Abstract:
A fuel injector for the direct injection of fuel into a combustion chamber of an internal combustion engine includes an energizable actuator, a valve needle, which is in operative connection with the actuator and acted upon by a restoring spring in a closing direction to actuate a valve-closure member, which forms a sealing seat together with a valve-seat surface formed at a valve-seat body. The valve-seat body includes at least two spray-discharge orifices. The pressure of the fuel flowing through the fuel injector is greater than 10 bar.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is directed to a fuel injector for the direct injection of fuel into an internal combustion engine.  
       BACKGROUND INFORMATION  
       [0002]     Published German patent document DE 196 25 059 discloses a fuel injector for the direct injection of fuel into a mixture-compressing internal combustion engine having external ignition, which injector provides a flow path for the fuel from a fuel intake to a spray-discharge orifice, in which flow path a plurality of fuel channels are arranged in front of the discharge orifice, the cross-section of the fuel channels determining the amount of fuel injected per time unit at the given fuel pressure. In order to influence the fuel distribution in an injected mixture cloud and to achieve selective skeining of the mixture cloud, at least a portion of the fuel channels is aligned such that in an open fuel injector the fuel jets exiting from the fuel channels are injected directly through the spray-discharge orifice.  
         [0003]     Particularly disadvantageous in the fuel injector of the aforementioned are the limited opportunities for intervening in the formation of the mixture cloud. Apart from varying the jet broadening and the alignment of the center-of-gravity axis of the mixture cloud, there is barely any possibility of influencing deviations from the conical shape, e.g., irregular mixture clouds and heterogeneously distributed jet penetration. Accordingly, the possibilities for lowering the fuel consumption and exhaust emissions are limited.  
       SUMMARY  
       [0004]     In the fuel injector according to the present invention, due to a high fuel pressure in the fuel-distributor line, it is possible to generate a mixture cloud that is of high atomization quality for a jet-directed combustion method without having to tolerate the disadvantages of fuel injectors with swirl inserts, e.g., high fuel consumption, coking of the valve tip, and increased emissions.  
         [0005]     The spray-discharge orifices end in widened regions which advantageously provide effective coking protection in the discharge region of the spray-discharge orifices.  
         [0006]     Due to a defined ratio l:d of overall length l or reduced length l′ on the intake side of the widened regions, and diameter d of spray-discharge orifices, it is possible to ensure that an optimal jet processing is able to be carried out.  
         [0007]     The at least two spray-discharge orifices may advantageously be implemented in the valve-seat body as desired, for instance on concentric or eccentric hole disks or hole ellipses, or along straight or curved rows.  
         [0008]     Furthermore, the center points of the spray-discharge orifices may be spaced apart from each other at uniform or different distances, just as the orientation of the axes of the spray-discharge orifices may be selected as desired.  
         [0009]     It is advantageous that none of the spray-discharge orifices is directed toward the spark plug so that coking of the spark gap and a shortened service life are able to be avoided.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows a schematic cross-sectional view of an exemplary embodiment of a fuel injector configured according to the present invention.  
         [0011]      FIG. 2  shows a cross-sectional view of a portion of the exemplary embodiment of a fuel injector shown in area II in  FIG. 1 .  
         [0012]      FIG. 3  shows an enlarged cross-sectional view of a portion of the exemplary embodiment in region III of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0013]      FIG. 1  shows a sectional view of an exemplary embodiment of a fuel injector  1  according to the present invention. It is in the form of a fuel injector for fuel-injection systems of mixture-compressing internal combustion engines having external ignition. Fuel injector  1  is suited for the direct injection of fuel into a combustion chamber (not shown further) of an internal combustion engine.  
         [0014]     Fuel injector  1  is composed of a nozzle body  2  in which a valve needle  3  is positioned. Valve needle  3  is in operative connection with a valve-closure member  4 , which cooperates with a valve-seat surface  6  located on a valve-seat member  5  to form a sealing seat. The valve-closure body has a substantially spherical shape, and in this way contributes to an offset-free guidance in valve-seat body  5 . In the exemplary embodiment, fuel injector  1  is an inwardly opening fuel injector, which has two spray-discharge orifices  7 . According to the present invention, spray-discharge orifices  7  are provided in valve-seat body and include widened regions  38 , which provide protection from coking. A detailed illustration of spray-discharge orifices  7  can be seen in  FIG. 2 , and further details are included in the following description.  
         [0015]     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 a gap  26  and braced against a connecting member  29 . Solenoid coil  10  is energized via a line  19  by an electric current, which may be supplied via an electrical plug contact  17 . Plug contact  17  is enclosed by plastic coating  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. On the other side of adjustment disk  15  is an armature  20  which, via a first flange  21 , is connected by force-locking to valve needle  3  joined to first flange  21  by a welding seam  22 . Braced on first flange  21  is a restoring spring  23 , which is prestressed by a sleeve  24  in the present example embodiment of fuel injector  1 .  
         [0017]     On the discharge-side of armature  20  is a second flange  34 , which is used as lower armature stop. It is joined to valve needle  3  in force-locking manner by a welding seem  35 . An elastic intermediate ring  33  is positioned between armature  20  and second flange  34  in order to damp armature bounce during closing of fuel injector  1 .  
         [0018]     Fuel channels  30  and  31  extend inside valve-needle guide  14  and armature  20 . Beveled sections  32 , which guide the fuel to the sealing seat, are formed at valve-closure member  4 . The fuel is supplied via a central fuel feed  16  and filtered by a filter element  25 . A seal  28  seals fuel injector  1  from a distributor line (not shown further). Another seal  36  provides sealing with respect to the cylinder head (not shown further) of the internal combustion engine.  
         [0019]     In the rest state of fuel injector  1 , restoring spring  23  acts upon first flange  21  at valve needle  3  against its lift direction, in such a way that valve-closure member  4  is retained in sealing contact against valve seat  6 . Armature  20  rests on intermediate ring  33 , which is supported on second flange  34 . When solenoid coil  10  is energized, it builds up a magnetic field which moves armature  20  in the lift direction against the spring tension of restoring spring  23 . Armature  20  carries along first flange  21 , which is welded to valve needle  3 , and thus carries valve needle  3  in the lift direction as well. Valve-closure member  4 , being in operative connection with valve needle  3 , lifts off from valve seat surface  6 , thereby causing the fuel guided to spray-discharge orifice  7  to be spray-discharged.  
         [0020]     In response to the coil current being turned off, once the magnetic field has sufficiently decayed, armature  20  falls away from inner pole  13  due to the pressure of restoring spring  23  on first flange  21 , whereupon valve needle  3  moves in the direction counter to the lift. As a result, valve closure member  4  comes to rest on valve-seat surface  6  and fuel injector  1  is closed. Armature  20  sets down on the armature stop formed by second flange  34 .  
         [0021]     As can be gathered from  FIG. 2 , the present invention provides for stepped spray-discharge orifices  7  in valve-seat body  5 . Spray-discharge orifices  7  widen into a widened region  38  along a discharge direction of the fuel. This measure provides protection from coking in the mouth regions of spray-discharge orifices  7 . A deposit of fuel in the region of the spray-discharge orifices would otherwise cause a buildup of combustion residue, which increasingly reduces the diameter of spray-discharge orifices  7  and thus the quantity of spray-discharged fuel. As a consequence, fuel injector  1  is limited in its function and no longer provides sufficient fuel for combustion in the combustion chamber of the internal combustion engine. Increased fuel consumption and poorer emission values are the result.  
         [0022]     In this undesirable scenario, an overall length l of spray-discharge orifices  7  may amount to 
 
l&gt;3· d  
 
 given a predefined diameter d of spray-discharge orifices  7 . For optimal jet processing, a fractional length l′ of spray-discharge orifices  7  on the inflow side (i.e., upstream) of widened region  38  must not exceed a specific value. The dimensions can be gathered from  FIG. 3 . The desired ratio of length l′ to diameter d (of narrow region of the orifice) thus is 
 
l′≦3· d.  
 
         [0023]     If no widened region  38  is provided, the following formula shall apply for overall length l of the spray-discharge orifice: 
 
l≦3· d.  
 
         [0024]     The dimensions indicated above have been shown in  FIG. 3 .  
         [0025]     Diameter d of spray-discharge orifices  7  amounts to  
       d   =       (       4   ·   c       π   ·   n   ·     p   0.5         )     0.5         
 
 where 
 
0.3≦c≦0.6 [mm 2  Mpa 0.5 ]. 
 
         [0026]     N denotes the number of spray-discharge orifices  7  and amounts to at least 2, p is the fuel pressure present in the fuel-distributor line, given in Mpa.  
         [0027]     Spray-discharge orifices  7  in valve-seat member  5  may be implemented in any desired location. The configuration of spray-discharge orifices  7  may be made up of one or a plurality of round or elliptical hole circles arranged concentrically or eccentrically with respect to each other or to a center point of valve-seat body  5 , or they may be made up of one or a plurality of straight or curved hole rows arranged in parallel, at an angle, an offset or without offset with respect to each other.  
         [0028]     The spacing between center points of spray-discharge orifices  7  may be of equal or different size, but should amount to at least 180% of diameter d of spray-discharge orifices  7  for reasons of production technology. The spatial orientation of a longitudinal axis of spray-discharge orifices  7  may differ for each spray-discharge orifice  7 . However, none of the longitudinal axes is directed toward a spark plug (not shown further) also arranged in the combustion chamber of the internal combustion engine. This prevents a shortened service life of the spark plug.  
         [0029]     The totality of all spray-discharge orifices  7  injects into the combustion chamber a mixture cloud whose center-of-gravity axis may be inclined between 0° and 70° in any spatial direction relative to a longitudinal axis  37  of fuel injector  1  and whose conical widening amounts to between 30° and 100°.  
         [0030]     Wall thickness t of valve-seat body  5  is calculated as follows: 
 
 t≧k·p   0.5  [mm], 
 
 where: 
 
 k=0.06 mm/Mpa 0.5  
 
 and fuel pressure p in the fuel-distributor line is indicated in Mpa. 
 
         [0031]     In accordance with wall thickness t, overall length l and reduced length l′ of spray-discharge orifices  7  result at the respective tilt of spray-discharge orifices  7 . Valve-seat body  5  is able to be processed in the corresponding regions in a simple manner.  
         [0032]     The present invention is not limited to the exemplary embodiment shown and described, but is also applicable to other spray-discharge orifices  7 , and also to any designs of inwardly opening, multi-hole fuel injectors  1 .