Underbody structure of electric vehicles

Abstract

This design ensures sufficient space inside the vehicle and prevents contact between the floor panel and the battery unit. [Solution] The undercarriage structure 100 of the electric vehicle includes a floor panel 1, a pair of side members 2, 2, a battery holding member 6, and an underbody flat cross member 8. The lower surface 2a of the side members protrudes downward relative to the lower surface 1b of the floor panel 1, and the battery unit 5 is positioned below the floor panel 1 and between the pair of side members 2, 2. The battery holding member 6 connects the side of the battery unit 5 to the lower surface 2a of the side members to hold the battery unit 5. The underbody flat cross member 8 extends in the vehicle width direction along the lower surface 1b of the floor panel 1 and is formed to be flat in the vehicle vertical direction, positioned above the battery unit 5, and the underbody flat cross member 8 is positioned inward in the vehicle width direction relative to the battery fixing portion 2x on the lower surface 2a of the side members to which the battery holding member 6 is fixed.

Description

[Technical Field]

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

[0002] A battery unit for supplying electric power to an electric motor is disposed 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 a structure for arranging a large battery unit below a floor panel is sometimes applied to the vehicle underbody structure of an electric vehicle.

[0003] As an example of a vehicle underbody structure having a structure for arranging a large battery unit below a floor panel, the structure disclosed in Patent Document 1 is known. In the structure disclosed in Patent Document 1, a front seat and a rear seat are arranged on a floor panel, and a battery pack (hereinafter referred to as a battery unit) extends below the floor panel in a range corresponding to a range extending from the feet of an occupant seated in the front seat to below the rear seat. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 2013-86609 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] Incidentally, in electric vehicles, there is a demand to maximize interior space while securing space for the battery unit located below the floor panel. From this perspective, one might consider adopting a structure that brings the floor panel and the top surface of the battery unit close together. However, simply bringing the floor panel and the top surface of the battery unit close together may result in contact between the floor panel and the battery unit. In particular, during a side collision where an impact load is applied to the side of the vehicle, there is a risk that the floor panel may deform and come into contact with the battery unit.

[0006] Therefore, the present invention aims to provide an undercarriage structure for an electric vehicle that can prevent contact between the floor panel and the battery unit during a side collision while ensuring sufficient space inside the vehicle. [Means for solving the problem]

[0007] To achieve the above objective, according to one aspect of the present invention, there is a vehicle understructure for an electric vehicle having a floor panel that constitutes the bottom of the passenger compartment, and a pair of side members that extend in the vehicle longitudinal direction along the outer side of the floor panel in the vehicle width direction, wherein the lower surfaces of the side members, which are the lower surfaces of each of the pair of side members, protrude downward from the lower surface of the floor panel, and a battery unit is disposed below the floor panel and between the pair of side members. The vehicle understructure for the electric vehicle includes a battery holding member provided corresponding to each of the pair of side members, which connects the side of the battery unit to the lower surface of the side member and holds the battery unit, and an underfloor flat cross member that extends in the vehicle width direction along the lower surface of the floor panel and is formed to be flat in the vehicle vertical direction, connecting the pair of side members, and is disposed above the battery unit, wherein the underfloor flat cross member is disposed inward in the vehicle width direction with respect to the battery fixing portion on the underside of the side member to which the battery holding member is fixed. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide an undercarriage structure for an electric vehicle that can prevent contact between the floor panel and the battery unit in the event of a side collision or a heavy object falling, while ensuring space inside the vehicle. [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 a partial underside view of the vehicle's understructure. [Figure 5] This is a partial cross-sectional view along the BB line shown in Figure 4. [Figure 6] This is an enlarged bottom view illustrating the positional relationship between the battery holding member of the vehicle's understructure and the underbody flat cross member. [Figure 7] This is an enlarged underside view of the main parts of the vehicle's understructure. [Figure 8] This is a perspective view from below of the main part of the vehicle's understructure. [Figure 9] This figure shows the state after the first member has been removed from the main part shown in Figure 8. [Figure 10] This is a perspective view from below of the portion of the underbody flat cross member that includes the central part. [Figure 11] This is an illustrative diagram showing an example of the deformation state of the floor panel of the vehicle's understructure during a side collision. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will now be described with reference to the accompanying drawings. Figures 1 to 3 are diagrams illustrating the vehicle understructure 100 of an electric vehicle according to one embodiment of the present invention. 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 direction 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 viewed from inside the vehicle.

[0011] (Overview of the vehicle's undercarriage) Referring to Figures 1 to 3, the vehicle understructure 100 includes a floor panel 1 and a pair of side members 2, 2. In this embodiment, the vehicle understructure 100 further includes an upper front cross member 3 and an under rear cross member 4. The vehicle understructure 100 is applied to the understructure of electric vehicles, such as electric vehicles that use an electric motor as a power source for vehicle propulsion, or hybrid vehicles that use 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. The passenger compartment V is equipped with a front seat S1 and a rear seat S2. Below the floor panel 1 is a battery unit 5 for supplying power to the electric motor (not shown). In other words, the vehicle understructure 100 is the understructure of an electric vehicle, with the front seat S1 and rear seat S2 provided above the floor panel 1 and the battery unit 5 for vehicle operation provided below the floor panel 1. 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 provided 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] In the illustrated example, 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 a central portion in the vehicle width direction of a lower portion 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 part of the floor panel 1.

[0015] In the illustrated example, the floor tunnel 10A extends over the entire length of a 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 (i.e., the panel body 10B), and has a groove-shaped cross-sectional shape opened downward 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. A front edge portion (front end portion) of the front flange portion 1Rb constitutes a 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 a region including the center on the front side of the rear floor panel 1R, and bulges upward of the vehicle. A front wall of the bulging portion 1Rc is continuous with a 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 side portions 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 side 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 is overlapped on 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-section 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 substantially groove-shaped cross-section that opens upward in 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. That is, in the vehicle lower structure 100, the side member lower surfaces 2a, which are the respective lower surfaces of the pair of side members 2, 2, protrude downward relative to the lower surface 1b of the floor panel 1, and the battery unit 5 is arranged below the floor panel 1 and between the pair of side members 2, 2.

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

[0020] The upper floor cross member 3 extends in the vehicle width direction along the upper surface 1a of the floor panel 1 and is a member that connects a pair of side members 2, 2. In this embodiment, the front seat S1 is located above the upper floor cross member 3 in the passenger compartment V. In the illustrated example, the upper floor cross member 3 is provided on the front end side of the seat portion of the front seat S1 and on the rear end side of the seat portion of the front seat S1 in the lower part of the front seat S1 in the vehicle longitudinal direction of the floor panel 1 (more specifically, the main floor panel 1M) (in other words, the lower front seat panel portion). That is, a pair of upper 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 portion), spaced apart from each other in the vehicle longitudinal direction. Each upper floor cross member 3 is joined to the upper surface 1a of the floor panel 1 (lower front seat panel portion) by spot welding or the like and protrudes upward from the vehicle.

[0021] Each floor-front 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-front 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-mounted front cross member 3 has a roughly hat-shaped cross section that opens downwards towards the vehicle. Four front seat brackets S3 are attached to the upper surface of each floor-mounted front cross member 3. The front seat brackets S3 are provided on the upper surface of each floor-mounted front cross member 3 at two locations 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 seat slide rail (not shown) is provided to connect the upper parts of two front seat brackets S3 that are aligned in the longitudinal direction of the vehicle, and the seating area of ​​each front seat S1 is positioned on the floor panel 1 so as to be slidable in the longitudinal direction of the vehicle via the two seat slide rails.

[0023] The vehicle width end of each floor front cross member 3 extends to the vicinity of the vehicle width outer edge of the main floor panel 1M. The front seat bracket S3 located on the outermost side in the vehicle width direction of the multiple front seat brackets S3 is joined to the upper surface of the side sill upper wall 2A2 of the side member 2 (side sill 2A) and the floor front cross member 3 by spot welding or the like. Thus, the floor front cross member 3 connects a pair of side members 2,2 by joining its vehicle width end to the corresponding side member 2 via the front seat bracket S3.

[0024] The underfloor rear cross member 4 extends in the vehicle width direction along the lower surface 1b of the floor panel 1 and is a member that connects a pair of side members 2,2 (here, a pair of rear side members 2B,2B). In this embodiment, the rear seat S2 is located above the underfloor rear cross member 4 in the passenger compartment V. In the illustrated example, the underfloor rear cross member 4 extends in the vehicle width direction along the lower surface 1b of the portion of the floor panel 1 (more specifically, the rear floor panel 1R) below the rear seat S2 (in other words, the rear seat lower panel portion) in the vehicle longitudinal direction and connects the pair of side members 2,2. In the illustrated example, the underfloor 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 underfloor rear cross member 4 is joined to the floor panel 1 and protrudes downward from the vehicle.

[0025] The underbody 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 S4 are attached to the upper surface 1a of the portion below the rear seat S2 (rear seat lower panel portion) in the longitudinal direction of the vehicle on the floor panel 1 (rear floor panel 1R). The rear seat brackets S4 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 S4. The ends of the underbody rear cross member 4 in the vehicle width direction are joined to the corresponding side members 2 (rear side members 2B).

[0026] 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).

[0027] 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 point of the underside of the vehicle body. When the battery unit is located below the floor panel, from the standpoint of ensuring minimum ground clearance, it is conceivable to offset the height of the floor panel towards the interior of the vehicle. However, this would reduce the interior space (especially the legroom for passengers sitting in the rear seats), which is undesirable from the standpoint of ensuring interior space. Considering both the need to ensure interior space and minimum ground clearance, the understructure 100 of the vehicle is positioned so that the floor panel 1 and the upper surface of the battery unit 5 (the upper battery surface 5d described later) are in close proximity. However, in order to prevent contact between the battery unit 5 and the floor panel 1 in the event of a side collision or when heavy objects fall, the understructure 100 of the vehicle has the structure described below.

[0028] (Detailed structure of the vehicle's undercarriage) Next, the detailed structure of the vehicle understructure 100 will be described. Figure 4 is a partial bottom view of the vehicle understructure 100, Figure 5 is a partial cross-sectional view along the BB line shown in Figure 4, and Figure 6 is an enlarged bottom view to explain the positional relationship between the battery holding member 6 and the underbody flat cross member 8, which will be described later. Figures 5 and 6 show the portion of the vehicle understructure 100 including the right-side main part. The right-side and left-side main parts of the vehicle understructure 100 are formed symmetrically with respect to the vehicle width direction, and the portion of the vehicle understructure 100 including the left-side main part has the same structure as shown in Figures 5 and 6, except that it is symmetrical.

[0029] Referring to Figures 2 to 6, 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 vehicle understructure 100 further includes battery holding members 6. The battery unit 5 is attached to the side members 2 via the battery holding members 6. The battery holding members 6 are provided corresponding to each of the pair of side members 2, 2, and connect the side of the battery unit 5 to the lower surface 2a of the side members, thereby holding the battery unit 5.

[0031] Specifically, 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. The battery holding member 6 is made of a thin steel plate and, for example, is crushed inward in the vehicle width direction by an impact load input from the outside in the vehicle width direction during a side collision, and also functions as an impact absorbing member that absorbs the impact load by this compressive deformation. The battery holding member 6, as an impact absorbing member, is formed to have low strength against external forces from the outside in the vehicle width direction so that it is crushed inward in the vehicle width direction with priority over other members during a side collision.

[0032] In the illustrated example, the battery holding member 6 has a generally trapezoidal outer shape when viewed from above or below the vehicle. 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 surface 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 side member bottom surface 2a, which is the bottom surface of the side member 2 (specifically, the side sill 2A), in the vehicle's vertical direction. The upper part of the battery outer surface 5a faces the side sill side wall 2A1 of the side sill 2A. A gap G is provided 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.

[0033] 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) (in other words, the lower surface of the lower side sill wall 2A3 of the side sill 2A) by fasteners such as bolts C1, and protrudes inward in the vehicle width direction from 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 C2. 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. The detailed fixing locations and fixing structure of the battery holding member 6 to the side member 2 will be described later.

[0034] Referring to Figures 1 and 2, although not particularly limited, in the illustrated example the vehicle understructure 100 includes a floor reinforcement panel 7. The floor reinforcement panel 7 is a panel 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 longitudinal direction of the vehicle, 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's vertical direction, and is joined to the floor panel 1 by spot welding or the like. Similar to the underbody flattened cross member 8 described later, the floor reinforcement panel 7 has a height (total height) in the vehicle's vertical direction that is sufficiently lower than, for example, the protruding height of the floor front cross member 3 in the vehicle's vertical direction, and is formed in a flattened shape in the vehicle's vertical direction.

[0035] 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.

[0036] The vehicle understructure 100 further includes an underbody flat cross member 8. The underbody flat cross member 8 extends in the vehicle width direction along the lower surface 1b of the floor panel 1 and is formed to be flat in the vehicle vertical direction, and is a member that connects a pair of side members 2, 2, and is located above the battery unit 5.

[0037] The underbody flat cross member 8 has, for example, a height (overall height) in the vehicle vertical direction that is lower than the vehicle vertical projection height of the upper front cross member 3, and is formed in a flat shape in the vehicle vertical direction.

[0038] The underbody flat cross member 8 is positioned inward in the vehicle width direction relative to the battery fixing portion 2x on the lower surface 2a of the side member 2 to which the battery holding member 6 is fixed. In other words, when viewed from below the vehicle, the battery fixing portion 2x provided on the lower surface 2a of the right side member 2, the underbody flat cross member 8, and the battery fixing portion 2x provided on the lower surface 2a of the left side member 2 are aligned in a line in the vehicle width direction. Furthermore, the vehicle understructure 100 has battery fixing portions 2x on each side member 2 that are located within the front-to-rear width range of the underbody flat cross member 8 in the vehicle's longitudinal direction.

[0039] Referring to Figures 4 to 6, specifically, multiple battery fixing parts 2x are provided on the lower surface 2a of the side member 2, and multiple battery flanges 5b are provided on the outer surface 5a of the battery unit 5. Although not particularly limited, in the illustrated example, battery fixing parts 2x are set at four locations spaced apart from each other in the vehicle's longitudinal direction on the lower surface 2a of each left and right side member 2 (the lower surface of the side sill lower wall 2A3). A bolt insertion hole is opened in each battery fixing part 2x through which a bolt C1 is inserted. A nut N is welded to the upper surface of the side sill lower wall 2A3 (more specifically, the side sill reinforcing member 9 which will be described later and is joined to the upper surface of the side sill lower wall 2A3) corresponding to the bolt insertion hole, and the bolt C1 inserted through the bolt insertion hole is screwed into the nut N. Furthermore, in the illustrated example, battery flanges 5b are provided protruding from four locations spaced apart from each other in the vehicle's longitudinal direction on the left and right outer surfaces 5a of the battery unit 5. Each battery flange 5b has a female thread into which a bolt C2 is screwed.

[0040] Then, bolt C1 is inserted from below through a cylindrical outer collar 6a, which is joined to the outer end of the battery holding member 6 in the vehicle width direction, and through the bolt insertion hole, which passes through the lower wall 2A3 of the side sill and the side sill reinforcing member 9, which will be described later, and is screwed into a nut N. As a result, the outer end of the battery holding member 6 in the vehicle width direction is fixed to the lower surface 2a of the side member via bolt C1 at each battery fixing part 2x. Also, bolt C2 is inserted from below through a cylindrical inner collar 6b, which is joined to the inner end of the battery holding member 6 in the vehicle width direction, and is screwed into the female thread of the battery flange 5b. As a result, the inner end of the battery holding member 6 in the vehicle width direction is fixed to the lower surface of each battery flange 5b via bolt C2. In this way, the battery unit 5, which is located below the floor panel 1 and between a pair of side members 2, 2, is held via the left and right battery holding members 6.

[0041] Furthermore, the underbody flat cross member 8 is aligned in the vehicle width direction with a portion of the multiple battery fixing parts 2x on each side member 2 (one of the last row in the illustrated example), and is positioned inward in the vehicle width direction relative to the battery fixing part 2x.

[0042] In the illustrated example, the front floor cross member 3 is aligned in the vehicle width direction with a portion of the multiple battery fixing parts 2x on each side member 2 (in this case, the frontmost one), and the rear floor cross member 3 is aligned in the vehicle width direction with a portion of the multiple battery fixing parts 2x on each side member 2 (in this case, the two middle ones). Although not particularly limited, in the illustrated example, the rear flange portion 3a of the front floor cross member 3 is aligned in the vehicle width direction with the frontmost battery fixing part 2x, the front flange portion 3b of the rear floor cross member 3 is aligned in the vehicle width direction with the second battery fixing part 2x from the front, and the rear flange portion 3a of the rear floor cross member 3 is aligned in the vehicle width direction with the third battery fixing part 2x from the front.

[0043] Referring to Figure 4, in this embodiment, the upper front cross member 3 is positioned in front of the vehicle relative to the lower flat cross member 8, and the lower rear cross member 4 is positioned behind the vehicle relative to the lower flat cross member 8. The lower flat cross member 8 is positioned in the longitudinal direction of the vehicle, within a range that overlaps with the center line X between the upper front cross member 3 and the lower rear cross member 4. In other words, the center line X is located between the front end and the rear end of the lower flat cross member 8. Furthermore, other cross members (in this case, the rear upper front cross member 3 and the lower rear cross member 4) are positioned approximately equally spaced in front of and behind the lower flat cross member 8. Specifically, the center line X is a virtual line extending in the vehicle width direction through the center point between the rear end of the rear upper front cross member 3 and the front end of the lower rear cross member 4.

[0044] In this embodiment, the underfloor flat cross member 8 extends along the lower surface 1b of the rear seat footwell panel portion 1c of the floor panel 1. 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. Each end of the underfloor flat cross member 8 in the vehicle width direction is joined to the inner side wall (side sill side wall 2A1) of the side member 2 (side sill 2A) in the vehicle width direction. The underfloor flat cross member 8 is also positioned in the gap G between the lower surface 1b of the floor panel 1 (rear seat footwell panel portion 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 G between the lower surface 1b of the floor panel 1 (rear floor panel 1R) and the upper surface 5d of the battery.

[0045] In the illustrated example, the floor reinforcement panel 7, the floor panel 1 (rear seat footwell panel section 1c), and the underbody flat cross member 8 are joined together in a layered manner. The underbody 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 floor reinforcement panel 7, floor panel 1, and underbody flat cross member 8 are joined together in a layered manner.

[0046] Next, the underbody flat cross member 8 will be described in more detail. Figure 7 is an enlarged bottom view of the main part of the vehicle understructure 100, Figure 8 is a perspective view of the main part of the vehicle understructure 100 viewed from below, Figure 9 shows the state in which the first member 81, which will be described later, has been removed from the main part shown in Figure 8, and Figure 10 is a perspective view of the portion of the underbody flat cross member 8 including the central part viewed from below. Figure 11 is an illustrative diagram showing an example of the deformation state of the floor panel 1 during a side collision. Note that in Figures 7 to 11, the battery unit 5 and battery holding member 6 have been removed, and in Figures 7 to 9, the portion of the underbody flat cross member 8 including the right end is shown.

[0047] Referring to Figures 4 to 8, in this embodiment, the underfloor flattened cross member 8 has a cross member body portion 8a, a first end flange 8b, and a second end flange 8c.

[0048] The cross member body portion 8a extends linearly in the vehicle width direction and is formed to be flat in the vehicle vertical direction, and constitutes the majority of the underbody flattened cross member 8. The cross member body portion 8a has a predetermined width in the vehicle longitudinal direction and extends in the vehicle width direction from the inner wall in the vehicle width direction of the right side member 2 (side sill side wall 2A1) to the inner wall in the vehicle width direction of the left side member 2 (side sill side wall 2A1).

[0049] The first end flange 8b is a flange that extends downward from one end of the cross member body 8a in the vehicle width direction. The first end flange 8b is joined to the upper part of the inner wall (side sill side wall 2A1) in the vehicle width direction of one of the pair of side members 2,2.

[0050] The second end flange 8c is a flange that extends downward from the other end of the cross member body 8a in the vehicle width direction. The second end flange 8c is joined to the upper part of the inner wall (side sill side wall 2A1) in the vehicle width direction of the other side member 2 of the pair of side members 2,2. Although not particularly limited, in the illustrated example, the first end flange 8b extends downward from the right end of the cross member body 8a and is joined to the right side member 2, and the second end flange 8c extends downward from the left end of the cross member body 8a and is joined to the left side member 2.

[0051] In other words, as shown in Figure 5, each end of the underbody flat cross member 8 in the vehicle width direction is generally bent downward. The corners of the bent portions at the ends of the underbody flat cross member 8 are positioned at the inner corners formed by the inner wall of the side member 2 in the vehicle width direction and the lower surface 1b of the floor panel 1, and the underbody flat cross member 8 is joined to the upper part of the inner wall of each side member 2 in the vehicle width direction and the lower surface 1b of the floor panel 1. As shown in Figures 4 and 5, both ends of the underbody flat cross member 8 in the vehicle width direction are joined to the inner wall of the side member 2, abutting perpendicularly against the inner wall of the side member 2 in the vehicle width direction. The length of each end flange 8b, 8c in the vehicle vertical direction is shorter than the length of the inner wall of the side member 2 in the vehicle vertical direction. Specifically, in the illustrated example, the length of each end flange 8b, 8c in the vehicle vertical direction is shorter than half the length of the inner wall of the side member 2, and is set to approximately one-third of the length of the inner wall.

[0052] In this embodiment, the components constituting the underfloor flat cross member 8 consist of a first component 81, a second component 82, and a main component 83. In other words, the components constituting the underfloor flat cross member 8 are divided into three parts, and the underfloor flat cross member 8 is formed as a single component by joining the three components (first component 81, second component 82, and main component 83) together.

[0053] The first member 81 is a member joined to one of the pair of side members 2,2. The first member 81 includes a first end flange 8b. In the illustrated example, the first member 81 has an L-shaped cross-section. The portion of the first member 81 extending in the vehicle's vertical direction constitutes the first end flange 8b and is joined to one of the side members 2 (the right side in this case) (the side sill side wall 2A1 of the side sill 2A), while the portion of the first member 81 extending inward in the vehicle's width direction is joined to the floor panel 1.

[0054] The second member 82 is a member joined to the other side member 2 of a pair of side members 2,2. The second member 82 includes a second end flange 8c. In the illustrated example, the second member 82 is formed symmetrically with the first member 81 and has an L-shaped cross-section. The portion of the second member 82 extending in the vehicle's vertical direction constitutes the second end flange 8c and is joined to the other side member 2 (the left side in this case) (the side sill side wall 2A1 of the side sill 2A), while the portion of the second member 82 extending inward in the vehicle's width direction is joined to the floor panel 1.

[0055] The main body member 83 is a member that connects the first member 81 and the second member 82. The main body member 83 is a member that constitutes the majority of the cross member main body portion 8a, and is formed to extend linearly in the vehicle width direction and to be flattened in the vehicle vertical direction. In the illustrated example, the main body member 83 has a length that is slightly shorter than the length between the pair of side members 2,2. That is, the main body member 83 extends from the vicinity of the side sill side wall 2A1 of the right side sill 2A to the vicinity of the side sill side wall 2A1 of the left side sill 2A. Furthermore, in the floor panel 1, the main body member 83 extends from the periphery of one side member 2 to the periphery of the other side member 2.

[0056] Each of the first member 81 and the second member 82 has an overlapping portion 8x that is joined to the corresponding outer end of the main body member 83 in the vehicle width direction, with the two members overlapping vertically. That is, in the right overlapping portion 8x, the first member 81 and the left end of the main body member 83 are overlapped vertically, and in the left overlapping portion 8x, the second member 82 and the right end of the main body member 83 are overlapped vertically. The length of each overlapping portion 8x in the vehicle width direction is approximately the same as or longer than the width of the underfloor flat cross member 8 in the vehicle longitudinal direction. Although not particularly limited, the length of each overlapping portion 8x in the vehicle width direction is longer than one-tenth of the panel width of the floor panel 1 (the length between the pair of side members 2,2).

[0057] The strength of each overlapping portion 8x against external forces from the outside in the vehicle width direction is set to be higher than, for example, the strength of the battery holding member 6, which acts as an impact absorbing member, against external forces from the outside in the vehicle width direction.

[0058] Furthermore, the inner ends (81a, 82a) of the first member 81 and the second member 82 in the vehicle width direction are located in the vehicle width direction at a position corresponding to or inside the inner end 6c of the battery holding member 6 in the vehicle width direction. Referring to Figure 5, the inner ends (81a, 82b) of the first member 81 and the second member 82 are located inside the inner end 6c of the battery holding member 6 in the vehicle width direction. Specifically, in the illustrated example, the inner ends (81a, 82b) of the first member 81 and the second member 82 are located inside the outer surface 5a of the battery unit 5 in the vehicle width direction.

[0059] In the illustrated example, multiple side sill reinforcing members 9 are provided inside each side sill 2A. The multiple side sill reinforcing members 9 are spaced apart from each other in the vehicle's longitudinal direction. In the illustrated example, nine side sill reinforcing members 9 are provided. Each side sill reinforcing member 9 extends from the lower side sill wall 2A3 to the upper side sill wall 2A1. Each side sill reinforcing member 9 has a lower flange 9a joined to the lower side sill wall 2A3, an upper flange 9b joined to the upper side sill wall 2A1, and a lateral flange 9c joined to the side sill side wall 2A2, and the lower side sill wall 2A3 and the upper side sill wall 2A1 are connected vertically via the side sill reinforcing member 9. Each side sill reinforcing member 9 partitions the inside of the side sill 2A in the vehicle's longitudinal direction and reinforces the side sill 2A.

[0060] In the illustrated example, in each side sill 2A, some of the multiple side sill reinforcing members 9 are provided at positions corresponding to the multiple battery fixing parts 2x. Specifically, four side sill reinforcing members 9, located in the 3rd, 4th, 5th, and 6th positions from the front out of the nine side sill reinforcing members 9, are provided at positions corresponding to the four battery fixing parts 2x. The nut N into which the bolt C1 is screwed is joined to the upper surface of the side sill reinforcing member 9 provided at the position corresponding to the battery fixing part 2x.

[0061] Furthermore, in relation to the underbody flat cross member 8, a portion of the multiple side sill reinforcing members 9 (in the illustrated example, the 7th side sill reinforcing member 9 from the front) is located above one of the battery fixing parts 2x that is aligned with the underbody flat cross member 8 in the vehicle width direction. In other words, a side sill reinforcing member 9 that is aligned with the underbody flat cross member 8 in the vehicle width direction is provided inside each side sill 2A.

[0062] In the illustrated example, the front floor cross member 3 is aligned in the vehicle width direction with some of the multiple side sill reinforcing members 9 on each side member 2 (in this case, the two on the front), and the rear floor cross member 3 is aligned in the vehicle width direction with some of the multiple side sill reinforcing members 9 on each side member 2 (in this case, the two in the middle). Although not particularly limited, in the illustrated example, the front flange portion 3b of the front floor cross member 3 is aligned in the vehicle width direction with the third side sill reinforcing member 9 from the front, the rear flange portion 3a of the front floor cross member 3 is aligned in the vehicle width direction with the fourth side sill reinforcing member 9 from the front, the front flange portion 3b of the rear floor cross member 3 is aligned in the vehicle width direction with the fifth side sill reinforcing member 9 from the front, and the rear flange portion 3a of the rear floor cross member 3 is aligned in the vehicle width direction with the sixth side sill reinforcing member 9 from the front.

[0063] Referring to Figures 4, 5, 7, and 8, the underbody flat cross member 8 has a pair of beads 8d, 8d extending in the vehicle width direction. The pair of beads 8d, 8d are spaced apart from each other in the vehicle longitudinal direction. Each bead 8d has a groove-shaped cross section that is open to the upper side of the vehicle and bulges downward. Each bead 8d extends continuously from the first end flange 8b to the second end flange 8c and is provided on approximately the entire underbody flat cross member 8 in the vehicle width direction.

[0064] Referring to Figures 8 and 9, the pair of beads 8d, 8d are formed on both the first member 81 and the main body member 83 in the overlapping portion 8x on the right side. In the illustrated example, the first member 81 overlaps the main body member 83 from below, and the pair of beads 8d, 8d of the first member 81 overlaps the pair of beads 8d, 8d of the main body member 83 from below. Also, the pair of beads 8d, 8d are formed on both the second member 82 and the main body member 83 in the overlapping portion 8x on the left side. In the illustrated example, the second member 82 overlaps the main body member 83 from below, and the pair of beads 8d, 8d of the second member 82 overlaps the pair of beads 8d, 8d of the main body member 83 from below.

[0065] Furthermore, a narrow bead section 8d1 is formed in the portion of each bead 8d corresponding to the overlapping portion 8x, having a narrower bead width than the bead width of the other portions. In detail, referring to Figure 8, in the overlapping portion 8x of the underfloor flat cross member 8, a part of the rear wall of the front bead 8b is recessed forward, and a part of the front wall of the rear bead 8b is recessed backward. As a result, a narrow bead section 8d1 is formed on the bead 8d of the overlapping portion 8x, and a widened groove section 8e is formed in the portion between the pair of beads 8d, 8d in the overlapping portion 8x (first member 81, second member 82), with a wider groove section 8e in the front-rear direction than the groove width between the pair of beads 8d, 8d in the other portions.

[0066] The underbody flat cross member 8 is joined to the floor panel 1 by spot welding or the like at its front and rear edges and in the portion between the pair of beads 8d, 8d (including the widened groove portion 8e). Multiple welding points spaced apart in the vehicle width direction are provided at the front edge, rear edge, and the portion between the pair of beads 8d, 8d (including the widened groove portion 8e) of the underbody flat cross member 8. In the widened groove portion 8e (overlapping portion 8x), multiple welding point groups spaced apart in the vehicle width direction are set in double rows in the vehicle's longitudinal direction. In other words, the density of multiple welding points to the floor panel 1 at both ends of the underbody flat cross member 8 in the vehicle width direction (left and right overlapping portions 8x) is set to be significantly higher than the density of multiple welding points to the floor panel 1 at other parts of the underbody flat cross member 8. Therefore, the strength of both ends of the underbody flat cross member 8 in the vehicle width direction (left and right overlapping portions 8x) is more reliably improved.

[0067] Referring to Figure 10, in the center of the underbody flat cross member 8 in the vehicle width direction, a constricted portion 8f is formed at the center of the pair of beads 8d, 8d in the vehicle width direction, constricting toward the center of the underbody flat cross member 8 in the vehicle longitudinal direction. In other words, the portion of the pair of beads 8d, 8d that intersects with the floor tunnel 10A is constricted toward the center of the underbody flat cross member 8 in the vehicle longitudinal direction. The underbody flat cross member 8 has a front central flange 8g1 and a rear central flange 8g2. The front central flange 8g1 protrudes forward relative to the constricted portion 8f, and the rear central flange 8g2 protrudes backward relative to the constricted portion 8f. The ends of each central flange (8g1, 8g2) are bent downward. Wiring fixing members C3, such as clips for fixing electrical wiring E, are fixed to the flat portions of each central flange (8g1, 8g2). In other words, electrical wiring fixing points for securing electrical wiring material E are provided on the flat portions of each central flange (8g1, 8g2). The electrical wiring material E is fixed to the upper surface of the underfloor flat cross member 8 via wiring fixing member C3 below the floor tunnel 10A.

[0068] According to the vehicle understructure 100 of this embodiment, (1) the underfloor flat cross member 8, which extends in the vehicle width direction along the lower surface 1b of the floor panel 1 and is positioned above the battery unit 5, is formed flat in the vehicle vertical direction, so that the floor panel 1 can be reinforced while securing space in the passenger compartment V and space for the battery unit 5. (2) The underfloor flat cross member 8 is positioned inward in the vehicle width direction with respect to the battery fixing portion 2x to which the battery holding member 6 on the lower surface 2a of the side member is fixed. Therefore, the strength against external forces (impact loads) that may be input from the outside in the vehicle width direction to the position corresponding to the underfloor flat cross member 8 during a side collision is increased by the battery holding member 6, and the strength reduction due to the flattened shape of the underfloor flat cross member 8 can be compensated for by the battery holding member 6. As a result, even if the underfloor flat cross member 8 is formed flat and thin in the vehicle vertical direction, sufficient strength against external forces input from the outside in the vehicle width direction can be easily secured. Therefore, contact between the battery unit 5 and the floor panel 1 during a side collision can be easily prevented. (3) Furthermore, the underfloor flat cross member 8 effectively improves the strength against external forces (impact loads) that may be applied from above when a heavy object is dropped onto the upper surface 1a of the floor panel 1 inside the passenger compartment V.

[0069] As described above, the vehicle understructure 100 can secure space inside the passenger compartment while preventing contact between the floor panel 1 and the battery unit 5 in the event of a side collision or a heavy object falling.

[0070] In this embodiment, the underbody flat cross member 8 is positioned in a range that overlaps with the center line X between the upper front cross member 3 and the underbody rear cross member 4 in the longitudinal direction of the vehicle. Therefore, the other cross members (the rear upper front cross member 3 and the underbody rear cross member 4), which are different from the underbody flat cross member 8, are positioned approximately evenly separated in front of and behind the underbody flat cross member 8. As a result, when an impact load is applied to the position corresponding to the underbody flat cross member 8 during a side collision, the impact load is distributed to the upper front cross member 3 and the underbody rear cross member 4, allowing the impact to be effectively absorbed.

[0071] In this embodiment, the underfloor flat cross member 8 extends along the lower surface 1b of the rear seat footwell panel 1c in the floor panel 1. Therefore, the rear seat footwell panel 1c can be reinforced while ensuring legroom for occupants seated in the rear seat S2. Furthermore, even when it is difficult to place sufficient reinforcing members on the upper surface 1a and lower surface 1b of the rear seat footwell panel 1c in order to ensure legroom for occupants seated in the rear seat S2 and space for the battery unit 5 located below the floor panel 1, the underfloor flat cross member 8 and battery holding member 6 effectively improve the strength against external forces during a side collision. In addition, the rear seat footwell panel 1c is susceptible to impact loads from the inside of the vehicle, not only from impact loads caused by falling heavy objects, but also from impact loads caused by the weight of occupants seated in the rear seat. By positioning the underfloor flat cross member 8 on the lower surface 1b of the rear seat footwell panel 1c, the underfloor flat cross member 8 can be used as a more effective reinforcing member.

[0072] In this embodiment, the main body portion 8a of the underbody flattened cross member 8 extends linearly in the vehicle width direction and is formed to be flat in the vehicle vertical direction. Therefore, when an external force (see the white arrow shown in Figure 11) is applied to the underbody flattened cross member 8 during a side collision, a deformation mode is induced in which the cross member main body portion 8a curves in an arc shape with the central part as the belly. As a result, the occurrence of bending of the underbody flattened cross member 8 in the vehicle vertical direction between the pair of side members 2, 2 is effectively suppressed. In addition, each end flange (8b, 8c) of the underbody flattened cross member 8 is joined to the upper part of the inner wall in the vehicle width direction of the side member 2. Therefore, as shown in Figure 11, the deformation mode induced in the cross member main body portion 8a during a side collision becomes an upward curving deformation that protrudes upward. As a result, during a side collision, the floor panel 1 curves upward following the upward curving deformation of the cross member main body portion 8a, and the floor panel 1 moves upward away from the battery top surface 5d of the battery unit 5. In this way, contact between the floor panel 1 and the battery unit 5 during a side collision can be more reliably prevented.

[0073] In this embodiment, (1) the underbody flat cross member 8 is formed as a single component by joining three members (first member 81, second member 82, and main body member 83) to each other. The first member 81 and the second member 82 at both ends are superimposed vertically on the corresponding outer ends of the main body member 83 in the vehicle width direction, and each has an overlapping portion 8x that is joined to the outer ends. The main body member 83 extends from the periphery of one side member 2 to the periphery of the other side member 2 in the floor panel 1. As a result, overlapping portions 8x with high strength against external forces from the outside in the vehicle width direction can be easily provided at both ends of the cross member main body portion 8a of the underbody flat cross member 8 that is along the lower surface 1b of the floor panel 1. Therefore, overlapping portions 8x with a strength higher than the compressive strength in the vehicle width direction of the battery holding member 6 as an impact absorbing member can be easily provided at both ends of the underbody flat cross member 8 (cross member main body portion 8a). (2) Moreover, the inner ends (81a, 82a) of the first member 81 and the second member 82 in the vehicle width direction are located in the vehicle width direction at a position corresponding to the inner end 6a of the battery holding member 6 in the vehicle width direction, or inward relative to the inner end 6a of the battery holding member 6 (in the illustrated example, they are located inward relative to the inner end 6a). As a result, the overlapping portion 8x is provided over the entire portion of the underbody flat cross member 8 that is directly above the battery holding member 6. Therefore, in the event of a side collision, the battery holding member 6 is crushed more reliably and preferentially to other members, and a portion of the input external force (impact load) is reliably transmitted to the entire underbody flat cross member 8. At this time, the overlapping portion 8x, which has high strength, deforms so that its inner ends (81a, 82a) are flipped upward while generally maintaining a linear shape. As a result, upward curvature deformation of the underbody flat cross member 8 (cross member main body 8a) is more reliably induced during a side collision, and contact between the floor panel 1 and the battery unit 5 during a side collision can be more reliably prevented.

[0074] Furthermore, since a pair of beads 8d extending in the vehicle width direction are formed on the underbody flat cross member 8, the strength against external forces input from the outside in the vehicle width direction is improved. And, since each bead 8d extends over almost the entire vehicle width direction of the underbody flat cross member 8, the amount of deformation of the underbody deformed cross member 8 and floor panel 1 in the upward curving deformation during a side collision can be reduced.

[0075] 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.

[0076] In this embodiment, the inner ends (81a, 82a) of the first member 81 and the second member 82 in the vehicle width direction are located inward relative to the inner end 6a of the battery holding member 6 in the vehicle width direction. However, the embodiment is not limited to this, and the inner ends may be located in a position corresponding to the inner end 6a, that is, directly above or near the inner end 6a. Furthermore, if upward curving deformation can be induced in the underbody flattened cross member 8 during a side collision, the inner ends (81a, 82a) of the first member 81 and the second member 82 in the vehicle width direction may be located outward relative to the inner end 6a of the battery holding member 6.

[0077] The installation location of the underfloor flat cross member 8 is not limited to the lower surface 1b of the rear seat footwell panel 1c. The underfloor flat cross member 8 can be appropriately positioned in a location on the floor panel 1 where there are no reinforcing members and which is disadvantageous against external forces during a side collision. For example, the underfloor flat cross member 8 may be provided on the lower surface 1b of the portion of the floor panel 1 located in front of the front seat lower panel below the front seat S1 (front seat footwell panel). In this case, the position of the battery fixing part 2x in the vehicle longitudinal direction should be set so that the underfloor flat cross member 8 is positioned inward in the vehicle width direction relative to the battery fixing part 2x.

[0078] Furthermore, the shape, extension direction, number, and location of the beads 8d of the underfloor flat cross member 8 can be set as appropriate. [Explanation of Symbols]

[0079] 1 Floor Panel 1a Top surface 1b Bottom side 1c Rear footwell 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 10A Floor Tunnel 10B Panel Unit 2,2 Pair of side members 2a Lower surface of side member 2x Battery mounting section 2A Side Sill 2A1 Side sill side wall 2A2 Side sill upper wall 2A3 Side sill lower wall 2B Rear side member 2B1 Inclined Member Section 2B2 Straight Member Section 3. Front cross member above floor 3a Rear flange section 3b Front flange section 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 6a Outer color 6b Inner Color 6c inner edge 7 Floor reinforcement panels 8. Underfloor flat cross member 8a Cross member main body 8b First end flange 8c Second end flange 8d, 8d pair of beads 8d1 Thin bead section 8e Widening groove section 8f Waist area 8g1 Center Front Flange 8g2 Center rear flange 8x overlapping area 81 First Member 81a Inner end 82 Second Member 82a inner edge 83 Main body components 9. Side sill reinforcing member 9a Lower flange 9b Upper flange 9c horizontal flange 100 Vehicle understructure C1 bolt C2 bolt C3 Wiring fixing component E Electrical wiring materials G Gap N Nut S1 Front Seats S2 Rear Seats S3 Front Seat Bracket S4 Rear Seat Bracket X Chuo Line V cabin

Claims

1. An undercarriage structure for an electric vehicle comprising a floor panel forming the bottom of the passenger compartment, and a pair of side members extending in the longitudinal direction of the vehicle along the outer side of the floor panel in the vehicle width direction, wherein the lower surfaces of each of the pair of side members protrude downward relative to the lower surface of the floor panel, and the battery unit is positioned below the floor panel and between the pair of side members, A battery holding member is provided corresponding to each of the pair of side members, connecting the side of the battery unit to the lower surface of the side member, and holding the battery unit. A flat underbody cross member that extends in the vehicle width direction along the lower surface of the floor panel and is formed to be flat in the vehicle vertical direction, connecting the pair of side members, and is positioned above the battery unit, Includes, The underbody structure of an electric vehicle is characterized in that the underbody flat cross member is positioned inward in the vehicle width direction with respect to the battery fixing portion on the lower surface of the side member to which the battery holding member is fixed.

2. The above-floor front cross member is positioned in front of the vehicle relative to the underfloor flat cross member, extends in the vehicle width direction along the upper surface of the floor panel, and connects the pair of side members, The rear underbody cross member is positioned at the rear of the vehicle relative to the aforementioned underbody flat cross member, extends in the vehicle width direction along the underside of the floor panel, and connects the pair of side members, It further includes, The underbody structure of an electric vehicle according to claim 1, wherein the underbody flat cross member is arranged in the longitudinal direction of the vehicle in a range that overlaps with the center line between the upper front cross member and the underbody rear cross member.

3. In the aforementioned passenger compartment, the front seats are positioned above the upper cross member above the floor, and the rear seats are positioned above the lower rear cross member above the floor. The underbody structure of an electric vehicle according to claim 2, wherein the underbody flat cross member extends along the lower surface of the rear footwell panel portion, which is the portion of the floor panel between the portion below the front seats and the portion below the rear seats in the longitudinal direction of the vehicle.

4. The underbody flattened cross member comprises a cross member main body portion that extends linearly in the vehicle width direction and is formed to be flat in the vehicle vertical direction, a first end flange extending downward from one end of the cross member main body portion in the vehicle width direction, and a second end flange extending downward from the other end of the cross member main body portion in the vehicle width direction. The first end flange is joined to the upper part of the inner wall in the vehicle width direction of one of the pair of side members. The vehicle understructure of an electric vehicle according to claim 1, wherein the second end flange is joined to the upper part of the inner wall in the vehicle width direction of the other side member of the pair of side members.

5. The components constituting the underfloor flat cross member consist of a first member joined to one of the pair of side members, a second member joined to the other of the pair of side members, and a main body member connecting the first member and the second member. Each of the first and second members is superimposed vertically on the corresponding outer end of the main body member in the vehicle width direction, and has an overlapping portion that is joined to the outer end. The main body member extends from the peripheral portion of one side member to the peripheral portion of the other side member in the floor panel. The vehicle understructure for an electric vehicle according to claim 4, wherein the inner ends of the first member and the second member in the vehicle width direction are located in the vehicle width direction at a position corresponding to the inner end of the battery holding member in the vehicle width direction or inward relative to the inner end of the battery holding member.

Images