Abstract:
The invention relates to a plug-in connector ( 1 ) for medium conduits comprising a plug-in part ( 4 ) sealingly introducible by means of a plug shank ( 6 ) into the receiving opening ( 16 ) of a connector counterpart ( 2 ) which is sealingly closable by means of latching means ( 18 ) for preventing the pull out thereof. For this purpose, a locking element ( 34 ) is movably connected to the plug-in part ( 4 ) in such a way that it locks the latching means ( 18 ) in a safety unscrewing-preventing position and releases in the unscrewing position for carrying out an unscrewing movement for freeing from locking.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT international patent application number PCT/EP2006/065603, filed Aug. 23, 2006 and DE patent application 20 2005 015 966.2, filed Oct. 10, 2005. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a plug-in connector for media conduits (pipelines or hose lines for hydraulic or pneumatic flow media), in particular for fuel lines, according to the preamble of claim  1 . 
       BACKGROUND OF THE INVENTION 
       [0003]    DE 298 24 260 U1 and the corresponding EP 0 999 398 B1 describes such a plug-in connector of the generic type in which the plug-in part has, as latching means, two latching arms which are formed integrally in one piece. The latching arms extend on diametrically opposite sides of the plug-in part with their free radially elastically moveable ends, in each case approximately parallel to the plugging axis in the direction opposed to the plug-in direction, i.e. in the release direction. When plugging in occurs, the latching arms engage with radial latching shoulders in corresponding latching contours within the receiving opening of the connector counterpart, an end activation section projecting outward from the receiving opening in each case so that the latching arms can be moved radially inward manually in order to release the latched connection. In this context, there is a description of a protective cap which can be plugged over the plug-in region from the outside in order to provide a seal against dirt. In addition, the protective cap also prevents undesired release of the plug-in part because, before the release activation of the latching arms, the protective cap firstly has to be removed because otherwise the latching arms or their activation sections are not accessible. This known embodiment requires a relatively large amount of installation space, and the protective cap is, as a separate part, subject to a considerable risk of being lost. 
         [0004]    U.S. Pat. No. 5,988,706 A describes a pipe which can be plugged with one end into a receiving part. In order to secure the pipe, it has an upset radial annular bead against which a securing element, seated on the pipe and composed of sheet metal, acts. This securing element is composed of an annular part which surrounds the pipe and two spring elastic latching arms which are located diametrically opposite one another and engage behind a step within the receiving part. In order to secure against release, a further hollow cylindrical ring is additionally arranged in a displaceable fashion on the pipe. This ring can be pushed axially into the region of the securing element. 
         [0005]    A very similar design is described in U.S. Pat. No. 5,806,898 A, in which case a profiled ring body is provided for securing purposes. 
         [0006]    DE 37 10 853 A1 describes a plug-in connection for a pipe. In this context, a receiving part has a cylindrical annular space into which the pipe and a securing sleeve which surrounds it and is made of plastic can be introduced. 
         [0007]    Finally, US 2003/0132631 A1 describes a further pipe connection with a sleeve-shaped securing element and a cap-like securing element composed of an elastic material. This securing element is specifically embodied in such a way that it can be fitted onto an angular region of the pipe. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is based on the object of providing a plug-in connector of the type mentioned at the beginning, which plug-in connector is distinguished by a particularly compact design, good handling with a low space requirement for manual release activation and by easy manufacture and assembly. 
         [0009]    According to the invention, this is achieved by means of the features of claim  1 . Advantageous embodiments are the subject matter of the dependent claims and of the following description. 
         [0010]    Accordingly, a locking element is captively and moveably connected to the plug-in part in such a way that in a secured position it blocks the latching means to prevent release, and in a release position it releases said latching means for a release movement which cancels the locked arrangement. The locking element expediently surrounds the plug-in part or its plug shank in certain areas, and can move radially between the plug shank and the latching arms or their activation sections in certain areas. In this secured position, the latching arms are blocked preventing a release movement which is directed radially inward. The plug-in connector according to the invention has a very compact shape due to its embodiment, in particular due to the arrangement and operative connection of the locking element to the plug-in part, and it ensures a high level of securing against undesired release accompanied by good handling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention will now be explained in more detail in a number of preferred variants of the locking element by means of a plurality of exemplary embodiments which are illustrated in the drawing, in which: 
           [0012]      FIG. 1  is a perspective view of a first embodiment of a plug-in connector according to the invention with a locking element in a secured position, 
           [0013]      FIG. 2  is an exploded view with a locking element illustrated at a distance, 
           [0014]      FIG. 3  is a side view of the connector without a locking element, 
           [0015]      FIG. 4  is a side view in the direction IV of the arrow as per  FIG. 3 , 
           [0016]      FIGS. 5 &amp; 6  are views, analogous to  FIGS. 3 and 4 , of the entire plug-in connector according to  FIG. 1  connected to the locking element, 
           [0017]      FIG. 7  is a three-view representation of the locking element of the first embodiment according to  FIGS. 1 to 6 , 
           [0018]      FIG. 8  comprises two views, analogous to  FIGS. 5 and 6 , in an embodiment variant and with additional representation, cut in half, of a connector counterpart, 
           [0019]      FIGS. 9 to 13  show representations of a second embodiment of the plug-in connector according to the invention, analogous to  FIGS. 1 to 7 , 
           [0020]      FIGS. 14 to 18  show further representations of a third embodiment, analogous to  FIGS. 9 to 13 , 
           [0021]      FIGS. 19 to 23  show a fourth embodiment in representations analogous to  FIGS. 14 to 18 , 
           [0022]      FIGS. 24 to 28  show further analogous representations of a fifth embodiment which is modified slightly compared to  FIGS. 19 to 23 , 
           [0023]      FIGS. 29 to 36  show representations of a further, preferred embodiment of the invention, specifically: 
           [0024]      FIG. 29  is a side view of the plug-in part in the secured position of the locking element, 
           [0025]      FIG. 30  is an enlarged cross section in the sectional plane XXX-XXX according to  FIG. 29 , 
           [0026]      FIG. 31  is a separate, highly enlarged perspective view of the locking element, 
           [0027]      FIG. 32  is a perspective view of the plug-in part according to  FIG. 29 , but in the release position of the locking element, 
           [0028]      FIG. 33  is a further perspective view of the side located diametrically opposite the view according to  FIG. 32 , but in the secured position according to  FIG. 29 , 
           [0029]      FIG. 34  is a side view of the plug-in part as in  FIG. 29 , but in a state in which it is plugged into a connector counterpart and in the release position of the locking element, 
           [0030]      FIG. 35  shows an enlarged partial view from  FIG. 34  with a connector counterpart in an axial section, and 
           [0031]      FIG. 36  shows a detail from  FIG. 35  in the secured position of the locking element. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    In the various figures of the drawing, identical parts are always provided with the same reference symbols. 
         [0033]    A plug-in connector  1  according to the invention is used to connect at least one media conduit (not illustrated) to a connector counterpart  2  in a rapid and releasable, pluggable and latchable fashion (see  FIGS. 8 ,  14 ,  17 ,  34  and  35 ). The plug-in connector  1  is composed of a plug-in part or plug-in section  4  in the form of a plug shank  6  and a conduit connection section  8  with at least one conduit outlet  10 . In the illustrated embodiments, the plug-in connector  1  is embodied as a T connector, with two conduit outlets  10  extending in opposite directions on the same axis, i.e. in accordance with a common conduit axis  12 . However, it is also possible for there to be two or more conduit outlets  10  with different conduit axes. The plug shank  6  defines a plugging axis  14 , with the conduit axis  12  extending transversely with respect to the plugging axis  14 . In this context it is possible, as in the illustrated preferred embodiments (cf. for example  FIGS. 8 and 29 ), for the plugging axis  14  and the conduit axis  12  to enclose an angle α≠90°. An embodiment where α=90° is however also possible. In addition, it is optionally also possible for there to be just one conduit outlet  10  which is oriented transversely with respect to the plugging axis  14 . In addition, it is also possible, at least in the embodiments according to  FIGS. 1 to 8  and  14  to  18 , for (just) one conduit outlet which is located opposite the plug shank  6  to be oriented in the direction of the plugging axis  14  (not illustrated). The conduit outlets  10  can be embodied as connectors for plugging on a respective conduit (not illustrated). 
         [0034]    According to  FIGS. 8 ,  14 ,  17 ,  34  and  35 , the plug shank  6  can be plugged in a seal-forming fashion into a receiving opening  16  of the connector counterpart  2 , and can be releasably locked, using latching means  18 , to prevent it from being pulled out. For the seal, the plug shank  6  is fitted with at least one sealing ring  22  in an annular groove  20 . 
         [0035]    The latching means  18  are preferably composed of two latching arms  26  which are located diametrically opposite one another, extend approximately parallel to the plugging axis  14  in the release direction (arrow  24 ), can move in a spring elastic fashion in the radial direction and are integrally connected at one end to the plug shank  6 . However, alternatively, a single latching arm  26  may already suffice, specifically in particular in applications of the plug-in connector  1  for pressureless media or in the event of a partial vacuum. However, it is also possible to provide more than two (for example three) latching arms  26  in a preferably radially symmetrical circumferential distribution. At their free ends which are located opposite one another and point in the release direction  24 , the latching arms  26  have end sections  28  which, in the plugged state (see for example  FIGS. 8 and 35 ), protrude outside the connector counterpart  2 . Each end section  28  is preferably connected to the associated latching arm  26  via a radial web section  28   a  in such a way that a radial gap  29  which is formed between the plug shank  6  and the latching arm  26  merges with a radially enlarged gap region  29   a  between the plug shank  6  and the end section  28  (see in particular  FIGS. 3 ,  11 ,  16 ,  21 ,  26  and  35 ). In the plugged-in state, the latching arms  26  engage in a positively locking, or at least frictionally locking, fashion behind a latching step  32  which is provided within the receiving opening  16  of the connector counterpart  2  (see in particular  FIG. 35 ). In order to release this latched connection, the latching arms  26  can be moved radially inward manually by means of the protruding end sections  28  in order to release a positively locking latched connection. In the case of a frictionally locking latched connection by means of faces which are beveled with respect to the plugging axis  14  (see  FIG. 35 ), the plug shank  6  can also simply be pulled out of the receiving opening  16  in a latching fashion. In this context, the latching means  18  can also be configured with different oblique faces in such a way that different forces have to be overcome in the plugging-in direction and the release direction. The plugging in will preferably be easier than the release, but the converse is also possible. This is described in more detail below for the embodiment according to  FIGS. 29 to 36  with reference to  FIG. 35 . 
         [0036]    The plug-in connector  1  is expediently embodied with its components, i.e. with the plug-in section  4 , with the latching arms  26  and preferably also with the conduit connection section  8 , as an integral, monolithic shaped part, in particular made of plastic. 
         [0037]    According to the invention, a locking element  34  is connected to the plug-in part  4  in a positively locking or frictionally locking fashion and as a result largely captively, and is connected so that it moves between a release position and a secured position in such a way that in the secured position, cf. for example  FIGS. 1 ,  5  and  6  and  FIGS. 29 ,  33  and  36 , it blocks the latching means  18  to prevent release, and in the release position, cf.  FIGS. 9 and 12  and  FIGS. 32 ,  34  and  35 , it releases said latching means  18  for a release movement which cancels the locked arrangement. The locking element  34  is preferably held on the plug-in part  4  so as to be moveable (slideable) in the axial direction in such a way that in the secured position it engages radially in the gap region  29   a , and preferably also partially in the gap  29  between the latching arms  26  and the plug shank  6 , that as a result the latching arms  26  are blocked to prevent a release movement which is directed radially inward. In the release position, the locking element  34  is axially outside (above) the gap region  29 ,  29   a  of the latching arms  26  and their end sections  28  in such a way that the latching arms  26  are released for their radial release movement. In this context, the locking element  34  is expediently secured in each of the two positions, in particular in a frictionally locking and latching fashion in relation to the plug-in part  4 . 
         [0038]    Different embodiment variants of the locking element  34  are explained below. 
         [0039]    In the first embodiment according to  FIGS. 1 to 7 , the locking element  34 , viewed in plan view and in the circumferential direction of the plug shank  6 , is embodied approximately in a C shape and preferably from plastic so that it can be slid radially onto the plug shank  6  and engages there around the plug shank  6  and as a result is guided in a self-locking and axially moveable fashion. A latching element  36  in the form of a latching arm which extends axially in the release direction  24  is provided diametrically opposite the opening region of the C-shaped locking element  34 . This latching element  36  interacts with two latching grooves  38 , spaced axially apart, on the plug shank  6  in such a way that the locking element  34  is secured in a latching fashion in the secured position and in the release position, respectively. An activation element  42  with a preferably rectangular shape is arranged in the plugging-in direction (arrow  40 ) underneath the latching element  36 . A force for moving the locking element  34  axially can be exerted manually or with a suitable tool using this clip-like, approximately radially protruding activation element  42 . In this context, the locking element  34  is guided in a slideable fashion on guide faces  44  ( FIG. 3 ) of the plug shank  6 . In the secured position, the locking element  34  blocks, with locking faces  46 , the latching arms  26  to prevent an opening movement radially inward in the direction of the plugging axis  14  by virtue of the fact that, according to  FIG. 5 , the locking element  34  engages with the locking faces  46  in the widened gap region  29   a  and an adjoining partial section of the gap  29 . In this first embodiment, the plug shank  6  has radially projecting support faces  47  for providing support against tilting in the receiving opening  16 . 
         [0040]    In the second embodiment according to  FIGS. 9 to 13 , the locking element  34  firstly corresponds largely to the first embodiment according to  FIGS. 1 to 7 ; however, it has additional elements. An activation section  48  in the form of a push button key, which is connected to the latching element  36  via an axial extension  50  of said latching element  36 , is therefore arranged on the actual C-shaped locking element  34 . The push button key-like activation section  48  has a surface which is oriented at a right angle to the plugging axis  14  and is arranged overall above the entire plug-in connector  1 . Reference is made in this regard in particular to  FIGS. 9 and 12 . By means of a web  52  which is formed on the underside of the activation section  48  and is adapted to the outer contour of the plug-in connector  1  ( FIG. 13 ), application of a pressure force on the activation section  48  is prevented from resulting in excessively large bending of the extension  50  and of the latching element  36 , and therefore impedes the axial movement of the locking element where possible. In addition, the locking element  34  has two guide webs  54  which extend parallel to one another axially in the plugging-in direction  40  on the underside. These guide webs  54  increase the protection against tilting of the locking element  34 . In this embodiment, two additional guide shoulders  56  are formed on the plug shank  6 , said shoulders  56  being arranged offset in each case by 90° between the latching arms  26 , and therefore diametrically opposite one another. The intermediate spaces which are produced as a result of this between the latching arms  26  and the guide shoulders  56  act as groove-like guides for the guide webs  54  of the locking element  34 . The guide webs  54  and the guide shoulders  56  have radially outer circumferential faces which lie together on a virtual cylindrical surface with an outer diameter which is adapted to the inner diameter of the receiving opening  16  in such a way that they serve to provide tilt-free guidance of the entire plug shank  6  in the receiving opening  16 . In the end regions, pointing in the release direction  24 , of the guide shoulders  56 , in each case a shoulder knob  58  is arranged, on which shoulder knob  58  the locking element  34  is supported in the secured position. In this context, in each case the stop knob  58  engages in a corresponding recess  60  in the C-shaped locking element  34 . Furthermore, in this second embodiment, a web shoulder  62  which extends in the longitudinal direction of the conduit axis  12  may be arranged on the upside of the plug-in connector  1  in order to control locking, said web shoulder  62  having an interruption  63  for receiving the activation section  48 . In this context, the embodiment is such that in the secured position of the locking element  34  the activation section  48  and the web shoulder  62  lie essentially in a common plane, said activation section  48  lying with its planar surface in said plane and said web shoulder  62  lying with its upper boundary edge in said plane. As a result, the correct secured position of the locking element  34  can easily be detected, i.e. seen and also checked. This embodiment therefore serves as a plug-in indicator. 
         [0041]    In the third embodiment according to  FIGS. 14 to 18 , the locking element  34  is embodied in an annular fashion and has a plurality of (two) latching elements  36  for positioning and a plurality of (two) shoulder-shaped activation elements  42 . In spite of the separate illustration in  FIG. 15 , this annular locking element  34  is seated in a nondetachable fashion on the plug shank  6 , see  FIGS. 14 and 17 . In one particular method, the locking element  34  can be injection molded onto the plug shank  6  in such a way that it surrounds it by virtue of the fact that the parts are composed of various plastic materials which do not connect to one another in a materially joined fashion. 
         [0042]    In the fourth embodiment according to  FIGS. 19 to 23 , the locking element  34  is embodied as a slide in an inverted U shape, which is pushed over the entire plug-in connector  1  from above. In this context, the locking element  34  engages over the plug-in connector  1  with two locking webs  64  and can be moved axially between the release position and the secured position. In its region which connects the locking webs  64 , a push button key-like activation element  66  is formed. The locking webs  64  have, at their free ends pointing in the plugging-in direction, locking knobs  68  which, in the secured position  7 , engage in the region of the end sections  28  of the latching arms  26  and in the gap regions  29   a  and in this way block the latching arms  26  (see  FIGS. 19 and 22 ). The latching elements  36  are formed by U-shaped cutouts in the region of the locking webs  64 , said latching elements  36  interacting with the latching grooves  38  on the plug shank  6  in order to position the locking element  34  in its two positions. The inner contour  70  on the underside of the activation element  66  (see  FIG. 23 ) is matched to the upper contour of the plug-in connector in such a way that a saving in installation space is achieved by interaction of the contours. The inner contour  70  and the mating contour of the plug-in connector are matched to one another by their geometry (for example radii and/or indents) in such a way that in the plugged-in and locked state virtually all the cavities are filled in. In the embodiment according to  FIGS. 19 to 23 , the push button key-like activation element  66  has an upper surface which is oriented parallel to the conduit axis  12  in accordance with the profile of said conduit axis  12  which is oblique with respect to the plugging axis  14  ( FIG. 22 ). 
         [0043]    The embodiment variant according to  FIGS. 24 to 28  differs therefrom in that the surface of the activation element  66  is oriented at right angles to the plugging axis  14  ( FIG. 27 ). For this purpose, according to  FIG. 26  the plug-in connector  1  has a recess with a corresponding mating face  72 . Moreover, this embodiment according to  FIGS. 24 to 28  corresponds to the fourth embodiment according to  FIGS. 19 to 23 . 
         [0044]    The embodiment according to  FIGS. 29 to 36 , which is particularly advantageous in many respects, corresponds firstly to the embodiments according to  FIGS. 1 to 7  and  FIGS. 9 to 13  in many features. In this context, the plug-in connector  1  or the plug-in section  4  with the plug shank  6  is preferably embodied in such a way, radially symmetrically with respect to the plugging axis  14 , that the essentially C-shaped locking element  34  can optionally be mounted on both diametrically opposite sides by radial plugging on. This means that all the components which interact with the locking element  34  are provided multiply and radially symmetrically with respect to one another (cf. in this respect  FIGS. 30 ,  32  and  33 , for example). 
         [0045]    Specific differences and particular features of the embodiment according to  FIGS. 29 to 36  compared to  FIGS. 1 to 7  and  9  to  13  will be explained below. 
         [0046]    The locking element  34  has just one axial guide web  54 , while the plug shank  6  has two rib-like guide shoulders  56  on each of its diametrically opposite sides. In this context, the guide web  54  of the locking element  34  engages between the guide shoulders  56  of the plug shank  6 . According to  FIG. 30 , the outer circumferential faces, curved in a circular arc shape in cross section, of the guide web  54  and of the guide shoulders  56  are located on a virtual cylinder face whose diameter is matched to the inner diameter of the receiving opening  16  of the connector counterpart  2  in such a way that good tilt-free guidance of the entire plug-in connector  1  in the receiving opening  16  is ensured. This guidance is preferably also supported by the fact that the outer faces of the latching arms  26  according to  FIG. 30  are also curved in a circular arc shape in cross section and lie on the same virtual cylinder face. 
         [0047]    According to  FIG. 31 , in this embodiment of the locking element  34  the latching element  36  which secures the two axial positions by interacting with the latching grooves  38  is formed by a rib-like projection directly on the inner circumference of the C-shaped locking element  34  or of the activation element  42 . In this context, the activation element  42  is advantageously mechanically reinforced by increased thickness, which is advantageous for activation by means of a tool, preferably by means of a screwdriver. At the free ends of the open sides of the C shape, the locking element  34  has latching elements  72  which point inward toward one another and with which the locking element  34  engages in a latching fashion around the plug shank  6  for securing purposes. 
         [0048]    Furthermore, the locking element  34  has first bolt sections  74  for engagement in the widened gap regions  29   a  between the plug shank  6  and the end sections  28  of the latching arms  26  as well as axially extended second bolt sections  76  which, in the secured position, engage relatively far into the gap  29  in the axial direction; see for this purpose in particular  FIG. 36 , according to which the second bolt sections  76  extend axially to just before the region of the latching shoulders  30 . In the unlocked release position ( FIG. 35 ), the latching arms  26  form a type of “projecting arms” which are freely elastically moveable in the radial direction. It is advantageous here if each latching arm  26  is integrally connected to the plug shank  6  via a radial connecting section  78  and in the process each connecting section  78  has a wall thickness which corresponds approximately to the wall thickness or the radial thickness of the latching arm  26 . As a result, the connecting section  78  acts similarly to a film hinge, which leads to a reduced radial force for radially moving the latching arms  26 . Nevertheless, in the secured position ( FIG. 36 ), a high degree of stability against release is ensured by virtue of the fact that each latching arm  26  is clamped in radially without play at both ends, i.e. on both sides of the latching shoulder  30 . 
         [0049]    In a further advantageous embodiment, the plug-in connector  1  has, on the (upper) side of the conduit connection section  8  lying opposite the plug-in section  4 , an, in particular, plate-shaped or disk-shaped pressure element  80  with a planar surface  80   a  which is oriented transversely, in particular at a right angle, with respect to the plugging axis  14 . The pressure element  80  is preferably arranged in such a way that the plugging axis  14  runs centrally through the pressure element  80  or its surface  80   a . A plug-in force can most satisfactorily be applied manually by means of the pressure element  80 . In addition, the pressure element  80  can also serve as a carrier for a mark or characterizing label. 
         [0050]    As has also already been mentioned above, the plug-in force which is to be applied for the purpose of plugging in is smaller than the release force which is necessary for pulling out. For this purpose, the latching shoulder  30  of each latching arm  26  preferably has, in structural terms, a first oblique face  82  which points in the plugging-in direction (arrow  40  in  FIG. 34 ) and a second oblique face  84 , opposite the first, (see  FIG. 36 ) which points in the release direction (arrow  24  in  FIG. 34 ). As is shown in  FIG. 35 , in this context the first oblique faces  82  enclose, with the plugging axis  14 , an acute, relatively small (flat) angle β, while the angle γ between the two oblique faces  84  and the plugging axis  14  is greater. In the illustrated example, the angle β is approximately 25° to 35°, in particular approximately 30°, and the angle γ is approximately 70° to 80°. Here, the latching step  32  is preferably also constructed within the connector counterpart  2  as an oblique face in such a way that in the release position of the locking element  34  the plug-in connector  1  can be released in a frictionally locking fashion by simply pulling it out by virtue of the fact that the latching shoulders  30  are moved radially inward over the respective oblique faces. 
         [0051]    Furthermore, it is advantageous if the plug-in connector  1  has, in the junction region between the plug-in section  4  and the conduit connection section  8 , a stop element  86  (or one on each diametrically opposite side) against which the locking element  34  moves axially into abutment in its upper release position. The stop element  86  therefore forms an end stop for upwardly limiting the movement of the locking element  34  in the release direction. As a result, a release force can advantageously also be applied to the plug-in connector  1  via the locking element  34  by means of a lever-like tool (screwdriver). 
         [0052]    In order to downwardly limit the axial movement of the locking element  34  in the plugging-in direction in the secured position (see in particular  FIG. 36 ), the plug-in connector  1  has in each case two stop knobs  58 —in turn preferably symmetrical on the two diametrically opposite sides—on the plug shank  6 , which stop knobs  58  advantageously also simultaneously serve, according to  FIG. 34 , as stops for limiting the plugging in of the plug shank  6  by bearing on the connector counterpart  2 . In this context, the stop knobs  58  are preferably dimensioned in such a way that in the plug-in position according to  FIG. 34  the latching arms  26  are axially free of force in the region of the latching shoulders  30  (cf. in this respect also  FIG. 35  according to which the latching shoulders  30  are slightly spaced apart from the latching step  32  in the axial direction). This is a particular advantage especially in the case of a partial vacuum of the medium or media. 
         [0053]    In order to obtain a particularly compact design with the smallest possible height protruding axially beyond the connector counterpart  2  the upper side of the locking element  34  is matched to the underside, adjoining the plug-in section  4 , of the conduit connection section  8  and the conduit outlet  10  in such a way that in its release position the locking element  34  holds or surrounds the conduit connection section  8  in certain areas. Specifically, this is achieved by virtue of the fact that according to  FIG. 31  the locking element  34  has, on its upper side, concave depressions  88  as a negative contour adapted to the circular cross-sectional contour of the conduit connection section  8  or of the conduit outlet  10 . At least one of these depressions  88  given an oblique position of the conduit connection section  8 , (cf. the angle α in  FIG. 29 ), fits tightly against the conduit connection section  8  in the release position (see  FIGS. 32 and 34 ). 
         [0054]    In order to permit the locking element  34  to be easily fitted or latched radially onto the plug shank  6 , the plug shank  6  expediently has, on its circumference, guide faces  90  which, for example, have an oblique or circular arc-shaped cross section (see  FIGS. 29 and 35 ) such that when said locking element  34  is fitted on radially the free sections of the C-shaped locking element  34  come to bear with the latching elements  72  on the guide faces  90  and as a result are spread elastically until ultimately the latching elements  72  engage in a frictionally locking and latching fashion around the plug shank  6 . 
         [0055]    To conclude it is to be noted that the plug-in connector according to the invention can be manufactured with a very small spatial shape in the embodiment according to the invention. For example, it can be configured for an inner diameter of the receiving opening  16  of the order of magnitude of approximately 8 mm. In this context the plug shank  6  has a plugging-in length of approximately 12 mm, measured from the free plugging-in end up to the support faces of the stop knobs  58 . 
         [0056]    One preferred use of the plug-in connector is for connecting at least one fuel return flow line or leakage oil line in a fuel injection system of an internal combustion engine, in particular in what is referred to as a common rail system of a diesel engine. Owing to the increasing conduit density in such engines, the installation space which is available for plug-in connections is becoming smaller and smaller in the injector region of the cylinder head. As a result of the possibly very small design, in particular the plugging-in length, of the plug-in connector according to the invention, the latter is also very well suited for such applications. 
         [0057]    The invention is not restricted to the illustrated and described exemplary embodiments but rather also comprises all the embodiments with the same effect within the sense of the invention. In addition, the invention has hitherto also not yet been restricted to a feature combination which is defined in claim  1  but rather can also be defined by any desired other combination of specific features of all the individual features which are disclosed in their entirety. This means that basically virtually any individual feature of claim  1  can be omitted or replaced by at least one individual feature which is disclosed at another point in the application. In this respect, claim  1  is merely to be understood as a first attempt at formulation of an invention.