Area of technology of the invention

The invention relates to a bumper beam having a hat-shaped profile, with a central flange and sides which have side flanges, wherein the central flange faces inward toward the vehicle, and the side flanges face outward from the vehicle, and the hat-shaped profile has a cover which is recessed into the hat-shaped profile and gives it a closed profile.

Background of the invention

EP1027231 illustrates such a bumper beam which has a cover which is welded to the flanges of the hat-shaped beam and is bent down into the hat- shaped profile in order to accommodate an energy-absorbing foam body.

Object of the invention An object of the invention is to control the deformation behaviour when collision stress is experienced.

Brief description of the invention According to the invention, the cover is welded to the sides of the hat- shaped profile, inside the profile. As a result of this, the cover stiffens the beam cross section and prevents collapse of the sides of the beam. The invention is defined by the claims. Brief description of the drawings

Figure 1 is an isometric view of a bumper beam, illustrating an exemplary embodiment of the invention; Figure 2 shows the bumper beam according to Fig. 1 , with its two elements separated; and

Figure 3 is a cross section through line 3 in Fig. 1.

Description of a the illustrated and preferred embodiment of the invention

The bumper beam of metal comprises a hat-shaped profile 11 and a cover 12. The hat-shaped profile is curved, and has a cross section which varies along the length of the profile. The profile has two fastening portions 13 and 14 for fastening the bumper beam to the vehicle.

The hat-shaped profile has a central member 15 and side members 16 and 17 which end in side flanges 18 and 19. The side flanges have reverse mem- bers 20 and 21. At the fastening portions, the sides of the hat-shaped profile have horizontal depressions 22-26 which extend in the longitudinal direction of the vehicle. The cover has vertical depressions 27-30 at the locations of the fastening portions 13 and 14, and horizontal depressions 31 and 32 between the fastening portions. The various depressions serve to reinforce the bumper beam and to im- prove its deformation behaviour in the various collision loads which may be experienced. The cover is recessed in the hat-shaped profile and is welded to the sides 16 and 17 inside the hat-shaped profile, with welds 33 and 34. The welds 33 and 34 support the sides 16 and 17 of the hat-shaped profile, and delay buckling of the sides 16 and 17 under collision stresses, and the beam is then deformed in a more advantageous manner, thereby increasing the absorption of energy. This enables use of a higher profile and/or a smaller sheet thickness, thereby saving weight while maintaining performance.

Both the cover and the hat-shaped profile are fabricated from hot- formed or cold-formed steel steel. Advantageously, the hat-shaped profile can be fabricated using the press-hardening technique, but the cover can be cold formed because the cover need not have as high an ultimate strength as the hat-shaped profile. The cover does not cover the end regions of the hat-shaped profile beyond the fastening portions; however, alternatively the cover may cover the entire hat-shaped profile.