Enhanced bumper system

Abstract

A bumper system (4) for a motor vehicle comprising a cross beam (1) which is globally orientated in a transverse direction (Y), said cross beam comprising a front wall (6) adapted to receive a crash impact force and a rear wall (5) opposed and spaced from said front wall, at least one absorber (2), at least an intermediate component (3) to attach the absorber (2) to the cross beam (1), said intermediate component (3) being connected to the rear wall (5) through a first contact area (10), distant from a longitudinal axis (LL), by an internal component distance, called L.sub.in, and an external component distance, called L.sub.out, which corresponds respectively to the minimum and maximum distance between said first contact area (10) and the longitudinal axis (LL), said longitudinal axis (LL) passing at mid width of the cross beam and being perpendicular to the transverse direction (Y), said intermediate component (3) being connected to the absorber (2) through a second contact area (20) distant from the longitudinal axis (LL) by an internal profile distance, called D.sub.in, and an external profile distance, called D.sub.out, which corresponds respectively to the minimum and maximum distance between the second contact (20) area and the longitudinal axis (LL), wherein a part of the intermediate component distant from the longitudinal axis (LL) by a distance comprised between L.sub.out and D.sub.out has a smaller bending stiffness (S.sub.interm) about a vertical axis (Z) than a part of the cross beam distant from the longitudinal axis (LL) by a distance comprised between L.sub.out and D.sub.in (S.sub.cross), said vertical axis (Z) being perpendicular to the transverse direction (Y) and the longitudinal axis (LL).

Claims

1. A bumper system (4) for a motor vehicle comprising A cross beam (1) which is globally orientated in a transverse direction (Y), said cross beam comprising a front wall (6) adapted to receive a crash impact force and a rear wall (5) opposed and spaced from said front wall, At least one absorber (2) At least an intermediate component (3) to attach the absorber (2) to the cross beam (1), Said intermediate component (3) being connected to the rear wall (5) through a first contact area (10), distant from a longitudinal axis (LL), by an internal component distance, called L.sub.in, and an external component distance, called L.sub.out, which corresponds respectively to the minimum and maximum distance between said first contact area (10) and the longitudinal axis (LL), said longitudinal axis (LL) passing at mid width of the cross beam and being perpendicular to the transverse direction (Y), Said intermediate component (3) being connected to the absorber (2) through a second contact area (20) distant from the longitudinal axis (LL) by an internal profile distance, called D.sub.in, and an external profile distance, called D.sub.out which corresponds respectively to the minimum and maximum distance between the second contact (20) area and the longitudinal axis (LL), wherein a part of the intermediate component distant from the longitudinal axis (LL) by a distance comprised between L.sub.out and D.sub.out has a smaller bending stiffness (S.sub.interm) about a vertical axis (Z) than a part of the cross beam distant from the longitudinal axis (LL) by a distance comprised between L.sub.out and D.sub.in (S.sub.cross), said vertical axis (Z) being perpendicular to the transverse direction (Y) and the longitudinal axis (LL), bending stiffness about a vertical axis (Z) being defined like the product of the modulus of elasticity of the beam by his area moment of inertia compared to the vertical axis (Z).

2. A bumper system (4) according to claim 1 wherein the said bending stiffness of a part of the intermediate component comprised between L.sub.out and D.sub.out (S.sub.interm) about the vertical direction (Z) is not constant between L.sub.out and D.sub.out and has a minimum bending stiffness (S.sub.interm, min) about the vertical axis (Z) and/or wherein the said bending stiffness of a part the cross beam comprised between L.sub.out and D.sub.in is not constant between L.sub.out and D.sub.in, and has a minimum bending stiffness (S.sub.cross, min) about the vertical axis (Z) and wherein the said minimum bending stiffness (S.sub.interm, min) of part the intermediate component is smaller than the said minimum bending stiffness of part the cross beam (S.sub.cross, min).

3. A bumper system (4) according to claim 1 wherein a part of the intermediate component distant from the longitudinal axis (LL) by a distance comprised between L.sub.out and D.sub.out has a minimum bending stiffness (S.sub.interm, min) about the vertical axis (Z) lower than 100%, more preferably lower than 50%, even more preferably lower than 10% or 1% than the minimum bending stiffness of a part of the cross beam distant from the longitudinal axis (LL) by a distance comprised between L.sub.out and D.sub.in (S.sub.cross, min).

4. A bumper system (4) according to claim 3 wherein the ratio S.sub.interm, min/S.sub.cross, min is preferably lower than 1, more preferably lower than 0.5, even more preferably lower than 0.1 or 0.01.

5. A bumper system (4) for a motor vehicle according to claim 1 wherein at least a part of the first and/or the second contact area is welded and/or bonded (101a, 101b, 201a, 201b).

6. A bumper system (4) for a motor vehicle according to claim 5 wherein the part of the first contact area and/or of the second contact area which being welded or bonded is non continuous.

7. A bumper system (4) for a motor vehicle according to claim 5 wherein the part of the first contact area, which is welded or bonded (101a, 101b), is distant from the longitudinal axis (LL) by a distance comprised between 0.8 L.sub.out and L.sub.out or between L.sub.in and 1.2 L.sub.in.

8. A bumper system (4) for a motor vehicle according to claim 1 wherein the intermediate component (3) is obtained by rolling, extruding, forging or casting.

9. A bumper system (4) for a motor vehicle according to claim 1 wherein the absorber has at least one outer wall (8, 8a, 8b) and wherein the intermediate component comprises a flange (30, 30a, 30b), connected to at least one outer wall (8, 8a, 8b) of the absorber.

10. A bumper system (4) for a motor vehicle according to claim 1 wherein the intermediate component (3) comprises reinforcements (40a, 40b).

11. A bumper system (4) for a motor vehicle according to claim 1, wherein the intermediate component (3) comprises additional means (50a, 50b) to attach additional functions.

12. A bumper system for a motor vehicle according to claim 1 wherein the intermediate component is outfitted with a through opening for the passage of a towing device or a towing eye (60).

13. Use of a bumper system according to claim 1 in a motor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further aspects, aims, advantages and features of the invention will emerge more clearly on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, with reference to the appended figures, wherein:

(2) FIG. 1 represents a perspective view of a bumper system comprising a cross beam, absorbers and intermediate components according to the invention;

(3) FIG. 2 represents a schematic section of the connection between the cross beam, one absorber and an intermediate component in the plan (X, Y);

(4) FIG. 3 represents a schematic section of the connection between the cross beam, one absorber and an intermediate component in the plan (Y, Z), showing the first and second contact area;

(5) FIG. 4 represents a schematic section of the connection between the cross beam, one absorber and an intermediate component in the plan (Y, Z), showing the location of the attachments;

(6) FIG. 5a is a perspective view of connection between the cross beam, one absorber and an intermediate component where the intermediate component has a flange, attached to the outer wall the profile member; FIG. 5b is a schematic section of the connection represented at FIG. 5a in the plan (X, Y).

(7) FIG. 6 is a perspective view of the connection between the cross beam and an intermediate component when the intermediate component has two flanges, attached to the outer walls of the profile member;

(8) FIG. 7 is a perspective view of the connection between the cross beam and an intermediate component when the intermediate component has reinforcement parts;

(9) FIG. 8 is a perspective view of the connection between the cross beam and an intermediate component when the intermediate component has additional means for adding functionalities;

(10) FIG. 9 is a perspective view of the connection between the bumper cross beam and an intermediate component where the intermediate component fulfils also the function of a towing eye;

(11) FIG. 10 is a variant of FIG. 9;

(12) FIG. 11 is a perspective view of the principle of RCAR bumper barrier test.

(13) FIG. 12 is a perspective view of the principle of pole barrier testpole barrier test.

(14) FIG. 13 is a section view of the connection between the cross beam and the absorber according to the prior art, without using an intermediate component.

(15) FIG. 14 is a section view of the connection between the cross beam and the absorber via an intermediate component according to the invention.

(16) FIG. 15 is a section of the bumper system according to the invention tested according to the RCAR bumper barrier test and the pole barrier test.

(17) FIG. 16 is a section of the cross beam tested according to the RCAR bumper barrier test and the pole barrier test.

(18) FIG. 17 is a section of the absorber tested according to the RCAR bumper barrier test and the pole barrier test.

(19) FIG. 18 represents the load that can sustain the bumper system in case of a frontal crash against a barrier, according to the RCAR bumper barrier test, when the cross beam is attached directly to the absorber or if an intermediate component according to the invention is used.

(20) FIG. 19 represents the load that can sustain the bumper system in case of a frontal crash against a pole when the cross beam is attached directly to the absorber or if an intermediate component according to the invention is used.

DETAILED DESCRIPTION OF THE INVENTION

(21) The invention will be better understood in reference to the figures. Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments may be illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. Moreover, the various embodiments and alternative embodiments are not mutually exclusive and may be combined with one another.

(22) FIG. 1 represents a perspective view of a bumper system (4) comprising a cross beam (1), two absorbers (2, 2′) and two intermediate components (3, 3′). The cross beam is curved and extending in a transverse direction (Y). It is constituted of an extrusion member with a length W and having a rear wall (5) and a front wall (6). The rear wall (5) is located in the inwardly edge of the curved cross beam. The front wall (6) is located in the outwardly edge of the curved cross beam. The rear wall is opposed and spaced from the front wall. The two absorbers (2, 2′) are positioned on the inwardly edge of the curved cross beam and are substantially positioned symmetrically to the longitudinal axis (LL). The longitudinal axis (LL) is passing at mid width W/2 of the cross beam. It may correspond with the symmetrical axis of a motor vehicle (not represented) on which the bumper system can be installed. This longitudinal axis is parallel with a longitudinal direction (X), said longitudinal direction (X) can also correspond to the driving direction of the vehicle (not represented).

(23) In between the cross beam (1) and an absorber (2, 2′) an intermediate component (3, 3′) is positioned. The intermediate component (3, 3′) is connected to the rear wall (5) of the cross beam (1) through a first contact area (10, 10′). In the case represented at FIG. 1, the first contact area corresponds to the whole surface of the intermediate component lying on the rear wall (5). However, in other embodiments where the curving of the cross beam is particularly pronounced in the zone where the intermediate component is positioned, the first contact area can correspond to only a part of the surface of the intermediate component lying on the rear wall and maybe formed by several non-contiguous surfaces.

(24) The intermediate component (3, 3′) is also connected to the absorber (2, 2′) through a second contact area (20, 20′).

(25) FIG. 2 is a cross-section of the left assembly cross beam/intermediate component/absorber represented at FIG. 1. The first contact area is distant from the longitudinal axis (LL), by an internal component distance, called L.sub.in, and an external component distance, called L.sub.out, which corresponds respectively to the minimum and maximum distance between said first contact area and the longitudinal axis (LL).

(26) The absorber (2) comprises a profile member (7) which extend parallel to the longitudinal direction (X). The profile member is attached at one end to an endplate (9) which permits to attach the absorber to longitudinal beam of the vehicle (not represented) and at the other end to the intermediate component, through a second contact area (20). The second contact area in the case represented at FIG. 2 corresponds to the whole section of the profile member (7). The second contact area is distant from the longitudinal axis (LL) by an internal profile distance, called D.sub.in, and an external profile distance, called D.sub.out, which corresponds respectively to the minimum and maximum distance between the second contact area and the longitudinal axis (LL).

(27) FIG. 3 is a cross section B-B of FIG. 2 showing the first contact area (10) and the second contact area (20).

(28) FIG. 4 corresponds to a similar embodiment of FIG. 3 but shows the location of the connections, where in the represented case corresponds to seam weld lines. In another embodiment (not represented), the connections could be performed by bonding or a mix of bonding and welding. In the represented case, the intermediate component is attached to the cross beam via seam weld line (101a, 101b) which is non continuous, i.e. the seam weld line is composed of two separate seam weld lines (101a, 101b) located on the two extremities of the first contact area; seam weld line 101a is positioned in an area distant of L.sub.out from the longitudinal axis LL and line 101b is distant from L.sub.in from the longitudinal axis LL. In another embodiment, the two separate seam weld lines can be located in an area distant from the longitudinal axis by a distance comprised between 0.8 L.sub.out and L.sub.out or between L.sub.in and 1.2 L.sub.in. The intermediate component is attached to the absorber via a seam weld line (201); it is peripheral and partly or fully encircled the second contact area (20).

(29) FIG. 5a and FIG. 5b represents a particular embodiment of the invention where the intermediate component has a flange (30), connected to the outer wall (8) of the absorber (2). The intermediate component is attached to the absorber via a seam weld line (201, 202) which is non continuous. The seam weld line is composed of two separate seam weld line (201 and 202) wherein one of these seam weld lines (202) correspond to the connection between the flange and the outer wall (8).

(30) FIG. 6 differs from FIG. 5 by the presence of two flanges (30a, 30b) in the intermediate component (3). In that case, each flange (30a, 30b) is connected to an outer wall of the absorber (8a, 8b). Each flange is attached via a seam weld line (202a, 202b).

(31) FIG. 7 represents a particular embodiment of the invention where the intermediate component comprises reinforcing parts (40a, 40b).

(32) FIG. 8 represents a particular embodiment of the invention where the intermediate component comprises attachment means (50a, 50b). The attachment means may permit to attach further components, like horns, electronic devices, reinforcement parts, lashing points or spot light.

(33) FIG. 9 and FIG. 10 represent the case where the intermediate component (3) is outfitted with a through opening for the passage of a towing device. FIG. 9 corresponds to the case where the thread for the towing hook (60) is attached separately to the intermediate component. The thread is in this case is included into an extra part which is attached to the intermediate component, for instance by welding or bonding. FIG. 10 corresponds to the case where the thread is integrated into the intermediate component. The intermediate component and the thread is monolithic, i.e. without the need of any external attachments. Preferably, it is obtained by extrusion.

EXAMPLE

(34) A RCAR bumper barrier test and a pole barrier test on a bumper system have been executed on two types of bumper system: a first bumper system, represented at FIG. 13 corresponding to prior art, i.e. without an intermediate component and a second bumper system represented at FIG. 14 corresponding to the invention. For both configurations, the same geometry of cross beam with three chambers, represented on FIG. 16, has been used with a total length of 1300 mm. The same absorbers, represented on FIG. 17, has been used and are positioned symmetrically around the longitudinal axis LL at a distance of 430 mm (see FIG. 15). The bumper system for both configurations is made in aluminium alloy, having a young modulus of 70 GPa.

(35) According to the prior art, the absorbers are welded directly to the cross beam. According to the invention, an intermediate component with a flange, made in aluminium alloy with a young modulus of 70 GPa and represented on FIG. 14 is placed between the cross beam and the absorber and is attached by welding to the cross beam through a first contact area and to the absorber through a second contact area. Table 1 shows the distance between the longitudinal axis LL and the first and second contact areas (also represented on FIG. 15). The corresponding area moment of inertia about the vertical Z axis of the part of the cross beam distant from the longitudinal axis (LL) by a distance comprised between L.sub.out and D.sub.in and the area moment of inertia about the vertical Z axis of the intermediate component distant between L.sub.out and D.sub.out are also included in Table 1. They have been calculated using the software CATIA V5.

(36) The corresponding bending stiffness is then deduced by multiplying the area moment of inertia by the young modulus of the material constituting the two elements (here aluminum).

(37) It can be observed that the bending stiffness of the intermediate component (S.sub.interm=84 Nm.sup.2) is much smaller than the bending stiffness of the cross beam (S.sub.cross=19460 Nm.sup.2), by a factor of 0.43%.

(38) TABLE-US-00001 TABLEAU 1 Intermediate cross beam component First Second Area Area contact contact moment Bending moment of Bending area area of inertia stiffness inertia stiffness L.sub.in L.sub.out D.sub.in D.sub.out I.sub.cross S .sub.cross I.sub.interm S.sub.interm (mm) (mm) (mm) (mm) (cm4) (Nm.sup.2) (cm4) (Nm.sup.2) 410 585 430 530 27.80 19460 0.12 84

(39) To perform the test, the bumper system (4) is fixed on the body-in-white longitudinals (13a, 13b), and said longitudinals are fixed on a bob-sled (16) as represented at FIG. 11 and FIG. 12. The RCAR bumper barrier test is conducted at 10.5 km/h and the pole barrier test at a speed ranging between 15 and 64 km/h.

(40) The energy absorption capacity of the bumper system during a crash is evaluated by the load displacement response. The area under the load-displacement curve is a measure of the energy absorbed. During a low speed impact, the bumper system has the function of preventing damage to the body in white. Hence, the maximum impact load transmitted through the system has to be limited. The maximal displacement is specified by the vehicle design. Indeed, it is needed that no damage of the cooling system, nor of security-relevant components occur during the crash.

(41) The ideal bumper system has a load-displacement response which acts as a step function; the load rapidly reaches the maximum value and remains there throughout the crash. For a given maximum displacement, higher load, better bumper system.

(42) The load-force versus the displacement for the two configurations with and without the intermediate components and for the two conditions of tests (RCAR bumper barrier and Pole barrier tests) are represented on FIGS. 18 and 19. The dashed lines correspond to the bumper system according to prior art (curve B), without an intermediate component and the bold lines to the bumper system according to the invention (curve A). In both cases, the curves correspond to simulated curves by FEM modelling.

(43) It can be observed that in the case of the RCAR bumper barrier test (FIG. 18), the bumper system with an intermediate component according to the invention (curve A), sustains for the smaller displacements a similar load compared to the prior art (curve B); but at higher displacements the force level is higher. This better behavior is attributed to the fact that the cross beam is still attached to the absorber via the intermediate component whereas in the case of the prior art, there is a damage initiated at the interface between the cross beam and the absorber. It can be mentioned that the presence of the intermediate component permits also to reduce the barrier intrusion, which is beneficial for the integrity of car components, such as cooling systems.

(44) During a certain range of displacement, the force sustained by the bumper system according to the invention is smaller than the corresponding force of the prior art due to the lower stiffness of the assembly, but it has no effect of the total energy absorption of the bumper system, which remain higher than the bumper system according to the prior art.

(45) A similar plot (FIG. 19) has been obtained during the pole barrier test. It is observed that the bumper system according to the invention (curve A) permits to sustain a higher load than a bumper system according to the prior art (Curve B).