Method for monitoring a switching position of an electromagnetically actuated fluid valve and fluid valve

Abstract

A method for monitoring a switching position of an electromagnetically actuated fluid valve is provided. The method according to the invention allows unwanted switching position changes US1 to US4 in the electromagnetically actuated fluid valve to be detected based on a detected current profile SV of the impressed coil current I, in particular based on anomalies A1 to A4 in the detected current profile SV. This provides a means of monitoring the switching positions of the electromagnetically actuated fluid valve without requiring the use of a separate position sensor.

Description

[0001] The present invention relates to a method for monitoring a switching position of an electromagnetically actuated fluid valve and to a fluid valve.

[0002] A fluid valve within the meaning of the present application is understood to mean, for example, a hydraulic valve or a pneumatic valve.

[0003] A well-known type of fluid valve is the binary-acting fluid valve, which has at least two ports and a switching element that can be moved into exactly two switching positions to create a first and a second state of the fluid valve. Such valves are also known as "black / white" valves. For example, the first state can be a closed state and the second state an open state. In this case, in the closed state, the switching element blocks at least one port of the fluid valve. In the open state, the switching element releases the at least one port of the fluid valve, so that this at least one port is connected to another port of the fluid valve in a fluid-conducting manner. Likewise, the first and second states of such a binary-acting fluid valve can differ, for example, in that they connect different ports of the fluid valve to one another.For example, in the first state, a first port A and a second port B can be fluidically connected to one another, and in the second state, the first port A and a third port C can be fluidically connected to one another. Various other configurations of the two states are conceivable. A key characteristic of a binary-acting fluid valve is that—in contrast to a proportional-acting fluid valve—a distinction is made between exactly two switching positions. The switching element can be, for example, a spool or a valve closing element that rests against a seat in the fluid valve, such as a valve cone.

[0004] In directly controlled (i.e., electromagnetically actuated), binary-acting fluid valves, the switching element is switched by an electromagnet against the force of a return element, such as a return spring. By energizing a coil of the electromagnet, an armature of the electromagnet and the switching element coupled to the armature are moved against the force of the return element from an initial switching position (e.g., closed or open) to a final switching position (e.g., open or closed). As soon as the coil is no longer energized, the return element automatically moves the switching element and the coupled armature of the electromagnet back to the initial switching position.The coupling between the armature and the switching element can, in a generally known manner, consist, for example, in a mechanical engagement of a valve tappet firmly connected to the armature on the switching element or in a continuous fixed connection between the armature and the switching element.

[0005] Due to external influences, such as vibrations and the like, it is fundamentally possible for the switching element to be moved back from its end switching position to its initial switching position by the return element, even though this is not desired. Such an unintentional change in the switching position of a fluid valve is problematic for the overall system in which the fluid valve in question is used. For applications where such an unintentional change in the switching position is more likely due to external conditions, it is therefore generally desirable to implement switching position monitoring to ensure that the desired switching position of the fluid valve is actually maintained.

[0006] For this purpose, the use of dedicated position sensors, for example, is known. These separate components detect the current position of the switching element in the fluid valve and thus enable monitoring of the current switching position. However, the use of such position sensors implemented as separate components leads to both increased costs and an increase in the potential sources of error in the overall system.

[0007] Against this background, it is an object of the present invention to provide a switching position monitoring device for an electromagnetically actuated fluid valve which makes the use of a separate position sensor superfluous.

[0008] The problem is initially solved by a method according to claim 1.

[0009] According to the invention, a method for monitoring the switching position of an electromagnetically actuated fluid valve is provided. The fluid valve comprises a switching element and at least one electromagnet with a coil and an armature, wherein the armature is coupled to the switching element for joint movement from an initial switching position to a final switching position. By energizing the coil, the armature is moved together with the switching element. The method comprises the following steps: - Impressing a coil current to switch the switching element by applying a coil voltage to the coil, - Recording the impressed coil current over time as a current curve, - Detection of an unwanted change in the switching position of the switching element based on an anomaly in the detected current curve.

[0010] Monitoring a switching position within the meaning of the present invention is understood in particular to mean monitoring the adherence or maintenance of a desired switching position. The coil current impressed in the coil of the electromagnet depends on the applied coil voltage (here initially: switching voltage), the ohmic resistance of the coil and the inductance of the coil. As a rule, a supply voltage is available in a higher-level fluid system in which the fluid valve is used, which is used to apply the coil voltage to the coil. In the simplest case, the supply voltage is applied directly to the coil. Typically, however, the coil voltage applied to the coil is set to defined values ​​by pulse width modulation (PWM) of the supply voltage or similar concepts. In this case, the coil voltage is initially set in particular to the value of a switching voltage.The ohmic resistance depends essentially on the temperature and changes sufficiently slowly that its rate of change is not reflected in the recorded current waveform. Accordingly, the ohmic resistance is assumed to be constant in the further analysis. However, any change in the inductance of the coil is directly reflected in the recorded current waveform. The inductance of the coil, in turn, is directly related to the position of the armature relative to the coil. A change in the position of the armature, which directly correlates with a change in the position of the switching element, always results in a change in the inductance of the coil. There is therefore a direct relationship between a change in the position of the switching element and the recorded current waveform. In other words, a change in the position of the switching element is directly reflected in the recorded current waveform.Thus, an unwanted change in the switching position of the switching element can be detected by identifying an anomaly in the recorded current waveform, in particular a deviation of the recorded current waveform from an expected current waveform or target current waveform. An anomaly is therefore understood to be a significant deviation from the target or expected value. In principle, the expected current waveform of the impressed coil current over a switching cycle of a fluid valve is known. However, if an unwanted change in the switching position occurs, this leads to an anomaly in the recorded current waveform (a significant target / expected value deviation), which can be identified. In this way, the switching position of the fluid valve or a change in the switching position of the fluid valve can be reliably monitored by identifying anomalies in the recorded current waveform.By detecting the applied coil current, unwanted switching position changes can be detected and the switching position of the fluid valve can be monitored accordingly, without the need for a separate position sensor. This saves both costs and installation space. Furthermore, the method according to the invention eliminates the need to actively influence the current flow in order to determine the current switching position of the fluid valve. Passive observation is entirely sufficient for this purpose.

[0011] The anomaly preferably comprises an increased gradient of the impressed coil current. In order to switch the switching element of the fluid valve from the initial switching position to the end switching position, the coil current is increased by applying the coil voltage equal to the value of the switching voltage. At a constant switching voltage, the coil current increases continuously, with the gradient decreasing as the coil current increases. During the movement of the switching element from the initial switching position to the end switching position, the detected current waveform experiences a characteristic kink, which is due to the change in inductance of the coil resulting from the movement of the armature. From this characteristic profile (kink) of the detected current waveform, the switching process of the switching element from the initial switching position to the end switching position can be recognized.After the switching element has moved to its end switching position, the coil current continues to rise continuously up to a switching current that depends on the applied switching voltage. However, if the switching element unintentionally moves back to the initial switching position during the coil current increase, the inductance in the coil changes due to the renewed movement of the armature and the coil current increases, for example, more quickly than if the switching element remained in the end switching position. Such an increased gradient of the impressed coil current can therefore directly detect an unintentional change in the switching position of the fluid valve. Depending on the circumstances, the increased gradient can be a predetermined relative value or can be determined and assessed using statistical methods, such as an outlier analysis or by calculating (moving) averages of the current curve over a plurality of switching cycles.

[0012] The anomaly expediently also includes an increased current value of the impressed coil current. In particular, the increased current value is higher than the switching current of the coil at a given switching voltage. When the switching operation is complete, the switching element is in the end switching position, and the coil current has reached the switching current dependent on the applied switching voltage, the coil current remains at this switching current as long as the coil voltage is kept constant at the value of the switching voltage. If, with an approximately constant coil current (switching current), the switching element inadvertently moves back to the initial switching position, this leads to an increase in the coil current above the switching current due to the change in the inductance of the coil. The increased current value thus makes it possible to directly detect an unintentional change in the switching position of the fluid valve.The same generally applies to the case of a constant coil current value, for example, also in the case of a constant holding current. Depending on the circumstances, the increased current value can be a predefined relative value, or it can be determined and evaluated based on statistical methods, such as an outlier analysis or by calculating (moving) averages of the current curve over a number of switching cycles.

[0013] The anomaly preferably comprises a positive slope of the impressed coil current. As a rule, the switching current induced by the switching voltage is significantly higher than the current that would be necessary to hold the switching element in the end switching position. In order to reduce power loss and thus increase the service life of the fluid valve, in particular of the electromagnet, it is therefore common practice to reduce the coil voltage applied to the coil after the switching operation from the switching voltage to a holding voltage. The holding voltage impresses a holding current in the coil that is below the switching current impressed by the switching voltage. By reducing the coil voltage, the impressed coil current drops from the switching current to the holding current that depends on the holding voltage. In other words, the impressed coil current has a negative slope until the holding current is reached.However, if the switching element is moved back from the end switching position to the initial switching position during this reduction of the coil current, the coil current temporarily increases again due to the change in inductance in the coil, thus having a positive gradient. This positive gradient of the applied coil current allows an unintentional change in the switching position of the fluid valve to be directly detected.

[0014] It is advantageous if the method further comprises the following steps: detecting an applied supply voltage and compensating the detected current waveform based on the detected supply voltage. Compensating the detected current waveform is understood in particular to mean, for example, calculating out fluctuations in the supply voltage. Fluctuations in the supply voltage can lead to fluctuations in the coil voltage and thus in the impressed coil current, which could potentially be falsely detected as anomalies. Therefore, if the actual applied supply voltage is known, such false detections of anomalies can be avoided by compensating the detected current waveform.

[0015] Preferably, applying the coil current to switch the switching element comprises the following steps: increasing the coil current to a switching current and reducing the coil current to a holding current. The switching current is not the current value at which the switching element performs the switching movement, but rather the saturation current in the coil, which depends on the switching voltage. As already described above, it is advantageous to reduce the switching current to a holding current to reduce power loss and increase the service life of the fluid valve.

[0016] It is useful to determine the holding current based on a characteristic profile in the recorded current waveform. As already described above, the recorded current waveform experiences a characteristic kink when the switching element moves from the initial switching position to the end switching position. This allows both the current switching position of the switching element to be identified and the absolute current value required to hold the switching element in the end switching position (minimum holding current) to be determined. To determine the holding current to be impressed into the coil, it is also advantageous to apply a safety factor to the determined minimum holding current.

[0017] Preferably, the method further comprises the following steps: outputting a switching signal to the fluid valve and / or outputting an error message to a higher-level control unit and / or outputting a warning to a user of the fluid valve and / or shutting down a fluid system connected to the fluid valve and / or increasing the coil voltage to restore the end switching position, in particular increasing the coil voltage to the switching voltage. Thus, upon detection of an unwanted change in the switching position of the fluid valve, an appropriate response can be triggered, for example, to avoid safety and other risks.

[0018] Advantageously, the method is carried out by a control unit assigned to the fluid valve. Preferably, the method is carried out by software implemented on the control unit, in particular a control program. Alternatively, the method can also be carried out by hardware implemented on the control unit, in particular a control circuit. The control unit assigned to the fluid valve can be a control unit integrated into the fluid valve or a higher-level control unit of a higher-level fluid system.

[0019] Furthermore, the object is achieved with an electromagnetically actuated fluid valve, in particular a hydraulic valve, having a switching element, at least one electromagnet, and a control unit associated with the fluid valve. The electromagnet has a coil and an armature coupled to the switching element. The control unit is designed to carry out the method according to one of the preceding claims. The control unit is preferably integrated into the fluid valve.

[0020] Preferably, the fluid valve is a binary-acting fluid valve. In particular, the binary-acting fluid valve comprises precisely one electromagnet. Such a "black / white" fluid valve, which has precisely two switching positions, is particularly suitable for implementing the method according to the invention. Alternatively, the concepts taught here are also applicable to a fluid valve with three or more clearly defined switching positions (non-proportional), in which two electromagnets can also be used to switch the switching element.

[0021] The fluid valve according to the invention makes it possible to ensure reliable monitoring of the fluid valve's switching positions without the need for a separate position sensor. This increases the operational reliability of the fluid valve while simultaneously saving both material costs and installation space.

[0022] The invention is explained in more detail below using an embodiment shown in the figures. These schematically show: Fig. 1 a side view of a fluid valve according to the invention according to an exemplary embodiment; Fig. 2 a partial sectional view of the fluid valve from Fig. 1; and Fig. 3 a diagram with an exemplary current and position curve over a switching cycle of the fluid valve from Fig. 1 to illustrate the method according to the invention.

[0023] Fig. 1 shows a side view of an exemplary embodiment of an electromagnetically actuated fluid valve according to the invention. The fluid valve in Fig. 1 is an electromagnetically operated hydraulic valve 10. More precisely, the hydraulic valve 10 is a directly controlled, binary-acting hydraulic valve 10 with an electromagnet 14 arranged in a housing 16 and a switching element 12 arranged in a valve housing 18 (see Fig. 2). The hydraulic valve 10 further comprises a connector 20 with a connector housing 22. Via the connector 20, the electromagnet 14 can be supplied with power and, if necessary, further signals and can communicate with a higher-level control unit of a higher-level hydraulic system (not shown). Furthermore, in this embodiment, a control unit 24 is arranged in the connector housing 22 (see Fig. 2). The control unit 24 can, of course, also be arranged in the valve housing 18, form a standalone component, or be part of a higher-level control unit of a higher-level hydraulic system. It is also conceivable, of course, that a device for wireless transmission of signals and data is provided next to the connector 20 or instead of the connector 20.

[0024] Fig. 2 is a purely schematic partial sectional view illustrating the essential elements and functions of the hydraulic valve 10. As in Fig. 2, the electromagnet 14 comprises a coil 26 and an armature 28. The armature 28 is coupled directly to the switching element 12 via a connecting rod 30 for joint movement. This can be a direct connection, as shown, or also, for example, a connection with a tappet or the like. The switching element 12, here a spool, is movably arranged in an axial bore 34 in the valve housing 18 of the hydraulic valve 10. The switching element 12 is urged from a side opposite the connecting rod 30 by a return spring 32 in the direction of the Fig. 2. In the present embodiment, the switching element 12 blocks two ports A and B of the hydraulic valve 10 in the initial switching position AS, so that no hydraulic fluid can flow via the hydraulic valve 10 between the ports A and B. In the initial switching position AS, the hydraulic valve 10 of the present embodiment is therefore closed.

[0025] If the coil 26 is energized, a magnetic force acts on the armature 28. As soon as this magnetic force overcomes the preload force of the return spring 32, the armature 28 moves with the switching element 12 in the direction of an end switching position ES of the hydraulic valve 10 until the end switching position ES is reached (see Fig. 3) and thus releases the connection between ports A and B. In the end switching position ES, the hydraulic valve 10 of the present embodiment is therefore open.

[0026] When the current supply to the coil 26 is subsequently switched off again, the return spring 32 presses the switching element 12 and the armature 28 back into the Fig. 2 shown initial switching position AS.

[0027] The following is based on Fig. 3 describes a method according to the invention for monitoring the switching position of the electromagnetically actuated hydraulic valve 10. In Fig. 3, the coil current I and the position P of the armature 28 or the switching element 12 are plotted against time t. Fig. 3 shows a current profile SV (solid line) and a position profile PV (dashed line), which correspond to a regular switching cycle of the hydraulic valve 10 from the initial switching position AS through the end switching position ES and back to the initial switching position AS. Deviations from the regular current profile SV and the regular position profile PV are shown as dotted lines.

[0028] The method according to the invention for monitoring the switching position of the electromagnetically actuated hydraulic valve 10 is carried out in the present case by a control program implemented in the control unit 24. First, the control unit 24 impresses a coil current I for switching the switching element 12 by applying a coil voltage to the coil 26. The impressed coil current I is recorded by the control unit 24 over time t as a current waveform SV. Based on the recorded current waveform SV, the control unit 24 detects unwanted switching position changes US1 to US4. Specifically, the control unit 24 is designed to detect anomalies A1 to A4 in the current waveform SV in order to detect the unwanted switching position changes US1 to US4, as will be described in more detail below.

[0029] For clarity, the diagram is in Fig. 3 is divided into time periods defined by times t0 to t7.

[0030] Between times t0 and t3, the coil voltage applied to the coil 12 has the value of a switching voltage, so that the coil current I is increased up to a switching current IS, which depends on the level of the switching voltage.

[0031] Between times t3 and t5, the coil voltage applied to the coil 12 has the value of a holding voltage, so that the coil current I drops between times t3 and t4 from the switching current IS to a holding current IH and then constantly maintains the value of the holding current IH.

[0032] After time t5, no coil voltage is applied to coil 12, so coil 12 is switched to freewheel mode. The coil current I subsequently drops from the holding current IH to zero.

[0033] At time t1, the magnetic force dependent on coil current I exceeds the preload force of return spring 32, so that armature 28 and switching element 12 begin to move from the initial switching position AS toward the end switching position ES. At time t2, armature 28 and switching element 12 have reached the end switching position ES. At time t6, the magnetic force dependent on coil current I drops again below the preload force of return spring 32, so that armature 28 and switching element 12 move back from the end switching position ES to the initial switching position AS by time t7.

[0034] As in the current SV in Fig. 3, the movements of the armature 28 with the switching element 12 between the times t1 and t2 as well as between the times t6 and t7 have an influence on the coil current I due to the change in inductance in the coil 26 triggered by the movement of the armature 28.

[0035] Due to the movement of the armature 28, the gradient of the coil current I flattens between times t1 and t2 up to a first turning point WP1 and then decreases to a second turning point WP2 at time t2, at which the armature 28 and the switching element 12 have reached the end switching position ES. From the second turning point WP2, the coil current increases again due to the applied coil voltage up to the switching current IS. The first turning point WP1 and the second turning point WP2 represent a characteristic profile in the recorded current curve SV, on the basis of which the control unit 24 determines the holding current IH. By detecting the second turning point WP2, the control unit 24 also clearly detects that the hydraulic valve 10 is now in the end switching position ES.

[0036] Between times t6 and t7, the movement of the armature 28 also causes the coil current I, which initially decreases in this range, to flatten until it increases again from a third reversal point WP3 to a fourth reversal point WP4 at time t7. At time t7, the armature 28 and the switching element 12 have returned to their initial switching position AS, so that the coil current I subsequently decreases from the fourth reversal point WP4 to zero. By detecting the fourth reversal point WP4, the control unit 24 thus clearly detects that the hydraulic valve 10 is back in the initial switching position AS.

[0037] The coil voltage applied to coil 26—and thus the coil current I impressed in coil 26—is controlled by control unit 24 via pulse width modulation (PWM) of an applied supply voltage. To compensate for the influence of voltage fluctuations in the applied supply voltage on the current waveform SV of the coil current I, control unit 24 detects the actual applied supply voltage.

[0038] In Fig. 3, unwanted switching position changes US1 to US4 in the position curve PV of the switching element 12 and the armature 28 are shown as dotted lines, which are detected by the control unit 24 based on anomalies A1 to A4 in the detected current curve SV. The unwanted switching position changes US1 to US4 in Fig. 3 illustrate situations in which the switching element 12 moves from the end switching position ES to the initial switching position AS, although the coil current I actually has a value at which the switching element 12 should remain in the end switching position ES. Reasons for the unwanted switching position changes US1 to US4 can lie in the environmental conditions under which the hydraulic valve 10 is used. For example, external vibrations on the hydraulic valve 10 can lead to the switching element 12 being moved back (possibly only temporarily) to the initial switching position AS. Fig. In the case illustrated in Figure 3, where the coil current I is reduced to the holding current IH to save energy and protect the electromagnet 14, the magnetic force of the electromagnet 14 on the switching element 12 also decreases, which in turn increases the likelihood of an unwanted change in switching position. Furthermore, damage to the hydraulic valve 10, for example, can also lead to unwanted changes in switching positions US1 to US4.

[0039] Every unwanted change in switch position US1 to US4 has an influence on the current curve SV of the coil current I, since the movement of the switching element 12 also causes the armature 28 to move within the coil 26, resulting in a change in inductance that is reflected in the recorded current curve SV. These changes in the recorded current curve SV represent anomalies A1 to A4 compared to the recorded current curve SV that would be expected under normal conditions (i.e., without unwanted changes in switch position US1 to US4). The current curve SV to be expected under normal conditions can, for example, be determined by the control unit 24 based on previous switching cycles. However, it is also conceivable that the expected current curve is permanently stored in the control unit 24. The anomalies A1 to A4 are therefore significant deviations from the expected value that are detected by the control unit 24 based on the recorded current curve SV.By detecting the anomalies A1 to A4, the control unit 24 detects the unwanted switch position changes US1 to US4.

[0040] Depending on the section of the switching cycle (or the current curve SV under normal conditions) in which the hydraulic valve 10 is located, the unwanted switching position changes US1 to US4 lead to different anomalies A1 to A4.

[0041] The Fig. The first unwanted change in switching position US1 shown in Figure 3 occurs in the section of the switching cycle in which the coil current I is still rising to the switching current IS after the switching element 12 has been switched to the final switching position ES. Due to the first unwanted change in switching position US1, the first anomaly A1 occurs in the form of an increased gradient of the impressed coil current I. The control unit 24 detects the first unwanted change in switching position US1 based on the increased gradient of the impressed coil current I.

[0042] Specifically, to detect an increased gradient of the impressed coil current I, the control unit 24 can, for example, detect the maximum gradient of the impressed coil current I between times t0 and t2 (switching element has switched). The gradient of the impressed coil current I generally flattens out as the coil current I increases. Consequently, the largest expected gradient of the coil current I over a switching cycle is close to time t0. Should the gradient of the impressed coil current I increase after time t2 beyond the maximum gradient detected up to time t2 (possibly subject to a safety factor of, for example, 5 to 10%), it can be concluded that there is an increased gradient of the impressed coil current I in the sense of the first anomaly A1.Alternatively or additionally, if the slope of the impressed coil current I increases again between time t2 and time t3, it can also be concluded that the first anomaly A1 has occurred. As already mentioned, the slope of the impressed coil current I continues to flatten as the coil current I increases until the switching current IS is reached. However, if the slope of the impressed coil current increases again from time t2 onwards instead of decreasing, it can also be concluded that the first anomaly A1 has occurred in the form of an increased slope of the impressed coil current I. A safety factor, for example, can also be used to detect a renewed increase in the slope of the impressed coil current I in order to minimize the occurrence of false detections.

[0043] The Fig. The second unwanted change in switching position US2 shown in Figure 3 occurs in the section of the switching cycle in which the coil current I has already reached the switching current IS after the switching element 12 has been switched to the end switching position ES and remains constant. Due to the second unwanted change in switching position US2, the second anomaly A2 occurs in the form of an increased current value of the impressed coil current I. The coil current I temporarily exceeds the switching current IS, which depends on the applied switching voltage. The control unit 24 detects the second unwanted change in switching position US2 based on the increased coil current I. Specifically, the increased coil current I can be detected based on a percentage or absolute increase in the expected switching current IS specified by the program. The second anomaly A2 simultaneously represents an increased gradient of the coil current I, which is also detected by the control unit 24.The control unit 24 also detects the second unwanted switch position change US2 based on the increased gradient of the impressed coil current I.

[0044] The Fig. The third unwanted switch position change US3 shown in Figure 3 occurs in the section of the switching cycle in which the coil current I is reduced to the holding current IH after the switching element 12 is switched to the end switching position ES. Due to the third unwanted switch position change US3, the third anomaly A3 occurs in the form of a positive gradient of the impressed coil current I. The control unit 24 detects the third unwanted switch position change US3 based on the positive gradient of the impressed coil current I. The third anomaly A3 simultaneously represents an increased gradient of the coil current I, which is also detected by the control unit 24. The control unit 24 also detects the third unwanted switch position change US3 based on the increased gradient of the impressed coil current I.

[0045] The Fig.The fourth unwanted change in switch position US4 shown in Figure 3 occurs in the section of the switching cycle in which the coil current I has reached the holding current IH after the switching element 12 has been switched to the end switching position ES. Due to the fourth unwanted change in switch position US4, the fourth anomaly A4 occurs in the form of a positive gradient of the impressed coil current I. The control unit 24 detects the fourth unwanted change in switch position US4 on the basis of the positive gradient of the impressed coil current I. The fourth anomaly A4 simultaneously represents an increased current value of the impressed coil current I compared to the holding current IH which is dependent on the holding voltage. The control unit 24 also detects the fourth unwanted change in switch position US4 on the basis of the increased current value of the impressed coil current I compared to the holding current IH.

[0046] As soon as the control unit 24 detects one of the unwanted switch position changes US1 to US4, the control unit 24 triggers a reaction to the detected unwanted switch position change. The reaction usually consists of forwarding a switching signal or error information to a higher-level control unit. This reaction can also consist of warning a user of the hydraulic valve 10, for example by triggering an alarm in the form of audio and / or visual signals. The reaction can also consist of shutting down a hydraulic system connected to the hydraulic valve 10 in order to avoid safety risks caused by the unwanted switch position change. The reaction can also consist of increasing the coil voltage to restore the end switch position ES, especially if the impressed coil current I has already been reduced to the holding current IH.A parallel or sequential combination of the described reactions upon detection of an unwanted switch position change US1 to US4 is also conceivable. For example, in parallel with an audio-visual warning to the user, the coil voltage can first be increased in order to restore the end switch position ES. The control unit 24 detects whether the end switch position 24 has actually been restored based on the characteristic inflection points WP1, WP2 in the recorded current waveform SV. If increasing the coil voltage does not restore the end switch position ES after a specified period of time, the control unit 24 can subsequently deactivate the hydraulic valve 10 and / or the higher-level hydraulic system.

[0047] Thus, the method according to the invention provides a possibility for reliably monitoring the switching positions of the electromagnetically actuated hydraulic valve 10 without the need for a separate position sensor. REFERENCE SYMBOL 10 Hydraulic valve 12 switching element 14 Electromagnet 16 housings 18 valve housing 20 plugs 22 connector housings 24 Control unit 26 coil 28 anchors 30 connecting rod 32 Return spring 34 axial bore A, B connections A1 to A4 anomalies AS initial switching position ES End switching position I coil current IH holding current IS switching current P Position of the armature or switching element PV position history SV current flow t time t0 to t7 time points US1 to US4 unwanted switch position changes WP1 to WP4 turning points

Claims

[1] Method for monitoring a switching position of an electromagnetically actuated fluid valve (10), wherein the fluid valve (10) has a switching element (12) and at least one electromagnet (14) with a coil (26) and an armature (28), wherein the armature (28) is coupled to the switching element (12) for joint movement from an initial switching position (AS) to an end switching position (ES), wherein by energizing the coil (26) the armature (28) is moved together with the switching element (12), and the method comprising the following steps: - impressing a coil current (I) for switching the switching element (12) by applying a coil voltage to the coil (26), - Recording the impressed coil current (I) over time (t) as a current curve (SV), - Detection of an unwanted change in the switching position (US1 to US4) of the switching element (12) based on an anomaly (A1 to A4) in the detected current curve (SV). [2] Method according to claim 1, characterized by that the anomaly (A1 to A4) includes an increased slope of the impressed coil current (I). [3] Method according to claim 1 or 2, characterized by that the anomaly (A1 to A4) includes an increased current value of the impressed coil current (I). [4] Method according to one of claims 1 to 3, characterized by that the anomaly (A1 to A4) includes a positive slope of the impressed coil current (I). [5] Method according to one of the preceding claims, characterized by that the method further comprises the following steps: - Detecting an applied supply voltage and - Compensate the detected current waveform (SV) based on the detected supply voltage. [6] Method according to one of the preceding claims, characterized by that the impression of the coil current (I) for switching the switching element (12) comprises: - Increasing the coil current (I) up to a switching current (IS), and - Reducing the coil current (I) to a holding current (IH). [7] Method according to claim 6, characterized by that the holding current (IH) is determined on the basis of a characteristic profile (WP1, WP2) in the recorded current curve (SV). [8] Method according to one of the preceding claims, characterized by that the method further comprises the following steps: - Outputting a switching signal to the fluid valve (10), and / or - Output of an error message to a higher-level control unit, and / or - issuing a warning to a user of the fluid valve (10), and / or - Switching off a fluid system connected to the fluid valve (10), and / or - Increase the coil voltage to restore the end switching position (ES). [9] Method according to one of the preceding claims, characterized by that the method is carried out by a control unit (24) associated with the fluid valve (10). [10] Electromagnetically actuated fluid valve (10), in particular a hydraulic valve, with a switching element (12), at least one electromagnet (14) and a control unit (24) associated with the fluid valve (10), wherein the electromagnet (14) has a coil (26) and an armature (28) coupled to the switching element (12), wherein the control unit (24) is designed to carry out the method according to one of the preceding claims. [11] Fluid valve (10) according to claim 10, characterized by that the fluid valve (10) is a binary-acting fluid valve (10).

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