Abstract:
Known fuel injectors have a valve-closure member, which cooperates with a sealing seat of a valve seat, and a flow exit region situated downstream from the sealing seat, the fuel spray generated by the fuel injectors having an average droplet diameter that is not small enough for future regulations governing exhaust emission. In the fuel injector according to the present invention the atomization is improved in a simple manner and the average droplet diameter is reduced without additional auxiliary power. The projections which influence the fuel flow are situated in the flow exit region.

Description:
BACKGROUND INFORMATION  
       [0001]    U.S. Pat. No. 4,759,335 describes a fuel injector, which has a valve-closure member cooperating with a sealing seat of a valve seat, and a flow outlet region downstream from the sealing seat. The known fuel injector generates a spray whose average droplet diameter is not small enough for future regulations governing exhaust emissions. 
       SUMMARY OF THE INVENTION  
       [0002]    The fuel injector according to the present invention has the advantage that the atomization is improved in a simple manner in that uneven regions or protrusions, which influence the fuel flow, are situated in the flow outlet region. This allows the average droplet diameter of the spray to be reduced without expending additional auxiliary energy, so that lower exhaust emissions are able to be achieved. 
         [0003]    It is especially advantageous if the flow outlet region is formed by a first wall and a second wall which is situated opposite the first wall, an exit gap being formed between the first wall and the second wall, since this makes the fuel jet exit the fuel injector in a defined manner. 
         [0004]    It is also advantageous if the second wall having a second flow edge ends downstream from the first wall having a first flow edge when viewed in the direction of the flow, since this constitutes an especially simple specific embodiment. 
         [0005]    According to an advantageous exemplary embodiment, the projections have a height—measured perpendicular to a surface of the flow exit region—that is less than 100 micrometers and greater than the roughness peaks of the surface area. 
         [0006]    It is very advantageous if the projections are situated in the exit gap because this promotes the generation of a so-called Karmann turbulence path whose periodically detaching vortexes produce turbulence so that the fuel jet disintegrates into smaller droplets than in the related art. 
         [0007]    Moreover, it is advantageous if the projections are positioned downstream from the first flow edge since the fuel jet then already disintegrates into many individual jets at the projections, the fuel jets having a large jet surface. 
         [0008]    Moreover, it is advantageous if the projections have a cylindrical, tetrahedral, pyramidal, conical, prism-shaped, rectangular, semispherical or nub-shaped form since this allows enough turbulence to be generated in the fuel jet exiting the fuel injector to induce the surface of the fuel jet to oscillate, thereby atomizing the fuel jet into very small droplets. 
         [0009]    Furthermore, it is advantageous if the height of the projections increases or decreases downstream in a continuous or stepped manner because the fuel jet is split into many individual jets at the projections, which then collide with other individual jets downstream less often. 
         [0010]    According to a second advantageous embodiment, the projections are situated in rows set up transversely to the flow, the rows being arranged at an offset with respect to each other, for instance. 
         [0011]    Furthermore, it is advantageous to generate the projections by rasping, micro-embossing, laser removal, etching, micro-electroplating or deposition of a coating since these are suitable methods for creating the projections. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]      FIG. 1  shows a first exemplary embodiment of a fuel injector. 
           [0013]      FIG. 2  shows a sectional plan view of the first exemplary embodiment. 
           [0014]      FIG. 3  shows a second exemplary embodiment. 
           [0015]      FIG. 4  shows a third exemplary embodiment. 
           [0016]      FIG. 5  shows a sectional plan view of the third exemplary embodiment. 
           [0017]      FIG. 6  shows a fourth exemplary embodiment. 
           [0018]      FIG. 7  shows a fifth exemplary embodiment. 
           [0019]      FIG. 8  shows a so-called A-valve. 
           [0020]      FIG. 9  shows a so-called I-valve. 
       
    
    
     DETAILED DESCRIPTION  
       [0021]      FIG. 1  shows a simplified view of a first exemplary embodiment of a fuel injector configured according to the present invention. 
         [0022]    The fuel injector is used to finely atomize fuel in the form of spray in order to lower the fuel consumption and exhaust emissions. In the so-called manifold injection, for instance, the fuel is injected into an intake manifold, or in the so-called direct injection it is injected directly into a combustion chamber of the internal combustion engine. 
         [0023]    The fuel injector has a valve housing  1  with an input port  2  for the fuel. Situated in valve housing  1  is a schematically illustrated actuator  3  for the axial adjustment of a valve needle  4 . Actuator  3  is, for instance, a magnetic armature which cooperates with an excitable coil, a hydraulic element, a piezoactuator or similar element. 
         [0024]    Valve needle  4  is provided in valve housing  1  so as to be axially displaceable and has, for instance, a needle shaft  7  facing actuator  3  and a valve-closure member  8  facing away from actuator  3 . Actuator  3  transmits its movement to needle shaft  7  of valve needle  4  directly or indirectly, thereby causing valve-closure member  8 , which cooperates with a valve seat  9 , to open or close the fuel injector in the direction of a valve axis  5 . The fuel injector has, for instance, a so-called ball-cone seat in which valve seat  9  has a conical design, for example, and valve-closure member  8  has a ball or radii section  10  that cooperates with valve seat  9 . However, the fuel injector may naturally also have a different design such as a ball-ball seat, a cone-cone seat or a cone-ball seat. When the fuel injector is closed, valve-closure member  8  sealingly rests against valve seat  9 , with line and surface contact across its entire circumference, which will be denoted as sealing seat  11  in the following text. 
         [0025]    Abutting downstream from valve seat  9  is a flow exit region  14  from which the fuel in the form of a so-called free jet is admixed to the air aspirated by the internal combustion engine. 
         [0026]    Flow exit region  14  is formed by a first wall  15  and a second wall  16  situated opposite first wall  15 , an exit gap  17  through which fuel  20  discharges when the fuel injector is opened being formed between first wall  15  and second wall  16 . First wall  15  extends from sealing seat  11  to a first flow edge  18 , and second wall  16  extends from sealing seat  11  to a second flow edge  19  in the flow direction. 
         [0027]    First wall  15  and second wall  16  may be joined to one another to make up one part, for instance, or each may also be provided on a separate part. Exit gap  17  is designed as a closed flow channel whose cross section may have various forms, for instance a circular, annular or rectangular form. Second wall  16  having second flow edge  19  ends on the side facing away from sealing seat  11  downstream from first flow edge  18  of first wall  15 . However, first flow edge  18  and second flow edge  19  may naturally also be situated in an identical plane perpendicular to valve axis  5 . 
         [0028]    According to the present invention, uneven regions or projections  22 , which project into the fuel stream and thereby influence or interfere with it, are situated in flow exit region  14 . 
         [0029]    Projections  22  have a raised design compared to, for instance, a surface area  23  of flow exit region  14  formed on second wall  16 , and a height, measured perpendicular to surface area  23 , that is less than  100  micrometers, for instance, and greater than the height of the roughness peaks of surface area  23 . 
         [0030]    Projections  22  may be situated adjacent to each other in any desired way, for instance in one or a plurality of rows  24  set up transversely to the flow ( FIG. 2 ). Rows  24  are situated behind each other when viewed in the flow direction; it is possible, for instance, to situate projections  22  of a row  24  at an offset with respect to projections  22  of adjacent rows  24 . 
         [0031]    Projections  22  may be placed in exit gap  17  and/or, if a second flow edge  19  is situated downstream, downstream from first flow edge  18 . Projections  22  may be provided on first wall  15  and/or second wall  16 . Projections  22  project from one of the two walls  15 ,  16  into exit gap  17  and may extend to wall  15 ,  16  lying opposite. 
         [0032]    Uneven regions or projections  22  have, for example, a cylindrical, tetrahedral, pyramidal, conical, prism-shaped, rectangular, semispherical, nub-shaped or similar design. 
         [0033]    The orientation of projections  22  relative to the flow is arbitrary; projections  22  may, for instance, be aligned in the direction of the flow via an edge or a surface. 
         [0034]    Pyramids or tetrahedrons have a form that is advantageous for the flow in that it avoids or at least reduces flow turbulence on the downstream side, so that no or only very few deposits form on the downstream side of the pyramids or tetrahedrons. 
         [0035]    The fuel is guided in valve housing  1  from input port  2  to valve-closure member  8  upstream from sealing seat  11 . When the fuel injector is opened, valve-closure member  8  lifts off from sealing seat  11 , so that fuel in the form of a fuel jet flows into exit gap  17  of flow exit region  14  via an outlet opening formed between valve-closure member  8  and valve seat  9 . 
         [0036]    In exit gap  17  the fuel jet is guided across the entire circumference via the area of flow exit region  14 , whereas, if second flow edge  19  lies downstream in the flow direction, the fuel jet as partially free jet is only partially guided along the circumference downstream from first flow edge  18 . The fuel jet leaves flow exit region  14  of the fuel injector downstream from second flow edge  19  as a completely free jet and disintegrates into many small individual droplets. The smaller the average droplet diameter, the lower the consumption of the internal combustion engine and the lower the exhaust emissions. 
         [0037]    The fuel jet discharging through exit gap  17  when the fuel injector is opened flows around and/or across projections  22 ; considerable turbulence is generated in the stream in the process, which induces oscillations on the surface of the fuel jet. Due to the oscillations on the surface of the fuel jet the fuel jet disintegrates into especially small droplets. This improvement in the atomization is achieved without expending additional energy. The arrangement of projections  22  in flow exit region  14  thus is a simple and cost-effective manner of generating smaller droplet diameters than in the related art. 
         [0038]    If projections  22  such as the pyramids and tetrahedrons have beveled surfaces, the fuel jet is split into many individual jets already when flowing around and/or across projections  22  since the flow, which follows the beveled surfaces, is deflected transversely to the main flow and tears off as free jet at the individual downstream edges of projections  22 . The individual jets generated at projections  22  have an overall larger jet surface than the fuel jet upstream from projections  22 . 
         [0039]    Projections  22  are generated also by, for instance, roughening, sand blasting, rolling, micro-embossing, laser removal, etching, micro-electroplating or deposition of a coating. 
         [0040]      FIG. 2  shows a plan, simplified partial view of the first exemplary embodiment according to  FIG. 1 . In the fuel injector according to  FIG. 2  the components that remain unchanged or act in the same manner as those in the fuel injector according to  FIG. 1  have been characterized by the same reference numerals. 
         [0041]      FIG. 3  shows a second exemplary embodiment of a fuel injector in a partial, simplified view. 
         [0042]    In the fuel injector according to  FIG. 3 , the components that remain unchanged or act in the same manner as those in the fuel injector according to  FIG. 1  and  FIG. 2  have been characterized by the same reference numerals. 
         [0043]    The fuel injector according to  FIG. 3  differs from the fuel injector according to  FIG. 1  in that projections  22  are not formed as pyramids, but as cylinders. 
         [0044]      FIG. 4  shows a third exemplary embodiment of a fuel injector in a partial, simplified view. 
         [0045]    In the fuel injector according to  FIG. 4 , the components that remain unchanged or act in the same manner as those in the fuel injector according to  FIGS. 1 through 3  are characterized by the same reference numerals. 
         [0046]    The fuel injector according to  FIG. 4  differs from the fuel injector according to  FIG. 1  in that projections  22  are not in the form of pyramids, but in the form of tetrahedrons. 
         [0047]    The height of projections  22  such as the tetrahedrons may increase or decrease in the flow direction in a stepwise or continuous manner. Since individual jets  26  tearing off at projections  22  tear off as free jets at different distances from surface area  23 , there are few collisions among individual jets  26 , so that they are retained and have a large surface. 
         [0048]    The height of projections  22  of a row  24  is constant, for instance, but it may also be modified according to a sine curve, for example. 
         [0049]      FIG. 5  shows a simplified plan view of a partial view of the third exemplary embodiment according to  FIG. 4 . In the fuel injector according to  FIG. 5 , the components that remain unchanged or act in the same manner as those in the fuel injector according to  FIG. 1  are characterized by the same reference numerals. 
         [0050]      FIG. 6  shows a fourth exemplary embodiment of a fuel injector in a partial, simplified view. 
         [0051]    In the fuel injector according to  FIG. 6 , the components that remain unchanged or act in the same manner as those in the fuel injector according to  FIGS. 1 through 5  are characterized by the same reference numerals. 
         [0052]    The fuel injector according to  FIG. 6  differs from the fuel injector according to  FIG. 1  in that projections  22  are in the form of nubs. 
         [0053]    Projections  22  are deposited by electroplating, for instance, as a patterned layer  25 . Patterned layer  25  is made up of a planar layer  26  on which semispherical projections  22 , for instance, are provided. Patterned layer  25  is made of chromium, for example. The diameter of semispherical projections  22  is between 0 and 30 micrometers, for instance. Patterned layer  25  may be produced with the aid of a known chrome patterning method. The thickness of patterned layer  25  continually decreases, for example at an edge of patterned layer  25  facing sealing seat  11 , so that a step, which would interfere with the flow of the fuel, is avoided. 
         [0054]    The production of patterned layer  25  requires no especially precise working of the surface and thus is simple and cost-effective. 
         [0055]      FIG. 7  shows a fifth exemplary embodiment of a fuel injector in a part-sectional, simplified view. 
         [0056]    In the fuel injector according to  FIG. 7  the components that remain unchanged or act in the same manner as those in the fuel injector according to  FIGS. 1 through 6  are characterized by the same reference numerals. 
         [0057]    The fuel injector according to  FIG. 7  differs from the fuel injector according to  FIG. 1  in that projections  22  are situated in exit gap  17  of flow exit region  14  and extend from first wall  15  to second wall  16 . 
         [0058]    Placing projections  22  in exit gap  17  causes a so-called wake vortex to be formed in the flow downstream from each projection  22 , such wake vortex also being known as Karmann turbulence path. With the flow, vortexes periodically detach from each projection  22 , which generate additional turbulence in the flow and in this manner promote the disintegration of the fuel jet into the smallest possible droplets. The smaller the cross-section of projection  22  exposed to the flow and the smaller the clearances between projections  22 , the higher the turbulence generated by the wake vortex. The mutual offset of individual rows  24  likewise increases the turbulence in the fuel jet. 
         [0059]      FIG. 8  shows in simplified form a so-called A-valve whose valve-closure member  8  executes an outwardly directed lift when viewed in the flow direction. 
         [0060]    In the fuel injector according to  FIG. 8  the components that remain unchanged or the act in the same manner as those in the fuel injector according to  FIGS. 1 to 7  are characterized by the same reference numerals. 
         [0061]    According to this exemplary embodiment, first wall  15  is formed on valve seat  9 , and second wall  16  is formed on valve-closure member  8 . Valve-closure member  8  widens in the flow direction from an end of needle shaft  7  facing away from actuator  3  up to second flow edge  19 , which is situated downstream from first flow edge  18  formed on valve seat  9  in the flow direction. Valve seat  9  widens downstream from sealing seat  11  up to first flow edge  18 . 
         [0062]    Exit gap  17  is provided between valve-closure member  8  and valve seat  9 . 
         [0063]    Projections  22  are provided, for instance, on valve-closure member  8  downstream from sealing seat  11  and upstream from second flow edge  19  and/or on valve seat  9  downstream from sealing seat  11  and upstream from first flow edge  18 . 
         [0064]      FIG. 9  shows a so-called I-valve in simplified form whose valve-closure member  8  executes an inwardly directed lift, counter to the flow direction. 
         [0065]    In the fuel injector according to  FIG. 9  the components that remain unchanged or act in the same manner as those in the fuel injector according to  FIGS. 1 to 8  are characterized by the same reference numerals. 
         [0066]    According to this exemplary embodiment, first wall  15  and second wall  16 , which are formed on a valve-seat body  31 , form exit gap  17 , which is configured as a flow channel. The flow channel has a cylindrical design, for instance, in a first region  29  downstream from the valve seat, and subsequently widens conically in the flow direction in a second region  30 . First flow edge  18  and second flow edge  19  lie in one plane. Projections  22  are situated in second region  30 , for example. 
         [0067]    When the fuel injector is open, the fuel is induced to rotate, for instance with the aid of a swirl disk (not shown), so that the stream entering exit gap  17  forms a rotationally symmetric lamella as a result of the centrifugal force and flows along first wall  15  and second wall  16 . The fuel flows around and across projections  22  in the process and is finely atomized downstream from projections  22 .