Method for operating a vehicle powertrain

Abstract

Method for operating a vehicle drive train (1) with a drive motor (2), with an output (3) and with a transmission (4) arranged in the power flow between the drive motor (2) and the output (3), the transmission being designed with at least one positive-locking switching element (A, F) and with several friction-locking switching elements (B, C, D, E) via which several gear pairs of a gear set (5) of the transmission (4) can be engaged and disengaged to represent different gear ratios (“1” to “R”) of the transmission, wherein only a part of the gear ratios (“1” to “R”), which are assigned to a gear ratio sub-range of the gear ratio range of the transmission, can be represented via the positive-locking switching element (A, F), wherein, if there is a requirement to represent a coasting operating state of the vehicle drive train (1), during which the drive motor (2) is engaged and the power flow between the output (3) in the area of ​​the transmission (4) is interrupted,The connected drive motor (2) is disconnected from the output (3) by opening one of the switching elements (A to F), which are kept in the closed operating state to represent the operating state present before the request to disconnect the connected drive motor (2), and subsequently the switching elements (A to F) are actuated depending on the current operating state profile of the vehicle drive train (1) with the connected drive motor (2) disconnected,that the switching elements (A to F) to be engaged in the transmission (4) to represent the gear ratio ("1" to "9") to be engaged when a request is made to engage the connected drive motor (2) to the output (3) are already partially engaged at the time of the request, and the connected drive motor (2) is connected to the output (3) by closing a further switching element (A to F) of the further switching elements (A to F), and the gear ratio ("1" to "9") requested depending on the current operating state of the vehicle drive train (1) is engaged in the transmission (4), wherein, when a request is made to represent the sailing operating state, starting from an operating state of the transmission (4) for which the positive-locking switching element (F) is closed, the closed positive-locking switching element (F) is converted into an open operating state.wherein, when a requirement exists to represent the sailing operating state starting from an operating state of the transmission (4), for the representation of which a further positive-locking switching element (A) is open, the opened further positive-locking switching element (A) is converted into a closed operating state when an operating state profile of the vehicle drive train (1) is determined which, upon a subsequent requirement to engage the connected drive motor (2), triggers the engagement of a gear ratio in the transmission (4), for the representation of which the further positive-locking switching element (A) must be engaged, characterized in that during the engagement process of the further switching element (A), a clutch (8), which is arranged in the power flow of the vehicle drive train between the drive motor (2) and the transmission (4),opened and the rotational speed (n_t) of a transmission input shaft (6) is reduced to zero by actuating at least one of the friction-locking switching elements (B, C, D) in order to generate a differential rotational speed required for closing the further positive-locking switching element (A) within a defined differential rotational speed range between the halves of the switching element of the further positive-locking switching element (A) which is in the open operating state.

Description

[0001] The invention relates to a method for operating a vehicle drive train according to the type defined in more detail in the preamble of patent claim 1.

[0002] A multi-speed transmission with nine forward gears and one reverse gear is known from DE 10 2008 000 429 A1. The multi-speed transmission comprises four planetary gear sets, eight rotating shafts, and six shift elements. The first and second planetary gear sets form a shiftable primary gear set, while the third and fourth planetary gear sets constitute a so-called main gear set. The carriers of the first and second planetary gear sets are coupled to one another via one of the rotating shafts, which is connected to an element of the main gear set. The ring gear of the first planetary gear set is coupled to the sun gear of the second planetary gear set via another shaft of the rotating shafts, which is detachably connectable to a drive shaft via a coupling.

[0003] The sun gear of the first planetary gear set can be coupled to a housing of the multi-speed transmission by means of a further shaft of the rotatable shafts via a brake and can be connected to the input shaft via a clutch. The ring gear of the second planetary gear set can be coupled to the housing by means of a shaft via a brake. Yet another shaft of the rotatable shafts is connected to at least one element of the main gear set and can be coupled to a housing via the brake. Another shaft of the rotatable shafts is connected to another element of the main gear set and can be connected to the input shaft via a shift element designed as a clutch, while an output shaft is connected to at least one other element of the main gear set. At least two of the shift elements of the multi-speed transmission are designed as positive shift elements that are only disengaged during upshifts.

[0004] To save fuel, vehicles are increasingly being equipped with so-called coasting functions in addition to so-called start-stop systems. These functions deactivate the combustion engine and decouple it from the rest of the drivetrain while driving. During such an activated coasting function, the vehicle's existing kinetic energy is used for propulsion instead of wasting it in the form of drag. This coasting function is already widespread in hybrid vehicles, but it is also increasingly being used in conventional vehicles with combustion engines.In contrast to start-stop systems, in which the engine is only switched off when a vehicle is stationary, the switching off of an engine designed as an internal combustion engine with the coasting mode function activated already takes place during a coasting mode of a vehicle, whereby the transmission then has to be supplied with hydraulic fluid via an additional electric pump, which, however, increases both the installation space required and the manufacturing costs of a transmission.

[0005] Comparable processes are known from the disclosures DE 10 2010 000 857 A1 and DE 10 2013 202 709 A1.

[0006] The present invention is based on the object of providing a method for operating a vehicle drive train with a transmission which is designed with at least one positive shifting element, by means of which a sailing operation of a vehicle designed with the vehicle drive train can be activated and deactivated in a simple and cost-effective manner with a high degree of spontaneity.

[0007] According to the invention, this object is achieved by a method having the features of patent claim 1.

[0008] The method according to the invention is intended for operating a vehicle drivetrain with a prime mover, an output drive, and a transmission arranged in the power flow between the prime mover and the output drive. The transmission is designed with at least one positive shifting element and several frictionally engaged shifting elements, via which several gear pairs of a gear set of the transmission can be engaged and disengaged to represent different transmission ratios. Only a portion of the ratios can be represented via the positive shifting element.

[0009] According to the invention, when a request is made to represent a coasting operating state of the vehicle drive train, during which the prime mover is engaged and the power flow between the output and the transmission is interrupted, the engaged prime mover is disconnected from the output by opening one of the switching elements, which are kept in a closed operating state to represent the operating state existing prior to the request to decouple the engaged prime mover. Subsequently, the switching elements are actuated depending on the current operating state profile of the vehicle drive train with the engaged prime mover disconnected,that the switching elements to be switched on to represent the gear ratio to be engaged in the event of a request to couple the engaged drive motor to the output in the transmission are already partially in the switched-on operating state at the time of the request, and the engaged drive motor is connected to the output by closing a further switching element of the further switching elements, and the gear ratio requested in the transmission depending on the current operating state of the vehicle drive train is engaged, wherein, when there is a request to display the sailing operating state, starting from an operating state of the transmission for which the positive-locking switching element is closed, the closed positive-locking switching element is transferred into an open operating state, wherein, when there is a request to display the sailing operating state, starting from an operating state of the transmission,for the representation of which a further positive-locking switching element is opened, the opened further positive-locking switching element is transferred into a closed operating state when an operating state curve of the vehicle drive train is determined which, in the case of a subsequent request to couple the engaged drive motor, triggers the engagement of a gear ratio in the transmission, for the representation of which the further positive-locking switching element is to be engaged, wherein during the engagement process of the further switching element, a clutch which is arranged in the power flow of the vehicle drive train between the drive motor and the transmission is opened and the speed of a transmission input shaft is guided towards zero by actuating at least one of the frictionally engaged switching elements,in order to generate a differential speed required for closing the further positive-locking switching element within a defined differential speed range between the switching element halves of the further positive-locking switching element in the open operating state.

[0010] With the procedure according to the invention, a sailing operating state that reduces the fuel consumption of a vehicle can be represented with little effort and an operating state of the vehicle drive train requested by a request to deactivate or exit the sailing operating state can be implemented or achieved with a high degree of spontaneity, particularly in the area of ​​the transmission, since during the activated sailing operating state, according to the invention, a so-called gear tracking is carried out depending on the operating state profile of the vehicle drive train, by means of which gear ratio to be represented depending on the currently existing operating state of the vehicle drive train can be engaged in the transmission within short operating times when the sailing operating state is exited.

[0011] The drive motor is in the engaged operating state both before the coasting mode is activated, during the activated coasting mode, and after the coasting mode is deactivated. This allows the transmission to be supplied with hydraulic fluid across the entire operating range of the vehicle drivetrain in a space-saving and cost-effective manner via a main transmission pump driven by the transmission input shaft, without the need for an electrically operated auxiliary pump that requires additional installation space and increases the transmission's manufacturing costs.

[0012] In an advantageous variant of the method according to the invention, when a request to display the coasting operating state is present, the closed positive-locking shifting element is transferred from a transmission operating state for which the positive-locking shifting element is closed to an open operating state. This procedure ensures that, when the drive engine is decoupled, drag torques in the transmission resulting from the closed operating state of the positive-locking shifting element impair the efficiency gain by activating the coasting operating state and avoid undesirable speeds that place a load on the transmission components, which are lower when the positive-locking shifting element is open.

[0013] In order to be able to implement a request to deactivate the sailing operating state with the greatest possible spontaneity, an additional positive-locking shifting element is transferred, upon a request to display the sailing operating state, from an operating state of the transmission for which the additional positive-locking shifting element is open, to its closed operating state when an operating state profile of the vehicle drive train is determined during which a subsequent request to couple the engaged drive engine or to deactivate the sailing operating state triggers the engagement of a gear ratio in the transmission, for which the additional positive-locking shifting element must be engaged. This provides a simple way of avoiding a situation in which a downshift is requested in the transmission when sailing is exited due to a driver-side load request, during which a dog-type shifting element must be engaged.This is made possible with little effort by the fact that the additional positive switching element is already transferred into its closed operating state during the sailing operating state of the vehicle drive train.

[0014] If the additional positive-locking shift element is closed when the output speed is lower than a threshold value, the actuation of the additional positive-locking shift element is based on a low-effort, speed-dependent claw conditioning strategy. For example, when coasting is initiated, the open positive-locking shift element is advantageously transferred to its closed operating state from an operating state of the vehicle drivetrain in which a high gear with a low ratio is engaged in the transmission at lower vehicle speeds. This is because deactivating the coasting operating state triggers a downshift in the transmission to a lower gear with a higher ratio anyway.In contrast, the latter procedure can be disruptive and disadvantageous in higher speed ranges of a vehicle, since the further positive switching element then cannot be kept in the closed operating state in order to display the then requested operating state of the transmission or the vehicle drive train when coasting is exited or when the coasting operating state is deactivated.

[0015] In general, the speed-dependent selection of whether the additional positive-locking switching element is switched on when entering the sailing operating state or is left in the open operating state achieves a high level of dynamics both during sailing entry and during sailing exit, since the additional positive-locking switching element is only transferred to its closed operating state during the activated sailing operating state if it is recognized that the additional positive-locking switching element is to be transferred to its closed operating state when the sailing operating state is deactivated in order to represent the requested operating state of the vehicle drive train.

[0016] If, during the engagement process of the further shifting element, a clutch which is arranged in the power flow of the vehicle drive train between the drive engine and the transmission is opened and the speed of a transmission input shaft is guided towards zero by actuating at least one of the frictionally engaged shifting elements in order to generate a differential speed required for closing the further positive-locking shifting element within a defined differential speed range between the shifting element halves of the further positive-locking shifting element in the open operating state, stalling of the drive engine is prevented with little effort if the speed of the transmission input of the transmission is to be guided essentially towards zero in order to synchronize the further positive-locking shifting element.

[0017] This procedure is particularly advantageous when the clutch is a torque converter lock-up clutch assigned to a hydrodynamic torque converter.

[0018] In order to create an at least approximately load-free operating state of the additional positive-locking switching element required for closing the additional positive-locking switching element, the transmission capacity of at least one frictionally engaged switching element is varied in a further advantageous variant of the method according to the invention. With this measure, for example, so-called tooth-on-tooth positions in the area of ​​the additional positive-locking switching element to be engaged can be easily resolved with little effort when the drive motor speed is greater than zero.

[0019] In addition to varying the transmission capacity of the friction-locking shift element, it is also possible to vary the speed of the drive motor in order to resolve a tooth-on-tooth position in the area of ​​the additional positive-locking shift element to be engaged. In addition to this or as an alternative, it can also be provided that the transmission capacity of the clutch between the drive motor and the transmission is varied in order to impose a disturbing torque on the transmission and break the blocking in the area of ​​the additional positive-locking shift element to be engaged.

[0020] Furthermore, it is also possible that during the engagement process of the additional positive-locking switching element to be engaged, a positive connection has already been established between the switching element halves to be engaged in the area of ​​the additional positive-locking switching element, but the additional positive-locking switching element has not yet reached its fully closed operating state and the closing process cannot be carried out to the desired extent despite a corresponding actuation in the closing direction. In this case, the torques that hinder the completion of the engagement process of the additional positive-locking switching element and are present at the additional positive-locking switching element can be reduced by varying the transmission capacity of at least one frictionally engaged switching element, and the complete insertion movement in the area of ​​the additional positive-locking switching element can be implemented to the desired extent.Such torques that hinder the closing process of a positive-locking switching element result, for example, from drag torques or other influences that can be reduced to the desired extent using the procedures described above in order to be able to operate a vehicle drive train with high dynamics and to ensure availability in the event of jammed claw switching elements.

[0021] The vehicle drive train and the transmission can be operated with a high degree of spontaneity if, when there is a request to represent a neutral operating state of the transmission, for which the power flow in the area of ​​the transmission is to be interrupted by corresponding actuation of the switching elements and for which the further positive switching element is to be opened, the transmission is prepared for the engagement of a gear ratio in the sailing operation of the vehicle drive train by keeping the further positive switching element in its closed operating state and selecting an actuation logic of the switching elements by means of which a neutral operating state of the transmission is represented in which the further positive switching element is in its closed operating state.

[0022] In addition to improving actuation spontaneity, the last-described variant of the method according to the invention achieves that a requested neutral operating state of the transmission is implemented using already known actuation sequences, thus eliminating the need to develop and implement additional actuation routines that require additional hardware resources. Furthermore, this variant of the method according to the invention creates a gear disengagement sequence that can be carried out within short operating times, during which the power flow is first completely reduced before the additional positive-locking shift element is disengaged to implement the neutral gear requested by the request for the neutral operating state of the transmission.

[0023] The sailing operating state can be deactivated in a simple manner with a high degree of spontaneity if, when the sailing operating state is activated and the connected drive engine is disconnected and when an operating state of the vehicle drive train exists in which the further positive switching element is closed and from which, upon a request to couple the drive engine, a gear ratio is to be engaged in the transmission, for the representation of which both the further positive switching element and the positive switching element are to be closed, the positive switching element is closed when an at least approximately synchronized operating state is reached.

[0024] In a variant of the method according to the invention which can be carried out with little control and regulation effort, the positive switching element is closed during an operating state of the vehicle drive train during which the speed of the output and / or the speed of the transmission input approaches a speed which corresponds to the synchronous speed which occurs when there is a request to deactivate the sailing operating state and a resulting request to couple the engaged drive motor in the transmission by closing the positive switching element with a simultaneously closed further positive switching element, if a differential speed between the switching element halves of the positive switching element present in the open operating state lies within a defined differential speed window.

[0025] In a further advantageous variant of the method according to the invention, the speed of the transmission input is increased by a positive engine intervention starting from the idle speed in the direction of the synchronous speed during an operating state of the vehicle drive train, during which the engaged drive engine is operated at the level of the idle speed and the synchronous speed of the transmission input, which is set when the gear ratio is engaged in the transmission by the closed further positive shift element and by additionally closing the positive shift element, is greater than the idle speed of the drive engine, whereby the vehicle drive train can be operated with a high degree of spontaneity when there is a corresponding requirement.

[0026] In order to be able to determine the synchronization point of the opened positive-locking shift element to the required extent within short operating times, in an advantageous variant of the method according to the invention, the transmission capability of a shift element between the drive motor and the transmission is guided to a defined level during the determination of the synchronization point of the opened positive-locking shift element, at which level the speed of the drive motor and the speed of the transmission input correspond at least approximately to one another.

[0027] In a further advantageous variant, the switching element between the drive motor and the transmission is at least partially opened during the closing of the positive switching element in order to avoid, with little effort, a compression of the drive motor during unfavorable operating conditions of the vehicle drive train.

[0028] For operation of the vehicle drivetrain characterized by a high degree of spontaneity, a further variant of the method according to the invention provides that during operating state curves of the vehicle drivetrain during which events that change the speed of the output, such as the actuation of a vehicle's service brake, occur and change the synchronization process of the positive-locking shift element to be engaged, as well as triggering a request to couple the engaged drive motor, a gear ratio is initially engaged in the transmission, for which the positive-locking shift element is open. Subsequently, a gear ratio is engaged in the transmission, for which a closed frictional-locking shift element must be disengaged and the positive-locking shift element must be closed.

[0029] This provides a simple way to prevent gear tracking from being forced during operating conditions in which the synchronous engagement of the positive shifting element is influenced by external factors such as braking intervention, a load request, or other measures that change the output speed, and to establish a power connection between the prime mover and the transmission. The required operating state of the vehicle drivetrain, and in particular the transmission, is first implemented by engaging a so-called support or synchronization gear in the transmission, followed by a pull downshift during which the positive shifting element is engaged.

[0030] If, during operating state curves of the vehicle drive train during which events take place which change the speed of the output and change the synchronization process of the positive shifting element to be engaged, such gear ratios are preparatoryly engaged in the transmission in each case that the synchronization point of the positive shifting element to be engaged can be reached due to the currently existing speeds of the output, the transmission input and the drive engine and the current gradients of the curves of these speeds and the positive shifting element is transferred into its closed operating state in at least an approximately synchronized operating state, the positive shifting element can be transferred into its closed operating state with a high degree of spontaneity within short operating times without further measures.Through this situational adaptation of the respectively prepared synchronization gear in the transmission, several speed windows can be selected, particularly during a coasting process of a vehicle, within which the positive switching element to be engaged has its synchronization point.

[0031] If the vehicle drive train is designed in the area between the prime mover and the transmission with a hydrodynamic torque converter and a torque converter lock-up clutch assigned to the torque converter, the torque converter lock-up clutch must be actuated depending on the respective operating state of the vehicle drive train and also depending on the respective requested operating state of the vehicle drive train and its transmission capacity must be varied if necessary in order to be able to carry out operating state changes of the vehicle drive train with a high degree of spontaneity without impairing driving comfort.

[0032] For example, it is particularly advantageous if the transmission capacity of the torque converter lock-up clutch is set to a level before the positive-locking shifting element or the further positive-locking shifting element is engaged, at which there is only a slight slip in the area of ​​the torque converter lock-up clutch or the torque converter clutch is operated without slip in order to minimize discontinuities in the course of a differential speed between shifting element halves of the positive-locking shifting elements.In the event that rotational irregularities in the area of ​​the drive machine distort the differential speed signal of the positive shift elements, the transmission capacity of the torque converter lock-up clutch is reduced to such an extent that the speed of the drive machine and the speed of the transmission input essentially correspond to one another, but speed vibrations of the drive machine are not fully impressed on the transmission input and are only introduced into the transmission in a damped manner during slip operation of the torque converter lock-up clutch.

[0033] This procedure is based on the knowledge that speed oscillations and varying differential speeds between the speed of the drive machine and the speed of the transmission input cause undesirable oscillations in the differential speed of the positive shift elements, which prevent a comfortable and load-free engagement of a positive shift element.

[0034] During the closing process of the positive-locking switching element or the further positive-locking switching element, there is the possibility during unfavorable operating state courses of the vehicle drive train that a torque is applied to the positive-locking switching elements which impairs the engagement or closing process of the positive-locking switching elements if the torque converter lock-up clutch is in the closed operating state or close to its closed operating state.

[0035] In order to be able to engage the clutch to the desired extent within a short operating time while simultaneously ensuring a high level of driving comfort, the transmission capacity of the torque converter lock-up clutch can be adjusted during the engagement of one of the positive shift elements in such a way that the torque converter lock-up clutch is operated with slipping and the torque applied to the positive shift element to be engaged is applied to the positive shift element at a level that favors the engagement of the positive shift element. This procedure offers a simple way of at least partially reducing the torque applied to the positive shift element to be engaged after the claw engagement by opening the torque converter lock-up clutch. In contrast to this, by engaging the torque converter lock-up clutch the torque in the area of ​​the positive shift element orThe torque applied to the further positive-locking shift element tends to increase, while opening the torque converter lockup clutch reduces the torque applied. With appropriate actuation of the torque converter lockup clutch, the likelihood of so-called claw jamming is reduced. This ensures greater transmission availability during an activated coasting mode.

[0036] If a request to deactivate the sailing operating state of the vehicle drivetrain requests an operating state of the vehicle drivetrain in which the positive shifting element is closed, the torque converter lock-up clutch is held in its closed operating state in a first phase of the target speed control of the positive shifting element to be closed. This ensures that the speed of the transmission input essentially corresponds to the speed of the drive engine. Shortly before the synchronous speed of the positive shifting element to be closed is reached, it is necessary to transfer the torque converter lock-up clutch to its open operating state in order to reduce or equalise the torque applied to the positive shifting element to be closed to the desired extent using the differential speed in the area of ​​the hydrodynamic torque converter.to dampen the torque applied to the positive-locking switching element to be closed during the engagement process to an extent that favors the engagement process of the positive-locking switching element, which in turn causes fewer claw jams and increases the availability of the transmission during the sailing operating state.

[0037] If the additional positive-locking switching element is closed when a requirement exists to implement a coasting operating state before the drive engine is switched off, it is possible in a simple manner to implement a hydraulic supply to the transmission via a main transmission pump driven by the drive engine and, if necessary, to implement an electrically driven auxiliary pump with a lower output. This, in turn, makes it possible to reduce the manufacturing costs of the transmission, as well as the installation space required and the load on the vehicle electrical system. In addition, the additional positive-locking switching element is located when exiting the coasting operating state towards an operating state of the vehicle drive train orof the transmission, to which the further positive-locking switching element is to be transferred into the closed operating state, is already in the closed operating state, whereby the transmission can be operated with high spontaneity and a requested operating state of the vehicle drive train can be represented within short operating times.

[0038] Alternatively, it can also be provided that the further positive-locking switching element is closed when a request is made to display a sailing operating state after the drive engine has been switched off, in which case the vehicle drive train can also be operated with a high degree of spontaneity when entering the sailing operating state, since the so-called engine stop release can occur immediately upon entering the sailing operating state. In addition, the vehicle drive train and also the transmission can be operated with a high degree of spontaneity even when exiting or leaving the sailing operating state if, upon exiting the sailing operating state, the vehicle drive train and the transmission are to be transferred to an operating state for which the further positive-locking switching element is to be transferred to or maintained in the open operating state.

[0039] If the gear set of the transmission is transferred into an at least partially locked operating state by actuating several frictionally engaged switching elements before the further positive-locking switching element is closed, in which a transmission input shaft is held in a rotationally fixed manner and a transmission output shaft connected to the output is rotatable, a defined operating state of the transmission is established, from which the further positive-locking switching element can be transferred into its closed operating state with little effort.

[0040] In an advantageous variant of the method according to the invention, the gear set of the transmission is held in the at least partially locked operating state at least until a speed of the prime mover is lower than a threshold value. This achieves rapid engine coasting with little effort and traverses a resonance speed range, which impairs driving comfort, during engine coasting within a short operating time. Furthermore, an undesirable increase in the speed of the transmission input or the transmission input shaft due to an excessively early withdrawal of the locked operating state of the gear set of the transmission during shutdown of the prime mover, which could potentially cause a load change in the vehicle drivetrain due to crossing of the speed profiles of the prime mover and the transmission input.

[0041] If a torque converter lockup clutch provided between the transmission and the prime mover for bypassing a hydrodynamic torque converter is transferred to a closed operating state when the coasting mode is activated and the prime mover is switched off, a synchronous speed of the transmission input speed corresponding to the operating state of the vehicle drivetrain to be represented can be set in a defined manner via a possible speed control of the prime mover speed. Furthermore, a so-called converter slip present in the area of ​​a hydrodynamic torque converter with the torque converter lockup clutch open does not need to be taken into account when specifying the target speed of the prime mover, thus reducing the operating effort required by the vehicle drivetrain.

[0042] The vehicle drive train and the transmission can be operated with a high degree of spontaneity if the further positive-locking switching element is transferred to its open operating state or is left in this state when there is a request to deactivate the sailing operating state and if the operating state of the transmission to be represented as a function of a current operating state profile of the vehicle drive train when the sailing operating state is deactivated can only be produced when the further positive-locking switching element is in the open state.

[0043] An increase in spontaneity when exiting the coasting mode is achieved by means of a further variant of the method according to the invention in that, when the power flow in the transmission area between the drive motor and the output is interrupted, all those frictionally engaged shifting elements that allow rotation of the transmission output shaft in the closed operating state are transferred to the closed operating state. By means of such a procedure, a large number of shifting elements are transferred to the closed operating state in a correspondingly designed transmission, for example, one that has a structural design similar to the multi-stage transmission described above and known from the prior art.Then, when leaving the coasting operating state, a required operating state in the transmission can be achieved to the desired extent within the desired short operating times by transferring fewer switching elements from their open operating state to their closed operating state than the number of switching elements already in the closed operating state that need to be deactivated or opened. This is advantageous because closed frictionally engaged switching elements can be transferred to their open operating state more quickly than open frictionally engaged switching elements can be transferred to their closed operating state.

[0044] The transmission can be operated with further improved spontaneity during an exit from the coasting mode if, with the coasting mode of the vehicle drivetrain activated, the actuation forces of the frictional shift elements are reduced to a level at which the frictional shift elements still exhibit a slip-free operating state and from which the shift elements can be fully engaged or disengaged within a short operating time. When exiting the coasting mode, the shift elements subjected to reduced pressure can be disengaged or emptied within a short operating time, starting from the lower actuation pressure level, and thus opened more quickly.At the same time, the switching elements that are to be fully switched on to represent the operating state that is to be established after deactivation of the sailing operating state can be transferred from the reduced pressure level to the fully switched on operating state more quickly than fully opened switching elements.

[0045] In one variant of the method according to the invention, the actuating forces of the shift elements, which are to be maintained or transferred to the closed operating state to represent the operating state of the vehicle drive train requested after leaving the coasting operating state of the vehicle drive train, are increased to the level corresponding to the required operating state, while the other frictionally engaged shift elements are opened. This, in turn, allows the required operating state of the transmission to be represented within a short operating time to the required or desired extent.

[0046] In a further variant of the method according to the invention which can be carried out with little operating effort, an interruption of the power flow between the drive engine and the output in the area of ​​the transmission is detected if a deviation between the speed of the transmission input shaft and the product of the speed of the transmission output shaft and the gear ratio engaged in the transmission at the current operating point of the vehicle drive train is greater than a limit value.

[0047] In a further advantageous variant of the method according to the invention, the current operating state of the vehicle drive train and the gear ratio to be engaged in the transmission upon exiting the coasting operating state are determined during the activated coasting operating state, wherein at least the shift elements that are to be engaged to represent the gear ratio to be engaged in the transmission upon exiting the coasting operating state are maintained in an operating state prepared for engagement of the shift elements. By means of this procedure, which characterizes a so-called gear tracking with the coasting operating state activated, it is achieved with little effort that a transmission can be transferred to the required operating state within a short operating time upon exiting the coasting operating state and can thus be operated with a high degree of spontaneity.

[0048] In a further advantageous variant of the method according to the invention, when there is a request to deactivate the sailing operating state and an associated request to display a gear ratio in the transmission that can be engaged when the further positive-locking shifting element is in the closed operating state and by means of at least the positive-locking shifting element in the transmission, a synchronization gear ratio is first engaged in the transmission. To display this gear ratio, the further positive-locking shifting element must be closed or held in the closed operating state and the positive-locking shifting element must be opened or held in the open operating state. To implement a subsequent gear ratio change starting from the synchronization gear ratio in the direction of the requested gear ratio, a friction-locking shift element must be deactivated and the positive-locking shifting element must be closed.This means that both the positive-locking switching element and the further positive-locking switching element can be converted from an open to a closed operating state within short operating times and with little control and regulation effort, starting from defined operating states of the transmission.

[0049] In an advantageous variant of the method according to the invention, discontinuities in the course of an output speed are avoided in that the frictional switching element which is to be opened in the area of ​​the transmission to separate the power connection between the drive engine and the output is only switched on when a blocking state of the gear set of the transmission is released when there is a request to leave the sailing operating state.

[0050] To further improve the transmission's actuation spontaneity, it can be provided that, when a request to deactivate the coasting mode is present, a check is performed to determine whether a gear ratio to be engaged in the transmission during the activated coasting mode, depending on the current operating state of the vehicle drivetrain, corresponds to a gear ratio that is to be engaged in the transmission depending on the event requesting deactivation of the coasting mode. If a deviation is detected, the gear ratio requested by the event is engaged in the transmission.This prevents, with little effort, the operating state requested and established by deactivating the sailing operating state from being immediately abandoned again in the course of a further gear ratio change immediately after exiting the sailing operating state, and the ultimately requested operating state from being established immediately upon exiting the sailing operating state in the transmission.

[0051] In a further advantageous variant of the method according to the invention, the drive motor is restarted upon exiting the coasting operating state, taking into account a transmission-side speed specification. The power flow between the drive motor and the output in the transmission area is only established when the speed of the drive motor exceeds the synchronous speed of the transmission input shaft, which corresponds to the speed of the transmission output shaft. The synchronous speed is established when the requested gear ratio is engaged in the transmission. This prevents undesirable speed crossover between the speed of the drive motor and the speed of the transmission output shaft, as well as a concomitant load change in the vehicle driveline, which adversely impairs driving comfort.

[0052] If there is a request to activate the sailing mode function starting from an operating state of the transmission for which the positive-locking switching element is closed, the closed positive-locking switching element is transferred into an open operating state in an advantageous variant of the method according to the invention, whereby undesirably high drag losses in the area of ​​the transmission are avoided in a simple manner.

[0053] Drag torques and component loads occurring in the area of ​​the transmission, which in turn result, among other things, from differential speeds in the area of ​​bearing points of the transmission, are reduced to the desired extent in an advantageous variant of the method according to the invention by transferring the transmission to the operating state in which the power flow between the drive motor and the output is interrupted by opening a frictional switching element and a transmission output shaft operatively connected to the output is rotatable.

[0054] If the frictional shift element to be actuated to engage the gear ratio relieving the load on the positive shift element is, when the sailing operating state is activated, initially transferred from a fully open operating state into an operating state in which the transmission capacity of the frictional shift element is zero and from which an increase in the actuating force causes an immediate increase in the transmission capacity, and then the transmission capacity of the frictional shift element is increased to a level that relieves the load on the positive shift element, the positive shift element can be transferred into an at least approximately load-free operating state with little control and regulation effort without causing discontinuities in the course of a torque applied in the area of ​​the output of the vehicle drive train.

[0055] If there is a request to activate the engine start-stop function of the vehicle drive train with the drive engine switched off at the same time, starting from an operating state of the vehicle drive train during which a sailing operation function of the vehicle drive train is activated, via which the switched off drive engine is decoupled from the output and the positive switching element is opened, and during which a speed of the output is greater than a defined speed at which a differential speed between switching element halves of the opened positive switching element lies within a speed range within which the positive switching element can be transferred to a closed operating state, the positive switching element is actuated in the closing direction in a further advantageous variant of the method according to the invention at the latest when the defined speed is reached.

[0056] By means of the procedure according to the invention described above, the sailing operating state of the vehicle drive train can be deactivated in a simple manner and with a high degree of spontaneity and the engine start-stop function of the vehicle drive train can be activated within short operating times, since the positive switching element to be engaged and in the open operating state can be converted to the closed operating state to the desired extent without additional measures during a coasting process of a vehicle designed with the vehicle drive train, during which the positive switching element to be engaged at least temporarily reaches an at least approximately synchronized operating state.

[0057] In order to avoid undesirably high loads in the area of ​​the positive-locking switching element to be engaged, the actuation of the positive-locking switching element in the closing direction is terminated in a simple variant of the method according to the invention when the open operating state of the positive-locking switching element is determined when the vehicle is stationary.

[0058] If the sequence of switching elements to be operated one after the other to partially lock the gear set is selected depending on the current operating state of the vehicle drive train, the sailing operating state can be activated with a high degree of spontaneity when a corresponding request is made and the vehicle drive train can be transferred to the operating state to be established by the request to deactivate the sailing operating state within short operating times and thus with a high degree of spontaneity.

[0059] An undesirably high increase in internal transmission drag torque is easily limited if the request to activate the sailing mode function is triggered when the engine start-stop function is activated at the same time when a defined threshold value of the output speed is exceeded.

[0060] Alternatively or additionally, in advantageous variants of the method according to the invention, the request to activate the sailing mode function with simultaneously activated engine start-stop function is triggered when the defined threshold value of the speed of the output is exceeded for longer than a predefined period of time or after driving a distance longer than a defined distance, whereby permanently excessive speeds in the transmission and, for example, dry running of bearing units of the transmission are avoided with little effort.

[0061] If a request is made to activate a coasting mode of the vehicle drive train while the engine start / stop function is simultaneously activated, the positive-locking switching element is opened in an advantageous variant of the method according to the invention, while the drive motor remains in both its decoupled and switched-off operating state. Using this procedure, a closed positive-locking switching element is transferred to its open operating state when the coasting mode is activated, resulting in only minimal losses and loads on the transmission during coasting.

[0062] If the sequence of switching elements to be actuated one after the other to partially lock the gear set is selected depending on the current operating state of the vehicle drive train, the sailing operating state can be deactivated with a high degree of spontaneity upon a corresponding request and the vehicle drive train can be transferred to the operating state to be established by the request to deactivate the sailing operating state within short operating times and thus with a high degree of spontaneity.

[0063] A request to activate the engine start-stop function starting from an operating state of the vehicle drive train, during which the transmission is currently being transferred in the direction of an operating state requested by the sailing operation function due to a previous request to activate the sailing operation function, is implemented with a high degree of spontaneity in a further variant of the method according to the invention in that the closed positive-locking switching element is left in its closed operating state and switching elements actuated by the request to activate the sailing operation function are actuated to the extent required to represent the operating state of the transmission to be represented by the request to activate the engine start-stop function.

[0064] In contrast to this, a request to activate the engine start-stop function is made starting from an operating state of the vehicle drive train during which the transmission is currently being transferred towards an operating state required for the representation of the operating state requested by the sailing operation function due to a previous request to activate the sailing operation function, the already opened positive-locking switching element is transferred into its closed operating state in a further advantageous variant and switching elements actuated by the request to activate the sailing operation function are actuated to the extent necessary to represent the operating state of the transmission to be represented by the request to activate the engine start-stop function in order to implement the request with a high degree of spontaneity.

[0065] In order to be able to transfer the positive shifting element to the requested extent within short operating times into its closed operating state, in a further advantageous variant of the method according to the invention for closing the positive shifting element, a gear ratio is first engaged in the transmission, for the representation of which the positive shifting element is to be held in the open operating state and at least one frictional shifting element is to be closed, wherein subsequently a gear ratio requested by the engine start-stop function is engaged by closing the positive shifting element and simultaneously opening the frictional shifting element in the transmission, and wherein during the gear ratio change a differential speed between shift element halves of the positive shifting element is guided to a level required for closing the positive shifting element.

[0066] Both the features specified in the patent claims and the features specified in the following embodiments of the subject matter according to the invention are suitable, either individually or in any combination with one another, for further developing the subject matter according to the invention.

[0067] Further advantages and advantageous embodiments of the subject matter according to the invention emerge from the patent claims and the exemplary embodiments described in principle below with reference to the drawing, wherein, for the sake of clarity, the same reference numerals are used for components with the same construction and function.

[0068] It shows: Fig. 1 a schematic representation of a vehicle drive train with a 9-speed automatic transmission; Fig. 2 a circuit diagram of the automatic transmission according to Fig. 1; Fig. 3 several curves of different operating variables of an automatic transmission according to Fig. 1 having vehicle drive train over time t, which is transferred as required into a sailing operating state, which is again deactivated at a later time; Fig. 4 a Fig. 3 corresponding representation of the trends of the operating variables, which during a period essentially correspond to the trends according to Fig. 3 set the operating state curve corresponding to the underlying operating state curve, whereby a shutdown process of a drive machine of the vehicle drive train is started as soon as the request to activate the sailing operating state is present; Fig. 5 the curves of the operating variables when the sailing operating state is activated and when the sailing operating state is exited in the direction of an operating state of the vehicle drive train to which a positive switching element is to be transferred or maintained in the closed operating state; Fig. 6 the curves of the operating variables of the vehicle drive train when the coasting mode is activated, which is only deactivated shortly before the vehicle comes to a standstill; Fig. 7 several curves of different operating variables of the vehicle drive train according to Fig. 1 over time t, which is transferred to a sailing operating state as required, which is deactivated again at a later time; Fig. 8 the curves of the operating variables of the vehicle drive train when the coasting operating mode is activated, which is only deactivated shortly before the vehicle comes to a standstill, whereby a synchronization point of a positive shift element to be engaged is reached at a constant speed of a drive motor of the vehicle drive train in conjunction with a special gear tracking system; Fig. 9 the curves of the operating variables of the vehicle drive train when the sailing operating mode is activated, which is deactivated before the vehicle comes to a standstill, whereby a synchronization point of a positive switching element to be engaged is established by means of a targeted engine intervention; Fig. 10 the curves of the operating variables of the vehicle drive train when the sailing operating mode is activated, which is deactivated by sharp deceleration of a vehicle running with the vehicle drive train; Fig. 11 the curves of the operating variables of the vehicle drive train when the sailing mode is activated, which is deactivated due to a power request from the driver; Fig. 12 several curves of different operating variables of the vehicle drive train according to Fig. 1 over time t, which occur during the implementation of a variant of the method according to the invention over time t; Fig. 13 several curves of different operating variables of the vehicle drive train according to Fig. 1, which occur during the implementation of a further variant of the method according to the invention over time t; Fig. 14 several curves of different operating variables of the vehicle drive train according to Fig. 1 over time t, which occur during the implementation of a variant of the method according to the invention over time t; Fig. 15 several curves of different operating variables of the vehicle drive train according to Fig. 1, which occur during the implementation of a further variant of the method according to the invention over time t; Fig. 16 several curves of different operating variables of the vehicle drive train according to Fig. 1 over time t, which occur during the implementation of a variant of the method according to the invention over time t; and Fig. 17 several curves of different operating variables of the vehicle drive train according to Fig. 1, which occur during the implementation of a further variant of the method according to the invention over time t.

[0069] Fig. 1 shows a highly schematic representation of a vehicle drive train 1 with a drive motor 2, with an output 3 and with a transmission 4 arranged in the power flow between the drive motor 2 and the output 3. The transmission 4 comprises six shift elements A to F, wherein the shift elements B, C, D and E are designed as frictional shift elements, while the shift elements A and F are positive shift elements. The shift elements C, D and F represent so-called brakes, while the shift elements B, E and A are designed as clutches. In general, several gear pairs of a gear set 5 of the transmission 4 are connected via the shift elements A to F to represent various Fig. 2 listed ratios “1” to “9” for forward travel and one ratio “R” for reverse travel can be switched on and off, whereby only some of the ratios “1” to “7” for forward travel can be represented via the positive switching element A in conjunction with the other switching elements B to E.

[0070] Fig. 2 shows a shift diagram of the transmission 4, wherein in the shift diagram the shift elements A to F are to be held or transferred to the closed operating state to represent one of the gear ratios "1" to "R", which are indicated by a circle, while the other shift elements A to F are to be transferred to their open operating state or held in this state. In addition, the penultimate column of the shift diagram shows the gear ratio value corresponding to the gear ratio "1" to "R" engaged in the transmission 4, while the last column of the shift diagram shows the gear step between each two adjacent gear ratios. The first gear ratio "1" for forward travel has a gear ratio of 4.70, while the second gear ratio "2" that can be engaged in the transmission 4 for forward travel has a gear ratio of 2.84.Between the first gear ratio "1" for forward drive and the second gear ratio "2" for forward drive, the transmission has a gear step of 1.65. Due to its design, transmission 4 has a total gear ratio spread of 9.81.

[0071] In addition, the shift elements A to F, which are to be kept in the closed operating state during an activated coasting operating state of the vehicle drive train 1 depending on the respective operating state of the vehicle drive train 1, are marked by a square, while a so-called coasting clutch, which is kept in the open operating state during the coasting operating state and is transferred to its closed operating state upon exiting the coasting operating state in order to couple the drive motor 2 to the output 3 in the area of ​​the transmission 4 to the required extent, is marked by a square arranged within a circle. The shift logic characterized by the squares and the squares arranged within the circles in the activated coasting operating state of the vehicle drive train 1 represents a so-called standard logic.For example, when the sailing operating state is activated using the standard switching logic during an operating state of the vehicle drive train 1 in which the second gear ratio "2" for forward travel is to be engaged in the transmission 4 when exiting the sailing operating state, the frictional switching element C is the sailing clutch, while the positive switching elements A and F are in the closed operating state.

[0072] When the sailing operating state is activated, the transmission 4 can alternatively also be operated according to a first variant of the switching logic, wherein the switching elements A to F which are then to be kept in the closed operating state are marked by a triangle, while the sailing clutch is the switching element F or E, which is each marked by a triangle arranged within a circle.

[0073] In addition, there is also the possibility that the transmission 4 is actuated according to a second variant of the switching logic when the sailing operating state is activated, wherein the switching elements to be kept in the closed operating state are each identified by a hexagon and the switching element E, D, C, B representing the sailing clutch is identified by a hexagon arranged within a circle.

[0074] The gear ratio range of transmission 4, comprising ratios “1” to “9” for forward travel, can essentially be functionally subdivided into three gear ratio subranges. A first gear ratio subrange comprises ratios “1” to “4”, for which both the positive shift element A and the positive shift element F must be held or transferred to the closed operating state and one of the frictional shift elements D, C, B or E must also be closed. The adjoining second gear ratio subrange comprises ratios “5” to “7”, for which only the positive shift element A must be held in the closed operating state alongside two further frictional shift elements B and E or C and E or D and E.The third gear ratio sub-range, which in turn follows the second gear ratio sub-range, comprises the gear ratios “8” and “9” for forward travel, which are engaged by simultaneously closing the three frictional shift elements C, D and E or D, B and E in transmission 4.

[0075] When changing gear ratios in the transmission 4 within a gear ratio sub-range, only one frictional shift element D, C, B or E or B, C, D or C, B needs to be switched off and another frictional shift element E, B, C, D or D, C, B or B, C needs to be switched on. In contrast to this, when changing gear ratios in the transmission 4, in which a gear ratio of one of the gear ratio sub-ranges is to be disengaged and a gear ratio of another gear ratio sub-range in the transmission 4 is to be engaged, at least one of the positive shift elements A and F needs to be switched on or off, which is implemented during normal driving operation of the vehicle drive train 1 by means of conventional switching routines.

[0076] However, if the vehicle drive train 1 is in its sailing operating state and the transmission 4 is actuated in the manner described in more detail below depending on the currently existing operating state of the vehicle drive train in such a way that when sailing is exited, the requested operating state of the vehicle drive train 1 can be represented by switching on only one of the switching elements A to F within short operating times and thus with high spontaneity, the procedures described in more detail below are to be carried out depending on the operating state.

[0077] On the transmission input side, the transmission 4 is operatively connected to the drive engine 2 via a hydrodynamic torque converter 7. In this case, the hydrodynamic torque converter 7 is assigned a so-called torque converter lock-up clutch 8, the transmission capacity of which is varied in a conventional manner depending on the operating state in order to minimize losses in the area of ​​the hydrodynamic torque converter 7. On the transmission output side, the transmission 4 is operatively connected to the output 3 via a transmission output shaft 9.

[0078] The transmission 4 in this case comprises four planetary gear sets P1 to P4, wherein the first and second planetary gear sets P1 and P2, which are preferably designed as minus planetary gear sets, form a switchable primary gear set, while the third planetary gear set and the fourth planetary gear sets P3 and P4 form a so-called main gear set. A sun gear S3 of the third planetary gear set P3 is in this case non-rotatably connected to a sun gear S4 of the fourth planetary gear set P4. The two sun gears S3 and S4 are non-rotatably connected to a housing-fixed component 10 when the positive shifting element F is in the closed operating state and rotate freely when the positive shifting element F is in the open operating state. The sun gear S3 meshes with planetary gears PR3, which are rotatably arranged on a planetary carrier ST3 of the third planetary gear set P3. Furthermore, the planetary gears PR3 mesh with a ring gear HR3 of the third planetary gear set P3.The sun gear S4 of the fourth planetary gear set P4 in turn meshes with planetary gears PR4, which are rotatably arranged on a planetary carrier ST4, which is rotationally fixedly coupled to the transmission output shaft 9. Additionally, the planetary gears PR4 mesh with a ring gear HR4 of the fourth planetary gear set P4, which in turn is rotationally fixedly connected to the planetary carrier ST3 of the third planetary gear set P3.

[0079] The planetary carrier ST3 of the third planetary gear set P3 can be brought into operative connection with the transmission input shaft 6 via the shifting element E. The ring gear HR3 of the third planetary gear set P3 is rotationally fixedly connected to a planetary carrier ST2 of the second planetary gear set P2, which in turn is rotationally fixedly connected to a planetary carrier ST1 of the first planetary gear set P1. Planetary gears PR2 rotatably mounted on the planetary carrier ST2 mesh with both a ring gear HR2 and a sun gear S2 of the second planetary gear set P2, wherein the ring gear HR2 can be rotationally fixedly connected to the housing-fixed component 10 via the frictional shifting element D. The sun gear S2 of the second planetary gear set P2 is in turn rotationally fixedly connected to a ring gear HR1 of the first planetary gear set P1, which meshes with planet gears PR1, which in turn mesh with a sun gear S1 of the first planetary gear set P1.The sun gear S1 is rotationally fixedly connected to the housing-fixed component via the frictional shifting element C and can be brought into operative connection with the transmission input shaft 6 via the frictional shifting element B. In addition, the sun gear S1 is rotationally fixedly connected to the ring gear HR 1 of the first planetary gear set P1 via the positive shifting element A when the shifting element B is in the closed operating state.

[0080] In order to be able to operate the vehicle drive train 1 with the lowest possible fuel consumption of the drive engine 2 and at the same time with high spontaneity, the vehicle drive train 1 is operated depending on the operating state in the manner described below using the illustrations in accordance with Fig. 3 to Fig. 17 in a manner described in more detail.

[0081] Fig. 3 to Fig. 6 show several curves of different operating variables of the vehicle drive train 1 over time t, wherein the vehicle drive train 1 is in a Fig. 3, the vehicle is in an operating state at the time T0 identified in more detail, at which the eighth gear ratio “8” or the ninth gear ratio “9” for forward travel is engaged in the transmission 4 and a speed n_mot of the drive motor 2 is greater than an idling speed n_motLL of the drive motor 2. At time T0, a request is made to display a sailing operating state of the vehicle drive train 1, during which the drive motor 2 is switched off and the power flow between the drive motor 2 and the output 3 is interrupted in the area of ​​the transmission 4. The request to activate the sailing operating state is made based on an operating state of the vehicle drive train 1 in which the drive motor 2 is switched on and connected to the output 3 via the transmission 4. Furthermore, a speed n_ab of the output 3 is greater than a threshold value that is greater than zero.When the eighth or ninth gear ratio “8” or “9” is engaged for forward travel, the positive shift element A is open.

[0082] To activate the sailing operating state, from time T1 onwards the frictional switching element E is lowered by a corresponding lowering of an actuating pressure p_E in the Fig. 3 is transferred into its open operating state up to a time T2 and thereby the power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is separated.

[0083] In addition, from time T0, the speed n_mot of the drive motor 2 is increasingly guided towards the idling speed n_motLL to the extent shown. The reduction in the transmission capacity of the frictional shift element E causes the speed n_t of the transmission input shaft 6, which is also referred to below as the turbine speed, to deviate from the product of the speed n_ab of the output 3 and the gear ratio i_zielgang_sas engaged in the transmission at time T0, from a time T3, which lies between times T1 and T2. If the deviation between the turbine speed n_t and the gear ratio i_zielgang_sas exceeds a threshold value kfl, the separate power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is detected. In this case, this is the case at a time T4, which lies between times T3 and T2.

[0084] At time T4, with the ninth gear ratio “9” engaged in gearbox 4 for forward travel, an actuation pressure p_C of the frictional switching element C is applied in the Fig. 3, the actuating pressure is abruptly increased to the level of a rapid filling pressure and maintained at this level until a time T5. Subsequently, the actuating pressure p_C is reduced to an intermediate pressure level at time T5 and ramped up via two successive pressure ramps to a time T6, at which the frictionally engaged switching element C is in a slip-free operating state. At time T6, the actuating pressure p_C is increased to a level at which the frictionally engaged switching element C is fully closed.

[0085] If the eighth gear ratio “8” for forward travel is engaged in transmission 4 at time T0, an actuating pressure p_B of the frictional switching element B is set in the manner described above between times T4 and T6 instead of the actuating pressure p_C in order to transfer the frictional switching element B, in addition to the frictional switching elements C and D, into the closed operating state.

[0086] When the frictional shift elements C, D, and B are in the closed operating state, the gear set 5 of the transmission 4 has a partially locked operating state in which the transmission input shaft 6 is held in a rotationally fixed manner and the transmission output shaft 9 connected to the output 3 is rotatable. In this operating state of the transmission 4, an actuation pressure p_A of the positive shift element A is increased, whereby the positive shift element A is transferred to its closed operating state. At the same time, the drive motor 2 is switched off, which is why the speed n_mot of the drive motor 2 drops towards zero. The corresponding request results from a curve MSF, which switches from the value 0 to 1 at time T6, thus activating the engine stop release. Thus, at time T6, the coasting operating state requested at time T0 is activated to the desired extent.

[0087] In this case, the coasting mode is initiated by a driver-side request, for example, by releasing the throttle and preferably applying the service brake. Additionally or alternatively, it is also possible for the coasting mode to be initiated by a higher-level driving strategy if a driver-side power request is not made and it is additionally determined that a route, for example, defined via a navigation system, can be completed at least partially in coasting mode with low fuel consumption.

[0088] In this case, the vehicle drive train 1 remains in the Fig. 3 up to a time T7 in the coasting mode. At time T7, for example, the driver presses the accelerator pedal again and requests a corresponding power from drive motor 2. This driver-side power request causes the MSF curve to switch from the value one to zero and the engine stop enable to be deactivated. This in turn leads to drive motor 2 being switched on and the speed n_mot of drive motor 2 increasing from time T7. To prevent an uncontrolled increase in the engine speed n_mot, a transmission-side engine target speed specification is issued, which is implemented according to the n_motEGS curve.By activating the engine target speed specification, the engine speed n_mot is raised at time T7 to a level that is above the speed of the transmission input shaft 6, which results from the product of the output speed n_ab and the gear ratio i_zielgang_sas to be engaged in the transmission 4 at time T7.

[0089] Since the vehicle drive train 1 is in an operating state at time T7 in which, with the coasting operating state deactivated in the transmission 4, the gear ratio engaged in the transmission 4 at time T0, i.e. the ninth gear ratio "9" or the eighth gear ratio "8" for forward travel, is to be engaged, the actuation pressure p_A of the positive shift element A is reduced at time T7 and the positive shift element A is transferred to its open operating state at time T7. At the same time, the actuation pressure p_C or the actuation pressure p_B of the frictional shift element C or B is reduced to zero in order to cancel the locking state of the gear set 5 created between times T4 and T6.

[0090] With increasing speed n_mot of the drive machine 2 and a release of the blocking state of the gear set 5, the turbine speed n_t increases from a time T8 following the time T7 and follows the course of the speed n_mot of the drive machine 2. From a time T9 following the time T8, the actuation pressure p_E of the frictionally engaged switching element E is in the Fig. 3, during a rapid filling phase lasting until time T10 and a subsequent filling equalization phase lasting until time T11. From time T9, the drive motor 2 is in speed control mode.

[0091] At time T11, the frictional shifting element E is in an operating state at which the transmission capacity of the frictional shifting element E is essentially equal to 0 and a further increase in the actuating pressure p_E results in an immediate increase in the transmission capacity of the frictional shifting element E. From time T11, the actuating pressure p_E is increased via a pressure ramp lasting until time T12. The actuating pressure p_E of the frictional shifting element E is increased in the present case at time T11 via the first pressure ramp following the fill equalization phase when the profile of the rotational speed n_mot of the prime mover 2 for the traction operation of the vehicle drive train 1 considered here has reached or even exceeded the profile n_ab*i_zielgang_sas and a differential speed Nd_Syn between the shifting element halves of the shifting element E to be engaged is close to the synchronous speed oris less than or equal to a threshold.

[0092] In contrast to this, the actuation pressure p_E of the switching element E to be engaged is increased to an extent not shown in more detail in the overrun mode of the vehicle drive train 1 from the time T11 via the first pressure ramp following the fill compensation phase if the profile of the speed n_mot of the drive machine 2 is below the profile n_ab*i_zielgang_sas or corresponds to this and a differential speed Nd_Syn between the switching element halves of the switching element E to be engaged is close to the synchronous speed or is less than or equal to a threshold value.

[0093] Subsequently, the actuation pressure p_E of the frictional shift element E is further increased via a further pressure ramp, the gradient of which is smaller than the pressure ramp present between times T11 and T12. At the end of the second pressure ramp, i.e., in this case, at time T13, the frictional shift element E is in a slip-free operating state, and the turbine speed n_t corresponds to the product of the output speed n_ab and the gear ratio i_zielgang_sas requested at time T7 and to be engaged in transmission 4, which in this case corresponds to either the ninth gear ratio "9" or the eighth gear ratio "8".

[0094] The engine speed n_mot is guided by the transmission-side engine target speed specification to a level above the curve n_ab*i_zielgang_sas in order to avoid undesirable speed crossover between the speed n_mot of the drive engine 2 and the turbine speed n_t resulting from the gear ratio to be engaged in the transmission 4 and the output speed n_ab during the establishment of the power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4. A speed crossover between the engine speed n_mot and the curve n_ab*i_zielgang_sas causes an undesirable load change in the vehicle drivetrain 1, which impairs driving comfort to an undesirable extent.

[0095] At time T14, the actuation pressure p_E of the frictional shift element E reaches the closing pressure level, and the operating state of the vehicle drive train 1 requested at time T7 is established to the desired extent at time T14. After time T14, from which the coasting operating state of the vehicle drive train 1 is terminated, any requested subsequent shifts can be performed in the transmission 4 to the desired extent.

[0096] The one in Fig. The operating state curve of the vehicle drive train underlying the curves shown in Figure 4 differs from that in Fig. 3 shown curves of the various operating variables of the vehicle drive train 1 underlying operating state curve of the vehicle drive train 1 in that the speed n_mot of the drive machine 2 during the operating state curve according to Fig. 4 is already reduced towards zero at time T5, ie in this case at the end of the rapid filling phase of the switching element C or B. In contrast, the engine speed n_mot of the drive machine 2 is reduced during the operating state according to Fig. 3 is only lowered towards zero at time T6, at which the actuating pressure p_C or p_B is raised to the closing pressure level.

[0097] The procedure according to Fig. 3 offers the possibility of implementing a hydraulic supply to the transmission 4 via a transmission main pump driven by the drive engine 2 via the transmission input shaft 6 and not shown in detail in the drawing, and of having to implement an electrically operated auxiliary pump of the transmission 4 with lower performance. In contrast to this, the hydraulic supply to the transmission 4 during the operating state of the vehicle drive train 1 from time T5 onwards is no longer to be taken over entirely by the transmission main pump but increasingly by the electrically driven auxiliary pump of the transmission 4, which is why this is required to implement the procedure according to Fig. 4 must be dimensioned accordingly.

[0098] Furthermore, the positive switching element A is Fig. 4 underlying operating state curve of the vehicle drive train 1 at time T6 is not transferred into its closed operating state. Since the request to deactivate the sailing operating state present at time T7 requires an operating state of the vehicle drive train 1 in the transmission 4 to be engaged in the eighth gear ratio "8" or the ninth gear ratio "9" for forward travel, for the representation of which the positive switching element A is to be transferred or maintained in the open operating state, the positive switching element A is left in its open operating state at time T7 and, in contrast to the operating state curve of the vehicle drive train 1 according to Fig. 3 not to be transferred to its open operating state at time T7.

[0099] This means that the Fig. 4 described procedure compared to the Fig. 3 has the advantage that at time T6 in the transmission 4, any tooth-on-tooth positions that may be present in the area of ​​the positive shifting element A due to the partially blocked operating state of the gear set 5 do not have to be resolved by appropriately varying the transmission capacity of one of the three simultaneously closed shifting elements C, D or B, and in the area of ​​the positive shifting element A, a differential speed between the shifting element halves of the positive shifting element A is created that is favorable for its engagement. In addition, any stress conditions in the area of ​​the positive shifting element A at time T7, at which the positive shifting element A is engaged during the Fig. 3 underlying operating state progression is transferred into its open operating state, not to be cancelled by correspondingly actuating the transmission capability of the switching element C or B which is then additionally to be switched off, before the positive switching element A can be transferred into its open operating state to represent the ninth gear ratio “9” or the eighth gear ratio “8” for forward travel.

[0100] In addition, the actuation of the frictional switching element E, which has to be transferred into its closed operating state in order to establish the power connection between the drive motor 2 and the output 3, can be transferred into its closed state with greater spontaneity from the time T7 at which the request to deactivate the sailing operating state of the vehicle drive train 1 is issued than during the Fig. 3 underlying operating state curve of the vehicle drive train 1 is possible.

[0101] In contrast, the Fig. 3, namely to transfer the positive switching element A into its closed operating state at time T6, in comparison to the Fig. 4 then offers advantages with regard to the spontaneity of the vehicle drive train 1 if a request to deactivate the sailing operating state of the vehicle drive train 1 requests an operating state of the vehicle drive train 1, for which one of the gear ratios "7" to "1" for forward travel is to be engaged in the area of ​​the transmission 4, for which the positive switching element A is to be transferred or held in its closed operating state, since this is then already in the closed operating state at the time T7.

[0102] Fig. 5 shows the curves of the operating variables of the vehicle drive train 1 according to Fig. 3 and Fig. 4 during an operating state progression of the vehicle drive train 1 after the time T6, at which the vehicle drive train 1 is already in the coasting operating state. Up to a time T15, a higher-level driving strategy recognizes that in the event of a possible exit from the coasting operating state of the vehicle drive train 1 in the transmission 4, the eighth gear ratio "8" or the ninth gear ratio "9" is to be engaged for forward travel. At time T15, with the coasting operating state of the vehicle drive train 1 activated, the driving strategy determines that in the transmission 4, the seventh gear ratio "7" is to be engaged for forward travel when exiting the coasting operating state. The positive shift element A is in the Fig. 3, it had already been transferred to its closed operating state at time T6.

[0103] Due to the determination of the driving strategy that from time T15 onwards the seventh gear ratio "7" is to be engaged in transmission 4 for forward travel, in order to increase the spontaneity of transmission 4 either the actuation pressure p_B of the frictional switching element B or the actuation pressure p_C of the frictional switching element C is reduced at time T15, while the actuation pressure p_D of the frictional switching element D is left at the closing pressure level of the switching element D. The actuation pressure p_B or actuation pressure p_C of the frictional switching element B or C is an offset value above a pressure value pf_min + Hys plus an offset value dependent on a hysteresis, which represents an actuation threshold above which the frictional switching elements B, C and D have a slip-free operating state when the coasting operating state is activated.

[0104] The pressure level pf_min + Hys plus a corresponding offset value corresponds to a pressure level above a transmission pressure level of the frictional shift elements B, C and D. This ensures that the frictional shift elements B, C and D remain in the closed operating state during the activated coasting operating state by being subjected to a pressure level of the respective actuation pressure p_B, p_C or p_D, but with a significantly lower transmission capacity. This offers the advantage that, in the event of a fault, the risk of over-determination of the gear set 5 of the transmission 4 is reduced, since when a corresponding torque is applied, the shift elements B, C, D are transferred to slip operation to the desired extent and thus a braking torque applied in the area of ​​the transmission output shaft 9 can be easily limited.

[0105] The spontaneity of the vehicle drive train 1 is increased, particularly in the area of ​​the transmission 4, in that, upon a corresponding request to deactivate the sailing operating state of the vehicle drive train 1 after the time T15, only the frictional switching element E has to be closed and the vehicle drive train 1 can be made available with the operating state requested by the request to deactivate the sailing operating state within short operating times t.

[0106] In this case, the vehicle drive train 1 remains in the coasting operating state even after time T15. The driving strategy determines at a subsequent time T16 that the curve n_ab*i_zielgang_sas has reached a value at which a possible request to deactivate the coasting operating state in turn requests an operating state of the vehicle drive train 1, for the establishment of which the sixth gear ratio "6" or the fifth gear ratio "5" must be engaged in the area of ​​the transmission 4. For this reason, at time T16, the actuation pressure p_C or the actuation pressure p_B of the frictional shift element C or the frictional shift element B is reduced to the extent shown from the pressure level above the threshold value pf_min + Hys plus an offset value taking a hysteresis into account in the direction of the closing pressure level in the Fig. 5, while the actuating pressure p_D of the frictionally engaged switching element D is reduced to a pressure level above the threshold value pf_min + Hys plus offset at time T17, at which the actuating pressure p_C or p_B reaches the closing pressure level.

[0107] At a time T18, a request is made to deactivate the sailing operating state of the vehicle drive train 1, wherein the exit from the sailing operating state of the vehicle drive train 1 takes place in the direction of an operating state of the vehicle drive train 1, for which either the sixth gear ratio "6" or the fifth gear ratio "5" for forward travel is to be engaged in the transmission 4. Since the shift elements A to D are already prepared at the time T18 for the representation of such a requested operating state of the vehicle drive train 1 and in particular of the transmission 4, from the time T18 onwards only the frictional shift element E is activated to the extent requested in the Fig. 5 into its closed operating state.

[0108] From time T18 onwards, the curve of the actuating pressure p_E of the frictional switching element E, the curve n_motEGS of the EGS engine target speed specification and the curve of the speed n_mot of the drive machine 2 essentially correspond to the Fig. 3 from time T9 onwards. Therefore, for the sake of clarity, reference is made to the above description regarding the actuation of the switching element E and the actuation of the drive motor 2 from time T18 onwards. Fig. 3 and the procedure explained therein concerning the actuation of the switching element E and the drive motor 2 from time T9. Generally, from time T9 or from time T18, the exit from the sailing mode occurs with simultaneous restart of the drive motor 2 and a speed control in the area of ​​the drive motor 2, which is also carried out simultaneously.

[0109] Fig. 6 shows the different curves of the operating variables of the vehicle drive train 1 from a time T20, which is between the times T15 and T16 according to Fig. 5 and at which the sailing operating state of the vehicle drive train 1 is activated. If a request to deactivate the sailing operating state is issued at time T20, the seventh gear ratio "7" for forward drive must be engaged in the area of ​​the transmission 4. The positive-locking switching element A is closed due to the applied actuation pressure p_A. At the same time, the frictional switching element D is also in the closed operating state and is subjected to an actuation pressure p_D having the closing pressure level, while the frictional switching element C is subjected to an actuation pressure p_C which is an offset value higher than the pressure value pf_min plus the offset value.

[0110] With increasing operating time t, with the sailing operating state of the vehicle drive train 1 still activated, the so-called sailing clutch logic determines at times T21, T22, T23, T24 and T25, via a gear tracking system that increases the spontaneity when exiting the sailing operating state of the vehicle drive train 1, that the sixth gear ratio "6", the fifth gear ratio "5", the third gear ratio "3", the second gear ratio "2" or the first gear ratio "1" in the transmission 4 is to be engaged. Therefore, at time T26, the actuation pressure p_D is reduced to the level above the pressure limit pf_min + Hys plus offset value, while the actuation pressure p_C is increased to the closing pressure level.To the same extent, after time T22, at time T27, the actuation pressure p_B of the frictional shift element B is brought to the closing pressure level, while the actuation pressure p_C of the frictional shift element C is reduced to the pressure level above the pressure limit pf_min + Hys plus the offset value. At time T23, no clutch logic change occurs, while at a time T28 following time T24, the actuation pressure p_C is again raised to the closing pressure level and the actuation pressure p_B of the frictional shift element B is reduced to the pressure level above the pressure limit pf_min + Hys plus the offset value, whereby the transmission 4 is prepared for the engagement of the second gear ratio "2" for forward travel.

[0111] From a time T 29 following the time T 25, the transmission 4 is prepared for engaging the first gear ratio “1” for forward travel by raising the actuating pressure p_D of the positive switching element D to the closing pressure level, while the actuating pressure p_C of the frictional switching element C is lowered to the pressure level above the pressure limit pf_min + Hys plus the offset value.

[0112] The latter procedure results from the fact that the vehicle speed continues to decrease during the observed operating state profile of the vehicle drive train 1 when the coasting operating state is activated, and the coasting clutch logic determines that with increasing operating time t, the gear to be engaged in the transmission upon leaving the coasting operating state changes and a lower gear or ratio must be engaged. Since the further positive-locking shift element F must be transferred to the closed operating state in order to represent the ratios "4" to "1" for forward travel, synchronization gears corresponding to the ratios "3" to "1" or the synchronization ratios "5", "6", or "7" must be engaged in the area of ​​the transmission 4 before engaging the ratios "3" to "1".

[0113] This means that if there is a request to deactivate the sailing operating state and an operating state of the vehicle drive train to be established for this purpose, for which the third gear ratio "3" is to be engaged in the transmission 4 for forward travel, the fifth gear ratio "5" is first engaged in the transmission 4 and then a downshift is carried out starting from the fifth gear ratio "5" in the direction of the third gear ratio "3", during which the further positive switching element F can then also be transferred into its closed operating state with little effort as required when the positive switching element A is already closed.

[0114] When the second gear ratio "2" for forward travel is to be engaged in transmission 4 as a result of a request to deactivate the sailing operating state, the sixth gear ratio "6" for forward travel is first engaged in transmission 4 and then the downshift is carried out starting from the sixth gear ratio "6" in the direction of the second gear ratio "2", during which the further positive switching element F is engaged in addition to the already closed switching element A. In addition, it is provided that the seventh gear ratio "7" is first engaged in transmission 4 and then the downshift is carried out starting from the seventh gear ratio "7" in the direction of the first gear ratio "1" if the first gear ratio "1" is to be engaged in the area of ​​transmission 4 as a result of a request to deactivate the sailing operating state of the vehicle drive train 1.Then, in addition to the already closed positive switching element A, the further positive switching element F can be transferred to its closed operating state to the desired extent.

[0115] In this case, at a time T30, the request to deactivate the sailing operating state in the area of ​​transmission 4 occurs, at which time the first gear ratio "1" for forward travel must be engaged in transmission 4. In order to transfer the additional positive shift element F to its closed operating state to the desired extent, the frictional shift element D and the positive shift element A are actuated with their actuating pressures p_D and p_A, which have the closing pressure level, from time T29 onwards. At time T30, the actuating pressures p_C and p_B are reduced to zero and the frictional shift elements C and B are transferred to their open operating state. In addition, the drive motor 2 is switched on, which is why the curve of the speed n_mot of the drive motor 2 increases in a controlled manner towards the idling speed n_motLL from time T30 onwards, depending on the EGS engine target speed specification.

[0116] At a time T31 following time T30, the frictional shifting element E is subjected to a filling compensation pressure during a rapid filling phase with a rapid filling pulse and a subsequent filling compensation phase, wherein the filling compensation phase in this case ends at a time T32. Subsequently, the actuation pressure p_E is increased via a first pressure ramp starting at time T32, whereby the synchronization ratio corresponding to the first gear ratio "1" or the seventh gear ratio "7" is engaged in the transmission 4. As the actuation pressure p_E of the frictional shifting element E continues to rise, the turbine speed n_t increases in the direction of the curve n_ab*i_zielgang_sas and corresponds to this at time T33, at which the shifting element E has its full transmission capacity.At time T33, the actuation pressure p_E of the frictional switching element E is again reduced to the level of the pressure threshold pf_min + Hys plus the offset value in order to transfer the additional positive switching element F to the desired extent into an operating state favorable for its engagement. In this case, a differential speed between the switching element halves of the additional positive switching element F is transferred into a differential speed window favorable for engagement, and the additional positive switching element F is subjected to the actuation pressure p_F required for engagement at a time T34 and transferred to its closed operating state.

[0117] At a time T35 shortly thereafter, it is detected that the additional positive-locking switching element F is in the closed operating state, since the curve of the turbine speed n_t at time T35 corresponds to the curve n_ab*i_zielgang_sas, which is known to occur when the first gear ratio "1" is engaged in a transmission 4. For this reason, at time T35, the actuation pressure p_E of the positive-locking switching element E is reduced to zero in the manner shown, and the frictionally engaged switching element E is fully opened, thus deactivating the coasting operation and the vehicle drive train 1 having the requested operating state.

[0118] The procedure according to the invention is particularly suitable for gearset concepts in conjunction with correspondingly designed shifting elements arranged in the gearset, in which the output of a vehicle drive train can rotate freely from the gearset of the transmission by opening a frictionally engaged shifting element. In the presently considered embodiment of the automatic transmission 4, this is shifting element E. By means of the additional shifting elements or the brakes D and C, one shifting element half of the positive-locking shifting element A or its rotational speed can be set to zero. In addition, the rotational speed of the additional shifting element half of the shifting element A and also of the transmission input shaft 6 can be set to zero by closing shifting element B when the coasting operating state of the vehicle drive train 1 is activated.Due to this active blocking of the gear set 5, pressure level changes of the actuating pressures of the shifting elements can be carried out dynamically during the gear adjustment described above and can be adjusted as in conventionally performed overlap shifts.

[0119] If shift elements B, C, or D are subjected to a pressure level above the filling pressure required to lock gear set 5, the locking of gear set 5 is maintained and the turbine speed n_t is zero. This enables rapid gear adjustment across the entire operating range of transmission 4, and filling shift elements B, C, or D via an electrically driven auxiliary pump of transmission 4 is not required. If a restart of prime mover 2 is requested by a corresponding request to deactivate the coasting operating state, the shift elements of transmission 4 that are not required to represent the requested operating state of the vehicle drive train can be easily deactivated by reducing the respective actuation pressure.

[0120] The particularly Fig. 5 and Fig. The gear tracking described in Figure 6 during the activated coasting mode of the vehicle drive train 1 in the area of ​​the transmission 4 can also be carried out in the opposite direction with increasing vehicle speed or with increasing output speed n_ab. Such an increase in the output speed occurs, for example, during downhill driving of a vehicle equipped with a vehicle drive train operable according to the invention. Furthermore, it is also possible for the vehicle speed to increase via an additional vehicle drive independent of the prime mover, such as an electric vehicle axle or the like.

[0121] Regardless of the event that increases the output speed, when the vehicle drive train transitions to the sailing operating state with the lower gear ratios “1” to “8” engaged in the transmission 4 for forward travel to the extent described above, the gear set 5 is first transferred to the partially blocked operating state by closing the switching elements B, C and D and then monitored in each case to determine whether an exit from the sailing operating state at the current operating point of the vehicle drive train requires a higher gear ratio to be engaged in the transmission 4 than at the time at which the sailing operating state of the vehicle drive train 1 was activated in order to represent the operating state of the vehicle drive train 1 that is then requested for this purpose.If this is the case, the transmission is actuated to the extent required by corresponding actuation of the switching elements A to F and is prepared for the gear ratio to be engaged in the area of ​​the transmission 4 depending on the respective operating point of the vehicle drive train in such a way that when exiting the sailing operating state, the requested operating state of the vehicle drive train can be represented within short operating times.

[0122] Fig. 7 to Fig. 11 each show several curves of different operating variables of the vehicle drive train 1 over time t, wherein the vehicle drive train 1 is Fig. 7, the vehicle is again in a driving operating state at which the eighth gear ratio "8" or the ninth gear ratio "9" for forward travel is engaged in the transmission 4 and a speed n_mot of the drive motor 2 is greater than an idle speed n_motLL of the drive motor 2. At time T130, a request is made to display a sailing operating state of the vehicle drive train 1, during which the drive motor 2 is engaged and the power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is interrupted. From time T130, the speed n_mot of the drive motor 2 is increasingly guided in the direction of the idle speed n_motLL to the extent shown. To activate the sailing operating state of the vehicle drive train 1, from time T131, the frictionally engaged switching element E is actuated by a corresponding reduction of the actuation pressure p_E in the range shown in Fig. 7 is transferred into its open operating state up to a time T132 and thereby the power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is separated.

[0123] The reduction in the transmission capacity of the frictional shift element E causes the speed n_t of the transmission input shaft 6 to deviate from the product of the speed n_ab of the output 3 and the gear ratio i_target_sas engaged in the transmission at time T130, starting at a time T133, which lies between times T131 and T132. If the deviation between the turbine speed n_t and the product of the speed n_ab times the gear ratio i_target_sas exceeds a threshold value kfl, the separate power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is detected. This is the case at a time T134, which lies between times T133 and T132.

[0124] At time T134, with the ninth gear ratio “9” engaged in gearbox 4 for forward travel, the actuation pressure p_C of the frictional switching element C is in the Fig. 7, the actuating pressure is abruptly increased to the level of the rapid filling pressure and maintained at this level until a time T135. Subsequently, the actuating pressure p_C is reduced to an intermediate pressure level at time T135 and, via two successive pressure ramps, is ramped up to a time T138, at which the frictionally engaged switching element C has a slip-free operating state. At time T136, the actuating pressure p_C is increased to a level at which the frictionally engaged switching element C is fully closed.

[0125] If the eighth gear ratio “8” for forward travel is engaged in transmission 4 at time T130, the actuation pressure p_B of the frictional switching element B is set in the manner described above instead of the actuation pressure p_C between times T134 and T136 in order to transfer the frictional switching element B, in addition to the frictional switching elements C and D, into the closed operating state.

[0126] When the frictional shift elements C, D, and B are in the closed operating state, the gear set 5 of the transmission 4 has a partially locked operating state, in which the transmission input shaft 6 is held in a rotationally fixed manner and the transmission output shaft 9 connected to the output 3 is rotatable. In this operating state of the transmission 4, the actuation pressure p_A of the positive shift element A is increased, thereby transferring the positive shift element to its closed operating state. At the same time, the drive motor 2 is operated at the idle speed n_motLL.

[0127] At a time T144, the closed operating state of the switching element A is detected, which is why both the actuating pressure p_B of the frictionally engaged switching element B and the actuating pressure p_C of the frictionally engaged switching element C are reduced to zero to the extent shown at time T144, whereby the sailing operating state of the vehicle drive train 1 requested at time T130 is activated to the desired extent at time T144.

[0128] In this case, the coasting mode is requested by a driver-side request, for example, by releasing the throttle and preferably applying the service brake. Additionally or alternatively, it is also possible for the coasting mode to be requested by a higher-level driving strategy if a driver-side power request is not made and it is additionally determined that a route, for example, defined via a navigation system, can be completed at least partially in coasting mode with low fuel consumption.

[0129] In this case, the vehicle drive train 1 remains in the Fig. 7 up to a time T137 in the coasting operating state. At time T137, the driver, for example, presses the accelerator pedal again and requests a corresponding power from the prime mover 2. This driver-side power request causes the speed n_mot of the prime mover 2 to increase from time T137. In order to prevent an uncontrolled increase in the engine speed n_mot, the prime mover 2 is operated in speed control mode from time T137 and a transmission-side engine target speed specification corresponding to the curve n_motEGS is carried out. By activating the engine target speed specification, the engine speed n_mot is increased from time T137 towards a level that lies above the speed n_t of the transmission input shaft 6, which results from the product of the output speed n_ab and the gear ratio i_zielgang_sas to be engaged in the transmission 4 at time T137.

[0130] Since the vehicle drive train 1 is in an operating state at time T137 at which, with the coasting operating state deactivated in the transmission 4, the gear ratio engaged in the transmission 4 at time T130, i.e. the ninth gear ratio "9" or the eighth gear ratio "8" for forward travel, is to be engaged, the actuation pressure p_A of the positive shift element A is reduced at time T137 and the positive shift element A is transferred to its open operating state at time T137. At a time T145 following the time T137, the open operating state of the positive shift element A is detected and the frictionally engaged shift element C or B is pre-filled via a rapid filling pulse lasting until a time T146.At time T146, the actuating pressure p_C or p_B is raised to an intermediate pressure level and, via two consecutive pressure ramps, ramped up to a further intermediate pressure level at time T147, at which the frictionally engaged switching element C or B has a slip-free operating state. At time T147, the actuating pressure p_C or p_B is raised to the closing pressure level at which the frictionally engaged switching element C or B is fully closed.

[0131] As the speed n_mot of the drive machine 2 increases, the turbine speed n_t also increases and follows the speed n_mot of the drive machine 2. From a time T138, the actuation pressure p_E of the frictional switching element E is Fig. 7, during a rapid filling phase lasting up to a time T139 and a subsequent filling equalization phase lasting up to a time T140, prepared for connection.

[0132] At time T140, the frictional shifting element E is in an operating state in which the transmission capacity of the frictional shifting element E is essentially zero and a further increase in the actuating pressure p_E results in an immediate increase in the transmission capacity of the frictional shifting element E. From time T140, the actuating pressure p_E is increased via a pressure ramp lasting until time T141. The actuating pressure p_E of the frictional shifting element E is increased in the present case at time T140 via the first pressure ramp following the fill equalization phase when the profile of the speed n_mot of the prime mover 2 for the traction operation of the vehicle drive train 1 considered here has reached or even exceeded the profile n_ab * i_zielgang_sas and a differential speed Nd_Syn between the shifting element halves of the shifting element E to be engaged is close to the synchronous speed oris less than or equal to a threshold.

[0133] In contrast to this, the actuation pressure p_E of the switching element E to be engaged is increased to an extent not shown in more detail in the overrun mode of the vehicle drive train 1 from the time T140 via the first pressure ramp following the fill compensation phase if the profile of the speed n_mot of the drive machine 2 is below the profile n_ab * i_zielgang_sas or corresponds to this and a differential speed Nd_Syn between the switching element halves of the switching element E to be engaged is close to the synchronous speed or is less than or equal to a threshold value.

[0134] Subsequently, the actuation pressure p_E of the frictional shift element E is further increased via a further pressure ramp, the gradient of which is smaller than the gradient of the pressure ramp present between times T140 and T141. At the end of the second pressure ramp, i.e., in this case at time T142, the frictional shift element E is in a slip-free operating state, and the turbine speed n_t corresponds to the product of the output speed n_ab and the gear ratio i_zielgang_sas requested at time T137 and to be engaged in transmission 4, which in this case corresponds to either the ninth gear ratio "9" or the eighth gear ratio "8".

[0135] Here too, the engine speed n_mot is guided to a level above the profile of the product n_ab*i_zielgang_sas by the transmission-side engine target speed specification in order to avoid an undesirable speed crossing between the speed n_mot of the drive machine 2 and the turbine speed n_t resulting from the gear ratio to be engaged in the transmission 4 and the output speed n_ab during the establishment of the power flow between the drive machine 2 and the output 3 in the area of ​​the transmission 4.

[0136] At time T143, the actuation pressure p_E of the frictionally engaged shifting element E reaches the closing pressure level, and the operating state of the vehicle drive train 1 requested at time T137 is established to the desired extent at time T143. After time T143, from which the coasting operating state of the vehicle drive train 1 is terminated, any requested subsequent shifts can be performed in the transmission 4 to the desired extent.

[0137] The to Fig. The procedure described in Figure 7, namely transferring the positive-locking switching element A into its closed operating state as early as time T136, offers advantages with regard to the spontaneity of the vehicle drive train 1 when a request to deactivate the sailing operating state of the vehicle drive train 1 requests an operating state of the vehicle drive train 1 for which one of the gear ratios “7” to “1” for forward travel is to be engaged in the area of ​​the transmission 4, for which the positive-locking switching element A is to be transferred or held into its closed operating state, since this is then already in the closed operating state at time T137.

[0138] This provides a simple way to prevent a situation where, in the event of a very likely coasting exit due to a driver-side load request, a downshift is requested during which the positive shifting element A must be transferred to its closed operating state. This avoids long shifting times and poor performance after coasting exit due to a claw downshift that must be carried out as required during coasting exit. During synchronization of the positive shifting element A to be engaged, the torque converter lock-up clutch 8 is opened in order to prevent the drive engine 2 from stalling due to the transmission input shaft 6 being held non-rotatably. Subsequently, during the activated coasting operating state, the control of the torque converter lock-up clutch 8 that was carried out before the request to activate the coasting operating state is released again.

[0139] Alternatively, it can also be provided that the vehicle drive train in the area between the drive engine and the transmission is designed only with a frictional switching element or a frictional clutch, which is operated in a controlled and / or regulated manner to an extent corresponding to the actuation of the converter lock-up clutch in order to synchronize the positive switching element A to be engaged to the desired extent and at the same time to prevent the drive engine 2 from stalling.

[0140] In order to ensure that the positive switching element A is engaged during a sail entry, it is possible to change the simultaneous actuation of the frictional switching elements B, C and D intended to close the positive switching element A by opening the frictional switching element B in order to resolve a tooth-on-tooth position present in the area of ​​the positive switching element A, since a large torque can be imposed on the positive switching element A by opening the frictional switching element B.

[0141] Additionally, it is also possible to provide an engine intervention in the area of ​​the drive engine 2, by means of which the speed n_mot of the drive engine 2 is increased starting from the idle speed n_motLL in order to impose a disturbance torque in the area of ​​the positive shifting element A that resolves the tooth-on-tooth position. Additionally or alternatively, it is also possible to briefly increase the transmission capacity of the torque converter lock-up clutch 8 in order to resolve the tooth-on-tooth position in the area of ​​the positive shifting element A by tearing open the partial blocking of the gear set 5.

[0142] In contrast, it is also possible that the positive-locking switching element A is partially closed by actuation in the closing direction, but has not reached its desired end position and thus its fully closed operating state. If a torque is applied to the positive-locking switching element A that prevents the complete closing of the positive-locking switching element A, the switching elements B, C and A continue to be actuated in the closing direction during the closing process of the switching element A, while the friction-locking switching element D is transferred to its closed operating state, whereby the torque applied to the positive-locking switching element A is reduced to an extent that favors the closing process and a so-called claw relief is carried out.

[0143] Such torques which impair the closing process of the positive switching element A result, among other things, from drag torques within the gearbox and other influences which already load the positive switching element with such a high torque during its closing process that a complete insertion movement is no longer possible.

[0144] The above mentioned Fig. The procedure described in Figure 7, which transfers the positive shifting element A into its closed operating state during the coasting start, offers considerable improvements with regard to the spontaneity of the vehicle drive train when coasting starting from gear ratios "9" or "8" at vehicle speeds below a threshold value, since when coasting exits, a lower gear must then be engaged in transmission 4 and the coasting exit will be associated with a downshift anyway. At higher vehicle speeds, however, this procedure can be disruptive and disadvantageous, since the positive shifting element A cannot be transferred into the closed operating state to represent an operating state of the vehicle drive train 1 requested by a coasting exit. Therefore, a speed-dependent definition of the claw conditioning strategy is provided in order to Fig. 7 described preconditioning of the positive switching element A during the activated sailing operating state of the vehicle drive train to operating ranges in which the preconditioning brings about an improvement in spontaneity.

[0145] This means that when sailing starts from operating states in which the gear ratio "9" or "8" is engaged in the transmission 4 for forward travel, the positive shifting element A is not transferred to its closed operating state if the vehicle speed is greater than the threshold value and an existing request to deactivate the sailing operating state is to represent an operating state of the vehicle drive train 1 in which the eighth gear ratio "8" or the ninth gear ratio "9" is engaged in the transmission 4 for forward travel, for the representation of which the positive shifting element A is to be transferred or maintained in the open operating state. Then, the positive shifting element A is left in its open operating state at time T136 and, in contrast to the operating state of the vehicle drive train 1 according to Fig. 7 not to be transferred to its open operating state at time T137.

[0146] This approach has, in comparison to the Fig. 7 has the advantage that at time T136 in the transmission 4, any tooth-on-tooth positions in the area of ​​the positive shifting element A due to the partially blocked operating state of the gear set 5 do not have to be resolved by appropriately varying the transmission capacity of one of the three simultaneously closed shifting elements C, D or B, and in the area of ​​the positive shifting element A, a differential speed between the shifting element halves of the positive shifting element A is created which is favorable for its engagement. In addition, any stress conditions in the area of ​​the positive shifting element A at time T137, at which the positive shifting element A is engaged during the Fig. 7 underlying operating state progression is transferred into its open operating state, not to be cancelled by correspondingly actuating the transmission capability of the switching element C or B which is then additionally to be switched off, before the positive switching element A can be transferred into its open operating state to represent the ninth gear ratio “9” or the eighth gear ratio “8” for forward travel.

[0147] In addition, the actuation of the frictional switching element E, which has to be transferred into its closed operating state in order to establish the power connection between the drive motor 2 and the output 3, can be transferred into its closed operating state with greater spontaneity from the time T137 at which the request to deactivate the sailing operating state of the vehicle drive train 1 is issued than during the Fig. 7 underlying operating state profile of the vehicle drive train 1 is possible. If the vehicle drive train 1 is in coasting mode and the transmission 4 is operated over longer operating times according to the second variant of the shift logic, so that the positive shift element A is already engaged and the shift element E is additionally held in the closed operating state, excessively high drag torques are permanently generated in the transmission 4 during constant driving operation. Therefore, after a defined operating time has elapsed, the transmission 4 is operated according to the first variant of the shift logic. One decision criterion as to whether the transmission 4 is permanently operated according to the first variant or the second variant of the shift logic when the coasting operating state of the vehicle drive train 1 is activated is the current gradient of the speed n_ab of the output 3.

[0148] If the vehicle drive train 1 is in the coasting operating state at an output speed n_ab, at which the eighth gear ratio "8" or the ninth gear ratio "9" is to be engaged in the event of an exit in the transmission 4, and if the transmission 4 is actuated according to the first variant or the second variant of the shift logic and both the positive shift element A and the frictional shift element E are in the closed operating state, then upon a request to display a neutral operating state of the transmission 4, to which the positive shift element is to be held or transferred to the open operating state, a gear jump in the direction of the seventh gear ratio "7" is carried out by the software before the neutral operating state is displayed. In this way, the neutral operating state of the transmission 4 is implemented in a simple manner as required while the positive shift element A is engaged at the same time.

[0149] This offers the advantage that the new shift logic, during which the positive shift element A is preconditioned in the coasting operating state of the vehicle drivetrain, can be implemented without a new shift sequence in the event of a requested gear disengagement process assigned the highest priority, and additional hardware resources are not required. Using this approach, existing shift sequences can continue to be executed with little effort, and gear disengagement sequences can be implemented with a high degree of spontaneity, since the frictional connection in the area of ​​transmission 4 is already completely reduced before the positive shift element A is transferred to its open operating state.

[0150] Fig. 8 shows the curves of the operating variables of the vehicle drive train 1 according to Fig. 7 during an operating state progression of the vehicle drive train 1 after time T136, at which the vehicle drive train 1 is already in the coasting operating state. At time T148, the transmission 4 is in an operating state at which only the positive shift element A in the transmission 4 is closed, while all other shift elements B to F are open. Up to time T149, a higher-level driving strategy recognizes that, in the event of a possible exit from the coasting operating state of the vehicle drive train 1, the seventh gear ratio "7" in the transmission 4 must be engaged for forward travel.At time T149, when the coasting operating state of the vehicle drive train 1 is activated, the driving strategy determines, depending on the current operating state profile of the vehicle drive train 1, that in the transmission 4, when exiting the coasting operating state, the sixth gear ratio "6" or, if the operating state profile deviates from this, the fifth gear ratio "5" is to be engaged for forward travel.

[0151] Due to the driving strategy determining that from time T149 onwards the sixth gear ratio “6” or the fifth gear ratio “5” is to be engaged in transmission 4 for forward travel, in order to increase the spontaneity of transmission 4 either the actuation pressure p_C of the frictional shifting element C or the actuation pressure p_B of the frictional shifting element B is raised at time T149 to the rapid fill pressure level of shifting element C or B, and at a subsequent time T150 is lowered to the level of the fill equalisation pressure and left at this pressure level until a time T151, which in this case represents the end of the fill equalisation phase of shifting element C or B. Following this, the actuation pressure p_C or p_B of shifting element C or B is raised over three successive pressure ramps up to a time T152 to a pressure level at which the frictional shifting element C or BB is in the closed operating state, whereby at time T152 the actuating pressure p_C or p_B is raised to the closing pressure level. With increasing operating time t, the output speed n_ab and thus the curve of the product n_ab * i_zielgang_sas decrease continuously to the extent shown.

[0152] If the transmission 4 is operated according to the standard sailing logic, after the time T152 the higher-level driving strategy determines that in addition to the positive switching element A, the further positive switching element F must also be transferred to its closed operating state in order to be able to engage one of the gear ratios “1” to “4” of the first gear ratio sub-range with high spontaneity in the transmission 4 when sailing out.

[0153] When switching elements A and B are closed at the same time, the differential speed dnF between the switching element halves of the further positive switching element F can be determined using the following formula: dnF=X*n_t+Y*n_ab

[0154] The variables X and Y represent factors that depend on the respective gear ratios of the individual gear sets of the transmission 4. When switching elements A and B are switched on simultaneously, in the exemplary embodiment of the transmission 4 considered, Fig. 1, the variable X has a value equal to -1.1, while Y is equal to -2.1. In contrast, when switching elements A and C are switched on simultaneously, X is equal to -0.739, while Y is again equal to -2.1.

[0155] In the present case, a favorable differential speed value between the switching element halves of the further positive-locking switching element F is determined via the formulaic relationship at time T153 for closing the further positive-locking switching element F, and the further positive-locking switching element F is transferred to its closed operating state by correspondingly increasing the actuation pressure p_F of the further positive-locking switching element F. At the same time, the actuation pressure p_C or p_B of the frictionally engaged switching element C or B is increased from time T153 in the Fig. 4 and reduced to zero by a time T154. The activation of the additional positive-locking switching element F and the subsequent deactivation of the frictional-locking switching element C or B causes the turbine speed n_t to initially adjust to the curve of the product n_ab * i_zielgang_sas and, from time T154, to return in the direction of the engine speed n_mot.

[0156] The change from the second gear ratio sub-range to the first gear ratio sub-range of the transmission 4 is thus implemented in a simple manner without additional measures while the sailing operating state of the vehicle drive train 1 is still activated. With increasing operating time t, starting from the operating state of the vehicle drive train 1 present at time T154, a further sailing operating state with a decreasing output speed n_ab can be carried out without further actuation of the transmission 4 and can also be deactivated with a high degree of spontaneity, since a possibly requested build-up of frictional connection in the area of ​​the transmission 4 between the drive engine 2 and the output 3 can then be implemented within short operating times by engaging the frictionally engaged shifting element B, C or D without additional actuation of the positively engaged shifting elements A and F.

[0157] In the present case, such a request is made at time T155, from which the actuating pressure p_C or p_B of the frictionally engaged switching element C or B is set to the extent shown via a rapid filling phase and a subsequent filling equalization phase, initially up to a time T156, for switching on the switching element C or B. Following time T156, the actuating pressure p_C or p_B is again raised, for example via three successive pressure ramps, up to a time T157 to a level at which the frictionally engaged switching element C or B is in a slip-free operating state and the actuating pressure p_C or p_B is raised to the closing pressure level of the frictionally engaged switching element C or B at time T157.

[0158] Alternatively, it is also possible for a vehicle equipped with the vehicle drive train 1 to roll towards a standstill from time T155 and for the vehicle drive train to be operated according to an engine start-stop function when the vehicle is at a standstill or already close to a standstill, and for the two positive-locking shift elements A and F to be engaged in the transmission 4 and for the other shift elements C, D, B and E to be in the open state. When the vehicle is at a standstill, the drive motor 2, which is decoupled from the output 3, is then switched off and, when requested, switched on for the vehicle to start moving, and for the shift element D, C, B or E, which is to be switched on to represent the requested starting ratio "1", "2", "3" or "4" for forward travel, to be switched on.

[0159] The above-described gear adjustment of the additional positive shifting element F takes place at virtually constant speeds n_mot and n_t of the drive motor 2 and the transmission input shaft 6, with a simultaneously changing speed n_ab of the output 3, whereby the additional positive shifting element F transitions to its synchronous state. To avoid perceptible reaction torques in the vehicle drive train 1 by the driver, the previously actuated shifting element C or B is deactivated after the additional positive shifting element F is closed.

[0160] The use of the additional positive-locking shift element F as a force-locking clutch is possible due to the almost load-free operating state of the additional positive-locking shift element F, which in turn results from the low torque transmitted via the hydrodynamic torque converter 7 while the torque converter lock-up clutch 8 is simultaneously open. During the determination of the synchronization point of the additional positive-locking shift element F to be engaged, the transmission capacity of the torque converter lock-up clutch 8 is adjusted such that the rotational speeds n_mot and n_t of the drive motor 2 and the transmission input shaft 6 correspond and in order to transfer the additional positive-locking shift element F into an operating state favorable for engagement.

[0161] Fig. 9 shows the curves of the operating variables of the vehicle drive train 1 according to Fig. 7 and Fig. 8 during an operating state curve of the vehicle drive train 1, in which the seventh gear ratio "7" for forward travel is engaged in the area of ​​the transmission 4 at a time T158 and the drive motor 2 is engaged. At time T158, the speed n_mot of the drive motor 2 is greater than the idling speed n_motLL of the drive motor 2 and a request is made to display the coasting operating state of the vehicle drive train 1, during which the drive motor 2 is engaged and the power flow between the drive motor 2 and the output 3 is interrupted in the area of ​​the transmission 4. From a time T159, the frictionally engaged switching element E is transferred to its open operating state to the same extent as from time T131, which the frictionally engaged switching element E has in this case at time T160. The engine speed n_mot is reduced towards the idle speed n_motLL and also reaches this at time T160.Due to the opened frictional switching element E, the power connection between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is separated, which is why the turbine speed n_t also drops towards the idle speed n_mot.

[0162] As the operating time t increases, the higher-level driving strategy detects that the vehicle drive train 1 is in an operating state at a time T161 in which, when there is a request to deactivate the sailing operating state in the area of ​​the transmission 4, the sixth gear ratio “6” or the fifth gear ratio “5” is to be engaged for forward travel. For this reason, the actuating pressure p_D of the frictionally engaged switching element D is suddenly reduced from the closing pressure level to an intermediate pressure level at time T161 and then continuously reduced along a pressure ramp up to a time T162 and reduced to zero at time T162. At the same time, the actuating pressure p_C or p_B of the frictionally engaged switching element C or B is raised to the rapid filling pressure level at time T161 and reduced to the level of the filling equalization pressure at a subsequent time T163.p_B remains at this level until a time T164.

[0163] Time T164 represents the end of the fill equalization phase of the frictional switching element C or B. From time T164, the actuating pressure p_C or p_B of the frictional switching element C or B is again increased, in this case, by way of example, via three successive pressure ramps up to time T162 to a pressure level at which the frictional switching element C or B is in a slip-free operating state. At time T162, the actuating pressure p_C or p_B is increased to the closing pressure level, whereby the frictional switching element C or B, in addition to the positive switching element A, is in the closed operating state.Starting from time T162, a change takes place on the software side in transmission 4 from the operating state of transmission 4 prepared for engagement of the fifth gear ratio “5” for forward travel to the operating state of transmission 4 prepared for engagement of the fourth gear ratio “4”, without any change in the clutch logic being made for this purpose.

[0164] At time T165, the higher-level driving strategy detects that when exiting coasting mode of vehicle drivetrain 1 in the area of ​​transmission 4, the second gear ratio "2" for forward travel must be engaged, which is why the actuation pressure p_B of frictional shifting element B is reduced to an intermediate pressure level at time T165, at which time the frictional shifting element B transitions to slip mode. At the same time, the actuation pressure p_C of frictional shifting element C is raised to the level of the rapid fill pressure and maintained at this level until time T166. Starting from time T165 to time T167, the actuation pressure p_B of frictional shifting element B is continuously reduced along a pressure ramp.After the fill equalization phase, which in this case ends at time T168, the actuating pressure p_C is increased during two subsequent pressure ramps up to time T167 to a pressure level at which the frictional switching element C is in a slip-free operating state. For this reason, the actuating pressure p_C is increased to the closing pressure level at time T167, while the actuating pressure p_B is reduced to zero at time T167.

[0165] At a time T169, the higher-level driving strategy determines an operating state of the vehicle drive train at which the first gear ratio "1" for forward travel is to be engaged when the coasting operating state is deactivated in transmission 4. Therefore, at time T169, the frictional switching element p_C is deactivated to the same extent as the frictional switching element B between times T165 and T170, and the frictional switching element D is transferred between times T169 and T170 via a rapid filling phase and a subsequent filling equalization phase as well as via a pressure ramp into its slip-free operating state and at time T170 into its fully closed operating state.

[0166] Thus, at time T170 in transmission 4, both shift element A and shift element D are closed. At time T171 following time T170, a request is made to deactivate the sailing operating state and to couple the drive motor 2. From time T171 onwards, the drive motor 2 is again in speed control mode and the engine speed n_mot is again increased according to the EGS engine target speed specification until the engine speed n_mot at time T172 is equal to the curve of the product n_ab * i_zielgang_sas. In this operating state, the further positive-locking shift element F is in its synchronous operating state, which is why the actuation pressure p_F of the further positive-locking shift element F in the Fig. 5, and the further positive shift element F is transferred to its closed operating state to the requested extent, whereby the first gear ratio "1" for forward travel is engaged in the transmission 4. The speed control mode of the drive motor 2 is terminated at time T173, whereby the coasting operating state of the vehicle drive train 1 is deactivated and subsequent shifts in the transmission 4 can be carried out using conventional shift sequences depending on the operating state.

[0167] The activation time of the further positive-locking switching element F to be activated is calculated from the gradient of the speed n_mot of the drive machine 2 as a function of a so-called switching time lead calculation, wherein the activation of the positive-locking switching element F is started at a time at which the engine speed n_mot is greater than or equal to the profile of the product n_ab * i_zielgang_sas and the differential speed in the area of ​​the opened further positive-locking switching element F is less than a threshold value. Fig. 9, the claw switching element F can be easily converted into its synchronous operating state by varying the engine speed n_mot.

[0168] If during the Fig. 8 described sequence for engaging the further positive shifting element F, the output speed changes with such a gradient that the synchronization point of the further positive shifting element F cannot be reached or set to the required extent with the current operating state of the transmission 4, it is provided to change the clutch logic at an early stage and to preparatorily engage the frictional shifting element C or the frictional shifting element D in the transmission 4 in addition to the positive shifting element A instead of the shifting element B in order to achieve a claw differential speed of at least approximately zero in the area of ​​the further positive shifting element F to be engaged while the drive motor 2 is simultaneously operated at the idle speed level.

[0169] In the Fig. 8, during which the operating state of the vehicle drive train is waited for, at which the turbine synchronous speed of the desired synchronization gear corresponds to the engine idle speed, an adjustment of the synchronization gear and the associated selection of a suitable speed window, within which the positive switching element F is in its synchronous operating state, prevents this speed window from being missed when the vehicle rolls to a stop and a brief effect on the output 3 occurs.

[0170] However, if the synchronization point of the positive switching element is in the respective Fig. 8 and Fig. 9 described extent cannot be reached or the synchronization point of the further positive switching element F to be connected can only be reached after an undesirably long operating time by means of one of the two procedures according to Fig. 8 or Fig. 9, the figures based on the illustrations in accordance with Fig. 10 and Fig. 11 procedures described in more detail below.

[0171] At a time T174, the sailing mode of vehicle drivetrain 1 is activated and only the positive shift element A is closed. The engine speed n_mot corresponds to the idle speed n_motLL. Due to the interrupted power transmission between the prime mover 2 and the output 3 in the area of ​​transmission 4, the turbine speed n_t is equal to the engine speed n_mot. The curve of the product n_ab * i_zielgang_sas lies above the idle speed n_motLL and decreases with a defined gradient. At time T175, the higher-level driving strategy recognizes that if sailing is aborted in transmission 4, the sixth gear ratio "6" or the fifth gear ratio "5" must be engaged for forward travel.

[0172] For this reason, at time T175, the actuating pressure p_C or p_B of the frictionally engaged switching element C or B is set for the activation of the switching element C or B via a rapid filling phase lasting until time T176 and a subsequent filling equalization phase ending at time T177. From time T177, the actuating pressure p_C or p_B is increased via three successive pressure ramps up to time T178 to the pressure level at which the frictionally engaged switching element C or B is in a slip-free operating state. Subsequently, the actuating pressure p_C or p_B is guided to its closing pressure level at time T178, and the frictionally engaged switching element C or B is in a fully closed operating state.The output speed n_ab and thus also the curve of the product n_ab * i_zielgang_sas decrease with a large gradient from time T178 due to a strong deceleration of the vehicle, which results, for example, from the driver applying the service brake.

[0173] Depending on the currently selected clutch logic, the differential speed of the positive shift element F to be engaged is determined using the formulaic relationship listed above, and it is determined that neither the Fig. 8 still with the Fig. 9, the further positive-locking switching element F can be transferred to its closed operating state. For this reason, at time T179, the actuating pressure p_E of the positive-locking switching element E is raised to the level of the rapid filling pressure and at time T180, it is lowered to the filling compensation pressure level. The filling compensation phase of the frictionally engaged switching element E ends, for example, at time T181. Subsequently, the actuating pressure p_E is raised to an intermediate pressure level during a first pressure ramp with a large gradient and is further raised during a further pressure ramp following at time T182, the gradient of which is smaller than the gradient of the first pressure ramp ending at time T182.

[0174] At time T183, the frictional shifting element E has a transmission capability at which the sixth gear ratio “6” or the fifth gear ratio “5” for forward travel is at least partially engaged due to the positive shifting element A already in the closed operating state and the frictional shifting element C or B also being engaged in the transmission 4.Starting from this operating state of the vehicle drive train 1, at which the turbine speed n_t corresponds at least briefly to the curve of the product n_ab * i_zielgang_sas, the transmission capacity is varied by appropriately adjusting the actuation pressure p_E of the frictionally engaged switching element E such that the curve of the turbine speed n_t and the curve of the product n_ab * i_zielgang_sas correspond at least approximately to one another over a longer operating time and the further positively engaged switching element F to be switched on has its synchronous operating state at time T184.For this reason, the actuation pressure p_F of the further positive-locking switching element F is increased at time T184 and a downshift is carried out in the transmission 4 starting from the sixth gear ratio “6” or starting from the fifth gear ratio “5” for forward travel in the direction of the third gear ratio “3” or in the direction of the second gear ratio “2”, whereby the further positive-locking switching element F is transferred to the requested closed operating state.

[0175] In order to be able to engage the further positive switching element F to the extent required for a high level of driving comfort, it is possible to set the actuation pressure p_E of the frictional switching element E from a time T185 in the Fig. 6 and to increase the transmission capacity of the frictional switching element E. With this measure, the gradient of the turbine speed n_t is reduced and the differential speed of the positive switching element F is kept over a longer period of time within a differential speed window required for the activation of the further positive switching element F.

[0176] The synchronization point of the further positive switching element F to be engaged may not be in the position to be Fig. 8 and Fig. 9 is achieved. In order to be able to transfer the positive switching element F to the required extent into its switched operating state with high spontaneity, the following Fig. The procedure described in section 11 is carried out when the driver requests a corresponding load.

[0177] At time T186, the coasting operating state of vehicle drivetrain 1 is again activated, and only the positive shift element A is in the closed operating state. The turbine speed n_t and the engine speed n_mot correspond to one another due to the interrupted power transmission between the prime mover 2 and the output 3 in the area of ​​the transmission 4. The engine speed n_mot is equal to the idle speed n_motLL, while the output speed n_ab is at a level such that the product of the output speed n_ab and the gear ratio i_zielgang_sas is greater than the engine idle speed n_motLL.

[0178] Again at time T187, the higher-level driving strategy determines, depending on the current operating state of the vehicle drivetrain 1, that when a request to deactivate the coasting operating state in the transmission 4 is made, the sixth gear ratio "6" or the fifth gear ratio "5" or the third gear ratio "3" for forward travel in the transmission is to be engaged. This results in the actuating pressure p_C or p_B of the frictional shift element C or B being set for the engagement of the frictional shift element C or B during a rapid fill phase and a subsequent fill equalization phase, which in this case ends at time T188. From time T188, the actuating pressure p_C or p_B is increased during three successive pressure ramps up to time T189 to a pressure level at which the frictional shift element C or B is in a slip-free operating state.

[0179] The actuation pressure p_C or p_B is raised to the closing pressure level at time T189 and the frictional switching element C or B next to the switching element A is transferred to its closed operating state. At a time T190 following time T189, a driver-side load request occurs, which causes the engine speed n_mot to increase from the idling speed n_motLL. Depending on the gradient of the engine speed n_mot, it is determined that switching on the additional positive switching element F is not possible without further measures, since the curve of the engine speed n_mot intersects the curve of the product n_ab * i_zielgang_sas at a large angle and actuation of the additional positive switching element F in the closing direction does not result in the desired switching on of the positive switching element F.

[0180] For this reason, at time T190, the actuation pressure p_E of the frictional shift element E is raised to the level of the rapid filling pressure and at time T191 is reduced to the filling compensation level. At time T192, the filling compensation phase is ended and the actuation pressure p_E is raised up to a first pressure ramp ending at time T193 and via a second pressure ramp extending to time T194, the gradient of which is smaller than the gradient of the first pressure ramp ending at time T193, to a pressure level at which the frictional shift element E has a transmission capacity such that the sixth gear ratio "6" or the fifth gear ratio "5" is at least partially engaged in the transmission 4. Following this, the actuation pressure p_E of the frictional shift element E is reduced from a time T195 along a steep pressure ramp ending at time T196.From time T196, the actuation pressure p_E is slightly reduced along a further pressure ramp with a flat gradient until time T197. This actuation of the frictionally engaged switching element E, in turn, causes the turbine speed n_t to adjust to the curve of the product n_ab * i_zielgang_sas until time T198 before time T197, and the additional positive-locking switching element F to be engaged is at its synchronization point and can be transferred to its closed operating state by increasing the actuation pressure p_F.

[0181] In order to be able to conveniently switch on the further positive switching element F, it is possible to set the actuating pressure p_F from a time T199 in the Fig. 10 to temporarily slightly increase the extent described above in order to adjust or flatten the gradient of the turbine speed n_t to an extent that is favorable for the connection process of the further positive switching element F.

[0182] Fig. Figure 12 shows several curves of various operating variables of the vehicle drive train 1 over time t. The vehicle drive train is in a Fig. 12, in a sailing operating state at which the speed n_mot of the drive motor 2 is zero and the power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is interrupted. The course of the product of the speed n_ab of the output 3 and the gear ratio i_zielgang_sas, which corresponds to a gear ratio determined as a function of the current operating state by means of a higher-level driving strategy and which is to be engaged in the transmission 4 when sailing is stopped or which is equal to the gear ratio currently engaged in the area of ​​the transmission 4 when the power flow is established between the drive motor 2 and the output 3 in the area of ​​the transmission 4, is greater than 0 and less than the idle speed n_motLL of the drive motor 2. The course of the product n_ab * i_zielgang_sas in the Fig. 12 shown in more detail over the operating time t with a steep gradient towards 0.

[0183] In transmission 4, at time T70, the positive-locking shift element A is initially closed, whereby the positive-locking shift element A is actuated in the closing direction with an actuation pressure p_A corresponding to the closing pressure level. In addition, the frictional-locking shift element C is also in the closed operating state at time T70 and is also actuated in the closing direction with an actuation pressure p_C corresponding to the closing pressure level. The other frictional-locking shift element E is fully open because the actuation pressure p_E that can be applied to the frictional-locking shift element E is zero.In addition, the frictional switching element B is subjected to an actuation pressure p_B, which has a pressure level that is an offset value above the pressure value pf_min + Hys plus a hysteresis-dependent offset value, which represents an actuation threshold above which the frictional switching elements B, C, and D have a slip-free operating state when the coasting operating state is activated. The additional frictional switching element F is also subjected to an actuation pressure p_F, which is why the additional frictional switching element F is also open.

[0184] Due to the deactivated drive motor 2 and the interrupted power flow in the area of ​​the transmission 4, the turbine speed n_t is zero. This operating state of the transmission 4 also results from the fact that, in addition to the frictional shift elements B and C, the frictional shift element D is subjected to an actuation pressure p_D that is above the pressure value pf_min + Hys.

[0185] At a time T71, a pressure ramp of the actuation pressure p_D of the frictional shifting element D ends, and the frictional shifting element D is in a slip-free operating state. In order to transfer the transmission 4 at time T71 into an operating state in which, in addition to the positive shifting element A, the frictional shifting element D is also fully closed in the transmission 4, the actuation pressure p_D is abruptly increased from the intermediate pressure level at time T71 to the closing pressure level. Essentially at the same time, the actuation pressure p_C of the frictional shifting element C is reduced from the closing pressure level to a pressure level that is an offset value above the pressure value pf_min + Hys, at which the frictional shifting element C still has a slip-free operating state.As the operating time t increases, the higher-level driving strategy detects that the output speed n_ab decreases towards zero and the vehicle comes to a standstill.

[0186] In order to be able to start the vehicle equipped with vehicle drive train 1 from a standstill with the desired high degree of spontaneity upon a corresponding driver request, a request to activate an engine start-stop function is issued at a time T72, which simultaneously deactivates the coasting function of vehicle drive train 1 and issues a request target_gear_sas = "1" to prepare transmission 4 for engagement of the first gear ratio "1" for forward travel. Activating the engine start-stop function results in a synchronization point of the additional positive-locking switching element F being determined depending on the gradient of the product n_ab * i_target_gear_sas, which, due to the activated engine start-stop function, is to be transferred to its closed operating state alongside the positive-locking switching element A.

[0187] In this case, it is determined that the additional positive-locking switching element F reaches its synchronization point required for engagement at time T73, which is why the actuating pressure p_F of the frictionally engaged switching element F is suddenly increased to the closing pressure level at time T73. The actuating pressure p_D of the frictionally engaged switching element D is reduced at time T73 to a pressure level that is an offset value above the pressure value pf_min + Hys. At time T74, the curve of the product n_ab * i_zielgang_sas is zero and the vehicle is at a standstill. At the same time, the closed operating state of the frictionally engaged switching element F is detected at time T74. Up to time T75, the vehicle is at a standstill with the engine start-stop function activated and the drive motor 2 is in the switched-off operating state.For this reason, the switching elements A to F are actuated or subjected to the pressure levels of the actuating pressures p_A to p_F present at time T74. At time T75, a request is made to engage the drive motor 2 and to couple the drive motor 2 to the output 3. For this reason, the engine speed n_mot increases to the extent shown toward the idle speed n_motLL.

[0188] Depending on the gear ratio “1”, “2” or “3” to be engaged in the gearbox 4 for forward travel, either the actuation pressure p_D, p_C or p_B of the frictional switching element D, C or B is Fig. 3, from time T75 to time T76, the pressure is initially raised to an intermediate pressure level at which the frictional switching element D, C or B is in the closed operating state. When the intermediate pressure level is reached at time T76, the actuating pressure p_D, p_C or p_B is suddenly raised to the closing pressure level, as a result of which, in addition to the two positive switching elements A and F, the frictional switching element D, C or B is additionally switched on in the transmission 4, and the gear ratio "1", "2" or "3" is engaged in the transmission.

[0189] In order not to impair the starting process of the drive machine 2, at time T75, depending on the gear ratio "1", "2" or "3" to be engaged in the transmission 4, the actuating pressures p_B and p_C, p_B and p_D or p_C and p_D are reduced from the pressure level above the pressure value pf_min + Hys to zero, whereby the partial blocking state of the gear set 5 of the transmission 4, in which the transmission input shaft 6 is held in a rotationally fixed manner, is removed. As the engine speed n_mot increases, the turbine speed n_t also increases from time T75 over the operating time t. In addition, the curve of the product n_ab * i_zielgang_sas also increases from time T77, whereby the turbine speed n_t is above the curve of the product n_ab * i_zielgang_sas.The deviation between the turbine speed n_t and the curve of the product n_ab * i_zielgang_sas results from a slip modulation in the area of ​​the frictional shift element D, C, or B to be engaged, which improves drivetrain comfort during engine start-up of the prime mover 2. At a time T78, the turbine speed n_t is equal to the curve of the product n_ab * i_zielgang_sas, since the frictional shift element D, C, or B to be engaged has already reached its slip-free operating state.

[0190] Depending on the respective driver request, the engine speed n_mot remains at the level of the idle speed n_motLL from a time T79 or increases increasingly, for example, according to the dashed line curve of the engine speed n_mot1.

[0191] Fig. 13 shows the Fig. 12 illustrates the curves of the operating variables of the vehicle drive train 1, starting from time T70 during an operating state curve of the vehicle drive train 1, during which it is determined at time T74 that the positive-locking switching element F is not transferred to its closed operating state to the desired extent by increasing the actuation pressure p_F. For this reason, at a further time T80 following time T74, the actuation pressure p_F of the positive-locking switching element F is reduced back to zero. Irrespective of this, from time T74 onwards, the engine start-stop function is activated and the coasting function of the vehicle drive train 1 is deactivated.

[0192] Depending on the gear ratio “1”, “2” or “3” to be engaged in the transmission 4 when the drive motor 2 is restarted for forward travel, at time T80 either the actuating pressure p_D, p_C or p_B of the frictional switching element D, C or B is raised from the pressure level above the pressure value pf_min + Hys to the closing pressure level, while the actuating pressures p_B and p_C, p_B and p_D or p_C and p_D of the frictional switching elements B and C or B and D or C and D are reduced to zero.

[0193] Since the vehicle equipped with the vehicle drive train 1 is at a standstill from the time T74 and the course of the product n_ab * i_zielgang_sas is equal to zero, the synchronization point of the positive shift element F to be engaged is in the Fig. 12 can no longer be achieved from time T73 onwards and the positive switching element F cannot be transferred to its closed operating state to the desired extent.

[0194] In order to be able to engage the respective gear ratio "1", "2" or "3" to be engaged in the transmission 4 with a high degree of spontaneity when the drive motor 2 is restarted, the actuating pressure p_E of the frictionally engaged switching element E is raised from the opening pressure level to the pressure level of the rapid filling pressure at a time T81 before a request for the engagement of the drive motor 2 and the coupling of the drive motor 2 to the output 3. The rapid filling phase of the frictionally engaged switching element E ends at a time T82, which is why the actuating pressure p_E is reduced to the pressure level of the filling equalization pressure and is left constant at this pressure level until the end of the filling equalization phase, in this case until time T83.Subsequently, the actuation pressure p_E is increased to an intermediate pressure level via a first pressure ramp lasting until a time T84, and then further increased along a second pressure ramp whose gradient is smaller than the gradient of the first pressure ramp ending at time T84. At a time T85, which simultaneously represents the end of the second pressure ramp, a request is issued to engage and couple the drive motor 2, which is why the engine speed n_mot increases from time T85 onward to the extent shown toward the idle speed n_motLL.

[0195] In order for the positive-locking switching element F to be switched into its closed operating state, the actuating pressure p_E is increased with a steep gradient from time T85 to a further intermediate pressure level, thereby increasing the transmission capacity of the frictionally engaged switching element E. The increase in the transmission capacity of the frictionally engaged switching element E causes both the curve of the product n_ab * i_zielgang_sas and the turbine speed n_t to increase from time T86. From time T87, the actuating pressure p_E of the frictionally engaged switching element E is again reduced with a steep gradient to the extent shown in order to reduce a differential speed in the area between the switching element halves of the frictionally engaged switching element F.Since the curve of the turbine speed n_t increasingly approaches the curve of the product n_ab * i_zielgang_sas over the operating time t, the actuating pressure p_E of the frictional switching element E is further reduced from a time T88 along a further pressure ramp whose gradient is smaller than the gradient of the pressure ramp provided between the times T87 and T88.

[0196] At a time T89, the turbine speed n_t essentially corresponds to the curve of the product n_ab * i_zielgang_sas, and it is detected that the positive-locking switching element F is in an operating state favorable for engagement. This results in the actuating pressure p_F being abruptly increased to the closing pressure level at time T89 to the extent shown, while the actuating pressure p_E of the frictionally engaged switching element E is reduced toward zero, and the frictionally engaged switching element E is transferred to its fully open operating state.

[0197] Due to the actuation of the frictional shifting element E described between times T81 and T89, in order to synchronize the positive shifting element F to be engaged, either the fifth gear ratio "5", the sixth gear ratio "6" or the seventh gear ratio "7" is engaged in the transmission 4, depending on the operating state of the transmission 4 at time T74, at least partially to synchronize the positive shifting element F, and then a downshift is carried out in the transmission 4, starting from the seventh gear ratio "7", the sixth gear ratio "6" or the fifth gear ratio "5" in the direction of the gear ratio "1", "2" or "3" to be engaged in the transmission 4, during which the positive shifting element F is engaged alongside the further positive shifting element A and the frictional shifting element D, C or B already engaged at time T80.

[0198] Fig. 14 again shows several curves of different operating variables of the vehicle drive train 1 over time t, wherein the vehicle drive train 1 is in a Fig. 14, the vehicle is in an operating state at which the two positive-locking switching elements A and F in the transmission 4 are closed, while the other frictionally engaged switching elements B, C, D, and E are in the open operating state and the drive motor 2 is switched off. The MSF curve has the value zero throughout the entire observed operating state curve of the vehicle drive train 1, since the engine stop enable is activated.

[0199] This operating state of the vehicle drive train 1 is established due to the activation of an engine start-stop function, via which the drive motor 2 is decoupled from the output 3 when the vehicle is stationary by opening the frictional switching elements B to E and the two positive switching elements A and F are kept in the closed operating state in order to be able to represent one of the gear ratios "1" to "4" for a start-up process of a vehicle equipped with the vehicle drive train 1 with high spontaneity, since in the transmission 4 one of these gear ratios can then be engaged within a short operating time by switching on the switching element D, the switching element C, the switching element B or the switching element E. Due to the fact that the output speed n_ab of the output 3 is greater than zero, the Fig. 14, where the variable i_zielgang_sas in turn corresponds to the gear ratio to be engaged in transmission 4 when exiting the engine start-stop function.

[0200] Due to drag torques within the transmission, the speed n_t of the transmission input shaft 6 is greater than zero. At a time T101, it is detected within a higher-level driving strategy that the clutch logic currently selected by the activated engine start-stop function is causing undesirably high drag torques in the transmission area due to the determined ratio between the turbine speed n_t and the output speed n_ab of the output 3. For this reason, a request is issued to implement a coasting mode function of the vehicle drivetrain 1, during which, depending on the current operating state of the vehicle drivetrain 1, the positive-locking switching element F is first to be transferred to its open operating state.

[0201] For this purpose, at time T101, an actuation pressure p_F of the positive-locking switching element F is abruptly reduced from the closing pressure level to zero. At a time T102 shortly thereafter, the open operating state of the positive-locking switching element F is detected while the positive-locking switching element A is simultaneously closed. Additionally, with the coasting function activated, an operating state of the vehicle drive train 1 is determined at which, upon deactivation of the coasting function in the transmission 4, the third gear ratio "3" for forward travel is to be engaged. Therefore, an actuation pressure p_B of the frictionally engaged switching element B is increased to a rapid-fill pressure level at time T102 and maintained at this pressure level until time T103.At time T103, the actuating pressure p_B of the frictional switching element B is abruptly reduced to the pressure level of the filling compensation pressure and is again left constant at this pressure level until the end of the filling compensation phase, in this case until a time T105.

[0202] Subsequently, the actuating pressure p_B is increased via two consecutive pressure ramps up to a time T106 to an intermediate pressure level at which the frictional switching element B is in its slip-free operating state. Upon reaching this operating state of the frictional switching element B, the actuating pressure p_B of the frictional switching element B is increased to the closing pressure level, whereby the frictional switching element B is completely closed.

[0203] In order to be able to transfer the positive switching element F to its open operating state to the desired extent at time T101, in a design of the transmission 4 in which the positive switching element F is subjected to hydraulic pressure for opening, it is possible to raise a system pressure of the transmission and to transfer a possibly installed electrical auxiliary oil supply to a higher power point if the actuating pressure p_F to be applied to the positive switching element F to be opened and acting in the opening direction depends on the system pressure or the electrical auxiliary oil supply designed as an electrical auxiliary pump.

[0204] During the fill equalization phase of the frictional switching element B, at a time T107, which in this case lies between times T103 and T105, an actuating pressure p_C of the frictional switching element C is raised to the rapid fill pressure level and maintained at this pressure level until the end of the rapid fill phase at time T108. At time T108, the actuating pressure p_C of the frictional switching element C is reduced to the fill equalization pressure level and maintained at this pressure level until time T106, at which time the frictional switching element B is transferred to its closed operating state. From time T106, the actuating pressure p_C of the frictional switching element C is also transferred to its slip-free operating state via two successive pressure ramps and transferred to its fully closed operating state by raising the actuating pressure p_C at time T109.

[0205] In addition, during the fill compensation phase of the frictional switching element C, an actuation pressure p_D of the frictional switching element D is raised to the rapid fill pressure level at a time T110 between times T108 and T106, and the actuation pressure p_D of the frictional switching element D is lowered to the fill compensation pressure level at a time T111 between times T106 and T109. The fill compensation phase of the frictional switching element D ends at a time T112, and the actuation pressure p_D is raised at time T112 via two pressure ramps up to time T113 to an intermediate pressure level, at which the frictional switching element D is also in a slip-free operating state.Upon reaching this operating state, the actuation pressure p_D of the frictional shift element D is again raised to the closing pressure level, whereby, in addition to the shift elements A, B, and C, the frictional shift element D is also in its fully closed operating state. When the frictional shift elements C, D, and E are in the closed operating state, the gear set 5 of the transmission 4 exhibits the partially locked operating state, in which the transmission input shaft 6 is held in a rotationally fixed manner and the transmission output shaft 9 connected to the output 3 is rotatable. For this reason, the turbine speed n_t decreases continuously toward zero starting at time T105.

[0206] Since the frictional switching element D is also transferred to its closed operating state at time T113, the sailing operating state of the vehicle drive train 1 requested at time T101 is activated to the desired extent at time T113.

[0207] In contrast to the previously described filling sequence of the frictional switching elements B, C and D, starting from an operating state of the vehicle drive train 1 at time T101, at which, when exiting the sailing mode function in the transmission 4 as the target gear according to the request zielgang_sas, the second gear ratio "2" for forward travel to establish the power flow between the drive engine 2 and the output 3, starting from the positive switching elements A and F in the closed operating state, first the frictional switching element C is transferred from time T102 to the extent corresponding to the actuation of the frictional switching element B into its closed operating state and already during the filling equalization phase of the frictional switching element C, the frictional switching element D instead of the frictional switching element C is prepared for engagement from time T107 to the extent described.Subsequently, instead of the frictional switching element D, the frictional switching element B is finally transferred into its closed operating state from time T111 to time T113.

[0208] In contrast, if an operating state of the vehicle drive train 1 exists at the time T101 at which the first gear ratio "1" for forward travel is to be engaged when the sailing operating state is deactivated in the transmission 4, first the switching element D, then the switching element C and then again the switching element B are each transferred to their closed operating state in order to achieve the advantages described later when exiting the sailing operating state of the vehicle drive train 1 during the activation of the sailing operating function between the times T101 and T113.

[0209] In the event that the positive switching element F is not in its open operating state despite corresponding actuation at time T102 or in the area of ​​the transmission 4 such high drag torques are determined by the higher-level driving strategy that a Fig. 3 described opening of the positive switching element, is described below to Fig. 4 is carried out in order to transfer the positive switching element F to its open operating state to the desired extent.

[0210] The one in Fig. 15 described curves of the operating variables of the vehicle drive train 1 according to Fig. 1 is based on an operating state curve at the time T102 of the vehicle drive train 1 which, except for the fact that in the area of ​​the transmission 4, higher drag torques are present at the positive shift element F than in the operating state of the vehicle drive train 1 at the time T102 according to Fig. 14. For this reason, the sailing mode is activated from time T102 according to Fig. 15 the frictional switching element B by increasing the actuating pressure p_B accordingly in the Fig. 4, a rapid filling pulse is applied to the frictional switching element E until time T104 and at time T104 is reduced to the level of the filling equalization pressure. Furthermore, at time T104, the frictional switching element E is subjected to a rapid filling pulse by increasing its actuating pressure p_E up to a time T114 and, during a subsequent filling equalization phase lasting until a time T115, is actuated with an actuating pressure p_E having a filling equalization pressure level and is thus prepared for activation. At time T115, the frictional switching element E has an operating state in which the transmission capacity of the frictional switching element E is essentially zero and an increase in the actuating force results in an immediate increase in the transmission capacity of the frictional switching element E.

[0211] In addition, the actuating pressure of the positive-locking switching element F to be switched off is reduced to zero shortly after time T114. From time T115, the actuating pressure p_E is increased along a first pressure ramp ending at time T116. Subsequently, the actuating pressure p_E of the frictionally engaged switching element E is continuously increased further via a subsequent further pressure ramp, which in this case ends at time T117 and has a smaller gradient than the pressure ramp provided between times T115 and T116. Following this, the actuating pressure p_E is again increased to a greater extent along a further pressure ramp, the gradient of which is in turn greater than the gradient of the pressure ramp between the time periods T116 and T117, until finally, at time T118, the open operating state of the positive-locking switching element is determined.The successive increase in the transmission capacity of the frictional switching element E relieves the load on the frictional switching element F or reduces the torque applied to the frictional switching element F, which counteracts the desired opening of the frictional switching element F. At time T118, the torque applied to the positive switching element F is reduced to such an extent by increasing the transmission capacity of the frictional switching element E that the positive switching element F transitions to its open operating state.

[0212] Upon detection of the open operating state of the frictional switching element F, the actuation pressure p_E of the frictional switching element E is reduced from time T118 to the extent shown along a pressure ramp with a large gradient until time T119 to an intermediate pressure level below the fill compensation pressure level, whereby the frictional switching element E is in the open operating state at time T119 at the latest. At time T119, the actuation pressure p_E is reduced again to zero, whereby the frictional switching element E transitions to its completely deactivated operating state.

[0213] Shortly thereafter, the actuating pressure p_B of the frictional switching element B is increased at a time T120 starting from the filling compensation pressure level in Fig. 14, the pressure is raised along the two pressure ramps to the intermediate pressure level at which the frictional switching element B is in a slip-free operating state. In order to fully engage the frictional switching element B, the actuating pressure p_B is suddenly raised to the closing pressure level at time T121, whereby the frictional switching element B is fully engaged. In the engaged operating state of the frictional switching element B, the frictional switching element C is initially subjected to a rapid filling pulse starting at time T122 and is prepared for engagement during a filling equalization phase that follows and lasts until time T123. At time T124, the frictional switching element C is in its slip-free operating state, which is why the actuating pressure is raised again to the closing pressure level at time T124 to the extent described above.

[0214] Before the end of the fill equalization phase of the frictional switching element C, the frictional switching element D is also subjected to a rapid fill pulse starting at time T125 and is prepared for engagement during a subsequent fill equalization phase lasting until time T126. At time T127, the frictional switching element D also has its slip-free operating state, which is why the actuation pressure p_D of the frictional switching element D is raised to the closing pressure level at time T127, whereby the vehicle drive train 1 is in its requested coasting operating state at time T127.

[0215] If at time T102 the higher-level driving strategy detects that if the activation of the sailing operating state is aborted, the second gear ratio "2" is to be engaged instead of the third gear ratio "3" for forward travel, the actuation pressure p_C of the frictional switching element C is applied instead of the actuation pressure p_B of the frictional switching element B at time T102 in the Fig. 4. After the rapid filling phase of the frictional switching element C has ended, the actuating pressure p_E of the frictional switching element E is adjusted accordingly to relieve the positive switching element F. Furthermore, at time T122, the actuating pressure p_D of the frictional switching element D and subsequently at time T125, the actuating pressure p_B of the frictional switching element B are adjusted to the extent described above in order to transfer the switching elements C and D to their fully closed operating state at times T124 and T127, respectively.

[0216] If, in contrast, an operating state of the vehicle drive train 1 is determined at time T102, from which the first gear ratio "1" for forward travel is to be engaged if the activation of the sailing mode function in the transmission 4 is aborted, the frictional switching element D is initially used to the extent described above from time T102 onwards. Fig. 4 instead of the frictional switching element B or the frictional switching element C, before the frictional switching element E is guided into the power flow of the transmission 4 to relieve the positive switching element F. Subsequently, the frictional switching element C is again first guided towards its fully closed operating state and, during the engagement process of the frictional switching element C, the frictional switching element B is also guided towards its fully closed operating state from time T125 onwards in order to ultimately activate the sailing operating state of the vehicle drive train 1 to the desired extent at time T127.

[0217] In addition, the procedures described in more detail below can be called up via the higher-level driving strategy in order to operate or actuate the vehicle drive train 1 and in particular the transmission 4 when there is a request to activate the sailing operating state of the vehicle drive train 1 during the activation process in such a way that a sailing exit triggered by current operating state changes of the vehicle drive train 1 can be implemented with a high degree of spontaneity and, at the same time, a high degree of driving comfort.

[0218] If there is a corresponding request to deactivate the sailing mode function during an operating state of the vehicle drive train 1 according to Fig. 3 before the time T101, the two positive switching elements F and A are left in the engaged operating state and, depending on the gear ratio to be engaged in the area of ​​the transmission 4, the frictional switching element to be engaged for this purpose is engaged within short operating times with the desired high level of spontaneity and, at the same time, high driving comfort.

[0219] In contrast, the data already transferred before time T114 to Fig. 15, the switching elements B, C or D actuated to the extent described, as well as the frictional switching element E, are emptied again and the positive switching elements F and A are left in the engaged operating state if a request to deactivate the sailing operation function is issued before the time T114 and the frictional switching element to be engaged in order to represent the requested operating state of the vehicle drive train 1 is subsequently engaged or the frictional switching elements are kept in the open operating state when the engine start-stop function is activated.

[0220] If the request to deactivate the sailing mode function is made at a time when the positive switching element F is already actuated in the opening direction and has switched to its open operating state due to the actuation, one of the ratios "5", "6" or "7" for forward travel is initially engaged in the transmission 4, for the representation of which the further positive switching element F is to be kept in the open operating state or transferred into this.

[0221] If, during activation of the coasting operating state of the vehicle drive train 1, the transmission 4 is actuated due to a current operating state of the vehicle drive train 1 in such a way that in the transmission 4, when coasting is exited with high spontaneity, the third gear ratio "3" for forward travel can only be engaged by engaging the positive shifting element F, then, when a request for deactivation of the coasting operating function is present, the fifth gear ratio "5" is first engaged in the transmission 4 and then the positive shifting element F is transferred to its closed operating state during a downshift towards the third gear ratio "3" in accordance with a conventional shifting sequence. At the same time, the frictional shifting element E is disengaged during the downshift from the fifth gear ratio "5" towards the third gear ratio "3".Depending on the respective requested operating state, the frictional switching element B is maintained in the closed operating state or transferred to its open operating state. The latter is the case, for example, when the engine start / stop function is activated and a decoupled operating state of the deactivated drive motor 2 is requested.

[0222] The frictional shift element B is thus transferred to its closed operating state when the vehicle is stationary and the two other frictional shift elements C and D are transferred to their open operating state if they are already filled or closed. If the shift elements C and D are not yet filled or closed, the filling process for the frictional shift elements C and D is no longer started. In addition to the frictional shift element B, the frictional shift element E must be transferred to its closed operating state in order to engage the fifth gear ratio “5” in the transmission to the required extent and then to synchronize the positive shift element to be engaged during the downshift starting from the fifth gear ratio “5” towards the third gear ratio “3” and to transfer it to the closed operating state.

[0223] In contrast, the frictional switching element C is closed or held in its closed operating state, while the frictional switching elements D and B are held in their open operating states or are transferred to them when the request to deactivate the sailing mode function is made for an operating state of the vehicle drive train 1 from which the second gear ratio "2" for forward travel is to be engaged in the transmission 4.In contrast to the previously described sailing exit in the direction of the third gear ratio “3” for forward travel, when sailing exit in the direction of the second gear ratio “2” for forward travel, instead of the synchronization gear “5” in the gearbox representing the positive shift element F to be engaged, the sixth gear ratio “6” is first engaged as the synchronization gear, and then the positive shift element F is synchronized in the direction of the second gear ratio “2” during a downshift starting from the sixth gear ratio “6” and in the process is transferred to its closed operating state.

[0224] If, however, the first gear ratio "1" for forward travel is to be engaged in transmission 4 during a coasting exit, the frictional shift element D must be closed or held in its closed operating state, while the other two frictional shift elements C and B must be opened or held in their open operating states. Subsequently, the further frictional shift element E is transferred to its closed operating state in order to initially engage the seventh gear ratio "7" in transmission 4, which represents the so-called synchronization gear for the positive shift element F to be engaged.

[0225] Starting from the seventh gear ratio “7” for forward travel then engaged in the area of ​​the transmission 4, a downshift towards the first gear ratio “1” for forward travel is carried out by switching off the frictional switching element E and by closing the positive switching element F, whereby the operating state of the vehicle drive train 1 to be established by the requested coasting exit is present.

[0226] In addition, in the event of a request for a coasting exit due to a load request during the previously described filling sequence of the frictional shift elements B, E, C and D, a further procedure can be selected via the higher-level driving strategy, via which, depending on a possible new target gear specification and the time at which the target gear change takes place during the filling sequence of the frictional shift elements B, E, C and D, the filling sequence is aborted or the next clutch B, E, C and D to be closed is selected in such a way that, starting from the prepared operating state of the transmission 3, a larger downshift gear step is possible.

[0227] Thus, when coasting exit is requested and a target gear change is initiated, starting from the third gear ratio "3" toward the second gear ratio "2," the frictional shift element C is transferred to its closed operating state, and the frictional shift elements B and D are opened or their filling is omitted. Subsequently, the frictional shift element E is closed again to engage the synchronization gear or the sixth gear ratio "6," and the positive shift element F to be engaged is engaged during the downshift toward the second gear ratio "2."

[0228] If, due to a load requirement, there is a coasting increase with a target gear change starting from the third gear ratio "3" towards the first gear ratio "1" for forward travel, the frictional shift element D is transferred to its closed operating state or left in this state, while the frictional shift elements B and C are transferred to their fully open operating state or left in this state. In addition, the frictional shift element E is closed in order to engage the synchronization gear in transmission 4 for the positive shift element F to be closed or the seventh gear ratio "7" and then to transfer and close the positive shift element F into its synchronized operating state during the downshift towards the first gear ratio "1".

[0229] Fig. 16 shows several curves of various operating variables of the vehicle drive train 1 over time t, wherein the vehicle drive train 1 is in a Fig. 16, the vehicle is in an operating state at which the second gear ratio "2" is engaged in the transmission 4 and the speed n_mot of the drive motor 2 is greater than the idling speed n_motLL of the drive motor 2. At time T40, a check is carried out to determine whether the drive motor 2 is to be switched off via an engine start-stop function or via a coasting operation function. Based on the previous operating state history of the vehicle drive train 1, a request is made at time T40 to display the coasting operation state of the vehicle drive train 1, during which the drive motor 2 is switched off and the power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is interrupted.

[0230] The request for activation of the coasting operating state is made starting from an operating state of the vehicle drive train 1 in which the prime mover 2 is engaged and connected to the output 3 via the transmission 4. Furthermore, the speed n_ab of the output 3 is greater than zero, whereby the vehicle equipped with the vehicle drive train 1 is in an operating state close to a standstill. As already explained above, in addition to the two positive shift elements A and F, the frictional shift element C is engaged and the second gear ratio "2" for forward travel is engaged in the transmission 4, while the shift elements B, D and E are each in the open operating state. For this purpose, the shift elements A to F are subjected to the required actuating pressures p_A to p_F.

[0231] To activate the sailing operating state, from a time T41 onwards, the frictional switching element E is activated by increasing the actuating pressure p_E in the Fig. 16, a rapid filling pulse is applied up to a time T42 and, during a subsequent filling equalization phase lasting up to a time T43, is actuated with an actuating pressure p_E having a filling equalization pressure level and is thus prepared for activation. At time T43, the frictionally engaged switching element E has an operating state in which the transmission capacity of the frictionally engaged switching element E is essentially zero and an increase in the actuating force results in an immediate increase in the transmission capacity of the frictionally engaged switching element E.

[0232] In addition, from time T40, the speed n_mot of the drive machine 2 is increasingly guided towards the idling speed n_motLL to the extent shown. The increase in the transmission capacity of the frictionally engaged switching element E from time T43 along a pressure ramp lasting up to time T44 causes the positive-locking switching element F to transition to an at least approximately load-free operating state and, at time T45, which lies between times T43 and T44, to be abruptly reduced from a pressure value corresponding to the closed operating state of the positive-locking switching element F to a pressure value corresponding to the open operating state of the positive-locking switching element F by appropriately setting an actuating pressure p_F of the positive-locking switching element F.The engagement of the frictional switching element E causes the positive switching element F to be transferred to at least a load-free operating state. The positive switching element F reaches this operating state at the switch-off time T45.

[0233] From time T44, the actuation pressure p_E of the frictionally engaged shift element E is increased along a further pressure ramp, the gradient of which is smaller than the pressure ramp provided between times T43 and T44, up to a time T46. Starting from the pressure level of the actuation pressure p_E present at time T46, the actuation pressure p_E is increased to a higher pressure level up to a time T47 along a third pressure ramp, the gradient of which is in turn greater than the gradients of the two previous pressure ramps. At time T47, it is detected that a speed n_t of the transmission input shaft 6, which is also referred to below as the turbine speed, deviates from a product of the speed n_ab of the output 3 and the gear ratio i_zielgang_sas currently engaged in the transmission 4 at time T40.If the deviation between the turbine speed n_t and the product of the speed n_ab of the output 3 and the gear ratio i_target_sas exceeds the threshold value kfl, the separate power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is detected. This is the case at time T47.

[0234] At time T47, the sixth gear ratio "6" is at least partially engaged in the transmission 4 by the shift elements C and A present in the closed operating state and by the at least partially engaged frictional shift element E. Since, when the coasting operating state is activated, it is recognized that at the current operating point of the vehicle drive train 1, when the coasting operating state is left in the transmission 4, the third gear ratio "3" for forward travel is to be engaged in the transmission instead of the sixth gear ratio "6" for forward travel with increasing operating time t, and in order to achieve the most efficient operation of the vehicle drive train 1, the power flow in the transmission 4 between the drive motor 2 to be switched off and the output 3 is to be separated, the frictional shift element B is switched on in the manner shown in Fig. 16, it is prepared for switching on or closing via a rapid filling phase lasting until a time T49 and a subsequent filling equalization phase ending at a time T50.

[0235] At time T51 following time T49, the request to shut down drive engine 2 is issued, causing the speed n_mot of drive engine 2 to decrease toward zero. The corresponding request results from the MSF curve, which switches from 0 to 1 at time T51, thus activating the engine stop enable. Thus, at time T45, the coasting mode requested at time T40 is activated to the desired extent.

[0236] Shortly after the time T47, at which the open operating state of the positive switching element F is detected, the frictional switching element E is opened from a time T52, which lies between the times T48 and T49, in the manner shown in Fig. 16, the pressure is first lowered via a pressure ramp lasting until time T51 and then abruptly reduced to zero at time T51, whereby the frictional switching element E changes into its fully open operating state and the power flow between the drive motor 2 and the output 3 in the area of ​​the transmission 4 is separated.

[0237] At time T50, the frictional switching element B is in an operating state at which the transmission capacity of the frictional switching element B is essentially zero and an increase in the actuating force of the frictional switching element B or the actuating pressure p_B causes an immediate increase in the transmission capacity of the frictional switching element B. From time T50, the actuating pressure p_B of the frictional switching element B is increased in the manner shown via two successive pressure ramps up to a time T53 at which the frictional switching element B is in the slip-free operating state. For this reason, the actuating pressure p_B of the frictional switching element B is increased abruptly at time T53 to the closing pressure level at which the frictional switching element B is fully closed.Thus, at time T53, the three shift elements A, B and C are closed, which is why the gear set 5 of the transmission 4 is in a partially blocked operating state in which the transmission input shaft 6 is held in a rotationally fixed manner and the transmission output shaft 9 connected to the output 3 is rotatable.

[0238] The coasting operating state or the coasting operating function is activated in the operating state profile of the vehicle drive train 1 described in more detail above, for example, starting from a near-standstill operating state of a vehicle when it is simultaneously detected that the speed profile of the output 3 has a positive gradient and the drive motor 2 is nevertheless to be transferred to its deactivated operating state. This is the case, for example, if a driver-side power request is not made while a vehicle is simultaneously driving downhill, or if a vehicle is designed with an electrically driven vehicle axle and it is detected that the current driver-side power request can be implemented by this alone.

[0239] When it is recognized that there is a request to activate the sailing operating state, the frictional clutch relieving the positive switching element F to be switched off or the frictional switching element E is actuated. During the filling process of the frictional switching element E and the associated build-up phase of the relief torque in the area of ​​the positive switching element E, the positive switching element F to be disengaged is actuated in the opening direction.

[0240] If the positive shifting element F is made almost torque-free by the relief torque built up in the area of ​​the frictional shifting element E, the positive shifting element F is opened without generating a relief shock in the vehicle drive train 1. If the open operating state of the positive shifting element F is determined, for example by a corresponding travel sensor in the area of ​​the positive shifting element F or a correspondingly determined speed reaction in the area of ​​the transmission 4, the relief torque built up in the area of ​​the frictional shifting element E is reduced by reducing the actuation pressure p_E and the resulting pressure reduction in the area of ​​the relief clutch or in the area of ​​the frictional shifting element E, and thus the output 3 is decoupled from the drive machine 2 and the transmission output is thus made frictionally free.

[0241] In this then existing operating state of the vehicle drivetrain 1, the resulting vehicle initially coasts with the drive motor 2 engaged. In order to be able to operate the vehicle drivetrain 1 with the drive motor 2 disengaged, frictionally engaged shifting elements of the transmission 4 are filled and transferred to their closed operating state depending on the currently existing operating state of the vehicle drivetrain 1. Since the transmission output shaft 9 and the output 3 connected thereto in a rotationally fixed manner can already rotate freely, the filling of the frictionally engaged shifting elements of the transmission 4 to be engaged and transferred to the closed operating state can be carried out within short operating times.

[0242] Based on this operating state of the vehicle drivetrain, with the coasting function activated, it is possible for the transmission 4 to be actuated accordingly depending on the respective operating state profile of the vehicle drivetrain in order to achieve an operating state with high spontaneity, which is established in the transmission area when the coasting operating state is left. For this purpose, the shift elements A to F are each actuated depending on the existing operating point of the vehicle drivetrain 1 and with the coasting function simultaneously activated, whereby the actuation of the shift elements A to F occurs to a significant extent depending on the speed of the output 3 and the vehicle speed in order to be able to represent the gear tracking required for high spontaneity.

[0243] Fig. 17 shows the Fig. 16 depicts the operating variables of the vehicle drive train 1, starting from an operating state at a time T54, at which the power flow between the drive motor 2 and the output 3 is established in the area of ​​the transmission 4 and the fourth gear ratio "4" for forward travel is engaged in the transmission 4. As can be seen from the shift diagram according to Fig. 2, to represent the fourth gear ratio "4" for forward travel in transmission 4, in addition to the two positive-locking shift elements A and F, the frictional-locking shift element E must also be closed. The speed n_mot of the prime mover 2 and the curve of the product n_ab * i_zielgang_sas are above the idle speed n_motLL. Up to a time T55, the curve of the product n_ab * i_zielgang_sas is equal to the curve of the turbine speed n_t.

[0244] Based on the current operating state history up to time T54, the higher-level driving strategy issues a request to activate the sailing function of vehicle drive train 1. To implement sailing operation, the positive-locking switching element F must be deactivated. Since a torque counteracting the opening process of the positive-locking switching element F is present at the positive-locking switching element F, the actuation pressure p_B of the friction-locking switching element B is abruptly increased from zero to the rapid-fill pressure level at time T55 and is kept constant at this pressure level until time T56.

[0245] At time T56, the actuation pressure p_B is reduced to the filling compensation pressure level and again maintained at this pressure level until time T57. From time T57, the actuation pressure p_B is increased starting from the filling compensation pressure level along a first pressure ramp, which in this case ends at time T58, with a defined gradient. At time T57, the frictional switching element B to be engaged has an operating state in which the transmission capacity of the frictional switching element B is zero, and an increase in the actuation pressure p_B acting in the closing direction of the frictional switching element B results in an immediate increase in the transmission capacity of the frictional switching element B. Due to the last-described change in operating state of the frictional switching element B, the positive switching element F to be disengaged is increasingly relieved from time T57.At a time T59 lying between the times T57 and T58, the positive-locking switching element F to be switched off has a relieved operating state such that the positive-locking switching element F changes into its open operating state as required by a sudden reduction of the actuating pressure p_F applied in the closing direction to the positive-locking switching element F to be switched off at the time T59, starting from the closing pressure level to zero.

[0246] From time T58, the pressure ramp is followed by a further pressure ramp of the actuation pressure p_B of the frictionally engaged switching element B to be engaged, the gradient of which is smaller than the gradient of the first pressure ramp ending at time T58. The second pressure ramp ends at time T60, at which the frictionally engaged switching element B to be engaged is essentially in the closed operating state. For this reason, the actuation pressure p_B is abruptly increased to the closing pressure level at time T60, and the frictionally engaged switching element B is transferred to its fully closed operating state. The actuation pressure p_E of the frictionally engaged switching element E is abruptly reduced from the closing pressure level to an intermediate pressure level above the pressure threshold pf_min + HYS at time T60.Subsequently, the actuating pressure p_E is guided along a pressure ramp, which in this case ends at a time T61, to an intermediate pressure level below the pressure threshold pf_min + HYS and is abruptly reduced to zero at the time T61, whereby the frictional switching element E changes into its fully open operating state.

[0247] By means of the procedure carried out between times T54 and T61, the positive shifting element F, which was engaged until time T59, is initially transferred to an at least approximately load-free operating state by at least partially engaging the fifth gear ratio "5" in transmission 4, for which the positive shifting element F must be transferred to the open operating state and the transmission capacity of the frictionally engaged shifting element B must be varied. Upon reaching the at least approximately load-free operating state at time T59, the positive shifting element F is opened to the extent described above, thus fulfilling the requirement to realize the sailing operating state with high spontaneity.

[0248] Depending on the current operating state of the vehicle drive train 1, it is determined in the area of ​​the higher-level driving strategy at a time T62, which in this case lies between times T60 and T61, that the third gear ratio "3" for forward travel must be engaged when sailing exits in the transmission 4. For this reason, at time T62 the actuation pressure p_C of the frictional switching element C is suddenly increased to the pressure level of the rapid filling pressure and kept constant at this level until the end of the rapid filling phase. Following this, the actuation pressure p_C of the frictional switching element C is increased, to an extent not shown in more detail, first to the pressure level of the filling equalization pressure and then, during two successive pressure ramps with different gradients, to the intermediate pressure level at which the frictional switching element C is in a slip-free operating state.When this operating state of the frictional switching element C is reached, the actuating pressure is raised to the closing pressure level and the frictional switching element C is completely closed. Reference symbol 1 vehicle powertrain 2 drive machine 3 Downforce 4 gearboxes 5 wheel set 6 Gearbox input shaft 7 hydrodynamic torque converter 8 torque converter lock-up clutch 9 Gearbox output shaft 10 housing-fixed component “1” to “9” gear ratio for forward drive “R” gear ratio for reverse A to F switching element HR1 to HR4 ring gear target gear_sas gear ratio currently to be engaged in the transmission i_zielgang_sas Translation kfl threshold MSF history n_ab speed of the output n_mot, n_mot1 Speed ​​of the drive machine n_motEGS Course of the EGS engine target speed specification n_motLL idle speed n_t turbine speed p_A Actuating pressure of switching element A p_B Actuating pressure of switching element B p_C Actuation pressure of switching element C p_D Actuating pressure of the switching element D p_E Actuating pressure of the switching element E p_F Actuating pressure of the switching element F P1 to P4 planetary gear set pf_min + Hys pressure threshold PR1 to PR4 planetary gear S1 to S4 sun gear ST1 to ST4 planetary gear t time T0 to T199 discrete time

Claims

[1] Method for operating a vehicle drive train (1) with a prime mover (2), with an output (3), and with a transmission (4) arranged in the power flow between the prime mover (2) and the output (3), which transmission is designed with at least one positive shifting element (A, F) and with a plurality of frictional shifting elements (B, C, D, E), via which a plurality of gear pairs of a gear set (5) of the transmission (4) can be engaged and disengaged to represent different gear ratios ("1" to "R") of the transmission, wherein only a portion of the gear ratios ("1" to "R") assigned to a gear ratio subrange of the gear ratio range of the transmission can be represented via the positive shifting element (A, F), wherein, upon a request to represent a coasting operating state of the vehicle drive train (1), during which the prime mover (2) is engaged and the power flow between the output (3) in the region of the transmission (4) is interrupted,the connected drive motor (2) is separated from the output (3) by opening one of the switching elements (A to F), which are kept in the closed operating state to represent the operating state existing before the request to uncouple the connected drive motor (2), and then the switching elements (A to F) are actuated depending on the current operating state of the vehicle drive train (1) with the connected drive motor (2) uncoupled,that the switching elements (A to F) to be engaged to represent the gear ratio ("1" to "9") to be engaged in the transmission (4) when a request is made to couple the engaged drive motor (2) to the output (3) are partially already in the engaged operating state at the time of the request, and the engaged drive motor (2) is connected to the output (3) by closing a further switching element (A to F) of the further switching elements (A to F), and the gear ratio ("1" to "9") requested depending on the current operating state of the vehicle drive train (1) is engaged in the transmission (4), wherein when a request is made to represent the coasting operating state, starting from an operating state of the transmission (4) for which the positive-locking switching element (F) is closed, the closed positive-locking switching element (F) is transferred into an open operating state,wherein, when there is a request to display the sailing operating state starting from an operating state of the transmission (4), for the display of which a further positive-locking switching element (A) is opened, the opened further positive-locking switching element (A) is transferred into a closed operating state when an operating state profile of the vehicle drive train (1) is determined which, in the case of a subsequent request to couple the engaged drive machine (2), triggers an engagement of a gear ratio in the transmission (4), for the display of which the further positive-locking switching element (A) is to be engaged, , characterized bythat during the engagement process of the further shifting element (A), a clutch (8) which is arranged in the power flow of the vehicle drive train between the drive engine (2) and the transmission (4) is opened and the speed (n_t) of a transmission input shaft (6) is guided towards zero by actuating at least one of the frictionally engaged shifting elements (B, C, D) in order to generate a differential speed required for closing the further positively engaged shifting element (A) within a defined differential speed range between shifting element halves of the further positively engaged shifting element (A) which is in the open operating state. [2] Method according to claim 1, characterized by that the further positive switching element (A) is closed when the speed (n_ab) of the output (3) is less than a threshold value. [3] Method according to one of claims 1 or 2, characterized bythat the transmission capacity of at least one frictional switching element (B, C, D) is varied in order to produce an at least approximately load-free operating state of the further positive switching element (A) required for closing the further positive switching element (A). [4] Method according to one of claims 1 to 3, characterized bythat when there is a request to display a neutral operating state of the transmission (4), in which the power flow in the area of ​​the transmission (4) is to be interrupted by corresponding actuation of the shift elements (A to F) and in which the further positive shift element (A) is to be opened, and when the coasting operating state of the vehicle drive train (1) is activated, the connected drive motor (2) is decoupled from the output (3) and the transmission (4) is prepared for the engagement of a gear ratio by holding the further positive shift element (A) in its closed operating state, an actuation logic of the shift elements (A to F) is selected, by means of which a neutral operating state of the transmission (4) is displayed, in which the further positive shift element (A) is in its closed operating state. [5] Method according to one of claims 1 to 4, characterized bythat when the sailing operating state is activated and the connected drive machine (2) is decoupled and when an operating state of the vehicle drive train (1) exists in which the further positive switching element (A) is closed and from which, upon a request to couple the drive machine (2), a gear ratio ("1" to "4") is to be engaged in the transmission (4), for the representation of which both the further positive switching element (A) and the positive switching element (F) are to be closed, the positive switching element (F) is closed when an at least approximately synchronized operating state is reached when the sailing operating state is deactivated. [6] Method according to one of claims 1 to 5, characterized bythat the positive switching element (F) is closed during an operating state of the vehicle drive train (1), during which the speed (n_ab) of the output (3) and / or the speed of the transmission input approaches a speed which corresponds to the synchronous speed which is set upon a request to deactivate the sailing operating state and a resulting request to couple the engaged drive motor (2) in the transmission (4) by closing the positive switching element (F) with a simultaneously closed further positive switching element (A), if a differential speed between the switching element halves of the positive switching element (F) present in the open operating state lies within a defined differential speed window. [7] Method according to one of claims 1 to 6, characterized bythat the speed (n_t) of the transmission input during an operating state of the vehicle drive train (1), during which the engaged drive motor (2) is operated at the level of the idle speed (n_motLL) and the synchronous speed of the transmission input, which is set when the gear ratio ("1", "2", "3", "4") is to be engaged in the transmission (4) by the closed further positive switching element (A) and by additionally closing the positive switching element (F), is greater than the idle speed (n_motLL) of the drive motor (2), is increased by a positive engine intervention starting from the idle speed (n_motLL) in the direction of the synchronous speed. [8] Method according to one of claims 1 to 7, characterized bythat the transmission capacity of the switching element (8) between the drive machine (2) and the transmission (4) is guided to a defined level during the determination of the synchronization point of the opened positive-locking switching element (F), at which level the rotational speed (n_mot) of the drive machine (2) and the rotational speed (n_t) of the transmission input correspond to one another at least approximately. [9] Method according to one of claims 1 to 8, characterized by that the switching element (8) between the drive engine (2) and the transmission (4) is at least partially opened during the closing of the positive switching element (F). [10] Method according to one of claims 1 to 9, characterized bythat during operating state curves of the vehicle drive train (1), during which events take place which change the speed (n_ab) of the output (3) and change the synchronization process of the positive switching element (F) to be engaged and trigger a request to couple the engaged drive machine (2), a gear ratio ("5", "6" or "7") is first engaged in the transmission (4), for which the positive switching element (F) is opened, and then a change is made in the transmission (4) to a gear ratio ("3", "2" or "1"), for which a closed frictional switching element (E) is to be switched off and the positive switching element (F) is to be closed. [11] Method according to one of claims 1 to 10, characterized bythat during operating state curves of the vehicle drive train (1), during which events take place which change the speed (n_ab) of the output (3) and change the synchronization process of the positive shifting element (F) to be engaged, such gear ratios ("3", "2" or "1") are preparatoryly engaged in the transmission (4) that the synchronization point of the positive shifting element (F) to be engaged can be reached due to the currently existing speeds (n_ab, n_t, n_mot) of the output (3), the transmission input and the drive machine (2) and the current gradients of the curves of these speeds and the positive shifting element (F) is transferred into its closed operating state in an at least approximately synchronized operating state.

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