Abstract:
A fuel injection valve for internal combustion engines having a valve body in which a bore is embodied, a valve seat face, at least one injection opening embodied on the end toward the combustion chamber of the bore, and at least one injection opening connecting the bore with the combustion chamber of the engine. A nozzle needle is longitudinally displaceably guided in the bore and on its end toward the combustion chamber it has a sealing face, which cooperates with the valve seat face and thus controls the at least one injection opening. The nozzle needle has a central longitudinal bore, in which an inner needle is disposed that is fixed immovably relative to the valve body. The nozzle needle is guided over at least part of its length on the inner needle, so that the nozzle needle is kept exactly centrally in the bore at all times.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 02/01094, filed on Mar. 26, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention is directed to an improved fuel injection valve for internal combustion engines. 
   2. Description of the Prior Art 
   A fuel injection valve for internal combustion engines of the kind with which this invention is concerned is known for instance from German Patent Disclosure DE 43 03 813 A1. A fuel injection valve of this kind has a valve body, in which a bore is embodied on whose end toward the combustion chamber a valve seat face and at least one injection opening are embodied. A pistonlike nozzle needle is disposed longitudinally displaceably in the bore and is guided sealingly in the bore in a portion remote from the combustion chamber. The nozzle needle tapers toward the combustion chamber, forming a pressure shoulder, and on its end toward the combustion chamber it changes over into a valve sealing face that cooperates with the valve seat face and thus by means of the longitudinal motion of the nozzle needle opens and closes the at least one injection opening. At the level of the pressure shoulder, a radial enlargement of the bore forms a pressure chamber, which continues, surrounding the nozzle needle, in the form of an annular conduit as far as the valve seat face. On its end remote from the combustion chamber, the nozzle needle is acted upon by a closing force exerted in the direction of the valve seat. At the same time, a hydraulic force acts on the nozzle needle counter to this closing force, which because of the fuel pressure in the pressure chamber and the attendant hydraulic force is exerted on the pressure shoulder. 
   In the substantially conical valve seat face, generally a plurality of injection openings are distributed uniformly over the circumference of the valve body. For uniform injection through all of these injection openings, it is important that in the opening motion of the nozzle needle, the nozzle needle and thus also the substantially conical valve sealing face remain precisely central relative to the bore and thus to the valve sealing face, so that a uniform flow of fuel out of the pressure chamber to the injection openings can be accomplished. Since the nozzle needle is now guided in the bore on the portion remote from the combustion chamber, once the valve sealing face lifts from the valve seat face, there is a very long free length of the nozzle needle between the guided portion and the valve seat face, so that it can easily happen that the nozzle needle will become tilted in the bore, resulting in an uneven inflow of fuel to the injection openings. Precisely at the beginning of the opening stroke motion when there is only a very small gap between the valve sealing face and the valve seat face, such tilting has a major influence on the injection pattern and hence on the quality of combustion. 
   SUMMARY AND ADVANTAGES OF THE INVENTION 
   The fuel injection valve of the invention has the advantage over the prior art that the nozzle needle is guided by an inner needle, so that exact centering in the bore is assured over the entire stroke range of the nozzle needle. The nozzle needle has a central longitudinal bore, in which the inner needle is disposed, and the inner needle is fixed relative to the valve body. In particular, the nozzle needle is guided in its end portion toward the valve seat on the inner needle, so that no tilting of the nozzle needle can occur in the region of the valve seat. 
   In an advantageous feature of the subject of the invention, the inner needle has at least two radially outward-protruding fixation ribs which rest on the inner wall of the bore and thus wedge the inner needle in the bore. This assures easy installation of the inner needle without having to make any structural changes or preparations for receiving the inner needle. It can also be provided that there are more than two fixation ribs, which are then preferably distributed uniformly over the circumference of the inner needle. 
   In another advantageous feature of the subject of the invention, the inner needle, in its middle region, has an undercut, so that only in an end portion toward the combustion chamber and an end portion remote from the combustion chamber is the nozzle needle is guided on the inner needle. This results in fewer friction losses between the inner needle and the outer needle, and the danger of seizing of the outer needle on the inner needle is reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Two exemplary embodiments of the fuel injection valve of the invention are described herein below, with reference to the drawings, in which: 
       FIG. 1  is a longitudinal section through a fuel injection valve of the invention; 
       FIG. 2 , an enlargement of  FIG. 1  in the region of the valve body; 
       FIG. 3 , a cross section through  FIG. 2  along the line III—III; and 
       FIG. 4 , an enlargement of  FIG. 1  in the region of the valve body of a further exemplary embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a longitudinal section through a fuel injection valve is shown. A valve holding body  1  is braced axially against a valve body  3  by a lock nut  4 . A bore  7  is embodied in the valve body  3 , and embodied on its end toward the combustion chamber is an essentially conical valve seat face  10 , in which there is at least one injection opening  9 . A nozzle needle  12  embodied in pistonlike fashion is disposed in the bore  7 , and on its end toward the combustion chamber it has a substantially frustoconical valve sealing face  17  which cooperates with the valve seat face  10 , so that upon contact of the valve sealing face  17  with the valve seat face  10 , the injection openings  9  are closed. The nozzle needle  12  is guided sealingly in the bore  7  in a portion remote from the combustion chamber, and the sealingly guided portion of the nozzle needle  12  has a larger diameter than the portion of the nozzle needle  12  end toward the combustion chamber, so that at the transition, a pressure shoulder  22  is formed. By a radial enlargement of the bore  7  at the level of the pressure shoulder  22 , a pressure chamber  16  is formed, which toward the combustion chamber continues in the form of an annular conduit surrounding the nozzle needle  12 , extending as far as the valve seat face  10 . Via an inlet conduit  30  extending in the valve body  3  and in the valve holding body  1 , the pressure chamber  16  communicates with a high-pressure connection  49 , by way of which fuel from a high-pressure fuel source, not shown in the drawing, can be pumped into the pressure chamber. In  FIG. 2 , for the sake of clarity, an enlarged view of  FIG. 1  in the region of the valve body  3  is shown, and  FIG. 3  shows a cross section through  FIG. 2  along the line III—III. The nozzle needle  12  has a central longitudinal bore  19 , which acts here as a guide bore and in which an inner needle  14  is disposed. The inner needle  14 , on its end toward the combustion chamber, has a contact face  11 , which is embodied conically and on which the also conically embodied valve seat face  10  rests. Because of the conical shape of the two faces, the contact face  11  is centrally fixed, so that the end toward the combustion chamber of the inner needle  14  is aligned precisely in the direction of the longitudinal axis  6  of the bore  7 . On the end remote from the combustion chamber, the inner needle  14  has three fixation ribs  20 , which extend outward radially from the inner needle  14 , where they are wedged in the bore  7 . The three fixation ribs  20  are distributed uniformly over the circumference of the inner needle  14 , so that the inner needle  14  is fixed immovably by the fixation ribs  20  in the valve body  3 , precisely in the direction of the longitudinal axis  6  of the bore  7 . Provision can also be made for there to be more than three fixation ribs  20  on the nozzle needle  12 , which are then likewise preferably distributed uniformly over the circumference of the inner needle  14 . The nozzle needle  12  has corresponding recesses  15 , which receive the fixation ribs  20  and thus assure the longitudinal displaceability of the nozzle needle  12  on the inner needle  14 . Between the end toward the combustion chamber of the fixation ribs  20  and the recess  15 , a gap  36  remains, which in the opening position of the nozzle needle as well assures that the nozzle needle  12  will not come to rest on the fixation ribs  20  of the inner needle  14 , and thus the inner needle  14  will not be improperly shifted out of its centrally fixed position by being constantly hit by the nozzle needle. 
   The nozzle needle  12  rests, on its end remote from the combustion chamber, on a cylindrical thrust pad  37 , which is disposed in a spring chamber  32  disposed in the valve holding body  1 . Between the end remote from the combustion chamber of the spring chamber  32  and the thrust pad  37  is a closing spring  34  prestressed for compression, which via the thrust pad  37  acts on the nozzle needle  12  and thus presses the nozzle needle  12  into its closing position—that is, when the valve sealing face  17  rests on the valve seat face  10 . A piston bore  38  is embodied in the valve holding body  1  coaxially with the bore  7  and discharges into the spring chamber  32 . A pressure piston  39  is disposed longitudinally displaceably in the piston bore  38  and on its end toward the combustion chamber it protrudes into the spring chamber  32 , which it rests on the thrust pad  37  and with its end face  41  remote from the combustion chamber it defines a control chamber  40 . The opening stroke of the nozzle needle  12  is stopped here by the impact of the pressure piston on the end remote from the combustion chamber of the piston bore  38 . The control chamber  40  communicates via an inlet throttle  42  with the inlet conduit  30  and via an outlet throttle  43  with a leak fuel chamber  48  embodied in the valve holding body  1 . This leak fuel chamber  48  communicates with a leak fuel system, not shown in the drawing, and is thus constantly pressureless. A magnet armature  45  is disposed in the leak fuel chamber  48 , and a sealing ball  47  is disposed on its end toward the control chamber  40 . The magnet armature  45  is urged by a spring  53  in the direction of the control chamber  40 , so that the sealing ball  47  is pressed onto the outlet throttle  43  and closes the outlet throttle  43 . 
   In the valve holding body  1 , there is an electromagnet  51 , surrounding the spring  43 , which when suitably supplied with current exerts an attracting force on the magnet armature  45 , thus pulling it in the direction of the electromagnet  51 , counter to the force of the spring  53 , so that the sealing ball  47  uncovers the outlet throttle  43 . If no current is supplied to the electromagnet  51 , the spring  53  presses the magnet armature  45  and thus the sealing ball  47  back onto the outlet throttle and thus closes off the control chamber  40  from the leak fuel chamber  48 . 
   The mode of operation of the fuel injection valve is as follows: Via the high-pressure connection  49 , fuel under high pressure is constantly carried as far as the inside of the pressure chamber  16 , so that a constant, predetermined high fuel pressure prevails in the pressure chamber  16 . The result is a hydraulic force on the pressure shoulder  22  of the nozzle needle  12  that is oriented in the direction of the thrust pad  37 . If no injection is meant to take place, then no current is supplied to the electromagnet  51 , and thus the outlet throttle  43  is closed by the sealing ball  47 . As a result, because of the inlet throttle  42 , the same pressure prevails in the control chamber  40  as in the inlet conduit  30  or in the pressure chamber  16 , resulting in a corresponding hydraulic force on the end face  41 , remote from the combustion chamber, of the pressure piston  39 . Since the pressure piston  39  has a larger diameter, and thus a larger hydraulically effective surface area, than the shoulder  22  on nozzle needle  12 , the force exerted by the pressure piston  39  on the nozzle needle  12  via the thrust pad  37  predominates, and thus the nozzle needle  12  stays in the closing position and closes the injection openings  9 . If an injection is to occur, then the electromagnet  51  is supplied with current, and the magnet armature  45  moves in the direction of the electromagnet  51 . As a result, the sealing ball  47  uncovers the outlet throttle  43 , and the control chamber  40  is made to communicate with the leak fuel chamber  48 . This causes the pressure in the control chamber  40  to drop, so that now the hydraulic force on the pressure shoulder  22  of the nozzle needle  12  predominates, and the nozzle needle lifts from the valve seat face  10  and uncovers the injection openings  9 . The closing spring  34  plays only a subordinate role here and serves primarily to keep the nozzle needle in the closed position when the fuel injection system has been shut off. If the injection is to be terminated, the electromagnet  51  is switched to be without current, and the high fuel pressure of the inlet conduit  30  builds up again in the control chamber  40 . 
   In installing the nozzle needle  12  and the inner needle  14  in the bore  7 , the procedure is for instance as follows; The inner needle  14  is introduced into the nozzle needle  12 , and then the two are introduced jointly into the bore  7 . The annular ribs  20  of the inner needle  14  are embodied here such that they have to be pressed into the bore  7 , resulting in an immovable fixation of the inner needle  14  in the bore  7  along the longitudinal axis  6  thereof. The nozzle needle  12  need not be fixed any further, because it is unambiguously disposed in the bore  7  by the fixation of the inner needle  14 . Next, the valve holding body  1 , with the pressure piston  39  already disposed in it and with the closing spring  34  and the thrust pad  37 , is braced against the valve body  3  by means of the lock nut  4 . 
   In  FIG. 4 , a further exemplary embodiment of the fuel injection valve of the invention is shown. Here, the inner needle  14  does not have a constant outer diameter; instead, between a first guide portion  114  toward the combustion chamber and a second guide portion  214  remote from the combustion chamber, it has an undercut  25 , in the vicinity of which the outer diameter of the inner needle  14  is reduced. The nozzle needle  12  is guided only over the first guide portion  114  and the second guide portion  214 , thus lessening the danger of seizing of the nozzle needle  12  on the inner needle  14 , and reducing both wear and friction of the nozzle needle  12  on the inner needle  14 . Provision can also be made to omit the second guide portion  214 ; then the nozzle needle  12  is guided on the inner needle  14  only over the first guide portion  114 . The nozzle needle  12  is already guided sealingly on its outer jacket face in the portion of the bore remote from the combustion chamber, and so guidance of the nozzle needle  12  on the inner needle  14  in this region is not absolutely necessary, depending on the demands made of the fuel injection valve. 
   The foregoing relates to 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.