Abstract:
An injector of a pressure-controlled fuel injection system includes a locally disposed hydraulic pressure booster, a device for centrally generating a control pressure for actuating the pressure booster, and a metering valve for regulating the fuel inflow to the pressure chamber of the pressure booster.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to an injector of a pressure-controlled fuel injection system with pressure boosting.  
           [0003]    2. Description of the Prior Art  
           [0004]    For the sake of better comprehension of the description and claims, some terms will now be defined: The fuel injection system of the invention is embodied as pressure-controlled. Within the scope of the invention, the term stroke-controlled fuel injection system is understood to mean that the opening and closing of the injection opening is done with the aid of a displaceable nozzle needle on the basis of the hydraulic cooperation of the fuel pressures in a nozzle chamber and in a control chamber. A pressure reduction within the control chamber causes a stroke of the nozzle needle. Alternatively, the deflection of the nozzle needle can be effected by means of a final control element (actuator). In a pressure-controlled fuel injection system of the invention, the nozzle needle is moved counter to the action of a closing force (spring) by the fuel pressure prevailing in the nozzle chamber of an injector, so that the injection opening is uncovered for an injection of the fuel from the nozzle chamber into the cylinder. The pressure at which fuel emerges from the nozzle chamber into a cylinder is called the injection pressure, while the term system pressure is understood to mean the pressure at which fuel is available or kept on hand within the fuel injection system. Fuel metering means delivering fuel to the nozzle chamber by means of a metering valve. In the unit fuel injector (UFI), the injection pump and the injector form a unit. One such unit per cylinder is built into the cylinder head and is driven either directly via a tappet or indirectly via tilt levers by the engine camshaft. The pump-line-nozzle system (PLN) operates by the same method. In that case, a high-pressure line leads to the nozzle chamber or nozzle holder.  
           [0005]    An injector of the type with which this invention is concerned is known for instance from European Patent EP 0 562 046 B1. In this injector (HGUI system produced by Caterpillar), air bubbles can form in the pressure chamber because of the suction created as the piston moves into the closing position. Another disadvantage of this injector is the quantity metering. Nor can a preinjection be performed with the aid of this injector.  
         OBJECT AND SUMMARY OF THE INVENTION  
         [0006]    The high pressure is generated only locally. The control pressure of the control fluid is conversely generated centrally and can perform still other functions (such as valve control). The throttling of the high pressure by the metering valve at the intake has the advantage of simple quantity regulation. The injection event can be initiated and terminated by a 3/2-way valve.  
           [0007]    Coupling two control valves for stroke-dependent pressure relief of the pressure chamber of the pressure booster makes it possible to embody an injector that is also capable of performing a preinjection.  
           [0008]    Embodying the piston of the pressure booster in two parts means a subdivision into two pressure chambers, so that the first pressure chamber, controlled by a metering valve, is separated from a second pressure chamber that communicates with a nozzle chamber of the injector. As a result of this arrangement, the suction of fuel into the first pressure chamber does not cause the formation of air bubbles in the first pressure chamber.  
           [0009]    Using a 2/2-way valve as a control valve for the pressure booster makes for a simple structural form of the injector with pressure boosting. A 3/2-way valve typically used is replaced by a 2/2-way valve and by the embodiment of a control conduit in the piston of the pressure booster. Integrating the control conduit with the piston reduces the space required for the injector.  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]    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 drawing, in which:  
         [0011]    [0011]FIG. 1 shows a first injector with a locally disposed pressure booster;  
         [0012]    [0012]FIG. 2 shows a second injector, with a coupling of two control valves in the pressure boosting;  
         [0013]    [0013]FIG. 3 shows the course of the stroke of valve elements of the control valves and the course of the pressure in the control chamber for an injector of FIG. 2;  
         [0014]    [0014]FIG. 4 shows a third injector with a two-part piston of the pressure booster;  
         [0015]    [0015]FIG. 5 shows a fourth injector with a 2/2-way control valve; and  
         [0016]    [0016]FIG. 6 shows a pressure booster in an alternative version to the pressure booster of FIG. 5.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    From FIG. 1 it can be seen that an injector  1  in a pressure-controlled fuel injection system includes a control valve  2 , a local pressure booster  3  that operates on a hydraulic basis, a metering valve  4 , and a nozzle needle  5 . The 3/2-way control valve  2  serves to connect a control chamber  6  on the low-pressure side of the pressure booster  3  either to a supply line  7 , in which a control fluid (such as oil, fuel, or a similar medium) that is at a centrally generated control pressure flows, or to a leak fuel line  8 . At suitable pressure inside the control chamber  6 , an outer piston  9  is moved in the direction of the nozzle needle  5  counter to the spring force of a closing spring  10 . In the process, an inner piston  11  is subjected to pressure via the outer piston  9  and displaced, causing compression of fuel in the pressure chamber  12  on the high-pressure side, which chamber can be filled with fuel with the aid of the metering valve  4 , a supply line  13 , and a check valve  14 . The filling is effected while the control chamber  6  is connected to the leak fuel line  8  (during pressure relief of the control chamber  6 ), in that fuel is aspirated into the pressure chamber  12  during the piston stroke (intake throttling, intake stroke of the piston  11 ). The aspirated fuel quantity is controlled by the metering valve  4 . From the pressure chamber  12 , the fuel that is at high pressure reaches a nozzle chamber  16  via the pressure line  15 . If the pressure in the nozzle chamber  16  exceeds the spring force of a closing spring  17 , the injection event is initiated. A pressure relief of a spring chamber  18  is effected by means of a further leak fuel line  19 .  
         [0018]    In FIG. 2, the functions of a first control valve  20  and a second control valve  21  in an injector  22  can be coupled. The filling of a control chamber  23  of a pressure booster  24  is regulated by a first displaceable valve element  25  of the first control valve  20 . The control chamber  23  can in turn be connected either to a supply line  26 , with a control fluid that is at a centrally generated control pressure, or to a leak fuel line  27 . The connection to the supply line  26  results in a fuel compression in a pressure chamber  28  that can be filled with the aid of a metering valve  29  and a supply line. If the first valve element  25  is moved outward (downward in FIG. 2) via a stroke h, then a second valve element  30  of the second control valve  21  is deflected as well and initiates a pressure relief within the pressure chamber  28 , by means of the resultant connection to a leak fuel line  31 . The buildup of high pressure in the pressure chamber  28  is interrupted. This interruption can be utilized for a preinjection at lesser fuel pressure. Upon further motion, the connection to the leak fuel line  31  is closed again, so that a main injection becomes possible. The control valves  20 ,  21  are in a pressure-balanced state (see the uniform cross-sectional diameter d). The stroke-dependent pressure ratios in the control chamber and the shaping of the injection course can be learned from FIG. 3.  
         [0019]    In FIG. 4, the inner piston used for pressure boosting in a pressure booster  32  is divided into two displaceable piston elements  33  and  34 , which are separated from one another by a first pressure chamber  35 . The cross sections e and the face areas acted upon by pressure are adapted to one another in such a way that a pressure boost of 1:1 occurs. From the volumetric adjustment in the pressure chamber  35 , the volumetric adjustment in a second pressure chamber  36  is also obtained. The disposition of the first pressure chamber  35  and metering valve  37  as well as an inlet  38  and the second pressure chamber  36  (injection control chamber) has the result that the suction of fuel into the first pressure chamber  35  does not cause the formation of air bubbles in the first pressure chamber  35 .  
         [0020]    [0020]FIG. 5 shows that instead of a 3/2-way valve as the control valve, a 2/2-way valve  39  can also be used. A control pressure is generated centrally in a rail (pressure reservoir) and is continuously applied to the control valve  39 . By opening the control valve  39 , control fluid that is at control pressure is carried into the control chamber  40 . A piston  41  is displaced as a result in the direction of the nozzle needle and compresses fuel in a pressure chamber  42 . If the piston  41  exceeds a piston stroke g, the control chamber  40  is pressure-relieved via a control conduit  43  (forming a slide valve in the piston  41 ). If the control valve  39  is closed simultaneously, a lesser pressure develops in the control chamber  40 . Because a closing spring  44  is provided, the piston  41  moves slowly back into its outset position. A slight overpressure is initially created in the control chamber  40 , but this drops to ambient pressure. The pressure drop can be reinforced by the opening of the nozzle needle.  
         [0021]    [0021]FIG. 6 shows an alternative version of the piston  41 , with a slide valve, by means of a piston  45  with a ball valve  46 .  
         [0022]    The control valves and metering valves shown are actuated via magnets or piezoelectric actuators and because of their dimensioning are in the pressure-balanced state.  
         [0023]    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.