Abstract:
A threaded pipe coupling is disclosed which comprises a connection stub, a pipe, and a union nut, and in which any leakage quantities that occur can be carried away through the union nut.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based on German Patent Application 10 2004 059 909.2 filed Dec. 13, 2004, upon which priority is claimed. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is directed to an improved threaded pipe coupling, comprising a connection stub, a pipe with a nipple, and a union nut. 
   2. Description of the Prior Art 
   Threaded pipe couplings have long been known in the prior art, and are used for instance in the high-pressure region of fuel injection systems for internal combustion engines. A threaded coupling of this kind may for instance be provided on both ends of a high-pressure line that is mounted between a common rail and an injector. 
   In some internal combustion engines, the problem arises that the injectors are located entirely inside the cylinder head cap of the engine. This means that only the high-pressure line is passed through the cylinder head cap. As a consequence, any leakages that occur at the threaded pipe coupling between the high-pressure line and the injector dilute and thin the motor oil which can cause engine damage. In rare cases, but these cannot be precluded, it is even possible for the leakages to get into the intake tube via the venting of the valve drive and thus can get into the combustion chambers of the engine. This can lead to dangerous situations. 
   OBJECT AND SUMMARY OF THE INVENTION 
   In the threaded pipe coupling of the invention, comprising a union nut, a pipe, and a connection stub, the danger mentioned above is precluded by providing that the leakage quantities that occur in the event of a leaking threaded pipe coupling cannot reach the motor oil of the engine but instead are diverted outside, that is, through the cylinder head cap of the engine. Outside, they can be collected and carried away, thus precluding thinning of the motor oil. 
   These advantages are attained according to the invention by a union nut for a threaded pipe coupling, having a graduated inner bore, in which a shoulder is embodied between the first portion and a second portion of the inner bore, and in which the first portion has a greater diameter than the second portion, by providing that at least one indentation is embodied on the shoulder; and that the at least one indentation extends from the first portion to the second portion. This indentation makes it possible for leakage that occurs between a nipple of the high-pressure line and the sealing face in the connection stub to be diverted through the shoulder out of the union nut. The indentation has no adverse effects on the contact pressure exerted on the nipple by the union nut. If the union nut is made long enough that one end of it protrudes through the cylinder head cap of the engine, it is then assured that the leakage cannot reach the motor oil of the engine but instead will be diverted to the outside. 
   Advantageous features of the union nut of the invention provide that the first portion has a female thread, so that the union nut can be screwed to a connection stub. 
   To assure that the leakage cannot get through the thread to reach the portion of the cylinder head that is wetted by motor oil, means are further provided according to the invention for sealing off the female thread. These means may alternatively or cumulatively be a groove in the inner bore for receiving a sealing ring, in particular a PTFE ring or an O-ring. However, it is also possible to coat the female thread with a sealing medium which is activated when the union nut is screwed together with the connection stub. 
   The advantages according to the invention can also be attained in a pipe having a nipple, that nipple having a sealing face and a bearing face, by providing that at least one indentation is embodied in the bearing face; and that the at least one indentation extends from an inside diameter to an outside diameter of the bearing face. In this embodiment of the threaded pipe coupling of the invention as well, it can be assured by the indentation in the bearing face that any leakages that occur can be carried through the threaded pipe coupling and diverted out of the cylinder head cap. 
   In pipes according to the invention, the sealing faces may be embodied as hemispherical, frustoconical, or flat. Correspondingly, it is possible to embody the bearing face as flat, hemispherical or frustoconical. However, the pipe of the invention is not limited to sealing faces and bearing faces of the aforementioned types. 
   The advantages of the invention can be attained in a connection stub for a threaded pipe coupling having an inner bore, having a sealing seat, and having a male thread, by providing that on the connection stub, there are means for sealing off the connection stub from a union nut. These means may be embodied as an annular groove, which serves to receive a sealing ring. The annular groove may be located in the region of the male thread or in a region adjoining it. Among others, PTFE rings or O-rings can be considered for the sealing rings. It is furthermore possible to coat the male thread with a sealing medium. 
   If the connection stub of the invention is embodied as an internally threaded stub, or in other words if the connection stub has an internal thread on its end opposite the male thread, then according to the invention it is further provided that a first biting edge is embodied concentrically with the inner bore, and outside the first biting edge there is a leakage bore, and that means are provided which seal off the leakage bores from the outside. These means may for instance be a sealing ring and/or a second biting edge. It is recommended that both the sealing ring and the second biting edge be made concentric with the inner bore, since as a result the production costs can be minimized, and the sealing action can be assured equally well over the entire circumference of the end face of the connection stub. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments, taken in conjunction with the drawings, in which: 
       FIG. 1  is a schematic illustration of an injector with a connection, in a side view and in section taken along the line A-A; and 
       FIGS. 2 through 4  show further exemplary embodiments. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a side view of an injector  1  is shown. On one end of the injector  1 , there are electrical terminals  3 . The other end of the injector  1  is screwed into the cylinder head (not shown) of an internal combustion engine in such a way that the tip  5  of the injector protrudes into the combustion chamber of the engine. 
   In some mass-produced internal combustion engines, the entire injector  1  is located below a cylinder head cap, not shown. This means that the entire injector  1  is bathed by motor oil of the engine. 
   A connection stub  7 , which has a male thread  9 , is embodied approximately in the middle of the injector  1 . With the aid of a union nut, not shown in  FIG. 1 , a pipe (also not shown) is screwed onto this connection stub  7 . During engine operation, the fuel located in the pipe is at a very high pressure of up to 1800 bar. If the threaded coupling of the pipe to the connection stub  7  should leak, then unless other provisions are made, fuel would get into the motor oil that surrounds the injector  1 . The resultant thinning of the motor oil adversely affects its lubricating properties and causes considerable damage to the engine. With the aid of a threaded pipe coupling according to the invention, which will be described in detail below in terms of the exemplary embodiments in conjunction with  FIGS. 2 ,  3  and  4 , the thinning of the motor oil from leakages from the threaded pipe coupling is reliably avoided. 
   In  FIG. 2 , a first exemplary embodiment of a threaded pipe coupling of the invention, comprising the connection stub  7 , a pipe  11 , and a union nut  13 , is shown in section. As can be seen from  FIG. 2 , the connection stub  7  has an inner bore  15 , which discharges into a frustoconical sealing seat  17 . 
   On its end toward the connection stub  7 , the pipe  11  has a nipple  19 . A sealing face  21  oriented toward the sealing seat  17  is embodied on the nipple  19 . 
   On the end of the nipple  19  opposite from the sealing face  21 , a bearing face  23  is embodied. A shoulder  25  of the union nut  13  presses against this bearing face  23  when the union nut  13  is screwed onto the male thread  9  of the connection stub  7 . As a result, the sealing face  21  of the nipple  19  is pressed against the sealing seat  17  of the connection stub  7  to produce a high-pressure-proof threaded coupling between the pipe  11  and the connection stub  7 . 
   The union nut  13  has a graduated inner bore  27   a  and  27   b . The shoulder  25  of the union nut  13  is embodied at the transition between the first portion  27   a  and the second portion  27   b  of the inner bore  27 . In the region of the first portion  27   a , there is a female thread  29 . 
   If a threaded pipe coupling of the prior art were to leak, fuel can pass through the threaded coupling between the female thread  29  and the male thread  9  to reach the motor oil that surrounds the injector and hence also the connection stub  7 . According to the invention, it can be provided that one or more indentations  35  are made in the shoulder  25  of the union nut, so that the leakage if it occurs can pass from the first portion  27   a  to the second portion  27   b  of the union nut  13 . If the portion  27   b  of the union nut  13  is made long enough that it protrudes out of a cylinder head cap (not shown), it is thus assured that the leakage in the annular gap between the inner bore  27   b  and the pipe  11  were passed to the outside, out of the regions of the engine that are lubricated by motor oil. 
   At the same time, it must also be assured that no fuel can get into the motor oil through the threaded coupling comprising the female thread  29  and the male thread  9 . This can be accomplished for instance by means of a suitable coating of a sealing medium applied onto the female thread  29  and/or of the male thread  9 . It is furthermore possible to provide an annular groove  31  into the connection stub  7 , which groove serves to receive a sealing ring  33 . The sealing ring  33  may be made for instance from PTFE (Teflon®) or an elastomer. Various cross-sectional shapes, such as square or round cross sections, may also be employed. It is also understood that it is unnecessary to form the annular groove  31  into the connection stub in the region of the male thread  9 . Alternatively, it is possible to form the annular groove  31  into the end of the male thread  9 , for example, so that it simultaneously takes on the function of a relief groove for the male thread  9 . 
   To improve the sealing action of the sealing ring  33 , it may also be provided that in the region of the sealing ring  33 , the union nut has a smooth cylindrical surface instead of a female thread  29 . Which of the variants mentioned will be preferred in an individual case is a structural provision that can be made by one skilled in the art as needed and with awareness of the other peripheral conditions. 
   For clarification of what has been said, a section taken along the line B-B is shown below  FIG. 2 . 
   In  FIG. 3 , a further exemplary embodiment of a threaded pipe coupling of the invention is shown. Identical components are identified by the same reference numerals, and what has been said in conjunction with  FIG. 2  applies accordingly. 
   The essential distinctions pertain to the sealing ring  33  and the nipple  19 . In the exemplary embodiment of  FIG. 3 , the sealing ring  33  is embodied as an O-ring. In contrast to the exemplary embodiment of  FIG. 2 , in the exemplary embodiment of  FIG. 3  the indentations  35  are made not in the union nut  13  but in the nipple  19  of the pipe  11 . The effect, namely that the leakage can pass from the first portion  27   a  through the indentations  35  into the portion  27   b  of the union nut  13 , is the same. 
   In the lower part of  FIG. 3 , a view is shown along the line B-B from above onto a pipe  11  of the invention, in which the indentations  35  are embodied in the nipple  19 . 
   In  FIG. 4 , an exemplary embodiment of a connection stub  7  of the invention is shown, in which an external thread  37  is provided on the end of the connection stub  7  opposite from the male thread  9 . The male thread  9  serves to screw on a union nut  13 , as has been explained in conjunction with the exemplary embodiments of  FIGS. 2 and 3 . In the exemplary embodiment of  FIG. 4 , the connection stub  7  is screwed into a component  39  with the aid of internal thread  38  in the component, which is shown engaged with the external thread  37  on the connection stub  7 . The component  39  may for instance be a cylinder head of an internal combustion engine. The component  39  has a through bore  41 , which is located in the extension of the inner bore  15  of the connection stub  7 . 
   So that no fuel can emerge from the end face  43  of the connection stub  7 , a first biting edge  45  is provided on the end face  43 . The first biting edge  45  is located concentrically with the inner bore and the through bore  41 . If the first biting edge  45  leaks during engine operation, the leakage could flow past the first biting edge  45  to reach the environment. To prevent this, a leakage bore  47  is made in the connection stub  7  of the invention; it discharges into the end face  43  of the connection stub  7 , outside the first biting edge  45 . To assure that the leakage will be carried away through the leakage bore  47 , a second biting edge  49  can for instance be provided, which is located concentrically with the first biting edge  45  and which surrounds the leakage bore  47 . This exemplary embodiment is shown on the right-hand side of  FIG. 4 . 
   Alternatively, it is also possible to place a sealing ring  51  in the step in the component  39 . This variant is shown on the left-hand side of  FIG. 4 . In both variants, it is possible for the leakage that occurs to be carried out of a housing cap  55  through the leakage bore  47 . Between the connection stub  7  and the housing cap  55 , a sealing ring  51  is provided. This sealing ring prevents motor oil, located for instance between the housing cap  55  and the component  39 , from being able to get into the environment. 
   The foregoing relates to preferred exemplary embodiments 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.