Abstract:
The invention relates to a fuel injection valve for internal combustion engines for injecting fuel under high pressure utilizing a nozzle needle interacting with a valve seat by longitudinal movements thereof, thus opening and closing at least one injection opening. The nozzle needle is subjected to a locking force directed toward the direction of the valve seat pressure in a control space. A control valve is configured in a valve body, by which the pressure in the control space can be adjusted. The control valve has a control valve space connected to the control space, in which a control valve member is disposed in a longitudinally movable manner, and opens and closes a connection of the control valve space to a leakage oil space by longitudinal movement. The control valve member is surrounded by pressure in the control valve space and configured such that no or very little resulting hydraulic force acts upon the control valve member in the longitudinal movement direction by the pressure in the control space, if the control valve member closes the connection of the control valve space to the leakage oil space.

Description:
[0001]    The invention relates to a fuel injection valve for internal combustion engines, of the kind used for injecting fuel into the combustion chamber of an internal combustion engine. 
       PRIOR ART 
       [0002]    Fuel injection valves, of the kind preferably used for injecting fuel directly into the combustion chamber of an internal combustion engine, have long been known from the prior art. In injection systems that operate on the so-called common rail principle, fuel compressed by means of a high-pressure pump is made available in a so-called rail and injected by means of injectors into the various combustion chambers of an internal combustion engine. The injection is triggered by means of a nozzle needle, which executes a longitudinal motion and thereby opens and closes one or more injection openings. Since in the injection of fuel at high pressure, in particular, it is not sensible or is impossible to move the nozzle needle directly by means of an electrical actuator, hydraulic forces that the compressed fuel exerts on the nozzle needle are employed for the triggering. For that purpose, a control chamber is embodied in the fuel injection valve, and the force of the control chamber acts directly or indirectly on the nozzle needle and presses it thereby against a nozzle seat, so that the nozzle needle closes the injection openings. By varying the pressure in the control chamber and thus the closing force on the nozzle needle, the longitudinal motion of the nozzle needle can be controlled in a purposeful way. 
         [0003]    The fuel pressure in the control chamber is varied by means of a control valve; the control chamber is made to communicate in alternation with a leak fuel chamber, in which a low pressure prevails, or this communication is interrupted by means of the control valve. From German Patent Disclosure DE 10 2004 030 445 A1, a fuel injection valve is known which has a control valve of this kind. The control valve is embodied there as a so-called 3/2-way valve, and it controls the communication of the control chamber on the one hand with the high-pressure source, from which the compressed fuel is delivered to the injection valve, and on the other to a leak fuel chamber that has low pressure. The control valve has a control valve member, which can be moved inside the control valve chamber by means of an electrical actuator, such as a magnet or piezoelectric actuator, and thus cooperates with a first control valve seat and a second control valve seat. If the control valve member is in contact with the first control valve seat, then the communication of the control valve chamber with the leak fuel chamber or to a leak fuel connection that has a communication with a low-pressure region is closed. Since both the outlet throttle restriction, which from the control chamber of the nozzle needle discharges into the control valve chamber, and the bypass throttle restriction, which connects the high-pressure conduit to the control conduit, open into the control valve chamber, the result is communication of the high-pressure conduit with the control chamber via the outlet throttle restriction. 
         [0004]    If the pressure is to be lowered in the control chamber, then by means of the electrical actuator the control valve member is moved away from the first control valve seat into contact with the second control valve seat. As a result, the communication of the control valve chamber with the leak fuel chamber is opened, while simultaneously the bypass throttle restriction, which connects the high-pressure conduit with the control valve chamber, is closed. The resultant communication of the outlet throttle restriction from the control chamber with the leak fuel chamber via the control valve chamber leads to an outflow of the fuel pressure in the control chamber and thus to a corresponding pressure reduction, which leads to a lowering of the closing pressure on the nozzle needle and finally to a motion of the nozzle needle away from the nozzle seat and for opening the injection openings. 
         [0005]    A control valve that functions quite similarly is further known from International Patent Disclosure WO 2006/067015 A1, which functions essentially in the same way. Once again, the control valve member is surrounded by the fuel pressure of the control valve chamber and thus is acted upon on all sides by the fuel pressure of the control valve chamber. The control valve functions as described above, in such a way that initially, the control valve member is in contact with the first control valve seat and is moved by an electrical actuator into the control valve chamber, until it is in contact with the second control valve seat. The control valve member has to be moved away from the first control valve seat counter to the fuel pressure in the control valve chamber. Since initially, at least approximately the same pressure as in the control chamber of the nozzle needle prevails in the control valve chamber, and this pressure in turn is approximately equivalent to the fuel high pressure supplied, this force is quite strong, so that a suitably powerful actuator with suitably high capacity is a prerequisite. 
         [0006]    Moreover, the known control valves have the disadvantage that the control valve member is prestressed toward the first control valve seat by a strong spring. This is necessary to ensure reliable closure of the control valve even whenever the hydraulic forces on the control valve member vary sharply because of the motion of the control valve member in the control valve chamber. However, a very strong closing spring has the disadvantage that the control valve member, even at relatively slight injection pressures, or in other words whenever only a slight fuel pressure prevails in the control valve chamber, is pressed against the first control valve seat by the very strong spring. The result is unnecessarily high wear at the first control valve seat, which can adversely affect the service life of the fuel injection valve. 
       ADVANTAGES OF THE INVENTION 
       [0007]    The fuel injection valve of the invention having the characteristics of claim  1  has the advantage over the prior art that fast, reliable switching of the injection is made possible by means of a control valve, and thus higher-quality injection and a longer service life of the injection valve are made possible. To that end, the control valve member, which is located in the control valve chamber, is embodied such that by the pressure in the control chamber, no resultant hydraulic force in the direction of the longitudinal motion of the control valve member is exerted. By this embodiment, the control valve member, when it is in contact with the first control valve seat, or in other words is in its closing position, is actually or practically force-balanced with respect to the leak fuel chamber. This makes it possible, by means of a relatively weak actuator, to move the control valve member quickly in the control valve chamber and to perform very fast switching operations. Since the control valve member is practically force-balanced, a relatively weak closing spring also suffices, which spring ensures that the control valve member, in the absence of further forces, and especially whenever the electrical actuator with which the control valve member is moved is off, remains in its position at the first control valve seat in which it closes the leak fuel chamber off from the control valve chamber. 
         [0008]    In a first advantageous feature, the control valve member is embodied in pistonlike fashion and cooperates with a first control valve seat for opening and closing a communication of the control valve chamber with the leak fuel chamber. The control valve member is guided, on its end remote from the control valve seat, in a sleeve. It is ensured by means of the sleeve that the end of the control valve member on the far side from the first control valve seat is not acted upon by the fuel pressure of the control valve chamber; instead, besides the outer surfaces of the control valve member, only the region with which the control valve member cooperates with the first control valve seat is acted on by the fuel pressure. If the diameter of the control valve member, in the region that is guided in the sleeve, is the same size as the diameter of the seat region in the vicinity of the first control valve seat, then, whenever the control valve member is in contact with the first control valve seat, no resultant hydraulic forces act on the control valve member, so that the control valve member is force-balanced. 
         [0009]    To ensure the movability of the control valve member, the chamber that is defined by the sleeve and the control valve member is a low-pressure chamber, which is pressure-relieved at all times. Advantageously, the low-pressure chamber communicates with the leak fuel chamber, in which a low pressure prevails at all times. 
         [0010]    The spring with which the control valve member is pressed against the first control valve seat is advantageously disposed between the sleeve and the control valve member in pressure-prestressed fashion, so that on the one hand, the control valve member is pressed against the first control valve seat, and on the other, the sleeve is pressed against the control valve chamber wall on the far site from the first control valve seat. 
         [0011]    In a further advantageous feature, the control valve member is embodied in boltlike form and has a blind bore, which originates at the end of the control valve member opposite from the first control valve seat, or in other words is open on the far side from the first control valve seat. An inner sleeve is disposed in sealing fashion in the blind bore, so that by means of the control valve member and the inner sleeve, a low-pressure chamber is defined which in turn advantageously communicates with a low-pressure chamber, preferably the leak fuel chamber, via a longitudinal bore extending in the inner sleeve. In this arrangement, the closing spring can be disposed in the interior of the low-pressure chamber, that is, between the inner guide sleeve and the control valve member, in pressure-prestressed fashion, so that the closing spring is not acted upon directly by the fuel pressure of the control valve chamber. 
         [0012]    In a further advantageous feature, the control valve chamber can be made to communicate with the fuel high pressure-carrying region of the fuel injection valve via a bypass throttle restriction. The bypass throttle restriction is disposed such that whenever the control valve member slides from the first control valve seat into the second control valve seat, the bypass throttle restriction is closed, while whenever the control valve member is in contact with the first control valve seat, the bypass throttle restriction ensures a rapid pressure buildup in the control valve chamber and thus also in the control chamber of the nozzle needle. 
     
    
     
       DRAWINGS 
         [0013]    In the drawings, various exemplary embodiments of the fuel injection valve of the invention are shown. 
           [0014]      FIG. 1  shows a longitudinal section through a fuel injection valve of the invention, in which only the essential portions are shown; 
           [0015]      FIG. 2  is an enlarged view of the control valve of  FIG. 1 ; 
           [0016]      FIG. 3 , in the same view as  FIG. 2 , shows a further exemplary embodiment of the fuel injection valve of the invention; and 
           [0017]      FIG. 4  schematically shows a further exemplary embodiment. 
       
    
    
     DESCRIPTION 
       [0018]      FIG. 1  shows a fuel injection valve  1  according to the invention in longitudinal section. The fuel injection valve  1  has a retaining body  2 , a valve body  4 , a throttle plate  6 , and a nozzle body  8 , which contact one another in that order. The components are pressed against one another by a tensioning nut  9 , which is braced on a shoulder of the nozzle body  8  and is retained on the retaining body  2  by means of a thread. In the nozzle body  8 , a pressure chamber  18  is embodied, in which a pistonlike nozzle needle  10  is disposed longitudinally displaceably. The nozzle needle  10 , on its end toward the combustion chamber, has a sealing face  11 , with which it cooperates with a nozzle seat  13  that is embodied on the end of the pressure chamber  14  toward the combustion chamber. One or more injection openings  12  originate at the nozzle seat  13 , and in the installed position of the fuel injection valve  1  they open directly into a combustion chamber of an internal combustion engine. The nozzle needle  10  is guided in a middle portion in the pressure chamber  14 , and the fuel is carried through a plurality of polished faces  14  to the injection openings  12 . 
         [0019]    The nozzle needle  10  is guided, on its end remote from the valve seat, in a sleeve  22 ; the sleeve  22  is pressed against the throttle disk  6  by a closing spring  18 , which surrounds the nozzle needle  10  and is braced, remote from the sleeve  22 , on a shoulder  16 . By means of the sleeve  22 , the face end of the nozzle needle  10  remote from the valve seat, and the throttle disk  6 , a control chamber  20  is defined, which is filled with fuel, so that by the pressure in the control chamber  20 , a hydraulic force is exerted on the face end, remote from the valve seat, of the nozzle needle  10  and exerts a force on the nozzle needle  10  in the direction of the nozzle seat  13 . 
         [0020]    An inlet conduit  25  is embodied in the retaining body  2 , the valve body  4 , and the throttle disk  6 , and by way of this conduit, compressed fuel is carried at high pressure from a high-pressure fuel source into the pressure chamber  14 . As shown further enlarged in  FIG. 2 , the inlet conduit  25  communicates with the control chamber  20  via an inlet throttle restriction  40  extending in the throttle disk  6 . Thus the same fuel pressure is always established between the high-pressure conduit  25  and the control chamber  20 , with a certain time lag. 
         [0021]    For controlling the fuel pressure in the control chamber  20 , a control valve  30  is provided in the valve body  4 ; the control valve  30  has a control valve chamber  31 , which is embodied as a hollow chamber in the valve body  4 . The control valve chamber  31  communicates with the control chamber  20  in the nozzle body  8  via an outlet throttle restriction  42 , which is embodied in the throttle disk  6 . A control valve member  34  is disposed longitudinally displaceably in the control valve chamber  31 , and the control valve member  34  has a pistonlike shape and, on its end remote from the throttle disk  6 , a mushroom-shaped widened portion, on which a sealing face  52  is embodied, with which face the control valve member  34  cooperates with a first control valve seat  37  that is embodied on the inside of the control valve chamber  31 . 
         [0022]    The control valve member  34 , on its end remote from the first control valve seat  37 , is guided in a sleeve  36 , which is braced by one end on the throttle disk  6 , and between which and the control valve member  34 , a spring  38  is disposed in pressure-prestressed fashion. By the force of the spring  38 , on the one hand the control valve member  34  is pressed against the first control valve seat  37 , and on the other the sleeve  36  is pressed against the throttle disk  6 . The motion of the control valve member  34  in the control valve chamber  31  takes place via a piston  32 , which is disposed in the retaining body  2  and is movable by an electrical actuator in its longitudinal direction, for instance by means of an electromagnet or a piezoelectric actuator. The piston  32  is located here in a leak fuel chamber  23 , which is pressure-relieved at all times and has a low fuel pressure. 
         [0023]    A low-pressure chamber  54 , which is pressure-relieved at all times via a leak fuel outlet  45 , is defined by the sleeve  36 , the control valve member  34 , and the throttle disk  6 . The leak fuel outlet  45  can for instance act as a communication with the leak fuel chamber  23 . 
         [0024]    The mode of operation of the fuel injection valve is as follows: At the onset of the injection, the control valve member  34 , driven by the spring  38 , is in contact with the first control valve seat  37 . The control valve chamber  31  communicates via the outlet throttle restriction  42  with the control chamber  20 , which in turn communicates via the inlet throttle restriction  40  with the high-pressure conduit  25 , so that a high fuel pressure, of the kind that also prevails in the inlet conduit  25 , is established both in the control chamber  20  and in the control valve chamber  31 . The low-pressure chamber  54  is without pressure, or is at only a very slight pressure, so that only slight forces on the control valve member  34  are exerted as a result of the pressure in the low-pressure chamber  54 . By means of the fuel pressure in the control chamber  20 , a hydraulic force in the direction of the nozzle seat  13  is exerted on the face end, remote from the valve seat, of the nozzle needle  10 , and this force presses the nozzle needle  10  against the nozzle seat  13 . Since the nozzle needle  10  is in contact with the nozzle seat  13 , the pressure chamber  14  is sealed off from the injection openings  12 , so that no fuel from the pressure chamber  14  can reach the combustion chamber of the engine. If an injection is to take place, then by means of an electrical actuator not shown in the drawings, moves against the piston  32  in the direction of the nozzle body  8 , as a result of which the control valve member  34  moves away from the first control valve seat  37  into contact with the second control valve seat  39 . As a result, a communication is triggered between the sealing face  52  of the control valve member  34  and the first control valve seat  37 , and this communication connects the control valve chamber  31  with the leak fuel chamber  23 , so that the pressure in the control valve chamber  31  rapidly drops. The replenishing fuel flowing into the control valve chamber  31  from the control chamber  20  via the outlet throttle restriction  42  also leads to a pressure drop in the control valve chamber  20 ; the outlet throttle restriction  42  and the inlet throttle restriction  40  are dimensioned such that more fuel flows away via the outlet throttle restriction  42  than flows in the same period of time from the high-pressure conduit  25  via the inlet throttle restriction  40 . The decreasing fuel pressure in the control chamber  20  leads to a reduced hydraulic force on the end face of the nozzle needle  10  remote from the valve seat, so that the hydraulic forces which otherwise act on the nozzle needle  10 , in particular on parts of the sealing face  11 , cause the nozzle needle  10  to lift from the nozzle seat  13  and to move in the direction of the throttle disk  6 , counter to the force of the spring  18 . As a result, a gap is opened up between the sealing face  11  and the nozzle seat  13 , and through this gap fuel flows out of the pressure chamber  14  to the injection openings  12  and is injected through the injection openings  12  into a combustion chamber of the engine. To terminate the injection, the electrical actuator is actuated once again, and the control valve member  34 , via the piston  32 , moves back into contact with the first control valve seat  37 . Since the communication of the control valve chamber  31  with the leak fuel chamber  23  is now interrupted, a high fuel pressure rapidly builds up again in the control chamber via the inlet throttle restriction  40 , and in the control valve chamber  31  as well, via the outlet throttle restriction  42 . 
         [0025]    The control valve member  34 , on its sealing face  52 , has a sealing edge  50 , with which the control valve member  34  contacts the first control valve seat  37 . The diameter of the sealing edge  50  is equivalent to the diameter of the control valve member  34 , in the portion thereof that is guided in the sleeve  36 . Since the fuel pressure of the control valve chamber  31  engages only the part of the sealing face  52  that is located radially outward from the sealing edge  50 , this hydraulic force is compensated for by a corresponding contrary force on the underside of the mushroom-shaped widened portion of the control valve member  34 , so that the control valve member  34  does not experience any hydraulic force operative in the direction of its longitudinal motion resulting from the fuel pressure in the control valve chamber  31  and is thus force-balanced. 
         [0026]    In  FIG. 3 , in the same view as in  FIG. 2 , a further exemplary embodiment of the control valve  30 ′ is shown; identical elements are identified by the same reference numerals, and a more-detailed description of the parts that are identical to those in  FIG. 2  will be dispensed with here. The control valve piston  34 ′ in this exemplary embodiment has a blind bore  33 , whose open end faces away from the first control valve seat  37 . In the blind bore  33 , there is an inner sleeve  48 , which has a longitudinal conduit  49  that extends over the entire length of the inner sleeve  48 . By means of the inner sleeve  48  and the control valve member  34 ′, a low-pressure chamber  54 ′ is defined, in which a spring  38 ′ is disposed. The spring  38 ′ is disposed here in pressure-prestressed fashion and ensures that the inner sleeve  48  is pressed against the throttle disk  6 , or in other words against the second control valve seat  39 ; the control valve member  34 ′ is also pressed against the first control valve seat  37 . Via the longitudinal bore  49 , the low-pressure chamber  54 ′ communicates with a leak fuel chamber  45 , so that the interior of the control valve member  34 ′, that is, the low-pressure chamber  54 ′, is pressureless at all times. 
         [0027]    To achieve the force equilibrium of the control valve member  34 ′, the sealing edge  50  of the control valve member  34 ′ is embodied such that it has the same diameter as the inner sleeve  48 . In the closed state of the control valve  30 ′, or in other words whenever the control valve member  34 ′ is in contact with the first control valve seat  37 , only the radially outer part of the sealing face  52 ′ is subjected to the fuel pressure in the control valve chamber  31 , which brings about a resultant hydraulic force in the direction of the second control valve seat  39 . At the same time, however, the face of the control valve member  34 ′ that is oriented toward the second control valve seat  39  is subjected to the fuel pressure in the control valve chamber  31  as well, so that the two hydraulic forces compensate for one another, and the control valve member  34 ′ is force-balanced. 
         [0028]    Otherwise, the function of the control valve  30 ′ is identical to the exemplary embodiment shown in  FIG. 2 , with the exception of the bypass throttle restriction  43 , which is additionally provided in the throttle disk  6 . The bypass throttle restriction  43  connects the pressure chamber  14  to the control valve chamber  31 , and the bypass throttle restriction  43  opens into the control valve chamber  31  in such a way that the bypass throttle restriction is closed by the control valve member  34 ′ when the latter is in contact with the second control valve seat  39 . As a result, with the control valve  30 ′ open, the pressure reduction in the control chamber  20  is prevented from slowing down and thus leading to a delayed opening of the nozzle needle  10 . Upon termination of the injection, or in other words once the control valve member  34 ′ moves back into contact with the first control valve seat  37 , however, the control valve chamber  31  is filled very quickly again with fuel at high pressure via the bypass throttle restriction  43 , so that the control chamber  20  is filled very quickly with fuel at high pressure not only via the inlet throttle restriction  40  but also by the inflow of fuel from the control valve chamber  31  via the outlet throttle restriction  42 , which leads to a fast closure of the nozzle needle  10 . This is important particularly so that the fuel will not, because of a slowly closing nozzle needle  10  at low pressure, trickle through the injection openings  12  into the combustion chamber of the engine, which would lead to high-pollution combustion. 
         [0029]    In  FIG. 4 , a further exemplary embodiment of the control valve  30 ″ of the invention is shown. This illustration is schematic and differs from the control valve of  FIG. 2  in that the low-pressure chamber  54  is not pressure-relieved via a leak fuel outlet  45  embodied in the throttle disk  6 , but instead is pressure-relieved via a longitudinal conduit  46 , extending in the control valve member  34 ″, and a transverse conduit  47 , intersecting the longitudinal conduit, that finally opens into an annular chamber  55  which is pressure-relieved via a leak fuel connection  56 . The annular chamber  55  is located downstream of the first control valve seat  37 ′, so that overall, the construction is simpler than when there is an additional leak fuel outlet  45  in the throttle disk  6  that [antecedent is leak fuel outlet  45 , not throttle disk  6 ] must communicate with the leak fuel chamber  23  via an additional conduit in the valve body  4 .