Increase of the compressibility of a bumper beam

Abstract

The bumper beam of a motor vehicle comprising a chassis and comprising at least one horizontal flank and at least one vertical flank extending longitudinally to the beam comprises at least one bearing member arranged so as to be supported on the chassis and to exert a reaction force in one direction on said at least one horizontal flank during the absorption of an impact by said beam, said bearing member being stronger than said at least one horizontal flank in the direction of the reaction force.

Claims

1. A bumper beam of a motor vehicle, the bumper beam comprising: a chassis, at least one horizontal flank and at least one vertical flank extending longitudinally to the beam, at least one bearing member configured to be supported on the chassis and to exert a reaction force in one direction on said at least one horizontal flank during absorption of an impact by said beam, the at least one bearing member including a blade, said at least one bearing member being stronger than said at least one horizontal flank in the direction of the reaction force, and the at least one horizontal flank being configured to be broken by the blade upon the impact.

2. The bumper beam according to claim 1, wherein the beam has a W-shaped profile and includes four horizontal flanks and three vertical flanks.

3. The bumper beam according to claim 1, wherein the beam comprises unidirectional fibres.

4. The bumper beam according to claim 1, further comprising bidirectional or multiaxial reinforcements in at least some of its vertical flanks, the bidirectional or multiaxial reinforcements being selected from ribbon, fabric, non-woven, and mat.

5. The bumper beam according to claim 1, wherein the at least one bearing member comprises a portion of an absorber configured to be supported on the chassis.

6. Beam according to claim 5, wherein the portion of the absorber is one side of the absorber.

7. The bumper beam according to claim 5, wherein the blade is fastened to the beam and to the portion of the absorber.

8. The bumper beam according claim 7, wherein the blade has generally a square shape.

9. Beam according to claim 5, wherein the at least one bearing member comprises a vertical flank of the beam.

10. Beam according to claim 7, wherein the at least one bearing member comprises several blades.

11. The bumper beam of claim 1, wherein: the at least one horizontal flank comprises two adjacent horizontal flanks; and the two adjacent horizontal flanks are configured to be broken by the blade upon the impact.

Description

(1) The invention will be better understood on reading the accompanying figures, which are given solely by way of example and not limiting in any way, in which:

(2) FIGS. 1 and 2 are perspective views of one end of a beam and its bearing member according to the invention, respectively before and after absorption of an impact.

(3) FIGS. 3 and 4 are cross-sectional views of the beam respectively of FIGS. 1 and 2,

(4) FIG. 5 is a graph against time of the force applied on a beam for which no horizontal flank breaks, and

(5) FIG. 6 is a graph similar to that of FIG. 5 for a beam for which some of the horizontal flanks break.

(6) In the following description, we use a motor vehicle coordinate system R(O, x, y, z), wherein O is the central point of the volume defined by the vehicle, axis (Ox) corresponds to the main vehicle axis and to the X direction, axis (Oy) corresponds to the horizontal direction perpendicular to the main vehicle axis and to the Y direction, and axis (Oz) is the vertical of the location and corresponds to the Z direction.

(7) For clarity, FIGS. 1 and 2 only show the left side of the bumper. However, the two sides of the bumper are composed of exactly the same parts and behave in the same way. The following description will therefore only consider the left side of the bumper, knowing that the right side can be deduced by symmetry with respect to the plane (Oxz).

(8) Referring to FIGS. 1 and 3, a bumper of the vehicle is provided with a beam 2 extending in the Y direction. This beam comprises four horizontal flanks 4 and three vertical flanks 6, each of these flanks comprising unidirectional fibers, for example carbon and glass fibers, which are highly resistant in the direction of their axis which coincides with the Y direction but considerably less resistant in any direction perpendicular to their axis. The vertical flanks further comprise bidirectional reinforcements, such as tape, fabric, mat or non-woven (stitched reinforcements), sandwiching the fibers in these flanks so as to make the latter resistant to any force along the direction of the main vehicle axis.

(9) As an example of embodiment, this type of beam can be produced using a pultrusion process. The horizontal flanks may have in their thickness carbon fibers representing a thickness of 2 mm, i.e. 2.10 m.sup.3, taken between two layers of glass fibers of thickness 1 mm, i.e. 1.10.sup.3 m. The vertical flanks may have in their thickness carbon fibers representing a thickness of 1.4 mm, i.e. 1.4.10 m.sup.3, sandwiched between two layers of glass fibers representing a thickness of 0.4 mm, i.e. 4.10.sup.4 m, these three fibre layers being sandwiched between two tape layers each having a thickness of 0.4 mm, i.e. 4.10.sup.4 m.

(10) The bumper is also provided with an absorber 12 attached to a side member (not shown) of the vehicle by attachment means 18, the side member itself being attached to the vehicle chassis, not shown here. The absorber is designed to absorb as much of the mechanical energy generated by an impact as possible, in order to deform the chassis as little as possible. The absorber is overmoulded on one end of the beam 2. Furthermore, a blade 14 having generally the shape of a square is fastened directly firstly to one side 13 of the absorber and secondly to a specific flank 16 amongst the vertical flanks of the beam. The blade 14 extends substantially in a plane perpendicular to the Z direction and has a small thickness, for example less than 1 cm. This type of configuration firstly allows the beam to be supported indirectly on the chassis, and secondly allows the blade to help absorb an impact. The side 13, the blade 14 and the flank 16 form a bearing member 10.

(11) It is considered that the bumper is subjected to a shock with partial front impact (i.e. offset to one side) on its left side. FIGS. 2 and 4 illustrate the condition of the beam 2 and of the bearing member 10 respectively before and after complete absorption of the impact by the vehicle. The obstacle with which the vehicle collides thereby generates a force applied to the bumper in the X direction, directed towards the rear of the vehicle. This force propagates in particular up to the bearing member 10, which firstly will partly absorb the energy through the absorber, and secondly will generate a reaction force applied in particular on the surface composed of the flank 16 in the X direction towards the front of the vehicle. Since this flank is thin in the direction of the reaction force and comprises bidirectional reinforcements, it will only dissipate a very small part of the impact energy, and the reaction force will apply in particular on the two adjacent horizontal flanks 4, which then compress until they break, thereby considerably increasing the bumper absorption stroke. The orientation of the blade 14 localises the force applied by the blade 14 on the flank 16 to favor breakage of the two adjacent horizontal flanks 4. FIG. 4 shows in particular that the lower horizontal flank 4, adjacent to the vertical flank 16 of the bearing member, broke after absorbing the impact, which reduced the incompressibility of the beam as illustrated by the vertical broken line. These two horizontal flanks 4 are also adjacent to the vertical flanks 6 which form the front of the beam 2. In other words, the horizontal flanks 4 of the beam 2 on which the bearing member 10 exerts its thrust is adjacent the front of the beam. The compressibility of the beam 2 is therefore increased near the front of the beam, i.e. near the area of the bumper in which the impact is applied.

(12) FIGS. 5 and 6 show the change in the force applied during an impact between an obstacle and the beam according to the displacement, in the vehicle coordinate system, of a point of contact between the obstacle and the bumper, respectively if none of the horizontal flanks break (curve 20) and if the two horizontal flanks adjacent to the vertical flank forming part of the bearing member break (curve 22). The two impacts are simulated under the same experimental conditions. Thus, the areas under these two curves, which represent the total mechanical energy dissipated, are equal.

(13) A key feature of the bumper is the maximum force to which it is subjected during absorption of the impact. We see that the value of this maximum force is reached firstly at a displacement of about 215 mm, i.e. 2.15.10.sup.1 m, and secondly that it is different depending on whether or not the beam breaks. Curve 20 shows that it is about 1.5.10.sup.5 N if the horizontal flanks do not break, and curve 22 that is about 1.4.10.sup.5 N if the bearing member breaks the two horizontal flanks adjacent thereto. This represents a difference of 1.10.sup.4 N between the two cases, which is not negligible. If the beam breaks locally, less force is transmitted to the chassis, which is therefore deformed much less, and to the passenger compartment housing the driver and any passengers.

(14) Obviously, numerous modifications can be made without leaving the scope of the invention.

(15) The beam profile may be different from that described above.

(16) The various flanks may include materials other than those described above. In particular, the horizontal flanks may comprise bidirectional reinforcements, but fewer than the vertical flanks so that the latter remain stronger than the horizontal flanks in the direction of the force applied during an impact.

(17) The thicknesses and distribution of the thicknesses in the flanks may be different from those described above.

(18) The blade can be replaced by a plurality of blades and these blades may be supported directly on the horizontal flanks to be broken.

(19) The absorber may be fastened to the chassis.