Abstract:
In a magnet coil arrangement having a wound coil former and having a metal housing surrounding the wound coil former, contact tabs are held in a plug-in base, one of which serves as a protective conductor connection. The contact tab serving as a protective conductor connection is held on the metal housing by a metallic connecting part. The free spaces between the wound coil former, the metal housing and the plug-in base are encapsulated with plastic. At the interfaces between the metal parts and plastic, moisture can enter the magnet coil arrangement. In order to prevent this moisture from getting into the connecting space, in which electric feed lines coming from the outside are connected to the contact tabs, in the area in which the connecting part engages in the contact tab, the contact tab serving as a protective conductor connection is arranged inside the plug-in base. Between the connecting part and the plug-in base there is arranged a sealing part, of which a first sealing face rests on the connecting part and a second sealing face rests on the plug-in base. The magnet coil arrangement is provided to operate valves which are used in fluid engineering.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to a magnet coil arrangement, in particular for operating valves. 
     A magnet coil arrangement of this type is disclosed by DE 43 41 087 C2. A coil former which is provided with an electric winding is arranged in a metal housing. A plug-in base provided with contact tabs is held on the metal housing by a metal connecting part. One of the contact tabs is connected to the metal housing via the connecting part as a protective conductor connection. The ends of the coil windings are connected to two further contact tabs. The free spaces between the wound coil former, the metal housing and the plug-in base are filled with plastic. Moisture can penetrate into the magnet coil arrangement through gaps at the interfaces between the metal housing and the plastic. In order to prevent the moisture entering the connecting space through the plug-in base along the contact tab serving as the protective conductor connection, a sealing ring which encloses the connecting part is provided between the contact tab serving as protective conductor connection and the metal housing. During the assembly preceding the encapsulation, the connecting part is pressed into a recess in the metal housing and into a recess in the contact tab. In the process, the sealing ring is clamped in between the metal housing and the contact tab. 
     Because of the curvature of the metal housing, the distance between the contact tab and the metal housing in the contact area of the sealing ring is of variable size, so that the sealing ring gives way outwardly to a greater or lesser extent. This leads to nonuniform deformation of the sealing ring over its circumference. The free circumferential surface of the sealing ring, that is to say the area of the sealing ring that is not resting on a metal part comes into contact with the plastic during encapsulation. As a result of the high temperature of the plastic during the encapsulation, the material of the sealing ring is highly thermally stressed. In addition, it is not ensured that, following the curing of the plastic, during which a certain shrinkage always has to be expected, a satisfactory sealing effect between the plastic and the surface of the sealing ring which is free before the encapsulation is ensured. There is therefore the risk that moisture which passes to the sealing ring via a gap between metal housing and the plastic, via a gap between the sealing ring and the plastic adjoining it and via the gap between the contact tab and the plug-in base or via the gap between the contact tab and the plastic, will nevertheless penetrate into the connecting space. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of providing a magnet coil arrangement of the type mentioned at the beginning which prevents liquid which has penetrated into the magnet coil arrangement via a gap between the metal housing and the plastic adjoining the latter being passed on into the connecting space. 
     In the magnet coil arrangement according to the invention, the sealing part touches neither the contact tab serving as a protective conductor connection nor the metal housing. Since the contact tab runs within the plug-in base in the area in which the connecting part engages in said contact tab, it is sufficient for the sealing part to rest on the connecting part on one side and on the plug-in base on the other side. Since the sealing part has a force applied to it even before the encapsulation of the magnet coil arrangement, the pressure of the plastic during encapsulation and in the following cooling phase plays no part in the sealing effect. In addition, the shrinkage of the plastic during cooling does not play any part in the sealing effect. The sealing part can be arranged between the connecting part and the plug-in base so as to seal both radially and axially. 
     If the sealing part is arranged to seal radially, it is advantageous to arrange the sealing part in a recess in the plug-in base which is matched to the outer contour of the sealing part, the recess is deeper than the thickness of the sealing part, the sealing part can give way in the axial direction that is to say in the installed state it assumes a substantially oval to egg-shaped cross section. A shoulder on the connecting part ensures that there is a defined distance between the metal housing and the surface of the plug-in base that faces it. If the outer diameter of the shoulder is greater than the inner diameter of the recess, no plastic reaches the sealing part during the encapsulation of the magnet coil arrangement. In addition, the part of the shoulder resting on the plug-in base prevents the connecting part being pulled out of the plug-in base under high tension. As an alternative to a radially sealing arrangement of the sealing part, the invention permits an axially sealing arrangement of the sealing part. In this case, the connecting part is provided with a collar which, when the connecting part is pressed into the contact tab held in the plug-in base, comes into contact with the plug-in base and in this way limits the force acting on the sealing part. In addition, the collar prevents the sealing part coming into contact with the hot plastic during encapsulation if the connecting part is rotationally symmetrical, at least in the sealing area, a commercially available and therefore cost-effective O ring can be used as the sealing part. If one side face of the plug-in base is provided with a projection between the outwardly pointing side and the side of the plug-in base that faces the metal housing, the result is a form-fitting connection which, even when there is high tension on the contact tabs or on the connecting part, prevents the plug-in base being pulled out of the plastic body. One or more recesses on the side of the plug-in base which faces the metal housing, said recesses surrounding the connecting part, improve the sealing effect in the boundary area between the plug-in base and the plastic used for the encapsulation, the recesses making initial melting easier during encapsulation or being effective as a labyrinth seal. If only that section of the contact tab serving as a protective conductor connection in which the connecting part engages is held in the plug-in base, the production of the plug-in base is simplified. Following the production of the plug-in base, the contact tab is pushed into a recess in the plug-in base. In this case, it is advantageous to arrange this recess at right angles to the recess provided for the connecting part. Even better sealing against penetration of moisture into the connecting space may be achieved if the contact tab serving as a protective conductor connection is held only in the plug-in base. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail below together with its further details by using exemplary embodiments which are illustrated in the drawings, in which 
     FIG. 1 shows a longitudinal section through part of a first magnet coil arrangement constructed in accordance with the invention, 
     FIG. 2 shows a section along the line A—A in FIG. 1, 
     FIG. 3 shows individual parts of the magnet coil arrangement illustrated in FIGS. 1 and 2 in the manner of an exploded drawing, 
     FIG. 4 shows a section corresponding to FIG. 2 through a second magnet coil arrangement according to the invention, 
     FIG. 5 shows a section corresponding to FIG. 1 through a third magnet coil arrangement according to the invention, and 
     FIG. 6 shows individual parts of the magnet coil arrangement illustrated in FIG. 5 in the manner of an exploded drawing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show various sections through part of a first magnet coil arrangement  10  constructed in accordance with the invention. Here, FIG. 1 shows a longitudinal section through the magnet coil arrangement  10  and FIG. 2 shows a transverse section along the line A—A in FIG.  1 . On the basis of FIG. 2, FIG. 3 shows individual parts of the magnet coil arrangement  10  illustrated in FIGS. 1 and 2 in the manner of an exploded drawing for the purpose of clarification. Identical components are provided with the same designations here. 
     A coil former  12  provided with a winding  11  is surrounded by a pot-like metal housing  13 . Arranged in a plug-in base  14  produced from electrically insulating material, for example plastic, are a contact tab  15  serving as a protective conductor connection and further contact tabs, to which the ends of the winding  11  are connected. The further contact tabs and the winding ends are not illustrated in FIGS. 1 to  3 , for reasons of clarity. The contact tab  15  is enclosed by the material of the plug-in base  14 , apart from the area  15   a  projecting into a connecting space  16 . During the production of the plug-in base  14 , the contact tab  15  is inserted into the injection mold and then encapsulated with plastic. In FIG. 2, the connecting space  16  is closed off by a cap  17  illustrated schematically. A circumferential seal  18  prevents moisture penetrating into the connecting space  16 . 
     A bolt-like metallic connecting part  21  is arranged in a recess  20 . The contact tab  15  is both held mechanically on the metal housing  13  via the connecting part  21  and also connected electrically to said metal housing  13 . In a recess  22  in the plug-in base  14 , running concentrically with the recess  20  and on the side facing the metal housing  13 , an O ring  23  serving as a sealing part is arranged. Both the recess  22  and the sealing area  21   a  of the connecting part  21  have a circular cross section in the sealing area. The inner diameter of the recess  22 , the outer diameter of the sealing area  21   a  and the O ring  23  are matched to one another in such a way that the O ring seals radially. In the axial direction of the connecting part  21 , the recess  22  is larger than the thickness of the O ring  23 . The O ring  23  can therefore give way in the axial direction. A shoulder  21   b , whose outer diameter is larger than the inner diameter of the recess  22 , closes the recess  22 . Its thickness determines the distance between the metal housing  13  and the plug-in base  14 . As shown in particular by FIG. 2, the shoulder  21   b  rests only linearly on the metal housing  13  because of the curvature of the latter. The connecting part  21  is provided with toothing  21   c , which is pressed into a corresponding through hole in the contact tab  15 . The connecting part  21  is also provided with further toothing  21   d , which is pressed into a corresponding through hole in the metal housing  13 . An internal thread  21   e  makes it possible to fix the cap  17  to the magnet coil arrangement  10  by means of a screw connection. The shoulder  21   b  additionally secures the connecting part  21  against being pulled out of the plug-in base  14 . 
     Before the encapsulation of the magnet coil arrangement  10 , the O ring  23  is pushed onto the sealing area  21   a . The connecting part  21  with the O ring  23  is then pressed into the plug-in base  14  until the shoulder  21   b  rests flush on the plug-in base  14 . The recess  22  is therefore closed in such a way that no plastic gets into the recess  22  during the subsequent encapsulation. In a further step, the toothing  21   d  of the connecting part  21  is pressed into the metal housing  13  until the shoulder  21   b  touches the metal housing  13 . The contact tab  15  is then electrically connected to the metal housing  13 , and the plug-in base  14  is held in a defined position on the metal housing  13  for the encapsulation operation. Following these preparatory steps, the coil former  12  provided with the winding  11  is guided into the metal housing  13 , and the ends of the winding  11  are electrically conductively connected to the connecting tabs assigned to them. This structure is encapsulated with plastic in the usual way. In the process, the heated plastic flows into the free spaces and fills them. The areas filled with plastic following the encapsulation, after curing, form a plastic body which, in FIGS. 1 and 2, is provided with the designation  25 . 
     As FIG. 1 illustrates, two side surfaces of the plug-in base  14  are provided with projections  14   a  and  14   b . The projections  14   a  and  14   b  are arranged between the outwardly pointing side  14   c  and that side  14   d  of the plug-in base  14  which faces the metal housing  13  and are constructed in such a way that even when there is high tension on the plug-in base  14 —be it via the contact tab  15 , via another contact tab or via the connecting part  21 —the plug-in base  14  cannot be pulled out of the plastic body  25 . 
     The side  14   d  of the plug-in base  14  which faces the metal housing  13  is provided with three recesses  14   e ,  14   f ,  14   g . The recesses  14   e ,  14   f ,  14   g  surround the connecting part  21  concentrically as intrinsically closed grooves. They are used as melting edges which, during the encapsulation of the magnet coil arrangement  10 , are initially melted by the hot plastic and fuse to the latter. The melting temperature of the plastic used for the plastic body  25  is selected to be higher for this purpose than the melting temperature of the plastic used for the plug-in base  14 . To the extent that complete fusing does not take place or is not intended, the recesses  14   e ,  14   f ,  14   g  serve as labyrinth seals, as they are known, which prevent moisture that has penetrated in being passed on. This makes it possible to seal off the interfaces between the plug-in base  14  and the plastic body  25  reliably against penetration of moisture. 
     By contrast, there is a different situation at the interfaces between metal and plastic, such as between the metal housing  13  and the plastic body  25  and also between the contact tab  15  and the plug-in base  14 . Here, gaps which permit the penetration of moisture cannot be avoided. It is therefore necessary for additional measures to be taken in order that no moisture which has penetrated from the outside via a gap between the metal housing  13  and the plastic body  25 , via a gap between the contact tab  15  and the plastic adjacent to the latter and belonging to the plug-in base  14 , gets into the connecting space  16 . According to the invention, for this purpose the O ring  23  serving as a sealing part is provided, which rests both on the connecting part  21  and on the plug-in base  14  in a radially sealing manner. Moisture which has penetrated via a gap between the metal housing  13  and the plastic body  25  can get only this far. However—as described above—because of the O ring  23 , no more moisture can get into the gap between the contact tab  15  and the plug-in base  14 , via which moisture would be passed on into the connecting space  16 . 
     The recess  22  and the shoulder  21   b  of the connecting part  21  form a chamber with a circularly annular cross section, in which the O ring  23  is protected against contact with the hot plastic compound during encapsulation. Since the O ring  23  does not come into direct contact with the hot plastic, the thermal stressing of the O ring  23  during encapsulation is only low. In addition, the mechanical stressing of the O ring  23  is low, since it has to seal off only radially but, in the direction of the axis of the connecting part  21 , can give way within the recess  22 . 
     FIG. 4 shows a second magnet coil arrangement  10 ′ according to the invention in an illustration corresponding to FIG.  2 . Here, identical parts are provided with the same designations. The cap that seals off the connecting space  16  is provided with the designation  17 ′. Differing from the cap  17  illustrated in FIG. 2, the cap  17 ′ rests with the seal  18  on the plug-in base  14 ′. The connecting part between the metal housing  13  and the contact tab  15  is provided with the designation  21 ′. The O ring  23  is arranged in an axially sealing manner between the plug-in base  14 ′ and a collar  21   b ′ of the connecting part  21 ′. The collar  21   b ′ limits the distance between the metal housing  13  and the plug-in base  14 ′. In addition, the collar  21   b ′ determines the distance between the surfaces of plug-in base  14 ′ and connecting part  21 ′, on which the O ring  23  rests. Therefore, the force acting on the O ring  23  in the direction of the axis of the connecting part  21 ′ is limited. It is not necessary for the O ring  23  also to rest on the connecting part  21 ′ so as to seal in the radial direction, since the sealing effect is already provided by the force acting on the O ring  23  in the axial direction. Since the inner diameter of the collar  21   b ′ is larger than the outer diameter of the O ring  23 , the O ring  23  can give way in the radial direction when acted on by an axial force. The collar  21   b , additionally prevents the O ring  23  coming into contact with the hot plastic during encapsulation. In this exemplary embodiment, too, moisture which has penetrated via a gap between the metal housing  13  and the plastic body  25  can get only as far as the O ring  23 . Because of the sealing provided by the O ring  23 , however, moisture which has penetrated cannot get further into the gap between the contact tab  15  and the plug-in base  14 ′, via which the moisture would then be passed on into the connecting space  16 . 
     FIGS. 5 and 6 show various sections through part of a third magnet coil arrangement  10 ″ constructed in accordance with the invention. In this case, FIG. 5 shows a section corresponding to FIG.  1  through the magnet coil arrangement  10 ″. FIG. 5 shows only that detail in which the magnet coil arrangement  10 ″ differs from the magnet coil arrangement  10  illustrated in FIG.  1 . For the purpose of illustration, FIG. 6 shows individual parts of the magnet coil arrangement  10 ″ illustrated in FIG. 5 in an exploded drawing corresponding to FIG.  2 . Identical components are provided with the same designations. 
     The third magnet coil arrangement  10 ″ differs from the magnet coil arrangements  10  and  10 ′ illustrated in FIGS. 1 to  4  with regard to the arrangement of the contact tab  15  in the plug-in base. In FIGS. 5 and 6, the latter is provided with the designation  14 ″. While, in the magnet coil arrangements  10  and  10 ′, the contact tab  15  is injection-molded into the plug-in base  14  (FIGS. 1 to  3 ) and  14 ′ (FIG.  4 ), the plug-in base  14 ″ is provided with an additional recess  28 , which is arranged at right angles to the recess  20  to accommodate the connecting part  21 . The recess  28  is used to accommodate the region of the contact tab  15  provided with the designation  15   b . The region  15   b  is provided with a through hole  29 . This arrangement has the advantage that the contact spring  15  does not need to be inserted into the injection mold during the production of the plug-in base  14 ″. The contact tab  15  is only inserted into the recess  20  in the plug-in base  14 ″ before the encapsulation of the magnet coil arrangement  10 ″. After the O ring  23  has been pushed onto the connecting part  21  until it makes contact with the shoulder  21   b , the connecting part  21  with the O ring  23  is pushed into the recess  20 , and the contact area  21   c  of the connecting part  21  is pressed into the through hole  29  in the contact tab  15  until the shoulder  21   b  rests on the plug-in base  14 ″. The contact tab  15  is therefore secured against slipping out of the plug-in base  14 ″ during the further processing steps. After the toothing  21   d  of the connecting part  21  has been pressed into the metal housing  13 , the further processing steps follow, as already described in connection with FIG.  3 . 
     The cap surrounding the connecting space is not illustrated in FIG.  5 . As illustrated in FIG. 2, it has to be constructed in such a way that it rests on the plastic body  25 .