Abstract:
A fuel injection valve in which a pistonlike outer valve needle is disposed longitudinally displaceably in a bore and cooperates with a valve seat to control at least one injection opening. A control chamber regulatable by a valve is provided and pressure in the control chamber exerts a closing force at least indirectly on the outer valve needle in the direction of the valve seat. A pressure face embodied on the outer valve needle is acted upon by the pressure in a pressure chamber, which is embodied between the outer valve needle and the wall of the bore and extends as far as the valve seat, so that an opening force on the outer valve needle results that is oriented counter to the closing force. An inner valve needle is guided in the outer valve needle and controls at least one additional injection opening and is acted upon by the pressure in the control chamber at least indirectly in the direction of the valve seat.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 02/01036 filed on Mar. 22, 2002. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   To reduce emissions and increase the efficiency of internal combustion engines with direct fuel injection, one goal is to inject the fuel into the combustion chamber of the engine in as finely-atomized a form as possible. To that end, first the injection pressure at which the fuel is injected through the fuel injection valve is increased. Second, the number of injection ports of the fuel injection valve is increased, so that the diameter of the individual injection ports can be reduced. The goal of this provision is to increase the energy of injection streams while at the same time reducing the droplet diameter. If very small quantities are to be fed, then when the pressures at the fuel injection valve are high the injection times are quite short. The course of combustion is consequently powerful and correspondingly noisy. 
   2. Description of the Prior Art 
   From European Patent Application EP 0 470 348 A1, for instance, a fuel injection valve of variable injection cross section is known, in which two rows of injection openings are embodied. These injection openings are controlled by an inner valve needle and a tube surrounding the valve needle; both the tube and the inner needle are acted on by closing springs, which press them into contact with a valve seat, as a result of which the injection openings are closed. If fuel at high pressure is introduced into corresponding pressure chambers, then the tube and the inner needle are acted upon by the fuel pressure in these pressure chambers. Depending on the pressure of the fuel introduced, either only the inner needle lifts from the valve seat and uncovers the first row of injection openings, or the inner needle and tube lift up from the valve seat successively, so that both rows of injection openings are opened in succession. The opening of the inner needle and the tube is accordingly pressure-controlled, so that the successive opening of the inner needle and the outer tube is achieved by means of a skillful design of the pressure faces and of the force of the closing springs. 
   Stroke-controlled fuel injection systems are also known from the prior art, in which a valve needle has a pressure face that is constantly urged in the opening direction by fuel at high pressure. The contrary force is generated not by a closing spring but rather hydraulically by a valve piston, which acts on the valve needle and in turn, because of the fuel pressure in a control chamber, exerts a closing force on the valve needle. As an example here, German Patent Disclosure DE 198 27 267 A1 can be named. By varying the fuel pressure in the control chamber, the closing force on the valve needle is changed, so that this needle is moved against the pressure face by the hydraulic force. Such stroke-controlled fuel injection systems are used in many modern internal combustion engines, especially for self-igniting engines in passenger cars. 
   A combination of the two systems, that is, of the variable injection cross section and the stroke-controlled injection system, would be especially advantageous to further optimize the combustion process. Until now, however, it was not possible without major effort to adopt the variable injection cross section to the stroke-controlled systems without making further modifications. Doing so requires complicated sealing edges or additional control valves, which are complicated to manufacture and expensive. 
   SUMMARY OF THE INVENTION 
   The fuel injection valve of the invention has the advantage over the prior art that with a stroke-controlled injection system, two rows of injection openings can be opened successively, and a shaping of the course of injection is thus possible without requiring additional control edges or control valves. An inner valve needle is guided in the outer valve needle, and each controlls at least one injection opening. In the fuel injection valve, a fuel-filled control chamber is embodied, by whose pressure the valve needles are urged at least indirectly in the direction of the valve seat. If the pressure in the control chamber changes, then the closing force exerted by the valve needles also changes, so that triggering of the injection openings is possible. 
   In an advantageous feature of the invention, a throttle connection is formed by the opening stroke motion of the outer valve needle, so that the inner valve needle is no longer acted upon by the pressure in the control chamber. As a result, the closing force on the inner valve needle is reduced in a simple way, without requiring a control edge or an additional valve. 
   In an advantageous feature, the outer valve needle is connected to an outer piston rod, whose end face is acted upon by the pressure in the control chamber and thereby generates the closing force on the valve needle. As a result, the function of the valve needle and of the pressure-actuated piston rod can advantageously be separated from one another and thus each designed optimally. 
   In a further advantageous feature, the throttle connection is formed between the face end of the piston rod and a stationary bottom face, so that the throttle connection can be embodied in a simple way that is accordingly easy to manufacture. 
   In another advantageous feature, the inner valve needle is also connected to an inner piston rod, whose face end is likewise acted upon by the pressure in the pressure chamber and thus generates the closing force on the inner valve needle. By this means as well, the function of the valve needle and of the piston rod can be separated. 
   In still another advantageous feature, the inner piston rod is guided in the outer piston rod, so that both piston rods are coaxial to one another. As a result, the connection of the outer piston rod to the outer valve needle, and of the inner valve needle to the inner piston rod, can advantageously be achieved in a simple way. 
   In a further advantageous feature, the inner piston rod, in the opening stroke motion of the inner valve needle, comes to rest on a stop face embodied on the inside of the outer piston rod. As a result, the stroke stop of the inner valve needle is realized in a simple way, without having to embody a stroke stop on the housing of the fuel injection valve. 
   In still another advantageous feature, the outer piston rod, on its end remote from the combustion chamber, has an inward-projecting region. As a result, an inner control chamber is defined by the outer valve needle, the inward-projecting region, and the inner valve needle, and this inner control chamber communicates with the control chamber, the communication being embodied in the form of a connecting bore. As a result, the pressure equalization between the control chamber and the inner control chamber and thus the closing force on the inner valve needle in the opening stroke motion can be adapted by means of the design of the valve needle, so that a defined, successive opening of the outer valve needle and the inner valve needle takes place, and thus the desired shaping of the injection course takes place as well. 
   In still another advantageous feature of the invention, the inner valve needle has a pressure face, which is not acted upon by the pressure in the pressure chamber until after the outer valve needle has lifted from the valve seat. As a result, an opening force on the inner valve needle is produced only when an injection is to occur. Because of this, no opening force acts on the inner valve needle between injections, and this needle always securely closes the injection openings assigned to it. 
   In still another advantageous feature of the invention, the pressure in the control chamber is established by a communication, controllable by a valve, with a leak fuel chamber. Thus for controlling the pressure, only this one 2/2-port directional control valve is required, since the inner throttle remains unchanged. 
   In another advantageous feature of the invention, the outer piston rod, in the opening stroke motion of the outer valve needle, closes the inner throttle at least partly. The result is a further drop in the pressure in the control chamber, so that the closing force on the inner valve needle decreases further. By means of a suitable design of the opening forces on the valve needles, it can be attained that the inner valve needle executes an opening stroke motion only after the outer valve needle has closed the inner throttle, and thus the injection openings are opened successively. In this way, the injection rate at the onset of the injection is less than during the main injection, in which all the injection openings are uncovered, so that a shaping of the injection course is achieved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages and advantageous features of the subject of the invention can be learned from the description contained below, with reference to the drawings, in which: 
       FIG. 1  shows a longitudinal section through a fuel injection valve of the invention; 
       FIG. 2  shows an enlargement of  FIG. 1  in the region marked II; 
       FIG. 3  shows an enlargement of  FIG. 1  in the region marked III; and 
       FIG. 4  shows the same detail as  FIG. 3 , but with the outer piston rod in a different switching position. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1 , one exemplary embodiment of the fuel injection valve of the invention is shown in longitudinal section. The fuel injection valve includes a housing  1 , which can be constructed in multiple parts. On its end region toward the combustion chamber, the housing  1  has a bore  3 , in which a pistonlike outer valve needle  10  is disposed. The outer valve needle  10  is guided sealingly in the bore  3  in a portion remote from the combustion chamber and tapers toward the combustion chamber, forming a pressure shoulder  9 . On the end toward the combustion chamber, the outer valve needle  10  changes into a conical pressure face  101  ( FIG. 2 ) and finally into a likewise conical valve sealing face  11 ; the pressure face  11 , in the closing position of the outer valve needle  10 , comes to rest on a valve seat  13  embodied on the end of the bore  3  toward the combustion chamber. In  FIG. 2 , an enlarged view of the detail marked II of  FIG. 1  is shown, in the region of the valve seat  13 . By means of a radial enlargement of the bore  3 , a pressure chamber  5  is formed in the housing  1  at the level of the pressure shoulder  9 , and this chamber continues in the form of an annular conduit, surrounding the outer valve needle  10 , as far as the valve seat  13 . A plurality of injection openings  7  are embodied in the valve seat  13 , arranged in a first row  107  of injection openings and a second row  207  of injection openings, disposed axially offset from it. Upon contact of the outer valve needle  10  with the valve seat  13 , this valve needle closes all the injection openings  7  off from the pressure chamber  5 , SO that no fuel from the pressure chamber can reach the injection openings  7 . 
   In the outer valve needle  10 , there is an inner valve needle  12 , which is pistonlike and which on its end toward the combustion chamber has a conical pressure face  112  and a valve sealing face  14 . If the inner valve needle  12  comes into contact with the valve seat  13 , then the valve sealing face  14  touches the valve seat  13  between the first row  107  of injection openings and the second row  207  of injection openings. By the interplay of the outer valve needle  10  and the inner valve needle  12 , the rows  107 ,  207  of injection openings can be made to communicate with the pressure chamber  5 . If the outer valve needle  10  with its valve sealing face  11  is resting on the valve seat  13 , then both rows  107 ,  207  of injection openings are closed off from the pressure chamber  5 . If only the outer valve needle  10  lifts from the valve seat  13 , while the inner valve needle  12  with its valve sealing face  14  rests on the valve seat  13 , then only the first row  107  of injection openings is made to communicate with the pressure chamber  5 , while the second row  207  of injection openings remains closed by the inner valve needle  12 . Not until the inner valve needle  12  also lifts from the valve seat  13  is the second row  207  of injection openings made to communicate with the pressure chamber  5 . 
   Via an inlet conduit  15  extending in the housing  1 , the pressure chamber  5  communicates with a high-pressure connection  17 , which communicates with a high-pressure fuel source, not shown in the drawing. When the internal combustion engine is in operation, the high-pressure fuel source here furnishes a predetermined high fuel pressure, so that in the inlet conduit  15  and thus also in the pressure chamber  5 , this fuel pressure always prevails and forms a high-pressure fuel region. 
   Remote from the combustion chamber toward the bore  3 , a piston bore  18  embodied as a blind bore is made in the housing  1 ; it has a bottom or end face  19 . An outer piston rod  20  is disposed longitudinally displaceably in the piston bore  18  and rests, with its face toward the combustion chamber, on the outer valve needle  10  and, with its face end  21  remote from the combustion chamber, it defines a control chamber  24  embodied on the end of the piston bore  18 . By means of a radial enlargement of the piston bore  18 , a spring chamber  8  is embodied in the housing  1 , in the end region of the piston rod  20  toward the combustion chamber, and a compression spring  42  is disposed with pressure prestressing in this spring chamber. The spring  42  is braced in stationary fashion on the end remote from the combustion chamber, and on its end toward the combustion chamber it rests on a spring plate  44 , which is connected to the outer piston rod  20 , so that the spring  42  exerts a force in the direction of the valve seat  13  on the outer piston rod  20  and thus also on the outer valve needle  10 . 
   In the outer piston rod  20 , there is an inner piston rod  22 , which is longitudinally displaceable in the outer piston rod  20 . On its end toward the combustion chamber, the inner piston rod  22  rests on the inner valve needle  12 , so that the inner piston rod  22  and the inner valve needle  12  move synchronously.  FIG. 3  shows an enlargement of  FIG. 1  in the region of the control chamber  24 . The control chamber  24  is defined by the bottom face  19 , the wall of the piston bore  18 , and the face end  21  of the outer piston rod  20 . The outer piston rod  20 , on its end remote from the combustion chamber, has an inward-projecting region  27 , so that the outer piston rod  20  and the face end  31 , remote from the combustion chamber, of the inner piston rod  22  define an inner control chamber  29 , which communicates with the control chamber  24  via a connecting bore  28  in the outer piston rod  20 . A stop face  23  is embodied in the interior of the outer piston rod  20  and limits the longitudinal motion of the inner piston rod  22 . In the closing position of the fuel injection valve, that is, when both the inner valve needle  12  and the outer valve needle  10  are resting on the valve seat  13 , an axial spacing remains between the stop face  23  and the face end  31 , remote from the combustion chamber, of the inner piston rod  22 . 
   The control chamber  24  communicates with the inlet conduit  15  via an inner throttle  25 . Moreover, via an outer throttle  26 , the control chamber  24  communicates with a leak fuel chamber  30  embodied in the housing  1 . A longitudinally movable magnet armature  34  is disposed in the leak fuel chamber  30  and has a sealing cone or ball  32  on its end toward the control chamber  24 . The magnet armature  34  is acted upon by a closing spring  38 , which presses the magnet armature  34  in the direction of the control chamber  24 . An electromagnet  36  is also disposed in the leak fuel chamber  30 ; when suitably supplied with current, it exerts an attracting force on the magnet armature  34  and moves it away from the control chamber  24 , counter to the force of the closing spring  38 . If no current is supplied to the electromagnet  36 , then the magnet armature  34  is pressed by the closing spring  38  in the direction of the control chamber  24 , and the sealing cone  32  closes the outer throttle  26 . When current is supplied to the electromagnet  36 , the magnet armature  34  is moved away from the control chamber  24 , and the sealing cone  32  uncovers the outer throttle  26 . In this position, fuel can flow out of the control chamber  24  into the leak fuel chamber  30 , via the outer throttle  26 . The magnet armature  34 , sealing cone  32 , and electromagnet  36  thus form a valve  33 . 
   The mode of operation of the fuel injection valve is as follows: In the closed state of the fuel injection valve, that is, when no fuel is injected through the injection openings  7  into the combustion chamber of the engine, the sealing cone  32  closes the outer throttle  26 . Through the inner throttle  25 , the same fuel pressure prevails in the control chamber  24  as in the inlet conduit  15 . The result is a hydraulic force on the face end  21  of the outer piston rod  20  and on the face end  31  of the inner piston rod  22 , which transmit this force to the outer valve needle  10  and the inner valve needle  12 , respectively, so that the valve needles  10 ,  12  are pressed into contact with the valve seat  13  and close the injection openings  7 . The ratio in terms of size between the face end  21  and the pressure shoulder  9 , or the pressure face  101  of the outer valve needle  10 , is designed such that in this state of the fuel injection valve, the hydraulic force on the face end  21  of the outer piston rod  20  predominates. If an injection of fuel into the combustion chamber is to be accomplished, current is supplied to the electromagnet  36 , as a result of which the magnet armature  34  and thus also the sealing cone  32  move away from the outer throttle  26  and cause the control chamber  24  to communicate with the leak fuel chamber  30  via the outer throttle  26 . The flow resistances of the inner throttle  25  and outer throttle  26  are designed such that the fuel pressure in the control chamber  24  drops as a result, in fact so far that the outer valve needle  10 , because of the pressure face  101  and the pressure shoulder  9 , experiences a greater hydraulic force than the hydraulic force in the control chamber  24  that now also acts on the face end  21  of the outer piston rod  20 . 
   As soon as the outer valve needle  10  lifts from the valve seat  13 , it uncovers the first row  107  of injection openings, through which fuel is now injected into the combustion chamber of the engine. As a result, the pressure face  112  of the inner valve needle  12  is now also acted upon by fuel pressure from the pressure chamber  5 , so that the inner valve needle  12  experiences an opening force. The remaining fuel pressure in the control chamber  24  is so high, however, that the hydraulic force on the face end  31  of the inner piston rod  22  still suffices to keep the inner valve needle  12  in the closing position, counter to the opening force. In the course of the opening stroke motion, the outer piston rod  20  finally comes into contact with the bottom face  19 , and as a result, by means of an additional throttle restriction  45  ( FIG. 4 ) that forms between the face end  21  of the outer piston rod  20  and the bottom face  19 , the control chamber  24  is largely closed off from the outer throttle  26 . This position of the outer piston rod  20  is shown in  FIG. 4 . As a result, the further inflow of fuel from the control chamber  24  to the outer throttle  26  is reduced, and the pressure in the inner control chamber  29  drops still further. Because of the now lower hydraulic pressure in the inner control chamber  29 , the inner valve needle  12 , driven by the hydraulic force on the pressure face  112 , and thus also the inner piston rod  22  move away from the valve seat  13 , so that the second row  207  of injection openings is opened. The inner piston rod  22  moves in the axial direction in this process, until it comes into contact with the stop face  23  of the outer piston rod  20 . By means of the successive opening of the two rows  107  and  207  of injection openings, a shaping of the injection course is achieved, in which at the onset of injection, fuel is injected into the combustion chamber of the engine with full pressure, but through only some of the injection openings  7 , while in the main injection, it is injected through all the injection openings  7  of both rows  107  and  207  of injection openings and thus also at a higher injection rate. To terminate the injection event, the current supply to the electromagnet  36  is stopped, and the sealing cone  32  on the magnet armature  34 , driven by the closing spring  38 , closes the outer throttle  26 ,  50  that because of the replenishing fuel flowing through the inner throttle  25 , the fuel pressure of the inlet conduit  15  builds up again in the control chamber  24  and presses both the outer piston rod  20  and the inner piston rod  22  in the direction of the valve seat  13 , so that the inner valve needle  12  and the outer valve needle  10  are moved back into the closing position. 
   Provision can also be made for injecting fuel through only the first row  107  of injection openings. For that purpose, the valve  33 , which is formed by the electromagnet  36 , the magnet armature  34 , and the sealing cone  32 , is closed again before the fuel pressure in the control chamber  24  has dropped so far that the inner valve needle  12  opens. The outer throttle  26  is then already closed again before the outer piston rod  20 , with its end face  21 , comes to rest on the bottom face  19  of the piston bore  18 . As a result, a hydraulic cushion is created between the end face  21  and the bottom face  19 ; it damps the opening motion of the outer piston rod  20  and prevents a pressure drop in the control chamber  24 , and so the inner piston rod  22  always exerts a sufficient closing force on the inner valve needle  12 . 
   Provision can also be made for the outer piston rod  20 , in the opening stroke motion of the outer valve needle  10 , to cover the inner throttle  25  partially, so that the cross section of the inner throttle  25  is reduced, but the inner throttle is not closed completely. This can be achieved for instance by means of a residual annular gap between the outer piston rod  20  and the wall of the piston bore  18 . The communication of the control chamber  24  with the outer throttle  26  is assured for instance by means of radially extending grooves on the face end  21  of the outer piston rod  20 . As a result, the fuel inflow into the control chamber  24  through the inner throttle  25  is reduced markedly, so that the fuel in the control chamber  24  and, via the connecting bore  28 , in the inner control chamber  29  as well drops further, and the inner piston rod  22  and thus the inner valve needle  12  open in the manner described above. 
   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.