Abstract:
A fuel injector for fuel-injection systems of internal combustion engines has a solenoid coil; a valve needle that is mechanically linked to the solenoid coil and acted upon by a restoring spring in a closing direction, in order to actuate a valve-closure member which, together with a valve-seat face, forms a sealing seat; and a sleeve, which prestresses the restoring spring. The sleeve is integrally formed with a filter element to form a one-part, deep-drawn filter sleeve, which has through-flow openings for filtering the fuel flowing through the fuel injector.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a fuel injector. 
   BACKGROUND INFORMATION 
   In the case of fuel injectors already known, fuel filters are press-fit into a fuel intake nipple and, thus, secured in place in it. This manner of fastening involves the risk of dust and cuttings forming, which can lead to the malfunction of the fuel injector. In addition, retaining collars for upper sealing rings are constructed as individual component parts. 
   A fuel injector, in which a fuel filter is manufactured in one piece with a retaining collar, is already known from German Published Patent Application No. 43 25 842. The retaining collar radially extends beyond the fuel intake nipple and has a lip outside the fuel intake nipple. The circumferential lip of the retaining collar forms, together with a groove on the outer circumference of the fuel intake nipple, a snap-in connection, by which the fuel filter is fastened in a defined manner. There is only a clearance fit between the base of the fuel filter and the inner wall of the fuel intake nipple, so that any build-up of shavings in the interior of the fuel injector is prevented. 
   In addition, European Patent No. 0 697 064 describes a filter, which is for a fuel injector having central fuel delivery and is form-locked to an adjusting sleeve for a restoring spring that keeps the fuel injector closed in the rest state. In this context, the filter is made out of a plastic frame, over which a mesh grating is laid. The filter is connected to the adjusting sleeve with the aid of a snap-in fastener, the adjusting sleeve preferably being made of metal. This allows the static rate of flow through the fuel injector to also be calibrated after the filter is inserted. 
   A particular disadvantage of the fuel injectors known from the above-mentioned, printed publications is the large amount of processing time spent in attaching the filter to either the adjusting sleeve or the fuel intake nipple. In addition, the filter and adjusting sleeve are made of different materials, whereby cuttings and dust are formed at the contact surfaces, predominantly on the plastic of the filter, which can lead to the malfunction of the fuel injector caused by the deposition of the particles. 
   SUMMARY OF THE INVENTION 
   The fuel injector of the present invention has the advantage over the background art that the sleeve for adjusting the dynamic flow rate is formed in one piece with the filter element, and therefore, on one hand, the position of the sleeve may easily be adjusted using the protruding filter element, and, on the other hand, quick and inexpensive manufacturing and assembly are rendered possible. 
   In this context, the combined filter sleeve is inexpensively manufactured by deep-drawing, so that a plastic frame having a filter grating attached to it may be dispensed with. 
   Through-flow openings are preferably provided, which may be introduced in large numbers into the filter sleeve in an exact manner, using laser drilling. 
   In particular, it is also advantageous that the flow rate may be adjusted with the filter already inserted, since contamination of the valve interior may be prevented by the adjusting tools. 
   Furthermore, it is advantageous that the filter sleeve may also be removed again, if necessary. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic of a section through an exemplary embodiment of a fuel injector constructed according to the present invention. 
       FIG. 2  shows an excerpt from region II of a schematic section through the exemplary embodiment represented in  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   A fuel injector  1  is designed, for example, in the form of an injection valve for fuel-injection systems of mixture-compressing, spark ignition engines. The fuel injector  1  represented is suitable for the direct injection of fuel into a combustion chamber, not shown, of an internal combustion engine. However, the present invention is also similarly suitable in the case of fuel injectors  1  for the injection of fuel into an intake manifold of the engine. 
   Fuel injector  1  includes a nozzle body  2 , in which a valve needle  3  is guided. Valve needle  3  is mechanically linked to a valve-closure member  4 , which interacts with a valve-seat surface  6  positioned on a valve-seat member  5 , to form a sealing seat. The fuel injector  1  in the exemplary embodiment is an inwardly opening fuel injector  1 , which has a spray orifice  7 . Nozzle body  2  is sealed from an outer pole  9  of a solenoid coil  10  by a seal  8 . Solenoid coil  10  is encapsulated in a coil housing  11  and wound onto a coil brace  12 , which lies against an inner pole  13  of solenoid coil  10 . Inner pole  13  and outer pole  9  are separated from each other by a gap  26  and are braced on a connecting member  29 . Solenoid coil  10  is energized via an electric line  19 , by an electric current which may be supplied via an electrical plug contact  17 . A plastic jacket  18 , which may be injection-molded onto inner pole  13 , encloses plug contact  17 . 
   Valve needle  3  is guided in a valve-needle guide  14 , which is disk-shaped. A paired adjustment disk  15  is used to adjust the lift. An armature  20  is situated on the other side of adjustment disk  15 . The former is frictionally connected by a flange  21  to a valve needle  3 , which is joined to flange  21  by a welded seam  22 . 
   A restoring spring  23 , which, in the present design of fuel injector  1 , is prestressed by a sleeve  24 , is braced against flange  21 . According to the present invention, the sleeve  24  that takes the form of an adjustment sleeve is formed in one piece with a filter element  25 . The component part formed in this manner is subsequently referred to as filter sleeve  34 . In this context, the filtering action is produced by through-flow openings  35 , which are introduced in an inflow end  36  of filter sleeve  34 . A discharge end  37  of filter sleeve  34  is formed in such a manner, that it may be used to adjust the initial spring tension of restoring spring  23 , and thus, to adjust the static rate of flow through fuel injector  1 . A detailed description of filter sleeve  34  may be gathered from the description relating to  FIG. 2 . 
   Fuel channels  30   a  through  30   c , which direct the fuel supplied via a central fuel inlet  16  to spray-discharge opening  7 , run in valve-needle guide  14 , in armature  20 , and on valve-seat member  5 . A seal  28  seals fuel injector  1  from a receiving bore pole, which is not shown in further detail and is, for example, in a fuel rail. 
   In the rest state of fuel injector  1 , armature  20  is acted upon by restoring spring  23  in a direction opposite to its lift direction, in such a manner, that valve-closure member  4  is held against valve seat  6  so as to create a seal. When solenoid coil  10  is excited, it generates a magnetic field which moves armature  20  in the lift direction, counter to the spring force of restoring spring  23 , the lift being given by a working gap  27  occurring in the rest position, between inner pole  13  and armature  20 . Flange  21 , which is welded to valve needle  3 , is also taken along by armature  20  in the lift direction. Valve-closure member  4 , which is mechanically linked to valve needle  3 , lifts off from the valve-seat surface, and fuel is discharged through spray-discharge opening  7 . 
   If the coil current is switched off, armature  20  falls away from inner pole  13  after sufficient decay of the magnetic field, due to the pressure of restoring spring  23 , whereupon flange  21 , which is mechanically linked to valve needle  3 , moves in a direction counter to the lift direction. Valve needle  3  is thereby moved in the same direction, whereby valve-closure member  4  sets down on valve seat surface  6 , and fuel injector  1  is closed. 
   In an excerpt of a cross-sectional view,  FIG. 2  shows the detail of fuel injector  1  of the present invention, which is designated in  FIG. 1  by II. 
   As mentioned previously, filter sleeve  34  is constructed such that through-flow openings  35  are formed at inflow end  36 , while discharge end  37  is formed in the shape of a sleeve, so that the initial tension of restoring spring  23  may be varied by pushing filter sleeve  34  into fuel injector  1 . 
   In this context, filter sleeve  34  is preferably formed out of metal, in order to ensure permanent clamping action during the entire service life of fuel injector  1 . The manufacturing is accomplished by deep-drawing, a manufacturing method that is simple and cost-effective. 
   In order to avoid high manufacturing costs for filter region  25  of filter sleeve  34 , small-diameter through-flow openings  35  are introduced in large numbers into inflow end  36  of filter sleeve  34 . This is preferably accomplished by laser drilling, since it allows extremely fine, low-volume bore holes to be produced. The diameter of through-flow openings  35  is preferably 0.04 to 0.05 mm, which means that dirt particles in the fuel may be filtered out to a satisfactory extent. In this context, the number of through-flow openings  35  depends on the available surface of filter region  25 . For example, the number of through-flow openings  35  may be increased by lengthening filter sleeve  34  or utilizing the surface of an inflow-side cover plate  38  of filter sleeve  34 . 
   In this manner, the interior of fuel injector  1  may be protected in two ways against contaminants that may cause malfunctions during the operation of fuel injector  1 . On one hand, the dynamic flow rate is adjusted by moving filter sleeve  34  when filter  25  is already installed, so that dirt from the adjusting tool may not reach the interior of the valve. On the other hand, cuttings and dust escape in response to filter  25  being pressed in at the end of the production line, whereby malfunctions caused by deposition of dust or larger particles are likewise prevented. 
   Combined filter sleeve  34  also allows the dynamic flow through fuel injector  1  to be adjusted in a simpler and more rapid manner. First of all, due to its greater overall length, filter sleeve  34  extends so far upstream into central fuel inlet  16 , that it may be moved, or if need be, removed more easily. On the other hand, filter sleeve  34  is situated considerably closer to the valve group after adjustment of the flow rate, so that the surface between filter sleeve  34  and the valve group becomes smaller, and the risk of contamination therefore decreases. 
   The present invention is not limited to the exemplary embodiments represented and is suitable for any designs of fuel injectors  1 , e.g. for manifold injectors  1  or fuel injectors  1  connected to a common-rail system.