Method and Control Device for Operating a Drive Train of a Motor Vehicle

Abstract

A method for operating a drive train of a motor vehicle for a reversing operation for changing from a forward gear to a reverse gear or vice versa when the motor vehicle is rolling at a speed less than a limit value, and in which a first shift element of the transmission is disengaged and a second shift element of the transmission is engaged, the method including receiving a target torque profile for a transmission output shaft for the reversing operation. The method further includes determining, based on the target torque profile for the transmission output shaft, target torque profiles for the first and second shift elements and the propulsion unit. Additionally, the method includes activating the first and second shift elements and the propulsion unit based on the respective target torque profile such that an actual torque profile follows the target torque profile for the transmission output shaft.

Claims

1-8: (canceled)

9. A method for operating a drive train (1) of a motor vehicle, the drive train (1) comprising a propulsion unit (2) and an automatic or automated transmission (4) connected between the propulsion unit (2) and a driven end (3), the method comprising: for a reversing operation for changing from a forward gear to a reverse gear or from the reverse gear to the forward gear, the reversing operation being carried out when the motor vehicle is rolling at a rolling speed less than a limit value, a first friction-locking shift element (5) of the transmission (4) being disengaged during the reversing operation and a second friction-locking shift element (6) of the transmission (4) being engaged during the reversing operation, the first friction-locking shift element (5) being a first shift element which is engaged in the forward gear and the second friction-locking shift element (6) being a second shift element which is disengaged in the forward gear for changing from the forward gear to the reverse gear, or the first friction-locking shift element (5) being one shift element which is engaged in the reverse gear and the second friction-locking shift element (6) being another shift element which is disengaged in the reverse gear for changing from the reverse gear to the forward gear: receiving a target torque profile for a transmission output shaft (9) of the transmission (4) for the reversing operation; determining, in accordance with the target torque profile for the transmission output shaft (9), a target torque profile for the first friction-locking shift element (5), a target torque profile for the second friction-locking shift element (6), and a target torque profile for the propulsion unit (2); and activating the first friction-locking shift element (5) in accordance with the target torque profile for the first friction-locking shift element (5), the second friction-locking shift element (6) in accordance with the target torque profile for the second friction-locking shift element (6), and the propulsion unit (2) in accordance with the target torque profile for the propulsion unit (2) such that an actual torque profile for the transmission output shaft (9) follows the target torque profile for the transmission output shaft (9).

10. The method of claim 9, wherein a time gradient of the target torque profile for the transmission output shaft (9) over time in a range defined about a zero crossing of the target torque profile is less than a limit value.

11. The method of claim 9, wherein determining the target torque profile for the first friction-locking shift element (5), the target torque profile for the second friction-locking shift element (6), and the target torque profile for the propulsion unit (2) comprises: determining for a first phase of the reversing operation, in which exclusively the first friction-locking shift element (5) to be disengaged for the reversing operation transmits torque, one target torque profile each exclusively for the first friction-locking shift element (5) and for the propulsion unit (2); determining for a second phase of the reversing operation, in which exclusively the second friction-locking shift element (6) to be engaged for the reversing operation transmits torque, one target torque profile each exclusively for the second friction-locking shift element (6) and for the propulsion unit (2); and determining for a third phase of the reversing operation, one target torque profile each for the first friction-locking shift element (5), the second friction-locking shift element (6), and the propulsion unit (2), wherein the first phase, the second phase, and the third phase are successive time phases, with the third phase being between the first phase and the second phase.

12. The method of claim 11, wherein, for the third phase: a target torque value of the first friction-locking shift element (5) which is valid at an end of the first phase and at a beginning of the third phase is stored, the target torque value of the first friction-locking shift element (5) is reduced to zero along a reduction characteristic curve from the end of the first phase to the beginning of the third phase, the target torque profile for the propulsion unit (2) is determined according to the target torque value of the first friction-locking shift element (5), the target torque profile for the second friction-locking shift element (6) is determined according to the target torque value of the first friction-locking shift element (5) and the reduction characteristic curve for the target torque value of the first friction-locking shift element (5).

13. The method of claim 12, wherein determining, for the first phase, the target torque profile (M.sub.K1sek-SOLL) for the first friction-locking shift element (5) and the target torque profile (M.sub.AN-SOLL) for the propulsion unit (2) comprises: determining, for the first phase, the target torque profile (M.sub.K1sek-SOLL) for the first friction-locking shift element (5) using: M.sub.K1sek-SOLL=(J.sub.1*{acute over ()}.sub.K1sek)*i.sub.1+(J.sub.2*{acute over ()}.sub.K2sek)*i.sub.2M.sub.AB-SOLL; and determining, for the first phase, the target torque profile (M.sub.AN-SOLL) for the propulsion unit (2) using: M.sub.AN-SOLL=(J.sub.AN*{acute over ()}.sub.AN)+(J.sub.1*{acute over ()}.sub.K1sek)*i.sub.1+(J.sub.2*{acute over ()}.sub.K2sek)*i.sub.2M.sub.AB-SOLL.

14. The method of claim 12, wherein, for the second phase, determining the target torque profile (M.sub.K2sek-SOLL) for the second friction-locking shift element (6) and the target torque profile (M.sub.AN-SOLL) for the propulsion unit (2) comprises: determining the target torque profile (M.sub.K2sek-SOLL) for the second friction-locking shift element (6) using: M.sub.K2sek-SOLL=(J.sub.2*{acute over ()}.sub.K2sek)*i.sub.2+(J.sub.1*{acute over ()}.sub.K1sek)*i.sub.1M.sub.AB-SOLL; and determining the target torque profile (M.sub.AN-SOLL) for the propulsion unit (2) using: M.sub.AN-SOLL=(J.sub.AN*{acute over ()}.sub.AN)+(J.sub.2*{acute over ()}.sub.K2sek)*i.sub.2+(J.sub.1*{acute over ()}.sub.K1sek)*i.sub.1M.sub.AB-SOLL.

15. The method of claim 14, wherein, for the third phase, determining the target torque profile (M.sub.K1sek-SOLL) for the first friction-locking shift element (5), the target torque profile (M.sub.K2sek-SOLL) for the second friction-locking shift element (6), and the target torque profile (M.sub.AN-SOLL) for the propulsion unit (2) comprises: determining the target torque profile (M.sub.K1sek-SOLL) for the first friction-locking shift element (5) using: M.sub.K1sek-SOLL=M.sub.K1sek-INI*(1k(t)); determining the target torque profile (M.sub.K2sek-SOLL) for the second friction-locking shift element (6) using M.sub.AN-SOLL=J.sub.An*{acute over ()}.sub.AN+M.sub.K1sek-INI; and determining the target torque profile (M.sub.AN-SOLL) for the propulsion unit (2) using: [M.sub.K1sek-INIJ.sub.1*{acute over ()}.sub.K1sek]*i.sub.1*(1k(t))+[M.sub.K2sek-SOLLJ.sub.2*{acute over ()}.sub.K2sek]*i.sub.2*k(t)+M.sub.AB-SOLL=0.

16. A control unit (20) for operating a drive train (1) of a motor vehicle, the control unit (20) being configured to automatically carry out the method of claim 9 on a control side.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Preferred developments can be found in the dependent claims and in the following description. Exemplary embodiments of the invention are explained in greater detail with reference to the drawing, without being limited thereto. Therein:

[0018] FIG. 1 shows a schematic diagram of a drive train of a motor vehicle,

[0019] FIG. 2 shows a time-dependency diagram in accordance with aspects of the invention, and

[0020] FIG. 3 shows a time-dependency diagram in accordance with aspects of the invention.

DETAILED DESCRIPTION

[0021] Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein.

[0022] FIG. 1 schematically shows a schematic diagram of a drive train 1 of a motor vehicle. The drive train 1 includes a propulsion unit 2 and a transmission 4 connected between the propulsion unit 2 and a drive output 3. The transmission 4 is an automatic, or automated, transmission having multiple shift elements. In FIG. 1, only two friction-locking shift elements 5, 6 are shown. The drive output 3 is shown as the driven wheels 7. An axle transmission 8 is connected between the automatic, or automated, transmission 4 and the drive output 3, as the driven wheels 7.

[0023] The invention relates to providing a reversing operation for the drive train 1, which reversing operation has reduced shift shocks, or jolts, in the drive train 1, preferably a shift shock-free and jolt-free reversing operation, i.e., when changing either from a forward gear to a reverse gear or from a reverse gear to a forward gear in the transmission 4 when the motor vehicle is rolling and the rolling speed thereof is less than a limit value.

[0024] FIG. 1 shows a first friction-locking shift element 5 of the transmission 4, which is to be disengaged for the reversing operation to be carried out. FIG. 1 also shows a second friction-locking shift element 6, which is to be engaged for the reversing operation.

[0025] In a change-over from the forward gear to the reverse gear, the first friction-locking shift element 5 is a shift element which is engaged in the forward gear and is disengaged in the reverse gear, i.e., is disengaged for the reversing operation. In this case, the second friction-locking shift element 6 is a shift element which is disengaged in the forward gear and is engaged in the reverse gear, i.e., is engaged for the reversing operation. If, in contrast, a reversing operation is to be carried out from a reverse gear to a forward gear, the first friction-locking shift element 5 is a shift element which is engaged in the reverse gear and disengaged in the forward gear, and the second friction-locking shift element is a friction-locking shift element which is disengaged in the reverse gear and engaged in the forward gear.

[0026] FIG. 1 shows effective moments of inertia J and transmission ratios i for these two friction-locking shift elements 5, 6.

[0027] The primary side of the particular shift element 5, 6 is acted on by the moment of inertia J.sub.AN, which is dependent in particular on the moment of inertia of the propulsion unit 2. The moment of inertia J.sub.AN is applied at the transmission input shaft 10.

[0028] The secondary side of the first friction-locking shift element 5 is acted on by the moment of inertia J.sub.1 of the assemblies of the transmission 4 that participate in the power flow and thus the torque transmission towards the transmission output shaft 9 relative to the first friction-locking shift element 5. A transmission ratio i.sub.1 is effective for these assemblies. The secondary side of the second friction-locking shift element 6 is acted on by the moment of inertia J.sub.2 of the assemblies of the transmission 4 that participate in the power flow and thus the torque transmission towards the transmission output shaft 9 relative to the second friction-locking shift element 6. The transmission ratio i.sub.2 is effective for these assemblies.

[0029] Furthermore, the secondary sides of both friction-locking shift elements 5, 6 are acted on by the moment of inertia JAB, which is dependent in particular on the moment of inertia of the drive output 3 and on the moment of inertia of the axle transmission 8.

[0030] If a reversing operation is then to be carried out with such a drive train 1 while the motor vehicle is rolling, a target torque profile M.sub.AB-SOLL (FIGS. 2 and 3) for the transmission output shaft 9 is specified on the control side for the reversing operation to be carried out.

[0031] According to the target torque profile M.sub.AB-SOLL (FIGS. 2 and 3) for the transmission output shaft 9, which is specified on the control side, target torque profiles are ascertained for the propulsion unit 2, and thus for the transmission input shaft 10, as well as for the two friction-locking shift elements 5, 6 of the transmission 4 participating in the reversing operation. The propulsion unit 2 as well as the shift elements 5, 6 are activated in accordance with such target torque profiles and, in fact, such that an actual torque profile for the transmission output shaft 9 corresponds to, or follows, the target torque profile M.sub.AB-SOLL for the transmission output shaft 9.

[0032] This is carried out by a torque balancing, which is discussed in greater detail further below.

[0033] FIG. 2 shows an example of a target torque profile M.sub.AB-SOLL for the transmission output shaft 9, which is illustrated for a reversing operation from a forward gear to a reverse gear.

[0034] According to FIG. 2, the target torque profile M.sub.AB-SOLL over time for the transmission output shaft is specified such that a time gradient of this target torque profile M.sub.AB-SOLL in a range 11 about a zero crossing of the target torque profile M.sub.AB-SOLL is less than a limit value. In FIG. 2, the zero crossing of the target torque profile M.sub.AB-SOLL occurs at the point in time t0. The gradient dM.sub.AB-SOLL/dt of the target torque profile for this zero crossing and in the range 11 about the zero crossing is less than the corresponding limit value.

[0035] Preferably, the target torque profile for the two friction-locking shift elements 5, 6 participating in the reversing operation and the target torque profile for the propulsion unit 2 are ascertained for successive time phases of the reversing operation according to the specified target torque profile M.sub.AB-SOLL for the transmission output shaft 9.

[0036] For a first time phase of the reversing operation, in which exclusively the first friction-locking shift element 5, which is to be disengaged for the reversing operation, transmits torque, one target torque profile each is ascertained exclusively for this first friction-locking shift element 5 and for the propulsion unit 2.

[0037] For a second time phase of the reversing operation, in which exclusively the second friction-locking shift element 6, which is to be engaged for the reversing operation, transmits torque, one target torque profile each is ascertained exclusively for this second friction-locking shift element 6 and for the propulsion unit 2.

[0038] For a third time phase of the reversing operation, which lies between the first time phase and the second time phase, one target torque profile each is ascertained for both friction-locking shift elements 5, 6 and for the propulsion unit 2.

[0039] For this third phase of the reversing operation, which lies between the first phase of the reversing operation and the second phase of the reversing operation, the target torque of the first friction-locking shift element 5, which is valid at the end of the first phase and at the beginning of the third phase, is frozen or stored. For the third phase, the frozen or stored target torque of the first friction-locking shift element 5 is reduced to zero along a reduction characteristic curve, in order to thus ascertain the target torque profile for the first friction-locking shift element 5.

[0040] For the third phase, the target torque profile for the propulsion unit 2 is determined according to the frozen or stored target torque of the first friction-locking shift element 5. In the third phase, the target torque profile for the propulsion unit 2 is constant.

[0041] The target torque profile for the second friction-locking shift element 6 is determined in the third phase also according to the frozen or stored target torque of the first friction-locking shift element 5, and also according to the reduction characteristic curve with which the target torque of the first friction-locking shift element 5 is reduced from the frozen or stored target torque.

[0042] For the first time phase of the reversing operation, in which exclusively the first friction-locking shift element 5 transmits torque, the target torque profile M.sub.K1sek-SOLL for the first friction-locking clutch 5 and the target torque profile M.sub.AN-SOLL for the propulsion unit are preferably determined as follows:

[00001]$M_{K1\mathrm{sek}-\mathrm{SOLL}}=\left(J_1*{\stackrel{}{}}_{K1\mathrm{sek}}\right)*i_1+\left(J_2*{\stackrel{}{}}_{K2\mathrm{sek}}\right)*i_2-M_{\mathrm{AB}-\mathrm{SOLL}}$$M_{\mathrm{AN}-\mathrm{SOLL}}=\left(J_{\mathrm{AN}}*{\stackrel{}{}}_{\mathrm{AN}}\right)+\left(J_1*{\stackrel{}{}}_{K1\mathrm{sek}}\right)*i_1+\left(J_2*{\stackrel{}{}}_{K2\mathrm{sek}}\right)*i_2-M_{\mathrm{AB}-\mathrm{SOLL}}$ [0043] wherein [0044] M.sub.K1sek-SOLL is the target torque profile of the first shift element 5, [0045] M.sub.AN-SOLL is the target torque profile of the propulsion unit 2, [0046] J.sub.1 is the moment of inertia acting on the secondary side of the first friction-locking shift element 5, [0047] {acute over ()}.sub.K1sek is the secondary-side angular speed of the first shift element 5, [0048] i.sub.1 is the transmission ratio which is effective for the secondary side of the first shift element 5, [0049] J.sub.2 is the moment of inertia acting on the secondary side of the second friction-locking shift element 6, [0050] {acute over ()}.sub.K2sek is the secondary-side angular speed of the second shift element 6, [0051] i.sub.2 is the transmission ratio which is effective for the secondary side of the second shift element 6, [0052] J.sub.AN is the moment of inertia at the transmission input shaft 10, [0053] {acute over ()}.sub.AN is the angular speed of the transmission input shaft 10, and [0054] M.sub.AB-SOLL is the target torque profile for the transmission output shaft 9.

[0055] For the second phase of the reversing operation, in which exclusively the second friction-locking shift element 6 participates in the torque transmission, the target torque profile M.sub.K2sek-SOLL for the second friction-locking clutch 6 and the target torque profile M.sub.AN-SOLL for the propulsion unit are preferably determined as follows:

[00002]$M_{K2\mathrm{sek}-\mathrm{SOLL}}=\left(J_2*{\stackrel{}{}}_{K2\mathrm{sek}}\right)*i_2+\left(J_1*{\stackrel{}{}}_{K1\mathrm{sek}}\right)*i_1-M_{\mathrm{AB}-\mathrm{SOLL}}$$M_{\mathrm{AN}-\mathrm{SOLL}}=\left(J_{\mathrm{AN}}*{\stackrel{}{}}_{\mathrm{AN}}\right)+\left(J_2*{\stackrel{}{}}_{K2\mathrm{sek}}\right)*i_2+\left(J_1*{\stackrel{}{}}_{K1\mathrm{sek}}\right)*i_1-M_{\mathrm{AB}-\mathrm{SOLL}}$ [0056] wherein [0057] M.sub.K2sek-SOLL is the target torque profile of the second shift element 6, [0058] M.sub.AN-SOLL is the target torque profile of the propulsion unit 2, [0059] J.sub.1 is the moment of inertia acting on the secondary side of the first friction-locking shift element 5, [0060] {acute over ()}.sub.K1sek is the secondary-side angular speed of the first shift element 5, [0061] i.sub.1 is the transmission ratio which is effective for the secondary side of the first shift element 5, [0062] J.sub.2 is the moment of inertia acting on the secondary side of the second friction-locking shift element 6, [0063] {acute over ()}.sub.K2sek is the secondary-side angular speed of the second shift element 6, [0064] i.sub.2 is the transmission ratio which is effective for the secondary side of the second shift element 6, [0065] J.sub.AN is the moment of inertia at the transmission input shaft 10, [0066] {acute over ()}.sub.AN is the angular speed of the transmission input shaft 10, and [0067] M.sub.AB-SOLL is the target torque profile for the transmission output shaft 9.

[0068] For the third phase of the reversing operation, which lies between the first phase of the reversing operation and the second phase of the reversing operation and in which both friction-locking shift elements 5, 6 participate in the torque transmission and in which a torque transmission is to be moved from the first friction-locking shift element 5 to the second friction-locking shift element 6, the target torque of the first friction-locking shift element 5, which is to be disengaged, is first frozen or stored, which target torque is valid at the beginning of the third phase and at the end of the first phase.

[0069] Then, the target torque profile for this first friction-locking shift element 5 is ascertained according to the frozen or stored target torque and a characteristic curve. By this characteristic curve, the frozen or stored target torque for the first friction-locking shift element 5 is reduced from the frozen or stored target torque to zero, for example, along a ramp or another characteristic curve. This characteristic curve is time-normalized.

[0070] Preferably, the target torque profile M.sub.K1sek-SOLL for the first friction-locking shift element 5 in the third phase is determined as follows:

[00003]$M_{K1\mathrm{sek}-\mathrm{SOLL}}=M_{K1\mathrm{sek}-\mathrm{INI}}*\left(1-k\left(t\right)\right)$ [0071] wherein [0072] M.sub.K1sek-SOLL is the target torque profile of the first shift element 5, [0073] M.sub.K1sek-INI is the target torque of the first shift element 5, which was frozen or stored at the beginning of the third phase or at the end of the first phase, and [0074] k(t) is the characteristic curve, which has been normalized over time t, for reducing the target torque of the first shift element 5 to zero.

[0075] For the third phase of the reversing operation, the target torque profile M.sub.AN-SOLL for the propulsion unit 2 is determined according to the frozen or stored target torque M.sub.K1sek-INI of the first friction-locking shift element 5 and is preferably constant.

[0076] Preferably, the target torque profile M.sub.AN-SOLL for the propulsion unit 2 in the third phase is determined as follows:

[00004]$M_{\mathrm{AN}-\mathrm{SOLL}}=J_{\mathrm{AN}}*{\stackrel{}{}}_{\mathrm{AN}}+M_{K1\mathrm{sek}-\mathrm{INI}}$ [0077] wherein [0078] M.sub.AN-SOLL is the target torque profile of the propulsion unit 2, [0079] M.sub.K1sek-INI is the target torque of the first shift element 5, which was frozen or stored at the beginning of the third phase or at the end of the first phase, [0080] J.sub.AN is the moment of inertia at the transmission input shaft 10, and [0081] {acute over ()}AN is the angular speed of the transmission input shaft 10.

[0082] For the third phase, the target torque profile M.sub.K2sek-SOLL for the second friction-locking shift element 6, which is to be engaged during the reversing operation, is determined according to the frozen or stored target torque M.sub.K1sek-INI of the first friction-locking shift element 5 and according to the reduction characteristic curve k(t) for the target torque of the first friction-locking shift element 5.

[0083] Preferably, the target torque profile M.sub.K2sek-SOLL for the second friction-locking shift element 6 in the third phase is determined as follows:

[00005]$\left[M_{K1\mathrm{sek}-\mathrm{INI}}-J_1*{\stackrel{}{}}_{K1\mathrm{sek}}\right]*i_1*\left(1-k\left(t\right)\right)+\left[M_{K2\mathrm{sek}-\mathrm{SOLL}}-J_2*{\stackrel{}{}}_{K2\mathrm{sek}}\right]*i_2*k\left(t\right)+M_{\mathrm{AB}-\mathrm{SOLL}}=0$ [0084] wherein [0085] M.sub.K1sek-INI is the target torque of the first shift element 5, which was frozen or stored at the beginning of the third phase or at the end of the first phase, [0086] J.sub.1 is the moment of inertia acting on the secondary side of the first friction-locking shift element 5, [0087] {acute over ()}.sub.K1sek is the secondary-side angular speed of the first shift element 5, [0088] i.sub.1 is the transmission ratio which is effective for the secondary side of the first shift element 5, [0089] J.sub.2 is the moment of inertia acting on the secondary side of the second friction-locking shift element 6, [0090] {acute over ()}.sub.K2sek is the secondary-side angular speed of the second shift element 6, [0091] i.sub.2 is the transmission ratio which is effective for the secondary side of the second shift element 6, [0092] M.sub.K2sek-SOLL is the target torque profile of the second shift element 6, [0093] M.sub.AB-SOLL is the target torque profile for the transmission output shaft 9. [0094] k(t) is the characteristic curve, which has been normalized over time t, for reducing the target torque of the first shift element 5 to zero.

[0095] The aforementioned equation is to be solved for the target torque M.sub.K2sek-SOLL of the second friction-locking shift element 6.

[0096] FIG. 3 shows multiple time curve profiles over time t, specifically the target torque profile M.sub.AB-SOLL for the transmission output shaft 9 as well as the target torque profiles M.sub.K1sek-SOLL, M.sub.K2sek-SOLL, which have been ascertained in accordance therewith, for the two friction-locking shift elements 5, 6 participating in the reversing operation, as well as the target torque profile M.sub.AN-SOLL for the propulsion unit 2. The period of time between the points in time t1, t2 corresponds to the first time phase 12 of the reversing operation, the period of time between the points in time t3, t4 corresponds to the second time phase 13 of the reversing operation, and the period of time between the points in time t2, t3 corresponds to the third phase 14 of the reversing operation.

[0097] In the first time phase 12 of the reversing operation, exclusively the target profile M.sub.K1sek-SOLL for the first friction-locking shift element 5, which is to be disengaged, as well as the target torque profile M.sub.AN-SOLL for the propulsion unit 2 are ascertained. The target torque profile M.sub.K2sek-SOLL for the second friction-locking shift element 6, which is to be engaged, is zero in the first phase 12.

[0098] In the second time phase 13 of the reversing operation, exclusively the target torque profile M.sub.K2sek-SOLL for the second friction-locking shift element 6, which is to be engaged, as well as the target torque profile M.sub.AN-SOLL for the propulsion unit 2 are ascertained. The target torque profile M.sub.K1sek-SOLL for the first friction-locking shift element 5, which is to be disengaged, is zero in the second phase 13.

[0099] In the third time phase 14 of the reversing operation, the target torque profiles M.sub.K1sek-SOLL, M.sub.K2sek-SOLL for the two friction-locking shift elements 5, 6, which participate in the reversing operation, as well as the target torque profile M.sub.AN-SOLL for the propulsion unit 2 are ascertained. At the end of the first phase and at the beginning of the third phase, i.e., at the point in time t2, the target torque profile M.sub.K1sek-SOLL for the first friction-locking shift element 5, which is to be disengaged, is frozen and stored as M.sub.K1sek-INI. Between the point in time t2 and point in time t3, i.e., in the third phase lying between the first phase and the second phase, the target torque profile M.sub.K1sek-SOLL for the first friction-locking shift element 5, which is to be disengaged, is reduced from the stored value M.sub.K1sek-INI to zero. At the point in time t2, therefore, k(t)=0 and at the point in time t3, this is k(t)=1. The characteristic curve k(t) is time-normalized. The point in time t2 corresponds to the time t=0% in the time-normalized characteristic curve. The point in time t3 corresponds to the time t=100% in the time-normalized characteristic curve. Between the points in time t2, t3, k(t) has a linear profile in FIG. 3. In some instances, the profile of k(t) between the points in time t2 and t3 is non-linear. Between points in time t2, t3, the target torque profile M.sub.AN-SOLL of the propulsion unit 2 is constant.

[0100] The curve profiles M.sub.K1sek-IST, M.sub.K2sek-IST visualize the torques transmitted via the two shift elements 5, 6 in accordance with the aforementioned target torques.

[0101] Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims. In the claims, reference characters corresponding to elements recited in the detailed description and the drawings may be recited. Such reference characters are enclosed within parentheses and are provided as an aid for reference to example embodiments described in the detailed description and the drawings. Such reference characters are provided for convenience only and have no effect on the scope of the claims. In particular, such reference characters are not intended to limit the claims to the particular example embodiments described in the detailed description and the drawings.

REFERENCE CHARACTERS

[0102] 1 drive train [0103] 2 propulsion unit [0104] 3 drive output [0105] 4 transmission [0106] 5 shift element [0107] 6 shift element [0108] 7 wheel [0109] 8 axle transmission [0110] 9 transmission output shaft [0111] 10 transmission input shaft [0112] 11 range [0113] 12 first phase [0114] 13 second phase [0115] 14 third phase