Method for operating a drive train of a working machine, drive train of a working machine, and working machine

Abstract

The invention relates to a method for operating a drive train (1) of a working machine, wherein a first electric motor (2) drives a working drive (6) of the working machine via a first transmission device (4), wherein a second electric motor (3) drives a traction drive (7) of the working machine via a second transmission device (5), and wherein during a shifting process of the second transmission device (5) from a relatively low gear stage to a relatively high gear stage, the rotational speed of the second electric motor (3) is reduced. The method according to the invention is characterized in that during the shifting process, a drive connection (22) is produced between the first electric motor (2) and the second transmission device (5) by means of a first clutch (8), so that during the shifting process, the first electric motor (2) drives (24, 25, 27, 28) the traction drive (7). The invention further relates to a corresponding drive train (1) and a working machine.

Description

Technical Field

[0001] The invention relates to a method for operating a drive train of a working machine, a drive train for a working machine and a corresponding working machine. Background Art

[0002] .Electrically driven working machines, such as wheel loaders, small loaders, telescopic handlers, dump trucks or excavators, are known from the prior art. Such electrically driven working machines are either purely electrically driven, i.e. they have only batteries or accumulators to supply them with energy. Or they are diesel-electric, i.e. the required energy is supplied by a diesel-driven generator, usually in combination with an electric buffer store, for example a capacitor of corresponding size. In all cases, the mechanical power required for the traction drive and the working drive is generated by one or more electric motors. Furthermore, hybrid electric working machines are also known, in which the required mechanical power is mainly generated by a combustion engine, usually a diesel engine. The electric motor provided in addition here usually performs a so-called power-boosting function.

[0003] Power-shiftable transmissions for working machines are also known, in which, during a shifting operation, a speed synchronization between the speed of the drive unit and the speed of the gear stage to be engaged is performed. In the case of an upshift operation, the speed of the drive unit is correspondingly reduced, while in the case of a downshift operation, the speed is correspondingly increased.

[0004] Against this background, DE 20 2014 000 738 U1 describes a purely electrically driven wheel loader having a first electric motor for a traction drive and a second electric motor for a working drive.

[0005] EP 0 962 597 A2 discloses a battery-operated working machine having two electric motors for the traction drive and a further electric motor for the working drive. The two electric motors for the traction drive are integrated into the front axle, each electric motor driving a wheel.

[0006] A planetary multi-speed transmission for a working machine is further known from DE 10 2010 063 503 A1. The multi-speed transmission comprises: a housing in which four planetary gear sets and a plurality of shafts are received; and

[0007] The shift element is formed by at least one brake and a plurality of clutches and by targeted actuation of the shift element eight different transmission ratios between the drive shaft and the output shaft can be described. The transmission of DE 10 2010 063 503 A1 allows power shifting.

[0008] However, a disadvantage of the known electrically driven working machines is that the speed synchronization of the gear stages involved in the shifting operation under power is more difficult than the same operation in a working machine driven by a combustion engine. The reasons for this are, on the one hand, the relatively large moment of inertia of the electric motor compared to the combustion engine and, on the other hand, the relatively large speed spectrum of the electric motor and, therefore, also correspondingly large speed differences. This conventionally requires that the clutch in the electrically driven working machine be dimensioned correspondingly larger and more powerful. However, this relatively larger and more powerful design of the clutch leads to an increased space requirement, an increased weight and increased production costs. Summary of the invention

[0009] .The object of the present invention is to propose an improved method for operating a drive train of a working machine.

[0010] According to the invention, this object is achieved by a method for operating a drive train of a working machine as described herein. Advantageous embodiments and further developments of the invention follow from this text.

[0011] The invention relates to a method for operating a drive train of a working machine, wherein a first electric motor drives a working drive of the working machine via a first transmission device, wherein a second electric motor drives a traction drive of the working machine via a second transmission device, and wherein during a shifting operation of the second transmission device from a lower gear stage to a higher gear stage, a speed reduction of the second electric motor is performed. The method according to the invention is characterized in that during the shifting operation, a drive connection is established between the first electric motor and the second transmission device via a first clutch, so that the first electric motor drives the traction drive during the shifting operation.

[0012] During a shifting operation from a lower gear stage to a higher gear stage, the first electric motor associated with the traction drive has to reduce its speed very quickly in order to establish the necessary speed synchronization between the clutch elements involved in the shifting operation. According to the prior art, this speed synchronization is performed via corresponding friction work between the clutch elements involved in the shifting operation, wherein, in particular in electric motors, relatively large speed differences occur which disadvantageously have to be balanced by particularly powerful and therefore heavy and expensive clutches. However, since the speed synchronization is performed by friction work, torque can continue to be transmitted from the second electric motor to the traction drive at any time during the shifting operation.

[0013] The method according to the invention proceeds from this: by advantageously enabling the traction drive to be driven by the first electric motor which is actually associated with the working drive during the shifting operation of the second transmission device, the second electric motor can be decoupled from the traction drive in terms of driving, and a new reduced speed can be set or adjusted without traction force losses in the traction drive. Thus, when implementing the method according to the invention, it is not necessary to achieve speed synchronization by friction work, so that the clutch of the second transmission device involved in the shifting operation can be designed to be relatively small and inexpensive.

[0014] Within the meaning of the invention, a shifting operation from a lower gear stage to a higher gear stage is understood to be a shifting operation from a gear stage with a relatively lower output speed and a relatively higher output torque to a gear stage with a relatively higher output speed and a relatively lower output torque.

[0015] Although it is conceivable and preferred to carry out the method according to the invention in the case of a downshift operation, that is to say in the case of a shift operation from a higher gear stage to a lower gear stage, this is generally not necessary, since in the case of speed synchronization in the sense of increasing the speed of the second electric motor, torque can be transmitted to the traction drive at any time during the shift operation.

[0016] The speed reduction of the second electric motor required for speed synchronization can preferably take place by energizing the second electric motor in a direction opposite to the current direction of rotation. Thus, an active braking torque is established, which allows an almost immediate speed reduction and synchronization of the second electric motor.

[0017] However, it is also possible and preferred to switch the second electric motor into generator mode so that, without energization, the required speed reduction or speed synchronization is caused solely by the electromagnetic braking force to which the rotor of the second electric motor is subjected due to the generator mode.

[0018] It is also conceivable and preferred to provide not only a single first electric motor or a second electric motor, but a plurality of first electric motors or a second electric motor, which can be connected to one another, for example, via an additive gear, or can be detachably connected to the first transmission device or the second transmission device in terms of drive.

[0019] Preferably, at least the second transmission arrangement has a plurality of gear stages in the form of forward gears and at least one gear stage in the form of a reverse gear. Particularly preferably, the number of forward gears corresponds to the number of reverse gears. The first transmission arrangement can also have more than one gear stage in the form of a forward gear. Furthermore, one or more gear stages of the first transmission arrangement in the form of a reverse gear are also conceivable.

[0020] According to a preferred embodiment of the invention, it is provided that the shifting operation is performed under power. Within the meaning of the invention, the expression "under power" refers to a state of the drive train in which torque is transmitted from the second electric motor or, during the shifting operation, also from the first electric motor to the traction drive, so that the working machine undergoes, for example, acceleration, or goes uphill at a constant speed on a slope. In particular, during the shifting operation, if the method according to the invention is not used, the transmission of torque would be interrupted unless a disadvantageously large, expensive and cumbersome clutch according to the prior art is used. In this sense, the advantages of the method according to the invention manifest themselves and especially in the shifting operation under power, since this is possible without interrupting the traction force and in the presence of a relatively small, inexpensive and low-power clutch. In effect, a drive train implementing the method according to the invention thus achieves the same power-shifting capability as a drive train provided with a relatively large, heavy and expensive clutch, without interrupting the traction force.

[0021] According to a further preferred embodiment of the invention, it is provided that during the gearshift operation, the first electric motor drives the traction drive and the working drive simultaneously. This has the advantage that the working drive is also not interrupted by the gearshift operation and can be used continuously. The drive connection is established between the first electric motor and the second transmission device only via the first clutch, so that during the gearshift operation, in addition to the power requirement of the working drive, the power requirement required by the traction drive can also be provided by the first electric motor.

[0022] According to a further preferred embodiment of the invention, it is provided that the first electric motor drives the traction drive only if the power difference between the power demand of the traction drive and the power that can be provided by the second electric motor during the gear shift operation is bridged. This means that the mechanical power provided by the first electric motor during the gear shift operation is advantageously increased exactly so that, on the one hand, the traction drive does not experience any power limitation due to the gear shift operation, but, on the other hand, does not experience any unwanted power increase. This has the advantage that the behavior of the traction drive is not affected by the gear shift operation. Thus, the power required by the operator of the working machine for the traction drive, for example, is also provided without restriction during the gear shift operation, for which purpose the power provided by the first electric motor is increased to the extent that the power provided by the second electric motor is reduced due to the gear shift operation. However, the total power provided to the traction drive is maintained.

[0023] According to a particularly preferred embodiment of the invention, it is provided that the first electric motor drives the traction drive only if the power demand of the working drive can be fully met during the gear shift operation. This has the advantage that in each case it is ensured that the working drive receives the required power demanded by the operator of the working machine even during the gear shift operation, so that a sudden power drop of the working drive, in particular a power drop not expected by the operator, can be avoided. A power drop of the working drive not expected by the operator can lead to a hazardous situation, for example, if a lifting device of a working machine operated by the working drive no longer receives the power required to hold the lifted load. On the other hand, a short-term power loss in the traction drive does not usually lead to a hazardous situation.

[0024] It is important that the power demand of the working drive is fully met by the first electric motor, in particular in situations where both the traction drive and the working drive make relatively high power demands which can no longer be provided by the first electric motor as a whole. Thus, if the required total power exceeds the maximum power that can be provided by the first electric motor, the demand of the working drive is fully met first. During the gearshift operation, the remaining residual power that can still be provided by the first electric motor is then available to the traction drive.

[0025] The invention further relates to a drive train for a working machine, comprising a first and a second electric motor and a first and a second transmission device, wherein the first electric motor and the first transmission device are associated with a working drive of the working machine, and wherein the second electric motor and the second transmission device are associated with a traction drive of the working machine. The drive train according to the invention is characterized in that a drive connection can be established between the first electric motor and the second transmission device via a first clutch. The drive train according to the invention therefore advantageously comprises all necessary devices and equipment to be able to implement the method according to the invention. This in turn leads to the advantages already described in conjunction with the method according to the invention.

[0026] In order to ensure that the method according to the invention is optimally implemented by the drive train according to the invention, the first electric motor and the second electric motor are preferably matched to each other in terms of the power they can provide and their torque-speed characteristics. This means that the maximum power that can be provided by the first electric motor advantageously varies in the range of 50% to 150%, in particular in the range of 80% to 120%, of the maximum power that can be provided by the second electric motor. Furthermore, the torque-speed characteristic of the first electric motor advantageously varies in the range of 50% to 150%, in particular in the range of 80% to 120%, of the torque-speed characteristic of the second electric motor.

[0027] The drive train preferably further comprises in each case its own power electronics or a single common power electronics for controlling or regulating the speed or torque of the first and second electric motors or the power to be provided by the first and second electric motors. It is also preferred that the drive train comprises an electronic control which controls or regulates the first and second electric motors via respective own power electronics or via common power electronics.

[0028] .According to a preferred embodiment of the invention, it is provided that the first electric motor and the second electric motor are arranged in a common housing. This allows the first electric motor and the second electric motor to be arranged in a drive train in a working machine in a space- and weight-saving manner. Furthermore, the common housing saves weight and costs compared to two separate housings. The first electric motor and the second electric motor can be mounted in a common housing (e.g. axially one after the other), wherein the motor output shafts can, for example, project out of the housing in opposite axial directions. However, an axially side-by-side arrangement in a correspondingly configured housing is likewise possible and preferred, so that the two motor output shafts can point, for example, in the same axial direction.

[0029] According to a preferred embodiment of the invention, it is provided that the second transmission arrangement is power-shiftable over a plurality of gear stages. This has the advantage that the power-shift capability that can be provided by the method according to the invention is ensured not only for a shift operation from a very specific lower gear stage to a very specific higher gear stage, but also for a plurality of gear stages. As a result, the drive train according to the invention becomes more flexible. This requires a correspondingly adapted speed-torque behavior and correspondingly configured performance, in particular the speed-torque behavior and performance of the first electric motor.

[0030] Particularly preferably, it is provided that the second transmission arrangement is power-shiftable in all gear stages. This allows the flexibility of the drive train according to the invention to be increased even further.

[0031] Particularly preferably, it is provided that the first transmission arrangement can be shifted or power-shifted by means of the method according to the invention via three second clutches. In practical applications, this has proven to be a good compromise between the flexibility due to a plurality of power-shiftable gear stages on the one hand and the space requirement, weight and production costs of the drive train on the other hand.

[0032] According to a further preferred embodiment of the present invention, it is provided that the drive train is configured to implement the method according to the present invention.

[0033] Preferably, it is provided that the first electric motor and / or the second electric motor is further configured to recover kinetic energy in a braking operation of the working machine. By means of the drive connection according to the invention which can be established between the first electric motor and the second transmission device via the first clutch, kinetic energy can advantageously be recovered by both the second electric motor and the first electric motor. For this purpose, the drive train further advantageously comprises an electrical energy storage device, to which the electrical energy supplied by the recovery operation can be supplied. In the recovery operation, the first electric motor and / or the second electric motor works as a generator and converts mechanical energy (i.e. kinetic energy) into electrical energy. If necessary, this electrical energy can then be drawn from the electrical energy storage device again in order to be supplied to the first electric motor and / or the second electric motor. Furthermore, it can also be provided that the electrical energy storage device can be charged with external electrical energy via a charging cable or other suitable charging device (e.g. an inductive charging device). The use of the first electric motor and / or the second electric motor for recovery further reduces the wear of the mechanical friction brakes.

[0034] The invention further relates to a working machine comprising a drive train according to the invention. The advantages already described in connection with the drive train according to the invention are also achieved for the working machine according to the invention.

[0035] According to a preferred embodiment of the invention, it is provided that the working machine is in the form of a wheel loader.

[0036] Alternatively, the working machine may also preferably be in the form of a dump truck, an excavator, a telescopic forklift or a tractor.

[0037] The present invention will be explained below by way of examples with reference to the embodiments shown in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In the attached figure:

[0039] . Figure 1 By way of example, a possible embodiment of a drive train according to the invention of a working machine is schematically shown.

[0040] . Figure 2 By way of example and in the form of a wheel diagram, another possible embodiment of a drive train 1 for a working machine according to the invention is shown.

[0041] . Figure 3 A possible embodiment of the method according to the invention for operating a drive train of a working machine is schematically shown by way of example in the form of a flow chart, and

[0042] . Figure 4By way of example, a torque curve of the traction drive, a speed curve of the traction drive and a power curve of the second electric motor and a power curve of the first electric motor during a gear shift operation are schematically shown.

[0043] In all figures, identical objects, functional units and similar components are denoted by the same reference numerals. These objects, functional units and similar components are identical in form with respect to their technical features, unless otherwise indicated explicitly or implicitly in the description. DETAILED DESCRIPTION

[0044] . Figure 1 By way of example, a schematic diagram of a method for a working machine (in Figure 1 1 . The drive train 1 shown by way of example comprises a first electric motor 2 and a second electric motor 3 as well as a first transmission device 4 and a second transmission device 5. The second transmission device 5 is configured to be power-shiftable over a plurality of gear stages. The first electric motor 2 and the first transmission device 4 are associated with a working drive 6 of the drive train 1, wherein the working drive 6 is in the form of a PTO (power take-off) interface 6, for example. On the other hand, the second electric motor 3 and the second transmission device 5 are associated with a traction drive 7 of the drive train 1. Furthermore, a drive connection can be established between the first electric motor 2 and the second transmission device 5 via a first clutch 8, wherein a drive connection can be established specifically from the first electric motor 2 to an intermediate shaft 5' of the second transmission device 5 according to the example. During a shifting operation of the second transmission device 5, the drive connection from the first electric motor 2 to the second transmission device 5 advantageously allows the traction drive 7 to be driven by the first electric motor 2 that is actually associated with the working drive 6. Thus, the second electric motor 3 can be decoupled from the traction drive 7 in terms of drive, and a speed synchronization in the sense of a speed reduction of the second electric motor 3 can be set or adjusted without any traction force loss in the traction drive 7. Therefore, when the method according to the invention is implemented, it is not necessary to achieve speed synchronization by friction work, so that the corresponding clutch of the second transmission device 4 can be designed to be relatively smaller and cheaper than a conventional clutch in the prior art. According to the example, the speed reduction of the second electric motor 3 required for speed synchronization is instead achieved by energizing the second electric motor 3 in a direction opposite to the current rotation direction.

[0045] . Figure 2 By way of example and in the form of a wheel diagram, a method for working a machine ( Figure 2 Another possible embodiment of the drive train 1 is shown in FIG. 1 . According to this example, Figure 2 The drive train 1 comprises a first electric motor 2 and a second electric motor 3 which are arranged in a common housing 9 . Figure 2The drive train 1 further comprises a first transmission device 4 and a second transmission device 5, wherein the first electric motor 2 and the first transmission device 4 are associated with a working drive 6 of the drive train 1. On the other hand, the second electric motor 3 and the second transmission device 5 are associated with a traction drive 7 of the drive train 1. A drive connection can be established between the first electric motor 2 and the second transmission device 5 via a first clutch 8, wherein a drive connection can be established from the first electric motor 2 to an intermediate shaft 5' of the second transmission device 5 according to the example. Thus, when the first clutch 8 is closed, the first electric motor 2 can drive the traction drive 7. According to the example, the second transmission device further comprises three second clutches 9, 9' and 9", in order to provide three shiftable gear stages of the second transmission device 5 by means of three different spur gear stages 10, 10', 10".

[0046] . Figure 3A possible embodiment of the method according to the invention for operating a drive train 1 of a working machine is schematically shown by way of example in the form of a flow chart. A first electric motor 2 of the drive train 1 drives a working drive 6 of the working machine via a first transmission device 4, and a second electric motor 3 of the drive train 1 drives a traction drive 7 of the working machine via a second transmission device 5. In method step 20, a shift operation of the second transmission device 5 from a lower gear stage to a higher gear stage is initiated by the operator of the working machine. The shift operation is initiated by the operation of a corresponding shift element of the working machine (according to the example, by means of a gear stage selection lever). In method step 21, the control device checks whether the first electric motor 2 associated with the working drive 6 of the working machine 1 still has sufficient power reserve to assist the shift operation and drive the working machine 6. According to the example, this is the case because the working drive 6 is not currently driven. Therefore, in the following method step 22, a drive connection is established between the first electric motor 2 and the second transmission device 5, which is achieved by closing the first clutch 8. In method step 23, the first clutch 8 is completely closed, and both the first electric motor 2 and the second electric motor 3 transmit power to the traction drive 7, that is, drive the traction drive 7. In method step 24, the second electric motor 3 reduces the power it transmits to the traction drive 7, wherein at the same time the first electric motor 2 increases the power it transmits to the traction drive 7. The increase in power transmitted by the first electric motor 2 corresponds exactly to the reduction in power transmitted by the second electric motor 3, so that during the shifting operation the power difference between the power requirement of the traction drive 7 and the power that can be provided by the second electric motor 3 is bridged. In the following method step 25, the second electric motor 3 reduces the power it transmits to the traction drive 7 to zero, while the first electric motor 2 further increases the power it transmits to the traction drive 7. The traction drive 7 is now driven only by the first electric motor 2. In step 26, the second clutch 9 of the second transmission device 5 involved in the shifting operation is opened, so that the drive connection of the second electric motor 2 to the traction drive 7 is interrupted. Then, the second electric motor 3 starts speed synchronization in the form of speed reduction. According to the example, the speed reduction is performed by switching the second electric motor 3 into generator mode with maximum current generation. As soon as the necessary speed reduction is completed and speed synchronization is achieved, the clutch 9' of the second transmission device 5, which is also involved in the gearshift operation, is closed. The drive connection between the second electric motor 3 and the traction drive 7 is thus established again. In method step 27, the first electric motor 2 reduces the power it transmits to the traction drive 7, while the second electric motor 3 increases the power it transmits to the traction drive 7 by the same amount. In this case, the reduction in the power transmitted by the first electric motor 2 corresponds exactly to the increase in the power transmitted by the second electric motor 3. The traction drive 7 thus receives a constant power supply.Finally, in method step 28, the first electric motor 2 no longer transmits any power to the traction drive 7. The traction drive 7 is once again driven only by the second electric motor 3. The first clutch 8 is opened and thus interrupts the drive connection between the first electric motor 2 and the second transmission device 5 or the traction drive 7. Thus, the shifting operation is completed. Since power has been transmitted from the first electric motor 2 or the second electric motor 3 to the second transmission device 5 or the traction drive 7 during the entire shifting operation, the shifting operation is performed under power. Therefore, the drive train 1 is power-shiftable.

[0047] . Figure 4 By way of example and schematically, a torque curve 30 of the traction drive 6, a speed curve 31 of the traction drive 6, and a power curve 32 of the second electric motor 3 and a power curve 33 of the first electric motor 2 during a shifting operation are shown. The shifting operation of the second transmission device 5 from a lower gear stage to a higher gear stage begins at time t1. At time t1, the traction drive 7 is driven only by the second electric motor 3 via the second clutch 9. The first clutch 8 for establishing a drive connection between the first electric motor 2 and the second transmission device 5 is open. The torque at the traction drive 7 decreases, while the speed increases. At time t2, the first clutch 8 closes. At the same time, the first electric motor 2 begins to transfer power to the traction drive 7. As soon as the first electric motor 2 transfers sufficient power to the traction drive 7, the second electric motor 3 is switched to generator mode in order to achieve a speed reduction. The torque at the traction drive 7 decreases further, and the speed at the traction drive 7 increases further. At time t3, the second clutch 9' is closed, while the first clutch 8 also remains closed. The closing of the second clutch 9' represents a change of the gear stage of the second transmission device 5. Also at time t3, the torque at the traction drive 7 drops further, and the speed at the traction drive 7 increases further. At time t4, the second electric motor 3 starts to transfer power to the second transmission device 5 and thus to the traction drive 7 again. At the same time, the first electric motor 2 reduces the power it transfers to the second transmission device 5 and thus to the traction drive 7. Both the first clutch 8 and the second clutch 9' are closed. The torque at the traction drive 7 drops further, and the speed at the traction drive 7 increases further. At time t5, the first clutch 8 is opened, and the drive connection between the first electric motor 2 and the second transmission device 5 or the traction drive 7 is thus interrupted. The second clutch 9' remains closed. The traction drive 7 is therefore once again completely driven by the second electric motor 6, and for this reason, the second electric motor 3 increases its power again. The power of the first electric motor 2 is reduced again. The torque at the traction drive 7 drops further again, and the speed at the traction drive 7 increases further again. Thus, the gearshift operation is completed.

[0048] Reference numerals

[0049] 1 Drive system

[0050] 2 First Electric Motor

[0051] 3 Second electric motor

[0052] 4 First transmission unit

[0053] 5 Second transmission device

[0054] 6 Working Driver

[0055] 7 Traction drive

[0056] 8 First Clutch

[0057] 9, 9', 9" Second Clutch

[0058] 10, 10', 10" spur gear stages

[0059] 11 Shared housing

[0060] 20 Start the gear shift operation

[0061] 21 Checking the power reserve

[0062] 22 Establishing a driver connection

[0063] 23 Full engagement of the first clutch

[0064] 24 The power of the second electric motor is reduced, and the power of the first electric motor is increased 25 The power of the second electric motor is further reduced, and the power of the first electric motor is further increased. 26 Opening and closing of the second clutch, speed synchronization

[0065] 27 The power of the first electric motor decreases, and the power of the second electric motor increases 28 The power of the second electric motor is further reduced, and the power of the first electric motor is further increased. 30 Torque curve of traction drive

[0066] 31 Speed ​​curve of traction drive

[0067] 32 Power curve of the second electric motor

[0068] 33 Power curve of the first electric motor

[0069] t1, t2, t3, t4 time

Claims

1. A method for operating a drive train (1) of a working machine, in, A first electric motor (2) drives a working drive (6) of the working machine via a first transmission device (4). wherein the second electric motor (3) drives the traction drive (7) of the working machine via a second transmission device (5), and wherein during a shifting operation of the second transmission device (5) from a lower gear stage to a higher gear stage, a speed reduction of the second electric motor (3) is performed, characterised in that during the gear shifting operation, a drive connection (22) is established between the first electric motor (2) and the second transmission device (5) via a first clutch (8), so that the first electric motor (2) drives the traction drive (7) (24, 25, 27, 28) via the second transmission device (5) during the gear shifting operation, and The first electric motor (2) drives the traction drive (7) only if the power difference between the power demand of the traction drive (7) and the power that can be provided by the second electric motor (3) is bridged (24, 25, 27, 28) during the gear shifting operation.

2. The method according to claim 1, It is characterized in that The shifting operation is performed under power.

3. The method according to any one of claims 1 and 2, It is characterized in that The first electric motor (2) drives the traction drive (7) and the working drive (6) (24, 25, 27, 28) simultaneously during the gear shifting operation.

4. The method according to claim 1, It is characterized in that The first electric motor (2) drives the traction drive (7) only if it is able to fully meet the power demand of the working drive (6) during the gear shifting operation.

5. A drive system (1) for a working machine, The drive train comprises a first electric motor (2) and a second electric motor (3) and a first transmission device (4) and a second transmission device (5). in, The first electric motor (2) and the first transmission device (4) are associated with a working drive (6) of the working machine, and wherein the second electric motor (3) and the second transmission device (5) are associated with a traction drive (7) of the working machine, It is characterized in that A drive connection can be established between the first electric motor (2) and the second transmission device (5) via a first clutch (8), so that the first electric motor (2) drives the traction drive (7) via the second transmission device (5), and The drive train (1) is configured to implement the method according to any one of claims 1 to 4.

6. The drive train (1) according to claim 5, It is characterized in that The first electric motor (2) and the second electric motor (3) are arranged in a common housing (11).

7. A drive train (1) according to any one of claims 5 and 6, It is characterized in that The second transmission device (5) is power-shiftable in a plurality of gear stages.

8. A working machine comprising a drive train (1) according to any one of claims 5 to 7.

9. The working machine according to claim 8, It is characterized in that The working machine is in the form of a wheel loader.

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