Drive system which actuates a second electric motor in order to generate a counteractive torque when a pushing aid is activated, and control method

Abstract

In particular, the invention relates to a drive system for an electric bicycle (F), said drive system being provided with control electronics (8) for controlling first and second electric motors (11, 12) and for activating a pushing aid. When the pushing aid is activated, a torque is transmitted from the first electric motor (11) to the output shaft (2) while the electric bicycle (F) is pushed by a user. Additionally, the second electric motor (12) is actuated in order to generate a torque which counteracts a rotation of the drive shaft (1).

Description

[0001] Drive system with control of a second electric motor for generating a counteracting torque when the push aid is activated and control method

[0002] Description

[0003] The proposed solution concerns in particular a drive system for an electric bicycle.

[0004] It is known to provide a push assist function via an electric motor drive unit of an electric bicycle, i.e., a so-called e-bike or pedelec, to assist a user when pushing the electric bicycle or starting off, for example, on an incline. The push assist function is typically triggered by an operating signal, for example, by operating a control element on the handlebars of the electric bicycle. The maximum speed achievable with the push assist function is set by the drive unit's control electronics and is usually limited by law. A maximum speed of 3 to 6 km / h is typically achieved with a push assist function.

[0005] When the push assist is activated, it is not uncommon for the drive shaft and pedals to be driven indirectly via friction torque, thus disturbing the user pushing the electric bike who is walking next to the electric bike.

[0006] Against this background, a drive system for an electric bicycle is proposed, in particular, which comprises two first and second electric motors, at least one planetary gear system, and control electronics, wherein the control electronics are provided for controlling the first and second electric motors and for activating a pushing aid. With the pushing aid or pushing aid function activated, a torque is transmitted from the first electric motor to the output shaft when a user pushes the electric bicycle. In a proposed drive system, the control electronics are further configured, when the pushing aid is activated, to control the second electric motor to generate a torque that counteracts a rotation of a drive shaft, to which a drive force applied by muscle power can be introduced in the drive system with the aid of at least one pedal crank.

[0007] For riding an electric bicycle, a proposed drive system can adjust a gear ratio of the planetary gear using the first and second electric motors (preferably continuously). The drive shaft and an output shaft of the drive system, provided for transmitting the drive power to a wheel of the electric bicycle, are coupled to one another via the at least one planetary gear. To drive the electric bicycle with a motor-generated assist force, which can be transmitted to the output shaft in addition to the drive force applied by human power, a torque generated by the first electric motor can be transmitted at least partially to the output shaft when riding the electric bicycle.The proposed solution is based on the basic idea of ​​utilizing such a design of the drive system with the first and second electric motors in order to prevent any disruptive co-rotation of the drive shaft and, in particular, of the associated cranks and pedals when the push assist is activated. As explained in the introduction, a push assist is particularly active when the electric bicycle is being pushed by a user. The drive system then provides assistance to drive the electric bicycle up to a predetermined maximum speed (e.g., 6 km / h). To provide this assistance in a forward direction, driving a first rotor shaft by the first electric motor is sufficient. In the proposed drive system, the second electric motor is used to generate a torque that counteracts any co-rotation of the drive shaft.

[0008] In particular, in this context, the control electronics are configured to control the second electric motor, when the pushing aid is activated, to generate a torque that counteracts a rotation of the drive shaft caused by the purely motor-driven drive of the output shaft. The second electric motor is thus controlled to generate a torque that precisely counteracts a rotation of the drive shaft caused by what is known as dragging of the drive shaft, which thus results, for example, from the fact that, due to friction, at least part of the (pushing aid) torque applied by the first electric motor is transmitted to the drive shaft via the planetary gear. The control electronics can be coupled to at least one sensor device of the drive system for detecting a rotational speed of the drive shaft.In such an embodiment, for example, the control electronics are configured to control the second electric motor to generate the torque counteracting the rotation of the drive shaft as a function of at least one sensor signal from the at least one sensor device. The generation of the torque by the second electric motor, in particular its magnitude, is thus dependent on at least one measured value from the at least one sensor device. For example, it can be provided that the control electronics control the second electric motor with the aim of ensuring that the rotational speed of the drive shaft is zero and that the drive shaft is therefore stationary. The at least one sensor signal provided by the at least one sensor device can thus be indicative, in particular, of the rotational speed of the drive shaft.A value for the (current) rotational speed of the drive shaft signaled by the sensor signal that deviates from zero and thus indicates a rotation of the drive shaft can thus serve as a control variable for the control electronics.

[0009] In principle, the at least one sensor device can comprise a speed sensor via which a speed (and thus an equivalent rotational speed) of the drive shaft can be measured.

[0010] In one embodiment, the control electronics comprise a controller, in particular a PI controller or PID controller, for controlling the torque to be generated by the second electric motor when the pushing aid is activated. The control electronics therefore implement a control system with the goal of ensuring that the drive shaft rotates by a maximum of a tolerated amount or not at all when the pushing aid is activated. For example, a setpoint for the rotational speed of the drive shaft can be stored as a reference variable for the controller of the control electronics. Such a setpoint can then be zero, for example, and thus correspond to 0 revolutions of the drive shaft or a standstill of the drive shaft.

[0011] In one design variant, the control electronics are configured to limit the torque to be generated by the second electric motor when the pushing assistance is activated to a maximum value. Limiting it to a maximum value, e.g. stored in a memory of the control electronics, can offer the advantage that the second electric motor is not or no longer controlled if it must be assumed that the drive shaft is being turned intentionally or necessarily even when the pushing assistance is activated. For example, when the pushing assistance is activated it should still be possible for a pedal crank connected to the drive shaft to be changed in its position, for example because a user wants to reposition a pedal connected to the pedal crank or the pedal crank or a pedal attached to it hits an obstacle.In such a case, the second electric motor would have to generate a comparatively large torque to counteract rotation of the drive shaft. By setting a maximum value for the torque to be generated when the push assist is activated, it is possible to ensure that the second electric motor does not counteract or even prevents rotation of the drive shaft when the push assist is activated if the user desires rotation of the drive shaft or if it could be advantageous.

[0012] For example, in this context the control electronics are configured, when the pushing aid is activated, to only (continue to) control the second electric motor to generate a torque that counteracts a rotation of the drive shaft if the torque to be generated does not exceed the maximum value. This includes, in particular, that the control electronics can be configured to at least temporarily suspend the control of the second electric motor when the pushing aid is activated and the torque already generated by the second electric motor if the torque to be generated would exceed the maximum value. Consequently, a torque counteracting a rotation of the drive shaft is not (or no longer) generated by the second electric motor when the pushing aid is activated in order to bring the drive shaft to a standstill if the torque required for this exceeds a maximum value.In the case of control electronics comprising a controller, a controller output can be limited to a small torque, i.e., a torque below the maximum value, for this purpose. This means that larger forces on the drive shaft and in particular on the pedal cranks connected to it, for example for a position correction by a user or a collision with an obstacle, are not compensated for and rotation of the drive shaft is permitted. The control device can therefore be configured not to apply any counteracting torque through the second electric motor if a crank force (and resulting crank torque) exceeding a threshold value is applied externally to the pedal crank(s), in particular via at least one pedal connected to it, and the drive shaft is rotated or accelerated as a result.This takes into account that such a crank force is applied by a force acting on the pedal crank(s) by a user (e.g., to correct the position of the pedals) or by an obstacle, and that any resulting rotation of the drive shaft should not be counteracted. The maximum value for limiting the control of the second electric motor when the push assist is activated can be specified, for example, by a torque value for a (second) rotor shaft to be driven by the second electric motor or by a torque value for the pedal crank(s) or the drive shaft.For example, it can be determined that if the crank force applied to the pedal crank or the drive shaft exceeds a threshold value, for example 10 Nm, the second electric motor should no longer be activated to generate a counteracting torque, since it can then be assumed that a force acting on the drive shaft is attributable to a user or an obstacle. Such a threshold value can be converted into a corresponding torque value for the rotor shaft to be driven by the second electric motor, which is stored in the control electronics for evaluation and, for example, limits the controller output. In principle, particularly in this context, it can be provided that a torque sensor is part of the drive system, via which a torque applied externally to the drive shaft can be measured in order to determine whether or not a counteracting torque should be applied by the second electric motor.

[0013] For example, the maximum value can be specified by a torque value in the range of 0.15 to 0.4 Nm for the rotor shaft to be driven by the second electric motor.

[0014] Part of the proposed solution is also a method for controlling a drive system of an electric bicycle. The drive system to be controlled comprises at least the following:

[0015] - a pedal crank connected to a drive shaft of the drive system for applying a driving force for driving the electric bicycle by means of muscle power,

[0016] - an output shaft that transmits the drive power to a wheel of the electric bicycle,

[0017] - at least one planetary gear, the transmission ratio of which can be adjusted by means of first and second electric motors and via which the input shaft and the output shaft are coupled to one another, wherein a torque generated by the first electric motor can be transmitted at least partially to the output shaft.

[0018] The drive system features an activatable push assist, which allows torque to be transmitted from the first electric motor to the output shaft when the user pushes the electric bicycle. The proposed method now provides for the second electric motor to be activated after the push assist is activated to generate a torque that counteracts rotation of the drive shaft.

[0019] An embodiment variant of a proposed control method can be implemented, in particular, by an embodiment variant of a proposed drive system. Accordingly, the advantages and features of embodiment variants of a proposed drive system explained above and below also apply to embodiment variants of a proposed control method, and vice versa.

[0020] Furthermore, a computer program product is proposed that contains instructions that, when executed by at least one processor of a control unit of a drive system of an electric bicycle comprising an electric motor drive unit, cause the at least one processor to execute an embodiment variant of a proposed control method. The at least one processor can thus be part of control electronics implemented with the control unit, via which, when the push assistance on the electric bicycle is activated, a second electric motor of the drive system can be controlled to generate a torque that counteracts the rotation of a drive shaft.

[0021] The attached figures illustrate possible embodiments of the proposed solution.

[0022] Here we show:

[0023] Figure 1 shows a 2D design for an electromotive

[0024] Drive unit of a variant of a proposed drive system;

[0025] Figure 2 shows schematically and in side view an electric bicycle with a proposed drive system;

[0026] Figure 3 shows a flow chart for an embodiment of a proposed control method.

[0027] Figure 2 illustrates an electric bicycle F with a drive system comprising an electric motor drive unit 10. The electric bicycle F has a frame 110, which here, for example, comprises a top tube, a down tube, and a seat tube, and to which the drive unit 10 is attached in the region of an intersection point of the seat tube and the down tube. Control electronics 8 and a sensor device 115 are part of the drive unit 10. Electric motors 11 and 12 (cf. Figure 1) of the drive unit 10 can be controlled via the control electronics 8, in particular to specify the level of an externally generated assist force for driving the electric bicycle F. The sensor device 115 is provided for the sensory detection of a rotational speed of the drive shaft (bottom bracket shaft) 1 of the drive unit 10. For this purpose, the sensor device 15 can comprise a rotational speed sensor, via which the rotational speed of the bottom bracket shaft 1 can be measured.A driver of the electric bicycle F can apply a driving force to the drive shaft 1 by muscle power via a pair of cranks 1A connected thereto and pedals provided thereon, to drive the electric bicycle F. Optionally, the sensor device 115 can also be provided for the sensory detection of a torque introduced at the drive shaft 1 by muscle power and can be designed, for example, with a torque sensor and / or a position sensor.

[0028] Via a belt or a chain 213 as a power transmission element, an output element of the drive unit A, for example a hollow output shaft 2 mounted coaxially to the bottom bracket shaft 1 (see Figure 1), is connected to a rear wheel 112 of the electric bicycle F in order to be able to drive the electric bicycle F. Assigned to this rear wheel 112 is, for example, a wheel sensor 114 for determining a driving speed of the electric bicycle F. Of course, the wheel sensor 114 can instead be provided on a front wheel 111 of the electric bicycle F.

[0029] The drive system of the electric bicycle F further comprises an operating unit 102. The operating unit 102 is, for example, attached in the area of ​​a handlebar of the electric bicycle F in Figure 2 and is connected to the control electronics 8 of the drive unit 10, typically via one or more cables. A user input can be detected via the operating unit 102 and used to control the drive unit 10. For example, the operating unit 102 comprises at least one display to inform a user of the electric bicycle F about

[0030] - the current operating status of the drive unit F, for example with regard to a set support level,

[0031] - a charge state of an energy storage device 9 which supplies the drive unit 10 with electrical energy and which, for example, contains at least one (rechargeable) battery, and / or - a set gear which specifies the transmission ratio with which a drive torque introduced by muscle power at the drive shaft 1 is transmitted to the output shaft 2 of the drive unit 10.

[0032] Figure 1 shows a 2D design for the drive unit 10 of Figure 2 comprising two electric motors 11 and 12.

[0033] The drive unit 10 has the drive shaft 1 and the output shaft 2, both of which are rotatably mounted in a housing 25 of the drive unit 10. The drive shaft 1 extends through the housing 25 and is connected on each side to a pedal crank 1A, via which a rider of the electric bicycle F can apply drive force using muscle power. The output shaft 2 protrudes from the housing 25 on only one side and is connected to a sprocket or a toothed belt pulley to drive the rear wheel 112 of the electric bicycle F from there.

[0034] The drive unit 10 has a first electric motor 11 with a first rotor shaft 3 and a second electric motor 12 with a second rotor shaft 4. The two electric motors 11 and 12 are connected via the control electronics 8 and form a continuously variable electric actuator. The control electronics 8 is also connected to the energy storage device 9. This allows the output shaft 2 to be driven purely electrically via the first electric motor 11. The energy storage device 9 can also be used as a braking energy storage device when braking power flows into the drive unit 10 at the output shaft 2.

[0035] The input shaft 1, the output shaft 2, and the two rotor shafts 3 and 4 are coupled via a multi-stage planetary gear 15, which has several gear stages with a first degree of freedom and at least one planetary gear stage 16 with a second degree of freedom. The gear stages here are designed as spur gear stages. However, toothed belt gear stages are also conceivable. The present three-shaft planetary gear stage 16 comprises a sun gear 17, a ring gear 18, and a planet carrier 19 with several planetary gears 20 mounted on planetary gear pins.

[0036] The elements of the drive unit 10 are distributed here, by way of example, across three shaft trains 21, 22, and 23, all of which are arranged parallel to one another within a space defined by the housing 25. The drive shaft 1, the output shaft 2, and the second rotor shaft 4 of the second electric motor 12 are arranged coaxially on the first shaft train 21. The three-shaft planetary gear stage 16 of the multi-stage planetary gear 15 is arranged on the second shaft train 22. The first rotor shaft 3 of the first electric motor 11 is arranged on a third shaft train 23. On the first shaft train 21, the outer (hollow) output shaft 2 encloses the inner drive shaft 1 on one side of the housing 25, and the second rotor shaft 4 encloses the drive shaft 1 on the other side of the housing 25.

[0037] Four gear stages 31 to 34 designed as spur gear stages serve to kinematically couple the elements of the drive unit 10, which are distributed across the three shaft trains 21, 22, and 23 and housed in the housing 25. The input shaft 1 on the first shaft train 21 is connected via a first spur gear stage 31 to a first coupling shaft 5 on the second shaft train 22. The output shaft 2 on the first shaft train 21 is connected via a second spur gear stage 32 to a second coupling shaft 6 on the second shaft train 22. The second rotor shaft 4 of the second electric motor 12 on the first shaft train 21 is connected via a third spur gear stage 33 to a third coupling shaft 7 on the second shaft train 22. This third coupling shaft also carries the sun gear 17.The first rotor shaft 3 of the first electric motor 11 on the third shaft train 23 is connected via a fourth spur gear stage 34 to the ring gear 18 of the planetary gear stage 16 on the second shaft train 22. On the second shaft train 22, the first coupling shaft 5 is connected to the planet carrier 19, the second coupling shaft 6 is connected to the ring gear 18, and the third coupling shaft is connected to the sun gear 17 of the planetary gear stage 16. Since the first rotor shaft 3 of the first motor 11 is connected to the ring gear 18 and thus to the output shaft 2, the drive unit 10 shown as an example has an output-side power split.

[0038] The first spur gear stage 31 increases the speed of the input shaft 1 to an absolute speed that is approximately three times higher than the first coupling shaft 5, which is connected to the second coupling shaft 6 via the planetary gear stage 16. The speed of the second coupling shaft 6 is transmitted to a speed of the output shaft 2 that is approximately 30% lower, e.g., lower, via the transmission ratio of the second spur gear stage 32.

[0039] In Figure 1, five arrangement levels 35, 36, 37, 38, and 39 are marked, the numbers of which increase in an axial direction 30. The axial direction 30 points from the point where the output shaft 2 exits the housing 25 into the housing 25.In Figure 1 it can be seen that the second spur gear stage 32 lies in the first arrangement plane 35 and that the planetary gear stage 16 and the fourth spur gear stage 34 lie in the second arrangement plane 36, which is offset in the axial direction 30 parallel to the first arrangement plane 35, and that the first spur gear stage 31 lies in a third arrangement plane 37, which is also offset in the axial direction 30 with respect to the second arrangement plane 36, and that the third spur gear stage 33 lies in a fourth arrangement plane 38, which is also offset in the axial direction 30 with respect to the third arrangement plane 37, and that the two electric motors 11 and 12 lie in a fifth arrangement plane 39, which is also offset in the axial direction 30 with respect to the fourth arrangement plane 38.

[0040] The planetary gear stage 16 and the fourth spur gear stage 34 can be located in the same second arrangement plane 36 because the gear of the fourth spur gear stage 34 on the second shaft train 22 has a larger pitch circle radius than the ring gear 18 of the three-shaft planetary gear stage 16. As a result, the ring gear 18 finds space within this gear of the fourth spur gear stage 34 in the second arrangement plane 36.

[0041] This axial arrangement of the spur gear stages 31, 32, 33 and 34 in the vicinity of the planetary gear stage 16 on the second shaft train 22, in conjunction with the illustrated distribution of the drive elements between the three shaft trains 21, 22 and 23, results in an extremely compact multi-stage planetary gear 15.

[0042] In the first arrangement level 35 with the second spur gear stage 32, a freewheel 40 is located between the input shaft 1 and the output shaft 2, for example in the form of a sprag type freewheel. The freewheel 40 can connect the input shaft 1 directly to the output shaft 2, particularly at a maximum gear ratio. The freewheel 40 also serves as overload protection for the drive unit 10 and, on the other hand, guarantees basic mechanical functionality of the drive unit 10 in the event of problems in the electrical system, for example, a voltage drop, or problems in the control / regulation, for example, caused by a failure of one or more sensors of the sensor device 115.

[0043] To facilitate the assembly of the remaining elements of the drive system 10 and their storage in the housing 25, the housing 25 has four housing parts. The housing 25 consists of a main housing 26 with a center web 27 connectable or connected thereto, a motor cover 28 connectable or connected to the main housing 26 on the side of the fifth arrangement level 39, and a gear cover 29 connectable or connected to the main housing 26 on the side of the first arrangement level 35, through which the output shaft 2 protrudes from the housing 25. In the drive unit 10 shown, the control electronics 8 additionally integrates a push-assist control. The drive system can thus be operated in a push-assist mode, for example, by generating an operating signal on the operating unit 102.A user can therefore activate a push assist function of the drive system via an operating signal, so that the user is assisted by the electric motor drive unit 10 when pushing the electric bicycle F. For this purpose, the control electronics 8 controls the first electric motor 10 to drive the electric bicycle F up to a speed of 6 km / h.

[0044] During the rotation of the output shaft 2, driven by the first electric motor 11, friction may cause at least a portion of the torque generated by the first electric motor 11 for the push assist to be transferred to the drive shaft 1 via the planetary gear 15, causing the drive shaft to be dragged along, thus also rotating (at a lower rotational speed). If a user pushing the electric bicycle F runs alongside the electric bicycle F, this co-rotation of the drive shaft 1 and the associated cranks 1A supporting the pedals may disrupt the drive shaft.

[0045] Against this background, the control electronics 8 are configured, when the pushing aid is activated, to control the second electric motor 12 to generate a torque that counteracts a rotation of the drive shaft 1. The control electronics 8 implements a closed-loop control for this purpose and has a PI controller or PID controller 80. The sensor signal from the speed sensor of the sensor device 115 is fed to this PI(D) controller 80 as an actual variable and thus a controlled variable. For this purpose, the speed of the drive shaft 1 is signaled to the control electronics 8, and here in particular to the PI(D) controller, via the speed sensor 115. When the pushing aid is activated, the control electronics 8 now controls the second electric motor 12 with the aim of ensuring that the speed of the drive shaft 10 becomes zero and that the drive shaft 1 thus remains stationary when the pushing aid is activated. For this purpose, a setpoint of zero, i.e., 0 revolutions, is set for the drive shaft 1 as the reference variable in the PI(D) controller 80.If a rotation of the drive shaft 1 is detected when the pushing aid is activated, a negative target torque for the second electric motor 12 is specified with the help of the control electronics 8 and its PI(D) controller. As a result, a torque generated by the second electric motor 12 on its second rotor shaft 4 counteracts a rotation of the drive shaft 1 and thus an adjustment of the pedal cranks 1A with the pedals attached thereto. In order to continue to ensure that a position of the pedal cranks 1A can be changed by a user when the pushing aid 1 is activated, or that the pedal cranks 1A can be displaced about a rotational axis of the drive shaft 1 if a pedal crank 1A or a pedal attached thereto strikes an obstacle, the controller output of the PI(D) controller 80 is limited to small torques.Larger forces on a pedal crank 1A are therefore not compensated for and the pedal cranks 1A can be adjusted by rotating the drive shaft 1 even when the pushing aid is activated.

[0046] For this purpose, a maximum value is stored, for example, in a memory 81 of the control electronics 8, which a torque to be generated by the second electric motor 12 must not exceed in order to bring the drive shaft 1 to a standstill when the pushing aid is activated. For example, the maximum value stored in the memory 81 corresponds to a torque value for the rotor shaft 4 to be driven by the second electric motor 12 in the range of 0.15 to 0.4 Nm, in particular exactly 0.3 Nm. A torque exceeding this torque (limit) value is not compensated for when the pushing aid is activated and rotation of the drive shaft 1 is detected by a sensor. In such a case, the second electric motor 12 is therefore not controlled at all to generate a counteracting torque.

[0047] The basic process of controlling the drive system of Figures 1 and 2 is also schematically illustrated using the flow chart in Figure 3.

[0048] If a pushing aid was activated in a first step S1, a subsequent step S2 (continuously) compares the actual rotational speed of the drive shaft 1 with a setpoint. Based on this comparison, the second electric motor 2 is controlled to bring the drive shaft 1 to a standstill, at least as long as the limitation of the controller output to the maximum torque (limit) value stored in memory 81 is not exceeded. The PI(D) controller 80 of the control electronics 8 thus controls the rotational speed or rpm of the drive shaft 1, as the controlled variable, to the setpoint of 0 as the reference variable.

[0049] With the proposed solution, when the shifting assistance is activated, it is possible to electronically prevent the pedal cranks 1A and the pedals attached to them from rotating (co-rotating), so that in particular the pedals do not collide with a user pushing the electric bicycle F who is walking next to the electric bicycle F. Nevertheless, when the pushing assistance is activated, the pedal cranks 1A and their pedals are not completely rigid or immobilized by the second electric motor 12. Rather, the position of the pedal cranks 1A and the pedals attached to them can still be corrected from the outside by the user or by an obstacle applying a sufficiently high crank force to at least one pedal crank 1A. A resulting rotation of the drive shaft 1, which is thus due to a crank force exceeding a threshold value, is not counteracted by the control electronics 8 and the second electric motor 12.In such a situation, only the first electric motor 11 for the activated pushing assistance remains active to drive the electric bicycle F.

[0050] List of reference symbols

[0051] drive shaft

[0052] Drive unit first electric motor second electric motor planetary gear

[0053] (Three-shaft) planetary gear stage sun gear

[0054] ring gear

[0055] Planet carrier output shaft

[0056] Planetary gear first shaft second shaft third shaft housing

[0057] Main body

[0058] Middle bridge

[0059] Motor cover Gearbox cover First rotor shaft Axial direction First spur gear stage Second spur gear stage Third spur gear stage Fourth spur gear stage First arrangement level Second arrangement level Third arrangement level Fourth arrangement level Fifth arrangement level Second rotor shaft

[0060] Freewheel first coupling shaft second coupling shaft third coupling shaft 8 Control electronics with push assist control via electric motor

[0061] 80 PI(D) controllers

[0062] 81 storage

[0063] 9 Energy storage

[0064] 102 Control panel

[0065] 110 (bicycle) frame

[0066] 111 front wheel

[0067] 112 rear wheel

[0068] 113 Belt / Chain

[0069] 114 Wheel sensor

[0070] 115 Sensor device F Electric bicycle

Claims

Claims 1. Drive system for an electric bicycle (F), with - a drive shaft (1) to which a pedal crank (1A) is connected for applying a driving force for driving the electric bicycle (F) by means of muscle power, - an output shaft (2) for transmitting the drive force to a wheel (112) of the electric bicycle (F), - a first electric motor (11), - a second electric motor (12), - a transmission device with at least one planetary gear (15), the transmission ratio of which can be adjusted by means of the first and second electric motors (11, 12) and via which the drive shaft (1) and the output shaft (2) are coupled to one another, wherein a torque generated by the first electric motor (11) can be transmitted at least partially to the output shaft (2), and - control electronics (8) for controlling the first and second electric motors (11, 12) and for activating a pushing aid, with which a torque is transmitted from the first electric motor (11) to the output shaft (2) when the electric bicycle (F) is pushed by a user, characterized in that the control electronics (8) is configured to control the second electric motor (12) to generate a torque when the pushing aid is activated, which counteracts a rotation of the drive shaft (1).

2. Drive system according to claim 1, characterized in that the Control electronics (8) is coupled to at least one sensor device (115) of the drive system for detecting a rotational speed of the drive shaft (1) and is configured to control the second electric motor (12) for generating the torque counteracting the rotation of the drive shaft (1) in dependence on at least one sensor signal of the at least one sensor device (115).

3. Drive system according to claim 2, characterized in that the control electronics (8) is configured to control the second electric motor (12) to generate the torque counteracting the rotation of the drive shaft (1) in dependence on the at least one sensor signal of the at least one sensor device (115) with the aim of controlling a rotational speed of the drive shaft (1) to zero.

4. Drive system according to claim 2 or 3, characterized in that the at least one sensor device (115) comprises a speed sensor.

5. Drive system according to one of the preceding claims, characterized in that the control electronics (8) comprises a controller (80) for regulating the torque to be generated by the second electric motor (12) when the pushing aid is activated.

6. Drive system according to claim 5, characterized in that a setpoint value for the rotational speed of the drive shaft (1) is stored as a reference variable for the controller (80).

7. Drive system according to one of the preceding claims, characterized in that the control electronics (8) are configured to limit the torque to be generated by the second electric motor (12) when the pushing aid is activated to a maximum value.

8. Drive system according to claim 7, characterized in that the control electronics (8) are configured, when the pushing aid is activated, to control the second electric motor (12) to generate a torque that counteracts a rotation of the drive shaft (1) only if the torque to be generated does not exceed the maximum value.

9. Drive system according to claim 8, characterized in that the control electronics (8) are configured to at least temporarily suspend the control of the second electric motor (12) when the pushing aid is activated and torque has already been applied by the second electric motor (12) if the torque to be generated would exceed the maximum value.

10. Drive system according to one of claims 7 to 9, characterized in that the maximum value is predetermined by a torque value for a rotor shaft (4) to be driven by the second electric motor (12) or by a torque value for the pedal crank (1A) or the drive shaft (1).

11. Drive system according to claim 10, characterized in that the maximum value is predetermined by a torque value in the range of 0.15 to 0.4 Nm for the rotor shaft (4) to be driven by the second electric motor (12).

12. Method for controlling a drive system of an electric bicycle (F), wherein the drive system - a pedal crank (T) is connected to a drive shaft (1) for muscle-powered application of a drive force for driving the electric bicycle (F), - an output shaft (2) transmits the drive force to a wheel (112) of the electric bicycle (F), - a transmission ratio of a planetary gear (15) is adjustable by means of first and second electric motors (11, 12), via which the drive shaft (1) and the output shaft (2) are coupled to one another, wherein a torque generated by the first electric motor (11) is at least partially transmittable to the output shaft (2), and - a pushing aid can be activated, with which a torque is transmitted from the first electric motor (11) to the output shaft (2) when the electric bicycle (F) is pushed by a user, characterized in that after activation of the pushing aid, the second electric motor (12) is controlled to generate a torque which counteracts a rotation of the drive shaft (1).

13. A computer program product containing instructions which, when executed by at least one processor of a control unit of a drive system of an electric bicycle (F) comprising an electric motor drive unit (10), cause the at least one processor to execute a method according to claim 12.

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