Vehicle rear structure
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2025-09-22
- Publication Date
- 2026-07-30
Smart Images
Figure JP2025033336_30072026_PF_FP_ABST
Abstract
Description
Rear vehicle structure
[0001] The present invention relates to a rear vehicle structure.
[0002] For the purpose of reducing the manufacturing cost of an automobile body, integration of a plurality of component parts into one component part by applying aluminum casting parts or the like has been promoted. Aluminum casting parts may be able to suppress the processing cost, but on the other hand, the material cost is relatively high compared with the component parts mainly made of the current steel material (steel plate). On the other hand, if some component parts can be integrated and made into an integrated body while maintaining the steel plate structure with a low material cost, omission of the manufacturing process by reducing the number of component parts will directly result in reduction of the manufacturing cost, which is superior to aluminum casting parts in terms of the total cost. Integrating component parts into an integrated body means manufacturing a plurality of parts made in different press processes as one component part in one press process by joining the component parts joined by spot-welding or the like in the joining process. By integrating component parts into an integrated body, part of the press process and the joining process can be omitted.
[0003] In addition, the component parts of an automobile body are designed and manufactured to have various performances and characteristics from the viewpoints of vehicle performance, weight, and the like. Therefore, when integrating a plurality of component parts into an integrated body, for example, it is required that each part has the performance and characteristics that the original component parts had before integration, such as a part of the integrated component parts being stronger than other parts.
[0004] So far, technologies for manufacturing component parts of an automobile body to have different performances and characteristics for each part have been proposed. For example, Patent Document 1 discloses a technology 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 member, and hot stamping forming is performed. According to this technology, it is said that only a specific portion of the overlapped hot stamping formed body can be partially strengthened while reducing the number of press dies.
[0005] Japanese Patent No. 6451327
[0006] The rear structure of an automobile, around the rear floor, is configured to include parts that actively deform during a rear-end collision to absorb crash energy, and parts that remain undeformed to protect the cabin area where the occupants are seated. For example, in the rear structure 5 of the vehicle shown in Figure 17, the pair of left and right rear side members 51 extending in the longitudinal direction of the vehicle have a front portion 51a that does not deform during a rear-end collision, and a rear portion 51b that actively deforms to absorb crash energy. In conventional rear side members 51, the parts corresponding to the front portion 51a and the rear portion 51b were manufactured using different pressing processes and joined at a joint 51c by spot welding. Furthermore, the material strength and thickness of the steel plates used as the material 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 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 the manufactured parts, necessitating safety design measures such as increasing the 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 collision performance was inferior to parts made by cold stamping of high-tensile steel sheet. "High-tensile steel sheet" generally refers to steel sheets 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 problems, and its objective is 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.
[0011] 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 which is integrally formed by cold pressing of a single high-tensile steel plate having two parts with different yield strengths and / or plate thicknesses, the boundary between the front and rear portions of the rear side member is located between a position 100 mm behind the rear end of the automobile's rear wheel and the rear end of the automobile's rear seat, and the sectional capacity of the front portion against the collision load applied to the rear side member during a rear collision of the automobile is 10% or more higher than the sectional capacity of the rear portion.
[0012] The aforementioned single high-tensile steel plate is formed by butt welding two high-tensile steel plates with different yield strengths and / or thicknesses, and it is preferable that the two joined high-tensile steel plates correspond to the two respective parts.
[0013] The aforementioned single high-tensile steel plate is preferably joined by spot welding with another high-tensile steel plate superimposed on all or part of the portion corresponding to the front side of the single high-tensile steel plate.
[0014] In this invention, the front and rear portions of a 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 strength in the front portion than in the rear portion. This allows the rear portion to deform and absorb collision energy during a rear-end collision, while the deformation of the front portion is suppressed, thereby suppressing deformation of the cabin area and protecting the occupants. Furthermore, according to this invention, unlike conventional rear side members, the joints where multiple parts corresponding to the front and rear portions are welded together do not fracture, thus suppressing a decrease in the amount of collision energy absorbed and improving collision performance. Moreover, according to this invention, manufacturing costs are reduced, productivity is improved, and weight reduction is achieved, improving mass efficiency in terms of collision performance.
[0015] Figure 1 shows the configuration of a vehicle rear structure according to an embodiment of the present invention ((a) a perspective view from below, (b) a side view when installed in an automobile). Figure 2 shows a specific example of a single high-tensile steel plate used for cold press forming of the rear side member in the vehicle rear structure according to this embodiment, in which two high-tensile steel plates with different yield strengths and / or plate thicknesses are joined by butt welding. Figure 3 is a top view showing a desirable deformation state of the rear side member in a rear collision test of an automobile. Figure 4 is a top view showing an undesirable deformation state of the rear side member in a rear collision test of an automobile. Figure 5 shows another specific example of a single high-tensile steel plate used for cold press forming of the rear side member in the vehicle rear structure according to this embodiment, in which another high-tensile steel plate is superimposed on a single high-tensile steel plate corresponding to the front part of the rear side member and joined by spot welding. Figure 6 shows a rear side member formed by cold press forming using a single high-tensile steel plate, in which another high-tensile steel plate is overlapped with the portion corresponding to the front side of the rear side member in a vehicle rear structure according to this embodiment, and joined by spot welding. Figure 7 shows the deformation state of the rear side member at the initial stage of a rear collision test of an automobile equipped with the vehicle rear structure according to Embodiment 1 of the present invention. Figure 8 shows the deformation state of the rear side member at the later stage of a rear collision test of an automobile equipped with the vehicle rear structure according to Embodiment 1 of the present invention. Figure 9 shows the deformation state of the rear side member at the initial stage of a rear collision test of an automobile equipped with the vehicle rear structure according to Embodiment 2 of the present invention. Figure 10 shows the deformation state of the rear side member at the later stage of a rear collision test of an automobile equipped with the vehicle rear structure according to Embodiment 2 of the present invention. Figure 11 shows the deformation state of the rear side member at the initial stage of a rear collision test of an automobile equipped with the vehicle rear structure according to Embodiment 3 of the present invention. Figure 12 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 shows the deformation state of the rear side member in the initial stages of a rear-end collision test of an automobile equipped with a vehicle rear structure according to a comparative example used as a comparison of the present invention. Figure 14 shows the deformation state of the rear side member in the later stages of a rear-end collision test of an automobile equipped with a vehicle rear structure according to a comparative example used as a comparison of the present invention. Figure 15 shows the deformation state of the rear side member in the initial stages of a rear-end collision test of an automobile equipped with a vehicle rear structure according to a conventional example used as a comparison of the present invention. Figure 16 shows the deformation state of the rear side member in the later stages of a rear-end collision test of an automobile equipped with a vehicle rear structure according to a conventional example used as a comparison of the present invention. Figure 17 shows the configuration of a conventional vehicle rear structure ((a) entire automobile, (b) rear of the vehicle, (c) vehicle rear structure).
[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 of 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 having two sections with different yield strengths and / or thicknesses.
[0018] In this application, integral molding refers to manufacturing 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, integral molding refers to manufacturing 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 butt welding (laser beam welding, etc.) of two high-tensile steel plates 21a and 21b with different yield strengths and / or plate thicknesses. 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 plate thickness of the high-tensile steel plates 21a and 21b should be appropriately selected, taking into consideration not only the cross-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. 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] Sectional strength is calculated by multiplying (the yield stress of the high-tensile steel plate 21a which forms the front portion 11a of the rear side member 11 or the high-tensile steel plate 21b which forms the rear portion 11b) by (the cross-sectional area of the section perpendicular to the compression direction of the front portion 11a or the rear portion 11b), and corresponds to the compressive failure strength. The cross-sectional area of the front portion 11a or the rear portion 11b is calculated by multiplying the plate thickness of the high-tensile steel plate corresponding to the front portion 11a or the rear portion 11b by the minimum line length in a cross-sectional direction 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. The rear-end collision test of the automobile 100 involved performing a collision analysis in which the 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 load-bearing capacity 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 load-bearing capacity of the front portion 11a and the rear portion 11b are the same. Furthermore, in calculating the cross-sectional load-bearing capacity, the cross-sectional line length was minimized near the boundary between the front portion 11a and the rear portion 11b, and was 220 mm in both cases. In addition, 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 side portion 11b is 308 mm 2 That was the case.
[0025] In Figure 3, the rear side member 11 shows deformation of the rear side portion 11b while the front side portion 11a remains unchanged, whereas in Figure 4, the rear side member 11 shows deformation of the front side portion 11a (indicated by the arrow in the figure). Therefore, the rear side member 11 in which the front side portion 11a remains unchanged, as shown in Figure 3, is considered a desirable deformation state, while the rear side member 11 in which the front side portion 11a is deformed, as shown in Figure 4, is considered an undesirable deformation state. The reasons for considering the case where the front side portion 11a does not deform as desirable are twofold: firstly, the deformation of the cabin area 105 is suppressed and occupants are protected by the absence of deformation of the front side portion 11a, and secondly, the collision energy can be sufficiently absorbed by the deformation of the rear side portion 11b while the front side portion 11a remains unchanged.
[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 an automobile 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 of the rear side member 11 and the determination results obtained in the rear-end collision test in which the sectional strength of the front section 11a and the rear section 11b were adjusted in various ways.
[0028]
[0029] In Table 1, the increase in sectional strength represents the increase in the sectional strength of the front portion 11a, relative to the sectional strength of the rear portion 11b. As shown in Table 1, it was found that if the sectional strength of the front portion 11a of the rear side member 11 is 9.5% or greater than the sectional strength of the rear portion 11b, no deformation is observed in the front portion 11a, and the deformation state of the rear side member 11 is desirable. In this invention, in order to reliably suppress the deformation of the front portion 11a, the sectional strength of the front portion 11a is specified to be 10% or more of the 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 position of boundary 11c was defined for the following reasons: During a rear-end collision of the 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 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 high 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 portion 11a and the rear portion 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. 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. 2 The sectional load-bearing capacity was set to 280kN.
[0036] Table 2 shows the deformation state of the rear side member 11 in 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]
[0038] As shown in Table 2, in Case 11 to Case 14 where the boundary 11c between the front side portion 11a and the rear side portion 11b is located behind the position 100 mm behind the rear end of the rear wheel 101, deformation occurred in the front side portion 11a. On the other hand, in Case 14 to Case 16 where the boundary 11c is located in front of the position 100 mm behind the rear end of the rear wheel 101, no deformation was observed in the front side portion 11a. From these results, it was found that it is desirable that the critical position on the rear side of the boundary 11c between the front side portion 11a and the rear side portion 11b is the position 100 mm behind the rear end of the rear wheel 101.
[0039] On the other hand, the critical position on the front side of the boundary 11c between the front side portion 11a and the rear side portion 11b was set as the vehicle longitudinal position of the rear end of the rear row seat 103. This is because when the boundary 11c is located in front of the rear end of the rear row seat 103 and a collision body collides with the rear surface of the automobile and the collision progresses, there is concern that deformation of the cabin area 105 will be induced and it will interfere with passenger protection.
[0040] Thus, in the vehicle rear structure 1 according to the present embodiment, by making the cross-sectional strength of the front side portion 11a of the rear side member 11 10% or more higher than that of the rear side portion 11b, when a rear-end collision occurs, the rear side portion 11b is deformed to absorb collision energy, and deformation of the front side portion 11a can be suppressed. Thereby, deformation of the cabin area 105 at the time of a rear-end collision can be suppressed, and passengers can be protected.
[0041] Further, the front side portion 11a and the rear side portion 11b of the rear side member 11 are integrally formed by cold pressing a single high-tensile steel sheet 21. Therefore, it is possible to suppress a decrease in the amount of collision energy absorbed due to breakage of the joint portion 51c as in the conventional rear side member 51 (see FIG. 17) in which a plurality of parts are joined by welding.
[0042] Furthermore, according to the vehicle rear structure 1 according to the present embodiment, since it does not require the production and joining of a plurality of parts as in the conventional rear side member 51 (FIG. 17), the manufacturing cost can be reduced, productivity can be improved, and weight can be reduced, improving the mass efficiency with respect to collision performance.
[0043] In the above description, a single high-tensile steel sheet 21 used for cold pressing was formed by butt-welding two high-tensile steel sheets 21a and 21b with different yield strengths and / or sheet thicknesses, as shown in FIG. 2. However, the present invention may be such that, for example, by cold pressing a single high-tensile steel sheet 41 (blank) shown in FIG. 5, the front side portion 31a and the rear side portion 31b of the rear side member 31 shown in FIG. 6 are integrally formed.
[0044] A single high-tensile steel sheet 41 shown in FIG. 5 is joined by spot welding (such as spot welding) in a state where another high-tensile steel sheet 45 is overlapped on a part of a portion 43a corresponding to the front side portion 31a of a single high-tensile steel sheet 43. Therefore, the high-tensile steel sheet 41 has two portions with different yield strengths and sheet thicknesses, namely, a portion 43a corresponding to the front side portion 31a and the high-tensile steel sheet 45, and a portion 43b corresponding to the rear side portion 31b.
[0045] In the rear side member 31 integrally formed by cold pressing the high-tensile steel sheet 41, the front side portion 31a is formed in a state where the high-tensile steel sheet 45 is overlapped on the high-tensile steel sheet 43, and the rear side portion 31b is formed by the high-tensile steel sheet 43. And the cross-sectional bearing capacity of the front side portion 31a is taken as the value obtained by calculating and adding the cross-sectional bearing capacities of the overlapped high-tensile steel sheets 43 and 45 respectively, and the cross-sectional bearing capacity of the rear side portion 31b is taken as the cross-sectional bearing capacity of the high-tensile steel sheet 43.
[0046] Even such a rear side member 31 obtained by cold press forming a single high-tensile steel sheet 41 falls within the scope of the integral molding of the present application, and compared with a conventional rear side member 51 (FIG. 17) composed of a plurality of parts, the pressing process and the joining process can be omitted, so that the manufacturing cost can be reduced and the productivity can be improved.
[0047] The high-tensile steel sheet 43 and the high-tensile steel sheet 45 used for the high-tensile steel sheet 41 are preferably selected appropriately in terms of yield strength and sheet thickness in consideration of not only the cross-sectional bearing capacities of the front side portion 31a and the rear side 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.
[0049] Tests were conducted to verify the effects of the present invention, and these will be described below. The test involved a rear crash test (crash speed 50 km / h) in which a barrier (crash test barrier) collided with the rear of a vehicle equipped with a rear vehicle structure, and the deformation state of the rear side member 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 having a rear side member 11 formed integrally by cold pressing of a front side portion 11a and a rear side portion 11b 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.
[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 plate thickness of 1.8 mm, and a high-tensile steel plate 21b with the same yield strength and a plate 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 stage of the collision (stroke 250 mm) and the later stage of the collision (stroke 750 mm).
[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> Example 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 is 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 in the initial stage of a collision (stroke 250 mm) and the later stage of a collision (stroke 750 mm), as viewed from below the automobile 100.
[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> Example 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 front part 31a of the 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 strength of the front portion 11a of the rear side member 11 was 413kN, and the sectional strength of the rear portion 11b was 246kN. The sectional strength 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 sectional strength of the front portion 11a is based on the yield strength of the high-tensile steel plate 43 (800 MPa) and the cross-sectional area (308 mm²). 2 The sectional strength of the high-tensile steel plate 43 is obtained by multiplying (plate thickness 1.4 mm × cross-sectional length 220 mm), and the yield strength of the high-tensile steel plate 45 is 1193 MPa and the cross-sectional area is 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 two values together. The sectional strength of the rear portion 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 stage of the collision (stroke 250 mm) and the later stage of the collision (stroke 750 mm).
[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 portion 31a, while only the rear portion 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 part 71a and the rear part 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 part 71a and the rear part 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 stage of the collision (stroke 250 mm) and the later stage of the collision (stroke 750 mm).
[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, and thus occupant protection is compromised. 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, and 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 stage of the collision (stroke 250 mm) and the later stage of the collision (stroke 750 mm).
[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 that of Example 2, in which 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.
[0073] According to the present invention, by integrally forming the rear side member from a single high-tensile steel sheet using cold press forming, it is possible to provide a vehicle rear structure that can sufficiently absorb collision energy during a rear-end collision while suppressing deformation of the cabin area, and further improve both productivity and mass efficiency.
[0074] 1 Rear vehicle structure 3 Rear vehicle structure 5 Rear vehicle structure 7 Rear vehicle structure 11 Rear side member 11a Front part 11b Rear part 11c Boundary 13 Rear cross member 21 High-tensile steel plate (blank) 21a High-tensile steel plate 21b High-tensile steel plate 31 Rear side member 31a Front part 31b Rear part 41 High-tensile steel plate (blank) 43 High-tensile steel plate 43a Part 43b Part 45 High-tensile steel plate 51 Rear side member 51a Front part 51b Rear part 51c Joint 71 Rear side member 71a Front part 71b Rear part 100 Automobile 101 Rear wheel 103 Rear seats 105 Cabin area 110 Barrier
Claims
1. A vehicle rear 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, wherein each rear side member is integrally formed by cold pressing of a single high-tensile steel plate having two portions with different yield strengths and / or plate thicknesses, the boundary between the front and rear portions of the rear side member is located between a position 100 mm behind the rear end of the rear wheel of the vehicle and the rear end of the rear row seats of the vehicle, and the sectional strength of the front portion against the collision load applied to the rear side member during a rear collision of the vehicle is 10% or more higher than the sectional strength of the rear portion.
2. The vehicle rear structure according to claim 1, wherein the single high-tensile steel plate is formed by butt welding two high-tensile steel plates having different yield strengths and / or plate thicknesses, and the two joined high-tensile steel plates correspond to each of the two parts.
3. The vehicle rear structure according to claim 1, wherein one high-tensile steel plate is joined by spot welding to all or part of the portion of the high-tensile steel plate corresponding to the front side portion, with another high-tensile steel plate superimposed on it.