Underbody structure

Abstract

To enhance the yield strength of a cross member against collision load and to improve the energy absorbing performance of a vehicle body lower part structure.SOLUTION: A vehicle body lower part structure 1 includes a floor panel 10, a side sill 20, a cross member 30, and a joining portion 40 of the floor panel 10 and the cross member 30. The side sill 20 has a hollow portion 20a and an impact absorbing portion 23. The impact absorbing portion 23 is connected to an inside wall portion 25 in a vehicle width direction of the side sill 20. The cross member 30 has: a plurality of wall portions including a top wall portion 31; and a plurality of ridge line portions 34. The plurality of ridge line portions 34 has a first ridge line portion A between the joining portion 40 and the top wall portion 31; and a second ridge line portion B. As viewed from the vehicle width direction, the first ridge line portion A and the second ridge line portion B are located in an area overlapping an area R where the impact absorbing portion 23 is disposed.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an underbody structure for an automobile. [Background technology]

[0002] In recent years, fuel efficiency regulations for automobiles have been tightened around the world, and the development of electric vehicles (EVs) is being promoted. Since electric vehicles have batteries placed under the floor, in order to protect the batteries during a collision, the structure under the vehicle body must absorb the collision energy. For example, in a collision where a utility pole comes into contact with the side of the vehicle body, the collision energy is absorbed by parts installed under the vehicle body, such as the side sill, cross member, and battery case. On the other hand, adopting high-strength materials or increasing the plate thickness of parts in order to improve the energy absorption performance leads to a significant increase in weight and cost. For this reason, it is desirable to achieve an improvement in energy absorption performance by structural improvements to the underbody.

[0003] As a technology relating to the underbody structure, Patent Document 1 discloses a structure in which a reinforcing member having projections and recesses is disposed inside a hollow automobile frame member. Patent Document 2 discloses a structure including a pair of rockers (side sills) and multiple cross members, with the distance between adjacent cross members set so that the bending reaction force of the rockers against an input load during a side collision is equal to or greater than the input load. Patent Document 3 discloses a structure in which a hat-shaped impact absorbing member having a pair of vertical walls is disposed inside the side sill, with a cross member disposed on the inside of the upper vertical wall in the vehicle width direction, and a battery side frame disposed on the inside of the lower vertical wall in the vehicle width direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 085383 [Patent Document 2] JP 2019-031219 A [Patent Document 3] Patent No. 6734709 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to maximize the energy absorption performance of the impact absorbing member during a side collision, it is preferable to plastically deform and crush the entire impact absorbing member. However, if the wall of the side sill to which the impact absorbing member is connected buckles early during a side collision, the posture of the impact absorbing member changes in accordance with the out-of-plane deformation of the side sill, and the impact load input to the impact absorbing member may not be transmitted as originally expected. In this case, the impact absorbing member does not exhibit the desired deformation behavior, and the undeformed portion of the impact absorbing member is likely to remain. Therefore, in order to maximize the energy absorption performance of the impact absorbing member, it is preferable to suppress the out-of-plane deformation of the wall of the side sill to which the impact absorbing member is connected.

[0006] Incidentally, the collision load transmitted to the cross member connected to the side sill is mainly transmitted via the impact absorbing member. Therefore, in the event of a side collision, the impact load is locally input to the cross member from the area where the impact absorbing member is arranged. When such a local load is input to the cross member, the flat surface constituting the cross member may bend, and excessive out-of-plane deformation may occur on the flat surface. In this case, out-of-plane deformation is induced on the vehicle interior wall of the side sill to which the cross member is connected, and as described above, a change in the posture of the impact absorbing member occurs in response to the out-of-plane deformation of the side sill, making it easier for the undeformed portion of the impact absorbing member to remain.

[0007] In other words, in order to promote plastic deformation of the impact absorbing member during a side collision and improve energy absorption performance, it is necessary to suppress the out-of-plane deformation of the interior wall of the side sill, but to do this, it is necessary to increase the strength of the cross member against the collision load transmitted through the impact absorbing member.

[0008] However, Patent Documents 1 to 3 do not disclose a structure for increasing the resistance of the cross member against a collision load.

[0009] The present invention has been made in consideration of the above circumstances, and has an object to increase the strength of a cross member against a collision load and improve the energy absorption performance of a vehicle lower body structure. [Means for solving the problem]

[0010] The present invention, which solves the above-mentioned problems, comprises a floor panel arranged under a vehicle body, a side sill provided at an end of the floor panel in the vehicle width direction and extending in the vehicle length direction, a cross member connected to the side sill and extending in the vehicle width direction, and a joint between the floor panel and the cross member, the side sill having a hollow portion extending in the vehicle length direction and a joint between the floor panel and the cross member, , made of metal material and an impact absorbing portion, the impact absorbing portion being disposed on the side sill. From the wall on the outside of the vehicle Vehicle width direction, inside wall Established over The cross member has a plurality of wall portions including a top wall portion, and a plurality of ridge portions extending in the vehicle width direction and sandwiched between the wall portions, the plurality of ridge portions having a first ridge portion and a second ridge portion between the joint portion and the top wall portion, the bending center of the first ridge portion being located on the inside of the cross member and the bending center of the second ridge portion being located on the outside of the cross member, and the first ridge portion and the second ridge portion being located in an area overlapping with the arrangement area of ​​the impact absorbing portion when viewed from the vehicle width direction. Effect of the Invention

[0011] According to the present invention, the strength of the cross member against a collision load can be increased, and the energy absorption performance of the vehicle lower body structure can be improved. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing an outline of a vehicle underbody structure according to an embodiment of the present invention; [Diagram 2] 2 is a diagram showing a cross section perpendicular to the axial direction (vehicle length direction) of the side sill. FIG. [Diagram 3] FIG. 4 is a perspective view showing the shape of a shock absorbing member. [Figure 4] 4 is a view of the impact absorbing member of FIG. 3 as viewed from the vehicle width direction. [Diagram 5] 1A to 1C are diagrams illustrating examples of the shape of a side sill. [Figure 6] 2 is a diagram showing a cross section perpendicular to the axial direction (vehicle width direction) of the cross member. FIG. [Figure 7] 1A to 1C are diagrams illustrating examples of shapes of a cross member. [Figure 8] 1A to 1C are diagrams illustrating examples of shapes of a cross member. [Figure 9] 1A to 1C are diagrams showing examples of the shape of a cross member having a first ridgeline portion and a second ridgeline portion. [Figure 10] 1A to 1C are diagrams showing examples of shapes of cross members that do not have either or both of a first ridgeline portion and a second ridgeline portion. [Figure 11] 13 is a diagram showing an example in which a reinforcing member is joined to a cross member. FIG. [Figure 12] 11A and 11B are diagrams illustrating examples of arrangement of reinforcing members. [Figure 13] 1A to 1C are diagrams illustrating examples of shapes of a cross member having a hollow portion. [Figure 14] 1 is a diagram showing an example in which a reinforcing member is joined to a cross member having a hollow portion. FIG. [Figure 15] FIG. 13 is a diagram showing an analytical model of a pole side impact simulation. [Figure 16] FIG. 13 is a diagram showing a simulation result. [Figure 17] FIG. 13 is a diagram showing a simulation result. [Figure 18] FIG. 13 is a diagram showing a simulation result. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this specification and the drawings, elements having substantially the same functional configuration are designated by the same reference numerals, and redundant description will be omitted.

[0014] FIG. 1 is a diagram showing an outline of a vehicle body underbody structure according to an embodiment of the present invention. FIG. 2 is a diagram showing a cross section perpendicular to the axial direction (vehicle length direction) of a side sill. FIG. 3 is a perspective view showing the shape of an impact absorbing member. FIG. 4 is a diagram showing the impact absorbing member of FIG. 3 as seen in the vehicle width direction. Note that the "X direction" shown in the drawings referred to in this specification is the vehicle width direction, the "Y direction" is the vehicle length direction, and the "Z direction" is the vehicle height direction. Note that "connection" between parts in this specification includes a state in which parts are in contact with each other as well as a state in which parts are joined together. Also, "joining" between parts in this specification includes joining by welding as well as joining by adhesive, for example.

[0015] The vehicle body understructure 1 includes a floor panel 10 arranged under the vehicle body, a side sill 20, and a cross member 30. The vehicle body understructure 1 can be applied to vehicles equipped with a vehicle body understructure having a floor panel, side sill, and cross member, such as hybrid cars, electric cars, and other cars powered by an internal combustion engine.

[0016] The side sill 20 is a member having a hollow portion 20a extending in the vehicle length direction (Y direction), and is disposed at an end of the floor panel 10 in the vehicle width direction (X direction).

[0017] The side sill 20 has an outer part 21, an inner part 22, and a shock absorbing part 23. Note that Fig. 1 shows the shape of the shock absorbing part 23 in schematic form, and Figs. 2 to 4 show the specific shape.

[0018] The outer part 21 and the inner part 22 are each hat-shaped, and the side sill 20 is formed into a hollow shape by joining a flange of the outer part 21 and a flange of the inner part 22 to each other. A collision load is input to a wall part of the side sill 20 on the outer side in the vehicle width direction (hereinafter, "outer side wall part 24") during a side collision. The floor panel 10 described above is connected to a wall part of the side sill 20 on the inner side in the vehicle width direction (hereinafter, "inner side wall part 25").

[0019] The impact absorbing portion 23 is a member that absorbs collision energy by its own plastic deformation during a collision, and extends in the vehicle length direction (Y direction) of the side sill 20. In this embodiment, the impact absorbing portion 23 is connected to the inner surfaces of both wall portions 24, 25 so as to be bridged between the vehicle outer side wall portion 24 and the vehicle inner side wall portion 25 at the center of the outer part 21 and the inner part 22 in the vehicle height direction (Z direction).

[0020] As shown in Figs. 2 to 4, the impact absorbing section 23 has a plurality of bottom surface portions 23a, two side surface portions 23b sandwiching the bottom surface portions 23a, and a top surface portion 23c connected to the upper end portion of each side surface portion 23b. Ridge portions 23d between the surfaces 23a to 23c each extend in the vehicle width direction (X direction). The impact absorbing section 23 has the bottom surface portion 23a, the two side surface portions 23b, and the top surface portion 23c continuously provided along the vehicle length direction (Y direction). Therefore, the shape of the impact absorbing section 23 is a wave shape having unevenness that continues along the vehicle length direction.

[0021] In this specification, the region where the shock absorbing parts 23 are arranged when viewed from the vehicle width direction (X direction) is referred to as the "arrangement region R of the shock absorbing parts 23." For example, in the shock absorbing part 23 shown in FIG. 4, the region from the bottom surface part 23a to the top surface part 23c is the arrangement region R of the shock absorbing parts 23.

[0022] The schematic configuration of the side sill 20 has been described above, but the configuration of the side sill 20 is not particularly limited, and a known configuration may be applied. As shown in Fig. 5, the side sill 20 may have a hollow portion 20a and a shock absorbing portion 23, for example, formed by extrusion molding. Note that the arrangement region R of the shock absorbing portion 23 in the example of Fig. 5 is the region between the lower surface and the upper surface of the shock absorbing portion 23.

[0023] The cross member 30 is a member extending in the vehicle width direction (X direction). In this embodiment, the cross member 30 extends so as to be bridged across a pair of side sills 20 extending in the vehicle length direction (Y direction), and both ends of the cross member 30 in the vehicle width direction are connected to the vehicle interior side wall portions 25 of the side sills 20. Note that, for example, one end of the cross member 30 in the vehicle width direction may be connected to the vehicle interior side wall portions 25 of the side sills 20, and the other end may be connected to a floor tunnel (not shown). In addition, the number of cross members 30 is not particularly limited, and multiple cross members 30 may be provided at intervals in the vehicle length direction (Y direction).

[0024] The following describes the shape of the cross member 30. Fig. 6 is a diagram showing a cross section perpendicular to the axial direction (vehicle width direction) of the cross member 30. Figs. 7 and 8 are diagrams showing examples of the shape of the cross member 30.

[0025] As shown in FIG. 6, the cross member 30 has a plurality of walls including a top wall portion 31, two vertical wall portions 32, and two flange portions 33.

[0026] An upper end of the vertical wall portion 32 is connected to an end portion of the top wall portion 31 in the vehicle length direction (Y direction). A lower end of the vertical wall portion 32 is connected to a flange portion 33. A ridge portion 34 sandwiched between the top wall portion 31, the vertical wall portion 32, and the flange portion 33 extends in the vehicle width direction (X direction). In the cross member 30 having such a shape, a hollow portion 30a extending in the vehicle width direction is formed by joining the flange portion 33 to the floor panel 10. Note that the black circles in the drawings referred to in this specification indicate the joint portion 40 of two adjacent parts.

[0027] The vertical wall portion 32 has a first wall portion 32a, a second wall portion 32b, and a third wall portion 32c. The first wall portion 32a and the third wall portion 32c each extend in the vehicle height direction (Z direction), and the second wall portion 32b is connected to the upper end of the first wall portion 32a and the lower end of the third wall portion 32c. Each ridge portion 34 sandwiched between each wall portion 32a to 32c extends in the vehicle width direction (X direction). The ridge portion 34 sandwiched between the first wall portion 32a and the second wall portion 32b has a bending center located inside the cross member 30 (inside the hollow portion 30a). The ridge portion 34 sandwiched between the second wall portion 32b and the third wall portion 32c has a bending center located outside the cross member 30 (outside the hollow portion 30a).

[0028] The vertical wall portion 32 is formed in a stepped shape due to the above-mentioned configuration. The ridge line portion 34 sandwiched between the first wall portion 32a and the second wall portion 32b, and the ridge line portion 34 sandwiched between the second wall portion 32b and the third wall portion 32c are located at positions overlapping with the arrangement region R of the impact absorbing portion 23 when viewed from the vehicle width direction (X direction).

[0029] In the following description, among the multiple ridges 34 present from the joint 40 with the floor panel 10 to the top wall 31, the ridges 34 whose bending centers are located inside the cross member 30 (inside the hollow portion 30a) and located in an area overlapping with the arrangement area R of the impact absorbing portion 23 as viewed from the vehicle width direction (X direction) may be referred to as the "first ridge A". Also, the ridges 34 whose bending centers are located outside the cross member 30 (outside the hollow portion 30a) and located in an area overlapping with the arrangement area R of the impact absorbing portion 23 as viewed from the vehicle width direction may be referred to as the "second ridge B". For example, in the cross member 30 shown in FIG. 6, the ridges 34 between the first wall portion 32a and the second wall portion 32b are the first ridge A, and the ridges 34 between the second wall portion 32b and the third wall portion 32c are the second ridge B.

[0030] That is, in the cross member 30 in this embodiment, when viewed from the vehicle width direction (X direction), the first ridge line portion A, the second ridge line portion B, and the second wall portion 32b between the first ridge line portion A and the second ridge line portion B are located in a region that overlaps with the arrangement region R of the impact absorbing portion 23. Also, a portion of the first wall portion 32a extending downward from the first ridge line portion A is located within the arrangement region R, and the remainder is located outside the arrangement region R. Also, a portion of the third wall portion 32c extending upward from the second ridge line portion B is located within the arrangement region R, and the remainder is located outside the arrangement region R.

[0031] The above is an explanation of the general configurations of the floor panel 10, side sills 20, and cross member 30 included in the vehicle body lower structure 1. The floor panel 10, side sills 20, and cross member 30 are formed from metal materials such as steel, aluminum alloy members, magnesium alloy members, etc., having a tensile strength of 440 to 2500 MPa.

[0032] According to the vehicle body underbody structure 1 of this embodiment, the vertical wall portion 32 of the cross member 30 is composed of a plurality of walls 32a to 32c, thereby improving the surface rigidity of the vertical wall portion 32. More specifically, even if the overall height (length in the vehicle height direction) of the vertical wall portion 32 in this embodiment is the same as that of a conventional vertical wall portion composed of a single wall portion, the height of each wall portion constituting the vertical wall portion 32 is low, thereby improving the surface rigidity of each wall portion. As a result, the surface rigidity of the entire vertical wall portion 32 is also increased, so that out-of-plane deformation of the vertical wall portion 32 is suppressed, and the resistance of the cross member 30 to a collision load is improved.

[0033] Furthermore, the collision load input to the cross member 30 is mainly transmitted from the arrangement region R of the impact absorbing portion 23, but in the cross member 30 of this embodiment, the first ridge line A and the second ridge line B are located at positions overlapping with the arrangement region R of the impact absorbing portion 23 when viewed from the vehicle width direction (X direction). Therefore, the collision load transmitted from the arrangement region R can be received by the first ridge line A and the second ridge line B, improving the resistance of the cross member 30 to the collision load.

[0034] Therefore, according to the vehicle underbody structure 1 of this embodiment, the resistance of the cross member 30 to a collision load during a side collision can be increased, and out-of-plane deformation of the vertical wall portion 32 of the cross member 30 can be suppressed. As a result, out-of-plane deformation of the vehicle interior wall portion of the side sill 20 to which the cross member is connected can also be suppressed, and plastic deformation of the impact absorbing portion 23 can be promoted. This makes it possible to improve the energy absorption performance of the vehicle underbody structure 1, as will be shown in the examples described later.

[0035] If the number of steps in the stepped vertical wall portion 32 becomes too large and the height of the wall portion of each step becomes too low, the boundaries between the steps become unclear, and the deformation behavior of the vertical wall portion 32 during a collision may become similar to that of a vertical wall portion composed of a single wall portion. A preferable upper limit for the number of steps in the vertical wall portion 32 varies depending on the shape of the cross member 30 and the size of the arrangement region R of the impact absorbing portion 23, but in order to enhance the effect of improving the surface rigidity of the vertical wall portion 32, it is preferable that the number of steps in the vertical wall portion 32 is, for example, 2 to 3.

[0036] 7, the top wall portion 31 of the cross member 30 may be located in a region overlapping with the arrangement region R of the impact absorbing portion 23 when viewed from the vehicle width direction (X direction). In this case, in addition to the ridge portion 34 between the first wall portion 32a and the second wall portion 32b, the ridge portion 34 between the top wall portion 31 and the third wall portion 32c also becomes the first ridge portion A, increasing the number of ridge portions that receive the collision load transmitted from the arrangement region R of the impact absorbing portion 23. This effectively increases the resistance of the cross member 30 to the collision load.

[0037] As shown in Fig. 8, a recess 35 may be formed in the top wall 31 of the cross member 30. The recess 35 shown in Fig. 8 has a bottom wall 35a and a side wall 35b. The side wall 35b is a wall between the bottom wall 35a and the top wall 31, and the ridge line 34 sandwiched between the bottom wall 35a and the side wall 35b extends in the vehicle width direction (Y direction). By forming such a recess 35 in the top wall 31, the number of ridge lines that receive a collision load increases, and the strength of the cross member 30 can be improved.

[0038] Moreover, the cross member 30 may be composed of a plurality of parts as shown in Fig. 8. In the example shown in Fig. 8, the cross member 30 is composed of a first part 36 and a second part 37. The first part 36 and the second part 37 each have a first ridge portion A and a second ridge portion B, and both parts are joined at the bottom wall portion 35a of the recess 35.

[0039] The shape of the cross member 30 is not limited to the shape described above, and may be, for example, the shape shown in FIG. 9. FIG. 9(a) shows an example in which only one of the two vertical wall portions 32 is formed in a stepped shape. FIG. 9(b) shows an example in which the bottom wall portion 35a of the recess 35 is not in contact with the floor panel 10. FIG. 9(c) shows an example in which the bottom wall portion 35a of the recess 35 is located within the arrangement region R of the impact absorbing portion 23. FIG. 9(d) shows an example in which the vertical wall portion 32 has four steps. FIG. 9(e) shows an example in which the vertical wall portion 32 has an inclined portion.

[0040] FIG. 9(f) shows an example in which the vertical wall portion 32 is not formed in a stepped shape, but the side wall portion 35b of the recessed portion 35 is formed in a stepped shape. In this example, the bottom wall portion 35a of the recessed portion 35 is joined to the floor panel 10, and a first ridge portion A and a second ridge portion B exist between the joint portion 40 and the top wall portion 31. This increases the surface rigidity of the side wall portion 35b, and increases the resistance of the cross member 30 to a collision load. In other words, the wall portion formed in a stepped shape is not limited to the vertical wall portion 32, and may be any wall portion between the joint portion 40 with the floor panel 10 and the top wall portion 31.

[0041] FIG. 10 is a diagram showing an example of the shape of a cross member 30 that does not have either or both of the first ridgeline portion A and the second ridgeline portion B. FIG. 10(a) is an example showing a cross member 30 in a general hat shape. FIG. 10(b) is an example in which the first ridgeline portion exists because the top wall portion 31 is located in an area overlapping with the arrangement area R of the shock absorbing portion 23, but the second ridgeline portion B does not exist. FIG. 10(c) is an example in which the vertical wall portion 32 is formed in a stepped shape, but the ridgeline portion 34 of each wall portion is located outside the arrangement area R of the shock absorbing portion 23. FIG. 10(d) is an example in which a recess 35 is formed in the top wall portion 31, but the first ridgeline portion A and the second ridgeline portion B do not exist.

[0042] Figure 10(e) shows an example of a cross member 30 having the same shape as the cross member 30 shown in Figure 9(f), but in which the bottom wall portion 35a of the recess 35 is not joined to the floor panel 10. In this cross member 30, the side wall portion 35b of the recess 35 is formed in a stepped shape, but since the bottom wall portion 35a is not joined to the floor panel 10, the contribution of this to improving the strength of the cross member 30 is low.

[0043] The shape of the cross member 30 has been described above, but as shown in FIG. 11, a reinforcing member 50 may be joined to the cross member 30. The reinforcing member 50 is formed so that the cross section in the axial direction (X direction) is U-shaped, and has a bottom surface portion 51 and two side surfaces 52 sandwiching the bottom surface portion 51. In the example shown in FIG. 11, the bottom surface portion 51 of the reinforcing member 50 is joined to the outer surface of the top wall portion 31 of the cross member 30, and the side surface portion 52 of the reinforcing member 50 is joined to the outer surface of the first wall portion 32a of the cross member 30. By providing such a reinforcing member 50, a closed cross section surrounded by the cross member 30 and the reinforcing member 50 is formed, and the surface rigidity of each wall portion of the cross member 30 can be improved. The bottom surface portion 51 of the reinforcing member 50 does not have to be in contact with the top wall portion 31 of the cross member 30.

[0044] The reinforcing member 50 may be shaped to extend over the entire length of the cross member 30, or, as shown in FIG. 12, multiple reinforcing members 50 may be arranged at intervals along the vehicle width direction (X direction).

[0045] In the above description, the cross member 30 is joined to the floor panel 10 to form the hollow portion 30a extending in the vehicle width direction (X direction). However, as shown in FIG. 13, the cross member 30 may be formed hollow by extrusion molding, for example. The cross member 30 has a top wall portion 31, two vertical wall portions 32, and a bottom wall portion 38 sandwiched between the two vertical wall portions 32, and the two vertical wall portions 32 and the floor panel 10 are joined by, for example, fillet welding. In this example, a first ridge portion A and a second ridge portion B are present between the joint portion 40 with the floor panel 10 and the top wall portion 31, which are located in an area overlapping with the arrangement area R of the impact absorbing portion 23. As a result, the vertical wall portion 32 is composed of a plurality of walls, and the surface rigidity of the vertical wall portion 32 is improved.

[0046] As shown in Fig. 14, the above-mentioned reinforcing member 50 may be provided on a cross member 30 having a hollow portion 20a. Also, the reinforcing member 50 and the cross member 30 shown in Fig. 14 may be integrally molded, for example, by extrusion molding.

[0047] Although an example of an embodiment of the present invention has been described above, the present invention is not limited to such an example. It is clear that a person skilled in the art can come up with various modified or revised examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention. EXAMPLES

[0048] Using the analytical model of the vehicle underbody structure shown in Fig. 15, a pole side impact simulation was carried out to simulate a side impact.

[0049] The side sill 20 of this analysis model is configured by two hat-shaped parts joined together at the flange portion. The impact absorbing part 23 is cuboid-shaped and is connected to the inner surface of the outer wall portion and the inner wall portion of the side sill 20 in the hollow portion of the side sill 20. The floor panel 10 is connected to the inner wall portion of the side sill 20. Two cross members 30 are arranged at an interval in the vehicle length direction (Y direction). The material of each part is steel plate with a tensile strength of 1180 MPa.

[0050] In this simulation, a pole with a radius of 127 mm was brought into contact with the outer wall of the side sill 20 and moved toward the inner side of the vehicle at a speed of 1 m / s. The contact position of the pole in the vehicle length direction (Y direction) is a position between the two cross members 30. In addition, restraint surfaces are set on the inner end faces of the floor panel 10 and the cross member 30 and the axial end face of the side sill 20. Specifically, the inner end faces of the floor panel 10 and the cross member 30 are completely restrained as rigid surfaces, and only deformation in the axial direction (Y direction) is restrained for the axial end face of the side sill 20.

[0051] A simulation was performed under the above conditions, and the energy absorption efficiency (amount of energy absorbed by the impact absorbing section / mass of the cross member) was calculated when the pole penetrated 85 mm. The results are shown in Figures 16 to 18. This simulation was performed on multiple models with different cross member shapes and the presence or absence of reinforcing members. When creating each model, the plate thickness t of the cross member was changed so that the total mass of the vehicle underbody structure was the same for each model.

[0052] 16, the model of Example 1 is a model in which the vertical wall portion of the cross member is formed in a stepped shape and has a first ridge line A and a second ridge line B that overlap with the arrangement area of ​​the impact absorbing portion. The model of Example 1 is superior in energy absorption efficiency to the models of Comparative Example 1 and Comparative Example 2 in which the first ridge line A and the second ridge line B do not exist.

[0053] As shown in Fig. 17, the models of Example 2 and Comparative Example 3 are models that do not have reinforcing members, unlike the model shown in Fig. 16. Even when reinforcing members are not provided in this way, the model of Example 2 in which the first ridgeline A and the second ridgeline B are present has superior energy absorption efficiency to the model of Comparative Example 3 in which the first ridgeline A and the second ridgeline B are not present. In particular, the model of Example 2 has a thinner cross member plate thickness than the model of Comparative Example 3, but has a higher energy absorption efficiency, which shows that the presence of the first ridgeline A and the second ridgeline B has a significant effect of improving surface rigidity.

[0054] As shown in FIG. 18, the models of all the examples have a higher energy absorption efficiency than the model of Comparative Example 2 (FIG. 16) in which the first ridgeline portion A and the second ridgeline portion B do not exist. [Industrial Applicability]

[0055] The present invention can be applied to the underbody structure of an automobile. [Explanation of symbols]

[0056] 1. Underbody structure 10 Floor Panel 20 Side sill 20a Hollow part 21 Outer parts 22 Inner parts 23 Shock absorbing part 23a Bottom part 23b Side part 23c Top section 23d Ridge 24 Vehicle exterior wall 25 Car interior wall 30 Cross member 30a Hollow part 31 Ceiling wall 32 Vertical wall section 32a 1st wall 32b 2nd wall part 32c 3rd wall section 33 Flange section 34 Ridgeline 35 Recess 35a Bottom wall 35b Side wall part 36 First Part 37 Second Part 38 Bottom wall 40 Joint 50 Reinforcement member 51 Bottom part 52 Side part A First ridge B Second ridge R Impact absorbing part placement area t Plate thickness

Claims

1. A floor panel located under the vehicle body; A side sill extending in a vehicle length direction is provided at an end of the floor panel in a vehicle width direction; A cross member connected to the side sill and extending in a vehicle width direction; a joint between the floor panel and the cross member, The side sill is A hollow portion extending in a vehicle length direction; A shock absorbing portion made of a metal material and disposed in the hollow portion, The impact absorbing portion is provided from a wall portion of the side sill on the vehicle outer side in the vehicle width direction to a wall portion on the vehicle inner side in the vehicle width direction, The cross member is A plurality of walls including a top wall; a plurality of ridge lines extending in a vehicle width direction and sandwiched between the wall portions; The plurality of ridge lines include a first ridge line and a second ridge line between the joint portion and the top wall portion, a bending center of the first ridge portion is located on the inner side of the cross member, A bending center of the second ridge portion is located on an outer side of the cross member, a shock absorbing portion that absorbs shocks from the shock absorbing member and that is disposed in a region overlapping the first ridge portion and the second ridge portion when viewed in a vehicle width direction;

2. A recess is formed in the top wall portion, The recess has a bottom wall and two side walls, The bottom wall portion is located between the two side wall portions, The vehicle underbody structure according to claim 1 , wherein a ridge portion sandwiched between the bottom wall portion and the two side wall portions extends in a vehicle width direction.

3. The cross member has a first component and a second component, the first component and the second component each have the first ridge portion and the second ridge portion, The vehicle underbody structure according to claim 2 , wherein the first component and the second component are connected to each other at the bottom wall portion.

4. A floor panel disposed under a vehicle body; A side sill extending in a vehicle length direction is provided at an end of the floor panel in a vehicle width direction; A cross member connected to the side sill and extending in a vehicle width direction; a joint between the floor panel and the cross member, The side sill is A hollow portion extending in a vehicle length direction; A shock absorbing portion is disposed in the hollow portion, The impact absorbing portion is connected to a wall portion of the side sill on the vehicle width direction inner side, The cross member is A plurality of walls including a top wall; a plurality of ridge lines extending in a vehicle width direction and sandwiched between the wall portions; The plurality of ridge lines include a first ridge line and a second ridge line between the joint portion and the top wall portion, a bending center of the first ridge portion is located on the inner side of the cross member, A bending center of the second ridge portion is located on an outer side of the cross member, the first ridge portion and the second ridge portion are located in a region overlapping with an arrangement region of the impact absorbing portion when viewed from a vehicle width direction, A recess is formed in the top wall portion, The recess has a bottom wall and two side walls, The bottom wall portion is located between the two side wall portions, A ridge portion between the bottom wall portion and the two side wall portions extends in a vehicle width direction, The cross member has a first component and a second component, the first component and the second component each have the first ridge portion and the second ridge portion, A vehicle underbody structure, wherein the first part and the second part are connected to each other at the bottom wall portion.

5. The vehicle underbody structure according to any one of claims 1 to 4, wherein the top wall portion is located in a region overlapping with the arrangement region of the impact absorbing portion when viewed in a vehicle width direction.

6. A reinforcing member is provided to reinforce the cross member, The reinforcing member has a bottom surface and two side surfaces, The bottom surface portion is located between the two side surfaces, A ridge portion sandwiched between the bottom surface portion and the two side surface portions extends in a vehicle width direction, The bottom surface portion is located above the top wall portion of the cross member, 6. The vehicle underbody structure according to claim 1, wherein the two side surface portions are each joined to a wall portion of the cross member other than the top wall portion.

7. The vehicle underbody structure according to claim 6 , wherein the reinforcing member is provided in a plurality of parts spaced apart from each other in a vehicle width direction.

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