Deformable front structure of a motor vehicle

Abstract

The invention relates to a deformable front structure of a motor vehicle comprising: a cradle adapted to extend transversely under an engine compartment of a motor vehicle, said cradle comprising two extensions extending parallel towards the front of said vehicle; a profiled crossmember (34) having two opposite ends (36, 38), said extensions respectively connecting said two opposite ends (36, 38) of said crossmember (34). Said two crossmember ends (36, 38) comprise preferential folding lines to cause the folding of said two ends (36, 38) along said preferential folding lines during an impact. Figure to be published with the abstract: Fig. 2

Description

Title of the invention: Deformable front structure of a motor vehicle

[0001] The present invention relates to a deformable front structure of a motor vehicle.

[0002] The deformation of the front structure aims to absorb the maximum energy during impacts in order to protect the equipment and people involved, whether they are inside the vehicle or outside.

[0003] Known motor vehicles usually comprise a passenger compartment and an engine compartment located at the front and delimited from the passenger compartment by an apron.

[0004] They also include two substantially parallel side members which extend longitudinally at a distance from each other through the bulkhead and into the engine compartment.

[0005] Substantially in line with the bulkhead and the engine compartment, the vehicle comprises a cradle which extends transversely and from which two extensions extend under the engine compartment. These two extensions themselves extend substantially in line with the two side members and are generally suspended there by means of a suspension member, or pendant.

[0006] The extensions are respectively extended themselves by shock absorbers commonly called “crash-boxes”.

[0007] And in addition, the two shock absorbers are connected together by a cross member which extends to the front.

[0008] Also, the sleepers are made from steel grades with a very high elastic limit and usually, according to continuous cold profiling processes. For example, martensitic steels are used whose elastic limit is of the order of 1200 MPa. The sleepers thus produced have relatively advantageous shock absorption properties. However, they are excessively expensive.

[0009] Thus, a problem which arises and which the present invention aims to solve is to provide deformable front structures having significant shock absorption capacities, but at more advantageous manufacturing costs.

[0010] In order to solve this problem, a deformable front structure of a motor vehicle is proposed comprising: a cradle adapted to extend transversely under an engine compartment of a motor vehicle, said cradle comprising two extensions extending parallel towards the front of said vehicle; and, a profiled crossmember having two opposite ends, said extensions respectively connecting said two opposite ends of said crossmember.

[0011] And, said two crossbar ends comprise preferential folding lines to cause said two ends to fold along said preferential folding lines upon impact.

[0012] Thus, a characteristic of the invention lies in the implementation of preferential folding lines in the crossmember. In this way, it is possible to do without shock absorbers, the role of which is then played by the ends of the crossmember. This significantly reduces the cost of the deformable front structure.

[0013] In addition, a lower-performance grade of steel can be used, the elastic limit of which is, for example, around 650 MPa, and which is therefore less expensive. Also, the strip steel is stamped to form the sleeper and consequently, it is obtained at a more advantageous cost, compared to sleepers obtained using cold profiling processes.

[0014] According to a particularly advantageous embodiment of the invention, said crosspiece is U-shaped, defining a bottom wall and two opposite wings facing each other, said two extensions being connected to said two opposite wings, while said bottom wall extends opposite said two extensions. Such a configuration promotes energy absorption as will be explained in more detail below. Furthermore, it will be observed that steel grades with a lower elastic limit are easier to connect by welding to other steels.

[0015] According to the invention, said two opposite wings preferably comprise, in each of said two crosspiece ends, two tongues extending projecting and facing one another opposite said bottom wall, and each of said two extensions is connected to said two tongues. The two tongues thus make it possible to locally increase the width of the wings of the crosspiece. In this way, the energy absorption capacities of the structure are increased.

[0016] Advantageously, according to the invention, each of said two extensions is connected to said two tabs by means of a plate. Thus, the free edges of the two tabs, opposite said bottom wall of the crosspiece, are preferably welded to the plate. The plate is itself adjusted flat on a receiving plate, which receiving plate is welded to the end of the extension, as will be explained in detail in the remainder of the description.

[0017] According to an alternative embodiment of the invention, each of said two tabs has a constriction to form said preferential folding lines. The constrictions are formed by two grooves extending opposite one another. Thus, the preferential folding lines extend between the two grooves.

[0018] According to another alternative embodiment of the invention, said two opposite wings have, in each of said two crosspiece ends, at least one recess to form said preferential folding lines. Preferably, the recess extends into the tabs, and consequently, the preferential fold lines extend at the tabs on either side of the recesses.

[0019] According to yet another alternative embodiment of the invention, said two opposite wings have, in each of said two crosspiece ends, grooves to form said preferential folding lines. Advantageously, the grooves also extend into the tabs to facilitate their deformation in the event of an impact.

[0020] According to a particularly advantageous embodiment of the invention, said two opposite wings have folded edges. In other words, the two wings have two edges folded back opposite each other. In this way, the quadratic moment of the crosspiece is significantly increased.

[0021] Furthermore, said crosspiece has, according to the invention, a plurality of pairs of local depressions made in the edges between said wings and said bottom wall. In other words, the two opposite edges of the crosspiece are substantially depressed symmetrically. In this way, preferential folding zones are also formed.

[0022] According to a particularly advantageous embodiment of the invention, said crosspiece is curved according to a convexity opposite said cradle.

[0023] Also, according to the invention, said crosspiece is stamped in a metallic material. Indeed, by using a steel grade with a lower elastic limit, less than 700 MPa for example, the crosspiece is easier to stamp. In addition, it is easy to weld it afterwards.

[0024] Compared to cold profiling processes, or "roll-forming" in English, stamping is much less expensive.

[0025] Other features and advantages of the invention will emerge from reading the description given below of particular embodiments of the invention, given for informational but non-limiting purposes, with reference to the appended drawings in which:

[0026] [Fig.l] is a schematic front right perspective view of a deformable front structure of a motor vehicle according to the prior art;

[0027] [Fig.2] is a schematic front right perspective view of an element of a deformable front structure according to the invention according to one embodiment;

[0028] [Fig.3A] is a schematic detail view of the object of [Fig.2] according to another embodiment; and,

[0029] [Fig.3B] is a schematic detail view of the object of [Fig.2] according to yet another mode of implementation.

[0030] [Fig.l] shows a deformable front structure 10 of a motor vehicle, according to the prior art.

[0031] It is inscribed in an orthogonal reference frame X, Y, Z, in which the X axis extends in a front-rear longitudinal direction of the motor vehicle, oriented towards the rear; the Y axis extends in a transverse direction of the vehicle, oriented from left to right when driving; and the Z axis extends in a vertical direction, oriented away from the ground.

[0032] The front structure 10 comprises a cradle 12 which extends transversely along the Y direction, and longitudinally along the -X component, at least partially under the engine compartment 14.

[0033] Furthermore, the structure 10 comprises extensions, a right extension 16 and a left extension 18, which are connected to the cradle 12 and extend substantially parallel to each other towards the front along the -X component.

[0034] The extensions 16, 18 extend substantially directly above the side members, which are not shown.

[0035] Also, in the extension of the extensions 16, 18, the front structure 10 comprises shock absorbers, or “crash-boxes”, right 20 and left 22.

[0036] And the two shock absorbers 20, 22 are connected together by a crosspiece 24.

[0037] The shock absorbers 20, 22 are tubular members capable of compressing axially in the event of an impact. They are connected to the extensions 16, 18 by means of a right 26 and left 28 connecting plate to which they are respectively welded. The connecting plates 26, 28 are themselves screwed onto right 30 and left 32 receiving plates which are integral with the extensions 16, 18.

[0038] Also, the receiving plates 30, 32 are usually suspended from the side members by means of suspension members or pendants. These latter, like the side members, are not shown here.

[0039] In accordance with the invention, the crosspiece 24 and the shock absorbers 20, 22 are replaced by a new crosspiece 34 as shown in [Fig. 2] and according to a first variant embodiment.

[0040] The crosspiece 34 has a right end 36 opposite a left end 38, which ends will act as shock absorbers as will be explained below. The right end 36 is symmetrical to the left end 38 with respect to the median plane Pm.

[0041] The crosspiece 34 is U-shaped and is obtained by cutting and stamping a metal strip. The metal strip is made of a steel grade having an elastic limit of less than 1000 MPa. Its elastic limit is advantageously less than 700 MPa. It is, for example, 660 MPa.

[0042] Such a grade of steel is easy to shape and stamp.

[0043] Thus, thanks to the cutting and the stamping, the crosspiece 34 has a bottom wall 40 and two opposite wings 42, 44 facing each other, erected relative to the bottom wall 40. The two opposite wings 42, 44 have two free edges 41, 43 and they define, with the bottom wall 40, two opposite edges 45, 47.

[0044] Also, the two opposite ends 36, 38 are symmetrical to each other with respect to a median plane Pm.

[0045] Furthermore, during the cutting operation, two opposite right tabs 46, 48 have been provided in the right end 36 and two opposite left tabs 50, 52 in the left end 38. The tabs 46, 48; 50, 52 extend projecting respectively from the wings 42, 44, according to the plane that they define, and opposite the bottom wall 40.

[0046] In addition, two opposite right oblong recesses 54, 56 have been provided in the right end 36 and, opposite, two opposite left oblong recesses 58, 60 in the left end 38.

[0047] The oblong recesses 54, 56; 58, 60 extend into the opposite wings 42, 44 and into the tongues 46, 48; 50, 52 respectively. They extend in a direction substantially perpendicular to the bottom wall 40 of the crosspiece 34.

[0048] The tabs 46, 48; 50, 52 have a width substantially equal to the height of the two opposite wings 42, 44. Also, the height of the tabs 46, 48; 50, 52 is between one third and two thirds of the height of the two opposite wings 42, 44.

[0049] Furthermore, during stamping, the free edges 41, 43 of the two opposite wings 42, 44 are bent back opposite each other to form two opposite flanged edges 62, 64. These two flanged edges 62, 64 make it possible to locally increase the quadratic moment of the edges of the crosspiece 34. In other words, they make it possible to significantly increase the resistance to deformation of the edges of the crosspiece 34.

[0050] In addition, the edges 45, 47 have pairs of wedge-shaped depressions 66, 68 made in close succession along the crosspiece 34. The depressions 66, 68 are made facing each other along the same cross-section of the crosspiece 34. Also, the pairs of depressions 66, 68 are spaced from each other by a distance between one and three times the width of the wings 42, 44. They are, for example, spaced from each other by a distance substantially equal to twice the width of the wings 42, 44.

[0051] These pairs of corner depressions 66, 68 make it possible to form preferential folding zones.

[0052] Also, the crosspiece 34 is connected to two connecting plates, a right connecting plate 70, and a left connecting plate 72 substantially identical to those described with respect to [ [Fig.l]]. It is connected thereto via the two pairs of tabs 46, 48; 50, 52 by means of weld beads 74. Thanks to the steel grade used to produce the crosspiece 34, it is easy to weld together the connecting plates 70, 72 and the tabs 46, 48; 50, 52. Only the weld beads 74 connecting two tabs 46, 50 to the connecting plates 78, 72 appear in [Fig.2]. The other two are masked by the crosspiece 34 itself.

[0053] In this way, the crosspiece 34 illustrated in [Fig.2] is suitable for installation at the end of the two extensions 16, 18 shown in [Fig.l], in place of the crosspiece 24 and its two shock absorbers 20, 22. The two connecting plates 70, 72 are then applied flat against the two receiving plates 30, 32 and are bolted there.

[0054] It will thus be observed that the two shock absorbers 20, 22 are dispensed with. In addition, this makes it possible to significantly shorten the engine compartment while benefiting from the usual absorption capacities.

[0055] Thus, during a frontal impact of the motor vehicle, the two opposite ends 36, 38 of the crossmember 34 act as shock absorbers.

[0056] According to the first variant embodiment as illustrated in [Fig.2], the two times two oblong recesses 54, 56; 58, 60 make it possible to delimit on each side bridges extending respectively in the tongues 46, 48; 50, 52, which bridges are capable of flexing during the impact. The preferential flexing of these bridges then contributes to the crushing of the ends 36, 38 of the crosspiece 34 according to the X component, and consequently, to the absorption of a significant quantity of energy.

[0057] Reference will be made to [Fig.3A] partially showing the left end 38' of the crosspiece 34', according to a second variant embodiment. The elements identical to those of [Fig.2] have the same references assigned a prime sign: "'". Also, [Fig.3A] illustrates the implementation of a constriction 76 at the base of the tongues 50', 52' thanks to two opposite grooves 78, 80. The tongues of the right end of the crosspiece 34, not shown here, have the same grooves.

[0058] In this way, during a frontal impact, the preferential folding lines are established from one groove bottom 78 to the other 80. And these preferential folding lines allow the controlled crushing of the left end 38'.

[0059] According to a third variant embodiment shown in [Fig.3B], where the elements identical to those of [Fig.2] have the same references assigned a double prime sign: “ ””, grooves 82, 84 are provided in the tabs 50”, 52”.

[0060] Thus, the preferential folding lines extend along the grooves 82, 84. And during a frontal impact, the tabs 50”, 52” fold along these grooves 82, 84.

Claims

Claims

1. Deformable front structure of a motor vehicle comprising: - a cradle (12) adapted to extend transversely under an engine compartment of a motor vehicle, said cradle (12) comprising two extensions (16, 18) extending parallel towards the front of said vehicle; - a profiled crossmember (34) having two opposite ends (36, 38), said extensions (16, 18) respectively connecting said two opposite ends (36, 38) of said crossmember (34); characterized in that said two crossmember ends (36, 38) comprise preferential folding lines to cause said two ends (36, 38) to fold along said preferential folding lines during an impact.

2. Deformable front structure according to claim 1, characterized in that said cross member (34) is U-shaped defining a bottom wall (40) and two opposite wings facing each other (42, 44), said two extensions (16, 18) being connected to said two opposite wings, while said bottom wall (40) extends opposite said two extensions (16, 18).

3. Deformable front structure according to claim 2, characterized in that said two opposite wings (42, 44) comprise in each of said two crosspiece ends (36, 38), two tongues (46, 48; 50, 52) extending projecting and facing each other opposite said bottom wall (40), and in that each of said two extensions (16, 18) is connected to said two tongues (46, 48; 50, 52).

4. Deformable front structure according to claim 3, characterized in that each of said two extensions (16, 18) is connected to said two tongues (46, 48; 50, 52) by means of a plate (70, 72).

5. Deformable front structure according to claim 3 or 4, characterized in that each of said two tabs (46, 48; 50, 52) has a constriction (76) to form said preferential folding lines.

6. Deformable front structure according to any one of claims 2 to 5, characterized in that said two opposite wings (42, 44) have, in each of said two crosspiece ends, at least one recess (54, 56; 58, 60) to form said preferential folding lines.

7. Deformable front structure according to any one of claims 2 to 6, characterized in that said two opposite wings (42, 44) have, in each of said two ends (36, 38) of the crosspiece, grooves (82, 84) to form said preferential folding lines.

8. Deformable front structure according to any one of claims 2 to 7, characterized in that said two opposite wings (42, 44) have fallen edges (62, 64).

9. Deformable front structure according to any one of claims 2 to 8, characterized in that said crosspiece (34) has a plurality of pairs of local depressions (66, 68) made in edges (45, 47) between said wings (42, 44) and said bottom wall (40).

10. Deformable front structure according to any one of claims 1 to 9, characterized in that said crosspiece (34) is curved according to a convexity opposite to said cradle (12).

11. Deformable front structure according to any one of claims 1 to 10, characterized in that said crosspiece (34) is stamped in a metallic material.

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