Vehicle lower body structure

Abstract

To provide a lower vehicle-body structure of a vehicle which can properly suppress the deformation of a side sill, without increasing the weight and manufacturing costs, in the small overlap collision of the vehicle.SOLUTION: A side sill 2 constituting a vehicle body, comprises a side sill outer 11 and a side sill inner 12. An upper-side side face portion 32A (upper face portion) and a lower-side side face portion 32B (lower face portion) of the side sill inner 12 are bent toward an inside of the side sill 2 to form a second bending portion 34 (bending portion). The side sill inner comprises: an upper-side slant face portion 36 and a lower-side slant portion 39 (slant portions) which slant in a direction where the side sill inner 12 gradually expands vertically as approaching the side sill outer 11; and a second upper face portion 37 and a second lower face portion 40 (vehicle-width-direction face portions) which extend in a vehicle width direction toward a vehicle inward side from the second bending portion 34.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] In a small overlap collision (i.e., a head-on collision in which a collision load is applied to a portion of the front of the vehicle in the vehicle width direction or less), one of the pair of side sills that make up the framework on both sides of the lower body of the vehicle is subjected to a collision load toward the rear and interior of the vehicle via the front wheel located in front of the side sill, which can cause the front end of the side sill to bend inward and narrow the interior space. Various vehicle body structures have been proposed to prevent this type of bending deformation of the side sill in a small overlap collision.

[0003] The vehicle body structure described in Patent Document 1 includes a side sill (rocker) with a closed cross-section structure extending in the longitudinal direction of the vehicle, and multiple reinforcing members are provided inside the front end of the side sill outer, which constitutes the outer side portion of the side sill, in order to reinforce the side sill. The reinforcing members are joined to the front portion (the surface facing the front of the vehicle), side portion (the surface facing the interior of the vehicle), and bottom surface of the inner surface of the side sill outer, thereby reinforcing the front end of the side sill outer from the inside and preventing bending deformation of the side sill in a small overlap collision. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-58749 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-described vehicle body structure, a reinforcing member is provided at the front end of the side sill outer to counter small overlap collisions. However, if the collision load during a small overlap collision increases due to factors such as an increase in vehicle size, there is a problem that the weight and cost of the reinforcing member increase in order to suppress deformation due to the large collision load.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a vehicle lower body structure that can suppress deformation of the side sill during a small overlap collision without increasing the weight and manufacturing costs of the side sill. [Means for solving the problem]

[0007] In order to solve the above problem, the underbody structure of a vehicle of the present invention comprises a side sill in which a side sill outer and a side sill inner, each extending in the fore-and-aft direction of the vehicle, cooperate to form a closed cross section, and a cross member joined to the side sill inner at a position rearward of the vehicle from the front end of the side sill and extending inward in the vehicle width direction from the side sill, wherein the side sill inner has an upper surface portion and a lower surface portion spaced downward from the upper surface portion, and the upper surface portion and the lower surface portion are each bent inward of the side sill, at least in the region between the front end of the side sill and the cross member in the fore-and-aft direction of the vehicle, and are provided with an inclined surface portion that extends from the bent portion toward the side sill outer and is inclined in a direction in which the side sill inner widens in the vertical direction as it approaches the side sill outer, and a vehicle width direction surface portion that extends in the vehicle width direction from the bent portion toward the interior of the vehicle.

[0008] According to this configuration, the upper and lower surfaces of the side sill inner are each bent inwardly of the side sill, at least in the region between the front end of the side sill and the cross member in the vehicle longitudinal direction, and are provided with an inclined surface portion that extends from the bent portion toward the side sill outer and inclines in the direction in which the side sill inner widens in the vertical direction as it approaches the side sill outer, and a vehicle width direction surface portion that extends in the vehicle width direction from the bent portion toward the inside of the vehicle. In this configuration, when a collision load is applied to the front end of the side sill in a rearward and transversely inward direction of the vehicle during a small overlap collision, a bending load is applied to the side sill with the joint between the cross member and the side sill inner as a fulcrum. As the bent portions of the upper and lower surfaces of the side sill inner displace inward in cross section, the inclined surfaces extending from the bent portions toward the side sill outer become increasingly inclined in the direction in which the side sill inner expands in the vertical direction, while the transverse surfaces extending from the bent portions toward the vehicle interior remain substantially parallel to the direction of the collision load. This allows the side sill inner itself to generate a high reaction force, thereby suppressing bending deformation of the side sill. Therefore, the above configuration eliminates the need for a reinforcing member inside the side sill as in conventional configurations, thereby suppressing deformation of the side sill during a small overlap collision without increasing the weight or manufacturing costs of the side sill.

[0009] In the above vehicle underbody structure, it is preferable that the upper surface of the cross member is located at the same height as the vehicle width direction surface portion of the upper surface portion of the side sill inner.

[0010] With this configuration, the side sill, which receives a bending load during a small overlap collision, can be supported by the cross member while suppressing twisting of the side sill.

[0011] In the above vehicle underbody structure, the cross member preferably has a first flange portion joined to the vehicle width direction surface portion of at least one of the upper surface portion and the lower surface portion of the side sill inner.

[0012] According to this configuration, at least one of the upper and lower surfaces of the side sill inner has a widthwise surface portion on the vehicle interior side of the bent portion joined to the first flange portion of the cross member, thereby suppressing deformation of the widthwise surface portion of the side sill inner during the deformation process of the side sill in a small overlap collision, and reliably maintaining the widthwise surface portion in a state approximately parallel to the direction of the collision load.

[0013] 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 upper surface portion and the lower surface portion, and the cross member has a second flange portion joined to the vertical wall portion of the side sill inner.

[0014] In this configuration, the vertical wall portion located at the inner end of the side sill inner in the vehicle width direction is joined to the second flange portion of the cross member, so that the side sill, which is subjected to bending loads during a small overlap collision, can be reliably supported by the cross member.

[0015] In the above-mentioned vehicle lower body structure, the side sill inner preferably has a vertical wall portion extending in the vertical direction at the inner end portion in the vehicle width direction and connecting the upper surface portion and the lower surface portion, and the vertical wall portion preferably has a bead extending in the fore-and-aft direction of the vehicle.

[0016] With this configuration, it is possible to improve the rigidity of the entire side sill, including the side sill inner, against bending deformation.

[0017] In the above vehicle underbody structure, it is preferable that the bead extends from the front end of the side sill to at least the rear end of the cross member.

[0018] With this configuration, the rigidity of the side sill from the front end of the side sill to the rear end of the cross member is improved by the bead, making it possible to effectively prevent bending deformation of the side sill when a collision load is input to the front end of the side sill during a small overlap collision.

[0019] In the above-mentioned lower body structure of the vehicle, it is preferable that the side sill inner further includes a pair of upper and lower flange portions provided at the ends of the upper surface portion and the lower surface portion on the side sill outer side, and that the side sill further includes a connecting plate portion connecting the pair of upper and lower flange portions of the side sill inner.

[0020] With this configuration, when a collision load is input to the front end of the side sill during a small overlap collision, a force acts on the upper and lower surfaces of the side sill inner in a direction that moves them apart vertically.However, because a pair of upper and lower flange portions provided at the ends of the upper and lower surfaces are connected by a connecting plate portion, the cross-sectional collapse of the upper and lower surfaces of the side sill inner can be suppressed by the tension of the connecting plate portion.

[0021] 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.

[0022] 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 tension of the connecting plate portion can reliably suppress the collapse of the cross-section of the upper and lower surfaces of the side sill inner.

[0023] 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.

[0024] With this configuration, it is possible to suppress cross-sectional deformation of the side sill inner while reducing the mass and cost of the connecting plate portion. [Effects of the Invention]

[0025] As described above, the vehicle lower body structure of the present invention can suppress deformation of the side sill during a small overlap collision without increasing the weight and manufacturing costs of the side sill. [Brief explanation of the drawings]

[0026] [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] FIG. 10 is an explanatory cross-sectional view showing deformation of a side sill during a small overlap collision. [Figure 7] 10 is a graph showing the change over time in bending load of a side sill during a small overlap collision in this embodiment and a comparative example. [Figure 8] 1 is a cross-sectional view of a typical side sill and cross member as a comparative example of the present invention. [Figure 9] 10 is an explanatory diagram showing stress distribution in the side sill of the present embodiment during a small overlap collision. FIG. [Figure 10] FIG. 10 is a diagram showing stress distribution in a side sill of a comparative example during a small overlap collision. [Figure 11] 10 is a graph showing the change over time in bending load of a side sill in an example in which the bead ends at the front end of the cross member as a modified example of the present invention, and in a comparative example. [Figure 12] 2 is a perspective explanatory view showing a bending load generated in the side sill of FIG. 1 during a vehicle side collision. FIG. [Figure 13] 5(a) to 5(d) are cross-sectional explanatory views showing the deformation process of a side sill during a vehicle side collision. [Figure 14] 6 is a graph showing changes over time in the bending moment of the side sill in this embodiment and a comparative example. [Figure 15] 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 16] FIG. 10 is a diagram showing a test vertical plate for examining the position of a bent portion. [Figure 17] 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

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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).

[0034] 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).

[0035] Specifically, the side sill outer 11 includes a vertical wall portion 21 extending in the up-down direction Z, an upper side surface portion 22A and a lower side surface portion 22B as a pair of side surface portions 22 extending in the vehicle width direction inward Y2 so as to widen in the up-down direction Z from both end portions of the vertical wall portion 21 toward the side sill inner 12, 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 inward Y2. The lower side surface portion 22B is located below the upper side surface portion 22A and spaced apart.

[0036] Each of the pair of side portions 22 (i.e., the upper side portion 22A and the lower side portion 22B) has a first bent portion 24 formed by bending the side portion 22 toward the inside of the side sill 2, a first portion 25 that starts from the first bent portion 24 and is located closer to the vertical wall portion 21 than the first bent portion 24, and a second portion 26 that starts from the first bent portion 24 and is located farther from the vertical wall portion 21 than the first bent portion 24.

[0037] 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.

[0038] When a bending load B2 (see FIG. 12) that bends the side sill 2 toward the inside of the vehicle is applied to the side sill 2 during a vehicle side collision (when an obstacle or the like collides with the vehicle from the outside of the vehicle to the side of the vehicle), compressive stress occurs in the vertical wall portion 21. Furthermore, in each of the pair of side surface portions 22, compressive stress occurs in the first portion 25 and tensile stress occurs in the second portion 26.

[0039] Therefore, in the side sill outer 11 of this embodiment, the first portion 25 (first portion) is configured to have higher rigidity than the second portion 26 (second portion) against a bending load B2 that compresses the vertical wall portion 21. In this embodiment, the first portion 25 is configured by joining two plate materials (a main plate material 20 and a 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 vertical wall portion 21, and the side portions 13b are joined to the first portion 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 vertical wall portion 21 and the first portion 25 of the pair of side surface portions 22 of the side sill outer 11 have high rigidity, while the second portion 26 without the patch 13 has low rigidity.

[0040] Furthermore, in the side surface portion 22 of this embodiment, the first portion 25 is formed by joining the main plate material 20 and the patch 13, and the second portion 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 first portion 25 to the rigidity of the second portion 26, with the first bent portion 24 as the boundary. In other words, the first portion 25 and the second portion 26 of this embodiment have uniform rigidity within their respective regions, but are configured so that the rigidity of the first portion 25 and the rigidity of the second portion 26 change abruptly at the first bent portion 24.

[0041] 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 to the outer surface Y1 of the main plate material 20 in the vehicle width direction is preferable because this makes the first portion 25 less likely to be crushed (deformed) in the event of a vehicle collision.

[0042] In this embodiment, as described above, the side surface portion 22 has a configuration in which the high-rigidity first portion 25 and the low-rigidity second portion 26 change discontinuously with the first bent portion 24 as the boundary, so that when a bending load B2 (see FIG. 12) is input to the side sill 2 during a vehicle side 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 first portion 25 at the first bent portion 24 and the second portion 16 is set to 30 degrees or less.

[0043] 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).

[0044] Specifically, the side sill inner 12 includes a vertical wall portion 31 extending in the up-down direction Z at its end on the inner side Y2 in the vehicle width direction, a pair of side surface portions 32 (i.e., an upper side surface portion 32A (upper surface portion) and a lower side surface portion 32B (lower surface portion)) extending from both ends of the vertical wall portion 31 toward the outer side Y1 in the vehicle width direction so as to widen in the up-down direction Z toward the side sill outer panel 11, and a pair of flange portions 33 extending upward Z1 and downward Z2 from the ends of the upper side surface portion 32A and the lower side surface portion 32B on the outer side Y1 in the vehicle width direction (i.e., toward the side sill outer panel 11). The lower side surface portion 32B (lower surface portion) is disposed below the upper side surface portion 32A (upper surface portion) and spaced apart Z2. When a bending load B2 (see FIG. 1) is applied to the side sill 2, tensile stress is generated in the vertical wall portion 31.

[0045] 3 and 5, a bead 31a for reinforcing the side sill inner panel 12 is provided near the middle of the vertical wall 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 vertical wall 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 a front end portion 2b (a connection portion with the hinge pillar 4) on the vehicle front side X1 of the side sill 2 to a position E at the end portion of the cross member 3 on the vehicle rear side X2.

[0046] The upper side surface portion 32A (upper surface portion) and the lower side surface portion 32B (lower surface portion) each include a second bent portion 34 (bent portion) 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 upper side surface portion 32A and the lower side surface portion 32B have a substantially stepped cross section having two steps.

[0047] Specifically, 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 (inclined surface portion) 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 (vehicle width surface portion) 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 (bent portion).

[0048] 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 (inclined surface portion) extending from an inner vehicle width direction Y2 end portion 38a of the first lower surface portion 38 toward the inner vehicle width direction Y2 and upper side Z1, and a second lower surface portion 40 (vehicle width direction surface portion) extending from the inner vehicle width direction Y2 end portion of the lower inclined surface portion 39 toward the inner vehicle width direction Y2 while forming the second bent portion 34 (bent portion). 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.

[0049] In other words, the side sill inner 12 is configured to have a pair of upper and lower second bending portions 34 that are bent 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, as bending portions formed by bending the upper side surface portion 32A (upper surface portion) and the lower side surface portion 32B (lower surface portion) toward the inside of the side sill 2.

[0050] The upper inclined surface portion 36 and the lower inclined surface portion 39 as inclined surface portions extend from the second bent portion 34 toward the side sill outer panel 11 and incline in a direction in which the side sill inner panel 12 widens in the up-down direction Z as it approaches the side sill outer panel 11. Furthermore, the second upper surface portion 37 and the second lower surface portion 40 as vehicle width direction surface portions extend in the vehicle width direction Y from the second bent portion 34 toward the vehicle interior side Y2.

[0051] In this embodiment, in order to suppress bending deformation of the side sill 2 during a small overlap collision, the upper side surface portion 32A (upper surface portion) and the lower side surface portion 32B (lower surface portion) of the side sill inner 12 may have the above-mentioned second bent portion 34 (bent portion), upper inclined surface portion 36 and lower inclined surface portion 39 (inclined surface portion), second upper surface portion 37 and second lower surface portion 40 (vehicle width direction surface portion) at least in the region between the front end portion 2b of the side sill 2 in the vehicle fore-and-aft direction X and the cross member 3, but may also have these portions over the entire length of the side sill 2.

[0052] The vertical wall portion 31 extends in the vertical direction Z and connects the vehicle width directional inner Y2 ends of the second upper surface portion 37 and the second lower surface portion 40, thereby achieving connection between the upper side surface portion 32A (upper surface portion) and the lower side surface portion 32B (lower surface portion).

[0053] 3 and 4, an end of a cross member 3 extending in the vehicle width direction Y is joined to the side sill inner panel 12. In this embodiment, the cross member 3 is joined to the side sill inner panel 12 at a position X2 that is further rearward than the front end 2b of the side sill 2, and extends from the side sill 2 toward the inside Y2 in the vehicle width direction.

[0054] The cross member 3 has three flange portions, a first flange portion 41, a second flange portion 42, and a third flange portion 43, which are joined at its end to the side sill inner panel 12. The first flange portion 41 extends from the upper surface 3a 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 side edge in the vehicle width direction Y1 of the side surface 3b (the surface facing the vehicle fore-and-aft direction X) of the cross member 3 and is joined to the vertical wall 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 side edge in the vehicle width direction Y1 of the bottom wall portion of the cross member 3 and is joined to the vertical wall portion 31.

[0055] To prevent twisting of the side sill 2 during a small overlap collision, the upper surface 3a of the cross member 3 is preferably located at the same height as the second upper surface portion 37 (surface portion in the vehicle width direction) of the side sill inner 12.

[0056] The above-mentioned first flange portion 41 extends from the upper surface 3a of the cross member 3 toward the outer side Y1 in the vehicle width direction and is joined to the second upper surface portion 37 of the side sill inner 12, but an additional first flange portion 41 may also extend from the lower surface of the cross member 3 toward the outer side Y1 in the vehicle width direction and be joined to the second lower surface portion 40 of the side sill inner 12.

[0057] As shown in FIG. 5, in the side sill 2 of this embodiment, the width L2 of the first portion 25, which is the first portion located on the outer side Y1 in the vehicle width direction 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 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 bent portion 24 when a bending load B2 (see FIG. 12) is input during a vehicle side collision, for example.

[0058] 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 B2 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.

[0059] 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.

[0060] 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.

[0061] The connecting plate portion 14 can be installed at any position in the vehicle longitudinal direction X inside the side sill 2. 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 constitutes the door opening 8 of the vehicle body 1 in the vehicle longitudinal direction X, thereby promoting buckling at the portion 2a.

[0062] 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.

[0063] The first bent portions 24 of the pair of side surface portions 22 are disposed so as to be equidistant from the vertical wall 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.

[0064] (Features of this embodiment) (1) In the lower body structure of the vehicle of this embodiment, as shown in FIG. 5 , the upper side surface portion 32A (upper surface portion) and the lower side surface portion 32B (lower surface portion) of the side sill inner 12 are each provided with a second bent portion 34 formed by bending the upper side surface portion 32A and the lower side surface portion 32B toward the inside of the side sill 2 at least in the region between the front end portion 2b of the side sill 2 and the cross member 3 in the vehicle longitudinal direction X, and are also provided with an upper inclined surface portion 36 and a lower inclined surface portion 39 (inclined surface portions) that extend from the second bent portion 34 toward the side sill outer 11 and incline in a direction in which the side sill inner 12 widens in the up-down direction Z as it approaches the side sill outer 11, and a second upper surface portion 37 and a second lower surface portion 40 (vehicle width direction surface portions) that extend from the second bent portion 34 in the vehicle width direction Y toward the vehicle interior side Y2.

[0065] 1-2 and 6, in the event of an overlap collision, a collision load A is input to the front end 2b of the side sill 2 via the front wheel W of the vehicle in the direction rearward X2 and inward Y2 in the vehicle width direction. At this time, a bending load B1 is input to the side sill 2 with the joint between the cross member 3 and the side sill inner panel 12 (near the end of the cross member 3 where the first to third flange portions 41-43 are provided) as a fulcrum.

[0066] As shown in FIG. 6 , when the second bent portions 34 of the upper side surface portion 32A and the lower side surface portion 32B of the side sill inner panel 12 are displaced inward in cross section after the input of the bending load B1, the upper inclined surface portion 36 and the lower inclined surface portion 39 extending from the second bent portion 34 toward the side sill outer panel 11 are increasingly inclined in the direction in which the side sill inner panel 12 widens in the up-down direction Z. Meanwhile, the second upper surface portion 37 and the second lower surface portion 40 extending from the second bent portion 34 toward the vehicle interior side Y2 are able to maintain a substantially parallel state to the direction of the collision load A (specifically, the horizontal direction, which is the same as the component of the collision load A in the vehicle width direction Y). This allows the side sill inner panel 12 itself to generate a high reaction force, thereby suppressing bending deformation of the side sill 2. Therefore, the above-described configuration eliminates the need for a reinforcing member inside the side sill 2 as in the conventional configuration, making it possible to suppress deformation of the side sill 2 during a small overlap collision without increasing the weight and manufacturing costs of the side sill 2. Although Figures 4 and 5 show a connecting plate portion 14 provided inside the side sill 2, the connecting plate portion 14 is not an essential component of the present invention, and it goes without saying that the above-mentioned effects can be achieved even without the connecting plate portion 14.

[0067] <Explanation about effectiveness verification> To verify the above-described effects, curve I in the graph of Fig. 7 shows the results of an investigation into the reaction force of the side sill 2 against bending load B1 when a collision load A is input to the front end 2b of the side sill 2 via the front wheel W of this vehicle in a direction rearward X2 and inward Y2 in the vehicle width direction during a small overlap collision, as shown in Figs. 1-2 and 6. The graph in Fig. 7 shows the change over time in bending load F acting on the side sill as a reaction force. Curve I in Fig. 7 shows the change over time in bending load for the side sill 2 of this embodiment, while curve II shows the change over time in bending load for a conventional side sill 50 shown in Fig. 8 as a comparative example.

[0068] 8 is composed of a side sill outer 51 and a side sill inner 52 of the same plate thickness, with 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 joined together, and the side sill inner 52 is joined to the end of the cross member 3. This side sill 50 does not have the second bent portion 34, the inclined surface portions (upper inclined surface portion 36 and lower inclined surface portion 39), and the vehicle width direction surface portions (second upper surface portion 37 and second lower surface portion 40) for increasing the reaction force in the side sill inner 52 as in this embodiment.

[0069] As is clear from the graph in Fig. 7, in the case of the side sill 2 of this embodiment, it is possible to maintain a high bending load as a reaction force against the bending load for a long period of time in a small overlap collision, as shown by curve I. In contrast, in the case of the side sill 50 of the comparative example in Fig. 8, it is clear that the bending load as a reaction force in a small overlap collision is lower than that of curve I above for almost the entire time, as shown by curve II.

[0070] Furthermore, when comparing the stress distribution acting on the side sill during a small overlap collision between the side sill 2 of this embodiment and the side sill 50 of the comparative example in Fig. 8, it can be seen that in the side sill 2 of this embodiment shown in Fig. 9, the areas of high stress near the joint with the cross member 3 in the side sill 2 (the dark areas in Fig. 9) are dispersed over a wide area, generating a high reaction force throughout the side sill 2. On the other hand, in the side sill 50 of the comparative example in Fig. 8 shown in Fig. 10, the areas of high stress near the joint with the cross member 3 (the dark areas in Fig. 10) are concentrated over a narrow area, and it can be seen that only a low reaction force can be generated throughout the side sill 50.

[0071] To further verify the operational effect of the side sill of the present invention, an example was also examined in which the bead 31a (see FIGS. 2 to 5) in the side sill 2 of this embodiment extends only to the front end of the cross member 3, rather than to the rear end, and the reaction force of the side sill against the bending load B1 during a small overlap collision was measured under the same conditions as above. The results are shown in curve I' of the graph in Figure 11. The graph in Figure 11 reveals that even in the modified example of the present invention (where the bead 31a is short) (curve I'), the bending load as a reaction force during a small overlap collision is higher for a longer period of time than in the case of the side sill 50 of the comparative example in Figure 8 (curve II).

[0072] Therefore, looking at the results of the graph in Figure 11 above, it can be concluded that even if the bead 31a extends only to the front end of the cross member 3, it is possible to maintain a high bending load as a reaction force if the structure has the second bend portion 34, inclined surface portions (upper inclined surface portion 36 and lower inclined surface portion 39), and vehicle width direction surface portions (second upper surface portion 37 and second lower surface portion 40) to increase the reaction force, as in the side sill 2 of this embodiment.

[0073] In addition, the modified example of the present invention (when the bead 31a is short) (curve I' in Figure 11) has a slightly lower maximum value of the bending load as a reaction force and a slightly shorter period of time during which the bending load is high than the side sill 2 of this embodiment (when the bead 31a is long) (curve I in Figure 7), so the structure in which the bead 31a extends to the rear end of the cross member 3, as in the side sill 2 of this embodiment, is preferable in that a high bending load can be obtained as a reaction force for a long period of time.

[0074] (2) In the vehicle lower body structure of this embodiment, the upper surface 3a of the cross member 3 shown in Figures 2 to 4 is preferably located at the same height as the second upper surface portion 37 of the upper side surface portion 32A (upper surface portion) of the side sill inner 12. In this case, the side sill 2, which receives a bending load B1 during a small overlap collision, can be supported by the cross member 3 while suppressing twisting of the side sill 2.

[0075] (3) In the lower body structure of the vehicle of this embodiment, it is preferable that the cross member 3 has a first flange portion 41 that joins to at least one of the second upper surface portion 37 and the second lower surface portion 40 (only the second upper surface portion 37 in Figures 2 to 4) on at least one of the upper side surface portion 32A and the lower side surface portion 32B of the side sill inner 12 (only the upper side surface portion 32A in Figures 2 to 4).

[0076] According to this configuration, in at least one of the upper side portion 32A and the lower side portion 32B of the side sill inner 12, at least one of the second upper surface portion 37 and the second lower surface portion 40, which is on the vehicle interior side Y2 rather than the second bent portion 34, is joined to the first flange portion 41 of the cross member 3, thereby suppressing deformation of at least one of the second upper surface portion 37 and the second lower surface portion 40 of the side sill inner 12 during the deformation process of the side sill 2 during a small overlap collision, and reliably maintaining the second upper surface portion 37 and the second lower surface portion 40 in a state approximately parallel to the direction of the collision load A.

[0077] (4) In the vehicle underbody structure of this embodiment, as shown in Figures 2 and 3, the side sill inner panel 12 includes a vertical wall portion 31 that extends in the up-down direction Z at its end on the inner side Y2 in the vehicle width direction and connects the upper side surface portion 32A (upper surface portion) and the lower side surface portion 32B (lower surface portion). The cross member 3 includes a second flange portion 42 that joins with the vertical wall portion 31 of the side sill inner panel 12. In this configuration, the vertical wall portion 31 located at the end on the inner side Y2 in the vehicle width direction of the side sill inner panel 12 is joined to the second flange portion 42 of the cross member 3, so that the side sill 2 that receives a bending load B1 during a small overlap collision can be reliably supported by the cross member 3.

[0078] In addition, in this embodiment, the cross member 3 has, in addition to the second flange portion 42, a third flange portion 43 that joins to the vertical wall portion 31 as shown in Figure 4, so that the side sill can be more reliably supported by the cross member 3.

[0079] (5) 2 to 5, in the vehicle lower body structure of this embodiment, the vertical wall portion 31 of the side sill inner panel 12 has a bead 31a extending in the vehicle fore-and-aft direction X. With this configuration, it is possible to improve the rigidity of the entire side sill 2 including the side sill inner panel 12 against bending deformation.

[0080] (6) In the vehicle lower body structure of this embodiment, the bead 31a extends from the front end 2b of the side sill 2 to at least the rear end (the position of line E in FIG. 3) of the cross member 3. With this configuration, the rigidity of the side sill 2 from the front end 2b of the side sill 2 to the rear end of the cross member 3 is improved by the bead 31a, so it is possible to effectively prevent bending deformation of the side sill 2 when a collision load A is input to the front end 2b of the side sill 2 during a small overlap collision.

[0081] (7) 5, the side sill inner panel 12 includes a pair of upper and lower flange portions 33 provided at the ends of the upper side surface portion 32A and the lower side surface portion 32B on the side of the side sill outer panel 11. The side sill 2 includes a connecting plate portion 14 connecting the pair of upper and lower flange portions 33 of the side sill inner panel 12.

[0082] In this configuration, when a collision load A is input to the front end 2b of the side sill 2 during a small overlap collision, a force acts on the upper side surface portion 32A and the lower side surface portion 32B of the side sill inner 12 in a direction that moves them apart in the vertical direction.However, since a pair of upper and lower flange portions 33 provided at the ends of the upper side surface portion 32A and the lower side surface portion 32B are connected by the connecting plate portion 14, it is possible to suppress cross-sectional collapse of the upper side surface portion 32A and the lower side surface portion 32B of the side sill inner 12 by the tension of the connecting plate portion 14.

[0083] (8) In the vehicle lower body structure of this embodiment, the connecting plate portion 14 is arranged in a portion of the side sill 2 in the vehicle longitudinal direction X that forms the door opening 8 of the vehicle body 1 (see FIG. 1).

[0084] 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, as described above, the connecting plate portion 14 is arranged in the part of the side sill 2 that constitutes the door opening 8, so that even in an area where there are no pillars, the tension of the connecting plate portion 14 can reliably suppress the collapse of the cross-section of the upper side surface portion 32A and the lower side surface portion 32B of the side sill inner 12.

[0085] (9) In both a small overlap collision and a side 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 therefore only a tensile load acts on it, so the connecting plate portion 14 does not require as much bending strength as the side sill outer 11 and the side sill inner 12. From this perspective, by configuring the connecting plate portion 14 so that its bending strength is smaller than the bending strengths of the side sill outer 11 and the side sill inner 12, it is possible to suppress cross-sectional deformation of the side sill inner 12 while keeping the mass and cost of the connecting plate portion 14 low. Moreover, it is possible to manufacture the connecting plate portion 14 from a thin, inexpensive material while achieving reliable buckling of the side sill 2.

[0086] (Deformation process of side sill 2 during a vehicle side collision) Next, with reference to FIGS. 13(a) to 13(d), the deformation process when the side sill 2 configured as described above receives a bending load B2 during a vehicle side collision will be shown.

[0087] 13(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. 12, a bending load B2 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.

[0088] 13(b), in the initial state of a vehicle side collision, when compressive stress acts on the vertical wall portion 21 of the side sill outer 11 of the side sill 2, the vertical wall portion 21 attempts to move toward the side sill inner 12 (inner side Y2 in the vehicle width direction), and in the pair of side surface portions 22 of the side sill outer 11, compressive stress acts on the first portion 25 and tensile stress acts on the second portion 26, with the first bent portion 24 as the boundary. Because the first portion 25 of the side surface portion 22 having the patch 13 has higher rigidity than the second portion 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.

[0089] As the first bent portion 24 moves inward of the side sill 2, the second portion 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 this process, while the first bent portion 24 is displacing inward of the side sill 2, the highly rigid first portion 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 vertical wall portion 21 moves toward the side sill inner panel 12, specifically, the vehicle width direction Y) during the deformation process. Therefore, the first portion 25 generates a high reaction force against the bending load B2. During this compression, the connecting plate portion 14 inhibits the upper and lower flange portions 23, 33 of the side sill 2 from moving apart vertically, generating a high reaction force against the bending load B2.

[0090] These reaction forces are shown in the graph of Figure 14, curve III, at time t1. BThe graph in Figure 14 shows the bending moment M that occurs in the side sill as a reaction force. B 14 shows the change over time of the bending moment in the side sill 2 of this embodiment, and curve IV shows the change over time of the bending moment in the conventional side sill 50 shown in FIG. 8 as a comparative example. The conventional side sill 50 shown in FIG. 8 does not have the first bent portion 24 and the second bent portion 34 that can trigger buckling, as in this embodiment.

[0091] 13(b), this corresponds to time t1 in the graph of FIG. 14, and at this time, curve III indicates that a high bending moment is generated as a reaction force of the side sill 2. On the other hand, curve IV at time t1 indicates that only a low bending moment is generated as a reaction force of the conventional side sill 50.

[0092] 13(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 vertical wall 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.

[0093] The reaction force of the side sill inner 12 is also clear from the height of the bending moment at time t2 of curve III in the graph of Fig. 14. That is, when the side sill 2 of this embodiment reaches the state shown in Fig. 13(c), this corresponds to time t2 in the graph of Fig. 14, and at this time, curve III indicates that a high bending moment is maintained as the reaction force of the side sill 2. From curve III, 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 vehicle width direction inward Y2 and maintains the reaction force of the side sill 2.

[0094] On the other hand, curve IV 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 III.

[0095] Furthermore, as shown in Figure 13(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.

[0096] The state of the side sill 2 of this embodiment in Fig. 13(d) corresponds to time t3 in the graph of Fig. 14. At time t3, curve III 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 IV.

[0097] (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 B2 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.

[0098] The graph in FIG. 15 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 VI. As is clear from the graph in Fig. 15, the side sill 2 of this embodiment (curve V) and the conventional side sill 50 (curve VI) 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.

[0099] (Other features of this embodiment) (11) 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 side 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.

[0100] 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 and the lower side surface portion 22B of the side sill outer panel 11 are displaced toward the inside of the cross section of the side sill 2. The first portions 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.

[0101] During this deformation of the side sill inner 12, the ends (the pair of flange portions 33 and their peripheral portions) 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 vertical wall 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.

[0102] 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.

[0103] 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.

[0104] (12) In the lower body structure of the vehicle of this embodiment, the width L2 of the first portion 25, which is located on the outer side Y1 of the vehicle width direction than the first bend 24 in the specified 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 total width L1 of the side sill 2 in the specified direction (vehicle width direction Y).

[0105] With this configuration, in the event of a side collision of the vehicle, buckling of the side sill 2 within the first portion 25 of the upper side portion 22A and the lower side portion 22B of the side sill outer 11 is suppressed, while the side sill 2 can be reliably bent at the first bending portion 24, which is the boundary between the first portion 25 and the second portion 26 of the upper side portion 22A and the lower side portion 22B, making it possible to generate a high reaction force at the upper side portion 22A and the lower side portion 22B.

[0106] 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 16 and 17. First, as shown in Figure 16, 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.

[0107] 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. 16, a 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, was calculated by computer simulation. 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. 17. It can be seen that the buckling strength is maximized when the bent portion 64 is provided at a height position of 1 / 4 of the total height b of the vertical plate 61.

[0108] From these results, it is believed that the buckling resistance is maximized when the position of the first bent portion 24 of the side sill 2 is a distance of 1 / 4 × L1 from the vertical wall 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 first portion 25 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) as described above, buckling of the side sill 2 within the first portion 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 first portion 25 and the second portion 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.

[0109] (13) In the vehicle underbody structure of this embodiment, the width L3 of the second upper surface portion 37 and the second lower surface portion 40 in a predetermined direction (vehicle width direction Y) in which the side sill outer panel 11 and the side sill inner panel 12 are aligned is set to be equal to or less than ¼ of the overall width L1 of the side sill 2 in the predetermined direction (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.

[0110] 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 specified direction (vehicle width direction Y) can be derived from the explanation using Figures 16 to 17 above using the same logic as for setting the width L2 of the first portion 25 above to be 1 / 4 or less of the overall width L1 of the side sill 2.

[0111] Furthermore, in the event of a small overlap collision, the front end 2b of the side sill 2 undergoes cantilever deformation, causing the side sill inner 12 to undergo compressive deformation. 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.

[0112] (14) In the vehicle underbody structure of this embodiment, a pair of side surface portions 22 (upper side surface portion 22A and lower side surface portion 22B) of the side sill outer panel 11 each include a first portion 25 located on the outer side (Y1) of the first bent portion 24 in the vehicle width direction and a second portion 26 located on the inner side (Y2) of the first bent portion 24 in the vehicle width direction. The first portion 25 is configured to have higher rigidity than the second portion 26. Therefore, even when the angle θ between the extension line of the first portion 25 at the first bent portion 24 and the second portion 26 is set to a small angle of 30 degrees or less, the second portions 26 of the upper side surface portion 22A and the lower side surface portion 22B of the side sill outer panel 11 are configured to have lower rigidity than the first portion 25. Therefore, during a vehicle side collision, the second portion 26 is tensilely deformed inward of the side sill 2, and the first bent portion 24 is displaced inward of the side sill 2, thereby reliably causing buckling of the side sill 2.

[0113] 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.

[0114] (15) 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) includes a first portion 25 that starts from the first bent portion 24 and is located closer to the vertical wall portion 21 than the first bent portion 24, and a second portion 26 that starts from the first bent portion 24 and is located farther from the vertical wall portion 21 than the first bent portion 24, and furthermore, the first portion 25 is configured to have higher rigidity than the second portion 26 against a bending load B2 that compresses the vertical wall 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 first portion 25 to the rigidity of the second portion 26, with the first bent portion 24 as the boundary. Therefore, during a vehicle side collision, as shown in FIG. 13(b), as the first bent portion 24 moves inward of the side sill 2, the second portion 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 this process, while the first bent portion 24 is displacing inward of the side sill 2, the highly rigid first portion 25 of each of the pair of side surface portions 22 becomes substantially parallel to the direction in which the vertical wall portion 21 moves toward the side sill inner panel 12 during the deformation process. Therefore, the first portion 25 generates a high reaction force against the bending load B2, thereby suppressing bending deformation of the side sill 2. As a result, when the bending load B2 is input to the side sill 2 during a vehicle side collision, the side sill 2 can absorb the impact by suppressing bending deformation and reliably buckling.

[0115] (16) 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.

[0116] (17) 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 vertically apart during bending deformation of the side sill 2 in the event of a vehicle side 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 moving apart in the vertical direction Z). This allows the side sill 2 to reliably buckle at the first bent portion 24 and the second bent portion 34.

[0117] (18) 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.

[0118] (19) In the vehicle lower body structure of this embodiment, the first portion 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 first portion 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.

[0119] (20) 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 vertical wall portion 21. With this configuration, when a bending load B2 is input to the side sill 2 during a vehicle side collision, the first bent portions 24 of the pair of side surface portions 22 can be simultaneously displaced inward, 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.

[0120] (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.

[0121] (B) In the side sill outer 11 of the above embodiment, the first portion 25 is formed by joining two plate materials, i.e., the main plate material 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 material, the plate thickness of the first portion 25 may be configured to be greater than the plate thickness of the second portion 26. In this configuration, the integral formation of the side sill outer 11 makes it possible to easily manufacture a buckling side sill 2.

[0122] (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]

[0123] 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 Vertical wall section 22 Side part 22A Upper side part 22B Lower side part 23 Flange 24 1st bend 25 Part 1 26 Part 2 31 Vertical wall section 31a Bead 32 Side part 32A Upper side part (top part) 32B Lower side part (bottom part) 33 Flange 34 2nd bending part 35 1st top section 36 Upper inclined surface section (slanted surface section) 37 Second upper surface section (vehicle width direction surface section) 38 1st bottom part 39 Lower slope section (slope section) 40 Second lower surface part (vehicle width direction surface part)

Claims

1. a side sill including a side sill outer and a side sill inner each extending in the vehicle longitudinal direction and cooperating to form a closed cross section; a cross member joined to the side sill inner at a position rearward of the vehicle relative to a front end of the side sill and extending inward in a vehicle width direction from the side sill; Equipped with The side sill inner 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 are each bent toward the inside of the side sill at least in a region between the front end of the side sill and the cross member in the vehicle longitudinal direction, and include an inclined surface portion that extends from the bent portion toward the side sill outer and is inclined in a direction in which the side sill inner increases in width in the up-down direction as it approaches the side sill outer, and a vehicle width direction surface portion that extends from the bent portion toward the vehicle interior in the vehicle width direction. A vehicle underbody structure characterized by:

2. 2. The vehicle underbody structure according to claim 1, An upper surface of the cross member is located at the same height as the vehicle width direction surface portion of the upper surface portion of the side sill inner. A vehicle underbody structure characterized by:

3. 3. The vehicle underbody structure according to claim 1, the cross member has a first flange portion joined to the vehicle width direction surface portion of at least one of the upper surface portion and the lower surface portion of the side sill inner; The vehicle's underbody structure.

4. 3. The vehicle underbody structure according to claim 1, the side sill inner includes a vertical wall portion extending in the up-down direction at an end portion on the inner side in the vehicle width direction and connecting the upper surface portion and the lower surface portion, The cross member includes a second flange portion that is joined to the vertical wall portion of the side sill inner. A vehicle underbody structure characterized by:

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

6. 6. The vehicle underbody structure according to claim 5, The bead extends from the front end of the side sill to at least the rear end of the cross member. A vehicle underbody structure characterized by:

7. 3. The vehicle underbody structure according to claim 1, The side sill inner further includes a pair of upper and lower flange portions provided at end portions of the upper surface portion and the lower surface portion on the side sill outer side, The side sill further includes a connecting plate portion that connects the pair of upper and lower flange portions of the side sill inner. A vehicle underbody structure characterized by:

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

9. 9. The vehicle underbody structure according to claim 8, 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:

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