DRIVE SYSTEM FOR AN ELECTRIC BICYCLE WITH RUN-THE-RUN OPERATION AND CONTROL METHOD

Description

[0001] The proposed solution concerns a drive system for an electric bicycle and a control method.

[0002] It is known to use two electric motors in combination with a superposition gear system with a planetary gear stage on an electric bicycle, i.e. on a so-called e-bike or pedelec, in order to continuously adjust the gear ratio between the drive and output. A corresponding drive system comprises, on the one hand, a drive shaft, via which a drive torque generated by a rider of the electric bicycle can be introduced and on which pedals are provided for this purpose. A drive torque introduced at the drive shaft and / or a torque generated by an electric motor is then transmitted to a wheel, usually a rear wheel of the electric bicycle, via an output shaft of the drive system that is to be coupled to a wheel of the electric bicycle.The drive shaft and the output shaft are coupled to one another via the superposition gearing, wherein a torque generated by a first electric motor of the two electric motors can be at least partially transmitted to the output shaft. A gear ratio can be continuously adjusted via the second electric motor of the two electric motors, so that the electric bicycle can be accelerated via a drive torque of the first electric motor without having to rotate the drive shaft faster or with greater force. The second electric motor thus also serves to support the torque generated by the first electric motor and, depending on the gear ratio, can rotate a rotor shaft in different directions of rotation. A drive device for an electric bicycle with a comparable superposition gearing and two electric motors is known, for example, from JP 2008-285069 A, WO 2019 / 166402 A1 or WO 2019 / 175022 A1.Document WO2019 / 166402A1 shows the preamble of claim 1.

[0003] The drive system known from WO 2019 / 175022 A1 provides for an emergency operation mode implemented by a freewheel. The freewheel ensures that muscle-powered power applied to the drive shaft can still be used to drive the electric bicycle, even if an energy storage device (e.g. a battery) of the drive system cannot provide electrical current to operate the first and second electric motors. The disadvantage of the emergency operation mode described in WO 2019 / 175022 A1, however, is that only a fixed gear ratio is specified and the gear ratio of the superposition gear can no longer be continuously varied. A continuously variable automatic transmission function, which is provided during normal operation of the drive system, is therefore no longer available.The fixed gear ratio in emergency mode can then, for example, correspond to the smallest gear ratio that can also be used in normal operation. However, with such a small gear ratio, only comparatively low speeds can be achieved, even when the drive shaft is rotated at a high pedaling frequency using muscle power.

[0004] Against this background, the proposed solution is based on the task of providing a drive system that is improved in this respect.

[0005] This object is achieved with a drive system of claim 1 and a control method of claim 12. A proposed drive system comprises at least a drive shaft, an output shaft for driving a wheel of an electric bicycle, a first electric motor which drives a first rotor shaft, a second electric motor which drives a second rotor shaft, a superposition gear whose transmission ratio is continuously adjustable with the aid of the first and second electric motors and via which the drive shaft and the output shaft are coupled to one another, wherein a torque generated by the first electric motor is at least partially transmittable to the output shaft, and an energy store for supplying the first and second electric motors with electrical current (during normal operation of the drive system).

[0006] In addition, control electronics (e.g. provided via control software) are provided for power control of the first and second electric motors in an emergency operation of the drive system. The emergency operation is active when the first and second electric motors cannot be supplied with electrical power via the energy storage device, for example because the energy storage device has been removed, is defective, or is empty. Via the control electronics, at least one of the first and second electric motors can then be operated at least temporarily as a generator in the emergency operation in order to convert (mechanical) power applied to the drive shaft by muscle power into electrical energy. This energy enables a continuous variation of the transmission ratio of the superposition gear even in emergency operation and can be controlled by the control electronics.

[0007] The basic idea of ​​the proposed solution is thus to provide control electronics that are configured to operate at least one of the first and second electric motors at least temporarily as a generator in the emergency mode, thus enabling a continuous variation of the gear ratio of the superposition gear even in the emergency mode. Consequently, in the emergency mode, the necessary electrical power for the automatic transmission function provided by the superposition gear is provided by at least one of the two electric motors, with the two electric motors being controlled accordingly via the provided control electronics. In this way, at least one of the electric motors can be used in generator mode to convert at least part of the mechanical power input by a rider of the electric bicycle into electrical power.

[0008] For example, the control electronics are configured to switch the drive system to emergency operation depending on an energy storage signal and then control the first and second electric motors differently than in normal operation. The energy storage signal signals to the control electronics whether sufficient electrical energy is still being provided by an energy storage device in the drive system. In this case, the signaling of a changed state and thus the switching to emergency operation can occur in particular through the absence of the energy storage signal. The energy storage signal is accordingly also suitable for signaling whether an energy storage device is still present at all. For example, the energy storage signal signals the presence of a faultlessly functioning energy storage device, i.e. a battery.If the battery has been removed, or is defective or empty, this is signaled to the control electronics via the energy storage signal, and the control electronics then switches the drive system to emergency operation. In the drive system's emergency operation, at least one of the first and second electric motors is then controlled by the control electronics differently than in normal operation, in order to continue to electronically continuously adjust the transmission ratio of the superimposed gear even in emergency operation.

[0009] In one embodiment, the control electronics are configured, for example, to control one of the electric motors in emergency operation with the aim of regulating an electrical energy balance within the drive system to zero. The control electronics are accordingly configured, for example, to process measurement signals which signal the power currently provided or consumed by the individual electric motors. Furthermore, the control electronics can, if necessary, also process measurement signals relating to the power consumption of any consumers present within the drive system or consumers coupled to the drive system. Depending on the power values ​​determined using these measurement signals and the resulting energy balance, the control electronics are then able to control one of the electric motors in emergency operation in such a way that the energy balance is regulated to zero.In other words, in emergency mode, the control electronics regulate the power of this electric motor in such a way that an energy balance of zero is achieved.

[0010] In one embodiment, the control electronics are set up in this context, for example, to control the second electric motor in accordance with normal operation, in which the first and second electric motors are supplied with electrical current via the energy storage device, and to control the first electric motor of the drive system with the aim of regulating an electrical energy balance within the drive system to zero.

[0011] The control electronics and the control system implemented thereby maintain the control of the second electric motor during the drive system's emergency operation as in normal operation. However, in contrast to normal operation, an energy balance-dependent control of the first electric motor is provided. As a rule, one of the electric motors is therefore operated as a generator and the other as a motor when the drive system's emergency operation is active.

[0012] As already explained above, in this context in particular, the control electronics for the power control of the first and second electric motors in emergency operation can be configured to take into account a power consumption of at least one consumer supplied with electrical energy via the drive system and / or a power loss for the control of the electric motors. Consequently, a corresponding power consumption and / or power loss can be detected and evaluated by the control electronics in order to control the one electric motor to a generator or motor operation (with varying power) depending on this.If, for example, the first electric motor is controlled by the power control in emergency operation with the aim of regulating an electrical energy balance within the drive system to zero, a power consumption of at least one consumer supplied with electrical energy via the drive system and / or a measured power loss also flows into the energy balance-dependent control of the first electric motor.

[0013] In one embodiment, the drive system comprises at least one energy buffer connected to the control electronics, which is designed and provided for buffering charge and thus for providing an intermediate circuit voltage. By providing an intermediate circuit with at least one associated energy buffer, emergency operation can be controlled more reliably if necessary.

[0014] For example, the control electronics can be configured to control one of the electric motors with the aim of maintaining the intermediate circuit voltage at a specific voltage value. A closed-loop control system provided by the control electronics then aims to maintain the intermediate circuit voltage, and thus the electrical energy present in the drive system, at a constant (voltage) value. The intermediate circuit voltage can also be measured continuously, as this provides direct feedback about the electrical energy present in the drive system. The control electronics can thus be configured to process a measurement signal representative of the current intermediate circuit voltage of the drive system. Based on this measurement signal, an actual voltage value can be determined and compared with at least one target voltage value.This target voltage value can be stored in a memory of the control electronics or made available to the control electronics via a separate voltage signal.

[0015] Using the measured value representative of the current intermediate circuit voltage, the control electronics can then, for example, control the first electric motor in such a way that, if the actual voltage value falls below a first target voltage value, the first electric motor is controlled to generate more power if the first electric motor is currently operating as a generator, or the first electric motor is controlled to consume less power if the first electric motor is currently operating as a motor.

[0016] In principle, particularly taking into account the power consumption of at least one consumer and / or power loss, it may happen that both the first electric motor and the second electric motor are operated in motor or generator mode during emergency operation. However, if the intermediate circuit voltage drops below the first target voltage value, the proposed design variant provides for the first electric motor to be driven more strongly toward generator mode in order to supply more energy to the drive system (if the first electric motor is already operating in generator mode) or to withdraw less energy from the drive system (if the first electric motor is currently operating in motor mode).

[0017] Alternatively or additionally, the control electronics can be set up to control the first electric motor depending on the measurement signal representative of the current intermediate circuit voltage, in such a way that if the actual voltage value rises above a second target voltage value, the first electric motor is controlled to generate less power when the first electric motor is currently operating as a generator, or the first electric motor is controlled to consume more power when the first electric motor is currently operating as a motor.

[0018] In this embodiment, it is therefore provided that the first electric motor is driven more strongly in the direction of motor operation in order to supply less energy to the drive system (if the first electric motor is currently operating as a generator) or to withdraw more energy (if the first electric motor is currently operating as a motor) when the intermediate circuit voltage rises above a certain setpoint.

[0019] In principle, the first and second target voltage values ​​can be identical, so that exactly one target voltage value is decisive for the control. In a combination of the two exemplary embodiments described above, to prevent a control system provided by the control electronics from intervening immediately when a certain target voltage value is exceeded or undershot, different first and second target voltage values ​​can be used. Consequently, within a tolerance range between the first target voltage value and the second target voltage value, the control electronics will not intervene, and thus the control of the first electric motor will not be changed.

[0020] One aspect of the present solution also concerns an electric bicycle with a proposed drive system.

[0021] Furthermore, a control method is proposed in which a drive system for an electric bicycle (a motor-assisted bicycle) is operated in emergency mode when the first and second electric motors of the drive system cannot be supplied with electrical power via an energy storage device. In this emergency mode, at least one of the first and second electric motors is operated at least temporarily as a generator in order to convert a (mechanical) power applied to a drive shaft of the drive system by muscle power into electrical energy, with which a continuous variation of a transmission ratio of a superposition gear of the drive system is enabled and controlled even in emergency mode.

[0022] An embodiment variant of a proposed control method can be implemented, in particular, with an embodiment variant of a proposed drive system. Accordingly, the advantages and features mentioned above and below for an embodiment variant of a proposed drive system also apply to embodiment variants of a proposed control method, and vice versa.

[0023] For example, an embodiment of a proposed control method can provide that in the emergency operation the second electric motor is controlled according to a normal operation in which the first and second electric motors are at least temporarily supplied with electrical current via the energy storage device (and if necessary only temporarily one of the electric motors is operated as a generator and supplies the energy storage device), and the first electric motor is controlled with the aim of regulating an electrical energy balance within the drive system to zero.

[0024] Consequently, in emergency operation, an energy balance-dependent power control and thus energy balance-dependent control of the first electric motor is also provided here.

[0025] Alternatively or additionally, the drive system can comprise at least one energy buffer for generating an intermediate circuit voltage in emergency operation for supplying electrical power to at least one of the electric motors. One of the electric motors can then be controlled with the aim of maintaining the intermediate circuit voltage at a specific voltage value. Consequently, a control system provided aims to maintain the intermediate circuit voltage for supplying the second electric motor at a constant voltage value in light of the changing mechanical power applied to the drive shaft by muscle power.

[0026] The proposed solution further comprises a computer program product, for example embodied by control software implemented in control electronics, which contains stored instructions which, when executed by at least one processor of the control electronics, cause the at least one processor to execute an embodiment variant of a proposed control method.

[0027] The attached figures illustrate exemplary embodiments of the proposed solution. In particular, the proposed solution can be used in combination with a drive system as already described in WO 2019 / 175022 A1. However, the proposed solution is not limited to this.

[0028] Here we show: Figure 1 Details of a control electronics for a power control of a drive system for an electric bicycle in an emergency operation, wherein this drive system is designed, for example, according to one of the embodiments of the Figures 4 to 7 can be constructed; Figure 2 a further development of the variant of the Figure 1 with an energy buffer and an energy balance-dependent control for a first electric motor of the drive system; Figure 3 shows a further development of the embodiment of the Figure 2 , which also provides an intermediate circuit voltage, but in contrast to the version of the Figure 2 is also used to control the first electric motor; Figure 4 shows a drive system known from the prior art with output-side power split; Figure 5 shows a structural design of the drive system according to Figure 4; Figure 6 shows a drive system known from the prior art with drive-side power split, Figure 7 shows a structural design of the drive system according to Figure 6 ; Figures 8A-8B Diagrams illustrating the operation of the drive system, where in the diagram the Figure 8A a power P of two electric motors of the drive system is plotted against a (driving) speed and in the diagram of the Figure 8B a speed of a drive shaft of the drive system to be caused by a rider of the electric bicycle above the speed v.

[0029] The Figures 4 and 5show a transmission structure and a 2D design of a prior art drive system 10 between a drive shaft 1 and an output shaft 2 in a gear housing 25 for use in an electric bicycle. The drive shaft 1 passes through the gear housing 25 and is connected on each side to a pedal crank, via which the rider drives the drive system 10. The output shaft 2 protrudes from the gear housing 25 on only one side and is connected to a sprocket or toothed belt pulley to drive the rear wheel of the bicycle.

[0030] The drive system 10 has a first motor 11 with a first rotor shaft 3. In this application, the motor is designed as an electric motor. The drive system 10 also has a second motor 12 with a second rotor shaft 4. The second motor 12 is also designed as an electric motor in this application. The two electric motors 11 and 12 are connected via a power controller 8 and thus form a continuously variable electric actuating gear. The power controller 8 is also connected to an energy storage device 9 in the form of a battery. This allows the output shaft 2 to be driven purely electrically via the first electric motor 11. The energy storage device 9 can then also be used as a braking energy storage device when braking power flows into the drive system 10 at the output shaft 2.

[0031] The input shaft 1, the output shaft 2, and the two rotor shafts 3 and 4 are coupled via a multi-stage superposition gear 15, which has several gear stages with a degree of freedom of 1 and at least one planetary gear stage 16 with a degree of freedom of 2. The gear stages here are designed as spur gear stages. However, toothed belt gear stages are also conceivable. The three-shaft planetary gear stage 16 has a sun gear 17, a ring gear 18, and a planet carrier 19 with several planet gears 20 mounted on planet gear pins.

[0032] The elements of the drive system 10 are distributed over three shaft trains 21, 22 and 23, which are all arranged parallel to each other in the available installation space of the gear housing 25.

[0033] The input 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 superposition gear 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.

[0034] On the first shaft train 21, the outer output shaft 2 encloses the inner drive shaft 1 on one side of the gear housing 25 and the second rotor shaft 4 encloses the drive shaft 1 on the other side of the gear housing 25.

[0035] The arrangement of the three-shaft planetary gear stage 16 on the second shaft train enables the use of a small-diameter sun gear 17. This, in turn, enables a large static gear ratio greater than |-4| with a still reasonably large ring gear 18. With such a large negative static gear ratio, the simple and therefore narrow planetary gears 20 become so large that sufficiently large, narrow ball bearings can be accommodated as planetary gear bearings. Overall, this results in a planetary gear stage 16 that is advantageously very short in the axial direction.

[0036] Four gear stages designed as spur gear stages serve to kinematically couple the elements of the drive system 10 distributed across the three shaft trains 21, 22, and 23. The input shaft 1 on the first shaft train 21 is connected to a first coupling shaft 5 on the second shaft train 22 via a first spur gear stage 31. The output shaft 2 on the first shaft train 21 is connected to a second coupling shaft 6 on the second shaft train 22 via a second spur gear stage 32. The second rotor shaft 4 of the second electric motor 12 on the first shaft train 21 is connected to a third coupling shaft 7 on the second shaft train 22 via a third spur gear stage 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 shaft train 23 is connected via a fourth spur gear stage to the ring gear 18 of the planetary gear stage 16 on the second shaft train 22.

[0037] The first spur gear stage 31 increases the speed of the input shaft 1 to an absolute speed approximately three times higher than that of 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 an approximately 30% lower speed of the output shaft 2 via the gear ratio of the second spur gear stage 32. The ratio of the gear ratios of the first spur gear stage 31 and the second spur gear stage 32, each defined as the ratio of the speed of the gear on the second shaft train 22 to the speed of the gear on the first shaft train 21, defines the maximum actuating coupling ratio between the first coupling shaft 5 and the second coupling shaft 6. For a high efficiency curve over the actuating coupling ratio in the actuating range, it is advantageous if the maximum and minimum actuating coupling ratios are approximately reciprocal. This can be easily achieved with such a design.

[0038] 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 first embodiment has a power split on the output side.

[0039] In the Figure 4 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 gearbox housing 25 into the gearbox housing 25. In the Figure 4it 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 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 superposition gear 15.

[0042] From the Figures 4 and 5It also becomes clear that the gear of the first spur gear stage 31 on the first coupling shaft 5 has a larger pitch circle radius than the sun gear 17 on the third coupling shaft 7. This means that when assembling the drive system 10, the sun gear 17 can be inserted through the gear on the first coupling shaft 5.

[0043] For easy assembly of the remaining elements of the drive system 10 and their mounting in the transmission housing 25, the transmission housing 25 has four essential housing parts. The transmission 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 transmission 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 transmission housing 25.

[0044] The Figure 5 The design shown illustrates possible bearing arrangements for all shafts of the drive system 10 in the gearbox housing 25 or on other shafts. The goal is to implement statically determinate bearing arrangements with large bearing spacing and small bearing sizes. These are good prerequisites for quiet and low-loss operation of all shafts.

[0045] The input shaft 1 is supported on the first shaft train 21 via a first bearing 41 in the output shaft 2 and a second bearing 42 in the motor cover 28. The input shaft 1 protrudes from the gearbox housing 25 on both sides and is subject to large radial loads from the drive. The bearings 41 and 42 are spaced as far apart as possible to ensure optimal support for the input shaft 1. The output shaft 2 is supported by a third bearing 43 in the gearbox cover 29 and by a fourth bearing 44 on the input shaft. The bearings 41 and 43 are arranged approximately radially around one another, so that the radial bearing load from bearing 41 is supported directly via bearing 43 in the gearbox housing 25.

[0046] The first rotor shaft 3 is supported by a fifth bearing 45 in the gearbox cover 29 and a sixth bearing 46 in the motor cover 28. However, the bearing 46 can also be positioned between the center web 27 and the rotor shaft 3 with similarly good performance.

[0047] The second rotor shaft 4 is mounted on the drive shaft 1 via a seventh bearing 47 and an eighth bearing 48. Bearing 47 can also be located between the rotor shaft 4 and the center web 27, but in this case it has a larger diameter. Bearing 48 could also be located between the rotor shaft 4 and the motor cover 28, but this would also require more axial and radial space.

[0048] On the second shaft train 22, several shafts are mounted one inside the other, but ultimately in the gearbox housing 25. The second coupling shaft 6 is the most heavily loaded shaft on the second shaft train 22 and is therefore designed as the innermost shaft, supported by a ninth bearing 49 in the gearbox cover 29 and a tenth bearing 50 in the center web 27. This results in a beneficially large bearing spacing. Alternatively, the bearing 50 can also be located in the engine cover 28.

[0049] The third coupling shaft 7 is supported on the second coupling shaft 6 via an eleventh bearing 51 and on the center web 27 via a twelfth bearing 52. The first coupling shaft 5 is supported on the third coupling shaft 7 via a thirteenth bearing 53 and on the second coupling shaft 6 via a fourteenth bearing 54. A fifteenth bearing 55 also transmits axial forces between the third coupling shaft 7 and the center web 27, and a sixteenth bearing 56 transmits axial forces between the first coupling shaft 5 and the third coupling shaft 7.

[0050] In the first arrangement level 35 with the second spur gear stage 32, there is a freewheel 40 between the input shaft 1 and the output shaft 2. This is preferably a sprag type freewheel because this type of freewheel has a high torque capacity and can utilize the hardened cylindrical surfaces of the shafts to be coupled. In the design according to Figure 5The freewheel has its own inner ring and its own outer ring.

[0051] If the control in the power control 8 limits the maximum torque of the second motor 12, an excessive drive torque that can no longer be supported by the second motor 12 accelerates the drive shaft 1 until the freewheel 40 automatically couples the drive shaft 1 with the output shaft 2. The freewheel 40 thus serves, on the one hand, as overload protection for the drive system and, on the other hand, guarantees basic mechanical function of the drive in the event of problems in the electrical system, for example, a voltage drop, or problems in the control / regulation, for example, a sensor failure.

[0052] For precise and reliable control of the drive system with a high level of drive comfort, the control system requires precise signals at short cycle times. A first resolver 57 with a sensor and encoder wheel for precise measurement of the angular position and speed is located on and around the first rotor shaft 3. A second resolver 58 is located on and around the second rotor shaft 4. A simple speed measuring system 59 also measures the speed of the drive shaft 1. The high-precision resolvers 57 and 58 are prerequisites for precise speed and / or torque control on the two motors 11 and 12. The additional and optional speed measuring system 58 on and around the drive shaft enables a certain degree of redundancy for greater system reliability. It can be used, for example, to check the plausibility of the resolver signals and enables a reduced-function emergency function in the event of a resolver failure.

[0053] On the gearbox housing 25, in the Figure 5An acceleration and inclination sensor 24, such as those used in many smartphones today, is also installed. The acceleration and inclination signals, combined with the knowledge of the transmitted power, allow conclusions to be drawn about the system weight and the dynamics of the drive torque. This information can be used in the power control system for faster and more convenient control.

[0054] The Figures 6 and 7 show a transmission structure and a 2D design of another drive system 10 known from the prior art between the input shaft 1 and the output shaft 2 in a transmission housing 25 for use in an electric bicycle.

[0055] In the first design, the first coupling shaft 5 is connected to the planetary carrier 9, and the second coupling shaft 6 is connected to the ring gear 18 of the planetary gear stage 20. In the second design, the first coupling shaft 5 is connected to the ring gear 18, and the second coupling shaft 6 is connected to the planetary carrier of the planetary gear stage 20. These are the only structural differences between the two designs.

[0056] Since the first rotor 3 of the first motor 11 is connected to the ring gear 18 via the fourth spur gear stage 34 in both embodiments (gear ratio in the range of |-8|), the speeds of the output shaft 2 and the first rotor shaft 3 are proportional in the first embodiment. In the second embodiment, the speeds of the drive shaft 1 and the first rotor shaft 3 are proportional. Both variants make technical sense. In an electrically assisted bicycle drive, the higher the electrical assistance, the more advantageous the first embodiment is, because the electrical assistance power then acts on the driven wheel via a more direct route from the energy storage device 9, primarily via the first motor 11.

[0057] In the design variants of the Figures 4 to 7The freewheel 40 enables emergency operation, which allows the drive system 10 to remain functional even if the energy storage device 9 is removed, defective, or empty. However, in this emergency operation, only a fixed gear ratio is provided, which corresponds to the lowest gear ratio in normal operation. Consequently, in emergency operation—despite the high pedaling frequency on the drive shaft 1—only comparatively low speeds can be achieved.

[0058] In this respect, the proposed solution provides a remedy, for which possible implementation variants are based on the Figures 1 , 2 and 3 are illustrated.

[0059] These design variants aim at providing control electronics 8.1, 8.2 for power control of first and second electric motors in emergency operation of a drive system, in which a superposition gear can be controlled with the help of the electric motors for a continuously variable transmission ratio. The design variants of the Figures 1 , 2 and 3 are thus particularly suitable for power control of the first and second electric motors 11 and 12 in a drive system 10 of an embodiment variant of the Figures 4 to 7 and are described below with reference to the design variants of the Figures 4 to 7 explained.

[0060] The control electronics 8.1, 8.2 of the Figures 1 , 2 and 3is represented by two control electronics parts 8.1 and 8.2, through which control signals are transmitted to one of the electric motors 11 and 12. Common to all variants of the Figures 1 , 2 and 3 that at least one of the electric motors, here, for example, the first electric motor 11, is operated at least temporarily as a generator in an emergency operation mode via the control electronics 8.1, 8.2 in order to convert mechanical power applied to the drive shaft 1 by muscle power into electrical energy, which further enables a continuous variation of the transmission ratio of the superposition gear 15 even in emergency operation. The control electronics components 8.1, 8.2 shown separately in the figures can of course be part of a uniform microcontroller and are shown separately in the figures merely for the sake of simplicity.

[0061] In the version of the Figure 1The control electronics 8.1, 8.2 (on the control electronics part 8.1) is coupled to the first electric motor 11 and evaluates an energy storage signal s 9 , which indicates - possibly also by its absence - whether the energy storage device 9 of the drive system 10 is functioning properly. In this case, the energy storage signal s 9 is understood to be an external or system-internal signal and thus also a signal that signals an undervoltage event, i.e. the occurrence of a voltage value in the system that is too low (compared to a stored reference value). In principle, a single, specific value of the energy storage signal or a specific course of the energy storage signal over time can be decisive for the switch to emergency operation. For example, the energy storage signal s 9 signals whether the energy storage device 9 and thus a battery of the drive system 10 has been removed, is defective, or is empty.If this is the case, the control electronics 8.1, 8.2 switches the drive system 10 into emergency operation and thus into another operating mode in which, in particular, the first electric motor 11 is operated differently from normal operation.

[0062] Thus, the second electric motor 12 is controlled via a control signal s 82 of the control electronics unit 8.2, as in normal operation, in order to continue to continuously vary the transmission ratio of the superposition gear 15 depending on the power to be delivered to the wheel of the electric bicycle and, accordingly, to maintain a moderate cadence on the drive shaft 1 even for a significantly higher travel speed. In contrast, the first electric motor 11 is controlled via a control signal s 81 in emergency operation such that an electrical energy balance is regulated to zero. For this purpose, the power L 11 , L 12 , and LV are determined within the drive system 10.Here, corresponding measurement signals are tapped in order to detect a power drop across the second electric motor 12 (power determination L 12 ), a power drop across at least one consumer V (power determination LV ) and the power of the first electric motor 11 (power determination L11) via measurement signals which are transmitted to the control electronics or its control electronics part 8.1.

[0063] The power lost at the second electric motor 12 is in the Figure 1is specified as P_(12), while the power drop across the consumer V is specified as P_(div). Using the control system provided by the control electronics 8.1, 8.2, the power to be made available to the first electric motor 11 is calculated as P_(11) with P_(11)=-P_(12)-P_(div). Depending on the determined energy balance and in particular the power P_(11) to be generated by the first electric motor 11, the control electronics 8.1, 8.2 generate the appropriate control signal s 81 for the first electric motor 11 at the control electronics part 8.1 in order to control it accordingly. As a rule (depending on the desired cadence, driving speed, and system design), the electric motor 11 operates as a generator, while the second electric motor 12 operates as a motor. This is illustrated by way of example in the diagrams Figures 8A and 8Bas a function of the speed of the electric bicycle achieved with the drive system 10. The diagram shows the Figure 8A the power P of the two electric motors 11 and 12 versus the speed v, while the diagram of the Figure 8B shows the rotational speed U of the drive shaft 1 to be achieved by the rider of the electric bicycle as a function of the speed v. From this it can be seen that both electric motors 11 and 12 are operated as generators or motors depending on the riding situation, in particular in order to be able to keep the rotation of the drive shaft 1 constant for the rider at a desired higher (riding) speed v.

[0064] However, situations may also arise during emergency operation in which both the first electric motor 11 and the second electric motor 12 are operated as a motor or generator, for example due to a higher power P_(div) being lost at at least one consumer. For example, consumer V can represent a lighting system that must be supplied to the electric bicycle.

[0065] In the version of the Figure 2The control electronics 8.1, 8.2 are coupled to an energy buffer 60. This energy buffer 60, formed, for example, by at least one intermediate circuit capacitor, a flywheel, a magnetic field arrangement, or a hydraulic pressure accumulator, buffers charge or energy and provides an intermediate circuit. The energy buffer 60 allows for better control of power losses and more stable control of emergency operation. The control electronics 8.1, 8.2, with the evaluation logic provided in the control electronics section 8.1, then strives, for example, to keep the energy balance during emergency operation at a constant value.

[0066] In a variant with an intermediate circuit capacitor, the control electronics 8.1, 8.2, with the evaluation logic provided in the control electronics section 8.1, for example, strive to keep the intermediate circuit voltage as constant as possible during emergency operation. Here, the first electric motor 11 continues to be operated in an energy balance-dependent manner. This means that, via the power measurements L 12 , LV , and L 11 , the first electric motor 11 is controlled, in particular, with the aid of the control signal s 81 in such a way that the energy balance is regulated to zero.

[0067] In the further training of Figure 3 An intermediate circuit capacitor 61 is provided as an energy buffer with an additional measuring tap for providing a measuring signal u IST to the control electronics 8.1, 8.2. This is how the design variant of the Figure 3In emergency operation, the first electric motor 11 is controlled as a function of a measured intermediate circuit voltage within the drive system 10, which is represented by the measurement signal u IST and made available to the control electronics section 8.1. The measurement signal u IST representative of the intermediate circuit voltage, or an actual voltage value determined therefrom, can then be compared with a target voltage value within the control electronics 8.1, 8.2 in order to control the first electric motor 11 such that the actual voltage value corresponds to the target voltage value or is at least approximated thereto.

[0068] A single, and therefore precisely one, target voltage value can be provided within the control electronics. However, it is also possible to provide two different target voltage values ​​that differ from each other by a tolerance range. The different target voltage values ​​are shown in the exemplary embodiment of the Figure 3 made available to the control electronics section 8.1 via signals u SOLL1 and u SOLL2.

[0069] The Figure 3The control system illustrated aims to keep the intermediate circuit voltage and thus the electrical energy present in the drive system 10 at a constant value. If, for example, the intermediate circuit voltage measured across the measuring point of at least one intermediate circuit capacitor 61 falls below a setpoint, for example u SOLL1 , the first electric motor 11 is driven more strongly toward generator operation via the control history 8.1, 8.2 in order to supply more energy to the drive system 10 (if the first electric motor 11 is already operating as a generator) or to withdraw less energy (if the first electric motor is currently operating as a motor).If, on the other hand, the intermediate circuit voltage rises above a setpoint, for example the setpoint u SOLL2 , the first electric motor 11 is driven more strongly in the direction of motor operation in order to supply less energy to the drive system 10 (if the first electric motor 11 is currently being operated as a generator) or to withdraw more energy (if the first electric motor 11 is already being operated as a motor). With power control via an intermediate circuit voltage, power losses can be automatically compensated for and the drive system 11 can be operated with smaller energy buffers and thus, for example, smaller intermediate circuit capacitors 61 (than in the design variant of the . Figure 2 ) are operated.

[0070] The proposed solution provides a drive system 10 which can provide a continuously variable automatic transmission function via a superposition gear 15 in an emergency mode even without an external energy supply and thus also without a (functional) energy storage device 9. In this emergency mode, a comparatively high driving speed can thus still be achieved even with a moderate pedaling frequency, in particular a higher driving speed than would be possible with a solution known from the prior art using only a freewheel 40, as in the embodiments of the Figures 4 to 7 is shown. List of reference symbols

[0071] 1Input shaft 2Output shaft 3First rotor shaft 4Second rotor shaft 5First coupling shaft 6Second coupling shaft 7Third coupling shaft 8Power control 8.1Control electronics part for first electric motor 9Energy storage 10Drive system 8.2Control electronics part for second electric motor 11First electric motor 12Second electric motor 15Superposition gear 16Three-shaft planetary gear stage PG 17Sun gear 18Ring gear 19Planet carrier 20Planet gears 21First shaft train 22Second shaft train 23Third shaft train 24Acceleration and inclination sensor 25Gearbox housing 26Main housing 27Center web 28Motor cover 29Gearbox cover 30Axis direction 31First spur gear stage 32Second spur gear stage 33Third spur gear stage 34Fourth spur gear stage 35First arrangement level 36Second arrangement level 37Third arrangement level 38Fourth arrangement level 39Fifth arrangement level 40Freewheel 41-56Bearing 57First resolver with sensor and encoder wheel 58Second resolver with sensor and encoder wheel 59Speed ​​measuring system 60Energy buffer 61Intermediate circuit capacitor L 11 , L 12 , LV Power determination s 81 , s 82 Control signal s 9 Energy storage signal u ACTUAL Measurement signal u SOLL1 , u SOLL2 Target signal VConsumer.

Claims

1. Drive system for an electric bicycle, having - a drive shaft (1), - an output shaft (2) for driving a wheel of the electric bicycle, - a first electric motor (11) which drives a first rotor shaft (3), - a second electric motor (12) which drives a second rotor shaft (4), - an overriding gear (15), the gear ratio of which is infinitely adjustable with the aid of the first and second electric motors (11, 12) and by way of 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 - an energy storage device (9) for supplying the first and second electric motors (11, 12) with electric current, wherein the drive system (10) comprises an electronic control unit (8.1, 8.2) which is specified to control the output of the first and second electric motors (11, 12) in an emergency operation of the drive system (10), wherein - the emergency operation is active when the first and second electric motors (11, 12) cannot be supplied with electric current by way of the energy storage device (9), characterized in that - the electronic control unit (8.1, 8.2) is specified to operate at least one of the first and second electric motors (11, 12) in emergency operation at least temporarily in a regenerative manner in order to convert an output applied to the drive shaft (1) by means of muscle force into electric energy by way of which an infinitely variable variation of the transmission ratio of the overriding gear (15), even in emergency operation, is enabled and is able to be controlled by the electronic control unit (8.1, 8.2).

2. Drive system according to Claim 1, characterized in that the electronic control unit (8.1, 8.2) for controlling the output of the first and second electric motors (11, 12) in emergency operation is specified to actuate one of the electric motors (11, 12) with the aim of adjusting an electrical energy balance within the drive system (10) to zero.

3. Drive system according to Claim 2, characterized in that the electronic control unit (8.1, 8.2) for controlling the output of the first and second electric motors (11, 12) in emergency operation is specified - to actuate the second electric motor (12) in accordance with normal operation, in which the energy storage device (9) supplies the first and second electric motors (11, 12) with electric current, and - to actuate the first electric motor (11) with the aim of adjusting an electrical energy balance within the drive system (10) to zero.

4. Drive system according to Claim 2 or 3, characterized in that the electronic control unit (8.1, 8.2) for controlling the output of the first and second electric motors (11, 12) in emergency operation is specified to take into account a power consumption of at least one consumer (V) supplied with electric energy by way of the drive system (10) and / or a power loss for adjusting the one electric motor (11).

5. Drive system according to one of the preceding claims, characterized in that the drive system (10) comprises at least one energy buffer (60, 61) which is connected to the electronic control unit (8.1, 8.2).

6. Drive system according to Claim 5, characterized in that the electronic control unit (8.1, 8.2) for controlling the output of the first and second electric motors (11, 12) in emergency operation is specified to actuate one of the electric motors (11, 12) with the aim of keeping a DC link voltage provided by way of the energy buffer (61) at a certain voltage value.

7. Drive system according to Claim 6, characterized in that the electronic control unit (8.1, 8.2) is specified to process a measurement signal (uIST) which is representative of the current DC link voltage of the drive system (10).

8. Drive system according to Claim 7, characterized in that the electronic control unit (8.1, 8.2) is specified to compare an actual voltage value recorded on the basis of the measurement signal (uIST) with at least one setpoint voltage value (uSOLL1, uSOLL2).

9. Drive system according to Claim 3 and according to Claim 8, characterized in that the electronic control unit (8.1, 8.2) is specified to actuate the first electric motor (11) as a function of the measurement signal (uIST) representative of the current DC link voltage, specifically in such a manner that, when the actual voltage value drops below a first setpoint voltage value (uSOLL1), - the first electric motor (11) is actuated to a higher generation of electricity when the first electric motor (11) is currently operated in a regenerative manner, or - the first electric motor (11) is actuated to a lower power consumption when the first electric motor (11) is currently operated as a motor.

10. Drive system according to Claim 3 and according to Claim 8 or 9, characterized in that the electronic control unit (8.1, 8.2) is specified to actuate the first electric motor (11) as a function of the measurement signal (uIST) representative of the current DC link voltage, specifically in such a manner that, when the actual voltage value increases beyond a second setpoint voltage value (uSOLL2), - the first electric motor (11) is actuated to a lower generation of electricity when the first electric motor (11) is currently operated in a regenerative manner, or - the first electric motor (11) is actuated to a higher power consumption when the first electric motor (11) is currently operated as a motor.

11. Electric bicycle having a drive system according to one of Claims 1 to 10.

12. Method for controlling a drive system (10) for an electric bicycle, wherein the drive system (10) comprises the following: - a drive shaft (1), - an output shaft (2) for driving a wheel of the electric bicycle, - a first electric motor (11) which drives a first rotor shaft (3), - a second electric motor (12) which drives a second rotor shaft (4), - an overriding gear (15), the gear ratio of which is infinitely adjustable with the aid of the first and second electric motors (11, 12) and by way of 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 - an energy storage device (9) for supplying the first and second electric motors (11, 12) with electric current, wherein the drive system (10) is operated in emergency operation when the first and second electric motors (11, 12) cannot be supplied with electric current by way of the energy storage device (9), characterized in that at least one of the first and second electric motors (11, 12) is operated in the emergency operation at least temporarily in a regenerative manner in order to convert an output applied to the drive shaft (1) by means of muscle force into electric energy by way of which an infinitely variable variation of the transmission ratio of the overriding gear (15), even in emergency operation, is enabled and controlled.

13. Method according to Claim 12, characterized in that in the emergency operation - the second electric motor (12) is actuated in accordance with normal operation in which the energy storage device (9) supplies the first and second electric motors (11, 12) with electric current, and - the first electric motor (11) is actuated with the aim of adjusting an electrical energy balance within the drive system (10) to zero.

14. Method according to Claim 12 or 13, characterized in that the drive system (10) comprises at least one energy buffer (60, 61) for generating a DC link voltage in emergency operation for supplying at least one of the electric motors (11, 12) with electric current, and one of the electric motors (11, 12) is actuated with the aim of keeping the DC link voltage at a certain voltage value.

15. Computer program product, comprising instructions which, when executed by at least one processor of an electronic control unit (8.1, 8.2) for a drive system (10) of an electric bicycle, prompt the at least one processor to carry out a method according to one of Claims 12 to 14.