Vehicle underbody structure

Abstract

A vehicle underbody structure includes: a cross member (30) disposed at a bottom of a vehicle and being a frame member long in a vehicle width direction; a plurality of pillars (50) disposed at intervals in the vehicle width direction and each protruding downward from a bottom surface of the cross member (30); and a brace arm (60) erected between the plurality of pillars (50).

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Japanese Patent Application No. 2022-061936, filed on April 1, 2022, the entire contents of which, including the description, claims, drawings and abstract, are incorporated herein by reference. Technical Field

[0003] This specification discloses a vehicle bottom structure having a crossbeam, which is a long, rectangular frame component in the vehicle width direction. Background Technology

[0004] Typically, a pair of longitudinal beams extending in the longitudinal direction and multiple crossbeams spanning between the longitudinal beams are provided at the bottom of a vehicle. Patent Document 1 discloses a vehicle bottom structure having such longitudinal beams (referred to as "lower side beams" in Patent Document 1) and crossbeams.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2021-112969

[0008] Here, the crossbeam is a skeletal component supporting the vehicle body, requiring high beam rigidity. Beam rigidity depends on the moment of inertia of its section, which is proportional to the first power of the crossbeam's longitudinal dimension and the cube power of its vertical dimension. Therefore, compared to the crossbeam's longitudinal dimension, the moment of inertia depends more heavily on the vertical dimension. To ensure sufficient beam rigidity, it is necessary to adequately ensure the crossbeam's vertical dimension as well.

[0009] However, increasing the vertical dimension of the crossbeam may correspondingly reduce the cabin space or decrease the space available for piping and wiring that should be located at the bottom of the vehicle.

[0010] Therefore, this specification discloses a vehicle bottom structure that can suppress the increase in the vertical dimension of the crossbeam and further improve the beam rigidity of the crossbeam. Summary of the Invention

[0011] The vehicle underbody structure disclosed in this specification is characterized by comprising: a crossbeam disposed at the bottom of the vehicle and being a long skeletal component in the vehicle width direction; a plurality of columns spaced apart in the vehicle width direction and each protruding downward from the bottom surface of the crossbeam; and a support arm mounted between the plurality of columns.

[0012] In a case where the cross member is deflected downward by a downward force, the posture of the column body protruding from the bottom surface of the cross member changes, and the separation distance between the adjacent column bodies changes. As described above, if the brace arm is provided between the plurality of column bodies, the change in the separation distance between the adjacent column bodies is effectively suppressed. Also, as a result, the deflection of the cross member can be effectively suppressed, and the rigidity of the cross member is improved.

[0013] In this case, it can also be that the linear member, which is a wiring or a piping, passes through the space surrounded by the cross member, the adjacent pair of the plurality of column bodies, and the brace arm, that is, the passage.

[0014] With this configuration, since a space for the linear member to pass through does not need to be prepared separately, the space at the bottom of the vehicle can be more effectively utilized.

[0015] Further, it can also be that a tunnel, which is raised upward of the floor panel and is long in the vehicle front-rear direction, is provided, the plurality of column bodies include a pair of column bodies adjacent in the vehicle width direction, and the vehicle width direction positions of the pair of column bodies are substantially the same as the vehicle width direction positions of the both ends of the tunnel in the vehicle width direction.

[0016] With this configuration, the inside space of the tunnel and the passage are substantially aligned in a straight line. As a result, the route of the linear member passing through both the inside space of the tunnel and the passage can be made substantially straight, and the bending and the flexing of the linear member can be effectively suppressed.

[0017] Further, it can also be that the cross member has a central portion and a pair of root portions located on both sides of the central portion in the vehicle width direction, the bottom surface of the central portion is located upward of the bottom surfaces of the root portions, the vertical direction dimension of the central portion is smaller than the vertical direction dimension of the root portions, and the plurality of column bodies protrude downward from the bottom surface of the central portion.

[0018] In this way, by providing the column bodies to the central portion, the vertical direction dimension of the entire beam member composed of the cross member, the column bodies, and the brace arm can be suppressed to be small.

[0019] In this case, it can also be that the cross member further has a transition portion between the central portion and the root portions, and the bottom surface of the transition portion is inclined so as to gradually approach upward as it approaches the central portion from the root portions.

[0020] In this way, by providing the transition portion, in which the vertical direction dimension gradually changes, between the central portion and the root portions, the stress concentration at the connection between the central portion and the root portions can be moderated. Also, as a result, the bending and the breaking of the cross member can be effectively suppressed.

[0021] Further, it can also be that the column body is substantially a box shape that forms a closed space between the bottom surface of the cross member.

[0022] By being configured in this way, the rigidity of the pillar can be improved, and deformation of the pillar and even flexing of the cross member can be effectively suppressed.

[0023] Further, the cross member can have a cross member upper portion and a cross member lower portion that are opposite in the up-down direction, the cross member upper portion having an extension portion that extends downward from a front lower edge of the cross member lower portion at the central portion, and the pillar can have a bottom wall that is opposite the cross member in the up-down direction, a rear wall that extends upward from a rear end of the bottom wall, and a pair of side walls that extend upward from both ends in the vehicle width direction of the bottom wall to engage with a bottom surface of the cross member, the front ends of the bottom wall and the side walls of the pillar engaging with the extension portion, and the portion of the extension portion that is opposite the rear wall of the pillar functioning as a front wall of the pillar.

[0024] By being configured in this way, the rigidity of the pillar can be further improved, and deformation of the pillar and even flexing of the cross member can be further effectively suppressed.

[0025] Further, the brace can be disposed within the up-down direction range of the cross member.

[0026] By being configured in this way, the up-down direction dimension of the entire cross member component composed of the cross member, the pillar, and the brace can be suppressed to be the same as a cross member component that does not have a pillar and a brace, and the cross member component can be prevented from becoming large.

[0027] Further, a pair of longitudinal members that are skeletal members that are long in the vehicle front-rear direction and that are connected to both ends in the vehicle width direction of the cross member can be further provided, and the brace can be disposed within the up-down direction range of the longitudinal members.

[0028] By being configured in this way, the up-down direction dimension of the entire vehicle floor structure composed of the cross member, the pillar, the brace, and the longitudinal members can be suppressed to be the same as a vehicle floor structure that does not have a pillar and a brace, and the vehicle floor structure can be prevented from becoming large.

[0029] According to the vehicle floor structure disclosed in this specification, the up-down direction dimension of the cross member can be suppressed from increasing, and the beam rigidity of the cross member can be further improved. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is an overall perspective view of a vehicle floor.

[0031] Figure 2 is a longitudinal sectional view of a cross member, and is Figure 1 is an A-A sectional view of

[0032] Figure 3 is a sectional perspective view taken with the B-B line of Figure 2 cut.

[0033] Figure 4 is a C-C sectional view. Figure 2

[0034] Figure 5 is a longitudinal sectional view showing a case where a downward force is applied to the cross beam.

[0035] Figure 6 is a longitudinal sectional view showing a case where a downward force is applied to the cross beam of the comparative example.

[0036] Figure 7 is a perspective view showing another example of the brace arm.

[0037] Figure 8 is a longitudinal sectional view of another vehicle floor structure.

[0038] Figure 9 is a longitudinal sectional view of another vehicle floor structure. DETAILED DESCRIPTION

[0039] Hereinafter, a vehicle floor structure will be described with reference to the drawings. Figure 1 is a perspective view of a vehicle floor. Further, in each drawing, "Fr", "Up", and "Rh" respectively indicate a front side, an upper side, and a right side of the vehicle.

[0040] As shown in Figure 1 , a floor panel 10 that functions as a floor surface of a passenger compartment is provided at a floor portion of the vehicle. The floor panel 10 is a panel material that extends in a horizontal direction. Further, the floor panel 10 is configured by combining a plurality of panel materials.

[0041] A longitudinal beam 20 is joined at both ends in a vehicle width direction of the floor panel 10. The longitudinal beam 20 is a skeletal member that is long in a vehicle front-rear direction. As shown in Figure 2 , the longitudinal beam 20 is configured by joining an inner longitudinal beam 22 and an outer longitudinal beam 24.

[0042] A tunnel 18 that is long in the vehicle front-rear direction is provided at a center in the vehicle width direction of the floor panel 10. The tunnel 18 is configured by causing the floor panel 10 to be raised upward of the vehicle. An inner side space of the tunnel 18 is passed through by a plurality of linear members 70 that are wiring or piping.

[0043] Further, a plurality of (two in the illustrated example) cross beams 30 are provided at the floor portion of the vehicle. The cross beam 30 is a skeletal member that is long in the vehicle width direction. Both ends in the vehicle width direction of the cross beam 30 are joined to the longitudinal beam 20.

[0044] The structure of the cross beam 30 will be described in detail with reference to Figures 2 to 4 . Figure 2 is a longitudinal sectional view of the cross beam 30, and is Figure 1 ​AA sectional view. Figure 3 It is Figure 2 A sectional perspective view of the BB line cut off. Figure 4 yes Figure 2 CC section view.

[0045] like Figure 3 , Figure 4 As shown, the crossbeam 30 is constructed by joining the upper part 32 and the lower part 34 of the crossbeam together. The upper part 32 of the crossbeam opens downward toward the vehicle and is a long, slot-shaped component in the vehicle width direction. More specifically, the upper part 32 of the crossbeam has: a top wall 32t that is substantially parallel to the horizontal direction; a front wall 32f that extends downward from the leading edge of the top wall 32t; a front flange 32ff that extends forward from the lower edge of the front wall 32f; a rear wall 32r that extends downward from the rear edge of the top wall 32t; and a rear flange 32rf that extends rearward from the lower edge of the rear wall 32r. In addition, the lower part 34 of the crossbeam has: a bottom wall 34b that is vertically opposite to the top wall 32t; a front flange 34ff that extends downward from the leading edge of the bottom wall 34b; a rear wall 34r that extends upward from the rear edge of the bottom wall 34b; and a rear flange 34rf that extends rearward from the upper edge of the rear wall 34r toward the rear of the vehicle. The front wall 32f of the upper part 32 of the crossbeam is joined to the front flange 34ff of the lower part 34 of the crossbeam, and the rear flange 32rf of the upper part 32 of the crossbeam is joined to the rear flange 34rf of the lower part 34 of the crossbeam via the floor panel 10.

[0046] Here, as Figure 2 As shown, the bottom surface (i.e., bottom wall 34b) of the crossbeam 30 is close to the upper surface (i.e., top wall 32t) at the center in the vehicle width direction, and the vertical dimension of the crossbeam 30 at the center in the vehicle width direction is smaller than that of the rest. In other words, in this example, the crossbeam 30 can be roughly divided into a central portion 36 with a small vertical dimension, a root portion 38 with a large vertical dimension, and a transition portion 40 between the central portion 36 and the root portion 38. The bottom wall 34b of the central portion 36 is located above the vehicle surface compared to the bottom wall 34b of the root portion 38.

[0047] Furthermore, the bottom wall 34b of the transition section 40 slopes upwards gradually from the root 38 toward the central section 36 (in other words, toward the inner side in the vehicle width direction). Thus, by providing the transition section 40, whose dimensions gradually change in the vertical direction, stress concentration at the connection between the central section 36 and the root 38 can be mitigated compared to the case without the transition section 40. As a result, deflection and breakage of the crossbeam 30 can be effectively suppressed.

[0048] Here, the bottom wall 34b is raised upward at the vehicle width direction center of the cross member 30 in order to pass the wire-like members 70 through the lower side of the cross member 30. That is, as described above, the plurality of wire-like members 70 that are the wiring or the piping pass the inner side of the passage 18. In order to pass the wire-like members 70, the central portion 36 that raises the bottom wall 34b upward is provided at the vehicle width direction center of the cross member 30.

[0049] Here, as shown in Figure 3 , Figure 4 , at the central portion 36, the front wall 32f of the cross member upper portion 32 extends to the lower side than the bottom wall 34b of the cross member lower portion 34. Hereinafter, the portion of the front wall 32f that extends to the lower side than the bottom wall 34b will be referred to as "extension portion 33".

[0050] A pair of pillars 50 is joined to the bottom surface of the cross member 30. The pillar 50 is a member that protrudes downward from the bottom surface of the cross member 30. The pillar 50 is provided at the central portion 36. The structure of the pillar 50 is not particularly limited as long as the pillar 50 has sufficient rigidity. In the present example, the pillar 50 is provided as a substantially box shape that forms an enclosed space 51 between the bottom surface of the cross member 30 and the pillar 50.

[0051] Specifically, the pillar 50 of the present example has a bottom wall 50b that opposes the bottom wall 34b of the cross member lower portion 34 in the up-down direction, a rear wall 50r that extends upward from the rear edge of the bottom wall 50b, and side walls 50s that extend upward from the vehicle width direction both ends of the bottom wall 50b. As shown in Figure 3 , Figure 4 , the upper end of the rear wall 50r is joined to the floor panel 10. In addition, the upper end of the side wall 50s is joined to the bottom surface of the cross member 30. Furthermore, the front end of the side wall 50s and the front end of the bottom wall 50b are joined to the extension portion 33 of the cross member upper portion 32. In this case, the portion of the extension portion 33 that opposes the rear wall 50r in the vehicle front-rear direction functions as a front wall 50f of the pillar 50. Furthermore, by this, at the lower side of the cross member 30, the enclosed space 51 is formed that is surrounded by the bottom surface of the cross member 30, the side wall 50s, the rear wall 50r, the bottom wall 50b, and the front wall 50f (i.e., a portion of the extension portion 33) of the pillar 50. In this way, by providing the pillar 50 as a box shape and further using a portion of the cross member upper portion 32 as the front wall 50f of the pillar 50, the rigidity of the pillar 50 is increased, and deformation of the pillar 50 is effectively prevented.

[0052] As shown in Figure 2 , a brace 60 is erected on the pair of pillars 50. The brace 60 is a substantially flat plate-like member that is long in the vehicle width direction. The vehicle width direction both ends of the brace 60 are fixed to the bottom wall 50b of the pillar 50. In addition, the brace 60 can be welded to the bottom wall 50b of the pillar 50, or can be fastened using a bolt or the like.

[0053] In summary, by erecting the brace 60 on the pair of pillars 50, a passage 42 surrounded by the pair of pillars 50, the brace 60, and the bottom wall 34b of the lower portion 34 of the cross member 30 is formed on the lower side of the central portion 36 of the cross member 30. In the present example, a linear member 70 that is a wiring or a pipe is caused to pass through this passage 42. Further, in the present example, the pillars 50 are disposed at positions overlapping the vehicle width direction both ends of the tunnel 18 when viewed in the vehicle front-rear direction. That is, the vehicle width direction positions of the vehicle width direction inner ends of the pillars 50 are made substantially the same as the vehicle width direction positions of the vehicle width direction both ends of the tunnel 18.

[0054] Next, the reason for providing the pillars 50 and the brace 60 will be described. Generally, the cross member 30 prevents deformation of the vehicle body by being pressed between the pair of side members 20. Therefore, the cross member 30 is required to have high beam rigidity. Also, in order to maintain the beam rigidity of the cross member 30 high, the cross-sectional moment of inertia of the cross member 30 needs to be high.

[0055] Here, in the conventional cross member 30, the pillars 50 and the brace 60 are not provided. In the case where the cross section of this conventional cross member 30 is regarded as a rectangle, the cross-sectional moment of inertia I of the cross member 30 is I = b x h 3 / 12. Further, b is the front-rear direction dimension of the cross member 30, and h is the up-down direction dimension of the cross member 30. From this formula, it is known that the cross-sectional moment of inertia I of the cross member 30 is proportional to the front-rear direction dimension b of the cross member 30 and is proportional to the cube of the up-down direction dimension h of the cross member 30, and that the cross-sectional moment of inertia I greatly depends on the up-down direction dimension h of the cross member 30 as compared with the front-rear direction dimension b. Therefore, it is known that, in order to increase the beam rigidity of the cross member 30, it is effective to increase the up-down direction dimension h of the cross member 30.

[0056] However, if the up-down direction dimension h of the cross member 30 is increased, the passenger room is correspondingly narrowed, or the space for passing the linear member 70 is narrowed. Also, if the thickness of the plate of the cross member 30 is increased, the cross-sectional moment of inertia I can be increased without increasing the up-down direction dimension h, but in this case, other problems such as an increase in material cost and an increase in vehicle weight are caused.

[0057] In order to solve such problems, the cross member 30 of the present example is provided with a pair of pillars 50 that project downward from the cross member 30 and a brace 60 that is erected between the pair of pillars 50. By being provided in this structure, it is possible to effectively suppress deflection without increasing the up-down direction dimension and the thickness of the plate of the cross member 30. In this regard, a comparative example will be described. Figure 5 is a sectional view showing the case where a downward force F is applied to the cross member 30. Further, Figure 6 is a sectional view showing the case where a downward force F is applied to the cross member 30* of the comparative example.

[0058] As Figure 6As shown, the cross member 30* of the comparative example is provided with the columnar bodies 50 at the same positions as the cross member 30 of the present example, and on the other hand, is not provided with the brace arms 60. In a case where a downward force F is applied to the cross member 30*, the cross member 30* is flexed convexly to the lower side. With this flexion, the posture of the columnar bodies 50 fixed to the bottom surface of the cross member 30* also changes. More specifically, the columnar bodies 50 are inclined in a manner that advances to the outer side in the vehicle width direction as it approaches the lower side, and thus the distance Ll between the lower ends of the pair of columnar bodies 50 expands compared to before the cross member 30* is flexed. In other words, the pair of columnar bodies 50 changes to an expanded tip shape. Since the comparative example cross member 30* is not provided with a member that restricts the change in posture of such columnar bodies 50, when a force F is applied, flexion of the cross member 30* and the change in posture of the columnar bodies 50 easily occur.

[0059] On the other hand, in the case of the cross member 30 of the present example, the brace arms 60 are provided to the pair of columnar bodies 50. In this case, even if the pair of columnar bodies 50 are to change to an expanded tip shape, the brace arms 60 restrict the change in distance Ll between the lower ends of the pair of columnar bodies 50. As a result, the change in posture of the columnar bodies 50 is firmly restricted. Moreover, since the change in posture of the columnar bodies 50 is restricted, flexion of the bottom surface of the cross member 30 to which the columnar bodies 50 are fixed, and even flexion of the entire cross member 30, is effectively suppressed. As a result, according to the present example, it is possible to suppress an increase in the up-and-down direction dimension and the plate thickness of the cross member 30, and effectively improve the beam rigidity of the cross member 30.

[0060] In addition, in the present example, the pair of columnar bodies 50 are arranged sufficiently separated in the vehicle width direction. Thus, it is possible to secure a passage 42 for passing the wire-like member 70 between the pair of columnar bodies 50. Moreover, as a result of this, it is not necessary to separately prepare a space for passing the wire-like member 70, and it is possible to effectively utilize the space of the vehicle floor.

[0061] In particular, in the present example, the position in the vehicle width direction of the inner side end of the columnar body 50 is made substantially the same as the position in the vehicle width direction of the both ends of the passage 18. By being configured in this manner, the inside space of the passage 18 and the inner side space of the passage 42 are arranged substantially straight. As a result, it is possible to make the route of the wire-like member 70 through both the inside space of the passage 18 and the passage 42 substantially straight, and it is possible to effectively suppress bending and flexing of the wire-like member 70. As a result, it is possible to simplify the wiring of the wire-like member 70.

[0062] In addition, in the present example, such a pillar 50 is provided in the central portion 36 that is small in the up-down direction. By providing the pillar 50 in the central portion 36, the up-down direction dimension of the beam member as a whole, which is composed of the cross beam 30, the pillar 50, and the brace 60, can be suppressed to be small. In particular, in the present example, the brace 60 is arranged in the up-down direction range of the cross beam 30 or in the up-down direction range of the longitudinal beam 20. By being configured in this way, the up-down direction dimension of the floor structure of the vehicle, which is composed of the cross beam 30 and the longitudinal beam 20, can be made the same as that of the prior art, and the enlargement of the floor structure can be effectively suppressed.

[0063] However, even if the brace 60 is provided, in the case where the pillar 50 itself is flexibly deformed, the cross beam 30 is flexed. However, in the present example, the pillar 50 is formed in a substantially box shape that forms an enclosed space 51 between the bottom surface of the cross beam 30. By being configured in this way, the rigidity of the pillar 50 can be improved, and the flexure of the pillar 50 itself can be effectively suppressed. As a result, the flexure of the cross beam 30 can be more effectively suppressed.

[0064] In particular, in the present example, a part of the extension portion 33 of the cross beam upper portion 32 functions as the front wall 50f of the pillar 50. In other words, in the present example, not only the upper end of the pillar 50 but also the front end is fixed to the panel material that constitutes the cross beam 30. By being configured in this way, the deformation and inclination of the pillar 50 can be more effectively suppressed. As a result, the flexure of the cross beam 30 can be more effectively suppressed.

[0065] Further, the structure described above is one example, and other structures can be appropriately changed as long as there are at least a plurality of pillars 50 that protrude downward from the bottom surface of the cross beam 30 and a brace 60 that is erected between the plurality of pillars 50. For example, in the above description, the brace 60 is formed in a substantially flat plate shape, but the shape of the brace 60 can be appropriately changed. Thus, for example, the brace 60 can be an angle material that is substantially L-shaped, T-shaped, or U-shaped in cross section. In addition, the brace 60 can be substantially box-shaped that has six mutually orthogonal faces. In addition, it is important that the brace 60 does not flex in the vehicle width direction. Thus, in order to suppress the flexure of the brace 60, as shown in FIG. 6, a rib 62 or a reinforcing rib 64 that is long in the vehicle width direction can be provided in the brace 60. Figure 7

[0066] ​Furthermore, the shape of the column 50 can be appropriately modified. Therefore, the column 50 is not limited to a box shape, but can also be plate-shaped or rod-shaped. Also, as long as the column 50 is fixed to the bottom surface of the crossbeam 30, its position is not limited. Therefore, the column 50 can also be positioned where it does not overlap with the two ends of the width direction of the passage 18 when viewed from the front-rear direction of the vehicle. Furthermore, the column 50 is not limited to the central part 36, but can also be located in other parts, such as the transition part 40. Additionally, the vertical dimensions of the column 50 and the support arm 60 are not particularly limited, and the support arm 60 can also be located below the lowest point of the crossbeam 30 and the lowest point of the longitudinal beam 20.

[0067] Furthermore, if there are two or more pillars (50), more can be set. For example, ... Figure 8 As shown, three pillars 50 can also be spaced apart in the vehicle width direction. By adopting this structure, the distance between two adjacent pillars 50 can be minimized, thus more effectively preventing the beam 30 from deflecting. Furthermore, in this example, the vertical dimension of the beam 30 varies according to the vehicle width direction, but it can also be arranged as shown... Figure 9 As shown, the vertical dimension of the crossbeam 30 is kept constant.

[0068] Label Explanation

[0069] 10 Floor panel, 18 Channel, 20 Longitudinal beam, 22 Inner longitudinal beam, 24 Outer longitudinal beam, 30, 30* Crossbeam, 32 Upper part of crossbeam, 33 Extension, 34 Lower part of crossbeam, 36 Central part, 38 Root, 40 Transition part, 42 Through passage, 50 Column, 50b Bottom wall, 50r Rear wall, 50s Side wall, 50f Front wall, 51 Enclosed space, 60 Support arm, 62 Rib, 64 Reinforcing rib, 70 Linear component.

Claims

1. A vehicle underbody structure characterized by comprising: Possessing: a cross member disposed at the bottom of a vehicle, which is a frame member long in the vehicle width direction; a plurality of pillars disposed at intervals in the vehicle width direction and each protruding downward from the bottom surface of the cross member; and a brace arm erected between the plurality of pillars, the cross member has a central portion and a pair of root portions on both sides of the central portion in the vehicle width direction, the cross member has a cross member upper portion and a cross member lower portion opposed in the vertical direction, the cross member upper portion has an extension portion in the central portion that extends downward further than the front lower edge of the cross member lower portion, the pillar has: a bottom wall opposed to the cross member in the vertical direction; a rear wall extending upward from the rear end of the bottom wall; and a pair of side walls extending upward from both ends of the bottom wall in the vehicle width direction to engage with the bottom surface of the cross member, the front ends of the bottom wall and the side walls of the pillar engage with the extension portion, the portion of the extension portion opposed to the rear wall of the pillar functions as a front wall of the pillar, the pillar is box-shaped with a closed space formed between the bottom surface of the cross member, on the lower side of the cross member, the closed space enclosed by the bottom surface of the cross member, the side walls, the rear wall, the bottom wall, and the front wall of the pillar is formed.

2. The vehicle bottom structure according to claim 1, characterized in that: a wire-like member that is a wiring or a pipe passes through the space enclosed by the cross member, the pillar, and the brace arm, that is, through the passage.

3. The vehicle bottom structure according to claim 2, characterized in that: the vehicle bottom structure further has a tunnel that is raised upward of the vehicle from a floor panel and is long in the vehicle front-rear direction, the plurality of pillars include a pair of pillars adjacent in the vehicle width direction, the vehicle width direction positions of the pair of pillars are substantially the same as the vehicle width direction positions of both ends of the tunnel in the vehicle width direction.

4. The vehicle bottom structure according to claim 1, characterized in that: the bottom surface of the central portion is located upward of the bottom surfaces of the root portions, so that the vertical direction dimension of the central portion is smaller than the vertical direction dimension of the root portions, the plurality of pillars protrude downward from the bottom surface of the central portion.

5. The vehicle bottom structure according to claim 4, characterized in that: the cross member further has a transition portion between the central portion and the root portions, the bottom surface of the transition portion is inclined so as to gradually approach upward as it approaches the central portion from the root portions.

6. The vehicle bottom structure according to any one of claims 1 to 5, characterized in that: the brace arm is disposed within the vertical direction range of the cross member.

7. The vehicle bottom structure according to any one of claims 1 to 5, characterized in that: the vehicle bottom structure further has a pair of side members connected to both ends of the cross member in the vehicle width direction, which are frame members long in the vehicle front-rear direction, the brace arm is disposed within the vertical direction range of the side members.

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