Abstract:
A fuel injection system for an internal combustion engine including a fuel injector which can be subjected to fuel at high pressure and is actuatable via a metering valve device by which the pressure in a pressure booster control chamber is controllable such that the pressure in a pressure booster pressure chamber, defined by a pressure booster piston, that can be filled with fuel from the high-pressure fuel source via a filling path in which a check valve is disposed and that is in communication with an injection valve member pressure chamber, is increased by the pressure booster piston such that an injection valve member opens for injecting fuel, whereupon fuel is positively displaced out of a damping chamber via a damping path, in which a damping throttle is disposed. To assure stable injection performance, the damping path is embodied such and connected in such a way to the filling path that the fuel positively displaced from the damping chamber via the damping throttle in an injection event reaches the filling path of the pressure booster pressure chamber via the damping path.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based on German Patent Application 10 2004 053 274.5 filed Nov. 4, 2004, upon which priority is claimed.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to an improved system for injecting fuel into a combustion chamber of an internal combustion engine, and more particularly to such a system having a fuel injector which can be subjected to fuel at high pressure via a high-pressure fuel source and which is actuatable via a metering valve device, by which device the pressure in a pressure booster control chamber is controllable such that the pressure in a pressure booster pressure chamber, defined by a pressure booster piston, that can be filled with fuel from the high-pressure fuel source via a filling path in which a check valve is disposed and that is in communication with an injection valve member pressure chamber, is increased by the pressure booster piston such that an injection valve member opens for injecting fuel, whereupon fuel is positively displaced out of a damping chamber via a damping path, in which a damping throttle is disposed.  
         [0004]     2. Description of the Prior Art  
         [0005]     From German Published Patent Disclosure DE 102 29 415 A1, a system for injecting fuel into a combustion chamber of an internal combustion engine is known, having a fuel injector which can be subjected to fuel at high pressure via a high-pressure source and which is actuatable via a metering valve. An injection valve member, which is urged in the closing direction by a closing force, is surrounded by a pressure chamber. To damp the opening speed of the injection valve member, such as a nozzle needle, without impairing its fast closure, the injection valve member is assigned a damping element that is movable independently of it and that defines a damping chamber and has at least one overflow conduit for connecting the damping chamber with a further hydraulic chamber. The damping element may be embodied as a damping piston, which is surrounded by the further hydraulic chamber.  
       OBJECT AND SUMMARY OF THE INVENTION  
       [0006]     The object of the invention is to create a system for injecting fuel into a combustion chamber of an internal combustion engine, having a fuel injector, which can be subjected to fuel at high pressure via a high-pressure fuel source and is actuatable via a metering valve device, by which device the pressure in a pressure booster control chamber is controllable such that the pressure in a pressure booster pressure chamber, defined by a pressure booster piston, that can be filled with fuel from the high-pressure fuel source via a filling path in which a check valve is disposed and that is in communication with an injection valve member pressure chamber, is increased by the pressure booster piston such that an injection valve member opens for injecting fuel, whereupon fuel is positively displaced out of a damping chamber via a damping path, in which a damping throttle is disposed, which fuel injection system can be produced economically and assures stable injection performance.  
         [0007]     In a system of this type, this object is attained in that the damping path is embodied such and connected in such a way to the filling path that the fuel positively displaced from the damping chamber via the damping throttle in an injection event reaches the filling path of the pressure booster pressure chamber via the damping path. The damping chamber, which may be defined by a separate damping piston or by the injection valve member, and the damping path with the damping throttle are also called a damping module. In the context of the present invention, it was discovered that in operation of the fuel injection system, the temperature in the damping module rises. The temperature increase in the damping module can be ascribed to the compression of the fuel volume enclosed in the damping chamber and to the depressurization losses in the damping throttle. The increased temperature in the damping module can lead to variable damping properties and instable injection performance. By the connection according to the invention of the damping path to the filling path, it is attained that the heated fuel, positively displaced out of the damping chamber, reaches the pressure booster pressure chamber the next time the pressure booster pressure chamber is filled via the filling path and is consequently injected. The heated fuel accordingly does not remain in the damping module. In the context of the present invention, the term “line” is understood to mean the same as the term “flow connecting means”. That is, a line as understood in the invention may also be a bore or a conduit.  
         [0008]     A preferred exemplary embodiment of the fuel injection system is characterized in that the filling path includes a filling path portion which connects the check valve with a control line that is in communication, via the metering valve device, with the high-pressure fuel source. Via the control line and the filling path portion, fuel subjected to high pressure reaches the pressure booster pressure chamber as a function of the switching position of the metering valve device.  
         [0009]     A further preferred exemplary embodiment of the fuel injection system is characterized in that the filling path includes a filling path portion which connects the check valve with an injection valve member spring chamber that is in communication, via the metering valve device, with the high-pressure fuel source. Via the injection valve member spring chamber and the filling path portion, fuel subjected to high pressure reaches the pressure booster pressure chamber as a function of the switching position of the metering valve device.  
         [0010]     A further preferred exemplary embodiment of the fuel injection system is characterized in that the damping path discharges into the filling path portion. Preferably, the damping path is markedly shorter than the filling path, and in particular shorter than the filling path portion.  
         [0011]     A further preferred exemplary embodiment of the fuel injection system is characterized in that the damping chamber is defined by a damping piston which has a damping chamber filling path by way of which the damping chamber is filled. The damping chamber filling path that is independent of the damping path assures that the damping chamber is filled with new, cold fuel. Good rinsing out of the damping chamber is thus assured.  
         [0012]     A further preferred exemplary embodiment of the fuel injection system is characterized in that the damping chamber is defined, in a damping chamber defining sleeve, by the end of the injection valve member remote from the combustion chamber. This has the advantage that a separate damping piston can be dispensed with.  
         [0013]     A further preferred exemplary embodiment of the fuel injection system is characterized in that the damping chamber is in communication with the control line via a damping chamber filling path. The damping chamber filling path that is dependent on the damping path assures that the damping chamber is filled with new, cold fuel. Good rinsing out of the damping chamber is thus assured.  
         [0014]     A further preferred exemplary embodiment of the fuel injection system is characterized in that a throttle and a check valve are disposed in the damping chamber filling path. It is thus assured, among other things, that no fuel from the damping chamber can escape via the damping chamber filling path.  
         [0015]     Further preferred exemplary embodiments of the fuel injection system are characterized in that the metering valve device and/or the injection valve member and/or the pressure booster piston is integrated with the fuel injector. As a result, a compact, multi-functional injector is created. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings, in which:  
         [0017]      FIG. 1  is a schematic illustration of a fuel injection system of the invention, in a longitudinal section through an injector in the state of repose, in a first exemplary embodiment;  
         [0018]      FIG. 2  shows a similar fuel injection system to  FIG. 1 , in a second exemplary embodiment; and  
         [0019]      FIG. 3  shows a similar fuel injection system to that of  FIGS. 1 and 2 , in a third exemplary embodiment.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     In  FIGS. 1 and 2 , a longitudinal section in shown through a common rail injector  1 , which is supplied with fuel that is at high pressure via an only schematically shown high-pressure reservoir  2 , also known as a common rail or as a high-pressure fuel source. From the interior of the high-pressure reservoir  2 , a fuel supply line  3  leads to a pressure booster  5 , and is integrated with the fuel injector  1 . The pressure booster  5  is surrounded by an injector housing  6 , which is shown only schematically in  FIGS. 1 and 2 .  
         [0021]     The injector housing  6  includes an injector body  7 , only the interior of which is shown in  FIGS. 1 and 2 , and a nozzle body  8 , which has a central guide bore  9 . An injection valve member  10 , also known as a nozzle needle, is guided movably back and forth in the guide bore  9 . The nozzle needle  10  has a tip  11 , on which a sealing face is embodied that cooperates with a sealing seat embodied on the end of the nozzle body  8  that protrudes into the combustion chamber. When the tip  11  of the nozzle needle  10  is resting with its sealing face on the sealing seat, at least one injection port and in particular a plurality of injection ports in the nozzle body  8  are closed.  
         [0022]     When the nozzle needle tip  11  lifts from its seat, then fuel subjected to high pressure is injected through the injection ports into the combustion chamber of the engine. The opening motion of the nozzle needle  10  is controlled via a metering valve device  12 , which in turn is triggered via a magnet valve. The metering valve device  12  is a 3/2-way valve which is integrated with the fuel injector  1 .  
         [0023]     A pressure shoulder  14  is embodied on the nozzle needle  10  and is disposed in a pressure chamber  15 , also called an injection valve member pressure chamber, in the nozzle body  8 . The nozzle needle  10  is prestressed by a nozzle spring  16  with its tip  11  against the associated nozzle needle tip. The nozzle spring  16  is received in a nozzle spring chamber  17 , which is recessed out of the injector body  7 . Via a connecting conduit  18 , the nozzle spring chamber  17  communicates with a pressure booster pressure chamber  22 .  
         [0024]     The pressure booster pressure chamber  22  is formed by a portion of a central bore in the injector body  7  that is embodied, toward the combustion chamber, as a blind bore. On its end remote from the combustion chamber, the bore widens to form a pressure booster control chamber  23 . In the blind bore, one end  24  of a pressure booster piston  25  is received such that it is movable back and forth. The end  24  of the pressure booster piston  25  has the form of a circular cylinder, which has a smaller diameter than an adjoining collar  21  of the pressure booster piston  25 . From the face end of the collar  21  remote from the combustion chamber, a plunger  20 , on whose end a spring plate  19  is embodied, protrudes into a pressure booster work chamber  26 , which is in communication with the high-pressure fuel source  2  via the fuel supply line  3 .  
         [0025]     The pressure booster pressure chamber  22  is defined by the end, toward the combustion chamber, of the circular cylinder  24  of the pressure booster piston  25 . The pressure booster control chamber  23  has the form of an annular chamber, which extends around the circular cylinder  24  into the injector body  7  and is defined by the end face, toward the combustion chamber, of the collar  21  of the pressure booster piston  25 . The end face remote from the combustion chamber of the collar  21  of the pressure booster piston  25  defines the pressure booster work chamber  26 . A nozzle spring  27  is fastened between the spring plate  19  and a stop  33  structurally connected to the injector housing, and by this spring the end of the pressure booster piston  25  remote from the combustion chamber is prestressed against the injector housing.  
         [0026]     The pressure booster control chamber  23  is in communication with the nozzle spring chamber  17  via a control line  28  in which a throttle  29  is provided. The pressure booster control chamber  23  is also in communication with the high-pressure reservoir  2 , via a connecting line  30  and the metering valve  12  as well as the supply line  3 . In the position of the metering valve  12  shown in  FIG. 1 , the pressure booster piston  25  is in pressure equilibrium, and the injector  1  is in the state of repose.  
         [0027]     When the metering valve  12  is put into its second position, the connecting line  30  is then made to communicate with a return line  31 , which is in communication with a low-pressure region. A connecting line  32 , in which a check valve  34  is disposed, originates at the control line  28  and discharges into the connecting conduit  18 , which communicates with the pressure booster pressure chamber  22 . Via the connecting line  32  and the check valve  34 , the pressure booster pressure chamber  22  is filled with fuel from the high-pressure reservoir  2 . The check valve  34  prevents a reverse flow of fuel out of the pressure booster pressure chamber  22 .  
         [0028]     From the connecting line  32 , a connecting line with a throttle  36  leads into an injection valve member control chamber  38 , which is defined in the nozzle body  8  by the end  41 , remote from the combustion chamber, of a damping piston  42 . The end  43  of the damping piston  42  toward the combustion chamber is embodied spherically and rests on the end of the nozzle needle  10  remote from the combustion chamber. In the state shown, a central through bore  45  is closed by a throttle in the damping piston  42 . The damping piston  42  is pressed with its end  43  toward the combustion chamber against the end of the nozzle needle  10  remote from the combustion chamber by the nozzle spring  16 .  
         [0029]      FIGS. 1 and 2  show similar fuel injection systems. The same reference numerals are therefore used to designate the same elements. The differences between the two exemplary embodiments will now be discussed below.  
         [0030]     In the exemplary embodiment shown in  FIG. 1 , a damping path in which the throttle  36  is disposed is identified by reference numeral  46 . The damping path  46  discharges into the connecting line  32  that extends between the check valve  34  and the control line  28 . A filling path for the pressure booster pressure chamber  22  is identified by reference numeral  47  in  FIG. 1 .  
         [0031]     In the exemplary embodiment shown in  FIG. 2 , a connecting line  62  (instead of the connecting line  32  in  FIG. 1 ) extends from the check valve  34  into the nozzle spring chamber  17 . A damping path in which the damping throttle  36  is disposed is identified by reference numeral  66  in  FIG. 2  and discharges into the connecting line  62 . A filling path is identified by reference numeral  67  in  FIG. 2 .  
         [0032]     The fuel injector  1  shown in  FIGS. 1 and 2  is controlled via the 3/2-way valve  12 . In the deactivated state of repose of the injector  1 , the pressure booster control chamber  23 , via the connecting line  30  and the metering valve  12 , is subjected to the same system pressure of the pressure booster work chamber  26 . The communication with the return  31  is closed. The pressure booster piston unit  25  is in pressure equilibrium, and no pressure boosting takes place. The nozzle needle  10  is closed.  
         [0033]     For activating the injector  1 , the pressure booster control chamber  23  is pressure-relieved. To that end, the pressure booster control chamber  23  is uncoupled from the pressure source  2  and is pressure-relieved into the return  31  via the connecting line  30 . The pressure in the pressure booster pressure chamber  22  is increased in accordance with the boosting ratio of the pressure booster  25  and carried onward, via the connecting line  18 , into the pressure chamber  15  at the nozzle needle  10 . The nozzle needle  10  begins to open, whereupon fuel from the damping chamber  38  must be positively displaced via the throttle  36 . As a result, the needle opening speed is reduced. The fuel that heats up upon depressurization via the throttle  36  into the damping path  46 ;  66  is carried into the filling path  47 ;  67  upstream of the check valve  34 .  
         [0034]     As long as the pressure booster control chamber  23 , which can also be called a differential pressure chamber of the pressure booster piston  25 , is pressure-relieved, the pressure booster  25  remains activated and compresses the fuel in the pressure booster pressure chamber  22 . The compressed fuel is carried onward to the nozzle needle  10  and injected.  
         [0035]     For terminating the injection, the differential pressure chamber  23  is disconnected from the return  31  by the control valve  12 , and is subjected to the supply pressure of the high-pressure fuel source  2 . As a result, rail pressure builds up in the connecting line  30  and the differential pressure chamber  23 . Simultaneously, the pressure in the pressure booster pressure chamber  22  and in the pressure chamber  15  drops to rail pressure. The nozzle needle  10  closes. In the process, the nozzle needle  10  separates from the damping piston  42  and executes a fast closing motion.  
         [0036]     The damping piston  42  is then restored by the nozzle spring  16 . In that process, the damping chamber  38  is filled via the central through bore  45 , which is also called the damping chamber filling path, and the opened sealing seat between the damping piston  42  and the nozzle needle  10 . The damping chamber filling path  45  is connected to the control line  28  in such a way that the filling is done with new, cold fuel. The result is a forced thorough rinsing of the damping chamber  38 .  
         [0037]     After the pressure equalization of the system, the pressure booster piston  25  is returned to its outset position by the pressure booster spring  27 , and the pressure booster pressure chamber  22  is filled via the filling path  47 ;  67  having the check valve  34 . This filling stream is embodied such that by means of it, the heated quantity is pumped out of the damping chamber  38 , or the damping path  46 ;  66 , into the pressure booster pressure chamber and consequently injected.  
         [0038]     In  FIG. 3 , a similar fuel injection system to those in  FIGS. 1 and 2  is shown. The same reference numerals are used for identifying identical elements. To avoid repetition, reference is made to the above description of  FIGS. 1 and 2 . Only the differences between the individual exemplary embodiments will be addressed below.  
         [0039]     In the exemplary embodiment shown in  FIG. 3 , a different nozzle needle  10  is used, and the damping piston ( 42  in  FIGS. 1 and 2 ) is dispensed with. In the exemplary embodiment shown in  FIG. 3 , flat faces  71 ,  72  are embodied on the nozzle needle  10 , and fuel can flow past these faces from the pressure chamber  15  to reach the tip  11  of the nozzle needle  10 . The nozzle needle  10  has a collar  73 , which is disposed in the pressure chamber  15 . The end of the nozzle needle  10  remote from the pressure chamber is guided in a nozzle needle control chamber defining sleeve  75 , which on its end remote from the combustion chamber has a biting edge that rests on part of the injector housing  6 .  
         [0040]     The nozzle needle control chamber defining sleeve  75  and the end of the nozzle needle  10  remote from the combustion chamber define the damping chamber  38 . A damping chamber filling path  76  originates at the damping chamber  38  and discharges into the control line  28 , and a check valve device  77  and a throttle  78  are disposed in this filling path  76 . The check valve  34  is in communication via a connecting line  79  with the pressure booster pressure chamber  22 . Via a connecting line  80 , the check valve  34  is in communication with the control line  28 . The damping path is identified in  FIG. 3  by reference numeral  86 . The filling path is identified in  FIG. 3  by reference numeral  87 .  
         [0041]     In the exemplary embodiment shown in  FIG. 3 , as in the preceding exemplary embodiments, upon opening of the nozzle needle  10  fuel is positively displaced out of the damping chamber  38  via the throttle  36  and depressurized, thereby damping the opening of the needle. The heated fuel is carried into the filling path via the damping path  86 . Upon needle closure, the damping chamber  38  is filled via the damping chamber filling path  76  and the larger throttle  78 , as a result of which new, cold fuel is introduced into the damping chamber  38 .  
         [0042]     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.