METHOD FOR ADAPTING THE PRESSURE OF A HYDROPUM OF A DRIVE ENGINE

Description

TECHNICAL AREA

[0001] The invention relates to a method for adapting a pressure of a hydraulic pump of a travel drive, preferably a method for learning a parameter of a pump characteristic or a pump characteristic curve or a calculation rule for adapting a pressure of a hydraulic pump of a travel drive. STATE OF THE ART

[0002] Hydrostatic drive systems for mobile work machines 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 an internal combustion engine—e.g., a diesel engine—and the hydraulic motors ultimately drive the mobile work machine—e.g., via a respective wheel.

[0003] The hydraulic pump in such travel drives often has an adjustable displacement. This allows, for example, the volume flow delivered by the hydraulic pump to be varied in a closed circuit at a constant engine speed, thus adjusting the output speed of the hydraulic motors or wheels—in other words, the travel speed of the mobile machine.

[0004] Hydrostatic axial piston pumps are used, among other things, in the travel drives of construction machinery. One function of these pumps is to limit the maximum permissible pressure. This is necessary, among other things, to limit torque and the maximum permissible pressure of the components.

[0005] In addition to the use of loss-prone pressure relief valves (the pump's flow rate is diverted to the tank), hydromechanical pressure control valves are also used. These valves limit the high pressure by reducing the pump's control pressure, thereby reducing the pump's displacement.

[0006] If the pump is electronically controlled, closed-loop pressure regulators or controlled solutions that are calibrated are sometimes used, as disclosed in patent application DE 10 2018 210685 A1.

[0007] The respective methods have several disadvantages.

[0008] The pressure relief valve causes high losses and subsequent thermal stress, which corresponds to additional costs. Furthermore, a pressure relief valve can only specify a fixed pressure. The hydraulic-mechanical pressure cutoff regulator generates additional costs, especially when electrically controlled. It is temperature-dependent and subject to tolerances and drift. Furthermore, the design for highly dynamic and stable behavior is very complex, and only a fixed pressure can be specified. Electronically controlled solutions with calibration are temperature-dependent and subject to tolerances and drift, and only a fixed pressure can be specified.

[0009] The electronic "closed loop" controller disclosed in DE 10 2018 210685 A1 has the following disadvantages: Designing for highly dynamic and stable behavior is complex; usually leads to high resource consumption on the control unit and is Complex to master and difficult to integrate into third-party control devices. The object of the invention, however, is to develop a method that eliminates the aforementioned disadvantages. SUMMARY

[0010] The invention is defined by the claims.

[0011] According to one embodiment of the present invention, a method for adapting a pressure of a hydraulic pump of a travel drive is provided, wherein the travel drive is provided with the hydraulic pump, which is coupled to a drive engine, for supplying pressure medium to a hydraulic motor of the travel drive that can be coupled to an output, wherein the hydraulic pump has an actuating cylinder with at least one cylinder chamber and a displacement volume that can be adjusted via it, and at least one electrically controllable pressure valve is provided, via which the cylinder chamber can be subjected to an adjusting actuating pressure, and with a device via which a pressure of the hydraulic pump can be regulated by influencing the actuating pressure, wherein the pressure can be regulated in a controlled manner, wherein the method comprises the following steps: a) Calculation of a maximum permissible control pressure taking into account the displacement of the hydraulic pump or a value representing this displacement, the rotational speed of the hydraulic pump and a maximum permissible pressure of the hydraulic pump; b) Recording the current pressure of the hydraulic pump; c) Comparison of the current pressure of the hydraulic pump with the maximum permissible pressure; d) Correction of the maximum permissible control pressure taking into account the difference between the current pressure of the hydraulic pump and the maximum pressure.

[0012] According to one embodiment of the present invention, a method for adapting a pressure of a hydraulic pump of a travel drive is provided, wherein the travel drive is provided with the hydraulic pump for supplying pressure medium to a hydraulic motor of the travel drive that can be coupled to an output, wherein the pressure generated by the hydraulic pump can be regulated by influencing a control pressure, wherein the method comprises the following steps: a) Calculating a maximum permissible control pressure taking into account a displacement of the hydraulic pump or a variable representing this displacement, the rotational speed of the hydraulic pump and a maximum permissible pressure of the hydraulic pump; b) Detecting the currently generated pressure of the hydraulic pump; c) Comparing the currently generated pressure of the hydraulic pump with the maximum permissible pressure; and d) Adapting the control pressure taking into account the difference between the current pressure of the hydraulic pump and the maximum permissible pressure by correcting a learning factor, which is preferably a parameter of a pump characteristic or a pump characteristic curve or a calculation rule.

[0013] This solution is particularly advantageous because it allows the hydraulic pump's behavior to always be adapted by correcting the learning factor. This is because the control pressure can be calculated taking into account the learning factor, which was corrected in the previous cycle.

[0014] According to the present invention, a method is provided, wherein the learning factor is learned in step d. by permanently storing the value in the control unit.

[0015] According to one embodiment of the present invention, a method is provided, the method further comprising the step of: e) Comparing the maximum permissible control pressure adapted in step d. with the control pressure calculated taking into account a driver's request and independently of the maximum permissible pressure of the hydraulic pump; f) Controlling the hydraulic pump with the smaller value between the control pressure calculated taking into account a driver's request and independently of the maximum permissible pressure of the hydraulic pump and the maximum permissible control pressure.

[0016] According to one embodiment of the present invention, a method is provided, wherein between steps b and c, it is checked whether predetermined conditions are met; wherein step c is performed if the predetermined conditions are met. According to one embodiment of the present invention, a method is provided, wherein one of the predetermined conditions is that the absolute value of the difference between the current pressure of the hydraulic pump and the maximum permissible pressure is greater than a predetermined value.

[0017] According to one embodiment of the present invention, a method is provided, wherein one of the predetermined conditions is that the absolute value of the difference between the current pressure of the hydraulic pump and the maximum permissible pressure for a predetermined time window is greater than a predetermined value.

[0018] According to one embodiment of the present invention, a method is provided, wherein in step e. the learning factor is corrected multiplicatively or additively.

[0019] According to one embodiment of the present invention, a method is provided, wherein, if the current pressure of the hydraulic pump is higher than the maximum permissible pressure, the learning factor is corrected downwards during said step d.

[0020] According to one embodiment of the present invention, a method is provided, wherein, if the current pressure of the hydraulic pump is less than the maximum permissible pressure and preferably further conditions are active (e.g. that the limitation is below control values ​​of the driver's request), the learning factor is corrected upwards during said step d.

[0021] According to one embodiment of the present invention, a method is provided, wherein, if the current pressure of the hydraulic pump is less than the maximum permissible pressure and the maximum permissible control pressure is less than the control pressure calculated taking into account a driver's request and independently of the maximum permissible pressure of the hydraulic pump, the learning factor is corrected upwards during said step d.

[0022] According to one embodiment of the present invention, a method is provided wherein the learning factor is reset during a vehicle calibration.

[0023] According to one embodiment of the present invention, a method is provided wherein if the difference between the learning factor before and after the correction is greater than a predetermined value, a diagnostic message is generated.

[0024] According to one embodiment of the present invention, a method is provided, wherein in step d. the currently generated and detected pressure is filtered to take pressure dynamics into account.

[0025] According to one embodiment of the present invention, a method is provided wherein the maximum permissible pressure of the hydraulic pump is different for traction and towing or braking operation. SHORT DESCRIPTION OF THE CHARACTERS

[0026] The present invention is described with reference to the accompanying figures, wherein like reference numerals refer to like parts and / or similar parts and / or corresponding parts of the system. Regarding the figures: Fig. 1 shows a hydraulic circuit diagram of a hydrostatic drive according to the state of the art, Fig. 2 shows characteristics of the hydrostatic drive according to the Figure 1 , and Fig. 3shows a more detailed block diagram of a method for controlling the hydrostatic drive of the method according to the prior art, Fig. 4 shows a simple block diagram of a method for adapting a pressure of a hydraulic pump of a travel drive according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention will now be described with reference to specific embodiments as shown in the accompanying figures. Nevertheless, 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.

[0028] Further modifications and variations of the present invention will be apparent to those skilled in the art. This description thus encompasses all modifications and / or variations of the present invention, the scope of which is defined by the claims.

[0029] According to Figure 1 A hydrostatic drive 1 has a hydraulic pump 2, which is fluidly connected in a closed hydraulic circuit via working lines 4 and 6 to a hydraulic motor (not shown) for supplying pressure to the motor. The hydraulic pump 2 is coupled to a drive motor (not shown) via a drive shaft 8 for transmitting torque. The coupling is not geared, so the speed of the drive motor and the hydraulic pump 2 are identical.

[0030] The hydraulic pump 2 is designed as an axial piston pump with a swashplate design and can be operated in both directions of rotation and in both pump and motor mode. It has an adjustable displacement volume VP and an adjustment device 10 designed as a double-acting hydraulic cylinder.

[0031] The hydraulic cylinder 10 has a first cylinder chamber 12 and a second cylinder chamber 14 opposing the first. The first cylinder chamber 12 is connected to the output of a first pressure reducing valve 18 via a first control pressure line 16. The latter is connected to a control pressure line 20, which can be supplied with control pressure medium via a control pressure connection pS and via a feed pump 22, which is located on the same drive shaft 8 as the hydraulic pump 2.

[0032] In the same way, the second cylinder chamber 14 is connected via a second control pressure line 24 to a second pressure reducing valve 26, which is connected to the control pressure line 20. The pressure reducing valves 18, 26 can be actuated electromagnetically, wherein the control pressure pa or pb resulting in the control pressure line 16 or 24 is proportional to a control current la or lb of the electromagnet a or b according to a valve characteristic curve. The control pressures pa, pb of the cylinder chambers 12, 14 can thus be controlled via the electromagnetic actuation of the pressure reducing valves 18, 26 by specifying the control currents la, lb. For this purpose, the electromagnets a, b of the pressure reducing valves 18, 26 are signal-connected to an electronic control unit 32 via a respective signal line 28 or 30.

[0033] Furthermore, the hydrostatic drive 1 has a speed detection unit 34, via which a speed n P of the hydraulic pump 2 can be detected and transmitted to the electronic control unit 32 via a signal line 36. Likewise, the drive 1 has a speed detection unit (not shown), via which the speed n M of the hydraulic motor can be detected and transmitted to the electronic control unit 32 via the signal line 38.

[0034] For safety-relevant pressure protection of the working lines 4, 6 against overload, the hydrostatic drive 1 has a pressure relief valve 40 each connected to the respective working line 4, 6. Both pressure relief valves 40 are connected by their outputs to a boost pressure line 44, which is connected to the boost pump 22. The boost pressure line 44 is fluidly connected to the control pressure line 20 via a throttle 42. When the pressure relief valves are activated, pressure medium is released into the boost pressure line 44, whereby energy losses are lower than if the release were to occur towards tank T. The pressure relief valves 40 each have a feed or suction function in the form of a check valve.

[0035] The hydrostatic drive 1 can be operated in traction mode as well as in towing or braking mode. In traction mode, the hydraulic pump 2 operates in pump mode; in braking mode, it operates in motor mode. Furthermore, the hydraulic pump 2 is reversible, meaning its displacement volume VP can be adjusted via the adjustment device 10 on either side of a neutral position with zero volume VP = 0. This allows a reversal of travel direction while maintaining the same direction of rotation of the drive shaft 8 and the prime mover (diesel engine).

[0036] The electronic control unit 32 is connected via a signal line 46 to an operator interface in the form of an accelerator pedal (not shown). A driver transmits a speed request to the electronic control unit 32 via the accelerator pedal. This request can affect both reversing and forward travel. If the accelerator pedal is actuated, this corresponds to traction or pumping operation of the hydraulic pump 2; if the accelerator pedal is released, this corresponds to braking or motoring operation of the hydraulic pump 2. The actuation of a service brake (not shown) also corresponds to braking or motoring operation of the hydraulic pump 2.

[0037] The control unit is designed such that it can determine the corresponding operation based on the aforementioned actuation. To select a direction of travel, the hydrostatic drive 1 also has an actuatable direction switch (not shown), which is signal-connected to the electronic control unit 32 via a signal line 48. Depending on its position, the hydraulic pump 2 is controlled in its reversed or non-reversed adjustment range, i.e., on either side of the neutral position of the displacement of the hydraulic pump 2. For further consideration, the following driving states are defined: Forward travel, traction operation: Pressurization of the first cylinder chamber 12 via the first control pressure line 16 and the first pressure reducing valve 18 with the first control pressure pa by controlling the first pressure reducing valve 18 with the control current 1a via the control unit 32 via the first signal line 28.

[0038] Forward travel, braking operation: Pressurization of the second cylinder chamber 14 via the second control pressure line 24 and the second pressure reducing valve 26 with the second control pressure pb by controlling the second pressure reducing valve 26 with the control current lb via the control unit 32 via the signal line 30.

[0039] Reverse travel, traction operation: Pressurization of the second cylinder chamber 14 via the chain 24, 26, 30, 32.

[0040] Reversing, braking operation: Pressurization of the first cylinder chamber 12 via the chain 16, 18, 28, 32.

[0041] In both shown embodiments of a hydrostatic travel drive 1, the hydraulic pump 2 is designed such that the pressure p present in the high-pressure line of the working lines 4, 6 counteracts the then effective control pressure pa or pb and acts in the direction of its own reduction. For this purpose, the hydraulic pump 2 has a structurally implemented control loop. In the present case of the hydraulic pump 2 designed as an axial piston pump with a swash plate design, this is implemented in such a way that a control disk of the hydraulic pump 2 is arranged twisted with respect to a rotational axis of its cylinder drum. The outlets of those cylinders that are connected to the pressure kidney control disk that has the pressure (high pressure) are thus arranged asymmetrically distributed with respect to a pivot axis of the swash plate. The end sections of the working pistons guided in the cylinders, which are supported on the swash plate, are then also asymmetrically distributed.The asymmetrically acting supporting forces of the working pistons result in a moment on the swash plate that swings back during pump operation and out during engine operation. Consequently, a relationship arises in the form of a pump characteristic curve or a characteristic map of pump characteristic curves of the hydraulic pump 2, in which the respective control pressure pa, pb can be described as a function of the pressure p and the displacement VP of the hydraulic pump 2, as well as its speed n P . These characteristic curves or characteristic maps are measured and stored in the electronic control unit 32 for processing, in particular for executing the method described below.

[0042] In Figure 2A characteristic of hydraulic pump 2 with open-loop control, i.e., with directly controlled displacement or stroke volume VP, is shown. The pressure p, or more precisely the pressure difference Δp between the working lines 4, 6, is plotted as a function of the displacement volume VP. The first control pressure pa of the first cylinder chamber 12 is plotted as a parameter. This increases starting from the origin 0 / 0. The limiting power is represented by the nominal power of the diesel engine P nominal, shown as a dashed curve. The starting point for the description is an unactuated accelerator or drive pedal and an engine rotating at idle speed.

[0043] As indicated by arrow 1, the operator first presses the accelerator pedal, increasing the speed of the prime mover (diesel) from idle to rated speed. Accordingly, the electronic control unit 32 generates a control signal or control current 1a for the hydraulic pump 2, more precisely for its first pressure reducing valve 18, depending on the speed of the diesel engine.

[0044] When the nominal speed of the drive unit is reached, a maximum travel speed of the travel drive 1 is obtained. Accordingly, the first control pressure pa is adjusted according to a value stored in the electronic control unit 32 according to Figure 1 stored characteristic map of hydraulic pump 2. Since there is no load yet, hydraulic pump 2 swings out fully to its maximum displacement V Pmax and delivers its maximum volume flow Q max at rated speed.

[0045] Due to the driving resistance that occurs when driving on a level surface, a pressure or load pressure p, for example 250 bar, is established. This process is described in Figure 2 symbolized by the arrow marked with the number 2. In the diagram according to Figure 2 A point Q is then reached, which lies on the curve P nomeng. At this point, the first control pressure pa at the rated speed is dimensioned such that the hydraulic power pQ max of hydraulic pump 2 corresponds to the rated power P nomeng.

[0046] If the load on the drive 1 increases, for example when driving uphill or when picking up gravel in the case of a wheel loader, the pressure p increases. Due to the aforementioned design of the hydraulic pump 2, in which the working pressure p counteracts the first control pressure pa in the direction of a reduction in the displacement VP during traction operation of the hydraulic pump 2 in forward travel, the pressure p pivots the pivoting cradle of the hydraulic pump 2 back, thereby slowing down the travel. The first control pressure pa remains unchanged during this time and corresponds to the straight line (arrow 3) intersecting point Q, representing the reduction in the displacement VP and the simultaneous increase in the pressure p or the pressure difference Δp.

[0047] Upon reaching a point L in the diagram according to Figure 2 a maximum permissible pressure p max or cut-off pressure, or a maximum permissible pressure difference Δp max is reached.

[0048] The task of the electronic control unit 32 is now to ensure that this limit p max , Δp max is not exceeded. Accordingly, with a further increasing load, no further increase in the pressure p occurs, as the first control pressure pa is reduced by the control unit 32 via the pressure reducing valve 18 according to Figure 1 is lowered in such a way that the pressure p max is not exceeded. Accordingly, one moves in accordance with Figure 2 along a block or limit curve extending horizontally from point L with a constant pressure p max or constant pressure difference Δp max to the left. Thus, if, for example, a maximum permissible pressure p max of, for example, 450 bar is set in the control unit 32, the control unit 32 intervenes according to the pressure cutoff according to the invention and reduces the first control pressure pa. This prevents the maximum permissible pressure p max from being exceeded even as the load continues to increase.

[0049] The following is a more detailed description of method 52, which allows the limitation of the maximum pressure p max.

[0050] As already mentioned, the input variables of the method are the determined or estimated displacement volume VP or the corresponding swivel angle α P of the hydraulic pump 2, its speed n P , as well as a predetermined limit of the pressure or working pressure p max , in this case of 450 bar.

[0051] According to Figure 1For each pressure limit p max , a pump characteristic or pump characteristic curve or calculation rule 82 is stored in the electronic control unit 32 for the operation of the hydraulic pump 2 in traction mode (pump mode) and 84 for the braking or motor mode of the hydraulic pump 2. The respective control pressure pa or pb is described as a function of the pump speed n P and the pump swivel angle α P (as a percentage of the maximum swivel angle). The control pressures pa and pb are also shown as a percentage of the maximum control or control pressure p smax available in the control pressure line 20. The scale of the second control pressure pb provided for the second control chamber 14 in motor mode extends from zero to -50%. The plus and minus signs represent the different effective directions of the pressure due to the opposing control chambers 12, 14.

[0052] Depending on the current values ​​n P , α P and p max of the operating state of the traction drive, the maximum permissible actuating pressure p amax for traction operation and p bmax for braking operation are initially determined according to method 52. This is done continuously with a fixed limit p max, since in particular α P changes during operation due to its load dependency. For traction operation, a required first actuating pressure p a68 is then adjusted, which results from the actuation of the accelerator pedal 68 according to Figure 1 The latter actuating pressure and the determined maximum permissible first actuating pressure p amax are compared by the control unit 32, and the smaller one is selected in step 86.

[0053] The same process occurs in step 88 with the maximum permissible second control pressure p bmax . The smaller of the control pressures selected from steps 86 and 88 is then multiplied by the maximum available control pressure p smax , resulting in a real control pressure pa or pb from the control pressure specified up to that point in percent. This is incorporated into a respective valve characteristic curve 90 or 92 for the pressure reducing valve 18 or 26, from which the corresponding control current la or lb for controlling the pressure reducing valve 18 or 26 is then determined.

[0054] In this way, the control pressures pa, pb required during normal driving operation and the maximum permissible control pressures p amax, p bmax are determined from the speed n P , the swivel angle α P , the pump characteristic curves 82, 84, the maximum permissible pressure p, the requested control pressure p a68 and the valve characteristic curves 90, 92, whereby the smaller of these leads to the control current la, lb. If the control pressure p a68 output according to the driver's request is above the limit p amax or p bmax, the control current pa or pb is limited or cut off.

[0055] In the method described above, the design for highly dynamic and stable behavior is very complex. In particular, the difficulty lies in generating the pump characteristics or the pump characteristic curve or the calculation rules that actually allow the limitation of p max and Δp max. In particular, the present invention will make it possible to compensate for tolerances, fluctuations in control behavior due to temperature and aging, and to dynamically adapt the permissible maximum pressures.

[0056] In the Figure 4 A method according to an embodiment of the present invention is shown which overcomes the above-mentioned problems.

[0057] The pump characteristic, or pump performance curve, or calculation rule (hereinafter referred to simply as "performance curves") depends on a learning factor, which is a parameter of the performance curves. The learning factor can be applied both multiplicatively and additively to the performance curve, allowing the performance curves to be adjusted upwards or downwards.

[0058] The first step 101 is analogous to the one in Figure 3 shown step 52. In particular, depending on the current values ​​n P , α P and p max of the operating state of the traction drive, the maximum permissible control pressure p amax for traction operation and p bmax for braking operation is first determined.

[0059] In the following step 102, the pressure difference Δp between the working lines 4, 6 is detected. Preferably, the currently generated and detected pressure p is filtered to account for pressure dynamics and to neglect fluctuations.

[0060] If the currently generated pressure p of hydraulic pump 2 is greater or less than the maximum permissible pressure p max , this indicates that the performance curves need to be corrected (either because the currently generated pressure p is too high or because it is too low). Therefore, the determined maximum permissible control pressure p amax for traction operation and p bmax for braking operation may need to be corrected.

[0061] However, additional conditions must be met to actually determine that a correction is necessary.

[0062] The first condition is that the generated pressure p that deviates from the maximum permissible pressure p max is undesirable. In other words, it must be verified that the reason why the pressure p generated by the pump deviates from the maximum pressure p max is not due to the driver's wishes, but rather to the performance characteristics used to calculate the maximum permissible control pressure p amax for traction operation and p bmax for braking operation in step 101.

[0063] If this condition and any additional conditions explained in the next section are met, the learning factor is adjusted upwards or downwards, and the learning factor is preferably learned so that this correction of the performance characteristics can be saved. In particular, the learning factors are permanently stored in the control unit so that the learned factors are already available upon restart.

[0064] Additional conditions may include: the absolute value of the difference between the currently generated pressure p of the hydraulic pump 2 and the maximum permissible pressure p max is greater than a predetermined value; and / or the absolute value of the difference between the currently generated pressure p of the hydraulic pump 2 and the maximum permissible pressure p max for a predetermined time window is greater than a predetermined value; and / or the pump is in the blocked state (estimated pump angle < defined value); and / or other conditions known to the person skilled in the art.

[0065] After the learning factor has been corrected, the maximum permissible control pressure p amax for train operation and p bmax for braking operation are recalculated based on the new learning factor.

[0066] The control pressures p amax and p bmax are then multiplied by the maximum available control pressure p smax, resulting in a real control pressure p amax or p bmax from the control pressure specified up to that point in percent.

[0067] In steps 103 and 104, parallel to steps 101 and 102, the control pressures pa and pb are first calculated as a percentage of the maximum control or control pressure p smax available in the control pressure line 20 (step 103), without taking into account the maximum pressure p max , and taking into account the actuation of the accelerator pedal 68. The control pressures pa and pb are then multiplied by the maximum available control pressure p smax , resulting in a real control pressure pa or pb from the control pressure specified up to that point as a percentage.

[0068] In step 105, the values ​​of the actuating pressures from steps 102 and 104 are compared and the minimum value for the actuating pressures is taken.

[0069] In step 106, these values ​​are included in the respective valve characteristic curve 90 or 92 for the pressure reducing valve 18 or 26, respectively, from which the associated control current la or lb for controlling the pressure reducing valve 18 or 26 is then determined.

[0070] The one with reference to Figure 4 The described procedure can always be active during driving and automatically detects which driving conditions are allowed to learn. The algorithm adapts to pressures that are too low or too high in overrun (negative pressures) and traction (positive pressures).

[0071] In addition, the learning factor can be reset during vehicle calibration and corrected and learned again during driving.

[0072] In a special case where the difference between the learning factor before and after the correction is greater than a specified value, a diagnostic message can be generated.

[0073] While the present invention has been described with reference to the embodiments described above, it will be apparent to those skilled in the art that it is possible to make various modifications, variations and improvements to the present invention in light of the above teachings and within the scope of the appended claims without departing from the scope of the invention.

[0074] Even though a maximum pressure has always been discussed, it is clear that the maximum permissible pressure p max of hydraulic pump 2 is different for traction and towing or braking operation.

[0075] Furthermore, the areas in which those skilled in the art would be familiar have not been described here in order not to unnecessarily obscure the invention described.

[0076] Accordingly, the invention is not to be limited by the specific illustrative embodiments, but only by the scope of the appended claims.

Claims

1. Method for adapting a pressure (p) of a hydraulic pump (2) of a traction drive (1), wherein the traction drive is provided with the hydraulic pump (2) for the purpose of supplying pressure medium to a hydraulic motor (78), which can be coupled to an output (80), of the traction drive (1), wherein the pressure (p) generated by the hydraulic pump (2) can be controlled by influencing an actuation pressure (pa, pb), wherein the method comprises the following steps: a. calculating a maximum permissible actuation pressure (pamax, pbmax) taking into account a swept volume (VP) of the hydraulic pump (2) or a quantity (αP) representing this swept volume (VP), the rotation speed (nP) of the hydraulic pump (2) and a maximum permissible pressure (pmax) of the hydraulic pump (2); b. sensing the currently generated pressure (p) of the hydraulic pump (2); c. comparing the currently generated pressure (p) of the hydraulic pump (2) with the maximum permissible pressure (pmax); and d. adapting the maximum permissible actuation pressure (pamax, pbmax) taking into account the difference between the current pressure (p) of the hydraulic pump (2) and the maximum permissible pressure (pmax) by way of a learning factor, which is a parameter of a pump characteristic or a pump characteristic curve or a calculation specification, being corrected, wherein the learning factor is learned in step d., wherein the learning factor is permanently stored in a control device, so that the learned factor will already be available at restart.

2. Method according to Claim 1, wherein the method further comprises the following step: e. comparing the maximum permissible actuation pressure (pamax, pbmax), which was adapted in step d., with the actuation pressure (pa, pb), which was calculated taking into account a driver's request and independently of the maximum permissible pressure (pmax) of the hydraulic pump (2); f. controlling the hydraulic pump with the smaller value between the actuation pressure (pa, pb), which was calculated taking into account a driver's request and independently of the maximum permissible pressure (pmax) of the hydraulic pump (2), and the maximum permissible actuation pressure (pamax, pbmax).

3. Method according to either of Claims 1 and 2, wherein a check is made between steps b. and c. as to whether predetermined conditions are met; wherein step c. is carried out when the predetermined conditions are met.

4. Method according to Claim 3, wherein one of the predetermined conditions is that the absolute value of the difference between the current pressure (p) of the hydraulic pump (2) and the maximum permissible pressure (pmax) is greater than a predetermined value.

5. Method according to Claim 4, wherein one of the predetermined conditions is that the absolute value of the difference between the current pressure (p) of the hydraulic pump (2) and the maximum permissible pressure (pmax) is greater than a predetermined value for a predetermined time window.

6. Method according to any of Claims 1 to 5, wherein the learning factor is multiplicatively or additively corrected in step e.

7. Method according to any of Claims 1 to 6, wherein, when the current pressure (p) of the hydraulic pump (2) is higher than the maximum permissible pressure (pmax), the learning factor is corrected downwards during said step d.

8. Method according to any of Claims 1 to 7, wherein, when the current pressure (p) of the hydraulic pump (2) is lower than the maximum permissible pressure (pmax) and the maximum permissible actuation pressure (pamax, pbmax) is lower than the control pressure (pa, pb) which was calculated taking into account a driver's request and independently of the maximum permissible pressure (pmax) of the hydraulic pump (2), the learning factor is corrected upwards during said step d.

9. Method according to any of Claims 1 to 8, wherein the learning factor is reset during vehicle calibration.

10. Method according to any of Claims 1 to 9, wherein, when the difference between the learning factor before and after the correction is greater than a predetermined value, a diagnostic message is generated.

11. Method according to any of Claims 1 to 10, wherein the current generated and sensed pressure (p) is filtered in step d. in order to take into account the pressure dynamics.

12. Method according to any of Claims 1 to 11, wherein the maximum permissible pressure (pmax) of the hydraulic pump (2) is different for overrun and traction or braking operation.