Underbody structure

Abstract

To provide a vehicle body lower structure which enables side frames to receive an impact weight along a vehicle body fore and aft direction which is input to a floor panel structure efficiently and also enables energy absorption by collapse of the floor panel structure etc. to proceed smoothly.SOLUTION: A vehicle body lower structure includes: a pair of side frames; a cross member; and a floor panel structure 15. The cross member has a pair of inclined extension parts 13s which extend from both ends of a center area in a vehicle width direction to the center side in a vehicle body fore and aft direction, bending at an obtuse angle. The floor panel structure 15 has reinforcement beads 23 which extend from an outer position in the vehicle body fore and aft direction relative to the cross member to the center side in the vehicle body fore and aft direction so as to contact with the cross member. The reinforcement bead 23 extends to a position such that the reinforcement bead 23 does not reach a joint part joined to the floor panel structure 15 at the center side in the vehicle body fore and aft direction of the cross member.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] As an underbody structure for a four-wheeled vehicle, there is one in which a cross member is connected to a pair of rear side frames extending substantially along the front-rear direction of the vehicle body, and a floor panel is joined to the pair of rear side frames and the cross member. In this type of underbody structure, when an impact load is input to the floor panel from the rear of the vehicle, it is desired that the load can be smoothly transmitted from the floor panel to the cross member, and that the energy of the impact load can be efficiently absorbed by the floor panel collapsing in the front and rear directions. Various technologies have been proposed to meet this demand (for example, see Patent Document 1).

[0003] The vehicle underbody structure described in Patent Document 1 has a reinforcing bead formed on a floor panel joined to a pair of rear side frames and a cross member, the reinforcing bead extending substantially along the vehicle front-rear direction. In the case of this vehicle underbody structure, when an impact load is input to the rear part of the floor panel from the rear of the vehicle, the reinforcing bead smoothly transmits the input load to the cross member. In addition, at this time, the floor panel reinforced by the reinforcing bead collapses, so that the energy of the impact load is efficiently absorbed.

[0004] In addition, the left and right underbody structures of four-wheeled vehicles Rear A cross member connected to a side frame by a cross member having a non-linear portion (bent portion) has been proposed (see, for example, Patent Document 2).

[0005] The vehicle underbody structure described in Patent Document 2 has a pair of inclined extensions that extend from both ends of a central region of a cross member in a vehicle width direction at an obtuse angle toward the front of the vehicle, and the outer ends of each inclined extension are connected to left and right rear side frames. A floor panel is joined to the left and right rear side frames and the cross member.

[0006] Even in such vehicle underbody structures, it is desirable to provide a reinforcing bead extending approximately along the fore-and-aft direction of the vehicle body on the floor panel structure (including cases consisting of multiple panels) to ensure smooth transmission of impact loads and improve the ability to absorb the energy of the impact load. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2000-16348 A [Patent Document 2] JP 2016-078658 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in a vehicle underbody structure that employs a cross member with an oblique extension, if a reinforcing bead extending generally along the vehicle longitudinal direction is applied to the floor panel structure, when an impact load along the vehicle longitudinal direction is input from the reinforcing bead to the cross member, the oblique extension of the cross member is likely to deform so as to open outward. When the oblique extension of the cross member deforms so as to open outward, the left and right side frames are pushed outward in the vehicle width direction, and are unable to efficiently absorb the input load. When the left and right side frames are unable to efficiently absorb the impact load, it becomes difficult to smoothly absorb energy due to the crushing of the floor panel structure, etc.

[0009] Therefore, the present invention aims to provide a vehicle underbody structure that can efficiently receive the impact load input to the floor panel structure in the fore-and-aft direction of the vehicle body by the side frames, and smoothly absorb the energy caused by the crushing of the floor panel structure, etc. The present invention will thereby contribute to the development of a sustainable transportation system. [Means for solving the problem]

[0010] In order to solve the above problems, the vehicle underbody structure according to the present invention employs the following configuration. That is, One Invention The vehicle body underbody structure according to the present invention includes a pair of side frames (e.g., rear side frames 10 in the embodiment) extending substantially along the vehicle body longitudinal direction at the rear or front side of the center in the vehicle longitudinal direction, a cross member (e.g., rear cross member 13 in the embodiment) connected to the pair of side frames, and a floor panel structure (e.g., floor panel structure 15 in the embodiment) joined to the pair of side frames and the cross member, and the cross member is disposed in a central region in the vehicle width direction (e.g., central extension portion 13c in the embodiment). The floor panel structure has a pair of inclined extension portions (e.g., inclined extension portion 13s in the embodiment) that extend from both ends of the cross member at an obtuse angle toward the center in the longitudinal direction of the vehicle body, and the floor panel structure has a reinforcing bead (e.g., reinforcing bead 23 in the embodiment) that extends from a position outside the cross member in the longitudinal direction of the vehicle body toward the center in the longitudinal direction of the vehicle body so as to contact the cross member, and the reinforcing bead extends to a position that does not reach the joint portion (e.g., front joint portion 35 in the embodiment) between the cross member and the floor panel structure on the central side in the longitudinal direction of the vehicle body. In the central region of the cross member, an installation portion (e.g., a support bracket 19r in the embodiment) of a part (e.g., a drive unit 18 in the embodiment) to be disposed under the vehicle body is fixed, and the reinforcing bead is disposed at a position intersecting the installation portion in the vehicle width direction. It is characterized by:

[0011] With the above-mentioned configuration, when an impact load is input from the fore-aft direction of the vehicle body through the floor panel structure, the impact load is transmitted along the reinforcing bead to the cross member. At this time, the reinforcing bead transmits the load to the cross member, but does not reach the joint between the cross member and the floor panel structure at the center of the vehicle body in the fore-aft direction. Therefore, the tension of the floor panel structure acts on the joint between the cross member and the floor panel structure at the center of the vehicle body in the fore-aft direction to suppress deformation of the inclined extension of the cross member. In other words, if the reinforcing bead extends across the joint between the cross member and the floor panel structure at the center in the vehicle's fore-aft direction, when the groove shape of the reinforcing bead is pushed open and deformed when an impact load is input, the tension of the floor panel structure will no longer act on the joint between the cross member and the floor panel structure at the center in the vehicle's fore-aft direction to suppress deformation of the oblique extension. In contrast, in the above configuration, since the reinforcing bead does not reach the joint between the cross member and the floor panel structure at the center in the vehicle's fore-aft direction, the tension of the floor panel structure will act on the joint between the cross member and the floor panel structure at the center in the vehicle's fore-aft direction to suppress deformation of the oblique extension of the cross member. Therefore, when an impact load is input from the front-rear direction of the vehicle body through the floor panel structure, the cross member receives the load from the reinforcing bead, which makes it difficult for the inclination angle of the inclined extension of the cross member to deform in an opening direction. Therefore, when this configuration is adopted, the bent portion of the cross member is prevented from deforming in the opening direction, and the impact load input to the floor panel structure can be efficiently received by the side frame.

[0013] In this case, the impact load along the fore-and-aft direction of the vehicle body input to the reinforcing bead is input to the portion of the central region of the cross member where the part installation portion is fixed. The portion of the central region of the cross member where the impact load is input through the reinforcing bead is reinforced by the part installation portion. This makes the central region of the cross member less likely to deform, and also makes it less likely that the opening-shaped deformation behavior of the reinforcing bead will be transmitted to the inclined extension side of the cross member.

[0014] A vehicle underbody structure according to another aspect of the present invention includes a pair of side frames (e.g., rear side frames 10 in the embodiment) extending substantially along the longitudinal direction of the vehicle body at a rear or front side of the center in the longitudinal direction of the vehicle body, a cross member (e.g., rear cross member 13 in the embodiment) connected to the pair of side frames, and a floor panel structure (e.g., floor panel structure 15 in the embodiment) joined to the pair of side frames and the cross member, the cross member extending from a central region in the vehicle width direction (e.g., central extension portion 13c in the embodiment) extending from a central region in the vehicle width direction (e.g., central extension portion 13c in the embodiment). the floor panel structure has a pair of inclined extension portions (e.g., inclined extension portion 13s in the embodiment) that extend from both ends of the cross member at an obtuse angle toward the center in the fore-aft direction of the vehicle body, the floor panel structure has a reinforcing bead (e.g., reinforcing bead 23 in the embodiment) that extends from a position outer than the cross member in the fore-aft direction of the vehicle body toward the center in the fore-aft direction of the vehicle body so as to contact the cross member, and the reinforcing bead extends to a position that does not reach the joint portion (e.g., front joint portion 35 in the embodiment) between the cross member and the floor panel structure on the center side in the fore-aft direction of the vehicle body, An installation portion (e.g., a support bracket 19r in the embodiment) of a part (e.g., a drive unit 18 in the embodiment) to be disposed under the vehicle body is fixed to the central region of the cross member, and the installation portion is fixed so as to straddle a bent portion (e.g., a bent portion 13b in the embodiment) between the central region of the cross member and the inclined extension portion. It is characterized by the fact that

[0015] In this case, the bent portion between the central region of the cross member and the inclined extension portion is strongly reinforced by the installation portion of the part. Therefore, when an impact load is input to the reinforcing bead from the fore-aft direction of the vehicle body, the installation portion of the part can suppress deformation originating from the bent portion of the cross member. Therefore, when this configuration is adopted, the impact load input to the floor panel structure can be more efficiently received by the side frame.

[0016] The reinforcing bead may extend beyond the joint between the cross member and the floor panel structure on the outer side in the vehicle longitudinal direction (for example, rear joint 30 in the embodiment) toward the center in the vehicle longitudinal direction.

[0017] In this case, the load input to the floor panel structure in the fore-and-aft direction of the vehicle body can be efficiently transmitted to the cross member through the reinforcing bead.

[0018] The reinforcing beads may be provided in multiple locations on the floor panel structure, spaced apart in the vehicle width direction, and the reinforcing bead that intersects with the inclined extension portion of the cross member may extend further toward the center in the fore-and-aft direction of the vehicle body than the reinforcing bead that intersects with the central region of the cross member.

[0019] In this case, by extending the reinforcing bead that intersects with the inclined extension portion of the cross member as far as possible toward the center in the fore-and-aft direction of the vehicle body, deformation of the inclined extension portion of the cross member can be suppressed while the impact load input to the floor panel structure can be efficiently transmitted to the cross member via multiple reinforcing beads. Effect of the Invention

[0020] In the vehicle underbody structure according to the present invention, the reinforcing bead of the floor panel structure extends to a position that does not reach the joint between the cross member and the floor panel structure at the center in the vehicle front-rear direction. Therefore, when an impact load is input in the vehicle front-rear direction, the input load is smoothly transmitted to the cross member via the reinforcing bead, and the inclined extension of the cross member can be prevented from deforming in the opening direction. Therefore, when the vehicle underbody structure according to the present invention is adopted, the impact load input to the floor panel structure along the vehicle front-rear direction can be efficiently received by the side frames, and energy absorption due to the crushing of the floor panel structure, etc. can proceed smoothly. Therefore, when the vehicle underbody structure according to the present invention is adopted, it can contribute to the development of a sustainable transportation system. [Brief description of the drawings]

[0021] [Figure 1] FIG. 2 is a bottom view of the vehicle according to the first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the vehicle according to the first embodiment taken along line II-II in FIG. [Diagram 3] FIG. 5 is a cross-sectional view similar to FIG. 2 of a vehicle according to a second embodiment. [Figure 4] FIG. 11 is a bottom view of a vehicle according to a second embodiment. [Diagram 5] FIG. 11 is a cross-sectional view similar to FIG. 2 of a vehicle according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. In the following description, the terms front, back, up, down, left and right refer to directions relative to the forward direction of the vehicle unless otherwise specified. In addition, in the appropriate places of the drawings, an arrow FR pointing to the front of the vehicle, an arrow UP pointing to the top of the vehicle, and an arrow LH pointing to the left side of the vehicle are indicated. In addition, in each embodiment described below, common parts are given the same reference numerals and some overlapping descriptions will be omitted.

[0023] First Embodiment Fig. 1 is a bottom view of the rear area of ​​a vehicle 1 according to this embodiment. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. A pair of rear side frames 10 (side frames) extending generally along the vehicle front-rear direction are disposed on both left and right sides of the rear region of the vehicle 1. The front ends of the left and right rear side frames 10 are connected to left and right side sills 11 disposed below and outside the vehicle width direction of the passenger compartment. The left and right side sills 11 extend along the vehicle front-rear direction. The front regions of the left and right rear side frames 10 are connected to each other by a front cross member 12 extending generally along the vehicle width direction. The rear regions of the left and right rear side frames 10 are connected to each other by a rear cross member 13 (cross member) extending generally along the vehicle width direction.

[0024] A front floor panel 14, which covers the lower part of the passenger compartment, is joined to the left and right side sills 11. A rear floor panel structure 15, which covers the lower part of the luggage compartment at the rear of the passenger compartment, is joined to the left and right rear side frames 10, the front cross member 12, and the rear cross member 13. The floor panel structure 15 has a double panel structure having an upper wall panel 16 and a lower wall panel 17, as will be described in detail later.

[0025] A drive unit 18 for driving the vehicle is supported on the front cross member 12 and the rear cross member 13. The front edge of the drive unit 18 is supported by a plurality of support blocks 70 joined to the rear edge of the front cross member 12, and the rear edge of the drive unit 18 is supported by the rear cross member 13. The plurality of support blocks 70 are fixed by welding to the rear edge of the front cross member 12 and to the underside of the front edge of the upper wall panel 16 of the floor panel structure 15. The drive unit 18 is fastened and fixed to the plurality of support blocks 70 and the respective undersides of the rear cross member 13 via vibration isolation mounts and support brackets 19f, 19r (not shown). In this embodiment, the drive unit 18 constitutes a component that is arranged below the vehicle body, and two support brackets 19r fastened to the underside of the rear cross member 13 constitute mounting portions for the components that are arranged below the vehicle body.

[0026] A pair of drive shafts 20 extend outward in the left-right direction of the vehicle body from the drive unit 18. The tip ends of the left and right drive shafts 20 are supported by the vehicle body via rear suspension devices (not shown). Rear wheels (not shown) are attached to the tip ends of the drive shafts 20.

[0027] As shown in Fig. 2, the floor panel structure 15 includes an upper wall panel 16 extending between the rear end of the front floor panel 14 (see Fig. 1) and the rear end of the vehicle body, a lower wall panel 17 extending below the upper wall panel 16 between the rear end of the rear cross member 13 and the rear end of the vehicle body, and a rear panel 21 connecting the rear ends of the upper wall panel 16 and the lower wall panel 17. The upper end of the rear cross member 13 is joined to approximately the middle part of the upper wall panel 16 in the vehicle fore-and-aft direction, and the front edge of the lower wall panel 17 is joined to the rear edge part of the lower end side. The lower wall panel 17 forms a box-shaped hollow part between itself and the rear half region of the upper wall panel 16.

[0028] Specifically, the left and right side edges of the lower wall panel 17 are bent upward and extend, and the bent upper edges are joined to the left and right side edges of the upper wall panel 16. The space between the front end of the lower wall panel 17 and the upper wall panel 16 is closed by the rear cross member 13, and the space between the rear end of the lower wall panel 17 and the upper wall panel 16 is closed by the rear panel 21. The box-shaped hollow portion thus formed extends rearward of the rear cross member 13 and the left and right rear side frames 10. A rear bumper 22 having a substantially hat-shaped cross section is joined to the central region of the rear end of the upper wall panel 16 and the lower wall panel 17 closed by the rear panel 21.

[0029] A plurality of (e.g., six) reinforcing beads 23 extending along the vehicle body front-rear direction are formed at approximately equal intervals in the vehicle width direction in the central region of the lower wall panel 17. The reinforcing beads 23 have a cross section that bulges downward or upward in a mountain shape extending along the vehicle body front-rear direction. Each reinforcing bead 23 extends from a position rearward of the rear cross member 13 (an outer position in the vehicle body front-rear direction) toward the front side of the vehicle body (the center side in the vehicle body front-rear direction) so as to contact the rear cross member 13.

[0030] As shown in Fig. 2, the rear cross member 13 is joined to the lower surface of the upper wall panel 16 to form a substantially rectangular closed cross section between the upper wall panel 16. The rear cross member 13 includes a central extending portion 13c (central region) extending along the vehicle width direction in a bottom view, and a pair of oblique extending portions 13s extending from outer ends on both sides of the central extending portion 13c in the vehicle width direction and bending at an obtuse angle toward the front side of the vehicle body (the center side in the vehicle front-rear direction). Bending portions 13b are provided between the central extending portion 13c and each oblique extending portion 13s. Note that the "bending" of the bending portions 13b provided between the central extending portion 13c and each oblique extending portion 13s is not limited to a form of bending at an angle, but also includes a form of bending in a curved manner.

[0031] In addition, as shown in Figure 2, the rear cross member 13 of this embodiment has a front plate 13f having a generally L-shaped cross section perpendicular to the vehicle width direction, and a rear plate 13r having a generally I-shaped cross section perpendicular to the vehicle width direction.

[0032] The front plate 13f has a vertical wall 24 extending in the up-down direction, and a lower wall 25 extending from the lower end of the vertical wall 24 toward the rear side of the vehicle. An upper flange 26 is provided at the upper end of the vertical wall 24, bending and extending toward the front side of the vehicle. The upper surface of the upper flange 26 is joined to the lower surface of the upper wall panel 16 of the floor panel structure 15. The portion of the upper wall panel 16 to which the upper flange 26 of the front plate 13f is joined does not have an uneven portion such as a reinforcing bead extending in the fore-and-aft direction of the vehicle body. The upper flange 26 is joined to a portion of the upper wall panel 16 that does not have an uneven portion extending in the fore-and-aft direction of the vehicle body. In this embodiment, the upper flange 26 of the front plate 13f forms a joint 35 with the floor panel structure 15 on the center side (front side) of the cross member in the vehicle front-rear direction. Hereinafter, this joint 35 will be referred to as the "front joint 35."

[0033] The rear plate 13r has a vertical wall 27 extending in the up-down direction behind the vertical wall 24 of the front plate 13f. An upper flange 28 is provided at the upper end of the vertical wall 27, bending and extending toward the front side of the vehicle. A lower flange 29 is provided at the lower end of the vertical wall 27, bending and extending toward the rear side of the vehicle. The upper surface of the upper flange 28 is joined to the lower surface of the upper wall panel 16 of the floor panel structure 15. The lower flange 29 faces the upper surface of the rear edge portion of the lower wall 25 of the front plate 13f in the up-down direction. The front edge portion of the lower wall panel 17 of the floor panel structure 15 is inserted between the lower flange 29 and the rear edge portion of the lower wall 25. The lower flange 29 and the lower wall 25 are fixed to each other by welding or the like, with the front edge portion of the lower wall panel 17 sandwiched between them. The front edge of the lower wall panel 17 is joined to the rear cross member 13 in a state where it is sandwiched between the lower flange 29 and the rear edge of the lower wall 25 . In this embodiment, the lower flange 29 and the rear edge of the lower wall 25 form a joint 30 with the floor panel structure 15 on the outer side (rear side) of the cross member in the vehicle front-rear direction. Hereinafter, this joint 30 will be referred to as the "rear joint 30."

[0034] The multiple reinforcing beads 23 formed on the lower wall panel 17 extend to a position that does not reach the front joint 35 on the front side of the rear cross member 13 in a bottom view of the vehicle. In other words, the multiple reinforcing beads 23 extend to a position that does not reach the joint between the cross member and the floor panel structure 15 on the center side in the longitudinal direction of the vehicle body. In the case of this embodiment, the multiple reinforcing beads 23 have their front ends in contact with the rear end of the rear joint 30 on the rear side of the rear cross member 13 and extend to a position that does not reach the front joint 35 on the front side of the rear cross member 13.

[0035] 1, the three reinforcing beads 23 in the left half region of the lower wall panel 17 are disposed at positions intersecting in the vehicle width direction with an extending portion of a support bracket 19r on the left side (upper side in FIG. 1) of the rear cross member 13. The left support bracket 19r is fixed to the underside of the lower wall 25 of the rear cross member 13 so as to straddle the bent portion 13b between the central extending portion 13c and the left inclined extending portion 13s of the rear cross member 13. The reinforcing bead 23L(23) located on the leftmost side among the reinforcing beads 23 in the left half region is disposed at a position intersecting with the left bent portion 13b.

[0036] Similarly, as shown in Fig. 1, the three reinforcing beads 23 in the right half region of the lower wall panel 17 are disposed at positions intersecting in the vehicle width direction with an extending portion of a support bracket 19r on the right side (lower side in Fig. 1) of the rear cross member 13. The right support bracket 19r is fixed to the underside of the lower wall 25 of the rear cross member 13 so as to straddle the bent portion 13b between the central extending portion 13c and the right inclined extending portion 13s of the rear cross member 13. The reinforcing bead 23R(23) located at the rightmost position among the reinforcing beads 23 in the right half region is disposed at a position intersecting with the right bent portion 13b.

[0037] As described above, in the vehicle body lower structure of this embodiment, the reinforcing bead 23 formed on the lower wall panel 17 of the floor panel structure 15 contacts the rear joint 30 of the rear cross member 13 and extends to a position not reaching the front joint 35 of the rear cross member 13. Therefore, when an impact load is input from the rear of the vehicle, the input load is smoothly transmitted to the rear cross member 13 via the reinforcing bead 23, and the deformation of the inclined extension 13s of the rear cross member 13 in the opening direction can be suppressed. That is, in this configuration, since the reinforcing bead 23 does not reach the front joint 35 of the rear cross member 13, the tension of the floor panel structure 15 (upper wall panel 16) acts on the front joint 35 of the rear cross member 13 with the floor panel structure 15 so as to suppress the deformation of the inclined extension 13s of the rear cross member 13 in the opening direction. Therefore, the impact load input to the floor panel structure 15 from the rear of the vehicle can be efficiently received by the left and right rear side frames 10. Therefore, when the underbody structure of this embodiment is adopted, energy absorption by crushing of the floor panel structure 15, etc. can proceed smoothly when an impact load is input from the rear of the vehicle. Therefore, when the underbody structure of this embodiment is adopted, it can contribute to the development of a sustainable transportation system.

[0038] In addition, in the vehicle body underbody structure of this embodiment, the reinforcing bead 23 is disposed at a position intersecting in the vehicle width direction with the installation portion (support bracket 19r) of the drive unit 18, which is a component disposed under the vehicle body. Therefore, an impact load input to the reinforcing bead 23 from the rear of the vehicle is input to a portion of the central extension portion 13c of the rear cross member 13 to which the installation portion (support bracket 19r) of the drive unit 18 is fixed. At this time, the portion of the central extension portion 13c of the rear cross member 13 to which the impact load is input through the reinforcing bead 23 is firmly reinforced by the installation portion (support bracket 19r) of the drive unit 18. Therefore, the rigidity of the central extension portion 13c of the rear cross member 13 is increased, making the central extension portion 13c less likely to deform, and the open-mouthed deformation behavior of the reinforcing bead 23 is also less likely to be transmitted to the inclined extension portion 13s side of the rear cross member 13. Therefore, when this configuration is adopted, energy absorption due to the crushing of the floor panel structure 15 etc. can proceed more smoothly when an impact load is input from the rear of the vehicle.

[0039] Furthermore, in the vehicle underbody structure of this embodiment, the installation portion (support bracket 19r) of the drive unit 18, which is a component disposed under the vehicle body, is fixed so as to straddle the bent portion 13b between the central extension portion 13c and the inclined extension portion 13s of the rear cross member 13. As a result, the bent portion 13b between the central extension portion 13c and the inclined extension portion 13s of the rear cross member 13 is firmly reinforced by the installation portion (support bracket 19r) of the drive unit 18. As a result, when an impact load is input from the rear of the vehicle body, deformation originating from the bent portion 13b of the rear cross member 13 can be suppressed by the installation portion (support bracket 19r) of the drive unit 18. Therefore, when this configuration is adopted, the impact load input to the floor panel structure 15 from the rear of the vehicle can be more efficiently received by the left and right rear side frames 10.

[0040] <Second embodiment> Fig. 3 is a cross-sectional view of the vehicle 101 of this embodiment similar to Fig. 2 of the first embodiment. Fig. 4 is a view of the vehicle 101 of this embodiment seen from below. In the vehicle 101 of this embodiment, the front regions of the left and right rear side frames (not shown) are connected to each other by a front cross member (not shown), and the rear regions are connected to each other by a rear cross member 13, as in the first embodiment. A floor panel structure 115 having a double panel structure is joined to the left and right rear side frames, the front cross member, and the rear cross member 13. The floor panel structure 115 includes an upper wall panel 16 and a lower wall panel 117, as in the first embodiment, and a plurality of (for example, six) reinforcing beads 123 extending along the vehicle body longitudinal direction are formed on the lower wall panel 117 at approximately equal intervals in the vehicle width direction. The reinforcing beads 123 have a cross section that bulges downward or upward in a mountain shape and extends along the vehicle body longitudinal direction. Each reinforcing bead 123 extends from a rearward position (an outer position in the vehicle body longitudinal direction) of the rear cross member 13 toward the front side of the vehicle body (the center side in the vehicle body longitudinal direction) so as to intersect with the rear cross member 13.

[0041] The rear cross member 13, like the first embodiment, has a central extending portion 13c (central region) extending along the vehicle width direction in a bottom view, and a pair of inclined extending portions 13s that extend from outer ends on both sides of the central extending portion 13c in the vehicle width direction at an obtuse angle toward the front side of the vehicle body (the center side in the vehicle front-rear direction). Bent portions 13b are provided between the central extending portion 13c and each inclined extending portion 13s. The rear cross member 13 has a front plate 13f and a rear plate 13r, like the first embodiment.

[0042] The front edge of the lower wall panel 117 of the floor panel structure 15 is inserted between the lower flange 29 of the rear plate 13r and the lower wall 25 of the front plate 13f. The front edge of the lower wall panel 117 extends to approximately the center of the lower wall 25 of the front plate 13f in the front-to-rear direction of the vehicle body. The lower flange 29 and the lower wall 25 are fixed to each other by welding or the like with the front edge of the lower wall panel 117 sandwiched therebetween. The front edge of the lower wall panel 117 is joined to the rear cross member 13 with it being sandwiched between the lower flange 29 and the rear edge of the lower wall 25. In this embodiment as well, the lower flange 29 and the rear edge of the lower wall 25 form a joint with the floor panel structure 115 on the outer side (rear side) of the cross member in the vehicle body fore-and-aft direction. Hereinafter, this joint will be referred to as the "rear joint 30." In addition, the upper flange 26 of the front plate 13f joined to the underside of the upper wall panel 16 forms a joint with the floor panel structure 115 on the central side (front side) of the cross member in the vehicle body fore-and-aft direction. Hereinafter, this joint will be referred to as the "front joint 35."

[0043] In this embodiment, the multiple reinforcing beads 123 have front ends that intersect with the rear end of the rear joint 30 on the rear side of the rear cross member 13, but extend to a position that does not reach the front joint 35 on the front side of the rear cross member 13. Therefore, the multiple reinforcing beads 123 extend beyond the joint (rear joint 30) between the cross member (rear cross member 13) and the floor panel structure 115 on the outer side in the vehicle front-to-rear direction, toward the center (front) in the vehicle front-to-rear direction.

[0044] Furthermore, the reinforcing bead 123L located on the leftmost side among the multiple reinforcing beads 123 is disposed so as to intersect with the left oblique extension portion 13s of the rear cross member 13, and the reinforcing bead 123R located on the rightmost side is disposed so as to intersect with the right oblique extension portion 13s of the rear cross member 13. The remaining four reinforcing beads 123C on the central side are disposed so as to intersect with the central extension portion 13c of the rear cross member 13.

[0045] 4, the front end portions 123Le, 123Re of the left and right reinforcing beads 123L, 123R are disposed further forward of the vehicle body than the front end portion 123Ce of the reinforcing bead 123C in the central region. In other words, the left and right reinforcing beads 123L, 123R intersecting with the inclined extension portion 13s extend further forward of the vehicle than the four reinforcing beads 123C in the central region intersecting with the central extension portion 13c of the rear cross member 13.

[0046] The vehicle body underbody structure of this embodiment has a basic configuration similar to that of the first embodiment, and therefore can obtain the same basic effects as those of the first embodiment described above.

[0047] Furthermore, in the vehicle body underbody structure of this embodiment, the multiple reinforcing beads 123 extend toward the front side of the vehicle body (toward the center in the vehicle body's fore-aft direction) beyond the rear joint 30 of the rear cross member 13 (the joint with the floor panel structure 115 on the outer side in the vehicle body's fore-aft direction). Therefore, impact load input to the floor panel structure 115 from the rear of the vehicle body can be efficiently transmitted to the rear cross member 13 through the multiple reinforcing beads 123. Therefore, when this configuration is adopted, the impact load input from the rear of the vehicle through the multiple reinforcing beads 123 can be more efficiently received by the left and right rear side frames, and energy absorption due to the crushing of the floor panel structure 115, etc. can proceed more smoothly.

[0048] Furthermore, in the vehicle body underbody structure of this embodiment, among the multiple reinforcing beads 123, the reinforcing beads 123L, 123R that intersect with the oblique extension portion 13s of the rear cross member 13 extend further toward the front side of the vehicle body (toward the center in the vehicle front-rear direction) than the reinforcing bead 123C that intersects with the central extension portion 13c. Therefore, the reinforcing beads 123L, 123R that intersect with the oblique extension portion 13s of the rear cross member 13 are extended to the front side of the vehicle body (toward the center in the vehicle front-rear direction) to the maximum extent, suppressing deformation of the oblique extension portion 13s, while efficiently transmitting an impact load input to the floor panel structure 115 to the rear cross member 13 via the multiple reinforcing beads 123.

[0049] <Third embodiment> FIG. 5 is a cross-sectional view of a vehicle 201 according to this embodiment similar to FIG. 2 of the first embodiment. In each of the above embodiments, the floor panel structure has a double panel structure having an upper wall panel and a lower wall panel, but the vehicle body lower structure of the vehicle 201 in this embodiment is composed of a single panel floor panel structure 215. In other words, the floor panel structure 215 is composed of a single rear floor panel 45 joined to the rear cross member 213 and a pair of rear side frames (not shown).

[0050] The rear cross member 213 has, for example, a front flange 51 and a rear flange 52 extending from the front upper end and the rear upper end of a cross member main body 50 having a generally U-shaped cross section that opens upward. The front flange 51 and the rear flange 52 are joined to the underside of the rear floor panel 45, spaced apart in the fore-and-aft direction of the vehicle body. In this embodiment, the front flange 51 of the rear cross member 213 forms a joint with the floor panel structure 215 on the central side of the cross member in the fore-and-aft direction of the vehicle body, and the rear flange 52 of the rear cross member 213 forms a joint with the floor panel structure 215 on the outer side of the cross member in the fore-and-aft direction of the vehicle body.

[0051] Although detailed illustrations are omitted, in this embodiment as well, the rear cross member 213 has a central extension portion (central region) that extends along the vehicle width direction when viewed from below, and a pair of inclined extension portions that extend at an obtuse angle from the outer ends on both sides of the central extension portion in the vehicle width direction toward the front side of the vehicle body (the center side in the fore-and-aft direction of the vehicle body).

[0052] In addition, the rear floor panel 45 (floor panel structure 215) is formed with a plurality of reinforcing beads 223 extending from a position rearward of the rear cross member 213 (an outer position in the vehicle's fore-and-aft direction) toward the front side of the vehicle body (toward the center in the vehicle's fore-and-aft direction) so as to contact the rear cross member 213. The multiple reinforcing beads 223 are formed on the rear floor panel 45 spaced apart in the vehicle width direction. In this embodiment, the multiple reinforcing beads 223 intersect with the rear flange 52 of the rear cross member 213 and extend to a position not reaching the front flange 51. The front flange 51, which is the joint on the front side of the rear cross member 213, is joined to a portion of the rear floor panel 45 that does not have an uneven shape such as a reinforcing bead.

[0053] In the vehicle body lower structure of this embodiment, the floor panel structure 215 is formed of a single rear floor panel 45, but the multiple reinforcing beads 223 intersect with the rear flange 52 and extend to a position not reaching the front flange 51. As a result, the tension of the floor panel structure 215 (rear floor panel 45) acts on the front joint (front flange 51) of the rear cross member 213 with the floor panel structure 215 so as to suppress deformation in the opening direction of the inclined extension of the rear cross member 213. Therefore, the left and right rear side frames can efficiently absorb the impact load input to the floor panel structure 215 from the rear of the vehicle. Therefore, in the case of this embodiment as well, when an impact load is input from the rear of the vehicle, energy absorption by the crushing of the floor panel structure 215 etc. can proceed smoothly.

[0054] The present invention is not limited to the above-mentioned embodiment, and various design modifications are possible without departing from the gist of the present invention. For example, in the above-mentioned embodiment, the central region of the rear cross member is provided with a central extension portion extending along the vehicle width direction, but the shape of the central region of the rear cross member is not limited to a shape extending along the vehicle width direction, and may be another shape such as a rectangular block shape. In addition, in the first and second embodiments, six reinforcing beads 23, 123 are provided on the lower wall panels 17, 117, respectively, but the number of reinforcing beads 23, 123 provided on the lower wall panels 17, 117 is not limited to six, and an appropriate number can be selected depending on the vehicle.

[0055] Although the above embodiment is directed to a vehicle body underbody structure at the rear of the vehicle, a similar configuration can also be adopted for a vehicle body underbody structure at the front. Specifically, in a structure in which a front cross member is joined to left and right front side frames extending substantially along the vehicle body longitudinal direction, and a floor panel is joined to the front side frames and the front cross member, a reinforcing bead may be formed on the floor panel in the same manner as described above.

[0056] In the above embodiment, the drive unit 18 is given as an example of a part that is disposed under the vehicle body and fixed to the cross member (rear cross member 13), but the part that is disposed under the vehicle body and fixed to the cross member is not limited to this. The part that is disposed under the vehicle body and fixed to the cross member may be, for example, a suspension part or a wiring holding part. [Explanation of symbols]

[0057] 10...Rear side frame (side frame) 13,213…Rear cross member (cross member) 13c...Central extension part (center area) 13s…Slope extension part 13b...Bending part 15,115,215…Floor panel structure 18...Drive unit (parts located under the vehicle body) 19r…Support bracket (installation part) 23,123,223…Reinforcing bead 30...Rear joint part (joint part) 35…Front joint (joint) 51...Front flange (joint) 52...Rear flange (joint)

Claims

1. A pair of side frames extending substantially along the front-rear direction of the vehicle body at a rear side or a front side of a center in the front-rear direction of the vehicle body; A cross member connected to the pair of side frames; a floor panel structure joined to the pair of side frames and the cross member, The cross member has a pair of inclined extending portions that extend from both ends of a central region in a vehicle width direction toward a center side in a vehicle front-rear direction while bending at an obtuse angle, the floor panel structure has a reinforcing bead extending from a position outside the cross member in the vehicle front-rear direction toward the center in the vehicle front-rear direction so as to contact the cross member, The reinforcing bead extends to a position not reaching a joint between the cross member and the floor panel structure on a center side in a vehicle front-rear direction, An installation portion for a component to be disposed under a vehicle body is fixed to the central region of the cross member, The vehicle underbody structure, wherein the reinforcing bead is disposed at a position intersecting the installation portion in the vehicle width direction.

2. A pair of side frames extending substantially along the front-rear direction of the vehicle body at a rear side or a front side of a center in the front-rear direction of the vehicle body; A cross member connected to the pair of side frames; a floor panel structure joined to the pair of side frames and the cross member, The cross member has a pair of inclined extending portions that extend from both ends of a central region in a vehicle width direction toward a center side in a vehicle front-rear direction while bending at an obtuse angle, the floor panel structure has a reinforcing bead extending from a position outside the cross member in the vehicle front-rear direction toward the center in the vehicle front-rear direction so as to contact the cross member, The reinforcing bead extends to a position not reaching a joint between the cross member and the floor panel structure on a center side in a vehicle front-rear direction, An installation portion for a component to be disposed under a vehicle body is fixed to the central region of the cross member, A vehicle underbody structure, characterized in that the installation portion is fixed so as to straddle a bent portion between the central region of the cross member and the inclined extension portion.

3. 3. The vehicle underbody structure according to claim 1, wherein the reinforcing bead extends beyond a joint between the cross member and the floor panel structure on an outer side in the vehicle longitudinal direction to a center side in the vehicle longitudinal direction.

4. The reinforcing beads are provided in a plurality on the floor panel structure at intervals in the vehicle width direction, 4. The vehicle underbody structure according to claim 3, wherein the reinforcing bead that intersects with the inclined extension portion of the cross member extends toward the center in the fore-and-aft direction of the vehicle body further than the reinforcing bead that intersects with the central region of the cross member.

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