Abstract:
A longitudinal beam for a motor vehicle and also to a method for the production of the longitudinal beam is disclosed. The longitudinal beam is produced from a lightweight metal profile. The extrusion direction of the lightweight metal profile runs transverse to the longitudinal direction of the longitudinal beam.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority from German Patent Application Number 10 2016 101 158.4, filed Jan. 22, 2016, the disclosure of which is hereby incorporated by reference herein in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a longitudinal beam for a motor vehicle as per the features in the preamble of Patent claim  1 . 
         [0003]    The present invention furthermore relates to a method for the production of such a longitudinal beam as per the features in the preamble of Patent claim  11 . 
       BACKGROUND OF THE INVENTION 
       [0004]    It is known from the prior art to assemble longitudinal beams in motor vehicles and to produce self-supporting motor vehicle bodies. These self-supporting motor vehicle bodies are mostly produced in this context from metallic materials. In particular, steel materials, but also lightweight metal materials, are used here. An aluminum alloy is used with preference as the lightweight metal material. 
         [0005]    At the front or at the rear, a self-supporting motor vehicle body of this type comprises longitudinal beams. The longitudinal beams serve on the one hand for producing a connection to cross-members arranged at a front or rear end, in particular incorporating crash boxes. However, the longitudinal beams also serve, for example, for receiving an axle subframe, but also an engine and/or gear mechanism. 
         [0006]    A longitudinal beam is formed as an elongate component profiled in cross section. A longitudinal beam can also be formed as a closed hollow profile component. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to specify a longitudinal beam and also a method for the production thereof, said longitudinal beam having a particularly low dead weight and being producible cost-effectively and with economical use of material. 
         [0008]    The aforementioned object is achieved according to the invention by a longitudinal beam for a motor vehicle as per the features in the patent claim  1 . 
         [0009]    The part of the object relating to the method is achieved according to the invention by a method in Patent claim  11 . 
         [0010]    Advantageous embodiment variants are described in the dependent patent claims. 
         [0011]    The longitudinal beam according to the invention for a motor vehicle is formed as an elongate component. It has a profiling in cross section. The profiling can vary in the longitudinal direction. The longitudinal beam is produced by shaping, the starting basis being an extruded lightweight metal profile. The longitudinal beam has differing wall thicknesses in certain length portions. According to the invention, the longitudinal beam is distinguished by the fact that the lightweight metal profile is extruded oriented transversely to the longitudinal direction of the longitudinal beam and was shaped after the extrusion. 
         [0012]    Within the context of the invention, the longitudinal direction does not necessarily have to run exactly at a 90° angle to the extrusion direction of the lightweight metal profile. It is also possible for a deviation of several degrees to prevail, in particular depending on the further processing by press forming, but in particular the longitudinal direction of the longitudinal beam runs oriented transversely to the extrusion direction of the lightweight metal profile. It is therefore preferable that the longitudinal direction of the longitudinal beam runs oriented between 70° and 110°, in particular between 80° and 100°, in relation to the actual extrusion direction of the lightweight metal profile. 
         [0013]    It is therefore possible firstly to extrude a lightweight metal profile having differing wall thicknesses in an extrusion cross section. Said lightweight metal profile is produced with an extrusion width which is smaller than a later processing width and also smaller than the length of the longitudinal beam. The lightweight metal profile is, however, extruded with an uneven extrusion cross section, for example an extrusion cross section running in wave form. 
         [0014]    In a subsequent processing step, said uneven extrusion cross section is widened, in particular flattened. This can be effected, for example, by the application of a compressive force from a top side or a bottom side and/or can be effected by the application of a tensile force at the respective ends of the extrusion cross section. Before or after the flattening or widening, the metal profile is cut to length. This provides semifinished products having a substantially board-like shape. These semifinished products are then processed by shaping, such that the longitudinal beam is provided with its final contour by shaping or by tensile compression shaping, deep drawing or three-dimensional press forming. Consequently, the longitudinal beam is formed as a component of three-dimensionally complex shape with differing wall thicknesses. According to the invention, however, the longitudinal direction of the longitudinal beam is oriented transversely to the original extrusion direction of the lightweight metal profile. This gives rise to the advantage that the wall thickness in certain length portions can be set by the extrusion process specifically to the respective demands in terms of loading, rigidity, crash performance and material use. The extrusion process can preferably be employed in such a manner that a greater wall thickness is produced in those length portions in which provision is made of small cross-sectional widths and/or cross-sectional heights of the later longitudinal beam. A thinner wall thickness can be used in those length portions which have a greater cross-sectional configuration compared to that mentioned above. The cross section of the actual longitudinal beam can then be produced in particular by the shaping. Said cross section can vary in the longitudinal direction. A substantially homogeneous wall thickness is then formed in each case in a cross section, however, with the wall thickness varying in the longitudinal direction of the longitudinal beam. 
         [0015]    It is possible to use conventional extrusion apparatuses capable of extruding extrusion widths of 30 cm, 40 cm, 50 cm. As a result of the flattening or widening which follows said extrusion process, however, it is possible to realize component lengths of more than 100 cm up to 150 cm or even 200 cm, such that the component length preferably corresponds to 1.5 times to 4 times the extrusion width. Wall thicknesses of between 1 mm and 10 mm are preferably extruded. In particular, the thinner wall thicknesses of 1 mm to 5 mm, in particular 1.5 mm to 3 mm, are formed. The greater wall thicknesses are preferably formed between 3 mm and 6 mm, in particular between 3.5 mm and 5 mm. 
         [0016]    In particular, it is therefore possible to produce a longitudinal beam in one piece and from the same material. However, the longitudinal beam can also be formed as a coupled assembly, and here in particular as a welded assembly. In the latter case, it is possible in particular to produce the longitudinal beam at least in certain length portions as a closed hollow profile. To this end, a closing plate is preferably coupled to the longitudinal beam in certain length portions. 
         [0017]    In a preferred embodiment variant of the invention, it is also possible, however, that the two parts of the longitudinal beam are produced in the form of an assembly by the method according to the invention and these two parts are coupled to one another after shaping. This affords the advantage that the two parts each have differing, varying wall thicknesses in certain length portions in a targeted manner for optimized weight. In particular, circumferential grooves can therefore be provided as a support, for example. In particular, these can be formed on the inner side of the hollow profile. It is therefore possible for a targeted compression of the longitudinal beam to be effected in the case of axial force introduction. 
         [0018]    A transition portion is preferably formed between two length portions adjacent in the longitudinal direction. Said transition portion is also referred to as a wall thickness transition. The transition portion furthermore preferably has a width extending in the longitudinal direction of the longitudinal beam, the width being formed so as to be smaller than or equal to 3 times, preferably 1.5 times, the greater wall thickness. Said wall thickness in the longitudinal section merges degressively, linearly or progressively from lesser to greater wall thickness or from greater to lesser wall thickness. This affords the advantage in particular that a corresponding wall thickness transition which does not display a notch effect in the subsequent flattening or widening operation can be produced initially in the extrusion process. Constrictions or cracking are avoided as a result. 
         [0019]    Alternatively, however, it is also conceivable that the wall thickness transition is formed in a step-like manner. The width of the wall thickness transition is therefore extremely small, preferably smaller than 1 mm. The wall thickness transition from lesser to greater wall thickness is made in accordance with the principle of a step and is made in the form of a jump. 
         [0020]    In particular, the greater wall thickness is greater than 1.3 times the lesser wall thickness, preferably greater than 1.5 times the respective adjacent lesser wall thickness. 
         [0021]    It is furthermore particularly preferable that the wall thickness transition is formed on the longitudinal beam only on one side. This means that one side with respect to the wall thickness transition is flat or even and the wall thickness transition is formed on the opposing side. As a result of the extrusion process, it is also possible with particular preference, however, that the wall thickness transition is formed on both sides of the longitudinal beam, consequently on a top side and on a bottom side. This also makes it possible in turn to produce the longitudinal beam with optimized weight and at the same time optimized stability by virtue of targeted variations in the wall thickness. 
         [0022]    In a further preferred embodiment variant, the longitudinal beam has a greater height in certain length portions, in particular in the installed position, compared to an adjacent length portion. In particular, this can be produced by a trimming operation. At the side of the lightweight metal profile which has been cut to length, said profile can be trimmed at the outer contour in such a manner that extensions directed upward or downward with respect to the installed position are formed, in order, for example, to receive add-on parts or the like. 
         [0023]    In addition or as an alternative, the longitudinal beam is formed in particular by coupling with a further part as a closed hollow profile. The longitudinal beam which is actually produced has, however, in particular a C-shaped, U-shaped, W-shaped or hat-shaped cross-sectional profile. The cross-sectional plane of the cross section of the longitudinal beam produced is oriented orthogonally in relation to the cross-sectional plane of the extrusion cross section of the lightweight metal profile. 
         [0024]    It is preferable that at least one length portion of thinner wall thickness is formed as a trigger in a length portion of the longitudinal beam, in particular in an end portion in the longitudinal direction. It is preferable that at least two, in particular three, four or more, length portions of thinner wall thickness are formed. These are spaced apart in parallel, such that, upon introduction of an axial force, a targeted compression or deformation of the longitudinal beam is brought about for energy reduction. The transition portions in the case of the trigger are in the form of a jump in particular and have a small width in the longitudinal direction. 
         [0025]    It is furthermore particularly preferable that an embodiment variant of the longitudinal beam provides that at least one hollow chamber is formed in certain length portions, consequently a cross section on the longitudinal beam is formed as a closed hollow profile. However, a further length portion is formed as an open hollow profile, for example has a C-shaped, W-shaped or hat-shaped form. This is formed in such a manner that a closing plate or a second part is coupled to the first part of the longitudinal beam in the length portion with the closed hollow profile. 
         [0026]    The present invention furthermore relates to a method for the production of a longitudinal beam having at least one of the aforementioned features. The method is distinguished according to the invention by the following method steps:
       extruding a lightweight metal profile with an uneven extrusion cross section and an extrusion width,   widening the extrusion width by flattening and/or pulling to give a processing width,   wherein individual semifinished products are obtained by cutting to length during or after the widening,   press-forming the semifinished product to give the longitudinal beam, wherein a trimming operation is carried out before, during or after the press-forming operation.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Further advantages, features and aspects of the invention are the subject of the following description. Preferred embodiment variants are shown in the schematic figures. These serve for a clear understanding of the invention. 
           [0032]      FIG. 1  shows a longitudinal beam produced according to the invention in a perspective view and also sectional views, 
           [0033]      FIG. 2  shows an optional closing plate for the longitudinal beam shown in  FIG. 1 , 
           [0034]      FIGS. 3 a  to 3 f    show a production method and also a longitudinal beam produced thereby with a closing plate, 
           [0035]      FIGS. 4 a  to 4 f    show a production method and also a longitudinal beam produced thereby in various views, 
           [0036]      FIG. 5  shows a cross-sectional view of the extruded lightweight metal profile, and 
           [0037]      FIGS. 6 a  and 6 b    show a longitudinal sectional view through the longitudinal beam according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0038]    In the figures, the same reference signs are used for the same or similar components, even if a repeated description is avoided for reasons of simplification. 
         [0039]      FIG. 1  shows a longitudinal beam  1  according to the invention in a perspective view. The longitudinal beam  1  has a contour of three-dimensionally complex shape produced by shaping. It can be seen with reference to the lines of intersection A-A and B-B and also the respectively illustrated cross-sectional view that the longitudinal beam  1  is formed at least in certain length portions as an open hollow profile and in particular as a hat-shaped, C-shaped or L-shaped cross-sectional profile. A respectively homogeneous wall thickness prevails in the cross section. 
         [0040]    In its longitudinal direction  2 , the longitudinal beam  1  has differing wall thicknesses W 1 , W 2 , W 3 , W 4 , W 5 , W 6 . This is indicated schematically in the longitudinal sectional view of a corresponding semifinished product  3 . The latter has a semifinished product length  4  which is greater than or equal to the length  5  of the longitudinal beam  1  itself. Shaping of the semifinished product  3  reduces the length  5  of the longitudinal beam  1  with respect to the semifinished products  4 . The wall thickness transitions  6  of the individual wall thicknesses W 1 , W 2 , W 3 , W 4 , W 5 , W 6  in relation to one another are formed only on a top side  7  (shown here). However, they could also be formed alternatively on a bottom side  8  or on the top side  7  and bottom side  8  (not shown in more detail). 
         [0041]      FIG. 1  shows, again by way of example, a transition portion  9  having a width  10  which is preferably smaller than or equal to the greatest adjacent wall thickness W 3 . The wall thickness merges from lesser wall thickness W 2  to greater wall thickness W 3  with a degressive progression. However, the wall thickness can also merge in a step-like manner or in the form of a jump (not shown in more detail). 
         [0042]    Two length portions  12 ,  13  of thinner wall thickness W 4 , W 6  are formed in a front end portion  11 . Upon the introduction of an axial force, these length portions  12 ,  13  can bring about a targeted deformation of the longitudinal beam  1 . They are also referred to as supports. The greater wall thicknesses W 1 , W 3 , W 5  can be the same, but can also differ from one another. The comparatively thinner wall thicknesses W 2 , W 4 , W 6  can likewise each be the same, but can also differ from one another. However, the longitudinal direction  2  is arranged running in a manner oriented transversely to a marked extrusion direction  14  of the lightweight metal profile (not shown in more detail). 
         [0043]      FIG. 2  shows an upper shell  15  for a longitudinal beam according to the invention, in particular as shown in  FIG. 1 . Said longitudinal beam would in this case be formed as the lower shell. The upper shell, too, has differing wall thicknesses W 1 , W 2 , W 3 , W 4 , W 5 , W 6  in its longitudinal section of the semifinished product  3 . These wall thicknesses W 1 , W 2 , W 3 , W 4 , W 5 , W 6  are formed analogously to the wall thicknesses shown in  FIG. 1 . The upper shell  15  and the lower shell for the longitudinal beam as shown in  FIG. 1  can be produced from the same semifinished product  3 . It is preferable, however, that the cut of the outer contour differs. The upper shell  15  and the lower shell are coupled to one another (not shown in more detail), in particular by a thermal joining process. 
         [0044]      FIGS. 3 c  to  f    show a further embodiment variant of a longitudinal beam  1  according to the invention. It can be seen that said longitudinal beam comprises, in its longitudinal direction  2 , length portions which have a greater height H and/or a greater cross-sectional area than adjacent length portions with a comparatively smaller height. By way of example, components (not shown in more detail) such as axles, body components or also engine mounts can be arranged here. It can be seen in particular with reference to the sectional view A-A in  FIG. 3 d    that the longitudinal beam  1  is coupled to a further profile  16  of C-shaped cross section, such that a closed hollow chamber  17  is formed. 
         [0045]      FIG. 3 a    shows a longitudinal sectional view through a widened semifinished product  3  as shown in  FIG. 3 b   . Wall thicknesses W 1 , W 2 , W 3 , W 4 , W 5  which differ from one another in certain length portions in the longitudinal direction  2  of the subsequently produced longitudinal beam  1  can readily be seen. The longitudinal direction is oriented transversely to the extrusion direction  14 . Wall thickness transitions  6  are shown between the individual wall thicknesses W 1 , W 2 , W 3 , W 4 , W 5 , here too, in turn, only on a top side  7 , but not on a bottom side  8 . For the coupling as shown in  FIG. 3 d   , it is advantageous for the bottom side  8  to have no wall thickness transitions. 
         [0046]      FIGS. 4 c  to  f    show a further embodiment of a longitudinal beam  1  in various views. It can be seen that a first part  18  of the longitudinal beam  1  is produced from a semifinished product  3  with wall thicknesses W 1 , W 2 , W 3 , W 4 , W 5  which differ from one another in cross section. A second part  19  in the form of a hollow profile formed with an open cross section is coupled to the first part  18 . This is effected, for example, by thermal joining. This gives rise to a closed hollow chamber  17 . As shown in  FIGS. 4 a  and  b   , a profile  16  is in turn firstly extruded and widened, in order to thereby produce differing wall thicknesses W 1 , W 2 , W 3 , W 4 , W 5  for the first part  18 . 
         [0047]      FIG. 5  furthermore shows an initially extruded lightweight metal profile  20  having an extrusion width  21  and differing wall thicknesses W 1 , W 2 . The extrusion width  21  here is smaller than a processing width  22 , shown by way of example in  FIG. 3 b   . The component length then corresponds to the processing width  22 , or is slightly smaller than the processing width  22  on account of the three-dimensional press forming. 
         [0048]      FIG. 6  shows a longitudinal section through a longitudinal beam  1  according to the invention, with a transition from a greater wall thickness W 1  to a lesser wall thickness W 2 . In the case of  FIG. 6 a   , the wall thickness transition  6  occurs both on the top side  7  and on the bottom side  8  of the longitudinal beam  1  according to the invention. Said longitudinal beam furthermore comprises a transition portion  9  extending by a width  10  in the longitudinal direction  2 , the width  10  being smaller than or equal to 3 times the greater wall thickness W 1 . In the transition portion  9 , the cross-sectional profile merges to the wall thickness W 2  progressively at the top side  7  and degressively at the bottom side  8 . 
         [0049]      FIG. 6 b    likewise shows a transition portion  9  in the form of a wall thickness jump likewise formed on the top side  7  but also on the bottom side  8 . The wall thickness jump  23  therefore has an extent in the longitudinal direction  2  preferably of smaller than or equal to 1 mm. In particular, the jump is made in a step-like manner. The illustrations in  FIGS. 6 a  and  b    can each also be formed only on a top side  7  or only on a bottom side  8 . The extrusion direction  14  is likewise shown. 
       REFERENCE SIGNS 
       [0000]    
       
         
           
               1 —Longitudinal beam 
               2 —Longitudinal direction of  1   
               3 —Semifinished product 
               4 —Semifinished product length 
               5 —Length of  1   
               6 —Wall thickness transition 
               7 —Top side 
               8 —Bottom side 
               9 —Transition portion 
               10 —Width of  9   
               11 —End portion 
               12 —Length portion 
               13 —Length portion 
               14 —Extrusion direction 
               15 —Upper shell 
               16 —Profile 
               17 —Hollow chamber 
               18 —First part 
               19 —Second part 
               20 —Lightweight metal profile 
               21 —Extrusion width 
               22 —Processing width 
               23 —Wall thickness jump 
             H—Height 
             W 1 —Wall thickness 
             W 2 —Wall thickness 
             W 3 —Wall thickness 
             W 4 —Wall thickness 
             W 5 —Wall thickness 
             W 6 —Wall thickness