is at least one operating mode from the following list of operating modes: - an ECO mode; - a race mode; - a hill-climbing mode; - a maximum support mode; and - a sliding aid mode.Method according to Claim 1 or 2, characterized in that the determination (10) of the variable setpoint rotational speed gradient is additionally carried out as a function of a comparison of the engine rotational speed (22) with the synchronous rotational speed (20).Method according to one of the preceding claims, characterized in that the determination (10) of the variable setpoint rotational speed gradient is additionally carried out as a function of at least one actuation of a crankshaft of the bicycle by a user.Method according to Claim 4, characterized in that the actuation has a pedaling moment introduced by the driver.Method according to one of the preceding claims, characterized in that the control (12) of the drive motor as a function of the variable setpoint rotational speed gradient comprises a comparison of an actual rotational speed gradient of the drive motor and the variable setpoint rotational speed gradient.Method according to one of the preceding claims, characterized in that the control (12) of the drive motor as a function of the variable setpoint rotational speed gradient comprises a presetting of an engine torque (52) as a function of the variable setpoint rotational speed gradient.Control device for a drive motor of a bicycle, wherein the drive motor is mechanically operatively connectable to an output element of the bicycle by means of a freewheel, wherein the control device is configured to receive a selected operating mode of at least a first selectable operating mode and a second selectable operating mode, to determine (10) a variable setpoint rotational speed gradient for the drive motor depending on the selected operating mode, and to control (12) the drive motor depending on the determined setpoint rotational speed gradient in order to bring a motor rotational speed (22) close to a synchronous rotational speed (20) of the freewheel.A bicycle having a drive motor, an output element and a freewheel, wherein the drive motor is mechanically operatively connectable to the output element of the bicycle by means of the freewheel, an operating device which is designed for selecting an operating mode for the drive train, and a control device, wherein the control device is designed to determine (10) a variable setpoint rotational speed gradient for the drive motor as a function of a selected one of at least a first selectable operating mode and a second selectable operating mode, and to control (12) the drive motor as a function of the determined setpoint rotational speed gradient in order to approximate a rotational speed (22) to a synchronous rotational speed (20) of the freewheel.

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