Vehicle body lower structure for electric vehicle

Abstract

A vehicle body lower structure 1 for an electric vehicle according to the present invention includes a pair of left and right side sills 10, a battery pack 20 in which a battery frame 23 is located on the outer peripheral side in the vehicle body width direction, and a floor cross member 30. The vehicle body lower structure 1 also has a battery mount 40 of which the cross section orthogonal to the vehicle body width direction is of a closed cross-sectional shape, an end part 40a on the vehicle inner side is connected to the lower surface of the battery frame 23, and an end part 40b on the vehicle outer side is connected to the lower surface of the side sill 10. The battery mount 40 has a closed cross-sectional shape part 41 having a closed cross-sectional shape, and a partition plate 43 that is provided in the central region of the closed cross-sectional shape part 41 and that forms a partition between the inner and outer sides of the vehicle. The closed cross-sectional shape part 41 is fabricated using a metal plate of lower tensile strength than the battery frame 23.

Description

Electric vehicle underbody structure

[0001] The present invention relates to an underbody structure for an electric vehicle in which a battery pack is mounted in a floor portion under the vehicle body.

[0002] In recent years, particularly in the automotive industry, environmental concerns have led to a shift from internal combustion engine vehicles to electric vehicles. Electric vehicles are equipped with a battery pack containing large batteries in the floor area under the vehicle body. Since batteries often use lithium-based materials, there is a risk of fire if the battery pack is damaged in a collision and leaks from the battery inside. Therefore, a structure that can protect the battery pack when mounted on the vehicle body is required.

[0003] Many structures for mounting a battery pack under the body of an electric vehicle or the like have been proposed. For example, Patent Document 1 discloses a structure in which a cross member extending in the vehicle width direction is attached to the lower part of a frame that forms the skeleton of a battery case that houses a tray (corresponding to the "battery pack" in this application) that houses a battery. Patent Document 2 discloses a structure in which a battery unit (corresponding to the "battery pack" in this application) including a lower case that houses a battery module is mounted on the underside of a floor panel by a cross member fixed to the underside of the lower case and side members that fix both ends of the cross member. Furthermore, Patent Document 3 discloses a structure in which an energy-absorbing member is fixed to a locker (corresponding to the "side sill" in this application) located on the outer side of the battery pack located below the floor panel in the vehicle width direction and that secures the battery pack to the vehicle body.

[0004] JP 2022-42851 A Japanese Patent No. 6197363 A Japanese Patent No. 2023-146163 A

[0005] In the structures of Patent Documents 1 to 3, the battery pack is mounted under the vehicle body by being supported by components provided below the battery pack (the cross member in Patent Document 1, the cross member in Patent Document 2, and the support section in Patent Document 3). Therefore, even if an attempt is made to increase the battery capacity in order to extend the driving range, the battery cannot be extended toward the ground side (below the vehicle body).

[0006] Furthermore, the structure of Patent Document 3 absorbs crash energy by compressive deformation of the energy absorbing material during a side collision of the vehicle, thereby reducing the load transmitted to the battery pack. However, if the energy absorbing material of Patent Document 3 begins to compressively deform before the side sill is fully crushed during a side collision, the side sill may not be crushed and may not be able to fully absorb the crash energy, thereby failing to reduce the load transmitted to the battery pack and resulting in insufficient crashworthiness. Furthermore, the energy absorbing material has a complex cross-section as a structure and is heavy, which may increase the weight of the vehicle body.

[0007] The present invention has been made to solve the above-mentioned problems, and its purpose is to provide an underbody structure for an electric vehicle that can mount a battery pack that allows the battery to be extended downward toward the vehicle body while ensuring sufficient collision performance in a side collision of the vehicle.

[0008] The underbody structure of an electric vehicle according to the present invention comprises a pair of left and right side sills disposed on the outer sides of the vehicle in the width direction of the vehicle and extending in the front-rear direction of the vehicle, a battery pack disposed between the pair of left and right side sills and having a battery frame disposed on the outer periphery in the width direction of the vehicle, and a floor cross member disposed on the upper surface of a floor panel disposed above the battery pack and extending in the width direction of the vehicle, the cross section perpendicular to the width direction of the vehicle being a closed cross section, and the floor cross member comprises a battery mount whose inner end is connected to the underside of the battery frame and whose outer end is connected to the underside of the side sill, and the floor cross member has a groove shape that is open to the lower side of the vehicle. The battery mount has a closed cross-sectional shape (a metal plate) with both ends abutting against the side surfaces of the left and right side sills, and the battery mount has a closed cross-sectional shape portion that forms the closed cross-sectional shape, and a partition plate that is provided within the closed cross-sectional shape portion so as to connect the upper surface and the lower surface and that separates the vehicle into an inside side and an outside side, and the closed cross-sectional shape portion is made of a metal plate that has a lower tensile strength than the battery frame.

[0009] Preferably, both ends of the groove shape in the floor cross member are open.

[0010] The vehicle may have a groove-shaped under-floor cross member that is installed between the floor panel and the battery pack, extends in the vehicle width direction, and has both ends abutting against the side surfaces of the left and right side sills.

[0011] The floor cross member may have a cross-sectional shape perpendicular to the vehicle body width direction that is substantially constant along the vehicle body width direction.

[0012] The battery mount may be made of three or more metal plates.

[0013] The under-floor cross member may comprise a continuous hat-shaped cross section member having at least three consecutive hat-shaped cross sections in a cross section perpendicular to the vehicle width direction, an upper metal plate covering the upper surface of the continuous hat-shaped cross section member, and a lower metal plate covering the lower surface of the continuous hat-shaped cross section member.

[0014] The under-floor cross member may be linear, and the cross-sectional shape perpendicular to the vehicle body width direction may be substantially constant along the vehicle body width direction.

[0015] The under-floor cross member may be linear, and the groove depth of the groove shape may be deeper toward the end on the vehicle outer side than the battery pack.

[0016] The side sill and the floor cross member are preferably made using steel plate with a tensile strength of 980 MPa or higher, and at least the closed cross-sectional shape portion of the battery mount is preferably made using steel plate with a tensile strength of 590 MPa or higher.

[0017] The under-floor cross member is preferably made of steel plate having a tensile strength of 980 MPa or higher.

[0018] According to the present invention, a battery pack can be mounted so that the battery can be expanded downward toward the vehicle body while ensuring sufficient crash performance in the event of a side collision.

[0019] FIG. 1 is a cross-sectional view showing the configuration of an underbody structure of an electric vehicle according to an embodiment of the present invention. FIG. 2 is a perspective view showing the shape of the tip of a floor cross member in an embodiment and an example of the present invention ((a) an open tip shape, (b) an open tip shape with an inwardly bent curved portion, and (c) a closed tip shape). FIG. 3 is a diagram showing a specific structure of a battery mount in an underbody structure according to an embodiment of the present invention. FIG. 4 is a cross-sectional view showing the configuration of an underbody structure according to another embodiment of the present invention. FIG. 5 is a diagram (part 1) showing an underfloor cross member of an underbody structure according to another embodiment of the present invention. FIG. 6 is a diagram (part 2) showing an underfloor cross member of an underbody structure according to another embodiment of the present invention. FIG. 7 is a diagram illustrating the groove depth of an underbody structure according to another embodiment of the present invention and an underfloor cross member. FIG. 8 is a diagram illustrating a crash analysis of a pole side impact test in an example. FIG. 9 is a diagram showing the underbody structure of an electric vehicle that was analyzed in a pole side impact test as a reference example in an example. FIG. 10 shows the position in the vehicle longitudinal direction (TL) at which the pole impacts the side of the vehicle in a side pole impact test of the examples ((a) TL = 520 mm (No. 1), (b) TL = 905 mm (No. 2), (c) TL = 1080 mm (No. 3), (d) TL = 1260 mm (No. 4), (e) TL = 1605 mm (No. 5)). FIG. 11 shows evaluation items for side impact performance in the examples ((a) input load to the battery pack, (b) amount of deformation of the battery pack). FIG. 12 shows deformation of the vehicle underbody structure of Example 1 in a pole side impact test in the examples ((a) cross-sectional view of the vehicle underbody structure at the start of the impact, (b) cross-sectional view of the vehicle underbody structure after the impact, (c) enlarged cross-sectional view of the side sill and its surroundings in the vehicle underbody structure after the impact). Figure 13 shows the deformation of the vehicle underbody structure of Example 2 in a pole side impact test in the examples ((a) cross-sectional view of the vehicle underbody structure at the start of the impact, (b) cross-sectional view of the vehicle underbody structure after the impact, (c) enlarged cross-sectional view of the side sill and its surroundings in the vehicle underbody structure after the impact).FIG. 14 is a diagram showing deformation of a vehicle underbody structure according to a reference example in a pole side collision test in an example ((a) cross-sectional view of the vehicle underbody structure at the start of the collision, (b) cross-sectional view of the vehicle underbody structure after the collision, and (c) enlarged cross-sectional view of the side sill and its surroundings in the vehicle underbody structure after the collision). FIG. 15 is a diagram showing the time history of deformation of a battery mound of a vehicle underbody structure according to Example 2 in a pole side collision test in an example ((a) start of the collision, (b) to (e) during the collision, (f) end of the collision). FIG. 16 is a graph showing the results of input loads to a battery pack determined by collision analysis of a pole side collision test in an example. FIG. 17 is a graph showing the results of deformation of a battery pack determined by collision analysis of a pole side collision test in an example.

[0020] An underbody structure 1 for an electric vehicle according to an embodiment of the present invention (hereinafter simply referred to as "underbody structure 1") includes a side sill 10, a battery pack 20, a floor cross member 30, and a battery mount 40, as shown as an example in FIG. 1. The underbody structure 1 according to this embodiment will be described below with reference to FIGS. 1 to 7. In the specification and drawings of this application, elements having substantially the same functions and configurations are designated by the same reference numerals, and redundant explanations are omitted or simplified. Furthermore, dimensions and other specific numerical values ​​shown in the specification and drawings are merely examples to facilitate understanding of the present invention and do not limit the present invention.

[0021] <Side Sills> The side sills 10 are a pair of left and right side sills arranged on the outer side of the vehicle in the vehicle width direction and extending in the fore-and-aft direction of the vehicle, and as shown in FIG. 1 , have a side sill inner 11 and a side sill outer 13.

[0022] The side sill inner 11 has a hat-shaped cross section that opens toward the outside of the vehicle in the vehicle width direction, and has a top plate portion 11a, a pair of vertical wall portions 11b extending from each of the upper and lower edges of the top plate portion 11a, and flange portions extending from each vertical wall portion 11b.

[0023] The side sill outer 13 has a hat-shaped cross section that opens toward the inside of the vehicle in the vehicle width direction, and has flange portions at each end on the upper and lower sides of the vehicle.

[0024] The side sill 10 has a flange portion of the side sill inner 11 joined to a flange portion of the side sill outer 13 at the upper side of the vehicle body, and a flange portion of the side sill inner 11 joined to a flange portion of the side sill outer 13 at the lower side of the vehicle body. As a result, the side sill inner 11 and the side sill outer 13 form a closed cross-sectional structure in the side sill 10.

[0025] <Battery Pack> As shown in FIG. 1 , the battery pack 20 houses battery cells 21 therein and is disposed between a pair of left and right side sills 10, with a battery frame 23 provided on the outer periphery in the vehicle body width direction.

[0026] In this embodiment, as shown in FIG. 1, the battery frame 23 has a substantially rectangular closed cross section perpendicular to the longitudinal direction of the vehicle body, and is joined to the side surface of the battery pack 20 in the vehicle width direction.

[0027] 1, the floor cross member 30 is provided for fastening a front seat (not shown), and is installed on the upper surface of a floor panel 31 that is installed above the battery pack 20, extending in the vehicle width direction. The floor cross member 30 has a linear groove shape that is open toward the lower side of the vehicle body, and both ends 30a abut against the side surfaces of the left and right side sills 10 (top plate portions 11a of the left and right side sill inner panels 11).

[0028] In the vehicle body understructure 1 according to this embodiment, three floor cross members 30 are provided at intervals in the fore-and-aft direction of the vehicle body. Both ends 30a of the groove shape of each floor cross member 30 are open, as shown in Fig. 2(a). The ends 30a may have an open shape, and may have rounded portions 30d bent inward from each end of a bottom portion 30b and a pair of wall portions 30c that form the groove shape, as shown in Fig. 2(b).

[0029] <Battery Mount> As shown in FIG. 1 , the battery mount 40 has a closed cross section perpendicular to the vehicle body width direction, with an end 40 a on the vehicle interior side connected to the underside of the battery frame 23 and an end 40 b on the vehicle exterior side connected to the underside of the side sill (the vertical wall portion 11 b on the vehicle body lower side of the side sill inner 11) (see FIG. 3( a) described later).

[0030] In this embodiment, as shown in FIG. 1, the battery mount 40 has an inner end 40a fastened to the vertical wall portion 11b of the side sill inner 11 on the lower side of the vehicle body by a fastening bolt 45, and an outer end 40b fastened to the underside of the battery frame 23 by a fastening bolt 47.

[0031] The battery mount 40 has a closed cross-sectional portion 41 that forms a closed cross-sectional shape, and a partition plate 43 that is provided in the center of the closed cross-sectional portion 41 in the vehicle width direction so as to connect the upper and lower surfaces and separate the battery mount 40 into an inside and outside of the vehicle. As the partition plate 43 is provided in the center of the closed cross-sectional portion 41, the battery mount 40 has a square-shaped cross-section in a cross section perpendicular to the fore-and-aft direction of the vehicle.

[0032] Furthermore, the closed cross-sectional portion 41 of the battery mount 40 is made using a metal plate having a lower tensile strength than the battery frame 23 .

[0033] 3A and 3B are diagrams showing an example of the specific structure of the battery mount 40, where FIG. 3A is an enlarged view of the battery mount 40 and its surroundings in the vehicle body lower structure 1, and FIG. 3B is a diagram showing a schematic view of the configuration of the battery mount 40.

[0034] The battery mount 40 is made of three steel plate parts: a steel plate part 41a, a steel plate part 41b, and a steel plate partition plate 43, which form the closed cross-sectional shape portion 41, and the parts are joined by spot welding at the areas surrounded by the dashed ovals in Figure 3(b).

[0035] In the vehicle underbody structure 1 according to this embodiment, the reason why deformation can be suppressed and the battery pack 20 can be protected by reducing the load input to the battery pack 20 will be explained below.

[0036] In the vehicle body underbody structure 1, the tip 30a of the floor cross member 30 abuts against the side surface of the side sill 10 (the top plate portion 11a of the side sill inner 11). As a result, when the side sill 10 deforms during a side collision and a load is input to the tip 30a of the floor cross member 30, the reaction force crushes the upper part of the side sill 10.

[0037] The closed cross-sectional portion 41 of the battery mount 40 has a partition plate 43 provided therein, and is made of a metal plate having a lower tensile strength than the battery frame 23 .

[0038] Therefore, the battery mount 40 resists the load that attempts to crush the side sill 10 during a side collision by maintaining the partition plate 43 in a closed cross-sectional shape, and is able to sufficiently increase the amount of collision energy absorbed by the side sill 10 and the battery mount 40 without being too tense or deforming too much.

[0039] Furthermore, since the vehicle body understructure 1 does not have a cross member that supports the battery pack 20 from below, as in the aforementioned Patent Documents 1 and 2, it is possible to extend the battery downward toward the vehicle body.

[0040] As described above, the vehicle body understructure 1 according to this embodiment can mount a battery pack that allows the battery to be extended downward toward the vehicle body while ensuring sufficient collision performance in the event of a side collision.

[0041] In the present invention, it is preferable that the cross-sectional shape of the floor cross member 30 perpendicular to the vehicle width direction is approximately constant along the vehicle width direction. An approximately constant cross-sectional shape means that the variation in the average groove depth of the floor cross member 30 in the vehicle width direction is within ±10%.

[0042] In this way, the cross-sectional shape of the floor cross member 30 is a straight line with little undulation that curves in the vehicle width direction and is generally constant along the vehicle width direction, making the floor cross member 30 less likely to bend (buckle) during a side collision. This allows the side sill 10 to be sufficiently crushed, resulting in high collision energy absorption.

[0043] In the above description, the tip 30a of the floor cross member 30 abuts against the top plate portion 11a of the side sill inner panel 11. However, in order to improve the vehicle body rigidity, the tip of the floor cross member 30 and the top plate portion 11a of the side sill inner panel 11 may be joined by a bracket or the like.

[0044] Furthermore, the floor cross member 30 of the vehicle body understructure 1 according to this embodiment does not have a groove-shaped closed tip 30e like the floor cross member 30' shown in Figure 2(c), but has an open tip 30a as shown in Figures 2(a) and 2(b). This ensures formability when producing the floor cross member 30 by press molding, and also enables weight reduction without compromising crash performance in the event of a side collision.

[0045] Furthermore, the cross-sectional shape of the floor cross member 30 perpendicular to the vehicle width direction is substantially constant along the vehicle width direction, which is not only convenient for mounting seats inside the vehicle cabin, but also has the effect of absorbing collision energy during a side collision and suppressing deformation toward the interior of the vehicle, thereby providing sufficient protection for not only the battery pack 20 but also the occupants.

[0046] The partition plate 43 on the battery mount 40 is preferably positioned in the range from the top plate portion 11a of the side sill inner 11 to the battery frame 23 in the width direction of the vehicle body so that it can maintain a closed cross-sectional shape without being crushed or opened in the vertical direction of the vehicle body.

[0047] Furthermore, battery mount 40 is not manufactured using a casting or extrusion material in which closed cross-sectional portion 41 and partition plate 43 are integrated, but is formed using three or more steel plate components. This allows the material strength, plate thickness, and welding method (number of welding spots) of each steel plate component (steel plate component 41a, steel plate component 41b, partition plate 43) that makes up battery mount 40 to be selected, and adjustments can be made to prevent excessive tension and deformation in response to the load input during a side collision of the vehicle.

[0048] Although the battery mount 40 shown in Fig. 3(b) is made of three steel plate parts, the battery mount may be made of four or more steel plate parts (for example, a closed cross-sectional portion formed of three steel plate parts).

[0049] Furthermore, because the battery mount 40 extends in the fore-and-aft direction of the vehicle body, collision performance can be ensured regardless of the position to which the collision load is input during a side collision. This provides an advantageous effect in meeting the "anywhere" requirements for protecting the battery regardless of the collision position. Furthermore, because the battery mount 40 extends in the fore-and-aft direction of the vehicle body, it can be expected to protect the battery pack 20 even during a frontal collision of the vehicle.

[0050] The closed cross-sectional shape of the battery mount 40 does not need to be substantially constant along the vehicle width direction. To reduce weight, the height of the battery mount 40 may decrease toward the outermost end of the battery mount 40 in the vehicle width direction, as shown in FIG. 1 . The decrease in height of the battery mount 40 toward the outermost end of the battery mount 40 in the vehicle width direction is preferably within a range of up to 33% compared to the center portion of the battery mount in the vehicle width direction. This prevents buckling at the battery mount's cross-sectional shape during a side collision and effectively absorbs collision energy. Furthermore, to increase the battery mount 40's resistance to side collisions, beads can be provided on the upper surface (41b1 in FIG. 3(a)) and lower surface (41a1 in FIG. 3(a)) of the battery mount 40 along the vehicle width direction. From the standpoints of effectiveness and formability, the bead height is preferably within 20% of the height of the center portion of the battery mount 40 in the vehicle width direction.

[0051] The present invention is not limited to the above-described vehicle body underbody structure 1, but may also be provided with an under-floor cross member 50, as in the vehicle body underbody structure 3 according to another embodiment shown in FIG.

[0052] <Under-floor cross member> The under-floor cross member 50 is arranged between the floor cross member 30 and the battery pack 20, and has a groove shape that extends linearly along the vehicle width direction, with both ends 50a abutting the side of the side sill 10 (the top plate portion 11a of the side sill inner 11).

[0053] Such an under-floor cross member 50 preferably has a groove shape that extends linearly along the vehicle width direction, and includes a continuous hat cross-sectional shape member 51, an upper metal plate 53, and a lower metal plate 55, as shown in FIG. 5 .

[0054] The continuous hat cross-sectional shape member 51 is a member formed so that three hat cross-sectional shapes are consecutively formed in a cross section perpendicular to the vehicle body width direction. The continuous hat cross-sectional shape member 51 has two hat cross-sectional shapes that open toward the upper side of the vehicle body and one hat cross-sectional shape that opens toward the lower side of the vehicle body between the two hat cross-sectional shapes, which are consecutively formed along the fore-and-aft direction of the vehicle body.

[0055] The upper metal plate 53 covers the upper surface of the continuous hat cross-sectional shaped member 51 and is provided so as to close the two hat cross-sectional openings that open toward the upper side of the vehicle body in the continuous hat cross-sectional shaped member 51. The upper metal plate 53 and the continuous hat cross-sectional shaped member 51 may be connected by one-side welding or bolts.

[0056] The lower metal plate 55 covers the underside of the continuous hat cross-section member 51 and is provided so as to connect the two hat cross-sectional top plate portions on the lower side of the vehicle body of the continuous hat cross-section member 51. The lower metal plate 55 and the continuous hat cross-section member 51 are preferably connected by spot welding.

[0057] In this way, the underfloor cross member 50 has a structure in which the continuous hat cross section shaped member 51 is sandwiched between the upper metal plate 53 and the lower metal plate 55, thereby increasing the bending rigidity against a side impact load and suppressing deformation of the underfloor cross member 50. This allows the underbody structure 3 to distribute and transmit the load input to the side of the underbody structure 3 during a side impact of the vehicle to the floor cross member 30 and the underfloor cross member 50, thereby further improving the protection performance of the battery pack 20.

[0058] The continuous hat cross-section member may have two outer hat cross-sections that open toward the bottom of the vehicle body and a central hat cross-section that opens toward the top of the vehicle body. In this case, the upper metal plate may be arranged to connect the top plates of the two outer hat cross-sections of the continuous hat cross-section member, thereby covering the top surface of the continuous hat cross-section member. The lower metal plate may be arranged to close the openings of the two outer hat cross-sections of the continuous hat cross-section member, thereby covering the bottom surface of the continuous hat cross-section member.

[0059] 5 is formed so that three hat cross sections are consecutively arranged. However, in the present invention, when an under-floor cross member is formed using a continuous hat cross section member, an upper metal plate, and a lower metal plate, the number of hat cross sections of the continuous hat cross section member is not limited to three, as long as it is three or more.

[0060] 4A and 4B, the under-floor cross member 50 may be linear and have a cross-sectional shape perpendicular to the vehicle width direction that is substantially constant along the vehicle width direction. This makes the under-floor cross member 50 less susceptible to folding deformation (buckling deformation) during a side collision, allowing the upper part of the side sill 10 to be sufficiently crushed, thereby achieving high collision energy absorption.

[0061] 4(c) and 6, the under-floor cross member 50 may be linear and have a groove depth that increases toward the tip on the vehicle outer side of the battery frame 23. This allows a wider area to be crushed on the side of the side sill 10 in the event of a side collision, thereby absorbing more of the collision energy.

[0062] As shown in Figure 7, the groove depth at the end 50b of the under-floor cross member 50 on the side sill 10 side is preferably no more than twice the groove depth at the central portion 50c, which has a constant cross-sectional shape (see Figures 7(b) and 7(c)). Figure 7(b) is a cross-sectional view of the central portion 50c in the vehicle width direction, and Figure 7(c) is a cross-sectional view of the end 50b in the vehicle width direction.

[0063] If the groove depth at the end 50b is more than twice that of the center, buckling is likely to occur due to the large shape change at the portion where the groove depth becomes deeper on the vehicle outer side than the battery pack 20. Therefore, when a load is input during a side collision, this portion may buckle, and the side sill 10 may not be sufficiently crushed. Therefore, it is recommended to set the bending radius at the position where the groove depth changes from a constant portion to about R30 to 60 to prevent abrupt bending.

[0064] In the present invention, both the side sills and floor cross members are preferably made using steel plates with a tensile strength of 980 MPa or higher. Examples of steel plates with a tensile strength of 980 MPa or higher include steel plates of 980 MPa, 1180 MPa, 1370 MPa, 1470 MPa, 1760 MPa, and 1960 MPa. Similarly to the side sills and floor cross members, the under-floor cross members are preferably made using steel plates with a tensile strength of 980 MPa or higher.

[0065] Furthermore, as mentioned above, the closed cross-sectional portion of the battery mount is made of a metal plate with a lower tensile strength than the side sill and floor cross member. Because the side sill and floor cross member are preferably made of steel plate with a tensile strength of 980 MPa or higher, the closed cross-sectional portion of the battery mount is preferably made of steel plate with a tensile strength of at least 590 MPa.

[0066] The partition plate of the battery mount does not necessarily have to be a metal plate with the same tensile strength as the closed cross-sectional shape portion; it is preferable to appropriately select a metal plate with a tensile strength that makes it difficult for the closed cross-sectional shape portion to be crushed or opened up and down.

[0067] Furthermore, since the battery frame reinforces and protects the battery pack against loads input during a side collision, it is preferable to fabricate it using a metal plate with high tensile strength (for example, a steel plate of 1180 MPa class or higher).

[0068] In the vehicle body underbody structure of the present invention, the locations and number of floor cross members can be appropriately set so that the collision load can be absorbed regardless of the location at which the collision load is input to the side of the electric vehicle, thereby more effectively protecting the battery pack.

[0069] The locations and number of under-floor cross members can be determined appropriately, just as with the floor cross members. Preferably, the under-floor cross members should be installed in positions that overlap the floor cross members in the fore-and-aft direction of the vehicle (see Figures 5 and 6). This allows the collision load to be efficiently distributed to the floor cross members and under-floor cross members, further improving the protection performance of the battery pack.

[0070] A specific analysis was carried out to verify the effects of the underbody structure for an electric vehicle according to the present invention, and the results will be described below.

[0071] In this example, as shown in Fig. 8, a collision analysis was performed on a pole side collision test in which a pole 103 was collided with the side of a vehicle 101 equipped with the above-described vehicle body underbody structure 1 (Fig. 1) or vehicle body underbody structure 3 (Fig. 4). In the collision analysis, the vehicle 101 was accelerated to 32 km / h, and the pole 103 was collided with the side of the vehicle 101 at a collision angle of 75°.

[0072] The vehicle underbody structure 1 includes a side sill 10, a battery pack 20, a floor cross member 30, and a battery mount 40 (Example 1). The vehicle underbody structure 3 includes the vehicle underbody structure 1 of Example 1, and an under-floor cross member 50 (Examples 2 and 3).

[0073] The battery pack 20 has a battery frame 23 disposed on the outer periphery in the vehicle width direction. The battery frame 23 was made using a steel plate with a tensile strength of 1470 MPa.

[0074] The floor cross member 30 has a groove shape extending in the vehicle width direction, with both ends 30a open, and is in contact with the side surfaces of the left and right side sills 10 (top plate portions 11a of the side sill inner panels 11). Two floor cross members 30 are arranged in positions that allow them to efficiently receive a pole in a pole side collision test.

[0075] As shown in Fig. 3, the battery mount 40 was made of three steel plates and had a closed cross-sectional portion 41 formed by steel plate parts 41a and 41b, and a partition plate 43 provided in the center of the closed cross-sectional portion 41. Steel plates with a tensile strength of 1180 Ma, which is lower than that of the battery frame 23, were used for the closed cross-sectional portion 41 and the partition plate 43. The partition plate 43 was provided at the same position in the vehicle width direction as the top plate portion 11a of the side sill inner panel 11.

[0076] In the vehicle underbody structure 3, the underfloor cross-member 50 includes a continuous hat cross-sectional member 51, an upper metal plate 53, and a lower metal plate 55, as shown in Figures 5 and 6. Example 2 of the invention is an underbody structure 3 that includes an underfloor cross-member 50 with a constant groove depth toward the end on the vehicle outer side of the battery pack 20, and Example 3 of the invention is an underbody structure 3 that includes an underfloor cross-member 50 with a deeper groove depth as shown in Figure 7.

[0077] In the vehicle underbody structure 1 according to Example 1, the side sills 10 and floor cross members 30 were made of steel plates with a tensile strength of 980 MPa, and the battery mount 40 was made of steel plates with a tensile strength of 1180 MPa. In the vehicle underbody structures 3 according to Examples 2 and 3, the tensile strength of the steel plates used for the side sills 10, floor cross members 30, and battery mount 40 was the same as in Example 1, and the underfloor cross member 50 was made of steel plates with a tensile strength of 1470 MPa.

[0078] In this embodiment, the vehicle body understructure 5 is used as a reference example, in which a ground-side cross member 60 is provided below the battery pack 20, as shown in FIG.

[0079] 9(a), the ground-side cross member 60 in the reference example is installed on the underside of the battery pack 20 and has a groove shape extending in the vehicle width direction. The ground-side cross member 60 is linear and has a cross-sectional shape perpendicular to the vehicle width direction that is approximately constant along the vehicle width direction, and an end portion 60a is connected to the underside of the side sill 10 (the vertical wall portion 11b on the lower side of the side sill inner panel 11).

[0080] Furthermore, the ground-side cross member 60 of the reference example includes a continuous hat cross-sectional shaped member, an upper metal plate, and a lower metal plate, similar to the underfloor cross member 50 of invention example 2. In the vehicle body understructure 5 of the reference example, four ground-side cross members 60 are installed at equal intervals in the fore-and-aft direction of the vehicle body.

[0081] In the vehicle body substructure 5 of the reference example, the side sills 10, floor cross member 30 and battery mount 40 are made of steel plate with the same tensile strength as the vehicle body substructure 1, and the ground side cross member 60 is made of steel plate with the same tensile strength as the under-floor cross member 50 of the vehicle body substructure 3.

[0082] Electric vehicles are subject to strict anywhere requirements that require the battery pack 20 to be protected regardless of the collision position of the pole 103 on the side of the vehicle 101. Therefore, in this embodiment, as shown in Fig. 10, five locations, No. 1 to No. 5, in the vehicle longitudinal direction (TL) were set as collision positions of the pole 103 (No. 1: TL = 520 mm, No. 2: TL = 905 mm, No. 3: TL = 1080 mm, No. 4: TL = 1260 mm, No. 5: TL = 1605 mm).

[0083] Then, a collision analysis of a pole side collision was performed for each collision position No. 1 to No. 5, and the load input to the battery pack 20 (input load to the battery pack) and the amount of deformation of the battery pack 20 (amount of deformation of the battery pack) were evaluated.

[0084] The input load to the battery pack was the reaction force (contact reaction force) generated in the battery frame 23 due to contact with the side sill inner panel 11 during the collision process, as shown in FIG. 11(a).

[0085] Regarding the deformation amount of the battery pack, as shown in Fig. 11(b), the length of the battery pack 20 in the vehicle width direction was measured at 12 locations in the fore-and-aft direction of the vehicle before and after deformation, and the difference between the lengths before and after deformation was calculated. The minimum distance between the inner surface of the battery pack 20 and the battery cells 21 before deformation was 11 mm. Therefore, in this example, the target deformation amount of the battery pack 20 was set to less than 10 mm, as a condition for preventing contact between the battery pack 20 and the battery cells 21 during a side collision with a pole.

[0086] Figure 12 shows the state of the vehicle underbody structure 1 before and after deformation obtained by collision analysis of a pole side collision test in which a pole 103 is collided with the side of a vehicle 101 equipped with the vehicle underbody structure 1 of Example 1 at a position TL=905 mm in the vehicle fore-and-aft direction (No. 2 in Figure 10(b)) (before deformation: Figure 12(a) , after deformation: Figures 12(b) and (c)). Figures 12(a) to (c) are cross-sectional views of the vehicle underbody structure 1 at the collision position (TL=905 mm) of the pole 103, and Figure 12(c) is an enlarged view of the battery mount 40 and its surroundings in Figure 12(b) .

[0087] As shown in FIGS. 12(b) and 12(c), the side sill 10 is completely crushed, which indicates that the collision energy is sufficiently absorbed.

[0088] Figure 13 shows the state of the vehicle underbody structure 3 before and after deformation obtained by collision analysis of a pole side collision test in which a pole 103 is collided with the side of a vehicle 101 equipped with the vehicle underbody structure 3 of Example 2 at a position TL=905 mm in the vehicle fore-and-aft direction (Figure 10(b)) (before deformation: Figure 13(a) , after deformation: Figures 13(b) and (c) ). Figures 13(b) and (c) are cross-sectional views of the vehicle underbody structure 3 at the collision position of the pole 103 (TL=905 mm), and Figure 13(c) is an enlarged view of the battery mount 40 and its surroundings in Figure 13(b) .

[0089] As shown in FIGS. 13(b) and 13(c), the side sill 10 is completely crushed, which indicates that it has sufficiently absorbed the collision energy.

[0090] 14 shows the state of the underbody structure 5 before and after deformation obtained by collision analysis of a pole side collision test in which a pole 103 is collided with the side of a vehicle 101 equipped with the underbody structure 5 of the reference example at a position TL=905 mm in the vehicle fore-and-aft direction (FIG. 10(b)), before deformation: FIG. 14(a), after deformation: FIGS. 14(b) and 14(c)). FIGS. 14(b) and 14(c) are cross-sectional views of the underbody structure 3 at the collision position of the pole 103 (TL=905 mm), and FIG. 14(c) is an enlarged view of the joint between the side sill 10 and the ground-side cross member 60 and the surrounding area in FIG. 14(b).

[0091] As shown in FIGS. 14(b) and 14(c), the side sill 10 is completely crushed, which indicates that it has sufficiently absorbed the collision energy.

[0092] 15 shows the time history of deformation of the battery mount 40 obtained by crash analysis of a pole side collision test of a vehicle 101 equipped with the vehicle body underbody structure 5 of Example 2. It can be seen that the battery mount 40 has a partition plate 43 provided in the center of the closed cross-sectional shape portion 41, which prevents the closed cross-sectional shape from being crushed too much as the side sill 10 is crushed after the start of the collision (FIGS. 15(b) to 15(d)).

[0093] 16 and 17 show the evaluation results of the input load to the battery pack and the amount of deformation of the battery pack obtained for each position in the fore-and-aft direction of the vehicle where the pole 103 hits. The input load to the battery pack shown in FIG. 16 was greater for Examples 1 to 3 than for the reference example, which was equipped with a ground-side cross member 60. However, the load input to the battery pack 20 was able to be kept below 160 kN. Also, Examples 2 and 3, which were equipped with an under-floor cross member 50, tended to have lower loads. Furthermore, Example 3, in which the groove depth was increased toward the end 50b of the under-floor cross member 50, had a lower load than Example 2, in which the groove depth was constant, except for collision position No. 5.

[0094] The deformation of the battery pack shown in Figure 17 was greater in Examples 1 to 3 than in the reference example, which was equipped with a ground-side cross member 60. However, it was still less than the target of 10 mm at all collision positions. As mentioned above, the gap between the battery pack 20 and the battery cell 21 at the start of the collision was 11 mm. Therefore, the results shown in Figure 17 show that even when the side sill 10 was completely crushed, a gap remained between the battery pack 20 and the battery cell 21.

[0095] Table 1 shows the vehicle weights of Examples 1 to 3 and the Reference Example, and the weight reductions relative to the Reference Example.

[0096]

[0097] As shown in Table 1, the vehicle body understructure 1 according to Example 1 does not have a ground-side cross member 60 on the underside of the battery pack 20 like the vehicle body understructure 5 according to the reference example, and is therefore 33.8 kg lighter than the reference example. Also, the vehicle body understructures 3 according to Examples 2 and 3 do not have a ground-side cross member 60 like Example 1, but the inclusion of an under-floor cross member 50 resulted in an increase in weight of 8.9 kg (Example 2) and 9.4 kg (Example 3).

[0098] The anywhere requirement for an electric vehicle in a side collision with a pole is a very difficult condition, but the vehicle underbody structure of the present invention achieved the target amount of deformation of the battery pack regardless of the pole collision position.

[0099] The vehicle underbody structure 5 of the reference example has a ground-side cross member 60 below the battery pack 20, so the battery cells 21 cannot be extended toward the ground (under the vehicle body). In contrast, none of the vehicle underbody structures 1 and 3 of invention examples 1 to 3 have a ground-side cross member below the battery pack 20. Therefore, according to the present invention, it has been demonstrated that a battery pack can be mounted so that the battery can be extended downward toward the vehicle body while ensuring sufficient collision performance and protecting the battery in a side collision of the vehicle, and that it is possible to increase the battery capacity for the purpose of extending the cruising range.

[0100] According to the present invention, it is possible to provide a vehicle body underbody structure for an electric vehicle that can mount a battery pack so that the battery can be extended downward toward the vehicle body while ensuring sufficient collision performance in a side collision of the vehicle.

[0101] DESCRIPTION OF SYMBOLS 1 Vehicle body understructure 3 Vehicle body understructure 5 Vehicle body understructure (reference example) 10 Side sill 11 Side sill inner 11a Top plate portion 11b Vertical wall portion 13 Side sill outer 20 Battery pack 21 Battery cell 23 Battery frame 30 Floor cross member 30a Tip 30b Bottom portion 30c Wall portion 30d R portion 30' Floor cross member (shape with closed tip) 30e Tip 31 Floor panel 40 Battery mount 40a Vehicle interior end portion 40b Vehicle exterior end portion 41 Closed cross section portion 41a Steel plate part 41a1 Lower surface of battery mount 41b Steel plate part 41b1 Upper surface of battery mount 43 Partition plate 45 Fastening bolt 47 Fastening bolt 50 Underfloor cross member 50a Tip 50b End 50c Center 51 Continuous hat cross section shaped member 53 Upper metal plate 55 Lower metal plate 60 Ground side cross member 60a End 101 Vehicle 103 Pole

Claims

1. An underbody structure for an electric vehicle comprising: a pair of left and right side sills arranged on the outer side of the vehicle in the width direction of the vehicle and extending in the fore-and-aft direction of the vehicle; a battery pack arranged between the pair of left and right side sills and with a battery frame arranged on the outer periphery in the width direction of the vehicle; and a floor cross member arranged on the upper surface of a floor panel installed above the battery pack and extending in the width direction of the vehicle, wherein the cross section perpendicular to the width direction of the vehicle is a closed cross section, and the battery mount has an inner end connected to the underside of the battery frame and an outer end connected to the underside of the side sill, the floor cross member has a groove shape that is open to the underside of the vehicle, and both ends abut against the side surfaces of the left and right side sills, the battery mount has a closed cross section portion that forms the closed cross section shape, and a partition plate that is arranged within the closed cross section portion so as to connect the upper surface and the lower surface and separates the inner side from the outer side of the vehicle, and the closed cross section portion is made of a metal plate with a lower tensile strength than the battery frame.

2. The vehicle body underbody structure for an electric vehicle according to claim 1, wherein both ends of the groove shape in the floor cross member are open.

3. The underbody structure of an electric vehicle as described in claim 1 or 2, further comprising a groove-shaped under-floor cross member that is installed between the floor panel and the battery pack, extends in the vehicle width direction, and has both ends abutting against the side surfaces of the left and right side sills.

4. An electric vehicle underbody structure as set forth in any one of claims 1 to 3, wherein the cross-sectional shape of the floor cross member perpendicular to the vehicle width direction is approximately constant along the vehicle width direction.

5. The underbody structure for an electric vehicle according to any one of claims 1 to 4, wherein the battery mount is made using three or more metal plates.

6. The underbody structure of an electric vehicle as described in claim 3, wherein the underfloor cross member comprises a continuous hat cross-sectional member having at least three consecutive hat cross-sectional shapes in a cross section perpendicular to the vehicle width direction, an upper metal plate covering the upper surface of the continuous hat cross-sectional member, and a lower metal plate covering the lower surface of the continuous hat cross-sectional member.

7. The underbody structure for an electric vehicle according to claim 3 or 6, wherein the underfloor cross member is linear and has a cross-sectional shape perpendicular to the width direction of the vehicle body that is substantially constant along the width direction of the vehicle body.

8. The underbody structure of an electric vehicle as described in claim 3 or 6, wherein the underfloor cross member is linear and the groove depth of the groove shape becomes deeper toward the end on the outer side of the vehicle than the battery pack.

9. An electric vehicle underbody structure according to any one of claims 1 to 8, wherein the side sill and floor cross member are made of steel plate with a tensile strength of 980 MPa or higher, and at least the closed cross-sectional shape portion of the battery mount is made of steel plate with a tensile strength of 590 MPa or higher.

10. An electric vehicle underbody structure according to any one of claims 3 to 8, wherein the underfloor cross member is made of steel plate having a tensile strength of 980 MPa or higher.

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