Suspension arm

Abstract

This invention provides a suspension arm that improves the fatigue life of the bush press-fit section formed by burring, while suppressing a significant increase in weight and reducing manufacturing costs, making it easy to manufacture. [Solution] The suspension arm 1 according to the present invention comprises an arm body 10 and a bush press-fitting portion 20 in which a bush is press-fitted into the inside of the cylindrical vertical wall portion 21, having a cylindrical vertical wall portion 21 and a curved portion 23 formed by burring the top plate portion 11 of the arm body 10, and a ring-shaped member 30 fitted to the outside of the cylindrical vertical wall portion 21, with its lower end 30c integrated with the top plate portion 11.

Description

Technical Field

[0001] The present invention relates to a suspension arm, which is a component of an automobile's undercarriage, and has a bush press-fitting portion into which a bush is press-fitted.

Background Art

[0002] In recent years, for the purpose of reducing the weight of automobiles, the use of high-tensile materials (high-tensile steel sheets) has promoted the thinning of the skeletal parts and undercarriage parts of automobiles. When the thickness of the suspension arm, which is an undercarriage part, is reduced, the rigidity of the bush press-fitting portion of the suspension arm decreases. Therefore, when a load in a direction perpendicular to the axial direction of the bush press-fitting portion is input to the bush during the running of the automobile, the stress generated near the curved portion of the bush press-fitting portion increases, and the curved portion and its vicinity of the bush press-fitting portion are likely to undergo fatigue failure.

[0003] As a technique applicable to this problem, for example, Patent Document 1 discloses a technique of attaching a reinforcing plate having a spherical head portion and a tail portion to a suspension arm including an arm body and a bush press-fitting portion formed by burring. In this technique, the reinforcing plate is arranged such that the spherical head portion is coaxially positioned with the short cylindrical portion of the bush press-fitting portion, and at least the tail portion is welded to the arm body of the suspension arm. Thereby, it is possible to sufficiently secure the cross-sectional shape of the transition portion from the bush press-fitting portion to the arm body of the suspension arm, and it is said that the necessary rigidity strength of the transition portion can be easily ensured.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The technology described in Patent Document 1 used a reinforcing plate having a tail portion extending longitudinally from an eye-shaped head to the main plate body of the arm, which inevitably led to a significant increase in weight. Furthermore, it was difficult to manufacture the eye-shaped head while positioning it coaxially with the short cylindrical portion in the bush press-fit section, and attaching the tail portion to the arm by welding was a problem, resulting in high manufacturing costs.

[0006] This invention was made to solve the above-mentioned problems, and aims to provide a suspension arm that improves the fatigue life of the bush press-fit portion and its vicinity, suppresses a significant increase in weight, and can be easily manufactured while keeping manufacturing costs down. [Means for solving the problem]

[0007] (1) The suspension arm according to the present invention comprises an arm body and a bush press-fitting portion having a cylindrical vertical wall portion and a curved portion formed by burring the top plate portion of the arm body, the inside of which a bush is press-fitted, The present invention is characterized by having a ring-shaped member that is fitted onto the outside of the cylindrical vertical wall portion and whose lower end is integrated with at least one of the curved portion or the top plate portion.

[0008] (2) In the items described in (1) above, The lower end of the ring-shaped member is welded to at least one of the curved portion or the top plate portion.

[0009] (3) In the case of the items described in (1) or (2) above, The ring-shaped member is characterized in that its outer surface lies outside the boundary between the curved portion and the top plate portion.

[0010] (4) In any of the items described in (1) to (3) above, The ring-shaped member is characterized in that its material is the same as that of the bush press-fit portion. [Effects of the Invention]

[0011] According to the present invention, the tensile stress generated in the curved portion of the bush press-fit section formed by burring and in its vicinity can be reduced, thereby extending the fatigue life of the bush press-fit section and its vicinity. Furthermore, according to the present invention, a significant increase in weight is suppressed in order to reinforce the bush press-fit section, and it can be manufactured easily while keeping manufacturing costs down. [Brief explanation of the drawing]

[0012] [Figure 1] This figure illustrates the bush press-fit portion and the ring-shaped member in a suspension arm according to an embodiment of the present invention ((a) top view, (b) cross-sectional view along B-B'). [Figure 2] This is a top view showing the entire suspension arm according to an embodiment of the present invention. [Figure 3] This is a top view showing the configuration of a conventional suspension arm. [Figure 4] This is a cross-sectional view illustrating the bush press-fit portion in a conventional suspension arm. [Figure 5] This diagram illustrates the load applied to a bush pressed into the bush press-fit section of a conventional suspension arm. [Figure 6] In the embodiment, as a conventional example, the CAE analysis model that models the bush press-fit portion and top plate portion of a conventional suspension arm is shown ((a) top view, (b) C-C' cross-sectional view). [Figure 7] In the example, as Invention Example 1, this figure shows a CAE analysis model that models the bush press-fit portion and top plate portion of the suspension arm according to the present invention ((a) top view, (b) D-D' cross-sectional view). [Figure 8] This figure shows a CAE analysis model in which the upper end of the vertical wall portion is modeled to be located below the upper end of the ring-shaped member in the embodiment ((a) top view, (b) E-E' cross section view). [Figure 9]In the embodiment, it is a diagram showing a CAE analysis model according to a comparative example used as a comparison target of the present invention ((a) top view, (b) cross-sectional view taken along F-F'). [Figure 10] In the embodiment, it is a diagram showing a bush to be press-fitted into the bush press-fitting portion of the CAE analysis model ((a) top view, (b) side view). [Figure 11] In the embodiment, it is a diagram for explaining a CAE analysis model in which a bush is press-fitted into a bush press-fitting portion and a load condition for loading a load on the bush in the CAE analysis model. [Figure 12] In the embodiment, it is a contour diagram showing the distribution of the first principal stress when a load is applied to the bush press-fitted into the bush press-fitting portion of the CAE analysis model. [Figure 13] In the embodiment, it is a graph showing the relationship between the distance X between the upper end of the vertical wall portion and the upper end of the ring-shaped member in the CAE analysis model and the maximum value of the first principal stress generated in the curved portion of the bush press-fitting portion. [Figure 14] In the embodiment, it is a diagram showing the force point, fulcrum point, and action point of the load when a load is applied to the bush of the CAE analysis model according to Invention Example 1. [Figure 15] In the embodiment, it is a diagram showing the force point, fulcrum point, and action point of the load when a load is applied to the bush of the CAE analysis model according to Invention Example 3.

Mode for Carrying Out the Invention

[0013] [Conventional Suspension Arm] Before explaining the suspension arm according to the embodiment of the present invention, the structure of the conventional suspension arm will be explained. In the following description, the drawings may show enlarged versions of key features for clarity, but the dimensions and proportions of each component may not be the same as those of the actual components. In the drawings of this application, the X-axis and Y-axis directions refer to the two orthogonal directions in the plane of the suspension arm viewed from above, and the Z-axis direction refers to the axial direction of the bush press-fit portion. Furthermore, in this specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant explanations are omitted or simplified.

[0014] Figure 3 shows, as an example, a conventional suspension arm 3 comprising an arm body 10 and a bush press-fitting section 20. The arm body 10 is manufactured by press forming of a metal plate (such as a steel plate) and has a top plate portion 11. As shown in Figure 4, which is a cross-sectional view taken along the line A-A' in Figure 3, the bush press-fit portion 20 has a cylindrical vertical wall portion 21 and a curved portion 23 formed by burring the top plate portion 11 of the arm body 10. The vertical wall portion 21 is formed in a cylindrical shape so as to protrude from the top plate portion 11, and as shown in Figure 5, a bush 50 (or ball bearing) is press-fitted inside it. The bush 50 (or ball bearing) is attached to the automobile body. The curved section 23 connects the top plate section 11 and the vertical wall section 21.

[0015] While the vehicle is in motion, a load is applied to the bush 50 from the vehicle body, as shown by the white arrow in Figure 5. At this time, tensile stress is generated near the curved portion 23 of the bush press-fit portion 20. If such tensile stress is repeatedly applied, the curved portion 23 and its vicinity may suffer fatigue failure.

[0016] [Embodiment] As an example, the suspension arm 1 according to an embodiment of the present invention, as shown in Figures 1 and 2, comprises an arm body 10 and a bush press-fit portion 20, similar to the conventional suspension arm 3 described above, and further includes a ring-shaped member 30. The ring-shaped member 30 is fitted onto the outside of the cylindrical vertical wall portion 21, and its lower end 30c is integrated with the top plate portion 11 by welding.

[0017] Thus, since the lower end 30c of the ring-shaped member 30 of the suspension arm 1 is integrated with the top plate portion 11, the rigidity of the curved portion 23 can be increased. Therefore, with the suspension arm 1, when a load perpendicular to the axial direction of the bush press-fit portion 20 is applied to the bush during vehicle operation, the stress generated in the curved portion 23 of the bush press-fit portion 20 and its vicinity can be reduced, thereby extending the fatigue life of the bush press-fit portion 20 and its vicinity.

[0018] Furthermore, since the ring-shaped member 30 does not have a tail portion extending from the bush press-fit portion 20 toward the arm body 10, as described in Patent Document 1 above, a significant increase in weight can be suppressed. Furthermore, since the suspension arm 1 has a ring-shaped member 30 fitted onto the outside of the cylindrical vertical wall portion 21, the ring-shaped member 30 can be easily positioned coaxially with the bush press-fit portion 20, allowing for easy manufacturing at a reduced cost.

[0019] In this embodiment, as shown in Figure 1, the upper end 30b of the ring-shaped member 30 was at the same height as the upper end 21a of the vertical wall portion 21. However, the upper end 30b may be at a lower position than the upper end 21a of the vertical wall portion 21. Preferably, the upper end 30b of the ring-shaped member 30 is at least at a height lower than the upper end 21a of the vertical wall portion 21 by the thickness of the bush press-fit portion 20. The reason for this will be explained in the embodiments described later.

[0020] Furthermore, the ring-shaped member 30 is not limited to one in which the entire circumference of the lower end 30c is welded to the top plate portion 11; it is sufficient if at least a portion of the lower end 30c is integrated. In this case, the portion of the lower end 30c that is integrated should be near the area in the curved portion 23 of the bush press-fit portion 20 where stress becomes high when a load is applied to the bush.

[0021] In the above description, the lower end 30c of the ring-shaped member 30 was integrated with the top plate portion 11, but it is sufficient if it is integrated with at least one of the curved portion 23 or the top plate portion 11. Furthermore, the integration of the lower end 30c of the ring-shaped member 30 with the curved portion 23 or the top plate portion 11 is not limited to welding, but may also be achieved by brazing, adhesive, or diffusion bonding.

[0022] To integrate the lower end 30c of the ring-shaped member 30 with the top plate portion 11, a fillet may be provided in the portion connecting the lower end 30c to the top plate portion 11. This helps to alleviate the tensile stress generated in the curved portion 23 of the bush press-fit portion 20.

[0023] Furthermore, as shown in Figure 1, it is preferable that the outer surface 30a of the ring-shaped member 30 is located outside the boundary 25 between the curved portion 23 and the top plate portion 11. The further the outer surface 30a of the ring-shaped member 30 is located outside, the longer the circumferential length of the bush press-fit portion 20 that resists the input of load to the bush (the arc length of the circumference traced by the outer surface of the ring-shaped member 30). This reduces the tensile stress in and near the curved portion 23, which is a cause of fatigue failure.

[0024] Generally, the surface of the suspension arm 1 is coated with a film such as cationic paint. However, if the film is damaged while the vehicle is in motion, the material of the ring-shaped member 30 and the material of the bush press-fit portion 20 will come into direct contact. If the ring-shaped member 30 and the bush press-fit portion 20 are made of different materials, direct contact may cause electrolytic corrosion. Therefore, it is desirable that the ring-shaped member 30 be made of the same material as the bush press-fit portion 20. For example, if the bush press-fit portion 20 is made of steel, it is desirable that the ring-shaped member 30 is also made of steel.

[0025] Furthermore, when fitting the ring-shaped member 30 onto the outside of the vertical wall portion 21 of the bush press-fit portion 20, commonly used methods such as press-fitting or shrink-fitting can be applied. Alternatively, threads may be cut on the outside of the vertical wall portion 21 and the inside of the ring-shaped member 30, and the ring-shaped member 30 may be screwed into the vertical wall portion 21. In addition, the inside of the ring-shaped member 30 may have a tapered shape in the axial direction. [Examples]

[0026] We have conducted a CAE analysis to verify the effects of the present invention, and will describe it below. The CAE analysis focused on a suspension arm equipped with a bush press-fit section formed by burring. The analysis determined the process of press-fitting the bush into the bush press-fit section and the stress generated when a load is applied to the bush.

[0027] Figure 6 shows a CAE analysis model 101 for the conventional suspension arm 3 shown in Figure 3 (conventional example). The CAE analysis model 101 comprises a top plate portion 111 and a bush press-fit portion 120 composed of a cylindrical vertical wall portion 121 and a curved portion 123. Hot-rolled steel sheet with a thickness of 2.0 mm and a pressure of 590 MPa is assumed to be the material for the top plate portion 111 and the bush press-fit portion 120.

[0028] In the CAE analysis model 101, the inner radius of the cylindrical vertical wall portion 121 was set to R25mm, the outer radius to R27mm, and the height from the top surface of the top plate portion 111 to the top end of the vertical wall portion 121 was set to 8mm. The radius of curvature on the inside of the curved portion 23 was set to 1mm, and the radius of curvature on the outside of the curved portion was set to 3mm. The outer radius of the top plate portion 111 was set to R58mm, and the width of the top plate portion 111 (the distance from the boundary 125 between the curved portion 123 and the top plate portion 111 to the outer end of the top plate portion 111) was set to 30mm. The top plate portion 11 and the bush press-fit portion 120 were element-divided using solid elements with a thickness of 0.4mm divided into 5 sections in the thickness direction.

[0029] Figure 7 shows a CAE analysis model 103 for the suspension arm 1 (see Figure 1) according to the present invention (Example 1 of the invention). The CAE analysis model 103 comprises a top plate portion 111, a bush press-fit portion 120 consisting of a cylindrical vertical wall portion 121 and a curved portion 123, and a ring-shaped member 130 fitted to the outside of the vertical wall portion 121. Hot-rolled steel sheet with a thickness of 2.0 mm and a pressure of 590 MPa was assumed as the material for the top plate portion 111, the bush press-fit portion 120, and the ring-shaped member 130.

[0030] In the CAE analysis model 103, the dimensions of the top plate portion 111 and the bush press-fit portion 120 (vertical wall portion 121 and curved portion 123) were the same as those of the CAE analysis model 101 in the conventional example. The ring-shaped member 130 has an inner radius of R27 mm and an outer radius of R29 mm. Its inner surface is formed to follow the vertical wall portion 121 and the curved portion 123, and its outer surface 130a is located outside the boundary 125 between the curved portion 123 and the top plate portion 111. Furthermore, the upper end 130b of the ring-shaped member 130 was made to the same height as the upper end 121a of the vertical wall portion 121, and the lower end 130c was integrated with the top plate portion 111. In addition, the ring-shaped member 130 was divided into five solid elements with a thickness of 0.4 mm in the thickness direction.

[0031] Figure 8 shows a CAE analysis model 105 in which the upper end 121a of the vertical wall portion 121 is positioned lower than the upper end 130b of the ring-shaped member 130. The CAE analysis model 105 comprises a top plate portion 111, a bush press-fit portion 120, and a ring-shaped member 130. The materials for the top plate portion 111, the bush press-fit portion 120, and the ring-shaped member 30 are assumed to be hot-rolled steel sheets with a thickness of 2.0 mm and a pressure of 590 MPa.

[0032] In the CAE analysis model 105, the dimensions of the top plate portion 111 and the bush press-fit portion 120 (vertical wall portion 121 and curved portion 123) were the same as those of the CAE analysis model 103 of Invention Example 1. Also, the distance between the upper end 130b of the ring-shaped member 130 and the upper end 121a of the vertical wall portion 121 was set to X (mm), and the other dimensions and shape were the same as those of the ring-shaped member 130 of Invention Example 1. Then, in CAE analysis model 105, the version with X set to 1.5 mm was designated as Invention Example 2, and the version with X set to 3.0 mm was designated as Invention Example 3.

[0033] Figure 9 shows CAE analysis model 107 used as a comparative example in the present invention (comparative example). The CAE analysis model 107 comprises a top plate portion 111 and a bush press-fit portion 120, and a ring-shaped member 140 fitted to the outside of the vertical wall portion 121 of the bush press-fit portion 120. The ring-shaped member 140 has its upper end 140b at the same position as the upper end 121a of the vertical wall portion 121, but its height is 7 mm, and there is a 1 mm gap between its lower end 140c and the top plate portion 111. The ring-shaped member 140 was also divided into elements using solid elements with a thickness of 0.4 mm, divided into five sections in the thickness direction of the plate.

[0034] Figure 10 shows a bush 150 that is pressed into the bush press-fitting section 120 of the CAE analysis model 101, etc. The bush 150 has a height of 50 mm, a radius of R25 mm at the top surface 150a, and a radius of R25.5 mm at the bottom surface 150b, with a taper so that the radius changes linearly from the top surface 150a to the bottom surface 150b. The bush 150 is assumed to be a rigid body and was modeled using shell elements.

[0035] In the examples, CAE analysis was performed using the following procedure. First, a CAE analysis was performed on the process of pressing the bush 150 into the bush press-fitting section 120 of each CAE analysis model (CAE analysis model 101, etc.). In this CAE analysis, with the top plate portion 111 restrained by a holder (not shown), the bush 150 was pressed in until the distance from the upper surface 150a of the bush 150 to the upper surface of the top plate portion 111 was 35 mm. Figure 11 shows, as an example, the state in which the bush 150 has been pressed into the bush press-fitting section 120 of the CAE analysis model 101 according to a conventional example.

[0036] Next, load input points were set at the center of the upper surface 150a and the center of the lower surface 150b of the bush 150, and the surface of the circumferential end of the bush press-fit section 120 into which the bush 150 was press-fitted was constrained so that it could not move in any of the X, Y, or Z axis directions. Then, as shown in Figure 11, a load of 150 kgf was applied in the -X axis direction to the load input point on the upper surface 150a of the bush 150, and a load of 150 kgf was applied in the +X axis direction to the load input point on the lower surface 150b, and the stress generated in the CAE analysis model 101, etc., was determined.

[0037] Figure 12 is a contour plot showing the distribution of the first principal stress in the CAE analysis model 101 for a conventional example in which the above loads were applied to the upper surface 150a and lower surface 150b of the bush 150. In Figure 12, the gray tones shown in the CAE analysis model 101 represent the magnitude of the first principal stress, with darker gray tones indicating a larger value for the first principal stress.

[0038] As shown in Figure 12, the first principal stress was maximum at the point in the curved portion 123 of the bush press-fit portion 120 where it intersects with the direction axis (X-axis) through which the load is applied to the bush 150 (indicated by the white arrow in the figure). Furthermore, although Figure 12 shows the results obtained for the CAE analysis model 101 relating to the conventional example, the first principal stress was also maximum at a similar point in the curved portion 123 in Invention Examples 1 to 3 and the Comparative Example.

[0039] Table 1 shows the maximum values ​​of the first principal stress obtained by CAE analysis for the conventional example, Invention Examples 1 to 3, and comparative example. [Table 1]

[0040] In the conventional example, the maximum value of the first principal stress was 419 MPa, but in Invention Example 1, it was 368 MPa, showing a 12% decrease. Furthermore, the maximum values ​​of the first principal stress in Invention Example 2 and Invention Example 3 were 370 MPa and 405 MPa, respectively, both of which were lower than in the conventional example. Furthermore, in the comparative example, the maximum value of the first principal stress was 549 MPa, which was 45% higher than that of Invention Example 1. This is because, as shown in Figure 9, in the comparative example, there is a gap between the ring-shaped member 140 and the top plate portion 111 and the curved portion 123, which causes stress concentration near the curved portion 123. These results indicate that the ring-shaped member 130 should be integrated with the top plate portion 111 by welding or other means, without leaving any gap between the lower end 130c and the top plate portion 111.

[0041] Figure 13 is a graph comparing the results of Invention Examples 1 to 3, with the distance X between the upper end 121a of the vertical wall portion 121 of the bush press-fit portion 120 and the upper end 130b of the ring-shaped member 130 on the horizontal axis and the maximum value of the first principal stress on the vertical axis. In Figure 13, the plot at X = 0.0 mm represents the result of Invention Example 1. As shown in Figure 13, the smaller the distance between the upper end 121a of the vertical wall portion 121 and the upper end 130b of the ring-shaped member 130, the smaller the maximum value of the first principal stress. However, when the distance X becomes smaller than the plate thickness (2 mm) of the bush press-fit portion 120, the effect of reducing the maximum value of the first principal stress remains almost unchanged. From this, it can be considered that if the upper end 130b of the ring-shaped member 130 is positioned higher than the upper end 121a of the vertical wall portion 121 by the thickness of the plate, a sufficient reduction in the maximum value of the first principal stress in the curved portion 123 of the bush press-fit portion 120 can be obtained.

[0042] The reason for the difference in the maximum value of the first principal stress between Invention Example 1 and Invention Example 3 is thought to be as follows. Figures 14 and 15 show the point of force application, fulcrum, and point of load application when the load shown in Figure 11 is applied to the bush in the CAE analysis model 103 according to Invention Example 1 and the CAE analysis model 105 according to Invention Example 3, respectively.

[0043] In Invention Example 1, as shown in Figure 14, when a load is applied to the point of force application on the upper surface 150a of the bush 150, the upper end 121a of the vertical wall portion 121 becomes the fulcrum, and the area near the curved portion 123 becomes the point of application.

[0044] In contrast, in Invention Example 3, as shown in Figure 15, the portion without the ring-shaped member is more easily deformed than the portion with the ring-shaped member, so there is a fulcrum between the upper end 121a of the vertical wall portion 121 and the upper end 130b of the ring-shaped member 130. Therefore, the distance in the Z direction between the point of force application and the fulcrum in Invention Example 3 is longer than in Invention Example 1, and the magnitude of the moment supported by the point of application is larger in Invention Example 3 by the difference in moment arms. As a result, it is thought that the maximum value of the first principal stress in Invention Example 3 is larger than that of Invention Example 1.

[0045] In summary, the present invention demonstrates that, in a suspension arm equipped with a bush press-fit portion formed by burring, the stress generated in the curved portion of the bush press-fit portion can be reduced. This result suggests that the fatigue life of the bush press-fit portion and its vicinity can be improved. [Explanation of Symbols]

[0046] 1. Suspension arm (invention) 3. Suspension arm (conventional technology) 10 Arm body 11 Top panel 20 Bush press-fit section 20 Ring-shaped member 20 Curved section 20a top end 21 Vertical wall section 21a top end 23 Curved section 25 Boundary 30 Ring-shaped member 30a outer surface 30b top end 30c bottom end 40 Ring-shaped member 40b top end 40c bottom end 50 Bush 50a top end 50b bottom end 101 CAE Analysis Model (Conventional Example) 103 CAE Analysis Model (Example 1 of Invention) 105 CAE Analysis Models (Examples 2 and 3) 107 CAE Analysis Model (Comparative Example) 111 Top panel 120 Bush press-fit section 121 Vertical wall section 121a top end 123 Curved section 125 Boundary 130 Ring-shaped member 130a outer surface 130b top end 130c bottom end 140 Ring-shaped member 140b top end 140c bottom end 150 bush 150a top 150b Bottom side

Claims

1. A suspension arm comprising an arm body, a cylindrical vertical wall portion and a curved portion formed by burring the top plate portion of the arm body, and a bush press-fit portion into which a bush is press-fitted, A suspension arm characterized by having a ring-shaped member that is fitted onto the outside of the cylindrical vertical wall portion and whose lower end is integrated with at least one of the curved portion or the top plate portion.

2. The suspension arm according to claim 1, characterized in that the lower end of the ring-shaped member is welded to at least one of the curved portion or the top plate portion.

3. The suspension arm according to claim 1 or 2, characterized in that the outer surface of the ring-shaped member is located outside the boundary between the curved portion and the top plate portion.

4. The suspension arm according to claim 1 or 2, characterized in that the ring-shaped member is made of the same material as the bush press-fit portion.

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