Abstract:
A fuel injector having an integrated ignition device includes a first electrode pair for igniting fuel which is injected directly into a combustion chamber of an internal combustion chamber through spray-discharge orifices of the fuel injector. The first electrode pair is made up of a ground electrode and a center electrode which are set apart by a spark gap. The fuel injector and the ignition device are situated in a shared housing. The ignition device has at least one additional spark gap and/or an additional electrode pair.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a fuel injector having an integrated ignition device. 
       BACKGROUND INFORMATION 
       [0002]    Published German patent document 102 14 167 describes a fuel injector which has an integrated ignition device. A first electrode and a second electrode form a spark gap on the discharge side of the spray-discharge orifices. One of the advantages of such a fuel injector-spark plug combination is the reduced installation space and the increased flexibility in the combustion-chamber design and the arrangement and sizing of the intake and exhaust valves. 
         [0003]    Particularly disadvantageous in the fuel injector described in the aforementioned German patent document is that the fuel-air mixture is ignited in only one location in the combustion chamber because of the only one spark gap. The time for the flame propagation in the combustion chamber is thus increased in a disadvantageous manner. 
       SUMMARY 
       [0004]    The fuel injector including an integrated ignition device according to the present invention has the advantage that the entire fuel-air mixture is ignited much faster. Since the overall combustion is therefore taking place much more rapidly, the efficiency is increased. In addition, lean end areas of the spray are avoided which ensures a smaller spread in the lambda range of the spray, resulting in reduced hydrocarbon emissions. Furthermore, the fuel injector having an integrated ignition device according to the present invention allows a higher exhaust-recirculation rate and/or lean stratified-charge operation which results in reduced nitrogen-oxide emissions. 
         [0005]    In an example embodiment, the electrode pairs are positioned in such a way that the spark gaps are distributed evenly about the spray-discharge orifices, and/or the spark gaps are positioned on a circle about the spray-discharge orifices. This provides a uniform ignition of the fuel-air mixture, and the fuel-air mixture may combust evenly and homogenously inside the combustion chamber. The time for the full ignition of the entire fuel-air mixture inside the combustion chamber is minimized. 
         [0006]    It is also advantageous to manufacture the housing from an electrically conductive material such as metal, for example. The housing may then be used as electrical pole or as ground electrode for the electrode pairs. 
         [0007]    Because the length of the spark plug amounts to only 50 to 300 micrometers, the ignition voltage may be selected to be low. In addition, a reduced thickness of the insulating bodies may be chosen. 
         [0008]    Moreover, it is advantageous to integrate a pressure sensor and/or a temperature sensor in the shared housing. This makes it easy to monitor states in the combustion chamber. Furthermore, no additional openings into the combustion chamber, which would be required for external sensors, will be necessary. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIG. 1  shows a schematic cross-sectional view of an example of a fuel injector without integrated ignition device. 
           [0010]      FIG. 2  shows a schematic cross-sectional view of the discharge-side region of an exemplary embodiment of the fuel injector having an integrated ignition device according to the present invention. 
           [0011]      FIG. 3  shows a plan view of the discharge-side end of the fuel injector having an integrated ignition device according to the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0012]    An exemplary embodiment of the present invention is described in the following by way of example. Identical components have been provided with matching reference numerals. 
         [0013]    Before giving a more detailed description of an exemplary embodiment according to the present invention in connection with  FIGS. 2 and 3 , to provide a better understanding of the present invention, a fuel injector without integrated ignition device shall be explained briefly with reference to  FIG. 1 . 
         [0014]    An example of a fuel injector  1  lacking an integrated ignition device, shown in  FIG. 1 , is designed in the form of a fuel injector  1  for fuel-injection systems of mixture-compressing internal combustion engines having externally supplied ignition. Fuel injector  1  is particularly suited for the direct injection of fuel into a combustion chamber (not shown) of an internal combustion engine. 
         [0015]    Fuel injector  1  lacking an integrated ignition device is made up of a nozzle body  2  in which a valve needle  3  is positioned. Valve needle  3  has on its discharge side a valve-closure member  4 , which cooperates with a valve-seat surface  6  disposed on a valve-seat member  5  to form a sealing seat. In the exemplary embodiment of  FIG. 1 , fuel injector  1  is an inwardly opening fuel injector  1 , which is provided with a spray orifice  7 . A seal  8  seals nozzle body  2  against an outer pole  9  of a solenoid coil  10 . Solenoid coil  10  is encapsulated in a coil housing  11  and wound on a coil brace  12  which rests against an inner pole  13  of solenoid coil  10 . Inner pole  13  and outer pole  9  are separated from one another by distance  26  and interconnected by a non-ferromagnetic connecting part  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 . Plug contact  17  is enclosed by a plastic coat  18 , which is extrudable onto inner pole  13 . 
         [0016]    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 (valve) lift. Armature  20  is disposed on the other side of adjustment disk  15 . Via a first flange  21 , it is in connection with valve needle  3 , which is joined to first flange  21  by a welded seam  22 . A helical restoring spring  23  is braced on first flange  21  and prestressed by a sleeve  24  in the example of fuel injector  1  shown in  FIG. 1 . 
         [0017]    Fuel channels  30 ,  31  and  32  extend in valve-needle guide  14 , armature  20  and along a guide element  36 . The fuel is supplied via a central fuel supply  16  and filtered by a filter element  25 . A rubber ring  28  seals fuel injector  1  against a fuel distributor line (not shown further), and a seal  37  seals it against a cylinder head (not shown further). 
         [0018]    On the spray-discharge side of armature  20  is an annular damping element  33  made of an elastomeric material. It rests on a second flange  34 , which is integrally joined to valve needle  3  via a welded seam  35 . 
         [0019]    In the quiescent state of fuel injector  1 , armature  20  is acted upon by a restoring spring  23  against its direction of lift, in such a way that valve-closure member  4  is held in sealing contact on valve-seat surface  6 . When excited, solenoid coil  10  generates a magnetic field which moves armature  20  in the lift direction, counter to the spring force of restoring spring  23 , the lift being defined by a working gap  27  occurring in the rest position between inner pole  12  and armature  20 . 
         [0020]    First flange  21 , which is welded to valve needle  3 , is taken along by armature  20  in the lift direction as well. Valve-closure member  4 , which is joined to valve needle  3 , lifts off from valve seat surface  6 , so that the fuel supplied under pressure is spray-discharged into the combustion chamber (not shown) through spray-discharge orifice  7 . 
         [0021]    If the coil current is interrupted, following sufficient decay of the magnetic field, armature  20  falls away from inner pole  13  due to the pressure of restoring spring  23 , whereupon first flange  21 , which is joined to valve needle  3 , moves in a direction counter to the lift direction. Valve needle  3  is thereby moved in the same direction, causing valve-closure member  4  to set down on valve seat surface  6  and fuel injector  1  to be closed. 
         [0022]      FIG. 2  shows a schematic cross-sectional view of the discharge-side region of an exemplary embodiment of a fuel injector  1  having an integrated ignition device according to the present invention. Illustrated fuel injector  1  is configured as a multi-hole valve and opens toward the inside of the combustion chamber. The integrated ignition device has two electrode pairs. A first electrode pair is made up of a first ground electrode  38  and a first center electrode  39 . A second electrode pair is made up of a second ground electrode  44  and a second center electrode  45 . 
         [0023]    Cylindrical nozzle body  2  of fuel injector  1  extends inside hollow-cylindrical housing  40  with a precise fit and ends on the spray-discharge-side end of housing  40 . Situated in housing  40  are a first hollow-cylindrical insulating body  42  in which first center electrode  39  extends, and a second hollow-cylindrical insulating body  47  in which second center electrode  45  extends. Insulating bodies  42 ,  47  are made from a ceramic material, for example. In other exemplary embodiments it is possible, for instance, to configure nozzle body  2  and housing  40  as one piece. Both insulating bodies  42 ,  47  project slightly beyond the discharge-side end of housing  40 . This serves the purpose of avoiding creeping currents between the electrodes. 
         [0024]    On the discharge side, both center electrodes  39 ,  45  initially exit from the two insulating bodies  42 ,  47  coaxially with respect to the center axis of the particular insulating body  42 ,  47 ; after a short distance, they then extend approximately at a right angle thereto. Both ground electrodes  38 ,  44  are affixed on opposite sides of spray-discharge orifices  7  in an electrically conductive manner by welding in the region of the outer edge of the discharge side of housing  40 . Starting from housing  40 , they initially extend parallel to the extension of the individually assigned center electrodes  39 ,  45 , and then bend at a right angle on the same level as center electrodes  39 ,  45 . The ends of individual center electrodes  39 ,  45  and the ends of individual ground electrodes  38 ,  44  are situated opposite each other and are spaced apart by spark gaps  41 ,  46  shown in greater detail in  FIG. 3 . 
         [0025]    As indicated by arrows in  FIG. 2 , the fuel emerging from the plurality of spray-discharge orifices  7  in the form of spray  43  is ignited at both spark gaps  41 ,  46 , and the arrows indicate the progression of the flame front of the ignited fuel-air mixture. The edge of spray  43 , or spark gaps  41 ,  46 , is situated such that spray  43  flows past spark gaps  41 ,  46  as closely as possible without coming into direct contact with or wetting them with fuel. Spray  43  flowing past at only a short distance also generates a so-called entrainment flow which deflects the ignition spark from the individual spark gap  41 ,  46  and in this way reliably ignites the fuel-air mixture. Since spark gaps  41 ,  46  are located at opposite sides of spray-discharge orifices  7 , two flame fronts propagate in the combustion chamber, which initially are directed away from one another, but then extend to a piston floor (not shown) and ultimately flow toward one another, as indicated by the arrows in  FIG. 2 . 
         [0026]    The time for the complete ignition of the fuel-air mixture in the combustion chamber (not shown) is nearly halved as a result. The two spark gaps  41 ,  46  are ignited simultaneously, an ignition with a time-offset being conceivable so as to take into account different propagation times of the two flame fronts in combustion-chamber geometries that are not symmetrical, for example. This may also become necessary if fuel injector  1  according to the present invention is not centrically disposed in a combustion-chamber roof (not shown). 
         [0027]    Introduced radially in the region of the discharge-side end of housing  40  are a temperature sensor  49  and a pressure sensor  48 . 
         [0028]      FIG. 3  shows a plan view of the discharge-side end of the fuel injector  1  having an integrated ignition device according to the present invention. Clearly visible are spark gaps  41 ,  46  on opposite sides of spray-discharge orifices  7 . However, in other exemplary embodiments according to the present invention, it is also possible to place more than two spark gaps  41 ,  46  around discharge orifices  7 , which spark gaps are then disposed about spray-discharge orifices  7  in a uniform or circular arrangement, for example. The end of first center electrode  39  and the end of first mass electrode  38  are facing toward each other. The end of second center electrode  45  and the end of ground electrode  44  are also directed toward each other. The areas of the ends of the individual electrodes  38 ,  39 ,  44 ,  45  oriented toward each other extend in parallel to each another. 
         [0029]    The clearances of the ends of the individual electrode pairs advantageously amount to only 50 to 300 micrometer. The magnitude of the ignition voltage may be lowered as a result, and the thickness of insulating bodies  42 ,  47  be reduced without detrimental effect on the reliability of fuel injector  1  having an integrated ignition device, since spray  43  flowing past generates the so-called entrainment flow, which deflects the only brief ignition spark and pulls it into the spray. 
         [0030]    The ignition of both spark gaps  41 ,  46  may be carried out either via an individual ignition coil (not shown) by a series connection, it being necessary in this case to install or implement one of the two ground electrodes  38 ,  44  in an insulating manner, or it may be carried out by a double-spark coil. 
         [0031]    The ignition of more than two spark gaps  41 ,  46  (n=number of spark gaps) may be realized either via an individual ignition coil, by a series connection, the ground electrodes of n−1 spark gaps then having to be installed in an insulating manner, or by using one or a plurality of double-spark coils or a combination of double-spark coils and single-spark ignition coils. 
         [0032]    Described fuel injector  1  having an integrated ignition device as sub-assembly may additionally be combined with one or a plurality of ignition coils disposed behind in the axial direction. 
         [0033]    The present invention is not restricted to the exemplary embodiments shown and may also be used, for instance, for outwardly opening or swirl-generating fuel injectors  1  having an integrated ignition device.