Abstract:
The invention relates to an injector for the fuel supply of an internal combustion engine, in particular in a motor vehicle. The injector has a piezoactuator for activating and/or actuating at least one nozzle needle to control the injection of fuel under high pressure through at least one nozzle spray hole. The piezoactuator is arranged with its shaft disposed in an actuator chamber of an injector body, and a high-pressure path directing the fuel under high pressure to at least one nozzle spray hole passes through the actuator chamber. In the injector according to the invention, the piezoactuator has an actuator foot at an end remote from the nozzle needle. The actuator foot has a sealing contour facing the nozzle needle and fitting in a sealing seat formed on the injector body remote from the nozzle needle.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an injector for supplying fuel to an internal combustion engine, in particular in a motor vehicle, having the characteristics of the preamble to claim  1 . 
       PRIOR ART 
       [0002]    Injectors of this kind are known for instance from German Patent Disclosure DE 10 2004 027 824 A1 and European Patent Disclosure EP 1 174 615 A2, and each include a piezoelectric actuator for triggering or actuating at least one nozzle needle, with the aid of which needle an injection of fuel that is at high pressure through at least one injection port is controllable. The piezoelectric actuator has a shaft, which expands longitudinally upon being supplied with current and which resumes its original shortened length upon the withdrawal of the current supply. An injector body of the injector contains an actuator chamber, in which the piezoelectric actuator with its shaft is disposed. In the known injectors, it is furthermore provided that a high-pressure path, which carries the fuel that is at high pressure to the at least one injection port, is passed through the aforementioned actuator chamber. As a consequence, the piezoelectric actuator is surrounded by the fuel that is at high pressure; the piezoelectric actuator is disposed in “wet” or “floating” fashion. 
         [0003]    In the known injectors, by supplying current to the piezoelectric actuator and withdrawing it, a control piston can be driven in order to lower the pressure in a control chamber for opening the nozzle needle. This involves direct, pressure-controlled needle control. In an inversely operated piezoelectric actuator, current is withdrawn from it to open the nozzle needle, while when the nozzle needle is closed current is supplied to it. 
         [0004]    In other designs of injectors, it is equally possible for the piezoelectric actuator to be used directly for driving the nozzle needle or a needle assembly that includes the nozzle needle, or for instance for triggering a servo valve. Still other designs of injectors with a piezoelectric actuator are also conceivable. 
         [0005]    In the aforementioned direct needle control, in order to reduce hydraulic boosting devices, it is necessary to provide the piezoelectric actuator with a relatively long shaft, so that the requisite strokes can be attained. However, in the production of the piezoelectric actuator and the injector body, production tolerances make deviations in planarity and concentricity unavoidable and can lead to an axial and angular offset of the components cooperating with one another. To achieve effective sealing off of the actuator chamber from the outside, however, the most exact possible angular orientation of the piezoelectric actuator within the injector body is necessary. This demand becomes more and more important, the greater the selected high pressure to which the fuel is subjected. In the meantime, in modern injection systems, the fuel can be subjected to a high pressure of 2000 bar. For the injector, a pressure tightness from the outside of up to 2400 bar is then for instance desired, so that even upon dynamic pressure peaks that occur in operation, leakage can be avoided. 
       ADVANTAGES OF THE INVENTION 
       [0006]    The injector of the invention having the characteristics of claim  1  has the advantage that by way of the cooperation of a sealing contour, embodied on an actuator foot, with a sealing seat, embodied on the injector body, the orientability of the piezoelectric actuator relative to the injector body during the assembly of the injector is improved. It is especially significant that the sealing contour of the actuator foot faces toward the nozzle needle and is seated axially in the direction of the nozzle needle in the sealing seat. In particular, it is thus possible to adapt the sealing contour and sealing seat to one another in such a way that the actuator foot, with its sealing contour resting in the sealing seat, forms an actuator seal that closes the actuator chamber. Depending on the axial force with which the sealing contour is seated in the sealing seat, more or less effective sealing off of the actuator chamber from outside can be attained. 
         [0007]    In an especially advantageous refinement, the actuator foot is prestressed by means of a prestressing device in the direction of the nozzle needle, in such a way that the sealing contour rests with initial tension in the sealing seat. By the selection of this axial initial tension, the tightness of the actuator seal can be adjusted to whichever pressure value is desired. In particular, the prestressing device can also be designed such that it is designed for introducing an initial tension that is so high that it leads to plastic deformation of the sealing seat and/or the sealing contour. In such an embodiment, even the tiniest deviations in shape can be compensated for by the deformation, in order to improve the effectiveness of the actuator seal. 
         [0008]    Further important characteristics and advantages of the injector according to the invention will become apparent from the dependent claims, the drawings, and the associated description in conjunction with the drawings. 
     
    
     
       DRAWINGS  
         [0009]    Exemplary embodiments of the invention are shown in the drawings and will be described in detail below; identical reference numerals pertain to identical or similar or functionally identical components. The drawings, each schematically, show the following: 
           [0010]      FIG. 1 , a simplified longitudinal section through an injector. 
           [0011]      FIG. 2 , an enlarged view in half cross section of a detail II of  FIG. 1 ; 
           [0012]      FIG. 3 , a further-simplified view in longitudinal section of an injector, but in a different embodiment. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0013]    In  FIGS. 1 through 3 , an injector  1  of an injection system, which serves to supply an internal combustion engine, in particular in a motor vehicle, with fuel, includes an injector body  2 , in which at least one nozzle needle  3 , or a nozzle body  4  that includes the nozzle needle  3 , is disposed. The nozzle body  4  is fixed on the rest of the injector body  2  by means of a nozzle tension nut  46  fitted over it. The injector  1  furthermore includes a piezoelectric actuator  5  with an actuator foot  6 , an actuator shaft  7 , and all actuator head  8 . The injector body  2  includes an actuator chamber  9 , in which the piezoelectric actuator  5  is disposed with at least its shaft  7 . 
         [0014]    Also embodied in the injector body  2  is a high-pressure path  10 , which leads from a high-pressure connection  11  of the injector  1 , embodied on the injector body  2 , to at least one injection port  12  of the injector  1 , also embodied on the nozzle body  4 , and which in operation of the injector  1  carries fuel that is at high pressure to the at least one injection port  12 . The high-pressure path  10  is extended through the actuator chamber  9 ; in other words, the actuator chamber  9  forms a component of the high-pressure path  10 , and the fuel at high pressure flows through it. 
         [0015]    The piezoelectric actuator  5  serves to trigger or actuate the nozzle needle  3 , in such a way that with the nozzle needle  3 , the injection of the fuel that is at high pressure through the at least one injection port  12  into an injection chamber  13  associated with the respective injector  1  can be controlled. For controlling the injection through the at least one injection port  12 , the nozzle needle  3  cooperates in a known manner with a needle seat  14 . To move the nozzle needle  3  out of the needle seat  14 , the needle must execute an opening stroke parallel to a longitudinal axis  15  of the injector  1  or injector body  2 . To that end, the pressure is lowered in a control chamber  16  by a suitable actuation of the piezoelectric actuator  5 . This control chamber  16  is defined in the radial direction by a control sleeve  17 . In the axial direction, the control chamber  16  is defined toward the nozzle needle  3  by an intermediate plate  18  and toward the piezoelectric actuator  5  by a control piston  19 . The control piston  19  is solidly connected to the actuator head  8  and plunges into the control sleeve  17 . The control sleeve  17  is supported with an adjustable stroke on the control piston  19  and is braced on the actuator head  8  by way of a closing compression spring  20 . Via the closing compression spring  20 , the control sleeve  17  is axially prestressed against the intermediate plate  18 . 
         [0016]    The piezoelectric actuator  5  may for instance be operated inversely. This means that in the outset state shown, in which the nozzle needle  3  is seated in the needle seat  14  and assumes its closing position, the piezoelectric actuator  5  is supplied with current and as a result expands axially. For opening the nozzle needle  3 , the supply of current to the piezoelectric actuator  5  is withdrawn, and as a result, its length, measured parallel to the longitudinal axis  15 , is reduced. Since the actuator foot  6  is disposed in stationary fashion on the injector body  2 , the actuator head  8  pulls back away from the nozzle needle  3  when the actuator shaft  7  becomes shorter. As a result, the control piston  19  is moved away from the nozzle needle  3 , causing the pressure in the control chamber  16  to fall. As a consequence, the pressure-controlled nozzle needle  3  can lift from the needle seat  14 , and the injection event begins. 
         [0017]    To enable bracing the piezoelectric actuator  5 , in the region of its actuator foot  6 , on the injector body  2  in stationary fashion, the actuator foot  6  has a sealing contour  21 , which faces toward the nozzle needle  3  and which rests in a sealing seat  22  that faces away from the nozzle needle  3  and is embodied on the injector body  2 . As a result, the actuator foot  6  can be braced axially on the injector body  2  in the direction toward the nozzle needle  3 . 
         [0018]    Preferably, the sealing contour  21  and sealing seat  22  are adapted to one another in such a way that the actuator foot  6 , together with its sealing contour  21  resting in the sealing seat  22 , forms an actuator seal  23 , which closes the actuator chamber  9 . With the aid of the actuator seal  23 , the actuator chamber  9  is axially closed on its end facing away from the nozzle needle  3 . To achieve the desired actuator seal  23 , the sealing contour  21  and the sealing seat  22  are each designed in the shape of a closed ring, extending in the circumferential direction relative to the longitudinal axis  15 . The sealing contour  21  and sealing seat  22  are furthermore preferably oriented concentrically to the longitudinal axis  15 . 
         [0019]    Besides the feasibility of the actuator seal  23 , the sealing contour  21  and sealing seat  22  can also be used to align the piezoelectric actuator  5  as exactly concentrically as possible to the central longitudinal axis  15  as the injector  1  is being put together. In that case, an embodiment that is especially advantageous is one in which the sealing contour  21  is designed in spherical form, in such a way that the sealing contour  21  extends spherically along a spherical segment. The associated virtual sphere is marked  24  in the drawings. Preferably, a center point  25  of the ball  24  is disposed Centrally in the actuator foot  6 . The spherical sealing contour  21  facilitates the axial orientation of the piezoelectric actuator  5  relative to the injector body  2 , thus improving the functionality in the collaboration between the control sleeve  17  and the control piston  19 . This mode of construction is especially advantageous if the piezoelectric actuator  5  has a comparatively long shaft  7 , which in  FIG. 1  is shown shortened markedly. 
         [0020]    The sealing seat  22  preferably has a conical shape, and as a result, regardless of manufacturing tolerances, linear contact is attained between the sealing contour  21  and the sealing seat  22 . As a result, a closed and hence effective actuator seal  23  is attained. 
         [0021]    To enhance the effectiveness of the actuator seal  23 , the actuator foot  6  is prestressed in the direction of the nozzle needle  3 , and as a result, the sealing contour  21  is seated with axial prestressing in the sealing seat  22 . The selected axial prestressing can be comparatively great; for instance, the set prestressing may be so great that tolerable plastic deformation occurs at the sealing seat  22  and/or at the sealing contour  21 . The aforementioned linear contact between the sealing contour  21  and the sealing seat  22  is made somewhat ribbonlike as a result. 
         [0022]    To enable introducing the desired axial prestressing into the actuator foot  6 , the injector  1  is equipped with a prestressing device  26 . In the exemplary embodiments shown, the prestressing device  26  includes a tension screw  27  and a clamping member  28 ; it is fundamentally also possible for the clamping member  28 , embodied here separately, to be embodied integrally with the tension screw  27 , or for the clamping member  28  to be formed by the tension screw  27 . It is equally possible for a tension nut to be used, instead of a tension screw  27 . 
         [0023]    The clamping member  28  has a support seat  29 , which faces toward the nozzle needle  3 . On the actuator foot  6 , on a side facing away from the nozzle needle  3 , a support contour  30  is embodied, which rests axially or is axially braced in the support seat  29 . To enable introducing the highest possible axial forces into the actuator foot  6 , it is expedient to design the support contour  30  and support seat  29  as closed rings and preferably to dispose them concentrically to the longitudinal axis  15 . It may also be advantageous here to design the support contour  30  in spherical form. The support contour  30  then extends spherically in a spherical segment. The sphere associated with the support contour  30  may have a different radius from the sphere associated with the sealing contour  21 . In the preferred example shown, the spheres of the two contours  21 ,  30  are on the one hand of equal size and are preferably identical. In other words, in the example shown, the spherical support contour  30  is likewise located on the virtual sphere  24  having the center point  25 . 
         [0024]    The support seat  29  is preferably designed conically, as a result of which a linear contact is attained between the support contour  30  and support seat  29  as well. Depending on the prestressing force, plastic deformation may also occur at the support seat  29  and/or the support contour  30 . 
         [0025]    The tension screw  27  has a male thread  31 , which cooperates with a complementary female thread  32  that is embodied on the injector body  2 . Thus the tension screw  27  can be screwed axially into the injector body  2 . In the process, the tension screw  27  presses the clamping member  28  in the axial direction against the actuator foot  6 . 
         [0026]    The clamping member  28  can be secured against torsional shifting about the longitudinal axis  15  with the aid of a torsion preventer  33 . For example, the torsion preventer  33  is formed by a securing pin  34 , which is braced on the injector body  2  and radially engages a securing slit  35  embodied on the outside of the clamping member  28 . The clamping member  28  is moreover preferably embodied as a ring, and as a result it includes a central opening  36 . Moreover, the tension screw  27  may, as here, be designed in sleevelike fashion, as a result of which it has a central passage  37 . The opening  36  and passage  37  form a terminal duct  38 , through which electrical terminals  39  of the piezoelectric actuator  5  are extended to the actuator foot  6  and through the actuator foot  6  as far as the actuator shaft  7  that is equipped with the piezoelectric elements. For this terminal duct  38 , the actuator foot  6  together with its support contour  30  resting on the support seat  29  can embody a terminal duct seal  45 , which closes the terminal duct  38  off from the outside at the actuator foot  6 . 
         [0027]    The injector  1  of the invention is distinguished in particular in that its piezoelectric actuator  5  can be oriented relatively precisely axially parallel to the longitudinal axis  15  during assembly, and this is achieved because of the intentional shaping and because of the collaboration of the sealing contour  21  and the sealing seat  22 . Moreover, with the aid of the clamping member  28 , which is secured on the injector body  2  in a manner fixed against relative rotation, it becomes possible to introduce very great prestressing forces via the tension screw  27 , without causing a change in the orientation that has been set between the piezoelectric actuator  5  and the injector body  2 . This is because the rotary motion of the tension screw  27  is not transmitted to the actuator foot  6  via the clamping member  28  that is secured against relative rotation. 
         [0028]    Via the high-pressure connection  11 , the injector  1  can be connected to a high-pressure source, which furnishes fuel that is at high pressure. For example, the high-pressure connection  11  is connected to a high-pressure line, which in turn communicates with a high-pressure pump. If a plurality of injectors  1  are connected to one common high-pressure line, then this is called a “common rail system”. 
         [0029]    In the embodiment shown in  FIGS. 1 and 2 , the injector body  2  is made in one piece, in the region that contains the actuator chamber  9 . In the embodiment shown in  FIG. 3 , the injector body  2 , in the region including the actuator chamber  9 , is made in at least two parts, namely being put together from a first injector body part  40  and a second injector body part  41 . The first injector body part  40  contains the actuator foot  6 . The second injector body part  41 , in the direction toward the nozzle needle  3 , adjoins the first injector body part  40 . The second injector body part  41  contains the entire actuator chamber  9 , or at least a substantial portion of it. The first injector body part  40  can contain a comparatively small portion of the actuator chamber  9 . In the present case, the high-pressure connection  1  is embodied on the first injector body part  40 . The two injector body parts  40 ,  41  are secured to one another via a connecting element  42 , which in particular may be sleevelike in embodiment. To be able to attain the desired pressure-proofness at the connecting point, marked  43 , between the two injector body parts  40 ,  41 , a ring seal  44  is additionally provided here. 
         [0030]    As a result of the multi-part mode of construction of the injector body  2  as shown in  FIG. 3 , it is possible for instance to embody the second injector body part  41  as a standard component, which is used identically in different variants of the injector  1 . The first injector body part  40  can then be designed differently for various variants of the injector  1 . By mounting different first injector body parts  40  on the standardized second injector body part  41 , various variants of the injector  1  can then be attained comparatively inexpensively.