Abstract:
The invention relates to an arrangement of stringed solenoid drives ( 1, 2, 3 ), particularly for solenoid valves, wherein each solenoid drive comprises a magnetic circuit with a yoke ( 4 ), moveable armature ( 5 ), and an excitation coil ( 6 ) arranged on the yoke. The magnetic circuits of neighboring solenoid drives have pre-magnetization with the same polarity and at least approximately the same strength. Due to the pre-magnetization, the magnetic potential difference between neighboring magnetic circuits is reduced. The pre-magnetization is thus carried out with the same polarity as the excitation by current flow in the excitation coil.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an in-line array of closely spaced solenoid drives in which each solenoid drive includes a magnetic circuit with a yoke, a movable armature, and an excitation winding disposed on the yoke. 
       BACKGROUND OF THE INVENTION 
       [0002]    There are various application fields for systems in which quite a number of magnetic circuits are placed in a relationship of mutual influence, without any magnetizable parts being in direct contact. This is the case, e.g., when a number of solenoid valves are disposed closely spaced in an in-line array. 
         [0003]    The smaller the solenoid valves in terms of their outer dimensions and the closer they are to be arranged next to each other for reasons of space, the greater the extent of undesirable mutual influence of the magnetic circuits on each other. This is accompanied by losses of energy. Magnetic flux does not stay within an apparatus, but flows off, ineffective in terms of power for this apparatus, via neighboring, magnetically conductive metal parts or is redirected to neighboring magnetic circuits. In the most unfavorable case, it may happen that a valve is unintentionally also switched when its neighboring valve switches. 
         [0004]    Solenoid valves that are arranged side by side therefore require a higher voltage for switching or are no longer responsive at all. 
       SUMMARY OF THE INVENTION 
       [0005]    The arrangement according to the invention serves to reduce the leakage flux to neighboring magnetic circuits and allows a reliable switching of solenoid valves disposed in an in-line array, with a minimum amount of energy applied. 
         [0006]    Specifically, the invention provides an in-line array of closely spaced solenoid drives in which each solenoid drive includes a magnetic circuit with a yoke, a movable armature, and an excitation winding disposed on the yoke. The magnetic circuits of adjacent solenoid drives have a pre-magnetization of same magnetic polarity and of at least approximately same strength as a magnetization caused by current flow in the excitation winding of each solenoid drive. The pre-magnetization causes the magnetic potential difference between neighboring magnetic circuits to be reduced. The pre-magnetization is thus effected with the same polarity as the excitation by current flow in the excitation winding. 
         [0007]    The pre-magnetization may be effected by means of permanent magnets or else by applying a bias current in the amount of a fraction of the normal exciting current to the excitation windings. 
         [0008]    Alternatively, the pre-magnetization is produced by an external magnetic field which is the same for all neighboring magnetic circuits. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will now be described in greater detail with reference to the accompanying drawings, in which: 
           [0010]      FIG. 1  shows a magnetic circuit of the type usually employed in solenoid valves; 
           [0011]      FIG. 2  shows a first arrangement, according to the invention, of permanent magnets on a magnetic circuit; 
           [0012]      FIG. 3  shows a plurality of (for example three) identical, closely adjacent magnetic circuits; 
           [0013]      FIG. 4  schematically shows the magnetic resistances on the closely adjacent magnetic circuits of  FIG. 3 ; 
           [0014]      FIG. 5   a  shows a schematic representation of magnetic circuits closely disposed in an in-line array, with pre-magnetization, but without current flow; 
           [0015]      FIG. 5   b  shows a schematic representation of the same magnetic circuits with pre-magnetization and current flow in the outer magnetic circuits; 
           [0016]      FIG. 5   c  shows a schematic representation of the same magnetic circuits without pre-magnetization, but with current flow in the outer magnetic circuits; 
           [0017]      FIG. 6  shows an arrangement, according to the invention, of a permanent magnet on a U-shaped yoke; and 
           [0018]      FIG. 7  shows an arrangement, according to the invention, of a bar magnet on a double-T-shaped yoke. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    A conventional magnetic circuit as shown in  FIG. 1  is comprised of a U-shaped yoke  4 , a winding  6  and an armature  5 . 
         [0020]    The magnetic circuit in  FIG. 2  is likewise comprised of a yoke  4 , a winding  6  and an armature  5 . In addition, at least two permanent magnets  7  and  8  are arranged on the limbs of the yoke  4 , the polarization of these permanent magnets being opposite to each other on their faces contacting the limbs. Accordingly, the permanent magnet  7  contacts one yoke limb by its south pole face and the permanent magnet  8  contacts the other limb by its north pole face. 
         [0021]    The permanent magnets  7  and  8  may either be seated both on the outer sides of the yoke limbs or both on the inner sides. 
         [0022]    To reinforce the effect, a plurality of magnets each with the same polarization direction may be stacked on each limb. 
         [0023]    Rather than carrying out the above described pre-magnetization of the magnetic circuits disposed in an in-line array by means of permanent magnets, an bias current feed may also be made use of. 
         [0024]      FIG. 3  illustrates a plurality of (for example three) identical magnetic circuits arranged side by side in a closely adjacent relationship. In the practical application, the distances between the individual magnetic circuits  1 ,  2  and  3  are minimal, i.e. smaller than shown in  FIG. 3 . The magnetic circuits are more particularly part of miniaturized solenoid valves. 
         [0025]    When the winding  6  in the magnetic circuit  2  is energized while the windings  6  of the two magnetic circuits  1  and  3  remain without a current, the yoke  4  of the magnetic circuit  2  made of a magnetic material is magnetized and will attract the armature  5  of the magnetic circuit  2 , likewise made of a magnetic material. 
         [0026]    The yokes  4  in the neighboring magnetic circuits  1  and  3  are pre-magnetized by the permanent magnets  7  and  8 . 
         [0027]    As a result, the difference of potential between the yoke  4  and the armature  5  within the magnetic circuit  2  is greater than the difference of potential between the yoke  4  of the magnetic circuit  2  and the yokes  4  of the neighboring magnetic circuits  1  and/or  3 . 
         [0028]    Consequently, only the magnetic circuit  2  will switch and the two neighboring magnetic circuits  1  and  3  will not. 
         [0029]    Ideally, any leakage flux from the magnetic circuit  2  to the magnetic circuits  1  or  3  will not occur or is at least greatly reduced. 
         [0030]      FIG. 4  schematically illustrates the effective magnetic resistances at and between the magnetic circuits. Of interest here are the air gap resistances between neighboring magnetic circuits. For the magnetic circuits  1  and  2 , the air gap resistances between opposite yoke limbs are denoted by RmL 121 , RmL 122  and RmL 123 , RmL 124 . While the magnetic air gap resistances are proportional to the distance, they are also inversely proportional to the surface area of the opposite surfaces. Since the distances are small and the surfaces are relatively large, the magnetic air gap resistance is correspondingly small. 
         [0031]    While an equipolar pre-magnetization using permanent magnets generates a small closing force, this closing force (with the permanent magnets being appropriately designed) is not sufficient for the armature to be attracted. 
         [0032]    Now, the advantage of the equipolar pre-magnetization using permanent magnets resides in that during the switching of neighboring devices, practically no more leakage flux develops between the devices. The reason for this is that opposite pole faces are always of the same name (irrespective of whether or not the devices are energized!), between which no magnetic flux arises. 
         [0033]      FIG. 5   a  schematically shows three magnetic circuits closely disposed in an in-line array, with a pre-magnetization having the same direction and strength, but without current flow. The direction of the hatching indicates the polarity and the density of the hatching indicates the strength of the magnetic flux. The pre-magnetization causes a small magnetic flux to develop in the ferromagnetic circuits, which, however, is too weak to cause the armatures of the magnetic circuits to be attracted. 
         [0034]    In  FIG. 5   b  it is assumed that the two outer magnetic circuits are energized while the one in the middle is not. In the outer magnetic circuits a strong magnetic flux develops which causes the armatures to be attracted. In the middle magnetic circuit no or only a very small leakage flux develops since owing to the pre-magnetization, the poles opposing each other are still of the same name, though of different strengths. Practically&#39; no flux line transition takes place between the north and south poles. 
         [0035]    In  FIG. 5   c , again the two outer magnetic circuits are energized, but there is no pre-magnetization. In the outer magnetic circuits a strong magnetic flux is produced, which causes the armature to be attracted. However, because of the small distance between the pole faces of the magnetic circuits, flux lines also close over the middle magnetic circuit and leakage flux develops. A magnetic polarization is produced at the middle magnetic circuit which is opposite to that of the outer magnetic circuits but which, in the most unfavorable case, may be sufficient to cause the armature of the middle device to be attracted although the middle magnetic circuit is not energized. 
         [0036]    Under these circumstances, the pre-magnetization, proposed according to the invention, of all of the magnetic circuits disposed in an in-line array turns out to be very effective for reducing the magnetic leakage fields by reducing the magnetic potential differences between neighboring magnetic circuits. 
         [0037]    In a further embodiment shown in  FIG. 6 , a U-shaped or C-shaped permanent magnet is engaged about the U-shaped yoke. 
         [0038]    In the embodiment shown in  FIG. 7 , the yoke is double-T-shaped. A bar-shaped or rod-shaped permanent magnet is inserted between the legs of the double-T-shaped yoke. 
         [0039]    Although the invention has been described hereinabove with reference to a specific embodiment, it is not limited to this embodiment and no doubt further alternatives will occur to the skilled person that lie within the scope of the invention as claimed.