Abstract:
A fuel injection device for an internal combustion engine includes a housing and a valve element which is arranged in the housing. The valve element interacts, in the region of a fuel outlet opening, with a valve seat. The valve element is embodied by at least one first part and at least one second part which are coupled to one another by means of a hydraulic coupler. The hydraulic coupler has a coupling chamber which is delimited at least partially by a sleeve which is guided on the first part of the valve element. Additionally a guide element guides an end region of the first part of the valve element, which end region being oriented toward the second part of the valve element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/050300 filed on 12 Jan. 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a fuel injection device for an internal combustion engine. 
     2. Description of the Prior Art 
     A fuel injection device is known from the market, which can be used to inject fuel directly into a combustion chamber of an internal combustion engine with which it is associated. To this end, a valve element is situated in a housing, which in the region of a fuel outlet opening, has a pressure surface that on the whole, acts in the opening direction of the valve element. At the opposite end of the valve element, there is a control surface that acts in the closing direction and delimits a control chamber. The control surface acting in the closing direction is on the whole larger than the pressure surface acting in the opening direction when the valve element is open. 
     When the fuel injection device is closed, a higher fuel pressure such as the pressure supplied by a fuel accumulator line (rail) acts on a region of the pressure surface acting in the opening direction and on the control surface acting in the closing direction. To open the valve element, the pressure acting on the control surface is reduced until the hydraulic force resultant acting on the pressure surface in the opening direction exceeds the force acting in the closing direction. This achieves an opening of the valve element. 
     A requirement for the function of this fuel injection device is a seal between the region in which the comparatively small pressure surface acting in the opening direction is situated and the region of the valve element in which the comparatively large control surface acting in the closing direction is situated. In the known fuel injection device, leakage fluid is conveyed out of the region of the seal via a leakage line. 
     The object of the present invention is to modify a fuel injection device of the type mentioned at the beginning so that it is as simple and inexpensive as possible and can be used at a very high operating pressure. In addition, the fuel injection device should function reliably, even when there are production tolerances. 
     SUMMARY AND ADVANTAGES OF THE INVENTION 
     In the fuel injection device according to the present invention, the hydraulic coupling of two separate parts of the valve element significantly increases the design freedom of the fuel injection device because the respective parts of the valve element can be optimally adapted to the location inside the fuel injection device. For example, the elastic properties of the valve element can, through an appropriate selection of the material used and the dimensions, be optimally adapted to the given area of use. Furthermore, the manufacture of the valve element as a whole is significantly simplified since in addition, parts with a constant diameter are used. This makes it possible for the fuel injection device to be constructed of simple parts, which on the one hand, facilitates production and on the other hand, permits a compact design. Furthermore, it is possible to continue to use numerous components of previous devices for implementation of the present invention. 
     Another advantage of the hydraulic coupler is the compensation of tolerances, which simplifies the production and assembly. The coupling of two parts of the valve element by means of a hydraulic coupler also permits the implementation of a certain movement damping. 
     The sleeve provided according to the present invention facilitates implementation of the hydraulic coupler and simplifies the housing work required. The guide element, which according to the present invention is provided separately from the housing, additionally minimizes an alignment error of the sleeve in relation to a sealing surface that cooperates with it on the housing. This can turn out to be particularly useful if the first part of the valve element is particularly long and if the sleeve is guided on the first part of the valve element in a particularly snug fashion. This minimizes or entirely eliminates leaks in the coupling chamber. It is therefore possible to dispense with a complex and cost-intensive calibration process. A wear-induced change in the functional properties of the fuel injection device according to the present invention is reduced. The guidance by means of the guide element compensates for production tolerances, thus assuring a reliable injector function. 
     The fuel injection device according to the present invention is particularly simple in terms of its construction if the sleeve rests against the guide element. In this case, a sealing surface can be embodied on the guide element against which the sleeve rests, exactly at right angles to the guide axis of the guide element thus minimizing to a particularly significant degree any misalignment of the sleeve guided on the first part in relation to the sealing surface on the guide element. 
     In a modification of this, the present invention proposes providing a fluid passage leading from one side of the guide element to the other in at least part of a guide region of the guide element or a complementary region of the first part of the valve element. This achieves a clear functional separation such that the guide region of the guide element has a pure guiding function and the sleeve has a purely sealing function. Such a separation of the functions permits an optimal layout. In a concrete modification of this, the fluid passage can be constituted by a guidance play between the guide element and the first part of the valve element. This is particularly easy to implement from a production engineering standpoint. 
     In another advantageous modification of the fuel injection device according to the present invention, the guide element includes a stroke stop for the second part of the valve element. This is advantageous primarily in those fuel injection devices with which comparatively large fuel quantities are to be injected, for example in commercial vehicles. In a fuel injection device of this kind, because of its multipart design, production tolerances in the longitudinal dimensions can lead to significant stroke tolerances. Prior to now, these were reduced through calibration of an adjusting element. To that end, before assembly of the individual parts of the fuel injection device, each relevant assembly dimension had to be measured in terms of its influence on the stroke tolerance. Based on these measurement values, it was possible to set the correct stroke value by selecting from a group of adjusting elements. 
     With the stroke stop for the second part of the valve element now being integrated into the guide element, it is possible to dispense with such a procedure, thus simplifying the assembly. If, however, other requirements make it necessary for the stroke of the second part of the valve element to be adjustable, then this can occur by placing a stroke adjusting element between the second part of the valve element and the stroke stop in or on the guide element. 
     The manufacture of the fuel injection device is further simplified if the guide element includes a through opening, preferably with a flow throttle, which connects a pressure chamber in the region of the valve seat to a high-pressure chamber. 
     In order to assure an optimum seal of the coupling chamber and of the high-pressure chamber or a fluid conduit, the guide element can be clamped between two housing bodies of the fuel injection device; its contact surfaces with the housing bodies are embodied so that the centers of their surface areas are situated at least approximately on a center axis of a guide region of the guide element. 
     According to another proposal of the present invention, the sleeve is acted on by a spring that rests against a shoulder embodied on the first part of the valve element. This permits the implementation of a unit that can be preassembled and includes at least the first part of the valve element, the sleeve, the spring, and possibly the guide element. In addition to saving time in the final assembly of the fuel injection device, this also prevents damages to the high-precision guidance between the sleeve and the first part of the valve element during the final assembly. In addition, this eliminates the otherwise necessary captive interim storage of the sleeve during the installation and calibration process of the spring. An interim storage of this kind eliminates the danger of the sleeve becoming contaminated, damaged, or even lost. Furthermore, this simplifies the housing and consequently its manufacture since now, a smooth through bore without a step can be provided to accommodate the valve element in the housing. This also improves the high-pressure strength of the fuel injection device and its greater reservoir volume (chamber between the valve element and through bore in the housing) leads to a reduction in pressure oscillations. 
     An alternative to this lies in the fact that the sleeve is acted on by a first spring that rests against a shoulder embodied on the one side of an annular element, whose other side is acted on by a second spring that rests at least indirectly against the housing and is coupled by means of a coupling element to the valve element in its closing direction. 
     The guide element can have a centering section, preferably a centering collar, which centers the guide element in relation to a housing body. This also at least indirectly centers the valve element and other regions of the housing that are spaced apart from the coupler. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Particularly preferred exemplary embodiments of the present invention will be explained in greater detail below in conjunction with the accompanying drawings. 
         FIG. 1  is a schematic depiction of an internal combustion engine equipped with a fuel injection device; 
         FIG. 2  is a schematic, partially sectional depiction of a first embodiment of the fuel injection device from  FIG. 1 ; 
         FIG. 3  is a detailed depiction of a region of the fuel injection device from  FIG. 2 ; 
         FIG. 4  is a top view of a guide element of the fuel injection device from  FIG. 3 ; 
         FIG. 5  is a section along the line V-V from  FIG. 4 ; 
         FIG. 6  is a depiction similar to  FIG. 2  of a region of a second embodiment of a fuel injection device; 
         FIG. 7  is a depiction similar to  FIG. 2  of a region of a third embodiment of a fuel injection device; 
         FIG. 8  is a depiction similar to  FIG. 2  of a fourth embodiment; and 
         FIG. 9  is a depiction similar to  FIG. 2  of a fifth embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , an internal combustion engine is labeled as a whole with the reference numeral  10 . Its primary function is to drive a motor vehicle that is not shown. A high-pressure delivery device  12  feeds fuel from a fuel tank  14  to a fuel pressure accumulator  16  (“rail”). In this rail, the fuel—for example diesel or gasoline—is stored at a very high pressure. A plurality of fuel injection devices  18  that inject the fuel directly into combustion chambers  20  associated with them are each connected to the rail  16  by means of a respective high-pressure connection  17 . Each of the fuel injection devices  18  has a respective low-pressure connection  21  via which they are connected to a low-pressure region, in this case the fuel tank  14 . 
     The fuel injection devices  18  can be embodied in a first embodiment corresponding to  FIGS. 2 and 3 : the fuel injection device  18  in the present exemplary embodiment depicted therein has a housing  22  with a nozzle body  24 , a main body  26 , and an end body  28 . It is also possible for the main body  26  and end body  28  to be of one piece with each other. In the longitudinal direction of the housing  22 , there is a step-shaped recess  30  in which a needle-like valve element  32  is contained. This needle-like valve element  32  is composed of two parts, namely a control piston  34  and a nozzle needle  36 . 
     The nozzle needle  36  has pressure surfaces  38  that delimit a pressure chamber  40  and whose hydraulic resultant force is oriented in the opening direction of the nozzle needle  36 . At its lower end in  FIG. 2 , the nozzle needle  36  cooperates with a valve seat (unnumbered) on the housing in a manner that is not shown in detail in  FIG. 2 . It is thus possible to disconnect fuel outlet openings  42  from the pressure chamber  40  or to connect them to it. The nozzle needle  36  has a section  44  with a smaller diameter and a section  46  with a larger diameter. The nozzle needle  36  is guided in a longitudinally movable fashion in the nozzle body  24  by means of the section  46 . 
     The control piston  34  is accommodated in the main body  26 . An end region  48  at the top of the control piston  34  in  FIG. 2  is embodied as a guide, which is accommodated and guided in a sleeve-like extension of the end body  28 . A spring  50  rests against a shoulder formed on the control piston  34  by means of an annular collar  52  and acts on the control piston  34  in the closing direction. The axial end surface at the top of the control piston  34  in  FIG. 2  constitutes a hydraulic control surface  54  acting in the closing direction of the valve element  32 . Together with the end body  28 , it delimits a control chamber  56 . 
     An inlet throttle  58 , which is provided in the sleeve-like extension of the end body  28 , connects the control chamber  56  to an annular chamber  60 , which, in the present case, is situated between the sleeve-like extension of the end body  28  and the main body  26  and is in turn connected to the high-pressure connection  17 . The annular chamber  60  is formed by means of the stepped recess  30  that are let into the main body  26 . The control chamber  56  is also connected to a 2/2-way switching valve  66  by means of an outlet throttle  64 , which is provided in the end body  28 . Depending on its switching position, this valve either connects the outlet throttle  64  to the low-pressure connection  21  or disconnects the two. The annular chamber  60  is also connected to the pressure chamber  40  via at least one conduit  68 . 
     A guide element  70  is clamped between the nozzle body  24  and the main body  26 . Its precise design is shown in  FIGS. 4 and 5 : according to these figures, the guide element  70  includes a base plate  72  and a cylindrical projection  74  that is formed onto the plate and constitutes a guide collar that has a centering function. Concentric to the projection  74 , the guide element  70  is provided with a guide bore  76  that constitutes a guide region and, in the installed positioned depicted in  FIGS. 2 and 3 , cooperates with a guide in the end region  77  at the bottom of the control piston  34  in  FIGS. 2 and 3 . The top and bottom surfaces of the base plate  72  are embodied as high-pressure sealing surfaces  78 , which, in the installed position, provide a reliable seal of the housing  22 , in particular of the annular chamber  60  and the chambers situated inside the guide element  70 , in relation to the surroundings of the fuel injection device  18 . The achievement of a good sealing action also depends on the position of the center point of the surface area in relation to the center axis. This is achieved through a corresponding embodiment of the outer contour of the base plate  72  so that the center point of the surface area is situated at least approximately on a center axis (not shown) of the guide bore  76 . 
     The underside of the base plate  72  has a bore shoulder  80  let into it, which is concentric to the guide bore  76  and has a greater diameter than it. The diameter of the bore shoulder  80  is also greater than the diameter of the section  46  of the nozzle needle  36 . In this way, the bore shoulder  80  constitutes a stroke stop for the nozzle needle  36  in a manner that will be explained in greater detail below. The base plate  72  of the guide element  70  also has an eccentric through opening or through bore  82  let into it, which is part of the conduit  68  in the installed position. In some instances in which the fuel injection device  18  is used in the internal combustion engine  10 , it is necessary for the through opening  82  to include a flow throttle of the kind depicted in  FIG. 2 . 
     An end surface  85 , which is embodied on the projection  74  and constitutes a sealing surface, is machined very precisely at right angles to the axis of the guide bore  76 . In the installed position shown in  FIGS. 2 and 3 , a sleeve  88  rests with a sealing edge  86  against the sealing surface and is guided with a small amount of play on the control piston  34 . The sleeve is pushed against the guide element  70  by a spring  90 , which in turn rests against the main body  26 . The sleeve  88  constitutes part of a hydraulic coupler  92  that couples the first part of the valve element  32 , namely the control piston  34 , to the second part of the valve element  32 , namely the nozzle needle  36 . To this end, the hydraulic coupler  92  includes a hydraulic coupling chamber that has subchambers  94   a  and  94   b  and is situated between the sleeve  88 , the guide element  70 , the end region at the bottom of the control piston  34  in  FIGS. 2 and 3 , and the end region at the top of the nozzle needle  36  in  FIGS. 2 and 3 . The volume constituted by the guidance play between the guide bore  76  and the guide  77  on the control piston  34  is dimensioned so that the subchambers  94 a and  94 b of the coupling chamber  94  constitute a coherent control volume without any hydraulic influence. This volume thus constitutes a fluid passage from one side to the other of the guide element  70 . Alternatively or in addition, the fluid passage can also include at least one groove in the guide bore  76  and/or at least one flattened region on the guide piston  34 . 
     The fuel injection device  18  shown in  FIGS. 2 and 3  functions as follows: in the initial state when the switching valve  66  is without current, the control chamber  56  is disconnected from the low-pressure connection  21  and is connected via the inlet throttle  58  to the high-pressure connection  17  and therefore to the rail  16 . Consequently, the same pressure prevails in the control chamber  56  as in the annular chamber  60 . It also prevails in the pressure chamber  40  via the conduit  68 . Due to certain inevitable leakages through the guidance of the nozzle needle  36  in the nozzle body  24  and the guidance of the sleeve  88  on the control piston  34 , this pressure also prevails in the coupling chamber  94   a ,  94   b . On the whole, this configuration yields a force acting in the closing direction of the valve element  32 , which presses the valve element  32  against the valve seat in the region of the fuel outlet openings  42  and which is exerted on the control piston  34  by the compression spring  50 . Consequently, fuel cannot emerge from the fuel outlet openings  42 . 
     If electrical current is then supplied to the switching valve  66 , then the outlet throttle  64  is connected to the low-pressure connection  21 . As a result, the pressure in the control chamber  56  decreases. On the whole, this yields a force acting in the opening direction of the control piston  34 , which begins to move upward in  FIGS. 2 and 3  in opposition to the force of the spring  50 . As a result, the pressure in the coupling subchamber  94   a  is reduced by the volume increase. The resulting pressure and force difference between the pressure surfaces  38  and an end surface  96  of the nozzle needle  36  that delimits the coupling subchamber  94   a  causes the nozzle needle  36  to also move upward in  FIGS. 2 and 3 , i.e. it lifts away from its valve seat in the region of the fuel outlet openings  42 . Consequently, fuel can flow from the rail  16  through the high-pressure connection  17 , the annular chamber  60 , the conduit  68 , and the pressure chamber  40  and can be injected via the fuel outlet openings  42  into the combustion chamber  20 . 
     The guide element  70  holds the valve element  32  and the control piston  34  in position in relation to the sealing edge  86 . This prevents a misalignment of the sleeve  88  in relation to the sealing surface  85 . Such a misalignment would lead to leakage between the annular chamber  60  and the coupling chamber  94   a ,  94   b  and therefore to a malfunction of the fuel injection device  18 . The stroke of the nozzle needle  36  is limited by the stroke stop  80 . As shown in  FIGS. 2 through 5 , stroke of the nozzle needle  36  can be implemented by machining the bore shoulder  80  or by machining a shoulder on the end surface  96  of the nozzle needle  36 . In this case, the sealing surface  78  simultaneously constitutes the stroke stop for the end surface  96  of the nozzle needle  36  (see  FIG. 6 ). 
     The control piston  34  is conveyed farther in its stroke motion. For this reason, the free stroke of the control piston  34  must always be greater than the maximum stroke of the nozzle needle  36 . Because of the narrow guidance play between the sleeve  88  and the control piston  34  and because of the resulting slight leakage into the coupling chamber  94   a ,  94   b , however, the control piston  34  is sharply braked in its stroke motion so that it can execute only a slight additional movement. 
     In an alternative exemplary embodiment shown in  FIG. 7 , a stroke adjusting element  97  is situated between the end surface  96  and the stroke stop  80  and also makes it possible to adjust a desired stroke of the nozzle needle  36 . 
     In order to terminate an injection, the switching valve  66  is brought back into its closed position in which it shuts off the connection between the control chamber  56  and the low-pressure connection  21 . Due to the presence of the inlet throttle  58 , the pressure in the control chamber  56  continuously increases. As a result, the control piston  34  is moved in the closing direction again since the pressure in the coupling chamber  94   a ,  94   b  is initially less than the pressure in the control chamber  56 . As a result, the pressure in the coupling chamber  94   a ,  94   b  increases again due to the decrease in volume, causing a closing motion of the nozzle needle  36 . 
       FIG. 8  shows an alternative embodiment of a fuel injection device  18 . Not only here, but essentially in all of the figures, those elements and regions that have functions equivalent to those of previously described elements and regions are provided with the same reference numerals and are not explained again in detail. For the sake of simplicity, the drawings essentially include only those reference numerals that are required for explanation of the differences in relation to a preceding exemplary embodiment. 
     By contrast with the exemplary embodiment shown in  FIGS. 2 and 3 , the spring  90 , which pushes the sleeve  88  encompassing the coupling subchamber  94   b  against the guide element  70 , does not rest against the main body  26 , but rather against the annular collar  52  and the shoulder that the latter constitutes. The two springs  90  and  50  thus engage the same annular collar  52  of the control piston  34 . The force component of the spring  90  acting in the opening direction must therefore be taken into account in the embodiment of the spring  50 . A further difference in relation to the exemplary embodiment shown in  FIGS. 2 and 3  lies in the two-part embodiment of the end body  28 . This end body is split so that the outlet throttle  64  is situated in the remaining end body  28  and the inlet throttle  58  is situated in the sleeve  99 , which is now a separate component. The spring  50  in this case pushes the sleeve  99  with its sealing surface or sealing edge (unnumbered) against the end body  28 , thus producing a sufficient separation of the annular chamber  60  from the control chamber  56 . 
     The advantage of the fuel injection device  18  shown in  FIG. 8  over the one shown in  FIGS. 2 and 3  lies in the fact that the control piston  34  can form a preassembled unit with the sleeve  99 , the spring  50 , the spring  90 , and the sleeve  88  so that in the subsequent assembly of all the components of the fuel injection device  18 , it is no longer necessary to separate the sleeves  99  and  88  from the control piston  34 . In addition, the recess  30  in the main body  26  of the housing  22  can be embodied as a smooth through bore, which permits the establishment of a comparatively large annular chamber  60  and a comparatively large reservoir volume for the fuel. 
       FIG. 9  shows a similar variant: here, in lieu of an annular collar  52  in the control piston  34 , a circumferential groove  100  is provided, into which an annular coupling element  102  is inserted against which in turn an annular element  104  rests, but only in the closing direction of the valve element  32 . This annular element  104  is engaged by the spring  90  on the one side and by the spring  50  on the other. Here, too, the control piston  34 , the sleeve  99 , the spring  50 , the sleeve  88 , the spring  90 , the coupling element  102 , and the annular element  104  can form a preassembled unit that can be stored as such and in the final assembly, can be inserted into the recess  30  in the main body  26  of the housing  22 . 
     The foregoing relates to the 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.