Patent Publication Number: US-9840996-B2

Title: Method for installing a sealing ring

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for installing a sealing ring on an injector, in particular a fuel injector for an internal combustion engine. 
     BACKGROUND INFORMATION 
     Fuel injectors which meter fuel under high pressure depending on the driving condition of the vehicle and inject the fuel in a fine spray directly into the combustion chamber of the internal combustion engine are used for direct injection in internal combustion engines designed as gasoline engines. Such a fuel injector is described in German Patent No. DE 199 46 602 A1, for example. Such a fuel injector is inserted into a bore of a cylinder head of the internal combustion engine that seals a combustion chamber in such a way that the injector tip provided with injection openings protrudes into the combustion chamber and the sealing ring situated on the fuel injector creates a combustion chamber seal between the fuel injector and the bore wall of the cylinder head bore. The sealing ring typically having a rectangular cross section is made of a less elastic plastic, e.g., polytetrafluoroethylene (PTFE). The sealing ring is inserted into a ring groove present in the fuel injector prior to installation of the fuel injector in the cylinder head. Since the inner diameter of the seal adapted to the diameter of the groove base of the ring groove is smaller than the diameter of the ring groove on the groove edge, an enlarging tool  11 —as schematically shown in  FIG. 1 —is placed on the tip of the fuel injector ( FIG. 1 a   ) and sealing ring  12  is pushed via enlarging tool  11  onto the fuel injector, whereby sealing ring  12  is enlarged and may thus be displaced on fuel injector  10  into ring groove  13  ( FIG. 1 b   ). Enlarging tool  11  is then removed from fuel injector  10  ( FIG. 1 c   ). Due to the low elasticity of the material of sealing ring  12 , sealing ring  12  initially remains enlarged and is not fully pressed into ring groove  13  ( FIG. 1 c   ). Therefore, sealing ring  12  is reshaped with the aid of a so-called calibration tool  14  to its final outer diameter, its predefined sealing dimension. Calibration tool  14  is placed on the tip of fuel injector  10  and is pushed over sealing ring  12  for this purpose ( FIG. 1 d   ). To reshape sealing ring  12 , calibration tool  14  has a hollow cone  15  which tapers against the slide-on direction with respect to the inner diameter, the smallest inner diameter on the side of hollow cone  15  facing away from fuel injector  10  being adapted to the desired sealing dimension of sealing ring  12 . During slide-on of calibration tool  14 , hollow cone  15  increasingly deforms sealing ring  12  until the desired outer diameter, the so-called sealing dimension, is achieved and simultaneously presses sealing ring  12  into ring groove  13 . During this calibration of sealing ring  12 , it is naturally pressed against the flank of ring groove  13  facing away from the combustion chamber. To prevent very high press-in forces and shearing off of sealing ring  12  during the installation of fuel injector  10  in the cylinder head, ring groove  13  filled by sealing ring  12  must not be overfilled by sealing ring  12 . Sealing ring  12  is therefore dimensioned in such a way that a residual ring gap  16  remains in ring groove  12  after reshaping. Since, as already mentioned, sealing ring  12  is pressed during the calibration process onto the flank of ring groove  13  facing away from the combustion chamber, this residual ring gap  16  is formed at the groove flank facing the combustion chamber. This residual ring gap  16  is filled by combustion residues during operation of the internal combustion engine, thus additionally protecting sealing ring  12  from the high thermal load of the exhaust gases in the combustion chamber. 
     When using fuels containing ethanol and preferably in the case of central installation of the fuel injector in the cylinder head, these combustion residues are lacking and hot particles become caught in the residual air gap. The hot particles may burn through the sealing ring, resulting in a leaky combustion chamber seal and consequent failure of the fuel injector. 
     SUMMARY 
     An example method of the present invention for installing the sealing ring may have the advantage that the reshaping process of the sealing ring caused by removal, not application, of the calibration tool results in shifting of the residual ring gap remaining in the ring groove toward the groove flank facing away from the combustion chamber. The sealing ring is supported by the groove flank of the ring groove facing the combustion chamber and retains this position even during installation in the cylinder head. As a result, hot particles are not able to become caught in front of the sealing ring and do not cause thermal damage to the sealing ring. 
     According to an advantageous specific embodiment of the present invention, the sealing ring is reshaped by a hollow cone which is formed in the calibration tool and tapers against the removal direction of the calibration tool from the fuel injector with respect to the inner cone diameter and whose smallest inner diameter is adapted to the predefined sealing dimension of the sealing ring. The calibration tool is placed on the fuel injector behind the sealing ring situated in the ring groove, is closed, and removed over the sealing ring from the fuel injector, thus pressing the sealing ring into the ring groove and reshaping it to its sealing dimension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is explained in greater detail on the basis of an exemplary embodiment in the following description illustrated in  FIG. 2 . 
         FIG. 1  shows an illustration of the conventional installation method for a sealing ring to be installed on a fuel injector in four individual method steps a through d. 
         FIG. 2  shows an illustration of an example of the installation method of the present invention for installing the sealing ring on a fuel injector in five individual method steps a through e, followed by installation of the injector in a cylinder head in a step f. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Fuel injector  20  for an internal combustion engine of a motor vehicle shown in a sectional side view in  FIG. 2  as an example of an injector is used for example for metered injection of finely sprayed fuel into the combustion chamber of an internal combustion engine and is inserted for this purpose into a cylinder head  300  sealing the combustion chamber of an internal combustion engine, the tip of fuel injector  20  protruding into the cylinder head  300  of the combustion chamber. Fuel injector  20  has a valve housing  21  and a valve seat support  22  protruding axially therefrom and having a smaller outer diameter than valve housing  21 . Valve seat support  22  is sealed in a conventional manner at an end facing away from valve housing  21  by a valve seat body not shown here on which a valve seat surrounding a valve opening is formed and to which a spray hole disk is attached downstream from the valve opening. A ring groove  23  is inserted from the outside into valve seat support  22  at an axial distance from the free end of valve seat support  22 . Ring groove  23  has two groove flanks  231  and  232  and a groove base  233  and a groove edge whose diameter is greater than the groove base diameter. A raised, circumferential bead  30  is molded as one piece, preferably in the center of groove base  233 , the outer diameter of the bead being slightly greater than the groove base diameter and its axial width being significantly smaller than the groove width. A sealing ring  24 , which seals fuel injector  20  with respect to a bore wall of a cylinder bore accommodating fuel injector  20  after installation of fuel injector  20  in the cylinder head of the internal combustion chamber, is inserted into ring groove  23 . Sealing ring  24  is made of a plastic, e.g., polytetrafluoroethylene (PTFE), which is not sufficiently elastic to be able to simply slide sealing ring  24  onto valve seat support  22  and then snap it into ring groove  23 . To allow for this, sealing ring  24  is enlarged via an enlarging tool  25  ( FIG. 2 a   ) and is inserted into ring groove  23 , and enlarged sealing ring  24  accommodated in ring groove  23  is reshaped with the aid of a calibration tool  26  ( FIG. 2 d   ) to a predefined sealing dimension that is smaller than the outer dimension of enlarged sealing ring  24 . Calibration tool  26  is placed for this purpose on fuel injector  20  and the reshaping process of sealing ring  24  is carried out during removal of calibration tool  26  from fuel injector  20 . This installation method is illustrated in five method steps in  FIG. 2 : 
     Enlarging tool  25  is initially placed on the tip of fuel injector  20 , more precisely on the front side of valve seat support  22 . Enlarging tool  25  has a cylinder section  251  having an outer diameter that is slightly greater than the outer diameter of valve seat support  22  and having a cone section  252  that is adjacent thereto and has an outer diameter that decreases toward the free end. As shown in  FIG. 2 a   , enlarging tool  25  is put on the free end of valve seat support  22  in such a way that cylinder section  251  of enlarging tool  25  is put on valve seat support  22  almost up to groove flank  231 . Sealing ring  24  is then pushed onto cone section  252  of enlarging tool  25  and is then pushed with a force F over cylinder section  251  of enlarging tool  25  into ring groove  23 . When being pushed over cone section  252 , sealing ring  24  is enlarged to the outer diameter of cylinder section  251  and generally retains this enlargement after being placed in ring groove  23  ( FIG. 1 b   ). After removal of enlarging tool  25  ( FIG. 1 c   ), calibration tool  26  is put on valve seat support  22  in the region between valve housing  21  and enlarged sealing ring  24  sitting in ring groove  23 . Calibration tool  26  is designed in two pieces for this purpose. For example,  FIG. 2 d    and  FIG. 2 e    show one of the parts of calibration tool  26  that can be put onto valve seat support  22  with another such part. Alternatively, calibration tool  26  may be in one piece and is then put on valve seat support  22  prior to the application of enlarging tool  25 . For reshaping sealing ring  24 , calibration tool  26  has a hollow cone  27 , which tapers against the removal direction of calibration tool  26  indicated in  FIG. 2 d    by arrow  29  from fuel injector  20 , i.e., its inner cone diameter decreases. If closed calibration tool  26  is removed from fuel injector  20 , hollow cone  27  shapes sealing ring  24  to the desired sealing dimension, which is determined by the smallest inner diameter of hollow cone  27 , and simultaneously presses sealing ring  24  into ring groove  23  ( FIG. 2 e   ), bead  30  being pressed at groove base  233  into sealing ring  24 . To prevent a ring groove  23  from being overfilled by sealing ring  24  during the reshaping process, sealing ring  24  is dimensioned in such a way that a residual ring gap  28  remains in ring groove  23  under all conditions of the reshaping process. Since sealing ring  24  is pressed against groove flank  231  of ring groove  23  facing away from housing  21  during the reshaping process which takes place during the removal of calibration tool  26 , this residual ring gap  28  is formed on groove flank  232  facing housing  21 . When installing fuel injector  20  in the cylinder head of the internal combustion engine, sealing ring  24  remains in this position since bead  30  reliably prevents possible pushing back of sealing ring  24  by frictional forces acting on the sealing ring. As a result, there is no ring gap between sealing ring  24  and the combustion chamber, so that hot particles do not become caught in front of sealing ring  24  and are not able to thermally damage sealing ring  24 .