A drive system and control method involving the operation of a second electric motor to generate counter-torque when Walk Assist is activated.

Abstract

In particular, the present invention relates to a drive system for an electric bicycle (F), the drive system comprising control electronic equipment (8) for controlling first and second electric motors (11, 12) and for activating walk assist. When walk assist is activated, torque is transmitted from the first electric motor (11) to the output shaft (2) while the electric bicycle (F) is being pushed by the user. Furthermore, the second electric motor (12) is operated to generate torque to counteract the rotation of the drive shaft (1).

Description

Technical Field

[0001] The proposed solution relates in particular to a drive system for an electric bicycle.

Background Art

[0002] It is known to provide walk assist for an electric bicycle, i.e., a so-called e-bike or pedelec, via an electric drive unit to assist the user when pushing the electric bicycle or, for example, starting on an uphill. Walk assist is typically activated in response to an operating signal, for example, by operating an operating element on the handlebar of the electric bicycle. The maximum speed of the electric bicycle achievable via walk assist is predefined by the control electronics of the drive unit and is usually legally restricted. In walk assist, a maximum speed of typically 3 to 6 km / h is achieved.

Summary of the Invention

Problems to be Solved by the Invention

[0003] When walk assist is activated, the drive shaft equipped with pedals is indirectly driven via frictional torque, which can sometimes interfere with the user pushing the electric bicycle walking alongside it.

Means for Solving the Problems

[0004] Against this backdrop, a drive system for an electric bicycle is proposed, comprising, in particular, two electric motors, a first and a second, at least one planetary gearbox, and control electronics. Here, the control electronics are provided for controlling the first and second electric motors and for activating walk assist. When walk assist or the walk assist function is activated, torque is transmitted from the first electric motor to the output shaft while the electric bicycle is being pushed by the user. In the proposed drive system, the control electronics are further configured to drive the second electric motor when walk assist is activated, thereby generating torque that counteracts the rotation of the drive shaft, which is the part to which human-powered driving force can be introduced into the drive system using at least one pedal crank.

[0005] For riding an electric bicycle, the proposed drive system uses first and second electric motors to set the gear ratio of a planetary transmission (preferably steplessly). The drive shaft and the output shaft of the drive system, which is provided to transmit driving force to the wheels of the electric bicycle, are coupled to each other via at least one planetary transmission. In order to drive the electric bicycle using motor-generated assist force that can be transmitted to the output shaft in addition to the driving force applied by human operation, the torque generated by the first electric motor is at least partially transmittable to the output shaft while riding the electric bicycle. The proposed solution is based on the basic idea of ​​utilizing such a configuration of a drive system with first and second electric motors to prevent unwanted co-rotation of the drive shaft, and in particular the pedal crank and pedal connected thereto, when the walk assist is activated. Thus, as described above, the walk assist is activated in particular when the electric bicycle is being pushed by the user. At that time, the drive system provides assist power to drive the electric bicycle up to a predetermined maximum speed (e.g., 6 km / h). For this assist power in the forward direction, it is sufficient to drive the first rotor shaft with a first electric motor. In the proposed drive system, a second electric motor is used to generate torque that counteracts the (co)rotation of the drive shaft.

[0006] In particular, in this context, the control electronics are configured to drive a second electric motor to generate a torque that counteracts the rotation of the drive shaft caused by the pure electric drive of the drive shaft when the walk assist is activated. The second electric motor is therefore operated to generate a torque that just counteracts the rotation of the drive shaft caused by so-called co-rotation of the drive shaft. This co-rotation occurs, for example, when at least a portion of the torque (of the walk assist) applied by the first electric motor is transmitted to the drive shaft via the planetary transmission due to friction.

[0007] Control electronics can be coupled to at least one sensor device of the drive system for obtaining the rotational speed of the drive shaft. In a variation of such an embodiment, the control electronics is configured to drive a second electric motor to generate a torque that counteracts the rotation of the drive shaft, for example, in response to at least one sensor signal from at least one sensor device. The torque generated by the second electric motor, in particular its magnitude, here depends on at least one measurement from at least one sensor device. For example, here it may be defined that the control electronics drive the second electric motor with the goal of making the rotational speed of the drive shaft zero and thus bringing the drive shaft to rest. Thus, at least one sensor signal provided by at least one sensor device may indicate, in particular, the rotational speed of the drive shaft. The value of the (current) rotational speed of the drive shaft notified by the sensor signal, which deviates from zero and indicates rotation of the drive shaft, can serve as a control quantity for the control electronics.

[0008] In principle, at least one sensor device may be equipped with a rotational speed sensor that can measure the rotational speed of the drive shaft (and the rotational speed that should be offset by it).

[0009] In a modified embodiment, the control electronics includes a controller, particularly a PI controller or PID controller, for adjusting the torque to be generated by the second electric motor when the walk assist is activated. As a result, the adjustment is performed via the control electronics, and this adjustment aims to ensure that when the walk assist is activated, the drive shaft rotates only within an acceptable range or does not rotate at all. For example, a target value for the rotational speed of the drive shaft can be stored as a reference variable for the controller of the control electronics. Such a target value can be, for example, zero, and thus corresponds to zero rotations or stationary position of the drive shaft.

[0010] In a modified embodiment, the control electronics are configured to limit the torque generated by the second electric motor to a maximum value when the walk assist is activated. For example, limiting the torque to a maximum value stored in the memory of the control electronics may provide the advantage that the second electric motor will not operate, or will no longer operate, when intentional or necessary rotation of the drive shaft should be expected, even when the walk assist is activated. Therefore, for example, when the walk assist is activated, it should also be possible to change the position of the pedal crank connected to the drive shaft. This could be, for example, when the user wants to change the position of the pedal connected to the pedal crank, or when the pedal crank or the pedal connected to it hits an obstacle. In such cases, it becomes necessary to generate a relatively large torque by the second electric motor in order to counteract the rotation of the drive shaft. Therefore, a maximum value adjusted accordingly is stored as the torque to be generated when the walk assist is activated. This ensures that, even when the walk assist is activated, the second electric motor does not counteract or prevent the rotation of the drive shaft when the user desires or when rotation may be advantageous.

[0011] For example, in this context, the control electronics are configured to drive a second electric motor to generate torque to counteract the rotation of the drive shaft, but only if the torque to be generated does not exceed the maximum value when the walk assist is activated. This includes, in particular, the control electronics being configured to at least temporarily interrupt the operation of the second electric motor if the torque to be generated would exceed the maximum value, even if the walk assist is activated and torque has already been applied by the second electric motor. Thus, if the torque required to keep the drive shaft stationary exceeds the maximum value, the torque to counteract the rotation of the drive shaft will no longer be applied by the second electric motor, even if the walk assist is activated. In the case of control electronics equipped with a controller, for this purpose, the controller output may be limited to a small torque, i.e., a torque below the maximum value. In this way, larger forces acting on the drive shaft, and especially the pedal crank connected thereto, due to, for example, user positioning or collision with an obstacle, are not counteracted, and rotation of the drive shaft is permitted. Therefore, the control device can be configured not to generate a counter-torque from the second electric motor when a crank force (and the resulting crank torque) exceeding a threshold is acting on the pedal crank from an external source, particularly via at least one pedal connected thereto, thereby causing the drive shaft to rotate or accelerate. In this case, it is taken into consideration that such a crank force is due to a force applied to the pedal crank by the user (e.g., for pedal position correction) or due to an obstacle, and that the resulting rotation of the drive shaft should not be hindered.

[0012] The maximum value for limiting the drive of the second electric motor when the walk assist is activated can be predetermined, for example, by the torque value of the (second) rotor shaft driven by the second electric motor, or by the torque value of the pedal crank or drive shaft. Therefore, for example, if the crank force acting on the pedal crank or drive shaft exceeds a threshold (e.g., 10 Nm), it can be determined that the second electric motor should not be driven to generate counter-torque, because in that case, it can be presumed that a force attributable to the user or an obstacle is acting on the drive shaft. Such a threshold can be converted into a corresponding torque value of the rotor shaft driven by the second electric motor. This torque value is stored in the control electronics in an evaluable format and, for example, limits the controller output. In principle, and especially in this context, a torque sensor capable of measuring the torque acting on the drive shaft from an external source can be included as part of the drive system to determine whether or not the second electric motor should generate counter-torque.

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

[0014] Part of the proposed solution is a method for controlling the drive system of an electric bicycle. The drive system to be controlled has at least the following: A pedal crank connected to the drive shaft of the drive system, which applies driving force to propel an electric bicycle through human operation. The output shaft that transmits the driving force to the wheels of an electric bicycle. A planetary transmission having an adjustable gear ratio using first and second electric motors, and coupling a drive shaft and an output shaft to each other, wherein the torque generated by the first electric motor can be transmitted to the output shaft, at least partially.

[0015] In this drive system, a walk assist is activated, in which torque is transmitted from a first electric motor to the output shaft when the electric bicycle is being pushed by the user. In the process of the proposed method, it is hereby specified that, after the walk assist is activated, a second electric motor is driven to generate torque to counteract the rotation of the drive shaft.

[0016] A modified embodiment of the proposed control method can be realized, in particular, by a modified embodiment of the proposed drive system. Therefore, the advantages and features of the embodiments of the proposed drive system described above and below also apply to embodiments of the proposed control method, and vice versa.

[0017] Furthermore, a computer program product is proposed that includes instructions, when executed by at least one processor of a control device for a drive system of an electric bicycle equipped with an electric drive unit, cause said at least one processor to execute a modified embodiment of the proposed control method. Thus, said at least one processor may be part of a control electronic device implemented together with the control unit, thereby driving a second electric motor of the drive system to generate torque that counteracts the rotation of the drive shaft when the walk assist is activated on the electric bicycle. [Brief explanation of the drawing]

[0018] The attached drawings illustrate possible embodiments of the proposed solution. These include: [Figure 1] This shows a 2D design drawing of an electric drive unit in one embodiment of the proposed drive system. [Figure 2] A schematic side view of an electric bicycle equipped with the proposed drive system is shown. [Figure 3] A flowchart of one embodiment of the proposed control method is shown. [Modes for carrying out the invention]

[0019] Figure 2 shows an electric bicycle F equipped with a drive system including an electric drive unit 10. The electric bicycle F has a frame 110, which, in this example, consists of an upper tube, a down tube, and a seat tube. The drive unit 10 is fixed to the frame 110 in the region where the seat tube and the down tube intersect. Part of the drive unit 10 is the control electronics 8 and the sensor device 115. The electric motors 11 and 12 of the drive unit 10 (see Figure 1) are controllable via the control electronics 8, which is in particular to pre-define the level of assist force generated by an external power source to drive the electric bicycle F. The sensor device 115 is provided to sensor-detect the rotational speed of the drive shaft (pedal shaft) 1 of the drive unit 10. For this purpose, the sensor device 15 may include a rotational speed sensor that can measure the rotational speed of the pedal shaft 1. The driving force for propelling the electric bicycle F can be applied to the drive shaft 1 by human operation by the driver of the electric bicycle F, via a pair of pedal cranks 1A connected thereto and the pedals provided thereon. If necessary, the sensor device 115 can also be provided for the acquisition of torque introduced to the drive shaft 1 by human operation, and can be configured, for example, using a torque sensor and / or a position sensor.

[0020] The output element of the drive unit A, for example, a hollow output shaft 2 (see Figure 1) supported coaxially with the pedal shaft 1, is connected to the rear wheel 112 of the electric bicycle F via a belt or chain 213 as a power transmission member, in order to enable the electric bicycle F to be driven. A wheel sensor 114 for determining the speed of the electric bicycle F is assigned to this rear wheel 112, for example. Of course, the wheel sensor 114 may be provided on the front wheel 111 of the electric bicycle F instead.

[0021] The drive system of the electric bicycle F further includes an operating component 102. In FIG. 2, the operating component 102 is fixed, for example, in the area of the handlebar of the electric bicycle F and is typically connected to the control electronics 8 of the drive unit 10 via one or more cables. User input can be obtained via the operating component 102 and used to control the drive unit 10. For example, the operating component 102 comprises at least one display for sending the following to the user of the electric bicycle F. For example, regarding the set assist level, the current operating state of the drive unit F, the charge state of the energy storage 9 that supplies electrical energy to the drive unit 10 (this energy storage includes, for example, at least one (rechargeable) battery), and / or the set gear stage, which defines the gear ratio when the drive torque input to the drive shaft 1 by manual operation is transmitted to the output shaft 2 of the drive unit 10.

[0022] FIG. 1 shows a 2D design proposal for the drive unit 10 of FIG. 2, which comprises two electric motors 11 and 12.

[0023] The drive unit 10 has a drive shaft 1 and an output shaft 2, both of which are rotatably supported within the housing 25 of the drive unit 10. The drive shaft 1 passes through the housing 25 and is connected on each side to a pedal crank 1A, via which the operator of the electric bicycle F can apply a driving force by manual operation. The output shaft 2 protrudes from the housing 25 on only one side and is connected from there to a sprocket or a toothed belt pulley in order to drive the rear wheel 112 of the electric bicycle F.

[0024] The drive unit 10 includes a first electric motor 11 having a first rotor shaft 3 and a second electric motor 12 having a second rotor shaft 4. The two electric motors 11 and 12 communicate via control electronic equipment 8 to form a continuous electrically operated transmission. The control electronic equipment 8 is also connected to an energy reservoir 9. Therefore, the output shaft 2 can also be driven purely electrically via the first electric motor 11. The energy reservoir 9 can also be used as a brake energy reservoir when brake power flows into the drive unit 10 at the output shaft 2.

[0025] The drive shaft 1, output shaft 2, and two rotor shafts 3 and 4 are coupled via a multi-stage planetary transmission 15 having multiple 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 are configured here as spur gear stages. However, toothed belt gear stages are also possible. In this example, the three-axis planetary gear stage 16 comprises a sun gear 17, a ring gear 18, and a planetary carrier 19 having multiple planetary gears 20 supported by planetary gear bolts.

[0026] The elements of the drive unit 10 are, in this example, distributed across three parallel shaft rows 21, 22, and 23 within the installation 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 coaxially arranged on the first shaft row 21. The three-axis planetary gear stages 16 of the multi-stage planetary transmission 15 are located on the second shaft row 22. The first rotor shaft 3 of the first electric motor 11 is located on the third shaft row 23. On the first shaft row 21, the outer (hollow) output shaft 2 surrounds the inner drive shaft 1 on one side of the housing 25, and the second rotor shaft 4 surrounds the drive shaft 1 on the other side of the housing 25.

[0027] Four gears 31-34, designed as spur gears, are used to kinematically couple the elements of the drive unit 10, which is distributed across three shaft rows 21, 22, and 23 and housed in a housing 25. The drive shaft 1 on the first shaft row 21 is connected to the first coupling shaft 5 on the second shaft row 22 via the first spur gear 31. The output shaft 2 on the first shaft row 21 is connected to the second coupling shaft 6 on the second shaft row 22 via the second spur gear 32. The second rotor shaft 4 of the second electric motor 12 on the first shaft row 21 is connected to the third coupling shaft 7 on the second shaft row 22 via the third spur gear 33. This third coupling shaft also carries the sun gear 17. The first rotor shaft 3 of the first electric motor 11 on the third axle train 23 is connected to the ring gear 18 of the planetary gear stage 16 on the second axle train 22 via the fourth spur gear stage 34. On the second axle train 22, the first connecting shaft 5 is connected to the planetary carrier 19, the second connecting shaft 6 is connected to the ring gear 18, and the third connecting 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 therefore to the output shaft 2, the drive unit 10 shown as an example has power splitting on the output side.

[0028] The first spur gear stage 31 increases the rotational speed of the drive shaft 1 to a greater absolute rotational speed of the first connecting shaft 5, which is, for example, about three times greater, and is connected to the second connecting shaft 6 via the planetary gear stage 16. The rotational speed of the second connecting shaft 6 is transmitted at a rotational speed, for example, about 30% lower than that of the output shaft 2, according to the gear ratio of the second spur gear stage 32.

[0029] In Figure 1, five alignment planes 35, 36, 37, 38, and 39 are marked, their numbers increasing in the axial direction 30. The axial direction 30 refers to the direction from where the output shaft 2 exits the housing 25 toward the inside of the housing 25. In Figure 1, the second spur gear stage 32 is located in the first alignment plane 35. The planetary gear stage 16 and the fourth spur gear stage 34 are located in the second alignment plane 36, which is offset in the axial direction 30 from the first alignment plane 35 and parallel to it. The first spur gear stage 31 is located in the third alignment plane 37, which is shifted in the axial direction 30 from the second alignment plane 36. Furthermore, the third spur gear stage 33 is located in the fourth alignment plane 38, which is shifted in the axial direction 30 from the third alignment plane 37. The two electric motors 11 and 12 are similarly located in the fifth alignment plane 39, which is shifted in the axial direction 30 from the fourth alignment plane 38.

[0030] 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 row 22 has a larger pitch circle radius than the ring gear 18 of the three-axis planetary gear stage 16. As a result, the ring gear 18 has space inside this gear of the fourth spur gear stage 34 in the second arrangement plane 36.

[0031] The configuration in which the spur gear stages 31, 32, 33, and 34 are axially positioned near the planetary gear stage 16 on the second shaft row 22, combined with the illustrated distributed arrangement of the drive elements to the three shaft rows 21, 22, and 23, results in an extremely compact multi-stage planetary transmission 15.

[0032] In the first arrangement plane 35 where the second spur gear stage 32 is located, the freewheel 40 is positioned between the drive shaft 1 and the output shaft 2, for example in the form of a sprag-type freewheel. The freewheel 40 can directly connect the drive shaft 1 to the output shaft 2, especially in the case of the maximum gear ratio. The freewheel 40 also functions, on the one hand, as overload protection for the drive unit 10, and on the other hand, in the event of electrical system malfunctions, such as voltage drops, or control / regulation failures caused, for example, by failure of one or more sensors of the sensor device 115.

[0033] For the easy assembly of the remaining elements of the drive system 10 and their support within the housing 25, the housing 25 has four housing components. The housing 25 consists of a main housing 26 to which a center land 27 is connectable or connected; a motor cover 28 to which a fifth arrangement plane 39 is connectable or connected; and a transmission cover 29 to which a first arrangement plane 35 is connectable or connected to the main housing 26, and which is the point where the output shaft 2 protrudes from the housing 25.

[0034] In the illustrated drive unit 10, the control electronics 8 further integrates walk assist control. Thus, the drive system can be driven in walk assist mode by generating an operating signal, for example, with the operating component 102. As a result, the user can activate the walk assist of the drive system via the operating signal, and consequently, when the electric bicycle F is being pushed, the user is assisted by the electric motor drive unit 10. For this purpose, the control electronics 8 drives the first electric motor 10 to drive the electric bicycle F up to a speed of 6 km / h.

[0035] During the rotation of the output shaft 2, which is motor-driven by the first electric motor 11, friction may cause at least a portion of the torque applied from the first electric motor 11 for walk assist to be transmitted to the drive shaft 1 via the planetary transmission 15, resulting in the drive shaft 1 rotating together, i.e., being rotated similarly (at a lower rotational speed). When a user pushing the electric bicycle F walks alongside the electric bicycle F, this co-rotation of the drive shaft 1 and the pedal crank 1A connected to it and supporting the pedals can be an obstacle.

[0036] Against this backdrop, the control electronics 8 is configured to drive a second electric motor 12 to generate a torque that counteracts the rotation of the drive shaft 1 when the walk assist is activated. The control electronics 8 performs adjustments for this purpose and has a PI controller or PID controller 80. The sensor signal from the rotational speed sensor of the sensor device 115 is supplied to this PI(D) controller 80 as a real variable, and therefore as a control variable. For this purpose, the rotational speed of the drive shaft 1 is signaled to the control electronics 8, and in this case the PI(D) controller in particular, via the rotational speed sensor 115. When the walk assist is activated, the control electronics 8 then drives the second electric motor 12 with the goal that the rotational speed of the drive shaft 10 becomes zero, and therefore the drive shaft 1 is stationary when the walk assist is activated. For this purpose, in the PI(D) controller 80, for example, a target value of zero, i.e., 0 rotations, is set as a reference variable for the drive shaft 1. When the Walk Assist is activated and rotation of the drive shaft 1 is detected, a negative target torque is predefined for the second electric motor 12 using the control electronic equipment 8 and its PI(D) controller. As a result, the torque generated by the second electric motor 12 at its second rotor shaft 4 counteracts the rotation of the drive shaft 1 and, therefore, the adjustment of the pedal crank 1A with the pedal fixed thereto.

[0037] When Walk Assist 1 is activated, the controller output of the PI(D) controller 80 is limited to a low torque to further ensure that the pedal crank 1A is displaced around the axis of rotation of the drive shaft 1 when the pedal crank 1A (or the pedal fixed thereto) comes into contact with an obstacle. Therefore, larger forces acting on the pedal crank 1A are not compensated, and the pedal crank 1A can be adjusted with rotation of the drive shaft 1, even when Walk Assist is activated.

[0038] For this purpose, for example, the memory 81 of the control electronic equipment 8 stores a maximum value that must not be exceeded by the torque generated by the second electric motor 12 to keep the drive shaft 1 stationary when the walk assist is activated. For example, the maximum value stored in memory 81 corresponds to a torque value in the range of 0.15 to 0.4 Nm, in particular, exactly 0.3 Nm, for the rotor shaft 4 driven by the second electric motor 12. Torque exceeding this torque (limit) value is not compensated when the walk assist is activated and the sensor detects that the drive shaft 1 is rotating. In such cases, as a result, the second electric motor 12 is not operated at all to generate counteracting torque.

[0039] The basic sequence for controlling the drive systems shown in Figures 1 and 2 is schematically illustrated with reference to the flowchart in Figure 3.

[0040] If walk assist is activated in the first step S1, in the subsequent step S2, a comparison between the actual rotational speed of the drive shaft 1 and a target value is performed (continuously). Based on this comparison, the second electric motor 12 is controlled to keep the drive shaft 1 stationary as long as it does not exceed the limit of the controller output based on the maximum torque (limit) value stored in memory 81. Therefore, the PI(D) controller 80 of the control electronic equipment 8 is used to control the rotational speed of the drive shaft 1, which is the controlled variable, to the target value 0, which is the reference variable.

[0041] The proposed solution makes it possible to prevent the pedal crank 1A and the pedal fixed thereto from rotating together in an electronically controlled manner when the walk assist is activated, and as a result, the pedal will not, in particular, strike a user pushing the electric bicycle F while running alongside it. Nevertheless, the pedal crank 1A, together with its pedal, is not completely rigidly or immobilely locked via the second electric motor 12 when the walk assist is activated. Rather, the pedal crank 1A and the pedal fixed thereto can still be corrected externally by the user or by an obstacle applying a sufficiently high cranking force to at least one of the pedal cranks 1A. No counteracting action is taken by the control electronic equipment 8 and the second electric motor 12 against the resulting rotation of the drive shaft 1, i.e., rotation caused by a cranking force exceeding a threshold. In such a situation, only the first electric motor 11 remains operational for the walk assist activated to drive the electric bicycle F. [Explanation of symbols]

[0042] 1 Drive shaft 10 Drive Unit 11. First electric motor 12. Second electric motor 15 Planetary transmission 16 (3-axis) planetary gear stage 17 Sun Gear 18 Ring Gear 19 Planetary Carriers 2 Output shafts 20 Planetary gears 21 First axis row 22 Second axis row 23 Third axis row 25 Housing 26 Main Housing 27 Centerland 28 Motor cover 29. Gearbox cover 3. First rotor shaft 30 Axis 31 First spur gear stage 32 Second spur gear stage 33 Third spur gear stage 34. Fourth spur gear stage 35 First arrangement plane 36. Second arrangement plane 37 Third arrangement plane 38. The fourth arrangement plane 39. Fifth arrangement plane 4. Second rotor shaft 40 Freewheel 5. First connecting shaft 6. Second connecting shaft 7. Third connecting shaft 8. Control electronic equipment with walk assist control using an electric motor. 80 PI(D) controller 81 memory 9 Energy storage devices 102 Operating parts 110 (bicycle) frame 111 Front Wheel 112 Rear wheel 113 Belt / Chain 114 Wheel Sensor 115 Sensor device F Electric Bicycle

Claims

1. A drive system for electric bicycles (F), A drive shaft (1) to which a pedal crank (1A) is connected for applying driving force to drive the electric bicycle (F) by human operation, An output shaft (2) for transmitting the aforementioned driving force to the wheels (112) of the electric bicycle (F), The first electric motor (11) and A second electric motor (12) and A transmission comprising at least one planetary gearbox (15), wherein the gear ratio of the planetary gearbox is adjustable using the first and second electric motors (11, 12), the drive shaft (1) and the output shaft (2) are coupled to each other via the planetary gearbox, and the torque generated by the first electric motor (11) is at least partially transmitted to the output shaft (2), Control electronic equipment (8) for controlling the first and second electric motors (11, 12) and for activating walk assist, wherein the walk assist transmits torque from the first electric motor (11) to the output shaft (2) when the electric bicycle (F) is pushed by the user, It has, The drive system is characterized in that the control electronic device (8) is configured to drive the second electric motor (12) to generate a torque that counteracts the rotation of the drive shaft (1) when the walk assist is activated.

2. The drive system according to claim 1, characterized in that the control electronic device (8) is coupled to at least one sensor device (115) of the drive system for acquiring the rotational speed of the drive shaft (1), and is configured to drive the second electric motor (12) to generate the torque that cancels out the rotation of the drive shaft (1) in response to at least one sensor signal of the at least one sensor device (115).

3. The drive system according to claim 2, characterized in that the control electronic device (8) is configured to drive the second electric motor (12) to generate the torque that cancels out the rotation of the drive shaft (1) in response to the at least one sensor signal of the at least one sensor device (115), with the goal of making the rotational speed of the drive shaft (1) zero.

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

5. The drive system according to any one of the preceding claims, characterized in that the control electronic equipment (8) includes a controller (80) for controlling the torque generated by the second electric motor (12) when the walk assist is activated.

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

7. The drive system according to any one of the preceding claims, characterized in that the control electronic device (8) is configured to limit the torque generated by the second electric motor (12) to a maximum value when the walk assist is activated.

8. The drive system according to claim 7, characterized in that the control electronic device (8) is configured to drive the second electric motor (12) to generate a torque to counteract the rotation of the drive shaft (1) only when the walk assist is activated and the generated torque does not exceed the maximum value.

9. The drive system according to claim 8, characterized in that the control electronic device (8) is configured to at least temporarily interrupt the operation of the second electric motor (12) if the generated torque exceeds the maximum value when the walk assist is activated and torque has already been applied by the second electric motor (12).

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

11. The 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 applied to the rotor shaft (4) driven by the second electric motor (12).

12. A method for controlling the drive system of an electric bicycle (F), wherein in the drive system, A pedal crank (T) for providing driving force to drive the electric bicycle (F) by human operation is connected to the drive shaft (1), The output shaft (2) transmits the driving force to the wheel (112) of the electric bicycle (F), The gear ratio of the planetary transmission (15) is adjustable using first and second electric motors (11, 12), the drive shaft (1) and the output shaft (2) are coupled to each other via the planetary transmission, and the torque generated by the first electric motor (11) can be transmitted to the output shaft (2) at least partially. Walk assist is activated so that when the electric bicycle (F) is pushed by the user, torque is transmitted from the first electric motor (11) to the output shaft (2). A method characterized in that, after the activation of the walk assist, the second electric motor (12) is operated to generate torque to counteract the rotation of the drive shaft (1).

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

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