suspension arm

Abstract

The suspension arm (1) has a main body (2). The main body (2) includes a curved portion (2a) that bends along its length and has a closed cross section. The main body (2) has an inner sidewall (2i), an outer sidewall (2o), a first sidewall (21), and a second sidewall (22). The inner sidewall (2i) corresponds to the inside of the bend of the curved portion (2a). The outer sidewall (2o) corresponds to the outside of the bend of the curved portion (2a). The first sidewall (21) connects one side edge of the inner sidewall (2i) to one side edge of the outer sidewall (2o). The second sidewall (22) connects the other side edge of the inner sidewall (2i) to the other side edge of the outer sidewall (2o) and is opposite to the first sidewall (21). The thickness (ta) of the inner sidewall (2i) is greater than the thickness (tb) of the outer sidewall (2o). When viewed in a cross section perpendicular to the length direction of the main body (2), the lengths of the first sidewall (21) and the second sidewall (22) are longer than the lengths of the inner sidewall (2i) and the outer sidewall (2o).

Description

Technical Field

[0001] This disclosure relates to a suspension arm, and more specifically to a suspension arm that is one of the components constituting the suspension of a vehicle such as an automobile. Background Technology

[0002] The vehicle is equipped with a suspension. The suspension includes suspension arms, which are components that connect the vehicle body and the wheels. For example, the upper arm and lower arm are equivalent to suspension arms.

[0003] Generally, a suspension arm has a main body, which includes a curved portion that bends along its length. Mounting portions are provided at both ends of the main body. One mounting portion is used for the connection between the wheel and the suspension arm. The other mounting portion is used for the connection between the vehicle body and the suspension arm. Therefore, in a vehicle, both ends (mounting portions) of the suspension arm are supported.

[0004] During vehicle operation, the suspension arms bear loads. To achieve good ride comfort, high stiffness is required for the suspension arms. Especially during cornering and braking, the suspension arms often bear high compressive loads along their length. Therefore, stiffness of the suspension arms against compressive loads along their length is particularly important.

[0005] Conventionally, suspension arms consist of two formed components stamped from steel sheets. These two components have symmetrical shapes, each with a wide U-shaped cross-section. The edges of the two components are joined together using arc welding to form a suspension arm with a closed cross-section (see, for example, Japanese Patent Application Publication No. 2004-262453 (Patent Document 1)). Because of its closed cross-section, the suspension arm exhibits high stiffness.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2004-262453 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] To improve a vehicle's fuel efficiency, weight reduction of the suspension arms is sought. As mentioned above, conventional suspension arms consist of two symmetrically formed components. Therefore, the plate thickness of conventional suspension arms is constant. By reducing the plate thickness of the two formed components, the overall plate thickness of the suspension arm can be reduced, thereby achieving weight reduction. However, in this case, the stiffness of the suspension arm is reduced, making it difficult to ensure good ride comfort.

[0011] The purpose of this disclosure is to provide a suspension arm that can achieve lightweight while ensuring stiffness.

[0012] Solution for solving the problem

[0013] The disclosed suspension arm comprises: a main body including a curved portion bending along its length direction and having a closed cross-section; a first mounting portion including a first hole; and a second mounting portion including a second hole. The first mounting portion is disposed at one end of the main body in the length direction. The second mounting portion is disposed at the other end of the main body in the length direction. The main body includes an inner sidewall, an outer sidewall, a first sidewall, and a second sidewall. The inner sidewall corresponds to the inner side of the curved portion. The outer sidewall corresponds to the outer side of the curved portion. The first sidewall connects one side edge of the inner sidewall to one side edge of the outer sidewall. The second sidewall connects the other side edge of the inner sidewall to the other side edge of the outer sidewall and is opposite to the first sidewall. The thickness of the inner sidewall is greater than the thickness of the outer sidewall. When viewed in a cross-section perpendicular to the length direction of the main body, the lengths of the first and second sidewalls are longer than the lengths of the inner and outer sidewalls.

[0014] The effects of the invention

[0015] The suspension arm disclosed herein can achieve lightweighting while ensuring stiffness. Attached Figure Description

[0016] Figure 1 This is a 3D view of the cantilever arm.

[0017] Figure 2 This is a side view of the analytical model used to illustrate the analytical conditions.

[0018] Figure 3 It is a graph summarizing the analysis results.

[0019] Figure 4 This is a perspective view of the suspension arm according to the first embodiment.

[0020] Figure 5 yes Figure 4 The exploded perspective view of the suspension arm is shown.

[0021] Figure 6 yes Figure 4 The side view of the suspension arm is shown.

[0022] Figure 7 yes Figure 6 A cross-sectional view at line VII-VII.

[0023] Figure 8 This is a cross-sectional view of the suspension arm according to the second embodiment.

[0024] Figure 9This is a cross-sectional view of the conventional suspension arm.

[0025] Figure 10 This is a diagram summarizing the analysis results of the embodiments. Detailed Implementation

[0026] The embodiments of this disclosure will be described below. Furthermore, while embodiments of this disclosure are illustrated by examples in the following description, this disclosure is not limited to these examples. Although specific numerical values ​​and specific materials are illustrated in the following description, this disclosure is not limited to these examples.

[0027] To address the aforementioned problems, the inventors of this application conducted repeated and in-depth research, resulting in the following insights. In this study, as an example of a suspension arm, an upper arm, which is one of the components constituting an independent suspension system, was employed.

[0028] Figure 1 This is a perspective view of the suspension arm 1A. The suspension arm 1A includes a main body 2, a first mounting portion 3, and a second mounting portion 4. The main body 2 is an elongated portion of the suspension arm 1A, disposed between the first mounting portion 3 and the second mounting portion 4. The main body 2 includes a curved portion 2a that bends along the length direction LD. The length direction LD in the suspension arm 1A is the direction in which the main body 2, including the curved portion 2a, extends. The length direction LD is not along the straight line connecting the first mounting portion 3 and the second mounting portion 4. The main body 2 has a closed cross-section.

[0029] The first mounting part 3 is provided at one end of the main body part 2 along the length direction LD. The second mounting part 4 is provided at the other end of the main body part 2 along the length direction LD. The first mounting part 3 has a first hole 5, which is used for the connection between the wheel (not shown) and the suspension arm 1A. The second mounting part 4 has a second hole 6, which is used for the connection between the vehicle body (not shown) and the suspension arm 1A.

[0030] In the vehicle, the suspension arm 1A is supported by a shaft member (not shown) passing through the first hole 5 and another shaft member (not shown) passing through the second hole 6. That is, both ends of the suspension arm 1A (the first mounted part 3 and the second mounted part 4) are supported.

[0031] The main body 2 includes an inner sidewall 2i, an outer sidewall 2o, a first sidewall 21, and a second sidewall 22. The inner sidewall 2i corresponds to the inner side of the bend in the curved portion 2a. The outer sidewall 2o corresponds to the outer side of the bend in the curved portion 2a. The first sidewall 21 connects one side edge of the inner sidewall 2i to one side edge of the outer sidewall 2o. The second sidewall 22 connects the other side edge of the inner sidewall 2i to the other side edge of the outer sidewall 2o. The second sidewall 22 is opposite to the first sidewall 21. The inner sidewall 2i, outer sidewall 2o, first sidewall 21, and second sidewall 22 form a closed cross section. The cross-sectional shape of the main body 2 perpendicular to the length direction LD is approximately rectangular. When viewed from a cross-section perpendicular to the length direction LD, the lengths of the first sidewall 21 and the second sidewall 22 are longer than the lengths of the inner sidewall 2i and the outer sidewall 2o.

[0032] When the suspension arm 1A is the upper arm, and the suspension arm 1A is mounted to the vehicle, the inner sidewall 2i is located on the upper side, and the outer sidewall 2o is located on the lower side. Additionally, for example, the first sidewall 21 faces the front of the vehicle, and the second sidewall 22 faces the rear of the vehicle. When the vehicle is turning, the suspension arm 1A experiences a high compressive load in the length direction LD.

[0033] right Figure 1 The cantilever 1A shown was subjected to CAE analysis. In the analysis, [the following was done / constructed / etc.]. Figure 1 The analytical model of the suspension arm 1A shown simulates the deformation of the suspension arm 1A under a compressive load along its length LD, based on actual conditions. Specifically, the first mounted part 3 is constrained to be able to rotate around the first hole 5, allowing the first mounted part 3 to rotate around the first hole 5. A load is applied from the second hole 6 toward the first hole 5 to the area around the second hole 6 of the second mounted part 4. For the suspension arm 1A, this load is a compressive load. The displacement of the second hole 6 in the load direction was also investigated. The displacement of the second hole 6 indicates the degree of deformation of the suspension arm 1A. The smaller the displacement of the second hole 6, the less easily the suspension arm 1A deforms, and the higher the stiffness of the suspension arm 1A.

[0034] CAE analysis was performed under multiple conditions. Figure 2 This is a side view of the analytical model used to illustrate the analytical conditions. Figure 2 The image shows a side view. Figure 1 The plane shown is the plane of the suspension arm 1A. From another perspective, in... Figure 2 The image shows the vehicle mounted on it, viewed from the front or rear. Figure 1 The plane shown is the plane of the suspension arm 1A. Figure 2 The first sidewall 21 is shown; the second sidewall is not shown. Figure 2 In the middle, the second sidewall is disposed behind the first sidewall 21, and its shape is the same as that of the first sidewall 21.

[0035] As in Figure 2 As indicated by double-dotted lines, the main body 2 of the suspension arm 1A is divided into many regions. Specifically, along the length direction LD of the suspension arm 1A... Figure 1 The inner sidewall 2i is divided into five regions: Bi, Ci, Di, Ei, and Fi. Similarly, the outer sidewall 2o is divided into five regions: Bo, Co, Do, Eo, and Fo, along the length direction LD of the suspension arm 1A. Likewise, the first sidewall 21 and the second sidewall (not shown) are each divided into five regions along the length direction LD of the suspension arm 1A. Furthermore, each region of the first sidewall 21 and the second sidewall is divided into three regions along a direction perpendicular to the length direction LD of the suspension arm 1A. In the inner sidewall 2i, regions Bi, Ci, and Di are included in the bend 2a. In the outer sidewall 2o, regions Bo, Co, and Do are included in the bend 2a.

[0036] for Figure 2 The analysis was conducted using the suspension arm 1A shown as a baseline condition, with the plate thickness set to be the same across the entire region. Furthermore, regarding... Figure 2 For each region shown, the plate thickness was changed to twice the thickness of the baseline condition, and analyses were performed for each of the changed conditions. The plate thickness of the cantilever 1A under the baseline condition was set to 2.6 mm. The material of the cantilever 1A was set to 780 MPa high-strength steel. The load applied to the second mounted part 4 was set to 10 N.

[0037] It is generally expected that stiffness will increase by increasing plate thickness. As mentioned above, by conducting analysis on each region under various conditions that increase plate thickness and investigating the displacement of the second hole 6, it is possible to verify the contribution of plate thickness in each region to the stiffness of the cantilever 1A.

[0038] Figure 3 This is a graph summarizing the results of the above analysis. Figure 3 The text shows that in Figure 2 The displacement of hole 6 under various conditions with different plate thicknesses in the regions shown.

[0039] Reference Figure 3 Under the reference conditions, the displacement of hole 6 in the second hole is 0.48 mm (refer to...). Figure 3(The dashed line in the diagram). Regardless of which region's plate thickness is increased, the displacement of the second hole 6 decreases relative to the reference condition. The decrease in displacement is particularly significant when the plate thickness of regions Bi, Ci, and Di, which are included in the bend 2a, and region Ei adjacent to region Di, is increased in the inner sidewall 2i. In the first sidewall 21 and the second sidewall 22, the decrease in displacement is also significant when the plate thickness of regions C1 and D1, which are close to these regions Bi, Ci, Di, and Ei, is increased. Even when the plate thickness of regions other than Bi, Ci, Di, Ei, C1, and D1 is increased, no significant decrease in displacement is observed.

[0040] Based on these results, the following is presented: The thickness (plate thickness) of the inner sidewall 2i contributes to the stiffness of the suspension arm 1A. Furthermore, the thickness (plate thickness) near the inner sidewall 2i in the first sidewall 21 and the second sidewall 22 also contributes to the stiffness of the suspension arm 1A. The thickness (plate thickness) of the outer sidewall 2o contributes little to the stiffness of the suspension arm 1A. The thickness (plate thickness) near the outer sidewall 2o in the first sidewall 21 and the second sidewall 22 also contributes little to the stiffness of the suspension arm 1A. In short, increasing the thickness of the inner sidewall 2i can further improve the stiffness of the suspension arm 1A compared to increasing the thickness of the outer sidewall 2o.

[0041] This situation arises from the mechanism described below.

[0042] When the cantilever arm 1A with the bend 2a is subjected to a compressive load along the length direction LD in its actual state, the compressive force is applied to the region of the inner sidewall 2i containing the bend 2a, causing compressive strain in that region. On the other hand, a tensile force is applied to the region of the outer sidewall 2o containing the bend 2a, causing tensile strain in that region. The region that experiences tensile strain does not deform outwards. In contrast, the region that experiences compressive strain deforms outwards. That is, the region of the inner sidewall 2i containing the bend 2a undergoes bending deformation.

[0043] Here, from the perspective of mechanics of materials, we examine the stiffness of a member whose plate thickness varies while maintaining a constant cross-sectional area. Under tensile force, the stiffness is related to the product of the first power of the plate thickness and Young's modulus. Conversely, under compressive force, the stiffness is related to the product of the nth power of the plate thickness (n: a value greater than 1 (e.g., an integer greater than 2)) and Young's modulus. This is based on the following reasoning: When compressive force is applied, the member undergoes local out-of-plane deformation. That is, local bending deformation of the member. The bending stiffness of a bending member depends on the moment of inertia of the section. This moment of inertia is related to the nth power of the plate thickness.

[0044] Therefore, in the cantilever 1A, if the thickness (plate thickness) of the inner sidewall 2i, which generates compressive strain due to bending deformation, is increased, the stiffness increases with respect to the nth power of the plate thickness. On the other hand, in the cantilever 1A, if the thickness (plate thickness) of the outer sidewall 2o, which generates tensile strain, is increased, the stiffness increases with respect to the first power of the plate thickness. Therefore, to further improve the stiffness of the cantilever 1A, it is sufficient to increase the thickness of the inner sidewall 2i rather than increasing the thickness of the outer sidewall 2o. In particular, even a slight increase in the thickness of the inner sidewall 2i can improve the stiffness of the cantilever 1A. This is because the stiffness increases with respect to the nth power of the plate thickness.

[0045] From another perspective, in the cantilever 1A, if the thickness (plate thickness) of the outer sidewall 2o, which generates tensile strain, is reduced, the stiffness decreases in relation to the first power of the plate thickness. Therefore, as long as the thickness (plate thickness) of the inner sidewall 2i is increased, the stiffness of the cantilever 1A can be ensured even if the thickness of the outer sidewall 2o is reduced by an amount greater than the increase in the thickness of the inner sidewall 2i.

[0046] In summary, in the suspension arm 1A having a curved portion 2a and bearing a compressive load in the longitudinal direction LD, it is possible to balance the stiffness of the suspension arm with weight reduction by increasing the thickness of the inner sidewall 2i and decreasing the thickness of the outer sidewall 2o by an amount greater than the increase in the thickness of the inner sidewall 2i. In this case, the thickness of the inner sidewall 2i is greater than the thickness of the outer sidewall 2o.

[0047] The cantilever arm of the embodiments disclosed herein is based on the above insights.

[0048] The cantilever arm of this disclosure includes: a main body including a curved portion bending along its length direction and having a closed cross-section; a first mounting portion including a first hole; and a second mounting portion including a second hole. The first mounting portion is disposed at one end of the main body in the length direction. The second mounting portion is disposed at the other end of the main body in the length direction. The main body includes an inner sidewall, an outer sidewall, a first sidewall, and a second sidewall. The inner sidewall corresponds to the inner side of the curved portion. The outer sidewall corresponds to the outer side of the curved portion. The first sidewall connects one side edge of the inner sidewall to one side edge of the outer sidewall. The second sidewall connects the other side edge of the inner sidewall to the other side edge of the outer sidewall and is opposite to the first sidewall. The thickness of the inner sidewall is greater than the thickness of the outer sidewall. When viewed in a cross-section of the main body perpendicular to the length direction, the lengths of the first and second sidewalls are longer than the lengths of the inner and outer sidewalls (first structure).

[0049] In the first structure of the suspension arm, the thickness of the inner sidewall is greater than the thickness of the outer sidewall. This is achieved by increasing the thickness of the inner sidewall and decreasing the thickness of the outer sidewall by an amount greater than the increase in the thickness of the inner sidewall. In this case, the suspension arm can be lightweighted by reducing the thickness of the outer sidewall, and the stiffness of the suspension arm can be ensured by increasing the thickness of the inner sidewall. In addition, the collision characteristics are also improved.

[0050] The cantilever arm of the first structure preferably has the following structure. The thickness ta of the inner sidewall, the thickness tb of the outer sidewall, the surface area Sa of the inner sidewall, and the surface area Sb of the outer sidewall satisfy the following equation (1). Furthermore, in the section of the inner sidewall perpendicular to the length direction at the bend, the moment of inertia Iz of the section when the thickness of the inner sidewall is ta and the thickness of the outer sidewall is tb is compared with the moment of inertia Iy of the section when the thicknesses of the inner sidewall and the outer sidewall are assumed to be "(Sa×ta+Sb×tb) / (Sa+Sb)", and satisfies the following equation (2):

[0051] ta>(Sa×ta+Sb×tb) / (Sa+Sb)>tb(1)

[0052] Iz>Iy×0.85(2) (Second structure).

[0053] In Equation (1), “(Sa×ta+Sb×tb) / (Sa+Sb)” represents the uniform thickness. The uniform thickness means the thickness at which the thickness of the entire area of ​​the inner and outer sidewalls is uniform, with the same cross-sectional shape and weight as the cantilever of the second structure. A cantilever with a uniform thickness is equivalent to a conventional cantilever with a constant plate thickness. According to the conditions in Equation (1), in the cantilever of the second structure, the thickness ta of the inner sidewall is greater than the plate thickness of the conventional cantilever, and the thickness tb of the outer sidewall is smaller than the plate thickness of the conventional cantilever. In this case, as described above, the cantilever can be lightweighted while ensuring its stiffness.

[0054] In Equation (2), Iy represents the moment of inertia of the section of the conventional cantilever with a uniform thickness. In Equation (2), Iz represents the moment of inertia of the section of the cantilever of the second structure, where the thickness ta of the inner sidewall is greater than the thickness tb of the outer sidewall. Generally, stiffness is determined by the moment of inertia of the section. However, as long as the condition of Equation (2) is met, the moment of inertia Iz of the section of the cantilever of the second structure can be smaller than that of the conventional cantilever. This is because, in the cantilever of the second structure, bending deformation related to the moment of inertia of the section is suppressed by increasing the thickness of the inner sidewall that generates compressive strain. Therefore, in the cantilever of the second structure, even if the moment of inertia Iz is smaller, the stiffness is improved.

[0055] The cantilever arm of the first or second structure preferably has the following structure: The first sidewall is divided into an inner first sidewall connected to an inner sidewall and an outer first sidewall connected to an outer sidewall. The second sidewall is divided into an inner second sidewall connected to an inner sidewall and an outer second sidewall connected to an outer sidewall. The main body includes a first member and a second member. The first member has an inner sidewall, an inner first sidewall, and an inner second sidewall. The second member has an outer sidewall, an outer first sidewall, and an outer second sidewall. The plate thickness of the first member is greater than the plate thickness of the second member. The first member and the second member are joined together by welding (third structure).

[0056] In the third type of cantilever arm, the main body is composed of two components: a first component and a second component. Specifically, the first component has an inner sidewall, and the second component has an outer sidewall with a shape different from the inner sidewall. Therefore, the first and second components have asymmetrical shapes. Furthermore, since the inner sidewall is thicker than the outer sidewall, the plate thickness of the first component is greater than that of the second component. For example, the first component can be formed by stamping a sheet of steel. The second component can be formed by stamping a sheet of steel that is thinner than the sheet used for the first component. The inner first sidewall of the first component is welded to the outer first sidewall of the second component, and the inner second sidewall of the first component is welded to the outer second sidewall of the second component. This forms a cantilever arm with a closed cross-section. In this third type of cantilever arm, the inner sidewall is also thicker than the outer sidewall. In conclusion, from a manufacturing point of view, the third type of cantilever arm is practical.

[0057] Furthermore, in the case of the third-structure cantilever, the welded joint connecting the first and second members exists on the first and second sidewalls. That is, there is no welded joint on the outer sidewall. Generally, if a welded joint exists in the area where tensile strain occurs, fatigue cracks are more likely to originate from that welded joint. The area in the cantilever where tensile strain occurs is the area within the bending portion of the outer sidewall. In conventional cantilevers, welded joints exist on both the inner and outer sidewalls. This is because two symmetrically formed members are joined together by welding. In conventional cantilevers, the welded joint exists on the outer sidewall, thus increasing the risk of fatigue cracks. On the other hand, in the third-structure cantilever, the welded joint does not exist on the outer sidewall, thus reducing the risk of fatigue cracks.

[0058] The cantilever arm of the third structure preferably has the following structure: the inner first sidewall of the first member and the outer first sidewall of the second member are welded together by a butt joint. The inner second sidewall of the first member and the outer second sidewall of the second member are welded together by a butt joint (fourth structure).

[0059] In the fourth structure's cantilever arm, the joint between the first and second components is achieved using butt joint welding. In this case, there is no overlap between the first and second components at the joint. Therefore, the fourth structure's cantilever arm can achieve both stiffness assurance and lightweighting while reducing the weight of the overlap.

[0060] The cantilever of the third structure may also have the following structure: The inner first sidewall of the first member and the outer first sidewall of the second member are welded together by a lap joint. The inner second sidewall of the first member and the outer second sidewall of the second member are welded together by a lap joint (the fifth structure).

[0061] In the cantilever of the fifth structure, the joint between the first and second members is welded using a lap joint. In this case, there is an overlap between the first and second members at the joint. Therefore, the cantilever of the fifth structure cannot achieve the weight reduction of the cantilever of the fourth structure, but it can balance stiffness and weight reduction.

[0062] Any of the suspension arms in structures 3 through 5 may also have the following structure. The first member includes: a first extension wall corresponding to the first mounting portion; and a first cylindrical portion formed on the first extension wall and corresponding to the first hole. The second member includes: a second extension wall opposite to the first extension wall and corresponding to the first mounting portion; and a second cylindrical portion formed on the second extension wall and corresponding to the first hole (structure 6).

[0063] The sixth type of suspension arm is suitable for cases where the main body is composed of a first member and a second member. In the sixth type of suspension arm, a first extension wall integral with the first member and a second extension wall integral with the second member form the first mounting portion of the suspension arm. For example, the first extension wall can be formed when the first member is stamped from a steel sheet. The second extension wall can be formed when the second member is stamped from a steel sheet.

[0064] Furthermore, in the suspension arm of the sixth structure, a first cylindrical portion integral with the first member and a second cylindrical portion integral with the second member form the first hole of the suspension arm. For example, the first cylindrical portion can be formed by performing a hole-making and flanging process on the first extended wall of the first member. The second cylindrical portion can be formed by performing a hole-making and flanging process on the second extended wall of the second member.

[0065] The first component and the second component are joined to form a suspension arm. In this suspension arm, the first extended wall and the second extended wall are opposite each other. Thus, the first mounting portion of the suspension arm is formed by the first extended wall and the second extended wall. Furthermore, the first cylindrical portion of the first component and the second cylindrical portion of the second component are arranged coaxially, and the top end of the first cylindrical portion of the first component approaches or contacts the top end of the second cylindrical portion. Thus, the first hole of the suspension arm is formed by the inner circumference of the first cylindrical portion and the inner circumference of the second cylindrical portion.

[0066] In conclusion, from a manufacturing point of view, the suspension arm of structure 6 is practical.

[0067] Any of the suspension arms in structures 3 through 6 may also have the following structure. The second member includes: a third extension wall corresponding to the second mounting portion; a first hole formed in the third extension wall and corresponding to the second hole; a fourth extension wall opposite to the third extension wall and corresponding to the second mounting portion; and a second hole formed in the fourth extension wall and corresponding to the second hole (structure 7).

[0068] The suspension arm of structure 7 is suitable for cases where the main body is composed of the first member and the second member. In the suspension arm of structure 7, the third and fourth extended walls, which are integral with the second member, face each other to form the second mounted portion of the suspension arm. For example, the third and fourth extended walls can be formed when the second member is stamped from a steel sheet.

[0069] Furthermore, in the suspension arm of the seventh structure, the first hole and the second hole of the second member form the second hole of the suspension arm. For example, the first hole and the second hole can be formed by drilling holes in the third extension wall and the fourth extension wall, respectively, so that the first hole and the second hole are arranged coaxially.

[0070] In conclusion, from a manufacturing point of view, the suspension arm of structure 7 is practical.

[0071] In a typical example, in any of the cantilever arms of structures 1 through 7, the radius of curvature of the inner sidewall at the bend is less than 200 mm (structure 8).

[0072] In the suspension arm of structure 8, the radius of curvature of the inner sidewall at the bend is relatively small. When the radius of curvature at the bend is small, the compressive strain generated on the inner sidewall tends to be large, making the stiffness of the suspension arm a concern. On the other hand, when the radius of curvature at the bend is larger than 200 mm, excessive compressive strain is less likely to occur on the inner sidewall, and the stiffness of the suspension arm is less of a concern. Therefore, according to the suspension arm of structure 8, even when stiffness is a concern, both stiffness and lightweight design can be achieved.

[0073] In a typical example, any one of the suspension arms in structures 1 through 8 is the upper arm (structure 9) that constitutes one of the components of an independent suspension system.

[0074] However, the suspension arm of structure 9 is not limited to the upper arm of an independent suspension system (e.g., double wishbone suspension, multi-link suspension, etc.). For example, the suspension arm can also be the lower arm of an independent suspension system, or it can be one of the components constituting other types of suspension systems.

[0075] The following is a reference to the appendix. Figure 1 Specific examples of the suspension arm in this embodiment will be described below. Identical or equivalent parts in the figures will be labeled with the same reference numerals without being described repeatedly.

[0076] [First Implementation]

[0077] Reference Figures 4-7 The suspension arm 1 of the first embodiment will be described. In this embodiment, as an example of the suspension arm 1, an upper arm, which is one of the components constituting an independent suspension type suspension device, is used.

[0078] Figure 4 This is a perspective view of the suspension arm 1 according to the first embodiment. Figure 5 yes Figure 4 The exploded perspective view of the suspension arm 1 shown. Figure 6 yes Figure 4 The side view of the suspension arm 1 is shown. Figure 6 The image shows the installation on the vehicle as viewed from the front or rear. Figure 4 The plane shown for suspension arm 1. Figure 6 The first sidewall 21 is shown; the second sidewall is not shown. Figure 6 In the middle, the second sidewall is disposed behind the first sidewall 21, and its shape is the same as that of the first sidewall 21. Figure 7 yes Figure 6 A cross-sectional view at line VII-VII. Figure 7 The cross-section shown is the section perpendicular to the length direction LD of the inner sidewall 2i at the bend 2a. That is, Figure 7 The cross section shown is the cross section of cantilever arm 1.

[0079] Reference Figures 4-7 In this embodiment, the suspension arm 1 and Figure 1 The suspension arm 1A shown also includes a main body 2, a first mounting portion 3, and a second mounting portion 4. The main body 2 includes a curved portion 2a that bends along the length direction LD. The cross-section of the main body 2 perpendicular to the length direction LD is a closed cross-section. That is, the main body 2 has a closed cross-section (see reference). Figure 7 ).

[0080] The first mounted part 3 is located at one end of the main body 2 along the length direction LD. The second mounted part 4 is located at the other end of the main body 2 along the length direction LD. The first mounted part 3 has a first hole 5. The first hole 5 is circular. The first hole 5 is used for the connection between the wheel (not shown) and the suspension arm 1. The second mounted part 4 has a second hole 6. The second hole 6 is circular. The second hole 6 is used for the connection between the vehicle body (not shown) and the suspension arm 1.

[0081] When the suspension arm 1 is installed in a vehicle, one axle member (not shown) passes through the first hole 5, and another axle member (not shown) passes through the second hole 6. The cross-sectional shape of each axle member is circular. In the vehicle, the suspension arm 1 is supported by the axle member passing through the first hole 5 and the axle member passing through the second hole 6. That is, both ends of the suspension arm 1 (the first mounted portion 3 and the second mounted portion 4) are supported.

[0082] The main body 2 includes an inner sidewall 2i, an outer sidewall 2o, a first sidewall 21, and a second sidewall 22. The inner sidewall 2i corresponds to the inside of the bend in the curved portion 2a. The outer sidewall 2o corresponds to the outside of the bend in the curved portion 2a. That is, the inner sidewall 2i is disposed on the inside of the bend in the curved portion 2a, and the outer sidewall 2o is disposed on the outside of the bend in the curved portion 2a. The first sidewall 21 connects one side edge of the inner sidewall 2i to one side edge of the outer sidewall 2o. The second sidewall 22 connects the other side edge of the inner sidewall 2i to the other side edge of the outer sidewall 2o. The second sidewall 22 is opposite to the first sidewall 21.

[0083] When the suspension arm 1 is the upper arm, and the suspension arm 1 is mounted on the vehicle, the curved portion 2a of the main body 2 is bent in a downward convex manner. Therefore, the inner sidewall 2i is located on the upper side, and the outer sidewall 2o is located on the lower side. In addition, the length direction LD of the suspension arm 1 is approximately aligned with the width direction of the vehicle. Therefore, for example, the first sidewall 21 faces the front of the vehicle, and the second sidewall 22 faces the rear of the vehicle. When the vehicle is turning, the suspension arm 1 bears a high compressive load in the length direction LD.

[0084] Reference Figure 6 and Figure 7In the suspension arm 1, the height H of the main body 2 is preferably greater than the width L of the main body 2. Here, the height H of the main body 2 corresponds to the height of the first side wall 21 and the second side wall 22. The height of the first side wall 21 is typically the same as the height of the second side wall 22. When viewed in a section perpendicular to the length direction LD, the height H of the main body 2 represents the length of the first side wall 21 and the second side wall 22. Similarly, when viewed in a section perpendicular to the length direction LD, the width L of the main body 2 represents the length of either the inner side wall 2i or the outer side wall 2o. In the example of this embodiment, when viewed in a section perpendicular to the length direction LD, the length of the inner side wall 2i is the same as the length of the outer side wall 2o. The ratio of height H to width L, H / L, is, for example, 1.0 to 4.0, preferably 1.5 to 3.5, and more preferably 2.0 to 3.0.

[0085] The suspension arm 1 in this embodiment is composed of a first component 11 and a second component 12. The first component 11 and the second component 12 are joined together by welding to form the suspension arm 1. The structure of the first component 11 and the second component 12 will be described in detail below.

[0086] In the main body 2, the first sidewall 21 is divided into an inner first sidewall 21i and an outer first sidewall 21o. The inner first sidewall 21i is connected to the inner sidewall 2i. The outer first sidewall 21o is connected to the outer sidewall 2o. Furthermore, in the main body 2, the second sidewall 22 is divided into an inner second sidewall 22i and an outer second sidewall 22o. The inner second sidewall 22i is connected to the inner sidewall 2i. The outer second sidewall 22o is connected to the outer sidewall 2o. The first member 11 includes the inner sidewall 2i, the inner first sidewall 21i, and the inner second sidewall 22i. The second member 12 includes the outer sidewall 2o, the outer first sidewall 21o, and the outer second sidewall 22o.

[0087] The first component 11 and the second component 12 are formed separately. The thickness of the first component 11 is greater than that of the second component 12. Therefore, the thickness ta of the inner sidewall 2i is greater than the thickness tb of the outer sidewall 2o (refer to...). Figure 7 Furthermore, the thicknesses of the inner first sidewall 21i and the inner second sidewall 22i are also greater than the thicknesses of the outer first sidewall 21o and the outer second sidewall 22o. This is because the thicknesses of the inner first sidewall 21i and the inner second sidewall 22i are the same as the thickness ta of the inner sidewall 2i, and the thicknesses of the outer first sidewall 21o and the outer second sidewall 22o are the same as the thickness tb of the outer sidewall 2o.

[0088] The materials of the first component 11 and the second component 12 are not particularly limited. However, the material strength of the second component 12 is preferably higher than that of the first component 11. This is because the thickness of the first component 11 is greater than that of the second component 12. Since the thickness of the first component 11 is greater than that of the second component 12, the strength of the component can be ensured even if the material strength of the first component 11 is lower than that of the second component 12. On the other hand, since the thickness of the second component 12 is less than that of the first component 11, the material strength of the second component 12 is preferably higher. The difference between the material strength of the first component 11 and the material strength of the second component 12 is, for example, 0 MPa to 250 MPa.

[0089] The inner first sidewall 21i of the first component 11 and the outer first sidewall 21o of the second component 12 are joined by welding. The inner second sidewall 22i of the first component 11 and the outer second sidewall 22o of the second component 12 are joined by welding. Thus, the first component 11 and the second component 12 are joined together to form a suspension arm 1 with a closed cross section of the main body 2.

[0090] Reference Figure 4 and Figure 5 In this embodiment, the first member 11 further includes a first extension wall 31 and a first cylindrical portion 51. The first extension wall 31 corresponds to the first mounted portion 3. The first cylindrical portion 51 corresponds to the first hole 5.

[0091] In the first member 11, a first extension wall 31 is provided at one end of the main body 2 in the length direction LD. The first extension wall 31 extends smoothly from the inner second side wall 22i of the first member 11. The first extension wall 31 and the inner second side wall 22i exist substantially in the same plane. The first extension wall 31 also extends smoothly from the inner side wall 2i and the inner first side wall 21i.

[0092] The first cylindrical portion 51 is formed in the first extended wall 31, extending from the inner second sidewall 22i. The first cylindrical portion 51 protrudes toward the side where the inner first sidewall 21i exists. The inner circumference of the first cylindrical portion 51 penetrates the inner second sidewall 22i. The inner diameter of the first cylindrical portion 51 is the same as the diameter of the first hole 5.

[0093] In this embodiment, the second member 12 further includes a second extension wall 32 and a second cylindrical portion 52. The second extension wall 32 corresponds to the first mounted portion 3. The second cylindrical portion 52 corresponds to the first hole 5.

[0094] In the second member 12, a second extension wall 32 is provided at one end of the main body 2 in the length direction LD. The second extension wall 32 extends smoothly from the outer first sidewall 21o of the second member 12. The second extension wall 32 and the outer first sidewall 21o are substantially on the same plane. The second extension wall 32 also extends smoothly from the outer sidewall 2o.

[0095] The second cylindrical portion 52 is formed in the second extended wall 32, extending from the outer first sidewall 21o. The second cylindrical portion 52 protrudes toward the side where the outer second sidewall 22o exists. The inner circumference of the second cylindrical portion 52 penetrates the outer first sidewall 21o. The inner diameter of the second cylindrical portion 52 is the same as the diameter of the first hole 5.

[0096] As described above, when the first member 11 and the second member 12 are joined by welding, the inner first sidewall 21i is joined to the outer first sidewall 21o, and the inner second sidewall 22i is joined to the outer second sidewall 22o. At this time, the portion of the first extended wall 31 extending from the inner second sidewall 22i is joined to the portion of the second extended wall 32 extending from the outer sidewall 20 by welding, and is also joined to the outer second sidewall 22o by welding.

[0097] With the first member 11 and the second member 12 engaged, the portion of the first extended wall 31 extending from the inner second side wall 22i is opposite to the portion of the second extended wall 32 extending from the outer first side wall 21o. Thus, the first mounted portion 3 of the suspension arm 1 is formed by the first extended wall 31 and the second extended wall 32.

[0098] Furthermore, when the first member 11 and the second member 12 are engaged, the first cylindrical portion 51 and the second cylindrical portion 52 are arranged coaxially, with the top end of the first cylindrical portion 51 approaching or contacting the top end of the second cylindrical portion 52. As a result, the first hole 5 of the suspension arm 1 is formed by the inner circumference of the first cylindrical portion 51 and the inner circumference of the second cylindrical portion 52.

[0099] Alternatively, contrary to the above, the first extension wall 31 may extend smoothly from the inner first sidewall 21i of the first member 11. In this case, the first extension wall 31 also extends smoothly from the inner sidewall 2i and the inner second sidewall 22i. A first cylindrical portion 51 is formed in the portion of the first extension wall 31 that extends from the inner first sidewall 21i. The first cylindrical portion 51 protrudes toward the side where the inner second sidewall 22i exists. The inner circumference of the first cylindrical portion 51 penetrates the inner first sidewall 21i.

[0100] In this case, contrary to the above, the second extended wall 32 extends smoothly from the outer second sidewall 22o of the second member 12. The second extended wall 32 also extends smoothly from the outer sidewall 2o. The portion of the second extended wall 32 extending from the outer second sidewall 22o is opposite to the portion of the first extended wall 31 extending from the inner first sidewall 21i. The second cylindrical portion 52 is formed in the portion of the second extended wall 32 extending from the outer second sidewall 22o. The second cylindrical portion 52 protrudes toward the side where the outer first sidewall 21o exists. The inner circumference of the second cylindrical portion 52 penetrates the outer second sidewall 22o.

[0101] In this embodiment, the second member 12 further includes a third extension wall 41, a first hole 61, a fourth extension wall 42, and a second hole 62. The third extension wall 41 and the fourth extension wall 42 correspond to the second mounted portion 4. The first hole 61 and the second hole 62 correspond to the second hole 6.

[0102] In the second member 12, the third extension wall 41 and the fourth extension wall 42 are provided at the other end of the main body 2 in the length direction LD. The third extension wall 41 extends smoothly from the outer first side wall 21o of the second member 12. The third extension wall 41 and the outer first side wall 21o are substantially coplanar. The fourth extension wall 42 extends smoothly from the outer second side wall 22o of the second member 12. The fourth extension wall 42 and the outer second side wall 22o are substantially coplanar. The third extension wall 41 and the fourth extension wall 42 also extend smoothly from the outer side wall 2o. The portions of the third extension wall 41 and the fourth extension wall 42 extending from the outer side wall 2o are integral. The portion of the third extension wall 41 extending from the outer first side wall 21o is opposite to the portion of the fourth extension wall 42 extending from the outer second side wall 22o. Thus, the third extension wall 41 and the fourth extension wall 42 form the second mounted portion 4 of the suspension arm 1.

[0103] A first hole 61 is formed in the third extension wall 41, extending from the outer first sidewall 21o. The first hole 61 penetrates the outer first sidewall 21o. A second hole 62 is formed in the fourth extension wall 42, extending from the outer second sidewall 22o. The second hole 62 penetrates the outer second sidewall 22o. The first hole 61 and the second hole 62 are circular holes with the same diameter as the second hole 6. The first hole 61 is formed in a manner that it is coaxially arranged with the second hole 62. Thus, the first hole 6 of the suspension arm 1 is formed by the first hole 61 and the second hole 62.

[0104] Alternatively, contrary to the above, the third extension wall 41, the first hole 61, the fourth extension wall 42, and the second hole 62 may be provided in the first member 11. In this case, in the first member 11, the third extension wall 41 and the fourth extension wall 42 are provided at the other end of the length direction LD of the main body 2. The third extension wall 41 extends smoothly from the inner first side wall 21i of the first member 11. The fourth extension wall 42 extends smoothly from the inner second side wall 22i of the first member 11. The third extension wall 41 and the fourth extension wall 42 also extend smoothly from the outer side wall 2o. The portions of the third extension wall 41 and the fourth extension wall 42 extending from the outer side wall 2o are integral. The portion of the third extension wall 41 extending from the inner first side wall 21i is opposite to the portion of the fourth extension wall 42 extending from the inner second side wall 22i.

[0105] In this case, a first hole 61 is formed in the third extended wall 41, extending from the inner first sidewall 21i. The first hole 61 penetrates the inner first sidewall 21i. A second hole 62 is formed in the fourth extended wall 42, extending from the inner second sidewall 22i. The second hole 62 penetrates the inner second sidewall 22i. The first hole 61 and the second hole 62 are formed coaxially.

[0106] Thus, the suspension arm 1 of this embodiment is composed of a first member 11 and a second member 12. In particular, the first member 11 has an inner sidewall 2i, and the second member 12 has an outer sidewall 2o with a shape different from that of the inner sidewall 2i. Therefore, the first member 11 and the second member 12 have asymmetrical shapes. In addition, the thickness of the first member 11 is greater than that of the second member 12.

[0107] The first component 11 can be formed by stamping a steel sheet. The second component 12 can be formed by stamping a steel sheet that is thinner than the steel sheet used for the first component 11. However, the forming methods for the first component 11 and the second component 12 are not limited to stamping.

[0108] Furthermore, the first extension wall 31, which becomes the first mounted part 3, can be formed when the first member 11 is stamped from a steel sheet. The second extension wall 32, which becomes the first mounted part 3, can be formed when the second member 12 is stamped from a steel sheet. The first cylindrical part 51, which becomes the first hole 5, can be formed by performing a hole-making and flanging process on the first extension wall 31 of the first member 11. The second cylindrical part 52, which becomes the first hole 5, can be formed by performing a hole-making and flanging process on the second extension wall 32 of the second member 12.

[0109] Furthermore, the third extension wall 41 and the fourth extension wall 42, which become the second mounted part 4, can be formed when the second member 12 is stamped from steel sheet. The first hole portion 61 and the second hole portion 62, which become the second hole 6, can be formed by performing hole-making on the third extension wall 41 and the fourth extension wall 42 before joining the first member 11 and the second member 12. However, there is no problem in forming the first hole portion 61 and the second hole portion 62, which become the second hole 6, even after joining the first member 11 and the second member 12.

[0110] Reference Figure 7 The cross-sectional shape of both the first component 11 and the second component 12 is a narrow U-shape. In this embodiment, the first component 11 and the second component 12 are joined by butt welding. Specifically, the open end (lower end) of the inner first sidewall 21i of the first component 11 is butt-jointed with the open end (upper end) of the outer first sidewall 21o of the second component 12 by welding. The open end (lower end) of the inner second sidewall 22i of the first component 11 is butt-jointed with the open end (upper end) of the outer second sidewall 22o of the second component 12 by welding. The welding method is not particularly limited, but arc welding is preferred. Laser welding can also be used.

[0111] In this case, the weld portion W that joins the first component 11 and the second component 12 exists on the first sidewall 21 and the second sidewall 22. That is, there is no weld portion on the outer sidewall 2o. In addition, in the case of a joint performed by butt joint welding, there is no overlap between the first component 11 and the second component 12 at the joint between the first component 11 and the second component 12.

[0112] In this embodiment, the thickness ta of the inner sidewall 2i and the thickness tb of the outer sidewall 2o are set to satisfy the above-described equations (1) and (2) in combination with the surface area Sa of the inner sidewall 2i and the surface area Sb of the outer sidewall 2o. For example, the thickness ta of the inner sidewall 2i (the plate thickness of the first member 11) is 2.9 mm, and the thickness tb of the outer sidewall 2o (the thickness of the second member 12) is 2.3 mm.

[0113] Reference Figure 6 In this embodiment, the radius of curvature R of the inner sidewall 2i at the bend 2a is 200 mm or less. When the portion of the inner sidewall 2i at the bend 2a is formed by connecting multiple bends with different radii of curvature, the minimum radius of curvature is 200 mm or less.

[0114] [Effect]

[0115] In the suspension arm 1 of this embodiment, the thickness ta of the inner sidewall 2i is greater than the thickness tb of the outer sidewall 2o. This situation occurs by increasing the thickness ta of the inner sidewall 2i and decreasing the thickness tb of the outer sidewall 2o by an amount greater than the increase in the thickness ta of the inner sidewall 2i. In this case, the suspension arm 1 can be lightweighted by reducing the thickness tb of the outer sidewall 2o, and the stiffness of the suspension arm 1 can be ensured by increasing the thickness ta of the inner sidewall 2i. In addition, the collision characteristics are also improved.

[0116] In particular, the thickness ta of the inner sidewall 2i and the thickness tb of the outer sidewall 2o are set in a manner that satisfies the above-described equations (1) and (2). According to the condition of equation (1), in the suspension arm 1 of this embodiment, the thickness ta of the inner sidewall 2i is greater than the plate thickness of a conventional suspension arm with a constant plate thickness, and the thickness tb of the outer sidewall 2o is smaller than the plate thickness of a conventional suspension arm. In this case, as described above, the suspension arm 1 can be lightweighted, and the stiffness of the suspension arm 1 can be ensured. In addition, as long as the condition of equation (2) is satisfied, the moment of inertia Iz of the section of the suspension arm 1 of this embodiment can be smaller than the moment of inertia Iy of the section of the conventional suspension arm.

[0117] Furthermore, the suspension arm 1 of this embodiment is composed of a first member 11 having an inner sidewall 2i and a second member 12 having an outer sidewall 2o. The first member 11 and the second member 12 are each formed separately. The first member 11 and the second member 12 are joined together by welding to form a suspension arm 1 with a main body 2 having a closed cross section. Therefore, from a manufacturing point of view, the suspension arm 1 of this embodiment is practical.

[0118] Furthermore, the first component 11 and the second component 12 are joined together by welding to form a suspension arm 1 having a first mounting portion 3 and a second mounting portion 4. From a manufacturing point of view, the suspension arm 1 of this embodiment is also practical.

[0119] Generally, if a welded portion exists in the area where tensile strain occurs, fatigue cracks are likely to originate from the welded portion. In the cantilever arm 1, the area where tensile strain occurs is the region within the bend 2a of the outer sidewall 2o. In this respect, in the case of the cantilever arm 1 of this embodiment, the welded portion W that joins the first member 11 and the second member 12 is not present in the outer sidewall 2o. Therefore, the risk of fatigue cracks is lower.

[0120] Furthermore, in the suspension arm 1 of this embodiment, there is no overlap between the first member 11 and the second member 12 at the joint. Therefore, it is possible to achieve both stiffness assurance and weight reduction while reducing the amount of overlap.

[0121] [Preferred Conditions]

[0122] Reference Figure 7 The preferred conditions for the height h11 of the first member 11 are described below. The height h11 of the first member 11 corresponds to the height of the inner first sidewall 21i in the first sidewall 21. The height of the inner first sidewall 21i, when viewed in a section perpendicular to the length direction LD, signifies the length of the inner first sidewall 21i. Furthermore, the height h11 of the first member 11 also corresponds to the height of the inner second sidewall 22i in the second sidewall 22. The height of the inner second sidewall 22i, when viewed in a section perpendicular to the length direction LD, signifies the length of the inner second sidewall 22i.

[0123] When the height h11 of the first member 11 is too large, the proportion of the inner first sidewall 21i relative to the height H of the first sidewall 21 becomes larger. Similarly, when the height h11 of the first member 11 is too large, the proportion of the inner second sidewall 22i relative to the height H of the second sidewall 22 becomes larger. In this case, the proportion of the first member 11 relative to the second member 12 becomes larger. As a result, the thickness of the first member 11 is greater than the thickness of the second member 12, and therefore the weight reduction of the suspension arm 1 may be suppressed. Therefore, the height h11 of the first member 11 is preferably not too large.

[0124] On the other hand, if the height h11 of the first member 11 is too small, the proportion of the inner first sidewall 21i relative to the height H of the first sidewall 21 becomes smaller. Similarly, if the height h11 of the first member 11 is too small, the proportion of the inner second sidewall 22i relative to the height H of the second sidewall 22 becomes smaller. In this case, the proportion of the first member 11 relative to the second member 12 becomes smaller. As a result, the weight reduction of the suspension arm 1 becomes significant. Conversely, the stiffness of the suspension arm 1 may decrease. Therefore, it is preferable that the height h11 of the first member 11 is not too small.

[0125] [Second Implementation]

[0126] Reference Figure 8 The suspension arm 1 of the second embodiment will be described. The suspension arm 1 of this embodiment is a modification of the suspension arm 1 of the first embodiment. Explanations that are repeated in the description of the first embodiment will be omitted as appropriate.

[0127] Figure 8 This is a cross-sectional view of the suspension arm 1 according to the second embodiment. Figure 8 With the above Figure 7 The cross-section shown corresponds to this.

[0128] Reference Figure 8In this embodiment, the first component 11 and the second component 12 are joined using a lap joint welding method. Specifically, the open edge (lower edge) of the inner first sidewall 21i of the first component 11 is overlapped with the open edge (upper edge) of the outer first sidewall 21o of the second component 12, and the two are joined by welding. The open edge (lower edge) of the inner second sidewall 22i of the first component 11 is overlapped with the open edge (upper edge) of the outer second sidewall 22o of the second component 12, and the two are joined by welding. The welding method is not particularly limited, but arc welding is preferred. Laser welding can also be used.

[0129] exist Figure 8 In the example shown, the inner first sidewall 21i of the first member 11 overlaps the outer surface of the outer first sidewall 21o of the second member 12, and the inner second sidewall 22i of the first member 11 overlaps the outer surface of the outer second sidewall 22o of the second member 12. However, the inner first sidewall 21i of the first member 11 may also overlap the inner surface of the outer first sidewall 21o of the second member 12, and the inner second sidewall 22i of the first member 11 may also overlap the inner surface of the outer second sidewall 22o of the second member 12.

[0130] In this embodiment, when viewed in a cross-section perpendicular to the length direction LD, the length of the inner sidewall 2i is different from the length of the outer sidewall 2o. In this case, the larger of the lengths of the inner sidewall 2i and the outer sidewall 2o when viewed in a cross-section perpendicular to the length direction LD is referred to as the width L of the main body 2.

[0131] In the case of the suspension arm 1 of this embodiment, similarly to the first embodiment, the welded portion W that joins the first member 11 and the second member 12 exists on the first sidewall 21 and the second sidewall 22. Furthermore, since the joint is performed by lap joint welding, there is an overlap M between the first member 11 and the second member 12 at the joint. The overlap M is approximately 5 mm. Therefore, compared to the first embodiment, the weight increases by an amount corresponding to the overlap M. Thus, the suspension arm 1 of this embodiment cannot achieve the weight reduction to the extent of the suspension arm 1 of the first embodiment, but it can achieve the same balance between ensuring rigidity and lightweighting as the suspension arm 1 of the first embodiment.

[0132] Example

[0133] To confirm the effectiveness of the suspension arm in this embodiment, a CAE analysis was performed using the same method as the CAE analysis described above. As Example 1 of the present invention, an analysis model of the suspension arm conceived in the first embodiment was created. In Example 1 of the present invention, as described above... Figure 7The first and second components shown are joined by welding via a butt joint. As Example 2 of the present invention, an analytical model of the cantilever arm conceived in the second embodiment was fabricated. In Example 2 of the present invention, as described above... Figure 8 The first component and the second component shown are joined by lap joint welding.

[0134] Furthermore, for comparison, an analytical model assuming the previous cantilever was created. Figure 9 This is a cross-sectional view of the conventional suspension arm 101. Figure 9 With the above Figure 7 and Figure 8 The cross-section shown corresponds to this. (Refer to...) Figure 9 In the comparative example, the suspension arm 101 is composed of two symmetrically formed members 111 and 112. The two formed members 111 and 112 have the same plate thickness. The two formed members 111 and 112 are joined together by lap joint welding. The welded portion W of the two formed members 111 and 112 exists on the inner sidewall 2i and the outer sidewall 2o.

[0135] In Examples 1 and 2 of the present invention, the thickness of the first component is 2.9 mm, and the thickness of the second component is 2.3 mm. That is, the thickness of the inner sidewall is 2.9 mm, and the thickness of the outer sidewall is 2.3 mm. Therefore, the thickness of the inner sidewall is greater than the thickness of the outer sidewall. In contrast, in the comparative example, the thickness of the two formed components 111 and 112 is 2.6 mm. Therefore, the thickness of the inner sidewall is the same as the thickness of the outer sidewall. In Examples 1 and 2 of the present invention, the ratio of height H to width L, H / L, is 2.5.

[0136] In the analytical models of Examples 1 and 2 of the present invention and the comparative examples, a load was applied from the second hole toward the first hole. The applied loads were set to 15 N and 40 N. The suspension arm was made of 780 MPa high-strength steel. The displacement in the load direction of the second hole was also investigated. Furthermore, the weight of the suspension arm was calculated from each analytical model.

[0137] Figure 10 This is a graph summarizing the analysis results of the embodiments. (See reference...) Figure 10 When either a load of 15N or 40N is applied, the displacement of Example 1 of the present invention is reduced relative to the displacement of the comparative example. That is, the stiffness of Example 1 of the present invention is improved. Furthermore, the weight of Example 1 of the present invention is reduced compared to the weight of the comparative example. In addition, the displacement of Example 2 of the present invention is the same as that of the comparative example. That is, the stiffness of Example 2 of the present invention is the same as that of the comparative example. Furthermore, the weight of Example 2 of the present invention is reduced compared to the weight of the comparative example.

[0138] This confirms that the suspension arm according to this embodiment can achieve lightweighting while ensuring stiffness.

[0139] The embodiments of this disclosure have been described above. However, the above embodiments are merely illustrative examples for implementing this disclosure. Therefore, this disclosure is not limited to the above embodiments, and can be implemented by appropriately modifying the above embodiments without departing from its spirit.

[0140] Explanation of reference numerals in the attached figures

[0141] 1. Suspension arm; 2. Main body; 2a. Bend; 2i. Inner sidewall; 2o. Outer sidewall; 21. First sidewall; 22. Second sidewall; 11. First component; 12. Second component; 21i. Inner first sidewall; 21o. Outer first sidewall; 22i. Inner second sidewall; 22o. Outer second sidewall; 3. First mounting part; 4. Second mounting part; 5. First hole; 6. Second hole; ta. Thickness of the inner sidewall; tb. Thickness of the outer sidewall.

Claims

1. A cantilever arm comprising: a main body including a curved portion bending along its length and having a closed cross-section; a first mounting portion disposed at one end of the main body along its length and including a first hole; and a second mounting portion disposed at the other end of the main body along its length and including a second hole, wherein... The main body comprises: The inner sidewall corresponds to the inner side of the bend in the curved portion; The outer sidewall corresponds to the outer side of the bend in the curved portion; A first sidewall, which connects one edge of the inner sidewall to one edge of the outer sidewall; and The second sidewall connects the other edge of the inner sidewall to the other edge of the outer sidewall and is opposite to the first sidewall. The thickness of the inner sidewall is greater than the thickness of the outer sidewall. When viewed in a cross-section perpendicular to the length direction of the main body, the lengths of the first sidewall and the second sidewall are longer than the lengths of the inner sidewall and the outer sidewall. The ratio of the height of the main body to the width of the main body is 2.0 or more and less than 4.

0.

2. The suspension arm according to claim 1, wherein, The thickness ta of the inner sidewall, the thickness tb of the outer sidewall, the surface area Sa of the inner sidewall, and the surface area Sb of the outer sidewall satisfy the following formula (1). Furthermore, in the cross section perpendicular to the length direction of the inner sidewall at the curved portion, the moment of inertia Iz of the cross section when the thickness of the inner sidewall is ta and the thickness of the outer sidewall is tb is compared with the moment of inertia Iy of the cross section when the thickness of the inner sidewall and the thickness of the outer sidewall are assumed to be "(Sa×ta+Sb×tb) / (Sa+Sb)", and satisfies the following equation (2). ta>(Sa×ta+Sb×tb) / (Sa+Sb)>tb (1) Iz>Iy×0.85 (2).

3. The suspension arm according to claim 1 or 2, wherein, The first sidewall is divided into an inner first sidewall connected to the inner sidewall and an outer first sidewall connected to the outer sidewall. The second sidewall is divided into an inner second sidewall connected to the inner sidewall and an outer second sidewall connected to the outer sidewall. The main body includes: The first component includes the inner sidewall, the first inner sidewall, and the second inner sidewall; and The second component includes the outer sidewall, the outer first sidewall, and the outer second sidewall. The thickness of the first component is greater than the thickness of the second component. The first component and the second component are joined together by welding.

4. The suspension arm according to claim 3, wherein, The inner first sidewall of the first component and the outer first sidewall of the second component are joined together by butt joint welding. The inner second sidewall of the first component and the outer second sidewall of the second component are joined together by welding through a butt joint.

5. The suspension arm according to claim 3, wherein, The inner first sidewall of the first component and the outer first sidewall of the second component are joined together by lap joint welding. The inner second sidewall of the first component and the outer second sidewall of the second component are joined together by lap joint welding.

6. The suspension arm according to claim 3, wherein, The first component includes: a first extended wall corresponding to the first mounted portion; and a first cylindrical portion formed in the first extended wall and corresponding to the first hole. The second component includes: a second extended wall opposite to the first extended wall and corresponding to the first mounted portion; and a second cylindrical portion formed on the second extended wall and corresponding to the first hole.

7. The suspension arm according to claim 3, wherein, The second component includes: a third extension wall corresponding to the second mounting portion; a first hole formed in the third extension wall and corresponding to the second hole; a fourth extension wall opposite to the third extension wall and corresponding to the second mounting portion; and a second hole formed in the fourth extension wall and corresponding to the second hole.

8. The suspension arm according to claim 1, wherein, The radius of curvature of the inner sidewall at the bend is less than 200 mm.

9. The suspension arm according to claim 1, wherein, The suspension arm is the upper arm that forms part of an independent suspension system.

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