Drive system with control electronics for actuating the electromotive drive using an active short-circuit in the event of a fault

Abstract

The invention relates to a drive system for an electric bicycle (F), comprising a driveshaft (1) for applying a drive force by means of muscle power in order to drive the electric bicycle (F), an output shaft (2) for transmitting the drive force to a wheel (112) of the electric bicycle (F), at least one electric motor (11, 12) for generating a supporting force by means of an external force, a transmission device (15) for coupling the driveshaft (1) to the output shaft (2) and for transmitting the supporting force to the output shaft (2), and control electronics (8) for controlling the at least one electric motor (11, 12), said control electronics being configured so as to actuate the at least one electric motor (11, 12) using an active short-circuit prior to switching to a torque-free state in response to at least one fault signal (fs).

Description

[0001] Drive system with control electronics for controlling the electric motor drive with an active short circuit in the event of a fault

[0002] Description

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

[0004] For drive systems for electric bicycles with at least one electric motor for the externally powered generation of an assist force, it is known to switch the at least one electric motor to a torque-free state in response to at least one error signal. Thus, it is necessary to switch the at least one electric motor to a torque-free and thus safe state if a safety-critical error is detected and, for example, reliable control of the at least one electric motor or the level of the assist force generated thereby is no longer possible.

[0005] However, an immediate and therefore sudden switching of the at least one electric motor to a torque-free state in response to a detected fault can take an electric bicycle rider completely by surprise while riding the electric bicycle. In particular, this can result in a sudden removal of a resistance previously exerted by the at least one electric motor, against which the rider pedals the electric bicycle. An immediate switching to the torque-free state can therefore, under certain circumstances, feel to an electric bicycle rider as if a drive chain on a conventional bicycle had broken. Particularly depending on the current riding situation, the immediate switching of the at least one electric motor to a torque-free state can therefore lead to injury for the electric bicycle rider.

[0006] The proposed solution aims to remedy this situation. A proposed drive system for an electric bicycle provides at least the following:

[0007] - a drive shaft for applying muscle-powered drive force to drive the electric bicycle,

[0008] - an output shaft for transmitting the drive power to a wheel of the electric bicycle,

[0009] - at least one electric motor for the externally powered generation of an auxiliary force,

[0010] - a transmission device for coupling the drive shaft and the output shaft and transmitting the assist force to the output shaft and

[0011] - control electronics for controlling the at least one electric motor, which is configured to control the at least one electric motor with an active short circuit in response to at least one error signal before the at least one electric motor is switched to a torque-free state via the control electronics.

[0012] The proposed solution is therefore based on the basic idea that in the event of a fault, which is electronically signaled by at least one fault signal, the at least one electric motor of the drive system is not immediately switched to a torque-free and thus safe state, but rather the at least one electric motor is first controlled at least once with an active short circuit. This ensures that, at least for the duration of the active short circuit, a resistance from the at least one electric motor is maintained at the drive shaft - albeit possibly lower than the situation before the fault signal was generated - and thus remains noticeable for the rider of the electric bicycle at the pedals connected to the drive shaft via pedal cranks. The risk of injury to the rider, e.g. due to a fall, can thus be reduced compared to a sudden switch to the torque-free state.

[0013] Control with an active short circuit also has the advantage that an active short circuit can be implemented even with only minimally functioning hardware and can therefore still be implemented even in the event of safety-critical errors signaled by the at least one error signal. Control with an active short circuit also prevents the at least one electric motor from accelerating a rotor (shaft) driven by the electric motor. Thus, when controlled with an active short circuit, the at least one electric motor can no longer provide any supporting force to rotate the drive shaft.Furthermore, it can be observed that by controlling the at least one electric motor with an active short circuit, a vibration that can be felt and / or heard by the rider of the electric bicycle can be caused in a housing of a drive unit of the drive system that accommodates the at least one electric motor. This can thus additionally communicate the occurrence of an error to the rider of the electric bicycle haptically and / or acoustically (possibly in addition to an alarm issued on a control unit of the drive system). This draws the rider's attention to the error, which typically results in the rider of the electric bicycle reducing the force with which they pedal. In this way, the rider of the electric bicycle is no longer surprised by a subsequent switching of the electric motor to the torque-free state.

[0014] In one embodiment, the control electronics of the drive system are configured to, in response to the at least one error signal, control the at least one electric motor with an active short circuit for a predetermined period of time before switching to the torque-free state. Thus, a period of time is stored in the control electronics for which the active short circuit will be maintained after the occurrence of the at least one error signal. For example, this period is in the range of one second.

[0015] Alternatively or additionally, the control electronics can be configured, in response to the at least one error signal, to control the at least one electric motor with a control sequence in which a first control with an active short circuit and a subsequent first switching to the torque-free state are followed by at least one further control with an active short circuit and at least one subsequent further switching to the torque-free state. In such an embodiment, the at least one electric motor is therefore initially only briefly switched to a torque-free state between at least two controls with an active short circuit, before finally a final switching to the torque-free state occurs and the at least one electric motor is held in the torque-free state.Alternating between phases with an active short circuit on the one hand and a torque-free state on the other can potentially further sensitize an electric bicycle rider to the occurrence of a fault and prepare them for the eventual switching and holding of at least one electric motor in the torque-free state. In this context, it can also be advantageous if a predetermined time period for the first activation with the active short circuit is longer than a second time period for the at least one subsequent activation with the active short circuit.If, for example, in a control sequence, first phases in which the at least one electric motor is controlled with an active short circuit alternate with second phases in which the at least one electric motor is switched to the torque-free state (until an end of the control sequence is reached at which the at least one electric motor is finally switched to the torque-free state), the lengths of the first phases can become shorter over time, in particular continuously shorter. With a periodic alternation between first and second phases, each lasting for a predetermined period, the proportion of the first phase in which the active short circuit is controlled can thus, for example, become smaller over time, in particular continuously shorter.By reducing the proportion of the first phases over time, it is possible to ensure that the resistance and thus the counterpressure felt by the rider of the electric bicycle on the pedals is continuously reduced before the resistance is completely eliminated when at least one electric motor switches to the torque-free state.

[0016] In principle, the first and second phases can alternate for a specified total period of time before finally switching to the torque-free state. For this purpose, the control electronics are then configured to control the at least one electric motor with alternating first and second phases for the specified total period of time in response to the at least one error signal.

[0017] The duration of the transition between the first and second phases until the final switching to the torque-free state in response to the at least one error signal can fundamentally also depend on whether a decreasing proportion of the first phases, in which the at least one electric motor is controlled with an active short circuit, has been reduced over time up to a threshold value. Control with an active short circuit thus ends with the first phases becoming shorter over time when the length of a first phase has reached a threshold value, for example, 0.

[0018] The control electronics can, in particular, be configured to periodically control the at least one electric motor with an active short circuit via control pulses. The control electronics are thus configured to generate pulsed short circuits for the at least one electric motor. This includes, for example, in combination with the embodiment variant explained above, in which phases with control of the active short circuit are reduced, a variant in which the control electronics is configured to reduce a duty cycle of the control pulses during the control sequence with increasing time. For example, the duration of the control pulse and thus its proportion of the period duration can be reduced at least for every third or second period duration. Alternatively, the period duration of the control pulses can be reduced continuously and thus immediately for each subsequent control pulse.

[0019] In one embodiment, the control electronics are further configured to control the at least one electric motor with an active short circuit only if at least one additional criterion is met. This additional criterion can, for example, relate to an operating parameter of the drive system. It has been shown that controlling the at least one electric motor with an active short circuit can even be disadvantageous in certain driving situations. In certain embodiments, it can therefore be advantageous to first check, in response to the at least one error signal, whether at least one additional criterion is also met before an active short circuit is triggered. If necessary, the control with an active short circuit in response to the at least one error signal occurs with a time delay in this way, namely only when the at least one additional criterion is also met.The fulfillment of a corresponding criterion can be detected electronically, for example.

[0020] In one embodiment, for example, the control electronics are configured to control the at least one electric motor with an active short circuit only when a speed of the at least one electric motor is above a threshold value. Such a configuration has proven particularly advantageous in drive systems that comprise first and second electric motors and in which a transmission device comprises at least one planetary gear whose transmission ratio can be adjusted using the first and second electric motors. In such drive systems, a torque generated by the first electric motor is at least partially transmitted to the output shaft. During normal operation, the second electric motor supports the driver torque applied by the driver and thus by muscle power, which results from the applied drive force.It is precisely this second electric motor that, during normal operation, provides the pedal resistance felt by the electric bike rider. Depending on the riding situation, the second electric motor drives its (second) rotor shaft to rotate in a positive direction (corresponding to a forward rotation of the second electric motor) or in the opposite, negative direction. If, for example, a fault occurs that ultimately leads to the electric motors switching to a torque-free state and detects that the second rotor shaft of the second electric motor is rotating in the opposite, negative direction, no active short circuit is initially triggered. Instead, the system waits until the direction of rotation changes and a corresponding measurement signal indicative of the rotation of the second rotor becomes positive (and thus exceeds a threshold value of 0).Only when this additional criterion is met is an active short circuit triggered for the first time, thus starting, for example, a control sequence explained above. For example, if the electric motor drive is no longer fully functional and the second rotor shaft is accelerated in a positive direction of rotation after a relatively short time due to the muscle power applied to the drive shaft by the electric bicycle rider, in the event of a fault, the rotational speed of the second rotor shaft will change from a negative value to a positive value after a short time, even if the current driving situation initially resulted in a negative rotational speed.

[0021] In principle, the control electronics can comprise a B6 bridge circuit for controlling the at least one electric motor. Such a B6 bridge circuit comprises, for example, six MOSFETs.

[0022] One or more error signals, which in particular trigger the switching of the at least one electric motor to the torque-free state, can be used to signal, for example, that the position of a rotor (a rotor shaft) of the at least one electric motor can no longer be detected and / or determined and / or, in the case of field-oriented control of the at least one electric motor via the control electronics, that a phase current measurement is no longer available. In the case of corresponding electronically detected errors, active commutation of the at least one electric motor is no longer possible, so that the at least one electric motor must always be finally switched to the torque-free and thus safe state. The proposed solution can be applied particularly in such error cases.

[0023] The proposed solution also relates to a method for controlling a drive system of an electric bicycle. The drive system includes at least the following: - a drive shaft for applying a drive force to propel the electric bicycle by muscle power,

[0024] - an output shaft for transmitting the drive power to a wheel of the electric bicycle,

[0025] - at least one electric motor for the externally powered generation of an assist force and

[0026] - a transmission device which couples the input shaft and the output shaft and is intended to transmit the assist force to the output shaft.

[0027] In the proposed control method, it is now provided that the at least one electric motor is controlled with an active short circuit in response to at least one error signal before switching to a torque-free state (at least once).

[0028] Embodiments of a proposed control method can be implemented, in particular, with embodiments of a proposed drive system. Accordingly, the advantages and features explained above and below for embodiments of a proposed drive system also apply to embodiments of a proposed control method, and vice versa.

[0029] 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, which is configured, in response to at least one error signal, to control the at least one electric motor with an active short circuit before switching to a torque-free state.

[0030] The attached figures illustrate possible embodiments of the proposed solution.

[0031] Here we show:

[0032] Figure 1 shows a 2D design for an electromotive

[0033] Drive unit of a variant of a proposed drive system; Figure 2 shows a schematic and side view of an electric bicycle with a proposed drive system;

[0034] Figure 3 shows an example of a B6 bridge circuit for the

[0035] Control electronics of Figure 1;

[0036] Figure 4 shows an example of a control sequence in which a control level for pulsed short circuits decreases with increasing time and thus shorter phases of a control with active short circuit alternate with longer phases in which an electric motor drive is switched to a torque-free state;

[0037] Figure 5 shows a flow chart for an embodiment of a proposed control method.

[0038] 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.

[0039] A belt or chain 213 as a power transmission link provides a

[0040] An output element of the drive unit A, for example a hollow output shaft 2 mounted coaxially with 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. A wheel sensor 114 for determining a driving speed of the electric bicycle F is assigned to this rear wheel 112, for example. Of course, the wheel sensor 114 can instead be provided on a front wheel 111 of the electric bicycle F.

[0041] 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

[0042] - the current operating status of the drive unit F, for example with regard to a set support level,

[0043] - a charge state of an energy storage device 9 supplying the drive unit 10 with electrical energy, which energy storage device 9 contains, for example, at least one (rechargeable) battery, and / or

[0044] - to inform about a set gear which specifies the ratio with which a drive torque introduced by muscle power at the input shaft 1 is transmitted to the output shaft 2 of the drive unit 10.

[0045] Figure 1 shows a 2D design for the drive unit 10 of Figure 2 comprising two electric motors 11 and 12.

[0046] The drive unit 10 has the drive shaft 1 and the output shaft 2, both of which are rotatably mounted in 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 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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 across the three shaft trains 21, 22, and 23, results in an extremely compact multi-stage planetary gear 15. 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 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, on the one hand, as overload protection for the drive unit 10 and, on the other hand, it guarantees a basic mechanical function of the drive unit 10 in the event of problems in the electrical system, for example in the event of a voltage drop, or in the event of problems in the control / regulation, for example caused by a failure of one or more sensors of the sensor device 115.

[0055] For easy assembly of the remaining elements of the drive system 10 and their mounting 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 gearbox 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.

[0056] The control electronics 8 of the electric motor drive unit 10 of Figures 1 and 2 comprise, in particular, a B6 bridge circuit 80 for controlling the first and second electric motors 11 and 12. Figure 3 shows an example of such a B6 bridge circuit with six MOSFETs, which is common in the prior art. In the event of a fault, the B6 bridge circuit 80 of the control electronics 8 can be switched off in order to switch the electric motors 11, 12 to a safe and torque-free state. For example, at least one fault signal f s The control electronics 8 can signal that a safety-critical error has been detected on the drive unit 10. This includes, for example, the error signal f sIt is signaled that a rotor position of at least one of the rotors 3, 4 can no longer be detected and / or determined by sensors or that, in the case of field-oriented control of the first and second electric motors 11, 12, a required phase current measurement is no longer available. In such a case, the control electronics 8 should switch the electric motors 11 and 12 to a torque-free state. However, in response to the presence of at least one error signal f s If a shift to the torque-free state is immediately triggered, this leads to the sudden loss of counterpressure on the pedals attached to the cranks 1A. A rider of the electric bicycle F would thus suddenly "pedal into the void," as would be the case if a drive chain broke on a conventional bicycle.

[0057] In order to reduce the risk of injury to a rider of an electric bicycle F in the event of a fault in the electric motor drive, the control electronics 8 are configured, in response to the at least one fault signal f snot to switch the electric motors 11 and 10 directly to a torque-free state, but to first control the second electric motor 12 at least once with an active short circuit. For the duration of the active short circuit, a counterpressure that is still noticeable to the rider of the electric bicycle F can be generated on the pedals, so that the rider of the electric bicycle 1 does not suddenly pedal into the void. Control with an active short circuit also offers the advantage that the active short circuit can be carried out even with minimally functioning hardware and the active short circuit cannot lead to an acceleration of the rotors 3, 4. Furthermore, when controlled with an active short circuit, it can also be observed that noticeable and audible vibrations are triggered on the housing 25 of the drive unit 10.In this way, the driver of the electric bicycle F can then be informed haptically and acoustically of the occurrence of a fault directly on the drive unit 10 in the event of a fault, so that the driver can already reduce the drive force applied to the drive shaft 1 and in particular to the pedal cranks 1A because he has been made aware of the fault that has occurred.

[0058] In order to introduce the rider of the electric bicycle F to the final and thus conclusive switching into the torque-free state, it may be advantageous to control the second electric motor E2 not only once for a predetermined period of time with an active short circuit when an error signal f sIt can also be provided that initial phases, in which control occurs with an active short circuit, alternate with second phases in which the electric motor drive is switched to a torque-free state. As time progresses, the initial phases can then be shortened, especially continuously.

[0059] Such a shortening of the first phases with an active short circuit is illustrated by way of example in Figure 4. In this case, a pulsed signal can be generated by the control electronics 8 to control the active short circuit. The pulse width PW1 of the corresponding (first) control pulse decreases with increasing time t, via a pulse width PW2 to a pulse width PW3. A duty cycle thus decreases over time t, i.e. the proportion of the first phase for a period T decreases over time. The ratio of the pulse duration for control with an active short circuit to the period T therefore decreases. Once the duty cycle has reached the value 0, the electric motors 11 and 12 are held in the torque-free state.

[0060] In the diagram in Figure 4, at least two control pulses with identical pulse widths PW1 or PW2 are followed, as an example, by control pulses with shorter pulse widths PW2 or PW3. However, it is of course also possible for the pulse widths PW1, PW2, and PW3, and thus the degree of control, to be continuously reduced, i.e., the pulse width of a subsequent control pulse is always shorter than that of a previous control pulse. Consequently, the control pulses shown in dashed lines would be omitted in Figure 4.

[0061] It should also be noted at this point that, for illustrative purposes, only three control pulses with different pulse widths PW1, PW2, and PW3 are shown in Figure 4. Of course, fewer or more than three control pulses with different pulse widths can be provided in a control sequence of the control electronics 8, in which first phases alternate with a control of the active short circuit and second phases with a switching to the torque-free state.

[0062] In a drive system which comprises two electric motors 11 and 12 similar to or identical to the drive unit 10, so that with their help a transmission ratio of the planetary gear 15 can be continuously adjusted, in certain driving situations the control of the second electric motor E2 with an active short circuit can also be disadvantageous, even though the error signal f sa safety-critical error has been signaled. During normal operation of the drive unit 10, it can obviously occur that the second rotor shaft 4 is driven by the second electric motor 12 at a negative speed and thus rotates in a negative direction. In such a case, it can be observed that an active short circuit can be detrimental.

[0063] Accordingly, for example, in the embodiment variant of Figure 1, it is provided that before the (first) activation with an active short circuit and thus a possible start of a control sequence according to Figure 4, the direction of rotation of the rotor shaft 4 of the second electric motor 12 is checked. If a negative speed is signaled by a sensor signal Sus from the sensor device 115 for the second rotor shaft 4, activation with an active short circuit is (initially) omitted. Only when the sensor signal Sus signals that the second rotor shaft 4 of the second electric motor 12 is stationary or rotating in the positive direction does activation with an active short circuit occur for the first time.This also takes advantage of the fact that in the event of a fault and thus a no longer fully functional electric motor drive, the rider of the electric bicycle F ensures that the rotor shaft 4 is accelerated in the positive direction of rotation after a comparatively short time through the drive force, which he / she (continues to) apply to the pedals attached to the cranks 1A using muscle power. The sensor signal Sn5 thus signals the fulfillment of an operating parameter of the drive system that characterizes a driving state of the electric bicycle F. Only when the corresponding criterion is met does control with an active short circuit occur.

[0064] The procedure outlined above for controlling the first and second electric motors 11, 12 in the event of a fault is illustrated again in Figure 5 for an embodiment variant of a proposed control method.

[0065] According to this, the first step S1 involves the detection of a safety-relevant error. Here, it is checked whether the error signal f s was generated and is therefore present. In a second step S2, a check is then performed based on the sensor signal Sus to determine whether the speed of the second electric motor 12 and thus of the second rotor shaft is greater than or equal to 0, i.e., whether the rotor shaft 4 is rotating in a forward direction. If this is not the case, the system waits and continues to monitor the speed.

[0066] If the speed of the second electric motor 12 or the rotor shaft 4 is greater than or equal to 0, a (first-time) activation with an active short circuit occurs. As explained in particular with reference to Figure 4, the active phase and thus the pulse duration of a control pulse for the active short circuit are then (continuously) reduced during a control sequence controlled by the control timer 8 until the torque-free state is maintained.

[0067] 1 drive shaft

[0068] 10 Drive unit

[0069] 11 first electric motor

[0070] 12 second electric motor

[0071] 15 planetary gears

[0072] 16 (three-shaft) planetary gear stage

[0073] 17 Sun gear

[0074] 18 ring gear

[0075] 19 planet carriers

[0076] 2 output shaft

[0077] 20 Planetary gear

[0078] 21 first shaft train

[0079] 22 second shaft train

[0080] 23 third shaft train

[0081] 25 housings

[0082] 26 Main housing

[0083] 27 Middle bridge

[0084] 28 Engine cover

[0085] 29 Gearbox cover

[0086] 3 first rotor shaft

[0087] 30 Axis direction

[0088] 31 first spur gear stage

[0089] 32 second spur gear stage

[0090] 33 third spur gear stage

[0091] 34 fourth spur gear stage

[0092] 35 first arrangement level

[0093] 36 second arrangement level

[0094] 37 third arrangement level

[0095] 38 fourth arrangement level

[0096] 39 fifth arrangement level

[0097] 4 second rotor shaft

[0098] 40 freewheel

[0099] 5 first coupling shaft

[0100] 6 second coupling shaft

[0101] 7 third coupling shaft 8 control electronics 80 B6 bridge 9 energy storage 102 control unit

[0102] 110 (Bicycle) frame 111 Front wheel

[0103] 112 Rear wheel 113 Belt / chain

[0104] 114 Wheel sensor 115 Sensor device F Electric bicycle fs Error signal PW1 , PW2, PW3 Pulse width T Period duration

[0105] S115 sensor signal

Claims

Claims 1. Drive system for an electric bicycle (F), with - a drive shaft (1) 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), - at least one electric motor (11, 12) for generating an auxiliary force by external power, - a transmission device (15) for coupling the drive shaft (1) and the output shaft (2) and transmitting the assist force to the output shaft (2) and - control electronics (8) for controlling the at least one electric motor (11, 12), which is configured, in response to at least one error signal (f s) to switch the at least one electric motor (11, 12) into a torque-free state, characterized in that the control electronics (8) is configured, in response to the at least one error signal (f s ) to control the at least one electric motor (11, 12) with an active short circuit before switching to the torque-free state.

2. Drive system according to claim 1, characterized in that the control electronics (8) are configured, in response to the at least one error signal (f s ) to control the at least one electric motor (11, 12) with an active short circuit for a predetermined period of time before switching to the torque-free state.

3. Drive system according to claim 1 or 2, characterized in that the control electronics (8) are configured, in response to the at least one error signal (f s) to control the at least one electric motor (11, 12) with a control sequence in which a first control with an active short circuit and a subsequent first switching to the torque-free state are followed by at least one further control with an active short circuit and at least one subsequent further switching to the torque-free state.

4. Drive system according to claim 3, characterized in that a predetermined first time period for the first activation with the active short circuit is greater than a second time period for the at least one further activation with the active short circuit.

5. Drive system according to claim 3 or 4, characterized in that the control electronics (8) are configured, in response to the at least one error signal (f s) to control the at least one electric motor (11, 12) with a control sequence in which first phases, in which the at least one electric motor (11, 12) is controlled with an active short circuit, and second phases, in which the at least one electric motor (11, 12) is switched to the torque-free state, alternate.

6. Drive system according to claim 5, characterized in that the length of the first phases of a control sequence becomes shorter with increasing time, in particular continuously shorter.

7. Drive system according to claim 5 or 6, characterized in that the control electronics (8) are configured, in response to the at least one error signal (f s ) to control the at least one electric motor (11, 12) for a predetermined total period of time with alternating first and second phases.

8. Drive system according to claim 6 or 7, characterized in that the control electronics (8) are configured, in response to the at least one error signal (f s ) to control the at least one electric motor (11, 12) with alternating first and second phases until the length of the first phases, which become shorter with increasing time, has reached a threshold value.

9. Drive system according to one of claims 5 to 8, characterized in that the control electronics (8) is configured to periodically control the at least one electric motor (11, 12) with an active short circuit via control pulses.

10. Drive system according to claim 6 and claim 9, characterized in that the control electronics (8) is configured to reduce a control level of the control pulses during the control sequence with increasing time.

11. Drive system according to one of the preceding claims, characterized in that the control electronics (8) is configured to connect the at least one electric motor (11, 12) with an active short circuit only upon fulfillment of at least one additional criterion, in particular only if an additional criterion relating to an operating parameter of the drive system is met.

12. Drive system according to claim 11, characterized in that the control electronics (8) are configured to control the at least one electric motor (11, 12) with an active short circuit only when a rotational speed of the at least one electric motor (12) is above a threshold value.

13. Drive system according to one of the preceding claims, characterized in that the drive system comprises a first electric motor (11) and a second electric motor (12) and the transmission device comprises at least one planetary gear (15) whose transmission ratio can be adjusted by means of the first and second electric motors (11, 12), wherein a torque generated by the first electric motor (11) can be transmitted at least partially to the output shaft (2).

14. Drive system according to claims 12 and 13, characterized in that the control electronics (8) is configured to control the first and second electric motors (11, 12) with an active short circuit only when a speed of the second electric motor (12) is above a threshold value.

15. Drive system according to one of the preceding claims, characterized in that the control electronics (8) comprises a B6 bridge circuit (80) for controlling the at least one electric motor (11, 12).

16. Drive system according to one of the preceding claims, characterized in that the at least one error signal (f s ) that the position of a rotor (3, 4) of the at least one electric motor (11, 12) can no longer be detected and / or determined and / or, in the case of field-oriented control of the at least one electric motor (11, 12) via the control electronics (8), a phase current measurement is no longer available.

17. Method for controlling a drive system of an electric bicycle (F), wherein the drive system - a drive shaft (1) is provided for applying a driving force for driving the electric bicycle (F) by means of muscle power, - an output shaft (2) is provided for transmitting the drive force to a wheel (112) of the electric bicycle (F), - at least one electric motor (11, 12) is provided for generating an auxiliary force by external power, - a transmission device (15) couples the drive shaft (1) and the output shaft (2) and is provided for transmitting the assist force to the output shaft (2) and - the at least one electric motor (11, 12) in response to at least one error signal (f s ) can be switched into a torque-free state, characterized in that in response to the at least one error signal (f s ) the at least one electric motor (11, 12) is controlled with an active short circuit before switching to the torque-free state.

18. 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 17.

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