JP7492682B2 - Vehicle underbody structure - Google Patents

Description

The present invention relates to a vehicle undercarriage.

In an electric vehicle, as disclosed in Patent Document 1, for example, the battery pack is fixed to the underside of the floor of the vehicle body, and a cross member is disposed on the vehicle front side of the battery pack. In this example, the cross member is joined to the side sill of the vehicle body side via a member such as an outrigger.

In addition, a front side frame extending forward of the vehicle is provided at the front of the floor, and a side frame bent portion is provided at the rear of the front side frame. The side frame bent portion is joined to the end of the cross member. With this configuration, when the front side frame receives an impact load due to, for example, a frontal collision, the impact load is urged to be transmitted to the side sill via the side frame bent portion, etc. This protects the battery pack from the impact load.

JP 2019-18821 A

However, in the above example, a configuration in which the impact load is transmitted from the front side frame to the side sill results in a redundant load transmission path, which may not result in the intended load transmission path. In other words, the impact load input to the front side frame may be transmitted in an unintended direction before being transmitted to the side sill, resulting in insufficient load transmission.

If the load transmission is insufficient, for example, stress may concentrate at the joint between the front side frame and the vehicle body, which may result in damage to the cabin or battery. Therefore, in a structure such as the above example, which has a bend in the load transmission path, there is room for improvement in terms of effectively transmitting the impact load input to the front side frame to the rear of the vehicle.

On the other hand, the battery pack of an electric vehicle is heavy and therefore accounts for a large proportion of the vehicle weight. As the battery pack is heavy, it has a large inertial force. If a frontal collision occurs while the vehicle is running, this inertial force will result in a large load acting in the forward direction of the vehicle on the front part of the battery case, which constitutes the outer part of the battery pack, and its surrounding area. For this reason, it is necessary to increase the rigidity of the front part of the battery pack, etc.

The present invention has been made to solve the above problems, and its purpose is to provide a vehicle underbody structure that ensures the rigidity of the front part of the battery pack and can effectively promote the load transfer of the front side members to the rear of the vehicle.

In order to achieve the above-mentioned objective, the vehicle undercarriage structure of the present invention comprises a front side member extending from a front portion of a floor portion of the vehicle toward the front of the vehicle, a side sill which is provided rearward of the front side member on the outside in the vehicle width direction and extends in the fore-and-aft direction of the vehicle, and a battery pack fixed to the underside of the floor portion, the front side member and the side sill being connected by a side brace extending in the vehicle width direction. In the vehicle undercarriage structure, a vehicle body joint extending in the fore-and-aft direction of the vehicle and joined to the floor portion is provided at the rear portion of the front side member, a battery bracket for fixing the battery pack is joined to the rear portion of the vehicle body joint, and a lower member extending inward in the vehicle width direction from the rear portion is joined to the rear portion of the front side member, the lower member has an upper stage portion joined to the floor portion and extending in the vehicle width direction, and a lower stage portion protruding downwardly of the vehicle relative to the upper stage portion and extending in the vehicle width direction, the length of the lower stage portion in the vehicle fore-and-aft direction relative to the length of the upper stage portion in the vehicle fore-and-aft direction is configured to become shorter toward the inside in the vehicle width direction, and a curved portion is provided at the rear of the lower stage portion that curves toward the rear of the vehicle as it moves toward the outside in the vehicle width direction, and the battery bracket is joined to the vehicle width outer portion of the curved portion .

The present invention makes it possible to ensure the rigidity of the front part of the battery pack and also effectively promote the load transfer from the front side member to the rear of the vehicle.

1 is a bottom view of a vehicle underbody structure according to the present invention, as viewed from below the vehicle. 2 is an enlarged bottom view showing a portion where a front side member, a lower member, and a side brace are joined in FIG. 1 . FIG. FIG. 3 is a bottom view showing a state in which the side brace in FIG. 2 has been removed. 3 is an enlarged bottom view showing an outer lower member and its periphery in FIG. 2 . FIG. 5 is a cross-sectional view taken along the line AA in FIG. 4. 2 is a perspective view of the lower member and the intermediate member of FIG. 1 as viewed from above the vehicle. FIG. FIG. 5 is a perspective view seen from the direction of arrow B in FIG. 4 . 8 is a perspective view showing a state in which an inner lower member and an outer lower member of FIG. 7 are removed. FIG. FIG. 9 is a perspective view showing a state in which the side brace in FIG. 8 is removed. 4 is a bottom view showing a modified example of the lower member in which the lower member and the outer lower member of FIG. 3 are integrally formed. FIG.

Below, an embodiment of a vehicle undercarriage structure according to the present invention will be described with reference to the drawings (Figs. 1 to 10). In the drawings, the direction of the arrow Fr indicates the front in the longitudinal direction of the vehicle. In the description of the embodiment, the "front (front end) and rear (rear end)" correspond to the front and rear in the longitudinal direction of the vehicle. The directions of the arrows L and R indicate the left and right sides in the vehicle width direction. In the description of the embodiment, the "left and right" correspond to the left and right sides when an occupant in the vehicle cabin faces forward of the vehicle. In addition, the arrow U indicates the upper side of the vehicle, and the arrow D indicates the lower side of the vehicle.

The vehicle underbody structure of this embodiment is the underbody structure of an electric vehicle having a battery that supplies power to a motor (not shown) for driving the wheels. The vehicle underbody structure has a front side member 10, a side sill 18, a lower member 21, a side brace 16, a battery pack 40, a battery bracket 50, and a front cross member 60.

As shown in Figures 1 and 2, the front side members 10 are highly rigid components that make up the vehicle body frame. The front side members 10 extend in the vehicle front-rear direction from both sides in the vehicle width direction at the front of the floor panel 71 that makes up the floor. The two front side members 10 are spaced apart in the vehicle width direction and are disposed on the vehicle width inner side of the wheel house panel 73 provided on the side of the vehicle body. A drive motor and other components are disposed between the two front side members 10.

Each front side member 10 has a rear inclined portion 12 and a front straight portion 11. The rear inclined portion 12 extends at an incline outward in the vehicle width direction from the front of the floor panel 71 toward the front of the vehicle. The rear portion of the rear inclined portion 12 is joined to the battery bracket 50. The configuration of the rear portion of the rear inclined portion 12 will be described later. The front straight portion 11 extends from the front end of the rear inclined portion 12 toward the front of the vehicle.

As shown in FIG. 9, the front side member 10 has a U-shaped cross section with an opening toward the top of the vehicle. For example, the inner wall 12a of the front side member 10 located at the rear inclined portion 12 is provided with an inner flange 12c (body joint) that protrudes inward in the vehicle width direction and extends in the vehicle front-rear direction, and the outer wall 12b is provided with an outer flange 12d (body joint) that protrudes outward in the vehicle width direction and extends in the vehicle front-rear direction. The inner flange 12c is inclined inward in the vehicle width direction toward the rear of the vehicle, and the outer flange 12d is inclined outward in the vehicle width direction toward the rear of the vehicle, and the inner flange 12c and the outer flange 12d are inclined so as to move away from each other toward the rear of the vehicle.

As shown in FIG. 2, the front portions of the inner flange 12c and the outer flange 12d are joined to a dash lower panel 72 that constitutes part of the floor of the vehicle body. As shown in FIG. 3, the battery bracket 50 is joined to the rear portions of the inner flange 12c and the outer flange 12d. The battery bracket 50 will be described later.

As shown in FIG. 1, the side sill 18 is a highly rigid member joined to both outer sides of the floor panel 71 in the vehicle width direction, and is disposed on the vehicle rear side of the wheel house panel 73, further outboard in the vehicle width direction than the front side member 10, and extends in the vehicle front-rear direction. The front part of the side sill 18 and the rear part of the rear inclined part 12 of the front side member 10 are connected by a side brace 16. The relationship between the side sill 18 and the rear inclined part 12 and the side brace 16 will be explained later.

As shown in Figures 1 to 4, a floor tunnel 71A is provided in the middle of the floor panel 71 in the vehicle width direction. The floor tunnel 71A is formed so that approximately the center of the floor panel 71 rises upward from the vehicle, and extends in the vehicle front-rear direction. In other words, by providing the floor tunnel 71A, an opening extending in the vehicle front-rear direction is formed in the underside of the floor panel 71.

The battery pack 40 is a heavy object that houses an internal battery and is fixed to the underside of the floor panel 71. The battery housed inside the battery pack 40 supplies power to, for example, a drive motor via a cable (not shown). The cable is routed, for example, inside the floor tunnel 71A and connected to the motor. The battery pack 40 includes a battery and a battery case that houses the battery, and in this embodiment, the battery case will be referred to as the battery pack 40.

As shown in FIG. 1, the battery pack 40 extends in the vehicle front-rear direction, and further extends in the vehicle width direction across the entire area between the side sills 18 on both sides. As shown in FIGS. 1 to 3, the front part of the battery pack 40 has a case straight part 41 and a case inclined part 42. The case straight part 41 is provided in the center of the front part of the battery pack 40 in the vehicle width direction, and extends in the vehicle width direction. The case inclined parts 42 are provided on both outer sides of the case straight part 41 in the vehicle width direction, and extend at an incline toward the rear of the vehicle as they move from the outer parts of the case straight part 41 in the vehicle width direction toward the outside in the vehicle width direction. In addition, the case straight part 41 and the case inclined part 42 form a case corner part 43 in the front part of the battery pack 40.

As shown in Figures 1 to 3, the front cross member 60 is disposed on the vehicle front side of the battery pack 40, is one of the members constituting the vehicle body frame, and is a member that extends in the vehicle width direction as a whole. The front cross member 60 has a member straight portion 61 and a member inclined portion 62. The member straight portion 61 is disposed between the rear inclined portions 12 of the front side members 10 on both sides in the vehicle width direction, and is a portion that extends in the vehicle width direction. The member inclined portion 62 is a portion that extends at an incline toward the rear of the vehicle as it moves from the outer portion of the member straight portion 61 in the vehicle width direction toward the outer side in the vehicle width direction. In addition, the member straight portion 61 and the member inclined portion 62 form a member corner portion 63 in the front cross member 60. In other words, the front cross member 60 is formed so that it is convex toward the front of the vehicle as a whole.

Although illustrations are omitted, the front cross member 60 is formed by joining together, for example, an upper member having an L-shaped cross section that forms the top surface and rear wall, and a lower member having an L-shaped cross section that forms the front wall and bottom. A flange that protrudes toward the rear of the vehicle is provided at the lower end of the rear wall of the upper member, and this flange is joined to the bottom surface 14 of the lower member; similarly, a flange that protrudes toward the front of the vehicle is provided at the upper end of the front wall of the lower member, and this flange is joined to the top surface of the upper member, thereby forming a hollow structure.

As shown in Figures 2 and 3, the battery bracket 50 is a member for attaching the battery pack 40 to the lower part of the floor of the vehicle body. The battery bracket 50 is joined to the battery pack 40 via the front cross member 60.

The battery bracket 50 is joined to the front wall located at the member corner 63 of the front cross member 60. A flange (not shown) that protrudes inward in the vehicle width direction and extends in the vehicle vertical direction is provided on the inside of the rear part of the battery bracket 50 in the vehicle width direction, and a flange (not shown) that protrudes outward in the vehicle width direction and extends in the vehicle vertical direction is provided on the outside of the vehicle width direction. These flanges are joined to the front wall located at the member corner 63 of the front cross member 60 by spot welding or the like.

As shown in Figures 1 to 3 when viewed from below the vehicle, the battery bracket 50 is joined to the rear of the inner flange 12c and the outer flange 12d provided on the rear inclined portion 12 of the front side member 10. In this example, the battery bracket 50 has a flat planar portion 51 extending from the member corner portion 63 toward the front of the vehicle. The planar portion 51 is joined to the rear of the rear inclined portion 12 via the outer lower member 27 and the side brace 16 described below. Here, the rear of the rear inclined portion 12, the outer lower member 27, the side brace 16, and the planar portion 51 of the battery bracket 50 are provided with bolt holes 52 that communicate with each other, and bolts are inserted through the bolt holes 52 to fasten these members together.

As shown in FIG. 3, the lower member 21 extends from the rear of the rear inclined portion 12 of the front side member 10 toward the inside in the vehicle width direction. In this embodiment, the lower member 21 is composed of an inner lower member 22 and an outer lower member 27 arranged side by side in the vehicle width direction. The inner lower member 22 and the outer lower member 27 are members that extend in the vehicle width direction, and the outer lower member 27 is joined to the outer end of the inner lower member 22.

As shown in FIG. 3, the inner lower member 22 is a hollow member that has a predetermined width in the vehicle front-rear direction and extends in the vehicle width direction, and has a cross-sectional shape with an opening on the upper side of the vehicle when viewed in the vehicle width direction. In this example, the vehicle width outer portion of the inner lower member 22 is located on the vehicle width inner portion at the rear of the rear inclined portion 12 of the front side member 10.

The inner side of the inner lower member 22 in the vehicle width direction is joined to the floor panel 71 located at the opening edge of the floor tunnel 71A, as shown in Figures 1 and 4. The inner side of the inner lower member 22 in the vehicle width direction is joined to an intermediate member 28 that extends in the vehicle width direction so as to straddle the floor tunnel 71A.

As shown in FIG. 3, the outer lower member 27 is a plate extending in the vehicle width direction, and the inner portion of the outer lower member 27 in the vehicle width direction is joined to the outer portion of the inner lower member 22 in the vehicle width direction. The outer lower member 27 is joined to the bottom portion 14 in a state where it covers a part of the bottom portion 14 of the rear inclined portion 12 of the front side member 10 from the underside of the vehicle.

In FIG. 1, the intermediate member 28, the left and right inner lower members 22, and the left and right outer lower members 27 form a single lower cross member that extends in the vehicle width direction.

As shown in FIG. 2, the side brace 16 extends at an angle toward the rear of the vehicle as it moves outward in the vehicle width direction, connecting the outer lower member 27 and the front portion of the side sill 18. Although not shown in detail, the side brace 16 has a U-shaped cross section that opens toward the top of the vehicle. Flanges 16c and 16d are provided on the upper portions of the front wall 16a and rear wall 16b that form the U-shaped cross section, and the flanges 16c and 16d are joined to the floor panel 71 by spot welding or the like. The flange 16c of the front wall 16a is joined to the floor panel 71 located near the rear of the wheel house panel 73.

The inner side of the underside of the U-shaped cross section of the side brace 16 is arranged to cover the bottom 14 at the rear of the rear inclined portion 12 of the front side member 10 via the outer lower member 27. The underside covering the front side member 10 is joined to the outer side of the bottom 14 of the rear inclined portion 12 of the front side member 10 by spot welding or the like. The underside is also joined to the outer lower member 27.

Here, the shape of the inner lower member 22 will be described in detail. As shown in Figs. 5 and 7, the inner lower member 22 has upper step portions 23, 24 that are joined to the floor portion and extend in the vehicle width direction, and a lower step portion 25 that protrudes downward from the upper step portions 23, 24 and extends in the vehicle width direction. In this example, the upper step portions 23, 24 have a front upper step portion 23 and a rear upper step portion 24, and the lower step portion 25 is disposed between the front upper step portion 23 and the rear upper step portion 24 in the vehicle front-rear direction. That is, as shown in Figs. 5 and 7, the inner lower member 22 has a convex cross section when viewed in the vehicle width direction.

3, 5 and 7, the front upper portion 23 is composed of a front upper wall surface 23A and a front upper surface 23B. The front upper wall surface 23A protrudes downward from the front end of the inner lower member 22, is a wall surface facing the front of the vehicle, and extends in the vehicle width direction. The outer side of the front upper wall surface 23A in the vehicle width direction is slightly inclined toward the front of the vehicle and is connected to a bulging portion of the front part of the outer lower member 27, which will be described later. The front upper surface 23B extends from the lower end of the front upper wall surface 23A toward the rear of the vehicle, is a surface facing the bottom of the vehicle, and extends in the vehicle width direction. A flange 23D is provided at the upper end of the front upper wall surface 23A, which protrudes forward of the vehicle and extends in the vehicle width direction. The flange 23D is joined to the floor panel 71.

As shown in Figures 5 and 7, the rear upper step portion 24 is composed of a rear upper wall surface 24A and a rear upper step surface 24B. The rear upper wall surface 24A protrudes downward from the rear end of the inner lower member 22, is a wall surface facing the rear of the vehicle, and extends in the vehicle width direction. In this example, as shown in Figure 7, the rear upper wall surface 24A has a straight portion 24Aa that extends in a straight line from the outer end of the inner lower member 22 in the vehicle width direction toward the outside in the vehicle width direction, and a rear bulging portion (bulging portion) 24Ab that bulges toward the rear of the vehicle as it moves from the outer end of the straight portion 24Aa toward the outside in the vehicle width direction. In addition, the rear upper step surface 24B extends forward from the lower end of the rear bulging portion 24Ab of the rear upper wall surface 24A, is a surface facing the lower side of the vehicle, and extends in the vehicle width direction. A flange 24D is provided at the upper ends of the straight portion 24Aa and the rear bulge portion 24Ab, and extends toward the rear of the vehicle in the vehicle width direction. The flange 24D is joined to the floor panel 71.

As shown in Figures 5 and 7, the lower portion 25 has a front lower wall surface 25A, a rear lower wall surface 25B, and a lower surface 25C. The front lower wall surface 25A protrudes downward from the rear end of the front upper surface 23B, is a wall surface facing the front of the vehicle, and extends in the vehicle width direction. In this example, as shown in Figure 2, the front lower wall surface 25A is inclined so as to curve toward the rear of the vehicle as it moves from the outer end of the inner lower member 22 in the vehicle width direction toward the inside in the vehicle width direction, and extends linearly from a predetermined position toward the inside in the vehicle width direction.

As shown in Figures 2 and 7, the rear lower wall surface 25B protrudes downward from the front end of the rear upper surface 24B, faces the rear of the vehicle, and extends in the vehicle width direction. In this example, the rear lower wall surface 25B forms a curved portion 25Ba that curves inwardly in the vehicle width direction from the inner end of the straight portion 24Aa of the rear upper wall surface 24A so as to be concave toward the front of the vehicle.

As shown in Figures 5 and 7, the lower surface 25C is a surface facing the underside of the vehicle so as to connect the lower end of the front lower wall surface 25A to the lower end of the rear lower wall surface 25B and the lower end of the rear upper wall surface 24A in the vehicle longitudinal direction, and extends in the vehicle width direction. As shown in Figures 2 and 7, by curving the front lower wall surface 25A and the rear lower wall surface 25B, the length of the lower surface 25C in the vehicle longitudinal direction is gradually shortened as it moves inward in the vehicle width direction.

In this embodiment, the length of the lower stage 25 in the vehicle longitudinal direction relative to the length of the upper stage is configured to become shorter toward the inside of the vehicle width direction. Here, the length of the upper stage is the distance between the front upper wall surface 23A and the rear upper wall surface 24A indicated by L1 in FIG. 2, and the length of the lower stage 25 in the vehicle longitudinal direction is the length of the lower stage surface 25C in the vehicle longitudinal direction indicated by L2 in FIG. 2.

The above-mentioned configuration allows the inner flange 12c and outer flange 12d, where the front side member 10 is joined to the vehicle body, to transmit impact loads to the battery bracket 50 located at the rear of the vehicle. In addition, the inner lower member 22 has a front upper stage 23, a rear upper stage 24, and a lower stage 25, and by setting the vehicle longitudinal lengths (L1, L2) of these as described above, the front side member 10 can be supported by the front upper stage 23, the rear upper stage 24, and the lower stage 25. As a result, deformation of the rear end of the front side member 10 in the vehicle width direction is suppressed, making it easier to transmit impact loads to the rear of the vehicle.

As shown in FIG. 4, the inner flange 12c and the outer flange 12d, which form the vehicle body joints, are arranged so that the distance between the inner flange 12c and the outer flange 12d in the vehicle width direction increases toward the rear of the vehicle, enabling effective load transmission to the battery bracket 50. Furthermore, this arrangement allows the number of joints (spot welding points) to the inner lower member 22 to be increased, further improving the rigidity of the joint between the front side member 10 and the inner lower member 22.

In this embodiment, the rear lower wall surface 25B located at the rear of the lower portion 25 has the curved portion 25Ba as described above, and the battery bracket 50 is joined to the outer side of the rear lower wall surface 25B in the vehicle width direction. In other words, the flat portion 51 of the battery bracket 50 is disposed on the outer side of the rear lower wall surface 25B in the vehicle width direction.

If the inner lower member 22 were shaped to extend linearly in the vehicle width direction, the load would be more easily transmitted along the linear (vehicle width) shape, and as a result, the load transmitted to the battery bracket 50 at the rear of the vehicle would be smaller. In contrast, in this embodiment, the lower section 25 is curved toward the rear of the vehicle, so the inner lower member 22 is more likely to transmit the load to the rear of the vehicle. Also, because the inner lower member 22 and the battery bracket 50 are joined, the impact load input from the front side member 10 can be easily transmitted to the battery bracket 50. Note that even if the curvature of the curve is small, it is possible to increase the load that can be transmitted to the rear of the vehicle.

In this embodiment, as shown in Figs. 4 and 7, the rear upper wall surface 24A of the rear upper stage 24 located on the vehicle rear side of the lower stage 25 is provided with a rear bulging portion 24Ab that bulges toward the vehicle rear relative to the lower stage 25, and the rear end of the front side member 10 is joined to the vertical wall located at the rear of the inner lower member 22. In detail, the straight portion 24Aa of the rear upper wall surface 24A of the inner lower member 22 is joined by spot welding or the like to the rear end flange 12e provided at the rear end of the rear inclined portion 12 of the front side member 10 shown in Figs. 8 and 9 (Fig. 7).

By providing the rear bulge 24Ab, the lower stage 25 and the rear upper stage 24 have different shapes, which reduces the surface area that resists the input of an impact load from the front of the vehicle and suppresses deformation. Suppressing deformation of the inner lower member 22 promotes the transmission of the impact load to the rear of the vehicle. Furthermore, because the lower stage 25 and the rear upper stage 24 have different shapes, the area of the rear upper wall surface 24A of the inner lower member 22 to which the rear end of the front side member 10 is joined is reduced, making it possible to distribute the load.

In this embodiment, as described above, the left and right lower members 21 and the intermediate member 28 form one cross member. As shown in Figs. 4 and 6, the intermediate member 28 has a front central upper step 28A and a rear central upper step 28B formed to connect to the front upper step 23 and the rear upper step 24 of the inner lower member 22, respectively, and a central lower step 28C formed to connect to the lower step 25. That is, the front central upper step 28A is provided on the vehicle front side of the central lower step 28C, and the rear central upper step 28B is provided on the vehicle rear side of the central lower step 28C.

The outer parts of the front and rear central upper stages 28A and 28B in the vehicle width direction are joined by spot welding or the like to the inner parts of the front upper stage 23 and the rear upper stage 24 in the vehicle width direction, respectively. In addition, the outer part of the central lower stage 28C in the vehicle width direction is joined by spot welding or the like to the inner part of the lower stage 25 in the vehicle width direction.

The intermediate member 28 straddles the floor tunnel 71A and is joined to the left and right lower members 21, so that the inner flange 12c and the outer flange 12d, where the front side member 10 is joined to the vehicle body, are prevented from moving inward and outward in the vehicle width direction due to impact load. As a result, the impact load input to the front side member 10 is facilitated to be transmitted to the battery bracket 50.

As shown in FIG. 6, the intermediate member 28 has a convex cross section when viewed in the vehicle width direction, with a central lower section 28C, a front central upper section 28A, and a rear central upper section 28B. A reinforcing member 29 is attached to the intermediate member 28. The reinforcing member 29 has a plate-shaped main body section 29A extending in the vehicle width direction, and vertical wall sections 29B extending downward from both outer ends of the main body section 29A in the vehicle width direction.

In this example, as shown in FIG. 6, the main body 29A of the reinforcing member 29 closes the opening formed at the lower ends of the front and rear walls constituting the central lower stage 28C, and is joined to the edge of the opening by spot welding or the like. In addition, the front and rear ends of the vertical wall portion 29B have flanges that protrude outward in the vehicle width direction, and the flanges are joined to the vehicle width direction sides of the front and rear walls of the central lower stage 28C by spot welding or the like.

If the convex shape of the intermediate member 28 were to deform so as to open in the vehicle fore-and-aft direction, the inner flange 12c and the outer flange 12d, where the front side member 10 is joined to the vehicle body, would move toward the inside of the vehicle, hindering the transmission of load in the vehicle fore-and-aft direction. In contrast, in this embodiment, a closed cross-sectional structure is formed, which makes it possible to prevent the convex shape of the intermediate member 28 from deforming in the vehicle fore-and-aft direction. In addition, by maintaining the closed cross-sectional structure, it is possible to maintain support rigidity in the vehicle width direction.

The description of this embodiment is merely an example for explaining the present invention, and does not limit the invention described in the claims. Furthermore, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications are possible within the technical scope described in the claims.

In this embodiment, the lower member 21 is composed of an inner lower member 22 and an outer lower member 27, but is not limited to this. For example, as shown in FIG. 10, the inner lower member 22 and the outer lower member 27 may be composed as a single member.

10: front side member 11: front straight portion 12: rear inclined portion 12a: inner wall 12b: outer wall 12c: inner flange (vehicle body joint portion)
12d Outer flange (body joint)
12e Rear end flange (rear end of front side member)
14 Bottom surface portion 16 Side brace 16a Front wall 16b Rear wall 16c Flange 18 Side sill 21 Lower member 22 Inner lower member 23 Front upper stage portion 23A Front upper wall surface 23B Front upper stage surface 23D Flange 24 Rear upper stage portion 24A Rear upper wall surface 24Aa Straight portion (vertical wall)
24Ab Rear bulge (bulge)
[0033] 24B Rear upper surface 24D Flange 25 Lower portion 25A Front lower wall surface 25B Rear lower wall surface 25Ba Curved portion 25C Lower surface 27 Outer lower member 28 Intermediate member 28A Front central upper portion 28B Rear central upper portion 28C Central lower portion 29 Reinforcement member 29A Main body portion 29B Vertical wall portion 40 Battery pack 41 Case straight portion 42 Case inclined portion 43 Case corner portion 50 Battery bracket 51 Flat portion 52 Bolt hole 60 Front cross member 61 Member straight portion 62 Member inclined portion 63 Member corner portion 71 Floor panel 71A Floor tunnel 72 Dash lower panel 73 Wheel house panel

Claims (4)

a front side member extending from a front portion of a floor portion of the vehicle toward the front of the vehicle; a side sill provided on an outer side in a vehicle width direction behind the front side member and extending in a front-rear direction of the vehicle; and a battery pack fixed to an underside of the floor portion,
The front side member and the side sill are connected by a side brace extending in a vehicle width direction,
a vehicle body joint extending in a vehicle front-rear direction and joined to the floor portion is provided at a rear portion of the front side member, and a battery bracket for fixing the battery pack is joined to a rear portion of the vehicle body joint;
A lower member is joined to a rear portion of the front side member, the lower member extending inward in a vehicle width direction from the rear portion,
The lower member is
An upper stage portion joined to the floor portion and extending in a vehicle width direction;
a lower stage portion that protrudes downward from the upper stage portion and extends in a vehicle width direction,
a length of the lower portion in the vehicle front-rear direction relative to a length of the upper portion in the vehicle front-rear direction is configured to be shorter toward an inner side in a vehicle width direction,
A curved portion is provided at a rear portion of the lower portion, the curved portion being curved toward the rear of the vehicle as it extends toward the outer side in the vehicle width direction,
The vehicle underbody structure , wherein the battery bracket is joined to an outer portion of the curved portion in a vehicle width direction . The upper stage portion, which is located on the vehicle rear side of the lower stage portion, is provided with a bulging portion that bulges toward the vehicle rear relative to the lower stage portion,
2. The vehicle underbody structure according to claim 1 , wherein a rear end portion of the front side member is joined to a vertical wall located at a rear portion of the lower member. A floor tunnel protruding upward from the vehicle is provided at a middle portion of the floor section in the vehicle width direction, and an intermediate member extending in the vehicle width direction so as to straddle the floor tunnel is provided on the lower surface side of the floor section,
a vehicle width direction outer portion of the intermediate member joined to a vehicle width direction inner portion of the lower member,
3. The vehicle underbody structure according to claim 2, wherein the intermediate member has a central upper stage portion formed to be connected to the upper stage portion of the lower member, and a central lower stage portion formed to be connected to the lower stage portion. The central upper stage is provided on the front and rear sides of the central lower stage in the vehicle front-rear direction,
the intermediate member has a convex cross-sectional shape having an opening toward the upper side of the vehicle, the central lower stage portion, the front central upper stage portion, and the rear central upper stage portion,
A plate-shaped reinforcing member extending in the vehicle width direction is provided to close the opening,
4. The vehicle underbody structure according to claim 3 , wherein the intermediate member and the reinforcing member form a closed cross-sectional structure.