Patent Publication Number: US-8528842-B2

Title: Fuel injector

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fuel injector. 
     BACKGROUND INFORMATION 
     From German Patent Document No. 198 16 315 A1, for instance, a fuel injector is discussed for the direct injection of fuel into the combustion chamber of an internal combustion engine, in particular. The fuel injector includes an armature cooperating with a solenoid coil, and a valve needle which is joined to the armature by force-locking and at which a valve-closure member is provided which forms a sealing seat together with a valve-seat surface. The valve needle has a first limit stop for the armature, which is able to move on the valve needle, the armature being additionally acted upon by a second restoring spring. Moreover, a stationary second limit stop for the armature is provided. The second restoring spring acts upon the armature counter to the lift direction, and in the non-excited state of the solenoid coil holds the armature against the second stop in such a way that the armature and the first stop formed on the valve needle are set apart by a predefined distance. 
     A particular disadvantage of the fuel injector of German Patent Document No. 198 16 315 A1 may be that, although a prestroke principle is realized which allows an improvement in the valve dynamics during opening of the fuel injector, armature bounce, which induces additional, undesired opening lifts of the valve needle, occurs during closing of the fuel injector when the armature returns to the neutral position. 
     SUMMARY OF THE INVENTION 
     In contrast, the fuel injector according to the exemplary embodiment of the present invention has the advantage that the armature is swingingly supported on the valve needle by a correspondingly disposed spring, and a prestroke may thus take place during the opening operation, but the armature is able to swing freely with respect to the valve needle during closing, so that additional opening lifts of the valve needle are able to be prevented. 
     Furthermore, it is advantageous that the spring is embodied as a simple helical spring und is slipped onto the valve needle. 
     The spring is advantageously positioned between a sleeve and a flange that is frictionally connected to the valve needle. The sleeve encapsulates the spring and the flange. 
     Another advantage is that the sleeve is able to be produced in an uncomplicated manner and be installed in the fuel injector on the armature. 
     Moreover, it is advantageous that a stop ring mounted to the housing is provided, which is used as lower armature stop. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic section through an exemplary embodiment of a fuel injector configured according to the exemplary embodiment of the present invention. 
         FIG. 2  shows an enlarged cutout from the exemplary embodiment of a fuel injector configured according to the exemplary embodiment of the present invention and shown in  FIG. 1 , in area II in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the present invention is described in the following by way of example. In this context, identical components have been provided with matching reference numerals in all of the figures. 
     An exemplary embodiment of a fuel injector  1  according to the present invention, shown in  FIG. 1 , is designed in the form of a fuel injector  1  for fuel-injection systems of mixture-compressing internal combustion engines having externally supplied ignition. Fuel injector  1  is particularly 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 nozzle body  2  in which a valve needle  3  is positioned. Valve needle  3  is mechanically linked to 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. Fuel injector  1  in the exemplary embodiment is an inwardly opening fuel injector, which is provided with a spray orifice  7 . 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 constriction  26  and interconnected by a non-ferromagnetic connecting part  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 a plastic coat  18 , which is extrudable onto inner pole  13 . 
     An armature  20  is positioned on valve needle  3  in a manner allowing movement. Armature  20  is set apart from a first flange  21  joined to valve needle  3  with force-locking by a welding seam  22 , by a prestroke gap  27 . Braced on first flange  21  is a restoring spring  23 , which is prestressed by a sleeve  24  in the present design of fuel injector  1 . A working air gap  33  is formed between a lower stop face of inner pole  13  and armature  20 . 
     Fuel channels  30  and  32  run in armature  20  and along a guide element  36 . The fuel is supplied via a central fuel supply  16  and filtered by a filter element  25 . Fuel injector  1  is sealed against a fuel distributor (not shown further) by a seal  28  and against a cylinder head (not shown further) by another seal  37 . 
     On the discharge-side of armature  20  is a second flange  34 , which is likewise joined to valve needle  3  by force-locking via a welding seam  35 . 
     According to the exemplary embodiment of the present invention, a cup-shaped sleeve  14  is provided, which is situated downstream of armature  20  and permanently connected thereto, in which a spring  31  is situated which is braced between sleeve  14  and second flange  34 . A stop ring  38 , mounted to the housing, is used as downstream armature stop. The measures according to the exemplary embodiment of the present invention are elucidated in greater detail in the following, with reference to  FIG. 2 . 
     In the neutral position of fuel injector  1 , return spring  23  acts upon valve needle  3  counter to its lift direction in such a way that valve-closure member  4  is retained in sealing contact against valve seat surface  6 . When excited, solenoid coil  10  generates a magnetic field which moves armature  20  in the lift direction, initially counter to the spring force of spring  31 , the prestroke, i.e., the free travel of the armature, being defined by a prestroke gap  27  occurring in the neutral position between first flange  21  and armature  20 . Following the prestroke travel, armature  20  is pulled to inner pole  13  of solenoid coil  10 , counter to the force of restoring spring  23 ; armature  20  takes along first flange  21 , which is welded to valve needle  3 , thereby taking it along in the lift direction as well. Valve-closure member  4 , which is connected to valve needle  3 , lifts off from valve seat surface  6 , and the fuel carried via fuel channels  30  and  32  is spray-discharged through spray-discharge orifice  7 . 
     If the coil current is interrupted, following sufficient decay of the magnetic field, armature  20  falls away from inner pole  13  due to the pressure of restoring spring  23 , whereupon first flange  21 , being joined to valve needle  3 , moves in a direction counter to the lift direction. Valve needle  3  is thereby moved in the same direction, causing valve-closure member  4  to set down on valve seat surface  6  and fuel injector  1  to be closed. Sleeve  14  simultaneously sets down on stop ring  38  mounted to the housing. 
     Due to second spring  31 , which is disposed between second flange  34  and a base part  40  of sleeve  14  as can be gathered from  FIG. 2 , armature  20  is situated on valve needle  3  in manner allowing it to swing freely. So-called first-order armature bounces are avoided in that during the closing movement of fuel injector  1  armature  20  is prevented from striking flange  34  when moving in the closing direction. Instead, it is caught by stop ring  38 . Armature  20  is thus braked by spring  31  during the closing movement. At the same time, the prestroke principle, which allows the opening dynamics of fuel injector  1  to be improved, is realized as well. 
     Sleeve  14  is fixedly connected to armature  20  via a collar  39 , for instance by welding, soldering or bonding. Stop ring  38  is mounted to the housing by pressing it in or welding it to outer pole  9  of fuel injector  1 , for example. 
     The present invention is not restricted to the exemplary embodiment shown, but also applicable to other forms of fuel injectors  1 .