Side member outer and ladder frame

Abstract

The side member outer (12) of the ladder frame (100) comprises a top plate (121), ridge sections (122a, 122b), and vertical walls (123a, 123b). Multiple beads (124) are formed on the top plate (121). Each bead (124) has a concave shape on the inside of the side member outer (12) and extends in the longitudinal direction of the side member outer (12). The side member outer (12) satisfies either (1) or (2) below. (1) The sum of the depths (d1) of the multiple beads (124) is 14.0 times or more the thickness (t) of the top plate (121). (2) The sum of the depths (d1) of the multiple beads (124) is less than 14.0 times the thickness (t) of the top plate (121), and 0.085 × L0 ≤ L1 ≤ 0.500 × L0.

Description

Technical Field

[0001] This disclosure relates to a side member outer and a ladder frame.

Background Art

[0002] The body of an automobile or the like includes various skeletal members. As the skeletal members, for example, those formed by shaping a metal plate into a predetermined shape are used.

[0003] For example, Patent Document 1 discloses a bumper reinforcement which is one of the skeletal members for a vehicle body. In Patent Document 1, the cross section of the bumper reinforcement has an open cross section in a groove shape. In the top plate of the bumper reinforcement, a central groove portion arranged at the center of the width and small groove portions arranged on both sides of the central groove portion are formed. In Patent Document 1, by setting the depth of the central groove portion and the small groove portions, and the interval between the small groove portions and the ridge line portions on both sides of the top plate within a predetermined range, suppression of breakage caused by deformation occurring when the bumper reinforcement is subjected to an impact is attempted.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, the body of large vehicles such as SUVs and pickup trucks, which are intended to travel on rough roads, sometimes employs a frame component called a ladder frame. A ladder frame includes left and right side members and multiple cross members that connect the side members to each other. The side members generally include a side member inner and a side member outer. The side member outer is positioned outside the side member inner in the vehicle width direction. The side member outer is joined to the side member inner and together with the side member inner forms a closed cross section.

[0006] In recent years, with the shift towards electric vehicles (EVs), ladder frames are required to have high strength from the perspective of battery protection. More specifically, in order to protect the battery located between the left and right side members, the side members are required to exhibit high strength against the load applied during a side collision. On the other hand, the side members are also required to suppress the increase in the weight of the vehicle, so the application of high-strength materials to side members is expected to expand in the future. However, because high-strength materials have low ductility, when side members are made of high-strength material, they become more prone to fracture due to deformation during a collision. In particular, there is concern about fracture occurring in the outer side member, which is located on the load-input side. To suppress fracture of the outer side member, it is important to reduce the strain during a collision.

[0007] The object of this disclosure is to provide a side member outer for a ladder frame that can reduce strain during a collision. [Means for solving the problem]

[0008] The side member outer of the ladder frame according to this disclosure comprises a top plate, two ridge sections, and two vertical walls. The ridge sections are continuous with both side edges of the top plate. The vertical walls are continuous with the ridge sections on the opposite side of the top plate. Multiple beads are formed on the top plate. Each bead has a concave shape on the inside of the side member outer and extends in the longitudinal direction of the side member outer. The side member outer satisfies either (1) or (2) below. (1) The sum of the depths of the multiple beads is 14.0 times or more the thickness of the tabletop. (2) The sum of the depths of the multiple beads is less than 14.0 times the thickness of the top plate, and in the cross-section of the side member outer, when L0 is the distance between two ridges and L1 is the minimum of the distance from one ridge to the bead and the distance from the other ridge to the bead, then 0.085 × L0 ≤ L1 ≤ 0.500 × L0. [Effects of the Invention]

[0009] The ladder frame side member outer according to this disclosure can reduce strain during a collision. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a perspective view showing a schematic configuration of a ladder frame according to an embodiment. [Figure 2] Figure 2 is a cross-sectional view of a side member including a side member outer according to an embodiment. [Figure 3] Figure 3 is a schematic perspective view showing a side member including the side member outer according to the embodiment. [Figure 4] Figure 4 is a schematic perspective view showing a side member including the side member outer according to the embodiment. [Figure 5] Figure 5 is a schematic perspective view showing a side member including the side member outer according to the embodiment. [Figure 6] Figure 6 is a cross-sectional view of a side member different from that shown in Figure 2. [Figure 7] Figure 7 is a perspective view of the side member used in the three-point bending analysis. [Figure 8] Figure 8 is a perspective view of another side member used in the three-point bending analysis. [Figure 9] Figure 9 is a graph showing the maximum value of the maximum principal strain at the edge of the side member outer for each comparative example and each embodiment. [Modes for carrying out the invention]

[0011] The side member outer of the ladder frame according to this embodiment comprises a top plate, two ridge sections, and two vertical walls. The ridge sections are continuous with both side edges of the top plate. The vertical walls are continuous with the ridge sections on the opposite side of the top plate. Multiple beads are formed on the top plate. Each bead has a concave shape on the inside of the side member outer and extends in the longitudinal direction of the side member outer. The side member outer satisfies either (1) or (2) below (first configuration). (1) The sum of the depths of the multiple beads is 14.0 times or more the thickness of the tabletop. (2) The sum of the depths of the multiple beads is less than 14.0 times the thickness of the top plate, and in the cross-section of the side member outer, when L0 is the distance between two ridges and L1 is the minimum of the distance from one ridge to the bead and the distance from the other ridge to the bead, then 0.085 × L0 ≤ L1 ≤ 0.500 × L0.

[0012] When a load is applied to the ladder frame from the top plate side of the side member outer during a side collision of the vehicle body, buckling may occur in the center of the top plate in the closed cross-section formed by the side member outer and the side member inner. If the center of the top plate buckles, deformation occurs in the side member outer that reduces the angle between the top plate and each vertical wall, and strain concentrates on the ridges on both sides of the top plate, potentially causing fracture at the ridges. In contrast, in the side member outer according to the first configuration, multiple beads are formed on the top plate. These beads increase the rigidity of the top plate, making it less likely for buckling to occur in the center of the top plate. As a result, deformation that reduces the angle between the top plate and each vertical wall in the side member outer is less likely to occur, and circumferential strain at the ridges is reduced. Therefore, fracture of the side member outer at the ridges can be suppressed.

[0013] In particular, the side member outer according to the first configuration is configured to satisfy the above condition (1) or (2). In the case of (1), since the total depth of the plurality of beads is 14.0 times or more the thickness of the top plate, the effect of improving the rigidity of the top plate by the beads is relatively high, and buckling of the central portion of the top plate is more easily suppressed. Therefore, regardless of the arrangement of the beads, the circumferential strain in the ridge line portion is likely to be reduced, and breakage at the ridge line portion is also less likely to occur. On the other hand, in the case of (2), the total depth of the plurality of beads is less than 14.0 times the thickness of the top plate, and the effect of improving the rigidity of the top plate by the beads is smaller compared to the case of (1). However, in the case of (2), a relatively large distance is ensured between the bead on the top plate and the ridge line portion. For example, when the bead is located near the ridge line portion, when the bead deforms while being crushed during a side impact of the vehicle body, the bead enters the inside of the side member outer, and the ridge line portion is easily bent in a form induced by the entry of this bead. Therefore, strain is likely to concentrate on the ridge line portion. In contrast, in the case of (2), the distance L1 from the ridge line portion to the bead is 0.085 times or more the distance L0 between the two ridge line portions. Thereby, when a load is input from the top plate side of the side member outer during a side impact of the vehicle body, deformation is dispersed over a wider range between the bead and the ridge line portion, and bending deformation occurs with a larger bending radius. Therefore, it is possible to prevent an increase in the strain of the ridge line portion due to the deformation of the bead while ensuring the effect of suppressing buckling of the top plate by the bead. Therefore, the strain in the ridge line portion is reduced, and breakage at the ridge line portion is less likely to occur.

[0014] Thus, according to the side member outer of the ladder frame according to the first configuration, the strain of the ridge line portion during a collision can be reduced. Therefore, breakage of the side member outer at the ridge line portion is less likely to occur.

[0015] The side member outer according to the first configuration can have a tensile strength of 780 MPa or more (second configuration). [[ID=!0]]

[0016] [[ID=!1]] [[ID=!2]]In the first or second configuration, the side member outer may have a plate thickness of 2.0 mm or more (third configuration). [[ID=!3]]

[0017] In the side member outer according to any one of the first to third configurations, the depth of each of the plurality of beads may be greater than 15 mm (fourth configuration).

[0018] The ladder frame according to the embodiment includes two side members and a plurality of cross members. The two side members each include a side member inner and a side member outer according to any one of the first to fourth configurations. The plurality of cross members connect the two side members (fifth configuration).

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In these drawings, the same or corresponding configurations are denoted by the same reference numerals, and the same description will not be repeated.

[0020] [Ladder Frame] FIG. 1 is a perspective view showing a schematic configuration of a ladder frame 100 according to an embodiment. Referring to FIG. 1, the ladder frame 100 is used for a vehicle body such as an automobile. The ladder frame 100 includes two side members 10 and a plurality of cross members 20.

[0021] The side member 10 is a member generally also referred to as a side rail in the ladder frame. The two side members 10 are arranged side by side in the left - right direction (vehicle width direction) of the vehicle body. Each of the side members 10 extends substantially in the front - rear direction (vehicle length direction) of the vehicle body. Each of the side members 10 can include a front portion 10F, an intermediate portion 10M, and a rear portion 10R. The front portion 10F is arranged forward of the rear portion 10R in the vehicle length direction. The intermediate portion 10M extends from the front portion 10F toward the rear portion 10R and connects the front portion 10F and the rear portion 10R.

[0022] Each of the side members 10 includes a side member inner 11 and a side member outer 12. The side member outer 12 is arranged outside the side member inner 11 in the vehicle width direction. The side member inner 11 and the side member outer 12 each extend in the longitudinal direction of the side member 10.

[0023] Multiple cross members 20 are arranged side by side in the vehicle length direction. Each cross member 20 extends substantially in the vehicle width direction. Each cross member 20 connects two side members 10. Each cross member 20 is joined to the side members 10, for example, by welding.

[0024] [Side Member] Figure 2 is a cross-sectional view of the side member 10 (section II-II in Figure 1). Figure 2 shows the cross-section of the side member 10 at the intermediate section 10M. The cross-section of the side member 10 refers to the cross-section obtained when the side member 10 is cut by a plane perpendicular to the longitudinal direction of the side member 10. Similarly, the cross-sections of the side member inner 11 and side member outer 12 included in the side member 10 refer to the cross-sections obtained when the side member 10 is cut by a plane perpendicular to the longitudinal direction of the side member 10 (the longitudinal direction of the side member inner 11 and side member outer 12), respectively.

[0025] Referring to Figure 2, the side member inner 11 is formed from a metal sheet. Preferably, the side member inner 11 is formed from a steel sheet. Typically, the side member inner 11 is formed by cold pressing a metal sheet. That is, the side member inner 11 is a cold-formed product. The side member inner 11 may include a top plate 111, two ridge sections 112a, 112b, and two vertical walls 113a, 113b.

[0026] With the side member 10 incorporated into the vehicle body, the top plate 111 is positioned inward in the vehicle width direction relative to the vertical walls 113a and 113b. The vertical walls 113a and 113b are positioned substantially aligned in the vertical direction (vehicle height direction) of the vehicle body. In a cross-sectional view of the side member inner 11, the vertical walls 113a and 113b may be positioned substantially parallel or non-parallel.

[0027] The ridge sections 112a and 112b are corner sections between the top plate 111 and the vertical walls 113a and 113b, respectively. The ridge sections 112a and 112b can have a substantially arc shape in cross-sectional view of the side member inner 11. The ridge sections 112a and 112b are continuous with both side edges of the top plate 111. The vertical walls 113a and 113b are continuous with the ridge sections 112a and 112b, respectively, on the opposite side of the top plate 111.

[0028] The side member outer 12 is formed from a metal sheet. Preferably, the side member outer 12 is formed from a steel sheet. The thickness of the side member outer 12 may be the same as or different from the thickness of the side member inner 11. The side member outer 12 is typically formed by cold pressing a metal sheet. That is, the side member outer 12 is a cold-formed product.

[0029] The side member outer 12 includes a top plate 121, two ridge sections 122a and 122b, and two vertical walls 123a and 123b.

[0030] With the side member 10 incorporated into the vehicle body, the top plate 121 is positioned outward in the vehicle width direction relative to the vertical walls 123a and 123b. The vertical walls 123a and 123b are positioned substantially aligned in the vehicle height direction. In a cross-sectional view of the side member outer 12, the vertical walls 123a and 123b may be positioned substantially parallel or non-parallel.

[0031] The ridge sections 122a and 122b are corner sections between the top plate 121 and the vertical walls 123a and 123b, respectively. The ridge sections 122a and 122b may have a substantially arc shape in cross-sectional view of the side member outer 12. The radius of curvature (inside of the bend) of the ridge sections 122a and 122b may be between 0.1 mm and 20.0 mm. The ridge sections 122a and 122b are continuous with both side edges of the top plate 121. The vertical walls 123a and 123b are continuous with the ridge sections 122a and 122b on the opposite side of the top plate 121, respectively.

[0032] With the side member 10 assembled into the vehicle body, the top plate 121 of the side member outer 12 faces the top plate 111 of the side member inner 11 in the vehicle width direction. The vertical wall 123a of the side member outer 12 is joined to the vertical wall 113a of the side member inner 11. The vertical wall 123b of the side member outer 12 is joined to the vertical wall 113b of the side member inner 11. As a result, the side member outer 12, together with the side member inner 11, forms a closed cross-section.

[0033] The vertical walls 123a and 123b of the side member outer 12 are joined to the vertical walls 113a and 113b of the side member inner 11, for example, at their tip ends (free ends). The vertical walls 123a and 123b may be joined to the vertical walls 113a and 113b on the outside of the side member inner 11, or they may be joined to the vertical walls 113a and 113b on the inside of the side member inner 11. The vertical walls 123a and 123b are joined to the vertical walls 113a and 113b, respectively, for example, by welding.

[0034] Continuing to refer to Figure 2, multiple beads 124 are formed on the top plate 121 of the side member outer 12. In this embodiment, two beads 124 are provided on the top plate 121. Each bead 124 has a concave shape on the inside of the side member outer 12. Each bead 124 extends in the longitudinal direction of the side member outer 12. The multiple beads 124 are arranged in the vehicle height direction in a cross-sectional view of the side member outer 12.

[0035] The top plate 121 includes a plurality of flat sections 121a, 121b, and 121c. Flat section 121a is the portion of the top plate 121 between the bead 124 closest to the edge section 122a and the edge section 122a. Flat section 121b is the portion of the top plate 121 between the bead 124 closest to the edge section 122b and the edge section 122b. Flat section 121c is the portion of the top plate 121 between adjacent beads 124 in a cross-sectional view of the side member outer 12. Each of the flat sections 121a, 121b, and 121c can have a substantially straight shape in a cross-sectional view of the side member outer 12.

[0036] Each bead 124 includes a bottom portion 1241, side portions 1242, 1243, and edge portions 1244, 1245. The bottom portion 1241 is positioned inside the side member outer 12 relative to the flat portions 121a, 121b, 121c. The side portions 1242, 1243 extend from the bottom portion 1241 toward the flat portions 121a, 121b, 121c in a cross-sectional view of the side member outer 12. In a cross-sectional view of the side member outer 12, one side portion 1242 is positioned toward the ridge portion 122a relative to the other side portion 1243. The bottom portion 1241 and the side portions 1242, 1243 may be substantially straight in a cross-sectional view of the side member outer 12. Edges 1244 and 1245 are continuous with side portions 1242 and 1243, respectively, on the opposite side of the bottom portion 1241. Edge 1244 is continuous with flat portion 121a or 121c. Edge 1245 is continuous with flat portion 121b or 121c. Edges 1244 and 1245 may have a substantially arc shape in cross-sectional view of the side member outer 12. The radius of curvature (inside the bend) of edges 1244 and 1245 is, for example, 0.1 mm or more and 20.0 mm or less.

[0037] Each bead 124 has a depth d1. In the cross-section of the side member outer 12, when the direction perpendicular to the straight line (the dashed line in Figure 2) connecting the boundary between one edge 1244 of the bead 124 and the flat portion 121a or 121c of the top plate 121, and the boundary between the other edge 1245 of the bead 124 and the flat portion 121b or 121c of the top plate 121 is defined as the depth direction, the distance in the depth direction from this straight line to the surface of the bead 124 is defined as the depth d1 of each bead 124. The boundary between the edge 1244 and the flat portion 121a or 121c is typically a radius end on the outer surface of the bend of the edge 1244, and is located on the opposite side of the side portion 1242. The boundary between the edge portion 1245 and the flat portion 121b or 121c is typically a radius end on the outer surface of the bend of the edge portion 1245, located on the opposite side of the side portion 1243.

[0038] The depth d1 of each bead 124 is, for example, 3.0 times or more the thickness t of the top plate 121. The depth d1 of each bead 124 may be 15.0 times or less the thickness t of the top plate 121. The depth d1 of each bead 124 is, for example, greater than 15 mm. The depth d1 of each bead 124 may be 20 mm or more. The depth d1 of each bead 124 may be the same as or different from the depth d1 of other beads 124.

[0039] The thickness t of the top plate 121 is the thickness measured at one of the flat sections 121a, 121b, or 121c. The thickness t is measured at one of the flat sections 121a, 121b, or 121c at a position at least 5.0 mm away from each bead 124 in the vehicle height direction. The thickness t is, for example, 2.0 mm or more, and may be 2.3 mm or more. The thickness t is preferably greater than 2.3 mm, and more preferably 2.6 mm or more. The thickness t may be 6.0 mm or less, for example 5.0 mm or less.

[0040] Each bead 124 has a width w1. The width w1 is the straight-line distance in the cross-section of the side member outer 12 from the boundary between one edge 1244 and the flat portion 121a or 121c to the boundary between the other edge 1245 and the flat portion 121b or 121c of the top plate 121. Although not particularly limited, the w1 of each bead 124 is, for example, 10 mm or more. The w1 of each bead 124 may be 100 mm or less. The width w1 of each bead 124 may be the same as or different from the width w1 of the other beads 124.

[0041] The side member outer 12 according to this embodiment is configured to satisfy either (1) or (2) below. (1) The sum of the depths d1 of the multiple beads 124, D1, is 14.0 times or more the thickness t of the top plate 121. (2) The sum of the depths d1 of the multiple beads 124, D1, is less than 14.0 times the thickness t of the top plate 121, and 0.085 × L0 ≤ L1 ≤ 0.500 × L0.

[0042] Regarding (2) above, L0 is the distance between the two ridge sections 122a and 122b in the cross-section of the side member outer 12. More specifically, in the cross-section of the side member outer 12, L0 is the straight-line distance from the boundary between one ridge section 122a and the flat section 121a of the top plate 121 to the boundary between the other ridge section 122b and the flat section 121b of the top plate 121. The boundary between the ridge section 122a and the flat section 121a is typically the radius end point on the flat section 121a side on the outer surface of the bent ridge section 122a. The boundary between the ridge section 122b and the flat section 121b is typically the radius end point on the flat section 121b side on the outer surface of the bent ridge section 122b. L0 may be, for example, 100 mm or more and 300 mm or less. In the cross-section of the side member outer 12, when the length of the side member outer 12 in a direction perpendicular to the straight line connecting the boundary between the ridge portion 122a and the flat portion 121a, and the boundary between the ridge portion 122b and the flat portion 121b, is defined as the height H of the side member outer 12, the height H of the side member outer 12 may be 20 mm or more and 100 mm or less.

[0043] L1 is the minimum of the distance from one of the ridge sections 122a and 122b to the bead 124 and the distance from the other ridge section 122a and 122b to the bead 124 in the cross-section of the side member outer 12. That is, if the distance from ridge section 122a to the bead 124 is smaller than the distance from ridge section 122b to the bead 124, then the distance from ridge section 122a to the bead 124 is set as L1, and if the distance from ridge section 122b to the bead 124 is smaller than the distance from ridge section 122a to the bead 124, then the distance from ridge section 122b to the bead 124 is set as L1. If the distance from the ridge portion 122a to the bead 124 and the distance from the ridge portion 122b to the bead 124 are equal, then either the distance from the ridge portion 122a to the bead 124 or the distance from the ridge portion 122b to the bead 124 may be used as L1.

[0044] In this embodiment, the distance from the ridge portion 122a to the bead 124 is the straight-line distance from the boundary between the ridge portion 122a and the flat portion 121a, as viewed in cross-section of the side member outer 12, to the boundary between the edge 1244 of the bead closest to the ridge portion 122a among the multiple beads 124 and the flat portion 121a. The distance from the ridge portion 122b to the bead 124 is the straight-line distance from the boundary between the ridge portion 122b and the flat portion 121b, as viewed in cross-section of the side member outer 12, to the boundary between the edge 1245 of the bead closest to the ridge portion 122b among the multiple beads 124 and the flat portion 121b.

[0045] The side member outer 12 can have a tensile strength of 780 MPa or more. Preferably, the side member outer 12 has a tensile strength of 980 MPa or more, and more preferably, a tensile strength of 1180 MPa or more. The tensile strength of the side member outer 12 may be the same as or different from the tensile strength of the side member inner 11. The tensile strength of the side member outer 12 can be measured by performing a tensile test in accordance with JIS Z 2241:2022 using a test piece obtained from the flat portion 121c located in the center of the top plate 121 in the vehicle height direction.

[0046] If it is difficult to obtain a test specimen for tensile testing from the top plate 121, the Vickers hardness of the top plate 121 may be measured, and the tensile strength of the side member outer 12 may be determined based on this Vickers hardness. Specifically, a test specimen is obtained from the flat section 121c located in the center of the top plate 121 in the vehicle height direction. Then, using this test specimen, a Vickers hardness test is performed in accordance with JIS Z 2244:2020 to measure the Vickers hardness of the flat section 121c. In the Vickers hardness test, the test force is set to 1 kgw (9.8 N), and the Vickers hardness is measured at 1 mm intervals along the longitudinal direction of the side member outer 12, at a position 1 / 4 of the plate thickness from the surface of the flat section 121c in the cross section of the flat section 121c. The average value of these Vickers hardnesses can be used as the Vickers hardness of the top plate 121. If the Vickers hardness of the top plate 121 is 240 HV or more and less than 300 HV, the side member outer 12 has a tensile strength of 780 MPa or more. If the Vickers hardness of the top plate 121 is 300 HV or more and less than 360 HV, the side member outer 12 has a tensile strength of 980 MPa or more. If the Vickers hardness of the top plate 121 is 360 HV or more, the side member outer 12 has a tensile strength of 1180 MPa or more.

[0047] Figures 3 to 5 are schematic perspective views showing the side member 10 including the side member outer 12 according to this embodiment. The side member outer 12 may be straight when viewed from the vertical wall 123a side (along the vehicle height direction), as shown in Figures 3 and 4, or it may be curved when viewed from the vertical wall 123a side, as shown in Figure 5.

[0048] Referring to Figures 3 to 5, the multiple beads 124 extend in the longitudinal direction of the side member outer 12. The beads 124 are provided on the top plate 121 so as to extend, for example, through the center of the longitudinal direction of the side member outer 12. Preferably, the beads 124 are provided at least between the joining positions of the cross member 20 to the side member 10. The beads 124 may be provided along the entire length of the top plate 121 in the longitudinal direction of the side member outer 12 as shown in Figure 3, or they may be provided on a part of the top plate 121 as shown in Figures 4 and 5. Preferably, the beads 124 have a length of 100 mm or more in the longitudinal direction of the side member outer 12. In other words, it is preferable that the side member outer 12 is configured to satisfy the above condition (1) or (2) in a range of 100 mm or more in its longitudinal direction.

[0049] [effect] In the side member outer 12 according to this embodiment, a plurality of beads 124 are formed on the top plate 121. This increases the rigidity of the top plate 121. Therefore, when a load is applied to the side member 10 from the top plate 121 side of the side member outer 12 during a vehicle collision, buckling of the central part of the top plate 121 in the cross-section of the side member outer 12 becomes less likely. As a result, deformation that reduces the angle between the top plate 121 and the vertical walls 123a and 123b in the side member outer 12 becomes less likely, and circumferential strain at the ridges 122a and 122b is reduced. Consequently, fracture of the side member outer 12 at the ridges 122a and 122b is more easily suppressed.

[0050] Furthermore, the side member outer 12 according to this embodiment is configured to satisfy the above-mentioned conditions (1) or (2). That is, the total depth D1 of the beads 124 provided on the top plate 121 is 14.0 times or more the thickness t of the top plate 121, or even if the total depth D1 of the beads 124 is less than 14.0 times the thickness t of the top plate 121, the beads 124 are arranged to satisfy 0.085 × L0 ≤ L1 ≤ 0.500 × L0. When the total depth D1 of the beads 124 is 14.0 times or more the thickness t, the rigidity of the top plate 121 is relatively high, and buckling of the top plate 121 is easily suppressed. Therefore, regardless of the arrangement of the beads 124, the circumferential strain of the ridge portions 122a and 122b during impact is easily reduced, and fracture of the side member outer 12 at the ridge portions 122a and 122b is less likely to occur.

[0051] On the other hand, if the sum of the depths d1 of the beads 124, D1, is less than 14.0 times the plate thickness t, the effect of the beads 124 on improving the rigidity of the top plate 121 will be small. However, since the distance L1 between the ridge portion 122a or 122b and the bead 124 closest to it is 0.085 times or more the distance L0 between the ridge portions 122a and 122b, when the vehicle body collides, the deformation is distributed over a wider area between the beads 124 and the ridge portions 122a and 122b, allowing for bending deformation with a larger bending radius. Therefore, bending of the ridge portions 122a and 122b caused by the deformation of the beads 124 is less likely to occur, and the concentration of strain in the ridge portions 122a and 122b is mitigated. Therefore, the circumferential strain of the ridge portions 122a and 122b during impact is easily reduced, and fracture of the side member outer 12 at the ridge portions 122a and 122b is less likely to occur. The distance L1 may be less than 0.500 times the distance L0 (L1 < 0.500 × L0). Preferably, the distance L1 is 0.400 times or less the distance L0 (L1 ≤ 0.400 × L0), and more preferably 0.300 times or less the distance L0 (L1 ≤ 0.300 × L0).

[0052] Generally, thin-walled automotive parts have low rigidity and are prone to bending when subjected to external forces, while thick-walled automotive parts have high rigidity and are less prone to bending when subjected to external forces. When the plate thickness of an automotive part is small, even if the distance from the ridge to the bead is not ensured when creating a bead on the top plate, the portion of the top plate from the ridge to the bead is prone to bending, and it is presumed that the ridge will deform with a relatively large bending radius. On the other hand, the side member outer 12 according to this embodiment is included in the ladder frame 100, and therefore typically has a relatively thick plate thickness of 2.0 mm or more. When the side member outer 12 is thick in this way, the portion of the top plate 121 between the ridges 122a, 122b and the bead 124 is less prone to bending compared to the case of a thin-walled part, and the bending radius of the ridges 122a, 122b when deformed is also likely to be smaller. Therefore, in this embodiment, by ensuring a sufficient distance L1 from the ridges 122a and 122b to the bead 124, the bending radius during deformation of the ridges 122a and 122b is increased. More specifically, by making the distance L1 between the ridge 122a or 122b and the bead 124 closest to it 0.085 times or more the distance L0 between the ridges 122a and 122b, when a load is applied to the side member outer 12 from the top plate 121 side, the top plate 121 deforms over a wider area near the ridges 122a and 122b. As a result, even with a side member outer 12 having a plate thickness of 2.0 mm or more, deformation with a large bending radius can be produced from the ridges 122a and 122b to the top plate 121. Therefore, strain is less likely to concentrate on the ridges 122a and 122b, and fracture of the ridges 122a and 122b is less likely to occur.

[0053] As described above, the side member outer 12 is included in the ladder frame 100 and therefore often has a relatively thick plate thickness of 2.0 mm or more. In this case, it is preferable that the depth d1 of each bead 124 is greater than 15 mm. If the depth d1 differs among the beads 124, it is preferable that the shallowest bead 124 among the multiple beads 124 has a depth d1 greater than 15 mm. By providing beads 124 greater than 15 mm on the top plate 121 of the thick side member outer 12, the rigidity of the top plate 121 can be effectively increased. As a result, deformation of the top plate 121 becomes less likely, and deformation of the ridge sections 122a and 122b that are continuous with the top plate 121 also becomes less likely. Therefore, strain concentration on the ridge sections 122a and 122b is less likely to occur, and fracture of the ridge sections 122a and 122b is less likely to occur.

[0054] In the side member outer 12 according to this embodiment, two beads 124 are formed on the top plate 121. However, as shown in Figure 6, three or more beads 124 may be formed on the side member outer 12. Even in this case, the side member outer 12 satisfies condition (1) or (2) regarding the depth d1 and arrangement of the beads 124.

[0055] In the side member outer 12 according to this embodiment, each bead 124 includes side portions 1242 and 1243. From the viewpoint of suppressing buckling of the central portion of the top plate 121, it is preferable that in the cross-section of the side member outer 12, at least the side portion of the side portions 1242 and 1243 located on the central portion side of the top plate 121 is substantially straight. More preferably, in the cross-section of the side member outer 12, both side portions 1242 and 1243 are substantially straight. When the side portion 1242 is substantially straight in the cross-section of the side member outer 12, from the viewpoint of effectively increasing the rigidity of the top plate 121, it is preferable that the angle between the side portion 1242 and the adjacent flat portion 121a or 121c of the top plate 121 is 120° or less. When the side portion 1243 of the side member outer 12 is substantially straight in cross-section, it is preferable that the angle between the side portion 1243 and the adjacent flat portion 121b or 121c of the top plate 121 is 120° or less, from the viewpoint of effectively increasing the rigidity of the top plate 121. The angle between each of the side portions 1242 and 1243 and the adjacent flat portion among the flat portions 121a, 121b, and 121c is, for example, 90° or more.

[0056] According to the side member outer 12 of this embodiment, the strain during impact at the ridge portions 122a and 122b is reduced, making fracture at the ridge portions 122a and 122b less likely. Therefore, a high-strength material can be applied to the side member outer 12. For example, the side member outer 12 can have a tensile strength of 780 MPa or more. Preferably, the side member outer 12 has a tensile strength of 980 MPa or more, more preferably 1180 MPa or more. In this case, the side member outer 12 can be made thinner and lighter while ensuring the necessary strength.

[0057] 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]

[0058] The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples.

[0059] To confirm the effects of this disclosure, a three-point bending analysis was performed on the side members 10 and 10A shown in Figures 7 and 8 using commercially available analysis software (LS-DYNA, manufactured by ANSYS). The side members 10 and 10A are long, closed-section members that mimic actual side members.

[0060] As shown in Figures 7 and 8, the side members 10 and 10A include a side member inner 11 and a side member outer 12. In the side member 10 shown in Figure 7, a plurality of beads 124 are formed on the top plate 121 of the side member outer 12, similar to the embodiment described above. On the other hand, in the side member 10A shown in Figure 8, no beads 124 are formed on the top plate 121 of the side member outer 12.

[0061] As shown in Figures 7 and 8, in this analysis, both longitudinal ends of the side members 10 and 10A were supported from the side of the side member inner 11 by support columns 30, and a pole (not shown) was pushed 50 mm into the side members 10 and 10A from the top plate 121 side of the side member outer 12. The maximum principal strain (circumferential strain) of the ridges 122a and 122b of the side member outer 12 at that time was evaluated. The diameter of the pole was 150 mm, and the radius of each support column 30 was 50 mm. The material of the side member inner 11 was a steel plate with a tensile strength of 1180 MPa and a plate thickness of 2.9 mm, and the material of the side member outer 12 was a steel plate with a tensile strength of 1180 MPa and a plate thickness of 2.9 mm.

[0062] In this analysis, the maximum principal strains of the ridge sections 122a and 122b were evaluated by changing the conditions for the number, size, and arrangement of beads 124. The conditions and evaluation results for beads 124 are shown in Table 1 and Figure 9.

[0063] [Table 1]

[0064] Referring to Table 1, in Comparative Example 1, no bead 124 is formed on the top plate 121 of the side member outer 12 (Figure 8). In contrast, in Comparative Example 2 and Examples 1 to 6, multiple beads 124 are formed on the top plate 121 of the side member outer 12 (Figure 7). In each of Comparative Example 2 and Examples 1 to 6, multiple beads 124 of the same depth d1 are provided on the top plate 121. In Comparative Example 2, the sum of the depths d1 of the beads 124, D1, is less than 14.0 times the plate thickness t, while L1 / L0 is less than 0.085, and neither of the conditions (1) and (2) described in the above embodiment is satisfied. As shown in Table 1 and Figure 9, in Comparative Example 2, the maximum value of the maximum principal strain of the ridge portions 122a and 122b of the side member outer 12 was greater than in Comparative Example 1.

[0065] In Examples 1 to 3, the sum of the depths d1 of the beads 124, D1, is less than 14.0 times the plate thickness t, while L1 / L0 is 0.085 or greater, thus satisfying the condition in (2) above. In Examples 1 to 3, the maximum values ​​of the maximum principal strains at the edges 122a and 122b of the side member outer 12 were significantly reduced compared to Comparative Examples 1 and 2.

[0066] In Examples 4 to 6, the sum of the depths d1 of the beads 124, D1, was 14.0 times or more the plate thickness t, thus satisfying the condition in (1) above. In Examples 4 to 6, the maximum value of the maximum principal strain in the ridge portions 122a and 122b of the side member outer 12 was significantly reduced compared to Comparative Examples 1 and 2. In particular, in Examples 4 and 6, the maximum value of the maximum principal strain was reduced compared to Comparative Examples 1 and 2, even though L1 / L0 was less than 0.085. That is, if the sum of the depths d1 of the beads 124, D1, is 14.0 times or more the plate thickness t, the strain in the ridge portions 122a and 122b can be reduced even when L1 / L0 is small.

[0067] This analysis confirmed that by forming multiple beads 124 on the top plate 121 of the side member outer 12 in such a way as to satisfy the conditions (1) or (2) above, it is possible to reduce the strain on the ridges 122a and 122b during a collision. [Explanation of symbols]

[0068] 100: Ladder Frame 10: Side Member 11: Side Member Inner 12: Side Member Outer 121: Top plate 122a, 122b: Ridgeline part 123a,123b: Vertical wall 124: Bead 20: Crossmember

Claims

1. It is the outer side member of the ladder frame, The tabletop and Two continuous ridge lines on both side edges of the aforementioned top plate, On the opposite side of the top plate, there are two vertical walls that are continuous with the ridge line, Equipped with, The aforementioned side member outer has a plate thickness of 2.0 mm or more. Each of the top plates has a concave shape on the inside of the side member outer and has a plurality of beads formed thereon that extend in the longitudinal direction of the side member outer. A side member outer that satisfies either (1) or (2) below. (1) The sum of the depths of the multiple beads is 14.0 times or more the thickness of the top plate. (2) The sum of the depths of the plurality of beads is less than 14.0 times the thickness of the top plate, and in the cross-section of the side member outer, when L0 is the distance between the two ridges and L1 is the minimum value of the distance from one of the ridges to the bead and the distance from the other of the ridges to the bead, then 0.085 × L0 ≤ L1 ≤ 0.500 × L0.

2. A side member outer according to claim 1, The side member outer is a side member outer having a tensile strength of 780 MPa or more.

3. A side member outer according to claim 1, The depth of each of the aforementioned multiple beads is greater than 15 mm for the side member outer.

4. It is a ladder frame, Two side members, each including a side member inner and a side member outer as described in any one of claims 1 to 3, Multiple cross members connecting the two side members, A ladder frame equipped with [a specific feature].

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