The invention pertains to a valve with a valve piston that can be moved linearly in a valve housing and a linear drive comprising a stator, which is immovably connected to the valve housing, and a rotor, which can be moved therein and acts upon the valve piston, wherein the stator is composed of a housing consisting of magnetically conductive material and at least one coil arranged therein, and wherein the rotor, which is separated from the stator by an air gap, consists of at least one permanent magnet with pole pieces that consist of magnetically conductive material and border on the respective pole of the permanent magnet.
A valve with the aforementioned features, which is driven by means of a linear drive, is described in DE 693 25 669 T2; with respect to the design of this linear drive, it is merely mentioned that it consists of a stator, which is connected to the valve housing by means of a permanent and rigid mechanical connection, and a rotor, which is arranged in a rotor chamber of the linear drive, mechanically coupled to the valve piston and separated from the stator by an air gap. If the known valve is realized in the form of a directional control valve with a valve piston that can be moved in both directions, a set of windings should be provided in the stator in order to cover both moving directions. According to a preferred design, the stator and the rotor should have the same length. No further detailed information with respect to the design of the stator and the rotor of the linear drive is provided in DE 693 25 669 T2.
A conventional design of a linear motor is insofar known from DE 11 2007 001 702 T5. In this case, the stator consists of a housing made of a magnetically conductive material, in which a sequence of abutting coils is arranged. The assigned rotor consists of multiple permanent magnets, which are arranged in a row and have alternately changing polarities, such that respectively identical magnetic poles face one another, wherein pole pieces consisting of a magnetically conductive material are respectively arranged between said magnetic poles and an outer pole piece respectively forms the end of the rotor.
In valves used in fluid technology applications, i.e. particularly in hydraulic and compressed-air applications, one generally encounters the problem that flow forces, which possibly may have to be overcome in addition to the restoring spring forces acting upon the valve piston, occur in dependence on the respective stroke of the valve piston, particularly when the valve piston is moved into the open position of the valve. Depending on the design of the valve, a corresponding increase of the flow forces occurs in this case during the stroke of the valve piston. It is therefore necessary to overcome this force counteracting the motion of the valve piston with a sufficient power reserve and a sufficiently high dynamic of the valve piston motion. In contrast, no high force is required for the return of the valve piston into its closed position because the flow force acts in an intensifying fashion in this case. Although direct drives for adjusting the valve piston in valves of this type have already been disclosed, for example, in DE 693 25 669 T2, these direct drives for the valve piston are mainly limited to smaller valves and valves with a larger design typically have to be operated with a pilot control featuring a smaller, directly driven valve.
Although DE 693 25 669 T2 describes a valve that is directly driven with a linear drive, the known valve is merely intended, in particular, for keeping the fluid, which is also present in the rotor chamber, free of magnetic foreign matter by retaining potentially present magnetic foreign matter in the rotor bore due to the magnetic force of the rotor. Consequently, the cited publication contains no references to designing the linear drive with consideration of the force progression occurring during the operation of the valve.
The invention therefore is based on the objective of making available a valve with the initially cited features, in which a direct drive can on the one hand be realized regardless of the size of the valve and the dynamic of valves directly driven by means of a linear drive is on the other hand improved.
This objective is attained with the content of the claims that follow this description and also disclose advantageous embodiments and enhancements of the invention.
The invention is based on the fundamental idea that, if a coil is embedded in the stator housing, an outer web is respectively arranged on their outer sides or, if multiple coils are embedded in the stator housing, an inner web is respectively arranged between the coils and an associated outer web is respectively arranged on the outer sides of the outermost coils, wherein the axial extents of inner webs and outer webs, permanent magnets and pole pieces are adapted to one another in such a way that, in order to realize an effective force increase when at least one coil is energized, at least one corner of a pole piece on the one hand and at least one corner of an outer web on the other hand lie opposite of one another in the stroke region of the valve piston in such a way that the magnetic fields of the permanent magnet and the energized coil are rectified and concentrated at this point in the air gap.
This fundamental idea is based on the consideration that forces acting upon the rotor in its moving direction are in a linear drive essentially generated at the material transitions in the air gap, namely in the form of iron/air gap/iron. The higher the magnetic flux density at the corresponding location in the air gap, the higher the forces generated by the linear drive. The magnetic flux density is composed of the contribution of the permanent magnet and the contribution of the energized coil or coils. In this case, the highest flux densities and therefore the desired force increases naturally occur in the air gap at the locations, at which the flow directions of the permanent magnet and the coil current are rectified and the iron parts of the stator and the rotor at the same time lie opposite of one another in the air gap with a relatively small transition surface. This positioning opposite of one another can also be described in that the edges of webs and pole pieces, which participate in the formation of the corresponding corner and face the air gap, just begin to overlap one another transverse to the moving direction of the rotor. If a decisive force increase occurs in such a position of the rotor relative to the stator, a corresponding force maximum does not necessarily have to exactly coincide with this geometric point because material-specific and manufacturing-specific circumstances are also influencing factors in this respect.
In the inventive design of the stator and the rotor, the rotor reaches intermediate positions, in which corners of pole pieces and corners of webs formed in the stator also lie opposite of one another with edges that are respectively aligned with one another. However, such positions of the rotor relative to the stator do not contribute anything to a force increase as long as both aforementioned prerequisites, namely the rectification of the flow directions in the permanent magnet and the coil and the opposite positioning of assigned corners of pole pieces and inner and outer webs, are not simultaneously fulfilled. In such constellations, the flow directions in the permanent magnet and the coil may either extend opposite to one another or large-surface iron parts of the rotor and the stator lie opposite of one another.
In its simplest implementation, the inventive idea can be realized, for example, in that a rotor featuring a permanent magnet with respectively outer pole pieces is in its starting position assigned to the coil with its outer webs arranged in the stator in such a way that the outer corner of the pole piece positioned in the direction of a working stroke of the valve lies in the starting position of the rotor defined by the deenergized coil opposite of the coil-side corner of the outer web of the stator positioned toward the direction of the working stroke such that a force increase occurs when the coil is energized with a field that is rectified referred to the field of the permanent magnet due to the immediately occurring concentration of the magnetic fields of the permanent magnet and the energized coil and the force of the linear drive acting upon the valve piston from the starting position of the rotor in the direction of the working stroke is thereby immediately increased.
Particularly in valves with a short stroke, such a force increase already suffices for moving the valve piston in the direction of a working stroke with the required dynamic. However, a corresponding design of the coil and the associated webs and of the permanent magnet and the associated pole pieces, as well as a corresponding choice of the intensity of the applied current, also makes it possible to realize a sufficient force increase for larger valves.
In advantageous embodiments of the invention with a different design, an arrangement of two or more coils is proposed, wherein an inner web is respectively arranged between the coils and the associated outer web is respectively arranged on the outer sides of the outermost coils. With respect to the function of the linear drive, it is in this case decisive that the coils are either wound in opposite directions if they are acted upon with the same current or that the coils are wound in the same direction if one coil is acted upon with a positive current and the other coil is acted upon with a negative current.
In such a basic design of the stator and the rotor with a larger number of coils and permanent magnets, the axial extents, i.e. the extents in the direction of the valve piston motion or rotor motion, of the permanent magnets and the pole pieces on the one hand and of outer and inner webs and therefore the coils arranged in the stator housing on the other hand may be realized differently, namely among one another as well as relative to one another.
In a first embodiment of the invention, it is therefore proposed that two coils with an inner web arranged between the coils and outer webs arranged on the respective outer sides of the coils are provided in the stator.
In this case, it would be conceivable, for example, that the axial extent of two coils and the inner web of the stator is identical to the axial extent of the rotor with a permanent magnet and two pole pieces, wherein the axial extent of the inner web of the stator either corresponds to the axial extent of the permanent magnet of the rotor such that two force increases, which simultaneously act upon the motion of the rotor and are therefore added to one another, are realized in the starting position of the rotor or the axial extent of the inner web of the stator is smaller than the axial extent of the permanent magnet of the rotor such that the first force increase is realized in the starting position of the rotor and a second force increase is realized after a predefined valve stroke has been reached.
Alternatively to the above-described exemplary embodiments, it would also be conceivable that the axial extent of two coils and the inner web of the stator is greater than the extent of the rotor with a permanent magnet and two pole pieces, wherein the distance of the edges of the outer webs of the stator bordering on the coils from the starting position of the rotor corresponds to the valve stroke, which is adapted to reaching a position of the valve piston that in turn is adapted to the progression of the flow forces, and wherein the axial extent of the inner web of the stator is once again identical to the axial extent of the permanent magnet of the rotor such that a first force increase is realized in the starting position of the rotor and a second force increase is realized after the predefined valve stroke has been reached, or wherein the axial extent of the inner web of the stator is smaller than the axial extent of the permanent magnet of the rotor such that a first force increase is realized after an initial valve stroke has been reached and a second force increase is realized after the predefined valve stroke has been reached.
It would furthermore be conceivable that the rotor is composed of at least two permanent magnets and at least three pole pieces, wherein a coil is assigned to at least one pole piece of the rotor in the stator. All in all, such a design may by all means comprise a larger (arbitrary) number of permanent magnets and associated pole pieces, wherein a pole piece is respectively arranged on the outer ends of the rotor structure. In this case, only one coil may be assigned to at least one pole piece of the rotor in the stator. Depending on the desired force-stroke characteristic of the valve piston motion, however, it would also be possible to respectively assign several coils to individual pole pieces of the rotor.
In an applicable simple exemplary embodiment of the invention with a rotor featuring several permanent magnets and several pole pieces, a coil may only be assigned to the central pole piece.
The inventive idea can also be applied to embodiments, for example, in which the stator features three coils with two inner webs arranged between said coils and two outer webs and in which the rotor is composed of a stack of at least three permanent magnets and pole pieces that are alternately arranged between the permanent magnets and on their outer sides, wherein at least one corner of a pole piece on the one hand and a corner of an inner web and/or an outer web on the other hand respectively lie opposite of one another either in the starting position of the rotor or when a predefined valve stroke is reached in order to realize an effective force increase when the coils are energized.
In this context, the inner webs and the outer webs of the stator may respectively have an identical axial extent and the pole pieces of the rotor may have axial extents that differ from one another, wherein the two outer pole pieces respectively have a smaller axial extent than the pole piece situated between the permanent magnets. Alternatively, the inner webs and the outer webs of the stator may respectively have a different axial extent and the outer pole pieces of the rotor may have an identical axial extent corresponding to half the axial extent of the pole piece situated between the permanent magnets.
In both above-described instances, the coils arranged in the stator may either have identical or different lengths.
In the implementation of the invention, it would generally be conceivable that the distances between the webs arranged in the stator are respectively identical to one another and the axial extents of the pole pieces in the rotor differ from one another or that the distances between the webs arranged in the stator differ from one another and the axial extents of all pole pieces in the rotor are respectively identical. Accordingly, the distances between the webs arranged in the stator may differ from one another and the axial extents of the pole pieces in the rotor may differ among one another or the distances between the webs arranged in the stator, as well as the axial extents of the pole pieces in the rotor, are respectively identical to one another.
If the invention is applied to directional control valves with a valve piston acting in both stroke directions of the valve, one prerequisite for this function is a symmetric design of the rotor and the stator referred to the axis of symmetry extending perpendicular to the moving direction of the rotor such that corresponding force increases are respectively realized in both moving directions of the rotor and of the valve piston driven thereby.
However, the invention can also be applied to valves realized in the form of plug-in valves with a valve piston acting in one stroke direction only. Since a corresponding force increase or force maximum only needs to be realized in one moving direction of the valve piston in this case, it is proposed that the rotor and the stator have an asymmetric design referred to the axis of symmetry extending perpendicular to the moving direction of the rotor.
If the force increase for the movement of the valve piston requires very high actuating forces, it would ultimately be conceivable to arrange several linear drives, which respectively consist of a stator and a rotor, parallel to one another in the moving direction of the valve piston, wherein the rotors of the linear drives are respectively connected to the valve piston.
An inventive linear drive can be used in connection with all conventional valve types; in this respect, the detailed internal design of the hydraulic valve is not important as long as the rotor of the linear drive is respectively connected to the valve piston of the hydraulic valve. Since the function of the inventive linear drive is respectively adapted to a starting position of the rotor and therefore of the valve piston, in which the at least one coil of the linear drive is energized in order to realize a working stroke of the valve piston, this starting position may, according to an exemplary embodiment of the invention, be realized by automatically adjusting the position of the valve piston in the deenergized state of the linear drive. In accordance with the corresponding prior art, the valve piston may for this purpose be held in the starting position, which corresponds to a central position, by means of springs acting upon the valve piston on both sides as it is common practice with directional control valves. However, other starting positions for the valve piston would also be conceivable, for example, in 2/2 directional control valves (e.g. cartridge valves), in which the valve piston is respectively displaced between two end positions only.
According to exemplary embodiments of the invention, the starting position of the valve piston adjusted, in particular, in the deenergized state of the linear drive may correspond to the closed position of the valve or, alternatively, to a working position of the valve piston, in which connections between valve housing ports are maintained open.
Exemplary embodiments of the invention are illustrated in the drawings and described in greater detail below. In these drawings:
Although
In order to directly drive the valve piston 13, a housing-like stator 21 consisting of a magnetically conductive material is arranged on one side of the valve housing 10 and rigidly connected to the valve housing 10. A rotor 22 is arranged in the annular space enclosed by the stator 21 and connected to the assigned end of the valve piston 13 by means of a connecting rod 29 such that the linear motion of the rotor 22 is converted into a displacement of the valve piston 13 in the housing bore 12 of the valve housing 10.
In the exemplary linear drive 20 illustrated in
According to
When the rotor 22, as well as the valve piston 13 coupled thereto, should once again be returned into the starting position (
In the exemplary embodiment illustrated in
According to the illustration in
The valve illustrated in
In the exemplary embodiment of a linear drive 20 illustrated in
This also applies accordingly to the stroke “−a” in the other moving direction, wherein the corners C, C′ of the pole piece 27 and the inner web 24 are positioned in front of one another in the starting position of the rotor 22 illustrated in
The exemplary embodiment illustrated in
In the exemplary embodiments of the linear drive 20 described above with reference to
A corresponding example is respectively illustrated in
Based on the above-described exemplary embodiments, the inventive design can also be realized with a greater number of coils 23 and inner webs 24 formed thereby on the one hand and/or with a greater number of permanent magnets 26 and pole pieces 27 on the other hand. The axial extents of pole pieces and/or permanent magnets 26, as well as of inner webs 24 and outer webs 25 predefined by the length of the coils 23 in the stator 21, may vary in this case. If two corners of the rotor 22 and the stator 21 respectively are simultaneously positioned in front of one another in different positions, a force increase occurs in the respective position of the rotor and the valve piston connected thereto whereas an increase of the stroke with a sufficiently high expenditure of force occurs if two corners of the rotor and the stator respectively are successively positioned in front of one another over the respective stroke of the rotor 22 or the valve piston.
These circumstances are elucidated below with reference to the exemplary embodiments schematically illustrated in
The characteristics of the object of these documents disclosed in the preceding description, the claims, the abstract and the drawings may be essential to the realization of the different embodiments of the invention individually, as well as in arbitrary combinations.
Number | Date | Country | Kind |
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10 2013 108 164.9 | Jul 2013 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/066363 | 7/30/2014 | WO | 00 |