Front Lower Suspension Arm Manufacturing Process

Abstract

The invention relates to a method for manufacturing a front lower suspension arm (16) of a motor vehicle (10), and the arm obtained in accordance with the method. Said method comprises the following steps: providing a first section of forgeable steel bar, and a second section of steel bar; forging said first section so as to form a first branch having a first end, and forming a second branch inclined relative to said first branch by defining an elbow and a lower surface, said second branch having a second end; extending said second section opposite said lower surface and welding said second section to said two branches, said elbow 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. Figure to be published with the abstract: Fig. 1

Description

Title of the invention: Method for manufacturing a front lower suspension arm

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

[0002] Also, it also relates to front lower suspension arms obtained in accordance with the method.

[0003] The front lower suspension arms are among the essential elements of pseudo-McPherson type suspensions, commonly used 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 of the arms 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 reinforcement piece welded inside the shell. In addition, a socket is advantageously welded at the level of the projecting elbow so that it can be pivotally mounted on the cradle.

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

[0008] Consequently, manufacturing front suspension arms while reducing the emission of greenhouse gases equivalent to CO2> comes up against the rate of recycled material usable in steel.

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

[0010] In order to solve this problem, and according to a first object, a method of manufacturing a front lower suspension arm of a motor vehicle is proposed, comprising the following steps: a first section of forgeable steel bar is provided, and a second section of steel bar is 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 an elbow 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 elbow 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 characteristic of the invention lies in the use of a forgeable steel bar section. In other words, steel wire is used in bars, originating from the steel industry of "long products", and not from the steel industry of "flat products" where steel strips are obtained by rolling. The steel industry of "flat products" emits overall much more CO2 equivalent greenhouse gases than that of "long products", because it tolerates much less recycled materials.

[0012] Also, the first section of steel is forged from raw steel 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 in the remainder of the description, the diameter of the sections will be chosen to obtain the required mechanical characteristics.

[0014] According to a particularly advantageous characteristic of the invention, said second section of steel bar is bent so as to form an extrados, and the second bent section is extended so that said extrados comes opposite said intrados of the first forged section. In other words, the two sections of steel bar have an average curvature and they are associated so that their curvatures are oriented in the same direction. In this way, it is easier to connect them by welding. In addition, the suspension arm extends in a more restricted 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 step of forging said first section advantageously comprises a rolling sub-step in which said first section is rolled. In this way, in a first sub-step, the first section is flattened.

[0017] Also, according to the invention, the forging step of said first section comprises a bending sub-step in which said first rolled section is bent. In other words, the flattened first section is forcibly bent. In this way, the inclination of the two branches of the suspension arm is then caused.

[0018] And, in accordance with the invention, the step of forging said first section comprises a stamping sub-step in which said 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 make it easier to implement the front and rear attachments respectively in the suspension arm.

[0021] Furthermore, during the forging step of said first section, said first end of said first branch is formed into a goose foot. In this way, the connection between the suspension arm and the wheel support is made easier, as will be explained in more detail in the remainder of 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 makes it possible to obtain good weldability. Furthermore, 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 required in the process according to the invention.

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

[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 partial schematic top view of a motor vehicle equipped with the subject 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 resulting from a step of the manufacturing method according to the invention;

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

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

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

[0032] [Fig.l] partially shows the front left top of a motor vehicle 10, and it is inscribed in an orthogonal reference frame X, Y, Z, in which the X axis extends in a longitudinal front-rear 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 in a rolling situation; and the Z axis extends in a vertical direction, oriented away from the ground.

[0033] [Fig.l] shows a chassis element 12 and a bodywork element 14 of the motor vehicle. Also, the chassis element 12 receives a left front lower suspension arm 16, making it possible to connect a left front wheel 18 and the chassis element 12.

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

[0035] The method of manufacturing the lower suspension arm 16 and its different steps will be described in detail below with reference to the flowchart of [Fig.2], as well as the result of each of these different steps 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 come from the steel industry of "long products", and consequently, can incorporate a high percentage of recycled steel products, commonly called: "scrap". This percentage of recycled steel products can be greater than 50%, and go up to 80%. Consequently, the greenhouse gas emissions to implement these steel products are much lower than the steel products directly derived from iron ore and with which "flat products" are produced.

[0038] As regards the steel bar intended to produce the first sections, a bainitic type steel will be chosen, for example. From the range of steels of this type, one will be chosen including, 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 in addition, given its low carbon content, it is easily weldable.

[0039] Also, the bar from 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, we will choose, for example, the same steel as that of the bar intended to make the first sections. On the other hand, its diameter extends 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 sub-step 28, the first section is rolled so as to flatten it overall 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 substantially 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 are shown in [Fig. 3], as well as an elbow 33.

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

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

[0046] This third stamping sub-step 32 makes it possible to plastically deform said first flattened and arched 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 arched section.

[0047] In this third sub-step 32, a first first end 40 of the first branch 29 is also formed in a goose foot shape. And in addition, a second recess 38 is made in a second first end 36 of the second branch 31.

[0048] The first flattened, arched 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 opposite a first intrados 44.

[0050] Parallel to the second forging step 26, in a particularly advantageously, the second section of steel bar is bent in a third bending step 46. 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] Then, in a fourth step 56, the second element 22 is extended, inside the first element 20, so that the second extrados 52 comes opposite the first intrados 44, and the first second end 48 comes into contact with the first first end 40, while the second second end 50 comes into contact with 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 produced at the joint between the first second end 48 and the first first end 40, and a second weld bead is produced 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 fastener, not shown, and the second recess 38 with a second fastener.

[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.l], the first attachment makes it possible to connect the suspension arm to the chassis element 12, towards the front of the vehicle, while the second attachment makes it possible to connect the suspension arm to the chassis element 12, towards the rear of the vehicle. As for the third attachment, it makes it possible to connect 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.l], makes it possible to connect on the right, a chassis element and a wheel support.

[0060] According to a particularly advantageous embodiment of the invention, and as illustrated in [Fig. 6], where the suspension arm 16' described above is found, during the second forging step 26, protrusions 60, 62 are formed which extend projecting from the intrados 44' of the first element 20'. These protrusions 60, 62 extend substantially as far as the second element 22', according to the embodiment shown here. They make it possible to carry out local stiffenings.

Claims

Claims

1. 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 relative to said first branch by defining an elbow (33) and a lower surface (44), said second branch (31) having a second end (36); - said second section is extended opposite said lower surface (44) and said second section is welded to said two branches (29, 31), said elbow (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. Manufacturing method according to claim 1, characterized in that, in addition, said second section of steel bar 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. 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 sub-step (28) in which said first section is rolled.

5. 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 sub-step (30) in which said first section is bent.

6. 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 sub-step (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 step (26) of said first section, an orifice (34) is made at the level of said elbow (33) and another orifice (28) in said second end (36) of said second branch (31).

8. 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 into a goose foot.

9. 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. Front lower suspension arm of a motor vehicle, obtained in accordance with the method according to any one of claims 1 to 9.

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