Abstract:
A fuel injector is described, particularly for fuel injector systems of internal combustion engines, including an actuator, a valve needle actuatable by the actuator for actuation of a valve-closure member, which together with a valve-seat surface forms a sealing seat, and a swirl device, having at least one swirl channel through which fuel flows having a tangential component regarding a longitudinal axis of the fuel injector. The axial position of a bypass disk, which is mechanically linked to a valve needle, determines a cross section of at least one bypass channel, which 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 direct injection of fuel into the combustion chamber of a mixture-compressing, spark-ignited internal combustion engine which on the downstream end of the fuel injector has a guide and seat area which is formed from three disk-shaped elements is known from 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 guides an axially movable valve needle penetrating through it, while a valve closing section of the valve needle cooperates with a valve-seat surface of the valve seat element. The swirl element has an inner opening area containing a plurality of swirl channels which are not connected to the outer periphery of the swirl element. The entire opening area extends fully over the axial thickness of the swirl element. 
   A particular disadvantage of the fuel injector known from the aforementioned document is the fixedly set swirl angle which cannot be adjusted to the different operating conditions of an internal combustion engine, such as partial load and full load operation. As a result, cone opening angle a of the injected mixture cloud also cannot be adjusted to the different operating conditions, which in turn results in inhomogeneities during combustion, increased fuel consumption, as well as increased exhaust gas emission. 
   SUMMARY OF THE INVENTION 
   The fuel injector according to the present invention has the advantage over the related art that the swirl is adjustable as a function of the operating state of the fuel injector, whereby a jet pattern may be produced which is adapted to the operating state of the fuel injector, resulting in an optimization of the mixture formation and the combustion process. 
   The simple design of the swirl producing components is particularly advantageous over the conventional swirl preparation, because they are extended by an easily manufacturable bypass disk which is connectable to the valve needle. 
   The possibility of combining the measures according to the present invention with fuel injectors having multi-stage lifts and of allocating different swirl intensities to the different lift positions is particularly advantageous. 
   The implementation of the measures according to the present invention is also advantageous in a fuel injector having continuous lift, because the desired modeling of the mixture cloud may be achieved in a simple manner using suitable geometry of the swirl channels. 
   It is also advantageous to design a swirl chamber in which the fuel components streaming through the swirl channels may be mixed with those coming from the bypass channel, thereby influencing the mixture cloud according to the requirements of the instantaneous operating condition. 
   The design of a catch, as well as the separation of the bypass disk from the valve needle, represent a particular advantage, since the opening operation of the fuel injector is not influenced by the bypass disk being raised while the valve needle initially performs a partial lift until the catch strikes the bypass disk. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a partial axial section through a first exemplary embodiment of a fuel injector according to the present invention. 
       FIG. 2A  shows an enlarged detail in area II of  FIG. 1 , the fuel injector being illustrated in its closed state. 
       FIG. 2B  shows an enlarged detail in area II of  FIG. 1 , the fuel injector being illustrated in its opened state. 
       FIG. 3A  shows a second exemplary embodiment of a fuel injector according to the present invention as the same detail illustration as in  FIG. 2A , the fuel injector being illustrated in its closed state. 
       FIG. 3B  shows a second exemplary embodiment of a fuel injector according to the present invention in the same way as in  FIG. 2B , the fuel injector being in its opened state. 
   

   DETAILED DESCRIPTION 
   A first exemplary embodiment of a fuel injector  1  designed according to the present invention illustrated in  FIG. 1  is used in particular for direct injection of fuel into the combustion chamber of a spark-ignited, mixture-compressing internal combustion engine. 
   Fuel injector  1  includes a solenoid  8  used as actuator  27  and is encapsulated in a coil housing  9 , a tubular internal pole  11  and an external pole  14  in the form of a sleeve, which is welded to nozzle body  2 . An armature  12  is mechanically linked to valve needle  3  which is configured as valve-closure member  4  in the spray-discharge direction. Valve-closure member  4  cooperates with valve-seat surface  6 , which is formed on a valve seat body  5 , to form a sealing seat. This exemplary embodiment is an inwardly opening fuel injector  1 . At least one spray-discharge orifice  7  is introduced in valve seat body  5 . 
   A swirl device  15 , which includes a guide disk  16 , a bypass disk  17  and swirl channels  18 , is provided on the upstream side of the scaling seat. Swirl device  15  is explained in greater detail in the description of  FIGS. 2A and 2B . 
   In the idle state of fuel injector  1 , armature  12  is acted upon by restoring spring  10  against a lift direction in such a way that valve-closure member  4  is held on valve-seat surface  6  in a sealing position. When solenoid  8  is energized, it generates a magnetic field, which moves armature  12  against the elastic force of restoring spring I 0  in the lift direction. Armature  12  also entrains valve needle  3  in the lift direction. Valve needle  3  and valve-closure member  4 , which have a one-piece design in the exemplary embodiment, are lifted from valve-seat surface  6 , whereby bypass disk  17 , friction-locked to valve needle  3  via weld  21 , also moves in the lift direction, so that bypass channel  19  is opened. Fuel is routed to the at least one spray-discharge orifice  7  through flow-through orifices  20  in guide disk  16 , as well as through bypass channel  19  and swirl channels  18  bypassing the sealing seat. A detailed illustration of the procedure is provided by  FIGS. 2A and 2B . 
   When the coil current is switched off, armature  12 , after sufficient decay of the magnetic field, drops away from internal pole  11  due to the force of restoring spring  10 , whereby valve needle  3 , being mechanically linked to armature  12 , moves against the lift direction, bypass disk  17  closes bypass channel  19 , valve-closure member  4  comes to rest on valve-seat surface  6 , and fuel injector  1  is closed. 
   In a partial, schematic axial section  FIG. 2A  shows fuel injector  1 , designed according to the present invention, in its closed state in area II of FIG.  1 . The enlarged illustration shows only those components which are relevant to the present invention. The design of the remaining components may be identical with a known fuel injector  1 . Elements already described are provided with the same reference symbols in all figures, so that a repeat description is unnecessary. 
   A mixture-compressing, spark-ignited engine has different requirements with regard to form, stoichiometry, and the penetration capability of the mixture cloud being injected into the combustion chamber in partial load operation as opposed to full load operation. During partial load operation the mixture cloud should have a relatively small opening angle α, a great penetration capability, a narrow core area due to the small opening angle α, with a richer mixture, and a very lean envelope, while during full load operation a wide opening angle α and with it an almost homogeneous filling of the cylinder with ignitable mixture is present. 
   The modeling of the parameters of the mixture cloud may be facilitated by influencing the swirl through the above-described measures according to the present invention. If the fuel exits the spray-discharge orifice with little swirl, a mixture cloud having a small opening angle α is injected, while a strong swirl causes the jet to widen more and thus the mixture cloud to have a wide opening angle α. The present invention is particularly advantageously applicable in connection with a fuel injector  1  having multi-stage lift or piezoelectric actuators  27 . 
   Swirl device  15  having a bypass channel  19 , as indicated in  FIG. 1 , allows the fuel flow rate to be configured by swirl device  15  as a function of the lift of valve needle  3  of fuel injector  1 . In the closed state of fuel injector  1 , as it is apparent in  FIG. 2A , bypass channel  19  is closed, and thus the fuel may only flow through swirl channels  18 . 
     FIG. 2B  shows fuel injector  1  according to the present invention in its opened state in the same detail as in FIG.  2 A. 
   If, according to the present exemplary embodiment, actuator  27  designed as a solenoid is actuated, then valve needle  3  is raised in a lift direction against the flow direction of the fuel, whereby bypass disk  17  which is connected to valve needle  3  by weld  21  is also moved in the lift direction. This results in the opening of bypass channel  19 , the amount of fuel that flows through depending on the axial position of valve needle  3 , i.e., on the distance of bypass disk  17  from an upstream side  22  of swirl channels  18 . The fuel flows via flow-through orifices  20  in guide disk  16  to bypass channel  19 . 
   While the flow in swirl channels  18  has a tangential component with regard to a longitudinal axis  26  of fuel injector  1 , the flow in bypass channel  19  has no tangential component but only a radial component. 
   Since the portion of fuel flowing through bypass channel  19  and the portion of fuel flowing through swirl channels  18  are reunited in swirl chamber  23 , a mixture cloud develops which contains swirled and unswirled components. This makes it possible, by having a suitable geometry of the swirl-generating components, to generate a mixture cloud which has the characteristics suitable for the operating condition of fuel injector  1 . 
     FIGS. 3A and 3B  illustrate a second exemplary embodiment of fuel injector  1  according to the present invention using the same view as in  FIGS. 2A and 2B . 
   Bypass disk  17  in the present second exemplary embodiment, in contrast to the first exemplary embodiment illustrated in  FIGS. 2A and 2B , is not connected to valve needle  3  by weld  21  or by pressure force, but is instead set on valve needle  3  in an axially movable manner. 
   Valve needle  3  has a catch  24  which is positively connected to valve needle  3  by weld  25  or by pressure force, etc. This design in particular is advantageously applicable in fuel injectors  1  having two-stage lifts. 
   If fuel injector  1  is closed, the same conditions as in the first exemplary embodiment of a fuel injector  1  according to the present invention, illustrated in  FIG. 2A , prevail. As is apparent in  FIG. 3A , bypass channel  19  is closed and fuel flows exclusively through swirl channels  18 . 
   If fuel injector  1  is switched to a first lift position, valve needle  3  performs a partial lift which, for example, accompanies only a slight lift of bypass disk  17  via catch  24  or no lift at all of bypass disk  17 ; therefore the fuel has a strong tangential swirl component downstream from the sealing seat. 
   If fuel injector  1  is switched to a second lift position, which corresponds to a greater lift, more fuel flows through wider opened bypass channel  19 , because catch  24  has raised bypass disk  17  further. This results in a displacement of the mass ratio between swirled and unswirled fuel, because more fuel flows through bypass channel  19  than through swirl channels  18 . Subsequently opening angle a of the injected mixture cloud decreases, while the penetration increases. 
   The present invention is not limited to the illustrated exemplary embodiments and it is particularly implementable in fuel injectors  1  having multi-stage lifts, in fuel injectors  1  having piezoelectric or magnetostrictive actuators  27 , and in any design variant of fuel injectors  1 .