Stiffening element for a motor vehicle

Abstract

The present invention relates to a structural element (2) for a motor vehicle, comprising a shell (4), the envelope of which defines a hollow body (6), and at least one stiffening element (8) housed in the hollow body (6) and overmolded onto the shell (4), the stiffening element (8) comprising at least one insert (10) formed of a composite material formed of at least one sheet of composite material.

Description

DESCRIPTION Title of the invention: Stiffening element for a motor vehicle

[0001] The present invention relates to the field of stiffening elements integrated within a motor vehicle to stiffen its structure.

[0002] Vehicles, and especially motor vehicles, are typically equipped with components such as mounting brackets and protective covers. These components are commonly subjected to stresses that can lead to degradation, such as plastic deformation. Consequently, the stresses applied to these components can impair their effectiveness for their intended use.

[0003] Therefore, it becomes necessary to provide methods for stiffening these elements. To this end, some of these elements are reinforced with ribs that increase their rigidity. These ribs can be formed by a manufacturing process in which a material is injected into a mold. Typically, the injected material is a thermoplastic resin that fills cavities within the mold to form the ribs. However, to ensure sufficient stiffness for the element being reinforced, these resin ribs are quite large relative to the dimensions of the element being stiffened.

[0004] Although such ribs can increase the stiffness of the element to be stiffened, they do not address the problems faced by the automotive industry.

[0005] Indeed, for performance reasons within the context of preserving natural resources and the environment, motor vehicles must meet weight and carbon footprint criteria. The ribs typically used to increase the rigidity of a component do not optimally address this dual constraint.

[0006] The present invention falls within this context and aims to overcome at least some of the drawbacks of the prior art. In particular, the present invention aims to provide an efficiently stiffened structural element with a low carbon footprint and limited weight, while ensuring optimal stiffening of the structural element.

[0007] Thus, the present invention relates to a structural element of a motor vehicle, comprising a shell whose outer shell defines a hollow body and at least one element stiffening element housed in the hollow body and overmolded onto the shell, the stiffening element comprising at least one insert formed of at least one sheet of composite material.

[0008] This composite material sheet, also known by the English term "organosheet", is a composite material formed from a continuous fabric of carbon or glass fibers integrated into a thermoplastic matrix.

[0009] This composite sheet replaces, at least in part, the use of resin for reinforcement in a given area of ​​the structural element. In other words, the use of an insert according to the invention, formed from at least one composite sheet, makes it possible to limit the amount of resin required to generate the desired local stiffness of the structural element, as the insert has a better carbon footprint and stiffening efficiency than resin. Indeed, the presence of the fiber fabric within the composite sheet, as described above, generates mechanical properties, at least in terms of stiffness, that are superior to those of a thermoplastic material alone, such as resin. This increased stiffness allows for a reduction in the required thickness of the material used and therefore a reduction in the weight of the structural element.

[0010] According to one feature of the invention, the stiffening element further comprises at least one resin overmolded onto at least one insert, said resin also being used to mold at least partially the hull. For example, said resin is the same as that used for injection molding the hull. It is understood that the stiffening element is formed by a combination of the insert, which has a rigid shape that does not change during the injection molding process of the structural element, and the resin, which is injected and takes the shape imposed by the injection mold. This resin allows for the formation of areas of the stiffening element distinct from that formed by the insert, and it allows the insert to be held within the hull.

[0011] Furthermore, as previously stated, the resin is overmolded onto the shell and the insert, so that the insert is at least partially embedded in the resin. Thus, the stiffening element is equipped with means, such as resin, to hold the insert in position relative to the shell; the resin acts as the bonding agent that secures the insert to the injected shell.

[0012] According to one feature of the invention, the insert has a first face and a second face delimited by a peripheral end edge opposite the shell and A free end edge opposite the peripheral end edge, the free end edge of the insert being at least partially covered by the resin of the stiffening element. In other words, the hollow body defined by the shell is configured to form an open face, and the insert extends into this shell such that one of its edges extends across this open face. The peripheral end edge of the insert is understood to be the edge(s) of this insert that are directly opposite, or in contact with, one of the walls of the shell delimiting the hollow body, and the free end edge is the edge of the insert that is not opposite the shell.

[0013] According to one feature of the invention, the resin helps to hold the insert laterally, and at least one of the first and second faces is at least partially covered with a strip of resin.

[0014] According to one feature of the invention, the peripheral end edge is disposed at least partly in contact with the hollow body.

[0015] According to one feature of the invention, the stiffening element has a rib matrix shape, at least one insert participating in making at least one of the ribs of the rib matrix and the resin making entirely at least one other of the ribs of the rib matrix.

[0016] According to one feature of the invention, the rib matrix comprises a plurality of first ribs among which at least one rib is formed at least in part by the insert and a plurality of second ribs intersecting the first ribs and formed of resin.

[0017] According to one feature of the invention, the insert is held in place by the second ribs.

[0018] According to one feature of the invention, the shell is made of a plastic material.

[0019] The invention also relates to a method for manufacturing a structural element using at least one mold having at least one slot configured so that a resin is injected into at least one slot to form the stiffening element and at least: - a first step during which an insert is placed in at least one slot of the mold, - a second step during which a resin is injected into the mold and is overmolded onto the insert and onto the shell present in the mold.

[0020] The shell can be inserted into the mold before the resin is injected, that is, prior to the second step. Alternatively, the shell can be formed directly in the mold using a bi-injection process. In this bi-injection process, the insert is placed in a slot in the mold, which is then closed. Next, the first material to form the shell is injected into the mold. This first material is injected before the second step. Then, the resin is injected into the mold as part of the second step.

[0021] According to one feature of the invention, the shell is thermoformed before the first step and introduced into the mold.

[0022] According to one feature of the invention, the shell is formed by injection into the mold before the stiffening element is formed.

[0023] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and several illustrative and non-limiting examples of embodiments given with reference to the attached schematic drawings on the other hand, in which:

[0024] [Fig.1] schematically represents a general view of a shell of a structural element;

[0025] [Fig.2] schematically represents a general view of the hull visible in figure 1 in which inserts are positioned;

[0026] [Fig.3] schematically represents a cross-sectional view, in a longitudinal-vertical plane, of the shell visible in figure 2 highlighting the junction between the insert and the shell;

[0027] [Fig.4] schematically represents a general view of a structural element according to the present invention;

[0028] [Fig.5] schematically represents a cross-sectional view of the structural element visible in Figure 4;

[0029] [Fig.6] schematically represents another cross-sectional view of the structural element visible in Figure 4, highlighting the overmolding of a resin onto the insert;

[0030] [Fig.7] schematically represents a mold for forming a structural element according to the present invention;

[0031] [Fig.8] schematically represents an alternative embodiment of the invention in which the structural element comprises a rib matrix.

[0032] The features, variants, and different embodiments of the invention may be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features, described hereafter in isolation from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0033] In the detailed description that follows, the terms "longitudinal," "transverse," and "vertical" refer to the orientation of a structural element according to the invention. A longitudinal direction corresponds to a principal elongation direction of the structural element, this longitudinal direction being parallel to a longitudinal axis L of a frame of reference L, V, T illustrated in the figures. A vertical direction corresponds to a direction parallel to a vertical axis V of the frame of reference L, V, T, this vertical axis V being perpendicular to the principal elongation direction of the structural element. Finally, a transverse direction corresponds to a direction parallel to a transverse axis T of the frame of reference L, V, T, this transverse axis T being perpendicular to the longitudinal axis L and to the vertical axis V.

[0034] Figure 1 illustrates a structural element 2 intended for use in a motor vehicle. The structural element 2 may, without limiting the invention, form an anti-squatting bump, intended to be positioned in the seat of a motor vehicle seat to control the occupant's pelvic movements under the seatbelt, or form a means of protection against battery shocks.

[0035] First and foremost, it should be noted that structural element 2, in the embodiment shown, is illustrated in a simplified manner. Of course, structural element 2 can have a more complex form and, in particular, be composed of a plurality of interconnected sub-elements.

[0036] Structural element 2 comprises a shell 4 made of a plastic material. This plastic material may be preferred over other materials for reasons of cost or implementation of specific manufacturing processes. The plastic material forming the shell 4 may be subjected to stresses inherent to the function performed. by the structural element 2 which can cause plastic deformation of the shell 4. It is understood that the plastic material used to form the shell 4 of the structural element has an intrinsic stiffness lower than other materials such as metallic materials.

[0037] The shell 4 has the shape of a hollow body with an outer shell, that is, the general shape of the shell 4, which creates a cavity. In the embodiment shown in the figures, the cavity formed by the hollow body 6 is delimited by various walls forming the outer shell of the shell 4, including two main longitudinal walls and two lateral walls located at the longitudinal ends of the shell. However, in alternative embodiments of the invention, the outer shell of the shell 4 delimiting the hollow body 6 may have other shapes and, in particular, may not have lateral walls, resulting in a "U" shape that opens the hollow body 6 at its longitudinal ends.

[0038] To increase its stiffness and enable it to withstand stresses within the motor vehicle, the structural element 2 includes a stiffening element 8 housed at least partially within the hollow body. The stiffening element 8 in the context of the invention comprises at least one insert 10 made of a composite material. Furthermore, as will be illustrated below, this stiffening element 8 includes additional elements of the insert 10 such that it is at least partially overmolded onto the shell 4.

[0039] In Figure 2, part of this stiffening element 8 is made visible in an embodiment where several inserts 10, here six in the example of Figure 2, are arranged in the hollow body 6.

[0040] It should be noted that in the embodiment shown, the stiffening element 8 comprises a plurality of inserts 10, but that, however, depending on the situation and in particular the shape taken by the shell 4 of the structural element 2 and the stresses to which this structural element 2 is likely to be subjected during its use on the motor vehicle it equips, the stiffening element 8 may comprise a single insert 10. Therefore, the description which follows in relation to an insert 10 applies mutatis mutandis to the other inserts 10 of the stiffening element 8.

[0041] Insert 10 is made of a composite material and is shaped like a sheet of composite material. More specifically, this sheet of composite material is a plate with high stiffness, giving it mechanical rigidity. This rigidity Its mechanical strength is sufficient to allow it to expand in a single plane of extension in the absence of constraints other than its own weight. More precisely, the high stiffness of the composite material sheet allows it to maintain a planar geometry, limiting any deformation or bending under low static or dynamic loads.

[0042] The composite sheet consists of a reinforcing element and a matrix. This reinforcing element is made of glass fibers and / or carbon fibers and / or aramid fibers and provides the insert 10 with significant mechanical properties in terms of strength and rigidity. The matrix is ​​made of a thermoplastic resin or a thermosetting matrix. The reinforcing element is embedded in the matrix so that the reinforcing element and the matrix form a single, unified unit. "Unified unit" means that the insert 10, formed by the reinforcing element and the matrix, forms a single, monolithic unit in which the reinforcing element cannot be separated from the matrix without damaging the insert 10.

[0043] In the preferred embodiment shown in the figures, the insert 10 is formed of a glass fiber fabric integrated into a thermoplastic matrix. The term "glass fiber fabric" means that the glass fibers are pre-entangled with each other so that a glass fiber mesh is formed and exhibits relative mechanical strength.

[0044] In one embodiment shown, the glass fibers are short fibers, however depending on the dimensions of the structural element 2, and more particularly of the hollow body 6, the glass fibers can be long fibers.

[0045] The shell 4 extends transversely, that is to say parallel to the transverse axis T between a first transverse end 12 and a second transverse end 14, these transverse ends 12, 14 being separated from each other by the hollow body 6. As mentioned previously, Figure 2 shows the main walls of the shell 4, which help to delimit the cavity formed by the hollow body 6, namely a first transverse end wall 16 of the hollow body 6 and a second transverse end wall 18.

[0046] More specifically, the first transverse end wall 16 and the second transverse end wall 18 of the hollow body 6 extend from a bottom wall 17, visible in Figure 3, to an external edge 19 of the hull 4 which extends each transverse end wall 16, 18 to form the perimeter of the hull 4.

[0047] The first transverse end wall 16 and the second transverse end wall 18 are opposite each other and form the largest dimension of the structural element 2, here the longitudinal dimension. In the embodiment shown, the first transverse end wall 16 and the second transverse end wall 18 are joined to each other, in addition to the bottom wall 17, by a first longitudinal end wall 21 and a second longitudinal end wall 23. This first longitudinal end wall 21 and this second longitudinal end wall 23 are respectively located at the longitudinal ends of the hollow body 6 and extend, like the first transverse end wall 16 and the second transverse end wall 18, from the bottom wall 17 to the outer edge 19 of the shell 4.

[0048] The insert 10 extends within the hollow body 6 by being in contact with the first transverse end wall 16 of the hollow body 6 which is proximal to the first transverse end 12 and in contact with the second transverse end wall 18 of the hollow body 6 which is proximal to the second transverse end 14. Such an arrangement of the insert 10 within the hollow body 6 allows it to form a bridge capable of supporting transverse forces applied from one transverse end 12, 14 to the opposite transverse end 12, 14.

[0049] Figure 3 illustrates a cross-sectional view of the structural element 2 in which two inserts 10 are installed in the hollow body 6 of the shell 4. As can be seen in Figure 3, the insert 10 has a first face 20 and a second face opposite the first face 20, delimited by a peripheral end edge 22 facing the shell 4 and a free end edge 24. The peripheral end edge 22 of the insert 10 is the end edge of the insert 10 that is directly opposite at least one of the walls of the shell 4 delimiting the hollow body 6. The free end edge 24 forms the end edge of the insert 10 that is not opposite said wall of the shell 4. Here, given the shape of the hollow body 6 forming a cavity, the peripheral end edge 22 extends over approximately two-thirds of the circumference of the insert. 10 and the free end edge 24 extends over approximately one third of the circumference of the insert 10.

[0050] The arrangement of the peripheral end edge 22 in relation to at least one of the walls of the hollow body 6 allows, in the event of a force being imposed on the wall of the corresponding shell 4, to come into contact with the insert and to allow the force to be taken up, which significantly improves the rigidity of the structural element 2.

[0051] More specifically, the peripheral end edge 22 is positioned, as shown in Figure 3, at least partially in contact with the hollow body 6. In the embodiment shown, the entire peripheral end edge 22 is in contact with the hollow core 6 so that the insert 10 has a shape compatible with that of the cavity delimited by the transverse end walls 16, 18 and the longitudinal end walls 21, 23 of the shell 4, and in particular an external profile that reproduces the inclination of the first transverse end wall 16, the second transverse end wall 18 and the bottom wall 17. This direct contact between the peripheral end edge 22 of the insert 10 and the shell 4 at the level of the hollow body 6 makes it possible, in particular, to limit the movements of the insert 10 when the force is transferred through the insert 10.

[0052] According to the invention, the stiffening element 8 is housed in the hollow body 6 and is overmolded onto the shell 4. For this purpose, the stiffening element 8 comprises, in addition to the insert 10, at least one resin 26 overmolded onto the insert 10 and onto the shell 4. In the embodiment shown in which the stiffening element 8 comprises a plurality of inserts 10, the resin 26 is overmolded onto each insert 10 and onto the shell 4.

[0053] This resin 26 allows the insert 10 of the stiffening element 8 to be held securely to the shell 4, and more specifically to the hollow body 6.

[0054] The resin 26 of the stiffening element 8 makes contact with the first transverse end edge 28 of the shell 4 and with the second transverse end edge 30 of the shell 4. This contact of the resin 26 with the shell 4, particularly at the first and second transverse end edges 28, 30, maximizes the adhesion of the resin 26 to the shell 4. Furthermore, it is noticeable in Figure 4 that the resin 26 of the stiffening element 8 is overmolded around the entire perimeter of the shell 4. Thus, the stiffening element 8 is securely bonded to the shell 4 without risk of separation of the stiffening element from the shell 4 under the effect of mechanical stresses.

[0055] Furthermore, the resin 26 extends from one transverse end edge 28, 30 to the other through the insert 10. More specifically, the resin 26 joins one transverse end edge 28, 30 to the other through the free end edge 24 of the insert 10 such that the free end edge 24 of the insert 10 is at least partially covered by the resin 26 of the stiffening element 8.

[0056] Indeed, as can be seen in Figure 5, the resin 26 forms a resin bridge 32 extending over the free end edge 24 of the insert 10. More precisely, this resin bridge 32 extends over the free end edge 24 between the first transverse end wall 16 and the second transverse end wall 18. To promote the mechanical hold of the insert 10, the resin band 32 extends continuously from the first transverse end wall 16 to the second transverse end wall 18.

[0057] Figures 5 and 6 highlight other characteristics of the resin, including the presence of a resin joint 34 and a resin band 36.

[0058] More specifically, the resin 26 of the stiffening element 8 has a resin joint 34 coming into contact with the first face 20 of the insert 10 and the shell 4 and with the second face of the insert 10 and the shell 4. This resin joint 34 allows, together with the resin bridge 32, to completely surround the insert 10, which improves the mechanical strength of the insert 10 within the hollow body 6.

[0059] The resin strip 36 contributes to maintaining the insert 10 laterally, that is, along a longitudinal component. This resin strip 36 extends at least over one and / or second face 20 of the insert 10, covering at least partially said face 20. More specifically, this resin strip 36 extends from the resin joint 34 to the resin bridge 32. It should be noted that, advantageously, the resin strip 36 extends along the insert 10 at its longest vertical dimension.

[0060] This resin band 36 also helps to reinforce the mechanical strength of the insert 10 within the hollow body 6. Thus, the resin 26 overmolded onto the insert 10 by means of the resin bridge 32, the resin joint 34 and the resin band 36 makes it possible to clamp the insert 10 and hold it in place within the hollow body 6 so that when forces are applied to the shell 4, the position of the insert 10 is not modified.

[0061] Figure 7 schematically illustrates a manufacturing process for the structural element 2. The mold 38 is formed in two parts, one of which is configured to receive the shell 4, shown here in dashed lines. This manufacturing process uses at least one mold 38, partially shown in Figure 7, comprising at least one slot 40 configured for the injection of resin 26 to form the stiffening element 2.

[0062] Furthermore, at least one slot 40 is configured to receive the insert 10 prior to resin injection. In light of what has been described previously, it is understood that the longitudinal dimension of the slot 40, that is, the dimension extending from a first face of the slot 40 intended to align with the first face 20 of the insert 10, when This is inserted into slot 40, and a second face of slot 40 intended to come opposite the second face of insert 10, is adjusted so that insert 10 is well positioned, i.e. without play, in slot 40. Also, at the level of slot 40, a channel, not visible in the figure, is made forming an impression in the first face of slot 40 and / or in the second face of slot 40 to form a clearance zone into which the resin can be injected to form the resin strip 36.

[0063] With this mold, the manufacturing process includes at least one first step in which the insert 10 is placed in the slot 40 of the mold 38. This arrangement is made so that the peripheral end edge 22 is flush with a peripheral part 37 of the mold 38. This arrangement makes it possible to form a space between the free end edge 24 of the insert 10 and a flat wall 42 of the mold 38 to form the resin bridge 32.

[0064] In a second stage of the manufacturing process, the resin 26 is injected into the mold so that this resin 26 is overmolded onto the insert 10. Thus, the injection of the resin 26 into the mold makes it possible to form the resin bridge 32, the resin joint 34 and the resin band 36.

[0065] It should be noted that prior to the second step, the mold 38 is closed so that the resin 26 spreads within the mold 38 into the spaces provided for this purpose. Furthermore, once the resin 26 has been injected into the mold 38, the resin 26 and the insert 10 are bonded to the shell 4. It should be noted that, depending on the mold 38 used to form the structural element 2, the resin 26 can be bonded simultaneously to the shell 4 and the insert 10, or with a slightly staggered time, taking into account the polymerization time of the resin 26, which varies depending on the material, i.e., the overmolded shell 4 or insert 10.

[0066] The shell 4 can be thermoformed before the first step of the manufacturing process. Thus, the shell 4 can directly form part of the mold 36 during the injection of the resin 26.

[0067] Alternatively, the shell 4 can be formed by injection in the mold 36 before the stiffening assembly 8 is formed. In this alternative, it is understood that the mold 36 is configured so that a first injection is carried out to form the shell 4 and then a second injection is carried out to form the stiffening element 8.

[0068] Figure 8 illustrates an alternative embodiment of the invention. In this alternative embodiment of the invention, the stiffening element 8 has a shape of rib matrix. This rib matrix comprises a plurality of first ribs 44 and a plurality of second ribs 46. Furthermore, this rib matrix is ​​housed in the hollow body 6 of the shell 4.

[0069] The first ribs 44 extend along a main transverse elongation direction, that is, from the first transverse wall 16 of the hollow body 6 to the second transverse wall 18. The second ribs 46 extend perpendicularly to the first ribs 44 such that the first ribs 44 and the second ribs 46 are in contact with each other. More precisely, in the embodiment shown, the second ribs 46 extend from the first longitudinal end wall 21 to the second longitudinal end wall 23. It should be noted that in an alternative embodiment, the second ribs 46 may extend strictly between two first ribs 44 or between a first rib 44 and a longitudinal end wall 21, 23.

[0070] The insert 10 participates in making at least one of the ribs 44, 46 of the rib matrix and the resin 26 participates in forming entirely at least one other of the ribs 44, 46 of the rib matrix.

[0071] When the insert 10 forms one of the first ribs 44, the second ribs 46 help to keep the insert 10 in contact with the hollow body 6. Also, it is not necessary to implement the resin strip 36 because the second ribs 46 help to hold the insert 10 laterally.

[0072] The invention as just described achieves its objective by proposing a structural element in which rigidity is reinforced by means of a stiffening element comprising an insert made of a composite material with optimized weight, strength and carbon footprint properties.

[0073] The present invention is not limited to the means and configurations described and illustrated herein, and also extends to any equivalent means and configuration as well as any technically operative combination of such means.

Claims

DEMANDS 1. Structural element (2) of a motor vehicle, comprising a shell (4) whose envelope defines a hollow body (6) and at least one stiffening element (8) housed in the hollow body (6) and overmolded onto the shell (4), the stiffening element (8) comprising at least one insert (10) formed of at least one sheet of composite material.

2. Structural element (2) according to claim 1, wherein the stiffening element (8) further comprises at least one resin (26) overmolded on at least one insert (10), said resin also being used to mold at least partially the shell (4).

3. Structural element (2) according to claim 2, in which the insert (10) has a first face (20) and a second face delimited by a peripheral end edge (22) opposite the shell (4) and a free end edge (24) opposite the peripheral end edge (22), the free end edge (24) of the insert (10) being at least partially covered by the resin (26) of the stiffening element (8).

4. Structural element (2) according to claim 3, in which the resin (26) helps to laterally retain the insert (10), at least one of the first face (20) and second face being at least partially covered with a strip of resin (36).

5. Structural element (2) according to any one of claims 3 and 4, wherein the peripheral end edge (22) is disposed at least partly in contact with the hollow body (6).

6. Structural element (2) according to any one of claims 2 to 5, wherein the stiffening element (8) has a rib matrix shape, at least one insert (10) participating in realizing at least one of the ribs of the rib matrix and the resin (26) fully realizing at least one other of the ribs of the rib matrix.

7. Structural element (2) according to claim 6, in which the rib matrix comprises a plurality of first ribs (44) among which at least one rib is formed at least in part by the insert (10) and a plurality of second ribs (46) secant to the first ribs (44) and formed of resin (26).

8. Structural element (2) according to claim 7, in which the insert (10) is held in contact by the second ribs (46).

9. Structural element (2) according to any one of claims 1 to 8, wherein the shell (4) is formed of a plastic material.

10. A method for manufacturing a structural element (2) according to any one of claims 1 and 3 to 9 in combination with claim 2, the manufacturing method employing at least one mold (38) having at least one slot (40) configured for injecting a resin (26) into at least one slot (40) to overmold the stiffening element (8) and at least: - a first step in which an insert (10) is placed in at least one slot (40) of the mold (38), - a second step in which a resin (26) is injected into the mold (38) and is overmolded onto the insert (10) and onto the shell (4) present in the mold (38).

11. Manufacturing method according to claim 10, wherein the shell (4) is thermoformed before the first step and introduced into the mold (38) or formed by injection into the mold (38) before the stiffening element (8) is formed.

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