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EP-4741263-A1 - VEHICLE BODY LOWER STRUCTURE FOR ELECTRIC VEHICLE

EP4741263A1EP 4741263 A1EP4741263 A1EP 4741263A1EP-4741263-A1

Abstract

An underbody structure for a battery electric vehicle according to the present invention includes: a pair of left and right side sills 10; a battery pack 20 disposed between the side sills 10; a floor cross member 30 having a groove shape extending linearly in a vehicle width direction; and a ground-side cross member 40 having a groove shape extending in the vehicle width direction, in which the side sills 10 each include a side sill inner 11 having a hat cross section and a side sill outer 13 having a groove shape. A side portion 11a of the side sill inner 11 and a surface portion 30a provided at an end of the floor cross member 30 in the vehicle width direction have substantially the same cross section orthogonal to a vehicle front-rear direction, and the side sill inner 11 is disposed such that ridge line sections 11b in a vehicle vertical direction overlap an upper end edge and a lower end edge of the surface portion 30a of the floor cross member 30.

Inventors

  • SAITO, TAKANOBU

Assignees

  • JFE Steel Corporation

Dates

Publication Date
20260513
Application Date
20240619

Claims (5)

  1. An underbody structure for a battery electric vehicle, the underbody structure comprising: a pair of left and right side sills disposed on the vehicle outer side in the vehicle width direction and extending in a vehicle front-rear direction; a battery pack disposed between the pair of left and right side sills; a floor cross member installed on a top surface side of the battery pack and extending in a vehicle width direction; and a ground-side cross member installed on a lower side of the battery pack and having a groove shape extending in a vehicle width direction, wherein the side sills each include: a side sill inner having a hat cross section opened toward the vehicle exterior side in the vehicle width direction, the side sill inner includes a side portion positioned on a vehicle interior side in the vehicle width direction, slope sections each continuous from one of an upper end edge and a lower end edge of the side portion to a vehicle exterior side via a ridge line section and inclined with respect to a vehicle horizontal direction, and a flange portion continuous from each of the slope sections; and a side sill outer having a groove shape opened toward the vehicle interior side in the vehicle width direction, the side sill outer includes a bottom part positioned on the vehicle exterior side in the vehicle width direction, and wall parts each bent from one of an upper end edge and a lower end edge of the bottom part toward the vehicle interior side and continuous, the flange portion of the side sill inner on an upper side of a vehicle body and an upper end portion of the side sill outer are joined to each other in a state in which an opening side of the side sill inner and an opening side of the side sill outer face each other, and the flange portion of the side sill inner on a lower side of the vehicle body and the bottom part of the side sill outer or the wall part of the side sill outer on the lower side of the vehicle body are joined to each other in the state in which the opening side of the side sill inner and the opening side of the side sill outer face each other, the floor cross member has a linear groove shape opened toward the lower side of the vehicle body and closed with surface portions provided at both ends in the vehicle width direction, each of the surface portions abutting on the side portion of one of the left and right side sill inners, the side portion of the side sill inner and the surface portion of the floor cross member have substantially a same cross section orthogonal to the vehicle front-rear direction, and the side portion of the side sill inner and the surface portion of the floor cross member are positioned such that the ridge line sections on the upper side and the lower side of the vehicle body of the side sill inner and the upper end edge and the lower end edge of the surface portion of the floor cross member overlap respectively in a vehicle vertical direction, and in the ground-side cross member, the groove shape is linear, a cross section orthogonal to the vehicle width direction is substantially constant in the vehicle width direction, and an end is connected to the wall part of the side sill outer on the lower side of the vehicle body.
  2. The underbody structure for a battery electric vehicle according to claim 1, wherein the ground-side cross member includes: a continuous hat cross-sectional shape member having at least three consecutive hat cross sections in a cross section orthogonal to the vehicle width direction; an upper metal plate covering a top surface of the continuous hat cross-sectional shape member; and a lower metal plate covering a lower surface of the continuous hat cross-sectional shape member.
  3. The underbody structure for a battery electric vehicle according to claim 1 or 2, wherein the floor cross member has the surface portion formed with end plates welded or bonded at both ends of the groove shape.
  4. The underbody structure of a battery electric vehicle according to claim 1 or 2, wherein a cross section of the floor cross member orthogonal to the vehicle width direction is substantially constant in the vehicle width direction.
  5. The underbody structure for a battery electric vehicle according to claim 1 or 2, wherein the side sill and the floor cross member are formed using a steel plate having a tensile strength greater than or equal to 980 MPa class, and the ground-side cross member is formed using a steel plate having a tensile strength greater than or equal to 590 MPa class.

Description

Field The present invention relates to an underbody structure of a battery electric vehicle in which a battery pack is disposed on the main floor of the underbody. Background In recent years, particularly in the automobile industry, replacement from internal combustion engine vehicles to battery electric vehicles or the like is progressing due to environmental issues. In battery electric vehicles or the like, a battery pack accommodating a large battery (battery) is disposed on the main floor of an underbody. In addition, Li-based materials are often used for the battery, and there is a risk of fire if the battery pack is damaged at the time of collision and liquid leakage from the battery occurs. Therefore, a structure for protecting the battery pack is required. In general, a battery electric vehicle or the like has a structure in which the battery pack is surrounded by a pair of left and right side sills disposed on both sides of a vehicle body and a floor cross member provided above the battery pack and connected to the left and right side sills. At the time of side collision (side impact), it is important that a side sill or the like is deformed by a collision load input to a side surface of the vehicle to absorb the collision energy (impact energy), thereby reducing the transfer load on the battery pack and suppressing the deformation. Therefore, for example, as disclosed in Patent Literatures 1 to 7, structures for protecting a battery pack at the time of side collision are proposed so far. Citation List Patent Literatures Patent Literature 1: JP 2020-83033 APatent Literature 2: Japanese Patent No. 6889419Patent Literature 3: JP 2020-189567 APatent Literature 4: JP 2021-88364 APatent Literature 5: JP 2022-77194 APatent Literature 6: Japanese Patent No. 6734709Patent Literature 7: Japanese Patent No. 6887469 Summary Technical Problem In the structures of Patent Literatures 1 to 3, a flange portion, formed at an end portion of a floor cross member (cross member in Patent Literature 2, and first and second cross members in Patent Literature 3) having a hat-shaped cross section, is connected to a side surface of a side sill (locker in Patent Literature 1). However, in these structures, deformation in which a floor cross member having the hat-shaped cross section is opened is likely to occur due to a collision load input at the time of side collision, and thus, collision energy cannot be sufficiently absorbed. Meanwhile, the structure of Patent Literature 4 includes a side sill (locker in Patent Literature 4) in which an outer portion and an inner portion are integrally molded, and the inner portion has an L-shaped deformed shape in cross section cut in a vehicle width direction. Therefore, it is difficult to manufacture the side sill having such a cross section by press forming, and there are problems of a decrease in the productivity and an increase in the manufacturing cost. In addition, in the structure of Patent Literature 4, a ladder shape impact absorption part (impact energy absorbing member) integrally formed in a side sill is provided in order to absorb collision energy input at the time of side collision; however, this leads to an increase in the weight of the vehicle body. Furthermore, in the structures of Patent Literatures 5 to 7, the end portion of the floor cross member is positioned above the side sill. Therefore, the side sill cannot be sufficiently crushed by the reaction force of a collision load transmitted to the floor cross member at the time of side collision, and the collision energy cannot be sufficiently absorbed. Furthermore, in the structures of Patent Literatures 5 to 7, since the floor cross member is partially in contact with the upper portion of the side sill or a part of a punch bottom, the side sill cannot be completely crushed at the time of side collision, and the absorption efficiency of collision energy is low. As described above, the conventional structures that protect the battery pack at the time of side collision cannot sufficiently absorb collision energy, and thus, there is a problem that the transfer load on the battery pack cannot be reduced to suppress deformation. Furthermore, in order to sufficiently absorb the collision energy, it is necessary to separately provide an impact absorption part (impact energy absorbing member), whereby the weight of the vehicle body increases. The present invention has been made to solve the above problems, and an object of the present invention is to provide an underbody structure of a battery electric vehicle capable of reducing a transfer load on a battery pack and suppressing deformation at the time of side collision of the battery electric vehicle without reducing weight efficiency. Solution to Problem To solve the problem and achieve the object, an underbody structure for a battery electric vehicle according to the present invention includes: a pair of left and right side sills disposed on the vehicle outer side in the