Suspension arm

Abstract

Suspension arm (10) which receives input from a road surface via a connecting component, wherein the suspension arm (10) has a hollow structure and comprises: an upper element (40) with a top plate (42) and a pair of side plates (44) and a lower element (50) with a bottom plate (52) and a pair of side plates (54), wherein the side plates (44) of the upper element (40) are welded to the side plates (54) of the lower element (50) at the edges of at least either the side plates (44) of the upper element (40) or the side plates (54) of the lower element (50), wherein the pairs of side plates (44, 54) of the upper or the lower element (40, 50) have protruding sections (48, 55) with a curved edge (47), and a weld seam (60) extends along this curved edge (47), thereby characterized that the weld (60) on the side plate (44,54) is curved in a direction towards the lower plate (42) or towards the upper plate (52).

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to a suspension arm of a vehicle and in particular to a welded structure in a suspension arm according to the preamble of claim 1. 2. Description of the relevant state of the art

[0002] A suspension arm of a vehicle is usually a hollow suspension arm in which outer edge ends of an upper plate element and a lower plate element, each having a U-shaped cross-section, are joined together by welding (see, for example, JP H06-143 953 A or DE 102 60 571 A1, which forms the basis for the preamble of claim 1).

[0003] In recent years, weight reduction for the entire vehicle has been strongly demanded to improve fuel efficiency, reduce emissions, and enhance handling. One solution for weight reduction in a suspension arm is to construct the arm with thinner plate elements; however, a reduction in the fatigue strength of the base material resulting from thinning the arm should be avoided. Since stresses often concentrate around a weld end near a lower ball joint attached to the suspension arm, the fatigue strength of the base material around the weld end must be particularly ensured. SUMMARY OF THE INVENTION

[0004] The present invention was made in view of such a circumstance, and one objective of it is to provide, in a suspension arm or control arm in which an upper element and a lower element, each having a substantially U-shaped cross-section, are joined together by welding, a welded structure which increases the fatigue strength of the base material around the weld ends.

[0005] To solve the above problem, a suspension arm according to one embodiment of the present invention relates to a hollow suspension arm or control arm with the features listed in claim 1. Advantageous further developments are the subject of the dependent claims.

[0006] According to this embodiment, the weld is curved and terminates near the joining component, so that any stress induced in the base material around the weld end can be generated and dissipated in a bending or curvature direction. Since the base material has a permissible stress in a bending direction that is higher than that in a tensile (or compressive) direction, curving the weld, thus creating stress around the weld end in a bending or curvature direction, can increase the fatigue strength of the base material around the weld end.

[0007] A side plate of the upper or lower element may have a substantially straight edge and a curved edge, which is curved from one end of the substantially straight edge, and the weld may terminate within the curved edge. By providing the curved edge on a side plate and performing welding along the curved edge, the weld may be curved before it terminates.

[0008] The weld along the curved edge can be inclined at a predetermined angle or greater to a stress direction near the weld end. For example, the weld can be inclined at 45 degrees or greater to a stress direction near the weld end. Furthermore, the weld along the curved edge near the weld end can be substantially perpendicular to a stress direction. By increasing the angle between the weld and a stress direction near the weld end, the bending or curvature direction component of a stress induced in the base material around the weld end can be increased, thereby enhancing the fatigue strength of the base material.

[0009] The suspension arm according to the embodiment is supported by a vehicle body at a first connecting section and a second connecting section, and a direction in which a load is transferred from the connecting component to the first connecting section and the second connecting section is defined as a load axis line by means of a first virtual point corresponding to the connecting component, a second virtual point corresponding to the first connecting section, and a third virtual point corresponding to the second connecting section. The weld seam may be curved away from the load axis line before it ends.By bending the weld seam with respect to the load axis line, the bending direction component of a stress induced in the base material around the weld end can be increased, and by increasing the distance between the weld end and the load axis line, a stress induced around the weld end can be reduced.

[0010] The weld on a side plate is curved in one direction, towards either the bottom or top plate. By positioning the weld end close to the bottom or top plate, the stress occurring around the weld end due to the applied force can be reduced. FIGURE DESCRIPTION

[0011] Only exemplary embodiments will now be described with reference to the attached figures, which are intended to be exemplary and not limiting, and where identical elements are numbered similarly in different figures, in which: Fig. 1 is a representation showing a configuration of a strut suspension device, Fig. 2 is a representation showing an upper surface of a suspension arm according to the present embodiment, Fig. 3. A representation is one that shows a section of the in Fig. The suspension arm shown in the diagram is seen along a line AA. Fig. 4A shows a welded structure in the suspension arm according to the present embodiment, Fig. 4 B a side face of an upper element, and Fig. 4C a side face of a lower element, Fig. 5 is a representation which shows a welded structure in a suspension arm provided as a comparative example from the prior art, Fig. 6A is a representation showing a section seen along a line DD near the weld end in the comparison example, and Fig. 6B is a representation showing a section seen along a line CC near the weld end in the present embodiment, and Fig. 7A is a perspective partial view of the welded structure in the suspension arm according to the comparison example, and Fig. Figure 7B is a perspective partial view of the welded structure in the suspension arm according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] The invention will now be described with reference to preferred embodiments. This is not intended to limit the scope of the present invention, but rather to illustrate the invention by way of example.

[0013] Fig. Figure 1 shows a configuration of a strut suspension device 1. A suspension arm or control arm 10 according to the present embodiment is designed as an L-shaped arm in which overlapping sections of side plates of an upper element and a lower element, each having a substantially U-shaped cross-section, are welded together. The suspension arm 10 is pivotally supported on a vehicle body at a first connecting section 14 and a second connecting section 16, each comprising a rubber bushing, and a lower ball joint 22 is attached to the suspension arm 10 via a bracket on a mounting section 12. The lower ball joint 22 is attached to a lower end of a steering knuckle 20, so that the mounting section 12 supports the steering knuckle 20 via the lower ball joint 22 in a way that allows it to pivot.The steering knuckle 20 is a support for rotatably mounting a wheel 30, and an upper section of the steering knuckle 20 is attached to a lower end of a strut 26 by means of a bracket 24. An upper end of the strut 26 is pivotally supported on the vehicle body via an upper bearing 28. The lower ball joint 22, as a connecting component, is attached to the mounting section 12 of the suspension arm 10, so that the suspension arm 10 receives input from a road surface via the lower ball joint 22.

[0014] Fig. Figure 2 shows an upper surface of the suspension arm 10 according to the present embodiment. The lower ball joint 22 is attached to the mounting section 12 via a bracket, and a force received by the wheel 30 from a road surface is transmitted to the suspension arm 10 via the lower ball joint 22. The first connecting section 14 and the second connecting section 16 are supported by the vehicle body, and a load received by the mounting section 12 is transmitted to the first connecting section 14 and the second connecting section 16.

[0015] In Fig. 2. A first virtual point 32 represents a virtual point corresponding to the lower ball joint 22, a second virtual point 34 represents a virtual point corresponding to the first connecting section 14, and a third virtual point 36 represents a virtual point corresponding to the second connecting section 16. More precisely, the first virtual point 32 corresponds to the center point of the lower ball joint 22, the second virtual point 34 corresponds to the center point of the first connecting section 14, and the third virtual point 36 corresponds to the center point of the second connecting section 16. A load transmitted within the suspension arm 10 acts to deform a virtual triangle having these three virtual points as its vertices.

[0016] Fig. Figure 3 shows a section of the image seen along a line AA. Fig. The suspension arm 10 shown in Figure 2 is a hollow arm comprising an upper element 40 with a top plate 42 and a pair of side plates 44, and a lower element 50 with a bottom plate 52 and a pair of side plates 54. That is, the suspension arm 10 has a so-called "hollow structure" in which the upper element 40 and the lower element 50 are joined by welding. Each of the upper element 40 and the lower element 50 is formed by pressing a sheet of steel. A side plate 44 of the upper element 40 and a side plate 54 of the lower element 50 are welded together, and in this example, an edge of the side plate 44 and a surface of the side plate 54 are joined in a weld section 60.Alternatively, the side plates 54 of the lower element 50 can be located outside the side plates 44 of the upper element 40 and can be joined together as an edge of a side plate 54 and a surface of a side plate 44.

[0017] Fig. Figure 4A shows a welded structure in the suspension arm 10 according to the present embodiment, wherein it shows a part of a side surface near the fastening section 12 from the direction of arrow B in Fig. 2 shows. A load axis line 80 in Fig. Figure 4A shows a direction in which an input received from a road surface via the lower ball joint 22 is transmitted between the first virtual point 32, the second virtual point 34, and the third virtual point 36 in the suspension arm 10. The load axis line 80 is a line virtually defined such that, when the suspension arm 10 is viewed from the direction of arrow B, a first axis line connecting the first virtual point 32 and the second virtual point 34 overlaps with a second axis line connecting the first virtual point 32 and the third virtual point 36. That is, the load axis line 80 is a line obtained by projecting a virtual triangle formed by the first virtual point 32, the second virtual point 34, and the third virtual point 36 onto the suspension arm 10 such that the first and second axis lines overlap.

[0018] A force acting at the first virtual point 32, which is the center point of the lower ball joint 22, is transmitted along the load axis 80 to the second virtual point 34 of the first connecting section 14 and the third virtual point 36 of the second connecting section 16. Similarly, an input received at the second virtual point 34 is transmitted along the load axis 80 to the first virtual point 32 and the third virtual point 36, and an input received at the third virtual point 36 is transmitted along the load axis 80 to the first virtual point 32 and the second virtual point 34. Thus, the load axis 80 indicates how a force acting at one of the virtual points is transmitted within the suspension arm 10 and dissipated via the other two virtual points.

[0019] If the suspension arm 10 is designed as an L-shaped arm which is essentially planar, the load axis line 80 is essentially parallel to the upper plate 42 of the upper element 40 or the lower plate 52 of the lower element 50, if the suspension arm 10 is supported by a [missing information] as in Fig. 4A shown side is seen from.

[0020] Fig. Figure 4B shows a side face of the upper element 40. The opposite side face of the upper element 40 is also configured to have the same shape.

[0021] The upper element 40 in the present embodiment comprises a projecting section 48 which projects downwards near a mounting section 12a on a side plate 44. The side plate 44 has an edge which extends substantially in a straight line towards the mounting section 12a (from left to right). Fig. 4B), and the edge is curved downwards due to the projecting section 48. More precisely, due to the presence of the projecting section 48, the edge of the side plate 44 is curved in a direction away from the load axis line 80 between a curvature start point 45, which is an end of the substantially straight edge, and a curvature end point 46. Hereinafter, the edge between the curvature start point 45 and the curvature end point 46 will be referred to as a curved edge 47. Therefore, the edge of the side plate 44 is curved upwards in the direction from the curvature end point 46, which is the end of the curved edge 47, towards the fastening section 12a.

[0022] Fig. Figure 4C shows a side face of the lower element 50. The opposite side face of the lower element 50 is also configured to have the same shape.

[0023] The lower element 50 in the present embodiment comprises a projecting section 55 which projects downwards near a fastening section 12b on a side plate 54. The projecting section 55 is shaped according to the shape of the projecting section 48 of the upper element 40 and is provided to ensure a welding gap for the curved edge 47 of the upper element 40. If the welding gap can be ensured, the projecting section 55 need not be provided.

[0024] Referring back to Fig. 4A The side plate 44 of the upper element 40 is arranged on the outside of the side plate 54 of the lower element 50, so that it overlaps. The side plate 44 of the upper element 40 and the side plate 54 of the lower element 50 are joined by welding in the overlap section, and the weld section 60 is formed between the edge of the side plate 44 and the surface of the side plate 54. A weld seam formed by the weld section 60 is curved and terminates at the point where the overlap of the side surfaces of the upper element and the lower element is closest to the lower ball joint 22.

[0025] Since the weld section 60 is formed along the edge of the side plate 44, the weld is essentially straight at a distance from the mounting section 12. Near the mounting section 12, however, the weld is curved from the curvature start point 45 along the curved edge 47 because the curved edge 47 is formed from the curvature start point 45. The weld then terminates before the curvature end point 46 of the curved edge 47, so that a weld end 62 is positioned before the curvature end point 46.

[0026] Since the weld end 62 is positioned at the curved edge 47, the direction of any stress acting on the base material around the weld end 62 can be altered compared to a case where the weld end is positioned at the end of the substantially straight weld. Furthermore, since the curved edge 47 is curved in a direction away from the load axis 80, the weld end 62 is positioned away from the load axis 80.

[0027] Before discussing the functions provided by the aforementioned welded structure according to the present embodiment, a comparison with the welded structure of the present embodiment is made. Fig. 5 showed a different welding structure.

[0028] Fig. Figure 5 shows a welded structure in a suspension arm 200 from the prior art. The suspension arm 200 comprises an upper element 100 and a lower element 110, each having a substantially U-shaped cross-section, and side plates 104 of the upper element 100 are joined to side plates 114 of the lower element 110 by welding. The lower ball joint 22 is attached to the suspension arm 200 at a mounting section 122. Compared to the suspension arm 10 according to the present embodiment, the suspension arm 200 of the prior art differs in that the upper element 100 is not provided with a protruding section 48 on a side plate 104, the lower element 110 is not provided with a protruding section 55 on a side plate 114, and the weld seam is substantially straight. With the exception of the above differences, the structure can be essentially identical to that in the present embodiment.

[0029] In contrast to the suspension arm 10 according to the present embodiment, since the upper element 100 does not have the protruding section 48, the edge of the side plate 104 is shaped such that it is substantially straight in a longitudinal direction, so that a weld formed by a weld section 120 is also substantially straight, and a weld end 64 is positioned at the end of the substantially straight weld. The weld structure described in the comparative technology is usually seen in a conventional suspension arm.

[0030] Since input from a road surface is transmitted to the suspension arm via the lower ball joint 22, the area surrounding a weld end located near the lower ball joint 22 is likely to become a stress concentration point. Consequently, in a suspension arm, the area surrounding a weld end near the lower ball joint 22 is likely to be one of the weakest sections with respect to the fatigue strength of the base material. One solution to ensure fatigue strength near a weld end is to make the plate thicker; however, this solution is not preferable because it does not meet the weight reduction requirement for suspension arms. In contrast, the weld structure in the suspension arm 10, according to the present embodiment, incorporates a design that enhances the fatigue strength of the base material near the weld end 62.The following describes the operating principles of the welded structure according to the present embodiment in comparison to the welded structure in the suspension arm 200 according to the comparative technique.

[0031] Fig. Figure 6A is an illustration showing a section view along a line DD near the weld end 64 in the comparative technique. Fig. Figure 6A shows a side plate 104 and a side plate 114 arranged at a distance from each other for the sake of clarity; however, the side plate 104 and the side plate 114 are actually in contact with each other. It is assumed here that a force is applied in a longitudinal direction of the vehicle to the first virtual point 32, which represents the center point of the lower ball joint 22.

[0032] When a load is applied to the first virtual point 32, distortion occurs in the upper element 100 and the lower element 110 of the suspension arm 200. At this point, the distortion dimensions in the upper element 100 and the lower element 110 differ depending on the difference in shape between the upper element 100 and the lower element 110, which form the attachment section 122 to which the lower ball joint 22 is attached. Accordingly, forces act in opposite directions on the upper element 100 and the lower element 110 near the weld end 64. Fig. Figure 6A shows the condition in which a tensile stress f1 acts on the side plate 104 of the upper element 100 near the weld end 64, and a compressive stress f2 acts on the side plate 114 of the lower element 110. The tensile stress f1 and the compressive stress f2 act in opposite directions, and conversely, a compressive stress can act on the side plate 104 and a tensile stress can act on the side plate 114.

[0033] In the prior art suspension arm 200, the direction in which the weld section 120 extends near the weld end 64 is essentially identical to the direction in which a load acts (stress direction). Accordingly, the stress directions on the front and rear surfaces of the side plate 104 are the same, and a stress in the tensile or compressive direction (hereinafter referred to as a "tension / compression direction") occurs near the weld end 64. Since it is known that the base material has an allowable stress in a tension / compression direction that is lower than that in a bending direction, applying a load near the weld end 64, where stresses often concentrate, in a tension / compression direction is not advantageous.Therefore, in the suspension arm 200, according to the comparative technique, the plate must be made thicker in order to increase the strength of the base material near the weld end 64, which could be one of the weakest sections.

[0034] Fig. Figure 6B is an illustrative representation showing a section viewed along a line CC near the weld end 62 in the present embodiment. As in Fig. 6A are a side plate 44 and a side plate 54 in Fig. Figure 6B shows them arranged at a distance from each other for ease of understanding, but in reality, side plate 44 and side plate 54 are in contact with each other.

[0035] When a load is applied in a longitudinal direction of the vehicle at the first virtual point 32, forces in opposite directions act on the upper element 40 and the lower element 50 of the suspension arm 10 near the weld end 62 due to the difference between the distortion dimensions caused in the upper element 40 and the lower element 50. Fig. Figure 6B shows the condition in which a tensile stress f1 acts on the side plate 44 of the upper element 40 near the weld end 62, and a compressive stress f2 acts on the side plate 54 of the lower element 50. The tensile stress f1 and the compressive stress f2 act in opposite directions, and conversely, a compressive stress can act on the side plate 44 and a tensile stress can act on the side plate 54.

[0036] In the suspension arm 10 according to the present embodiment, the weld along the curved edge 47 is substantially perpendicular to a stress direction near the weld end 62, which is the end of the weld. Accordingly, near the weld end 62, the stress directions on the front and rear surfaces of the side plate 44 of the upper element 40 are opposite to each other, and a stress in a bending direction occurs in the base material near the weld end 62. Since the base material has a permissible stress in a bending direction that is greater than that in a tensile / compressive direction, inducing a stress in a bending direction near the weld end 62 allows the plate to be manufactured thinner and increases the fatigue strength of the base material.

[0037] Fig. Figure 7A is a perspective partial view of the welded structure in the suspension arm 200 according to the state of the art, and Fig. Figure 7B is a perspective partial view of the weld structure in the suspension arm 10 according to the present embodiment. As can be seen from the figures, in the prior art suspension arm 200, the weld section 120 extends in the directions of the stresses f1 and f2, so that a tensile / compressive stress is caused in the base material around the weld end 64. In the suspension arm 10 according to the present embodiment, on the other hand, the weld section 60 is formed along the curved edge 47, and the weld seam is arranged substantially perpendicular to the directions of the stresses f1 and f2, so that a bending stress is caused in the base material around the weld end 62. Thus, in the suspension arm 10, the weld seam is curved before it ends, which causes a bending stress in the base material around the weld end 62.By creating a stress in a bending direction instead of a tensile / compressive direction around the weld end 62, the fatigue strength of the base material, which has a higher permissible stress in a bending direction, can be increased, which makes it possible to thin the base material.

[0038] In the Fig. At the curved edge 47 shown in Figure 4A, the weld ends at a position where the weld is substantially perpendicular to the direction in which the side plate 44 extends. However, the weld may end at a different position within the curved edge 47. For example, the weld may end at a position between the position shown as the weld end 62 and the curvature start point 45 in Figure 4A. Fig.4A. By curving the weld seam with respect to the load axis line 80 before the weld seam is completed, the tensile / compressive component of a stress induced near the weld end 62 can be reduced, while the bending component of the stress can be increased compared to the case where the weld seam ends without being curved. Thus, by terminating the weld seam within the curved edge 47, the fatigue strength of the base material around the weld end 62 can be increased. The weld seam along the curved edge 47 is preferably inclined near the weld end 62 at a predetermined angle or greater, such as 45 degrees or more, to a stress direction.If the weld seam near the weld end 62 is inclined at a predetermined angle or greater to a stress direction, the ratio of the bending direction component to the tension / compression direction component in the stress can be increased.

[0039] Furthermore, by curving the weld seam in a direction away from the load axis 80 and positioning the weld end 62 within the curved edge 47, the distance between the weld end 62 and the load axis 80 can be increased. A greater distance from the load axis 80 reduces the induced stress. Therefore, by positioning the weld end 62 further away from the load axis 80, a stress induced near the weld end 62 can be reduced. Similarly, by curving the weld seam towards the base plate 52 to increase the distance between the weld end 62 and the load axis 80, a stress induced near the weld end 62 can be reduced, thus further increasing the fatigue strength of the base material near the weld end 62.

[0040] The present invention has been described with regard to the embodiment. The embodiment is intended to be illustrative only, and it will be obvious to those skilled in the art that various modifications could be developed for a combination of components or processes, and that such modifications also fall within the scope of the present invention.

[0041] In this embodiment, a side plate 44 has a projecting section 48 that extends downwards. Alternatively, as a modification, the side plate 44 can have a recess that extends upwards. In this case as well, stress in a bending direction can be induced around the weld end by curving the weld and allowing it to terminate near the lower ball joint 22. Such a weld structure according to the modification is particularly effective when the load axis 80 is located below the weld, but its application is not limited to this.

[0042] Furthermore, as previously described, in this embodiment the side plates 54 of the lower element 50 are overlapped and thus welded from the outside by the side plates 44 of the upper element 40. Conversely, the side plates 44 of the upper element can be overlapped and thus welded from the outside by the side plates 54 of the lower element 50. In this case, each of the side plates 54 can have a protruding section that projects upwards, such that the weld is curved along the curved edge of the protruding section and terminates near the lower ball joint 22. That is, the curved edge can be curved in a direction towards the upper plate 42, so that the weld terminates near the upper plate 42.Thus, the vertical positions of the upper element 40 and the lower element 50 in the suspension arm 10 are relative, and the vertical positional arrangement relationship described in the embodiment can be reversed.

Claims

[1] Suspension arm (10) receiving input from a road surface via a connecting component, the suspension arm (10) having a hollow structure and comprising: an upper element (40) with a top plate (42) and a pair of side plates (44) and a lower element (50) with a bottom plate (52) and a pair of side plates (54), wherein the side plates (44) of the upper element (40) are welded to the side plates (54) of the lower element (50) at the edges of at least either the side plates (44) of the upper element (40) or the side plates (54) of the lower element (50), wherein the pairs of side plates (44, 54) of the upper or the lower element (40, 50) have protruding sections (48, 55) with a curved edge (47), and a weld (60) along this curved edge (47). proceeds characterized by, that the weld (60) on the side plate (44, 54) is curved in a direction towards the lower plate (42) or towards the upper plate (52). [2] Suspension arm (10) according to claim 1, wherein the side plate (44, 54) of the upper element (40) or of the lower element (50) has a straight edge and a curved edge (47) which is curved from one end of the straight edge, and the weld (60) terminates within the curved edge (47). [3] Suspension arm (10) according to one of claims 1 or 2, wherein: the suspension arm (10) is supported on a first connecting section (14) and a second connecting section (16) of a vehicle body and a direction in which a load is transferred from the connecting component to the first connecting section (14) and the second connecting section (16) is defined as a load axis line (80) by means of a first virtual point (32) corresponding to the connecting component, a second virtual point (34) corresponding to the first connecting section (14) and a third virtual point (36) corresponding to the second connecting section (16), and the weld seam (60) is curved in a direction away from the load axis line (80).

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