Body substructure of electric automobile

Abstract

To provide a body substructure of an electric automobile that protects a battery in the case of a lateral collision.SOLUTION: A body substructure of an electric automobile in accordance with the present invention includes a pair of left and right side sills 10, a battery pack 20 interposed between the side sills 10, a floor cross member 30 shaped like a groove extending linearly in a body width direction, and a ground-side cross member 40 shaped like a groove extending in the body width direction. The side sill 10 includes a side sill inner piece 11 whose section is shaped like a hat, and a side sill outer piece 13 shaped like a groove. A flank 11a of the side sill inner piece 11 and a surface 30a at a distal end in the body width direction of the floor cross member 30 have substantially identical sectional shapes that are orthogonal to a body fore-and-aft direction. A ridge part 11b in a body vertical direction of the side sill inner piece 11 is disposed to overlap an upper edge and lower edge of the surface 30a of the floor cross member 30.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 disposed in a floor portion under the vehicle body. [Background technology]

[0002] In recent years, especially in the automobile industry, there has been a shift from gasoline engine vehicles to electric vehicles due to environmental issues. Electric vehicles have a battery pack housing a large battery in the floor area under the vehicle body. Li-based materials are often used in batteries, and there is a risk of fire if the battery pack is damaged in a collision and leaks battery fluid, 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 a floor cross member that is provided above the battery pack and connects to the left and right side sills. During a side collision, it is important that the side sills, etc., deform due to the collision load input to the side of the vehicle and absorb the collision energy, thereby reducing the load input to the battery pack and suppressing its deformation. Therefore, structures for protecting the battery pack during a side collision have been proposed, for example as disclosed in Patent Documents 1 to 7. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-83033 A [Patent Document 2] Patent No. 6889419 [Patent Document 3] JP 2020-189567 A [Patent Document 4] Patent Publication No. 2021-88364 [Patent Document 5] JP 2022-77194 A [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 floor cross member with a hat-shaped cross section (a cross member in Patent Document 2, and a first and second cross members in Patent Document 3) is connected to the side of a side sill (a rocker in Patent Document 1). However, with these structures, the floor cross member with a hat-shaped cross section is prone to deformation that opens up due to the collision load input during a side collision, making it impossible to fully 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 part and an inner part are integrally molded, and the inner part 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, and there are problems with 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 in order 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 that in the event of a side collision, the side sill cannot be sufficiently crushed by the reaction force of the collision load transmitted to the floor cross member, and therefore the collision energy cannot be sufficiently absorbed. In addition, in the structures of Patent Documents 5 to 7, the floor cross member is in partial contact with the upper part of the side sill or part of the punch bottom, so that the side sill cannot be completely crushed in the event of a side collision, resulting in low efficiency in absorbing collision energy.

[0008] As described above, the conventional structure for protecting the battery pack during a side collision cannot fully absorb the collision energy, and therefore cannot reduce the load input to the battery pack to suppress deformation. Furthermore, in order to fully absorb the collision energy, it is necessary to provide a separate impact absorbing part (collision energy absorbing member), which increases the vehicle weight.

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide an underbody structure for an electric vehicle that can reduce the load input to a battery pack and suppress deformation during a side collision of the electric vehicle without reducing weight efficiency. [Means for solving the problem]

[0010] (1) The vehicle body underbody structure of the present invention includes a pair of left and right side sills disposed on outer sides of the vehicle in a width direction of the vehicle body and extending in a front-rear direction of the vehicle body; 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 ground-side cross member is provided on the underside of the battery pack and has a groove shape extending in the vehicle width direction, The side sill is a side sill inner having a hat-shaped cross section that has a side portion located on the vehicle interior side in the vehicle width direction, an inclined surface portion that is continuous from each of an upper end edge and a lower end edge of the side portion to an exterior side of the vehicle via a ridge portion and is inclined with respect to the horizontal direction of the vehicle body, and a flange portion that is continuous from each inclined surface portion; and a groove-shaped side sill outer having a bottom surface portion located on the outer side of the vehicle in the vehicle width direction, and wall surface portions bending and continuing from each of an upper end edge and a lower end edge of the bottom surface portion toward the inner side of the vehicle, the groove-shaped side sill outer opening toward the inner side of the vehicle in the vehicle width direction, The side sill inner and the side sill outer are joined together with their opening sides facing each other, and the flange portion of the side sill inner on the upper side of the vehicle body and the upper end portion of the side sill outer, and the flange portion of the side sill inner on the lower side of the vehicle body and the bottom portion or the wall portion on the lower side of the vehicle body of the side sill outer are joined together, The floor cross member is a linear groove shape that opens toward the lower side of the vehicle body and has a surface portion at both ends in the vehicle body width direction, and each surface portion abuts against the side surface portion of each of the left and right side sill inner panels, the side surface portion of the side sill inner and the surface portion of the floor cross member have substantially the same cross-sectional shape perpendicular to the vehicle front-rear direction, and the ridge portions of the side sill inner on the upper side and the lower side of the vehicle body and the upper and lower edges of the surface portion of the floor cross member are positioned so as to overlap in the vehicle vertical direction, The ground side cross member is characterized in that the groove shape is straight and the cross-sectional shape perpendicular to the vehicle width direction is approximately constant along the vehicle width direction, and the end portion is connected to the wall portion on the lower side of the vehicle body of the side sill outer.

[0011] (2) In the above (1), The ground side 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; and a lower metal plate covering the underside of the continuous hat cross section shaped 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 surface portion.

[0013] (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 approximately constant along the vehicle body width direction.

[0014] (5) In any one of (1) to (4) above, 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 in that it is formed using a steel plate with a tensile strength of 590 MPa or more. Effect of the Invention

[0015] In the present invention, the side sill can be sufficiently crushed by the reaction force of the load input to the side sill and transmitted to the floor cross member during a side collision, thereby obtaining high collision energy absorption. This reduces the load input to the battery pack during a side collision and suppresses deformation of the battery pack, thereby preventing damage to the battery and protecting it, thereby enabling the manufacture of a safe electric vehicle. Furthermore, in the present invention, the cross-sectional shape of the side sill inner can be made small, making it possible to reduce the weight of the vehicle body without deteriorating the side collision performance. [Brief description 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. [Diagram 2] 1A and 1B are diagrams illustrating the configuration of the underbody structure of an electric vehicle according to an embodiment of the present invention ((a) a conventional underbody structure and its deformation behavior during a side collision, (b) an enlarged view of the side sill and its surroundings of the underbody structure of an electric vehicle according to the present embodiment). [Diagram 3] 1A to 1C are diagrams showing the structure of a ground-side cross member of the vehicle body underbody structure of an electric vehicle according to an embodiment of the present invention ((a) orthogonal cross-sectional view in the vehicle body width direction, (b) orthogonal cross-sectional view in the vehicle body fore-and-aft direction, (c) enlarged view of the orthogonal cross-section in the vehicle body width direction). [Figure 4] FIG. 1 is a diagram for explaining a side collision analysis in an embodiment. [Diagram 5] 1A and 1B are diagrams showing a vehicle underbody structure according to an embodiment of the present invention ((a) is a perspective view from above the vehicle body, and (b) is a perspective view from below the vehicle body). [Figure 6] FIG. 2 is a diagram showing the position in the vehicle longitudinal direction (TL) at which a pole collides with the side of a test electric vehicle in the examples. [Figure 7] FIG. 2 is a diagram for explaining evaluation items for side collision performance in the examples ((a) input load to a battery pack, (b) deformation amount of the battery pack). [Figure 8] 1A and 1B are diagrams showing a vehicle underbody structure of a reference example used for comparison with the vehicle underbody structure of the invention in the embodiment ((a) is a perspective view from below the vehicle body, and (b) is an orthogonal cross-sectional view in the fore-and-aft direction of the vehicle body). [Figure 9] 1A and 1B are diagrams showing deformation during a side collision of a vehicle equipped with an underbody structure according to an embodiment of the present invention and a reference embodiment of the present invention ((a) Reference embodiment of the present invention, (b) Example of the present invention). [Figure 10] 1A and 1B are diagrams showing deformation during a side collision of a vehicle equipped with an underbody structure according to an embodiment of the present invention and a reference embodiment of the present invention ((a) Reference embodiment of the present invention, (b) Example of the present invention). [Figure 11] In the examples, this is a graph showing the results of evaluation items obtained in a side collision test targeting the vehicle body underbody structures of Example 1 and Reference Example 1 ((a) input load to the battery pack, (b) deformation amount of the battery pack). [Figure 12] In the examples, this is a graph showing the results of evaluation items obtained in a side collision test targeting the vehicle body underbody structures of Example 2 and Reference Example 2 ((a) input load to the battery pack, (b) deformation amount of the battery pack). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] 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 ground-side cross member 40, as shown as an example in Fig. 1. Hereinafter, the underbody structure 1 according to this embodiment will be described with reference to Figs. 1 and 2. In this specification and the drawings, elements having the same functional configuration are denoted by the same reference numerals and redundant explanations will be omitted.

[0018] 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 panel 11 has a hat-shaped cross section that opens toward the vehicle exterior in the vehicle width direction. The side sill inner panel 11 has a side surface portion 11a located on the vehicle interior side in the vehicle width direction, and an inclined surface portion 11c that is inclined with respect to the horizontal direction of the vehicle body and continues from each of the upper and lower edges of the side surface portion 11a to the vehicle exterior via a ridge portion 11b. The side sill inner panel 11 further has a flange portion 11d that is continuous with each inclined surface portion 11c.

[0020] The side sill outer 13 has a groove shape that opens toward the vehicle interior in the vehicle width direction. The side sill outer 13 has a bottom surface portion 13a located on the vehicle exterior in the vehicle width direction, and wall surface portions 13b that are bent and continue from the upper and lower edges of the bottom surface portion 13a toward the vehicle interior. In this embodiment, the side sill outer 13 further has a flange portion 13c that continues from the wall surface portion 13b on the upper side of the vehicle body to the upper side of the vehicle body. In addition, as described below, it is preferable that the lower wall portion 13b of the side sill outer 13 be shaped to extend in the vehicle body width direction to a position where it can be connected to the end portion 40a of the ground side cross member 40, in order to ensure connection with the end portion 40a of the ground side cross member 40.

[0021] The side sill inner 11 and the side sill outer 13 are arranged with their opening sides facing each other, and a flange portion 11d on the upper side of the vehicle body of the side sill inner 11 is joined to a flange portion 13c which is the upper end portion of the side sill outer 13. Furthermore, a flange portion 11d on the lower side of the vehicle body of the side sill inner 11 is joined to a bottom portion 13a of the side sill outer 13.

[0022] As shown in FIG. 1, the battery pack 20 is disposed between a pair of left and right side sills 10, and includes a battery cell 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] 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 body width direction. Furthermore, the floor cross member 30 is a linear groove shape that opens toward the lower side of the vehicle body and has surface portions 30a at both ends in the vehicle body width direction, and each surface portion 30a abuts against the side surface portions 11a of the left and right side sill inner panels 11. The surface portions 30a of the floor cross member 30 may be in contact with the side surface portions 11a of the side sill inner panels 11, or may be joined with a bracket or the like.

[0024] The side surface portion 11a of the side sill inner 11 and the surface portion 30a of the floor cross member 30 have substantially the same cross-sectional shape perpendicular to the front-rear direction of the vehicle body, and are also substantially in the same position in the vertical direction of the vehicle body. Therefore, the ridge lines 11b on the upper and lower sides of the side sill inner panel 11 and the upper and lower edges of the surface portion 30a of the floor cross member 30 are positioned so as to overlap in the vertical direction of the vehicle body.

[0025] As shown in FIG. 1, the ground-side cross member 40 is disposed on the underside of the battery pack 20 and has a groove shape extending in the vehicle body width direction.

[0026] The ground side cross member 40 has a straight groove shape and a cross-sectional shape perpendicular to the vehicle body width direction that is approximately constant along the vehicle body width direction, and its end portion 40a in the vehicle body width direction is connected to the wall portion 13b on the lower side of the side sill outer 13.

[0027] There is no particular limitation on the method of connecting the end 40a of the ground-side cross member 40 and the lower wall surface portion 13b of the side sill outer 13. For example, the upper surface (upper metal plate 43 shown in FIG. 2(b)) of the end 40a on the vehicle interior side of the ground-side cross member 40 and the lower wall surface portion 13b of the side sill outer 13 may be fastened with a fixing bolt or joined by welding (spot welding, etc.).

[0028] The reason why the load input to the battery pack 20 is reduced in the vehicle body underbody structure 1 according to this embodiment, thereby suppressing deformation of the battery pack 20 and protecting the battery pack 20, will be explained below with reference to FIG. 2.

[0029] In the conventional vehicle body underbody structure 3, as shown in Fig. 2(a)(i), the cross-sectional height of the side surface portion 51a of the side sill inner panel 51 is higher than the cross-sectional height of the surface portion 30a of the floor cross member 30, and the cross-sectional shapes perpendicular to the vehicle front-rear direction are different. Furthermore, the surface portion 30a of the floor cross member is structured to abut against the upper portion of the side surface portion 51a of the side sill inner panel 51. In the case of the conventional vehicle underbody structure 3, as shown in Fig. 2(a)(ii), the side sill 50 cannot be sufficiently crushed by the reaction force from the floor cross member 30 during a side collision of the vehicle, and the structure has low efficiency in absorbing collision energy. As a result, a load is input to the battery pack 20, causing the battery pack 20 to deform.

[0030] In contrast, in the vehicle body underbody structure 1 according to this embodiment, as shown in Fig. 2(b), the cross-sectional shapes of the side surface portion 11a of the side sill inner panel 11 and the surface portion 30a of the floor cross member 30 are substantially the same. The ridge portion 11b in the vertical direction of the vehicle body of the side sill inner panel 11 and the upper and lower edges of the surface portion 30a of the floor cross member 30 are positioned so as to overlap in the vertical direction of the vehicle body.

[0031] As a result, in the event of a side collision of the vehicle, the vehicle body understructure 1 can transmit a collision load from the side sill outer 13 to the upper and lower edges of the surface portion 30a of the floor cross member 30 via the upper and lower inclined surface portions 11c of the side sill inner 11. The vehicle body understructure 1 can transmit a reaction force from the floor cross member 30 to the ridge portion 11b of the side sill inner 11, so that the side sill 10 can be sufficiently crushed and the efficiency of absorbing collision energy can be improved. As a result, the input of the load to the battery pack 20 can be reduced, and deformation of the battery pack 20 can be suppressed.

[0032] In the vehicle body lower structure 1, the floor cross member 30 has a closed shape with faces 30a provided at both ends of the groove shape, and abuts against the side surface 11a of the side sill inner 11. This makes it possible to prevent a reduction in strength caused by deformation of the groove shape, such as opening, even if the side sill 10 deforms during a side collision and a load is input to the end of the floor cross member 30.

[0033] Furthermore, in the vehicle body understructure 1, the ground-side cross member 40 is installed on the underside of the battery pack 20, so that the load input to the side of the vehicle body understructure 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. In particular, by making the groove shape of the ground side cross member 40 linear and making the cross-sectional shape perpendicular to the vehicle body width direction substantially constant along the vehicle body width direction, the cross-sectional height of the side sill outer 13 can be maximized. As a result, it is possible to increase the collision absorption energy due to the deformation of the side sill outer 13. Furthermore, by making the groove shape of the ground side cross member 40 linear and making the cross-sectional shape perpendicular to the vehicle body width direction substantially constant along the vehicle body width direction, the ground side cross member 40 is structured to be less prone to bending deformation (buckling deformation) in the event of a side collision, and the load input to the battery pack 20 can be reduced.

[0034] In this way, according to the vehicle body underbody structure 1, the side sill 10 can be sufficiently crushed in the event of a side collision to increase the collision absorption energy, thereby reducing the input load to the battery pack 20 and suppressing the amount of deformation of the battery pack 20.

[0035] Furthermore, the cross-sectional height of the side surface portion 11a of the side sill inner 11 is lower than the bottom surface portion 13a of the side sill outer 13, and a flange portion 11d continuing from the side surface portion 11a via an inclined surface portion 11c on the lower side of the vehicle body is connected to the bottom surface portion 13a of the side sill outer 13. This allows the cross-sectional shape of the side sill inner 11 to be small without reducing the collision energy absorption in the event of a side collision, which contributes to weight reduction.

[0036] 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 underbody structure 1 according to this embodiment, the cross-sectional shape of the side sill inner 11 can be made small, making it possible to reduce the weight of the vehicle body without deteriorating the side collision performance.

[0037] In the above description, the inclined surface portion 11c on the lower side of the vehicle body of the side sill inner 11 is connected to the bottom surface portion 13a of the side sill outer 13, but the present invention is not limited to this, and it may also be connected to the wall surface portion 13b on the lower side of the vehicle body of the side sill outer 13.

[0038] There is also no particular limitation on the inclination angle of the inclined surface portion 11c of the side sill inner 11, and it may be set appropriately depending on the cross-sectional shape of the side surface portion 11a and the arrangement and connection portion of the side sill outer 13. However, there are cases where the closed cross section formed by the side sill inner 11 and the side sill outer 13 is required to ensure the frontal collision performance of the vehicle and to accommodate various harnesses. Therefore, it is preferable that the inclination angle of the inclined surface portion 11c (the acute angle formed by the horizontal plane of the vehicle body and the inclined surface portion 11c on the lower side of the vehicle body) is 20° or more. From the viewpoint of transmitting the reaction force received by the ridge line portion 11b of the side sill inner panel 11 from the floor cross member 30, the inclination angle of the inclined surface portion 11c of the side sill inner panel 11 on the vehicle body lower side is preferably 45° or less.

[0039] Furthermore, it is preferable that the 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 3.

[0040] The continuous hat cross-sectional shape member 41 is a member formed so that three hat cross-sectional shapes are continuous in a cross section perpendicular to the vehicle body width direction. The continuous hat cross-sectional shape member 41 shown in Fig. 3(c) is formed so that 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 are continuous along the vehicle body front-rear direction.

[0041] The upper metal plate 43 covers the upper surface of the continuous hat cross section shaped member 41 and is provided so as to close the two hat cross section shaped openings that open towards the upper side of the vehicle body in the continuous hat cross section shaped member 41. The upper metal plate 43 and the continuous hat cross section shaped member 41 may be connected by one-sided welding or bolts.

[0042] The lower metal plate 45 covers the lower surface of the continuous hat cross-sectional shaped member 41 and is provided so as to connect the two hat cross-sectional shaped top plate portions that open toward the upper side of the vehicle body. The lower metal plate 45 and the continuous hat cross-sectional shaped member 41 may be connected by one-sided welding or bolts.

[0043] In this manner, by sandwiching the continuous hat cross-sectional shaped member 41 between the upper metal plate 43 and the lower metal plate 45, the bending rigidity against a side impact load can be increased, and the ground-side cross member 40 can be structured to be less prone to bending deformation (buckling deformation). This makes it possible to reduce the load input to the battery pack 20 during a side impact.

[0044] Although the continuous hat cross-sectional shape member 41 shown in FIG. 3(c) 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.

[0045] 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 central 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 top plate portions of the two outer hat cross sections of the continuous hat cross section shaped component to cover the top surface of the continuous hat cross section shaped component, and the lower metal plate may be provided to cover the bottom surface of the continuous hat cross section shaped component by closing the opening of the hat cross section in the middle of the continuous hat cross section shaped component.

[0046] In the present invention, the floor cross member may have a groove shape with faces at both ends and 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 any of spot welding, laser welding, and arc welding.

[0047] However, the floor cross member may be formed integrally by drawing, with the linear groove shape and the closed shapes at both ends.

[0048] Furthermore, in the present invention, it is preferable that the floor cross member has a straight groove shape without undulations curved in the vehicle body width direction, and 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 may mean that the change in the cross-sectional shape in the vehicle body width direction is 90% or less of the groove height at the end.

[0049] In this way, the cross-sectional shape of the floor cross member is a straight line with no undulations curved in the vehicle width direction and is generally constant along the vehicle width direction, making it difficult for the floor cross member to bend (buckle) in the event of a side collision. This allows the side sill to be sufficiently crushed, resulting in high collision energy absorption.

[0050] In the vehicle body underbody structure of the present invention, the positions and number of floor cross members can be appropriately set so that the collision load can be received 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.

[0051] Also, like the floor cross-member, it is preferable that the change in cross-sectional shape of the ground-side cross-member in the vehicle width direction is less than 1.2 times that of the central portion. Furthermore, the positions and number of the pair of left and right ground-side cross members may be appropriately set in the same manner as for the floor cross members. Preferably, the ground-side cross members are installed in positions that overlap the floor cross members in the fore-aft direction of the vehicle body. This allows the collision load to be efficiently distributed to the floor cross members and the ground-side cross members, further improving the protection performance of the battery pack.

[0052] The height of the surface of the floor cross member that abuts on the side of the side sill inner is preferably determined so that the upper edge of the surface of the floor cross member overlaps the range of the ridgeline on the upper end side of the side of the side sill inner (the range in the vertical direction of the vehicle body between the R end of the ridgeline on the side part side and the R end of the inclined surface part side at the bending R of the ridgeline), and the lower edge of the surface of the floor cross member overlaps the range of the ridgeline on the lower end side of the side of the side sill inner. Also, the height of the surface of the floor cross member is preferably 100 mm or less in relation to the passenger compartment space, and more preferably 40 to 60 mm.

[0053] In the present invention, the side sill and floor cross member are preferably formed using a steel plate 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.

[0054] Moreover, the ground-side cross-member is preferably formed using a steel plate having a tensile strength of 590 MPa or more. After the side sill outer 13 is crushed in a side collision, the collision load input to the vehicle body is directly transmitted to the end 40a of 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, and if the ground-side cross-member 40 breaks due to bending deformation, the collision energy absorption performance is significantly reduced. For this reason, it is preferable that the ground-side cross member be formed using steel plate which has higher ductility than the steel plate used for the side sill and floor cross member, and it is preferable that it be formed using steel plate of 590 MPa class or higher which has the same tensile strength as the floor cross member, or which has a lower tensile strength and higher ductility than the floor cross member.

[0055] By using steel plates with these tensile strengths to manufacture the side sills, 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, making it possible to efficiently absorb collision energy. EXAMPLES

[0056] A specific analysis was carried out to verify the effect of the underbody structure according to the present invention, and the results will be described below.

[0057] In this example, a collision analysis was performed on a pole side impact test in which a side of a vehicle 101 equipped with the vehicle body underbody structure 1 shown in FIG. 1 in the above-described embodiment was collided with a pole 103 from the outside of the vehicle in the width direction of the vehicle body, as shown in FIG. 3 (example of the invention).

[0058] As described in the embodiment, the vehicle body underbody structure 1 includes the side sill 10, the battery pack 20, the floor cross member 30, and the ground-side cross member 40.

[0059] The floor cross members 30 are provided for fastening the front seats (not shown), and as shown in FIG. 5(a), two of them are installed with a gap between them in the front-rear direction of the vehicle body. Each of the two floor cross members 30 has a groove shape extending in the vehicle body width direction, and is closed by providing a surface portion 30a at both ends thereof, and is abutted against the side surfaces of the left and right side sills 10 (side surface portions 11a of the side sill inners 11).

[0060] As shown in FIG. 5(b), four ground-side cross members 40 were installed at intervals in the front-rear direction of the vehicle body on the underside of the battery pack.

[0061] Each ground-side cross member 40, as shown in Fig. 3 above, 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 Figs. 3(b) and (c), 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.

[0062] In the vehicle body lower structure 1 according to this embodiment, the side sill 10 and the floor cross member 30 are formed using steel plate with a tensile strength of 980 MPa class, and the ground side cross member 40 is formed using steel plate with a tensile strength of 980 MPa class.

[0063] In this embodiment, 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. 4).

[0064] In an electric vehicle, there is a strict requirement for an anywhere requirement that the battery pack 20 can 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. 6, five points No. 1 to No. 5 in the vehicle body longitudinal direction (TL) are 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.

[0065] The input load to the battery pack was determined to be the reaction force (contact reaction force) generated in the battery frame 23 due to contact with the side sill inner panel 11 during a collision, as shown in FIG. 7(a).

[0066] Batteries installed in electric vehicles and other vehicles are required to comply with the United Nations Convention Regulation "UN ECE R100-0.2.Part.II," which specifies a crush test (impact test) as a test item for evaluating the safety of batteries in the event of a vehicle collision. In this crush test, the test subject (battery pack) is crushed with a force of 100 kN to 105 kN for a starting period of less than 3 minutes and a holding period of 100 ms to 10 s, 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 crush test of the United Nations Convention Regulation "UN ECE R100-0.2. Part. II."

[0067] On the other hand, as for 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 points in the vehicle front-rear direction, and the difference between the deformation amount and the deformation amount was obtained. Here, the minimum distance between the inner surface of the battery pack 20 and the battery cell 21 before deformation was 11 mm, taking into account the plate thickness of the battery pack 20. Therefore, in this embodiment, the target deformation amount of the battery pack was less than 10 mm, as a condition for preventing contact between the battery pack 20 and the battery cell 21 during a side collision with a pole.

[0068] In this embodiment, invention examples 1 and 2 are provided, which have different widths of the battery pack 20. In invention example 1, the battery pack 20 has a standard width (the distance between the battery pack 20 and the side sill inner panel 11 in the vehicle width direction is 90 mm). On the other hand, in invention example 2, the battery pack 20 has a width that is 60 mm wider than the standard width (the distance between the battery pack 20 and the side sill inner panel 11 in the vehicle width direction is 60 mm).

[0069] Furthermore, in this embodiment, as shown in FIG. 8, a vehicle body underbody structure 3 having a side sill inner 51 having a side portion 51a having a cross-sectional height higher than the surface portion 30a of the floor cross member 30 is used as a reference example. In the vehicle body understructure 3, the side sill 50 is formed by joining a hat-shaped side sill outer 53 and a side sill inner 51, and the battery pack 20, floor cross member 30 and ground side cross member 40 are the same as those in the vehicle body understructure 1 according to the example of the invention. Furthermore, the surface portion 30a of the floor cross member 30 is abutted against the upper portion of the side surface portion 51a of the side sill inner 51, and both end portions 40a in the vehicle width direction of the ground side cross member 40 are connected to the lower wall surface portions 51b of the side sill inner 51.

[0070] Comparing the side sill inner 51 of the reference example (FIG. 8) with the side sill inner 11 of the invention example (FIG. 1), the cross-sectional shape of the side sill inner 11 of the invention example is smaller. Therefore, the vehicle underbody structure 1 of the invention example is 5.1 kg lighter in weight than the vehicle underbody structure 3 of the reference example.

[0071] Then, for the reference example, a collision analysis of a pole side impact was performed in the same manner as for the vehicle body understructure 1 of the invention example, and the vehicle body understructure 3 with the battery pack 20 having a standard width was designated as Reference Example 1, and the vehicle body understructure 3 with the width of the battery pack 20 being 60 mm wider than the standard width was designated as Reference Example 2.

[0072] Fig. 9 shows the deformation behavior during a pole side collision process in which a pole 103 is collided against the side of a vehicle 101 equipped with a vehicle body understructure 1 (invention example 1) and a vehicle body understructure 3 (reference example 1) with a battery pack 20 as a reference width. Note that the results shown in Fig. 9 are for a case in which the pole is collided at a position TL = 905 mm in the vehicle front-rear direction (Fig. 6(b)).

[0073] In reference example 1, as shown in Figure 9(a), the surface portion 30a of the floor cross member 30 abuts against the upper portion of the side portion 51a of the side sill inner 51, so that the lower portion of the side sill inner 51 remains uncrushed, suggesting that the collision energy is not sufficiently absorbed.

[0074] In contrast, in Example 1, as shown in FIG. 9(b), the side sill 10 is completely crushed, and it is understood that the collision energy is sufficiently absorbed.

[0075] Fig. 10 shows the deformation behavior during a pole side collision process in which a pole 103 is collided against the side of a vehicle 101 equipped with a vehicle body understructure 1 (invention example 2) and a vehicle body understructure 3 (reference example 2) in which the width of the battery pack 20 is 60 mm wider than the reference width. The results shown in Fig. 10 are for a case in which the pole 103 is collided at a position TL = 905 mm in the vehicle longitudinal direction (Fig. 6(b)).

[0076] Even when the width of the battery pack 20 is made 60 mm wider than the standard width, in the vehicle body underbody structure 3 of reference example 2, the lower part of the side sill inner 51 remains uncrushed, suggesting that the collision energy is not sufficiently absorbed. In contrast, in the vehicle body underbody structure 1 according to Example 2, the side sill 10 is completely crushed, thereby sufficiently absorbing the collision energy.

[0077] FIG. 11 shows 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, when the battery pack 20 has a reference width. The input load to the battery pack in Example 1 of the invention was equal to or lower than that in Reference Example 1 at all collision positions, and was significantly lower than the target of 105 kN.

[0078] Similarly, the deformation amount of the battery pack in Example 1 was equal to or smaller than that of Reference Example 1 at all collision positions, and was less than the target 10 mm.

[0079] 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 fore-and-aft direction of the vehicle where the pole 103 collides when the width of the battery pack 20 is made 60 mm wider than the reference width. The input load to the battery pack in Example 2 of the invention was equal to or lower than that in Reference Example 2 at all collision positions, and was the target 105 kN or less.

[0080] Similarly, the deformation amount of the battery pack in Example 2 of the invention was equal to or smaller than that of Reference Example 2 at all collision positions, and was less than the target 10 mm.

[0081] Although the anywhere requirement for electric vehicles in a pole side collision is a very difficult condition, it has been demonstrated that the vehicle body understructure 1 according to the present invention can achieve the target deformation amount of the battery pack regardless of the pole collision position and protect the battery. Furthermore, it has been shown that the vehicle body understructure 1 according to the present invention can reduce the weight of the vehicle body without degrading the side collision performance. [Explanation of symbols]

[0082] 1. Underbody structure 3. Underbody structure 10 Side sill 11 Side sill inner 11a Side part 11b Ridgeline 11c Slope section 11d Flange part 13 Side sill outer 13a Bottom part 13b Wall section 13c Flange 20 Battery Pack 20a End 21 Battery Cells 23 Battery frame 30 Floor cross member 30a side part 40 Ground side cross member 40a End 41 Continuous hat-shaped section member 41a Top plate 43 Upper metal plate 45 Lower metal plate 50 Side sill 51 Side sill inner 51a Side part 51b Wall section 53 Side sill outer 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 ground-side cross member is provided on a lower surface side of the battery pack and has a groove shape extending in a vehicle width direction. The side sill is a side sill inner having a hat-shaped cross section that has a side portion located on the vehicle interior side in the vehicle width direction, an inclined surface portion that is continuous from each of an upper end edge and a lower end edge of the side portion to an exterior side of the vehicle via a ridge portion and is inclined with respect to the horizontal direction of the vehicle body, and a flange portion that is continuous from each inclined surface portion; and a groove-shaped side sill outer having a bottom surface portion located on the outer side of the vehicle in the vehicle width direction, and wall surface portions bending and continuing from each of an upper end edge and a lower end edge of the bottom surface portion toward the inner side of the vehicle, the groove-shaped side sill outer opening toward the inner side of the vehicle in the vehicle width direction, The side sill inner and the side sill outer are joined together with their opening sides facing each other, and the flange portion of the side sill inner on the upper side of the vehicle body and the upper end portion of the side sill outer, and the flange portion of the side sill inner on the lower side of the vehicle body and the bottom portion or the wall portion on the lower side of the vehicle body of the side sill outer are joined together, The floor cross member is a linear groove shape that opens toward the lower side of the vehicle body and has a surface portion at both ends in the vehicle body width direction, and each surface portion abuts against the side surface portion of each of the left and right side sill inner panels, the side surface portion of the side sill inner and the surface portion of the floor cross member have substantially the same cross-sectional shape perpendicular to the vehicle front-rear direction, and the ridge portions of the side sill inner on the upper side and the lower side of the vehicle body and the upper and lower edges of the surface portion of the floor cross member are positioned so as to overlap in the vehicle vertical direction, The 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 an end portion is connected to the wall portion on the lower side of the vehicle body of the side sill outer.

2. The ground side 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; 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 surface portion.

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.

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