Vehicle body lower part structure

Abstract

This vehicle body lower part structure comprises: a floor panel 1; a battery pack 2 disposed below the floor panel 1; a first cross member 4 and a second cross member 5 which extend in parallel in the vehicle width direction; and a longitudinal member 6. The longitudinal member 6 is bridged across the first cross member 4 and the second cross member 5 and is joined to the floor panel 1. The battery pack 2 is fastened to the longitudinal member 6.

Description

Underbody structure

[0001] The present invention relates to a vehicle underbody structure.

[0002] As vehicle electrification advances, vehicles are often equipped with large battery packs. In battery electric vehicles (BEVs), large battery packs are sometimes fixed under the floor of the vehicle body. Patent Document 1 discloses a vehicle underbody structure in which a large battery pack is mounted under the floor. In the structure disclosed in Patent Document 1, the battery pack is fixed to a pair of side sills provided on both side edges of the floor and to multiple parallel cross members that span the width of the vehicle and are bridged between the pair of side sills.

[0003] Japanese Patent Application Laid-Open No. 2018-202887

[0004] Battery packs have a robust structure to protect the battery modules inside them in the event of a vehicle accident. In the vehicle underbody structure disclosed in Patent Document 1, the battery pack is fixed to the cross member of the floor panel as described above. Therefore, in the event of a side collision, the battery pack functions as a reinforcing member, improving the buckling strength of the cross member. However, the general floor surface between the cross members of the floor panel has low surface rigidity and is prone to vibration, which is disadvantageous in terms of noise and vibration performance. On the other hand, if the battery pack is fixed to the general floor surface instead of the cross member to suppress this vibration, the vibration can be suppressed, but the cross member is not reinforced, resulting in a decrease in the vehicle's side collision performance.

[0005] An object of the present invention is to provide a vehicle underbody structure that can achieve both side impact performance and noise and vibration performance.

[0006] A vehicle underbody structure according to an aspect of the present invention includes a floor panel, a battery pack disposed below the floor panel, first and second cross members extending parallel to the vehicle width direction, and a vertical member spanning between the first and second cross members. The vertical members are joined to the floor panel. The battery pack is fastened to the vertical members.

[0007] According to the vehicle underbody structure according to the above aspect, it is possible to achieve both opposite side impact performance and noise and vibration performance.

[0008] Fig. 1 is a cross-sectional view of a vehicle underbody structure according to an embodiment. Fig. 2 is a plan view showing a main portion of the vehicle underbody structure. Fig. 3 is a perspective view showing a vertical member of the vehicle underbody structure. Fig. 4 is an exploded perspective view showing the vertical member. Fig. 5 is a cross-sectional view of the vertical member. Fig. 6 is a perspective view showing a battery pack of the vehicle underbody structure. Fig. 7 is an exploded perspective view of the battery pack.

[0009] Hereinafter, a vehicle undercarriage structure according to an embodiment will be described with reference to the drawings. In the following description, components having the same functions as those already described will be assigned the same reference numerals and will not be described again. In each drawing, FR and RR indicate the front and rear in the vehicle longitudinal direction, respectively, LH and RH indicate the left and right in the vehicle width direction, and UP and DN indicate the upper and lower, respectively. In the following description, the left and right in the vehicle width direction, and the front, front side, rear and rear sides in the vehicle longitudinal direction will be simply referred to as the left, right, front, front side, rear and rear side, respectively.

[0010] The vehicle equipped with the underbody structure is a battery electric vehicle (BEV). As shown in FIGS. 1 and 2 , the vehicle includes a battery pack 2 that occupies almost the entire area below a floor panel 1 of the passenger compartment (see FIGS. 6 and 7 ). A pair of side sills 3 are welded to both sides of the floor panel 1, which is a pressed steel plate. Note that only the passenger compartment-facing half of the side sills 3 (the sill inner panels) is shown in the figures. The floor panel 1 also includes a first cross member 4 and a second cross member 5 that extend parallel to the vehicle width direction and span the pair of side sills 3. The second cross member 5 is located rearward of the first cross member 4. The first cross member 4 and the second cross member 5 are each formed by spot welding flanges on both side edges of a pressed steel plate with a hat-shaped cross section to the floor panel 1.

[0011] The first cross member 4 and the second cross member 5 improve the surface rigidity of the floor panel 1 and suppress vibration of the floor panel 1. In other words, the first cross member 4 and the second cross member 5 improve sound and vibration performance. Furthermore, during a side collision of the vehicle, the collision load is input to the side sill 3. The collision load input to the B-pillar during a side collision is also transmitted to the side sill 3. The side sill 3 has a closed cross section so that it can withstand the collision load. The first cross member 4 and the second cross member 5 suppress inward bending of the side sill 3 during a side collision and suppress buckling of the floor panel 1. This structure suppresses deformation of the vehicle body during a collision and improves side collision performance.

[0012] The floor panel 1 is also provided with a pair of vertical members 6 that extend in the fore-and-aft direction of the vehicle and are bridged between the first cross member 4 and the second cross member 5. One of the vertical members 6 is located on the left side of the vehicle, dividing the width of the floor panel 1 at a ratio of approximately 1:3, and is located below the front left seat. The other vertical member 6 is located on the right side of the vehicle, dividing the width of the floor panel 1 at a ratio of approximately 3:1, and is located below the front right seat. The battery pack 2 is fixed to the vehicle body by having both side edges thereof fastened to the side sills 3 and by being fastened to the vertical members 6 via bolts 7, which are fasteners provided on the upper surfaces of the battery packs.

[0013] The battery pack 2 houses multiple battery modules (not shown). Each battery module houses multiple battery cells. As shown in FIGS. 6 and 7 , the case of the battery pack 2 mainly comprises a frame 2a, a bottom plate 2b, and a top plate 2c. The front wall 2f and rear wall 2r of the frame 2a are made of die-cast aluminum, and the side wall 2s is made of extruded aluminum. A side bracket 2d is fixed to the side wall 2s for fastening the battery pack 2 to the side sill 3. The bottom plate 2b is formed by laminating and joining multiple pressed metal plates. The top plate 2c is made of a single pressed metal plate.

[0014] A pair of inner cross members 2m extending parallel to the vehicle width direction are provided within the frame 2a, spanning a pair of side walls 2s. Each inner cross member 2m is formed from a machined aluminum extrusion. The frame 2a also includes an inner member spanning two of the front wall 2f, the inner cross member 2m, and the rear wall 2r in the vehicle's fore-and-aft direction. These inner members are also formed from aluminum extrusion. A bracket 2e is attached to the front inner cross member 2m for fastening the battery pack 2 to the vertical member 6.

[0015] 5 , the bolt 7 includes a base plate 7a that is fastened to the bracket 2e with the top plate 2c interposed therebetween, and a weld bolt 7b that is fixed to the base plate 7a. The weld bolt 7b projects upward, i.e., toward the floor panel 1. The bolt 7 is fastened to the vertical member 6 by a mating nut 8. That is, the battery pack 2 is fixed to the vehicle body by fastening the bolt 7 to the vertical member 6, i.e., to the floor panel 1, in addition to fastening the side bracket 2d to the side sill 3 described above.

[0016] To protect the battery modules housed inside, the battery pack frame 2a is formed into the aforementioned sturdy ladder frame structure using aluminum die-cast or extruded aluminum. The vertical members 6 are fastened to the internal cross members 2m that form the ladder frame structure of the battery pack 2 frame 2a via bolts 7 and brackets 2e. In addition, the top plate 2c of the battery pack 2 is sandwiched between the floor panel 1 and the base plate 7a of the bolts 7, preventing surface vibration of the floor panel 1 and the top plate 2c. As a result, sound and vibration performance is improved.

[0017] As shown in Figures 3 to 5, each vertical member 6 may be formed of two members: a member main body 6a and a reinforcing member 6b. In this embodiment, the front end of the member main body 6a is spot welded to the upper surface of the first cross member 4, and the rear end is spot welded to the upper surface of the second cross member 5. The member main body 6a and the reinforcing member 6b are pressed steel plates. In plan view, the member main body 6a and the reinforcing member 6b may overlap, and both sides of the member main body 6a and the reinforcing member 6b may be spot welded to the floor panel 1. More specifically, both ends of the reinforcing member 6b in the vehicle width direction may be joined to the floor panel 1 by spot welding together with both side edges of the member main body 6a in the vehicle width direction. Both side edges of the member main body 6a may also be spot welded to the floor panel 1 at areas other than the overlapping portions with the reinforcing member 6b. Furthermore, the front and rear ends of the reinforcing member 6b may also be spot welded to the upper surface of the floor panel 1 (or the flange of the second cross member 5) using holes or notches formed therein.

[0018] In this embodiment, the thickness of the member main body 6a and the thickness of the reinforcing member 6b are the same. The member main body 6a is formed of a so-called 440 MPa-class high-tensile steel plate for formability, and the reinforcing member 6b is formed of a so-called 980 MPa-class ultra-high-tensile steel plate for strength. That is, the tensile strength of the material of the reinforcing member 6b may be greater than the tensile strength of the material of the member main body 6a. The member main body 6a primarily connects the first cross member 4 and the second cross member 5 and improves the surface rigidity of the floor panel 1 between the first cross member 4 and the second cross member 5. On the other hand, the reinforcing member 6b primarily aims to improve the strength of the fastening point of the battery pack 2 to the floor panel 1. For this reason, the reinforcing member 6b is formed of a material with a greater tensile strength than the member main body 6a. In this way, the vertical member 6 may be formed of two members, the member main body 6a and the reinforcing member 6b, each with a different function. The thickness of the member main body 6a and the reinforcing member 6b may be different. For example, the thickness of the member main body 6a may be thicker than the thickness of the reinforcing member 6b. In this case, the surface rigidity of the floor panel 1 between the first cross member 4 and the second cross member 5 can be further improved. As a result, vibration of the floor panel 1 can be further suppressed, and sound and vibration performance can be further improved. Furthermore, the thickness of the reinforcing member 6b may be thicker than the thickness of the member main body 6a. For example, if the required tensile strength cannot be obtained simply by forming the reinforcing member 6b from a material with high tensile strength, the required tensile strength can be obtained by increasing the thickness of the reinforcing member 6b.

[0019] As shown in FIG. 4 , the member main body 6a has an access hole 6c for the nut 8, which is used to fasten the bolt 7 of the battery pack 2 to the reinforcing member 6b. The reinforcing member 6b has a circular seat 6d for the nut 8. An insertion hole for the bolt 7 is formed in the center of the seat 6d. An insertion hole for the bolt 7 is also formed in the floor panel 1 to match the insertion hole in the reinforcing member 6b. The back surface of the seat 6d is in surface contact with the front surface of the floor panel 1. Reinforcing beads 6e may be formed on the right and left sides of the seat 6d. The reinforcing beads 6e are formed by forming annular embossments around the periphery of the seat 6d that protrude above the seat 6d. The reinforcing beads 6e may be formed between the seat 6d and a flange that is spot-welded to the floor panel 1.

[0020] The effects of the vehicle underbody structure according to this embodiment will be described.

[0021] (1) The vehicle body understructure of this embodiment includes a floor panel 1, a battery pack 2 disposed below the floor panel 1, first and second cross members 4 and 5 extending parallel to the vehicle width direction, and vertical members 6. The vertical members 6 span between the first and second cross members 4 and 5 and are also joined to the floor panel 1. The battery pack 2 is fastened to the vertical members 6. Because the vertical members 6 are joined to the general floor surface of the floor panel 1 between the first and second cross members 4 and 5, the surface rigidity of the floor panel 1 is improved. This suppresses vibration of the floor panel 1 between the first and second cross members 4 and 5. As a result, sound and vibration performance is improved.

[0022] Furthermore, the first cross member 4 and the second cross member 5 are fastened to the battery pack 2, which has a robust structure, via the vertical members 6. During a side collision, a collision load input to the vehicle body from the side of the vehicle is transmitted from the side sill 3 to the first cross member 4 and the second cross member 5. At this time, the first cross member 4 and the second cross member 5 are reinforced by the battery pack 2, which has a robust structure, via the vertical members 6, and buckling thereof is suppressed. As a result, deformation of the vehicle body during a collision can be suppressed, and opposite side collision performance is improved. In other words, the vehicle body underbody structure of this embodiment can achieve both opposite side collision performance and sound and vibration performance.

[0023] (2) In the vehicle body lower structure of this embodiment, the vertical member 6 includes a member main body 6a and a reinforcing member 6b. The reinforcing member 6b is directly joined to the floor panel 1, and fasteners (bolts 7 in this embodiment) are fastened to the reinforcing member 6b. The front and rear ends of the member main body 6a are joined to the first cross member 4 and the second cross member 5, respectively. The member main body 6a is joined to the floor panel 1 so as to overlap the reinforcing member 6b in a plan view. In this way, by forming the vertical member 6 from two members formed with separate main functions, i.e., the member main body 6a and the reinforcing member 6b, it is possible to realize a vertical member 6 that is small in size but has sufficient strength.

[0024] Although it is possible to form the vertical member 6 as a single member, achieving the required strength results in a large size. For example, if the vertical member is made of only a material with low tensile strength (e.g., high-tensile steel plate), the size will be large. Specifically, it may be necessary to increase the height of the reinforcing bead 6e or widen the width to ensure a large embossed diameter around the seat surface 6d. When the vertical member 6 is disposed below the front seats as in the above embodiment, a high height of the vertical member 6 may interfere with the underside of the front seats, or a wide width of the vertical member 6 may make it impossible to place an air conditioning outlet below the front seats. On the other hand, if the vertical member is made of only a material with high tensile strength (e.g., ultra-high-tensile steel plate) so that a small cross-sectional area is sufficient, formability will be poor. By forming the vertical member 6 from two members, the member main body 6a and the reinforcing member 6b, as in the present embodiment, a vertical member 6 with sufficient strength can be realized while being small in size.

[0025] (3) Furthermore, in the vehicle body undercarriage structure of this embodiment, both ends of the reinforcing member 6b in the vehicle width direction are joined to both side edges of the member main body 6a in the vehicle width direction. Although the member main body 6a and the reinforcing member 6b may be joined with the floor panel 1 interposed therebetween, it is preferable that the member main body 6a and the reinforcing member 6b be joined directly to their side edges in this manner. This effectively improves the strength of the vertical member 6, and sufficient strength can be obtained while keeping the size of the vertical member 6 small.

[0026] (4) In addition, in the vehicle underbody structure of this embodiment, the tensile strength of the material of the reinforcing member 6b is greater than the tensile strength of the material of the member main body 6a. As described above, by forming the vertical member 6 from two components, the member main body 6a and the reinforcing member 6b, it is possible to realize a vertical member 6 that is small in size but has sufficient strength. Here, by forming the reinforcing member 6b from a material with a greater tensile strength, it is possible to ensure the formability of the member main body 6a while effectively improving the strength of the reinforcing member 6b, which serves as the direct fastening point for the battery pack 2. This prevents damage to the fastening point and further reinforces (prevents buckling) the first cross member 4 and the second cross member 5 via the vertical member 6 by the battery pack 2, thereby further improving side impact performance.

[0027] (5) Furthermore, in the vehicle underbody structure of this embodiment, the fastener is a bolt 7 protruding from the upper surface of the battery pack 2, and the reinforcing member 6b has a seating surface 6d for a nut 8 that is fastened to the bolt 7. A reinforcing bead 6e is formed around the seating surface 6d of the reinforcing member 6b. In this way, by ensuring the seating surface 6d that comes into surface contact with the surface of the floor panel 1 and by forming the reinforcing bead 6e around the seating surface 6d, the strength of the fastening point of the battery pack 2 can be further improved.

[0028] (6) In the vehicle underbody structure of this embodiment, the reinforcing bead 6e is formed to protrude upward from the seat surface 6d, thereby ensuring the cross-sectional area of ​​the reinforcing member 6b and improving the rigidity of the reinforcing member 6b.

[0029] The above-described embodiments are merely examples described to facilitate understanding of the invention. The technical scope of the invention is not limited to the specific technical matters disclosed in the above-described embodiments, but also includes various modifications, changes, alternative technologies, etc. that can be easily derived therefrom.

[0030] For example, in the above embodiment, the components are joined by spot welding, but arc welding or laser welding may be used in combination, or the components may be joined by arc welding or laser welding alone. Furthermore, instead of joining by welding, joining using a structural adhesive may also be employed.

[0031] Furthermore, in the above embodiment, the fasteners provided on the upper surface of the battery pack 2 are bolts 7, but nuts or members with bolt holes may be provided as fasteners on the upper surface of the battery pack 2. In this case, bolts may be used instead of the nuts 8 described above to fasten the battery pack 2 to the vertical members 6. In this case, the bearing surface 6d of the reinforcing member 6b serves as the bearing surface for the head of the bolt.

[0032] REFERENCE SIGNS LIST 1 Floor panel 2 Battery pack 4 First cross member 5 Second cross member 6 Vertical member 6a Member body 6b Reinforcement member 6d Seat surface 6e Reinforcement bead 7 Bolt (fastener) 8 Nut

Claims

1. A vehicle body lower structure comprising a floor panel, a battery pack disposed below the floor panel, a first cross member extending in the vehicle width direction, a second cross member disposed in parallel with the first cross member and extending in the vehicle width direction, and a longitudinal member extending in the vehicle longitudinal direction and bridging between the first cross member and the second cross member and joined to the floor panel, wherein the battery pack is fastened to the longitudinal member.

2. The vehicle body lower structure according to claim 1, wherein the longitudinal member includes a reinforcing member to which a fastener is fastened and joined to the floor panel, and a member body having front and rear ends joined to the first cross member and the second cross member respectively and overlapping the reinforcing member in plan view and joined to the floor panel.

3. The vehicle body lower structure according to claim 2, wherein both ends of the reinforcing member in the vehicle width direction are joined to both side edges of the member body in the vehicle width direction respectively.

4. The vehicle body lower structure according to claim 2 or 3, wherein the tensile strength of the material of the reinforcing member is greater than the tensile strength of the material of the member body.

5. The vehicle body lower structure according to any one of claims 2 to 4, wherein the fastener is a bolt protruding from the upper surface of the battery pack, the reinforcing member has a seating surface to which the bolt is fastened, and a reinforcing bead is formed around the seating surface of the reinforcing member.

6. The vehicle body lower structure according to claim 5, wherein the reinforcing bead is formed to protrude upward from the seating surface.

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