"Method for managing an axial piston machine taking into account a zero case"

Abstract

TITLE: "Method for managing an axial piston machine taking into account a zero case" Method for managing an axial piston machine (10) whose discharge flow rate is continuously adjustable with a double-acting regulating cylinder (20) with: * one chamber (21) has an electric pressure regulating valve (30), and the other chamber (22) is connected to an electric 3 / 2-way spool (32). The setpoint pressure difference (dpX-cons) has a zero case (60) in which the difference (dpX-cons) is practically zero, * a positive case (61) with a positive difference (dpX-cons), * a negative case (62) with a negative difference (dpX-cons). We calculate a first and a second setting pressure (p-DRE; p-3 / 2), and determine whether we are in the zero case (60), the positive case (61) or the negative case (62), to use the setting pressure (p-DRE, or p-3 / 2), to supply the pressure regulating valve (30). Figure 3

Description

Title of the invention: “Method for managing an axial piston machine taking into account a zero case” FIELD OF THE INVENTION

[0001] The present invention relates to a method for managing an axial piston machine. STATE OF THE ART

[0002] According to the document "Axial piston pump A4VG Baureihe 35" (adjustable axial piston pump 4AVG series 35) from Bosch Rexroth AG (order number RD92035 . edition 12.02.2020), an axial piston machine with inclined glass is known, the delivery flow of which is adjusted with a double-acting adjusting cylinder moving to the zero position so that for the same drive direction, the delivery direction is reversed by adjusting the rocker alone. In the ET adjustment, both adjustment chambers of the adjusting cylinder are connected to a pressure adjustment valve in the form of a pressure reducing valve. In the event of a failure of the electrical excitation, it is not unequivocally established which flow rate is adjusted.

[0003] This method is not desirable for hydraulic fan drives. The fan must generally rotate at its maximum rotation speed when the electrical control fails (integrated safety method).

[0004] Document DE 10 2010 020 528 A1 presents a fan drive having a closed hydraulic circuit which essentially comprises the axial piston machine described above. The control cylinder is controlled in this case by a pressure control valve in the form of a pressure reducing valve with an increasing or positive characteristic curve and with a 4 / 2-way slide valve, the two control valves each having an electrical adjustment. The circuit is designed so that in the event of failure of the electrical control, the axial piston machine automatically sets itself to a maximum amplitude delivery flow so that both fan rotors rotate at maximum speed.

[0005] Furthermore, the circuit is designed so that the current applied to the pressure adjustment valve does not abruptly change the adjustment pressure difference at the zero crossing. At the zero crossing, the corresponding adjustment current drops to zero and then rises again, and only the 4 / 2-way slide valve switches abruptly.

[0006] The disadvantage of this control is that it requires a special valve block for the control valves which are specially adapted to the fan drive. If instead of the above fail-safe behavior another behavior is desired, then the valve block must be modified.

[0007] DISCLOSURE AND ADVANTAGES OF THE INVENTION

[0008] The present invention aims to overcome the drawbacks of known solutions and to this end relates to a method for managing an axial piston machine whose delivery flow rate is continuously adjustable with a double-acting adjustment cylinder comprising two adjustment chambers acting in opposite directions,

[0009] this method comprising the following steps consisting of:

[0010] a) using a corresponding axial piston machine, with an adjustment chamber to which an electrically controlled pressure adjustment valve is connected,

[0011] * the other adjustment chamber being connected to a 3 / 2-way slide valve with control electric,

[0012] b) provide a setpoint adjustment pressure difference with:

[0013] * a zero case defined as the case in which the setting pressure difference of the deposit is practically zero,

[0014] * a positive case defined as the case in which the setting pressure difference of setpoint is positive and does not fall below the zero case,

[0015] * a negative case defined as a case in which the pressure difference of setpoint adjustment is negative and does not go below the zero case,

[0016] c) calculating a first and a second setting pressure,

[0017] * in the context of a case distinction, we determine whether we are in the zero case, in the positive case or in the negative case,

[0018] * the result of the case distinction being taken into account for the calculation of the first and the second adjustment pressure,

[0019] d) supplying current to the pressure adjustment valve as a function of the first adjustment pressure and supplying current to the 3 / 2-way slide valve as a function of the second adjustment pressure.

[0020] The invention has the advantage of producing the axial piston machine only with commercially available control valves to provide integrated safety. At the same time, the appropriate choice of the direction of adjustment and the mounting location of the two control valves allows a large number of drive variants without requiring special mechanical designs instead of catalog components. It is sufficient to adapt the program of the control device to the selected control valves.

[0021] Step a) is preferably carried out before the other process steps. This step enables the integrated, safe behavior of the fan drive; the other details of [Fig. 1] will be developed below. This implementation, however, has the consequence that when the setpoint pressure difference passes through zero, the pressure control valve is abruptly moved discontinuously. This is remedied by the other process steps b), c), d). Consequently, we avoid imposing harsh operation on the axial piston motor, especially if it is part of a fan drive.

[0022] The setpoint adjustment pressure difference is then practically zero if the adjustment of the pressure adjustment valve and the 3 / 2-way slide valve does not guarantee that the actual adjustment pressure difference is definitely positive or negative. This is the zero case as long as the actual adjustment pressure difference, which has actually been adjusted, can vary around zero due to adjustment inaccuracies.

[0023] Steps b), c), d) of the method are preferably applied at least partly in the form of a computer program executed by a control device of the axial piston engine; the control device preferably comprises a programmable digital computer or an FPGA circuit (programmable logic device comprising a programmable gate array).

[0024] The pressure control valve and the 3 / 2-way slide valve are preferably connected directly to the control chamber associated with them. They are preferably each designed as an integrated valve, installed integrally in a bore opening into the control chamber concerned.

[0025] According to another characteristic, steps b), c), d), are executed during the operation of the axial piston machine, continuously and in parallel or quasi-parallel. The indicated steps are preferably executed discretely in time over a large number of calculation cycles which follow one another at the calculation interval; in each calculation cycle all steps b), c), d are taken into account. Within a calculation cycle, the different calculation steps are executed successively, which corresponds to a quasi-parallel calculation. The calculation interval is preferably constant, for example equal to 1 ms. Such a computer program can be applied by the Simulink programming system from the company Matlab. Other programming languages ​​C or C++ can also be used.

[0026] The calculation phase of each calculation cycle is preferably without calculation feedback (live); the calculation feedback is carried out on the successive calculation cycles. The calculation feedback is different from the physical feedback on the real axial piston machine, for example in the context of the control loop described with reference to [Fig.2] with two real pressure sensors.

[0027] In step d), it is possible to provide for supplying the pressure adjustment valve with a first adjustment current and the 3 / 2-way slide valve with a second adjustment current, the first adjustment current being calculated with an inverse model of the pressure adjustment valve from the first adjustment pressure and the second adjustment current being calculated with an inverse model of the 3 / 2-way slide valve from the second adjustment pressure. In the simplest case, the models are static models. In the case of the pressure adjustment valve, the static model is the valve characteristic curve that associates a first adjustment pressure with each adjustment current; this association depends on the pressure at the control input of the pressure regulating valve. This model calculates according to the physical / effect relationship. The corresponding inverse model works in the opposite way by associating a first adjustment current with each adjustment pressure. Thus it works in the opposite direction to the cause / effect relationship, in the opposite direction.

[0028] Within the scope of the method of the invention, dynamic models can be used which take into account the speed with which the valve responds to a change in the control current. The static model of the 3 / 2-way spool distinguishes only two discrete switching stages of the 3 / 2-way spool. One switching state is preferably prestressed by a return spring so that the second control current is zero. In the other state, the second control current is large enough so that the force of the return spring can be safely switched quickly. The current with which the actuating electromagnet of the 3 / 2-way spool holds permanently and without overheating can be considered as the second control current. The second control pressure is the pressure at the control input or the pressure at the control return, both of which pressures are known during operation of the axial piston machine.The pressure at the control inlet is, for example, predefined by adjusting a supply pressure limiting valve; this setting is usually fixed.

[0029] It is also possible in step d) to calculate the first and second setting pressure respectively for the zero case, the positive case and the negative case; and in step d), the above case distinction selects one of the results of the three calculations. In the quasi-parallel calculation described above of the method design developed above, the calculation time of a calculation cycle practically does not vary and remains the same regardless of the state of the axial piston machine. Thus, it is simply guaranteed that the calculation time required in each calculation cycle is less than the calculation time interval.

[0030] According to a characteristic, in step d), in the zero case, a first and a second pair are calculated comprising respectively the first and the second adjustment pressure, the first pair having a second adjustment pressure equal to the pressure at the control input; the first adjustment pressure is calculated as a function of this second adjustment pressure and the difference in setpoint adjustment pressure; with the second pair, the second pressure is calculated equal to the control feedback pressure, the first adjustment pressure being calculated as a function of this second adjustment pressure and the difference in setpoint adjustment pressure;

[0031] depending on the last case mentioned in the context of the distinction of cases and / or possibly, a future forecast case, we decide to use the first or the second pair for the calculation result. The calculation then simply consists of providing the evoked numerical values ​​which are stored in memory, preferably as parameters of the control device. The first adjustment pressure is preferably equal to the sum of the setpoint adjustment pressure difference and the second adjustment pressure. The second adjustment pressure can thus only take positive values, the setpoint adjustment pressure difference taking positive and negative values. The decision regarding which pair to use is preferably made based on the derivative of the setpoint adjustment pressure difference as a function of time. Further details will be given with reference to [Fig. 3].

[0032] According to a characteristic, in the zero case of step (d), the first and second pairs are calculated and from the decision mentioned, one of the two calculation results is selected. Thus, it is simply guaranteed that the calculation time required for each calculation cycle remains less than the calculation time interval.

[0033] According to another characteristic, in step c), in the positive case, the second adjustment pressure is equal to the control return pressure; the first adjustment pressure is then calculated from this second adjustment pressure and the difference in setpoint adjustment pressure.

[0034] According to another characteristic, in the context of step c), in the negative case, the second adjustment pressure is equal to the pressure at the control input, the first adjustment pressure then being calculated from this second adjustment pressure and the difference in setpoint adjustment pressure.

[0035] According to another characteristic, in step a), the axial piston machine has:

[0036] - a first and a second working connection,

[0037] - a first and a second pressure sensor with which we measure respectively a first and a second actual pressure at the first or second associated working connection and in step b), the setpoint adjustment pressure difference is calculated as a function of the first and second actual pressures and a predefined setpoint discharge pressure difference. This calculation is preferably done so that the difference between the first and second actual pressures approximates the setpoint discharge pressure difference. The calculation can be done in the direction of a regulation. Preferably, the calculation is that of a linear regulator, for example a PID regulator. This regulation can be superimposed on a pilot control.In the pilot control, the path is planned according to which, from a setpoint discharge pressure difference, a planned setpoint discharge pressure difference is determined, which in the pilot control is in good agreement with the actual discharge difference. In this way, sudden changes in the calculation of the setpoint discharge pressure difference, which cannot be obtained with a difference, are taken into account. actual discharge pressure which considerably complicates the calculation of the pilot control.

[0038] This pilot control can use an inverse model of an axial piston machine such as, for example, those described in documents DE 10 2019210 003 A1 or DE 10 2021 200 693 A1, the first document describing trajectory planning. The pilot control can also be applied without combination with regulation.

[0039] According to another feature, in step a), an axial piston machine is used, equipped with a rotational speed sensor which measures the actual rotational speed of the machine, the setpoint adjustment pressure difference being calculated as a function of the actual rotational speed in the direction of a pilot control. The actual rotational speed is preferably taken into account in the inverse model of the axial piston machine. Brief description of the drawings

[0040] The present invention will be described below in more detail with the aid of embodiments shown in the accompanying drawings in which:

[0041] [Fig. 1] hydraulic diagram of an axial piston machine according to the invention,

[0042] [Fig.2] part of a regulation diagram implemented by the method of the invention,

[0043] [Fig.3] another part of the regulation diagram of [Fig.2], and

[0044] [Fig.4] diagram explaining the inverse model of the pressure adjustment valve.

[0045] DESCRIPTION OF AN EMBODIMENT

[0046] [Fig.l] shows the hydraulic diagram of an axial piston machine 10 according to the invention. This axial piston machine 10 comprises a main pump 18 and a feed pump 13 driven by a common motor shaft 19. The rotational speed of the motor shaft 19 is measured with a rotational speed sensor 70 preferably installed in a fixed manner on the axial piston machine 10.

[0047] The main pump 18 is an axial piston pump whose delivery flow rate can be adjusted continuously, preferably with a tilting cradle. The tilting cradle is movably coupled to the adjusting piston of a double-acting adjusting cylinder 20. The adjusting cylinder 20 has a first and a second adjusting chamber 21, 22 in which the respective pressure corresponds to the numerical values ​​p-DRE and p-3 / 2 in [Fig. 3]; these pressures act in opposite directions on the adjusting piston. The first adjusting chamber 21 is connected by a fluid connection directly to the pressure adjusting valve 30; this is preferably in the form of a pressure reducing valve, electrically controlled by a control electromagnet 31. The second adjusting chamber 22 is connected by a direct fluid connection to the 3 / 2-way slide valve 32, electrically controlled by a control electromagnet 33 and returned to a pre-stressed position by a return spring 34; in this position, the control input is open (open position). The pressure regulating valve 31 and / or the 3 / 2-way spool 32 are preferably respectively controlled by an electrical voltage whose working ratio is chosen to have on average an intensity whose numerical value corresponds to the value i-DRE or i-3 / 2. For this, preferably respectively a digitally implemented current regulating circuit is used which is at most preferably calculated by the control device also applying the method of the invention.

[0048] The pressure control valve 30 here has a positive characteristic curve so that its currentless state corresponds to the lowest pressure in the control return 16, applied to the first control chamber 21. The 3 / 2-way spool is open currentless so that for this currentless state, the high pressure will be applied to the control inlet 15 of the second control chamber 22. The present main pump 18 is regulated by passing through the zero delivery flow. Correspondingly, the currentless state, regulates a maximum delivery flow in amplitude as long as the motor shaft 19 rotates. The corresponding direction of rotation is designed so that the fan rotor 41 rotates correspondingly in the desired direction of the cooling air delivery.This behavior is desired in the majority of fan drive cases so that even if the electrical control fails, the cooling of the thermal engine will be sufficient.

[0049] The feed pump 13 is for example 17 a vane pump. It draws the pressurized fluid from the reservoir 18 and delivers it on one side to the control inlet 15 and on the other side via the feed valve 23, to the closed hydraulic circuit. In [Fig.l], all the reservoir references 17 refer to the same reservoir. The pressurized fluid is preferably a liquid and very preferably hydraulic fluid. The outlet of the feed pump 13 is connected to a feed pressure limiting valve 14. The flow rate of the feed pump 13 is sufficiently high during most of the operating time of the axial piston machine 10 so that the feed pressure limiting valve 14 is triggered and the pressure in the control inlet 15 is defined by the setting of the feed pressure limiting valve 14.The supply pressure limiting valve 14 is here fixedly adjusted by an electrically controlled supply pressure limiting valve.

[0050] The first and second working connections 11, 12 of the main pump 18 or of the axial piston machine 10 are connected by a fluid connection, here in the sense of a closed hydraulic circuit, to a hydraulic motor 40. The hydraulic motor 40 directly drives a fan rotor 41 which cools, for example, the combustion engine of a relatively large vehicle, in particular a mobile machine. The present invention is primarily intended for this application, although it can also be used in other applications. The target discharge pressure difference described below can be regulated, for example, by a main control circuit with which the rotational speed of the fan rotor 41 is adjusted using it as a controlled variable. The method according to the invention is sufficient for the first and second pressure sensors 71, 72 and the rotational speed sensor 70 without necessarily requiring any other sensor.For example, it is possible to optionally use a tilt angle sensor connected to the main pump 18 or another rotation speed sensor installed on the hydraulic motor 40 to improve the operating behavior of the overall system.

[0051] The first pressure sensor 71 measures a first actual pressure pA in the first working connection 11. The second pressure sensor 72 measures a second actual pressure pB in the second working connection 12.

[0052] It should however be noted that the two supply valves 23 compensate for leaks by supplying the pressurized fluid from the supply pump 13 to the closed hydraulic circuit. It is possible to envisage an axial piston machine 10 equipped with a flushing valve to take, beyond the leaks mentioned above, in a targeted manner, pressurized fluid from the closed hydraulic circuit to avoid overheating of its pressurized fluid. This risk is low in the case of this fan drive.

[0053] [Fig. 2] shows a part of a control diagram implemented by the method of the invention. The part of the control diagram of [Fig. 2] can be applied in multiple variants without departing from the scope of the invention. For example, it is possible to use only the pilot control with the path planning filter 50 and the inverse model 51 of the axial piston machine. It is also possible to consider using only the regulator 52. In each case, the overall system operates; [Fig. 2] shows the most complete variant with the best operating characteristics.

[0054] For the axial piston machine, a setpoint discharge pressure difference dp-cons is predefined from the outside; this difference is that of the first and second measured sensor pressures, i.e. the first and second actual pressures pA; pB set to the setpoint discharge pressure difference dp-cons.

[0055] This adjustment is carried out as quickly as possible, first of all by a pilot control based on the inverse model 51 of the axial piston machine. The description of document DE 10 2019210 003 A1 gives mathematical formulas which model the behavior of the axial piston machine. Document DE 10 2021 200 693 A1 describes a method with which the mathematical model of the axial piston machine is experimentally determined. All these models have in common that they provide usable results by inversion only if the timing diagram of the discharge pressure difference used at the inlet can be effectively adjusted on a real axial piston machine.

[0056] The setpoint discharge pressure difference dp-cons can, however, have sudden variations which are not those of the actual discharge pressure difference because the latter can only vary continuously. This is why the setpoint discharge pressure difference dp-cons is first applied to a path planning filter 50 before applying it to the inverse model 51 of the axial piston machine. In the simplest case, the path planning filter 50 is a low-pass filter whose limit frequency is set in a fixed manner. This makes it possible to simply eliminate the sudden variations mentioned above.However, the path planning filter 50 described in document DE 10 2019 210 003 Al makes it possible to make the best use of the available power of the axial piston machine to achieve, within the framework of the pilot control, a particularly rapid approach to the setpoint discharge pressure difference dp-cons.

[0057] In addition to the modified setpoint discharge pressure difference, the measured values ​​of the sensors, namely the actual rotational speed (n) of the motor shaft and the first and second actual pressures pA, pB, are also applied to the inverse model 51 of the axial piston machine to calculate the model 51. The result then provided by the inverse model 51 of the axial piston machine is the setpoint adjustment pressure difference dpX-cons, which must be set in theory to bring the actual discharge pressure difference and the setpoint discharge pressure difference dp-cons closer together as quickly as possible. This theoretical value may not correspond perfectly to the actual conditions. Therefore, a control 50 is combined (superimposed) with the pilot control.

[0058] The control variable of the regulator 52 is preferably another setpoint control pressure difference additively combined 54 with the pilot control to obtain the value dpX-cons. It is also conceivable to apply the control variable of the regulator 52 to a suitable point of the inverse model 51 of the axial piston machine to improve the control behavior.

[0059] On the input side of the regulator 52, the actual discharge pressure difference is first calculated as the difference 53 between the first and second actual pressures pA, pB. The control deviation is the difference 53 between the setpoint discharge pressure difference dpX-cons and the actual discharge pressure difference 55. The control deviation is applied to the controller 52 which is preferably a continuous linear controller, in particular a PID controller. The controller 52 applies a cycle-based calculation method discretely in time, preferably within the input.

[0060] [Fig. 3] shows another part of the control diagram of [Fig. 2]. The interface between Figures 2, 3 is the setpoint adjustment pressure difference dpX-cons which is also the primary input quantity of the process according to the invention.

[0061] According to the invention, in particular control valves are used, namely a pressure control valve and a 3 / 2-way slide valve. This choice has considerable advantages in the context of driving a fan, since different variants of conventional fans can be produced with the same components. In particular, the side of the control cylinder to which the pressure control valve is associated can be freely selected, and the 3 / 2-way slide valve is then installed on the other side. This advantage comes at the cost of a significant disadvantage avoided by the present invention. In particular, the control behavior of the control valves for a setpoint control pressure difference dpX-cons must be equal to zero, which corresponds to a significant discontinuity of the two control valves. The control valves cannot be used with a purely hydraulic, conventional control device, even if they are actuated hydraulically.Therefore, within the framework of the invention, a method is applied which is preferably implemented by a programmable digital computer which has a microprocessor.

[0062] The discontinuity mentioned above is taken into account by distinguishing three cases, namely: a zero case 60, a positive case 61 and a negative case 62. In the zero case 60, the difference in setpoint adjustment pressure dpX-cons is practically zero, which also includes cases in which, due to adjustment inaccuracies, it is not certain whether the actual adjustment pressure difference, actually set, is positive or negative.

[0063] In the positive case 61, the setpoint adjustment pressure difference dpX-cons is positive and there is no zero case 60. In the positive case 61, the second adjustment chamber is connected by the 3 / 2-way slide valve to the control return so that in the second adjustment chamber the pressure is practically zero. In the case of the pressure adjustment valve of [Fig.l], with an increasing characteristic curve, the current i-DRE increases practically proportionally to the setpoint adjustment pressure difference dpX-cons. The corresponding relationship is shown in [Fig.4].

[0064] In the negative case 62, the setpoint adjustment pressure difference dpX-cons is negative but there is no zero case. The second adjustment chamber is then connected to the control input by the 3 / 2-way slide valve so that a high pressure prevails in the second adjustment chamber; this pressure is at the same time defined as the maximum pressure to which the pressure adjustment valve is set. In the case of the pressure adjustment valve of [Fig.l], with a positive characteristic curve, the current i-DRE decreases in a manner practically inversely proportional to the amplitude of the desired setpoint adjustment pressure difference dpX-cons.

[0065] In the zero case 60, two zero adjustment positions can be available for the adjustment valves (30, 32 [Fig.l]). Thus, the two adjustment chambers are connected to the control input or the two adjustment chambers (21, 22, [Fig.l]) are connected to the control return. In both cases of zero adjustment, zero pressure is applied to the adjustment piston. Theoretically, the pressure adjustment valve should not be set to an intermediate value. But in practice this is unavoidable, in particular for the transition from the positive case 61 to the negative case 62 or vice versa (zero crossing). This problem is remedied by a corresponding switching, only if this is actually necessary and then it is carried out in a particularly rapid manner.

[0066] For this purpose, the four possible cases for the first and second adjustment pressure p-DRE are preferably calculated continuously and almost simultaneously; p-3 / 2, i.e. in the case of zero adjustments as a constant and only for a distinction of cases 63, the one of the four cases which will be used to control the adjustment valves (30, 32 of [Fig.l]) is fixed.

[0067] This distinction of case 63 is simple if one is incontestably in the positive case or in the negative case 61, 62. The situation is more delicate if there is a crossing through zero. For this one can envisage adjusting the difference in setpoint adjustment pressure dpX-cons, abruptly by passing through zero. This sub-case, results in a simple distinction of cases, between the positive case and the negative case 61, 62, to have the desired result; the discontinuity necessarily caused by the adjustment system is not disturbed by the discontinuous adjustment of the difference in setpoint adjustment pressure dpX-cons.

[0068] If the zero crossing is carried out by a continuous adjustment of the setpoint adjustment pressure difference dpX-cons, with the derivative of the setpoint adjustment pressure difference as a function of time, the zero crossing is theoretically expected. A short time before the theoretical zero crossing, a respective zero adjustment is made which does not require abrupt adjustment of the adjustment valves. During the zero case 60, the setpoint adjustment pressure difference dpX-cons is continued to be observed. If unilaterally leaves the zero case 60 in a zero crossing, the other zero adjustment is done abruptly.

[0069] The inverse model 64 of the pressure control valve determines the first control current i-DRE required to set the desired pressure. This can be done with the static model of [Fig.4] which is simply a valve characteristic curve. Alternatively, a dynamic model can be used which takes into account how quickly the pressure control valve reacts to changes in the first control current i-DRE. Because of the particularly rapid adjustment desired for the zero case 60, it is advantageous to have a dynamic inverse model 64.

[0070] With the inverse model 65 of the 3 / 2-way spool, the second setting current i-3 / 2 required to set the desired pressure is determined. The basic switching characteristic here only allows a principle to be distinguished in two cases. In the first case, i-3 / 2 is equal to zero. In the other case, i-3 / 2 is as large as possible without risking overheating of the corresponding actuating electromagnet (33 [Fig.l]). During the switching period, a second setting current i-3 / 2 can be set, which is larger than in the subsequent period in which the 3 / 2-way spool is to maintain its setting. This results in rapid switching on the one hand and minimizes current consumption and the risk of overheating on the other.

[0071] [Fig. 4] shows a diagram representing the inverse model of the pressure control valve. This is a static model in the form of a valve characteristic curve. The horizontal axis represents the (average) current in the actuating magnet and the vertical axis represents the pressure at the outlet of the pressure control valve. The pressure control valve is preferably designed to have at least a monotonic characteristic curve. This ensures the possibility of a unambiguous inversion of the model. For a predefined first control pressure p-DRE, it is then sufficient to set only the first control current i-DRE.

[0072] The present characteristic curve is practically linear. In the context of preferential numerical calculation, the present quality of approximation is sufficient in itself because the residual non-linearity is compensated by the inverse model without risk of technical drawback.

[0073] NOMENCLATURE OF MAIN ELEMENTS

[0074] 10 Axial piston machine

[0075] 11 First working connection

[0076] 12 Second working connection

[0077] 13 Power strip

[0078] 14 Supply pressure limiting valve

[0079] 15 Command Input

[0080] 16 Return of order

[0081] 17 Tank

[0082] 18 Main pump

[0083] 19 Motor shaft

[0084] 20 Adjustment cylinder

[0085] 21 First adjustment chamber

[0086] 22 Second adjustment chamber

[0087] 23 Feed valve

[0088] 30 Pressure adjustment valve

[0089] 31 Electromagnet for actuating the pressure adjustment valve

[0090] 32 3 / 2 way drawer

[0091] 33 Electromagnet for actuating the 3 / 2-way spool

[0092] 40 Hydraulic motor

[0093] 41 Fan rotor

[0094] 50 Path planning filter

[0095] 51 Inverse model of the axial piston machine

[0096] 52 Regulator

[0097] 53 Actual value / setpoint value comparison

[0098] 54 Combination of pilot control and regulation

[0099] 55 Determination of the difference in actual discharge pressure

[0100] 60 Case zero

[0101] 61 Positive case

[0102] 62 Negative case

[0103] 63 Distinction of cases

[0104] 64 Reverse model of the pressure adjustment valve

[0105] 65 Reverse model of the 3 / 2-way drawer

[0106] 70 Rotation speed sensor

[0107] 71 First pressure sensor

[0108] 72 Second pressure sensor

[0109] dpX-cons Difference of the setpoint adjustment pressure

[0110] dp-cons Difference of the set discharge pressure [YES] i-DRE First adjustment current

[0112] i-3 / 2 Second adjustment current

[0113] pA First actual pressure

[0114] pB Second actual pressure

[0115] n Actual rotation speed

[0116] p-DRE First adjustment pressure

[0117] p-3 / 2 Second adjustment pressure

Claims

Claims

1. Method for controlling an axial piston machine (10) whose delivery flow rate is continuously adjustable with a double-acting adjustment cylinder (20) having two adjustment chambers (21, 22) acting in opposite directions: method comprising the following steps: a) providing an axial piston machine (10), followed by an adjustment chamber (21), to which an electrically controlled pressure adjustment valve (30) is connected, * the other adjustment chamber (22) being connected to an electrically controlled 3 / 2-way spool (32), b) providing a setpoint adjustment pressure difference (dpX-cons) with: * a zero case (60) defined as a case in which the setpoint adjustment pressure difference (dpX-cons) is practically zero, * a positive case (61) defined as a case in which the setpoint adjustment pressure difference (dpX-cons) is positive and does not fall below the zero case (60),* a negative case (62) defined as a case in which the setpoint adjustment pressure difference (dpX-cons) is negative and does not fall below the zero case (60), c) calculating a first and a second adjustment pressure (p-DRE; p_3 / 2), * within the framework of a case distinction (63) determining whether one is in the zero case (60), in the positive case (61) or in the negative case (62), * the result of the case distinction (63) being taken into account for calculating the first and second adjustment pressures (p-DRE, p_3 / 2), d) supplying current to the pressure adjustment valve (30) as a function of a first adjustment pressure (p-DRE) and supplying current to the 3 / 2-way slide valve (31) as a function of the second adjustment pressure (p-3 / 2).,

2. A method according to claim 1, wherein during operation of the axial piston machine (10), steps b), c) and d) are applied continuously and in parallel or quasi-parallel to each other.

3. Method according to one of the preceding claims, according to which in step d) the pressure control valve (30) is supplied with a first control current (i-DRE), * by supplying the 3 / 2-way slide valve (32) with a second control current (i-3 / 2), * by calculating the first control current (i-IDRE) with an inverse model (64) of the pressure control valve (30) from the first control pressure (p-DRE), * by calculating the second control current (i-3 / 2) with an inverse model (65) of the 3 / 2-way slide valve (32) from the second control pressure (p-3 / 2).

4. Method according to one of the preceding claims, according to which * in step d) the first and second adjustment pressure (p-DRE; p-3 / 2) are calculated each time for the zero case (60), the positive case (61) and the negative case (62), and * with the case decision (63) according to step b) one of the results of the three calculations is selected.

5. Method according to one of the preceding claims, according to which * in step d), in the zero case (60) a first and a second pair are calculated which respectively comprise the first and the second adjustment pressure (p-DRE; p-3 / 2), * for the first pair, the second adjustment pressure (p-3 / 2) is equal to the pressure in the control input (15), * the first adjustment pressure (p-DRE) is calculated as a function of this second pressure (p_3 / 2) and the setpoint adjustment pressure difference (dpX-cons), * for the second pair, the second adjustment pressure (p_3 / 2) is equal to the pressure in the control return (16), * the first adjustment pressure (p-DRE) is calculated as a function of this second adjustment pressure (p-DRE) and the setpoint adjustment pressure difference (pdX-cons), * depending on the last case in the case distinction (63) and / or where appropriate the future forecast case, it is decided to use the first or second pair of calculation results.

6. Method according to claim 5, according to which in the zero case (60) of step d), the first and the second pair are calculated, and * depending on the decision according to claim 5, one of the two calculation results is selected.

7. Method according to one of the preceding claims, according to which * in step c), in the positive case (61), the second adjustment pressure (p-3 / 2) is equal to the pressure in the control return (16), * the first adjustment pressure (p-DRE) is calculated as a function of this second adjustment pressure (p-3 / 2) and the difference in setpoint adjustment pressure (dpX-cons).

8. Method according to one of the preceding claims, according to which * in step c), in the negative case (62) the second adjustment pressure (p-3 / 2) is equal to the pressure in the control inlet (15), * the first adjustment pressure (p-DRE) is calculated as a function of this second adjustment pressure (p-3 / 2) and the difference in setpoint adjustment pressure (dpX-cons).

9. Method according to one of the preceding claims, according to which - in step a), an axial piston machine (10) is used with a first and a second working connection (11, 12), * a first and a second pressure sensor (71, 72) being provided for measuring a first or a second actual pressure (pA; pB) in the first or the second working connection (11, 12), - in step b) the setpoint adjustment pressure difference (dpX-cons) is calculated as a function of the first and the second actual pressure (pA; pB) and a predefined setpoint delivery pressure difference (dp-cons).

10. A method according to claim 9, wherein in step a) an axial piston machine (10) with a first rotational speed sensor (70) is used, * with this rotation speed sensor (70) the actual rotation speed (n) of the axial piston machine (10) is measured, and * the setpoint pressure difference (dpX-cons) in the direction of a pilot control is calculated as a function of the actual rotation speed (n).

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