Abstract:
The invention relates to an injector for injecting fuel into combustion chambers of internal combustion engines. According to the invention, a valve seat of a control valve is designed as a flat seat that has a planar valve seat surface. A circumferential edge located on the face of a sleeve of the control valve rests on the planar valve seat surface when the control valve is closed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/059593 filed on Sep. 12, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an injector for injecting fuel into combustion chambers. 
     2. Description Of The Prior Art 
     European Patent Disclosure EP 1 612 403 A1 describes a common rail injector with a control valve, in pressure equilibrium in the axial direction, for blocking and opening a fuel outflow course from a control chamber. By means of the control valve, the fuel pressure inside the control chamber can be varied. The control chamber is supplied via a pressure conduit with fuel from a pressure chamber communicating hydraulically with a high-pressure fuel reservoir. Varying the fuel pressure inside the control chamber adjusts a nozzle needle between an opening position and a closing position; in its opening position, the nozzle needle enables the flow of fuel into the combustion chamber of an internal combustion engine. The control valve has a valve sleeve, which is adjustable in the axial direction by means of an electromagnetic drive and which cooperates with a stationary, conical valve seat face in a sealing fashion. In long-term use of the known injector, wear can be observed in the region of the valve seat. Because of the seat wear, a circular-annular surface develops on both the valve seat and the valve sleeve, and as a consequence the control valve is no longer in pressure equilibrium, and the opening characteristic of the control valve is subject to major changes over the service life of the injector. The opening behavior of the control valve is highly pressure-dependent over the course of time, which leads to marked changes in the injection quantities. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is therefore the object of the invention to propose an injector having a control valve whose opening characteristic remains at least substantially constant over its service life. 
     The invention is based on the concept of providing, instead of a raised and for instance conical valve seat, a valve seat embodied as a flat seat that has a planar valve seat face; the planar valve seat face cooperates in sealing fashion with a face-end encompassing edge of the valve sleeve of the control valve. The encompassing edge extends axially from the valve sleeve. With the control valve closed, the valve sleeve is pressed with its face-end encompassing edge against the planar valve seat face. Because of the combination of a planar valve seat face and the radially narrow contact area (encompassing edge) of the valve sleeve, it is assured that despite unavoidable wear, no pressure engagement face for the fuel pressure in the axial direction is created on the valve sleeve; thus the opening characteristic is essentially preserved over the service life of the control valve. To obtain a control valve that is in pressure equilibrium in the axial direction, the encompassing edge or in other words the contact edge with which the valve sleeve rests on the planar valve seat face must be formed by the inner circumference of the valve sleeve. In other words, the diameter of the encompassing edge, in the case of a control valve that is axially in pressure equilibrium, is equal to the inside diameter of the valve sleeve in its guidance portion on the guide bolt that absorbs the axial pressure forces. 
     The effects of wear on the opening characteristic of the control valve are minimal if an annular face, extending radially outward from the encompassing edge, forms an angle with the valve seat face. 
     This angle must be dimensioned such that first, the wear of the valve sleeve and of the valve seat is minimal, and second, flow forces on the valve sleeve, which are caused by fuel that flows into a low-pressure chamber surrounding the valve sleeve when the control valve is open, are minimized. It has been found that depending on the injection pressures for which the injector is designed, angles in a range between approximately 0.5° and 20° between the valve seat face and the annular face are suitable. Preferably, the angle is between approximately 1° and 10°; optimal results are attained at an angle of approximately 5°. 
     For implementing a safety concept, in a refinement of the invention, for the sake of the axial pressure equilibrium a defined pressure engagement face can be provided, which assures that if a maximum fuel pressure inside the valve sleeve is exceeded, the valve sleeve lifts from the planar valve seat and the fuel that is at an impermissible overpressure can thus flow out into a low-pressure chamber. In particular, the pressure engagement face is dimensioned such that at fuel pressures above 2100 bar, and in particular above 2200 bar, the valve sleeve lifts from the valve seat counter to the force of a valve spring. 
     In a refinement of the invention, it is advantageously provided that the pressure engagement face is embodied as an encompassing pressure step. This kind of pressure engagement face is easy to produce with high precision. 
     Preferably, the encompassing edge with which the valve sleeve rests on the planar valve seat face is disposed with radial spacing from the inner surface, guided on the guide bolt, of the valve sleeve. The pressure engagement face, preferably embodied as an encompassing pressure step, is located in a region between this inner surface and the encompassing edge. 
     Angular errors between the valve sleeve and the planar valve seat are minimized if the guide bolt is embodied integrally with a component that forms or has the valve seat. The guide bolt extends in the axial direction into the valve sleeve from a region radially inside the planar valve seat face. 
     Angular errors between the valve sleeve and the valve seat face can be further reduced by providing that the valve sleeve, in a feature of the invention, is embodied integrally with an armature plate of the actuator embodied as an electromagnetic drive. 
     Advantageously, the fuel outflow course extends through the component having the valve seat axially into the guide bolt and from there radially out of the guide bolt into an annular chamber inside the valve sleeve. From there, when the valve sleeve is lifted from the valve seat, the fuel can flow radially into a low-pressure chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, characteristics and details of the invention will become apparent from the ensuing description of preferred exemplary embodiments and from the drawings, in which: 
         FIG. 1  shows a schematic sectional view of an injector; 
         FIG. 2  shows one possible embodiment of a detail of  FIG. 1 ; and 
         FIG. 3  shows an alternative embodiment of the detail of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawings, identical components and components with the same functions are identified by the same reference numerals. 
     In  FIG. 1 , the parts of a common rail injector  1  that are essential to control are shown schematically. Inside a nozzle body  2 , an elongated nozzle needle  3  is guided movably in the axial direction. The nozzle needle  3 , on its needle tip, not shown, has a closing face with which it can be brought into tight contact with a needle seat, also not shown, inside the nozzle body a  2 . When the nozzle needle  3  is seated on the needle seat, the emergence of fuel from a nozzle hole array, not shown, is blocked. Conversely, if it is lifted from the needle seat, then fuel can flow out of a pressure chamber  4  in the axial direction along the nozzle needle  3  through the nozzle hole array and there, essentially at the high pressure (rail pressure), can be injected into a combustion chamber. The fundamental construction of an injector  1  is known. In this respect, see German Patent Disclosure DE 100 24 703 A1. 
     The injector  1  has a throttle plate  5 , which extends in sleevelike fashion downward in the plane of the drawing into the nozzle body  2 . A control chamber  7  is defined by the sleevelike portion of the throttle plate  5  and the face end  6  of the nozzle needle  3 . The control chamber  7  communicates with the pressure chamber  4  via a pressure conduit  8  having an inlet throttle restriction  9 , and the pressure chamber in turn communicates with a high-pressure fuel reservoir, via a supply line, not shown. Via the pressure conduit  8 , fuel at high pressure can thus flow into the control chamber  7 . From the control chamber  7 , a fuel outflow path  10  with an outflow throttle restriction  11  leads in the axial direction. Via the fuel outflow path  10 , when a control valve  12  is open, fuel can flow out of the control chamber  7  into a low-pressure chamber  13 . The flow cross sections of the inflow throttle restriction  9  and outflow throttle restriction  11  are adapted to one another such that the inflow through the pressure conduit  8  is less than the outflow through the fuel outflow path  10 , and accordingly, when the control valve  12  is open, there is a net outflow of fuel from the control chamber  7 . The resultant pressure drop in the control chamber  7  causes the closing force to drop below the opening force and causes the nozzle needle  3  to lift from its needle seat. 
     The fuel outflow path  10  leads through the throttle plate  5  with the outflow throttle restriction  11  into a component  14  disposed above it in the plane of the drawing. The component  14  has a valve seat  22  (fiat seat) with a planar valve seat face  15  of the control valve  12 , and when the control valve is closed, a valve sleeve  16  of the control valve  12  rests sealingly on the valve seat face  15 . For that purpose, the valve sleeve  16  is urged by spring force by a valve spring  17  onto the valve seat face  15  in the axial direction. The valve spring  17  is braced at the top in terms of the plane of the drawing on an injector body  18  and on the opposite end on a spring guide part  19 , which in turn rests on the valve sleeve  16 . The valve sleeve  16  is penetrated in the axial direction by a guide bolt  25 , on the outer face of which it is guided. The guide bolt  25  is embodied integrally with a cylindrical portion of the component  14 . 
     The valve spring  17  is disposed inside an electromagnet  20 . When current is supplied to the electromagnet  20 , an armature plate  21 , embodied integrally with the valve sleeve  16 , is moved axially in the direction of the electromagnet  20 , as a result of which the valve sleeve  16  lifts from the valve seat face  15  counter to the spring force of the valve spring  17 , which in turn enables the flow of fuel out of the control chamber  7  via the fuel outflow path  10  into the low-pressure chamber  13 . From there, the fuel can flow out to a tank via a return line, not shown. The pressure inside the low-pressure chamber  13 , depending on the operating state, amounts to between approximately 0 and 10 bar, while conversely the fuel pressure inside the pressure chamber  4  is between approximately 1800 and 2000 bar. 
     As can be seen from  FIG. 2 , the valve seat face  15  of the valve seat  22  is planar, and the valve seat face  15  extends transversely to the longitudinal center axis  23  of the valve sleeve  16 . With an axially extending, face-end encompassing edge  24 , the valve sleeve  16  rests on the valve seat face  15  when the control valve  12  is closed. The encompassing edge  24  is embodied on the inside diameter d 1  of the valve sleeve  16 . In other words, the diameter d 2  of the valve sleeve  16  at the encompassing edge  24  is equivalent to the diameter d 1  of the valve sleeve  16  in the guidance portion on the guide bolt  25 . Because the diameter d 2  is equivalent to the diameter d 1 , the control valve  12  in  FIG. 2  is in pressure equilibrium in the axial direction. This means that no pressure forces, or only minimal pressure forces, act on the valve sleeve  16  in the axial direction. 
     The encompassing edge  24  is adjoined in the radial direction outward by a conical annular face  27 . In the exemplary embodiment shown, this annular face forms an angle α of approximately 5° with the planar valve seat face  15 . 
     It can also be seen from  FIG. 2  that the fuel outflow course changes over from an axial portion to a radial portion and discharges into an annular chamber  26  defined on one side by the guide bolt  25  and on the other by the valve sleeve  16 . 
     The injector  1  in  FIG. 1  may also be embodied as shown in  FIG. 3 . In this variant embodiment as well, a planar valve seat face  15  is provided. In a distinction from the exemplary embodiment in  FIG. 2 , the diameter d 2  of the valve sleeve  16  in the region of the encompassing edge  24  is not equivalent to the diameter d 1  of the valve sleeve  16  in the guidance region immediately radially outside the guide bolt  25 . The diameter d 2  is slightly greater than the diameter d 1 , as a result of which, an annular pressure engagement face  28  embodied as a pressure step is formed on the valve sleeve  16 . This pressure engagement face  28  prevents damage to or destruction of the injector if a maximum allowable fuel pressure inside the control valve  12  is exceeded. The pressure engagement face  28  is dimensioned such that if an impermissible pressure level, for instance of approximately 2200 bar, is reached, the valve sleeve  16  lifts from the valve seat  22 , and fuel can thus flow out into the low-pressure chamber  13 . 
     In the same way as in the exemplary embodiment of  FIG. 2 , in the exemplary embodiment of  FIG. 3  as well a radially outer conical face  27  adjoins the encompassing edge  24 , which with the planar valve seat face  15 , or its imaginary extension, forms an angle α of approximately 5°. 
     The foregoing relates to the 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.