Vehicle body front structure, method for designing vehicle body front structure, and method for manufacturing vehicle body front structure

Abstract

A vehicle body front structure (1) is provided with: a pair of left and right front side members (11) extending in the front-rear direction of a vehicle body and having a closed cross-sectional structure; and a crash box (21) extending from the front end of each front side member (11) toward the front side of the vehicle body and having a closed cross-sectional structure. The ratio (Fx1 / Fx2) of the axial force (Fx1) of a cross section where the length of the cross-sectional line of the closed cross-sectional structure in the crash box (21) is minimum to the axial force (Fx2) of a cross section where the length of the cross-sectional line of the closed cross-sectional structure in the front side member (11) is minimum is equal to or less than a predetermined critical axial force ratio. The thickness and tensile strength of each metal plate for the front side member (11) and the crash box (21) are set.

Description

Technical Field

[0001] The present invention relates to a vehicle body structure having a pair of left and right front side members extending in the front-rear direction of the vehicle body, and a crash box extending from the front end of each front side member toward the front side of the vehicle body, a design method for the vehicle body structure, and a manufacturing method for the vehicle body structure. Background Technology

[0002] In recent years, electric vehicles, which reduce CO2 emissions compared to gasoline vehicles, have become increasingly popular as an environmental countermeasure. Increasing battery capacity is effective in extending the driving range of electric vehicles, but this increases vehicle weight, becoming a major cause of increased collision energy during a collision. Therefore, electric vehicles require a body structure capable of effectively absorbing collision energy. Previously, front body structures were known to absorb collision energy during a frontal collision (front crash) by compressing the front longitudinal beams in the longitudinal direction (axial crush). In such a frontal collision, the front side of the front longitudinal beam compresses in the longitudinal direction of the vehicle body, and the rear side folds and deforms in a manner that protrudes outward in the width direction and downward in the vertical direction of the vehicle body. Therefore, it absorbs the collision energy input to the front structure of the vehicle body and prevents the deterioration of occupant protection performance (occupant injury value) caused by the intrusion of body parts such as the dashboard into the passenger compartment due to the engine, motor and other vehicle-mounted components.

[0003] Typically, in the compression and bending deformation of vehicle body components, even with the same stroke, compression deformation can absorb more collision energy. Therefore, for example, Patent Document 1 discloses a front body structure that creates a stiffness difference between the front and rear sides of the front side frame (equivalent to the front longitudinal beam of this application), and that each region alternately exhibits a stiffness difference in the vehicle's longitudinal direction. Furthermore, in this technology, during a frontal collision, compression deformation begins from the front side of the relatively less stiff front side frame, followed by compression deformation from the rear side of the relatively more stiff front side frame. This allows the front longitudinal beam to undergo smooth, bellows-shaped compression deformation along its entire length, thus maximizing the absorption of collision energy.

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2021-66202 Summary of the Invention

[0005] The problem that the invention aims to solve In the front structure of the vehicle body, a collision energy-absorbing box is installed in front of the front longitudinal beam. During a frontal collision, this box further absorbs collision energy by compressing and deforming in the longitudinal direction. In frontal structures with such longitudinal beams and collision energy-absorbing boxes, relatively low-strength steel with a tensile strength of around 440 MPa is used to allow for sufficient compression and deformation of the box. Furthermore, the front longitudinal beams mostly use high-strength steel with a tensile strength of 780 MPa or higher. Moreover, to meet the requirement of increasing collision energy absorption in frontal collisions of electric vehicles, research is underway to use steel with a tensile strength of 980 MPa or higher (ultra-high strength steel) for the collision energy-absorbing box.

[0006] In such cases, it is important to achieve the required amount of collision energy absorption by compressing and deforming the front side of the energy-absorbing box and the front longitudinal beam. However, even by simply increasing the strength of the steel plate used for the energy-absorbing box, bending deformation of the front longitudinal beam may sometimes occur before the energy-absorbing box undergoes sufficient compressive deformation. In such cases, the energy-absorbing box cannot adequately absorb the collision energy, resulting in failure to meet the specified collision performance requirements, such as the amount of vehicle body deformation. Therefore, to achieve high strength in the energy-absorbing box, it is important to bend and deform the front longitudinal beam after the energy-absorbing box has undergone sufficient compressive deformation. Furthermore, to achieve the above objective, it is considered sufficient to appropriately determine the thickness and material strength of the steel plates and other metal plates used for the energy-absorbing box and the front longitudinal beam.

[0007] However, the technology disclosed in Patent Document 1 effectively absorbs collision energy by compressing and deforming the front longitudinal beam in a smooth, corrugated manner along its entire length. Therefore, Patent Document 1 does not disclose or provide any guidance on determining the appropriate plate thickness and material strength of the collision energy-absorbing box based on its relationship with the front longitudinal beam.

[0008] In addition, for battery-powered electric vehicles, besides ensuring the specified collision energy absorption performance, a compact front structure is required to ensure sufficient battery space. Moreover, to achieve a compact front structure, it is necessary to adequately absorb collision energy in a frontal collision, even with minimal compression deformation of the energy-absorbing box and front longitudinal beams.

[0009] However, with respect to the technology in Patent Document 1, the load input during a frontal collision is significantly reduced only in relation to the reduced rigidity of the front longitudinal beam. Therefore, to ensure the amount of collision energy absorbed by compressive deformation during a frontal collision, the front longitudinal beam needs to be lengthened to increase the amount of compressive deformation. Thus, with the technology in Patent Document 1, it is not possible to simultaneously ensure the collision energy absorption performance of the front structure of an electric vehicle and achieve compactness.

[0010] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a front body structure that can simultaneously achieve the specified collision performance and compactness in frontal collisions, a design method for the front body structure, and a manufacturing method for the front body structure.

[0011] Methods for solving problems The present invention relates to a front vehicle structure comprising a pair of left and right front longitudinal beams extending in the longitudinal direction of the vehicle body and having a closed cross-section structure, and a collision energy-absorbing box extending from the front end of each front longitudinal beam toward the front of the vehicle body and having a closed cross-section structure. This is achieved by minimizing the axial force F of the cross-section of the aforementioned closed cross-section structure within the collision energy-absorbing box. x1 The axial force F of the section with the minimum section length of the closed section structure in the aforementioned front longitudinal beam. x2 The ratio of F x1 / F x2 The thickness and tensile strength of the metal plates for the aforementioned front longitudinal beam and the aforementioned collision energy-absorbing box are set in a manner that is below a predetermined critical ratio of axial force, so that in the event of a frontal collision with the vehicle, after the aforementioned collision energy-absorbing box has been sufficiently compressed and deformed, the aforementioned front longitudinal beam is bent and deformed.

[0012] The present invention relates to a design method for a vehicle front structure, comprising a pair of left and right front longitudinal beams extending in the longitudinal direction of the vehicle and having a closed cross-section, and a collision energy-absorbing box extending from the front end of each front longitudinal beam toward the front side of the vehicle and having a closed cross-section, wherein the design is such that, in a frontal collision, after the collision energy-absorbing box has been sufficiently compressed and deformed, the front longitudinal beams bend and deform. The method includes: a vehicle model acquisition step, acquiring a vehicle model having the aforementioned vehicle front structure, and defining an intrusion evaluation area for evaluating the intrusion amount of the vehicle model's body components toward the passenger compartment side in a frontal collision; and a minimum cross-section length determination step, determining, for each of the aforementioned collision energy-absorbing box and the aforementioned front longitudinal beam in the acquired vehicle model, a minimum cross-section length (a cross-section where the line length in the cross-sectional direction is the minimum). (Minimum); Axial force ratio calculation step: For the aforementioned collision energy-absorbing box and the aforementioned front longitudinal beam in the aforementioned vehicle model, calculate the axial force in the aforementioned minimum section with various plate thicknesses and tensile strengths, and calculate the ratio of the axial force calculated for the aforementioned collision energy-absorbing box to the axial force calculated for the aforementioned front longitudinal beam; Body component passenger compartment side intrusion calculation step: Perform a collision analysis related to the aforementioned frontal collision of the aforementioned vehicle model with various plate thicknesses and tensile strengths, and calculate the intrusion of the aforementioned body components towards the passenger compartment side in the aforementioned intrusion evaluation area set in the aforementioned vehicle model during the aforementioned frontal collision; Critical axial force ratio determination The steps involve determining the relationship between the axial force ratio calculated using various plate thicknesses and tensile strengths in the aforementioned axial force ratio calculation step and the intrusion amount of the aforementioned body component towards the passenger compartment side in the aforementioned intrusion amount evaluation area calculated using the aforementioned collision analysis of the aforementioned vehicle model with various plate thicknesses and tensile strengths in the aforementioned body component passenger compartment side intrusion amount calculation step, and determining the critical axial force ratio at which the aforementioned intrusion amount reaches saturation at a substantially constant value; and the plate thickness and tensile strength determination step, which, among the axial force ratios calculated for various combinations of plate thicknesses and tensile strengths, determines the combination of plate thicknesses and tensile strengths that is below the critical axial force ratio determined in the aforementioned critical axial force ratio determination step.

[0013] It is possible that, in the aforementioned axial force ratio calculation step, the weights of the aforementioned collision energy-absorbing box and the aforementioned front longitudinal beam in the aforementioned combinations of plate thickness and tensile strength are calculated; and in the aforementioned plate thickness and tensile strength determination step, among the combinations of plate thickness and tensile strength in which the axial force ratio becomes below the aforementioned critical axial force ratio, the combination of plate thickness and tensile strength in which the total weight of the aforementioned collision energy-absorbing box and the aforementioned front longitudinal beam calculated in the aforementioned axial force ratio calculation step is the minimum is determined.

[0014] It is possible that, in the aforementioned steps of determining plate thickness and tensile strength, among the combinations of plate thickness and tensile strength where the axial force ratio is below the aforementioned critical axial force ratio, the combination of plate thickness and tensile strength where the axial force calculated for the aforementioned collision energy absorption box is the largest is determined.

[0015] The present invention relates to a method for manufacturing a front body structure, wherein, through the design method of the present invention, for each of the front longitudinal beam and the collision energy absorption box of the aforementioned front body structure, a combination of plate thickness and tensile strength is determined; using the determined combination of plate thickness and tensile strength, an axial force F is generated for a cross-section having a minimum cross-sectional length in the aforementioned closed cross-section structure of the aforementioned collision energy absorption box. x1 The axial force F of the section with the minimum section length of the closed section structure in the aforementioned front longitudinal beam. x2 The ratio of F x1 / F x2 The front structure of the vehicle body that becomes the aforementioned front longitudinal beam and the aforementioned collision energy absorption box below the aforementioned critical axial force ratio.

[0016] Invention Effects According to the present invention, in a frontal collision, after the collision energy-absorbing box is sufficiently crushed axially, the front longitudinal beam can be bent and deformed, thereby suppressing the intrusion of body components towards the passenger compartment to a predetermined level and sufficiently absorbing collision energy. Furthermore, according to the present invention, without reducing collision energy absorption and the amount of body component intrusion towards the passenger compartment during a frontal collision, the vehicle body can be made lighter and more compact, contributing to improved commercial viability. Attached Figure Description

[0017] [ Figure 1 ] Figure 1 This is a diagram illustrating an example of the configuration of the front structure of a vehicle body according to an embodiment of the present invention.

[0018] [ Figure 2 ] Figure 2 It is a diagram illustrating the compression deformation of the front longitudinal beam and the bending deformation of the collision energy absorption box in the front structure of the vehicle body during a frontal collision.

[0019] [ Figure 3 ] Figure 3 It is a graph that schematically represents the load-stroke curve of the front structure of a vehicle body during a frontal collision.

[0020] [ Figure 4 ] Figure 4 It is a schematic diagram showing the time-varying loads generated by the collision energy absorption box and the front longitudinal beam during a frontal collision of a vehicle body frontal structure with only high strength of the collision energy absorption box.

[0021] [ Figure 5 ] Figure 5 It is a diagram schematically showing the time-varying loads generated by the collision energy absorption box and the front longitudinal beam respectively during a frontal collision of the vehicle body structure, which is obtained by increasing the strength of the front longitudinal beam in accordance with the increase of the strength of the collision energy absorption box.

[0022] [ Figure 6 ] Figure 6 It is a graph illustrating the relationship between the axial force ratio, which is the ratio of the axial force of the collision energy absorption box to the axial force of the front longitudinal beam, and the amount of front bulkhead intrusion caused by the deformation of the dash lower panel towards the passenger compartment during a frontal collision of the vehicle. It is also a graph in which the critical axial force ratio is the axial force ratio at which the amount of front bulkhead intrusion reaches saturation at a substantially constant value.

[0023] [ Figure 7 ] Figure 7 This is a diagram illustrating an example of the cross-sectional shape of the front longitudinal beam and the collision energy absorption box of the vehicle body front structure according to an embodiment of the present invention, which are orthogonal to the longitudinal direction of the vehicle body.

[0024] [ Figure 8 ] Figure 8 This is a flowchart illustrating the process flow in the design method of the front structure of a vehicle body according to an embodiment of the present invention.

[0025] [ Figure 9 ] Figure 9 This is a diagram illustrating the crashworthiness analysis of an offset collision as a frontal collision of a vehicle in the embodiment.

[0026] [ Figure 10 ] Figure 10 This is a diagram showing the location of the front bulkhead intrusion, which is the amount of deformation of the lower front bulkhead towards the passenger compartment caused by a frontal collision of the vehicle, in an embodiment.

[0027] [ Figure 11 ] Figure 11 The load-stroke curves of the front structure of the vehicle body obtained by collision analysis during a frontal collision in the embodiments are ((a) Invention Example (No. 3), (b) Comparative Example (No. 4)).

[0028] [ Figure 12 ] Figure 12 The diagram shows the front bulkhead intrusion, footbrake intrusion, and collision energy absorption (collision energy absorption box EA) of the inventive examples (No. 1, 3, 10) and comparative example (No. 4) obtained by collision analysis during a frontal collision of the vehicle in the embodiments. Detailed Implementation

[0029] Before describing the vehicle front structure and its design method according to embodiments of the present invention, the process of the present invention will be explained. In the accompanying drawings of this application, the X direction, Y direction, and Z direction represent the vehicle front-rear direction, vehicle width direction, and vehicle vertical direction, respectively.

[0030] <The Process of Invention> Figure 2 This is a schematic diagram illustrating the front structure 1 of a vehicle body, which includes a front longitudinal beam 11 and a collision energy absorption box 21, as the subject of this invention.

[0031] like Figure 1 As shown, the front longitudinal beam 11 extends in the longitudinal direction of the vehicle body, and its rear end connects to the lower front bulkhead 31, which separates the vehicle's cabin (passenger compartment) and the front structure 1 of the vehicle body. Furthermore, in a frontal collision, the front longitudinal beam 11 compresses and deforms (axial crush) in the longitudinal direction (trail-to-rear direction of the vehicle body), and folds and bends in a direction orthogonal to the longitudinal direction (outer side in the left-right direction of the vehicle body or lower side in the vertical direction of the vehicle body) (bending crush). Additionally, as... Figure 2 As shown, the front longitudinal beam 11 is subjected to bending stiffeners 13, thereby inducing bending deformation starting from the bending stiffeners 13 during a frontal collision. Additionally, as... Figure 7 As shown in (b), the front longitudinal beam 11 has a closed cross-section structure perpendicular to the length direction.

[0032] The collision energy-absorbing box 21 extends from the front end of the front longitudinal beam 11 towards the front of the vehicle body, and undergoes corrugated compression deformation (axial crushing) in the longitudinal direction during a frontal collision. Furthermore, to induce corrugated compression deformation in the longitudinal direction (length direction) of the vehicle body during a frontal collision, for example... Figure 2 As shown, the collision energy-absorbing box 21 has multiple reinforcing ribs 23 along its length. Additionally, as... Figure 7 As shown in (c), the collision energy-absorbing box 21 has a closed cross-section structure perpendicular to the length direction.

[0033] Figure 3 This is a schematic diagram illustrating the load-stroke curves of the frontal structure 1 of the vehicle body during a frontal collision. Figure 3 In this context, the value obtained by integrating the load with the distance (travel) (the area enclosed by the curve) represents the amount of collision energy absorbed.

[0034] As disclosed in Patent Document 1, in the front body structure 1 with a bending reinforcing rib 13 applied to the front longitudinal beam 11, the bending deformation caused by the bending reinforcing rib 13 significantly reduces the load, thus inducing smooth compressive deformation of the front longitudinal beam 11. However, in order to obtain the same amount of collision energy absorption as the front body structure 1 without the bending reinforcing rib 13 applied to the front longitudinal beam 11 (a conventional front body structure), the total length of the front longitudinal beam 11 and the collision energy absorption box 21 needs to be increased, thereby increasing the stroke (deformation amount) until the front longitudinal beam 11 undergoes bending deformation. Figure 3 x in A →x A ').

[0035] In contrast, from a lightweighting perspective, by using high-strength metal sheets (e.g., high-tensile steel sheets) in the impact energy absorption box 21, the yield strength during a frontal collision is improved. Figure 3 (F→F' in the middle), and the subsequent load also increases. Therefore, it is believed that the required travel (deformation) to achieve the same amount of collision energy absorption as previous front body structures can be suppressed. Figure 3 x in A →x B ).

[0036] However, even if only the metal plate used for the collision energy absorption box 21 is made stronger, if the front longitudinal beam 11 bends and deforms in the middle of the compression deformation of the collision energy absorption box 21, it will also hinder the compression deformation of the collision energy absorption box 21, and reduce the amount of collision energy absorbed.

[0037] Therefore, the inventors of this application conducted in-depth research on this topic. As a result, they conceived of a way to appropriately balance the axial forces of the collision energy-absorbing box 21 and the front longitudinal beam 11 by increasing the strength of the front longitudinal beam 11 in accordance with the increased strength of the collision energy-absorbing box 21. Axial force refers to the allowable load (bearing capacity) in the length direction of components with closed cross-section structures such as the collision energy-absorbing box 21 and the front longitudinal beam 11, which is represented by Equation (1) described later.

[0038] Furthermore, it was found that by appropriately balancing the axial forces of the collision energy-absorbing box 21 and the front longitudinal beam 11, and by increasing the strength of the collision energy-absorbing box 21, smooth, corrugated compressive deformation can be promoted after the buckling deformation of the collision energy-absorbing box 21 begins. As a result, the collision energy can be adequately absorbed by the collision energy-absorbing box 21, and the intrusion of body components towards the passenger compartment can be kept below a specified level, thereby improving the safety of the passenger compartment. The appropriate balancing of the axial forces of the collision energy-absorbing box 21 and the front longitudinal beam 11 will be explained below.

[0039] Figure 4 and Figure 5 shows the load - stroke curve when the front body structure 1 having the front side member 11 and the crash energy absorber 21 is deformed by a crash load applied from the front side to the rear side of the vehicle. Figure 2 The load - stroke curve shown as such is a graph schematically showing the change in the load received by the front side member 11 with respect to the amount of deformation (stroke) of the front body structure 1 in the longitudinal direction of the vehicle. Figure 4 and Figure 5 As shown by the solid line in

[0040] As Figure 4 When a crash load is applied to the front body structure 1 during a frontal collision of the vehicle, first, the crash energy absorber 21 first undergoes a small elastic (compressive) deformation in the longitudinal direction of the vehicle (elastic deformation in the compression direction). Then, the crash energy absorber 21 starts to buckle and compress (axial crushing) under the load F1 (amount of deformation d1), reaches a fully crushed state, and thus the crushing ends (amount of deformation d2). Next, the front side member 11 undergoes a transitional elastic deformation, and when it receives the transmitted load F3, it starts to buckle and bend (amount of deformation d3), reaches the endurance (maximum load), and thus completes the bending deformation (amount of deformation d4).

[0041] If only the crash energy absorber 21 is strengthened by applying high - tensile steel sheets, as Figure 4 shown by the dashed line in

[0042] On the contrary Figure 5The dashed line indicates that, corresponding to the increased strength of the impact energy absorption box 21, the front longitudinal beam 11 is also strengthened by using high-tensile steel plates, and the load at which the front longitudinal beam 11 begins to buckle and bend is set to F3' (F3'>F3). In this case, after the impact energy absorption box 21 has fully compressed and deformed to a completely crushed state and the crushing ends (deformation amount d2), the bending deformation of the front longitudinal beam 11 can begin (deformation amount d3>d2), thus not hindering the compression deformation of the impact energy absorption box 21.

[0043] In addition, if the thickness of the closed section structure of the impact energy absorption box 21 is increased or the section line length of the closed section structure is increased, the impact energy absorption box 21 will not be easily compressed and deformed without increasing its strength. Even so, the load at which the impact energy absorption box 21 begins to buckle and compress and deform will be higher. Therefore, just like the case of increasing the strength of the impact energy absorption box 21, it will hinder the compression and deformation of the impact energy absorption box 21.

[0044] In order to fully compress and deform the impact energy absorption box 21 until the front longitudinal beam 11 begins to bend and deform, the inventors of this application, focusing on the balance of endurance in the impact energy absorption box 21 and the front longitudinal beam 11, conceived of making appropriate adjustments to the plate thickness and tensile strength of the impact energy absorption box 21 and the front longitudinal beam 11.

[0045] Next, the inventors of this application investigated how to properly balance the load-bearing capacity of the impact energy-absorbing box 21 and the front longitudinal beam 11. Therefore, firstly, the inventors of this application used the axial force, expressed by the following equation (1), as an indicator corresponding to the load-bearing capacity of the impact energy-absorbing box 21 and the front longitudinal beam 11. Axial force refers to an indicator of the design allowable load (loading capacity / load bearing capacity) in the direction of the component's length. When the design allowable load is set as a buckling load, the yield strength can also be used instead of the tensile strength in equation (1).

[0046] Axial force (N) = Section length (mm) × Plate thickness (mm) × Tensile strength (MPa) ···(1) Furthermore, regarding the balance of axial forces between the collision energy absorption box 21 and the front longitudinal beam 11, the axial force F of the collision energy absorption box 21 is determined. x1 Axial force F relative to front longitudinal beam 11 x2 The ratio (=F) x1 / F x2 ) that is, the axial force ratio (F) X )express.

[0047] Furthermore, an investigation was conducted into whether the balance of axial forces in the collision energy-absorbing box 21 and the front longitudinal beam 11 could be appropriately adjusted based on such a specified axial force ratio. Therefore, by changing various combinations of the plate thickness and tensile strength of the collision energy-absorbing box 21 and the front longitudinal beam 11, the relationship between the axial force ratio of the collision energy-absorbing box 21 and the front longitudinal beam 11 and the amount of intrusion of the vehicle body components towards the passenger compartment during a frontal collision was investigated. The results are as follows: Figure 6 As shown, when the axial force ratio is below a specified value, the intrusion of the body components reaches saturation at a certain constant level.

[0048] In this application, the ratio of the axial force of the collision energy-absorbing box 21 to the front longitudinal beam 11 at the point when the intrusion of the vehicle body components towards the passenger compartment side reaches saturation is referred to as the critical axial force ratio. Furthermore, Figure 6 The axial force ratio F is the result of setting various combinations of plate thickness and material strength as shown in Table 1 (described later) for both the front longitudinal beam 11 and the impact energy absorption box 21. x The chart is obtained by drawing the amount of intrusion of the front bulkhead as a body component toward the passenger compartment.

[0049] In this way, regarding the balance of axial forces in the collision energy absorption box 21 and the front longitudinal beam 11, it was found that it can be adjusted in such a way that the ratio of axial forces in the collision energy absorption box 21 and the front longitudinal beam 11 is below the critical axial force ratio.

[0050] That is, it is known that by determining the plate thickness and tensile strength (or yield strength) of the collision energy-absorbing box 21 and the front longitudinal beam 11 in a suitable way so that the axial force ratio of the collision energy-absorbing box 21 to the front longitudinal beam 11 is below the critical axial force ratio, the balance of the load-bearing capacity in the collision energy-absorbing box 21 and the front longitudinal beam 11 can be properly balanced. Furthermore, in the front body structure 1 where the axial force ratio of the collision energy-absorbing box 21 to the front longitudinal beam 11 is properly balanced, in the event of a frontal collision, the front longitudinal beam 11 can be bent and deformed after the collision energy-absorbing box 21 has undergone sufficient compression deformation. As a result, it is understood that the intrusion of body components toward the passenger compartment can be suppressed to below a specified level, and collision energy can be sufficiently absorbed through the compression deformation of the collision energy-absorbing box 21. The present invention was made based on the above research results, and its specific structure will be described below.

[0051] Front Structure of Vehicle Body As an example, Figure 1 The diagram shows a front body structure 1 according to an embodiment of the present invention. The front body structure 1 includes a pair of left and right front longitudinal beams 11 extending in the longitudinal direction of the vehicle body and having a closed cross-section structure, and a collision energy absorption box 21 extending from the front end of each front longitudinal beam 11 toward the front side of the vehicle body and having a closed cross-section structure.

[0052] like Figure 7As shown, the front longitudinal beam 11 is, for example, a closed cross-section structure formed by joining the inner part 11a of the front longitudinal beam with a hat-shaped cross-section and the outer part 11b of the front longitudinal beam with a panel shape.

[0053] like Figure 7 As shown, the collision energy-absorbing box 21 is, for example, a closed cross-section structure formed by joining an inner part 21a of a U-shaped cross-section collision energy-absorbing box and an outer part 21b of a U-shaped cross-section collision energy-absorbing box. Additionally, as... Figure 1 As shown, in the front structure 1 of the vehicle body, a bumper beam 33 extending in the width direction of the vehicle body is connected to the front end of each collision energy absorption box 21.

[0054] Furthermore, in the front structure 1 of the vehicle body, the axial force F of the collision energy absorption box 21 is reduced. x1 Axial force F of front longitudinal beam 11 x2 The ratio of F x1 / F x2 The thickness and tensile strength of the metal plates for the front longitudinal beam 11 and the impact energy absorption box 21 are set in a predetermined manner to achieve the critical axial force ratio. x1 This is given in the section where the line length of the closed section structure in the impact energy absorption box 21 is minimized. Additionally, the axial force F of the front longitudinal beam 11... x2 It is given in the section where the line length of the closed section structure in the front longitudinal beam 11 is the minimum.

[0055] Thus, the front structure 1 of the vehicle body becomes such that, in the event of a frontal collision, after the collision energy absorption box 21 is fully compressed and deformed, the front longitudinal beam 11 is bent and deformed.

[0056] In this way, according to the front body structure 1 of this embodiment, the front longitudinal beam 11 can be bent and deformed after the collision energy absorption box 21 is sufficiently compressed and deformed during a frontal collision. As a result, the intrusion of the body components toward the passenger compartment can be kept below a predetermined level without increasing the longitudinal length of the front longitudinal beam 11, and the collision energy absorption box 21 can sufficiently absorb the collision energy.

[0057] Furthermore, in this invention, if the axial force ratio between the collision energy-absorbing box 21 and the front longitudinal beam 11 is below a predetermined critical axial force ratio, then metal plates with increased tensile strength and reduced thickness can be used for the collision energy-absorbing box 21 and the front longitudinal beam 11. As a result, the vehicle body can be made lighter and more compact without reducing collision energy absorption during a frontal collision or the intrusion of body components into the passenger compartment, thus contributing to improved commercial viability of the automobile.

[0058] As mentioned above Figure 6As shown, the critical axial force ratio can be determined using a value based on the amount of deformation of the body components (e.g., the lower front panel 31) towards the passenger compartment side during a frontal collision, i.e., the amount of passenger compartment intrusion.

[0059] In addition, regarding the lower limit of the axial force ratio, as long as it is within the range of the thickness and tensile strength (or yield strength) of the metal plate (e.g., steel plate) actually used for the front longitudinal beam 11 and the impact energy absorption box 21, it will not cause a large difference in the amount of passenger compartment intrusion.

[0060] For example, in Figure 1 In the front structure 1 of the vehicle body shown, the steel plates actually used as raw materials for the front longitudinal beam 11 and the collision energy absorption box 21 have a thickness of 1.2mm to 2.3mm and a tensile strength of 270MPa to 1470MPa. In this case, among the steel plates that can be used as the collision energy absorption box 21, the axial force F... x1 The minimum steel plate thickness is 1.8 mm, and the tensile strength is 270 MPa. Furthermore, among the steel plates suitable for use as the front longitudinal beam 11, the axial force F... x2 The thickest steel plates are 1.0 mm (outer part) and 1.6 mm (inner part), with a tensile strength of 1470 MPa. Therefore, the axial force ratio of 0.15, resulting from the combination of these steel plate thicknesses and tensile strengths, becomes the lower limit. Furthermore, in the front body structure 1 with an axial force ratio of 0.15, after the collision energy absorption box 21 is sufficiently axially crushed, the front longitudinal beam 11 bends and deforms, and no increase in the intrusion of body components towards the passenger compartment is observed.

[0061] <Design Methodology for Front Body Structure> The design method for the front structure of a vehicle body involved in the embodiments of the present invention is a design Figure 1 The method describes a front body structure 1, as shown, comprising a pair of left and right front longitudinal beams 11 and a collision energy absorption box 21. Furthermore, the design method of the front body structure according to this embodiment is such that, in the event of a frontal collision, the collision energy absorption box 21 is sufficiently compressed and deformed, and then the front longitudinal beams 11 are bent and deformed.

[0062] like Figure 8 As shown, the design method for the front structure of the vehicle body involved in this embodiment includes: a vehicle model acquisition step S1, a minimum section length determination step S3, an axial force ratio calculation step S5, and a passenger compartment side intrusion calculation step S7 for vehicle body components. Furthermore, as... Figure 8 As shown, the design method for the front structure of the vehicle body involved in this embodiment includes: a critical axial force ratio determination step S9, and a plate thickness and tensile strength determination step S11. Hereinafter, the design of the aforementioned... Figure 1 The front structure 1 of the vehicle body shown is referred to Figure 8 and Figure 9 The steps described above will be explained.

[0063] Steps to Obtain a Vehicle Model In the vehicle model acquisition step S1, a vehicle model with the front body structure 1 is acquired, and the parameters are set... Figure 9 The portion of the vehicle model 101 shown is used to evaluate the amount of intrusion of its body components toward the passenger compartment during a frontal collision. In this embodiment, the frontal collision of the vehicle model 101 is as follows: Figure 9 As shown, the offset collision is considered against the collision object 103. In this embodiment, the body component that evaluates the intrusion of the vehicle model 101 towards the passenger compartment side during a frontal collision is the lower front panel 31. Figure 1 Then, as Figure 10 As shown, an intrusion evaluation section 31a is set on the lower front panel 31, and the intrusion amount towards the passenger compartment in each intrusion evaluation section 31a is calculated.

[0064] Steps for determining the minimum cross-sectional length of the section line. In step S3, which determines the minimum cross-sectional length, the minimum cross-sectional length is determined for each of the collision energy-absorbing box 21 and the front longitudinal beam 11 in the front structure 1 of the obtained vehicle model 101. In this embodiment, for... Figure 7 In (a) shown in the figure, the collision energy absorption box 21 and the front longitudinal beam 11 of the front body structure 1 are each, as the section with the smallest section length in the section perpendicular to the length direction, the AA section with stiffener 23 and bent stiffener 13 are respectively determined. Figure 7 (c) in the middle), BB section ( Figure 7 (b) in the middle.

[0065] Steps for calculating the axial force ratio In step S5, which calculates the axial force ratio, the axial force F in the minimum section with the defined cross-sectional length for the collision energy absorption box 21 and the front longitudinal beam 11 in the vehicle model 101 is first calculated using equation (1). x1 and F x2 Then, in step S5 of the axial force ratio calculation, the axial force F calculated for the collision energy absorption box 21 is determined. x1 The axial force F calculated for the front longitudinal beam 11 x2 The ratio of F x1 / F x2 (=Axial force ratio F) x In step S5, the axial force F is calculated for various combinations of the thickness and tensile strength (or yield strength) of the metal plate (e.g., steel plate) actually used for the front longitudinal beam 11 and the impact energy absorption box 21. x1 F x2 and axial force ratio Fx .

[0066] ≪Steps for calculating passenger compartment side intrusion of vehicle body components≫ In step S7, which calculates the intrusion amount of the vehicle body components to the passenger compartment side, a frontal collision analysis is first performed on the vehicle model 101, which has various combinations of plate thickness and tensile strength set for the metal plates used for the front longitudinal beam 11 and the collision energy absorption box 21. Then, the intrusion amount of the vehicle body components (lower front panel 31) in the intrusion evaluation area 31a set in the vehicle model 101 to the passenger compartment side is calculated during the frontal collision.

[0067] The collision analysis of vehicle model 101 in step S7 of the calculation of passenger compartment side intrusion of body components can be performed by executing collision analysis software.

[0068] Steps for determining the critical axial force ratio In the critical axial force ratio determination step S9, the critical axial force ratio is determined by calculating the relationship between the axial force ratio calculated in step S5 and the intrusion amount calculated in step S7 of the passenger compartment side intrusion amount calculation of the body component. The axial force ratio is calculated in step S5 for various combinations of the plate thickness and tensile strength of the metal plates used for the front longitudinal beam 11 and the collision energy absorption box 21. On the other hand, the intrusion amount of the body component is the value calculated in step S7 of the passenger compartment side intrusion amount calculation of the body component by crash analysis of the vehicle model 101, which sets various combinations of the plate thickness and tensile strength of the metal plates used for the front longitudinal beam 11 and the collision energy absorption box 21.

[0069] Furthermore, in the critical axial force ratio determination step S9, the relationship between the axial force ratio and the intrusion amount of the vehicle body component can be as follows: Figure 6 As illustrated in the example. Figure 6 As shown, the intrusion of the body components decreases as the axial force ratio decreases, but when the axial force ratio is below 0.69, the intrusion reaches saturation within a roughly constant range (within ±20%). Therefore, the critical axial force ratio can be determined to be 0.69.

[0070] Steps for determining plate thickness and tensile strength In step S11, the combination of plate thickness and tensile strength of the metal plate used for the front longitudinal beam 11 and the impact energy absorption box 21 is determined to be below the critical axial force ratio determined in step S9. In determining the combination of plate thickness and tensile strength of the metal plate used for the front longitudinal beam 11 and the impact energy absorption box 21, it can be selected from various combinations of plate thickness and tensile strength for which the axial force ratio was calculated in step S5.

[0071] According to the design method of the front body structure according to the embodiments of the present invention, the front body structure 1 can be designed such that, in the event of a frontal collision, after the collision energy absorption box 21 has been sufficiently compressed and deformed, the front longitudinal beam bends and deforms. Furthermore, a vehicle equipped with such a front body structure 1 can, in the event of a frontal collision, reduce the intrusion of body components towards the passenger compartment to a predetermined level without increasing the longitudinal length of the front longitudinal beam 11, and can sufficiently absorb collision energy through the collision energy absorption box 21.

[0072] In the step of determining plate thickness and tensile strength, any combination of plate thickness and tensile strength that results in an axial force ratio below the critical axial force ratio can be appropriately determined. However, in the step of determining plate thickness and tensile strength, for example, as described below, weight can be used as an indicator to determine plate thickness and tensile strength.

[0073] In this case, firstly, in step S5 of calculating the axial force ratio, the weights of the front longitudinal beam 11 and the impact energy absorption box 21 are calculated in addition to the axial force ratio for various combinations of plate thicknesses and tensile strengths of the metal plates used for the front longitudinal beam 11 and the impact energy absorption box 21.

[0074] Then, in the plate thickness and tensile strength determination step S11, among the combinations of plate thickness and tensile strength that have an axial force ratio below the critical axial force ratio, the combination of plate thickness and tensile strength that minimizes the total weight of the front longitudinal beam 11 and the collision energy absorption box 21 calculated in the axial force ratio calculation step is determined. Thus, a front body structure 1 that ensures collision performance and achieves vehicle body lightweighting can be designed.

[0075] The above explanation addresses the case where weight is used as an indicator to determine the optimal plate thickness and tensile strength. However, the rigidity of the front structure of the vehicle body and the amount of collision energy absorbed can also be used as indicators. When determining the combination of plate thickness and tensile strength for the metal plate used in the collision energy absorption box 21 of the front longitudinal beam 11 using the amount of collision energy absorbed by the collision energy absorption box 21 as an indicator, in the step of determining plate thickness and tensile strength, the axial force ratio F... x Among the combinations of plate thickness and tensile strength that fall below the critical axial force ratio, the axial force F calculated for the impact energy absorption box 21 is determined. x1 This results in the combination of maximum plate thickness and tensile strength. Consequently, it promotes sufficient compressive deformation of the impact energy absorption box 21 and maximizes the endurance of the impact energy absorption box 21, thereby maximizing the amount of impact energy absorbed (the value obtained by integrating the load with the distance (stroke) in the load-stroke curve).

[0076] Furthermore, in this embodiment, the passenger compartment side intrusion calculation step S7 uses a full vehicle model, which models the entire vehicle, as the vehicle model 101. However, it can also be a partial vehicle model, which models the front body structure and surrounding body parts of the vehicle.

[0077] Furthermore, the design method for the front structure of a vehicle body according to this embodiment can also be implemented using a computer-based design apparatus for the front structure of a vehicle body. Moreover, in the design apparatus for the front structure of a vehicle body, the computer can execute programs for each step of the design method for the front structure of a vehicle body.

[0078] <Manufacturing Method of Front Body Structure> In the manufacturing method of the front body structure according to the embodiments of the present invention, the design method of the front body structure according to the above-described embodiments of the present invention determines the combination of plate thickness and tensile strength for the front longitudinal beam 11 and the collision energy absorption box 21 of the front body structure 1. Then, using the metal plate with the determined combination of plate thickness and tensile strength, an axial force F is generated for the cross-sectional line length of the closed cross-section structure in the collision energy absorption box 21 to be minimized. x1 The axial force F of the section line length of the closed section structure in the front longitudinal beam 11 is the minimum. x2 The ratio of F x1 / F x2 The front body structure 1, consisting of the front longitudinal beam 11 and the collision energy absorption box 21, is determined to be below the critical axial force ratio determined in step S9.

[0079] According to the manufacturing method of the front body structure of the present invention, a front body structure 1 can be manufactured such that, in a frontal collision, after the collision energy-absorbing box 21 is sufficiently compressed and deformed, the front longitudinal beam 11 bends and deforms. Furthermore, a vehicle equipped with a front body structure 1 manufactured in this way can reduce the intrusion of body components towards the passenger compartment to a predetermined level or less during a frontal collision. Moreover, the collision energy can be sufficiently absorbed by the collision energy-absorbing box 21 without increasing the longitudinal length of the front longitudinal beam 11.

[0080] Example An analysis was conducted to verify the effectiveness of the present invention, which is described below. In the analysis, such as... Figure 9 As shown, a front structure 1 (of the vehicle body) is used. Figure 1The vehicle model 101 is used as the target for offset collision, in which the collision body 103 collides with the front of the vehicle model 101 while offset from the center of the vehicle body width direction. Then, based on the analysis of the offset collision, the optimal plate thickness and tensile strength are determined so that the front longitudinal beam 11 can bend and deform after the collision energy absorption box 21 in the front structure 1 of the vehicle body is sufficiently compressed and deformed.

[0081] First, obtain Figure 1 The vehicle model 101 of the front body structure 1 shown is configured with intrusion evaluation areas for evaluating the amount of intrusion of body parts toward the passenger compartment side during a frontal collision. In this embodiment, the lower front bulkhead 31 and the foot brake (not shown) are used as body parts for evaluating the amount of intrusion toward the passenger compartment side. Then, as... Figure 10 As shown, six intrusion evaluation points 31a are set for the lower front panel 31. In addition, the foot brake itself is set as an intrusion evaluation point.

[0082] Next, regarding Figure 7 In (a) of the vehicle model 101, the collision energy absorption box 21 and the front longitudinal beam 11 in the front body structure 1 are each defined as the minimum cross-sectional section with the smallest cross-sectional length as section AA. Figure 7 (c) in the middle), BB section ( Figure 7 (b) in the middle.

[0083] Next, the axial force F in the minimum section of the collision energy absorption box 21 and the front longitudinal beam 11 is calculated separately. x1 and F x2 And calculate the axial force ratio F x (=F) x1 / F x2 The axial force ratio F is calculated for various combinations of plate thickness and tensile strength of the metal plates used for the front longitudinal beam 11 and the impact energy absorption box 21. x The axial forces of the impact energy absorption box 21 and the front longitudinal beam 11 were calculated using JSOL's ARUP software PRIMER 1.80 (Oasys Primer ver. 1.80 for LS-DYNA). Additionally, the weights of the impact energy absorption box 21 and the front longitudinal beam 11 were calculated based on various combinations of the plate thickness and tensile strength of the metal plates used for the front longitudinal beam 11 and the impact energy absorption box 21.

[0084] Table 1 shows the combinations of plate thickness and tensile strength set in the impact energy absorption box 21 and the front longitudinal beam 11, and the axial force and axial force ratio F of the impact energy absorption box 21 and the front longitudinal beam 11 calculated for each combination. x .

[0085] [Table 1] Next, an offset collision analysis was performed on vehicle model 101 with various combinations of plate thickness and tensile strength. The intrusion of the body components in the intrusion evaluation area of ​​vehicle model 101 towards the passenger compartment was calculated. In the collision analysis, the initial speed of vehicle model 101 was set to 64 km / h.

[0086] Next, the axial force ratio F between the impact energy absorption box 21 and the front longitudinal beam 11, calculated for each plate thickness and tensile strength combination shown in Tables No.1 to No.10, is determined. x The relationship between the intrusion amount and the intrusion amount in the evaluation area determined by the collision analysis of vehicle model 101 is plotted. Then, the critical axial force ratio is determined based on the plotted relationship between the axial force ratio and the intrusion amount. Figure 6 The graph shown is a plot of the relationship between the axial force ratio and the front bulkhead intrusion. See Table 1 and... Figure 6 As shown, in the region where the axial force ratio is greater than 0.69 (No. 2 and No. 4 in Table 1), the front bulkhead intrusion tends to decrease as the axial force ratio decreases. Furthermore, in the region where the axial force ratio is less than 0.69 (No. 1, No. 3, No. 5 to No. 10 in Table 1), the front bulkhead intrusion is approximately constant within ±20%, regardless of the axial force ratio. Therefore, the critical axial force ratio relative to the front bulkhead intrusion is determined to be 0.69.

[0087] In Table 1, for the impact energy-absorbing box 21 and the front longitudinal beam 11 with plate thicknesses and tensile strengths shown in No. 1, No. 3, and No. 5 to No. 10, the axial force ratio F x For the reason Figure 6 The critical axial force ratio is determined to be below the following values. Therefore, the front body structure 1 of the vehicle body, which has the combination of these plate thicknesses and tensile strengths, including the impact energy absorption box 21 and the front longitudinal beam 11, is within the scope of the present invention (example of the invention).

[0088] In contrast, in Table 1, for the impact energy-absorbing box 21 and the front longitudinal beam 11 with the combinations of plate thickness and tensile strength shown in No. 2 and No. 4, the axial force ratio F x Greater than by Figure 6 The value of the critical axial force ratio is determined. Therefore, the front body structure 1 of the vehicle body, which has the combination of these plate thicknesses and tensile strengths, including the impact energy absorption box 21 and the front longitudinal beam 11, is outside the scope of the present invention (comparative example).

[0089] In addition, Table 1 shows the weight difference between the impact energy absorption box 21 and the front longitudinal beam 11 in each combination of plate thickness and tensile strength involved in No.2 to No.10, based on the weight when the plate thickness of the impact energy absorption box 21 and the front longitudinal beam 11 is set to No.1.

[0090] In the invention examples shown in No.3, No.6 to No.9, compared with No.1, the impact energy absorption box 21 and the front longitudinal beam 11 are lightweight without reducing the amount of front panel intrusion by increasing the tensile strength of the impact energy absorption box 21 and the front longitudinal beam 11 and reducing the plate thickness.

[0091] Figure 11 As an example, the load-stroke curve is shown in the collision analysis of the vehicle model 101 with offset collision, which is set by the combination of the plate thickness and tensile strength of the collision energy absorption box 21 and the front longitudinal beam 11 as shown in Table 1 No.3 (Example 2 of the Invention) and No.4 (Comparative Example 2).

[0092] also, Figure 12 The diagram shows a summary chart of the results for the front bulkhead intrusion, foot brake intrusion, and collision energy absorption (energy absorption EA) of the collision energy absorption box in the inventive examples (No. 1, No. 3, and No. 10) and comparative example (No. 4). Figure 11 and Figure 12 In the context of collision energy absorption box EA, the amount of collision energy absorbed by the collision energy absorption box 21 due to the compression deformation of the collision energy absorption box 21 is measured from the distance and time until the front longitudinal beam 11 begins to buckle (bending deformation).

[0093] When the combination of the plate thickness and tensile strength of the impact energy-absorbing box 21 and the front longitudinal beam 11 is set as shown in Table 1 (Example 1 of the Invention), such as Figure 11 (a) and Figure 12 As shown, the energy absorption capacity (EA) of the impact energy-absorbing box at the point where the front longitudinal beam 11 begins to buckle (668.8 mm) and at a time of 0.041 s is 58.5 kN·m. Additionally, the front bulkhead intrusion is 22.5 mm and the foot brake intrusion is 15.0 mm.

[0094] In Table 1, No. 3 (Example 2 of the Invention), in the combination of the plate thickness and tensile strength of the impact energy absorption box 21 and the front longitudinal beam 11, the axial force ratio F x The axial force ratio F is greater than that of No.1 (Example 1) (No.1: 0.50, No.3: 0.69) and No.3 (Example 2). x It is equal to the critical axial force ratio (=0.69). Furthermore, as... Figure 11As shown in (a), smooth, corrugated compressive deformation of the impact energy absorption box 21 can be promoted until the front longitudinal beam 11 begins to buckle (bending deformation). Therefore, compared to No. 1 (Example 1), the impact energy absorption box EA is increased by 6.6% (No. 3: 62.4 kN·m, No. 1: 58.5 kN·m), the front bulkhead intrusion is reduced by 9% (No. 3: 20.4 mm, No. 1: 22.5 mm), and the foot brake intrusion is reduced by 20% (No. 3: 12.0 mm, No. 1: 15.0 mm). Furthermore, compared to No. 1 (Example 1), the axial force F of the impact energy absorption box 21 in No. 3 (Example 2) is... x1 The energy absorption capacity of the impact energy absorption box 21 is 53% larger (No.1: 304.9kN, No.3: 466.1kN). Due to the sufficient compression deformation of the impact energy absorption box 21, the energy absorption capacity of the impact energy absorption box EA of No.3 (Example of the Invention) is increased by 6.6% compared with No.1 (Example of the Invention) (No.3: 62.4kN·m, No.1: 58.5kN·m).

[0095] In Table 1, No. 4 (Comparative Example 2), in the combination of the plate thickness and tensile strength of the impact energy absorption box 21 and the front longitudinal beam 11, the axial force ratio F x Greater than the critical axial force ratio of 0.69 (=0.84), such as Figure 11 As shown in (b), the distance until the front longitudinal beam 11 begins to buckle (bending deformation) is 18% shorter than that in No. 1 (Example 1 of the Invention) (No. 4: 550.6 mm, No. 1: 668.8 mm), which is insufficient to allow the compressive deformation of the impact energy absorption box 21 to progress sufficiently. Therefore, in No. 4 (Comparative Example 2), although the tensile strength of the steel plate used for the impact energy absorption box 21 was set to 1180 MPa, which increased the axial force by 87% compared to No. 1 (Example 1 of the Invention) (No. 4: 568.8 kN, No. 1: 304.9 kN), the EA amount of the impact energy absorption box was reduced by 12.8% compared to No. 1 (Example 1 of the Invention) (No. 4: 51.0 kN·m, No. 1: 58.5 kN·m). Furthermore, in No.4 (Comparative Example 1), by reducing the amount of compression deformation of the collision energy-absorbing box 21 until the front longitudinal beam 11 begins to bend and deform, the intrusion of the front bulkhead increased by 73% (No.4: 38.9 mm, No.1: 22.5 mm) and the intrusion of the foot brake increased by 58% (No.4: 23.7 mm, No.1: 15.0 mm).

[0096] In Table 1, No. 10 (Example 8 of the Invention), the combination of plate thickness and tensile strength of the impact energy-absorbing box 21 and the front longitudinal beam 11, compared with No. 1 (Example 1 of the Invention), shows that the axial force ratio F xThe reduction (No. 1: 0.50, No. 10: 0.19) promotes smooth, corrugated axial crushing of the impact energy-absorbing box until the front longitudinal beam 11 begins to buckle (bending deformation). Therefore, compared to No. 1 (Example 1), in No. 10 (Example 8), the front bulkhead intrusion is reduced by 11% (No. 10: 20.0 mm, No. 1: 22.5 mm), and the foot brake intrusion is reduced by 18% (No. 10: 12.3 mm, No. 1: 15.0 mm). No. 10 (Example 8) uses steel plates with lower tensile strength than No. 1 (Example 1) for the impact energy-absorbing box 21 (No. 1: 440 MPa grade, No. 10: 270 MPa grade), thus reducing the impact energy-absorbing box EA by 57% (No. 10: 25.3 kN·m, No. 1: 58.5 kN·m).

[0097] In this embodiment, the axial force ratio and the weight of the front longitudinal beam 11 and the collision energy absorption box 21 were calculated for the case where the combination of plate thickness and tensile strength was changed, and the optimal combination of plate thickness and tensile strength was determined from the viewpoint of lightweighting the front structure 1 of the vehicle body.

[0098] Table 2 shows the results of axial force ratios for various combinations of plate thickness and tensile strength.

[0099] In addition, Table 3 shows the weight difference of the front longitudinal beam 11 and the impact energy absorption box 21 based on the impact energy absorption box 21 and the front longitudinal beam 11 involved in Table 1 No.1 (Example 1 of the invention) for various combinations of plate thickness and tensile strength, and the weight difference obtained by adding them together.

[0100] [Table 2] [Table 3] In Table 2, the axial force ratio, and in Table 3, the total weight difference between the front longitudinal beam 11 and the impact energy absorption box 21, the columns filled in gray indicate the axial force ratio. Figure 6 The critical axial force ratio shown is the combination of plate thickness and tensile strength below (≤0.69).

[0101] According to the results shown in Tables 2 and 3, when the plate thickness of the front longitudinal beam 11 is set to 1.0 mm for the inner part 11a (inner part) and 1.6 mm for the outer part 11b (outer part), and the tensile strength is set to 1470 MPa, and the plate thickness of the impact energy absorption box 21 is set to 1.2 mm, and the tensile strength is set to 1470 MPa, the absolute value of the total weight difference between the front longitudinal beam 11 and the impact energy absorption box 21 is the largest, which is -2151.2 g. This shows that the combination of plate thickness and tensile strength shown in Tables 2 and 3 is the most suitable.

[0102] Furthermore, the combination of plate thickness and tensile strength that maximizes the collision energy absorption (collision energy absorption EA) of the collision energy absorption box 21 is the combination of the columns filled in gray in Table 2 that is below the critical axial force ratio (≤0.69) for the axial force F calculated for the collision energy absorption box 21. x1 This forms the largest possible combination. In this embodiment, it can be determined that: the plate thickness of the front longitudinal beam 11 is set to 1.2 mm for the inner part 11a (inner part) and 1.8 mm for the outer part 11b (outer part), and the tensile strength is set to 1470 MPa; the plate thickness of the impact energy absorption box 21 is set to 1.4 mm and the tensile strength is set to 1470 MPa.

[0103] As shown above, according to the present invention, in the event of a frontal collision, after the collision energy-absorbing box has been sufficiently compressed and deformed, the front longitudinal beam can be bent and deformed, thereby suppressing the intrusion of body components toward the passenger compartment to a predetermined level, thus ensuring the amount of collision energy absorbed. Furthermore, it has been demonstrated that the vehicle body can be lightweight without compromising collision performance (collision energy absorption and the amount of body component intrusion into the passenger compartment).

[0104] Industrial availability According to the present invention, a design method for a front body structure capable of simultaneously achieving specified collision performance and a compact design in a frontal collision, a method for manufacturing a front body structure, and a method for manufacturing a front body structure are provided.

[0105] Explanation of reference numerals in the attached figures 1. Front structure of the vehicle body 11 Front longitudinal beam 11a Inner side component of front longitudinal beam 11b Front longitudinal beam outer side member 13 Bending stiffeners 21 Collision Energy Absorption Box 21a Collision energy absorption box inner part 21b External component of the impact energy absorption box 23 Reinforcing ribs 31 Front lower panel 31a Site for evaluating intrusion amount 33 Bumper 101 vehicle models 103 Colliders

Claims

1. A front structure of a vehicle body, comprising a pair of left and right front longitudinal beams extending in the longitudinal direction of the vehicle body and having a closed cross-section, and a collision energy absorption box extending from the front end of each front longitudinal beam toward the front side of the vehicle body and having a closed cross-section, wherein the front structure of the vehicle body, The axial force F is used to minimize the cross-sectional line length of the closed cross-section structure in the impact energy absorption box. x1 The axial force F of the section with the minimum section length of the closed section structure in the front longitudinal beam. x2 The ratio of F x1 / F x2 The thickness and tensile strength of the metal plates for the front longitudinal beam and the collision energy-absorbing box are set in a manner that determines a predetermined critical axial force ratio, so that in a frontal collision, the front longitudinal beam bends after the collision energy-absorbing box has been sufficiently compressed and deformed.

2. Design method for the front structure of the vehicle body, wherein, In a front body structure comprising a pair of left and right front longitudinal beams extending in the longitudinal direction of the vehicle and having a closed cross-section, and a collision energy-absorbing box extending from the front end of each front longitudinal beam toward the front of the vehicle body and having a closed cross-section, the front longitudinal beams are designed such that, in a frontal collision, the collision energy-absorbing box is sufficiently compressed and deformed, and then the front longitudinal beams are bent and deformed. The design method for the front body structure includes: The vehicle model acquisition step involves acquiring a vehicle model with the aforementioned front body structure and setting an intrusion evaluation location for evaluating the intrusion of the vehicle model's body components toward the passenger compartment side during a frontal collision. The step of determining the minimum section length involves determining the minimum section length for each of the collision energy-absorbing box and the front longitudinal beam in the obtained vehicle model. The axial force ratio calculation step involves calculating the axial force in the minimum section with a set plate thickness and tensile strength for each of the collision energy absorption box and the front longitudinal beam in the vehicle model, and calculating the ratio of the axial force calculated for the collision energy absorption box to the axial force calculated for the front longitudinal beam. The steps for calculating the passenger compartment side intrusion of the body component are as follows: a collision analysis is performed on the vehicle model with the various plate thicknesses and tensile strengths set for a frontal collision, and the intrusion of the body component to the passenger compartment side in the intrusion evaluation area set in the vehicle model is calculated during the frontal collision. The critical axial force ratio determination step involves determining the relationship between the axial force ratio calculated in the previous step (using various plate thicknesses and tensile strengths) and the intrusion amount of the body component towards the passenger compartment side in the intrusion evaluation area calculated in the previous step (using collision analysis of the vehicle model with various plate thicknesses and tensile strengths). This determines the critical axial force ratio at which the intrusion amount reaches saturation at a substantially constant value. The plate thickness and tensile strength determination step involves identifying, among the axial force ratios calculated for various combinations of plate thickness and tensile strength, the combinations of plate thickness and tensile strength that fall below the critical axial force ratio determined in the critical axial force ratio determination step.

3. The design method for the front structure of the vehicle body as described in claim 2, wherein, In the step of calculating the axial force ratio, the weights of the impact energy-absorbing box and the front longitudinal beam are calculated in the various combinations of plate thickness and tensile strength. In the plate thickness and tensile strength determination step, among the combinations of plate thickness and tensile strength where the axial force ratio is below the critical axial force ratio, the combination of plate thickness and tensile strength that minimizes the total weight of the collision energy absorption box and the front longitudinal beam calculated in the axial force ratio calculation step is determined.

4. The design method for the front structure of the vehicle body as described in claim 2, wherein, In the step of determining plate thickness and tensile strength, among the combinations of plate thickness and tensile strength where the axial force ratio is below the critical axial force ratio, the combination of plate thickness and tensile strength where the axial force calculated for the impact energy absorption box is the largest is determined.

5. A manufacturing method for the front structure of a vehicle body, wherein, Using the design method for the front structure of the vehicle body according to any one of claims 2 to 4, the combination of plate thickness and tensile strength is determined for each of the front longitudinal beam and the collision energy absorption box of the front structure of the vehicle body. Using a metal plate with a defined combination of thickness and tensile strength, an axial force F is generated at a cross-sectional length that minimizes the length of the closed cross-section structure in the impact energy-absorbing box. x1 The axial force F of the section with the minimum section length of the closed section structure in the front longitudinal beam. x2 The ratio of F x1 / F x2 The front longitudinal beam and the collision energy absorption box form the front structure of the vehicle body when the critical axial force ratio is below the specified value.

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