Shock absorption member

Abstract

To provide a shock absorption member which is light, and can bend and deform at convenient points, so as to achieve high energy absorption efficiency.SOLUTION: A shock absorption member 1 includes a cylindrical body 30 and a reinforcement 40. The reinforcement 40 satisfies at least one of a first condition having a vertical plate 41 and a first plane part width-thickness ratio r1 of 10 or more and 50 or less, and a second condition having a transverse plate 42 and a second plane part width-thickness ratio r2 of 10 or more and 50 or less. The reinforcement 40 has a first portion R1, a second portion R2, and a third portion R3 sequentially along a longitudinal direction. In the second portion R2, a bend-start part having at least one of a plate thickness thinner than those of the first and third portions R1, R3 and tensile strength lower than those of the first and third portions R1, R3 is formed with a connection position with the cylindrical body 30 included in the bend-start part.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an impact absorbing member. [Background technology]

[0002] In recent years, fuel efficiency regulations have become stricter around the world, and automakers are promoting the weight reduction of vehicle bodies. At the same time, vehicle crash safety standards have also become stricter, so there is a demand for both weight reduction and improved crash performance. Furthermore, in response to fuel efficiency regulations in various countries and the trend toward carbon neutrality, the electrification of automobile power sources is progressing. Compared to conventional vehicle structures with internal combustion engines, the electrification of power sources has led to changes in the vehicle body structure, such as an increase in vehicle weight and a reduction in the engine compartment. One example is the shortening of the front nose of the vehicle body. In order to maintain high collision safety while shortening the vehicle nose, a structure that can obtain high energy absorption efficiency with a short deformation stroke is required.

[0003] In particular, for parts such as front side members and rear side members that actively undergo plastic deformation to absorb collision energy during a vehicle collision, structures that can dramatically improve energy absorption performance are required. Also, because such parts play a role in minimizing the external force applied to occupants during a collision, it is ideal for them to have a deformation mode that can shorten the deformation stroke while suppressing sudden load fluctuations.

[0004] The deformation of the member includes bellows deformation and serpentine deformation. The bellows deformation refers to a deformation in which out-of-plane deformation occurs on all of the side surfaces constituting a component, but the center line in the longitudinal direction of the component hardly bends at all. On the other hand, meandering deformation occurs when bending occurs at multiple points along the longitudinal direction of a component, in which out-of-plane deformation occurs mainly on one of the side surfaces that make up the component, and the center line of the component in the longitudinal direction also bends. Comparing the above two deformation modes, it can be said that bellows deformation absorbs a greater amount of impact energy than serpentine deformation if the impact force is applied from an ideal direction. However, since the input direction of the impact force is not limited to one direction, for example, if the impact force is applied obliquely to the longitudinal direction of the component, the amount of energy absorbed by bellows deformation drops significantly. In contrast, serpentine deformation (folding deformation) can flexibly respond to the direction of the impact force to a certain extent, and therefore can stably absorb impact energy. Patent documents 1 and 2 show examples of structures that absorb impact energy by folding deformation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-174121 A [Patent Document 2] International Publication No. 2021 / 192188 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 discloses a vehicle rear structure that absorbs impact energy during a rear collision. In this vehicle rear structure, a rear frame and a tank lower frame that are disposed below the rear frame are disposed in a pair on the left and right sides of the vehicle body, and the rear frame has a displacement-load characteristic that makes the ratio of load F to displacement S (F / S) larger than that of the tank lower frame, and the tank lower frame employs a configuration in which cross-sectional deformation is suppressed so that the load does not drop suddenly after reaching the maximum bending strength.

[0007] Here, as described above, in addition to weight reduction and improved collision performance, the impact absorbing member is also required to shorten the deformation stroke. One way to reduce weight is to use light alloys such as aluminum as a material, but due to the low material strength, it is not possible to improve collision performance and shorten the deformation stroke. Therefore, another idea is to use high-strength steel plates with high tensile strength and then reduce the plate thickness. However, for example, if the plate thickness is simply reduced in the rear frame disclosed in Patent Document 1, out-of-plane deformation is likely to occur at any point in the rear frame, and the position of the break starting point becomes unclear. From the viewpoint of impact energy absorption, it is not acceptable to break anywhere, and if the joints do not break at the designed position, the designed energy absorption amount cannot be obtained. In that case, the original high energy absorption amount, which should be superior to bellows deformation, cannot be exhibited. In other words, simply increasing the material strength and reducing the plate thickness does not allow the advantages of the folding deformation to be expressed to a high level, and the deformation stroke cannot be shortened. The same is true for Patent Document 2. Patent Document 2 discloses a structure including a skeletal member having a closed cross-sectional structure and a reinforcing member disposed within the skeletal member. In this structure, if the plate thickness of the skeletal member is simply reduced in order to reduce the weight, out-of-plane deformation is likely to occur at each part of the skeletal member, and the position of the breakage starting point becomes unclear. Therefore, there is room for further study to maximize the advantages of the folding deformation and further shorten the deformation stroke.

[0008] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an impact absorbing member which is lightweight yet capable of bending and deforming smoothly at its joints, thereby exhibiting high energy absorption efficiency. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention employs the following means. (1) One aspect of the present invention is A shock absorbing member having a hollow tube and a reinforcement fixedly disposed inside the hollow tube, the shock absorbing member being long in one direction, The hollow tube is made of a steel material having a tensile strength of 650 MPa or more and 1600 MPa or less, and the reinforcement is made of a steel material having a tensile strength of 590 MPa or more and 1600 MPa or less; A cross section perpendicular to the longitudinal direction of the impact absorbing member, The hollow tube has a top wall portion having a flat portion overall width dimension W1 (mm) and a wall thickness t1 (mm), and a pair of side wall portions provided on both sides of the top wall portion and having a flat portion overall width dimension W2 (mm) and a wall thickness t1 (mm), The reinforcement has at least one of a vertical plate having one end joined to the top wall portion, a total number of n1 plates, and a total plate thickness of t2 (mm), and a horizontal plate connecting the pair of side wall portions, a total number of n2 plates, and a total plate thickness of t3 (mm); The reinforcement is At least one of the following conditions is satisfied: a first condition in which the first flat portion width-thickness ratio r1 according to the vertical plate and the following formula 1 is 10 or more and 50 or less; and a second condition in which the second flat portion width-thickness ratio r2 according to the horizontal plate and the following formula 2 is 10 or more and 50 or less. having a first portion, a second portion, and a third portion aligned in sequence along the longitudinal direction; In the second portion, A plate thickness that is thinner than both the first portion and the third portion, and a tensile strength lower than both the first portion and the third portion; A bend starting point having at least one of the above is formed including a connection position with the hollow tube. r1=((W1-t2) / (n1+1)) / t1...(Formula 1) r2=((W2-t3) / (n2+1)) / t1...(Formula 2)

[0010] According to the impact absorbing member described in (1) above, when the bending start point is set in the top wall of the hollow tube, the top wall at the start of bending deformation tends to sink inwardly into the hollow tube. When only the first condition is satisfied, the vertical plate continues to support the top wall while resisting the force that tends to sink. This prevents the top wall from sinking, and also prevents the gap between the pair of side walls that tends to occur as the top wall sinks. In this way, the hollow tube is supported by the reinforcement from the inside. Alternatively, when only the second condition is satisfied, the spacing between the pair of side walls is constrained by the horizontal plate. This constraint prevents the top wall from sinking in to expand the gap between the pair of side walls, and the top wall is indirectly supported. Therefore, in this case as well, the hollow tube is supported from the inside by the reinforcement. Alternatively, when both the first and second conditions are satisfied, in addition to suppressing sinking of the top wall, the gap between the pair of side walls is also suppressed. Therefore, due to the synergistic effect of both, the hollow tube is more firmly supported from the inside by the reinforcement. In this way, the hollow tube is reinforced at each position in the longitudinal direction by the reinforcement. In addition, the hollow tube satisfies at least one of the first condition that the first flat portion width-thickness ratio r1 is 10 or more and 50 or less, and the second condition that the second flat portion width-thickness ratio r2 is 10 or more and 50 or less. As a result, even if the thickness t1 of the hollow tube is thinned for the purpose of weight reduction, the top wall portion or the side wall portion does not easily deform out of plane. If out-of-plane deformation occurs at an unintended position, the way of compressive deformation at that portion becomes unstable, so that the out-of-plane deformed portion may be easily or difficult to break. As a result, there is a risk of bending deformation occurring at an unintended position of the hollow tube. On the other hand, in this embodiment, at least one of the first condition and the second condition is satisfied. As a result, it is possible to suppress out-of-plane deformation of the hollow tube at an unintended portion, and therefore the thickness t1 can be thinned to reduce the weight of the impact absorbing member. On the other hand, since the second portion of the impact absorbing member has at least one of a thickness thinner than both the first portion and the third portion and a tensile strength lower than both the first portion and the third portion, the bending strength of the second portion is relatively lower than the bending strength of the first portion and the bending strength of the third portion. By combining this relative strength difference with at least one of the first condition and the second condition described above, the impact absorbing member can be bent and deformed smoothly with the second portion as the bending origin. In addition, the impact energy applied to the impact absorbing member is absorbed mainly by the reinforcement while bending and deforming with the second portion as the starting point, so that the amount of energy absorption can be increased.

[0011] (2) The impact absorbing member according to the above (1) may be as follows: the tensile strength of the folding origin portion in the second region is equal to the tensile strengths in the first region and the third region; A thickness ratio obtained by dividing the total thickness t2 at the break origin in the second location by an average thickness ta3 (mm) which is the average value of the total thickness t3 in the first location and the total thickness t3 in the third location satisfies 1 / 3 to (ta3-0.2) / ta3. According to the shock absorbing member described in (2) above, since the upper limit of the thickness ratio at the break point is (ta3-0.2) / ta3, the minimum thickness difference required for the shock absorbing member to bend smoothly at the break point can be ensured. Also, since the lower limit of the thickness ratio at the break point is 1 / 3, there is an advantage that the shock absorbing member can be deformed reliably at a predetermined position regardless of the load conditions in the actual usage environment.

[0012] (3) The impact absorbing member according to the above (1) may be as follows: The total thickness t2 at the folding start point in the second region is equal to an average thickness ta3 (mm) which is an average value of the total thickness t3 in the first region and the total thickness t3 in the third region; A tensile strength ratio obtained by dividing the tensile strength E1 (MPa) of the folding starting portion in the second region by an average tensile strength Ea2 (MPa) which is the average value of the tensile strength in the first region and the tensile strength in the third region satisfies (Ea2-100) / Ea2~2. According to the shock absorbing member described in (3) above, since the upper limit of the tensile strength ratio at the folding start point is 2, it is possible to ensure the minimum tensile strength difference required for the shock absorbing member to bend smoothly at the folding start point position. Also, since the lower limit of the tensile strength ratio at the folding start point is (Ea2-100) / Ea2, there is an advantage that deformation can be reliably achieved at a predetermined position regardless of the load conditions in the actual usage environment.

[0013] (4) The impact absorbing member according to the above (1) may be as follows: a thickness ratio obtained by dividing the total thickness t2 at the folding starting point in the second region by an average thickness ta3 (mm) which is an average value of the total thickness t3 in the first region and the total thickness t3 in the third region satisfies 1 / 3 to (ta3-0.2) / ta3; A tensile strength ratio obtained by dividing the tensile strength E1 (MPa) of the folding starting portion in the second region by an average tensile strength Ea2 (MPa) which is the average value of the tensile strength in the first region and the tensile strength in the third region satisfies (Ea2-100) / Ea2~2. According to the shock absorbing member described in (4) above, the synergistic effect of the combination of (2) and (3) above makes the difference in bending strength between the bending start point and its surroundings clearer, and the shock absorbing member can be bent smoothly at the bending start point. The reasons for each upper and lower limit values ​​are as described above.

[0014] (5) In the impact absorbing member according to any one of the above (1) to (4), In the direction along the longitudinal direction, A length dimension Lr1 (mm) of the bend starting point and a length dimension Lr2 (mm) of the reinforcement may satisfy Lr2>Lr1>(1 / 2)×Lr2. According to the shock absorbing member described in (5) above, by setting the lower limit of the length Lr1 of the folding start portion as described above, the bending strength difference between the folding start portion and its surroundings can be made clearer, and the shock absorbing member can be folded and deformed smoothly at the folding start portion. Also, by setting the upper limit of the length dimension Lr1 of the folding start portion as described above, the out-of-plane deformation region can be made smaller, which is advantageous in that a higher energy absorption amount can be obtained.

[0015] (6) In the impact absorbing member according to any one of the above (1) to (4), When the reinforcement is viewed in a cross section perpendicular to the longitudinal direction at a position including the folding start point, A width dimension Wr1 (mm) of the bend starting point and a width dimension Wr2 (mm) between the center of the reinforcement and the connection position may satisfy Wr2≧Wr1>(1 / 3)×Wr2. According to the shock absorbing member described in (6) above, by setting the lower limit of the width dimension Wr1 of the folding start portion as described above, the bending strength difference between the folding start portion and its surroundings can be made clearer, and the shock absorbing member can be bent smoothly at the folding start portion. Also, by setting the upper limit of the width dimension Wr1 of the folding start portion as described above, it is possible to reduce the relative weak area, which has the advantage of allowing a higher energy absorption amount to be obtained.

[0016] (7) In the impact absorbing member according to any one of the above (1) to (4), the following may be performed: The first condition is met; In a cross-sectional view perpendicular to the longitudinal direction, a flange formed at the one end of the vertical plate is spot welded to the top wall portion. According to the shock absorbing member described in (7) above, by adopting a surface joint using a flange, it is possible to more reliably prevent out-of-plane deformation at unexpected locations in the top wall portion, compared to, for example, a line joint in which the plate thickness of the one end of the vertical plate is the joint line. In addition, by adjusting the pitch and area of ​​spot welding, it is possible to fine-tune the distribution of the joint strength along the longitudinal direction of the shock absorbing member, for example.

[0017] (8) In the impact absorbing member according to any one of the above (1) to (4), the following may be performed: The second condition is met; In a cross-sectional view perpendicular to the longitudinal direction, flanges formed on both ends of the horizontal plate are spot-welded to each of the pair of side wall portions. According to the impact absorbing member described in (8) above, by adopting a surface joint using a flange, it is possible to more reliably prevent out-of-plane deformation at unexpected locations in the pair of side wall portions, compared to, for example, a line joint in which the plate thickness at both ends of the horizontal plate is used as the joint line. In addition, by adjusting the pitch and area of ​​spot welding, it is possible to fine-tune the distribution of the joint strength along the longitudinal direction of the impact absorbing member, for example.

[0018] (9) The impact absorbing member according to the above (1) may be as follows: The hollow tube is A hat-shaped member having a hat top portion whose cross section perpendicular to the longitudinal direction is the top wall portion and the pair of side wall portions connected to both sides of the hat top portion; a plate-like member joined to the hat-shaped member and facing the hat top; Both the first condition and the second condition are met; In a cross section perpendicular to the longitudinal direction, The total number n1 is 1 and the total number n2 is 1, The vertical plate is fixed in a spanning state between the hat top and the plate-like member, The horizontal plate is fixed between the pair of side wall portions in a state where it crosses the vertical plate. According to the shock absorbing member described in (9) above, when viewed in a cross section perpendicular to the longitudinal direction, the hollow tube is supported from the inside by the surface formed by the combination of the vertical plates and the horizontal plates. Therefore, the bending strength of the reinforcement can be increased over its entire length, so that the maximum load (barrier reaction force) can be increased and this maximum load can be maintained for a long time, thereby increasing the amount of energy absorption.

[0019] (10) The impact absorbing member according to the above (1) may be as follows: The hollow tube is a hat-shaped member having a hat top portion whose cross section perpendicular to the longitudinal direction is the top wall portion and a pair of side wall portions connected to both sides of the hat top portion; a plate-like member joined to the hat-shaped member and facing the hat top; Both the first condition and the second condition are met; In a cross section perpendicular to the longitudinal direction, The total number n1 is 1 and the total number n2 is 1, One end of the horizontal plate is joined to one of the pair of side wall portions, and the other end of the horizontal plate is joined to the other of the pair of side wall portions, The one end of the vertical plate is joined to the top of the hat, and the other end of the vertical plate is joined to a position between the one end and the other end of the horizontal plate. According to the shock absorbing member described in (10) above, when viewed in a cross section perpendicular to the longitudinal direction, the hollow tube is supported from the inside by the surface formed by the combination of the vertical plates and the horizontal plates. Therefore, the bending strength of the reinforcement can be increased over its entire length, so that the maximum load (barrier reaction force) can be increased and this maximum load can be maintained for a long time, thereby increasing the amount of energy absorption. Effect of the Invention

[0020] According to the impact absorbing member according to each of the above aspects of the present invention, it is lightweight, yet can bend and deform smoothly at its joints, thereby achieving high energy absorption efficiency. [Brief description of the drawings]

[0021] [Figure 1] 1 is a perspective view of a vehicle body in which an impact absorbing member according to an embodiment of the present invention is applied to a front side member and a rear side member. [Diagram 2] 1 is a perspective view of the shock absorbing member, with a part cut away to show the inside of the shock absorbing member, in which the illustration of the break point is omitted. [Diagram 3] FIG. 4 is a perspective view showing an example of a reinforcement provided in the impact absorbing member. [Figure 4] FIG. 11 is a perspective view showing another example of a reinforcement provided in the impact absorbing member. [Diagram 5] FIG. 11 is a perspective view showing another example of a reinforcement provided in the impact absorbing member. [Figure 6] FIG. 11 is a perspective view showing another example of a reinforcement provided in the impact absorbing member. [Figure 7] FIG. 3 is a schematic diagram for explaining dimensions of each part of the impact absorbing member, and is a cross-sectional view taken along the line BB in FIG. 2. [Figure 8] 3(a) to 3(d) are diagrams showing modified examples of the impact absorbing member, respectively, and are cross-sectional views taken along the line BB in FIG. 2. [Figure 9] 5(a) to (e) are diagrams showing other modified examples of the impact absorbing member, respectively, and are cross-sectional views taken along the line BB in FIG. [Figure 10] 5(a) to (d) are diagrams showing still other modified examples of the impact absorbing member, respectively, and are cross-sectional views taken along the line BB in FIG. [Figure 11] 5(a) to (c) are diagrams showing still other modified examples of the impact absorbing member, respectively, and are cross-sectional views taken along the line BB in FIG. [Figure 12] 5(a) to (e) are diagrams showing still other modified examples of the impact absorbing member, respectively, and are cross-sectional views taken along the line BB in FIG. [Figure 13] 5(a) to (g) are diagrams showing still other modified examples of the impact absorbing member, respectively, and are cross-sectional views taken along the line BB in FIG. [Figure 14] 5(a) to (e) are diagrams showing still other modified examples of the impact absorbing member, respectively, and are cross-sectional views taken along the line BB in FIG. [Figure 15] FIG. 1 is a diagram illustrating the impact absorbing member used in the first embodiment, in which (a) is a side view showing the impact absorbing member before a load is applied along the longitudinal direction, and (b) is a side view showing the impact absorbing member after it has been subjected to the load and has undergone out-of-plane deformation. [Figure 16] FIG. 10 is a diagram for explaining the first embodiment, and is a graph in which the horizontal axis indicates the ratio W / t and the vertical axis indicates the out-of-plane deformation amount δ. [Figure 17]12(a) and 12(b) are diagrams for explaining the impact absorbing member used in the second embodiment, in which FIG. 12(a) is a cross-sectional view corresponding to FIG. 7 or FIG. 12(a), and FIG. [Figure 18] 11A and 11B are diagrams illustrating the second embodiment, in which (a) is a perspective view of a bent and deformed portion in the impact absorbing member of Case A, and (b) is a perspective view of a bent and deformed portion in the impact absorbing member of Case B. FIG. [Figure 19] FIG. 3 is a diagram showing the impact absorbing member used in the third embodiment, and is a cross-sectional view taken along line BB in FIG. 2. Of these, Cases 000 and 005 are comparative examples, while Cases 001 to 004 are examples of the invention that are provided with various reinforcements. [Figure 20] 11 is a perspective view showing how a load is applied in the third embodiment, (a) showing the state before bending deformation and (b) showing the state after bending deformation. [Figure 21] 13 is a bar graph comparing maximum loads in the third embodiment, in which the horizontal axis indicates each case number and the vertical axis indicates maximum load (kN). [Figure 22] 13 is a bar graph comparing the amount of energy absorption in the third embodiment, in which the horizontal axis indicates each case number and the vertical axis indicates the amount of energy absorption (kJ). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, a shock absorbing member according to an embodiment of the present invention and various modified examples thereof will be described with reference to the drawings. As shown in Fig. 1, the impact absorbing member of this embodiment can be used as a front side member FM or a rear side member RM, which are frame members of an automobile. When the impact absorbing member is used as a front side member FM, it is disposed on the vehicle front FW side relative to the passenger compartment C. On the other hand, when the impact absorbing member is used as a rear side member RM, it is disposed on the vehicle rear RW side relative to the passenger compartment C. The impact absorbing member is a hollow tube that is long in one direction, and in either case of use as a front side member FM or a rear side member RM, it is disposed so that one end side in the longitudinal direction faces the vehicle front and the other end side in the longitudinal direction faces the vehicle rear.

[0023] Although details will be described later, the impact absorbing member has a rectangular cross section perpendicular to its longitudinal direction, and includes a hat-shaped member and a plate-shaped member. The hat-shaped member has a cross section perpendicular to the longitudinal direction that is a hat top that is a top wall portion, and a pair of side walls that are connected to both sides of the hat top. The plate-shaped member is joined to the hat-shaped member and faces the hat top. The shock absorbing member absorbs impact force by bending deformation rather than bellows deformation. Hereinafter, the area that undergoes bending deformation shown in Fig. 1 will be given the reference symbol 1, and will be described while illustrating this as the shock absorbing member 1. Also, a case where the trigger for the bending deformation (the trigger for folding) is set in the top wall will be described as an example.

[0024] 2, the impact absorbing member 1 of this embodiment is a cylindrical part that is long in the longitudinal direction along its center line CL. The impact absorbing member 1 has a rectangular cross section perpendicular to the center line CL, and includes a hat-shaped member 10, a plate-shaped member 20, and a reinforcement 40.

[0025] The hat-shaped component 10 has one top wall portion 11 , a pair of side wall portions 12 , and a pair of flange portions 13 . The top wall 11 forms the hat top of the hat-shaped member 10, which has a hat shape when viewed along the center line CL. The top wall 11 is a long plate that is long in a direction parallel to the center line CL, and the outer width dimension and plate thickness are constant at each position in the extending direction. The outer width dimension referred to here includes the ridge lines EL formed along both side edges of the top wall 11. The top wall 11 has a flat upper surface and a flat lower surface. The outer width dimension and thickness of the top wall 11 do not necessarily have to be constant at each position along the center line CL, and may be slightly changed so as to be different at each position along the center line CL according to the needs of the part design. Similarly, the upper and lower surfaces of the top wall 11 do not necessarily have to be flat, and may have some unevenness according to the needs of the part design.

[0026] The pair of side walls 12 include a left side wall 12a and a right side wall 12b. The left side wall 12a is a vertical wall integrally connected to one of both side edges of the top wall 11. In a cross section perpendicular to the center line CL, the angle between the left side wall 12a and the top wall 11 may be 90° or slightly larger than 90°. The left side wall 12a has a substantially constant width and a substantially constant thickness. The left side wall 12a has a flat outer surface and a flat inner surface. The right side wall portion 12b is a vertical wall integrally connected to the other of both side edges of the top wall portion 11. In a cross section perpendicular to the center line CL, the angle between the right side wall portion 12b and the top wall portion 11 may be 90° or an angle slightly larger than 90°. The right side wall portion 12b has a substantially constant width dimension and a substantially constant plate thickness. The right side wall portion 12b has a flat outer surface and a flat inner surface.

[0027] The left side wall portion 12a and the right side wall portion 12b are each a long plate that is long in a direction parallel to the center line CL when viewed in a cross section perpendicular to the longitudinal direction of the impact absorbing member 1, and the outer height dimension and plate thickness at each position in the extending direction are constant. The outer height dimension referred to here also includes the portion of the ridge line EL formed along each upper edge of the left side wall portion 12a and the right side wall portion 12b. The left side wall portion 12a and the right side wall portion 12b have a flat outer side surface and a flat inner side surface. The outer width dimensions and thicknesses of the left side wall portion 12a and the right side wall portion 12b do not necessarily have to be constant at each position along the center line CL, and may be slightly changed so as to be different at each position along the center line CL as required for part design. Similarly, the outer and inner surfaces of the left side wall portion 12a and the right side wall portion 12b do not necessarily have to be flat, and may have some unevenness as required for part design.

[0028] The pair of flange portions 13 includes a left flange portion 13a and a right flange portion 13b. The left flange portion 13a is integrally connected to the lower edge of the left side wall portion 12a. The left flange portion 13a is a band-shaped plate having a substantially constant width and thickness, and is elongated in the direction along the center line CL. The left flange portion 13a has a flat upper surface and a flat lower surface. The right flange portion 13b is integrally connected to the lower edge of the right side wall portion 12b. The right flange portion 13b is a band-shaped plate having a substantially constant width and thickness, and is elongated in the direction along the center line CL. The right flange portion 13b has a flat upper surface and a flat lower surface. The width and thickness of the left and right flange portions 13a, 13b do not necessarily have to be constant at each position along the center line CL, and may be changed at each position along the center line CL as required for part design. Similarly, the upper and lower surfaces of the left and right flange portions 13a, 13b do not necessarily have to be flat, and may have some irregularities depending on the shape of the plate-like member 20.

[0029] A ridge line EL parallel to the center line CL is formed between the top wall 11 and the left side wall 12a. A ridge line EL parallel to the center line CL is also formed between the top wall 11 and the right side wall 12b. The pair of ridge lines EL are parallel to each other and also to the center line CL. The combination of the top wall portion 11, the left side wall portion 12a, and the right side wall portion 12b forms a generally trapezoidal shape in a cross section perpendicular to the center line CL. Furthermore, by combining this combination with the left flange portion 13a and the right flange portion 13b, a hat-shaped member 10 is formed, the cross section perpendicular to the longitudinal direction of which is hat-shaped. This hat-shaped member 10 is obtained by pressing a die-cut plate material. The material of the hat-shaped member 10 is a metal, and a high-strength steel plate with a tensile strength of 650 MPa or more and 1600 MPa or less can be suitably used.

[0030] The plate-shaped member 20 is a long metal plate along the center line CL, and a high-strength steel plate having a tensile strength of 650 MPa or more and 1600 MPa or less can be suitably used. The plate-shaped member 20 has a flat upper surface and a flat lower surface. The plate-shaped member 20 is welded to the left flange portion 13a and the right flange portion 13b at both side edges thereof. This forms a closed cross section between the hat-shaped member 10 and the plate-shaped member 20. In this manner, the hat-shaped member 10 and the plate-shaped member 20 form a cylindrical body 30. The width and thickness of the plate-like member 20 do not necessarily have to be constant at each position on the center line CL, and may vary slightly at each position along the center line CL as required for part design. Similarly, the upper and lower surfaces of the plate-like member 20 do not necessarily have to be flat, and may have some irregularities as required for part design.

[0031] Next, the reinforcement 40 will be described. The reinforcement 40 has a folding trigger at the center position in the longitudinal direction. Since there are multiple variations in the folding trigger, the basic configuration of the reinforcement 40 itself will be described first, and then the folding trigger will be described.

[0032] 2, the reinforcement 40 has a vertical plate 41 and a horizontal plate 42. The reinforcement 40 is divided into a first region R1, a second region R2, and a third region R3 that are aligned in this order along the longitudinal direction. The vertical plate 41 is a single strip-shaped plate having a substantially constant width and thickness except for the second portion R2, and is long in the direction along the center line CL. The vertical plate 41 has a flat left side and a flat right side except for the second portion R2. Although the vertical plate 41 is a single strip-shaped plate, it is apparently divided into two by a horizontal plate 42 that intersects at the center position in the height direction when viewed in a cross section perpendicular to the longitudinal direction of the impact absorbing member 1. The upper and lower portions of the two divided vertical plate 41 have the same height and length dimensions.

[0033] 3 has the same thickness at each position in the longitudinal direction. On the other hand, in the upper part of the vertical plate 41, the thickness of at least a part of the second region R2 is thinner than the thicknesses of the first region R1 and the third region R3. That is, in the upper part of the vertical plate 41, a rectangular region in the second region R2 serves as a folding starting point BP whose thickness is thinner than that of the surrounding region. More specifically, the thickness ratio obtained by dividing the thickness t2 (mm) at the break start point BP (the total thickness if there are multiple vertical plates 41) by the average thickness ta3 (mm), which is the average of the thickness t3 (mm) at the first region R1 (the total thickness if there are multiple vertical plates 41) and the thickness t3 (mm) at the third region R3 (the total thickness if there are multiple vertical plates 41), satisfies 1 / 3~(ta3-0.2) / ta3.

[0034] The fold origin BP can be formed, for example, by a tailor welded blank (TWB) in which a plate material having a recess formed in the upper center portion so as to be substantially U-shaped in side view and a plate material to be joined to the recess and having a thickness thinner than the other plate material are prepared, and these are joined by welding to form one vertical plate 41. Alternatively, the vertical plate 41 having the fold origin BP can be formed by a tailor rolled blank (TRB).

[0035] The horizontal plate 42 is a strip-shaped plate having a substantially constant width and thickness, and is long in the direction along the center line CL. The horizontal plate 42 has a flat upper surface and a flat lower surface. Although the horizontal plate 42 is a strip-shaped plate, when viewed in a cross section perpendicular to the longitudinal direction of the impact absorbing member 1, it is apparently divided into two by a vertical plate 41 that intersects at the center position in the width direction. The left and right portions of the two-part horizontal plate 42 have the same width, thickness, and length.

[0036] The reinforcement 40 has a "+" shape when viewed in a cross section perpendicular to the longitudinal direction of the impact absorbing member 1. The center line CL of the impact absorbing member 1 passes through the intersection between the vertical plate 41 and the horizontal plate 42. The vertical plate 41 and the horizontal plate 42 can be joined by, for example, welding. When viewed in a cross section perpendicular to the longitudinal direction of the impact absorbing member 1, the vertical plate 41 has its upper end (one end) joined to the widthwise center of the lower surface of the top wall portion 11, and its lower end joined to the widthwise center of the upper surface of the plate-like member 20. At this time, the upper edges of the first portion R1 and the third portion R3 of the vertical plate 41 and the upper edge of the folding point BP in the second portion R2 are directly joined to the lower surface of the top wall portion 11. In this way, the top wall portion 11 is supported mainly by the vertical plate 41 and the plate-like member 20. That is, the top wall portion 11 is supported by three regions: the first portion R1 and the third portion R3, which are relatively thick, and the second portion R2, which has the folding point BP, which is relatively thin.

[0037] The horizontal plate 42 has a left end (one end) joined to the center in the height direction of the inner surface of the left side wall portion 12a and a right end (the other end) joined to the center in the height direction of the inner surface of the right side wall portion 12b when viewed in a cross section perpendicular to the longitudinal direction of the impact absorbing member 1. In this way, the horizontal plate 42 restrains the left side wall portion 12a and the right side wall portion 12b so that the distance therebetween is kept constant.

[0038] A high-strength steel plate having a tensile strength of 650 MPa or more and 1600 MPa or less can be suitably used as the reinforcement 40. That is, the reinforcement 40 can be manufactured by intersecting a vertical plate 41 and a horizontal plate 42 made of the high-strength steel plate with each other and then welding them together. Furthermore, the impact absorbing member 1 can be manufactured by welding the reinforcement 40 into the cylindrical body 30. The arrangement of the reinforcement 40 inside the cylindrical body 30 at this time is as described above with reference to FIG. 2. Although the vertical plate 41 is manufactured by TWB or TRB, the material of the folding start point BP is the same as that of the other parts, and only the plate thickness is different. Therefore, the tensile strength of the folding start point BP in the second part R2 and the tensile strengths in the first part R1 and the third part R3 are both equal and are 650 MPa or more and 1600 MPa or less.

[0039] Next, the breakage trigger will be described. 2, the upper surface of the top wall portion 11 is set to be on the inner side of the bending when it breaks at the center position in the longitudinal direction of the impact absorbing member 1. This setting is mainly performed by combining the arrangement of the impact absorbing member 1 in the vehicle and the setting of the position of the bending trigger of the reinforcement 40. The shock absorbing member 1 can be arranged inside the vehicle by shifting the point of application of the shock load to the side closer to the top wall portion 11 than the center line CL, as will be described later with reference to FIG. 16(a).

[0040] On the other hand, the position of the folding trigger is set by dividing the reinforcement 40 into a first portion R1, a second portion R2, and a third portion R3 arranged in order along the longitudinal direction, as shown in Fig. 2. Among these, the bending strength of the second portion R2 is set lower than the bending strengths of the first portion R1 and the third portion R3. This allows the shock absorbing member 1 to bend and deform with the upper surface of the top wall portion 11 on the inner side at the position overlapping with the second portion R2. The above-mentioned relative bending strength difference can be obtained by the arrangement of the folding start portion BP.

[0041] In the configuration illustrated in FIG. 3, the width dimension Wr1 (mm) of the folding start portion BP is set equal to the height dimension of the upper portion of the vertical plate 41. That is, the entire width dimension Wr2 (mm) of the vertical plate 41 between the widthwise center position where the center line CL of the reinforcement 40 passes and the upper edge position which is the connection position with the top wall portion 11 is set as the folding start portion BP having a thin plate thickness. However, this is not limited to this form, and for example, as shown in FIG. 4, the folding start portion BP may be formed at a position that is 1 / 3 the width of the upper portion of the vertical plate 41 and includes the upper edge of the vertical plate 41. More specifically, the width dimension Wr1 (mm) and the width dimension Wr2 (mm) may satisfy Wr2≧Wr1>(1 / 3)×Wr2. In both cases of FIG. 3 and FIG. 4, it is preferable to arrange the folding start portion BP so that it divides the upper edge portion of the vertical plate 41 at the position of the second region R2 by including the upper edge portion of the vertical plate 41.

[0042] As shown in Fig. 5, the folding start point BP may be formed on the horizontal plate 42 instead of the vertical plate 41. In this case, it is preferable that the folding start point BP is formed at the center of the horizontal plate 42 in the longitudinal direction, at one position each on the left and right portions with the vertical plate 41 in between. It is also preferable that the folding start point BP on the left portion and the folding start point BP on the right portion have the same shape and size (same width, same length, same plate thickness). This makes it possible to make the bending strengths on the left and right sides of the center line CL of the shock absorbing member 1 equal to each other, so that the bending direction in which the upper surface of the top wall portion 11 is on the inside of the bending can be controlled with high precision. 5, the number of fold start points BP formed on the horizontal plate 42 is two, but the total number may be an even number of 2 or more. In this case, too, it is preferable that the fold start points BP on the left portion and the fold start points BP on the right portion are the same size and number. Furthermore, the folding start points BP may be formed on both the vertical plate 41 and the horizontal plate 42 as described above.

[0043] In the configuration illustrated in FIG. 5, the width dimension Wr1 (mm) of the folding start portion BP is set equal to the width dimension of the left or right portion of the horizontal plate 42. That is, the entire width dimension Wr2 (mm) between the widthwise center position of the horizontal plate 42, through which the center line CL of the reinforcement 40 passes, and the side edge position, which is the connection position with the left side wall portion 12a or the right side wall portion 12b, is set as the folding start portion BP having a thin plate thickness. However, the present invention is not limited to this form, and the folding start portion BP may be formed at a position that is 1 / 3 the width of the left or right portion of the horizontal plate 42 and includes the side edge of the horizontal plate 42, as shown in FIG. 6. More specifically, the width dimension Wr1 (mm) and the width dimension Wr2 (mm) may satisfy Wr2≧Wr1>(1 / 3)×Wr2. In both cases of Figures 5 and 6, it is preferable to include both side edge portions of the horizontal plate 42 so that each folding start portion BP is positioned so as to divide both side edge portions of the horizontal plate 42 at the position of the second region R2.

[0044] The above-described configuration of Fig. 3 or 4 may be combined with the configuration of Fig. 5 or 6. That is, the folding start portion BP may be formed at the position of the second region R2 for both the vertical plate 41 and the horizontal plate 42. In this case, the width dimension Wr1 of the folding start portion BP formed in the vertical plate 41 may be equal to the width dimension Wr1 of the folding start portion BP formed in the horizontal plate 42, or may be different from each other.

[0045] In the above example, the breakage starting points BP are formed by reducing the plate thickness. Alternatively, the breakage starting points BP may be formed by partially reducing the tensile strength. That is, the thickness t2 at the folding start point BP in the second region R2 (total thickness when there are multiple vertical plates 41) may be equal to the average thickness ta3 of the thickness t3 at the first region R1 (total thickness when there are multiple vertical plates 41) and the thickness t3 at the third region R3 (total thickness when there are multiple vertical plates 41) may be equal to each other. In addition, the tensile strength ratio obtained by dividing the tensile strength E1 (MPa) of the folding start point BP in the second region R2 by the average tensile strength Ea2 (MPa) which is the average value of the tensile strength at the first region R1 and the tensile strength at the third region R3 may satisfy (Ea2-100) / Ea2~2. Such a tensile strength difference is obtained by joining the folding start point BP made of a material different from the material of the vertical plate 41 or the horizontal plate 42 by the TWB. Furthermore, both the vertical plate 41 and the horizontal plate 42 in the second region R2 may be provided with folding start points BP having a relatively low tensile strength.

[0046] In order to prevent out-of-plane deformation from occurring in unintended locations, the impact absorbing member 1 having the reinforcement 40 and the tubular body 30 described above, both the first region R1 and the third region R3 satisfy both the first condition that (1) the first region R1 has a vertical plate 41 and the first planar portion width-thickness ratio r1 according to the following formula 1 is 10 or more and 50 or less, and (2) the second condition that the second region R1 has a horizontal plate 42 and the second planar portion width-thickness ratio r2 according to the following formula 2 is 10 or more and 50 or less.

[0047] r1=((W1-t2) / (n1+1)) / t1...(Formula 1) r2=((W2-t3) / (n2+1)) / t1...(Formula 2)

[0048] These formulas 1 and 2 will be explained below with reference to FIG. 7, but first FIG. Fig. 7 is a schematic diagram for explaining the dimensions of each part at the position of the first part R1 or the third part R3 of the impact absorbing member 1, and corresponds to the cross-sectional view taken along line BB in Fig. 2. Note that in Fig. 7, the following illustrations are used for ease of understanding. First, the curvature of the curved portions (rounded portions) at the ridge lines EL is shown to be larger than the actual curvature. Each curved portion is a corner portion that connects the top wall portion 11 to the left side wall portion 12a and the right side wall portion 12b, respectively, and has a predetermined radius of curvature. 7, the pair of left and right side walls 12a, 12b are parallel to each other. The plate-like member 20 and the left and right flanges 13a, 13b are integrated without any joints between them. The position of the vertical plate 41 in the left-right direction is slightly offset from the position of the center line CL. Similarly, the position of the horizontal plate 42 in the up-down direction is slightly offset from the position of the center line CL. The plate thickness of the vertical plate 41 and the plate thickness of the horizontal plate 42 are made different from each other.

[0049] Equations 1 and 2 will be explained with reference to FIG. First, the symbol W1 in Equation 1 is the overall flat width dimension (unit: mm) of the flat top wall 11 having an upper surface that is the inner side of the bend in the rectangular cylindrical body 30. This overall flat width dimension W1 does not include the curved portion (rounded portion) including the ridge line EL. For example, if the width of the flat portion of the top wall 11 is w1 (mm) and w2 (mm) with respect to the joint position with the upper edge of the vertical plate 41 as the boundary, W1 = w1 + w2 + t2. Here, the thickness of the top wall 11 within the range of the overall flat width dimension W1 is t1 (mm). As will be described later, the total plate thickness of the vertical plate 41 is t2 (mm).

[0050] W2 is the overall flat width dimension (unit: mm) of each of the flat left side wall portion 12a and the flat right side wall portion 12b that are connected to both sides of the top wall portion 11 via a pair of bends. This overall flat width dimension W2 does not include the bend (rounded portion) including the ridge line EL and the bend (rounded portion) formed between the left flange portion 13a and the right flange portion 13b (not shown). For example, when the flat widths of each side wall portion 12 are w3 (mm) and w4 (mm) with respect to the joint position with the horizontal plate 42 as the boundary, W2 = w3 + w4 + t3. The thickness of the top wall portion 11 within the range of this overall flat width dimension W2 is t1 (mm), which is the same as the top wall portion 11. Also, as described later, the total plate thickness of the horizontal plate 42 is t3 (mm).

[0051] In the case of the impact absorbing member 1 of this embodiment, the symbol t2 in formula 1 is the plate thickness (total plate thickness, in mm) of the vertical plate 41 whose upper end (one end) is joined to the top wall portion 11 and whose total number is one (n1=1). The symbol t3 in formula 2 is the plate thickness (total plate thickness, in mm) of the horizontal plate 42 which connects the left side wall portion 12a and the right side wall portion 12b and whose total number is one (n2=1). As shown in FIG. 7, the total plate thickness t2 may be thicker than the total plate thickness t3, or conversely, the total plate thickness t3 may be thicker than the total plate thickness t2, or the total plate thickness t2 and the total plate thickness t3 may be equal.

[0052] The symbol n1 in the formula 1 is the total number of the vertical plates 41 in the reinforcement 40, which is one (n1=1) in the impact absorbing member 1 of this embodiment. If a configuration is provided with multiple vertical plates 41 and the plate thicknesses of the vertical plates 41 differ from one another, n1 will be the total number thereof, and the total plate thickness t2 will be the sum of the plate thicknesses of all the vertical plates 41. The symbol n2 in the formula 2 is the total number of the horizontal plates 42 in the reinforcement 40, which is 1 (n2=1) in the impact absorbing member 1 of this embodiment. If a configuration is provided with multiple horizontal plates 42 and the plate thicknesses of the horizontal plates 42 differ from one another, n2 will be the total number of the horizontal plates 42, and the total plate thickness t3 will be the total value of the plate thicknesses of all the horizontal plates 42. Therefore, the first flat portion width-thickness ratio r1 means the average flat portion width of the range of the flat portion overall width W1 of the top wall portion 11 that is not supported by the vertical plates 41 divided by the plate thickness t1 of the top wall portion 11. Also, the second flat portion width-thickness ratio r2 means the average flat portion width of the range of the flat portion overall width W2 of the side wall portion 12 that is not supported by the horizontal plates 42 divided by the plate thickness t1 of the side wall portion 12.

[0053] By providing the reinforcement 40 and satisfying the first condition that the first flat portion width-thickness ratio r1 obtained by Equation 1 is 10 or more and 50 or less, it is possible to prevent out-of-plane deformation at unintended locations in the top wall portion 11. Similarly, by satisfying the second condition that the second flat portion width-thickness ratio r2 obtained by Equation 2 is 10 or more and 50 or less, it is possible to prevent out-of-plane deformation at unintended locations in each side wall portion 12. It is possible to satisfy either one of the first condition and the second condition, or to satisfy both.

[0054] Here, the out-of-plane deformation will be described. Under the above-mentioned cross-sectional structure, a method for reducing the weight of the impact absorbing member 1 is to reduce the plate thickness t1 of the cylindrical body 30. In this case, in the case of a conventional structure without the reinforcement 40, the wide flat portion indicated by the flat portion overall width dimension W1 and the wide flat portion indicated by the flat portion overall width dimension W2 are not supported, so that out-of-plane deformation is likely to occur. The out-of-plane deformation here refers to a deformation in which the wall portion is undulating toward the inside and outside of the cylindrical body 30 in the cross section of FIG. 7. If the plate thickness t1 is made thin, it becomes unclear at which part of the cylindrical body 30 this out-of-plane deformation occurs. It is desirable for the impact absorbing member 1 to absorb impact energy by bending in a predetermined bending direction with a predetermined position as the bending starting point. However, when out-of-plane deformation occurs in the cylindrical body 30, that part may be easily broken or, conversely, may be difficult to break. As a result, there is a risk that the desired energy absorption amount cannot be obtained because the bending deformation cannot be performed as previously set.

[0055] In contrast, in the cross section shown in FIG. 7, the inside of the cylindrical body 30, which has a single large opening cross section in the conventional configuration, is divided into multiple (four) small opening cross sections by combining the vertical plates 41 and the horizontal plates 42. Of course, it can be said that the occurrence of out-of-plane deformation of the top wall portion 11 can be suppressed more than in the conventional structure just by supporting the top wall portion 11 with the vertical plates 41. However, the impact absorbing member 1 of the present embodiment does not only that, but also divides the opening cross section into small sections by combining the vertical plates 41 and the horizontal plates 42, and further specifies the range of the first flat portion width-thickness ratio r1 according to the above formula 1 and the range of the second flat portion width-thickness ratio r2 according to the above formula 2 for each of the range of the top wall portion 11 that is not supported by the vertical plates 41 and the range of the left side wall portion 12a and the right side wall portion 12b that is not supported by the horizontal plates 42. This makes it possible to reduce the plate thickness t1 while suppressing out-of-plane deformation. Therefore, the shock absorbing member 1 can be folded and deformed at desired positions to obtain high energy absorption efficiency, while also being lightweight.

[0056] This point will be described below based on the bending deformation that occurs when an impact force is applied to the impact absorbing member 1 along its longitudinal direction. When a folding start point is set in the top wall 11 of the cylindrical body 30, the top wall 11 at the beginning of folding deformation tends to sink toward the inside of the cylindrical body 30. The vertical plate 41 continues to support the top wall 11 while resisting the force that tends to sink. This prevents the top wall 11 from sinking. In addition, the gap between the left side wall portion 12a and the right side wall portion 12b is constrained by the horizontal plate 42. This constraint prevents the top wall portion 11 from sinking so as to expand the gap between the left side wall portion 12a and the right side wall portion 12b, and indirectly supports the top wall portion 11. In this way, the cylindrical body 30 is firmly supported from the inside by the reinforcement 40 due to the synergistic effect of the support of the top wall portion 11 by the vertical plate 41 and the constraint between the left side wall portion 12a and the right side wall portion 12b by the horizontal plate 42.

[0057] In this way, the cylindrical body 30 is reinforced at each position in the longitudinal direction by the reinforcement 40. In addition, the cylindrical body 30 satisfies both the first condition that the first flat portion width-thickness ratio r1 is 10 or more and 50 or less, and the second condition that the second flat portion width-thickness ratio r2 is 10 or more and 50 or less. Here, if the first flat portion width-thickness ratio r1 or the second flat portion width-thickness ratio r2 is less than 10, the plate thickness is thick and it is difficult to obtain the weight reduction effect by the reinforcement 40. On the other hand, if the first flat portion width-thickness ratio r1 or the second flat portion width-thickness ratio r2 is more than 50, the plate thickness becomes too thin and it is difficult to obtain the effect of preventing out-of-plane deformation by the reinforcement 40.

[0058] As described above, if out-of-plane deformation occurs at an unintended position, the manner in which compressive deformation occurs at that portion becomes unstable, and the out-of-plane deformed portion may be easily or not easily broken. As a result, there is a risk of bending deformation occurring at an unintended portion of the cylindrical body 30. On the other hand, the shock absorbing member 1 satisfies both the first and second conditions, and therefore, out-of-plane deformation at an unintended portion of the cylindrical body 30 can be suppressed, and therefore the plate thickness t1 can be made thinner to reduce the weight.

[0059] In addition, since the shock absorbing member 1 has the folding start portion BP illustrated in Figures 3 to 6, the bending strength of the second portion R2 is relatively lower than the bending strength of the first portion R1 and the bending strength of the third portion R3. This allows the shock absorbing member 1 to bend and deform at good joints with the second portion R2 as the folding start portion. In addition, the impact energy applied to the shock absorbing member 1 is absorbed mainly by the reinforcement 40 while folding and deforming with the second portion R2 as the folding start portion, so the amount of energy absorption can be increased.

[0060] In the above embodiment, the reinforcement 40 having a "+" shape is fixedly disposed inside the cylindrical body 30, but other than that, various forms exemplified in Fig. 8 to Fig. 14 can also be adopted. Fig. 8 to Fig. 14 correspond to the cross-sectional view taken along line BB in Fig. 2.

[0061] In FIG. 8(a), the horizontal plate 42 divides the internal space of the cylindrical body 30 into two in the vertical direction. That is, the vertical plate 41 is omitted, and the horizontal plate 42 restricts the distance between the left side wall portion 12a and the right side wall portion 12b. A flange is formed on one of the two side edges of the horizontal plate 42, and this flange is fixed by spot welding in a state of surface contact with the left side wall portion 12a. Similarly, a flange is formed on the other of the two side edges of the horizontal plate 42, and this flange is fixed by spot welding in a state of surface contact with the right side wall portion 12b. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed on each of the two side edges of the horizontal plate 42. In FIG. 8(b), the internal space of the cylindrical body 30 is also divided vertically into two by the horizontal plate 42. That is, the vertical plate 41 is omitted, and the horizontal plate 42 restricts the distance between the left side wall portion 12a and the right side wall portion 12b. One of the two side edges of the horizontal plate 42 is fixed by laser arc welding in a state where it is abutted against the left side wall portion 12a. Similarly, the other of the two side edges of the horizontal plate 42 is fixed by laser arc welding in a state where it is abutted against the right side wall portion 12b. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, folding start portions BP are formed at both positions including the side edges of the horizontal plate 42.

[0062] In FIG. 8(c), the internal space of the cylindrical body 30 is divided into two in the left-right direction by the vertical plate 41. That is, the horizontal plate 42 is omitted, and the top wall portion 11 is supported by the vertical plate 41. A flange is formed at the upper end of the vertical plate 41, and this flange is fixed to the top wall portion 11 by spot welding while being in surface contact with the top wall portion 11. Similarly, a flange is formed at the lower end of the vertical plate 41, and this flange is fixed to the plate-like member 20 by laser arc welding while being in surface contact with the plate-like member 20. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at a position including the upper end of the vertical plate 41. In Fig. 8(d), the internal space of the cylindrical body 30 is also divided into two in the left-right direction by the vertical plate 41. That is, the horizontal plate 42 is omitted, and the top wall portion 11 is supported by the vertical plate 41. The upper end of the vertical plate 41 is fixed by laser arc welding in a state where it is abutted against the top wall portion 11. Similarly, the lower end of the vertical plate 41 is fixed by laser arc welding in a state where it is abutted against the plate-like member 20. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at a position including the upper end of the vertical plate 41.

[0063] In FIG. 9(a), the internal space of the cylindrical body 30 is divided into three parts in the vertical direction by two horizontal plates 42. That is, the vertical plate 41 is omitted, and the distance between the left side wall portion 12a and the right side wall portion 12b is restricted by two horizontal plates 42. Flanges are formed on one of the two side edges of each horizontal plate 42, and these flanges are fixed by spot welding in a state of surface contact with the left side wall portion 12a. Similarly, flanges are formed on the other side edges of each horizontal plate 42, and these flanges are fixed by spot welding in a state of surface contact with the right side wall portion 12b. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, folding start portions BP are formed at both positions including the side edges of each horizontal plate 42. In FIG. 9(b), the internal space of the cylindrical body 30 is also divided into three parts in the vertical direction by two horizontal plates 42. That is, the vertical plate 41 is omitted, and the distance between the left side wall portion 12a and the right side wall portion 12b is restricted by two horizontal plates 42. One of both side edges of each horizontal plate 42 is fixed by laser arc welding in a state where it is abutted against the left side wall portion 12a. Similarly, the other of both side edges of each horizontal plate 42 is fixed by laser arc welding in a state where it is abutted against the right side wall portion 12b. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, the folding start portion BP is formed at both positions including each side edge of each horizontal plate 42.

[0064] In FIG. 9(c), the internal space of the cylindrical body 30 is divided into three parts in the left-right direction by two vertical plates 41. That is, the horizontal plate 42 is omitted, and the top wall portion 11 is supported by the two vertical plates 41. The upper ends of the vertical plates 41 are connected, and the connected parts are fixed to the top wall portion 11 by spot welding in a surface-jointed state. Meanwhile, flanges are formed at the lower ends of the vertical plates 41, and these flanges are fixed to the plate-like member 20 by laser arc welding in a surface-contact state. In this example, the two vertical plates 41 are formed by press-forming one steel plate into an inverted U-shaped cross section, but two separate vertical plates 41 may be used. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at a position including the upper end edge of each vertical plate 41. In FIG. 9(d), the internal space of the cylindrical body 30 is divided into three parts in the left-right direction by two vertical plates 41. That is, the horizontal plate 42 is omitted, and the top wall portion 11 is supported by two vertical plates 41. Flanges are formed at the upper end of each vertical plate 41, and these flanges are fixed to the top wall portion 11 by spot welding in a surface-jointed state. Meanwhile, the lower end of each vertical plate 41 is connected, and this connected part is fixed to the plate-like member 20 by spot welding in a surface-jointed state. In this example, the two vertical plates 41 are formed by press-forming one steel plate into a U-shaped cross section, but two separate vertical plates 41 may be used. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at a position including the upper end edge of each vertical plate 41.

[0065] In FIG. 9(e), the internal space of the cylindrical body 30 is divided into three parts in the left-right direction by two vertical plates 41. That is, the horizontal plate 42 is omitted, and the top wall portion 11 is supported by the two vertical plates 41. The upper ends of the vertical plates 41 are connected, and the connected parts are fixed to the top wall portion 11 by spot welding in a surface-joined state. Meanwhile, a wide flange is formed at the lower end of each vertical plate 41. One of these flanges is fixed to the left flange portion 13a by spot welding, and the other is fixed to the right flange portion 13b by spot welding. Between the lower ends of the two vertical plates 41, the space formed between them is sealed by a narrow plate-like member 20. That is, the plate-like member 20 is fixed to each flange connected to the lower ends of the two vertical plates 41 by spot welding. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. On the other hand, only in the second region R2, a folding starting point BP is formed at a position including the upper end edge of each vertical plate 41.

[0066] 10(a), the internal space of the cylindrical body 30 is divided into three by a combination of one vertical plate 41 and one horizontal plate 42. That is, one of the two side edges of the horizontal plate 42 is fixed by laser arc welding in a state where it abuts against the left side wall portion 12a. Similarly, the other of the two side edges of the horizontal plate 42 is fixed by laser arc welding in a state where it abuts against the right side wall portion 12b. The upper end of the vertical plate 41 is fixed by laser arc welding in a state where it is abutted against the top wall portion 11. The height dimension of the vertical plate 41 is about half of that shown in FIG. 2, and its lower end is fixed by laser arc welding in a state where it is abutted against the center position in the width direction of the horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into three parts: two spaces partitioned by the top wall portion 11, the left side wall portion 12a and the right side wall portion 12b, the vertical plate 41, and the horizontal plate 42, and one space partitioned by the horizontal plate 42, the left side wall portion 12a and the right side wall portion 12b, and the plate-like member 20. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. On the other hand, only in the second portion R2, a folding start portion BP is formed at least one of a position including the upper end edge of the vertical plate 41 and a position including both side edges of the horizontal plate 42.

[0067] 10(b), the internal space of the cylindrical body 30 is divided into three by a combination of one vertical plate 41 and one horizontal plate 42. That is, a flange is formed on one of both side edges of the horizontal plate 42, and this flange is fixed by spot welding in a state of surface contact with the left side wall portion 12a. Similarly, a flange is formed on the other of both side edges of the horizontal plate 42, and this flange is fixed by spot welding in a state of surface contact with the right side wall portion 12b. In addition, a flange is formed at the upper end of the vertical plate 41, and this flange is fixed by laser arc welding in a state of surface contact with the top wall portion 11. The height dimension of the vertical plate 41 is about half that of the embodiment shown in FIG. 2, and a flange is formed at its lower end, and this flange is fixed by spot welding in a state of surface contact with the center position of the horizontal plate 42 in the width direction. In this way, the internal space of the cylindrical body 30 is divided into three parts: two spaces partitioned by the top wall portion 11, the left side wall portion 12a and the right side wall portion 12b, the vertical plate 41, and the horizontal plate 42, and one space partitioned by the horizontal plate 42, the left side wall portion 12a and the right side wall portion 12b, and the plate-like member 20. The cross-sectional configuration of this example is almost the same in each part of the first part R1, the second part R2, and the third part R3. On the other hand, only in the second part R2, a folding start part BP is formed at at least one of a position including the upper end edge of the vertical plate 41 and a position including both side edges of the horizontal plate 42.

[0068] 10(c), the internal space of the cylindrical body 30 is divided into three by a combination of one vertical plate 41 and one horizontal plate 42. That is, one of the two side edges of the horizontal plate 42 is fixed by laser arc welding in a state where it abuts against the left side wall portion 12a. Similarly, the other of the two side edges of the horizontal plate 42 is fixed by laser arc welding in a state where it abuts against the right side wall portion 12b. The upper end of the vertical plate 41 is fixed by laser arc welding in a state where it abuts against the center of the width of the horizontal plate 42. The height dimension of the vertical plate 41 is about half of that shown in FIG. 2, and its lower end is fixed by laser arc welding in a state where it abuts against the center of the width of the plate-like member 20. In this way, the internal space of the cylindrical body 30 is divided into three parts: one space partitioned by the top wall 11, the left side wall 12a and the right side wall 12b, and the horizontal plate 42, and two spaces partitioned by the horizontal plate 42, the left side wall 12a and the right side wall 12b, the vertical plate 41, and the plate-like member 20. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at a position including both side edges of the horizontal plate 42.

[0069] 10(d), the internal space of the cylindrical body 30 is divided into three by a combination of one vertical plate 41 and one horizontal plate 42. That is, a flange is formed on one of both side edges of the horizontal plate 42, and this flange is fixed by spot welding in a state of surface contact with the left side wall portion 12a. Similarly, a flange is formed on the other of both side edges of the horizontal plate 42, and this flange is fixed by spot welding in a state of surface contact with the right side wall portion 12b. A flange is formed at the upper end of the vertical plate 41, and this flange is fixed by spot welding in a state where it is abutted against the center position in the width direction of the horizontal plate 42. The height dimension of the vertical plate 41 is about half that of the embodiment shown in FIG. 2, and a flange is formed at its lower end, and this flange is fixed by laser arc welding in a state where it is in surface contact with the center position in the width direction of the plate-like member 20. In this way, the internal space of the cylindrical body 30 is divided into three parts: one space partitioned by the top wall portion 11, the left side wall portion 12a and the right side wall portion 12b, and the horizontal plate 42, and two spaces partitioned by the horizontal plate 42, the left side wall portion 12a and the right side wall portion 12b, the vertical plate 41, and the plate-like member 20. The cross-sectional configuration of this example is almost the same in each part of the first part R1, the second part R2, and the third part R3. Meanwhile, only in the second part R2, a folding start part BP is formed at a position including both side edges of the horizontal plate 42.

[0070] 11(a), the internal space of the cylindrical body 30 is divided into four parts by a combination of two vertical plates 41 and one horizontal plate 42. In this example, the vertical plates 41 and parts of the horizontal plates 42 are integrally formed by pressing a single steel plate. A flange is formed on one of the two side edges of the horizontal plate 42, and this flange is fixed by spot welding in surface contact with the left side wall portion 12a. Similarly, a flange is formed on the other of the two side edges of the horizontal plate 42, and this flange is fixed by spot welding in surface contact with the right side wall portion 12b. The horizontal plate 42 includes a left portion joined to the left side wall portion 12a and a right portion joined to the right side wall portion 12b, as well as a central portion connecting the left and right portions that are spaced apart from each other. This central portion is a separate part and is fixed to the left and right portions by spot welding. The portion connecting the upper ends of the two vertical plates 41 is a flange that is surface-joined at the center position in the width direction of the top wall portion 11. This flange is joined to the top wall portion 11 by spot welding. The lower ends of the two vertical plates 41 are integral with the horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into four spaces: three spaces partitioned by the top wall 11, the left side wall 12a and the right side wall 12b, the two vertical plates 41, and the horizontal plate 42, and one space partitioned by the horizontal plate 42, the left side wall 12a and the right side wall 12b, and the plate-like member 20. The cross-sectional configuration of this example is almost the same in each of the first region R1, the second region R2, and the third region R3. Meanwhile, only in the second region R2, a folding start portion BP is formed at least in one of the positions including the upper end edges of the vertical plates 41 and the positions including both side edges of the horizontal plate 42.

[0071] 11(b), the internal space of the cylindrical body 30 is also divided into four parts by combining two vertical plates 41 and one horizontal plate 42. In this example, the vertical plate 41 and a part of the horizontal plate 42 are also integrally formed by pressing a single steel plate. A flange is formed on one of the two side edges of the horizontal plate 42, and this flange is fixed by spot welding in surface contact with the left side wall portion 12a. Similarly, a flange is formed on the other of the two side edges of the horizontal plate 42, and this flange is fixed by spot welding in surface contact with the right side wall portion 12b. The horizontal plate 42 includes a left portion joined to the left side wall portion 12a, a right portion joined to the right side wall portion 12b, and a central portion connecting the left and right portions that are arranged apart from each other. This central portion is a separate part and is fixed to the left and right portions by spot welding. The portion connecting the lower ends of the two vertical plates 41 is a flange that is surface-joined at the center position in the width direction of the plate-shaped member 20. This flange is joined to the plate-shaped member 20 by spot welding. The upper ends of the two vertical plates 41 are integral with the horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into four spaces: one space partitioned by the top wall 11, the left and right side walls 12a and 12b, and the horizontal plate 42, and three spaces partitioned by the horizontal plate 42, the left and right side walls 12a and 12b, the two vertical plates 41, and the plate-like member 20. The cross-sectional configuration of this example is substantially the same in each of the first region R1, the second region R2, and the third region R3. Meanwhile, only in the second region R2, a folding start portion BP is formed at a position including both side edges of the horizontal plate 42.

[0072] In Fig. 11(c), the internal space of the cylindrical body 30 is divided into four parts by a combination of two vertical plates 41 and one horizontal plate 42. In this example, when forming the hat-shaped member 10, the central portion of the top wall portion 11 in the width direction is press-molded so as to be recessed toward the inside of the cylindrical body 30. Two vertical plates 41 are formed in this recessed portion. The top wall portion 11 also includes a left portion and a right portion spaced apart from each other by the recessed portion, and a central portion connecting the left portion and the right portion. This central portion is a separate part and is fixed to each of the left portion and the right portion by spot welding. A flange is formed on one of the two side edges of the horizontal plate 42, and this flange is fixed by spot welding in surface contact with the left side wall portion 12a. Similarly, a flange is formed on the other of the two side edges of the horizontal plate 42, and this flange is fixed by spot welding in surface contact with the right side wall portion 12b. The lower ends of each vertical plate 41, i.e., the recessed portions, are fixed by spot welding in surface contact with the center position of the horizontal plate 42 in the width direction. In this way, the internal space of the cylindrical body 30 is divided into four spaces: three spaces partitioned by the top wall 11, the left side wall 12a and the right side wall 12b, the two vertical plates 41, and the horizontal plate 42, and one space partitioned by the horizontal plate 42, the left side wall 12a and the right side wall 12b, and the plate-like member 20. The cross-sectional configuration of this example is almost the same in each of the first region R1, the second region R2, and the third region R3. Meanwhile, only in the second region R2, a folding start portion BP is formed at least in one of the positions including the upper end edges of the vertical plates 41 and the positions including both side edges of the horizontal plate 42.

[0073] 12(a), the internal space of the cylindrical body 30 is divided into four parts by a combination of one vertical plate 41 and one horizontal plate 42. That is, one of the two side edges of the horizontal plate 42 is fixed by laser arc welding in a state where it abuts against the left side wall portion 12a. Similarly, the other of the two side edges of the horizontal plate 42 is fixed by laser arc welding in a state where it abuts against the right side wall portion 12b. The upper end of the vertical plate 41 is fixed by laser arc welding in abutment against the top wall portion 11. Similarly, the lower end of the vertical plate 41 is fixed by laser arc welding in abutment against the plate-like member 20. The vertical plate 41 is joined by laser arc welding at a center position in the height direction to a center position in the width direction of the horizontal plate 42 in a state intersecting (orthogonal) thereto. In this way, the internal space of the cylindrical body 30 is divided into four spaces by the top wall 11, the left side wall 12a, the right side wall 12b, the vertical plate 41, the horizontal plate 42, and the plate-like member 20. The cross-sectional configuration of the present example is substantially the same for each of the first region R1, the second region R2, and the third region R3. Meanwhile, only in the second region R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42.

[0074] 12(b), the internal space of the cylindrical body 30 is also divided into four parts by combining one vertical plate 41 and one horizontal plate 42. That is, a flange is formed on one of both side edges of the horizontal plate 42, and this flange is fixed by spot welding in a state of surface contact with the left side wall portion 12a. Similarly, a flange is formed on the other of both side edges of the horizontal plate 42, and this flange is fixed by spot welding in a state of surface contact with the right side wall portion 12b. A flange is formed at the upper end of the vertical plate 41, and this flange is fixed by laser arc welding in a state of surface contact with the top wall portion 11. Similarly, a flange is formed at the lower end of the vertical plate 41, and this flange is fixed by laser arc welding in a state of surface contact with the plate-like member 20. In this way, the internal space of the cylindrical body 30 is divided into four spaces by the top wall 11, the left side wall 12a, the right side wall 12b, the vertical plate 41, the horizontal plate 42, and the plate-like member 20. The cross-sectional configuration of the present example is substantially the same for each of the first region R1, the second region R2, and the third region R3. Meanwhile, only in the second region R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42.

[0075] In the example of FIG. 12(c), the internal space of the cylindrical body 30 is also divided into four by a combination of one vertical plate 41 and one horizontal plate . In this example, the hat-shaped member 10 is formed by combining a first member having a cross-sectional shape perpendicular to the longitudinal direction that is generally inverted U-shape (or narrow hat-shape) with a second member that is L-shaped. Of this first member, an upper wall portion forms part of the ceiling wall portion 11. Furthermore, one of a pair of vertical wall portions provided in the first member is a vertical plate 41, and the other is the right side wall portion 12b. Flanges are formed at the lower end of the vertical plate 41 and at the lower end of the right side wall portion 12b. Of these, the flange formed at the lower end of the vertical plate 41 is fixed by laser arc welding in a state of surface contact with the plate-shaped member 20. On the other hand, the flange formed at the lower end of the right side wall portion 12b is fixed by spot welding in a state of surface contact with the plate-shaped member 20.

[0076] Of the second member, the upper wall portion forms part of the top wall portion 11, and the vertical wall portion forms the left side wall portion 12a. A small flange is formed on the edge of the upper wall portion of the second member, and this flange is fixed by laser arc welding in a state of surface contact with the upper end of the vertical wall portion of the first member. In addition, a flange is formed on the lower end of the second member, and this flange is fixed by spot welding in a state of surface contact with the plate-like member 20. A flange is formed on one of the opposite side edges of the horizontal plate 42, and this flange is fixed by spot welding in surface contact with the left side wall portion 12a. Similarly, a flange is formed on the other opposite side edge of the horizontal plate 42, and this flange is fixed by spot welding in surface contact with the right side wall portion 12b. The vertical plate 41 is joined at its height center position by laser arc welding in a state where it intersects (orthogonally) with the width center position of the horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into four spaces by the top wall 11, the left side wall 12a, the right side wall 12b, the vertical plate 41, the horizontal plate 42, and the plate-like member 20. The cross-sectional configuration of the present example is substantially the same for each of the first region R1, the second region R2, and the third region R3. Meanwhile, only in the second region R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42.

[0077] In the example of FIG. 12(d), the internal space of the cylindrical body 30 is also divided into four by a combination of one vertical plate 41 and one horizontal plate . In this example, a cylindrical body 30 is combined with a pair of angle bars each having an L-shaped cross section perpendicular to the longitudinal direction to form a rectangular closed cross-sectional space. That is, a flange is formed on only one of the two end edges of each angle bar. These flanges are then fixed by spot welding to the other angle bar, which is the connecting partner, in a face-to-face contact state. By fixing these two flange portions to the other, the closed cross-sectional space is formed between the two angle bars.

[0078] A pair of smaller first and second angle members are combined in the closed cross-sectional space in a "+" shape to form a vertical plate 41 and a horizontal plate 42. The first angle member has a substantially L-shaped cross section perpendicular to the longitudinal direction, and flanges are formed at both ends. One of these flanges is fixed by spot welding in a surface-contact state to the top wall portion 11, and the other is fixed by spot welding in a surface-contact state to the right side wall portion 12b. On the other hand, the second angle member has a substantially L-shaped cross section perpendicular to the longitudinal direction, and flanges are formed at both ends. One of these flanges is fixed by spot welding in a surface-contact state to the left side wall portion 12a, and the other is fixed by spot welding in a surface-contact state to the plate-shaped member 20. In addition, a recess is formed at the corner of the second angle member, and the corner of the first angle member is fixed by adhesion into this recess. Therefore, in this example, the vertical wall of the first angle iron and the vertical wall of the second angle iron are combined to form one vertical plate 41. Furthermore, the horizontal wall of the first angle iron and the horizontal wall of the second angle iron are combined to form one horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into four spaces by the top wall 11, the left side wall 12a, the right side wall 12b, the vertical plate 41, the horizontal plate 42, and the plate-like member 20. The cross-sectional configuration of the present example is substantially the same for each of the first region R1, the second region R2, and the third region R3. Meanwhile, only in the second region R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42.

[0079] In the example of FIG. 12(e), the internal space of the cylindrical body 30 is also divided into four parts by a combination of one vertical plate 41 and one horizontal plate . In this embodiment, the cylindrical body 30 is formed by combining four angle bars, each of which has an L-shaped cross section perpendicular to its longitudinal direction. Flanges are formed on both end edges of each angle bar. Furthermore, two flat plate-like plates are fixed by laser arc welding in a state where they are crossed (orthogonal) at the center position in the width direction, thereby forming a reinforcement 40 including a vertical plate 41 and a horizontal plate 42. Then, the upper and lower ends of the vertical plate 41 and the left and right ends of the horizontal plate 42 are spot welded in a state where they are sandwiched between the flanges of the four angle irons so that the reinforcement 40 is disposed in the center, thereby forming a cylindrical body 30 including a top wall portion 11, a left side wall portion 12a, a right side wall portion 12b, and a plate-like member 20. In this way, the internal space of the cylindrical body 30 is divided into four spaces by the top wall 11, the left side wall 12a, the right side wall 12b, the vertical plate 41, the horizontal plate 42, and the plate-like member 20. The cross-sectional configuration of the present example is substantially the same for each of the first region R1, the second region R2, and the third region R3. Meanwhile, only in the second region R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42.

[0080] In the example of FIG. 13(a), the internal space of the cylindrical body 30 is also divided into four parts by a combination of one vertical plate 41 and one horizontal plate . In this example, the reinforcement 40, which includes a vertical plate 41 and a horizontal plate 42, is formed by joining two angle bars by spot welding at their respective corners. That is, two angle bars are prepared, each of which has a substantially L-shaped cross section perpendicular to the longitudinal direction and has chamfered corners. Then, these angle bars are joined by spot welding with their chamfers in surface contact with each other. As a result, the wall of one angle bar and the wall of the other angle bar become parallel to each other, forming the vertical plate 41. Similarly, the other wall of one angle bar and the other wall of the other angle bar become parallel to each other, forming the horizontal plate 42. Then, the edges of each angle bar are butted against the top wall 11, the left side wall 12a, the right side wall 12b, and the plate-like member 20, respectively, and are joined by laser arc welding. As a result, the internal space of the cylindrical body 30 is divided into four spaces by the vertical plate 41 and the horizontal plate 42. The cross-sectional configuration of this example is almost the same for each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least at one of a position including the upper end edge of the vertical plate 41 and a position including both side edges of the horizontal plate 42.

[0081] In the example of FIG. 13(b), the internal space of the cylindrical body 30 is also divided into four parts by a combination of one vertical plate 41 and one horizontal plate . In this example, the corners of two angle bars are joined by spot welding to form the reinforcement 40 having a vertical plate 41 and a horizontal plate 42. That is, two angle bars are prepared, each of which has a substantially L-shaped cross section perpendicular to the longitudinal direction and has chamfered corners. A flange is formed on one of a pair of edges of each angle bar. The chamfers of these angles are in surface contact with each other and spot welded together, so that the wall of one angle and the wall of the other angle are parallel to each other to form a vertical plate 41. Similarly, the other wall of one angle and the other wall of the other angle are parallel to each other to form a horizontal plate 42. The reinforcement 40 formed as described above is joined by spot welding with each flange in surface contact with the left side wall portion 12a and the right side wall portion 12b. In addition, the edge portion of the reinforcement 40 where the flange is not formed is butted against the top wall portion 11 and the plate-like member 20, respectively, and joined by laser arc welding. As a result, the internal space of the cylindrical body 30 is divided into four spaces by the vertical plate 41 and the horizontal plate 42. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and a position including both side edges of the horizontal plate 42.

[0082] In the example of FIG. 13(c), the internal space of the cylindrical body 30 is also divided into four by a combination of one vertical plate 41 and one horizontal plate . In this example, the reinforcement 40 including the vertical plate 41 and the horizontal plate 42 is formed by spot welding the side surfaces near the corners of two angle irons. That is, two angle irons having a substantially L-shaped cross section perpendicular to the longitudinal direction are prepared. Then, these angle irons are joined by spot welding with the side surfaces near the corners of each of them overlapping and in surface contact with each other. As a result, the wall portion of one angle iron and the wall portion of the other angle iron become parallel to each other, forming the vertical plate 41. Similarly, the other wall portion of one angle iron and the other wall portion of the other angle iron become parallel to each other, forming the horizontal plate 42. Then, the edges of each angle bar are butted against the top wall 11, the left side wall 12a, the right side wall 12b, and the plate-like member 20, respectively, and are joined by laser arc welding. As a result, the internal space of the cylindrical body 30 is divided into four spaces by the vertical plate 41 and the horizontal plate 42. The cross-sectional configuration of this example is almost the same for each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least at one of a position including the upper end edge of the vertical plate 41 and a position including both side edges of the horizontal plate 42.

[0083] In the example of FIG. 13(d), the internal space of the cylindrical body 30 is also divided into four parts by a combination of one vertical plate 41 and one horizontal plate . In this example, the corners of two angle bars are joined together by spot welding to form the reinforcement 40, which includes a vertical plate 41 and a horizontal plate 42. That is, two angle bars having a substantially L-shaped cross section perpendicular to the longitudinal direction are prepared. A flange is formed on one of a pair of edges of each angle bar. Then, these angle bars are joined by spot welding with the sides near the corners of each angle bar overlapping and in surface contact with each other. As a result, the wall of one angle bar and the wall of the other angle bar are parallel to each other, forming the vertical plate 41. Similarly, the other wall of one angle bar and the other wall of the other angle bar are parallel to each other, forming the horizontal plate 42. The reinforcement 40 formed as described above is joined by spot welding with each flange in surface contact with the left side wall portion 12a and the right side wall portion 12b. In addition, the edge portion of the reinforcement 40 where the flange is not formed is butted against the top wall portion 11 and the plate-like member 20, respectively, and joined by laser arc welding. As a result, the internal space of the cylindrical body 30 is divided into four spaces by the vertical plate 41 and the horizontal plate 42. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and a position including both side edges of the horizontal plate 42.

[0084] In the example of FIG. 13(e), the internal space of the cylindrical body 30 is also divided into four parts by a combination of one vertical plate 41 and one horizontal plate . In this example, the corners of one angle bar and one pressed plate are joined together by spot welding to form the reinforcement 40 including a vertical plate 41 and a horizontal plate 42. That is, one angle bar having a substantially L-shaped cross section perpendicular to the longitudinal direction and one pressed plate having a substantially S-shaped cross section by bending at right angles at two locations in the width direction are prepared. Flanges are formed on both of a pair of edges of the angle bar. Also, flanges are formed on both of a pair of edges of the pressed plate.

[0085] The side surface of the angle bar near the corner and the side surface of the pressed plate near the corner are joined by laser arc welding while being in surface contact with each other. As a result, the wall of the angle bar and the wall of the pressed plate become parallel to each other to form a vertical plate 41. Similarly, the other wall of the angle bar and the other wall of the pressed plate become parallel to each other to form a horizontal plate 42. One flange of the angle iron is spot welded to the top wall 11 in surface contact, and the other flange is spot welded to the right side wall 12b in surface contact. In addition, one flange of the pressed plate is spot welded to the left side wall 12a in surface contact, and the other flange of the pressed plate is spot welded to the lower part of the right side wall 12b in surface contact. Furthermore, a plate-shaped member 20 having flanges formed on both ends is prepared, and each flange is joined to the hat-shaped member 10 by spot welding. In addition, the plate-shaped member 20 is joined by laser arc welding in a state where one of the two bent portions of the press-processed plate that is not joined to the angle bar is in contact with the widthwise center position of the plate-shaped member 20. As a result, the internal space of the cylindrical body 30 is divided into four spaces by the vertical plate 41 and the horizontal plate 42. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least at one of a position including the upper end edge of the vertical plate 41 and a position including both side edges of the horizontal plate 42.

[0086] In the example of FIG. 13(f), the internal space of the cylindrical body 30 is also divided into four parts by a combination of one vertical plate 41 and one horizontal plate . In this example, the corners of one angle bar and one pressed plate are joined together by spot welding to form a reinforcement 40 including a vertical plate 41 and a horizontal plate 42. That is, one angle bar having a substantially L-shaped cross section perpendicular to the longitudinal direction and one pressed plate having a substantially S-shaped cross section by bending at right angles at two locations in the width direction are prepared. Flanges are formed on both of a pair of edges of the angle bar. Also, a flange is formed on one of a pair of edges of the pressed plate.

[0087] The side surface of the angle bar near the corner and the side surface of the pressed plate near the corner are joined by laser arc welding while being in surface contact with each other. As a result, the wall of the angle bar and the wall of the pressed plate become parallel to each other to form a vertical plate 41. Similarly, the other wall of the angle bar and the other wall of the pressed plate become parallel to each other to form a horizontal plate 42. One flange of the angle iron is spot welded to the top wall 11 in surface contact, and the other flange is spot welded to the right side wall 12b in surface contact. In addition, the flange of the pressed plate is spot welded to the left side wall 12a in surface contact, and the flange-free edge of the pressed plate is spot welded to the right flange 13b at the lower end of the right side wall 12b in surface contact. Then, a plate-like member 20 narrower than the lower opening width of the hat-shaped member 10 is prepared. Then, one edge of the plate-like member 20 is joined by laser arc welding in a state where it is in contact with the one of the two bent portions of the press-processed plate that is not joined to the angle material. Furthermore, the other edge of the plate-like member 20 is joined by spot welding in a state where it is in surface contact with the left flange portion 13a at the lower end of the left side wall portion 12a. As a result, the internal space of the cylindrical body 30 is divided into four spaces by the vertical plate 41 and the horizontal plate 42. The cross-sectional configuration of this example is almost the same in each of the first portion R1, the second portion R2, and the third portion R3. Meanwhile, only in the second portion R2, a folding start portion BP is formed at at least one of a position including the upper end edge of the vertical plate 41 and a position including both side edges of the horizontal plate 42.

[0088] In FIG. 13(g), the internal space of the cylindrical body 30 is divided into six parts by a combination of two vertical plates 41 and one horizontal plate . In this example, a first press-processed plate formed in two stages by press processing and a second press-processed plate formed in one stage by press processing are prepared. Then, both corners of the upper stage of the second press-processed plate are joined by laser arc welding to both corners of the lower stage of the first press-processed plate in face contact. As a result, the first press-processed plate and the second press-processed plate are integrated to form a reinforcement 40. In this reinforcement 40, two vertical walls of the first press-processed plate and two vertical walls of the second press-processed plate are connected to form two vertical plates 41. Also, two horizontal walls of the first stage of the first press-processed plate and one horizontal wall of the second press-processed plate are connected to form one horizontal plate 42.

[0089] Then, this reinforcement 40 is incorporated and fixed in the hat-shaped member 10. That is, the higher step (upper end) of the first press-processed plate is joined by spot welding in a state where it is in surface contact with the top wall portion 11. Furthermore, each side wall of the lower step of the first press-processed plate is joined by spot welding in a state where it is in surface contact with the left side wall portion 12a and the right side wall portion 12b. Finally, both side edges of the second press-processed plate are joined by spot welding in a state where it is sandwiched between the left flange portion 13a, the right flange portion 13b, and the plate-like member 20. In this way, the internal space of the cylindrical body 30 is divided into six spaces: three spaces partitioned by the top wall 11, the left and right side walls 12a and 12b, the two vertical plates 41, and the horizontal plate 42, and three spaces partitioned by the horizontal plate 42, the left and right side walls 12a and 12b, the two vertical plates 41, and the plate-like member 20. The cross-sectional configuration of this example is almost the same in each of the first region R1, the second region R2, and the third region R3. Meanwhile, only in the second region R2, a folding start portion BP is formed at least in one of the positions including the upper end edges of the vertical plates 41 and the positions including both side edges of the horizontal plate 42.

[0090] In FIG. 14(a), one vertical plate 41 and one horizontal plate 42 are combined to divide the internal space of the cylindrical body 30 into four parts. In this example, two hollow tubes are prepared, each of which has a cross section that is roughly shaped like the letter "9" with the left and right reversed. A flange is formed on the edge of the open part of the "9" shape. The two hollow tubes are assembled so that their cross-sectional shapes perpendicular to the longitudinal direction are rotationally symmetrical to each other. Then, the flange of one hollow tube is joined to the other hollow tube by laser arc welding in a face-to-face contact state. This joining is performed at two places. As a result, the outer peripheral parts of both hollow tubes are assembled to each other to form a cylindrical body 30. That is, an outer shape part corresponding to the top wall 11, the left side wall 12a, the right side wall 12b, and the plate-like member 20 is formed. At the same time, the vertical wall of one hollow tube and the vertical wall of the other hollow tube are connected to each other in the cylindrical body 30 to form a vertical plate 41. Similarly, the horizontal wall of one hollow tube and the horizontal wall of the other hollow tube are connected to each other in the cylindrical body 30 to form a horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into four spaces defined by the vertical plate 41 and the horizontal plate 42. In this example, the cross-sectional configurations of the first portion R1, the second portion R2, and the third portion R3 are substantially the same. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42.

[0091] In FIG. 14(b), one vertical plate 41 and one horizontal plate 42 are combined to divide the internal space of the cylindrical body 30 into four parts. In this example, two hollow tubes with a cross section shaped like the letter "8" are prepared. These hollow tubes are formed by bending a single plate material at right angles in various places, and both ends of the material are machined into flanges. Next, the flanges of each hollow tube are pre-joined by laser arc welding.

[0092] The two hollow tubes thus prepared are stacked and bonded together, one of which is the lower stage and the other being the upper stage. The side walls of the two hollow tubes are then joined together by laser arc welding, so that the two hollow tubes are integrated into one. As a result, the outer peripheries of both hollow tubes are combined with each other to form a cylindrical body 30. That is, an outer shape portion corresponding to the top wall portion 11, the left side wall portion 12a, the right side wall portion 12b, and the plate-like member 20 is formed. At the same time, the vertical wall of one hollow tube and the vertical wall of the other hollow tube are connected to each other within the cylindrical body 30 to form a vertical plate 41. Similarly, the horizontal wall of one hollow tube and the horizontal wall of the other hollow tube are connected to each other within the cylindrical body 30 to form a horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into four spaces defined by the vertical plate 41 and the horizontal plate 42. In this example, the cross-sectional configurations of the first portion R1, the second portion R2, and the third portion R3 are substantially the same. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42.

[0093] In FIG. 14(c), the internal space of the cylindrical body 30 is also divided into four by a combination of one vertical plate 41 and one horizontal plate . In this example, a hollow tube is formed by bending a single plate material at multiple points to form three rectangular spaces. These three rectangular spaces are arranged in an inverted L shape, with the lower left corner of the page open. Flanges are formed on both side edges of the plate material that forms the hollow tube. These flanges are joined by laser arc welding in an overlapping state to the wall portion that forms the adjacent rectangular space.

[0094] Then, a generally L-shaped angle bar is attached to the corner of the hollow tube so as to cover the corner and form a fourth rectangular space. Flanges are formed on both side edges of the angle bar. These two flanges are then joined by laser arc welding in a state of surface contact with the side wall surface of the hollow tube. In this way, by combining the hollow tube material and the angle bar, the outer peripheries of both are combined with each other to form a cylindrical body 30 having a rectangular outer shape. That is, the outer shape parts corresponding to the top wall 11, the left side wall 12a, the right side wall 12b, and the plate-like member 20 are formed. At the same time, within this cylindrical body 30, a part of the hollow tube material forms a vertical plate 41, and another part forms a horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into four spaces defined by the vertical plate 41 and the horizontal plate 42. In this example, the cross-sectional configurations of the first portion R1, the second portion R2, and the third portion R3 are substantially the same. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42.

[0095] In FIG. 14(d), the internal space of the cylindrical body 30 is also divided into four by a combination of one vertical plate 41 and one horizontal plate . In this example, two molded bodies approximately shaped like the letter "9" are obtained by roll forming. A flange is formed on the edge of only one of these molded bodies. Then, this flange is brought into surface contact with the edge of the other molded body and joined by laser arc welding. In addition, the corners of each molded body are butted against each other and joined by laser arc welding. This joint portion becomes the center position of the cylindrical body 30. In this way, an intermediate body having three rectangular spaces arranged in an L-shape is obtained by using a pair of molded bodies. The intermediate body has an open corner at the top right corner of the page.

[0096] Then, a substantially L-shaped angle bar is attached to the corner of the intermediate body so as to cover the corner and form a fourth rectangular space. Flanges are formed on both side edges of the angle bar. These two flanges are then joined by laser arc welding in a state of surface contact with the side wall surface of the intermediate body. In this way, by combining the formed body and the angle bar, the outer peripheries of both are combined with each other to form a cylindrical body 30 having a rectangular outer shape. That is, the outer shape parts corresponding to the top wall 11, the left side wall 12a, the right side wall 12b, and the plate-like member 20 are formed. At the same time, within this cylindrical body 30, a part of the intermediate body forms a vertical plate 41, and another part forms a horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into four spaces defined by the vertical plate 41 and the horizontal plate 42. In this example, the cross-sectional configurations of the first portion R1, the second portion R2, and the third portion R3 are substantially the same. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42.

[0097] In FIG. 14(e), the internal space of the cylindrical body 30 is also divided into four by a combination of one vertical plate 41 and one horizontal plate . In this example, four hollow tubes with rectangular cross sections are prepared. These hollow tubes are then glued together in two vertical rows and two horizontal rows. The joints on the outer circumference are then firmly joined by laser arc welding. In this manner, by combining the four hollow tubular materials, the outer peripheries of each material are combined with each other to form a cylindrical body 30 having a rectangular outer shape. That is, the outer shape parts corresponding to the top wall 11, the left side wall 12a, the right side wall 12b, and the plate-like member 20 are formed. At the same time, within this cylindrical body 30, parts of each hollow tubular material are combined with each other to form a vertical plate 41 and a horizontal plate 42. In this way, the internal space of the cylindrical body 30 is divided into four spaces defined by the vertical plate 41 and the horizontal plate 42. In this example, the cross-sectional configurations of the first portion R1, the second portion R2, and the third portion R3 are substantially the same. Meanwhile, only in the second portion R2, a folding start portion BP is formed at least in one of a position including the upper end edge of the vertical plate 41 and positions including both side edges of the horizontal plate 42. EXAMPLES

[0098] [First Example] A rectangular tubular member with both end faces closed by lids was considered as an impact absorbing member, and the relationship between the out-of-plane deformation amount δ and the flat portion width-to-thickness ratio W / t when a load was applied along the longitudinal direction of the impact absorbing member was obtained by numerical calculation.

[0099] First, the shock absorbing member 1A shown in Fig. 15(a) was placed vertically on the base BS. This shock absorbing member 1A is a rectangular tubular member whose cross section perpendicular to each position in its longitudinal direction is a square, and its upper and lower ends are closed by lids. This shock absorbing member 1A was set to be placed in an upright state with its central axis perpendicular to the upper surface of the base BS. The length of the shock absorbing member 1A was L = 200 (mm). The width of each side in a cross section perpendicular to the longitudinal direction of the shock absorbing member 1A was W (mm), and the plate thickness was t (mm). The width W (mm) was changed to eight stages, 5 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, and 70 mm. In addition, the plate thickness t (mm) was changed to three stages, 1.0 mm, 1.6 mm, and 2.0 mm. By combining these widths W (mm) and plate thicknesses t (mm), multiple shock absorbing members 1A with various dimensions and shapes were assumed when the flat portion width-plate thickness ratio W / t was changed within a range of 70 or less. The tensile strength of the material of each shock absorbing member 1A was unified to 1180 MPa, and no reinforcement was provided.

[0100] After placing each shock absorbing member 1A in an upright position as shown in Fig. 15(a), an impact force F was applied in the compressive direction through the central axis to the rigid wall that was the lid at the top end of the shock absorbing member 1A. The speed at which the rigid wall moved downward on the paper was set to 5 m / s, and the load was applied until buckling deformation began. The timing at which buckling deformation began was determined to be the point at which the load supported by the shock absorbing member 1A decreased. Then, as shown in Fig. 15(b), the amount of out-of-plane deformation of the shock absorbing member 1A after it has been subjected to the impact force F was determined as δ (mm). This out-of-plane deformation amount δ (mm) indicates the maximum deformation amount of the bulge of the outer surface after the out-of-plane deformation, based on the outer surface before the application of the impact force F. In this manner, the relationship between the out-of-plane deformation amount δ and the flat portion width-to-plate thickness ratio W / t was determined for each of the shock absorbing members 1A, and these were plotted in the graph shown in Fig. 16.

[0101] As a result, as shown in Figure 16, in the impact absorbing member 1A having a flat portion width-to-thickness ratio W / t of less than 10, the strength was too high to undergo out-of-plane deformation, so no knots were generated and the impact force F could not be adequately absorbed. On the other hand, as shown in FIG. 16, in the impact absorbing member 1A with a flat width-thickness ratio W / t of 10 or more and 70 or less, axial crushing occurred as a result of out-of-plane deformation. It was confirmed that the out-of-plane deformation amount δ (mm) at this time remained constant or increased slightly when the flat width-thickness ratio W / t was 50 or less, but increased rapidly when the flat width-thickness ratio W / t exceeded 50. From this, it can be seen that the out-of-plane deformation suddenly becomes unstable when the flat width-thickness ratio W / t exceeded 50. Although the impact absorbing member 1A of the first embodiment does not correspond to the invention example because it does not have a reinforcement, it was confirmed that in order to appropriately control the out-of-plane deformation of the impact absorbing member 1A to cause bending deformation, the flat width-thickness ratio W / t is set to 10 or more and 50 or less.

[0102] [Second Example] In the second embodiment, the influence of the first flat portion width-thickness ratio r1 and the second flat portion width-thickness ratio r2 described in FIG. 7 on the behavior of the bending deformation of the impact absorbing component was obtained and confirmed by numerical calculation. First, as shown in Fig. 17, a shock absorbing member 1B having the same configuration as the shock absorbing member 1 shown in Fig. 2 was assumed. The length L (mm) of the shock absorbing member 1B was set to 400 mm, the plate thickness t (mm) to 1.0 mm, the tensile strength of the material to 1180 MPa, and the breakage start point to the center position in the longitudinal direction of the top wall. Also, it was equipped with a reinforcement 40 having the same "+" shape as in Fig. 2. On the other hand, in this shock absorbing member 1B, w1 (mm), w2 (mm), w3 (mm), and w4 (mm) shown in FIG. 7 were set to be equal width dimensions. Two cases were assumed, one where the width dimensions were 50 mm and the other where they were 70 mm. Thus, two cases were set: Case-A, which is an example of the invention in which the first flat portion width-thickness ratio r1 and the second flat portion width-thickness ratio r2 are equal to 50 (r1=50 and r2=50), and Case-B, which is a comparative example in which the first flat portion width-thickness ratio r1 and the second flat portion width-thickness ratio r2 are equal to 70 (r1=70 and r2=70). An impact force F was applied along the longitudinal direction to each of the shock absorbing members 1B of Case-A and Case-B, as shown in FIG. 17(b), to cause bending deformation.

[0103] As a result, in Case-A (example of the invention) shown in FIG. 18(a), the position of the assumed break point coincided with the actual break point. On the other hand, in Case-B (comparison example) shown in FIG. 18(b), the actual break occurred at a position shifted from the assumed break point. Comparing the out-of-plane deformation of both cases, the out-of-plane deformation was kept small in the example of the invention in FIG. 18(a). On the other hand, the out-of-plane deformation was large in the comparison example in FIG. 18(b). It was presumed that the occurrence of this large out-of-plane deformation caused the actual break point to shift from the assumed break point. From the above, it has been confirmed that in order to suppress out-of-plane deformation, it is not sufficient to simply provide the reinforcement 40, and it is necessary to set at least one of the first planar portion width-thickness ratio r1 and the second planar portion width-thickness ratio r2 within an appropriate range (10 to 50).

[0104] [Third Example] A third embodiment of the present invention will be described below with reference to Figures 19 to 22. In this third embodiment, the maximum load and the amount of energy absorption when collision energy is applied to a plurality of impact absorbing members having different reinforcement conditions are calculated by numerical calculation.

[0105] That is, first, six types of impact absorbing members having various cross-sectional shapes shown in Fig. 19 were prepared. Fig. 19 is a cross-sectional view of the impact absorbing member taken along line BB in Fig. 2. Of these, Case 000 shows a comparative example that does not include the reinforcement 40. Case 005 also shows a comparative example in which the reinforcement method is different. Case 001 shows an example of the invention in which only one horizontal plate 42 is provided as the reinforcement 40. This horizontal plate 42 has folding start portions BP on both side edges at the position of the second region R2 shown in FIG. Case 002 shows an example of the invention in which only one vertical plate 41 is provided as the reinforcement 40. This vertical plate 41 has a folding start portion BP at the upper edge at the position of the second region R2 shown in FIG. Case 003 is an example of the invention in which one horizontal plate 42 and one vertical plate 41 are crossed in a "+" shape as the reinforcement 40, and is the same as the configuration illustrated in Figures 2 and 12(a). These vertical plate 41 and horizontal plate 42 are provided with folding start parts BP on both side edges and the upper edge at the position of the second region R2 shown in Figure 2. Case 004 is an example of the invention in which one vertical plate 41 of half the height is joined between the widthwise center of one horizontal plate 42 and the top wall portion 11, and has the same configuration as the example shown in Fig. 10(a). These vertical plate 41 and horizontal plate 42 have folding start parts BP on both side edges and the upper edge at the position of the second part R2 shown in Fig. 2. Case 005 is a comparative example in which a U-shaped reinforcing member 10A, the cross section of which is similar to that of the hat-shaped member 10, is joined to the inner peripheral surface of the hat-shaped member 10.

[0106] For each of the shock absorbing members shown in Case 000 to Case 005, a load F parallel to the longitudinal direction of the shock absorbing member was applied as collision energy while both ends were held rotatably around a horizontal axis as shown in FIG. 20(a). At this time, the position of the center line of the shock absorbing member was offset in the height direction from the input position of the collision energy, and then the collision energy was applied. More specifically, the load F was applied in the horizontal direction at a position closer to the top wall portion than the center line of the shock absorbing member. As a result, the shock absorbing member was folded from the state shown in FIG. 20(a) before folding deformation to the state shown in FIG. 20(b) after folding deformation, with the top wall portion 11 as the folding starting point.

[0107] The maximum load results for each case are shown in Table 1 below and Figure 21. In Figure 21, the horizontal axis shows each case number, and the vertical axis shows the maximum load (kN). Similarly, the energy absorption results for each case are shown in Table 1 below and Figure 22. In Figure 22, the horizontal axis shows each case number, and the vertical axis shows the energy absorption (kJ).

[0108] [Table 1]

[0109] As shown in FIG. 22, all of Cases 001 to 004 belonging to the invention examples obtained a higher energy absorption amount than Case 000 without reinforcement. The same was true for Case 005, which is a comparative example, but as shown in Table 1, the weight was significantly increased compared to Case 000. On the other hand, all of Cases 001 to 004 belonging to the invention examples have a weight increase compared to Case 000 that is only slightly increased. Therefore, it is possible to reduce the weight of the entire part by reducing the plate thickness of Cases 001 to 004 belonging to the invention examples until the energy absorption amount is the same as that of Case 000 or shortening the deformation stroke. Therefore, it was confirmed that the configuration of the invention example can exhibit high energy absorption efficiency by folding and deforming at good joints while being lightweight.

[0110] The gist of the present invention is summarized below. (1) One embodiment of the present invention is an impact absorbing member 1 that is long in one direction and includes a cylindrical body (hollow tube) 30 and a reinforcement 40 fixedly arranged inside the cylindrical body 30, the cylindrical body 30 being made of steel having a tensile strength of 650 MPa or more and 1600 MPa or less, and the reinforcement 40 being made of steel having a tensile strength of 590 MPa or more and 1600 MPa or less. Also, when viewed in a cross section perpendicular to the longitudinal direction of the impact absorbing member 1, the cylindrical body 30 has a top wall portion 11 having a flat portion overall width dimension W1 (mm) and a plate thickness t1 (mm), and a pair of side wall portions 12 provided on both sides of the top wall portion 11 and having a flat portion overall width dimension W2 (mm) and a plate thickness t1 (mm). Also, when viewed in a cross section perpendicular to the longitudinal direction of the impact absorbing member 1, the reinforcement 40 has at least one of a vertical plate 41 having one end joined to the top wall portion 11, a total number of n1 plates (n1 is an integer of 1 or more) and a total plate thickness of t2 (mm), and a horizontal plate 42 connecting the pair of side wall portions 12, a total number of n2 plates (n2 is an integer of 1 or more) and a total plate thickness of t3 (mm). The reinforcement 40 satisfies at least one of a first condition that the reinforcement 40 has a vertical plate 41 and the first planar portion width-thickness ratio r1 according to the following formula 1 is 10 or more and 50 or less, and a second condition that the reinforcement 40 has a horizontal plate 42 and the second planar portion width-thickness ratio r2 according to the following formula 2 is 10 or more and 50 or less. Further, the reinforcement 40 has a first portion R1, a second portion R2, and a third portion R3 arranged in this order along the longitudinal direction. In addition, the reinforcement 40 has a break origin portion BP in the second portion R2, the break origin portion BP having at least one of a plate thickness thinner than both the first portion R1 and the third portion R3 and a tensile strength lower than both the first portion R1 and the third portion R3, the break origin portion BP including the connection position with the tubular body 30. r1=((W1-t2) / (n1+1)) / t1...(Formula 1) r2=((W2-t3) / (n2+1)) / t1...(Formula 2)

[0111] (2) The impact absorbing member 1 described in (1) above may be configured as follows. That is, the tensile strength of the folding start point BP in the second region R2 may be equal to the tensile strengths in the first region R1 and the third region R3. In addition, the thickness ratio obtained by dividing the total thickness t2 at the folding start point BP in the second region R2 by the average thickness ta3 (mm) which is the average of the total thickness t3 in the first region R1 and the total thickness t3 in the third region R3 may satisfy 1 / 3 to (ta3-0.2) / ta3.

[0112] (3) The impact absorbing member 1 described in (1) above may be configured as follows. That is, the total thickness t2 at the folding start point BP in the second region R2 may be equal to the average thickness ta3 (mm) which is the average of the total thickness t3 at the first region R1 and the total thickness t3 at the third region R3. In addition, the tensile strength ratio obtained by dividing the tensile strength E1 (MPa) at the folding start point BP in the second region R2 by the average tensile strength Ea2 (MPa) which is the average of the tensile strength at the first region R1 and the tensile strength at the third region R3 may satisfy (Ea2-100) / Ea2~2.

[0113] (4) The impact absorbing member 1 described in (1) above may be configured as follows. That is, the thickness ratio obtained by dividing the total thickness t2 at the folding start point BP in the second region R2 by the average thickness ta3 (mm) which is the average of the total thickness t3 at the first region R1 and the total thickness t3 at the third region R3 may satisfy 1 / 3 to (ta3-0.2) / ta3. In addition, the tensile strength ratio obtained by dividing the tensile strength E1 (MPa) at the folding start point BP in the second region R2 by the average tensile strength Ea2 (MPa) which is the average of the tensile strength at the first region R1 and the tensile strength at the third region R3 may satisfy (Ea2-100) / Ea2 to 2.

[0114] (5) In the impact absorbing member 1 described in any one of (1) to (4) above, the length dimension Lr1 (mm) of the break origin portion BP in the direction along the longitudinal direction and the length dimension Lr2 (mm) of the reinforcement 40 may satisfy Lr2>Lr1>(1 / 2)×Lr2.

[0115] (6) In the impact absorbing member 1 described in any one of (1) to (5) above, when the reinforcement 40 is viewed in a cross section perpendicular to the longitudinal direction at a position including the break origin BP, the width dimension Wr1 (mm) of the break origin BP and the width dimension Wr2 (mm) between the center of the reinforcement 40 and the connection position may satisfy Wr2≧Wr1>(1 / 3)×Wr2.

[0116] (7) In the impact absorbing member 1 described in any one of (1) to (6) above, while satisfying the first condition, a flange formed at one end of the vertical plate 41 may be spot welded to the top wall portion 11 in a cross-sectional view perpendicular to the longitudinal direction.

[0117] (8) In the impact absorbing member 1 described in any one of (1) to (7) above, while satisfying the second condition, in a cross-sectional view perpendicular to the longitudinal direction, flanges formed on both ends of the cross plate 42 may be spot welded to each of a pair of side wall portions 12.

[0118] (9) The impact absorbing member described in (1) above may be configured as follows. That is, the cylindrical body 30 may have a hat-shaped member 10 having a hat top whose cross section perpendicular to the longitudinal direction is a top wall portion 11 and a pair of side walls 12 connected to both sides of the hat top, and a plate-shaped member 20 joined to the hat-shaped member 10 and facing the hat top. In addition, both the first condition and the second condition may be satisfied. In addition, when viewed in a cross section perpendicular to the longitudinal direction, the total number n1 may be 1 and the total number n2 may be 1, and the vertical plate 41 may be fixed in a state of being stretched between the hat top and the plate-shaped member 20. In addition, a horizontal plate 42 may be fixed between the pair of side walls 12 in a state of being crossed with the vertical plate 41.

[0119] (10) The impact absorbing member 1 described in (1) above may be configured as follows. That is, the cylindrical body 30 may have a hat-shaped member 10 having a hat top whose cross section perpendicular to the longitudinal direction is a top wall portion 11 and a pair of side walls 12 connected to both sides of the hat top, and a plate-shaped member 20 joined to the hat-shaped member 10 and facing the hat top. In addition, both the first condition and the second condition may be satisfied. In addition, in a cross section perpendicular to the longitudinal direction, the total number n1 may be 1 and the total number n2 may be 1, and one end of the horizontal plate 42 may be joined to one of the pair of side walls 12, and the other end of the horizontal plate 42 may be joined to the other of the pair of side walls 12. In addition, one end of the vertical plate 41 may be joined to the hat top, and the other end of the vertical plate 41 may be joined to a position between one end and the other end of the horizontal plate 42. [Explanation of symbols]

[0120] 1. Shock absorbing material 10 Hat-shaped member 11 Ceiling wall, hat top 12 Side wall 12a Left side wall (side wall) 12b Right side wall (side wall) 20 Plate-shaped member 30 Cylindrical body (hollow tube) 40 Reinforce 41 Vertical Board 42 Horizontal board BP Fold starting point R1 1st part R2 2nd part R3 3rd part

Claims

1. A shock absorbing member having a hollow tube and a reinforcement fixedly disposed inside the hollow tube, the shock absorbing member being long in one direction, The hollow tube is made of a steel material having a tensile strength of 650 MPa or more and 1600 MPa or less, and the reinforcement is made of a steel material having a tensile strength of 590 MPa or more and 1600 MPa or less; A cross section perpendicular to the longitudinal direction of the impact absorbing member, The hollow tube has a top wall portion having a flat portion overall width dimension W1 (mm) and a wall thickness t1 (mm), and a pair of side wall portions provided on both sides of the top wall portion and having a flat portion overall width dimension W2 (mm) and a wall thickness t1 (mm), The reinforcement has at least one of a vertical plate having one end joined to the top wall portion, a total number of n1 plates, and a total plate thickness of t2 (mm), and a horizontal plate connecting the pair of side wall portions, a total number of n2 plates, and a total plate thickness of t3 (mm); The reinforcement is At least one of the following conditions is satisfied: a first condition in which the first flat portion width-thickness ratio r1 according to the vertical plate and the following formula 1 is 10 or more and 50 or less; and a second condition in which the second flat portion width-thickness ratio r2 according to the horizontal plate and the following formula 2 is 10 or more and 50 or less. having a first portion, a second portion, and a third portion aligned in sequence along the longitudinal direction; In the second portion, A plate thickness that is thinner than both the first portion and the third portion, and a tensile strength lower than both the first portion and the third portion; a bending start portion having at least one of the above is formed including a connection position with the hollow tube; A shock absorbing member characterized by: r1=((W1-t2) / (n1+1)) / t1...(Formula 1) r2=((W2-t3) / (n2+1)) / t1...(Formula 2)

2. the tensile strength of the folding origin portion in the second region is equal to the tensile strengths in the first region and the third region; A thickness ratio obtained by dividing the total thickness t2 at the folding starting point in the second portion by an average thickness ta3 (mm) which is an average value of the total thickness t3 in the first portion and the total thickness t3 in the third portion satisfies 1 / 3 to (ta3-0.2) / ta3; The impact absorbing member according to claim 1 .

3. The total thickness t2 at the folding start point in the second portion is equal to an average thickness ta3 (mm) which is an average value of the total thickness t3 in the first portion and the total thickness t3 in the third portion; a tensile strength ratio obtained by dividing the tensile strength E1 (MPa) of the folding starting portion in the second region by an average tensile strength Ea2 (MPa) which is an average value of the tensile strength in the first region and the tensile strength in the third region satisfies (Ea2-100) / Ea2-2; The impact absorbing member according to claim 1 .

4. A thickness ratio obtained by dividing the total thickness t2 at the folding start point in the second portion by an average thickness ta3 (mm) which is an average value of the total thickness t3 in the first portion and the total thickness t3 in the third portion satisfies 1 / 3 to (ta3-0.2) / ta3; a tensile strength ratio obtained by dividing the tensile strength E1 (MPa) of the folding starting portion in the second region by an average tensile strength Ea2 (MPa) which is an average value of the tensile strength in the first region and the tensile strength in the third region satisfies (Ea2-100) / Ea2-2; The impact absorbing member according to claim 1 .

5. In the direction along the longitudinal direction, The length dimension Lr1 (mm) of the bend starting point and the length dimension Lr2 (mm) of the reinforcement satisfy Lr2>Lr1>(1 / 2)×Lr2. The impact absorbing member according to any one of claims 1 to 4.

6. When the reinforcement is viewed in a cross section perpendicular to the longitudinal direction at a position including the folding start point, A width dimension Wr1 (mm) of the bend starting point and a width dimension Wr2 (mm) between the center of the reinforcement and the connection position satisfy Wr2 ≧ Wr1 > (1 / 3) × Wr2. The impact absorbing member according to any one of claims 1 to 4.

7. The first condition is satisfied; In a cross-sectional view perpendicular to the longitudinal direction, a flange formed at the one end of the vertical plate is spot welded to the top wall portion; The impact absorbing member according to any one of claims 1 to 4.

8. The second condition is satisfied; In a cross-sectional view perpendicular to the longitudinal direction, flanges formed on both ends of the horizontal plate are spot-welded to each of the pair of side wall portions; The impact absorbing member according to any one of claims 1 to 4.

9. The hollow tube is a hat-shaped member having a hat top portion whose cross section perpendicular to the longitudinal direction is the top wall portion and a pair of side wall portions connected to both sides of the hat top portion; a plate-like member joined to the hat-shaped member and facing the hat top; Both the first condition and the second condition are satisfied; In a cross section perpendicular to the longitudinal direction, The total number n1 is 1 and the total number n2 is 1, The vertical plate is fixed in a spanning state between the hat top and the plate-like member, The horizontal plate is fixed between the pair of side wall portions in a state where the horizontal plate crosses the vertical plate; The impact absorbing member according to claim 1 .

10. The hollow tube is a hat-shaped member having a hat top portion whose cross section perpendicular to the longitudinal direction is the top wall portion and a pair of side wall portions connected to both sides of the hat top portion; a plate-like member joined to the hat-shaped member and facing the hat top; Both the first condition and the second condition are satisfied; In a cross section perpendicular to the longitudinal direction, The total number n1 is 1 and the total number n2 is 1, One end of the horizontal plate is joined to one of the pair of side wall portions, and the other end of the horizontal plate is joined to the other of the pair of side wall portions, one end of the vertical plate is joined to the top of the hat, and the other end of the vertical plate is joined to a position between the one end and the other end of the horizontal plate; The impact absorbing member according to claim 1 .

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