Abstract:
A fuel injection valve for internal combustion engines, having a housing in which an outer valve needle and an inner valve needle guided in it are disposed in a bore. The outer valve needle controls an outer row of injection openings, and the inner valve needle controls an inner row of injection openings, to which rows of injection openings fuel is delivered at an injection pressure through a high-pressure conduit embodied in the housing. A control pressure chamber in the housing can be made to communicate with the high-pressure conduit, and by means of its pressure, a closing force is exerted at least indirectly on the inner valve needle. The high-pressure conduit communicates with a control chamber, by whose pressure a closing force is exerted at least indirectly on the outer valve needle, and the control chamber communicates with the control pressure chamber. A control valve is disposed in a housing, and by means of the control valve, the control chamber can be made to communicate with a leak fuel chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 03/00210 filed on Jan. 27, 2003. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is directed to an improved fuel injection valve for internal combustion engines. 
   2. Description of the Prior Art 
   One fuel injection valve known for instance from published, nonexamined German patent application DE 41 15 477 A1 includes an outer valve needle and an inner valve needle guided in it are located in a housing. Both valve needles cooperate, by their end toward the combustion chamber, with a valve seat face in which there are two rows of injection openings. The outer row of injection openings is controlled by the outer valve needle, and the inner row of injection openings is correspondingly controlled by the inner valve needle. Through a high-pressure conduit embodied in the housing, the injection openings are supplied with fuel at high pressure, which emerges, controlled by the valve needles, through the injection openings and from there is injected into the combustion chamber of the engine. 
   A control chamber is embodied in the housing of the fuel injection valve, and its pressure acts on the face end of a pressure piston which is connected to the inner valve needle. In this way, via the pressure in the control chamber, a closing force on the inner valve needle is produced, which keeps this valve needle in contact with the valve seat face. The control chamber can communicate with the injection pressure via a control valve, or can be relieved into a leak fuel chamber, so that the pressure in the control chamber can be controlled in this way. The opening pressure on the inner and outer valve needles is generated, in this known valve by the imposition of fuel pressure on a pressure face, embodied on each of the valve needles; the pressure at which the valve needles open is called the opening pressure. 
   The known fuel injection valve has the disadvantage, however, that the closing force on the outer valve needle is not generated hydraulically but rather via a fixedly prestressed closing spring. The opening pressure of the outer valve needle is therefore not regulatable, and it can be injected through the outer row of injection openings only at a minimum pressure equivalent to the opening pressure of the outer valve needle. Moreover, the prior art has the disadvantage that the control valve that regulates the pressure in the control chamber is embodied as a 3/2-way valve with a slide seat, so that it is relatively complicated and hence expensive to produce. It is thus not possible in the known fuel injection valve to control the injection cross section arbitrarily. 
   SUMMARY AND ADVANTAGES OF THE INVENTION 
   The fuel injection valve of the invention has the advantage over the prior art that both the inner and the outer valve needle can be triggered via only a single control valve. A control chamber is embodied in the housing and communicates with the high-pressure conduit and furthermore with a control pressure chamber. Through the pressure in the control chamber, a closing force is exerted at least indirectly on the outer valve needle. In the housing, there is a control valve by which the control chamber can be made to communicate with a leak fuel chamber, so that the pressure in the control chamber and, because of the communication with the control chamber, in the control pressure chamber as well can be lowered to markedly below the injection pressure via the control valve, so that the closing force on the inner and outer valve needle can be controlled. Via a suitable switching characteristic of the control valve and suitably dimensioned inlets and outlets from the control chamber and of its communication with the control pressure chamber, a separate triggering of the outer valve needle, or selectively of both valve needles, can be achieved. 
   In an advantageous feature of the subject of the invention, the control valve has a valve chamber, which communicates with the control chamber, and also has a valve member, which is controlled by an actuator. The actuator is advantageously embodied as an electric actuator and in particular as a piezoelectric actuator. As a result, the valve member can be controlled precisely, and the valve member can be moved directly to the desired position. 
   In a further advantageous feature, in a first switching position, the valve member cooperates with a first valve seat, and in a second switching position it cooperates with a second valve seat; in the first switching position, the valve chamber is sealed off from the leak fuel chamber, and in the second switching position it communicates with the leak fuel chamber. By means of this valve member, the pressure in the control chamber can be controlled precisely and without any significant time lag. 
   In a further advantageous feature, the valve chamber of the control valve can be made to communicate with the high-pressure conduit via a connecting conduit, and when the valve member is in contact with the second valve seat, it closes the connecting conduit. Upon relief of the control chamber, the connecting conduit thus becomes inoperative and does not impede the further function of the pressure regulation in the control chamber. Upon actuation of the control valve and upon motion of the valve member toward the first valve seat, the high-pressure conduit is uncovered, and fuel can flow at the injection pressure into the valve chamber and from there into the control chamber. As a result, after the end of the injection, a high pressure is built up very quickly in the control chamber, so that a strong closing force on the outer valve needle and thus also on the inner valve needle results. 
   In a further advantageous feature, an outer pressure piston is disposed in a housing; it communicates with the outer valve needle, and its end face defines the control chamber. In this way, as a result of the pressure in the control chamber, a hydraulic force on the end face of the outer pressure piston is produced, so that a closing force is exerted on the outer valve needle. Because of the separation of the function of the pressure face subjected to pressure and of the valve needle, the two parts can be optimized separately from one another. 
   In still another advantageous feature, the outer pressure piston, in the opening stroke motion of the outer valve needle, comes to rest on a wall of the control chamber, interrupting the communication of the control chamber with the high-pressure conduit. As a result, when the fuel injection valve is open, fuel no longer flows into the control chamber, and thus the leak fuel losses of the fuel injection valve are minimized. 
   In another advantageous feature, the control pressure chamber is embodied in the outer pressure piston and communicates with the control chamber through a bore in the outer pressure piston. This construction allows direct triggering of the inner valve needle, which is located inside the outer valve needle, and furthermore results in a very space-saving construction. 
   In an advantageous feature, a pressure markedly lower than the injection pressure, this lower pressure preferably being atmospheric pressure, prevails in the leak fuel chamber. The lower the pressure in the leak fuel chamber, the greater are the pressure differences from the injection pressure, so that correspondingly greater forces on the inner and outer valve needle can also be achieved, and hence shorter switching times. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One exemplary embodiment of the fuel injection valve of the invention is described herein below, with reference to the drawings, in which: 
       FIG. 1  is a longitudinal section through a fuel injection valve of the invention in its essential region; 
       FIG. 2 , an enlargement of  FIG. 1  in the region of the end toward the combustion chamber of the injection valve, this detail marked II in  FIG. 1 ; 
       FIG. 3 , an enlargement of  FIG. 1  in the region marked III; and 
       FIG. 4 , a cross section through the detail shown in  FIG. 3 , taken along the line injection IV—IV. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1 , a longitudinal section is shown through a fuel injection valve of the invention, the fuel injection valve having a housing  1 , which has a valve body  3 , an intermediate body  7 , an intermediate disk  9 , a control body  12 , and a retaining body  14 , with these components each resting on one another in the order recited. All these parts of the housing  1  are pressed against one another by their contact faces by means of a lock nut  5 . A high-pressure conduit  10  embodied in the housing  1  communicates with a high-pressure fuel source, not shown in the drawing, and extends as far as the inside of the valve body  3  through the retaining body  14 , the control body  12 , the intermediate disk  9 , and the intermediate body  7 . In the valve body  3 , the high-pressure conduit  10  discharges into a pressure chamber  26 , which is embodied as a radial enlargement of a bore  16  embodied in the valve body  3 . The bore  16 , on its end toward the combustion chamber, is closed off by a seat face  24 , and injection openings  30  are embodied in the seat face  24  that connect the bore  16  to the combustion chamber of the engine. A pistonlike outer valve needle  20  is disposed in the bore  16  and is guided sealingly in a portion of the bore  16  remote from the combustion chamber. Beginning at the guided portion, the outer valve needle  20  tapers toward the combustion chamber, forming a pressure shoulder  27 , and on its end toward the combustion chamber it changes into a valve sealing face  32 , with which it rests on the seat face  24  in the closing position. An annular conduit  28  is embodied between the outer valve needle  20  and the wall of the bore  16  and connects the pressure chamber  26  to the seat face  24 ; the pressure shoulder  27  is disposed at the level of the pressure chamber  26 . In the closing position, the outer valve needle  20  closes off the injection openings  30  from the fuel in the annular conduit  28 , so that only when the outer valve needle  20  has lifted from the seat face  24  can fuel flow to the injection openings  30 . 
   The outer valve needle  20  is embodied as a hollow needle and has a longitudinal bore  21 . An inner valve needle  22  is disposed longitudinally displaceably in the longitudinal bore  21 , and with its end toward the combustion chamber it also comes to rest, in the closing position, on the seat face  24 .  FIG. 2  shows an enlargement of the detail marked II in  FIG. 1 , that is, the region of the seat face  24 . The injection openings  30  in the seat face  24  are grouped into one outer row  130  of injection openings and one inner row  230  of injection openings. The outer valve needle  20 , on its end toward the combustion chamber, has a conical valve sealing face  32 , which has a larger opening angle than the likewise conically embodied seat face  24 . As a result, on the outer edge of the sealing face  32 , a sealing edge  34  is embodied, which in the closing position of the outer valve needle  20  comes to rest on the seat face  24 . The sealing edge  34  is disposed upstream of the outer row  130  of injection openings, so that when the sealing edge  34  is in contact with the seat face  24 , the injection openings of the outer row  130  are sealed off from the annular conduit  28 . On the end toward the combustion chamber of the inner valve needle  22 , a conical pressure face  36  is embodied, which in turn borders on a likewise conical face  38  that forms the end of the inner valve needle  22 . At the transition from the pressure face  36  to the conical face  38 , a sealing edge  37  is embodied, which in the closing position of the inner valve needle  22  comes to rest on the seat face  24 . The contact of the sealing edge  37  is effected here between the outer row  130  and the inner row  230  of injection openings, so that upon contact of the inner valve needle  22  with the seat face  24 , only the inner row  230 , but not the outer row  130 , of injection openings is sealed off from the annular chamber  28 . 
     FIG. 3  shows an enlargement of  FIG. 1  in the detail marked III, that is, in the region of the intermediate body  7 , intermediate disk  9 , and control body  12 . A piston bore  45  is disposed in the intermediate body  7 , and a pressure piston  40  is disposed in this bore and rests with an end toward the combustion chamber on the outer valve needle  20 . By means of a radial enlargement of the piston bore  45 , a spring chamber  43  is embodied, in which a closing spring  44 , which surrounds the outer pressure piston  40  over part of its length, is disposed with compressive prestressing between a contact face  41  of the spring chamber  43  and an annular face  39  of the outer pressure piston  40 . Because of the prestressing of the closing spring  44 , the outer pressure piston  40  is pressed in the direction of the valve body  3 , and thus the outer valve needle  20  is also pressed in the direction of the seat face  24 . A guide bore  47  is embodied in the longitudinal direction in the outer pressure piston  40 , and in it an inner pressure piston  42  is guided that rests with its end, toward the combustion chamber, on the inner valve needle  22 . The inner pressure piston  42  is longitudinally displaceable in the outer pressure piston  40  and moves synchronously with the inner valve needle  22 . 
   The piston bore  45 , face end  51 , remote from the combustion chamber, of the outer pressure piston  40 , and the intermediate disk  9  define a control chamber  50 , which communicates with a control pressure chamber  52  via a connecting bore  55  embodied in the outer pressure piston  40 ; the control pressure chamber  52  is defined by the guide bore  47  and by the face end  53 , remote from the combustion chamber, of the inner pressure piston  42 . The control chamber  50  communicates with the high-pressure conduit  10  via an inlet throttle  70  and with a valve chamber  68 , embodied in the control body  12 , via an outlet throttle  72 . A valve member  60  is disposed in the valve chamber  68 ; it is embodied essentially hemispherically and forms a control valve  58 . A flattened side of valve member  60  is oriented toward the intermediate disk  9 , while a hemispherical side of the valve member  60  is connected to a pressure piece  48  that is guided in a receiving body  13  disposed in the retaining body  14 . The pressure piece  48  is longitudinally displaceable by means of an actuator  46  and as a result also moves the valve member  60  within the valve chamber  68 ; the actuator is embodied here as a piezoelectric actuator, for example. The pressure piece  48  is surrounded by a leak fuel chamber  78 , which because of its communication with a leak fuel system, not shown in the drawing, is always at a low pressure. Remote from the intermediate disk  9  in the valve chamber  68 , there is a first valve seat  62 , with which the valve member  60  can come into contact with its spherical valve sealing face  66 . Opposite the first valve seat  62  in the valve chamber  68 , there is a second valve seat  64 , with which the valve member  60  can come into contact with its flattened side. A connecting conduit  74 , which likewise discharges into the valve chamber  68  and which communicates with the high-pressure conduit  10  via a transverse conduit  76 , is closed by contact of the valve member  60  with the second valve seat  64 .  FIG. 4  shows a cross section through  FIG. 3  along the line IV—IV. The course of the transverse conduit  76  as a semicircular groove on the contact face, toward the intermediate body  7 , of the intermediate disk  9  is clearly shown here. In the cross section shown, the inlet throttle  70 , outlet throttle  72 , connecting conduit  74  and high-pressure conduit  10  are also readily visible. 
   The function of the fuel injection valve is as follows: At the onset of the injection cycle, the fuel injection valve is in the closing position; that is, both the outer valve needle  20  and the inner valve needle  22  are in contact with the seat face  24  and close both the inner row  230  and the outer row  130  of injection openings. Since the valve member  60  is resting on the first valve seat  62 , both the control chamber  50  and the control pressure chamber  52  communicate with the high-pressure conduit  10  via the inlet throttle  70 , so that in both the control chamber  50  and the control pressure chamber  52 , the high fuel pressure of the high-pressure conduit  10  prevails; this pressure is equivalent to the injection pressure. The face end  51  of the outer pressure piston  40  has a larger hydraulically operative face than the pressure shoulder  27  of the outer valve needle  20 , so that the outer valve needle  20  remains in the closing position. The force of the closing spring  44  plays only a subordinate role here; the closing spring  44  serves primarily to keep the outer valve needle  20  in the closing position when the engine is not in operation. In the valve chamber  68  as well, because of the communication via the connecting conduit  74  and also via the outlet throttle  72 , the pressure in the high-pressure conduit  10  prevails. In the leak fuel chamber  78 , conversely, a low pressure prevails, which as a rule is approximately equivalent to atmospheric pressure. 
   If an injection is to take place, the actuator  46  is actuated, and the valve member  60  moves together with the pressure piece  48  away from the first valve seat  62  toward the second valve seat  64 . As a result, the valve chamber  68  is made to communicate with the leak fuel chamber  78 , so that the valve chamber  68  and the control chamber  50  as well are pressure-relieved via the outlet throttle  72 . By means of the contact of the valve member  60  with the second valve seat  64 , the connecting conduit  74  is closed, so that no further fuel can flow into the valve chamber  68  via the transverse conduit  76 . The inlet throttle  70  and the outlet throttle  72  are dimensioned such that although the pressure in the control chamber  50  does drop, it does not drop to the level of the leak fuel chamber  78 . Because of the dropping pressure in the control chamber  50 , the hydraulic force on the face end  51  of the outer pressure piston  40  decreases, so that now the hydraulic force on the pressure shoulder  27  predominates. The outer valve needle  20  thereupon lifts from the seat face  24 , and fuel flows out of the annular chamber  28  to the outer row  130  of injection openings, and from there is injected into the combustion chamber of the engine. As a result of the lifting of the outer valve needle  20 , the pressure face  36  of the inner valve needle  22  is now also acted upon by fuel, but this force is not sufficient to overcome the hydraulic force on the face end  53  of the inner pressure piston  42 , since for that purpose the pressure in the control chamber  50  is still too high. The outer valve needle  20  and the outer pressure piston  40  move away from the combustion chamber until such time as the face end  51  of the outer pressure piston  40  comes to rest on the intermediate disk  9 . 
   When fuel is to be injected into the combustion chamber of the engine through only the outer row  130  of injection openings, for instance for the sake of a pilot injection, then at that instant, the valve member  60  must be moved again by the actuation of the actuator  46 , so that the communication between the valve chamber  68  and the leak fuel chamber  78  is interrupted. As a result, the communication between the high-pressure conduit  10  and the valve chamber  68  via the connecting conduit  74  is reestablished, so that fuel flows at injection pressure out of the high-pressure conduit  10  via the outlet throttle  72  and the inlet throttle  70  into the control chamber  50 . There, a high fuel pressure level builds up again, which presses the outer pressure piston  40  and thus also the outer valve needle  20  back into the closing position again. 
   Conversely, if the injection is to be done through the entire injection cross section, that is, through all the injection openings  30 , then the valve member  60  remains in contact with the second valve seat  64 . Because of the contact of the face end  51  of the outer pressure piston  40  with the intermediate disk  9 , the inlet throttle  70  is closed. The pressure in the control pressure chamber  52  can thus drop further via the outlet throttle  72  and the communication of the valve chamber  68  with the leak fuel chamber  78 , until the hydraulic force on the pressure face  36  of the inner valve needle  22  is greater than the hydraulic force on the face end  53  of the inner pressure piston  42 . The inner valve needle  22 , with its sealing edge  37 , now lifts from the seat face  24 , and fuel is additionally injected through the inner row  130  of injection openings. Here as well, the injection is terminated by actuating the actuator  46 , so that the valve member  60  moves back into contact with the first valve seat  62  again. In the manner already described above, high fuel pressure is now once again carried into the control chamber  50  and, via the connecting bore  55 , into the control pressure chamber  52  as well. As a result, both the inner valve needle  22  and the outer valve needle  20  close the injection openings  30  off again from the annular conduit  28 . 
   Besides the timing control for opening only the outer row of injection openings, a selective opening can also be attained by means of a middle position of the control valve  58 . By means of the piezoelectric actuator  46 , the valve member  60  is moved into a middle position between the first valve seat  62  and the second valve seat  64 , so that all the connections with the valve chamber  68  are opened. As a result, fuel flows on the one hand out of the valve chamber  68  into the leak fuel chamber  78  and on the other flows constantly into the valve chamber  68  via the connecting conduit  74 , so that only a certain pressure drop occurs in the valve chamber  68 , but the pressure is still markedly above the pressure in the leak fuel chamber  78 . This pressure is sufficient to keep the inner valve needle  22  in its closing position, but the closing force on the outer valve needle  20  has now been reduced to such an extent that the outer valve needle opens. Once again, the injection is terminated as already described above by switching of the control valve  58 . 
   In this exemplary embodiment, the actuator  46  is preferably a piezoelectric actuator. The valve member  60  in the valve chamber  68  requires only a short stroke for its function, of the kind that as a rule can be brought to bear by a piezoelectric actuator. If necessary, a hydraulic booster may be provided, with which longer strokes can be achieved and which is quite well known from the prior art. Furthermore, piezoelectric actuators offer the advantage that they can switch extremely fast. It is thus possible without problems, in the manner described above, to perform a precise preinjection through only the outer row  130  of injection openings. 
   The foregoing relates to preferred exemplary embodiments in 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.