Abstract:
A fuel injection valve for internal combustion engines is supplied from a high-pressure fuel reservoir with high-pressure fuel that at the same time also serves to actuate the injection valve needle of the fuel injection valve. The injection valve needle is actuated via a tappet, which defines a control pressure chamber that is supplied with high-pressure fuel via a Z-throttle and can be relieved via an outlet throttle which is controlled by a magnet valve. The control pressure chamber is enclosed in an insert by the tappet guided in a cylindrical bore, and this insert receives not only the cylindrical bore but also a flat armature, a tappet of the flat armature, and a valve member of the magnet valve. The insert is braced on the housing on the injection valve by the magnet valve housing.

Description:
PRIOR ART 
     The invention is based on a fuel injection valve for internal combustion engine. In one such fuel injection valve, known from European Patent Disclosure EP B1 0 304 747, the insert has a peglike part, which is inserted into a suitable blind bore of the housing of the fuel injection valve and with its face end closes a guide bore, inside of the guide bore a tappet is guided that acts on the other end on the injection valve needle. In the known version, the control pressure chamber is accommodated in an axial bore of the insert and communicates, via a throttle, with a further control chamber portion located immediately above the tappet in the guide bore. Between the insert and the tappet, an insert receiving this throttle is provided. The stroke of the tappet can be adjusted by varying the thickness of the insert. 
     The magnet valve in this version has a magnet valve housing with an axially protruding apron, by way of which the insert is held in its position on the housing of the fuel injection valve. The armature of the magnet valve is guided along the inside circumference of the apron and is located in principal between the upper end of the insert and the core of the electromagnet that actuates the armature. This version entails a major effort to adjust the stroke of the valve member of the magnet valve. It involves the risk that if the armature comes into direct contact with the associated core of the electromagnet, magnetic sticking can disadvantageously occur, which considerably impairs the functioning, and particularly the switching speed of the magnet valve. 
     ADVANTAGES OF THE INVENTION 
     By means of the fuel injection valve of the invention as defined hereinafter, a compact design with considerable advantages in terms of production and assembly is attained. Because the insert now receives not only the guide for the valve member of the magnet valve but also the cylinder with the movable wall that encloses the control pressure chamber, a single production unit is created which is easy to make and easy to assemble. It is in particular highly advantageous that the armature is embodied as a flat armature and is adjustable in a cup-shaped recess of the insert, with one rim of the insert protruding past the armature located in the closing position and ending directly in the plane that defines the final stroke position of the armature. Thus, an association of the electromagnet of the magnet valve with the valve seat disposed in the insert can be established in a simple way, and this association can be adjusted exactly by simply reworking the height of the rim of the insert. In a very simple way, it, is then possible by placing a shim between the rim of the insert and the housing or the core of the electromagnet, to define a residual air gap; upon excitation of the electromagnet, the armature moves with its rim into contact with the shim that defines its stroke toward the magnet, specifically in a narrow surface region in the rim region of the outer circumference of the armature. It is thus assured that when the excitation of the electromagnet is turned off, and under the influence of a closing spring, the armature quickly and securely returns the valve closing member to the closing position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The sole FIGURE is a cross sectional view of one-half of an injection valve along its longitudinal axis. 
    
    
     DETAILED DESCRIPTION 
     The drawing shows a part of the fuel injection valve of the invention. An injection valve needle, not identified by reference numeral and of the kind also disclosed in the reference cited at the outset is guided in the housing  1  of the fuel injection valve. This injection valve needle, on one end, has a well known conical sealing face, which cooperates with a likewise conical valve seat in the housing  1 , and when the injection valve needle is on its valve seat, it closes injection bores, while when the injection valve needle is lifted it opens the bones. The injection bores can lead directly away from the conical valve seat or from a blind bore adjoining the conical valve seat. Recent injection systems prefer the first option. On the end toward the valve seat, the valve needle surrounds an annular chamber, which extends as far as a pressure chamber on the other end of the annular chamber that communicates constantly with a high-pressure fuel source, not shown, in the form of a high-pressure reservoir. To that end, the housing of the fuel injection valve has an inlet  5 . In a conventional version, the tappet  3  is placed on the valve needle and is tightly guided, on an end remote from the valve needle, in a cylindrical bore  4 . By way of the length of the part located outside the cylindrical bore, the tappet is positioned spaced apart from the housing, and a compression spring acting in the closing direction is also provided, which engages either the tappet or the injection valve needle. 
     On a face end  6  forming a movable wall, the tappet  3  encloses a control pressure chamber  7  in the cylindrical bore  4  with the closed end thereof; this chamber communicates with the inlet  5  via an inlet throttle  8 , also known as a Z-throttle. To attain this, the cylindrical bore  4  is made inside a cylindrical insert  10 , which is made from a part that is stepped on its outer circumference. A part  12  of the smallest diameter in the stepped part is inserted into a housing bore  13  of the housing  1 . This smallest part  12  is followed by a part  14  of medium diameter, which is inserted into a correspondingly wider-diameter part of the housing bore  13  and finally changes over, via a shoulder  16 , into a flange-like part  17 . This part  17  rests with a shoulder on a corresponding shoulder  18  of the housing  1  and is received in a cylindrical recess  19  that is formed by a neck  20  that protrudes from the housing  1 . An end region of the smaller-diameter part  12  that adjoins the middle part  14  protrudes into the part of the housing bore  21  that otherwise receives the middle part  14  and with the annular chamber forms an annular chamber  23 , into which the inlet  5  discharges. On the other end, the Z-throttle leads away from the annular chamber  23 , so that the control pressure chamber  7  can be supplied with fuel via the inlet, the annular chamber  23 , and the Z-throttle  8 . Seals are also provided above and below this annular chamber  23 , to seal the annular chamber off from the outside. 
     The cylindrical bore  4  is accommodated in the region of the smaller-diameter part  12  of the cylindrical insert. A relief line in the form of a bore  25  leads axially away, inside this part, from the control pressure chamber  7  and changes over to an outlet throttle  26  which in turn ends in a conical valve seat  28  that adjoins a relief chamber. This valve seat is the valve seat of a magnet valve  29 , which has an electromagnet  30  with a magnet core  31 , a magnet coil  32  embedded in the core, and a magnet valve housing  34  receives the magnet core and coil. The magnet valve housing is screw threaded to the housing of the injection valve by means of a tension nut  35 , which is coupled via a collar  36  to the shoulder  37  of the magnet valve housing. The tension nut has a female thread, which is screwed onto a male thread on the neck  20 . This operation presses the magnet valve housing against the flange-like part  17  of the cylindrical insert  10 , so that the insert comes into solid contact with its shoulder  16  on the shoulder  17  of the housing. And is thus fixed in the housing of the fuel injection valve. 
     The magnet valve  29  also has a flat armature  40 , which comes to rest inside a recess  42  on the face end of the flange-like part  17  of the insert  10 . The recess  42  is defined circumferentially by a rim  43 , on whose face end  44  the face end of the magnet valve housing acts. Connected to the armature is an axially extending tappet  45 , which is part of the valve member and is guided in a guide bore  47  of the insert  10  that is coaxial with the cylindrical bore  4 . On the end of the tappet remote from the flat armature  40 , the tappet has a receptacle  49  for a ball  50 , which cooperates as a valve member with the valve seat  28 . The receptacle may be embodied as a separate part, which is displaceable crosswise to the actuation direction of the tappet  45 , in order to compensate for errors of alignment resulting from tolerances in production. 
     The flat armature  40  is also loaded by a compression spring  52 , which is accommodated in an axial bore in the interior of the magnet core  31  and is braced there. This spring moves the valve member  50  to the closing position when the electromagnet is not excited. The magnet core  31 , toward the flat armature  40 , has a flat termination face  53 , which is located in the same plane as the face end of the magnet valve housing or protrudes somewhat past it. Thus exact machining of this surface can be done in a simple way. So that the armature, upon excitation of the electromagnet, will not come into direct contact with the termination face of the magnet core  31 , a shim  55  which fits over a peripheral region of the flat armature  40  is fastened between the edge  54  of the magnet valve housing  34  and the face end  44  of the rim  43  of the insert  10 . Thus when the electromagnet is excited, the flat armature  40  meets only this shim  55  and is not exposed to remanent magnetic forces. This shim may be embodied antimagnetically. If the edge  54  of the magnet valve housing  34  recedes relative to the termination face  53 , then the shim  55  can be made correspondingly thicker. 
     In operation of the fuel injection valve, the control pressure chamber  7  is constantly put at the high pressure, which also prevails in the high-pressure fuel reservoir, via the Z-throttle  8  when the magnet valve is closed. Since the face end  6  of the tappet  3  has a larger surface area than a sealing face acting in the opening direction that is present in a known manner on the injection valve needle, the valve needle is kept in the closing position by the high pressure prevailing in the control pressure chamber. As soon as the magnet valve is excited, the control pressure chamber can be opened to the relief chamber via the bore  25  and the throttle  26 . The relief chamber is formed by the entire chamber enclosed by the tappet guide and the recess  42 . The relief line communicating with the relief chamber is not identified by reference numeral in the drawing. If the magnet valve closes again because the excitation of the electromagnet is turned off, then the original high-pressure builds up again rapidly in the control pressure chamber  7  via the throttle  8 , and the valve needle is then moved into the closing position by the force resulting from this pressure. 
     The embodiment of the insert with the rim  43  also makes a very favorable adaptation of the geometric dimensions of the valve member to those of the flat armature  40  possible. Advantageously, for exact setting of the dimensions, the ball  50  is replaced by a larger-diameter ball, which puts the flat armature  40  in a position that corresponds to its position when the electromagnet is excited. In this position, the flat armature  40  and the rim  43  of the insert are machined jointly, so that a common plane is created. The stroke of the flat armature  40  can thus be adjusted exactly to the desired dimension. The residual air gap is also set exactly by means of the thickness of the shim  55 . The entire arrangement has the advantage that the insert can easily be machined to the required dimensions and is fastened in an equally simple way, together with the housing of the magnet valve, in the housing of the injection valve. 
     The foregoing relates to a preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.