Abstract:
A fuel injector ( 1 ) for fuel injection systems of internal combustion engines, in particular for direct injection of fuel into the combustion chamber of an engine, includes an actuator ( 10 ), a valve needle ( 3 ) which is mechanically linked to the actuator ( 10 ) and is acted upon by a restoring spring ( 23 ) in a closing direction to actuate a valve closing body ( 4 ), which together with a valve seat face ( 6 ) forms a sealing seat, and it has a sleeve ( 24 ) which pre-stresses the restoring spring ( 23 ). The sleeve ( 24 ) is plastically deformable so that the cross section of a flow-through channel ( 46 ) of the sleeve ( 24 ) is variable by mechanical action.

Description:
BACKGROUND INFORMATION  
         [0001]    The present invention is based on a fuel injector according to the preamble of claim 1 and a method of adjusting a fuel injector according to the preamble of claim 11.  
           [0002]    German Patent Application 40 23 828 A1 describes a fuel injector and a method of adjusting a fuel injector. To adjust the amount of fuel to be delivered during the opening and closing operation of the electromagnetically operable fuel injector, a magnetically conductive material, e.g., in the form of a powder which alters the magnetic properties of the internal pole is introduced into a blind hole, and thus the magnetic force is varied until the actual measured flow rate of the medium corresponds to the predetermined setpoint flow rate.  
           [0003]    Similarly, German Patent Application 40 23 826 A1 describes the insertion of an equalizing bolt into a blind hole of an internal pole having a recess on its periphery to the extent that the measured actual amount corresponds to the predetermined setpoint amount, and thus varying the magnetic force until this is achieved.  
           [0004]    German Patent Application 195 16 513 A1 describes a method of adjusting the dynamic flow rate of a fuel injector. In this case, an adjusting element situated close to the magnetic coil outside the flow path of the medium is adjusted. In doing so, the magnetic flux in the magnetic circuit, and thus the magnetic force, changes, so it is possible to influence and adjust the flow rate. Adjustment can be performed with either wet or dry fuel injectors.  
           [0005]    German Patent Application 42 11 723 A1 describes a fuel injector and a method of adjusting the dynamic flow rate of a fuel injector, in which an adjusting sleeve having a longitudinal slot is pressed into a longitudinal bore in a connection up to a predetermined depth, the dynamic actual flow rate of the injector is measured and compared with a setpoint flow rate and the pressed-in adjusting sleeve which is under a tension acting radially is pushed forward until the measured actual flow rate matches the predetermined setpoint flow rate.  
           [0006]    In German Patent Application 44 31 128 A1, to adjust the dynamic flow rate of a fuel injector, the valve housing undergoes deformation due to the action of a deformation tool on the outer perimeter of the valve housing. The size of the residual air gap between the core and the armature, and thus the magnetic force, is varied in this way, thereby making it possible to influence and adjust the flow rate.  
           [0007]    One disadvantage of the group of methods which influence the magnetic flux in the magnetic circuit is in particular the high expense with regard to production costs, because the required static flow tolerances must be guaranteed, although this is difficult to implement. In particular, measurements of magnetic fields are complicated to perform and require a test field.  
           [0008]    One disadvantage of the group of mechanical adjustment methods is in particular the high degree of inaccuracy to which these methods are subject. Furthermore, the opening and closing times of a fuel injector may be shortened only at the expense of the electric power, so the electric load on the components and on the controllers is increased.  
           [0009]    In particular, the method known from German Patent Application 44 31 128 A1, where the residual air gap between the core and the armature is varied by deformation of the valve housing, permits only a very inaccurate correction of the flow rate because shear stresses in the nozzle body may have a negative effect on the direction and magnitude of the deforming force. Therefore, a high manufacturing precision is necessary for all parts.  
         ADVANTAGES OF THE INVENTION  
         [0010]    The fuel injector according to the present invention having the characterizing features of claim 1 and the method according to the present invention for adjusting a fuel injector having the features of claim 11 have the advantage over the related art that the adjustment sleeve is capable of plastic deformation, and in this way the cross section of a flow channel provided in the sleeve may be varied easily by mechanical action using a stamping tool.  
           [0011]    Advantageous refinements of the fuel injector characterized in claim 1 and the method characterized in claim 11 for adjusting a fuel injector are possible through the measures characterized in the subclaims.  
           [0012]    It is advantageous in particular that an annular insert made of soft metal is inserted into the intake end of the sleeve and may be deformed without affecting the stability of the sleeve.  
           [0013]    The design of a throttle zone in the flow channel of the sleeve having a peripheral collar projecting into the flow channel is advantageous inasmuch as this specific design of the throttle zone supports the desired deformation of the inlet end of the sleeve.  
           [0014]    It is especially advantageous to provide an external thread on the sleeve and an internal thread in the central recess in the fuel injector, because the sleeve is thereby stable in its position in the central recess in the fuel injector and is prevented from slipping, while it is easily brought into a different position using a corresponding adjusting tool due to the thread.  
           [0015]    Also advantageous is the design of the recess in the sleeve on the inlet side, e.g., in the form of a hexagon socket which is designed so that an adjusting tool which is mechanically linked to the sleeve does not act on the annular soft metal insert.  
           [0016]    It is also especially advantageous that the restoring spring is supported on an intermediate ring which is inserted between the sleeve and the restoring spring in the central recess in the fuel injector, because in this way it is possible to rotate the sleeve with an adjusting tool without the restoring spring rotating with it. This prevents metal shavings from being deposited on the restoring spring. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0017]    Embodiments of the present invention are illustrated in simplified form in the drawing and are explained in greater detail in the following description:  
         [0018]    [0018]FIG. 1 shows a schematic diagram of a section through an embodiment of a fuel injector according to the related art.  
         [0019]    [0019]FIG. 2A shows a detail of a schematic diagram of a section through a first embodiment of the fuel injector according to the present invention, approximately in area II in FIG. 1 before performing a first adjustment according to the method of the present invention.  
         [0020]    [0020]FIG. 2B shows the sleeve shown in FIG. 2A after performing the adjustment according to the method of the present invention.  
         [0021]    [0021]FIG. 2C shows a detail of the sleeve corresponding to a second embodiment.  
         [0022]    [0022]FIG. 3A shows a detail of a schematic diagram of a section through a third embodiment of the fuel injector according to the present invention in area II in FIG. 1 before performing a first step of a second adjustment according to the method of the present invention.  
         [0023]    [0023]FIG. 3B shows the sleeve in FIG. 3A after performing the first step of the method.  
         [0024]    [0024]FIG. 4 shows a detail of a schematic diagram of a section through the embodiment according to FIG. 3 during the second step of the second adjustment according to the method of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0025]    Before describing three embodiments of a fuel injector  1  according to the present invention in greater detail on the basis of FIGS. 2 through 4, a fuel injector  1  already known and having the same design as the embodiments except for the measures according to the present invention will first be explained briefly with regard to its essential components on the basis of FIG. 1.  
         [0026]    Fuel injector  1  is designed in the form of a fuel injector for fuel injection systems of engines having spark ignition of a fuel-air mixture. Fuel injector  1  is suitable in particular for direct injection of fuel into a combustion chamber (not shown) of an internal combustion engine.  
         [0027]    Fuel injector  1  has a nozzle body  2  in which a valve needle  3  is guided. Valve needle  3  is mechanically linked to a valve closing body  4  which cooperates with a valve seat face  6  situated on a valve seat body  5  to form a tight seat. In this embodiment, fuel injector  1  is an inwardly opening fuel injector  1  having an injection orifice  7 . Nozzle body  2  is sealed by a seal  8  with respect to stationary pole  9  of a magnetic coil  10 . Magnetic coil  10  is encapsulated in a coil housing  11  and is wound on a field spool  12  which is in contact with an internal pole  13  of magnetic coil  10 . Internal pole  13  and stationary pole  9  are separated by a gap  26  and are supported on a connecting component  29 . Magnetic coil  10  is energized by electric current supplied via a line  19  and an electric plug contact  17 . Plug contact  17  is surrounded by a plastic sheathing  18  which may be integrally molded on internal pole  13 .  
         [0028]    Valve needle  3  is guided in a valve needle guide  14  designed in the form of a disk. A matching adjustment disk  15  is used to adjust the lift. On the other side of adjustment disk  15  there is an armature  20  which is in a friction-locked connection with valve needle  3  via a flange  21 , the valve needle being connected to flange  21  by a weld  22 . A restoring spring  23  sits on flange  21  and is pre-stressed by a sleeve  24  in the present design of fuel injector  1 . Fuel channels  30   a  through  30   c  which carry the fuel supplied through a central fuel supply  16  and filtered through a filter element  25  to injection orifice  7  run in valve needle guide  14 , armature  20  and on valve seat body  5 . Fuel injector  1  is sealed with respect to a fuel line (not shown) by a seal  28 .  
         [0029]    In the resting state of fuel injector  1 , armature  20  is acted upon by restoring spring  20  against its direction of lift so that valve closing body  4  is held sealingly against valve seat  6 . When magnetic coil  10  is energized, it creates a magnetic field which moves armature  20  in the direction of lift against the elastic force of restoring spring  23 , the lift being predetermined by a working gap  27  between internal pole  12  and armature  20  in the resting position. Armature  20  also entrains flange  21 , which is welded to valve needle  3 , in the direction of lift. Valve closing body  4 , which is mechanically linked to valve needle  3 , is lifted up from the valve seat face, and the fuel carried through fuel channels  30   a  through  30   c  is injected through injection orifice  7 .  
         [0030]    When the coil current is turned off, armature  20  drops back from internal pole  13  due to the pressure of restoring spring  21  after the magnetic field has declined sufficiently, so that flange  21 , which is mechanically linked to valve needle  3 , moves against the direction of lift. Valve needle  3  is thus moved in the same direction, so that valve closing body  4  is placed on valve seat face  6  and fuel injector  1  is closed.  
         [0031]    In an excerpt of a sectional diagram, FIGS.  2 A-C show approximately the detail of fuel injector  1  labeled as II in FIG. 1 before stamping and two embodiments of the detail labeled as III in FIG. 2A after stamping.  
         [0032]    In an excerpt of a sectional diagram, FIG. 2A shows the detail labeled as II in FIG. 1 of fuel injector  1 , filter element  25  which is present in central fuel supply  16  in FIG. 1 having been removed and instead stamping tool  44  being inserted into central recess  47  of fuel injector  1 . In the present embodiment, sleeve  24  has a throttle zone  40  which has a peripheral collar  41  projecting into a flow channel  46  of sleeve  24 .  
         [0033]    If stamping tool  44 , which is in central recess  47  of fuel injector  1 , is pressed against inlet end  43  of sleeve  24  with a defined force, the sleeve is compressed slightly. Therefore, the cross section of flow channel  46  of sleeve  24  is reduced in the area of throttle zone  40  because the material of sleeve  24  may only be displaced into throttle zone  40  due to the manner in which sleeve  24  is installed in central recess  47  of fuel injector  1 .  
         [0034]    [0034]FIG. 2B shows a diagram of sleeve  24  in area III in FIG. 2A after stamping, in which case inlet end  43  of sleeve  24  has a slightly compressed and thus reduced cross section in the area of throttle zone  40 . The flow rate of fuel flowing through fuel injector  1  per unit of time is thus reduced.  
         [0035]    Since this procedure could be reversed only by replacing sleeve  24 , it is necessary for fuel injector  1  to have a higher actual flow rate before adjusting the flow rate than the ideal flow rate to be achieved.  
         [0036]    [0036]FIG. 2C shows a variant of sleeve  24  after the stamping operation, in this case with an annular insert  39 , preferably made of soft metal, being inserted into inlet  43  of sleeve  24 . This variant has the advantage that sleeve  24  need not be made entirely of a deformable soft metal, but instead may be made of a stable metal, so the stability of sleeve  24  with respect to deformation is maintained.  
         [0037]    Throttle zone  40  is thus formed by annular insert  39  so that sleeve  24  is designed as a cylinder having a cylindrical flow channel  46 .  
         [0038]    [0038]FIGS. 3A and 3B show another embodiment of fuel injector  1  according to the present invention, FIG. 3A sowing the first step of the method according to the present invention for adjusting a fuel injector  1 , FIG. 3B showing the condition of sleeve  24  after the first method step, and FIG. 4 showing the second step of the method according to the present invention for adjusting a fuel injector  1 .  
         [0039]    In an excerpt of a sectional diagram, FIG. 3A shows the detail labeled as II in FIG. 1 of fuel injector  1  before stamping; FIG. 3B shows the detail labeled as IV in FIG. 3A after stamping.  
         [0040]    In the present embodiment, sleeve  24  has a recess  46   a  on the inlet side and a recess  46   b  on the outlet side, throttle zone  40  being formed between them. Sleeve  24  is provided with an external thread  49  which works together with an internal thread  50  of central recess  47  of fuel injector  1 . Sleeve  24  is screwed into central recess  47  of fuel injector  1  by thread  49  and thread  50 . The inlet side of recess  46 A of sleeve  24  is designed so that a corresponding adjusting tool  52  may be rotatably engaged with sleeve  24 . The inlet side of recess  46 A may have a hexagon socket section or a triangle socket section, for example.  
         [0041]    Filter element  25  illustrated in FIG. 1 is again replaced by stamping tool  44  to perform the first step of the method according to the present invention for adjusting a fuel injector  1 . Sleeve  24  is stamped by stamping tool  44  in the area of throttle zone  40  in the inlet side of recess  46 A, slightly deforming the metal of sleeve  24  in the area of throttle zone  40 . This reduces the static flow through fuel injector  1 .  
         [0042]    In an excerpt of a sectional diagram, FIG. 3B shows the detail labeled as IV in FIG. 3A with a reduction in cross section of flow-through channel  46  of sleeve  24  after the stamping operation.  
         [0043]    In an excerpt of a sectional diagram, FIG. 4 shows the detail labeled as II in FIG. 1 of fuel injector  1 , illustrating the second step of the method according to the present invention for adjusting fuel injector  1 .  
         [0044]    To adjust the dynamic flow through fuel injector  1 , sleeve  24  is adjusted in its axial position in central recess  47  of fuel injector  1  using adjusting tool  52 , which may be a hexagon socket wrench, a screwdriver or a similar tool, for example. The deeper sleeve  24  is screwed into central recess  47 , the lower is the dynamic flow through fuel injector  1 . This is due to the fact that restoring spring  23  is acted upon by sleeve  24  with a greater pre-stress, so that fuel injector  1  opens later and closes sooner.  
         [0045]    To prevent restoring spring  23  from also turning as sleeve  24  rotates, an intermediate ring  48  is inserted between sleeve  24  and restoring spring  23 , restoring spring  23  being supported on this intermediate ring. This measure prevents metal shavings from being detached from the wall of central recess  41 , and thus clogging fuel channels  30   a  through  30   c  as well as injection orifice  7 , due to the rotation of restoring spring  23  with it when sleeve  24  is twisted into central recess  47 .  
         [0046]    The present invention is not limited to the embodiments presented here and is also suitable for fuel injectors  1  having piezoelectric or magnetostrictive actuators, for example. In addition, the present invention may also be used to produce hydraulic and pneumatic throttles that are not adjustable.