Vehicle rear structure

Abstract

By integrally forming the rear side members from a single high-tensile steel sheet using cold press forming, this vehicle rear structure effectively absorbs collision energy during a rear-end collision while suppressing deformation of the cabin area, thereby improving both productivity and mass efficiency. [Solution] The vehicle rear structure 1 according to the present invention is equipped with a pair of rear side members 11 arranged on both sides in the width direction of the automobile 100 and extending in the front-rear direction. Each rear side member 11 is integrally formed by cold pressing a single high-tensile steel plate 21 having two parts with different yield strengths and / or plate thicknesses. The boundary 11c between the front part 11a and the rear part 11b of the rear side member 11 is located between a position 100 mm behind the rear end of the rear wheel 101 of the automobile 100 and the rear end of the rear row seat 103. The cross-sectional strength of the front part 11a against the collision load applied to the rear side member 11 during a rear collision of the automobile 100 is 10% or more higher than the cross-sectional strength of the rear part 11b.

Description

Technical Field

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

Background Art

[0002] In order to reduce the manufacturing cost of an automobile body, integration of a plurality of components into one component by applying aluminum cast parts or the like has been promoted. Aluminum cast parts may be able to suppress processing costs, but the material cost is relatively high compared to the current components mainly made of steel materials (steel plates). On the other hand, if some components can be integrated and made into an integrated body while maintaining the steel plate structure with low material cost, omission of the manufacturing process by reducing the number of components will directly reduce the manufacturing cost, which is advantageous over aluminum cast parts in terms of total cost. Note that integrating components into one means manufacturing a component made by joining a plurality of parts manufactured in different press processes by spot welding or the like in a joining process as one component in one press process, and part of the press process and the joining process can be omitted.

[0003] In addition, components of an automobile body are designed and manufactured to have various performances and characteristics from the viewpoints of vehicle performance, weight, etc. Therefore, when integrating a plurality of components into one, for example, it is required that each part has the performance and characteristics that the original components had before integration, such as a part of the integrated component being stronger than other parts.

[0004] So far, technologies for manufacturing components of an automobile body to have different performances and characteristics for each part have been proposed. For example, Patent Document 1 discloses a technique in which a plurality of reinforcing steel plates are overlapped and welded only to a portion formed at a specific portion of a material steel plate of a vehicle body component, and hot stamping is performed. According to this technique, it is said that only a specific portion of the overlapped hot stamping body can be partially strengthened while reducing the number of press dies.

Prior Art Documents

[0005] [Patent Document 1] Patent No. 6451327 [Overview of the project] [Problems that the invention aims to solve]

[0006] The rear structure of an automobile, particularly around the rear floor, is configured to include parts that actively deform during a rear-end collision to absorb collision energy, and parts that remain undeformed to protect the cabin area where the occupants are seated. For example, in the vehicle rear structure 5 shown in Figure 17, the pair of left and right rear side members 51 extending in the longitudinal direction of the vehicle are configured such that the front portion 51a is a part that does not deform during a rear collision, and the rear portion 51b is a part that actively deforms to absorb collision energy. In such conventional rear side members 51, the parts corresponding to the front section 51a and the rear section 51b were manufactured using different pressing processes and joined at the joint 51c by spot welding. The material strength and thickness of the steel plates used for the parts corresponding to the front section 51a and the rear section 51b were appropriately set so that the part corresponding to the front section 51a would not deform during a rear-end collision, while the part corresponding to the rear section 51b would deform to absorb collision energy.

[0007] It is considered that the hot stamping technology described in Patent Document 1 can be applied to manufacture the rear side member 51, which can absorb collision energy and protect the cabin area, by integrating it through a steel plate pressing process.

[0008] However, in actual production, hot stamping technology resulted in significant dimensional variations in manufactured parts, necessitating safety design measures such as increasing plate thickness. Consequently, even when integrated rear side members were manufactured using hot stamping technology, the weight increased, resulting in a problem where the part mass ratio (mass efficiency) to crash performance was inferior to parts cold-pressed from high-tensile steel. In general, "high-tensile steel plate" refers to a steel plate with a tensile strength of 340 MPa or higher, and the same meaning is used in this application.

[0009] Furthermore, hot stamping technology involves heating and cooling the steel blank during the pressing process, resulting in slow production speeds and failing to meet the demand for integrated components aimed at reducing manufacturing costs. Therefore, there was a need for a technology that could satisfy both productivity and mass efficiency requirements by manufacturing integrated rear side members through cold pressing of a single high-tensile steel sheet.

[0010] The present invention was made to solve the above-mentioned problems, and aims to provide a vehicle rear structure that can sufficiently absorb collision energy during a rear collision while suppressing deformation of the cabin area, and further improve both productivity and mass efficiency, by integrally forming the rear side member by cold press forming of a single high-tensile steel plate. [Means for solving the problem]

[0011] (1) The vehicle rear structure according to the present invention comprises a pair of rear side members arranged on both sides in the width direction of the automobile and extending in the front-rear direction, Each of the aforementioned rear side members is integrally formed by cold pressing a single high-tensile steel sheet having two portions with different yield strengths and / or thicknesses. The boundary between the front and rear portions of the rear side member is located between a point 100 mm behind the rear end of the rear wheel of the vehicle and the rear end of the rear seats of the vehicle. The present invention is characterized in that the cross-sectional strength of the front portion against the collision load applied to the rear side member during a rear-end collision of the vehicle is 10% or more higher than the cross-sectional strength of the rear portion.

[0012] (2) In the items described in (1) above, The aforementioned single high-tensile steel plate is formed by butt welding together two high-tensile steel plates with different yield strengths and / or plate thicknesses. The invention is characterized in that the two joined high-tensile steel plates correspond to each of the two parts.

[0013] (3) In the items described in (1) above, The aforementioned high-tensile steel plate is characterized in that one high-tensile steel plate is joined by spot welding to all or part of the portion corresponding to the front side of one high-tensile steel plate, with another high-tensile steel plate superimposed on it. [Effects of the Invention]

[0014] In this invention, the front and rear portions of the rear side member are integrally formed by cold pressing a single high-tensile steel sheet having two portions with different yield strengths and / or thicknesses, resulting in a higher cross-sectional load-bearing capacity in the front portion than in the rear portion. As a result, during a rear-end collision, the rear portion deforms to absorb collision energy while deformation of the front portion is suppressed, thereby suppressing deformation of the cabin area and protecting the occupants. Furthermore, according to the present invention, unlike conventional rear side members, the joint where multiple parts corresponding to the front and rear sections are welded together does not break, thus suppressing a decrease in the amount of collision energy absorbed, and an improvement in collision performance can be expected. Furthermore, according to the present invention, manufacturing costs can be reduced and productivity can be improved, and weight can be reduced, thereby improving mass efficiency in terms of collision performance. [Brief explanation of the drawing]

[0015] [Figure 1]It is a figure showing the configuration of a vehicle rear structure according to an embodiment of the present invention ((a) perspective view from below, (b) side view in a state of being disposed on an automobile). [Figure 2] In the vehicle rear structure according to the present embodiment, it is a figure showing a specific example of a single high-tensile steel sheet used for cold press forming of a rear side member, in which two high-tensile steel sheets having different yield strengths and / or sheet thicknesses are joined by butt welding. [Figure 3] It is a top view showing a desirable deformation state of a rear side member in a rear collision test of an automobile. [Figure 4] It is a top view showing an undesirable deformation state of a rear side member in a rear collision test of an automobile. [Figure 5] In the vehicle rear structure according to the present embodiment, it is a figure showing another specific example of a single high-tensile steel sheet used for cold press forming of a rear side member, in which another high-tensile steel sheet is overlapped and joined by spot welding at a portion corresponding to the front side portion of the rear side member in a single high-tensile steel sheet. [Figure 6] It is a figure showing a rear side member cold press formed using a single high-tensile steel sheet joined by spot welding in a state where another high-tensile steel sheet is overlapped at a portion corresponding to the front side portion of the rear side member in a single high-tensile steel sheet. [Figure 7] It is a figure showing a deformation state of a rear side member at the initial stage of a collision in a rear collision test of an automobile equipped with a vehicle rear structure according to Example 1 of the present invention. [Figure 8] It is a figure showing a deformation state of a rear side member at the later stage of a collision in a rear collision test of an automobile equipped with a vehicle rear structure according to Example 1 of the present invention. [Figure 9] It is a figure showing a deformation state of a rear side member at the initial stage of a collision in a rear collision test of an automobile equipped with a vehicle rear structure according to Example of the present invention. [Figure 10] It is a figure showing a deformation state of a rear side member at the later stage of a collision in a rear collision test of an automobile equipped with a vehicle rear structure according to Example 2 of the present invention. [Figure 11] This figure shows the deformation state of the rear side member in the initial stages of a rear-end collision test of an automobile equipped with the rear vehicle structure according to Embodiment 3 of the present invention. [Figure 12] This figure shows the deformation state of the rear side member in the later stages of a collision during a rear-end collision test of an automobile equipped with the rear vehicle structure according to Embodiment 3 of the present invention. [Figure 13] This figure shows the deformation state of the rear side member at the initial stage of a collision in a rear-end collision test of an automobile equipped with a comparative vehicle rear structure according to the present invention. [Figure 14] This figure shows the deformation state of the rear side member in the later stages of a collision during a rear-end collision test of an automobile equipped with a vehicle rear structure according to a comparative example used as a comparison for the present invention. [Figure 15] This figure shows the deformation state of the rear side member at the initial stage of a rear-end collision test of an automobile equipped with a conventional vehicle rear structure used as a comparison for the present invention. [Figure 16] This figure shows the deformation state of the rear side member in the later stages of a collision during a rear-end collision test of an automobile equipped with a conventional vehicle rear structure used as a comparison for the present invention. [Figure 17] This diagram shows the configuration of a conventional vehicle rear structure ((a) entire vehicle, (b) rear of vehicle, (c) rear structure of vehicle). [Modes for carrying out the invention]

[0016] As shown in Figure 1, the vehicle rear structure 1 according to an embodiment of the present invention comprises a pair of left and right rear side members 11 disposed on both sides in the vehicle width direction of the automobile 100 and extending in the vehicle front-rear direction, and a rear cross member 13 disposed between the rear side members 11 and extending in the vehicle width direction, with both ends connected to the sides of each rear side member 11.

[0017] Each rear side member 11 is integrally formed by cold pressing a single high-tensile steel sheet, which has two sections with different yield strengths and / or thicknesses.

[0018] In this application, integral molding refers to the production of the rear side member 11 as a single part using a set of mold series. However, integral molding may also be considered in cases where the press molding process for a press-formed product is divided into multiple stages, and a mold is required for each stage. In such cases, however, integral molding refers to the production of the rear side member 11 in which the front part 11a and the rear part 11b (see Figure 1) are integrated into a single piece in the final press stage.

[0019] Furthermore, in this embodiment, as shown in Figure 2, a single high-tensile steel plate 21 (blank) is used, which is formed by joining two high-tensile steel plates 21a and 21b with different yield strengths and / or plate thicknesses by butt welding (laser welding, etc.). Then, by cold pressing the high-tensile steel plate 21, the portion of the high-tensile steel plate 21a becomes the front portion 11a of the rear side member 11, and the portion of the high-tensile steel plate 21b becomes the rear portion 11b. The yield strength and thickness of the high-tensile steel plates 21a and 21b should be appropriately selected, taking into consideration not only the sectional strength of the front portion 11a and the rear portion 11b of the rear side member 11, but also the formability of the cold press.

[0020] In the cold-pressed rear side member 11, the boundary 11c between the front portion 11a and the rear portion 11b is located between a position 100 mm behind the rear end of the rear wheel 101 of the automobile 100 and the rear end of the rear seat 103 of the automobile 100. Here, the position 100 mm behind the rear end of the rear wheel 101 and the rear end of the rear seat 103 are positions in the longitudinal direction of the vehicle.

[0021] Furthermore, in the rear side member 11, the cross-sectional strength of the front portion 11a against the collision load applied to the rear side member 11 during a rear-end collision of a vehicle is 10% or more higher than the cross-sectional strength of the rear portion 11b.

[0022] The sectional strength is calculated by multiplying (the yield stress of the high-tensile steel plate 21a which forms the front part 11a of the rear side member 11 or the high-tensile steel plate 21b which forms the rear part 11b) by (the cross-sectional area of ​​the section perpendicular to the compression direction of the front part 11a or the rear part 11b), and corresponds to the compressive failure strength. The cross-sectional area of ​​the front part 11a or the rear part 11b is calculated by multiplying the plate thickness of the high-tensile steel plate corresponding to the front part 11a or the rear part 11b by the minimum cross-sectional line length of the section perpendicular to the compression direction.

[0023] In the vehicle rear structure 1 according to this embodiment, the cross-sectional strength of the front portion 11a and the rear portion 11b of the rear side member 11 and the position of the boundary 11c were determined based on the deformation state of the rear side member 11 after conducting a rear-end collision test of the automobile 100 shown in Figures 3 and 4. Here, the rear-end collision test of the automobile 100 was a collision analysis in which a barrier 110 was collided with the rear of the automobile 100 at a predetermined collision speed.

[0024] Figure 3 shows the case where the cross-sectional strength of the front portion 11a of the rear side member 11 is higher than that of the rear portion 11b, whereas Figure 4 shows the case where the cross-sectional strength of the front portion 11a and the rear portion 11b are the same. Furthermore, in calculating the cross-sectional strength, the minimum cross-sectional length for both the front portion 11a and the rear portion 11b was 220 mm, near the boundary between them. Additionally, the plate thickness was 1.6 mm for the front portion 11a and 1.4 mm for the rear portion 11b, and the cross-sectional area of ​​the front portion 11a was 352 mm². 2 The rear section 11b is 308 mm 2 That was the case.

[0025] In Figure 3, the rear side member 11 shows deformation at the rear side portion 11b while the front side portion 11a remains unchanged, whereas in Figure 4, the rear side member 11 shows deformation at the front side portion 11a (indicated by the arrow in the figure). Therefore, as shown in Figure 3, a rear side member 11 in which the front portion 11a is not deformed is considered a desirable deformation state, and as shown in Figure 4, a rear side member 11 in which the front portion 11a is deformed is considered an undesirable deformation state. The reason why the case in which the front portion 11a is not deformed is considered desirable is twofold: firstly, the deformation of the cabin area 105 can be suppressed and the occupants can be protected by the front portion 11a not deforming while the rear portion 11b deforms, allowing for sufficient absorption of collision energy.

[0026] Based on the deformation state of the rear side member 11 during a rear-end collision, the cross-sectional load-bearing capacity of the front portion 11a and the rear portion 11b of the rear side member 11, and the position of the boundary 11c were determined through prior studies.

[0027] In the preliminary study, a rear-end collision test was first conducted on a vehicle 100 equipped with a vehicle rear structure 1 in which the sectional strength of the front section 11a and the rear section 11b was adjusted by changing the yield strength of the high-tensile steel plates 21a and 21b in the high-tensile steel plate 21 shown in Figure 2, and the deformation state of the rear side member 11 was determined. Table 1 shows the deformation state and judgment results of the rear side member 11 obtained in rear-end collision tests in which the cross-sectional load-bearing capacity of the front side portion 11a and the rear side portion 11b were adjusted in various ways.

[0028] [Table 1]

[0029] In Table 1, the increase in sectional strength is the increase in sectional strength of the front section 11a when the sectional strength of the rear section 11b is used as the reference. As shown in Table 1, if the cross-sectional strength of the front portion 11a of the rear side member 11 is 9.5% or more greater than the cross-sectional strength of the rear portion 11b, no deformation is observed in the front portion 11a, indicating a desirable deformation state for the rear side member 11. In this invention, in order to reliably suppress the deformation of the front portion 11a, the cross-sectional strength of the front portion 11a is specified to be 10% or more of the cross-sectional strength of the rear portion 11b.

[0030] Next, we will explain the appropriate position of the boundary 11c between the front portion 11a and the rear portion 11b of the rear side member 11.

[0031] The location of boundary 11c was defined for the following reasons: During a rear-end collision of automobile 100, the collision load is applied to the rear side member 11 as the rear of the vehicle is crushed, causing it to deform. As the collision progresses and the deformation of the rear side member 11 reaches the rear wheels 101, the rear wheels 101 take on the responsibility for the collision load, suppressing deformation of the cabin area.

[0032] However, if the boundary 11c in the rear side member 11 is too far to the rear, a high collision load will be applied to the front part 11a, which has higher cross-sectional strength, causing it to deform before the deformation of the rear side member 11 reaches the rear wheel 101, thus inducing deformation of the cabin area 105.

[0033] Furthermore, if the boundary 11c is located too far forward, the rear side member 11 located below the cabin area 105 will begin to deform in the initial stages of a rear-end collision, inducing deformation of the cabin area 105. Therefore, the boundary 11c between the front section 11a and the rear section 11b must be in an appropriate position.

[0034] Therefore, rear-end collision tests were conducted by changing the position of the boundary 11c between the front part 11a and the rear part 11b of the rear side member 11 in various ways, and the deformation state of the rear side member 11 was determined. The rear-end collision test, similar to the cross-sectional strength test described above, involved collision analysis in which the barrier 110 was collided with the rear of the automobile 100 at a predetermined collision speed (see Figures 3 and 4).

[0035] In the rear-end collision test, the front section 11a was made of high-tensile steel plate with a tensile strength of 1470 MPa (yield strength of 1193 MPa) and a thickness of 1.6 mm, with a cross-sectional area of ​​352 mm². 2 The cross-sectional strength was set to 420kN. In addition, the rear section 11b was made of high-tensile steel plate with a tensile strength of 980MPa class (yield strength of 800MPa) and a plate thickness of 1.6mm, with a cross-sectional area of ​​308mm². 2The sectional load-bearing capacity was set to 280kN.

[0036] Table 2 shows the deformation state of the rear side member 11 during a rear-end collision test for vehicle rear structure 1 with various changes in the position of the boundary 11c between the front side portion 11a and the rear side portion 11b. The deformation state of the rear side member 11 shown in Table 2 is classified as either deformed or not deformed depending on whether or not plastic deformation occurred in the front side portion 11a during the rear-end collision process.

[0037] [Table 2]

[0038] As shown in Table 2, in Cases 11 to 14, where the boundary 11c between the front part 11a and the rear part 11b is located more than 100 mm behind the rear end of the rear wheel 101, deformation occurred in the front part 11a. In contrast, in Cases 14 to 16, where the boundary 11c is located more than 100 mm behind the rear end of the rear wheel 101, no deformation was observed in the front part 11a. From these results, it was found that the critical position on the rear side of the boundary 11c between the front part 11a and the rear part 11b is preferably 100 mm behind the rear end of the rear wheel 101.

[0039] On the other hand, the critical position on the forward side of the boundary 11c between the front section 11a and the rear section 11b was set to the position of the rear end of the rear row seat 103 in the longitudinal direction of the vehicle. This is because if the boundary 11c is located in front of the rear end of the rear row seat 103, there is a concern that if an impacting object collides with the rear of the vehicle and the collision progresses, deformation of the cabin area 105 may be induced, impairing occupant protection.

[0040] Thus, in the vehicle rear structure 1 according to this embodiment, by making the cross-sectional load-bearing capacity of the front portion 11a of the rear side member 11 10% or more higher than that of the rear portion 11b, the rear portion 11b deforms during a rear-end collision to absorb collision energy, while the deformation of the front portion 11a is suppressed. As a result, deformation of the cabin area 105 during a rear-end collision is suppressed, and occupants can be protected.

[0041] Furthermore, the front portion 11a and the rear portion 11b of the rear side member 11 are integrally formed by cold pressing a single high-tensile steel plate 21. Therefore, unlike conventional rear side members 51 (see Figure 17) in which multiple parts are joined by welding, the fracture of the joint portion 51c and the resulting decrease in collision energy absorption can be suppressed.

[0042] Furthermore, according to the vehicle rear structure 1 of this embodiment, since it does not require the fabrication and joining of multiple parts as in the conventional rear side member 51 (Figure 17), manufacturing costs are reduced, productivity is improved, and weight can be reduced, improving mass efficiency in terms of collision performance.

[0043] In the above description, the single high-tensile steel sheet 21 used for cold pressing was, as shown in Figure 2, made by butt welding together two high-tensile steel sheets 21a and 21b with different yield strengths and / or thicknesses. However, the present invention may also be one in which the front portion 31a and the rear portion 31b of the rear side member 31 shown in Figure 6 are integrally formed by cold pressing a single high-tensile steel plate 41 (blank) as shown in Figure 5.

[0044] As shown in Figure 5, a single high-tensile steel plate 41 is formed by joining another high-tensile steel plate 45 to a portion of the front portion 43a of a single high-tensile steel plate 43 by spot welding (such as spot welding), with the latter overlapping the former. Therefore, the high-tensile steel plate 41 has two portions with different yield strengths and plate thicknesses: the portion 43a and high-tensile steel plate 45 corresponding to the front portion 31a, and the portion 43b corresponding to the rear portion 31b.

[0045] In the rear side member 31, which is integrally formed by cold pressing of high-tensile steel plate 41, the front portion 31a is formed by overlapping a high-tensile steel plate 45 with a high-tensile steel plate 43, and the rear portion 31b is formed by high-tensile steel plate 43. The sectional strength of the front portion 31a is calculated and added together by calculating the sectional strengths of the overlapping high-tensile steel plate 43 and high-tensile steel plate 45, and the sectional strength of the rear portion 31b is the sectional strength of the high-tensile steel plate 43.

[0046] Even a rear side member 31 formed by cold press forming of a single high-tensile steel sheet 41 falls under the category of integral molding as defined in this invention. Compared to a conventional rear side member 51 (Figure 17) composed of multiple parts, pressing and joining processes can be omitted, thereby reducing manufacturing costs and improving productivity.

[0047] Furthermore, the yield strength and thickness of the high-tensile steel plates 43 and 45 used in the high-tensile steel plate 41 should be appropriately selected, taking into consideration not only the sectional strength of the front portion 31a and rear portion 31b of the rear side member 31, but also the formability of cold pressing.

[0048] Furthermore, although the high-tensile steel plate 41 shown in Figure 5 was formed by overlapping another high-tensile steel plate 45 onto a portion of the front side portion 31a of a single high-tensile steel plate 43, it is also possible for another high-tensile steel plate 45 to be overlapped and joined over the entire portion 43a. [Examples]

[0049] Tests were conducted to verify the effects and benefits of the present invention, and these will be described below. The test involved a rear-end collision test (collision speed 50 km / h) in which a barrier collided with the rear of a vehicle equipped with a rear structure, and the deformation state of the rear side members was investigated.

[0050] For the rear-end collision test, the boundary between the front and rear sections of the rear side member was positioned 15 mm behind the rear end of the rear wheel. The cross-sectional length of the rear side member was set to 220 mm, the minimum length near the boundary between the front and rear sections. The cross-sectional strength was adjusted by varying the yield strength and thickness of the high-tensile steel plates corresponding to the front and rear sections of the rear side member.

[0051] <Example 1> Example 1 concerns a vehicle rear structure 1, which is made of a high-tensile steel plate 21 as shown in Figure 2 and has a rear side member 11 in which the front part 11a and the rear part 11b are integrally formed by cold pressing as shown in Figure 1, and a rear cross member 13 disposed between the left and right rear side members 11.

[0052] The high-tensile steel plate 21 was formed by butt welding a high-tensile steel plate 21a with a tensile strength of 1470 MPa (yield strength of 1193 MPa) and a thickness of 1.8 mm, and a high-tensile steel plate 21b with the same yield strength and a thickness of 1.4 mm. In Example 1, the sectional yield strength of the front part 11a of the rear side member 11 was 472 kN, and the sectional yield strength of the rear part 11b was 367 kN. The sectional yield strength of the front part 11a was 28.6% higher than that of the rear part 11b, which was within the scope of the present invention.

[0053] Figures 7 and 8 show the deformation state of the rear side member 11 of the automobile 100 as viewed from below, during the initial (stroke 250 mm) and late (stroke 750 mm) stages of the collision.

[0054] As shown in Figures 7 and 8, during the collision process from the initial to the later stages of the collision, the rear side member 11 shows no deformation at the front portion 11a, while only the rear portion 11b deforms, thus preventing deformation of the cabin area. Furthermore, the total collision energy absorbed by the rear side member 11 in Example 1 was 35.7 kJ.

[0055] <Example 2> Embodiment 2 concerns a vehicle rear structure 1 having a rear side member 11 in which the front side portion 11a and the rear side portion 11b are integrally molded as shown in Figure 1, using a high-tensile steel plate 21 as shown in Figure 2, and a rear cross member 13 disposed between the left and right rear side members 11.

[0056] The high-tensile steel plate 21 was formed by joining two high-tensile steel plates: 21a, which has a tensile strength of 1470 MPa (yield strength of 1193 MPa) and a thickness of 1.6 mm, and 21b, which has a tensile strength of 980 MPa (yield strength of 800 MPa) and a thickness of 1.6 mm, by butt welding.

[0057] In Example 2, the sectional load-bearing capacity of the front portion 11a of the rear side member 11 was 420kN, and the sectional load-bearing capacity of the rear portion 11b was 281kN. The sectional load-bearing capacity of the front portion 11a was 49.5% higher than that of the rear portion 11b, which was within the scope of the present invention.

[0058] Figures 9 and 10 show the deformation state of the rear side member 11 of the automobile 100 in the initial stage of the collision (stroke 250 mm) and the later stage of the collision (stroke 750 mm), as viewed from below.

[0059] As shown in Figures 9 and 10, during the collision process from the initial to the later stages of the collision, the rear side member 11 shows no deformation at the front portion 11a, while only the rear portion 11b deforms, thus preventing deformation of the cabin area. Furthermore, the total collision energy absorbed by the rear side member 11 in Example 2 was 33.6 kJ.

[0060] <Example 3> Embodiment 3 concerns a vehicle rear structure 3 having a rear side member 31 in which the front side portion 31a and the rear side portion 31b are integrally molded using the high-tensile steel plate 41 shown in Figure 5, as shown in Figure 6, and a rear cross member 13 disposed between the left and right rear side members 31.

[0061] The high-tensile steel plate 41 is formed by spot welding a high-tensile steel plate 45, which has a tensile strength of 1470 MPa (yield strength of 1193 MPa) and a thickness of 1.4 mm, to a portion of the 43a corresponding to the front side portion 31a of a high-tensile steel plate 43, which has a tensile strength of 980 MPa (yield strength of 800 MPa) and a thickness of 1.4 mm, while overlapping it.

[0062] In Example 3, the sectional load-bearing capacity of the front portion 11a of the rear side member 11 was 413 kN, and the sectional load-bearing capacity of the rear portion 11b was 246 kN. The sectional load-bearing capacity of the front portion 31a was 67.9% higher than that of the rear portion 31b, which was within the scope of the present invention. The cross-sectional strength of the front section 11a is based on the yield strength of the high-tensile steel plate 43, which is 800 MPa, and the cross-sectional area is 308 mm². 2 The sectional strength of high-tensile steel plate 43 is calculated by multiplying (plate thickness 1.4 mm × cross-sectional length 220 mm) by the yield strength of high-tensile steel plate 45 (1193 MPa) and cross-sectional area (140 mm²). 2 The sectional strength of the high-tensile steel plate 45 was calculated by multiplying it by (plate thickness 1.4 mm × cross-sectional length 100 mm) and adding the values. The sectional strength of the rear section 11b was calculated by multiplying it by the yield strength of the high-tensile steel plate 43 (800 MPa) and its cross-sectional area (308 mm²). 2 The value was calculated by multiplying (plate thickness 1.4 mm × cross-sectional line length 220 mm).

[0063] Figures 11 and 12 show the deformation state of the rear side member 31 of the automobile 100 as viewed from below, during the initial (stroke 250 mm) and late (stroke 750 mm) stages of the collision.

[0064] As shown in Figures 11 and 12, during the collision process from the initial to the later stages of the collision, the rear side member 31 shows no deformation at the front side 31a, while only the rear side 31b deforms, thus preventing deformation of the cabin area. Furthermore, the total collision energy absorbed by the rear side member 31 in Example 2 was 35.4 kJ.

[0065] <Comparative Example> The comparative example concerns a vehicle rear structure 7 having a rear side member 71 in which the front portion 71a and the rear portion 71b are integrally molded by hot stamping technology, and a rear cross member 13 disposed between the left and right rear side members 71 (see Figures 13 and 14). The rear side member 71 was made from a 1.6 mm thick high-tensile steel plate with a tensile strength of 1.5 GPa (yield strength of 1200 MPa) after die hardening, and the cross-sectional yield strength of both the front portion 71a and the rear portion 71b was 422 kN, which was outside the scope of the present invention.

[0066] Figures 13 and 14 show the deformation state of the rear side member 71 of the automobile 100 as viewed from below, during the initial (stroke 250 mm) and late (stroke 750 mm) stages of the collision.

[0067] As shown in Figures 13 and 14, the front portion 71a of the rear side member 71 is deformed from the initial stage of the collision (the area enclosed by the oval circle in the figure), which means that deformation of the cabin area cannot be suppressed, thus impairing occupant protection. The total energy absorption of the rear side member 71 in Example 3 was 32.3 kJ, which was lower than that of Examples 1 to 3 described above.

[0068] <Conventional Example> The conventional example, as shown in Figure 17, concerns a vehicle rear structure 5 having a conventional rear side member 51 made by joining multiple parts, and a rear cross member 13 disposed between the left and right rear side members 51. Furthermore, since the rear side member 51 is not integrally formed by cold pressing of a single high-tensile steel plate, with the front part 51a and the rear part 51b being the same, it falls outside the scope of the present invention.

[0069] In the conventional example, the front part 51a of the rear side member 51 was formed by cold pressing using a high-tensile steel plate with a tensile strength of 1470 MPa (yield strength of 1193 MPa) and a plate thickness of 1.6 mm, while the rear part 51b was formed by cold pressing using a high-tensile steel plate with a tensile strength of 980 MPa (yield strength of 800 MPa) and a plate thickness of 1.6 mm. Furthermore, the front part 51a and the rear part 51b were joined by spot welding, and the joint 51c was located 15 mm behind the rear end of the rear wheel.

[0070] Figures 15 and 16 show the deformation state of the rear side member 51 of the automobile 100 as viewed from below, during the initial (stroke 250 mm) and late (stroke 750 mm) stages of the collision.

[0071] As shown in Figures 15 and 16, spot welding fracture occurred at the joint 51c in the initial stages of the collision, preventing the absorption of the collision energy. As a result, deformation occurred in the front part 51a in the later stages of the collision (indicated by the oval circle in the figure), making it impossible to suppress the deformation of the cabin area and thus compromising occupant protection. The total energy absorption of the rear side member 51 in the conventional example was 32.1 kJ, which was lower than in Example 2, where the cross-sectional strength of the front part 51a and the rear part 51b were equivalent.

[0072] In summary, the vehicle rear structure according to the present invention has been shown to absorb collision energy by deforming the rear portion of the rear side member during a rear-end collision, while suppressing deformation of the front portion of the rear side member, thereby suppressing deformation of the cabin area and protecting the occupants. [Explanation of Symbols]

[0073] 1. Rear structure of the vehicle 3. Rear structure of the vehicle 5. Rear structure of the vehicle 7. Rear structure of the vehicle 11 Rear side member 11a Front side 11b Rear side 11c boundary 13 Rear cross member 21 High-tensile steel plate (blank) 21a high tensile strength steel plate 21b high tensile strength steel plate 31 Rear side member 31a Front side 31b Rear side 41 High-tensile steel plate (blank) 43 High tensile strength steel plate 43a Part 43b Part 45 High tensile steel plate 51 Rear side member 51a Front side 51b Rear side 51c joint 71 Rear side member 71a Front side 71b Rear side 100 automobiles 101 Rear wheel 103 Rear seats 105 Cabin Area 110 Barrier

Claims

1. A rear vehicle structure comprising a pair of rear side members arranged on both sides in the width direction of the vehicle and extending in the front-rear direction, Each of the aforementioned rear side members is integrally formed by cold pressing a single high-tensile steel sheet having two portions with different yield strengths and / or thicknesses. The boundary between the front and rear portions of the rear side member is located between a point 100 mm behind the rear end of the rear wheel of the vehicle and the rear end of the rear seats of the vehicle. A vehicle rear structure characterized in that the cross-sectional strength of the front portion against the collision load applied to the rear side member during a rear-end collision of the vehicle is 10% or more higher than the cross-sectional strength of the rear portion.

2. The aforementioned single high-tensile steel plate is formed by butt welding together two high-tensile steel plates with different yield strengths and / or plate thicknesses. The vehicle rear structure according to claim 1, characterized in that the two joined high-tensile steel plates correspond to each of the two parts.

3. The vehicle rear structure according to claim 1, characterized in that the single high-tensile steel plate is joined by spot welding to all or part of the portion of the single high-tensile steel plate corresponding to the front side portion, with another high-tensile steel plate superimposed on it.

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