Vehicle lower body structure

Abstract

To provide a lower vehicle-body structure of a vehicle which can properly increase the bending resistance of a side sill without increasing its weight and manufacturing costs.SOLUTION: A side sill 2 constituting a vehicle, comprises a side sill outer 11 and a side sill inner 12. Each of an upper-side side face portion 22A (upper face portion) and a lower-side side face portion 22B (lower face portion) of the side sill outer 11 comprises a first bending portion bent 24 toward an inside of the side sill 2. The side sill inner 12 comprises: an upper-side side face portion 32A provided with a series of a first upper face portion 35, an upper-side slant face portion 36 and a second upper face portion 37, which are aligned in a vehicle width direction Y, and a lower-side side face portion 32B provided with a series of a first lower face portion 38, a lower-side slant face portion 39 and a second lower face portion 40, which are aligned in the vehicle width direction Y. The side sill inner 12 comprises a pair of upper-and-lower second bending portions 34 which are bent toward an inside of the side sill 2 at respective positions between the second upper face portion 36 and the upper-side slant face portion 37 and between the second lower face portion 40 and the lower-side slant face portion 39.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] In the above-described vehicle body structure, it is conceivable to adopt a structure that reduces the cross-sectional width of the side sill in order to secure space within the vehicle cabin. However, if the cross-sectional width of the side sill is reduced, the moment of inertia of the side sill will decrease, and there is a risk that it will not be able to generate sufficient bending strength (in other words, bending rigidity) to suppress deformation within the vehicle cabin when a side collision load is input to the side sill. Furthermore, if the side sill is reinforced to obtain sufficient bending strength (for example, by adding reinforcing members or increasing the thickness of the side sill), the weight and manufacturing costs of the side sill will increase.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a vehicle lower body structure that can increase the bending strength of the side sill without increasing the weight and manufacturing costs of the side sill. [Means for solving the problem]

[0008] In order to solve the above problems, the vehicle underbody structure of the present invention is a vehicle underbody structure including a side sill in which a side sill outer and a side sill inner each extending in the vehicle longitudinal direction cooperate to form a closed cross section, the side sill outer having an upper surface portion and a lower surface portion spaced downward from the upper surface portion, the upper surface portion and the lower surface portion each having a first bent portion formed by bending toward the inside of the side sill, and the side sill inner having a first upper surface portion extending in the vehicle width direction and an upper inclined surface extending inward and downward in the vehicle width direction from an inner end of the first upper surface portion a second upper surface portion extending inward in the vehicle width direction from the inner end of the upper inclined surface portion; a first lower surface portion extending in the vehicle width direction at a position spaced downward from the first upper surface portion; a lower inclined surface portion extending inward and upward in the vehicle width direction from the inner end of the first lower surface portion; and a second lower surface portion extending inward in the vehicle width direction from the inner end of the lower inclined surface portion, and further the side sill inner has a pair of upper and lower second bending portions that bend toward the inside of the cross section of the side sill between the second upper surface portion and the upper inclined surface portion, and between the second lower surface portion and the lower inclined surface portion.

[0009] With this configuration, when a collision load is applied to the side sill from the side during a vehicle side collision, the first bent portions of the upper and lower surfaces of the side sill outer are displaced toward the inside of the cross section of the side sill. Portions of the upper and lower surfaces outward of the first bent portions in the vehicle width direction become substantially parallel to the lateral force during deformation, causing a high reaction force to be generated and crushed in the vehicle width direction. During deformation of the side sill inner, the outer ends of the side sill inner are extended upward and downward, respectively, causing the first upper surface portion, second upper surface portion, first lower surface portion, and second lower surface portion of the side sill inner to deform and bulge outward of the cross section of the side sill. However, at the same time, the pair of upper and lower second bent portions of the side sill inner are displaced toward the outside of the cross section of the side sill, allowing the first upper surface portion, second upper surface portion, first lower surface portion, and second lower surface portion to maintain a substantially parallel state to the direction of the collision load. Therefore, the first upper surface portion, second upper surface portion, first lower surface portion, and second lower surface portion of the side sill inner support the side sill outer during deformation, generating a higher reaction force and suppressing bending deformation of the side sill. As a result, the side sill can generate a high resistance to a side collision load at both the side sill outer and side sill inner, and it is possible to increase the bending strength of the side sill without increasing its weight or manufacturing costs.

[0010] In the above-mentioned lower body structure of the vehicle, it is preferable that the width of the portion located outside the first bent portion in the vehicle width direction is set to be 1 / 4 or less of the total width of the side sill in the vehicle width direction.

[0011] With this configuration, in the event of a vehicle collision, buckling of the skeletal member at the portions of the upper and lower surfaces of the side sill outer that are located outside the first bend in the vehicle width direction is suppressed, while the upper and lower surfaces can be reliably bent at the first bend, making it possible to generate a high reaction force at the upper and lower surfaces.

[0012] In the above-described vehicle lower body structure, it is preferable that the width of the second upper surface portion and the second lower surface portion in the vehicle width direction is set to be 1 / 4 or less of the overall width of the side sill in the vehicle width direction.

[0013] With this configuration, when a bending load is input during a vehicle side collision or the like, buckling at the second upper surface portion and the second lower surface portion is suppressed, and the side sill can be reliably buckled at the second bent portion.

[0014] In the above-mentioned vehicle lower body structure, the upper surface portion and the lower surface portion of the side sill outer each have a first portion located outside the first bent portion in the vehicle width direction and a second portion located inside the first bent portion in the vehicle width direction, and the first portion is configured to have higher rigidity than the second portion, and it is preferable that the angle between the extension line of the first portion at the first bent portion and the second portion is set to 30 degrees or less.

[0015] In this configuration, the upper and lower surface portions of the side sill outer each include a first portion located outward in the vehicle width direction from the first bent portion and a second portion located inward in the vehicle width direction from the first bent portion, and the first portion is configured to have higher rigidity than the second portion. Therefore, even when the first bent portion is formed at a small angle of 30 degrees or less as described above, the second portion located inward in the vehicle width direction from the first bent portion on the upper and lower surface portions of the side sill outer is configured to have lower rigidity than the first portion located outward in the vehicle width direction. Therefore, during a vehicle collision, the second portion is tensilely deformed inward of the side sill, and the first bent portion is displaced inward of the side sill, ensuring buckling of the side sill.

[0016] In the above-mentioned vehicle lower body structure, each of the side sill outer and the side sill inner has a pair of upper and lower flange portions, and the flange portions of the side sill outer and the side sill inner are joined to form the closed cross section, and it is preferable that the flange portions 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 portion is sandwiched between the pair of upper and lower flange portions of the side sill outer and inner panels and connects the pair of upper and lower flange portions. Therefore, even if the pair of upper and lower flange portions attempt to displace vertically apart during bending deformation of the side sill during a vehicle collision, the connecting plate portion suppresses the vertical displacement of the pair of upper and lower flange portions. This allows the side sill to reliably buckle at the first bent portion and the second 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 first bend and the second bend.

[0022] In the above-mentioned vehicle lower body structure, it is preferable that the side sill inner has a vertical wall portion extending in the vertical direction at the inner end portion in the vehicle width direction and connecting the second upper surface portion and the second lower surface portion, and that the vertical wall portion has a bead portion extending in the vehicle fore-and-aft direction.

[0023] According to this configuration, the vertical wall portion of the side sill inner has a bead portion, which makes it possible to improve the rigidity of the side sill against bending deformation. [Effects of the Invention]

[0024] As described above, according to the vehicle underbody structure of the present invention, the bending strength of the side sill can be increased without increasing the weight and manufacturing costs of the side sill. [Brief explanation of the drawings]

[0025] [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

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The side sill 2, which is a skeletal member of the vehicle body 1, comprises a side sill outer 11, a side sill inner 12 located on the vehicle widthwise inner side Y2 of the side sill outer 11, and a connecting plate portion 14 sandwiched between the side sill outer 11 and the side sill inner 12.

[0030] 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.

[0031] 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.

[0032] 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).

[0033] 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).

[0034] Specifically, the side sill outer 11 includes a compression surface portion 21, which is a vertical wall extending in the up-down direction Z, and in which compressive stress is generated when a bending load B (see FIG. 1) that bends the side sill 2 toward the vehicle interior side is input to the side sill 2 during a vehicle side collision (when an obstacle or the like collides with the vehicle from the vehicle exterior side to the side), a pair of side surface portions 22, that is, an upper side surface portion 22A (upper surface portion) and a lower side surface portion 22B (lower surface portion), extending from both ends of the compression surface portion 21 toward the vehicle width direction inner side Y2 so as to widen in the up-down direction Z, and a pair of flange portions 23 extending upward Z1 and downward Z2 from the ends of the pair of side surface portions 22 on the vehicle width direction inner side Y2. The lower side surface portion 22B is located below the upper side surface portion 22A and spaced apart.

[0035] Each of the pair of side portions 22 (i.e., the upper side portion 22A and the lower side portion 22B) includes a first bent portion 24 formed by bending the side portion 22 toward the inside of the side sill 2, a compression side region 25 which is a first portion starting from the first bent portion 24 and 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 which is a second portion starting from the first bent portion 24 and located farther 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.

[0036] 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.

[0037] The compression-side region 25 (first portion) is configured to have higher rigidity than the tension-side region 26 (second portion) 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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).

[0042] Specifically, the side sill inner 12 comprises a tensile surface portion 31 (vertical wall portion) which is a vertical wall extending in the vertical direction Z at its end on the inner side Y2 of the vehicle width direction 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 of the vehicle width direction so as to spread 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, respectively, from the ends of the pair of side surface portions 32 on the outer side Y1 of the vehicle width direction.

[0043] 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 (vertical wall portion) 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 (outward in the vehicle width direction Y1) of the side sill 2. 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] As shown in FIG. 5, in the side sill 2 of this embodiment, the width L2 of the compression side region 25, which is the first portion located on the outer side Y1 in the vehicle width direction Y, is set to be ¼ or less of the overall width L1 of the side sill 2 in the vehicle width direction Y. This ensures that the side sill 2 can buckle reliably at the first bend 24 when a bending load B is input during a vehicle side collision or the like.

[0051] 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 vehicle width direction Y is set to be ¼ or less of the overall width L1 of the side sill 2 in the 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] (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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] These reaction forces are shown in the graph of Figure 8, where the bending moment M B The graph in Figure 8 shows the bending moment M that occurs in the side sill as a reaction force. B8 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] (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.

[0069] 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.

[0070] (Features of this embodiment) (1) The lower body structure of the vehicle of this embodiment has a structure in which the cross-sectional width of the side sill 2 is reduced to ensure interior space, but in order to obtain a high reaction force in the event of a vehicle collision, the side sill inner 12 has not only the first bent portion 24 of the side sill outer 11, but also a second bent portion 34 and four upper and lower surfaces (first upper surface portion 35, second upper surface portion 37, first lower surface portion 38, second lower surface portion 40) (i.e., four side walls) extending in the vehicle width direction Y.

[0071] In this configuration, when a collision load is input from the side to the side sill 2 during a vehicle side collision, the first bent portions 24 of the upper side surface portion 22A (upper surface portion) and the lower side surface portion 22B (lower surface portion) of the side sill outer panel 11 are displaced toward the inside of the cross section of the side sill 2. The compressed-side regions 25, which are first portions of the upper side surface portion 22A and the lower side surface portion 22B that are on the outer side Y1 in the vehicle width direction than the first bent portions 24, become substantially parallel to the lateral input during the deformation process, and are therefore crushed in the vehicle width direction Y while generating a high reaction force.

[0072] During this deformation of the side sill inner 12, the ends (the pair of flanges 33 and their surroundings) of the upper side surface portion 32A and the lower side surface portion 32B of the side sill inner 12 on the vehicle width direction outer side Y1 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 12 attempt to deform so as to bulge outward from the cross section of the side sill 2. However, at the same time, the second bent portions 34 of the upper side surface portion 32A and the lower side surface portion 32B of the side sill inner 12 attempt to displace outward from the cross section of the side sill 2, so that the first upper surface portion 35, the second upper surface portion 37, the first lower surface portion 38, and the second lower surface portion 40 can maintain a state substantially 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 support the side sill outer 11 during deformation, and can generate a higher reaction force, thereby suppressing bending deformation of the side sill 2.

[0073] Therefore, the side sill 2 can generate high resistance to side collision loads at both the side sill outer 11 and the side sill inner 12, and it is possible to increase the bending strength of the side sill 2 without increasing the weight and manufacturing costs of the side sill 2.

[0074] In other words, in the side sill 2 of this embodiment, the first and second upper surface portions 35, 37 and the first and second lower surface portions 38, 40 support the side sill outer panel 11 during deformation, and are able to generate a high reaction force. Note that if the side sill inner panel 12 simply has the second bent portions 34 provided on the upper side surface portion 32A (upper surface portion) and the lower side surface portion 32B (lower surface portion), i.e., if the upper side surface portion 32A and the lower side surface portion 32B simply have a dogleg-shaped cross section, during lateral input, there are few portions of the upper side surface portion 32A and the lower side surface portion 32B that are parallel to the input direction when the second bent portions 34 move outward of the side sill 2 (for example, only the second upper surface portion 37 and the second lower surface portion 40 located on the inner side Y2 of the side sill inner 12 in the vehicle width direction), and therefore a high reaction force cannot be generated.

[0075] (2) In the lower body structure of the vehicle of this embodiment, the width L2 of the compression side region 25, which is the first part located on the outer side Y1 of the vehicle width direction Y than the first bend portion 24, is set to be 1 / 4 or less of the total width L1 of the side sill 2 in the vehicle width direction Y.

[0076] With this configuration, in the event of a vehicle collision, buckling of the side sill 2 within the compression side region 25 of the upper side surface portion 22A (upper surface portion) and the lower side surface portion 22B (lower surface portion) 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 upper side surface portion 22A and the lower side surface portion 22B, making it possible to generate a high reaction force at the upper side surface portion 22A and the lower side surface portion 22B.

[0077] 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.

[0078] 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.

[0079] From these results, it is believed that the buckling resistance is highest when 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 vehicle width direction Y, as described above, buckling of the side sill 2 within the compression-side region 25 is suppressed, while the side sill 2 is 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 upper side surface portion 22A and the lower side surface portion 22B, and a high reaction force can be generated in the upper side surface portion 22A and the lower side surface portion 22B.

[0080] (3) In the vehicle lower body structure of this embodiment, the width L3 of the second upper surface portion 37 and the second lower surface portion 40 in the vehicle width direction Y is set to be equal to or less than ¼ of the overall width L1 of the side sill 2 in the vehicle width direction Y. By setting the width L3 of the second upper surface portion 37 and the second lower surface portion 40 in this manner, buckling at the second upper surface portion 37 and the second lower surface portion 40 can be suppressed when a bending load is input during a vehicle side collision or the like, and the side sill 2 can be reliably buckled at the second bent portion 34.

[0081] Furthermore, the fact that the width L3 of the second upper surface portion 37 and the second lower surface portion 40 should be set to be 1 / 4 or less of the overall width L1 of the side sill 2 in the vehicle width direction Y can be derived from the explanation using Figures 10 to 11 above using the same logic as for setting the width L2 of the compression side region 25 to be 1 / 4 or less of the overall width L1 of the side sill 2.

[0082] Furthermore, in the event of a small overlap collision (i.e., a head-on collision in which the collision load is applied partially to an area of ​​one-fourth or less of the front of the vehicle), the side sill inner 12 is compressed and deformed due to cantilever deformation of the vehicle front side X1 end 2b of the side sill. However, by setting the width L3 of the second upper surface portion 37 and the second lower surface portion 40 as described above, a high reaction force can also be obtained from the side sill inner 12, making it possible to prevent large cross-sectional deformation of the side sill 2.

[0083] (4) In the vehicle lower body structure of this embodiment, the pair of side surface portions 22 (upper side surface portion 22A (upper surface portion) and lower side surface portion 22B (lower surface portion)) of the side sill outer panel 11 each include a compression-side region 25, which is a first portion located on the outer side Y1 of the first bent portion 24 in the vehicle width direction, and a tension-side region 26, which is a second portion located on the inner side Y2 of the first bent portion 24 in the vehicle width direction. The compression-side region 25 is configured to have higher rigidity than the tension-side region 26. Therefore, even when the angle θ between the extension line of the compression side region 25 at the first bend 24 and the tension side region 26 is set to a small angle of 30 degrees or less, the tension side region 26 at the upper side surface portion 22A and the lower side surface portion 22B of the side sill outer 11 is configured to have lower rigidity than the compression side region 25, so that in the event of a vehicle collision, the tension side region 26 is tensilely deformed toward the inside of the side sill 2, while the first bend 24 is displaced toward the inside of the side sill 2, thereby ensuring buckling of the side sill 2.

[0084] 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 (upper side portion 22A and lower side portion 22B) of the side sill outer 11 cannot be secured in a structure where 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 cross section during a vehicle side collision.

[0085] (5) Moreover, in the configuration of this side sill outer 11, each side surface portion 22 (upper side surface portion 22A and lower side surface portion 22B) has 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.

[0086] (6) 5, in the vehicle lower body structure of this embodiment, the flange portions 23, 33 of the side sill outer panel 11 and the side sill inner panel 12 constituting 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. This 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 inside the vehicle cabin. This makes it possible to ensure space inside the vehicle cabin while suppressing bending deformation of the side sill 2 and maintaining impact absorption performance.

[0087] (7) 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 suppresses displacement of the pair of upper and lower flange portions 23, 33 in the up-down direction Z (i.e., the pair of flange portions 23 (and the pair of flange portions 33) from separating vertically from each other). This allows the side sill 2 to reliably buckle at the first bent portion 24 and the second bent portion 34.

[0088] (8) 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.

[0089] (9) In the vehicle underbody structure of this embodiment, the side sill inner panel 12 includes a tensile surface portion 31, which is a vertical wall portion that extends in the up-down direction Z at an end portion on the inner side Y2 in the vehicle width direction and connects the second upper surface portion 37 and the second lower surface portion 40. The tensile surface portion 31 has a bead 31a (see FIGS. 2 to 5) that extends in the vehicle front-rear direction X. With this configuration, the tensile surface portion 31, which is a vertical wall portion of the side sill inner panel 12, has the bead 31a, which can improve the rigidity of the side sill 2 against bending deformation.

[0090] (10) 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.

[0091] (11) 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.

[0092] (12) 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.

[0093] (Variation) (A) The side sill outer 11 of this embodiment is manufactured by joining together the main plate material 20, which is two plates made of steel or the like, and the patch 13 and then press-forming them, but the present invention is not limited to this, and the patch 13 may be omitted. However, having the patch 13 allows the side sill outer 11 to buckle more reliably at the first bent portion 24.

[0094] (B) 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] (C) 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 a side sill outer and a side sill inner 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 by integrating the corresponding side sill outer and side sill inner, respectively. In this case, too, it is possible to achieve the same effects as the side sill 2 in the above embodiment. [Explanation of symbols]

[0096] 1. Body 2 Side sill 3 Cross members 8 Door Opening 11 Side sill outer 12 Side sill inner 13 Patch 14 Connecting plate part 20 Main plate material 21 Compression surface 22 Side part 22A Upper side face part (upper face part) 22B Lower side face part (lower face part) 23 Flange part 24 First bending part 25 Compression side region (first part) 26 Tension side region (second part) 31 Tension face part 31a Bead 32 Side face part 32A Upper side face part 32B Lower side face part 33 Flange part 34 Second bending part 35 First upper face part 36 Upper inclined face part 37 Second upper face part 38 First lower face part 39 Lower inclined face part 40 Second lower face part

Claims

1. A vehicle underbody structure including a side sill having a side sill outer and a side sill inner each extending in a vehicle longitudinal direction and cooperating to form a closed cross section, The side sill outer includes an upper surface portion and a lower surface portion spaced downward from the upper surface portion, the upper surface portion and the lower surface portion each include a first bent portion formed by being bent toward the inside of the side sill, the side sill inner includes a first upper surface portion extending in the vehicle width direction, an upper inclined surface portion extending inward and downward in the vehicle width direction from an inner end portion of the first upper surface portion, a second upper surface portion extending inward in the vehicle width direction from the inner end portion of the upper inclined surface portion, a first lower surface portion extending in the vehicle width direction at a position spaced downward from the first upper surface portion, a lower inclined surface portion extending inward and upward in the vehicle width direction from the inner end portion of the first lower surface portion, and a second lower surface portion extending inward in the vehicle width direction from the inner end portion of the lower inclined surface portion, Furthermore, the side sill inner has a pair of upper and lower second bent portions that bend toward the inside of the cross section of the side sill between the second upper surface portion and the upper inclined surface portion and between the second lower surface portion and the lower inclined surface portion. A vehicle underbody structure characterized by:

2. 2. The vehicle underbody structure according to claim 1, a width of a portion located outward in the vehicle width direction from the first bent portion in the vehicle width direction is set to be ¼ or less of the total width of the side sill in the vehicle width direction; A vehicle underbody structure characterized by:

3. 3. The vehicle underbody structure according to claim 1, The width of the second upper surface portion and the second lower surface portion in the vehicle width direction is set to be ¼ or less of the overall width of the side sill in the vehicle width direction. A vehicle underbody structure characterized by:

4. 3. The vehicle underbody structure according to claim 1, the upper surface portion and the lower surface portion of the side sill outer each include a first portion located outward in the vehicle width direction from the first bent portion and a second portion located inward in the vehicle width direction from the first bent portion, The first portion is configured to be stiffer than the second portion; An angle between an extension line of the first portion and the second portion of the first bent portion is set to 30 degrees or less. A vehicle underbody structure characterized by:

5. 3. The vehicle underbody structure according to claim 1, Each of the side sill outer and the side sill inner has a pair of upper and lower flange portions, The flange portion of the side sill outer and the flange portion of the side sill inner are joined to form the closed cross section, The flange portion is disposed outward in the vehicle width direction from the cross-sectional center of the side sill. A vehicle underbody structure characterized by:

6. 6. The vehicle underbody structure according to claim 5, 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:

7. 7. The vehicle underbody structure according to claim 6, 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:

8. 3. The vehicle underbody structure according to claim 1, the side sill inner includes a vertical wall portion extending in a vertical direction at an end portion on an inner side in a vehicle width direction and connecting the second upper surface portion and the second lower surface portion, The vertical wall portion has a bead extending in the vehicle front-rear direction. A vehicle underbody structure characterized by:

Images