Patent Publication Number: US-6702346-B2

Title: Bumper beam arrangement

Description:
TECHNICAL FIELD 
     This invention relates to a bumper beam arrangement for a vehicle, comprising a bumper beam that has an open profile with a top end and two sides, wherein the beam is mounted on two crash boxes, which protrude into the profile and are mounted to the top end of the profile. 
     DESCRIPTION OF PRIOR ART 
     To mount bumper beams in crash boxes is known for example from EP-0763448 A1, DE-19537186 A1, DE-4127381 A1, and U.S. Pat. No. 3,998,485 A1. The crash boxes take up energy in a crash by being plastically deformed axially. The strength of the crash boxes can be designed for high-speed crashes, but crash boxes can alternatively be designed for low speed crashes. 
     U.S. Pat. No. 3,998,485 A1 shows crash boxes for low speed crashes in the form of tubes with a constant cross section, in which a bumper beam with a U-formed cross section is mounted. When a crash box is axially compressed, the two sides of the bumper beam will be forced into the body of the vehicle and cause damages also in a crash at very low speed. In a light offset crash on one of the crash boxes, this crash box will be axially compressed while the bumper beam will practically not be deformed. Yet, the bumper beam will damage the vehicle body. Conical crash boxes are shown at the rear of the tube formed crash boxes and these conical crash boxes are adapted not to be deformed until the tube formed crash boxes have been compressed. 
     Bumper beams having hat profile are shown for example in WO-94/0770. 
     OBJECT OF INVENTION 
     It is an object of the invention to reduce the risk of damage on the body in low velocity crashes and in particular in such offset crashes. To this end, the crash boxes taper off and protrudes into the profile with their narrow ends so that the crash boxes force the sides of the profile to widen the profile and make it flatter when the crash boxes are axially compressed. The invention is defined by the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a bumper beam of a passenger vehicle, mounted to the vehicle in accordance with the invention. 
     FIG. 2 is a section taken along the line  2 — 2  in FIG.  1  and it shows one of two crash boxes shown in FIG.  1 . 
     FIGS. 3-6 correspond to FIG. 2, but they are shown in various stages of compression of the crash box shown in FIG. 2 when the bumper beam hits a barrier. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows one end of a vehicle, for example a passenger car, which has a bumper beam  11  mounted in two crash boxes  12 , 13 , which are mounted in a structural part of the vehicle body. In the figures, the crash boxes are shown mounted on the ends of the side rails (side beams)  15 , 16  of the vehicle body. In the figure, a panel  17  is shown, which may be a front panel or a rear panel of the vehicle and such a panel has often an enlargement  18  in the middle so as to give place for a radiator or a spare wheel. The bumper beam is usually curved as shown in order to give place for such an enlargement  18 . A non-illustrated shell of plastics usually hides the bumper beam. 
     FIG. 2 is a section through the crash box  12  and the bumper beam  11  and it is taken along line  2 — 2  in FIG.  1 . The bumper beam  11  has an open profile shown as a hat profile with a crown comprising a top or central flange  20  and two sides or webs  21 , 22  that end in two side flanges (brims)  23 , 24 . The bumper beam  11  is mounted with its top end  20  in one end of the crash box  12  so that the crash box extends into the bumper beam and fills out a major part of the cross section of the bumper beam. The crash box  12  may have a round, rectangular or square cross section and it widens towards its mounting to the vehicle as shown so that it is wider at its base than the distance between the two sides of the bumper beam. It has deformation guides  25 . 
     The FIGS. 3-6 show in a sequence the compression of the crash box  12  when the bumper beam hits a barrier  28 . The crash box folds and the folds forces the sides  21 , 22  of the bumper beam outwards so that the bumper beam flattens out. Therefore, the sides of the bumper beam will not hit the panel  17 . In low velocity crashes and in particular in low velocity off-set crashes on only one of the crash boxes, the crash box and the bumper beam will be the only parts that are damaged. The other parts of the vehicle, that is, the panel  17  in FIG. 1, will not be damaged.