Abstract:
In order to solve the problem, in the case of a trailer coupling comprising a ball neck supporting a coupling ball, and also comprising a socket receptacle for a socket for the power supply of units acting on the coupling ball, the socket having a socket housing with a housing sleeve, which is provided with an insertion opening, and the insertion opening being closable by a cover that is mounted pivotably on the housing sleeve, of being able to mount the sockets as conveniently and easily as possible, it is proposed that the socket receptacle has a receiving channel, into which the housing sleeve extends starting from a first side of the socket receptacle, that the housing sleeve bears against the first side of the socket receptacle via a bearing surface, and that the housing sleeve is fixed to the socket receptacle by a retaining element, which is fitted starting from a second side of the socket receptacle and which is supported on the socket receptacle and is connected to the housing sleeve by a latched connection.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This patent application claims the benefit of German application No. 10 2014 108 071.8, filed Jun. 6, 2014, the teachings and disclosure of which are hereby incorporated in their entirety by reference thereto. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a trailer coupling comprising a ball neck supporting a coupling ball, and also comprising a socket receptacle for a socket for the power supply of units acting on the coupling ball, the socket having a socket housing with a housing sleeve, which is provided with an insertion opening, and the insertion opening being closable by a cover that is mounted pivotably on the housing sleeve. 
     Trailer couplings of this type are known from the prior art. 
     Here, units that act on the coupling ball are to be understood to be either towing ball couplings of trailers, which act on the coupling ball such that a hinged connection to the trailer is produced via the coupling ball, or load carriers, for example bicycle racks, which act on the coupling ball and are mounted thereon, the entire load carrier being supported exclusively by the coupling ball and the ball neck. 
     In trailer couplings of this type there is the problem of being able to mount the socket as conveniently and easily as possible. 
     SUMMARY OF THE INVENTION 
     This problem is solved in accordance with the invention in a trailer coupling of the type described in the introduction in that the socket receptacle has a receiving channel, into which the housing sleeve extends starting from a first side of the socket receptacle, in that the housing sleeve bears against the first side of the socket receptacle via a bearing surface, and in that the housing sleeve is fixed to the socket receptacle by a retaining element, which is fitted starting from a second side of the socket receptacle and which is supported on the socket receptacle and is connected to the housing sleeve by a latched connection. 
     The advantage of the solution according to the invention is considered to be constituted by the fact that a simple possibility is thus created for fixing the housing sleeve to the socket receptacle without connecting the socket housing to the socket receptacle by screws, which was the case previously. 
     In addition, the solution according to the invention with the provision of a latched connection also has the advantage that the latched connection can be configured such that it can adapt to different embodiments of the socket receptacle with usual tolerances. 
     In view of the fixing of the retaining element on the socket receptacle, a wide range of possibilities are conceivable. 
     In accordance with an advantageous solution the retaining element is supported in the receiving channel. 
     Here, the receiving channel may have recesses, for example, in which the retaining element is supported. 
     However, in accordance with an advantageous solution, the retaining element is supported on a conically widening wall region of the receiving channel. 
     In particular, the conically widening wall region is configured here such that it widens in the direction of the second side of the socket receptacle, such that a retaining element inserted into the receiving channel from the second side can be supported on the conical wall region narrowing in the direction of the first side. 
     Alternatively or additionally, the retaining element is supported via a supporting flange on a side of the socket receptacle opposite the first side. 
     In addition, it is advantageous when the socket is fixed in the socket receptacle in a manner fixed against rotation. 
     By way of example, this would be possible by fixing the housing sleeve in the housing receptacle in a manner fixed against rotation, for example by means of positively-locking elements. 
     However, in accordance with a particularly advantageous solution, the retaining element is secured on the socket receptacle in a manner fixed against rotation by positively-locking elements. 
     A securing of the retaining element in a manner fixed against rotation has the advantage that on the one hand there is the possibility of securing the retaining element, in the region of which a cable guide usually extends, in an unambiguous manner, fixed against rotation, and on the other hand there is the possibility to vary the orientation of the housing sleeve relative to the retaining element. 
     In particular, the retaining element has a positively-locking element, which enters into a rotationally fixed positively-locking connection with a positively-locking element of the socket receptacle. 
     These positively-locking elements could be formed for example as toothings and counter-toothings, or as any non-rotationally symmetrical structures, which are formed in a manner corresponding to one another. 
     In accordance with a particularly favourable solution, the socket receptacle, as positively-locking element, has a pocket extending from the second side of the socket receptacle into the receiving channel. 
     In this case the retaining element expediently has a body engaging with the pocket, such that the positively-locking elements are formed by the body and the pocket. 
     In particular, the positively-locking elements expediently extend parallel to a fitting direction of the retaining element, such that the positively-locking elements engage with one another by fitting the retaining element. 
     With regard to an orientation of the retaining element and the housing sleeve relative to one another, no further details have been provided in conjunction with the previously explained exemplary embodiments. 
     In accordance with an advantageous solution, the retaining element and the housing sleeve are connectable to one another in a manner fixed against rotation relative to one another in at least one rotary position, preferably in various rotary positions. 
     This means that it is possible to fix the housing sleeve in at least one rotary orientation, preferably in different rotary orientations, relative to the retaining element. 
     By way of example, in order to fix the retaining element and the housing sleeve relative to one another in at least one rotary position, the retaining element and the housing sleeve are connected in a manner fixed against rotation by positively-locking elements. 
     Positively-locking elements of this type could be, for example, radial toothings, which mesh with one another. 
     In the case of radial toothings of this type, it is also possible to select a different orientation of the housing sleeve relative to the retaining element in the case of the connection between housing sleeve and retaining element. 
     A solution that is particularly expedient is one in which at least one of the positively-locking elements is arranged on the housing sleeve and/or the retaining element in a number of angular positions about the centre axis, the other positively-locking element engaging with the first-mentioned positively-locking element such that it is possible, already by means of the number of angular positions of the first-mentioned positively-locking element, to bring the other positively-locking element into engagement with one of the positively-locking elements in one of these angular positions. 
     By way of example, the positively-locking elements for fixing the housing sleeve and the retaining element to one another in a rotationally fixed manner also extend parallel to the fitting direction. 
     With regard to the establishment of the latched connection between the retaining element and the housing sleeve, a wide range of solutions are conceivable. 
     In accordance with an advantageous solution the latched connection is effective in a position-independent manner within a latching region extending in the fitting direction. 
     This means that the latched connection has a latching region extending in the fitting direction, and that the latched connection is effective within this latching region, irrespective of the position within the latching region at which the latched connection occurs. 
     With a latched connection of this type it is thus possible to mount the socket in the socket receptacle in a tolerance-insensitive manner, i.e. the socket receptacle can be produced with considerable tolerances, in particular considerable tolerances with regard to the distance of the first side from the second side and/or the design of the receiving channel, and the socket nevertheless always can be mounted in a reliable, simple and secure manner in that the latched connection is effective in a position-independent manner within the latching region, such that for example a varying spacing of the first side from the second side and/or a varying diameter of the receiving channel can be compensated for by a different positioning of the retaining element relative to the housing sleeve and thus by sliding on the retaining element to a different extent in the fitting direction. 
     A position-independent latching region of this type can be provided preferably in that the retaining element is latchable to the housing sleeve in that either the housing sleeve or the retaining element has a latching toothing with a series of latching teeth extending parallel to the fitting direction and the retaining element or the housing sleeve has a counter-toothing with at least one latching tooth meshing with the series of latching teeth. 
     Due to the extension of the series of latching teeth of the latching toothing in the fitting direction, it is possible to define the extension of the latching region within which the latched connection is effective in a position-independent manner. 
     However, the solution according to the invention can also be developed advantageously by further features effective within the scope of a trailer coupling. 
     In accordance with a particularly expedient solution, the retaining element is formed as part of a housing cover for closing the housing sleeve on a side opposite the insertion, in particular a rear-side opening of the housing sleeve. 
     The fixing of the housing sleeve in the socket receptacle can thus be combined in a simple manner with the mounting of a cover for closing the housing sleeve. 
     In addition, with a trailer coupling according to the invention, a sensor is provided in the ball neck or in the coupling ball, such that a sensor connection line also has to run in the region of the receiving channel. 
     In accordance with an advantageous solution, the receiving channel has an indentation for receiving a sensor connection line. 
     In addition, in accordance with a further advantageous solution, the sensor connection line alternatively or additionally is guided along an outer surface of the retaining element, such that for example it is possible to guide the sensor connection line between the outer surface of the retaining element and the receiving channel, in particular the indentation in the receiving channel. 
     Alternatively, it is advantageously possible to form the retaining element such that it has a guide for the sensor connection line, in particular a channel as guide for the sensor connection line, such that the sensor connection line can run in the guide or the channel of the retaining element. 
     Here, the guide or the channel of the retaining element preferably lies outside the outer surface of the retaining element, such that, for example, the guide or the channel may also be arranged such that they are arranged in the indentation of the receiving channel. 
     Alternatively to the guide of the sensor connection line in the region of the receiving channel or in the region around the retaining element, in particular between the retaining element and the receiving channel, the sensor connection line is guided in the housing cover of the socket in accordance with a further advantageous solution. 
     In this case the housing cover provides an expedient possibility for providing a plug connection for the plug connection line. 
     This plug connection could be formed here such that it lies loosely in the housing cover. 
     However, in accordance with a particularly advantageous solution, the plug connection is fixed to the housing cover, in particular is fixed detachably. 
     In accordance with another advantageous solution, a plug connector element of a plug connector for the sensor connection line is integrated in the housing cover. 
     With this solution it is thus no longer possible to fix the plug connector within the housing, but instead the fixing is already provided in that a plug connector element of the plug connector is integrated in the housing cover. 
     In accordance with a further advantageous solution a receiving space for an electrical or electronic circuit is provided in the housing cover. 
     An electronic circuit of this type can be used in many ways. 
     By way of example, this electronic circuit could be an electronic circuit associated with a sensor or an electronic circuit comprising or cooperating with control elements for the trailer coupling or monitoring elements for the trailer coupling. 
     Here, the electronic circuit may also comprise additional switching elements operable for example from the housing cover, or also display elements arranged on the housing cover, in particular integrated in the housing cover. 
     In accordance with a particularly favourable solution, the housing cover has a receiving space for an electronic circuit connected to the sensor connection line, such that this electronic circuit may be, for example, an evaluation circuit or control circuit for a sensor system connected to the sensor connection line. 
     With regard to a sensor system connected to the sensor connection line, no further details have been provided previously. 
     In accordance with an advantageous solution, the sensor connection line is guided to a sensor system associated with a ball neck. 
     A sensor system of this type for example may be an angle of inclination sensor, which is integrated in the coupling ball or the ball neck, in particular a region of the ball neck adjoining the coupling ball. 
     However, a sensor system of this type may also be a load sensor, which is integrated in the coupling ball or in the ball neck. 
     A load sensor of this type can be formed for example as a supporting load sensor, which detects merely the supporting load that acts on the coupling ball and/or the ball neck. 
     However, a sensor of this type may also be configured as a sensor detecting the load of the coupling ball and/or the ball neck as a whole, which not only detects the supporting load, but also all other forces acting on the coupling ball and/or the ball neck. 
     Further features and advantages of the invention will be disclosed in the following description and will be presented in the drawings showing illustrations of some exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic side view of a motor vehicle having a trailer coupling; 
         FIG. 2  shows an illustration of the trailer coupling that is mountable on the vehicle; 
         FIG. 3  shows a first exemplary embodiment of a ball neck of a trailer coupling according to the invention with coupling ball; 
         FIG. 4  shows a view of the first exemplary embodiment of the ball neck in the direction of the arrow A in  FIG. 3  without socket inserted into the socket receptacle; 
         FIG. 5  shows an enlarged view of the socket receptacle without inserted socket; 
         FIG. 6  shows an illustration of the ball neck of the first exemplary embodiment of the trailer coupling according to the invention similarly to  FIG. 4  with inserted socket; 
         FIG. 7  shows a section along line  7 - 7  in  FIG. 6 ; 
         FIG. 8  shows a section along line  8 - 8  in  FIG. 7 ; 
         FIG. 9  shows a perspective illustration of the housing sleeve of the socket housing without housing cover; 
         FIG. 10  shows a perspective illustration of the housing cover for the socket according to  FIG. 9  in accordance with the first exemplary embodiment of the trailer coupling according to the invention; 
         FIG. 11  shows an enlarged illustration of a latching toothing between the retaining element and the housing sleeve; 
         FIG. 12  shows an illustration similarly to  FIG. 4  in a second exemplary embodiment of the trailer coupling according to the invention; 
         FIG. 13  shows a section similarly to  FIG. 7  in the second exemplary embodiment of the trailer coupling according to the invention; 
         FIG. 14  shows a section similarly to  FIG. 13  in a third exemplary embodiment of a trailer coupling according to the invention; 
         FIG. 15  shows a section along line  15 - 15  in  FIG. 14  through the housing cover of the third exemplary embodiment of the trailer coupling according to the invention; 
         FIG. 16  shows a section similarly to  FIG. 7  through a fourth exemplary embodiment of the trailer coupling according to the invention; 
         FIG. 17  shows a section similarly to  FIG. 7  through a fifth exemplary embodiment of the trailer coupling according to the invention; 
         FIG. 18  shows a section similarly to  FIG. 7  through a sixth exemplary embodiment of the trailer coupling according to the invention; and 
         FIG. 19  shows a section similarly to  FIG. 7  through a seventh exemplary embodiment of the trailer coupling according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A motor vehicle illustrated in  FIG. 1  and designated as a whole by  10  comprises a motor vehicle body  12 , which carries a bumper unit  16  on a rear end  14 . A crossmember  22  of a coupling carrier unit  20  is provided on the rear side  18  of the rear end  14  covered by the bumper unit  16  and on the bumper unit  16  and is fixed by side supports  24  to the rear end  14  of the motor vehicle body  12  in that the side supports  24  extend parallel to a longitudinal direction  26  of the motor vehicle body  12  and are fixed to the rear end  14  in side regions  28  thereof. 
     The coupling carrier unit  20  is also provided with a bearing unit designated as a whole by  30 , the bearing base  32  of said bearing unit being fixedly connected to the crossmember  22 . 
     The bearing unit  30  also comprises a bearing element designated as a whole by  34 , which is connected to a first end  42  of a ball neck designated as a whole by  40 , which extends from the first end  42  to a second end  44  and at the second end  44  thereof carries a coupling ball designated as a whole by  46 . 
     The bearing element  34  may be a bearing element fixedly connected to the bearing base  32  or a bearing element that is mountable removably on the bearing base  32 . 
     Alternatively however, the bearing element  34  may be a pivot bearing element, which is pivotable relative to the bearing base  32  about a pivot axis designated by  36 , such that the ball neck  40  is pivotable from the working position A illustrated in  FIG. 2  by solid lines into a rest position R illustrated by dashed lines, in which the ball neck  40  extends, starting from the bearing base  32 , transversely to the longitudinal direction  26  of the motor vehicle body  12  and therefore along the crossmember  22 . 
     The ball neck  40  thus runs, in the rest position R illustrated by dashed lines, transversely to a vertical longitudinal centre plane  38  of the motor vehicle body  12  and also of the coupling carrier unit  20 , the vertical longitudinal centre plane  38  thus also running parallel to the longitudinal direction  26 . 
     Further, the pivot axis  36  also runs preferably transversely to the longitudinal centre plane  38 , but inclined relative to the vertical longitudinal centre plane  38  by an angle, the angle being less than 70° and more than 20°. 
     An exemplary embodiment of a ball neck  40  of this type is illustrated in an enlarged manner in  FIG. 3 , the ball neck  40  being formed integrally on the bearing element  34  and the bearing element  34  in this case is formed as a pivot bearing element for pivotable mounting on the bearing base  32 . 
     In the illustrated exemplary embodiment of the ball neck  40 , this carries, at the second end  44  thereof, a ball attachment  48 , which has a circumferential surface running cylindrically relative to a ball centre axis  50  and running at a radial distance around the ball centre axis  50 , which distance is smaller than a radius of the coupling ball  46 . 
     In the illustrated exemplary embodiment of the ball neck  40 , this has, as illustrated in  FIGS. 3 to 5 , a housing receptacle  60 , which is integrated in one piece in the ball neck  40  and is formed in the manner of an annular body  62 , which lies between a ball neck portion  64 , which extends from the first end  42  of the ball neck  40  to the annular body  62 , and a second ball neck portion  66 , which extends from the annular body  62  to the second end of  44  the ball neck. 
     The annular body  62  of the housing receptacle  60  encloses a receiving channel of the housing receptacle  60 , which receiving channel is denoted as a whole by  72  and extends from a first end face  74  of the annular body  62  to a second end face  76  of the annular body  62  and forms a centre axis  78 , which runs transversely to the longitudinal centre plane  38 , and here may be inclined with respect to the longitudinal centre plane  38  by an acute angle, but preferably runs perpendicularly to the longitudinal centre plane  38 . 
     The receiving channel  72  is formed here by a channel inner wall  82  enclosing said receiving channel, which channel inner wall has, adjacently to the first end face  74 , a wall region  84  running substantially cylindrically to the centre axis  78  and running around the centre axis  78  and also has a wall region  86  starting from the wall region  84  and widening conically to the second end face  76 , which wall region  86  thus runs, at the transition to the second end face  76 , at a larger radial distance from the centre axis  78  than in the vicinity of the cylindrical wall region  84 . 
     In addition, the receiving channel  72  is provided with positively-locking elements  92 , which are formed as pockets  94 , which widen radially relative to the conical wall region  86 , extend starting from the cylindrical wall region  84  in the direction of the second end face  76 , and have pocket openings  96  arranged in the end face  76 , such that the pockets  94  are accessible via the pocket openings  96  arranged in the second end face  76 . 
     Besides the positively-locking elements  92 , a cable guide groove  102  running in the first ball neck portion  64  leads into the conical wall region  86  and has an opening  104  leading into the conical wall region  86  and adjoining the second end face  76 . 
     The cable guide groove  102  is set back both in relation to the second end face  76  and also in relation to a surface  68  of the first ball neck portion  64 . 
     As illustrated in  FIGS. 3 and 6 to 10 , a socket designated as a whole by  110  is inserted into the socket receptacle  60  and has a socket housing designated as a whole by  112 , which engages with the socket receptacle  60 . 
     The socket housing  112  comprises, in turn, a housing sleeve  114 , which is provided with an insertion opening  116 . 
     The insertion opening  116  is closable by a cover  118 , which is mounted on the housing sleeve  114  by means of a cover hinge designated as a whole by  122  so as to be pivotable about a pivot axis  124 . 
     The cover hinge  122  is formed integrally on a collar  126  adjoining the insertion opening  116 , which collar forms a bearing surface  128  which can be placed against the first end face  74  of the socket receptacle  60  and by means of which the socket housing  112  bears against the socket receptacle  60  in the mounted position and is fixed against a movement in the direction of the second end face  76 . 
     The housing sleeve  114  extends from the insertion opening  116  to a rear-side opening  132 , which is closable by a housing cover  134 . 
     The housing cover  134  overlaps the rear-side opening  132  with a covering body  136 , on which a retaining element  138  is integrally formed, which engages around the housing sleeve  114  on an outer peripheral side  142 . 
     In order to connect the housing cover  134  to the housing sleeve  114 , the housing sleeve  114  has, on the outer peripheral side  142  thereof, latching toothings  144  close to the rear-side opening  132 , which have a plurality of successive latching teeth  148  in a direction parallel to a centre axis  146  of the socket housing  112 . 
     By way of example, latching toothings  144  arranged opposite one another in pairs are formed identically with regard to the arrangement of the latching teeth  148 , the latching teeth  148  of different pairs possibly being arranged offset relative to one another in the direction of the centre axis  146  in order to enable an even more precise positioning of the retaining element  138  relative to the housing sleeve in the direction of the centre axis  146  than is predefined by the distance of the latching teeth  144 , specifically in that the latching is established in each case by at least one pair of mutually opposed latching toothings  144 , whereas another pair or other pairs do not contribute to the latching in this position. 
     A counter-toothing  152  formed integrally on the retaining element  138  engages with this latching toothing  148 , as illustrated in  FIG. 11 , and has at least one latching tooth  154 , but possibly may also have further latching teeth  154 . 
     The latching toothing  144  and the counter-toothing  152  are preferably formed such that, as the retaining element  138  is slid on in a fitting direction  156 , which runs parallel to the centre axis  146 , the two toothings  144  and  152  mesh with one another and latch with one another securely, preferably non-detachably. 
     The housing cover  134  is fitted in the fitting direction  156  until the retaining element  138  bears against the socket receptacle  60 , such that the entire socket  110  is thus held on the socket receptacle  60  securely against movements in the direction of the centre axis  78  of the receiving channel  72 , since on the one hand the bearing surface  128  bears against the first end face  74  of the socket receptacle  60 , and on the other hand the retaining element  138  is supported on the socket receptacle  60 . 
     The retaining element  138  can be supported on the socket receptacle  60  by a supporting flange  158  protruding radially beyond the retaining element  138 , which supporting flange can bear against the second end face  76  and secures the retaining element  138  against a movement in the direction of the first end face  74 . 
     This can be implemented alternatively or additionally in that the retaining element  138  is provided with a conically extending outer surface  162 , which faces the wall region  86  extending conically in relation to the centre axis  78  and which in particular has the same cone angle as the conically extending wall region  86 , such that, by fitting the retaining element  138  on the housing sleeve  114 , the housing sleeve  114  is centred on account of the conical outer surface  162  bearing against the conical wall region  86  and is supported against a movement of the retaining element  138  in the direction of the first end face  74 . 
     Here, the outer surface  162  can also be provided with outwardly protruding scraper fins  163 , which ensure a further improved fit and contribute to the tolerance compensation. 
     In addition, the housing sleeve  114  is also centred radially by the cylindrical wall region  84  of the channel inner wall  82  in the region in a region adjoining the collar  126 , such that the socket housing  112  is thus securely fixed in the socket receptacle  60 . 
     The fact that, for example, the latching toothing  144  has a plurality of latching teeth  148  and the counter-toothing  152  is thus latchable with the latching toothing  144  in a plurality of latching positions corresponding to the plurality of latching teeth  148  makes it possible, when fitting the retaining element  138  to the housing cover  134  and sliding it in the fitting direction  156 , to compensate for dimensional tolerances in the region of the annular body  62 , which are created during production of the annular body  62  as a forged part. 
     The socket  110  can thus be mounted in the socket receptacle  60  in a simple and reliable manner, and also in a manner insensitive to dimensional tolerances. 
     In order to secure the socket  110  in a manner fixed against rotation, the retaining element  138  is provided with positively-locking elements  172  in the form of wedge bodies  174 , which is introducible into the pockets  94  as the retaining element  138  is fitted in the fitting direction  156  over the pocket openings  96 , such that the retaining element  138  is fixed in the ring body  62  in a manner fixed against rotation by the positively-locking elements  172  cooperating with the positively-locking elements  92 . 
     The positioning by the wedge bodies  174  by way of example can be made even less sensitive to tolerance in that the wedge bodies  174  are provided with outwardly protruding scraper fins  175 . 
     Merely an additional rotationally fixed fixing of the housing sleeve  114  relative to the retaining element  138  is thus also necessary. 
     This is achieved in that the housing sleeve  114  is provided in an end portion  182  carrying the latching toothings  144  with slits  184  extending parallel to the centre axis  146 , which slits are engaged by webs  186  formed integrally on the retaining element  138  and protruding radially in the direction of the centre axis  146 . 
     The slits  184  are preferably arranged around the centre axis  146  at equal angular distances, and the corresponding webs  186  are also arranged at equal angular distances, such that it is possible to fix the housing sleeve  114  with a positive engagement and in a manner fixed against rotation relative to the retaining element  138  in various rotary positions, and to thus predefine different rotary positions of the housing sleeve  114  relative to the retaining element  138 . 
     In a second exemplary embodiment of a trailer coupling according to the invention, those parts that are identical to those of the first exemplary embodiment are provided with the same reference signs, and therefore reference can be made fully to the comments relating to the first exemplary embodiment with regard to the description of these parts. 
     In the second exemplary embodiment a sensor system  202  is associated for example with the second ball neck portion  66  and/or the coupling ball  46 , a sensor connection line  204  being guided to said sensor system and running through a channel  206 , which passes through the ball neck portion  66 , the ball attachment  48  and possibly the coupling ball  46 , and which likewise leads into the receiving channel  72  of the socket receptacle  60 , such that the sensor connection line  204  is to be continued within the receiving channel  72 . 
     A sensor system  202  of this type is, for example, an angle of inclination sensor for measuring an angle of inclination between the ball neck  40  and a towing ball coupling provided on a trailer drawbar and/or a sensor system for measuring forces acting on the coupling ball  46  and/or the ball neck  40 . 
     For this purpose, as illustrated in  FIGS. 12 and 13 , a stepped recess  212  is provided in the wall region  86 , specifically directly adjacent to the second end face  76 , and runs from a mouth region  214  of the channel  206  in the receiving channel  72 , said mouth region being arranged in a manner recessed relative to the channel inner wall  82 , to the cable guide groove  102 , more specifically in particular runs on a side of the conical wall region  86  facing away from the positively-locking elements  92 . 
     In the simplest case it is possible, as illustrated in  FIG. 13 , to allow the sensor connection line  204  to run between the outer surface  162  of the retaining element  138  and the stepped indentation  212  from the mouth region  214  to the cable guide groove  102 , and then to combine this in the cable guide groove  102  with a socket supply line  106  to form a cable harness  108 , or to allow this to continue in this cable harness to a connection unit on the motor vehicle. 
     In a third exemplary embodiment of the trailer coupling according to the invention, illustrated in  FIGS. 14 and 15 , the sensor connection  204 , for protection thereof, is guided on the retaining element  138 ′ in such a way that a supporting web  222  running parallel to the outer surface  162  of the retaining element  138  is arranged on the supporting flange  158  in the region of the supporting flange  158  facing towards the stepped indentation  212  and runs at a distance from the outer surface  162  of the retaining element  138 ′, such that a U-shaped channel  224  is created between the supporting web  222  and the retaining element  138 ′, in which channel the sensor connection line  204  is laid and by which the connection line  204  is guided, such that this can run in the retaining element  138 ′, in a manner protected against mechanical influences, guided from the mouth region  214  to the cable guide groove  102 . 
     In addition, in this third exemplary embodiment of the trailer coupling according to the invention, all those elements identical to those of the first exemplary embodiment are also provided with the same reference signs, and therefore reference can be made fully to the comments relating to the first exemplary embodiment with regard to the description of these parts. 
     In a fourth exemplary embodiment, illustrated in  FIG. 16 , the connection line  204  coming from the sensor system  202  is introduced into the housing cover  134 ″ from the mouth region  214  through the retaining element  138 ″ and is connected by means of a plug connection  232 , which is fixed to the housing cover  134 ″, preferably to the covering body  136  of the housing cover  134 ″, to a sensor line  234  also guided in the cable harness  108  with the socket supply line  106 , such that the cable harness  108  comprising the socket supply line  106  can be equipped in advance with the sensor line  234 , which can then be connected within the housing cover  134 ″ via the plug connection  232  to the sensor connection line  204  coming from the sensor system  202 . 
     In addition, in the fourth exemplary embodiment, all those elements identical to those of the above exemplary embodiments are provided with the same reference signs, and therefore reference can be made fully to the comments relating to these exemplary embodiments. 
     In a fifth exemplary embodiment of a trailer coupling according to the invention, illustrated in  FIG. 17 , those parts identical to those of the above exemplary embodiments are provided with the same reference signs, and therefore reference can be made fully to the comments relating to the above exemplary embodiments, in particular the first exemplary embodiment, with regard to the description of these parts. 
     In contrast to the above exemplary embodiments, in this exemplary embodiment the housing cover  134 ′″ is formed such that it is also provided with an electronic circuit  242  associated with the sensor system  202 , for example an evaluation circuit for the sensor system  202 , the circuit  242  preferably being arranged and held on an inner side of the covering body  136 ′″ in a receiving space  238  of the housing cover  134 ′″. 
     In this exemplary embodiment a socket housing  244  is also formed integrally on the retaining element  138 ′″, in which socket housing plug contact units  246  are arranged, into which contact pins  248  of the sensor connection line  204  are pluggable, such that a connection between the sensor connection line  204  and the circuit  242  is producible via a plug connection  252 , of which the socket housing  244  and the plug contact units  246  are integrated in the housing cover  234 ′″. 
     In addition, in the fifth exemplary embodiment, all those elements identical to those of the above exemplary embodiments are provided with the same reference signs, and therefore reference can be made fully to the comments relating to these exemplary embodiments. 
     In a sixth exemplary embodiment of a trailer coupling according to the invention, illustrated in  FIG. 18 , in contrast to the above exemplary embodiments, the housing sleeve  114 ″″ is provided itself with a cover  262 , the cover  262  engaging for example via a retaining region  264  with the housing sleeve  114 ″″ and is thus connected to the housing sleeve  114 ″″ either with positive engagement or by other fastening possibilities, such as adhesive bonding. 
     However, the housing sleeve is still fixed by the retaining element  138 ″″, which also still has the supporting flange  158 ″″, which is supported on the second end face  76  of the ring body  62 . Here, the housing sleeve  114 ″″ is fixed by the retaining element  138 ″″ in the same manner as described in conjunction with the above exemplary embodiments. 
     In addition, in the sixth exemplary embodiment, all those elements identical to the above exemplary embodiments are provided with the same reference signs, and therefore reference can be made fully to the comments relating to the above exemplary embodiments. 
     In a seventh exemplary embodiment, illustrated in  FIG. 19 , the retaining element  138 ′″″, similarly to the third exemplary embodiment illustrated in  FIGS. 14 and 15 , is provided with the supporting web  222 ′″″, such that the channel  224 ′″″ is formed, in which the sensor connection line  204  can be guided by the retaining element  138 ′″″ from the mouth region  214  to the cable guide groove  102 . 
     In addition, in the seventh exemplary embodiment, all those elements identical to the above exemplary embodiments are provided with the same reference signs, and therefore reference can be made fully to the comments relating to these exemplary embodiments. 
     In all exemplary embodiments a contact carrier  272  is provided in the socket  110  within the socket housing  112 , in which contact carrier plug contacts  274  are provided, which can be connected to a plug that is pluggable into the socket  110 . 
     The plug contacts  274  are contacted in turn by a contact plug designated as a whole by  276 , which in turn has contact elements  278 , which are connected on the one hand to the plug contacts  274  in the plugged-in state of the contact plug  276  and on the other hand are connected to individual cores  282  of the socket supply line  106 .