Abstract:
The invention relates to a vehicle dashboard crossmember ( 2 ) including a crossbar which extends lengthwise along a generatrix line (G) that is directed substantially along the width of the vehicle body and transversely relative to the direction of travel of said vehicle, as well as at least one connection flange ( 3, 4 ) designed to enable said crossbar ( 2 ) to be attached to said body, said crossbar ( 2 ) consisting, over at least a portion of the length thereof, of a load-bearing web ( 10 ) that has a side wall ( 11 ) rounded about said generatrix line (G) so as to have, in a cross-section perpendicular to the generatrix line, a first arm ( 12 ) and a second arm ( 13 ) that are connected to one another via a common connection portion ( 14 ) and which thus define a cavity ( 15 ), and of a reinforcing brace ( 20 ) made of a fibrous composite material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2013/061389, which was filed Jun. 3, 2013 and which claims the priority to French application 1255343 filed on Jun. 7, 2012 the content (text, drawings and claims) of which is incorporated here by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to the general domain of crossmembers used in vehicle construction, and more specifically to crossmembers which are mounted to the vehicle body, transverse to the drive direction, to provide means for mounting the dashboard of the vehicle as well as various accessories such as climate control unit, steering column, fuse box, glove compartment, etc. 
     It is known that crossmembers generally comprise a crossbar made of steel tubing which extends between two mounting flanges securing the bar to the body of the vehicle, and which is usually also supported by a central strut attached to the floor of the vehicle. 
     Although known crossmembers generally perform satisfactorily, particularly because of their rigidity, they may nevertheless have some drawbacks. 
     Their fabrication may require particularly heavy, cumbersome and costly tooling, including for instance shear presses and welding machines, as well as stamping presses specially equipped with the necessary punches and dies. 
     In addition, the relatively heavy weight of known crossmembers complicates their manipulation during assembly and contributes to making the vehicle heavy, negatively affecting the fuel consumption of the vehicle. 
     Finally, it is often difficult to arrange the crossmember in the proper way in order to avoid the likelihood of resonance phenomena propagating towards the cabin which emanate from engine compartment vibrations or the vehicle body. 
     SUMMARY 
     Consequently, the goal of the invention is to propose a new crossmember for a vehicle dashboard which combines light weight and high mechanical properties, as required for the application, and especially with vibrational performance, rigidity and behavior comparable or superior than that of known metallic tubing. 
     Another goal of the invention is to propose a new fabrication method for dashboard crossmembers which provides a light weight and robust crossmember, which is versatile and simple, fast and inexpensive to implement. 
     The goals of the invention are achieved by means of a dashboard crossmember for a vehicle, the crossmember comprising a crossbar extending lengthwise according to a generating line G, intended to be oriented according to the width of the vehicle body, transverse to the driving direction of the vehicle, and at least one connecting flange designed for mounting the crossbar to the body of the vehicle, the crossmember being characterized in that the crossbar is formed, at least over a portion of its length, on the one hand by a first part forming a carrier core with a bulging lateral wall around the generating line G, in order to present, in a section perpendicular to the generating line, a first branch and a second branch connected with each other by a common connection part and bordering in this way a cavity, and on the other hand by a second part, different from the first part, forming a back brace made of a fiber reinforced composite material containing fibers arranged in a matrix, and which links the first branch with the second branch. 
     The goals of the invention are also achieved by means of a fabrication method for a vehicle dashboard crossmember which must be equipped with a crossbar extending lengthwise according to a generating line G, intended to be oriented according to the width of the vehicle body, transverse to the driving direction of the vehicle, and at least one connecting flange for mounting the crossbar to the body of the vehicle, the method being characterized in that it comprises a fabrication step (a) for the carrier core intended to form the basic structure of the crossbar over at least a portion of the length of the crossbar. In this step a rigid carrier core with bulging wall is created by curving or bending, for instance by means of bending or stamping operations, a basic blank of fibrous composite sheet, around the generating line G in order to form, according to a section perpendicular to the generating line, a first branch and a second branch connected with each other by a common connecting part and bordering in this way a cavity. The method further includes a step (b) in which a rigid back brace is fabricated from fibrous composite material, followed by a step (c) in which the preformed back brace is assembled to the branches of the carrier core, preferably at a distance from the connecting part, in order to form, over at least a portion of the length of the crossbar, a reinforced tubular stub. 
     Advantageously, the crossmember combines the light weight of a hollow carrier core with the structural strength of tubing with relatively large volume, due to the reinforcement provided by the reinforcing back brace which stabilizes the branches of the core, and in this way significantly improves the resistance of the assembly against flexion, torsion, impact and buckling. 
     Advantageously, the use of a brace of fibrous composite material, preferably with a polymer matrix, provides excellent mechanical properties, and specifically great robustness and high rigidity, by means of a material which is relatively light, less dense and generally lighter than a metallic alloy, which results in a lighter crossmember assembly. 
     In addition, this composite material is undeniably easy to form, so that its use in the method according to the invention results in lower cost for raw material, energy, or tooling. 
     The ease of forming of the composite material is reflected in the great freedom of choice relative to forms and dimensions of the reinforcing brace, so that it can be adapted to a multitudes of variants, and furthermore associated either with a same carrier core, or several types of carrier cores, in order to obtain the combination which gives the best performance, for a given vehicle, in terms of mechanical strength and/or vibrational characteristics. 
     Advantageously, with this kind of differentiation in the parts constituting the crossmember, whereby the form, dimensions or constituting material of each part can be adapted independently from the other parts, the modular character of the crossmember gives the method great versatility. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objectives, characteristics and advantages of the invention will be presented in more detail in the following description, and with reference to the attached drawings, provided strictly for illustrative and non-limiting purposes, among which: 
         FIG. 1  is an exploded perspective view illustrating an example of a dashboard crossmember made in accordance with the claimed invention. 
         FIG. 2  is a perspective view illustrating the assembled crossmember of  FIG. 1 . 
         FIGS. 3A and 3B  are perspective views illustrating a sheet with fibers crossing at an angle used to produce a variant of a reinforcing brace employed in the crossmembers of  FIGS. 1 and 2  as well as, respectively, the brace obtained in this way starting from such a sheet. 
         FIGS. 4A and 4B  are perspective views illustrating a sheet with continuous lengthwise fibers used to produce a variant of the carrier core employed in the crossmembers of  FIGS. 1 and 2  as well as, respectively, the carrier core obtained in this way starting from such a sheet. 
         FIGS. 5, 6, 7 and 8  are transverse sectional views illustrating construction variants for the reinforcing brace employed in the crossmembers according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     A dashboard crossmember  1  for a vehicle comprises a crossbar  2  extending lengthwise according to a generating line G intended to be oriented according to the width of the vehicle body (not shown), transverse to the driving direction (forward-reverse) of the vehicle, as well as at least one connecting flange  3 ,  4  designed for mounting the crossbar  2  to the body of the vehicle (not shown). 
     It is understood that the invention relates also to a vehicle (not shown), and particularly an automotive vehicle, equipped with the dashboard crossmember  1 . 
     Preferably, as illustrated in  FIGS. 1 and 2 , the crossmember  1  comprises at least two connecting flanges,  3 ,  4  arranged lengthwise on both sides of the crossbar  2 , at the extremities of the latter, so that the flanges can be attached to both sides (left and right) of the vehicle body, so that once mounted the crossmember extends transverse to the drive direction of the vehicle, and approximately over the whole width of the vehicle. 
     Preferably, the crossmember includes a strut  5  anchored to the floor of the vehicle and supporting crossbar  2 . The strut  5  is in an intermediate position at a distance from the two connecting flanges  3 ,  4  of the crossmember. The crossmember preferably includes a mounting fork  6 , which preferably is deformable in case of impacts, and for instance is made of steel. The mounting fork  6  connects the crossmember, and more particularly crossbar  2 , to a forward portion of the vehicle body, approximately facing the steering column. 
     By convention, and for ease of description, the horizontal forward/reverse driving direction of the vehicle is designated by “X”, the transverse direction of the vehicle, which corresponds in general with the lengthwise extension of the crossmember  1  and more particularly of the crossbar  2  according to generating line G is designated by “Y” and the vertical direction, which forms with the preceding directions a direct trihedral, is designated by “Z”. 
     The crossbar  2  is constituted over at least a portion of its length L2, on the one hand by a first part forming carrier core  10  which has a bulging side wall  11  around the generating line G, in order to present, in a section PS perpendicular to the generating line, a first branch  12  and a second branch  13  connected to each other by a common connecting part  14 , and bordering a cavity  15 , which opens preferably opposite the connecting part  14 , as illustrated in  FIGS. 1 and 5 to 8 , and on the other hand by a second part, different from the first, which forms a reinforcing brace  20  made of fibrous composite material containing fibers  21  arranged in a matrix  22 , and which connects branch  12  with the second branch  13 . 
     According to a variant embodiment, corresponding with  FIG. 5 , the shape of reinforcing brace  20  conforms to the concave face of wall  11 , and therefore of cavity  15 . 
     According to other embodiments, corresponding with  FIGS. 6, 7, and 8 , the reinforcing brace  20  can connect the first branch  12  with the second branch  13  at a distance from the connecting part  14 , in the way of a cover closing cavity  15 , opposite the connecting part, and preferably according to a path which is not symmetric to that of wall  11 . 
     The cavity  15  can remain empty, or on the contrary be filled with foam  23 , such as polymer foam, in order to improve the capacity of the crossmember  1  to dampen or absorb vibrations. 
     According to another variant, corresponding for instance with the example of  FIG. 5 , the cavity  15  can be occupied at least partially by partitions or ribs  24 , backing up the concave face of the brace  20 , and, through its intermediary the concave face of wall  11 . 
     Preferably, the carrier core  10 , forming the hollow basic structure of the crossbar  2  extends over at least 50%, at least 75%, at least 80%, at least 90%, or over the whole length L2 of the crossbar, and more generally the whole length of the crossmember  1 . 
     Advantageously, the carrier core  10  can form a beam type support structure, capable of supporting the crossbar over its whole length, and particularly of ensuring at least partially if not completely the rigidity of the crossbar  2 , and especially of absorbing the compressive, tensile, torsional, or bending stresses that the crossbar is subjected to inside the vehicle. 
     Preferably, the carrier core follows a generating line G, or “central axis of generation” which is mostly straight, particularly in the lengthwise central portion of the crossbar  2 , and preferably parallel to the Y direction of the vehicle. 
     It can however be envisaged that the generating line G is locally curved, and particularly that it presents, for instance towards its extremities, elbows  25  corresponding for instance with one of the deviations ΔX, ΔZ in X and/or Z, as illustrated in  FIGS. 1, 2 and 4B  in order, for instance to adapt, or to reinforce, the structural rigidity of the crossmember  1 . 
     Preferably, the convex bulging of the wall  11 , and more generally of the crossbar  2  is intended to be oriented towards the cabin of the vehicle, towards the rear, while the brace  20  is disposed in the back portion of the crossmember, towards the front of the vehicle, the body and hood side, preferably according to a vertical plane. 
     Preferably, the solid wall of the carrier core  10  follows a convex contour regularly bent in a U or in an Ω shape, as illustrated in  FIGS. 1, 2, 4B and 5 to 8 . 
     Although it is possible that the bulging of the wall  11  can be created by a broken line comprising a succession of adjacent segments (straight or curved) separated by folds, preference is given to a gradual and smooth curvature, which avoids stress concentrations and simplifies the construction of the core in a single piece and in a single forming pass, while preserving the integrity of the material constituting the core  10 . 
     For this purpose, the connecting part  14  can, for instance, have a substantially arcuate outline, and more particularly a half-circle, which the branches  12  and  13 , which are preferably parallel to each other, border tangentially. 
     The free extremities of the first branch  12  and of the second branch  13  preferably have flat mounting flaps  26  against which the reinforcing brace  20  locates. 
     Preferably, the flaps  26  can be formed in one piece with wall  11 , by means of tabs folded preferably towards the exterior. 
     In addition, the flaps  26  situated on both sides of the cavity  15 , can be in the same plane, and preferably located in the same vertical plane (parallel to the plane delimited by the Y and Z directions), in order to facilitate gluing and flat mounting of the brace  20  against the core  10 . 
     Preferably, the assembly formed in this manner has an asymmetric transverse section, and preferably forms a tunnel of which the carrier core  10  forms the archway, like a spout, and the reinforcing brace  20  closes the base like a cover. 
     In any case, the assembly and more specifically the superimposition of the carrier core  10  and the brace  20 , whether or not there is a cavity between these elements, results in the presence inside the crossbar  2  of a preferably straight reinforced section T, with a length corresponding with the distance of overlap between the core  10  and the brace  20 , and which is relatively simple to produce. 
     Although it is possible that the reinforcing brace  20  extends over more than 50%, 75% or even the whole length L10 of the carrier core, and more generally the length L2 of the crossbar, the reinforcing brace  20  covers preferably at least 25%, at least 30%, and preferably approximately 35% or 40% of the length L2 of the crossbar  2 , and more generally of the crossmember  1 , as illustrated in  FIGS. 1 and 2 . 
     The length L20 of the brace, measured according to the generating line G, and therefore the length of the reinforced section T, is preferably smaller than the length L10 of the core  10 , and more generally than the length L2, preferably equal to the length L2 of the crossbar. 
     The width of brace  20  can be equal to the width of the carrier core  10 , if necessary including mounting flaps  26 , as illustrated in  FIGS. 1 and 5 to 8 . 
     In a particularly preferential manner, the reinforced section T combining the core  10  and the brace  20  covers, or corresponds exclusively with, the section of the crossbar  2  to which are attached the first connecting flange  3  (on the left in  FIGS. 1 and 2 ), the strut  5  and the fork  6 . 
     It is indeed in the above defined triangular zone that the crossbar  2  is mechanically most stressed, and where it requires the most robust structure. 
     The length L20 of the brace  20  and its position relative to the core along the generating line G can therefore be determined, if necessary, in order to define a partial coverage necessary and sufficient for reinforcing the triangular zone, which leads to material savings by not unnecessarily reinforcing the rest of the crossbar  2 ; the brace  20  can for instance be interrupted starting from the strut  5 , and the reinforcement can be omitted between the section, situated beyond the strut  5 , and up to the second mounting flange  4  (here on the right). 
     If necessary, it can also be envisaged to provide several distinct reinforcing braces  20  distributed at a distance from each other along the crossbar  2 , and more preferably along the same carrier core  10 , in order to create a plurality of reinforced sections in the critical zones of the crossbar  2 . 
     Preferably, the reinforced brace  20  is formed by a plate with folds or reliefs  27  with heights preferably greater than the base thickness E30 of the blank  30  used to produce the plate, whereby the reliefs  27  form ribs between branches  12 ,  13  connected by the plate contributing to the rigidity of the plate, as illustrated in  FIGS. 1, 3B, 7 and 8 . 
     Advantageously, such stiffening reliefs  27  can be obtained by stamping, bending, or ribbing, and contribute to raising the torsional modulus and the bending modulus of the brace  20 , and in this way its torsion, flexion or buckling strength, while preserving its thinness and light weight. 
     The reinforcing brace  20  preferably has abutment shoulders which protrude inside the cavity  15 , between the first and second branch  12 ,  13  in order to offer to the branches  12 ,  13  a support to prevent their moving closer to each other, as illustrated for instance in  FIG. 7 . 
     Advantageously, the brace  20  can form in this way a particularly strong column which effectively opposes the transverse crushing of the carrier core  10 . 
     Preferably, the shoulders  31  can form secant planes with the mounting legs  32  which locate against the flaps  26 , which results in a reinforced fixation and abutment effect in two distinct directions, approximately square to each other. 
     If necessary, the tie rod role of the brace  20  opposing the separation of the branches  12 ,  13  (and more particularly opening of the U shape), for instance under influence of torsion around the generating line G, can also be reinforced by this extension of contact and fixation surfaces. 
     Preferably, the shoulders  31  can coincide with all or part of the stiffening reliefs  27 , as illustrated in  FIG. 7 . 
     It is however possible that, according to another variant embodiment, the stiffening reliefs  27  can be oriented towards the outside of the cavity, in this case protruding forward, as illustrated in  FIG. 8 . 
     The core  10  can be made of the same material as the reinforcing brace  20 , or from a different material. 
     In a particularly preferential manner, just like the reinforcing brace  20 , the carrier core  10  is also made of a fibrous composite material, comprising fibers  33  arranged in a matrix  34 . 
     The reinforcing fibers  21 ,  33  of the brace  20  or the core  10  can be comprised of glass, carbon or aramid fibers, etc. 
     The matrices  22 ,  34  are preferably made of one or more polymer materials, such as polypropylene or polyamide, and more preferentially of one or more resin type thermoplastic polymers. 
     Compared to a metallic construction, the use of these composite materials advantageously results in a reduced weight crossbar  2 , and therefore crossmember  1 , while preserving, because of the reinforcement fibers  21 ,  33 , the high elasticity module, the great rigidity, and the high resistance to traction, bending and buckling, under lateral compression stresses or shearing forces. 
     For this purpose, the crossbar  2  preferably has a hollow or tubular structure, delimited by a relatively thin composite skin, with low density relative to metal, but highly rigid and tough. 
     Furthermore, such fibrous composite materials can simplify the forming of the parts, while limiting the loss of raw material. 
     Obviously it is possible that core  10  and brace  20  are made of the same fibrous composite material, if necessary oriented in similar manner relative to the generating line G. 
     The fibrous composite material employed for the carrier core  10  preferably has a matrix  34 , and/or fiber  33  composition, and/or fiber  33  orientation, and/or fiber  33  density which is different than the fibrous composite material used for the reinforcing brace  20 . 
     As an example, to form the core  10 , a composite of carbon fibers  33  can be used containing preferably 90% of the fibers at 0 degrees (in line with the generating line) and 10% of fibers at 90% (transverse to the generating line), as illustrated in  FIG. 4A , and to form the brace  20 , a composite with crossed glass fibers  21 , arranged preferentially half at +45 degrees, and half at −45 degrees, as illustrated in  FIG. 3A . 
     Advantageously, by combining the materials in this way, the different lateral portions of the reinforced section T can be given locally differentiated mechanical properties, the combination of which improves the mechanical strength and/or the vibrational characteristics of the assembly. 
     Preferably, the carrier core  10  and/or the brace  20  are formed in one piece from a single sheet of composite  30 ,  35  (also called “patch”, which is a specific example of the “blank” adapted to composite technology) as shown in  FIGS. 4A and 3A  respectively. 
     In this way, substantial material savings can be realized, and in addition the parts can be formed rapidly, preferably each in a single cutting operation followed by a single striking operation, and more particularly in one thermoforming operation under a press, from one and the same corresponding patch  30 ,  35 , which makes the fabrication method suitable for the production rates of the automotive industry, with cycle times of a few minutes, or even less than one minute. 
     Although particularly thin and light weight (resulting from the thickness of one patch  30 ,  35 ), the parts thus obtained are nevertheless particularly robust and homogenous, due to their fabrication in one piece. 
     The reinforcing brace  20  and/or the core  10  preferably have a plurality of continuous fibers  21 ,  33  parallel with each other and extending without interruption from one edge to the other of the brace  20 , respectively from one edge to the other of the carrier core  10 . 
     This continuity of fibers  21 ,  33  advantageously improves the mechanical strength of the corresponding patches  30 ,  35  and therefore of the parts obtained from these patches. 
     The orientation of the continuous fiber mesh or matrix can be chosen so that it corresponds with the direction of the most severe stresses to which the part is subjected. 
     If necessary, the fibers of the same patch can be arranged according to two crossed patterns of continuous fibers superimposed or interlaced in the manner of textile. 
     As an example, the carrier core  10  can comprise, preferably a majority, of continuous warp yarn fibers  33 C disposed parallel to the generating line G, in the manner of lengthwise tie rods, and if necessary continuous weft yarn fibers  33 T perpendicular to the warp fibers, especially in a ratio of 90%-10% such as described above, each fiber pattern  33 C,  33 T joining in this manner without interruption one corresponding cut edge of a preferably rectangular patch  35 , with the opposite cut edge, as illustrated in  FIG. 4A . 
     Preferably, the fibers  21  of the reinforcing brace  20  are arranged, at least partially, in a crossed pattern, for at least 25%, or 50%, according to an angle of +30 degrees to +60 degrees, and preferably of +45 degrees relative to the generating line G, and for at least 25%, or 50%, according to an angle of −30 degrees to −60 degrees, and preferably of −45 degrees relative to the generating line G. 
     In this way, the fibers can continuously connect, preferably at ±45 degrees, one cut edge of the corresponding patch  30 , which is preferably rectangular, with the adjacent cut edge. 
     As illustrated in  FIGS. 1, 2 and 5 to 8 , the carrier core  10 , and more generally the crossbar  2 , can be coated over its whole length or part of its length, on at least one of its faces, or on two faces, with a non-metallic coating layer  40 , made preferably through over-molding, in a polymer material, preferably a composite material and different from the composite material which constitutes the carrier core  10  and/or brace  20 . 
     The coating layer  40  can, for instance, be created in a polypropylene or polyamide type polymer material, if necessary reinforced with short non-continuous fibers, with individual lengths smaller than 25 mm, or 10 mm, or ultra-short fibers measuring between 2 mm and 4 mm, and specifically in PA6GF60. 
     Advantageously, such material is particularly suitable to be formed by injection over-molding on the carrier core  10 , which locally backed by the brace  20  forms the true functional armature of the crossbar  2 . 
     Such coating layer  40  can be used to add to the crossmember  1 , and more particularly to the crossbar  2 , elements providing additional functions, and not contributing to, or only marginally contributing to, the structural strength of crossbar  2 , such as for instance leg or eyelet type mounting interfaces used for mounting to the crossmember accessories as the climate control group, the radio, the glove compartment, etc. 
     Advantageously, all or part of the mounting interfaces, until now made of metal, can be replaced by elements in a (second) composite material, reducing in this way the weight of the crossmember  1 . 
     The coating layer  40  can also be used to add point ribbing  24  in the cavity  15  ( FIG. 5 ), and/or along the exterior surface of the bulging wall  11  ( FIGS. 5 to 8 ), and/or a rib backing  24 , or a filling, of visible stiffening reliefs  27  of the brace  20  ( FIG. 7 ). 
     As illustrated in  FIG. 7 , the coating layer can comprise for this purpose on the one hand a thin base plate with constant thickness conforming to the outside surface of the reinforcing brace  20  along the generating line G, the base plate being locally reinforced by transverse ribs  24  or partitions with height equal to the height of the stiffening reliefs  27 , and on the other hand by covering arch type ribs conforming to the outside surface of the bulging wall  11 . 
     In this way it can be also envisaged to back up the reinforced section T by means of transverse ribbing  24  over-molded from each side, or over the whole lateral periphery of the section. 
     The crossmember  1  can therefore have a generally multi-layered structure differentiated in its composition and function, comprising at least a first carrying armature layer formed by the core  10 , and if necessary the brace  20 , preferably made from preformed patches  30 ,  35  with continuous fibers, and a second coating layer  40  offering for instance additional mounting interfaces, preferably formed by over-molding in a composite with short fibers. 
     According to a variant embodiment, the mounting flange(s)  3 ,  4  can be made of a fibrous composite material, which can be identical for both flanges, even coming from the same material from which the core  10  is made. 
     Of course, a person skilled in the art will be able to adapt the invention to his needs by isolating or combining all or part of the above mentioned characteristics. 
     The invention also relates to a method for fabricating a dashboard crossmember  1  for a vehicle, which must be provided with a crossbar  2 , extending lengthwise according to a generating line G, intended to be oriented according to the width of the vehicle body, transverse to the driving direction of the vehicle, and at least one mounting flange  3 ,  4  designed for mounting the crossbar to the body of the vehicle. 
     The method of fabricating the dashboard crossmember comprises a step (a) in which a carrier core  10  is fabricated, which is intended to form the basic structure of the crossbar  2  over at least part of the length of the crossbar. In this step a rigid carrier core  10  with a bulging wall is made by curving or bending, for instance by bending or stamping, a base blank  35 , from a fibrous composite sheet, around the generating line G in order to form, in a section perpendicular to the generating line, a first branch  12  and a second branch  13  which are connected to each other by a common connecting part  14  and which border a cavity  15 . The method further includes a step (b) of fabricating a composite reinforcing brace  20  in which a rigid reinforcing brace  20  is produced in a fibrous composite material, followed by an assembly step (c) in which the preformed reinforcing brace  20  is attached to branches  12 ,  13  of the carrier core  10 , preferably at a distance from the connecting part  14 , in order to form, over at least a portion of the length L2 of the crossbar, a reinforced tubular section T. 
     Advantageously, the assembly of the separately preformed core  10  and brace  20  can be created by any appropriate assembly method, particularly at the interface of the flaps  26  and the mounting legs  32 , and specifically by riveting, welding, for instance by hot welding or ultrasonic welding, by gluing, for instance with epoxy or polyurethane type structural glue, or by interlacing the fibers of one of the patches  30  with the fibers of the adjacent patch  35  through a stitching operation, if necessary through the intermediary of fiber sutures made for this purpose through the patches. 
     Advantageously, a solidly connected “all composite” base sub-assembly is obtained in this manner, which is particularly light and strong. 
     The over-molding of the coating layer  40  on the base sub-assembly can take place after this first assembly step, followed by the mounting of the strut  5  and the fork  6 .