Method and control device for operating a drive train

Abstract

A method for operating a drive train of a hybrid vehicle, wherein the drive train has a plurality of drive units (1, 2), a transmission (3), and an output (4), wherein a first drive unit (1), namely an internal combustion engine, acts on a first transmission shaft (6), wherein a second drive unit (2), namely an electric machine, acts on a second transmission shaft (7), wherein the transmission (3) comprises positive shifting elements (9), at least one frictional shifting element (10), and at least one planetary gear set (5), characterized in that when, in order to carry out a gear change from an actual gear to a target gear, a positive shifting element (9) closed in the actual gear is opened and / or a positive shifting element (9) open in the actual gear is closed, the shifting element (9) to be opened is made load-free and / or the shifting element (9) to be closed is speed-synchronized, namely bythat, depending on a torque applied to the output (4), a torque provided by one of the drive units (1, 2) is increased and a torque provided by another of the drive units (1, 2) is reduced in order to reduce a torque transmitted by the positive-locking switching element (9) to be opened and / or to synchronise the positive-locking switching element (9) to be closed, wherein, if at least one of the drive units (1, 2) reaches a torque limit before the positive-locking switching element (9) to be opened has been made load-free and / or the positive-locking switching element (9) to be closed has been synchronised, by closing the at least one frictional switching element (10), the torque transmitted by the positive-locking switching element (9) to be opened is further reduced until the same is made load-free, and / or by closing the at least one frictional switching element (10), thepositive switching element (9) is further synchronized until the same is speed synchronized.,

Description

The invention relates to a method for operating a drive train of a hybrid vehicle. The invention furthermore relates to a control device for operating a drive train of a hybrid vehicle.Drive trains of hybrid vehicles comprise a plurality of drive units, namely a first drive unit designed as an internal combustion engine and a second drive unit designed as an electric machine, a transmission and an output. In such a drive train, the first drive unit can act on a first transmission shaft of the transmission and the second drive unit can act on a second, different transmission shaft of the transmission. The first transmission shaft on which the internal combustion engine acts is then preferably a transmission input shaft. The second transmission shaft on which the electric machine acts is then preferably an internal transmission shaft. The transmission of the drive train comprises a plurality of shift elements, which can be designed as frictional shift elements and / or positive shift elements. Furthermore, the transmission of the drive train comprises at least one planetary gear set.The present invention relates to a method and a control device for operating a drive train of a motor vehicle, in which a first drive unit acts on a first transmission shaft and a second drive unit acts on a second, different transmission shaft of the transmission, wherein the transmission comprises a plurality of positively locking shift elements and at least one frictionally locking shift element and at least one planetary gear set.When a gear change from an actual gear to a target gear is to be carried out in such a drive train, at least one form-locking shift element that is closed in the actual gear must be opened and subsequently at least one form-locking shift element that is open in the actual gear must be closed.In order to be able to open a closed, positively locking shifting element, the same must be released from load. To close an open, positive-locking switching element, it is necessary to synchronize the same.In principle, it is possible to implement the load release of a form-locking shift element to be opened and the rotational speed synchronization of a form-locking shift element to be closed in that a torque is increased at one of the drive assemblies of the hybrid vehicle and a torque is reduced at another of the drive assemblies of the hybrid vehicle, preferably in such a way that, on the one hand, an output torque effective at the output is maintained and, on the other hand, the load release or the rotational speed synchronization is carried out. In this case, a state can be established in which one of the drive assemblies or also both drive assemblies of the hybrid vehicle reach a torque limit, such that the torque provided by the same cannot be increased further or cannot be reduced further. In this case, the load release or the rotational speed synchronization cannot be carried out to the end, so that a shift or a gear change cannot be carried out completely, but rather must be aborted. This is disadvantageous.There is therefore a need for a method and a control device for operating a drive train, with the aid of which it is possible to successfully end the load disengagement and / or the speed synchronization of the respective positive-locking shift element even if at least one drive unit strikes a torque limit during load disengagement and / or during the speed synchronization of a positive-locking shift element, in order to be able to successfully end the shift or the gear change in this way.On the basis of this, the object of the invention is to create a novel method for operating a drive train and a control device for carrying out the method, with the aid of which shifts or gear changes can be successfully completed even if at least one of the drive assemblies encounters a torque limit.This object is achieved by a method for operating a drive train according to claim 1.According to the invention, when, for carrying out a gear change from an actual gear to a target gear, a form-fitting shift element which is closed in the actual gear is opened and / or a form-fitting shift element which is opened in the actual gear is closed, the form-fitting shift element which is to be opened is set free of load and / or the form-fitting shift element which is to be closed is synchronized in terms of the rotational speed, namely in that, depending on a torque which is present at the output, a torque which is provided by one of the drive assemblies is increased and a torque which is provided by another of the drive assemblies is reduced in order to reduce a torque which is transmitted by the form-fitting shift element which is to be opened and / or to synchronize the form-fitting shift element which is to be closed, wherein, in this case, at least one of the drive assemblies abuts a torque limit before the form-fitting shift element which is to be opened is set free of load and / or the form-fitting shift element which is to be closed is to be synchronized, The torque transmitted by the positive shifting element to be opened is further reduced by closing at least one frictional shifting element until the same is released from load, and / or the positive shifting element to be closed is further synchronized by closing at least one frictional shifting element until the same is synchronized in speed.The present invention proposes for the first time that, when a drive unit of a hybrid vehicle strikes a torque limit during load release and / or during rotational speed synchronization, so that the torque of the drive unit cannot be changed any further in a desired direction, the load release and / or the rotational speed synchronization is successfully completed by at least one frictionally engaging shift element of the transmission being brought into slip in order to transmit or support it via the same torque. With the invention it is possible to be able to safely complete a circuit even under unfavourable operating conditions.According to a preferred development, a frictional shifting element is slippingly closed, which is opened in the actual gear. This frictional shifting element is also open in the target gear. This makes it possible to ensure that a suitable frictional shifting element is used for load release or rotational speed synchronization of a positive-locking shifting element, which is available on the basis of a shifting matrix of the transmission depending on the engaged actual gear and on the target gear to be engaged.Preferably, for load-releasing the form-locking shift element to be opened, the friction-locking shift element is actuated in such a way that the friction-locking shift element supports exactly enough torque that the form-locking shift element to be opened becomes load-free, and the latter is subsequently actuated to be opened after the load-releasing of the form-locking shift element to be opened. Alternatively, for load-releasing the form-locking shift element to be opened, the friction-locking shift element is actuated in such a way that the friction-locking shift element is closed along a setpoint characteristic curve in the direction of a setpoint value in which it supports more torque in a slipping manner than is required for load-releasing the form-locking shift element to be opened, wherein the form-locking shift element to be opened is actuated for opening already before the load-releasing thereof. With both variants, a form-fitting shifting element to be provided free of load can be reliably opened.The control device according to the invention is defined in claim 8.Preferred refinements emerge from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawings, without being restricted thereto. The following shows: FIG. 1 is a schematic of a powertrain; FIG. 2 shows a first diagram for illustrating the method according to the invention; FIG. 3 shows a second diagram to illustrate the method according to the invention; FIG. 4 shows an exemplary transmission diagram of a transmission in which the method according to the invention can be used; FIG. 5 shows a first shift matrix for the transmission of FIG. 4 ; and FIG. 6 shows a second shift matrix for the transmission of FIG. 4.The invention relates to a method and a control device for operating a drive train of a hybrid vehicle. FIG. 1 shows a diagram of a drive train of a hybrid vehicle, in which the method according to the invention can preferably be used.The drive train of FIG. 1 comprises two drive units 1, 2, a transmission 3 and an output 4. the transmission 3 comprises at least one planetary gear set 5. the two drive units 1, 2 act on different transmission shafts of the transmission 3, namely the first drive unit 1 acts on a first transmission shaft 6 and the second drive unit 2 acts on a second, different transmission shaft 7.In the exemplary embodiment shown, the first drive unit 1 is an internal combustion engine which acts on the first transmission shaft 6, which in the exemplary embodiment shown is the transmission input shaft of the transmission 3. In the exemplary embodiment shown, the second drive unit 2 is an electric machine which acts on the second transmission shaft 7 of the transmission 3, wherein the second transmission shaft 7 is provided by the planetary gear set 5 in the exemplary embodiment shown, namely by a ring gear thereof in the exemplary embodiment shown. The second transmission shaft 7 is an in-transmission shaft. A transmission output shaft 8 of the transmission 3 acts on an output 4 of the drive train in order ultimately to provide a driver's desired torque at the output 4. In the exemplary embodiment shown in FIG. 1, the first drive unit 1 is a drive unit external to the transmission, and the drive unit 2 is a drive unit internal to the transmission. In the preferred exemplary embodiment shown in FIG. 1, only two drive units are present. The drive train accordingly comprises an internal combustion engine and an electric machine.According to FIG. 1, the transmission 3 comprises a plurality of shift elements, wherein FIG. 1 shows only two form-locking shift elements 9 and one frictional shift element 10 by way of example. Thus, a form-locking shift element 9 according to FIG. 1 is connected between the transmission input shaft 6 and the planetary gear set 5, and a form-locking shift element 9 is connected between the planetary gear set 5 and the transmission output shaft 8. The two form-fitting switching elements 9 are, for example, claw switching elements. The frictional shifting element 10 can be designed as a clutch or brake.In the exemplary embodiment of FIG. 1, a separating clutch 11 is connected between the first drive unit 1 and the transmission input shaft 6 of the transmission 3, which separating clutch is preferably designed as a frictional separating clutch, it being possible for the first drive unit 1 to be decoupled from the transmission input shaft 6 via the separating clutch 11. The separating clutch 11 is an optional component group and can also be omitted.FIG. 1 furthermore shows a control device 12 which, in the exemplary embodiment shown, controls and / or regulates the operation of the first drive unit 1 and of the transmission 3 including the second drive unit 2. This control device 12 is preferably a hybrid control device of a motor vehicle. The control device 12 exchanges data with both the first drive unit 1 and the transmission 3 according to the dashed arrows in order to control and / or regulate the operation of the first drive unit 1, the transmission 3 and the second drive unit 2.The transmission 3, which comprises the shift elements 9 and 10 and the planetary gear set 5, is a stepped automatic transmission having a plurality of powershiftable gears.In each engaged actual gear of the transmission 3, a first number of shift elements 9, 10 of the transmission 3 is closed and a second number of shift elements 9, 10 is open.In order to carry out a shift or a gear change from the current actual gear to a target gear, a shift element which is closed in the actual gear must be opened and a shift element which is opened in the actual gear must be closed. It is to be assumed below that, in order to carry out a gear change from the actual gear to the target gear, a form-locking shift element 9 which is closed in the actual gear must be opened and a form-locking shift element 9 which is opened in the actual gear must be closed. To open a previously closed, positive-locking shifting element 9, the same must be previously released from load; to close it, a previously opened, positive-locking shifting element must be synchronized in speed. Otherwise, form-locking shift elements cannot be reliably opened or closed.FIG. 2 illustrates details according to the invention for opening a form-locking shift element 9 that is closed in the actual gear. FIG. 2 thus shows a plurality of torque profiles M over time t, namely a torque profile of the first drive unit 1 with reference numeral 13, a torque profile of the second drive unit 2 with reference numeral 14, and a torque profile of the form-locking shift element 9 that is closed in the actual gear and is to be opened subsequently with reference numeral 15.An actual gear is engaged in the transmission 3 before the time t and the hybrid vehicle is traveling in this actual gear, namely in such a way that both drive units 1, 2 each provide a constant torque before the time t 1 according to the signal curves 13 and 14, and that the subsequently openable, form-locking shift element 9 transmits a constant torque according to the signal curve 15 before the time t 1.At the time t 1, there is a shift request for carrying out a gear change from the actual gear to a target gear, wherein for this purpose the closed, form-locking shift element 9, which is closed in the actual gear, must be opened.Starting at the time t 1, a load release of the form-locking shifting element 9 to be subsequently opened is carried out for this purpose, namely in that, according to the signal profile 15, the torque transmitted by the form-locking shifting element 9 to be subsequently opened is reduced, namely in that, for this purpose, depending on the torque prevailing at the output 4, preferably while maintaining the torque prevailing at the output 4, according to the signal profile 13, the torque provided by the first drive unit 1 is increased and the torque 14 provided by the second drive unit 2 is reduced, wherein, according to FIG. 2, the torque 14 provided by the drive unit 2 experiences a sign change between the times t 1 and t 2, that is to say changes from a traction torque to a thrust torque.FIG. 2 shows a torque limit for the torque 14 that can be provided by the second drive unit 2 with the reference numeral 16. FIG. 2 thus shows that the torque 14 of the second drive unit 2 reaches this torque limit 16 at the time t 2, so that the torque 14 of the second drive unit 2 cannot be reduced further beginning at the time t 2.At the time t 2, however, according to the signal profile 15, the form-locking shifting element 9 to be opened for the gear change is not yet free of load, but instead it still transmits torque at the time t 2.This state can be established, for example, when the hybrid vehicle is braked greatly, i.e. a braking torque is effective at the output 4, which braking torque cannot be supported by the second drive unit 2 under load free conditions of the positive-locking shift element 9 to be opened, as a result of the torque limit 16 of the second drive unit 2.In methods known from practice, the shift would then have to be aborted, since the form-locking, to-be-opened shifting element 9 could then not be reliably opened.However, it is proposed in the sense of the present invention that, when one of the drive units, in FIG. 2, the second drive unit 2, reaches a torque limit, namely the torque limit 16 in FIG. 2, before the positively engaging shift element 9 to be opened for carrying out the gear change has been released from load, a frictionally engaging shift element 10 of the transmission 3 is caused to slip beginning at the time t 2 according to the signal profile 17, as a result of which the frictionally engaging shift element 10 supports the torque which the second drive unit 2 cannot support further as a result of the torque limit 16 being reached.Between the times t 2 and t 3, the torque 14 of the drive unit 2, the torque limit 16 of which has been reached, is accordingly not lowered further, but rather a frictional shifting element 10 is brought into slip in order to support via the same torque, wherein the torque 13 provided by the drive unit 1 is likewise increased further between the times t 2 and t 3 in order to set the positive shifting element 9 free of load in combination of the torques 13 and 14 applied by the drive units 1 and 2 with the torque 17 supported by the frictional shifting element 10. At the time t 3, the positive shifting element 9 to be opened is released from load, so that then in FIG. 2 at the time t 3 the positive shifting element 9, which is closed in the actual gear and is open in the target gear, can be opened.According to a first alternative, the load release of the form-locking shift element 9 that is closed and to be opened in the actual gear takes place in such a way that for this purpose the frictional shift element 10 of the transmission 3 is controlled in such a way that the frictional shift element 10 is guided along a setpoint characteristic curve, preferably along a ramp, to a setpoint torque with which the frictional shift element 10 supports exactly enough torque that the form-locking shift element 9 to be opened becomes load-free, wherein subsequently, i.e. when at the time t 3 the form-locking shift element 9 to be opened has been released, the same is controlled to be opened in order thus to disengage the form-locking shift element 9.According to a second alternative, it is provided that for the load release of the form-locking shift element 9 to be opened, the frictional shift element 10 is controlled in such a way that the frictional shift element 10 is slip-closed along a setpoint characteristic curve, preferably along a setpoint ramp, in the direction of a setpoint torque with which the frictional shift element 10 supports more torque in a slip-like manner than is actually required for the load release of the form-locking shift element 9 to be opened, so that in this case the point at which the form-locking shift element 9 to be opened becomes load-free is traversed. In this case, the form-locking shifting element 9 to be opened is then already controlled to open before the load release thereof, so that when that point at which the form-locking shifting element 9 becomes load-free is reached, the form-locking shifting element 9 is automatically disengaged or opened.In FIG. 2, after the load release and opening of the positive-locking shifting element 9 to be opened, the frictional shifting element 10 remains slipping according to the signal profile 17. In contrast to this, it is also possible that, with the load release of the form-locking shifting element 9 to be opened and after the disengagement or opening thereof at the time t 3, the slip at the frictionally engaging shifting element 10 is reduced again by the latter being opened completely.With the procedure described with reference to FIG. 2, when, in order to carry out a gear change when the form-locking shift element 9 to be opened is released, at least one of the drive assemblies 1, 2 of the hybrid vehicle reaches a torque limit before the form-locking shift element 9 has actually been released, the form-locking shift element 9 to be opened can subsequently be released by load, in that at least one frictional shift element 10 of the transmission 3 supports torque during slipping operation. In this case, a frictionally engaging shift element 10 is brought into slip, which is actually open in the actual gear. This frictional shifting element 10, which is used for releasing the load of the positive shifting element 9 to be opened, can also be opened in the target gear or alternatively be closed in the target gear.The invention is described below with reference to FIG. 3 for the case in which, when a shift or a gear change is carried out, a form-locking shift element 9 that is open in actual gear is to be closed, wherein for this purpose this form-locking shift element 9 to be closed has to be subjected to a rotational speed synchronization.FIG. 3 shows a plurality of temporal signal curves over time t, namely with signal curve 18 a torque provided by a first drive unit 1, with signal curve 19 a torque provided by a second drive unit 2 and with signal curve 20 a torque transmitted by a frictionally engaging shift element 10. Signal curve 21 shows a rotational speed curve of first drive unit 1 and signal curve 20 shows a rotational speed curve of second drive unit 2.Before the time t 1, in FIG. 3 the actual gear is driven, and the drive units 1, 2 accordingly each provide a constant torque 18, 19 before the time t 1. At the time t 1, a gear change is requested and preferably an openable, form-locking shifting element 9 of the transmission 3 is disengaged at the time t 1. Subsequently, a form-locking shift element 9 that is opened in the actual gear and is to be closed for the target gear is to be closed, for which purpose, between the times t 1 and t 3, this form-locking shift element 9 that has previously been opened and is to be closed is subjected to a rotational speed synchronization.For synchronizing the rotational speed of the form-locking shift element 9 to be closed, rotational speeds 21 and 22 of the drive assemblies 18 and 19 are first adjusted between the points in time t 1 and t 2 via the torques 18 and 19 provided by the drive assemblies 1 and 2 such that the form-locking shift element 9 to be closed is at least partially synchronized, wherein the torque 18 of the drive assembly 1 reaches a torque limit 23 at the point in time t 2, so that then starting with the point in time t 2 the torque 18 of the first drive assembly 1 cannot be changed further.According to practice, starting at the time t2, the rotational speeds 21 and 22 of the drive units 1 and 2 would then remain on the dashed rotational speed profiles 21', 22', and the rotational speed synchronization could therefore not be concluded to the rotational speed levels 21", 22'' of the target gear which would be required for the rotational speed synchronization of the form-locking shift element 9 to be closed. The circuit would then have to be aborted after practice.However, in order to be able to successfully end the speed synchronization at the time t2 when the torque limit 23 of the first drive unit 1 is reached, according to the invention, starting at the time t2 according to the signal curve 20, a frictionally engaging shift element 10 of the transmission 3 is caused to slip, so that the same torque is transmitted, whereby then between the times t2 and t3 the speeds 21, 22 of the drive units 1, 2 can be raised or lowered to the speed levels 21", 22" of the target gear to be engaged, which are required for speed synchronization, so that the same do not remain at the speed levels 21', 22'.The situation that, when synchronizing the rotational speed of an open, positively locking shift element to be subsequently closed, one of the drive assemblies reaches its torque limit can be established, for example, when the output drive 4 is accelerated so strongly, for example as a result of a downhill travel, that target rotational speeds for the drive assemblies change in such a way that the dynamics of the drive assemblies 1, 2 are not sufficient to lead the same to their rotational speed levels 21", 22".By closing a frictionally engaging shift element 10, the drive assemblies can then be supported in order to be able to successfully complete a shift despite the achievement of a torque limit at one of the drive assemblies or both of the drive assemblies.FIG. 4 schematically shows an exemplary transmission 3 in which the method according to the invention can be used.The transmission 3 has an input shaft 6, an output shaft 7, a first planetary gear set 5 aand a second planetary gear set 5 b. The first and second planetary gear sets 5 a, 5 bare designed as minus gear sets. The first planetary gear set 5 ais constructed as a stepped planetary gear set, the planetary gears PL 1 of which have two different effective diameters. A first sun gear E 111 of the first planetary gear set 5 ais in mesh with the larger effective diameter of the planetary gears PL 1. A second sun gear E 112 of the first planetary gear set 5 ais in mesh with the smaller effective diameter of the planetary gears PL 1. The second sun gear E 112 of the first planetary gear set 5 ais continuously connected to a sun gear E 12 of the second planetary gear set 5 b. A carrier E 21 of the first planetary gear set 5 ais continuously connected to a ring gear E 32 of the second planetary gear set 5 b. The first and second planetary gear sets 5 a, 5 bthus form a so-called Simpson gear set.In the embodiment of the transmission 3 according to FIG. 1, there are two possibilities for arranging the output shaft 8, a first possibility for forming the output shaft 8 is formed by a toothing, not shown, which is formed on a section of that coupling shaft which connects the carrier E 21 of the first planetary gear set 5 awith the ring gear E 32 of the second planetary gear set 5 b. A second possibility, which is designated in FIG. 1 as output shaft 8', consists of a coaxial arrangement of the output shaft 8' with respect to the input shaft 6 at opposite axial ends of the transmission 3.The input shaft 6 can be connected to the carrier E 22 of the second planetary gear set 5 bvia a first positively locking shifting element 9 a. Via a second positively locking shifting element 9 b, the input shaft 6 can be connected to the second sun gear E 112 of the first planetary gear set 5 a. Via a frictional shifting element 10 a, the input shaft 6 can be connected to the first sun gear E 111 of the first planetary gear set 5 a. A ring gear E 31 of the first planetary gear set 5 acan be fixed in a rotationally fixed manner via a third positively locking shift element 9 cin that it is shiftably connected to a housing of the transmission 3 via the shift element 9 c.Optionally, a further frictionally engaging shifting element 10 bis provided, by means of which the first sun gear E 111 of the first planetary gear set 5 acan be fixed in a rotationally fixed manner in that it is shiftably connected to the housing of the transmission 3 via the shifting element 10 b.The transmission 3 further comprises an electric machine 2, which has a rotatably mounted rotor R and a stator S 1 fixed in a rotationally fixed manner. The rotor R is permanently connected in a rotationally fixed manner via a transmission shaft 7 to the first sun gear E 111 of the first planetary gear set 5 a.FIG. 5 shows a shift matrix for a transmission 3 of FIG. 4 without the shift element 10 b. The rows of the shift matrix show five forward gears G 1 to G 5, two electrodynamic operating modes EDA 1, EDA 2 and a first electrical operating mode E 1. In the columns of the shift pattern, an 'x' represents which of the shift elements 9 a, 9 b, 9 c, 10 aare closed in which forward gear G 1 to G 5 or operating mode EDA 1, EDA 2, E 1. FIG. 6 shows a shift matrix for a transmission 3 of FIG. 4 with the shift element 10 b.The method can be used in the transmission 3 of FIG. 4, for example, when the form-locking shift element 9 bis to be opened and the form-locking shift element 9 ais to be closed when a gear change is to be carried out from the actual gear G 2 to the target gear G 3. If, for example, the form-locking shifting element 9 bcannot be released from load alone as a result of too great a braking torque at the output via the drive assemblies and / or the form-locking shifting element 9 acannot be synchronized in rotational speed alone as a result of too great an acceleration during a downhill travel via the drive assemblies, the frictional shifting element 10 aor 10 bcan be brought into slip in order to further reduce the torque transmitted by the form-locking shifting element 9 bto be opened until the same is released from load and / or in order to further synchronize the form-locking shifting element 9 ato be closed until the same is synchronized in rotational speed.The invention further relates to a control device 12 for operating a drive train of a hybrid vehicle. When, in order to carry out a gear change from an actual gear to a target gear, a form-fitting shift element 9 closed in the actual gear is opened and / or a form-fitting shift element 9 opened in the actual gear is closed, the control device 12 sets the shift element 9 to be opened on the control side in a load-free manner and / or in a speed-synchronized manner, the control device 12 increases the shift element 9 to be closed on the control side, namely in that the control device 12 increases a torque provided by one of the drive assemblies 1, 2 on the control side as a function of a torque present at the output 4, and reduces a torque provided by another of the drive assemblies 1, 2 on the control side, in order to reduce a torque transmitted by the form-fitting shift element 9 to be opened and / or synchronize the form-fitting shift element 9 to be closed, wherein, in this case, at least one of the drive assemblies 1, 1, increases in a torque manner which is to be controlled, In the embodiment of FIG. 2, the control device 12 strikes against a torque limit before the positive shifting element 9 to be opened is released and / or the shifting element to be closed has been synchronized, by actuating at least one frictional shifting element 10 for closing, the torque transmitted by the positive shifting element 9 to be opened is further reduced until the same is released and / or by closing at least one frictional shifting element 10, the positive shifting element 9 to be closed is further synchronized until the same is synchronized in speed. The control device 12 is preferably an electronic transmission control device.Reference numerals denote reference numerals1 First drive assembly / internal combustion engine 2 Second drive assembly / electric machine 3 Transmission 4 Output 5 Planetary gear set 5 a Planetary gear set 5 b Planetary gear set 6 First transmission shaft / transmission input shaft 7 Second transmission shaft 8 Transmission output shaft 8' Transmission output shaft 9 Positive shifting element 9 a Positive shifting element 9 b Positive shifting element 9 c Positive shifting element 10 Frictional shifting element 10 a Frictional shifting element 10 b Frictional shifting element 11 Disconnect clutch 12 Control device 13 Curve profile 14 Curve profile 15 Curve profile 16 Curve profile 17 Curve profile 18 Curve profile 19 Curve profile 20 Curve profile 21 Curve profile 22 Curve profile 23 Curve profile

Claims

Method for operating a drive train of a hybrid vehicle, wherein the drive train has a plurality of drive units (1, 2), a transmission (3) and an output (4), wherein a first drive unit (1), namely an internal combustion engine, acts on a first transmission shaft (6), wherein a second drive unit (2), namely an electric machine, acts on a second transmission shaft (7), wherein the transmission (3) comprises form-locking shift elements (9), at least one frictional shift element (10) and at least one planetary gear set (5), characterized in that, when a form-locking shift element (9) closed in the actual gear is opened and / or a form-locking shift element (9) opened in the actual gear is closed in order to carry out a gear change from an actual gear to a target gear, a form-locking shift element (9) closed in the actual gear is opened, the shifting element (9) to be opened is set free of load and / or the shifting element (9) to be closed is synchronized in rotational speed, namely in that, depending on a torque applied to the output (4), a torque provided by one of the drive assemblies (1, 2) is increased and a torque provided by another of the drive assemblies (1, 2) is reduced in order to reduce a torque transmitted by the positive shifting element (9) to be opened and / or to synchronize the positive shifting element (9) to be closed, wherein, if at least one of the drive assemblies (1, 2) hereby abuts a torque limit before the positive shifting element (9) to be opened is set free of load and / or the positive shifting element (9) to be closed has been synchronized, by closing the at least one frictional shifting element (10) the torque transmitted by the positive shifting element (9) to be opened is further reduced until the same is set free of load, and / or by closing the at least one frictional shifting element (10), the positive shifting element (9) to be closed is further synchronized until the same is synchronized in speed.Method according to Claim 1, characterized in that the form-locking shift element (9) to be opened is released from load and opened before the form-locking shift element (9) to be closed is synchronized in speed and closed.Method according to Claim 1 or 2, characterized in that the at least one frictionally engaging shift element (10) is closed in a slipping manner, which shift element is open in the actual gear.Method according to Claim 3, characterized in that the frictional shifting element (10) is also open in the target gear.Method according to one of Claims 1 to 4, characterized in that, in order to release the positive-locking shift element (9) to be opened, the frictional-locking shift element (10) is actuated in such a way that the frictional-locking shift element (10) supports exactly enough torque that the positive-locking shift element (9) to be opened becomes free of load, and the latter is subsequently actuated to open after the positive-locking shift element (9) to be opened has been released of load.Method according to one of Claims 1 to 4, characterized in that, in order to release the load of the form-locking shift element (9) to be opened, the frictional shift element (10) is actuated in such a way that the frictional shift element (10) is closed along a setpoint characteristic curve in the direction of a setpoint value in which it supports more torque in a slipping manner than is required for releasing the load of the form-locking shift element (9) to be opened, the form-locking shift element (9) to be opened being actuated for opening already before the load release of the latter.Method according to Claim 5 or 6, characterized in that the frictional shift element (10) which is operated in a slipping manner for load release is opened again after the positive shift element (9) which is to be opened has been load-released.Control device (12) for operating a drive train of a hybrid vehicle, wherein the drive train has a plurality of drive units (1, 2), a transmission (3) and an output (4), wherein a first drive unit (1), namely an internal combustion engine, acts on a first transmission shaft (6), wherein a second drive unit (2), namely an electric machine, acts on a second transmission shaft (7), wherein the transmission (3) comprises form-locking shift elements (9), at least one friction-locking shift element (10) and at least one planetary gear set (5), characterized in that the control device (12) is opened when, for carrying out a gear change from an actual gear to a target gear, a form-locking shift element (9) closed in the actual gear is opened and / or a form-locking shift element (9) opened in the actual gear is closed, the shifting element (9) to be opened is load-free on the control side and / or the shifting element (9) to be closed is speed-synchronized on the control side, namely in that the control device increases a torque provided by one of the drive assemblies (1, 2) on the control side as a function of a torque present at the output (4) and reduces a torque provided by another of the drive assemblies (1, 2) on the control side in order to reduce a torque transmitted by the positive shifting element (9) to be opened and / or synchronize the positive shifting element (9) to be closed, wherein when at least one of the drive assemblies (1, 2) thereby abuts a torque limit before the positive shifting element (9) to be opened is load-free and / or the shifting element to be closed has been synchronized, the control device, by actuating at least one frictional shifting element (10) to close, then the positive shifting element (9) to be opened, is disengaged and / or the shifting element to be closed is synchronized, The positive shifting element (9) is further reduced in torque transmitted by the positive shifting element (9) until it is released from load, and / or by closing at least one frictional shifting element (10), the positive shifting element (9) to be closed is further synchronized until it is synchronized in speed.

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