Abstract:
According to the invention, several outward-projecting tongues are formed on the built-in housing part of a parallelepipedal built-in unit and a frame whose inner width is greater than the mounting dimension of the built-in housing, is configured on the front panel that is to be fixed on the built-in housing part. Grooves which are allocated to the tongues and corresponding sliding surfaces are formed on the interior of the frame, the grooves and surfaces cooperating with certain elasticity in the frame to form a one-way snap-on connection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation of international application PCT/DE01/02083, filed Jul. 6, 2002 and which designated the United States, and claims priority to German application 20110888.7, filed Jun. 30, 2001, the both of which are herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to means for connecting a front panel of a parallelepiped built-in unit to the built-in housing of the latter, the front panel being assigned to a narrow side of the built-in housing.  
         [0003]     If the abovementioned built-in unit is a tachograph used in a motor vehicle, then the front panel thereof, in addition to satisfying esthetic requirements, also constitutes a functional part in which are formed, for example, a window cut-out for a display, button shafts and guide slots assigned to the data cards of the driver and passenger, and possibly also a discharge slot for a printout.  
         [0004]     The connecting means between the front panel and the built-in housing of such a tachograph thus have to have a high level of positioning accuracy in relation to the subassemblies arranged in the built-in housing, i.e. the display, various buttons, a printing unit and the data-card assemblies, and have to avoid changes in position as a result of material fatigue on account of vibrations which are inevitable during operation of a motor vehicle and on account of the fluctuations in temperature which prevail at the installation location. On the other hand, the recordings of tachographs, in particular the recordings relating to the working and rest periods, are at risk of manipulation, with the result that it has to be ensured that tampering which cannot be subsequently detected, for example through a gap between the front panel and built-in housing, is reliably prevented.  
         [0005]     Quite apart from the fact that they are not suitable for mass production on account of the outlay in respect of components and installation, it is also the case that conventional screw connections secured by lead seals do not fulfill these conditions, inter alia, because the amount of installation space which is necessary for fitting a plurality of screw connections on the front side is not available and, as experience has shown, the lead-seal caps which secure the screws do not perform a reliable sealing function. In contrast, hooks or claws integrally formed on the front panel, in order to be sufficiently resilient for a latching connection between the front panel and the built-in housing, require a certain length and amount of free space. In addition to the risk of such connecting means breaking, this type of fastening is tolerance-critical, with the result that a front panel, in some circumstances, cannot be installed or an unstable connection which is no longer free of play is possibly established over time on account of vibrations and extreme change in temperature.  
       SUMMARY OF THE INVENTION  
       [0006]     The object of the present invention has thus been to provide means which allow the front panel of a parallelepipedal tachograph to be installed on the built-in housing of the latter in a manner which is compatible with mass production, which ensure a constant function, in particular in respect of preventing tampering, in the operation environment in the motor vehicle, and which are straightforward to produce.  
         [0007]     This object is achieved in that a frame is formed on the front panel, and the clear width of this frame is greater than the installation dimensions of the built-in housing, in that outwardly oriented tongues/tabs are integrally formed at least on two opposite wall elements of the built-in housing essentially at right angles to the respective wall plane, and in that grooves assigned to the tongues/tabs are formed in the frame.  
         [0008]     The solution according to the invention provides the advantage of a one-way snap-in connection which is quick to install, ensures that the front panel is seated permanently on the built-in housing and in the case of which preferably the entire front panel is included in the necessary elastic deformation, the relatively long sliding surfaces provided allowing the frame to expand during installation of the front panel. Removal of the front panel without damage or destruction is only possible using a specific tool, with the result that the connection according to the invention also performs a sealing function, to be precise without additional components being necessary. On the other hand, tampering is prevented because the frame covers over the connecting means to a relatively great extent and the location of the connecting means, i.e. the tongues/tabs and the grooves assigned to the tongues/tabs on the inside of the frame is not visible from the outside. It has further been noted that the connection according to the invention is largely free of forces in the installed state and thus ensures dimensional stability for the front panel, which is preferably produced from plastic. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0009]     The invention is explained in more detail hereinbelow with reference to drawings, in which:  
         [0010]      FIG. 1  shows a front view of a tachograph,  
         [0011]      FIG. 2  shows an enlarged partial illustration of a side view of the tachograph according to  FIG. 1 ,  
         [0012]      FIG. 3  shows a perspective illustration of the built-in housing of the tachograph according to the invention, and  
         [0013]      FIG. 4  shows a partial section along section line A in  FIG. 1  with the printer drawer removed. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     In  FIG. 1, 1  designates a front panel which closes off a built-in housing  2  ( FIGS. 2 and 3 ) of a tachograph on the front side.  3  designates a window cut-out through which it is possible to read a display  4 . Furthermore, a plurality of buttons  5 ,  6 ,  7  and  8  are guided in the front panel  1 . In this case, the buttons  5  and  8  serve for the task of the driver and passenger logging on, and the buttons  6  and  7  serve for releasing the respective data cards assigned to the driver and passenger. A covering  9  closes a plug socket used for diagnostic purposes. Guide slots  10  and  11  which are countersunk in a funnel-like manner serve for the introduction of the driver&#39;s data card into the respective reading/writing assemblies of the tachograph, these being located in the built-in housing  2  and preferably being assigned to a printed circuit board  12  ( FIG. 3 ). Recesses  13  and  14  of the bead-like protrusion  15  of the front panel  1  serve for access for the purpose of removing a data card. The front panel  1  further contains a cut-out  16  which is covered by a front wall  17  of a drawer assigned to a printing device, to be precise such that the front wall  13  is incorporated in terms of design, in particular in a surface-flush manner, in the front surface of the front panel  1 .  
         [0015]     Merely for the sake of completeness, it should be mentioned that the drawer is assigned connecting means which, in the case where recording material is to be refilled, can be unlocked by confirmation of a button  18 .  19  designates an outlet opening for the printed recording material. A button  20  serves for initiating printing. By means of a rocker switch  21  which is likewise arranged in the drawer, it is possible to select various functions and memories and, for example in conjunction with the buttons  5  and  8 , to enquire the working-period data of the driver and passenger.  22  designates a lead-seal cap which is assigned to a screw which connects the front panel  1  to the built-in housing  2 . Pairs of openings  23 ,  24  and  25 ,  26  serve for the introduction of clamp-like tools for removing a tachograph from an installation compartment or a suitable opening in an instrument panel. In this case, the legs of the clamps, as can be gathered from  FIG. 2 , interact with resilient claws  27  and  28  which are formed on u-shaped components  29  which, for their part, are fastened on the side walls  30  and  31  of the built-in housing  2  by means of screws  32  and  33 .  
         [0016]     The built-in housing  2 , which according to  FIG. 3  is only partly fitted out, comprises a cover part  34  and a base part  35 . The cover part  34  has a cover plate  36 , on which the side walls  30 ,  31  and a rear wall  37  are integrally formed. The base part  35  is formed by a base plate  38  and by legs which are integrally formed on the base plate  38  and are assigned in an overlapping manner to the side walls  30 ,  31  and the rear wall  37  of the cover part  34 , one leg being designated  39 . Tabs  40  and  41 , which are bent out of the side walls, and catches  42  and  43 , which are integrally formed on the legs, are used to join the cover part  34  and base part  35  together in a bayonet-like manner. Moreover, the tabs  40 ,  41  form platforms which are used for fastening the printed circuit board  12 . The built-in housing  2 , furthermore, is assigned a structural part  44  which, on the one hand, serves for stiffening purposes by being connected to a side wall  31  of the rear wall  37 , the base plate  38 , the cover plate  36  and the printed circuit board  12  and, on the other hand, forms a securing means for the display  4  or for a display subassembly, comprising the display  4 , a printed circuit board assigned to the display  4 , and the buttons  5 ,  6 ,  7  and  8 , and on which is integrally formed a guide rail which is assigned to the drawer of the printing device. The second guide rail of the drawer is fastened on the side wall  30 .  45  designates a plug connector which symbolically illustrates the positioning of the display subassembly in relation to the printed circuit board  12 .  46  constitutes a support which is formed on the structural part  44 , engages through the printed circuit board  12  and interacts with the base plate  38 .  
         [0017]     As can further be seen from  FIG. 3 , stiffening strips  47  and  48  with tongues  49 ,  50 ,  51  and  52 ,  53  formed thereon are integrally formed on those end sides of the cover plate  36  and base plate  38  which are directed toward the front panel  1 . Bent tabs  54  and  55  are located at the ends of the side walls  30 ,  31  of the cover part  34 , preferably in the same plane as the tongues  49 ,  50 ,  51 ,  52 ,  53 . Two angled elements  56 ,  57  which are formed from the side walls  30 ,  31  serve as stops during the installation of the tachograph. A lug which is integrally formed on the base plate  38 , and is designated  58 , is used in the operation of fitting the abovementioned screw secured by the lead-seal cap  22 .  
         [0018]     The partial section illustrated by  FIG. 4  and the side view in  FIG. 2  show that a peripheral frame  59  which is integrally formed on the front panel  1  engages over the built-in housing  2  to a relatively great extent and thus covers the regions where the connecting means between the front panel  1  and the built-in housing  2  are located, these connecting means being rendered inaccessible. The tongues  49 ,  50 ,  51 ,  52 ,  53  and the tabs  54 ,  55  are each assigned grooves  60  which are formed in the frame  59  and of which the locking flanks  61 , corresponding to the tongues and tabs, are located in one or different planes and are formed essentially at right angles to the direction of installation of the front panel  1 .  62  designates sliding surfaces which are respectively assigned to each groove  60 . A plurality of ribs  63 , which stiffen the front panel  1 , are designed such that their end surfaces  64  are located in the front plane of the strips  47 ,  48 , possibly also the side walls  30 ,  31 , and serve as stop during installation of the front panel  1 . It should also be mentioned that the flanks  61  may also be formed such that they are not at right angles to the direction of installation of the front panel  1 , whereby, in one case, removal of the front panel  1  would be facilitated and in the other case, e.g. with undercut grooves  60 , removal would be made more difficult and the sealing function would be enhanced.