Patent Publication Number: US-6901915-B2

Title: Fuel injection device for an internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 02/03140 filed on Aug. 23, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is directed to an improved fuel injection system for an internal combustion engine of the type having a high pressure pump and a fuel injector for each cylinder of the engine. 
   2. Description of the Prior Art 
   One fuel injection system of the type with which this invention is concerned is known from European Patent Disclosure EP 0 957 261 A1. For each cylinder of the engine, this known fuel injection system has one high-pressure fuel pump and one fuel Injection valve communicating with it. The high-pressure fuel pump has a pump piston, which is driven in a reciprocating motion by the engine and which defines a pump work chamber that communicates with a pressure chamber of the fuel injection valve. The fuel Injection valve has an Injection valve member, by which at least one injection opening is controlled, and which is movable by the pressure prevailing in the pressure chamber in an opening direction counter to a closing force. By means of an electrically controlled control valve, a communication of the pump work chamber with a relief chamber is controlled in order to control the fuel injection. When the pressure in the pump work chamber and thus in the pressure chamber of the fuel injection valve reaches the opening pressure, the injection valve member moves In the opening direction and uncovers the at least one injection opening. The injection cross section that is controlled by the injection valve member in the process is always the same size. This does not enable optimal fuel injection under all engine operating conditions. 
   SUMMARY OF THE INVENTION 
   The fuel injection system of the invention has the advantage over the prior art that by means of the second injection valve member, an additional injection cross section can be opened or closed with the at least one injection opening as a function of engine operating parameters, so that the injection cross section can be adapted optimally to engine operating conditions. 
   Various advantageous features and refinements of the fuel injection system of the invention are disclosed. One embodiment makes simple control of the control pressure in the control chamber possible. In another this control can be attained without requiring any additional component. A further embodiment makes it possible upon the supply onset of the pump piston initially to uncover only a slight injection cross section with the at least one injection opening, and upon a greater stroke of the pump piston additionally to uncover a larger injection cross section with the at least one second injection opening. The stroke length of the pump piston beyond which the at least one second injection opening is opened may be varied. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the invention will become apparent from the description contained herein below, taken in conjunction with the drawings, in which: 
       FIG. 1  shows a fuel injection system for an internal combustion engine schematically in a first exemplary embodiment; 
       FIG. 2  is an enlarged view of a detail of a fuel injection valve, marked II in  FIG. 1 ; and 
       FIG. 3  shows the fuel injection system in a second exemplary embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIGS. 1-3 , a fuel injection system for an internal combustion engine of a motor vehicle is shown. The engine is preferably a self-igniting internal combustion engine. The fuel injection system is embodied as a so-called unit injector or pump-line-nozzle system and for each cylinder of the engine has one high-pressure fuel pump  10  and one fuel injection valve  12  communicating with it. In an embodiment as a pump-line-nozzle system, the high-pressure fuel pump  10  is disposed at a distance from the fuel injection valve  12  and communicates with it via a line. In the exemplary embodiments shown, the fuel injection system is embodied as a unit injector, in which the high-pressure fuel pump  10  and the fuel injection valve  12  communicate directly with one another and form a structural unit. The high-pressure fuel pump  10  has a pump piston  18 , guided tightly in a cylinder bore  16  in a pump body  14 , and this piston is driven in a reciprocating motion by a cam  20  of a camshaft of the engine, counter to the force of a restoring spring  19 . In the cylinder  16 , the pump piston  18  defines a pump work chamber  22 , in which in the pumping stroke of the pump piston  18  fuel is compressed at high pressure. In the intake stroke of the pump piston  18 , fuel from a fuel tank  24  of the motor vehicle is delivered to the pump work chamber  22  in a manner not shown in further detail. 
   The fuel injection valve  12  has a valve body  26 , which can be embodied in multiple parts and in which a first injection valve member  28  is guided longitudinally displaceably in a bore  30 . In its end region toward the combustion chamber of the cylinder of the engine, the valve body  26  has at least one first injection opening, and preferably a plurality of first injection openings  32 , which are distributed over the circumference of the valve body  26 . The first injection valve member  28 , in its end region toward the combustion chamber, has a sealing face  34 , which for instance is approximately conical, and which cooperates with a valve seat  36  embodied in the end region of the valve body  26  oriented toward the combustion chamber, and from this valve seat or downstream of it, the first injection openings  32  lead away. Between the injection valve member  28  and the bore  30  in the valve body  26 , toward the valve seat  36 , there is an annular chamber  38 , which in its end region remote from the valve seat  36  changes over, by means of a radial widening of the bore  30 , into a pressure chamber  40  that surrounds the first injection valve member  28 . At the level of the pressure chamber  40 , as a result of a cross-sectional reduction, the first injection valve member  28  has a pressure shoulder  42 . The end of the first injection valve member  28  remote from the combustion chamber is engaged by a first prestressed closing spring  44 , by which the first injection valve member  28  is pressed toward the valve seat  36 . The first closing spring  44  is disposed in a first spring chamber  46  of the valve body  26 , which chamber adjoins the bore  30 . 
   The first injection valve member  28  of the fuel injection valve  12  is embodied as hollow, and in it, a second injection valve member  128  is guided displaceably in a bore embodied coaxially in the injection valve member  28 . By means of the second injection valve member  128 , at least one second injection opening  132  in the valve body  26  is controlled. The at least one second injection opening  132  is offset toward the combustion chamber in the direction of the longitudinal axis of the injection valve members  28 ,  128  from the at least one first injection opening  32 . The second injection valve member  128 , in its end region toward the combustion chamber, has a sealing face  134 , which for instance is approximately conical, and which cooperates with a valve seat  136 , embodied in the valve body  26  in its end region toward the combustion chamber, from which or downstream of which valve seat the second injection openings  132  lead away. The second injection valve member  128  can be embodied in two parts and can have one part, toward the combustion chamber, that has the sealing face  134  and one second part, pointing away from the combustion chamber, that adjoins the first part. Near the end toward the combustion chamber of the second injection valve member  128 , a pressure face  142  is embodied on the injection valve member, and when the first injection valve member  28  is opened, the pressure prevailing in the pressure chamber  40  acts on this pressure face. 
   A second spring chamber  146  is embodied in the valve body  26 , adjacent to the first spring chamber  46  in the direction away from the combustion chamber, and in this second spring chamber, a second closing spring  144 , acting on the second injection valve member  128 , is disposed. The first injection valve member  28  protrudes with its end into the first spring chamber  46  and is braced on the first closing spring  44 . The first closing spring  44  is braced with its end remote from the first injection valve member  28  on a sleeve  47 , which is disposed between the first spring chamber  46  and the second spring chamber  146  and which for instance is press-fitted into the valve body  26 . The second injection valve member  128  protrudes through the sleeve  47  into the second spring chamber  146 , and it is braced on the second closing spring  144  via a spring plate  147 . The second closing spring  144  is braced, by its end remote from the second valve member  128 , on the bottom of the second spring chamber  146 . By means of the spring plate  147 , a control chamber  50  is defined in the second spring chamber  146 . 
   From the pump work chamber  22 , a conduit  52  leads through the pump body  14  and the valve body  26  into the pressure chamber  40  of the fuel injection valve  12 . By means of an electrically controlled valve  23 , a communication of the pump work chamber  22  with a relief chamber is controlled; by way of example, the fuel tank  24  can serve at least indirectly as this relief chamber, or a region in which a pressure that is somewhat elevated compared to the fuel tank  24  is maintained can serve as the relief chamber. As long as no fuel injection is to occur, the control valve  23  is intended to keep the communication of the pump work chamber  22  with the relief chamber open, so that high pressure cannot build up in the pump work chamber  22 . When a fuel injection is to occur, the pump work chamber  22  is disconnected from the relief chamber by the control valve  23 , so that upon the pumping stroke of the pump piston  18 , high pressure can build up in the pump work chamber  22 . The control valve  23  can be embodied as a magnet valve or as a piezoelectric valve. 
   The fuel injection system is shown in a first exemplary embodiment in  FIGS. 1 and 2 . In the first exemplary embodiment, the pump piston  18  has a conduit  60 , extending in this piston, that discharges at one end into the pump work chamber  22 , in a portion on the face end of the pump piston  18  extending in the direction of the longitudinal axis of the pump piston  18 , and on the other end discharges into a portion, extending approximately radially to the longitudinal axis of the pump piston  18 , at the jacket face of the pump piston  18  at some distance from the face end. The radial portion of the conduit  60  can for instance be embodied diametrically continuously by the pump piston  18 . In the pump body  14 , in the cylinder bore  16 , an encompassing annular groove  62  is embodied, which communicates with the control chamber  50  via a conduit  63  extending through the pump body  14  and the valve body  26 . Thus by means of the pump piston  18 , as a function of its stroke, a communication of the control chamber  50  with the pump work chamber  22  is controlled. The pump work chamber  22  serves as a pressure source for controlling the pressure in the control chamber  50 . At a slight pumping stroke of the pump piston  18  into the pump work chamber  22 , the orifice of the conduit  60  is located on the jacket face of the pump piston  18 , coinciding with the annular groove  62 , so that the control chamber  50  communicates with the pump work chamber  22 . As the pumping stroke of the pump piston  18  lengthens into the pump work chamber  22 , the orifice of the conduit  60  is offset from the annular groove  62  on the jacket face of the pump piston  18 , so that the control chamber  50  is disconnected from the pump work chamber  22 . 
   Between the camshaft of the engine having the cam  20  and the pump piston  18 , an intermediate shaft  70  is disposed, on which a transmission element  71  in the form of a two-armed tilt lever is disposed, which lever rolls with one end over the cam  20 , for instance via a roller  72 , and is pivotably connected by its other end to the pump piston  18 . It is provided that the location of the intermediate shaft  70  having the tilt lever  71  is variable, as a result of which the outset stroke position of the pump piston  18  can be varied. In  FIG. 1 , the intermediate shaft  70  with the tilt lever  71  and the left half of the pump piston  18  is shown in solid lines in a first position, in which the pump piston  18  has an outset stroke position in which the pump piston  18  plunges relatively far into the cylinder bore  16  in the pump body  14 . In  FIG. 1 , the intermediate shaft  70  with the tilt lever  71  and the right half of the pump piston  18  is shown in dashed lines in a second position, in which the pump piston  18  in its outset stroke position plunges to a lesser extent than in the first position into the cylinder bore  16  in the pump body  14 . 
   An adjustment of the location of the intermediate shaft  70  can be made for instance by means of a hydraulic adjusting device  74 , by which the bearing of the intermediate shaft  70  is shifted. Alternatively, the adjusting device  74  can be embodied as an eccentric element, by which the bearing of the intermediate shaft  70  is shifted. 
   The function of the fuel injection system in the first exemplary embodiment will now be explained. Upon the intake stroke of the pump piston  18 , the control valve  23  is opened, so that fuel from the fuel tank  24  reaches the pump work chamber  22 . In the pumping stroke of the pump piston  18 , the onset of the fuel injection is defined as a result of the fact that the control valve  23  closes, so that the pump work chamber  22  is disconnected from the relief chamber, and high pressure builds up in the pump work chamber  22 . As a function of engine operating parameters, the intermediate shaft  70  is adjusted to the requisite position by the adjusting device  74 . When the pump piston  18  is in the outset stroke position shown in the right-hand half of  FIG. 1 , control chamber  50  communicates with the pump work chamber  22 , so that a high control pressure prevails in the control chamber  50 . If the pressure in the pump work chamber  22  and thus in the pressure chamber  40  of the fuel injection valve  12  is so high that the pressure force generated by it on the first injection valve member  28  via the pressure shoulder  42  is greater than the force of the first closing spring  44 , then the fuel injection valve  12  opens, because the first injection valve member  28  lifts with its sealing face  34  from the valve seat  36  and uncovers the at least one first injection opening  32 . The control pressure in the control chamber  50  acts via the spring plate  147  on the second injection valve member  128  and reinforces the closing spring  144 , so that the pressure force, acting on the second injection valve member  128  via the pressure face  142  as a result of the pressure prevailing in the pressure chamber  40  does not suffice to open the second injection valve member  128 . Thus with the first injection openings  32  of the fuel injection valve  12 , only a portion of the total injection cross section is opened, and accordingly only a slight fuel quantity is injected. 
   When the pump piston  18  executes its supply stroke further, the conduit  60  in the pump piston  18  moves away from coincidence with the annular groove  62 , and so the control chamber  50  is disconnected from the pump work chamber  22 . The control chamber  50  preferably communicates with a relief chamber via at least one throttle restriction, so that the pressure in the control chamber  50  decreases. In this case, now only the force of the second closing spring  144 , and possibly a slight pressure force, act on the second injection valve member  128 , so that the pressure force acting on the second injection valve member  128  via the pressure face  142  as a result of the pressure prevailing in the pressure chamber  40  does suffice to open the second injection valve member  128  as well, so that the at least one second injection opening  132  is uncovered as well. Thus the entire injection cross section of the fuel injection valve  12  is opened, and a larger fuel quantity is injected. The end of the fuel injection is determined by the opening of the control valve  23 , as a result of which the pump work chamber  22  communicates with the relief chamber, and high pressure can no longer build up in it. 
   The pump piston  18  can have one further conduit  65 , which upon a maximal stroke of the pump piston  18  into the pump work chamber  22  comes into coincidence with the annular groove  62  and establishes a communication with a relief chamber. At the maximal stroke of the pump piston  18 , the control chamber  50  thus communicates with a relief chamber and is pressure-relieved. 
   It can be provided that the injection cross sections formed by the first injection openings  32  and the second injection openings  132  are at least of approximately equal size, so that when only the first injection valve member  28  is opened, half of the total injection cross section is uncovered. Alternatively, it can be provided that the first injection openings  32  form a larger or smaller injection cross section than the second injection openings  132 . 
   When the pump piston  18  is in its outset stroke position shown in the left half of  FIG. 1 , the conduit  60  of the pump piston  18  is not in coincidence with the annular groove  62 , and so the control chamber  50  is disconnected from the pump work chamber  22 . In this case, when the opening pressure in the pump work chamber  22  is reached, both injection valve members  28  and  128  open at least approximately simultaneously, and the total injection cross section of the fuel injection valve  12  is uncovered. 
   The variation in the position of the intermediate shaft  70  and thus in the outset stroke position of the pump piston  19  by the adjusting device  74  is effected as a function of such engine operating parameters as the rpm, load, and temperature, and optionally still other operating parameters. The adjusting device  74  is triggered by an electric control unit  76 , by which the control valve  23  is also triggered. If, taking these operating parameters into account, only a slight fuel quantity is to be injected at the onset of the fuel injection, then by means of the control unit  76 , the adjusting device  74  is triggered in such a way that the intermediate shaft  70  and thus the pump piston  18  are in the outset stroke position of the pump piston shown in the right half of  FIG. 1 , and at the onset of the fuel injection, only the first injection valve member  28  of the fuel injection valve  12  opens. If taking these operating parameters into account, only a greater fuel quantity is to be injected even at the outset of the fuel injection, then by means of the control unit  76 , the adjusting device  74  is triggered in such a way that the intermediate shaft  70  and thus the pump piston  18  are in the outset stroke position of the pump piston shown in the left half of  FIG. 1 , and even at the outset of the fuel injection, both injection valve members  28  and  128  of the fuel injection valve  12  open. If the engine has a plurality of cylinders, then one high-pressure fuel pump  10  for each cylinder is provided, but for driving it only one camshaft  20  and one intermediate shaft  70  is provided. For varying the position of the intermediate shaft  70  and the outset stroke position of the pump pistons  18  of all the high-pressure fuel pumps  10 , only a single adjusting device  74  is needed. 
   In  FIG. 3 , the fuel injection system is shown in a second exemplary embodiment, in which the fundamental layout is the same as in the first exemplary embodiment. In a departure from the first exemplary embodiment, however, in the second exemplary embodiment it is not the pump work chamber  22  that is used as a pressure source for controlling the pressure in the control chamber  50 , but rather a fuel inlet, through which upon the intake stroke of the pump piston  18 , fuel is delivered to the pump work chamber  22 . Communicating with the fuel inlet is a fuel conduit  80  embodied in the pump body  14 ; this conduit discharges at the jacket of the cylinder bore  16  in which the pump piston  18  is guided. In a region offset circumferentially from the orifice of the fuel conduit  80 , the conduit  63  that leads to the control chamber  50  discharges at the jacket of the cylinder bore  16 . In the pump piston  18 , a conduit  82  is embodied, which extends for instance radially to the longitudinal axis of the pump piston  18  and which discharges at the jacket of the of the pump piston  18 . By means of the pump piston  18 , as a function of its stroke position, the communication of the fuel conduit  80  with the conduit  63  to the control chamber  50  is controlled by the conduit  82  of the pump piston. In  FIG. 3 , the intermediate shaft  70  with the pump piston  18  is again shown in various positions. In an outset stroke position shown in the right half of the pump piston  18  in  FIG. 3 , the conduit  82  of the pump piston  18  is in coincidence with the orifice of the fuel conduit  80  and with the orifice of the conduit  63  leading to the control chamber  50 , so that the control chamber  50  communicates with the fuel conduit  80 . In the control chamber  50 , the elevated pressure in the fuel conduit  80  is thus operative, so that in the fuel injection valve  12 , the second injection valve member  128  remains in its closed position, and only the first injection valve member  28  opens. In the outset stroke position shown for the left half of the pump piston  18 , the conduit  82  of the pump piston  18  is not in coincidence with the orifice of the fuel conduit  80  and the orifice of the conduit  63  leading to the control chamber  50 , but instead is offset from them, so that the control chamber  50  is disconnected from the fuel conduit  80 . Thus an elevated pressure is not operative in the control chamber  50 , and in the fuel injection valve  12 , both injection valve members  28  and  128  open. 
   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.