Component carrier
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Application Ser. No. G 90/12,844.3, filed Sep. 9, 1990, in the Federal Republic of Germany, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a component carrier for circuit boards equipped with electrical and electronic components. These circuit boards are insertable on guide rails and are equipped with two parallel side walls, at least four parallel front and rear module rails which connects the side walls and support the guide rails. In order to fasten the module rails, the side walls are equipped with groups of fastening elements in the form of fastening holes and pins that project on the interior. The end faces of the module rails are provided with blind holes to accommodate fastening screws that pass through the fastening holes and with profiles against whose longitudinal sides the pins lie. 
     The invention is used for component carriers of any type and dimension which are intended to accommodate circuit boards and are assembled in the manner of a rack of two side walls and at least four module rails that connect the side walls. 
     In order to connect the module rails with the side walls of a component carrier, fastening elements are known which are provided at the side walls and cooperate with the end faces of the module rails where blind holes are provided. To produce defined fastenings, it is further known to provide low, block-shaped pins on the interior of the side walls with the aid of which the position of the module rails is fixed so as to secure them against twisting. The drawback is here that, in view of the unavoidable tolerances with which components to be connected are generally produced, inaccuracies with respect to the assembled component carrier must be accepted. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to configure the fastening elements for fastening the module rails to the side walls of a module carrier so that, with only little expenditure for technology and while compensating manufacturing tolerances, accurate assembly is possible and twisting of the module rails relative to the side walls is effectively prevented. 
     This is accomplished in a component carrier of the above-mentioned type in that each group of the fastening elements provided at the side walls includes four fixing pins that are arranged in the corners of a rectangle and form two pairs. Each group has an associated fastening hole and each module rail has a profile that matingly fits into the space between each pair of fixing pins. This configuration of the fastening elements can be produced at little expense, permits simple and quick as well as accurate assembly of the parts of a component carrier and permits the use of different module rail profile configurations. 
     Advantageously the fixing pins have the shape of a circular cylinder which ensures good compensation of manufacturing tolerances. pattern; 
     According to a further feature of the invention, the fastening hole of each group of fastening elements lies on the extension of the short center line of the rectangle. This symmetrical arrangement permits the mirror-image attachment of the same fastening elements to the interior of the two facing side walls. 
     Good protection against twisting is realized if the long side of the rectangle is at least three times longer than its short side. 
     In order to provide for adaptation to relatively low module rails, the fastening hole is seated in close proximity to the long side of the rectangle. 
     A very accurate fit of the module rails in the fastening elements of the side walls is realized if the module rails are provided with milled fixing recesses at both ends in which the fixing pins matingly engage. 
     In order to provide for adaptation to the shape of the fixing pins, the milled fixing recesses are advisably given a trough shape. 
     For reasons of economical manufacture, the length of the milled fixing recesses will only slightly exceed the height of the fixing pins. 
     In order to be able to produce component carriers having module rails spaced at different depths so as to accommodate short circuit boards, an edge row of groups composed of four fixing pins and an associated fastening hole are provided alongside the upper edge and the lower edge of the side walls. 
     In the region of the center of the side walls, two center rows of parallel groups composed of four fixing pins arranged back to back and an associated fastening hole may be provided. This configuration of the component carrier permits the attachment of additional profiled rails in the center to also accommodate reduced height circuit boards at two superposed levels. 
     According to a further, advantageous feature of the component carrier, an additional row of supplemental holes is provided between the two center rows. These supplemental holes are arranged in pairs and lie on the connecting lines of the short sides of the two rectangles. A central profiled rail at the end face is equipped with bores and, utilizing one of the supplemental holes on each side, is screwed to the respective side wall; its cross-sectional profile engages matingly in the space between the fixing pins of the one group and in the space between the fixing pins of the other group. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described in greater detail for one embodiment thereof and with reference to the two attached drawing figures. The drawings show in: 
     FIG. 1, a simplified perspective view, to a reduced scale, of a component carrier equipped with module rails for circuit boards that are insertable on guide rails; 
     FIG. 2, an enlarged perspective view of part of a module rail of the component carrier of FIG. 1; 
     FIG. 3, a detail view marked &#34;X&#34; of the (rear) side wall of the component carrier of FIG. 1, including a group of fastening elements according to the invention composed of four fixing pins and a fastening hole; 
     FIG. 4, a vertical sectional view of a component carrier corresponding to FIG. 1, approximately in actual size, including two front and two rear module rails and a profiled rail fastened in the center. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The component carrier 1 shown in FIG. 1 is intended to accommodate a larger number of insertable circuit boards 2 which are equipped with electrical and electronic components (not shown). Component carrier 1 is composed of two rectangular, parallel side walls 3 and 4, two front module rails 5 and 6 and two rear module rails 7 and 8. 
     The four module rails 5 to 8, which are manufactured of drawn aluminum, connect the two side walls 3 and 4 with one another. Upper and lower guide rails 9 and 10 are clamped by means of resilient clamping elements to each front module rail 5 and 6 and one rear module rail 7 and 8, respectively, transversely to module rails 5 to 8, with these clamping elements being snapped into rows of equidistant long holes 11 provided in the longitudinal direction of module rails 5 to 8. 
     The identically configured guide rails 10 which are pressed of plastic are provided at their upper sides with a guide groove 12 for the circuit boards 2 to be inserted. This guide groove is equipped with hole arrangements 13 for the components (not shown). 
     For fastening of module rails 5 to 8, the side walls 3 and 4 are provided with groups 14 of fastening elements. Each one of these identically configured groups 14 includes four fixing pins 16, 17, 18 and 19 which are disposed in the corners of a rectangle 15--indicated in dashed lines in FIG. 3--so as to form two pairs 16, 17 and 18, 19. These fixing pins 16 to 19 project from the two interior faces of side walls 3 and 4. Each one of groups 14 has an associated fastening hole 20 (FIG. 3). These fastening elements serve to fasten module rails 5 to 8 to the side walls 3 and 4 of component carrier 1. 
     The end face 21 of each module rail 5 to 8 (see FIG. 2) is provided with a blind bore 22 that is provided with an internal thread and serves to receive a fastening screw 23 passing through fastening hole 20. Module rails 5 to 8 have a profile in which, when module rails 5 to 8 are screwed to side walls 3 and 4, fixing pins 16 to 19 lie against their long sides in such a way that parts of the profile engage matingly in the spaces 24 between each pair 16, 17 and 18, 19, as indicated in FIG. 4. The four fixing pins 16 to 19 have the shape of a circular cylinder, see FIG. 3. 
     The fastening hole 20 of each group 14 of the fastening elements lies in the extension of the short centerline 25 of rectangle 1 in the direction toward the edge of side walls 3 and 4 and is seated in close proximity to the long side 26 of rectangle 15. The long side 26 of the narrow rectangle 15, in whose corners the four fixing pins 16 to 19 are arranged is three times longer than its short side 27. 
     Module rails 5 to 8 are provided with milled fixing recesses 29 and 30--see FIG. 2--at their two sides 28 in an arrangement which corresponds to the profile of module rails 5 to 8. When module rails 5 to 8 are installed, fixing pins 17 and 19 lie against the sides of the recesses in a mating manner. The two oppositely disposed fixing pins 16 and 18 here contact the sides of module rails 5 to 8 at the corresponding locations. The depth of milled fixing recesses 29 and 30 may be selected so that the profiles of module rails 5 to 8 more or less tightly sit in the spaces 24 between the two pairs 16, 17 and 18, 19 of fixing pins 16 to 19. 
     Milled fixing recesses 29, 30 at the ends 28 of profiled rails 5 to 8 are given a trough shape; their cross section is semi-circular and corresponds to the circular cross section of fixing pins 16 to 19. The length 1 of milled fixing recesses 29, 30 only slightly exceeds the height h of fixing pins 16 to 19. 
     As can be seen particularly well in the vertical sectional view of the component carrier 1 shown in FIG. 4, an edge row 31 of groups 14 comprising four fixing pins 16, 17, 18, 19 that project toward the interior and an associated fastening hole 2 is provided along each of the upper edges 32 and the lower edges 33 of side walls 3, 4. The four module rails 5, 6, 7 and 8 are fastened to side wall 4 and their profiles matingly engage in the spaces 24 between each pair 16, 17 and 18, 19 of the four fixing pins 16 to 19. In FIG. 4, the two front module rails 5 and 6 have a somewhat differently configured profile than the two rear module rails 7 and 8. 
     In the center of side walls 3 and 4, two center rows 34 and 35 of parallel groups 14 each composed of four fixing pins 16 to 19 and one associated fastening hole 20 are provided back to back. With the aid of these two rows of fasting elements, two further central front module rails and two further central rear module rails (not shown) can be fastened between the two side walls 3 and 4 to which corresponding guide rails (not shown) can be clamped. In this way, component carrier 1 can be equipped with circuit boards of a lower height at two superposed levels. 
     Between the two center rows 34 and 35 of groups 14 of fastening elements, an additional row 36 of supplemental holes 37 and 38 is provided in side walls 3 and 4. These supplemental holes are arranged in pairs between the respective back-to-back groups 14 and lie on the connecting lines 39 between the short sides 27 of the two rectangles 19. By using one of the two supplemental holes 37, a profiled rail 40 is disposed at side walls 3 and 4. It carries a central, end-face bore 41 for a screw 42 provided for fastening it to side wall 4. 
     Profiled rail 40 has an essentially U-shaped cross-sectional profile, with a bore 41 being provided in its thickened U-base. As can be seen in FIG. 4, the two legs of the U of the cross-sectional profile of the installed profiled rail 40 engage matingly in the space 24 between the fixing pins of the one group 14 as well as in the space 24 between the fixing pins of the other group 14. This profiled rail 40 which is provided as a center support for rear wall plates is also provided with milled fixing recesses 43 that are disposed at the interior faces of the two legs of the U and may be fastened, based on the proposed arrangement of two supplemental holes 37 and 38, selectively so as to be oriented toward the front or toward the back. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.