Vehicle lower body structure

Abstract

To provide a lower vehicle-body structure of a vehicle in which a frame member can attain impact absorption by securely generating the buckling, while suppressing its bending deformation, when the bending load is applied to the frame member in the vehicle collision.SOLUTION: A lower vehicle-body structure of a vehicle is provided with a frame member 2 having a closed-cross section. The frame member 2 comprises a first portion 11 and a second portion 12. The first portion 11 comprises a compression face portion 21 and a pair of side face portions 22. The side face portion 22 comprises: a bending portion 24; a compression-side area 25 which is positioned on a side of the compression face portion 21 relative to the bending portion 24 with the bending portion 24 being a starting point and where a compressive stress is generated when the bending load is applied; and a tension-side area 26 which is positioned on a side away from the compression face portion 21 relative to the bending portion 24 with the bending portion 24 being a starting point and where a tensile stress is generated when the bending load is applied. The compression-side area 25 is configured to have higher rigidity than the tension-side area 26.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an underbody structure of a vehicle. [Background technology]

[0002] Conventionally, in the lower body structure of a vehicle, among the skeletal members that make up the vehicle's skeleton, skeletal members such as side sills that are subjected to bending loads during a vehicle collision are required to have a cross-sectional structure that combines bending strength and impact absorption (so-called disposable cross-sections or performance-maximizing cross-sections) from the perspective of reducing vehicle weight and costs.

[0003] Patent Document 1 discloses a side sill structure with a bent portion for impact absorption. The side sill is a member with a closed cross-sectional structure extending in the longitudinal direction of the vehicle on both sides of the vehicle body, and includes two components: a side sill outer and a side sill inner. The side sill outer and side sill inner each have a pair of flanges, and the side sill outer and side sill inner are combined by joining the flanges to form the closed cross-sectional structure.

[0004] The side sill outer is a component formed by pressing a uniformly thick steel or other plate material into a cross-sectional shape (hat cross-section) with a pair of flanges. The pair of upper and lower side sections of the side sill outer each have a bent section formed by bending inward toward the side sill. This allows the side sill outer to begin buckling at the bent section during a side collision (side impact), etc., and the entire side sill can absorb impact by buckling while maintaining a certain degree of bending strength. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-104832 Summary of the Invention [Problem to be solved by the invention]

[0006] The flange portion of the side sill outer is typically positioned at the same position as the bottom edge of the door in the vehicle width direction. However, to ensure sufficient space within the vehicle cabin, it is possible to adopt a structure in which the flange portions of the side sill inner and outer are positioned outward in the vehicle width direction from the center of the cross section of the side sill. In such a structure, the width of the side portion of the side sill outer cannot be ensured in the vehicle width direction, which reduces the formability of the side portion during press molding of the side sill outer. This reduced formability makes it difficult to obtain a sufficient angle for the bending portion of the side portion of the side sill outer, making it difficult to set a trigger for buckling of the side sill. Therefore, with such a structure, it is difficult for the side sill to reliably buckle and absorb the impact when a bending load is applied to the side sill during a vehicle collision.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a vehicle lower body structure that is capable of suppressing bending deformation of a skeletal member and reliably buckling to absorb impact when a bending load is input to the skeletal member during a vehicle collision. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides an underbody structure for a vehicle that includes a skeleton member having a first portion and a second portion extending in the same direction that cooperate to form a closed cross section, the first portion including a compression surface portion in which a compressive stress occurs when a bending load is input to the skeleton member, and a pair of side portions extending from both ends of the compression surface portion toward the second portion, and each of the pair of side portions includes a bent portion formed by bending the side portion toward the inside of the skeleton member, a compression-side region that is located on the compression surface portion side of the bent portion with the bent portion as a starting point, and in which a compressive stress occurs when the bending load is input, and a tension-side region that is located on the compression surface portion side of the bent portion with the bent portion as a starting point, and in which a tensile stress occurs when the bending load is input, and the compression-side regionthroughout the area is characterized in that it is configured to have higher rigidity than the tension side region against the bending load that compresses the compression surface portion.

[0009] In this configuration, of the first and second portions that form the closed cross section of the skeleton member, the first portion has a compression surface portion where compressive stress occurs when a bending load is input to the skeleton member, and a pair of side surfaces extending from both ends of the compression surface portion toward the second portion. The side surfaces have bent portions formed by bending the side surfaces toward the inside of the skeleton member.

[0010] With this configuration, when a bending load is input to the skeletal member during a vehicle collision, compressive stress acts on the compressed surface portion of the first part, causing the compressed surface portion to move toward the second part, and at the pair of side portions of the first part, the bent portions that are bent toward the inside of the skeletal member tend to move toward the inside of the skeletal member.

[0011] In this configuration, each side surface portion has a compression side region that is located on the compression surface side of the bent portion, starting from the bent portion, and a tension side region that is located on the side away from the compression surface side of the bent portion, starting from the bent portion. throughout the area The compression side regions of the pair of side surfaces are configured to have higher rigidity than the tension side regions against a bending load that compresses the compression surface portions. Therefore, in the event of a vehicle collision, as the bent portions move inward of the frame member, the tension side regions are tensilely deformed inward of the frame member, and the bent portions are displaced inward of the frame member, causing buckling of the frame member. At this time, during the process in which the bent portions are displaced inward of the frame member, the high-rigidity compression side regions of the pair of side surfaces are throughout the area In the process of deformation, the compressed surface portion becomes substantially parallel to the direction of movement toward the second portion. throughout the area This generates a high reaction force against the bending load, making it possible to suppress bending deformation of the frame member. As a result, when a bending load is input to the frame member during a vehicle collision, the frame member can absorb the impact by suppressing bending deformation and reliably buckling.

[0012] In the above-described vehicle lower body structure, it is preferable that the angle between the extension line of the compression-side region and the tension-side region in the bent portion is set to 30 degrees or less.

[0013] With this configuration, even when the bent portion is formed at a small angle of 30 degrees or less as described above, the tension side region is configured to have lower rigidity than the compression side region, so that in the event of a vehicle collision, the tension side region undergoes tensile deformation inward of the skeletal member, while the bent portion displaces inward of the skeletal member, ensuring buckling of the skeletal member.

[0014] In the above-mentioned vehicle lower body structure, it is preferable that the width of the compression side region in a predetermined direction in which the first part and the second part are aligned is set to be 1 / 4 or less of the overall width of the skeletal member in the predetermined direction.

[0015] With this configuration, in the event of a vehicle collision, buckling of the skeletal member within the compression side region of the side portion in the first part is suppressed, while the side portion is able to bend reliably at the bending portion which is the boundary between the compression side region and the tension side region, making it possible to generate a high reaction force at the side portion.

[0016] In the above-mentioned vehicle lower body structure, it is preferable that the skeletal member is a side sill that extends in the fore-and-aft direction of the vehicle on both sides of the vehicle body and has a closed cross section, the first part is a side sill outer that has a pair of upper and lower flange portions and constitutes the outer part of the side sill in the vehicle width direction, the second part is a side sill inner that has a pair of upper and lower flange portions and constitutes the inner part of the side sill in the vehicle width direction, the side sill is constituted by joining the flange portions of the side sill outer and the side sill inner, and the flange portions of the side sill outer and the side sill inner are positioned outward in the vehicle width direction from the center of the cross section of the side sill.

[0017] With this configuration, the flanges of the side sill outer and inner panels that make up the side sill are positioned outward in the vehicle width direction from the center of the cross section of the side sill, which makes it easier to position the door opening defined by these flanges outward in the vehicle width direction, making it easier to ensure space inside the vehicle.As a result, it is possible to ensure space inside the vehicle while suppressing bending deformation of the side sill and maintaining its impact absorption performance.

[0018] In the above-mentioned vehicle lower body structure, it is preferable that the side sill further includes a connecting plate portion that is sandwiched between the pair of upper and lower flange portions of the side sill outer and the pair of upper and lower flange portions of the side sill inner and connects the pair of upper and lower flange portions.

[0019] According to this configuration, the connecting plate is sandwiched between the pair of upper and lower flanges of the side sill outer and inner panels, connecting the pair of upper and lower flanges. Therefore, even if the pair of upper and lower flanges attempt to move apart vertically during bending deformation of the side sill during a vehicle collision, the connecting plate suppresses the vertical displacement of the pair of upper and lower flanges. This allows the side sill to reliably buckle at the bent portion.

[0020] In the above-described vehicle lower body structure, the connecting plate portion is preferably disposed in a portion of the side sill that defines a door opening of the vehicle body in the longitudinal direction of the vehicle.

[0021] The door opening of a vehicle body is an area where there are no pillars extending in the vertical direction, and where the support rigidity of the side sill is weak. However, as described above, the connecting plate portion is positioned in the part of the side sill that forms the door opening, so even in an area where there are no pillars, the side sill can reliably buckle at the bending portion.

[0022] In the above vehicle underbody structure, the connecting plate portion preferably has a bending strength smaller than the bending strengths of the side sill outer and the side sill inner.

[0023] In the event of a vehicle collision, the connecting plate is pulled in the vertical direction by the pair of upper and lower flanges, and therefore only a tensile load acts on it, so the connecting plate does not require as much bending strength as the side sill outer and inner. From this perspective, by configuring the connecting plate so that its bending strength is lower than the bending strength of the side sill outer and inner, it is possible to manufacture the connecting plate from a thin, inexpensive material while achieving reliable buckling of the side sill.

[0024] In the above vehicle lower body structure, the compression side region is preferably formed by joining two plate members.

[0025] According to this configuration, the compression side area of ​​the side portion of the side sill outer is formed by joining two plate materials, so that a buckling side sill can be easily manufactured by joining two plate materials in the side sill outer.

[0026] In the above-described vehicle underbody structure, the side sill outer may be configured so that the plate thickness of the compression side region is greater than the plate thickness of the tension side region.

[0027] With this configuration, the side sill outer is configured so that the plate thickness in the compression side region is greater than the plate thickness in the tension side region, so that a buckling side sill can be easily manufactured by integrally forming the side sill outer.

[0028] In the above-described vehicle lower body structure, it is preferable that the bent portions of the pair of side surfaces are arranged at equal distances from the compression surface portion.

[0029] With this configuration, when a bending load is input to the frame member during a vehicle collision, the bent portions of the pair of side surfaces can be displaced inward simultaneously, allowing the side sill to reliably buckle at the respective bent portions of the pair of side surfaces. [Effects of the Invention]

[0030] As described above, according to the vehicle lower body structure of the present invention, when a bending load is input to a skeletal member during a vehicle collision, the skeletal member can absorb impact by suppressing bending deformation and reliably buckling. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a perspective view showing the overall configuration of a vehicle body including an underbody structure for a vehicle according to an embodiment of the present invention; [Figure 2] FIG. 2 is an enlarged plan view showing the arrangement of the side sill, cross member, and hinge pillar of FIG. 1. [Figure 3] FIG. 2 is an enlarged perspective view showing the arrangement of the side sill, cross member, and hinge pillar of FIG. 1. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2. [Figure 5] FIG. 5 is a cross-sectional view of the side sill of FIG. 4. [Figure 6] 5(a) to 5(d) are cross-sectional explanatory views showing the deformation process of a side sill during a vehicle side collision. [Figure 7] 1 is a cross-sectional view of a typical side sill as a comparative example of the present invention. [Figure 8] 6 is a graph showing changes over time in the bending moment of the side sill in this embodiment and a comparative example. [Figure 9] 6 is a graph showing the change over time in the torsional moment of the side sill in this embodiment and in a comparative example. [Figure 10] FIG. 10 is a diagram showing a test vertical plate for examining the position of a bent portion. [Figure 11]10 is a graph showing the change in the buckling strength ratio when the ratio of the distance from the top end of the vertical plate to the bent portion to the total height of the vertical plate is changed. DETAILED DESCRIPTION OF THE INVENTION

[0032] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle underbody structure according to an embodiment of the present invention will be described in detail below with reference to the drawings.

[0033] As shown in FIGS. 1 to 4 , a vehicle body 1 to which an underbody structure for a vehicle according to an embodiment of the present invention is applied includes, as skeletal members constituting the framework of the vehicle body 1, a pair of side sills 2 extending in the vehicle longitudinal direction X at positions spaced apart on both sides of the vehicle width direction Y, and a cross member 3 extending in the vehicle width direction Y and connecting the pair of side sills 2. Furthermore, on both sides of the vehicle width direction Y, other skeletal members are provided, extending upward from the side sills 2 in the vehicle longitudinal direction X in this order, as pillars spaced apart from one another. The side sills 2 of this embodiment extend in the vehicle longitudinal direction X between the hinge pillars 4 and the rear pillar 6. Furthermore, a front pillar 7 is provided, extending from the upper end of the hinge pillar 4 toward the upper end of the center pillar 5, one spaced apart rearward X2 of the vehicle. The side sills 2, the hinge pillars 4, the center pillars 5, and the front pillars 7 form a door opening 8 at the front of the vehicle. A door (not shown) is attached to the door opening 8 (specifically, the portion of the hinge pillar 4 that forms the door opening 8) so as to be able to be opened and closed freely. In addition, a floor panel 9 that forms the floor of the vehicle body 1 is provided between the pair of side sills 2.

[0034] As shown in Figures 4 and 5, the side sill 2 is a generally cylindrical member that extends in the vehicle fore-and-aft direction X on both sides of the vehicle body 1 and has a closed cross-section C, and has a pair of flange portions 23 and a pair of flange portions 33, which will be described later, that protrude upward Z1 and downward Z1, respectively.

[0035] The side sill 2, which is a skeletal member of the vehicle body 1, comprises a first part, a side sill outer 11, a second part, a side sill inner 12, which is located on the inner side Y2 in the vehicle width direction relative to the side sill outer 11, and a connecting plate part 14 sandwiched between the side sill outer 11 and the side sill inner 12.

[0036] The side sill outer 11 is made up of two plates such as steel (main plate 20 and patch 13), and the side sill inner 12 and the connecting plate portion 14 are made up of one plate such as steel.

[0037] The side sill outer 11 has a pair of upper and lower flange portions 23 and is a member that constitutes the outer side Y1 of the side sill 2 in the vehicle width direction. The side sill inner 12 has a pair of upper and lower flange portions 33 and is a member that constitutes the inner side Y2 of the side sill 2 in the vehicle width direction.

[0038] The side sill 2 is formed by joining the flange portion 23 of the side sill outer 11 and the flange portion 33 of the side sill inner 12. That is, the closed cross section C of the side sill 2 is formed by the side sill outer 11 and the side sill inner 12, which extend in the same direction (the vehicle longitudinal direction X in this embodiment), cooperating with each other (specifically, joining together).

[0039] The following provides a more detailed description of the configuration of the side sill outer 11. As shown in Figures 4 and 5, the side sill outer 11 of this embodiment is formed by joining together a main plate material 20, which is two plate materials made of steel or the like, and a patch 13, and then press-forming the main plate material 20 into a hat-shaped cross section (i.e., a shape having a pair of flange portions 23).

[0040] Specifically, the side sill outer 11 is a vertical wall extending in the vertical direction Z and includes a compression surface portion 21 in which compressive stress is generated when a bending load B (see Figure 1) that bends the side sill 2 toward the inside of the vehicle is input to the side sill 2 during a vehicle side collision (when an obstacle or the like collides with the vehicle from the outside to the side of the vehicle), a pair of side surface portions 22 that extend from both ends of the compression surface portion 21 to the inside Y2 in the vehicle width direction so as to spread in the vertical direction Z toward the side sill inner 12, and a pair of flange portions 23 that extend upward Z1 and downward Z2 from the ends of the pair of side surface portions 22 on the inside Y2 in the vehicle width direction, respectively.

[0041] Each of the pair of side surface portions 22 includes a first bent portion 24 formed by bending the side surface portion 22 toward the inside of the side sill 2, a compression-side region 25 that starts from the first bent portion 24 and is located closer to the compression surface portion 21 than the first bent portion 24, and in which compressive stress occurs when a bending load B is input, and a tension-side region 26 that starts from the first bent portion 24 and is located away from the compression surface portion 21 than the first bent portion 24, and in which tensile stress occurs when a bending load B is input. The first bent portion 24 corresponds to the bent portion of the present invention.

[0042] The first bent portion 24 is formed by bending the side surface portion 22 (specifically, the portion corresponding to the side surface portion 22 of the main plate material 20) toward the inside of the side sill 2.

[0043] The compression-side region 25 is configured to have higher rigidity than the tension-side region 26 against a bending load B that compresses the compression surface portion 21. In this embodiment, the compression-side region 25 is configured by joining two plate materials (the main plate material 20 and the patch 13). The patch 13 shown in FIG. 5 is joined to the inside of the main plate material 20. The patch 13 has a main body portion 13a and a pair of side portions 13b formed by bending both side portions of the main body portion 13a. The main body portion 13a is joined to the compression surface portion 21, and the side portions 13b are joined to the compression-side region 25. The positions of the tips of the side portions 13b coincide with the positions of the first bent portions 24. As a result, the compression surface portion 21 of the side sill outer 11 and the compression-side region 25 of the pair of side surface portions 22 have high rigidity, while the tension-side region 26, where the patch 13 is not present, has low rigidity.

[0044] Furthermore, in the side surface portion 22 of this embodiment, the compression-side region 25 is formed by joining the main plate material 20 and the patch 13, and the tension-side region 26 is formed only by the main plate material 20. As a result, the side surface portion 22 is configured so that the rigidity of the side surface portion 22 changes discontinuously from the rigidity of the compression-side region 25 to the rigidity of the tension-side region 26, with the first bent portion 24 as the boundary. In other words, the compression-side region 25 and the tension-side region 26 of this embodiment each have a uniform rigidity, but are configured so that the rigidity of the compression-side region 25 and the rigidity of the tension-side region 26 change abruptly at the first bent portion 24.

[0045] The patch 13 may be joined to either the outer surface Y1 or the inner surface Y2 of the main plate material 20 in the vehicle width direction, but joining it to the outer surface Y1 of the main plate material 20 in the vehicle width direction is preferable because this makes the compression side region 25 less likely to be crushed (deformed) in the event of a vehicle collision.

[0046] In this embodiment, as described above, the side surface portion 22 has a configuration in which the high-rigidity compression-side region 25 and the low-rigidity tension-side region 26 change discontinuously with the first bent portion 24 as a boundary, so that when a bending load B is input to the side sill 2 during a vehicle collision, the side sill 2 is likely to buckle at the first bent portion 24. Therefore, as shown in Fig. 5, the side sill 2 can reliably buckle even if the angle θ between the extension line of the compression-side region 25 at the first bent portion 24 and the tension-side region 16 is set to 30 degrees or less.

[0047] Next, a detailed description will be given of the configuration of the side sill inner 12. As shown in Figures 4 and 5, the side sill inner 12 is formed by press-forming a single sheet of steel or other plate material into a hat-shaped cross section (i.e., a shape having a pair of flange portions 23).

[0048] Specifically, the side sill inner 12 comprises a tensile surface portion 31 which is a vertical wall extending in the vertical direction Z and in which tensile stress is generated when a bending load B (see Figure 1) is input to the side sill 2, a pair of side surface portions 32 (i.e., an upper side surface portion 32A and a lower side surface portion 32B) which extend from both ends of the tensile surface portion 31 to the outer side Y1 in the vehicle width direction so as to widen in the vertical direction Z toward the side sill outer 11, and a pair of flange portions 33 which extend upward Z1 and downward Z2 from the ends of the pair of side surface portions 32 on the outer side Y1 in the vehicle width direction, respectively.

[0049] 3 and 5, a bead 31a for reinforcing the side sill inner panel 12 is provided near the middle of the tensile surface portion 31 in the up-down direction Z so as to extend in the extension direction of the side sill inner panel 12 (i.e., the vehicle front-rear direction X). The bead 31a is formed by recessing the middle of the tensile surface portion 31 inward of the side sill 2 (outward in the vehicle width direction Y1). As shown in FIG. 3, the bead 31a in this embodiment extends from the vehicle front side X1 end 2b of the side sill 2 (the connection portion with the hinge pillar 4) to a position E of the vehicle rear side X2 end of the cross member 3.

[0050] Each of the pair of side surface portions 32 (i.e., the upper side surface portion 32A and the lower side surface portion 32B) has a second bent portion 34 formed by bending toward the inside of the side sill 2, and two surfaces extending in the vehicle width direction Y (see the surfaces indicated by the reference numerals 35, 37, 38, and 40 in FIG. 5). In other words, the side surface portion 32 has a substantially stepped cross section with two steps.

[0051] Specifically, of the pair of side surface portions 32, the upper side surface portion 32A comprises a first upper surface portion 35 extending in the vehicle width direction Y, an upper inclined surface portion 36 extending from the vehicle width inner Y2 end portion 35a of the first upper surface portion 35 to the vehicle width inner Y2 and downward Z2, and a second upper surface portion 37 extending from the vehicle width inner Y2 end portion of the upper inclined surface portion 36 to the vehicle width inner Y2 while forming the second bent portion 34.

[0052] The lower side surface portion 32B also includes a first lower surface portion 38 extending in the vehicle width direction Y at a position spaced downward from the first upper surface portion 35, a lower inclined surface portion 39 extending from an inner Y2 end portion 38a of the first lower surface portion 38 toward the inner Y2 and upper Z1 sides in the vehicle width direction, and a second lower surface portion 40 extending from the inner Y2 end portion of the lower inclined surface portion 39 toward the inner Y2 side in the vehicle width direction while forming the second bent portion 34. The lower side surface portion 32B has a shape that is axisymmetrical to the upper side surface portion 32A. Therefore, in the vehicle width direction Y, the first lower surface portion 38 has the same width as the first upper surface portion 35, the lower inclined surface portion 39 has the same width and inclination angle as the upper inclined surface portion 36, and the second lower surface portion 40 has the same width as the second upper surface portion 37.

[0053] That is, the side sill inner 12 is configured to have a pair of upper and lower second bending portions 34 that bend toward the inside of the cross section of the side sill 2 between the second upper surface portion 37 and the upper inclined surface portion 36, and between the second lower surface portion 40 and the lower inclined surface portion 39.

[0054] The tensile surface portion 31 extends in the up-down direction Z and connects the vehicle width direction inner Y2 ends of the second upper surface portion 37 and the second lower surface portion 40 to each other.

[0055] As shown in FIGS. 3 and 4 , an end of the cross member 3 extending in the vehicle width direction Y is joined to the side sill inner panel 12. The cross member 3 has three flange portions, a first flange portion 41, a second flange portion 42, and a third flange portion 43, joined to the side sill inner panel 12 at its end. The first flange portion 41 extends from the upper surface of the cross member 3 toward the outer side in the vehicle width direction Y1 and is joined to the second upper surface portion 37 of the side sill inner panel 12. The second flange portion 42 extends in the vehicle fore-and-aft direction X from the outer edge in the vehicle width direction Y1 of the side surface of the cross member 3 (the surface facing the vehicle fore-and-aft direction X) and is joined to the tensile surface portion 31 of the side sill inner panel 12. The third flange portion 43 extends upward Z1 (i.e., toward the interior of the cross member 3) from the outer edge in the vehicle width direction Y1 of the bottom wall portion of the cross member 3 and is joined to the tensile surface portion 31.

[0056] As shown in FIG. 5, in the side sill 2 of this embodiment, the width L2 of the compression side region 25 in the predetermined direction (vehicle width direction Y) in which the side sill outer 11 and the side sill inner 12 are aligned is set to be ¼ or less of the overall width L1 of the side sill 2 in the predetermined direction (vehicle width direction Y). This ensures that the side sill 2 can buckle reliably at the first bend portion 24 when a bending load B is input during a vehicle side collision or the like.

[0057] Furthermore, as shown in FIG. 5, the width L3 of the second upper surface portion 37 and the second lower surface portion 40 in the predetermined direction (vehicle width direction Y) in which the side sill outer 11 and the side sill inner 12 are aligned is set to be 1 / 4 or less of the overall width L1 of the side sill 2 in the predetermined direction (vehicle width direction Y). Therefore, when a bending load B is input during a vehicle side collision or the like, buckling at the second upper surface portion 37 and the second lower surface portion 40 is suppressed, and the side sill 2 can reliably buckle at the second bent portion 34.

[0058] Also, as shown in Figure 5, the flange portions 23, 33 (particularly the flange portions 23, 33 protruding upward Z1) of the side sill outer 11 and the side sill inner 12 are the reference for the position of the door opening 8 in Figure 1 (position in the vehicle width direction Y), but are positioned outside the cross-sectional center O of the side sill 2 in the vehicle width direction Y1, making it possible to ensure space inside the vehicle.

[0059] As shown in Figures 4 and 5, the connecting plate portion 14 is sandwiched between a pair of upper and lower flange portions 23 of the side sill outer 11 and a pair of upper and lower flange portions 33 of the side sill inner 12, connecting the pair of upper and lower flange portions 23 and the pair of upper and lower flange portions 33.

[0060] The connecting plate portion 14 can be installed at any position inside the side sill 2 in the vehicle longitudinal direction X. However, as shown in FIG. 1, it is preferable that the connecting plate portion 14 is arranged to reinforce a portion 2a of the side sill 2 that forms the door opening 8 of the vehicle body 1 in the vehicle longitudinal direction X and promote buckling at that portion 2a.

[0061] The connecting plate portion 14 has a configuration in which the bending strength of the connecting plate portion 14 is smaller than the bending strength of the side sill outer 11 and the side sill inner 12. Specifically, the connecting plate portion 14 is made of a plate material that is thinner than the main plate material 20 and the patch 13 that constitute the side sill outer 11, and the plate material that constitutes the side sill inner 12.

[0062] The first bent portions 24 of the pair of side surface portions 22 are arranged so as to be equidistant from the compressed surface portion 21. That is, in this configuration, the first bent portions 24 of the side sill outer 11 are positioned symmetrically in the up-down direction.

[0063] (Side sill 2 deformation process) Next, with reference to FIGS. 6(a) to 6(d), the deformation process when the side sill 2 configured as described above receives a bending load B during a vehicle side collision will be shown.

[0064] 6(a), during a vehicle side collision, that is, when an obstacle S collides with the side sill 2 from the outer side Y1 in the vehicle width direction toward the inner side Y2 in the vehicle width direction, a collision load is input from the side to the side sill 2. As a result, as shown in FIG. 1, a bending load B that bends the side sill 2 toward the interior of the vehicle is input to the side sill 2, which is fixed at both ends in the vehicle fore-and-aft direction X by vehicle body components such as the hinge pillar 4 and the center pillar 5.

[0065] 6(b), in the initial state of a vehicle side collision, when a compressive stress acts on the compressed surface portion 21 of the side sill outer 11 of the side sill 2, the compressed surface portion 21 attempts to move toward the side sill inner 12 (the vehicle width direction inner side Y2), and in the pair of side surface portions 22 of the side sill outer 11, a compressive stress acts in a compressed-side region 25 and a tensile stress acts in a tension-side region 26, with the first bent portion 24 as the boundary. Because the compressed-side region 25 having the patch 13 of the side surface portion 22 has higher rigidity than the tension-side region 26, even if the first bent portion 24 is at a small angle (30 degrees or less), the first bent portion 24 is encouraged (induced) to move toward the inside of the side sill 2.

[0066] As the first bent portion 24 moves inward of the side sill 2, the tension-side region 26 undergoes tensile deformation inward of the side sill 2, causing the first bent portion 24 to displace inward of the side sill 2 and buckle the side sill 2. At this time, while the first bent portion 24 is displacing inward of the side sill 2, the high-rigidity compression-side region 25 of each of the pair of side surface portions 22 becomes substantially parallel to the direction of the collision load (i.e., the direction in which the compression surface portion 21 moves toward the side sill inner panel 12, specifically the vehicle width direction Y) during the deformation process. Therefore, the compression-side region 25 generates a high reaction force against the bending load B. Furthermore, during this compression, the connecting plate portion 14 suppresses the vertical movement of the upper and lower flange portions 23, 33 of the side sill 2 away from each other, generating a high reaction force against the bending load B.

[0067] These reaction forces are shown in the graph of Figure 8, where the bending moment M BThe graph in Figure 8 shows the bending moment M that occurs in the side sill as a reaction force. B 8 shows the change over time of the bending moment in the side sill 2 of this embodiment, and curve II shows the change over time of the bending moment in the conventional side sill 50 shown in FIG. 7 as a comparative example. The conventional side sill 50 shown in FIG. 7 is composed of a side sill outer 51 and a side sill inner 52 of the same plate thickness, and has a structure in which a pair of flange portions 51a of the side sill outer 51 and a pair of flange portions 52a of the side sill inner 52 are joined together. This side sill 50 does not have the first bent portion 24 and the second bent portion 34 that could trigger buckling, as in this embodiment.

[0068] 6(b), corresponds to time t1 in the graph of FIG. 8, and at this time, curve I indicates that a high bending moment is generated as a reaction force of the side sill 2. On the other hand, curve II at time t1 indicates that only a low bending moment is generated as a reaction force of the conventional side sill 50.

[0069] 6(c), as time progresses further after the start of the vehicle side collision, the deformation of the side sill outer panel 11 and the deformation of the side sill inner panel 12 progress. During the deformation process of the side sill inner panel 12, the ends (the pair of flange portions 33 and their surrounding areas) of the pair of side surface portions 32 (the upper side surface portion 32A and the lower side surface portion 32B) of the side sill inner panel 12 on the outer side Y1 in the vehicle width direction are extended upward Z1 and downward Z2, respectively, and the first and second upper surface portions 35, 37 and the first and second lower surface portions 38, 40 of the side sill inner panel 12 attempt to deform so as to bulge outward in the cross section of the side sill 2. However, at the same time, the second bent portions 34 of the pair of side surface portions 32 of the side sill inner 12 tend to displace outward in the cross section of the side sill 2, so that the first and second upper surface portions 35, 37 and the first and second lower surface portions 38, 40 can maintain a state that is approximately parallel to the direction of the collision load (i.e., the direction in which the compressed surface portion 21 moves toward the side sill inner 12, specifically the vehicle width direction Y). Therefore, the first and second upper surface portions 35, 37 and the first and second lower surface portions 38, 40 of the side sill inner 12 can support the side sill outer 11 during deformation and generate a higher reaction force, making it possible to suppress bending deformation of the side sill 2.

[0070] The reaction force of the side sill inner 12 is also clear from the height of the bending moment at time t2 of curve I in the graph of Fig. 8. That is, when the side sill 2 of this embodiment reaches the state shown in Fig. 6(c), this corresponds to time t2 in the graph of Fig. 8, and at this time, curve I indicates that a high bending moment is maintained as the reaction force of the side sill 2. From curve I, it can be seen that not only the side sill outer 11 has the first bent portion 24 but also the side sill inner 12 has the second bent portion 34, which effectively suppresses buckling of the side sill 2 toward the inner side Y2 in the vehicle width direction, thereby maintaining the reaction force of the side sill 2.

[0071] On the other hand, curve II at time t2 shows that the bending moment as a reaction force of the conventional side sill 50 reaches only a lower level than curve I.

[0072] Furthermore, as shown in Figure 6(d), as time progresses after the start of the vehicle side collision, the second bent portion 34 of the side sill inner 12 moves outward from the side sill 2, causing the side sill inner 12 to deform and protrude outward, generating a reaction force.

[0073] The state of the side sill 2 of this embodiment in Fig. 6(d) corresponds to time t3 in the graph of Fig. 8. At time t3, curve I shows that the bending moment as the reaction force of the side sill 2 gradually decreases, but the decrease in reaction force is suppressed, and the reaction force is maintained at a level that is sufficiently higher than that of the conventional side sill 50, shown by curve II.

[0074] (Regarding twisting of side sill 2) In the bending deformation of the side sill 2 described above, we looked at the reaction force as a bending moment when a bending load B is applied to the side sill 2 during a vehicle side collision. However, the side sill 2 of this embodiment, by having the first bent portion 24 and the second bent portion 34 as described above, is capable of generating a high reaction force even when a torsional moment acts around an axis extending in the vehicle fore-and-aft direction X.

[0075] The graph of FIG. 9 shows the torsional moment M T The time variation of the torsional moment M in the conventional side sill 50 of FIG. T The change over time in this relationship is shown by curve IV. As is clear from the graph in Fig. 9, the side sill 2 of this embodiment (curve III) and the conventional side sill 50 (curve IV) generate similar levels of torsional moment as a reaction force in the early stage when the torsional moment starts to be input, but after that, the side sill 2 of this embodiment maintains a higher torsional moment as a reaction force than the conventional side sill 50.

[0076] (Features of this embodiment) (1) The lower body structure of the vehicle of this embodiment is a structure in which the width dimension of a pair of upper and lower side portions 22 of the side sill outer 11 which cooperate with the side sill inner 12 to form the closed cross section C of the side sill 2 cannot be secured, and in order to solve the problem of displacing the first bent portion 24 of the pair of side portions 22 toward the inside of the cross section during a side collision of the vehicle, so as to ensure buckling of the side sill 2, a rigidity difference is provided with the first bent portion 24 of the side portion 22 of the side sill outer 11 as a boundary so that the compression side region 25 of the side portion 22 of the side sill outer 11 has high rigidity, and this acts as a trigger for buckling, making it easier for the side sill 2 to buckle at the first bent portion 24.

[0077] 5, the side sill outer 11 includes a compression surface portion 21 where a compressive stress occurs when a bending load B is input to the side sill 2, and a pair of side surface portions 22 extending from both ends of the compression surface portion 21 toward the side sill inner 12. The side surface portions 22 include first bent portions 24 formed by bending the side surface portions 22 toward the inside of the side sill 2.

[0078] With this configuration, when a bending load B is input to the side sill 2 during a vehicle collision, as shown in Figure 6 (b), a compressive stress acts on the compression surface portion 21 of the side sill outer 11, causing the compression surface portion 21 to move toward the side sill inner 12, and at the pair of side surface portions 22 of the side sill outer 11, the first bent portions 24 that are bent toward the inside of the side sill 2 tend to move toward the inside of the side sill 2.

[0079] Moreover, in the configuration of this side sill outer 11, each side surface portion 22 includes a compression-side region 25 that starts from the first bent portion 24 and is located closer to the compression surface portion 21 than the first bent portion 24, and a tension-side region 26 that starts from the first bent portion 24 and is located away from the compression surface portion 21 than the first bent portion 24, and furthermore, the compression-side region 25 is configured to have higher rigidity than the tension-side region 26 against a bending load B that compresses the compression surface portion 21. In other words, the side surface portion 22 is configured so that the rigidity of the side surface portion 22 changes discontinuously from the rigidity of the compression-side region 25 to the rigidity of the tension-side region 26, with the first bent portion 24 as the boundary. Therefore, during a vehicle collision, as shown in FIG. 6( b), as the first bent portion 24 moves inward of the side sill 2, the tension-side region 26 undergoes tensile deformation inward of the side sill 2, causing the first bent portion 24 to displace inward of the side sill 2 and buckle. During the process of the first bent portion 24 displacing inward of the side sill 2, the high-rigidity compression-side region 25 of each of the pair of side surface portions 22 becomes substantially parallel to the direction in which the compression surface portion 21 moves toward the side sill inner panel 12 during the deformation process. Therefore, the compression-side region 25 generates a high reaction force against the bending load B, thereby suppressing bending deformation of the side sill 2. As a result, when bending load B is input to the side sill 2 during a vehicle collision, the side sill 2 can absorb impact by suppressing bending deformation and reliably buckling.

[0080] (2) In the vehicle lower body structure of this embodiment, the angle θ between the extension line of the compression-side region 25 of the first bent portion 24 and the tension-side region 26 is set to 30 degrees or less. With this configuration, even when the first bent portion 24 is formed at a small angle θ of 30 degrees or less as described above, the tension-side region 26 is configured to have lower rigidity than the compression-side region 25. Therefore, during a vehicle collision, the tension-side region 26 is tensile-deformed inward of the side sill 2, while the first bent portion 24 is displaced inward of the side sill 2, thereby reliably causing buckling of the side sill 2.

[0081] In other words, in the side sill 2 of this embodiment, even if the width dimension of the pair of upper and lower side portions 22 of the side sill outer 11 cannot be secured and the angle θ of the first bent portion 24 of the side sill outer 11 cannot be sufficiently secured, the side sill 2 can reliably buckle while displacing the first bent portion 24 of the pair of side portions 22 inward in the cross section during a vehicle side collision.

[0082] (3) In the lower body structure of the vehicle of this embodiment, the width L2 of the compression side region 25 in a predetermined direction (vehicle width direction Y) in which the side sill outer 11 and the side sill inner 12 are aligned is set to be 1 / 4 or less of the overall width L1 of the side sill 2 in that predetermined direction (vehicle width direction Y).

[0083] With this configuration, in the event of a vehicle collision, buckling of the side sill 2 within the compression side region 25 of the side portion 22 of the side sill outer 11 is suppressed, while the side sill 2 is able to bend reliably at the first bending portion 24, which is the boundary between the compression side region 25 and the tension side region 26 of the side portion 22, making it possible to generate a high reaction force at the side portion 22.

[0084] Here, the optimal position of the bent portion within the entire width of the side sill to promote buckling will be examined with reference to Figures 10 and 11. First, as shown in Figure 10, the entire width of the side sill in the vehicle width direction is considered as a model of a single vertical plate 61. The upper and lower ends of the vertical plate 61 are connected to and restrained by end plates 62 and 63.

[0085] In order to approach the full plastic moment, which is the full potential of the vertical plate 61 and serves as an index of the ideal buckling strength of the vertical plate 61, it is conceivable to provide a bent portion 64 in the vertical plate 61 as a shape change point (i.e., a point at which the vertical plate 61 buckles). Using a model in which the vertical plate 61 buckles and bends at the bent portion 64 when a vertical bending load acts on the vertical plate 61, as shown in FIG. 10, a computer simulation was performed to determine the buckling strength ratio R, which serves as an index of the magnitude of the reaction force of the vertical plate 61 when the bent portion 64 is provided at a position a distance b' from the upper end of the vertical plate 61 within the total height b of the vertical plate 61. As a result, the relationship between the ratio b' / b of the distance b' to the total height b of the vertical plate 61 and the buckling strength ratio R (the ratio to the ideal buckling strength) is shown in the graph of FIG. 11. It can be seen that the buckling strength is maximized when the bent portion 64 is provided at a height of 1 / 4 of the total height b of the vertical plate 61.

[0086] From these results, it is believed that the buckling resistance will be highest if the position of the first bent portion 24 of the side sill 2 is a distance of 1 / 4 × L1 from the compression surface portion 21 with respect to the overall width L1 of the side sill 2. Based on these verification results, it is concluded that if the width L2 of the compression-side region 25 is set to be 1 / 4 or less of the overall width L1 of the side sill 2 in the specified direction (vehicle width direction Y) as described above, buckling of the side sill 2 within the compression-side region 25 will be suppressed, while the side sill 2 will be able to bend reliably at the first bent portion 24, which is the boundary between the compression-side region 25 and the tension-side region 26 in the side surface portion 22, and a high reaction force will be generated in the side surface portion 22.

[0087] (4) In the vehicle underbody structure of this embodiment, the framework members are side sills 2 that extend in the vehicle longitudinal direction X on both sides of the vehicle body 1 and have a closed cross section C. Of the two parts that make up the framework member, the first part is a side sill outer 11 that has a pair of upper and lower flange portions 23 and that constitutes the portion of the side sill 2 on the outer side Y1 in the vehicle width direction. Of the two parts that make up the framework member, the second part is a side sill inner 12 that has a pair of upper and lower flange portions 33 and that constitutes the portion of the side sill 2 on the inner side Y2 in the vehicle width direction. The side sill 2 is constituted by joining the pair of flange portions 23 of the side sill outer 11 and the pair of flange portions 33 of the side sill inner 12.

[0088] 5, in the configuration of this embodiment, the flange portions 23, 33 of the side sill outer 11 and the side sill inner 12 that constitute the side sill 2 are disposed on the outer side Y1 in the vehicle width direction from the cross-sectional center O of the side sill 2, which makes it easier to position the door opening 8 of the vehicle body 1, defined by these flange portions 23, 33, on the outer side Y1 in the vehicle width direction, making it easier to ensure space within the vehicle cabin. Therefore, it is possible to ensure space within the vehicle cabin while suppressing bending deformation of the side sill 2 and maintaining impact absorption performance.

[0089] (5) In the vehicle underbody structure of this embodiment, the side sill 2 includes a connecting plate portion 14. The connecting plate portion 14 is sandwiched between the pair of upper and lower flange portions 23, 33 of the side sill outer panel 11 and the side sill inner panel 12, connecting the pair of upper and lower flange portions 23 and the pair of upper and lower flange portions 33. Therefore, even if the pair of upper and lower flange portions 23, 33 attempt to displace in a direction separating vertically during bending deformation of the side sill 2 in the event of a vehicle collision, the connecting plate portion 14 prevents the pair of upper and lower flange portions 23, 33 from displacing in the vertical direction Z (i.e., the pair of flange portions 23 (and the pair of flange portions 33) from separating from each other in the vertical direction Z). This allows the side sill 2 to reliably buckle at the first bent portion 24.

[0090] (6) In the vehicle lower body structure of this embodiment, the connecting plate portion 14 is arranged in the side sill 2 in the vehicle longitudinal direction X at a portion 2a (see FIG. 1) that constitutes the door opening 8 of the vehicle body 1. The door opening 8 of the vehicle body 1 is an area where there are no pillars extending in the vertical direction Z, and where the support rigidity of the side sill 2 is weak. However, because the connecting plate portion 14 is arranged in the side sill 2 at the portion 2a that constitutes the door opening 8 as described above, the side sill 2 can reliably buckle at the first bent portion 24, even in an area where there are no pillars.

[0091] (7) In the vehicle underbody structure of this embodiment, the connecting plate portion 14 is configured so that its bending strength is lower than that of the side sill outer 11 and the side sill inner 12. During a vehicle collision, the connecting plate portion 14 is pulled in the vertical direction by the pair of upper and lower flange portions 23, 23, 33, 33, and only a tensile load acts on the connecting plate portion 14. Therefore, the connecting plate portion 14 does not require as much bending strength as the side sill outer 11 and the side sill inner. From this perspective, by configuring the connecting plate portion 14 so that its bending strength is lower than that of the side sill outer 11 and the side sill inner 12, it becomes possible to manufacture the connecting plate portion 14 from a thin, inexpensive material while achieving reliable buckling of the side sill 2.

[0092] (8) In the vehicle lower body structure of this embodiment, the compression side region 25 of the side sill outer 11 is formed by joining two plate materials, namely, the main plate material 20 and the patch 13. According to this configuration, since the compression side region 25 of the side surface portion 22 of the side sill outer 11 is formed by joining two plate materials, it is possible to easily manufacture a buckling side sill 2 by joining the two plate materials in the side sill outer 11.

[0093] (9) In the vehicle lower body structure of this embodiment, the first bent portions 24 of the pair of side surface portions 22 of the side sill outer panel 11 are arranged so as to be equidistant from the compression surface portion 21. With this configuration, when a bending load B is input to the side sill 2 during a vehicle collision, the first bent portions 24 of the pair of side surface portions 22 can be displaced inward simultaneously, and the side sill 2 can be reliably buckled at the locations of the first bent portions 24 of the pair of side surface portions 22.

[0094] (Variation) (A) In the side sill outer 11 of the above embodiment, the compression-side region 25 is formed by joining two plates, i.e., the main plate 20 and the patch 13, but the present invention is not limited to this. When the side sill outer 11 is formed from a single plate, the plate thickness of the compression-side region 25 may be configured to be greater than the plate thickness of the tension-side region 26. In this configuration, the integral formation of the side sill outer 11 makes it possible to easily manufacture a buckling side sill 2.

[0095] (B) The side sill 2 in the above embodiment is configured by joining the side sill outer 11 and the side sill inner 12, which are separate members, as an example of the first and second portions working together to form the closed cross section C, but the present invention is not limited to this, and the side sill may be configured such that the side sill outer and the side sill inner corresponding to the first and second portions, respectively, are integrated. In this case, too, it is possible to achieve the same effects as the side sill 2 in the above embodiment.

[0096] (C) In the above embodiment, the side sill 2 is shown as an example of a frame member to which the present invention is applied, but the present invention is not limited thereto. The technology of the present invention can be applied to any frame member constituting the vehicle body that is subjected to a bending load during a vehicle collision. For example, frame members to which the present invention is applied include not only the side sills described above, but also cross members 3, dash cross members, floor frames, and rear frames that extend in the vehicle width direction Y. For example, in the case of the cross member 3, the upper surface of the member (upper member) constituting the upper side of the cross member 3 is the compression surface portion, and the portions of the upper surface extending downward from both ends in the vehicle front-rear direction X are the pair of side surface portions. [Explanation of symbols]

[0097] 1. Body 2 Side sill (framework) 3 Cross member (framework member) 8 Door Opening 11 Side sill outer (first part) 12 Side sill inner (second part) 13 Patch 14 Connecting plate part 20 Main plate material 21 Compression surface 22 Side part 23 Flange 24 1st bending part (bending part) 25 Compression side region 26 Tension side region 31 Tensile surface 31a Bead 32 Side part 33 Flange 34 2nd bending part 35 1st top section 36 Upper slope section 37 Second top section 38 1st bottom part 39 Lower slope section 40 Second bottom part

Claims

1. A vehicle underbody structure including a framework member having a first portion and a second portion extending in the same direction and cooperating to form a closed cross section, The first portion is a compression surface portion in which a compressive stress occurs when a bending load is input to the framework member; a pair of side surfaces extending from both ends of the compression surface portion toward the second portion; Equipped with The pair of side surfaces each include: a bent portion formed by bending the side surface portion toward the inside of the framework member; a compression side region that is located on the compression surface portion side of the bent portion from the bent portion as a starting point and in which a compressive stress occurs when the bending load is input; a tension side region that is located on a side away from the compression surface portion from the bent portion as a starting point and in which a tensile stress occurs when the bending load is input; Equipped with The entire compression-side region is configured to have higher rigidity than the tension-side region against the bending load that compresses the compression surface portion. A vehicle underbody structure characterized by:

2. 2. The vehicle underbody structure according to claim 1, The angle between the extension line of the compression-side region and the tension-side region in the bent portion is set to 30 degrees or less. A vehicle underbody structure characterized by:

3. 3. The vehicle underbody structure according to claim 2, a width of the compression-side region in a predetermined direction in which the first portion and the second portion are aligned is set to be ¼ or less of the total width of the framework member in the predetermined direction; A vehicle underbody structure characterized by:

4. 4. The vehicle underbody structure according to claim 3, the framework members are side sills that extend in the vehicle longitudinal direction on both sides of the vehicle body and have a closed cross section, the first portion is a side sill outer having a pair of upper and lower flange portions and constituting an outer portion of the side sill in the vehicle width direction, the second portion is a side sill inner having a pair of upper and lower flange portions and constituting an inner portion of the side sill in the vehicle width direction, The flange portion of the side sill outer and the flange portion of the side sill inner are joined to form the side sill, The flange portions of the side sill outer and the side sill inner are disposed outward in the vehicle width direction from the center of a cross section of the side sill. A vehicle underbody structure characterized by:

5. 5. The vehicle underbody structure according to claim 4, The side sill further includes a connecting plate portion that is sandwiched between the pair of upper and lower flange portions of the side sill outer and the pair of upper and lower flange portions of the side sill inner and connects the pair of upper and lower flange portions. A vehicle underbody structure characterized by:

6. 6. The vehicle underbody structure according to claim 5, The connecting plate portion is disposed in a portion of the side sill that defines a door opening of the vehicle body in the vehicle longitudinal direction. A vehicle underbody structure characterized by:

7. 7. The vehicle underbody structure according to claim 5 or 6, The connecting plate portion has a bending strength smaller than the bending strengths of the side sill outer and the side sill inner. A vehicle underbody structure characterized by:

8. The vehicle underbody structure according to any one of claims 1 to 6, The compression side region is formed by joining two plate materials. A vehicle underbody structure characterized by:

9. The vehicle underbody structure according to any one of claims 4 to 6, The side sill outer is configured so that the plate thickness of the compression side region is greater than the plate thickness of the tension side region. A vehicle underbody structure characterized by:

10. The vehicle underbody structure according to any one of claims 1 to 6, The bent portions of the pair of side surfaces are arranged so as to be equidistant from the compression surface portion. A vehicle underbody structure characterized by:

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