Manufacturing process for front lower suspension arms

Abstract

The invention relates to a method for manufacturing a front lower suspension arm (16) of a motor vehicle (10), and the arm obtained according to the method. The method comprises the following steps: a first section of forgeable steel bar and a second section of steel bar are provided; the first section is forged to form a first branch having a first end, and a second branch inclined relative to the first branch by defining a bend and an intrados, the second branch having a second end; the second section is extended opposite the intrados and welded to the two branches, the bend being adapted to receive a front attachment and the second end being adapted to receive a rear attachment, while the first end is adapted to be connected to a wheel support. Figure to be published with the abstract: Fig. 1

Description

Title of the invention: Method for manufacturing front lower suspension arms

[0001] The present invention relates to a method for manufacturing lower front suspension arms of a motor vehicle.

[0002] It also relates to lower front suspension arms obtained in accordance with the process.

[0003] The front lower suspension arms are among the essential elements of pseudo-McPherson type suspensions, commonly implemented on motor vehicles.

[0004] They are mounted articulated on the front cradle of the vehicle, on the right and on the left, and they receive at their end a wheel support or spindle.

[0005] Each arm has two main branches inclined relative to each other, forming a projecting elbow. One of the branches is then connected to the cradle of the motor vehicle at its free end, towards the rear of the vehicle and at the elbow, towards the front of the vehicle, while the other branch is connected to a wheel support.

[0006] The arms are usually made from a main shell stamped from a steel plate and an additional reinforcing piece welded inside the shell. In addition, a bushing is advantageously welded at the protruding elbow to allow it to pivot on the cradle.

[0007] The flat steels used are hot-rolled steels. The hot-rolling process for steels requires the use of materials with a recycled content of less than 30%. However, the more recycled material is used in steel, the fewer greenhouse gases are produced.

[0008] Consequently, manufacturing front suspension arms while reducing CO2 equivalent greenhouse gas emissions is limited by the rate of usable recycled material in steel.

[0009] Also, a problem which arises and which the present invention aims to solve, is precisely to manufacture front suspension arms while lowering the emission of greenhouse gas equivalent CO2.

[0010] In order to solve this problem, and according to a first object, a method for manufacturing a front lower suspension arm for a motor vehicle is proposed, comprising the following steps: a first section of forgeable steel bar and a second section of steel bar are provided; said first section is forged so as to form a first branch having a first end, and to form a second branch inclined relative to said first branch by defining a bend and an intrados, said second branch having a second end; and said second section is extended opposite said intrados and said second section is welded to said two branches, said bend being adapted to receive a front attachment and said second end being adapted to receive a rear attachment, while said first end is adapted to be connected to a wheel support.

[0011] Thus, a feature of the invention lies in the use of forgeable steel bar sections. In other words, steel wire is used, sourced from the "long products" steel industry, and not from the "flat products" steel industry where steel strips are obtained by rolling. The "flat products" steel industry emits significantly more CO2 equivalent greenhouse gases overall than the "long products" industry, because it tolerates far fewer recycled materials.

[0012] Also, the first section of steel, from raw steel, is forged to form two inclined branches, then the second section is welded onto the first section using weld beads to obtain a structural part.

[0013] As will be explained later in the description, the diameter of the sections will be chosen to obtain the required mechanical characteristics.

[0014] According to a particularly advantageous feature of the invention, the second section of steel bar is bent to form an extrados, and the second bent section is extended so that the extrados is opposite the intrados of the first forged section. In other words, the two sections of steel bar have a moderate curvature and are joined so that their curvatures are oriented in the same direction. This makes it easier to join them by welding. Furthermore, the suspension arm extends within a smaller space.

[0015] According to a preferred embodiment of the invention, said second section is welded to said first and second ends of the first forged section. In this way, the first and second ends of the first section are perfectly held in a fixed position relative to each other. In other words, the mechanical resistance to deformation of the suspension arm is greatly improved.

[0016] Furthermore, and in accordance with the invention, the forging step of said first section advantageously comprises a rolling substep in which said first section is rolled. Thus, in a first substep, the first section is flattened.

[0017] Also, according to the invention, the forging step of said first section includes a bending substep in which said first rolled section is bent. In other words, the first flattened section is forced into a bend. In this way, the inclination of the two arms of the suspension arm is caused.

[0018] And, in accordance with the invention, the forging step of said first section comprises a stamping sub-step in which the first section is stamped. In this way, the first rolled and curved section is plastically deformed while hot in a die.

[0019] Also, during this stamping sub-step, it is advantageous to also deform the material to the point of creating localized recesses in the first rolled and curved section.

[0020] Preferably, according to the invention, during the forging step of said first section, an orifice is made at said elbow and another orifice in said second end of said second branch. Such orifices facilitate the installation of the front and rear fasteners respectively in the suspension arm.

[0021] Furthermore, during the forging stage of said first section, said first end of said first branch is formed into a crow's foot. In this way, the connection between the suspension arm and the wheel support is made easier, as will be explained in more detail later in the description.

[0022] According to the invention, a first section of forgeable steel bar is provided, the steel comprising less than 0.30% carbon. Such a steel with a relatively low carbon content allows for good weldability. Moreover, it is also suitable for forging. Preferably, the second section of steel bar is made of the same steel.

[0023] The range of bainitic steels fully meets the requirements of the process according to the invention.

[0024] According to a second object, the invention relates to a front lower suspension arm of a motor vehicle, obtained in accordance with the process as described above.

[0025] 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:

[0026] [Fig.1] is a partial schematic top view of a motor vehicle equipped with the object of the invention;

[0027] [Fig.2] is a flowchart of the different stages of the manufacturing process according to the invention;

[0028] [Fig.3] is a schematic top view of an element from a step of the manufacturing process according to the invention;

[0029] [Fig.4] is a schematic top view of another element from another stage of the manufacturing process according to the invention;

[0030] [Fig.5] is a schematic top view of the two elements shown in [Fig.3], [Fig.4], combined; and,

[0031] [Fig.6] is a schematic top view of the object of [Fig.5], according to an alternative embodiment.

[0032] Fig. 1 shows partially the front left top of a motor vehicle 10, and it is inscribed in an orthogonal coordinate system X, Y, Z, in which the X axis extends along a longitudinal front-to-rear direction of the motor vehicle, oriented towards the rear; the Y axis extends along a transverse direction of the vehicle, oriented from left to right when in a driving situation; and the Z axis extends along a vertical direction, oriented away from the ground.

[0033] Figure 1 shows a chassis element 12 and a body element 14 of the motor vehicle. The chassis element 12 receives a left front lower suspension arm 16, which connects a left front wheel 18 to the chassis element 12.

[0034] The lower left front suspension arm 16 comprises two elements, a first element 20 and a second element 22 connected to the first element 20.

[0035] The manufacturing process of the lower suspension arm 16 and its various stages will be described in detail below with reference to the flowchart of [Fig.2], as well as the result of each of these different stages with reference to [Fig.3], [Fig.4] and [Fig.5].

[0036] Thus, in accordance with a first step 24, a first section of steel bar and a second section of steel bar are provided.

[0037] Steel bars are produced from the "long products" steel industry and, consequently, can incorporate a high percentage of recycled steel products, commonly referred to as "scrap metal." This percentage of recycled steel products can exceed 50% and reach up to 80%. As a result, the greenhouse gas emissions from the production of these steel products are significantly lower than those from steel products directly derived from iron ore, which are used to manufacture "flat products."

[0038] Regarding the steel bar intended for making the first sections, a bainitic steel will be chosen, for example. From the range of steels of this type, one will be selected that includes, for example: up to 30% carbon, 0.25% silicon, 1.00% manganese, 0.50% nickel, 1.00% molybdenum, and 0.10% niobium. Such a steel is then easily forged and, moreover, given its low carbon content, is easily weldable.

[0039] Also, the bar in which the first sections are made has a diameter between 15 mm and 25 mm, for example 20 mm.

[0040] As for the steel bar intended to make the second sections, the same steel as that used for the bar intended to make the first sections will be chosen, for example. However, its diameter will range between 8 mm and 15 mm.

[0041] According to a second forging step 26, including three sub-steps which will be described below, the first section of steel bar is forged.

[0042] In a first rolling substep 28, the first section is rolled so as to flatten it globally and also to flatten it locally at its two ends and in an intermediate zone located between the two ends. This intermediate zone is advantageously located approximately equidistant from the two ends. The first flattened section then defines a first average plane.

[0043] In a second sub-step 30 of bending, the first flattened section is bent substantially at the level of said intermediate zone, and around an axis substantially perpendicular to said first average plane, forming two branches, a first branch 29 and a second branch 31, which can be seen on the [Fig.3], as well as a bend 33.

[0044] The two branches 29, 31 are inclined to each other at an angle greater than 90°. This angle of inclination is, for example, 100°.

[0045] And in a third stamping substep 32, the first flattened and curved section is stamped. This step is carried out hot. The other substeps 28, 30 can also be carried out hot.

[0046] This third sub-step 32 of stamping allows plastic deformation of said first flattened and curved section, in particular in the intermediate zone in which a first recess 34 is also made. This first recess 34 is made at the level of the elbow 33 of the first flattened and curved section.

[0047] In this third substep 32, a first first end 40 of the first branch 29 is also formed in a goose foot shape. And furthermore, a second hollowing 38 is made in a second first end 36 of the second branch 31.

[0048] The first flattened, curved and stamped section as shown in [Fig.3], constitutes the first element 20. It defines a mean plane parallel to the plane of [Fig.3]

[0049] Also, it defines a first extrados 42 opposed to a first intrados 44.

[0050] In parallel with the second forging step 26, in a particularly advantageous, a third step 46, of bending, is carried out, to bend the second section of steel bar. This step is in no way limiting.

[0051] In this way, a second curved section is obtained as shown in [Fig.4] and constituting the second element 22. It has a first second end 48 opposite a second second end 50. In addition, it has a second extrados 52 opposite a second intrados 54.

[0052] Next, in a fourth step 56, the second element 22 is extended inside the first element 20, so that the second extrados 52 is opposite the first intrados 44, and the first second end 48 is applied against the first first end 40, while the second second end 50 is applied against the second first end 36. Such a situation is illustrated in the [Fig.5].

[0053] Also, in a fifth step 58, a first weld bead is made at the joint between the first second end 48 and the first first end 40, and a second weld bead is made at the joint between the second second end 50 and the second first end 36.

[0054] This results in a rigid suspension arm.

[0055] Also, the first recess 34 is subsequently equipped with a first attachment, not shown, and the second recess 38 with a second attachment.

[0056] As for the first first end 40 of the first branch 29 in goose foot, it is equipped with a third attachment, not shown.

[0057] As illustrated in [Fig. 1], the first attachment connects the suspension arm to the chassis element 12 at the front of the vehicle, while the second attachment connects the suspension arm to the chassis element 12 at the rear of the vehicle. The third attachment connects the suspension arm to the wheel support.

[0058] Also, the suspension arm extends along a plane substantially parallel to the horizontal plane X, Y.

[0059] Furthermore, a right front suspension arm symmetrical to the left front suspension arm 16 as illustrated in [Fig.1], allows to connect on the right, a chassis element and a wheel support.

[0060] According to a particularly advantageous embodiment of the invention, as illustrated in [Fig. 6], which shows the suspension arm 16' described above, during the second forging step 26, projections 60, 62 are formed which extend outwards from the intrados 44' of the first element 20'. These projections 60, 62 extend substantially to the second element 22', according to the embodiment shown here. They allow for local stiffening.

Claims

Demands

1. A method for manufacturing a front lower suspension arm of a motor vehicle, characterized in that it comprises the following steps: - a first section of forgeable steel bar is provided, and a second section of steel bar; - said first section is forged so as to form a first branch (29) having a first end (40), and to form a second branch (31) inclined with respect to said first branch by defining a bend (33) and an intrados (44), said second branch (31) having a second end (36); - said second section is extended opposite said intrados (44) and said second section is welded to said two branches (29, 31), said bend (33) being adapted to receive a front attachment and said second end (36) being adapted to receive a rear attachment, while said first end (40) is adapted to be connected to a wheel support.

2. A manufacturing method according to claim 1, characterized in that furthermore, said second steel bar section is bent so as to form an extrados (52), and in that the second bent section is extended so that said extrados (52) comes opposite said intrados (44) of the first forged section.

3. Manufacturing method according to claim 1 or 2, characterized in that said second section is welded to said first (40) and second (36) ends of the first forged section.

4. A manufacturing method according to any one of claims 1 to 3, characterized in that the forging step (26) of said first section comprises a rolling substep (28) in which said first section is rolled.

5. A manufacturing method according to any one of claims 1 to 4, characterized in that the forging step (26) of said first section comprises a bending substep (30) in which said first section is bent.

6. A manufacturing method according to any one of claims 1 to 5, characterized in that the forging step (26) of said first section comprises a stamping substep (32) in which said first section is stamped.

7. A manufacturing method according to any one of claims 1 to 6, characterized in that, during the forging stage (26) of said first section, an orifice (34) is operated at the level of said elbow (33) and another orifice (28) in said second end (36) of said second branch (31).

8. A manufacturing method according to any one of claims 1 to 7, characterized in that, during the forging step (26) of said first section, said first end (40) of said first branch (29) is formed in a goose foot shape.

9. A manufacturing method according to any one of claims 1 to 8, characterized in that a first section of forgeable steel bar is provided, the steel comprising less than 0.30% carbon.

10. Lower front suspension arm of a motor vehicle, obtained according to the method according to any one of claims 1 to 9.

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