Method and control unit for operating a motor vehicle

Abstract

Method for operating a motor vehicle with a drive unit (1), a transmission (2) having several switching elements (9, 10, 11, 12, 13) and an output (14), wherein the transmission (2) is designed as an automatic or automated transmission and is connected between the drive unit (1) and the output (14), wherein in each frictional gear of the transmission (2) a first number of the switching elements (9, 10, 11, 12, 13) of the transmission (2) are closed or engaged and a second number of the switching elements (9, 10, 11, 12, 13) of the transmission (2) are open or disengaged, wherein, depending on at least one operating condition of the motor vehicle, the drive unit (1) is switched off by the control system and the transmission (2) is brought into a non-load-bearing state, where, depending on at least one operating condition of the motor vehicle, the drive unit (1) is subsequently started via the control system and the transmission (2) is brought into a friction-locked state, wherein in the non-friction-locked state of the transmission (2) one less switching element of the transmission (2) is actuated to close and thus one more switching element of the transmission (2) is actuated to open than in a friction-locked state of the transmission (2), characterized by the fact that Then, when the motor vehicle is rolling with the drive unit (1) switched off and the transmission (2) not in frictional engagement, it is checked whether the synchronous speed of the gear of the transmission (2) that is engaged from the non-frictional state of the transmission (2) to bring it into the frictional state is above or below a first limit value that depends on the fictitious idle speed of the drive unit (1), whereby, depending on whether the synchronous speed is above or below the first limit value that depends on the fictitious idle speed of the drive unit (1), an adapted frictional engagement mode is selected when engaging the gear and thus when bringing the transmission into the frictional state.

Description

[0001] The invention relates to a method for operating a motor vehicle. Furthermore, the invention relates to a control unit for carrying out the method.

[0002] From DE 10 2007 001 499 A1, a method for operating a motor vehicle's drivetrain is known, wherein the drivetrain comprises a drive unit provided by an internal combustion engine and a transmission connected between the drive unit and an output shaft. With an active start / stop system for the drive unit, a speed monitor or a torque monitor checks during the drive unit's start-up process whether a requested power transmission is established in the transmission.

[0003] According to current technology, a start / stop system for a motor vehicle's drive unit is only used when the vehicle is stationary, i.e., when the vehicle is not rolling. When stationary, depending on at least one operating condition of the vehicle, the start / stop system can deactivate the drive unit and put the transmission into a disengaged state. Subsequently, depending on at least one operating condition of the vehicle, the drive unit can be restarted and the transmission put back into a engaged state. Extending the start / stop system beyond stationary operation is not currently possible, as proper power transmission cannot be guaranteed in the transmission while the vehicle is rolling using methods known from the prior art.

[0004] Based on this, the invention aims to create a novel method for operating a motor vehicle and a control unit for operating a motor vehicle.

[0005] This problem is solved by a method for operating a motor vehicle according to claim 1.

[0006] According to the invention, when the motor vehicle is rolling with the drive unit switched off via the start / stop system and the transmission not in frictional engagement, it is checked whether the synchronous speed of the gear of the transmission that is engaged from the non-frictional state of the transmission to bring it into the frictional state is above or below a first limit value that depends on the fictitious idle speed of the drive unit, wherein, depending on whether the synchronous speed is above or below the first limit value that depends on the fictitious idle speed of the drive unit, an adapted frictional engagement mode is selected when engaging the gear and thus when bringing the transmission into the frictional state.

[0007] The invention makes it possible to extend the start / stop system for a drive unit to use while the vehicle is rolling. According to the invention, when the vehicle is rolling with the drive unit deactivated via the start / stop system and the transmission in non-engaged state, the system checks whether the synchronous speed of the transmission gear that is engaged from the non-engaged state to the engaged state is above or below the first limit value, which depends on the hypothetical idle speed of the deactivated drive unit. Depending on this, a suitable engagement mode is selected for engaging the gear. This ultimately allows the start / stop system for the drive unit to be used reliably even while the vehicle is rolling.

[0008] Then, when the synchronous speed is above the first limit value, a first friction-based engagement mode is selected for engaging the gear and thus bringing the transmission into the friction-based state. Preferably, in the first friction-based engagement mode, the drive unit is started on the control side, and the transmission input speed is increased towards the synchronous speed by means of a speed control of the drive unit, and then the shift element of the transmission, which is to be closed to engage the friction-based gear, is preferably fully closed.

[0009] Then, if the synchronous speed is below the first limit, and if the speed of the drive unit is still greater than a second limit, a second power transmission mode is selected for engaging the gear and thus bringing the transmission into the frictional state. Preferably, in this second power transmission mode, the drive unit is started at the control unit, and the transmission input speed is reduced to the synchronous speed by partially closing the transmission's shift element (the one to be closed for engaging the frictional gear). Subsequently, the transmission's shift element (the one to be closed for engaging the frictional gear) is preferably fully closed.

[0010] Then, if the synchronous speed is below the first limit, and if the speed of the drive unit remains below the second limit, a third type of power transmission is selected for engaging the gear and thus bringing the transmission into the frictional state. Preferably, in this third type of power transmission, the drive unit is started at the control unit, and the transmission input speed is brought towards the synchronous speed by partially closing the transmission's shift element (the one to be closed for engaging the frictional gear). Subsequently, the transmission's shift element (the one to be closed for engaging the frictional gear) is preferably fully closed.

[0011] With the three types of frictional connection established above, the drive unit can always be reliably started and frictional connection established in the transmission of a vehicle that is rolling with the drive unit switched off and the transmission not frictionally engaged.

[0012] According to a further advantageous development, if the synchronous speed changes from a value above the first limit value to a value below the first limit value, the system switches from the first to the second frictional connection type. If the synchronous speed is below the first limit value and the speed of the drive unit changes from a value above the second limit value to a value below the second limit value, the system switches from the second to the third frictional connection type. Finally, if the synchronous speed is below the first limit value and the speed of the drive unit changes from a value below the second limit value to a value that is offset above the second limit value, the system switches from the third to the second frictional connection type.Then, when the synchronous speed changes from a value below the first limit to a value that is offset above the first limit, the system switches from the second frictional connection mode to the first. This is preferred to avoid switching back and forth between the different frictional connection modes too frequently.

[0013] The control unit according to the invention is defined in claim 7.

[0014] Preferred embodiments are described in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. The drawing shows: Fig. 1 a powertrain diagram of a motor vehicle with a gearbox; Fig. 2 a shift matrix of the gearbox of the Fig. 1; Fig. 3 a first time diagram to illustrate the invention; Fig. 4 a second time diagram to illustrate the invention; Fig. 5 a third time diagram to illustrate the invention; Fig. 6. A fourth time diagram to illustrate the invention.

[0015] The invention relates to a method and a control unit for operating a motor vehicle and a control unit for carrying out the method.

[0016] Fig. Figure 1 shows a highly schematic representation of the powertrain of a motor vehicle with an automatic transmission. Figure 2. The powertrain of the Fig. 1 comprises a drive unit 1, the automatic transmission 2 and an output 14, wherein the automatic transmission 2 is positioned between the drive unit 1 and the output 14.

[0017] The automatic transmission 2 has several gear sets 3, 4, 5, and 6, as well as several switching elements 9, 10, 11, 12, and 13 that interact with these gear sets. Switching elements 9 and 10 are also referred to as switching elements A and B, and switching elements 11, 12, and 13 are also referred to as switching elements C, D, and E. Switching elements A and B, as well as switching elements C, D, and E, are friction-based switching elements; specifically, switching elements A and B are brakes, and switching elements C, D, and E are clutches.

[0018] Fig. Figure 2 shows a shift matrix of the automatic transmission 2 of the Fig. 1. Fig. 2 can be seen that with the gearbox 2 the Fig. 1. A total of eight forward gears and one reverse gear can be provided. In each of these traction-transmitting gears, a first number of switching elements, namely three switching elements, are closed, whereas a second number of switching elements, namely two switching elements, are open in each traction-transmitting gear. The switching elements that are closed in the respective traction-transmitting gear are in Fig. 2 is marked by a dot. Thus, in forward gear 1, switching elements A, B, and C are closed, and in forward gear 2, switching elements A, B, and E are closed. In reverse gear, switching elements A, B, and D are closed. The switching elements closed in forward gears 3, 4, 5, 6, 7, and 8 also follow from the switching matrix of the Fig. 2.

[0019] Fig. Figure 1 shows that the drive unit 1 is coupled to a transmission input shaft 7 and the output 14 to a transmission output shaft 8. Depending on the gear selected in the transmission 2, the transmission 2 converts speeds and torques, thus providing the tractive force of the drive unit 1 at the output 14.

[0020] In particular, a converter is connected between the drive unit 1 and the transmission input shaft 7, which is in Fig. Figure 1 is not shown. Such a converter has a turbine, the turbine being coupled to the transmission input shaft 7. Furthermore, a converter has a pump, a freewheel, and a converter lock-up clutch. The design of such a converter is familiar to the person skilled in the art.

[0021] Instead of a converter, a starting clutch can also be connected between the drive unit 1 and the transmission input shaft 7.

[0022] It should be noted that the in Fig. 1 shown gearbox 2, which the in Fig. The switching matrix shown in Figure 2 is exemplary in nature. The invention can also be used in motor vehicles with other transmission configurations.

[0023] Like the switching matrix of the Fig. 2 can be taken from, in each traction force-transmitting or force-locking gear of the transmission 2 a first defined number of switching elements 9 to 10 are closed or engaged and a second defined number of switching elements 9 to 13 are open or disengaged. Fig. 2 can be seen that in each friction-fit gear three switching elements are closed and two switching elements are open.

[0024] It is already known from practice that, depending on at least one operating condition of the vehicle, the start / stop system can deactivate the drive unit 1 and put the transmission 2 into a non-engaged state. In this non-engaged state, which the transmission 2 assumes when the drive unit 1 is deactivated by the start / stop system, one shift element of the transmission 2 is activated less frequently to engage and thus one shift element is activated more frequently to disengage than in a fully engaged gear or a fully engaged state of the transmission 2. When the drive unit 1 is deactivated, it can coast to a stop or its rotational speed can decrease. When its rotational speed reaches zero, it comes to a complete stop.Furthermore, it is known in practice that, following the control-side shutdown of the drive unit 1 via the start / stop system, the drive unit 1 of the vehicle can be restarted at the control-side and the transmission 2 returned to a positive-locking state, depending on at least one further operating condition of the vehicle. For this purpose, only a switching element of the transmission 2 needs to be activated to close.

[0025] The invention presented here relates to such details of a method and control unit for operating a motor vehicle, by means of which the start / stop automatic system is not limited to use when the vehicle is stationary, but can instead be extended to a rolling motor vehicle.

[0026] When the vehicle is rolling with the drive unit deactivated and the transmission 2 in a non-engaged state, it is checked whether the synchronous speed of the gear of transmission 2 that is selected to bring it into a engaged state, starting from the non-engaged state, lies above or below a first limit value that depends on the hypothetical idle speed of the drive unit 1. When a drive unit 1 is deactivated, its idle speed corresponds to its hypothetical idle speed. Depending on whether the synchronous speed is above or below the first limit value (dependent on the hypothetical idle speed of the drive unit 1), an appropriate engagement mode is selected to engage the gear and thus bring the transmission 2 into a non-engaged state.

[0027] Then, if the synchronous speed of the exit gear, i.e., the gear of transmission 2 which is engaged from the non-friction-locking state of transmission 2 to bring it into the friction-locking state, is above the first limit value, a first friction-locking configuration is selected for engaging the gear and thus for bringing the transmission into the friction-locking state.

[0028] Then, if the synchronous speed of the exit gear, i.e., the gear of transmission 2 which is engaged from the non-friction-locked state of transmission 2 to bring it into the friction-locked state, is below the first limit value, and if, furthermore, the speed of the drive unit 1 is greater than a second limit value, a second friction-locking mode is selected for engaging the gear and thus bringing transmission 2 into the friction-locked state.

[0029] However, if the synchronous speed of the exit gear is below the first limit value, and if the speed of the drive unit 1 is still less than the second limit value, a third type of frictional connection is chosen for engaging the gear and thus for bringing the transmission 2 into the frictional state.

[0030] The three friction-based connection types differ from each other. Depending on whether the synchronous speed is above or below the first limit value, which depends on the fictitious no-load speed of the drive unit, and depending on whether the speed of drive unit 1 is less than or greater than the second limit value, an appropriate friction-based connection type is selected.

[0031] Further details of the inventive method for operating a motor vehicle are given below with reference to Fig. 3, Fig. 4, Fig. 5 to Fig. 6 described.

[0032] In Fig. Figure 3 shows the synchronous speed of the exit gear over time t with the signal curve 15, i.e. the synchronous speed of that gear of the transmission 2 which is engaged when the motor vehicle is rolling with the drive unit 1 stopped and the transmission 2 not engaged, when the transmission 2 is to be transitioned from a non-engaging state to a friction-engaging state.

[0033] Furthermore, in Fig. Figure 3 shows the following over time t as a function of the drive unit speed 16 of the drive unit 1 sectors X, Y and Z, which illustrate which of the three frictional connection types is selected in each case. This occurs when the synchronous speed 15 is greater than that of the fictitious no-load speed n. LEER of the drive unit 1 dependent first limit value n G1 If the first frictional connection type X is selected, it will be chosen.

[0034] The first limit n G1is greater than the fictitious idle speed n by a positive offset. LEER , i.e., the fictitious idle speed of the drive unit 1.

[0035] Then, when in Fig. 3 at time t1 the synchronous speed 15 of the exit gear starting from a value above the first limit n G1 to a value below the first limit n G1 When the system changes, it switches from the first frictional connection type X to the second frictional connection type Y. In this process, the drive unit speed 16 is initially still greater than a second limit value n. G2 , which is below the fictitious idle speed n LEER of the drive unit 1.

[0036] Then, when the synchronous speed 15 of the exit gear is below the first limit n G1 lies and the drive unit speed 16 changes from a value above the second limit value n G2 to a value below the second limit n G2When the system changes, it switches from the second frictional connection type Y to the third frictional connection type Z.

[0037] Then, when the synchronous speed 15 of the exit gear is below the first limit value n G1 lies and the drive unit speed 16 is below the second limit value n G2 changes to a value that is above the second limit by a defined offset n G2 When the third frictional connection type Z is in place, the system switches back to the second frictional connection type Y.

[0038] Then, if at time t2 the synchronous speed 15 of the exit gear, starting from a value below the first limit n G1 changes to a value that is above the first limit n by a defined offset Δn G1 When the vehicle is in place, the system switches from the second frictional connection type Y to the first frictional connection type X.

[0039] Then, if the synchronous speed 15 of the exit gear, i.e., the gear of transmission 2 that is engaged when transmission 2 is moved from the non-friction-locked state to the friction-locked state, is above the first limit n G1 lies, which is based on the fictitious idle speed n LEER The first frictional engagement type X is selected for engaging the gear and thus bringing the transmission 2 into the frictional state, depending on the drive unit 1, with details of the first frictional engagement type X described below with reference to Fig. 4 will be described.

[0040] Then, if the synchronous speed 15 of the exit gear is below the first limit n G1 lies, and if the drive unit speed 16 continues to be greater than the second limit value n G2If the gear is engaged and thus the transmission 2 is moved from the non-friction-locked state to the friction-locked state, the second friction-locking configuration Y is selected, which is described below with reference to Fig. 5 is described.

[0041] Then, when the synchronous speed is below the first limit n G1 lies, and if the drive unit speed remains 16 less than the second limit value n G2 For engaging the gear and thus transitioning the transmission from a non-friction-locked state to a friction-locked state, the third friction-lock type Z is selected, which is described below with reference to Fig. 6 is described.

[0042] In Fig. Figure 4 shows the curves 15, 16 and 17 over time t, namely a time course of the synchronous speed 15, the time course of the drive unit speed 16 of the drive unit 1 and the time course 17 of the speed of the transmission input shaft 7. Furthermore, curves 18 and 19 are shown, namely curve 18 a time-based pressure control of the switching element of the transmission 2 to be closed for engaging the respective friction-fit gear and curve 19 a torque of the drive unit 1.

[0043] Before time t3 of the Fig. 4. The start / stop system deactivated the drive unit 1 at the control end and put the transmission 2 into a non-engaged state. In Fig. 4. With the drive unit 1 switched off at the control unit, the drive unit speed 16 is zero. The synchronous speed 15 of the disengagement gear, i.e., the gear of the transmission 2 that is engaged from the non-friction-locked state of the transmission 2 to bring it into the friction-locked state, is greater than the first limit n. G1 .

[0044] At time t3, operating conditions for exiting the vehicle exist, on the basis of which the start / stop system starts the drive unit 1 on the control side and brings the transmission 2 into the friction-locked state.

[0045] Following time t3, the frictional gear is then engaged in gearbox 2 using the first frictional transmission method by closing the corresponding switching element of gearbox 2, thereby establishing a frictional connection in gearbox 2.

[0046] The first type of frictional connection Fig. 4 is subdivided into the in Fig. The pressure control phases I to VI of the transmission 2's closing switching element are shown in Figure 4. Following time t3, a defined period is initially waited in Phase I before the switching element is rapidly filled in Phase II. Both Phase I and Phase II are time-controlled and are therefore carried out for a defined period. Upon completion of Phase II, i.e., the rapid filling, the process transitions to the time-controlled Phase III, a filling equalization phase. After the predetermined time for the filling equalization phase III has elapsed, the control pressure for the closing switching element is increased in Phase IV, preferably along a ramp, for a defined period, up to the pressure level of Phase V, at which the switching element does not yet transmit any torque.Phase V remains active and its pressure level unchanged until, via active speed control for the drive unit 1, the speed of the transmission input shaft 7 has been guided into a defined band around the synchronous speed 15. Then, when the speed of the transmission input shaft 7 has been guided into this band around the synchronous speed 15 via the speed control for the drive unit 16, Phase V is terminated and, in Phase VI, the shift element of the transmission 2, which is to be closed to engage the respective positive gear, is fully closed, preferably along the line shown. Fig. The ramp shown in section 4 is time-controlled. At the end of phase VI, power is transmitted in the transmission, so that driving then takes place in a positive-locking gear.

[0047] According to curve 19 of the Fig. 4. A control-side torque limit for the drive unit 1 is inactive during the first friction-based power transmission mode described above. The drive unit torque can be controlled up to its maximum during speed control.

[0048] Then, if a converter is connected between the transmission 2 and the drive unit 1, a converter lock-up clutch is closed or at least in controlled operation during the first power transmission type described above, in order to quickly or with a short response time bring the transmission input speed towards the synchronous speed.

[0049] Then, if the synchronous speed 15 of the disengagement gear of the transmission 2 is below the first limit value nG1, which depends on the fictitious idle speed of the drive unit 1, and if the speed of the drive unit 1 is also greater than a second limit value nG2, the second frictional engagement mode is selected for engaging the gear and thus bringing the transmission 2 into the frictional state, with details of this being provided in Fig. 5 are shown. Fig. Figure 5 shows the curves 15, 16, 17, 18, and 19 over time t, where curve 15 represents the synchronous speed of the positive-locking gear to be engaged, curve 16 the speed of the drive unit 1, and curve 17 the speed of the transmission input shaft 7. Curve 18 represents the pressure control of the switching element of the transmission 2 to be closed, and curve 19 a torque of the drive unit 1.

[0050] In Fig. At time t3, operating conditions for exiting the vehicle are again present, based on which the start / stop system starts the drive unit 1 at the control end and the transmission 2 is brought into the frictional state. At time t3, in Fig. 5 the synchronous speed 15 smaller than that of the fictitious idle speed n LEER of the drive unit 1 dependent limit value n G1and the rotational speed of the drive unit 1 is greater than the second limit value n G2 .

[0051] In the second type of force-fit construction of the Fig. In the time-controlled phase I of the pressure control 18, a defined period of time is waited until the rapid filling of the closing switching element of the transmission 2 takes place in the time-controlled phase II of the pressure control 18. The time-controlled phase II of the pressure control 18 is followed by the time-controlled phase III of the pressure control 18, which is again a time-controlled filling equalization phase.

[0052] Phase III of the pressure control 18 is followed by the time-controlled phase IV of the pressure control 18, in which the switching pressure for the switching element to be closed is increased in a time-controlled manner, preferably along a ramp, to the pressure level at the beginning of phase V, at which the switching element does not yet transmit any torque.

[0053] Subsequently, in phase V of the pressure control 18, the switching pressure is further increased, but with a lower gradient than in phase IV. Phase V is not time-controlled, but rather event-controlled, such that phase V ends when the speed of the transmission input shaft 7 has been reduced to a range around the synchronous speed via the second power transmission method, thus establishing synchronous conditions. If this occurs, phase V ends, and the switching element to engage the gear is then fully closed by the time-controlled phase VI. In phase V of the pressure control 18 of the second power transmission method of the Fig. 5 can transmit the torque to the switching element to be closed.

[0054] According to curve 19 of the Fig. 5 is a control-side torque limit for the drive unit 1 active in the second frictional connection type described above.

[0055] Then, when a converter is connected between the transmission 2 and the drive unit 1, the converter lock-up clutch is open during the second power transmission type described above.

[0056] So while in Fig. 4. In phase V, the switching element to be closed is only closed to the extent that it cannot yet transmit a torque. Fig. 5. The switching element to be closed is already closed to the point where it can transmit torque to reduce the speed at the transmission input 7 towards the synchronous speed. If the synchronous conditions between the speed of the transmission input shaft 7 and the synchronous speed are met, phase VI begins, in which the switching element of the transmission 2 is then fully closed in a time-controlled manner.

[0057] Then, when the synchronous speed 15 of that exit gear of the transmission 2 is below the first limit value n which depends on the fictitious idle speed of the drive unit 1 G1 lies, and if the drive unit speed remains 16 less than the second limit value n G2 If the gear is engaged and the transmission 2 is thus brought into the frictional state, the third frictional engagement type is selected, with details in Fig. 6 are shown.

[0058] In Fig. Figure 6 shows the curves 15, 16, 17, 18, and 19 over time t, where curve 15 represents the synchronous speed of the positive-locking gear to be engaged, curve 16 the speed of the drive unit 1, and curve 17 the speed of the transmission input shaft 7. Curve 18 represents the pressure control of the switching element of the transmission 2 to be closed, and curve 19 a torque of the drive unit 1.

[0059] In Fig. At time t3, operating conditions for exiting the vehicle are again present, based on which the start / stop system starts the drive unit 1 at the control end and the transmission 2 is brought into a positive-lock state. At time t3, in Fig. 5 the synchronous speed 15 smaller than the first limit value n dependent on the fictitious idle speed of the control-side deactivated drive unit 1 G1, furthermore the rotational speed of the drive unit 1 is less than the second limit value n G2 .

[0060] In the third type of force-fit connection, the Fig. 6. First, the drive unit 1 is started by the control system, and in phase I of the pressure control 18, a defined waiting period is observed until, in the time-controlled phase II of the pressure control 18, the rapid filling of the switching element of the gearbox 2 to be closed takes place. The length of phase I depends on when the rotational speed of the drive unit 1 and the gearbox input speed of the gearbox 2 have reached their respective first threshold values. Phase III of the pressure control 18, which is a filling compensation phase, follows the time-controlled phase II of the pressure control 18. The length of phase III depends on when the rotational speed of the drive unit 1 and the gearbox input speed of the gearbox 2 have reached their respective second threshold values.

[0061] Phase III of the pressure control 18 is followed by the time-controlled Phase IV of the pressure control 18, in which the switching pressure for the switching element to be closed is increased in a time-controlled manner, preferably along a ramp, to the pressure level at the beginning of Phase V, at which the switching element is not yet transmitting any torque. Subsequently, in Phase V of the pressure control 18, the switching pressure is further increased, but with a lower slope than in Phase IV. Phase V is not time-controlled, but rather event-controlled, such that Phase V ends when, via the third force-locking mechanism, the rotational speed of the transmission input shaft 7 has been brought into a range around the synchronous speed, thus establishing synchronous conditions. If this occurs, Phase V ends, and the switching element to be closed for gear engagement is then fully closed by the time-controlled Phase VI.In phase V of the pressure control 18 of the third force-lock formation type of the . Fig. 6 can transmit torque to the switching element to be closed.

[0062] According to curve 19 of the Fig. 6 is a control-side torque limitation for the drive unit 1 active in the third frictional connection type described above.

[0063] Then, when a converter is connected between the transmission 2 and the drive unit 1, the converter lock-up clutch is open during the second power transmission type described above.

[0064] It is therefore in line with the present invention that, when a motor vehicle is rolling after being brought to a standstill by the start / stop system, it is checked whether the synchronous speed of the disengagement gear of the transmission 2, which is engaged to transition the transmission 2 from a non-friction-locked state to a friction-locked state, is above or below the first limit value, which depends on the fictitious idle speed of the drive unit 1. If this synchronous speed of the disengagement gear is above the first limit value, the first friction-lock mode is used.

[0065] Then, if the synchronous speed of the exit gear is below this first limit value, which depends on the fictitious idle speed of the drive unit, it is further checked whether the speed of the drive unit is above or below a second limit value. Depending on this, the second or third frictional engagement mode is used to bring the transmission into the frictional state.

[0066] In a simplified embodiment, the second limit value is selected such that the second frictional engagement mode is used when the drive unit 1 is running and the third frictional engagement mode is used when the drive unit 1 is stationary, namely when the synchronous speed of the exit gear is below the first limit value, which depends on the fictitious no-load speed of the drive unit 1. However, the second limit value can also be selected differently.

[0067] The invention further relates to a control unit for operating a motor vehicle, wherein the control unit is preferably an electronic transmission control unit.

[0068] Then, when the vehicle is rolling with the drive unit 1 switched off and the transmission 2 not in frictional engagement, the control unit checks whether the synchronous speed of the gear of transmission 2, which is engaged from the non-frictional state of transmission 2 to bring it into frictional engagement, is above or below a first limit value dependent on the fictitious idle speed of the drive unit 1, whereby, depending on whether the synchronous speed is above or below the first limit value dependent on the fictitious idle speed of the drive unit 1, the control unit selects an adapted frictional engagement mode when engaging the gear and thus bringing the transmission into frictional engagement, in the manner described above.

[0069] The control unit comprises means for carrying out the method, namely hardware-related means and software-related means. The hardware-related means include data interfaces for exchanging data with the assemblies involved in carrying out the method according to the invention, such as control valves of the switching elements and a speed sensor, which serves to measure the transmission input speed. Furthermore, the transmission control unit comprises, as hardware-related means, a memory for data storage and a processor for data processing. As software-related means, the control unit comprises program modules for carrying out the method according to the invention. Reference sign 1 drive unit 2 automatic transmissions 3 wheelset 4 wheelset 5 wheelset 6 wheelset 7 Gearbox input shaft 8 Gearbox output shaft 9 Switching element A 10 Switching element B 11 Switching element C 12 Switching element D 13 Switching element E 14 Drive 15 Curve progression Synchronous speed 16 Curve progression Drive unit speed 17 Curve of gearbox input speed 18 Curve progression pressure control 19 Curve of drive unit torque Phase I Phase II Phase III Phase IV V Phase Phase VI n G1 first limit n G2 second limit value n LEER Idle speed Δn Offset t time t1 Time t2 time t3 time

Claims

Method for operating a motor vehicle with a drive unit (1), a transmission (2) having several switching elements (9, 10, 11, 12, 13) and an output (14), wherein the transmission (2) is designed as an automatic or automated transmission and is connected between the drive unit (1) and the output (14), wherein in each frictional gear of the transmission (2) a first number of the switching elements (9, 10, 11, 12, 13) of the transmission (2) are closed or engaged and a second number of the switching elements (9, 10, 11, 12, 13) of the transmission (2) are opened or disengaged, wherein, depending on at least one operating condition of the motor vehicle, the drive unit (1) is deactivated by a control system and the transmission (2) is brought into a frictionless state.wherein, depending on at least one operating condition of the motor vehicle, the drive unit (1) is subsequently started via the start / stop system and the transmission (2) is brought into a friction-locked state, wherein in the non-friction-locked state of the transmission (2) one less switching element of the transmission (2) is actuated to close and thus one more switching element of the transmission (2) is actuated to open than in a friction-locked state of the transmission (2), characterized in that when the motor vehicle is rolling with the drive unit (1) stopped and the transmission (2) not in friction-locked state, it is checked whether a synchronous speed of the gear of the transmission (2) which is engaged from the non-friction-locked state of the transmission (2) to bring it into the friction-locked state is above or below a first limit value dependent on the fictitious idle speed of the drive unit (1),where, depending on whether the synchronous speed is above or below the first limit value which depends on the fictitious idle speed of the drive unit (1), an adapted frictional engagement mode is selected when the gear is engaged and thus when the transmission is brought into the frictional state. The method according to claim 1, characterized in that, when the synchronous speed is above the first limit value, a first frictional connection type is selected for engaging the gear and thus bringing the transmission into the frictional state; when the synchronous speed is below the first limit value and the speed of the drive unit is also greater than a second limit value, a second frictional connection type is selected for engaging the gear and thus bringing the transmission into the frictional state; when the synchronous speed is below the first limit value and the speed of the drive unit is also less than the second limit value, a third frictional connection type is selected for engaging the gear and thus bringing the transmission into the frictional state. The method according to claim 2, characterized in that, when the synchronous speed changes from a value above the first limit value to a value below the first limit value, the system switches from the first frictional connection type to the second frictional connection type; when the synchronous speed is below the first limit value and the speed of the drive unit changes from a value above the second limit value to a value below the second limit value, the system switches from the second frictional connection type to the third frictional connection type; when the synchronous speed is below the first limit value and the speed of the drive unit changes from a value below the second limit value to a value that is offset above the second limit value, the system switches from the third frictional connection type to the second frictional connection type.When the synchronous speed changes from a value below the first limit value to a value that is offset above the first limit value, the system switches from the second frictional connection type to the first frictional connection type. Method according to claim 2 or 3, characterized in that in the first frictional connection configuration the drive unit (1) is started on the control side and a transmission input speed of the transmission (2) is increased towards the synchronous speed by means of a speed control of the drive unit (1) and then the switching element of the transmission (2) to be closed for engaging the frictional gear is preferably completely closed. Method according to one of claims 2 to 4, characterized in that in the second frictional transmission configuration the drive unit (1) is started on the control side and a transmission input speed of the transmission (2) is reduced to the synchronous speed by partially closing the switching element of the transmission (2) to engage the frictional gear, and then the switching element of the transmission (2) to engage the frictional gear is preferably completely closed. Method according to one of claims 2 to 5, characterized in that in the third frictional transmission configuration the drive unit (1) is started on the control side and a transmission input speed of the transmission (2) is brought towards the synchronous speed by partially closing the switching element of the transmission (2) to engage the frictional gear, and subsequently the switching element of the transmission (2) to engage the frictional gear is preferably completely closed. Control unit for operating a motor vehicle with a drive unit (1), a transmission (2) having several switching elements (9, 10, 11, 12, 13) and an output (14), wherein the transmission (2) is designed as an automatic or automated manual transmission and is connected between the drive unit (1) and the output (14), wherein the control unit, in each engaged, friction-fit gear of the transmission (2), controls a first number of the switching elements (9, 10, 11, 12, 13) of the transmission (2) to close and a second number of the switching elements (9, 10, 11, 12, 13) of the transmission (2) to open, depending on at least one operating condition of the motor vehicle, the control unit shuts down the drive unit (1) via a start / stop system and puts the transmission (2) into a friction-free state.Subsequently, depending on at least one operating condition of the motor vehicle, the drive unit (1) is started via the start / stop system and the transmission (2) is brought into a friction-fit state, in the non-friction-fit state of the transmission (2) one less switching element of the transmission (2) is actuated to close and thus one more switching element of the transmission (2) is actuated to open than in a friction-fit state of the transmission (2), characterized in that the control unit, when the motor vehicle is rolling with the drive unit (1) switched off and the transmission (2) in a non-friction-fit state, checks whether the synchronous speed of the gear of the transmission (2) that is engaged from the non-friction-fit state of the transmission (2) to bring it into the friction-fit state is above or below a first limit value that depends on the fictitious idle speed of the drive unit (1),the control unit selects an adapted power transmission mode when engaging the gear and thus transitioning the transmission into the power-locked state, depending on whether the synchronous speed is above or below the first limit value. Control unit according to claim 7, characterized in that, when the synchronous speed is above the first limit value, it selects a first frictional connection type for engaging the gear and thus bringing the transmission into the frictional state; when the synchronous speed is below the first limit value and the speed of the drive unit is also greater than a second limit value, it selects a second frictional connection type for engaging the gear and thus bringing the transmission into the frictional state; when the synchronous speed is below the first limit value and the speed of the drive unit is also less than the second limit value, it selects a third frictional connection type for engaging the gear and thus bringing the transmission into the frictional state. Control unit according to claim 8, characterized in that it switches from the first frictional connection type to the second frictional connection type when the synchronous speed changes from a value above the first limit value to a value below the first limit value; then, when the synchronous speed is below the first limit value and the speed of the drive unit changes from a value above the second limit value to a value below the second limit value, it switches from the second frictional connection type to the third frictional connection type; then, when the synchronous speed is below the first limit value and the speed of the drive unit changes from a value below the second limit value to a value that is offset above the second limit value, it switches from the third frictional connection type to the second frictional connection type.when the synchronous speed changes from a value below the first limit value to a value that is offset above the first limit value, switching from the second frictional connection type to the first frictional connection type. Control unit according to claim 8 or 9, characterized in that, in the first power transmission configuration, it starts the drive unit (1) on the control side and increases a transmission input speed of the transmission (2) towards the synchronous speed by means of a speed control of the drive unit (1) and then actuates the switching element of the transmission (2) to engage the positive gear, preferably to close completely, and / or, in the second power transmission configuration, it starts the drive unit (1) on the control side and reduces a transmission input speed of the transmission (2) towards the synchronous speed by actuating the switching element of the transmission (2) to engage the positive gear, to partially close it, and then actuates the switching element of the transmission to engage the positive gear, preferably to close completely.and / or in the third type of power transmission, the drive unit (1) is started on the control side and a transmission input speed of the transmission (2) is converted to the synchronous speed by actuating the switching element of the transmission (2) to partially close it in order to engage the power-engaging gear, and subsequently actuates the switching element of the transmission to preferably fully close it in order to engage the power-engaging gear.

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