FRONT ARM SUPPORT FOR MOTOR VEHICLES

Description

[0001] The present invention relates to the field of vehicles, and in particular to motor vehicles. The invention concerns a vehicle front foot structure, a vehicle comprising such a structure, and a method for manufacturing such a front foot structure.

[0002] Generally, the front (US 2005 / 046237 A1) and rear pillars of a vehicle are uprights located towards the front or rear of the body side, between a wheel well and a door opening. The pillars have different geometries, specific to their location at the front or rear of the vehicle.

[0003] A front leg can be composed of several structural parts assembled together by welding or riveting. figure 1 This assembly comprises a set of parts welded together to form a front pillar 1. The various parts thus assembled include a front reinforcement pillar 3, an upper front pillar gusset 5, and a front reinforcement 7 on the passenger side. In a frontal impact, the resulting forces are transmitted to the vehicle structure via the side members and the A-pillars, forming two load paths. A third load path includes the front reinforcement on the passenger side 7, arranged on each side of the vehicle at the wheel arch to transmit the forces received to the side members and the A-pillars via the upper front pillar gussets 5 and the front pillar reinforcements 3.

[0004] In particular, in a frontal collision with minimal front overlap, known as a "small overlap" collision, the lateral part of the vehicle's front structure is subjected to significant stress. This type of collision occurs when an impactor dents the front of the vehicle, making contact with only a portion of the front end, including the lateral edge. This type of collision is exemplified by a head-on collision between two vehicles positioned slightly apart. In this type of impact, the front reinforcement on the passenger side, opposite the impactor, will bear the brunt of the stress. If the mechanical strength of this reinforcement is insufficient, it will deform excessively during the impact, allowing the impactor to push against the wheel, which will then load the front wheel and cause it to move towards the rear of the vehicle.Furthermore, if the front strut is not sufficiently strong, it risks being forced backward under the stress transmitted by the front reinforcement during an impact. The risk of intrusion into the passenger compartment is then significant. It is essential to find a balance between the mechanical strength of the reinforcement and the front strut to ensure both the deformation of the front of the vehicle and the reinforcement itself, allowing for energy absorption during an impact while minimizing intrusion into the passenger compartment.

[0005] A known problem arising from the assembly of these different parts is a sealing issue that would be beneficial to resolve. Furthermore, the automotive industry is constantly seeking solutions to reduce vehicle manufacturing costs and weight. Finally, there is an ongoing focus on improving mechanical performance and impact resistance. This is why several other types of front strut structures have already been proposed.

[0006] Document FR2926056 describes a reinforced front foot for vehicles comprising an upper part, or gusset, and a lower part, or front foot reinforcement. The front foot reinforcement is a single piece with various stampings that stiffen it to improve its performance in limiting front foot rotation in the event of a frontal impact.

[0007] Document FR2800698 proposes a front pillar structure that combines the front pillar reinforcement and the upper front pillar gusset into a single piece. The resulting piece extends substantially vertically and includes beam end supports for its connection to the side member, the window pillar, and the front reinforcement on the passenger compartment side. The piece is preferably made from a single piece of lightweight metal casting, particularly aluminum or a lightweight metal alloy, particularly an aluminum alloy.

[0008] Document EP2080689 describes a lateral reinforcement device intended to be fitted to a front section of a motor vehicle. The device comprises an elongated reinforcement element, which is intended to be fixed to the vehicle body structure at a side wall of the front section by extending, in the longitudinal direction of the vehicle, between a front pillar of the vehicle adjacent to the side wall and a front end of the front section, with the longitudinal axis of the reinforcement element directed substantially parallel to the longitudinal direction.

[0009] The invention aims to address the drawbacks and problems encountered in the prior art by proposing a new, more watertight front pillar structure. The invention also aims to provide a new, lighter front pillar structure. The invention further aims to improve vehicle performance in the event of a small overlap frontal collision. Finally, the invention aims to provide a more economical method for manufacturing such a structure.

[0010] To this end and according to a first aspect, the invention relates to a front foot of a vehicle consisting of a stamped part comprising a central body intended to extend vertically, so as to show a lower end and an upper end and lateral edges, the front foot being remarkable in that it further comprises a front extension extending from one of said lateral edges of said central body, so that said central body and said extension form a single piece.

[0011] As can be understood from the definition just provided, the invention is remarkable in that it combines three structural parts—namely, the upper front pillar gusset, the front pillar reinforcement, and the front reinforcement on the passenger compartment side—into a single unit. In doing so, the invention addresses the sealing problems encountered in the prior art. The invention also reduces the overall weight of the vehicle. Finally, the invention simplifies the vehicle assembly process since it eliminates the need to assemble these different parts, thereby lowering overall production costs.

[0012] In a preferred embodiment, the central body includes, at its lower end, a mounting area for attaching to a longitudinal member and / or, at its upper end, a mounting area for attaching to a window frame. The central body performs the functions of a front leg reinforcement and an upper front leg gusset.

[0013] Advantageously, the aforementioned extension before: extends from one of said lateral edges of said central body in a substantially horizontal direction; and / or extends from one of said lateral edges of said central body to a height between the lower and upper extremities of the central body; and / or forms with the central body an arc-shaped circular form intended to form a wheel arch; preferably the central angle α intercepting said arc-shaped circular is greater than or equal to 45°.

[0014] According to a preferred embodiment, the central body and / or the front extension include at least one reinforcing rib; preferably, the front extension includes at least one reinforcing rib arranged to extend horizontally.

[0015] According to one embodiment of the invention, the front foot is made of ultra-high yield strength steel having, after hot stamping, a mechanical strength Rm of at least 1200 MPa as measured according to ISO 6892-1:2016 and an elongation at break of at least 3% as measured according to ISO 6892-1:2016.

[0016] Alternatively, the central body of said front foot has a mechanical resistance greater than the mechanical resistance shown by its front extension; preferably, the central body has a mechanical resistance Rm of at least 1200 MPa and the front extension has a mechanical resistance Rm between 300 and 1150 MPa, the mechanical resistance being measured according to ISO 6892-1:2016.

[0017] Alternatively, the thickness of the central body is greater than that of the front extension. That is to say, the thickness of the part forming the central body is greater than the thickness of the part forming the extension.

[0018] According to a second aspect, the invention relates to an assembly comprising a front foot as defined in the first aspect, the assembly further comprising a reinforcing piece configured to overlap at least partially the upper end of said central body and said front extension. Said reinforcing piece is assembled to the foot by welding.

[0019] According to a third aspect, the invention relates to a reinforcing piece notable in that it consists of a hot-drawn steel piece configured to have a shape complementary, at least in part, to the upper end of the central body and the front extension of a front foot as described in the first aspect, so as to be able to be superimposed on it. Preferably, said reinforcing piece is made of steel having, after hot drawing, a tensile strength Rm of between 400 and 1100 MPa, the tensile strength being measured according to ISO 6892-1:2016.

[0020] According to a fourth aspect, the invention relates to a vehicle remarkable in that it comprises at least one front foot as defined according to the first aspect, or an assembly according to the second aspect.

[0021] According to a fifth aspect, the invention relates to a method for manufacturing a front foot according to the first aspect, the central body of said front foot exhibits a mechanical resistance greater than the mechanical resistance shown by its front extension, the method being remarkable in that it comprises a differential hardening operation including at least: a step of heating a steel blank to a temperature beyond which the steel structure becomes austenitic; a step of hot drawing the heated blank in a drawing tool having at least two zones; and a step of differentially quenching the different zones, such that at least one zone of the drawing tool is cooled at a cooling rate higher than the cooling rate applied to another zone.

[0022] Preferably, the differential hardening operation includes, during the stamping step, an additional step of heating a portion of the stamped blank in at least one area, so that at the time of the hardening step at least one area of ​​the stamping tool is brought to a temperature higher than the temperature shown by another area of ​​said tool.

[0023] According to a sixth aspect, the invention relates to a method for manufacturing a front foot according to the first aspect, the central body of said front foot exhibits a mechanical resistance greater than the mechanical resistance shown by its front extension, the method being remarkable in that it comprises a laser splicing operation including: a laser welding step of at least two sheet metal elements arranged adjacently so as to form a sheet metal blank comprising at least two portions showing different mechanical characteristics from each other, and a hot stamping step of such a blank so as to form a front foot comprising a central body and an extension showing different mechanical characteristics from each other.

[0024] The invention will be well understood and other aspects and advantages will become clear upon reading the following description, given by way of example and with reference to the attached drawing, according to which: there figure 1 represents an assembly forming a forefoot structure according to prior art, and the figure 2 represents an assembly forming a front foot structure according to the invention.

[0025] In the following description, the term "include" is synonymous with "include" and is not restrictive in that it permits the presence of other elements in the structure, vehicle, or front strut reinforcement component to which it refers. It is understood that the term "include" includes the term "consist of." In the various figures, the same reference numerals designate identical or similar elements. The terms "lower," "upper," "front," and "rear" are understood in relation to the overall orientation of the vehicle. The term "lower" indicates a closer proximity to the ground in the vertical direction than the term "upper." The term "front" indicates a forward-facing position of a vehicle in the horizontal direction, and the term "rear" indicates a rearward-facing position of a vehicle in the same direction.The term "horizontal part" will define a portion of a vehicle component extending between a front end and a rear end of said component. The unit of measurement MPa stands for "Mega Pascals".

[0026] There figure 1 Having been discussed in the introductory section, we will now refer to the figure 2 .

[0027] The invention proposes a front foot 9 of a vehicle consisting of a stamped part comprising a central body 11 intended to extend vertically when mounted in the vehicle, so as to show a lower end 13 and an upper end 15 and lateral edges, the front foot 9 being notable in that it further comprises a front extension 17 extending from one of said lateral edges of said central body 11, such that said central body 11 and said front extension 17 form a single piece.

[0028] According to a preferred embodiment, the central body 11 includes, at its lower end 13, a mounting area for a side rail and, at its upper end 15, a mounting area for a window jamb. The central body 11 thus performs the functions of the front leg reinforcement pieces and the upper front leg gusset of the prior art. The mounting areas for the side rails or window jambs include at least one wall and / or at least one bearing edge against which at least a portion of a wall of a side rail or window jamb contacts.

[0029] The front extension 17 of the front strut 9 according to the invention performs the function of the front reinforcement on the passenger compartment side of the prior art. As such, the front extension 17 extends from one of the lateral edges of the central body 11 in a substantially horizontal direction towards the front of the vehicle in which the front strut 9 is intended to be mounted, and / or at a height between the lower end 13 and the upper end 15 of the central body 11. The front strut 9 has a general three-pronged cross shape, each prong representing a load path in the event of a frontal impact. Preferably, one of the prongs, namely the front extension 17, has an arched profile.

[0030] According to an advantageous configuration, the front extension 17 forms, with the central body 11 and partly with its lower part, an arc-shaped form intended to create a wheel arch. Preferably, the central angle α intercepting said arc is greater than or equal to 45°, preferably the angle α is greater than or equal to 50°, more preferably the angle α is greater than or equal to 55°, and even more preferably the angle α is greater than or equal to 60°. This configuration is particularly advantageous for impact resistance with a small overlap. Indeed, in the prior art, the assembly of different parts did not allow for a satisfactory connection between the rebates at the wheel arch. On the figure 1It can be seen that the curve defining the wheel arch is interrupted at the junction between the front pillar reinforcement 3 and the front reinforcement 7 on the passenger compartment side. This break reduces impact resistance due to a wedge effect, making the assembly less robust. Having only one piece, as in the invention, allows for better control of the part's geometry and improved performance in managing impacts with small overlaps.

[0031] According to a preferred embodiment, the central body 11 and / or the front extension 17 include at least one reinforcing rib (not shown). Preferably, the front extension 17 includes at least one reinforcing rib arranged to extend horizontally. The presence of one or more reinforcing ribs provides rigidity to the front leg 9.

[0032] According to a first embodiment of the invention, the front foot 9 can be homogeneous in its mechanical characteristics. Those skilled in the art would then benefit from using an ultra-high yield strength steel for its manufacture, having a tensile strength Rm of at least 1200 MPa as measured according to ISO 6892-1:2016 and an elongation at break of at least 3% as measured according to ISO 6892-1:2016. Steels with such characteristics are available on the market, for example, those marketed by ArcelorMittal under the trade name Usibor ©< 1500 or 22MnB5. These steel grades, after hot drawing, exhibit a yield strength Re of 1100 MPa, a tensile strength Rm of 1500 MPa, and an elongation at break A ≥ 6%.

[0033] According to another embodiment of the invention, the central body 11 and the front extension 17 have different mechanical characteristics. In particular, the central body 11 of the front foot 9 has a higher mechanical resistance than the mechanical resistance shown by its front extension 17. Thus, ideally, the central body 11 has a mechanical resistance Rm of at least 1200 MPa, while the front extension 17 has a mechanical resistance Rm between 300 and 1150 MPa, the mechanical resistance being measured according to ISO 6892-1:2016. Preferably, the mechanical resistance Rm exhibited by the central body 11 is at least 1300 MPa, more preferably at least 1400 MPa, and even more preferably at least 1500 MPa. Preferably, the front extension 17 has a mechanical resistance between 350 and 1100 MPa, preferably between 400 and 1000 MPa, more preferably between 400 and 900 MPa, and more preferably still between 450 and 800 MPa.

[0034] Steels that can be used in the field of hot stamping of automotive structural parts can be classified according to their mechanical characteristics and in particular by their mechanical strength characteristic Rm as measured according to ISO 6892-1:2016 as well as their elastic properties indicated by their elongation at break A or by their yield strength Re, also measured according to ISO 6892-1:2016.

[0035] When steel is deformed, this deformation is reversible and proportional to the load as long as it remains within the steel's elastic deformation range. When the load becomes too great, the steel enters the plastic deformation range, in which the deformations undergone by the steel are irreversible. The yield strength (Re) of a steel is the stress (unit load) that defines the boundary between the plastic and elastic ranges. When a force is applied to steel beyond its yield strength, the resulting deformation is therefore irreversible. Tensile strength (Rm) represents the maximum allowable stress for a steel. When a force is applied to steel beyond its tensile strength limit, it will break. Elongation at break (A) represents the maximum allowable relative deformation of a steel before it breaks.

[0036] We can thus distinguish between mild steels showing a yield strength of 300 to 350 MPa, high yield strength (HLE) steels showing a yield strength of 400 to 700 MPa, very high yield strength (THLE) steels showing a yield strength of 800 to 1000 MPa and ultra high yield strength (UHLE) steels showing a yield strength of 1100 to 1500 MPa.

[0037] Therefore, when it exhibits homogeneous mechanical properties, the front foot 9 according to the invention will preferably be made of ultra-high-strength steel. Whereas, when it has areas with different mechanical properties, the front foot 9 according to the invention will preferably comprise a central body 11 made of very high-strength steel and a front extension 17 made of high-strength steel.

[0038] Alternatively, when the front foot 9 according to the invention has homogeneous mechanical properties, it can be made of a steel having a lower mechanical resistance than an ultra-high yield strength steel, such as for example a very high yield strength or high yield strength steel, the thicknesses then being chosen to obtain the desired mechanical resistance of the different parts of said front foot.

[0039] According to a preferred embodiment of the invention, when comprising portions exhibiting different mechanical characteristics, the front foot 9 can be formed by hot stamping with differential cooling. An example of a hot stamping tool with differential cooling is described in document FR2927828. The manufacturing process includes a differential hardening operation comprising at least: a step of heating a steel blank to a temperature beyond which the steel structure becomes austenitic; a step of stamping the heated blank in a stamping tool having at least two zones; a step of differentially quenching the different zones, such that at least one zone of the stamping tool is cooled at a cooling rate higher than the cooling rate applied to another zone.

[0040] According to a known principle, the higher the cooling rate of a steel part, the higher its final mechanical strength. Therefore, according to the invention, the central body 11 of the front foot 9 will be cooled at a higher quenching rate than that used for cooling the front extension 17.

[0041] Preferably, the differential hardening operation includes, during the drawing step, an additional heating step of a portion of the drawn blank in at least one area, such that, at the time of the hardening step, at least one area of ​​the drawing tool is at a temperature higher than that of another area of ​​said tool. The tool then comprises a so-called hot zone and a so-called cold zone. The portion(s) of the front foot 9 located in the so-called hot zone will exhibit lower mechanical strength than the portion(s) of the front foot 9 located in the so-called cold zone. Therefore, according to the invention, the central body 11 of the front foot 9 will be formed in a so-called cold zone of the drawing tool, while its front extension 17 will be formed in a so-called hot zone of said tool.

[0042] The choice of heating temperatures and cooling rates will be easily adapted by a person skilled in the art according to the initial characteristics of the steel used and the desired final characteristics.

[0043] According to another preferred embodiment of the invention, when comprising portions exhibiting different mechanical characteristics, the front foot 9 can be formed by laser joining. Laser joining is a technique known to those skilled in the art, which consists of placing two or more blanks against each other and welding them together by laser welding to form a sheet metal blank comprising at least two adjacent parts exhibiting different mechanical and elastic characteristics. The blank obtained by laser joining is then hot-drawn within a single die to obtain a part exhibiting different mechanical characteristics in different areas.In cases where the front foot has inconsistent mechanical properties, different mechanical properties for the central body 11 and the front extension 17 can be achieved by using sheet metal blanks of different thicknesses and / or blanks made from different grades of steel for said central body 11 and said front extension 17. For example, the central body 11 can be made from a sheet metal blank of ultra-high-strength steel and the extension 17 from a sheet metal blank of high-strength steel, or the central body 11 can be made from a sheet metal blank thicker than the sheet metal blank used for the extension 17. A combination of different sheet metal thicknesses and grades can also be considered.A person skilled in the art will know how to choose the thicknesses and / or grades of steel to obtain the desired mechanical characteristics of the different parts forming the front foot of the invention.

[0044] According to a preferred embodiment, where necessary, the front leg 9 is reinforced by a reinforcing piece 19. This reinforcing piece 19 is a hot-drawn steel piece configured to have a shape complementary, at least in part, to the upper end 15 of the central body 11 and to the front extension 17 of a front leg, so as to be able to overlap it. Optionally, said reinforcing piece includes at least one stiffening rib (not shown). Preferably, said reinforcing piece 9 is made of steel having, after hot drawing, a tensile strength Rm of between 400 and 1100 MPa, the tensile strength being measured according to ISO 6892-1:2016. The reinforcing piece 19 is welded to the front leg 9. The weld points are arranged both on the bottom of the piece and on the rebates.

Claims

1. A front foot (9) of a vehicle consisting of a stamped piece comprising a centre body (11) intended to extend vertically, so as to show a lower end (13) and an upper end (15) and lateral edges, the front foot (9) being characterised in that it further comprises a front extension (17) extending from one of said lateral edges of said centre body (11), so that said centre body (11) and said front extension (9) form a single component.

2. Front foot (9) according to claim 1, wherein the central body (11) comprises at the level of its lower end (13) a zone for fixing to a spar and / or at the level of its upper end (15) a zone for fixing to a bay upright.

3. Front foot (9) according to either of Claims 1 and 2, characterised in that the said front extension (17): - extends from one of said lateral edges of said central body (11) in a substantially horizontal management, and / or - extends from one of said lateral edges of said central body (11) to a height between the lower (13) and upper (15) ends of the central body (11); and / or - forms with the central body (11) an arc of a circle shape intended to form a wheel arch; preferably the angle α at the compound intercepting said arc of a circle is greater than or equal to 45°.

4. Front foot (9) according to one of Claims 1 to 3, characterised in that the central body (11) and / or the front extension (17) comprise at least one reinforcing rib; preferably, the front extension (17) comprises at least one reinforcing rib arranged to extend horizontally.

5. Front foot (9) according to one of Claims 1 to 4, characterised in that: - said front leg (9) is made of ultra high elastic limit steel having, after hot stamping, a mechanical strength Rm of at least 1200 MPa as measured according to ISO 6892-1:2016 and an elongation at break of at least 3 % as measured according to ISO 6892-1:2016; or - the central body (11) of the said front foot (9) has a mechanical strength greater than the mechanical strength shown by its front extension (17); preferably, the central body (11) has a mechanical strength Rm of at least 1200 MPa and the front extension (17) has a mechanical strength Rm of between 300 and 1150 MPa, the mechanical strength being measured according to the standard ISO 6892-1:2016.

6. Front foot (9) according to one of Claims 1 to 5, characterised in that the thickness of the central body (11) is greater than that of the front extension (17).

7. Assembly comprising a front leg (9) according to one of Claims 1 to 6, characterised in that it further comprises a reinforcing component (19) configured to be superposed at least in part on the upper end of said central body (11) and on said front extension (17).

8. Assembly according to claim 7, wherein said reinforcing component (9) is made of a hot-drawn steel component, and is realised of a steel having, after hot stamping, a mechanical strength Rm of between 400 and 1100 MPa, the mechanical strength being measured according to ISO standard 6892-1:2016.

9. Vehicle characterised in that it comprises a front leg (9) according to one of Claims 1 to 6, or an assembly according to one of Claims 7 or 8.

10. Method for manufacturing a front foot (9) according to one of Claims 1 to 5, the central body (11) of the said front foot (9) having a mechanical strength greater than the mechanical strength shown by its front extension (17), the method being characterised in that it comprises a differential tempering task comprising at least: - a step of heating a steel blank to a temperature beyond which the steel structure becomes austenitic; - a step of hot stamping of the heated blank in a stamping tool having at least two zones; and - a step of differential quenching of the different zones, such that at least one zone of the stamping tool is cooled at a higher cooling rate than the cooling rate of another zone; preferably, the differential tempering task comprises, during the stamping step, an additional step of heating a portion of the stamped blank to the level of at least one zone, such that, at the time of the tempering step, at least one zone of the stamping tool is brought to a temperature higher than the temperature shown by another zone of said tool.

11. Method for manufacturing a front leg (9) according to one of Claims 1 to 6, the central body (11) of said front leg (9) having a mechanical strength greater than the mechanical strength shown by its front extension (17), the method being characterised in that it comprises a laser butting task comprising: - laser welding of at least two sheet items disposed adjacent to each other so as to form a sheet blank comprising at least two portions exhibiting different mechanical characteristics from each other, and - step of hot stamping of such a blank so as to form a front foot (9) comprising a central body (11) and a front extension (17) exhibiting different mechanical characteristics from each other.