Underbody of vehicle

Abstract

An underbody of a vehicle includes a floor member formed by extrusion to extend in a vehicle width direction. A plurality of floor members are provided so that the plurality of floor members are continuously provided adjacent to each other in the vehicle length direction. The upper surface of the floor component forms the floor of the vehicle, and the lower surface of the floor component forms the upper battery box. The underbody also includes first weld regions each formed within a boundary region between the lower surfaces of adjacent floor members to interconnect the adjacent floor members. The first welding region is formed by friction stir welding and extends in a vehicle width direction.

Description

Technical Field

[0001] The present invention relates to the underbody of a vehicle, and more particularly, to a body floor that forms the lower part of the vehicle. Background Art

[0002] For electric vehicles, increasing the driving range is an important development goal. To improve the driving range of electric vehicles, strategies include increasing the battery capacity by increasing the number of battery cells and reducing the weight of electric vehicle components. Merely increasing the battery capacity by adding more battery cells inevitably causes an increase in the weight of the added battery cells, thus limiting the effect of improving the driving range.

[0003] Therefore, many manufacturers focus on solutions for lightening the battery system itself or reducing the vehicle weight, while maximizing the installation of battery cells by making the most effective use of the limited vehicle space.

[0004] Meanwhile, the batteries of electric vehicles are generally installed in the lower part of the vehicle body. Specifically, the batteries are installed in the lower part of the vehicle body by interconnecting a plurality of battery modules, accommodating the battery modules in a battery box, and mounting the battery box to the lower part of the vehicle body located below the vehicle body. Technologies are being developed to accommodate the battery modules in a lower battery box and enable the body floor to serve as an upper battery box to eliminate a separate upper battery box.

[0005] The above matters disclosed in this section are only for enhancing the understanding of the general background of the present invention, and should not be regarded as an admission or an implication in any form that these matters constitute related art known to those of ordinary skill in the art. Summary of the Invention

[0006] In view of the above problems, an object of the present invention is to provide a coupling structure of floor members, which are formed by extrusion in the vehicle width direction and are provided in a plurality, such that the plurality of floor members are continuously arranged adjacent to each other in the vehicle length direction. The upper surface of the floor member forms the floor of the vehicle, and the lower surface of the floor member forms an upper battery box.

[0007] According to one aspect of the present invention, the above and other objects can be achieved by providing a bottom body including a floor member formed by extrusion and extending in the vehicle width direction. The floor members are provided in plurality such that the plurality of floor members are continuously arranged adjacent to each other in the vehicle length direction. In particular, the upper surfaces of the plurality of floor members constitute the floor of the vehicle, and the lower surfaces of the plurality of floor members constitute the upper battery box. Each first welding region is formed in a boundary region between the lower surfaces of adjacent floor members among the plurality of floor members, such that the adjacent floor members are interconnected. The first welding region is formed by friction stir welding (FSW) and extends in the vehicle width direction.

[0008] One of the adjacent floor members may be recessed upward by a part at one end to be stepped, thereby forming a stepped portion, and the other of the adjacent floor members may form a flange portion at the other end, and the flange portion extends facing the stepped portion formed in the one floor member. The stepped portion and the flange portion may be in surface contact with each other, such that the lower surfaces of the adjacent floor members are disposed on the same plane. The stepped portion and the flange portion may be welded to each other by friction stir welding, thereby forming a corresponding first welding region.

[0009] The plurality of floor members may include a plurality of members formed by extrusion to have different heights respectively.

[0010] Reinforcing partition walls extending in the vehicle width direction may be provided inside each floor member to divide the interior of the floor member into a plurality of closed cross-sections.

[0011] Additional reinforcing partition walls may be provided inside the floor member at positions adjacent to the stepped portion or the flange portion to provide a supporting force against the welding pressure generated during friction stir welding.

[0012] The bottom body may further include a second welding region, and each second welding region is formed in a boundary region between the upper surfaces of adjacent floor members among the plurality of floor members, such that the adjacent floor members are interconnected. The second welding region may be formed by metal inert gas (MIG) welding and may extend in the vehicle width direction.

[0013] The floor member may include a first member and a second member. The height of the first member may be greater than the height of the second member.

[0014] The first members may be provided in plurality such that the plurality of first members are continuously arranged and connected to each other in the vehicle length direction. The second member may be disposed outside the first member and connected to the outermost one of the first members.

[0015] The seat mounting part may be formed on the upper surface of the first member to mount a vehicle seat thereon.

[0016] The floor member may further include a third member and a fourth member, each of the third member and the fourth member including a vertical partition wall having a downwardly extending end portion. The third member or the fourth member may be disposed outside the first member or the second member and may be coupled to the first member or the second member.

[0017] The vertical partition walls formed on the third member and the fourth member may respectively constitute the front partition wall and the rear partition wall of the upper battery box.

[0018] One end of the first member may be recessed upward by a part to be stepped, thereby forming a first stepped portion, and a first flange portion extending toward an adjacent floor member may be formed at the other end of the first member. One end of the second member may be recessed upward by a part to be stepped, thereby forming a second stepped portion, and a second flange portion extending toward an adjacent floor member may be formed at the other end of the second member.

[0019] A plurality of first members may be provided such that the plurality of first members are continuously provided in the vehicle longitudinal direction. The first stepped portion of one of the adjacent first members among the first members and the first flange portion of the other of the adjacent first members may be welded to each other by friction stir welding under the condition that the first stepped portion and the first flange portion are in surface contact with each other. The second stepped portion of the second member and the first flange portion of one of the adjacent first members may be welded to each other by friction stir welding under the condition that the second stepped portion and the first flange portion are in surface contact with each other, or the first stepped portion of the other of the first members and the second flange portion of the adjacent second member may be welded to each other by friction stir welding under the condition that the first stepped portion and the second flange portion are in surface contact with each other.

[0020] The floor member may further include a third member and a fourth member, each of the third member and the fourth member including a vertical partition wall having a downwardly extending end portion. The third member may be recessed upward by a part at one end to be stepped, thereby forming a third stepped portion, and the fourth member may form a fourth flange portion at the other end, and the fourth flange portion extends toward one of the adjacent floor members.

[0021] A plurality of second members may be provided. The third stepped portion of the third member and the second flange portion of an adjacent second member may be welded to each other by friction stir welding under the condition that the third stepped portion and the second flange portion are in surface contact with each other. The fourth flange portion of the fourth member and the second stepped portion of the other adjacent second member may be welded to each other by friction stir welding under the condition that the fourth flange portion and the second stepped portion are in surface contact with each other. Description of the Drawings

[0022] Through the following detailed description in conjunction with the accompanying drawings, the above and other objects, features, and other advantages of the present invention should be more clearly understood. In the drawings:

[0023] Figure 1 Shows the installation of the battery on the lower side;

[0024] Figure 2 Shows along Figure 1 A cross-sectional view taken along line A-A' in;

[0025] Figure 3 Shows the upper surface of the floor according to an embodiment of the present invention;

[0026] Figure 4 Shows a cross-sectional view of a floor member provided with an additional reinforcing partition wall;

[0027] Figure 5 Is a cross-sectional view taken along line B-B' in; and Figure 3 Shown in; and

[0028] Figure 6 Shows the upper surface of the floor provided with a seat mounting portion. Detailed Embodiments

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Regardless of the reference numerals in the drawings, the same or similar elements are denoted by the same reference numerals, and repeated descriptions thereof are omitted.

[0030] In the following description of the embodiments of the present invention, when the detailed description of the known functions and configurations involved herein may obscure the subject matter of the embodiments of the present invention, these detailed descriptions are omitted. In addition, the embodiments of the present invention should be more clearly understood from the accompanying drawings, and moreover, the present invention is not limited by the drawings, and it should be understood that all changes, equivalent methods, and alternative methods that do not depart from the spirit and technical scope of the present invention are included in the present invention.

[0031] Although terms such as "first", "second", etc. may be used herein to describe various elements, these elements are not limited by these terms. These terms are only used to distinguish one element from another.

[0032] Unless otherwise clearly stated, the singular expression includes the plural meaning.

[0033] In this specification, terms such as "comprising", "including", etc. are intended to indicate the presence of features, quantities, steps, operations, elements, components, or combinations thereof, but do not exclude the presence of other features, quantities, steps, operations, elements, components, or any combinations or any additions thereof.

[0034] In the case where one component is "connected" or "linked" to another component, it should be understood that the component can be directly connected or linked to another component, or other components may exist therebetween. In contrast, in the case where one component is "directly connected" or "directly linked" to another component, it should be understood that no other components exist therebetween.

[0035] When the components, devices, elements, etc. of the present invention are described as having a certain use or performing a certain operation, function, etc., the component, device, or element should be regarded as "configured / constructed" to meet the use or perform the operation or function.

[0036] Figure 1 The installation of the battery on the lower side is shown. Refer to Figure 1 , since the weight of the battery 200 in the vehicle is quite large, considering the vehicle center of gravity, vehicle driving stability, etc., the battery 200 is installed below the floor 100 of the vehicle.

[0037] For a conventional battery, its battery module is installed in the lower battery box, the upper battery box is coupled to the lower battery box, and the final structure (i.e., the assembled structure) is coupled to the vehicle body.

[0038] In an embodiment of the present invention, the structure of a separate upper battery box is omitted. Instead, as Figure 1 shown, the floor 100 of the vehicle serves as the upper battery box, that is, it replaces the function of the omitted upper battery box.

[0039] In other words, the floor 100 of the vehicle forms the interior space of the vehicle and provides space for installing the seat mounting portion. In addition, the lower battery box 300 (in which the battery is installed or accommodated) can be coupled to the lower part of the floor 100.

[0040] Since the battery is a sensitive electronic device, the battery should be isolated from the external environment as much as possible. For this purpose, in the conventional case, a sealant is coated on the battery to prevent water or foreign objects from entering from outside the vehicle body.

[0041] However, the sealant is not sufficient to ensure perfect airtightness and watertightness. In particular, it may be difficult for the seal to ensure high-pressure watertight performance. For electric vehicles, achieving perfect airtightness and watertightness is crucial. In particular, in the present invention where the upper battery box is omitted, the necessity is even greater.

[0042] To ensure perfect airtightness and watertightness, the present invention proposes to ensure airtightness and watertightness by welding the coupling members while minimizing the use of the sealant.

[0043] In the present invention, the floor of the vehicle is not a single-board type floor manufactured by a general pressing process, but a floor with a closed cross-section manufactured by an extrusion process.

[0044] Conventionally, a single-board type floor is manufactured using a set of molds with easily adjustable sizes. However, in the case of manufacturing a floor by an extrusion process, the extrusion is carried out under the condition of inserting a blank into the mold. For this reason, the extrusion size of the floor in the vehicle width direction is restricted.

[0045] For this reason, the floor 100 of the vehicle is manufactured by interconnecting a plurality of floor members 10 formed by extrusion in the vehicle width direction.

[0046] Each floor member 10 can be molded by extruding aluminum or an aluminum alloy. Accordingly, the floor member 10 has an upper surface and a lower surface. When a plurality of floor members 10 are continuously arranged adjacent to each other in the vehicle length direction and are joined to each other, their upper surfaces constitute the floor of the vehicle, and their lower surfaces constitute the upper battery box.

[0047] Hereinafter, a joining structure for joining floor members to ensure airtightness and watertightness will be described.

[0048] Figure 2 Shows a cross-sectional view taken along Figure 1 the line A-A' in Figure 1 , that is, a cross-sectional view of the floor taken along the line A-A' in the middle. Refer to Figure 2 , the floor is formed by joining a plurality of floor members 10 to each other.

[0049] Adjacent floor members among the plurality of floor members 10 are joined to each other, and the position where the adjacent floor members 10 are joined to each other is a first welding area W1 formed within a boundary area between the lower surfaces of two adjacent floor members 10. The first welding area W1 is formed by friction stir welding. When friction stir welding is performed in the vehicle width direction, the first welding area W1 extends along the vehicle width direction.

[0050] Figure 3 Shows the upper surface of the floor according to an embodiment of the present invention. Refer to Figure 3 , the first welding area W1 is formed within the boundary area between adjacent floor members in the vehicle width direction.

[0051] Specifically, as shown in Figure 2 and Figure 3 , each of the plurality of floor members 10 is recessed upward by a part to be stepped to form a stepped portion 101, and a flange portion 102 is formed, and the flange portion 102 extends to face the stepped portion 101 formed by another adjacent floor member 10.

[0052] In other words, adjacent floor members 10 are arranged such that the stepped portion 101 formed in one of the adjacent floor members 10 and the flange portion 102 formed in the other of the adjacent floor members 10 face each other, and then the flange portion 102 is inserted into the space defined by the stepped portion 101 (for example, below the stepped portion 101) so that the stepped portion 101 and the flange portion 102 are in surface contact with each other. Accordingly, the lower surfaces of the adjacent floor members 10 are disposed in the same plane.

[0053] Thereafter, the friction stir welding machine performs friction stir welding while moving along the flange portion 102 and the stepped portion 101 extending in the vehicle width direction, thereby forming the first welding region W1. With the first welding region W1, the adjacent floor members 10 are coupled to each other.

[0054] In one embodiment, the plurality of floor members 10 may include a plurality of members having different heights formed by extrusion. A part of these members may be formed to have a height greater than the height of the remaining other members of these members, thereby providing a seat mounting portion (on which a seat will be mounted). Another part of these members may be formed to extend downward more than the remaining other members, and thus, may be used as a partition wall surrounding the battery 200.

[0055] As described above, the floor members 10 having various heights can be manufactured, the stepped portion 101 and the flange portion 102 are formed in each floor member 10, and the adjacent floor members 10 are coupled to each other by the coupling between the stepped portion 101 or the flange portion 102 of one of the adjacent floor members 10 and the flange portion 102 or the stepped portion 101 of the other of the adjacent floor members 10. Thus, the floor 100 can be obtained.

[0056] In another embodiment, the reinforcing partition wall 1 may be formed inside each floor member 10 to extend in the vehicle width direction such that the interior of the floor member 10 is divided into a plurality of closed cross-sections. When manufacturing the floor member 10, a mold can be manufactured such that the reinforcing partition wall 1 is disposed in the vehicle length direction.

[0057] Since the reinforcing partition wall 1 is disposed in the vehicle length direction, a plurality of closed cross-sections can be formed inside the floor member 10, and the resulting floor 100 can ensure the stiffness against side collisions through the plurality of closed cross-sections.

[0058] In an embodiment, the pressure applied to the flange portion 102 during the friction stir welding process is about 6500 N. For this reason, one side surface of the floor member 10 bulges in the direction of the pressure applied during the friction stir welding.

[0059] However, since the stepped portion 101 and the flange portion 102 of the floor member 10 are respectively formed at the ends of the lower surface of the floor member 10, and the vertical walls 2 are respectively formed at the ends of the floor member 10 to constitute a closed cross-section of the floor member 10, the walls 2 can withstand the pressure applied to the stepped portion 101 and the flange portion 102 during friction stir welding, thereby preventing the one side surface of the floor member 10 from bulging.

[0060] Another reinforcing partition wall 1 can be added inside the floor member 10 at a position adjacent to the stepped portion 101 or the flange portion 102 to provide a reliable supporting force to resist the welding pressure generated during friction stir welding.

[0061] In other words, referring to Figure 4 , the additional reinforcing partition wall 1 is provided at a portion of the floor member 10 adjacent to the stepped portion 101 or the flange portion 102, and the additional reinforcing partition wall 1 is formed to extend in the direction in which the pressure generated during friction stir welding is applied, whereby the supporting force to resist the welding pressure can be ensured.

[0062] Through the first welding area W1 formed by friction stir welding, the airtightness and watertightness of the lower surfaces of adjacent floor members 10 can be ensured, and the upper surfaces of adjacent floor members 10 can be welded to each other by metal inert gas (MIG) welding, thereby achieving a firm connection of multiple floor members 10.

[0063] Referring to Figure 2 , a boundary area is formed between the upper surfaces of adjacent floor members 10, and adjacent floor members 10 can be in surface contact with each other in a direction perpendicular to the ground. However, it is difficult to weld the inside of the floor member 10 by friction stir welding. For this reason, the boundary area between the upper surfaces of the floor members 10 can be welded by MIG welding to form the second welding area W2, whereby a firm connection between the floor members 10 can be achieved.

[0064] Similar to the first welding area W1, the second welding area W2 also extends in the vehicle width direction. Therefore, not only can the floor members 10 be connected to each other through the first welding area W1 to ensure watertightness and airtightness, but also a firm connection between the floor members 10 can be achieved through the second welding area W2.

[0065] Since, as described above, multiple floor members 10 can have different heights, the second welding area W2 can be formed on the upper surface of the floor members 10 by performing MIG welding.

[0066] When multiple floor members 10 are connected together by friction stir welding and MIG welding as described above, airtightness and watertightness can be achieved. In addition, the floor 100 formed by multiple floor members 10 can ensure sufficient stiffness to resist external collisions.

[0067] In particular, when a plurality of floor members 10 are joined together, a plurality of chambers capable of distributing external impacts can be formed, thereby protecting the battery 200 from external impacts.

[0068] In an embodiment, a side seal may be joined to the side of the floor 100 to protect the battery 200 disposed at the side surface of the lower battery case 300 and to ensure watertightness and airtightness at the side of the floor 100.

[0069] Hereinafter, the bottom body of a vehicle according to an embodiment of the present invention will be described in detail. Figure 5 is a cross-sectional view taken along line B-B’ in Figure 3

[0070] As described above, the floor member 10 may include a plurality of members 11, 12, 13, and 14 having different heights formed by extrusion.

[0071] Specifically, the floor member 10 may include a first member 11, a second member 12, a third member 13, and a fourth member 14. Each member will be described below.

[0072] The first member 11 may be disposed at a position closer to the inside of the floor than the remaining members, and a plurality of first members 11 may be continuously disposed along the vehicle length direction such that the plurality of first members 11 are joined to each other. In other words, the first member 11 may be located deeper inside the floor than the other members, and a plurality of them may be arranged consistently along the vehicle length direction. In this case, the outermost first member among the plurality of first members 11 may be joined to the second member 12, and the middle first member among the plurality of first members 11 may be joined to another first member 11.

[0073] Figure 6 A seat mounting portion 500 is shown, on which a vehicle seat is mounted. In particular, the seat mounting member 500 may be formed on the upper surface of the first member 11. Accordingly, the height of the first member 11 may be formed to be higher than the height of the second member 12.

[0074] The third member 13 and the fourth member 14 may be respectively disposed at the foremost end and the rearmost end of the floor 100. In some cases, the third member 13 and the fourth member 14 may be joined on the outside of the first member 11 or on the outside of the second member 12.

[0075] The third member 13 and the fourth member 14 respectively include vertical partition walls 135, 145, each of which has an end portion extending downward. The vertical partition walls 135, 145 formed in the third member 13 and the fourth member 14 constitute the front partition wall and the rear partition wall of the upper battery case, thereby protecting the battery 200 from external impacts. ​

[0076] In the following, reference is made to Figure 5 the connection of the first member to the fourth member.

[0077] One end of the first member 11 is recessed upward by a part to be stepped, thereby forming a first stepped portion 111. A first flange portion 112 extending toward an adjacent floor member is formed at the other end of the first member 11. In addition, one end of the second member 12 is recessed upward by a part to be stepped, thereby forming a second stepped portion 121. A second flange portion 122 extending toward an adjacent floor member is formed at the other end of the second member 12.

[0078] The connection method between adjacent first members 11 is as follows. When the first flange portion 112 of one of the adjacent first members 11 and the first stepped portion 111 of the other adjacent first member 11 (which is disposed adjacent to the first flange portion 112) are in surface contact with each other, they are welded to each other by friction stir welding. Thus, the adjacent first members 11 are connected to each other.

[0079] In this case, the boundary region between the upper surfaces of the adjacent first members 11 is welded by MIG welding. Thus, a firm connection between the first members 11 can be achieved.

[0080] The connection method between the first member 11 and the second member 12 is as follows. When the first flange portion 112 of the first member 11 and the second stepped portion 121 of the second member 12 (which is disposed adjacent to the first flange portion 112) are in surface contact with each other, they are welded to each other by friction stir welding. Thus, the first member 11 and the second member 12 are connected to each other.

[0081] In addition, the first stepped portion 111 of the first member 11 and the second flange portion 122 of the second member 12 disposed adjacent to the first stepped portion 111 are welded to each other by friction stir welding under the condition that the first stepped portion 111 and the second flange portion 122 are in surface contact with each other. Thus, the first member 11 and the second member 12 are connected to each other.

[0082] In this case, the boundary region between the upper surfaces of the first member 11 and the second member 12 is welded by MIG welding. Accordingly, a firm connection between the first member 11 and the second member 12 can be achieved.

[0083] Although both the third member 13 and the fourth member 14 can be connected to the first member 11, the following description is given in connection with the case where both the third member 13 and the fourth member 14 according to an embodiment of the present invention are connected to the second member 12.

[0084] First, one end of the third member 13 may be recessed upward by a part to be stepped, whereby a third stepped portion 131 may be formed. A fourth flange portion 142 extending toward the adjacent floor member may be formed at the other end of the fourth member 14.

[0085] The connection between the second member 12 and the third member 13 may be carried out as follows. The third stepped portion 131 of the third member 13 and the second flange portion 122 of the second member 12 (which is disposed adjacent to the third stepped portion 131) are welded to each other by friction stir welding when the third stepped portion 131 and the second flange portion 122 are in surface contact with each other. Thus, the second member 12 and the third member 13 are connected to each other.

[0086] In this case, the boundary region between the upper surfaces of the second member 12 and the third member 13 is welded by MIG welding. Accordingly, a firm connection between the second member 12 and the third member 13 can be achieved.

[0087] The connection between the second member 12 and the fourth member 14 may be carried out as follows. The fourth flange portion 142 of the fourth member 14 and the second stepped portion 121 of the second member 12 (which is disposed adjacent to the fourth flange portion 142) are welded to each other by friction stir welding when the fourth flange portion 142 and the second stepped portion 121 are in surface contact with each other. Thus, the second member 12 and the fourth member 14 are connected to each other.

[0088] In this case, the boundary region between the upper surfaces of the second member 12 and the fourth member 14 is welded by MIG welding. Accordingly, a firm connection between the second member 12 and the fourth member 14 can be achieved.

[0089] According to the present invention, the floor of the vehicle may also function as an upper battery box. Accordingly, the weight of the vehicle can be reduced by the weight eliminated due to the omission of the upper battery box.

[0090] In addition, friction stir welding and MIG welding can be used to ensure airtightness and watertightness to prevent foreign matters from entering the battery.

[0091] Although some embodiments of the present invention have been disclosed for illustrative purposes, those of ordinary skill in the art should understand that various modifications, additions, and substitutions can be made without departing from the scope and spirit of the present invention disclosed in the appended claims.

Claims

1. A bottom body of a vehicle, comprising: A plurality of floor members that extend in the width direction of the vehicle and are continuously arranged adjacent to each other in the length direction of the vehicle, wherein the upper surfaces of the plurality of floor members constitute the floor of the vehicle, and the lower surfaces of the plurality of floor members constitute an upper battery box; and A first welding area, each first welding area being formed within a boundary area between the lower surfaces of adjacent floor members among the plurality of floor members, wherein the first welding area is configured to extend in the width direction of the vehicle and interconnect adjacent floor members among the plurality of floor members.

2. The bottom body according to claim 1, wherein: One of the adjacent floor members is recessed upward by a part at one end to form a stepped portion, and the other of the adjacent floor members is formed with a flange portion at the other end, and the flange portion extends facing the stepped portion formed on the one floor member; The stepped portion and the flange portion are in surface contact with each other, such that the lower surfaces of the adjacent floor members are disposed on the same plane; and The stepped portion and the flange portion are welded to each other by friction stir welding to form a corresponding first welding area.

3. The bottom body according to claim 1, wherein, The plurality of floor members include a plurality of members formed by extrusion and having different heights respectively.

4. The bottom body according to claim 2, wherein, A reinforcing partition wall extending in the width direction of the vehicle is provided inside each of the floor members to divide the interior of the floor member into a plurality of closed cross-sections.

5. The bottom body according to claim 4, wherein, An additional reinforcing partition wall is provided inside the floor member at a position adjacent to the stepped portion or the flange portion to provide a supporting force against the welding pressure generated during friction stir welding.

6. The bottom body according to claim 1, further comprising: A second welding area, each second welding area being formed within a boundary area between the upper surfaces of adjacent floor members among the plurality of floor members, wherein the second welding area is formed by metal inert gas welding and extends in the width direction of the vehicle to interconnect adjacent floor members among the plurality of floor members.

7. The bottom body according to claim 1, wherein: The plurality of floor members include at least one first member and a second member; and The height of the at least one first member is greater than the height of the second member.

8. The bottom body according to claim 7, wherein: The at least one first member includes a plurality of first members continuously arranged in the length direction of the vehicle, wherein the plurality of first members are connected to each other; and The second member is disposed outside the plurality of first members and is connected to the outermost first member among the plurality of first members.

9. The bottom body according to claim 7, wherein, A seat mounting portion is formed on the upper surface of the at least one first member and is configured to mount a seat thereon.

10. The bottom body according to claim 7, wherein: The plurality of floor members further include a third member and a fourth member, and each of the third member and the fourth member includes a vertical partition wall having an end portion extending downward; and The third member or the fourth member is disposed outside the at least one first member or the second member and is coupled to the at least one first member or the second member.

11. The bottom body according to claim 10, wherein, The vertical partition walls formed in the third member and the fourth member respectively constitute the front partition wall and the rear partition wall of the upper battery box.

12. The bottom body according to claim 7, wherein: One end of the at least one first member is recessed upward by a part to be stepped, thereby forming a first stepped portion, and a first flange portion extending toward an adjacent floor member among the plurality of floor members is formed at the other end of the at least one first member; And One end of the second member is recessed upward by a part to be stepped, thereby forming a second stepped portion, and a second flange portion extending toward an adjacent floor member among the plurality of floor members is formed at the other end of the second member.

13. The bottom body according to claim 12, wherein: The at least one first member includes a plurality of first members continuously arranged in the longitudinal direction of the vehicle; When the first stepped portion of one of the adjacent first members among the plurality of first members and the first flange portion of the other of the adjacent first members are in surface contact with each other, they are welded to each other by friction stir welding; And The second stepped portion of the second member and the first flange portion of one of the first members adjacent thereto are welded to each other by friction stir welding when the second stepped portion and the first flange portion are in surface contact with each other, or the first stepped portion of the other of the first members and the second flange portion of the second member adjacent thereto are welded to each other by friction stir welding when the first stepped portion and the second flange portion are in surface contact with each other.

14. The bottom body according to claim 13, wherein: The floor member further includes a third member and a fourth member, and each of the third member and the fourth member includes a vertical partition wall having an end portion extending downward; and One end of the third member is recessed upward by a part to be stepped, thereby forming a third stepped portion, and a fourth flange portion extending toward one of the floor members adjacent thereto is formed at the other end of the fourth member.

15. The bottom body according to claim 14, wherein: The second member is provided in a plurality; The third stepped portion of the third member and the second flange portion of one of the second members adjacent thereto are welded to each other by friction stir welding when the third stepped portion and the second flange portion are in surface contact with each other; and The fourth flange portion of the fourth member and the second stepped portion of the other second member adjacent thereto are welded to each other by friction stir welding when the fourth flange portion and the second stepped portion are in surface contact with each other.

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