DE19921920A1 - Overload protection method for automobile automatically-operated friction clutch controls gear used for moving off of vehicle to prevent damage to clutch - Google Patents

Abstract

The overload protection method detects the loading of the friction clutch (22), for indication of an overload condition, for only permitting moving off of the automobile in a given number of gears, e.g. first gear or reverse gear, or for controlling the moving off of the automobile to inhibit overloading of the friction clutch, e.g by limiting the engine revs.

Description

The present invention relates to a method for protecting a automated friction clutch of a vehicle against overload.

DE 198 15 259 A1 discloses a procedure in which when it is determined that the clutch of a vehicle is in a Overload condition has reached, the clutch is controlled such that the torque that can be transmitted from this is repeated spontaneously and repeatedly changes so that the vehicle jerks. Because of this Jerky, the driver is made aware that the clutch in is an overload condition and it is his in a corresponding manner Should adapt driving style. If this does not lead to the desired reaction, see above following the jerking phase, the clutch will move towards the clutch position to increase the slip occurring in this reduce.

The problem with such an approach is that of overloading reactions arising from various measures taken by the driver could easily be avoided and thus the risk of coupling damage has not been removed.

It is the object of the present invention to act reliably Method for protecting an automated friction clutch Provide vehicle against overload.

According to a first aspect of the present invention, this object is achieved by a method for protecting a friction clutch, in particular an automated friction clutch, of a vehicle against overload, comprising the steps:

• a) determining the load condition of the friction clutch,
• b) Determine whether the determined load condition is an overload state is
• c) when the determined load condition is an overload condition, take overload protection measures.

This method then provides that the overload protection measures include at least one of the following measures:

• 1. c ₁ ) Allowing starting of the vehicle only in selected one of a plurality of starting gears provided in a transmission arrangement,
• 2. c ₂ ) preventing the vehicle from starting in an excessively stressful manner.

These measures c ₁ ) and c ₂ ) ensure that, if the overload of the clutch has been detected beforehand, for example when driving, during a subsequent starting procedure which can be carried out subsequently, the clutch can only be started in a manner which is gentle on the clutch.

This can be achieved, for example, that the intended Starting gears at least the first, the second and the reverse gear the transmission arrangement and that the selected gears include first and reverse gear.

Furthermore, it is possible that the vehicle is started in one Kickdown mode and / or if the speed is above a limit speed a drive unit is prevented.

If it is recognized that the driver is attempting to start in a mode which does not comply with measures c ₁ ) or c ₂ ), it can be provided that with measure c ₁ ) and / or measure c ₂ ) starting by holding the Friction clutch is prevented in a disengaging position or in the region of the disengaging position, and / or that, if the transmission arrangement is an automated transmission arrangement, the engagement of one of the unselected gear stages is prevented.

An essential driving mode that contributes to overloading a clutch is the creep driving mode or the starting mode. In both of these states, the clutch is generally only partially engaged, and low speed driving is made possible by slip occurring in the clutch. This state is particularly relevant for the functionality of a clutch when it has already been recognized that the clutch was previously overloaded. According to a further aspect, the present invention therefore provides that the method further comprises determining whether the vehicle is operating in a crawl or start mode, and that, when the vehicle is operated in a crawl or start mode, overload protection measures for Reduction of the clutch load when creeping or when starting to be taken. This can be realized, for example, in that the overload protection measures include a measure c ₃ ) for setting the friction clutch in the direction of an engagement position. Alternatively or additionally, it is possible that the overload protection measures include a measure c ₄ ) for reducing the power output of the drive unit.

It goes without saying that these measures, as well as measures to be described below, can be combined with measures c ₁ ) and c ₂ ), since measures c ₁ ) and c ₂ ) initially ensure that and how the vehicle can be set in motion, and measures c ₃ ) and c ₄ ) then relieve the clutch when the vehicle is moving in a specific mode, namely the crawl or start mode, when the clutch is previously overloaded.

In order to impair the starting or crawling operation of the vehicle as little as possible, but nevertheless to ensure a suitable relief of the clutch, it is proposed that measure c ₃ ) and / or measure c ₄ ) are preferably carried out periodically repeatedly. This means that after the measures c ₃ ) and c ₄ ) have been initiated or taken, they are canceled again, ie the originally predefined state is restored and then initiated or taken repeatedly.

In order to avoid that immediately after a vehicle has been put into motion, for example in conformity with measures c ₁ ) or c ₂ ), further measures that may not be absolutely necessary are proposed that measure c ₃ ) or / and measure c ₄ ) is initiated if at least one of the following conditions is met:

• - Since the start of a creeping or starting process a first predetermined period of time has passed,
• - the since the beginning of the creeping or starting process in the The friction work introduced into the friction clutch has a limit reached,
• - The output torque of the drive unit has one reaches or lies in a certain value Area,
• - The speed of the drive unit has a certain value reached or is in a certain range.

Creeping or starting operations generally take a predetermined amount of time. This knowledge can also be used to take overload protection measures in that the overload protection measures include a measure c ₅ ) for placing the friction clutch in a disengaging position or a position in the area of the disengaging position if a since the beginning of the creeping or starting process second predetermined period of time has passed.

Another critical state that occurs during driving operation, i.e. a state that can occur, for example, after a starting process has been carried out in conformity with measures c ₁ ) -c ₄ ), is a shifting process in which a large speed difference occurs after the new gear is engaged exists between the transmission input side and the drive unit. This is, for example, an engaging process in the Schubbe. In order to be able to provide relief for the clutch even in this state, it is proposed that the overload protection measures include a measure c ₆ ) for setting the speed of the drive unit to a speed to be expected after performing a switching operation on a transmission input side of a transmission arrangement. As already indicated, the shift process can include a shift from a higher gear to a lower gear, ie a transition to overrun.

By adjusting the speed on both sides of the friction clutch, it is ensured that the slip occurring in the clutch and thus the frictional power generated are as low as possible when engaging. Since this measure c ₆ ) in the sense of the present invention is an overload protection measure, that is, it is only taken if it was actually recognized beforehand that the clutch is in an overload state, in other driving states if the clutch is not overloaded, for example when engaging after switching to a lower gear, the engine braking effect can be fully exploited, since the mentioned speed adjustment is then essentially not carried out. This ultimately leads to a relief of the braking system of a vehicle.

The above-mentioned state, that after or when performing a switching operation, there are relatively strongly different speeds on both sides of the friction clutch, occurs particularly when the switching operation includes a gear shift, i.e. there is at least between an output gear stage and a newly engaged or engaged gear stage another skipped gear. If such a shifting process occurred, even measure c ₆ ) could possibly not lead to a complete adjustment of the speeds on both sides of the friction clutch within the time available. In order to avoid this, it is proposed according to a further aspect of the present invention that the overload protection measures include a measure c ₇ ) for preventing gear changes in which at least one gear step is skipped. Since in this way it is ensured in the overload state that only one gear stage can be shifted to the immediately following gear stage in the shift sequence, it is ensured that the speed difference occurring in the gearbox arrangement after the shifting operation has been carried out is in the range the friction clutch is kept very low, with the result that, on the one hand, the slip that occurs is minimized and, on the other hand, measure c ₇ ) can reliably lead to the speed adjustment.

This measure c ₇ ) can be implemented, for example, by preventing a shifting process by holding the friction clutch in a disengaging position or in the area of the disengaging position and / or when the gear arrangement is an automated gear arrangement, engaging a gear step, in which at least one gear step is skipped from an initial gear step, is prevented.

An essential condition that stresses the clutch is, as already described above, the slip condition. The longer a slip condition lasts, the greater the load on the clutch. In other words, in a state where slip must occur, e.g. B. during a coupling process of the friction clutch can contribute to relieving the clutch in that the duration of such a state is minimized as much as possible. According to a further aspect of the present invention, it is therefore proposed that the overload protection measures include a measure c ₈ ) for reducing a period of time for carrying out a coupling operation of the friction clutch with respect to a corresponding period of time in the absence of an overload state and / or in the case of a state of lower overload.

Another measure that can contribute to relieving a clutch, especially when a slip condition occurs in the area of driven wheels such that the speed of the driven wheels is lower than that of non-driven wheels is measure c ₉ ), in which when performing a coupling process and when slip occurs in the area of driven wheels, the friction clutch is adjusted in the direction of a disengaging position. This is, for example, a state in which a coupling process is carried out when the vehicle is moving on slippery ground and the driven wheels are suddenly blocked. By setting the coupling in the direction of the disengaging position, considerable relief can be provided.

If it is further provided that after or during the placement of the Friction clutch in the direction of the disengaging position the speed of the Drive unit on a in the area of an input side of a transmission order is present speed, then it is ensured that when the friction clutch is engaged, the engine braking effect is minimized and in a corresponding manner that achieved in the clutch Friction work is minimized.  

For example, it can be provided that after or during the Setting the speed of the drive unit to that on an input side of the transmission arrangement, the present speed, the friction clutch is put back towards the engagement position.

Another measure that relieves the load on the clutch after performing a gearshift or when engaging is a measure c ₁₀ ), in which, when a gear change from a lower gear to a higher gear is to be carried out, increasing the output torque or the power output of a drive unit after the switching operation in the gear arrangement is limited or delayed until the friction clutch is substantially fully engaged.

Although when taking the various previously mentioned Protective measures of the driver through the reaction of the vehicle in the general knowledge that protective measures have been initiated, it is advantageous if an additional optical or / and an acoustic warning signal is generated if such Overload protection measures are to be taken.

Furthermore, it is advantageous to ensure that when the driver consciously wants to go into a state in which the clutch load only is very small, possibly less than in a current state, in which overload protection measures are taken, it is proposed that the method according to the invention further comprises a step d) at least partially, preferably essentially completely Cancellation of overload protection measures. For example be provided that step d) is carried out if after Take overload protection measures to carry out the Step b) leads to the result that an overload condition is not is present.  

For example, step d) can be carried out if Lifting measures, e.g. B. the substantially complete depression an accelerator pedal.

Such cancellation measures do not lead to a corresponding one Reaction of the vehicle, this could result in a state in which in contrast to the expected further relief of the clutch even greater stress occurs. It is therefore proposed that if the substantially complete depression of the accelerator pedal does not leads to a corresponding reaction of the vehicle, the drive unit gat is brought into a non-operational state.

Furthermore, it can then be provided that the drive unit after expiration a third predetermined period of time since substantially full continuously depressing the accelerator pedal to the non-operating state brought. The drive unit is once out of operation brought, can by pressing an ignition switch or this will be started again automatically.

The present invention will hereinafter be described with reference to the accompanying Figure, which schematically shows a drive system in a motor vehicle represents, described in detail.

The figure schematically shows the view of a drive system 10 , as is implemented, for example, in a vehicle. The drive system 10 comprises a drive unit 12 , for. B. an internal combustion engine 12 having a power control arrangement 14 , which power control arrangement 14 comprises any area of the drive unit 12 in which an influence on the power output can be taken. So comprising said power actuator assembly 14 is a throttle, the ignition system, the spark plugs, the injection system, the valve actuation means, etc. The power actuator assembly 14 is under control of a control means 16 based on various specifications or running conditions of the drive unit for outputting a desired torque or to control a desired performance. A drive shaft, for example a crankshaft 18 , is connected to an input side 20 of a friction clutch, generally designated 22. In a manner known per se, this input side 20 can comprise a flywheel, for example a two-mass flywheel or the like. In the drive system 10 shown, the friction clutch 22 is an automated friction clutch 22 , which has an actuator arrangement 24 for actuating the same. The actuator assembly 24 is under control of the control device 16 , so that by outputting appropriate control commands, the friction clutch 22 is brought into a desired state, for example engagement state, disengagement state or an intermediate slip state, in which only part of the torque output by the drive unit is transmitted can. The control device 16 also receives, for example, from an actuator arrangement 24 assigned and not shown. Sensor arrangement Information about the current actuating state of the friction clutch 22 . The output side 26 , for example a clutch disk 26 , of the friction clutch 22 is coupled to a transmission input shaft 28 of a transmission designated 30 . This transmission 30 may, for example, be an automated manual transmission, in which shift commands entered by a shift lever 32 are detected by a sensor arrangement 34 , corresponding shift commands or shift intention commands are passed to the control device 16 and then by the control device 16 in coordination with the actuation of the actuator arrangement 24 Friction clutch 22, an actuator arrangement 36 of the transmission 30 is driven to disengage or engage the desired gear stages.

A transmission output shaft 38 drives shafts 42 , 44 via a differential 40 , to which driven wheels 46 , 48 are coupled.

When operating such a drive system, the friction clutch 22 may be overloaded. An overload of such a friction clutch 22 generally occurs when there is a slip condition over a long period of time, ie there is a speed difference between the drive shaft 18 and the transmission input shaft 28 . Due to the frictional heat generated in the slip state, ie, friction work introduced into the friction clutch 22 , damage can occur in the area of the friction linings. It is therefore monitored according to the present invention, the load condition of the clutch and when it is decided that the overload condition represents a state in which the risk of damage to the friction clutch, especially the friction linings thereof, can not be excluded, will be described below Overload protection measures taken.

It is in the operation of such a drive system 10, the friction clutch 22 continuously or periodically checked for the load condition. This can be done, for example, by adding up the friction work introduced into the clutch for a given time window into the past, starting from a moment that is currently available. Ultimately, this means that the friction power introduced into the clutch is determined, for example as the product of the transferable clutch torque with the slip occurring in the friction clutch 22 , as known from DE 198 15 259 A1. If it is recognized that the friction power introduced exceeds a certain limit value, this can be interpreted as a criterion for the fact that, due to the friction power introduced, the clutch or the friction linings have now been heated in such a way that an overload condition must be detected. This decision can also be made, for example, based on the temperature in the area of the clutch or on the friction linings thereof. Once it has been decided in the method according to the invention that the clutch is in an overloaded state, the overload protection measures described below are then initiated. It is pointed out that the overload protection measures described in detail below are based in part on different operating states of the vehicle and, depending on the operating state in which the vehicle is currently operated, one or more of these measures can be taken. This means that in a drive system that uses a friction clutch or in a procedure for protecting this friction clutch against overloading, the measures described below can be implemented in any combination or individually, and when several measures are implemented, the appropriate measures are then dependent on the operating state is accessed.

A first relevant operating state is the start-up state. If, for example, the vehicle is stopped in an overloaded state of the clutch, for example for stopping at a traffic light, the situation can occur that due to a previously very high load on the clutch even when the clutch is disengaged and not currently is loaded, the presence of an overload condition is still detected. In this case, a first measure according to the invention ensures that the load on the clutch is kept as low as possible when the vehicle is subsequently started up. On the one hand, this can be done in that starting is only permitted in selected gear stages from otherwise available starting gear stages. In general, starting in such drive systems is permitted in the first, second or reverse gear. If there is an overload condition, second gear can be excluded, so that starting is only possible in first gear or in reverse gear. In this way it can be ensured that the slip phase is kept as short as possible when starting. This measure can be achieved in that, for example, when the second gear is engaged in this state in order to start with this gear, the control device 16 continues to control the actuator arrangement 24 in such a way that the friction clutch 22 is held in the disengaged state. This measure alone is already effective, even if the transmission 30 is not an automated transmission. If, as shown in the figure, the transmission 30 is an automated transmission, this overload protection measure can additionally or alternatively be implemented by not engaging the second gear stage, for example by engaging the first gear instead of the second gear.

A further possibility of relieving the load on the clutch in the start-up state in the event of a previously recognized overload is to prohibit kickdown operation, ie the maximum adjustment of the power control arrangement 14 or the start-up in the manner of a “race start”. In this state, the engine speed is first turned up and then the gear is engaged at a very high speed and the clutch is engaged. These measures can be implemented, for example, by suitable control of the power control arrangement 14 or by the fact that the friction clutch is not brought into the engaged state even in this state.

If the vehicle is then brought into the starting or crawling mode, that is to say the vehicle is operated in a maneuvering mode, for example, this also means a relatively high load on the clutch, since such a driving mode is generally realized with the approval of a certain clutch slip . In order to avoid further overloading of the clutch in this state, the clutch can, for example, be placed increasingly in the direction of the engagement position, so that the slip is reduced and the speed of the drive unit is forced. This has the consequence that the load on the clutch is continuously reduced by the reduced slip and the possibly equally reduced power output. Alternatively, it is possible in this state that the power output of the drive unit 12 is continuously reduced by correspondingly controlling the power control arrangement 14 , ie by intervening in the injection quantity, hiding individual cylinders, adjusting the ignition angle and / or acting on the throttle system , if necessary up to the engine idling range. The clutch is actuated in parallel in such a way that engine stalling is prevented, ie the clutch is controlled in the direction of disengaging. This can also reduce the load on the clutch.

These two measures described above in crawl or Startup status can be initiated immediately when a such driving condition is recognized, but can also additionally depending on certain parameters. So can For example, a timer can be provided, starting with the Detecting such a driving condition a predetermined time of z. B. counts two seconds and then when the time runs out, one becomes of these measures taken. Alternatively, it is possible for this special Process to observe the friction work introduced into the clutch and then when the friction work introduced a certain limit exceeds to initiate the measures. Also the engine torque or the starting speed are monitored and if certain setpoints one of the measures can be initiated. Still is it is possible to carry out these measures repeatedly, d. H. a Initiate or take action, for example the clutch continuously engage or the performance of the engine continuously drive back, then cancel this measure and immediately subsequently or after a specified waiting time. The Decide which of the parameters mentioned above to do this is used to initiate one of the measures, for example also based on how strong the previously recognized Overload condition. Different limits can be defined and depending on which of the limits have already been exceeded, this can then  Initiate these overload protection measures based on a specific one of the parameter sizes.

In particular when performing a creeping or starting process generally to be expected that such an operation a be certain time period, for example in the range of four seconds. After this time, possibly after a of the measures described above has already been taken, recognized that this crawl or start still is not is finished, the clutch can be further protected in one fully disengaged. The indentation or restarting can then only be permitted again, for example if it is detected that the clutch is no longer overloaded Condition is. The provision of a certain waiting time can also be realized his.

A condition that often occurs during driving and is very stressful for a friction clutch is clutch engagement in overrun mode. This occurs, for example, when changing from a higher gear to a lower gear and when the clutch is engaged, the speed on the output side 26 of the clutch is significantly higher than on the input side 20 . Since the drive unit 12 must be dragged up with respect to its speed in such a coupling process, considerable friction work is performed in the area of the friction clutch. In order to avoid this, especially if it has already been recognized that the clutch itself is already overloaded, measure can be provided according to a further overload protection that in this state the speed of the drive unit is then adjusted to a speed that the the transmission input side, ie the clutch output side 26 , corresponds to the present or expected speed. It is then not possible to use the engine braking torque in this overload state, but priority is given to the protection of the clutch. In other operating states in which the clutch is not overloaded, this measure is then not carried out or only to a reduced extent, so that the existing engine braking torque can be used at least partially.

Furthermore, it can be provided in the present invention that the skipping of gear steps is not permitted when switching operations are carried out. Again, either by holding the friction clutch 22 in the disengaged state or - if an automated transmission is present - can be responded to by preventing the engagement of gear steps, which would mean skipping another gear step.

Another measure when engaging the clutch to keep the clutch load as low as possible is to reduce the amount of time required to carry out the coupling process. Such automated friction clutches 22 are generally controlled in the direction of engagement by predetermined time ramps. According to the invention, these ramps can be steeper in the presence of an overload state of the clutch than in no or less overloaded states, which is done at the expense of comfort, but leads to a significant reduction in friction work.

Another driving situation, which requires the taking of overload protection measures, in particular in the overloaded state of a friction clutch, is the occurrence of a blocking of the driven wheels when clutching. This condition can occur in particular when the vehicle is operated on slippery ground, for example a snow-covered road, and is shifted from a higher gear to a lower gear, so that the vehicle switches to overrun. In order to keep the generated friction work of the clutch as low as possible, for example, if it is detected that the driven wheels are rotating more slowly than the non-driven wheels, the clutch can first be controlled in the direction of disengaging as an overload protection measure. It can then be acted on by means of the Steuereinrich device on the power control arrangement 24 to bring the speed of the drive unit 12 to the speed on the output side 26 of the friction clutch 22 . If this has been achieved or, if necessary, already during the adjustment of the speed of the drive unit 12 , the clutch can then be gradually put back in the direction of the engagement position, since the load occurring is now significantly reduced. In the normal driving state, ie when the clutch is not under load, this measure can be suppressed in order to be able to use the braking torque of the drive unit 12 .

Another driving state in which damage to the clutch can be generated, particularly when the clutch is already overloaded, is clutch engagement in train operation, that is to say in a state in which driving of the torque is conducted from the drive unit 12 to the transmission 30 . In such switching operations, the engine torque or the speed of the same is generally regulated downward, so that during the phase during which the drive train is interrupted by the clutch on the one hand and by the position of the transmission on the other hand, the drive unit is prevented from revving up. When the shifting process in the transmission is then completed, that is to say, in conditions in which no overloading of the friction clutch 22 has been detected, the engine torque is increased again before or accompanying the clutch in the direction of the engagement position, in order to restore the torque demanded by the driver based on the throttle position Get performance. If there is an overload condition, this upward adjustment of the engine torque can be delayed, take place more slowly or only up to a certain limit, and only when the clutch is essentially completely closed or the torque that can be transmitted by this means a threshold value of z. B. 50-70% of the maximum transmissible torque is reached, the engine torque is adjusted to the value that corresponds to that required by the accelerator pedal position. In this way, a further load on the clutch can be kept within acceptable limits if an overload is already detected when carrying out a clutch operation in train operation.

The measures described above to protect against friction clutch before overload due to the engagement in the clutch system, the transmission or the engine management when driving in generally noticeable to the driver. However, it can be an advantage Driver also by acoustic and / or visual warning signals on it point out that the vehicle or the clutch system in one Condition is in which another massive burden of damage of the clutch system could lead so that the driver on his own can already take measures to relieve the clutch contribute.

Once the measures for protecting the clutch from overloading mentioned above have been taken, it is advantageous to end them not only when the routine check has shown that the clutch is no longer in an overloaded state, but when the driver is Possibility to end the protective measures through active intervention. This active intervention can take place, for example, by actuating a switch provided for this purpose, but can also be done, for example, by the driver depressing the accelerator pedal essentially completely. Since depressing the accelerator pedal in the area of its maximum deflection position should generally result in the vehicle being brought into a state in which the friction clutch is fully engaged and the load is then significantly reduced, a can also be done very quickly in this way Relief of the clutch can be achieved. If this depression of the accelerator pedal does not lead to the desired reaction, ie the vehicle speed does not increase to a corresponding extent, which can be the case, for example, if the vehicle is on a steep slope or if the tires are directly on a very high curb, this could represent a great danger for the clutch, since the drive unit 12 demands a great deal of power, which in the end, however, is completely consumed in friction work in the friction clutch. In this case, it is advantageous to switch off the drive unit 12 immediately or at least after a predetermined period of time has elapsed, or to stall by closing the clutch. Once this has taken place, the drive unit can be started again by a start / stop function implemented in the control device 16 or by actuating the ignition lock, a predetermined safety time being also possible here during which the clutch has been switched off since the drive unit was switched off the possibility is given to cool down again, so that when the drive unit 12 is restarted it may already be in a state which is not an overload state.

The foregoing description shows that by the present invention a large number of measures is planned, all of which Drive system can be implemented to operate in a wide variety conditions of a vehicle to be able to take measures that already exist If the clutch is overloaded, ensure relief or at least for a reduced load on the clutch.

Claims (28)

1. A method for protecting a friction clutch, in particular an automated friction clutch ( 22 ), of a vehicle against overload, comprising the steps:

• a) determining the load state of the friction clutch ( 22 ),
• b) determining whether the determined load condition is an overload condition,
• c) if the determined load condition is an overload condition, taking overload protection measures,

characterized in that the overload protection measures include at least one of the following measures:

• 1. c ₁ ) Allowing the vehicle to start only in selected one of a plurality of starting gears provided in a transmission arrangement ( 30 ),
• 2. c ₂ ) Preventing the vehicle from starting in an excessively stressful manner in the friction clutch ( 22 ).

2. The method according to claim 1, characterized in that the intended starting gears comprise at least the first, the second and the reverse gear of the transmission arrangement ( 30 ) and that the selected gears comprise the first and the reverse gear. 3. The method according to claim 1 and claim 2, characterized in that the starting of the vehicle in a kickdown mode and / or at a speed above a limit speed of a drive unit ( 12 ) is prevented. 4. The method according to any one of claims 1 to 3, characterized in that in the measure c ₁ ) and / or the measure c ₂ ) starting by holding the friction clutch ( 22 ) in a disengaging position or in the region of the disengaging position is prevented, or / and that, if the transmission arrangement ( 30 ) is an automated transmission arrangement, the engagement of one of the unselected gear stages is prevented. 5. The method according to the preamble of claim 1 or one of the Claims 1 to 4, characterized in that the method further comprises determining whether the vehicle is operated in a crawl or start mode, includes, and that when the vehicle is in a crawl or Start-up mode is operated, overload protection measures for Reduction of the clutch load when crawling or when Starting to be taken. 6. The method according to claim 5, characterized in that the overload protection measures include a measure c ₃ ) for setting the friction clutch ( 22 ) in the direction of an engagement position. 7. The method according to claim 5 or 6, characterized in that the overload protection measures include a measure c ₄ ) to reduce the power output of the drive unit ( 12 ). 8. The method according to claim 6 or 7, characterized in that the measure c ₃ ) and / or the measure c ₄ ) are preferably carried out periodically repeatedly. 9. The method according to any one of claims 6 to 8, characterized in that measure c ₃ ) and / or measure c ₄ ) are initiated if at least one of the following conditions is met:

• a first predetermined period of time has passed since the start of a crawling or starting process,
• - The friction work introduced into the friction clutch ( 22 ) since the beginning of the creeping or starting process has reached a limit value,
• - The output torque of the drive unit ( 12 ) has reached a certain value or is in a certain range,
• - The speed of the drive unit ( 12 ) has reached a certain value or is in a certain range.

10. The method according to any one of claims 6 to 9, characterized in that the overload protection measures include a measure c ₅ ) for setting the friction clutch ( 22 ) in a disengaging position or a position in the region of the disengaging position if since the beginning of the crawl or Starting process has passed a second predetermined period of time. 11. The method according to the preamble of claim 1 or one of claims 1 to 10, characterized in that the overload protection measures include a measure c ₆ ) for adjusting the speed of the drive unit ( 12 ) to a after performing a switching operation on a transmission input side ( 28th ) a gear arrangement ( 30 ) expected speed. 12. The method according to claim 11, characterized in that the switching process is a switching of a higher gear into a lower gear.   13. The method according to the preamble of claim 1 or one of claims 1 to 12, characterized in that the overload protection measures include a measure c ₇ ) to prevent switching operations in which at least one gear step is skipped. 14. The method according to claim 13, characterized in that a switching operation is prevented in that the friction clutch ( 22 ) is held in a disengaging position or in the region of the disengaging position and / or that when the gear arrangement ( 30 ) is an automated gear arrangement , the insertion of a gear step, in which at least one gear step is skipped starting from an output gear step, is prevented. 15. The method according to the preamble of claim 1 or one of claims 1 to 14, characterized in that the overload protection measures include a measure c ₈ ) to reduce a period of time for performing an engagement process of the friction clutch ( 22 ) with respect to a corresponding period of time in the absence of an overload condition or / and when there is a low overload condition. 16. The method according to the preamble of claim 1 or one of claims 1 to 15, characterized in that the overload protection measures include a measure c ₉ ), in which when performing a coupling process and when slip occurs in the area of driven wheels ( 46 , 48 ) the friction clutch ( 22 ) is adjusted in the direction of a disengaging position. 17. The method according to claim 16, characterized in that the slip state is a state in which the speed of the driven wheels ( 46 , 48 ) is lower than that of non-driven wheels. 18. The method according to claim 16 or 17, characterized in that after or during the setting of the friction clutch ( 22 ) in the direction of the disengaging position, the speed of the drive unit ( 12 ) to a present in the area of an input side ( 28 ) of a gear arrangement ( 30 ) is provided. 19. The method according to claim 18, characterized in that after or during the setting of the speed of the drive unit ( 12 ) on the on an input side ( 28 ) of the gear arrangement ( 30 ) present speed, the friction clutch ( 22 ) again in the direction of the engagement position becomes. 20. The method according to the preamble of claim 1 or one of claims 1 to 19, characterized in that the overload protection measures further include a measure c ₁₀ ), in which, when in a transmission arrangement ( 30 ) a shift from a lower gear to one higher gear stage is to be carried out, the increase in the output torque or the power output of a drive unit ( 12 ) after performing the switching operation in the transmission arrangement ( 30 ) is limited or delayed until the friction clutch ( 22 ) is substantially fully engaged or the moment transmitted by it Threshold reached. 21. The method according to any one of claims 1 to 20,  further comprising generating an optical warning signal or / and an acoustic warning signal if overload protection measures are to be taken. 22. The method according to any one of claims 1 to 21, further comprising a step d) for at least partially, preferably substantially completely eliminating the overload protective measures. 23. The method according to claim 22, characterized in that step d) is then carried out, if, after taking overload protection measures, a new one Carrying out step b) leads to the result that a Overload condition not present. 24. The method according to claim 22 or 23, characterized in that step d) is then carried out, if lifting measures are taken. 25. The method according to claim 24, characterized in that the lifting measures in substantially complete depression of an accelerator pedal. 26. The method according to claim 25, characterized in that when the substantially complete depression of the accelerator pedal does not lead to a corresponding reaction of the vehicle, the drive unit ( 12 ) is brought into an inoperative state. 27. The method according to claim 26, characterized in that the drive unit ( 12 ) is brought into the inoperative state after a third predetermined period of time since the substantially full depression of the accelerator pedal. 28. The method according to claim 26 or 27, characterized in that after bringing the drive unit ( 12 ) into the non-operating state, the drive unit ( 12 ) is started again automatically or by actuation of an ignition switch.