ELECTRICAL DETERMINING OF CHARACTERISTIC VALUES OF MAGNETIC SWITCH VALVES

Abstract

The invention relates to a method for determining a characteristic value of a magnetic switch valve. The magnetic switch valve can be switched from a closed switch state into an open switch state, via the movement of a rotor by means of a switching magnet applied with current against a conservative restoring force. According to the invention, during the switching of the switch valve from the open state into the closed state, the time course of the current flowing through the switching magnet and/or of the voltage at the switching magnet is measured. The characteristic value to be measured is evaluated from this time course. It was recognised that every movement of the rotor against the switching magnet induced a voltage in same. Now the voltage at the switching magnet is regulated at a constant value, for one, the voltage induced by the movement can be observed as a control deviation in the short term. For another, the induced voltage causes a current flow through the switching magnets. Based on this, the kinematics of the rotor can be deduced. Given that the switching magnet has an ohmic resistance, energy is also dissipated via the current flow. This energy is the key to determining the switching path covered by the rotor when switching between the closed and the open state. The invention also relates to a measuring device that is particularly suitable for the method.

Claims

1. A method for determining a characteristic value of a magnetic switch valve (1), which can be switched from a closed switch state (A) into an open switch state (B), via the movement of a rotor (2) by a switching magnet (3) applied with current against a conservative restoring force (4), wherein the characteristic value belongs to a group comprising: the time required for switching the switch valve from the open switch state into the closed switch state, the spring constant of the restoring force (4), the coefficient of friction effective during the valve actuation and the switching path (AH), which the rotor (2) covers when switching between the closed (A) and the open (B) state, characterized in that during the switching of the switch valve (1) from the open (B) into the closed (A) state, the time course of the current (I) flowing through the switching magnet and/or of the voltage (U) at the switching magnet is measured, and the characteristic value is determined from this time course.

2. The method according to claim 1, characterized in that during the switching of the switch valve (1) from the open (B) into the closed (A) state, the time course of the current flowing through the switching magnet and/or of the voltage at the switching magnet is measured while controlling the voltage (U) at the switching magnet to a constant value.

3. The method according to claim 1, characterized in that additionally the time course of the current (1) when switching from the closed (A) to the open (B) state and/or the current required for switching the valve (1) from the closed state (A) into the open state (B) and/or the voltage required for this switching and/or the ohmic resistance of the switching magnet (3) and/or the time course of the voltage (U) when switching from the closed (A) into the open (B) state and/or from the open (B) into the closed state (A) are measured and used for determining the characteristic value.

4. The method according to claim 1, characterized in that during the switching from the closed (A) into the open state (B) by the mechanical work against the restoring force (4), stored potential energy, which is converted into electric energy when switching from the open (B) into the closed (A) state by the movement of the rotor (2) against the switching magnet (3) and is dissipated at the ohmic resistor thereof, is evaluated from the time course of the current (I) and/or the voltage (U).

5. The method according to claim 4, characterized in that the temporal attenuation course is determined with which the energy stored in the magnetic circuit consisting of rotor (2) and switching magnet (3) is dissipated when the position of the rotor (2) is fixedly held in the open and/or closed state

6. The method according to claim 5, characterized in that the attenuation course is determined under the boundary condition that the switching magnet (3) is short-circuited or that the voltage (U) at the switching magnet (3) is controlled to a constant value.

7. The method according to claim 5, characterized in that the attenuation course is determined by an extrapolation of the time course of the current (I) and/or the voltage (U) on the basis of the time period, in which the application of current to the switching magnet (3) has already been interrupted but the rotor (2) has not yet been set into motion by the restoring force (4), and/or by a curve fit at maxima, which have been induced in the current course (I) and/or in the voltage course (U) when switching into the closed state (A) by the repeated bouncing of the rotor (2) at the end position thereof.

8. The method according to claim 5, characterized in that the attenuation course is determined from the temporal current response of the switching magnet (3) to a voltage which is applied in the closed state (A) and which is not sufficient for switching into the open state (B).

9. The method according to claim 5, characterized in that the stored potential energy is evaluated as an integral over the attenuation course for the open state (B) between a first point in time, at which the rotor (2) begins to move when switching from the open (B) into the closed (A) state by the restoring force (4), and a second point in time, at which the rotor (2) first strikes the end position thereof during this switching operation.

10. The method according to claim 5, characterized in that the stored potential energy is evaluated as an integral over the measured current course (I) and/or the voltage course (U) between a first point in time, at which the rotor (2) begins to move by the restoring force (4) when switching from the open (B) into the closed (A) state, and a second point in time, at which the measured current course (I) or respectively the measured voltage course (U) has the same current value or respectively the same voltage value as the attenuation course for the closed state (A) at the first point in time.

11. The method according to claim 1, characterized in that the point in time, at which the time course of the current (I) and/or the voltage (U) achieves a local maximum after the beginning of the switching from the open (B) into the closed (A) state, is evaluated as a point in time, at which the rotor (2) strikes the end position thereof.

12. The method according to claim 1, characterized in that as a point in time t.sub.1 at which the rotor (2) begins to move by the restoring force (4) when switching from the open (B) into the closed (A) state, that point in time is evaluated at which the rotor (2) hereby induces a voltage or respectively current signal in the switching magnet (3).

13. A device for determining characteristic values of a magnetic switch valve (1), which can be switched from a closed switch state (A) into an open switch state (B) via the movement of a rotor (2) by a switching magnet (3) applied with current against a conservative restoring force, characterized by a driver unit (5) for applying a voltage or current course to the switching magnet (3), said voltage or current course switching the valve (1) from the open switch state (B) into the closed switch state (A); a meter (6, 8) for measuring the time course of the current (I) flowing through the switching magnet (3) and/or of the voltage (U) at the switching magnet during the closing process and an evaluation unit (7), which determines a characteristic value of the magnetic switch valve from this time course (I).

14. The device according to claim 13, characterized in that the evaluation unit (7) is capable of determining a characteristic value from the time course (I, U) from a group, wherein this group comprises: the time required for switching the switch valve from the open switch state into the closed switch state, the spring constant of the restoring force (4), the coefficient of friction effective during the valve actuation and the switching path (AH), which the rotor (2) covers when switching between the closed (A) and the open (B) state.

15. The device according to claim 13, characterized in that the evaluation unit (7) is capable of extracting the point in time at which the rotor (2) is set into motion during the closing process and/or the point in time at which the rotor (2) achieves the end position thereof in the closed switch state (A) from the time course (I, U).

16. The device according to claim 13, characterized in that said device comprises a further meter (8) for measuring the time course of the voltage (U) applied to the switching magnet (3) or respectively the time course of the current (I) flowing through the switching magnet (3) during the closing process, so that the evaluation unit (7) receives the time course of the current (I) as well as the time course of the voltage (U) as an input.

17. The device according to claim 13, characterized in that the evaluation unit (7) has an integrator for the time course of the voltage (U) and/or for the time course of the current (I).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In the drawings:

[0055] FIG. 1 shows an exemplary embodiment of the device according to the invention.

[0056] FIG. 2 shows the determination of the switching path using attenuation courses, which are fit to the measured time course of the current through the switching magnet.

[0057] FIG. 3 shows the determination of the switching path using an attenuation course separately measured after closing the valve.

[0058] FIG. 4 shows the determination of the spring constant for the restoring force and the coefficient of friction for the valve actuation from the measured time course of the current through the switching magnet.

DETAILED DESCRIPTION

[0059] FIG. 1 shows an exemplary embodiment of the device according to the invention. The magnetic switch valve 1 blocks a line 10 here in the closed switch state A; in the open switch state B enables the flow through the line, 10. The switch valve 1 is controlled by a rotor 2, which can be pulled by means of an energized switching magnet 3 against the force of a spring 4 from the closed switch state A into the open switch state B. In so doing, the rotor 2 covers the switching path (rotor stroke) AH.

[0060] A universal power supply having selectable voltage or current specification is provided as a driver unit 5. This driver unit 5 is capable of applying a voltage course or a current course to the switching magnet 3, which switches the valve 1 from the open switch state B into the closed switch state A.

[0061] Furthermore, a digital ammeter 6 for measuring the current flowing the switching magnet 3 and a digital volt meter 8 for measuring the voltage applied to the switching magnet are provided. The digital outputs of both instruments are supplied to a measuring computer, which functions as an evaluation unit 7 and in each case plots the time course. The measuring computer is equipped with a software, which determines the points in time at which the rotor 2 is set into motion during the closing process and at which said rotor strikes in the end position thereof in the closed switch state A. Thus, the spring constant of the restoring force 4, the coefficient of friction during the valve actuation and the time required for closing the valve 1 are known. The software can also numerically integrate the time course of the voltage U and/or the current; thus enabling the rotor stroke to be determined.

[0062] The device is therefore a compact measuring place, with which all important characteristic values of magnetic switch valve can be determined.

[0063] FIG. 2 shows the determination of the switching path AH according to one exemplary embodiment of the method according to the invention. A voltage was applied to the switching magnet 3 according to a time profile that is reflected by the curve U. The voltage was in each case consistently controlled to a target value. The measured time course of the current through the switching magnet is indicated in curve I. At the beginning of the measurement a constant abruptly reduced to 0. The voltage actually applied to the magnet 3 indicated by the curve U could thereupon naturally only react with a final flank steepness. After that, the current I through the magnet 3 fell almost linearly until the rotor 2 began to move as a result of the effect of the restoring force 4, which manifested itself in a turning point in the current curve I. The curve K.sub.1 is fitted in the region before the turning point. The curve K.sub.1 indicates the temporal attenuation course, with which the energy stored in the magnetic circuit consisting of rotor 2 and switching magnet 3 is dissipated during the fixedly held position of the rotor 2 in the open state.

[0064] As a result of the movement of the rotor 2 against the switching magnet 3, an additional voltage and therefore also an additional current were induced through the switching magnet. This led to the fact that the drop in the current through the switching magnet 3 initially flattened out until it finally even reversed into an increase. At the point in time, as the rotor 2 first struck in the end position thereof, the acceleration acting on said rotor and therefore also the induced current were the greatest. This is shown by a local maximum in the current curve I at the point in time t.sub.2. The point in time t.sub.1, at which the rotor 2 begins to set itself in motion due to the effect of the restoring force, was determined as the point in time, at which the curve K.sub.1 had the same current value as the curve K.sub.2 at the point in time t.sub.2 of the first local maximum. The integral

ΔE=∫.sub.t1.sup.t2R.sub.MV.Math.K.sub.1.sup.2dt

[0065] concerning the curve K.sub.1 between the times t.sub.1 and t.sub.2 was evaluated as the amount of energy, which had been stored as potential energy by carrying out mechanical work against the restoring force 4. The restoring force 4 was supplied in this exemplary embodiment by a conventional valve spring.

[0066] The determined amount of energy ΔE was converted via the force law for springs into the switching path (rotor stroke) AH in order to have compressed the spring when opening the valve. This is the difference

AH=s.sub.1−s.sub.0

between the entire tensioning distance s.sub.1 of the spring if the valve member is at the upper stop and the pre-tensioning distance s.sub.0 of the valve during installation. The following applies:

[00001]$s_1=\sqrt{\frac{2.Math.\mathrm{Eges}}{D}},\mathrm{where}.Math..Math.E_{\mathrm{ges}}=E_0+\Delta .Math..Math.E$

[0067] wherein E.sub.0 is the energy in the, if applicable, pre-tensioned spring.

[0068] Because the pre-tensioning force of the fast switching magnetic valves are adjusted very precisely according to the prior art, The energy E.sub.0 according to the equation:

E.sub.0=½.Math.D.Math.s.sub.0.sup.2

is very well known. D denotes the spring constant of the valve spring, which is likewise very exactly known.

[0069] The following equation therefore applies to switch valves with and without pre-tensioning by a spring:

[00002]$\mathrm{AH}=\frac{F.Math..Math.0}{D.Math..Math.2}+\sqrt{\frac{F.Math..Math.0}{D}}+\frac{R}{D}.Math.{\int }_{t.Math..Math.1}^{t.Math..Math.2}.Math.I^2.Math.\mathrm{dt}$

[0070] where

[0071] I . . . measured current

[0072] D . . . spring constant of the spring

[0073] F . . . pre-tensioning force of the spring

[0074] The sought switching path (rotor stroke) can clearly be determined from the measured variable I and the variables D and F.sub.0 known from the construction and the assembly of the valve.

[0075] After the first strike in the end position, the rotor 2 springs once again back in order to subsequently in each case again reach this end position, which in turn led in each case to a further local maximum in the current curve I. Between the point in time t.sub.1 and the point in time, at which the rotor 2 finally assumes its rest position, the current I runs approximately piecewise parabolic, wherein a new parabola begins after each local maximum. Some of these parabolas are plotted in FIG. 2 as dotted lines.

[0076] FIG. 3 shows the determination of the switching path AH using a further exemplary embodiment of the method according to the invention, which dispenses with the fitting of curves to the measured current course through the switching magnet. In the diagram, the voltage U at the switching magnet, the measured current I.sub.1 flowing through the switching magnet 3 as well as a current I.sub.2 measured after the closing of the valve 1 for determining the attenuation course of the magnetic circuit in the closed state are plotted.

[0077] The voltage curve 3 begins with a steep ascent in the direction of the target value predetermined at the voltage control. Said curve overshoots the target value before it remains constant on this target value. The current through the switching magnet 3 lags temporally behind the applied voltage due to the inductance of the coil. The valve 1 is initially still in the closed state. As soon as the current through the switching magnet 3 is sufficient to draw the rotor 2 into the open position, a buckling occurs in the current curve I.sub.1. The current value, whereat this occurs, is denoted with I.sub.an. Voltage U and current I remain constant for a certain amount of time. The ohmic resistance was determined from the quotient U/I.sub.1. Subsequently, the target value for the voltage at the switching magnet was reduced from 3 to 0. The actual voltage U reacted subsequently with a final flank steepness. Along with the voltage at the switching magnet 3, the current I.sub.1 flowing through the switching magnet 3 also dropped. I.sub.1 was not initially sufficient to hold the valve 1 open. At a point in time t.sub.2, the restoring force 4 first prevailed over the remaining holding force of the switching magnet 3, and the rotor 2 began to move in the direction of the closed position. This point in time can be seen in FIG. 3 in the voltage curve as a small control deviation. This control deviation is superimposed in FIG. 3 by means of an overshoot that the voltage U carries out beyond the target value 0 thereof into the negative area.

[0078] Analogous to FIG. 2, several local maxima appear in the measured current I.sub.1 in FIG. 3, which were caused by the fact that the rotor 2 repeatedly struck against the closed end position thereof. After the rotor 2 finally had reached the end position thereof, the feed of the switching magnet 3 was switched to current control and a current value I.sub.3 was set, which lay below the current value I.sub.an for opening the valve 1. The actually flowing current was plotted starting from the right edge of the diagram in the current curve I.sub.2, wherein progression was made in the rearward direction on the time axis. The curve I.sub.2 is the temporal current response of the switching magnet 3 to a voltage that is applied in the closed state of the valve 1 and is not sufficient to switch into the open state. Said curve I.sub.2 was evaluated as an attenuation course with which the energy stored in the magnetic circuit consisting of rotor 2 and switching magnet 3 is dissipated when the rotor 2 is in a fixedly held position in the closed state.

[0079] The potential energy ΔE stored by means of the mechanical work against the restoring force 4 was now evaluated as an integral via the measured current

|ΔE|=∫.sub.t1.sup.t2R.sub.MV.Math.I.sub.1.sup.2dt

[0080] The right integration limit is the point in time t.sub.2, at which the rotor 2 began the motion in the direction of the closed position. The left integration limit t.sub.1 is the point in time at which the measured current I.sub.1 has the same current value I.sub.4 as the attenuation curve I.sub.3 at the point in time t.sub.2. The area under the curve I.sub.1, which corresponds to the amount of energy ΔE determined in this manner, is depicted shaded in FIG. 3. Analogous to FIG. 2, the switching path AH was determined on this amount of energy ΔE, around which switching path the spring had been compressed during the opening of the valve.

[0081] If the voltage U.sub.inj at the injector of the switching magnet 3 in the time period between t.sub.1 and t.sub.2 is not 0 volts, the formula stated above for calculating the energy difference ΔE is to be corrected as follows:

ΔE=U.sub.inj.Math.I.sub.1dt−∫.sub.t1.sup.t2R.sub.MV.Math.I.sub.1.sup.2dt

[0082] FIG. 4 clarifies the determination of the spring constant of the restoring force 4 as well as the determination of the coefficient of friction for the valve actuation using the measured data shown in FIG. 3. t.sub.1 denotes here the point in time at which the rotor 2 began the movement thereof in the direction of the closed position; this point in time can be seen by means of a small control deviation in the current curve U. The rotor 2 struck in each case the end position thereof at the points in time t.sub.2, t.sub.3, and t.sub.4. The information regarding the spring constant of the valve spring 4 is contained in the time difference between the points in time t.sub.1, t.sub.2, t.sub.3, and t.sub.4. The coefficient of friction for the valve actuation lies in the decrease of the amplitude in the current curve I.sub.1 between the individual maxima at the points in time t.sub.2, t.sub.3 and t.sub.4.