Impact absorption member and vehicle body

Abstract

To provide an impact absorption member having lighter weight and capable of achieving high collision resistance performance, and a vehicle body including the impact absorption member.SOLUTION: An impact absorption member 4 is provided in a vehicle body 1, and includes a closed cross section part formed along a predetermined longitudinal direction and having a cross section orthogonal to the longitudinal direction being a closed cross-sectional shape. The impact absorption member includes: a low strength part 51; a high strength part 53 aligned with the low strength part and having a plate thickness direction center part having a higher Vickers hardness than a Vickers hardness of a plate thickness direction center part of the low strength part; and a bonding part 52 bonding the low strength part and the high strength part. The maximum bending angle of the high strength part is set according to the maximum bending angle of the low strength part.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a shock-absorbing member and a vehicle body.

Background Art

[0002] While automobiles are required to reduce CO2 emissions, the standard values for collision safety are becoming stricter. Therefore, for automotive members, such as shock-absorbing members, weight reduction and improvement of collision safety are required, and material selection and structural design of shock-absorbing members are important. In particular, for the center pillar, which is an important member for protecting occupants during a side collision of an automobile, more advanced knowledge of material selection and structural design is required. From the viewpoint of occupant protection, high strength is required for the upper part of the center pillar so as not to deform, and thus the application of high-strength materials is effective. On the other hand, since the lower part of the center pillar is required to absorb energy, a material with a good balance between strength and fracture resistance is required. Therefore, a tailor-welded blank (TWB) capable of arranging two different materials on a single blank from the viewpoint of weight reduction is useful as a material for the center pillar. As a TWB material, the TWB material described in Patent Document 1 can be exemplified.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] From the perspective of reducing CO2 emissions, each automobile manufacturer is rapidly advancing the development of electric vehicles. In automobiles that transmit the output rotation of an internal combustion engine to the wheels, such as gasoline engine vehicles and diesel engine vehicles, due to the structure of the side sill, when a side collision occurs, the side sill connected to the lower part of the center pillar greatly deforms and rotates, and the center pillar also tends to deform. Therefore, the deformation of the center pillar was local.

[0005] On the other hand, in an electric vehicle, a battery is arranged on the side of the side sill. And in order to protect this battery, an impact absorbing member for protecting the battery is installed in the side sill, etc., and the side sill is reinforced, and the side sill has a structure that is difficult to deform. Thus, in an electric vehicle where the side sill tends to be difficult to deform due to the structure of battery protection, at the time of a side collision, as the deformation amount of the side sill is relatively small, the deformation amount of the center pillar tends to increase for impact absorption. In particular, in the center pillar outer formed from TWB and having a higher tensile strength in the upper part compared to the lower tensile strength, the lower end part of the high-strength upper part (the part near the welding line with the lower part) is also greatly deformed being dragged by the deformation of the low-strength lower part, and there is a possibility of base material fracture. Since it is preferable that base material fracture possibility does not occur from the perspective of ensuring impact absorption performance, it is preferable to suppress such base material fracture possibility. To suppress the base material fracture possibility, it is conceivable to increase the plate thickness of the center pillar outer, but increasing the plate thickness of the center pillar outer is not preferable because it increases the weight of the center pillar outer. In order to increase the impact absorption performance at the time of a side collision while making the center pillar outer lighter, it is preferable to reduce the thickness of the steel plate constituting the center pillar outer while increasing its strength, and further suppress the possibility of member fracture at the time of a side collision.

[0006] One of the objects of the present invention is to provide an impact absorbing member that can achieve higher lightweight and impact resistance performance, and a vehicle body equipped with the same.

Means for Solving the Problem

[0007] The present invention relates to an impact absorbing member and a vehicle body described below.

[0008] (1) An impact absorbing member provided in a vehicle body, formed along a predetermined longitudinal direction, and including a portion having a closed cross-sectional shape perpendicular to the longitudinal direction, a low-strength portion, a high-strength portion having a central portion in the plate thickness direction that is arranged in the longitudinal direction with the low-strength portion and has a Vickers hardness higher than that of the central portion in the plate thickness direction of the low-strength portion, a joint portion that joins the low-strength portion and the high-strength portion, and an impact absorbing member in which the maximum bending angle of the high-strength portion is set according to the maximum bending angle of the low-strength portion.

[0009] According to this configuration, for example, by increasing the maximum bending angle of the material of the high-strength portion, the difference between the maximum bending angle of the material of the high-strength portion and the maximum bending angle of the material of the low-strength portion can be reduced. By setting the bending angle in this way, even in the material of the high-strength portion with high strength due to high Vickers hardness, high bending performance can be exhibited. Therefore, even when the high-strength portion is plastically deformed relatively largely due to the plastic deformation of the low-strength portion during a side collision, the deformability of the high-strength portion can be increased, and the possibility of fracture of the high-strength portion near the joint portion can be suppressed. In addition, the high-strength portion can be applied to a location where high strength is required from the viewpoint of occupant protection. Here, when a material with low Vickers hardness (low strength) is used to ensure high bendability, it is necessary to increase the plate thickness in order to reduce the amount of deformation on the occupant side, which leads to an increase in mass. On the other hand, according to the above configuration, since the Vickers hardness of the high-strength portion is high, the high-strength portion is of high strength, and while improving the impact absorption performance during a collision such as a side collision, the high-strength portion can be made thinner to achieve weight reduction of the impact absorbing member. In this way, by applying a material that combines Vickers hardness (strength) and bendability as the high-strength portion, an impact absorbing member having high impact absorption performance through light weight and suppression of fracture possibility can be realized.

[0010] (2) The difference between the maximum bending angle of the high-strength portion and the maximum bending angle of the low-strength portion is 100 degrees or less, and the impact-absorbing member according to (1) above.

[0011] According to this configuration, at the time of a side collision of the vehicle, it is possible to more reliably achieve suppression of the possibility of fracture of the high-strength portion following the bending deformation of the low-strength portion. Therefore, an impact-absorbing member having high impact-absorbing performance through suppression of the possibility of fracture can be realized.

[0012] (3) The Vickers hardness at the central portion in the plate thickness direction of the high-strength portion is 500 HV or more, and the impact-absorbing member according to (1) or (2) above.

[0013] According to this configuration, the strength difference (strength ratio) between the high-strength portion and the low-strength portion is large, and there is a tendency that the difference in bendability between the material of the high-strength portion and the material of the low-strength portion is likely to be large. That is, when the Vickers hardness of the high-strength portion is 500 HV or more, at the time of a side collision, due to the bending deformation of the high-strength portion following the bending deformation of the low-strength portion, there is a tendency that the possibility of fracture is likely to occur in the high-strength portion. Thus, when the Vickers hardness of the high-strength portion is 500 HV or more, the problem of the possibility of fracture in the high-strength portion becomes prominent. Even in such a case, by setting the maximum bending angle of the high-strength portion according to the maximum bending angle of the low-strength portion, the possibility of fracture of the high-strength portion at the time of a side collision can be suppressed.

[0014] (4) The Vickers hardness at the central portion in the plate thickness direction of the low-strength portion is 150 HV or more, and the impact-absorbing member according to any one of (1) to (3) above.

[0015] According to this configuration, at the time of a side collision, while increasing the impact energy absorption effect due to the plastic deformation of the low-strength portion, excessive plastic deformation of the high-strength portion can be suppressed, and while enhancing the impact-absorbing performance, the amount of intrusion of the high-strength portion into the cabin side of the vehicle body can be reduced.

[0016] (5) The ratio HV1 / HV2 of the Vickers hardness HV1 at the center in the plate thickness direction of the high-strength portion to the Vickers hardness HV2 at the center in the plate thickness direction of the low-strength portion is 1.3 or more, and the impact-absorbing member according to any one of the above (1) to (4).

[0017] According to this configuration, the strength difference (strength ratio) between the high-strength portion and the low-strength portion is large, and the difference in bendability between the material of the high-strength portion and the material of the low-strength portion tends to be large. That is, when HV1 / HV2 is 1.3 or more, at the time of a side collision, the high-strength portion with a high Vickers hardness is likely to be broken by the bending deformation of the high-strength portion that follows the bending deformation of the low-strength portion. Thus, when HV1 / HV2 is 1.3 or more, the problem of the requirement for suppressing breakage possibility in the high-strength portion becomes prominent. Even in such a case, by setting the maximum bending angle of the high-strength portion according to the maximum bending angle of the low-strength portion, the breakage possibility of the high-strength portion at the time of a side collision can be suppressed.

[0018] (6) The difference between the maximum bending angle of the low-strength portion and the maximum bending angle of the high-strength portion is 30 degrees or less, and the impact-absorbing member according to any one of the above (1) to (5).

[0019] According to this configuration, at the time of a side collision, the high-strength portion can sufficiently follow the bending deformation of the low-strength portion and bend. As a result, the breakage possibility of the high-strength portion at the time of a side collision can be suppressed.

[0020] (7) The impact-absorbing member is a center pillar that includes a pillar inner and a pillar outer and is arranged along the vertical direction of the vehicle body. The pillar outer includes the low-strength portion, the joint portion, and the high-strength portion. The high-strength portion is arranged above the low-strength portion, and the impact-absorbing member according to any one of the above (1) to (6).

[0021] According to this configuration, in the case of a side collision, in the pillar outer part of the center pillar that receives most of the impact load, since the material of the high-strength part arranged above the low-strength part has enhanced bendability, it is possible to more surely suppress the occurrence of breakage in the high-strength part. Therefore, the effect of protecting the occupant by the center pillar can be more surely exhibited.

[0022] (8) The center pillar is provided with a pair of upper and lower brackets for supporting a door installed behind the center pillar. The joint portion is the impact absorbing member according to (7) disposed at a position lower than the height position of the lower end of the upper bracket.

[0023] According to this configuration, the impact load input from the upper bracket (impact load input point) located far from the side sill to the center pillar can be received by the high-strength part. Therefore, the amount of deformation of the center pillar toward the occupant side due to a side collision can be made smaller.

[0024] (9) The joint portion is the impact absorbing member according to (8) disposed at a position higher than the height position of the upper end of the lower bracket.

[0025] According to this configuration, a sufficient range of the low-strength part can be ensured. Therefore, it is possible to achieve both impact absorption by the low-strength part in cooperation with the side sill at the initial stage of a side collision and deformation suppression of the center pillar toward the occupant side by the high-strength part receiving the impact load from the upper bracket at the later stage of the side collision.

[0026] (10) The joint portion is the impact absorbing member according to (8) disposed at a position lower than the height position of the lower end of the lower bracket.

[0027] During a side collision, the side sill may undergo torsional deformation about an axis along the front-rear direction. When the side sill is torsionally deformed in this way, by arranging the joint portion at a position lower than the height position of the lower end of the lower bracket, a high-strength portion can be installed near the side sill where the amount of deformation is large during a side collision. Therefore, during a side collision, the deformation of the center pillar that follows the intrusion of the side sill into the cabin due to the torsional deformation of the side sill can be suppressed by the high-strength portion. As a result, the amount of intrusion of the center pillar into the cabin can be made smaller, and furthermore, the torsional deformation of the side sill can be suppressed.

[0028] (11) The vehicle body further includes a side sill joined to the lower portion of the center pillar, arranged along the front-rear direction of the vehicle body, and having a closed cross-sectional shape in a cross-section orthogonal to the front-rear direction. The side sill includes an outer wall arranged on the outer side in the width direction of the vehicle body in the side sill. The lower portion of the center pillar includes an overlapping portion arranged to cover the side sill at the connection location with the side sill. The overlapping portion is along the side sill down to a position below the height position of half the height in the vertical direction of the outer wall of the side sill, and is the impact-absorbing member according to any one of (7) to (9) above.

[0029] According to this configuration, since the joint area between the center pillar and the side sill can be increased, the stress acting between the side sill and the center pillar during a side collision can be reduced. Further, the load transmitted from the center pillar to the side sill during a side collision is mainly received by the vehicle body as a torsional moment. Therefore, it is possible to suppress deformation of the closed cross-sectional shape of the side sill, particularly deformation of the side sill outer. Even when a side collision occurs, since the original closed cross-sectional shape of the side sill before the collision is difficult to change, the side sill has high torsional rigidity and the torsional angle of the side sill during a side collision can be reduced. Thereby, the intrusion amount of the center pillar and the side sill into the cabin can be reduced. On the other hand, for example, by devising the arrangement so that the center pillar does not reach the lower end of the side sill, the center pillar does not become unnecessarily heavy, and it is possible to highly balance the improvement of the reinforcement effect of the side sill by the lower shape of the center pillar and the suppression of the weight increase of the center pillar.

[0030] (12) The Vickers hardness on the surface in the plate thickness direction of the high-strength portion is at least 100 HV lower than the Vickers hardness at the center portion in the plate thickness direction of the high-strength portion, and the impact absorbing member according to any one of (1) to (11) above.

[0031] According to this configuration, the maximum bending angle of the high-strength portion can be increased. Therefore, during a side collision, the high-strength portion can more surely follow the bending deformation of the low-strength portion, suppressing the possibility of breakage in the high-strength portion and improving the impact absorption performance.

[0032] (13) A high-strength portion softening layer is provided in the high-strength portion in the plate thickness direction from the surface, The Vickers hardness at the center portion in the plate thickness direction of the portion where the high-strength portion softening layer is provided in the high-strength portion is 500 HV or more, The thickness of the high-strength portion softening layer is 80 μm or more and 5% or more and 20% or less of the plate thickness of the portion where the high-strength portion softening layer is provided, The Vickers hardness of the high-strength part softening layer on the surface is 0.5 times or more and less than 0.9 times the Vickers hardness at the center in the plate thickness direction of the portion where the high-strength part softening layer is provided. The high-strength part softening layer has, in the plate thickness direction, a first hardness change region that is a region from the surface to 40% of the thickness of the high-strength part softening layer, and a second hardness change region that is a region of the high-strength part softening layer that is not the first hardness change region. The absolute value ΔHV1 of the hardness change in the plate thickness direction in the first hardness change region is greater than the absolute value ΔHV2 of the hardness change in the plate thickness direction in the second hardness change region, for the impact absorbing member according to (12).

[0033] According to this configuration, since the Vickers hardness at the center in the plate thickness direction of the high-strength part is 500 HV or more, the effect of improving the deformability due to the softening layer in the high-strength part becomes remarkable. Also, if the thickness of the high-strength part softening layer is 20% or less of the above plate thickness, since the proportion of the high-strength part softening layer in the steel plate that is the material of the high-strength part is small, the load resistance required for the high-strength part can be maintained. On the other hand, if the thickness of the high-strength part softening layer is 80 μm or more and 5% or more of the above plate thickness, the deformability due to the high-strength part softening layer can be sufficiently exhibited. Also, if the Vickers hardness of the surface of the high-strength part is 0.5 times or more the Vickers hardness at the center in the plate thickness direction, the load resistance during collision, particularly in the latter stage of the stroke during collision, can be improved. On the other hand, if the Vickers hardness of the surface of the high-strength part is less than 0.9 times the Vickers hardness at the center in the plate thickness direction, the deformability can be sufficiently improved. Also, if ΔHV1 is greater than ΔHV2, sufficient load characteristics can be obtained.

[0034] (14) The Vickers hardness on the surface in the plate thickness direction of the low-strength part is at least 100 HV lower than the Vickers hardness at the center in the plate thickness direction of the low-strength part, for the impact absorbing member according to any one of (1) to (13).

[0035] According to this configuration, the maximum bending angle of the low-strength portion can be made larger. Therefore, it is possible to suppress cracking in the low-strength portion during a side collision and improve the impact absorption performance. As a result, since the high-strength portion has a high Vickers hardness and high strength, it is possible to suppress the amount of intrusion into the vehicle interior and improve the occupant protection effect. In the low-strength portion, while ensuring the absorption amount of impact energy, the thickness of the low-strength portion can be further reduced to lightweight the vehicle body. Further, even when the low-strength portion is formed of a high-strength material having a higher Vickers hardness, the possibility of fracture of the low-strength portion can be suppressed, so that the amount of the low-strength portion entering the inside of the vehicle body during a side collision can be made smaller.

[0036] (15) The low-strength portion is provided with a low-strength portion softening layer in the plate thickness direction from the surface, The Vickers hardness of the central portion in the plate thickness direction of the portion where the low-strength portion softening layer is provided in the low-strength portion is 150 HV or more, The thickness of the low-strength portion softening layer is 80 μm or more and 5% or more and 20% or less of the plate thickness of the portion where the low-strength portion softening layer is provided, The Vickers hardness of the low-strength portion softening layer on the surface is 0.5 times or more and less than 0.9 times the Vickers hardness of the central portion in the plate thickness direction of the portion where the low-strength portion softening layer is provided, The low-strength portion softening layer has a first hardness change region which is a region from the surface to 40% of the thickness of the low-strength portion softening layer in the plate thickness direction, and a second hardness change region which is a region of the low-strength portion softening layer that is not the first hardness change region, The absolute value ΔHV1’ of the hardness change in the plate thickness direction in the first hardness change region is larger than the absolute value ΔHV2’ of the hardness change in the plate thickness direction in the second hardness change region, the impact absorption member according to (14).

[0037] According to this configuration, when the Vickers hardness at the center in the plate thickness direction in the low-strength part is 150 HV or more, the effect of improving the deformability due to the low-strength part softening layer in the low-strength part becomes remarkable. Further, if the thickness of the low-strength part softening layer is 20% or less of the above plate thickness, the ratio of the low-strength part softening layer in the steel plate which is the material of the low-strength part is small, so that the load resistance required for the low-strength part can be maintained. On the other hand, if the thickness of the low-strength part softening layer is 80 μm or more and 5% or more of the above plate thickness, the deformability due to the low-strength part softening layer can be sufficiently exhibited. Further, if the Vickers hardness of the surface of the low-strength part is 0.5 times or more the Vickers hardness at the center in the plate thickness direction, the load resistance during collision, particularly in the latter stage of the stroke during collision, can be improved. On the other hand, if the Vickers hardness of the surface of the low-strength part is less than 0.9 times the Vickers hardness at the center in the plate thickness direction, the deformability can be sufficiently improved. Further, if ΔHV1’ is larger than ΔHV2’, sufficient load characteristics can be obtained.

[0038] (16) A vehicle body comprising a center pillar and a side sill joined to the lower part of the center pillar. A vehicle body, wherein at least one of the center pillar and the side sill is the impact absorbing member according to any one of (1) to (15) above.

[0039] According to this configuration, a vehicle body that is lighter and has high collision resistance performance can be realized.

Effects of the Invention

[0040] According to the present invention, an impact absorbing member that is lighter and has high collision resistance performance can be realized.

Brief Description of the Drawings

[0041]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0042] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a shock-absorbing member applied to an automobile will be described.

[0043] FIG. 1 is a schematic left side view showing a main part of a vehicle body 1 to which a shock absorbing member according to an embodiment of the present invention is applied. FIG. 2 is a cross-sectional view orthogonal to the vertical direction Z of a closing surface portion 46 of a center pillar 4 along line II-II in FIG. 1, and illustration of the back side of the cross-section is omitted. FIG. 3 is a schematic cross-sectional view of a main part for explaining a coupling state between a side sill outer 15 and a pillar outer 41 of a center pillar 4 along line III-III in FIG. 1, showing a cross-section orthogonal to the front-rear direction X of the vehicle body 1. Hereinafter, unless otherwise specified, explanations will be given while appropriately showing FIGS. 1 to 3.

[0044] The vehicle body 1 is a part of a vehicle, and an example of the vehicle can be an automobile. As an example of the automobile, a passenger car can be cited. As an example of the above passenger car, a sedan type passenger car, a coupe type passenger car, a hatchback type passenger car, a minivan type passenger car, an SUV (Sport Utility Vehicle) type passenger car, etc. can be cited. Further, in the present embodiment, a configuration in which the vehicle is a BEV (Battery Electric Vehicle) will be described as an example.

[0045] In the present embodiment, the vehicle body 1 is formed of a material including a steel plate. As the steel plate, an aluminum-plated steel plate can be exemplified, but other steel types such as a zinc-plated steel plate may also be used. The plating on the plated steel plate is not particularly limited, but examples include hot-dip galvanizing, alloyed hot-dip galvanizing, electro-galvanizing, Zn-Ni plating (electro-alloyed zinc plating), Sn plating, Al-Si plating, alloyed electro-galvanizing, hot-dip zinc-aluminum alloy plating, hot-dip zinc-aluminum-magnesium alloy plating, hot-dip zinc-aluminum-magnesium-Si alloy plating, zinc vapor deposition Al plating, etc. Further, the plating treatment can be performed by passing the steel plate through a continuous line.

[0046] The vehicle body 1 includes a front pillar 2, a roof rail 3, a center pillar 4, a side sill 5, and a side sill rear 6.

[0047] The front pillar 2 has a cross-sectional shape in a cross-section orthogonal to the longitudinal direction of the front pillar 2 that has an endless closed shape (closed cross-sectional shape). The front pillar 2 has a front pillar upper 11 that is coupled to the roof rail 3 toward the rear as it goes upward, and a front pillar lower 12 disposed below the front pillar upper 11. The front pillar lower 12 is formed, for example, in an L shape in a side view. The lower rear edge portion 12a of the front pillar lower 12 is open toward the rear.

[0048] The roof rail 3 is disposed on the roof portion of the vehicle body 1 and extends rearward from the front pillar upper 11.

[0049] The side sill 5 is provided at the lower part of the outer portion in the width direction Y of the vehicle body 1. The side sill 5 is joined to the lower part (lower overlapping portion 47) of the center pillar 4 and is disposed along the longitudinal direction X of the vehicle body 1. The side sill 5 has an endless closed cross-sectional shape in a cross-section orthogonal to the longitudinal direction X.

[0050] The side sill 5 has a side sill outer 15 and a side sill inner 16 arranged in the width direction Y.

[0051] The side sill outer 15 and the side sill inner 16 each have a cross-sectional shape orthogonal to the longitudinal direction X formed in a hat shape, and cooperate to form the closed cross-sectional shape in the side sill 5. The side sill outer 15 is disposed outside the side sill inner 16 in the width direction Y.

[0052] The side sill outer 15 and the side sill inner 16 are formed of, for example, a steel plate. The tensile strength of the side sill outer 15 and the side sill inner 16 is not particularly limited, but a value of 980 MPa or more can be exemplified.

[0053] The side sill outer 15 has an upper flange 151, an upper wall 152 extending outward in the width direction Y from the upper flange 151, an outer wall 153 extending downward from the upper wall 152 and disposed at the outermost side in the width direction Y in the side sill 5, a lower wall 154 extending inward in the width direction Y from the outer wall 153, and a lower flange 155 extending downward from the lower wall 154.

[0054] The side sill inner 16 has an upper flange 161, an upper wall 162 extending inward in the width direction Y from the upper flange 161, an inner wall 163 extending downward from the upper wall 162, a lower wall 164 extending outward in the width direction Y from the inner wall 163, and a lower flange 165 extending downward from the lower wall 164.

[0055] The upper flanges 151 and 161 are joined to each other by welding, adhesion, or the like. Similarly, the lower flanges 155 and 165 are joined to each other by welding, adhesion, or the like.

[0056] The front portion 5a of the side sill 5 is fitted into the front pillar lower 12 of the front pillar 2 and joined to the front pillar lower 12 by welding, adhesion, or the like. And the side sill 5 extends rearward from the lower rear edge portion 12a of the front pillar lower 12. The rear portion 5b of the side sill 5 is fitted into the side sill rear 6 and joined to the side sill rear 6 by welding, adhesion, or the like.

[0057] The side sill rear 6 is disposed behind the side sill 5. The side sill rear 6 is a hollow member extending along the front-rear direction X. The cross-sectional shape of the side sill rear 6 in a cross-section orthogonal to the longitudinal direction of the side sill rear 6 is formed in a closed shape such as a rectangle (closed cross-sectional shape). The side sill 5 extends forward from the front edge portion 6a of the side sill rear 6.

[0058] The battery unit 18 is installed at a location that has advanced inward in the width direction Y from the side sill 5 (the side of the side sill 5). The battery unit 18 is disposed below the floor panel 7 that extends inward in the width direction Y from the side sill 5. The battery unit 18 has a battery case 18a and a battery 18b housed in the battery case 18a. The battery 18b supplies electric power via a cable or the like to an electric motor for driving wheels (not shown) or the like. The battery case 18a is fixed to a member of the vehicle body 1 such as the floor panel 7 by a fixing member such as a bolt (not shown). The battery unit 18 is also installed near the center pillar 4 and is aligned with a lower overlapping portion 47 (to be described later) of the center pillar 4 in the width direction Y. The battery unit 18 is disposed adjacent to the side sill 5 in the width direction Y (for example, at a distance of less than 10 cm). The battery case 18a protects the battery 18b in cooperation with the side sill 5 and the center pillar 4 during a side collision.

[0059] A reinforcing member 20 is disposed inside the side sill 5. The reinforcing member 20 is provided to suppress the transmission of an impact to the battery unit 18 during a side collision. The specific shape of the reinforcing member 20 is not limited. When an impact load equal to or greater than a certain value acting inward in the width direction Y from the side sill outer 15 acts, the reinforcing member 20 absorbs the impact by collapsing while plastically deforming inward in the width direction Y. In the present embodiment, the reinforcing member 20 is disposed so as to be aligned with the battery unit 18 in the width direction Y, and the cross-sectional shape orthogonal to the front-rear direction X is a shape in which a plurality of rectangles are arranged in the width direction Y. The reinforcing member 20 is fixed to, for example, the inner wall 163 of the side sill inner 16. The reinforcing member 20 is installed, for example, at at least a part of the side sill 5 in the front-rear direction X and may be installed over the entire area of the side sill 5.

[0060] Also, around the center pillar 4, a floor cross member (not shown) is disposed on the side of the side sill 5.

[0061] During a side collision in the side sill 5, particularly when a side collision occurs at the lower overlapping portion 47 between the center pillar 4 and the side sill 5, the side sill 5 sets the lower rear edge portion 12a of the front pillar 2 as the front fastening position, the lower overlapping portion 47 of the center pillar 4 as the intermediate fastening position, the front edge portion 6a of the side sill rear 6 as the rear fastening position, and the location where the floor cross member is arranged as the inner fastening position, and receives an impact load from an object. When the impact load is equal to or greater than a certain level, the side sill 5 absorbs the impact load while plastically deforming inward in the width direction Y.

[0062] Since the reinforcing member 20 is installed inside the side sill 5, a greater impact load is required to deform the reinforced side sill 5 during a side collision. Therefore, both the amount of bending deformation and the amount of torsional deformation of the side sill 5 are small. On the other hand, since the center pillar 4 receives a relatively large impact load, it plastically deforms significantly toward the cabin 1 side.

[0063] In this embodiment, the side sill rear 6 is described as the member constituting the rear fastening position. However, it does not have to be like this. For example, other members such as the lower end portion of the C pillar connected to the rear end of the side sill 5 may constitute the rear fastening position. The rear fastening position may be the rear fastening point when the side sill 5 plastically deforms under an impact load during a side collision, and the specific example of the member constituting the rear fastening position is not limited. Similarly, for the front fastening position, the specific example of the member constituting the front fastening position is not limited. When a member other than the side sill rear 6 constitutes the rear fastening position, the side sill rear 6 does not have to exist in the vehicle body 1.

[0064] The center pillar 4 is arranged behind the front pillar 2 and is formed along the vertical direction Z (a predetermined longitudinal direction) from the roof rail 3 to the side sill 5. The center pillar 4 is an impact absorbing member that absorbs impacts during a side collision of the vehicle body 1.

[0065] The center pillar 4 has an upper overlapping portion 45 joined to the roof rail 3, a blocking portion 46 disposed below the upper overlapping portion 45 and above the side sill 5, and a lower overlapping portion 47 as a lower portion disposed below the blocking portion 46 and arranged to cover the outer surface of the side sill 5 at the connection location with the side sill 5.

[0066] Further, the center pillar 4 includes a pillar outer 41, a pillar inner 42, and a reinforcing patch 43 disposed between the pillar outer 41 and the pillar inner 42. The upper overlapping portion 45, the blocking portion 46, and the lower overlapping portion 47 are formed by the pillar outer 41 and the pillar inner 42. The patch 43 is a member formed by pressing a blank and is joined to at least one of the pillar outer 41 and the pillar inner 42. The patch 43 may be omitted.

[0067] In the blocking portion 46, the pillar outer 41 and the pillar inner 42 each have a hat-shaped cross-sectional shape orthogonal to the vertical direction Z. By joining the pillar outer 41 and the pillar inner 42 to each other, the blocking portion 46 has a closed cross-sectional shape in a cross-section orthogonal to the vertical direction Z. The pillar outer 41 is disposed outside the pillar inner 42 in the width direction Y.

[0068] The pillar outer 41 in the blocking portion 46 has a front flange 411, a front wall 412 extending outward in the width direction Y from the front flange 41, a side wall 413 extending rearward from the front wall 412, a rear wall 414 extending inward in the width direction Y from the side wall 413, and a rear flange 415 extending rearward from the rear wall 414.

[0069] The pillar inner 42 in the closing surface portion 46 has a front flange 421, a front wall 422 extending inward in the width direction Y from the front flange 421, a side wall 423 extending rearward from the front wall 422, a rear wall 424 extending outward in the width direction Y from the side wall 423, and a rear flange 425 extending rearward from the rear wall 424. Note that the pillar inner 42 may have a flat plate shape, and the cross-sectional shape orthogonal to the vertical direction Z may be a shape that is substantially straight in the front-rear direction X. In this case, the front wall 422 and the rear wall 424 are omitted, and the front flange 421, the side wall 423, and the rear flange 425 are arranged along the front-rear direction X.

[0070] The front flanges 411 and 421 are joined to each other by welding, adhesion, or the like. Similarly, the rear flanges 415 and 425 are joined to each other by welding, adhesion, or the like.

[0071] A more specific configuration of the closing surface portion 46 will be described later.

[0072] Next, the configuration of the lower overlapping portion 47 will be described in more detail. The pillar inner 42 in the lower overlapping portion 47 is joined to the side sill inner 16 by welding, adhesion, or the like.

[0073] In the present embodiment, the pillar outer 41 in the lower overlapping portion 47 may simply be referred to as the overlapping portion 47.

[0074] The overlapping portion 47 is arranged so as to cover the outer surface of the side sill 5 from the outside in the width direction Y at the connection portion of the pillar outer 41 of the center pillar 4 with the side sill 5.

[0075] The overlapping portion 47 has an upper flange 471, an upper wall 472 extending outward in the width direction Y from the upper flange 471, and an outer side wall 473 extending downward from the upper wall 472.

[0076] The upper flange 471 is joined to the outer surface 151a of the upper flange 151 of the side sill outer 15 by welding, adhesion, or the like.

[0077] The upper wall 472 is preferably arranged in contact along the upper surface 152a of the upper wall 152 of the side sill outer 15, and may or may not be joined to the upper surface 152a by welding, adhesion or the like.

[0078] The outer wall 473 is preferably arranged in contact along the outer surface 153a of the outer wall 153 of the side sill outer 15, and may or may not be joined to the outer surface 153a by welding, adhesion or the like. In the present embodiment, the lower end 473b of the outer wall 473 is the lower end of the overlapping portion 47. Note that the lower end 473b of the overlapping portion 47 may be arranged along the upper wall 152 instead of along the outer wall 153 of the side sill outer 15.

[0079] As shown by the two-dot chain line in FIG. 3, it is preferable that the lower end 473b (the overlapping portion 47) of the outer wall 473 extends below the height position 153b which is half of the height in the vertical direction Z of the outer wall 153 of the side sill 5. The height position 153b is the central position of the length in the vertical direction Z at the location where it overlaps with the central portion of the outer wall 473 in the front-rear direction X of the outer wall 153. The length of the outer wall 153 in the vertical direction Z is the length between the upper end 153c and the lower end 153d in the vertical direction Z at the location where it overlaps with the central portion of the outer wall 473 in the front-rear direction X of the outer wall 153. The upper end 153c of the outer wall 153 is the starting point of the curved portion from the outer wall 153 to the upper wall 152 in the side sill outer 15. The lower end 153d of the outer wall 153 is the starting point of the curved portion from the outer wall 153 to the lower wall 154 in the side sill outer 15. When the lower end 473b of the outer wall 473 extends below the height position 153b, the lower end 473b may be arranged below the position advanced 1 / 6 of the length of the outer wall 153 in the vertical direction Z from the height position 153b (the position 1 / 3 from the bottom of the length of the outer wall 153 in the vertical direction Z), or may be arranged below the position advanced 1 / 4 of the length of the outer wall 153 in the vertical direction Z from the height position 153b (the position 1 / 4 from the bottom of the length of the outer wall 153 in the vertical direction Z), or may be arranged below the position advanced 1 / 3 of the length of the outer wall 153 in the vertical direction Z from the height position 153b (the position 1 / 6 from the bottom of the length of the outer wall 153 in the vertical direction Z).

[0080] By arranging the overlapping portion 47 in this manner, the joint area between the center pillar 4 and the side sill 5 can be increased, so that the stress acting between the side sill 5 and the center pillar 4 during a side collision can be reduced. Further, the load transmitted from the center pillar 4 to the side sill 5 during a side collision is mainly received by the vehicle body 1 as a torsional moment. Therefore, it is possible to suppress deformation of the closed cross-sectional shape of the side sill 5, particularly the side sill outer 15. Even when a side collision occurs, since the original closed cross-sectional shape of the side sill 5 before the collision is difficult to change, the side sill 5 has high torsional rigidity and can reduce the torsional angle of the side sill 5 during a side collision. As a result, the intrusion amount of the center pillar 4 and the side sill 5 into the cabin 10 can be reduced. On the other hand, when the arrangement is devised so that the center pillar 4 does not reach the lower end (lower flange 155) of the side sill 5, the center pillar 4 does not become unnecessarily heavy, and it is possible to highly balance the improvement of the reinforcement effect of the side sill 5 by the lower shape of the center pillar 4 and the suppression of the weight increase of the center pillar 4.

[0081] The lower end 473b of the overlapping portion 47 is preferably a linear end along the front-rear direction X. With this configuration, the vehicle body 1 can receive the load transmitted from the center pillar 4 to the side sill 5 as a torsional moment over the entire area where the overlapping portion 47 is arranged in the front-rear direction X. Therefore, it is possible to more reliably suppress crushing of the closed cross-sectional shape of the side sill 5, particularly the side sill outer 15.

[0082] The center pillar 4 is provided with a pair of upper and lower brackets 61, 62 for supporting the door 8 installed behind the center pillar 4.

[0083] Each of the brackets 61 and 62 may be a plate-like member formed by press-working a steel plate, or may be a block-like member formed by cutting a steel material or the like. Each of the brackets 61 and 62 constitutes a part of a hinge mechanism that connects the center pillar 4 and the door 8. Door shafts 63 and 64 are installed between each of the brackets 61 and 62 and the door 8. Further, a pair of upper and lower brackets 65 and 66 corresponding to the brackets 61 and 62 are installed on the door 8. The brackets 61 and 62 and the corresponding brackets 65 and 66 are connected via the corresponding door shafts 63 and 64. The door 8 is opened and closed by moving around the door shafts 63 and 64.

[0084] Each of the brackets 61 and 62 is fixed to the pillar outer 41 of the center pillar 4 by welding or a fixing member such as a bolt. Each of the brackets 61 and 62 is preferably fixed to the side wall 413 in particular within the pillar outer 41. With this configuration, with respect to the impact load input to the pillar outer 41 via each of the brackets 61 and 62, due to the high hardness, a high-strength part 53 formed of a material with high strength and high bending deformation ability is provided, so that the impact absorption effect of the center pillar 4 can be made higher. The lower bracket 62 is installed on the cut-off surface part 46 in the vicinity of the overlapping part 47 of the center pillar 4. The upper bracket 61 is installed above the lower bracket 62 and is separated from the lower bracket 62. The upper bracket 61 is installed, for example, in the vicinity of the lower end 8a of the window opening in the door 8.

[0085] (More detailed configuration of the pillar outer) The material of the pillar outer 41 is a tailor-welded blank (TWB) formed as a single member by joining two separately formed blanks. By press-working this material, the pillar outer 41 is formed.

[0086] As described above, the pillar outer 41 in the center pillar 4 includes a low-strength portion 51, a joint portion 52, and a high-strength portion 53. The lower portion of the pillar outer 41 is constituted by the low-strength portion 51, and the upper portion is constituted by the high-strength portion 53. In the present embodiment, during a side collision, in the pillar outer 41 that receives most of the impact load among the center pillars 4, since the material of the high-strength portion 53 disposed above the low-strength portion 51 has enhanced bendability, the possibility of breakage in the high-strength portion 53 can be more reliably suppressed. Therefore, the occupant protection effect by the center pillar 4 can be more reliably exhibited.

[0087] As described above, the pillar outer 41 includes a low-strength portion 51, a high-strength portion 53 that is arranged in the vertical direction Z with the low-strength portion 51 and has a Vickers hardness HV1 higher than the Vickers hardness HV2 of the low-strength portion 51, and a joint portion 52 that joins the low-strength portion 51 and the high-strength portion 53. In the present embodiment, the Vickers hardness HV2 of the low-strength portion 51 and the Vickers hardness HV1 of the high-strength portion 53 respectively refer to the Vickers hardness at the center in the plate thickness direction of the low-strength portion 51 and the Vickers hardness at the center in the plate thickness direction of the high-strength portion 53. The central portion in this embodiment refers to most of the steel plate portion when there is no plating layer, and when there is a plating layer, it refers to most of the steel plate base material immediately below the plating layer. When there is an alloy layer between the plating layer and the steel plate base material in addition to the plating layer, most of the steel plate base material immediately below the alloy layer is referred to as the central portion.

[0088] Here, a layer containing at least one of the plating layer and the alloy layer is referred to as a plating film. When the plating film exists, the thickness of the plating film is measured, and the position corresponding to the thickness of the plating film in the plate thickness direction from the surface of the steel sheet including the plating film is defined as the boundary position between the plating film and the steel sheet base material. In the present embodiment, the "plate thickness" refers to the thickness of the base material portion obtained by subtracting the plating film thickness on the steel sheet surface side and the plating film thickness on the steel sheet back side from the total plate thickness of the steel sheet including the plating film. Further, unless otherwise specified, the surface of the low-strength portion 51 and the surface of the high-strength portion 53 each refer to the surface of the steel sheet base material. Also, the plating film thickness is measured by a high-frequency glow discharge optical emission surface analyzer (GDS). The specific measurement method will be described below.

[0089] Determine three arbitrary measurement positions from the regions of the low-strength portion 51 or the high-strength portion 53 that have the plating film, respectively. At each measurement point, while sputtering from the surface of the plating film, measure the concentration of each element of Fe, Mn, Zn, Si, Al, O, Cr, Ni, Mg, Cu, and Sn.

[0090] Analyze the content of each element in the depth direction and obtain the depth until the Fe concentration first becomes 90 mass% or more. Then, obtain the average value of the depths at each measurement point, and use this average value as the plating film thickness of the low-strength portion 51 or the high-strength portion 53. If the Fe concentration does not reach 90 mass% or more up to the depth that can be analyzed by one GDS measurement, that is, if the plating film thickness is greater than the measurable depth, at an arbitrary position different from the measured positions within the same region, polish and remove the plating film corresponding to 80% - 90% of the previous measured depth. After grasping the depth of the plating film removed by polishing from the change in plate thickness before and after polishing, perform a new GDS analysis from the surface after polishing, and combine the measurement results of the first and subsequent measurements to measure the plating film thickness. Even when there is a structure other than the plating film on the surface of the steel sheet base material, the boundary position between the steel sheet base material and the other structure can be measured by the above measurement method.

[0091] As a GDS measuring device, for example, a Marcus type high-frequency glow discharge emission analyzer GD-Profiler2 (manufactured by HORIBA) is used. At this time, for example, the discharge conditions are 35 W, the Ar pressure during measurement is 600 Pa, the discharge range is 4 mmφ in diameter, the electrode distance is 0.15 mm to 0.25 mm, and the measurement pitch in the plate thickness direction is 0.01 μm to 0.05 μm for measurement.

[0092] (Maximum bending angles of the high-strength part and the low-strength part) The maximum bending angle θ1 of the high-strength part 53 is set according to the maximum bending angle θ2 of the low-strength part 51. The maximum bending angle can be obtained by the VDA bending test (VDA238-100:2017) standardized by the German Automobile Industry Association (VDA). Figures 4A and 4B are schematic diagrams for explaining the bending test. Figure 4A is a plan view of the test piece S before the test, and Figure 4B shows the test piece S, the punch P, and the roll R. As shown in Figures 4A and 4B, this VDA bending test is a test in which the test piece S placed on two rolls R, R is deformed into a V shape by pushing it between the rolls R, R with a punch P having a tip radius of 0.4 mm. The length of the test piece S is in the range of 60 mm from the value obtained by adding 10 mm to the distance between the centers of the rolls R, R. The width of the test piece S is in the range of 10 mm to 60 mm. The test piece S is taken from the high-strength part 53 so that the direction with a curvature radius of 500 mm or more is the length direction of the test piece S. The test piece S is deformed so as to be V-shaped when viewed along the width direction as shown in Figure 4B. The ridge line L generated by the bending of the test piece S at this time is a line along the width direction of the test piece S. The load of the punch P and the stroke of the punch P at this time are measured. Then, the maximum bending angle is calculated from the stroke when the load of the punch P that has increased since the start of the test decreases by 60 N from the maximum load due to the occurrence of breakage at the apex of the bending of the test piece S, thereby evaluating the fracture resistance characteristics of the test piece S. The formula for calculating the maximum bending angle from the stroke uses the formula described in Annex D of VDA238-100 mentioned above. When the test piece S does not break even at a stroke of 14 mm, the value obtained by the formula for calculating the maximum bending angle from the bending angle at a stroke of 14 mm is taken as the maximum bending angle of the test piece S.

[0093] In this embodiment, by cutting out a part of the high-strength portion 53, for example, near the upper bracket 61, as a test piece S and performing a VDA bending test, the maximum bending angle θ1 of the high-strength portion 53 can be calculated. Further, by cutting out a part of the low-strength portion 51, for example, near the lower bracket 62, as a test piece S and performing a VDA bending test, the maximum bending angle θ2 of the low-strength portion 51 can be calculated. The number of tests for the high-strength portion 53 in the VDA bending test is set to 3, and the average value of the measurement results of the three test pieces S is taken as the maximum bending angle θ1 of the high-strength portion 53. Similarly, the number of tests for the low-strength portion 51 in the VDA bending test is set to 3, and the average value of the measurement results of the three test pieces S is taken as the maximum bending angle θ2 of the low-strength portion 51.

[0094] The low-strength portion 51 forms, in the pillar outer 41, an overlapping portion 47 and a part of the cutoff surface portion 46 on the overlapping portion 47 side (lower side). The joint portion 52 is a portion formed by joining the material of the low-strength portion 51 and the material of the high-strength portion 53. The joint portion 52 exists as a portion where the material of the low-strength portion 51 and the material of the high-strength portion 53 are joined before press-forming the material of the low-strength portion 51 and the material of the high-strength portion 53 to form the pillar outer 41. When the low-strength portion 51 and the high-strength portion 53 are joined by laser welding, the low-strength portion 51 and the high-strength portion 53 face each other in the longitudinal direction of the pillar outer 41 in the vicinity of the joint portion 52. On the other hand, when the low-strength portion 51 and the high-strength portion 53 are joined by spot welding, the low-strength portion 51 and the high-strength portion 53 face each other in the plate thickness direction of the pillar outer 41 in the vicinity of the joint portion 52. The joint portion 52 is preferably arranged straight in the front-rear direction X. Thereby, the strength distribution of the pillar outer 41 in the front-rear direction X can be made more uniform around the joint portion 52. The joint portion 52 does not have to be straight in the front-rear direction X. The joint portion 52 only needs to join at least a part of the low-strength portion 51 and the high-strength portion 53 in the front-rear direction X. The low-strength portion 51 is arranged below the joint portion 52, and the high-strength portion 53 is arranged above the joint portion 52. The high-strength portion 53 forms, in the pillar outer 41, a part of the upper overlapping portion 45 side of the cutoff surface portion 46 and the upper overlapping portion 45.

[0095] In this embodiment, since the side sill 5 is reinforced by the reinforcing member 20, during a side collision, the amount of deformation of the side sill 5 is small, and the bending deformation of the center pillar 4 is mainly caused rather than the torsional deformation of the side sill 5. Since the amount of plastic deformation of the side sill 5 is small in this way, the center pillar 4 will be greatly plastically deformed to absorb the impact. At this time, the low-strength portion 51 is greatly plastically deformed inward in the width direction Y to absorb the impact. And since the high-strength portion 53 is high-strength to suppress the collision with the occupant, the amount of plastic deformation inward in the width direction Y tends to be smaller than the amount of plastic deformation of the low-strength portion 51. On the other hand, in the vicinity of the joint portion 52, the amount of plastic deformation of the high-strength portion 53 also increases following the plastic deformation of the low-strength portion 51 inward in the width direction Y.

[0096] Therefore, in the present embodiment, the maximum bending angle θ1 of the high-strength portion 53 is set according to the maximum bending angle θ2 of the low-strength portion 51. Thereby, for example, by increasing the maximum bending angle θ1 of the material of the high-strength portion 53, the difference between the maximum bending angle θ1 of the material of the high-strength portion 53 and the maximum bending angle θ2 of the material of the low-strength portion 51 is reduced. By setting the bending angle in this way, even in the material of the high-strength portion 53 with high Vickers hardness and high strength, high bending performance can be exhibited. Therefore, even when the high-strength portion 53 is plastically deformed relatively largely due to the plastic deformation of the low-strength portion 51 of the pillar outer 41 during a side collision, the deformability of the high-strength portion 53 can be increased, and the possibility of breakage of the pillar outer 41 (high-strength portion 53) near the joint portion 52 can be suppressed. In addition, the upper portion of the center pillar 4 is required to have high strength from the viewpoint of occupant protection. Here, when a material with low Vickers hardness (low strength) is used in the member above the joint portion 52 to ensure high bendability, it is necessary to increase the plate thickness in order to reduce the amount of deformation toward the occupant side, which leads to an increase in mass. On the other hand, in the present embodiment, since the Vickers hardness of the high-strength portion 53 is increased, the high-strength portion 53 has high strength, and while improving the impact absorption performance at the time of a collision such as a side collision, the high-strength portion 53 can be made thinner to achieve weight reduction of the pillar outer 41. In this way, by applying a material that achieves both Vickers hardness (strength) and bendability as the high-strength portion 53 to the upper portion of the center pillar 4, a center pillar 4 having high impact absorption performance that is lightweight and suppresses the possibility of breakage can be realized.

[0097] The difference Δθ between the maximum bending angle θ1 of the high-strength portion 53 and the maximum bending angle θ2 of the low-strength portion 51 is preferably 100 degrees or less. By setting the difference Δθ of the bending angle to 100 degrees or less, during a side collision of the vehicle, the bending deformation of the high-strength portion 53 following the bending deformation of the low-strength portion 51 can be more surely achieved. Therefore, a center pillar 4 having high impact absorption performance through suppression of the possibility of breakage can be realized.

[0098] (Thickness of the low-strength portion and the high-strength portion) The thicknesses of the low-strength portion 51 and the high-strength portion 53 may be the same or different. Examples of the thicknesses of the low-strength portion 51 and the high-strength portion 53 include 0.8 mm to 2.6 mm. By setting the thickness to 0.8 mm or more, the strength of the pillar outer 41 can be made sufficiently high, and the amount of deformation of the center pillar 4 inward in the width direction Y during a side collision can be made smaller. By setting the thickness to 2.6 mm or less, it is possible to prevent the center pillar 4 from becoming too heavy.

[0099] Examples of the lower limits of the respective thicknesses of the low-strength portion 51 and the high-strength portion 53 include 0.8 mm, 1.0 mm, and 1.2 mm, and examples of the upper limits include 1.6 mm, 1.8 mm, 2.0 mm, 2.2 mm, 2.3 mm, and 2.5 mm. As is clear from the above, the respective thicknesses of the low-strength portion 51 and the high-strength portion 53 are preferably 1.0 mm to 2.5 mm, also 1.2 mm to 2.3 mm, also 1.2 mm to 2.2 mm, also 1.2 mm to 2.0 mm, also 1.2 mm to 1.8 mm, and also 1.2 mm to 1.6 mm.

[0100] (Vickers hardness of the low-strength portion) The Vickers hardness HV2 at the center in the thickness direction of the low-strength portion 51 may be 150 HV or more, 300 HV or more, 400 HV or more, or 500 HV or more in order to exhibit high impact absorption performance. The upper limit of the Vickers hardness HV2 of the low-strength portion 51 is not particularly limited, but examples include 500 HV, 400 HV, and 300 HV from the viewpoint of more surely suppressing the possibility of breakage during a side collision. Thus, as an example of the Vickers hardness HV2 of the low-strength portion 51, 150 HV to 500 HV can be exemplified.

[0101] (Vickers hardness of the high-strength portion) The Vickers hardness HV1 at the center in the thickness direction of the high-strength portion 53 is preferably 300 HV or more, may be 400 HV or more, may be 500 HV or more, may be 600 HV or more, may be 750 HV or more, may be 800 HV or more, may be 900 HV or more, may be 950 HV or more, may be 1000 HV or more, may be 1050 HV or more, may be 1100 HV or more, from the viewpoint of making the displacement amount of the high-strength portion 53 toward the cabin 10 side (inside in the width direction Y) smaller during a side collision. The upper limit of the Vickers hardness HV1 of the high-strength portion 53 is not particularly limited, but 1100 HV, 1050 HV, 1000 HV, 950 HV, 900 HV, 800 HV, 750 HV, 650 HV, 600 HV, 550 HV, 500 HV can be exemplified from the viewpoint of more surely suppressing the possibility of breakage during a side collision. Thus, as a preferable example of the Vickers hardness HV1 of the high-strength portion 53, 300 HV to 1100 HV can be exemplified, and as a more preferable example, 500 HV to 1100 HV can be exemplified.

[0102] (Method for measuring Vickers hardness of low-strength portion and high-strength portion) In the present embodiment, the method for measuring the Vickers hardness at the center in the thickness direction of the low-strength portion 51 or the high-strength portion 53 is as follows. A cross section perpendicular to the plate surface of a sample cut out from, for example, a part near the lower bracket 62 of the low-strength portion 51 or a part near the upper bracket 61 of the high-strength portion 53 is taken, the sample of the measurement surface is prepared, and it is subjected to a hardness test. The method for preparing the measurement surface is carried out in accordance with JIS Z 2244:2020. After polishing the measurement surface using silicon carbide paper from #600 to #1500, it is finished to a mirror surface using a liquid in which diamond powder with a particle size of 1 μm to 6 μm is dispersed in a diluent such as alcohol or pure water. The hardness test is carried out in accordance with JIS Z 2244:2020. Using a micro-Vickers hardness tester, at the 1 / 2 position of the sample thickness, with a test force of 1 kgf, 10 points are measured so that the distance between the centers of the indentations is 3 times or more the average diagonal length of the indentations, and the average value is taken as the Vickers hardness of the low-strength portion 51 or the high-strength portion 53.

[0103] Furthermore, by setting the Vickers hardness HV2 of the low-strength portion 51 to 150 HV or more and the Vickers hardness HV1 of the high-strength portion 53 to 500 HV or more, it is possible to increase the impact energy absorption effect due to the plastic deformation of the low-strength portion 51 during a side collision, suppress excessive plastic deformation of the high-strength portion 53, enhance the impact absorption performance, and reduce the amount of intrusion of the upper portion of the center pillar 4 toward the cabin 10 side.

[0104] In particular, when the Vickers hardness HV1 of the high-strength portion 53 is 500 HV or more, the strength difference (strength ratio) between the high-strength portion 53 and the low-strength portion 51 is large, and the difference in bendability between the material of the high-strength portion 53 and the material of the low-strength portion 51 tends to be large. That is, when the Vickers hardness HV1 of the high-strength portion 53 is 500 HV or more, during a side collision, there is a tendency for the high-strength portion 53 to be prone to breakage due to the bending deformation of the high-strength portion 53 following the bending deformation of the low-strength portion 51. Thus, when the Vickers hardness HV1 of the high-strength portion 53 is 500 HV or more, the problem of breakage possibility in the high-strength portion 53 becomes prominent. Even in such a case, by setting the maximum bending angle θ1 of the high-strength portion 53 according to the maximum bending angle θ2 of the low-strength portion 51, the possibility of breakage of the high-strength portion 53 during a side collision can be suppressed.

[0105] (An example of the combination of the Vickers hardness of the low-strength portion and the Vickers hardness of the high-strength portion) As an example of the combination of the Vickers hardness HV2 of the low-strength portion 51 and the Vickers hardness HV1 of the high-strength portion 53, the Vickers hardness HV1 of the high-strength portion 53 can be exemplified as 480 HV to 750 HV, and the Vickers hardness HV2 of the low-strength portion 51 can be exemplified as 150 HV to 480 HV (less than the Vickers hardness HV1 of the high-strength portion 53). As more specific preferable combinations, the following three combinations can be exemplified. Example 1) Vickers hardness HV1 of the high-strength portion 53 and Vickers hardness HV2 of the low-strength portion 51: 600 HV and 350 HV Example 2) Vickers hardness HV1 of the high-strength portion 53 and Vickers hardness HV2 of the low-strength portion 51: 600 HV and 420 HV Example 3) Vickers hardness HV1 of the high-strength part 53 and Vickers hardness HV2 of the low-strength part 51: 720 HV and 480 HV

[0106] In all of the above three examples, the ratio HV1 / HV2 of the Vickers hardness HV1 of the high-strength part 53 to the Vickers hardness HV2 of the low-strength part 51 is 1.3 or more. Thus, when HV1 / HV2 is 1.3 or more, the strength difference (strength ratio) between the high-strength part 53 and the low-strength part 51 is large, and the difference in the bendability between the material of the high-strength part 53 and the material of the low-strength part 51 tends to be large. That is, when HV1 / HV2 is 1.3 or more, during a side collision, the high-strength part 53 with a high Vickers hardness is likely to break due to the bending deformation of the high-strength part 53 following the bending deformation of the low-strength part 51. Thus, when HV1 / HV2 is 1.3 or more, the problem of the requirement for suppressing breakage possibility in the high-strength part 53 becomes prominent. Even in such a case, by setting the maximum bending angle θ1 of the high-strength part 53 according to the maximum bending angle θ2 of the low-strength part 51, the breakage possibility of the high-strength part 53 during a side collision can be suppressed. HV1 / HV2 is preferably 1.4 or more, and 1.5 or more.

[0107] The higher the Vickers hardness HV1 of the high-strength part 53, the smaller the plate thickness required for the required impact absorption performance can be made. On the other hand, cracks are likely to occur during press working of the low-strength part 51 and the high-strength part 53, and during a side collision. Therefore, by appropriately setting the Vickers hardness and the plate thickness, and further improving the maximum bending angle θ1 of the high-strength part 53, the center pillar 4 that is lightweight and has excellent impact absorption performance can be realized.

[0108] (Combination of the maximum bending angle of the low-strength part and the maximum bending angle of the high-strength part) As the maximum bending angle θ2 of the low-strength portion 51, angles from 135 degrees to 50 degrees can be exemplified, and within this range, 135 degrees, 70 degrees, 60 degrees, and 50 degrees can be exemplified. Also, as the maximum bending angle θ1 of the high-strength portion 53, angles from 60 degrees to 40 degrees can be exemplified, and within this range, 60 degrees, 50 degrees, and 40 degrees can be exemplified. Therefore, the difference Δθ between the maximum bending angle θ1 of the high-strength portion 53 and the maximum bending angle θ2 of the low-strength portion 51 may be 95 degrees or less, or 85 degrees or less, or 75 degrees or less, or 30 degrees or less, or 20 degrees or less, or 10 degrees or less, or 0 degrees. The minimum value of the difference Δθ is 0 degrees.

[0109] The ratio θ1 / θ2 of the maximum bending angle θ1 of the high-strength portion 53 to the maximum bending angle θ2 of the low-strength portion 51 may be 40 / 135 = approximately 0.30 or more, or 50 / 135 = approximately 0.37 or more, or 60 / 135 = approximately 0.44 or more, or 40 / 70 = approximately 0.57 or more, or 40 / 60 = approximately 0.67 or more, or 50 / 70 = approximately 0.71 or more, or 50 / 60 = approximately 0.83 or more, or 60 / 70 = approximately 0.86 or more. The upper limit of the ratio θ1 / θ2 is, for example, 1.00. Note that the upper limit of the ratio θ1 / θ2 may also be 0.95 or 0.90. As is clear from the above, the ratio θ1 / θ2 may be 0.30 to 1.00, or 0.37 to 0.95, or 0.44 to 0.90, or 0.57 to 0.90, or 0.67 to 0.90, or 0.71 to 0.90, or 0.86 to 0.90.

[0110] (Combination of Vickers hardness and maximum bending angle) Regarding Examples 1) to 3) of the preferable combinations of the above-described high-strength portion 53 and low-strength portion 51, the difference Δθ between the maximum bending angle θ2 of the low-strength portion 51 and the maximum bending angle θ1 of the high-strength portion 53 will be described below. Example 1) Vickers hardness HV1 of the high-strength part 53 and Vickers hardness HV2 of the low-strength part 51: When HV1 is 600 HV and HV2 is 350 HV, the difference Δθ between the maximum bending angle θ2 of the low-strength part 51 and the maximum bending angle θ1 of the high-strength part 53 is 30 degrees. Example 2) Vickers hardness HV1 of the high-strength part 53 and Vickers hardness HV2 of the low-strength part 51: When HV1 is 600 HV and HV2 is 420 HV, the difference Δθ between the maximum bending angle θ2 of the low-strength part 51 and the maximum bending angle θ1 of the high-strength part 53 is 20 degrees. Example 3) Vickers hardness HV1 of the high-strength part 53 and Vickers hardness HV2 of the low-strength part 51: When HV1 is 720 HV and HV2 is 480 HV, the difference Δθ between the maximum bending angle θ2 of the low-strength part 51 and the maximum bending angle θ1 of the high-strength part 53 is less than 15 degrees.

[0111] As is clear from the above description, it is preferable that the difference Δθ between the maximum bending angle θ2 of the low-strength part 51 and the maximum bending angle θ1 of the high-strength part 53 is 30 degrees or less. With this configuration, during a side collision, the high-strength part 53 can sufficiently follow the bending deformation of the low-strength part 51 and undergo bending deformation. As a result, the possibility of breakage of the high-strength part 53 during a side collision can be suppressed.

[0112] Note that the difference Δθ between the maximum bending angle θ1 of the high-strength part 53 and the maximum bending angle θ2 of the low-strength part 51 is preferably set according to the Vickers hardness HV1 of the high-strength part 53 and the Vickers hardness HV2 of the low-strength part 51. In this case, the greater the difference between the Vickers hardness HV1 of the high-strength part 53 and the Vickers hardness HV2 of the low-strength part 51, the greater the tendency for the difference Δθ in bending angle to be large. On the other hand, within the range of the above difference Δθ, the maximum bending angle θ1 of the high-strength part 53 and the maximum bending angle θ2 of the low-strength part 51 are set.

[0113] For example, when the Vickers hardness HV2 of the low-strength part 51 is 200 HV and the Vickers hardness HV1 of the high-strength part 53 is 600 HV, the difference Δθ in bending angle may be 90 degrees or less. Also, when the Vickers hardness HV2 of the low-strength part 51 is 200 HV and the Vickers hardness HV1 of the high-strength part 53 is 480 HV, the difference Δθ in bending angle may be 85 degrees or less.

[0114] When the Vickers hardness HV2 of the low-strength part 51 is 350 HV and the Vickers hardness HV1 of the high-strength part 53 is 600 HV, the difference Δθ in bending angle may be 30 degrees or less. Also, when the Vickers hardness HV2 of the low-strength part 51 is 350 HV and the Vickers hardness HV1 of the high-strength part 53 is 480 HV, the difference Δθ in bending angle may be 20 degrees or less.

[0115] When the Vickers hardness HV2 of the low-strength part 51 is 420 HV and the Vickers hardness HV1 of the high-strength part 53 is 600 HV, the difference Δθ in bending angle may be 20 degrees or less. Also, when the Vickers hardness HV2 of the low-strength part 51 is 420 HV and the Vickers hardness HV1 of the high-strength part 53 is 480 HV, the difference Δθ in bending angle may be 10 degrees or less.

[0116] When the Vickers hardness of the low-strength part 51 is 350 HV to 470 HV and the Vickers hardness of the high-strength part 53 is 430 HV to 530 HV, the difference Δθ in bending angle may be 25 degrees or less, 20 degrees or less, 15 degrees or less, or 10 degrees or less. By being such a relationship between the respective Vickers hardnesses of the low-strength part 51 and the high-strength part 53 and the difference Δθ in bending angle, the high-strength part 53 can sufficiently follow the bending deformation of the low-strength part 51 and undergo bending deformation during a side collision. As a result, the possibility of breakage of the high-strength part 53 during a side collision can be suppressed. The lower limit of the difference Δθ in bending angle in this case is 0 degrees.

[0117] (Height position of the joint part) In a side collision, the impact load acts on the pillar outer 41 from the door 8 via the brackets 61, 62, 65, and 66. Therefore, at the pillar outer 41, the joint portions with the brackets 61 and 62 become the input points of the impact load during a side collision. More specifically, when another vehicle collides with the vehicle from the side as a collision vehicle, at the initial stage of the collision, due to the shape of the collision vehicle (the shape where the lower front part of the collision vehicle protrudes forward with respect to the upper front part of the vehicle), the input from the collision vehicle to the lower side of the vehicle tends to increase. For this reason, at the initial stage of the collision, in addition to the side sill 5, it is necessary to absorb the impact in the portion of the center pillar 4 near the side sill 5, and it is desirable that the lower part of the center pillar 4 can be plastically deformed significantly. Therefore, the input from the lower bracket 62, which receives more of the impact at the initial stage of the collision among the brackets 61 and 62 for the door 8, is preferably received at the low-strength portion 51 as in this embodiment. On the other hand, at the later stage of the collision, since the upper part of the collision vehicle also collides with the vehicle, an impact is also input to the upper bracket 61 among the brackets 61 and 62. From the perspective of occupant protection, it is desired to suppress plastic deformation as much as possible in the center pillar 4 near the upper bracket 61. Therefore, the impact load from the upper bracket 61 is preferably received at the high-strength portion 53 as in this embodiment.

[0118] In this embodiment, the joint portion 52 is arranged at a position lower than the height position of the lower end 61b of the upper bracket 61. Thereby, the impact load input from the upper bracket 61 (the impact load input point) located at a position far from the side sill 5 to the center pillar 4 can be received at the high-strength portion 53. Therefore, the amount of deformation of the center pillar 4 toward the occupant side due to a side collision can be made smaller.

[0119] Preferably, as in the present embodiment, the joint portion 52 is disposed at a height position between the lower end 61b of the upper bracket 61 and the upper end 62a of the lower bracket 62 in the vertical direction Z of the vehicle body 1. Thereby, a sufficient range of the low-strength portion 51 can be secured. Therefore, it is possible to achieve both shock absorption by the low-strength portion 51 cooperating with the side sill 5 at the initial stage of a side collision and suppression of deformation of the center pillar 4 toward the cabin 10 side by the high-strength portion 53 receiving the impact load from the upper bracket 61 at the later stage of the side collision.

[0120] The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. The present invention can be variously modified within the scope described in the claims. In the following, configurations different from the above-described embodiments and modified examples will be mainly described, and the same reference numerals will be given to the same configurations and detailed descriptions thereof will be omitted.

[0121] <Modification Example 1> In the above-described embodiment, a configuration in which substantially no difference is provided in the strength distribution in the thickness direction in the steel plate base material has been described as an example. However, this does not have to be the case. FIG. 5 is a longitudinal sectional view along the thickness direction and the vertical direction Z of the pillar outer 41 in the vicinity of the joint portion 52 in Modification Example 1, and illustration of the back side of the cross section is omitted. As shown in FIG. 5, a high-strength portion softening layer 55 may exist in at least one of the vicinity of the outer surface 53a and the vicinity of the inner surface 53b of the high-strength portion 53. In Modification Example 1, high-strength portion softening layers 55 exist in both the vicinity of the outer surface 53a and the vicinity of the inner surface 53b, and a central portion 56 exists between the high-strength portion softening layers 55.

[0122] (Range of existence of high-strength portion softening layer) It is preferable that each high-strength part softening layer 55 is directly connected to the entire area of the joint part 52 in that it can enhance the effect of suppressing the possibility of fracture during a side collision near the joint part 52. Each high-strength part softening layer 55 preferably exists near the joint part 52 even if it is not directly connected to the joint part 52. In either case, whether each high-strength part softening layer 55 is directly connected to the joint part 52 or not, it is preferable that each high-strength part softening layer 55 exists up to a position higher than the upper end 61a of the upper bracket 61 starting from near the joint part 52. Thereby, during a side collision, the bending deformation ability of the high-strength part 53 accompanying the bending deformation of the low-strength part 51 can be enhanced, and the possibility of fracture of the high-strength part 53 can be suppressed. In particular, in each high-strength part softening layer 55, if it is connected to the joint part 52 across the entire longitudinal direction (front-rear direction X) of the joint part 52, the effect of suppressing the possibility of fracture of the high-strength part 53 can be made higher. If each high-strength part softening layer is formed across the entire area of the high-strength part 53 in the vertical direction Z, the effect of suppressing the possibility of fracture of the high-strength part 53 can be made higher.

[0123] (Overview of the thickness range of the high-strength part softening layer) Each high-strength part softening layer 55 is formed, for example, by reducing the carbon content in the blank which is the material of the high-strength part 53 in the vicinity of the portion that becomes the outer surface 53a and the portion that becomes the inner surface 53b (the portion that becomes the high-strength part softening layer 55) compared to the portion that becomes the central part 56 of the blank. The method of forming the high-strength part softening layer 55 is not particularly limited, and any method may be used. In this modification example, it is preferable that each high-strength part softening layer 55 is provided with a predetermined thickness from the corresponding surfaces and in that it can increase the maximum bending angle θ1 of the high-strength part 53 while sufficiently ensuring the strength of the high-strength part 53. The lower limit of the predetermined thickness is, for example, 80 μm, and the upper limit is, for example, 200 μm.

[0124] (Overview of the Vickers hardness distribution of the high-strength part softening layer and the overview of the Vickers hardness of the central part) In each high-strength part softening layer 55, the Vickers hardness is decreased as the distance from the 1 / 2 thickness position of the high-strength part 53 increases. Among each high-strength part softening layer 55, the portions that become the surfaces 53a and 53b have the lowest Vickers hardness in the high-strength part 53, and are, for example, at least 100 HV lower than the Vickers hardness of the central part 56. As the upper limit of the difference in Vickers hardness between the surfaces 53a and 53b and the central part 56 of the high-strength part 53, 250 HV, 300 HV, 350 HV, 400 HV, 500 HV, 550 HV, 600 HV, and 650 HV can be exemplified. Note that when simply referring to "the Vickers hardness of the high-strength part 53", it means the Vickers hardness at the central part 56.

[0125] In the first modified example 1 in which each high-strength part softening layer 55 is provided in the high-strength part 53, compared with the case where the high-strength part softening layer 55 is not provided (embodiment), the maximum bending angle θ1 of the high-strength part 53 can be increased by, for example, about 20 degrees.

[0126] Thus, the Vickers hardness at the surfaces 53a and 53b in the thickness direction of the high-strength part 53 is at least 100 HV lower than the Vickers hardness at the central part 56 at the center in the thickness direction of the high-strength part 53. Thereby, the maximum bending angle θ1 of the high-strength part 53 can be made larger. Therefore, when a side collision occurs, the high-strength part 53 can more reliably follow the bending deformation of the low-strength part 51, suppressing the occurrence of cracks in the high-strength part 53 and improving the impact absorption performance.

[0127] An example of the configuration of the high-strength part 53 will be described more specifically.

[0128] (Vickers hardness of the central part of the high-strength part) It is preferable that the Vickers hardness of the central portion 56 in the thickness direction of the portion provided with the high-strength portion softening layer 55 is 500 HV or more. When the Vickers hardness of the central portion 56 is 500 HV or more, the effect of improving the deformability due to the high-strength portion softening layer 55 in the high-strength portion 53 becomes remarkable. It is preferable that the Vickers hardness of the central portion 56 is 600 HV or more, and more preferably 700 HV or more. The upper limit of the Vickers hardness of the central portion 56 is not particularly limited, but in view of formability and the like, it is preferably 900 HV or less, and more preferably 800 HV or less. Thus, as an example of the preferable lower limit of the Vickers hardness of the central portion 56, 500 HV, 550 HV, 600 HV, 700 HV, 720 HV, 750 HV can be cited. Further, as an example of the preferable upper limit of the Vickers hardness of the central portion 56, 1100 HV, 1050 HV, 1000 HV, 950 HV, 900 HV, 850 HV, 800 HV can be cited. As is clear from the above, the Vickers hardness of the central portion 56 may be 500 HV to 1100 HV, or 550 HV to 1050 HV, or 600 HV to 1000 HV, or 700 HV to 950 HV, or 720 HV to 900 HV, or 750 HV to 850 HV, or 750 HV to 800 HV. Further, the Vickers hardness of the central portion 56 may be 550 HV to 1000 HV, or 550 HV to 950 HV, or 550 HV to 900 HV, or 550 HV to 850 HV, or 550 HV to 800 HV.

[0129] (Combination of Vickers hardness of central portion and maximum bending angle difference) As the Vickers hardness of the low-strength portion 51 (the central portion of the low-strength portion 51) in Modification 1, 350 HV to 530 HV can be cited. When the Vickers hardness of the low-strength portion 51 is 350 HV to 530 HV and the Vickers hardness of the central portion 56 of the high-strength portion 53 is 550 HV to 1050 HV, the difference Δθ in bending angle may be 30 degrees or less, 25 degrees or less, 20 degrees or less, 15 degrees or less, 10 degrees or less, or 5 degrees or less. The lower limit of the difference Δθ in bending angle is preferably 0 degrees. By virtue of the relationship between the Vickers hardness at the central portions of such low-strength portion 51 and high-strength portion 53 and the difference Δθ in bending angle, the high-strength portion 53 can sufficiently follow the bending deformation of the low-strength portion 51 and undergo bending deformation during a side collision. As a result, the possibility of fracture of the high-strength portion 53 during a side collision can be suppressed. Incidentally, the Vickers hardness of the central portion 56 of the high-strength portion 53 described above may be in the range of 350 HV to 770 HV.

[0130] (Details of the thickness of each high-strength portion softening layer) The thickness of each high-strength portion softening layer 55 in the plate thickness direction is preferably 80 μm or more and 5% or more and 20% or less of the plate thickness at the portion where each high-strength portion softening layer 55 is provided. If the thickness of each high-strength portion softening layer 55 is 20% or less of the above plate thickness, the proportion of each high-strength portion softening layer 55 in the steel plate which is the material of the high-strength portion 53 is small, so that the load resistance required for the high-strength portion 53 can be maintained. The thickness of each high-strength portion softening layer 55 is preferably 17% or less of the above plate thickness, and more preferably 14% or less. On the other hand, when the high-strength portion softening layer 55 is provided over the entire surface of the steel plate which is the material of the high-strength portion 53, if the thickness of each high-strength portion softening layer 55 is 80 μm or more and 5% or more of the above plate thickness, the deformability by the high-strength portion softening layer 55 can be sufficiently exhibited. The thickness of each high-strength portion softening layer 55 is more preferably 8% or more of the above plate thickness. As is clear from the above, the thickness of each high-strength portion softening layer 55 may be 5% to 17% of the above plate thickness, 5% to 14%, 8% to 20%, 8% to 17%, or 8% to 14%.

[0131] (Method for Measuring Thickness Position of Boundary between High-Strength Part Softening Layer and Central Part) Next, a method for measuring the boundary between the high-strength part softening layer 55 and the central part 56 will be described. FIG. 6 is an image diagram for explaining an example of the method for measuring the boundary between the high-strength part softening layer 55 and the central part 56. A cross-section perpendicular to the plate surface of the sample taken from the high-strength part 53 is taken, and after the sample preparation of the measurement surface is performed, it is subjected to a hardness test. The preparation of the measurement surface is carried out so that the Vickers hardness near the surface of the sample is accurately measured, with as little unevenness as possible and no burrs generated near the surface. Here, a cross-section polisher manufactured by JEOL is used, and the measurement surface is sputtered by an argon ion beam. At this time, in order to suppress the generation of streak-like unevenness on the measurement surface, a sample rotation holder manufactured by JEOL is used to irradiate the measurement surface with an argon ion beam from 360-degree directions.

[0132] For the sample with the measurement surface prepared, the Vickers hardness is measured using a micro-Vickers hardness tester. The region corresponding to the softening layer of the sample is measured from the surface of the sample in a direction perpendicular to the surface (plate thickness direction) with a test force of 50 gf.

[0133] The measurement position on the outermost surface of the sample shall be at a thickness position of 20 μm from either of the two surfaces of surfaces 53a and 53b (when there is a plating layer, it refers to the surface of the steel plate base material directly under the plating layer; when there is an alloy layer between the plating layer and the steel plate base material in addition to the plating layer, it refers to the surface of the steel plate base material directly under the alloy layer). When measuring the boundary between the high-strength part softening layer 55 and the central part 56, the measurement points shall be at equal intervals of 5 μm or more and 15 μm or less in the plate thickness direction, and the distance between the centers of the depressions shall be 3 times or more the average diagonal length of the depressions. Depending on the average diagonal length of the depressions, there may be cases where it is not possible to secure a center distance of the depressions of 3 times or more the average diagonal length in a row along the plate thickness direction. In such cases, measurements shall be taken while varying the positions in the direction orthogonal to the plate thickness direction and also varying the positions in the plate thickness direction. Thereby, it is possible to satisfy the measurement conditions of having equal intervals of 5 μm or more and 15 μm or less in the plate thickness direction and having the distance between the centers of the depressions be 3 times or more the average diagonal length of the depressions. Measurements shall be taken from a thickness position of 20 μm from the surface to a position of 1 / 2 of the plate thickness in the plate thickness direction.

[0134] (Method for calculating the slope of the Vickers hardness at each thickness position after measurement of the boundary between the high-strength part softening layer and the central part) When measuring the boundary between the high-strength part softening layer 55 and the central part 56, the slope of the Vickers hardness at each thickness position after Vickers hardness measurement shall be, for example, the slope Δbi obtained from the Vickers hardness at a plurality of consecutive points (3 points). The slope Δbi is calculated from the following formula (1).

Equation

[0135] Of the three measurement points where the slope Δbi obtained by the formula (1) first becomes 0.5 (HV / μm) or less in order from the surface side of the high-strength portion 53, the thickness position of the measurement point closest to the steel plate surface is defined as the thickness position of the boundary between the high-strength portion softened layer 55 and the central portion 56.

[0136] (Relationship between Vickers hardness of high-strength portion softened layer and Vickers hardness of central portion) The Vickers hardness of the high-strength portion softened layer 55 on the surfaces 53a, 53b of the high-strength portion 53 is preferably 0.5 times or more and less than 0.9 times the Vickers hardness of the central portion 56 in the portion where the high-strength portion softened layer 55 is provided.

[0137] (Method for measuring Vickers hardness of central portion of high-strength portion) The method for measuring the Vickers hardness of the central portion 56 is as follows. A cross-section perpendicular to the plate surface of the sample cut out from the high-strength portion 53 is taken, the sample preparation of the measurement surface is carried out, and it is subjected to a hardness test. The method for preparing the measurement surface is carried out in accordance with JIS Z 2244:2020. After polishing the measurement surface using silicon carbide paper from #600 to #1500, it is finished to a mirror surface using a liquid in which diamond powder with a particle size of 1 μm to 6 μm is dispersed in a diluent such as alcohol or pure water. The hardness test is carried out in accordance with JIS Z 2244:2020. Using a micro-Vickers hardness tester, at the 1 / 2 position of the plate thickness of the sample, with a test force of 1 kgf, dents are measured at 10 points at a distance between centers that is 3 times or more the average diagonal length of the dents, and the average value is taken as the Vickers hardness of the central portion 56.

[0138] (Method for measuring Vickers hardness of surface of high-strength portion) The Vickers hardness of the surface of the high-strength portion 53 is measured in accordance with the Vickers hardness test described in JIS Z 2244:2020 for the cross-section obtained by cutting along the plate thickness direction of the high-strength portion 53.

[0139] Regarding the above cross-section, after sample preparation of the measurement surface, it is subjected to a hardness test. The preparation of the measurement surface is carried out so that the unevenness is as small as possible and no burrs are generated near the surface in order to accurately measure the Vickers hardness near the surface of the sample. Here, using a cross-section polisher made by JEOL, the measurement surface is sputtered with an argon ion beam. At this time, in order to suppress the occurrence of streak-like unevenness on the measurement surface, an argon ion beam is irradiated onto the measurement surface from 360-degree directions using a sample rotation holder made by JEOL.

[0140] For the sample with the measurement surface prepared, the Vickers hardness is measured using a micro-Vickers hardness tester. At this time, the measurement point is set to a thickness position of 20 μm from the surface of the high-strength part 53. When there is a plating layer on the high-strength part 53, the thickness position is 20 μm from the surface of the steel plate base material directly under the plating layer. When there is an alloy layer between the plating layer and the steel plate base material in addition to the plating layer on the high-strength part 53, the measurement point is set to a thickness position of 20 μm from the surface of the steel plate base material directly under the alloy layer. At the position at the above-mentioned thickness from the surface of the sample, 10 indentations are measured in the direction perpendicular to the plate surface (plate thickness direction) with a test force of 10 gf at a distance between the centers that is 3 times or more the average diagonal length of the indentation, and the average value is taken as the Vickers hardness of the surface of the high-strength part 53.

[0141] If the Vickers hardness of the surface of the high-strength part 53 is 0.5 times or more that of the Vickers hardness of the central part 56, the load resistance during impact, particularly in the latter stage of the stroke during impact, can be improved. It is more preferable that the high-strength part softening layer 55 has a Vickers hardness of 0.6 times or more that of the Vickers hardness of the central part 56 on the surface of the high-strength part 53. On the other hand, if the Vickers hardness of the surface of the high-strength part 53 is less than 0.9 times that of the Vickers hardness of the central part 56, the deformability can be sufficiently improved. It is more preferable that the high-strength part softening layer 55 has a Vickers hardness of less than 0.8 times that of the Vickers hardness of the central part 56 on the surface of the high-strength part 53.

[0142] (Change in Vickers hardness in the high-strength part softening layer) FIG. 7 is an image diagram for explaining an example of the change in Vickers hardness in the high-strength part softening layer 55. As shown in FIG. 7, the high-strength part softening layer 55 preferably has, in the plate thickness direction, a first hardness change region that is a region from the surfaces 53a and 53b to 40% of the thickness of the high-strength part softening layer 55, and a second hardness change region that is a region of the high-strength part softening layer that is not the first hardness change region. The absolute value ΔHV1 of the hardness change in the plate thickness direction in the first hardness change region is preferably greater than the absolute value ΔHV2 of the hardness change in the plate thickness direction in the second hardness change region. If ΔHV1 is greater than ΔHV2, sufficient load characteristics can be obtained.

[0143] The absolute value ΔHV1 of the hardness change in the first hardness change region is preferably 100 HV or more and less than 200 HV. If ΔHV1 is 100 HV or more, stress concentration during bending deformation can be more effectively alleviated, and the bending characteristics can be further improved. Also, if ΔHV1 is less than 200 HV, the effect of alleviating stress concentration during bending deformation is further enhanced, and better bending characteristics can be obtained. Therefore, when ΔHV1 is 100 HV or more and less than 200 HV, good bending characteristics can be obtained, and the deformability of the high-strength part 53 can be improved. Specifically, in the latter stage of the stroke during a collision, the drop in load immediately after the load peak can be made gentle. Therefore, as described above, the absolute value ΔHV1 of the hardness change in the first hardness change region is preferably 100 HV or more and less than 200 HV. Note that the lower limit of ΔHV1 is preferably 100 HV, while the upper limit may be less than 200 HV, less than 300 HV, or less than 400 HV.

[0144] (Method for Measuring Vickers Hardness of the First and Second Hardness Change Regions of the High-Strength Part Softening Layer) Next, a method for measuring the hardness of the first hardness change region and the second hardness change region will be described. After a cross-section perpendicular to the plate surface of the sample taken from the high-strength portion 53 is taken and the sample preparation of the measurement surface is performed, it is subjected to a hardness test. The preparation of the measurement surface is carried out so that the unevenness is as small as possible and no burrs are generated in the vicinity of the surface in order to accurately measure the Vickers hardness in the vicinity of the surface of the sample. Here, a cross-section polisher manufactured by JEOL is used, and the measurement surface is sputtered by an argon ion beam. At this time, in order to suppress the occurrence of streak-like unevenness on the measurement surface, a sample rotation holder manufactured by JEOL is used to irradiate the measurement surface with an argon ion beam from 360-degree directions.

[0145] For the sample with the measurement surface prepared, the Vickers hardness is measured using a micro-Vickers hardness tester. The region corresponding to the softened layer of the sample is measured from the surface of the sample in the direction perpendicular to the plate surface (plate thickness direction) with a test force of 10 gf. At this time, although the total number of measurement points varies depending on the plate thickness of the sample, the number of measurement points for calculating ΔHV1 and ΔHV2 described later is set according to the description in JIS Z 2244:2020.

[0146] The thickness of the high-strength portion softened layer 55 is 80 μm or more and 5% or more and 20% or less of the plate thickness in the portion where the high-strength portion softened layer 55 is provided. The first hardness change region is the region from the surface of the high-strength portion softened layer 55 to 40% of the thickness. In this embodiment, starting from the surface of the high-strength portion 53, it exists at a thickness position of at least, for example, 40 μm and at most, for example, 80 μm.

[0147] The measurement position on the outermost surface side of the sample shall be at a thickness position of 20 μm from the surface (when there is a plating layer, it refers to the surface of the steel plate base material directly below the plating layer; when there is an alloy layer between the plating layer and the steel plate base material in addition to the plating layer, it refers to the surface of the steel plate base material directly below the alloy layer). The measurement point at this 20-μm thickness position shall be a point different from the measurement point at the time of measuring the Vickers hardness of the surface of the high-strength portion 53 described above. For the measurement of the first hardness change region, at equal intervals of 15 μm or less in the plate thickness direction and at a center-to-center distance of at least three times the average diagonal length of the indentation, the indentation is measured at at least two positions in the plate thickness direction. Depending on the average diagonal length of the indentation, there may be cases where only one point can be measured in a row along the plate thickness direction for the first hardness change region. In this case, the measurement is performed while varying the position in the direction perpendicular to the plate thickness direction and also varying the position in the plate thickness direction. Thereby, while satisfying the measurement conditions of equal intervals of 15 μm or less in the plate thickness direction and a center-to-center distance of the indentations of at least three times the average diagonal length of the indentation, the Vickers hardness is measured at at least two points for the first hardness change region.

[0148] The thickness of the softened layer 55 of the high-strength portion is 80 μm or more and 5% or more and 20% or less of the plate thickness at the portion where the softened layer 55 of the high-strength portion is provided. The Vickers hardness of the second hardness change region is measured in the range excluding the first hardness change region among this thickness range. When the thickness of the softened layer 55 of the high-strength portion is 80 μm to 200 μm, the second hardness change region exists in the range of the thickness position of at least 32 μm to 80 μm (a thickness range of 48 μm) and at most 80 μm to 200 μm (a thickness range of 120 μm) starting from the surface of the high-strength portion 53. The second hardness change region is measured at least at two positions in the plate thickness direction at intervals of 15 μm or less and at a distance between centers that is 3 times or more the average diagonal length of the indentation. Depending on the average diagonal length of the indentation, it may not be possible to measure two adjacent points at intervals determined in a row along the plate thickness direction for the second hardness change region. In this case, measurements are made while varying the positions in the direction orthogonal to the plate thickness direction and also varying the positions in the plate thickness direction. Thereby, while satisfying the measurement condition that the intervals are 15 μm or less in the plate thickness direction and the distance between the centers of the indentations is 3 times or more the average diagonal length of the indentation, the Vickers hardness of the second hardness change region is measured. The second hardness change region may be measured on the same row as the first hardness change region. The second hardness change region may be measured, for example, at a total of 4 points including 1 point near the boundary with the first hardness change region, 1 point near the boundary with the central portion 58, and 2 points between these 2 points. When the second hardness change region exists up to 200 μm from the steel plate surface, the measurement points of the first hardness change region and the second hardness change region can be measured at the respective thickness positions of, for example, 20 μm, 35 μm, 50 μm, 65 μm, 80 μm, 95 μm, 110 μm, 125 μm, 140 μm, 155 μm, 170 μm, 185 μm, 200 μm from the steel plate surface.

[0149] In the case of a sample in which the softened layer 55 of the high-strength portion is disposed on both sides of the central portion 56 of the high-strength portion 53, the same measurement is performed from the first surface side of the sample and further from the second surface side opposite to the first surface.

[0150] (Method for calculating the absolute value ΔHV1 of the hardness change after measurement of the first hardness change region) ΔHV1 is calculated by the following procedure. That is, from all the measurement points included in the region (first hardness change region) from the surface of the sample cut out from the high-strength portion 53 to 40% of the total thickness 40 of the high-strength portion softening layer 55, the hardness gradient Δa of the first hardness change region is calculated by Equation (2). Here, ai is the ratio (%) of the distance from the surface at the i-th measurement point to the total thickness of the softening layer, ci is the Vickers hardness (HV) at ai, and n is the total of all the measurement points included in the region (first hardness change region) from the surface to 40% of the total thickness of the softening layer.

[0151]

Number

[0152] Here, Δa: Gradient of the change in hardness in the plate thickness direction in the first hardness change region (HV / %) ai: Ratio (%) of the distance from the surface at the i-th measurement point to the total thickness of the softening layer ci: Average value (HV) of the Vickers hardness at three different points at the i-th measured thickness position n: Total of all the measurement points included in the first hardness change region on the first surface side That is.

[0153] In the case of a sample in which the high-strength portion softening layers 55 are arranged on both sides of the central portion 56, based on the Vickers hardness measurement results from the first surface side, Δa1 on the first surface side is obtained from Equation (2), and further, based on the Vickers hardness measurement results from the second surface side, Δa2 on the second surface side is obtained from Equation (2). The arithmetic mean of Δa1 and Δa2 can be taken as Δa.

[0154] ΔHV1 can be obtained by multiplying Δa obtained by Equation (2) by the ratio of the plate thickness direction thickness of the first hardness change region to the total thickness of the softening layer.

[0155] (Method for calculating the absolute value ΔHV2 of the hardness change after measurement of the second hardness change region) ΔHV2 is calculated by the following procedure. That is, from all the measurement points included in the region from 40% to 100% of the thickness of the entire high-strength part softening layer 55 on the surface side of the sample (the second hardness change region), the hardness gradient ΔA of the second hardness change region is calculated by Equation (3). Here, Ai is the ratio (%) of the distance from the surface at the i-th measurement point to the thickness of the entire softening layer, Ci is the Vickers hardness (HV) at Ai, and N is the total of all the measurement points included in the region from 40% to 100% of the thickness of the entire softening layer on the surface side (the second hardness change region).

[0156] [Number]

[0157] Here, ΔA: Gradient of the change in hardness in the plate thickness direction in the second hardness change region (HV / %) Ai: Ratio (%) of the distance from the surface at the i-th measurement point to the thickness of the entire softening layer Ci: Average value of the Vickers hardness (HV) at three different points at the i-th measured thickness position N: Total of all the measurement points included in the first surface side second hardness change region is.

[0158] In the case of a sample in which the high-strength part softening layers 55 are arranged on both sides of the central part 56, based on the Vickers hardness measurement results from the first surface side, ΔA1 on the first surface side is obtained from Equation (3), and further, based on the Vickers hardness measurement results from the second surface side, ΔA2 on the second surface side is obtained from Equation (3). The arithmetic mean of ΔA1 and ΔA2 can be taken as ΔA.

[0159] ΔHV2 can be obtained by multiplying ΔA obtained by Equation (3) by the ratio of the plate thickness direction thickness of the second hardness change region to the thickness of the entire softening layer.

[0160] In addition, the reason why the effect of preventing cracking can be exerted due to the large maximum bending angle θ1 during a side collision is mainly the high-strength part softening layer 55 on the outer surface 53a side. Therefore, it is not necessary to provide the high-strength part softening layer 55 on the inner surface 53b side. In this case, the inner surface 53b side has the same Vickers hardness as the central part 56, and the high-strength part softening layer 55 exists only on the outer surface 53a side.

[0161] <Modified Example 2> In the above-described embodiment, the configuration in which no softening layer is formed in the low-strength part 51 has been described as an example. However, it does not have to be like this. FIG. 8 is a longitudinal sectional view along the plate thickness direction and the vertical direction Z of the pillar outer 41 in the vicinity of the joint part 52 in Modified Example 2, and the illustration on the back side of the cross section is omitted. As shown in FIG. 8, a low-strength part softening layer 57 may exist in the low-strength part 51. In this case, the low-strength part softening layer 57 exists both near the outer surface 51a and near the inner surface 51b of the low-strength part 51. In this case, in the plate thickness direction of the low-strength part 51, the low-strength part softening layers 57 exist on both sides, and the central part 58 exists between the low-strength part softening layers 57.

[0162] (Vickers hardness of the central part of the low-strength part) Even when the Vickers hardness of the central part 58 of the low-strength part 51 exceeds 300 HV, for example, is 400 HV, it may be possible to avoid the possibility of fracture during a side collision. However, in a configuration where the Vickers hardness of the central part 58 exceeds 300 HV, the presence of the low-strength part softening layer 57 can significantly enhance the effect of suppressing the possibility of fracture of the low-strength part 51 during a side collision. As an example of a preferable lower limit of the Vickers hardness of the central part 58, 300 HV, 350 HV, 400 HV, 420 HV, 450 HV can be mentioned. Also, as an example of a preferable upper limit of the Vickers hardness of the central part 58, 530 HV, 500 HV, 480 HV, 450 HV can be mentioned. As is clear from the above, the Vickers hardness of the central part 58 may be 300 HV to 530 HV, may be 350 HV to 500 HV, may be 400 HV to 480 HV, or may be 420 HV to 450 HV.

[0163] (Combination of Vickers hardness at the central part and maximum bending angle difference) When the Vickers hardness of the low-strength part 51 is 420 HV to 530 HV and the Vickers hardness of the central part 56 of the high-strength part 53 is 550 HV to 1050 HV, the difference Δθ in bending angle may be 50 degrees or less, 45 degrees or less, 40 degrees or less, 35 degrees or less, 30 degrees or less, or 25 degrees or less. The lower limit of the difference Δθ in bending angle is preferably 0 degrees. By virtue of the relationship between the Vickers hardness at the central part of each of the low-strength part 51 and the high-strength part 53 and the difference Δθ in bending angle like this, when a side collision occurs, the high-strength part 53 can sufficiently follow the bending deformation of the low-strength part 51 and be bent and deformed. As a result, the possibility of breakage of the high-strength part 53 during a side collision can be suppressed. Incidentally, the Vickers hardness of the central part 56 of the high-strength part 53 described above may be in the range of 550 HV to 770 HV.

[0164] (Existence range of the low-strength part softening layer) When the joint portion 52 is at the height position between the lower end 61b of the upper bracket 61 and the upper end 62a of the lower bracket 62 (when in the position shown in FIG. 1), it is preferable that each low-strength portion softening layer 57 on the respective surfaces 51a and 51b of the low-strength portion 51 exists from a position higher than the upper end 62a of the lower bracket 62 to a position lower than the lower end 62b of the lower bracket 62. Thereby, each low-strength portion softening layer 57 can be arranged so as to cover the lower bracket 62 that deforms the most in the vehicle body 1 during a side collision, and it is possible to suppress the possibility of breakage of the low-strength portion 51 and improve the impact energy absorption amount of the low-strength portion 51 through the improvement of the bending deformation ability of the low-strength portion 51 by each low-strength portion softening layer 57. The low-strength portion softening layer 57 may be formed over the entire area of the low-strength portion 51 in the vertical direction Z. In particular, as will be described later, when the joint portion 52 is at a position lower than the lower end 62b of the lower bracket 62 (when in the position shown in FIG. 9), it is preferable that the low-strength portion softening layer 57 is formed over the entire area of the low-strength portion 51 in the vertical direction Z. In this case, the range of the low-strength portion 51 in the center pillar 4 is relatively narrow, and the entire area of the low-strength portion 51 tends to deform during a side collision. Therefore, it is possible to suppress the possibility of breakage of the low-strength portion 51 and improve the impact energy absorption amount of the low-strength portion 51 through the improvement of the bending deformation ability of the low-strength portion 51 by the low-strength portion softening layer 57.

[0165] (Outline of the thickness range of the low-strength portion softening layer) Each low-strength portion softening layer 57 is formed, for example, in a blank that is the material of the low-strength portion 51 by reducing the carbon content in the vicinity of the portion that becomes the outer surface 51a and the portion that becomes the inner surface 51b (the portion that becomes the low-strength portion softening layer 57) compared to the portion that becomes the central portion 58 of the blank. The method of forming the low-strength portion softening layer 57 is not particularly limited, and any method may be used. In this modification, it is preferable that each low-strength portion softening layer 57 is provided with a predetermined thickness from the corresponding surfaces 51a and 51b in terms of being able to increase the maximum bending angle of the low-strength portion 51 while sufficiently ensuring the strength of the low-strength portion 51. The lower limit of the predetermined thickness is, for example, 80 μm, and the upper limit is, for example, 200 μm.

[0166] (Overview of the Vickers hardness distribution of the low-strength part softening layer and the overview of the Vickers hardness of the central part) In each low-strength part softening layer 57, the Vickers hardness is decreased as the distance from the 1 / 2 thickness position of the low-strength part 51 increases. Among the low-strength part softening layers 57, the portions that become the surfaces 51a, 51b have the lowest Vickers hardness in the low-strength part 51, and are, for example, at least 100 HV to 250 HV lower than the Vickers hardness of the central part 58. In this case, the Vickers hardness of the low-strength part 51 refers to the Vickers hardness in the central part 58.

[0167] In the second modified example 2 in which each low-strength part softening layer 57 is provided in the low-strength part 51, the maximum bending angle of the low-strength part 51 can be increased by, for example, about 20 degrees compared to the case (embodiment) where the low-strength part softening layer 57 is not provided.

[0168] In this way, the Vickers hardness at the surfaces 51a, 51b in the thickness direction of the low-strength part 51 is at least 100 HV lower than the Vickers hardness at the central part 58 at the center in the thickness direction of the low-strength part 51. As a result, the maximum bending angle of the low-strength part 51 can be made larger. Therefore, during a side collision, the low-strength part 51 can more surely follow the bending deformation of the center pillar 4, suppressing the occurrence of cracks in the low-strength part 51 and increasing the shock absorption performance. As a result, since the high-strength part 53 has a high Vickers hardness and is high-strength, the intrusion amount into the vehicle interior can be suppressed and the occupant protection effect can be increased. In the low-strength part 51, while ensuring the absorption amount of shock energy, the thickness of the low-strength part 51 can be further reduced to lightweight the vehicle body 1. Also, even when the low-strength part 51 is formed of a high-strength material with a higher Vickers hardness, the possibility of breakage of the low-strength part 51 can be suppressed, so that the amount of entry of the low-strength part 51 into the inside of the vehicle body during a side collision can be made smaller.

[0169] An example of the configuration of the low-strength part 51 will be described more specifically.

[0170] (Vickers hardness of the central part of the low-strength part) It is preferable that the Vickers hardness of the central portion 58 in the plate thickness direction in the portion where the low-strength portion softening layer 57 is provided is 150 HV or more. When the Vickers hardness of the central portion 58 is 150 HV or more, the strength at the time of side collision in the low-strength portion 51 can be sufficiently ensured. The Vickers hardness of the central portion 58 may be greater than 200 HV, may be 250 HV or more, may be 300 HV or more, may be 400 HV or more, or may be 500 HV or more. The upper limit of the Vickers hardness of the central portion 58 is not particularly limited, but in view of the followability to the deformation of the center pillar 4 at the time of side collision, etc., it is preferably 500 HV or less.

[0171] (Details of the thickness range of each low-strength portion softening layer) The thickness of each low-strength portion softening layer 57 in the plate thickness direction is preferably 80 μm or more and 5% or more and 20% or less of the plate thickness in the portion where each low-strength portion softening layer 57 is provided. If the thickness of each low-strength portion softening layer 57 is 20% or less of the above plate thickness, the ratio of each low-strength portion softening layer 57 in the steel plate which is the material of the low-strength portion 51 is small, so the load resistance required for the low-strength portion 51 can be maintained. The thickness of each low-strength portion softening layer 57 is preferably 17% or less of the above plate thickness, and more preferably 14% or less. On the other hand, when the low-strength portion softening layer 57 is provided over the entire surface of the steel plate which is the material of the low-strength portion 51, if the thickness of each low-strength portion softening layer 57 is 80 μm or more and 5% or more of the above plate thickness, the deformation ability by the low-strength portion softening layer 57 can be sufficiently exhibited. The thickness of each low-strength portion softening layer 57 is more preferably 8% or more of the above plate thickness. As is clear from the above, the thickness of each low-strength portion softening layer 57 may be 5% - 17% of the above plate thickness, may be 5% - 14%, may be 8% - 20%, may be 8% - 17%, or may be 8% - 14%.

[0172] (Method for measuring the thickness position of the boundary between the low-strength portion softening layer and the central portion) The method for measuring the boundary between the low-strength portion softening layer 57 and the central portion 58 is the same as the method for measuring the boundary between the high-strength portion softening layer 55 and the central portion 56.

[0173] (Calculation method of the slope of Vickers hardness at each thickness position after measurement of the boundary between the low-strength part softening layer and the central part) The calculation method of the slope of Vickers hardness at each thickness position after Vickers hardness measurement during the boundary measurement between the low-strength part softening layer 57 and the central part 58 is the same as the calculation method of the slope of Vickers hardness at each thickness position after Vickers hardness measurement during the boundary measurement between the high-strength part softening layer 55 and the central part 56.

[0174] (Relationship between the Vickers hardness of the low-strength part softening layer and the Vickers hardness of the central part) The Vickers hardness of the low-strength part softening layer 57 on the surfaces 51a, 51b of the low-strength part 51 is preferably not less than 0.5 times and less than 0.9 times the Vickers hardness of the central part 58 in the portion where the low-strength part softening layer 57 is provided.

[0175] (Measurement method of the Vickers hardness of the central part of the low-strength part) The measurement method of the Vickers hardness of the central part 58 of the low-strength part 51 is the same as the measurement method of the Vickers hardness of the central part 56 of the high-strength part 53.

[0176] (Measurement method of the Vickers hardness of the surface of the low-strength part) The measurement method of the Vickers hardness of the surface of the low-strength part 51 is the same as the measurement method of the Vickers hardness of the surface of the high-strength part 53.

[0177] If the Vickers hardness of the surface of the low-strength part 51 is not less than 0.5 times the Vickers hardness of the central part 58, the load resistance during collision, particularly during the latter stage of the stroke during collision, can be improved. The low-strength part softening layer 57 more preferably has a Vickers hardness not less than 0.6 times the Vickers hardness of the central part 58 on the surface of the low-strength part 51. On the other hand, if the Vickers hardness of the surface of the low-strength part 51 is less than 0.9 times the Vickers hardness of the central part 58, the deformability can be sufficiently improved. The low-strength part softening layer 57 more preferably has a Vickers hardness less than 0.8 times the Vickers hardness of the central part 58 on the surface of the low-strength part 51.

[0178] (Vickers hardness change in the low-strength softened layer) FIG. 7 is also an image diagram for explaining an example of the Vickers hardness change in the low-strength softened layer 57. As shown in FIG. 7, the low-strength softened layer 57 preferably has a first hardness change region which is a region from the surfaces 51a and 51b to 40% of the thickness of the low-strength softened layer 57 in the plate thickness direction, and a second hardness change region which is a region in the low-strength softened layer 57 that is not the first hardness change region. The absolute value ΔHV1' of the hardness change in the plate thickness direction in the first hardness change region is preferably greater than the absolute value ΔHV2' of the hardness change in the plate thickness direction in the second hardness change region. If ΔHV1' is greater than ΔHV2', sufficient load characteristics can be obtained.

[0179] The absolute value ΔHV1' of the hardness change in the first hardness change region is preferably 100 HV or more and less than 200 HV. If ΔHV1' is 100 HV or more, the stress concentration during bending deformation can be more effectively relieved, and the bending characteristics can be further improved. Also, if ΔHV1' is less than 200 HV, the effect of relieving the stress concentration during bending deformation is further enhanced, and better bending characteristics can be obtained. Therefore, when ΔHV1' is 100 HV or more and less than 200 HV, good bending characteristics can be obtained, and the deformability of the low-strength portion 51 can be improved. Specifically, in the latter stage of the stroke during a collision, the drop of the load immediately after the load peak can be made gentle. Therefore, as described above, the absolute value ΔHV1' of the hardness change in the first hardness change region is preferably 100 HV or more and less than 200 HV. Note that the upper limit of ΔHV1' is preferably less than 200 HV, while the lower limit may be 50 HV, may exceed 50 HV, may be 55 HV, may be 60 HV, or may be 100 HV.

[0180] (Method for measuring Vickers hardness of the first and second hardness change regions of the low-strength softened layer) The method for measuring the hardness of the first hardness change region and the second hardness change region in the low-strength portion 51 is the same as the method for measuring the hardness of the first hardness change region and the second hardness change region in the high-strength portion 53.

[0181] In the case of a sample in which the low-strength portion softening layers 57 are arranged on both sides of the central portion 58 of the low-strength portion 51, the same measurement is performed from the first surface side of the sample, and further from the second surface side opposite to the first surface.

[0182] (Method for calculating the absolute values ΔHV1’ and ΔHV2’ of the hardness change after measuring the first and second hardness change regions) The method for calculating ΔHV1’ and ΔHV2’ in the low-strength portion 51 is the same as the method for calculating ΔHV1 and ΔHV2 in the high-strength portion 53.

[0183] It should be noted that the low-strength portion softening layer 57 on the outer surface 51a side mainly contributes to the effect of preventing cracking due to the large maximum bending angle during side impact. Therefore, the low-strength portion softening layer 57 may not be provided on the inner surface 51b side. In this case, the inner surface 51b side has the same Vickers hardness as the central portion 58, and the low-strength portion softening layer 57 exists only on the outer surface 51a side.

[0184] It should be noted that in this Modification 2, the high-strength portion softening layer 55 may not be provided in the high-strength portion 53. In this case, most of the steel plate base material in the high-strength portion 53 is formed by the central portion 56. When there is a plating layer in the high-strength portion 53, the steel plate base material starts from directly below the plating layer. When there is an alloy layer between the plating layer and the steel plate base material in addition to the plating layer in the high-strength portion 53, the steel plate base material starts from directly below the alloy layer.

[0185] <Modification 3> In the above-described embodiment, an example has been described in which the vehicle is a BEV and is provided with a reinforcing member 20 for protecting the battery 18b from side collisions inside the side sill 5. However, this does not have to be the case. FIG. 9 is a schematic left side view for explaining a modified example 3 in which the reinforcing member 20 is not installed inside the side sill 5. As shown in FIG. 9, in the case of a vehicle equipped with an internal combustion engine such as a gasoline engine or a diesel engine, and the battery is not installed on the side (inside in the width direction Y) of the side sill 5, the reinforcing member 20 may not be installed inside the side sill 5. In addition, even in a vehicle equipped with an internal combustion engine, it is common to install a member for reinforcement inside the side sill 5. The vehicle shown in FIG. 9 may be a PHEV (Plug-in Hybrid Electric Vehicle). When the vehicle is a PHEV, the driving battery for driving the wheels is fixed to the floor panel 7 or the like with a relatively large distance (for example, a distance greater than 10 cm) in the width direction Y from the side sill 5.

[0186] In such a configuration, during a side collision, the amount of deformation of the side sill 5 tends to increase, and furthermore, the side sill 5 undergoes torsional deformation. Since the amount of plastic deformation of the side sill 5 is relatively large in this way, the amount of impact energy absorbed by the side sill 5 is large, and the side sill 5 and the center pillar 4 share the impact absorption. When the amount of impact energy absorbed by the center pillar 4 is small, in order to suppress the contact between the vehicle body 1 and the occupant, it is preferable that the range of the low-strength portion 51 that plastically deforms greatly inward in the width direction Y to absorb the impact is narrowed, and the high-strength portion 53 that reduces the amount of plastic deformation of the vehicle body 1 inward in the width direction Y is arranged close to the side sill 5.

[0187] Therefore, in this modification, the joint portion 52 is arranged at a height position below the upper end 62a of the lower bracket 62 in the vertical direction Z, and in particular, it is preferably arranged at a height position below the lower end 62b of the lower bracket 62 in the vertical direction Z. The joint portion 52 is arranged, for example, above the side sill 5 below the lower end 62b. In the vehicle shown in FIG. 9, during a side collision, the side sill 5 undergoes torsional deformation about an axis along the front-rear direction X. When the side sill 5 undergoes torsional deformation in this way, by arranging the joint portion 52 in the above-described manner, the high-strength portion 53 can be installed near the side sill 5 where the amount of deformation is large during a side collision. Therefore, during a side collision, the deformation of the pillar outer 41 following the intrusion of the side sill 5 into the cabin 10 side due to the torsional deformation of the side sill 5 can be suppressed by the high-strength portion 53. As a result, the amount of intrusion of the center pillar 4 into the cabin 10 side can be made smaller, and furthermore, the torsional deformation of the side sill 5 can be suppressed.

[0188] <Modification 4> In the above-described embodiment, the form in which the lower end 473b of the overlapping portion 47 of the pillar outer 41 is arranged along the outer wall 153 of the side sill outer 15 has been described as an example. However, it does not have to be like this. FIG. 10 is a schematic cross-sectional view of the main part of Modification 4 regarding a modification of the overlapping portion 47 of the pillar outer 41, showing a cross-section orthogonal to the front-rear direction.

[0189] The overlapping portion 47 of Modification 4 has, in addition to the upper flange 471, the upper wall 472, and the outer wall 473, a lower wall 474 that extends inward in the width direction Y from the outer wall 473.

[0190] The outer wall 473 is arranged up to the lower end of the outer surface 153a of the outer wall 153 of the side sill outer 15.

[0191] The lower wall 474 is preferably arranged along and in contact with the lower surface 154a of the lower wall 154 of the side sill outer 15, and is joined to this lower surface 154a by welding, adhesion, or the like. In this embodiment, the lower end 474b (lower tip) of the lower wall 474 is the lower end of the overlapping portion 47.

[0192] In this way, since the overlapping portion 47 extends to the lower wall 474 of the side sill outer 15, the center pillar 4 is configured to hold the lower part of the side sill 5. As a result, the joint area between the center pillar 4 and the side sill 5 can be increased, so that the stress acting between the side sill 5 and the center pillar 4 during a side collision can be reduced. Further, the load transmitted from the center pillar 4 to the side sill 5 during a side collision is received by the vehicle body 1 as a torsional moment. Therefore, deformation of the closed cross-sectional shape of the side sill 5, particularly the side sill outer 15, can be suppressed. Even when a side collision occurs, since the original closed cross-sectional shape of the side sill 5 before the collision is difficult to change, the side sill 5 has high torsional rigidity, and the torsional angle of the side sill 5 during a side collision can be reduced. Thereby, the intrusion amount of the center pillar 4 and the side sill 5 into the cabin 10 can be reduced. On the other hand, by devising the arrangement so that the center pillar 4 does not reach the lower end (lower flange 155) of the side sill 5, the center pillar 4 does not become unnecessarily heavy, and it is possible to highly balance the improvement of the reinforcing effect of the side sill 5 by the lower shape of the center pillar 4 and the suppression of the weight increase of the center pillar 4.

[0193] The lower end 474b of the overlapping portion 47 is, for example, a linear end along the front-rear direction X. With this configuration, the vehicle body 1 can receive the load transmitted from the center pillar 4 to the side sill 5 as a torsional moment over the entire area where the overlapping portion 47 is arranged in the front-rear direction X. Therefore, it is possible to more reliably suppress the occurrence of crushing in the closed cross-sectional shape of the side sill 5, particularly the side sill outer 15.

[0194] In Modification 4, the height position of the joint portion 52 is preferably between the height position of the lower end 61b of the upper bracket 61 and the height position of the upper end 62a of the lower bracket 62, as described in the embodiment. Since the overlapping portion 47 extends to the lower wall 474 of the side sill outer 15, at the time of a side collision, the overlapping portion 47 acts in the same manner as the reinforcing member 20, and deformation of the side sill 5 is suppressed. In this case, by setting the height position of the joint portion 52 to the above-described position, a sufficient range of the low-strength portion 51 can be ensured. Therefore, it is possible to achieve both impact absorption by the low-strength portion 51 cooperating with the side sill 5 at the initial stage of a side collision and suppression of deformation of the center pillar 4 toward the cabin 10 side by the high-strength portion 53 receiving the impact load from the upper bracket 61 at the later stage of the side collision.

[0195] Note that in Modification 4, the height position of the joint portion 52 may be arranged at a position lower than the height position of the lower end 62b of the lower bracket 62. Further, although the reinforcing member 20 is illustrated in FIG. 10 showing Modification 4, the reinforcing member 20 may be omitted.

[0196] <Other Modifications> Further, in the above-described embodiment and modifications, the center pillar has been described as an example of the impact absorbing member of the present invention. However, this is not necessarily the case. As the impact absorbing member of the present invention, a side sill may be adopted. In this case, for example, the vicinity of the overlapping portion 47 in the side sill outer 15 is made into a low-strength portion 51, and a high-strength portion 53 is arranged on the front fastening position side or the rear fastening position side in the side sill 5. In this case, at the time of a side collision, while exerting an impact absorption effect in the vicinity of the overlapping portion 47 in the side sill 5, entry of the side sill 5 into the cabin 10 can be more reliably suppressed by the high-strength portion in the front side portion or the rear side portion of the side sill 5. Note that the impact absorbing member of the present invention may be applied other than to the center pillar and the side sill.

Example

[0197] A model of the vehicle body 1 described in the embodiment (Figs. 1 to 3) was created by a computer. The configurations of the example and the comparative example in the model of the vehicle body 1 are as follows. (Configuration of the example) Vickers hardness HV1 and plate thickness of the high-strength portion 53 of the pillar outer 41: 600 HV, 1.2 mm. The high-strength portion 53 is the material described in Modification 1 and includes a high-strength portion softening layer 55. Vickers hardness HV2 and plate thickness of the low-strength portion 51 of the pillar outer 41: 350 HV, 1.4 mm (Configuration of the comparative example) Vickers hardness HV1 and plate thickness of the high-strength portion 53 of the pillar outer 41: 1000 HV, 1.2 mm. The high-strength portion 53 does not include the high-strength portion softening layer 55 described in Modification 1. Vickers hardness HV2 and plate thickness of the low-strength portion 51 of the pillar outer 41: 150 HV, 1.4 mm (Configurations common to the example and the comparative example) Vickers hardness and plate thickness of the pillar inner 42: 350 HV, 1.3 mm Vickers hardness and plate thickness of the patch 43: 600 HV, 1.2 mm

[0198] The particular differences between the comparative example and the example are as follows. Difference Δθ between the maximum bending angle θ1 of the high-strength portion 53 and the maximum bending angle θ2 of the low-strength portion 51 in the comparative example: 105 degrees Difference Δθ between the maximum bending angle θ1 of the high-strength portion 53 and the maximum bending angle θ2 of the low-strength portion 51 in the example: 20 degrees

[0199] For the comparative example and the example, the presence or absence of cracks in the pillar outer 41 when a side collision occurred on the vehicle body 1 was measured by computer simulation. The side collision conditions were set according to the IIHS (Insurance Institute for Highway Safety). Specifically, the test conditions were such that a collision load was applied to the center pillar under conditions assuming a full-car collision.

[0200] As a result, in the comparative example, cracks occurred in the front wall 412 and the rear wall 414 of the high-strength portion 53 near the joint portion 52. On the other hand, in the example, no cracks occurred. Thus, the example was able to ensure impact absorption performance by suppressing cracks while being thin and lightweight and not cracking even during a side collision.

Industrial Applicability

[0201] The present invention can be widely applied as an impact absorption member.

Explanation of Signs

[0202] 1 Vehicle body 4 Center pillar (impact absorption member) 5 Side sill 8 Door 20 Reinforcing member 41 Pillar outer 42 Pillar inner 47 Overlapping portion 51 Low-strength portion 52 Joint portion 53 High-strength portion 61 Bracket 61a Upper end of the upper bracket 62 Bracket 153 Outer wall Z Vertical direction (longitudinal direction) θ1 Maximum bending angle of the high-strength portion θ2 Maximum bending angle of the low-strength portion

Claims

1. A shock absorption member provided on a vehicle body, formed along a predetermined longitudinal direction, and including a portion having a closed cross-sectional shape in a cross-section orthogonal to the longitudinal direction, a low-strength portion, a high-strength portion arranged in parallel with the low-strength portion in the longitudinal direction and having a central portion in the plate thickness direction with a Vickers hardness higher than that of the central portion in the plate thickness direction of the low-strength portion, a joint portion joining the low-strength portion and the high-strength portion, and comprising, wherein a maximum bending angle of the high-strength portion is set according to a maximum bending angle of the low-strength portion. A shock absorption member.

2. The shock absorption member according to claim 1, wherein a difference between the maximum bending angle of the high-strength portion and the maximum bending angle of the low-strength portion is 100 degrees or less.

3. The shock absorption member according to claim 1, wherein the Vickers hardness of the central portion in the plate thickness direction of the high-strength portion is 500 HV or more.

4. The shock absorption member according to claim 3, wherein the Vickers hardness of the central portion in the plate thickness direction of the low-strength portion is 150 HV or more.

5. The Vickers hardness HV at the center in the plate thickness direction of the high-strength portion １ and the Vickers hardness HV at the center in the plate thickness direction of the low-strength portion ２ and the ratio HV １ / HV ２ is 1.3 or more, and the impact-absorbing member according to claim 3.

6. The shock absorption member according to claim 1, wherein a difference between the maximum bending angle of the low-strength portion and the maximum bending angle of the high-strength portion is 30 degrees or less.

7. The shock absorption member is a center pillar provided with a pillar inner and a pillar outer and arranged along the vertical direction of the vehicle body, the pillar outer includes the low-strength portion, the joint portion, and the high-strength portion, and the high-strength portion is arranged above the low-strength portion. The shock absorption member according to any one of claims 1 to 6.

8. A pair of upper and lower brackets for supporting a door installed behind the center pillar are provided on the center pillar, and the joint portion is arranged at a position lower than a height position of a lower end of the upper bracket. The shock absorption member according to claim 7.

9. The shock absorption member according to claim 8, wherein the joint portion is arranged at a position higher than a height position of an upper end of the lower bracket.

10. The shock absorption member according to claim 8, wherein the joint portion is arranged at a position lower than a height position of a lower end of the lower bracket.

11. The vehicle body further includes a side sill joined to a lower portion of the center pillar and arranged along the front-rear direction of the vehicle body and having a closed cross-sectional shape in a cross-section orthogonal to the front-rear direction, and the side sill includes an outer wall arranged on an outer side in the width direction of the vehicle body in the side sill. The lower part of the center pillar is provided with an overlapping portion arranged to cover the side sill at the connection portion with the side sill. The overlapping portion is along the side sill down to a position below the height of the upper and lower halves of the outer wall of the side sill, the impact absorbing member according to claim 7.

12. The Vickers hardness on the surface in the plate thickness direction of the high-strength portion is at least 100 HV lower than the Vickers hardness at the center in the plate thickness direction of the high-strength portion, the impact absorbing member according to claim 1.

13. The high-strength portion is provided with a high-strength portion softening layer in the plate thickness direction from the surface. The Vickers hardness at the center in the plate thickness direction of the portion where the high-strength portion softening layer is provided in the high-strength portion is 500 HV or more. The thickness of the high-strength portion softening layer is 80 μm or more and 5% or more and 20% or less of the plate thickness of the portion where the high-strength portion softening layer is provided. The Vickers hardness of the high-strength portion softening layer on the surface is 0.5 times or more and less than 0.9 times the Vickers hardness at the center in the plate thickness direction of the portion where the high-strength portion softening layer is provided. The high-strength portion softening layer has a first hardness change region which is a region from the surface to 40% of the thickness of the high-strength portion softening layer in the plate thickness direction, and a second hardness change region which is a region of the high-strength portion softening layer that is not the first hardness change region. The absolute value ΔHV1 of the hardness change in the plate thickness direction in the first hardness change region is larger than the absolute value ΔHV2 of the hardness change in the plate thickness direction in the second hardness change region, the impact absorbing member according to claim 12.

14. The Vickers hardness on the surface in the plate thickness direction of the low-strength portion is at least 100 HV lower than the Vickers hardness at the center in the plate thickness direction of the low-strength portion, the impact absorbing member according to claim 1.

15. The low-strength portion is provided with a low-strength portion softening layer in the plate thickness direction from the surface. The Vickers hardness at the center in the plate thickness direction of the portion where the low-strength portion softening layer is provided in the low-strength portion is 150 HV or more. The thickness of the low-strength portion softening layer is 80 μm or more and 5% or more and 20% or less of the plate thickness of the portion where the low-strength portion softening layer is provided. The Vickers hardness of the low-intensity part softening layer on the surface is 0.5 times or more and less than 0.9 times the Vickers hardness of the central part in the plate thickness direction of the part where the low-intensity part softening layer is provided. The low-intensity part softening layer has a first hardness change region that is a region from the surface to 40% of the thickness of the low-intensity part softening layer in the plate thickness direction, and a second hardness change region that is a region of the low-intensity part softening layer that is not the first hardness change region. The absolute value ΔHV1' of the hardness change in the plate thickness direction in the first hardness change region is greater than the absolute value ΔHV2' of the hardness change in the plate thickness direction in the second hardness change region. The impact-absorbing member according to claim 14.

16. A center pillar and a side sill joined to the lower part of the center pillar. A vehicle body, wherein at least one of the center pillar and the side sill is the impact-absorbing member according to claim 1.

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