Abstract:
A fuel injector includes a solenoid coil, which cooperates with an armature acted upon by a restoring spring, the armature forming an axially movable 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. In addition, a valve sleeve is provided whose wall thickness varies across its axial extension.

Description:
BACKGROUND INFORMATION  
       [0001]     Described in German Patent Application No. DE 40 03 227, for instance, is a fuel injector, which has a core enclosed by a solenoid coil; an armature via which a valve closure body cooperating with a fixed valve seat is actuable by a connection pipe soldered to the armature; and a tubular metal intermediate part, which is sealingly connected by welding to an end of the core facing the armature by its one end and to a tubular connecting part by its other end; and at least one bracket-type conductive element which crosses over the solenoid coil and is connected, by welding, to the connecting part by its end facing the valve closure member and to the core by its other end. The welding of two overlapping components of the fuel injector is implemented in a cross-section reduction of one of the two parts to be welded.  
         [0002]     A particular disadvantage of the fuel injector known from the aforementioned printed publications 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 their strength and flexural stiffness which may lead to considerable resonances as a result of housing parts having different thicknesses and to related noise development during operation of the fuel injector.  
       SUMMARY OF THE INVENTION  
       [0003]     The fuel injector according to the present invention has the advantage that the wall thickness of the valve sleeve of the fuel injector varies. As a result, it is adapted to the specific requirements in the various regions. Resonances are attenuated so that the noise development is dampened as well. This has no negative effect on the stability of the valve sleeve and the saturation behavior of the magnetic field in the region of the working air gap.  
         [0004]     In an advantageous manner the wall thickness is reduced in a discharge direction of the fuel, so that the relevant parts do not suffer any loss in stability.  
         [0005]     It is also advantageous that the valve sleeve diameter also tapers in the region of the reduced wall thickness, which makes the fuel injector more compact and lighter.  
         [0006]     Furthermore, it is advantageous that the supply pipe which conveys the fuel to the sealing seat may be formed in one piece with the valve sleeve, so that the fuel injector may likewise have a more compact and shorter design. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0007]      FIG. 1  shows a schematic section through an exemplary embodiment of a fuel injector configured according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0008]      FIG. 1  shows a sectional, schematic 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.  
         [0009]     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 .  
         [0010]     Coil brace  3  is penetrated by a valve sleeve  5  which has a tubular design and according to the present invention varies in its material thickness. The measures of the present invention will be described in greater detail below.  
         [0011]     A support pipe  6  wedged inside or welded to valve sleeve  5  may be used as inner pole of solenoid coil  2 . Valve housing  4 , for example, may be used as outer pole of solenoid coil  2 . Downstream from support pipe  6  is an armature  7  which is integrally formed with a valve needle  8 . Flow-through orifices  9 , which guide the fuel flowing through fuel injector  1  toward a sealing seat, are provided in valve needle  8 .  
         [0012]     Valve needle  8  is in operative connection—preferably by welding—with a valve-closure member  10  which has a spherical shape 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 in a spray-orifice plate  12 , from which the fuel is injected into the intake manifold (not shown further).  
         [0013]     In the rest state of fuel injector  1 , armature  7  is acted upon by a restoring spring  14  in such a way 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 support pipe  6  and is 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 . Via an intake pipe  24 , a recess  15  and flow-through orifices  9 , the fuel conveyed by a central fuel supply  18  flows through fuel injector  1  to the sealing seat and to spray-discharge orifice  13 .  
         [0014]     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. 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 coating  22  which may be sprayed onto valve sleeve  5  or onto intake pipe  24 .  
         [0015]     If an electric current is supplied to magnetic coil  2  via an electrical line (not shown further), a magnetic field will be generated that, if sufficiently strong, pulls armature  7  into magnetic 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 support pipe  6 . The movement of armature  7  also carries along in the lift direction valve needle  8  integrally formed with armature  7 , so that valve-closure member  10  lifts off from valve-seat body  11  and fuel is conveyed to spray-discharge orifice  13 .  
         [0016]     Fuel injector  1  is closed as soon as the electric current energizing magnetic coil  2  has been switched off and the magnetic field has decayed to such a degree that restoring spring  14  presses armature  7  away from support pipe  6 , thereby moving valve needle  8  in the discharge direction and valve-closure member  10  coming to rest on valve-seat body  11 .  
         [0017]     Due to flexural vibrations, fuel injectors have a tendency to emit interfering noise during operation. This is caused by the form of valve sleeve  5  which has a support function on the one hand, but on the other hand must be thin enough in its material thickness to allow a satisfactory build-up of the magnetic field in the region of the working air gap.  
         [0018]     As mentioned above, valve sleeve  5  has a tubular design and according to the present invention varies in its wall thickness in order to limit noise emissions. An inflow-side region  25  into which supply pipe  24  is inserted, has a heavier design than a downstream region  26 . The wall thickness of valve sleeve  5  in the inflow-side region is approximately 0.5 mm, while the downstream region has a wall thickness of approximately 0.3 mm.  
         [0019]     In addition, the cross section of valve sleeve  5  is variable as well. In region  25  having greater material strength the cross section is larger, which leads to higher stability of valve sleeve  5 ; the cross section is smaller in region  26  having lower material strength.  
         [0020]     The tapering of valve sleeve  5  occurs at a collar  27  which separates the regions having high material thickness and those having low material thickness and also the regions having different cross sections.  
         [0021]     Due to the greater wall thickness of inflow-side region  25  of valve sleeve  5 , it may also be formed in one piece with supply pipe  24 , which constitutes an advantageous further development of fuel injector  1  with respect to compactness and overall length.  
         [0022]     The present invention is not limited to the exemplary embodiment shown. In particular, any combination of the individual features is possible.