Vehicle underbody structure

Abstract

The objective is to provide a vehicle underbody structure that can efficiently transmit side impact loads from one side sill to the other side sill. [Solution] The lower body structure of the vehicle 1 comprises a pair of left and right side sills 3 extending in the vehicle longitudinal direction at both ends in the vehicle width direction of the front floor panel 4, and a plurality of floor cross members 6 that connect the pair of left and right side sills 3 in the vehicle width direction and are fixed to the upper surface of the front floor panel 4. The floor cross member 6 comprises a front cross member 20 provided at the front of the vehicle, a rear cross member 40 provided at a predetermined distance from the front cross member 20 at the rear of the vehicle, and an intermediate cross member 30 provided between the front cross member 20 and the rear cross member 40 in the vehicle longitudinal direction and fixed to the front cross member 20 and the rear cross member 40, respectively.

Description

Technical Field

[0001] This invention relates to a lower body structure of a vehicle provided with a cross member that connects a pair of left and right side sills provided on both ends in the vehicle width direction in the vehicle width direction.

Background Art

[0002] In vehicles such as automobiles, in order to suppress deformation of the passenger compartment due to a collision load from the side of the vehicle, a cross member may be provided on the floor panel so as to connect a pair of left and right side sills provided on both ends in the vehicle width direction. Thereby, the side collision load, which is a collision load from the side of the vehicle, can be transmitted from one side sill to the other side sill via the cross member.

[0003] For example, in Patent Document 1, a plurality of cross members that connect a pair of left and right side sills in the vehicle width direction are fixed to the upper surface of the floor panel, and the side collision load can be transmitted via the plurality of cross members. Thereby, it is said that the side collision load can be dispersedly transmitted from one side sill to the other side sill.

[0004] In order to efficiently transmit the side collision load applied from the side of such a vehicle from one side sill to the other side sill, it is conceivable to improve the rigidity of the cross member. However, when the rigidity of the cross member is improved, there are problems such as compression of the space in the passenger compartment and an increase in weight due to an enlarged cross-sectional area of the cross member. For this reason, a lower body structure of a vehicle that can efficiently transmit the side collision load from one side sill to the other side sill is required.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The purpose of this invention is to provide a vehicle underbody structure that can efficiently transmit a side impact load from one side sill to the other side sill. [Means for solving the problem]

[0007] This invention is a lower body structure for a vehicle comprising a pair of left and right side sills extending in the longitudinal direction of the vehicle at both ends of the floor panel in the vehicle width direction, and a plurality of cross members connecting the pair of left and right side sills in the vehicle width direction and fixed to the upper surface of the floor panel, wherein the cross members include a first cross member provided at the front of the vehicle, a second cross member provided at a predetermined distance from the first cross member at the rear of the vehicle, and a third cross member provided between the first cross member and the second cross member in the longitudinal direction of the vehicle and fixed to the first cross member and the second cross member respectively.

[0008] The cross member includes a cross member with an open cross section shape that forms a closed cross section with the floor panel, or a cross member with a closed cross section shape such as a cylindrical body. The side sill and the cross member may be connected by both ends of the cross member being directly connected to the side sill, or they may be connected via seat mounting brackets or gussets provided at both ends of the cross member.

[0009] This invention makes it possible to efficiently transmit side impact loads from one side sill to the other side sill. More specifically, a pair of left and right side sills extending in the longitudinal direction of the vehicle are connected in the vehicle width direction at both ends of the floor panel in the vehicle width direction, and a first cross member, a second cross member, and a third cross member are provided fixed to the upper surface of the floor panel. The third cross member is fixed to the first cross member and the second cross member, respectively. As a result, the first, second, and third cross members, which are fixed to each other, can work together with the floor panel to improve the rigidity of the vehicle body against side impact loads, which are collision loads from the side of the vehicle. Therefore, the lower body structure of the vehicle can efficiently transmit side impact loads, such as those caused by a narrow object such as a utility pole colliding with the side of the vehicle, from one side sill to the other side sill.

[0010] In this way, the vehicle's lower body structure, with its first and second cross members, third cross members fixed to each of the first and second cross members, and floor panel working together, improves the rigidity of the vehicle body and efficiently transmits side impact loads from one side sill to the other. Therefore, the vehicle's lower body structure can suppress deformation of the side sills, cross members, floor panel, etc., caused by side impact loads resulting from the vehicle's side colliding with a narrow object.

[0011] In one embodiment of this invention, the first cross member may be provided with a front mounting portion for attaching the front side of the front seat in a vehicle, and the second cross member may be provided with a rear mounting portion for attaching the rear side of the front seat.

[0012] This invention enables the lower body structure of a vehicle to efficiently transmit side impact loads from one side sill to the other side sill at a position close to the vehicle's center of gravity. More specifically, the center of gravity of a vehicle is generally set close to the front seats in the longitudinal direction of the vehicle. A third cross member is positioned between a first cross member, which has a front mounting section for attaching the front side of the front seats (located close to the vehicle's center of gravity in the longitudinal direction), and a second cross member, which has a rear mounting section for attaching the rear side of the front seats. This allows the lower body structure of the vehicle to improve rigidity in a position close to the vehicle's center of gravity, thus enabling efficient transmission of side impact loads from one side sill to the other in a position close to the vehicle's center of gravity.

[0013] Specifically, if a narrow object collides with the side of a vehicle off-center from the vehicle's center of gravity, the vehicle body rotates around the center of gravity, distributing the side impact load. In contrast, if a narrow object collides with the side of a vehicle towards its center of gravity, the side impact load is concentrated on the vehicle body without being distributed.

[0014] In the lower body structure of the vehicle, as described above, a third cross member is fixed to the first and second cross members, as well as to the floor panel, between a first cross member, which has a front mounting section for attaching the front side of the front seat, and a second cross member, which has a rear mounting section for attaching the rear side of the front seat. Therefore, the third cross member, positioned below the front seat, can improve rigidity at a position close to the vehicle's center of gravity. As a result, even if a narrow object collides with the side of the vehicle towards the vehicle's center of gravity, the concentrated side impact load on the vehicle body can be efficiently transmitted from one side sill to the other.

[0015] Furthermore, in the lower body structure of the vehicle, a third cross member is fixed between the first and second cross members in the longitudinal direction of the vehicle, and is positioned below the front seats. Therefore, even with the third cross member, space can be secured in the footwell area of ​​the front seats.

[0016] In another aspect of this invention, the cross member may be configured with a substantially M-shaped cross-section extending in the vehicle width direction. This invention makes it possible to improve the rigidity of each cross member compared to a cross member configured with a hat-shaped cross section. Therefore, the lower body structure of the vehicle can more efficiently transmit side impact loads from one side sill to the other.

[0017] In another aspect of this invention, a tunnel portion projecting upward is formed at the center of the floor panel in the vehicle width direction, and the cross member may span the tunnel portion and connect the left and right pair of side sills in the vehicle width direction.

[0018] According to this invention, a cross member that straddles a tunnel section extending in the longitudinal direction of the vehicle at the center of the vehicle width direction is connected to a pair of left and right side sills in the vehicle width direction. Therefore, the lower body structure of the vehicle can reliably transmit side impact loads from one side sill to the other side sill compared to a pair of cross members that connect a pair of left and right side sills with the tunnel section in between.

[0019] In another aspect of this invention, the tunnel section has side wall sections facing each other in the vehicle width direction, the cross member comprises a front flange section extending forward of the vehicle and a rear flange section extending backward of the vehicle, and the front flange section and the rear flange section may be joined to the side wall section.

[0020] This invention allows the cross members to form a closed cross section even in the side walls of the tunnel section, thereby improving the rigidity of the tunnel section and the rigidity of the cross members spanning the tunnel section. Consequently, the lower body structure of the vehicle can suppress deformation of the tunnel section and efficiently transmit side impact loads across the tunnel section from one side sill to the other.

[0021] As an aspect of the present invention, the rear flange portion of the first cross member may be fixed by overlapping it above the front flange portion of the third cross member, and the rear flange portion of the third cross member may be fixed by overlapping it above the front flange portion of the second cross member.

[0022] According to the present invention, since the first cross member, the second cross member, and the third cross member can be easily attached to the floor panel, the efficiency of the fixing work for fixing the cross members to the floor panel can be improved.

[0023] Further, when the front seat mounting portions and the rear seat mounting portions for mounting the front seat in the vehicle are provided on the first cross member and the second cross member, it is possible to suppress the downward displacement of the front seat. Specifically, the first cross member can be supported by the third cross member, and the third cross member can be supported by the second cross member. Therefore, it is possible to regulate the downward displacement of the cross member accompanying the upward displacement of the tunnel portion due to the side impact load. Accordingly, in the lower body structure of the vehicle, when the front seat mounting portions and the rear seat mounting portions for mounting the front seat in the vehicle are provided on the first cross member and the second cross member, it is possible to suppress the downward displacement of the front seat.

[0024] As an aspect of the present invention, the side sill and the cross member may be joined such that the upper surfaces of the side sill and the cross member are aligned in the vehicle vertical direction. The above side sill and the cross member being joined such that the upper surface of the side sill and the upper surface of the cross member are aligned in the vehicle up-down direction means that the upper surface of the side sill and the upper surface of the cross member may be joined so as to be arranged side by side in the vehicle width direction, or may be joined such that a part of the upper surface of the cross member overlaps the upper surface of the side sill. Further, when the upper surface of the side sill is an inclined surface inclined in the vehicle up-down direction with respect to the vehicle width direction, it means being joined such that the upper surface of the cross member is arranged in the range from the upper end position to the lower end position of the inclined upper surface of the side sill in the vehicle up-down direction.

[0025] According to this invention, ridge line portions which are higher in rigidity than other portions in the side sill and the cross member are in substantially the same position in the vehicle up-down direction although their extending directions are substantially orthogonal to each other in plan view. That is, the ridge line portion of the floor cross member and the ridge line portion of the side sill are continuous. Therefore, the lower body structure of the vehicle can efficiently transmit a side impact load from one side sill to the other side sill. Note that the ridge line portion extending in the vehicle front-rear direction forming the upper surface of the side sill in the side sill and the ridge line portion extending in the vehicle width direction forming the upper surface of the cross member in the cross member are higher in rigidity than other portions in their respective members.

[0026] As an aspect of this invention, a battery unit may be provided below the floor panel, and a connecting portion may be provided which is fastened to a fastening member inserted through the upper surface of the cross member overlapped with the tunnel portion to connect the cross member and the battery unit.

[0027] According to this invention, in the central portion in the vehicle width direction, the upward displacement of the cross member and the tunnel portion due to a side impact load is suppressed by the battery unit connected via the fastening member and the connecting portion. For this reason, the lower body structure of the vehicle can reliably transmit a side impact load from one side sill to the other side sill.

[0028] In another aspect of this invention, the upper surface of the cross member is provided with a groove that is recessed downward and extends in the vehicle width direction, and the length of the groove in the tunnel section in the vehicle longitudinal direction may be longer than the length of the groove in other sections in the vehicle longitudinal direction.

[0029] This invention provides a seating surface for fixing the cross member and the battery unit, and also improves the rigidity of the cross member. As a result, the lower body structure of the vehicle can securely fix the cross member and the battery unit, and the upward displacement and deformation of the cross member can be further suppressed. [Effects of the Invention]

[0030] This invention provides a vehicle underbody structure that can efficiently transmit side impact loads from one side sill to the other side sill. [Brief explanation of the drawing]

[0031] [Figure 1] An external perspective view showing the appearance of the lower part of the vehicle body as seen from the front. [Figure 2] A plan view showing the external appearance of the lower body of a vehicle in a top-down view. [Figure 3] An external perspective view showing the appearance of key parts of the lower body of the vehicle from a rearward view. [Figure 4] Cross-sectional view taken along arrow AA in Figure 2. [Figure 5] Cross-sectional view taken along the CC arrow in Figure 2. [Figure 6] Enlarged cross-sectional view of the main part in Figure 5. [Figure 7] Cross-sectional view taken along arrow BB in Figure 2. [Modes for carrying out the invention]

[0032] One embodiment of this invention will be described below with reference to the drawings. Vehicle 1 in this embodiment is, for example, an electric vehicle equipped with a floor cross member 6 that connects a pair of left and right side sills 3 in the vehicle width direction, approximately in the center of the front floor panel 4 in the vehicle's longitudinal direction. The lower body structure in the passenger compartment of such vehicle 1 will be described in detail with reference to Figures 1 to 7.

[0033] Figure 1 shows an external perspective view of the lower body of vehicle 1 from a forward view, Figure 2 shows a plan view of the lower body of vehicle 1, and Figure 3 shows an external perspective view of the main part of the lower body of vehicle 1 from a rear view. Figure 4 shows a cross-sectional view of the main part as seen by arrow AA in Figure 2, Figure 5 shows a cross-sectional view of the main part as seen by arrow CC in Figure 2, Figure 6 shows an enlarged cross-sectional view of the main part circled in Figure 5, and Figure 7 shows a cross-sectional view of the main part as seen by arrow BB in Figure 2.

[0034] Furthermore, in the diagram, arrows Fr and Rr indicate the front-rear direction, with Fr indicating the front and Rr indicating the rear. Additionally, arrows Rw and Lw indicate the vehicle width direction, with Rw indicating the right direction and Lw indicating the left direction. Moreover, arrows Uh and Dh indicate the vehicle's vertical direction, with Uh indicating the top of the vehicle and Dh indicating the bottom of the vehicle.

[0035] As shown in Figures 1 and 2, the lower body of vehicle 1 includes a dash panel 2 that separates the engine compartment from the passenger compartment in the longitudinal direction of the vehicle, a pair of left and right side sills 3 that extend from the lower ends of both ends of the dash panel 2 in the vehicle width direction toward the rear of the vehicle, and a front floor panel 4 that is positioned between the left and right side sills 3 and forms the floor surface of the passenger compartment.

[0036] As shown in Figures 1, 2, and 3, the front floor panel 4 has a roughly tunnel-shaped tunnel section 5 that bulges upward from the front to the rear of the vehicle, located near the approximate center in the vehicle width direction. In addition, a floor cross member 6 is fixed to the upper surface of the front floor panel 4, near the center in the vehicle's longitudinal direction, straddling the tunnel section 5 and connecting a pair of left and right side sills 3 in the vehicle width direction. A battery unit 7 is also located below the front floor panel 4, connected to a high-rigidity part of the vehicle body.

[0037] Specifically, the dash panel 2 is a panel member having thickness in the front-to-rear direction of the vehicle, and its lower part is formed in a curved shape toward the rear of the vehicle. A front floor panel 4 is provided extending toward the rear of the vehicle from the lower end of this dash panel 2.

[0038] The side sills 3 consist of a pair of left and right sills that extend from the lower ends of both ends in the vehicle width direction of the dash panel 2 toward the rear of the vehicle, and the cross-sectional shape in the longitudinal section along the vehicle width direction is configured to form a closed section with a substantially rectangular cross-section. That is, at the corners of the upper surface portion of the side sills 3, ridge portions 3a are formed that extend in the front-rear direction of the vehicle at predetermined intervals in the vehicle width direction.

[0039] As shown in Figures 2 and 4, the front floor panel 4 is a panel member having thickness in the vertical direction of the vehicle, with its front end connected to the lower end of the dash panel 2, and both ends in the vehicle width direction joined to the side sills 3. A tunnel portion 5 that protrudes upward toward the vehicle is formed approximately in the center of the front floor panel 4 in the vehicle width direction, as described above.

[0040] As shown in Figures 3 and 4, the tunnel section 5 is formed in a roughly hat-shaped cross-section, projecting upwards in a roughly trapezoidal shape, and extends from the front end to the rear end of the front floor panel 4 in the longitudinal direction of the vehicle. The front end of the tunnel section 5 is joined to the dash panel 2. The console bracket 10 covers the front end portion of the tunnel section 5.

[0041] More specifically, as shown in Figures 3 and 5, the tunnel section 5 consists of a pair of left and right side walls 51 that rise from the front floor panel 4 and are inclined toward the center in the vehicle width direction as they extend upward, and a substantially planar tunnel upper section 52 that connects the upper ends of the pair of left and right side walls 51. The height of the side walls 51 relative to the front floor panel 4 is slightly higher than the height of the side sills 3 relative to the front floor panel 4.

[0042] The upper part of the tunnel 52 is inclined downward towards the rear of the vehicle when it is in front of the front cross member 20 (described later), and extends almost horizontally along the longitudinal direction of the vehicle when it is behind the front cross member 20. As shown in Figures 5 and 6, in the central portion of the upper part 52 of the tunnel configured in this way, multiple through-holes 53 that penetrate in the vertical direction of the vehicle are provided at predetermined intervals in the longitudinal direction of the vehicle.

[0043] As shown in Figure 2, the floor cross member 6 connects the left and right side sills 3 in the vehicle width direction and is composed of a front cross member 20, an intermediate cross member 30, and a rear cross member 40, all of which have a roughly M-shaped cross section and are fixed to the upper surface of the front floor panel 4.

[0044] As shown in Figures 2, 3, and 4, the front cross member 20, the intermediate cross member 30, and the rear cross member 40 span the tunnel section 5 that extends in the longitudinal direction of the vehicle, connecting the left and right pair of side sills 3 in the vehicle width direction, and are arranged in this order from the front to the rear of the vehicle. In other words, the front cross member 20, the intermediate cross member 30, and the rear cross member 40 connect the left and right pair of side sills 3 in a nearly linear manner in plan view at a position near the center of the front floor panel 4 in the longitudinal direction of the vehicle.

[0045] As shown in Figures 2 and 3, the front cross member 20 is positioned in front of the intermediate cross member 30 and extends in the vehicle width direction, straddling the tunnel section 5. More specifically, the front cross member 20 has a straddling section 21 in the central part in the vehicle width direction that straddles the tunnel section 5, and a pair of left and right member bodies 22 that extend in the vehicle width direction between the outer end of the straddling section 21 in the vehicle width direction and the side sill 3.

[0046] As shown in Figures 2 and 3, the straddle portion 21 is formed to rise upward along the tunnel portion 5 relative to the member body 22. On the outer portion of the straddle portion 21 in the vehicle width direction, a front inner seat bracket 211 for attaching the front seat (not shown) is provided so as to straddle the boundary portion with the member body 22.

[0047] As shown in Figures 2 and 3, the front inner seat bracket 211 is roughly box-shaped with an open outer side in the vehicle width direction and a central portion projecting upward in the vehicle width direction, and its vertical cross-sectional shape along the vehicle width direction forms a closed cross-sectional shape with the front floor panel 4 and the tunnel section 5. The upper end surface of the front inner seat bracket 211 configured in this way is set above the upper part 52 of the tunnel and has a front inner mounting hole 212 for attaching the front of the front seat. The front inner seat bracket 211, the tunnel section 5, and the front cross member 20 are fixed together by welding, such as spot welding.

[0048] As shown in Figure 2, the member body 22 extends continuously in the vehicle width direction from the outer end of the straddle portion 21 in the vehicle width direction, and is joined to a pair of left and right side sills 3 via front outer seat brackets 221 provided at both ends in the vehicle width direction.

[0049] The front outer seat bracket 221 is substantially symmetrical to the front inner seat bracket 211. More specifically, the front outer seat bracket 221 is formed in a substantially mountain shape with the central part in the vehicle width direction protruding upward, and is substantially box-shaped with openings on the outer side in the vehicle width direction and below the vehicle. The longitudinal cross-sectional shape along the vehicle's front-rear direction is closed by the side sill 3 and the member body 22. The front outer seat bracket 221 of this shape has a ridge portion 221a at its upper part.

[0050] Furthermore, the upper surface of the front outer seat bracket 221 on the vehicle side is joined to the side sill 3, and the upper surface of the front outer seat bracket 221 on the vehicle side is fixed to the connecting portion 25, which will be described later, by welding such as spot welding. The front outer seat bracket 221, which connects the side sill 3 and the connecting portion 25, is set above the side sill 3 and has a front outer mounting hole 222 on its upper end surface for attaching the front part of the front seat.

[0051] As shown in Figure 4, the front cross member 20, which connects the side sills 3 while straddling the tunnel section 5, has a pair of flange sections 23 on both sides in the vehicle's longitudinal direction, extending along the vehicle's width direction and in the vehicle's longitudinal direction. The flange sections 23 and the front floor panel 4 are joined by welding, such as spot welding. As a result, the front cross member 20 and the front floor panel 4 form a closed cross section.

[0052] The flange portion 23 in the straddle portion 21 is inclined along the vehicle width direction at both ends, while the central portion of the flange portion 23 in the vehicle width direction is approximately horizontal along the upper part 52 of the tunnel (see Figure 5). Thus, the flange portion 23 provided on the straddle portion 21 that protrudes upward toward the vehicle is fixed to the tunnel portion 5 that constitutes the front floor panel 4 by spot welding or the like. Here, of the pair of flange portions 23 extending in the longitudinal direction of the vehicle, the flange portion 23 at the front of the vehicle is designated as the front flange portion 23a, and the flange portion 23 at the rear of the vehicle is designated as the rear flange portion 23b.

[0053] As shown in Figure 4, such a front cross member 20 is formed in a roughly M-shape in a longitudinal section along the vehicle's longitudinal direction. More specifically, the front cross member 20 has a pair of front and rear upright portions 24 at the inner ends of the flange portion 23 in the vehicle's longitudinal direction, which are inclined toward the opposing side of the flange portion 23 as they extend upward towards the vehicle, and a connecting portion 25 that connects the upper ends of the upright portions 24 from one end to the other in the vehicle's width direction.

[0054] The connecting portion 25 is set so that its upper surface aligns with the upper surface of the side sill 3 in the vehicle's vertical direction, and is joined to the side sill 3 via the front outer seat bracket 221. In other words, the side sill 3 and the connecting portion 25 are connected by the front outer seat bracket 221.

[0055] Furthermore, as shown in Figures 2 and 4, a groove 26 is provided in the central part of the connecting section 25 in the vehicle's longitudinal direction, extending downward to approximately half the length of the upright section 24 in the vehicle's vertical direction, and extending in the vehicle's width direction from one end to the other of the front cross member 20. The lower surface of the groove 26 is joined to a convex portion of the front floor panel 4, which is formed in a wave-like shape along the vehicle's longitudinal direction.

[0056] In the central portion of the groove 26 in the straddle portion 21, the width in the vehicle longitudinal direction is configured to be longer than the width in the vehicle longitudinal direction of the groove 26 in other parts such as the member body 22. More specifically, in the central portion of the straddle portion 21, the groove width is wider than that of the groove 26 in other parts such as the member body 22, and it is formed in a hexagonal shape in plan view (see Figure 2). Furthermore, in the central portion of the groove 26 in the straddle portion 21, a cross member through hole 261 is provided that penetrates in the vehicle vertical direction and is inserted through the through hole 53 (see Figures 5 and 6).

[0057] As shown in Figure 4, the front cross member 20 configured in this way has a pair of left and right ridges 20a extending in the vehicle width direction, spaced at a predetermined distance in the vehicle front-rear direction, formed at the corners between the upright portion 24 and the connecting portion 25, and at the corners of the groove 26 in the connecting portion 25.

[0058] Furthermore, the front cross member 20 and the side sill 3 are connected via the front outer seat bracket 221 such that the ridge portion 20a formed at the corner between the upright portion 24 and the connecting portion 25, and the ridge portion 3a on the side sill 3, which is set so that the upper surface of the side sill 3 and the upper surface of the connecting portion 25 are aligned in the vehicle's vertical direction, are continuous via the ridge portion 221a of the front outer seat bracket 221 (see Figure 3).

[0059] Furthermore, the ridge portion 20a extending in the vehicle width direction formed on the front cross member 20 is more rigid than other parts (flat portions) of each member, similar to the ridge portion 3a extending in the vehicle longitudinal direction formed on the corner portion of the upper surface of the side sill 3.

[0060] The intermediate cross member 30, positioned on the rear side of the vehicle relative to the front cross member 20, has substantially the same configuration as the front cross member 20. More specifically, as shown in Figures 2, 3, and 4, the intermediate cross member 30 is provided to extend in the vehicle width direction, straddling the tunnel section 5. In the center in the vehicle width direction, it has a straddling section 31 that straddles the tunnel section 5, and a pair of left and right member bodies 32 that extend in the vehicle width direction between the outer end of the straddling section 31 in the vehicle width direction and the side sill 3.

[0061] Since the straddle portion 31 has substantially the same configuration as the straddle portion 21, except that it is not equipped with a front inner seat bracket 211, a detailed explanation will be omitted. The member body 32 has substantially the same configuration as the member body 22, except that a pair of gussets 321 are provided instead of a pair of front outer seat brackets 221.

[0062] The gusset 321 is roughly box-shaped with openings on the outer side in the vehicle width direction and below the vehicle, and its longitudinal cross-sectional shape along the vehicle width direction forms a closed cross-section with the front floor panel 4 and tunnel section 5 and the intermediate cross member 30. The gusset 321 configured in this way is fixed to the left and right pair of side sills 3 and member body 32 by welding, such as spot welding. The gusset 321 has a ridge portion 321a at its upper part.

[0063] More specifically, the upper outer surface of the gusset 321 is joined to the upper surface of the side sill 3 by welding such as spot welding, and the upper inner surface of the gusset 321 is joined to the connecting portion 35, which corresponds to the connecting portion 25 described later, by welding such as spot welding.

[0064] Similar to the front cross member 20, the intermediate cross member 30 is formed in a roughly M-shape in its longitudinal section along the vehicle's longitudinal direction. More specifically, the intermediate cross member 30 consists of a flange portion 33, an upright portion 34, and a connecting portion 35. In the central portion of the connecting portion 35 in the vehicle's longitudinal direction, a groove 36 having a cross member through hole 361 is provided, similar to the groove 26, extending in the vehicle's width direction (see Figures 4, 5, and 6).

[0065] Here, the flange portion 33, the upright portion 34, the connecting portion 35, the groove 36, and the cross member through hole 361 have substantially the same configuration as the flange portion 23, the upright portion 24, the connecting portion 25, the groove 26, and the cross member through hole 261, so a detailed explanation is omitted. In addition, the intermediate cross member 30, similar to the front cross member 20, has a pair of left and right ridge portions 30a that extend in the vehicle width direction at a predetermined distance in the vehicle front-rear direction, at the corner portion between the upright portion 34 and the connecting portion 35, and at the corner portion of the groove 36 in the connecting portion 35.

[0066] Furthermore, as described above, the upper surface of the connecting portion 35 and the upper surface of the side sill 3 are set to be aligned in the vertical direction of the vehicle, and the gusset 321 is joined to each of them. As a result, the ridge portion 30a formed at the corner between the upright portion 34 and the connecting portion 35 and the ridge portion 3a of the side sill 3, which is set to be aligned in the vertical direction of the vehicle on their upper surfaces, are continuous via the ridge portion 321a of the gusset 321, and the intermediate cross member 30 and the side sill 3 are connected via the gusset 321 (see Figures 5 and 6).

[0067] The rear cross member 40, located at the rear of the vehicle relative to the intermediate cross member 30, has substantially the same configuration as the front cross member 20. More specifically, as shown in Figures 2, 3, and 4, the rear cross member 40 is provided to extend in the vehicle width direction, straddling the tunnel section 5. In the center in the vehicle width direction, it has a straddling section 41 that straddles the tunnel section 5, and a pair of left and right member bodies 42 that extend in the vehicle width direction between the outer end of the straddling section 41 in the vehicle width direction and the side sill 3.

[0068] The straddle portion 41 has substantially the same configuration as the straddle portion 21, and at both ends of the straddle portion 41 in the vehicle width direction, rear inner seat brackets 411 for attaching the front seat (not shown) are provided so as to straddle the boundary portion with the member body 42.

[0069] The rear inner seat bracket 411 is roughly box-shaped with openings on the outer side in the vehicle width direction and on the lower side of the vehicle. Its longitudinal cross-sectional shape along the vehicle width direction forms a closed cross-section with the front floor panel 4, the tunnel section 5 and the rear cross member 40. The rear inner seat bracket 411 also has a rear inner mounting hole 412 on its upper end surface for attaching the front part of the front seat. The rear inner seat bracket 411 and the tunnel section 5 are fixed together by welding, such as spot welding.

[0070] The member body 42 has substantially the same configuration as the member body 22 and is joined to a pair of left and right side sills 3 by rear outer seat brackets 421 provided at both ends in the vehicle width direction.

[0071] The rear outer seat bracket 421 is substantially symmetrical to the rear inner seat bracket 411. More specifically, the rear outer seat bracket 421 is substantially box-shaped with openings on the outer side in the vehicle width direction and below the vehicle, and its longitudinal cross-sectional shape along the vehicle's front-rear direction forms a closed cross-section with the front floor panel 4 and tunnel section 5 and the rear cross member 40. The rear outer seat bracket 421, configured in this way, is fixed to the left and right pair of side sills 3 and member body 42 by welding, such as spot welding. The rear outer seat bracket 421 has a ridge portion 421a at its upper part.

[0072] More specifically, the upper surface of the rear outer seat bracket 421 on the vehicle side is joined to the upper surface of the side sill 3 by welding such as spot welding, and the upper surface of the rear outer seat bracket 421 on the vehicle side is joined to the connecting portion 45, which will be described later, by welding such as spot welding. The rear outer seat bracket 421 has a rear outer mounting hole 422 on its upper end surface for attaching the front part of the front seat.

[0073] Similar to the front cross member 20, the rear cross member 40 is formed in a roughly M-shape in its longitudinal section along the vehicle's longitudinal direction (see Figure 4). More specifically, the rear cross member 40 consists of a flange portion 43, an upright portion 44, and a connecting portion 45. In the central portion of the connecting portion 45 in the vehicle's longitudinal direction, a groove 46 is provided that extends in the vehicle width direction and has a cross member through-hole 461, similar to the groove 26.

[0074] Here, the flange portion 43, the upright portion 44, the connecting portion 45, the groove 46, and the cross member through hole 461 have substantially the same configuration as the flange portion 23, the upright portion 24, the connecting portion 25, the groove 26, and the cross member through hole 261, so a detailed explanation is omitted. Also, similar to the front cross member 20, the rear cross member 40 has a pair of left and right ridge portions 40a that extend in the vehicle width direction at a predetermined distance in the vehicle longitudinal direction, at the corner portion between the upright portion 44 and the connecting portion 45, and at the corner portion of the groove 46 in the connecting portion 45 (see Figure 4).

[0075] As described above, the upper surface of the connecting portion 45 is set to align with the upper surface of the side sill 3 in the vehicle's vertical direction, and the rear outer seat bracket 421 is joined to each of them. As a result, the rear cross member 40 and the side sill 3 are connected via the rear outer seat bracket 421 so that the ridge portion 40a formed at the corner between the upright portion 44 and the connecting portion 45 and the ridge portion 3a of the side sill 3, which is set to align with the upper surfaces in the vehicle's vertical direction, are continuous via the ridge portion 421a of the rear outer seat bracket 421.

[0076] The front cross member 20, intermediate cross member 30, and rear cross member 40, configured in this way, are fixed to each other as shown in Figure 4. More specifically, the front flange portion 33a of the intermediate cross member 30, which is located at the front of the vehicle, is positioned above the rear flange portion 23b of the front cross member 20, which is located at the rear of the vehicle, and is joined to the front floor panel 4. Furthermore, the rear flange portion 33b of the intermediate cross member 30, which is located at the rear of the vehicle, is positioned above the front flange portion 43a of the rear cross member 40, which is located at the front of the vehicle, and is joined to the upper surface of the front floor panel 4 via the front flange portion 43a.

[0077] Here, the front inner seat bracket 211 and the front outer seat bracket 221 provided on the front cross member 20 can be used to attach the front of the front seat to the vehicle, and the rear inner seat bracket 411 and the rear outer seat bracket 421 provided on the rear cross member 40 can be used to attach the rear of the front seat to the vehicle. In other words, in the longitudinal direction of the vehicle, the intermediate cross member 30, which is positioned between the front cross member 20 and the rear cross member 40, is positioned below the front seat to the vehicle.

[0078] The battery unit 7, located below the front floor panel 4, is a roughly rectangular structure in plan view and consists of battery modules 71 arranged side by side in the vehicle width direction and a housing 72 that houses and holds the battery modules 71 inside (see Figures 1, 4, and 5).

[0079] The battery module 71 is, for example, a lithium-ion battery in which multiple battery cells are electrically connected, and is formed in a roughly rectangular shape in plan view, which is long in the front-rear direction of the vehicle. As shown in Figures 5 and 6, the housing 72 is formed as a roughly rectangular, roughly annular shape in plan view, which serves as the frame for the battery unit 7, and is connected to a high-rigidity part of the vehicle body via a plurality of connecting members 80. More specifically, the housing 72 comprises a battery frame 73, a bottom plate portion 74 that closes the opening on the lower side of the vehicle in the battery frame 73, and a top plate portion 75 that closes the opening on the upper side of the vehicle in the battery frame 73. The high-rigidity part of the vehicle body refers to the side sill 3, the rear cross member that connects the sill and side frame in the vehicle width direction (not shown), and the torque box that connects the front part of the side sill 3 to the front side frame.

[0080] The battery frame 73 is a highly rigid frame that is roughly rectangular in plan view, and is configured to fasten and secure the housed battery module 71. The battery frame 73 is also fastened and secured to highly rigid parts of the vehicle body, such as the side sill 3 and other structural members that form the body's skeletal structure.

[0081] As shown in Figure 6, the central portion of the battery frame 73 in the vehicle width direction is provided with a longitudinal frame 76 that connects the front and rear frames of the rectangular battery frame 73 in the vehicle longitudinal direction, an intermediate frame 77 positioned above the longitudinal frame 76, and a support portion 78 that supports the intermediate frame 77.

[0082] As shown in Figures 6 and 7, the longitudinal frame 76 is formed in a roughly hat-shaped cross-section that protrudes roughly rectangularly upwards from the vehicle in a cross-section along the vehicle width direction, and connects the front and rear frames of the rectangular battery frame 73 in the longitudinal direction of the vehicle. The longitudinal frame 76 also has a flange (not shown) extending in the vehicle width direction from the front end to the rear end in the longitudinal direction of the vehicle, and the flange and the bottom plate portion 74 are joined by welding such as spot welding. As a result, the longitudinal frame 76 improves the rigidity of the battery frame 73 and the rigidity of the central portion of the bottom plate portion 74 in the vehicle width direction.

[0083] As shown in Figures 6 and 7, the intermediate frame 77 has a concave cross-sectional shape that opens upward in a cross-section along the longitudinal direction of the vehicle, and is positioned above the vehicle at a predetermined distance from the upper surface of the longitudinal frame 76. In addition, an intermediate through-hole 771, which is circular in plan view and penetrates vertically, is provided at a predetermined distance in the longitudinal direction of the vehicle, so as to be positioned opposite the through-hole 53 provided in the upper part 52 of the tunnel on the vehicle's lower side.

[0084] As shown in Figure 6, the support portion 78 is a support member that supports the intermediate frame 77 at a predetermined distance above the vehicle on the upper surface of the longitudinal frame 76. Specifically, the lower end portion of the support portion 78 is connected to the longitudinal frame 76, and the upper end portion of the support portion 78 is connected to the outer portion in the vehicle width direction on the lower surface of the intermediate frame 77. In this way, the support portion 78 supports the intermediate frame 77 above the longitudinal frame 76 on the vehicle at a predetermined distance from the longitudinal frame 76. The height of the support portion 78 is set so that the distance between the upper surface of the intermediate frame 77 and the lower surface of the top plate portion 75 in the vehicle vertical direction is equal to the distance between the upper surface of the top plate portion 75 and the lower surface of the tunnel upper portion 52 in the vehicle vertical direction.

[0085] As shown in Figure 5, the bottom plate portion 74 is a plate material having thickness in the vertical direction and is configured to be fastened and fixed to the battery frame 73. As shown in Figures 5 and 6, the top plate portion 75 is a plate material having thickness in the vertical direction and is configured to be fastened and fixed to the upper surface of the battery frame 73. Furthermore, as shown in Figure 7, the top plate portion 75 has multiple circular top plate through holes 751 that penetrate in the vertical direction of the vehicle, positioned opposite the through holes 53 and intermediate through holes 771 in the front-rear direction of the vehicle. Note that the top plate through holes 751 have substantially the same shape as the through holes 53 and intermediate through holes 771 in a plan view. Connecting members 80 are positioned between the top plate through holes 751 and intermediate through holes 771, and between the top plate through holes 751 and through holes 53, respectively.

[0086] As shown in Figures 5 and 6, the connecting member 80 connects the tunnel section 5 and the battery unit 7 via fastening bolts V. More specifically, as shown in Figure 6, the connecting member 80 is integrally formed from a shaft portion 81 extending axially along the vertical direction of the vehicle and a main body portion 82 extending to one side of the shaft portion 81 in the axial direction.

[0087] The shaft portion 81 is formed in a substantially cylindrical shape with screw threads on its outer surface that can be threaded onto a nut N (see Figures 6 and 7). The axial length of the shaft portion 81 is shorter than the distance between the front-rear frame 76 and the intermediate frame 77 along the vertical direction of the vehicle.

[0088] As shown in Figures 6 and 7, the main body portion 82 is formed to a length equal to the distance between the upper surface of the intermediate frame 77 and the lower surface of the top plate portion 75. Also, as shown in Figure 6, the main body portion 82 has a larger diameter than the diameter of the shaft portion 81 and is formed in a substantially cylindrical shape that extends from the shaft portion 81. When the shaft portion 81 is inserted through the intermediate through hole 771, the lower end surface of the main body portion 82 abuts against the upper surface of the intermediate frame 77, and the upper end surface abuts against the lower surface of the top plate portion 75.

[0089] Furthermore, as shown in Figure 6, the main body portion 82 of the connecting member 80 has a screw hole 821 recessed from the upper end surface along the axial direction. Specifically, the screw hole 821 of the main body portion 82 has substantially the same structure as the screw hole of the nut N, and is formed from the upper end surface of the main body portion 82 to near the approximate center in the axial direction of the main body portion 82. The screw hole 821 configured in this way allows the shaft portion 81 of the separate connecting member 80 to be screwed in from above the vehicle. The fastening bolt V, which fastens the connecting member 80 from above the vehicle, is a hexagonal bolt with the same diameter as the shaft portion 81 and is screwed into a threaded hole 821 provided at the upper end of the main body portion 82 of the connecting member 80 (see Figure 6).

[0090] As shown in Figures 5, 6, and 7, the connecting member 80 configured in this way connects the tunnel section 5, the floor cross member 6, and the battery unit 7. More specifically, a nut N is fastened to the shaft portion 81 of a connecting member 80, which is positioned between the top plate portion 75 and the intermediate frame 77, and the shaft portion 81 of another connecting member 80, which is inserted through a through hole 751 of the top plate portion 75 from above the vehicle, is screwed into the connecting member 80 positioned between the top plate portion 75 and the intermediate frame 77, thereby fixing the top plate portion 75 to the connecting member 80 positioned between the top plate portion 75 and the intermediate frame 77.

[0091] Furthermore, a connecting member 80, positioned between the top plate portion 75 and the intermediate frame 77, has a shaft portion 81 that is inserted through a through hole 751 in the top plate portion 75 screwed into a screw hole 821 in the connecting member 80, which is positioned between the top plate portion 75 and the intermediate frame 77. The connecting member 80 is positioned between the top plate portion 75 and the tunnel upper portion 52, in contact with the upper surface of the top plate portion 75 and the lower surface of the tunnel upper portion 52 (see Figures 5, 6, and 7). Fastening bolts V are then fastened to the connecting member 80 positioned between the top plate portion 75 and the tunnel upper portion 52 from the inside of the vehicle, by passing through cross member through holes 261, 361, and 461 provided in the straddling portions 21, 31, and 41 of the front cross member 20, intermediate cross member 30, and rear cross member 40 that straddle the tunnel portion 5, and through holes 53 provided in the tunnel upper portion 52 of the tunnel portion 5 (see Figures 5, 6, and 7).

[0092] In this manner, the connecting member 80 positioned between the top plate portion 75 and the intermediate frame 77, and the connecting member 80 positioned between the top plate portion 75 and the upper part of the tunnel 52, connect the tunnel portion 5, the floor cross member 6, and the battery unit 7 in the lower body structure of the vehicle 1 by fastening fastening bolts V.

[0093] Thus, in the lower body structure of vehicle 1, as shown in Figure 7, a plurality of connecting members 80 are arranged in the longitudinal direction of the vehicle between the top plate portion 75 and the upper part of the tunnel 52 so as to correspond to the positions of through holes 53 which are provided at predetermined intervals in the longitudinal direction of the vehicle. These connecting members 80 are connected to the tunnel portion 5 and the floor cross member 6, with the upper end surface of the connecting member 80 in contact with the lower surface of the upper part of the tunnel 52 and the lower end surface of the connecting member 80 in contact with the upper surface of the top plate portion 75, with the battery unit 7 which houses and holds the battery module 71 inside the housing 72.

[0094] Furthermore, the battery unit 7, which is connected to the pair of left and right side sills 3 that are structural members of the vehicle body 1, is fixed to each other, and the front cross member 20, intermediate cross member 30, and rear cross member 40 that connect the pair of left and right side sills 3 across the tunnel section 5 are connected and fixed to the tunnel section 5 at the upper part 52 of the tunnel section 5, which is the central part in the width direction of the vehicle. As a result, the rigidity of the vehicle body 1 is improved in the lower body structure of the vehicle 1.

[0095] Thus, the lower body structure of the vehicle 1 comprises a pair of left and right side sills 3 extending in the longitudinal direction of the vehicle at both ends in the vehicle width direction of the front floor panel 4, and a plurality of floor cross members 6 that connect the pair of left and right side sills 3 in the vehicle width direction and are fixed to the upper surface of the front floor panel 4. The floor cross members 6 include a front cross member 20 provided at the front of the vehicle, a rear cross member 40 provided at a predetermined distance from the front cross member 20 at the rear of the vehicle, and an intermediate cross member 30 provided between the front cross member 20 and the rear cross member 40 in the longitudinal direction of the vehicle and fixed to the front cross member 20 and the rear cross member 40, respectively.

[0096] As a result, the lower body structure of vehicle 1 can efficiently transmit side impact loads from one side sill 3 to the other side sill 3 in the vehicle width direction. More specifically, a pair of left and right side sills 3 extending in the longitudinal direction of the vehicle are connected in the vehicle width direction at both ends of the front floor panel 4 in the vehicle width direction, and a front cross member 20, a rear cross member 40, and an intermediate cross member 30 are provided fixed to the upper surface of the front floor panel 4. The intermediate cross member 30 is fixed to the front cross member 20 and the rear cross member 40, respectively. As a result, the front cross member 20, intermediate cross member 30, and rear cross member 40, which are fixed to each other, can work together with the front floor panel 4 to improve the rigidity of the vehicle body against side impact loads, which are collision loads from the side of the vehicle. Therefore, the lower body structure of the vehicle 1 can efficiently transmit side impact loads, such as those caused by a narrow object such as a utility pole colliding with the side of the vehicle, from one side sill 3 to the other side sill 3.

[0097] In this way, the lower body structure of vehicle 1, with its front cross member 20 and rear cross member 40, the intermediate cross member 30 fixed to the front cross member 20 and rear cross member 40 respectively, and the front floor panel 4 working together to improve the rigidity of the vehicle body, and efficiently transmits side impact loads from one side sill 3 to the other side sill 3 in the vehicle width direction. Therefore, the lower body structure of vehicle 1 can suppress deformation of the side sills 3, floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40), front floor panel 4, etc., due to side impact loads caused by a narrow collision object hitting the side of the vehicle.

[0098] Furthermore, the front cross member 20 is provided with a front inner seat bracket 211 and a front outer seat bracket 221 for attaching the front side of the front seat in the vehicle 1, and the rear cross member 40 is provided with a rear inner seat bracket 411 and a rear outer seat bracket 421 for attaching the rear side of the front seat.

[0099] As a result, the lower body structure of vehicle 1 can efficiently transmit side impact loads from one side sill 3 to the other side sill 3 at a position close to the center of gravity of vehicle 1. More specifically, the center of gravity of vehicle 1 is generally set close to the front seats in the longitudinal direction of the vehicle. Between the front cross member 20, which is equipped with front inner seat brackets 211 and front outer seat brackets 221 that attach to the front side of the front seats, and the rear cross member 40, which is equipped with rear inner seat brackets 411 and rear outer seat brackets 421 that attach to the rear side of the front seats, an intermediate cross member 30 is positioned and fixed to each of them. As a result, the lower body structure of vehicle 1 can improve the rigidity of the vehicle body close to the center of gravity of vehicle 1, and thus can efficiently transmit side impact loads from one side sill 3 to the other side sill 3 in a position close to the center of gravity of vehicle 1.

[0100] Specifically, if a narrow object collides with the side of vehicle 1, deviating from the vehicle's center of gravity, the vehicle body rotates around the vehicle's center of gravity, thus distributing the side impact load. In contrast, if a narrow object collides with the side of vehicle 1, directed towards the vehicle's center of gravity, the side impact load is concentrated on the vehicle body without being distributed.

[0101] In the lower body structure of vehicle 1, as described above, an intermediate cross member 30 is fixed to the front cross member 20 and the rear cross member 40, as well as to the front floor panel 4, between the front cross member 20, which is provided with a front inner seat bracket 211 and a front outer seat bracket 221 for attaching the front side of the front seats, and the rear cross member 40, which is provided with a rear inner seat bracket 411 and a rear outer seat bracket 421 for attaching the rear side of the front seats. Therefore, the intermediate cross member 30, positioned below the front seats, can improve rigidity at a position close to the center of gravity of vehicle 1. As a result, even if a narrow object collides with the side of the vehicle towards the center of gravity of vehicle 1, the concentrated side impact load applied to the vehicle body can be efficiently transmitted from one side sill 3 to the other side sill 3.

[0102] Furthermore, in the lower body structure of vehicle 1, an intermediate cross member 30, fixed to the front cross member 20 and the rear cross member 40 in the longitudinal direction of the vehicle, is positioned below the front seats. Therefore, even with the intermediate cross member 30, space can be secured in the footwell area of ​​the front seats.

[0103] Furthermore, since the floor cross members 6 (front cross member 20, intermediate cross member 30, and rear cross member 40) are configured with a roughly M-shaped cross section extending in the vehicle width direction, the rigidity of each floor cross member 6 (front cross member 20, intermediate cross member 30, and rear cross member 40) can be improved compared to when the cross members are configured with a hat-shaped cross section. Therefore, the lower body structure of the vehicle 1 can transmit side impact loads more efficiently from one side sill 3 to the other side sill 3.

[0104] Furthermore, a tunnel section 5 is formed at the center of the front floor panel 4 in the vehicle width direction, and the floor cross members 6 (front cross member 20, intermediate cross member 30, rear cross member 40) straddle the tunnel section 5 and connect the left and right pair of side sills 3 in the vehicle width direction.

[0105] In the lower body structure of vehicle 1 configured in this way, a floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) that straddles a tunnel section 5 extending in the longitudinal direction of the vehicle at the center of the vehicle width direction is connected to a pair of left and right side sills 3 in the vehicle width direction. Therefore, the lower body structure of vehicle 1 can reliably transmit side impact loads from one side sill 3 to the other side sill 3 compared to a pair of floor cross members 6 (front cross member 20, intermediate cross member 30, rear cross member 40) that connects a pair of left and right side sills 3 with the tunnel section 5 in between.

[0106] Furthermore, the tunnel section 5 has side wall sections 51 facing each other in the vehicle width direction, and the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) has front flange sections 23a, 33a, 43a extending forward of the vehicle and rear flange sections 23b, 33b, 43b extending rearward of the vehicle. The front flange sections 23a, 33a, 43a and the rear flange sections 23b, 33b, 43b are joined to the side wall sections 51.

[0107] As a result, the floor cross members 6 (front cross member 20, intermediate cross member 30, rear cross member 40) can form a closed cross section even at the side wall portion 51 of the tunnel section 5, thereby improving the rigidity of the tunnel section 5 and improving the rigidity of the floor cross members 6 (front cross member 20, intermediate cross member 30, rear cross member 40) that straddle the tunnel section 5. Therefore, the lower body structure of the vehicle 1 can suppress deformation of the tunnel section 5 and efficiently transmit side impact loads across the tunnel section 5 from one side sill 3 to the other side sill 3.

[0108] Furthermore, the rear flange portion 23b of the front cross member 20 is fixed by overlapping it with the upper part of the 33a of the intermediate cross member 30, and the rear flange portion 33b of the intermediate cross member 30 is fixed by overlapping it with the upper part of the front flange portion 43a of the rear cross member 40. This allows the front cross member 20, intermediate cross member 30, and rear cross member 40 to be easily attached to the front floor panel 4. Therefore, the efficiency of the fixing work for fixing the front cross member 20, intermediate cross member 30, and rear cross member 40 to the front floor panel 4 can be improved.

[0109] Furthermore, in the lower body structure of vehicle 1, the front inner seat bracket 211, front outer seat bracket 221, rear inner seat bracket 411, and rear outer seat bracket 421 are provided on the front cross member 20 and rear cross member 40, respectively, to which the front seats of vehicle 1 are attached. This prevents the front seats from being displaced downwards from the vehicle.

[0110] More specifically, the lower body structure of vehicle 1 supports the front cross member 20 with the intermediate cross member 30, and the intermediate cross member 30 with the rear cross member 40. Therefore, the downward displacement of the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) due to the upward displacement of the tunnel section 5 caused by a side impact load can be restricted. Consequently, the lower body structure of vehicle 1 can suppress the downward displacement of the front seats when the front inner seat bracket 211, front outer seat bracket 221, rear inner seat bracket 411, and rear outer seat bracket 421, to which the front seats of vehicle 1 are attached, are provided on the front cross member 20 and the rear cross member 40.

[0111] Furthermore, the side sill 3 and the floor cross member 6 (front cross member 20, middle cross member 30, rear cross member 40) are joined so that the upper surface of the side sill 3 and the upper surface of the floor cross member 6 (front cross member 20, middle cross member 30, rear cross member 40) are aligned in the vertical direction of the vehicle.

[0112] As a result, the ridge sections 3a and 20a, 30a, and 40a of the side sill 3 and floor cross member 6 (front cross member 20, intermediate cross member 30, and rear cross member 40), which are more rigid than other parts, are located at approximately the same position in the vertical direction of the vehicle, although their extension directions are approximately perpendicular in a plan view. In other words, the ridge sections 20a, 30a, and 40a of the floor cross member 6 (front cross member 20, intermediate cross member 30, and rear cross member 40) and the ridge section 3a of the side sill 3 are continuous. Therefore, the lower body structure of vehicle 1 can efficiently transmit side impact loads from one side sill 3 to the other side sill 3.

[0113] Furthermore, a battery unit 7 is located below the front floor panel 4, and a connecting member 80 is provided to fasten it to the battery unit 7 by fastening bolts V inserted from the upper surface of the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) which is superimposed on the tunnel section 5, thereby connecting the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) and the battery unit 7.

[0114] As a result, in the central part in the width direction of the vehicle, the upward displacement of the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) and the tunnel section 5 due to a side impact load is suppressed by the battery unit 7 connected via fastening bolts V and connecting members 80. Therefore, the lower body structure of the vehicle 1 can reliably transmit the side impact load from one side sill 3 to the other side sill 3.

[0115] Furthermore, the upper surfaces of the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) are provided with grooves 26, 36, and 46 that are recessed downwards and extend in the vehicle width direction. The length of the grooves 26, 36, and 46 in the tunnel section 5 in the vehicle longitudinal direction is longer than the length of the grooves 26, 36, and 46 in the vehicle longitudinal direction at other locations.

[0116] This ensures a seating surface for fixing the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) to the battery unit 7, and also improves the rigidity of the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40). As a result, the lower body structure of the vehicle 1 can reliably fix the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) to the battery unit 7, and further suppresses upward displacement and deformation of the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40).

[0117] In the correspondence between the structure of this invention and the embodiments described above, the floor panel of this invention corresponds to the front floor panel 4 of the embodiment, and similarly, hereinafter, The cross member corresponds to the floor cross member 6. The first cross member corresponds to the front cross member 20, The second cross member corresponds to the rear cross member 40. The third cross member corresponds to the intermediate cross member 30, The front mounting section corresponds to the front inner seat bracket 211 and the front outer seat bracket 221. The rear mounting section corresponds to the rear inner seat bracket 411 and the rear outer seat bracket 421. The front flange portion corresponds to the front flange portions 23a, 33a, and 43a. The rear flange section corresponds to the rear flange sections 23b, 33b, and 43b. The fastening member corresponds to the fastening bolt V, The connecting portion corresponds to the connecting member 80, but this invention is not limited to the configuration of the above-described embodiment, and many embodiments can be obtained.

[0118] For example, the floor cross members 6 (front cross member 20, intermediate cross member 30, rear cross member 40) have an open cross-sectional shape that forms a closed cross-section with the front floor panel 4, but are not limited to this. The floor cross members 6 (front cross member 20, intermediate cross member 30, rear cross member 40) may also be joined to the front floor panel 4 with a closed cross-sectional shape such as a cylindrical body.

[0119] Furthermore, the side sill 3 and the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) are indirectly joined to the upper surface of the side sill 3 and the upper surface of the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40), which are at approximately the same height, via the front outer seat bracket 221, gusset 321, and rear outer seat bracket 421. However, this configuration is not limited to this one, as long as the ridge portion 3a and the ridge portions 20a, 30a, and 40a are continuous.

[0120] For example, the side sill 3 and the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) may be joined so that the upper surface of the side sill 3 and the upper surface of the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) are aligned in the vehicle width direction. Alternatively, the floor cross member 6 (front cross member 20, intermediate cross member 30, rear cross member 40) may be positioned so that a portion of its upper surface overlaps the upper surface of the side sill 3, and the side sill 3 and the floor cross member 6 may be joined directly or indirectly at the overlapping portion.

[0121] Furthermore, if the upper surface of the side sill 3 is an inclined surface that slopes in the vertical direction of the vehicle with respect to the vehicle width direction, the upper surfaces of the floor cross members 6 (front cross member 20, intermediate cross member 30, rear cross member 40) may be directly or indirectly joined so that they are positioned in the vertical direction of the vehicle within the range from the upper end to the lower end of the inclined upper surface of the side sill 3. [Explanation of Symbols]

[0122] 1…Vehicle 3... Side sill 4…Front floor panel 5...Tunnel section 6…Floor cross member 7…Battery unit 20…Front cross member 26… recessed groove 30…Intermediate cross member 36…Diamond groove 40...Rear cross member 46…Diamond groove 51... Side wall section 80…Connecting member 211…Front inner seat bracket 221…Front outer seat bracket 411... Rear inner seat bracket 421... Rear outer seat bracket 23a...Front flange section 23b...Rear flange section 33b...Rear flange section 33a...Front flange section 43a...Front flange section 43b...Rear flange section V... Fastening bolt

Claims

1. A pair of left and right side sills extending in the front-to-rear direction of the vehicle are located at both ends of the floor panel in the vehicle width direction, The left and right side sills are connected in the vehicle width direction, and the system includes a plurality of cross members fixed to the upper surface of the floor panel, The aforementioned cross member is The first cross member located at the front of the vehicle, A second cross member is provided at a predetermined distance from the first cross member at the rear of the vehicle, The vehicle has a third cross member provided between the first cross member and the second cross member in the longitudinal direction of the vehicle, and fixed to each of the first and second cross members. The lower body structure of the vehicle.

2. The first cross member is provided with a front mounting portion for attaching the front side of the front seat in the vehicle. The second cross member is provided with a rear mounting portion for attaching the rear side of the front seat. The lower body structure of the vehicle according to claim 1.

3. The cross member is configured to have a roughly M-shaped cross-section that extends in the vehicle width direction. The lower body structure of a vehicle according to claim 1 or claim 2.

4. At the center of the floor panel in the vehicle width direction, a tunnel portion is formed that protrudes upward. The cross member spans the tunnel section and connects the left and right pair of side sills in the vehicle width direction. The lower body structure of a vehicle according to claim 1 or claim 2.

5. The tunnel section has side walls facing each other in the vehicle width direction, The cross member comprises a front flange portion extending forward of the vehicle and a rear flange portion extending rearward of the vehicle. The front flange portion and the rear flange portion are joined to the side wall portion. The lower body structure of the vehicle according to claim 4.

6. The rear flange portion of the first cross member is superimposed and fixed on the front flange portion of the third cross member. The rear flange portion of the third cross member is fixed in place by overlapping it with the front flange portion of the second cross member. The lower body structure of a vehicle according to claim 5.

7. The side sill and the cross member are, The upper surface of the side sill and the upper surface of the cross member are joined together so that their positions are aligned in the vertical direction of the vehicle. The lower body structure of a vehicle according to claim 1 or claim 2.

8. A battery unit is provided below the floor panel. A connecting portion is provided that fastens with a fastening member inserted from the upper surface of the cross member, which is superimposed on the tunnel portion, thereby connecting the cross member and the battery unit. The lower body structure of the vehicle according to claim 4.

9. The upper surface of the cross member is provided with a groove that is recessed downward and extends in the direction of the vehicle width. The length of the groove in the tunnel section in the vehicle longitudinal direction is longer than the length of the groove in other locations in the vehicle longitudinal direction. The lower body structure of a vehicle according to claim 8.

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