DE102008025683A1 - Method for controlling a traction drive - Google Patents

Abstract

The invention relates to a method for controlling a traction drive (1) with a primary drive machine (2) and a hydrostatic transmission (3) connected thereto. First, a position of a travel command setting device (13) is detected. On the basis of the determined position of the drive command setting device (13), an operating point for a primary drive machine (2) is determined. Furthermore, an adjustment of the hydrostatic transmission (3) is determined. On the basis of the detected position of the driving command setting device (13), a target output torque of the traction drive (1) is determined, from which a required drive power of the primary drive machine (2) is determined. Based on the required drive power, the operating point of the primary drive machine (2) is determined.

Description

The The invention relates to a method for controlling a traction drive with a primary prime mover and an associated one stepless transmission.

A method for controlling a hydrostatic drive is from the DE 38 06 194 A1 known. The control described there is self-learning and processor-controlled. By means of a transmitter, such as an accelerator pedal, a speed for a diesel engine is specified. The control contains adjustable characteristic curves with which a maximum permissible pressure can be set as a function of the given diesel engine speed. Depending on the pressure actually resulting from the load condition, a delivery volume of the hydrostatic pump of the hydrostatic transmission is adjusted.

Problematic At the known control it is that changes to the Characteristics of the control behavior are difficult to implement. So must by the self-learning process in each case an idle curve the prime mover are recorded. The flexibility is limited to the adaptation of the permissible maximum pressure of the diesel engine.

It It is therefore the object of the invention to provide a control method for to create a hydrostatic drive in which a lighter Intervention in the control characteristic is possible.

The The object is achieved by the method having the features of the claim 1 solved.

at The method according to the invention is used for driving a traction drive with a continuously variable, in particular a hydrostatic Transmission first a move command and a vehicle condition determined. It is z. B. a position of a Fahrbefehlvorgabevorrichtung and detects a vehicle speed. Such a driving command presetting device can be a throttle or an accelerator pedal. From the detected Position of the drive command setting device is a vehicle target torque and from this an operating point for a primary Engine determined. At the determined operating point is Ensures that the primary prime mover has a sufficient power to satisfy the requirements according to driving lever specification generated. In addition to the operating point is also the Adjustment of the hydrostatic transmission, ie their transmission ratio determined. According to the invention is based on the Detected position of the Fahrbefehlvorgabevorrichtung a target output torque the traction drive determines from the required drive power and ultimately the operating point of the primary prime mover is determined. This is in contrast to the prior art means the position of the Fahrbefehlvorgabevorrichtung no longer easy a target speed for the most as a diesel engine executed primary drive machine specified. Rather, initially set by an operator Driving lever position of a torque request, the target output torque, assigned by the operator. Based on this moment requirement So the target output torque of the traction drive is then in a second step, the required driving power of the primary Determined drive, which for the realization of the target output torque is required.

After all is the determined required drive power accordingly set an operating point of the primary drive machine. In particular, in diesel engines there is no immediate Relationship between the position of the drive command setting device and a target speed of the diesel engine. The operating point is rather determined from the map of the diesel engine, wherein a selection criterion is the previously determined required drive power is. The determination of the operating point in the map can thus be made considerably more flexible and in particular areas with particular consider favorable fuel consumption. following For the sake of simplicity, it will merely be a hydrostatic transmission also used for other continuously variable transmissions.

advantageous Further developments of the method according to the invention are set forth in the subclaims.

It is advantageous to first determine a vehicle target speed based on a physical model of the drive train or of the entire vehicle from the setpoint output torque of the travel drive. From this vehicle target speed, the transmission ratio of the hydrostatic transmission is then determined. The determination of the transmission ratio of the hydrostatic transmission from the target output torque on the target vehicle speed has the advantage that instead of a complex consideration of an acceleration torque, a simple addition of the actual vehicle speed can be done. This is the calculation and in particular the parameterization of the control simplified.

According to one Another preferred embodiment is for determination the target output torque of the respectively determined position of the drive command setting device a value of 0 up to one from the rated power of the prime mover associated with the resulting moment. However, this results in a relatively large load sensitivity, since each actually available power at a speed considering the Pressing the diesel engine with increasing speed increasingly below the rated power of the diesel engine.

In another, particularly preferred embodiment therefore, every detected position of the travel command setting device a value from 0 to one out of the at an actual operating point associated with the prime mover moment. This will each ensures that regardless of the position of the drive command setting device for the remaining pedal travel or lever travel of the travel command default device the actually available free drive power the primary drive machine is available. At each travel command default position "feels" the operator therefore, what additional power him Drive machine still offers.

Preferably is also used in determining the gear ratio of the hydrostatic transmission considered a vehicle load torque. The vehicle load torque is in particular from the suppression the drive machine determined. The pressure is the deviation the actual speed of a target speed of the primary drive machine designated. The determination of the vehicle load torque from the push the prime mover has the advantage that only one deviation the actual resulting engine speed is required by the predetermined target speed. This is already happening by using a simple speed sensor allows.

According to one Another preferred embodiment is the vehicle load torque in contrast, from the control unit of the primary drive machine directly read. However, such an approach is only possible if the control unit, for example, the injection system a diesel engine via a corresponding signal the vehicle load torque or the actual delivered drive power of the diesel engine available provides.

The Determination of the vehicle target speed is preferably carried out by integration of an initially determined vehicle target acceleration. It is in a particularly simple way, the relationship between exploited the desired output torque and the target acceleration. The Calculation of the vehicle target speed by integration of the Vehicle roll acceleration ensures that practically the total determination of the gear ratio of the hydrostatic transmission can be carried out by calculation can. The pressure-controlled adjusting devices, for example at a usual speed-dependent high pressure adjustment are required, can thus be omitted. The procedure to drive the traction drive is thus essentially in one Integrate control unit and can be accordingly simple be parameterized.

The gear ratio for the hydrostatic transmission is according to the Finally, preferred embodiment of the by Integration determined vehicle target speed and the actual speed determined the primary drive machine. In this way can also be adjusted to the translation of the hydrostatic Gear are determined purely by calculation, with the setting the pump swivel angle or the motor swivel angle starting from the gear ratio individually Characteristics are set.

there it is particularly preferred that the integration of the vehicle target acceleration for determining the vehicle target speed over the entire time since a system start.

One preferred embodiment of the invention Method will be with reference to the figures in the following description explained in detail. Show it:

1 a schematic representation of a used for the control according to the method according to the invention hydrostatic drive;

2 an exemplary map for scaling the position of the Fahrbefehlvorgabevorrichtung;

3 a signal flow diagram to illustrate the implementation of the method according to the invention proceedings;

4 an exemplary map of a diesel engine running primary prime mover.

In the 1 is a schematic representation of a traction drive 1 to recognize the implementation of the method according to the invention. The traction drive 1 comprises a primary drive machine, which in the illustrated embodiment as a diesel engine 2 is executed. The diesel engine 2 is with a hydrostatic transmission 3 connected.

The hydrostatic transmission 3 includes an adjustable hydraulic pump 4 and a likewise adjustable hydraulic motor 5 , The transmission ratio of the hydrostatic transmission 3 is determined by the set delivery volume of the hydraulic pump 4 and the set displacement of the hydraulic motor 5 established. In the illustrated embodiment, the hydrostatic transmission is 3 by connecting the hydraulic pump 4 and the hydraulic motor 5 realized in a closed circuit. Both hydrostatic machines, which are preferably axial piston machines of the bent axis or swash plate type, are designed for operation in two opposite directions of flow. This allows the direction of travel without the need for a mechanical transmission by changing the direction of the hydraulic pump 4 to adjust.

The diesel engine 2 is with the hydraulic pump 4 via a drive shaft 6 connected. Instead of the direct drive of the hydraulic pump 4 can also be a between the diesel engine 2 and the hydraulic pump 4 arranged gear can be provided. The transmission can be designed as a transfer case, which is provided for example a power take-off for driving further possibly also hydraulic consumers.

To drive the vehicle is the hydraulic motor 5 via an output shaft 7 with a powered vehicle axle 8th connected. The representation of the individual driven vehicle axle is merely an example. Likewise, the output shaft 7 be connected to another transfer case, for example, to realize a multi-axis drive.

To implement a determined operating point of the diesel internal combustion engine 2 is an injection system 9 intended. The injection system 9 For example, it may have its own injection control unit, via which the injection quantity of an injection pump (not explicitly shown) of the injection system 9 is set.

For adjusting the delivery volume of the hydraulic pump 4 is a first adjustment 10 intended. In a corresponding manner is to adjust the absorption volume of the hydraulic motor 5 a second adjusting device 11 intended. The first adjusting device 10 and the second adjusting device 11 may be, for example, electro-proportional adjusting devices, as they are known for controlling swash plate angles in axial piston machines.

By means of a central control unit 12 , in which the inventive method for driving substantially expires, both the injection system 9 as well as the first and the second adjusting device 10 . 11 of the hydrostatic transmission 3 driven. This is done by the central control unit 12 Defines default values, which via appropriate lines, such as a bus system, to the injection system 9 , the first adjusting device 10 and the second adjusting device 11 be transmitted.

The central control unit 12 detected for the diesel engine 2 a by a target speed n _D, set operating point and for the first adjustment 10 and the second adjusting device 11 in each case a control signal, for example for a proportional magnet in the case of an electro-proportional adjustment of the hydraulic pump 4 and the hydraulic motor 5 ,

To determine the control signals is by the central control unit 12 determines a position of a travel command presetting device. In the illustrated embodiment of the 1 the travel command default device is an accelerator pedal 13 , The position of the accelerator pedal 13 is via an accelerator pedal sensor 14 determined and corresponds to a value from 0 to 100%. Furthermore, the central control unit 12 the actual speed n _{D, is} the diesel engine 2 fed. This can be done, for example, via a correspondingly returned signal of the injection system 9 respectively. Is such a signal of the injection system 9 not available, such as a speed sensor on the drive shaft 6 provide and its signal to the central control unit 12 supply. The accelerator pedal 13 can also starting from a basic position to -100% and + 100% adjustable.

Further, the vehicle speed v _is by means of a vehicle speed sensor 15 determined. This can, for example, the speed of the output shaft 7 and to the central control unit 12 pass on, where, taking into account the Radgetriebeübersetzungen and / or a final drive transmission ratio, the actual vehicle speed v _is determined.

For carrying out the method according to the invention, first of all a specific and by the position sensor 14 determined position of the _{Fahrbefehlvorgabevorrichtung} a vehicle _{target torque} M _{Fzg, shall be} determined. In general, a vehicle torque is calculated according to the following equation:

Where M _{Fzg is} the vehicle _torque , MD that is actually the hydrostatic transmission 3 supplied drive torque of the diesel engine 2 , r the translation of the hydrostatic transmission 3 as the ratio of the stroke volume of the hydraulic pump V _gP to the stroke volume of the hydraulic _motor 5 V _gM and i _rad the Radgetriebeuntersetzung, which is defined as the speed of the hydraulic motor 5 to the speed of the driven wheel. At the same time, this definition also takes into account an axis ratio.

There are two possibilities, the determined position of the accelerator pedal 13 to assign a vehicle target torque. In general, the following relationship between the vehicle torque and the power of the primary drive engine is generally used:

Where n _{D is} the actual speed of the primary prime _mover , V _{Fzg, is} the actual speed of the vehicle and r _{rad is} the radius of the driven wheels. In the right-hand part of the equation, the dependence of the vehicle _torque M _Fzg on the power of the primary drive _machine P _{D can be recognized} , taking into account the power of any additional load P _NV present.

Since with decreasing vehicle _speeds V _Fzg, the vehicle _torque would go in the direction of infinity, is a limitation of the maximum torque by pressure relief valves in the hydrostatic transmission 3 provided. This limitation is made according to the equation:

Where M is _{Fzg, max is} the maximum vehicle _torque , V _{gM is} the displacement of the _{hydraulic motor} 5 and p _max through the pressure relief valves in the closed circuit of the hydrostatic transmission 3 maximum permissible working pressure.

According to a first, simple embodiment, the scaling of the ascertained accelerator pedal position takes place such that when the accelerator pedal is fully depressed (100% position) the vehicle target torque is calculated according to the above equation, taking into account the absolute maximum drive power P _{D, max, abs of} the diesel internal combustion engine 2 is determined. In the rest position of the accelerator pedal 13 (0% position) is the vehicle _{target torque} M _Fzg, however _{, should} equal zero. The scaling can z. B. be linear.

In this determination, one of the position of the accelerator pedal 13 however, it is not considered that the actual vehicle power torque P _{D, max} (n _{D, is} ) is the actual speed of the diesel engine 2 as well as their pressure depends and with increasing pressure is smaller than the absolute maximum power P _{D, max, abs of} the diesel engine 2 ,

For this first possibility is in the 2 a map for scaling the accelerator pedal 13 shown. From the diagram of 2 it can be seen that the accelerator pedal 13 starting from its zero position in two directions can be swung out, which corresponds to a forward drive or a reverse drive. Furthermore, the limitation of the maximum vehicle _torque M _Fzg can be recognized by the pressure relief _valves . The diagram shows this by an operator by means of the accelerator pedal 13 predetermined vehicle _{target torque} M _{Fzg, is} in dependence on the vehicle _speed v _{FZg, is} .

According to a second, particularly preferred embodiment, when the accelerator pedal is fully depressed, the vehicle pedal is scaled 13 (100% position) not the rated power of the primary prime mover 2 but rather takes into account the drive power actually available at the set operating point. The 100% position of the accelerator pedal 13 Thus, a vehicle _{target torque} M _{Fzg to be} assigned, which is the maximum torque M _{D, max} available at the actual _{diesel engine speed} n _D, taken into account. In the 0% position of the accelerator pedal 13 is of course again the assigned vehicle _{target torque} M _{Fzg, should} equal to zero. The latter possibility has the advantage that the torque scaling of the usable torque of the diesel engine 2 always over the entire accelerator pedal path. The Restpedalweg the accelerator pedal 13 thus always the currently available power reserve of the diesel engine 2 assigned. Thus, in contrast to the first-mentioned scaling example, there is no dead pedal travel in which an operator depresses the accelerator pedal 13 changes in position, but no reaction of the vehicle takes place.

The sequence of the method according to the invention will be described below with reference to FIGS 3 explained. First, as already explained above, for each position of the accelerator pedal 13 in the central control unit 12 an assigned vehicle _{target torque} M _{Fzg is to be} determined. The scaling is schematic with step 1 designated. In step S2, this vehicle _target torque M _{Fzg is to be} freed from the load torque of the vehicle. In the illustrated example, the load torque from the depression of the diesel engine 2 certainly. For this purpose, initially starting from the vehicle _{target torque} M _Fzg, a target rotational speed n _{D, should} the diesel engine 2 determined. This setpoint speed n _{D, should} also be through the central control unit 12 determined and the injection system 9 of the traction drive 1 supplied as a control variable.

To determine the target speed n _D, the diesel engine should 2 is first from the vehicle _{target torque} M _Fzg, the required for the realization of this torque drive power is determined (S3). The specification of Solldrehzal n _{D, should} then be based on a map of the diesel engine 2 , This will be explained below with reference to the 4 still explained. After in step S4, the target speed for the diesel engine 2 was determined, in addition, for example by means of a speed sensor, not shown, the actual speed n _{D, is} the diesel engine 2 determined. In step S5, from the target rotational speed n _{D, soll} and the actual rotational speed n _D, the rotational speed depression Δn _{D is} determined. From the depression Δn _D and the actual diesel engine speed n _{D, is} based on a known relationship, as a map in the central control unit 12 that is actually stored by the diesel engine 2 generated moment M _{D, is} determined. From the one by the diesel engine 2 provided torque M _{D, is} taking into account the transmission ratio r of the hydrostatic transmission 3 and the wheel gear ratio i _rad in step S7 as well as other factors influencing the moment, such as friction losses, a simplified vehicle _{load torque} M _Fzg, estimated _est , which disregards a proportion to the actual acceleration share. This estimated simplified vehicle _{load torque} M _{Fzg, est} is subtracted from the vehicle _{target torque} M _{Fzg, which is} determined from the accelerator pedal _position, and a simplified vehicle _{target acceleration} a 'F _{zg, soll is} calculated from the difference _torque thus obtained in step S9.

This generated torque M _{D, is} equivalent to that of the diesel engine hydrostatic transmission 3 actually provided drive torque, if auxiliary consumers are not available. In general, the input torque of the hydrostatic transmission 3 corresponds to the following relationship: M D is, = f ((n D should - n D is, ) P, n D is, ) - (M. NV ) (IV)

Here, M _{NV is} the load torque of the secondary consumers and f ((n _{D, soll} - n _{D, is} ) p, n _{D, is} ) stored as a map relationship between that of the diesel engine 2 generated torque and the determined diesel pressure Δ _nD at a certain diesel engine speed n _{D, is} .

Generally, the relationship between the vehicle _{load torque} M _{Fzg, load is given} by the following equation:

In this case, the first link of the right side gives the simplified vehicle _{load moment} M _{Fzg, est} and the second link a to the actual acceleration a _{Fzg, is apportioned} part of the load torque of the vehicle. Here m is the total vehicle mass and r _rad the radius of the driven wheel.

From the difference between the vehicle _{target torque} M _{Fzg, should} and the vehicle _load, a target acceleration a _{Fzg, should be} calculated for the vehicle. This takes into account in a difference between the vehicle _{target torque} M _{Fzg, should} and the vehicle _load M _{Fzg, load} , as calculated according to the above equation, also the _{load component} attributable to the acceleration component and is calculated according to the following relationship:

The respective vehicle _{target speed} V _{Fzg, should} result from integration of the vehicle _{target acceleration} a _Fzg determined according to the above context _{, should be} by integration. If one chooses integration limits from the system start (t = 0) up to the current time t, the following relationship results:

wobei die tatsächliche Dieseldrehzahl n_D,ist zu berücksichtigen ist.The relationship between this vehicle _{target speed} V _{Fzg, soll} and the transmission ratio r to be set of the hydrostatic transmission 3 is given by the equation:

where the actual diesel speed n _{D, is} to be considered.

In the calculation of the vehicle _{target speed} V _{Fzg, it should also be} shown that, due to the relationship according to equation VI, the integration via the vehicle _{target acceleration} a _{Fzg should} ultimately _be able to be reduced to an addition of the _actual vehicle _speed . The vehicle _{target speed} V _{Fzg, should} result in:

Coming back to the presentation of the procedure in the 3 Thus, the simplified vehicle _{load torque} V _{Fzg, est} of the vehicle _{target torque} V _{Fzg, shall be} deducted in step S2, since instead of integrating the vehicle _{actual acceleration} a _Fzg, an addition of the vehicle _{actual speed} V _{Fzg is} to _{be performed} at a later time ,

From the difference between the vehicle _{target torque} V _{Fzg, soll} and the simplified vehicle _{load torque} V _{Fzg, est} , a simplified vehicle _{target acceleration} a ' _{Fzg, soll is} determined in step S9. After the vehicle _{actual speed} V _Fzg , is then added in the further step S10 via this simplified vehicle _{target acceleration} a ' _{Fzg, should be} integrated. This vehicle _speed V _{Fzg, is} in a simple manner, for example via the speed _sensor 15 determine. An integration with respect to this proportion in the determination of the vehicle _{target speed} V _{Fzg, should} thus be avoided.

Using the actual _{diesel engine speed} n _D, then, from the vehicle _{target speed} V _Fzg, the transmission ratio r is to be determined. With the aid of this transmission ratio r, the delivery volume V _gP for the hydraulic pump is subsequently determined by means of a first characteristic curve 4 and a second characteristic, the displacement _volume V _{gM of} the _{hydraulic motor} 5 determined. These are given by way of example in method step S12. First, the displacement V _{gM of} the _{hydraulic motor} 5 maintained at its constant, maximum value while the swing angle of the hydraulic pump 4 along a ramp is increased linearly from a minimum value up to the maximum delivery volume. Upon reaching the maximum delivery volume of the hydraulic pump 4 is then along the second part of the dashed curve, the displacement V _{gM of} the _{hydraulic motor} 5 reduces and thus accelerates the vehicle on.

In the 4 is an example of a map of a diesel internal combustion engine 2 shown. In the diesel map is determined after determining a power requirement resulting from the traction drive 1 As well as the additional existing consumers composed, determines an optimal diesel engine speed, taking into account the specific fuel consumption. In addition to the diesel engine speed, the efficiency of the hydrostats will be considered 4 . 5 considered. Instead of increasing the power of the diesel engine 2 along the points 16 to 23 , Which would allow an increase in the diesel power or the output torque at a constant speed, starting from a point A (idle), the diesel speed is increased to the point B. This increase in diesel speed has the advantage that the hydraulic motor 5 can be operated in the range of improved efficiency. By increasing the speed of the diesel engine, larger engine swivel angles of the hydraulic motor can be achieved 5 be realized, with the efficiency of the hydraulic motor 5 thereby improved. From point B, the speed of the diesel engine 2 in the direction of the point C is increased so that as long as possible operation of the reciprocating engines 4 . 5 of the hydrostatic transmission 3 in a good efficiency range is possible. The exact adjustment of the curve as well as the required support points are determined by means of an optimization function, which takes into account the driving comfort and / or the driving performance to be achieved in addition to the consumption. Instead of the optimization function, a map can be used, in addition to consumption and power also enters the speed.

wobei p_SpHD der aktuelle Druck in dem Hochdruckspeicher und p_SpND der Druck im Niederdruckspeicher ist, der zum Volumenstromausgleich erforderlich ist. Bei dem beschriebenen Ausführungsbeispiel ist der Fahrantrieb 1 mit einer Druckwiege bestehend aus einem Hochdruckspeicher und einem Niederdruckspeicher verbunden. Die oben angegebene Beziehung gilt ohne Berücksichtigung der Wirkungsgrade. Gleichzeitig muss sichergestellt werden, dass die Dieselbrennkraftmaschine 2 nicht in den Schubbetrieb geht. Der Motorschwenkwinkel des Hydromotors 5 muss daher folgende Bedingung erfüllen:

In a vehicle with a drive of the 1 is in a simple way, the recovery of braking energy feasible. For this purpose, an unillustrated high-pressure accumulator with the suction side of the hydraulic pump 4 connected. That by the diesel engine 2 available to drive torque is reduced accordingly due to the provided high pressure. The vehicle target torque is calculated in this case according to:

where p _{SpHD is} the current pressure in the high-pressure _accumulator and p _{SpND is} the pressure in the low-pressure _accumulator required for volume flow _compensation . In the described embodiment, the traction drive 1 connected to a pressure cradle consisting of a high pressure accumulator and a low pressure accumulator. The above relationship applies without regard to the efficiencies. At the same time, it must be ensured that the diesel engine 2 does not go into overrun. The engine swivel angle of the hydraulic motor 5 must therefore fulfill the following condition:

The Invention is not the illustrated embodiment bound. Rather, individual features of the invention are also Method combined with each other.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3806194 A1 [0002]

Claims (10)

Method for controlling a traction drive ( 1 ) with a primary drive machine ( 2 ) and an associated continuously variable transmission ( 3 ), comprising the following method steps: - detecting a position of a drive command setting device (S1), - determining an operating point (A, B, C) for a primary drive machine ( 2 ) based on a travel command ( 13 , S4) and a current vehicle state, - determining a transmission ratio (r) of the hydrostatic transmission ( 3 ), characterized in that based on the detected position of the travel command presetting device ( 13 ) a vehicle rolling moment of the traction drive ( 1 ) is determined from which a required drive power is determined (S3), based on the required drive power of the operating point (A, B, C) of the primary drive machine ( 2 ). A method according to claim 1, characterized in that from the target output torque (M _{Fzg, soll} ) a vehicle _{target speed} (V _{Fzg, soll} ) is determined based on a physical model of a powertrain or the vehicle (S10) and the transmission ratio (r) of the continuously variable transmission ( 3 ) is determined from the vehicle target speed (S11). A method according to claim 1 or 2, characterized in that for determining the vehicle _{target torque} (M _{Fzg, soll} ) the determined position of the driving command _{setting device} ( 13 ) is assigned a value of zero up to a torque resulting from the rated power of the prime mover (S1). A method according to claim 1 or 2, characterized in that for determining the vehicle _{target torque} (M _{Fzg, soll} ) the determined position of the driving command _{setting device} ( 13 ) is a value from zero to one of the at an actual operating point (A, B, C) of the prime mover ( 2 ) is assigned to the resulting moment (S1). Method according to one of claims 1 to 4, characterized in that for determining the transmission ratio (r) of the hydrostatic transmission ( 3 ) A vehicle _{load torque} (M _{Fzg, est} ) is taken into account. A method according to claim 5, characterized in that the vehicle _{load torque} (M _{Fzg, est} ) is determined from a suppression of the prime mover. A method according to claim 5, characterized in that the vehicle _{load torque} (M _{Fzg, est} ) from a control unit (g) of the _{prime mover} ( 2 ) is read out. A method according to claim 2, characterized in that the vehicle _{target speed} (V _{Fzg, should} ) from an initially determined vehicle _{target acceleration} (a _{Fzg, should} ) is determined by integration (S10). A method according to claim 8, characterized in that from the vehicle _target speed (V _{Fzg, soll} ) and the actual speed (n _{D, is} ) of the primary drive _machine ( 2 ) the transmission ratio (r) for the hydrostatic transmission ( 3 ) is determined. A method according to claim 8 or 9, characterized in that the integration of the vehicle _{target acceleration} (a _{Fzg, soll} ) over the entire time since the system start (0-t) takes place.