Determining armature stroke by measuring magnetic hysteresis curves

Abstract

The invention relates to a method for producing a valve (1) that can be electromagnetically actuated which method comprises an electromagnet (2, 2a, 2b), an armature (3) that can be moved by the electromagnet (2, 2a, 2b), and a valve body (5), having means (4, 4a, 4b, 4c) for converting a movement of the armature (3) into an opening or closing of the valve (1), wherein the electromagnet (2, 2a, 2b) and the armature (3) are inserted into the valve body (5), wherein, before the electromagnet (2, 2a, 2b) is inserted into the valve body (5), a magnetic hysteresis curve (10) of a combination (6) of the electromagnet (2, 2a, 2b) having a test armature (3a) lying against said electromagnet (2, 2a, 2b) is recorded, the slope m.sub.1 of a first, substantially linear curve segment (11) of the hysteresis curve (10) is determined in the unsaturated state, and, from the slope m.sub.1, the slope m.sub.1* of a curve segment (31) of a hysteresis curve (30) of the finally assembled valve (1) having the armature (3) lying continuously against the electromagnet (2, 2a, 2b) is determined, said curve segment corresponding to the first curve segment (11). The invention further relates to a method for determining the armature stroke AH, wherein the magnetic energy E in the air gap (9) formed between the armature (3) and the electromagnet (2, 2a, 2b) is evaluated from the difference between the first slope m.sub.0 and the second slope m.sub.1*.

Claims

1. A method for ascertaining a hysteresis curve of an electromagnetically actuatable valve (1) made of an electromagnet (2, 2a, 2b), an armature (3) that is movable by way of the electromagnet (2, 2a, 2b), and a valve body (5) with means (4, 4a, 4b, 4c) for converting a movement of the armature (3) into opening or closing of the valve (1), wherein the electromagnet (2, 2a, 2b) and the armature (3) are inserted into the valve body (5), the method comprising recording a magnetic hysteresis curve (10) of a combination (6) of the electromagnet (2, 2a, 2b) with a test armature (3a) contacting said electromagnet (2, 2a, 2b) prior to inserting the electromagnet (2, 2a, 2b) into the valve body (5), ascertaining the slope m.sub.1 of a first, substantially linear curve portion (11) of the hysteresis curve (10) in an unsaturated state, and ascertaining, from the slope m.sub.1, the slope m.sub.1* of a curve portion (31), corresponding to the first curve portion (11), of a hysteresis curve (30) of the fully assembled valve (1) with an armature (3) permanently in contact with the electromagnet (2, 2a, 2b).

2. The method as claimed in claim 1, characterized in that the slope m.sub.1* is ascertained by way of a specified first functional relationship from the slope m.sub.1.

3. The method as claimed in claim 2, characterized in that the armature (3) is fastened to the electromagnet (2, 2a, 2b) on at least one fully assembled valve (1) and the hysteresis curve (30) is recorded in this state for the purposes of ascertaining the first functional relationship.

4. The method as claimed in claim 1, characterized in that the slope m.sub.2 of a second, substantially linear curve portion (12) of the hysteresis curve (10) of the combination (6) is additionally ascertained in the saturated state prior to inserting the electromagnet (2, 2a, 2b) into the valve body (5).

5. The method as claimed in claim 4, characterized in that the current I.sub.0 at which a linear continuation (13) of the second curve portion (12) toward the current axis I intersects the current axis I is additionally ascertained.

6. The method as claimed in claim 4, characterized in that a further magnetic hysteresis curve (20) of the valve (1) is recorded after assembling the valve (1), wherein the slope m.sub.3 of a second, substantially linear curve portion (22) of the further magnetic hysteresis curve (20), corresponding to the second curve portion (12) of the magnetic hysteresis curve (10), in the saturated state is ascertained.

7. The method as claimed in claim 6, characterized in that the current I.sub.1 at which a linear continuation (23) of the second curve portion (22) toward the current axis I intersects the current axis I is additionally ascertained.

8. The method as claimed in claim 7, characterized in that the difference in terms of magnitude I between the current I.sub.1 and the current I.sub.0 is ascertained and the valve (1) is classified as faulty if the difference in terms of magnitude I exceeds a specified threshold value.

9. The method as claimed in claim 2, characterized in that a correlation and/or a second functional relationship (8) between the slopes m.sub.1 and m.sub.2 is ascertained from the slopes m.sub.1 and m.sub.2.

10. The method as claimed in claim 9, characterized in that the second functional relationship (8) establishes a linear relationship between the ratio m.sub.2/m.sub.1 and the current value I.sub.0.

11. The method as claimed in claim 1, characterized in that the slope m.sub.1, the slope m.sub.2, the slope m.sub.1*, and/or the first functional relationship, and/or the second functional relationship (8), and/or the correlation between the slopes m.sub.1 and m.sub.2 is noted on the electromagnet (2, 2a, 2b), and/or on a machine-readable information carrier (7) connected to the electromagnet (2, 2a, 2b) and/or unambiguously linked to the electromagnet (2, 2a, 2b) in a database.

12. The method as claimed in claim 1, characterized in that a multiplicity of electromagnets (2, 2a, 2b) are classified according to the value of the slopes m.sub.1 and/or m.sub.2, and/or according to the second functional relationship (8) and/or the correlation between the slopes m.sub.1 and m.sub.2.

13. A method for determining an armature stroke (AH) on an electromagnetically actuatable valve (1) comprising an electromagnet (2, 2a, 2b) and an armature (3) that is movable by the electromagnet (2, 2a, 2b), the method comprising recording a magnetic hysteresis curve (20) of the valve (1), determining a first slope m.sub.0 of a first, substantially linear curve portion (21) of the hysteresis curve (20) of the valve (1) in the unsaturated state, and evaluating the magnetic energy E in the air gap (9) formed between the armature (3) and the electromagnet (2, 2a, 2b) from the difference between the first slope m.sub.0 and a second slope m.sub.1* of the first, substantially linear curve portion (11), corresponding to the first curve portion (21) of the hysteresis curve (20), of a further magnetic hysteresis curve (10), which the valve (1) would have in the case of an armature (3) secured on the electromagnet (2, 2a, 2b).

14. The method as claimed in claim 13, wherein the valve (1) comprises a valve body (5) and wherein the electromagnet (2, 2a, 2b), the armature (3), and means (4, 4a, 4b, 4c) for converting a movement of the armature (3) into an opening or closing of the valve (1) are arranged within the valve body (5), characterized in that, for the purposes of ascertaining the second slope m.sub.1*, at least one reference value m.sub.1 that was ascertained prior to inserting the electromagnet (2, 2a, 2b) into the valve body (5) is used for said slope m.sub.1*.

15. The method as claimed in claim 13, characterized in that the second slope m.sub.1* is ascertained from the slope m.sub.3 of a second linear curve portion (22) of the magnetic hysteresis curve (20) of the valve (1) in the saturated state in conjunction with a second functional relationship (8) and/or a correlation between the slopes m.sub.1, m.sub.2 of curve portions (11, 12) of the further hysteresis curve (10).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further measures that improve the invention are illustrated in more detail below, together with the description of the preferred exemplary embodiments of the invention on the basis of the figures.

(2) In the figures:

(3) FIG. 1a shows a schematic illustration of an electromagnetically actuatable valve.

(4) FIG. 1b shows a combination of electromagnet and test armature.

(5) FIG. 2 shows a section of the hysteresis curve measured on the combination.

(6) FIG. 3 shows a section of the hysteresis curve measured on the fully assembled valve.

(7) FIG. 4 shows the functional relationship between the slope ratio and the current, ascertained in a mass examination of electromagnets.

(8) FIG. 5 shows a complete hysteresis curve of the valve.

(9) FIG. 6a shows deviations between a first hysteresis curve and a second hysteresis curve.

(10) FIG. 6b shows the reverse case where, within a batch of five electromagnets, the respective hysteresis curves measured in the combination with a test armature only differ significantly in the saturated state, while the hysteresis curves extend practically parallel to one another in the unsaturated state.

(11) FIG. 6c shows the case where, within a batch of three electromagnets, the respective hysteresis curves measured in the combination with a test armature differ significantly both in terms of their slopes in the unsaturated range and in terms of their slopes in the second curve portions in the saturated range.

DETAILED DESCRIPTION

(12) According to FIG. 1a, the valve 1, illustrated here in an exemplary manner as a 2/2 valve, comprises a valve body 5 with an inlet 1a and an outlet 1b. The valve 1 controls the through-flow of a medium between the inlet 1a and the outlet 1b. To this end, an electromagnet 2 is arranged within the valve body 5, said electromagnet consisting of a ferromagnetic magnetic core 2a and a coil 2b wound on the ferromagnetic magnetic core 2a. Attached to the electromagnet 2 is a machine-readable information carrier 7, which contains a barcode with reference values. These reference values were measured on a combination 6 of the electromagnet 2 with a test armature 3a prior to the insertion of the electromagnet 2 into the valve body 5.

(13) In the valve 1, an armature 3 is arranged relative to the electromagnet 2 in such a way that the electromagnet 2 can attract the armature 3. Then, the actuator 4c of the valve 1 is transferred by way of a coupling mechanism 4a from the position shown in FIG. 1a, in which the valve 1 is closed, into the position not shown in FIG. 1a, in which the valve 1 is open, against the restoration force exerted by the valve spring 4b. Together, the coupling mechanism 4a, the valve spring 4b and the actuator 4c form the means 4 for converting the movement of the armature 3 into opening or closing of the valve 1.

(14) In the closed position of the valve 1, shown in FIG. 1a, there is an air gap 9 between the armature 3 and the electromagnet 2. By contrast, if the armature 3 is attracted to the electromagnet 2, this air gap 9 vanishes. The width of the air gap 9 in the closed position, in which the armature 3 has dropped off the electromagnet 2, corresponds to the armature stroke AH of the valve 1.

(15) Together, the electromagnet 2 and the armature 3 form a magnetic circuit which is permeated by magnetic flux . Two flux lines of this magnetic flux are plotted in FIG. 1a in an exemplary manner.

(16) FIG. 1b shows the combination 6 of the electromagnet 2 and the test armature 3a, using which at least the slope m.sub.1 of a curve portion 11 of a hysteresis curve 10 in the unsaturated state is ascertained as a reference value. The test armature 3a is held in contact with the magnetic core 2a of the electromagnet 2 by means that are not illustrated in FIG. 1b, even if there is no current passing through the coil 2b of the electromagnet 2.

(17) FIG. 2 shows a section of the hysteresis curve 10 that was recorded on the combination 6 of the electromagnet 2 and the test armature 3a. The magnetic flux is plotted against the current I through the coil 2b of the electromagnet 2. In a first curve portion 11, which represents the unsaturated state of the electromagnet 2, the hysteresis curve 10 extends substantially linearly with a slope m.sub.1, and so (I)=m.sub.1.Math.I+c.sub.1 with a constant c.sub.1 applies approximately in this curve portion 11. In a second curve portion 12, which represents the saturated state of the electromagnet 2, the hysteresis curve 10 likewise extends substantially linearly with a slope m.sub.2, and so (I)=m.sub.2.Math.I+c.sub.2 with a constant c.sub.2 applies approximately in this curve portion 12. A linear continuation 13 of this second curve portion 12 with the same slope m.sub.2 toward the current axis I intersects the current axis I at the current value I.sub.0. The section of the hysteresis curve 10 illustrated in FIG. 2 was recorded proceeding from the saturated state of the electromagnet 2. Thus, proceeding from the highest current I through the coil 2b of the electromagnet 2, the current I was successively reduced.

(18) FIG. 3 shows a section of the hysteresis curve 20 that was recorded on the fully assembled valve 1. In a manner analogous to FIG. 1, the magnetic flux in the magnetic circuit of the valve 1 formed by the electromagnet 2 and armature 3 is plotted against the current I through the coil 2b of the electromagnet 2. In a manner analogous to FIG. 1, the current I was successively reduced starting from the highest value of the current I in the saturated state of the electromagnet 2.

(19) In the unsaturated state, the hysteresis curve 20 also has a first curve portion 21, in which it extends substantially linearly with a slope m.sub.0. Thus, (I)=m.sub.0.Math.I+c.sub.0 with a constant c.sub.0 applies approximately in this curve portion 21. In a second curve portion 22, which represents the saturated state, the hysteresis curve 20 likewise extends substantially linearly with a slope m.sub.3. In this curve portion 22, (I)=m.sub.3.Math.I+c.sub.3 with a constant c.sub.3 applies approximately. The linear continuation 23 of the curve portion 22 with the same slope m.sub.3 toward the current axis I intersects the current axis I at the current value I.sub.1.

(20) For comparison purposes, FIG. 3 additionally plots the curve portion 31 of the hysteresis curve 30 shown in FIG. 2, which the fully assembled valve would have in the case of an armature permanently in contact with the electromagnet. In this curve portion 31, (I)=m.sub.1*.Math.I+c.sub.1* applies approximately with a constant c.sub.1*.

(21) It is clear from the profile of the hysteresis curve 20 proceeding from the second curve portion 22 toward lower current values I that the armature 3 dropping off the electromagnet 2 reduces the magnetic flux in a discontinuous fashion. The reason for this is that the air gap 9 forms between the armature 3 and the electromagnet 2 as a result of the armature 3 dropping off and magnetic energy E is stored in the air gap 9. This energy E corresponds to the area between the first curve portion 21 of the hysteresis curve 20 and the first curve portion 31 of the hysteresis curve 30. The wanted armature stroke H is establishable from the energy E.

(22) FIG. 4 shows a second functional relationship 8 between the slope ratio m.sub.2/m.sub.1 and the current I.sub.0, said functional relationship having been ascertained in mass examinations of electromagnets 2. The second functional relationship 8 corresponds to equation (3). Each measurement point characterized by a rhombus as a symbol represents an electromagnet 2 for which the second functional relationship 8 approximately applies. Each measurement point characterized by a circle as a symbol represents an electromagnet 2 that significantly deviates from the second functional relationship 8. Two groups 8a and 8b of such outliers can be identified in FIG. 4. Electromagnets 2 that are conspicuous in this manner are preferably sorted out as rejects.

(23) For better understanding, FIG. 5 shows a complete hysteresis curve 20 of the valve 1 in the case of symmetric control. Proceeding from the highest current value I in the saturated state, the branch 28 is initially passed over to lower currents I. In the process, the substantially linearly extending second curve portion 21 is passed over first. Following this second curved portion 21, the magnetic flux in the descending curve portion 24 reduces superlinearly before, at the point 27a, the armature 3 drops off the electromagnet 2 as a result of the restoration force exerted by the valve spring 4b of the valve 1 and the air gap 9 is formed between the armature 3 and the electromagnet 2. This manifests itself in a discontinuous drop in the magnetic flux T. Subsequently, the branch 28 of the hysteresis curve 20 merges into the first curve portion 21 in the unsaturated state. Here, the curve of the magnetic flux is approximately linear in relation to the current I.

(24) In the lower left quadrant of FIG. 5, the branch 28 of the hysteresis curve 20 merges into an attracting curve portion. At the point 26b, the armature 3 is attracted to the electromagnet 2, which manifests itself in a small discontinuity in the curve profile.

(25) If the current I is subsequently increased again in the saturated state, the branch 29 of the hysteresis curve 20 is passed over. Here, the hysteresis curve 20 merges again into a decreasing curve portion 24, in which the armature 3 drops off the electromagnet 2 at the point 27b. When the branch 29 of the hysteresis curve 29 passes over into the upper right-hand quadrant, the next attracting curve portion 25 starts. At the point 26a, the armature 3 is attracted to the electromagnet 2 again.

(26) In a manner analogous to FIG. 3, the linear continuation 23 of the second curve portion 21 toward the current axis I and the current value I.sub.1, at which the continuation 23 intersects the current axis I, are also plotted in FIG. 5.

(27) On the basis of a few examples, FIG. 6 elucidates how the individual variation between the various electromagnets 2 can influence the profile of the hysteresis curve 10 of a combination 6 of the respective electromagnet 2 with the test armature 3a.

(28) FIG. 6a shows deviations between a first hysteresis curve 10 and a second hysteresis curve 10a of the type that may be caused, for example, by differences in the heat treatment of the magnetic cores 2a of different electromagnets 2, or else by a different chemical composition of the magnetic powder used for both magnetic cores 2a. In the saturated state, which is represented by the second curve portion 12, the profiles of the two hysteresis curves 10 and 10a are identical. Consequently, the deviation in the composition of the magnetic cores 2a does not modify the slope m.sub.2 in the second curve portion 12 and does not modify the current I.sub.0, at which the linear continuation 13 of the second curve portion 12 intersects the current axis I, either. However, the profiles of the first curve portions 11 and 11a in the unsaturated state are different and, in particular, also have different slopes m.sub.1.

(29) FIG. 6b shows the reverse case where, within a batch of five electromagnets 2, the respective hysteresis curves 10, 10a-10d measured in the combination 6 with a test armature 3a only differ significantly in the saturated state, while the hysteresis curves 10, 10a-10d extend practically parallel to one another in the unsaturated state. Thus, for example, the second curve portions 12 and 12a of the hysteresis curves 10 and 10a have different slopes m.sub.2 in the saturated state and the linear continuations 13 and 13a of these two curve portions 12 and 12a in the direction of the current axis I intersect the current axis I with different currents I.sub.0. By contrast, the slope m.sub.1 in the unsaturated state is virtually identical for all hysteresis curves 10, 10a-10d.

(30) By contrast, FIG. 6c shows the case where, within a batch of three electromagnets 2, the respective hysteresis curves 10, 10a, 10b measured in the combination 6 with a test armature 3a differ significantly both in terms of their slopes m.sub.1 in the unsaturated range and in terms of their slopes m.sub.2 in the second curve portions 12, 12a in the saturated range. Accordingly, the linear continuations 13, 13a of the second curve portions 12, 12a in the direction of the current axis I also intersect the current axis I at different currents I.sub.0.

(31) Provided that the individual variation between electromagnets 2 only manifests itself in such modifications of the hysteresis curve 10, which modify m.sub.1, m.sub.2, and I.sub.0 in a correlated manner, the production method can be applied in a simplified form. Then, it is possible to dispense with recording a hysteresis curve 10 for each individual electromagnet 2. Instead, it is sufficient to measure a sample of a few electromagnets 2 of a batch of the nominally identically dimensioned and manufactured electromagnets 2 and ascertain the functional relationship 8 according to equation (3) therefrom. By way of example, it is possible, for this sample, to use reference valves in which the armature 3 is attached to the electromagnet 2 as a test armature 3a. Then, m.sub.1 can be evaluated for all further electromagnets 2 of the batch according to equation (4).