Abstract:
A fuel injection valve has a connection piece for a fuel-supply line, a valve-seat support having a valve-seat body provided with a valve opening, a solenoid for activating a valve member, which controls the valve opening, and a plastic extrusion coat enclosing the connection piece, the solenoid and the valve-seat support. To achieve a cost-effective manufacture by requiring fewer components for the injection valve and providing a reduction in the assembly costs, the connection piece and the valve-seat support are made of plastic and designed as one-piece plastic housing together with the plastic extrusion coat. The yoke element for closing the magnetic circuit of the solenoid, which extends across the magnetic core and magnetic armature, is a magnetic material extrusion coat, which encloses the solenoid coil and adjoins the magnetic core in a gapless manner and ends in front of the magnetic armature with a gap clearance.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an injection valve for fuel injection, in particular for internal combustion engines of motor vehicles.  
       BACKGROUND INFORMATION  
       [0002]     In an injection valve for fuel-injection systems of internal combustion engines, e.g., as described in German patent document DE 195 03 224, the connection piece is machine-cut from a steel pipe and accommodates the plastic coil brace of the electromagnet wound with the excitation winding and simultaneously forms the magnetic core of the electromagnet. The valve-seat support, which is likewise made from a steel pipe, is joined to the bottom side of the coil brace; it partially encloses the magnetic armature connected to the plastic valve needle, the magnetic armature being guided in the valve-seat support so as to be displaceable by sliding and partially projecting into the coil brace. The magnetic yoke between the magnetic core or connection piece and the magnetic armature is formed by a sleeve-type, ferromagnetic intermediate piece, which is permanently affixed between coil brace and connection piece, i.e., magnetic core, and encloses the magnetic armature via a section projecting beyond the connection piece or magnetic core, in a manner that allows sliding displacement of the magnetic armature. The magnetic armature made from magnetically soft steel is plated with hard chromium to protect it from wear. The plastic valve needle is extruded onto the magnetic armature.  
       SUMMARY  
       [0003]     An injection valve according to the present invention provides the advantage of a less complicated and more cost-effective manufacture since the injection valve is made up of considerably fewer components than the conventional injection valves; in addition, these components are able to be produced by simple injection molding methods. The reduced number of components requires fewer assembly steps and thus less assembly time and is more cost-effective with respect to automatic assembly machines and jointing machines. The manufacturing steps are limited to placing the magnetic core fitted with the magnetic coil in an extrusion die, die casting the magnetic yoke element from magnetic material, subsequent injection-molding of the magnetic yoke element with solenoid coil and iron core to produce the plastic housing, and inserting valve member with valve-closure spring and valve-seat support having the spray-orifice disk in the prefabricated plastic housing. The production steps for the injection molding may be carried out with the aid of a so-called cube system, which uses a block-shaped extrusion die having vertical junction planes, which is rotated by 90° following each production step in order to implement the next production step. At 0°, the cylindrical magnetic core supporting the magnetic coil is inserted; at 90°, the extrusion coating of magnetic coil and magnetic core with the magnetic material takes place in which a gapless connection to the magnetic core is produced. At 180°, the plastic-extrusion coating to produce the plastic housing is carried out, and at 270°, the finished plastic housing with the valve-seat support as well as the connection piece and connection lug for the solenoid coil formed thereon is removed.  
         [0004]     According to an example embodiment of the present invention, labyrinth seals are provided between the plastic housing and the extrusion coat, which is made of magnetic material and encloses the solenoid coil; the labyrinth seals are made up of peripheral meshing, which is produced in the extrusion die and extends between the extrusion coat of magnetic material and injection-molded plastic housing in a concentric manner with respect to the magnetic core. This labyrinth seal, in conjunction with the use of fuel-tight plastic for the plastic housing, prevents the escape of fuel from the flow path of the fuel.  
         [0005]     According to an example embodiment of the present invention, the solenoid coil has a coil brace, which is made of plastic and slipped over or extruded onto the magnetic core, and an excitation winding, which is wound onto the coil brace. Concentric circumferential labyrinth seals, which are made up of meshing between the coil brace and the extrusion coat made of magnetic material, are once again provided between the coil brace and the extrusion coat of magnetic material for the purpose of sealing from the flow path of the fuel.  
         [0006]     In an alternative example embodiment of the present invention the coil brace is omitted and the excitation coiling is made of baked enamel wire and directly wound onto the magnetic core.  
         [0007]     According to an example embodiment of the present invention, the valve member is made of plastic and carries an elastomer seal, which cooperates with the valve-seat body and is used to seal the valve opening from the flow path of the fuel. The valve member is produced together with elastomer seal in a two-component injection molding process.  
         [0008]     According to an example embodiment of the present invention, the magnetic armature situated on the valve member is made of a magnetically conductive plastic, and the valve member, elastomer seal and magnetic armature are produced in a three-component injection molding process. This achieves additional cost savings due to the simplified manufacture of the valve member.  
         [0009]     According to an example embodiment of the present invention, the valve-seat member having the valve opening is likewise made of plastic and permanently joined to the plastic housing, e.g., by laser beam welding, once it has been inserted in the valve-seat support region of the plastic housing.  
         [0010]     As an alternative, the valve-seat member may also be made of metal in the conventional manner, sealed from the plastic housing by a ring seal, and safeguarded against axial displacement by a spray-orifice plate which cuts into the plastic housing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows a longitudinal cross-sectional view of an exemplary embodiment of an injection valve for fuel injection.  
         [0012]      FIG. 2  shows a longitudinal half-section of an injection valve according to an additional exemplary embodiment.  
         [0013]      FIGS. 3 through 5  show three exemplary embodiments of the injection valve, shown in half section, which are modified with respect to the integration of the valve-seat member in the plastic housing. 
     
    
     DETAILED DESCRIPTION  
       [0014]     The injection valve for fuel-injection systems, e.g., of motor vehicles, shown in longitudinal section in  FIG. 1 , has a plastic housing  10 , made of a fuel-tight plastic, at whose one end a connection piece  12  is formed and at whose other end a valve-seat support  13  is formed. Connection piece  12  and valve-seat support  13  are combined into one piece by plastic coat  11  lying between them, in order to form complete plastic housing  10 . Connection piece  12  is used to connect the injection valve to a fuel-supply line  30 , a so-called rail. Valve-seat support  13  accommodates a valve-seat body  14  in which a valve opening  15  is located, which is surrounded by a valve seat  141 . Valve opening  15  is connected to connection piece  12  via a fuel-flow path  16  provided in the interior of plastic housing  11 . A valve member  17 , which cooperates with a valve seat  141  formed on valve-seat body  14 , is used to control valve opening  15  for the purpose of spray-discharging fuel via valve opening  15 . A valve-closure spring  18  presses valve member  17  onto valve seat  141  and thereby closes valve opening  15 . A solenoid  19  opens the injection valve by lifting valve member  17  off valve seat  141 , counter to the force of valve-closure spring  18 , by energizing solenoid  19 . Solenoid  19  is encased by plastic coat  11 , which is situated between connection piece  12  and valve-seat support  13  and connects them to one another to form one piece.  
         [0015]     Solenoid  19  is made up of a hollow-cylindrical magnetic core  20  made of ferromagnetic material through which fuel flow path  16  is guided; a solenoid coil  21 ; a magnetic armature  22  affixed on valve member  17 , the magnetic armature likewise having an axial bore for plastic fuel-flow path  16  and lying coaxially with respect to magnetic core  20 ; and a magnetic yoke element  23 , which closes the magnetic circuit via magnetic core  20  and magnetic armature  22 .  
         [0016]     To achieve a simplified valve design with few components and low assembly costs, solenoid coil  21  is situated directly on magnetic core  20 , and magnetic core  20  with solenoid coil  21  is placed in an injection-molding die, which is extrusion-coated with a magnetically conductive material—denoted as magnetic material in brief—to yield magnetic yoke element  23 , a gapless connection being produced between magnetic material extrusion coat  24  and magnetic core  20 . The component premanufactured in this manner is placed inside another injection-molding die with whose aid plastic housing  10  is injection-molded. The component is enveloped by plastic coat  11 , and the regions of connection piece  12  and valve-seat support  13  are injection-molded onto plastic coat  11  at the same time. Finished plastic housing  10 , in which complete solenoid  19 —with the exception of magnetic armature  22 —is already integrated, is removed from the injection-molding die.  
         [0017]     In the exemplary embodiment of  FIG. 1 , solenoid coil  21  has a coil brace  26  made of plastic and an excitation winding  27 , which is wound onto coil brace  26  and made of enameled armature wire. Excitation winding  27  is wound onto premanufactured coil brace  26  and connected via the ends of its windings to plug pins  25  held on coil brace  26 . Wound coil brace  26  is slipped over magnetic core  20 . As an alternative, coil brace  26  is produced by extrusion-coating magnetic core  20  with plastic material and then winding up excitation winding  27  and fitting it with plug pins  25 . To seal excitation winding  27  from fuel-flow path  16 , two labyrinth seals  28 , which are concentric with respect to the housing axis, are provided between magnetic material extrusion coat  24  and plastic housing  10 , and two labyrinth seals  29 , which likewise extend concentrically, are provided between coil brace  26  and magnetic material extrusion-coat  24 . Each labyrinth seal  29  is realized by meshing between the mutually abutting components, i.e., magnetic material extrusion coat  24  and plastic housing  10  on the one side, and magnetic material extrusion coat  24  and coil brace  26  on the other side.  
         [0018]     To complete the injection valve, valve-closure spring  18 , valve member  17  with magnetic armature  22  affixed thereon, and valve-seat body  14  must still be inserted in plastic housing  10  having integrated solenoid  19 . To adjust the valve lift, valve seat body  14  is positioned in the region of valve-seat support  13  of plastic housing  10  with the utmost precision and anchored on plastic housing  10  in a manner that prevents axial displacement. Valve-closure spring  18 , accommodated in magnetic core  20 , is braced on magnetic armature  22  and on an adjustment sleeve  31 , which is inserted in magnetic core  20  and anchored therein. The initial stress of valve-closure spring  18  is specified by means of adjustment sleeve  31 . In addition, downstream from valve-seat body  14  in the flow direction of the fuel, there is a spray-orifice plate  32  having spray orifices  33 , which is either affixed on plastic housing  10  or on valve-seat body  14 , so that the fuel discharging from valve opening  15  when the injection valve is open is spray-discharged via spray orifices  33  of spray-orifice plate  32 . The injection valve is sealed from the bore wall in the cylinder head of a combustion engine or an internal combustion engine via a sealing ring  34  and attached to fuel-supply line  30  or rail via its region of plastic housing  10  formed as connection piece  12  and joined to fuel-supply line  30  or rail in a fuel-tight manner by laser-beam welding.  
         [0019]     In the exemplary embodiment of  FIG. 1 , sleeve-type valve member  17 , sealed at one sleeve end and provided with flow-through openings  173  for the fuel, is made of plastic and has an elastomer seal  35  on its end region that comes into contact with valve seat  141  on valve-seat body  14 ; elastomer seal  35  presses onto valve seat  141  when the injection valve is closed and in this manner seals valve opening  15  from fuel-flow path  16 . Valve member  17  and elastomer seal  35  are advantageously produced in a two-component injection-molding process. Magnetic armature  22  is affixed on valve member  17  as separate component. Magnetic armature  22  is advantageously made of a magnetically conductive plastic (magnetic plastic) and produced in a three-component injection-molding process together with valve member  17  and elastomer seal  35 .  
         [0020]     In the exemplary embodiment of  FIG. 1 , valve-seat body  14  is likewise made of plastic and permanently affixed inside plastic housing  10  by laser-beam welding. Formed on spray-orifice plate  32  is a flexible annular region  321 , which is prestressed and, due to its excess spring force, “claws” into the inner wall of plastic housing  10  via a ring edge  322 .  
         [0021]     In an alternative embodiment, shown in  FIG. 5 , of valve-seat body  14  made of plastic, valve-seat body  14  has integrally formed pegs  36  on its bottom side facing spray-orifice plate  32 , which are able to be guided through congruent openings  37  in spray-orifice plate  32 . Spray-orifice plate  32  is placed on the bottom side of valve-seat member  14  in such a way that pegs  36  project through openings  37 . Pegs  36  are then deformed in their end region projecting beyond spray-orifice plate  32 , for instance with the aid of ultrasound or by hot-stamping, so that a type of plastic-rivet connection is produced between valve-seat body  14  and spray-orifice plate  32 .  
         [0022]     The injection valve according to the exemplary embodiment shown in  FIG. 2  is modified in several aspects with respect to the previously described injection valve. For instance, the coil brace in solenoid coil  21  has been omitted, and excitation winding  27  made of baked enamel wire is wound directly onto hollow-cylindrical magnetic core  20 . The winding ends of excitation winding  27  are affixed inside a plastic part  38  enclosed by magnetic material extrusion coat  24 . Plug pins  39 , connected to the winding ends of excitation winding  27 , lead out of this plastic part  38  through plastic housing  10 . When magnetic material extrusion coat  24  is extruded, plastic part  38  having plug pins  39  connected to excitation winding  27  is placed in the injection die as well and is thereby already fixed in place in the subsequent injection molding of plastic housing  10 . Fuel-supply line  30 , or rail, has been provided with plug sockets  40 , which are situated in a recess  41  and contacted by plug pins  39 , which slide into plug sockets  40  when connection piece  12 , which is integrally formed on plastic housing  10 , is slipped over fuel-supply line  30 . Plug sockets  40  are connected to electrical connection leads (not shown) in order to energize excitation coil  27 . To seal from the fuel, sealing rings  42  are placed in recess  41  accommodating sockets  40 , each of which seals one plug pin  39  on the bottom side of socket  40  facing plastic housing  10  from the wall of recess  41  in fuel-supply line  30 . Sealing ring  42  may be omitted if plug pins  39  are provided with texture  47  such as meshing or heavy ribbing. In  FIG. 2 , texture  47  is additionally indicated in a sectional area of plug pin  39 . Since the materials of plastic coat  11  and plug pins  39  have different coefficients of thermal expansion, mutual gripping comes about between plastic coat  11  and plug pins  39  in the region of texture  47 , so that fluid-tight sealing of plug pins  39  is achieved.  
         [0023]     In the exemplary embodiment of  FIG. 2 , valve-seat body  14  is made of metal in the conventional manner and sealed from the inner wall of plastic housing  10  by a sealing ring  43 , which lies in a circumferential groove  44  in valve-seat body  14 . Spray-orifice plate  32  downstream from valve-seat body  14  has the same shape and is affixed inside plastic housing  10  as described in connection with  FIG. 1 . Valve-seat body  14  is fixed in place on spray-orifice plate  32  by laser-beam welding, for instance and, due to ring edge  322  of spray-orifice plate  32 , which claws into the inner wall of plastic housing  10 , is secured in a manner that prevents axial displacement. Valve member  17  is made of metal in the conventional manner and made up of a sleeve-shaped valve needle  171  having radial bores  174  for the passage of fuel, and a valve-closure top  172 , which is welded onto the front end of valve needle  171  and cooperates with valve seat  141  formed on valve-seat body  14 . Magnetic armature  22  is placed on the end of valve needle  171  facing away from valve-closure top  172  and welded thereto.  
         [0024]      FIGS. 3 and 4  show two additional exemplary embodiments for affixing a valve-seat body  14  made of metal inside plastic housing  10 . Valve-seat body  14  has a circumferential groove  44 , like valve-seat body  14  in  FIG. 2 , in which sealing ring  43  is situated, which seals with respect to the inner wall of plastic housing  10 . In the exemplary embodiment of  FIG. 3 , valve-seat body  14  and spray-orifice plate  32  are fixed in place with the aid of a prestressed profile ring  45 , which has excessive spring tension and buries itself in the wall of plastic housing  10  by its saw-tooth-type profile formed on the outer circumference.  
         [0025]     In the exemplary embodiment of  FIG. 4 , valve-seat body  14  is widened in the press-in direction, i.e., its diameter increases in the press-in direction. A profile edge  46  is formed at its end face having the largest diameter, which buries itself in the inner wall of plastic housing  10  and thus prevents further axial displacement of valve-seat body  14 . Spray-orifice plate  32  is affixed on the bottom side of valve-seat body  14 , by welding, for instance.