Abstract:
A bumper system for an automotive vehicle includes a unitary bumper beam substrate which defines upper and lower channel sections which are capped for part of their length by stiffening elements which provide localized increased strength and resistance to elastic buckling and collapsing of the bumper beam.

Description:
TECHNICAL FIELD 
   This invention relates to an automotive bumper having a beam substrate which is locally strengthened to achieve performance characteristics appropriate for the bumpers of automotive vehicles, with reduced weight and cost. 
   BACKGROUND 
   Automotive bumpers must have the capability to manage impact energy without suffering excessive damage. To meet this requirement, most bumper beams have an invariant sectional configuration characterized by longitudinally invariant strength not only in bending, but also in compression and in resistance to buckling. Each of these characteristics must be sufficient to protect a vehicle against excessive damage. However, a bumper having an invariant cross section exhibiting the same bulk operational characteristics as the present inventive bumper, will weigh, and likely cost, more than the present bumper because the impact reaction of a bumper, in compression, for example, occurs primarily through the frame horns. As a result, much of the strength characterizing the entire length of a conventional, longitudinally invariant, bumper is not needed, and cannot be utilized. As a result, the unusable structure is in essence, wasted. 
   The present inventive bumper uses a localized, structurally modified beam substrate to react against impact loading, especially those reacted through the frame horns of a vehicle, while at the same time providing savings in material, weight, and cost. 
   SUMMARY 
   A bumper for an automotive vehicle includes a unitary beam substrate defining a plurality of channels. A plurality of stiffening caps is applied to the plurality of channels, so as to form a plurality of box sections. The present bumper preferably extends laterally across a vehicle. The stiffening caps do not extend across the entire bumper, however, but rather are applied only to portions of the beam substrate extending inboard from either end of the beam. In addition to the stiffening caps applied to the outboard sections of the beam substrate, a center stiffening cap is applied to a midpoint or middle section or center section of the beam substrate. 
   The stiffening caps applied to the outboard sections and, for that matter, the midpoint of the beam substrate, are unitary and are formed as segments joined by longitudinally extending stiffening beads. 
   According to another aspect of the present invention, a beam substrate used in the present bumper includes a generally vertical front face, an upwardly opening channel section cantilevered from an upper portion of the front face, and a downwardly opening channel section cantilevered from a lower portion of the front face. The beam substrate also includes an upper mounting flange extending downwardly from the upper channel section, and a lower mounting flange extending upwardly from the lower channel section. These mounting flanges are used to make a connection with mounting plates which attach the bumper to left and right frame horns of the vehicle. 
   It is an advantage of the present bumper system that superior strength and dynamic performance during impact are achieved with a bumper having lower weight and cost than other prior art bumpers. 
   It is a further advantage of the present invention that the bumper system may be built around a roll formed or extruded beam substrate providing excellent strength, but at lower manufacturing cost, as compared with prior art bumpers. 
   It is a further advantage of the present invention that the performance characteristics of the present bumper may be tuned more readily than is the case with prior art bumpers, because of the ability to change the operating characteristics of the upper and lower stiffening caps applied to the outboard portions of the beam substrate. 
   It is a further advantage of a bumper system according to the present invention that a multiple box beam structure may be created locally, so as to give localized higher performance sections of the resultant bumper beam without the need for maintaining a higher performance section, and concomitant weight and cost, across the entire width of the bumper. 
   Other advantages, as well as objects and features of the present invention will become apparent to the reader of this specification. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an automotive vehicle having a bumper system according to the present invention. 
       FIG. 2  is a perspective view of the inventive bumper system according to the present invention. 
       FIG. 3  is a sectional view of a beam substrate and stiffening caps, taken along the line  3 - 3  of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown in  FIG. 1 , vehicle  10  has bumper  12  with bumper cover  14  providing a finish for the bumper. Bumper cover  14  is applied to bumper beam substrate  16 , which is shown in  FIG. 1  as being attached to left frame horn  18   a , it being understood that bumper beam substrate  16  will also be attached to right frame horn  18   b  ( FIG. 2 ). 
     FIG. 3  is a sectional view of a capped portion of the bumper beam, including substrate  16 , upper stiffening end cap  22 , and lower stiffening end cap  24 . Upper cap  22  is applied to a portion of upwardly opening channel section  44 , and lower cap  24  is applied to downwardly opening channel section  48 . Upwardly opening channel section  44  and downwardly opening channel section  48  are cantilevered from generally vertical front face  40 . Center stiffening cap  30  is shown in  FIG. 2 . 
     FIG. 2  illustrates that stiffening caps  22  and  24  are applied to beam substrate  16  across only portions of substrate  16  extending inboard from the ends of substrate  16  to positions which are slightly inboard from frame horns  18   a  and  18   b . This means that the total weight of caps  22  and  24 , and bumper  12 , will be much less than would be the case were caps  22  and  24  to be applied to the entire longitudinal length of substrate  16 .  FIG. 2  shows further that frame horns  18   a  and  18   b  are equipped with crush zones  20 , which assist in managing longitudinally directed impact loads. 
   Center cap  30  is placed near the midpoint of bumper beam substrate  16 , so as to provide increased torsional, bending, and warping stiffness for bumper  12 . Upper stiffening end caps  22  and lower caps  24  include longitudinal beads  26  ( FIG. 2  see longitudinal direction, “L”), which cause a delay in the elastic buckling of bumper  12  and increase the resistance of beam substrate  16  to axial collapse. In essence, end caps  22  and  24  transform upwardly opening channel section  44 , and downwardly opening channel section  48  into box section beams extending generally horizontally across a portion of vehicle  10 . A similar transformation occurs with respect to mounting plates  34 , which are shown in  FIG. 2  as being attached to upper mounting flange  52  and lower mounting flange  54 . Mounting plates  34  produce a large box beam by enclosing a segment of the rear portion of beam substrate  16 . 
   Controlled axial collapse of bumper  12  is achieved in part through the use of internal collapse zones which are indicated at  22   a  and  44   a  at the upper portion of beam  16 , with  24   a  and  48   a  defining a collapse zone at the lower portion of beam  16 . The impact performance of bumper  12  may be tuned or adjusted by changing the strength of end caps  22  and  24 , without the need for revision of beam  16 . 
   While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.