Abstract:
A fuel injector includes a solenoid coil, which cooperates with an armature acted upon by a restoring spring, the armature forming an axially displaceable valve part together with a valve needle. A valve-closure member, which forms a sealing seat together with a valve-seat body, is provided on the valve needle. A sealing of the valve sleeve is provided by a rubber disk affixed underneath the solenoid coil, which solenoid coil, which is axially prestressed, is pressed onto the rubber disk.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. FIELD OF THE INVENTION  
         [0002]     The present invention relates to a fuel injector.  
         [0003]     2. DESCRIPTION OF RELATED ART  
         [0004]     Published German patent document DE 40 03 227 describes a fuel injector which includes a core surrounded by a solenoid coil, an armature by which a valve-closure member cooperating with a fixed valve seat is actuable with the aid of a connecting tube welded to the armature; a tubular metal intermediate part which, by welding, is sealingly connected to an end of the core facing the armature via its one end, and to a tubular connecting part via its other end; and at least one bracket-type conducting element, which overlaps the solenoid coil and, by welding, is connected to the connecting part by its end facing the valve-closure member, and to the core via its other end. In each case, the welding of two overlapping components of the fuel injector is implemented in a region having a reduced cross section of one of the two components to be welded to one another.  
         [0005]     A particular disadvantage of the fuel injector described in the aforementioned German patent document is that the production of the connections between the individual components of the fuel injector is complicated and thus time- and cost-intensive. Furthermore, the welded points are loaded thermally and thus lose some of their strength and flexural stiffness, which may lead to considerable resonances due to the different thicknesses of housing parts as well as to related noise development during operation of the fuel injector. In addition, a support ring, which is injection-molded underneath the seal on the side of the intake manifold, has the effect that contact points between the housing and valve sleeve are not reliably sealed, which may lead to problems due to poor sealing, especially in turbo-operation of the engine.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The fuel injector according to the present invention has the advantage of allowing reliable axial sealing between the housing and the valve sleeve by a fuel-resistant elastomer. This seal is a disk, e.g., made of rubber, which has the advantage that the utilized sealing element is simple and cost-effective. Another advantage is that the rubber disk requires only little space within the valve, which is reduced even further by compression of the rubber disk after installation.  
         [0007]     During installation of the fuel injector, the axial force may be advantageously transmitted from the top to the rubber disk via the solenoid coil, by way of a projection provided on the end face of the coil brace, so that the rubber disk is pressed against the solenoid coil and the flange of the valve housing with sufficient force, thereby further improving the sealing.  
         [0008]     The height and form of the projection are configured such that the coil is always pressed onto the rubber disk when the top is installed in its final position. This reliable sealing has the advantage that it is independent of the tolerances of the individual components; compensation of the tolerances is accomplished by selective deformation of the projection, and the coil is axially prestressed in a play-free manner.  
         [0009]     Furthermore, the axial prestressing by the projection provided on the end face facing the top ensures that the hydraulic pressure of the elastic mass will not cause any additional axial displacement of the coil during injection-molding of the plug connector, which might damage the soldering of coil and plug clip.  
         [0010]     It is advantageous that an inner radius of the disk is smaller than a radius of a valve sleeve. Moreover, it is advantageous that the inner radius of the disk is dimensioned such that sealing of the valve sleeve occurs. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0011]      FIG. 1  shows a schematic cross-sectional view of an exemplary embodiment of a fuel injector according to the present invention.  
         [0012]      FIG. 2  shows a schematic cross-sectional view of a portion of the fuel injector configured according to the present invention.  
         [0013]      FIG. 3  shows a schematic cross-sectional view of a portion of the fuel injector configured according to the present invention, according to a second exemplary embodiment.  
         [0014]      FIG. 4  shows a schematic cross-sectional view of a portion of the fuel injector configured according to the present invention, according to a third exemplary embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]      FIG. 1  shows a schematic sectional representation of a longitudinal section through an exemplary embodiment of a fuel injector  1  designed according to the present invention, the fuel injector being suited, in particular, for the injection of fuel into an intake manifold (not shown further) of an internal combustion engine.  
         [0016]     Fuel injector  1  includes a solenoid coil  2 , which is wound on a coil brace  3 . Coil brace  3  is encapsulated in a cup-shaped valve housing  4 .  
         [0017]     Coil brace  3  is penetrated by a valve sleeve  5  having a tubular design. Downstream from inner pole  6  is an armature  7 , which is connected with a valve needle  8 .  
         [0018]     Valve needle  8  is in operative connection with a valve-closure member  10 , which has a spherical form in the exemplary embodiment and forms a sealing seat together with a valve-seat body  11 . Downstream from the sealing seat at least one spray-discharge orifice  13  is formed from which the fuel is injected into the intake manifold (not shown further).  
         [0019]     In the rest state of fuel injector  1 , armature  7  is acted upon by a restoring spring  14  with such a force that fuel injector  1  is held closed by the contact pressure of valve-closure member  10  on valve-seat body  11 . Restoring spring  14  is situated in a recess  15  of armature  7  or inner pole  6  and prestressed by an adjusting sleeve  16 . On the inflow side of adjusting sleeve  16 , a cup-shaped filter element  17  is preferably pressed into valve sleeve  5 . The fuel, which is conveyed via a central fuel supply  18 , traverses fuel injector  1  through an intake pipe  24 , recess  15 , and flows to valve-seat body  11  and to spray-discharge orifice  13 .  
         [0020]     For the purpose of installation on a fuel-distributor line (not shown further), fuel injector  1  is provided with a seal  19  in the region of central fuel supply  18 . An additional seal  20  seals the connection (not shown further) between fuel injector  1  and the intake manifold. The intake manifold is not shown further here since it is unimportant for the essence of the present invention. Solenoid coil  2  is energized via a line by an electric current, which may be supplied via an electrical plug contact  21 . Plug contact  21  is enclosed by a plastic extrusion coating  22 , which may be sprayed onto valve sleeve  5  or intake pipe  24 .  
         [0021]     If an electric current is supplied to solenoid coil  2  via an electrical line (not shown further), a magnetic field will be generated that, if sufficiently strong, pulls armature  7  into solenoid coil  2 , counter to the force of restoring spring  14  and counter to the flow direction of the fuel. This closes a working gap  23  formed between armature  7  and inner pole  6 . The movement of armature  7  also carries along in the lift direction valve needle  8 , which is integrally joined to armature  7 , so that valve-closure member  10  lifts off from valve-seat body  11  and fuel is spray-discharged via spray-discharge orifice  13 .  
         [0022]     Fuel injector  1  is closed as soon as the electric current energizing solenoid coil  2  is turned off and the magnetic field has decayed to the point where restoring spring  14  presses armature  7  away from inner pole  6 , which causes valve needle  8  to move in the discharge direction and valve-closure member  10  to come to rest on valve-seat body  11 .  
         [0023]     Valve sleeve  5  has a tubular design. According to the present invention, a disk  25  made of an elastomeric material, e.g., a rubber disk  25 , is provided between valve housing  4  and valve sleeve  5 , disk  25  constituting reliable sealing of valve sleeve  5 , an inner radius of disk  25  being smaller than a radius of valve sleeve  5 . The inner radius of disk  25  is dimensioned such that sealing of valve sleeve  5  is accomplished. This is shown in the drawings of  FIG. 1  to  FIG. 4 . Moreover, coil brace  3  has at least one projection  27  on an end face  30  facing a top  28  of the coil chamber, e.g., at its inner diameter, the projection being shown in  FIG. 3 . During installation, axial forces are transmitted from top  28  to rubber disk  25  via end face  30  facing top  28  and via solenoid coil  2 /coil brace  3 . Rubber disk  25  may be installed either as loose component or, for instance, be fixedly installed on coil brace  3  by cementing.  
         [0024]      FIG. 4  shows a coil brace having at its downstream end a radially peripheral collar  12 , which is situated circumferentially on the lower end face of coil brace  3 , radially outside of rubber disk  25 , and which rests against the shoulder of valve housing  4  in a clamped state of rubber disk  25 . As an alternative to a circumferential collar, it is also possible to provide a plurality of nubs on the lower end of coil brace  3  in a radially symmetrical manner.  
         [0025]     The projection may be present in the form of a partial ring  27 A, as shown in  FIG. 3 , the dimensions of its cross section  27 B being small compared to the radial extension of end face  30  facing top  28 . Both the height and cross section  27 B of projection  27  are dimensioned such that solenoid coil  2  is pressed onto rubber disk  25  regardless of the tolerances of the individual components; the tolerances are compensated for by selective deformation of projection  27 . It is also possible to place a plurality of projections  27  across the circumference of coil brace  3 .  
         [0026]     An axial, play-free initial stress is imparted to solenoid coil  2 , it being ensured that the hydraulic pressure brought about by the elastic mass during plug-connection extrusion coating  22  will not cause any additional axial displacement of solenoid coil  2 .  
         [0027]     The present invention is not limited to the illustrated exemplary embodiments. In particular, any combination of the individual features is possible.