Torsion crossmember for an axle, axle comprising such a crossmember, and method for manufacturing such a crossmember

Abstract

The invention relates to a torsion crossmember (6) for an axle (1), the torsion crossmember comprising a metal strip that has two longitudinal edges (10, 11) and is folded back on itself about a longitudinal axis, wherein the two longitudinal edges (10, 11) are welded to one another so as to form a closed section; the torsion crossmember (6) comprising at least one central region (Zc) and two end regions (Ze1, Ze2) which are respectively located at two opposite ends of the torsion crossmember (6); the metal strip having a thickness eext. in the end regions (Ze1, Ze2) and a thickness ecent. in the central region (Zc); the thickness eext. being greater than the thickness ecent.

Description

[0001] DESCRIPTION

[0002] Title of the invention: Torsion beam for an axle, axle comprising such a beam, and method for manufacturing such a beam

[0003] The invention relates to the field of motor vehicles.

[0004] The invention relates more specifically to a torsion crossmember for an axle, in particular for a flexible rear axle, of a motor vehicle and a method for manufacturing such a crossmember.

[0005] A flexible rear axle, also called a deformable axle or semi-rigid axle, is a common component in motor vehicles. The flexible axle is typically paired with coil springs and shock absorbers that work together to absorb shocks and maintain vehicle stability.

[0006] The flexible axle consists of two axle arms, each connecting one of the rear wheels to the vehicle body. The front end of each axle arm is articulated to the vehicle body via a flexible joint, while the rear end is fitted with an axle head that serves as a mounting point for a wheel bearing. The flexible axle also includes a torsion beam connecting the two axle arms. The compact size and low weight of such flexible axles make them a preferred solution for entry-level and compact vehicles.

[0007] When the wheels move unevenly relative to the vehicle chassis, for example on an uneven surface or when turning, this asymmetrical movement causes the axle arms to rotate at different angles. This generates torsion in the crossmember, whose torsional stiffness applies a restoring force.

[0008] The torsion beam is subjected to significant stresses during driving: it must support the vehicle's weight as well as the dynamic forces generated by road irregularities. Furthermore, the torsion beam undergoes large-amplitude bending and torsional deformations to control camber (wheel inclination) and steering (wheel direction) movements induced by cornering, as well as vertical oscillations caused by road irregularities. To optimize its cost, the torsion beam is generally manufactured from a stamped metal strip, the longitudinal edges of which are welded together, and whose thickness is specifically designed to meet the fatigue and impact resistance requirements experienced by the wheels in the most stressed areas.

[0009] However, these torsion beams have drawbacks due to their considerable thickness, necessary to meet the aforementioned fatigue and impact resistance criteria, resulting in high weight and cost. Yet, in the context of reducing carbon dioxide emissions from internal combustion engine vehicles and increasing the range of electric vehicles, it is essential to find solutions to minimize the weight of vehicle components.

[0010] Also, a problem that arises and that the present invention aims to solve is to provide a torsion crossmember for an axle that has a lower mass while ensuring resistance to the stresses exerted on it.

[0011] In order to solve this problem, and according to a first design, a torsion beam for an axle is proposed, comprising a metal strip having two longitudinal edges and folded back on itself around a longitudinal axis, the two longitudinal edges being welded to each other to form a closed section; said torsion beam comprising at least a central zone and two extreme zones located respectively at two opposite ends of the torsion beam; the metal strip having an external thickness e in the extreme zones and a thickness e C ent. in the central zone; the external thickness being greater than the centr. thickness; the closed section having an average perimeter p e xt. in extreme areas and an average perimeter p C em. in the central zone; the average perimeter p e xt. being greater than the average perimeter pcent..

[0012] The amount of material is therefore lower in the less stressed areas: This is the case for the central zone of the cross member, which is subjected to a lower level of stress than its ends. The torsion cross member can thus have a lower mass while still providing sufficient resistance to the stresses exerted upon it.

[0013] According to embodiments, such a crossbeam may include one or more of the following characteristics.

[0014] According to one embodiment, 0.8 p e xt. pcent. 0.7 p e xt.

[0015] According to one embodiment, the cross member comprises two intermediate zones which are respectively positioned between the central zone and one or the other of the two extreme zones, the metal strip having a thickness eint. in the intermediate zones with e e xt. > eint. > e Cent. ; the closed section having an average perimeter pint, in the intermediate zones with Pext. > Pint. > Pcent..

[0016] In one embodiment, the torsion beam is longitudinally curved with an upward convexity, such that the central zone is higher than the extreme zones. This curvature optimizes the mechanical and elastokinematic performance of the torsion beam (specifically, it increases its ability to generate a greater roll-induced steering angle than would be achieved without it), its durability, and its interaction with the axle, while simultaneously reducing mass and improving vehicle handling. Furthermore, a torsion beam with the aforementioned characteristics exhibits greater bending capacity than a torsion beam made, for example, from a tubular structure.

[0017] According to one embodiment, the torsion cross member has an internal section which decreases from each extreme zone towards the central zone.

[0018] According to one embodiment, the closed section comprises a lower part and an upper part; the lower part gradually approaching the upper part, longitudinally from each extreme zone towards the central zone.

[0019] According to a second aspect, the invention relates to an axle comprising two axle arms, each of which is equipped with an axle head for fixing a wheel bearing and is connected to each other by a torsion cross member of the aforementioned type.

[0020] According to a third aspect, the invention also relates to a method for manufacturing a torsion beam comprising: - supplying a sheet having at least a first zone having a thickness e Cas well as a second zone and a third zone having a thickness eext, the second and third zones being arranged longitudinally on either side of the first zone, the thickness eext being greater than the thickness e C em. ;

[0021] - to cut and shape said sheet metal so as to obtain a metal strip which has two longitudinal edges and is folded over itself around a longitudinal axis with the two longitudinal edges arranged edge to edge, the first zone, the second zone and the third zone forming respectively a central zone and two extreme zones; said metal strip having a cross-section having an average perimeter p e xt. in extreme areas and an average perimeter p C ent. in the central zone; the perimeter p e xt. being greater than the perimeter p C ent. ; and

[0022] - weld the two longitudinal edges together so as to close the section.

[0023] According to some embodiments, such a process may include one or more of the following characteristics.

[0024] According to one embodiment, during welding, the welding energy is varied during the longitudinal movement of a welding torch along the longitudinal edges, with the welding energy being higher in the extreme areas than in the central area.

[0025] According to one embodiment, the sheet metal comprises a fourth zone and a fifth zone, each having a thickness eint., with eext. > eint. > e Cent; the fourth zone being positioned longitudinally between the first and second zones, and the fifth zone being positioned longitudinally between the first and third zones; and wherein the sheet metal is cut and shaped so that the fourth and fifth zones respectively form two intermediate zones, and the metal strip has an average perimeter pint, in the intermediate zones with p e xt. > Pint. > Pcent-

[0026] According to one embodiment, the welding energy in the intermediate zones is higher than in the central zone and lower than in the extreme zones.

[0027] Other features and advantages of the invention will become apparent from the following description of particular embodiments of the invention, given by way of example but not limitation, with reference to the attached drawings in which: [Fig. 1] is a top view of a rear flexible axle of a motor vehicle according to one embodiment.

[0028] [Fig. 2] is a bottom view of the rear flexible axle of figure 2.

[0029] [Fig. 3] is a front view of the rear flexible axle of figures 1 and 2.

[0030] [Fig. 4] is a top view of the torsion beam of the flexible axle shown in figures 1 to 3.

[0031] [Fig. 5] is a cross-sectional view of the torsion beam along the longitudinal section plane YY shown in Figure 4.

[0032] [Fig. 6] is a side view of one of the extreme areas of the torsion cross member.

[0033] [Fig. 7] is a cross-sectional view of the torsion beam along the transverse cutting plane XX.

[0034] [Fig. 8] is a schematic representation illustrating the manufacturing process of the torsion cross member shown in figures 4 to 7.

[0035] The orientations expressed in the description are given with reference to an orthonormal XYZ coordinate system, shown in the figures, in which X represents the longitudinal direction of the vehicle, oriented from front to back, Y the transverse direction of the vehicle, oriented to the right, and Z the vertical direction oriented upwards of the vehicle in its usual position, resting on its wheels.

[0036] Figures 1 and 2 represent a flexible axle 1 of a rear axle of a motor vehicle. It has an H-shaped structure.

[0037] Axle 1 comprises two axle arms 2, 3. One end of each axle arm 2, 3, namely its front end 4, is articulated to the vehicle body via a flexible joint 5. Such a flexible joint 5 comprises, for example, an elastomer bushing mounted radially between two metal bushings. It thus allows limited rotation of the axle arms 2, 3 relative to the body while filtering vibrations and shocks.

[0038] The axle arms 2 and 3 are connected to each other by a torsion beam 6. The torsion beam 6 is fixed, and advantageously welded, at each of its extreme points Ze1 and Ze2 to a respective axle arm 2 or 3. The torsion beam 6 is capable of deforming in bending and torsion, particularly when cornering or when the vehicle encounters irregularities in the road, thus allowing limited relative movement of the rear wheels with respect to each other.

[0039] Each axle arm 2, 3 is equipped with a suspension cup 7 which is welded to said axle arm 2, 3 and which supports one end of one of the suspension springs. Each axle arm 2, 3 is also equipped with a mounting bracket 8 to which one end of a suspension damper, not shown, is attached.

[0040] Each of the axle arms 2, 3 is also equipped with an axle head 9, which is designed to secure a wheel bearing to said axle arm 2, 3. The axle head 9 is made of metal, preferably steel, and is attached and welded to the axle arm 2 at one rear end of said axle arm 2. The axle head 9 serves as the mounting point for the wheel bearing and, for this purpose, has holes for receiving fasteners, not shown.

[0041] The torsion beam 6 is formed from at least one metal strip that is folded back on itself around a longitudinal axis so that the longitudinal edges 10, 11 of the metal strip are positioned edge to edge. The longitudinal edges 10, 11 are further welded to each other by means of a weld 12, thus forming a closed section. The weld 12 is formed on a median longitudinal line along the torsion beam 6 and positioned at the apex of its upper part 14.

[0042] As can be seen for example in figure 3, the torsion cross member 6 is longitudinally curved, which means that the longitudinal axis of the torsion cross member 6 has a curvature with a convexity oriented upwards, along the Z axis. Thus, the central zone Zc of the cross member is at a higher height than that of its extreme zones Ze1, Ze2 which are each welded to a respective axle arm 2, 3.

[0043] As illustrated in Figure 5, the internal cross-section of the torsion beam 6 decreases from its extreme zones Ze1 and Ze2 to its central zone Zc, meaning it gradually narrows towards the central zone Zc. More specifically, the lower portion 13 of the closed cross-section of the torsion beam 6 gradually approaches the upper portion 14 from the ends towards the center. Thus, the lower portion 13 of the closed cross-section gradually curves inwards towards the upper portion 14, from the extreme zones Ze1 and Ze2 of the torsion beam 6 to its central zone Zc. Therefore, this lower portion 13 is either straight, as shown in Figure 6, or exhibits an outward curvature in the extreme zones Ze1 and Ze2 of the torsion beam 6, while it exhibits an inward curvature in the upper portion 14 in the central zone Zc, as shown in Figure 7.Thus, at the center of the torsion cross member 6, the lower part 13 of the closed section has a U-shape protruding inside the upper part 14.

[0044] The metal strip has a variable thickness. In one embodiment, this is achieved by a rolling process: the metal is passed between rollers at controlled temperatures and pressures, and the distance between the rollers and the applied pressure are adjusted to vary the thickness. In other embodiments, the thickness variation of the metal strip is achieved by locally thinning it through stretching or crushing in the appropriate directions.

[0045] More specifically, the thickness of the metal strip forming the torsion cross member 6 varies longitudinally along the length of the torsion cross member 6: it increases from the central zone Zc of the torsion cross member 6 towards the extreme zones Ze1, Ze2.

[0046] As schematically represented in figures 4 and 5, the torsion cross member 6 can be divided into five zones: namely a central zone Zc, two extreme zones Ze1, Ze2 and two intermediate zones Zi1, Zi2 which are arranged on either side of the central zone Zc, between it and one of the extreme zones Ze1, Ze2.

[0047] The metal strip has a thickness of e C ent. in the central zone Zc, a thickness eext. in the extreme zones Ze1, Ze2 and a thickness eint. in the intermediate zones Zi1, Zi2. The aforementioned thicknesses satisfy the following inequalities: eext. > eint. > e CFor example, the thickness of the metal strip is between 2 and 3 mm, which means that e C ent. > 2 mm and that eext. <3mm.

[0048] Thus, the sheet metal thickness is most important in areas where a higher stress concentration is expected and less important in areas where a lower stress concentration is expected.

[0049] Furthermore, the perimeter of the closed section varies longitudinally along the length of the torsion beam 6: it increases from the central zone Zc towards the extreme zones Ze1, Ze2. Thus, the metal strip has average perimeters of the closed section which are designated:

[0050] - percent in the central zone Zc;

[0051] - pim. in the intermediate zones Zi 1, Zi2; and

[0052] - pext. in the extreme zones Ze1, Ze2; and which respect the following inequalities: p ext. > pint. > pcent..

[0053] The average perimeters of the closed section correspond to the average value of the perimeter of the closed section - that is to say the total length of the edges delimiting the section of the torsion beam 6 in a transverse plane, orthogonal to its longitudinal direction - in the corresponding area.

[0054] The amount of material is thus further reduced in the least stressed areas, which makes it possible to further reduce the mass and cost of the torsion beam 6.

[0055] With reference to figure 8, a manufacturing process for such a torsion cross member 6 will be described below, according to a particular embodiment.

[0056] The torsion beam is manufactured from a sheet of rolled steel with five zones of varying thicknesses corresponding to the five aforementioned zones, namely Ze1, Zi1, Zc, Zi2, and Ze2. In a first step E1, called forming, the sheet undergoes an initial stamping operation to shape the lower part 13 of the torsion beam 6. Then, in a second step E2, called trimming, the longitudinal edge strips of the sheet are cut to define the longitudinal edges 10, 11, which will subsequently be welded together. The trimming is carried out in such a way as to progressively reduce the width of the sheet from the extreme zones Ze1 and Ze2 towards the central zone Zc, thus allowing the perimeter of the closed section of the resulting torsion beam 6 to vary accordingly.During the third step E3, called lifting, the longitudinal edges 10, 1 1 are straightened on each side of the imprint forming the lower part 13. Finally, during the fifth and sixth steps E5 and E6, called rolling, the longitudinal edges 10, 1 1 are rolled and folded in order to obtain the desired section.

[0057] Subsequently, the longitudinal edges 10 and 11 are welded together to close the section of the torsion beam 6. The welding operations can be carried out by arc welding, such as MAG welding (Metal Active Gas), also known as gas-activated arc welding. Advantageously, during the welding operations, the welding energy, and more specifically the current value, is varied as the welding torch moves longitudinally along the torsion beam 6. Specifically, the welding energy is highest when the welding torch is in the thickest areas, namely the extreme zones Ze1 and Ze2, and lowest when the welding torch is in a thinner area, namely the central zone Zc. Furthermore, the welding energy is advantageously between these two values ​​in the intermediate zones Zi1 and Zi2.

[0058] Adapting the welding energy to the thickness of the different areas allows:

[0059] - on the one hand, to avoid damaging the metal strip in the central zone Zc and the intermediate zones Zi1, Zi2, where excessive welding energy could cause perforations; and

[0060] - on the other hand, to maintain sufficient fusion energy in the extreme zones Ze1, Ze2 to ensure effective welding.

[0061] Although the invention has been described in connection with several particular embodiments, it is clearly evident that it is by no means limited to them and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention, as defined by the claims.

[0062] The use of the verb "comporter", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or steps than those stated in a claim.

[0063] In claims, any reference sign in parentheses should not be interpreted as a limitation of the claim.

Claims

DEMANDS

1. A torsion beam (6) for an axle (1) comprising a metal strip having two longitudinal edges (10, 11) and folded back on itself about a longitudinal axis, the two longitudinal edges (10, 11) being welded to each other so as to form a closed section; said torsion beam (6) comprising at least one central zone (Zc) and two extreme zones (Ze1, Ze2) which are respectively located at two opposite ends of the torsion beam (6); the metal strip having an external thickness eext in the extreme zones (Ze1, Ze2) and a thickness ec C ent. in the central zone (Zc); the external thickness eext. being greater than the external thickness e C ent. ; the closed section having an average perimeter p e xt. in the extreme zones (Ze1, Ze2) and an average perimeter p C ent. in the central zone (Zc); the perimeter p e xt. being greater than the perimeter pcent..

2. A torsion cross member (6) according to claim 1, wherein the cross member comprises two intermediate zones (Zi1, Zi2) which are respectively positioned between the central zone (Zc) and one or the other of the two extreme zones (Ze1, Ze2), the metal strip having a thickness eint. in the intermediate zones (Zi1, Zi2) with eext. > eint. . > e C ent. ; the closed section having an average perimeter pint, in the intermediate zones (Zi 1 , Zi2) with p e xt. > pint. . > pcent.

3. Torsion cross member (6) according to claim 1 or 2, wherein the torsion cross member (6) is longitudinally curved with an upwardly oriented convexity such that the central zone (Zc) is at a height greater than that of the extreme zones (Ze1, Ze2).

4. Torsion cross member (6) according to any one of claims 1 to 3, wherein the torsion cross member (6) has an internal section which decreases from each extreme zone (Ze1, Ze2) towards the central zone (Zc).

5. Torsion cross member (6) according to any one of claims 1 to 3, wherein the closed section comprises a lower part (13) and an upper part (14) and wherein the lower part (13) gradually approaches the upper part (14), longitudinally from each extreme zone (Ze1, Ze2) towards the central zone (Zc).

6. Axle (1) comprising two axle arms (2, 3) which are each equipped with an axle head (9) for fixing a wheel bearing and are connected to each other by a torsion cross member (6) according to any one of claims 1 to 5.

7. A method for manufacturing a torsion beam comprising: - provide a sheet metal comprising at least one first zone having a thickness e C em as well as a second zone and a third zone having a thickness eext, the second zone and the third zone being arranged longitudinally on either side of the first zone, the thickness eext being greater than the thickness e C em. ; - to cut and shape said sheet metal so as to obtain a metal strip having two longitudinal edges (10, 11) and folded over itself around a longitudinal axis with the two longitudinal edges (10, 11) arranged edge to edge, the first zone, the second zone and the third zone forming respectively a central zone (Zc) and two extreme zones (Ze1, Ze2); said metal strip having a cross-section with an average perimeter p e xt. in the extreme zones (Ze1, Ze2) and an average perimeter p C ent. in the central zone (Zc); the perimeter p ext. being greater than the perimeter p C ent. ; and - weld the two longitudinal edges (10, 1 1 ) together so as to close the section.

8. A manufacturing method according to claim 7, wherein, during welding, the welding energy is varied during the longitudinal movement of a welding torch along the longitudinal edges (10, 11), the welding energy being stronger in the extreme zones (Ze1, Ze2) than in the central zone (Zc).

9. A method for manufacturing a torsion beam according to claim 7 or 8, wherein the sheet metal comprises a fourth zone and a fifth zone, each having a thickness eint., with eext. > eint. > e Cthe fourth zone being positioned longitudinally between the first and second zones, and the fifth zone being positioned longitudinally between the first and third zones; and wherein the sheet metal is cut and shaped so that the fourth and fifth zones respectively form two intermediate zones (Zi 1, Zi2) and the metal strip has an average perimeter of 1 / 2 in the intermediate zones (Zi 1, Zi2) with 1 / 2. e xt. > pim > pcent.

10. A method for manufacturing a torsion beam according to claims 8 and 9 taken in combination, wherein the welding energy in the intermediate zones (Zi1, Zi2) is higher than in the central zone (Zc) and lower than in the extreme zones (Ze1, Ze2).

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