Patent Publication Number: US-2005127209-A1

Title: Director plate having smooth exits

Description:
TECHNICAL FIELD  
      The present invention relates to fuel injectors for internal combustion engines; more particularly, to fuel injectors for injection of fuel into the cylinders of such engines; and most particularly, to such a fuel injector including a director plate having fuel passage exits with minimal raised rims, burrs, and break-edges.  
     BACKGROUND OF THE INVENTION  
      Fuel injected internal combustion engines are well known. In such an engine, the injection tip of the fuel injector is positioned forward of the intake valve and includes a perforated plate, known in the art as a “director plate,” for dispersing and directing fuel injected from the injector toward the intake valve of the combustion chamber. As is well known in the automotive arts, the configuration and positioning of a director plate with respect to the injector tip and the combustion chamber intake valve are critical elements in the distribution of fuel into the combustion chamber. For example, a director plate may have a plurality of fuel passages therethrough, and the axes of the passages may be inclined radially and/or tangentially from the axis of the director plate. Director plates, including fuel passages, are formed typically of a stainless steel as by precision stamping from sheet stock. Other forming processes for fuel passages are known, such as electrical discharge machining (EDM), laser drilling, and the like; however, stamping is an inexpensive and generally accepted process for forming fuel passages in director plates.  
      A known problem can arise during use of fuel injectors equipped with director plates, and especially stamp-formed director plates. Such director plates can accumulate deposits of fuel-related materials around the exits of the fuel passages, both on the surface of the plates and along the passage walls adjacent the exits. Such deposits are undesirable, can affect the spray pattern of fuel, and can grow large enough to cause a fuel injector to fail due to flow restriction. If the injector cannot be cleaned, the only practical remedy is replacement of the fuel injector, which is inconvenient, time-consuming, and expensive.  
      What is needed in the art is a fuel injector having a director plate that does not readily accumulate fuel-related deposits around the exits of the fuel passages.  
      It is a principal object of the present invention to provide a fuel injector having a director plate that does not readily accumulate fuel-related deposits around the exits of the fuel passages.  
     SUMMARY OF THE INVENTION  
      Briefly described, a director plate for a fuel injector in accordance with the invention includes a plurality of fuel passages extending therethrough between an inlet surface and an exit surface of the director plate. The passage and exit surfaces are extremely smooth, having an average surface roughness (R a ) less than about 0.2 μm, and preferably less than 0.1 μm. The corners of the exits are sharp and are free of features such as break-edges, burrs, and remelt. The surface quality may be obtained via any means of surface finishing, and the invention is defined by the quality of the surfaces and not by the means of attaining such quality. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
       FIG. 1  is an elevational cross-sectional view of a portion of a fuel injector including a director plate;  
       FIG. 2  is an enlarged cross-sectional view of the director plate shown in  FIG. 1 ;  
       FIG. 3  is an enlarged view of the area shown in Circle  3  in  FIG. 2 , showing a fuel passage in accordance with the invention;  
       FIG. 4  is a view like that shown in  FIG. 3 , showing a prior art fuel passage and exit having stamping-residual passage damage and raised exit rim;  
       FIG. 5  is a view like that shown in  FIG. 4 , showing the beginning of accumulation of fuel-related deposits around the raised exit rim;  
       FIG. 6  is a view like that shown in  FIG. 5 , showing severe accumulation of fuel-related deposits around the raised exit rim; and  
       FIG. 7  is a topological schematic drawing of an idealized crystal surface showing relative preference of material adsorption sites. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Referring to  FIGS. 1 and 2 , there is shown a fuel injector  10  for use in injecting fuel at the intake valve  12  of an internal combustion engine  14 . An end portion  16  of injector  10  includes an injector body  18  surrounding an injector nozzle  20  press-fit into a bore  22  in body  18 . A director plate  24 , formed as a shallow cup, is disposed on the end of nozzle  20  and retained in place by a retainer  26  also pressed into bore  22 . A central opening  28  in retainer  26  permits fuel to be injected from director plate  24  into chamber  12 . Plate  24  includes a plurality of passages  30  therethrough between a fuel inlet surface  32  and a fuel exit surface  34 , the passages having respective fuel inlets  33  and exits  35 . Plate  24  is formed typically by stamping from sheet stock of a stainless steel such as AISI  430  or  304 L. The sheet stock typically has a thickness of about 0.150-0.200 μm, and the passages have a comparable diameter, in the range of about 0.150-0.300 μm, depending in part upon the number of passages selected. Passages are stamped in the direction  36  from inlet surface  32  through exit surface  34 , which is also the fuel flow direction. The axes of the passages typically are inclined by an angle  37  from the surface normal  39 , typically about 190, which incline may be radial, tangential, or both, from the axis of the plate and injector.  
      Referring now to  FIGS. 4 through 6 , a prior art director plate  24  that is formed by stamping typically exhibits distortion and tearing of the metal structure of the passage walls  41 , especially near the exit side of the punching. Such distortion is known in the art as “break-edge”  38 . Further, punching is known to leave a slight raised, irregular rim  40  around the exit opening  42  ( FIG. 4 ). Heretofore, these artifacts of punching have been considered in the art to be trivial and of no practical consequence. However, we have found surprisingly that they are of great importance in the premature impairment and eventual failure of fuel injectors. Examinations of prior art director plates  24  after periods of use show that burrs and crevices in and adjacent to rim  40  are sites for accumulation of fuel-related deposits  44  ( FIG. 5 ). With continued plate use, these deposits can continue to grow to a size  44 ′ ( FIG. 6 ) sufficient to cause the fuel injector to fail to deliver its intended volume and spray pattern of fuel into the combustion chamber.  
      The tendency for deposits to form on rough surfaces and break-edges can be explained in terms of preferred adsorption sites on a crystal surface. While not essential to the invention, the following theory is offered to explain the success of the invention. Referring to  FIG. 7 , a topological schematic drawing  45  of an idealized crystal surface  46  is shown. Surface  46  includes a discontinuity  48  such as would result from formation of break-edge  38  and rim  40  ( FIG. 4 ). Discontinuity  48  results in a ledge  50  having two walls  52 , 54 , and a corner  56  having three walls  58 , 60 , 62 . Particle A is deposited on surface  46  and has only one side in contact therewith. Particle B is deposited on ledge  50  and thus has two sides in contact with walls  52  and  54 . Particle C is deposited in corner  56  and thus has three sides in contact with walls  58  and  60  and  62 . Because particles are bonded to substrates by the total surface energy available, Particle C will be adsorbed more strongly than Particle B, which will be more strongly adsorbed than Particle A. Therefore, fuel-related deposits are seen to form most readily on surfaces including corners and ledges, which are constituents of any rough surfaces such as break-edges  38  and burred rim  40 .  
      What is now recognized by the inventors is that surface roughness in the vicinity of passage exit opening  42  is very critical to formation of deposits, and therefore, smoother surfaces in these regions are highly desirable. Referring to  FIG. 3 , an improved director plate  24 ′ in accordance with the invention is substantially free of significant roughness in regions in and around passage exit opening  42 ′ of passage  30 ′, and especially at passage exit corner  43 . “Significant roughness” is defined herein as being a surface having a numerical roughness average (R a ) less than about 0.2 μm, and preferably less than about 0.1 μm, where R a  is the arithmetic mean of the departures of the roughness profile from the mean line. Such levels of smoothness can be achieved by any of several well-known means, including but not limited to mechanical polishing, magnetorheological finishing, and laser polishing. The scope of the invention is not limited by any selected means of surface smoothing, including initially forming passages having no break-edge and/or rim deformation.  
      While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.