Abstract:
Disclosed is a fuel injection device comprising a housing and a valve element disposed therein and cooperating with a valve seat located in the area of at least one fuel discharge port. The valve element is composed of several parts while at least two parts of the valve element are coupled to each other via a hydraulic coupler.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2006/062779 filed on May 31, 2006. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an improved fuel injection device for an internal combustion engine with direct fuel injection. 
     2. Description of the Prior Art 
     A fuel injection device with which the fuel can be injected directly into a combustion chamber, assigned to it, of an internal combustion engine is known on the market. For that purpose, a valve element is disposed in a housing, and in a region of a fuel outlet opening, the valve element has a pressure face that acts overall in the opening direction of the valve element. On the opposite end of the valve element, there is a control face acting in the closing direction, which defines a control chamber. The control face acting in the closing direction is larger overall than the pressure face that when the valve element is open acts in the opening direction. 
     When the fuel injection device is closed, in a region of the pressure face acting in the opening direction aid of the control face acting in the closing direction, a high fuel pressure prevails, of the kind furnished for instance by a fuel collection line (or “rail”). For opening the valve element, the pressure applied to the control face is lowered, until the hydraulic force resultant, acting in the opening direction, at the pressure face exceeds the force acting in the closing direction. As a results opening of the valve element is accomplished. 
     A prerequisite for the mode of operation of this fuel injection device is sealing between every region in which the comparatively small pressure face, acting in the opening direction, is present, and the region of the valve element in which the comparatively large control face, acting in the closing direction, is present. Leakage fluid, in the known fuel injection device, is carried away from the region of the seal via a leakage line. 
     The object of the present invention is to refine a fuel injection device of the type defined at the outset in such a way that it is as simple and economical as possible in construction and can be used at a very high operating pressure. 
     SUMMARY AND ADVANTAGES OF THE INVENTION 
     In the fuel injection device of the invention, as a result of the hydraulic coupling of two separate parts of the valve element, the freedom in designing the fuel injection device is increased considerably, since the various parts of the valve element can each be optimally adapted to the specific location inside the fuel injection device. For instance, the elastic properties of the valve element can be optimally adapted to the intended region of use by means of a suitable choice of the material employed and of the dimensions. Moreover, the manufacture of the valve element overall is substantially simplified, since parts of constant diameter can also be used. This makes a simpler construction of the fuel injection device possible, with simpler parts; this both facilitates production and also makes a smaller mode of construction possible. For implementing the present invention, it is furthermore possible to continue to use numerous components of previous devices. 
     A further advantage of the hydraulic coupler is the compensation for tolerances, which simplifies both production and assembly. Coupling two parts of the valve element by means of a hydraulic coupler moreover makes it possible to implement a certain motion damping. By means of a sleeve element, the hydraulic coupler can be implemented very simply. 
     It is especially advantageous if in all the chambers that surrounds the valve element and are located between a control chamber and a pressure chamber, at least approximately the high fuel pressure that prevails at the high-pressure connection prevails during operation (the valve element “floats” in high pressure), and if the valve element has a hydraulic control face acting in the closing direction and a hydraulic pressure face acting in the opening direction. This means nothing other than that in such a device, a pressure step that was previously required between the pressure face and the control face is no longer necessary. A valve element that “floats” in high pressure can be implemented for instance by providing that the recess in which the valve element overall is received communicates with the high-pressure connection. By means of a larger control face (acting in the closing direction), secure closure of the valve element is also assured in the event of a lessening, caused by wear to the seat toward the housing, of the difference in surface area and an attendant reduction in the force acting in the closing direction (drift in the closing force). 
     Since a pressure step with a low-pressure chamber required for it can be dispensed with and the valve element overall “floats” in the high pressure, a low-pressure region is no longer present. Hence no leakage can occur between the high-pressure region and such a low-pressure region, and thus the corresponding sealing and a requisite leakage line for the purpose can be dispensed with. Dispensing with a pressure step also means that the valve element rests statically with only a comparatively low closing force on the valve seat toward the housing, which lessens the aforementioned drift. 
     The fuel injection device of the invention furthermore operates at high efficiency, since the leakage existing in earlier devices between the valve element and the housing is no longer present. As a consequence, a return line can be designed smaller. 
     If the end face, located in the hydraulic coupler, of the part of the valve element that is remote from the fuel outlet openings of the fuel injection device is larger than the end face of the other part, then when the valve element is open, a hydraulic spring acting in the closing direction is “tensed” by the hydraulic coupler, which reinforces a secure closure of the valve element. 
     If the pressure face and control face are at least approximately the same size, then the valve element overall is in pressure equilibrium, with suitably high dynamics. The force excess in the closing direction required for the closure can be implemented in this case by a slight throttling in the region of the pressure face, and/or by throttling of the fuel flow that reaches the pressure face. 
     The assembly of the fuel injection device is simplified if the valve element is received in its entirety in a high-pressure chamber that communicates with the high-pressure connection. The high-pressure chamber car furthermore function as a damping volume, by means of which pressure waves and consequently wear to a valve seat can be reduced. In addition, the precision of the injection quantities upon multiple injection increases. Furthermore, manufacture is simplified, since a separate high-pressure bore for connecting the pressure chamber to the high-pressure connection can be dispensed with. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Especially preferred exemplary embodiments of the present invention will be described in further detail below in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a schematic view of an internal combustion engine with a fuel injection device; 
         FIG. 2  is a schematic, partly sectional view of a first embodiment of the fuel injection device of  FIG. 1 ; 
         FIG. 3  is a view similar to  FIG. 2  of a second embodiment; 
         FIG. 4  is a view similar to  FIG. 2  of a third embodiment; 
         FIG. 5  is a view similar to  FIG. 2  of a fourth embodiment; 
         FIG. 6  is a view similar to  FIG. 2  of a fifth embodiment; 
         FIG. 7  is a view similar to  FIG. 2  of a sixth embodiment, 
         FIG. 8  is a view similar to  FIG. 2  of a seventh embodiment; and 
         FIG. 9 , a detail marked IX of  FIG. 8  in a three-dimensional view. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , an internal combustion engine is identified overall by reference numeral  10 . It serves to drive a motor vehicle, not shown. A high-pressure pumping device  12  pumps fuel from a fuel tank  14  into a fuel pressure reservoir  16  (or “rail”). The fuel—diesel or gasoline—is stored in it at very high pressure. Each by means of a respective high-pressure connection  17 , a plurality of fuel injection devices  18  are connected to the rail  16  and inject the fuel directly into combustion chambers  20  assigned to them. The fuel injection devices  18  each also have a low-pressure connection  21 , by way of which they communicate with a low-pressure region, in this case the fuel tank  14 . 
     The fuel injection devices  18  in a first embodiment may be embodied in accordance with  FIG. 2 : The fuel injection device  18  shown there includes a housing  22  with a nozzle body  24 , a main body  26 , and an end body  28 . In the housing  22 , in its longitudinal direction, there is a stepped recess  30 , in which a needle-like valve element  32  is received. This valve element is embodied in two parts, with a control piston  34  and a nozzle needle  36 . 
     The nozzle needle  36 , on its lower end in terms of  FIG. 2 , has a conical pressure face  38   a , which defines a pressure chamber  40 . In the region of the pressure face  38   a , the nozzle needle  36  cooperates in a manner not show in detail in  FIG. 2  with a valve seat of the housing. In this way, fuel outlet openings  42  can be disconnected from the pressure chamber  40  or made to communicate with it. It is understood that whenever the nozzle needle  36  rests with the pressure face  38   a  on the valve seat of the housing, only a region of the pressure face  38   a  located upstream of the valve seat is subjected to the pressure prevailing in the pressure chamber  40 . Not until the nozzle needle  36  lifts from the valve seat is an increased pressure also applied to a region of the pressure face  38   a  located downstream of the valve seat. However, this is not shown in the drawing, for the sake of simplicity. 
     The nozzle needle  36  has one portion  44  of smaller diameter and one portion  46  of larger diameter. Between them is a shoulder which likewise forms a pressure face acting in the opening direction of the valve element  32 ; this pressure face is identified by reference numeral  38   b . With the portion  46 , the nozzle needle  36  is guided longitudinally displaceably in the nozzle body  24 . 
     The control piston  34  is guided in the main body  26 . Its lower end extends, with an end face  48  that in the present exemplary embodiment is chamfered conically, into a widening of the recess  30  that forms a coupling chamber  50 . This chamber will be addressed in further detail hereinafter. An axial end face  51  of the nozzle needle  36 , which is the upper end face in terms of  FIG. 2 , protrudes into the coupling chamber  50 . The upper end, in terms of  FIG. 2 , of the control piston  34  extends into a widened region of the recess  30 , so that in this region between the valve element  32  and the wall of the recess  30 , an annular chamber  52  is formed. A sleeve  54  is slipped onto the upper end region, in terms of  FIG. 2 , of the control piston  34  and is pressed with a sealing edge (without a reference numeral) against the end body  28  by a spring  55  that is braced on the control piston  34  via an annular collar  56 . 
     The upper axial end face, in terms of  FIG. 2 , of the control piston  34  forms a hydraulic control face  58  that acts in the closing direction of the valve element  32 . Together with the sleeve  54  and the end body  28 , it defines a control chamber  60 . This chamber communicates with the annular chamber  52  via an inlet throttle restriction  62 , which is present in the sleeve  54 . The control chamber  60  furthermore communicates with a 3/2-way switching valve  66 , by means of a combined inlet and outlet throttle restriction  64  that is present in the end body  28 . Depending on the switching position, this valve causes the inlet and outlet throttle restriction  64  to communicate selectively with the high-pressure connection  17  or the low-pressure connection  21 . The annular chamber  52 , via a conduit  68 , likewise communicates constantly with the high-pressure connection  17 , as does the pressure chamber  40  via a conduit  70 . 
     It should be noted that in the exemplary embodiment shown in  FIG. 2 , the portion  46  of the nozzle needle  36  has the same diameter D 1  as the control piston  34  (diameters D 2  and D 3 ). From this, it can also be seen that the two pressure faces  38   a  and  38   b  (upstream and downstream of the valve seat), projected onto a plane perpendicular to the longitudinal axis of the valve element  32 , when the valve element has lifted from the valve seat, form the same total hydraulically effective surface area as the control face  58 . 
     The fuel injection device  18  shown in  FIG. 2  functions as follows: In the outset state, with the switching valve  66  currentless, the control chamber  60  communicates, via the combined inlet and outlet throttle restriction  64  as well as the inlet throttle restriction  62 , with the high-pressure connection  17  and thus with the rail  16 . The high rail pressure thus prevails in the control chamber  60 . This pressure also prevails in the annular chamber  52  via the conduit  68  and in the pressure chamber  40  via the conduit  70 . Because of certain unavoidable leakage flows as a result of the guidance of the nozzle needle  36  in the nozzle body  24  and of the control piston  34  in the main body  26 , rail pressure prevails in the coupling chamber  50  as well. 
     Since as has already been mentioned above, when the valve element  32  is closed, only a portion of the pressure face  38   a  is acted upon by the high pressure prevailing in the pressure chamber  40 , the total with the pressure face  38   b  is a somewhat lesser hydraulic force acting in the opening direction, compared to the force acting on the control face  58  in the closing direction. As a result of this force difference and of the spring  55 , the valve element  32  is pressed against the valve seat in the region of the fuel outlet openings  42  (in this state, the control piston  34  rests with its end face  48  on the end face  51  of the nozzle needle  36 ). Accordingly, fuel is unable to exit through the fuel outlet openings  42 . 
     If current is now supplied to the switching valve  66 , the communication of the combined inlet and outlet throttle restriction  64  with the high-pressure connection  17  is interrupted, and this combined throttle restriction communicates instead with the low-pressure connection  21 . As a result of the throttling action of the combined inlet and outlet throttle restriction  64  and of the inlet throttle restriction  62 , the pressure in the control chamber  60  drops. 
     Because the difference in pressure and force between the end face  48  and the control face  58  of the control piston  34 , the control piston  34  now begins to move upward in  FIG. 2 , counter to the force of the spring  55 . The pressure in the coupling chamber  50  thus drops as a result of the increase in volume. Because of the difference in pressure and force that now occurs between the end face  51  and the pressure faces  38   a  and  38   b , the nozzle needle  36  also moves upward in  FIG. 2 ; that is, it lifts from its valve seat in the region of the fuel outlet openings  42 , so that now the region of the pressure face  38   a  located downstream of the valve seat also acts in the opening direction, which reinforces the opening process. Thus fuel from the rail  16  can be injected into the combustion chamber  20 , via the high-pressure connection  17 , the conduit  68 , the annular chamber  52 , the conduit  70 , the pressure chamber  40 , and the fuel outlet openings  42 . 
     To terminate an injection, the switching valve  66  is put back into its closed position, in which the inlet and outlet throttle restriction  64  communicates with the high-pressure connection  17 . The pressure in the control chamber  60  now rises to rail pressure again. As a result, the control piston  34  is stopped and moved back in the closing direction, since the pressure in the coupling chamber  50  is initially less than in the control chamber  60 . As a consequence, the pressure in the coupling chamber  50  rises up to the rail pressure, because of the reduction in volume. 
     In the case being observed now, in which the control piston  34  has the same diameter D 2  as the portion  46  of the nozzle needle (diameter D 1 ), the control piston  34  only now becomes seated again with the end face  48  on the end face  51  of the nozzle needle  36 . By means of the spring  55 , the intrinsically pressure-balanced valve element  32  is now closed. With a decreasing stroke of the valve element  32 , the nozzle needle  36  begins to throttle the flow in the region of the pressure face  38   a , causing the pressure prevailing there to drop. As a result, the closure of the valve element  32  is hydraulically reinforced. As soon as the nozzle needle  36  again rests on the valve seat in the region of the fuel outlet openings  42 , the injection is terminated. 
     From the above functional description, it can be seen that by means of the coupling chamber  50 , the nozzle needle  36  is hydraulically coupled with the control piston  34 . The end face  48 , coupling chamber  50 , and end face  51  in this respect taken together form a hydraulic coupler  71 . It can also be seen that between the pressure chamber  40  and the control chamber  60 , in the form of the annular chamber  52  and the coupling chamber  50 , only those chambers, surrounding the valve element  32 , in which at least intermittently and at least approximately the high rail pressure applied also to the high-pressure connection  17  or in the rail  16 , are present. In other words, the valve element  32  “floats” in high-pressure fuel. 
     In  FIG. 3 , an alternative embodiment of a fuel injection device  18  is shown. Here as well as in the exemplary embodiments that follow, those elements and regions that have equivalent functions to elements and regions described above are identified by the same reference numerals and will not be described again in detail. For the sake of simplicity, not all the reference numerals are entered, either. 
     In a distinction from the exemplary embodiment shown in  FIG. 2 , the switching valve  66  in the fuel injection device shown in  FIG. 3  is embodied as a 2/2-way switching valve. With this valve, the control chamber  60 , via the device that in this case is embodied only as an outlet throttle restriction  64 , can either be made to communicate with the low-pressure connection  21  or be separated from it. Moreover, a throttle restriction  72  is provided in the conduit  70  that connects the annular chamber  52  to the pressure chamber  40 . As a consequence, the pressure in the pressure chamber  40  when the valve element  32  is open is somewhat below the rail pressure. In this way, the closing process of the valve element  32  is simplified or accelerated. It is understood that the throttle restriction  72  may also be disposed at some other point between the high-pressure connection  17  and the pressure chamber  40 , for instance in the conduit  68 . 
     In the embodiment shown in  FIG. 4 , the diameters D 2  and D 33  of the control piston  34  are larger than the diameter D 1  of the portion  46  of the nozzle needle  36 . As a consequence, during the opening process, or in other words with the switching valve  66  open, the pressure in the coupling chamber  50  drops, and the nozzle needle  36  very quickly returns to being in contact with the control piston  34 . Moreover, as a result in the opening stroke of the valve element  32 , by means of the hydraulic coupler  71 , a “hydraulic spring” acting on the control piston  34  in the closing direction is tensed, and this reinforces the ensuing closing process, even given the fact that the valve element  32  in the open state is intrinsically pressure-balanced. 
     In the embodiment shown in  FIG. 5 , the coupling chamber  50  is formed not between the valve element  32  and the housing  22  but rather between the valve element  32  and an additional sleeve  74 . This sleeve is urged against the nozzle body  24  by a spring  76 , which is braced on the main body  26 . The control piston  34  in  FIG. 5  furthermore has a larger diameter D 3  above the annular collar  56  than below the annular collar  56  (diameter D 2 ). This permits an additional degree of freedom in determining the closing and opening properties of the fuel injection device  18 . The sleeve  74  permits a marked increase in size of the annular chamber  52 , which simplifies the manufacture and design of the main body  26 . Moreover, the increased volume of the annular chamber  52  assures an improved damping property, for instance for damping pressure waves. In addition, in the embodiment shown in  FIG. 5 , the sleeve  54  is integral with the end body  28 . 
     In  FIG. 6 , a fifth embodiment of the fuel injection device is shown, which is substantially the same as the embodiments of  FIGS. 2 through 5 , except that the control piston  34 , like the nozzle needle  36 , is guided in the nozzle body  24  rather than in the main body  26 . This has the advantage that the guides for the nozzle needle  36  and the control piston  34 , which are formed by a bore  25  in the nozzle body  24 , can be manufactured with high precision. The diameter D 1  of the nozzle needle  36  and the diameter D 2  of the control piston  34  can be the same or different, and as a result the volume of the coupling chamber  50  can be varied. By means of a portion of reduced diameter, provided on the control piston  34  or on the nozzle needle  36 , the volume of the coupling chamber  50  can also be varied, and thus the performance of the coupler  71  can be varied. 
     In  FIG. 7 , a sixth embodiment of the fuel injection device is show, in which the fundamental construction is the same as in the embodiment of  FIG. 5 , but in which one additional throttle restriction  86  is provided, which is disposed in the connection of the pressure chamber  40  with the high-pressure connection  17 . In the version in  FIG. 7 , the additional throttle restriction  86  is disposed in a branch of the conduit  68  leading to the pressure chamber  40 , and upstream of the additional throttle restriction  86  the connection leads from the conduit  68  into the control chamber  60 , in which the inlet throttle restriction  62  is disposed. Between the sleeve  54  and the main body  26 , there is a sealing element, by which the annular chamber  52  is subdivided into two separate annular chamber regions  52   a  and  52   b . The connection with the control chamber  60  extends though the annular chamber region  52   a  and the inlet throttle restriction  62  in the sleeve  54  into the control chamber  60 . Thus the additional throttle restriction  86  is operative only in the connection with the pressure chamber  40 , which discharges into the annular chamber region  52   b  and from there leads onward into the pressure chamber  40 . 
     In an embodiment shown in  FIG. 8  which has been modified compared to  FIG. 7 , it is provided that the annular chamber  52  is subdivided into two separate annular chamber regions  52   a  and  52   b  by a sealing element  87  fastened between the main body  26  and the sleeve  54 . The control piston  34 , on its end disposed in the sleeve  54 , has an enlarged diameter D 4 , by way of which the control piston  34  is guided in the sleeve  54 . Hence there is an annular gap between the remaining shaft, disposed in the sleeve  54 , of the control piston  34  and the sleeve  54 . The high-pressure connection  17  discharges into the annular chamber region  52   a , from which the connection into the control chamber  60  with the inlet throttle restriction  62  leads away. A connection into the annular gap between the shaft of the control piston  34  and the sleeve  54  also leads away from the annular chamber region  52   a  via the additional throttle restriction  86 , and the annular gap is in communication with the annular chamber region  52   b . The communication of the annular chamber region  52   b  and hence of the pressure chamber  40  with the high-pressure connection  17  is thus effected via the additional throttle restriction  86 , which however is not operative for the communication of the control chamber  60  with the high-pressure connection  17 . 
     In  FIG. 9 , a further embodiment of the fuel injection device is shown, which is suitable in particular for the embodiment of  FIG. 8  but is also suitable for all the other embodiments described above. In  FIG. 9 , the sleeve  54  is shown, in which the control piston  34  is guided with its end of increased diameter. The inlet throttle restriction  62  is formed here by a plurality of bores  63  of very small diameter, for instance approximately 4 to 9 such bores, which are preferably made in the sleeve  54  by laser drilling. The bores  63  are distributed over the circumference of the sleeve  54 , and the diameter of the bores  63  can amount to approximately 0.1 mm. The inlet and/or outlet region of the bores  63  may be rounded, for instance by means of a hydroerosive process. The bores  63 , in addition to the throttling function, also have the function of a filter, so that an additional filter in the region of the high-pressure connection  17  may optionally be dispensed with. Clogging of the inlet throttle restriction  62  is unlikely, because of the multiple bores  63 . The additional throttle restriction  86  in the communication with the pressure chamber  40  can also be formed by a plurality of bores  88  of small diameter in the sleeve  54 , as is shown in  FIG. 9 . For forming the throttle restriction  86 , approximately 20 to 50 bores  88 , for instance, may be provided, which can each have a diameter of approximately 0.1 mm. The bores  88  are distributed over the circumference of the sleeve  54 . Also shown in  FIG. 9 , is the sealing element  87 , by which the two annular chamber regions  52   a  and  52   b  of  FIG. 8  are separated from one another. 
     The foregoing relates to a preferred exemplary embodiment 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.