Abstract:
An injector for a fuel injection system is proposed, having an at least partial compensation for the hydraulic forces acting on the nozzle needle. In addition, the fuel volume to be controlled is reduced, so that short control times are possible.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC application of PCT/DE 00/03597 filed on Oct. 12, 2000. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on an injector for a fuel injection system for internal combustion engines, having a nozzle needle protruding into the valve control chamber. 
     2. Description of the Art 
     Injectors that are controlled by a magnet valve or a piezoelectric actuator are known. Regardless of the type of control, improvements in emissions and fuel consumption as well as noise produced by the internal combustion engine can be attained, among other provisions, by shortening the control times of the injectors. Shortened control times mean that the metering of the injection quantities is done more precisely, and that the course of injection can be designed with greater freedom. Finally, in modern internal combustion engines in motor vehicles, the available space is increasingly tight, which demands injectors of compact structure. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is the primary object of the invention to furnish an injector for a fuel injection system for internal combustion engines whose control times are shortened and whose external dimensions are especially compact. 
     This object is attained according to the invention by an injector for a fuel injection system for internal combustion engines, having a valve control chamber controlling a nozzle needle, in which the valve control chamber is defined by an end face of the nozzle needle. 
     This injector has the advantage that by the omission of a long thrust rod and a valve piston, the number of components and the mass inertia of the moving parts of the injector are reduced. This makes short control times possible. In addition, the valve control chamber can be brought closer to the injection nozzle, making thinner nozzle needles possible as well. This effect contributes to a further reduction in the moving masses inside the injector. 
     With the omission of multiple components and the possible reduction in size of the components that remain, a marked reduction in the structural size of the injector is attained. The diameter ratios of the injector of the injection are approximately equivalent to those of an injection nozzle of the prior art. 
     Furthermore, in the version of the injector according to the invention, no leakage can occur in the closed state, so that there is also no need to provide a leaking oil outlet. 
     In a variant of the invention, it is provided that the valve control chamber is disposed in a valve body, so that the injector can be produced simply and economically. 
     In another version of the invention, the valve body protrudes into a pressure chamber, so that a compact design of the injector is attained and the number of sealing points remains low. 
     The invention furthermore provides that the pressure chamber communicates with a high-pressure fuel reservoir via an inlet conduit; that the valve control chamber communicates at least indirectly with a high-pressure fuel reservoir via an inlet throttle; and that the valve control chamber communicates with the pressure chamber via an inlet throttle, so that the requisite hydraulic connections between the valve control chamber, pressure chamber and high-pressure fuel reservoir can be achieved in a simple way. 
     The invention also provides that the valve control chamber can be made to communicate with a fuel return, via an outlet conduit, an outlet throttle, and a control valve, in particular a 2/2-way control valve or 2/3-way control valve, so that the pressure in the valve control chamber can be reduced by opening the control valve. As a consequence, the nozzle needle uncovers the sealing seat, and the injection begins. 
     A variant of the invention provides that the outlet conduit and an outlet throttle are disposed in the valve body, so that a further reduction in the requisite installation space is attained. 
     Further features of the invention provide that a closing spring braced against the valve body and at least indirectly against the nozzle needle is present in the pressure chamber; the closing spring is braced against a shoulder of the nozzle needle; or that a closing spring braced against the injector and against the nozzle needle is present in the valve control chamber, so that in the absence of fuel pressure the injector is always closed, and thus the uncontrolled outflow of fuel into the combustion chamber is prevented. 
     In one embodiment of the invention, it is provided that the diameter of the end face of the nozzle needle is greater than the diameter of the sealing line between the nozzle needle and a nozzle needle seat, so that for the same pressure in the valve control chamber and pressure chamber, the resultant hydraulic force always brings about a closure of the injector. 
     Further in the invention, it is provided that the control valve is actuated by a piezoelectric actuator, so that the control times of the injector of the invention are shortened further. 
     The object stated above is also attained by a fuel injection system for internal combustion engines, having a high-pressure fuel pump and having at least one injector having a valve control chamber controlling a nozzle needle, characterized in that the valve control chamber is defined by an end face of the nozzle needle, so that the fuel injection system of the invention can be used in internal combustion engines in which both a compact design and very short control times are required. 
     In a variant of the invention, the fuel injection system has a high-pressure fuel reservoir, so that the advantages of the injector according to the invention also benefit common rail fuel injection systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Further features and advantages of the invention can be learned from the ensuing description, taken with the single FIGURE of the drawing which is a fragmentary cross section through an 309 injection of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawing in detail, in an injector of the invention. Via a high-pressure connection  1 , the fuel, not shown, is carried through an inlet conduit  3  into a pressure chamber  5  of an injection nozzle  7 . The fuel originates in and has the presure of the high-pressure fuel reservoir (common rail), not shown. Via an inlet throttle  8 , a valve control chamber  9  communicates with the pressure chamber  5 . Via a control valve  11 , shown in only fragmentary fashion, the valve control chamber  9  can be made to communicate with a pressureless fuel return, not shown. Between the valve control chamber  9  and the control valve  11 , there are an outlet conduit  13  and an outlet throttle  14 . 
     The housing  15  of the injector is connected by a union nut  16  to a cap  17 . The cap  17  furthermore fixes a valve body  19  that protrudes into the pressure chamber  5 . In the valve body  19 , there is a guide bore  20 , having the diameter d 2 , for a nozzle needle  21 . The valve control chamber  9  disposed in the valve body  19  is defined by an end face  23  of the nozzle needle. 
     Between the valve body  19  and the housing  15 , there is a conical sealing seat  25 , which seals off the pressure chamber  5  from its surroundings. A cup spring  26  fastened between the cap  17  and the valve body  19  presses the valve body  19  permanently and with constant force against the sealing seat  25 . 
     The nozzle needle  21  prevents the fuel, which is under pressure, from flowing between injections out of the injection nozzle  7  through an injection port  27  into the combustion chamber, not shown. This is accomplished in that the nozzle needle  21  is pressed into a nozzle needle seat  29  and thus seals off the inlet conduit  3  from the combustion chamber, not shown. A circular sealing line forms between the nozzle needle  21  and the nozzle needle seat  29 . The diameter of the sealing line is designated as d 1 . 
     A closing spring  33  is present between a shoulder  31  of the nozzle needle  21  and the valve body  19 . The spring assures that the nozzle needle  21  is always closed when the fuel lacks any overpressure. 
     When the control valve  11  is closed, the same pressure prevails in both the valve control chamber  9  and the pressure chamber  5 . Via the end face  23 , this pressure exerts a hydraulic force acting on the nozzle needle  21  in the direction of the nozzle needle seat  29 . The same pressure exerts a hydraulic force, acting in the opposite direction, on the annular face defined by the diameters d 1  and of nozzle needle  21 . The resultant hydraulic force acts on the nozzle needle  21  in the direction of the nozzle needle seat  29 , because the end face  23  is larger than the annular face defined by the diameters d 1  and d 2 . 
     The injection nozzle  7  opens when the control valve  11  is opened and as a consequence the pressure in the valve control chamber  9  collapses. In that case, the resultant hydraulic force acts in the direction of the control valve  11  and lifts the nozzle needle  21  from the nozzle needle seat  29 . The fuel can thus flow out of the pressure chamber  5  into the combustion chamber via the injection port  27 , and the injection begins. 
     When the control valve  11 , which can be embodied as a 2/2-way control valve or a 2/3-way control valve, closes again, a high pressure builds up again in the valve control chamber  9 , and this high pressure is equal to the pressure in the pressure chamber  5 , so that the resultant hydraulic force presses the nozzle needle  21  back into the nozzle needle seat  29 , and the injection ends. 
     An especially advantageous feature of the injector of the invention is that it is very compact in structure. The diameter of an injector of the invention is equivalent to that of an injection nozzle of the prior art. Furthermore, the masses of the moving parts are very low, since a valve piston and a thrust rod can be omitted and the nozzle needle has very small dimensions. This leads to very short control times of the injector, which can be fully utilized particularly conjunction with a piezoelectric actuator-actuated control valve  11 . The tiniest possible preinjection quantities can for instance be realized. The low number of components also has cost advantages for production. Finally, no leakage losses occur, either. 
     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.