Structural members

Abstract

The structural member (100) comprises a first mounting portion (11), a second mounting portion (12), a third mounting portion (13), a first vertical wall (31), a second vertical wall (32), a third vertical wall (33), and a top plate (20). The second vertical wall (32) includes a curved portion (321). The curved portion (321) is adjacent to the second mounting portion (12) and curves concavely inward from the structural member (100) in a plan view of the structural member (100). When the height of the second vertical wall (32) in the curved section (321) is H [mm], the radius of curvature of the curved section (321) in a plan view of the structural member (100) is R [mm], and the Vickers hardness of the second vertical wall (32) is Hv [HV], the structural member (100) satisfies any of the conditions (1) to (6) relating to height H, radius of curvature R, and Vickers hardness Hv.

Description

Technical Field

[0005] , , ,

[0001] This disclosure relates to a structural member for a vehicle.

Background Art

[0002] Multiple structural members are used in vehicles such as automobiles. For example, Patent Document 1 discloses a lower arm as an example of a structural member for a vehicle. In Patent Document 1, the lower arm includes an arm member and a reinforcing member. The reinforcing member includes a reinforcing member body and a flange. The reinforcing member body faces the top plate of the arm member. The flange protrudes from the reinforcing member body toward the top plate of the arm member while being arranged with a gap from the top plate. In Patent Document 1, the reinforcing member body branches into a first branch portion and a second branch portion, and the flange is arranged along the branch portion of the reinforcing member body.

[0003] Patent Document 2 also discloses a lower arm as an example of a structural member for a vehicle. In Patent Document 2, the lower arm includes an arm member and a reinforcing member. The reinforcing member includes a bottom wall portion facing the top wall portion of the arm member and a flange portion. The reinforcing member is provided over a wide range of the arm member. In the lower arm of Patent Document 2, the flange portion of the reinforcing member is arranged at a position close to the load input point. For example, the length from the attachment portion of the vehicle body side part to the flange portion is 83% or more of the length from the attachment portion of the vehicle body side part to the attachment portion of the wheel side part which is the load input point.

Prior Art Documents

Patent Documents

[0004] <F

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Structural components for vehicles are required to possess various properties. One of the properties required for structural components is strength (yield strength) against external forces. The object of this disclosure is to provide a structural component for vehicles that can improve yield strength. [Means for solving the problem]

[0006] The structural member for a vehicle according to this disclosure comprises a first mounting portion for attaching the wheels of the vehicle, a second mounting portion and a third mounting portion for attaching the body of the vehicle, a first vertical wall, a second vertical wall, a third vertical wall, and a top plate. The first vertical wall extends from the first mounting portion side to the second mounting portion side. The second vertical wall extends from the second mounting portion side to the third mounting portion side. The third vertical wall extends from the first mounting portion side to the third mounting portion side. The top plate is continuous with each of the first vertical wall, the second vertical wall, and the third vertical wall. The second vertical wall includes a curved portion. The curved portion is adjacent to the second mounting portion. In a plan view of the structural member, the curved portion curves concavely inward. When the height of the second vertical wall in the curved section is H [mm], the radius of curvature of the curved section in a plan view of the structural member is R [mm], and the Vickers hardness of the second vertical wall is Hv [HV], the structural member satisfies any of the following conditions (1) to (6). (1) The conditions 184 ≤ Hv < 243 and H ≥ 0.690R + 12.8 are satisfied. (2) The conditions are 243 ≤ Hv < 305 and H ≥ 0.611R + 9.6. (3) The end of the second vertical wall opposite the top plate is a free end, satisfying 305 ≤ Hv < 367 and H ≥ 0.425R + 8.5. (4) A flange portion is provided continuously on the end of the second vertical wall opposite to the top plate, satisfying 305 ≤ Hv < 367 and H ≥ 0.244R + 19.4. (5) The end of the second vertical wall opposite the top plate is a free end, satisfying 367 ≤ Hv and H ≥ 0.205R + 12.5. (6) A flange portion is provided continuously on the end of the second vertical wall opposite to the top plate, satisfying 367≦Hv and H≧0.125R+17.5. [Effects of the Invention]

[0007] According to this disclosure, the load-bearing capacity of structural members can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic perspective view showing a structural member according to an embodiment. [Figure 2] Figure 2 is another perspective view schematically showing a structural member according to the embodiment. [Figure 3] Figure 3 is a plan view of the structural members shown in Figures 1 and 2. [Figure 4A] Figure 4A is a cross-sectional view taken along line IV-IV in Figure 3. [Figure 4B] Figure 4B is a cross-sectional view taken along line IV-IV in Figure 3. [Figure 5] Figure 5 is a cross-sectional view of the VV section of Figure 3. [Figure 6A] Figure 6A is a schematic diagram showing the configuration of a press molding apparatus for manufacturing structural members according to the embodiment. [Figure 6B] Figure 6B is a schematic diagram showing the configuration of a press molding apparatus for manufacturing structural members according to the embodiment. [Figure 7A] Figure 7A is a schematic diagram illustrating the operation of the press forming apparatus shown in Figures 6A and 6B. [Figure 7B] Figure 7B is a schematic diagram illustrating the operation of the press forming apparatus shown in Figures 6A and 6B. [Figure 8A] Figure 8A is a graph showing the relationship between the height and radius of curvature of the curved section obtained from press forming analysis. [Figure 8B] Figure 8B is a graph showing the relationship between the height and radius of curvature of the curved section obtained from press forming analysis. [Figure 9] Figure 9 is a graph showing F / t for the first embodiment. [Figure 10] Figure 10 is a graph showing the receding force load for Examples 1 to 3 of the second embodiment. [Modes for carrying out the invention]

[0009] The structural member for a vehicle according to the embodiment includes a first attachment portion for attaching a wheel of the vehicle, a second attachment portion and a third attachment portion for attaching the vehicle body of the vehicle respectively, a first vertical wall, a second vertical wall, a third vertical wall, and a top plate. The first vertical wall extends from the first attachment portion side to the second attachment portion side. The second vertical wall extends from the second attachment portion side to the third attachment portion side. The third vertical wall extends from the first attachment portion side to the third attachment portion side. The top plate is continuous with each of the first vertical wall, the second vertical wall, and the third vertical wall. The second vertical wall includes a curved portion. The curved portion is adjacent to the second attachment portion. The curved portion curves inwardly concave in a plan view of the structural member. When the height of the second vertical wall in the curved portion is H [mm], the radius of curvature of the curved portion in a plan view of the structural member is R [mm], and the Vickers hardness of the second vertical wall is Hv [HV], the structural member satisfies any one of the following conditions (1) to (6) (the first configuration). (1) It satisfies 184 ≤ Hv < 243 and H ≥ 0.690R + 12.8. (2) It satisfies 243 ≤ Hv < 305 and H ≥ 0.611R + 9.6. (3) The end of the second vertical wall on the side opposite to the top plate is a free end, it satisfies 305 ≤ Hv < 367, and H ≥ 0.425R + 8.5. (4) A flange portion is provided continuously at the end of the second vertical wall on the side opposite to the top plate, it satisfies 305 ≤ Hv < 367, and H ≥ 0.244R + 19.4. (5) The end of the second vertical wall on the side opposite to the top plate is a free end, it satisfies 367 ≤ Hv, and H ≥ 0.205R + 12.5. (6) A flange portion is provided continuously at the end of the second vertical wall on the side opposite to the top plate, it satisfies 367 ≤ Hv, and H ≥ 0.125R + 17.5.

[0010] The structural member according to the first configuration includes a first vertical wall, a second vertical wall, a third vertical wall, and a top plate continuous with these. In this structural member, a curved portion that curves inwardly in a plan view of the structural member is provided at a position adjacent to the mounting portion (second mounting portion) on the vehicle body side of the second vertical wall. The second vertical wall has a relatively large height H at the curved portion. More specifically, the height H of the second vertical wall at the curved portion is set so as to satisfy any one of the conditions (1) to (6) together with the radius of curvature R of the curved portion in the plan view of the structural member and the Vickers hardness Hv of the second vertical wall. Thereby, the rigidity of the curved portion is improved, and when an external force is input to the structural member, out-of-plane deformation of the structural member in the curved portion and its vicinity is likely to be suppressed. Therefore, the strength (endurance) of the structural member against external forces is likely to be improved.

[0011] The structural member according to the first configuration may further include a first reinforcing member. The first reinforcing member is, for example, arranged on the side of the third mounting portion with respect to the curved portion. The first reinforcing member can include a reinforcing member main body and a flange. The reinforcing member main body may face the top plate with a gap and be joined to the second vertical wall. The flange may project from the reinforcing member main body toward the top plate side and be joined to the top plate (second configuration).

[0012] In the structural member according to the embodiment, since the height H of the second vertical wall at the curved portion satisfies any one of the conditions (1) to (6), the rigidity of the curved portion is improved. As a result of the improved rigidity of the curved portion in the vicinity of the second mounting portion, for example, when a load in the front-rear direction is input to the first mounting portion on the wheel side, the load on the portion of the structural member located on the side of the third mounting portion rather than the curved portion is likely to increase, and torsional deformation may occur in this portion. Therefore, in the second configuration, the first reinforcing member is arranged on the side of the third mounting portion with respect to the curved portion. In the first reinforcing member, the reinforcing member main body is joined to the second vertical wall, and the flange is joined to the top plate to suppress out-of-plane deformation of the top plate. As a result, when a load in the front-rear direction is input to the first mounting portion, torsional deformation of the structural member on the side of the third mounting portion with respect to the curved portion is suppressed, and the entire structural member is less likely to buckle.

[0013] In the structural member relating to the second configuration, the flange may be continuous with respect to the reinforcing member body on the opposite side of the second vertical wall (third configuration).

[0014] In the third configuration, the flange of the first reinforcing member is continuous with the main body of the reinforcing member on the opposite side of the second vertical wall and is joined to the top plate at this position. In this case, when a load is applied to the first mounting portion in the front-rear direction, the first reinforcing member makes it easier to suppress torsional deformation of the structural member on the third mounting portion side relative to the curved portion. Therefore, buckling of the entire structural member is further reduced.

[0015] A structural member relating to the second or third configuration may further include a second reinforcing member. The second reinforcing member is positioned, for example, on the first mounting side relative to the first reinforcing member. The second reinforcing member may be joined to each of the first vertical wall, the second vertical wall, and the third vertical wall (fourth configuration).

[0016] In the fourth configuration, a second reinforcing member is provided on the structural member in addition to the first reinforcing member. These reinforcing members help to suppress overall torsional deformation of the structural member when a load is applied to the first mounting portion in the longitudinal direction. As a result, the applied load is more easily transmitted to the structural member without causing buckling. Consequently, the structural member can exhibit excellent strength against loads in the longitudinal direction.

[0017] In the structural member relating to the fourth configuration, the second reinforcing member may be joined to the curved portion (fifth configuration).

[0018] In the structural member relating to the fifth configuration, the height from the top plate of the joint between the curved portion and the second reinforcing member may be 20 mm or more (sixth configuration).

[0019] Embodiments of this disclosure will be described below with reference to the drawings. In these drawings, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated.

[0020] [Structural Member Composition] Figures 1 and 2 are schematic perspective views showing the structural member 100 according to this embodiment. The structural member 100 is used in vehicles such as automobiles. The structural member 100 is, for example, a chassis component of an automobile. Chassis components include suspension arms such as lower arms and upper arms. In this embodiment, an example in which the structural member 100 is a front lower arm will be described.

[0021] Referring to Figures 1 and 2, the structural member 100 comprises mounting parts 11, 12, and 13, a top plate 20, and vertical walls 31, 32, and 33. The structural member 100 may further comprise reinforcing members 40 and 50.

[0022] The mounting portion 11 is provided on the structural member 100 for attaching the vehicle's wheels. When the structural member 100 is assembled into the vehicle, the mounting portion 11 is positioned outward in the vehicle width direction (left-right direction) relative to the mounting portions 12 and 13. The mounting portion 11 is provided with, for example, a ball joint. The structural member 100 is attached to the wheels via, for example, a ball joint and a steering knuckle.

[0023] The mounting portion 12 is provided on the structural member 100 for attaching the vehicle body. The mounting portion 12 is positioned inward in the vehicle width direction relative to the mounting portion 11 when the structural member 100 is assembled into the vehicle. The mounting portion 12 is provided with, for example, a cylindrical collar 121. The structural member 100 is attached to the vehicle body via, for example, a bush and a suspension member that are press-fitted into the collar 121.

[0024] The mounting portion 13 is provided on the structural member 100 for attaching the vehicle body. When the structural member 100 is assembled into the vehicle, the mounting portion 13 is positioned inward in the vehicle width direction relative to the mounting portion 11. When the structural member 100 is assembled into the vehicle, the mounting portion 13 is positioned behind the mounting portion 12. For example, a bushing is provided on the mounting portion 13. The structural member 100 is attached to the vehicle body, for example, via the bushing and suspension members.

[0025] The top plate 20 and vertical walls 31, 32, 33 are typically formed from metal plates. The top plate 20 and vertical walls 31, 32, 33 may also be formed from steel plates. The vertical walls 31, 32, 33 are formed integrally with the top plate 20. The top plate 20 and vertical walls 31, 32, 33 can have a thickness of, for example, 0.4 mm or more. The thickness of the top plate 20 and vertical walls 31, 32, 33 may be 1.0 mm or more. The thickness of the top plate 20 and vertical walls 31, 32, 33 may be 6.0 mm or less, or 4.0 mm or less.

[0026] The top plate 20 intersects the vertical direction of the vehicle when the structural member 100 is incorporated into the vehicle. In this embodiment, the wheel-side mounting portion 11 and the vehicle body-side mounting portion 13 are provided on the top plate 20. More specifically, the mounting portion 11 may include a recess 111 provided on the end face of the top plate 20. The mounting portion 13 may include a through hole 131 that penetrates the top plate 20 in the thickness direction. For example, a ball joint is mounted in the recess 111. For example, a bush is press-fitted into the through hole 131.

[0027] The top plate 20 is provided with through holes 21. The through holes 21 are located near the mounting portion 12 and penetrate the top plate 20 in the direction of its thickness. The through holes 21 are used, for example, to pass tools through when assembling the structural member 100 to the vehicle.

[0028] The top panel 20 is continuous with each of the vertical walls 31, 32, and 33. The vertical walls 31, 32, and 33 are connected by the top panel 20.

[0029] Vertical wall 31 extends from the mounting portion 11 side to the mounting portion 12 side. Vertical wall 32 extends from the mounting portion 12 side to the mounting portion 13 side. Vertical wall 33 extends from the mounting portion 11 side to the mounting portion 13 side.

[0030] The reinforcing member 40 is positioned on the mounting portion 13 side of the structural member 100. The reinforcing member 40 includes a reinforcing member body 41 and at least one flange 42. The reinforcing member body 41 faces the top plate 20 with a gap between them. The reinforcing member body 41 is joined to the vertical wall 32. The flange 42 is provided continuously with the reinforcing member body 41. The flange 42 is joined to the top plate 20.

[0031] The reinforcing member 50 is a separate component from the reinforcing member 40. In the structural member 100, the reinforcing member 50 is positioned on the mounting portion 11 side relative to the reinforcing member 40. The reinforcing member 50 may, for example, have a plate shape. The reinforcing member 50 faces the top plate 20 with a gap between them. The reinforcing member 50 may be provided with through holes 51 corresponding to the through holes 21 in the top plate 20. The reinforcing member 50 is joined to each of the vertical walls 31, 32, and 33.

[0032] The reinforcing members 40 and 50 are typically made of metal plates. The reinforcing members 40 and 50 may also be made of steel plates. The thickness of the reinforcing members 40 and 50 may be the same as or different from the thickness of the top plate 20 and the vertical walls 31, 32, and 33. The thickness of the reinforcing member 40 may be the same as or different from the thickness of the reinforcing member 50.

[0033] The structure of the structural member 100 will be described in more detail below with reference to Figures 3 to 5. Figure 3 is a plan view of the structural member 100. Figure 3 shows the structural member 100 as seen from the top plate 20 side. Figures 4A and 4B are cross-sectional views taken along line IV-IV in Figure 3. Figure 5 is a cross-sectional view taken along line VV in Figure 3.

[0034] Referring to Figure 3, the structural member 100 has an overall curved shape in its plan view. That is, the structural member 100 is curved overall when viewed along the direction corresponding to the vertical direction of the vehicle into which it is incorporated. Hereinafter, with respect to the structural member 100, the direction corresponding to the vertical direction of the vehicle will simply be referred to as the vertical direction.

[0035] Referring to Figure 3, vertical wall 31 is positioned on the outside of the curve of structural member 100 relative to vertical wall 33. Vertical wall 32 is also positioned on the outside of the curve of structural member 100 relative to vertical wall 33. Vertical walls 32 and 33 include curved portions 321 and 331, respectively.

[0036] The curved portion 321 is the part of the vertical wall 32 that curves inward in a concave shape when viewed from above. The curved portion 321 is adjacent to the mounting portion 12. The curved portion 321 is positioned, for example, next to the collar 121 provided on the mounting portion 12. The curved portion 331 is the part of the vertical wall 33 that curves inward in a concave shape when viewed from above.

[0037] Figures 4A and 4B schematically show the cross-section of the structural member 100 at the location of the curved portion 321. The cross-section of the structural member 100 is the cross-section of the structural member 100 when cut by a plane along the vertical direction. Figures 4A and 4B show the cross-section of the structural member 100 passing through the top plate 20, the curved portion 321 of the vertical wall 32, and the vertical wall 33. However, Figure 4B shows an example of a different cross-section of the structural member 100 from that in Figure 4A.

[0038] Referring to Figures 4A and 4B, the top plate 20 is continuous with the vertical walls 32 and 33, respectively. In a cross-sectional view of the structural member 100, the top plate 20 may have straight sections 22 and 23 adjacent to the vertical walls 32 and 33, respectively. In this embodiment, a recess 24 is provided between the straight sections 22 and 23 in the top plate 20. In the example in Figures 4A and 4B, the through-hole 21 for tools is formed on the bottom surface of the recess 24. However, the top plate 20 does not necessarily have to have a recess 24. The top plate 20 may be entirely linear in a cross-sectional view of the structural member 100.

[0039] The vertical wall 32 includes a vertical wall body 322 and a ridge portion 323. The ridge portion 323 is provided continuously with the top plate 20. The vertical wall body 322 is connected to the top plate 20 via the ridge portion 323. That is, the ridge portion 323 is the corner portion between the top plate 20 and the vertical wall body 322. The ridge portion 323 may have a curved shape that protrudes outward from the structural member 100 in a cross-sectional view of the structural member 100. In the examples of Figures 4A and 4B, the ridge portion 323 is provided continuously with the straight portion 22 of the top plate 20.

[0040] The vertical wall body 322 extends substantially vertically in a cross-sectional view of the structural member 100. The vertical wall body 322 may be substantially straight in a cross-sectional view of the structural member 100. The vertical wall body 322 may be parallel or non-parallel to the vertical direction in a cross-sectional view of the structural member 100. In the example in Figure 4A, the end of the vertical wall body 322 opposite to the top plate 20 is a free end. On the other hand, in the example in Figure 4B, a flange portion 324 is continuously provided at the end of the vertical wall body 322 opposite to the top plate 20. As shown in Figure 4B, the flange portion 324 protrudes from the vertical wall body 322 to the outside of the structural member 100 in a cross-sectional view of the structural member 100. The flange portion 324 may be provided only on the curved portion 321 of the vertical wall 32, or it may be provided to extend beyond the curved portion 321 toward the mounting portion 13 (Figure 3).

[0041] The vertical wall 32 has a height H in the curved portion 321. As in the example in Figure 4A, when the end of the vertical wall 32 opposite to the top plate 20 is a free end, the height H is the vertical distance from the end of the vertical wall 32 on the top plate 20 side to the free end of the vertical wall 32 in the curved portion 321. On the other hand, as in the example in Figure 4B, when a flange portion 324 is continuously provided at the end of the vertical wall 32 opposite to the top plate 20, the height H is the vertical distance from the end of the vertical wall 32 on the top plate 20 side to the surface of the flange portion 324 opposite to the top plate 20 in the curved portion 321. The end of the vertical wall 32 on the top plate 20 side is the end of the vertical wall 32 on the top plate 20 side on the outer surface of the structural member 100, and is the boundary between the curved ridge portion 323 and the straight portion 22 of the top plate 20 in a cross-sectional view. The end of the vertical wall 32 on the top plate 20 side may also be the R-end on the top plate 20 side of the outer surface of the ridge portion 323.

[0042] In a cross-sectional view of the structural member 100, the vertical wall 33 is positioned on the opposite side of the top plate 20 from the vertical wall 32. The vertical wall 33 includes a vertical wall body 332 and a ridge portion 333. The ridge portion 333 is provided continuously with the top plate 20. The vertical wall body 332 is connected to the top plate 20 via the ridge portion 333. That is, the ridge portion 333 is the corner portion between the top plate 20 and the vertical wall body 332. The ridge portion 333 may have a curved shape that protrudes outward from the structural member 100 in a cross-sectional view of the structural member 100. In the examples of Figures 4A and 4B, the ridge portion 333 is provided continuously with the straight portion 23 of the top plate 20.

[0043] The vertical wall body 332 extends substantially vertically in a cross-sectional view of the structural member 100. The vertical wall body 332 may be substantially linear in a cross-sectional view of the structural member 100. The vertical wall body 332 may be parallel or non-parallel to the vertical direction in a cross-sectional view of the structural member 100. In this embodiment, the end of the vertical wall body 332 opposite to the top plate 20 is a free end. However, a flange portion (not shown) may be continuously provided at the end of the vertical wall body 332 opposite to the top plate 20.

[0044] The reinforcing member 50 is spaced vertically away from the top plate 20. The reinforcing member 50 is joined to the vertical wall 32. The reinforcing member 50 is joined to the vertical wall 32, for example, by welding. In this embodiment, the reinforcing member 50 is joined to the curved portion 321 of the vertical wall 32. However, the reinforcing member 50 may be joined to a portion of the vertical wall 32 other than the curved portion 321.

[0045] In this embodiment, the reinforcing member 50 is joined to the inner surface of the vertical wall 32. That is, the reinforcing member 50 is joined to the vertical wall 32 on the side of the top plate 20, beyond the free end or flange portion 324 of the vertical wall 322. In the example shown in Figures 4A and 4B, the end face of the reinforcing member 50 is joined to the inner surface of the vertical wall body 322 with abutting against it. However, the reinforcing member 50 may also be joined to the inner surface of the vertical wall body 322 with its end bent upward or downward.

[0046] In this embodiment, the reinforcing member 50 is joined to the curved portion 321 of the vertical wall 32, for example, by welding. When the height from the top plate 20 of the joint between the curved portion 321 and the reinforcing member 50 is h, the height h may be 20 mm or more. The height h is the vertical distance from the top plate 20 side end of the vertical wall 32 (curved portion 321) on the outer surface of the structural member 100 to the outer surface of the reinforcing member 50. The height h is less than or equal to the height H of the vertical wall 32 in the curved portion 321.

[0047] The reinforcing member 50 is also joined to the vertical wall 33. The reinforcing member 50 is joined to the vertical wall 33, for example, by welding.

[0048] In this embodiment, the reinforcing member 50 is joined to the inner surface of the vertical wall 33. That is, the reinforcing member 50 is joined to the vertical wall 33 on the side of the top plate 20, beyond the free end or flange portion (not shown) of the vertical wall 33. In the example shown in Figures 4A and 4B, the end face of the reinforcing member 50 is joined to the inner surface of the vertical wall body 332 in a butt-to-butt position. However, the reinforcing member 50 may also be joined to the inner surface of the vertical wall body 332 with its end bent upward or downward.

[0049] Although not shown in the illustrations, the reinforcing member 50 is also joined to the vertical wall 31 (Figures 2 and 3). The reinforcing member 50 can be joined to the vertical wall 31 in the same manner as the vertical walls 32 and 33. That is, the reinforcing member 50 may be joined with its end face abutting against the inner surface of the vertical wall 31, or it may be joined to the inner surface of the vertical wall 31 with its end bent upward or downward. The reinforcing member 50 is joined to the vertical wall 31, for example, by welding.

[0050] Returning to Figure 3, the curved portion 321 of the vertical wall 32 has a radius of curvature R. The radius of curvature R is the radius of curvature of the curved portion 321 in a plan view of the structural member 100. The radius of curvature R is, for example, 20 mm or more and 60 mm or less.

[0051] The radius of curvature R of the curved section 321 can be measured, for example, as follows: In a plan view of the structural member 100, evaluation points are placed at intervals of, for example, 5.0 mm on the end of the vertical wall 32 on the top plate 20 side, and the radius of curvature of the arc passing through three consecutive evaluation points can be taken as the radius of curvature of the vertical wall 32 at the positions of these evaluation points. For example, the curved section 321 is the range of the vertical wall 32 where evaluation points with a radius of curvature of 20 mm or more and 60 mm or less are consecutive. The average value of the radii of curvature of the evaluation points located within the curved section 321 can be taken as the radius of curvature R.

[0052] The structural member 100 is configured to satisfy any of the following conditions (1) to (6) with respect to the radius of curvature R [mm] of the curved portion 321, the height H [mm] of the vertical wall 32 in the curved portion 321 (Figures 4A and 4B), and the Vickers hardness Hv [HV] of the vertical wall 32. (1) The conditions 184 ≤ Hv < 243 and H ≥ 0.690R + 12.8 are satisfied. (2) The conditions are 243 ≤ Hv < 305 and H ≥ 0.611R + 9.6. (3) The end of the vertical wall 32 opposite to the top plate 20 is a free end (Figure 4A), and the conditions 305 ≤ Hv < 367 and H ≥ 0.425R + 8.5 are satisfied. (4) A flange portion 324 is provided continuously on the end of the vertical wall 32 opposite to the top plate 20 (Figure 4B), satisfying 305 ≤ Hv < 367 and H ≥ 0.244R + 19.4. (5) The end of the vertical wall 32 opposite to the top plate 20 is a free end, and the conditions 367≦Hv and H≧0.205R+12.5 are satisfied. (6) A flange portion 324 is provided continuously on the end of the vertical wall 32 opposite to the top plate 20, satisfying 367≦Hv and H≧0.125R+17.5.

[0053] The Vickers hardness Hv of the vertical wall 32 can be measured as follows: A test specimen having a cross-section along the thickness direction of the vertical wall 32 is cut from the curved section 321, and a Vickers hardness test is performed using this specimen in accordance with JIS Z 2244-1:2024. In the Vickers hardness test, the Vickers hardness is measured with a test force of 1 kgw (9.8 N) at a position 1 / 4 of the thickness from the surface of the vertical wall 32 (test specimen). The obtained Vickers hardness is the Vickers hardness Hv of the vertical wall 32.

[0054] The height H of the vertical wall 32 in the curved section 321 may be set to satisfy any of the above conditions (1) to (6), for example, 20 mm or more. The height H may be 25 mm or more. The height H may be 50 mm or less, or 45 mm or less.

[0055] The reinforcing member 40 is positioned on the mounting portion 13 side relative to the curved portion 321 of the vertical wall 32. The reinforcing member 40 may also be positioned near the through hole 131 of the mounting portion 13. Figure 5 schematically shows a cross-section of the structural member 100 at the position of the reinforcing member 40. Figure 5 shows a cross-section of the structural member 100 passing through the top plate 20, vertical walls 32, 33, and the reinforcing member 40.

[0056] Referring to Figure 5, the main body 41 of the reinforcing member 40 is separated vertically from the top plate 20. The reinforcing member main body 41 is joined to the vertical wall 32. The reinforcing member main body 41 is joined to the vertical wall 32, for example, by welding. The reinforcing member main body 41 may have a substantially straight shape in a cross-sectional view of the structural member 100. The reinforcing member main body 41 extends from the vertical wall 32 toward the vertical wall 33 in a cross-sectional view of the structural member 100. However, the reinforcing member main body 41 does not reach the vertical wall 33.

[0057] In this embodiment, the reinforcing member body 41 is joined to the inner surface of the vertical wall 32. That is, the reinforcing member body 41 is joined to the vertical wall 32 on the side of the top plate 20, beyond the free end or flange portion 324 (Figure 4B) of the vertical wall 32. In the example shown in Figure 5, the end face of the reinforcing member body 41 is joined to the inner surface of the vertical wall body 322 with abutting against it. However, the reinforcing member body 41 may also be joined to the inner surface of the vertical wall body 322 with its end bent upward or downward.

[0058] In the reinforcing member 40, the flange 42 is provided continuously with the reinforcing member body 41. The flange 42 protrudes from the reinforcing member body 41 toward the top plate 20. In this embodiment, the flange 42 is continuous with respect to the reinforcing member body 41 on the opposite side of the vertical wall 32. The flange 42 is positioned between the vertical wall 32 and the vertical wall 33. The flange 42 can face each of the vertical walls 32 and 33.

[0059] The flange 42 is joined to the top plate 20. The flange 42 is joined to the top plate 20, for example, by welding. In this embodiment, a recess 24 is formed in the top plate 20. The flange 42 may be joined to the top plate 20 at the location of the recess 24.

[0060] In this embodiment, the flange 42 is joined to the top plate 20 with its end face abutting against the top plate 20. However, the flange 42 may also be joined to the top plate 20 with its end bent.

[0061] [Method for manufacturing structural members] The structural member 100 can be manufactured by press forming of a metal sheet. Of the structural member 100, the curved portion 321 of the vertical wall 32 has a small radius of curvature R in plan view and is a relatively difficult part to form. In this embodiment, the method for forming this curved portion 321 will be described.

[0062] A press forming apparatus 60, as shown in Figures 6A and 6B, can be used to form the curved portion 321 of the vertical wall 32. By press forming the blank 70 using the press forming apparatus 60, the curved portion 321 of the vertical wall 32 (Figures 3 and 4A or 4B) can be formed. Referring to Figure 6A, the press forming apparatus 60 comprises a punch 61, a die 62, a blank holder 63, and at least one shim-shaped spacing holder 64.

[0063] The punch 61 and blank holder 63 are configured to be movable relative to the die 62 in the pressing direction P. The shim-shaped spacing holder 64 is positioned between the die 62 and the blank holder 63 to maintain a predetermined distance between the die 62 and the blank holder 63. The shim-shaped spacing holder 64 may also be positioned on the blank holder 63.

[0064] Figure 6B schematically shows the relationship between the punch 61, die 62, blank holder 63, and shim-shaped spacing holder 64 when viewed from the press direction P. Referring to Figure 6B, when viewed from the press direction P, the edge 611 of the punch 61 on the die 62 side (punch edge) extends along the edge 621 of the die 62 on the punch 61 side (die edge). When viewed from the press direction P, the punch edge 611 may be substantially parallel to the die edge 621 throughout its entirety.

[0065] The die edge 621 includes a curved portion 621a. The curved portion 621a curves convexly toward the punch 61 when viewed from the pressing direction P. The curved portion 621a is the part for forming the curved portion 321 (Figure 3, and Figure 4A or Figure 4B) of the vertical wall 32 of the structural member 100.

[0066] The blank holder 63 is positioned to correspond to a portion of the die edge 621. More specifically, when viewed from the pressing direction P, the blank holder 63 is positioned to correspond to the curved portion 621a of the die edge 621.

[0067] When viewed from the press direction P, the distance C between the punch-side edge (holder edge) 631 of the blank holder 63 and the die edge 621 changes along the die edge 622. The distance C between the holder edge 631 and the die edge 621 is smallest at the curved portion 621a. The distance C is the distance between the holder edge 631 and the die edge 621 on the perpendicular line to the extending direction of the die edge 621 when viewed from the press direction P. The minimum value of the distance C is, for example, smaller than the clearance between the punch edge 611 and the die edge 621 when viewed from the press direction P. The minimum value of the distance C may be 0 mm. In this case, when viewed from the press direction P, the holder edge 631 and the die edge 621 overlap at the point where they are closest to each other. When the minimum value of the distance C is greater than 0 mm, when viewed from the press direction P, the entire holder edge 631 is positioned on the opposite side of the punch 61 from the die edge 621. In this embodiment, the distance C between the holder edge 631 and the die edge 621 is minimized at the top of the curved portion 621a.

[0068] Viewed from the pressing direction P, the wire length of the holder edge 631 at the point where the gap C between it and the die edge 621 is smallest is, for example, 0.5 to 2.5 times the wire length of the curved portion 621a of the die edge 621. The wire length of the curved portion 621a may be the product of the clamping angle θ (rad) and the radius of curvature of the curved portion 621a. The clamping angle θ is the angle formed by the tangents at both ends of the curved portion 621a when viewed from the pressing direction P. The clamping angle θ may be 1 / 3π (rad) or more and 2 / 3π (rad) or less.

[0069] Figures 7A and 7B are schematic diagrams illustrating the operation of the press forming apparatus 60. Figures 7A and 7B show a cross-section of the press forming apparatus 60 along the pressing direction P at the position of the curved portion 621a of the die edge 621. Referring to Figure 7A, when forming the curved portion 321 of the vertical wall 32 of the structural member 100 (Figures 3 and 4A or 4B), first, the blank 70 is placed between the punch 61 and the blank holder 63 and the die 62. Then, the blank 70 is sandwiched and pressed between the die 62 and the blank holder 63. The portion of the blank 70 located on the punch 61 may be pressed down by a pad (not shown).

[0070] Referring to Figure 7B, with the blank 70 sandwiched between the die 62 and the blank holder 63, the die 62 and the punch 61 are brought relatively closer in the pressing direction P. This causes the blank 70 to be pushed towards the die 62 by the punch 61. If the flange portion 324 is not provided on the curved portion 321 of the vertical wall 32 (Figure 4A), as shown in Figure 7B, the pushing (forming) by the punch 61 is completed after the blank 70 has been completely pulled out from between the die 62 and the blank holder 63. If the flange portion 324 is provided on the curved portion 321 of the vertical wall 32 (Figure 4B), the pushing (forming) by the punch 61 is completed with a portion of the blank 70 remaining between the die 62 and the blank holder 63. This makes it possible to form the curved portion 321 of the vertical wall 32 of the structural member 100 (Figures 1 and 2).

[0071] When the blank 70 is pulled out from between the die 62 and the blank holder 63, the distance between the die 62 and the blank holder 63 is adjusted to the thickness s of the shim-shaped spacing retainer 64. The shim-shaped spacing retainer 64 is provided in the area of ​​the die 62 or the blank holder 63 other than the area where the blank 70 is clamped. When the thickness of the blank 70 is t, the thickness s of the shim-shaped spacing retainer 64 is set to satisfy 0.1t ≤ s < 1.0t. The thickness s may also satisfy 0.1t ≤ s ≤ 0.75t.

[0072] By using such a punch 61, die 62, blank holder 63, and shim-shaped spacing holder 64, a curved portion 321 having a height H that satisfies any of the above conditions (1) to (6) can be formed.

[0073] Specifically, when the blank 70 is pushed towards the die 62 by the punch 61 to perform forming, the blank 70 is pulled toward the die edge 621 (Figure 6B). The portion of the blank 70 that is pulled toward the curved portion 621a (Figure 6B) of the die edge 621 is stretched in the direction of the extension of the curved portion 621a as it is pulled toward the curved portion 621a, and its thickness decreases. However, in the press forming apparatus 60 described above, the distance C between the holder edge 631 and the die edge 621, as viewed from the pressing direction P, is minimized at the curved portion 621a. Therefore, compressive stress can be applied in the thickness direction by the die 62 and the blank holder 63 up to the vicinity of the curved portion 621a to the portion of the blank 70 that is pulled toward the curved portion 621a and experiences a decrease in thickness. This makes it possible to suppress the occurrence of cracks in the blank 70.

[0074] In addition, in forming using the press forming apparatus 60, when the blank 70 is pulled towards the die edge 621, the distance between the die 62 and the blank holder 63 is controlled to the thickness s of the shim-like spacing holding portion 64 that satisfies 0.1t ≤ s < 1.0t. This reduces the compressive stress and compressive strain acting on the blank 70 when the edge of the blank 70 is pulled out from between the die 62 and the blank holder 63. Therefore, the reduction in plate thickness caused by compressive stress can be mitigated.

[0075] As a result, the curved section 321, which has a relatively small radius of curvature R and a relatively large height H, is more easily formed without cracking.

[0076] Figures 8A and 8B are graphs showing the relationship between the height H and radius of curvature R of the curved portion 321 obtained from press forming analysis using commercially available analysis software (LS-DYNA, Ansys). Figure 8A shows the analysis results for each Vickers hardness Hv when the curved portion 321 is formed without leaving the flange portion 324, and Figure 8B shows the analysis results for each Vickers hardness Hv when the curved portion 321 is formed with the flange portion 324 remaining. Figures 8A and 8B show the height H and radius of curvature R at which forming became impossible when attempting to form the curved portion 321 using a normal press forming apparatus that does not have a shim-shaped spacing holder 64, and where the gap C between the holder edge 631 and the die edge 621 is not minimized at the curved portion 621a of the die edge 621. In this analysis, forming was deemed impossible when the damage value I, expressed by the following formula, at the free end of the vertical wall 32 or the tip of the flange portion 324 was greater than or equal to the standard value. The standard value for damage value I was determined by a separate stretch flange forming test, specifically a test in which a saddle-shaped molded product simulating a stretch flange shape was obtained by press forming, to confirm the formability of each material. The damage value I was defined as the value at which the material could not be formed in this stretch flange forming test.

[0077]

number

[0078] Referring to Figure 8A, when the curved portion 321 is formed by normal press forming without leaving the flange portion 324, the height H that could not be formed is expressed as a linear equation of the radius of curvature R for each Vickers hardness Hv as follows. • If Hv=184: H=0.690R+12.8 • If Hv=243: H=0.611R+9.6 • If Hv=305: H=0.425R+8.5 • If Hv=367: H=0.205R+12.5

[0079] Referring to Figure 8B, when the curved portion 321 is formed by normal press forming while leaving the flange portion 324 intact, the height H that could not be formed can be expressed as a linear equation of the radius of curvature R for each Vickers hardness Hv as follows. • If Hv=305: H=0.244R+19.4 • If Hv=367: H=0.125R+17.5

[0080] In contrast, when the curved portion 321 is formed by press forming in this embodiment using the punch 61, die 62, blank holder 63, and shim-shaped spacing holding portion 64, it has been confirmed that it is possible to form even a height H that could not be formed by normal press forming. In other words, in the structural member 100 according to this embodiment, the height H of the curved portion 321 can be set to satisfy any of the above conditions (1) to (6).

[0081] [effect] In the structural member 100 according to this embodiment, a curved portion 321 is provided in the vertical wall 32 at a position adjacent to the mounting portion 12 on the vehicle body side. The height H of the vertical wall 32 in the curved portion 321 is greater than that of a typical structural member. More specifically, the height H of the vertical wall 32 in the curved portion 321 is set to satisfy any of the above conditions (1) to (6). As a result, the rigidity of the curved portion 321 is improved, and when an external force is applied to the structural member 100, out-of-plane deformation of the structural member 100 is more easily suppressed in and around the curved portion 321. In particular, when a load in the longitudinal direction (reverse force) is applied to the mounting portion 11 on the wheel side, the structural member 100 becomes less susceptible to out-of-plane deformation. Therefore, the strength (yield strength) of the structural member 100 is more easily improved against external forces, such as a reverse force.

[0082] In the structural member 100 according to this embodiment, the height H of the vertical wall 32 in the curved portion 321 is large, thereby improving the rigidity of the curved portion 321. As a result of the improved rigidity of the curved portion 321 near the mounting portion 12, when a retraction force is applied to the mounting portion 11 on the wheel side, the load on the portion of the structural member 100 behind the curved portion 321 tends to increase, and torsional deformation may occur in that portion. In contrast, in this embodiment, a reinforcing member 40 is positioned on the mounting portion 13 side of the curved portion 321, in other words, behind the curved portion 321. In the reinforcing member 40, the reinforcing member body 41 is joined to the vertical wall 32, and the flange 42 is joined to the top plate 20 to suppress out-of-plane deformation of the top plate 20. As a result, when a retraction force is applied to the mounting portion 11, torsional deformation of the structural member 100 at a position behind the curved portion 321 is easily suppressed, and the entire structural member 100 becomes less prone to buckling.

[0083] In this embodiment, the flange 42 of the reinforcing member 40 is continuous with the reinforcing member body 41 on the opposite side of the vertical wall 32 and is joined to the top plate 20 at this position. In this case, when a receding force is applied to the mounting portion 11, the effect of the reinforcing member 40 in suppressing torsional deformation of the structural member 100 is improved. Therefore, buckling of the entire structural member 100 becomes less likely.

[0084] However, the flange 42 does not necessarily have to be continuous with the reinforcing member body 41 on the opposite side of the vertical wall 32. The flange 42 may be continuous with the reinforcing member body 41 on the mounting portion 11, 12 side, or on the mounting portion 13 side. Alternatively, the flange 42 may be continuous with the reinforcing member body 41 on the mounting portion 11, 12 side and / or on the mounting portion 13 side, in addition to the opposite side of the vertical wall 32. In this case, the flange 42 may extend uninterrupted from the opposite side of the vertical wall 32 to the mounting portion 11, 12 side and / or the mounting portion 13 side, or it may be divided between the opposite side of the vertical wall 32 and the mounting portion 11, 12 side and / or the mounting portion 13 side.

[0085] In this embodiment, in addition to the reinforcing member 40, a reinforcing member 50 is provided on the structural member 100. The reinforcing members 40 and 50 make it easier to suppress the overall torsional deformation of the structural member 100 when a receding force is applied to the mounting portion 11. As a result, buckling of the structural member 100 is less likely to occur, and the applied load is more easily transmitted to the structural member 100. Therefore, the structural member 100 can exhibit excellent strength against receding forces.

[0086] In this embodiment, the height H of the vertical wall 32 in the curved section 321 is relatively large. This makes it easier to join the reinforcing member 50 to the curved section 321. For example, the reinforcing member 50 can be welded to the curved section 321 while ensuring a height h of 20 mm or more from the top plate 20 at the joint between the curved section 321 and the reinforcing member 50. Thus, the joining work between the reinforcing member 50 and the curved section 321 is simplified.

[0087] However, the structural member 100 according to this embodiment does not necessarily have to include the reinforcing member 50. The structural member 100 may include the reinforcing member 40 but not the reinforcing member 50. Alternatively, the structural member 100 may not include either the reinforcing member 40 or 50.

[0088] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit. [Examples]

[0089] The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples.

[0090] [First Embodiment] To confirm the effects of this disclosure, a collision analysis was performed on a structural member having a shape similar to the structural member 100 according to the above embodiment, using commercially available structural analysis software (Abaqus, manufactured by Dassault Systèmes K.K.). More specifically, the load-bearing capacity of the structural member 100 against a load (backward force) directed from the front to the rear of the vehicle was investigated by varying the combination of the height H of the vertical wall 32 in the curved section 321, the radius of curvature R of the curved section 321, and the Vickers hardness Hv of the vertical wall 32. The conditions and results of this analysis are shown in Table 1 and Figure 9.

[0091] [Table 1]

[0092] In this analysis, the strength of the structural member 100 was evaluated by the ratio of the reaction force (recession load) F when a recession force is applied to the mounting part 11 to the plate thickness t of the vertical wall 32: F / t [kN / mm]. The evaluation standard value for F / t was set to 6.0, requiring that the plastic strain of the side frame component near the structural member 100 be less than 0.01 when a recession force is applied to the structural member 100. When F / t is 6.0 or greater, the structural member 100 is judged to meet the performance requirements for strength (indicated by "○" in Table 1), and when F / t is less than 6.0, the structural member 100 is judged to not meet the performance requirements for strength (indicated by "×" in Table 1).

[0093] Referring to Table 1 and Figure 9, it was confirmed that the structural member 100 satisfies the performance requirements when any of conditions (1) to (6) are satisfied. On the other hand, it was confirmed that the structural member 100 does not satisfy the performance requirements when none of conditions (1) to (6) are satisfied. Therefore, it can be said that when any of conditions (1) to (6) are satisfied, the deformation of the structural member 100 is suppressed when a setback force is applied, and the load-bearing capacity of the structural member 100 is improved.

[0094] [Second Example] A collision analysis was performed on a structural member having a shape similar to the structural member 100 according to the above embodiment, using commercially available structural analysis software (Abaqus, manufactured by Dassault Systèmes K.K.). More specifically, a load directed from the front to the rear of the vehicle (reverse force) was input to the mounting part 11, and the reaction force (reverse force load) to this load was investigated. The results of this analysis are shown in Figure 10.

[0095] Examples 1 to 3 all satisfy the above condition (3), with the height H of the vertical wall 32 in the curved section 321 being 30 mm, the radius of curvature R of the curved section 321 being 30 mm, and the Vickers hardness Hv of the vertical wall 32 being 305 HV. In Example 1, the analysis was performed on a structural member 100 that was not provided with reinforcing members 40 and 50. In Example 2, the analysis was performed on a structural member 100 that was provided with reinforcing member 40 but not with reinforcing member 50. In Example 3, the analysis was performed on a structural member 100 that was provided with both reinforcing members 40 and 50. The analysis conditions other than the presence or absence of reinforcing members 40 and 50 were common to Examples 1 to 3.

[0096] As shown in Figure 10, in Example 2, where reinforcing member 40 was provided on the structural member 100, the receding force load increased significantly compared to Example 1, where reinforcing members 40 and 50 were not provided on the structural member 100. In Example 3, where reinforcing members 40 and 50 were provided on the structural member 100, the receding force load was even greater than in Example 2.

[0097] This analysis confirmed that by providing a reinforcing member 40 on the mounting portion 13 side relative to the curved portion 321, torsional deformation of the structural member 100 is suppressed and the receding force load increases. Therefore, it can be said that the reinforcing member 40 makes it easier to suppress buckling of the structural member 100. Furthermore, it was confirmed that by providing reinforcing members 40 and 50, torsional deformation of the structural member 100 is further suppressed and the receding force load increases even further. In other words, by providing reinforcing member 50 in addition to reinforcing member 40, buckling of the structural member 100 is more easily suppressed. [Explanation of symbols]

[0098] 100: Structural member 11: Mounting section (first mounting section) 12: Mounting section (second mounting section) 13: Mounting section (third mounting section) 20: Tabletop 31: Vertical wall (First vertical wall) 32: Vertical wall (Second vertical wall) 321: Curved section 324: Flange section 33: Vertical wall (Third vertical wall) 40: Reinforcement member (first reinforcement member) 41: Reinforcement member body 42: Flange 50: Reinforcement member (second reinforcement member)

Claims

1. A structural component for a vehicle, A first mounting portion for attaching the wheels of the vehicle, A second mounting portion and a third mounting portion for attaching the vehicle body, respectively, A first vertical wall extending from the first mounting portion to the second mounting portion, A second vertical wall extending from the second mounting portion side to the third mounting portion side, A third vertical wall extending from the first mounting portion to the third mounting portion, A top plate continuous with each of the first vertical wall, the second vertical wall, and the third vertical wall, Equipped with, The second vertical wall is adjacent to the second mounting portion and includes a curved portion that curves inward in a concave shape when viewed in plan of the structural member. A structural member that satisfies any of the following conditions (1) to (6), where H [mm] is the height of the second vertical wall in the curved portion, R [mm] is the radius of curvature of the curved portion in a plan view of the structural member, and Hv [HV] is the Vickers hardness of the second vertical wall. (1) The conditions 184 ≤ Hv < 243 and H ≥ 0.690R + 12.8 are satisfied. (2) The conditions 243 ≤ Hv < 305 and H ≥ 0.611R + 9.6 are satisfied. (3) The end of the second vertical wall opposite to the top plate is a free end, and the conditions 305 ≤ Hv < 367 and H ≥ 0.425R + 8.5 are satisfied. (4) A flange portion is provided continuously at the end of the second vertical wall opposite to the top plate, satisfying 305 ≤ Hv < 367 and H ≥ 0.244R + 19.

4. (5) The end of the second vertical wall opposite to the top plate is a free end, and 367 ≤ Hv and H ≥ 0.205R + 12.5 are satisfied. (6) A flange portion is provided continuously at the end of the second vertical wall opposite to the top plate, satisfying 367 ≤ Hv and H ≥ 0.125R + 17.

5.

2. A structural member according to claim 1, further, The curved portion is provided with a first reinforcing member positioned on the third mounting portion side, The first reinforcing member is, A reinforcing member body is positioned opposite the top plate with a gap between them and is joined to the second vertical wall, A flange that protrudes from the reinforcing member body toward the top plate and is joined to the top plate, Structural members, including those mentioned above.

3. A structural member according to claim 2, The flange is a structural member that is continuous with respect to the reinforcing member body on the side opposite to the second vertical wall.

4. A structural member according to claim 2 or 3, further, A structural member comprising a second reinforcing member positioned on the first mounting side with respect to the first reinforcing member and joined to each of the first vertical wall, the second vertical wall, and the third vertical wall.

5. A structural member according to claim 4, The second reinforcing member is a structural member that is joined to the curved portion.

6. A structural member according to claim 5, A structural member wherein the height from the top plate of the joint between the curved portion and the second reinforcing member is 20 mm or more.

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