Field of the invention

The invention relates to a lightweight bumper beam according to the preamble of claim 1.

Background of the invention

For certain markets low speed crash regulations admits the use of much simpler and lighter bumper systems compared to the European and US market. This has typically called for thin, lightweight monoblock bumper systems with relative poor performance if they are to be tested in a high-speed crash test or the RCAR Allianz Crash Repair Test, commonly known as the AZT-crash test.

However, in recent years, manufacturers have asked for

performance improvements of bumper beams of the above- mentioned type so as to make them capable of taking higher load and energy levels in high speed crash tests. Future trends also seem to point towards that AZT-crash will be a mandatory requirement in the majority of current markets.

Object of the invention

An object of the invention is thus to improve the stability and increase the load and energy levels capable of being taken up by a bumper beam having a typical lightweight monoblock design .

A further object is to strengthen the attachment of a towing tube if the lightweight bumper beam according to the invention is provided with such towing tube. Brief description of the invention

According to the invention these objects are achieved by a lightweight bumper beam, comprising an elongated U-shaped monoblock cross member provided at respective end with an attachment portion for attachment to a body in white of a vehicle, characterized in that each attachment portion is provided with two elongated reinforcing means extending between an inner top surface of the elongated U-shaped

monoblock cross member and a bracket of said attachment portion, that said elongated reinforcing means being arranged at a distance relative to each other so as to form a space therebetween, and that said distance being smallest at an intermediate portion of said two elongated reinforcing means.

Preferred embodiments of the lightweight bumper beam are defined in the dependent claims.

Brief description of the drawings

The invention is described in more detail below with reference being made to non-limiting examples shown on the appended drawings, in which

- Fig. 1 is a perspective view obliquely from above of an inventive bumper beam with an attachment portion at each end for attachment to a body in white of a vehicle (not shown),

- Fig. 2 is an enlarged view obliquely from above of a first embodiment of two elongated reinforcing means provided at respective attachment portion of the inventive bumper beam,

- Fig. 3 is an enlarged view obliquely from above of a second embodiment of two elongated reinforcing means provided at respective attachment portion of the inventive bumper beam,

- Fig. 4 is an enlarged view from above of the second

embodiment of two elongated reinforcing means shown in Fig. 3, - Fig. 5 is a schematic sectional view from above of the inventive bumper beam provided with a towing tube with fitted towing hook at one of the attachment portions, and

- Fig. 6 is a schematic sectional view from above of an enlarged partial view obliquely from above of the towing tube with fitted towing hook at one of the attachment portions.

Description of preferred embodiments

In the description and claims below the definition of a lightweight monoblock design of a bumper beam is a bumper beam which in its own, without any reinforcing means or crash boxes, and only by occasional attachment plates can be mounted to a vehicle and used as a complete bumper system. Thus, such a bumper system comprises only one energy absorbing part acting as crash boxes and cross member combined. Fig. 1 shows a lightweight bumper beam 1 comprising an

elongated generally U-shaped monoblock cross member 2 provided at respective end 3 with an attachment portion 4 for

attachment to a body in white of a vehicle (not shown) .

As shown in Figs. 2 to 6, each attachment portion 4 is provided with two elongated reinforcing means 11, 12 extending between an inner top surface 5 (Fig. 5) of the elongated U- shaped monoblock cross member 2 and a bracket 6 of said attachment portion 4. The two elongated reinforcing means 11, 12 are placed essentially in in the longitudinal direction of the vehicle and welded, for instance, at their respective end to the bracket 6 and the inner top surface of the elongated U- shaped monoblock cross member 2, i.e. to the inside surface of the cross member 2.

The two elongated reinforcing means 11, 12 are designed specifically to interact with each other during the buckling sequence of the attachment portion (s) 4 in case of a crash, thus raising the deformation resistance of said attachment portion(s) 4 considerably.

More particular, the two elongated reinforcing means 11, 12 are arranged at a distance X relative to each other so as to form a space 20 therebetween. Said distance X being smallest at an intermediate portion 13 of said two elongated

reinforcing means 11, 12. See Fig. 4.

In a preferred embodiment, each of said two elongated

reinforcing means 11, 12 is formed of sheet metal and has a general U-shape and each having at least a partially curved inner 14 and outer 15 surfaces. The outer surface 15 of the respective two elongated reinforcing means 11, 12 is directed towards each other which means that said distance X being smallest at the intermediate 13 portion of said curved outer surfaces 15. See Fig. 4

The curvature of the two elongated reinforcing means 11, 12 makes for pronounced initiation of the buckling sequence and early on, the two reinforcing means simply fold towards each other. This helps to keep the initial peak load down. As soon as the outer surfaces 15 of two reinforcing means touch each other, the resistance ramps up and the load level rises significantly .

For best stability the two elongated reinforcing means 11, 12 are mounted standing upwards, orthogonal to an inner upper and lower face of the attachment portion 4 of the elongated U- shaped monoblock cross member 2.

The basic function of the two elongated reinforcing means 11, 12 also works in other shapes, as long as the curvature of the elongated reinforcing means are aimed towards each other and thus interfere during deformation.

In a preferred embodiment, as shown in Figs. 2, 5 and 6, in each attachment portion 4 one of the elongated reinforcing means, i.e. the elongated reinforcing means 12, is provided with a straight intermediate portion 12a, and another

elongated reinforcing means, i.e. the elongated reinforcing means 11, is provided with straight portions 11a, lib at the ends attached to the inner top surface 5 of the elongated U- shaped monoblock cross member 2 and the bracket 6 of said attachment portion 4, respectively.

In the embodiment shown in Figs. 3 and 4, the two elongated reinforcing means 11, 12 have each an evenly progressing curvature . To increase the resistance to buckling the elongated U-shaped monoblock cross member 2 further comprises, at each end of respective leg 2a of the U, a rim 7 forming part of and extending in the longitudinal direction and over a major portion or the hole length of the elongated U-shaped monoblock cross member 2. Said rim 7 is preferably bent in such a way that an edge 7a thereof is directed parallel with respective leg 2a of the U such as to form a hat-shaped lightweight bumper beam 1.

In Fig. 5, the lightweight bumper beam 1 is provided with a towing tube 30 arranged in at least one of said spaces 20 formed between said outer surface 15 of said respective elongated reinforcing means 11, 12. A towing hook 31 is preferably by means of threads attached to said towing tube 30 when needed. A hole 32 is made in line with the towing tube 30 in a front surface 10 of the elongated U-shaped monoblock cross member 2.

The towing tube 30 has preferably an elongated cylindrical form, and to enable the towing tube 30 to be arranged in said space 20 each of said elongated reinforcing means 11, 12 is provided with a depression 16, preferably having a partial cylindrical form. See Figs. 2 and 3, for instance. In the embodiment shown in Fig. 3, said depressions 16 may have the same shape and extend preferably at least 60% of the length of each elongated reinforcing means 11, 12, and in the embodiment shown in Fig. 2 the depression 16 of one of the elongated reinforcing means, i.e. the elongated reinforcing means 12, extends to at least one 12b of the ends of the elongated reinforcing means 12 while the depression 16 of the other elongated reinforcing means 11 is shaped as in Fig. 3.

As seen in Fig. 6, at least a portion of the towing tube 30 is arranged to abut on the outer surface 15 of each of said depression 16 formed in respective elongated reinforcing means 11, 12. The towing tube 30 extends at least between said depressions 16 and said bracket 6 of said attachment portion 4.

Thus, as can be inferred from the above-stated the elongated reinforcing means 11, 12 are aimed to increase high speed and AZT-performance of the monoblock bumper beam 1 while

maintaining light weight and stability.

Since the elongated reinforcing means 11, 12 are added at the inside of said attachment portion 4 of the monoblock bumper beam 1, it leaves the manufacturer with the possibility of a very light bumper for the low requirement markets, and with the option of adding the elongated reinforcing means 11, 12 for increased stability and load levels on other markets, making an adaptable cross over-bumper beam.

Thus, when the elongated reinforcing means 11, 12 are added the inside of each attachment portion 4 of the monoblock bumper beam 1, said attachment portions 4 act as reinforced crash boxes .

As can be inferred from the above, lightweight bumper beam 1 according to the invention is of monoblock type having integrated crash boxes.