Abstract:
A power-split transmission which is designed to be operated with either first or second deceleration logics. The second deceleration logic has a higher deceleration dynamic than the first deceleration logic, and is designed to disengage an engaged range clutch immediately so as to reduce the transmission ratio by way of a hydrostatic unit with a maximum dynamic. A method of operating the transmission includes: monitoring various vehicle parameters while the vehicle is operated with the first deceleration logic; detecting that at least one set limit value has been exceeded while the vehicle operated with the first deceleration logic; activating the second deceleration logic, to immediately disengage an engaged range clutch; reducing a transmission ratio to a maximum using the hydrostatic unit, the hydrostatic unit being displaced with a maximum dynamic; and engaging the range clutch and activating the first deceleration logic.

Description:
[0001]    This application claims priority from German patent application serial no. 10 2016 200 992.3 filed Jan. 25, 2016. 
       FIELD OF THE INVENTION 
       [0002]    The invention concerns a power-split transmission device for a vehicle and a method for operating such a transmission device, such that the transmission device can in particular be used in a mobile working machine. 
       BACKGROUND OF THE INVENTION 
       [0003]    Vehicle drive-trains of mobile working machines, in particular wheel loaders, are more and more often built with continuously variable power-split transmission devices which are made with a variator, a reversing transmission and range clutches. In the area of the reversing transmission spur gear stages or planetary gearsets are usually provided, such that the travel direction of the working machine is determined by the corresponding engagement of disk clutches. Driving ranges, within which a transmission ratio of the power-split transmission can be varied continuously by means of the variator, are obtained by coupled planetary gearsets or spur gear stages. To obtain driving range changes, as a rule disk clutches are used as the shifting elements. Furthermore, the variator is often designed as a hydrostatic transmission with hydrostatic units that can in each case be operated as a pump or a motor in combination with a power-splitting arrangement. 
         [0004]    When the transmission ratio of the power-split transmission device is adjusted, for example starting from small transmission ratios toward larger transmission ratios, in each case one or more driving ranges are respectively passed through in part or totally, and for this the hydrostatic unit has to be swiveled several times over the complete driving range. For example, if two driving ranges which have to be completely passed through are considered, then around 0.5 to 1.0 seconds are needed for passing through the driving ranges and a further 150 to 200 ms are needed for the necessary driving range change, so that in total approximately 0.65 to 1.2 seconds pass by until a maximum transmission ratio is produced in the area of the transmission device. When a wheel loader drives onto a pile or heap, the load imposed from outside increases, in particular the deceleration, in less than 0.2 seconds. The control speed or speed of change of the transmission ratio in the area of the transmission device is therefore, disadvantageously, too low to avoid unacceptable decelerations of the rotational speed of a drive engine when driving onto a heap. Owing to the high control speeds of the hydrostatic unit required in combination with the unavoidable dead time associated with a driving range change, new methods are needed in order to satisfy the strict requirements for dynamics and for the protection of the engine and the transmission. 
         [0005]    For example, DE 10 2013 222 693 A1 discloses a method for operating a vehicle drive-train with a drive engine and a power-split transmission device that can be brought, on the input side, into functional connection with the drive engine, which on its output side can be connected to a drive output, and whose transmission ratio in the area of a variator can be varied continuously, and with a shifting element which is arranged in the power flow of the vehicle drive-train between the drive engine and the drive output and whose transmission capacity can be varied continuously. The transmission capacity of the shifting element is varied as a function of the torque to be transmitted at the time in the drive-train between the drive engine and the drive output, and if the torque applied is greater than a defined threshold value, the shifting element changes to slipping operation. 
       SUMMARY OF THE INVENTION 
       [0006]    The purpose of the present invention is to provide a power-split transmission device and a method for operating the transmission device, which show greater deceleration dynamics in order to protect the transmission device and the drive engine in unfavorable operating situations. 
         [0007]    This objective is achieved by the transmission device and method for operating the same as described below. 
         [0008]    According to the invention, the power-split transmission device for a vehicle is provided in order to connect a drive engine arranged on its input side to a drive output arranged on its output side. The transmission device comprises a hydrostatic unit for the continuous adjustment of a transmission ratio and at least one range clutch for coupling the transmission device to the drive output, wherein the transmission device is designed to be operated with a first and a second deceleration logic such that the second deceleration logic has a higher deceleration dynamic than the first deceleration logic, and wherein the second deceleration logic is provided in order to immediately open a closed range clutch so as to reduce the transmission ratio by means of the hydrostatic unit with maximum dynamic. 
         [0009]    Preferably, the transmission ratio of the hydrostatic unit is displaced toward zero transmission ratio with maximum gradient regardless of the driving range at the time. In particular the drive engine is an internal combustion engine, preferably a Diesel engine and serves to propel the vehicle. The transmission ratio of the transmission device is adjusted by active displacement of the hydrostatic unit. In particular, for this a yoke of the hydrostatic unit is moved between a zero position and a maximum deflection. Moreover, the at least one range clutch is provided in order to couple a driving range of the hydrostatic unit, within which the transmission ratio can be varied continuously, to the drive output. Furthermore, it is conceivable for the transmission device to have a plurality of range clutches, each range clutch being provided in order to couple a respective driving range to the drive output. 
         [0010]    The first deceleration logic represents essentially a normal operating condition of the transmission device. During normal operation when the vehicle decelerates, for example when it is braked from a high speed down to rest, all the driving ranges are passed through. Thus, depending on the number of driving ranges, a plurality of driving range changes are carried out. An actual reciprocal transmission ratio follows a nominal transmission ratio set by the hydrostatic device. By definition the actual reciprocal transmission ratio is equal to the quotient of the drive output rotational speed and the drive input rotational speed of the transmission device. 
         [0011]    In contrast, the second deceleration logic represents an emergency shift of the transmission device provided in order to protect the transmission device and the drive engine. During the second deceleration logic the nominal transmission ratio follows the actual reciprocal transmission ratio. In particular, the second deceleration logic is activated for highly dynamic driving movements of the vehicle. A highly dynamic driving movement is understood to mean, for example, when a wheel loader climbs up a solid heap at speed. In such a case a high deceleration dynamic occurs whose result is that the nominal transmission ratio cannot follow the actual reciprocal transmission ratio. The second deceleration logic has higher deceleration dynamics than the first deceleration logic. When the second deceleration logic is activated a closed range clutch is opened immediately. This separates the transmission device and the drive engine from the drive output. Moreover, this makes it possible for the nominal transmission ratio to be reduced by means of the hydrostatic unit with the maximum dynamics. Thus, the various driving ranges are no longer passed through. Maximum dynamics is understood to mean that a maximum nominal transmission ratio gradient is used. This makes it possible for the nominal transmission ratio to follow the reciprocal transmission ratio. 
         [0012]    According to a preferred embodiment, three range clutches are provided in order to obtain three driving ranges, such that in each driving range the transmission ratio can be adjusted continuously by means of the hydrostatic unit. To accelerate the vehicle, the first range clutch is closed and the nominal transmission ratio is adjusted by means of the hydrostatic unit to the synchronous transmission ratio for the driving range change. During the driving range change from the first driving range to the second driving range the first and second range clutches are synchronized with one another, and the second range clutch is closed while the first range clutch is opened. As soon as the driving range change has been completed, the nominal transmission ratio in the second driving range is adjusted by means of the hydrostatic unit to the synchronous transmission ratio for the next driving range change. During the driving range change from the second to the third driving range, the second and third range clutches are synchronized with one another and the third range clutch is closed while the second range clutch is opened. As soon as this driving range change has been completed, the nominal transmission ratio in the third driving range is adjusted by means of the hydrostatic unit. During deceleration, in particular when braking the vehicle from the third driving range down to rest, the three driving ranges are passed through in the reverse sequence. 
         [0013]    The method according to the invention for operating the above-mentioned power-split transmission device comprises essentially the following process steps: monitoring of various vehicle parameters while the vehicle is operated with a first deceleration logic, detection that while the vehicle is being operated with the first deceleration logic at least one established limit value has been exceeded, activation of the second deceleration logic whereby a closed range clutch is opened immediately, maximum reduction of a transmission ratio by means of the hydrostatic unit, wherein the hydrostatic unit is displaced with a maximum dynamic, and closing the range clutch and activation of the first deceleration logic. Thus, the second deceleration logic is activated as soon as it is seen from the vehicle parameters monitored that the deceleration dynamics of the first deceleration logic no longer suffice for the nominal transmission ratio to be adapted to the actual reciprocal transmission ratio. To assess when the deceleration dynamics of the first deceleration logic are no longer sufficient, limit values for various vehicle parameters are defined. These vehicle parameters are monitored and if at least one established limit value is exceeded, the second deceleration logic is activated. In other words, the exceeding of at least one established limit value serves as the triggering condition for activating the second deceleration logic. 
         [0014]    Below, preferred triggering conditions for activating the second deceleration logic are described. Preferably, the second deceleration logic is activated when at least one triggering condition has been fulfilled. According to a further preferred embodiment, the second deceleration logic is activated when all the triggering conditions have been fulfilled. It is conceivable, moreover, to weight the various triggering conditions to different extents. In particular, it is envisaged that several more highly weighted triggering conditions bring about the activation of the second deceleration logic. Advantageously the activation of the second deceleration logic can be countermanded in some circumstances, particularly when information about a lifting frame or scoop position of the vehicle is known. 
         [0015]    Preferably, the second deceleration logic is activated when at least one actual drive output rotational speed gradient is smaller than a fixed limit value. The actual drive output rotational speed gradient is in particular a measure of the deceleration of the vehicle and describes how quickly the drive output rotational speed is changing and especially how quickly the vehicle is decelerating. 
         [0016]    Preferably, the second deceleration logic is activated when at least one high pressure in the transmission device is higher than an established limit value. The high pressure in the transmission device is a measure for the loading of the hydrostatic unit and must not exceed a maximum limit value in order not to compromise the function of the hydrostatic unit. If the high pressure in the transmission device is above a transmission-damaging maximum pressure for a certain time, an emergency shift is triggered. Thus, the triggering condition is a maximum operating time above the transmission-damaging maximum pressure. For this, when the maximum pressure is exceeded a count value is incremented. When the high pressure falls below the maximum pressure, the count is decremented. If the maximum operating time is reached, the second deceleration logic is activated. 
         [0017]    Preferably, the second deceleration logic is activated when at least an engine rotational speed and/or an engine rotational speed gradient is smaller than an established limit value. The drive engine is operated at an engine rotational speed that is within an acceptable range. A reduction of the engine rotational speed below the acceptable range can result in stalling of the engine or, in the worst case, to engine damage. Moreover, the engine rotational speed gradient describes how quickly the engine rotational speed is changing. Preferably, the second deceleration logic is activated when at least a reduction of the engine rotational speed is larger than an established limit value. 
         [0018]    Preferably, the second deceleration logic is activated when at least a load on the drive engine is greater than an established limit value. The loading of the drive engine is preferably expressed as a percentage. 
         [0019]    Preferably, the second deceleration logic is activated when at least a nominal reciprocal transmission ratio gradient is smaller than an established limit value. Thus, the second deceleration logic is activated in order to increase the nominal reciprocal transmission ratio gradient. This makes it possible for the nominal reciprocal transmission ratio to follow the actual reciprocal transmission ratio. 
         [0020]    Preferably, when the second deceleration logic is activated the range clutch is reduced to a filling equalization pressure, in order thereafter, from that pressure level, to begin a torque-controlled engagement of the range clutch. In that way the range clutch operates without emptying completely, so that a torque can be built up more rapidly at the range clutch. 
         [0021]    According to a preferred example embodiment, the range clutch is closed as soon as the actual reciprocal transmission ratio reaches a limit value. In particular, a zero position is defined as the limit value. Moreover, the limit value can also be larger than zero and then the range clutch is designed more efficiently. 
         [0022]    In a further preferred example embodiment, a range clutch is closed as soon as a rotational speed difference reaches a limit value. The limit value of the rotational speed difference depends on the power of the range clutch. This, the range clutch can be closed even with a larger rotational speed difference if the range clutch is correspondingly more efficient and can perform the necessary shifting work and shifting power. 
         [0023]    Preferably, the opening of the closed range clutch when the second deceleration logic is activated, is associated with an actuation of the brakes of the vehicle. When the second deceleration logic is activated, owing to the opening of the range clutch the drive-train is free, and the vehicle can therefore roll backward. To enable backward rolling and a more rapid closing of the range clutch, the activation of the second deceleration logic is associated with an actuation of the vehicle&#39;s brakes. In particular, the brakes are actuated below a certain drive output rotational speed. The brake of the vehicle can be both a holding brake and a service brake. 
         [0024]    Preferably, conditions are also envisaged which allow activation of the first deceleration logic while the vehicle is being operated with the second deceleration logic. In particular, the first deceleration logic is activated again when the friction performance and/or the friction work at the range clutch exceeds a limit value. Furthermore, the first deceleration logic is activated again when a maximum time of operating with the second deceleration logic has been exceeded. Preferably, the maximum time for operating the vehicle with the second deceleration logic amounts to a few seconds. In addition, the first deceleration logic is activated again when, after a maximum operating time of the second deceleration logic, an actual drive output rotational speed has fallen to a certain value. 
         [0025]    In particular, the power-split transmission device according to the invention can be used for providing drive power, and therefore in a mobile working machine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Below, an example embodiment of the invention is described in more detail with reference to the drawings, in which the same or similar elements are provided with the same indexes and which show: 
           [0027]      FIG. 1 : A very schematic block circuit representation of a vehicle drive-train comprising a power-split transmission device according to the invention with a hydrostatic device, 
           [0028]      FIG. 2 : A diagram to illustrate a variation of a transmission ratio of the hydrostatic unit and an actual reciprocal transmission ratio that depends on it, 
           [0029]      FIG. 3 : A diagram to illustrate a variation of a nominal reciprocal transmission ratio, the transmission ratio of the hydrostatic unit, and the actual reciprocal transmission ratio that depends on it, when the second deceleration logic is activated in a third driving range, 
           [0030]      FIG. 4 : A diagram to illustrate a variation of a nominal reciprocal transmission ratio, the transmission ratio of the hydrostatic unit, and the actual reciprocal transmission ratio that depends on it, when the second deceleration logic is activated in a second driving range, 
           [0031]      FIG. 5 : A diagram to illustrate a variation of a nominal reciprocal transmission ratio, the transmission ratio of the hydrostatic unit, and the actual reciprocal transmission ratio that depends on it, when the second deceleration logic is activated in a first driving range, 
           [0032]      FIG. 6 : A diagram to illustrate a variation of the nominal reciprocal transmission ratio and the actual reciprocal transmission ratio when the second deceleration logic is activated, and 
           [0033]      FIG. 7 : A diagram to illustrate the variation of the closing torque at a first range clutch. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    As shown in  FIG. 1 , a vehicle drive-train comprises a drive engine  2  and a continuously variable power-split transmission device  1  that can be coupled thereto. In this case the drive engine  2  is in the form of an internal combustion engine, but in other embodiments of the drive-train it can also be an electric machine or a combination of an internal combustion engine and an electric machine. On the transmission output side the transmission device  1  is in functional connection with a drive output  3  so that a drive torque produced by the drive engine  2 , converted in accordance with the transmission ratio set in the area of the transmission device  1 , is provided as the drive output torque in the form of a corresponding traction force. The transmission device  1  comprises a hydrostatic unit  4  for the continuous adjustment of the transmission ratio, three range clutches  5   a,    5   b,    5   c  for coupling the transmission device  1  to the drive output  3 , and a reversing clutch  9  for enabling the vehicle to drive in the forward and in the reversing direction. Embodiments with only one range clutch  5   a,    5   b,    5   c  are also conceivable. Usually, a clutch (not shown here) for forward driving and a clutch (also not shown) for driving in reverse are arranged in the reversing clutch. However, the reversing clutch can also be in the form of a dual shifting element, which means that for the respective actuation of the clutches for driving forward or in reverse a single, common actuator is operated. Furthermore, in the area between the drive engine  2  and the transmission device  1 , an auxiliary power take-off  6  in the form of a working hydraulic system can be acted upon by torque from the drive engine  2 ,. According to the invention, the transmission device  1  is designed to be operated with a first and a second deceleration logic such that the second deceleration logic has higher deceleration dynamics than the first deceleration logic. For this the second deceleration logic is designed so as to immediately open whichever range clutch  5   a,    5   b,    5   c  is closed, in order to reduce the transmission ratio by means of the hydrostatic unit  4  with the maximum dynamic. During this the reversing clutch remains constantly dosed in the shifting position for forward driving. 
         [0035]    According to  FIGS. 2, 3, 4 and 5 , starting from a high transmission ratio the transmission device  1  is in each case adjusted in the direction toward lower transmission ratios. In the diagrams, time is plotted along the abscissa and the transmission ratio along the ordinate. 
         [0036]      FIG. 2  shows how a transmission ratio  10  of the hydrostatic unit  4  is adjusted in the respective driving range  7   a,    7   b,    7   c  in accordance with a first deceleration logic in order to reduce an actual reciprocal transmission ratio  11 . The transmission ratio  10  of the hydrostatic unit  4  is understood to be a nominal transmission ratio of the hydrostatic unit  4 , namely a desired transmission ratio of the hydrostatic unit  4 . By definition, the actual reciprocal transmission ratio  11  is equal to the quotient of a drive output rotational speed and a drive input rotational speed of the transmission device  1 , the drive output rotational speed and the drive input rotational speed preferably being measured by a sensor in each case. During any driving range change  8   a,    8   b  the actual reciprocal transmission ratio  11  and the transmission ratio  10  of the hydrostatic unit  4  cannot be adjusted. In a third driving range  7   c  the transmission ratio  10  of the hydrostatic unit  4  is adjusted from high transmission ratios, analogously to the actual reciprocal transmission ratio  11 , in the direction of a first synchronous point  13   a  toward lower transmission ratios. In a first driving range change  8   a  the third and second range clutches  5   c,    5   b  are synchronized. The second range clutch  5   b  is closed and the third range clutch  5   c  is opened. The second driving range is activated. In the second driving range  7   b  the actual reciprocal transmission ratio  11  decreases toward a second synchronous point  13   b,  whereas the transmission ratio  10  of the hydrostatic unit  4  increases to higher values. In a second driving range change  8   b  the second and first range clutches  5   b,    5   a  are synchronized. The first range clutch  5   a  is closed and the second range clutch  5   b  is opened. The first driving range  7   a  is activated. In the first driving range  7   a  the transmission ratio  10  of the hydrostatic unit  4  is adjusted from a high transmission ratio, analogously to the actual reciprocal transmission ratio  11 , in the direction of the stationary point toward lower transmission ratios. The first deceleration logic is provided for normal deceleration operation, wherein the actual reciprocal transmission ratio  11  is set in accordance with the transmission ratio  10  of the hydrostatic unit  4 . Accordingly, the actual reciprocal transmission ratio  11  follows the transmission ratio  10  of the hydrostatic unit  4 . 
         [0037]    When higher dynamics are required, in particular as regards the adjustment dynamics of the transmission ratio, the first deceleration logic comes up against its limits. In other words, in the event of an exceptional deceleration the transmission ratio cannot be adjusted quickly enough so the transmission ratio  10  of the hydrostatic unit  4  cannot follow the actual reciprocal transmission ratio  11 . As a result, either the rotational speed of the drive engine  2  is reduced too much or a high pressure in the hydrostatic unit  4  reaches unacceptably high values which can damage the transmission device  1 . According to the invention, it is then proposed to operate the transmission device  1  with a second deceleration logic having higher deceleration dynamics than the first deceleration logic. 
         [0038]      FIG. 3  shows how, when the second deceleration logic has been activated in the third driving range  7   c,  the transmission ratio  10  is adjusted in order to obtain a desired nominal reciprocal transmission ratio  15  which substantially matches the actual reciprocal transmission ratio  11 . When the second deceleration logic is activated the third, closed range clutch  5   c  is opened immediately so that the stress on the drive engine  2  and the transmission device  1  is reduced. The reversing clutch  9  remains closed. During a waiting period  12 , the transmission ratio  10  of the hydrostatic unit  4  is adjusted with the existing nominal dynamic until the second range clutch  5   b  is fully open so that the second range clutch  5   b  no longer transmits any torque. After the end of the waiting period  12 , the transmission ratio  10  of the hydrostatic unit  4  is adjusted directly to the zero position with the maximum dynamic. Thereafter, the first range clutch  5   a  is engaged and the first driving range  7   a  is activated, so that there is no traction force interruption. 
         [0039]      FIG. 4  shows how, when the second deceleration logic in the second drive range  7   b  has been activated, the transmission ratio  10  of the hydrostatic unit  4  is adjusted in order to obtain the desired nominal reciprocal transmission ratio  15  in such manner that it substantially matches the actual reciprocal transmission ratio  11 . When the second deceleration logic is activated the second, closed range clutch  5   b  is opened immediately, such so that the load on the drive engine  2  and the transmission device  1  is reduced. The reversing clutch  9  remains closed. During a waiting period  12 , the transmission ratio  10  of the hydrostatic unit  4  is not adjusted, but is unchanged, since here a normal adjustment would be accompanied by an increase in the transmission ratio  10  of the hydrostatic unit  4  in the direction of the second synchronous point  13   b  during the deceleration. After the end of the waiting period  12 , the transmission ratio  10  of the hydrostatic unit  4  is adjusted directly to the zero position with the maximum dynamic. The first range clutch  5   a  is then engaged and the first drive range  7   a  is activated such that no or only a small interruption of the traction force take place. 
         [0040]      FIG. 5  shows how, when the second deceleration logic in the first drive range  7   a  has been activated, the transmission ratio  10  of the hydrostatic unit  4  is adjusted in order to obtain the desired nominal reciprocal transmission ratio  15  in such manner that it substantially matches the actual reciprocal transmission ratio  11 . This adjustment of the transmission ratio  10  of the hydrostatic unit  4  is identical to the adjustment of the transmission ratio  10  of the hydrostatic unit  4  in the third drive range  7   c  according to  FIG. 3 . When the second deceleration logic is activated the first, closed range clutch  5   a  is opened immediately. The reversing clutch  9  remains closed. During a waiting period  12 , the transmission ratio  10  of the hydrostatic unit  4  is adjusted with the existing nominal dynamic. After the end of the waiting period  12 , the transmission ratio  10  of the hydrostatic unit  4  is adjusted directly to the zero position with the maximum dynamic. The first range clutch  5   a  is then engaged again. 
         [0041]      FIG. 6  is a diagram showing the respective variations of the nominal transmission ratio  10  and the actual transmission ratio of the hydrostatic unit  4 , with time plotted along the abscissa and transmission ratio along the ordinate. The actual transmission ratio of the hydrostatic unit  4  represents a real variation of the transmission ratio, whereas the nominal transmission ratio  10  of the hydrostatic unit  4  is a desired variation of the transmission ratio of the hydrostatic unit  4 . When the second deceleration logic has been activated the transmission ratio of the hydrostatic unit  4  is adjusted in the direction toward zero. This return is carried out with the gradient  16   a  as far as a threshold value  17   a.  Thereafter, a yoke of the hydrostatic unit  4 —not shown here—is readjusted as a function of the actual transmission ratio of the hydrostatic unit  4 . During this readjustment of the actual transmission ratio of the hydrostatic unit  4 , the nominal transmission ratio of the hydrostatic unit  4  is adjusted with a second gradient  16   b,  which is smaller than the first gradient  16   a,  in order to achieve smooth regulation.  FIG. 6  describes the case in which after passing through zero the vehicle rolls slightly backward. In that case the nominal transmission ratio below the zero position is set to the lowest threshold value  17   b.  In other words, the hydrostatic unit  4  overshoots. This reduces a rotational speed difference when the first range clutch  5   a  is engaged. 
         [0042]      FIG. 7  is a diagram showing a variation of a closing torque of the first range clutch  5   a,  wherein time is plotted along the abscissa and closing torque along the ordinate. When the second deceleration logic has been activated and the closed range clutch  5   a,    5   b,    5   c  concerned has been opened, the first range clutch  5   a  is engaged. This engagement of the first range clutch  5   a  follows an exactly defined, torque-controlled process. The loading limits of the first range clutch  5   a  in relation to friction performance and friction work must not be exceeded. Due to the starting by means of the first range clutch  5   a,  traction force is quickly built up again in the forward direction. To begin with, an initial first closing torque  18   a  is applied at the first range clutch  5   a.  Starting from that closing torque  18   a,  the torque is increased during a time interval as far as a second closing torque  18   b,  whereby the first range clutch  5   a  produces a frictional connection between the transmission device  1  and the drive output  3 . The second closing torque  18   b  is chosen such that a predetermined friction performance is not exceeded, but at the same time sufficient closing torque is built up to stop the vehicle from rolling backward and bring it to rest. After a minimum time interval  19 , the first range clutch  5   a  is closed in that the closing torque is increased to a third closing torque  18   c  by way of a maximum gradient. However, this only takes place if after the lapse of the minimum time interval  19  a predefined maximum rotational speed difference of the clutch is not exceeded. If the rotational speed difference at the clutch is exceeded, the torque is maintained until the rotational speed difference falls below the predefined maximum rotational speed difference of the clutch and only then is the clutch closed completely. Accordingly the range clutch  5   a  is closed, whereby the first deceleration logic is activated again. 
       Indexes 
       [0000]    
       
           1  Transmission device 
           2  Drive engine 
           3  Drive output 
           4  Hydrostatic unit 
           5   a  to  5   c  Range clutch 
           6  Auxiliary power take-off 
           7   a  to  7   c  Driving range 
           8   a,    8   b  Driving range change 
           9  Reversing clutch 
           10  Nominal transmission ratio 
           11  Actual reciprocal transmission ratio 
           12  Waiting time 
           13   a,    13   b  Synchronous point 
           14  Actual transmission ratio 
           15  Nominal reciprocal transmission ratio 
           16   a,    16   b  Gradient 
           17   a,    17   b  Threshold value 
           18   a  to  18   c  Closing torque 
           19  Minimum time interval