Vehicle underbody structure

Abstract

The objective is to provide a vehicle underbody structure that can ensure desired side impact performance even when the floor panel is joined to the side sill above the center position in the vertical direction of the vehicle. [Solution] The lower body structure of the vehicle 1 comprises a floor cross member 6 connecting a pair of left and right side sills 3, an upper member 70 fixed to the upper floor panel surface 4a which is the upper surface of the front floor panel 4, and having a cross member upper surface 711 that protrudes upward of the vehicle and faces upward of the vehicle, and a lower member 80 fixed to the lower floor panel surface 4b which is the lower surface of the front floor panel 4, and protruding downward of the vehicle, and the side sills 3 and the floor cross member 6 are joined so that the upper side sill surface 3c and the cross member upper surface 711 are aligned in the vertical direction of the vehicle, and the front floor panel 4 positioned between the upper member 70 and the lower member 80, the upper member 70 and the lower member 80 form a closed cross section in the longitudinal direction.

Description

Technical Field

[0001] The present invention relates to a lower vehicle body structure of a vehicle, for example, in which a floor panel is joined above a central position in the vehicle vertical direction with respect to left and right side sills.

Background Art

[0002] Generally, the lower vehicle body structure of recent vehicles includes a pair of left and right side sills extending in the vehicle front-rear direction, a floor panel provided between the pair of left and right side sills, and a floor cross member fixed to the upper surface of the floor panel and connecting the pair of left and right side sills in the vehicle width direction.

[0003] And in such a lower vehicle body structure of a vehicle, as shown in Patent Document 1, with respect to a collision load from the side of the vehicle (hereinafter referred to as a side collision load) during a side collision, the pair of left and right side sills are configured to transmit the collision load to the opposite side in the vehicle width direction by a floor cross member connecting the pair of left and right side sills in the vehicle width direction. Specifically, the lower vehicle body structure of the vehicle transmits a side collision load acting on one of the pair of left and right side sills to the other side sill via a floor cross member extending in the vehicle width direction.

[0004] Thus, in order to efficiently transmit the side collision load from one side sill to the other side sill, the lower vehicle body structure of the vehicle aligns the positions in the vehicle vertical direction of the upper surfaces where the ridge line portions of the side sill and the floor cross member are formed, and it is necessary to increase the cross-sectional strength of the floor cross member in a longitudinal section along the vehicle front-rear direction (hereinafter referred to as a front-rear direction longitudinal section).

[0005] However, as shown in Patent Document 1, for example, an electric vehicle may have a floor panel disposed above the vehicle because a battery is disposed under the floor. Then, the floor panel is joined above the central position in the vehicle vertical direction with respect to the side sill.

[0006] Thus, when the floor panel is joined to the side sill above the central position in the vehicle's vertical direction, the upper surfaces of the side sill and the floor cross member, where relatively strong ridges are formed, can be aligned in the vehicle's vertical direction, allowing the ridges to be continuous. However, the cross-sectional area of ​​the floor cross member in the longitudinal direction becomes smaller, and there is a risk that sufficient cross-sectional strength cannot be ensured. Therefore, it cannot be said that side impact loads can be efficiently transmitted from one side sill to the other, and there is room for improvement. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-055473 [Overview of the project] [Problems that the invention aims to solve]

[0008] In view of the above-mentioned problems, the present invention aims to provide a lower vehicle body structure that can ensure desired side impact performance even when the floor panel is joined to the side sill above the central position in the vertical direction of the vehicle. [Means for solving the problem]

[0009] This invention is characterized by a lower vehicle body structure comprising a pair of left and right side sills extending in the vehicle longitudinal direction at both ends of the floor panel in the vehicle width direction, and a floor cross member extending in the vehicle width direction and connecting the pair of left and right side sills, wherein the side sills have a side sill upper surface facing upward of the vehicle and form a closed cross section in the longitudinal section along the vehicle width direction, and the floor cross member comprises an upper member fixed to the floor panel upper surface, which is the upper surface of the floor panel, and projecting upward of the vehicle, and an upper cross member having an upper cross member surface facing upward of the vehicle, and a lower member fixed to the floor panel lower surface, which is the lower surface of the floor panel, and projecting downward of the vehicle, wherein the side sills and the floor cross member are joined so that the upper surface of the side sills and the upper surface of the cross member are aligned in the vehicle vertical direction, and the floor panel, which is positioned between the upper member and the lower member, the upper member and the lower member form a closed cross section in the longitudinal section along the vehicle longitudinal direction.

[0010] The floor cross member, which extends in the vehicle width direction and connects the left and right pair of side sills as described above, may be connected to the side sills by being directly connected at both ends, or it may be connected via seat mounting brackets or gussets provided at both ends.

[0011] Furthermore, the above-mentioned side sill and floor cross member are joined so that the upper surface of the side sill and the upper surface of the cross member are aligned in the vehicle's vertical direction. This means that the upper surface of the side sill and the upper surface of the cross member may be joined so that they are aligned in the vehicle's width direction, or a portion of the upper surface of the cross member may overlap the upper surface of the side sill. Moreover, the above-mentioned side sill and floor cross member refer to the case where the upper surface of the side sill is an inclined surface that slopes in the vehicle's vertical direction with respect to the vehicle's width direction, and the upper surface of the cross member is positioned in the vehicle's vertical direction within the range from the upper end to the lower end of the inclined upper surface of the side sill.

[0012] This invention makes it possible to ensure the desired side impact performance even when the floor panel is joined to the side sill above the center position in the vertical direction of the vehicle. Specifically, the lower body structure of the vehicle comprises a pair of left and right side sills extending in the longitudinal direction of the vehicle at both ends of the floor panel in the vehicle width direction, and a floor cross member extending in the vehicle width direction and connecting the pair of left and right side sills. The side sills have an upper side sill surface facing upwards of the vehicle and form a closed cross section in the longitudinal section along the vehicle width direction (hereinafter referred to as the widthwise longitudinal section).

[0013] Furthermore, the floor cross member comprises an upper member fixed to the upper surface of the floor panel, which is the upper surface of the floor panel, and projecting upwards toward the vehicle, and having an upper surface of the cross member facing upwards toward the vehicle, and a lower member fixed to the lower surface of the floor panel, which is the lower surface of the floor panel, and projecting downwards toward the vehicle.

[0014] The side sill and the floor cross member are joined so that the upper surface of the side sill and the upper surface of the cross member are aligned in the vertical direction of the vehicle. The ridge portion extending in the vehicle's longitudinal direction, which forms the upper surface of the side sill, and the ridge portion extending in the vehicle's width direction, which forms the upper surface of the floor cross member, are more rigid in each member than other parts. Thus, although the extension directions of the highly rigid ridge portions in each member are approximately perpendicular in a plan view, they are located at approximately the same position in the vertical direction of the vehicle. In other words, the ridge portion of the floor cross member and the ridge portion of the side sill are continuous. Therefore, the lower body structure of the vehicle can efficiently transmit side impact loads from one side sill to the other side sill.

[0015] Furthermore, the floor panel positioned between the upper member and the lower member, the upper member, and the lower member form a closed cross section in the longitudinal section in the front-rear direction. Therefore, the cross-sectional area of ​​the floor cross member, which functions as a load transmission member in the vehicle width direction that transmits a side impact load from one side sill to the other side sill, in the longitudinal section along the vehicle's front-rear direction can be increased compared to the cross-sectional area of ​​the floor cross member that is composed only of an upper member fixed to the upper surface of the floor panel.

[0016] Therefore, the cross-sectional strength of the floor cross member in the longitudinal section along the vehicle's longitudinal direction is increased, as it functions as a transmission member that transmits the side impact load from one side sill to the other side sill, and the side impact load can be efficiently transmitted from one side sill to the other side sill. Consequently, in the lower body structure of the vehicle in which the floor panel is joined to the side sill above the central position in the vehicle's vertical direction, the desired side impact performance can be ensured.

[0017] In an embodiment of this invention, the upper member may have an upper member ridge portion that extends in the vehicle width direction, and the upper member may have three or more upper member ridge portions that are spaced apart in the vehicle front-rear direction.

[0018] This invention allows for a further increase in the cross-sectional strength of the upper member because the upper ridge portion, which is more rigid than other parts of the upper member, comprises three or more such ridge portions. Therefore, the cross-sectional strength of the floor cross member, which forms a closed cross section with the upper member whose cross-sectional strength has been further increased and the lower member via the floor panel, can be further increased. Thus, the lower body structure of the vehicle can improve its function as a load transmission member in the vehicle width direction.

[0019] In another aspect of this invention, the lower member may have a ridge portion extending in the vehicle width direction as the lower member ridge portion, and the lower member may have three or more of these lower member ridge portions positioned at intervals in the vehicle front-rear direction.

[0020] This invention makes it possible to further increase the cross-sectional strength of the lower member because there are three or more lower ridge portions in the lower member that are more rigid than other parts. Therefore, with the upper and lower members having further increased cross-sectional strength, the cross-sectional strength of the floor cross member that forms a closed cross-section via the floor panel can be further increased. Thus, the lower body structure of the vehicle can further improve its function as a load transmission member in the vehicle width direction.

[0021] Furthermore, in an embodiment of this invention, the floor cross member has joining portions provided at both ends in the vehicle width direction and joined to the side sills, and a main body portion between the joining portions on both sides in the vehicle width direction, and the upper member constituting the main body portion protrudes upward toward the vehicle and is arranged at intervals in the vehicle longitudinal direction, and has an upper convex portion having the upper surface of the cross member, and an upper concave portion connecting the upper convex portions in the vehicle longitudinal direction and arranged below the vehicle from the upper surface of the cross member, and in the longitudinal section in the longitudinal direction, the upper members are arranged at intervals The lower member, which constitutes the main body portion, is formed in a substantially M-shape in cross-section by the convex portion and the upper concave portion, and has a lower convex portion that protrudes downward toward the vehicle and is spaced apart in the longitudinal direction of the vehicle, and a lower concave portion that connects the lower convex portions in the longitudinal direction of the vehicle and is positioned above the lower end of the lower convex portion and is concave, and in a longitudinal cross-section along the longitudinal direction of the vehicle, the lower convex portion and the lower concave portion, which are spaced apart, are formed in a substantially inverted M-shape in cross-section, and the upper member and the lower member may be joined by the upper concave portion and the lower concave portion.

[0022] The joint portions provided at both ends in the vehicle width direction and joined to the side sill may be a part of the floor cross member continuous with the main body portion, or may be seat mounting brackets or gussets provided at both ends.

[0023] According to this invention, the cross-sectional strength of the floor cross member can be further increased. Specifically, it has a joint portion provided at both ends in the vehicle width direction and joined to the side sill, and a main body portion between the joint portions on both sides in the vehicle width direction. The upper member constituting the main body portion protrudes upward of the vehicle and is arranged at intervals in the vehicle longitudinal direction, and has an upper convex portion having the upper surface of the cross member, and an upper concave portion that connects the upper convex portions in the vehicle longitudinal direction and is arranged below the vehicle from the upper surface of the cross member. In the longitudinal cross section in the front-rear direction, the upper convex portion and the upper concave portion arranged at intervals are formed in a substantially M-shaped cross section. Therefore, at least six upper ridge line portions extending in the vehicle width direction and spaced apart in the vehicle longitudinal direction are formed on the upper member. Thereby, it is possible to configure the upper member having a high cross-sectional strength while forming a low height in the vehicle up-down direction.

[0024] Also, the lower member constituting the main body portion protrudes downward of the vehicle and has a lower convex portion arranged at intervals in the vehicle longitudinal direction, and a lower concave portion that connects the lower convex portions in the vehicle longitudinal direction and is arranged above the vehicle from the lower end of the lower convex portion and is concave. In the longitudinal cross section in the front-rear direction, the lower convex portion and the lower concave portion arranged at intervals are formed in a substantially inverted M-shaped cross section. Therefore, at least six lower ridge line portions extending in the vehicle width direction and spaced apart in the vehicle longitudinal direction are formed on the lower member. Thereby, it is possible to configure the lower member having a high cross-sectional strength while forming a low height in the vehicle up-down direction.

[0025] Furthermore, the upper member and the lower member are joined by the upper concave portion and the lower concave portion. As a result, in the floor cross member that forms a closed cross-section through the floor panel, a closed cross-section can be formed by each of the upper convex portion and the lower convex portion that are spaced apart by a predetermined interval in the vehicle longitudinal direction. Therefore, two closed cross-sections can be formed in the floor cross member constituted by the upper member and the lower member, and the cross-sectional strength of the floor cross member can be further improved. Thus, the lower body structure of the vehicle can further improve its function as a load transmission member in the vehicle width direction.

[0026] Also, as an aspect of this invention, the floor panel is provided with a floor convex portion that extends along the vehicle width direction and protrudes in either the vehicle vertical direction. The upper concave portion, the floor convex portion, and the lower concave portion are laminated in the vehicle vertical direction, and the upper member and the lower member may be joined by the upper concave portion and the lower concave portion via the floor convex portion. The floor convex portion that protrudes in either the vehicle vertical direction as described above may protrude upward or downward of the vehicle.

[0027] According to this invention, the floor convex portion is provided on the floor panel, extends along the vehicle width direction, and protrudes in either the vehicle vertical direction. The upper concave portion, the floor convex portion, and the lower concave portion are laminated in the vehicle vertical direction, and the upper member and the lower member are joined by the upper concave portion and the lower concave portion via the floor convex portion.

[0028] Therefore, compared with the case where the upper concave portion and the lower concave portion are laminated with the flat floor panel sandwiched therebetween to form the floor cross member with a closed cross-section, while suppressing the protruding height of the upper convex portion or the lower convex portion with respect to the floor panel on the side opposite to the direction in which the floor convex portion protrudes to be low, the cross-sectional height of the floor cross member that forms a closed cross-section can be ensured.

[0029] Therefore, the cross-sectional strength of the floor cross member, which is composed of the upper member and the lower member, can be further improved. Thus, the lower body structure of the vehicle can further improve its function as a load transmission member in the vehicle width direction.

[0030] In another aspect of this invention, the upper member and the lower member may be provided with flange portions that are aligned with the vehicle width direction and protrude in the vehicle's longitudinal direction, and the upper member and the lower member may be joined to the floor panel by the flange portions.

[0031] This invention allows the upper member and the lower member to be securely fixed to the floor panel by the flange portion. Therefore, the floor cross member, with the floor panel sandwiched between the upper member and the lower member, can reliably form a closed cross section.

[0032] In another aspect of this invention, a plurality of beads extending in the vehicle's longitudinal direction may be formed on the flange portion formed along the vehicle's width direction, spaced apart in the vehicle's width direction. This invention makes it possible to improve the shape retention of the flange portion, which is formed to be long in the vehicle width direction. Therefore, the shape retention of the upper member and the lower member having the flange portion can be improved.

[0033] In another aspect of this invention, the floor cross member may include a first floor cross member positioned approximately in the center of the floor panel in the vehicle's longitudinal direction, and a second floor cross member positioned at a predetermined distance from the first floor cross member towards the rear of the vehicle.

[0034] This invention allows the floor cross members, which form a closed cross section with respect to the floor panel, to be provided at two locations separated by a predetermined distance in the longitudinal direction of the vehicle. Therefore, the transmission performance of collision loads during side impacts in the vehicle width direction by the floor cross members can be improved. Therefore, in the lower body structure of the vehicle in which the floor panel is joined to the side sill above the central position in the vertical direction of the vehicle, the desired side impact performance can be ensured. [Effects of the Invention]

[0035] The present invention provides a vehicle underbody structure that can ensure desired side impact performance even when the floor panel is joined to the side sill above the central position in the vertical direction of the vehicle. [Brief explanation of the drawing]

[0036] [Figure 1] An external perspective view showing the appearance of the lower part of the vehicle body as seen from the front. [Figure 2] A plan view showing the external appearance of the lower body of a vehicle in a top-down view. [Figure 3] A plan view showing the exterior appearance of the lower body of the vehicle from a bottom view. [Figure 4] Enlarged view of the main part of the cross-section in the direction of arrow AA in Figure 2. [Figure 5] Enlarged view of the main part of the cross-section in the direction of arrow BB in Figure 2. [Figure 6] Enlarged view of the main part of the cross-section in the direction of arrow CC in Figure 2. [Figure 7] Enlarged view of the main part of the cross-section in the direction of arrow DD in Figure 2. [Figure 8] A schematic cross-sectional view of the beads formed on the concave and flange portions, viewed from the front-rear direction of the vehicle. [Modes for carrying out the invention]

[0037] One embodiment of this invention will be described below with reference to the drawings. Vehicle 1 in this embodiment is, for example, an electric vehicle in which the front floor panel 4 is joined to the side sill 3 above the center position in the vertical direction of the vehicle. The lower body structure in the passenger compartment of such vehicle 1 will be described in detail with reference to Figures 1 to 8.

[0038] Figure 1 shows an external perspective view of the lower body of vehicle 1 from a forward view of the vehicle, Figure 2 shows a plan view of the lower body of vehicle 1, Figure 3 shows a bottom view of the lower body of vehicle 1, Figure 4 shows an enlarged cross-sectional view of the main part as seen by arrow AA in Figure 2, Figure 5 shows an enlarged cross-sectional view of the main part as seen by arrow BB in Figure 2, Figure 6 shows an enlarged cross-sectional view of the main part as seen by arrow CC in Figure 2, Figure 7 shows an enlarged cross-sectional view of the main part as seen by arrow DD in Figure 2, and Figure 8 shows a schematic cross-sectional view of the bead 66 formed on the concave parts 72, 82 and flange part 65 as seen from the front-rear direction of the vehicle.

[0039] More specifically, Figure 4 shows an enlarged cross-sectional view of the area where the first floor cross member 6A and the second floor cross member 6B are located, as seen from the direction of arrow AA extending in the longitudinal direction of the vehicle in Figure 2, with the side sill 3 and the front seat bracket 62 shown as dashed lines.

[0040] Figure 5 shows an enlarged cross-sectional view of the vicinity of the right side sill 3 in the vehicle width direction, as seen from the BB arrow extending in the vehicle width direction in Figure 2, and the first floor cross member 6A is shown with a dashed line. Figure 6 shows an enlarged cross-sectional view of both ends and the central part in the vehicle width direction, as seen from the CC arrow extending in the vehicle width direction in Figure 2, and the first floor cross member 6A is shown with a dashed line. Figure 7 shows an enlarged cross-sectional view of both ends and the central part in the vehicle width direction, as seen from the DD arrow extending in the vehicle width direction in Figure 2.

[0041] Furthermore, in the diagram, arrows Fr and Rr indicate the front-rear direction, with Fr indicating the front and Rr indicating the rear. Additionally, arrows Rw and Lw indicate the vehicle width direction, with Rw indicating the right direction and Lw indicating the left direction. Moreover, arrows Uh and Dh indicate the vehicle's vertical direction, with Uh indicating the top of the vehicle and Dh indicating the bottom of the vehicle.

[0042] As shown in Figures 1 and 2, the lower body of vehicle 1 includes a dash panel 2 that separates the engine compartment from the passenger compartment in the longitudinal direction of the vehicle, a pair of left and right side sills 3 that extend from the lower ends of both ends of the dash panel 2 in the vehicle width direction toward the rear of the vehicle, and a front floor panel 4 that is positioned between the left and right side sills 3 and forms the floor surface of the passenger compartment.

[0043] As shown in Figures 1 and 2, the front floor panel 4 has a roughly tunnel-shaped bulge 5 extending from the front to the rear of the vehicle, near the approximate center in the vehicle width direction. Also, as shown in Figures 1 and 2, a floor cross member 6 connecting a pair of left and right side sills 3 in the vehicle width direction is fixed to the front floor panel 4 on the lower body of the vehicle 1. A battery unit (not shown) is located below the front floor panel 4.

[0044] Furthermore, the lower body of the vehicle 1 includes a first floor cross member 6A and a second floor cross member 6B as floor cross members 6 that connect the left and right side sills 3 in the vehicle width direction. The first floor cross member 6A is positioned approximately in the center of the front floor panel 4 in the vehicle's longitudinal direction, and the second floor cross member 6B is positioned at a predetermined distance from the first floor cross member 6A towards the rear of the vehicle.

[0045] Each component will be explained in detail below. The dash panel 2 is a panel member having thickness in the front-to-rear direction of the vehicle, and its lower part is formed in a curved shape toward the rear of the vehicle. A front floor panel 4 is provided extending toward the rear of the vehicle from the lower end of this dash panel 2.

[0046] The side sills 3 consist of a pair of left and right sills that extend from the lower ends of both sides in the vehicle width direction of the dash panel 2 toward the rear of the vehicle, and the cross-sectional shape of the longitudinal section along the vehicle width direction (hereinafter referred to as the width direction longitudinal section) is configured to form a closed section with a substantially rectangular cross-section.

[0047] More specifically, the side sill 3 is formed in a roughly rectangular shape, slightly longer in the vehicle's vertical direction than in the vehicle's width direction, by assembling a roughly hat-shaped side sill outer 3a projecting outward in the vehicle's width direction and a roughly hat-shaped side sill inner 3b projecting inward in the vehicle's width direction. The upper surface of the side sill 3, which has a roughly rectangular shape in its longitudinal cross-section in the vehicle's width direction, is called the side sill upper surface 3c. The surface of the side sill 3 that runs along the vehicle's vertical direction is called the side surface 3d, and a side sill ridge 3e is formed at the corner between the side sill upper surface 3c and the side surface 3d.

[0048] As shown in Figures 1 to 5, the front floor panel 4 is a substantially flat panel member having thickness in the vertical direction of the vehicle, with its front end connected to the lower end of the dash panel 2, and the front of the front floor panel 4 is inclined upward toward the dash panel 2 as it approaches the front of the vehicle. The side of the front floor panel 4 facing upwards towards the vehicle is designated as the upper floor panel surface 4a, and the side facing downwards towards the vehicle is designated as the lower floor panel surface 4b.

[0049] Furthermore, a tunnel section 5, which will be described later, is formed approximately in the center of the front floor panel 4 in the vehicle width direction, and protrudes upward toward the vehicle. The tunnel section 5 is joined to the dash panel 2 at its front end, and its rear end extends to the front of the first floor cross member 6A, which will be described later.

[0050] Furthermore, two floor protrusions 4c (see Figure 4) are formed on the front floor panel 4, one approximately in the center of the vehicle's longitudinal direction and the other at a predetermined distance further rearward, with the protrusions extending upward toward the vehicle. Furthermore, the front floor panel 4 is provided with connecting pieces 4d at both ends in the vehicle width direction, which are bent upwards and joined to the side surface 3d of the side sill 3.

[0051] As shown in Figures 5 to 7, the front floor panel 4, configured in this way, is fixed by bringing the joining piece 4d of the front floor panel 4 into contact with the inner side surface 3d in the vehicle width direction of the side sill 3, which is formed in a substantially rectangular shape that is slightly longer in the vehicle height direction than in the vehicle width direction in a cross-section in the vehicle width direction. At this time, the front floor panel 4 is fixed so as to be located above the center position of the vehicle in the vehicle height direction with respect to the side sill 3, which is formed in a substantially rectangular shape that is slightly longer in the vehicle height direction than in the vehicle width direction.

[0052] The floor cross member 6 is provided at both ends in the vehicle width direction and comprises seat brackets 622 and 64 that connect to the side sills 3, and a main body portion 60 that forms the space between the seat brackets 622 and 64, connecting the left and right side sills 3 in the vehicle width direction. In addition, the main body portion 60 of the floor cross member 6 forms multiple cross member ridge portions 61 that extend in the vehicle width direction.

[0053] The main body portion 60 of the floor cross member 6 is constructed by sandwiching the front floor panel 4 from the vertical direction of the vehicle between an upper member 70 with a roughly M-shaped cross section extending in the vehicle width direction and fixed to the upper surface 4a of the floor panel 4 of the front floor panel 4, and a lower member 80 with a roughly inverted M-shaped cross section extending in the vehicle width direction and fixed to the lower surface 4b of the floor panel 4.

[0054] As shown in Figure 4, the upper member 70, which has a roughly M-shaped cross section, has upper member ridge sections 70a that form a plurality of cross member ridge sections 61 extending in the vehicle width direction, spaced at predetermined intervals in the vehicle's longitudinal direction, and is formed in a roughly inverted concave shape with an open cross section that is open to the lower part of the vehicle in the longitudinal direction.

[0055] More specifically, the upper member 70 comprises upper convex portions 71 that are arranged at predetermined intervals in the vehicle's longitudinal direction and protrude upward in the vehicle's longitudinal section, upper concave portions 72 that are arranged between the upper convex portions 71 and are positioned below the vehicle's cross member upper surface 711 of the upper convex portions 71, and flange portions 65 that protrude in the vehicle's longitudinal direction from the lower end of the outer surface 712 of the upper convex portions 71.

[0056] The upper convex portion 71 has, in its longitudinal cross section in the front-rear direction, a substantially horizontal upper cross member surface 711, an outer surface 712 extending downward and outward from the outer side of the upper cross member surface 711 in the vehicle's front-rear direction, and an inner surface 713 extending downward and inward from the inner side of the upper cross member surface 711 in the vehicle's front-rear direction. In addition, a flange portion 65 is provided at the lower end of the outer surface 712 for fixing to the upper floor panel 4a of the front floor panel 4.

[0057] Furthermore, the inner surface 713 is formed with a shorter inclination length than the outer surface 712 in the front-to-back cross-section. Specifically, in the front-to-back cross-section, the inner surface 713 is formed to be about half the length of the outer surface 712.

[0058] The upper concave portion 72 is formed substantially horizontally in a longitudinal cross section in the longitudinal direction of the vehicle, so as to connect the lower ends of the inner surfaces 713 of the upper cross member surfaces 711, which are provided on both sides in the longitudinal direction of the vehicle, in the longitudinal direction of the vehicle. Therefore, the upper concave portion 72 is positioned below the upper cross member surface 711 of the upper convex portion 71 and above the flange portion 65.

[0059] Furthermore, as shown in Figure 2, multiple beads 66 (see Figure 8) are formed at intervals in the vehicle width direction on the upper concave portion 72 formed between the upper convex portions 71 and the flange portion 65, projecting upwards on the vehicle and extending in the vehicle's longitudinal direction. Specifically, the beads 66 are formed in the flange portion 65 extending in the vehicle width direction, covering approximately one-third of the width on both sides. In addition, the beads 66 are formed in the upper concave portion 72 extending in the vehicle width direction, covering approximately one-third of the width on both sides and a small amount in the central portion.

[0060] As described above, the upper member 70 is formed such that upper member ridges 70a (cross member ridges 61) extending in the vehicle width direction are formed at the corners between the cross member upper surface 711 and the outer surface 712, the corners between the cross member upper surface 711 and the inner surface 713, the corners between the outer surface 712 and the flange portion 65, and the corners between the inner surface 713 and the upper concave portion 72, and is formed in a roughly M shape when viewed from the vehicle width direction.

[0061] As shown in Figure 4, the lower member 80, which has a roughly inverted M-shaped cross section, has lower member ridge sections 80a that form a plurality of cross member ridge sections 61 extending in the vehicle width direction, spaced at predetermined intervals in the vehicle's longitudinal direction, and is formed in a roughly concave shape with an open cross section that is open above the vehicle in the longitudinal direction.

[0062] More specifically, in the longitudinal section in the front-rear direction, it comprises lower convex portions 81 arranged at predetermined intervals in the front-rear direction of the vehicle and projecting upwards toward the vehicle, lower concave portions 82 arranged between the lower convex portions 81 and positioned above the vehicle above the bottom surface 811 of the cross member of the lower convex portions 81, and flange portions 65 projecting in the front-rear direction of the vehicle from the upper end of the outer surface 812 of the lower convex portions 81.

[0063] The lower convex portion 81 has, in its longitudinal cross section in the front-rear direction, a substantially horizontal cross member bottom surface 811, an outer surface 812 extending outward and upward of the vehicle on the outer side of the cross member bottom surface 811 in the vehicle's front-rear direction, and an inner surface 813 extending inward and upward of the vehicle on the inner side of the cross member bottom surface 811 in the vehicle's front-rear direction. In addition, a flange portion 65 is provided at the upper end of the outer surface 812 for fixing to the lower surface 4b of the floor panel of the front floor panel 4.

[0064] Furthermore, the inner surface 813 is formed with a longer inclination length than the outer surface 812 in the front-to-back cross-section. Specifically, in the front-to-back cross-section, the inner surface 813 is formed to be about twice the length of the outer surface 812.

[0065] The lower concave portion 82 is formed substantially horizontally in a longitudinal cross section in the longitudinal direction of the vehicle, so as to connect the upper ends of the inner surfaces 813 of the cross member bottom surfaces 811, which are provided on both sides in the longitudinal direction of the vehicle, in the longitudinal direction of the vehicle. Therefore, the lower concave portion 82 is positioned above the flange portion 65, which is positioned above the cross member bottom surface 811 of the lower convex portion 81.

[0066] Furthermore, as shown in Figure 3, multiple beads 66 (see Figure 8) are formed at intervals in the vehicle width direction on the lower concave portion 82 formed between the lower convex portions 81 and the flange portion 65, projecting downwards from the vehicle and extending in the vehicle's longitudinal direction. Specifically, the beads 66 are formed on the flange portion 65 extending in the vehicle width direction, excluding approximately the central 1 / 4 of the vehicle width direction. Also, the beads 66 are formed on the lower concave portion 82 extending in the vehicle width direction, covering the entire area in the vehicle width direction.

[0067] As described above, the lower member 80 is formed such that lower member ridges 80a (cross member ridges 61) extending in the vehicle width direction are formed at the corners between the cross member bottom surface 811 and the outer surface 812, the corners between the cross member bottom surface 811 and the inner surface 813, the corners between the outer surface 812 and the flange portion 65, and the corners between the inner surface 813 and the lower concave portion 82, and is formed in a substantially inverted M shape when viewed from the vehicle width direction.

[0068] The upper member 70 and lower member 80 formed in this way are arranged such that the upper member 70 is positioned above the front floor panel 4 on the vehicle, and the lower member 80 is positioned below the front floor panel 4 on the vehicle so as to correspond to the upper member 70 in the vehicle's vertical direction. In other words, the upper member 70 and lower member 80 are positioned and fixed so as to sandwich the front floor panel 4 from both sides in the vehicle's vertical direction, thereby forming the floor cross member 6.

[0069] More specifically, as shown in Figure 4, in the front floor panel 4, the upper member 70 and the lower member 80 are positioned such that the upper concave portion 72 and the lower concave portion 82 are located relative to a floor convex portion 4c that extends in the vehicle width direction and protrudes upward toward the vehicle.

[0070] Then, the flange portion 65 of the upper member 70, positioned on the upper surface 4a of the front floor panel 4, and the flange portion 65 of the lower member 80, positioned on the lower surface 4b of the front floor panel 4, are joined together with the front floor panel 4 in between. At this time, the upper concave portion 72 of the upper member 70, the floor convex portion 4c of the front floor panel 4, and the lower concave portion 82 of the lower member 80 are stacked in the vertical direction of the vehicle. The upper concave portion 72 of the upper member 70 and the lower concave portion 82 of the lower member 80, which are stacked in this way, are joined together with the floor convex portion 4c of the front floor panel 4 in between.

[0071] As a result, the front floor panel 4, upper member 70, and lower member 80 are fixed, and a floor cross member 6 can be formed that sandwiches the front floor panel 4 and forms a closed cross section. Specifically, a closed cross section is formed when the front floor panel 4 is sandwiched from the vehicle's vertical direction by the upper convex portion 71 and lower convex portion 81 on one side in the vehicle's longitudinal direction, and a closed cross section is formed when the front floor panel 4 is sandwiched from the vehicle's vertical direction by the upper convex portion 71 and lower convex portion 81 on the other side in the vehicle's longitudinal direction. In other words, a closed cross section is formed by the upper convex portion 71 and lower convex portion 81 on both sides in the vehicle's longitudinal direction of the upper concave portion 72, floor convex portion 4c, and lower concave portion 82 which are stacked and fixed in the vehicle's vertical direction.

[0072] As shown in Figure 4, in the longitudinal cross-section, the distance between the front floor panel 4 and the cross member bottom surface 811 in the vehicle's vertical direction is smaller than the distance between the front floor panel 4 and the cross member upper surface 711 in the vehicle's vertical direction. In other words, the height of the floor cross member 6 protruding downward from the floor panel bottom surface 4b of the front floor panel 4 can be made lower than the height of the floor cross member 6 protruding upward from the floor panel upper surface 4a of the front floor panel 4. However, since the floor convex portion 4c, which stacks the upper concave portion 72 and the lower concave portion 82, is located higher in the vehicle than other parts of the front floor panel 4, it is positioned approximately in the center between the cross member upper surface 711 and the cross member bottom surface 811 in the vehicle's longitudinal direction.

[0073] In other words, the closed cross section of the floor cross member 6, which is composed of an upper convex portion 71 and a lower convex portion 81 that sandwich the front floor panel 4, is located higher up on the vehicle relative to the front floor panel 4. However, with respect to the floor convex portion 4c, which is stacked with the upper concave portion 72 and the lower concave portion 82 located in the center of the floor cross member 6 in the vertical direction of the vehicle, it protrudes to the same extent on both sides in the vertical direction of the vehicle.

[0074] Furthermore, in the main body portion 60, the joints between the flange portions 65 of the upper member 70 and the lower member 80 and the front floor panel 4 are spaced apart in the vehicle's longitudinal direction, with the joints between the upper concave portion 72 and the lower concave portion 82 and the floor convex portion 4c located between them. Since the floor convex portion 4c protrudes upward from the front floor panel 4, the joints between the upper concave portion 72 and the lower concave portion 82 and the floor convex portion 4c are located above the vehicle in the vehicle's vertical direction compared to the joints between the flange portions 65 of the upper member 70 and the lower member 80 and the front floor panel 4, which are spaced apart in the vehicle's longitudinal direction.

[0075] Furthermore, at these joint locations, the cross-sectional strength in the longitudinal section in the front-rear direction of the main body portion 60 is lower than at other parts. Therefore, in the main body portion 60 of the floor cross member 6, the joint locations between the upper concave portion 72 and the lower concave portion 82 and the floor convex portion 4c are positioned higher on the vehicle than when they are aligned in a straight line in the front-rear direction with the joint locations between the flange portions 65 of the upper member 70 and the lower member 80, which are spaced apart in the front-rear direction of the vehicle, and the front floor panel 4. This arrangement allows for the construction of a floor cross member 6 with higher cross-sectional strength.

[0076] Furthermore, the upper convex portion 71 of the upper member 70 is fixed to the upper surface 4a of the floor panel of the front floor panel 4, which is fixed to the side sill 3, which is formed in a roughly rectangular shape that is slightly longer in the vertical direction of the vehicle than in the width direction of the vehicle, so that it is located above the center of the vehicle in the vertical direction. The upper surface 3c of the side sill 3 and the upper surface 711 of the cross member of the upper convex portion 71 are formed at approximately the same height in the vertical direction of the vehicle.

[0077] As described above, the floor cross member 6, which forms a closed cross section with the upper member 70 and the lower member 80, consists of a first floor cross member 6A located near the center of the front floor panel 4 in the vehicle's longitudinal direction, and a second floor cross member 6B located at a predetermined distance from the first floor cross member 6A and at the rear of the vehicle.

[0078] Of the floor cross members 6, the first floor cross member 6A at the front of the vehicle is equipped with a front seat bracket 62. The front seat bracket 62 consists of a front inner seat bracket 621 positioned in the center in the vehicle width direction of the first floor cross member 6A, and front outer seat brackets 622 positioned on both outer sides.

[0079] The front inner seat bracket 621 is roughly box-shaped, elongated in the vehicle width direction, with an opening at the bottom of the vehicle. The inner portion of the front seat in the vehicle width direction is attached to the upper surface of the front inner seat bracket 621. The front inner seat bracket 621 is fixed to the first floor cross member 6A by welding, such as spot welding.

[0080] The front outer seat brackets 622 are positioned on both sides of the first floor cross member 6A in the vehicle width direction and are configured to attach the outer portion of the front seat in the vehicle width direction to their upper surfaces. The front outer seat brackets 622 are roughly mountain-shaped when viewed from the front-rear direction of the vehicle, and are roughly box-shaped with an opening at the bottom of the vehicle. They are equipped with flange portions 623 (623a, 623b) extending in the vehicle width direction on both sides in the vehicle width direction. The front outer seat brackets 622 also have a ridge at the top (see Figure 4).

[0081] Specifically, the inner flange portion 623a on the inner side in the vehicle width direction of the front outer seat bracket 622, which is formed in a roughly V-shape when viewed from the front-rear direction of the vehicle, is joined and fixed to the upper surface 711 of the cross member of the upper member 70 that constitutes the first floor cross member 6A. In contrast, the outer flange portion 623b on the outer side in the vehicle width direction of the front outer seat bracket 622, which is formed in a roughly V-shape when viewed from the front-rear direction of the vehicle, is joined and fixed to the upper surface 3c of the side sill 3.

[0082] Thus, the first floor cross member 6A is joined to the side sill 3 via a front outer seat bracket 622, which has an inner flange portion 623a that is joined and fixed to the upper surface 711 of the cross member of the upper member 70, and an outer flange portion 623b that is joined and fixed to the upper surface 3c of the side sill 3.

[0083] Of the floor cross members 6, the second floor cross member 6B at the rear of the vehicle is equipped with a rear outer seat bracket 64. The rear outer seat bracket 64 is positioned on both outer sides in the vehicle width direction of the second floor cross member 6B. The rear outer seat bracket 64 is positioned on both sides in the vehicle width direction of the second floor cross member 6B and is configured to attach the outer portion of the rear of the front seat in the vehicle width direction to its upper surface. Note that the rear inner seat bracket, which attaches the inner portion of the rear of the front seat in the vehicle width direction, is not shown in the illustration.

[0084] The rear outer seat bracket 64 has a main body portion 641 that is approximately square in plan view and fixed to the upper convex portion 71 of the upper member 70 that constitutes the second floor cross member 6B, and a flange portion 642 that extends outward in the vehicle width direction from the main body portion 641. The rear outer seat bracket 64 has a ridge at its upper part (see Figure 4).

[0085] Furthermore, the main body portion 641 is fixed to the second floor cross member 6B by welding, such as spot welding, and the flange portion 642 is fixed by joining it to the upper surface 3c of the side sill 3. Thus, the second floor cross member 6B is joined to the side sill 3 via a rear outer seat bracket 64 which has a main body portion 641 that is joined and fixed to the upper surface 711 of the cross member of the upper member 70, and a flange portion 642 that is joined and fixed to the upper surface 3c of the side sill 3.

[0086] As described above, the first floor cross member 6A, which is joined to the side sill 3 via the front outer seat bracket 622, and the second floor cross member 6B, which is joined to the side sill 3 via the rear outer seat bracket 64, have their upper cross member upper surface 711 of the upper member 70 that constitutes them, which is in approximately the same position as the upper side sill surface 3c of the side sill 3 in the vehicle's vertical direction.

[0087] Therefore, the upper member ridge portion 70a (cross member ridge portion 61) extending in the vehicle width direction in the first floor cross member 6A and the second floor cross member 6B is continuous with the side sill ridge portion 3e formed at the corner between the upper side sill surface 3c and the side surface 3d of the side sill 3, via the ridge portion of the front outer seat bracket 622 and the ridge portion of the rear outer seat bracket 64.

[0088] More specifically, the upper member ridges 70a (cross member ridges 61) formed on both sides in the vehicle longitudinal direction of the upper convex portion 71 of the upper member 70 that constitutes the floor cross member 6 (6A, 6B) which is connected to the upper surface 3c of the side sill 3 via the front outer seat bracket 622 and the rear outer seat bracket 64, and the side sill ridges 3e formed at the corner between the upper surface 3c of the side sill 3 and the side surface 3d, extend in different directions and are connected via the front outer seat bracket 622 and the rear outer seat bracket 64, but are in approximately the same position in the vehicle vertical direction and are continuous via the front outer seat bracket 622 and the rear outer seat bracket 64.

[0089] As described above, the lower body structure of vehicle 1 comprises a pair of left and right side sills 3 extending in the longitudinal direction of the vehicle at both ends in the vehicle width direction of the front floor panel 4, and a floor cross member 6 extending in the vehicle width direction and connecting the pair of left and right side sills 3. The side sills 3 have a side sill upper surface 3c facing upwards of the vehicle and have a closed cross section in the longitudinal section along the vehicle width direction. The floor cross member 6 is fixed to the floor panel upper surface 4a, which is the upper surface of the front floor panel 4, and protrudes upwards of the vehicle, and also extends upwards of the vehicle. The floor cross member 6 comprises an upper member 70 having an upper cross member upper surface 711 facing downwards, and a lower member 80 fixed to the lower floor panel surface 4b, which is the lower surface of the front floor panel 4, and protruding downwards from the vehicle. The side sill 3 and the floor cross member 6 are joined so that the upper side surface 3c of the side sill and the upper cross member upper surface 711 are aligned in the vertical direction of the vehicle. The front floor panel 4, which is positioned between the upper member 70 and the lower member 80, along with the upper member 70 and the lower member 80, form a closed cross section in the longitudinal section along the front-rear direction of the vehicle.

[0090] This configuration ensures the desired side impact performance even when the front floor panel 4 is joined to the side sill 3 above the vehicle's vertical center position. Specifically, the lower body structure of vehicle 1 comprises a pair of left and right side sills 3 extending in the longitudinal direction of the vehicle at both ends in the vehicle width direction of the front floor panel 4, and a floor cross member 6 that extends in the vehicle width direction and connects the pair of left and right side sills 3. The side sills 3 have a side sill upper surface 3c facing upwards of the vehicle and have a closed cross section in the longitudinal section in the width direction.

[0091] Furthermore, the floor cross member 6 includes an upper member 70 fixed to the upper floor panel surface 4a, which is the upper surface of the front floor panel 4, and having an upper cross member surface 711 that protrudes upward and faces upward, and a lower member 80 fixed to the lower floor panel surface 4b, which is the lower surface of the front floor panel 4, and protruding downward.

[0092] The side sill 3 and the floor cross member 6 are joined so that the upper surface 3c of the side sill and the upper surface 711 of the cross member are aligned in the vertical direction of the vehicle. The side sill ridge portion 3e that extends in the longitudinal direction of the vehicle and forms the upper surface 3c of the side sill 3, and the cross member ridge portion 61 (upper member ridge portion 70a) that extends in the width direction of the vehicle and forms the upper surface 711 of the floor cross member 6, are more rigid in each member than other parts. Thus, although the extension directions of the highly rigid ridge portions (3e, 61) in each member are approximately perpendicular in a plan view, they are located at approximately the same position in the vertical direction of the vehicle. In other words, the cross member ridge portion 61 (upper member ridge portion 70a) of the floor cross member 6 and the side sill ridge portion 3e of the side sill 3 are continuous. Therefore, the lower body structure of the vehicle 1 can efficiently transmit side impact loads from one side sill 3 to the other side sill 3.

[0093] Furthermore, the front floor panel 4, positioned between the upper member 70 and the lower member 80, along with the upper member 70 and the lower member 80, form a closed cross section in the longitudinal direction. Therefore, the cross-sectional area of ​​the floor cross member 6, which functions as a load transmission member in the vehicle width direction that transmits a side impact load from one side sill 3 to the other side sill 3, in the longitudinal direction along the vehicle can be increased compared to the cross-sectional area of ​​a floor cross member composed only of an upper member fixed to the upper surface 4a of the floor panel.

[0094] Therefore, the cross-sectional strength of the floor cross member 6 in the longitudinal direction is increased, as it functions as a transmission member that transmits the side impact load from one side sill 3 to the other side sill 3, and the side impact load can be efficiently transmitted from one side sill 3 to the other side sill 3. Thus, in the lower body structure of a vehicle 1 in which the front floor panel 4 is joined to the side sill 3 above the central position in the vertical direction of the vehicle, the desired side impact performance can be ensured.

[0095] Furthermore, in the upper member 70, the ridge portion extending in the vehicle width direction is defined as the upper member ridge portion 70a, and the upper member 70 has three or more upper member ridge portions 70a located at intervals in the vehicle longitudinal direction. This configuration allows for a further increase in the cross-sectional strength of the upper member 70, as there are three or more upper ridge sections that are more rigid than other parts of the upper member 70.

[0096] Therefore, the cross-sectional strength of the floor cross member 6, which forms a closed section with the upper member 70 having further increased cross-sectional strength and the lower member 80 via the front floor panel 4, can be further increased. Thus, the lower body structure of the vehicle 1 can improve its function as a load transmission member in the vehicle width direction.

[0097] Furthermore, in the lower member 80, the ridge portion extending in the vehicle width direction is defined as the lower member ridge portion 80a, and the lower member 80 has three or more lower member ridge portions 80a located at intervals in the vehicle's longitudinal direction. This configuration allows for a further increase in the cross-sectional strength of the lower member 80, as there are three or more lower ridge sections that are more rigid than other parts of the lower member 80.

[0098] Therefore, with the upper member 70 and lower member 80 having further increased cross-sectional strength, the cross-sectional strength of the floor cross member 6, which forms a closed cross-section via the front floor panel 4, can be further increased. Thus, the lower body structure of the vehicle 1 can further improve its function as a load transmission member in the vehicle width direction.

[0099] Furthermore, the floor cross member 6 has seat brackets 622 and 64 provided at both ends in the vehicle width direction and joined to the side sill 3, and a main body portion 60 between the seat brackets 622 and 64 on both sides in the vehicle width direction. The upper member 70 of the main body portion 60 protrudes upward toward the vehicle and is spaced apart in the vehicle longitudinal direction, and has an upper convex portion 71 having the cross member upper surface 711, and an upper concave portion 72 connecting the upper convex portions 71 in the vehicle longitudinal direction and positioned below the cross member upper surface 711. In the longitudinal section in the longitudinal direction, the upper convex portion 71 and the upper concave portion 72, which are spaced apart, form a roughly M-shaped cross section. The lower member 80 of the main body portion 60 has lower convex portions 81 that protrude downward toward the vehicle and are spaced apart in the longitudinal direction of the vehicle, and lower concave portions 82 that connect the lower convex portions 81 in the longitudinal direction of the vehicle and are positioned above the lower end of the lower convex portions 81 and are concave. In the longitudinal section in the longitudinal direction, the lower convex portions 81 and lower concave portions 82, which are spaced apart, form a roughly inverted M shape in cross-section. The upper member 70 and the lower member 80 are joined by the upper concave portion 72 and the lower concave portion 82.

[0100] This configuration further increases the cross-sectional strength of the floor cross member 6. Specifically, it has front outer seat brackets 622 provided at both ends in the vehicle width direction and joined to the side sill 3, and a main body portion 60 between the front outer seat brackets 622 on both sides in the vehicle width direction. The main body portion 60 of the upper member 70 protrudes upward toward the vehicle and is spaced apart in the vehicle longitudinal direction, and has upper convex portions 71 having the upper surface 711 of the cross member, and upper concave portions 72 connecting the upper convex portions 71 in the vehicle longitudinal direction and being located below the upper surface 711 of the cross member. In the longitudinal section in the longitudinal direction, the upper convex portions 71 and upper concave portions 72, which are spaced apart, form a roughly M-shaped cross section. As a result, the upper member 70 has at least six upper member ridge portions 70a extending in the vehicle width direction, spaced apart in the vehicle longitudinal direction. This makes it possible to construct an upper member 70 with high cross-sectional strength while keeping the vehicle's vertical height low.

[0101] Furthermore, the main body portion 60 of the lower member 80 protrudes downward toward the vehicle and has lower convex portions 81 that are spaced apart in the vehicle's longitudinal direction, and lower concave portions 82 that connect the lower convex portions 81 in the vehicle's longitudinal direction and are positioned above the lower end of the lower convex portions 81 and are concave. In the longitudinal section in the longitudinal direction, the lower convex portions 81 and lower concave portions 82, which are spaced apart, form a roughly inverted M-shape in cross-section. As a result, the lower member 80 has at least six lower member ridge portions 80a that extend in the vehicle's width direction and are spaced apart in the vehicle's longitudinal direction. This makes it possible to construct a lower member 80 with high cross-sectional strength while keeping the vehicle's vertical height low.

[0102] Furthermore, the upper member 70 and the lower member 80 are joined at the upper concave portion 72 and the lower concave portion 82. As a result, in the floor cross member 6 which forms a closed cross section via the front floor panel 4, a closed cross section can be formed at the upper convex portion 71 and the lower convex portion 81, which are separated by a predetermined distance in the longitudinal direction of the vehicle. Therefore, two closed cross sections can be formed in the floor cross member 6 composed of the upper member 70 and the lower member 80, further improving the cross-sectional strength of the floor cross member 6. Thus, the lower body structure of the vehicle 1 can further improve its function as a load transmission member in the vehicle width direction.

[0103] Furthermore, the front floor panel 4 is provided with a floor convex portion 4c that extends along the width direction of the vehicle and protrudes in either the vertical direction of the vehicle. The upper concave portion 72, the floor convex portion 4c, and the lower concave portion 82 are stacked in the vertical direction of the vehicle, and the upper member 70 and the lower member 80 are joined via the floor convex portion 4c, with the upper concave portion 72 and the lower concave portion 82 being joined together.

[0104] In this configuration, the upper concave portion 72, the floor convex portion 4c provided on the front floor panel 4 which extends along the vehicle width direction and protrudes in either the vertical direction of the vehicle, and the lower concave portion 82 are stacked in the vertical direction of the vehicle, and the upper member 70 and the lower member 80 are joined by the upper concave portion 72 and the lower concave portion 82 via the floor convex portion 4c.

[0105] Therefore, compared to the case where a flat front floor panel 4 is sandwiched between the upper concave portion 72 and the lower concave portion 82 to form a closed-section floor cross member 6, it is possible to keep the protrusion height of the lower convex portion 81 relative to the front floor panel 4 on the underside of the vehicle, opposite to the direction in which the floor convex portion 4c protrudes, low while ensuring the cross-sectional height of the floor cross member 6 that forms a closed section.

[0106] Therefore, the cross-sectional strength of the floor cross member 6, which is composed of the upper member 70 and the lower member 80, can be further improved. Thus, the lower body structure of the vehicle 1 can further improve its function as a load transmission member in the vehicle width direction.

[0107] Furthermore, the upper member 70 and the lower member 80 are provided with flange portions 65 that run along the width direction of the vehicle and protrude in the front-rear direction of the vehicle, and the upper member 70 and the lower member 80 are joined to the front floor panel 4 by the flange portions 65.

[0108] This configuration allows the upper member 70 and the lower member 80 to be securely fixed to the front floor panel 4 by the flange portion 65. Therefore, the floor cross member 6, with the front floor panel 4 sandwiched between the upper member 70 and the lower member 80, can reliably form a closed cross section.

[0109] Furthermore, since multiple beads 66 extending in the vehicle's longitudinal direction are formed at intervals in the vehicle's width direction on the flange portion 65 formed along the vehicle's width direction, the shape retention of the flange portion 65, which is formed to be long in the vehicle's width direction, can be improved. Therefore, the shape retention of the upper member 70 and lower member 80 having flange portions 65 can be improved.

[0110] Furthermore, since multiple beads 66 extending in the vehicle's longitudinal direction are formed at intervals in the vehicle's width direction in the concave portions 72 and 82 formed along the vehicle's width direction, the shape retention of the long concave portions 72 and 82 in the vehicle's width direction can be improved. Therefore, the shape retention of the upper member 70 and lower member 80 having concave portions 72 and 82 on which the bead 66 is formed can be improved.

[0111] Furthermore, the floor cross member 6 includes a first floor cross member 6A positioned approximately in the center of the front floor panel 4 in the vehicle's longitudinal direction, and a second floor cross member 6B positioned at a predetermined distance from the first floor cross member 6A towards the rear of the vehicle.

[0112] This configuration allows for the installation of two floor cross members 6, which form a closed cross section on either side of the front floor panel 4, at predetermined intervals in the longitudinal direction of the vehicle. This improves the transmission performance of collision loads during side impacts in the width direction of the vehicle by the floor cross members 6. Therefore, in the lower body structure of the vehicle 1 in which the front floor panel 4 is joined to the side sill 3 above the central position in the vertical direction of the vehicle, the desired side impact performance can be ensured.

[0113] In the correspondence between the structure of this invention and the embodiments described above, The floor panel of this invention corresponds to the front floor panel 4. The same applies to the following: The connecting portion corresponds to the front outer seat bracket 622, This invention is not limited to the configuration of the embodiments described above, and many other embodiments can be obtained.

[0114] For example, in the embodiment described above, the first floor cross member 6A is joined to the side sill 3 via front outer seat brackets 622 provided on both sides in the vehicle width direction, and the second floor cross member 6B is joined to the side sill 3 via rear outer seat brackets 64 provided on both sides in the vehicle width direction. However, the main body portion 60 may also be joined to the side sill 3 via gussets provided on both sides in the vehicle width direction, or both ends of the main body portion 60 may be directly joined to the side sill 3. Furthermore, the cross member upper surface 711 of the upper member 70 constituting the main body portion 60 may be extended outward in the vehicle width direction and joined to the side sill upper surface 3c of the side sill 3.

[0115] Furthermore, although the side sill 3 described above was formed with a rectangular cross section that was slightly longer in the vehicle-rear direction than in the vehicle-width direction, the upper surface 3c of the side sill 3 may be an inclined surface that slopes toward the center in the vehicle-width direction. In this case, the upper surface 711 of the cross member of the upper member 70 that constitutes the floor cross member 6 should be positioned in the range between the upper end position and the lower end position of the inclined side sill outer 3a in the vehicle-vertical direction.

[0116] Furthermore, although the floor convex portion 4c of the front floor panel 4, which is formed by stacking the upper concave portion 72 of the upper member 70 and the lower concave portion 82 of the lower member 80, is formed to protrude upward toward the vehicle, the floor convex portion 4c may also protrude downward toward the vehicle. In this case, the lower member 80 described above would be positioned above the vehicle of the front floor panel 4 and fixed to the upper surface 4a of the floor panel, and the upper member 70 would be positioned below the vehicle of the front floor panel 4 and fixed to the lower surface 4b of the floor panel, which would reduce the protrusion height of the floor cross member 6 upward toward the vehicle. [Explanation of symbols]

[0117] 1…Vehicle 3... Side sill 3c... Top of the side sill 4…Front floor panel 4a... Top surface of floor panel 4b...Underside of floor panel 4c... Floor protrusion 6…Floor cross member 6A…First floor cross member 6B...2nd floor cross member 60…Body part 70... Upper Member 70a... Upper member ridge section 71… Upper convex part 72... Upper concave part 80...Roamember 80a...Lower member ridge section 81... Lower convex part 82...Lower concave section 622…Front outer seat bracket 711... Top surface of the cross member

Claims

1. A pair of left and right side sills extending in the front-to-rear direction of the vehicle are located at both ends of the floor panel in the vehicle width direction, It includes a floor cross member that extends in the vehicle width direction and connects the left and right pair of side sills, The aforementioned side sill has an upper side sill surface facing upwards of the vehicle, and has a closed cross-section in the longitudinal section along the vehicle width direction. The aforementioned floor cross member is An upper member is fixed to the upper surface of the floor panel, which is the upper surface of the floor panel, and protrudes upward of the vehicle, and has an upper surface of a cross member that faces upward of the vehicle, It comprises a lower member fixed to the lower surface of the floor panel, which is the lower surface of the floor panel, and protruding downwards from the vehicle, The side sill and the floor cross member are, The upper surface of the side sill and the upper surface of the cross member are joined together so that their positions are aligned in the vertical direction of the vehicle. The floor panel, positioned between the upper member and the lower member, the upper member, and the lower member form a closed cross section in the longitudinal section along the vehicle's longitudinal direction. The lower body structure of the vehicle.

2. In the upper member, the ridge portion extending in the vehicle width direction is defined as the upper member ridge portion. The upper member has three or more upper member ridges that are spaced apart in the longitudinal direction of the vehicle. The lower body structure of the vehicle according to claim 1.

3. In the lower member, the ridge portion extending in the vehicle width direction is defined as the lower member ridge portion. The lower member has three or more lower member ridges that are spaced apart in the longitudinal direction of the vehicle. The lower body structure of the vehicle according to claim 2.

4. The floor cross member has connecting portions provided at both ends in the vehicle width direction and joined to the side sill, and a main body portion between the connecting portions on both sides in the vehicle width direction. The upper member that constitutes the main body portion is The upper convex portion, which protrudes upward toward the vehicle and is arranged at intervals in the longitudinal direction of the vehicle, and which has the upper surface of the cross member, The upper convex portions connect to each other in the vehicle's longitudinal direction, and the cross member has an upper concave portion positioned below the vehicle's upper surface. In the longitudinal section along the vehicle's front-rear direction, the upper convex portion and the upper concave portion, which are spaced apart, form a roughly M-shaped cross-section. The lower member constituting the main body portion is The lower convex portion protrudes downward toward the vehicle and is arranged at intervals in the longitudinal direction of the vehicle, The lower convex portions are connected to each other in the vehicle's longitudinal direction, and the lower concave portion is positioned above the lower end of the lower convex portion and is concave. In the longitudinal section along the vehicle's front-rear direction, the lower convex portion and the lower concave portion, which are spaced apart, form a roughly inverted M-shape in cross-section. The upper member and the lower member are joined at the upper recessed portion and the lower recessed portion. The lower body structure of the vehicle according to claim 3.

5. The floor panel is provided with a floor protrusion that extends along the vehicle width direction and protrudes in either the vertical direction of the vehicle. The upper concave portion, the floor convex portion, and the lower concave portion are stacked in the vertical direction of the vehicle. The upper member and the lower member are joined via the floor convex portion, and the upper concave portion and the lower concave portion are joined together. The lower body structure of the vehicle according to claim 4.

6. The upper member and the lower member are, A flange portion is provided that is aligned with the vehicle width direction and protrudes in the vehicle's front-rear direction. The upper member and the lower member are joined to the floor panel by the flange portion. The lower body structure of the vehicle according to claim 1.

7. Multiple beads extending in the vehicle's longitudinal direction are formed at intervals in the vehicle's width direction on the flange portion formed along the vehicle's width direction. The lower body structure of a vehicle according to claim 6.

8. The floor cross member comprises a first floor cross member positioned approximately in the center of the floor panel in the vehicle's longitudinal direction, The vehicle is equipped with a second floor cross member positioned at a predetermined distance from the first floor cross member at the rear of the vehicle. The lower body structure of the vehicle according to claim 1.

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