Patent Publication Number: US-6712295-B2

Title: Fuel injection valve for internal combustion engines

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 00/00910 filed on Aug. 4, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to an improved fuel injection valve for internal combustion engines, preferably internal combustion engines with self ignition. 
     2. Description of the Prior Art 
     In one known fuel injection valve, disclosed in German Utility Model 298 14 934, a bore is embodied in a valve body, and in the bore a pistonlike valve member is disposed longitudinally displaceably; by its longitudinal motion, the valve member controls the opening of at least one injection opening. The valve member is urged in the closing direction by a closing force and has a pressure face, which is disposed in a pressure chamber that can be filled with high fuel pressure. Filling the pressure chamber with fuel at high pressure makes it possible to exert a hydraulic force on the pressure face that is oriented counter to the closing force and thus brings about the opening stroke motion of the valve member. The device for generating the closing force is embodied in a valve holding body, which has a longitudinal axis and is braced axially against the valve body. A high-pressure connection is located on the valve holding body and discharges into an inlet conduit that penetrates the valve holding body longitudinally and extends through the contact face between the valve body and the valve holding body as far as the inside of the pressure chamber of the valve body. The contact face is accordingly a high-pressure sealing face and must have a correspondingly good seal. 
     The bracing of the valve holding body against the valve body if effected by a lock nut, which surrounds the valve body and contacts an annular-disklike contact face, embodied on the valve body, that faces away from the valve holding body. On the valve holding body, there is a male thread engaged by the lock nut with a corresponding female thread, so that the valve body is braced against the valve holding body by the screwing action of the lock nut. As a result, a good seal is achieved at the high-pressure sealing face between the valve holding body and the valve body, and the inlet conduit that passes through the high-pressure sealing face, that is, the contact face of the valve holding body at the valve body, is securely sealed off. 
     In the known fuel injection valves, the thread, embodied on the outer jacket face of the valve holding body and engaged by the lock nut, is embodied as a fine thread. The flanks of the thread courses form an angle of about 60° with the longitudinal axis of the thread and thus also with the longitudinal axis of the valve holding body. Thus because of the axial bracing of the lock nut, along with the axially operative force component on the screw faces, a force component acting in the radial direction to the longitudinal axis of the valve holding body is also obtained, which expands the lock nut. This limits the maximum attainable pressure per unit of surface area at the high-pressure sealing face between the valve holding body and the valve body, so that at high pressures in the inlet conduit, sealing problems can occur. 
     SUMMARY OF THE INVENTION 
     The fuel injection valve of the invention has the advantage over the prior art that the contact flanks of the male thread embodied on the valve holding body and of the female thread embodied on the lock nut are at least approximately perpendicular to the longitudinal axis of the valve holding body, so that upon the bracing of the lock nut, these contact flanks are pressed against one another without substantial radial forces on the lock nut being engendered. As a result, greater axial clamping forces can be exerted on the valve body and the valve holding body, and a higher pressure per unit of surface area can thus be achieved at the high-pressure sealing face between the two bodies. Expansion of the lock nut from radial force components thus no longer occurs. This is especially advantageous in fuel injection valves that work with a so-called common rail system, because in that case a constantly high fuel pressure prevails in the valve body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will become apparent from the detailed description contained below, taken with the drawings, in which: 
     FIG. 1 is a longitudinal section through a fuel injection valve of the invention; 
     FIG. 2 shows an enlarged detail of FIG. 1 in the region of the male thread of the valve holding body; and 
     FIG. 3 shows a further exemplary embodiment of a fuel injection valve of the invention in longitudinal section. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a fuel injection valve of the invention in longitudinal section. A valve holding body  1  is braced axially against a valve body  3 . The valve body  3  is embodied with a graduated diameter and tapers toward the combustion chamber, so that an annular-disklike contact face  24  oriented toward the combustion chamber is formed on its outer jacket face. A lock nut  5  grips the valve body  3  and rests on the contact face  24 , extending to beyond the valve body  3 . On the inner jacket face of the lock nut  5 , at the level of the valve holding body  1 , a female thread  44  is formed, which engages a male thread  42  embodied on the outer jacket face of the valve holding body  1 ; this male thread  42  has a longitudinal axis  8 . Hence turning the lock nut  5  moves the lock nut  5  in the axial direction and thus braces the valve body  3 , with its end face remote from the combustion chamber, against the valve holding body  1 , so that the contact face of the valve body  3  at the valve holding body  1  is embodied as a high-pressure sealing face  30 . 
     Embodied in the valve body  3  is a bore  7 , which originates on the face end of the valve body  3  remote from the combustion chamber and changes over, on its end toward the combustion chamber, into a valve seat  20 . The valve seat  20  is embodied substantially conically and has at least one injection opening  22 , by way of which the bore  7  communicates with the combustion chamber of the engine. A pistonlike valve member  10  is disposed in the bore  7  and is guided sealingly in the bore  7  in a portion remote from the combustion chamber, while toward the combustion chamber it tapers, forming a pressure shoulder  16 . On its end toward the combustion chamber, the valve member  10  changes over into a valve sealing face  18 , which is embodied substantially conically and cooperates with the valve seat  20  to control the at least one injection opening  22 . In the valve body  3 , at the level of the pressure shoulder  16 , a pressure chamber  14  is embodied by a radial enlargement of the bore  7 ; the pressure chamber continues in the form of an annular conduit, surrounding the valve member  10 , as far as the valve seat  20 . An inlet conduit  12  embodied in the valve body  3  and in the valve holding body  1  discharges into the pressure chamber  14  and communicates by its other end with a source of high fuel pressure, not shown in the drawing. Via this inlet conduit  12 , the pressure chamber  14  can be filled with fuel at high pressure. 
     In the valve holding body  1 , there is a spring chamber  32  embodied as a bore, in which a guide piece  40  is disposed that is connected to the end face, remote from the combustion chamber, of the valve member  10 . The guide piece  40  is embodied cylindrically here and is guided in the spring chamber  32 . The guide piece  40  has at least one lateral recess  41 , which connects the bore  7  to the spring chamber  32 . A closing spring  34  embodied as a helical compression spring is disposed with pressure prestressing between the guide piece  40  and the end face, remote from the combustion chamber, of the spring chamber  32 . This closing spring  34  surrounds a tappet  36 , which is disposed in a guide bore  38  that discharges into the spring chamber  32 , and with its face end toward the valve member  10 , this tappet rests on the guide piece  40 . By means of a device not shown in the drawing, a controllable closing force acts on the face end of the tappet  36  remote from the combustion chamber; this force is capable of urging the tappet  36  in the direction of the valve seat  20 . In the closed state of the fuel injection valve, that is, when the valve sealing face  18  is resting on the valve seat  20 , a predetermined high fuel pressure prevails in the pressure chamber  14  because of the communication with the high-pressure fuel source. As a result of this high fuel pressure, a hydraulic force on the pressure shoulder  16  is produced, resulting in an opening force acting on the pressure shoulder  16  in the direction away from the valve seat  20 . The closing force on the tappet  36 , which also acts on the valve member  10  via the guide piece  40 , predominates over this opening force, however, so that the valve member  10  remains in the closing position. The closing spring  34  still has a reinforcing effect at this time. If an injection of fuel is to take place, then the closing force on the tappet  36  is reduced, and the hydraulic force on the pressure shoulder  16  is now capable of moving the valve member  10  in the opening direction, that is, away from the valve seat  20 , counter to the closing force on the tappet  36  and to the spring force of the closing spring  34 . As a result, the valve sealing face  18  lifts from the valve seat  20 , the injection openings  22  are uncovered, and fuel flows out of the pressure chamber  14  through the injection openings  22  into the combustion chamber of the engine. Via the inlet conduit  12 , fuel at high pressure is constantly resupplied from the high-pressure fuel source. The end of the injection is brought about in turn by increasing the closing force on the tappet  36 , so that the valve member  10 , as a result of the force ratios described above, returns to its closing position. 
     In FIG. 2, an enlargement in the region of the overlap of the lock nut  5  and the valve holding body  1  is shown. The male thread  42  on the valve holding body  1  has an oblique flank  46  in every thread course; this flank forms an angle β with the longitudinal axis  8  of the male thread  42 . The contact flank  52  facing the oblique flank  46  conversely forms an angle α with the longitudinal axis  8  of the male thread  42 , and this angle is preferably within the range about 85° to 95°, and more preferably approximately 90°. The female thread  44  of the lock nut  5  is embodied so that it engages the male thread  42  of the valve holding body  1 . Each thread course of the female thread  44  has one oblique flank  48 , which once the lock nut  5  has been screwed in faces the oblique flank  46  of the male thread  42 . The two oblique flanks  46 ,  48  are not generally pressed together, however, since the lock nut  5  is axially braced against the valve holding body  1 . The flank of the female thread  44  facing the oblique flank  48  is embodied as a contact flank  50  and is preferably within the range of about 85° to 95°, and more preferably approximately perpendicular to the longitudinal axis  8  of the valve holding body  1  and corresponding to the angle α of flank  52 . The contact flank  50  rests on the contact flank  52  of the male thread  42 , so that when the lock nut  5  is screwed in tightly, an axially acting force is transmitted from the lock nut  5  via the outer contact flank  50  onto the contact flank  52  of the male thread  42  of the valve holding body  1 . Since the two contact flanks  50 ,  52  contacting one another are approximately perpendicular to the longitudinal axis  8  of the male thread  42  and thus also approximately perpendicular to the bracing direction of the valve body  3 , there is no, or only a slight, resultant force component in the radial direction relative to the longitudinal axis  8  upon the lock nut  5 . Accordingly no expansion of the lock nut  5  from the tightening occurs, and hence at the high-pressure sealing face  30 , or in other words the contact face of the valve body  3  at the valve holding body  1 , a very high pressure per unit of surface area can be achieved and accordingly an adequately good seal of the inlet conduit  12  at its transition from the valve holding body  1  to the valve body  3 . 
     In FIG. 3, as an alternative to the design shown in FIG. 1, a fuel injection valve is shown in longitudinal section in which there is a shim  6  between the valve holding body  1  and the valve body  3 , thus creating two high-pressure sealing faces: first, at the transition from the valve holding body  1  to the shim  6 , and second, from the shim  6  to the valve body  3 . In this kind of design as well, because of the thread according to the invention on the inside of the lock nut and on the outer jacket face of the valve holding body  1 , an optimized pressure per unit of surface area is obtained, and thus improved tightness of the inlet conduit  12  at its transition from the valve holding body  1  to the valve body  3  because of the high-pressure sealing faces. 
     Alternatively to the fuel injection valves shown in FIGS. 1 and 3, it can also be provided that the lock nut with its female thread engages a male thread disposed on the outer jacket face of the valve body  3 . In that case, the lock nut is braced on a contact face, embodied on the valve holding body  1  facing away from the valve body  3 , that in this case as well, a bracing of the valve body  3  and valve holding body  1  against one another can be effected. 
     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.