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 engaged, friction-fit 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, where, depending on at least one operating condition of the motor vehicle, a sailing mode is entered, wherein, to enter the sailing mode of the motor vehicle, starting from a friction-locked gear, a switching element of the transmission (2) is actuated to open, so that in a non-friction-locked sailing gear one switching element is less closed and thus one switching element is more open than in a friction-locked gear, wherein, in the sailing mode of the motor vehicle with the drive unit (1) switched off, the respective closed and open switching elements of the transmission (2) are changed depending on at least one operating condition of the motor vehicle to maintain the sailing gear, characterized by the fact that then, when the drive unit (1) is started, the gearbox input speed of the gearbox (2) and the speed of the drive unit (1) are evaluated to conclude that the gearbox (2) is improperly preloaded, in which the gearbox is blocked on the input side and can rotate freely on the output side.

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] German patent application DE 10 2011 005 320 A1 discloses a method for operating a motor vehicle comprising a drive unit, a transmission, and an output shaft, wherein the transmission is connected between the drive unit and the output shaft. The transmission is an automatic or automated manual transmission. According to DE 10 2011 005 320 A1, depending on at least one operating condition of the motor vehicle, a coasting mode is activated or entered, and subsequently, depending on at least one operating condition of the motor vehicle, the coasting mode is deactivated or exited.During the journey of the motor vehicle with the combustion engine running and coupled to the drive system, the sailing mode is activated when a driver-requested torque dependent on accelerator pedal operation or a driving torque specified by a driver assistance system remains within a defined range for a defined time and when the current acceleration or deceleration of the motor vehicle also remains within a defined range.

[0003] From DE 10 2011 005 284 A1, a method for initiating a coasting mode is known in which a torque converter lock-up clutch of a torque converter is closed or brought into a state with low slip. Furthermore, the transmission capacity of a shift element that transmits torque in a driving gear is reduced, so that slip occurs at the same element.

[0004] DE 10 2014 219 598 A1 discloses details for terminating the sailing mode and thus details for exiting a sailing operation. According to this, to terminate the sailing mode, a target gear is specified for the transmission and a speed control is set for the drive unit. During speed control, the system monitors which switching elements of the transmission are to be considered closed, and a monitoring function is triggered when a defined number of switching elements are considered closed.

[0005] From DE10 2015 220 999 A1, it is known that when a sailing mode is entered, the closed and open switching elements of the transmission are adjusted or changed depending on at least one operating condition of the vehicle. This ensures that when exiting sailing mode, a suitable, friction-fit gear can be engaged in the transmission as quickly and smoothly as possible. Thus, when the closed and open switching elements are adjusted in sailing mode, a change from the current sailing gear to a target sailing gear occurs during sailing mode, with one more switching element being open in each sailing gear than in a friction-fit gear. To exit sailing mode, only one additional switching element of the transmission needs to be closed, starting from the current sailing gear, to engage a friction-fit gear in the transmission.

[0006] Further methods for operating a motor vehicle with a drive unit, a transmission having several switching elements and a drive, wherein a sailing mode is entered depending on at least one operating condition of the motor vehicle, are also known from documents DE 10 2017 203 790 B3, DE 10 2015 209 949 A1 and DE 10 2016 208 751 A1.

[0007] As explained above, it is known that in each engaged, friction-fit gear of the transmission, a defined first number of the transmission's shift elements are closed or engaged, and a defined second number of the transmission's shift elements are open or disengaged. In coasting mode, compared to a friction-fit gear, one more shift element of the transmission is open, and thus one fewer shift element is closed. It is also known that in coasting mode, depending on at least one operating condition of the vehicle, the non-friction-fit coasting gears are adjusted, whereby in each non-friction-fitted, adjusted coasting gear, only one more shift element is open compared to a friction-fit gear.

[0008] When sailing with the engine off, it is currently only possible to check, during the sailing gear adjustment in sailing mode, whether a positive-locking gear or an over-determined transmission is unintentionally formed during the gear adjustment while sailing, in motor vehicles known from practice.

[0009] In a friction-based gear, torque can be transmitted from the transmission input towards the transmission output. In an over-constrained gear, at least one more shift element is closed than in a friction-based gear.

[0010] Currently, it is not possible to check whether a gearbox misalignment develops during gear selection while the engine is off during coasting mode. With a misaligned gearbox, the output side may rotate freely, but the input side is blocked. It is desirable to be able to detect this condition reliably.

[0011] 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.

[0012] This problem is solved by a method according to claim 1. According to the invention, when the drive unit is started, the gearbox input speed and the speed of the drive unit are evaluated to determine if the gearbox is improperly preloaded, in which the gearbox is blocked on the input side but can rotate freely on the output side. By evaluating the gearbox input speed and the speed of the drive unit that result from the start-up of the drive unit, a misaligned gearbox can be determined simply and reliably. The start-up of the drive unit can be initiated, for example, by switching from sailing with the drive unit stationary to sailing with the drive unit running, or by the control system when exiting sailing mode.The restart of the drive unit can also be triggered by a monitoring function on the control side without changing the driving strategy, for example to check whether the transmission is incorrectly tensioned when the vehicle has been operated in sailing mode with the drive unit switched off for a certain period of time.

[0013] According to a first embodiment of the invention, if, to start the drive unit, a starting element of the motor vehicle is brought into a defined slip to provide slip decoupling, and if, during slip decoupling, the resulting transmission input speed is less than a first threshold value and simultaneously, the resulting difference between the speed of the drive unit and the transmission input speed is greater than a second threshold value, then a conclusion is drawn that the transmission is improperly preloaded. This first embodiment of the invention is advantageously applicable to motor vehicles that use slip decoupling to start the drive unit. It allows for a simple and reliable conclusion to be drawn that the transmission is improperly preloaded.

[0014] According to a second embodiment of the invention, if no slip decoupling is used to start the drive unit, and if, without slip decoupling, the resulting transmission input speed is less than a first threshold value and simultaneously the difference between the speed of the drive unit and the transmission input speed is less than a second threshold value, then a faulty transmission is inferred. This second embodiment of the invention is advantageously used to detect a faulty transmission when no slip decoupling is used to start the drive unit.

[0015] The control unit according to the invention is defined in claim 6.

[0016] 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 a first variant of the invention; and Fig. 4. A second time diagram to illustrate a second variant of the invention.

[0017] 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.

[0018] 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.

[0019] 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 positive-locking and thus traction-transmitting forward gears and one positive-locking and thus traction-transmitting reverse gear can be provided. In each of these traction-transmitting gears, a defined first number of switching elements, namely three switching elements, are closed, whereas a defined second number of switching elements, namely two switching elements, are open in each traction-transmitting and thus positive-locking gear.

[0020] The switching elements, which are closed in the respective force-locking and thus force-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.

[0021] 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.

[0022] Between the drive unit 1 and the transmission input shaft 7 is in Fig. In the embodiment shown in Figure 1, a torque converter 15 is used as a hydrodynamic starting element. Such a torque converter 15 has a turbine 16, which is coupled to the transmission input shaft 7. Furthermore, the torque converter 15 has a pump 17 and a torque converter lock-up clutch 18. The design of such a torque converter is familiar to those skilled in the art. Instead of a torque converter, a starting clutch can also be used as the starting element between the drive unit 1 and the transmission input shaft 7. An internal transmission clutch can also serve as the starting element.

[0023] 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 transmissions.

[0024] Like the switching matrix of the Fig. 2 can be taken from, in each force-locking and thus traction-transmitting gear of the transmission 2 a first defined number N of the switching elements 9 to 10 are closed or engaged and a second defined number M of the switching elements 9 to 13 are open or disengaged. Fig. It can be deduced from Figure 2 that in each friction-transmitting gear, N=3 switching elements are closed and M=2 switching elements are open. It is already known that when a friction-transmitting gear is engaged in the transmission 2 and the vehicle is traveling in this friction-transmitting gear, a coasting mode is entered depending on at least one operating condition of the vehicle. To enter coasting mode, a switching element of the transmission 2, which is closed in the friction-transmitting gear, is actuated to open from a friction-transmitting gear.

[0025] In sailing mode, one less switching element is closed, and thus one more switching element is open, compared to a friction-based gear, so that the power transmission in gearbox 2 is interrupted. The switching elements of gearbox 2 that are closed in sailing mode form a non-friction-based and therefore non-traction-transmitting sailing gear.

[0026] Furthermore, it is already known that after entering a sailing mode, it is possible to exit sailing mode again depending on at least one operating condition of the vehicle. For this purpose, a switching element is closed from sailing mode to engage a positively driven gear that transmits traction.

[0027] Furthermore, it is already known that in the sailing mode of the motor vehicle, the closed and open switching elements of transmission 2 are adjusted or changed depending on at least one operating condition of the motor vehicle. This ensures that the non-power-engaged and therefore non-traction-transmitting sailing gear is adjusted in sailing mode. This adjustment of the sailing gear allows for a spontaneous and comfortable exit from sailing mode.

[0028] As explained above, in each frictional gear of transmission 2, a defined first number of shift elements 9 to 13 are closed and a defined second number of shift elements 9 to 13 are open. When the vehicle's coasting mode is active, one more shift element of transmission 2 is open in coasting mode than in a frictional gear. The shift elements that are closed in coasting mode define the so-called non-frictional coasting gear, from which a shift to a frictional gear can be initiated to exit coasting mode by closing another shift element.

[0029] When tracking the non-force-locking and therefore non-traction-transmitting sail gears in sailing mode, it can happen that a switching element that should open during gear tracking fails to open, but instead remains closed.

[0030] During sailing mode, a state can develop in which a number of switching elements are closed that corresponds to the number of switching elements closed in a force-locking and thus traction-transmitting gear. If one of the in Fig. If the two switching element combinations shown are closed, an undesired force transmission can then develop during sailing mode, originating from the transmission input shaft 7 in the direction of the transmission output shaft 8.

[0031] Furthermore, a state can develop in which a larger number of switching elements are closed in sailing mode than in a force-locking and thus traction-transmitting gear, resulting in an overdetermined transmission.

[0032] Furthermore, if, during gear selection in sailing mode, a switching element of the transmission 2 that is to be opened cannot be opened or disengaged, a state of faulty preload on the transmission 2 can develop, in which the transmission output shaft 8 and thus the transmission 2 can rotate freely on the output side, but the transmission input shaft 7 and thus the transmission 2 is blocked on the input side. In the case of the transmission Fig. 1. This is the case when switching elements A, C, and E are closed during sailing mode. With an incorrectly preloaded gearbox, the gearbox is neither frictionally engaged nor capable of transmitting tractive force, nor is it over-constrained. Although a number of switching elements are closed in an incorrectly preloaded gearbox, corresponding to the number of switching elements closed in a frictionally engaged and thus tractive force-transmitting gear, no tractive force can be transmitted from the gearbox input shaft 7 to the gearbox output shaft 8 due to the combination of closed switching elements.

[0033] When sailing with the propulsion unit switched off, an undesirable force-locking gearbox or an undesirable over-constrained gearbox can be detected, and this is already implemented in practice. However, it is not yet possible to reliably detect a faultily preloaded gearbox.

[0034] Then, when the motor vehicle is in sailing mode with the drive unit switched off, and the respective closed and open switching elements of the transmission are changed depending on at least one operating condition of the motor vehicle to maintain the sailing gear, the transmission input speed of the transmission 2 or the speed of the transmission input shaft 7 and the speed of the drive unit 1 are evaluated when the drive unit 1 is started or restarted, in order to conclude that the transmission 2 is improperly preloaded, in which the transmission 2 can rotate freely on the output side at the transmission output shaft 8, but is blocked on the input side at the transmission input shaft 7.The invention relates to a transmission that is incorrectly pre-tensioned in such a way, in which a number of switching elements are closed that corresponds to the number that is closed in a force-locking and thus traction-transmitting gear, but in which, on the basis of the combination of the closed switching elements, no traction force can be transmitted from the transmission input shaft 7 towards the transmission output shaft 8, depending on the speed of the input shaft 7 of the transmission 2 and depending on the speed of the drive unit 1, which are then formed when, starting from the sailing mode with the drive unit stationary, the drive unit 1 is started.

[0035] In a first embodiment of the invention, it is provided that, in order to start the drive unit 1 from the sailing mode with the drive unit 1 stationary, a slip decoupling is used by bringing a starting element of the motor vehicle, which is preferably switched between the transmission 1 and the transmission 2, into a defined slip.

[0036] In the powertrain of the Fig. 1. Slip decoupling is ensured by bringing the torque converter lock-up clutch 18 into a defined slip. If no torque converter 15 is engaged between drive unit 1 and transmission 2, but rather a starting clutch, this starting clutch can be brought into a defined slip to achieve slip decoupling. Alternatively, an internal transmission shift element can also be brought into a defined slip to achieve slip decoupling.

[0037] According to the first variant, the rotational speed of the transmission input shaft 7 of transmission 2, as well as the rotational speed of the drive unit 1, are recorded and evaluated when slip decoupling is active and the drive unit 1 is started. If the resulting transmission input speed of transmission 2 is less than a first threshold value S1 and simultaneously the difference between the rotational speed of the drive unit 1 and the transmission input speed of transmission 2 is greater than a second threshold value S2, then a conclusion is drawn that transmission 2 is incorrectly preloaded.

[0038] Further details of this first variant of the invention will emerge from Fig. 3. In Fig. Figure 3 shows two rotational speed curves n over time t: curve n1 represents the rotational speed of the transmission input shaft 7, and curve n2 represents the rotational speed of the drive unit 1. Before time t1, the vehicle is coasting with the drive unit stationary. At time t1, the drive unit 1 is to be started or partially started. According to the first variant, the drive train is... Fig. 1 the converter lock-up clutch 18 defined in slippage.

[0039] Fig. 3 can be deduced that after time t1, i.e. after the start-up of the drive unit 1, the rotational speed n1 at the transmission input shaft 7 is or remains smaller than the first threshold value S1, while at the same time a developing difference Δn between the rotational speed n2 of the drive unit 1 and the rotational speed n1 of the transmission input shaft 7 of the transmission 2 is or becomes larger than the threshold value S2.

[0040] In Fig. At time t2, it is detected that the difference Δn between the rotational speed n2 of the drive unit 1 and the rotational speed n1 of the transmission input shaft 7 of the transmission 2 is greater than the threshold value S2, and simultaneously the transmission input speed n1 is less than the first threshold value S1. At time t2, a conclusion is then drawn that the transmission 2 is improperly preloaded.

[0041] It may be possible to limit this monitoring after the start-up of the drive unit 1 at time t1 to a maximum monitoring duration, i.e., to conclude that the gearbox 2 is incorrectly preloaded only if, within the maximum monitoring duration after the start-up of the drive unit 1 at time t1, the developing gearbox input speed of the gearbox 2 is or remains below the first threshold value and, at the same time, the developing difference between the speed of the drive unit 1 and the gearbox input speed of the gearbox 2 is or becomes above the second threshold value.

[0042] As already explained, a faulty gearbox 2 corresponds to a state of gearbox 2 in which a number of switching elements are closed that corresponds to the number closed in a frictionally engaged and thus force-transmitting gear of gearbox 2, but in which, based on the combination of closed switching elements, no tractive force can be transmitted from the gearbox input towards the gearbox output. In the gearbox of Fig. 1 corresponds to the combination of switching elements A, C and E.

[0043] The invention allows for the conclusion that the transmission is improperly preloaded even if no slip decoupling is used when starting the drive unit 1. For this purpose, after starting the drive unit 1, the rotational speed at the transmission input shaft 7 of the transmission 2 and the rotational speed of the drive unit 1 are again recorded and evaluated. This evaluation is performed such that if, without slip decoupling after starting the drive unit 1, the resulting transmission input speed of the transmission 2 is less than a first threshold value and, simultaneously, the difference between the rotational speed of the drive unit and the transmission input speed of the transmission is or remains less than a second threshold value, then a conclusion is drawn that the transmission 2 is improperly preloaded.

[0044] Details of the inventive method according to the second variant, i.e., the variant without slip decoupling when starting the drive unit 1, are described below with reference to Fig. 4 described.

[0045] In Fig. Figure 4 shows two speed profiles over time t: speed n1 is the speed of the transmission input shaft 7, and speed n2 is the speed of the drive unit 1. Before time t1, the vehicle is sailing with the drive unit stopped.

[0046] At time t1, the drive unit is to be started or restarted. During this process, in Fig. 4. No slip decoupling is used. The rotational speeds n1 and n2 that develop after the desired start of the drive unit 1 are monitored.

[0047] In Fig. 4. Both the rotational speed n1 of the transmission input shaft 7 and the difference between the rotational speed n2 of the drive unit 1 and the rotational speed n1 of the transmission input shaft 7 remain smaller than a threshold value S. In Fig. 4 corresponds to the threshold S1 and the threshold S2.

[0048] If, without slip decoupling, both the developing rotational speed n1 at the gearbox input and the resulting difference between the rotational speed of the drive unit 1 and the rotational speed at the gearbox input are and remain below the threshold value S, a conclusion is drawn that the gearbox 2 is incorrectly preloaded. This monitoring takes place for a defined period until time t2. Fig.4. If, after the start of the drive unit 1, the rotational speed n1 of the transmission input shaft 7 and the difference between the rotational speed n2 of the drive unit 1 and the rotational speed n1 of the transmission input shaft 7 both remain below the threshold value S at time t1 until time t2, then at time t2 it is concluded that the transmission 2 is improperly preloaded.

[0049] The invention further relates to a control unit for operating a motor vehicle, specifically for carrying out the method described above. In each engaged, friction-fit gear of the transmission 2, the control unit controls a first number of switching elements of the transmission 2 to close and a second number of switching elements of the transmission 2 to open.

[0050] Depending on at least one operating condition of the motor vehicle, the control unit can control the transmission 2 to enter and exit a sailing mode, whereby, to enter a sailing mode, the control unit, starting from a force-engaged and thus traction-transmitting gear, controls a switching element of the transmission 2 to open, so that in a non-force-engaged and thus non-traction-transmitting sailing gear, one switching element is less closed and thus one switching element of the transmission 2 is more open than in a force-engaged and thus traction-transmitting gear.

[0051] In sailing mode, the control unit controls the switching elements of gearbox 2 to maintain the sailing gear, depending on at least one operating condition.

[0052] Then, when the control unit activates drive unit 1 from a sailing mode with drive unit 1 stationary, the control unit evaluates both the transmission input speed of the transmission and the speed of drive unit 1 to conclude, based on these speeds, that the transmission is improperly preloaded. This involves evaluating both the speed at the transmission input shaft 7 of transmission 2 and the difference between the speed of drive unit 1 and the speed of the transmission input shaft 7, as described above.

[0053] When sailing with the drive unit 1 switched off, if the drive unit 1 needs to be started, this can be caused by switching from sailing mode with the drive unit switched off to sailing mode with the drive unit running. Furthermore, the drive unit 1 can be started when exiting sailing mode. It is also possible for the monitoring system according to the invention to start the drive unit 1 without changing the sailing strategy, specifically when sailing has already taken place for a defined period with the drive unit 1 switched off and, for example, based on other monitoring functions, there is a high probability that a gearbox is misaligned.

[0054] 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 speed sensors, which serve for the metrological measurement of the monitored rotational speeds. Furthermore, the 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. 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 converters 16 Turbine 17 Pump 18 Torque converter lock-up clutch

Claims

[1] 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 engaged, friction-fit 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, where, depending on at least one operating condition of the motor vehicle, a sailing mode is entered, wherein, to enter the sailing mode of the motor vehicle, starting from a friction-locked gear, a switching element of the transmission (2) is actuated to open, so that in a non-friction-locked sailing gear one switching element is less closed and thus one switching element is more open than in a friction-locked gear, wherein, in the sailing mode of the motor vehicle with the drive unit (1) switched off, the respective closed and open switching elements of the transmission (2) are changed depending on at least one operating condition of the motor vehicle to maintain the sailing gear, characterized by , that then, when the drive unit (1) is started, the gearbox input speed of the gearbox (2) and the speed of the drive unit (1) are evaluated to conclude that the gearbox (2) is improperly preloaded, in which the gearbox is blocked on the input side and can rotate freely on the output side. [2] Method according to claim 1, characterized by , that to start the drive unit (1) a starting element of the motor vehicle is brought into a defined slip to provide slip decoupling. [3] Method according to claim 2, characterized by , that if, during slip decoupling, the resulting transmission input speed of the transmission (2) is less than a first threshold value and simultaneously a resulting difference between the speed of the drive unit (1) and the transmission input speed of the transmission (2) is greater than a second threshold value, it is concluded that the transmission (2) is improperly preloaded. [4] Method according to claim 1, characterized by , that no slip decoupling is used to start the drive unit (1). [5] Method according to claim 4, characterized by, that if, without slip decoupling, the resulting transmission input speed of the transmission (2) is less than a first threshold value and simultaneously a resulting difference between the speed of the drive unit (1) and the transmission input speed of the transmission (2) is less than a second threshold value, it is concluded that the transmission (2) is improperly preloaded. [6] 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 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) a first number of switching elements (9, 10, 11, 12, 13) of the transmission (2) to close and a second number of 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 transmission (2) is controlled to enter a sailing mode, To enter sailing mode from a positive-locking gear, a switching element of the transmission (2) is actuated to open, so that in a non-positive-locking sailing gear one switching element is less closed and thus one more switching element is open than in a positive-locking gear, In the sailing mode of the motor vehicle with the drive unit switched off (1), the control of the respective closed and open switching elements of the transmission (2) changes depending on at least one operating condition of the motor vehicle to maintain the sailing gear, characterized by , that The control unit then, when the drive unit (1) is started, evaluates on the one hand the transmission input speed of the transmission (2) and on the other hand the speed of the drive unit (1) in order to conclude that the transmission (2) is improperly preloaded, in which the transmission (2) is blocked on the input side and can rotate freely on the output side. [7] Control unit according to claim 6, characterized by , that the control unit for starting the drive unit (1) controls a starting element of the motor vehicle to provide slip decoupling. [8] Control unit according to claim 7, characterized by, that the control unit concludes that the transmission (2) is incorrectly preloaded when, during slip decoupling, the resulting transmission input speed of the transmission (2) is less than a first threshold value and simultaneously a resulting difference between the speed of the drive unit (1) and the transmission input speed of the transmission (2) is greater than a second threshold value. [9] Control unit according to claim 6, characterized by , that the control unit does not use slip decoupling to start the drive unit (1). [10] Control unit according to claim 9, characterized by, that the control unit concludes that the transmission (2) is incorrectly preloaded if, without slip decoupling, the resulting transmission input speed of the transmission (2) is less than a first threshold value and simultaneously a resulting difference between the speed of the drive unit (1) and the transmission input speed of the transmission (2) is less than a second threshold value.

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