Patent Publication Number: US-2005116058-A1

Title: Control of a pressure exchanger by displacement of an injection valve member

Description:
TECHNICAL FIELD  
      Both pressure-controlled and stroke-controlled injection systems can be used to supply fuel to combustion chambers of autoignition internal combustion engines. In addition to unit injectors and unit pumps, accumulator injection systems are also used as fuel injection systems. Accumulator (common rail) injection systems advantageously make it possible to adapt the injection pressure to the load and speed of the autoignition internal combustion engine. Achieving high specific outputs and reducing emissions of the autoignition engine generally require the highest possible injection pressure.  
     PRIOR ART  
      For strength reasons, the achievable pressure level in accumulator injection systems currently in use is limited to approximately  1600  bar at this time. In order to further increase the pressure in accumulator injection systems, common rail systems employ pressure boosters.  
      DE 199 10 970 A1 relates to a fuel injection apparatus. This fuel injection apparatus has a pressure booster unit, which is disposed between a pressure accumulator and a nozzle chamber and whose pressure chamber is connected to the nozzle chamber via a pressure line. In addition, a bypass line is provided, which is connected to the pressure accumulator. The bypass line is connected directly to the pressure line. The bypass line can be used for a pressure injection and is disposed parallel to the pressure chamber so that the bypass line is continuously independent of the movement and position of a moving pressure fluid in the pressure booster unit. This feature increases the flexibility of the injection. A differential chamber can be connected to a leakage line via a 2/2-way valve and there is a connection from the differential chamber to the pressure accumulator. A valve device, which is disposed outside the injector at an arbitrary point between the pressure accumulator and the injector, is associated with the pressure booster unit in order to control it.  
      DE 190 40 526 A1 also relates to a fuel injection apparatus. This fuel injection apparatus has a pressure booster unit, which is disposed between a pressure accumulator and a nozzle chamber and has a moving piston unit for boosting the pressure of the fuel to be supplied to the nozzle chamber. In order to control the pressure booster unit, the piston unit has a transition from a larger piston cross-section to a smaller piston cross-section and a differential chamber formed as a result of this. The differential chamber is connected to the pressure accumulator by means of a filling path that contains a filling valve. This permits a reduction of the control quantity during the triggering of the pressure booster unit and permits a rapid resetting of the piston unit.  
      In view of ever-increasing standards regarding emissions and noise production in autoignition internal combustion engines, further steps must be taken in the injection system in order to meet the stricter limit values to be expected in the near future.  
     DEPICTION OF THE INVENTION  
      With the design proposed according to the invention, it is possible to control a fuel injector of a fuel injection system with an actuator, which makes it possible to significantly reduce the complexity and costs of production. In particular, the design proposed according to the invention makes it possible to produce a pressure booster by making direct use of the movement of an injection valve element advantageously embodied as a nozzle needle, thus eliminating the need for a separate actuator. The pressure booster can be switched on with the opening movement of the injection valve element. The pressure booster contains a piston unit, which separates the working chamber of the pressure booster from its control chamber and can be set with a partial stroke, the passage of which permits the pressure booster to be switched on. This achieves considerable advantages with regard to the design of a fuel injector with a pressure booster. For example, it is possible to execute multiple preinjections into the combustion chamber of an autoignition internal combustion engine without activating the pressure booster. It is therefore possible to execute a preinjection, which occurs at a pressure level that essentially corresponds to the pressure level prevailing inside a high-pressure accumulator (common rail). After the piston unit of the pressure booster has traveled its set stroke distance, a main injection can be executed with an activated pressure booster, thus resulting in the production of a high pressure level during the main injection, which has a favorable effect on the emissions of autoignition internal combustion engines and is higher than the pressure prevailing inside a high-pressure accumulator (common rail). This makes it possible to achieve a boot-shaped injection since the first injection phase (preinjection phase) occurs at a lower pressure and then a pressure increase to the boosted injection pressure occurs. The activation of the pressure booster can produce a pressure increase up to the maximal permissible pressure during the main injection phase when the injection valve element is in the open position. Furthermore, the design proposed according to the invention makes it possible to achieve the pressure booster before the closing of the injection valve element that is preferably embodied as a nozzle needle, which makes it possible to prevent pressure surges above the maximal injection pressure when the needle closes. This has a favorable effect on the service life of the fuel injection system in an autoignition internal combustion engine. In addition, the design according to the invention can execute a secondary injection phase at a very high injection pressure after the main injection phase, as well as a stepped secondary injection that follows the main injection by a somewhat longer time span. 
    
    
     DRAWINGS  
      The invention will be explained in detail below in conjunction with the drawings.  
       FIG. 1  shows an embodiment version of a pressure booster actuated by an injection valve element in a first state,  
       FIG. 2  shows the embodiment version of the design proposed according to the invention according to  FIG. 1 , with a pressure booster in a second state,  
       FIG. 3  shows another embodiment version of a pressure booster that can be actuated by an injection valve element, with two valve elements guided one inside the other, and  
       FIG. 4  shows an embodiment version of a pressure booster actuated by an injection valve element, with two valve elements, one of which is spring-loaded. 
    
    
     EMBODIMENT VERSIONS  
       FIG. 1  shows a first embodiment version of a pressure booster that can be actuated by an injection valve element, depicted in a first state in which the control chamber of the pressure booster is disconnected from the return, i.e. from the low-pressure region of the fuel injection system.  
      Starting from a high-pressure source  1 , which can be embodied, for example, as a high-pressure accumulator (common rail), a high-pressure inlet  2  extends to a pressure booster  3 . The high-pressure inlet  2  has a high-pressure line  7  that can contain a check valve  8 . Parallel to the high-pressure line  7 , the high-pressure inlet  2  from the high-pressure source  1  acts on a parallel branch  11  that can contain a filling valve  10 . Another branch  12  extends parallel to it, which contains a throttle restriction  13 . The first parallel branch that contains the filling valve  10  and the additional parallel branch  12  that contains the throttle restriction  13  feed into a control chamber  15  of the pressure booster  3 . The pressure booster  3  also has a working chamber  14 , which likewise communicates with the high-pressure source  1  via the high-pressure inlet  2 .  
      A piston unit  17  separates the working chamber  14  and the control chamber  15  inside the pressure booster  3 . The piston unit  17  can be comprised of one piece or of multiple parts and has a section with a larger diameter, whose end surface delimits the working chamber  14  of the pressure booster  3 , and a piston part with a smaller diameter than this, whose lower end surface delimits a compression chamber  18  of the pressure booster  3 . The compression chamber  18  of the pressure booster  3  has a compression line  20  extending from it, which at its other end, unites with the high-pressure inlet  7  that contains the check valve  8  and transitions with it into a nozzle chamber inlet  9 . The control chamber  15  of the pressure booster  3  contains a spring element  16 , which acts on an underside of the piston unit  17  and is supported against the bottom of the control chamber  15 . The pressure booster  3  is disposed inside the injector body  5 ; the control chamber  15  of the pressure booster  3  has a control line  19  that is in turn connected to an annular chamber  33  of a valve element  27 .  
      The nozzle inlet  9 , which is fed by both the high-pressure line  7  and the compression line  20  extending from the compression chamber  18 , feeds into a nozzle chamber  36  at a junction point  37 .  
      A high-pressure branch  22  that contains an inlet throttle element  23  branches off from the nozzle chamber inlet  9 . The high-pressure branch  22  feeds into a control chamber  21  inside a nozzle body  6  of the fuel injector  4 . The control chamber  21  can be pressure-relieved by means of a control valve  25  embodied as a 2/2-way valve. An outlet throttle element  24  is provided between the control valve  25  (2/2-way valve) and the control chamber  21 . A low-pressure return  26  extends from the low-pressure side of the control valve  25  (2/2-way valve) and feeds into a fuel tank, not shown here, of a motor vehicle. The control valve  25  can be either a solenoid valve or as a valve that is actuated by a piezoelectric actuator. In addition, the control valve  25  can also be embodied as a servo valve or as a valve that can be actuated directly.  
      The fuel injector  4  shown in  FIG. 1  has an injection valve element  34 , which is advantageously embodied as a nozzle needle. In the embodiment version according to  FIG. 1 , the injection valve element  34  is acted on by a one-piece valve element  27 , which can be embodied as a valve piston. The end surface  29  of the one-piece valve element  27  delimits the control chamber  21 , which can be filled via the inlet throttle restriction  23  and can be pressure-relieved via the outlet throttle restriction  24 . Under the control chamber  21 , the one-piece valve element  27  embodied as a valve piston is encompassed by an annular chamber  33  into which the control line  19  feeds, which connects the annular chamber  33  to the control chamber  15  of the pressure booster  3 . The annular chamber  33  is provided with a control edge  31  that cooperates with a control edge  30  provided on the one-piece valve element  27 . In the depiction according to  FIG. 1 , the control edges  30  and  31  overlap each other by a stroke distance h 1 , see reference numeral  32 . Below the one-piece valve element  27 , the nozzle body  6  contains another hydraulic chamber that has a second low-pressure return  26 . 2  branching from it, which also leads to the fuel tank of the motor vehicle, not shown in  FIG. 1 .  
      The nozzle chamber inlet  9  acts on the nozzle chamber  36  of the fuel injector  4  inside the nozzle body  6  with highly pressurized fuel so that a hydraulic force is generated, which acts in the opening direction on a pressure shoulder  35  provided on the circumference surface of the injection valve element  34 . Starting from the nozzle chamber  36  inside the nozzle body  6 , an annular gap  38  extends to a seat  40  of the injection valve element  34  at the end oriented toward the combustion chamber. Under the seat  40  at the end oriented toward the combustion chamber, injection openings  39  are provided, which can be embodied, for example, as annular rows of openings, in the form of one or more circular arrangements of openings extending concentrically to one another. In the position of the injection valve element  34  shown in  FIG. 1 , the injection openings  39  are closed by the injection valve element  34 , which has traveled into the seat  40  at the end oriented toward the combustion chamber so that no fuel can flow into a combustion chamber  41  of the autoignition internal combustion engine. In the depiction according to  FIG. 1 , the reference numeral  42  indicates the position of the injection valve element  34  in which it closes the injection openings  39 . No injection of fuel into the combustion chamber  41  of the autoignition internal combustion engine occurs in this position of the injection valve element  34 .  
      The fuel injection system has a number of fuel injectors  4  that corresponds to the number of cylinders of the autoignition internal combustion engine; each of the fuel injectors  4  has a pressure booster  3  and each fuel injector  4  is associated with a control valve  25 . In the working state shown in  FIG. 1 , i.e. when the injection openings are closed  42 , the control valve  25 , which is preferably embodied as a 2/2-way control valve, is in its closed position, i.e. the control chamber  21  of the injection valve element  34  is disconnected from the low-pressure return  26 . The overlapping of the control edge  31  on the nozzle body  6  and the control edge  30  on the one-piece valve element  27  closes the sliding seal constituted by the control edges  30  and  31 . The injection valve element  34  is disposed in its position  42  that closes the injection openings  39  at the end oriented toward the combustion chamber and the piston unit  17  of the pressure booster  3  is pressure-balanced so that no pressure boosting is taking place. In this state shown in  FIG. 1 , the filling valve  10  in the first parallel line  11  that branches off from the high-pressure inlet  2  is open and the piston unit  17  of the pressure booster  3  is disposed in its starting position. The pressure prevailing inside in the high-pressure accumulator (common rail), to name an example of a high-pressure source  1 , is connected via the open filling valve  10  to the back chamber  15  of the pressure booster  3  and travels via the check valve  8  contained in the high-pressure line  7  to the control chamber  21  of the fuel injector  4  as well as to its nozzle chamber  36 . In this operating state, an injection can occur at any time at the pressure level prevailing in the high-pressure source  1 , i.e. the rail pressure level.  
      However, if the control valve  25 , which can preferably be embodied as a 2/2-way valve, is switched into its open position, then the control chamber  21  is pressure-relieved via the outlet throttle  24  into the first low-pressure return  26 . 1  on the low-pressure side of the fuel injector  4 . Because of the dropping pressure in the control chamber  21  of the fuel injector  4 , the hydraulic forces acting on the pressure shoulder  35  of the injection valve element  34  predominate and the injection valve element  34  opens. An injection of fuel into the combustion chamber  41  of the autoignition internal combustion engine through the injection openings  39  at the end oriented toward the combustion chamber begins at the pressure level supplied by the high-pressure source  1 . Because of the series connection of the one-piece valve element  27  with the injection valve element  34 , when an opening movement of the injection valve element  34  occurs, the end surface  29  of the one-piece valve element  27  travels into the control chamber  21  of the fuel injector  4 . If this stroke motion exceeds the stroke distance h 1  (reference numeral  32 ), then the control edges  30  and  31  are no longer in the state shown in  FIG. 1 , i.e. the overlapping state, but are instead open so that the sliding seal is open. As a result, the control chamber  15  of the pressure booster  3  is connected to the second low-pressure return  26 . 2  via the control line  19  that connects the control chamber  15  to the annular chamber  33 . Since the control chamber  15  of the pressure booster  3  is now pressure-relieved into the low-pressure region and the filling valve  10  closes, the piston unit  17  of the pressure booster  3  is no longer pressure-balanced; as a result, the pressure inside the working chamber  14  of the pressure booster  3  predominates and the bottom end surface of the piston unit  17  travels into the compression chamber  18 . The piston unit  17  of the pressure booster  3  travels into the compression chamber  18  in accordance with the pressure area ratios of this piston unit  17 , thus supplying the nozzle chamber  36  with a boosted pressure—i.e. a higher pressure than can be supplied to it by the high-pressure source  1  alone—via the combustion chamber line  20 , which feeds into the nozzle inlet  9  along with the high-pressure line  7  from the high-pressure source  1 . When the lower end surface of the piston unit  17  travels into the compression chamber  18 , it compresses the fuel in the chamber so that a higher, i.e. boosted, pressure prevails in the nozzle chamber  36  via the nozzle inlet  9 .  
      When the stroke distance h 1  (reference numeral  32 ) is exceeded, then the injection occurs at a boosted, i.e. higher, pressure. This makes it possible to achieve a boot-shaped injection. The first injection phase, e.g. the preinjection phase, takes place at the pressure level supplied by the high-pressure source  1 , e.g. embodied in the form of a high-pressure accumulator (common rail), and is followed by another injection phase at a significantly higher injection pressure level, which is generated a result of the pressure area ratios in the piston unit  17  of the pressure booster  3  and is communicated via the compression chamber line  20  to the nozzle chamber  36  contained in the nozzle body  6  of the fuel injector  4 .  
       FIG. 2  shows the embodiment version of a fuel injector according to  FIG. 1 , with a pressure booster in a second state.  
       FIG. 2  shows that the housing control edge  31  in the nozzle body  6  and the control edge  30  of the one-piece valve element  27  are not overlapping, which produces a low-pressure connection  50  between the control chamber  15  of the pressure booster  3  via the control line  19 , which into the annular chamber  33  that encompasses the one-piece valve element  27 . The control chamber  15  is thus pressure-relieved via the second low-pressure return  26 . 2  so that the piston unit  17 , due to the pressure prevailing in the working chamber  14  of the pressure booster  3 , compresses the fuel volume contained in the compression chamber  18  of the pressure booster  3  and conveys it via the compression chamber line  20  and the nozzle inlet  9  into the nozzle chamber  36  of the nozzle body  6 . The injection valve element  34  of the fuel injector  4  is then disposed in its retracted position  51 , i.e. its open position, so that fuel is injected via the nozzle chamber  36 , the annular gap  38 , and the opened injection openings  39  into the combustion chamber  41  of the autoignition internal combustion engine at a very high pressure, which corresponds to the pressure-boosted, increased pressure level.  
      In order to terminate the injection, the control valve  25 , which is preferably embodied as a 2/2-way valve, is closed so that a pressure increase occurs in the control chamber  21  of the injection valve element  34 . Due to the action on the end surface  29  of the one-piece valve element  27 , the injection valve element  34  that cooperates with it moves in the closing direction. When the control edge  31  on the nozzle body  6  is reached, the control edges  30  and  31  overlap each other so that the sliding seal they produce is closed. This closes the connection of the control chamber  15  via the control line  19  and the annular chamber  33  into the low-pressure return  26 , thus deactivating the pressure booster  3 . The injection valve element  34  moves further in the direction of its seat  40  at the end oriented toward the combustion chamber and thus at a later point, closes the injection openings  39  that feed into the combustion chamber  41  of the autoignition internal combustion engine. Since the pressure booster  3  is already deactivated, pressure surges that occur with the closing of the injection valve element  34  are compensated for.  
      The shut-off time of the pressure booster  3 , i.e. the moment at which the control edges  30  and  31  overlap each other, can be optimally matched to the end of the respective injection phase by adjusting the stroke distance h 1  (reference numeral  32 ) and the closing speeds of the injection valve element  34  and the valve element  27 . With small injection quantities, such as in a preinjection, the injection valve element  34 , which is preferably embodied as a nozzle needle, cannot be completely opened along the entire stroke distance h 1  (reference numeral  32 ), as a result of which the pressure booster  3  remains deactivated. Consequently, any number of preinjections can be executed without an activated pressure booster  3 . In preinjections for conditioning the combustion mixture contained in the combustion chamber  41 , the preinjections are executed at the pressure level supplied by the high-pressure source  1 , for example a high-pressure accumulator (common rail), and not at the increased pressure level that can be achieved by means of the pressure booster  3 . The number and duration of the respective preinjection phases, as well as the duration of the main injection at an increased pressure level, can be set by adjusting the triggering time of the control valve  25 .  
       FIG. 3  shows another embodiment version of a pressure booster that is actuated by an injection valve element, with two valve elements guided one inside the other.  
      The fuel injector  4  shown in  FIG. 3 , which is for supplying fuel to an autoignition internal combustion engine, also has a pressure booster  3  integrated into the injector body  5 . Via a high-pressure inlet  2 , the high-pressure source  1  acts on a high-pressure line  7 , a first parallel branch  11 , an additional parallel branch  12 , and the working chamber  14  of the pressure booster  3 . The first parallel branch  11  contains a filling valve  10  and the additional parallel branch  12  contains a throttle restriction  13 . The high-pressure line  7  contains a check valve  8 .  
      Analogous to the pressure booster  3  shown in  FIG. 1 , the pressure booster  3  in the additional embodiment version in  FIG. 3  has a piston unit  17  that divides the working chamber  14  from the control chamber  15 . The underside of the piston unit  17  acts on the compression chamber  18  in the injector body  5  of the pressure booster  3  and, branching off from this compression chamber  18 , the compression chamber line  20  leads to the nozzle chamber inlet  9  and unites with the high-pressure line  7  from the high-pressure source  1 .  
      By contrast with the embodiment version of the design proposed according to the invention shown in  FIGS. 1 and 2 , the injection valve element  34  according to the depiction in  FIG. 3  is acted on by a multi-part valve element  28 . The multi-part valve element  28  has a first valve element  28 . 1  with an additional, second valve element  28 . 2  encompassing it. The first valve element  28 . 1  and the additional valve element  28 . 2  can be embodied as piston-shaped. An annular surface  60  on the second valve element  28 . 2  partially delimits the control chamber  21 . The second valve element  28 . 2  contains an opening  61  via which an end surface  62  of the first valve element  28 . 1  can be acted on by the pressure prevailing in the control chamber  21 . According to this embodiment version, a stroke distance h 1  (reference numeral  32 ) is established between the inner, first valve element  28 . 1 , i.e. its end surface  62 , and a collar at the opening  61  in the second valve element  28 . 2  of the multi-part valve element  28 . The second valve element  28 . 2  has a control edge  30  that cooperates with a seat of a valve chamber  63 . The control line  19  from the control chamber  15  of the pressure booster  3  feeds into the valve chamber  63  above the seat. A first return line  64  branches off from the valve chamber  63  and leads to the low-pressure side of the fuel supply system. The first valve element  28 . 1  has a piston extension  66  that has a smaller diameter than the piston part of the first valve element  28 . 1 . The piston extension  66  passes through an additional cavity, which is disposed underneath the valve chamber  63  in the nozzle body  6  and contains a closing spring  67 . The end surface of the piston extension  66  rests against the end surface of the injection valve element  34 , which is preferably embodied as a nozzle needle.  
      When the pressure in the control chamber  21  is relieved by the control valve  25 , which is preferably embodied as a 2/2-way valve, and the nozzle chamber  36  of the injection valve element  34  is acted on at the same time, a hydraulic force builds up in the nozzle chamber  36  via the nozzle chamber inlet  9 , which force acts on the pressure shoulder  35  of the injection valve element  34 . The injection valve element  34  opens, thus allowing the execution, for example, of a preinjection via the injection opening  39  into a combustion chamber, not shown here, of an internal combustion engine. The preinjection, however, occurs only at the pressure level prevailing in the high-pressure source  1  since the pressure booster  3  is not activated at this point. With further pressure-relief of the control chamber  21 , the end surface  62  of the inner, first valve element  28 . 1  comes into contact with the collar-shaped stop of the second, outer valve element  28 . 2  and carries the outer, second valve element  28 . 2  along with it in the opening direction. As a result, the control edge  30  on the outer circumference of the second valve element  28 . 2  opens the connection of the control chamber  15  to the first return line  64  via the control line  19  and the valve chamber  63  so that the pressure in the control chamber  15  of the pressure booster  3  is relieved. The piston unit  17  of the pressure booster  3  thus travels into the compression chamber  18  so that fuel is conveyed at an increased pressure via the compression chamber line  20 , the nozzle chamber inlet  9 , and the junction point  37  into the nozzle chamber  36  in the nozzle body  6 . It is now possible to execute a subsequent injection into the combustion chamber of the autoignition internal combustion engine at an increased pressure level that corresponds to the pressure boosting of the pressure booster  3 . In addition to the first return line  64  that branches off from the valve chamber  63 , the additional embodiment version of a fuel injector according to the invention shown in  FIG. 3  has a second return line  65  into the low-pressure region of the fuel supply system, which branches off from the cavity containing the closing spring element  67  above the injection valve element  34 . In the depiction according to  FIG. 3 , the reference numeral  68  indicates the stop point at which, with further pressure-relief of the control chamber  21 , the end surface  62  of the inner, first valve element  28 . 1  comes to rest against the outer, second valve element  28 . 2  and carries it along with it in the opening direction.  
      The remaining components of the fuel injector  4  according to the embodiment version shown in  FIG. 3  that are not discussed in detail above essentially correspond to the components that have already been described in the embodiment version of the fuel injector according to the invention in  FIGS. 1 and 2 .  
       FIG. 4  shows an embodiment version of a pressure booster that is actuated by an injection valve element, with two valve elements, one of which is embodied as spring-loaded.  
      From the high-pressure source  1 , the high-pressure inlet  2  extends via a high-pressure line branch  7  that contains a check valve  8  and via a first parallel branch  1   1  and an additional parallel branch  12  to the control chamber  15  of the pressure booster  3 . In addition, the high-pressure source  1 , which is embodied for example as a high-pressure accumulator (common rail), acts on the working chamber  14  of the pressure booster  3  directly. The working chamber  14  and the control chamber  15  of the pressure booster  3  are separated from each other by a piston unit  17 , the end surface of the piston unit  17  oriented toward the working chamber  14  having a larger diameter than the end surface of the piston unit  17  that delimits the compression chamber  18  of the pressure booster  3 . The compression chamber  18  inside the injector body  5  of the fuel injector  4  has a compression chamber line  20  branching off from it, which unites with the high-pressure line  7  containing the check valve  8  and transitions into the nozzle chamber inlet  9 .  
      The control chamber  21  inside the fuel injector  4  is acted on with pressure via a high-pressure branch  22  with an inlet throttle restriction  23  and can be pressure-relieved into the low-pressure return  26  via an outlet throttle restriction  24  through actuation of a control valve  25 .  
      A multi-part valve element  28  is also used in the embodiment version of the fuel injector  4  shown in  FIG. 4 . The multi-part valve element  28  that acts on the injection valve element  34  in the nozzle body  6  of the fuel injector  4  includes a first valve element  28 . 1  whose end surface  62  delimits the control chamber  21 . The first valve element  28 . 1  has a piston extension  66  whose bottom end surface rests against the end surface of the injection valve element  34 . The first valve element  28 . 1  is encompassed by a second, additional valve element  28 . 2 ; a continuous gap  72  is provided between the first valve element  28 . 1  and the second valve element  28 . 2 . By contrast with the embodiment version shown in  FIG. 3 , the second valve element  28 . 2  does not delimit the control chamber  21 , but is instead disposed underneath the first valve element  28 . 1  and its annular surface  60  is acted on by a spring element  70 . The spring element  70  rests against the top  71  of the valve chamber  63  in the nozzle body  6  of the fuel injector  4 .  
      The spring element  70  contained in the valve chamber  63  presses the control edge  30  of the second, sleeve-shaped valve element  28 . 2  into its closed position so that the valve seat between the control edge  30  and the housing edge  31  of the valve chamber  63  is closed in the idle position and the pressure booster  3  is deactivated. Since the control edges  30  on the second valve element  28 . 2  and the control edge  31  on the valve chamber  63  close the seat, it is not possible for the pressure in the control chamber  15  to be relieved into the valve chamber  63  via the line  19  so that the piston unit  17  between the working chamber  14  and the control chamber  15  of the pressure booster  3  is disposed in its starting position. A corresponding pressure shoulder inside the valve chamber  63  can serve to generate a closing hydraulic compression force in order to increase the closing force on the control edge  30 .  
      After the triggering of the control valve  25 , which is preferably embodied as a 2/2-way control valve, a pressure-relief occurs in the control chamber  21  so that the end surface  62  of the first valve element  28 . 1  travels into this chamber. If the control chamber  21  above the end surface  62  of the first valve element  28 . 1  is pressure-relieved until the end surface of the injection valve element  34  comes to rest against the lower annular surface of the second valve element  28 . 2 , i.e. if the stroke distance h 1  (reference numeral  32 ) is exceeded, then the injection valve element  34  activates the pressure booster  3  since the hydraulic force acting on the pressure shoulder  35  in the nozzle chamber  36  opens the sealed seat between the control edges  30  on the second valve element  28 . 2  and the control edge  31  of the valve chamber  63 , and a pressure decrease in the control chamber  15  of the pressure booster  3  can occur via the line  19  leading into the first low-pressure return  64 . As a result, the fuel compressed in the compression chamber  18  of the pressure booster  3  is supplied to the nozzle chamber  36  via the compression chamber line  20 , the nozzle chamber inlet  9 , and the junction point  37  at which the nozzle chamber inlet  9  adjoins the nozzle chamber  36 . With an appropriate pressure-relief of the control chamber  21  of the injection valve element  34  within certain limits, i.e. so that the retraction path of the injection valve element  34  is less than the stroke distance h 1  (reference numeral  32 ), the design shown in  FIG. 4  can produce preinjections at the pressure level prevailing in the high-pressure source  1 ; a longer-lasting pressure-relief of the control chamber  21  above the injection valve element  34  activates the pressure booster  3  and a main injection phase with rate-shaping can be executed at an increased pressure level. In accordance with the triggering cycle of the control valve  25 , one or more preinjection phases can be executed, depending solely on the triggering times and the triggering program of the control valve  25 , which preferably can be embodied as a 2/2-way valve. In the embodiment versions proposed according to the invention and shown respectively in  FIGS. 1 and 2  and in  FIGS. 3 and 4 , with less than a certain needle stroke h 1  (reference numeral  32 ), an injection of fuel into the combustion chamber  41  of an autoignition internal combustion engine can be executed at a first pressure level that corresponds, for example, to the pressure level of a high-pressure source  1 . Once the needle stroke h 1  (reference numeral  32 ) is exceeded, the injection valve element  34  activates the pressure booster  3  so that a subsequent injection then occurs at an increased pressure level. On the one hand, this permits the production of a boot-shaped injection since the first injection phase (preinjection) occurs at a lower pressure level than the subsequent main injection. The activation of the pressure booster  3  through the vertical stroke motion of the injection valve element  34  causes an increased pressure level to occur at precisely the moment required in terms of process engineering, in accordance with the combustion progression occurring in the combustion chamber  41  of the autoignition internal combustion engine. In the range of small injection quantities, the injection valve element  34  can carry out a preinjection by executing a pressure-relief of the control chamber  21 , this pressure-relief being controlled with regard to its relief duration in such a way as not to exceed the stroke distance h 1  (reference numeral  32 ) so that the pressure booster  3  remains deactivated. The design proposed according to the invention can therefore execute any number of preinjections at a pressure level that is low in comparison that which is produced when the pressure booster  3  is activated, thus allowing the fuel injector  4  according to the design proposed according to the invention to be operated with only one control valve  25 .  
      Reference Numeral List  
     
         
           1  high-pressure source (common rail)  
           2  high-pressure inlet  
           3  pressure booster  
           4  fuel injector  
           5  injector body  
           6  nozzle body  
           7  high-pressure line  
           8  check valve  
           9  nozzle chamber inlet branch  
           10  filling valve  
           11  first parallel branch  
           12  second parallel branch  
           13  throttle restriction  
           14  working chamber  
           15  control chamber  
           16  spring element  
           17  piston unit  
           18  compression chamber  
           19  control line for control chamber  
           20  compression chamber line  
           21  control chamber  
           22  high-pressure branch to control chamber  
           23  inlet throttle restriction  
           24  outlet throttle restriction  
           25  control valve (2/2-way valve)  
           26 . 1  first low-pressure return  
           26 . 2  second low-pressure return  
           27  one-piece valve element  
           28  multi-part valve element  
           28 . 1  first valve element  
           28 . 2  second valve element  
           29  end surface of one-piece valve element  
           30  control edge of valve element  
           31  control edge of housing  
           32  stroke distance h 1    
           33  annular chamber of valve element  
           34  injection valve element  
           35  pressure shoulder  
           36  nozzle chamber  
           37  junction point of nozzle chamber inlet  
           38  annular gap  
           39  injection opening  
           40  seat at end oriented toward the combustion chamber  
           41  combustion chamber  
           42  closed injection opening  
           50  low-pressure connection  
           51  injection valve element  34  (retracted position)  
           52  open injection openings  
           60  annular surface of second valve element  
           61  opening  
           62  end surface of first valve element  
           63  valve chamber  
           64  first return line  
           65  second return line  
           66  piston extension  
           67  closing spring  
           68  stop of first valve element on second valve element  
           70  spring element for second valve element  
           71  stop for spring element  
           72  overflow gap