Abstract:
A fuel injection device for internal combustion engines which under the control of a control unit supplies fuel injection valves with fuel from a high-pressure fuel source. The fuel injection valve has an injection valve member, whose opening and closing position is determined by a pressure acting upon the injection valve member set in a control chamber. To perform an injection, the pressure in the control chamber must be relieved, which is accomplished with a control valve that opens two different outflow cross sections of an outflow conduit of the control chamber in succession. It is thus possible to accomplish an adapted opening of a fuel injection valve member for a preinjection and a main injection.

Description:
BACKGROUND OF THE INVENTION 
     The invention is based on a fuel injection device for internal combustion engines. In one such fuel injection device, known from German Patent Disclosure DE 196 24 001 A1, the valve chamber in a first version communicates with the control chamber without any reduction in cross section. Upon actuation by the piezoelectric actuator, the control valve makes the outflow cross section to the outflow conduit either fully open or the central valve closes the outflow cross section. In another version, the valve chamber communicates with the control chamber via a connecting conduit, and the connecting conduit is coaxial with the valve seat on the side of the outflow conduit. By actuation of the control valve member by the piezoelectric actuator, either the outflow cross section from the valve chamber to the outflow conduit is fully opened or closed, or to attain a preinjection, the control valve member is moved away from the valve seat toward the outflow conduit to the entrance of the connecting conduit and to the valve chamber; as a consequence of this motion, the control chamber is briefly opened to the outflow conduit via the valve chamber. For an ensuing main injection, the control valve member is moved into a middle position, in which both the cross section toward the outflow conduit and the cross section of the connecting conduit into the valve chamber are fully opened. This embodiment has the disadvantage that to relieve the pressure in the control chamber, only a single, geometrically defined outflow cross section to the outflow conduit exists. The preinjection quantity in the second version described is such that the speed of adjustment of the control valve member by the piezoelectric actuator and the geometrically defined travel of the control valve member are predetermined variables for the degree of relief of the pressure in the control chamber. In particular, the maximum relief cross section is the same for both the relief for the preinjection and for the relief for the main injection, which is disadvantageous in view of any fine adaptation of the opening speed of the injection valve in various operating conditions. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The fuel injection device according to the invention has an advantage that two different outflow cross sections can be established in succession, by making two different connection cross sections to the control chamber as a function of the position of the control valve member. It is thus possible to graduate the outflow cross section as a function of the stroke. Particularly for a slight relief of the control pressure in the control chamber, a first, smaller outflow cross section can come into effect, with which the preinjection stroke of the injection valve member can be set with greater precision. For the main injection, a large outflow cross section is subsequently available, which allows a fast motion of the injection valve member. 
     Advantageously, a cross section that is additional to the first connection cross section is provided as the second connection cross section. This makes it possible to attain a large effective change in cross section. The first connection cross section is located in a space-saving way in the intermediate valve member, where sufficiently large flow cross section is furnished on the outer circumference. The second connection cross section can be defined by the flow cross section at the interstices between the longitudinal ribs, which is determined by the stroke of the intermediate valve member, which uncovers a certain flow cross section between the sealing seat shoulder and the sealing face. 
     In a further feature crosswise connections that are always open are furnished between the connecting conduit of the valve member and the valve chamber, so that this connecting conduit is ready as an always-open first connection cross section, to which a further, second connection cross section is added when the intermediate valve member is opened. 
     It is also advantageous to close the connecting conduit in the intermediate valve member when the control valve member contacts the intermediate valve member; thus the cross section of the connecting conduit is furnished not in the intermediate valve member, but along the outer circumference of the intermediate valve member. 
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a fuel injection device with fuel supply from a high-pressure fuel reservoir, and with a fuel injection valve of known design; 
     FIG. 2 shows a first exemplary embodiment of the invention, with a control valve member that actuates a first embodiment of an intermediate valve member; 
     FIGS.  3   a  through  3   c  show the stroke courses of the injection valve member, control valve member and intermediate valve member of the exemplary embodiment of FIG. 2; 
     FIG. 4 shows a modification of the exemplary embodiment of FIG. 2, with an intermediate valve member whose connecting conduit can be closed by the control valve member; and 
     FIGS.  5   a  through  5   b  show the stroke courses of the injection valve member, control valve member and intermediate valve member of the exemplary embodiment of FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A fuel injection device with which a wide variation of the fuel injection with regard to the injection quantity and the instant of injection is possible at high injection pressures and at little expense is achieved by a so-called common rail system. This makes a different kind of high-pressure fuel source available than exists with the usual high-pressure fuel injection pumps. However, the invention is also applicable in principle to conventional fuel injection pumps. Nevertheless, its use in a common rail injection system is especially advantageous. 
     In the common rail injection system shown in FIG. 1, a high-pressure fuel reservoir  1  is provided as the high-pressure fuel source, and it is supplied with fuel by a high-pressure fuel feed pump  2  by a fuel supply container  4 . The pressure in the high-pressure fuel reservoir  1  is detected by a pressure sensor  6  and delivered in the form of a signal to an electric control unit  8 , which via a pressure control valve  5  controls the pressure in the high-pressure fuel reservoir. Alternatively, the supply quantity of the high-pressure fuel pump can be varied in this way. The control unit also controls the opening and closing of high-pressure fuel injection valves  9 , which are supplied for injection with fuel from the high-pressure fuel reservoir. 
     In a known version, the fuel injection valve  9  has a valve housing  11 , which on one end, that is, the end intended for mounting in the engine, has injection ports  12 , whose outlet from the interior of the fuel injection valve is controlled by an injection valve member  14 . This valve member is embodied in the example being described as an elongated valve needle, which on one end has a conical sealing face  15  that cooperates with an inner valve seat on the valve housing, and from there the injection ports  12  lead away. The injection ports can also begin at a bore that adjoins the valve seat. The valve needle is guided in a longitudinal bore  13  by its upper end, remote from the sealing face  15 , and is urged in the closing direction on the end remote from the sealing face  15  and emerging from the longitudinal bore  13  by a compression spring  18 . Between where it is guided in the longitudinal bore  13  and the valve seat, the valve needle  14  is surrounded by an annular chamber  19 , which discharges into a pressure chamber  16  that in turn communicates constantly, via a pressure line  17 , with the high-pressure fuel reservoir  1 . In the region of this pressure chamber, the valve needle  14  has a pressure shoulder  20 , by which it is acted upon by the pressure in the pressure chamber  16 , counter to the force of the spring  18 , in the direction of lifting of the sealing face  15  from the valve seat. 
     The valve needle is also actuated by a tappet  21 , whose face end  22 , remote from the valve needle  14 , defines a control chamber  24  in a tappet guide bore  23 . This control chamber communicates constantly with the pressure line  17 , or the high-pressure fuel reservoir  1 , via an inflow conduit  26  in which an inflow throttle  28  is provided. The inflow conduit discharges from the side into the control chamber  24  and cannot be closed. Coaxially with the tappet  21 , a connecting conduit  29  leads away from the control chamber  24  and discharges into a valve chamber  30  of a control valve  31 . In the connecting conduit, which at the same time is an outflow conduit, a diameter limitation is provided, preferably in the form of an outflow throttle  32 . The detailed structure of the control valve  31  is shown more specifically in the exemplary embodiments of FIGS. 2 and 3. A common feature of these exemplary embodiments is that the control valve  31  includes a control valve member  34 , which comprises a valve tappet  35 , the valve tappet  35  is guided in a tappet bore  36 , and a valve head  37 , is located on an end of the control valve member  34  that protrudes into the valve chamber  30 . On the end of the valve tappet  35  opposite the valve head, a spring plate  38  is provided, a compression spring  39  is supported on the spring plate  38  that seeks to urge the control valve member into the closing position. In the opposite direction, the control valve member  34  is acted upon by a piston  40 , which is part of a piezoelectric actuator  41  and upon excitation of the piezoelectric element the control valve member is positioned in different opening positions depending on the degree of excitation of the piezoelectric element. The piston can either be joined directly to the piezoelectric element of the piezoelectric actuator, or it can be moved by this element, by means of a hydraulic or mechanical intensification. 
     For a more-detailed illustration of the embodiment of the control valve  31  according to the invention, the control valve will be described in further detail in conjunction with FIG.  2 . Once again, the end of the tappet  21  is shown, which actuates the valve needle  14 . The tappet  21 , with a face end  22  acting as a movable wall, encloses the control chamber  24  in the tappet guide bore  23 . The upward adjustment of the tappet  21 , in the opening direction of the injection valve member  14 , is limited by a stop  42  that leaves an outer annular chamber  43  open, into which the inflow conduit  26  discharges. The connecting conduit  29  leads axially away in the region of the stop  42  and discharges into the valve chamber  30 . This valve chamber has a circular- cylindrical circumferential wall  45 , which changes over at a conical valve seat  46  into an annular chamber  48  surrounding the valve tappet  35 . From this annular chamber, an outflow conduit  49  leads to a fuel return or to a relief chamber. 
     The valve head  37  disposed on the end of the valve tappet  35  has a conical valve head sealing face  51 , remote from the entrance of the connecting conduit  29  into the valve chamber  30 , and this sealing face cooperates with the valve seat  46  and thus controls the communication between the valve chamber  30  and the annular chamber  48  or the adjoining outflow conduit  49 . The annular chamber  48  is formed by a recess on the circumference of the valve tappet  35 , adjacent to the sealing face  51  of the valve head  37 , and this recess communicates with the tappet bore  36  leading away from the valve chamber  30 . 
     The side of the valve head toward the connecting conduit  29  has a flat face end  53 , which upon actuation of the valve tappet  35  comes into contact with a face end  54  of an intermediate valve member  57 , which forms an intermediate valve  56 , and upon further actuation of the valve tappet  35 , the intermediate valve member  57  is moved out of its closing position. 
     The intermediate valve member  57  has ribs  59  on its outer circumference, between which flow cross sections are formed and which are guided by their face ends in a guide bore  60 . Toward the valve chamber  30 , the guide bore  60  narrows via a sealing seat shoulder  62 , to form a connecting bore  63  that discharges into the valve chamber  30  coaxially with the guide bore. The sealing seat shoulder  62  thus acts as the valve seat of the intermediate valve member. 
     The part of the intermediate valve member  57  that has the ribs  59  tapers, adjoining the ribs, via a conical sealing face  64  to form a cylindrical actuating portion  65 , which protrudes through the connecting bore with a clearance from the connecting bore into the valve chamber  30 . On the opposite side, the intermediate valve member  57  is loaded by a closing spring  68 , which puts the intermediate valve member with its sealing face  64  into contact with the sealing seat shoulder  62 . The closing spring  68  is supported at the transition between the guide bore  60  and the portion  29  leading onward of the outflow conduit, which discharges into the control chamber  24  coaxially with the guide bore  60 . 
     Extending through the intermediate valve member  57  is an axial connecting conduit  69 , which also connects the valve chamber  30  with the control chamber  24  via the portion  29  of the outflow conduit, when the intermediate valve member  57  is in its closing position. The connecting conduit can be embodied as a stepped bore, of which one stepped bore portion  70 , located toward the control chamber  24  and having a smaller diameter, determines a first connection cross section. On the side of the valve chamber  30  in the region of the actuating portion  65 , at least one recess  71  leads away from the connecting conduit  69 , extending crosswise to it, in such a way that upon contact of the flat face end  53  of the valve head  37  with the face end  54  of the intermediate valve member  57 , the communication between the control chamber  24  and the control chamber  30  is preserved, and the portion  70  of the connecting conduit  69  continues to determine the connection cross section. 
     The mode of operation of the embodiment of FIG. 2 is such that to trip a fuel injection with the aid of the control valve  31 , the pressure in the control chamber  24  is lowered by opening the outflow conduit  29 ,  70 ,  69 ,  30 ,  48 ,  49 . With decoupling by the throttle  28  in the inflow conduit  26 , the pressure in the control chamber  24  drops in such a way that the valve member opens under the influence of the opening forces in the pressure chamber  16 , counter to the force of the spring  18 . The degree of opening of the injection valve member  14  can be varied by means of the magnitude of the control chamber, or the quantity of the pressure fluid or fuel flowing out there. If the control valve member  34  executes only a partial stroke, such that the face end  53  does not come into contact with the intermediate valve member  57 , then this determines the maximum flow through the portion  70  of the connecting conduit  69 . The relief rate and thus the stroke of the injection valve member  14  are correspondingly slight. Hence only a slight fuel injection quantity, for instance for introducing a preinjection quantity into the combustion chamber, is pumped. However, if a larger fuel quantity is meant to gain injection, then the control valve member  34  opens fully and comes into contact with the intermediate valve member  57  and lifts the valve member  57  from the sealing seat shoulder  62  via the actuating portion  65  and thus in addition to the first connection cross section makes a second connection cross section available, the latter being determined by the portion  70 . The second connection cross section can be determined either by the flow cross section between the sealing seat shoulder  62  and the sealing face  64 , or by the remaining flow area between the ribs  59 . By means of the now-added second connection cross section, the relief of the control chamber  24  is faster and greater in extent, so that the injection valve member  14  can be opened to the intended extent, for instance with a stroke determined by the contact of its end face  22  with the stop  42 . 
     The partial relief of the control chamber  24  for performing the preinjection has the advantage that upon closure of the control valve member  34 , the pressure can build up again very rapidly, since the pressure has not been reduced as much as it would otherwise be reduced. 
     The functional sequence described can be understood better from FIGS.  3   a  through  3   c . FIG.  3   a  shows the stroke of the injection valve member  14  over time. The stroke of the injection valve member for the preinjection V and the stroke of the injection valve member for performing the main injection H can be seen. These strokes are interrupted by an injection pause P. In FIG.  3   b , the stroke of the control valve member  34  required for the purpose is shown, represented by a short stroke V s  and a long stroke H s . In FIG.  3   c , finally, the stroke Z of the intermediate valve member over time is plotted, with the association with the stroke H s  of the control valve member  34  and the stroke H for the main injection of the injection valve member  14 . 
     In FIG. 4, a second exemplary embodiment of the invention is shown, in a modification of the version of FIG.  2 . With an otherwise identical construction, the difference here is that the valve head  134  instead of the flat face end  53  now has a conical face end  73 , embodied as a sealing face, which cooperates with a face end, embodied as a valve seat  74 , of the intermediate valve member  157 . The valve seat  74  surrounds the axial connecting conduit  69 , provided in the intermediate valve member  57  of FIG. 2, in the region of its outlet at the actuating portion  65  into the valve chamber  30 . Instead of a leaf spring  68  provided in the exemplary embodiment of FIG. 2, a spiral spring  168  is now provided, which loads the intermediate valve member  157  from the side of the control chamber  24  and keeps the intermediate valve  157  with its sealing face  64  in contact with the sealing seat shoulder  62 , as long as the intermediate valve member  157  has not been displaced by the control valve member  134 . In this version, the portion  70  of the connecting conduit  69  again forms the first connection cross section between the control chamber  24  and the valve seat  62 , but the connection is closed whenever the control valve member  134  comes into contact with the intermediate valve member  157  by seating the on the conical valve head  137  on the conical valve seat  74 . Now, however, by lifting of the intermediate valve member  157 , the second connection cross section between the ribs  59 , or between the sealing seat shoulder  62  and the sealing face  64 , is opened. The second connection cross section is designed such that the second connection is correspondingly larger than the first connection cross section  70  of the portion of the connecting conduit  69 , taking into account the fact that here the flow cross section of the second connection cross section takes the place of the flow cross section of the first connection cross section. This design can be more favorable in an individual instance, to make it possible to define the second connection cross section more exactly. 
     In FIG.  5   a , analogously to FIG.  3   a , the stroke of the injection valve member  14  is plotted over time, again with the stroke V for the preinjection and the stroke H for the main injection. From FIG.  5   b , it can be seen that in the present case the further advantage of the feature of FIG. 4 is that the control valve member, to interrupt the fuel injection between the preinjection V and main injection H, does not have to be returned to its original closing position. As indicated by the curve course S, the control valve member  134  executes a strokes hV in the process comes into contact with the conical valve seat  74  of the intermediate valve member. Over the travel distance between the closing position of the control valve member  134  at its conical valve seat  46  and its contact with the conical valve seat  74 , the relief of the control chamber  24  takes place, determined by the first connection cross section of the portion  70  of the connecting conduit  69 , which leads to the preinjection. After that, with the closure of the connecting conduit  69 , the pressure in the control chamber  24  can build up again and can close the injection valve member. For the main injection, the control valve member  134  is moved onward up to the stroke h h , and in the process it opens the intermediate valve member as indicated by the stroke curve Z. With this opening of the intermediate valve, the relief of the control chamber  24  takes place at a higher relief rate, and accordingly the opening stroke of the injection valve member that is required for the main injection is made possible. 
     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.