Method for operating a drive of a mobile work machine

Abstract

The invention relates to a method for operating a hydrostatic drive of a mobile work machine, wherein the hydrostatic drive comprises a hydraulic pump (12) with an adjustable delivery rate and at least one hydraulic motor (3) which are connected to one another in a hydraulic circuit; the hydraulic pump (12) is driven by a drive motor; and the at least one hydraulic motor (3) is configured to drive a wheel of the mobile work machine. The method is characterized by the following steps: a) detecting a speed which corresponds to the current speed of the mobile work machine or a variable which is based thereon; b) determining a speed setpoint value which represents a setpoint value for the speed detected in step a); c) taking into account the speed setpoint value determined in step b), controlling the speed detected in step a) by changing an actuation variable for the hydraulic pump (12) while a defined rotational speed of the drive motor is being requested; d) increasing the load exerted on the drive motor by the drive while the speed is being controlled in step c); and e) storing the current value of the actuation variable for the hydraulic pump (12) if, when the load is increased in step d), it is determined that an operating variable of the drive motor or an operating variable of the hydrostatic drive has reached a first target value.

Description

[0001] Robert Bosch GmbH

[0002] 415635 - Mumcu

[0003] Method for operating a drive system of a mobile working machine

[0004] TECHNICAL AREA

[0005] The present disclosure relates to a method for operating a drive system of a mobile working machine and a corresponding drive system.

[0006] STATE OF THE ART

[0007] Hydrostatic drive systems for mobile machinery are known, in which a hydraulic pump and one or more hydraulic motors are connected in a closed hydraulic circuit. The hydraulic pump is driven by a drive motor – e.g., a diesel engine – and the hydraulic motors ultimately drive the mobile machinery – e.g., via a wheel.

[0008] The hydraulic pump in such drive systems often has an adjustable delivery volume. This allows, for example, the flow rate delivered by the hydraulic pump in a closed circuit to be changed while the drive motor is running at a constant speed, thereby adjusting the output speed of the hydraulic motors or the wheels – and thus the driving speed of the mobile machine.

[0009] Furthermore, it is known that the hydraulic motor(s) are also adjustable in their displacement volume. This makes it possible, for example, to initially increase the hydraulic pump's delivery volume from zero to its maximum value when starting up the mobile machine in question, and then to reduce the hydraulic motor's displacement volume from its maximum for faster speeds. This reduction increases the output speed while maintaining a constant flow rate.

[0010] It is advantageous if the control of the hydraulic pump and hydraulic motors is matched to the power output of the drive motor. On the one hand, the power available from the drive motor should be fully available to the drive system when needed, so that the maximum speed of the machine can be achieved. On the other hand, overloading of the drive motor, which can lead to stalling in an internal combustion engine, should be avoided. This disclosure relates to a method for matching the control of the hydraulic pump and hydraulic motors to the power output of the drive motor.

[0011] Electrically variable displacement hydraulic pumps are often used in the drive systems of construction machinery. In these pumps, the delivery volume, which is set at a specific control current, depends on the pump's speed and operating pressure. Hydraulic pumps with this type of control can automatically reduce the delivery volume at a given control current if the load increases. However, for optimal control, the control current must be matched to the drive motor's power output, which is typically speed-dependent.

[0012] Hydraulic motors in construction machinery drive systems are often controlled via an electroproportional adjustment of the displacement volume, whereby the displacement volume adjustment can be used as a control variable to regulate the operating pressure in the hydrostatic drive. The setpoint pressure for such control of the operating pressure influences the power consumed by the drive system and must therefore also be matched to the power output of the drive motor.

[0013] The control currents for the hydraulic pump and the pressure setpoints for pressure regulation, which depend on the speed of the drive motor and are described above, can be roughly set based on technical data from data sheets. However, due to the variation in component properties between units and the often incomplete technical data available for mobile machinery, it is generally advisable to fine-tune the settings for each individual machine to achieve optimal results.

[0014] The current state of the art involves manual adjustment by the operator of the mobile work machine through analysis of measurement data and iterative modification of the relevant parameters during commissioning. Such manual adjustment has the disadvantage of being time-consuming, requiring trained personnel, and the result of the adjustment can depend on which operator performs the adjustment.

[0015] The present invention is based on the objective of creating a method for matching the control of hydraulic pumps and hydraulic motors to the power of the drive motor, which avoids the aforementioned disadvantages.

[0016] SUMMARY

[0017] According to one embodiment of the present invention, a method for operating a drive system of a mobile working machine, for example a wheel loader, a telescopic handler, a municipal vehicle, or an excavator, is provided, wherein the hydrostatic drive system comprises a hydraulic pump with adjustable delivery volume, for example an axial piston pump of swashplate design, and at least one hydraulic motor, for example an axial piston motor of swashplate design with electroproportional control of the swivel angle, which are connected to each other in a hydraulic circuit, wherein the hydraulic pump is driven by a drive motor, for example a diesel engine, and the at least one hydraulic motor is configured to drive a wheel of the mobile working machine, for example the two wheels of the rear axle via a cardan shaft and a differential gear, characterized in thatthat the method comprises the following steps: a) detecting a speed corresponding to the current speed of the mobile working machine or a variable dependent thereon, for example, the rotational speed of the at least one hydraulic motor; b) determining a target speed value, which represents a setpoint for the speed detected in step a), wherein the target speed value is determined, for example, before the execution of the method from the displacement volumes of the hydraulic pump and the at least one hydraulic motor, and corresponds to setting the hydraulic pump to a maximum delivery volume; c) controlling the speed detected in step a), taking into account the target speed value determined in step b), by changing a control variable for the hydraulic pump, for example, by changing an electric current, while a defined rotational speed of the drive motor is requested.for example, the rated speed of the drive motor; d) increasing the load acting on the drive motor by the drive system, for example, by applying the service brake or by increasing a driving resistance on a roller test bench, while the speed is being controlled in step c); e) storing the current value of the control variable for the hydraulic pump, for example, storing the electrical current as a parameter for a characteristic curve in an electronic control unit, if, when increasing the load in step d), it is determined that an operating variable of the drive motor or an operating variable of the hydrostatic drive system has reached a first target value, for example, if the mechanical power supplied by the drive motor has reached a first target power value.

[0018] According to one embodiment of the present invention, a method is provided, wherein the method comprises the following further step: controlling the hydraulic pump by means of a first function in which the value for the control variable of the hydraulic pump stored in step e) is entered, for example by means of a characteristic curve that provides the current for controlling the hydraulic pump as a function of the speed of the drive motor, so that the hydraulic pump is controlled in such a way that a power absorbed by the hydraulic pump is matched to a mechanical power of the drive motor.

[0019] According to one embodiment of the present invention, a method is provided wherein, in step d), the load is increased by actuating the service brake of the mobile working machine. Increasing the load by means of the service brake is advantageous because it does not require any additional devices or measures to increase the load during the execution of the method, since a service brake is generally present on every working machine with a drive system.

[0020] According to one embodiment of the present invention, a method is provided in which steps a), b), c), and e) are executed automatically, and the operator of the mobile work machine can interrupt the execution of these steps by means of an input device on the mobile work machine. Automatic execution of these steps is advantageous because it eliminates time-consuming manual steps, requires no specially trained personnel, and the result of the method is reproducible and independent of the operator of the mobile work machine. The ability to interrupt the method is advantageous because it allows the operator to stop the mobile work machine at any time in safety-critical situations.

[0021] According to one embodiment of the present invention, a method is provided wherein the operating parameter of the drive motor mentioned in step e) corresponds to a rotational speed of the drive motor, or to a torque generated by the drive motor, or to a power generated by the drive motor, or wherein the operating parameter of the hydrostatic drive mentioned in step e) corresponds to a rotational speed of the hydraulic pump, or to a torque received by the hydraulic pump, or to a power received or delivered by the hydraulic pump, or to a power received or delivered by the at least one hydraulic motor. While the method according to the invention serves to match the control of the hydrostatic drive to the mechanical power supplied by the drive motor, this power can be determined from various operating parameters.Depending on the equipment of a specific mobile working machine, in particular depending on the drive motor and the available sensors, only certain operating parameters can be determined, so that the method according to the invention can only be applied to a specific working machine using these determinable operating parameters.

[0022] According to one embodiment of the present invention, a method is provided wherein the displacement volume of the at least one hydraulic motor of the drive is adjustable, for example via an electroproportional swivel angle control, wherein the adjustment of the swivel angle of the hydraulic motor can serve to control the pressure differential in the hydrostatic drive, and wherein the method comprises the following additional steps: f) controlling the hydraulic pump with a control value that sets the hydraulic pump to a maximum delivery volume, wherein this control value can be obtained, for example, from a data sheet for the hydraulic pump; g) determining a pressure differential corresponding to a current difference between the pressures prevailing in the inlet and outlet lines of the hydraulic pump, for example, using two pressure sensors, each arranged at a working port of the hydraulic pump;h) Increasing the load exerted on the drive motor by the drive system, for example by applying the service brake, while the hydraulic pump is set to a maximum delivery volume in step f); i) Storing the pressure difference determined in step g), for example by storing the determined pressure difference as a parameter for a characteristic curve in an electronic control unit, if, during the increase in load in step h), it is determined that an operating parameter of the drive motor or an operating parameter of the hydrostatic drive system has reached a second target value, for example, if the mechanical power supplied by the drive motor has reached a second power target value.

[0023] According to one embodiment of the present invention, a method is provided, wherein the method comprises the following further step: controlling the at least one adjustable hydraulic motor by means of a second function, which incorporates the pressure difference stored in step i), for example by means of a characteristic curve that specifies a pressure setpoint for pressure control as a function of the speed of the drive motor, wherein the change in the swivel angle of the at least one hydraulic motor serves the pressure control, so that a power absorbed by the hydrostatic drive is matched to a mechanical power of the drive motor.

[0024] According to one embodiment of the present invention, a computing unit is provided which is configured to carry out a method according to the invention. According to one embodiment of the present invention, a mobile working machine is provided which has a hydrostatic drive and a computing unit which is configured to carry out a method according to the invention, wherein the hydrostatic drive comprises a hydraulic pump with adjustable delivery volume and at least one hydraulic motor which are connected to each other in a hydraulic circuit, wherein the hydraulic pump is driven by a drive motor and the at least one hydraulic motor is configured to drive a wheel of the mobile working machine.

[0025] According to one embodiment of the present invention, a computer program is provided which causes a computing unit to perform a method according to the invention when it is executed on the computing unit.

[0026] BRIEF DESCRIPTION OF THE FIGURES

[0027] The present invention is described with reference to the accompanying figures, where identical reference numerals refer to identical parts and / or to similar parts and / or to corresponding parts of the system. Regarding the figures:

[0028] Figure 1 schematically shows a circuit diagram of a drive system according to the state of the art.

[0029] Figure 2 schematically shows, using an activity diagram, the determination and storage of a control current for the hydraulic pump for an embodiment of the invention.

[0030] Figure 3 schematically shows, using an activity diagram, the determination and storage of a pressure setpoint for the control of a hydraulic motor for an embodiment of the invention.

[0031] DETAILED DESCRIPTION

[0032] The present invention is described below with reference to certain embodiments as shown in the accompanying figures. However, the present invention is not limited to the specific embodiments described in the following detailed description and shown in the figures; rather, the described embodiments merely illustrate some aspects of the present invention, the scope of which is defined by the claims.

[0033] Further modifications and variations of the present invention are obvious to those skilled in the art. The present description therefore encompasses all modifications and / or variations of the present invention whose scope of protection is defined by the claims. Figure 1 shows a circuit diagram for a drive system in which the method according to the invention is carried out. Only the components essential to the invention are described.

[0034] The drive system comprises an axial piston pump 12, on whose housing two working ports A and B are formed. A hydraulic motor 3 is hydraulically connected to the axial piston pump 12 via these working ports A and B and via working lines of a closed circuit. A wheel (not shown) is non-rotatably coupled to an output shaft of the hydraulic motor 3. This forms a drive system for a mobile working machine (not shown in detail).

[0035] The axial piston pump 12 is equipped with a swashplate 2, whose pump swivel angle op mp is adjustable via an adjusting unit 4a. This is achieved using a double-acting actuating cylinder 6, which has a first actuating pressure chamber 81 and a counteracting second actuating pressure chamber 82.

[0036] A first control pressure acts in the first actuating pressure chamber 81 in the direction of an increase in the swivel angle a. Pmp and thus towards an increase in the pump delivery volume V P . In contrast, a second actuating pressure in the second actuating pressure chamber 82 acts in the direction of a reduction of the swivel angle a. Pmp and thus towards a reduction in the pump delivery volume V P In this process, a control pressure differential can be defined, which by definition always increases in the direction of a larger pump swivel angle a. Pmp or the pump delivery volume V P It works.

[0037] The drive mechanism of the axial piston pump 12, and subsequently a feed pump 14, are driven via a drive shaft 10. The drive shaft 10 is driven by a diesel engine (drive motor, not shown), whose crankshaft rotates at a certain speed. The drive shaft 10 therefore rotates at the same or a proportionally different pump speed.

[0038] The pump speed, together with the control pressure differential, acts in the direction of an increase in the pump swivel angle a. Pmp More precisely, an increase in pump speed has this effect.

[0039] When the axial piston pump 12 shown supplies the hydraulic motor 3 via its working ports A and B, working port B is assumed to be the high-pressure port when the mobile working machine is moving forward. Accordingly, the working line connected to working port B is labeled high pressure (HP), while the other working line is labeled low pressure (LP). The high pressure (HP) acts in the direction of a reduction of the pump swashplate angle ap. mp .

[0040] The two control pressures are controlled via two pressure reducing valves 18i, 182. Each of these has an electric solenoid a, b, which is connected to the electronic control unit 16 via an electrical line 20i, 2O2. The two pressure reducing valves 181, 182 are designed such that the respective control pressure is proportional to the respective current.

[0041] The two pressure reducing valves 181, 182 are supplied on the inlet side via a feed pressure line 22 from the feed pump 14.

[0042] An input device 26 for transmitting the driver's request to the electronic control unit 16 is connected via an electrical line 25, wherein the input device 26 preferably comprises an accelerator pedal and a brake pedal.

[0043] The aforementioned hydraulic motor 3, acting as a secondary machine, is connected to the two working lines HD and ND of the closed circuit. The motor has a displacement V. m is adjustable via an electric adjustment unit 4b, which is connected to the electronic control unit 16 via an electrical line 24.

[0044] The electronic control unit 16 determines and sets the control currents for the axial piston pump 12, which flow via electrical lines 20i and 2O2, and the control current for the hydraulic motor, which flows via electrical line 24. For the usual driving functions of the drive system, a current characteristic curve is stored in the electronic control unit 16, which specifies the control current for the axial piston pump 12 depending on the speed of the drive motor and the direction of travel requested by the driver. The electronic control unit 16 also regulates the pressure differential between the high-pressure (HP) and low-pressure (LP) working lines by adjusting the displacement volume of the hydraulic motor 3 using the current flowing via electrical line 24. The target pressure for this pressure regulation is defined by a pressure characteristic curve that depends on the speed of the drive motor.The drive motor transmits its current rotational speed to the electronic control unit 16 via an electronic message.

[0045] The determination of a control current for at least one of the support points of the aforementioned current characteristic curve and the determination of a pressure setpoint for at least one of the support points of the aforementioned pressure characteristic curve are carried out during the commissioning of the mobile working machine by implementing the method according to the invention, in particular for the rated speed of the drive motor, wherein the rated speed is the speed at which the drive motor can provide maximum power. This aligns the control of the axial piston pump 12 and the hydraulic motor 3 with the power of the drive motor, in particular with the maximum available power of the drive motor, so that the available power of the drive motor can be drawn from the drive system without overloading the drive motor. This alignment is described below.

[0046] Figure 2 shows the determination of a pressure setpoint for the control of the pressure difference in the hydrostatic drive using an activity diagram, where the starting node 200 indicates the starting point of the activity diagram.

[0047] In step 201, the inventive method for determining a target pressure value is started by the driver by changing a first parameter in the electronic control unit 16 using a service tool. From this point on, the usual driving functions of the drive system are temporarily unavailable until the method is terminated. The service tool is executed on a computer connected to the electronic control unit 16. The method described below can be terminated at any time by resetting the aforementioned parameter.

[0048] The activity diagram continues via merging node 202 to step 203, which involves requesting a constant speed of the drive motor. This request is made via an electronic message transmitted from the electronic control unit 16 to the electronic control unit of the drive motor. The following describes the procedure for when the aforementioned nominal speed of the drive motor is requested. The requested speed can be set by the operator using the service tool, allowing the procedure to be performed at other drive motor speeds as well. In step 203, the control current for the axial piston pump 12 is also set to a value that overrides the pump, setting it to its maximum delivery volume.

[0049] In step 204, the pressure differential in the hydrostatic drive is determined in the electronic control unit 16 by evaluating the signals from two pressure sensors connected to the electronic control unit 16, one pressure sensor being arranged on each working line of the axial piston pump 12. In step 205, the current speed of the drive motor is subtracted from the requested speed of the drive motor to calculate a speed difference. This speed difference, which represents a measure of the load on the drive motor, is compared with a target value ZA for the speed difference, where the target value ZA corresponds to a desired load on the drive motor at the requested speed. The greater the load on the drive motor, the greater the speed difference.The target value ZA for the speed difference can be derived, for example, from the data sheet of the drive motor or from measurements during the load of the drive motor on a test bench or during the operation of the mobile working machine.

[0050] Step 206 represents a decision point. If the speed difference calculated in step 205 is smaller than the target value ZA, which corresponds to an insufficient load on the drive motor, the process continues with step 208. Otherwise, it continues with step 207.

[0051] Step 208 involves displaying a message to the operator indicating that the brake pedal of the mobile work machine needs to be pressed slightly harder. This message is displayed on a display unit of the mobile work machine, for example, as a percentage. The operator then increases the pressure on the brake pedal accordingly, thereby increasing the load that the drive system exerts on the drive motor. Step 203 is then reached again via merge node 202 and continued from there.

[0052] Step 207 involves saving a support point in the aforementioned pressure curve, where the pressure curve specifies a target pressure value that depends on the rotational speed of the drive motor. As already mentioned, this pressure curve is evaluated during the normal driving function of the drive system to determine the current target pressure value. The support point to be saved is determined by the rotational speed of the drive motor requested in step 203 and by the pressure difference determined in step 204. After the support point is saved, the procedure for determining a target pressure value is automatically terminated, so that the normal driving functions of the drive system are available to the operator again. If the operator of the machine wants to set another support point at a different rotational speed of the drive motor, the procedure must be restarted from step 201.

[0053] The end node 209 is then reached, indicating that the execution of the activity diagram is complete. Figure 3 schematically illustrates the determination of a control current for the axial piston pump 12 for a support point of the aforementioned current characteristic curve using an activity diagram, with the start node 300 indicating the starting point of the activity diagram.

[0054] In step 301, the operator starts the inventive method by changing a second parameter in the electronic control unit 16 using the aforementioned service tool. From this point on, the usual driving functions of the drive system are temporarily unavailable until the method is terminated. The method described below can also be terminated at any time by resetting this second parameter. In an alternative embodiment, the method described in Fig. 3 is executed directly following the method described in Fig. 2, without the operator of the work machine having to separately start the execution of the method described in Fig. 3 using the second parameter. In this alternative embodiment, step 303 is reached directly after step 207 via the merging node 302.

[0055] Step 303, which involves requesting a constant speed of the drive motor, is reached via merging node 302 in the activity diagram. The procedure is described below for the case where the aforementioned rated speed of the drive motor is requested. The requested speed can be set by the operator using the service tool, so the procedure can also be performed at other drive motor speeds. In step 303, a speed setpoint for the machine is also determined in the electronic control unit 16. This speed setpoint is selected to correspond to a speed at which the axial piston pump 12 is set to its maximum delivery volume.

[0056] In step 304, the current speed of the working machine is determined in the electronic control unit 16 using a speed sensor located on the hydraulic motor 3 of the drive.

[0057] In step 305, the speed of the working machine determined in step 304 is controlled by the electronic control unit 16, taking into account the speed setpoint determined in step 303, using a control current for the axial piston pump 12 as the manipulated variable. Depending on the requested direction of travel, which the operator of the working machine specifies via a direction selector lever, either the current in electrical line 20i or 202 is changed, and the other electrical line is kept de-energized. In step 306, the current speed of the drive motor is subtracted from the requested speed of the drive motor to calculate a speed difference.This speed difference, which, as already mentioned, represents a measure of the load on the drive motor, is compared with a target value ZB for the speed difference. The target value ZB is chosen to be slightly larger than the target value ZA used in step 205, for example, by approximately 100 revolutions per minute or by approximately 5%. The target value ZB for the speed difference thus corresponds to a higher drive motor output than the target value ZA. The target value ZB for step 306 is chosen to be larger than the target value ZA for step 205 so that the control current to be stored in step 308 for the axial piston pump 12 is sufficiently large to set the axial piston pump 12 to its maximum delivery volume when the pressure differential prevailing in the hydrostatic drive is set to the pressure setpoint stored in step 207.In this way, an axial piston pump 12 set to maximum delivery volume only begins to reduce its delivery volume under increasing load once the hydraulic motor 3 is already set to its maximum displacement volume. Such control of the hydrostatic drive is generally advantageous for its efficiency.

[0058] Step 307 represents a decision point. If the speed difference calculated in step 306 is smaller than the target value ZB, which corresponds to insufficient load on the drive motor, the process continues with step 309. Otherwise, it continues with step 308.

[0059] Step 309 displays a message to the operator indicating that the brake pedal of the mobile work machine needs to be pressed slightly harder, as described in step 208. The operator applies more pressure to the brake pedal accordingly, thereby increasing the load that the drive system exerts on the drive motor. Step 303 is then accessed again via merge node 302 and continued from there.

[0060] Step 308 involves saving a support point in the aforementioned current characteristic curve, where, as already mentioned, the current characteristic curve specifies a control current for the axial piston pump 12 that depends on the rotational speed of the drive motor. The support point being saved is determined by the rotational speed of the drive motor requested in step 303 and by the control current set in step 305. After the support point is saved, the procedure for determining the control current is automatically terminated, so that the usual driving functions of the drive system are available again. If the operator of the machine wants to set another support point at a different rotational speed of the drive motor, the procedure must be restarted with step 301. Afterward, the end node 310 is reached, which indicates that the execution of the activity diagram is complete.

[0061] While the present invention has been described with reference to the embodiments described above, it is clear to the person skilled in the art that it is possible to describe various modifications, variations, and improvements of the present invention in the

[0062] to realize the above-described teaching and within the scope of the attached claims without deviating from the scope of protection of the invention.

[0063] Furthermore, the areas in which experts would likely be knowledgeable have not been described here in order to avoid unnecessarily obscuring the described invention. Accordingly, the invention is not intended to be limited by the specific illustrative embodiments, but only by the scope of protection defined in the accompanying claims.

Claims

Claims 1. A method for operating a hydrostatic drive system of a mobile working machine, wherein the hydrostatic drive system comprises a hydraulic pump (12) with adjustable delivery volume and at least one hydraulic motor (3) connected to each other in a hydraulic circuit, wherein the hydraulic pump (12) is driven by a drive motor and the at least one hydraulic motor (3) is configured to drive a wheel of the mobile working machine, characterized in that the method comprises the following steps: a) detecting a speed corresponding to a current speed of the mobile working machine or a variable dependent thereon; b) determining a speed setpoint that represents a setpoint for the speed detected in step a);c) Controlling the speed recorded in step a) taking into account the speed setpoint determined in step b) by changing a control variable for the hydraulic pump (12) while a defined speed of the drive motor is requested; d) Increasing the load acting on the drive motor by the drive system while the speed is controlled in step c); e) Storing the current value of the control variable for the hydraulic pump (12) when, during the increase in load in step d), it is determined that an operating variable of the drive motor or an operating variable of the hydrostatic drive system has reached a first target value.

2. The method of claim 1, wherein the method comprises the following further step: controlling the hydraulic pump (12) by means of a first function in which the value for the control variable of the hydraulic pump (12) stored in step e) is entered, such that the hydraulic pump (12) is controlled in such a way that a power absorbed by the hydraulic pump (12) is matched to a mechanical power of the drive motor.

3. Method according to one of the preceding claims, wherein in step d) the load is increased by actuating the service brake of the mobile working machine.

4. Method according to any of the preceding claims, wherein steps a), b), c) and e) are performed automatically, wherein the driver of the mobile working machine can interrupt the execution of these steps by an input via an input device (26) of the mobile working machine.

5. Method according to one of the preceding claims, wherein the operating parameter of the drive motor mentioned in step e) corresponds to a speed of the drive motor or a torque generated by the drive motor or a power generated by the drive motor, or the operating parameter of the hydrostatic drive mentioned in step e) corresponds to a speed of the hydraulic pump (12) or a torque received by the hydraulic pump (12) or a power received or delivered by the hydraulic pump (12) or a power received or delivered by the at least one hydraulic motor (3).

6. A method according to any one of the preceding claims, wherein the at least one hydraulic motor (3) of the drive system is adjustable in its displacement volume, and wherein the method comprises the following additional steps: f) controlling the hydraulic pump (12) with a control value that sets the hydraulic pump (12) to a maximum delivery volume; g) determining a pressure differential corresponding to a current difference between the pressures prevailing in the two working lines (HP, LP) of the hydraulic pump (12); h) increasing the load acting on the drive motor by the drive system while the hydraulic pump (12) is set to a maximum delivery volume by step f); i) storing the pressure differential determined in step g) if, during the increase in load in step h), it is determined that an operating parameter of the drive motor or an operating parameter of the hydrostatic drive system has reached a second target value.

7. Method according to claim 6, wherein the method comprises the following further step: controlling the at least one adjustable hydraulic motor (3) by means of a second function which incorporates the pressure difference stored in step i), such that a power absorbed by the hydrostatic drive is matched to a mechanical power of the drive motor.

8. Computing unit configured to perform a method according to any of the preceding claims.

9. Mobile working machine comprising a computing unit according to claim 8 and a hydrostatic drive, wherein the hydrostatic drive comprises a hydraulic pump (12) with adjustable delivery volume and at least one hydraulic motor (3) connected to each other in a hydraulic circuit, wherein the hydraulic pump (12) is driven by a drive motor and the at least one hydraulic motor (3) is configured to drive a wheel of the mobile working machine.

10. Computer program that causes a computing unit to perform a method according to any one of claims 1 to 7 when executed on the computing unit.

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