Method for operating axial piston machine taking into account zero

Abstract

The invention relates to a method for operating an axial piston machine. According to the invention, the method comprises the following steps: a) providing a corresponding axial piston machine in which an electrically adjustable pressure regulating valve is connected to one of the regulating chambers and the other regulating chamber is connected to an electrically adjustable 3 / 2 path switching valve; b) providing a setpoint regulating pressure difference, where a zero condition is defined as a condition where the setpoint regulating pressure difference is substantially zero, where a positive condition is defined as a condition where the setpoint regulating pressure difference is positive, where a negative condition is defined as a condition where the setpoint regulating pressure difference is negative; c) a first and a second control pressure are calculated, whether a zero condition, a positive condition or a negative condition is present is ascertained within a condition distinguishing range, and the result of the condition distinguishing is taken into account when the first and the control pressure are calculated; and d) energizing the pressure regulating valve according to the first regulating pressure and energizing the 3 / 2 path switching valve according to the second regulating pressure.

Description

Technical Field

[0001] The invention relates to a method for operating an axial piston machine. Background Art

[0002] The data sheet "Axial Piston Variable-Modulating Pump A4VG Series 35" (order number RD92035; edition 12 February 2020) of Bosch Rexroth AG discloses an axial piston machine of swash plate design whose displacement can be adjusted across zero by means of a double-acting regulating cylinder, so that the delivery direction can be reversed simply by adjusting the cradle while the drive rotation direction remains the same. In ET control, the two regulating chambers of the regulating cylinder are each connected to a pressure regulating valve in the form of a pressure reducing valve. In the event of a failure of the electrical control, it is not possible to reliably determine which displacement is present.

[0003] This behavior is undesirable for hydraulic fan drives, where the fan should normally rotate at maximum speed in the event of a failure of the electric control (fail-safe behavior).

[0004] DE 10 2010 020 528 A1 describes a fan drive having a closed hydraulic circuit which essentially comprises the axial piston machine described above. The regulating cylinder is here controlled by a pressure regulating valve in the form of a pressure reducing valve with an increasing or positive characteristic curve and by a 4 / 2-way switching valve, wherein the two regulating valves can be electrically controlled separately. The switching is designed so that in the event of a failure of the electrical control, the axial piston machine automatically sets the maximum displacement in terms of value, so that the two fan impellers rotate as fast as possible.

[0005] Furthermore, the switching is designed so that the current at the pressure regulating valve does not need to be adjusted in a step-like manner at the zero crossing of the regulating pressure difference. At the zero crossing, the corresponding regulating current drops to zero and then rises again, wherein only the 4 / 2-way switching valve is switched in a step-like manner.

[0006] The disadvantage of this control is that a special valve body is required for the regulating valve, which is specifically matched to the fan drive. If other behaviors are desired instead of the above-mentioned failsafe behavior, the valve body must be changed. Summary of the invention

[0007] The invention has the advantage that the known axial piston machine can be manufactured using only control valves available from the catalogue in such a way that the above-described failsafe behavior is achieved. At the same time, a large number of drive variants can be realized by suitable selection of the control direction and the installation location of the two control valves, without requiring a special mechanical design compared to the known catalogue components. Only the program of the control device must be adapted to the selected control valve arrangement.

[0008] According to claim 1, a method for operating an axial piston machine is provided, wherein the displacement of the axial piston machine can be continuously adjusted by means of a double-acting control cylinder having two oppositely acting control chambers, wherein the method comprises the following steps:

[0009] a) providing a corresponding axial piston machine, wherein an electrically adjustable pressure regulating valve is connected to one of the regulating chambers, wherein the other regulating chamber is connected to an electrically adjustable 3 / 2-way switching valve;

[0010] b) providing a nominal regulated pressure difference, wherein a zero case is defined as a case where the nominal regulated pressure difference is substantially zero, wherein a positive case is defined as a case where the nominal regulated pressure difference is positive, wherein the nominal regulated pressure difference does not belong to the zero case, and wherein a negative case is defined as a case where the nominal regulated pressure difference is negative, wherein the nominal regulated pressure difference does not belong to the zero case;

[0011] c) calculating a first and a second control pressure, wherein within the scope of a situation differentiation it is ascertained whether a zero situation, a positive situation or a negative situation is present, wherein the result of the situation differentiation is taken into account in the calculation of the first and the first control pressure;

[0012] d) The pressure regulating valve is energized as a function of the first regulating pressure and the 3 / 2-way switching valve is energized as a function of the second regulating pressure.

[0013] Step a) is preferably carried out before all other steps of the method. This step can be used to initiate a failsafe behavior of the fan drive, wherein the following reference is made to Figure 1 Further details are explained. However, this design has the consequence that the pressure regulating valve is preferably adjusted in a step-like manner at the zero crossing of the setpoint regulating pressure difference. This is taken into account in the remaining method steps b), c) and d). Thus, an abrupt operating behavior of the axial piston machine is avoided, especially when the axial piston machine is used as a component of a fan drive.

[0014] If the actual control differential pressure cannot be guaranteed to be either reliably positive or reliably negative by adjusting the pressure regulating valve and the 3 / 2-way switching valve, the setpoint control differential pressure is essentially zero. Therefore, the zero case exists as long as the actual control differential pressure actually set may fluctuate around zero due to control inaccuracies.

[0015] Steps b), c) and d) of the method are preferably implemented at least in the form of a computer program which is executed by a control device of the axial piston machine, wherein the control device preferably comprises a programmable digital computer and / or an FPGA.

[0016] The pressure regulating valve and the 3 / 2-way switching valve are preferably directly connected to the assigned regulating chamber, respectively. They are preferably configured as built-in valves, respectively, which are fixedly installed in a borehole, which opens into the relevant regulating chamber.

[0017] Advantageous developments and refinements of the invention are described in the dependent claims.

[0018] It can be provided that steps b), c) and d are performed continuously and in parallel or quasi-parallel to one another during the operation of the axial piston machine. The steps mentioned are preferably performed in a time-distributed manner in a large number of calculation cycles that follow one another with a calculation time interval, wherein all steps b), c) and d are taken into account in each calculation cycle. Within a calculation cycle, the individual calculation steps can be performed successively, wherein then quasi-parallel calculations are mentioned. The calculation time interval is preferably constant, wherein it is, for example, 1 ms. Such a computer program can be programmed, for example, with the programming system Matlab Simulink. However, it can also be programmed in the programming language C or C++ or in any other programming language.

[0019] The calculation process within a single calculation cycle preferably does not contain any calculation feedback (feedforward), wherein the calculation feedback is carried out in successive calculation cycles. The calculation feedback mentioned should be consistent with the calculation feedback in a real axial piston machine, for example in a reference Figure 2 A physical feedback within the scope of the described control loop comprising two real pressure sensors is differentiated.

[0020] It can be provided that within the scope of step d), the pressure regulating valve is energized with a first regulating current, wherein the 3 / 2-way switching valve is energized with a second regulating current, wherein the first regulating current is calculated from the first regulating pressure by means of an inverse model of the pressure regulating valve, wherein the second regulating current is calculated from the second regulating pressure by means of an inverse model of the 3 / 2-way switching valve. In the simplest case, the model mentioned is a static model. In the case of the pressure regulating valve, such a static model is a valve characteristic curve, which assigns a first regulating pressure to each first regulating current, wherein this assignment depends on the pressure in the control inlet of the pressure regulating valve. Such a model is calculated along a physical cause-effect relationship. The corresponding inverse model, on the contrary, assigns a first regulating current to each first regulating pressure. It works in the opposite direction relative to the cause-effect relationship mentioned. Within the scope of the method according to the invention, a dynamic model can be used, which takes into account how quickly the relevant valve reacts to changes in the regulating current. The static model of the 3 / 2-way switching valve only distinguishes between two discrete switching states of the 3 / 2-way switching valve. The switching state is preferably preloaded by a return spring so that the second regulating current is zero. In another state, the second control current is then so great that the force of the return spring is overcome reliably and quickly. It is conceivable that the second control current is a current that the actuating magnet of the 3 / 2-way switching valve can just withstand permanently without overheating. The second control pressure is either the pressure in the control inlet or the pressure in the control return, both pressures being known during operation of the axial piston machine. The pressure in the control inlet is predetermined, for example, by adjusting the feed pressure limiting valve, wherein this adjustment is usually performed in a fixed manner.

[0021] It can be provided that within the scope of step d) the first and second control pressures are calculated for the zero case, the positive case and the negative case, wherein one of the results of the three calculations mentioned is selected as a function of the case distinction mentioned in step d). Within the scope of the quasi-parallel calculation explained above, the above-described method design achieves that the time for calculating a calculation cycle does not substantially fluctuate, regardless of the state of the axial piston machine. This can ensure in a simple manner that the required calculation time in each calculation cycle is less than the calculation time interval.

[0022] It can be provided that within the scope of step d), a first and a second pairing, each comprising a first and a second regulating pressure, is calculated in the zero case, wherein in the first pairing the second regulating pressure is equal to the pressure in the control inlet, wherein the first regulating pressure is calculated as a function of this second regulating pressure and a setpoint regulating pressure difference, wherein in the second pairing the second regulating pressure is equal to the pressure in the control return port, wherein the first regulating pressure is calculated as a function of this second regulating pressure and a setpoint regulating pressure difference, wherein a decision is made as a function of the last situation existing within the scope of the situation distinction and / or as a function of the situation that may exist in the future, whether the first pairing or the second pairing is used as the calculation result. In this case, "calculation" means the straightforward provision of the mentioned values, which are preferably stored as parameters in the control device. The first regulating pressure is preferably equal to the sum of the setpoint regulating pressure difference and the second regulating pressure. The second regulating pressure can here assume only positive values, wherein the setpoint regulating pressure difference can assume both positive and negative values. The decision as to which pairing to use is preferably made as a function of the time derivative of the setpoint regulating pressure difference. For further details, refer to the following Figure 3 To explain.

[0023] It can be provided that the first and second pairings are calculated within the scope of the zero case of step d), wherein one of the two calculation results is selected according to the above-mentioned decision. Thus, it can be ensured in a simple manner that the required calculation time in each calculation cycle is less than the calculation time interval.

[0024] It can be provided that within the scope of step c) in the positive case the second control pressure is equal to the pressure in the control return, wherein the first control pressure is calculated as a function of the difference between this second control pressure and the setpoint control pressure.

[0025] It can be provided that within the scope of step c) in the negative case the second control pressure is equal to the pressure in the control inlet, wherein the first control pressure is calculated as a function of the difference between this second control pressure and the setpoint control pressure.

[0026] It can be provided that within the scope of step a), an axial piston machine with a first and a second working interface is provided, wherein a first and a second pressure sensor are provided, by means of which the first and the second pressure sensor can respectively measure the first or the second actual pressure at the respectively assigned first or the second working interface, wherein within the scope of step b), the rated regulating pressure difference is calculated according to the first and the second actual pressures and according to the predetermined rated delivery pressure difference. The last-mentioned calculation is preferably carried out in such a way that the difference formed by the first and the second actual pressures is close to the rated delivery pressure difference. The calculation can be carried out in the sense of regulation. The calculation mentioned preferably includes calculations for a linear regulator, such as a PID regulator. It is possible to superimpose a precontrol on this regulation. Within the scope of the precontrol, a trajectory plan can be implemented, in which the planned rated delivery pressure difference is ascertained from the rated delivery pressure difference, and the rated delivery pressure difference can be well coordinated with the corresponding actual delivery pressure difference within the scope of the precontrol. Here, in particular, a step-like change in the rated delivery pressure difference is taken into account, which cannot be achieved with the actual delivery pressure difference and which makes the calculation for the precontrol significantly difficult. Within the scope of such a pilot control, an inverse model of an axial piston machine, such as described in DE 10 2019 210 003 A1 or DE 10 2021 200 693 A1, can be used, wherein the first-mentioned patent application also describes a trajectory planning. It goes without saying that the pilot control can also be implemented without superimposed regulation.

[0027] It can be provided that within the scope of step a), an axial piston machine with a rotational speed sensor is provided, wherein the actual rotational speed of the axial piston machine can be measured with the rotational speed sensor, wherein the setpoint control pressure difference is calculated as a function of the actual rotational speed in the sense of a pilot control. The mentioned actual rotational speed is preferably taken into account in an inverse model of the axial piston machine.

[0028] It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively described combination but also in other combinations or alone, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention is described in detail below with the aid of the accompanying drawings.

[0030] Figure 1 A hydraulic circuit diagram of an axial piston machine according to the present invention is shown;

[0031] Figure 2 A portion of a control diagram for implementing the method according to the invention is shown;

[0032] Figure 3 Shows Figure 2another part of the reconciliation chart in

[0033] Figure 4 A graph illustrating an inverse model of a pressure regulating valve is shown. DETAILED DESCRIPTION

[0034] Figure 1 The hydraulic circuit diagram of the axial piston machine 10 according to the invention is shown. The axial piston machine 10 comprises a main pump 18 and a feed pump 13, which are driven by a common drive shaft 19. The actual rotational speed n of the drive shaft 19 can be measured by means of a rotational speed sensor 70, which is preferably fixedly attached to the axial piston machine 10.

[0035] The main pump 18 is designed as an axial piston, wherein its displacement can preferably be continuously adjusted by means of a pivoting cradle. The cradle is coupled to the movement of the control piston of a dual-acting control cylinder 20. The control cylinder 20 has a first and a second control chamber 21; 22, wherein the pressures therein (whose values ​​correspond to Figure 3 The first regulating chamber 21 is directly fluidically connected to a pressure regulating valve 30, which is preferably designed as a pressure reducing valve, wherein the pressure regulating valve can be electrically adjusted by means of an actuating magnet 31. The second regulating chamber 22 is directly fluidically connected to a 3 / 2-way switching valve 32, which can be electrically adjusted by means of an actuating magnet 33, wherein the actuating magnet is preloaded by means of a return spring 34 into a position in which the control inlet 15 is connected (so-called open position). The pressure regulating valve 30 and / or the 3 / 2-way switching valve 32 are preferably respectively actuated by a voltage, the duty cycle of which is selected so that, on average, a current is generated, the value of which corresponds to i_DRE or i_3 / 2. For this purpose, preferably a digitally implemented current control loop is always used, which is preferably calculated at most by a control device, which also executes the method according to the invention.

[0036] The pressure regulating valve 30 has a positive characteristic curve here, so that in its de-energized state, the low pressure in the control return port 16 exists in the first regulating chamber 21. The 3 / 2-way switching valve is open when it is de-energized, so that in its de-energized state, the high pressure in the control inlet 15 exists in the second regulating chamber 22. The current main pump 18 can be adjusted across the zero displacement. Correspondingly, in the de-energized state, as long as the drive shaft 19 rotates, the maximum displacement is set in numerical terms. The corresponding rotation direction is designed in this way so that the fan impeller 41 rotates according to the desired cooling air delivery direction. This behavior is welcome in most cases of fan drives in order to produce sufficient cooling of the internal combustion engine to be cooled even when the electric control fails.

[0037] The feed pump 13 can be designed as a vane pump, for example. It draws in pressure fluid from the tank 17 and delivers it on the one hand to the control inlet 15 and on the other hand via the feed valve 23 into the closed hydraulic circuit. Figure 1 In the drawings, all tank symbols 17 represent the same tank. The pressure fluid is preferably a liquid and preferably at most a hydraulic oil. The outlet of the feed pump 13 is connected to the feed pressure limiting valve 14. The delivery flow of the feed pump 13 is so great during the main operating time of the axial piston machine 10 that the feed pressure limiting valve 14 is triggered, so that the pressure in the control flow inlet 15 is defined by adjusting the feed pressure limiting valve 14. The feed pressure limiting valve 14 is fixedly adjusted here, wherein an electrically adjustable feed pressure limiting valve can be used.

[0038] The first and second working interfaces 11; 12 of the main pump 18 or the axial piston machine 10 are fluidically connected to the hydraulic motor 40 in the sense of a closed hydraulic circuit. The hydraulic motor 40 directly drives the fan impeller 41, which cools, for example, the internal combustion engine of a larger vehicle, especially a mobile working machine. The present invention is mainly designed for this application, wherein it can of course also be used for other applications. The set delivery pressure difference explained below can be used as a control variable in a superimposed control loop (with which the speed of the fan impeller 41 is regulated). Here, the first and second pressure sensors 71; 72 and the speed sensor 70 according to the method of the present invention should be sufficient, wherein other sensors are not mandatory. It goes without saying that, for example, a swivel angle sensor on the main pump 18 or another speed sensor on the hydraulic motor 40 can be used optionally to improve the operating behavior of the overall system.

[0039] A first actual pressure p_A at the first working port 11 can be measured by the first pressure sensor 71 , and a second actual pressure p_B at the second working port 12 can be measured by the second pressure sensor 72 .

[0040] The two feed valves 23 are also mentioned, via which pressure fluid can be conveyed from the feed pump 13 into the closed hydraulic circuit in order to compensate for leakages. It is conceivable to equip the axial piston machine 10 with flushing valves, by means of which pressure fluid can be removed in a targeted manner from the closed hydraulic circuit over the aforementioned leakages, so that the pressure fluid there does not overheat. However, this risk is less in the case of current fan drives.

[0041] Figure 2 A section of a control diagram for implementing the method according to the invention is shown. Figure 2The parts shown in the figure can be subjected to a great deal of variation without departing from the scope of the invention. For example, it is possible to use only a precontrol with a trajectory planning filter 50 and an inverse model 51 of the axial piston machine. It is also conceivable to use only a regulator 52. In any case, an operational overall system is produced, in which Figure 2 The most expensive variant with the best operating characteristics is shown.

[0042] A setpoint delivery pressure difference dp_soll is externally predetermined for the axial piston machine, wherein the difference between the first and second actual pressures p_A, p_B measured by the first and second pressure sensors is to be adjusted to the setpoint delivery pressure difference dp_soll.

[0043] In order to make this adjustment as fast as possible, a precontrol is first provided, which is based on an inverse model 51 of the axial piston machine. The following mathematical formula is described in the specification of DE 10 2019 210 003 A1, with which the behavior of the axial piston machine can be modeled. DE 102021 200 693 A1 describes a method with which a mathematical model of the axial piston machine can be determined in an empirically determined manner. All these models have in common that, in the case of a time curve of the delivery pressure difference that can actually be adjusted and used as an input quantity in a real axial piston machine, the model only provides a result that is then available when it is reversed.

[0044] However, the set delivery pressure difference dp_soll can have a step-like change that cannot occur in the actual delivery pressure difference, because this actual delivery pressure difference can only change continuously. Therefore, before the set delivery pressure difference dp_soll is delivered to the inverse model 51 of the axial piston machine, it is first delivered to the trajectory planning filter 50. The trajectory planning filter 50 is a low-pass filter with a fixed set limit frequency in the simplest case. As a result, the mentioned steps can be eliminated in a simple way. However, it is preferred to use the trajectory planning filter 50 disclosed in DE 10 2019 210 003 A1, with which the effective power of the axial piston machine can be utilized as best as possible, so as to achieve a particularly fast approach to the set delivery pressure difference dp_soll within the scope of the pre-control.

[0045] In addition to the modified setpoint delivery pressure difference, the measured values ​​of the sensor, i.e. the actual rotational speed n of the drive shaft and the first and second actual pressures p_A; p_B, are also supplied to the inverse model 51 of the axial piston machine in order to calculate the model 51. As a result, the inverse model 51 of the axial piston machine provides a setpoint control pressure difference dpX_setpoint, which must be set theoretically, in order to achieve a quicker approach of the actual delivery pressure difference to the setpoint delivery pressure difference dp_setpoint. It goes without saying that this theoretical value does not perfectly correspond to the actual situation. Therefore, the regulation 50 is superimposed with the precontrol.

[0046] The manipulated variable of the regulator 52 is here a further setpoint differential pressure which is additively superimposed 54 on the pilot-controlled setpoint differential pressure to obtain dpX_setpoint. It is conceivable to use the manipulated variable of the regulator 52 at a suitable point in the inverse model 51 of the axial piston machine to improve the control behavior.

[0047] On the inlet side of the regulator 52, the actual delivery pressure difference is first calculated 55 as a difference 53 consisting of the first and second actual pressures p_A; p_B. The control deviation is generated from the difference 53 consisting of the setpoint delivery pressure difference dp_setpoint and the actual delivery pressure difference. The control deviation is supplied to the regulator 52, which is preferably designed as a continuous linear regulator, in particular as a PID regulator. The regulator 52 is preferably calculated in a time-dispersed manner within the scope of the round-based calculation method explained at the beginning.

[0048] Figure 3 Shows Figure 2 Another part of the adjustment chart in . Figure 2 and 3 The interface of forms a setpoint control pressure difference dpX_setpoint, which is also a primary input variable of the method according to the invention.

[0049] In the scope of the present invention, in particular, regulating valves, that is, pressure regulating valves and 3 / 2-way switching valves are used. This choice has significant advantages for fan drives, because different fan variants common on the market can be realized with the same components. In particular, it is possible to freely choose on which side of the regulating cylinder the pressure regulating valve should be arranged, wherein the 3 / 2-way switching valve is arranged on the other side. This advantage is exchanged for the significant disadvantages eliminated by the present invention. In particular, the regulating behavior of the regulating valve has a significant discontinuity for the rated regulating pressure difference dpX_soll equal to zero, and the significant discontinuity involves two regulating valves. Therefore, the current regulating valve cannot be used with conventional purely hydraulic control devices, even if the regulating valve can be hydraulically operated. Therefore, within the scope of the present invention, such a method is used, which is preferably implemented with the aid of a programmable digital computer, and the digital computer particularly includes a microprocessor.

[0050] The aforementioned discontinuity is taken into account by distinguishing between three cases, namely a zero case 60, a positive case 61 and a negative case 62. In the zero case 60, the setpoint control pressure difference dpX_setpoint is essentially zero, wherein the case should also be detected in which it is not certain whether the actual control pressure difference actually set is positive or negative due to control inaccuracies.

[0051] In the positive case 61, the setpoint control pressure difference dpX_setpoint is positive, wherein there is no zero case 60. In the positive case 61, the second control chamber is connected to the control return via the 3 / 2-way switching valve, so that essentially zero pressure exists in the second control chamber. Figure 1 For the pressure regulating valve shown in FIG. 1 , which has a rising characteristic curve, the current i_DRE increases approximately proportionally to the desired setpoint regulating pressure difference dpX_setpoint. The corresponding relationship is Figure 4 Shown in.

[0052] In the negative case 62, the setpoint differential pressure dpX_setpoint is negative, wherein there is no zero case. In this case, the second control chamber is connected to the control inlet via the 3 / 2-way switching valve, so that a high pressure prevails in the second control chamber, wherein this pressure simultaneously defines the maximum pressure that can be set with the pressure regulating valve. Figure 1 For the pressure regulating valve shown in FIG. 1 , which has a positive characteristic curve, the current i_DRE decreases approximately inversely proportionally to the value of the desired setpoint control pressure difference dpX_setpoint.

[0053] In the zero condition 60, the two zero adjustments of the control valve (at Figure 1 Either the two control chambers can be connected to the control flow inlet, or the two control chambers (in Figure 1 21; 22) can be connected to the control return. In both cases of zero regulation, an effective zero pressure acts on the regulating piston. Theoretically, the pressure regulating valve should not be adjusted to an intermediate value. However, this is unavoidable in practice, especially when there is a change from the positive situation 61 to the negative situation 62 or vice versa (zero crossing). This problem is addressed in that the corresponding change is only carried out when it is actually necessary, and the change is then carried out particularly quickly.

[0054] For this purpose, the first and second control pressures p_DRE are preferably calculated continuously and quasi-simultaneously; all four conceivable cases of p_3 / 2 or, in the case of zero control, are provided as a constant, wherein it is only determined within the scope of the case distinction 63 which of the four cases is used to control the control valve (in Figure 1 30; 32).

[0055] If there is clearly a positive or negative case 61; 62, then this case distinction 63 is simple. It becomes difficult if a zero crossing occurs. It is conceivable here that the setpoint control pressure difference dpX_set should be set in a step-like manner across zero. In this subcase, a simple case distinction between positive and negative cases 61; 62 already leads to the desired result, wherein the discontinuity caused by the control system does not interfere with the discontinuous adjustment of the setpoint control pressure difference dpX_set.

[0056] If a zero crossing occurs within the scope of a continuous control of the setpoint differential pressure dpX_set, it is possible to predict when the theoretical zero crossing will occur by observing the derivative of the setpoint differential pressure over time. A zero control is then set for a short period of time before the theoretical zero crossing, which does not require a step-like adjustment of the control valve. The setpoint differential pressure dpX_set continues to be observed during the zero situation 60. If the zero situation 60 is clearly left in the sense of a zero crossing, another zero control is set in a step-like manner.

[0057] The inverse model 64 of the pressure regulating valve is used to determine the first regulating current i_DRE required to set the desired pressure. Figure 4 , which is simply the valve characteristic curve. However, it is also conceivable to use a dynamic model that takes into account how quickly the pressure regulating valve reacts to changes in the first regulating current i_DRE. Due to the particularly fast regulation expected in the zero case 60, a dynamic inverse model 64 is advantageous.

[0058] The second regulating current i_3 / 2 required for setting the desired pressure is determined by the inverse model 65 of the 3 / 2-way switching valve. Due to the basic switching characteristics, only two cases can be distinguished here in principle. In one case, i_3 / 2 is equal to zero. In the other case, i_3 / 2 is as large as possible, without the possibility of a corresponding actuating magnet (in Figure 1 Overheating of the 3 / 2-way switching valve (reference numeral 33 in the figure). It is conceivable that during the switching time period a second regulating current i_3 / 2 is set that is greater than in a later time period, in which the 3 / 2-way switching valve is only intended to maintain its position. This allows, on the one hand, a fast switching to be achieved, while on the other hand, current consumption and the risk of overheating are reduced to a minimum.

[0059] Figure 4 A diagram is shown which illustrates an inverse model of a pressure regulating valve. This is a static model in the form of a valve characteristic curve. The (average) current in the actuating magnet is plotted on the horizontal axis, the pressure at the outlet of the pressure regulating valve being plotted on the vertical axis. The pressure regulating valve is preferably designed in such a way that it has at least a monotonic characteristic curve. This ensures the unambiguous reversibility of the model. If a first regulating pressure p_DRE is predetermined, there is only one possible first regulating current i_DRE which is to be set for this purpose.

[0060] The current characteristic curve is approximately linear. Within the scope of the preferred digital control, the current approximation quality is adequate without any problems, since the remaining nonlinearities are compensated by the inverse model without having to worry about technical disadvantages.

[0061] Finally, reference is made to a parallel patent application by the applicant of the present invention having the same priority date, which relates to further details of the axial piston machine according to the invention.

[0062] List of reference numerals:

[0063] 10 Axial piston machine

[0064] 11 First working interface

[0065] 12 Second working interface

[0066] 13 Feed pump

[0067] 14 Feed pressure limiting valve

[0068] 15 Control flow inlet

[0069] 16 Control reflux port

[0070] 17 Tanks

[0071] 18 Main pump

[0072] 19 Drive shaft

[0073] 20 Adjustment cylinder

[0074] 21. First conditioning room

[0075] 22 Second Conditioning Room

[0076] 23 Feed valve

[0077] 30 Pressure regulating valve

[0078] 31. Actuating magnet for pressure regulating valve

[0079] 32 3 / 2 way switching valve

[0080] 33 Actuating magnet for 3 / 2-way switching valve

[0081] 40 Hydraulic motor

[0082] 41 Fan impeller

[0083] 50 Trajectory Planning Filter

[0084] 51 Inverse model of axial piston machine

[0085] 52 Regulator

[0086] 53 Rated and actual value comparison

[0087] 54 Superposition of pre-control and regulation

[0088] 55 Determination of actual delivery pressure difference

[0089] 60 Zero Case

[0090] 61 Positive situation

[0091] 62 Negative situation

[0092] 63 Situation Distinction

[0093] 64 Inverse Model of Pressure Regulating Valve

[0094] 65 Inverse Model of 3 / 2-Way Switching Valve

[0095] 70 Speed ​​sensor

[0096] 71 First pressure sensor

[0097] 72 Second pressure sensor

[0098] dpX_soll Rated regulated pressure difference

[0099] dp_soll Rated delivery pressure difference

[0100] i_DRE First regulation current

[0101] i_3 / 2 Second regulation current

[0102] p_A First actual pressure

[0103] p_B Second actual pressure

[0104] n Actual speed

[0105] p_DRE First regulation pressure

[0106] p_3 / 2 Second adjustment pressure

Claims

1. A method for operating an axial piston machine (10) whose displacement can be continuously adjusted by means of a double-acting regulating cylinder (20) comprising two oppositely acting regulating chambers (21; 22), the method comprising the following steps: a) providing a corresponding axial piston machine (10), wherein an electrically adjustable pressure regulating valve (30) is connected to one of the regulating chambers (21), wherein the other regulating chamber (22) is connected to an electrically adjustable 3 / 2-way switching valve (32); b) providing a setpoint regulating pressure difference (dpX_soll), wherein a zero case (60) is defined as a case where the setpoint regulating pressure difference (dpX_soll) is substantially zero, wherein a positive case (61) is defined as a case where the setpoint regulating pressure difference (dpX_soll) is positive, wherein the setpoint regulating pressure difference (dpX_soll) does not belong to the zero case (60), wherein a negative case (62) is defined as a case where the setpoint regulating pressure difference (dpX_soll) is negative, wherein the setpoint regulating pressure difference (dpX_soll) does not belong to the zero case (60); c) calculating a first and a second control pressure (p_DRE; p_3 / 2), wherein within the scope of a situation differentiation (63) it is determined whether a zero situation (60), a positive situation (61) or a negative situation (62) is present, wherein the result of the situation differentiation (63) is taken into account in the calculation of the first and the second control pressure (p_DRE; p_3 / 2); d) energizing the pressure regulating valve (30) according to a first regulating pressure (p_DRE) and energizing the 3 / 2-way switching valve (31) according to a second regulating pressure (p_3 / 2).

2. The method according to claim 1, In this case, steps b), c) and d) are carried out continuously and in parallel or quasi-parallel to one another during operation of the axial piston machine (10).

3. The method according to any one of the preceding claims, Within the scope of step d), the pressure regulating valve (30) is energized with a first regulating current (i_DRE), the 3 / 2-way switching valve (32) is energized with a second regulating current (i_3 / 2), the first regulating current (i_DRE) is calculated from a first regulating pressure (p_DRE) with the aid of an inverse model (64) of the pressure regulating valve (30), and the second regulating current (i_3 / 2) is calculated from a second regulating pressure (p_3 / 2) with the aid of an inverse model (65) of the 3 / 2-way switching valve (32).

4. The method according to any one of the preceding claims, In step d), the first and second control pressures (p_DRE; p_3 / 2) are calculated for the zero case (60), the positive case (61) and the negative case (61), respectively, wherein one of the results of the three calculations is selected depending on the case differentiation (63) mentioned in step d).

5. The method according to any one of the preceding claims, In step d), a first and a second pairing are calculated in the zero case (60), each comprising a first and a second control pressure (p_DRE; p_3 / 2), wherein in the first pairing the second control pressure (p_3 / 2 / ) is equal to the pressure in the control inlet (15), wherein the first control pressure (p_DRE) is calculated as a function of this second control pressure (p_3 / 2) and a setpoint control pressure difference (dpX_set), wherein in the second pairing the second control pressure (p_3 / 2) is equal to the pressure in the control return (16), wherein the first control pressure (p_DRE) is calculated as a function of this second control pressure (p_DRE) and a setpoint control pressure difference (dpX_set), wherein it is determined whether the first pairing or the second pairing is used as the calculation result as a function of the last existing case and / or as a function of a case that may exist in the future as desired within the case differentiation (63).

6. The method according to claim 5, The first and second pairings are calculated within the scope of the zero case (60) of step d), wherein one of the two calculation results is selected according to the decision mentioned in claim 5.

7. The method according to any one of the preceding claims, Within the scope of step c), in the positive case (61), the second control pressure (p_3 / 2) is equal to the pressure in the control return (16), wherein the first control pressure (p_DRE) is calculated as a function of this second control pressure (p_3 / 2) and a setpoint control pressure difference (dpX_setpoint).

8. The method according to any one of the preceding claims, In the negative case (61) within step c), the second control pressure (p_3 / 2) is equal to the pressure in the control flow inlet (15), wherein the first control pressure (p_DRE) is calculated as a function of this second control pressure (p_3 / 2) and a setpoint control pressure difference (dpX_setpoint).

9. The method according to any one of the preceding claims, Within the scope of step a), an axial piston machine (10) having a first and a second working interface (11; 12) is provided, wherein a first and a second pressure sensor (71; 72) are provided, by means of which a first or a second actual pressure (p_A; p_B) at the respectively assigned first or second working interface (11; 12) can be measured, respectively, wherein within the scope of step b), the setpoint regulating pressure difference (dpX_setpoint) is calculated based on the first and the second actual pressures (p_A; p_B) and based on a predetermined setpoint delivery pressure difference (dp_setpoint).

10. The method according to claim 9, In step a), an axial piston machine (10) having a rotational speed sensor (70) is provided, wherein the rotational speed sensor (70) is capable of measuring an actual rotational speed (n) of the axial piston machine (10), wherein the setpoint control differential pressure (dpX_setpoint) is calculated in the sense of a pilot control as a function of the actual rotational speed (n).

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