Car body understructure for electric automobile

Abstract

To provide a car body understructure for an electric automobile, which protects a battery at the time of side crashing.SOLUTION: A car body understructure 1 for an electric automobile comprises: a pair of left and right side sills 10; a battery pack 20 disposed between the side sills 10; a floor cross member 30 disposed on the top side of the battery pack 20 to extend in a car body width direction; and a set of left and right ground cross members 40 each having a groove shape extending outside the automobile and installed at both ends 20a in the car body width direction on the bottom surface of the battery pack 20. The floor cross member 30 has a linear groove shape opened toward the lower side of the car body and closed at both tips 30a. The tips 30a abut against the side surfaces of the side sills 10. Each ground cross member 40 has the linear groove shape ans is roughly uniform in a sectional shape in the car body width direction. An end 40a inside the automobile is connected to the bottom surface of the battery pack 20, and an end 40b outside the automobile is connected to the bottom surfaces of the side sills 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, particularly in the automotive industry, environmental issues have led to a shift from internal combustion engine vehicles to electric vehicles. Electric vehicles have a battery pack containing large cells (batteries) located 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 and leaks during a collision, so a structure to protect the battery pack is required.

[0003] In general, electric vehicles and the like have a structure in which a battery pack is surrounded by a pair of left and right side sills arranged on both sides of the vehicle body and floor cross members provided above the battery pack and connected to the left and right side sills. In the event of a side collision, it is important that the side sills and the like deform due to the collision load input to the side of the vehicle, thereby absorbing the collision energy and reducing the load input to the battery pack and suppressing its deformation. Therefore, structures for protecting the battery pack in the event of a side collision have been proposed, as disclosed in Patent Documents 1 to 7, for example. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-83033 [Patent Document 2] Patent No. 6889419 [Patent Document 3] Japanese Patent Publication No. 2020-189567 [Patent Document 4] Patent Publication No. 2021-88364 [Patent Document 5] Japanese Patent Publication No. 2022-77194 [Patent Document 6] Patent No. 6734709 [Patent Document 7] Patent No. 6887469 Summary of the Invention [Problem to be solved by the invention]

[0005] In the structures of Patent Documents 1 to 3, a flange portion formed at the end of a hat-shaped cross-section floor cross-member (a cross-member in Patent Document 2, and a first and second cross-member in Patent Document 3) is connected to the side of a side sill (a rocker in Patent Document 1). However, with these structures, the hat-shaped cross-section floor cross-member is prone to deformation that causes it to open when subjected to a collision load input during a side collision, making it impossible to adequately absorb collision energy.

[0006] Furthermore, the structure of Patent Document 4 includes a side sill (called a rocker in Patent Document 4) in which an outer portion and an inner portion are integrally molded, and the inner portion has an irregular L-shaped cross section cut along the vehicle body width direction. Therefore, it is difficult to manufacture a side sill having such a cross section by press molding, resulting in problems such as reduced productivity and increased manufacturing costs. Furthermore, the structure of Patent Document 4 has a ladder-shaped impact absorbing section (collision energy absorbing member) integrally formed within the side sill to absorb the collision energy input during a side collision, but this results in an increase in the vehicle weight.

[0007] Furthermore, in the structures of Patent Documents 5 to 7, the end of the floor cross member is located above the side sill, so in the event of a side collision, the reaction force of the collision load transmitted to the floor cross member cannot sufficiently crush the side sill, and the collision energy cannot be sufficiently absorbed.

[0008] As such, conventional structures for protecting battery packs during side collisions have the problem that they are unable to fully absorb the collision energy, making it impossible to reduce the load input to the battery pack and suppress deformation. Furthermore, in order to fully absorb the collision energy, a separate impact absorbing part (collision energy absorbing member) must be provided, which increases the vehicle weight.

[0009] 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 reduce the load input to the battery pack and suppress deformation during a side collision without increasing the vehicle weight. [Means for solving the problem]

[0010] (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; a floor cross member disposed on an upper surface side of the battery pack and extending in the vehicle body width direction; a pair of left and right ground-side cross members installed at both ends in the vehicle width direction on the underside of the battery pack and having groove shapes extending from the both ends toward the outside of the vehicle, The floor cross member has a linear groove shape that opens toward the lower side of the vehicle body and has both closed ends, and the both ends abut against the side surfaces of the left and right side sills, Each ground-side cross member is characterized in that the groove shape is linear and the cross-sectional shape perpendicular to the vehicle width direction is approximately constant along the vehicle width direction, and the end on the inside of the vehicle is connected to the underside of the battery pack and the end on the outside of the vehicle is connected to the underside of the side sill.

[0011] (2) In the above (1), Each of the ground side cross members 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.

[0012] (3) In the above (1) or (2), The floor cross member is characterized in that end plates are welded or glued to both ends of the groove shape to form the closed shape.

[0013] (4) In the above (1) or (2), 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.

[0014] (5) In the above (1) or (2), The side sill and the floor cross member are formed using steel plates with a tensile strength of 980 MPa or higher, The ground-side cross member is characterized by being formed using a steel plate having a tensile strength of 590 MPa or more. [Effects of the Invention]

[0015] In the present invention, the load input to the battery pack during a side collision is reduced, suppressing deformation of the battery pack, thereby preventing damage to the battery and protecting it, thereby enabling the manufacture of a safe electric vehicle that protects the battery pack during a side collision. [Brief explanation of the drawings]

[0016] [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]1A and 1B are diagrams illustrating a ground-side cross member in an underbody structure of an electric vehicle according to an embodiment of the present invention ((a) cross section perpendicular to the longitudinal direction of the vehicle body, (b) cross section perpendicular to the width direction of the vehicle body). [Figure 3] FIG. 10 is a diagram illustrating a side collision analysis in the embodiment. [Figure 4] 1A and 1B are diagrams showing a vehicle underbody structure that was the subject of a side collision test analysis in the examples ((a) is a perspective view from above the vehicle body, and (b) is a plan view from below the vehicle body). [Figure 5] In the embodiment, this is a diagram explaining the ground-side cross member in the vehicle body underbody structure of an electric vehicle ((a) perpendicular cross section of the battery pack and ground-side cross member in the vehicle body width direction, (b) perpendicular cross section of the ground-side cross member in the vehicle body width direction). [Figure 6] FIG. 1 is a diagram showing the position in the longitudinal direction (TL) of the vehicle body at which a pole collides with the side of the electric vehicle tested in the examples. [Figure 7] 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 8] In the embodiment, (a) is a diagram showing the length of a ground-side cross member in a vehicle underbody structure according to an example of the invention, and (b) is a diagram showing the ground-side cross member in a vehicle underbody structure according to a reference example. [Figure 9] 1A and 1B are diagrams showing a cross member on the ground side in a vehicle underbody structure according to a reference example in an embodiment ((a) is a cross section perpendicular to the longitudinal direction of the vehicle body, and (b) is a cross section perpendicular to the width direction of the vehicle body). [Figure 10] In the examples, these figures show the deformation of a vehicle equipped with a vehicle body underbody structure according to an example of the invention during a side collision ((a) plan view from below the vehicle body, (b) cross-sectional view of the vehicle body underbody structure at the start of the collision, (c) cross-sectional view of the vehicle body underbody structure after the collision). [Figure 11] In the example, this figure shows the deformation during a side collision of a vehicle equipped with a body undercarriage structure having different lengths of ground-side cross member ((a) ground-side cross member length: 245 mm, (b) ground-side cross member length: 165 mm). [Figure 12]1 is a graph showing the results of evaluation items obtained in a side collision test in an example ((a) input load to a battery pack, (b) amount of deformation of a battery pack). DETAILED DESCRIPTION OF THE INVENTION

[0017] The vehicle body understructure 1 of an electric vehicle according to an embodiment of the present invention (hereinafter simply referred to as "vehicle body understructure 1") comprises a side sill 10, a battery pack 20, a floor cross member 30, and a ground-side cross member 40, as shown as an example in Figure 1. Hereinafter, a vehicle body underbody structure 1 according to this embodiment will be described with reference to FIGS. In this specification and drawings, elements having the same functional configuration are denoted by the same reference numerals, and redundant explanations will be omitted.

[0018] <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.

[0019] 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 the upper and lower sides of the top plate portion 11a, and flange portions 11c extending from each vertical wall portion 11b.

[0020] 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 13c at each end on the upper and lower sides of the vehicle.

[0021] In the side sill 10, the flange portion 11c of the side sill inner 11 and the flange portion 13c of the side sill outer 13 are joined at the upper side of the vehicle body, and the flange portion 11c of the side sill inner 11 and the flange portion 13c of the side sill outer 13 are joined at 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.

[0022] <Battery pack> As shown in FIG. 1, the battery pack 20 is disposed between a pair of left and right side sills 10, and includes battery cells 21 mounted therein. In this embodiment, the battery pack 20 is supported by a battery frame 23 disposed on the outer periphery in the vehicle width direction.

[0023] <Floor cross member> As shown in Fig. 1, the floor cross member 30 is installed on the upper surface side of the battery pack 20 and extends in the vehicle width direction. The floor cross member 30 opens toward the lower side of the vehicle body, and both ends 30a in the vehicle width direction are closed, linear groove shapes, and both ends 30a abut against the side surfaces of the left and right side sills 10. In the vehicle body underbody structure 1 shown in Fig. 1, both ends 30a of the floor cross member 30 abut against the top plate portions 11a of the side sill inner panels 11, which are the side surfaces of the side sills 10. In order to improve the rigidity of the vehicle body, both ends of the floor cross member 30 and the top plate portion 11a of the side sill inner 11 may be joined by brackets or the like.

[0024] <Ground-side cross member> As shown in Figure 1, the ground-side cross members 40 are installed on both end portions 20a of the underside of the battery pack 20 in the vehicle width direction, and are a pair of left and right members each having a groove shape extending from both end portions 20a toward the outside of the vehicle.

[0025] Each ground-side cross-member 40 has a groove shape that is linear along the vehicle body width direction and a cross-sectional shape perpendicular to the vehicle body width direction that is approximately constant along the vehicle body width direction, with an inboard end 40a connected to the underside of the battery pack 20 and an outboard end 40b connected to the underside of the side sill 10. In the vehicle body understructure 1 shown in FIG. 1 , the outboard end 40b of each ground-side cross-member 40 is connected to the lower vertical wall portion 11b of the side sill inner 11, which is the underside of the side sill 10.

[0026] There is no particular restriction on the method of connecting the outer end 40b of the ground-side cross member 40 to the underside of the side sill 10. For example, the upper surface (upper metal plate 43 shown in FIG. 2(b)) of the inner end 40a of the ground-side cross member 40 to the lower vertical wall portion 11b of the side sill inner 11 may be fastened with a fixing bolt or connected by welding. It is also advisable to ensure a predetermined gap between the outer end 40b of the ground-side cross member 40 and the flange portion 11c on the vehicle body lower side of the side sill inner 11. This is to prevent the ground-side cross member 40 from forming a load transfer path for the collision load input to the vehicle body before the side sill outer 13 is crushed during a side collision.

[0027] In the vehicle underbody structure 1 according to this embodiment, the reason why deformation of the battery pack 20 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.

[0028] In the vehicle body lower structure 1, the floor cross member 30 has a groove-shaped configuration with both ends 30a closed and abutting against the side surface of the side sill 10 (top plate portion 11a of the side sill inner 11). As a result, even if the side sill 10 deforms during a side collision and a load is input to the end 30a of the floor cross member 30, a reduction in strength due to deformation of the groove shape of the end 30a, such as opening, can be prevented.

[0029] Furthermore, by installing a pair of left and right ground-side cross members 40 on the underside of the battery pack 20, the load input to the side of the vehicle body lower structure 1 can be distributed and transmitted to the floor cross member 30 and the ground-side cross member 40. This makes it possible to more effectively improve the protection performance of the battery pack 20.

[0030] Furthermore, the pair of left and right ground-side cross members 40 are separately connected to both ends 20a of the underside of the battery pack 20 in the vehicle width direction, which prevents a significant increase in vehicle weight due to the installation of the ground-side cross members 40. The range (length) of the inboard end 40a of each ground-side cross member 40 connected to both ends 20a of the underside of the battery pack 20 should preferably be at least 50 mm in the vehicle width direction.

[0031] As described above, the underbody structure 1 for an electric vehicle according to this embodiment can reduce the load input to the battery pack 20 during a side collision and suppress deformation of the battery pack 20. This makes it possible to manufacture a safe electric vehicle that protects the battery even during a side collision. Furthermore, in the vehicle body undercarriage structure 1 of this embodiment, by installing a pair of left and right ground-side cross members 40 at both ends 20a of the underside of the battery pack 20 in the vehicle width direction, the vehicle body can be made lighter without reducing side collision performance.

[0032] In the present invention, it is preferable that each ground-side cross member 40 has a groove shape extending in the vehicle width direction, and is configured to include a continuous hat cross-sectional shape member 41, an upper metal plate 43, and a lower metal plate 45, as shown in Figure 2.

[0033] The continuous hat cross-sectional shape member 41 is a member formed so that three hat cross-sectional shapes are consecutively formed in a cross section perpendicular to the vehicle width direction. The continuous hat cross-sectional shape member 41 shown in Fig. 2(b) 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 front-rear direction of the vehicle body.

[0034] The upper metal plate 43 covers the upper surface of the continuous hat cross-sectional shaped member 41 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 41. The upper metal plate 43 and the continuous hat cross-sectional shaped member 41 may be connected by one-side welding or bolts.

[0035] The lower metal plate 45 covers the underside of the continuous hat cross-section shaped member 41 and is provided so as to connect the two hat cross-section shaped top plate portions 41a that open toward the upper side of the vehicle body. The lower metal plate 45 and the continuous hat cross-section shaped member 41 may be connected by one-side welding or bolts.

[0036] In this way, by sandwiching the continuous hat cross-sectional shaped member 41 between the upper metal plate 43 and the lower metal plate 45 and making it linear along the vehicle width direction, it is possible to increase bending rigidity against a side collision load and suppress deformation of the ground-side cross member 40. As a result, in the event of a side collision, the lower side of the side sill 10 is sufficiently crushed, allowing for better absorption of collision energy.

[0037] Although the continuous hat cross-sectional shape member 41 shown in FIG. 2(b) is formed so as to have three consecutive hat cross-sectional shapes, in the present invention, the continuous hat cross-sectional shape member may be formed so as to have at least three consecutive hat cross-sectional shapes.

[0038] In addition, in the present invention, the continuous hat cross-sectional shaped member may be arranged so that the two outer hat cross-sectional shaped openings face toward the lower side of the vehicle body and the middle hat cross-sectional shaped opening faces toward the upper side of the vehicle body. In this case, the upper metal plate may be provided to connect the two outer hat-shaped top plates 41a of the continuous hat cross-section member to cover 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 by closing the hat cross-sectional opening in the middle of the continuous hat cross-section member.

[0039] In the present invention, the floor cross member may have a groove shape extending in the vehicle width direction, with both ends closed, and preferably has end plates welded or bonded to both ends of the groove shape to form a closed shape. Here, the welding of the end plates may be by spot welding, laser welding, or arc welding.

[0040] However, the floor cross member may be formed by integrally forming the linear groove shape and the closed shapes at both ends by drawing.

[0041] Furthermore, in the present invention, it is preferable that the floor cross member has a straight groove shape that is curved in the vehicle body width direction without any undulations, and that the cross-sectional shape perpendicular to the vehicle body width direction is approximately constant along the vehicle body width direction. Here, the cross-sectional shape being approximately constant means that the change in the groove height of the cross-sectional shape in the vehicle body width direction is within ±10% of the average groove height of the floor cross member in the vehicle body width direction.

[0042] In this way, the cross-sectional shape of the floor cross member is a straight line with no curves in the vehicle width direction, and is generally constant along the vehicle width direction, making it less likely for the floor cross member to bend (buckle) in a side collision. This allows the upper part of the side sill to be sufficiently crushed, resulting in high collision energy absorption.

[0043] Furthermore, as with the floor cross member, the linear groove shape of the ground side cross member means that the cross-sectional shape perpendicular to the vehicle body width direction is approximately constant along the vehicle body width direction, and it is preferable that the change in the cross-sectional shape in the vehicle body width direction is within ±10% of the average value of the groove height of the ground side cross member in the vehicle body width direction.

[0044] In the vehicle body underbody structure of the present invention, the installation position and number of floor cross members can be appropriately set so that the collision load can be absorbed and the battery pack can be protected more effectively regardless of the position at which the collision load is input to the side of the electric vehicle.

[0045] The positions and number of the left and right ground-side cross members can be determined appropriately, just as with the floor cross members. Preferably, the ground-side cross members should be installed in positions that overlap the floor cross members in the fore-and-aft direction of the vehicle. This allows the collision load to be efficiently distributed between the floor cross members and the ground-side cross members, further improving the protection performance of the battery pack.

[0046] In the present invention, the side sills and floor cross members are preferably formed using steel plates having a tensile strength of 980 MPa or higher. Examples of steel plates having 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 classes.

[0047] Furthermore, because the outer end 40b of the ground-side cross member faces the flange portion 11c of the side sill inner panel 11 on the vehicle body lower side, after the side sill outer panel 13 is crushed in a side collision, the collision load input to the vehicle body is directly transmitted to the ground-side cross member 40 (see FIG. 1). However, the ground-side cross member 40 is more susceptible to bending deformation than the floor cross member 30. If the ground-side cross member 40 breaks due to bending deformation, its collision energy absorption performance will be significantly reduced. Therefore, in the present invention, the ground-side cross member is preferably formed using a steel plate with the same or higher ductility than the steel plate used for the side sill and floor cross member. In particular, it is preferable that the ground-side cross member be formed using a steel plate with a tensile strength of 590 MPa or higher, which has a lower tensile strength but a higher ductility than the floor cross member.

[0048] By using steel plates with these tensile strengths to manufacture the side sills, floor cross members, and ground-side cross members, the upper and lower parts of the side sills can be sufficiently crushed in the event of a side collision, allowing collision energy to be absorbed efficiently. [Example]

[0049] A specific analysis was carried out to verify the effects of the vehicle underbody structure according to the present invention, and the results will be described below.

[0050] In this example, a collision analysis was performed on a pole side collision test in which the side of a vehicle 101 equipped with the vehicle body undercarriage 1 shown in Figure 1 in the above-mentioned embodiment was collided with a pole 103 from the outside of the vehicle in the vehicle width direction, as shown in Figure 3 (example of the invention).

[0051] As described in the embodiment, the vehicle body understructure 1 includes the side sill 10, the battery pack 20, the floor cross member 30, and the ground-side cross member 40.

[0052] The floor cross members 30 are provided for fastening the front seats (not shown), and as shown in FIG. 4(a), two of them are installed at a distance in the longitudinal direction of the vehicle body. The two floor cross members 30 each have a groove shape extending in the vehicle width direction, with both ends 30a closed, and are in contact with the side surfaces of the left and right side sills 10 (top plate portions 11a of the side sill inners 11).

[0053] As shown in Figure 4(b), the ground-side cross members 40 are installed on the underside of the battery pack 20 so as to extend outward from both ends 20a in the vehicle width direction of the vehicle body, and consist of a pair of left and right ground-side cross members each having a groove shape extending in the vehicle width direction. In the vehicle body understructure 1, four pairs of ground-side cross members 40 are installed at intervals in the fore-and-aft direction of the vehicle body.

[0054] As shown in Fig. 5, each ground-side cross member 40 is configured to include a continuous hat cross-sectional shape member 41, an upper metal plate 43, and a lower metal plate 45. Each ground-side cross member 40 has a linear groove shape, a cross-sectional shape perpendicular to the vehicle body width direction that is approximately constant along the vehicle body width direction, and a groove height of 12.6 mm.

[0055] In the vehicle body lower structure 1 according to this embodiment, the side sill 10 and floor cross member 30 are formed using steel plate with a tensile strength of 980 MPa, and the ground side cross member 40 is formed using steel plate with a tensile strength of 980 MPa.

[0056] In this example, a collision analysis was performed on a pole side collision test in which a vehicle 101 accelerated to 32 km / h was made to collide with a pole 103 at a collision angle of 75° (FIG. 3).

[0057] In an electric vehicle, there is a strict requirement for anywhere protection of 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. 6, 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). 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.

[0058] 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. 7(a).

[0059] Batteries installed in electric vehicles and other vehicles are required to comply with the United Nations Convention on the Electrical and Electronic Devices Industry (UN ECE R100-0.2.Part.II), which specifies a crushing test (impact test) as a test item for evaluating the safety of batteries in the event of a vehicle collision. In this crushing test, the device under test (battery pack) is crushed with a force of 100kN to 105kN for a starting period of less than 3 minutes and a holding period of 100ms to 10s, and the presence or absence of signs of battery shattering, electrolyte leakage, fire, or explosion is evaluated (Internet<URL:https: / / www.mlit.go.jp / jidosha / un / UN_R100.pdf> [Retrieved on June 21, 2020]). Therefore, in this embodiment, the target value of the input load to the battery pack is set to 105 kN or less, which is the load applied to the battery in the crushing test of the United Nations Convention Regulation "UN ECE R100-0.2.Part.II."

[0060] On the other hand, regarding the deformation amount of the battery pack, as shown in Fig. 7(b), the length of the battery pack 20 in the vehicle width direction before and after deformation was measured at 12 locations in the longitudinal direction of the vehicle, 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, taking into account the plate thickness of the battery pack 20. Therefore, in this example, the target deformation amount of the battery pack 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.

[0061] In this example, as shown in Figures 8(a)(i) to (iii), collision analysis was performed on three cases of vehicle body understructures 1 in which the lengths of each ground-side cross member 40 were 245 mm, 165 mm, and 85 mm, and the effect of the length of the ground-side cross member 40 was examined.

[0062] Furthermore, in this embodiment, as shown in Figure 8(b), a vehicle body understructure 51 having a ground-side cross member 60 extending in the vehicle body width direction and having both ends 60a connected to the left and right side sills 10 was used as a reference example, and a collision analysis of a pole side collision was performed in the same way as the vehicle body understructure 1 of the invention example.

[0063] 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 has a linear groove shape and 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).

[0064] Furthermore, the ground-side cross member 60 of the reference example, like the ground-side cross member 40 of the invention example, is configured to include a continuous hat cross-sectional shaped member 61, an upper metal plate 63, and a lower metal plate 65, as shown in Figure 9. The ground-side cross member 60 has a groove height of 12.6 mm, as shown in Figure 9(c). In the vehicle body understructure 51 according to the reference example, four ground-side cross members 60 are installed at equal intervals in the front-rear direction of the vehicle body.

[0065] Figure 10 shows the state of the vehicle body understructure 1 before and after deformation during a pole side collision process in which a pole 103 collides with the side of a vehicle 101, in which the length of the ground-side cross member 40 according to the example of the invention is 165 mm, at a position TL=905 mm in the vehicle fore-and-aft direction (Figure 6(b)) (before deformation: Figure 10(b), after deformation: Figure 10(c)). Figures 10(b) and (c) are cross-sectional views of the vehicle body understructure 1 at the collision position (TL=905 mm) of the pole 103.

[0066] As shown in Figure 10(c), the outer-side tip 30a of the floor cross-member 30 is deformed, and the outer-side end 40b of the ground-side cross-member 40 is bent but not crushed. On the other hand, the side sill 10 is completely crushed, which indicates that it has sufficiently absorbed the collision energy. In particular, after the side sill outer 13 is crushed, the lower part of the side sill 10 is sufficiently crushed because the outer-side end 40b of the ground-side cross-member 40 is connected to the underside of the side sill 10 (the vertical wall portion 11b of the side sill inner 11). 10(c), even if the side sill 10 is completely crushed, there is still a gap between the battery pack 20 and the battery cell 21. This indicates that the battery cell 21 is protected from damage caused by the deformation of the battery pack 20.

[0067] Figure 11 shows the deformation of the vehicle body undercarriage 1 obtained by a collision analysis in which a pole is collided with the side of a vehicle 101 at a position TL = 1605 mm in the fore-and-aft direction of the vehicle body (Figure 6(e)) for vehicles 101 in which the lengths of each ground-side cross member 40 are 245 mm and 165 mm.

[0068] Compared to when the length of each ground-side cross member 40 was 245 mm, when the length of each ground-side cross member 40 was 165 mm, the side sill 10 was significantly deformed toward the inside of the vehicle, as shown in Figure 11(b).

[0069] FIG. 12 shows the evaluation results of the input load to the battery pack and the deformation of the battery pack obtained for each position in the front-rear direction of the vehicle body where the pole 103 collides. The input load to the battery pack did not vary significantly depending on the length of the ground-side cross member 40, and was always below the target value of 105 kN.

[0070] The deformation of the battery pack increased as the length of the ground-side cross member 40 became shorter, and for lengths of 85 mm and 165 mm, the result exceeded the target of 10 mm at impact position No. 5 (Figure 6(e), TL = 1605 mm). However, for other impact positions (No. 1 to No. 4) and for a ground-side cross member 40 with a length of 245 mm, the results were similar to those of the reference example and were less than the target of 10 mm.

[0071] The anywhere requirement for an electric vehicle in a side collision with a pole is a very difficult condition, but with the vehicle body underbody structure 1 of the present invention, it has been demonstrated that if the length of the ground-side cross member 40 is appropriately selected (in the embodiment, at least 245 mm or more), the target deformation amount of the battery pack can be achieved regardless of the pole collision position, and the battery can be protected. [Explanation of symbols]

[0072] 1 Underbody structure 10 Side sill 11 Side sill inner 11a Top plate 11b Vertical wall section 11c Flange 13 Side sill outer 13c Flange 20 Battery Pack 20a End 21 battery cells 23 Battery frame 30 Floor cross member 30a tip 40 Ground side cross member 40a Inside end of the car 40b Outside edge of the vehicle 41 Continuous hat-shaped cross-section member 41a Top plate 43 Upper metal plate 45 Lower metal plate 51 Underbody structure 60 Ground side cross member 60a End 61 Continuous hat-shaped cross-section member 63 Upper metal plate 65 Lower metal plate 101 vehicles 103 Paul

Claims

1. A pair of left and right side sills disposed on the outer side 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; A floor cross member is provided on an upper surface side of the battery pack and extends in a vehicle body width direction; a pair of left and right ground-side cross members each having a groove shape extending from the both ends toward an outer side of the vehicle, the left and right ground-side cross members being installed at both ends in a vehicle width direction on a lower surface of the battery pack, The floor cross member is a linear groove shape that opens toward the lower side of the vehicle body and has both closed ends, and the both ends abut against the side surfaces of the left and right side sills, This is an electric vehicle underbody structure, characterized in that each ground side cross member has a groove shape that is straight and a cross-sectional shape perpendicular to the vehicle width direction that is approximately constant along the vehicle width direction, and the end on the inside of the vehicle is connected to the underside of the battery pack, and the end on the outside of the vehicle is connected to the underside of the side sill.

2. Each of the ground side cross members 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; 2. The vehicle underbody structure of an electric vehicle according to claim 1, further comprising: a lower metal plate covering a lower surface of the continuous hat cross section shaped member.

3. 3. The vehicle body underbody structure for an electric vehicle according to claim 1, wherein the floor cross member has end plates welded or bonded to both ends of the groove shape to form the closed shape.

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. The side sill and the floor cross member are formed using 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 the ground side cross member is formed using a steel plate having a tensile strength of 590 MPa or more.

Images