JP2006182278A - Lower arm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compose a lower arm of sheet metal by bending a single sheet metal in such a way that cross sectional form is gradually changed. <P>SOLUTION: This lower arm 1 comprises a sheet metal, having a roughly rectangular cross section comprising a bottom surface 16, a left side surface 14 and a right side surface 15 having a roughly pentagonal side view, and a front upper surface 12 and a rear upper surface 13 respectively provided along a bent front upper edge 18 and a bent rear upper edge 19 of the left side surface 14 and the right side surface 15. The front upper surface 12 and the rear upper surface 13 are parted forward and rearward at an intersection of the front upper edge 18 and the rear upper edge 19 to be independently bent to gradually change the cross sectional form along the front upper edge 18 and the rear upper edge 19, that are bent in a ridge form or a trough form, of the left side surface 14 and the right side surface 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lower arm that supports a wheel with respect to a chassis frame in an automobile or the like.

  In automobiles and the like, as can be seen in Patent Document 1, the lower arm that supports the wheel with respect to the chassis frame varies in shape or size depending on the design specifications for each vehicle type, but particularly requires high rigidity. For example, Patent Document 2 discloses a cast iron lower arm having a substantially rectangular shape in cross section and a stabilizer attachment portion side in a substantially rectangular shape in a cross section located between the stabilizer attachment portion and the vehicle body side attachment portion. A lower arm with a substantially cross-shaped side is proposed. The lower arm has a high rigidity by specifying a cross-sectional shape and including a stabilizer.

  The lower arm is required to have high rigidity, but at the same time it is desirable that it be lightweight. From now on, as seen in Patent Document 3, a sheet metal lower arm in which a pair of members formed in a predetermined shape are joined and made hollow is also used. The lower arm made of sheet metal is usually integrated by forming a flat plate-like member on the lower surface side, abutting a U-shaped member having a lower part opened on this member, and welding the abutting portion. The U-shaped member having a U-shaped cross section forms a lower arm having a gradually changing cross section by curving convex left and right side surfaces and an upper surface, and realizes high rigidity by increasing the cross section coefficient.

JP 07-304461 A Japanese Unexamined Patent Publication No. 2000-142052 JP 07-096731 A

  Unless a complicated shape is required based on the design specifications for each vehicle type, it can be said that a lightweight and highly rigid sheet metal lower arm is preferable. However, the conventional lower arm made of sheet metal has a flat plate-like lower surface in order to realize a gradually changing cross-section for the purpose of increasing the section modulus, and is covered with a U-shaped cross-section member on both sides. The edges were welded together. This increases the number of parts that may cause thermal deformation associated with welding, and makes it difficult to manufacture an accurate sheet metal lower arm. In addition, a sheet metal lower arm consisting of two members needs to be die-cut, molded or processed on separate production lines and then welded again on the welding line, increasing the number of manufacturing processes and The installation area was increased and the manufacturing cost of the sheet metal lower arm was increased. Therefore, a sheet metal lower arm whose cross-sectional shape gradually increases or decreases was examined in order to manufacture by bending a single sheet metal.

  What has been developed as a result of the study is the bottom surface, the left side surface and the right side surface of a substantially pentagonal shape in side view, and the front upper surface and the rear upper surface that respectively follow the bent front upper edge and rear upper edge of the left side surface and right side surface. A lower arm made of a sheet metal having a substantially square cross section, wherein the front upper surface and the rear upper surface are divided into front and rear at the intersection of the front upper edge and the rear upper edge and bent individually, and the bottom surface, the front upper surface or the rear upper surface is the left side surface Alternatively, the unfolded original plate cut at the upper edge or lower edge of the right side surface is bent along the front upper edge, rear upper edge or lower edge of the left side surface and right side surface, and the upper edge or lower edge of the left side surface or right side surface is bent. Front upper edge and rear upper bent to the chevron or valley shape of the left side and right side by welding the other end against one of the cut bottom, front top, back top, left side or right side The lower arm is obtained by gradually increasing or decreasing the cross-sectional shape along the edge.

  The lower arm of the present invention has a structure in which the cross-sectional shape is linearly increased or decreased linearly, and has a front upper edge that is bent into a mountain shape or a valley shape on the left side surface and the right side surface of the substantially pentagonal shape when viewed from the side. Bend the front upper surface and the rear upper surface in a chevron or valley shape along the rear upper edge (or the edge if separated from the rear upper surface), and make the front upper surface and the rear upper surface be the left side or right side. On the other hand, it can be individually bent and can be developed as one original plate. Here, “front” and “rear” in the lower arm of the present invention are names for convenience of explanation, and one of the extending directions of the lower arm is “front”, and the other remaining direction of the lower arm is “rear”. Call. The lower arm is a member that connects the chassis frame and the wheel. For example, the chassis frame attachment portion is attached to the “front” and the axle attachment portion is attached to the “rear” for support. Moreover, you may attach an axle attachment part between the divided | segmented front upper surface and rear upper surface.

  When the lower arm is formed from the unfolded original plate, the manner of abutting each surface differs depending on whether the bottom surface, the front upper surface, or the rear upper surface is cut by the upper edge or the lower edge of the left side surface or the right side surface. For example, the front upper surface may be welded by abutting the edge of either the left side surface or the right side surface, or by abutting the edge of the front upper surface on either the left side surface or the right side surface. Similarly, the rear upper surface may be welded by abutting the edge of either the left side surface or the right side surface, or by abutting the edge of the rear upper surface against either the left side surface or the right side surface. Further, the bottom surface may be welded by abutting the edge of either the left side surface or the right side surface, or by abutting the edge of the bottom surface on either the left side surface or the right side surface.

  A specific lower arm can have the following configuration. That is, the unfolded original plate is provided with a left side surface and a right side surface at the front upper edge on the left and right sides of the front upper surface, a bottom surface with a lower edge on the right side of the right side surface, and a rear upper edge on the right side of the left side surface. A rear upper surface is provided as a boundary, the original plate is bent according to the front upper edge, rear upper edge or lower edge of the left side surface and the right side surface, the bottom edge is set to the left side, and the right side edge is set to The lower arm is formed by gradually increasing and decreasing the cross-sectional shape along the front upper edge and the rear upper edge that are bent into a mountain shape or a valley shape on the left side surface and the right side surface by abutting and welding to the rear upper surface. This lower arm has a diagonal position relationship between the abutting portion of the left side surface and the bottom surface and the abutting portion of the right side surface and the rear upper surface on the rear upper surface side where there are two welding sites by abutting, The load on the welding site can be distributed. The lower arm may be provided with a bottom surface on the left side of the left side surface with the lower edge as a boundary and a rear upper surface on the right side of the right side surface with the rear upper edge as a boundary due to the left-right mirror surface symmetry of the above configuration.

  As another example, the unfolded original plate is provided with a left side surface and a right side surface on the right and left sides of the bottom surface, with the front upper surface on the right side of the right side and on the right side of the right side surface. The rear upper surface is provided separately with the rear upper edge as a boundary, and the original plate is bent along the front upper edge, rear upper edge or lower edge of the left side surface and right side surface, and the edge of the left side surface is front front surface and rear upper surface. A lower arm whose cross-sectional shape is gradually increased or decreased along the front upper edge and the rear upper edge bent in a chevron shape or a valley shape on the left side surface and the right side surface by welding to each other. This lower arm has one welded part on each of the front upper surface and the rear upper surface, and both welded parts are aligned on the same line in plan view, so that welding is facilitated, and in particular, the production line can be simplified. The lower arm may be provided with a front upper surface on the left side of the left side surface with the front upper edge as a boundary and a rear upper surface on the left side of the left side surface with the rear upper edge as a boundary due to the left-right mirror surface symmetry of the above configuration. .

  The lower arm of the present invention may be configured such that the bottom surface, the front upper surface, or the rear upper surface are divided into left and right and overlapped. That is, a sheet metal having a substantially rectangular cross section comprising a bottom surface, a left side surface and a right side surface having a substantially pentagonal shape in side view, and a front upper surface and a rear upper surface that respectively follow the bent front upper edge and rear upper edge of the left side surface and right side surface. A lower arm made of the front, upper and rear upper surfaces are divided into front and rear at the intersection of the front upper edge and rear upper edge and bent individually, and the bottom surface, front upper surface or rear upper surface is divided into left and right and separated. The left and right side surfaces are bent by bending the shape of the original plate according to the front upper edge, rear upper edge or lower edge of the left side surface and right side surface, and then overlapping the bottom surface, front upper surface or rear upper surface and welding them. It may be a lower arm whose cross-sectional shape is gradually increased or decreased following the front upper edge and rear upper edge bent in a mountain shape or valley shape.

  In this case, the specific lower arm is as follows. That is, the unfolded original plate is provided with a left side surface and a right side surface on the left and right sides of the front upper surface with the front upper edge as a boundary, and on the left side of the left side surface with one of the outer layer bottom surface or the inner layer bottom surface with the lower edge as a boundary. One of the rear upper surface of the outer layer or the rear upper surface of the inner layer is provided on the right with the rear upper edge as the boundary, the other of the outer layer bottom surface or the inner layer bottom surface is provided on the right side of the right side surface, and the rear upper edge is defined on the left side of the right side surface. The other upper surface after the outer layer or the upper surface after the inner layer is provided, and the original plate is bent along the front upper edge, the rear upper edge or the lower edge of the left side surface and the right side surface, and the outer layer bottom surface, the inner layer bottom surface, the outer layer rear upper surface, and the inner layer rear surface. The lower arm is formed by gradually increasing and decreasing the cross-sectional shape along the front upper edge and the rear upper edge bent in a mountain shape or a valley shape on the left side surface and the right side surface by overlapping and welding the upper surface.

  According to the present invention, it is possible to manufacture a sheet metal lower arm whose cross-sectional shape is gradually increased or decreased by bending from one original sheet. This is because the lower arm of the present invention is a structure in which the cross-sectional shape is linearly increased or decreased linearly, and only the upper surface is mountain-shaped, and the upper surface is divided into a front upper surface and a rear upper surface, so that the developed shape is a single original plate. This is the effect of being able to be configured. As a result, it is possible to perform the processes from die cutting of the original plate to bending and welding in a series of production lines, and the lower arm can be efficiently manufactured. This facilitates quality control of the lower arm and improves the quality of the lower arm, and also reduces the manufacturing cost associated with the improvement of production efficiency.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a suspension device 4 for a rear wheel to which an example of the lower arm 1 of the present invention is applied, FIG. 2 is a perspective view of the lower arm 1 of the present example as viewed from the rear, and FIG. 3 is a lower arm 1 of the present example. 4 is a bottom view of the lower arm 1 of the present example, FIG. 5 is a side view of the lower arm 1 of the present example, FIG. 6 is a plan view of the unfolded original plate 11 of the lower arm 1 of the present example, and FIG. FIG. 8 is a cross-sectional view of the lower arm 1 of this example on the upper surface 12, and FIG. 8 is a cross-sectional view of the lower arm 1 of this example on the rear upper surface 13. In the following example, the lower arm 1 composed of the left side surface 14 and the right side surface 15 having a substantially pentagonal shape in side view, that is, a substantially mountain shape in side view, having a front upper edge 18 and a rear upper edge 19 bent in a convex manner will be described. The lower arm having the bent front upper edge and the rear upper edge in the side view substantially pentagonal shape, that is, the left side surface and the right side surface in the side view substantially valley shape is easily understood from the following example, and the description thereof is omitted. .

  The lower arm of the present invention employs a structure in which the cross-sectional shape linearly increases or decreases gradually. As can be seen from FIG. 1, for example, the suspension device 4 can be configured to support a rear wheel axle (an axle, not shown) by a pair of left and right lower arms 1 and 1. In this case, at the front end of the lower arm 1 formed by bending the original plate 11 (see FIG. 6), the front end pipe 42 constituting the chassis frame mounting portion, the clearance between the front upper surface 12 and the rear upper surface 13 and the rear end of the lower arm 1 An intermediate pipe 43 and a rear end pipe 44, each constituting an axle mounting portion, are attached. A rubber bush or the like is inserted into each pipe 42, 43, 44.

  As shown in FIGS. 2 to 5, the lower arm 1 of this example has a substantially trapezoidal bottom surface 16 that is widened from front to back, a lower edge 17 that is a boundary between the bottom surface 16, and an arc shape. Left side of a substantially mountain shape in a side view surrounded by a front edge 111, a rear edge 112 and an intermediate edge 113, a long front upper edge 18 with a downward slope before, and a short rear upper edge 19 with a downward slope after Plane view following the front upper edge 12 of the plane 14 and right side 15, the front upper edge 18 of the left side 14 and right side 15, and the rear upper edge 19 of the left side 14 and right side 15 The rear upper surface 13 is substantially trapezoidal. That is, in this example, the lower arm 1 made of sheet metal is configured to increase or decrease the cross-sectional shape along the front upper surface 12 and the rear upper surface 13 while gradually widening the bottom surface 16 from the front to the rear.

  The original plate 11 forming the lower arm 1 has a developed shape as shown in FIG. That is, the original plate 11 is provided with a left side surface 14 and a right side surface 15 having a substantially mountain shape in side view with a front upper edge 18 as a boundary on the left and right sides of the front upper surface 12 having a substantially trapezoidal shape in plan view, A bottom surface 16 having a substantially trapezoidal shape in plan view is provided with a boundary 17 and a rear upper surface 13 having a substantially trapezoidal shape in plan view is provided to the right of the left side surface 14 with a rear upper edge 19 as a boundary. As described above, the lower arm 1 of the present invention includes the unfolded original plate 11, so that the original plate 11 can be obtained, for example, by stamping from a continuously drawn steel plate by press forming.

  In the original plate 11 of this example, jig fitting holes 114 are provided in the front upper surface 12, the left side surface 14, the right side surface 15, and the bottom surface 16 in order to position a reference surface for bending. The original plate 11 is first fitted with a jig (not shown, the same applies hereinafter) in a jig fitting hole 114 on the front upper surface 12 and the front upper surface 12 is used as a reference surface, and the front upper edge 18 is bent and the left side surface 14 is used. And the right side surface 15 is bent. Next, a jig is fitted into the jig fitting hole 114 of the right side surface 15 and the right side surface 15 is used as a reference surface, and the bottom surface 16 is bent using the lower edge 17 as a bending edge. Thereby, as seen in FIG. 7, the edge of the bottom surface 16 can be abutted against the inside of the left side surface 14, and fillet welding can be performed, and the molding of the first half portion of the lower arm 1 is completed. The cross section of the edge of the bottom surface 16 may be cut out and groove welding may be performed (the same applies to fillet welding below).

  Finally, a jig is fitted into the jig fitting hole 114 of the left side surface 14, and the rear upper surface 13 is bent with the left side surface 14 as a reference surface and the rear upper edge 19 of the left side surface 14 as a bending edge. As a result, as shown in FIG. 8, the edge of the right side surface 15 can be abutted against the inside of the rear upper surface 13, and fillet welding can be performed, and the entire molding of the lower arm 1 is completed. The folding order of the respective surfaces may be different. For example, the rear upper surface is divided into two stages, and the left side surface and the right side surface are preliminarily folded halfway and then folded until the edge of the right side surface abuts. It may be. The lower arm 1 that has been molded in this way becomes a product if the front end pipe 42 as the chassis frame attachment portion and the intermediate pipe 43 and the rear end pipe 44 as the axle attachment portion are attached as necessary.

  The lower arm of the present invention adopts a structure in which the cross-sectional shape is linearly increased or decreased linearly, and the configuration of the original plate can be freely set as long as the original upper plate and the rear upper surface can be bent individually. You can choose. 9 is a perspective view of another example of the lower arm 2. FIG. 10 is a plan view of the other example of the lower arm 2. FIG. 11 is a bottom view of the example of the lower arm 2. FIG. FIGS. 13A and 13B are plan views of a developed original plate of the lower arm 2, and FIG. 14 is a cross-sectional view of the lower arm 2 of the present example on the front upper surface 22 or the rear upper surface 23. For simplification of illustration, the jig fitting hole 214 is not shown in FIGS.

  As shown in FIGS. 9 to 12, the lower arm 2 of the present example is substantially the same as the above-described lower arm 1 (see FIG. 2), and has a substantially trapezoidal bottom in plan view widened from the front to the rear. 26, a lower edge 27 serving as a boundary with the bottom surface 26, an arc-shaped front edge 211, a rear edge 212 and an intermediate edge 213, a long front upper edge 28 having a downward slope before, and a short length having a downward slope after A substantially mountain-shaped left side surface 24 and right side surface 25 surrounded by a rear upper edge 29, a front surface 22 having a substantially trapezoidal shape in plan view following the front upper edge 28 of the left side surface 24 and the right side surface 25, and A rear upper surface 23 having a substantially trapezoidal shape in plan view following the rear upper edge 29 of the left side surface 24 and the right side surface 25 is formed. This means that the same lower arm can be configured even if the developed shapes are different, and shows the diversity of the present invention.

  The original plate 21 forming the lower arm 2 has a developed shape as shown in FIG. 13 and includes a left side surface 24 and a right side surface 25 that are substantially mountain-shaped in side view with the lower edge 27 as a boundary on the left and right sides of the bottom surface 26 that is substantially trapezoidal in plan view. A front trapezoidal front upper surface 22 with a front upper edge 28 as a boundary to the right of the right side 25, and a rear trapezoidal rear upper surface 23 with a rear upper edge 29 as a boundary to the right of the right side 25 Are provided. The original plate 21 of this example is also provided with jig fitting holes 214 on the right side surface 25 and the bottom surface 26 in order to position a reference surface for bending.

  In the original plate 21, first, a jig is fitted into the jig fitting hole 214 of the bottom surface 26, and the left side surface 24 and the right side surface 25 are bent using the bottom surface 26 as a reference surface and the lower edge 27 as a bending edge. Then, a jig is fitted into the jig fitting hole 214 of the right side surface 25, the right side surface 25 is used as a reference surface, and the front upper edge 28 and the rear upper edge 29 of the right side surface 25 are bent as front edges. 22 and rear upper surface 23 are bent. As a result, as shown in FIG. 14, the edge of the left side surface 24 can be abutted against the inside of the front upper surface 22 and the rear upper surface 23, so that fillet welding can be performed, and the entire molding of the lower arm 2 is completed. In the lower arm 2 of this example, only the size of the cross-sectional shape is different, and the cross-section on the front upper surface 22 and the cross-section on the rear upper surface 23 are similar to those shown in FIG. The lower arm 2 which has been molded in this way becomes a product if the front end pipe 42 as the chassis frame attaching portion and the intermediate pipe 43 and the rear end pipe 44 as the axle attaching portion are attached as necessary.

  Further, the lower arm of the present invention can be formed not only from the front upper edge, the rear upper edge, or the lower edge, which is a bent edge, but also from an unfolded original plate that is divided into left and right sides. 15 is a rear perspective view of another example of the lower arm 3, FIG. 16 is a plan view of the further example of the lower arm 3, FIG. 17 is a bottom view of the example of the lower arm 3, and FIG. FIG. 19 is a plan view of a developed original plate of the lower arm 3, FIG. 20 is a cross-sectional view of still another lower arm 3 on the front upper surface 32, and FIG. 21 is a rear upper surface 31. It is sectional drawing of the lower arm 3 of another example. For simplification of illustration, the jig fitting hole 314 is not shown in FIGS.

  As shown in FIGS. 15 to 18, the lower arm 3 of this example is substantially the same as the above-described lower arm 1 (see FIG. 2), and has a substantially trapezoidal bottom in plan view widened from the front to the rear. 36, a lower edge 37 serving as a boundary with the bottom surface 36, an arc-shaped front edge 311, a rear edge 312 and an intermediate edge 313, a long front upper edge 38 having a downward slope in front, and a short length having a downward slope after A substantially mountain-shaped left side surface 34 and right side surface 35 surrounded by a rear upper edge 39, a front surface 32 having a substantially trapezoidal shape in plan view following the front upper edge 38 of the left side surface 34 and the right side surface 35, and The rear upper surface 33 includes a substantially trapezoidal shape in plan view that follows the rear upper edge 39 of the left side surface 34 and the right side surface 35.

  The original plate 31 forming the lower arm 3 has a developed shape as shown in FIG. 19, and a left side surface 34 and a right side surface 35 are provided on the left and right sides of the front upper surface 32 with a front upper edge 38 as a boundary. The outer layer bottom surface 362 is provided on the right side of the left side surface 34, the inner layer rear upper surface 331 is provided on the right side of the left side surface 34, and the inner layer bottom surface 361 is provided on the right side of the right side surface 35 of the lower edge 37. The rear upper surface 332 is provided on the left side of 35 with the rear upper edge 39 as a boundary. That is, the original plate 31 forming the lower arm 3 of this example has a left-right symmetrical shape in which the rear upper surface 33 and the bottom surface 36 are divided into left and right. The original plate 31 of this example is also provided with jig fitting holes 314 on the front upper surface 32, the left side surface 34, and the right side surface 35 in order to position a reference surface for bending.

  In the original plate 31, first, a jig is fitted into a jig fitting hole 314 on the front upper surface 32, and the left upper surface 34 and the right side surface 35 are bent using the front upper surface 32 as a reference surface and the front upper edge 38 as a bending edge. Next, a jig is fitted into the jig fitting hole 314 on the right side surface 35, the right side surface 35 is used as a reference surface, the inner layer bottom surface 361 is bent with the lower edge 37 of the right side surface 35 as a bending edge, A jig is fitted into the jig fitting hole 314 on the left side surface 34, the left side surface 34 is used as a reference surface, the lower edge 37 of the left side surface 34 is bent, and the outer layer bottom surface 362 is bent. The rear upper surface 331 of the inner layer is bent using the rear upper edge 39 of the surface 34 as a bending edge. Thus, as seen in FIG. 20, the inner layer bottom surface 361 and the outer layer bottom surface 362 can be overlapped and fillet welded, and the molding of the first half of the lower arm 3 is completed.

  Finally, a jig is fitted into the jig fitting hole 314 of the right side surface 35, the right side surface 35 is used as a reference surface, the rear upper edge 39 of the right side surface 35 is bent, and the rear upper surface 332 of the outer layer is bent. Thus, as shown in FIG. 21, the inner layer rear upper surface 331 and the outer layer rear upper surface 332 can be overlapped and welded to fillet, and the entire molding of the lower arm 3 is completed. The bending order of each surface may be different, but if fillet welding is performed with the inner layer bottom surface 361 and outer layer bottom surface 362 of the welded portion overlapped first, the shape of the lower arm during molding is good, and handling is easy. Therefore, prior to fillet welding of the inner layer rear upper surface 331 and the outer layer rear upper surface 332, the order in which the inner layer bottom surface 361 and the outer layer bottom surface 362 are first overlapped and the fillet welding is performed is preferable. The lower arm 3 which has been molded in this manner becomes a product if the front end pipe 42 as the chassis frame attaching portion and the intermediate pipe 43 and the rear end pipe 44 as the axle attaching portion are attached as necessary.

It is a perspective view showing the suspension device for rear wheels to which an example of the lower arm of the present invention is applied. It is the perspective view which looked at the lower arm of this example from back. It is a top view of the lower arm of this example. It is a bottom view of the lower arm of this example. It is a side view of the lower arm of this example. It is a top view of the original plate of the developed shape of the lower arm of this example. It is sectional drawing of the lower arm of this example in a front upper surface. It is sectional drawing of the lower arm of this example in a back upper surface. It is the perspective view which looked at the lower arm of another example from back. It is a top view of the lower arm of another example. It is a bottom view of the lower arm of another example. It is a side view of the lower arm of another example. It is a top view of the original plate of the developed shape of the lower arm of another example. It is sectional drawing of the lower arm of this example in a front upper surface or a rear upper surface. Furthermore, it is the perspective view which looked at the lower arm of another example from back. It is a top view of the lower arm of another example. It is a bottom view of the lower arm of another example. It is a side view of another example of the lower arm. Furthermore, it is a top view of the original plate of the developed shape of the lower arm of another example. It is sectional drawing of the lower arm of another example in a front upper surface. It is sectional drawing of the lower arm of another example in a back upper surface.

Explanation of symbols

1 Lower arm
114 Jig fitting hole
12 Front top
13 Rear top
14 Left side
15 Right side
16 Bottom
17 Lower edge
18 Front upper edge
19 Rear upper edge 2 Lower arm
22 Front top
23 Rear upper surface
24 Left side
25 Right side
26 Bottom
27 Lower edge
28 Front upper edge
29 Rear upper edge 3 Lower arm
32 Front top
33 Rear top
331 Upper surface after inner layer
332 Upper surface after outer layer
34 Left side
35 Right side
36 Bottom
361 Bottom of inner layer
362 Outer layer bottom
37 Lower edge
38 Front upper edge
39 Rear upper edge
42 Front end pipe
43 Intermediate pipe
44 Rear end pipe

Claims (11)

Made of a sheet metal having a substantially rectangular cross section comprising a bottom surface, a left side surface and a right side surface having a substantially pentagonal shape in side view, and a front upper surface and a rear upper surface that respectively follow the bent front upper edge and rear upper edge of the left side surface and right side surface. Lower arm, the front upper surface and the rear upper surface are divided forward and backward at the intersection of the front upper edge and the rear upper edge and bent individually, and the bottom surface, front upper surface or rear upper surface is the upper edge or lower side of the left side or right side The base plate of the developed shape cut at the edge is bent according to the front upper edge, rear upper edge or lower edge of the left side and right side, and the bottom surface, front upper surface, and rear are cut at the upper edge or lower edge of the left side or right side By butt-welding the other edge to one of the top, left, or right side surfaces, the cross section gradually changes along the front upper edge and rear upper edge that bend in a chevron or valley shape on the left side surface and right side surface. Lower arm with increased or decreased shape. The lower arm according to claim 1, wherein the front upper surface is welded by contacting an end edge of either the left side surface or the right side surface. The lower arm according to claim 1, wherein the front upper surface is welded by abutting an edge of the front upper surface against either the left side surface or the right side surface. The lower arm according to claim 1, wherein the rear upper surface is welded by abutting an edge of either the left side surface or the right side surface. The lower arm according to claim 1, wherein the rear upper surface is welded by abutting the edge of the rear upper surface against either the left side surface or the right side surface. The lower arm according to claim 1, wherein the bottom surface is welded by abutting the edge of either the left side surface or the right side surface. The lower arm according to claim 1, wherein the bottom surface is welded by abutting the edge of the bottom surface against either the left side surface or the right side surface. The unfolded original plate is provided with a left side and a right side on the left and right of the front upper surface with the front upper edge as a boundary, a bottom surface with a lower edge on the right of the right side, and a rear upper edge on the right of the left side A rear upper surface is provided, and the original plate is bent according to the front upper edge, rear upper edge or lower edge of the left side surface and right side surface, and the bottom edge is on the left side and the right side edge is on the rear upper surface. The lower arm according to claim 1, wherein the cross-sectional shape is gradually increased or decreased along the front upper edge and the rear upper edge bent in a chevron shape or a valley shape on the left side surface and the right side surface by abutting and welding respectively. The unfolded original plate is provided with a left side and a right side on the right and left sides of the bottom surface, with the front upper surface on the right side of the right side and the front upper surface on the right side of the right side, and with the rear upper edge on the right side of the right side. A rear upper surface is provided separately, and the original plate is bent according to the front upper edge, rear upper edge, or lower edge of the left side surface and right side surface, and the edge of the left side surface is abutted against the front upper surface and the rear upper surface, respectively, and welded. The lower arm according to claim 1, wherein the cross-sectional shape is gradually increased or decreased along the front upper edge and the rear upper edge bent in a mountain shape or valley shape on the left side surface and the right side surface. Made of a sheet metal having a substantially rectangular cross section comprising a bottom surface, a left side surface and a right side surface having a substantially pentagonal shape in side view, and a front upper surface and a rear upper surface that respectively follow the bent front upper edge and rear upper edge of the left side surface and right side surface. Lower arm, front upper surface and rear upper surface are divided into front and rear at the intersection of front upper edge and rear upper edge and bent individually, and the bottom, front upper surface or rear upper surface is divided into left and right and divided into left and right shapes By bending the original plate according to the front upper edge, rear upper edge, or lower edge of the left side surface and right side surface, and then welding by overlapping the bottom surface, front upper surface, or rear upper surface divided into left and right sides, Alternatively, a lower arm formed by gradually increasing or decreasing the cross-sectional shape along the front upper edge and rear upper edge bent in a valley shape. The unfolded original plate is provided with a left side and a right side on the left and right of the front upper surface, with the front upper edge as a boundary, and on the left side of the left side with one of the outer layer bottom surface or the inner layer bottom surface with the lower edge as a boundary. One of the rear upper surface of the outer layer or the rear upper surface of the inner layer is provided with the rear upper edge as a boundary, the other of the bottom surface of the outer layer or the lower surface of the inner layer is provided on the right side of the right side surface, and the outer layer with the rear upper edge on the left side of the right side surface. The rear upper surface or the inner layer rear upper surface is provided, and the original plate is bent according to the front upper edge, rear upper edge or lower edge of the left side surface and the right side surface, and the outer layer bottom surface, the inner layer bottom surface, the outer layer rear upper surface, and the inner layer rear upper surface; 11. The lower arm according to claim 10, wherein the cross-sectional shape is gradually increased or decreased along the front upper edge and the rear upper edge bent in a chevron shape or a valley shape on the left side surface and the right side surface by superposing and welding each of them.

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