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. 1a) 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. 1b). Enlarging tool 11 is then removed from fuel injector 10 (FIG. 1c). 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. 1c). 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. 1d). 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.
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 sealing the combustion chamber of an internal combustion engine, the tip of fuel injector 20 protruding into 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. 2a) 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. 2d) 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. 2a, 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. 1b). After removal of enlarging tool 25 (FIG. 1c), 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. 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. 2d 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. 2e), 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.
Patent Application
20120216781
