Patent Publication Number: US-6908043-B2

Title: Fuel injection device for internal combustion engines

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 02/03449 filed on Sep. 14, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is directed to an improved fuel injection system including a plurality of injectors for injecting fuel into the cylinders of an internal combustion engine. 
   2. Description of the Prior Art 
   In a fuel injection system of illustrated in  FIG. 1  of German Patent Disclosure DE 199 39 419 A1, the injection pressure is also used as the control pressure for a control chamber. For a preinjection and a postinjection, a local pressure reservoir is necessary. 
   SUMMARY OF THE INVENTION 
   The fuel injection system of the invention has the advantage over the prior art that by means of a stepped piston, the high pressure for the injection and the control pressure for the control chamber are generated separately from one another. As a result, preinjections and/or postinjections that are controllable exactly are possible. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Two exemplary embodiments of the fuel injection system of the invention are explained in further detail in the ensuing description, taken in conjunction with the drawings, in which: 
       FIG. 1  schematically shows the essential components of a first fuel injection system of the invention, with a graduated pump piston and with a closing piston acting on the valve member; and 
       FIG. 2  schematically shows the essential components of a second fuel injection system of the invention, with a graduated pump piston and with a deflection piston acting on the valve member. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The fuel injection system shown in  FIG. 1  for an internal combustion engine includes a unit injector (UI)  1 , in which the fuel is compressed to a higher injection pressure by means of a pump piston  2  and is carried away via an injection line  3  to an injection valve (injector)  4  protruding into the combustion chamber of the engine to be supplied. One unit injector  1  per engine cylinder is built into a cylinder head. The pump piston  2  is driven by a cam  5  of the engine camshaft counter to the action of a restoring spring  6 . 
   In an axial guide bore  7  of the injection valve  4 , a pistonlike valve member (nozzle needle)  8  with a conical valve sealing face  9  is displaceably supported; this face is pressed by a closing spring  10  against a conical valve seat face  11  of the valve housing and closes the injection openings  12  provided there. The injection line  3  discharges in the injection valve  4  into an annular nozzle chamber  13 , from which an annular gap between the guide bore  7  and the valve member  8  extends as far as the valve seat face  11 . In the region of the nozzle chamber  13 , the valve member  8  has a first control face  14 , embodied as a pressure shoulder, at which the fuel delivered via the injection line  3  engages the valve member  8  in the opening direction (that is, inward). The face end of the valve member  8  remote from the valve sealing face  9  is engaged by a closing piston  15 , whose face end remote from the valve sealing face  9  forms a second control face  16 . The second control face  16  defines a control chamber  17  and acts in the valve closing direction. 
   The pump piston  2 , with its face end remote from the cam  5 , defines a first compression chamber  18  communicating with the injection line  3 , and with an annular shoulder  19 , it defines a second compression chamber  20 , which communicates with the control chamber  17  via a throttle  21 . The two compression chambers  18 ,  20  each communicate via a respective check valve  22 ,  23  with a supply line  24  for the fuel. The first compression chamber  18 , from which the injection line  3  begins, can be made to communicate via a first valve  25 , and the control chamber  17  can be made to communicate via a second valve  26 , with a relief line (leak fuel)  27 . The two valves  25 ,  26  are embodied as 2/2-way valves with piezoelectric actuators  28 ,  29 . In the first compression chamber  18 , the high pressure for the injection is generated, and in the second compression chamber  20 , the high pressure for the control function of the control chamber  17  is generated. The second control face  16  is larger than the first control face  14 , so that when the valves  25 ,  26  are closed and there is an identical high pressure in the nozzle chamber  13  and in the control chamber  17 , the valve member  8  closes the injection openings  12 . 
   During the pumping stroke of the pump piston  2 , the two compression chambers  18 ,  20  are filled with fuel via the supply line  24 . By means of the compression stroke of the pump piston  2 , when both valves  25 ,  26  are closed, the fuel located in the compression chambers  18 ,  20  is compressed to a higher pressure; the check valves  22 ,  23  prevent the return flow of compressed fuel back into the supply line  24 . 
   During the compression stroke of the pump piston  2  and with the control chamber  17  pressure-relieved (that is, with the second valve  26  open), the onset of the injection event is initiated by closure of the first valve  25 . The higher injection pressure builds up in the first compression chamber  18  and thus in the nozzle chamber  13  as well. As soon as the fuel pressure prevailing in the nozzle chamber  13  suffices to open the valve member  8  under pressure control, counter to the action of the closing spring  10 , the fuel is injected into the combustion chamber. If the second valve  26  is now closed as well, then a higher fuel pressure builds up in the second compression chamber  20  and thus in the control chamber  17  as well. The control chamber  17  is no longer pressure-relieved, and so the valve member  8  closes the injection openings  12 . Opening the second valve  26  relieves the control chamber  17  of pressure again, and the valve member  8  opens under stroke control, so that a postinjection at the fuel pressure prevailing in the nozzle chamber  13  is performed. If the fuel pressure prevailing in the nozzle chamber  13  no longer suffices to open the valve member  8 , then the closing spring  10  closes the valve member  8 , and the injection event is ended. 
   The fuel injection system shown in  FIG. 2 , instead of a closing piston, uses a deflection piston  115 , whose face end remote from the valve sealing face  9  forms the second control face  116  and defines the control chamber  117 . The closing spring  110  is braced on the end of the deflection piston  115  remote from the second control face  116  and on a head  128  of the valve member  108 . The deflection piston  115  and the head  128  are guided displaceably in a common axial guide bore  129  of the injection valve  104 . 
   When the second valve  26  is open, the control chamber  117  is pressure-relieved via the relief line  27 , and the deflection piston  115  is displaced into its outermost position in the valve opening direction, so that the fuel pressure prevailing in the nozzle chamber  13  suffices to open the valve member  108  counter to the closing spring  110 . When the second valve  26  is closed, the deflection piston  115  is displaced in the valve closing direction by the fuel pressure prevailing in the control chamber  117 , and as a result the closing spring  110  is compressed so much that the fuel pressure prevailing in the nozzle chamber  13  no longer suffices to open the valve member  108 . 
   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.