Abstract:
The method for producing and securing an apertured disk for a fuel injector is distinguished by the use of the following method steps: a) making available a flat, metallic sheet having a constant thickness, b) reducing the thickness in one region of the sheet by impressing or embossing, c) introducing at least one spray-discharge opening in the region having reduced thickness, d) machining the sheet until an apertured disk having predefined outside dimensions is attained, and e) securing the apertured disk on a valve-seat member of the fuel injector in such a way that a lower end face of the valve-seat member overlaps an intake region of the apertured disk produced by the thickness reduction, such that the at least one spray-discharge opening is covered.

Description:
BACKGROUND INFORMATION  
       [0001]     German Patent Application No. DE 41 21 310 describes a fuel injector which has a valve-seat member, on which a fixed valve seat is formed. A valve-closure member, which is axially movable in the injector, cooperates with this valve seat formed in the valve-seat member. Adjoining the valve-seat member in the downstream direction is a flat jet-directional plate in which, facing the valve seat, an H-shaped depression is provided as an intake region. Adjoining the H-shaped intake region in the downstream direction are four spray-discharge orifices, so that a fuel to be discharged can be distributed over the intake region toward the spray-discharge orifices. In so doing, the flow geometry in the jet-directional plate is not to be influenced by the valve-seat member. Rather, a flow passage is implemented downstream of the valve seat in the valve-seat member so far that the valve-seat member has no influence on the opening geometry of the jet-directional plate.  
       SUMMARY OF THE INVENTION  
       [0002]     The method of the present invention for producing and securing an apertured disk has the advantage that particularly small apertured-disk thicknesses are easily attainable. Since according to the present invention, the spray-discharge openings are introduced in the thickness-reduced middle region of the apertured disk, it is possible to form a plurality of spray-discharge openings having very small spray-orifice diameters in the apertured disk, while maintaining known and customary ratios of length to diameter of each individual spray-discharge opening. Consequently, an apertured disk produced according to the present invention and mounted on a fuel injector guarantees the finest uniform atomization of the fuel, a particularly high atomization quality and a jet formation adapted to the specific requirements being attained.  
         [0003]     The impressing or embossing process employed for reducing the thickness of the apertured disk may advantageously be used with low expenditure for forming apertured disks in very large quantities.  
         [0004]     In particularly advantageous manner, the apertured disk produced according to the present invention is mounted in such a way on a fuel injector that the apertured disk, disposed downstream of a valve seat, has an opening geometry for a complete axial passage of the fuel, the opening geometry being bounded by a valve-seat member encompassing the fixed valve seat. The valve-seat member therefore already assumes the function of influencing the flow in the apertured disk. An S-twist is especially advantageously attained in the flow for improving the fuel atomization, since a lower end face of the valve-seat member covers the spray-discharge openings in the apertured disk.  
         [0005]     The S-twist in the flow, attained by the geometrical arrangement of the valve-seat member and the apertured disk, allows the formation of bizarre jet forms having high atomization quality. The apertured disks, in conjunction with suitably implemented valve-seat members for single-jet, dual-jet and multi-jet sprays, permit jet cross-sections in countless variants. Using such a fuel injector, it is possible to reduce the exhaust emissions of the internal combustion engine, and fuel consumption is able to be reduced as well. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  shows a partially depicted injector having an apertured disk downstream of the valve-seat member.  
         [0007]      FIG. 2  shows an enlarged representation of the valve-seat part made up of the valve-seat member and apertured disk.  
         [0008]      FIG. 3  shows schematically the method step of impressing or embossing. 
     
    
     DETAILED DESCRIPTION  
       [0009]      FIG. 1  partially shows a valve in the form of an injector for fuel injection systems of mixture-compressing internal combustion engines having externally supplied ignition. The injector has a tubular valve-seat support  1 , in which a longitudinal opening  3  is formed concentrically with respect to a longitudinal valve axis  2 . Situated in longitudinal opening  3  is a, for example, tubular valve needle  5 , which is securely joined at its downstream end  6  to a, for instance, spherical valve closure member  7 , at whose periphery, five flattenings  8 , for example, are provided for the fuel to flow past.  
         [0010]     The fuel injector is actuated in a known manner, e.g. electromagnetically. A schematically indicated electromagnetic circuit having a solenoid coil  10 , an armature  11  and a core  12  is used for axially moving valve needle  5  and, as such, for opening the injector against the spring force of a restoring spring (not shown) and for closing the injector. Armature  11  is connected to the end of valve needle  5  facing away from valve-closure member  7  by, for example, a welded seam formed by a laser, and is aligned with core  12 .  
         [0011]     A guide opening  15  of a valve-seat member  16 , which is sealingly mounted by welding into the downstream end of valve-seat support  1  facing away from core  12 , in longitudinal opening  3  running concentrically with respect to longitudinal valve axis  2 , is used for guiding valve-closure member  7  during the axial movement. At its lower end face  17  facing away from valve-closure member  7 , valve-seat member  16  is concentrically and securely joined to a, for instance, cup-shaped apertured disk  20 . Apertured disk  20  is implemented with a base part  24  and a retention rim  26 . Retention rim  26  extends in the axial direction facing away from valve-seat member  16 , and is bent outwardly in conical fashion up to its end. Valve-seat member  16  and apertured disk  20  are joined, e.g., by a first peripheral and impervious welded seam  25 , formed by a laser, in an outer annular region of base part  24 . For reasons of fatigue strength of the injector, apertured disk  20  should have a thickness of at least 0.2 mm in this securing region. In the region of retention rim  26 , apertured disk  20  is moreover joined to the wall of longitudinal opening  3  in valve-seat support  1 , e.g., by a peripheral and impervious second welded seam  30 .  
         [0012]     According to the present invention, a middle region  33  of base part  24  of apertured disk  20  is reduced in thickness compared to the outer annular region of base part  24  and compared to retention rim  26 . At least one, however, ideally a plurality of spray-discharge openings  34 , is introduced in this middle region  33 . In this context, spray-discharge openings  34  are advantageously located in the outer edge region of thickness-reduced middle region  33 , which, for example, is circular, so that lower end face  17  of valve-seat member  16  covers spray-discharge openings  34 , which means downstream of valve seat  29  between an outlet orifice  31  in valve-seat member  16  and spray-discharge openings  34  in apertured disk  20 , in each case the fuel flow takes an S-shaped course.  
         [0013]     The insertion depth of the valve-seat part, made up of valve-seat member  16  and cup-shaped apertured disk  20 , into longitudinal opening  3  determines the size of the lift of valve needle  5 , since the one end position of valve needle  5  when solenoid coil  10  is not energized is determined by the contact of valve-closure member  7  against valve seat  29  of valve-seat member  16 , valve seat  29  tapering conically downstream. When solenoid coil  10  is energized, the other end position of valve needle  5  is determined, e.g., by the seating of armature  11  on core  12 . Therefore, the path between these two end positions of valve needle  5  represents the lift. Valve-closure member  7  cooperates with valve seat  29 .  
         [0014]     Valve-seat member  16  is formed with its lower outlet orifice  31  in such a way that lower end face  17  of valve-seat member  16  partially forms an upper covering of an intake region  40  of apertured disk  20 , formed by the depression in middle region  33  of apertured disk  20 , and thus determines the entry area of fuel into apertured disk  20 . In the exemplary embodiment shown in  FIG. 1 , outlet orifice  31  has a smaller diameter than the diameter of an imaginary circle on which spray-discharge openings  34  of apertured disk  20  are situated. Because of the radial displacement of spray-discharge openings  34  with respect to outlet orifice  31 , an S-shaped flow pattern of the medium, here the fuel, results toward each individual spray-discharge opening  34 , which is indicated clearly in  FIG. 2  by arrows  36 .  
         [0015]     The so-called S-twist within apertured disk  20  having several sharp reroutings of the flow impresses a strong, atomization-promoting turbulence on the flow. The velocity gradient transversly to the flow is thereby particularly strongly pronounced. It is an expression for the change in velocity transversely to the flow, the velocity in the middle of the flow being perceptibly greater than in the vicinity of the walls. The increased shear stresses in the fluid resulting from the velocity differences promote the disintegration into fine droplets near spray-discharge openings  34 . Since because of the impressed radial component, the flow in the outlet is detached on one side, it experiences no calming because there is a lack of contour guidance. The fluid exhibits an especially high velocity at the detached side. The atomization-promoting turbulences and shear stresses are therefore not dissipated in the outlet. Due to the S-twist, a high-frequency turbulence is generated in the fluid, this turbulence causing the jet to disintegrate into suitably fine droplets immediately after exiting apertured disk  20 .  
         [0016]      FIG. 2  shows an enlarged representation of the valve part formed by valve-seat member  16  and apertured disk  20 , in order to clearly indicate the S-shaped flow pattern, denoted by arrows  36 , toward each spray-discharge opening  34 .  FIG. 3  shows schematically the impression method step.  
         [0017]     In a first method step, not shown, a flat metallic sheet  20 ′ having a constant thickness is made available. This sheet  20 ′ has a thickness of approximately  0 . 2  mm, for example, which is retained outside of region  33  even after application of the method steps according to the present invention. For instance, sheet  20 ′ is a stainless steel material such as 1.4404, 1.4301 or SUS304, having a tensile strength of 500 to 700 N/mm 2  and an original hardness of 160±15 HV. For reasons of long-term endurance of the fuel injector, apertured disk  20  should have a minimum thickness of 0.2 mm at least in its annular region of base part  24 , in which apertured disk  20  is secured to valve-seat member  16  by welded seam  25 . In order to optimally adhere to the ratio of length to diameter of each individual spray-discharge opening  34  from the standpoint of fluid mechanics, given the predefined minimum thickness, the spray-orifice diameters are likewise largely predefined with a minimum value. If, for reasons of improved atomization and spray conditioning, a plurality of spray-discharge openings  34  having very small spray-orifice diameters, e.g. less than 0.2 mm, is now to be formed in apertured disk  20 , it is advantageous in region  33  of spray-discharge openings  34 , to reduce the thickness of sheet  20 ′, from which the later apertured disk  20  is formed.  
         [0018]     In a further method step, thickness is reduced by impressing, a depression  40 ′ thereby being formed in sheet  20 ′ ( FIG. 3 ). This depression  40 ′ has, for example, a frustoconically inclined or cylindrical limiting wall. Given an original thickness of sheet  20 ′ of 0.12 mm to 0.25 mm, the thickness reduction in region  33 , accomplished by impressing, may amount to approximately 0.05 mm to 0.1 mm. A stamping tool  41  is indicated symbolically in  FIG. 3 . During the impressing process, a plastic deformation is carried out and material of sheet  20 ′ is displaced and piled up a little bit on the contact side of stamping tool  41  around depression  40 ′. This displaced material can easily be distributed in a rolling process. By this rolling or method also called “stamping”, the mound around impressed region  33  is uniformly distributed radially outwardly, resulting in a negligible increase in thickness in the region immediately outside of impressed region  33 .  
         [0019]     As an alternative to impressing, the thickness of sheet  20 ′ may also be reduced in region  33 , in which spray-discharge openings  34  are located, by so-called embossing. It is a stamping-bending operation, similar to deep drawing, as a further possibility for cold-working a metal. Embossing is suitable for forming intake region  40  of apertured disk  20  in particular when the hardness of the material to be deformed is greater or considerably greater than 160 HV. During the embossing process, material is pushed out on the bottom side of sheet  20 ′ facing away from the contact side of embossing tool  41 ′. This protruding material is subsequently removed again by grinding, for example, so that the bottom side of sheet  20 ′, i.e., of apertured disk  20 , is even.  
         [0020]     After thickness has been reduced by impressing or embossing, in a further method step, the at least one spray-discharge opening  34  is introduced in region  33  of sheet  20 ′. Sheet  20 ′ is thereupon finish-machined until apertured disk  20  is obtained with its predefined outside dimensions. However, apertured disk  20  may also already be provided with the desired outside dimensions prior to introducing spray-discharge openings  34  by separating it from sheet  20 ′, for example, by punching out, cutting out, or in a similar manner. The at least one spray-discharge opening  34  is introduced by punching, eroding or laser drilling.  
         [0021]     As already described in detail above, in conclusion, apertured disk  20  is secured according to the present invention in a manner that the flow approaches spray-discharge openings  34  in an S-shape, since in the mounted state of apertured disk  20 , material of valve-seat member  16  overlaps spray-discharge openings  34  radially inwardly.  
         [0022]      FIG. 1  shows, by way of example, a cup-shaped apertured disk  20 , mounted on a fuel injector, which, because of its retention rim  26 , is able to be mounted in a particularly secure and reliable manner. However, the method steps of the present invention for producing an apertured disk  20  are by no means limited to such geometrical designs of apertured disks  20 . Rather, apertured disks  20  which are completely flat or bent differently are also able to be reduced in thickness according to the present invention in a region  33 .