Abstract:
A solenoid arrangement comprises a pole tube which is axially subdivided into a pole core section, a transition section, and a tube section. A magnetic flux between the pole core section and the tube section is interrupted by the transition section. An armature is movably guided in the pole tube and has, at its end facing the pole core section, a flange which axially projects from an end face. According to the invention, the pole core section has a stepped depression into which the armature can plunge and which, starting from the transition section, is subdivided into an annular collar, a shoulder, and a notch which is set back axially and radially. An axial dimension of the collar exceeds an axial dimension of the flange.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2009/005250 filed on Jul. 20, 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 
     One such solenoid arrangement is known from German Patent Disclosure DE 197 07 587 A1. A pressure-proof solenoid has, in addition to the pole tube, a coil for actuating an armature that is axially movably guided in an armature chamber of the pole tube. The pole tube essentially comprises the following: a pole piece—also called a pole core—which can be screwed into a valve housing via a central thread; a nonmagnetic adapter piece; and a tubular piece, which adjoins the adapter and is closed on the face end, on the side remote from the pole piece, by means of a component acting as a stroke limiter. The pole piece, the adapter piece, the tube piece, and the stroke limiter define the armature chamber for the armature that cooperates with the coil. The armature is connected to a tappet, which penetrates the pole piece in the axial direction and serves to actuate a valve slide of a hydraulic valve. The nonmagnetic adapter piece serves to divert the magnetic flux into the armature. This nonmagnetic adapter piece can be embodied in annular-conical form, for attaining a favorable characteristic force-travel curve. In the production, however, such shaping involves effort and expense. Especially in simply switching magnets, the simplest possible geometry of the adapter piece should be employed in the production. 
     Examples for how an armature in cooperation with a pole piece can be contoured are given in German Patent Disclosure DE 103 27 875 B4. However, in terms of production, this discloses pole pieces of quite complicated shape. 
     In conventional, easy to manufacture solenoids, the characteristic force-travel curve at present usually does not have an optimal course. Specifically, for actuating hydraulic switching valves or proportional valves, even at short to medium strokes of the control piston, strong flow forces, oriented counter to the actuation, must be overcome and they increase only slightly in the further course of the stroke. Moreover, the flow forces are often effective over only a narrowly defined portion of the stroke. Conversely, conventional solenoids develop a strong force only in the final portion of the stroke. Aside from this, the force development is not very localized and is usually embodied as uniform or with a slight ascending slope over a wide stroke range. This requires large solenoids, with correspondingly high consumption of material and energy. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to disclose an improved solenoid arrangement which can be adapted structurally in a simple way to the actuation force characteristic curve of a valve. 
     This object is attained by a solenoid arrangement according to the invention. 
     The embodiment of a bolster on the armature and of a graduated indentation in the pole core, with a countersunk feature for receiving the bolster, can be achieved in manufacture by simple means. The greater length of the collar in comparison to the bolster on the armature has the effect that over the stroke course of the armature in the actuation operation, edges and boundary lines or boundary faces of the pole piece come into coincidence, in succession and spaced apart from one another, with corresponding segments of the armature. First, coincidence occurs between a face-end inner boundary line of the collar and end face of the armature. As the stroke continues, the bolster then plunges into the countersunk feature, moving past a shoulder of the indentation. In this way, the characteristic force-stroke curve can be designed such that over a defined portion of the stroke, namely along the course of the armature between the two edges, a targeted plateau-like elevation of the force occurs. The solenoid arrangement according to the invention is simple in construction and can be produced favorably. It can be adapted optimally to the flow force characteristic curves, for instance of switching valves. By means of the structural form described, the force even decreases again in the end region of the armature stroke, or in other words after the bolster plunges into the countersunk feature. This contributes to reduced stress on the nonstick disk, to less switching noise, and to a faster switching time. Overall, with the valve arrangement of the invention, at less electrical power, greater valve forces or flow forces can be overcome, and switching valves in particular can be actuated safely and efficiently. 
     Accordingly, the object is also attained by a valve arrangement which has a solenoid arrangement of this kind. 
     In particular, the valve is combined with a solenoid arrangement that in its characteristic curve is adapted optimally to the flow force conditions of the valve. The adaptation is effected structurally simply, by way of the geometric length ratios of the collar and bolster. In a clear way, the location of the aforementioned edges, for instance, is adapted to the course of the opening cross section of the valve along the actuation stroke. 
     In an advantageous feature of the present invention, the transition segment is formed of a nonmagnetic material, and a separation segment between the transition segment and the collar is oriented essentially perpendicular to a center axis of the pole tube. Precisely with such simply geometries at the separation segment, characteristic curves that are well adapted to a valve can be attained by means of the embodiment according to the invention of the armature and the pole core segment. It is especially simple to manufacture, for instance using resistance welding—such as capacitor discharge welding or medium-frequency welding—for joining the pole piece and the separating ring that forms the transition segment. 
     Preferably, a nonstick disk is disposed between the end face of the armature and the shoulder of the pole piece. A comparatively large area is available there, so that the nonstick disk withstands even heavy loads. The nonstick disk could even be drawn over onto the bolster and thus rest in captive fashion on the end face of the armature. 
     The described geometry at the armature and the pole core segment can also be utilized to damp an impact of the armature on the pole core. To that end, a radial gap between the bolster and the countersunk feature is dimensioned correspondingly narrowly. The fluidic damping is then effected via the positive displacement of fluid out of an outer annular chamber between the armature—or more precisely its end face and the bolster—and the shoulder of the indentation. 
     Preferably, in a valve arrangement having the solenoid arrangement of the invention, a first position of the armature, in which position the end face of the armature is facing a boundary line of the end face of the collar, is equivalent to a slight degree of opening of the valve, or in other words to a position of the valve piston at which flow forces become definitive. A second position of the armature, at which an end face of the bolster of the armature is facing the shoulder of the indentation, is equivalent to a greater degree of opening of the valve, at which the valve piston has already nearly completed its opening stroke and in which the flow forces are receding again. This can for instance be from 25% to 75% of the opening stroke of the valve piston. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention and its advantages will be described in further detail below with reference to the exemplary embodiment shown in the drawings. 
         FIG. 1  shows a solenoid arrangement in a schematic sectional view; 
         FIG. 2  shows an detail of  FIG. 1  around the region of the working air gap; and 
         FIG. 3  shows a characteristic curve of the solenoid arrangement of the invention, in comparison with a flow force characteristic curve of a valve and a characteristic curve of a conventional solenoid. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In  FIG. 1 , a solenoid arrangement  1  for actuating a valve slide of a hydraulic valve (not shown) is shown. The solenoid arrangement  1  has a fluid-tight pole tube  3 . The pole tube  3  has a pole core segment  5 , a separation segment  7 —in the claims also called a transition segment—a tube segment  9 , and a closure piece  11 —also called a stroke limiter. The pole core segment  5 , separation segment  7 , tube segment  9 , and closure piece  11  form a circular-cylindrical receiving chamber for an armature  13 . A tappet  15  is guided in the pole core segment  5  and protrudes from it on the outer face end of the pole core segment  5 . 
     By means of a thread  17  on the pole core segment  5 , the pole tube  3  is screwed into a valve housing of the hydraulic valve. A coil component is slipped onto the pole tube  3 . It includes the actual coil  19  as well as a housing of magnetic material (not shown), which acts as a yoke for a magnetic circuit that includes the pole tube  3 . The separation segment  7  interrupts the magnetic circuit in the vicinity of the working air gap  21  between the armature  13  and the pole core segment  5  and forces the magnetic field lines to transfer from the pole core segment  5  to the armature  13 . 
     The armature  13 , on its face end toward the pole core segment  5 , is provided with a bolster  24  that protrudes from the end face  22 . A nonstick disk  25  is placed on the circular-annular end face  22 . This nonstick disk, for securing, can optionally be drawn onto the bolster  24 . Axial fluid compensation conduits  27  penetrate the armature  13 . They discharge at an end face  29  of the bolster  24 . 
     The pole core segment, on its inside, has a graduated indentation  31  for receiving the armature portion oriented toward it. This indentation  31  is divided up as follows: A collar  33  protrudes in circular-annular fashion past an inner end face  34  of the pole core segment  5 . The end face  34  also forms a shoulder for a central countersunk feature  36 . 
     The inside diameter of the collar  33  is equivalent to the inside diameter of the separation segment  7  and to the inside diameter of the tube segment  9 . The inside diameter of the countersunk feature  36  is selected such that the bolster  24  can plunge into the countersunk feature  36 . Via a gap between the bolster  24  and the countersunk feature  36 , fluidic damping of the armature motion in the terminal position can be attained. The damping volume is located in an annular chamber that is defined by the bolster  24 , the end face  22 , the end face  34 , and the collar  33 . 
     The region around the working air gap  21  is shown enlarged in  FIG. 2 . The essentially circular-tubular form of the separation segment  7 , which has no cone, can be seen. A pole tube  3  with this kind of separation segment can be joined together from tubular or cup-shaped semifinished products, for instance by means of electrical resistance welding. The nonstick disk  25 ′ shown is a variant of that in  FIG. 1 . The nonstick disk  25 ′ is placed in the working air gap  21  and rests on the end face  34 . It can optionally be secured there. 
     The bolster  24  is defined on its face end by an outer annular edge  41 . There is also an annular edge  40  at the transition from the end face  22  of the armature into the jacket face of the armature. An imaginary, circular boundary line  42  is located at the transition from the collar  33  to the separation segment  7 , and at this line the magnetizability of the pole tube  3  changes abruptly in its axial course. Between the end face  34  and the countersunk feature  36 , the annular edge  43  is present in the graduated indentation  31  of the pole core segment  5 . This annular edge can be chamfered or rounded. 
       FIG. 3  shows a characteristic force-stroke curve  50  of a conventional solenoid arrangement, for instance an actuation magnet, of the kind described in DE 197 07 587 A1 referred to at the outset; a characteristic force-stroke curve  52  of the solenoid arrangement  1  of the invention; and an characteristic actuation force-stroke curve  54  (in dashed lines) of a typically directly actuated switching valve of the rated size 6 or 10. The stroke is subdivided into ranges B 1  through B 6 . The length of the ranges is on the order of magnitude of 1 to 2 mm each, for example. The characteristic curve  54  of the valve has a basic line, which rises to the range B 1  and is dictated by the usual action of a restoring spring on the valve piston and by the friction of the valve piston in the valve bore. However, the flow forces acting on the valve piston in the opening operation have a major effect on the characteristic curve  54 . They cause the sharp rise, which can be seen in the ranges B 2  and B 3  of the characteristic curve  54 , in the requisite actuation force. After the valve has been connected fully through, flow forces are no longer definitive, as the curve  54  in the range B 1  shows. 
     Upon an electrical actuation of the solenoid arrangement  1  by a supply of current to the coil  19 , the following procedure takes place: From a terminal position at the closure piece  11  or from contact with the tappet  15 —as shown in FIG.  1 —the armature  13  begins to move in the direction of the pole core segment  5 . The motion begins in the range B 6  or at the transition from the range B 5  to the range B 4 —in this case contact with the tappet  15  occurs—with initially low force, as indicated by the line  52 . The range B 3  is the portion of the course of motion at which the annular edge  40  of the armature  13  crosses over the boundary line  42  with the collar. Between the annular edge  40  and the boundary line  42 , there is a high density of magnetic field lines in the working air gap. When the armature  13  with the annular edge  40  plunges into the collar  33 , a pronounced decrease occurs in the magnetic field energy present in the working air gap. As a result, the characteristic curve  52  rises steeply from the range B 4  to the range B 3 . 
     Once the armature  13  has passed the boundary line  42 , a further range of high field line density is present between the annular edge  41  at the bolster  24  of the armature  13  and the annular edge  43  of the graduated indentation  31 . As the armature  13  plunges to an increasing extent into the graduated indentation  31 , the high force can therefore be maintained, until the armature plunges, with the bolster  24 , into the countersunk feature  36 . This can be seen in the characteristic curve  52  in the range B 2  and at the transition from the range B 2  to the range B 1 . Over the further course of the armature  13 , only the volume, filled with only a few magnetic field lines, in the countersunk feature  36  is now reduced. The force accordingly drops in the range B 1 . The motion ends when the armature  13 , with the nonstick disk  25  or  25 ′, rests on the end face  34 . A gap remains between the end face  29  of the bolster  24  and the bottom of the countersunk feature  36 . 
     By the selection of the axial disposition of the boundary line  42  and the annular edge  43 , or in other words of the length of the collar  33 , and by means of a suitable length of the bolster  24 , a plateau-like increase in the magnetic force can thus be attained over a comparatively wide stroke range in the characteristic force-stroke curve  52  of the solenoid arrangement  1 . The difference in length between the collar  33  and the bolster  24  approximately produces the length of the plateau of the characteristic force-stroke curve  52  in the ranges B 2  and B 3 . For that purpose, at the beginning and in the end phase of the armature stroke—the ranges B 4  through B 6  and the range B 1 —the magnetic force is correspondingly reduced—in each case in comparison to the characteristic curve  50  of a conventional magnet with the same electrical power. 
     The solenoid arrangement  1  described is excellently well suited for actuating a switching multiposition valve. The typical actuation force characteristic curve  54  on the stroke of the valve slide, as noted, has a significant increase because of flow forces upon the enlargement of the opening cross section, until full valve opening is attained. This can be seen as a plateau in the actuation force in the ranges B 2  and B 3  of the characteristic curve  54 . By means of the length of the bolster  24  and the collar  33 , among other ways, the solenoid arrangement  1  is now designed such that the plateau of the actuation force in the characteristic curve  54  is covered by the plateau-like increase in the magnetic force in the characteristic curve  52 . Thus over each portion of the armature stroke, sufficient magnetic force for securely connecting the valve through exists. Because of the steep rise in the magnetic force in the range B 4  of the characteristic curve  52 , sufficient magnetic force is also present even at the beginning of the stroke of the valve slide, when the prestressing of the restoring spring has to be overcome. The decrease in magnetic force in the range B 1  coincides with the decrease in the flow forces once the valve has been connected fully through. Moreover, because of the decrease in force, the nonstick disk  25  or  25 ′ is less severely stressed by the impact of the armature  13  striking it. The impact noise is slight as well. The armature  13  returns to its outset position faster after the coil  19  has been shut off. 
     The use of the solenoid arrangement of the invention has been described in terms of the exemplary embodiment for a switching multiposition valve for performing the opening stroke that is closed when with current. It is understood that it can also be employed with a switching multiposition valve for performing the closing stroke that is open when without current. The solenoid arrangement of the invention can furthermore be used for actuating a proportional valve as well. Then a plurality of bolsters disposed in stages can also be provided on the armature, and a correspondingly multiply graduated indentation on the pole piece, which indentation receives the bolsters each in suitable countersunk features, can be employed. 
     A further variant is to embody the collar  33  conically. Then, as a result of the above-described shape of the armature  13  with the bolster  24  and of the graduated indentation  31 , the proportional range can be extended over a wider stroke range. 
     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.