Vehicle underbody structure

Abstract

To provide a vehicle lower part structure capable of suppressing floor vibration by improving the rigidity of a floor panel while suppressing generation of a weight increase.SOLUTION: A vehicle lower part structure 100 includes a floor panel 102 forming a floor surface of a vehicle and a first cross member 110 extending in the vehicle width direction on the upper side of the floor panel. The floor panel includes a bead which is a protruding bead 124 upward of the vehicle and crosses the first cross member and extends in the cross direction of the vehicle and is joined to the first cross member and swollen parts 128, 130, 132, 134 formed in regions 140, 142, 144, 146 partitioned by the first cross member and the bead and swelling downward of the vehicle. The bead includes adjacent parts 148, 150 which are adjacent to the swollen parts and extend in the vehicle cross direction, and a wide part 152 which continues to the adjacent part, has a wider width in the vehicle width than the adjacent part and overlaps on the first cross member.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Vehicles such as automobiles are equipped with a vehicle underbody structure having a floor panel that forms the floor surface of the vehicle (for example, Patent Document 1). Patent Document 1 describes a floor panel structure of a vehicle body having a plurality of frame members arranged in the front-rear direction and the width direction of the vehicle body, and a floor panel connected to the frame members.

[0003] The floor panel of Patent Document 1 has a panel region. The panel region is surrounded by a frame member and / or a vibration regulating portion that regulates the vibration region. A high-rigidity portion protruding in the vertical direction of the vehicle is formed within the panel region, and a low-rigidity portion is formed around the high-rigidity portion. Furthermore, a portion of the high-rigidity portion is formed so as to contact the frame member and / or the vibration regulating portion.

[0004] In Patent Document 1, a high-rigidity portion is formed within the panel region of the floor panel, and a low-rigidity portion is formed around the high-rigidity portion, so that vibration energy is concentrated in the low-rigidity portion due to the difference in rigidity between the high-rigidity portion and the low-rigidity portion. Furthermore, it is said that a part of the high-rigidity portion is formed so as to contact the frame member and / or the vibration regulating portion, so that the rigidity of the high-rigidity portion can be significantly increased.

[0005] Patent document 1 also states that vibration energy that is highly concentrated in low-rigidity areas within the panel area is converted into thermal energy due to the damping capacity of the material that makes up the floor panel, resulting in a reduction in the vibration energy of the entire panel area and a reduction in acoustic radiation from the panel area. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-335576 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the floor panel structure of Patent Document 1, the low-rigidity parts within the panel area are still arranged around the high-rigidity parts and the vibration regulating parts. Therefore, in this floor panel structure, the low-rigidity parts within the panel area become the starting points of deformation, generating local modes (local deformation) in the vibration area, making it difficult to sufficiently reduce floor vibration.

[0008] In addition, in the floor panel structure of Patent Document 1, it is possible to consider a method of increasing the rigidity of the floor panel and reducing floor vibration by adding and arranging other members such as reinforcing members, but this method would result in an increase in the weight of the floor panel structure.

[0009] In view of the above problems, the present invention has an object to provide a vehicle underbody structure that can increase the rigidity of a floor panel and reduce floor vibration while suppressing an increase in weight. [Means for solving the problem]

[0010] In order to solve the above problems, a typical configuration of the present invention comprises a floor panel that forms the floor surface of the vehicle, and a first cross member extending in the vehicle width direction above the floor panel, wherein the floor panel has a bead that convex upwardly of the vehicle, intersecting the first cross member and extending in the fore-and-aft direction of the vehicle and joined to the first cross member, and a bulge portion that is formed within an area partitioned by the first cross member and the bead and bulges downwardly of the vehicle, and the bead includes an adjacent portion that extends in the fore-and-aft direction of the vehicle adjacent to the bulge portion, and a wide portion that is continuous with the adjacent portion, is wider in the vehicle width direction than the adjacent portion, and overlaps the first cross member. Effect of the Invention

[0011] According to the present invention, it is possible to provide a vehicle underbody structure that can increase the rigidity of a floor panel and reduce floor vibration while suppressing an increase in weight. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing an outline of a vehicle underbody structure according to an embodiment of the present invention; [Diagram 2] 2 is an enlarged top view showing a part of the vehicle undercarriage structure of FIG. 1. [Diagram 3] 3 is an enlarged top view showing a part of the vehicle undercarriage structure of FIG. 2. [Figure 4] 3A to 3C are diagrams showing cross sections of the vehicle underbody structure of FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A typical configuration of one embodiment of the present invention comprises a floor panel that forms the floor surface of the vehicle, and a first cross member extending in the vehicle width direction above the floor panel, wherein the floor panel has a bead that convex upwardly of the vehicle, intersecting the first cross member and extending in the fore-and-aft direction of the vehicle and joined to the first cross member, and a bulge portion that is formed within an area partitioned by the first cross member and the bead and bulges downwardly of the vehicle, and the bead includes an adjacent portion that extends in the fore-and-aft direction of the vehicle adjacent to the bulge portion, and a wide portion that is continuous with the adjacent portion, is wider in the vehicle width direction than the adjacent portion, and overlaps the first cross member.

[0014] In the above configuration, a bead and a bulge are formed in the floor panel to provide a height difference, and the bead is further formed with an adjacent portion adjacent to the bulge and a wide portion overlapping the first cross member. This causes a vibration mode in which the bulge of the floor panel vibrates up and down, generating a load in the vertical direction. In the above configuration, this vertical load can be transmitted from the bulge to the adjacent portion of the adjacent bead, and further transmitted from the wide portion continuous with the adjacent portion to the first cross member, thereby dispersing it. In other words, the surface rigidity of the floor panel can be improved by overlapping the first cross member with the wide portion.

[0015] Furthermore, when a vertical load is input to the bead from the bulging portion of the floor panel, the vertical load can be transmitted and dispersed from the adjacent portion of the bead to the first cross member via the wide portion. Furthermore, the floor panel has an improved vertical rigidity by intentionally creating a height difference between the upwardly convex bead and the bulging portion bulging downward of the vehicle, and the adjacent portion and the wide portion are formed continuously with the upwardly convex bead, resulting in a shape that can distribute the load without adding other members such as reinforcing members. Therefore, with the above configuration, it is possible to increase the rigidity of the floor panel and reduce floor vibration while suppressing weight increase, thereby improving the NV (Noise and Vibration) characteristics of the vehicle.

[0016] The vehicle underbody structure may further include a second cross member extending in the vehicle width direction on the vehicle front side of the first cross member, across the bulge, and the bead may also overlap the second cross member.

[0017] As a result, the wide portion of the bead of the floor panel overlaps with the first cross member, and a predetermined portion of the bead (for example, the front end portion) also overlaps with the second cross member that is spaced from the first cross member toward the front of the vehicle. This reduces the difference in rigidity between the wide portion of the bead that overlaps with the first cross member and the predetermined portion that overlaps with the second cross member, preventing deformation due to the difference in rigidity and further suppressing floor vibration.

[0018] The bulge portion of the above-mentioned floor panel has a curved portion that bends from an adjacent portion of the bead along one or both of the first cross member or the second cross member, and the bead may further include a shape-changing portion that connects the adjacent portion and the wide portion along the curved portion of the bulge portion.

[0019] In this way, the bead includes a shape-changing portion that connects the adjacent portion and the wide portion. The shape-changing portion of the bead is shaped to follow the curved portion of the bulging portion of the floor panel, and therefore changes shape, for example, from the wide portion toward the adjacent portion so that the width in the vehicle width direction narrows as it approaches the curved portion. Therefore, in the floor panel, the shape-changing portion of the bead approaches the curved portion of the bulging portion of the floor panel, narrowing the width in the vehicle width direction of the area between the shape-changing portion and the curved portion of the bulging portion, and deformation of this area can be suppressed.

[0020] In addition, the shape-changing portion of the bead changes gradually because it follows the curved portion of the bulge. This prevents the occurrence of weak spots that would occur from abrupt changes in shape. Furthermore, the wide portion of the bead can utilize the rigidity of the bulge by being close to the shape-changing portion of the curved portion of the bulge. This allows the bead to reliably distribute the load input to the first cross member by the wide portion that overlaps the first cross member.

[0021] If the bulge does not have a curved portion and has a shape close to a rectangle, for example, stress may concentrate at the corners, which may become the starting point of deformation. In contrast, in the above configuration, the curved portion is formed in the bulge, which prevents stress from concentrating and suppresses deformation of the bulge.

[0022] The floor panel further has a flat portion located between the shape-changing portion of the bead and the curved portion of the bulge, and the height of the flat portion in the vertical direction of the vehicle is preferably intermediate between the bead and the bulge.

[0023] This allows the flat portion of the floor panel to be the base surface that serves as the reference for the height in the vertical direction of the vehicle. In this case, in the floor panel, the bead is convex toward the upper side of the vehicle from the flat portion, which is the base surface, and the bulge portion bulges toward the lower side of the vehicle from the flat portion. As a result, the shape change portion of the bead protrudes toward the upper side of the vehicle from the curved portion of the bulge portion. Also, in the floor panel, the shape change portion of the bead that protrudes toward the upper side of the vehicle is located near the curved portion of the bulge portion, so that the load input to the bulge portion can be easily transmitted from the curved portion of the bulge portion to the shape change portion, and further, the load can be easily transmitted from the shape change portion via the wide portion to the first cross member that overlaps the wide portion.

[0024] The above vehicle undercarriage structure further includes a side sill extending in the fore-and-aft direction of the vehicle along the edge of the floor panel, and a rear cross member extending in the vehicle width direction, spaced apart from the rear of the first cross member, connecting the side sills, and the bead preferably extends to the rear cross member.

[0025] Therefore, when a load is input from the bulging portion of the floor panel to the bead, this load is not only transmitted and dispersed from the portion adjacent to the bead through the wide portion to the first cross member, but also to the rear cross member, thereby increasing the rigidity of the floor panel and reducing floor vibration. EXAMPLES

[0026] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific values ​​shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are given the same reference numerals to avoid repeated explanations, and elements not directly related to the present invention are not shown.

[0027] Fig. 1 is a diagram showing an overview of a vehicle underbody structure 100 according to an embodiment of the present invention. Fig. 1(a) shows the vehicle underbody structure 100 as viewed obliquely from above. Fig. 1(b) is a cross-sectional view of the vehicle underbody structure 100 taken along line AA in Fig. 1(a). In each of the following drawings, the front-rear direction of the vehicle is indicated by arrows Front and Back, the left and right directions in the vehicle width direction are indicated by arrows Left and Right, and the top-bottom direction of the vehicle is indicated by arrows Up and Down.

[0028] 1(a), the vehicle underbody structure 100 includes a floor panel 102 that forms the floor surface of the vehicle, a pair of side sills 104, 106, and a floor tunnel 108. The pair of side sills 104, 106 extend in the front-rear direction of the vehicle along the edge of the floor panel 102. The floor tunnel 108 extends in the front-rear direction of the vehicle at the center of the floor panel 102 in the vehicle width direction and protrudes upward.

[0029] The vehicle underbody structure 100 further includes first cross members 110, 112, second cross members 114, 116, and a rear cross member 118. The first cross members 110, 112 are disposed above the floor panel 102 and extend in the vehicle width direction between the side sills 104, 106 and the floor tunnel 108, respectively.

[0030] The second cross members 114, 116 are disposed above the floor panel 102, spaced apart from the first cross members 110, 112 on the vehicle front side, and extend in the vehicle width direction between the side sills 104, 106 and the floor tunnel 108. Note that the first cross members 110, 112 and the second cross members 114, 116 are provided with a plurality of seat mounting brackets 120.

[0031] The rear cross member 118 extends in the vehicle width direction, spaced apart from the first cross members 110, 112 on the vehicle rear side, and connects the side sills 104, 106. Since the vehicle undercarriage structure 100 has a left-right symmetrical structure as shown in Fig. 1(a), only the structure on the left side in the vehicle width direction will be described below unless otherwise necessary.

[0032] Here, the vehicle underbody structure 100 includes a battery pack 122 disposed under the floor panel 102 as shown in FIG. 1(b). For this reason, in the vehicle underbody structure 100, reinforcing members such as side members extending in the vehicle front-rear direction cannot be disposed on the floor panel 102, making it difficult to increase the rigidity of the floor panel 102. Even if an appropriate reinforcing member could be disposed on the floor panel 102, it would result in an increase in the weight of the vehicle underbody structure 100. The battery pack 122 is joined to a battery cross member 122a shown in FIG. 1(b). The battery cross member 122a extends in the vehicle width direction and connects the side sills 104, 106 to each other below the battery pack 122.

[0033] Therefore, the vehicle underbody structure 100 employs a configuration that can improve the NV characteristics of the vehicle by increasing the rigidity of the floor panel 102 to reduce floor vibration while suppressing an increase in weight. That is, the vehicle underbody structure 100 further includes beads 124, 126 formed on the floor panel 102, and a plurality of bulges 128, 130, 132, 134 shown in Fig. 2. Note that the bead 126 has the same shape and function as the bead 124, and therefore the following description will focus on the bead 124 and the configuration around it.

[0034] Fig. 2 is an enlarged top view showing a portion of the vehicle underbody structure 100 shown in Fig. 1. In the figure, the positions of a first cross member 110 and a second cross member 114 extending in the vehicle width direction above the floor panel 102 are indicated by dashed lines.

[0035] The bead 124 of the floor panel 102 protrudes upward in the vehicle direction, intersects with the first cross member 110, extends in the fore-and-aft direction of the vehicle, and is joined to the first cross member 110. A predetermined portion of the bead 124 (e.g., a front end portion 136) overlaps and is joined to the second cross member 114, and a rear end portion 138 extends to the rear cross member 118. The second cross member 114 is spaced apart from the first cross member 110 on the front side of the vehicle, and extends in the vehicle width direction across the bulging portions 128, 130 of the floor panel 102. The rear cross member 118 is spaced apart from the first cross member 110 on the rear side of the vehicle, across the bulging portions 132, 134.

[0036] The bulging portions 128, 130, 132, 134 of the floor panel 102 are portions that bulge downward of the vehicle and are formed within areas 140, 142, 144, 146, respectively, defined by the first cross member 110, the second cross member 114, the rear cross member 118 and the bead 124.

[0037] The bead 124 also includes adjacent portions 148, 150 and a wide portion 152. The adjacent portions 148, 150 extend in the vehicle front-rear direction adjacent to the bulging portions 128, 130, 132, 134, respectively, as shown in Figure 2. The wide portion 152 is continuous with the adjacent portions 148, 150 and is wider in the vehicle width direction than the adjacent portions 148, 150. The wide portion 152 also overlaps the first cross member 110.

[0038] In this way, the floor panel 102 has a convex bead 124 formed above the vehicle and bulging portions 128, 130, 132, and 134 that bulge below the vehicle, creating a height difference, and the bead 124 also has adjacent portions 148, 150 adjacent to the bulging portions 128, 130, 132, and 134, and a wide portion 152 that overlaps the first cross member 110.

[0039] Therefore, in the vehicle underbody structure 100, even if a vibration mode in which the bulges 128, 130, 132, 134 of the floor panel 102 vibrate up and down occurs, the vertical load generated from this vibration can be transmitted to the adjacent portions 148, 150 of the bead 124 adjacent to the bulges 128, 130, 132, 134, and further transmitted and dispersed from the wide portion 152 continuing to the adjacent portions 148, 150 to the first cross member 110. As a result, the first cross member 110 and the wide portion 152 overlap, thereby improving the surface rigidity of the floor panel 102.

[0040] In addition, in the vehicle undercarriage structure 100, when a vertical load is input to the bead 124 from the bulging portions 128, 130, 132, and 134 of the floor panel 102, this vertical load can be transmitted and dispersed from the adjacent portions 148, 150 of the bead 124 to the first cross member 110 via the wide portion 152.

[0041] In this way, floor panel 102 improves vertical rigidity by intentionally creating a height difference between upwardly convex bead 124 and bulging portions 128, 130, 132, 134 that bulge downward of the vehicle, and further, by forming adjacent portions 148, 150 and wide portion 152 continuously with upwardly convex bead 124, it has a shape that makes it possible to disperse vibrations and loads without adding other members such as reinforcing members. Therefore, vehicle underbody structure 100 can increase the rigidity of floor panel 102 while suppressing weight increase, reducing floor vibrations, and improving the NV characteristics of the vehicle.

[0042] Additionally, in the floor panel 102, the wide portion 152 of the bead 124 overlaps the first cross member 110, and further, the front end 136 of the bead 124 overlaps the second cross member 114. As a result, in the bead 124, the difference in rigidity between the wide portion 152 overlapping the first cross member 110 and the front end 136 overlapping the second cross member 114 is small, preventing deformation due to the rigidity difference and further suppressing floor vibration.

[0043] Furthermore, in the floor panel 102, the rear end 138 of the bead 124 extends to the rear cross member 118. Therefore, in the vehicle undercarriage structure 100, when a load is input from the bulging portions 128, 130, 132, 134 of the floor panel 102 to the bead 124, this load is not only transmitted and dispersed from the adjacent portions 148, 150 of the bead 124 via the wide portion 152 to the first cross member 110, but can also be transmitted and dispersed from the rear end 138 to the rear cross member 118. This can further increase the rigidity of the floor panel 102 and reduce floor vibration.

[0044] Fig. 3 is an enlarged view of a portion of the vehicle underbody structure 100 of Fig. 2. The bulging portion 128 of the floor panel 102 has a curved portion 154. The curved portion 154 is shaped to bend from the portion 148 adjacent to the bead 124 along the first cross member 110 as shown in the figure.

[0045] The bead 124 further includes a shape changing portion 156. The shape changing portion 156 is a portion that connects the adjacent portion 148 and the wide portion 152 along the curved portion 154 of the bulging portion 128. Since the shape changing portion 156 of the bead 124 has a shape that follows the curved portion 154 of the bulging portion 128 as shown in the figure, the shape changes, for example, from the wide portion 152 toward the adjacent portion 148 so that the width in the vehicle width direction becomes narrower as it approaches the curved portion 154.

[0046] As a result, in floor panel 102, shape-changing portion 156 of bead 124 and curved portion 154 of bulge portion 128 come closer to each other, thereby narrowing the width in the vehicle width direction of area 158 between shape-changing portion 156 and curved portion 154 of bulge portion 128, thereby suppressing deformation of this area 158.

[0047] Furthermore, because shape-changing portion 156 of bead 124 follows curved portion 154 of bulge 128, the shape changes gradually. This prevents floor panel 102 from having weak portions caused by sudden changes in shape.

[0048] In addition, the wide portion 152 of the bead 124 can utilize the rigidity of the bulging portion 128 by having a shape change portion 156 that is continuous with the wide portion 152 approach the curved portion 154 of the bulging portion 128. Furthermore, the wide portion 152 of the bead 124 is joined to and overlapped with the first cross member 110 at a joint 160 shown in FIG.

[0049] Therefore, wide portion 152 of bead 124 can reliably distribute the load input to first cross member 110. Note that first cross member 110 is joined, for example at joint 162, to a portion of floor panel 102 where bead 124 is not formed.

[0050] If bulging portion 128 of floor panel 102 did not have curved portion 154 and had a shape close to a rectangle, for example, stress would concentrate at the corners, which could become the starting point of deformation. In contrast, vehicle underbody structure 100 forms curved portion 154 at bulging portion 128 of floor panel 102, thereby preventing stress concentration and suppressing deformation of bulging portion 128.

[0051] Although the configuration of the bead 124 and the bulge 128 has been described for the floor panel 102, the present invention is not limited to this, and the bulge 128 may be formed with a curved portion that curves from the adjacent portion 148 along the second cross member 114 (see FIG. 2). The arrangement and shape of the front end 136 of the bead 124 relative to this curved portion may be the same as the arrangement and shape of the adjacent portion 148, the wide portion 152, and the shape-changing portion 156 of the bead 124 relative to the curved portion 154. Furthermore, the configuration of the bead 124 and the bulge 128 may be applied as the configuration of the bead 124 and the other bulges 130, 132, 134, thereby providing similar functions, etc.

[0052] Fig. 4 is a diagram showing each cross section of the vehicle underbody structure 100 in Fig. 2. Note that point D shown in Fig. 4 indicates the position in the vehicle width direction of the adjacent portion 148 of the bead 124 (see Fig. 3). Also, dotted line E shown in Fig. 4 indicates the height in the vehicle up-down direction that is the base plane of the floor panel 102.

[0053] In the cross section BB of Fig. 4(a), floor panel 102 smoothly connects bulging portions 128, 130 that bulge below the vehicle below dotted line E indicating the height of the base surface, to adjacent portions 148 of bead 124 that are adjacent to bulging portions 128, 130 and protrude above the vehicle above the base surface. For this reason, in floor panel 102, a height difference can be provided between bulging portions 128, 130 and adjacent portions 148 of bead 124 to increase rigidity, and further, the areas between bulging portions 128, 130 and adjacent portions 148 do not become starting points of deformation, so floor vibration can be sufficiently suppressed.

[0054] The floor panel 102 further has a flat portion 164 shown in FIG. 3. The flat portion 164 is located between the shape change portion 156 of the bead 124 and the curved portion 154 of the bulging portion 128. The dotted line F shown in FIG. 3 indicates the end of the flat portion 164 on the bead 124 side. Furthermore, the point of the flat portion 164 that intersects with the dotted line F at a position along the line CC in FIG. 3 is the end 165 on the bead 124 side. Here, the shape change portion 156 has a width in the vehicle width direction that is larger than the adjacent portion 148 by a dimension La, based on the end 165 of the flat portion 164 on the bead 124 side, at a position along the line CC in FIG. 3 (see FIG. 4(b)). Furthermore, the flat portion 164 has a width in the vehicle width direction that is a dimension Lb, based on the end 165 on the bead 124 side, at a position along the line CC in FIG. 3 (see FIG. 4(b)).

[0055] 4(b), the height in the vehicle vertical direction of flat portion 164 of floor panel 102 is midway between shape change portion 156 of bead 124 and bulging portions 128, 130, and is at the same vehicle vertical height as dotted line E. That is, in floor panel 102, flat portion 164 can function as a basic surface that serves as a reference for the height in the vehicle vertical direction.

[0056] 4(b), in floor panel 102, bead 124 is convex toward the upper side of the vehicle from flat portion 164, which is the basic surface, and bulging portions 128, 130 bulge toward the lower side of the vehicle from flat portion 164. For this reason, shape change portion 156 of bead 124 protrudes toward the upper side of the vehicle more than curved portion 154 of bulging portion 128.

[0057] 3 and 4(b), the shape-changing portion 156 of the bead 124 that protrudes above the vehicle is located near the curved portion 154 of the bulging portion 128. Therefore, in the vehicle undercarriage structure 100, the load input to the bulging portion 128 can be easily transmitted from the curved portion 154 of the bulging portion 128 to the shape-changing portion 156 of the bead 124, and can also be easily transmitted from the shape-changing portion 156 via the wide portion 152 to the first cross member 110 that overlaps the wide portion 152.

[0058] As described above, according to the vehicle underbody structure 100, by forming the bead 124 and multiple bulges 128, 130, 132, 134 on the floor panel 102, it is possible to increase the rigidity of the floor panel 102 and reduce floor vibration while suppressing weight increase.

[0059] Although the preferred embodiment of the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such an embodiment. It is clear that a person skilled in the art can think of various modifications or alterations within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present invention. [Industrial Applicability]

[0060] The present invention can be used in a vehicle underbody structure. [Explanation of symbols]

[0061] 100... vehicle underbody structure, 102... floor panel, 104, 106... side sill, 108... floor tunnel, 110, 112... first cross member, 114, 116... second cross member, 118... rear cross member, 120... seat mounting bracket, 122... battery pack, 122a... battery cross member, 124, 126... bead, 128, 130, 132, 134... bulging portion, 136... front end of bead, 138... rear end of bead, 140, 142, 144, 146, 158... area, 148, 150... adjacent portion, 152... wide portion, 154... curved portion, 156... shape change portion, 160, 162... joint, 164... flat portion

Claims

1. A floor panel that forms a floor surface of the vehicle; a first cross member extending in a vehicle width direction above the floor panel; a battery pack disposed under the floor panel, The floor panel is a bead that is convex toward an upper portion of a vehicle, that intersects with the first cross member, that extends in a front-rear direction of the vehicle, and that is joined to the first cross member; a bulge portion formed within an area defined by the first cross member and the bead and bulging outwardly toward a vehicle bottom, The bead is an adjacent portion adjacent to the bulge portion and extending in the vehicle front-rear direction; a wide portion that is continuous with the adjacent portion, has a width in the vehicle width direction greater than that of the adjacent portion, and overlaps the first cross member, The vehicle underbody structure further includes a second cross member extending in a vehicle width direction on a vehicle front side of the first cross member across the bulge portion, A vehicle underbody structure, characterized in that a front end of the bead also overlaps the second cross member.

2. The bulging portion of the floor panel has a curved portion that bends from an adjacent portion of the bead along one or both of the first cross member and the second cross member, 2. The vehicle underbody structure according to claim 1, wherein the bead further includes a shape change portion that connects the adjacent portion and the wide portion along a curved portion of the bulging portion.

3. The floor panel further has a flat portion located between the shape change portion of the bead and the curved portion of the bulge portion, 3. The vehicle underbody structure according to claim 2, wherein a height of the flat portion in the vehicle vertical direction is intermediate between the bead and the bulge.

4. The vehicle undercarriage further comprises: a side sill extending in a vehicle front-rear direction along an edge of the floor panel; a rear cross member extending in a vehicle width direction and spaced apart from the first cross member on the vehicle rear side and connecting the side sills to each other, 4. The vehicle underbody structure according to claim 1, wherein the bead extends to the rear cross member.

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