Abstract:
A rear frame for a motor vehicle has a profile part manufactured from cast metal. The profile part has two legs, which are connected to one another via a cover element, and an attachment element. In this way, the rear frame has a particularly high stability and may be manufactured particularly cost-effectively.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application No. 102008059274.9, filed Nov. 27, 2008, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The invention relates to a rear frame for a self-supporting vehicle body of a motor vehicle having a girder and having a profile part of the girder, which has multiple legs, and a vehicle body of a motor vehicle having such a rear frame. 
     BACKGROUND 
     In rear frames, the girders are frequently manufactured from sheet-metal profiles and are known from practice. The rear frames are incorporated into a vehicle body comprising sheet-metal shells. To manufacture such girders, a plurality of plates is stamped and deep-drawn. The plates are subsequently connected to one another in a welding method, for example. The number and the concrete configuration of the plates is required in order to ensure the stability of the girder and in particular produce sufficient crash safety of the entire rear frame. In addition, attachment elements are fastened to the girders to attach auxiliary frames or spring struts. The known rear frame thus requires complex manufacturing. Unnecessary material accumulations, which result in an increased weight, arise due to the overlap of the plates required for welding. 
     Vehicle bodies are also known in which individual node points of the vehicle body comprise cast parts, while the frame parts connecting the nodes are implemented in sheet-metal shell construction. In addition, implementing the front crossbeam of a vehicle body as a cast part is known. 
     The invention is based on at least the problem of refining a rear frame of the type cited at the beginning so that it is particularly simple to produce and has high stability. 
     SUMMARY 
     This problem is solved according to an embodiment of the invention in that the profile part is manufactured from cast metal. 
     The form of the girder may be selected essentially freely through this design. Furthermore, in a single component, a closed box profile or profiles deviating from a box profile may be generated with little effort. In this way, the rear frame according to an embodiment of the invention is producible particularly cost-effectively. Furthermore, this results in particularly high bending rigidity and torsion rigidity of the rear frame according to an embodiment of the invention. The particularly high rigidity results in high crash safety and driving safety of the motor vehicle having the rear frame according to an embodiment of the invention. 
     Of course, components to be connected to the profile part may be produced using nearly arbitrary methods. It contributes to further reducing manufacturing costs of the rear frame according to an embodiment of the invention if a cover element, which connects the legs of the profile part, is manufactured from cast metal. The cover element forms a box shape having particularly high bending rigidity together with the profile part through the connection of the legs. 
     For example, the cover element may be welded to the profile part. It contributes to reducing the processing steps for manufacturing the girder, however, if the cover element is integrally cast with the profile part. The profile part and/or the cover element preferably have recesses and/or cross-sectional changes for weight reduction and for targeted influence of the rigidity. Such recesses may be generated easily in the cast metal during the manufacturing in the casting method. No further method step for weight reduction is necessary according to the production method in this way. 
     According to another embodiment of the invention, it contributes to reducing the manufacturing costs of the girder if an attachment element provided for attaching a further component to the girder is integrally manufactured with the profile part from cast metal. The integral manufacturing of the attachment element contributes to reducing the number of components to be joined to the rear frame according to an embodiment of the invention. During the assembly of the rear frame according to an embodiment of the invention, the further component can simply be moved toward the attachment element and subsequently welded or screwed thereto. The attachment element thus contributes to simplifying the assembly of the rear frame. Furthermore, the girder can be manufactured correctly for the load in a particularly simple manner by an appropriate design of a casting mold for manufacturing the attachment element integrally cast with the profile part. Further reinforcements, as in sheet-metal shell constructions, are not necessary thanks to the embodiments of the invention. 
     The rear frame according to an embodiment of the invention has a particularly high stability if the attachment element is implemented as an attachment flange for a crossbeam. 
     The construction effort for introducing operating forces of the motor vehicle into the rear frame according to an embodiment of the invention may be kept particularly low if the attachment element is implemented as a spring plate for supporting a spring element of a rear wheel of the motor vehicle. 
     According to another advantageous embodiment of the invention, the attachment element contributes to increasing the rigidity of the girder if the attachment element, which is implemented as a spring plate, is made conical and extends over a subarea of the leg. 
     An auxiliary frame for receiving various components in the rear area of the motor vehicle may be easily installed according to another advantageous embodiment of the invention if the attachment element is implemented as a bearing bush for a rear axle auxiliary frame. A substantial advantage of this design is additionally that the multiple bearing eyes are situated on a common girder. In this case, the integral manufacturing of the components of the girder with the bearing eyes results in a reduction of tolerances, because the bearing eyes are on a common component. The bearing bush can be a bearing eye, a screw bush, or another arbitrarily designed element for attaching the auxiliary frame, for example. 
     The attachment of the girder to a plate, in particular a side plate or a floor plate of the motor vehicle, is particularly simple according to an advantageous embodiment of the invention if the cover element forms a box shape with a base of the profile part which connects the ends of the legs and if a connection flange is situated on the free ends of at least one of the legs. This connection flange may be generated in the casting method of the profile part and in this way does not require any further processing steps. The connection flange can be angled from the at least one leg or protrude linearly beyond the cover element and allows the simple welding to the plate. The plate preferably connects connection flanges situated on both legs and thus contributes to stiffening the girder. 
     It contributes to further increasing the stability of the rear frame according to an embodiment of the invention if threaded bolts for screwing the girder to a further component connect the cover element and the profile part to one another. This design is suitable in particular for attaching a rear wheel suspension arm to the girder. This rear wheel suspension arm may be screwed on easily using the threaded bolts. 
     The rear frame according to an embodiment of the invention has a particularly low weight if the cast metal is a light metal. 
     The girder of the rear frame according to an embodiment of the invention may be connected easily to adjoining components in a welding method if the cast metal is a cast steel and has a wall thickness of approximately 1 to 5 mm. 
     At least one object of the invention is also a self-supporting vehicle body, which is manufactured in sheet-metal shell construction, of a motor vehicle having a rear frame, as previously described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  shows a motor vehicle having a rear frame according to an embodiment of the invention; 
         FIGS. 2-4  show multiple embodiments of girders of the rear frame according to an embodiment of the invention from  FIG. 1 ; 
         FIG. 5  shows an attachment of a crossbeam to a girder of the rear frame according to an embodiment of the invention from  FIG. 1 ; 
         FIG. 6  shows an attachment of an auxiliary frame to a girder of the rear frame according to an embodiment of the invention from  FIG. 1 ; 
         FIG. 7  shows an attachment of a spring element to a girder of the rear frame according to an embodiment of the invention from  FIG. 1 ; and 
         FIG. 8  shows an attachment of a rear axle suspension arm to a girder of the rear frame according to an embodiment of the invention from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
       FIG. 1  shows a motor vehicle having a motor vehicle body and having a rear frame  1  of the motor vehicle body in a side view. The motor vehicle has two front wheels  2  and two rear wheels  3 . The rear wheels  3  are linked to a girder  4  of the rear frame  1 . 
       FIG. 2  shows a subarea of the girder  4  of the rear frame  1  from  FIG. 1  in perspective. The girder  4  has a profile part  5  and a cover element  6 . The profile part  5  has a base  7  having legs  8 ,  9  protruding from the base  7 . The cover element  6  connects the legs  8 ,  9  in a central area. The girder  4  has a bend  10  for guiding it laterally past the rear wheels  3  from  FIG. 1  and is manufactured integrally from cast metal. 
       FIG. 3  shows a further embodiment of the girder  4  of the rear frame  1  from  FIG. 1  in perspective. It differs from that from  FIG. 2  in that the cover element  6  is fastened to the free ends of the legs  8 ,  9  spaced apart from the base  7  of the profile part  5 . Otherwise, the girder  4  is constructed as described in  FIG. 2 . 
       FIG. 4  shows a further embodiment of the girder  4  of the rear frame  1  from  FIG. 1  in perspective, having recesses  11  situated in the cover element  6  to save weight. Furthermore, connection flanges  12 ,  13  are situated on the ends of the legs  8 ,  9  facing away from the base  7 . A plate  14  can be fastened on these connection flanges  12 ,  13 . The plate  14  is shown for exemplary purposes by dot-dash lines here and connects the two connection flanges  12 ,  13  of the legs  8 ,  9  to one another. Otherwise, the girder  4  is constructed as described in  FIG. 2 . 
       FIG. 5  shows the girder  4  of the rear frame  1  from  FIG. 1 , in which an attachment element  15  is implemented as an attachment flange for attaching a crossbeam  16  and is manufactured integrally with one of the legs  8 . The attachment element  15  is situated at the height of the cover element  6 , so that the crossbeam  16  is led up into the girder  4 . The crossbeam  16  can be constructed like the girder  4  described in  FIGS. 2 through 4 , of course. The crossbeam  16  is shown schematically by dot-dash lines to simplify the drawing. 
       FIG. 6  shows the girder  4  of the rear frame  1  from  FIG. 1 , in which multiple attachment elements  17 ,  18  are implemented as bearing bushes for an auxiliary frame  19 . The auxiliary frame  19  connects the attachment elements  17 ,  18  and is shown very simplified by dot-dash lines in the drawing. 
       FIG. 7  shows the girder  4  of the rear frame  1  from  FIG. 1 , in which an attachment element  20  is implemented as a spring plate. A spring element  21 , shown by dot-dash lines, for supporting the rear wheels  3  from  FIG. 1 , is supported on the attachment element  20 , which is implemented as a spring plate. The attachment element  20  is shaped conically and is guided over a subarea of the legs  8 ,  9  of the profile part  5 . 
       FIG. 8  shows the girder  4  of the rear frame  1  from  FIG. 1 , in which multiple threaded bolts  22  for attaching a further component  23 , shown by dot-dash lines in the drawing, connect the cover element  6  and the base  7  of the profile part  5  to one another. 
     While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.