Method for operating a motor vehicle transmission

Abstract

The invention relates to a method for operating a motor vehicle transmission. The transmission device is provided with a driving shaft, an output shaft, a first friction clutch, a second friction clutch, a first sub-transmission device and a second sub-transmission device. The first friction clutch is closed for the coupling of the drive shaft to the output shaft in the first force flow path by means of the first partial transmission, and the second friction clutch is closed for the coupling of the drive shaft to the output shaft in the second force flow path by means of the second partial transmission. The output shaft is braked within the range of a braking function in such a way that the drive shaft is coupled to the output shaft simultaneously by means of the first partial transmission with a first gear ratio and by means of the second partial transmission with a second gear ratio as the braking function is activated, and the two friction clutches are closed in a temporally consistent manner for the simultaneous coupling. The friction clutch is only closed in a sliding mode during braking. The respective load capacities of the friction clutches are taken into account when the slip operation is performed.

Description

Field of the Invention

[0001] The invention relates to a method for operating a motor vehicle transmission, in particular an agricultural machine transmission, having a drive shaft, an output shaft, a first friction clutch, a second friction clutch, a first sub-transmission and a second sub-transmission, wherein the drive shaft is configured to couple the motor vehicle transmission on the drive side to at least one drive of the motor vehicle, and the output shaft is configured to establish a coupling of the motor vehicle transmission on the output side to the drive wheels of the motor vehicle, wherein, for the coupling of the drive shaft to the output shaft via the first sub-transmission in a first power flow path, the first friction clutch is closed, and wherein, for the coupling of the drive shaft to the output shaft via the second sub-transmission in a second power flow path which is at least sectionally parallel to the first power flow path, the second friction clutch is closed. Furthermore, the invention also relates to a controller, a computer program product and a data carrier. Background Art

[0002] In motor vehicle transmissions, multi-speed transmissions are known, which are each composed of a plurality of sub-transmissions. In such motor vehicle transmissions, the respective power flow guidance between the respective drive shaft and the respective output shaft can be achieved by the sub-transmissions in power flow paths which are at least sectionally parallel to each other, wherein the respective power flow guidance by the respective sub-transmissions is mostly established here by means of the associated friction clutches. Thereby, the power shiftability of the respective motor vehicle transmission can be obtained in such a way that, when guiding the power flow through one sub-transmission, the next gear ratio has already been switched out in another sub-transmission which is not currently in the power flow, and finally the gear shift has to be completed by simply switching between the friction clutches. When two friction clutches are combined into a dual clutch, such a motor vehicle transmission is also often referred to as a dual-clutch transmission.

[0003] Furthermore, such a motor vehicle transmission can also be used as a transmission group in an agricultural machine transmission implemented in a modular structure, wherein the motor vehicle transmission having a plurality of sub-transmissions can form a split gear group or a main gear group of the agricultural machine transmission here. Thereby, it can be achieved that the gear shifts which mostly only take place in the split gear group and the main gear group during the continuous operation of the respective agricultural or municipal commercial vehicle can be carried out under load and thus with a high level of comfort.

[0004] EP 2 916 044 A1 discloses a sectional drive device which is configured for an agricultural and commercial vehicle, such as a tractor. Herein, the drive device consists of a plurality of drive device groups, and one of the drive device groups is designed as a motor vehicle drive device implemented according to the dual-clutch drive device type. Herein, in addition to having a drive shaft (at which the motor vehicle drive device can be coupled to a drive machine on the drive side within the motor vehicle drive train of the commercial vehicle through an upstream intermediate placed drive device group) and an output shaft (at which the motor vehicle drive device can establish a coupling with the drive wheels of the commercial vehicle on the output side within the motor vehicle drive train), the motor vehicle drive device further has a first sub-drive device and a second sub-drive device. Herein, a plurality of different transmission ratios can be switched out in each of the sub-drive devices. Wherein, when a single sub-drive device is in a state where one of the transmission ratios is switched out, the drive shaft can be coupled to the output shaft in the corresponding force flow path by closing the associated friction clutch. Based on the force flow paths achievable through the sub-drive devices, the power shift capability of the motor vehicle drive device can be achieved by switching between the friction clutches.

[0005] In the field of commercial vehicles, it is known to apply continuous brakes to relieve the burden on the corresponding service brakes. In heavy goods vehicles, retarders are often used as continuous brakes, while in agricultural and commercial vehicles, the continuous brakes are usually designed as engine braking brakes. Summary of the Invention

[0006] Starting from the above prior art, the object of the present invention now is to achieve a braking function through appropriate operation of the motor vehicle drive device, wherein this should be achieved in a simple and reliable manner at the same time.

[0007] This object is solved from the method technical perspective by the preamble of claim 1 in combination with its characterizing part. The subsequent dependent claims respectively reflect advantageous improvement schemes of the present invention. Additionally, the controller for executing the above method is the subject matter of claims 11 and 12. Furthermore, claim 13 also relates to a computer program product and claim 14 relates to a data carrier.

[0008] According to the invention, a motor vehicle transmission is operated within the scope of the method according to the invention, which has a drive shaft, an output shaft, a first friction clutch, a second friction clutch, a first sub-transmission and a second sub-transmission. The drive shaft is arranged to couple the motor vehicle transmission on the drive side to at least one drive machine of the motor vehicle, and the output shaft is used to establish the coupling of the motor vehicle transmission on the output side to the drive wheels of the motor vehicle. Here, for the coupling of the drive shaft to the output shaft in a first power flow path via the first sub-transmission, the first friction clutch is closed, and for the coupling of the drive shaft to the output shaft in a second power flow path that is at least sectionally parallel to the first power flow path via the second sub-transmission, the second friction clutch is closed.

[0009] Thus, a motor vehicle transmission operated within the scope of the method according to the invention includes a drive shaft and an output shaft, wherein the drive shaft is used for the connection on the drive side of the motor vehicle transmission in the state where the motor vehicle transmission is installed in the motor vehicle, and the output shaft is used for the connection on the output side of the motor vehicle transmission. The motor vehicle transmission is designed to enable the power flow guidance from at least one drive machine of the motor vehicle to the drive wheels of the motor vehicle, so that the motor vehicle transmission is a driving transmission. For this purpose, in the installed state of the motor vehicle transmission and during the power flow guidance, a coupling with at least one drive machine is established at the drive shaft, and a connection with the drive wheels of the motor vehicle is made at the output shaft.

[0010] The motor vehicle transmission is preferably used for agricultural or municipal commercial vehicles, so that the motor vehicle transmission is especially an agricultural machinery transmission. Particularly preferably, the motor vehicle transmission is here part of a sectional transmission implemented in a sectional structure, where the motor vehicle transmission is especially arranged as the main gear group of the sectional transmission. Thus, in the installed state of the motor vehicle transmission, a connection with the transmission group upstream of the drive side can be established at the drive shaft, and / or a connection with the transmission group downstream of the output side can be established at the output shaft.

[0011] Within a motor vehicle transmission, on the one hand, the drive shaft can be coupled to the output shaft in a first power flow path via a first sub-transmission of the motor vehicle transmission, for which purpose the first friction clutch is closed. On the other hand, the drive shaft can also establish a coupling with the output shaft in a second power flow path that is at least sectionally parallel to the first power flow path, in such a way that the power flow is guided through a second sub-transmission of the motor vehicle transmission. For this purpose, the second friction clutch is closed. Here, when the coupling is established, a respective transmission ratio is realized between the drive shaft and the output shaft via the respective sub-transmission, wherein within the respective sub-transmission, preferably different transmission ratios can be switched out by selectively actuating the switching elements of the respective sub-transmission, in particular. In addition, the two sub-transmissions preferably differ with respect to the transmission ratios that can be realized between the drive shaft and the output shaft, so that a switching between different transmission ratios (as gears of the motor vehicle transmission) can be effected by switching between the available power flow paths. Here, this switching can be based on the respective couplings established by the respective friction clutches and is effected by switching between the friction clutches under load.

[0012] The second power flow path being "at least sectionally" parallel to the first power flow path means, in the sense of the present invention, that these two power flow paths can also have overlapping portions with each other. Thus, for example, when the power flow is guided through one of the sub-transmissions, it is possible for the power flow to be guided via regions of the other sub-transmission.

[0013] In particular, a plurality of transmission stages are provided within the respective sub-transmission, which are preferably each designed as a spur gear stage here. Here, there can also be transmission stages that are available for power flow guidance via both sub-transmissions. In particular, respective switching elements are assigned to the individual transmission stages, and when the switching elements are actuated, the respective assigned transmission stages can be connected into the power flow. In addition, the respective sub-transmission preferably has a respective assigned input shaft, which, on the one hand, can be coupled to the output shaft via at least one transmission ratio stage of the motor vehicle transmission by actuating the corresponding switching element, and on the other hand, can be coupled to the drive shaft via the respective friction clutch, in particular.

[0014] The two friction clutches are each designed as clutches in which torque transmission occurs in a friction-locked manner. In particular, the individual friction clutches are here implemented as friction clutches for wet operation. Specifically, the individual friction clutches can here be multi-plate clutches. Particularly preferably, the individual friction clutches can be power-shifted here, that is to say, they are able to establish a coupling between the drive shaft and the output shaft while the two clutch halves are loaded. In order to completely shift out the transmission ratio between the drive shaft and the output shaft, the respective friction clutch is here completely closed, wherein the torque transmission through the respective friction clutch here first occurs in a sliding manner during the closing process, that is, there is a rotational speed difference between the clutch halves of the friction clutch, and only then is rotational speed synchronization established between the clutch halves, and the clutch is completely closed.

[0015] The technical teaching now included in the present invention is that, within the scope of the braking function, braking of the output shaft is carried out in such a way that the drive shaft is simultaneously coupled to the output shaft by means of a first sub-transmission with a first transmission ratio and by means of a second sub-transmission with a second transmission ratio different from the first transmission ratio upon activation of the braking function. Here, for this simultaneous coupling, the two friction clutches are closed in a temporally coincident manner, wherein at least one of the friction clutches is only closed in a sliding manner during the braking function, i.e., only in its respective sliding operation. The respective load capacity of at least one friction clutch is also taken into account when carrying out the respective sliding operation.

[0016] In other words, the braking function can be carried out when operating a motor vehicle transmission, and the output shaft is braked when carrying out the braking function. In order to carry out the braking function, the first friction clutch and the second friction clutch are closed in a temporally coincident manner, which results in the drive shaft being coupled to the output shaft in a temporally coincident manner by means of the first sub-transmission and the second sub-transmission. Thereby, coupling with the first transmission ratio is achieved by means of the first sub-transmission, and coupling with a second transmission ratio different from the first transmission ratio is achieved by means of the second sub-transmission. However, here, at least one of the two friction clutches only operates in its respective sliding operation and is thus only closed in a sliding manner, rather than being completely closed. The respective sliding operation of at least one friction clutch during the execution of the braking function is designed taking into account the respective load capacity of at least one friction clutch.

[0017] Here, the advantage of the operation of this motor vehicle transmission is that by simultaneously closing two friction clutches and coupling the drive shaft to the output shaft via two force flow paths with different transmission ratios, braking of the output shaft and thus braking of the drive wheels of the motor vehicle coupled to the output shaft are achieved. However, here, jamming of the motor vehicle transmission does not occur because at least one of the friction clutches closes only in a sliding manner during its respective sliding operation. Therefore, when at least one friction clutch closes during its respective sliding operation, it ensures the gradual elimination of the respective rotational speed difference, which causes braking of the output shaft based on the full closure of the other friction clutch or also a sliding closure and based on the different transmission ratios of the two sub-transmissions. Since the load capacity of the friction clutch is also considered when designing the respective sliding operation of at least one friction clutch, overload and damage of the sliding friction clutch can be reliably excluded here. In summary, a retarder-like braking function is thus achieved by the motor vehicle transmission.

[0018] The important point of the present invention is that within the scope of the braking function, the coupling of the drive shaft to the output shaft via two sub-transmissions with different transmission ratios is completed in time to achieve braking of the output shaft. However, here, in order to avoid jamming of the motor vehicle transmission and only achieve braking of the output shaft, at least one of the respective friction clutches must close only in a sliding manner when coupling via the respective sub-transmission.

[0019] According to an embodiment of the present invention, the respective sliding operation of at least one friction clutch is limited within the respective sliding value range, where the frictional power to be generated during the sliding operation by the respective friction clutch is in the fatigue strength range of the respective friction clutch in any case. Thus, within the scope of the braking function, overload of the respective friction clutch that may occur is reliably excluded because the respective friction clutch operates in a non-critical range anyway during its sliding operation. Here, the fatigue strength range is especially defined by the range in which the respective friction clutch can operate within the respective sliding value range for a long time because cooling especially by lubricating oil occurs here.

[0020] According to an alternative design feasibility solution of the present invention, there is no limitation within the sliding value range for the respective sliding operation of at least one friction clutch, wherein during the operation of at least one friction clutch in its respective sliding operation, the respective current load of the friction clutch is known. In this way, advantageously, based on the lack of limitation, a higher braking effect can also be achieved by at least one friction clutch in the sliding state. Preferably, the respective current load is known, preferably calculated, by knowing the respective current friction power of the individual friction clutch. Here, based on the friction power, the load of at least one friction clutch can be reliably inferred.

[0021] Alternatively or additionally, when the respective current load of an individual friction clutch exceeds a determined boundary value, the braking function is terminated. The advantage is that, thus, by appropriately defining the boundary value, overload of the respective friction clutch can be excluded, in such a way that the braking function is terminated before the overload occurs. If the respective current load is known based on the respective current friction power, then the determined boundary value is the friction power boundary value.

[0022] Another embodiment of the present invention is that during the execution of the braking function, the respective sliding operation of at least one friction clutch is adjusted respectively depending on the braking torque to be achieved on the output shaft. Here, within the scope of the present invention, this adjustment can be done either in the sense of control or in the sense of regulation.

[0023] Preferably, in at least one friction clutch, for adjusting the respective sliding operation, the respective operating pressure is adjusted here depending on the braking torque to be achieved. In this way, the respective sliding of the respective friction clutch can be precisely adjusted by the respective hydraulic or pneumatic adjustment actuator of the respective friction clutch. Alternatively or additionally, the respective current transmission ratio of the respective sub-transmission is taken into account when adjusting the respective sliding operation of at least one friction clutch.

[0024] According to a design feasibility solution of the present invention, during the execution of the braking function, two friction clutches operate simultaneously only in their respective sliding operations respectively. The advantage is that, thus, the load is distributed to the two friction clutches. Particularly preferably, the sliding operation of the friction clutch is designed such that the generation of the braking torque is distributed at least as evenly as possible to the two friction clutches, which correspondingly also results in an even distribution of the load to the two friction clutches.

[0025] In an improved solution of the present invention, the drive shaft is decoupled on the drive side along with the activation of the braking function and during the execution of the braking function. In this way, it is possible to prevent at least one drive machine connected to the drive shaft from being dragged.

[0026] The subject matter of the invention also includes a control, in particular a transmission control of a motor vehicle transmission. The control is configured to initiate the closing of a first friction clutch in the motor vehicle transmission for the connection of a drive shaft and an output shaft via a first sub-transmission in a first force flow path. In addition, the control is also designed to initiate the closing of a second friction clutch in the motor vehicle transmission for the connection of a drive shaft and an output shaft via a second sub-transmission in a second force flow path at least partially parallel to the first force flow path. The control is also configured to perform a braking function to brake the output shaft, with the activation of the braking function, the drive shaft and the output shaft are connected simultaneously via the first sub-transmission with a first transmission ratio and via the second sub-transmission with a second transmission ratio different from the first transmission ratio. In this case, the control is designed to cause the simultaneous closing of two friction clutches for the execution of the braking function, wherein the respective closing of at least one of the friction clutches is performed only in a slipping manner in the respective slipping operation during the braking function, and wherein the control is configured to take into account the respective load capacity of at least one friction clutch when performing the respective slipping operation. In addition, the control is configured to implement one or more of the above-mentioned variants of the method of the invention for adjusting the actuator.

[0027] The method of the present invention can also be embodied as a computer program product, which, when executed on a processor (e.g., a processor of the above-mentioned controller), instructs the processor to execute the corresponding method steps related to the subject of the invention by software. In this regard, the subject of the present invention also includes a computer-readable medium on which the above-mentioned computer program product is stored in a callable manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The advantageous embodiment of the invention to be explained below is shown in the accompanying drawings, in which:

[0029] Figure 1 It is a schematic diagram of a motor vehicle drive train for agricultural or municipal commercial vehicles;

[0030] Figure 2 is a flow chart of a method for implementing a braking function according to one embodiment of the present invention;

[0031] Figure 3 The present invention is a flowchart of a method for realizing a braking function according to a feasible design solution of the present invention. DETAILED DESCRIPTION

[0032] according to Figure 1Schematic view of a motor vehicle drive train 1 of a motor vehicle in the form of a commercial vehicle for agricultural or municipal use, in particular a tractor. A sectional transmission 4 is provided between a drive machine 2 in the form of an internal combustion engine and the drive wheels 3. In addition to other transmission groups, the sectional transmission includes a power-shiftable motor vehicle transmission 5. The motor vehicle transmission 5 is coupled to the upstream transmission group at a drive shaft 6 and a coupling to the drive wheels 3 is established at an output shaft 7 of the motor vehicle transmission 5. Furthermore, the motor vehicle transmission 5 has a first sub-transmission 8 and a second sub-transmission 9, each of which is assigned an input shaft 10 or 11.

[0033] On the one hand, a first transmission ratio of the first sub-transmission 8 is achieved by coupling the input shaft 10 of the first sub-transmission 8 to the output shaft 7 via a spur gear stage 12 by actuating a switching element 13. On the other hand, a second transmission ratio can also be switched in the first sub-transmission, in such a way that the input shaft 10 of the first sub-transmission can be coupled to the input shaft 11 of the second sub-transmission 9 via the spur gear stage 12 and a spur gear stage 14 by actuating a switching element 15, and then the force flow is further guided from the input shaft of the second transmission to the output shaft 7 via a spur gear stage 16 by actuating a switching element 17.

[0034] Here, a first transmission ratio of the second sub-transmission 9 is also achieved when the second transmission ratio of the first sub-transmission 8 is switched, wherein, when the switching element 17 is actuated, the input shaft 11 of the second sub-transmission 9 is coupled to the output shaft 7 via a spur gear stage 16. Furthermore, a coupling of the input shaft 11 of the second sub-transmission 9 to the output shaft 7 with a second transmission ratio of the second sub-transmission 9 can be achieved in such a way that the switching elements 13 and 14 are closed simultaneously and thus a coupling of the input shaft 11 to the output shaft 7 via the spur gear stage 14 is carried out. Due to the related inclusion of the spur gear stage 12 in the force flow, this also results in switching out the first transmission ratio of the first sub-transmission 8 at the same time.

[0035] Now, in order for the drive shaft 6 to be able to be coupled to the output shaft 7 via the respective sub-transmission 8 or 9, a first friction clutch 18 and a second friction clutch 19 are also provided in the motor vehicle transmission 5, both of which are designed as wet-running friction clutches. Here, the closing of the first friction clutch 18 enables a coupling between the input shaft 10 of the first sub-transmission 8 and the drive shaft 6 via a spur gear stage 20, whereby, when one of the transmission ratios of the first sub-transmission 8 is switched out simultaneously, a force flow from the drive shaft 6 to the output shaft 7 can occur in a first force flow path.

[0036] If, however, the second friction clutch 19 is closed, this results in the coupling of the drive shaft 6 to the input shaft 11 of the second subtransmission 9 via the cylindrical gear stage 21. Here, the power flow from the drive shaft 6 to the output shaft 7 is effected in a second power flow path that is at least sectionally parallel to the first power flow path by simultaneously switching one of the transmission ratios of the second subtransmission 9 and thereby enabling the power flow through the second subtransmission 9. The corresponding switching of the transmission ratios in the subtransmissions 8 and 9, the closing of the friction clutches 18 and 19, and the switching processes in the other transmission groups are effected in the sectional transmission 4 by the controller 22, which is shown in Figure 1 as shown.

[0037] In connection with the above-described motor vehicle transmission 5, the method according to the invention will be explained below, by means of which braking functions for braking the associated motor vehicle can be implemented respectively. Here, the method according to the invention can in principle also be implemented in motor vehicle transmissions of different designs having a plurality of subtransmissions, in which the switching processes can be effected automatically or in an automated manner by a controller.

[0038] Figure 2 FIG. shows a flow chart of a first embodiment of a method according to the invention for implementing a braking function. Here, at the start of the method, in a first step S1 it is first queried whether a braking preset exists, i.e., whether braking of the respective vehicle is actually to be effected. If the result of step S1 is negative, then it jumps back to before step S1, preferably starting a new query in step S1 after the expiration of a defined time window.

[0039] If, however, a braking preset exists, then after step S1, step S2 is entered, in which in the motor vehicle transmission 5 one possible transmission ratio each is simultaneously switched out in the two subtransmissions 8 and 9. Here, the switched-out transmission ratios are different from one another with respect to the transmission ratio respectively implemented between the drive shaft 6 and the output shaft 7. In step S2, the drive shaft 6 is also decoupled from the upstream drive machine 2 by effecting a neutral gear in the transmission group upstream of the motor vehicle transmission 5.

[0040] Following step S2, step S3 is entered, in which the braking torque T Brems to be implemented on the output shaft 7 is determined according to the braking preset. Then in step S4, according to this braking torque T Brems the actuation pressures p 1 and p 2, they are used to control two friction clutches 18 and 19 so as to perform the simultaneous coupling of the output shaft 7 and the drive shaft 6 with a switched transmission ratio through two sub-transmissions 8 and 9 during the slip operation of the two friction clutches 18 and 19, and thereby, generate the required braking torque T on the output shaft 7 Brems . Herein, the respective slip values of the respective friction clutches 18 or 19 are determined respectively, wherein when selecting the slip values, the respective transmission ratios of the respective sub-transmissions 8 or 9 are considered, and at least approximately uniform load distribution to the two friction clutches 18 and 19 is also performed. Then in step S5, the determined operating pressures p 1 and p 2 are used to control the friction clutches 18 and 19.

[0041] Following step S5, in step S6, the current friction powers P Reib1 and P Reib2 are calculated, which are generated by the friction clutches 18 and 19 under the slip operation respectively set in step S5. Then, in the subsequent step S7, the calculated friction powers P Reib1 and P Reib2 of the friction clutches 18 and 19 are compared with the respective (in the form of predetermined friction power boundary values P Reib, Grenz1 and P Reib, Grenz2 ) boundary values of the friction clutches 18 and 19. If the two calculated friction powers P Reib1 and P Reib2 are herein lower than the respective friction power boundary values P Reib, Grenz1 and P Reib, Grenz2 , then after step S7, it enters step S8, and if the respective friction power P Reib1 or P Reib2 exceeds one of the friction power boundary values P Reib, Grenz1 or P Reib, Grenz2 , then it switches to step S9. In this step S9, the braking function is terminated by completely disconnecting the two friction clutches 18 and 19 again.

[0042] And in step S8, it is queried whether there is still a braking demand currently. If this is the case, it jumps back before step S3, and if there is a lack of braking demand at this time, it also enters step S9.

[0043] In addition, Figure 3 shows a flowchart of a method for implementing a braking function according to a second design feasibility solution of the present invention. Herein, this method basically corresponds to the process of the foregoing variant according to Figure 2 , the difference being that after step S3, it enters step S10. In this step S10, the operating pressures p of the two friction clutches 18 and 19 are also obtained1* and p 2* , they are used to control two friction clutches 18 and 19 so as to generate the required braking torque T on the output shaft 7 Brems . However, here, each sliding value and thus the respective operating pressure p 1* or p 2* of each of the respective friction clutches 18 or 19 is limited by a maximum value, wherein the frictional power to be generated by the respective friction clutches 18 or 19 is in the fatigue strength range of the respective friction clutches 18 or 19 in any case. Subsequently, in step S11, the operating pressures p 1* and p 2* selected in this way are used to control the friction clutches 18 and 19.

[0044] After step S11, in step S12, it is queried whether there is still a braking demand at present. In the affirmative case, it jumps back to before step S3. And if the result in step S12 is negative, it proceeds to step S13, in which the braking function is terminated by completely disengaging the two friction clutches 18 and 19.

[0045] Here, the braking function can be realized in a simple and at the same time reliable manner by means of the operation of the motor vehicle transmission according to the invention.

[0046] Reference numerals

[0047] 1 Motor vehicle drive train

[0048] 2 Driving machine

[0049] 3 Driving wheel

[0050] 4 Grouped transmission

[0051] 5 Motor vehicle transmission

[0052] 6 Drive shaft

[0053] 7 Output shaft

[0054] 8 First sub - transmission

[0055] 9 Second sub - transmission

[0056] 10 Input shaft

[0057] 11 Input shaft

[0058] 12 Cylindrical gear stage

[0059] 13 Switching element

[0060] 14 Cylindrical gear stage

[0061] 15 Switching element

[0062] 16 Cylindrical gear stage

[0063] 17 Switching element

[0064] 18 Friction clutch

[0065] 19 Friction clutch

[0066] 20 Cylindrical gear stage

[0067] 21 Cylindrical gear stage

[0068] 22 Controller

[0069] T Brems Braking torque

[0070] p 1 Actuating pressure

[0071] p 2 Actuating pressure

[0072] P Reib1 Frictional power

[0073] P Reib2 Frictional power

[0074] P Reib, Grenz1 Frictional power limit value

[0075] P Reib, Grenz2 Frictional power limit value

[0076] p 1* Actuating pressure

[0077] p 2* Actuating pressure

[0078] S1 to S13 Individual steps

Claims

1. A method for operating a motor vehicle transmission (5), in particular an agricultural machinery transmission, the motor vehicle transmission comprising a drive shaft (6), an output shaft (7), a first friction clutch (18), a second friction clutch (19), a first sub-transmission (8) and a second sub-transmission (9), the drive shaft being arranged for coupling the motor vehicle transmission (5) on the drive side to at least one drive engine (2) of a motor vehicle, the output shaft being used for establishing a coupling of the motor vehicle transmission (5) on the output side to a drive wheel (3) of the motor vehicle, wherein: The first friction clutch (18) is closed for coupling the drive shaft (6) to the output shaft (7) via the first sub-transmission (8) in a first force flow path, and the second friction clutch (19) is closed for coupling the drive shaft (6) to the output shaft (7) via the second sub-transmission (9) in a second force flow path at least partially parallel to the first force flow path, wherein the output shaft (7) is braked within the scope of a braking function in that the drive shaft (6) is braked along with the braking function. The activation of the braking function is simultaneously coupled to the output shaft (7) via the first sub-transmission (8) with a first transmission ratio and via the second sub-transmission (9) with a second transmission ratio different from the first transmission ratio, wherein for this simultaneous coupling, the two friction clutches (18, 19) are closed in time coincidence, and at least one of the friction clutches (18, 19) is closed only in a slipping manner in the respective slipping operation during the braking function, and the respective load capacity of at least one friction clutch (18, 19) is taken into account when performing the respective slipping operation.

2. The method according to claim 1, characterized in that The respective slip operation of the at least one friction clutch (18, 19) is limited to a respective slip value range, wherein the friction power to be generated by the respective friction clutch (18, 19) in the respective slip operation is always within the fatigue strength range of the respective friction clutch (18, 19).

3. The method according to claim 1, characterized in that The respective slipping operation of the at least one friction clutch (18, 19) is not limited to a slip value range, wherein the respective current load of the friction clutch (18, 19) is determined during operation of the at least one friction clutch (18, 19) in the respective slipping operation.

4. The method according to claim 3, characterized in that By means of the respective current friction power (P Reib, Grenz2 ) is known and preferably calculated to know the respective current loads.

5. The method according to claim 3 or 4, characterized in that: The braking function is terminated when the respective current load of the individual friction clutches (18, 19) exceeds a certain limit value.

6. The method according to any one of the preceding claims, characterized in that When the braking function is performed, the braking torque (T Brems ) to adjust the respective slipping operation of the at least one friction clutch (18, 19).

7. The method according to claim 6, characterized in that For the at least one friction clutch (18, 19), for setting the respective slipping operation, depending on the braking torque to be achieved (T Brems ) to adjust the respective operating pressures (p1, p2; p 1* 、p 2* ).

8. The method according to claim 6 or 7, characterized in that: When adjusting the respective slipping operation of the at least one friction clutch (18, 19), the respective current transmission ratio of the respective component transmission (8, 9) is taken into account.

9. The method according to any one of the preceding claims, characterized in that During the execution of the braking function, the two friction clutches (18, 19) are simultaneously closed only in the respective slipping mode.

10. The method according to claim 9, characterized in that The sliding operation of the friction clutch (18, 19) is designed so that the braking torque (T Brems ) is generated and distributed as evenly as possible to the two friction clutches (18, 19).

11. The method according to any one of the preceding claims, characterized in that Accompanying activation and while the braking function is being performed, the drive shaft (6) is decoupled on the drive side.

12. A control unit (22), in particular a transmission control unit, which is configured to initiate the closing of a first friction clutch (18) in a motor vehicle transmission unit (5) for coupling a drive shaft (6) via a first sub-transmission (8) in a first force flow path to an output shaft (7), wherein: The controller (22) is also configured to initiate the closing of the second friction clutch (19) in the motor vehicle transmission (5) for coupling the drive shaft (6) with the output shaft (7) via a second sub-transmission (9) in a second force flow path at least partially parallel to the first force flow path, wherein the controller (22) is configured to perform a braking function to brake the output shaft (7) and, accompanying the activation of the braking function, to brake the drive shaft (6) simultaneously via the first sub-transmission (8) at a first transmission ratio and via the second sub-transmission (9) at a second force flow path at least partially parallel to the first force flow path. The device (9) is coupled to the output shaft (7) at a second transmission ratio different from the first transmission ratio, wherein the controller (22) is configured to cause the two friction clutches (18, 19) to close in a timely manner for the execution of the braking function, and to perform the respective closing of at least one of the friction clutches (18, 19) in a respective slipping operation only in a slipping manner during the braking function, and wherein the controller (22) is configured to take into account the respective load capacity of at least one friction clutch (18, 19) when performing the respective slipping operation.

13. The control unit (22) according to claim 12, further configured to carry out the method according to any one or more of claims 2 to 11.

14. A computer program product for a controller (22) according to claim 12 or 13, by means of which the method according to any one or more of claims 1 to 11 can be performed, wherein: A routine for operating the motor vehicle transmission (5) is implemented by corresponding control instructions stored in software.

15. Data carrier having a computer program product according to claim 14.

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