Abstract:
The invention relates to a solenoid wherein a magnetic discontinuity is formed in the pole tube reducing the effective material thickness, such as by reducing the thickness, particularly the wall thickness of the magnetically active material, the front face of the armature facing the pole core and a bottom face in the interior of the pole tube at the pole core each have a contour allowing mutual axial overlapping. This enables advantageous influencing of the force-stroke characteristic curve of the solenoid with low production effort.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2009/004816 filed on Jul. 3, 2009. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a solenoid arrangement. The invention also relates to a valve arrangement. 
     2 Description of the Prior Art 
     The solenoid arrangement of this generic type is often used in fluidics as a drive for actuating hydraulic or pneumatic valves. 
     Actuation magnets in fluidics are usually of modular construction and have a pole tube which is fluid-tight except for a through opening for the tappet and in which the armature is movable. A coil body is slipped over the pole tube. The coil body is secured with a nut. A separating ring of nonmagnetic material is typically welded in place between a pole core segment and a tube segment of the pole tube. As a result, the magnetic field lines in the pole tube pass from the pole core segment to the armature. Only in that way can a working air gap filled with field lines develop. 
     Precisely with switching valves, solenoids of the simplest possible construction are employed. For example, German Patent Application 10 2008 030 748 of the present Applicant describes a pole tube which, in order to generate the requisite discontinuity between the pole core and the tube segment, has a reduced material thickness in the vicinity of the transition segment. In that case, a secondary magnetic flux through the transition segment is tolerated for the sake of simpler production of the pole tube. These pole tubes are also called thin—turned pole tubes, since the reducing in the material thickness is typically done by turning on a lathe. However—in comparison to the usable magnetic flux sent through the working air gap—that requires a considerable secondary flux. If a thin-turned pole tube is used instead of a conventional pole tube, the presumptive force loss for a solenoid is about 10%, on the condition that the coil capacity is identical. Moreover, solenoids with thin-turned pole tubes often have a force-stroke characteristic curve that is very unfavorable for the valve actuation, as the characteristic curve  42  for a conventional solenoid in  FIG. 3  shows. The actuation force rises significantly just before the armature makes contact with the pole core. A fluidic valve, however, requires a sufficient actuation force over a greater stroke range. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is the object of the present invention to disclose an improved solenoid arrangement, which in particular has a characteristic curve suited to the valve actuation. 
     This object is attained by a solenoid arrangement according to the invention. 
     In a solenoid in which a magnetic discontinuity in the pole tube is formed by means of reducing the effective material thickness—such as a reduction in the thickness and in particular the wall thickness of the magnetically effective material—the invention is based in general on the concept of providing both the face end, toward the pole core segment, of the armature and a bottom, provided in the interior of the pole tube on the pole core segment, with a respective contour that allows a mutual axial overlap. This makes advantageous variation of the force-stroke characteristic curve of the solenoid possible, at low production cost. 
     An embodiment in which the transition segment between the pole core segment and the tube segment of the pole tube has a reduced wall thickness, is especially preferred. In addition, by means of a protruding bolster, a step is formed on the armature. The bottom face on the pole core segment is likewise stepped by means of a cylindrical countersunk feature. The bolster of the armature can be received in the countersunk feature, such that at least a segment of the bolster dips into the countersunk feature when the armature contacts the bottom face. 
     In this way, the force-stroke characteristic curve of the solenoid arrangement can be designed such that a sufficient actuation force is available over a greater range of the characteristic curve. Because of the mode of construction according to the invention, the magnetic field lines are concentrated more strongly on the region between the armature and the bottom face of the pole core segment. As a result, over the course of the armature as it moves from its terminal position remote from the pole core to where the bolster dips into the countersunk feature, a strong actuation force is available. Just before the bolster dips into the countersunk feature, the actuation force rises markedly. After this plunge, the actuation force drops. Over the remaining course of the armature stroke until it contacts the bottom face, a moderate actuation force is available. Because of the reduced actuation force in the final stroke segment, the mechanical load on the pole tube, and on a nonstick disk that may be present between the armature and the pole core segment, is also reduced. Furthermore, better switching times are achieved. 
     By means of the solenoid arrangement of the invention, valves that usually require strong actuation forces right at the outset of an opening operation of the valve slide can be triggered or connected through securely. Because of the strong actuation force that is already present in a segment of the stroke remote from the pole core, it is possible to use a relatively weakly dimensioned coil. The required electrical current for the actuation is reduced, compared to conventional solenoids. Moreover, a solenoid arrangement can now be furnished that even when using thin-turned pole tubes has a precisely defined characteristic curve that is largely independent of production-dictated variations. In the present application, for the sake of simplicity, the term “thin-turned pole tube” is used. However, this term is meant to apply generally to solenoid arrangements having a pole tube that has a reduced wall thickness in the transition segment between the pole core and the tube segment. The reduced wall thickness can be created not only by turning but also by other processes. Examples that can be named are roller-burnishing, round-kneading, or stretching of a bar-shaped semifinished product, or molding of a ring of nonmagnetic material, as described in the aforementioned German Patent Application 10 2008 030 748 of the present Applicant. All these methods for reducing the wall thickness in the transition segment are meant to be included in the term “thin-turned pole tube”. 
     The object is also attained by a valve arrangement which is equipped with a solenoid arrangement of this kind. By adaptation of the contours, especially the length of the bolster and optionally the length of a collar on the pole core segment, the force-stroke characteristic curve of the solenoid arrangement can be optimally adapted to the actuation force requirements of the valve arrangement. 
     The aforementioned contours can have the most various forms. For example, bolsterlike, annular conical and spherical caplike protuberances are suitable. They need not necessarily be concentric to the axis of motion of the armature, but the concentric form does make them easier to manufacture. The respective counterpart contour preferably has geometrically complementary countersunk features. 
     Preferably, as noted, the pole core segment, the transition segment, and the tube segment are embodied in one piece from a magnetic material. This allows especially inexpensive manufacture of the pole tube. The manufacture is especially simple if the transition segment has a radial groove in an outer face of the pole tube. The transitions from the radial groove to the pole core segment and from the radial groove to the tube segment can be rounded, to prevent fissuring. 
     The bolster can be embodied as somewhat shorter than a collar segment of the pole core. As a result, the slight increase of force effected by the collar segment can be used in the segment of the characteristic curve that is remote from the pole core. 
     In a preferred feature of the present invention, a radial gap between the bolster and the countersunk feature is dimensioned such that in a terminal position associated with the pole core segment, a motion of the armature is fluidically damped. As a result, the mechanical load on the pole tube and optionally on a nonstick disk placed between the armature and the pole core segment is lessened. 
     In an especially preferred feature of the present invention, a first position of the armature, in which the end face of the armature is facing an end, toward the pole core segment, of the transition segment, and/or a second position of the armature, in which an end face of the bolster of the armature is facing the bottom face of the pole core segment, is disposed in accordance with an expected profile of forces for flow forces acting on the valve slide in an opening operation. 
     Preferably, the second position of the armature corresponds to a nearly completely open flow cross section. At that point, the flow-caused restoring forces on the valve slide countersunk feature. The reduced actuation forces once the bolster dips into the countersunk feature are still sufficient to connect the valve fully through. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention and its advantages are described in greater detail below in terms of the exemplary embodiment shown in the drawings. 
         FIG. 1  shows a partial section view through a solenoid arrangement of the present invention, with a pole tube secured to a valve housing, with a coil body seated on the pole tube, and with a housing surrounding the coil body. 
         FIG. 2  shows a section through the pole tube of the solenoid arrangement shown in  FIG. 1 ; and 
         FIG. 3  shows a force-stroke characteristic curve of the solenoid arrangement of the invention, in comparison to a force-stroke characteristic curve of a conventional solenoid. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows the typical construction of a solenoid  1 , of the kind used for actuating switching valves in fluidics, having a pole tube according to the invention inserted therein. On a valve housing  3 , a pole tube  5  of the solenoid  1  is screwed into the valve bore. A magnet coil  7  is slipped onto the pole tube  5 . The magnet coil  7  is secured on the pole tube  5  by means of a nut  9 . At a transition segment  14 , the pole tube is constricted in terms of its external radius. 
       FIG. 2  shows the construction of the pole tube  5 , and the armature guided in it, in accordance with the present invention. A pole tube body  11  is furnished in the form shown, from a ferromagnetic steel, such as goods in bar form, by metal-cutting machining. 
     The pole tube body  11  is subdivided axially into a pole core  12 , a transition segment  14 , and a tube segment  16 . The overall bushlike shape of the pole tube body  11  allows the insertion of an armature  20  into a central bore  18 . The bore  18 , on its end remote from the pole core  12 , at the opening of the tube segment  16 , is later provided with a closure piece (not shown)—also called a stroke limiter—which at the same time has a thread for securing the nut  9 . 
     An annular-conical collar  22  protrudes from the pole core  12 . Via a rounded area, this collar merges with a tube segment  16 . In comparison to the pole core  12  and the tube segment  16 , the outer circumferential surface of the pole tube  5  is constricted by a radial groove at the transition segment  14 . Via a further rounded area  24  and an obliquely positioned conical outer face, the transition segment  14  merges with the tube segment  16 . 
     The armature  20  is supported axially displaceably in the bore  18 . A nonstick disk  26  is placed in the working air gap between the armature  20  and the pole core  12 . 
     The armature  20  is contoured, on its face end toward the pole core  12 , by a step: A cylindrical bolster  30  protrudes from the annularly embodied end face  28 . 
     In the bottom face  32  of the bore  18 , there is a countersunk feature  34  that corresponds geometrically with the bolster  30 . This means that the bolster  30  can dip into the countersunk feature  34 . Both the axial length and the radial length of the bolster  30  are selected with regard to the desired characteristic curve form, as will be described hereinafter. The depth of the countersunk feature  34  is selected such that, taking into account the nonstick disk  26 , there is still a gap between the bottom of the countersunk feature  34  and the end face of the bolster  30  even when the armature  20  is in its terminal position toward the pole core. 
       FIG. 3  shows the force-stroke characteristic curve  40  of the solenoid arrangement  1  of the invention, in comparison to the force-stroke characteristic curve  42  of a conventional solenoid arrangement, which though it has a thin-turned pole tube does not have contouring of the armature face end toward the pole core or of the bottom of the bore  18  at the pole core  12 . 
     In the solenoid arrangement  1  of the invention, as the characteristic curve  40  compared to the characteristic curve  42  shows, it was possible to attain a more-pronounced increase in the actuation force in an early segment  40   a  of the stroke process. At this point the armature  20  is still at a great distance from the pole core  12 . The contours of the end face of the armature and of the bottom face of the pole core  12 , that is, of the bolster  30  and the countersunk feature  34 , do not yet axially overlap. 
     The characteristic curve  40  rises more steeply as the armature  20  approaches closer to the pole core  12 , until in the segment  40   b  a plateau develops. The segment  40   b  corresponds to a position of the armature  20  in which the bolster  30  is located just before the bottom face  32  and in other words has not yet dipped into the countersunk feature  34 . 
     With the embodiment of the axial overlap, which in this example is when the bolster  30  dips into the countersunk feature  34 , the characteristic curve  40  initially falls, in the segment  40   c . Upon contact of the armature  20  with the pole core  12 , the characteristic curve  40  finally rises moderately and concludes with the retention force  40   d , but no longer goes higher than the plateau reached in segment  40   b.    
     The influence of the annular-conical collar  22  on the characteristic curve  40  an also on the characteristic curve  42  is marginal. In the stroke range  44 , at most, a minimal bulge in the characteristic curve  42  can be seen. The rise in the characteristic curve  40  attained by the contouring of the armature  20  and of the bottom of the pole core  12  far exceeds any influence on the part of the annular-conical collar. 
     By adaptation of the axial length of the bolster  30 , the location of the plateau segment  40 b of the characteristic curve  40  can be varied. The radial length of the bolster  30  and the size of the radial gap between the bolster  30  and the countersunk feature  34  have an influence on the height of the plateau and on the variously strongly pronounced nature of the protuberance of the characteristic curve  40  compared to the characteristic curve  42 . The air gap from the bottom of the countersunk feature that remains, in the terminal position of the armature  20  on the pole core  12 , has an influence on the retention force  40   d . In particular by the described adaptations of the armature contour and the bottom contour, the characteristic curve  40  is adapted to the actuation force characteristic curve of a fluidic valve in such a way that a range in which strong actuation forces are required—such as from the onset of opening of a fluid path in the valve until the path is completely open—is approximately equivalent to the plateau segment  40   b . Thus flow forces that act in the closing direction of the valve, especially, are securely overcome, and the valve slide is connected through from every actuation state. 
     Especially with proportional valves, in which the position of the valve slide is controlled by the actuation force acting counter to a spring and furnished by the solenoid  1 , the characteristic curve  40  that falls near  40   c  is advantageous. The result on the position axis is a very narrow sectional range between the spring characteristic curve  42  and the force-stroke characteristic curve  40 . The desired position of the valve slide can thus be triggered very precisely, and with little deviation, by means of the supply of electrical current to the solenoid  1 . 
     The invention is based generally on the concept of providing both the face end, toward the pole core segment, of the armature and a bottom, provided in the interior of the pole tube on the pole core segment, with a respective contour that allows a mutual axial overlap. This makes advantageous variation of the force-stroke characteristic curve of the solenoid possible, at low production cost. 
     The foregoing relates to the preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.