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

Abstract

The invention relates to a method for operating a drive train (1) of a work machine, wherein a working drive (6) of the work machine is driven by a first electric motor (2) via a first gear arrangement (4), a travel drive (7) of the work machine is driven by a second electric motor (3) via a second gear arrangement (5), and during a gear shift of the second gear arrangement (5), the rotational speed of the second electric motor (3) is synchronized and the temperature of the second electric motor (3) is recorded. The claimed method is characterized in that the rotational speed is synchronized by supplying current to the second electric motor (3), and in the case of exceeding a threshold temperature, at least one measure is carried out to relieve the thermal load of the second electric motor (3). The invention further relates to a corresponding drive train (1) and a work machine.

Description

Field of the Invention

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

[0002] . Electrically driven work machines are known in the prior art, such as wheel loaders, compact loaders, reach stackers, dump trucks, or excavators. Such electrically driven work machines are either purely electrically driven, i.e., they only have a battery or accumulator to supply them with energy, or diesel-electrically driven, i.e., the required energy is supplied by a diesel-driven generator, usually in combination with an electrical buffer memory, such as a capacitor of a corresponding size. In all cases, the mechanical power required for the traction drive and the work drive is generated by one or more electric motors. In addition, hybrid electric work machines are also known, in which the required mechanical power is mainly generated by a combustion engine (usually a diesel engine). The additionally provided electric motors usually perform a so-called boosting function.

[0003] . Power-shiftable transmissions for work machines are also known, in which, during a gearshift operation, a speed synchronization is performed between the speed of the drive unit and the speed of the gear stage to be engaged. In the case of an upshift operation, the speed of the drive unit is correspondingly reduced, while in the case of a downshift operation, this speed is correspondingly increased. The speed synchronization is thus achieved via the frictional work between the clutch elements.

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

[0005] . A planetary multi-stage transmission for a work machine is further known from DE 10 2010 063 503 A1. The multi-stage transmission includes: a housing, four planetary gear sets and a plurality of shafts received in the housing; and shift elements formed by at least one brake and a plurality of clutches, and eight different transmission ratios between the drive shaft and the output shaft can be described by targeted actuation of the shift elements. The transmission of DE 10 2010 063 503 A1 allows power shifting.

[0006] . A method for preventing the starting clutch from being overloaded during a starting operation in a higher gear of a manual-automatic transmission is known from DE 10 2007 046 735 A1. In the event that the starting clutch actually or potentially overheats, an emergency downshift is performed.

[0007] . However, a drawback of known electrically driven working machines is that gear stage speed synchronization involved in a gearshift operation under power is more difficult compared to the same operation in a working machine driven by a combustion engine. The reason for this is that, on the one hand, the moment of inertia of the electric motor is relatively larger compared to that of the combustion engine, but mainly that the speed spectrum of the electric motor is significantly larger, so there can be a correspondingly larger speed difference that must be synchronized accordingly. In the case of repeated gearshifts, especially within short time intervals, this can also lead to a high thermal load on the electric motor.

[0008] . It is an object of the present invention to provide an improved method for operating a drive train of a working machine. Summary of the Invention

[0009] . According to the present invention, this object is achieved by the method for operating a drive train of a working machine described herein. Advantageous embodiments and further developments of the present invention result from this.

[0010] . The present invention relates to a method for operating a drive train of a working machine, wherein a working drive of the working machine is driven by a first electric motor via a first transmission device, wherein a traction drive of the working machine is driven by a second electric motor via a second transmission device, wherein during a gearshift operation of the second transmission device, speed synchronization of the second electric motor is carried out, and wherein the temperature of the second electric motor is detected. The method according to the present invention is characterized in that this speed synchronization is carried out by exciting the second electric motor, and in that if a limit temperature is exceeded, at least one measure is carried out to relieve the thermal load on the second electric motor.

[0011] .Thus, the method according to the invention provides for the operation of a drive train for a work machine by means of two electric motors, namely a first electric motor and a second electric motor. The first electric motor is associated in a dedicated manner with a working drive, and the second electric motor is associated in a dedicated manner with a traction drive. During a gearshift operation in the second transmission device, i.e., the traction transmission, the speed synchronization of the elements involved in the gearshift operation, including the second electric motor, must be carried out separately. In the prior art, speed synchronization is typically carried out by the frictional work in the clutch involved in the gearshift operation, which, however, leads to clutch wear and thus requires a correspondingly loadable clutch design. According to the invention, the speed synchronization during the gearshift operation of the second transmission device is thus carried out via the second electric motor itself, i.e., by correspondingly exciting the second electric motor. Depending on the direction of the current, the excitation causes the generation of a corresponding torque and thus either an increase or a decrease in the speed of the second electric motor. Thus, the speed difference does not have to be eliminated by the frictional work of the clutch involved in a specific gearshift operation. The clutch can thus be designed more compactly and with less power, thereby reducing costs and weight. However, depending on the speed change of the second electric motor necessary for speed synchronization, it may be necessary to excite it with a relatively high current in order to generate the torque required for rapid torque changes. However, the higher current causes a corresponding, usually undesirable heating of the second electric motor, and for this reason, it is therefore advantageous to continuously detect the temperature of this second electric motor or at least to detect it regularly at specific time intervals. If it is then determined that a previously fixed limit temperature has been exceeded, at least one measure is carried out to relieve the thermal load on the second electric motor so that the second electric motor can cool down or at least no longer heat up further. This prevents damage to the second electric motor and extends its service life.

[0012] .In the sense of the present invention, excitation is understood to mean not only supplying current to the electric motor from the outside to allow the electric motor to generate torque, but also additionally converting the electric motor into generator mode so that the speed reduction required for speed synchronization is generated by the electromagnetic braking force exerted on the rotor of the second electric motor due to the generator mode. Excitation of the electric motor thus also takes place, but in this case the current is not supplied from the outside but is generated in the electric motor. However, in both cases, the current is applied to the coil windings of the electric motor, i.e., the coil windings are excited. Thus, the excitation of the second electric motor is understood to refer to both external excitation and conversion to generator mode.

[0013] . During a gearshift operation from a lower gear stage to a higher gear stage, the second electric motor associated with the traction drive must very quickly reduce its speed in order to establish the necessary speed synchronization. Conversely, during a gearshift operation from a higher gear stage to a lower gear stage, the second electric motor must very quickly increase its speed in order to achieve speed synchronization.

[0014] . The temperature of the second electric motor is preferably detected via a sensor configured for this purpose, such as a sensor operating by the Seebeck effect or an infrared sensor. However, alternatively and preferably, the temperature of the second electric motor can also be detected by means of a temperature model calculation of the second electric motor.

[0015] . It is preferably provided that the first transmission device, i.e. the working transmission, is also designed to be shiftable. In this case, the method according to the invention is also particularly advantageously used for the first electric motor.

[0016] . It is further conceivable and preferably not only a single first electric motor or a second electric motor is provided, but also a plurality of first electric motors or second electric motors, which can be coupled to each other via an accumulator drive, for example, or can be detachably connected to the first transmission device or the second transmission device in terms of drive.

[0017] . Preferably, at least the second transmission device 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 device can also have more than one gear stage in the form of a forward gear. In addition, one or more gear stages in the form of a reverse gear of the first transmission device are also conceivable. However, due to the ability of the electric motor to change the direction of rotation, it is not always necessary to provide a reverse gear.

[0018] .According to a preferred embodiment of the invention, when the second transmission device is in the form of a manual / automatic transmission, the at least one measure is to apply a shift hysteresis to the shift points of the second transmission device. In a manual / automatic transmission, the shift point represents the operating point at which a shift operation to the next higher or lower gear stage typically occurs. The shift point can be influenced, for example, by the motor load, the motor speed, the speed of the transmission elements associated with the engaged gear stage, the speed of the work machine, the detected inertial coasting or traction mode of the work machine, or also by the detected ground gradient. By applying a hysteresis to the shift point, this one shift point is divided into two different, direction-related shift points, where one of the two shift points is only used in the case of a downshift operation and the other of the two shift points is only used in the case of an upshift operation. The directionality causes the operating point for starting the shift operation to be reached later. For example, a shift hysteresis can be applied to a shift point specified in a speed-related manner, typically 10 km / h, such that this shift point is divided into a shift point at 8 km / h and a shift point at 12 km / h. In order to delay the start of the shift operation, that is, to reach the operating point for starting the shift operation later, the shift point at 8 km / h is only used for downshift operations and the shift point at 12 km / h is only used for upshift operations. Thus, a downshift occurs later when the work machine decelerates and an upshift occurs later when the work machine accelerates. Thus, especially in the case of frequent speed changes near the initial shift point, the number of shift operations can be reduced. Together with the number of shift operations, the frequency of the speed synchronization performed is also reduced and thus the thermal load on the second electric motor is reduced.

[0019] .Particularly preferably, the shift hysteresis is applied not only to one shift point of the second transmission device, but also to a plurality of shift points or all shift points.

[0020] .This shift hysteresis can also preferably be applied to one or more shift points of the first transmission device.

[0021] .According to a further preferred embodiment of the invention, the at least one measure is to assist the speed synchronization by means of a clutch. This means that the speed synchronization is not only carried out by exciting the second electric motor, but is additionally assisted by the friction process of the corresponding clutch of the second transmission device. Thus, the thermal load on the second electric motor is also correspondingly reduced.

[0022] .Particularly preferably, the at least one measure can also be to carry out the speed synchronization solely by means of the corresponding clutch of the second transmission device. In this case, therefore, the second electric motor is not used at all for speed synchronization. Accordingly, the thermal load on the second electric motor is significantly reduced.

[0023] .Preferably provided is that the thermal load of the first electric motor is also reduced because the clutch of the first transmission device assists in speed synchronization or the speed synchronization is performed entirely by the clutch of the first transmission device.

[0024] .According to a further preferred embodiment of the invention, provided is that the at least one measure is to enhance the cooling of the second electric motor. For example, the supply pump of the cooling circuit for cooling the second electric motor can operate at a higher capacity, or an additional cooling device, such as a radiator, can be activated to cool the cooling fluid.

[0025] .Also preferably provided is that not only the cooling of the second electric motor is enhanced, but also additionally or alternatively the cooling of the clutch of the second transmission device involved in the shifting operation is enhanced. As a result, the clutch can contribute more to the necessary speed synchronization through additional frictional work, and thus contribute to a greater extent to reducing the thermal load of the second electric motor.

[0026] .Preferably provided is that the thermal load of the first electric motor is also reduced by enhancing the cooling of the first electric motor or the cooling of the clutch of the first transmission device.

[0027] .According to a further preferred embodiment of the invention, provided is that the at least one measure is to establish a drive connection between the working drive and the traction drive such that the traction drive is additionally or solely driven by the first electric motor. This means that the first electric motor, which is actually associated with the working drive and provided for the working drive, can also additionally drive the traction drive via a drive short circuit between the working drive and the traction drive. This in turn advantageously enables the excitation and thus the thermal load of the second electric motor to be reduced to the same extent as the contribution of the first electric motor to the traction drive.

[0028] .According to a particularly preferred embodiment of the invention, provided is that the driving of the traction drive by the first electric motor is carried out while taking into account the temperature of the first electric motor. This has the advantage that reducing the thermal load of the second electric motor does not cause thermal overload of the first electric motor. On the contrary, the contribution of the first electric motor to the traction drive does not exceed the range allowed by its own thermal reserve. Therefore, damage or overload of the first electric motor can be avoided.

[0029] .In particular, provided is that the first electric motor drives the traction drive and the working drive simultaneously. This has the advantage that the working drive is also driven and is continuously available. Then the first electric motor only additionally provides the power requirement needed by the traction drive.

[0030] . Particularly preferably, it is provided that the traction drive is driven by the first electric motor only when the power required by the working drive can still be provided by the first electric motor. Thus, the traction drive is driven by the first electric motor only if or only because the power required by the working drive can be continuously supplied to the working drive. This has the advantage that it ensures that in any case the working drive always receives the power required and demanded by the operator of the working machine, thereby avoiding a sudden power drop of the working drive, especially an unexpected power drop for the operator. It is important that the power requirements of the working drive are fully met by the first electric motor, especially in cases where both the traction drive and the working drive have relatively high power requirements but these requirements cannot all be met by the first electric motor.

[0031] . Preferably, it is provided that via a drive connection, the working drive can also be additionally or solely driven by the second electric motor.

[0032] . According to a further preferred embodiment of the invention, it is provided that the at least one measure is to limit the permitted operating range of the second electric motor. This means that the permitted operating range is restricted, especially restricted to a relatively low power range. For example, the power range can be specified by respectively limiting the operating voltage or the operating current to a specific maximum limit power. As a result, excitation with a relatively high current can be avoided, thereby reducing the thermal load of the second electric motor and enabling the second electric motor to cool down.

[0033] . In particular, the permitted operating range can be restricted not only by limiting the operating voltage or the operating current, but also additionally or alternatively by limiting the motor speed to a specific limit speed.

[0034] . The restriction of the specific operating range, or the specific limit power or limit speed, can advantageously be selected according to the temperature of the second electric motor detected in a specific situation. For example, if the limit temperature is only slightly exceeded, this may initially result in a slight restriction of the permitted operating range, such as restricting it to a maximum of 75% of the maximum power of the second electric motor. However, if the limit temperature is significantly exceeded, this may result in an immediate and very severe restriction of the operating range, such as restricting it to a maximum of 50% of the maximum power.

[0035] . Preferably, it is provided that the permitted operating range of the first electric motor can also be restricted in order to reduce the thermal load of the first electric motor.

[0036] .According to a further preferred embodiment of the present invention, provided is that the at least one measure is to prevent upshifting in the second transmission device. That is, the selected gear stage of the second transmission device cannot be further increased, thereby reducing the thermal load on the second electric motor. Preventing upshifting preferably takes the form of preventing the corresponding shifting operation, which is possible in, for example, a manual / automatic transmission and is particularly simple and effective via a correspondingly configured control software. Since the gear stage can no longer be upshifted by an upshifting operation, the maximum travel speed of the work machine is limited. In addition, since the power demand in a lower gear stage is generally lower than that in a higher gear stage, the thermal load on the second electric motor can be reduced. In addition, preventing upshifting avoids the corresponding shifting operation and the necessary speed synchronization associated therewith, which also helps to reduce the thermal load on the second electric motor.

[0037] .Preferably provided is that upshifting prevention is also provided in the first transmission device to reduce the thermal load on the first electric motor.

[0038] .On the other hand, downshifting of the engaged gear stage of the second transmission device can continue to be permitted. Although this initially requires speed synchronization, it then results in a relatively lower power demand from the second electric motor and thus reduces the thermal load on the second electric motor.

[0039] .The present invention further relates to a drive train for a work machine, wherein the drive train includes a work drive having a first transmission device and a first electric motor; and a traction drive having a second transmission device and a second electric motor, wherein the work drive can be driven by the first electric motor via the first transmission device, and wherein the traction drive can be driven by the second electric motor via the second transmission device. The drive train according to the present invention is characterized in that a drive connection can be established between the work drive and the traction drive via a coupling clutch. The drive train according to the present invention thus advantageously includes the necessary devices and components capable of performing the method according to the present invention. This in turn results in the advantages already described in connection with the method according to the present invention.

[0040] .The drive train preferably further includes its own power electronics or a single shared power electronics for controlling or regulating the speed or torque of the first electric motor and the second electric motor or the power provided by the first electric motor and the second electric motor.

[0041] .Equally preferably, the drive train includes an electronic control device which controls or regulates the first electric motor and the second electric motor via respective own power electronics or via a common power electronics. The control device can also additionally control the first transmission unit and / or the second transmission unit. The control device itself advantageously includes a microprocessor and an electronic memory, and the method according to the invention is particularly preferably stored in the electronic memory in the form of a software algorithm executable by the microprocessor.

[0042] .Equally preferably, the drive train further includes at least one cooling device for cooling the first electric motor, the second electric motor, the first transmission unit and / or the second transmission unit.

[0043] .Further preferably, the second transmission device can be power-shifted at multiple gear stages.

[0044] .The first transmission device preferably has a relatively simple form as a reduction gear. If the first transmission device includes multiple shiftable gear stages, these gear stages are preferably power-shiftable.

[0045] .According to a preferred embodiment of the invention, 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 space-saving and weight-saving manner in the drive train of the working machine. In addition, compared with two separate housings, the common housing saves weight and cost. The first electric motor and the second electric motor can be installed, for example, axially one behind the other in the common housing, wherein the motor output shafts can, for example, point out of the housing in opposite axial directions. However, an axial side-by-side arrangement in a correspondingly configured housing is equally possible and preferred, such that the two output shafts can, for example, point in the same axial direction.

[0046] .According to a further preferred embodiment of the invention, the drive train is configured to implement the method according to the invention.

[0047] .Preferably provided is that the first electric motor and / or the second electric motor is further configured to recover kinetic energy during a braking operation of the drive train. By means of the drive connection that can be established between the first traction drive and the working drive via the first clutch according to the invention, the 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 includes an electrical energy storage, to which the electrical energy supplied by the recovery operation can be supplied. During the recovery operation, the first electric motor and / or the second electric motor operates as a generator and converts the kinetic energy of the working machine into electrical energy. If required, this electrical energy can subsequently be extracted from the electrical energy storage in order to supply power to the first electric motor and / or the second electric motor. It can also be provided that the electrical energy storage can be charged with external electrical energy via a charging cable or other suitable charging means, such as an inductive charging means. Using the first electric motor and / or the second electric motor for recovery additionally reduces the wear of the mechanical friction brake.

[0048] .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 can also be obtained from the working machine according to the invention.

[0049] .According to a preferred embodiment of the invention, the working machine is in the form of a wheel loader, an autodumper, an excavator, a telescopic handler or a tractor.

[0050] .The invention will be explained below by way of example with reference to the embodiments shown in the drawings. Description of the Drawings

[0051] .In the drawings:

[0052] . Figure 1 Possible embodiments of a drive train for a working machine according to the invention are shown by way of example and in the form of a wheel diagram,

[0053] . Figure 2 Another possible embodiment of a drive train for a working machine according to the invention is shown by way of example and in the form of a wheel diagram, and

[0054] . Figure 3 The excitation curve of the second electric motor and the curve of the temperature of the associated second electric motor over time are shown by way of example.

[0055] .In all the drawings, the same objects, functional units and similar components are denoted by the same reference signs. These objects, functional units and similar components are formally identical in terms of their technical features, unless the description explicitly or implicitly shows otherwise. Detailed Description

[0056] . Figure 1 A possible embodiment of the drive train 1 according to the invention for a work machine ( Figure 1 not shown) is shown by way of example and in the form of a wheel diagram. According to the example, Figure 1 the drive train 1 includes a first electric motor 2 and a second electric motor 3, which are arranged in a common housing 11. Both the first electric motor 2 and the second electric motor 3 each have an associated temperature sensor 2', 3' for continuously detecting the temperature of the first electric motor 2 or the second electric motor 3. Figure 1 The drive train 1 further includes 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 the 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 the traction drive 7 of the drive train 1. According to the example, the second transmission device 5 further includes three additional, power-shiftable clutches 9, 9' and 9", and three shafts 5, 5' and 5" 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". During the shifting operation of the second transmission device 5, the previously closed clutch 9, 9' or 9" opens, and at the same time the previously open clutch 9, 9' or 9" closes. In order to enable the clutch 9, 9' or 9" to close, the elements of the gear stage to be shifted must first be speed-synchronized. According to the example, the speed synchronization is carried out by means of a corresponding excitation of the second electric motor 3. However, due to the necessary rapid speed changes and the associated high current intensity, this also results in significant heating in the second electric motor 3. In order to reduce the thermal load on the second electric motor 3, a drive connection can be established between the first transmission device 4 and the second transmission device 5 via the connecting clutch 8, wherein, according to the example, a drive connection can be established from the first electric motor 2 to the shaft 5' of the second transmission device 5. Thereby, when the connecting clutch 8 is closed, the first electric motor 2 can drive the traction drive 7. According to the example, this occurs whenever it is necessary to reduce the thermal load on the second electric motor 3. By additionally driving the traction drive 7 by the first electric motor 2, the second electric motor 3 can be operated at a lower operating point, thereby reducing the excitation of the second electric motor 3 and thus also reducing the thermal load on the second electric motor 3.

[0057] . Figure 2 Another possible embodiment of the drive train 1 according to the invention for a work machine ( Figure 2 not shown) is shown by way of example and in the form of a wheel diagram. Figure 2 The drive train 1 differs from the drive train 1 only in that a drive connection can be established from the first electric motor 2 to the traction drive 7: According to the example, this drive connection extends from the first electric motor 2 to the shaft 5" of the second transmission device 5.

[0058] . Figure 3 The excitation curve 20 (shown on the y-axis) of the second electric motor 3 and the associated temperature of the second electric motor 3 (likewise shown on the y-axis) are shown by way of example as a function of time t (shown on the x-axis) in curve 21. At time t 0 , the second electric motor 3 is operating with current I 0 and has temperature T 0 . Although the current I 0 causes the second electric motor 3 to continuously heat up, the increased heat is dissipated via the cooling system to achieve a dynamic thermal equilibrium. At time t 1 , a gearshift operation is carried out in the second transmission device 5, and for this reason, speed synchronization is required. Speed synchronization is achieved by briefly exciting the second electric motor 3 with current I 1 . This also causes the temperature to suddenly rise to value T 1 . Then the working machine continues its travel uniformly until time t 2 , where, at time t 2 , a gearshift operation is carried out again in the second transmission device 5. The again required speed synchronization and thus the required high excitation I 2 of the second electric motor 3 cause the temperature to rise further, this time reaching value T 2 . Temperature T 2 is only slightly below the limit temperature T 极限 . At time t 3 , a further gearshift operation occurs, which in turn causes the excitation to briefly rise to current intensity I 3 , and causes the temperature to rise to value T 3 . At this time, the temperature T 3 of the second electric motor also exceeds the limit temperature T 极限 . As a result, when the limit temperature T 极限 is exceeded, a number of measures are carried out to reduce the thermal load on the second electric motor 3. According to the example, first a shift hysteresis is applied to all shift points of the second transmission device 5 to avoid or at least postpone further gearshift operations. And the cooling of the second electric motor 3 is intensified. Finally, a drive connection is established between the working drive 6 and the traction drive 7 such that the traction drive 7 is additionally driven by the first electric motor 2. As a result of the last-mentioned measure for reducing the thermal load on the second electric motor 3, the excitation of this second electric motor can be reduced to value I 4 . The temperature of the second electric motor 3 then drops rapidly.

[0059] Reference numerals

[0060] 1 Drive train

[0061] 2 First electric motor

[0062] 2' Temperature sensor of the first electric motor

[0063] 3 Second electric motor

[0064] 3' Temperature sensor of the second electric motor

[0065] 4 First transmission device

[0066] 5 Second transmission device

[0067] 6 Working drive

[0068] 7 Traction drive

[0069] 8 Connecting clutch

[0070] 9, 9', 9" Clutch

[0071] 10, 10', 10" Spur gear stage

[0072] 11 Common housing

[0073] 20 Excitation of the second electric motor

[0074] 21 Temperature of the second electric motor

[0075] t 0、 t 1、 t 2、 t 3 Time

[0076] I 0、 I 1、 I 2、 I 3 Current

[0077] T 0、 T 1、 T 2、 T 3 Temperature

Claims

1. A method for operating a drive train (1) of a work machine, wherein, a working drive (6) of the work machine is driven by a first electric motor (2) via a first transmission device (4), and wherein a traction drive (7) of the work machine is driven by a second electric motor (3) via a second transmission device (5), wherein, during a gearshift operation of the second transmission device (5), speed synchronization of the second electric motor (3) is performed, and wherein the temperature of the second electric motor (3) is detected, wherein the speed synchronization is carried out by exciting the second electric motor (3), and if a limit temperature is exceeded, at least one measure is performed to reduce the thermal load on the second electric motor (3), characterized in that the second transmission device (5) is in the form of a manual / automatic transmission, the at least one measure includes applying a shift hysteresis to the shift points of the second transmission device (5), and by applying the shift hysteresis to the shift points, the shift points are divided into two different, direction-dependent shift points.

2. The method according to claim 1, characterized in that, the at least one measure includes assisting the speed synchronization by means of clutches (9, 9', 9").

3. The method according to any one of claims 1 to 2, characterized in that, the at least one measure includes enhancing the cooling of the second electric motor (3).

4. The method according to any one of claims 1 to 2, characterized in that, the at least one measure includes establishing a drive connection between the working drive (6) and the traction drive (7) such that the traction drive (7) is additionally or solely driven by the first electric motor (2).

5. The method according to claim 4, characterized in that, while taking into account the temperature of the first electric motor (2), the first electric motor (2) drives the traction drive (7).

6. The method according to any one of claims 1 to 2, characterized in that, the at least one measure includes restricting the permitted operating range of the second electric motor (3).

7. The method according to any one of claims 1 to 2, characterized in that, the at least one measure includes preventing an upshift in the second transmission device (5).

8. A drive train (1) for a work machine, wherein, the drive train (1) comprises: a working drive (6) having a first transmission device (4) and having a first electric motor (2); and a traction drive (7) having a second transmission device (5) and having a second electric motor (3), wherein the working drive (6) can be driven by the first electric motor (2) via the first transmission device (4), and wherein the traction drive (7) can be driven by the second electric motor (3) via the second transmission device (5), It is characterized in that a drive connection can be established between the working drive (6) and the traction drive (7) via a coupling clutch (8), and the drive train (1) is configured to carry out the method according to any one of the preceding claims.

9. The drive train (1) according to claim 8, characterized in that the first electric motor (2) and the second electric motor (3) are arranged in a common housing (11).

10. A working machine, the working machine comprising a drive train (1) according to any one of claims 8 to 9.

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