Method, computing unit and computer program for closing a form-fitting coupling on a vehicle with hydrostatic drive

Abstract

The present invention relates to a method for closing a form-fitting coupling (6, 6l, 6r) on a vehicle with hydrostatic drive (30a, 30b), wherein the coupling (6, 6l, 6r) is arranged between the hydrostatic drive (30a, 30b) and at least one wheel (1vl, 1vr, 1hl, 1hr) of a first axle (10, 20) of the vehicle, and a vehicle, a computing unit and a computer program for carrying out the method. The method according to the invention comprises producing a contact between the at least two coupling parts of the form-fitting coupling (6, 6l, 6r); setting a first displacement volume (Vg1) in a first flow direction of the hydraulic pump (5) in order to exert a force in a first direction of rotation of the hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr); and setting a second displacement volume (Vg2) in a second flow direction of the hydraulic pump (5), which is opposite to the first flow direction, in order to exert a force in a second direction of rotation of the hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr) which is opposite to the first direction of rotation.

Description

[0001] Method, computing unit and computer program for closing a positive-locking clutch on a vehicle with hydrostatic drive

[0002] Description

[0003] The present invention relates to a method for closing a positive-locking clutch on a vehicle with a hydrostatic drive, wherein the clutch is arranged between the hydrostatic drive and at least one wheel of a first axle of the vehicle, as well as to a vehicle, a computing unit and a computer program for carrying out the method.

[0004] Background of the invention

[0005] Hydrostatically driven vehicles, such as agricultural, forestry, or construction machinery, typically have a so-called work mode and a so-called road mode. Work mode provides high traction at low speed, while road mode provides high speed with low traction. Accordingly, in work mode, all axles of the vehicle are preferably driven, while in road mode, one driven axle is sufficient.

[0006] A driven axle is a vehicle axle on which torque generated by a drive unit and converted by the hydrostatic drive is transmitted via one or more drive shafts to the vehicle's wheels located on that axle. The wheels are driven by one or more hydraulic motors, with a single hydraulic motor driving all wheels on the drive axle, or one hydraulic motor per wheel.

[0007] To provide the required drive power in both driving modes, at least one of the vehicle axles can be mechanically engaged and disengaged. For this purpose, positive-locking clutches, such as claw clutches, can be used, which can transmit high torques with a compact design. However, positive-locking clutches should only be engaged or opened and closed when the vehicle is stationary, in particular to prevent torque peaks on positive-locking elements that are only slightly engaged.

[0008] Closing such a positive-locking coupling when stationary can be problematic, since there is a certain probability that positive-locking elements of opposing coupling parts cannot slide into each other due to an unfavourable position relative to each other.

[0009] Disclosure of the invention

[0010] According to the invention, a method for closing a positive-locking clutch on a vehicle with a hydrostatic drive, a vehicle with a hydrostatic drive and at least one positive-locking clutch, as well as a computing unit and a computer program for implementing the method are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0011] The method enables reliable engagement of a positive-locking clutch in a hydrostatic drive train at a standstill, without requiring position determination of the clutch components, e.g., using a position sensor. Position determination can be performed conventionally to align the clutch components and ensure that the clutch is fully engaged before starting off. Clutch damage due to insufficient connection of the clutch components when the vehicle starts off is avoided. Multiple shift attempts and the resulting delay in starting off are avoided.

[0012] The hydrostatic drive of the vehicle comprises at least one hydraulic pump with adjustable displacement volume and at least one hydraulic motor, which according to one embodiment can also have an adjustable displacement volume. In particular, the hydrostatic drive can contain a closed fluid circuit, wherein, for example, hydraulic oil can serve as the fluid. The hydraulic pump can be an axial piston pump, in particular a bent-axis or swash-plate pump, whose displacement volume is adjusted by means of a pivoting angle of a pivot axis or a swash plate. The hydraulic pump can be driven by a drive unit, for example by an internal combustion engine, in particular a diesel engine, or an electric motor, etc. The hydraulic motor can also be an axial piston motor, in particular a bent-axis or swash-plate motor with adjustable displacement volume.

[0013] The vehicle can, for example, be an agricultural machine, in particular a self-propelled agricultural machine (field sprayer, forage harvester, combine harvester, etc.), a forestry machine, or a construction machine (roller, crawler, etc.). In particular, the vehicle can have at least two axles, with at least drive elements of a first axle being connected to a hydraulic motor by means of the positive coupling. Drive elements of a second axle can be connected to a hydraulic motor by means of a fixed connection, but can also be connected via a coupling (positive or other type). The terms "first" and "second" axle serve only to distinguish the described axle configurations and do not limit the number of axles on the vehicle to two. Instead, there can be multiple axles with at least one positive coupling and multiple axles with a detachable and / or fixed connection.The drive elements can be, for example, drive shafts and / or gears. Each axle can contain at least two wheels, which can be configured to accommodate tires, belts, or chains.

[0014] The at least one positive coupling is arranged between the hydraulic drive and at least one wheel of the first axle of the vehicle and includes at least two coupling parts, one of which can be connected to the at least one wheel, or to a drive element of the at least one wheel, and another of which can be connected to the at least one hydraulic motor of the hydraulic drive. The further coupling element can be mounted on an output shaft of the hydraulic motor.

[0015] In particular, the positive coupling can be a claw coupling. In one embodiment, it can be arranged, for example, between the hydraulic motor and a differential gear of a first axle, e.g., a rear axle, of the vehicle, so that both wheels of this axle are connected to a single hydraulic motor by means of the positive coupling. In a further embodiment, the wheels of the first axle can be driven individually, i.e., each wheel can be connected to a separate hydraulic motor. In this case, the positive coupling can be arranged between the hydraulic motor and the wheel.

[0016] The hydrostatic drive can include at least one additional hydraulic motor to drive the wheels of the second axle, e.g., a front axle, of the vehicle in the same way, either jointly or separately. The hydraulic motor can be permanently or couplingly connected to a differential gear or a drive element of the wheels on the second axle. At least one brake, in particular a holding or parking brake, can also be attached to the second axle, which can brake the wheels of the second axle.

[0017] Specifically, contact is established between the at least two coupling parts of the positive-locking coupling. This can be achieved in a known manner, for example, by displacing at least one of the two coupling parts in the axial direction, e.g., by means of a sliding sleeve, which can be arranged on the output shaft of the hydraulic motor or on a drive shaft on the first axis in a rotationally fixed and axially displaceable manner. The at least one coupling part can be displaced until the two coupling parts slide into each other or—in a "tooth-on-tooth" position—touch each other and their positive-locking elements come into contact, e.g., by being pressed against each other by an adjusting force introduced via the sliding sleeve.

[0018] Furthermore, a first displacement volume is set in a first flow direction of the hydraulic pump in order to exert a force in a first direction of rotation of the hydraulic motor. In other words, by setting the first displacement volume on the hydraulic pump, a volume flow is conveyed to the hydraulic motor, which exerts a force on the output shaft of the motor and the coupling part arranged thereon. In embodiments of the invention, this can occur before the coupling parts touch, so that the coupling part on the output shaft of the motor also rotates in the first direction of rotation. In embodiments of the invention, this can occur prior to or only after the coupling parts touch, whereby a force is exerted on the output shaft of the motor which overcomes a contact force between the two coupling parts and moves the coupling part located on the output shaft in the first direction of rotation.When using an axial piston pump, to set the first displacement volume, a swivel angle of a swash plate or inclined axis of the pump can be increased in a first direction until the first displacement volume is reached. This continuously increases the displacement volume and thus the force or torque. To determine the first displacement volume, for example, a relationship between swivel angle and displacement volume determined in advance and stored in a computer unit in the vehicle can be used. Alternatively or additionally, the displacement volume of the hydraulic pump can be measured. It is also possible to set a swivel angle or another suitable control variable of the hydraulic pump directly instead of the first displacement volume.

[0019] Subsequently, a second displacement volume is set in a second flow direction of the hydraulic pump, which is opposite to the first flow direction. When using an axial piston pump, the second displacement volume can be set analogously to the first displacement volume by pivoting the swash plate / swash plate axis in a second direction, which is opposite to the first direction.

[0020] This reverses the direction of the flow in the hydraulic pump, so that it now exerts an opposing force on the drive shaft of the hydraulic motor and moves the coupling part located thereon in a second direction of rotation opposite to the first direction of rotation. This creates a reciprocating movement of the output shaft of the hydraulic motor, which can break the tooth-on-tooth position of the coupling parts and cause them to slide into each other.

[0021] The above-described adjustment of the first and second displacement volumes can be repeated one or more times, e.g., for a predetermined number of times, in embodiments of the invention, whereby an oscillating rotation is generated on the output shaft of the hydraulic motor, which further improves the positive connection of the coupling parts.

[0022] According to one embodiment, the first and second displacement volumes can each be adjusted by ramping the adjustable displacement volume in the first and second flow directions of the hydraulic pump. When using an axial piston pump, for example, the pivot angle of the swash plate / swash plate axis can be increased in the first / second direction at a constant angular velocity until the first / second displacement volumes are reached.

[0023] According to one embodiment, the ramp-like adjustment of the first and second displacement volumes can be performed continuously. For example, the swash plate / swash axis can first be swashed at a constant angular velocity in the first direction until the first displacement volume is reached, and then, starting from the first displacement volume, can be swashed in the second direction until the second displacement volume is reached.

[0024] According to one embodiment, an amount of the first and second displacement volume of the hydraulic pump can be the same, whereby a uniform oscillating rotation is established on the output shaft of the hydraulic motor, which further facilitates the positive connection of the coupling parts in contact.

[0025] According to one embodiment, the first displacement volume can be set for a first predetermined time and the second displacement volume for a second predetermined time. This allows the maximum force to be applied to both sides of the output shaft for the first and second predetermined times, respectively, which can further accelerate the initiation of the positive connection. In particular, the first and second predetermined times can be the same. However, depending on the design of the positive coupling or its positive engagement elements, different times can also be selected for the first and second predetermined times if necessary.

[0026] According to one embodiment, the first displacement volume of the hydraulic pump can be adjusted until a first pressure difference between an inlet and an outlet of the hydraulic motor reaches or exceeds a first predetermined value. Similarly, the second displacement volume of the hydraulic pump can be adjusted until a second pressure difference between the inlet and the outlet of the hydraulic motor reaches or exceeds a second predetermined value. The predetermined value for the first and second pressure differences can be set such that, by means of the pressure difference, a torque can be exerted on the output shaft that is sufficient to initiate rotation of the contacted coupling parts. In other words, the predetermined value for the first / second pressure difference can be set to a value with which a contact force (friction) between the two coupling parts can be overcome.In this way, if the coupling parts are already positively connected, torque at the coupling output can be limited and unwanted vehicle movement can be prevented or at least reduced.

[0027] In particular, the value for the first and / or second pressure difference can be determined depending on a force that creates the positive locking of the coupling parts, for example, depending on an adjusting force that presses the positive locking elements against each other via a sliding sleeve. This can ensure that the contact force (friction) between the two coupling parts is reliably overcome and that the coupling parts rotate relative to each other.

[0028] According to one embodiment, the displacement volume of the hydraulic motor can be set to a maximum value, at least during the adjustment of the first and second displacement volumes at the hydraulic pump. As a result, the volume flow provided by the hydraulic pump is not throttled at the hydraulic motor, and this flow can be fully converted into torque for rotating the output shaft, with the exception of unavoidable flow and leakage losses.

[0029] According to one embodiment, the displacement volume of the hydraulic motor can be set to a value that is greater than a minimum possible displacement volume and less than the maximum possible displacement volume, at least during the adjustment of the first and second displacement volumes on the hydraulic pump. Since this method eliminates the need to wait for the maximum possible displacement volume to be reached, the time required by the hydraulic motor to provide the torque needed to overcome the contact force (friction) can be reduced, thereby reducing the duration of the entire switching process.

[0030] According to one embodiment, a displacement volume of the at least one additional hydraulic motor on the second axle can be set to a minimum value at least during the adjustment of the first and second displacement volumes on the hydraulic pump. When using an axial piston motor, its pivot angle can be set to zero, so that no torque is generated on an output shaft of the additional hydraulic motor.

[0031] Additionally, the at least one brake on the second axle can be actuated at least during the adjustment of the first and second displacement volumes on the hydraulic pump. In this way, unwanted vehicle movement can be prevented even more reliably.

[0032] A computing unit according to the invention, e.g. a control unit of a vehicle with a hydrostatic drive, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0033] Implementing a method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is also advantageous, as this entails particularly low costs, especially if an executing control unit is also used for additional tasks and is therefore already present. Suitable data storage devices for providing the computer program include, in particular, magnetic, optical, and electrical storage devices, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0034] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0035] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0036] The invention is illustrated schematically in the drawings using an exemplary embodiment and is described in detail below with reference to the drawings.

[0037] Description of the figures Figures 1a and 1b each schematically show an example of a vehicle according to an embodiment of the invention.

[0038] Figures 2a and 2b each schematically show an example of methods for closing a positive coupling according to an embodiment of the invention.

[0039] Detailed description of the drawing

[0040] Figures 1a and 1b each schematically show an example of a vehicle according to an embodiment of the invention. The vehicle can be, for example, an agricultural machine, in particular a self-propelled agricultural machine (field sprayer, forage harvester, combine harvester, etc.), a forestry machine, or a construction machine (roller, crawler, etc.).

[0041] The vehicle illustrated schematically and by way of example in Figure 1a has a front axle 10 and a rear axle 20, to whose unspecified drive shafts two wheels 1vl, 1vr, 1hl, Ihr are each mounted. These wheels are driven by a hydrostatic drive 30 via a differential gear 7v, 7h and a wheel hub gear 2vl, 2vr, 2hl, 2hr on each wheel 1vl, 1vr, 1hl, Ihr. Also mounted on the front axle 10 are two parking brakes 3l, 3r, which block the wheels 1vl, 1vr of the front axle 10 when the vehicle is stationary.

[0042] The hydrostatic drive 30a of the vehicle shown comprises a hydraulic pump 5 with adjustable displacement and two hydraulic motors 4v, 4h, which also have an adjustable displacement. In this case, the hydrostatic drive contains a closed fluid circuit in which, for example, hydraulic oil can serve as the energy-transmitting fluid. The hydraulic pump 5 can be an axial piston pump, in particular a bent-axis or swash-plate pump, whose displacement is adjusted by means of a pivot angle of a pivot axis or a swash plate. The hydraulic pump 5 can be driven by a drive unit (not shown), for example by an internal combustion engine, in particular a diesel engine, via its input shaft.This is indicated by two opposing arrows on the input shaft of hydraulic pump 5 and the designations M, n, which indicate that a torque M and a speed n are introduced into the input shaft. The hydraulic motors 4v, 4h can also be axial piston motors, in particular bent-axis motors, or swashplate motors with adjustable displacement.

[0043] An unspecified output shaft of the hydraulic motor 4v, which is arranged on the front axle 10, is fixedly connected to the differential gear 7v on the front axle 10. On the rear axle 20, however, an unspecified output shaft of the corresponding hydraulic motor 4h is connected by means of a positive coupling 6 to the differential gear 7h on the rear axle 20. In the present case, the positive coupling 6 is a dog clutch 6. This makes it possible to separate the hydraulic motor 4h from the drive elements on the rear axle 20, e.g. in a road driving mode in which little drive torque is required. In this case, the vehicle is only driven via the hydraulic motor 4v on the front axle 10 and the wheels 1hl, Ihr of the rear axle run freely.

[0044] If the wheels 1hl, ihr on the rear axle are to be driven again, e.g. due to increased traction requirements, the hydraulic motor 4h must be reconnected to the differential gear 7h via the claw clutch 6.

[0045] The vehicle illustrated schematically and exemplarily in Figure 1b differs from the one shown in Figure 1a in that no differential gear 7v, 7h is attached to the front and rear axles 10, 20, but rather the wheels 1vl, 1vr, 1hl, I hr are driven by separate hydraulic motors 4vl, 4vr, 4hl, 4hr. Consequently, the hydrostatic drive 30b shown in Figure 1b has two hydraulic motors 4vl, 4vr on the front axle, whose output shafts are firmly connected to a drive shaft of the front axle. In addition, the hydrostatic drive comprises two hydraulic motors 4hl, 4hr, which are arranged on the rear axle and are each connected by means of a claw clutch 6l, 6r to the corresponding wheel hub gears 2hl, 2hr on the rear wheels 1hl, I hr.In this case, one coupling part is attached to the output shaft of the corresponding hydraulic motor 4hl, 4hr and another coupling part is attached to an unspecified input shaft of the corresponding wheel hub gear 2hl, 2hr.

[0046] The switching of a claw clutch 6, 61, 6r, as shown in Figures 1a and 1b, can only take place when stationary and there is a risk that form-locking elements of opposing clutch parts cannot slide into one another due to an unfavorable position relative to one another.

[0047] Figures 2a and 2b each schematically show an example of a method for closing a positive-locking clutch, such as the claw clutch shown in Figures 1a and 1b, according to an embodiment of the invention. This method enables reliable engagement of a hydraulic motor 4h, 4I, 4hr of the hydrostatic drive 30a, 30b at a standstill using the claw clutch 6, 6I, 6r, for example, when the clutch parts are in a "tooth-tooth" position relative to one another.

[0048] Figure 2a shows a diagram in which a control variable of a hydraulic pump 5 is plotted against a time t during a closing process of a claw clutch 6, 6I, 6r. In the present case, the hydraulic pump 5 is an axial piston pump 5 with adjustable displacement, and the control variable is a target displacement volume Vg of the axial piston pump during the closing process of the claw clutch 6, 6I, 6r. By specifying the target displacement volume Vg, for example, a swivel angle of the axial piston pump can be set, which then determines an actual displacement volume of the pump. Instead of the target displacement volume Vg, the swivel angle of the axial piston pump can also be used directly as the control variable.

[0049] For example, time t1 marks a point in time during the closing process of the claw clutch 6, 6I, 6r, in which both clutch parts are in contact with each other, but due to their position relative to each other, do not form a positive connection. From this point in time t1, for example, a ramp-shaped curve of the target displacement volume Vg is set, starting from a neutral position of the swash plate / inclined axis of the axial piston pump 5. The value "A1" denotes the ramp time in which the target displacement volume Vg of the axial piston pump 5 is increased from zero, with the swash plate / inclined axis in the neutral position, to a first displacement volume Vg1, whereupon the target displacement volume is increased with the ramp time "A2" to the second displacement volume Vg2. The values ​​"B1" and "B2" indicate a duration during which the first and second displacement volumes Vg1 and Vg2 are kept constant, respectively.The value "C1" denotes the ramp time in which the target displacement volume Vg of the axial piston pump 5 is reduced from the first displacement volume Vg1 to zero, and the value "C2" denotes the ramp time in which the target displacement volume Vg of the axial piston pump 5 is reduced from the second displacement volume Vg2 to zero. The values ​​"D1" and "D2" denote an amplitude of the target displacement volume Vg for the first and second first displacement volumes Vg1 and Vg2.

[0050] In the diagram shown here, the target displacement volume Vg is first increased in a first direction during ramp time "A1" up to the first displacement volume Vg1, which is then held constant for the holding period "B1." After the holding period "B1" has elapsed, the target displacement volume Vg is reduced in the first direction during ramp time "C1" to zero, and then, starting at time t2, is increased in the opposite direction during ramp time "A2" up to the second displacement volume Vg2. This is held constant for the holding period "B2" and then reduced back to zero during ramp time "C2." In the diagram shown here, the ramp times "A1," "A2," "C1," "C2," the holding periods "B1" and "B2," and the amplitudes "D1" and "D2" for setting the first and second target displacement volumes Vg1 and Vg2 are selected to be equal. However, it is also possible to parameterize these sizes differently.Furthermore, it is possible to specify a separately adjustable time for each individual step of this process (separated by the vertical dashed lines, numbered with Roman numerals I to VI), allowing increasing and decreasing demands on the target displacement volume to be set separately. Furthermore, it is possible to reduce individual ramp times or all ramp times to zero, resulting in rectangular signal curves. Furthermore, it is possible to reduce the holding times "B1" and "B2" to zero.

[0051] The ramp-shaped adjustment of the first displacement volume Vg1 causes a ramp-shaped increasing volume flow in a first direction of the axial piston pump 5 and the ramp-shaped adjustment of the second displacement volume Vg2 causes a ramp-shaped increasing volume flow in a second, opposite direction of the axial piston pump 5. The respective volume flows are conveyed to the hydraulic motor and there lead to an alternating force on its output shaft, whereby an oscillating rotation is generated on the output shaft of the hydraulic motor, which causes a positive connection of the coupling parts in contact.

[0052] Figure 2b shows another example of specifying a ramp-like curve for the target volume flow Vg. In this diagram, in addition to the target volume flow Vg, a differential pressure dp in the hydraulic circuit is also shown, which can be determined, for example, by means of a pressure measurement upstream and downstream of the hydraulic motor 6, 6I, 6R. The value "D" in this context denotes a pressure amplitude of this differential pressure dp. This pressure amplitude "D" is used in the present example to set the holding period "B." It can be seen that the differential pressure dp increases as soon as the target displacement volume reaches the first displacement volume Vg1. When the differential pressure reaches a predetermined value dpi, the holding period "B," during which the first displacement volume is kept constant, is ended, and the target displacement volume Vg is reduced in the first direction.Similarly, the ramp-shaped adjustment of the second displacement volume Vg2 proceeds in the opposite direction. In this case, the pressure difference reverses due to the flow reversal in pump 5 at time t2 and drops to the predetermined value dp2, at which the holding period "B," during which the second displacement volume Vg2 is kept constant, ends. The predetermined values ​​for the pressure difference dpi, dp2 can be determined based on the required forces on the output shaft of the hydraulic motor 6, 61, 6r. For example, these can each be set to a value that can overcome a contact force between the two clutch parts. In this way, if the clutch parts have already been positively connected, a torque at the clutch output can be limited and unwanted vehicle movement can be prevented or at least reduced.

Claims

Claims 1 . Method for closing a positive-locking clutch (6, 6I, 6r) with at least two clutch parts, which is arranged between a hydrostatic drive (30a, 30b) and at least one wheel (1vl, 1vr, 1hl, ihr) of a first axle (10, 20) of a vehicle, wherein the hydrostatic drive (30a, 30b) has at least one hydraulic pump (5) with adjustable displacement volume and at least one hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr), comprising the steps of: a) establishing contact between the at least two clutch parts of the positive-locking clutch (6, 6I, 6r); b) setting a first displacement volume (Vg1) in a first flow direction of the hydraulic pump (5) in order to exert a force in a first direction of rotation of the hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr);and c) setting a second displacement volume (Vg2) in a second flow direction of the hydraulic pump (5) opposite to the first flow direction in order to exert a force in a second direction of rotation of the hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr) opposite to the first direction of rotation; 2. The method according to claim 1, comprising repeating steps b) and c) a predetermined number of times.

3. Method according to claim 1 or 2, wherein the first and the second displacement volume (Vg1, Vg2) are each adjusted by ramp-like or step-like increasing and reducing the adjustable displacement volume in the first and second flow directions of the hydraulic pump (5).

4. Method according to one of the preceding claims, wherein steps b) and c) are carried out continuously.

5. Method according to one of the preceding claims, wherein an amount of the first and second displacement volumes (Vg1, Vg2) of the hydraulic pump (5) is equal.

6. Method according to one of the preceding claims, wherein the first displacement volume (Vg1) is set for a first predetermined time (H) and the second displacement volume (Vg2) is set for a second predetermined time (H).

7. The method according to any one of claims 1 to 5, wherein the first displacement volume (Vg1) of the hydraulic pump (5) is adjusted until a first pressure difference (dpi) between an inlet and an outlet of the hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr) exceeds a first predetermined value, and the second displacement volume (Vg2) of the hydraulic pump (5) is adjusted until a second pressure difference (dp2) between an inlet and an outlet of the hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr) exceeds a second predetermined value.

8. Method according to one of the preceding claims, wherein the hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr) has an adjustable displacement volume which is set at least during steps b) and c) to a maximum value or to a predetermined value which is smaller than the maximum value and greater than a minimum value.

9. Method according to one of the preceding claims, wherein the hydrostatic drive (30a, 30b) has at least one further hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr) with an adjustable displacement volume, which is connected to at least one wheel (1vl, 1vr, 1hl, 1hr) of a second axle (10, 20) of the vehicle, and a displacement volume of the at least one further hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr) is set to a minimum value at least during steps b) and c).

10. Method according to one of the preceding claims, wherein the second axle (10, 20) of the vehicle has at least one brake (3I, 3r), and the brake (3I, 3r) is actuated at least during steps b) and c).

11. A computing unit comprising a processor configured to carry out the method according to any one of the preceding claims.

12. Vehicle comprehensive a hydrostatic drive (30a, 30b) with at least one hydraulic pump (5) with adjustable displacement and at least one hydraulic motor (4v, 4h, 4vl, 4vr, 4hl, 4hr); at least one positive coupling (6, 6l, 6r) with at least two coupling parts, which is arranged between the hydraulic drive (30a, 30b) and at least one wheel (1vl, 1vr, 1hl, 1hr) of an axle (10, 20) of the vehicle; and a computing unit according to claim 11.

13. A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method according to claims 1 to 10.

14. A computer-readable data carrier on which the computer program according to claim 13 is stored.

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