Method and control device for operating a drive train

Abstract

The invention relates to a method for operating a drive train of a motor vehicle, which has an internal combustion engine (1), an electric machine (4) and a group transmission (2) with a main transmission (9) and a range group (11), wherein the internal combustion engine (1) is coupled to an input shaft (6) of the group transmission (2) via a shiftable disconnect clutch (5), wherein the electric machine (4) is also coupled to the input shaft. Then, when the motor vehicle travels with the disconnect clutch (5) engaged, and using the range group (11) and the main transmission (9), a downshift is to be carried out, and the electric machine (4) cannot be used to synchronise the shifting elements, the following is carried out: The motor vehicle is accelerated in such a way that a rotational speed of the internal combustion engine (1) is brought to a target rotational speed. Subsequently, a load reduction is carried out on a shifting element of the main transmission (9) to be disengaged to carry out the downshift, and same is disengaged. Subsequently, the input shaft (6) is synchronized to a first target rotational speed and the shifting element of the main transmission (9) to be engaged in order to carry out the downshift is engaged. At the same time or subsequently, the range group (11) is transferred into neutral, the input shaft (6) is synchronised to a second target rotational speed via the internal combustion engine (1), and a shifting element of the range group (11) to be engaged to carry out the downshift is engaged.

Description

[0001] ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0002] Method and control unit for operating a drive train

[0003] The invention relates to a method for operating the drivetrain of a motor vehicle, wherein the drivetrain comprises an internal combustion engine as the first drive unit, an electric machine as the second drive unit, and an automated transmission group connected between the drive units and an output shaft, wherein the internal combustion engine is coupled to an input shaft of the transmission group via a switchable disconnect clutch, wherein the electric machine is also coupled to the input shaft of the transmission group, and wherein the transmission group comprises several sub-transmissions, namely at least one main transmission and a range group connected downstream of the main transmission. The invention further relates to a control unit for operating such a drivetrain.

[0004] DE 10 2007 043 694 A1 discloses a group transmission comprising a main transmission, a range group connected downstream of the main transmission, and a splitter group connected upstream of the main transmission. The main transmission and splitter group are designed as reduction gears with countershafts, one of which has a transmission brake engaged. An internal combustion engine is coupled to an input shaft of the group transmission via a disconnect clutch, and an output shaft is coupled to an output shaft of the group transmission. Shifting is possible within the group transmission, and according to DE 10 2007 043 694 A1, the transmission brake is used to synchronize the shifting elements.

[0005] DE 10 2013 211 225 A1 discloses a group transmission for a motor vehicle, which in turn comprises a main transmission, a range group connected downstream of the main transmission, and a splitter group connected upstream of the main transmission, wherein an internal combustion engine and an electric machine are coupled to the input shaft of the group transmission. The internal combustion engine is coupled to the input shaft of the group transmission via a disconnect clutch, while the electric machine is permanently coupled to the input shaft of the group transmission via a planetary gear stage. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0006] The group transmission for a hybrid drive arrangement disclosed in DE 10 2013 211 225 A1 does not include a transmission brake. In one version, the electric machine is used to synchronize the switching elements.

[0007] If the electric machine for synchronizing the switching elements is unavailable, for example due to a malfunction or failure of a high-voltage system, it is currently not reliably possible to perform shifts in the transmission. This can then lead to the vehicle breaking down.

[0008] Based on this, there is a need for a method for operating a motor vehicle drive train with an automated group transmission, in which a downshift can be reliably carried out even when the electric machine cannot be used for switching element synchronization, with the involvement of the range group and the main transmission.

[0009] The invention is based on the objective of creating a novel method for operating a drive train of a motor vehicle and a control unit for carrying out the method.

[0010] This problem is solved by a method for operating a drive train according to claim 1 and by a control unit according to claim 9.

[0011] Then, when the motor vehicle is driving with the disconnect clutch engaged, and a downshift is to be performed in the range transmission, at least involving the range group and the main transmission, and the electric machine cannot be used for shift element synchronization, the following steps must be taken to perform the downshift:

[0012] The vehicle is accelerated in such a way that the internal combustion engine's speed is brought up to a target speed. In doing so, the engine speed is increased. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0013] Subsequently, a load reduction is carried out on a positive-locking switching element of the main gearbox designed to execute the downshift, and the same is then designed to bring the main gearbox into neutral.

[0014] The input shaft is then synchronized to a first target speed, and subsequently the positive-locking shift element of the main gearbox, required for downshifting, is engaged. To synchronize the input shaft of the range gearbox to the first target speed, the speed of the internal combustion engine is reduced.

[0015] Simultaneously with the insertion of the positive-locking switching element of the main transmission or subsequently thereafter, the range group is moved into neutral, the input shaft is synchronized to a second target speed via the combustion engine and a switching element of the range group to be inserted for the execution of the downshift is inserted.

[0016] The invention proposes a method that enables reliable downshifting in a hybrid drive system's transmission group that lacks a transmission brake, specifically when the electric motor cannot be used for shift element synchronization. In the method according to the invention, the internal combustion engine is used to synchronize shift elements as far as possible to perform a downshift involving both the main transmission and the downstream range group. First, the drivetrain is conditioned by accelerating the vehicle and bringing the internal combustion engine to its target speed. Subsequently, a shift is performed first in the main transmission and then in the range group to ultimately execute the downshift.

[0017] Preferably, when accelerating the motor vehicle, the internal combustion engine's speed is increased to a target speed that is lower than the maximum permissible operating speed of the internal combustion engine by an offset or a factor. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0018] The target engine speed, to which the engine speed is adjusted for conditioning the drivetrain, is set so that the engine runs at the highest possible speed and yet does not overspeed after downshifting. This ensures the highest possible engine speed even during relatively long shifts with large gear changes. This is particularly advantageous for reliable downshifting.

[0019] Preferably, if the first target speed is greater than the idle speed of the internal combustion engine, the input shaft of the range gearbox is synchronized to the first target speed via the internal combustion engine, and the positive-locking shift element of the main gearbox, which is to be engaged to perform the downshift, is activated for engagement upon reaching the first target speed. In this case, the disconnect clutch between the internal combustion engine and the input shaft can remain closed, and the synchronization of the input shaft to the first target speed is carried out exclusively via the internal combustion engine.

[0020] Preferably, if the first target speed is lower than the idle speed of the internal combustion engine, the input shaft is first guided towards the first target speed via the internal combustion engine. The disconnect clutch is then opened at an internal combustion engine speed higher than its idle speed, and the input shaft is subsequently synchronized to the first target speed via friction losses in the transmission. The positive-locking shift element of the main transmission, which is used to perform the downshift, is activated upon reaching the first target speed or even before. In this case, the input shaft speed is synchronized to the first target speed first via the internal combustion engine with the disconnect clutch closed, and then, with the disconnect clutch open, via friction losses in the transmission.Opening the disconnect clutch prevents the idle speed control of the internal combustion engine from engaging. This is preferred for comfort reasons and also to ensure advantageous synchronization of the input shaft of the transmission. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30.

[0021] To synchronize the input shaft of the group gearbox to the first target speed, the speed of the internal combustion engine is reduced in both cases with the disconnect clutch closed, preferably using an engine braking device of the internal combustion engine, which may be designed, for example, as a decompression brake, primary retarder or the like.

[0022] Preferably, if a splitter group upstream of the main transmission is also involved in the downshift, a positive-locking switching element designed for downshifting is installed in the splitter group after the range group has been shifted into neutral and before the input shaft of the range transmission has been synchronized to the second target speed. A positive-locking switching element is also inserted in the splitter group to execute the downshift. If the splitter group is also involved in the upshift, the switching of the splitter group occurs between the shifting of the main transmission and the shifting of the range group.

[0023] Preferably, downshifting is performed when, after a downshift request is received, it is determined, based on a current and / or future driving situation, particularly driving resistance and / or road gradient, that downshifting can be performed without assistance from the electric motor. This serves to verify whether, when a downshift request is received, the downshift can indeed be performed without the involvement of the electric motor for switching element synchronization. Only if this is the case will the downshift be performed when a downshift request is received; otherwise, the downshift is prevented and not executed. This prevents the control system from triggering an impractical downshift.

[0024] Preferred embodiments are described in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. The drawing shows:

[0025] Fig. 1 shows an exemplary schematic of a motor vehicle powertrain, namely a hybrid drive arrangement with a range gearbox; ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0026] Fig. 2 is a signal flow diagram to illustrate the invention.

[0027] The invention presented here relates to a method for operating a drive train of a motor vehicle with an automated group transmission and a control device for carrying out the method.

[0028] Fig. 1 shows a scheme of a motor vehicle drive train with a first drive unit designed as an internal combustion engine 1, with an automated group transmission 2, with an output 3 and with a second drive unit designed as an electric machine 4.

[0029] The internal combustion engine 1 is coupled to an input shaft 6 of the transmission 2 via a disconnect clutch 5, also referred to as a starting clutch. The disconnect clutch 5 is a friction-fit switching element. When the disconnect clutch 5 is open, the internal combustion engine 1 is disengaged from the input shaft 6 of the transmission 2. When the disconnect clutch 5 is closed, either fully or partially closed, the internal combustion engine 1 is coupled to the input shaft 6 of the transmission 2.

[0030] In the illustrated embodiment, the electric machine 4 is permanently coupled to the input shaft 6 of the group gearbox 2, specifically via a planetary gear 30 in Fig. 1. In addition to the planetary gear 30, a disconnect clutch (not shown) can also be connected between the electric machine 4 and the input shaft 6 of the group gearbox 2.

[0031] The output 3 is coupled to an output shaft 8 of the group gearbox 2.

[0032] In the illustrated embodiment, the group transmission 2 comprises a main transmission 9, a split group 10 upstream of the main transmission 9 in terms of drive technology, and a range group 11 downstream of the main transmission 9 in terms of drive technology.

[0033] The main transmission 9 is also referred to as the main group. The main transmission 9 of the group transmission 2 is a direct-drive transmission with a reduction gear and has two countershafts 21, 22. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0034] In the illustrated embodiment, the main transmission 9 is configured with three gear ratios G1, G2, and G3 for forward travel and one gear ratio R for reverse travel. The loose gears of gear ratios G1, G2, and R are each rotatably mounted on a main shaft and can be switched via associated switching elements 15, 16, 18, and 19, which are designed as positive-locking claw switching elements. In Fig. 1, switching element 15 is designated as switching element C, switching element 16 as switching element D, switching element 18 as switching element E, and switching element 19 as switching element F. The associated fixed gears are arranged non-rotatably on the countershafts 21 and 22. The two switching elements 15 and 16 (or C and D) and the two switching elements 18 and 19 (or E and F) each form a switching assembly 17 or 20, respectively.

[0035] The splitting unit 10 of the transmission group 2, which is upstream of the main transmission 9, is designed in two stages in the illustrated embodiment and is also of a reduction gear design, with the two gear ratios K1 and K2 of the splitting unit 10 forming two switchable input constants of the main transmission 9. The two gear ratios K1 and K2 have a smaller gear ratio difference. The splitting unit 10 of the transmission group 2 is optional and can also be omitted. The loose gear of the first gear ratio K1 is rotatably mounted on the input shaft 6. The loose gear of the second gear ratio K2 is rotatably mounted on the main shaft. The fixed gears of both gear ratios K1 and K2 of the splitting unit 10 are each rotationally fixed to the input-side extended reduction shafts 21 and 22 of the main transmission 9. Synchronized switching elements 12 and 13, so-called synchronous switching elements, of the splitting unit 10 are combined into a common switching assembly 14.In Fig. 1, switching element 12 is designated as switching element A and switching element 13 as switching element B. Switching elements 12 and 13 are designed as positive-locking claw switching elements.

[0036] The range group 11 of the group gearbox 2, which is downstream of the main gearbox 9, is also designed as a two-stage system, but as a planetary gearbox 24. The sun gear 25 is non-rotatably connected to the main shaft of the main gearbox 9, which is extended on the output side. The planet carrier 27 is non-rotatably coupled to the output shaft 8 of the group gearbox 2. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0037] The ring gear 26 of the planetary gear 24 is connected to a shift assembly 23 with two synchronized shift elements 28, 29, by which the range group 11 can be alternately switched to a slow-speed stage by connecting the ring gear 26 to a stationary housing part 7 and to a high-speed stage by connecting the ring gear 26 to the planet carrier 27. In Fig. 1, the shift element 28 is designated as shift element G and the shift element 29 as shift element H. The shift elements 28, 29 are designed as positive-locking claw shift elements.

[0038] In Fig. 1, an optional oil pump 31 engages the countershaft 22 and can be driven from the countershaft 22.

[0039] It should be noted here that the embodiment of the group transmission 2 shown in Fig. 1 is preferred, but optional. The invention can also be used in conjunction with other group transmissions.

[0040] The present invention relates to a method by which it is possible to perform a shift, namely downshifting, at least with the involvement of the section group 11 and the main transmission 9, in a group transmission 2 which is part of a hybrid powertrain configuration of a motor vehicle, and in which, due to the omission of a transmission brake, the electric machine 4 is used to synchronize shifting elements when shifting is carried out in the group transmission 2, even if, for example, the electric machine 4 cannot be used for shifting element synchronization due to a fault or failure of a high-voltage system.

[0041] Initially, it is assumed that the vehicle is traveling with the disconnect clutch 5 at least partially engaged, and in particular fully engaged, and that during the vehicle's travel, a downshift request exists to execute a downshift in the range transmission 2 involving the area group 11 and the main transmission 9. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0042] A downshift request can be detected, for example, based on the driver's accelerator pedal input, particularly when the driver releases the accelerator pedal, indicating a desire for a lower speed. This can be interpreted by the transmission control unit as a downshift request. A downshift request can also be inferred from brake pedal input.

[0043] If such a downshift request exists, it is preferably first checked whether the downshift can actually be carried out without assistance from the electric machine 4. For this purpose, it can be estimated, based on a current and / or future driving situation, in particular driving resistance and / or road gradient, whether the desired downshift can actually be carried out without switching element synchronization by the electric machine 4.

[0044] To determine driving resistance and / or road gradient, sensors installed in the drivetrain, such as tilt sensors, as well as models for calculating or estimating the vehicle mass, can be used. Furthermore, GPS data about the road ahead can be provided by a GPS system. Based on these input parameters, driving resistance and / or road gradient can be determined in order to estimate, depending on these parameters, whether a downshift can be performed when a downshift is requested, specifically when the electric motor 4 is not available for synchronizing the shift element.

[0045] Only if it is determined that, in the event of a downshift request, the downshift can be executed by the electric machine 4 even without switching element synchronization, is the downshift triggered and enabled by the control system. Otherwise, the execution of the downshift is suppressed by the control system and not carried out. If it is determined that the downshift to be performed can be carried out by the electric machine 4 without switching element synchronization, the drivetrain is subsequently conditioned by bringing the speed of the internal combustion engine 1 up to a target speed. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0046] When bringing the internal combustion engine 1 up to the target speed, the motor vehicle is accelerated, whereby the speed of the internal combustion engine 1 is preferably increased to a speed that is smaller than the maximum permissible operating speed of the internal combustion engine by a defined offset or factor.

[0047] In particular, the target speed for the internal combustion engine 1 is determined such that the internal combustion engine 1 rotates at the highest possible speed and yet does not overspeed after downshifting. This ensures, on the one hand, the highest possible connection speed even during relatively long shifts with large gear changes, and on the other hand, it ensures that a large proportion of the differential speed can be reduced by the engine braking system of the internal combustion engine 1 until it reaches idle speed.

[0048] After preconditioning the drive train by accelerating the motor vehicle and bringing the speed of the internal combustion engine 1 up to the target speed, a load reduction is subsequently carried out on a positive-locking switching element of the main transmission 9 designed to execute the downshift, in particular by reducing torque at the internal combustion engine 1 at a preferably constant speed.

[0049] The load reduction frees the positive-locking switching element of the main gearbox 9, which is designed to execute the downshift, in order to subsequently engage it and move the main gearbox 9 into neutral. The range gearbox 2, and thus the drive train, is then open and no longer frictionally engaged.

[0050] After the main gearbox 9 is shifted into neutral, the input shaft 6 of the range gearbox 2 is synchronized to a first target speed. This also ensures speed adjustment of the intermediate shafts 21, 22. After the input shaft 6 of the range gearbox 2 has been synchronized to the first target speed, a positive-locking shift element of the main gearbox 9, which is required to perform the downshift, can be engaged and thus closed. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0051] By synchronizing the input shaft 6 of the group gearbox 2 to the first target speed, the positive-locking switching element of the main gearbox 9, which is to be inserted to execute the downshift, is therefore synchronized.

[0052] Then, when the first target speed is greater than the idle speed of the internal combustion engine 1, the input shaft 6 of the range gearbox 2 is synchronized to the first target speed via the internal combustion engine 1, specifically via an engine braking device of the same, designed, for example, as a decompression brake or primary retarder. The disconnect clutch 5 can remain closed during this process. To execute the downshift, the positive-locking shift element of the main gearbox 9 is then activated for engagement, namely when the first target speed is reached.

[0053] If, however, the first target speed to which the input shaft 6 of the transmission 2 is synchronized with the disconnect clutch 5 closed is lower than the idle speed of the internal combustion engine, the input shaft 6 of the transmission 2 is first guided towards the first target speed via the internal combustion engine 1, specifically its engine braking device, with the disconnect clutch 5 closed. Subsequently, the disconnect clutch 5 is opened at a speed of the internal combustion engine 1 that is higher than its idle speed, in order to then synchronize the input shaft 6 of the transmission 2 to the first target speed via friction losses of the transmission 2. Opening the disconnect clutch 5 at a speed higher than the idle speed prevents the idle speed governor of the internal combustion engine 1 from being activated due to the engine speed falling below idle.This is preferred for reasons of comfort on the one hand, and to ensure proper synchronization on the other. The positive-locking shift element of the main transmission 9, which is to be engaged for downshifting, is activated either when the first target speed is reached or even before, i.e., when there is still a differential speed at the shift element to be engaged. In this case, a controlled ratchet action is used to engage the shift element of the main transmission 9 required for the downshift. This differential speed is, in particular, less than 300 rpm. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30.

[0054] Simultaneously with the engagement of the positive-locking switching element of the main transmission 9, which is to be engaged to execute the downshift, or alternatively immediately following this, the range group 11 is shifted into neutral, the input shaft 6 of the range transmission 2 is synchronized to a second target speed via the internal combustion engine 1, and a switching element of the range group 11, which is to be engaged to execute the downshift, is engaged. During the synchronization of the input shaft 6 of the range transmission 2 to the second target speed, the speed of the internal combustion engine 1 is increased. By synchronizing the input shaft 6 of the range transmission 2 to this second target speed, the positive-locking switching element of the range group 11, which is to be engaged to execute the downshift, is synchronized.

[0055] Then, if the split group 10 upstream of the main gearbox 9 is also involved in the execution of the downshift, the split group 10 is switched after the range group 9 has been moved into neutral and before the input shaft 6 of the group gearbox 2 has been synchronized to the second target speed, namely a positive locking switching element to be designed for the execution of the downshift is placed in the split group and a positive locking switching element of the split group 10 to be inserted for the execution of the downshift.

[0056] The invention is described below with reference to the signal flow diagram of Fig. 2 for the implementation of a downshift from gear 7 to gear 6, wherein in gear 7 the switching elements A, E and G of the group transmission 2 of Fig. 1 are closed, and wherein in gear 6 the switching elements B, C and H of the group transmission 2 of Fig. 2 are closed.

[0057] Block 32 corresponds to an initial state of the vehicle in which it is traveling with gear 7 engaged, i.e., with shift elements A, E, and G closed, and with the disconnect clutch 5 engaged. In Block 32, depending on driver accelerator and / or brake pedal actuation, it is determined, for example, that a downshift request exists and that the downshift can be executed even without the electric motor 4 participating in the shift element synchronization. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0058] Therefore, in block 32 the drivetrain is conditioned for the downshift to be performed by accelerating the vehicle in such a way that the speed of the internal combustion engine 1 is brought to a target speed.

[0059] In a subsequent block 33, the positive-locking switching element to be designed for the execution of the downshift in the main transmission 9, in the case of execution of the downshift from gear 7 to gear 6 the switching element E, is set to be unloaded and the transmission is moved into neutral by its design.

[0060] In the following blocks 34, 35 and 36, the input shaft 6 of the group transmission 2 is then synchronized to a first target speed, specifically in block 34 via the engine braking device of the internal combustion engine 1. Should the first target speed be lower than the idle speed of the internal combustion engine, the disconnect clutch 5 must subsequently be opened in block 35 and then, in a subsequent block 36, the transmission input shaft 6 of the group transmission 2 must be synchronized to the first target speed via friction losses or drag losses in the group transmission 2.

[0061] After synchronizing the speed of the transmission input shaft 6 to the first target speed, the positive-locking shift element of the main transmission 9, which is to be engaged for the downshift, is engaged. In the case of downshifting from gear 7 to gear 6, this is the positive-locking shift element C. This engagement of the positive-locking shift element in the main transmission 9, which is to be closed for the downshift, is visualized in Fig. 2 by block 37. The positive-locking shift element of the main transmission 9 can also be resynchronized and engaged using ratchets.

[0062] In Fig. 2, simultaneously with the engagement of the main transmission 9 according to block 38 of Fig. 2, the range group 11 is moved to neutral by activating the positive-locking switching element to be designed for the execution of the downshift in range group 11, namely the switching element G when downshifting from gear 7 to gear 6. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0063] When performing the downshift from gear 7 to gear 6, the split group 10 is involved, so that after the area group 11 is transferred to neutral according to block 39, a switching operation takes place in the split group 10, namely by disengaging the switching element A and engaging the switching element B when performing the downshift from gear 7 to gear 6.

[0064] After switching the split group 10, the input shaft 6 of the group gearbox 2 is synchronized to the second target speed in a block 40, with the disconnect clutch 5 closed, via the internal combustion engine 1. The speed of the internal combustion engine 1 is preferably increased in this process.

[0065] After the input shaft 6 of the transmission group 2 has been synchronized to the second target speed, the shift element of range group 11 required for the downshift is engaged. In the case of downshifting from gear 7 to gear 6, this is shift element H, according to block 41. Subsequently, according to block 42, the vehicle travels in gear 6; the downshift has been completed.

[0066] Then, if the first target speed to which the input shaft 6 of the group gearbox 2 is to be synchronized when shifting the main gearbox 9 is greater than the idle speed of the internal combustion engine 1, blocks 35 and 36 are not activated. The disconnect clutch 5 then remains closed.

[0067] If the split group 10 is not involved in the execution of the downshift, block 39 of Fig. 2 is not executed. This is the case, for example, when downshifting from gear 7, in which the switching elements A, E and G are closed, to gear 5, in which the switching elements A, C and H are closed, as well as when downshifting from gear 7 to gear 3, in which the switching elements A, D and H are closed.

[0068] The invention further relates to a control unit configured to automatically execute the above-described method. The control unit has hardware and software means for this purpose. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0069] Hardware components include data interfaces for exchanging data with the assemblies involved in carrying out the method according to the invention, for example, for controlling the combustion engine 1 and the switching elements involved in executing the upshift. Hardware components also include a processor for data processing and a memory for data storage. Software components include program modules implemented in the control unit for carrying out the method.

[0070] ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0071] Reference mark

[0072] 1 Internal combustion engine

[0073] 2-group gearbox

[0074] 3 Drive

[0075] 4 electric machine

[0076] 5 Disconnect coupling

[0077] 6 Input wave

[0078] 7 Housing part

[0079] 8 Output wave

[0080] 9 Main gearboxes

[0081] 10 Split group

[0082] 11 Area Group

[0083] 12 Synchronous switching element

[0084] 13 Synchronous switching element

[0085] 14 shift package

[0086] 15 switching element

[0087] 16 switching element

[0088] 17 shift package

[0089] 18 switching element

[0090] 19 Switching element

[0091] 20 shift package

[0092] 21 Countershaft

[0093] 22 Countershaft

[0094] 23 Shift package

[0095] 24 planetary gears

[0096] 25 sun wheel

[0097] 26 Ring gear

[0098] 27 planetary carriers

[0099] 28 switching element

[0100] 29 Switching element

[0101] 30 planetary gears

[0102] 31 Oil pump

[0103] 32 Block ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30

[0104] Block 33

[0105] Block 34

[0106] 35 Block

[0107] 36 Block

[0108] Block 37

[0109] 38 Block

[0110] Block 39

[0111] 40 blocks

[0112] Block 41

[0113] 42 Block

Claims

ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30 Patent claims 1. A method for operating a drivetrain of a motor vehicle, wherein the drivetrain comprises an internal combustion engine (1) as the first drive unit, an electric machine (4) as the second drive unit, and an automated transmission (2) connected between the drive units and an output (3), wherein the internal combustion engine (1) is coupled to an input shaft (6) of the transmission (2) via a switchable disconnect clutch (5), wherein the electric machine (4) is also coupled to the input shaft (6) of the transmission (2), wherein the transmission (2) comprises several sub-transmissions, namely at least one main transmission (9) and a range group (11) connected downstream of the main transmission (9), characterized in that when the motor vehicle is driving with the disconnect clutch (5) engaged,In the group transmission (2), a downshift is to be carried out at least with the involvement of the range group (11) and the main transmission (9), and the electric machine (4) cannot be used for shift element synchronization. The following steps are carried out to execute the downshift: the vehicle is accelerated such that the speed of the internal combustion engine (1) is brought to a target speed; subsequently, a load reduction is carried out on a positive-locking shift element of the main transmission (9) designed for the execution of the downshift, and the same is subsequently engaged to bring the main transmission (9) into neutral; subsequently, the input shaft (6) is synchronized to a first target speed, and subsequently the positive-locking shift element of the main transmission (9) to be engaged for the execution of the downshift is engaged; overlapping or subsequently, the range group (11) is brought into neutral.the input shaft (6) is synchronized to a second target speed via the internal combustion engine (1) and a switching element of the range group (11) to be inserted for the execution of the downshift is engaged. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30 2. Method according to claim 1, characterized in that when accelerating the motor vehicle, the speed of the internal combustion engine (1) is increased as a target speed to a speed which is smaller by an offset or a factor than the maximum permissible traction operating speed of the internal combustion engine (1).

3. Method according to claim 1 or 2, characterized in that by synchronizing the input shaft (6) of the group transmission (2) to the first target speed, the positive-locking switching element of the main transmission (9) to be inserted for carrying out the downshift is synchronized.

4. Method according to claim 1, 2 or 3, characterized in that by synchronizing the input shaft (6) of the group transmission (2) to the second target speed, the positive-locking switching element of the range group (11) to be inserted for carrying out the downshift is synchronized.

5. Method according to one of claims 1 to 4, characterized in that when the first target speed is greater than an idle speed of the internal combustion engine (1 ), the input shaft (6) of the group transmission (2) is synchronized to the first target speed via the internal combustion engine and the positive-locking switching element of the main transmission (9) to be engaged for the execution of the downshift is actuated for engagement upon reaching the first target speed.

6. Method according to claim 5, characterized in that when the first target speed is less than the idle speed of the internal combustion engine (1), the input shaft (6) of the group transmission (2) is first guided via the internal combustion engine (1) in the direction of the first target speed, the disconnect clutch (5) is opened at a speed of the internal combustion engine (1) that is greater than its idle speed, and the input shaft (6) is subsequently synchronized to the first target speed via friction losses of the group transmission (2), wherein the positive-locking switching element of the main transmission (9) to be engaged for the execution of the downshift is actuated either upon reaching the first target speed or even before. ZF Friedrichshafen AG File 305280 Friedrichshafen 2024-10-30 7. Method according to one of claims 1 to 6, characterized in that, when a split group (10) upstream of the main transmission (9) is also involved in the execution of the downshift, a positive-locking switching element to be designed for the execution of the downshift is designed and a positive-locking switching element to be inserted for the execution of the downshift is designed in the split group (10) after the range group (9) has been moved to neutral and before the input shaft (6) of the range transmission (2) has been synchronized to the second target speed.

8. Method according to one of claims 1 to 7, characterized in that the downshifting is then carried out when, after a downshifting request has been made, it is recognized, based on a current and / or future driving situation, in particular a driving resistance and / or a road inclination, that the downshifting can be carried out without support from the electric machine (4).

9. Control unit for operating a drive train of a motor vehicle, wherein the drive train comprises as a first drive unit an internal combustion engine (1), as a second drive unit an electric machine (4), and an automated group transmission (2) connected between the drive units and an output (3), wherein the internal combustion engine (1) is coupled to an input shaft (6) of the group transmission (2) via a switchable disconnect clutch (5), and wherein the electric machine (4) is also coupled to the input shaft (6) of the group transmission (2), wherein the group transmission (2) comprises several sub-transmissions, namely at least one main transmission (9) and a range group (11) connected downstream of the main transmission (9) in terms of drive technology, characterized in that the control unit is configured for the automatic, control-side execution of the method according to one of claims 1 to 8.

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