Abstract:
A door impact beam for a motor vehicle includes a formed metal sheet defined by a longitudinal axis and having a tubular cross section which has a closed circumference in a center portion of the metal sheet, and is configured with open circumference at both end portions of the metal sheet which adjoin the center portion in a direction of the longitudinal axis. Each end portion is defined by an opening angle which continuously increases from the center portion to respective ends of the end portions.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application, Serial No. 10 2009 011 378.9, filed Mar. 5, 2009, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     The present invention relates, in general, to a door impact beam. 
     The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
     Door impact beams are used in motor vehicles as door reinforcement to protect occupants from injury in the event of an impact from the side, and are typically made of tubes or tubular cross sections, for example extrusion profiles or also press parts. Tubular cross sections have the drawback that in areas in which stress is less they generally have a same cross section as in those areas which encounter maximum stress. For that reason, tubular profiles have been oversized in some areas. To optimize weight, it is therefore required to subsequently cut the tubular cross sections to size, causing separate manufacturing steps. This in turn adversely affects manufacturing costs. 
     It would therefore be desirable and advantageous to provide an improved door impact beam which obviates prior art shortcomings and is simple in structure with optimum weight and which can be produced in a cost-efficient manner. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a door impact beam for a motor vehicle includes a formed metal sheet defined by a longitudinal axis and having a tubular cross section which has a closed circumference in a center portion of the metal sheet, and is configured with open circumference at both end portions of the metal sheet which adjoin the center portion in a direction of the longitudinal axis, each said end portions defined by an opening angle which continuously increases from the center portion to respective ends of the end portions. 
     The final configuration of the door impact beam is already established by the contour of the metal sheet which has been cut to size, i.e. there is no need for a later manufacturing step. The weight is optimized therefore beforehand. The manufacturing process is more cost-efficient than would be the case when a tubular structure has to be cut to size later. 
     According to another advantageous feature of the present invention, a reinforcement plate can be arranged in the center portion along an inner side of the metal sheet and may extend about a circumferential area of less than 360°. The reinforcement plate bears flatly upon and is secured to the later inner side of the door impact beam of the metal sheet which is still unformed but cut to size. The reinforcement plate may be connected to the metal sheet by material union or formfittingly, e.g. through welding, clinching/compression. A subsequent forming step involved a forming of the patched metal sheet in such a way that the center portion has a closed cross section whereas the end portions have an open, round cross section. Also the reinforcement plate receives its final configuration during forming of the metal sheet. The forming process is preferably executed in two stages. In a first stage, the metal sheet is formed into a U-shape. The second stage involves the shaping into the partly closed O-shaped cross sectional contour. 
     The opening angle of the end portions increases from the central portion of the door impact beam to the ends of the end portions. The increase is advantageously continuous in the absence of jumps so as to prevent stress peaks. The cross sectional configuration, i.e. the radius, the elliptic or, when overlap is involved, helical contour of the cross section remains hereby preferably constant. 
     In an unformed initial state, the center portion of the metal sheet may have a rectangular geometry with preferably parallel length sides, followed in longitudinal direction by trapezoidal end portions, respectively, which taper to their free end. 
     The transition between the end portions and the central portion may be configured in such a way that the distance of the length sides of the end portions in this transition is smaller than a width of the center portion. Thus, there is a stepped width with a stepped jump in the transition. It is, of course, also conceivable to make the distance of the length sides the same as the width of the center portion. 
     The reinforcement plate arranged in the center portion of the door impact beam may conform to the geometry of the center portion and also configured in the form of a rectangle. In this case, the reinforcement plate is spaced from the length sides in the center portion and has a length which corresponds to 40% to 100%, preferably 40% to 70%, of a length of the center portion. A flat contact of the reinforcement plate upon the center portion provides a local reinforcement of the door impact beam at a location where maximum stress is encountered in the event of a side impact. The wall thickness of the metal sheet can be reduced by optimizing the cut and suitable positioning of the reinforcement plate, resulting overall in a weight reduction. 
     According to another advantageous feature of the present invention, the metal sheet may have length side zones which overlap in the center portion. It may also be conceivable to shape the metal sheet in such a way that the length sides are end-to-end in the center portion. Both cases result in a center portion of the door impact beam having the closed and in relation to the end portions more stable cross section for attaining the necessary stiffness. The length side zones or the length sides of the metal sheet can then be connected to one another, e.g. welding, locally in two regions through material union. 
     After the forming process, the end portions have a toroidal cross section. As a consequence of the trapezoidal shape of the end portions in the unformed state, an opening angle increases in a direction towards the free ends of the end portions. The opening angle may theoretically start at 0°, preferably it may start in a range from 10° to 100°. At the free ends of the end portions, the opening angle may range between 120° and 180°, so that the required stability of the door impact beam is still ensured also at the end portions. Advantageously, the opening angle is 180°. To optimize the door impact beam, the end portions may be configured differently, for example with respect to their length. 
     According to another advantageous feature of the present invention, the opening angle of the reinforcement plate, realized during forming, may be greater than the opening angle of the end portions in the transition to the center portion. In this way, the section modulus is especially high in the center portion. Of course, it is not precluded within the scope of the invention to select the angle identical or smaller when the door impact beam should be less stiff. 
     The geometry of the door impact beam is governed by the cut of the metal sheet so that additional refinishing operations can be omitted in order to optimize weight. It is also conceivable within the scope of the invention, to provide fastening brackets directly, when the metal sheet is cut to size, for allowing attachment of the door impact beam to a door structure. The fastening brackets are brought into the desired position, when the metal sheet is formed. Of course, it is also possible to provide fastening brackets as separate components on the free ends of the end portions. This causes, however, an additional manufacturing step. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
         FIG. 1  is a schematic illustration of an unformed metal sheet for a door impact beam; 
         FIG. 2  is a side view of the metal sheet of  FIG. 1  after undergoing a forming process; 
         FIG. 3  is a cross section of one variation of a formed metal sheet; 
         FIG. 4  is a cross section of another variation of a formed metal sheet; 
         FIG. 5  is a side view of a formed metal sheet; 
         FIG. 6  is a cross section of end portions of the metal sheet, taken along the line I-I in  FIG. 5 ; 
         FIG. 7  is a cross section of end portions of the metal sheet, taken along the line II-II in  FIG. 5 ; 
         FIG. 8  is a schematic illustration of a free end of an end portion; and 
         FIG. 9  is a schematic illustration of a formed metal sheet with press parts. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
     Turning now to the drawing, and in particular to  FIG. 1 , there is shown a schematic illustration of a metal sheet, generally designated by reference numeral  1 , in its still unformed initial state, for producing a door impact beam. The metal sheet  1  has a center portion  2  of rectangular shape. Adjoining both sides of the center portion  2  in longitudinal direction are trapezoidal end portions  3 ,  4 , respectively. The end portions  3 ,  4  have length sides  5 ,  6  at distances A 1 , A 2  which are greater in a transition  7  to the center portion  2  than at the free ends  8 ,  9  of the end portions  3 ,  4 . In this non-limiting exemplified embodiment, the distances Al, A 2  for both end portions  3 ,  4  are of same size. Of course, it is equally conceivable to make the distances from end portion to end portion different. 
     The distance A 2  of the length sides  5 ,  6  in the transition  7  to the center portion  2  is smaller than a width B 1  of the center portion  2 . In accordance with another, not shown, embodiment, a distance of the length sides of the end portions may be made of same size in the transition to the center portion as the width of the center portion in order to attain a transition, substantially free of notch stress, from the end portions to the center portion. 
     A reinforcement plate  10  bears approximately in the middle of the center portion  2  flatly upon the later inner side  11  of the metal sheet  1  and has a length L 1  ( FIG. 2 ) which is about 50% of a length L 2  of the center portion  2 . In addition, the reinforcement plate  10  has a width B 2  which is smaller than a width B 1  of the center portion  2  so that the reinforcement plate  10  does not extend beyond the length sides  12 ,  13  of the center portion  2 . As a result, the door impact beam is reinforced at a location where maximum stress can be expected. 
       FIG. 2  shows a side view of the metal sheet  1  after the latter has been shaped into a tubular profile with circular cross section. As a consequence of the trapezoidal configuration of the end portions  3 ,  4 , the latter taper continuously starting from the transition  7  to the free ends  8 ,  9 . The length sides  5 ,  6  of the end portions  3 ,  4  and an imaginary prolongation of the length sides  12 ,  13  of the center portion  2  define hereby angles W 1 , W 2 , respectively, of at least 10° at the free ends  8 ,  9  of the end portions  3 ,  4 . The angles W 1 , W 2  of the end portions  3 ,  4  may hereby differ, for example as a consequence of a different length of the end portions  3 ,  4 . The door impact beam may therefore be configured asymmetric in relation to its transverse center axis MQE. 
       FIG. 3  shows a cross section of center portion  2  of a formed metal sheet  1  with a round, tubular cross section. The inner radius is designated with R. In this embodiment, the metal sheet  1  has been shaped in such a way that the length side zones  14 ,  15  of the metal sheet  1  overlap. It can be seen that the reinforcement plate  10  does not extend beyond the length side zones  14 ,  15  of the center portion  2  but rests evenly and flatly upon the inner side  11  of the metal sheet  1 . The opening angle W 3  of the reinforcement plate  10  and the radius R can be defined by the degree of overlap of the length side zones  14 ,  15 . 
     A further possibility of a cross sectional configuration of the metal sheet  1  is shown in  FIG. 4 . In this case, the metal sheet  1  is shaped in such a way that the length sides  5 ,  6  are joined end-to-end. In this embodiment, the opening angle W 3  is greater than the opening angle W 3  of the reinforcement plate  10  of  FIG. 3 . 
     The joining process for the embodiment of  FIG. 3  as well as for the embodiment of  FIG. 4  may be realized through material union for example. 
       FIG. 5  shows a side view of the formed metal sheet  1  of  FIG. 4  with two section planes I-I and II-II. 
       FIGS. 6 and 7  show cross sections of the section planes I-I, of the end portions  3 ,  4  of  FIG. 5 . As can be seen, the opening angle W 4  of the end portions  3 ,  4  is smaller in the transition  7  to the center portion  2  than the opening angle W 3  of the reinforcement plate  10 . As a consequence of the trapezoidal shape of the end portions  3 ,  4 , the opening angle W 4  is greater to the free ends  8 ,  9  than the opening angle W 3  of the reinforcement plate  10 , however not greater than 180°. 
       FIG. 8  shows a free end  16  of an end portion  17  formed in one piece with attachment brackets  18  for securement of the door impact beam to a door. The attachment brackets  18  may be provided already at a time when the basic shape of the unbent metal sheet is cut. 
       FIG. 9  shows a door impact beam in accordance with the invention with separate attachment brackets  19  at the free ends  20 ,  21  of the end portions  22 ,  23  for attachment to a door. 
     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 
     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: