WO2022090771A1

WO2022090771A1 - Bumper assembly for an automotive vehicle

Info

Publication number: WO2022090771A1
Application number: PCT/IB2020/060153
Authority: WO
Inventors: Nicolas TOUPIN; Yves DROUADAINE
Original assignee: Arcelormittal
Priority date: 2020-10-29
Filing date: 2020-10-29
Publication date: 2022-05-05

Abstract

Bumper assembly (2) for an automotive vehicle (1) comprising at least a main beam (3) and two crash boxes (22), said bumper assembly (2) consisting of a central portion (4) corresponding to the part of the bumper assembly (2) extending transversally in between said two crash boxes (22) and including said crash boxes (22), and two side portions (5) corresponding to the part of the bumper assembly (2) extending outside of the crash boxes (22) in the transverse direction, said side portions (5) each comprising a proximal edge (10), which is the edge of the side portion (5) located the closest to the central portion (4) and a distal edge (36), which is the edge of the side potion (5) located furthest away from the central portion (4), wherein each distal edge (36) longitudinally faces a corresponding wheel (6).

Description

Bumper assembly for an automotive vehicle

The present invention relates to protection and reinforcement elements in the car industry, and more specifically relates to a bumper assembly for an automotive vehicle. The present invention also relates to a process for manufacturing such a bumper assembly.

Bumper beams are known to be attached to the front and rear ends of an automotive vehicle, in order to absorb a part of the energy generated by any possible shock and to act as anti-intrusion parts. For this matter, bumper beams are known for having good strength and impact characteristics. The bumper beam is aimed to protect the driver and other passengers in case of rear or front impact due for example to a road accident.

WO 2018/091948 discloses a bumper beam having an 8-shaped cross section, extending in a transverse direction regarding the automotive vehicle. This bumper beam is made of a roll formed steel sheet and comprises an upper beam and a lower beam separated by a central wall extending transversally. The specific 8-shaped cross section of the bumper beam allows for very good energy absorption during an impact and increases the resistance to buckling under the compressive load generated by the impact. However, this design focuses on absorbing energy in the central part of the bumper beam, i.e. in between the two crash boxes affixed to the front rails.

New crash test regulations and ever-increasing safety consciousness of the public and automotive manufacturers, are prompting to consider the consequence of a crash not only for the occupants of the vehicle but also for the occupants of the partner vehicle in case of a head-on collision between two vehicles.

In the light of this new direction, known designs, such as the bumper beam disclosed in WO 2018/091948, do not address the issue of penetration into the partner vehicle of the mechanical structure of the vehicle situated outside of the transverse perimeter delimited by the crash boxes. For example, the fenders, the wheels etc. are all hard elements that can penetrate the partner vehicle and cause severe damage to the structure and, which is most preoccupying, to the occupants of the partner vehicle. This point is becoming of increasing concern to vehicle designers because of the appearance of new crash test regulations, which take into account the consequences of the crash on the partner vehicle of a head-on collision. For example, the new Moveable Progressive Deformable Barrier (MPDB) test of the European New Car Assessment Program (Euro-NCAP), in which a vehicle is impacted by a barrier travelling at 50km/h and overlapping 50% of the vehicle width equipped with a honeycomb structure and sensors which can be analyzed after the test to evaluate the penetration depth, homogeneity and severity of the tested vehicle into the barrier simulating a partner vehicle. Because the test results are estimated in terms of homogeneity of the penetration into the partner vehicle, it is important to have a front structure and in particular a bumper assembly, which distributes the crash energy as much as possible. Furthermore, it is also important to have a bumper assembly which contributes to shielding the partner vehicle from penetration of elements of the vehicle located behind the bumper assembly.

The aim of the present invention is therefore to remedy the drawbacks of the prior art by providing a bumper assembly that enhances security by optimizing impact energy absorption and by contributing to the safety of the occupants of the partner vehicle in case of a head-on collision.

The present invention also allows to ensure that the above described technical effects are met even in the case of a vehicle having rounded front edges, as is frequently the case with current vehicles. Indeed, rounded front edges of the outer skin of the vehicle are now easily achievable thanks to e.g. plastic molding and they are a popular design choice.

For this purpose, a first object of the present invention consists of a bumper assembly, comprising at least a main beam and two crash boxes, said bumper assembly consisting of a central portion corresponding to the part of the bumper assembly extending transversally in between said two crash boxes and including said crash boxes, and two side portions corresponding to the part of the bumper assembly extending outside of the crash boxes in the transverse direction, said side portions each comprising a proximal edge, which is the edge of the side portion located the closest to the central portion and a distal edge, which is the edge of the side potion located furthest away from the central portion, wherein each distal edge longitudinally faces a corresponding wheel.

A bumper assembly having the above described characteristics exhibits a very good crash resistance and good protection of the occupants both of the considered vehicle and of the partner vehicle in the case of a head-on collision.

According to other optional features of the bumper assembly according to the invention, considered alone or according to any possible technical combination:

-the tangent to the side portion at its distal edge forms with the transverse direction of the vehicle an angle comprised between 0° and 90°.

-the bumper assembly has an outer contour, which is defined as the line delimiting the top part of the bumper assembly on the side facing the outside of the vehicle, wherein Lcenter is the length of the outer contour corresponding to the central portion and wherein Lsidel , Lside2 are the lengths of the outer contour corresponding respectively to a first and second side portion of the bumper assembly and wherein Lsidel + Lside2 > 0,5*Lcenter.

-Lwheels being the distance between the outer parts of the wheels measured in the transverse direction of the vehicle, Lcenter + Lsidel + Lside2 > Lwheels.

-the bumper assembly further comprises two side reinforcements one on either side of said bumper assembly, wherein said side reinforcements extend at least over the entire width of each side portion.

An object of the present invention is also a vehicle having a bumper assembly corresponding to the above described characteristics.

An object of the present invention is also a process to manufacture a bumper assembly having the above described characteristics and a process to manufacture a vehicle having the above described characteristics.

Other characteristics and advantages of the invention will be described in greater detail in the following description.

The invention will be better understood by reading the following description, which is provided purely for purposes of explanation and is in no way intended to be restrictive, with reference to: - Figure 1 , which represents a top view of an automotive vehicle having a front end equipped with a bumper assembly according to a particular embodiment of the invention;

- Figure 2, which represents a top view of a first embodiment of the bumper assembly of the invention;

- Figure 3, which represents a perspective view of a detail of the bumper assembly of figure 2;

- Figure 4, which represents a cross section view following line IV-IV of the bumper assembly of figure 2;

- Figure 5, which represents an assembly sequence of the bumper assembly of figure 2;

- Figure 6, which represents a top view of a second embodiment of the bumper assembly of the invention;

- Figure 7, which represents a perspective view of a detail of the bumper assembly of figure 6;

- Figure 8, which represents a cross section view following line VI I l-VIII of the bumper assembly of figure 6;

- Figure 9, which represents an assembly sequence of the bumper assembly of figure 6;

- Figure 10 to figure 13, which represent a top view of a kinematic of deformation of the bumper assembly during a front crash.

- Figure 14, which represents a top view of a specific embodiment of the bumper assembly of the invention;

In the following description, the terms “upper”, “lower”, “front”, “rear”, “transverse” and “longitudinal” are defined according to the usual directions of a mounted vehicle. More particularly, the terms “upper”, “lower”, “up”, “down”, “bottom” and “top” are defined according to the elevation direction of the vehicle, the terms “front”, “rear”, “forward”, “backward” and “longitudinal” are defined according to the front I rear direction of the vehicle and the term “transverse” is defined according to the width of the vehicle. The term “height” refers to the distance between two points, lines, surfaces or volumes as measured in the horizontal direction. The terms “substantially perpendicular” define an angle of 90° +/- 15° and the terms “substantially parallel” define an angle of 0° +/- 15°.

A sheet has a top and bottom face, which are also referred to as a top and bottom side or as a top and bottom surface. The distance between said faces is designated as the thickness of the sheet. The thickness can be measured for example using a micrometer, the spindle and anvil of which are placed on the top and bottom faces. In a similar way, the thickness can also be measured on a formed part.

A blank of steel refers to a flat sheet of steel, which has been cut to any shape suitable for its use.

The yield strength, the ultimate tensile strength and the uniform and total elongation are measured according to ISO standard ISO 6892-1 , published in October 2009.

The bending angle is measured according to the VDA-238 bending standard. For a same material, the bending angle depends on the thickness. For the sake of simplicity, the bending angle values of the current invention refer to a thickness of 1.5mm. If the thickness is different than 1.5mm, the bending angle value needs to be adjusted by the following calculation where a1 ,5 is the bending angle at 1 ,5mm, t is the thickness, and at is the bending angle for thickness t:

The bending angle of a part is a way to measure the ability of the part to resist deformation without the formation of cracks.

According to figure 1 , an automotive vehicle 1 , that will simply be named “vehicle” in the following, comprises a bumper assembly 2 extending in a general transverse direction. Said bumper assembly 2 corresponds either to the front bumper beam, as depicted in the attached figures, or the rear bumper beam.

The general characteristics of the bumper assembly 2 according to the invention will first be described.

Referring to figure 2, the bumper assembly 2 comprises at least a main beam 3 extending in a general transverse direction and two crash boxes 22 extending in a general longitudinal direction. Said crash boxes 22 are located on either side of the vehicle and longitudinally facing respective side members 25, as depicted on 1 .

Referring to figure 14, the bumper assembly 2 consists of a central portion 4 and two side portions 5. Said central portion 4 corresponds to the part of the bumper assembly 2 extending transversally in between said two crash boxes 22 and including said crash boxes 22. Said side portions 5 correspond to the two outer parts of the bumper assembly 2 extending outside of the crash boxes 22 in the transverse direction. The limit between said central portion 4 and side portions 5 is materialized by the dashed lines 33 in figures 2, 14 and 35 in figure 6.

Each side portion 5 comprises a proximal edge 10, which is the edge of the side portion 5 located the closest to the central portion 4 and a distal edge 36, which is the edge of the side potion 5 located furthest away from the central portion 4.

Each distal edge 36 is associated to a corresponding wheel 6. For example, in the case where the bumper assembly is the front bumper assembly, the wheel 6 corresponding to the right-hand distal edge is the front right-hand side wheel. For example, in the case where the bumper assembly is the rear bumper assembly, the wheel 6 corresponding to the right-hand distal edge is the rear right-hand side wheel.

Referring to figure 1 , according to the present invention, the distal edge 36 of each side portion 5 longitudinally faces its corresponding wheel 6. By “longitudinally faces”, it is meant that any line extending in a longitudinal direction of the vehicle 1 from the distal edge 36 towards its corresponding wheel 6 will intercept said corresponding wheel 6.

In a particular embodiment, as depicted on figure 14, the angle 45 formed between the outside of the tangent 44 to a side portion 5 at its distal edge 36 and the transverse direction of the vehicle is comprised between 0° and 90°.

Referring to figure 14, the outer contour 50 (depicted as a dashed line on figure 14) of the bumper assembly 2 is defined as the line delimiting the top part of the bumper assembly 2 on the side facing the outside of the vehicle. The outside of the vehicle faces towards the rear in the case of a rear bumper and towards the front in the case of a front bumper. The outer contour 50 of the central portion 4 of the bumper assembly has a shape which generally follows the design of the central part of the corresponding end of the vehicle. If said central part of the vehicle is straight, the outer contour 50 of the central portion 4 will extend transversally in a generally straight line. If said central part is curved, which is mostly the case nowadays when looking at passenger vehicles for example, the outer contour 50 of the central portion 4 will extend transversally following a bow-shaped line, as depicted in figures 1 and 2 for example.

The outer contour 50 of the side portions 5 also needs to fit in to the space afforded by the design of the sides of the corresponding end of the vehicle, and in particular it only has the amount of space afforded by the front or rear overhang in the longitudinal direction. The front or rear overhang is the distance separating respectively the front or rear wheels from the outer skin of the vehicle at the front or the rear.

Referring to figure 14, Lcenter is defined as the length of the outer contour 50 corresponding to the central portion 4 and Lsidel , Lside2 are the lengths of the outer contour 50 corresponding respectively to a first and second side portion 5 of the bumper assembly 2. In other words, Lcenter is the length of the outer contour between the two proximal edges 10, while Lsidel , Lside2 are the length of the outer contour between each of the corresponding proximal and distal edges 10, 36.

In a particular embodiment, Lsidel +Lside2 > 0,5*Lcenter.

For example, Lcenter = 1 193mm, Lsidel = Lside2 = 527mm and thus Lsidel + Lside2 = 1054, Lcenter*0,5 = 596.5mm, verifying indeed the inequality Lsidel +Lside2 > 0,5*Lcenter.

Referring to figure 1 , Lwheels is the distance between the outer parts of the wheels 6 measured in the transverse direction of the vehicle 1. In a particular embodiment, Lcenter + Lsidel + Lside2 > Lwheels.

The bumper assembly 3 comprises at least a main beam 3 and two crash boxes 22.

The main beam 3 is the main structural element of the assembly and is destined to withstand the high loads generated during a front impact, prevent intrusion and transmit the efforts to the rest of the energy absorbing elements of the vehicle’s structure. For example, the main beam 3 is made by roll forming a high strength steel or by hot stamping a press-hardenable steel, both technologies being well known to the skilled person.

In a particular embodiment, the main beam 3 is made by roll-forming a fully martensitic steel sheet having a carbon content comprised between 0,15% and 0,5% and having an ultimate tensile strength above 1500MPa. Advantageously, using such a high strength steel will afford very good anti-intrusion properties to the main beam 3. For example, the main beam 3 is made by roll forming a steel sheet having a thickness comprised between 1 ,0mm and 2,0mm.

In a particular embodiment, the main beam 3 is made by hot stamping a press-hardening steel. Hot stamping is a forming technology which involves heating a steel sheet up to a temperature at which the microstructure of the steel has at least partially transformed to austenite, forming the blank at high temperature by stamping it and quenching the formed part to obtain a microstructure having a very high strength. Hot stamping allows to obtain very high strength parts with complex shapes and no springback. In order to yield the described benefits of hot stamping, the material used is known as press-hardening material, which has a chemical composition allowing it to form the desired hardened microstructure when submitted to the above described hot stamping process. It should be understood that the thermal treatment to which a part is submitted includes not only the above described thermal cycle of the hot stamping process itself, but also a subsequent paint baking step, performed after the part has been painted in order to bake the paint. The mechanical properties of hot stamped parts below are those measured after the paint baking step, in case a paint baking step has indeed been performed.

According to an embodiment, the steel composition of the main beam 3 comprises for example, in % weight: 0.20% < C < 0.25%, 1.1 % < Mn < 1.4%, 0.15% < Si < 0.35%, < Cr < 0.30%, 0.020% < Ti < 0.060%, 0.020% < Al < 0.060%, S < 0.005%, P < 0.025%, 0.002% < B < 0.004%, the remainder being iron and unavoidable impurities resulting from the elaboration. With this composition range, the tensile strength of the main beam 3 after hot stamping is comprised between 1300 and 1650 MPa. For example, the main beam 3 is made of Usibor 1500®. For example, the steel composition of the main beam 3 comprises, in % weight: 0.24% < C < 0.38%, 0.40% < Mn < 3%, 0.10% < Si < 0.70%, 0.015% < Al < 0.070%, Cr < 2%, 0.25% < Ni < 2%, 0.015% < Ti < 0.10%, Nb < 0.060%, 0.0005% < B < 0.0040%, 0.003% < N < 0.010%, S < 0,005%, P < 0,025%, %, the remainder being iron and unavoidable impurities resulting from the elaboration. With this composition range, the tensile strength of the main beam 3 after press-hardening is higher than 1800 MPa. For example, the main beam 3 is made of Usibor 2000®.

According to an embodiment, the main beam 3 is made by forming a tailor welded blank. Tailor welded blanks are made by assembling together, for example by laser welding together, several sheets of steel, known as sub-blanks, in order to optimize the performance of the part in its different areas, to reduce overall part weight and to reduce overall part cost. For example, the material used to manufacture the portion of the main beam 3 corresponding to the central portion 4 will have a different composition and / or different thickness than the material corresponding to the side portions 5.

According to an embodiment, the main beam 3 is made by forming a tailor rolled blank. A tailor rolled blank is a blank having multiple thicknesses which has been manufactured by differential rolling of a steel sheet.

The crash boxes 22 play the double role of absorbing energy by compressing through controlled buckling upon impact and of connecting the bumper assembly 2 to the rest of the vehicle. Generally, the crash boxes 22 are seen as fuses in case of a low speed impact, during which they will deform by controlled buckling thus protecting the rest of the vehicle structure. Also, the crash boxes 22 are generally designed so that the bumper assembly 2 can be easily removed and replaced in case of a low speed impact, thereby lowering the repair costs. The crash boxes generally comprise an energy absorption element 20 and a connecting plate 21 . Said energy absorption element 20 having a first end 40 attached to the bumper assembly 2 and a second end 41 attached to the connecting plate 21 . The bumper assembly 2 is attached to the rest of the vehicle 1 by attaching said connecting plates 21 to the corresponding side member 25 of the vehicle 1 , for example by screwing it through holes provided in the connecting plates 21. Advantageously, using a reversible mechanical assembly such as screwing allows to easily replace the bumper assembly 2 in case of damage, without affecting the rest of the vehicle structure.

In a particular embodiment, the energy absorption element 20 is made by cold stamping a steel sheet having a chemical composition comprising in weight %: 0.13% < C < 0.25%, 2.0 % < Mn < 3.0%, 1 .2% < Si < 2.5%, 0.02% < Al < 1 .0%, with 1 .22% < Si+AI < 2.5%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, Ti < 0.05 %, the remainder being Fe and unavoidable impurities and having a microstructure comprising between 8% and 15% of retained austenite, the remainder being ferrite, martensite and bainite, wherein the sum of martensite and bainite fractions is comprised between 70% and 92%. With this composition, the steel sheet has, as measured in the rolling direction, a yield strength comprised between 600MPa and 750MPa and an ultimate tensile strength comprised between 980MPa and 1300MPa while keeping a total elongation above 19%. Advantageously, by using such a high strength, high elongation material to manufacture the energy absorption element 20, it is possible to absorb a high amount of energy during a crash.

In a particular embodiment, the energy absorption element 20 is made by cold stamping a steel sheet having a chemical composition comprising in weight %: %: 0.15% < C < 0.25%, 1 .4 % < Mn < 2.6%, 0.6% < Si < 1 .5%, 0.02% < Al < 1 .0%, with 1 .0% < Si+AI < 2.4%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, the remainder being Fe and unavoidable impurities and having a microstructure comprising between 10% and 20% of retained austenite, the remainder being ferrite, martensite and bainite. With this composition, the steel sheet has, as measured in the rolling direction, a yield strength comprised between 850MPa and 1060MPa and an ultimate tensile strength comprised between 1 180MPa and 1330MPa while keeping a total elongation above 13%. Advantageously, by using such a high strength, high elongation material to manufacture the energy absorption element 20, it is possible to absorb a high amount of energy during a crash.

In a particular embodiment, the energy absorption element 20 is made by cold stamping a steel sheet having, as measured in the rolling direction, a yield strength comprised between 700MPa and 820MPa and an ultimate tensile strength comprised between 1050MPa and 1 180MPa while keeping a total elongation above 14%. Advantageously, by using such a high strength, high elongation material to manufacture the energy absorption element 20, it is possible to absorb a high amount of energy during a crash.

For example, the energy absorption element 20 is made by cold stamping a steel sheet having an initial thickness comprised between 0,7mm and 1 ,5mm.

In a particular embodiment, the bumper assembly 2 further comprises side reinforcements 7 on either side. Said side reinforcements 7 are attached to the main beam 3. Different embodiments of said side reinforcements 7 will be disclosed further on. The side reinforcements 7 play the role of reinforcing the structure of the bumper assembly 2 in order for example to compensate for the absence of the main beam 3 over at least part of the side portions 5, or in order to compensate for weaknesses in the main beam 3 over the side portions 5 brought on by the forming process, or in order to simply add additional reinforcement in the side portions 5.

Specific advantages of the bumper assembly 2 according to the invention will now be described referring to figures 10 to 13. These figures represent a kinematic of a crash test according to the above described Euro-NCAP MPDB standard. In this example, the bumper assembly 2 is the front bumper of the vehicle. However, it should be understood that the below disclosed technical effects of the bumper assembly 2 according to the present invention also apply in the case of a rear bumper assembly according to the invention, for example when the vehicle is submitted to an impact coming from the rear.

The Movable Progressive Deformable Barrier (MPDB) is depicted by reference 31 . The MPDB impacts the front of the vehicle at 50km/h with a transverse overlap of 50%

Figure 10 depicts the situation just before the impact. Figure 1 1 to 13 show the progressive deformation of the vehicle front structure as the MPDB penetrates the vehicle.

In a first step, depicted in figure 1 1 , the impact of the MPDB bends the central portion 4 of the bumper assembly 2 and compresses the crash box 22 facing the MPDB, which folds onto itself under the load.

As the barrier progresses (figure 12), the deformation of the central portion 4 continues and the front member 25 starts to the deform under the compressive load. At this stage, the considered side portion 5 moves backwards under the effect of the deformation of the bumper assembly 2, until the corresponding distal edge 36 reaches the longitudinally facing front wheel 6. The proximal edge 10 of the side portion 5 on the side of the impact is held in place by the corresponding crash box 22, while the distal edge 36 of said side portion is pushed onto the wheel 6 under the effect of the progression of the MPDB 31. As a result, said side portion 5 will have a tendency to unfold. This movement, associated with the fact that the side portion 5 is made of high strength steels, and in a particular embodiment is further reinforced through the use of a side reinforcement 7, has the effect of absorbing a high amount of crash energy during the impact.

Figure 13 depicts the situation when the MPDB has moved even further to penetrate the front structure. The lever effect exerted on the side portion 5 by the wheel 6 can be clearly seen.

On top of the above described energy absorption advantage of the unfolding of the side portion 5, said side portion 5 also brings about the benefit of distributing the impact energy over a very large width, up to the wheels 6 of the vehicle and also has the effect of shielding the partner vehicle (simulated by the MPDB in case of the Euro-NCAP test) from the penetration of the wheel 6 during the crash. The side portion 5 therefore contributes to increasing the safety not only of the occupants of its own vehicle, but also of the partner vehicle in case of a head on collision.

Advantageously, the longer the length of the outer contour 50 of the side portion 5, the more material there is to absorb energy by unfolding of the side portion 5 and the more material there is to shield the partner vehicle from the penetration of the wheel during impact. For example, it is advantageous to have side portions 5 such that Lsidel + Lside2 > 0,5*Lcenter, as previously disclosed.

Likewise, it is advantageous to have a bumper assembly 2 covering the entire width between the two wheels 6 when it unfolds, in order to ensure good shielding of the partner vehicle. In other words, it is advantageous to have a bumper assembly 2 verifying Lcenter + Lsidel + Lside2 > Lwheels.

Looking at the angle 45, it can be seen from the above described crash test sequence that there is an advantage of keeping said angle in between 0° and 90°. Indeed, if the angle 45 is above 90°, which means that the side portion 5 starts to bend back towards the central portion 4, the above described unfolding behavior during impact will not take place. Instead of having the effect of unfolding the side portion 5, the impact will have the effect of crushing the side portion 5 unto itself or towards the center of the vehicle. This will likely not absorb the same amount of energy and also will not ensure that the partner vehicle is shielded from the penetration of the wheel 6 when the impact progresses, thus resulting in potential issues for the passengers of the considered vehicle and of the partner vehicle in the case of a head on collision.

According to figures 2 to 5, a first embodiment of the bumper assembly 2 of the invention will now be described.

In this embodiment, the main beam 3 extends along the central portion 4 and along the side portions 5 up to the distal edge 36 of said side portion 5. The bumper assembly 2 further comprises side reinforcements 7.

As depicted in figure 3, each side reinforcement 7 comprises a reinforcement element 14, said element 14 comprising a vertical wall 26 and two opposite lateral walls 27 substantially perpendicular to said vertical wall 26 so that the reinforcement element 14 has a generally U-shaped cross section.

In a particular embodiment depicted on figure 3, the reinforcement element 14 comprises three successive straight portions linked by a first and second curvatures 12, 13.

In a particular embodiment, not depicted in the attached figures, the reinforcement element 14 comprises a plurality of n straight portions, n being greater than 2, for example 4, 5 or more successive straight portions.

In a particular embodiment, not depicted in the attached figures, the reinforcement element 14 has a smooth continuously curved shape.

For example, the reinforcement element 14 is made by forming a steel sheet having the following mechanical characteristics: the yield strength is comprised between 570 and 720 MPa, and the ultimate tensile strength is comprised between 780 and 920 MPa. For example, the steel sheet used to make the reinforcement element 14 has a thickness comprised between 0,9mm and 1 ,5mm. As depicted in figure 2, an inner face of the corresponding reinforcement element 14 is attached to the main beam 3 facing a rear wall 8 of said main beam 3. In the current description, for clarity sake, the terms “front” and “rear” are used relative to a front beam assembly 2 - in the case of a beam assembly 2 corresponding to a rear bumper according to the invention, the terms front and rear should be interchanged.

As depicted on figure 4, the crash bod 22 is attached to the base wall 26 of the reinforcement element 14. This connection is made for example by welding, for example using metal active gas welding (MAG welding). Figure 4 depicts an embodiment in which MAG welding was used to attach the crash box 22 to the base wall 26, the weld seams are depicted by the reference 29. In a particular embodiment depicted in figure 4, the energy absorption element 20 has a general rectangular cross section, comprising four corrugated lateral walls 28. The corrugated shape of the lateral walls 28 allows to control the buckling behavior of the absorption element 20 when submitted to a compressive load, as is well known to the skilled person.

The main beam 3 comprises a front wall 9 extending towards the exterior of the vehicle 1 , and the opposite rear wall 8 extending towards the interior of the vehicle 1. Furthermore, the beam 3 comprises an upper wall 10 and an opposite lower wall 1 1 , both extending perpendicularly to the rear and front walls 8, 9. Finally, the beam 3 comprises a central wall 23 dividing the beam 3 into an upper hollow body and an adjacent lower hollow body, said central wall 23 extending perpendicularly to both rear and front walls 8, 9.

For example, the main beam 3 according to the present embodiment is manufactured according to a process comprising the following steps:

-Roll forming a sheet into a continuous 8-shaped cross section,

-bending the thus obtained roll formed shape to imprint the general curvature of the central portion 4 and cutting it to the length of the main beam 3 destined to be mounted on the vehicle (the bending and cutting operation can be carried in any order, some industrial operations being more suited to bending before cutting and vice versa), -In the case when the side portions 5 are made from a succession of straight planes, it can be interesting to from transverse cutouts 42, as depicted on figure 2, on the sides of the beam 3. These cutouts are located in the areas destined to form the curvatures 12, 13. The cutouts 42 allow for further bending of the very high strength steel used in these areas,

-Further bending the side portions of the bumper beam 3 to form the curvatures 12, 13. This operation is made possible even on roll formed very high strength steels, which will resist the high bending angle, thanks to the above described cutouts 42. Indeed, without cutouts 42, the bending of the semi-finished roll formed main beam 3 to form the curvatures 12, 13 would necessitate extremely high bending strength and could result in either cracks or folds forming around the curvatures 12, 13, or even both problems simultaneously. Thanks to the presence Furthermore, the width of the cutouts 42 in the transverse direction can be advantageously designed so that the edges of the cutouts in the rear wall 8 touch each other at the end of the bending operation. This provides the double advantage of minimizing the necessary cutout width (said cutouts 42 introduce a structural weakness in the part and should be kept to a minimum), while at the same time providing a useful physical cue to the manufacturer (the process cannot go further once the appropriate bending angle is reached).

Once the bumper beam 3 has been obtained through the above described process, the bumper assembly 2 is formed by a process comprising the following steps:

-Attaching the opposite lateral walls 27 of the reinforcement element 14 to the upper wall 10 and to the lower wall 1 1 of the beam 3 (see figure 4). This operation is performed for example by laser welding (the weld seam is depicted as reference 30 on figure 4). Laser welding is advantageously applied in this case because it allows to weld the parts together with only one access point from the outside. Laser welding can be performed either to ensure a continuous joint between the reinforcement element 14 and the bumper beam 3, or to form a dis-continuous joint between the two parts, also known as laser stitches. The advantage of a continuous joint is that it provides the best possible assembly strength and ensures optimal cooperation between the parts. On the other hand, laser stitches can be used as a good compromise between a good assembly strength and an improved productivity thanks to the shorter distance to be welded.

-Referring to figure 5, the thus obtained first assembly 24 formed by the association between the bumper beam 3 and the reinforcement elements 14 is then secured to the corresponding energy absorption element 20. This assembly step is for example performed by MAG welding, as mentioned previously. MAG welding is particularly advantageous in this type of configuration involving already formed parts, having nonlinear shapes and possibly exhibiting some geometrical differences from one part to another, due to the industrial tolerances on the parts and the presence of local distortions due, among others, to springback when using very high strength steels. Indeed, thanks to the presence of a welding wire, MAG welding can accommodate for some shape variations, by filling up the gaps with more or less wire. MAG welding is also a very commonly used technology in the automotive industry which provides very high strength assemblies at industrial productivity rates.

-The thus formed bumper assembly 2 is then ready to be assembled to the rest of the vehicle structure, for example by welding, the connecting plates 21 of the crash box 22 to the corresponding side members 25 of the vehicle 1 .

Advantageously, thanks to the above described structure and forming process of the bumper assembly 2, it is possible to form a bumper assembly 2 having an important overall curvature and length of the side portions 5. The cutouts 42, which make it possible to obtain such a shape also allow to control the above described unfolding behavior of the side portions 5 - indeed the material will start to unfold first in the areas of the cutouts 42. The areas of the onset of unfolding can therefore be controlled and adjusted thanks to the positioning of the cutouts 42. ON the other hand, said cutouts 42 weaken the resistance of the main beam 3 in the side portions. This structural weakness is compensated by the presence of the side reinforcement 7, embodied by the reinforcement elements 14. Thus, the bumper assembly exhibits in said side portions a very high strength, a high resistance in case of crash and a very good energy absorption and shielding properties in case of a head on collision as was described previously. Referring to figures 6 to 9, a second embodiment of the bumper assembly 2 according to the invention will now be described.

In this second embodiment, the main beam 3 extends only over the central portion 4. The bumper assembly 2 further comprises side reinforcements 7, which make up the side portions 5 and connect to the main beam 3 in the area of the crash boxes 22.

Each reinforcement structure 7 comprises two reinforcement elements 15, 16, respectively a rear reinforcement element 16 provided to face the rear wall 8 of the main beam 3 and a front reinforcement element 15 provided to face the front wall 9 of the main beam 3. In the current description, for clarity sake, the terms “front” and “rear” are used relative to a front beam assembly 2 - in the case of a beam assembly 2 corresponding to a rear bumper according to the invention, the terms front and rear should be interchanged.

As depicted on figure 9, each reinforcement element 15, 16 comprises a fastening section 17 provided to be attached to the main beam 3, and an adjacent strengthening section 18 forming the corresponding side portion 5 of the bumper assembly 2.

As depicted on figure 7, the fastening section 17 has a generally U-shaped cross section and comprises a substantially plane base wall 26a and two lateral walls 27a both perpendicular to the base wall 26a. The strengthening section 18 of each reinforcement element 15, 16 also comprises a base wall 26b and two lateral walls 27b both perpendicular to the base wall 26b. In a particular embodiment, the base wall 26b of each strengthening section 18 advantageously comprises a longitudinal groove 19, reinforcing and stiffening the corresponding strengthening section 18. When the side reinforcement 7 is attached to the main beam 3, the two reinforcement elements 15, 16 are facing each other and the corresponding grooves 19 of said reinforcement elements 15, 16 are also facing each other. In addition, the outer faces of both groove 19 are in contact.

Each reinforcement element 15, 16 is for example made of by forming a steel sheet having the following mechanical characteristics: the yield strength is comprised between 570 and 720 MPa, and the ultimate tensile strength is comprised between 780 and 920 MPa. For example, the reinforcement elements, 15, 16 are made from a steel sheet having a thickness comprised between 0,9 and 1 ,5mm.

As depicted in figure 6, the beam assembly 2 according to the second embodiment also comprises two crash boxes 22 as described above. The connector plate 21 of each crash box 22 is attached to the corresponding side member 25 of the vehicle 1 , while the opposite end of the absorption element connector 22 is attached to the outer face of the fastening section 17 of the rear reinforcement element 16.

Turning to figure 8, the crash box 22 is attached to the base wall 26a of the fastening section 17 of the rear reinforcement element 16, for example via MAG welding, for the same reasons as described above. The MAG weld seams are depicted by references 29.

Finally, the opposite lateral walls 27a of the fastening section 17 of the rear reinforcement element 16 are attached to each other and to the upper wall 10 and to the lower wall 1 1 of the main beam 3, for example by laser welding, for the same reasons as explained above. The laser welds are depicted by reference 30 on figure 8.

Figure 9 depicts an example of possible assembly sequence of the bumper assembly 2 according to the second embodiment.

-In a first step, a first assembly 24a is provided by securing, for example by welding, each side reinforcement 7 to the main beam 3. More precisely, the lateral walls of the fastening section 17 of each rear reinforcement element 16 are attached for example by laser welded respectively to the lower and upper walls 10, 1 1 of the main beam 3, said rear reinforcement elements 16 facing the rear wall 8 of the main beam 3. Then, the lateral walls 26a of the fastening section 17 of each front reinforcement element 15 are attached for example by laser welding to the lateral walls 26a of the corresponding rear reinforcement element 16, said front reinforcement elements 15 facing the front wall 9 of the main beam 3. Finally, in the specific examples when grooves 19 have been practiced in the reinforcing elements 15, 16, the facing grooves 19 of the rear and front reinforcement elements 15, 16 can be attached together, for example by spot welding, to further reinforce the assembly. In a second step, a second assembly is provided by securing, for example by welding, each connecting plate 21 to the second ends 41 of the corresponding energy absorption element 20 thus forming the two crash boxes 22.

In a third step, a final bumper assembly 2 is provided by securing, for example by welding, the first ends 40 of each crash box 22 to the outer face of the fastening section 17 of the corresponding rear reinforcement element 16.

The bumper assembly 2 is then ready to be assembled to the vehicle 1 by securing each connecting plate 21 of the absorption element connector 22 to the corresponding side member 25 of the vehicle 1. Said assembly can be performed for example by screwing said connecting plate 21 to said front member 25 through holes provided within the connecting plate 21 .

Advantageously, thanks to the above described structure and forming process of the bumper assembly 2a, it is possible to form a bumper assembly 2a having an important overall curvature of the side portions 5 and which exhibit in said side portions a very high strength and high resistance in case of crash.

Claims

CLAIMS ) Bumper assembly (2) for an automotive vehicle (1 ) comprising at least a main beam (3) and two crash boxes (22), said bumper assembly (2) consisting of a central portion (4) corresponding to the part of the bumper assembly (2) extending transversally in between said two crash boxes (22) and including said crash boxes (22), and two side portions (5) corresponding to the part of the bumper assembly (2) extending outside of the crash boxes (22) in the transverse direction, said side portions (5) each comprising a proximal edge (10), which is the edge of the side portion (5) located the closest to the central portion (4) and a distal edge (36), which is the edge of the side potion (5) located furthest away from the central portion (4), wherein each distal edge (36) longitudinally faces a corresponding wheel (6). ) Bumper assembly (2) according to claim 1 , wherein the tangent (44) to the side portion (5) at its distal edge (36) forms with the transverse direction of the vehicle (1 ) an angle (45) comprised between 0° and 90°. ) Bumper assembly (2) according to claim 1 or 2, having an outer contour (50), which is defined as the line delimiting the top part of the bumper assembly (2) on the side facing the outside of the vehicle, wherein Lcenter is the length of the outer contour (50) corresponding to the central portion (4) and wherein Lsidel , Lside2 are the lengths of the outer contour (50) corresponding respectively to a first and second side portion 5 of the bumper assembly (2) and wherein Lsidel + Lside2 > 0,5*Lcenter. ) Bumper assembly (2) according to any one of claims 1 to 3, wherein Lwheels is the distance between the outer parts of the wheels 6 measured in the transverse direction of the vehicle (1 ), and wherein Lcenter + Lsidel + Lside2 > Lwheels. ) Bumper assembly (2) according to any one of claims 1 to 4, further comprising two side reinforcements (7) one on either side of said bumper assembly (2), wherein said side reinforcements (7) extend at least over the entire width of each side portion (5). ) Vehicle (1 ) having a bumper assembly (2) according to any one of claims 1 to 5.