Abstract:
A fuel injection device comprising a high-pressure pump supplying a fuel to a high-pressure area in which an injector for injecting fuel into an internal combustion engine cylinder is arranged. An electric control unit for controlling fuel injection by at least one injector is provided. A pressure adjusting valve which adjusts a pressure in the high-pressure area and controls a connection between said high pressure area and a low-pressure fuel-filled area is controlled by the control unit. When the pressure adjusting valve is not controlled by the control unit it is placed in an open switching position in such a way that the connection between the high- low-pressure areas is opened, thereby preventing a gas formation in the high pressure area when the internal combustion engine is switched off and the fuel is cooled.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a 35 USC 371 application of PCT/EP 2006/050445 filed on Jan. 25, 2006. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is directed to an improved fuel injection device for an internal combustion engine. 
   2. Description of the Prior Art 
   A fuel injection device, known from DE 100 04 617 A, has a high pressure pump that delivers fuel into a high-pressure region in which for example one high-pressure accumulator, a so-called rail, is provided. An injector for fuel injection is provided for each cylinder of the engine; each injector is connected to the high-pressure accumulator via a hydraulic line. An electric control unit is provided for controlling the fuel injection by means of the injectors. Both the lines to the injectors and the injectors themselves are components of the high-pressure region. A pressure control valve that is triggered by the control unit is provided for setting a certain pressure in the high-pressure region. The pressure control valve controls a connection between the high-pressure region and a low-pressure region. When the pressure control valve is triggered by the control unit, it opens the connection between the high-pressure region and the low-pressure region so that fuel can flow out of the high-pressure region into the low-pressure region. In new fuel injection devices, the high-pressure region is completely leak-tight. When the internal combustion engine is switched off after long operation, the fuel contained in the high-pressure region is heated. Upon subsequent cooling, the complete leak-tightness of the high-pressure region can cause a degassing of the fuel to occur. This impedes the restarting of the internal combustion engine since it is first necessary to displace the gas in the high-pressure region. 
   SUMMARY AND ADVANTAGES OF THE INVENTION 
   The fuel injection device according to the invention has the advantage over the prior art that when the internal combustion engine is switched off and the control unit is not triggering the pressure control valve, the high-pressure region is connected to the low-pressure region, thus preventing a degassing of the fuel in the high-pressure region. No additional structural complexity is required in comparison to the known fuel injection device. 
   Advantageous embodiments and modifications of the fuel injection device according to the invention are disclosed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Several exemplary embodiments of the invention are described herein below, with reference to the drawings, in which: 
       FIG. 1  is a simplified depiction of a fuel injection device for an internal combustion engine according to a first exemplary embodiments, 
       FIG. 2  is an enlarged depiction of an injector of the fuel injection device, 
       FIG. 3  is an enlarged depiction of a pressure control valve of the fuel injection device, and 
       FIG. 4  shows the fuel injection device according to a second exemplary embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 through 4  show a fuel injection device for a multicylinder internal combustion engine that is preferably an autoignition engine of a motor vehicle. The fuel injection device has a high-pressure pump  10  that delivers the fuel at a high pressure. Each cylinder of the internal combustion engine is provided with an injector  12  that is able to inject the fuel into the combustion chamber of the cylinder. Only some of the injectors  12  are shown in  FIGS. 1 through 3 ; other injectors up to the last injector  12   d  are indicated by dots. 
   As shown in  FIG. 2 , the injector  12  has a fuel injection valve  14 , which injects fuel into the combustion chamber of the cylinder, and has an electrically triggered actuator  16 . The actuator controls the opening and closing motion of an injection valve member  15  of the fuel injection valve  14 . The actuator  16  is preferably a piezoelectric actuator, whose size changes as a function of an electrical voltage applied to it. This size change can perform a switching function that is capable of opening or closing the injection valve member  15 . An electronic control unit  18  triggers the actuator  16 . The actuator  16  is situated in a fuel-filled chamber  20  in a housing  22  of the injector  12 . The actuator  16  can, for example, act on a piston  17  that delimits a control chamber  19 ; the pressure prevailing in the control chamber  19  acts on the injection valve member  15  in the closing direction. A prestressed spring  21  holds the piston  17  in contact with the actuator  16 . In addition, a prestressed spring  23  acts on the injection valve member  15  in the closing direction. When the control unit  18  causes an electrical voltage to be applied to the actuator  16 , it expands and pushes the piston  17  into the control chamber  19 , causing a high pressure to prevail therein, which holds the injection valve member  15  in its closed position so that no fuel injection occurs. When the control unit  18  does not supply any electrical voltage to the actuator  16 , then it reduces in size so that the spring  21  moves the piston  17  out of the control chamber  19 , thus causing the pressure to drop in the control chamber  19 . Then the high pressure acting on the injection valve member  15  in the opening direction moves it into its open position in opposition to the pressure prevailing in the control chamber  19  and in opposition to the force of the spring  23  so that an injection of fuel occurs. 
   In the fuel injection device according to a first exemplary embodiment shown in  FIG. 1 , the high-pressure pump  10  delivers fuel into a reservoir  26 . A fuel supply pump  30  that draws from a fuel tank  32  supplies fuel to the high-pressure pump  10 . A fuel metering device  34  that is able to change the fuel quantity delivered by the high-pressure pump  10  can be provided between the fuel supply pump  30  and the high-pressure pump  10 . For example, the fuel metering device  34  is able to adjust a variable flow cross section. The control unit  18  triggers the fuel metering device  34 . 
   The injectors  12  are each connected to the reservoir  26  via a respective hydraulic line  36 . The high-pressure region of the fuel injection device includes the reservoir  26 , the hydraulic lines  36  from the reservoir  26  to the injectors  12 , and the injectors  12  themselves. The high-pressure region contains a pressure sensor  40  that sends the control unit  18  a signal for the pressure prevailing in the high-pressure region. The high-pressure region also contains a pressure control valve  42  that the control unit  18  triggers in order to maintain a predetermined pressure in the high-pressure region. The pressure control valve  42  controls a connection  44  between the high-pressure region and a fuel-filled low-pressure region; the low-pressure region can be the fuel tank  32  or a region upstream or downstream of the fuel supply pump  30 . The pressure sensor  40  and the pressure control valve  42  can be situated at any point in the high-pressure region, for example in the high-pressure pump  10 , in the hydraulic line  24  between the high-pressure pump  10  and the reservoir  26 , in the reservoir  26 , in a line  36  between the reservoir  26  and the injectors  12 , or in an injector  12 . Aside from the connection  44  controlled by the pressure control valve  42 , the high-pressure region has no other connection to the environment and is completely leak-tight. 
   As is shown in  FIG. 3 , the pressure control valve  42  has a valve member  46  with a for example spherical closing element  47  that cooperates with a valve seat  48  and that has the capacity to be moved by an electric actuator  50 , for example an electromagnet or a piezoelectric actuator, in opposition to a return spring  52 . In this case, the control unit  18  triggers the actuator  50 . The return spring  52  acts on the valve member  46  in its opening direction in which its closing element  47  is lifted away from the valve seat  48 , thus opening the connection  44  between the high-pressure region and the low-pressure region. When the control unit  18  triggers the actuator  50 , the actuator keeps the valve member  46 —in opposition to the return spring  52  and in opposition to the pressure prevailing in the high-pressure region—in its closed position in which its closing element  47  rests against the valve seat  48  so that the high-pressure region is disconnected from the low-pressure region. The pressure prevailing in the high-pressure region, for example in the reservoir  26 , acts on the valve member  46  in its opening direction in which it is lifted away from the valve seat  48  and thus opens the connection  44  between the high-pressure region and the low-pressure region. If the actuator  50  is being not triggered, then the pressure prevailing in the high-pressure region opens the valve member  46  in opposition to the force of the closing spring  52 , thus opening the connection  44  to the low-pressure region. During operation of the internal combustion engine, the control unit  18  triggers the fuel metering device  34  and the pressure control valve  42  so that a predetermined pressure that is required for the fuel injection to occur builds up in the high-pressure region. The pressure sensor  40  sends the control unit  18  a signal for the actual pressure in the high-pressure region. 
   When the internal combustion engine is switched off, the pressure control valve  42  is no longer being, triggered by the control unit  18  and therefore assumes its open switched position, as a result of which the high-pressure region is connected to the low-pressure region. When the fuel contained in the high-pressure region cools, it is thus possible for the volume in the high-pressure region to be replenished with fuel from the low-pressure region so that no gas can form in the high-pressure region. With a subsequent starting of the internal combustion engine, the control unit  18  triggers the pressure control valve  42  so that it moves into its closed position. When the high-pressure pump  10  delivers fuel, high pressure builds back up again quickly in the high-pressure region so that the engine can be operated after a short starting time. 
   In a second exemplary embodiment of the fuel injection device shown in  FIG. 4 , the design is essentially the same as in the first exemplary embodiment, but no reservoir  26  is provided. A first injector  12   a , which is preferably the injector of the engine situated the closest to the high-pressure pump  10 , is connected to the high-pressure pump  10  via a hydraulic line  56 . The next injector  12   b  is connected to the first injector  12   a  via a hydraulic line  58 . The remaining injectors  12  are connected to one another in series via respective hydraulic lines  58 . The hydraulic lines  56  and  58  each are each connected to the chamber  20  in the respective injector  12 . The high-pressure region of the fuel injection device that includes the hydraulic lines  56 ,  58  and the injectors  12  is provided with the pressure sensor  40  and the pressure control valve  42 , as in the first exemplary embodiment. The pressure sensor  40  and the pressure control valve  42  can, for example, be situated in the high-pressure pump  10 , in the line  56  between the high-pressure pump  10  and the injector  12   a , or in a line  58  between the injectors  12 . The pressure control valve  42  is embodied the same as in the first exemplary embodiment so that when it is not being triggered by the control unit  18 , it assumes its open switched position in which the connection  44  is open between the high-pressure region and the low-pressure region. In the fuel injection device according to the second exemplary embodiment, it is also alternatively possible for not only the first injector  12   a  to be connected directly to the high-pressure pump  10 , but also for the last injector  12   d  to be connected directly to the high-pressure pump via a hydraulic line  56 , as indicated with dashed lines in  FIG. 4 . The fuel injected through the fuel injection valve  14  of the injector  12  is drawn from the chamber  20  in which the actuator  16  is situated. The chamber  20  has a sufficiently large volume to permit the storage of the fuel volume required for the fuel injection. The volume of the chamber  20  can be between 1 and 5 cm 3 , for example approximately 2 cm 3 . 
   The foregoing relates to a preferred exemplary embodiment 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.