Vehicle undercarriage

Abstract

The rigidity of the section including the intersection of the cross member and the floor tunnel will be improved. [Solution] The vehicle understructure 100 includes a floor panel 1 having a floor tunnel 10A and a panel body 10B, and an upper floor cross member 3. The upper floor cross member 3 intersects with the floor tunnel 10A in a state where it overlaps the floor tunnel 10A from above the vehicle. The floor tunnel 10A has an upper wall 11, a side wall 12 consisting of a lower side wall portion 12A located below the upper floor cross member 3 and a continuous side wall portion continuous with the lower side wall portion 12A, and a projection portion 13 formed by a portion of the side wall 12 that includes at least a part of the lower side wall portion 12A protruding outward in the vehicle width direction and having a lateral inclined surface 13a. The lower part of the overlapping portion 3A of the upper floor cross member 3 is formed as a recessed portion 31 that is recessed upward on the vehicle, and the recessed portion 31 has a joining inclined wall portion 31a that extends along the lateral inclined surface 13a and joins to the lateral inclined surface 13a.

Description

[[Technical Field]]

[0001] The present invention relates to a vehicle underbody structure. [[Background Art]]

[0002] Battery units for supplying electric power to an electric motor are arranged below a floor panel of an electric vehicle such as an electric vehicle that uses an electric motor as a power source for vehicle travel, or a hybrid vehicle that uses a combination of an electric motor and an internal combustion engine as a power source. In recent years, battery units have been increasing in size, and large-sized battery units are arranged below floor panels. In many cases, a floor tunnel that extends in the vehicle front-rear direction and bulges upward toward the vehicle is formed at the center of the floor panel in the vehicle width direction, and the floor panel is configured to include the floor tunnel and panel bodies extending from the floor panel to both sides in the vehicle width direction.

[0003] As an example of a vehicle underbody structure having a structure in which a battery unit is arranged below a floor panel having a floor tunnel, the structure disclosed in Patent Document 1 is known. In the structure disclosed in Patent Document 1, a cross member extends in the left-right direction (the vehicle width direction) across a center tunnel (hereinafter referred to as a floor tunnel), and the cross member intersects the floor tunnel in a state where the cross member overlaps the floor tunnel from above the vehicle. [[Prior Art Documents]] [[Patent Documents]]

[0004] [[Patent Document 1]] Japanese Unexamined Patent Publication No. 2022-159767 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0005] Incidentally, when the cross member overlaps the floor tunnel from above the vehicle and intersects with it, a structural gap is likely to occur between the cross member and the side wall of the floor tunnel at the intersection, and welding the cross member and floor tunnel together is difficult from a manufacturing standpoint. For this reason, the cross member and floor tunnel are generally not joined to each other at the intersection, and this intersection may become a weak point in the floor panel, suggesting room for improvement from the perspective of improving vibration characteristics.

[0006] Therefore, the present invention aims to provide a vehicle understructure having a structure that can improve the rigidity of the portion including the intersection of the cross member and the floor tunnel. [Means for solving the problem]

[0007] To achieve the above objective, according to one aspect of the present invention, a vehicle understructure is provided which includes a floor panel having a floor tunnel extending in the longitudinal direction of the vehicle and bulging upward from the vehicle at the center of the vehicle width direction in the underside of the vehicle, and panel bodies extending on both sides in the vehicle width direction from the floor tunnel, and a floor cross member extending in the vehicle width direction along the upper surface of the floor panel, wherein the floor cross member intersects with the floor tunnel while overlapping it from above the vehicle. In the vehicle understructure, the floor tunnel has an upper wall facing upward over the vehicle, a side wall extending along the vehicle width end of the upper wall, the side wall consisting of a lower side wall portion located below the floor cross member and a continuous side wall portion continuous with the lower side wall portion, and a protruding portion formed by the side wall projecting outward in the vehicle width direction with respect to at least a portion of the lower side wall portion, the protruding portion having a lateral inclined surface that slopes toward the panel body as it moves from the inside in the vehicle width direction toward the outside in the vehicle width direction, and the lower part of the overlapping portion of the floor cross member that overlaps with the floor tunnel is formed as a concave shape recessed upward over the vehicle, and the concave shape has a joining inclined wall portion that extends along the lateral inclined surface and joins to the lateral inclined surface. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a vehicle understructure having a structure that can improve the rigidity of the portion including the intersection of the cross member and the floor tunnel. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view of the undercarriage structure of an electric vehicle according to an embodiment of the present invention. [Figure 2] This is a top view of the vehicle's understructure. [Figure 3] This is a partial cross-sectional view along line AA shown in Figure 2. [Figure 4] This is an enlarged perspective view of the main parts of the vehicle's understructure. [Figure 5] This is a perspective view of the vehicle's undercarriage with the floor crossmember removed. [Figure 6] This is a top view of the vehicle's understructure with the floor cross member removed. [Figure 7] This is an enlarged perspective view of the main part of the floor panel. [Figure 8] This is an enlarged top view of the main part of the floor panel. [Figure 9] Figure 8 is a cross-sectional view of the floor panel along the BB line. [Figure 10] This is a partial cross-sectional view along the CC line shown in Figure 2. [Figure 11] This is a partial cross-sectional view along the DD line shown in Figure 2. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figures 1 to 3 are diagrams illustrating a vehicle understructure 100 according to one embodiment of the present invention, where Figure 1 is a perspective view, Figure 2 is a top view, and Figure 3 is a partial cross-sectional view along line AA shown in Figure 2. In each of the figures described below, the direction of arrow Fr indicates the front in the vehicle's longitudinal direction, the direction of arrow U indicates the upward in the vehicle's vertical direction, and the directions of arrows R and L indicate the right and left in the vehicle width direction when viewing the front of the vehicle from inside the passenger compartment.

[0011] (Overview of the vehicle's undercarriage) Referring to Figures 1 to 3, the vehicle understructure 100 includes a floor panel 1, a pair of side members 2, 2, and an upper floor cross member 3. In this embodiment, the vehicle understructure 100 further includes an underfloor rear cross member 4. In this embodiment, the vehicle understructure 100 is applied to the understructure of an electric vehicle, such as an electric vehicle that uses an electric motor as a power source for vehicle propulsion, or a hybrid vehicle that uses a combination of an electric motor and an internal combustion engine as a power source.

[0012] The floor panel 1 is a panel member that constitutes the bottom of the passenger compartment V where the front seat S1 and rear seat S2 are located. In this embodiment, a battery unit 5 for supplying power to the electric motor (not shown) is located below the floor panel 1. In other words, the vehicle understructure 100 is the understructure of an electric vehicle in which the front seat S1 and rear seat S2 are located above the floor panel 1, and the battery unit 5 for vehicle operation is located below the floor panel 1 and below the floor cross member 3. The floor panel 1 forms a floor section that separates the space inside the passenger compartment V where the front seat S1 and rear seat S2 are located from the space outside the vehicle. The floor panel 1 is a member made of steel plate that extends from the lower part of the front of the passenger compartment (e.g., the dashboard panel) toward the rear of the vehicle. The width dimension of the floor panel 1 is approximately the width dimension of the vehicle body. In the illustrated example, in the front area of ​​the passenger compartment V, the driver's seat S1 and the passenger seat S1 are located spaced apart from each other in the width direction. In other words, the two separate front seats S1 are positioned above the floor panel 1. The rear seats S2 are a so-called bench-type seat that is not separated on either side.

[0013] In the illustrated example, the floor panel 1 is composed of a main floor panel 1M on which the front seat S1 is provided and a rear floor panel 1R on which the rear seat S2 is provided. The rear end 1Ma of the main floor panel 1M and the front end 1Ra of the rear floor panel 1R are overlapped vertically and joined to each other by spot welding or the like. The front seat S1 is located above the main floor panel 1M and in the front area of ​​the vehicle compartment V. The rear seat S2 is located above the rear floor panel 1R and in the rear area of ​​the vehicle compartment V, and is spaced rearward relative to the front seat S1.

[0014] The floor panel 1 includes a floor tunnel 10A and a panel body 10B. The floor tunnel 10A extends in the vehicle front-rear direction at the center in the vehicle width direction of the lower part of the vehicle and bulges upward of the vehicle. The panel body 10B extends from the floor tunnel 10A to both sides in the vehicle width direction. That is, the panel body 10B extends from the lower end of the floor tunnel 10A to both the right side in the vehicle width direction and the left side in the vehicle width direction, and constitutes most of the floor panel 1.

[0015] In the illustrated example, the floor tunnel 10A extends over the entire main floor panel 1M in the vehicle front-rear direction. The floor tunnel 10A is formed integrally with other portions of the main floor panel 1M (that is, the panel body 10B), and has a groove-shaped cross-sectional shape opened toward the lower side of the vehicle when viewed in the vehicle front-rear direction. The floor tunnel 10A bulges upward of the vehicle with a generally trapezoidal outer shape.

[0016] In the illustrated example, the rear floor panel 1R includes a front flange portion 1Rb and a bulging portion 1Rc. The front edge (front end portion) of the front flange portion 1Rb constitutes the front end portion 1Ra of the rear floor panel 1R, and extends in the vehicle front-rear direction and the vehicle width direction. The bulging portion 1Rc occupies most of the area including the center on the front side of the rear floor panel 1R, and bulges upward of the vehicle. The front wall of the bulging portion 1Rc is continuous with the rear end of the front flange portion 1Rb and constitutes an inclined front wall 1Rc1 that extends rearward of the vehicle and obliquely upward from the rear end.

[0017] The pair of side members 2, 2 extend in the vehicle front-rear direction along the vehicle width-direction outer portion of the floor panel 1. That is, the pair of side members 2, 2 are spaced apart from each other in the vehicle width direction, and each side member 2 extends along the vehicle width-direction outer portion of the floor panel 1. The side member is composed of a side sill 2A provided at a position generally corresponding to the main floor panel 1M, and a rear side member 2B provided at a position generally corresponding to the rear floor panel 1R. The front portion of the rear side member 2B overlaps the side sill side wall 2A1 facing inward in the vehicle width direction at the rear portion of the side sill 2A, and extends along the side sill side wall 2A1. The floor tunnel 10A extends in the vehicle front-rear direction between the pair of side sills 2A, 2A.

[0018] Specifically, the side sill 2A has a hat-shaped cross-sectional shape that opens outward in the vehicle width direction. The vehicle width-direction outer edge portion of the main floor panel 1M is joined to the upper surface of the side sill upper wall 2A2 of the side sill 2A by spot welding or the like. The rear side member 2B has, for example, a generally groove-shaped cross-sectional shape that opens upward of the vehicle. The vehicle width-direction outer edge portion of the rear floor panel 1R is joined to the rear side member 2B from above the vehicle by spot welding or the like so as to close the opening of the rear side member 2B. The lower portion of the side member 2 composed of the side sill 2A and the rear side member 2B protrudes downward relative to the lower surface 1b of the floor panel 1.

[0019] Referring to FIG. 3, the rear side member 2B includes an inclined member portion 2B1 extending obliquely upward toward the rear of the vehicle from the front portion joined to the side sill 2A, and a straight member portion 2B2 linearly extending toward the rear of the vehicle from the rear end of the inclined member portion 2B1 to the rear end of the side member 2.

[0020] The floor cross member 3 extends in the vehicle width direction along the upper surface 1a of the floor panel 1. The floor cross member 3 is a member for connecting a pair of side members 2,2. In the illustrated example, the floor cross member 3 is provided on the front end side and the rear end side of the seat of the front seat S1 in the lower part of the floor panel 1 (main floor panel 1M in the illustrated example) in the vehicle longitudinal direction (in other words, the lower front seat panel section). That is, a pair of floor cross members 3,3 are arranged on the upper surface 1a of the lower part of the floor panel 1 (lower front seat panel section), spaced apart from each other in the vehicle longitudinal direction. Each floor cross member 3 is joined to the upper surface 1a of the floor panel 1 (lower front seat panel section) by spot welding or the like, and protrudes upward from the vehicle.

[0021] Each floor cross member 3 overlaps with the floor tunnel 10A from above the vehicle and intersects with the floor tunnel 10A. In other words, the floor cross member 3 follows the upper surface 1a of the floor panel 1, overlapping with the floor tunnel 10A and the panel body 10B from above the vehicle, and is joined to the floor tunnel 10A and the panel body 10B, and when viewed from above the vehicle, it intersects with the floor tunnel 10A.

[0022] Each floor cross member 3 has a roughly hat-shaped cross section that opens downwards towards the vehicle. Multiple seat brackets (X1, X2, X3, X4) supporting seats (front seats S1 in the illustrated example) are provided (attached) to the upper surface of each floor cross member 3. In the illustrated example, the seat brackets are provided at two locations on the upper surface of each floor cross member 3 corresponding to the seating area of ​​the right front seat S1 and at two locations corresponding to the seating area of ​​the left front seat S1. A slide rail (not shown) is provided to connect the upper parts of two of the seat brackets that are aligned in the longitudinal direction of the vehicle, and the seating areas of each front seat S1 are positioned on the floor panel 1 so as to be slidable in the longitudinal direction of the vehicle via the two slide rails.

[0023] The vehicle width end of each floor cross member 3 extends to the vicinity of the vehicle width outer edge of the main floor panel 1M. The outermost seat brackets (X3, X4) of the plurality of seat brackets (X1, X2, X3, X4) in the vehicle width direction are joined to the upper surface of the side sill upper wall 2A2 of the side member 2 (side sill 2A) and the floor cross member 3 by spot welding or the like. Therefore, the floor cross member 3 connects a pair of side members 2, 2 by joining its vehicle width end to the side member 2 via the seat brackets (X3, X4).

[0024] In this embodiment, the multiple seat brackets (X1, X2, X3, X4) include a first inner seat bracket X1, a second inner seat bracket X2, a first outer seat bracket X3, and a second outer seat bracket X4. The first inner seat bracket X1 and the second inner seat bracket X2 are adjacent to each other, spaced apart in the vehicle width direction, on the inner side (floor tunnel 10A side) in the vehicle width direction. In the illustrated example, the first inner seat bracket X1 is located on the right side in the vehicle width direction, and the second inner seat bracket X2 is located on the left side in the vehicle width direction. The first outer seat bracket X3 and the second outer seat bracket X4 are each located on the outermost side in the vehicle width direction of the four seat brackets (X1, X2, X3, X4). In the illustrated example, the first outer seat bracket X3 is located on the outermost right side, and the second outer seat bracket X4 is located on the outermost left side.

[0025] The underbody rear cross member 4 extends in the vehicle width direction along the lower surface 1b of the portion of the floor panel 1 (rear floor panel 1R) below the rear seat S2 (in other words, the panel portion below the rear seat) in the vehicle longitudinal direction, and is a member that connects a pair of side members 2,2 (here, a pair of rear side members 2B,2B). In the illustrated example, the underbody rear cross member 4 extends in the vehicle width direction along the rear corner portion 1Rd so as to cover the rear corner portion 1Rd formed by the front flange portion 1Rb and the inclined front wall 1Rc1 of the rear floor panel 1R from below. The underbody rear cross member 4 is joined to the floor panel 1 and protrudes downward from the vehicle.

[0026] The underfloor rear cross member 4 has a roughly hat-shaped cross section that opens upwards towards the vehicle. Multiple (four in the illustrated example) rear seat brackets Y for supporting the rear seat S2 are attached to the upper surface 1a of the portion below the rear seat S2 (rear seat lower panel portion) in the vehicle longitudinal direction of the floor panel 1 (rear floor panel 1R). The rear seat brackets Y are provided at the front of the bulging portion 1Rc. The seating portion of the rear seat S2 is positioned on the floor panel 1 (rear floor panel 1R) by being attached to the multiple rear seat brackets Y. Each end of the underfloor rear cross member 4 in the vehicle width direction is joined to the corresponding side member 2 (rear side member 2B).

[0027] As mentioned above, the battery unit 5 is located below the floor panel 1. The battery unit 5 has a generally box-shaped exterior with a height in the vertical direction of the vehicle that is approximately the same as the height of the side sill 2A. The space (allowable placement space) for arranging the battery unit 5 below the floor panel 1 extends outward in the vehicle width direction to the inner side surface in the vehicle width direction of the inner side wall of the side member 2 (side sill side wall 2A1 of the side sill 2A).

[0028] In general, a certain minimum ground clearance must be ensured at the underside of the vehicle, which is the distance from the road surface to the lowest surface of the underside of the vehicle body. When the battery unit is located below the floor panel, one might consider offsetting the height of the floor panel towards the interior of the vehicle to ensure the minimum ground clearance. However, this would reduce the interior space, which is undesirable from the standpoint of ensuring interior space. Considering both the need to ensure interior space and the minimum ground clearance, the understructure 100 of the vehicle is positioned, as in conventional designs, with the battery unit 5 positioned as close as possible to the lower surface 1b of the floor panel 1.

[0029] Referring to Figures 2 and 3, in the vehicle understructure 100, the battery unit 5 extends over approximately the entire area below the main floor panel 1M of the floor panel 1 in the longitudinal direction of the vehicle. The front end of the battery unit 5 is located below the front part of the main floor panel 1M in the longitudinal direction of the vehicle, and the rear end of the battery unit 5 extends beyond the rear end 1Ma of the main floor panel 1M and the inclined front wall 1Rc1 of the bulge 1Rc of the rear floor panel 1R to the rear of the vehicle, and is located below the central part of the bulge 1Rc in the longitudinal direction of the vehicle.

[0030] The battery unit 5 is attached to the side member 2 via a battery holding member 6. The battery holding member 6 is a member for attaching the outer portion of the battery unit 5 in the vehicle width direction to the side member 2, and for example, has a rectangular cylindrical cross-sectional shape and extends in the longitudinal direction of the vehicle. In the illustrated example, the battery holding member 6 has a generally trapezoidal outer shape when viewed from the top or bottom direction of the vehicle in a plan view. The battery unit 5 has a battery flange 5b that protrudes outward in the vehicle width direction from the battery outer surface 5a, which is the outer side in the vehicle width direction. In the illustrated example, the battery bottom surface 5c, which is the bottom surface of the battery unit 5, is located below the bottom surface 2a of the side member 2 (specifically, the side sill 2A) in the vehicle vertical direction. The upper part of the battery outer surface 5a faces the side sill side wall 2A1 of the side sill 2A. There is also a gap between the battery top surface 5d, which is the top surface of the battery unit 5, and the bottom surface 1b of the floor panel 1.

[0031] In the illustrated example, the battery holding member 6 extends in the longitudinal direction of the vehicle. The battery holding member 6 is fixed to the lower surface 2a of the side member 2 (side sill 2A) by fasteners such as bolts (not shown), and protrudes inward in the vehicle width direction beyond the side sill side wall 2A1 of the side sill 2A. The inner end of the battery holding member 6 in the vehicle width direction abuts against the lower surface of the battery flange 5b and is fixed to the battery flange 5b by fasteners such as bolts (not shown). In this way, the battery unit 5 is attached to the side member 2 so as to connect the pair of side members 2,2 (a pair of side sills 2A,2A) via the left and right battery holding members 6.

[0032] (Detailed structure of the vehicle's undercarriage) Next, the detailed structure of the vehicle understructure 100 will be explained, focusing mainly on the intersection of the floor tunnel 10A and the floor cross member 3 and the surrounding structure. Figure 4 is an enlarged perspective view of the main part of the vehicle understructure 100, and Figures 5 to 8 are diagrams illustrating the vehicle understructure 100 with the floor cross member 3 removed. Figure 5 is a perspective view, Figure 6 is a top view, Figure 7 is an enlarged perspective view of the main part of the floor panel 1, and Figure 8 is an enlarged top view of the main part of the floor panel 1. Figure 9 is a cross-sectional view of the floor panel 1 along the BB line shown in Figure 8, Figure 10 is a partial cross-sectional view along the CC line shown in Figure 2, and Figure 11 is a partial cross-sectional view along the DD line shown in Figure 2. Note that in Figures 6 and 8, the outer shape of the floor cross member 3 is shown by a dashed line.

[0033] Referring to Figures 1, 2, 5, and 6, in the illustrated example, the vehicle understructure 100 includes a floor reinforcement panel 7. The floor reinforcement panel 7 is positioned on the upper surface 1a of the rear seat footwell panel portion 1c, which is the portion of the floor panel 1 between the portion below the front seat S1 (front seat lower panel portion) and the portion below the rear seat S2 (rear seat lower panel portion) in the vehicle longitudinal direction, and is joined to the upper surface 1a. The floor reinforcement panel 7 is a steel plate panel for reinforcing the floor panel 1 from above, that is, a member that is flattened in the vehicle vertical direction, and is joined to the floor panel 1 by spot welding or the like. The floor reinforcement panel 7, like the underbody flattened cross member 8 described later, has a height (total height) in the vehicle vertical direction that is sufficiently lower than, for example, the protruding height of the floor cross member 3 in the vehicle vertical direction, and is formed in a flattened shape in the vehicle vertical direction.

[0034] The floor reinforcement panel 7 is provided in a plan view taken from one side in the vertical direction of the vehicle, within the area that fits inside the outer shape of the battery unit 5. In the illustrated example, the floor reinforcement panel 7 is provided adjacent to the floor tunnel 10A on each side in the vehicle width direction of the floor tunnel 10A and is joined to the rear seat footwell panel 1c. In other words, the pair of floor reinforcement panels 7,7 are arranged along the floor tunnel 10A, and the floor tunnel 10A is sandwiched between the pair of floor reinforcement panels 7,7.

[0035] Referring to Figures 2 and 3, in the illustrated example, the vehicle understructure 100 further includes an underfloor flat cross member 8. The underfloor flat cross member 8 extends in the vehicle width direction along the lower surface 1b of the rear seat footwell panel portion 1c of the floor panel 1 and is formed flat in the vehicle vertical direction, connecting a pair of side members 2, 2. The underfloor flat cross member 8 has a height (overall height) in the vehicle vertical direction that is lower than, for example, the protruding height of the upper floor cross member 3 in the vehicle vertical direction, and is formed in a flat shape in the vehicle vertical direction. The underfloor flat cross member 8 is joined to the lower surface 1b of the rear seat footwell panel portion 1c by spot welding or the like. The ends of the underfloor flat cross member 8 in the vehicle width direction are joined to the inner side walls (side sill side walls 2A1) of the side members 2 (side sills 2A) in the vehicle width direction. The underfloor flat cross member 8 is positioned in the gap between the lower surface 1b of the floor panel 1 (rear seat footwell panel section 1c) and the upper surface 5d of the battery unit 5. The lower surface 4a of the underfloor rear cross member 4 faces the upper surface 5d of the battery, and the underfloor rear cross member 4 is located in the gap between the lower surface 1b of the floor panel 1 (rear floor panel 1R) and the upper surface 5d of the battery. The upper floor reinforcement panel 7, the floor panel 1 (rear seat footwell panel section 1c), and the underfloor flat cross member 8 are joined together in a layered manner. The underfloor flat cross member 8 extends along the lower surface 1b of the rear seat footwell panel section 1c over the entire width of the vehicle, and the upper floor reinforcement panel 7, the floor panel 1 (rear seat footwell panel section 1c), and the underfloor flat cross member 8 are joined together in a layered manner.

[0036] Referring to Figures 1, 2, and 4, as mentioned above, each floor cross member 3 overlaps the floor tunnel 10A from above the vehicle, and when viewed from above the vehicle, it intersects the floor tunnel 10A.

[0037] Referring to Figures 5 to 12, the floor tunnel 10A has an upper wall 11, a side wall 12, and a protruding portion 13.

[0038] The upper wall 11 faces upwards towards the vehicle and extends in the longitudinal direction of the vehicle, forming the top of the floor tunnel 10A. The upper wall 11 has an overlapping upper wall portion 11a that overlaps with the floor cross member 3. In the illustrated example, the tunnel height H1 at the overlapping upper wall portion 11a of the floor tunnel 10A (i.e., the height in the vehicle's vertical direction from the panel body 10B to the upper surface of the overlapping upper wall portion 11a of the floor tunnel 10A, see Figures 10 and 11) is lower than the tunnel height H2 (see Figure 9) in other areas (i.e., areas that do not intersect with the floor cross member 3). Furthermore, both the tunnel height H1 at the overlapping upper wall portion 11a of the floor tunnel 10A and the tunnel height H2 in other areas are smaller (lower) than the member height H3 of the floor cross member 3 (i.e., the maximum height in the vehicle's vertical direction from the lower surface of the floor cross member 3 to the upper surface of the member upper wall 3a).

[0039] The side walls 12 are walls that extend along the vehicle-width end of the upper wall 11. The side walls 12 of the floor tunnel 10A that bulges upward above the vehicle are provided at both the one end of the upper wall 11 in the vehicle-width direction and the other end of the upper wall 11 in the vehicle-width direction. In other words, one side wall 12 extends downward from one edge of the upper wall 11 in the vehicle-width direction, and the other side wall 12 extends downward from the other edge of the upper wall 11 in the vehicle-width direction. In other words, each side wall 12 is a vertical wall that connects the panel body 10B and the vehicle-width end of the upper wall 11.

[0040] Each side wall 12 consists of a lower side wall portion 12A located below the floor cross member 3 and a continuous side wall portion 12B that is continuous with the lower side wall portion 12A. In other words, the lower side wall portion 12A is located directly below the floor cross member 3 and overlaps with the floor cross member 3 when viewed from above the vehicle, while the continuous side wall portion 12B extends in the longitudinal direction of the vehicle, continuous with the lower side wall portion 12A, and does not overlap with the floor cross member 3 when viewed from above the vehicle.

[0041] The protruding portion 13 is a portion of the side wall 12 that includes at least a part of the lower side wall portion 12A and protrudes outward in the vehicle width direction. In other words, the protruding portion 13 is a portion of the side wall 12 that includes at least a part of the lower side wall portion 12A and protrudes outward in the vehicle width direction more than other parts, and constitutes a part of the side wall 12. Therefore, the protruding portion 13, like other parts, connects the panel body 10B and the vehicle width direction end of the upper wall 11. The protruding portion 13 is provided on both the right side wall 12 and the left side wall 12. Furthermore, the left protruding portion 13 and the right protruding portion 13 are formed in a symmetrical shape to each other.

[0042] The protruding portion 13 has a lateral inclined surface 13a that slopes toward the panel body 10B as it moves from the inside in the vehicle width direction toward the outside in the vehicle width direction. In other words, the lateral inclined surface 13a is the outer surface of the portion of the side wall 12 that constitutes the protruding portion 13, and is facing outward in the vehicle width direction and diagonally upward, and is inclined downward toward the outside in the vehicle width direction. The lateral inclined surface 13a has a predetermined width in the vehicle front-rear direction and extends in the vehicle width direction, and in a plan view seen from above the vehicle, it is visible as a rectangular surface with the vehicle width direction as its longitudinal direction.

[0043] The floor panel 1 is formed by pressing a steel plate, and the side wall 12 of the floor tunnel 10A, which is part of the floor panel 1 and bulges upward above the vehicle, is inclined even in the continuous side wall section 12B from the viewpoint of formability. In other words, both the lower side wall section 12A and the continuous side wall section 12B have a predetermined width when viewed from above the vehicle. However, the width in the vehicle width direction of the lateral inclined surface 13a of the lower side wall section 12A when viewed from above the vehicle is greater than the width in the vehicle width direction of the inclined surface of the continuous side wall section 12B when viewed from above the vehicle.

[0044] Referring to Figure 9, the inclination angle θ1 of the lateral inclined surface 13a with respect to the upper surface (horizontal plane) of the upper wall 11 is smaller than the inclination angle θ2 (a predetermined angle slightly less than 90 degrees) of the inclined surface of the continuous side wall portion 12B with respect to the upper surface (horizontal plane) of the upper wall 11 (θ1 < θ2). Thus, the lateral inclined surface 13a of the protrusion 13 is inclined with a gentler slope than the inclined surface of the portion of the continuous side wall portion 12B of the side wall 12 where the protrusion 13 is not provided. Therefore, the length of the protrusion 13 in the vehicle width direction including the lateral inclined surface 13a (protrusion length) is set to a value sufficiently large compared to the tunnel height (H1, H2) of the floor tunnel 10A. Also, in the illustrated example, the length of the protrusion 13 in the vehicle width direction including the lateral inclined surface 13a is set to be approximately the same as the length of the upper wall 11 of the floor tunnel 10A in the vehicle width direction. In other words, the tunnel width, which is the width of the floor tunnel 10A in the vehicle width direction, is widened by the protrusion 13. In the illustrated example, the tunnel width in the portion including the protrusion 13 is set to approximately three times the tunnel width in other areas that do not have the protrusion 13.

[0045] Specifically, in the illustrated example, the protrusion 13 is formed on each side wall 12, straddling the boundary between the lower side wall portion 12A and the continuous side wall portion 12B. In other words, the protrusion 13 extends not only to the lower side wall portion 12A but also to the continuous side wall portion 12B, and is formed to protrude into the continuous side wall portion 12B when viewed from above the vehicle. In the illustrated example, in the region of the lower side wall portion 12A, the protrusion 13 is formed on a part of the lower side wall portion 12A adjacent to the front boundary and on a part of the lower side wall portion 12A adjacent to the rear boundary.

[0046] In this embodiment, the protrusions 13 are individually provided on the parts of the overlapping upper wall portion 11a of the side wall 12 that correspond to the four corners. Therefore, when viewed from above the vehicle, the four protrusions 13 protrude outward in the vehicle width direction from the four corners of the overlapping upper wall portion 11a. More specifically, the four protrusions 13 are provided as legs that extend outward in the vehicle width direction at the point where the floor tunnel 10A and the floor cross member 3 overlap when viewed from above the vehicle. In the illustrated example, the four corners are, when viewed from above the vehicle, the front right inner corner formed by the front edge of the floor cross member 3 and the right continuous side wall portion 12B, the front left inner corner formed by the front edge of the floor cross member 3 and the left continuous side wall portion 12B, the rear right inner corner formed by the rear edge of the floor cross member 3 and the right continuous side wall portion 12B, and the rear left inner corner formed by the rear edge of the floor cross member 3 and the left continuous side wall portion 12B. The four protrusions 13 are provided below the front floor cross member 3 and below the rear floor cross member 3, respectively. In other words, the floor panel 1 has a total of eight protrusions 13.

[0047] Referring to Figures 4, 9 through 11, the lower part of the overlapping portion 3A of the floor cross member 3, which overlaps with the floor tunnel 10A, is formed as a recessed portion 31 that is recessed upwards towards the vehicle. The recessed portion 31 has a joining inclined wall portion 31a that extends along the lateral inclined surface 13a of the protruding portion 13 and joins to the lateral inclined surface 13a. The recessed portion 31 has a pair of left and right joining inclined wall portions 31a, 31a, corresponding to the left lateral inclined surface 13a and the right lateral inclined surface 13a. The recessed portion 31 also has a joining horizontal wall portion 31b that connects the upper end of the left joining inclined wall portion 31a and the upper end of the right joining inclined wall portion 31a. The joining horizontal wall portion 31b extends horizontally along the upper surface of the overlapping upper wall portion 11a of the floor tunnel 10A and joins to the overlapping upper wall portion 11a.

[0048] Specifically, each floor cross member 3 has an upper member wall 3a, a front member wall 3b extending downward from the front edge of the upper member wall 3a, a rear member wall 3c extending downward from the rear edge of the upper member wall 3a, a front member flange 3d extending forward from the lower end of the front member wall 3b, and a rear member flange 3e extending rearward from the lower end of the rear member wall 3c.

[0049] The concave portion 31, when viewed from the front-rear direction of the vehicle, is generally trapezoidal groove-shaped, recessed upwards towards the vehicle, and penetrates in the front-rear direction of the vehicle. The front flange 3d and rear flange 3e of the member are bent in the concave portion 31, and the joining inclined wall portion 31a and joining horizontal wall portion 31b of the concave portion 31 are formed from parts of the front flange 3d and rear flange 3e of the member. The lower parts of the front wall 3b and rear wall 3c of the member are cut out in the concave portion 31. The upper wall 3a of the member extends generally flat over its entire length in the width direction of the vehicle. In other words, the floor cross member 3 does not bend in the vertical direction of the vehicle at the overlapping portion 3A in order to cross over the floor tunnel 10A. In the vehicle understructure 100, in order to prioritize securing space for the passenger compartment V, the lower part of the floor cross member 3 is recessed upwards towards the vehicle at the overlapping portion 3A, thereby allowing the floor cross member 3 to cross the floor tunnel 10A.

[0050] Each floor cross member 3 is joined to the upper surface 1a of the floor panel 1 by spot welding or the like. Specifically, each flange (3d, 3e) of the floor cross member 3 is joined to the floor tunnel 10A and the panel body 10B at multiple locations spaced apart in the vehicle width direction. At the overlapping section 3A, the joining inclined wall portion 31a of each flange (3d, 3e) abuts against the lateral inclined surface 13a of the protruding portion 13 of the floor tunnel 10A and is joined, and the joining horizontal wall portion 31b of each flange (3d, 3e) abuts against the overlapping upper wall portion 11a of the floor tunnel 10A and is joined.

[0051] In this embodiment, the protruding portion 13 has a lateral inclined surface 13a, as well as a front inclined surface 13b and a rear inclined surface 13c, and is formed in a mountain-like shape that protrudes outward in the vehicle width direction when viewed from the vertical direction of the vehicle. The front inclined surface 13b connects the front end of the lateral inclined surface 13a to the upper surface of the panel body 10B. The rear inclined surface 13c connects the rear end of the lateral inclined surface 13a to the upper surface of the panel body 10B. In a cross-sectional view of the protruding portion 13 cut by a virtual plane extending in the longitudinal direction of the vehicle, it has a trapezoidal groove-shaped cross-section that protrudes upward of the vehicle, and the width of the protruding portion 13 in the longitudinal direction of the vehicle narrows as it moves outward in the vehicle width direction.

[0052] In this embodiment, a recessed portion 13d is formed between the upper end of the side wall 12 and the upper end of the lateral inclined surface 13a in the protruding portion 13, recessing downwards towards the vehicle. In other words, the formation of the recessed portion 13d causes the lateral inclined surface 13a to be interrupted just below and in front of the upper end of the side wall 12. Furthermore, the upper end of the lateral inclined surface 13a is located one step lower and outward in the vehicle width direction relative to the upper end of the side wall 12 (or upper wall 11), and the lateral inclined surface 13a extends from this position one step lower and outward in the vehicle width direction relative to the upper end of the side wall 12 to the lower end (panel body 10B). Therefore, as shown in Figure 8, the ridge line 14 formed by the upper wall 11 and the side wall 12 in the floor tunnel 10A extends continuously and linearly in the portion corresponding to the lower side wall portion 12A and the portion corresponding to the continuous side wall portion 12B of the side wall 12. In the illustrated example, the recessed portion 13d is formed in a V-groove shape.

[0053] In this embodiment, an adhesive layer G is interposed between the protruding portion 13 of the floor tunnel 10A and the concave portion 31 of the floor cross member 3. Specifically, for example, at the intersection (overlapping portion) of the floor tunnel 10A and the floor cross member 3, the adhesive is applied to at least one of the floor tunnel 10A and the floor cross member 3, and the floor cross member 3 is then placed on top of the floor tunnel 10A. As a result, the adhesive layer G is interposed, for example, between the lateral inclined surface 13a and the joining inclined wall portion 31a, and between the overlapping upper wall portion 11a and the joining horizontal wall portion 31b. In this state, the lateral inclined surface 13a and the joining inclined wall portion 31a are further joined by spot welding, and the overlapping upper wall portion 11a and the joining horizontal wall portion 31b are further joined by spot welding. The adhesive layer G may also be interposed in the gap between the relief portion 13d and the concave portion 31. As the adhesive constituting the adhesive layer G, for example, an adhesive having vibration damping properties is used.

[0054] In this embodiment, the vehicle understructure 100 further includes a cross member reinforcing member 9. The cross member reinforcing member 9 is a reinforcing member for reinforcing the floor cross member 3. The cross member reinforcing member 9 is joined to the overlapping portion 3A of the floor cross member 3 from above the vehicle and extends in the vehicle width direction. The cross member reinforcing member 9 is provided at both the overlapping portion 3A of the front floor cross member 3 and the overlapping portion 3A of the rear floor cross member 3.

[0055] Specifically, the cross member reinforcing member 9 has a roughly hat-shaped cross section that opens downwards towards the vehicle, similar to the floor cross member 3, and overlaps the overlapping portion 3A of the floor cross member 3 from above the vehicle, covering a part of the floor cross member 3. The cross member reinforcing member 9 includes a reinforcing upper wall 91, a reinforcing front wall 92 extending downwards from the front edge of the reinforcing upper wall 91, a reinforcing rear wall 93 extending downwards from the rear edge of the reinforcing upper wall 91, a reinforcing front flange 94 extending forwards from the lower end of the reinforcing front wall 92, a reinforcing rear flange 95 extending rearward from the lower end of the reinforcing rear wall 93, a first reinforcing leg 96 extending downwards from one end of the reinforcing upper wall 91 in the vehicle width direction (right side in the illustrated example), and a second reinforcing leg 97 extending downwards from the other end of the reinforcing upper wall 91 in the vehicle width direction (left side in the illustrated example).

[0056] The vehicle's vertical height of the cross member reinforcing member 9 is set to a value greater than the vehicle's vertical height of the floor cross member 3 at the overlapping section 3A, and the reinforcing upper wall 91 is spaced above the vehicle relative to the member upper wall 3a. The reinforcing front wall 92 extends along the member front wall 3b and is joined to the member front wall 3b by spot welding or the like. The reinforcing rear wall 93 extends along the member rear wall 3c and is joined to the member rear wall 3c by spot welding or the like. The reinforcing front flange 94 is bent to match the shape of the joining inclined wall section 31a and joining horizontal wall section 31b that constitute the concave section 31 of the member front flange 3d. The reinforcing front flange 94 extends along the upper surface of the member front flange 3d and is joined to the member front flange 3d by spot welding or the like. More specifically, the reinforced front flange 94, the member front flange 3d (joining inclined wall portion 31a, joining horizontal wall portion 31b), and the floor panel 1 (lateral inclined surface 13a of the protruding portion 13 of the floor tunnel 10A, overlapping upper wall portion 11a) are joined in a three-layer stack. The reinforced rear flange 95 extends along the upper surface of the member rear flange 3e and is joined to the member rear flange 3e by spot welding or the like. More specifically, the reinforced rear flange 95, the member rear flange 3e (joining inclined wall portion 31a, joining horizontal wall portion 31b), and the floor panel 1 (lateral inclined surface 13a of the protruding portion 13 of the floor tunnel 10A, overlapping upper wall portion 11a) are joined in a three-layer stack. The first reinforcing leg 96 and the second reinforcing leg 97 each have an L-shaped cross section. The lower part of each leg (96, 97) is bent outward in the vehicle width direction and is joined to the member upper wall 3a of the floor cross member 3 by spot welding or the like.

[0057] Furthermore, the vehicle-width end 9a of the cross member reinforcing member 9 (see Figures 10 and 11) is located above the vehicle relative to the joint inclined wall 31a. Specifically, one end 9a of the cross member reinforcing member 9 in the vehicle-width direction (right side in the illustrated example) includes the first reinforcing leg 96, and the other end 9a of the cross member reinforcing member 9 in the vehicle-width direction (left side in the illustrated example) includes the second reinforcing leg 97. The vertical walls extending vertically from the first reinforcing leg 96 are located above the vehicle relative to the approximate center of the longitudinal direction of the right-side joint inclined wall 31a, and the vertical walls extending vertically from the second reinforcing leg 97 are located above the vehicle relative to the approximate center of the longitudinal direction of the left-side joint inclined wall 31a. The lower parts of each reinforcing leg (96, 97) are bent outward in the vehicle-width direction. More specifically, the cross member reinforcing member 9 is longer than the upper wall 11 of the floor tunnel 10A in the vehicle width direction, and the cross member reinforcing member 9 extends to a position outside the center of the lateral inclined surface 13a in the vehicle width direction.

[0058] In this embodiment, the cross member reinforcing member 9 is positioned between the first inner seat bracket X1 and the second inner seat bracket X2, which are adjacent to each other and spaced apart in the vehicle width direction, above the overlapping portion 3A of the floor cross member 3. One end 9a of the cross member reinforcing member 9 in the vehicle width direction (right side in the illustrated example) is sandwiched between the floor cross member 3 and the first inner seat bracket X1 and joined to the floor cross member 3 and the first inner seat bracket X1. The other end 9a of the cross member reinforcing member 9 in the vehicle width direction (left side in the illustrated example) is sandwiched between the floor cross member 3 and the second inner seat bracket X2 and joined to the floor cross member 3 and the second inner seat bracket X2.

[0059] Specifically, the first inner seat bracket X1 and the second inner seat bracket X2 are formed in a symmetrical shape. In the illustrated example, the height of each inner seat bracket (X1, X2) provided on the front floor cross member 3 is set to be greater than the height of each inner seat bracket (X1, X2) provided on the rear floor cross member 3. The front inner seat brackets (X1, X2) and the rear inner seat brackets (X1, X2) are formed in the same shape as each other, except that their heights are different.

[0060] Each inner seat bracket (X1, X2) has a bracket head Xa and a bracket body Xb. The bracket head Xa constitutes the head (top) of the inner seat bracket (X1, X2). The bracket head Xa is formed in a box shape that opens downwards towards the vehicle. The aforementioned slide rail is fastened to the bracket head Xa using a weld nut N welded to the back surface of the bracket head Xa and a bolt (not shown). The bracket head Xa covers the upper part of the bracket body Xb and is joined to the upper part of the bracket body Xb. The bracket body Xb constitutes the base of the inner seat bracket (X1, X2). The bracket body Xb is also formed in a generally box shape that opens downwards towards the vehicle.

[0061] Specifically, the bracket body Xb has an upper wall Xb1, a front wall Xb2, a rear wall Xb3, an inner leg Xb4, and an outer leg Xb5. The upper wall Xb1 faces the top wall of the bracket head Xa and is spaced downward from the top wall. The rigidity of the upper part of the inner seat brackets (X1, X2) is increased by a double wall formed by the top wall of the bracket head Xa and the upper wall Xb1, thereby improving the support rigidity of the slide rail. The front wall Xb2 extends downward from the front edge of the upper wall Xb1, along the upper part of the reinforcing front wall 92 of the cross member reinforcing member 9, and is joined to the reinforcing front wall 92. The rear wall Xb3 extends downward from the rear edge of the upper wall Xb1, along the upper part of the reinforcing rear wall 93 of the cross member reinforcing member 9, and is joined to the reinforcing rear wall 93. The inner leg Xb4 of the main body extends downward from the inner edge in the vehicle width direction of the upper wall Xb1 of the main body. The lower part of the inner leg Xb4 is bent toward the center in the vehicle width direction and joined to the reinforcing upper wall 91 of the cross member reinforcing member 9. The outer leg Xb5 of the main body extends downward from the outer edge in the vehicle width direction of the upper wall Xb1 of the main body. The lower part of the outer leg Xb5 is bent outward in the vehicle width direction. In the right-side first inner seat bracket X1, the lower part of the outer leg Xb5 of the main body abuts against the upper surface of the bent lower part of the first reinforcing leg 96 of the cross member reinforcing member 9. In this state, the lower part of the outer leg Xb5 of the main body, the lower part of the first reinforcing leg 96 (end 9a), and the member upper wall 3a of the floor cross member 3 are joined in a triple layer. Similarly, in the second inner seat bracket X2 on the left side, the lower part of the main body outer leg Xb5, the lower part of the second reinforcing leg 97 (end 9a), and the upper wall 3a of the floor cross member 3 are joined in a triple layer. Each inner seat bracket (X1, X2) is joined to the cross member reinforcing member 9 by the main body inner leg Xb4 and the main body outer leg Xb5, straddling the upper corner of the end 9a of the cross member reinforcing member 9. In this way, each end 9a of the cross member reinforcing member 9 is sandwiched between the floor cross member 3 and the corresponding inner seat bracket (X1, X2), and joined to the floor cross member 3 and the corresponding inner seat bracket (X1, X2).

[0062] In the vehicle understructure 100 according to this embodiment configured as described above, (1) the floor cross member 3 intersects with the floor tunnel 10A in a state where it overlaps with the floor tunnel 10A from above the vehicle, and the floor tunnel 10A has an upper wall 11 facing above the vehicle, a side wall 12 extending along the vehicle width direction end of the upper wall 11 and consisting of a lower side wall portion 12A located below the floor cross member 3 and a continuous side wall portion 12B continuous with the lower side wall portion 12A, and a protruding portion 13 formed by a portion of the side wall 12 including at least a part of the lower side wall portion 12A protruding outward in the vehicle width direction and having a lateral inclined surface 13a that is inclined to approach the panel body 10B as it goes from the inside in the vehicle width direction to the outside in the vehicle width direction. With this configuration, the protrusion 13 having a lateral inclined surface 13a improves the rigidity of the floor panel 1 itself around the intersection of the floor cross member 3 and the floor tunnel 10A, and the tunnel width of the floor tunnel 10A around the intersection is widened by the protrusion 13. (2) The lower part of the overlapping portion 3A of the floor cross member 3 that overlaps with the floor tunnel 10A is formed as a recessed portion 31 that is recessed upwards on the vehicle, and the recessed portion 31 has a joining inclined wall portion 31a that extends along the lateral inclined surface 13a and joins to the lateral inclined surface 13a. With this configuration, the recessed portion 31 at the lower part of the overlapping portion 3A of the floor cross member 3 overlaps with the portion of the floor tunnel 10A that has been widened by the protrusion 13, so that the joining range at the intersection of the floor tunnel 10A and the floor cross member 3 is widened. This widening of the joining range expands the range in which deformation (displacement) of the floor panel 1 can be suppressed by joining the floor tunnel 10A and the floor cross member 3. Moreover, since the concave portion 31 of the floor cross member 3 has a joining inclined wall portion 31a that joins to the lateral inclined surface 13a of the protruding portion 13 of the floor tunnel 10A, it becomes easier to align the floor cross member 3 and the floor tunnel 10A with each other.As a result, at the intersection of the floor cross member 3 and the floor tunnel 10A, a gap is less likely to occur between the concave portion 31 of the floor cross member 3 and the side wall 12 of the floor tunnel 10A, thereby more effectively improving the joint strength between the floor cross member 3 and the floor panel 1, and providing a structure that is advantageous in terms of improving vibration characteristics and other aspects. In this way, the vehicle understructure 100 has a structure that can improve the rigidity of the portion including the intersection of the floor cross member 3 and the floor tunnel 10A.

[0063] In this embodiment, the cross member reinforcing member 9, which is joined to the overlapping portion 3A of the floor cross member 3 from above the vehicle and extends in the vehicle width direction, has its vehicle width direction end 9a positioned above the vehicle relative to the joining inclined wall portion 31a of the concave portion 31 of the floor cross member 3. With this configuration, the rigidity around the concave portion 31 of the floor cross member 3 is reliably increased by the cross member reinforcing member 9. This reduces the deformation of the concave portion 31 of the floor cross member 3 during side collisions (side impacts) such as pole collisions. Moreover, since the concave portion 31 is reinforced by the cross member reinforcing member 9, which is a separate member from the floor cross member 3, the overall height of the floor cross member 3 is reduced. As a result, sufficient space can be easily secured in front of the feet of the occupants sitting in the rear seat S2 (i.e., below the seat of the front seat S1), and rear passenger comfort can be easily ensured. Furthermore, since the cross member reinforcing member 9 is formed as a separate component from the floor cross member 3, the rigidity around the concave portion 31 can be improved without worsening the moldability of the part.

[0064] In this embodiment, each end 9a of the cross member reinforcing member 9 is sandwiched between the floor cross member 3 and the corresponding inner sheet brackets (X1, X2), and is joined to the floor cross member 3 and the corresponding inner sheet brackets (X1, X2). By providing such a joining structure around the concave portion 31, the rigidity around the concave portion 31 is efficiently increased.

[0065] In this embodiment, the protrusions 13 are individually provided on the parts corresponding to the four corners of the overlapping upper wall portion 11a of the side wall 12. With this configuration, the four protrusions are regularly arranged around the intersection of the floor cross member 3 and the floor tunnel 10A. As a result, the rigidity of the floor panel 1 itself around the intersection of the floor cross member 3 and the floor tunnel 10A is efficiently improved.

[0066] In this embodiment, the protruding portion 13 has a lateral inclined surface 13a as well as a front inclined surface 13b and a rear inclined surface 13c, and is formed in a mountain-like shape that protrudes outward in the vehicle width direction when viewed from the vertical direction of the vehicle. With this configuration, the abrupt change in the shape of the floor panel 1 at the protruding portion 13 is reduced, thereby improving the moldability of the floor panel 1.

[0067] In this embodiment, a recessed portion 13d is formed between the upper end of the side wall 12 and the upper end of the lateral inclined surface 13a of the protruding portion 13, and the ridge line 14 formed by the upper wall 11 and the side wall 12 of the floor tunnel 10A extends continuously and linearly in the portion corresponding to the lower side wall portion 12A and the portion corresponding to the continuous side wall portion 12B. With this configuration, the straightness of the ridge line 14 is maintained. In other words, the ridge line 14 below the floor cross member 3 extends linearly in the longitudinal direction of the vehicle, continuously with the ridge line 14 that runs back and forth relative to the floor cross member 3, and the straightness of the ridge line 14 is maintained without interruption below the floor cross member 3. As a result, the rigidity of the floor tunnel 10A in the longitudinal direction of the vehicle is reliably ensured.

[0068] In this embodiment, an adhesive layer G is interposed between the protruding portion 13 of the floor tunnel 10A and the concave portion 31 of the floor cross member 3. When adhesive is used to join the floor tunnel 10A and the floor cross member 3, it is easier to interpose the adhesive layer G between the concave portion 31 of the floor cross member 3 and the side wall 12 of the floor tunnel 10A, where gaps are less likely to occur at the intersection of the floor cross member 3 and the floor tunnel 10A. As a result, the bonding strength is improved by adhesive bonding. Furthermore, by joining the floor cross member 3 and the floor tunnel 10A by both welding and adhesive bonding, the bonding strength is further improved. With adhesive bonding, the bonding length and bonding range can be easily increased, thus easily improving the bonding strength, and also improving the rigidity and reducing vibration at the intersection of the floor cross member 3 and the floor tunnel 10A.

[0069] In this embodiment, the vehicle understructure 100 is applied to the understructure of an electric vehicle in which a battery unit 5 for vehicle operation is provided below the floor panel 1 and below the floor cross member 3. In such an electric vehicle, the floor panel is located higher than in a general vehicle driven by an internal combustion engine in order to secure space for the battery unit below the floor panel. Furthermore, in electric vehicles, the tunnel height of the floor tunnel is sacrificed and kept relatively low in order to secure space inside the vehicle, and the effect of improving floor rigidity by the tunnel height of the floor tunnel tends to be reduced. In contrast, in the vehicle understructure 100, the rigidity of the floor panel 1 itself is improved by the protruding portion 13, and the rigidity of the portion including the intersection of the floor cross member 3 and the floor tunnel 10A is improved by the joint inclined wall portion 31a of the concave portion 31 and the lateral inclined surface 13a of the protruding portion 13, so that floor rigidity can be secured even if the tunnel height (H1, H2) of the floor tunnel 10A is low.

[0070] In the illustrated example, each inner seat bracket (X1, X2) is composed of two parts (bracket head Xa and bracket body Xb). As a result, by increasing the localized plate thickness (for example, increasing the plate thickness of the bracket head Xa), it is possible to ensure seat support rigidity (seat mounting rigidity) while suppressing an increase in the weight of the bracket. Furthermore, because the bracket is composed of two parts, the degree of freedom in adjusting the position of the seat mounting point during manufacturing is increased, and the position of the seat mounting point in the vehicle's longitudinal direction, vehicle's vertical direction, and vehicle's width direction can be easily set within the required accuracy. As a result, the sliding performance of the slide rail is improved, the accuracy of the seat height position is improved, and the height difference between the left and right seats is eliminated.

[0071] Furthermore, since the rear footwell panel 1c is reinforced by a flat floor reinforcement panel 7 joined to the upper surface 1a of the rear footwell panel 1c, the rear footwell panel 1c can be reinforced while ensuring sufficient legroom for occupants seated in the rear seats S2. In addition, since the floor reinforcement panel 7 is positioned within a predetermined range that fits inside the outer shape of the battery unit 5 in a plan view from one side in the vertical direction of the vehicle, deformation of the rear footwell panel 1c is reduced, and contact between the rear footwell panel 1c and the battery unit 5 can be efficiently prevented.

[0072] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and further modifications and changes are possible based on the technical concept of the present invention.

[0073] For example, the protrusion 13 may be formed integrally below the floor cross member 3 without being divided into front and rear sections. The protrusion 13 may not have a relief portion 13d, and the upper end of the lateral inclined surface 13a may be located on the ridge line 14. The adhesive layer G may not be provided, and the joint between the floor cross member 3 and the floor tunnel 10A may be made by welding alone. The vehicle understructure 100 is not limited to the understructure of an electric vehicle, but may also be applied to the understructure of a vehicle that uses an internal combustion engine as a power source instead of a battery unit 5. In this case, for example, by lowering the tunnel height (H1, H2) of the floor tunnel 10A and lowering the position of the floor panel 1, the interior space can be expanded downwards compared to conventional vehicles that use an internal combustion engine as a power source. [Explanation of Symbols]

[0074] 1 Floor Panel 1M Main Floor Panel 1Ma rear end 1R Rear Floor Panel 1Ra front end 1Rb Front flange section 1Rc bulge 1Rc1 Slanted front wall 1Rd Rear corner 1a Top surface 1b Bottom side 1c Rear footwell panel 10A Floor Tunnel 10B Panel Unit 11 Upper wall 11a Overlapping upper wall section 12 Side wall 12A Lower side wall 12B Continuous side wall section 13 Protrusion 13a Horizontal slope 13b Front slope 13c Back slope 13d Escape Club 14 Ridge 2,2 Pair of side members 2a Bottom side 2A Side Sill 2A1 Side sill side wall 2A2 Side sill upper wall 2B Rear side member 2B1 Inclined Member Section 2B2 Straight Member Section 3. Floor cross member 3A Overlapping section 31 Concave shape part 31a Joint inclined wall section 31b Joint horizontal wall section 3a Member upper wall 3b Member front wall 3c Member rear wall 3D Member Front Flange 3e Member rear flange 4. Underfloor rear cross member 4a Bottom side 5 Battery Unit 5a Battery outer surface 5b Battery flange 5c battery bottom 5d battery top 6 Battery holding member 7 Floor reinforcement panels 8. Underfloor flat cross member 9 Cross member reinforcing member 9a end 91 Reinforced upper wall 92 Reinforced front wall 93 Reinforced rear wall 94 Reinforced flange 95 Reinforced flange 96. First reinforcement leg 97 Second Reinforcement Leg 100 Vehicle understructure G adhesive layer H1 Tunnel height (height of floor tunnel) H2 Tunnel height (height of floor tunnel) H3 Member height (height of floor cross member) N Weld Nut S1 Front Seats S2 Rear Seats X1 First Inner Seat Bracket X2 Second Inner Seat Bracket Xa Bracket Head Xb Bracket Body Xb1 console top wall Xb2 front wall Xb3 main body rear wall XB4 Inner Legs Xb5 body outer legs X3 1st outer seat bracket X4 2nd outer seat bracket Y Rear seat bracket V cabin θ1 Tilt angle θ2 Tilt angle

Claims

1. A vehicle understructure comprising: a floor panel having a floor tunnel extending in the longitudinal direction of the vehicle and bulging upward from the vehicle at the center of the vehicle width direction in the underside of the vehicle, and panel bodies extending from the floor tunnel to both sides in the vehicle width direction; and a floor cross member extending in the vehicle width direction along the upper surface of the floor panel, wherein the floor cross member intersects the floor tunnel in a state where it overlaps the floor tunnel from above the vehicle; The aforementioned floor tunnel is The upper wall overlooking the vehicle, A side wall extending along the vehicle width end of the upper wall, comprising a lower side wall portion located below the floor cross member and a continuous side wall portion continuous with the lower side wall portion, A projection is formed such that a portion of the side wall, including at least a part of the lower side wall, protrudes outward in the vehicle width direction, and the projection has a lateral inclined surface that is inclined to approach the panel body as it moves from the inside in the vehicle width direction to the outside in the vehicle width direction, It has, The lower part of the overlapping portion of the floor cross member that overlaps with the floor tunnel is formed as a concave shape that is recessed upwards towards the vehicle. The vehicle understructure is characterized in that the concave portion has a joining inclined wall portion that extends along the lateral inclined surface and joins to the lateral inclined surface.

2. The cross member reinforcing member is further joined to the overlapping portion of the floor cross member from above the vehicle and extends in the vehicle width direction, The vehicle understructure according to claim 1, wherein the end of the cross member reinforcing member in the vehicle width direction is located above the vehicle with respect to the joint inclined wall portion.

3. The floor cross member is provided with a plurality of seat brackets that support the seats. The plurality of seat brackets include a first inner seat bracket and a second inner seat bracket that are adjacent to each other and spaced apart in the vehicle width direction above the overlapping portion. One end of the cross member reinforcing member in the vehicle width direction is sandwiched between the floor cross member and the first inner seat bracket, and is joined to the floor cross member and the first inner seat bracket. The other end of the cross member reinforcing member in the vehicle width direction is sandwiched between the floor cross member and the second inner seat bracket and joined to the floor cross member and the second inner seat bracket, as described in claim 2.

4. The upper wall of the floor tunnel has an overlapping upper wall portion that overlaps with the floor cross member, The vehicle understructure according to claim 1, wherein the protruding portions are individually provided in the portions of the side wall corresponding to the four corners of the overlapping upper wall portion.

5. The vehicle understructure according to claim 4, wherein the protruding portion has a front inclined surface connecting the front end of the lateral inclined surface and the upper surface of the panel body, and a rear inclined surface connecting the rear end of the lateral inclined surface and the upper surface of the panel body, and is formed in a mountain-shaped form that protrudes outward in the vehicle width direction when viewed from the vertical direction of the vehicle.

6. Between the upper end of the side wall and the upper end of the lateral inclined surface of the protruding portion, a recessed portion is formed that is recessed downwards towards the vehicle. The vehicle understructure according to claim 1, wherein the ridge line formed by the upper wall and the side wall in the floor tunnel extends continuously and linearly in the portion corresponding to the lower side wall portion and the portion corresponding to the continuous side wall portion.

7. The vehicle understructure according to claim 1, wherein an adhesive layer is interposed between the protruding portion of the floor tunnel and the concave portion of the floor cross member.

8. The vehicle understructure according to claim 1, wherein a battery unit for vehicle operation is arranged below the floor panel and below the floor cross member.

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