Abstract:
A fuel injector, in particular a fuel injector for fuel-injection systems of internal combustion engines, includes a valve needle cooperating with a valve-seat surface to form a sealing seat, and has an armature engaging with the valve needle, the armature being axially moveable on the valve needle and damped by a damping element made of an elastomer. The damping element is positioned in a recess of the armature at the valve needle in such a way that the valve needle is connected to the armature in the radial direction via the damping element.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a fuel injector. 
   BACKGROUND INFORMATION 
   U.S. Pat. No. 4,766,405 describes a fuel injector that includes a valve-closure member which is joined to a valve needle and cooperates with a valve-seat surface formed on a valve-seat member to form a sealing seat. For the electromagnetic actuation of the fuel injector, a magnetic coil is provided which cooperates with an armature that is joined to the valve needle by force-locking. An additional mass having a cylindrical form is provided around the armature and the valve needle, the mass being connected to the armature via an elastomeric layer. 
   The disadvantage with this is particularly the costly design that includes an additional component. In addition, the large surfaced elastomer ring is disadvantageous for the pattern of the magnetic field and hinders the closing of the field lines, and thus the achievement of high attractive forces during the opening movement of the fuel injector. 
   U.S. Pat. No. 4,766,405 describes another embodiment of a fuel injector in which, for damping and debouncing, an additional cylindrical mass is provided around the armature and the valve needle, which is moveably braced and held in its position by two clastomeric rings. When the valve needle strikes the sealing seat, this second mass can move relative to the armature and the valve needle and prevent bouncing of the valve needle. 
   The disadvantage of this described specific embodiment is the additional cost and space requirement. Also, the armature itself is not decoupled, so that its momentum increases the bouncing tendency of the valve needle. 
   U.S. Pat. No. 5,299,776 describes a fuel injector having a valve needle and an armature, where the armature is movably guided on the valve needle. The armature movement in the lift direction of the valve needle is limited by a first stop and its movement counter to the lift direction by a second stop. Within certain limits, the axial play of the armature, defined by the two stops, leads to a decoupling of the inert mass of the valve needle on the one hand, and the inert mass of the armature on the other hand. This counteracts to some extent a bouncing back of the valve needle from the valve-seat surface upon closing of the fuel injector. However, since the axial position of the armature relative to the valve needle is totally undefined by the free movement of the armature relative to the valve needle, bounces are avoided only to a limited extent. In particular, in the design of the fuel injector of U.S. Pat. No. 5,299,776 it is not avoided that the armature strikes the stop facing the valve-closure member during the closing movement of the fuel injector, thereby rapidly transmitting its momentum to the valve needle. This sudden transfer of linear momentum may cause additional bounces of the valve-closure member. 
   Furthermore, it is known in practice to fasten the armature, which is movably positioned on the valve needle, by using an elastomeric ring so that it is movably clamped in its position. For this purpose, the armature is held between two stops, an elastomeric ring being situated between the armature and lower stop. With this arrangement, however, the problem arises that a borehole through the armature is necessary for the supply of fuel to the valve-sealing seat. The bore through the armature is implemented close to the valve needle, so that it may occur that the elastomeric ring covers the bore. 
   SUMMARY OF THE INVENTION 
   In contrast, the fuel injector according to the present invention has the advantage over the related art that a damping element radially damps the armature and the valve needle with respect to one another in that a hollow-cylindrical elastomeric part is slid over the valve needle and the two components are together inserted in a recess of the armature. In this way, both needle bounce and armature bounce are damped in an effective manner. 
   In an advantageous manner, the surfaces of the damping element are vulcanized in order to produce better adhesion between the damping element made of elastomeric material and the metallic components, valve needle and armature. 
   Particularly advantageous is the separation of the fuel path through the fuel injector from the damping element, the damping element thus remaining undamaged and being unable to stray from its position under the influence of the fuel pressure, thereby extending the service life of the fuel injector. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic section through an exemplary embodiment of a fuel injector configured according to the present invention, in an overall view; and 
       FIG. 2  shows a schematic longitudinal section through the fuel injector configured according to the present invention as shown in  FIG. 1 , in area II in FIG.  1 . 
   

   DETAILED DESCRIPTION 
   An exemplary embodiment of a fuel injector  1  configured according to the present invention as shown in  FIG. 1  is designed in the form of a fuel injector 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 in operative connection with valve-closure member  4 , which cooperates with a valve-seat surface  6 , located 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 one spray-discharge orifice  7 . Nozzle body  2  is sealed from outer pole  9  of a magnetic coil  10  by a seal  8 . Magnetic coil  10  is encapsulated in a coil housing  11  and wound on a coil brace  12 , which rests against an inner pole  13  of magnetic coil  10 . Inner pole  13  and outer pole  9  are separated from one another by a constriction  26  and are interconnected by a non-ferromagnetic connecting part  29 . Magnetic coil  10  is energized via a line  19  by an electric current which may be supplied via an electrical plug contact  17 . A plastic extrusion coat  18 , which maybe extruded onto inner pole  13 , encloses plug contact  17 . 
   Valve needle  3  is guided in a valve-needle guide  14 , which is disk-shaped. A paired adjustment disk  15  is used to adjust the (valve) lift. Armature  20  is on the other side of adjustment disk  15 . Via a first flange  21 , it is in force-locking connection to valve needle  3  which is connected to first flange  21  by a welded seam  22 . Braced on first flange  21  is a restoring spring  23  which is provided with an initial stress by a sleeve  24  in the present design of fuel injector  1 . Downstream from armature  20  is a second flange  31 , which is connected to valve needle  3  by force-locking via a welded seam  33  and serves as lower armature stop. 
   Fuel channels  30   a  through  30   c  run in valve-needle guide  14 , in armature  20  and valve-seat member  5 . The fuel is supplied 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). 
   According to the present invention, fuel injector  1 , in a recess  34  of armature  20 , is provided with a damping element  32  which is designed as a hollow cylinder and penetrated by valve needle  3 . Damping element  32  maybe made of an elastomeric material, such as rubber, and is joined by force-locking to armature  20  on one side, and to valve needle  3  on the other side, in such a manner that the axial movements of the mentioned components are damped with respect to each other. In this way, it is possible to prevent armature bounce both during the opening in the upper lift position and also during closing of fuel injector  1  in the lower lift position of armature  20 . 
   The measures according to the present invention are represented in detail in FIG.  2  and explained more clearly in the following description. 
   In the rest state of fuel injector  1 , armature  20  is acted upon by restoring spring  23  in a direction opposite to its lift direction, in such a manner that valve-closure member  4  is sealingly held against valve seat  6 . In response to excitation of magnetic coil  10 , it generates a magnetic field which moves armature  20  in the lift direction, counter to the spring force of restoring spring  23 , the lift being predefined by a working gap  27  which occurs in the rest position between inner pole  12  and armature  20 . First flange  21 , which is welded to valve needle  3 , is taken along by armature  20  in the lift direction as well. Valve-closure member  4 , being in connection with valve needle  3 , lifts off from valve-seat surface  6 , and the fuel is spray-discharged through spray-discharge orifice  7 . 
   In response to interruption of the coil current, 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 connected to valve needle  3 , moves in a direction counter to the lift. 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. 
   In a part-sectional view,  FIG. 2  shows an enlarged view of region II in FIG.  1 . Shown are armature  20  with damping element  32  and the inflow-side end of valve needle  3 . For the sake of clarity, the remaining components situated in this region have been omitted. 
   As already mentioned earlier, fuel injector  1  in its preferred embodiment has a damping element  32  which is positioned in an axial recess  34  of armature  20 . 
   Damping element  32  is designed as a hollow cylinder and preferably made of an elastomeric material, such as rubber. For the force-locking connection of damping element  32  to armature  20  and to valve needle  3 , damping element  32  is provided with vulcanized layers  35   a  and  35   b , which rest against recess  34  of armature  20  and valve needle  3  and, by pressure and static friction, provide for an elastic connection between armature  20  and valve needle  3 . Damping element  32  is restricted in its axial length only by the axial length of recess  34  of armature  20 . The length and the wall thickness of damping element  32  are selected mainly under the aspect of manufacturing and assembly technology and also durability during continuous operation. 
   The movements of armature  20  and of valve needle  3  with respect to one another may be effectively damped by the elastic connection, thereby avoiding armature bounce at first sleeve  21  during opening of fuel injector I and at second sleeve  31  during closing of fuel injector  1 . The movement of valve needle  3  is also damped, so that valve-needle bounce in the sealing seat is likewise avoided. As a consequence, the dynamics of fuel injector  1  are improved, so that it is possible to realize shorter opening and closing times in combination with faster switching cycles and smaller and more precise metered quantities. 
   By a separation of the fuel path through fuel injector  1 , which guides fuel through armature  20  by way of fuel channels  30   a , from damping element  32  in recess  34  of armature  20 , damping element  32  is not damaged by the corrosive fuel. There is also no danger of damping element  32  leaving recess  34  of armature  20 , due to the prevailing fuel pressure, and being consequently damaged. Slight movements along valve needle  3 , on the other hand, do not affect the functioning. 
   The present invention is not limited to the exemplary embodiment shown and is also applicable, for instance, to outwardly opening fuel injectors  1 .