Electric automobile vehicle body lower part structure

Abstract

To provide an electric automobile vehicle body lower part structure that allows a battery pack to be mounted such that a battery can be expanded downward below a vehicle body while ensuring sufficient collision performance at the time of a side collision.SOLUTION: The electric automobile vehicle body lower part structure 1 of the present invention comprises a pair of left and right side sills 10, a battery pack 20 with a battery frame 23 arranged on the outer periphery in the vehicle width direction, and a floor cross member 30, and is provided with a battery mount 40 whose cross section perpendicular to the vehicle width direction is a closed cross section, and whose inner end 40a is connected to the underside of the battery frame 23 and whose outer end 40b is connected to the underside of the side sill 10. The battery mount 40 has a closed cross section portion 41 having a closed cross section shape and a partition plate 43 provided in the center of the closed cross section portion 41 to separate the inner and outer sides of the vehicle, and the closed cross section portion 41 is made of a metal plate having a tensile strength lower than that of the battery frame 23.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[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. [Background technology]

[0002] In recent years, the automotive industry in particular has been moving away from internal combustion engine vehicles and towards electric vehicles due to environmental concerns. Electric vehicles are equipped with a battery pack containing large cells (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, so a structure that can protect the battery pack when mounted on the vehicle body is required.

[0003] Many battery packs have been proposed for electric vehicles and other vehicles. For example, Patent Document 1 discloses a structure in which a cross member extending in the vehicle width direction is provided at the bottom of a frame that forms the skeleton of a battery case that stores a tray that houses a battery (corresponding to the "battery pack" in this application). Patent document 2 also discloses a structure in which a battery unit (corresponding to the "battery pack" in this application) equipped with a lower case that houses a battery module is mounted on the underside of the floor panel using 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 that is located on the vehicle width outer side of the battery pack located below the floor panel and fixed to a rocker (corresponding to the "side sill" in this application), and that includes an energy absorbing material that fixes the battery pack to the vehicle body. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-42851 [Patent Document 2] Patent No. 6197363 [Patent Document 3] Japanese Patent Publication No. 2023-146163 Summary of the Invention [Problem to be solved by the invention]

[0005] In the structures of Patent Documents 1 to 3, the battery pack is supported by parts provided below the battery pack (the cross member in Patent Document 1, the cross member in Patent Document 2, and the support part in Patent Document 3), and is mounted under the vehicle body. Therefore, even if the battery capacity is increased to extend the driving range, the battery cannot be extended toward the ground (below the vehicle body).

[0006] Furthermore, the structure of Patent Document 3 absorbs collision energy by compressively deforming 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 the material may not be able to fully absorb the collision energy, thereby failing to reduce the load transmitted to the battery pack and resulting in insufficient collision performance. 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 aims to provide an 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. [Means for solving the problem]

[0008] (1) The vehicle body underbody structure of the electric vehicle according to the present invention includes a pair of left and right side sills disposed on the outer sides of the vehicle in the width direction of the vehicle body and extending in the front-rear direction of the vehicle body; 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 vehicle body width direction; a floor cross member that is installed on an upper surface side of a floor panel that is installed above the battery pack and that extends in the vehicle body width direction, a battery mount having a closed cross section perpendicular to the vehicle body width direction, an inner end connected to a lower surface of the battery frame, and an outer end connected to a lower surface of the side sill; The floor cross member has a groove shape that opens downward toward the vehicle body, and both ends thereof abut against the side surfaces of the left and right side sills, The battery mount has a closed cross-sectional shape portion that forms the closed cross-sectional shape, and a partition plate that is arranged within the closed cross-sectional shape portion to connect the upper and lower surfaces and separate the vehicle interior from the vehicle exterior, and is characterized in that the closed cross-sectional shape portion is made using a metal plate that has a lower tensile strength than the battery frame.

[0009] (2) In the above (1), The floor cross member is characterized in that both ends of the groove shape are open.

[0010] (3) In the above (1) or (2), The vehicle is characterized by having 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 the sides of the left and right side sills.

[0011] (4) In any one of (1) to (3) above, The floor cross member is characterized in that the cross-sectional shape perpendicular to the vehicle body width direction is substantially constant along the vehicle body width direction.

[0012] (5) In any one of (1) to (4) above, The battery mount is characterized in that it is made using three or more metal plates.

[0013] (6) In the above (3), The under-floor cross member is a continuous hat cross-sectional shape member having at least three consecutive hat cross-sectional shapes in a cross section perpendicular to the vehicle body width direction; an upper metal plate covering an upper surface of the continuous hat cross section shaped member; and a lower metal plate covering the lower surface of the continuous hat-shaped cross-section member.

[0014] (7) In the above (3) or (6), The under-floor cross member is linear, and has a cross-sectional shape perpendicular to the vehicle body width direction that is substantially constant along the vehicle body width direction.

[0015] (8) In the above (3) or (6), The under-floor cross member is linear, and the groove depth of the groove shape increases toward the end on the vehicle outer side of the battery pack.

[0016] (9) In any one of (1) to (8) above, The side sill and the floor cross member are made of steel plates with a tensile strength of 980 MPa or higher, The battery mount is characterized in that at least the closed cross-sectional shape portion is made of a steel plate having a tensile strength of 590 MPa or higher.

[0017] (10) In any one of (3) to (8) above, The under-floor cross member is characterized in that it is made using a steel plate with a tensile strength of 980 MPa or higher. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a cross-sectional view showing a configuration of an underbody structure of an electric vehicle according to an embodiment of the present invention. [Figure 2] 1. An oblique view showing the shape of the tip of a floor cross member in an embodiment and example of the present invention ((a) shape with an open tip, (b) shape with an open tip and an inwardly bent R portion, (c) shape with a closed tip). [Figure 3] 1 is a diagram showing a specific structure of a battery mount in a vehicle underbody structure according to an embodiment of the present invention; [Figure 4] FIG. 4 is a cross-sectional view showing the configuration of a vehicle underbody structure according to another embodiment of the present invention. [Figure 5] FIG. 10 is a view (part 1) showing an under-floor cross member of a vehicle underbody structure according to another embodiment of the present invention. [Figure 6] FIG. 10 is a view (part 2) showing an under-floor cross member of a vehicle underbody structure according to another embodiment of the present invention. [Figure 7] 10A and 10B are diagrams illustrating a vehicle underbody structure according to another embodiment of the present invention and a groove depth of an under-floor cross member. [Figure 8] FIG. 10 is a diagram illustrating a collision analysis of a pole side collision test in an embodiment. [Figure 9] FIG. 1 is a diagram showing the underbody structure of an electric vehicle that was analyzed in a pole side collision test as a reference example in the examples. [Figure 10]Figure 1 shows the longitudinal (TL) position of the vehicle body at which the pole collides with the side of the vehicle in the pole side impact test of the example ((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)). [Figure 11] FIG. 2 is a diagram illustrating evaluation items for side collision performance in the examples ((a) input load to the battery pack, (b) deformation amount of the battery pack). [Figure 12] In the examples, these figures show the deformation of the vehicle body underbody structure of Example 1 in a pole side impact test ((a) cross-sectional view of the vehicle body underbody structure at the start of the impact, (b) cross-sectional view of the vehicle body underbody structure after the impact, (c) enlarged cross-sectional view of the side sill and its surroundings in the vehicle body underbody structure after the impact). [Figure 13] In the examples, these figures show the deformation of the vehicle body understructure of Example 2 of the invention in a pole side impact test ((a) cross-sectional view of the vehicle body understructure at the start of the impact, (b) cross-sectional view of the vehicle body understructure after the impact, (c) enlarged cross-sectional view of the side sill and its surroundings in the vehicle body understructure after the impact). [Figure 14] In the examples, these figures show the deformation of the vehicle body underbody structure of the reference example in a pole side impact test ((a) cross-sectional view of the vehicle body underbody structure at the start of the impact, (b) cross-sectional view of the vehicle body underbody structure after the impact, (c) enlarged cross-sectional view of the side sill and its surrounding area in the vehicle body underbody structure after the impact). [Figure 15] 1A and 1B are diagrams showing the time history of deformation of a battery mount of a vehicle body underbody structure according to Example 2 in a pole side impact test ((a) at the start of the impact, (b) to (e) during the impact, (f) at the end of the impact). [Figure 16] 10 is a graph showing the results of input loads to a battery pack obtained by crash analysis of a pole side crash test in an example. [Figure 17] 10 is a graph showing the results of the deformation amount of the battery pack obtained by collision analysis of a pole side collision test in the examples. DETAILED DESCRIPTION OF THE INVENTION

[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, as shown as an example in Fig. 1, a side sill 10, a battery pack 20, a floor cross member 30, and a battery mount 40. Below, the underbody structure 1 according to this embodiment will be described with reference to Figs. 1 to 7. In the specification and drawings of this application, elements having substantially the same functions and configurations are denoted 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 for facilitating understanding of the present invention, and do not limit the present invention.

[0021] <Side sill> The side sills 10 are a pair of left and right side sills disposed on the outer side of the vehicle in the width direction of the vehicle body and extending in the front-rear direction of the vehicle body. As shown in FIG.

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

[0025] <Battery pack> As shown in FIG. 1, the battery pack 20 houses battery cells 21 inside 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 width direction.

[0026] In this embodiment, as shown in FIG. 1, the battery frame 23 has a generally 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] <Floor cross member> 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 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 on 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 panel portions 11a of the left and right side sill inner panels 11).

[0028] In the vehicle body underbody structure 1 according to this embodiment, three floor cross members 30 are provided at intervals in the front-rear 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). Both ends 30a may have an open shape, and may have an R portion 30d bent inward from each end of the bottom portion 30b and 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 cross section of the battery mount 40 perpendicular to the vehicle width direction has a closed cross section, and the end 40a on the vehicle interior side is connected to the underside of the battery frame 23, and the end 40b on the vehicle exterior side is connected to the underside of the side sill (the vertical wall portion 11b on the vehicle 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 panel 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] 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 closed cross-sectional portion 41 in the vehicle width direction so as to connect the upper and lower surfaces and separate the vehicle into an inside and outside side. In this way, because partition plate 43 is provided in the center of closed cross-sectional portion 41, battery mount 40 has a square-shaped cross section in a cross section perpendicular to the vehicle front-rear direction.

[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] Figure 3 shows an example of the specific structure of the battery mount 40, where Figure 3(a) is an enlarged view of the battery mount 40 and its surroundings in the vehicle body lower structure 1, and Figure 3(b) is 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 surrounded by the dashed ovals in Figure 3(b) are joined by spot welding.

[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 lower 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 tries 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 above-mentioned Patent Documents 1 and 2, the battery can be extended downwards in the vehicle body.

[0040] As described above, the vehicle body understructure 1 according to this embodiment can mount a battery pack such that the battery can be expanded downward of the vehicle body while ensuring sufficient crash 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. Here, "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 curved in the vehicle width direction and is approximately 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 tip 30e that is closed like the floor cross member 30' shown in Fig. 2(c), but has an open tip 30a as shown in Fig. 2(a) and (b). This ensures formability when the floor cross member 30 is produced 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 is preferably located in the battery mount 40 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 shape portion 41 and partition plate 43 are integrated, but is formed using three or more steel plate parts. This allows the material strength, plate thickness, and welding method (number of spots) of each steel plate part (steel plate part 41a, steel plate part 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 from three steel plate parts, the battery mount may also be made from four or more steel plate parts (for example, a closed cross-sectional portion formed from 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, which is advantageous in terms of "anywhere" requirements for protecting the battery regardless of the collision position. Furthermore, because the battery mount 40 extends in the longitudinal direction of the vehicle body, it is expected to protect the battery pack 20 even in the event of 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, and for weight reduction purposes, the height of the battery mount 40 may decrease toward the outermost end in the vehicle width direction, as shown in Fig. 1 etc. Preferably, the decrease in height of the battery mount 40 toward the outermost end in the vehicle width direction is within a range of up to 33% compared to the center portion in the vehicle width direction. This prevents buckling at the battery mount's location where the cross-sectional shape changes during a side collision, enabling collision energy to be effectively absorbed. Additionally, to increase the resistance of the battery mount 40 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 standpoint of effectiveness and formability, it is preferable that the bead height be within 20% of the height of the center 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 width direction of the vehicle body, with both ends 50a abutting against the side surfaces of the side sill 10 (top panel portion 11a of the side sill inner 11).

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

[0054] The continuous hat cross-sectional shape member 51 is a member formed so that three hat cross-sections are continuous in a cross section perpendicular to the vehicle width direction. The continuous hat cross-sectional shape member 51 is formed so that two hat cross-sections that open toward the upper side of the vehicle body and one hat cross-section that opens toward the lower side of the vehicle body between the two hat cross-sections are continuous along the front-to-rear 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-sectional shaped member 51 and is provided so as to connect the two hat cross-sectional shaped top plate portions on the lower side of the vehicle body of the continuous hat cross-sectional shaped member 51. The lower metal plate 55 and the continuous hat cross-sectional shaped 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 vehicle underbody structure 3 to distribute and transmit the load input to the side of the vehicle 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-sectional member may have two outer hat cross-sectional shapes that open downward toward the vehicle body, and a central hat cross-sectional shape that opens upward toward the vehicle body. In this case, the upper metal plate may be provided 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, and the lower metal plate may be provided to cover the bottom surface of the continuous hat cross section member, thereby closing the openings of the two outer hat cross sections of the continuous hat cross section member.

[0059] 5 is formed so that three hat cross sections are connected in a row. 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] 4(a) and 4(b), 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 bending (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 Fig. 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 Figs. 7(b) and 7(c)). Fig. 7(b) is a cross-sectional view of the central portion 50c in the vehicle width direction, and Fig. 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 large shape changes in the area where the groove depth is deeper on the vehicle outer side than the battery pack 20. Therefore, when a load is input during a side collision, this area buckles, and there is a risk that the side sill 10 will not be sufficiently crushed. Therefore, it is advisable 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 sill and the floor cross member are preferably made of steel plate having a tensile strength of 980 MPa or higher. Examples of steel plate having a tensile strength of 980 MPa or higher include steel plate of 980 MPa, 1180 MPa, 1370 MPa, 1470 MPa, 1760 MPa, and 1960 MPa classes. Similarly to the side sills and floor cross members, the under-floor cross members are preferably made of 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 like 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. [Example]

[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 understructure 1 (Fig. 1) or vehicle body understructure 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 body understructure 1 includes a side sill 10, a battery pack 20, a floor cross member 30, and a battery mount 40 (Example 1 of the invention). The vehicle body understructure 3 is the vehicle body understructure 1 of invention example 1 further provided with an under-floor cross member 50 (invention 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] 3, the battery mount 40 has a closed cross-sectional shape portion 41 formed by steel plate parts 41a and 41b, and a partition plate 43 provided in the center of the closed cross-sectional shape portion 41, and was made using three steel plates. For the closed cross-sectional shape portion 41 and the partition plate 43, steel plates with a tensile strength of 1180 Ma, which is lower than that of the battery frame 23, were used. The partition plate 43 is provided at the same position as the top plate portion 11a of the side sill inner 11 in the vehicle width direction.

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

[0077] In the vehicle underbody structure 1 according to Example 1, the side sills 10 and the floor cross members 30 were made of steel plates with a tensile strength of 980 MPa, and the battery mounts 40 were made of steel plates with a tensile strength of 1180 MPa. In the vehicle body understructures 3 of invention examples 2 and 3, the tensile strength of the steel plates used for the side sills 10, floor cross members 30 and battery mounts 40 was the same as that of invention example 1, and the under-floor cross member 50 used steel plates with a tensile strength of 1470 MPa.

[0078] In this embodiment, a vehicle body understructure 5 in which a ground-side cross member 60 is provided below the battery pack 20 as shown in FIG. 9 is used as a reference example.

[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 11).

[0080] Furthermore, the ground-side cross member 60 of the reference example is configured to include a continuous hat cross-sectional shaped member, an upper metal plate, and a lower metal plate, similar to the under-floor cross member 50 of the invention example 2. In the vehicle body understructure 5 according to the reference example, four ground-side cross members 60 were installed at equal intervals in the front-rear 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 plates with the same tensile strength as the vehicle body substructure 1, and the ground-side cross member 60 is made of steel plates with the same tensile strength as the under-floor cross member 50 of the vehicle body substructure 3.

[0082] In an electric vehicle, strict anywhere requirements are imposed to protect the battery pack 20 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 positions No. 1 to No. 5 in the vehicle body 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 of the collision positions No. 1 to No. 5, and the load input to the battery pack 20 side (input load to the battery pack) and the deformation amount of the battery pack 20 (deformation amount 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 body before and after deformation, and the difference between the lengths before and after deformation was calculated. Here, 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 in the event of a side collision with a pole.

[0086] FIG. 12 shows the state of the vehicle body understructure 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 body understructure 1 according to Example 1 at a position TL=905 mm in the vehicle fore-and-aft direction (FIG. 10(b), No. 2) (before deformation: FIG. 12(a); after deformation: FIGS. 12(b) and (c)). Note that FIGS. 12(a) to (c) are cross-sectional views of the vehicle body understructure 1 at the collision position (TL=905 mm) of the pole 103, and FIG. 12(c) is an enlarged view of the battery mount 40 and its surroundings in FIG. 12(b).

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

[0088] Fig. 13 shows the state of the vehicle body understructure 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 body understructure 3 according to Example 2 at a position TL = 905 mm in the vehicle fore-and-aft direction (Fig. 10(b)) (before deformation: Fig. 13(a); after deformation: Figs. 13(b) and (c)). Figs. 13(b) and (c) are cross-sectional views of the vehicle body understructure 3 at the collision position (TL = 905 mm) of the pole 103, and Fig. 13(c) is an enlarged view of the battery mount 40 and its surroundings in Fig. 13(b). do.

[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] FIG. 14 shows the state of the vehicle body understructure 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 vehicle body understructure 5 according to the reference example at a position TL=905 mm in the vehicle longitudinal direction (FIG. 10(b)) (before deformation: FIG. 14(a); after deformation: FIG. 14(b) and (c)). Note that FIGS. 14(b) and (c) are cross-sectional views of the vehicle body understructure 3 at the collision position (TL=905 mm) of the pole 103, and FIG. 14(c) is an enlarged view of the joint between the side sill 10 and the ground-side cross member 60 in FIG. 14(b) and the surrounding area.

[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] Fig. 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 deformation amount of the battery pack obtained for each position in the front-rear direction of the vehicle body where the pole 103 collides. Although the input load to the battery pack shown in Figure 16 was greater in Invention Examples 1 to 3 than in the reference example in which a ground-side cross member 60 was provided, the load input to the battery pack 20 was able to be kept below 160 kN. Also, a tendency for the load to be lower was observed in invention examples 2 and 3, which were provided with an under-floor cross member 50. Furthermore, invention 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 invention 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 in which the ground-side cross member 60 was provided, but 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 still existed between the battery pack 20 and the battery cell 21.

[0095] Table 1 shows the vehicle weights of invention examples 1 to 3 and the reference example, and the weight reductions relative to the reference example. [Table 1]

[0096] As shown in Table 1, the vehicle body understructure 1 of Example 1 of the invention is 33.8 kg lighter than the reference example because it does not have a ground-side cross member 60 on the underside of the battery pack 20 like the vehicle body understructure 5 of the reference example. In addition, although the vehicle body understructures 3 of Invention Examples 2 and 3 do not have a ground-side cross member 60, as in Invention Example 1, the provision of an under-floor cross member 50 resulted in an increase in weight of 8.9 kg (Invention Example 2) and 9.4 kg (Invention Example 3).

[0097] 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.

[0098] The vehicle body understructure 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 (toward the bottom of the vehicle body). In contrast, none of the vehicle body understructures 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 it is possible to install a battery pack that allows the battery to be expanded downward toward the vehicle body while ensuring sufficient collision performance in a side collision of the vehicle to protect the battery, and to increase the battery capacity with the aim of extending the cruising range. [Explanation of symbols]

[0099] 1 Underbody structure 3 Underbody structure 5. Underbody structure (example) 10 Side sill 11 Side sill inner 11a Top plate 11b Vertical wall section 13 Side sill outer 20 Battery Pack 21 battery cells 23 Battery frame 30 Floor cross member 30a tip 30b bottom 30c wall 30d R section 30' Floor Cross Member (Closed End) 30e tip 31 Floor Panel 40 Battery Mount 40a Inside end of the car 40b Outside edge of the vehicle 41 Closed cross section shape part 41a Steel plate parts 41a1 Underside of battery mount 41b Steel plate parts 41b1 Top of the battery mount 43 Partition 45 Fastening bolt 47 Fastening bolt 50 Underfloor cross member 50a tip 50b end 50c central part 51 Continuous hat-shaped cross-section member 53 Upper metal plate 55 Lower metal plate 60 Ground side cross member 60a End 101 vehicles 103 Paul

Claims

1. a pair of left and right side sills disposed on the outer sides of the vehicle in the vehicle width direction 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 vehicle body width direction; a floor cross member disposed on an upper surface side of a floor panel disposed above the battery pack and extending in a vehicle width direction, a battery mount having a closed cross section perpendicular to the vehicle body width direction, an inner end connected to a lower surface of the battery frame, and an outer end connected to a lower surface of the side sill; The floor cross member has a groove shape that opens downward toward the vehicle body, and both ends thereof abut against the side surfaces of the left and right side sills, 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 an upper surface and a 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.

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

3. 3. The vehicle body understructure of claim 1, 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 the side surfaces of the left and right side sills.

4. 3. The vehicle body underbody structure for an electric vehicle according to claim 1, wherein the cross-sectional shape of the floor cross member perpendicular to the vehicle body width direction is substantially constant along the vehicle body width direction.

5. 3. The vehicle body underbody structure for an electric vehicle according to claim 1, wherein the battery mount is made of three or more metal plates.

6. The under-floor cross member is a continuous hat cross-sectional shape member having at least three continuous hat cross-sectional shapes in a cross section perpendicular to the vehicle body width direction; an upper metal plate covering an upper surface of the continuous hat cross section shaped member; 4. The vehicle body underbody structure of an electric vehicle according to claim 3, further comprising: a lower metal plate covering a lower surface of the continuous hat-shaped cross-section member.

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

8. 4. The vehicle body understructure of claim 3, wherein the underfloor cross member is linear, and the groove depth of the groove shape becomes deeper toward the end on the vehicle outer side than the battery pack.

9. The side sill and the floor cross member are made of steel plates with a tensile strength of 980 MPa or higher, 3. The vehicle body underbody structure for an electric vehicle according to claim 1, wherein at least the closed cross-sectional shape portion of the battery mount is made of a steel plate having a tensile strength of 590 MPa or more.

10. 4. The electric vehicle underbody structure according to claim 3, wherein the under-floor cross member is made of a steel plate having a tensile strength of 980 MPa or more.

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