Abstract:
A fuel injector for fuel injection systems of internal combustion engines has a solenoid operable via an electric wire, a valve sleeve in an injection-side area forming an external sheathing of the fuel injector, and a valve housing. The fuel injector has a plastic sleeve, which contains the solenoid and the electric wire and can be pushed onto the valve sleeve.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is directed to a fuel injector and a method for assembling a fuel injector.  
       BACKGROUND INFORMATION  
       [0002]     Fuel injectors normally have a number of metallic housing parts, which are provided with a plastic coating after assembly. German Published Patent Application No. 101 22 353, for example, describes a fuel injector of this type.  
         [0003]     German Published Patent Application No. 197 12 591 also describes a fuel injector which is composed of two pre-assembled independent modules. A function part essentially includes an electromagnetic circuit and a sealing valve, while a connecting part essentially comprises a hydraulic connector and an electric connector. In the fully assembled fuel injector, electric connecting elements and hydraulic connecting elements of the two modules cooperate in such a way as to ensure the electric and hydraulic connection.  
         [0004]     The disadvantage of the known fuel injectors is in particular that the assembly of such a fuel injector is made complicated and cost-intensive by the plastic coating.  
         [0005]     Furthermore, when coating with liquid plastic, components are shifted from their original positions, which increases the reject rate in the manufacture of the fuel injectors.  
       SUMMARY OF THE INVENTION  
       [0006]     The fuel injector according to the present invention and the method according to the present invention for assembling a fuel injector have the advantage over the related art that the fuel injector may be assembled from two modules without the need for complicated connecting elements by inserting a hydraulic cartridge into a pre-manufactured plastic sleeve.  
         [0007]     Quicker assembly is thus possible in fewer work steps, and the expensive plastic coating, which is subject to defects, may be omitted. In addition, the individual modules may be manufactured in a simple way because they contain no complicated components.  
         [0008]     The plastic sleeve advantageously includes the hydraulic and electric connection, as well as the solenoid and its electric contact wire, while the hydraulic module includes the remaining components forming the magnetic circuit and the valve.  
         [0009]     It is furthermore advantageous that the hydraulic module is situated in a preferably deep-drawn pipe.  
         [0010]     It is also advantageous that the pipe has a peripheral groove and a sealing ring, which seals off the hydraulic module from the plastic sleeve.  
         [0011]     The hydraulic module is advantageously fixed, after insertion into the plastic sleeve, by clamping action; however, it may be additionally secured by gluing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  schematically shows a longitudinal section through an example of a fuel injector according to the related art.  
         [0013]      FIG. 2A  shows a schematic illustration of a hydraulic cartridge for use in a fuel injector according to the present invention.  
         [0014]      FIG. 2B  shows a schematic illustration of a plastic sleeve for use in a fuel injector according to the present invention.  
         [0015]      FIG. 2C  shows a schematic illustration of an exemplary embodiment of a fully assembled fuel injector according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  first shows, to better illustrate the measures according to the present invention, a highly simplified sectional view of the essential components of a fuel injector  1  according to the related art. Fuel injector  1  is suitable in particular for injecting fuel into an inlet pipe (not illustrated in detail) of an internal combustion engine.  
         [0017]     Fuel injector  1  includes a solenoid  2 , which is wound onto a field spool  3 . Field spool  3  is encapsulated in a valve housing  4 , which is used as the external pole of solenoid  2  and is closed by a cover  5 . Solenoid  2  is contacted by an electric wire  6 . A tube-shaped valve sleeve  7 , which is extended by an insert sleeve  8  for supplying fuel, goes through field spool  3 .  
         [0018]     Fuel injector  1  is assembled according to the related art in such a way that valve sleeve  7  is manufactured first and provided with insert sleeve  8 , and subsequently the components solenoid  2 , valve housing  4 , and cover  5  are axially pushed onto valve sleeve  7  of fuel injector  1 . After pre-assembly, a plastic sheathing  9  is extruded onto the metallic components of fuel injector  1 . It includes a connector  10  for connecting the electric lead (not shown) for solenoid  2 .  
         [0019]     On the inlet side, fuel injector  1  is sealed off from the fuel distribution line (not shown) by a seal  11  and, on the downstream side, from the inlet pipe of the engine by another seal  12 .  
         [0020]     Fuel injector  1  may be operated, for example, via an armature  13  cooperating with solenoid  2 , in conjunction with a valve needle  14 , whose valve closing body  15  closes an injection opening  16 . Injection opening  16  is opened by lifting valve needle  14  and is closed by re-lowering valve needle  14  with the help of a restoring spring  17 , for example, which is pre-stressed by an adjusting sleeve  18 . An internal pole  19  of the solenoid is pressed into valve sleeve  7 .  
         [0021]     The above-mentioned components must be installed in valve sleeve  7  individually and in a given sequence for assembling fuel injector  1 . Internal pole  19  must be inserted first, then adjusting sleeve  18 , restoring spring  17 , and finally armature  13  including valve needle  14  and valve closing body  15 . A valve seat body  20  having injection opening  16  is finally inserted into valve sleeve  7 .  
         [0022]     As schematically shown in  FIGS. 2A through 2C , the assembly of fuel injector  1  is simplified according to the present invention in that first a plastic sleeve  22  is manufactured, which already includes solenoid  2  and the required electric contact wiring  6  and plug  10 , which are then provided with a hydraulic module  21  of fuel injector  1  in an additional assembly step.  
         [0023]     Hydraulic module  21  is schematically illustrated in  FIG. 2A . It includes a pipe  23 , into which internal pole  19 , adjusting sleeve  18 , restoring spring  17 , the component which includes armature  13 , valve needle  14  and valve closing body  15 , and finally valve seat body  20  having injection opening  16  are installed. This latter component is responsible for preventing the individual components from falling out of pipe  23 .  
         [0024]     On the inlet side, pipe  23  has a peripheral groove  24 , in which a sealing ring  25  for sealing off hydraulic module  21  from plastic sleeve  22  is situated. Pipe  23  is manufacturable in a simple way, for example, as a deep-drawn part. Hydraulic module  21  is compact, easy to assemble, and reliable, being transportable in bulk without risk of damage.  
         [0025]     Plastic sleeve  22  is schematically illustrated in  FIG. 2B . It already has plug  10  molded onto it, a hydraulic connection  29  for connecting to a fuel distribution line (not shown), electric wiring  6  and solenoid  2 . On the inlet side of solenoid  2 , a recess  26  is formed, which divides plastic sleeve  22  into two parts, which are connected by a web  27 . Electric wiring  6  for contacting solenoid  2  is located in web  27 .  
         [0026]     A cover  28  is provided for further assembling fuel injector  1  as shown in  FIG. 2C . Cover  28  is radially snapped over hydraulic module  21  of fuel injector  1  during assembly.  
         [0027]     The assembly of fuel injector  1  includes the following steps: inserting pre-assembled hydraulic module  21  into the likewise pre-manufactured plastic sleeve  22 , radially pushing cover  28  into recess  26 , and finally fitting valve housing  4  onto hydraulic module  21 . As an alternative, hydraulic module  21  may also be connected to plastic sleeve  22  by gluing.  
         [0028]     Assembly may thus be kept very simple without welding, soldering, or other joining procedures. Nevertheless, hydraulic module  21  is reliably and hermetically connected to plastic sleeve  22 . Complicated connections and connecting components for electrically and hydraulically connecting the two modules may be omitted in full.  
         [0029]     The present invention is not limited to the exemplary embodiment illustrated and may be applied to any other types of fuel injector  1 , e.g., to fuel injectors  1  for direct injection or to fuel injectors  1  in conjunction with a common rail system. In particular, any combinations of the individual features are possible.