DE102006046164A1 - Protecting shift elements in motor vehicle automatic gearbox involves applying torque to overloaded element in opposition to normal operation as result of protection function for shifts involving overloaded shift element - Google Patents

Abstract

The method involves turning off one shift element and turning on another when shifting from one gear to another, whereby different load characteristics are determined for individual shift elements and are compared with threshold values to activate a protection function. For shifts involving an overloaded shift element a torque is applied to the overloaded element in opposition to normal operation as result of the protection function.

Description

The The invention relates to a method for protecting switching elements in an automatic transmission of a motor vehicle with the features of Preamble of claim 1.

In the DE 102 33 699 A1 a method for protecting switching elements in an automatic transmission of a motor vehicle is described in which separate load characteristics are determined for individual switching elements of the transmission, for example, for individual multi-plate clutches. The load characteristic values result from the sum of the friction work occurring at the respective shift element, which is determined based on a differential speed and an actuating pressure on the shift element. If the load characteristic value of a switching element exceeds a limit value, then a protective function for the overloaded switching element is activated. For this purpose, the current circuit is still terminated and locked the associated, overloaded switching element for further switching operations for a certain period. Thus, gears in which the overloaded switching element is in the torque flow, can no longer be inserted.

In contrast, is it is the object of the invention to provide a method for protecting switching elements to propose in an automatic transmission of a motor vehicle, which is a high availability allows the transmission and which in particular the use of all gears even with one or more overloaded Switching elements allows. According to the invention Problem solved by a method having the features of claim 1.

According to the invention is at Circuits in the gearbox involving the overloaded switching element is due to the protective function, a torque on the overloaded Switching element opposite reduced to normal operation. The gearbox will then be in normal operation operated or a circuit is then carried out in normal operation, when the Load characteristic of none of the switching elements involved in the circuit greater than the respectively associated Limit is. The reduction of the torque can, for example by a reduction of the output torque of an engine of the Motor vehicle, by opening a arranged between the engine and transmission starting clutch and / or by a reduction of the transferable from the switching element Torque, the so-called clutch torque realized during the circuit become.

In order to it will be overloaded Switching element only minimally loaded in a circuit, so that no additional overload may occur and the switching element from damage due to further overload protected is. This will ensure that always, even if individual switching elements overloaded are, all gears of the transmission can be used. A driver or an automatic switching program can always use the target gear free from all courses of the gearbox.

An overload of switching elements, in particular in a so-called manual mode of the Gear occur in which the driver by means of a suitable Operating device, such as a selector lever, set the target gear directly can. As a result, it may happen that a with respect to the load of the switching elements unfavorable Gear is engaged and it is thus an overload of a switching element comes. Furthermore can the driver by repeated, short successive circuits overload cause a switching element. One way, such and on it following overloads to prevent would be to no longer allow the manual mode in case of a recognized overload or, as described above, to lock individual aisles. This would be the functionality of the transmission severely restrict and would be also from the driver not immediately understand, making it the dissatisfaction of Driver come can. By applying the method according to the invention, the manual mode continue to be allowed, as the switching elements by the reduction sufficiently relieved of the torque and thus protected. Thus, the full functionality of the transmission can be maintained, to have to at most losses in terms of the switching times or regarding the at a circuit for the propulsion available standing torque to be accepted.

The Switching elements are in particular as friction clutches or brakes, For example, hydraulically actuated Multi-plate clutches or brakes of automatic transmissions with several coupled planetary gear sets executed. The transmission of this type has, in particular, a starting element Automated starting clutch between engine and gearbox, in particular a wet-running starting clutch.

When Starting element can also be, for example, a hydrodynamic Serve torque converter.

The Switching elements can Also, for example, as synchronizations of the individual gears of a Change-speed gearbox, in particular with an automated starting clutch.

The method of determining the load characteristics is not included in the present invention Foreground. It is only necessary that load characteristics which characterize the level of load of the individual switching elements be determined. As a load characteristic of a switching element, for example, the temperature of the switching element can be estimated by means of a temperature model. The temperature model takes into account a quantity of heat released at the switching element which is determined as a function of the rotational speed difference and the torque on the switching element. In addition to the amount of heat, a heating and cooling behavior of the switching element is taken into account. In this case, further influencing variables, such as a temperature of a transmission oil, an outside temperature and / or a vehicle speed can be taken into account.

It is also possible the load characteristic by adding up the friction work or the To determine friction loss. In this case, the load characteristic at not actuated Switching element can also be reduced.

It is not necessary for that All switching elements of the transmission load characteristics are determined. For switching elements, where an overload very unlikely, can be waived. An example for a Such switching element is a switching element, the only for one reverse gear needed becomes.

The Load characteristics can be compared with a limit that applies to all switching elements. The limit value may be, for example, operating variables of the motor vehicle, such as for example, a transmission oil temperature or an outside temperature depend. But it is also possible that for each switching element a separate limit is used. This can take into account specific properties of the switching element and also of farm sizes of the Depend on motor vehicle. In addition, can the limit value over change the life of the switching element and in particular as a function an estimated one Wear of the Switching element become smaller. The wear can, for example, due to the number of operations of the switching element and / or the load characteristics which have occurred estimated become.

The Protective function for a circuit can be activated if the load characteristic value of the switching element switching on or off the associated limit value Has. It is activated especially when the overloaded Switching element additionally burdened by the upcoming circuit becomes. Will that be overloaded Switching element not burdened by the upcoming circuit, the protection function is not activated. This is the protective function activated only when absolutely necessary.

If a switching element is loaded by the circuit is of the Type of circuit depends, where distinguished between so-called train-up, train-back, thrust-up and thrust-reverse circuits becomes. The name is derived from whether the motor vehicle while the circuit is in traction or in overrun mode. In train operation gives the prime mover from a positive torque, which for Drive the motor vehicle is used. In overrun mode, the prime mover becomes from the powered vehicle wheels over the Drivetrain dragged, so the prime mover takes a torque, the so-called pushing moment on. There are train-up and thrust-reverse circuits, and train-reverse and thrust-high circuits basically the same, leaving only between two groups of circuits must be distinguished.

at Pull-up and push-back circuits usually finds a positive overlap with powershift transmissions instead of. This means that in one phase of the shift the clutch torque the disconnecting switching element reduces and at the same time Clutch torque of the switching element switching is increased. In this phase, both switching elements are charged, so that at Such a circuit, the protective function is activated when the switching on or off the switching element is overloaded.

at Train Re and boost-high-circuits is usually the power-shift transmissions Clutch torque of the switching off switching element so long on so-called release torque reduced until the speed of the prime mover approximately has reached a synchronous speed of the target gear. Only then will increases the clutch torque of the switching element switching. Since the connection of the switching element takes place only after adjusting the speed is the switchable switching element in such a circuit quasi not loaded. Therefore, at an upcoming train return or Thrust-high circuit only activates the protection function if that disconnecting switching element overloaded is.

In Embodiment of the invention is in a train-up and / or a push-back circuit Engine intervention performed. The engine intervention serves to smooth and support the Circuit. This is due to the engine intervention in a train-high circuit specifically reduces the torque of the prime mover and targeted at a push-reverse circuit elevated. As a result of the protective function of the engine intervention is compared to Normal operation earlier and / or stronger carried out.

In normal operation, the engine intervention is included power-shift transmissions usually after the overlap, so then take place when the shutdown switching element is fully opened and the switching element is fully or almost completely switched on. As a result of the protective function of the engine intervention takes place in particular before the switching off switching element is completely switched off. The engine intervention takes place in particular at the same time or even before it starts to reduce the clutch torque of the switching-off switching element. The torque changed by the engine engagement is achieved in particular even before the reduction of the clutch torque.

Of the Engine intervention is only terminated when the speed the prime mover has reached the synchronous speed of the target gear, the circuit is so quasi finished. Below the synchronous speed is understood the speed of the prime mover, which is at fully inserted Target gear at the current vehicle speed results.

Under a stronger one Motoreingriff is understood that by the engine intervention set torque of the prime mover stronger than in normal operation of one from the driver deviates by a gas pedal set desired torque.

The Measure of Time shift and / or the degree of gain of the engine intervention can thereby from the load value of the overloaded switching element dependent be.

By the former or stronger ones Motoreingriff the involved switching elements, in particular in the overlapping phase relieved, so that there are no further overloads.

In Embodiment of the invention is the clutch torque of the switching Switching element when switching on a, compared to a Connection torque limited in normal operation lower limiting torque. The connection torque is in particular only at or after reaching set the synchronous speed of the target gear. The clutch torque the switching element switches in conjunction with the engine intervention the change the speed of the prime mover, whereby the switching element additionally loaded becomes. By limiting the clutch torque is the load reduced the switching element switching.

The All actions taken as a result of the protective function cause one Reduction of vehicle acceleration during the gear change, the Switching time changed not essential. But since all courses are available, this is accepted.

During the previously described circuits, the gearbox was over the Starting element connected to the drive machine.

In Embodiment of the invention is between the prime mover and arranged the transmission an automated startup clutch. at a train high and / or a train high and / or a push downshift As a result of the protective function, the starting clutch is opened, wherein including a partial opening to understand. Thus, the transmission is at least during the circuit partially decoupled from the prime mover, so that at the Switching elements acting torques are greatly reduced. Next to the open the starting clutch is also the torque of the prime mover adjusted so that the speed to the synchronous speed of the target gear is adjusted.

In order to the switching elements are maximally relieved, although in Purchase is made that no load switching is performed, so while the circuit no drive torque transmitted to the driven vehicle wheels becomes.

One particularly effective method results from the combination of both described procedures. If a load characteristic exceeds a first limit, is in a first stage of the protective function in a train-up and / or a Thrust downshift the engine intervention earlier and / or stronger carried out. Give these protective measures not out and over a load characteristic a second, higher limit, so is in a second stage of protection in such circuits opened the starting clutch between the engine and transmission.

The precautions can so optimally adapted to the load of the switching elements and a for the current state of the switching elements minimum switching time reached become.

In an embodiment of the invention, a so-called release torque of the switching off switching element is set in a train-reverse and / or a push-upshift. The release torque is used to transmit torque between the prime mover and the driven vehicle wheels during the shift. The level of the release torque determined in a train-return circuit, the height of the driving of the motor vehicle serving torque at the vehicle wheels during the circuit. As a result of the protective function is the said release torque less than in normal operation. Thus, the switching off switching element is relieved, being accepted that the available during the circuit for the drive of the motor vehicle torque is lower than the normal operation. The transmission remains connected to the prime mover during the shift.

Further Embodiments of the invention will be apparent from the description and the Drawing forth. embodiments The invention are shown in simplified form in the drawing and explained in more detail in the following description.

there demonstrate:

1 a drive train of a motor vehicle having an automatic, load-shiftable transmission,

2a . 2 B temporal representation of state variables in a train-high-circuit in normal operation,

3a . 3b time representation of state variables in a train-high-circuit with activated first stage of the protective function,

4a . 4b Timing of state variables in a train-high circuit with activated second stage of the protection function and

5a . 5b Timing of state variables in a train-return circuit.

According to 1 has a powertrain 10 via a prime mover 11 , which is designed as a gasoline engine. The prime mover 11 is from a controller 29 controlled, which is in signal communication with sensors and actuators, not shown. The control device 29 For example, a speed of the prime mover 11 capture and a given torque of the prime mover 11 to adjust. To adjust the torque, the control device 29 For example, change a fuel injection amount and a throttle position. In order to achieve a rapid reduction of the torque of the drive machine, for example during an engine intervention during a shift, the control device 29 also adjust a firing angle in the direction of late. The control device 29 stands with an accelerator pedal 30 in signal connection. By means of the accelerator pedal 30 For example, a vehicle driver can set a driver's desired torque, which is given by the control device 29 unless other higher priority requirements exist.

The prime mover 11 is by means of an automated starting clutch 12 with a transmission input shaft 13 an automatic, powershift transmission 14 connected. The starting clutch 12 and the gearbox 14 are from a controller 27 controlled, which is in signal communication with sensors and actuators, not shown. The control device 27 can thus operating variables of the starting clutch 12 and the transmission 14 , such as speed or temperature. In addition, the control device 27 by means of an actuator, not shown, the starting clutch 12 open and close and thus a transferable torque of the starting clutch 12 to adjust.

The gear 14 is designed as a planetary gear change gearbox. The gear 14 is very schematic and has two gears 16 and 17 , which with a transmission output shaft 18 connected and via two switching elements in the form of couplings 19 and 20 alternatively be inserted. In a circuit of an original gear, such as gear 16 , in a target gear, for example gear 17 , the clutch will 19 off and the clutch 20 switched on.

The couplings 19 . 20 can also via actuators, not shown, from the controller 27 be opened and closed. The control device 27 Can use circuits in the transmission 14 carry out. Circuits can by the driver by means of a selector lever 28 be requested or from the controller 27 be triggered automatically.

From the transmission output shaft 18 becomes a speed and a torque by means of a drive shaft 23 to a axle drive 24 transmitted, which in a conventional manner the torque via two output shafts 25 to drive wheels 26 transfers.

The control device 27 is with the controller 29 the prime mover 11 in signal connection. The control device 27 may request a deviating from the driver torque torque, which then by the controller 29 is set. In particular, the control device 27 at a circuit in the transmission 14 a change in the delivered torque, so request a so-called engine intervention.

In particular, the transmission may be a planetary gear change transmission according to DE 199 10 299 C1 be educated. In contrast to DE 199 10 299 C1 is replaced in the present drive train, the hydrodynamic torque converter by a starting clutch. The content of DE 199 10 299 C1 is hereby explicitly incorporated in the This application has been incorporated.

The functions of the control device 29 and the controller 27 may also be combined in one device or split into more than two devices.

The control device 27 intended for the two clutches 19 . 20 separate load characteristics. The controller appreciates this 27 the at the clutches 19 . 20 if there is slip at the clutches dissipated amount of energy. The necessary operating parameters of the couplings 19 . 20 are determined from measured or determined from maps parameters. The speed difference at the clutches 19 . 20 is determined from measured speeds before and after the clutches. The torque at the clutches 19 . 20 becomes from the output torque of the prime mover 11 , the transmittable torque of the starting clutch 12 and any translation between starting clutch 12 and the couplings 19 . 20 calculated.

E_a_i:

abgeschätzte Wärmemenge für eine Kupplung

i

i = 19: Kupplung 19, i = 20: Kupplung 20

Δn_i:

Drehzahldifferenz an Kupplung i

M_i:

Drehmoment an Kupplung i

Δt:

Zeitraster der Abarbeitung

The estimate is in a fixed time cycle of, for example 20 ms performed. The determined operational variables are assumed to be constant for the duration between two estimation steps, so that the estimation is determined according to the following formula: E_a i = ΣΔn i · M i · .DELTA.t With

E_a _i :

estimated amount of heat for a clutch

i

i = 19: clutch 19 , i = 20: clutch 20

Δn _i :

Speed difference on clutch i

M _i :

Torque on clutch i

.delta.t:

Time frame of processing

Based on this estimate of the amount of energy E_a _i temperatures of the couplings 19 . 20 T_K ₁₉ , T_K _{20 of} the coupling 19 . 20 estimated. This heating and Abkühlkuren the couplings 19 . 20 Heeded the construction of the couplings 19 . 20 , take into account the speed of the motor vehicle, the outside temperature and / or the amount of energy dissipated. This allows the current temperatures of the clutches 19 . 20 be estimated very accurately. The estimation of the temperatures can continue after a shutdown of the motor vehicle, so as to provide meaningful starting values for the temperatures when the motor vehicle is restarted.

In a circuit request for the transmission 14 checks the control device 27 whether one of the switching devices in the form of one of the clutches involved in the new target gear shift is in the form of one of the clutches 19 . 20 overloaded. For this purpose, the control device checks 27 whether one of the estimated temperatures T_K ₁₉ , T_K _{20 is} greater than a first limit value associated therewith in the form of first limit temperatures T_limit1 ₁₉ , T_limit1 ₂₀ . The limit temperatures T_Grenz1 ₁₉ , T_Grenz1 ₂₀ depend on the design of the clutch and on an estimated wear of the clutches. Wear is estimated from the number of clutch actuations and the amount of energy dissipated. The limit temperatures T_Grenz1 ₁₉ , T_Grenz1 ₂₀ decrease with increasing wear.

Is not one of the clutches 19 . 20 overloaded, the circuit is executed in a normal operation.

Is the overload of one of the clutches 19 . 20 determined, then checks the control device 27 which kind of circuit should be executed. For this purpose, the control device determines 27 based on the output torque of the prime mover 11 whether the motor vehicle is in thrust or in train operation. If the torque is greater than a definable threshold of, for example, 20 Nm, train operation is detected. With the additional information as to whether the requested shift is an upshift or downshift, the type of shift, whether it be a train up, a train back, a shift up or down shift, can be specified ,

These the requested circuit is a train-reverse or thrust-high circuit, so will be afterwards checked, whether the connecting or disconnecting clutch is overloaded. If the switching Clutch overloaded is, the circuit is executed in normal operation. Is on the other hand, the shutdown Clutch overloaded, This activates a protection function, which is described in detail below becomes.

If the requested circuit is a pull-up or a push-back circuit, a protection function will definitely be activated. The type of protection depends on the estimated temperatures of the switching on and off clutches. If one of the estimated temperatures is greater than an associated second, compared to the first temperature limit T_Grenz1 _i larger temperature limit T_Grenz2 _i (eg T_Grenz2 ₁₉ , T_Grenz2 ₂₀ ) so a second stage of the protection function is activated. If both estimated temperatures are smaller than the associated second temperature limit values T_Grenz2 _i , a first stage of the protective function is activated.

In a transmission with more than two gears, the estimates described are the Temperature and wear, as well as the test for overheating performed for all switching elements.

In 2a and 2 B are time profiles of state variables of the drive train in a train-high circuit in normal operation shown. In 2a the speeds of the prime mover and the transmission input shaft are shown. Since the starting clutch is closed, the two speeds are always the same size. In 2 B are the torque of the prime mover (dashed line 31 ), the clutch torque of the switching off switching element (dot-dash line 32 ) and the clutch torque of the switching element (dotted line 33 ). The torque transfer from the disconnecting to the switching element is started at time t1, whereupon immediately the clutch torque of the switching element switching off a ramp to 0 and increased in the same time the clutch torque of the switching element switching on a Zuschaltmoment M_z at the same level. This phase is referred to as the so-called overlap phase. After completion of the overlap phase at time t2, the torque of the prime mover is reduced via a Zündwinkeleingriff to a torque value M_m1. As a result, the rotational speed of the engine starts to decrease from time t2 until it reaches the synchronous speed n_sync_h of the target gear at time t3. Then the engine intervention is terminated and the torque of the prime mover is raised again to the level before the circuit, which corresponds to the desired moment of the driver. The circuit is complete.

In 3a and 3b the time profiles of the same state variables are shown in a train-high circuit with activated first stage of the protection function. The starting clutch remains closed during the circuit, so that the two speeds are still the same size. The torque transfer from the disconnecting to the switching element is also started at time t1. Then, in this case, first an engine intervention is performed and the torque of the prime mover (dashed line 34 ) is reduced to a torque value M_m2 smaller than the torque value M_m1. In addition, from the time t1, the clutch torque of the switching element switching off (dot-dash line 35 ) lowered to 0 via a ramp. At the same time, the clutch torque of the switching element (dotted line 36 ) along a ramp to a first limiting torque M_b1, which is smaller than the Zuschaltmoment M_z increase. After the clutch torque of the switching off switching element has reached 0 at time t2, the speed of the prime mover starts to decrease until it has reached the synchronous speed n_sync_h of the target gear at the time t4, which is later than the time t3. Then the engine intervention is terminated and the torque of the prime mover is raised again to the level before the circuit, which corresponds to the desired moment of the driver. At the same time, the clutch torque of the engaging shift element is abruptly increased by the limiting torque M_b1 to the Zuschaltmoment M_z. The circuit is complete.

If The torque reduction is not reduced very quickly with an ignition intervention can be, but only along a ramp, so are the clutch moments only after reaching the reduced torque value of the prime mover changed.

In 4a and 4b are the time courses of the same state variables plus the transferable torque of the starting clutch in a train-high circuit with activated second stage of the protection function shown. The starting clutch is opened at the circuit, so that the speed of the prime mover (solid line 37 in 4a ) at times by the speed of the transmission input shaft (dashed line 38 in 4a ) deviates. The circuit is also started at time t1. Then, in this case, first the torque of the prime mover (dashed line 39 ) is reduced to 0 along a ramp and with a small time delay the starting clutch is opened, ie the transmittable torque of the starting clutch (solid line 42 ) is reduced to 0 along a ramp. The starting clutch is fully open at time t5. Then, the clutch torque of the switching off switching element (dash-dotted line 40 ) suddenly lowered to 0. At the same time, the clutch torque of the switching element (dotted line 41 ) along a ramp to a second limiting moment M_b2 which is smaller than the first limiting momentum M_b1. As a result, the speed of the prime mover begins to decrease, whereas the speed of the transmission input shaft remains unchanged. The rotational speed of the engine reaches at time t6 the synchronous speed n_sync_h of the target gear. Then, the clutch torque of the switching element is abruptly increased by the limiting torque M_b2 on the Zuschaltmoment M_z. At the same time, the starting clutch is closed again. Somewhat time-delayed, the torque of the prime mover is raised again along a ramp to the level before the shift, which corresponds to the desired torque of the vehicle driver. The driver's desired torque is reached at time t7, which the circuit is completed.

Push-back circuits be basically driven with intermediate gas. For this purpose, the switching off switching element open. By means of a speed control, the speed of the prime mover led to the synchronous speed of the new gear. After that, the switching will be Switching element switched lossless.

In 5a and 5b are time profiles of state variables of the drive train in a train-return circuit in normal operation and with activated protection function shown. In 5a the speeds of the prime mover and the transmission input shaft are shown. Since the starting clutch is closed, the two speeds are always the same size. In 5b are the torque of the prime mover (dashed line 43 ), the clutch torque of the switching off switching element in normal operation (solid line 44a ), the clutch torque of the disconnecting switching element with activated protection function (dot-dash line 44b ) and the clutch torque of the switching element (dotted line 45 ). The circuit is started at time t10, whereupon immediately the clutch torque of the switching-off switching element is lowered via a ramp to a release torque. The release torque with activated protection function M_f_s is smaller than the release torque in normal operation M_f_n. After reaching the release torque at time t11, the speed of the prime mover increases, with a representation of the differences between normal operation and activated protection function has been omitted. As soon as the rotational speed of the drive engine has reached or slightly exceeded the synchronous speed n_sync_r of the target gear, the clutch torque of the disengaging shift element is reduced to 0 via a ramp from time t12, and the clutch torque of the engaging clutch is simultaneously increased to an engagement torque. This is done at time t13, which completes the circuit.

The described procedures for a train-return circuit are analogously applicable to a push-high circuit. But it is also possible, that in push-upshifts the starting clutch is opened.

Claims (9)

Method for protecting switching elements in an automatic transmission of a motor vehicle, in which, when shifting from an original gear to a target gear, a shifting element ( 19 . 20 ) is switched off and another is switched on, wherein - for individual switching elements ( 19 . 20 ) of the transmission ( 14 ) separate load characteristics (T_K ₁₉ , T_K ₂₀ ) are determined, - the load characteristics (T_K ₁₉ , T_K ₂₀ ) are compared with limit values (T_Grenz1 ₁₉ , T_Grenz1 ₂₀ , T_Grenz2 ₁₉ , T_Grenz2 ₂₀ ) and - when a limit value (T_Grenz1 ₁₉ , T_Grenz1 ₂₀ , T_Grenz2 ₁₉ , T_Grenz2 ₂₀ ) by a load characteristic value (T_K ₁₉ , T_K ₂₀ ) a protective function for the associated, overloaded switching element ( 19 . 20 ) is activated, characterized in that in circuits in the transmission ( 14 ), where the overloaded switching element ( 19 . 20 ), as a result of the protective function, a torque on the overloaded switching element ( 19 . 20 ) is reduced compared to a normal operation. A method according to claim 1, characterized in that the protective function is activated only in circuits in which the overloaded switching element ( 19 . 20 ) is additionally charged. Method according to claim 1 or 2, characterized, that - at a train high and / or a push downshift a motor intervention performed and - of the Engine intervention as a result of the protective function earlier and / or stronger than in normal operation is performed. Method according to Claim 3, characterized in that the engine intervention takes place before the switching-off switching element ( 19 . 20 ) is completely switched off. A method according to claim 3 or 4, characterized in that a clutch torque of the switching element ( 19 . 20 ) is limited in the connection to a, in comparison to a Zuschaltmoment (M_z) in normal operation lower limiting torque (M_b1). Method according to claim 5, characterized in that that the Zuschaltmoment (M_z) until after or after reaching a synchronous speed (n_sync_h) of the target gear is set. Method according to claim 1 or 2, characterized in that between a drive machine ( 11 ) and the transmission ( 14 ) an automated start-up clutch ( 12 ) is arranged and in a train-up and / or a train-up and / or a push-down circuit as a result of the protective function, the starting clutch ( 12 ) is opened. The method of claim 1 or 2, characterized in that on exceeding - a first limit value (T_Grenz1 _19, T_Grenz1 ₂₀₎ through a loading characteristic value (T_K _19, T_K ₂₀₎ a method according to any one of claims 3 to 6, and - A second, higher limit value (T_Grenz2 ₁₉ , T_Grenz2 ₂₀ ) by a load characteristic (T_K ₁₉ , T_K ₂₀ ) instead of a method according to claim 7 is performed. Method according to one of the preceding claims, characterized characterized in that at a train-back and / or a push-upshift - a release torque the switching off switching element is set and - said Release torque due to the protective function is lower than in normal operation.