Method for controlling an actuating device of a slide valve

Abstract

The invention relates to a method for controlling an actuating device of a slide valve (2), wherein the actuating device comprises at least one electromagnetic pressure control valve (4) which is hydraulically connected to at least one control pressure chamber of the slide valve, wherein the at least one pressure control valve can be controlled with at least one electrical control current, wherein pressure medium provided at at least one working connection has a control pressure value corresponding to at least one control current intensity, wherein a control signal (72) is detected (110) and a target control pressure value (76) and a desired piston speed (80) are determined (120, 130) from the control signal;wherein a pressure difference value (90) is determined (140) from the desired piston speed, which corresponds to the pressure drop (56) that occurs between the at least one working connection and the corresponding at least one control pressure chamber during a piston movement (50) at the desired piston speed due to the at least one volume flow (52); wherein a compensated target control pressure value (94) is determined (150) as the sum or difference of the target control pressure value (76) and the pressure difference value (90); and wherein the at least one pressure control valve is controlled (160) with at least one electrical control current that has at least one control current intensity that corresponds to the compensated target control pressure value.

Description

[0001] The present invention relates to a method for controlling an actuating device of a slide valve as well as a computing unit and a computer program for its execution. Background of the invention

[0002] In hydraulic systems, the flow of pressure fluid to and from hydraulic consumers can be controlled by means of directional control valves or slide valves. A slide valve, for example, has a slide or piston that is continuously adjustable in the longitudinal direction, whereby the adjustment of the piston can be hydraulically controlled by at least one electromagnetic pressure control valve. At least one actuating surface (e.g., end face) of the piston is subjected to a pressure fluid under a so-called control pressure via the at least one pressure control valve. Disclosure of the invention

[0003] According to the invention, a method for controlling an actuating device of a slide valve, as well as a computing unit and a computer program for implementing the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the subclaims and the following description.

[0004] In detail, the method according to the invention relates to the control of an actuating device of a slide valve having a piston with at least one actuating surface that delimits a corresponding at least one control pressure chamber, wherein the actuating device has at least one electromagnetic pressure control valve, each with a working connection that is hydraulically connected to a corresponding one of the at least one control pressure chambers. The at least one pressure control valve can be controlled with at least one electrical control current, wherein pressure medium provided at the at least one working connection has a control pressure value that corresponds to at least one control current intensity of the at least one electrical control current.

[0005] The invention makes use of the measure of determining a target control pressure value and a desired piston speed from a control signal, of determining a pressure difference value from the desired piston speed, which pressure difference corresponds to the pressure drop that occurs during a piston movement with the desired piston speed due to at least one volume flow between the working connection of the at least one pressure control valve and the corresponding at least one control pressure chamber, and of controlling the at least one pressure control valve with at least one electrical control current that has at least one control current intensity that corresponds to a compensated target control pressure value that is determined as the sum of the target control pressure value and the pressure difference value. By means of the measure according to the invention, during the control orDuring the piston movement, unwanted positional deviations of the valve spool, which result from the fact that the pressure actually acting on the piston differs from the control pressure value at at least one pressure control valve due to the pressure drop, are avoided or at least reduced.

[0006] The pressure drop is primarily caused by constrictions in the hydraulic connection (e.g., a hydraulic line or a hydraulic channel) between the pressure control valve(s) and the control pressure chamber(s). A pressure drop can also occur due to friction of the pressure medium (even with an unchanged line cross-section).

[0007] According to one embodiment, the control signal is determined using an operating device, in particular a joystick, which is configured to detect a user input. Alternatively, the control signal is based on a signal detected by the operating device. For example, the operating device can be used to control a hydraulic consumer supplied with pressure medium via the slide valve by a user of a work machine in which the hydraulic consumer and the slide valve are installed. The control signal can also be obtained, for example, by filtering or similar means from a signal detected by the operating device.

[0008] According to one embodiment, the control signal corresponds to a desired piston position of the piston, wherein the control signal is, in particular, a desired speed of a hydraulic consumer supplied with pressure medium via the slide valve. Different piston positions typically correspond to different or differently sized volume flows to the hydraulic consumer.

[0009] According to one embodiment, the target control pressure value is the control pressure value at which the piston assumes the desired piston position in a stationary state. This means that if the target control pressure value is present, the piston would assume the desired piston position in a state in which there are no volume flows into and / or out of the at least one control pressure chamber, i.e., when there is no movement of the piston. In a stationary state, the target control pressure value (i.e., the control pressure at the at least one working connection) is also present at the at least one actuating surface of the piston.

[0010] According to one embodiment, the desired piston speed is determined from a profile of the desired piston position; in particular by differentiation or filtering.

[0011] According to one embodiment, the actuating device has at least one spring element that exerts a preload on the piston, wherein the preload by the at least one spring element is taken into account when determining the target control pressure value. According to an additional or alternative embodiment, at least one end stop of the piston can be taken into account when determining the target control pressure value. For example, it can be taken into account that the preload must first be overcome in order to achieve the piston movement. For example, a characteristic curve can be provided that indicates a relationship between control pressure values ​​and piston position.

[0012] According to one embodiment, the determination of the pressure difference value is based on a relationship between the at least one volume flow and the pressure difference value, wherein the relationship is given by at least one formula and / or at least one characteristic map. According to a further embodiment, the at least one formula and / or the at least one characteristic map is determined by a throttle equation and / or an orifice equation and / or similar equations and / or simulations and / or test runs. The use of the throttle or orifice equation is helpful, for example, when correspondingly shaped bottlenecks are present in the hydraulic connection between the pressure control valve and the control pressure chamber.

[0013] According to one embodiment, the at least one pressure control valve is configured to provide pressure medium at its working connection, which pressure medium has an output pressure value that corresponds to or is assigned to the control current intensity of the control current with which the pressure control valve is actuated. If the actuating device has only one pressure control valve, the control pressure value is equal to the output pressure value. If the actuating device has two pressure control valves, the control pressure value is equal to the difference between the output pressure values ​​of the two pressure control valves. In particular, the control pressure value can therefore have negative values.

[0014] A computing unit according to the invention, e.g. a control unit of a hydraulic system of a mobile work machine, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0015] Implementing a method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is also advantageous, as this entails particularly low costs, particularly if an executing control unit is also used for other tasks and is therefore already present. Suitable data storage devices for providing the computer program include, in particular, magnetic, optical, and electrical storage devices, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0016] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0017] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0018] The invention is illustrated schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing. Character description Fig. 1 shows an exemplary arrangement with a hydraulically operated slide valve, whereby control pressures are generated via electromagnetically operated pressure control valves. Fig. Figure 2 shows an example relationship between piston position and control pressure, as it can occur in a slide valve. Fig. 3 shows an example of a relationship between a pressure difference caused by the pressure drop at constrictions and a volume flow, as it occurs in a slide valve / / an arrangement according to Fig. 1 can be given. Fig. 4 illustrates steps of a method according to an embodiment of the invention. Detailed description of the drawing

[0019] Fig. 1 shows an exemplary arrangement with a hydraulically operated slide valve 2 or control valve, wherein control pressures are generated via electromagnetically operated pressure control valves 4 (so-called pilot valves), ie the slide valve is hydraulically actuated in an electromagnetically piloted manner.

[0020] The spool valve 2 (or directional control valve) has a spool or piston 6 (also referred to as the main spool or main piston), whose position (longitudinally) can be continuously shifted between end positions or end stops. Volume flows to and from a hydraulic consumer 8 (e.g., a hydraulic cylinder), which is hydraulically connected to working ports of the spool valve 2, occur according to the position of the piston. In a spool valve, openings can be guided through the valve body in which the piston is mounted, and grooves can be provided on the circumferential surface of the piston.

[0021] The spool valve is actuated hydraulically, i.e. the piston has actuating surfaces or pressure surfaces, the pressurisation of which by means of a pressurised (control pressure or pilot pressure) pressure medium (hydraulic fluid, in particular a hydraulic oil) causes a force on the piston. The actuating surfaces delimit chambers formed in the valve body of the spool valve 2, also referred to in this application as control pressure chambers, into which chambers the pressure medium containing the control pressure can flow in order to pressurise the actuating surfaces. In the example shown, two opposing actuating surfaces are provided on the piston, which delimit two control pressure chambers in the valve body supplied with pressure medium via the pressure regulating valves 4. If the actuating surfaces have the same surface area, the force acting on the piston results from the pressure difference between the control pressures in the two control pressure chambers.If the area is different, the difference must be taken into account accordingly.

[0022] In addition to the hydraulic actuation by the control pressures, spring elements 10 are provided which cause opposing spring forces on the piston, so that without control pressures (or with equal forces caused by the control pressures) the piston 6 is adjusted to a neutral position not shown in more detail.

[0023] The piston position results from the interaction between control pressures and spring characteristics. This is exemplified in Fig. 2, in which the piston position 20 is plotted against the (total) control pressure 22, i.e., the pressure difference between the control pressures, and a piston position characteristic curve 24 is shown. As can be seen, there are values ​​for the (total) control pressure for which the piston position does not change. This is the case, for example, below (in terms of magnitude) the preloads 26 of the spring elements and at the end stops 29, i.e., above (in terms of magnitude) corresponding upper control pressure values ​​28.

[0024] Referring to Fig. 1, the pressure control valves 4 each have a pressure connection 40 (or pressure supply connection), which is hydraulically connected, for example, via a hydraulic line to a control pressure medium source in which a sufficient pressure level is generated, for example, by a hydraulic pump, a return flow connection 42, which is hydraulically connected, for example, to a tank for pressure medium, and a working connection 44, which is hydraulically connected to one of the control pressure chambers of the slide valve 10. The pressure control valves 4 are each continuously adjustable between a first position, in which the working connection 44 is hydraulically connected to the return flow connection 42 and no volume flow of pressure medium is possible between the working connection 44 and the pressure connection 40, and a second position, in which the working connection 44 is hydraulically connected to the pressure connection 40 and no volume flow of pressure medium is possible between the working connection 44 and the return flow connection 42.The pressure control valves 4 are each pre-tensioned into the first position. The adjustment towards the second position is effected by an electromagnet to which an electrical control current can be applied. A hydraulic control line is also provided (typically internal to the respective pressure control valve) which directs the pressure of the pressure medium at the working port 44 to a control surface which effects an adjustment towards the first position. Overall, a pressure of the pressure medium at the working port 44 is maintained which is dependent on the electrical control current through the electromagnet. Each control current strength, i.e. each control current strength, can be assigned a pressure or pressure value, also referred to as the output pressure value, of the pressure medium at the working port 44, i.e., with regard to the actuation of the slide valve, each control current strength can be assigned a pressure value.Conversely, each desired (and technically possible) pressure value can be assigned an electrical control current strength with which the pressure value is achieved when the pressure control valve or its electromagnet is actuated with a control current that has the control current strength. If the piston is actuated, as in . Fig. 1, adjusted by two opposing control pressures, and two pressure control valves 4 are provided, a control pressure value or a pressure difference can be assigned to each pair of control currents, i.e., the difference between the two output pressure values, which is caused by the two control currents with the control currents. Conversely, each desired control pressure value or each desired (and technically possible) pressure difference can be assigned at least one pair of control currents, or generally several pairs of control currents.

[0025] To control the slide valve 2 by controlling the pressure control valves 4, an electronic controller 12 (i.e. a computing unit, e.g. a control unit of the hydraulic system or of a working machine in which it is used) is provided, which is designed to generate the electrical control currents or to initiate their generation. The pressure control valves can be controlled by means of a PWM signal (PWM: pulse width modulation or pulse length modulation), whereby the control currents result as control currents averaged (by inductances of the electromagnets); the control current strengths then depend, for example, on a duty cycle of the respective PWM signal. The control current strengths are thereby determined by the electronic controller 12 based on a control signal which, for example,as an operating signal by an operator input detected by a joystick 14, wherein the control current strengths are determined based on the level of the control signal (which corresponds, for example, to the joystick deflection).

[0026] The Fig. The exemplary slide valve 2 shown in Figure 1 is actuated by two control pressures. Alternatively, actuation can also occur with only one control pressure, with the pressure being applied via a (single) pressure control valve controlled by an electric control current, and with a spring element that preloads the piston in a direction opposite to the control pressure. The above statements apply accordingly in this case.

[0027] In general, therefore, at least one pressure regulating valve, e.g. one or two pressure regulating valves, is provided with which the slide valve is actuated, i.e. with which its piston is adjusted. An actuating device for the slide valve is therefore formed, which has at least one pressure regulating valve. The actuating device can furthermore have at least one spring element. The actuating device causes the piston of the slide valve to be adjusted, wherein the at least one electromagnetic pressure regulating valve is controlled by at least one electrical control current, so that a control pressure value is assumed at at least one working output (which corresponds to the control current strength of the at least one electrical control current). If there is only one pressure regulating valve (i.e. only one hydraulically pressurised actuating surface of the slide valve), the control pressure value is the output pressure value of this one pressure regulating valve.With two pressure control valves (i.e. two oppositely acting hydraulically pressurized actuating surfaces of the slide valve), the control pressure value is given by the difference between the output pressure values ​​of the two pressure control valves.

[0028] In Fig. 1 shows a situation in which a displacement or movement 50 of the piston 6 occurs. Accordingly, there is a (displacement) volume flow 52 (of pressure medium) into one of the control pressure chambers and a (displacement) volume flow 52 out of the other of the control pressure chambers. These volume flows each cause a pressure drop 56 at throttle elements, valves or other structural constrictions 16 that are located between the respective pressure control valve 4 and the control pressure chamber connected to it. The pressure drops 56 result in an effective (total) control pressure 58 (or an effective pressure difference) at the piston, which is different from the (total) control pressure that would result at the pressure control valves 4 in a stationary state, i.e. with the piston not moving, for given control current intensities. The pressure difference resulting from the pressure drop at the constrictions means that the actual oreffective control pressure value acting on the piston from the control pressure value corresponding to the control current strengths or the control current strength.

[0029] Fig. Figure 3 shows a corresponding relationship between a pressure difference 60, caused by the pressure drop at constrictions 52, and a volume flow for a slide valve connected in this way. Pressure 62 is plotted against volume flow 64.

[0030] Fig. 4 illustrates steps of a method according to an embodiment of the invention. Steps of the method sequence are shown on the right of the figure, which are illustrated on the left using corresponding diagrams. In the diagrams, respective variables (signal level, various pressures, piston position / speed) are plotted as respective curves against time 70 as the horizontal axis. The method represents a method for controlling an actuating device of a slide valve having an adjustable piston with at least one actuating surface that delimits a corresponding at least one control pressure chamber. The actuating device has at least one electromagnetic pressure control valve with a working connection that is hydraulically connected to one of the at least one control pressure chamber.The at least one pressure control valve is designed to provide pressure medium at the working outlet (provided that the pressure control valve itself is supplied with pressure medium at a sufficiently high pressure, ie provided that pressure medium at a sufficiently high pressure is provided at a pressure connection of the pressure control valve, e.g. by a pressure medium source), which has an output pressure that corresponds to a control current strength of a control current with which the pressure control valve is controlled.

[0031] In step 110, a control signal, e.g., a joystick signal, can be detected. The diagram shows an exemplary control signal curve 72 plotted against time 70, with the vertical axis showing the control signal level 74 (which corresponds, e.g., to the deflection of the joystick) in suitable units. The control signal indicates, e.g., a desired speed of a hydraulic consumer supplied with pressure medium via the slide valve (e.g., a hydraulic cylinder, as in Fig. 1). The corresponding volume flows to and from the hydraulic consumer are controlled by the slide valve, i.e., they correspond to specific piston positions. Accordingly, the at least one pressure control valve can be controlled with at least one electrical control current, wherein the pressure medium provided at the at least one working connection has a control pressure value that corresponds to or is assigned to at least one control current strength of the at least one electrical control current.

[0032] In step 120, a target control pressure value can be determined from the control signal. A target control pressure curve 76 determined from the control signal curve 72 is plotted against time 70 in the diagram, with the height 78 of the target control pressure corresponding to the vertical axis (again in suitable units). The target control pressure value is determined such that the displacement of the piston of the slide valve corresponds to the control signal when the target control pressure value acts on the piston. The target control pressure value is the pressure value from which, when it is actually applied, the force acting on the piston results, i.e., with a piston pressurized on both sides (as in Fig. 1) the pressure difference between the output pressures of the pressure control valves and, in the case of a piston pressurized on one side, the one output pressure. The diagram shows the case of a piston pressurized on both sides, so the target control pressure value can also assume negative values ​​as a pressure difference.

[0033] When determining the target control pressure value from the control signal, the characteristic of the valve, such as Fig. 2. (Start) control pressures 27, which are selected according to the preloads of the spring elements, are shown. The (start) control pressures 27 (which are assumed when the control signal is not equal to zero) are selected such that the force caused by them on the piston is somewhat smaller in magnitude than the force caused by the preloads of the spring elements in order to prevent unwanted opening of the valve due to component tolerances, i.e. a (start) control pressure is specified which does not yet cause any valve movement or valve opening. As can be seen, these should be overcome by the target control pressure value in order to correspond to the control signal. Since the target control pressure value corresponds to a piston position, a target piston position (not shown) can also be determined from the control signal in an analogous manner (instead of or in addition to the target control pressure value).

[0034] In step 130, a desired piston speed is determined from the target control pressure value or the target control pressure curve 76, which results when the target control pressure value is actually applied. A corresponding piston speed curve 80 is shown in the diagram. A corresponding piston position curve 82 is also shown. The desired piston position can, for example, also be determined directly from the control signal or correspond to it. In this case, the desired piston speed can be determined from the desired piston position (by differentiation and / or filtering). The vertical axis corresponds to the height 84 of the desired piston speed and the position 86 (relative to a reference position) of the piston, each in suitable units. Here it can be seen that the piston movement starts later than the target control pressure, and the maximum position, i.e.an end stop is reached while the desired control pressure is still increasing.

[0035] In step 140, based on the desired piston speed determined in step 130, a pressure difference value (or a pressure correction value or a pressure drop value) is determined, which is caused by the pressure drop caused by the volume flow of pressure medium through constrictions between the pressure control valve and the control pressure chambers. For this purpose, a functional relationship between volume flow and pressure difference or pressure difference values, such as in Fig.3. The relationship can be determined from the known structure of the hydraulic system, i.e. in particular the geometry of the hydraulic connections between the pressure control valves and the control pressure chambers or the constrictions located therein, e.g. by calculations using corresponding equations (e.g. throttle equation and / or orifice equation and / or similar equations) and / or simulations. Additionally or alternatively, pressure measurements or other measurements obtained in test runs can be used. The relationship can be stored in the electronic control system in the form of corresponding formulas and / or characteristic maps. The volume flow results from the piston speed if the piston diameter is known.

[0036] Shown is a pressure difference curve 90 (the pressure difference value), which results from the piston speed curve 80 (the desired piston speed), with the pressure value 92 of the pressure drop plotted on the vertical axis. Depending on the different directions of movement of the piston, the pressure difference can assume positive and negative values.

[0037] In step 150, a compensated target control pressure value is determined, the height 96 of which, or pressure value, is plotted on the vertical axis. The compensated target control pressure value is determined from the target control pressure value and the pressure difference value, i.e., as the sum of the target control pressure value and the pressure difference value (each related to the same point in time). A corresponding compensated target control pressure curve 94 is shown in the corresponding diagram. Instead of the sum, a difference can also be formed to determine the compensated target control pressure value if a different sign is selected for one of the variables.

[0038] In step 160, the electrical control currents or the electrical control current (in the case of a piston pressurized on one side) are determined according to the compensated target control pressure, i.e., such that in the static case (without piston movement), the compensated target control pressure value would be reached if the pressure control valves or the pressure control valve (or their electromagnets) were controlled with control currents having the control currents or with a control current having the control current. Furthermore, the pressure control valves or the pressure control valve are controlled with control currents having the control currents determined in this way or with a control current having the control current strength determined in this way.

Claims

[1] Method for controlling an actuating device of a slide valve (2) which has a piston (6) with at least one actuating surface which delimits a corresponding at least one control pressure chamber, wherein the actuating device has at least one electromagnetic pressure regulating valve (4) each with a working connection (44) which is hydraulically connected to a corresponding one of the at least one control pressure chamber, wherein the at least one pressure regulating valve is controllable with at least one electrical control current, wherein pressure medium provided at the at least one working connection has a control pressure value which corresponds to at least one control current strength of the at least one electrical control current, comprising: Detecting (110) a control signal (72) and determining (120, 130) a target control pressure value (76) and a desired piston speed (80) from the control signal; Determining (140) from the desired piston speed a pressure difference value (90) which corresponds to the pressure drop (56) which occurs during a piston movement (50) at the desired piston speed due to the at least one volume flow (52) between the working connection of the at least one pressure control valve and the corresponding at least one control pressure chamber; Determining (150) a compensated target control pressure value (94) as the sum or difference of the target control pressure value (76) and the pressure difference value (90); and Controlling (160) the at least one pressure control valve (4) with at least one electrical control current having at least one control current intensity corresponding to the compensated target control pressure value. [2] Method according to claim 1, wherein the control signal (72) is determined with an operating device, in particular a joystick (14), which is configured to detect a user input. [3] Method according to claim 1 or 2, wherein the control signal (72) corresponds to a desired piston position of the piston (6); wherein the control signal is in particular a desired speed of a hydraulic consumer (8) which is supplied with pressure medium via the slide valve (2). [4] Method according to claim 3, wherein the target control pressure value (76) is the control pressure value at which the piston (2) assumes the desired piston position in a stationary state. [5] Method according to claim 3 or 4, wherein the desired piston speed (80) is determined from a profile of the desired piston position (82); in particular by differentiation or filtering. [6] Method according to one of the preceding claims, wherein the actuating device has at least one spring element (10) which effects or exerts a preload on the piston (2), wherein the preload by the at least one spring element is taken into account in the determination (10) of the target control pressure value (76). [7] Method according to one of the preceding claims, wherein at least one end stop of the piston (2) is taken into account in the determination (120) of the target control pressure value (76). [8] Method according to one of the preceding claims, wherein the determination (140) of the pressure difference value (90) is based on a relationship between the at least one volume flow (52) and the pressure difference value, which is given by at least one formula and / or at least one characteristic map. [9] Method according to claim 8, wherein the at least one formula and / or the at least one characteristic map is determined by a throttle equation and / or an orifice equation and / or simulations and / or test runs. [10] Method according to one of the preceding claims, wherein each of the at least one pressure control valve (4) is arranged to provide pressure medium at its working connection (44) which has an output pressure value which corresponds to or is assigned to the control current intensity of the control current with which the pressure control valve is controlled; wherein the control pressure value is equal to the output pressure value if the actuating device has only one pressure control valve, or the control pressure value is equal to the difference between the output pressure values ​​of the two pressure control valves if the actuating device has two pressure control valves (4). [11] Computing unit (16) comprising a processor configured to carry out the method according to any one of the preceding claims. [12] A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method according to claims 1 to 10. [13] A computer-readable data carrier on which the computer program according to claim 12 is stored.

Images