Method for shifting a powershift motor vehicle transmission, a powershift motor vehicle transmission and agricultural vehicle

Abstract

The invention relates to a method for shifting a powershift motor vehicle transmission (100), wherein the motor vehicle transmission (100) comprises at least a first powershift clutch (310) and a second powershift clutch (320), as well as a main clutch (200), wherein during a shifting operation, the pressure in the first powershift clutch (310) is reduced from a closing pressure to an opening pressure, so that the first powershift clutch (310) opens, and the pressure in the second powershift clutch (320) is increased from an opening pressure to a closing pressure, so that the second powershift clutch (320) closes. The method according to the invention is characterized in that the pressure in the main clutch (200) is reduced during the shifting operation to such an extent that it is lower than the pressure in the second powershift clutch (320) during the shifting operation.The invention further relates to a power-shiftable motor vehicle transmission and a corresponding agricultural vehicle.

Description

[0001] The present invention relates to a method for shifting a power-shiftable motor vehicle transmission according to the preamble of claim 1, a power-shiftable motor vehicle transmission according to the preamble of claim 7 and a corresponding agricultural vehicle.

[0002] It is known in the prior art that agricultural or municipal vehicles, and especially tractors, typically require different driving ranges due to their wide range of applications. This necessitates a large spread between the slowest and fastest gears in the transmission of such a vehicle. Furthermore, the transmission of such a vehicle typically requires small geometric step increments between the individual gears, allowing for a high number of gears in combination with the large spread. To achieve this large number of gears with reasonable effort, transmissions for agricultural or municipal vehicles are often designed in modular units. One such modular unit is typically the so-called...Split group or powershift group, designed for shifting gears under load. The frictional energy generated during powershift is comparatively high and increases exponentially with the number of gears to be skipped.

[0003] In this context, EP 2 916 044 A1 discloses a modular motor vehicle transmission designed for use in an agricultural vehicle, for example, a tractor. The motor vehicle transmission comprises several transmission groups, one of which is a dual-clutch transmission.

[0004] German patent DE 19 711 820 A1 describes a shifting process for a dual-clutch transmission in which gears can be skipped. In this process, one clutch is controlled without applying torque by transferring the engine torque to another clutch. Only after the new gear has been engaged is the engine torque transferred back to the first clutch.

[0005] From US 9 862 388 B2 a method is known in which, in the event of an overheated clutch of a dual clutch transmission, a certain slip of the clutch is allowed and the total load is distributed between both clutches.

[0006] DE 10 349 220 B4 describes a method for shifting a dual-clutch transmission in which, during a gear change on the same countershaft, for example from sixth to second gear, the clutch of the other countershaft assists with speed adjustment using a suitably selected auxiliary gear, and, to reduce the load on the synchronizer, the starting clutch assists with speed adjustment of the respective input shaft. In this process, a large portion of the frictional power of the synchronizer is transferred to the disengagement clutch.

[0007] DE 101 90 489 B4 describes a method for controlling a gear change in a transmission, wherein the transmission has a starting clutch and at least one shift clutch for switching the gear ratios. The engine torque can be controlled by means of a control unit and an actuator, and the clutches can be controlled by means of at least one further actuator.Transmission synchronization is controlled in four steps: In the first step, the torque that can be transmitted by the starting clutch is reduced; in the second step, the torque balance between the torque that can be transmitted by the starting clutch and the torque that can be transmitted by a shift clutch of the target gear is determined; in the third step, the torque that can be transmitted by the starting clutch is further reduced until a turning point of the transmission input speed is detected; and in the fourth step, the torque that can be transmitted by the starting clutch is regulated to the value of the equilibrium torque.

[0008] CN 103 097 777 A discloses a method for a vehicle with a main clutch that enables the transmission of torque from an engine shaft to a primary shaft. The vehicle's transmission includes two further clutches, each of which enables the transmission of torque from the primary shaft to a secondary shaft. First, the two further clutches are placed in their slip state. Then, the main clutch is placed in its slip state. Subsequently, the torque transmitted by the first clutch is reduced, and the torque transmitted by the second clutch is increased. Finally, when the torque transmitted by the first clutch reaches zero, two torque instructions are given to the second clutch and the main clutch, which cause a reduction in the rotational speed of the primary shaft until a target value is reached.Once this is reached, the second clutch is moved into its locked position and then the torque of the engine shaft is controlled to synchronize the engine shaft and the primary shaft, after which the main clutch is also moved into its locked position.

[0009] However, conventional powershift transmissions have the disadvantage that the clutches capable of powershifting—especially when skipping one or more gears is required—must be comparatively large and robust to absorb the resulting frictional energy. This results in high inertia within the drivetrain and a large drag torque, which in turn reduces the drivetrain's efficiency. Furthermore, large and robust clutches are expensive and require considerable installation space.

[0010] It is an object of the invention to propose an improved method for shifting a power-shiftable motor vehicle transmission.

[0011] This problem is solved according to the invention by the method for shifting a load-shiftable motor vehicle transmission according to claim 1. Advantageous embodiments and further developments of the invention are described in the dependent claims.

[0012] The invention relates to a method for shifting a power-shiftable motor vehicle transmission, wherein the motor vehicle transmission comprises at least a first power-shift clutch and a second power-shift clutch as well as a main clutch, wherein during a shifting operation a pressure in the first power-shift clutch is reduced starting from a closing pressure, so that the first power-shift clutch no longer transmits torque, and a pressure in the second power-shift clutch is increased starting from an opening pressure, so that the second power-shift clutch transmits torque.

[0013] A method is provided that enables shifting from one gear of a powershift-capable motor vehicle transmission to another gear of the same powershift-capable motor vehicle transmission. These gears are powershift-capable gears. The gears can be adjacent or non-adjacent. For example, the shift can occur from second gear to first or third gear. Similarly, the shift can also occur from second gear to fourth, fifth, or sixth gear. Furthermore, the shift can, in principle, occur in both directions, i.e., to higher gears and to lower gears.

[0014] In the context of the invention, the opening pressure is understood to be the pressure at which the first or second power-shift clutch no longer transmits torque. Typically, the opening pressure is therefore 0 Pa. However, it is also conceivable that the first or second power-shift clutch no longer transmits torque at higher pressures, for example, because they are designed as pressureless open clutches, which are held open by a return spring in the pressureless state.

[0015] The opening pressure of the first power shift clutch may differ from the opening pressure of the second power shift clutch, for example due to different restoring forces or other component tolerances.

[0016] In the context of the invention, the closing pressure is understood to be the pressure at which the first or second power shift clutch is closed and transmits full torque.

[0017] The closing pressure of the first power shift clutch may also differ from the closing pressure of the second power shift clutch, either due to the previously mentioned different restoring forces of a possible restoring spring or simply due to component tolerances.

[0018] During the switching process, the pressure in the first power shift clutch is reduced to such an extent that it is moved from the closed, torque-transmitting state to the open, non-torque-transmitting state. The pressure in the first power shift clutch is accordingly reduced from the closing pressure to the opening pressure.

[0019] Conversely, in the second power shift clutch, the pressure is increased to such an extent that it is moved from the open, non-torque-transmitting state to the closed, torque-transmitting state. The pressure in the second power shift clutch is thus increased from the opening pressure to the closing pressure.

[0020] The first and second power shift clutches are advantageously hydraulically actuated multi-plate clutches, in particular wet-running, hydraulically actuated multi-plate clutches.

[0021] The first and second power shift clutches are preferably open when depressurized, i.e., they do not transmit any torque in the depressurized state.

[0022] In addition to the first and second powershift clutches, the vehicle transmission also includes a main clutch. The main clutch is advantageously designed as a friction clutch, for example, also as a multi-plate clutch, and in particular as a hydraulically actuated, wet multi-plate clutch. Opening the main clutch advantageously allows for the complete interruption of torque transmission in the vehicle transmission, regardless of the selected gear.

[0023] The power-shiftable motor vehicle transmission is preferably not a so-called dual-clutch transmission.

[0024] According to the invention, the pressure in the main clutch is reduced during the shifting process to such an extent that the torque transmission capacity of the main clutch is lower than that of the second power-shift clutch. This reduces the main clutch's ability to transmit torque during the shifting process below the level of the second power-shift clutch.

[0025] This means that the main clutch is actuated with such pressure that – for example, in the case of a multi-plate clutch – adjacent plates, or inner and outer plates of the main clutch, no longer have sufficient static friction to prevent slippage against each other, even when transmitting comparatively lower torques than the second powershift clutch. In other words, the main clutch is deliberately engaged in a "slipping" manner to prevent the second powershift clutch from "slipping" as well.

[0026] According to the invention, when speed synchronization is required in a vehicle transmission due to the shifting process, the frictional work necessary for this synchronization takes place in the main clutch instead of the second powershift clutch. Since the main clutch is generally much more robust and efficient than the comparatively small powershift clutches, it can absorb correspondingly more frictional energy without being damaged or destroyed. This allows, for example, one or more gears to be skipped during shifting, which naturally leads to particularly high frictional work. Skipping just one gear, for instance, increases the frictional energy fourfold compared to shifting into an adjacent gear.Skipping two gears increases frictional energy ninefold, skipping three gears sixteenfold, and skipping four gears twenty-fivefold. This would typically lead to the immediate destruction of the second powershift clutch. However, the inventive method keeps the frictional energy away from the second load-shift clutch and instead directs it to the main clutch, which can absorb such loads.

[0027] According to a preferred embodiment of the invention, the opening pressure and closing pressure of the first and second power-shift clutches are identical. To achieve identical opening and closing pressures in both clutches, it may be necessary to compensate for component tolerances. Identical opening and closing pressures simplify the control of the two power-shift clutches.

[0028] Advantageously, additional load-shift couplings are also provided; in particular, a total of three, six or nine load-shift couplings are provided, which advantageously all have an identical opening and closing pressure.

[0029] According to the invention, it is further provided that the pressure in the main clutch is only increased again when the first powershift clutch has reached its opening pressure and the second powershift clutch has reached its closing pressure, whereby at the intersection of the two characteristic curves the torque of both powershift clutches is equal, so that the slippage transfers to the other clutch and the torque of the main clutch is lower than that of the powershift clutches, and at the intersection the pressure of the two powershift clutches is between the opening and closing pressures. This means that the main clutch remains "slipping" until the first and second powershift clutches have completed the shifting process. Thus, in principle, there is an uninterrupted load transfer from the first powershift clutch to the second powershift clutch. However, since during the shifting process, i.e.,During load transfer, the torque transmission capacity of the main clutch is lower than that of the second powershift clutch. Due to the speed difference caused by the shifting process, frictional work is generated in the main clutch. By only increasing the pressure in the main clutch back to its previous output pressure (the closing pressure of the main clutch) with a time delay after the second powershift clutch closes and the first powershift clutch opens, it is ensured that the frictional work required for speed synchronization is generated predominantly in the main clutch and kept away from the second clutch.

[0030] According to a further preferred embodiment of the invention, it is provided that at a point in time when the torque transmission capacity of the first power-shift clutch and the torque transmission capacity of the second power-shift clutch are equal, the torque transmission capacity of the main clutch is lower than that of the first and second power-shift clutches. During the shifting process, the torque transmission capacity of the first power-shift clutch must be reduced and simultaneously the torque transmission capacity of the second power-shift clutch must be increased, so that at a certain point in the shifting process there is an intersection between the two torque transmission capacities. At this intersection, where the torque transmission capacity of the first power-shift clutch and the torque transmission capacity of the second clutch are equal, there is a risk of frictional work being generated in the two power-shift clutches.To protect the first and second powershift clutches, the pressure in the main clutch, and thus its torque transmission capacity, is reduced during the shifting process to a level lower than the combined torque transmission capacity of the first and second powershift clutches at their intersection point. This ensures that speed synchronization, and therefore frictional work, occurs primarily in the main clutch.

[0031] Advantageously, the pressure in the main clutch is reduced at the beginning of the shifting process to a pressure that is lower than the pressure of the first and second power shift clutches at the intersection.

[0032] According to a particularly preferred embodiment of the invention, the torque transmission capacity in the main clutch is adjusted during the shifting process according to the drive torque to be transmitted, with the torque transmission capacity being greater at high drive torques than at low drive torques. Higher pressure enables the transmission of higher drive torques. By adjusting the pressure in the main clutch to the respective drive torque to be transmitted during the shifting process, comparatively rapid speed synchronization can be achieved even at high drive torques. This not only enables fast shifting but also helps to keep the load on the main clutch low, since the pressure can be quickly increased back to the engagement pressure. This reduces the time during which friction work occurs in the main clutch.

[0033] It should be clarified that the closing pressure in the main clutch after the shifting process is independent of the drive torque being transmitted. Only during the shifting process is the pressure in the main clutch increased back to the closing pressure relatively quickly at comparatively higher drive torques. This ensures that the main clutch always resumes torque transmission after approximately the same time period, regardless of the torque being transmitted.

[0034] According to a further preferred embodiment of the invention, the torque transmission capacity of the main clutch is reduced before the torque transmission capacity of the first power-shift clutch is reduced. Thus, the first power-shift clutch is protected from overload due to friction work at all times during the shifting process. Instead, the friction work is introduced into the main clutch from the very beginning of the shifting process.

[0035] According to a further preferred embodiment of the invention, it is provided that the second load-shift clutch is subjected to a pressure pulse before the pressure in the second load-shift clutch is increased to the closing pressure.

[0036] The pressure pulse preferably has a duration of 100 ms to 400 ms. The pressure pulse facilitates faster filling of the piston chamber and thus a faster switching process.

[0037] The invention further relates to a power-shiftable motor vehicle transmission, comprising at least a first power-shift clutch and a second power-shift clutch as well as a main clutch, wherein the motor vehicle transmission is configured to reduce the pressure in the first power-shift clutch from a closing pressure during a shifting operation, so that the first power-shift clutch no longer transmits torque, and to increase the pressure in the second power-shift clutch from an opening pressure, so that the second power-shift clutch transmits torque, wherein the motor vehicle transmission is further configured to reduce the pressure in the main clutch during the shifting operation to such an extent that the torque transmission capacity of the main clutch is lower than the torque transmission capacity of the second power-shift clutch.

[0038] According to the invention, the pressure in the main clutch is only increased again when the first power shift clutch has reached the opening pressure and the second power shift clutch has reached the closing pressure, wherein at the intersection of the two characteristic curves the torque of both power shift clutches is equal, so that the slipping is transferred to the other clutch and the torque of the main clutch is lower than that of the power shift clutches and at the intersection the pressure of the two power shift clutches is between the opening and closing pressure. This results in the same advantages for the inventive powershiftable motor vehicle transmission as already described in connection with the inventive method.

[0039] According to a preferred embodiment of the invention, the vehicle transmission is designed as a range transmission comprising a powershift group and a synchronizer group. This allows the vehicle transmission to provide a large number of gear ratios with a wide spread. Powershift operations in the powershift group can be carried out using the method according to the invention, whereby speed synchronization is essentially achieved via the main clutch.

[0040] According to a particularly preferred embodiment of the invention, the powershift assembly comprises at least three powershift clutches. This provides a sufficient number of powershiftable gear stages with a sufficient powershiftable spread for most applications.

[0041] Advantageously, the power shift group can comprise nine power shift clutches.

[0042] According to a further preferred embodiment of the invention, it is provided that the motor vehicle transmission is designed to carry out the method according to the invention.

[0043] The invention relates to an agricultural vehicle comprising a motor vehicle transmission according to the invention. Thus, the advantages of the invention also apply to the agricultural vehicle.

[0044] The invention is explained below by way of example with reference to embodiments shown in the figures.

[0045] They show: Fig. 1 by way of example a pressure profile in a first power shift clutch, a second power shift clutch and a main clutch during a shifting operation with and without the method according to the invention in a power shiftable motor vehicle transmission, Fig. 2. For example, a typical power shift clutch and a typical main clutch are shown in direct size comparison. Fig. 3. An exemplary and schematic representation of a possible embodiment of a load-shiftable motor vehicle transmission according to the invention.

[0046] Identical objects, functional units, and comparable components are designated across all figures using the same reference symbols. These objects, functional units, and comparable components are identical in their technical characteristics unless explicitly or implicitly stated otherwise in the description.

[0047] Fig. Figure 1a shows an example of a pressure profile in a first power-shift clutch 310, a second power-shift clutch 320 and a main clutch 200 during a shifting operation without the method according to the invention in a power-shiftable motor vehicle transmission 100. The x-axis shows the time profile and the y-axis shows the respective pressure.

[0048] For example, the first power shift clutch 310 and the second power shift clutch 320 are identical in construction, so that they have an identical torque transmission capability at an identical pressure.

[0049] The pressure curve in the first power shift clutch 310 is represented by curve 20, the pressure curve in the second power shift clutch 320 by curve 30 and the pressure curve in the main clutch 200 by curve 40.

[0050] Curve 20 thus represents the torque transmission capability of the first power shift clutch 310, curve 30 the torque transmission capability of the second power shift clutch 320 and curve 40 the torque transmission capability of the main clutch 200.

[0051] Since the pressure profile of the main clutch 200 is not changed without the method according to the invention, the curve 40 is accordingly designed as a straight line in this case, i.e., the main clutch 200 remains closed and transmitting torque during the entire switching process.

[0052] To initiate the switching process, at time t1 the second load-switching clutch 320, which is to be moved from the open state to the closed state during the switching process, is first subjected to a pressure pulse 31. For example, the pressure pulse 31 has a duration of 300 ms.

[0053] After the pressure pulse 31 subsides, at time t2 the pressure in the first power shift clutch 310 is reduced from the closing pressure to such an extent that the first power shift clutch 310 transmits only a reduced torque at time t3.

[0054] At time t2, the pressure in the second power shift clutch 320 is also increased, so that the second power shift clutch 320 begins to transmit increasing torque. At time t3, the pressure in the first and second power shift clutches 310, 320 is equal, so that at this time – due to their identical design – the first and second power shift clutches 310, 320 have the same torque transmission capacity. At time t3, the first and second power shift clutches 310, 320 are therefore slipping equally and thus subject to a comparatively high amount of frictional work.

[0055] To avoid a sudden jolt in the drivetrain, the second power-shift clutch 320 is, for example, filled with pressure relatively slowly, so that it only closes completely at time t4. For example, there is a 1 s interval between time t3 and time t4, during which the frictional work required for speed synchronization is introduced into the second power-shift clutch 320. Since the second power-shift clutch 320 is relatively compact, it can easily be thermally damaged by the introduction of high frictional energies.

[0056] Fig. Figure 1b, in contrast, shows a pressure profile in a first power-shift clutch 310, a second power-shift clutch 320, and a main clutch 200 during a shifting operation according to the inventive method in a power-shiftable motor vehicle transmission 100. The x-axis again shows the time profile, and the y-axis shows the respective pressure.

[0057] For example, the shifting process takes place in the identical motor vehicle transmission 100 of the Fig. 1a. That is, the first power shift clutch 310 and the second power shift clutch 320 are identical in construction, so that they have an identical torque transmission capability at an identical pressure.

[0058] The pressure curve in the first power shift clutch 310 is again represented by curve 20, the pressure curve in the second power shift clutch 320 by curve 30 and the pressure curve in the main clutch 200 by curve 40.

[0059] Curve 20 also represents the torque transmission capability of the first power shift clutch 310, curve 30 the torque transmission capability of the second power shift clutch 320 and curve 40 the torque transmission capability of the main clutch 200.

[0060] To initiate the switching process, the following is also done according to the exemplary embodiment of the Fig. 1b at time t1, the second load-switching clutch 320, which is to be moved from the open state to the closed state during the switching process, is subjected to a pressure pulse 31. As an example, the pressure pulse 31 again has a duration of 300 ms.

[0061] During pressure pulse 31, the pressure—and thus the torque transmission capacity—in the main clutch 200 is reduced at time t5. At time t6, pressure pulse 31 ends, and simultaneously, the further reduction of pressure in the main clutch 200 ceases. Instead, the pressure and torque transmission capacity are initially held constant. At time t7, the torque transmission capacity of the second power-shift clutch 320 begins to increase, and the torque transmission capacity of the first power-shift clutch 310 begins to decrease.

[0062] The reduction in the torque transmission capacity of the first power-shift clutch 310 remains unchanged compared to the state of the art and as also in Fig. Figure 1a shows that the increase in the torque transmission capacity of the second power-shift clutch 320 also remains unchanged until time t8, at which the torque transmission capacity in the first and second power-shift clutches 320 is equal. Fig. 1a.

[0063] In contrast to Fig. 1a is in Fig. 1b However, according to the inventive method, the torque transmission capacity of the main clutch 200 at time t8 is lower than both the torque transmission capacity of the first power-shift clutch 310 and the torque transmission capacity of the second power-shift clutch 320. This allows the frictional work required for speed synchronization to be performed in the main clutch 200 from time t8 onwards, as the main clutch 200 is comparatively more robust and efficient than the first power-shift clutch 310 and the second power-shift clutch 320. This also makes it possible for the second power-shift clutch 320 to reach the closing pressure and be fully closed by time t9, so that consequently no friction can occur in the second power-shift clutch 320. Frictional work is only introduced into the second power-shift clutch 320 between times t7 and t8, for example, 0.1 s.However, this time period is so short that no damage can occur to the second power shift clutch 320.

[0064] From time t9 until time t 10 The pressure in the main clutch 200 is now increased according to the exemplary curve 40 until the main clutch 200 is engaged at time t. 10 is completely closed again. Between times t9 and t 10 This also includes speed synchronization in the main clutch 200, which lasts, for example, 0.9 s.

[0065] Thus, the same switching process can be carried out within the same time period, namely within 1 second, as in Fig. 1a. However, 90% of the frictional work required for speed synchronization is advantageously shifted to the more efficient main clutch 200.

[0066] Fig. Figure 2 shows, as an example in direct size comparison, a typical 300-series power shift clutch with a friction surface of 88,000 mm². 2 ( Fig. 2a). In contrast, a typical main clutch 200 is shown, which has a friction surface of 236000 mm². 2 exhibits ( Fig. 2b). This size difference illustrates the greater performance of the main clutch 200 compared to the power shift clutch 300.

[0067] Fig. Figure 3 shows an exemplary and schematic embodiment of a possible embodiment of a power-shiftable motor vehicle transmission 100 according to the invention. The power-shiftable motor vehicle transmission 100 comprises, for example, six power-shift clutches 310, 320, 330, 340, 350 and 360 as well as a main clutch 200.

[0068] During a switching operation, the pressure in a first power shift clutch 310 is reduced, for example, from a closing pressure to such an extent that the previously closed first power shift clutch 310 no longer transmits any torque.

[0069] In a second power shift clutch 320, the pressure is increased from an opening pressure to such an extent that the second power shift clutch 320 transmits torque.

[0070] During the shifting process, the pressure in the main clutch 200 is also reduced to such an extent that the torque transmission capacity of the main clutch 200 is lower than the torque transmission capacity of the second power shift clutch 320.

[0071] This allows the majority of the frictional work required for speed synchronization to be diverted into the main clutch 200. Reference sign 20 Pressure curve in the first power shift clutch 30 Pressure curve in the second power shift clutch 31 Pressure pulse 40 Pressure curve in the main clutch 100 Powershift automotive transmissions 200 Main clutch 300 power shift clutch 310 first power shift clutch 320 second power shift clutch

Claims

[1] Method for shifting a powershift motor vehicle transmission (100), wherein the motor vehicle transmission (100) comprises at least a first powershift clutch (310) and a second powershift clutch (320) as well as a main clutch (200), wherein, during a switching operation, a pressure in the first power-shift clutch (310) is reduced starting from a closing pressure, so that the first power-shift clutch (310) no longer transmits torque, and a pressure in the second power-shift clutch (320) is increased starting from an opening pressure, so that the second power-shift clutch (320) transmits torque, wherein a pressure in the main clutch (200) is reduced during the switching operation to such an extent that a torque transmission capacity of the main clutch (200) is lower than a torque transmission capacity of the second powershift clutch (320), characterized bythat the pressure in the main clutch (200) is only increased again when the first powershift clutch (310) has reached the opening pressure and the second powershift clutch (320) has reached the closing pressure, wherein at the intersection point of the two characteristic curves the torque of both powershift clutches (310, 320) is equally high, so that the slipping is transferred to the other clutch (310, 320) and the torque of the main clutch (200) is lower than that of the powershift clutches (310, 320) and at the intersection point the pressure of the two powershift clutches (310, 320) is between the opening and closing pressure. [2] Method according to claim 1, characterized by that the opening pressure in the first and second powershift clutch (310, 320) are identical and that the closing pressure in the first and second powershift clutch (310, 320) are identical. [3] Method according to at least one of claims 1 to 2, characterized bythat at a time when the torque transmission capacity of the first powershift clutch (310) and the torque transmission capacity of the second powershift clutch (320) are equal, the torque transmission capacity of the main clutch (200) is lower than in the first and second powershift clutches (310, 320). [4] Method according to claim 3, characterized by that the torque transmission capacity in the main clutch (200) is adjusted during the switching process in accordance with a drive torque to be transmitted, wherein the torque transmission capacity is greater at a high drive torque than at a low drive torque. [5] Method according to at least one of claims 1 to 4, characterized by that the torque transmission capacity of the main clutch (200) is reduced before the torque transmission capacity of the first powershift clutch (310) is reduced. [6] Method according to at least one of claims 1 to 5, characterized by that the second powershift clutch (320) is subjected to a pressure pulse (31) before the pressure in the second powershift clutch (320) is increased to the closing pressure. [7] Powershift motor vehicle transmission (100), comprising at least a first powershift clutch (310) and a second powershift clutch (320) and a main clutch (200), wherein the motor vehicle transmission (100) is designed to reduce a pressure in the first powershift clutch (310) during a shifting operation starting from a closing pressure, so that the first powershift clutch (310) no longer transmits torque, and to increase a pressure in the second powershift clutch (320) up to a closing pressure, so that the second powershift clutch (320) transmits torque, wherein the motor vehicle transmission (100) is further designed to reduce a pressure in the main clutch (200) during the shifting operation to such an extent that a torque transmission capacity of the main clutch (200) is lower than a torque transmission capacity of the second powershift clutch (320), characterized bythat the pressure in the main clutch (200) is only increased again when the first powershift clutch (310) has reached the opening pressure and the second powershift clutch (320) has reached the closing pressure, wherein at the intersection point of the two characteristic curves the torque of both powershift clutches is the same, so that the slipping is transferred to the other clutch and the torque of the main clutch is lower than that of the powershift clutches and at the intersection point the pressure of the two powershift clutches is between the opening and closing pressure. [8] Motor vehicle transmission (100) according to claim 7, characterized by that the motor vehicle transmission (100) is designed as a group transmission which comprises a powershift group and a synchronous group. [9] Motor vehicle transmission (100) according to claim 8, characterized by that the powershift group comprises at least three powershift clutches (310, 320, 330). [10] Motor vehicle transmission (100) according to at least one of claims 7 to 9, characterized by that the motor vehicle transmission (100) is designed to carry out a method according to at least one of claims 1 to 6. [11] Agricultural utility vehicle comprising a motor vehicle transmission (100) according to at least one of claims 7 to 10.

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