Abstract:
A fuel injector ( 1 ) is provided with a magnetic coil ( 10 ), which cooperates with an armature ( 20 ) acted upon by a restoring spring ( 23 ), the armature forming an axially movable valve part together with a valve needle ( 3 ). A valve-closure member ( 4 ), which forms a sealing seat with a valve-seat member ( 5 ), is provided at the valve needle ( 3 ). A flange ( 14 ), which penetrates the armature ( 20 ) through an opening ( 19 ) of the armature ( 20 ) and which is connected to the valve needle ( 3 ) by force-locking, has at least one radial fuel channel ( 11 ) with whose aid an inner chamber ( 29 ) of the fuel injector ( 1 ) is able to be connected to a recess ( 22 ) of the valve needle ( 3 ) upon actuation of the fuel injector ( 1 ).

Description:
FIELD OF THE INVENTION 
   The present invention related to a fuel injector. 
   BACKGROUND INFORMATION 
   As an example, from German Published Patent Application No. DE 196 26 576 an electromagnetically actuable fuel injector is known, in which, for the electromagnetic actuation, an armature cooperates with an electrically energizable magnetic coil, and the lift of the armature is transmitted to a valve-closure member via a valve needle. The valve-closure member cooperates with a valve-seat surface to form a sealing seat. A plurality of fuel channels is provided in the armature. The armature is reset by a resetting spring. 
   Disadvantageous in the fuel injector known from German Published Patent Application No. DE 196 26 576 is, in particular, that the fuel quantity q dyn  flowing through the fuel injector cannot be metered with sufficient precision when the valve-closure member lifts off from the sealing seat. The ratio of maximally sprayed-off fuel quantity relative to minimally sprayed-off fuel quantity, q max /q min , is relatively low. The characteristic curve of the fuel injector, which represents the profile of the dynamic flow rate q dyn  as a function of the valve needle lift, is relatively flat, so that considerable fluctuations occur in the dynamic flow rate. 
   SUMMARY OF THE INVENTION 
   In contrast, the fuel injector according to the present invention has the advantage over the related art that at least one fuel channel is disposed in the valve interior in such a way that its cross section is closed off when the fuel injector is closed, so that the interior of the fuel injector is not connected to the opening of the valve needle. When the fuel injector opens, the fuel channel is released, thereby obtaining an approximately stepped characteristic curve. 
   It is advantageous, in particular, that the at least one fuel channel is formed in a flange that penetrates the armature of the magnetic circuit and is frictionally connected to the valve needle. This simple design eliminates a costly design for the armature&#39;s free path. 
   It is also advantageous that the fuel channel is covered by an appropriately formed shoulder of the inner pole of the fuel injector, thereby dispensing with additional components. 
   Also advantageous, in particular, is the tubular valve needle whose orifice allows both the plug connection with the flange and also a conveying of the fuel. 
   Moreover, it is advantageous that the at least one fuel channel is dimensioned such that it does not act as a throttle, so that no lift throttling takes place. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  shows a schematic section through an exemplary embodiment of a fuel injector designed according to the present invention, in the closed state. 
       FIG. 1B  shows a schematic section through an exemplary embodiment of a fuel injector designed according to the present invention, in the open state. 
       FIG. 2  shows a schematic representation of the dynamic flow rate q dyn  as a function of the valve needle lift of the fuel injector according to the present invention, as represented in FIGS.  1 A and  1 B. 
   

   DETAILED DESCRIPTION 
     FIGS. 1A and 1B  show a part-sectional view of an exemplary embodiment of fuel injector  1 , designed according to the present invention, in the closed state. It is designed in the form of a fuel injector  1  for fuel injection systems of mixture-compressing internal combustion engines with externally supplied ignition. Fuel injector  1  is suited for the direct injection of fuel into a combustion chamber (not shown) of an internal combustion engine. 
   Fuel injector  1  is made up of a tubular 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  disposed on a valve-seat member  5  to form a sealing seat. In the exemplary embodiment, fuel injector  1  is an inwardly opening fuel injector  1 , which has a spray-discharge orifice  7 . 
   Nozzle body  2  is connected to an outer pole  9  of a magnetic coil  10  by a welding seam  8 . Magnetic coil  10  is wound on a coil brace  12 , which rests against an inner pole  13  at magnetic coil  10 . Magnetic coil  10  is energized via an electric line (not shown further) by an electric current, which may be supplied via an electrical plug contact  17 . A plastic coating  18 , which may be extruded onto inner pole  13 , encloses plug contact  17 . 
   Valve needle  3 , via a flange  14  which is inserted into the tubularly designed valve needle  3  and connected to valve needle  3  by a welding seam  15 , is connected to an armature  20  in a force-locking manner. Flange  14  reaches through armature  20  through an opening  19  of armature  20 . A restoring spring  23 , which in the present design of fuel injector  1  is prestressed by a sleeve  31 , is supported on flange  14 . 
   According to the present invention, at least one radially extending fuel channel  11  is formed in flange  14  on the inflow-side of armature  20 , the fuel channel allowing the fuel to pass into valve needle  3  upon opening of fuel injector  1 . In the closed state of fuel injector  1 , the at least one fuel channel  11  is closed off by a shoulder  24  of inner pole  13  from an inner chamber  29  of fuel injector  1 , which is formed in inner pole  13  of fuel injector  1 . 
   The fuel is supplied to fuel injector  1  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). 
   In the rest state of fuel injector  1 , illustrated in  FIG. 1A , restoring spring  23  acts upon flange  14  in such a way that it comes to rest against an end face  30  on the inflow side of armature  20 . In this way, armature  20  is likewise acted upon by a restoring spring  23 , so that valve-closure member  4  formed at valve needle  3  is sealingly held at valve-seat surface  6 . A working gap  27 , formed between end face  30  of armature  20  and inner pole  13 , is opened. 
   In the closed state of fuel injector  1 , the at least one fuel channel  11 , which is formed in flange  14 , is covered by shoulder  24  of inner pole  13 , in such a way that no fuel is able to flow through fuel channel  11 . The further functioning of fuel injector  1  during the opening process is explained in greater detail in FIG.  1 B. 
   In a part-sectional, schematic representation,  FIG. 1B  shows a longitudinal section through the exemplary embodiment of a fuel injector  1 , designed according to the present invention as shown in  FIG. 1A , in the open state. Identical components have been provided with the same reference numerals in  FIGS. 1A and 1B . 
     FIG. 1B  shows the fuel injector  1  designed according to the present invention in the open state. Fuel channel  11  formed in flange  14  connects inner chamber  29  of fuel injector  1  to opening  22  of valve needle  3 , so that fuel, which is supplied via central fuel supply  16  and filtered by filter element  25 , is able to be guided to the sealing seat via axial bore  21  of flange  14  and opening  22  of valve needle  3 . Valve needle  3  has a plurality of flow-through orifices  26  through which the fuel discharges from opening  22  of valve needle  3 . 
   When magnetic coil  10  is energized by means of the electric line (not shown further), a magnetic field is built up which pulls armature  20  to inner pole  13 , counter to the force of restoring spring  23 , thereby closing working gap  27  between end face  30  on the inflow-side of armature  20  and inner pole  13 . 
   Since flange  14  penetrates armature  20  through its opening  19 , flange  14  with armature  20  is moved in the lift direction upon actuation of fuel injector  1 , thereby moving valve needle  3 , which is frictionally connected to flange  14  via welding seam  15 , in the lift direction as well. At the same time, the at least one fuel channel  11  is unblocked. This allows fuel, supplied via central fuel supply  16  via inner chamber  29  of fuel injector  1 , to flow through the at least one fuel channel  11  into opening  22  of valve needle  3 . The fuel then reaches the sealing seat via flow-through orifices  26  and is spray-discharged into the combustion chamber (not shown further) via spray-discharge orifice  7 . 
   When the coil current is switched off, armature  20 , due to the pressure of restoring spring  23 , falls away from inner pole  13  after the magnetic field has decayed sufficiently, whereupon valve needle  3 , which is in operative connection to flange  14 , moves in a direction counter to the lift direction. As a result, valve closure member  4  comes to rest on valve-seat surface  6 , and fuel injector  1  is closed. Armature  20  comes to rest against the armature stop formed by second flange  31 . 
     FIG. 2  shows a schematic representation of flow-rate quantity q dyn  flowing through fuel injector  1  as a function of the lift of valve needle  3  of fuel injector  1 . 
   By the afore-described arrangement of at least one fuel channel  11 , it is possible to set, or model, a characteristic curve representing the dynamic flow rate q dyn  of fuel through fuel injector  1  as a function of a lift of valve needle  3 . By an appropriate lift adjustment of valve needle  3 , as much fuel will flow through fuel injector  1  as is required to obtain the necessary flow-rate precision. 
   By shoulder  24  covering the at least one fuel channel  11 , no fuel is able to flow to the sealing seat at the beginning of the opening process. Only when the at least one fuel channel  11  is released, will the dynamic flow rate q dyn  rise quickly and in an approximately step-by-step manner, to a saturation value, as illustrated in FIG.  2 . 
   The described measures are able to improve the dynamics of fuel injector  1  and to lower the production cost, since the design of an armature free path is omitted and the minimal fuel quantity flowing through fuel injector  1  is able to be minimized. 
   The at least one fuel channel  11  is dimensioned such that it will not act as a throttle, but, upon release, will allow an unthrottled fuel flow through fuel injector  1 . 
   The present invention is not limited to the exemplary embodiments shown and is also applicable, for instance, to fuel injectors  1  of mixture-compressing, self-ignitable internal combustion engines.