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

Abstract

The invention relates to 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 central thickness ecent in the central zone (Zc); the external thickness being greater than the central thickness. Figure to be published with the abbreviation: Fig. 5

Description

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

[0001] The invention relates to the field of motor vehicles.

[0002] 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.

[0003] A flexible rear axle, also called a deformable axle or semi-rigid axle, is a component commonly used in motor vehicles. The flexible axle is generally associated with coil springs and shock absorbers that work together to absorb shocks and maintain vehicle stability.

[0004] The flexible axle comprises two axle arms, each connecting one of the rear wheels to the vehicle body. To achieve this, 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 to each other. The reduced size and low weight of such flexible axles make them a preferred solution for entry-level and compact vehicles.

[0005] When the wheels undergo uneven movement relative to the vehicle chassis, for example on an uneven surface or when turning, this asymmetrical movement causes the axle arms to rotate to different degrees. This generates torsion at the crossmember, whose torsional stiffness applies a restoring force.

[0006] The torsion beam is subjected to significant stresses during driving: it must support the weight of the vehicle as well as the dynamic forces generated by road irregularities. Furthermore, the torsion beam is subjected to large-amplitude bending and torsional deformations in order to control the camber (wheel inclination) and steering (wheel direction) movements induced by cornering, as well as the vertical oscillations caused by road irregularities.

[0007] To optimize its cost, the torsion cross member is generally made from a stamped metal strip, the longitudinal edges of which are welded together and the thickness of which is specifically designed to meet the fatigue and shock resistance requirements experienced by the wheels in the most stressed areas.

[0008] 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. Given 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.

[0009] Also, a problem which arises and which the present invention aims to solve is to provide a torsion crossmember for an axle which has a lower mass while ensuring resistance to the stresses exerted on it.

[0010] In order to solve this problem, and according to a first object, a torsion cross member for an axle is proposed comprising a metal strip which has two longitudinal edges and is folded over itself around a longitudinal axis, the two longitudinal edges being welded to each other so as to form a closed section; said torsion cross member comprising at least a central zone and two extreme zones which are respectively located at two opposite ends of the torsion cross member; the metal strip having an ext. thickness in the extreme areas and an ecent. thickness in the central area; the ext. thickness being greater than the ecent. thickness. the closed section having an average perimeter pext in the extreme areas and an average perimeter pcent. in the central area; the average perimeter pext. being greater than the average perimeter pcent.

[0011] The amount of material is therefore lower in the less stressed areas: This is the case for the central area 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 on it.

[0012] According to embodiments, such a cross member may include one or more of the following characteristics.

[0013] According to one embodiment, 0.8 pext. > pcent. > 0.7 pext

[0014] According to one embodiment, the cross member comprises two intermediate zones which are respectively positioned between the central zone and either of the two extreme zones, the metal strip having a thickness eint. in the intermediate zones with eext > eint >ecent. The closed section exhibiting an average perimeter pint. in the intermediate zones with Pext. > Pint > Pcent.

[0015] According to 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 (more precisely, it increases its ability to generate a greater roll-induced steering angle than would be obtained without it), its durability, and its interaction with the axle, while reducing mass and improving the vehicle's handling. Furthermore, it is observed that the torsion beam with the aforementioned characteristics exhibits greater bending capacity than a torsion beam made, for example, from a tubular structure.

[0016] According to one embodiment, the torsion cross member has an internal section which decreases from each extreme zone towards the central zone.

[0017] 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.

[0018] According to a second aspect, the invention relates to an axle comprising two axle arms which are each equipped with an axle head for fixing a wheel bearing and are connected to each other by a torsion cross member of the aforementioned type.

[0019] According to a third aspect, the invention also relates to a method for manufacturing a torsion crossmember comprising: - provide a sheet comprising at least a first zone having an ecent thickness as well as a second zone and a third zone having an eext thickness, the second zone and the third zone being arranged longitudinally on either side of the first zone, the eext thickness being greater than the ecent thickness; - to cut and shape said sheet metal so as to obtain a metal strip having two longitudinal edges and 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 pext. in the extreme zones and an average perimeter pcent. in the central zone; the perimeter pext being greater than the perimeter pcent; and - weld the two longitudinal edges together so as to close the section.

[0020] According to embodiments, such a process may include one or more of the following characteristics.

[0021] According to one embodiment, during welding, the welding energy is varied during the longitudinal movement of a welding torch along the edges longitudinal, the welding energy being stronger in the extreme zones than in the central zone.

[0022] According to one embodiment, the sheet metal comprises a fourth zone and a fifth zone, each having a thickness eint, with eext > eint >ecent; the fourth zone being positioned longitudinally between the first zone and the second zone, and the fifth zone being positioned longitudinally between the first zone and the third zone; and in which 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 pext. > Pint. >Pcent*

[0023] According to one embodiment, the welding energy in the intermediate zones is stronger than in the central zone and weaker than in the extreme zones.

[0024] 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 accompanying drawings in which:

[0025] [Fig-1] is a top view of a rear flexible axle of a motor vehicle according to a particular embodiment.

[0026] [Fig.2] is a view from below of the rear flexible axle of the [Fig.2].

[0027] [Fig.3] is a front view of the rear flexible axle of figures 1 and 2.

[0028] [Fig.4] is a top view of the torsion beam of the flexible axle shown in figures 1 to 3.

[0029] [Fig.5] is a cross-sectional view of the torsion beam along the cutting plane longitudinal YY represented in [Fig.4].

[0030] [Fig.6] is a side view of one of the extreme areas of the torsion cross member.

[0031] [Fig.7] is a cross-sectional view of the torsion beam along the cutting plane transversal XX.

[0032] [Fig.8] is a schematic representation illustrating the manufacturing process of the torsion cross member shown in figures 4 to 7.

[0033] The orientations expressed in the description are given with reference to an orthonormal XYZ frame, 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.

[0034] Figures 1 and 2 represent a flexible axle 1 of a rear axle of a motor vehicle. It has an H-shaped structure.

[0035] The axle 1 has 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 An elastic joint 5. Such an elastic joint 5 comprises, for example, an elastomer ring mounted radially between two metal rings. It thus allows limited rotation of the axle arms 2, 3 relative to the body while filtering vibrations and shocks.

[0036] The axle arms 2, 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 ends Z1, Z2 to a respective axle arm 2, 3. The torsion beam 6 is capable of deforming in bending and torsion, particularly when turning or when the vehicle encounters irregularities in the road, which allows limited relative movement of the rear wheels with respect to each other.

[0037] 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.

[0038] Each of the axle arms 2, 3 is also equipped with an axle head 9 which is intended 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 a rear end of said axle arm 2. The axle head 9 serves as a mounting point for the wheel bearing and, for this purpose, has openings for receiving fastening elements, not shown.

[0039] The torsion cross member 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, thereby forming a closed section. The weld 12 is formed on a median longitudinal line along the torsion cross member 6 and positioned at the apex of its upper part 14.

[0040] As can be seen for example in [Fig.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 area Zc of the cross member is at a higher height than its extreme areas Zel, Ze2 which are each welded to a respective axle arm 2, 3.

[0041] As illustrated in [Fig. 5], the internal cross-section of the torsion beam 6 decreases from its extreme zones Zel, Ze2 to its central zone Zc, i.e., it gradually narrows towards the central zone Zc. More specifically, the lower part 13 of the closed section of the torsion beam 6 gradually approaches the upper part 14, from the ends towards the center. Thus, the lower part 13 of the closed section gradually rises towards the interior of the The upper portion 14 extends from the extreme zones Zel, Ze2 of the torsion beam 6 to its central zone Zc. Thus, the lower portion 13 is either straight, as shown in [Fig. 6], or has an outward curvature in the extreme zones Zel, Ze2 of the torsion beam 6, while it has an inward curvature within the upper portion 14 in the central zone Zc, as shown in [Fig. 7]. Therefore, at the center of the torsion beam 6, the lower portion 13 of the closed section has a U-shape projecting into the upper portion 14.

[0042] The metal strip has a variable thickness. To achieve this, according to one embodiment, the metal strip is obtained 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. According to other embodiments, the variation in thickness of the metal strip is obtained by locally thinning it by stretching or crushing in the appropriate directions.

[0043] More particularly, 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 Zel, Ze2.

[0044] 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 Zel, Ze2 and two intermediate zones Zil, Zi2 which are arranged on either side of the central zone Zc, between it and one of the extreme zones Zel, Ze2.

[0045] The metal strip has a thickness ecent in the central zone Zc, a thickness eext. in the extreme zones Zel, Ze2 and a thickness eint. in the intermediate zones Zil, Zi2. The aforementioned thicknesses respect the following inequalities: eext. > eint > ecent. As an example, the thicknesses of the metal strip are between 2 and 3 mm, which means that ecent > 2 mm and that eext. < 3 mm.

[0046] Thus, the thickness of the sheet metal is most important in areas where a higher stress concentration is expected and less important in areas where a lower stress concentration is expected.

[0047] 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 Zel, Ze2. Thus, the metal strip has average perimeters of the closed section which are designated: - Point in the central zone Zc; - pint in the intermediate zones Zil, Zi2; and - ext. in extreme zones Zel, Ze2; and which respect the following inequalities: pext > pint > pcent.

[0048] 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 cross member 6 in a transverse plane, orthogonal to its longitudinal direction - in the corresponding area.

[0049] 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 cross member 6.

[0050] With reference to [Fig.8], a manufacturing process for such a torsion cross member 6 will be described below, according to a particular embodiment.

[0051] The torsion cross member is manufactured from a sheet of rolled steel having five zones of different thicknesses corresponding to the five aforementioned zones, namely Zel, Zil, 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 cross member 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 Zel and Ze2 towards the central zone Zc, thus allowing the perimeter of the closed section of the torsion cross member 6 thus produced to vary accordingly.During the third step E3, called lifting, the longitudinal edges 10, 11 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, 11 are rolled and folded to obtain the desired section.

[0052] Subsequently, the longitudinal edges 10, 11 are welded together so as to close the section of the torsion cross member 6. The welding operations can in particular be carried out by arc welding, such as MAG welding (acronym for "Metal Active Gas" in English) also referred to as arc welding with active gas.

[0053] Advantageously, during welding operations, the welding energy, and more particularly the current value, is varied during the longitudinal movement of the welding torch along the torsion beam 6. More specifically, the welding energy is greatest when the welding torch is in the thickest areas, namely the extreme zones Z1 and Z2, and lower when the welding torch is in a thinner area, namely the central zone Z1. Furthermore, the welding energy is advantageously between these two values ​​in the intermediate zones Z1 and Z2.

[0054] Adapting the welding energy to the thickness of the different areas allows: - on the one hand, to avoid damaging the metal strip in the central zone Zc and the intermediate zones Zil, Zi2, where excessive welding energy could cause perforations; and - on the other hand, to maintain sufficient fusion energy in the extreme Zel, Ze2 zones to ensure effective welding.

[0055] 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.

[0056] The use of the verb "comprise", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0057] In the claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

Demands

1. A torsion cross member (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 cross member (6) comprising at least one central zone (Zc) and two extreme zones (Zel, Ze2) which are respectively located at two opposite ends of the torsion cross member (6); the metal strip having an ext. thickness in the extreme zones (Zel, Ze2) and an ecent. thickness in the central zone (Zc); the ext. thickness being greater than the ecent. thickness; the closed section having a mean perimeter pext in the extreme zones (Zel, Ze2) and a mean perimeter pcent. in the central zone (Zc); the pext perimeter being greater than the pcent perimeter.

2. A torsion cross member (6) according to claim 1, wherein the cross member comprises two intermediate zones (Z1, Zi2) which are respectively positioned between the central zone (Zc) and either of the two extreme zones (Z1, Ze2), the metal strip having a thickness eint in the intermediate zones (Z1, Zi2) with eext. > eint.. >eœnt. ; the closed section having a mean perimeter pint in the intermediate zones (Z1, Zi2) with pext. > 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 (Zel, 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 (Zel, 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 (Zel, 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 cross member comprising: - providing a sheet having at least a first zone having a thickness ecent and 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 ecent; - cutting and shaping said sheet so as to obtain a metal strip which has two longitudinal edges (10, 11) and is 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 (Zel, Ze); said metal strip having a cross-section having a mean perimeter pext in the extreme zones (Zel, Ze) and a mean perimeter pcent.in the central zone (Zc); the perimeter pext being greater than the perimeter pcent; and - weld the two longitudinal edges (10, 11) 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 (Zel, 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 > ecent; the fourth zone being positioned longitudinally between the first zone and the second zone, and the fifth zone being positioned longitudinally between the first zone and the third zone; and in which the sheet metal is cut and shaped so that the fourth and fifth zones respectively form two intermediate zones (Z1, Zi2) and the metal strip has an average perimeter pint in the intermediate zones (Z1, Zi2) with Pext. Pint .>Pcent*

10. A method for manufacturing a torsion cross member according to claims 8 and 9 taken in combination, wherein the welding energy in the intermediate zones (Zil, Zi2) is stronger than in the central zone (Zc) and weaker than in the extreme zones (Zel, Ze2).

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