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 allowing for easy manufacturing at a reduced cost. [Solution] The suspension arm 1 according to the present invention comprises an arm body 10 and a ring-shaped member 30 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 bush press-fit portion 20 into which a bush is press-fitted inside the cylindrical vertical wall portion 21, and a cylindrical wall portion 31 fitted inside the cylindrical vertical wall portion 21 and an outward-facing flange portion 33 extending from the lower end of the cylindrical wall portion 31 toward the top plate portion 11, wherein the outer peripheral end 33b of the outward-facing flange portion 33 is located at or outside the boundary 25 between the curved portion 23 and the top plate portion 11 and is in contact with the top plate portion 11.

Description

Technical Field

[0001] The present invention relates to a suspension arm which is an undercarriage component of an automobile and includes a bush press-fit portion into which a bush is press-fitted.

Background Art

[0002] In recent years, for the purpose of reducing the weight of automobiles, the thickness of frame components and undercarriage components of automobiles has been reduced through the use of high-tensile steel sheets. When the thickness of a suspension arm, which is an undercarriage component, is reduced, the rigidity of the bush press-fit portion of the suspension arm decreases. Therefore, when a load in a direction perpendicular to the axial direction of the bush is input to the bush while the automobile is running, the stress generated in the vicinity of the curved portion of the bush press-fit portion increases, which causes a problem that the curved portion of the bush press-fit portion and the vicinity thereof are prone to fatigue fracture.

[0003] As a technique applicable to this problem, for example, Patent Document 1 discloses a technique for attaching a reinforcing plate having a circular head portion and a tail portion in a suspension arm including an arm body and a bush press-fit portion formed by burring. In this technique, the reinforcing plate is disposed such that the circular head portion is coaxial with the short cylindrical portion of the bush press-fit portion, and at least the tail portion is welded to the arm body of the suspension arm. It is stated that this makes it possible to sufficiently secure the cross-sectional shape of the transition portion from the bush press-fit portion of the suspension arm to the arm body, and easily ensure the required rigidity and strength of the transition portion.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem 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, a cylindrical vertical wall portion formed by burring the top plate portion of the arm body, and a bush press-fit portion having a curved portion between the vertical wall portion and the top plate portion, in which a bush is press-fitted into the inside of the cylindrical vertical wall portion, The ring-shaped member comprises a cylindrical wall portion that is fitted inside the cylindrical vertical wall portion, and an outward-facing flange portion that extends from the lower end of the cylindrical wall portion toward the top plate portion, The outward-facing flange portion is characterized in that its outer peripheral end is located at or outside the boundary between the curved portion and the top plate portion and is in contact with the top plate portion.

[0008] (2) The suspension arm according to the present invention comprises an arm body, 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, and a bush press-fitted into the bush press-fitting portion, The bush comprises a bush body and a ring-shaped member attached to the outer circumferential surface of the bush body. The ring-shaped member has a cylindrical wall portion that fits inside the cylindrical vertical wall portion, and an outward-facing flange portion that extends from the lower end of the cylindrical wall portion toward the top plate portion, The outward-facing flange portion is characterized in that its outer peripheral end is located at or outside the boundary between the curved portion and the top plate portion and is in contact with the top plate portion.

[0009] (3) In the case of the items described in (1) or (2) above, The outward-facing flange portion is characterized in that its outer peripheral end is welded or brazed to the top plate portion and integrated with it.

[0010] (4) In any of the items described in (1) to (3) above, The cylindrical wall portion is characterized in that its upper end is located at a height greater than or equal to the upper end of the vertical wall portion.

[0011] (5) In any of the items described in (1) through (4) above, The ring-shaped member is characterized by being made of the same material as the bush press-fit portion. [Effects of the Invention]

[0012] 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, the bush press-fit section can be reinforced while suppressing a significant increase in weight, and it can be manufactured easily while keeping manufacturing costs down. [Brief explanation of the drawing]

[0013] [Figure 1] This figure illustrates the bush press-fit portion and the ring-shaped member in a suspension arm according to Embodiment 1 of the present invention ((a) top view, (b) cross-sectional view along A-A'). [Figure 2] This is a top view showing the entire suspension arm according to Embodiment 1 of the present invention. [Figure 3] This is a top view showing the configuration of a conventional suspension arm. [Figure 4]It is a cross-sectional view illustrating the bush press-fitting portion in a conventional suspension arm. [Figure 5] It is a diagram illustrating a load applied to a bush press-fitted into a bush press-fitting portion in a conventional suspension arm. [Figure 6] It is a diagram showing a CAE analysis model obtained by modeling the bush press-fitting portion and top plate portion of a conventional suspension arm in an example ((a) top view, (b) C-C' cross-sectional view). [Figure 7] It is a diagram showing a bush to be press-fitted into the bush press-fitting portion of a CAE analysis model in an example ((a) top view, (b) side view). [Figure 8] It is a diagram illustrating a CAE analysis model in which a bush is press-fitted into a bush press-fitting portion, and load conditions applied to the bush in the CAE analysis model, in an example. [Figure 9] It is a contour diagram showing the distribution of a first principal stress when a load is applied to a bush press-fitted into the bush press-fitting portion of a CAE analysis model according to a conventional example in an example. [Figure 10] It is a diagram showing a CAE analysis model obtained by modeling a suspension arm in which a ring-shaped member is fitted inside a bush press-fitting portion in an example. [Figure 11] It is a diagram illustrating a CAE analysis model in which the upper end of the cylindrical wall portion of the ring-shaped member is positioned lower than the upper end of the vertical wall portion of the bush press-fitting portion in an example. [Figure 12] It is a graph showing the relationship between the width a of the outward flange portion in the CAE analysis models according to the invention example and comparative example, and the maximum value of the first principal stress generated at the curved portion of the bush press-fitting portion, in an example. [Figure 13] It is a graph showing the relationship between the distance b between the upper end of the cylindrical wall portion and the upper end of the vertical wall portion of the bush press-fitting portion in the CAE analysis model according to the invention example, and the maximum value of the first principal stress generated at the curved portion of the bush press-fitting portion, in an example. [Figure 14]In an embodiment, this is a diagram showing an analysis result when the upper end of the cylindrical wall portion in the CAE analysis model is too far below the upper end of the vertical wall portion of the bush press-fit portion, and the ring-shaped member comes off from the bush press-fit portion. [Figure 15] It is a diagram illustrating the configuration of a conventional bush. [Figure 16] It is a diagram illustrating the suspension arm according to the second embodiment of the present invention ((a) top view, (b) B-B' cross-sectional view). [Figure 17] It is a diagram showing the configuration of a bush in the suspension arm according to the second embodiment of the present invention. [Figure 18] It is a diagram showing another aspect of a bush in the suspension arm according to the second embodiment of the present invention. Mode for Carrying Out the Invention

[0014] [Conventional Suspension Arm] Before describing the suspension arms according to the first and second embodiments of the present invention, the structure of a conventional suspension arm will be described. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant descriptions are omitted or simplified. Further, in the present application, terms such as "upper end", "lower end", "upper surface" and "lower surface" represent the positions of respective parts based on the state where the suspension arm is installed in an actual vehicle. Furthermore, the X-axis direction and Y-axis direction shown in the drawings of the present application are two orthogonal directions on a plane when the suspension arm is viewed from above, and the Z-axis direction indicates the axial direction of the bush press-fit portion. However, these terms relating to positions and directions do not limit the arrangement, orientation, etc. of the suspension arm according to the present invention.

[0015] FIG. 3 shows, as an example, a conventional suspension arm 3 including an arm main body 10 and a bush press-fit portion 20. The arm main body 10 is processed by press molding of a metal plate (such as a steel plate), and has a top plate portion 11.

[0016] As shown in Figure 4, which is a cross-sectional view taken along the line B-B' in Figure 3, the bush press-fit portion 20 has a cylindrical vertical wall portion 21 formed by burring the top plate portion 11 of the arm body 10, and a curved portion 23 between the vertical wall portion 21 and the top plate portion 11. 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.

[0017] 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.

[0018] [Embodiment 1] As an example, the suspension arm 1 according to Embodiment 1 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 comprises a ring-shaped member 30.

[0019] The ring-shaped member 30 has a cylindrical wall portion 31 that is fitted inside the cylindrical vertical wall portion 21, and an outward-facing flange portion 33 that extends from the lower end of the cylindrical wall portion 31 toward the top plate portion 11. The outward-facing flange portion 33 has its outer peripheral end 33b located outside the boundary 25 between the curved portion 23 and the top plate portion 11 (the end of the curved portion 23 on the top plate portion 11 side), and is in contact with the top plate portion 11.

[0020] Thus, in the suspension arm 1, the cylindrical wall portion 31 of the ring-shaped member 30 is fitted inside the vertical wall portion 21 of the bush press-fit portion 20, so the bush 50 (see Figure 5) is press-fitted inside the cylindrical wall portion 31 of the ring-shaped member 30.

[0021] Furthermore, since the outer peripheral end 33b of the outward-facing flange portion 33 of the ring-shaped member 30 of the suspension arm 1 is in contact with the top plate portion 11, it can resist the load applied to the bush when the vehicle is in motion. In addition, since the outer peripheral end 33b of the outward-facing flange portion 33 is located outside (towards the top plate portion 11) of the boundary 25 of the bush press-fit portion 20, the circumferential length of the wire (arc length of the outer peripheral end 33b) that resists the load applied to the bush is longer compared to the conventional suspension arm 3. As a result, in the suspension arm 1, the tensile stress generated in the curved portion 23 of the bush press-fit portion 20 and its vicinity during vehicle operation can be reduced, and the fatigue life of the bush press-fit portion 20 and its vicinity can be extended.

[0022] Furthermore, since the ring-shaped member 30 does not have a tail portion that extends 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 inside 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.

[0023] In the ring-shaped member 30 shown in Figure 1, the portion from the boundary 25 on the upper surface 33a of the outward-facing flange portion 33 to the outer peripheral end 33b is in contact with the lower surface 11a of the top plate portion 11. However, in the present invention, it is sufficient that at least the outer peripheral end 33b of the outward-facing flange portion 33 is in contact with the lower surface 11a.

[0024] The outer peripheral end 33b of the outward-facing flange portion 33 is not particularly restricted in terms of position, as long as it is on the side of the top plate portion 11 (outside) of the boundary 25 between the curved portion 23 and the top plate portion 11. However, it is preferable that the further outward the outer peripheral end 33b is, the longer the circumferential wire length that resists the load applied to the bush becomes, further reducing the tensile stress that could lead to fatigue failure.

[0025] Furthermore, although the ring-shaped member 30 had an outer peripheral end 33b of the outward-facing flange portion 33 in contact with the lower surface 11a of the top plate portion 11, it is preferable that the outer peripheral end 33b be integrated with the top plate portion 11 by welding, brazing, or adhesive. This ensures reliable resistance to the load applied to the bush and further reduces the tensile stress generated in the curved portion 23 of the bush press-fit portion 20 and its vicinity.

[0026] The area where the outer peripheral end 33b of the outward-facing flange portion 33 is welded, brazed, or bonded to the top plate portion 11 does not need to be the entire circumference of the outer peripheral end 33b if the direction of the load applied to the bush is known in advance. It may be limited to the curved portion 23 of the bush press-fit portion 20 and the area in its vicinity where stress is high.

[0027] As shown in Figure 1(b), it is preferable that the upper end 31a of the cylindrical wall portion 31 of the ring-shaped member 30 is located at a height equal to or greater than the upper end 21a of the vertical wall portion 21. This is because if the upper end 31a of the cylindrical wall portion 31 is lower than the upper end 21a of the vertical wall portion 21, the tensile stress may be higher compared to the case where they are at the same height.

[0028] Furthermore, if the upper end 31a of the cylindrical wall portion 31 is too low, the ring-shaped member 30 may come off the bush press-fit portion 20 when a load is applied to the bush. For this reason, it is desirable that the position of the upper end 31a of the cylindrical wall portion 31 be at least the thickness of the bush press-fit portion 20 above the boundary 27 between the curved portion 23 and the vertical wall portion 21 of the bush press-fit portion 20 (the end of the R curve on the vertical wall portion 21 side of the curved portion 23, see Figure 1(b)). The case where the upper end 31a of the cylindrical wall portion 31 is located below the upper end 21a of the vertical wall portion 21 will be explained again in the embodiment described later.

[0029] Furthermore, generally, a coating is formed on the surface of the suspension arm 1 by cationic coating or the like. However, if the coating 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.

[0030] When fitting the ring-shaped member 30 into the inner side 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 inner side of the vertical wall portion 21 and on the outer side of the cylindrical wall portion 31 of the ring-shaped member 30, and the cylindrical wall portion 31 may be screwed into the vertical wall portion 21. Furthermore, the outer side of the cylindrical wall portion 31 may have a tapered shape in the axial direction (the z-axis direction in Figure 1(b)).

[0031] In the above description, as shown in Figure 1(b), the ring-shaped member 30 has an outward-facing flange portion 33 that protrudes outward (towards the top plate portion 11) from the lower end of the cylindrical wall portion 31, and the cross-section of one side of the ring-shaped member 30 is approximately L-shaped. However, even if the lower end of the cylindrical wall portion of the ring-shaped member protrudes below the outward-facing flange portion and the cross-section of one side is approximately T-shaped, this does not impair the effects of the present invention.

[0032] [Embodiment 2] The suspension arm 1 according to Embodiment 1 (Figure 1) required a step during assembly in which a ring-shaped member 30 was fitted into the bush press-fit portion 20.

[0033] Conventional bushings 50, as shown in Figure 15, have a metal core 51a surrounded by an elastic body 51b made of hard rubber or the like, and the outer surface of the elastic body 51b is covered with a metal sheath 51c. Therefore, if a bushing 50 with a ring-shaped member 30 pre-attached to its outer surface (sheath 51c) is used, the suspension arm 1 can be easily assembled without the need for the step of fitting the ring-shaped member 30 into the bushing press-fit portion 20.

[0034] Based on the above, the suspension arm 5 according to Embodiment 2 of the present invention comprises, as shown in Figure 16, an arm body 10, a bush press-fitting portion 20 formed by burring the top plate portion 11 of the arm body 10, and a bush 60 press-fitted into the bush press-fitting portion 20.

[0035] The bush press-fit portion 20, similar to Embodiment 1, has a cylindrical vertical wall portion 21 and a curved portion 23 that connects the vertical wall portion 21 and the top plate portion 11. As shown in Figure 16, the bush 60 comprises a bush body 61 and a ring-shaped member 63 attached to the outer circumferential surface of the bush body 61.

[0036] The bush body 61, like the bush 50 shown in Figure 15, has a metal core 51a, an elastic body 51b provided around the core 51a, and a metal sheath 51c covering the outer surface of the elastic body 51b, as shown in Figure 17.

[0037] The ring-shaped member 63 is the same as the ring-shaped member 30 according to Embodiment 1, and has a cylindrical wall portion 63a that is fitted inside the cylindrical vertical wall portion 21, and an outward-facing flange portion 653 that extends from the lower end of the cylindrical wall portion 63a toward the top plate portion 11. The outward-facing flange portion 63b has its outer peripheral end 63c located at or outside the boundary 25 between the curved portion 23 and the top plate portion 11, and is in contact with the top plate portion 11.

[0038] Thus, in the suspension arm 5, similar to the suspension arm 1 according to Embodiment 1, the tensile stress generated in the curved portion 23 of the bush press-fit portion 20 and its vicinity during vehicle operation can be reduced, thereby extending the fatigue life of the bush press-fit portion 20 and its vicinity. Furthermore, if the bush 60, which has a ring-shaped member 63 attached to the bush body 61, is manufactured in advance in a separate process, the suspension arm 5 can be easily assembled without the need for the process of press-fitting the ring-shaped member 30 into the bush press-fitting portion 20, as described above for the suspension arm 1 in Embodiment 1.

[0039] There are no particular limitations on the method of attaching the ring-shaped member 63 to the outer circumferential surface of the bush body 61, but for example, it may be attached by filling the inside of the cylindrical wall portion 63a of the ring-shaped member 63 with the bush body 61.

[0040] The outward-facing flange portion 63b of the ring-shaped member 63 is preferably integrated with the top plate portion 11 of the arm body 10 by welding or brazing its outer peripheral end, similar to the ring-shaped member 30 in Embodiment 1. Furthermore, it is preferable that the material of the ring-shaped member 63 and the height of the upper end of the cylindrical wall portion 63a are the same as those of the ring-shaped member 30 in Embodiment 1.

[0041] In the above description, the bush 60 had a bush body 61 in which the outer circumferential surface of an elastic body 61a was covered with a sheath portion 61c. However, in another embodiment of the suspension arm 5 according to Embodiment 2, instead of the sheath portion 51c, the bush 60A may have a bush body 61A in which the outer circumferential surface of a bush body 61A consisting of a core portion 51a and an elastic body 51b is covered with a ring-shaped member 53, as shown in Figure 18.

[0042] In this case, the bush 60A can be assembled by filling the inside of the cylindrical wall portion 63a of the ring-shaped member 63 with the elastic body 51b, thus eliminating the need to cover the outer surface of the elastic body 61b with the sheath portion 51c by filling or the like, as shown in the bush 60 in Figure 17.

[0043] Furthermore, the cylindrical wall portion 63Aa of the ring-shaped member 63A shown in Figure 18 was positioned so that its upper end was at the same height as the upper end of the bush body 61A. However, in the present invention, the upper end of the cylindrical wall portion 61A1 may be positioned below the upper end of the bush body 61A, as long as it is at a height equal to or greater than the upper end of the vertical wall portion 21 (Figure 16) of the bush press-fit portion 20.

[0044] Furthermore, the outward-facing flange portion 63Ab of the ring-shaped member 63A protrudes outward from the lower end of the cylindrical wall portion 31, and the cross-section of one side of the ring-shaped member 63 is approximately L-shaped. However, the ring-shaped member may also have a lower end of the cylindrical wall portion protruding below the outward-facing flange portion, resulting in a cross-section of approximately T-shape on one side, or the lower end of the cylindrical wall portion may be located at a height higher than the lower end of the bush body. [Examples]

[0045] 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 on the top plate of the arm body by burring. The analysis investigated the process of press-fitting the bush into the bush press-fit section and the stresses generated in and around the bush press-fit section when a load is applied to the bush.

[0046] Figure 6 shows a CAE analysis model 103 for the conventional suspension arm 3 shown in Figure 3 (conventional example). The CAE analysis model 103 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 was assumed as the material for the top plate portion 111 and the bush press-fit portion 120.

[0047] In the CAE analysis model 103, 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 upper end 121a 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 (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.

[0048] Figure 7 shows the bush 150 to be pressed into the bush press-fit section 120 of the CAE analysis model 103. The bush 150 has a height of 50 mm, a radius of R25 mm at a position 5 mm below the upper surface 150a, and a radius of R25.5 mm at the lower surface 150b. It is tapered so that the radius changes linearly from the upper surface 150a to the lower surface 150b. The bush 150 is a rigid body and was modeled using shell elements.

[0049] In the embodiment, first, a CAE analysis was performed on the process of pressing the bush 150 into the bush press-fitting section 120 of the CAE analysis model 103. 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 8 shows the state in which the bush 150 is pressed into the bush press-fitting section 120 of the CAE analysis model 103.

[0050] 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, respectively, and the surface of the peripheral edge of the top plate portion 111 was constrained so that it could not move in the X-axis, Y-axis, or Z-axis direction. Then, as shown in Figure 8, 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 103 was determined.

[0051] Figure 9 is a contour map showing the distribution of the first principal stress in CAE analysis model 103 for a conventional example under the load conditions shown in Figure 8. In Figure 9, the gray tones shown in CAE analysis model 103 represent the magnitude of the first principal stress, with darker gray tones indicating a larger value for the first principal stress.

[0052] As shown in Figure 9, 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).

[0053] Next, CAE analysis was performed on the suspension arm 1 according to the present invention. Figure 10 shows a CAE analysis model 101 for the suspension arm 1 (see Figure 1) according to the present invention. The CAE analysis model 101 comprises a top plate portion 111, a bush press-fitting portion 120 consisting of a cylindrical vertical wall portion 121 and a curved portion 123, and a ring-shaped member 130 fitted inside 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 and the bush press-fitting portion 120.

[0054] In the CAE analysis model 101, 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 (Figure 6) related to the conventional example. The ring-shaped member 130 has a cylindrical wall portion 131 and an outward-facing flange portion 133 that extends from the lower end of the cylindrical wall portion 131 toward the top plate portion 111. The outward-facing flange portion 133 has its outer peripheral end 133b of the upper surface 133a located on the side of the top plate portion 111 that is closer to the top plate portion 111 than the boundary 125 between the curved portion 123 and the top plate portion 111, and is in contact with the top plate portion 111.

[0055] In the CAE analysis model 101, the ring-shaped member 130 is treated as a rigid body, and the surface of the ring-shaped member 30 shown in Figure 1 (the outer surface of the cylindrical wall portion 31, the upper surface 33a of the outward-facing flange portion 33, the outer peripheral end 33b, and the side end face 33c) is modeled using shell elements. The side end face 133c is provided in the CAE analysis model 101 to prevent the calculation from stopping due to the outer peripheral end 133b of the outward-facing flange portion 133 coming into contact with the bush press-fit portion 120 during the CAE analysis.

[0056] In the CAE analysis model 101, the cylindrical wall portion 131 had an inner radius of R27 mm and an outer radius of R29 mm, and the width a of the outward flange portion 133 and the distance b between the upper end 131a of the cylindrical wall portion 131 and the upper end 121a of the vertical wall portion 121 were varied.

[0057] Regarding the width a, if it is 3 mm or more, the outer peripheral end 133b of the outward-facing flange portion 133 is located outside the boundary 125 and contacts the top plate portion 111, so it falls within the scope of the present invention (inventive example). In contrast, if it is less than 3 mm, the outer peripheral end 133b is not located outside the boundary 125 and does not contact the top plate portion 111, so it falls outside the scope of the present invention (comparative example).

[0058] With respect to distance b, if it is 0 mm or more, as shown in Figure 10, the upper end 131a of the cylindrical wall portion 131 is located at a height equal to or greater than the upper end 121a of the vertical wall portion 121, which falls within the preferred range of the present invention (example of invention). In contrast, when the distance b is less than 0 mm, as shown in Figure 11, the upper end 131a of the cylindrical wall portion 131 is located below the upper end 121a of the vertical wall portion 121. Therefore, although this is outside the preferred range of the present invention, it is within the scope of the present invention (example of invention).

[0059] In CAE analysis model 101, virtual load input points (not shown) were set at the same positions as the centers of the upper surface 150a and lower surface 150b of the bush 150 in the conventional CAE analysis model 103 shown in Figure 8. Then, with the surface of the peripheral edge of the top plate portion 111 constrained, a load was applied in the same manner as in CAE analysis model 103 in Figure 8, and the stress generated in CAE analysis model 101 due to the load applied to the ring-shaped member 130 in conjunction with the virtual load input points was determined.

[0060] In the CAE analysis model 101 relating to the inventive example and comparative example, the first principal stress was maximum in the curved portion 123, similar to the CAE analysis model 103 relating to the conventional example shown in Figure 9.

[0061] Figure 12 is a graph with the width a of the outward flange portion 133 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 12, the plot where a=0mm represents the maximum value of the first principal stress in the CAE analysis model 103 for a conventional example that does not use the ring-shaped member 30.

[0062] As shown in Figure 12, the maximum value of the first principal stress was as large as or larger than the conventional example where a=0mm when the width a was 2mm, but with the exception of this case, the maximum value of the first principal stress generally tended to decrease with increasing width a.

[0063] The reason the maximum value of the first principal stress increased when the width a was 2 mm is that the outer peripheral end 133b of the outward-facing flange portion 133 came into contact with the curved portion 123 of the bush press-fit portion 120. When the width a is 3 mm or more, the outer peripheral end 133b of the outward-facing flange portion 133 is located on the side of the top plate portion 111 that is greater than the boundary 125 between the curved portion 123 and the top plate portion 111, and contacts the top plate portion 111. As the width a increases, the length of the circumferential wires resisting the input load increases, so the maximum value of the first principal stress decreases monotonically.

[0064] Figure 13 is a graph in which the horizontal axis represents the distance b between the upper end 131a of the cylindrical wall portion 131 and the upper end 121a of the vertical wall portion 121, and the vertical axis represents the maximum value of the first principal stress.

[0065] When the distance b is a positive value (=2 mm), that is, when the upper end 131a of the cylindrical wall portion 131 is above the upper end 121a of the vertical wall portion 121, the maximum value of the first principal stress was approximately the same as when the distance b = 0 mm (the upper end 131a of the cylindrical wall portion 131 is at the same height as the upper end 121a of the vertical wall portion 121).

[0066] On the other hand, when the distance b is a negative value, that is, when the upper end 131a of the cylindrical wall portion 131 is lower than the upper end 121a of the vertical wall portion 121, the maximum value of the first principal stress increases as the absolute value of the distance b increases. However, the maximum value of the first principal stress was lower compared to the conventional example and comparative example shown in Figure 12.

[0067] Furthermore, when distance b was -6 mm, applying a load resulted in the ring-shaped member 130 detaching from the bush press-fit portion 120, as shown in Figure 14.

[0068] We investigated the range of distance b that is preferable to prevent the ring-shaped member 130 from coming off the bush press-fit portion 120. When distance b was -6 mm, the upper end 131a of the cylindrical wall portion 131 was 1 mm higher than the boundary 127 (the R-end on the vertical wall portion 121 side of the curved portion 123, see Figures 6(b) and 11). In contrast, when distance b was -4 mm, the upper end 131a of the cylindrical wall portion 131 was 3 mm higher than the boundary 127.

[0069] Here, as mentioned above, the plate thickness of the bush press-fit portion 120 was 2 mm. Therefore, when the distance b is -6 mm, the upper end 131a of the cylindrical wall portion 131 is located at a height less than the plate thickness than the boundary 127 between the vertical wall portion 121 and the curved portion 123, whereas when the distance b is -4 mm, the upper end 131a of the cylindrical wall portion 131 is located at a height greater than or equal to the plate thickness than the boundary 127.

[0070] Therefore, in order to prevent the ring-shaped member 130 from coming off the bush press-fit portion 120, it is preferable that the upper end 131a of the cylindrical wall portion 131 be at a height greater than or equal to the plate thickness of the boundary 127 between the vertical wall portion 121 and the curved portion 123 of the bush press-fit portion 120.

[0071] Furthermore, it was shown that it is more preferable to make the upper end 131a of the cylindrical wall portion 131 greater than or equal to the upper end 121a of the vertical wall portion 121 of the bush press-fit portion 120, as this can reduce the maximum value of the first principal stress.

[0072] In summary, the present invention demonstrates that the tensile stress generated in the curved portion of the bush press-fit section formed by burring and in its vicinity can be reduced, suggesting that the fatigue life of the bush press-fit section and its vicinity can be extended. [Explanation of Symbols]

[0073] 1. Suspension arm (Embodiment 1) 3. Suspension arm (conventional) 5. Suspension arm (Embodiment 2) 10 Arm body 11 Top panel 11a Bottom side 20 Bush press-fit section 21 Vertical wall section 21a top end 23 Curved section 25 Boundary 27 Boundary 30 Ring-shaped member 31 Cylinder wall 31a top end 33 Outward flange portion 33a Top side 33b Outer edge 33c Side end surface 50 Bush 51a Core 51b Elastic body 51c Sheath 60, 60A bushings 61, 61A Bushing Body 63, 63A Ring-shaped member 63a, 63Aa Cylinder wall 63b, 63Ab Outward-facing flange section 63c Outer edge 101 CAE Analysis Model (Example of Invention) 103 CAE Analysis Model (Conventional Example) 111 Top panel 120 Bush press-fit section 121 Vertical wall section 121a top end 123 Curved section 125 Boundary 127 Boundary 130 Ring-shaped member 131 Cylinder wall 131a top end 133 Outward flange section 133a Top side 133b Outer edge 133c Side end face 150 bush 150a top 150b Bottom side

Claims

1. A suspension arm comprising: an arm body; a cylindrical vertical wall portion formed by burring the top plate portion of the arm body; and a bush press-fit portion having a curved portion between the vertical wall portion and the top plate portion, into which a bush is press-fitted. The ring-shaped member comprises a cylindrical wall portion that is fitted inside the cylindrical vertical wall portion, and an outward-facing flange portion that extends from the lower end of the cylindrical wall portion toward the top plate portion, The suspension arm is characterized in that the outward-facing flange portion has its outer peripheral end located at or outside the boundary between the curved portion and the top plate portion, and is in contact with the top plate portion.

2. A suspension arm comprising an arm body, a bush press-fitting section having a cylindrical vertical wall and a curved section formed by burring the top plate portion of the arm body, and a bush press-fitted into the bush press-fitting section, The bush comprises a bush body and a ring-shaped member attached to the outer circumferential surface of the bush body. The ring-shaped member has a cylindrical wall portion that fits inside the cylindrical vertical wall portion, and an outward-facing flange portion that extends from the lower end of the cylindrical wall portion toward the top plate portion, The suspension arm is characterized in that the outward-facing flange portion has an outer peripheral end located at or outside the boundary between the curved portion and the top plate portion, and is in contact with the top plate portion.

3. The suspension arm according to claim 1 or 2, characterized in that the outward-facing flange portion is integrated with the top plate portion by welding or brazing its outer peripheral end.

4. The suspension arm according to claim 1 or 2, characterized in that the upper end of the cylindrical wall portion is located at a height greater than or equal to the upper end of the vertical wall portion.

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

6. The suspension arm according to claim 3, characterized in that the material of the ring-shaped member is the same as the material of the bush press-fit portion.

Images