Patent Publication Number: US-6988681-B2

Title: Fuel injection valve

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fuel injector. 
     BACKGROUND INFORMATION 
     A fuel injector that includes a nozzle body which is tubular on its downstream side, and at whose downstream end a sealing seat and a spray discharge opening are positioned, is described in German Published Patent Application No. 198 49 210. The tubular portion of the nozzle body is insertable into a receiving bore of a cylinder head. The nozzle body is sealed with respect to the receiving bore of the cylinder head, which has a diameter corresponding to the radial extension of the nozzle body, with a seal that has approximately the geometry of a hollow cylinder. 
     For positional retention of the seal on the nozzle body, the nozzle body includes a circumferential groove which is made, for example, by turning down the nozzle body and into which the seal is inserted. Elastic materials that may be slid over the nozzle body for installation in the groove may be used as materials. 
     A further fuel injector, in which a sealing element is positioned on the nozzle body, is described in German Published Patent Application No. 198 08 068. The seal is made of a metallic material, and expands in the radial direction under the influence of the temperature created by the combustion process. This may be implemented either by manner of a shape-memory alloy or the use of a bimetallic seal. A groove in the nozzle body may be used for retention, as in the case of German Published Patent Application No. 198 49 210. 
     During operation of the internal combustion engine, the metal sealing ring heats up and expands. The sealing effect is thus enhanced during operation. For easier assembly, the metal seal has a slightly smaller diameter than the receiving bore that is introduced into the cylinder head for the fuel injector. 
     A disadvantage of the sealing approach described in German Published Patent Application No. 198 49 210 is the high temperature acting on the seal. With direct-injection internal combustion engines, full-throttle strength of nonmetallic seal materials may not be ensured. 
     The approach described in German Published Patent Application No. 198 08 068 has the disadvantage that the sealing effect of the metallic seal is temperature-dependent. After a cold start of the internal combustion engine, it takes some time for the materials in the vicinity of the combustion chamber to be heated by the combustion process sufficiently to reach, by thermal conduction, a temperature in the seal that results in the requisite geometrical change. In addition to the seal described, a further seal is used in order to seal the combustion chamber with respect to the exterior during initial operation of the internal combustion engine, so that compression pressure is not lost. 
     The complex materials that are used in the manufacture of metallic seals which deform in temperature-dependent fashion are also disadvantageous. A shape-memory alloy has a transition temperature matched to the application. Close tolerances in the manufacturing process are useful in guaranteeing this transition temperature. The result is to increase not only development costs for the alloy but also costs for utilization in series production. 
     The use of a bimetallic seal requires retention of the seal on a nozzle body, which serves as countermember upon deformation. Installation of the bimetallic element e.g. in a groove is difficult, however, since the properties of the metals change if one of the two metals experiences an inelastic deformation during installation 
     SUMMARY OF THE INVENTION 
     The fuel injector according to the present invention may provide the advantage that only a change in the geometry of the nozzle body results in sealing. Because the sealing ridges are configured in one piece with the nozzle body, the seal is required to have a sealing function only with regard to the contiguous component. Another consequence is that no materials that may be damaged as a result of the temperatures that occur are used in the immediate vicinity of the combustion chamber. The purely metallic seal is a constituent of a component that is used in any case, so that furthermore no additional corrosion protection (for example, due to possible contact corrosion) is necessary. 
     The one-piece configuration reduces the production complexity of the fuel injector, and moreover ensures low rejection rates because one assembly step may be omitted. 
     The successive positioning of multiple sealing ridges may be advantageous especially in terms of the reliability of the sealing effect. The identical geometry of the individual enlargements simplifies manufacture, so that tool costs may be reduced. 
     It may be additionally advantageous that an increase in the number of sealing elements does not result in an increase in the number of components of the fuel injector. The sealing ridges may be machined in different quantities out of the same nozzle body blank. 
     The use of an adapter sleeve as contiguous component may allow the sealing of the unit comprising the fuel injector plus adapter sleeve with respect to the cylinder head to be shifted to a location that is less critical in terms of temperature. 
     An example embodiment of a fuel injector according to the present invention is depicted in the drawings and is explained in the description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic partial section through an example embodiment of a fuel injector according to the present invention. 
         FIG. 2  is a schematic section, in portion II of  FIG. 1 , through the fuel injector according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     For better comprehension of the present invention, an example embodiment of a fuel injector  1  according to the present invention will first be explained briefly with reference to  FIG. 1  in an overall presentation in terms of its constituents. 
     Fuel injector  1  is embodied in the form of a fuel injector  1  for fuel injection systems of mixture-compressing, sparkignited internal combustion engines. Fuel injector  1  is suitable for direct injection of fuel into a combustion chamber (not depicted) of an internal combustion engine. 
     Fuel injector  1  includes a nozzle body  2  in which a valve needle  3  is positioned. Valve needle  3  is in working engagement with a valve closure element valve-closure member which coacts with a valve-seat surface  6 , positioned on a valve seat element  5 , to form a sealing seat. In the example embodiment, fuel injector  1  is an electromagnetically actuated fuel injector  1  that possesses at least one spray discharge opening  7 . Nozzle body  2  is sealed by a seal  8  with respect to an external pole  9  of a magnet coil  10 . Magnet coil  10  is encapsulated in a coil housing  11  and wound onto a coil support  12  that rests against an internal pole  13  of magnet coil  10 . Internal pole  13  and external pole  9  are separated from one another by a gap  26 , and are supported on a connecting component  29 . Magnet coil  10  is energized, via a conductor  19 , by an electrical current that may be conveyed via an electrical plug contact  17 . Plug contact  17  is surrounded by a plastic sheath  18  that may be injection-molded onto internal pole  13 . 
     Valve needle  3  is guided in a valve needle guide  14  that is of disk-shaped configuration. Paired with the latter is an adjusting disk  15  that serves to adjust the valve needle stroke. Located on the upstream side of adjusting disk  15  is an armature  20 . The latter is joined nonpositively, via a flange  21 , to valve needle  3 , which is joined to flange  21  by manner of a weld seam  22 . Braced against flange  21  is a return spring  23  which, in the present configuration of fuel injector  1 , is preloaded by a sleeve  24  pressed into internal pole  13 . 
     Fuel conduits  30   a  through  30   c  extend in valve needle guide  14 , in armature  20 , and in a guidance disk  31 . A filter element  25  is positioned in a central fuel inlet  16 . Fuel injector  1  is sealed with respect to a fuel line (not depicted) by manner of a seal  28 . 
     When fuel injector  1  is in the idle state, armature  20  is impinged upon opposite to its linear stroke direction, via flange  21  on valve needle  3 , by return spring  23 , so that valve-closure member  4  is held in sealing contact on valve seat  6 . Upon energization of magnet coil  10 , the latter establishes a magnetic field that moves armature  20  in the linear stroke direction against the spring force of return spring  23 , the linear stroke is defined by a working gap  27  that is present, in the idle position, between internal pole  13  and armature  20 . Armature  20  also entrains flange  21 , which is welded to valve needle  3 , in the linear stroke direction. Valve-closure member  4  lifts off from valve-seat surface  6 , and fuel is discharged from spray discharge opening  7 . 
     When the coil current is shut off and once the magnetic field has decayed sufficiently, armature  20  falls away from internal pole  13  onto flange  21  as a result of the pressure of return spring  23 , thereby moving valve needle  3  against the linear stroke direction. Valve-closure member  4  is thereby placed onto valve-seat surface  6 , and fuel injector  1  is closed. 
     Fuel injector  1  according to the present invention is sealed with respect to an adapter sleeve  32  by manner of at least one sealing ridge  31  that is positioned as a radial enlargement on nozzle body  2 . Instead of adapter sleeve  32  depicted in the example embodiment, any contiguous component may be used. Adapter sleeve  32  may allow fuel injectors  1  to be installed into a cylinder head that would require changes to the outside dimensions of fuel injector  1 . Adapter sleeve  32  includes at its downstream end a tubular part  35 , the inner radial extension of tubular part  35  corresponding to the outer radial extension of nozzle body  2 . Tubular part  35  has a cylindrical inner contour. Adapter sleeve  32  is sealed with respect to the cylinder head in a manner that is not depicted. 
     The length of tubular part  35  of adapter sleeve  32  is at least sufficient that all the sealing ridges  31  provided for sealing of nozzle body  2  together include a smaller extension in the axial direction than tubular part  35  of adapter sleeve  32 , and thus are positioned within tubular part  35 . Sealing ridges  31 , which are positioned circumferentially around cylindrical nozzle body  2  as radially enlarged regions, include an outer radial extension which is somewhat greater than the inner radial extension of tubular part  35  of adapter sleeve  32 . When nozzle body  2  is inserted into adapter sleeve  32 , a press-fit join which assumes the sealing function is thus produced between nozzle body  2  and adapter sleeve  32 . Since adapter sleeve  32  is in turn sealed (in a manner not depicted) with respect to the cylinder head, it is not possible for the pressure in the combustion chamber (not depicted) to escape into its surroundings. 
     Nozzle body  2  is of cylindrical configuration, its outer radial extension (especially downstream of sealing ridges  31 ) is somewhat smaller than the outer radial extension of sealing ridges  31 . The contact area between nozzle body  2  and adapter sleeve  32  is thereby limited to sealing ridges  31 . The surface pressure resulting from the press-fit join and the small contact area ensures the sealing effect. Sealing ridges  31  positioned successively in the axial direction have identical cross sections. 
     Instead of adapter sleeve  32 , fuel injector  1  may also be installed directly into a cylinder head of a direct-injection internal combustion engine. For that purpose, the cylinder head includes a receiving orifice for fuel injector  1  that corresponds, at least in a subregion, to the geometry of adapter sleeve  32 , so that when fuel injector  1  is in the installed position, sealing ridges  31  of nozzle body  2  seal fuel injector  1  with respect to the receiving orifice of the cylinder head. As an alternative to the identical geometry of the individual sealing ridges  31  in the example embodiment depicted, sealing ridges  31  may also be embodied with differing cross sections. 
       FIG. 2  is an enlarged depiction of the sealing portion of nozzle body  2  shown in FIG.  1 . Sealing ridges  31  constitute the only contact areas between nozzle body  2  and adapter sleeve  31 , and thus generate the sealing surface pressure. Upstream and downstream from sealing ridges  31 , an air gap  34  is formed as a result of the smaller radial extension of nozzle body  2  as compared to the inner radial extension of adapter sleeve  32 . 
     External radii  33  of sealing ridges  31  in the region of the contact surface against adapter sleeve  32  are selected to be sufficiently large that chips may not be shaved off from adapter sleeve  32  upon assembly. Chip-free assembly is especially important in the context of direct installation into a cylinder head, since the metal chips would fall directly into the combustion chamber.