Method for determining the switching position of a directly controlled hydraulic valve, method for controlling a directly controlled hydraulic valve, hydraulic valve and hydraulic system

Abstract

Method for determining the switching position of a directly controlled hydraulic valve (11), wherein the hydraulic valve (11) comprises a valve element (12) and an electromagnet (13) with an armature (A) and a coil (S), wherein the armature (A) is coupled to the valve element (12) for joint movement between different switching positions, wherein the method is carried out by a control unit (14) assigned to the hydraulic valve (11) and comprises the following steps: - impressing a coil current in the coil (S) of the electromagnet (13), wherein the coil current is composed of an actuating current and a measuring current profile (MS1, MS2) superimposed on the actuating current; - Recording the impressed coil current over time (t) as a current curve; - determining a compensation characteristic value of the hydraulic valve (11) on the basis of the detected current curve; - determining a temperature- and inductance-dependent position characteristic value of the electromagnet (13) of the hydraulic valve (11) on the basis of the detected current profile; and - Calculating the switching position of the hydraulic valve (11) based on the compensation characteristic value and the position characteristic value; characterized in that the temperature- and inductance-dependent position characteristic value is a current decrease rate in the detected current profile, which is determined during a decay interval of the measuring current profile (MS1, MS2).

Description

[0001] The present invention relates to a method for determining the switching position of a directly controlled hydraulic valve, a method for controlling a directly controlled hydraulic valve as well as a hydraulic valve and a hydraulic system.

[0002] In directly controlled, i.e. electromagnetically actuated, hydraulic valves, a valve element of the hydraulic valve is coupled to an armature of an electromagnet of the hydraulic valve for joint movement between different switching positions of the hydraulic valve. This coupling can, for example, consist of a fixed connection between the armature and the valve element or in the contact of a valve tappet that is firmly connected to the armature against the valve element. By energizing a coil of the electromagnet, the armature and the valve element are moved between the different switching positions against the force of a return element, usually a return spring. By moving the valve element between the different switching positions, at least one connection of the hydraulic valve is blocked or released. As a result, a volume flow of hydraulic fluid flows through the hydraulic valve that depends on the switching position of the valve element.The valve element can be a valve piston or a valve seat element.

[0003] The variable switching position of the valve element creates a variable opening cross-section of the hydraulic valve, which in turn provides a variable volume flow through the hydraulic valve. For this purpose, a regulated actuating current is injected into the coil of the electromagnet, upon which the switching position of the hydraulic valve depends. However, the actual switching position of the hydraulic valve also depends on other boundary conditions (disturbance variables), such as friction- and / or temperature-dependent hysteresis effects, the system pressure of a higher-level hydraulic system, and the ambient or system temperature, which can, for example, influence the properties of the electromagnet.

[0004] In order to adjust the flow rate provided by such a directly controlled hydraulic valve as precisely and reproducibly as possible, it is therefore desirable to compensate for such disturbances as much as possible. Such compensation is typically achieved by providing a dedicated position sensor that measures the actual current switching position of the hydraulic valve, i.e., the switching position of the valve element and / or the armature. Based on the measured switching position, a downstream position control can then be performed to regulate the flow rate provided by the hydraulic valve.

[0005] However, such dedicated position sensors for detecting the switching position of a hydraulic valve are usually complex components, the use of which not only increases costs, but also increases the required installation space and also increases the complexity and thus the susceptibility to errors of the overall system.

[0006] From DE 10 2022 202 224 B3, methods are also known which enable the switching position of a directly controlled hydraulic valve with two electromagnets for actuating the valve element on the non-actuated electromagnet to be determined.

[0007] From the generic DE 10 2015 213 206 A1 a method for determining a position of a movable armature of an electromagnetic actuator is known, in which the position is determined via the frequency of an oscillating signal in an oscillating system.

[0008] From DE 10 2018 203 215 A1 a method for determining the position of a solenoid valve is known, in which the inductance of the coil is determined from a detected coil current and the position of a valve tappet is deduced from the determined inductance.

[0009] Against this background, it is an object of the present invention to provide an improved possibility for controlling the volume flow via a directly controlled hydraulic valve, which is also applicable to directly controlled hydraulic valves with only a single electromagnet for actuating the valve element.

[0010] The problem is solved, first, by a method for determining the switching position of a directly controlled hydraulic valve according to claim 1. The hydraulic valve comprises a valve element and an electromagnet with an armature and a coil. The armature is coupled to the valve element for joint movement between different switching positions. The method is carried out by a control unit assigned to the hydraulic valve and comprises the following steps: - Impressing a coil current in the coil of the electromagnet, wherein the coil current is composed of an actuating current and a measuring current profile superimposed on the actuating current; - Recording the impressed coil current over time as a current curve; - Determining a compensation characteristic of the hydraulic valve based on the detected current curve; - Determining a position characteristic of the hydraulic valve based on the detected current curve; and - Calculate the switching position of the hydraulic valve based on the compensation characteristic value and the position characteristic value.

[0011] According to the invention, the electromagnet of the hydraulic valve is not only supplied with the actuating current to switch the hydraulic valve. Rather, the measuring current profile is superimposed on the actuating current, and the coil current impressed in the coil of the electromagnet, which represents the combination of the actuating current and the measuring current profile, is measured. In other words, the actuating current and the measuring current profile are impressed in the coil of the electromagnet simultaneously and recorded together as a current waveform. The compensation characteristic value and the position characteristic value are determined from the recorded current waveform in order to calculate the actual current switching position of the hydraulic valve. Thus, by superimposing the measuring current profile on the actuating current and by recording the impressed coil current, the switching position of the hydraulic valve can also be determined on the actuated electromagnet of the hydraulic valve.This makes it possible to perform precise position or volume flow control even with directly controlled hydraulic valves with only a single electromagnet to actuate the valve element, without the need for a dedicated position sensor in the form of a separate component. The method according to the invention can save both costs and installation space, and it also increases the reliability of the system in which the hydraulic valve is used, since fewer system components are required overall.

[0012] The term "determination" as used here encompasses one or more process steps such as controlling, measuring, and / or calculating to determine the corresponding value. System-specified values can also be used for the determination.

[0013] The control unit comprises, in particular, a current sensor for measuring the current in the coil of the electromagnet and a solenoid controller that controls the actuation of the electromagnet in a generally known manner using a supply voltage. The control unit is, in particular, an electronic control unit.

[0014] Preferably, the measuring current profile has a maximum measuring amplitude dependent on the current actuation current. In particular, the measuring current profile has a variable measuring amplitude that depends on the actuation amplitude of the current actuation current. In particular, the current actuation current is recorded separately, and the maximum measuring amplitude is set depending on the recorded current actuation current. It should be noted that temporary current peaks above the set maximum measuring amplitude can also occur. However, due to their short duration and the inertia of the overall system, these peaks do not lead to a movement of the valve element that is significant for the volume flow through the hydraulic valve.For hydraulic valves where there is a particularly large amplitude difference between the minimum and maximum actuating current, the variable maximum measuring amplitude can ensure that the amplitude of the measuring current profile is not lost in the actuating amplitude of the actuating current.

[0015] Furthermore, it is expedient if the measuring current profile has a maximum measuring amplitude corresponding to a dither amplitude. In particular, the dither amplitude amounts to up to 20% of the actuation amplitude of the current actuation current of the electromagnet. The use of dither signals is known, for example, from the field of continuous hydraulic valves. A rectangular alternating current signal (dither frequency) with a low amplitude (dither amplitude) is superimposed on an actuation direct current in order to cause the valve element of the continuous hydraulic valve to oscillate, thereby avoiding static friction and reducing hysteresis effects. In abstract terms, the dither amplitude of a hydraulic valve corresponds to an amplitude that leads to a slight movement of the valve element, which in particular lies above a minimum actuation current of the hydraulic valve.The fact that the maximum measurement amplitude "corresponds to a dither amplitude" should also be understood to mean that temporary current peaks above the dither amplitude can also occur. However, due to their short duration and the inertia of the overall system, these peaks do not lead to a movement of the valve element that is significant for the volume flow through the hydraulic valve. The measurement current profile can therefore, in particular, have a maximum measurement amplitude that lies above a minimum actuation current of the hydraulic valve and itself leads to slight movements of the valve element, which, however, do not have a significant influence on the switching position of the hydraulic valve. It is also conceivable that the measurement current profile has a measurement frequency that corresponds to a dither frequency.

[0016] Preferably, the compensation characteristic of the hydraulic valve is a temperature-dependent compensation characteristic of the electromagnet. In particular, the temperature-dependent compensation characteristic of the electromagnet is the electrical resistance, in particular the copper resistance, of the coil of the electromagnet, which is determined during a holding interval of the measurement current profile in which the measurement amplitude is kept constant. Alternatively, the temperature-dependent compensation characteristic of the electromagnet is a current rise rate in the recorded current curve, which is determined during a rise interval of the measurement current profile in which the measurement amplitude increases. This allows a temperature dependency to be taken into account and compensated for when determining the switching position of the hydraulic valve.

[0017] According to the invention, the position characteristic of the hydraulic valve is a temperature- and inductance-dependent position characteristic of the electromagnet. According to the invention, the temperature- and inductance-dependent position characteristic of the electromagnet is a current decrease rate in the detected current curve, which is determined during a decay interval of the measured current profile in which the measurement amplitude decreases. The temperature dependence can be compensated by offsetting it with the compensation characteristic. The inductance of an electromagnet depends in particular on the position of the armature within the coil, so that the position of the armature in the coil and thus the switching position of the hydraulic valve can be calculated via the inductance dependence of the position characteristic.

[0018] Furthermore, the problem is solved by a method for controlling a directly controlled hydraulic valve. The hydraulic valve comprises a valve element and an electromagnet with an armature and a coil. The armature is coupled to the valve element for joint movement between different switching positions. The method is carried out by a control unit assigned to the hydraulic valve and comprises the following steps: - Determining the switching position of the hydraulic valve by the method described above for determining a switching position of a hydraulic valve; and - Controlling the switching position of the hydraulic valve based on the determined switching position.

[0019] By controlling the switching position of the hydraulic valve, the volume flow flowing through the hydraulic valve can be controlled. Thus, the invention implements a position or volume flow control for the hydraulic valve, which no longer requires the use of a separate position sensor in the form of a standalone component and can also be used in directly controlled hydraulic valves with only a single electromagnet to actuate the valve element.

[0020] Furthermore, the problem is solved by a hydraulic valve with a valve element and an electromagnet with an armature and a coil. The armature is coupled to the valve element for joint movement between different switching positions. The hydraulic valve further comprises an integrated control unit configured to perform one of the above-described methods for determining a switching position of a directly controlled hydraulic valve and for controlling a directly controlled hydraulic valve.

[0021] Furthermore, the object is achieved by a hydraulic system with a hydraulic valve. The hydraulic valve comprises a valve element and an electromagnet with an armature and a coil. The armature is coupled to the valve element for joint movement between different switching positions. The hydraulic system further comprises a control unit assigned to the hydraulic valve, which is configured to carry out one of the above-described methods for determining a switching position of a directly controlled hydraulic valve and for regulating a directly controlled hydraulic valve. The control unit is preferably integrated into the hydraulic valve.

[0022] The invention is explained in more detail below with reference to embodiments shown in the figures. These schematically show: Fig. 1 shows a hydraulic system with a direct-acting hydraulic valve according to an exemplary embodiment of the present invention; Fig. 2 a flowchart of a method according to the invention; Fig. 3 a diagram illustrating a first measuring current profile; and Fig. 4 a diagram illustrating a second measuring current profile.

[0023] In Fig. 1 shows a hydraulic system 10 of an exemplary embodiment of the present invention with a directly controlled hydraulic valve 11 and an electronic control unit 14 assigned to the hydraulic valve 11. The hydraulic valve 11 comprises a valve element 12, an electromagnet 13, and a return element 15, which is schematically illustrated here as a return spring. The hydraulic valve 11 is a directly controlled, proportional 2 / 2-way seat valve. In the present embodiment, the valve element 12 is therefore a valve closing element which, in the closed switching position of the hydraulic valve 11, rests against a seat in the housing of the hydraulic valve 11 and blocks the two ports of the hydraulic valve 11 from one another, so that no hydraulic fluid can flow via the hydraulic valve 11.

[0024] The electromagnet 13 comprises a coil S and an armature A. By energizing the coil S of the electromagnet 13 with an actuating current, the armature A of the electromagnet 13, which is coupled to the valve element 12 for movement between the different switching positions of the hydraulic valve 11, moves with the valve element 12 against the restoring force of the restoring element 15. Depending on the actuating amplitude of the actuating current, the hydraulic valve 11 can be brought into different switching positions continuously between its closed switching position and its fully open switching position and a variable volume flow of hydraulic fluid can be provided via the hydraulic valve 11.

[0025] The coil S is energized by the control unit 14 assigned to the hydraulic valve 11, which is shown here as separate from the hydraulic valve 11. The signal connection between the electromagnet 13 of the hydraulic valve 11 and the control unit 14 is shown in Fig. 1 is shown schematically as a dashed line. However, it is also conceivable that the control unit 14 is integrated into the hydraulic valve 11, for example, in a housing of the electromagnet 13, and is in turn connected via signaling to a higher-level control unit of the hydraulic system 10.

[0026] The control unit 14 thus actuates the hydraulic valve 11 via its electromagnet 13. Furthermore, the control unit 14 is configured to carry out the method according to the invention for determining the switching position of the hydraulic valve 11. For this purpose, the control unit 14 superimposes a measuring current profile on the actuating current for switching the hydraulic valve 11 and records the coil current impressed in the coil S over time t as a current profile, as explained in detail below.

[0027] In Fig. 3 shows an exemplary first measurement current profile MS1 over time t. For the first measurement current profile MS1 from Fig. 3, the measurement amplitude IM is increased during a rise interval T1, T1' (time t1 to t2, t2') up to a defined maximum measurement amplitude IMmax, held at the maximum measurement amplitude IMmax during a first hold interval T2, T2' (time t2, t2' to t3), then the voltage for generating the coil current is removed during a decay interval T3, T3' (time t3 to t4, t4') until the measurement amplitude IM has reached a defined minimum measurement amplitude IMmin, and finally, the measurement amplitude IM is held at the minimum measurement amplitude IMmin during a second hold interval T4, T4' (time t4, t4' to t5). Therefore, no voltage is applied to the coil during the decay interval T3, T3'. As a result, the coil current drops during the decay interval T3, T3' in freewheeling from the defined maximum measuring amplitude IMmax to the defined minimum measuring amplitude IMmin and is maintained there until time t5.In this case, the time interval t1 to t5 corresponds to a dither period of the hydraulic valve 11.

[0028] Depending on how far the armature A is located within the coil S, i.e. the current position of the valve element 12, the inductance of the coil S varies, which is why a different length of the decay interval T3, T3' of the measuring amplitude IM results in freewheeling. Fig. 3 shows a first decay interval T3 and a second decay interval T3', each representing the time required for the measurement amplitude IM to decrease from its defined maximum value IMmax to the defined minimum value IMmin. The longer second decay interval T3' (dashed curve in Fig. 3) corresponds to a case in which the armature A is located further inside the coil S, so the inductance of the coil S is higher than in the case of the shorter decay interval T3 (solid curve in Fig. 3). The switching position of the hydraulic valve 11 can be derived from the length of the decay interval T3, T3'. Fig. 3 it can also be seen that the length of the rise interval T1, T1' also depends on the position of the armature A within the coil S.

[0029] In this case, the first measuring current profile MS1 is Fig. 3, a dither signal is used to measure the position of armature A within coil S. Accordingly, the dither period from t1 to t5 is selected such that for all switching positions of hydraulic valve 11 (positions of armature A within coil S), the decay interval T3, T3', during which the measurement amplitude IM drops in freewheeling from the maximum measurement amplitude IMmax to the minimum measurement amplitude IMmin, is shorter than half the dither period from time t3 to time t5. This ensures that a reliable determination of the switching position of hydraulic valve 11 is possible using the dither signal.

[0030] In Fig. 4 shows an alternative second measurement current profile MS2, which also alternates between a defined maximum measurement amplitude IMmax and a defined minimum measurement amplitude IMmin. In the second measurement current profile MS2 in Fig. 4, however, the measuring amplitude IM is not held at its maximum value IMmax, but is switched to freewheel mode immediately upon reaching the maximum measuring amplitude IMmax. Furthermore, the measuring amplitude IM is not held when the minimum measuring amplitude IMmin is reached, but is immediately increased again to the maximum measuring amplitude IMmax. In the second measuring current profile MS2, the rise time of the measuring amplitude IM during the rise interval T5, T5' is also one of the parameters to be recorded. This rise time depends on the position of the armature A in the coil S, which results in a shorter first rise interval T5 (solid curve in Fig. 4) and a longer second rise interval T5' (dashed curve in Fig. 4) for the two in Fig. 4 curves shown as examples. Analogous to Fig. 4 also results in a shorter first decay interval T6 and a longer second decay interval T6'. In a generally known manner, the length of the rising interval T5 and the length of the falling interval T6 of the measuring amplitude IM in the second measuring current profile MS2 are a measure of the position of the armature A within the coil S and the switching position of the hydraulic valve 11.

[0031] The maximum measurement amplitude IMmax and the minimum measurement amplitude IMmin are variable for both the first measurement current profile MS1 and the second measurement current profile MS2 and are set by the control unit 14 depending on the detected current actuation current or its actuation amplitude. In particular, in the present embodiment, the control unit 14 sets the maximum measurement amplitude IMmax such that it corresponds to a dither amplitude of the hydraulic valve 11. As a result, the Fig. 3 and Fig. The cyclical repetition of the measurement current profiles MS1 and MS2 shown in Figure 4 and the resulting alternation between the maximum measurement amplitude IMmax and the minimum measurement amplitude IMmin constantly keeps the valve element 12 of the hydraulic valve 11 in slight oscillating movements. These oscillating movements prevent static friction of the valve element 12 and thus reduce hysteresis effects when switching the hydraulic valve 11.

[0032] With reference to the Fig. 2 to 4, the method according to the invention for determining a switching position of the hydraulic valve 11, which is carried out by the control unit 14, is described below.

[0033] In step S1, a coil current is impressed into the coil S of the electromagnet 13, which consists of an actuating current and a measuring current profile MS1, MS2 superimposed on the actuating current. The actuating current is in this case a regulated direct current for switching the hydraulic valve 11 to a switching position dependent on the actuating current. As described above, Fig. 3 an exemplary first measuring current profile MS1 and in Fig. 4 shows an exemplary second measurement current profile MS2. The coil current impressed in the coil S in step S1 is thus, in a first alternative, the sum of the actuating current for switching the hydraulic valve 11 and the first measurement current profile MS1, or, in a second alternative, the sum of the actuating current for switching the hydraulic valve 11 and the second measurement current profile MS2.

[0034] In step S2, the impressed coil current is recorded over time as a current curve by the control unit 14. Step S2 takes place in parallel with the impression of the coil current from step S1.

[0035] In step S3, a compensation characteristic value of the hydraulic valve 11 is determined by the control unit 14 based on the detected current profile. In this case, the compensation characteristic value is a temperature-dependent compensation characteristic value. When using the first measurement current profile MS1, the temperature-dependent compensation characteristic value is the copper resistance of the coil S and is determined during the first holding interval T2, T2'. When using the second measurement current profile MS2, the temperature-dependent compensation characteristic value is the current rise rate of the coil current and is determined during the rise interval T5, T5' of the second measurement current profile MS2. The current rise rate of the coil current from the measurement current profile MS2 also depends on the position of the armature A in the coil S and the exciting voltage.The voltage dependence can be compensated in a known manner by measuring the supply voltage via which the control unit 14 actuates the electromagnet 13.

[0036] In step S4, a position characteristic of the hydraulic valve 11 is determined by the control unit 14 based on the detected current profile. When using both the first and the second measuring current profile MS1, MS2, the position characteristic is a temperature- and inductance-dependent position characteristic, namely the current decay rate of the coil current, and is determined during the decay interval T3, T3' of the first measuring current profile MS1 or during the decay interval T6, T6' of the second measuring current profile MS2.

[0037] In step S5, the control unit 14 calculates the current switching position of the hydraulic valve 11 based on the compensation characteristic value and the position characteristic value. The temperature dependence of the current decrease rate of the coil current (position characteristic value) is calculated using the determined copper resistance of the coil or the determined current rise rate of the coil current (compensation characteristics), which enables a precise calculation of the current switching position of the hydraulic valve 11. The coil S and the armature A of the electromagnet 13 of the hydraulic valve 11 are thus used in parallel both to actuate the valve element 12 and to determine the switching position of the hydraulic valve 11 based on the detected current profile.

[0038] As a result, in the optional step S6, the control unit 14 can regulate the switching position of the hydraulic valve 11 or the volume flow flowing through the hydraulic valve 11 on the basis of the determined switching position.

[0039] Thus, a switching position and volume flow control for the hydraulic valve 11 is realized, which does not require the use of dedicated position sensors and at the same time is also suitable for directly controlled hydraulic valves with only a single electromagnet for actuating the hydraulic valve. REFERENCE SYMBOL 10 Hydraulic system 11 direct-acting hydraulic valve 12 Valve element 13 Electromagnet 14 Control unit 15 Reset element A anchor IM measurement amplitude IMmax maximum measurement amplitude IMmin minimum measurement amplitude MS1 first measuring current profile MS2 second measuring current profile S coil S1 to S6 process steps t time t1 to t5 time points T1, T1' Rise interval of the first measuring current profile T2. T2' first hold interval of the first measurement current profile T3, T3' Decay interval of the first measuring current profile T4, T4' second hold interval of the first measuring current profile T5, T5' Rise interval of the second measuring current profile T6, T6' Decay interval of the second measuring current profile

Claims

[1] Method for determining the switching position of a directly controlled hydraulic valve (11), wherein the hydraulic valve (11) comprises a valve element (12) and an electromagnet (13) with an armature (A) and a coil (S), wherein the armature (A) is coupled to the valve element (12) for joint movement between different switching positions, wherein the method is carried out by a control unit (14) associated with the hydraulic valve (11) and comprises the following steps: - impressing a coil current in the coil (S) of the electromagnet (13), wherein the coil current is composed of an actuating current and a measuring current profile (MS1, MS2) superimposed on the actuating current; - Recording the impressed coil current over time (t) as a current curve; - determining a compensation characteristic value of the hydraulic valve (11) on the basis of the detected current curve; - determining a temperature- and inductance-dependent position characteristic value of the electromagnet (13) of the hydraulic valve (11) on the basis of the detected current profile; and - Calculating the switching position of the hydraulic valve (11) on the basis of the compensation characteristic value and the position characteristic value; characterized by that the temperature and inductance-dependent position characteristic is a current decrease rate in the detected current curve, which is determined during a decay interval of the measuring current profile (MS1, MS2). [2] Method according to claim 1, characterized by that the measuring current profile (MS1, MS2) has a maximum measuring amplitude (IMmax) that depends on the current actuation current. [3] Method according to one of the preceding claims, characterized by that the measuring current profile (MS1, MS2) has a maximum measuring amplitude (IMmax) which corresponds to a dither amplitude. [4] Method according to one of the preceding claims, characterized bythat the compensation characteristic of the hydraulic valve (11) is a temperature-dependent compensation characteristic of the electromagnet (13). [5] Method for controlling a directly controlled hydraulic valve (11), wherein the hydraulic valve (11) comprises a valve element (12) and an electromagnet (13) with an armature (A) and a coil (S), wherein the armature (A) is coupled to the valve element (12) for joint movement between different switching positions, wherein the method is carried out by a control unit (14) associated with the hydraulic valve (11) and comprises the following steps: - Determining the switching position of the hydraulic valve (11) by a method according to one of the preceding claims; and - Controlling the switching position of the hydraulic valve (11) based on the determined switching position. [6] Hydraulic valve (11) with a valve element (12) and an electromagnet (13) with an armature (A) and a coil (S), wherein the armature (A) is coupled to the valve element (12) for joint movement between different switching positions, wherein the hydraulic valve (11) further comprises an integrated control unit (14) which is designed to carry out a method according to one of the preceding claims. [7] Hydraulic system (10) with a hydraulic valve (11), wherein the hydraulic valve (11) comprises a valve element (12) and an electromagnet (13) with an armature (A) and a coil (S), wherein the armature (A) is coupled to the valve element (12) for common movement between different switching positions, wherein the hydraulic system (10) further comprises a control unit (14) assigned to the hydraulic valve (11) and designed to carry out a method according to one of claims 1 to 5. [8] Hydraulic system (10) according to claim 7, characterized by that the control unit (14) is integrated into the hydraulic valve (11).

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