Open section bumper reinforcement

Abstract

The present invention comprises a top panel (210), two walls (211, 222), and two ridge sections (231, 232), the tensile strength of the top panel (210) and the walls (221, 222) is 1470 MPa or greater, each of the two ridge sections (231, 232) extends in the lengthwise direction of the top panel (210) between the top panel (210) and each of the walls (221, 222), a cross section in the center of the lengthwise direction is a trench-shaped open cross section, the top panel (210) comprises, at the widthwise center thereof, a center trench (260) extending in the lengthwise direction in the cross section, the top panel (210) comprises small trenches between the center trench (260) and each of the ridge sections (231, 232) in the cross section, the depth of trench in the center is 15-25 times inclusive of the sheet thickness of the top panel (210) in the cross section, the depth of the small trenches (240, 250) is 2-13 times inclusive of the sheet thickness of the top panel (210), and the spacing between the small trenches (240, 250) and the ride sections (231, 232) is smaller than or equal to 30 times of the sheet thickness of the top panel (210).

Description

[Technical Field]

[0001] The present disclosure relates to an open section bumper reinforcement. This application claims priority based on Japanese Patent Application No. 2022-006845, filed on January 20, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conventionally, automotive frame members have been made by processing metal plate-shaped members into a predetermined cross-sectional shape. When a product having a frame member is subjected to a collision impact, the frame member is required to achieve a desired deformation mode and efficiently absorb the impact. For example, Patent Document 1 discloses a bumper reinforcement material that has a small groove and a large groove surrounding the small groove for the purpose of increasing the peak load and increasing the amount of energy absorption.

[0003] Such frame members are required to be lightweight and have sufficient load-bearing capacity. In recent years, with the stricter collision safety standards for automobiles and other vehicles and the stricter fuel economy regulations, there is a demand for high-strength, lightweight frame members. In order to meet these demands, development is underway to develop lightweight frame members that use so-called high-strength materials with high tensile strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5329188 Summary of the Invention [Problem to be solved by the invention]

[0005] The bumper reinforcement used for a vehicle bumper absorbs impact by deforming members during a vehicle collision. When the bumper reinforcement breaks, it can no longer absorb impact, so the bumper reinforcement is required not to break until a certain amount of deformation occurs during a vehicle collision. Using a high-strength material for the member can enhance the performance of the member. However, while using a high-strength material enables the member to be both high-strength and lightweight, there is a problem that high-strength materials have poor ductility and the member may break during deformation. For this reason, there were limitations when using high-strength materials for bumper reinforcements.

[0006] The present disclosure has been made in view of the above, and an object thereof is to provide an open-section bumper reinforcement capable of suppressing breakage caused by deformation that occurs when a member is impacted.

Means for Solving the Problem

[0007] (1) The open-section bumper reinforcement according to one aspect of the present disclosure includes a top plate, two walls, and two ridge lines, the tensile strength of the top plate and the wall is 1470 MPa or more, each of the two ridge lines extends between the top plate and the wall in the longitudinal direction of the top plate, the cross-section at the central portion in the longitudinal direction is an open section having a groove shape, in the cross-section, the top plate includes a central groove portion extending in the longitudinal direction at the center of the width, in the cross-section, the top plate includes small groove portions between the central groove portion and each of the ridge lines, in the cross-section, the depth of the central groove portion at the center is 15 times or more and 25 times or less the plate thickness of the top plate, the depth of the small groove portion is 2 times or more and 13 times or less the plate thickness of the top plate, the distance between the small groove portion and the ridge line is 30 times or less the plate thickness of the top plate. (2) In the open-section bumper reinforcement described in (1) above, in the cross-section, The total length of the flat portions (L1, L2) between the ridge line portion and the small groove portion and the total length of the flat portions (L3, L4) between the central groove portion and the small groove portion may be 18% or less of the distance between the ridge line portions. (3) In the open-section bumper reinforcement according to (1) above, In the cross section, The central groove portion and the small groove portion each have a flat bottom, The total length of the extension length (L7) of the bottom of the central groove portion, the extension lengths (L5, L6) of the bottom of the small groove portion, the extension lengths (L1, L2) of the flat portion between the ridge line portion and the small groove portion, and the extension lengths (L3, L4) of the flat portion between the central groove portion and the small groove portion may be 25% or less of the distance between the ridge line portions. (4) In the open-section bumper reinforcement according to any one of (1) to (3) above, In the cross section, The width of the small groove portion may be 5 times or more and 30 times or less the plate thickness. (5) In the shock-absorbing member according to any one of (1) to (4) above, The tensile strength of the top plate and the wall may be 1760 MPa or more.

Advantages of the Invention

[0008] According to the open-section bumper reinforcement of the present disclosure, breakage due to deformation caused when the member is subjected to an impact can be suppressed.

Brief Description of the Drawings

[0009] [Figure 1] It is a schematic perspective view of an open-section bumper reinforcement according to an embodiment of the present disclosure. [Figure 2] It is a schematic cross section of an open-section bumper reinforcement according to an embodiment of the present disclosure. [Figure 3] It is a schematic cross section showing the vicinity of a groove portion of an open-section bumper reinforcement according to an embodiment of the present disclosure. [Figure 4]It is a schematic cross-section showing an example of one groove portion of an open-section bumper reinforcement according to an embodiment of the present disclosure. [Figure 5] It is a schematic cross-section showing an example of the other groove portion of an open-section bumper reinforcement according to an embodiment of the present disclosure. [Figure 6] It is a schematic cross-section showing an example of the central groove portion of an open-section bumper reinforcement according to an embodiment of the present disclosure. [Figure 7] It is a schematic cross-section of an open-section bumper reinforcement according to an embodiment of the present disclosure. [Figure 8] It is a schematic top view of an open-section bumper reinforcement according to an embodiment of the present disclosure, which is a view of the open-section bumper reinforcement seen from a direction perpendicular to the plate surface of the first plate portion. [Figure 9] It is a diagram for explaining a modified example of the groove portion or the central groove portion according to the present disclosure, and is a schematic cross-section showing the vicinity of the groove portion of the open-section bumper reinforcement. [Figure 10] It is a diagram for explaining another modified example of the groove portion or the central groove portion according to the present disclosure, and is a schematic cross-section showing the vicinity of the groove portion of the open-section bumper reinforcement. [Figure 11] It is a graph showing the results of Example 1 of the present disclosure. [Figure 12] It is a schematic top view of an open-section bumper reinforcement according to an embodiment of the present disclosure, which is a view showing a deformation mode when the depth of the groove portion is 1 times the plate thickness. [Figure 13] It is a schematic top view of an open-section bumper reinforcement according to an embodiment of the present disclosure, which is a view showing a deformation mode when the depth of the groove portion is 2 times the plate thickness. [Figure 14] It is a schematic top view of an open-section bumper reinforcement according to an embodiment of the present disclosure, which is a view showing a deformation mode when the depth of the groove portion is 13 times the plate thickness. [Figure 15] It is a schematic top view of an open-section bumper reinforcement according to an embodiment of the present disclosure, which is a view showing a deformation mode when the depth of the groove portion is 17.8 times the plate thickness. [Figure 16]10 is a graph showing the relationship between the depth of the groove and the opening angle between the side walls when the open cross section bumper reinforcement according to the embodiment of the present disclosure is deformed by an external force. [Figure 17] 10 is a graph showing the relationship between the depth of a groove and plastic strain when an open cross section bumper reinforcement according to an embodiment of the present disclosure is deformed by an external force. [Figure 18] FIG. 10 is a schematic top view of an open cross-section bumper reinforcement according to an embodiment of the present disclosure, illustrating a deformation mode when the depth of the central groove is set to less than 15 times the thickness of the top plate. [Figure 19] FIG. 10 is a schematic cross-sectional view of an open cross-section bumper reinforcement according to an embodiment of the present disclosure, showing a deformation mode when the depth of the central groove is set to less than 15 times the thickness of the top plate. [Figure 20] FIG. 10 is a schematic top view of an open cross-section bumper reinforcement according to an embodiment of the present disclosure, illustrating a deformation mode when the depth of the central groove is set to 15 times or more the thickness of the top plate. [Figure 21] FIG. 10 is a schematic cross-sectional view of an open cross-section bumper reinforcement according to an embodiment of the present disclosure, showing a deformation mode when the depth of the central groove is set to 15 times or more the thickness of the top plate. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described using examples, but it is clear that the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be used as examples, but other numerical values and materials may be used as long as the effects of the present disclosure are obtained. Furthermore, the components of the following embodiments can be combined with each other.

[0011] [Embodiment] FIG. 1 illustrates a bumper reinforcement with an open cross-section according to an embodiment. The bumper reinforcement with an open cross-section refers to a bumper reinforcement having an open cross-section with a groove-shaped cross-section. In the present disclosure, the cross-section of the bumper reinforcement with an open cross-section refers to a cross-section perpendicular to the longitudinal direction of the bumper reinforcement with an open cross-section. FIG. 1 is a perspective view of the bumper reinforcement 200 with an open cross-section. The cross-section of the bumper reinforcement 200 in front of FIG. 1 is a cross-section that crosses the central position in the longitudinal direction of the bumper reinforcement 200. The bumper reinforcement 200 with an open cross-section according to the embodiment is a groove-shaped member as shown in FIG. 1. The bottom of the groove-shaped cross-section is also referred to as the top plate portion (top plate) or the first plate portion 210. When the bumper reinforcement with an open cross-section is mounted on a vehicle, the bottom is arranged to face the traveling direction (vehicle length direction) of the vehicle. The side walls (walls) of the groove-shaped cross-section are also referred to as the second plate portions 221 and 222. The side walls are located on the sides of the bottom and are arranged to face each other in the vehicle height direction of the vehicle. Specifically, the bumper reinforcement 200 with an open cross-section has the following configuration. That is, the bumper reinforcement 200 with an open cross-section includes a first plate portion 210 (top plate), two second plate portions 221 and 222 (walls), and two ridge line portions 231 and 232. Each of the two ridge line portions 231 and 232 extends in the longitudinal direction of the first plate portion 210 between the first plate portion 210 and the second plate portion 221 and between the first plate portion 210 and the second plate portion 222. The bumper reinforcement 200 with an open cross-section has an open cross-section with a groove-shaped cross-section at the central portion in the longitudinal direction. In the cross section of the open cross section bumper reinforcement 200, the first plate portion 210 has a central groove 260 extending in the longitudinal direction at the center of its width, and grooves 240, 250 (small grooves) disposed between the central groove 260 and the ridge portion 231 and between the central groove 260 and the ridge portion 232, respectively. The open cross section bumper reinforcement 200 is an elongated member and has a longitudinal direction and a lateral direction perpendicular to the longitudinal direction. The longitudinal direction is the direction in which the open cross section bumper reinforcement 200, which is an elongated member, extends. In FIG. 1, the longitudinal direction of the open cross section bumper reinforcement 200 is parallel to the Z coordinate axis. The X coordinate axis and the Y coordinate axis in FIG. 1 are parallel to the lateral direction of the open cross section bumper reinforcement 200. The X coordinate axis, the Y coordinate axis, and the Z coordinate axis in FIG. 1 are perpendicular to each other. That is, when the open cross section bumper reinforcement is mounted on a vehicle, the X coordinate axis is the vehicle height direction, the Y coordinate axis is the vehicle length direction, and the Z coordinate axis is the vehicle width direction.

[0012] In the example of FIG. 1 , the first plate portion 210 is a substantially flat plate-shaped portion except for groove portions 240, 250, and a central groove portion 260, which will be described later, and extends in the longitudinal direction of the open cross section bumper reinforcement 200. The first plate portion 210 has a constant thickness. In the open cross section bumper reinforcement 200, the surface of the first plate portion 210 on the outside of the groove shape is called the top plate front surface 210a, and the surface of the first plate portion 210 on the inside of the groove shape is called the top plate back surface 210b. When the direction parallel to the longitudinal direction of the open cross section bumper reinforcement 200 is defined as the length direction of the first plate portion 210, the first plate portion 210 has a constant length in the length direction of the first plate portion 210.

[0013] The second plate portions 221 and 222 are generally flat plate-shaped portions that extend in the longitudinal direction of the open cross section bumper reinforcement 200. The second plate portion 221 has a constant thickness. In the open cross section bumper reinforcement 200, the surfaces of the second plate portions 221 and 222 on the outside of the groove shape are referred to as the wall surface 221a and the wall surface 222a, respectively, and the surfaces of the second plate portions 221 and 222 on the inside of the groove shape are referred to as the wall back surface 221b and the wall surface 222b, respectively. When the direction parallel to the longitudinal direction of the open cross section bumper reinforcement 200 is defined as the length direction of the second plate portions 221 and 222, the second plate portions 221 and 222 have a constant length in the length direction of the second plate portions 221 and 222. When the direction orthogonal to the length direction of the second plate portion 221 and the thickness direction of the second plate portion 221 is defined as the width direction of the second plate portion 221, the second plate portion 221 has a constant length in the width direction of the second plate portion 221. When the direction orthogonal to the length direction of the second plate portion 222 and the thickness direction of the second plate portion 222 is defined as the width direction of the second plate portion 222, the second plate portion 222 has a constant length in the width direction of the second plate portion 222. Note that the first plate portion 210, the second plate portion 221, and the second plate portion 222 may be provided with holes, notches, beads, welds, etc.

[0014] Ridge line 231 is a portion connecting first plate portion 210 and second plate portion 221, and extends in the longitudinal direction of open cross section bumper reinforcement 200. Because second plate portion 221 is inclined with respect to first plate portion 210, ridge line 231 connecting them has a curved shape that describes a curved line in the transverse cross section of open cross section bumper reinforcement 200. Similarly, ridge line 232 is a portion connecting first plate portion 210 and second plate portion 222, and extends in the longitudinal direction of open cross section bumper reinforcement 200. Because second plate portion 222 is inclined with respect to first plate portion 210, ridge line 232 connecting them has a curved shape that describes a curved line in the transverse cross section of open cross section bumper reinforcement 200.

[0015] The second plate portion 221 being inclined with respect to the first plate portion 210 means that the plate surface of the first plate portion 210 and the plate surface of the second plate portion 221 are not parallel. Similarly, the second plate portion 222 being inclined with respect to the first plate portion 210 means that the plate surface of the first plate portion 210 and the plate surface of the second plate portion 222 are not parallel. Furthermore, a direction parallel to the longitudinal direction of the open cross section bumper reinforcement 200 is defined as the length direction of the ridge portion 231 or the ridge portion 232. The outer surface of the bent ridge portion 231 is defined as the ridge outer surface 231a, and the inner surface of the bent ridge portion 231 is defined as the ridge inner surface 231b. The top plate surface 210a and the wall surface 221a are connected to the ridge outer surface 231a, and the top plate back surface 210b and the wall back surface 221b are connected to the ridge inner surface 231b. Similarly, the surface on the outside of the bend of the ridge portion 232 is referred to as the ridge outer surface 232a, and the surface on the inside of the bend of the ridge portion 232 is referred to as the ridge inner surface 232b. The top plate surface 210a and the wall surface 221a are connected to the ridge outer surface 232a, and the top plate back surface 210b and the wall back surface 221b are connected to the ridge inner surface 232b. The ridge outer surface 231a side (or the ridge outer surface 232a side) may be referred to as the outside of the open cross section bumper reinforcement 200, and the ridge inner surface 231b side (or the ridge inner surface 232b side) may be referred to as the inside of the open cross section bumper reinforcement 200. Specifically, the ridge portion 231 or the ridge portion 232 refers to the range in which the radius of curvature R of the ridge outer surface 231a or the ridge outer surface 232a is 30 mm or less in the cross section of the open cross section bumper reinforcement 200. The portion where the radius of curvature R exceeds 30 mm is considered to be included in the first plate portion 210, the second plate portion 221, or the second plate portion 222.

[0016] One edge (first plate edge 210A) of the first plate portion 210 extending in the longitudinal direction of the open cross-section bumper reinforcement 200 is connected to one edge (ridge line edge 231A) of one ridge line portion 231 extending in the longitudinal direction of the open cross-section bumper reinforcement 200. An edge (second plate edge 221A) of the second plate portion 221 extending in the longitudinal direction of the open cross-section bumper reinforcement 200 is connected to the other edge (ridge line edge 231B) of the ridge line portion 231 extending in the longitudinal direction. Further, the other edge (first plate edge 210B) of the first plate portion 210 extending in the longitudinal direction of the open cross-section bumper reinforcement 200 is connected to one edge (ridge line edge 232A) of the other ridge line portion 232 extending in the longitudinal direction of the open cross-section bumper reinforcement 200. An edge (second plate edge 222A) of the other second plate portion 222 extending in the longitudinal direction of the open cross-section bumper reinforcement 200 is connected to the other edge (ridge line edge 232B) of the ridge line portion 232 extending in the longitudinal direction.

[0017] The first plate portion 210 is provided with groove portions 240 and 250 that pass through the central position in the longitudinal direction of the open cross-section bumper reinforcement 200 and extend along the ridge line portion 231. Here, when the open cross-section bumper reinforcement 200 absorbs the impact during a collision and undergoes deformation such that the width of the first plate portion 210 becomes narrower, there is a concern that the cross-sections of the central groove side ridge lines 266 and 267 of the central groove portion 260 described later will be deformed into acute angles and the central groove side ridge lines 266 and 267 will break. Therefore, the groove portions 240 and 250 are provided to relieve the deformation of the central groove side ridge lines 266 and 267. In the embodiment, the depths d1 and d2 of the groove portions 240 and 250 are shallower than the central groove portion 260 (details will be described later). When the direction parallel to the longitudinal direction of the open-section bumper reinforcer 200 is defined as the length direction of the groove portion 240 and the groove portion 250, the groove portion 240 and the groove portion 250 each have a constant length in their respective length directions. The central position in the longitudinal direction of the open-section bumper reinforcer 200 means a position included in a range of 20% of the longitudinal length of the open-section bumper reinforcer 200 from the central position that bisects the longitudinal length of the open-section bumper reinforcer 200. That the groove portion 240 (or the groove portion 250) extends along the ridge line portion 231 (or the ridge line portion 232) means that the groove portion 240 (or the groove portion 250) is arranged to be substantially parallel to a part of the adjacent ridge line portion 231 (or the ridge line portion 232).

[0018] A central groove portion 260 that passes through the central position in the longitudinal direction of the open-section bumper reinforcer 200 and extends in the longitudinal direction of the open-section bumper reinforcer 200 is provided in the first plate portion 210. The central groove portion 260 is located between the groove portion 240 and the groove portion 250. When the direction parallel to the longitudinal direction of the open-section bumper reinforcer 200 is defined as the length direction of the central groove portion 260, the central groove portion 260 has a constant length in its length direction. The groove portion 240, the groove portion 250, and the central groove portion 260 may extend substantially parallel to each other.

[0019] FIG. 2 is a cross-section of the central position in the longitudinal direction of the open-section bumper reinforcer 200 of FIG. 1. The groove portion 240, the groove portion 250, and the central groove portion 260 protrude in a direction intersecting the plate surface of the first plate portion 210 (the top plate surface 210a and the back surface 210b of the top plate opposite to the top plate surface 210a). In the example of FIG. 2, the groove portion 240, the groove portion 250, and the central groove portion 260 protrude toward the side (the back surface 210b side of the top plate) where the second plate portion 221 and the second plate portion 222 are located with respect to the first plate portion 210.

[0020] In the open cross-section bumper reinforcement 200 according to the embodiment, in the cross-section at the longitudinal center position of the open cross-section bumper reinforcement 200, when the average plate thickness of the first plate portion 210 is t, a part of the groove portion 240 is located in a range of 30t in a direction parallel to the plate surface of the first plate portion 210 from the boundary b1 between the first plate portion 210 and one ridge line portion 231 toward the first plate portion 210 side. In other words, at the longitudinal center position of the open cross-section bumper reinforcement 200, the distance between the groove portion 240 and the ridge line portion 231 is 30 times or less the plate thickness of the first plate portion 210. In the present disclosure, the distance refers to the so-called distance between the ends, not the distance between the centers. Further, in a plane orthogonal to the longitudinal direction of the open cross-section bumper reinforcement 200 at the longitudinal center position of the open cross-section bumper reinforcement 200, a part of the groove portion 250 is located in a range of 30t in a direction parallel to the plate surface of the first plate portion 210 from the boundary b3 between the first plate portion 210 and the other ridge line portion 232 toward the first plate portion 210 side. In other words, at the longitudinal center position of the open cross-section bumper reinforcement 200, the distance between the groove portion 250 and the ridge line portion 232 is 30 times or less the plate thickness of the first plate portion 210.

[0021] FIG. 3 is a cross-section of the vicinity of the groove portion 240 of the open cross-section bumper reinforcement 200 of FIG. 2. FIG. 3 is a cross-section of the longitudinal center position of the open cross-section bumper reinforcement 200 of FIG. 1.

[0022] In the example of FIG. 3 , groove 240 has a groove bottom 241 and a pair of groove side portions 242 and 243. Groove bottom 241 is connected at each end to groove side portions 242 and 243 via a pair of groove bottom-side ridge portions 244 and 245. Groove side portions 242 and 243 are connected to first plate portion 210 via groove side-side ridge portions 246 and 247. Groove bottom 241, groove side portions 242 and 243, groove bottom-side ridge portions 244 and 245, and groove side-side ridge portions 246 and 247 extend in the length direction of groove 240. These ridge portions refer to the ranges where the radius of curvature R on the outer sides of the ridge portions is 30 mm or less in a cross section of open cross section bumper reinforcement 200. A portion where the radius of curvature R exceeds 30 mm is considered to be included in the groove bottom 241, the groove side 242, or the groove side 243. The groove bottom 241 has a bottom inner surface 241a located inside the groove 240 (on the side of the groove side portions 242 and 243) and a bottom outer surface 241b opposite the bottom inner surface 241a.

[0023] In a cross section of the open cross section bumper reinforcement 200, of the boundaries between the first plate portion 210 and the groove portion 240 (boundaries between the first plate portion 210 and groove side ridge portions 246 and 247), the boundary closer to the ridge portion 231 (the boundary between the first plate portion 210 and the groove side ridge portion 246) is designated as groove boundary gb1, and the other boundary (the boundary between the first plate portion 210 and the groove side ridge portion 247) is designated as groove boundary gb2. As shown in Fig. 3, in a cross section at the longitudinal center position of the open cross section bumper reinforcement 200, a distance L1 from boundary b1 to groove boundary gb1 in a direction parallel to the plate surface of the first plate portion 210 is less than 30t.

[0024] As shown in FIG. 3, the boundary b1 between the first plate portion 210 and the ridge line portion 231 means the position where the first plate portion edge 210A and the ridge line edge 231A are in contact. The direction parallel to the plate surface of the first plate portion 210 means the direction parallel to the plate surface of the first plate portion 210 in the range from the boundary b1 to the groove portion 240 in the cross section of the open cross-section bumper reinforcement 200. That the part of the groove portion 240 is located in the above range means that at least a part of the groove portion 240 (the groove bottom portion 241, the groove side portions 242 and 243, the groove bottom side ridge line portions 244 and 245, or the groove side side ridge line portions 246 and 247) exists in the above range.

[0025] In the cross section of the open cross-section bumper reinforcement 200, the distance between the groove boundary gb1 and the groove boundary gb2 is defined as the width w1 of the groove portion 240. The width w1 of the groove portion 240 does not have to be constant in the longitudinal direction of the open cross-section bumper reinforcement 200.

[0026] As shown in FIG. 4, in the cross section of the open cross-section bumper reinforcement 200, the distance from the inner surface of the groove (the bottom inner surface 241a) of the groove farthest from the straight line l to the straight line l in the direction orthogonal to the straight line l passing through the boundaries gb1 and gb2 is defined as the depth d1 of the groove portion 240. Here, when the open cross-section bumper reinforcement 200 absorbs the impact during a collision, the groove boundary gb1 and the groove boundary gb2 approach each other, and the opening angle between the second plate portion 221 and the second plate portion 222 increases. At this time, the larger the depth d1 of the groove portion 240, the larger the opening angle between the second plate portion 221 and the second plate portion 222. If the depth d1 of the groove portion 240 is small and the opening angle between the second plate portion 221 and the second plate portion 222 is small, strain concentrates on the central groove side portions 262 and 263 and the central groove side side ridge line portions 266 and 267 of the central groove portion 260 described later, and there is a concern about breakage at the location where the strain concentrates. If the depth d1 of the groove portion 240 is large and the opening angle between the second plate portion 221 and the second plate portion 222 is large, strain concentrates on the groove side portions 242 and 243 and the groove side side ridge line portions 246 and 247 of the groove portion 240, and there is a concern about breakage at the location where the strain concentrates. Figures 12 to 15 are diagrams showing the deformed states of the open-section bumper reinforcer 200 at a stroke of 70 mm when the depth d1 of the groove portion 240 and the depth d2 of the groove portion 250 (described later) are 1.4 mm, 2.8 mm, 18.2 mm, and 25.0 mm, respectively. The average plate thickness t of the open-section bumper reinforcer 200 is 1.4 mm. In other words, the depth d1 of the groove portion 240 and the depth d2 of the groove portion 250 in Figures 12 to 15 are 1t, 2t, 13t, and 17.8t, respectively. Also, in Figures 12 to 15, the width of the central groove portion 260 is 14 mm and the depth is 23 mm. The radii of curvature of the bottom-side ridge lines 264 and 265 of the central groove portion are 6 mm. The radii of curvature of the side-side ridge lines 246, 247, 256, and 257 of the groove portion are 5 mm. The radii of curvature of the bottom-side ridge lines 244, 245, 254, and 255 of the groove portion are 4 mm. The radii of curvature of the ridge lines 231 and 232 are 8 mm. The center-to-center distances between the central groove portion 260 and the groove portions 240 and 250 in the width direction are 32.97 mm each. The distances between the boundary b1 and the groove boundary gb1, and between the boundary b3 and the groove boundary gb3 are 17.66 mm each. Figure 16 is a graph showing the relationship between the magnitudes of the depth d1 of the groove portion 240 and the depth d2 of the groove portion 250 under the above-described conditions, and the opening angle between the second plate portion 221 and the second plate portion 222 during deformation at a stroke of 70 mm of the open-section bumper reinforcer 200. Figure 17 is a graph showing the relationship between the magnitudes of the depth d1 of the groove portion 240 and the depth d2 of the groove portion 250 under the above-described conditions, and the equivalent plastic strain amount during deformation at a stroke of 70 mm of the open-section bumper reinforcer 200. From Figures 12 to 15 and Figure 16, it can be seen that the larger the depth d1 of the groove portion 240 and the depth d2 of the groove portion 250, the greater the tendency for the opening angle between the second plate portion 221 and the second plate portion 222 to increase. In FIG. 17, when the fracture threshold is set to 0.3, it can be seen that the depth d1 of the groove portion 240 and the depth d2 of the groove portion 250 exceed the fracture threshold when they are 2.8 mm or less or 18.2 mm or more. That is, when the depth d1 of the groove portion 240 and the depth d2 of the groove portion 250 are 2.8 mm or less, the opening angle between the second plate portion 221 and the second plate portion 222 becomes small, so it is considered that strain concentrates on the central groove portion side portions 262 and 263 of the central groove portion 260 and the central groove portion side portion side ridge lines 266 and 267. When the depth d1 of the groove portion 240 and the depth d2 of the groove portion 250 are 18.2 mm or more, the opening angle between the second plate portion 221 and the second plate portion 222 becomes large, so it is considered that strain concentrates on the groove portion side portions 242 and 243 of the groove portion 240, the groove portion side portion side ridge lines 246 and 247, the groove portion side portions 252 and 253 of the groove portion 250, and the groove portion side portion side ridge lines 256 and 257. In order to avoid such concentration of local strain, the depth d1 of the groove portion 240 is preferably as follows. That is, in the cross section in the longitudinal direction of the open cross-section bumper reinforcement 200 at the central position in the longitudinal direction of the open cross-section bumper reinforcement 200, the depth d1 of the groove portion 240 is preferably 2t to 13t. In other words, in the cross section at the central portion in the longitudinal direction of the open cross-section bumper reinforcement 200, the depth of the groove portion 240 is preferably 2 times or more and 13 times or less the plate thickness of the first plate portion 210. When the depth d1 of the groove portion 240 is 2t to 13t, there is an advantage that the deformation of the first plate portion 210 during a collision can be alleviated and the generated strain can be suppressed. More preferably, the depth d1 of the groove portion 240 is 4t to 10t. Note that the depth d1 of the groove portion 240 does not have to be constant in the longitudinal direction of the open cross-section bumper reinforcement 200.

[0027] Also, as shown in FIG. 5, the configuration of the groove portion 250 is the same as that of the groove portion 240. The groove portion 250 has a groove bottom portion 251 and a pair of groove side portions 252 and 253. The groove bottom portion 251 is connected to the respective groove side portions 252 and 253 via a pair of groove bottom side ridge line portions 254 and 255 at each end. Each of the groove side portions 252 and 253 is connected to the first plate portion 210 via groove side portion side ridge line portions 256 and 257. The groove bottom portion 251, the groove side portions 252 and 253, the groove bottom side ridge line portions 254 and 255, and the groove side portion side ridge line portions 256 and 257 extend in the longitudinal direction of the groove portion 250. These ridge line portions mean a range where the curvature radius R outside the ridge line portion is 30 mm or less in a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 200. A portion where the curvature radius R exceeds 30 mm is regarded as being included in the groove bottom portion 251, the groove side portion 252, or the groove side portion 253. The groove bottom portion 251 has a bottom inner surface 251a located inside the groove portion 250 (on the side of the groove side portions 252 and 253) and a bottom outer surface 251b opposite to the bottom inner surface 251a.

[0028] In the cross-section of the open-section bumper reinforcement 200, of the boundaries between the first plate portion 210 and the groove portion 250 (the boundaries between the first plate portion 210 and the groove side portion side ridge line portions 256 and 257), the boundary closer to the ridge line portion 232 (the boundary between the first plate portion 210 and the groove side portion side ridge line portion 256) is defined as the groove boundary gb3, and the other boundary (the boundary between the first plate portion 210 and the groove side portion side ridge line portion 257) is defined as the groove boundary gb4. As shown in FIG. 5, in the cross-section at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the distance L2 from the boundary b3 in the direction parallel to the plate surface of the first plate portion 210 to the groove boundary gb3 is less than 30t.

[0029] As shown in FIG. 5, the boundary b3 between the first plate portion 210 and the ridge line portion 232 means the position where the first plate portion edge 210B and the ridge line edge 232A are in contact. The direction parallel to the plate surface of the first plate portion 210 means the direction parallel to the plate surface of the first plate portion 210 in the range from the boundary b3 to the groove portion 250 in the cross section of the open cross-section bumper reinforcement 200. That the part of the groove portion 250 is located in the above range means that at least a part of the groove portion 250 (the groove bottom portion 251, the groove side portions 252 and 253, the groove bottom side ridge line portions 254 and 255, or the groove side side ridge line portions 256 and 257) exists in the above range.

[0030] In the cross section of the open cross-section bumper reinforcement 200, the distance between the groove boundary gb3 and the groove boundary gb4 is defined as the width w2 of the groove portion 250. The width w2 of the groove portion 250 does not have to be constant in the longitudinal direction of the open cross-section bumper reinforcement 200.

[0031] Also, similar to the case of the groove portion 240, in the cross section of the open cross-section bumper reinforcement 200, the distance from the inner surface of the groove (the bottom inner surface 251a) farthest from the straight line l to the straight line l in the direction orthogonal to the straight line l passing through the boundaries gb3 and gb4 is defined as the depth d2 of the groove portion 250. At this time, similar to the conditions of the groove portion 240 described above, in the cross section at the central position in the longitudinal direction of the open cross-section bumper reinforcement 200, the depth d2 of the groove portion 250 is preferably 2t to 13t. In other words, in the cross section at the central portion in the longitudinal direction of the open cross-section bumper reinforcement 200, the depth of the groove portion 250 is preferably not less than 2 times and not more than 13 times the plate thickness of the first plate portion 210. When the depth d2 of the groove portion 250 is 2t to 13t, there is an advantage that the deformation of the first plate portion 210 during a collision can be alleviated and the generated strain can be suppressed. The depth d2 of the groove portion 250 is more preferably 4t to 10t. Note that the depth d2 of the groove portion 250 does not have to be constant in the longitudinal direction of the open cross-section bumper reinforcement 200.

[0032] As shown in FIG. 3, on a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 200 at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the boundaries b1 and b2 are points on the plate surface on the bending outer side of the ridge line portion 231. Also, as shown in FIG. 3, on a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 200 at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the groove boundaries gb1 and gb2 are points on the plate surface on the bending outer side of the groove-side ridge line portions 246 and 247. Similarly, as shown in FIG. 5, on a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 200 at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the boundaries b3 and b4 are points on the plate surface on the bending outer side of the ridge line portion 232. Also, as shown in FIG. 5, on a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 200 at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the groove boundaries gb3 and gb4 are points on the plate surface on the bending outer side of the groove-side ridge line portions 256 and 257.

[0033] FIG. 6 is a cross-section near the central groove portion 260 of the open-section bumper reinforcement 200 in FIG. 2. FIG. 6 is a cross-section at the central position in the longitudinal direction of the open-section bumper reinforcement 200 in FIG. 1.

[0034] In the example of FIG. 6, the central groove portion 260 has a central groove bottom portion 261 and a pair of central groove side portions 262 and 263. The central groove bottom portion 261 is connected to the respective central groove side portions 262 and 263 via a pair of central groove bottom side ridge line portions 264 and 265 at each end. Each of the central groove side portions 262 and 263 is connected to the first plate portion 210 via a central groove side portion side ridge line portion 266 and 267. The central groove bottom portion 261, the central groove side portions 262 and 263, the central groove bottom side ridge line portions 264 and 265, and the central groove side portion side ridge line portions 266 and 267 extend in the longitudinal direction of the central groove portion 260. These ridge line portions mean a range in the cross section of the open cross-section bumper reinforcement 200 where the radius of curvature R outside the ridge line portion is 30 mm or less. A portion where the radius of curvature R exceeds 30 mm is regarded as being included in the central groove bottom portion 261 or the central groove side portion 262 or the central groove side portion 263. The central groove bottom portion 261 has a central groove bottom inner surface 261a located inside the central groove portion 260 (on the side of the central groove side portions 262 and 263) and a central groove bottom outer surface 261b on the side opposite to the central groove bottom inner surface 261a.

[0035] In a plane orthogonal to the longitudinal direction of the open cross-section bumper reinforcement 200, the boundaries between the first plate portion 210 and the central groove portion 260 are defined as a central groove boundary cb1 and a central groove boundary cb2. In the example of FIG. 2, the central groove boundary cb1 is located on the groove portion 240 side, and the central groove boundary cb2 is located on the groove portion 250 side. As shown in FIG. 6, at the cross section at the central position in the longitudinal direction of the open cross-section bumper reinforcement 200, the central groove boundary cb1 and the central groove boundary cb2 are points on the plate surface on the outer side of the bend of the central groove side portion side ridge line portions 266 and 267.

[0036] The distance between the central groove boundary cb1 and the central groove boundary cb2 in the cross section of the open cross-section bumper reinforcement 200 is defined as the width w3 of the central groove portion 260. The width w3 of the central groove portion 260 does not have to be constant in the longitudinal direction of the open cross-section bumper reinforcement 200.

[0037] The method for determining the depth of the central groove portion 260 is the same as that for the groove portion 240 and the like. As shown in FIG. 6, in a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 200, the distance from the inner surface of the groove portion (the inner surface 261a of the bottom of the central groove portion) farthest from the straight line l to the straight line l in the direction orthogonal to the straight line l passing through the boundaries cb1 and cb2 is defined as the depth d3 of the central groove portion 260. Here, FIGS. 18 to 21 are diagrams showing the deformed states of the open-section bumper reinforcement 200 at a stroke of 70 mm when the depth d3 of the central groove portion 260 is 10 mm and 21 mm. The average plate thickness t of the open-section bumper reinforcement 200 is 1.4 mm. In other words, the depth d3 of the central groove portion 260 in FIGS. 18 to 21 is 7.1t and 15t, respectively. In FIGS. 18 to 21, the depth d1 of the groove portion 240 and the depth d2 of the groove portion 250 are each 8 mm. Other conditions are the same as those in FIGS. 12 to 15 described above. If the depth d3 of the central groove portion 260 is not sufficient, as shown in FIGS. 18 and 19, when absorbing an impact, the width of the first plate portion 210 is deformed to become wider, and the second plate portion 221 and the second plate portion 222 are deformed to close. Therefore, in the cross-section in the longitudinal direction of the open-section bumper reinforcement 200 at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the depth d3 of the central groove portion 260 is 15t or more. Since the depth d3 of the central groove portion 260 is 15t or more, as shown in FIGS. 20 and 21, the width of the first plate portion 210 is deformed to become narrower, and the second plate portion 221 and the second plate portion 222 are deformed to open. By this, there are advantages of being able to suppress the strain generated at the time of a collision and improving the member strength by increasing the sectional rigidity. Incidentally, if the depth d3 of the central groove portion 260 is too deep, the mass increases due to the increase in the central groove portion side portions 262 and 263 of the central groove portion 260. Thereby, the energy absorption amount per mass decreases. Therefore, the depth d3 of the central groove portion 260 is more preferably 15t to 25t. In other words, in the cross-section at the central portion in the longitudinal direction of the open-section bumper reinforcement 200, the depth of the groove (central groove portion 260) at the center is 15 times or more and 25 times or less the plate thickness of the first plate portion 210. Note that the depth d3 of the central groove portion 260 does not have to be constant in the longitudinal direction of the open-section bumper reinforcement 200.

[0038] As shown in FIG. 2, the central groove portion 260 is located between the groove portion 240 and the groove portion 250. That is, in the cross-section of the open-section bumper reinforcement 200 at the central position in the longitudinal direction of the open-section bumper reinforcement 200, from the ridge line portion 231 side toward the ridge line portion 232 side, via the first plate portion 210, the groove portion 240, the central groove portion 260, and the groove portion 250 are located in this order. In the cross-section at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the first plate portion 210 is divided into four by the groove portion 240, the groove portion 250, and the central groove portion 260.

[0039] In the embodiment, the above-described boundary is also the R stop on the plate surface on the bending outer side of the ridge line portion.

[0040] It is more preferable that the total length of central groove portion 260 is 50 to 90% of the total length of ridge line portion 231 or ridge line portion 232. This allows high collision performance to be exhibited even when the outside of the central portion of open cross section bumper reinforcement 200 is subjected to collision deformation.

[0041] The average thickness t of the first plate portion 210 is determined by the following method. In a cross section at the longitudinal center of the open cross section bumper reinforcement 200, the thickness is measured at five or more arbitrary positions of the first plate portion 210, excluding the groove portion 240, the groove portion 250, and the central groove portion 260, using a micrometer. The arithmetic mean value of the thickness measurements at these positions is defined as the average thickness t.

[0042] In the example embodiment, the grooves 240, 250, and central groove 260 are convex toward the side of the first plate portion 210 where the second plate portions 221 and 222 are located (top plate back surface 210b side), but the grooves 240, 250, or central groove 260 may be convex toward the side opposite the side of the first plate portion 210 where the second plate portions 221 and 222 are located (top plate front surface 210a side). That is, the grooves 240, 250, or central groove 260 provided in the first plate portion 210 may be convex toward either the outside or the inside of the open cross section bumper reinforcement 200. The grooves 240, 250, and central groove 260 may be convex in opposite directions.

[0043] The open cross section bumper reinforcement 200 according to the embodiment has a tensile strength of 1470 MPa or more. That is, for example, the tensile strength of the first plate portion 210 and the second plate portions 221 and 222 is 1470 MPa or more. By making the tensile strength of the open cross section bumper reinforcement 200 1470 MPa or more, a certain yield stress can be ensured and distortion can be suppressed. The tensile strength of the open cross section bumper reinforcement 200 is determined as follows. Specifically, a sample of a size conforming to the JIS No. 5 tensile test, the JIS No. 13B tensile test, or the JIS No. 14B tensile test is obtained from the first plate portion 210 or the second plate portions 221 and 222 of the open cross section bumper reinforcement 200. The tensile strength of this sample is measured using a universal testing machine or a hydraulic servo strength testing machine according to a method conforming to JIS Z 2241, and this tensile strength is defined as the tensile strength of the open cross section bumper reinforcement 200. If it is not possible to obtain a test piece specified by JIS, a micro-tensile test piece may be used as the sample. For the micro-tensile test, the width and thickness of the parallel section are preferably 0.2 to 2.0 mm, and the test piece shape is preferably one that applies a uniform load within the parallel section of the tensile test. Wire-cut electrical discharge machining is preferably used for processing the test piece. For example, the test piece in the Journal of the Japan Welding Society, Vol. 75 (2006), No. 6, pp. 461-465 (https: / / www.jstage.jst.go.jp / article / jjws / 75 / 6 / 75_6_461 / _pdf / -char / ja) can be used as the micro-tensile test piece.

[0044] Here, in the cross section of the open cross section bumper reinforcement 200 according to the embodiment, the extension length of the flat portion between the ridge line portion 231 and the groove portion 240 is defined as L1. The extension length of the flat portion between the ridge line portion 232 and the groove portion 250 is defined as L2. The extension length of the flat portion between the central groove portion 260 and the groove portion 240 is defined as L3. The extension length of the flat portion between the central groove portion 260 and the groove portion 250 is defined as L4. In this case, it is more preferable that the total extension length of L1, L2, L3, and L4 is 18% or less of the distance between the ridge line portion 231 and the ridge line portion 232. That is, in the cross-section in the longitudinal direction of the open-section bumper reinforcement 200 at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the length of the first plate portion 210 excluding the groove portion 240, the groove portion 250, and the central groove portion 260 is more preferably 18% or less with respect to the length from the boundary b1 between the first plate portion 210 and one ridge line portion 231 to the boundary b3 between the first plate portion 210 and the other ridge line portion 232. Thereby, the cross-sectional area of the entire open-section bumper reinforcement 200 can be reduced, and the performance per unit mass of the open-section bumper reinforcement 200 can be enhanced.

[0045] As shown in FIG. 7, in the cross-section in the longitudinal direction of the open-section bumper reinforcement 200 at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the first plate portion 210 is divided into four parts, namely, ranges 211, 212, 213, and 214 by the groove portion 240, the groove portion 250, and the central groove portion 260. The length of the first plate portion 210 excluding the groove portion 240, the groove portion 250, and the central groove portion 260 is defined as the total length of the respective lengths L1, L2, L3, and L4 of the ranges 211, 212, 213, and 214.

[0046] In the cross-section in the longitudinal direction of the open-section bumper reinforcement 200 at the central position in the longitudinal direction of the open-section bumper reinforcement 200, the straight-line distance L0 from the boundary b1 between the first plate portion 210 and one ridge line portion 231 to the boundary b3 between the first plate portion 210 and the other ridge line portion 232 is defined as the length from the boundary b1 to the boundary b3.

[0047] In the cross-section of the open-section bumper reinforcement 200 according to the embodiment, the central groove portion 260, the groove portion 240, and the groove portion 250 each have a flat bottom. Here, in the cross-section of the open-section bumper reinforcement 200, the extension length of the bottom of the central groove portion 260 is denoted as L7. The extension lengths of the bottoms of the groove portion 240 and the groove portion 250 are denoted as L5 and L6, respectively. At this time, it is more preferable that the total extension lengths of L1, L2, L3, L4, L5, L6, and L7 are 25% or less of the interval between the ridge line portion 231 and the ridge line portion 232. That is, the groove portion 240, the groove portion 250, and the central groove portion 260 each have a flat bottom (groove bottom portion 241, groove bottom portion 251, and central groove bottom portion 261), and the sum of the lengths of these bottoms and the length of the first plate portion 210 excluding the groove portion 240, the groove portion 250, and the central groove portion 260 is more preferably 25% or less with respect to the length from the boundary b1 between the first plate portion 210 and one ridge line portion 231 to the boundary b3 between the first plate portion 210 and the other ridge line portion 232. Thereby, the radius of curvature of each ridge line portion of the open cross-section bumper reinforcement 200 can be increased, the reduction in plate thickness generated during the manufacture of the open cross-section bumper reinforcement 200 can be suppressed, and the component performance during a collision can be exhibited. Further, when the above ratio is 25% or less, the demerit that the press load increases when press-forming due to the small radius of curvature of the ridge line portions of the groove portion 240, the groove portion 250, and the central groove portion 260 can be avoided.

[0048] As shown in FIG. 7, when the lengths of the groove bottom portion 241, the groove bottom portion 251, and the central groove bottom portion 261 in the longitudinal cross-section of the open cross-section bumper reinforcement 200 at the central position in the longitudinal direction of the open cross-section bumper reinforcement 200 are L5, L6, and L7, respectively, the sum of the lengths of the bottoms (groove bottom portion 241, groove bottom portion 251, and central groove bottom portion 261) and the length of the first plate portion 210 excluding the groove portion 240, the groove portion 250, and the central groove portion 260 is the sum of the lengths of L1, L2, L3, L4, L5, L6, and L7. Also, the length L5 of the groove bottom portion 241 or the length L6 of the groove bottom portion 251 is more preferably 0 to 4t, and the length L7 of the central groove bottom portion 261 is more preferably 0 to 6t.

[0049] In the example of the open cross-section bumper reinforcement 200 according to the embodiment, in the cross-section at the central position in the longitudinal direction of the open cross-section bumper reinforcement 200, each range of the first plate portion 210 and the groove bottom portion 241, the groove bottom portion 251, and the central groove bottom portion 261 are parallel to each other. However, these parts do not have to be parallel to each other, and the above-described definition of length can also be applied in that case.

[0050] The open-section bumper reinforcement 200 according to the embodiment preferably has a longitudinal length of 700 to 1500 mm. Further, in the open-section bumper reinforcement 200 according to the embodiment, it is more preferable that the widthwise length of the first plate portion 210 (the length from the boundary b1 to the boundary b3) is 30 to 160 mm. Further, in the open-section bumper reinforcement 200 according to the embodiment, it is more preferable that the widthwise lengths of the second plate portions 221 and 222 are 30 to 160 mm.

[0051] In the open-section bumper reinforcement 200 according to the embodiment, deformation occurs when a load equal to or greater than a certain level is applied in a direction orthogonal to the longitudinal direction of the open-section bumper reinforcement 200 or in the longitudinal direction of the open-section bumper reinforcement 200, and in a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 200, the ridge lines 231 and 232 move in the deformation direction. At this time, a tensile force or a compressive force is applied to the first plate portion 210 or the second plate portions 221 and 222 connected to the ridge lines 231 and 232 in a direction orthogonal to the longitudinal direction of the open-section bumper reinforcement 200. In the open-section bumper reinforcement 200 according to the embodiment, these tensile forces or compressive forces are relaxed, local deformation can be suppressed, and as a result, breakage due to deformation can be suppressed. Since the groove portion and the central groove are appropriately provided in the first plate portion 210, the rigidity when the first plate portion 210 attempts to deform out of the plane is increased. Thereby, the member strength and the mass efficiency of the absorbed energy of the open-section bumper reinforcement 200 can be enhanced. Further, since the amount of deformation of the first plate portion 210 until the target performance is reached can be suppressed, local deformation can be more effectively suppressed and material breakage can be reduced.

[0052] In the cross-section of the open-section bumper reinforcement 200 according to the above embodiment, it is preferable that the widths of the groove portion 240 and the groove portion 250 are 5 times or more and 30 times or less the plate thickness of the open-section bumper reinforcement 200. That is, it is preferable that the width of the groove portion is 5t to 30t. When the width of the groove portion is 5t to 30t, there is an advantage that local deformation occurring in the plane of the first plate portion can be suppressed and breakage can be more reliably suppressed.

[0053] In the open-section bumper reinforcement according to the above embodiment, the average plate thickness t of the first plate portion is preferably 0.8 to 2.3 mm in order to enhance the mass effect of the open-section bumper reinforcement. When the average plate thickness t is large, the press-forming load of the groove portion and the central groove portion becomes high and manufacturing becomes difficult, and furthermore, it is difficult to enhance the member performance per unit mass. Therefore, the average plate thickness t of the first plate portion is more preferably 1.4 mm or less. Further, the average plate thickness t of the first plate portion is more preferably 0.8 mm or more in order to exhibit collision performance by utilizing the rigidity of the plate thickness and further suppress local deformation by the rigidity.

[0054] As shown in FIG. 8, the length of the groove portion 240 or the groove portion 250 may be shorter than the length of the first plate portion 210, and the length of the central groove portion 260 may be shorter than the length of the first plate portion 210. The groove portion 240 or the groove portion 250 may extend over the longitudinal direction of the open-section bumper reinforcement 200, and the central groove portion 260 may extend over the longitudinal direction of the open-section bumper reinforcement 200. The groove portion 240, the groove portion 250, or the central groove portion 260 may extend so as to pass through the central position in the longitudinal direction of the open-section bumper reinforcement 200 (the position of line c in FIG. 8).

[0055] In the open-section bumper reinforcement according to the above embodiment, it is preferable that the total length of the groove portion is 50 to 90% of the total length of the ridge line portion. By the total length of the groove portion being 50 to 90% of the total length of the ridge line portion, high collision performance can be exhibited even when a collision deformation is received outside the central portion of the open-section bumper reinforcement.

[0056] In the open-section bumper reinforcement according to the above embodiment, the tensile strength of the top plate (first plate portion 210) and the two walls (second plate portions 221 and 222) is more preferably 1760 MPa or more. Thereby, compared with a material having a tensile strength of 1470 MPa or more, higher collision performance can be exhibited.

[0057] In the open-section bumper reinforcement according to the above embodiment, a flange portion may be formed at an edge of the first plate portion or the second plate portion that extends in the longitudinal direction and is not connected to the ridge line portion among the edges.

[0058] In the open-section bumper reinforcement according to the above embodiment, the groove portion or the central groove portion may have a cross-sectional shape formed of a curve as shown in FIG. 9 or FIG. 10, or a V-shaped cross-sectional shape including a curve in part. FIG. 9 is a cross section at the central position in the longitudinal direction of the open-section bumper reinforcement 300. The groove portion 340 provided in the open-section bumper reinforcement 300 as shown in FIG. 9 has a groove bottom portion 341 whose cross section is formed of a curve. The groove bottom portion 341 is connected to the first plate portion 310 via a pair of groove ridge line portions 346 and 347 at each end. In the open-section bumper reinforcement 300, the surface of the first plate portion 310 outside the groove shape is referred to as the top plate surface 310a, and the surface of the first plate portion 310 inside the groove shape is referred to as the top plate back surface 310b. The groove bottom portion 341 has a bottom inner surface 341a located inside the groove portion 340 and a bottom outer surface 341b opposite to the bottom inner surface. In a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 300, one of the boundaries between the first plate portion 310 and the groove portion 340 (the boundaries between the first plate portion 310 and the groove ridge line portions 346 and 347) is defined as the groove boundary gb1 (the boundary between the first plate portion 310 and the groove ridge line portion 346), and the other boundary (the boundary between the first plate portion 310 and the groove ridge line portion 347) is defined as the groove boundary gb2. On the plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 300 at the central position in the longitudinal direction of the open-section bumper reinforcement 300, the groove boundaries gb1 and gb2 are points on the plate surface on the outer side of the bend of the groove ridge line portions 346 and 347. The distance between the groove boundary gb1 and the groove boundary gb2 in a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 300 is defined as the width of the groove portion 340. The width of the groove portion 340 does not have to be constant in the longitudinal direction of the open-section bumper reinforcement 300. Also, in a plane orthogonal to the longitudinal direction of the open-section bumper reinforcement 300, the distance from the inner surface (bottom inner surface 341a) of the groove, which is the farthest from the straight line, to the straight line in the direction orthogonal to the straight line passing through the boundaries gb1 and gb2 (not shown) is defined as the depth of the groove portion 340.

[0059] FIG. 10 is a cross-section of the open cross-section bumper reinforcement 400 at the longitudinal center. As shown in FIG. 10, a groove 440 provided in the open cross-section bumper reinforcement 400 has a groove bottom 441 and a pair of groove side portions 442 and 443, each of which has a curved cross section. The groove bottom 441 is connected to the groove side portions 442 and 443, which are connected to the first plate portion 410 via groove ridge portions 446 and 447. In the open cross-section bumper reinforcement 400, the surface of the first plate portion 410 on the outside of the groove shape is referred to as the top plate surface 410a, and the surface of the first plate portion 410 on the inside of the groove shape is referred to as the top plate back surface 410b. The groove bottom 441 has a bottom inner surface 441a located inside the groove 440 and a bottom outer surface 441b opposite the bottom inner surface. In a plane perpendicular to the longitudinal direction of the open cross section bumper reinforcement 400, one of the boundaries between the first plate portion 410 and the groove portion 440 (the boundaries between the first plate portion 410 and the groove ridge portions 446 and 447) is defined as groove boundary gb1 (the boundary between the first plate portion 410 and the groove ridge portion 446), and the other boundary (the boundary between the first plate portion 410 and the groove ridge portion 447) is defined as groove boundary gb2. In a cross section at the longitudinal center of the open cross section bumper reinforcement 400, the groove boundary gb1 and the groove boundary gb2 are defined as points on the plate surface on the bending outer side of the groove ridge portions 446 and 447. The distance between the groove boundary gb1 and the groove boundary gb2 in the cross section of the open cross section bumper reinforcement 400 is defined as the width of the groove portion 440. The width of the groove portion 440 does not have to be constant in the longitudinal direction of the open cross section bumper reinforcement 400. In addition, in the cross section of open cross section bumper reinforcement 400, the distance from the inner surface of the groove farthest from a straight line (not shown) passing through boundaries gb1 and gb2 in a direction perpendicular to the straight line to the line (bottom inner surface 441a) is defined as the depth of groove 440. In the case of the shape shown in Fig. 9 or 10, the definition of the ridge line of the groove is the same as in the above embodiment.

[0060] The open cross section bumper reinforcement according to the above embodiment is preferably used as a vehicle member such as a front bumper reinforcement or a rear bumper reinforcement.

[0061] [Manufacturing method] The open-section bumper reinforcement according to the above embodiment may be manufactured by performing hot stamping, cold pressing, roll forming, or extrusion on a single steel plate.

Example

[0062] (Example 1) In Example 1, on the CAE simulation, the performance of the open-section bumper reinforcement according to the above-described embodiment was evaluated by changing the position and depth of the groove portion of the open-section bumper reinforcement having the shape shown in FIG. 1 and the like.

[0063] In this example, the plate thickness t of the open-section bumper reinforcement was set to 1.4 mm.

[0064] In the cross section at the central position in the longitudinal direction of the open-section bumper reinforcement, the width of the groove portion was set to 30 mm, and the curvature radius outside the ridge line portion of the ridge line portion on the side of the groove portion side was set to 8 mm. Also, the curvature radius of the outer surface of the ridge line of the ridge line portion connecting the first plate portion and the second plate portion was set to 9.4 mm, the length in the width direction of the second plate portion was set to 50 mm, and the angle between the plate surface of the first plate portion and the plate surface of the second plate portion was set to 96 degrees. Further, the length in the longitudinal direction of the open-section bumper reinforcement was set to 1400 mm, and the length of the groove portion in the longitudinal direction of the open-section bumper reinforcement was set to 100% of the length of the open-section bumper reinforcement. The definitions of these lengths and the like were as described in the description of the embodiment. Note that the open-section bumper reinforcement of Comparative Example 1 was not provided with a groove portion.

[0065] For each experimental example, the tensile strength was as shown in Table 1. The material data used in the CAE simulation was obtained by prototyping open-section bumper reinforcements for each material with different strength classes, obtaining samples of a size conforming to JIS No. 4 test pieces from the second plate portion, and measuring the tensile strength of these samples using a universal testing machine (SDW-9103 manufactured by Imada Seisakusho) by a method conforming to JIS Z 2241.

[0066] In each experimental example, the distance L from the boundary between the first plate portion and the ridge line portion to the groove portion boundary in the direction parallel to the top plate surface and the back surface of the top plate in the cross section at the longitudinal center position of the open cross-section bumper reinforcement was as shown in Table 1. As described in the embodiment, the distance L was defined as the boundary between the first plate portion and the ridge line portion in the direction parallel to the plate surface of the first plate portion to the groove portion boundary (the boundary closer to the ridge line portion among the boundaries between the first plate portion and the groove portion) in the cross section at the longitudinal center position of the open cross-section bumper reinforcement. The distance L is shown as a multiple of the plate thickness t.

[0067] In each experimental example, the depth of the groove portion in the cross section at the longitudinal center position of the open cross-section bumper reinforcement was as shown in Table 1. As described in the embodiment, the depth d was defined as the distance from the inner surface of the groove portion farthest from this straight line to the straight line in the direction perpendicular to the straight line passing through the two boundaries in the cross section of the open cross-section bumper reinforcement. The depth d is shown as a multiple of the plate thickness t.

[0068] Also, for the open cross-section bumper reinforcements of each experimental example, their performance was measured. In the evaluation of the component performance of the impact absorption portion of this example, the maximum reaction force per unit member mass and the maximum equivalent plastic strain generated up to a stroke of 70 mm were measured. When the result was a maximum reaction force of 5.5 (N / g) or more and a maximum equivalent plastic strain of 0.3 or less, it was rated as "Good", and when the result was outside this range, it was evaluated as "No good".

[0069]

Table 1

[0070] As shown in Table 1, it can be understood that the open cross-section bumper reinforcements of Invention Examples 1 to 7 according to the present disclosure have good component performance.

[0071] (Example 2) In Example 2, the performance of the open-section bumper reinforcement according to the above-described embodiment was evaluated. Specifically, for the open-section bumper reinforcement having a shape as shown in FIG. 1 and the like and the open-section bumper reinforcement provided with one or two groove portions, the plastic strain when receiving a deformation of a predetermined stroke was measured.

[0072] In this example, the plate thickness t of the open-section bumper reinforcement was set to 1.4 mm. The method for measuring the plate thickness was the same as that in Example 1.

[0073] In the open-section bumper reinforcement A, as shown in FIG. 1 and the like, two groove portions and a central groove portion located between these groove portions were provided. In the open-section bumper reinforcement A, in the cross section at the central position in the longitudinal direction, the width of the two groove portions was 17 mm and the depth was 5.7t, the width of the central groove portion was 35 mm, and the depth was 16t. Further, in the cross section at the central position in the longitudinal direction of the open-section bumper reinforcement, the distances L1 and L2 from the boundary between the first plate portion and the ridge line portion in the direction parallel to the top plate surface and the back surface of the top plate to the groove boundary were set to 5t (≤30t).

[0074] In the open-section bumper reinforcement B, two groove portions were provided. In the open-section bumper reinforcement B, in the cross section at the central position in the longitudinal direction, the width of the two groove portions was 17 mm and the depth was 16t. The distance from the boundary between the first plate portion and the ridge line portion in the direction parallel to the top plate surface and the back surface of the top plate to the groove boundary (the boundary closer to the ridge line portion among the boundaries between the first plate portion and the groove portion) was set to 31t (>30t).

[0075] In the open-section bumper reinforcement C, one groove portion was provided. In the open-section bumper reinforcement C, in the cross section at the central position in the longitudinal direction, the width of the groove portion was 17 mm and the depth was 16t. The distance from the boundary between the first plate portion and the ridge line portion in the direction parallel to the top plate surface and the back surface of the top plate to the groove boundary was set to 40t (>30t).

[0076] For all of the open-section bumper reinforcements A to C, the radius of curvature on the outer side of the ridge line portion of the side ridge line portion of the groove is 9.4 mm, and the radius of curvature on the outer side of the ridge line portion of the side ridge line portion of the central groove is 9.4 mm. Also, the radius of curvature of the outer surface of the ridge line of each ridge line portion connecting the first plate portion and the second plate portion is 9.4 mm, the length in the width direction of the first plate portion is 130 mm, the lengths in the width direction of the two second plate portions are 66 mm, and the angle between the plate surface of the first plate portion and the plate surface of the second plate portion is 96 degrees. Also, the length in the longitudinal direction of the open-section bumper reinforcement is 1400 mm, and the length of the groove portion in the longitudinal direction of the open-section bumper reinforcement is 100% of the length of the open-section bumper reinforcement. The definitions of these lengths and the like were as described in the description of the embodiment.

[0077] Also, for all of the open-section bumper reinforcements A to C, the tensile strength was 2000 MPa. The method for measuring the tensile strength was the same as in Example 1.

[0078] For the open-section bumper reinforcements A to C as described above, a three-point bending test was carried out using CAE simulation to press down the central portion of the open-section bumper reinforcement. From the results of this test, for each of the open-section bumper reinforcements A to C, the maximum load per unit mass and the deformation up to a stroke of 70 mm were calculated, and from this, the maximum equivalent plastic strain at a stroke of 70 mm was calculated. The results are shown in FIG. 11.

[0079] The reason for adopting the maximum equivalent plastic strain at a stroke of 70 mm is as follows. When the amount of deformation reaches a stroke of 70 mm, since the peak of the load of the open-section bumper reinforcement has passed, 70 mm of stroke is the amount of stroke that satisfies the yield strength performance of the open-section bumper reinforcement. On the other hand, regarding fracture, since the deformation progresses up to a stroke of 70 mm and there is a risk of an increase in strain, the fracture risk was determined based on the maximum equivalent plastic strain amount at a stroke of 70 mm. As a criterion for judging the fracture risk, when the maximum equivalent plastic strain amount at a stroke of 70 mm exceeded 0.26, it was judged that there was a fracture risk.

[0080] As shown in Fig. 11, it is understood that the open-section bumper reinforcement A has a strain amount below the standard and a fracture risk suppressed with respect to the open-section bumper reinforcements B or C.

[0081] As shown in Fig. 11, in the open-section bumper reinforcement A according to the present disclosure, the maximum yield strength per mass is 4.32 (N / g). From this, it is understood that the present disclosure can provide a structure with a low fracture risk and a high mass efficiency with respect to the maximum load.

[0082] (Example 3) In Example 3, on the CAE simulation, the performance of the open-section bumper reinforcement according to the above-described embodiment was evaluated by changing the positions and depths of the groove portions and the central groove portion of the open-section bumper reinforcement having the shape shown in Fig. 1 and the like.

[0083] In this example, the plate thickness t of the open-section bumper reinforcement was set to 1.4 mm.

[0084] In the cross-section at the central position in the longitudinal direction of the open-section bumper reinforcement, the widths of the two groove portions were set to 15 mm, and the radii of curvature outside the ridge lines of the ridge line portions on the side portions of the groove portions were set to 5 mm. Also, the width of the central groove portion was set to 15 mm, and the radius of curvature outside the ridge line of the ridge line portion on the side portion of the central groove portion was set to 5 mm. Further, the radii of curvature of the outer surfaces of the ridge lines of the two ridge lines connecting the first plate portion and the second plate portion were set to 9.4 mm, the length in the width direction of the first plate portion was set to 140 mm, the lengths in the width direction of the two second plate portions were set to 50 mm, and the angles between the plate surface of the first plate portion and the plate surfaces of the respective second plate portions were set to 96 degrees. Also, the length in the longitudinal direction of the open-section bumper reinforcement was set to 1400 mm, and the length of the groove portion in the longitudinal direction of the open-section bumper reinforcement was set to 100% of the length of the open-section bumper reinforcement. The definitions of these lengths and the like were the same as those in the description of the embodiment. Note that the open-section bumper reinforcements of Comparative Example 2 and Comparative Example 3 were not provided with groove portions.

[0085] The tensile strengths in each experimental example were as shown in Table 2. The method for measuring the tensile strength was the same as in Example 1.

[0086] In each experimental example, the distances L1 and L2 from the boundary between the first plate portion and each ridge line portion to the boundary of each groove portion in the transverse direction at the central position in the longitudinal direction of the open-section bumper reinforcement, in the direction parallel to the top plate surface and the back surface of the top plate, were as shown in Table 2. The distance L1 or the distance L2 was defined as the boundary between the first plate portion and the ridge line portion in the direction parallel to the plate surface of the first plate portion to the groove portion boundary (the boundary closer to the ridge line portion among the boundaries between the first plate portion and the groove portion) in the transverse section at the central position in the longitudinal direction of the open-section bumper reinforcement, as described in the description of the embodiment. The distance L1 or the distance L2 is shown as a multiple of the plate thickness t.

[0087] In each experimental example, the depth (d1 or d2) of the groove portion and the depth d3 of the central groove portion in the transverse section at the central position in the longitudinal direction of the open-section bumper reinforcement were as shown in Table 2. The depths d1 to d3 were defined as the distances from the inner surface of the groove portion farthest from this straight line to the straight line in the direction orthogonal to the straight line passing through the two boundaries in the transverse section of the open-section bumper reinforcement, as described in the description of the embodiment. The depths d1 to d3 are shown as multiples of the plate thickness t.

[0088] Also, the performance of the open-section bumper reinforcement of each experimental example was measured. In the evaluation of the component performance of the shock absorption portion of this example, the maximum reaction force per unit member mass and the maximum equivalent plastic strain generated up to a stroke of 70 mm were measured. When the result was a maximum reaction force of 5.5 (N / g) or more and a maximum equivalent plastic strain of 0.3 or less, it was evaluated as "Good", and when the result was outside this range, it was evaluated as "No good".

[0089]

Table 2

[0090] As shown in Table 2, it is understood that the open-section bumper reinforcements of Invention Examples 1 to 7 according to the present disclosure have good component performance.

[0091] (Example 4) In Example 4, similar to Example 3, for the open-section bumper reinforcement having the shape shown in FIG. 1 and the like, by changing the ratio that the length of the first plate portion excluding the two groove portions and the central groove portion occupies with respect to the length from the boundary between the first plate portion and one ridge line portion to the boundary with the other ridge line portion, the performance of the open-section bumper reinforcement was evaluated.

[0092] In this example, the plate thickness t of the open-section bumper reinforcement was 1.4 mm.

[0093] In the cross-section at the central position in the longitudinal direction of the open-section bumper reinforcement, the width of the two groove portions was 20 mm, and the radius of curvature outside the ridge line portion of the ridge line portion on the side of the groove portion side was 5 mm. Also, the width of the central groove portion was 44 mm, and the radius of curvature outside the ridge line portion of the ridge line portion on the side of the central groove portion side was 5 mm. Further, the radius of curvature of the outer surface of the ridge line of the two ridge line portions connecting the first plate portion and the second plate portion was 9.4 mm. The length in the width direction of the first plate portion was 103.3 mm in Invention Examples 1 to 3 and 104.7 mm in Invention Examples 4 to 6. The length in the width direction of the two second plate portions was 50 mm, and the angle between the plate surface of the first plate portion and the plate surfaces of the respective second plate portions was 96 degrees. Also, the length in the longitudinal direction of the open-section bumper reinforcement was 1400 mm, and the length of the groove portion in the longitudinal direction of the open-section bumper reinforcement was 100% of the length of the open-section bumper reinforcement. The definitions of these lengths and the like were as described in the description of the embodiment.

[0094] The tensile strength in each experimental example was 1470 MPa. The method for measuring the tensile strength was the same as that in Example 1.

[0095] In each experimental example, the distances L1 and L2 from the boundary between the first plate portion and the respective ridge line portions to the respective groove boundaries in the direction parallel to the top plate surface and the back surface of the top plate in the cross-section at the central position in the longitudinal direction of the open-section bumper reinforcement were as shown in Table 3 or Table 4. The definitions of the distance L1 or the distance L2 were the same as those in Example 3. The distance L1 or the distance L2 was shown as a multiple of the plate thickness t.

[0096] In each experimental example, the depths (d1 or d2) of the groove portions and the depth d3 of the central groove portion in the cross section at the longitudinal center position of the open cross-section bumper reinforcement were as shown in Table 3 or Table 4. The definitions of the depths d1 to d3 are the same as those in Example 3. The depths d1 to d3 are shown as multiples of the plate thickness t.

[0097] In the cross section at the longitudinal center position of the open cross-section bumper reinforcement, the first plate portion is divided into four by two groove portions and a central groove portion. The lengths of the divided first plate portions are denoted as L1, L2, L3, and L4 respectively, and the lengths of the bottoms of the two groove portions and the central groove portion in the same cross-sectional view are denoted as L5, L6, and L7 respectively. Also, the straight-line distance L0 from the boundary between the first plate portion and one ridge line portion to the boundary between the first plate portion and the other ridge line portion in the same cross-sectional view is taken as the length from boundary to boundary.

[0098] Table 3 shows the ratio of (L1 + L2 + L3 + L4) to L0 in each experimental example. Table 4 shows the ratio of (L1 + L2 + L3 + L4 + L5 + L6 + L7) to L0 in each experimental example.

[0099] Also, the performance of the open cross-section bumper reinforcement of each experimental example was measured. In the evaluation of the component performance of the impact absorption portion of this example, the maximum load and the maximum equivalent plastic strain at the time of a stroke of 70 mm were evaluated. When the result was a maximum reaction force of 5.5 (N / g) or more and a maximum equivalent plastic strain of 0.3 or less, it was rated as "Good", and when the result was a maximum reaction force of 5.5 (N / g) or more and a maximum equivalent plastic strain of 0.25 or less, it was evaluated as "Very Good".

[0100]

Table 3

[0101] As shown in Table 3, it is understood that the member strength is improved by setting the ratio of (L1 + L2 + L3 + L4) to L0 to 18% or less. In the cross-section of the open-section bumper reinforcement, by increasing the ratio occupied by the ridge lines of the groove portions, the total amount of ridge line strength increases, and as a result, it is considered that the member strength is improved.

[0102]

Table 4

[0103] As shown in Table 4, it is understood that the member strength is improved by setting the ratio of (L1 + L2 + L3 + L4 + L5 + L6 + L7) to L0 to 25% or less. In the cross-section of the open-section bumper reinforcement, by increasing the ratio occupied by the ridge lines of the groove portions, the total amount of ridge line strength increases, and as a result, it is considered that the member strength is improved.

Industrial Applicability

[0104] According to the open-section bumper reinforcement of the present disclosure, since breakage caused by deformation occurring when the member is impacted can be suppressed, it is extremely useful industrially.

Explanation of Reference Numerals

[0105] 200 Open-section bumper reinforcement 210 First plate portion 221, 222 Second plate portions 231, 232 Ridge line portions 240, 250 Groove portions 241, 251 Bottoms of the groove portions 242, 243, 252, 253 Side portions of the groove portions 244, 245, 254, 255 Ridge line portions at the sides of the bottoms of the groove portions 246, 247, 256, 257 Ridge line portions at the sides of the side portions of the groove portions 260 Central groove portion 261 Bottom of the central groove portion 262, 263 Side portions of the central groove portion 264, 265 Ridge line portions at the sides of the bottom of the central groove portion 266, 267 Lateral ridge part of the central groove side

Claims

1. It comprises a top plate, two walls, and two ridge line portions, the tensile strength of the top plate and the walls is 1470 MPa or more, each of the two ridge line portions extends between the top plate and the walls in the longitudinal direction of the top plate, the cross-section at the central portion in the longitudinal direction is an open cross-section with a groove shape, in the cross-section, the top plate has a central groove portion extending in the longitudinal direction at the center of the width, in the cross-section, the top plate has small groove portions respectively between the central groove portion and the ridge line portions, in the cross-section, the depth of the central groove portion at the center is 15 times or more and 25 times or less of the plate thickness of the top plate, the depth of the small groove portion is 2 times or more and 13 times or less of the plate thickness of the top plate, the distance between the small groove portion and the ridge line portion is 30 times or less of the plate thickness of the top plate, in the cross-section, the central groove portion and the small groove portion each have a flat bottom, the total of the extension length (L7) of the bottom of the central groove portion, the extension lengths of the bottoms (L5, L6) of the small groove portions, the extension lengths of the flat portions (L1, L2) between the ridge line portion and the small groove portions, and the extension lengths of the flat portions (L3, L4) between the central groove portion and the small groove portions is 25% or less of the distance between the ridge line portions characterized in that it is an open cross-section bumper reinforcer.

2. in the cross-section, the total of the extension length of the flat portions (L1, L2) between the ridge line portion and the small groove portion and the extension length of the flat portions (L3, L4) between the central groove portion and the small groove portion is 18% or less of the distance between the ridge line portions, characterized in that it is the open cross-section bumper reinforcer according to Claim 1.

3. in the cross-section, the width of the small groove portion is 5 times or more and 30 times or less of the plate thickness, characterized in that it is the open cross-section bumper reinforcer according to Claim 1 or 2.

4. the tensile strength of the top plate and the walls is 1760 MPa or more characterized in that it is the open cross-section bumper reinforcer according to Claim 1 or 2.

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