Abstract:
A fuel injector for fuel injection systems in internal combustion engines, including an actuator, a valve needle operable by the actuator for operating a valve-closure member, which, together with a valve-seat surface forms a sealing seat and a swirl device including at least one swirl channel, through which fuel flows with a tangential component relative to a longitudinal axis of the fuel injector. The axial position of a plunger element determines a cross-section of at least one bypass channel that bypasses the at least one swirl channel without a tangential component.

Description:
FIELD OF THE INVENTION 
     The present invention relates to A fuel injector. 
     BACKGROUND INFORMATION 
     A fuel injector for the direct injection of fuel into the combustion chamber of a mixture-compressing, spark-ignited internal combustion engine, the fuel injector including a guide and seat area formed by three disk-shaped elements at the downstream end of the fuel injector is described in German Published Patent Application No. 197 36 682. A swirl element is embedded between a guide element and a valve seat element. The guide element is used to guide an axially movable valve needle that protrudes through the guide element while a valve closing section of the valve needle cooperates with a valve seat surface of the valve seat element. The swirl element includes an inner opening area with multiple swirl channels that are not connected to the outer circumference of the swirl element. The entire opening area extends completely across the axial thickness of the swirl element. 
     A disadvantage of the fuel injectors described in the publication cited above is the fixedly set swirl angle which may not be adapted to the different operating states of an internal combustion engine such as partial load and full load operation. As a result, it is also not possible to adapt the cone apex angle α of the injected mixture cloud to the various operating states, which results in non-homogeneities during combustion, increased fuel consumption, as well as increased exhaust gas emission. 
     SUMMARY OF THE INVENTION 
     In contrast, the present invention may provide the advantage that the swirl is adjustable as a function of the operating state of the internal combustion engine, making it possible to produce a jet pattern adapted to the operating state of the internal combustion engine. This makes it possible to optimize both the mixture formation and the combustion process. 
     An advantage may be the configuration of the swirl-producing components, which in contrast to conventional swirl formation, are only augmented by a plunger element, which is simple to manufacture and which is slidable onto the valve needle. The plunger element may be activated by a suitable control unit, for example by a piezoelectric, electromagnetic or hydraulic manner. 
     It may also be an advantage that the swirl disk of the conventional swirl formation may be taken over without modification. 
     In addition, the funnel-shaped, recessed form of the valve-seat member, which makes it possible to deform the swirl disk elastically and accordingly adjust the swirl, is simple to manufacture. 
     It may be advantageous that the downstream end of the plunger element include a radial bevel, whose inclination corresponds to that of the funnel-shaped valve-seat member, as a result of which the swirl disk is uniformly deformed and non-homogeneities are prevented. 
     Also of advantage is the possibility to switch the plunger element into the position appropriate to the present operating state of the fuel injector independently of the lift of the valve needle. 
     An example embodiment of the present invention is shown in the drawings and explained in the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an axial section through a first example embodiment of a fuel injector according to the present invention. 
     FIG. 2 shows an enlarged detail taken from the fuel injector according to the present invention in area II in FIG.  1 . 
     FIG. 3A shows a schematic representation of the jet apex angle α of a mixture cloud injected into the combustion chamber for various operating states of a fuel injector. 
     FIG. 3B shows a schematic representation of the jet apex angle α of a mixture cloud injected into the combustion chamber for various operating states of a fuel injector. 
     FIG. 4 shows a schematic view of an example embodiment of the swirl disk of the fuel injector according to the present invention. 
     FIG. 5A shows a schematic representation of the function of the fuel injector according to the present invention in area V in FIG.  2 . 
     FIG. 5B shows a schematic representation of the function of the fuel injector according to the present invention in area V in FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     Before an example embodiment of a fuel injector  1  according to the present invention is described in greater detail based on FIGS. 2 through 5, the components of fuel injector  1  according to the present invention will be explained briefly in general terms based on FIG.  1 . Fuel injector  1  is configured in the form of a fuel injector for fuel injection systems of mixture-compressing, spark-ignited internal combustion engines. Fuel injector  1  is suitable for the direct injection of fuel into a combustion chamber (not shown) of an internal combustion engine. 
     Fuel injector  1  includes a nozzle body  2  in which a valve needle  3  is arranged. Valve needle  3  is mechanically linked with a valve-closure member  4 , which cooperates with a valve seat surface  6  arranged on a valve-seat member  5  to form a sealing seat. In the example embodiment, fuel injector  1  is an inwardly opening fuel injector  1  including at least one spray-discharge orifice  7 . Nozzle body  2  is sealed off from outer pole  9  of a solenoid  10  by a seal  8 . Solenoid  10  is encapsulated in a coil housing  11  and wound on a coil frame  12  which is in contact with an inner pole  13  of solenoid  10 . Inner pole  13  and outer pole  9  are separated by a gap  26  and are supported by a connecting component  29 . Solenoid  10  is energized by an electric current which may be supplied by an electric plug contact  17  via a line  19 . Plug contact  17  is enclosed by a plastic sheathing  18  which may be extruded onto inner pole  13 . 
     Valve needle  3  is guided in a valve needle guide  14  which is configured in the shape of a disk. A matched adjusting disk  15  is used to adjust the lift. An armature  20  is located on the other side of adjusting disk  15 . Armature  20  is friction-locked to valve needle  3  via a first flange  21 , valve needle  3  is connected to first flange  21  by a weld  22 . A restoring spring  23  is supported on first flange  21 , which in the present configuration of fuel injector  1  is pre-stressed by a sleeve  24 . 
     A second flange  31 , which is connected to valve needle  3  by a weld  33 , is used as a lower armature stop. An elastic intermediate ring  32  which rests on second flange  31  prevents rebounding when fuel injector  1  is closed. 
     A guide disk  34 , including at least one swirl channel  35 , is arranged on the inlet side of the sealing seat. Together with a sleeve-shaped plunger element  36  in the example embodiment, guide disk  34  produces the swirl formation of the fuel jet, which is a function of the operating state of fuel injector  1 . In the example embodiment, plunger element  36  is configured as a hollow cylinder and slipped onto valve needle  3 . Using a control unit, which is not shown here, as well as an actuating mechanism, also not shown in greater detail, which, e.g., act on plunger sleeve  36  by a electromagnetic, hydraulic or piezoelectric manner, it is possible to deform swirl disk  34  elastically during the operation of fuel injector  1  so that a bypass channel  37  is closed and consequently a swirl may be produced in the fuel flowing through swirl disk  34 . 
     As a result, the fuel flowing through fuel injector  1  in partial load operation has a lesser swirl, whereby a jet apex angle α of a mixture cloud injected into the combustion chamber (not shown) of the internal combustion engine is kept smaller, while in full load operation a greater swirl also produces a larger jet apex angle α. Accordingly, the mixture may be kept richer or leaner, making it possible to achieve optimum combustion. Swirl disk  34  and the plunger element are shown in greater detail in FIGS. 2 and 4 while the mode of operation of the components is explained in FIGS. 5A and 5B. 
     Fuel channels  30   a  to  30   c  run in valve needle guide  14 , in armature  20  and in a guide disk  42 . The fuel is supplied via a central fuel supply  16  and is filtered through a filter element  25 . A seal  28  seals off fuel injector  1  from a fuel line, which is not shown in greater detail. 
     When fuel injector  1  is in its idle state, restoring spring  23  applies force to armature  20  against the direction of its lift so that valve-closure member  4  is held in sealing contact against valve seat  6 . When solenoid  10  is energized, it builds up a magnetic field which moves armature  20  in the direction of its lift against the elastic force of restoring spring  23 , the lift is predetermined by a working gap  27  in the idle state, located between inner pole  12  and armature  20 . Armature  20  entrains flange  21 , which is welded to valve needle  3 , also in the lift direction. Valve-closure member  4 , which is mechanically linked with valve needle  3 , lifts from valve seat surface  6  and the fuel is spray-discharged. Plunger element  36  may be controlled independently of the lift of valve needle  3  and displaced into the axial position appropriate to the particular operating state. 
     When the coil current is switched off, the pressure of restoring spring  23  causes armature  20  to drop away from inner pole  13  after sufficient decay of the magnetic field, as a result of which flange  21 , which is mechanically linked to valve needle  3 , moves against the lift direction. This moves valve needle  3  in the same direction, as a result of which valve-closure member  4  settles on valve seat surface  6  and fuel injector  1  is closed. 
     In a partial, simplified axial sectional view, FIG. 2 shows fuel injector  1  configured according to the present invention in area II of FIG.  1 . Elements already described are provided with matching reference symbols in all figures. In order to implement the aforementioned adjustment of the swirl, fuel injector  1  configured according to the present invention includes, in addition to plunger element  36 , a funnel-shaped hollow  43  in an inlet-side face  39  of valve-seat member  5 . Hollow  43  runs radially from the outside to the inside so that valve seat surface  6  closes hollow  43  off from spray-discharge orifice  7 . 
     At a downstream end  40 , plunger element  36  includes a bevel  44 , the inclination of which corresponds to the inclination of funnel-shaped hollow  43 . 
     If, when fuel injector  1  is open, fuel flows through fuel channel  30   c  formed in guide disk  42 , the fuel receives a more or less strong swirl as a function of the position of plunger element  36 . 
     In FIG. 2, plunger element  36  is in an operating position in which there is no effect on swirl disk  34 , which is thus not elastically deformed. As a result, a bypass channel  37  is opened, which makes it possible for the fuel to flow radially from the outside to the inside without taking on a swirl. This is made possible by funnel-shaped hollow  43  in inflow-side face  39  of valve-seat member  5  since it causes a gap  45  to form between swirl disk  34  and valve-seat member  5 . The tangential component of the fuel flow is thus very small with the result that the widening of the jet pattern of the mixture cloud injected into the combustion chamber is slight, jet apex angle α remains small and the mixture cloud has a high penetration capacity. 
     In order to illustrate the requirements for the mixture cloud injected into the combustion chamber for two different operating states of a fuel injector  1  (partial load range and full load range), FIGS. 3A and 3B show the desired mixture cloud formed for each case. 
     In partial load operation, a mixture-compressing, spark-ignited internal combustion engine places different requirements on the form, the stoichiometry and the penetration capacity of the mixture cloud injected into the combustion chamber than in full load operation. In partial load operation, the mixture cloud, as shown in FIG. 3A, should have a relatively small apex angle α, a high penetration capacity, a narrow core area due to the small apex angle α with a richer mixture and a very lean envelop, while a large apex angle α as shown in FIG.  3 B and consequently an almost homogeneous filling of the cylinder with a combustible mixture is required in full load operation. 
     The measures according to the present invention described here make it possible to model the parameters of the mixture cloud by influencing the swirl. If, for example, the fuel exits from spray-discharge orifice  7  with low swirl, a mixture cloud having a small apex angle α is injected, while a strong swirl produces a large jet widening and accordingly a mixture cloud having a large apex angle α. It is possible to adjust the strength of the swirl through the axial position of plunger element  36 . 
     In a schematic view, FIG. 4 shows an example embodiment of swirl disk  34  of fuel injector  1  according to the present invention. 
     The shape of swirl disk  34  illustrated in FIG. 4 includes six swirl channels  35  which are arranged in a star-shaped pattern with equal spacing. At their radial outer ends  46 , swirl channels  35  include widenings  47 . Valve needle  3  penetrates swirl disk  34 , as a result of which a swirl chamber  48  is created between valve needle  3  and swirl disk  34 , into which swirl channels  35  open. 
     Widenings  47  are configured and arranged in such a manner that the fuel flowing through fuel channel  30   c  enters gap  45  between valve-seat member  5  and swirl disk  34  without taking on a swirl and thus uses bypass channel  37  instead of swirl channels  35 . The fuel may thus be spray-discharged without a tangential component, as a result of which the jet has the high penetration capacity required. 
     In a detailed section of area V of FIG. 2, FIGS. 5A and 5B show schematically the mode of operation of plunger element  36  for swirl formation. FIG. 5A shows the position of plunger element  36  already illustrated in FIG. 2 in which there is no effect on swirl disk  34  and accordingly no swirling of the fuel. The matching of the inclination of wedge-shaped bevel  44  of the downstream end  40  of plunger element  36  with funnel-shaped hollow  43  of inflow-side face  39  of valve-seat member  5  is apparent in FIG.  5 A. 
     If fuel injector  1  is opened by operating actuator  10  and lifting valve needle  3  off valve seat surface  6 , fuel flows through fuel channel  30   c  to swirl disk  34 . If plunger element  36  is not operated, swirl disk  34  is separated from valve-seat member  5  by gap  45 , as a result of which it is possible for the fuel to bypass swirl channels  35  formed in swirl disk  34  and flow via outside radial widenings  47  of swirl channels  35  and through gap  45 , or bypass channel  37  thus formed, to the sealing seat without swirl. The flow is indicated in FIG. 5A by an arrow. 
     FIG. 5B shows fuel injector  1  according to the present invention also in the open state. Compared to FIG. 5A, plunger element  36  is displaced in the downstream direction and presses on swirl disk  34 . The matching inclination of bevel  44  and of hollow  43  causes swirl disk  34  to be uniformly elastically deformed by plunger element  36  and pressed against valve-seat member  5 , as a result of which bypass channel  37  or gap  45  is closed and the fuel flows though swirl channels  35 . As a result, the flow receives a component in the tangential direction causing fuel swirled after the sealing seat to be spray-discharged via spray-discharge orifice  7 . This is also indicated in FIG. 5B by an arrow. 
     The present invention is not limited to the example embodiment shown and it may be used with fuel injectors  1  including piezoelectric or magnetostrictive actuators  27  and with any configuration variants of fuel injectors  1 .