Patent Document

CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation of copending International Application No. PCT/DE02/00400 filed Feb. 4, 2002 and claiming a priority date of Feb. 6, 2001, which designates the United States. 

   TECHNICAL FIELD OF THE INVENTION 
   The invention relates to a fuel injection nozzle for an internal combustion engine. 
   BACKGROUND OF THE INVENTION 
   A fuel injection nozzle of this kind used in injection systems for injecting fuel under high pressure into the combustion chamber of an internal combustion engine is known, for example, from EP-B-0 637 686. This injection nozzle has a nozzle body and a nozzle holder which are screwed together by means of a lock nut with interposed stop shim. Mounted in a guide bore of the nozzle body is an axially displaceable valve needle which seals injection ports disposed in a valve seat at the lower end of the guide bore in the idle state. The guide bore of the valve needle is additionally widened at one point to form a pressure chamber to which fuel is fed at high pressure via an inlet bore. In the region of the pressure chamber, the valve needle has a pressure shoulder to which the highly pressurized fuel can be applied. In a blind bore in the nozzle holder there is disposed a pressure pin loaded by helical compression springs. The pressure pin cooperates with the valve needle via a feed-through implemented in the stop shim and presses said valve needle onto the valve seat in the nozzle body with a preset holding force in the idle condition. However, if the fuel pressure exerted on the pressure shoulder of the valve needle exceeds this holding force in the pressure chamber of the nozzle body, the valve needle lifts from the valve seat and moves axially in the direction of the stop shim until the end face of the valve needle strikes the stop shim, thereby limiting the maximum lift of the valve needle and therefore the amount of fuel injected. For implementing travel limiting for the valve needle, the adjacent surfaces of the stop shim, the nozzle holder and the nozzle body are implemented precisely level in order to ensure reliable sealing to the outside against the fuel which is at a pressure of up to 1500 bar. However, such planicity of the adjacent surfaces is difficult to achieve. 
   WO 00/60233 discloses a fuel injection valve for a common rail fuel injection system having a plurality of injector modules which are disposed axially one above the other and are axially tensioned against each other with a union nut, the two touching end faces of two successive injector modules forming sealing surfaces. In order to reduce the amount of sealing surface to be machined and therefore the manufacturing costs, the end face of an injector module, for example of a stop element, is provided with a recess of low planicity, said recess being produced in the end face of the injector module by laser ablation or electron beam ablation. However, with the known methods, only one end face of the injector module can be processed at a time, which means that the production process is time-consuming and therefore expensive. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to provide a fuel injection nozzle wherein the sealing surfaces on a stop element can be manufactured quickly and precisely. 
   This object can be achieved by a method for producing a fuel injection nozzle for an internal combustion engine, comprising the steps of:
     providing a nozzle body in which a valve needle with a stop is displaceably disposed,   providing a nozzle holder in which a pressure pin is displaceably disposed, and   providing a disk-shaped stop element in a region between the nozzle body and the nozzle holder,   axially tensioning the nozzle body and the nozzle holder against one another in such a way that the stop element forms a first sealing surface which bears on a nozzle holder section, and a second sealing surface which bears on a nozzle body section, and   producing at least one cutout in the two sealing surfaces in a single manufacturing operation.   

   The object can also be achieved by a method for manufacturing a fuel injection nozzle for an internal combustion engine, comprising the steps of:
     disposing a valve needle with a stop displaceably within a nozzle body,   disposing a pressure pin displaceably within a nozzle holder,   providing a disk-shaped stop element in a region between the nozzle body and the nozzle holder,   axially tensioning the nozzle body and the nozzle holder against one another in such a way that the stop element forms a first sealing surface which bears on a nozzle holder section, and a second sealing surface which bears on a nozzle body section, and   producing at least one cutout in the two sealing surfaces in a single manufacturing operation.   

   The cutout can be punched, drilled and/or stamped. The cutout extends all the way through the stop element from the first to the second sealing surface. The method may further comprise the step of deepening the cutout by a predetermined axial depth in the first and the second sealing surface. The cutout may have a circular, oval or polygonal shape. The method may further comprise the step of providing the cutout in the edge region of the stop element. 
   Furthermore, the object can be achieved by a fuel injection nozzle for an internal combustion engine, comprising a nozzle body in which a valve needle with a stop is displaceably disposed, a nozzle holder in which a pressure pin is displaceably disposed, and a disk-shaped stop element which is provided in a region between the nozzle body and the nozzle holder, wherein the nozzle body and the nozzle holder being axially tensioned against one another in such a way that the stop element forms a first sealing surface which bears on a nozzle holder section, and a second sealing surface which bears on a nozzle body section, wherein the first and the second sealing surfaces each incorporate at least one cutout for the purpose of increasing the contact pressure of the sealing surfaces, and wherein the bilateral cutouts being implemented evenly opposite one another in the sealing surfaces. 
   The cutout may extend all the way through the stop element from the first to the second sealing surface. The cutout can be deepened by a predetermined axial depth in the first and the second sealing surface. The cutout may have a circular, oval or polygonal shape. The cutout can be provided in the edge region of the stop element. 
   Accordingly, a disk-shaped stop element disposed in a region between a nozzle body and a nozzle holder has sealing surfaces with at least one cutout on both sides. Through the provision of the cutouts, the surface areas of the two sealing surfaces on the end faces of the stop element are reduced, causing an increased contact pressure between, on the one hand, a nozzle holder section and the first sealing surface lying opposite thereto and, on the other, between a nozzle body section and the second sealing surface lying opposite thereto. Because of the smaller first and second sealing surface compared to an overall end face of the stop element, a high contact pressure and a high-pressure-tight connection is produced when the nozzle holder and the nozzle body are pretensioned against one another. This ensures, even with a high fuel pressure, a reliable seal between the nozzle holder section on the end face of the nozzle holder and the first sealing surface of the stop element as well as between the second sealing surface of the stop element and the nozzle body section on the end face of the nozzle body. 
   According to the invention, the cutouts in the first and second sealing surfaces are punched, drilled and/or stamped. This means that the process for producing the cutout is very quick and therefore inexpensive. Particularly in the case of punching, a cutout can be produced in the stop element with high precision and in any shape. With production of the cutout according to the invention by means of punching, drilling and/or stamping, it is possible to make the cutouts in both sealing surfaces simultaneously in a single operation, so that the production process for the sealing surfaces on the stop element is considerably simplified. 
   For low-cost production it has been found advantageous if the cutout runs all the way through the disk-shaped stop element from the first to the second sealing surface, the bilateral cutouts being easily manufacturable by punching or drilling of the stop element. In contrast to milling of the cutouts, punching allows greater geometrical scope for creating the sealing surfaces while at the same time reducing production costs. 
   According to another implementation of the invention it is preferred that the cutout is implemented in such as way that it is deepened by a predetermined amount in the first and the second sealing surface, the cutouts on the first and the second sealing surface being possibly provided by bilateral stamping, for example. Bilateral stamping in turn ensures machining of two sealing surfaces in a single operation. 
   To achieve an even contact pressure on the first and/or second sealing surface of the stop element, it has been found advantageous if the cutout has a circular, oval or polygonal shape. Contours of this kind can be quickly and precisely produced by means of punching, it being possible to selectively influence the contact pressure exerted by the sealing surfaces on the opposite nozzle holder section or nozzle body section by means of a predefined shaping of the cutout. 
   In certain applications it offers advantages if the cutout is provided bilaterally in the edge region of the sealing surfaces of the stop element. This increases the contact pressure in the inner region of the first and the second sealing surface. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be explained in greater detail with reference to the accompanying drawings: 
       FIG. 1  shows a longitudinal section through a first embodiment of the fuel injection nozzle according to the invention; 
       FIG. 2  shows a plan view of a stop element of a fuel injection nozzle in a second embodiment; 
       FIG. 3  shows a sectional view of the stop element from  FIG. 2  along the line III—III; 
       FIG. 4  shows a plan view of a stop element of a fuel injection nozzle in a third embodiment; 
       FIG. 5  shows a sectional view of the stop element from  FIG. 4  along the line V—V; 
       FIG. 6  shows a plan view of a stop element of a fuel injection nozzle in a fourth embodiment; and 
       FIG. 7  shows a sectional view of the stop element from  FIG. 6  along the line VII—VII. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows an essentially rotationally symmetrical fuel injection nozzle in a first embodiment wherein a nozzle body  2  is tensioned against a nozzle holder  6  by a union nut  4 . In a first guide bore  8  in the nozzle body  2  a valve needle  10  is displaceable mounted in the axial direction. At its front end, the valve needle  10  is provided with an essentially conical tip which cooperates with the valve seat in the nozzle body  2  which has a plurality of injection ports (not shown). In a central area the guide bore  8  is widened to form a pressure chamber  12  in which the valve needle  10  has a pressure shoulder  14 . The pressure chamber  12  is connected to a high-pressure inlet bore (not shown) implemented in the nozzle body  2  and via which fuel is fed under high pressure to the pressure chamber  12 . 
   The nozzle holder  6  has a second guide bore  9  whose longitudinal axis is in line with the longitudinal axis of the first guide bore  8  in the nozzle body  2 . There is additionally implemented in the walls of the nozzle holder  6  a high-pressure inlet bore (not shown) which is connected to the high-pressure inlet bore in the nozzle body  2  in order to feed in fuel. There is provided in the second guide bore  9  in the nozzle holder  6  a pressure pin  16  that can be displaced axially and which is in active connection with a drive (not shown) which applies a required holding pressure to the pressure pin  16 . This drive can be provided electromagnetically or piezoelectrically or even by means of a spring mechanism. 
   The pressure pin  16  acts on the valve needle  10  via an interposed transmission body  18 , the valve needle  10 , the pressure pin  16  and the transmission body  18  being disposed in axial alignment in order to achieve good power transmission. In the front area of the second guide bore  9  there is implemented a spring chamber  20  in which a spring force adjustment disk  21  is disposed. On the  21  spring force adjustment disk, a helical spring  22  is supported at one end. The other end of the helical spring  22  cooperates with an end face of the transmission body  18 , said helical spring  22  being designed in such a way that, in the unpressurized state when no fuel pressure is present in the pressure chamber of the nozzle body  2 , it presses the valve needle  10 , via the transmission body  18 , against the valve seat in the nozzle body  2 , thereby preventing fuel from being injected. 
   A disk-shaped stop element  26  is inserted between opposite end faces of the nozzle holder  6  and of the nozzle body  2 , said stop element  26  having a central feed-through  28  through which the transmission body  18  protrudes sectionally as the active connection between the pressure pin  16  and the valve needle  10 . The stop element  26  is of annular form and fastened via fixing bores  32  to the nozzle holder  6  on the one hand and to the nozzle body  2  on the other. The stop element  26  has a first, upper sealing surface  30  which bears on a nozzle holder section  23  on the end face of the nozzle holder  6 , and a second, lower sealing surface  31  which bears on a nozzle body section  24  on the end face of the nozzle body  2 . The nozzle holder section  23  and the nozzle body section  24  in each case form sealing surfaces which cooperate with the sealing surfaces  30 ,  31  on the end faces of the stop element  26 , the nozzle union nut  4  which engages a shoulder of the nozzle body  2  and presses the nozzle body  2  axially in the direction of the nozzle holder  6 , providing axial pretensioning of the nozzle holder  6 , of the stop element  26  and of the nozzle body  2  against one another, thereby producing a high contact pressure at their end faces. This means that the high-pressure inlet bores as well as the guide bores  8 ,  9  and the feed-through  28  are reliably sealed against each other and to the outside. 
   At its end opposite the transmission body  18 , the valve needle  10  has a stop  34 . In the idle position the valve needle  10  is seated on the valve seat because of the holding pressure acting via the pressure pin  16  on the transmission body  18  and the valve needle  10  and closes the injection ports so that no fuel is injected into the internal combustion engine. If the fuel pressure which is present in the pressure chamber  12  of the guide bore  8  and which acts on the pressure shoulder  14  on the valve needle  10  exceeds the holding pressure acting on the valve needle  10  via the pressure pin  16  and the transmission body  18 , the valve needle  10  lifts from the valve seat and moves axially against the pressure pin  16  and the transmission body  18  until the stop  34  of the valve needle  10  strikes the stop element  26 , thereby limiting the maximum travel of the valve needle  10 . This maximum travel essentially determines the amount of fuel injected via the injection ports. The stop element  26  disposed between the end face  23  of the nozzle holder  6  and the end face  24  of the nozzle body  2  provides a simple means of meeting the required tolerances for the maximum travel. The stop element  26  can be manufactured as a simple turned part, e.g. made of hardened steel, the bilateral end faces of the stop element  26  being implemented as sealing surfaces  30 ,  31  having at least one cutout (not shown in  FIG. 1 ). By means of the cutouts, a surface area of the sealing surfaces  30 ,  31  is reduced and the sealing effect is increased. 
     FIG. 2  shows a plan view of a stop element  26  of a fuel injection nozzle.  FIG. 2  provides a top view of the upper, first sealing surface  30  of the stop element  26 . The stop element  26  has at its center the feed-through  28  for the transmission body (not shown in  FIG. 2 ) which protrudes through the feed-through  28  in the installed condition. Additionally provided in this disk-shaped stop element  26  are two oval cutouts  36  disposed mirror-symmetrically on the sealing surface  30 . In addition, a third kidney-shaped cutout  36  is implemented in the sealing surface  30 . To attach the stop element  26  to the end faces of the nozzle holder  6  and of the nozzle body  2 , two fixing bores  32  are distributed over the sealing surface  30 . A fuel inlet bore  33  is additionally provided in the stop element  26 . 
   In  FIG. 3  shows a sectional view of the stop element  26  shown in  FIG. 2  along the line III—III. As can be seen from  FIG. 3 , the cutouts  36  in the first sealing surface  30  extend all the way through the thickness of the stop element  26  from the first sealing surface  30  to the second sealing surface  31 . This extending of the cutouts  36  all the way through can be achieved quickly in a simple and precise manner by punching them out from the material of the stop element  26 . Between the cutouts implemented as punchings there is provided a web  38  which provides a stop surface for the stop  34  of the valve needle  10 . 
     FIG. 4  illustrates a stop element  26  of a fuel injection nozzle according to a third embodiment. As can be seen from the plan view of the first sealing surface  30  of the stop element  26 , in this case an individual cutout  36  is implemented on the sealing surface  30 . The cutout  36  has a polygonal shape which is implemented evenly over the sealing surface  30  and is mirror-symmetrical about the two central axes of the essentially circular stop element  26 . Two fixing bores  32  and a fuel inlet bore  33  are provided in the edge region of the stop element  26 . 
     FIG. 5  shows a sectional view of the stop element  26  along the line V—V according to  FIG. 4 , the cutout  36  being provided in the stop element  26  both on the upper, first sealing surface  30  and on the lower, second sealing surface  31 . In the center of the stop element  26  is the feed-through  28  for the transmission body. The cutout  36  has a predetermined axial depth h of at least 0.02 mm in each sealing surface  30 ,  31 . Each cutout  36  therefore incorporates non-bearing and therefore non-sealing surface regions  40  which are made deeper compared to the sealing surfaces  30 ,  31  so that an axial height difference exists between each sealing surface  30 ,  31  and the surface region  40  of the cutout  36 . 
     FIG. 6  shows a plan view of another embodiment of the stop element  26  wherein the four cutouts  36  are formed in the edge region of the sealing surface  30 . The cutouts  36  are in this case semicircular and disposed mirror-symmetrically about both central axes of the disk-shaped stop element  26 , the shape of the cutouts  36  according to  FIGS. 4 to 6  being produced, for example, by bilateral stamping of the stop element  26 . 
     FIG. 7  shows a sectional view of the stop element  26  along the line VII—VII according to  FIG. 6 , the feed-through  28  extending from the first sealing surface  30  all the way through the stop element  26  to the second sealing surface  31 . The sealing surfaces  30 ,  31  are raised compared to the surface regions  40  of the cutouts  36 .

Technology Category: f