EP1963138A1

EP1963138A1 - A bumper beam

Info

Publication number: EP1963138A1
Application number: EP06835870A
Authority: EP
Inventors: Martin Weiman
Original assignee: Gestamp Hardtech AB
Current assignee: Gestamp Hardtech AB
Priority date: 2005-12-15
Filing date: 2006-12-15
Publication date: 2008-09-03
Also published as: SE0502759L; WO2007084044A1; EP1963138A4; SE528353C2

Abstract

A bow-shaped bumper beam for vehicles has a hat-shaped profile with a central flange (11), two webs (12, 13) and side flanges (14, 15). The beam has side attachment portions (20, 21) at which the side flanges form attachment surfaces (30- 33) for attachment onto the vehicle with the central flange of the hat profile facing outwards. The central flange is asymmetrically broader at its centre than at the attachment portions, and the web on the side on which the central flange is most narrow has deformation triggers in the form of holes (35, 36) in association with the attachment surfaces.

Description

A Bumper Beam

Technical Field

The present invention relates to a bumper beam, which has a hat-shaped profile with a central flange, two webs and side flanges, wherein the beam has side attachment portions where the side flanges form attachment surfaces for attachment onto the vehicle with the central flange of the hat profile facing outwards.

Aim of the Invention and Brief Description of the Invention

It is an object of the invention to obtain good deformation properties for a bumper beam in the case in which the height of the vehicle's attachment portion does not correspond to the desired height of the bumper beam. The invention is characterised in that the central flange is asymmetrically broader at its centre than at the attachment portions, and in that the web on the side at which the central flange is most narrow has deformation triggers in association with the attachment surfaces.

Brief Description of the Drawings The drawings show a bumper beam that is solely one embodiment of the invention.

Figure 1 is a perspective view of the bumper beam. Figure 2 is a view seen from below. Figure 3 is a view seen from above. Figure 4 is a view seen towards the vehicle. Figure 5 is a section taken along the line 5-5 in Figure 3. Figure 6 is a section taken along the line 6-6 in Figure 3.

Description of Illustrated and Preferred Embodiment

The bow-shaped bumper beam shown in the figures is made of metal. It is appropriate that it is made of hardenable sheet steel that has been hot-stamped and hardened in one step in what is known as the "press-hardening" process. The steel has a high strength, and may have a yield strength greater than 900 MPa (N/mm²), for example greater than 1100 MPa or greater than 1200 MPa. The bumper beam is a hat-shaped beam (it has a hat profile) with a central flange 11 , two webs 12, 13 and two side flanges 14, 15. The bumper beam has an open cross- section. The webs and the central flange form the crown of the hat beam. The central flange has an elongated brace in the form of a longitudinal depression 16. This may extend along the complete length of the bumper beam, as is shown in the drawings, or only along a part of the beam. This longitudinal depression may be deeper than shown and it may in an extreme case be so deep that the beam obtains the profile of a double hat. Alternatively, two narrower longitudinal depressions may be used. The web has a weakened bend 17, 18 that functions as a deformation trigger.

The beam has two attachment portions 20, 21 , where the side flanges have flat parts 30-33, which lie in one plane and have holes 22, 23, 24 such that they can be attached by bolts to flat attachment plates on the vehicle. The webs 12, 13 are highest at their attachment portions and they are lowest in the centre, as is shown by the cross-sections according to Figures 5 and 6. The profile height of the beam in the centre is in the example shown approximately 40% of the maximum profile height. It is appropriate that the profile height at the centre is less than 2/3 of the maximum profile height, and preferably less than half of this height, in order in this way to reduce the weight of the beam. It is, however, desired in certain cases to have a large profile height also in the centre.

The side flanges 14, 15 have edges 26, 27 that are bent upwards along the complete extent between the attachment portions 20, 21 , while the side flanges otherwise lack bent edges. The bent edges make the beam stiffer and provide better deformation properties. The sections 5 and 6 show the profile of the beam, these sections are shown at a uniform scale and are self-explanatory. The web 12 is convex such that the beam obtains an asymmetric cross-section, since the attachment surfaces of the vehicle for the bumper beam are positioned too high to enable the beam to be made symmetrical. Also a number of holes and recesses depend on the design of the particular vehicle and are not described in detail. They may, for example, be adapted for a towing eyelet to pass through the beam or they may be adapted for the positioning of the beam during its mounting. In the event of collision loading, in particular central collision loading, the bumper beam experiences a turning moment due to the fact that it is asymmetric, since the web 12 bulges outwards such that the central flange becomes broader on that side. The other web 13 does not bulge outwards which makes the central flange narrower on that side. The bumper beam tends to twist downwards and inwards when it is placed under load. The web 13 has two holes 35, 36 not only in association with the attachment surface 30 of the side flange 14, but also at its attachment surface 32, i.e. at the attachment portions 20, 21. These holes provide a weakening and they act as additional deformation triggers, initiating the deformation when collision loading occurs. It is appropriate that the holes cut off the weakened bend 17. Twisting of the beam is avoided in that the web 13 is deformed more readily in association with the attachment surfaces than the web 12 is deformed. This entails that the load from the collision that is transferred to the structure lying behind is more evenly distributed between the upper and the lower side flanges 14, 15. By having two (or more) holes that are separated by a narrow band 37, the tolerance is maintained during the forming. It is possible to have one large hole rather than two small holes, but this could reduce the forming tolerance. It is possible alternatively that deformation is initiated by other means than holes, for example by the formation of folds, but the use of holes is preferred.

As is made most clear by Figure 4, the side flanges 14, 15 have been given a transverse dent 29 at all four transitions between their plane portions 30-33 at the attachment portions and their central part with folded-up edges 26, 27. These dents 29 in association with the beginning of the folded-up edges are readily straightened when the beam is bent during a collision, and they reduce in this way the local tension in these sensitive regions of the side flanges, and reduce the risk of cracks forming.

Buckling of the bumper beam gives greater damage the closer to the centre it occurs, since the moment arm relative to the attachment is greatest there. If the profile is strong and does not bend, it would be possible for a thin pole to buckle the profile giving a rapid collapse. If the profile yields more readily, in that it has a profile height that becomes less towards the centre, the buckling will be reduced or delayed, and the motion of the rail towards the vehicle will be reduced. The longitudinal depression 16 provides reinforcement against local buckling of the profile in the middle portion, but it does not hinder yielding.

The beam described above is manufactured from hot-formed and hardened sheet steel, suitably boron-alloyed manganese steel. It may alternatively be manufactured by the cold forming of high-strength cold-forming steel. It does not need to be a functionally open profile as that which is shown; it may have members that couple the side flanges together. It may also be manufactured from another metal than steel, such as aluminium.

Claims

1. A bumper beam for vehicles, with a hat-shaped profile having a central flange (11), two webs (12, 13) and side flanges (14, 15), wherein the beam has side attachment portions (20, 21 ) at which the side flanges form attachment surfaces (30-33) for attachment onto the vehicle with the central flange of the hat profile facing outwards, characterised in that the central flange (11) is asymmetrically broader at its centre than at the attachment portions and that the web (13) on the side on which the central flange is most narrow has deformation triggers (35, 36) in association with the attachment surfaces.

2. The bumper beam according to claim 1 , characterised in that the said triggers are constituted by holes (35, 36) in the web.

3. The bumper beam according to claim 2, characterised in that the said triggers are constituted by several neighbouring holes (35, 36).

4. The bumper beam according to any one of the preceding claims, characterised in that the profile height of the beam (11) decreases continuously from the attachment surfaces (20, 21) towards the centre, such that the profile height at the centre is less than 2/3 of the maximum profile height at the attachment portions.