Sub-frame structure of automobile

Abstract

A subframe structure (1) for an automobile according to the present invention is provided with a pair of left and right longitudinal members (10) and a cross member (20), the cross member (20) having: a hollow member (21) having a substantially rectangular cross-section disposed on a straight line connecting left and right suspension arm connecting sections (11) on the front side of the automobile; and a plate-shaped member (23) which is formed in a plate shape from a single metal plate and is disposed further toward the rear side of the vehicle than the substantially rectangular cross-section hollow member (21), the rear ends (23a1) of both side edge portions (23a) being located further toward the rear side of the vehicle than the suspension arm connection portion (13) on the rear side of the vehicle, the plate-shaped member (23) having a rib portion (25), and the rib portion (25) being disposed on the rear end portion (23a1) of both side edge portions (23a) of the plate-shaped member (23). The rib portion is formed so as to be convexly curved from the vehicle rear side toward the center in the vehicle width direction toward the vehicle front side, and the rib width gradually increases from the curved center toward both ends.

Description

TECHNICAL FIELD

[0001] The present application relates to a sub-frame structure of an automobile which improves the stiffness against various loads input from a suspension arm, other automotive parts at the time of running. BACKGROUND

[0002] A sub-frame which combines a suspension arm with a vehicle body is provided on the vehicle body of an automobile. The sub-frame generally has a structure in which both end portions of a cross member extending in the vehicle width direction are connected to a pair of side members extending in the vehicle front-rear direction. Also, on the sub-frame, there are a structure in which two cross members are provided separated from each other in the vehicle front-rear direction and which is in a check mark shape when viewed from above, and a structure in which one cross member is provided on the rear side of the vehicle and which is in an H shape when viewed from above. Further, the side members and the cross member are not limited to a structure in which they are different members and are connected by other members, and there is also a structure in which the side members and the cross member are integrated.

[0003] The sub-frame deforms not only due to the load input from the suspension arm at the time of running of the vehicle, but also due to the load input from the stabilizer, the steering gear box, and other automotive parts assembled to the sub-frame, and the mounting portion mounted to the vehicle body, and thus high stiffness is required. Also, the high stiffness of the sub-frame improves the ride comfort, and increases the value of the automobile.

[0004] In addition, in the case of a gasoline powered automobile, the sub-frame is generally configured to avoid the engine, but this is not necessary in the case of a battery electric vehicle. However, the battery electric vehicle needs to be equipped with a battery, and thus the weight of the vehicle increases. Therefore, in the sub-frame of the battery electric vehicle, a structure which further improves the stiffness is required.

[0005] So far, several technologies related to the performance and structure required for the sub-frame structure of an automobile have been proposed, for example, as disclosed in Patent Documents 1 to 3.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT DOCUMENTS

[0008] Patent Document 1: Japanese Patent Application Publication No. 2020-50213

[0009] Patent Document 2: Japanese Patent Application Publication No. 2022-074054

[0010] Patent Document 3: Japanese Patent Application Publication No. 2020-164094 SUMMARY

[0011] Problem to be Solved by the Invention

[0012] In a subframe of an automobile, as described above, in addition to the load input from the suspension arm at the time of running, high rigidity with respect to various directions of the load input from other vehicle body members, which are assembled to the subframe, and a mounting portion mounted to the vehicle body is required. In particular, in a subframe of an electric automobile, from the viewpoint of energy efficiency of the automobile, light weight is also required. In order to achieve light weight of the subframe, in the case where the subframe is manufactured by press forming of a metal sheet, it is effective to make the sheet thickness thin, but if the sheet thickness is made thin, the rigidity is generally reduced, and thus high rigidity and light weight are in a trade-off relationship. In addition, as the car performance reduced when the sheet thickness is made thin, there are crashworthiness, deformation strength at the time of input of a primary load, fatigue strength, and the like, but they can be solved by applying a metal material having high strength. However, in a general metal material, even if the strength is increased, the elastic coefficient is hardly changed, and thus high rigidity due to high strength of the metal material cannot be expected.

[0013] Thus, in a subframe of an automobile (particularly, an electric automobile), a structure in which high rigidity is achieved regardless of the strength of the metal material is required. However, the subframes of Patent Literature 1 and Patent Literature 2 are subframes in which crashworthiness in which a front crash of a vehicle is assumed is improved, and are not subframes in which rigidity with respect to various directions of the load input from the suspension arm, other vehicle body members, and the mounting portion mounted to the vehicle body is improved.

[0014] In addition, the subframe of Patent Literature 3 connects the first longitudinal beam and the second longitudinal beam in a skew structure by a connecting member provided separately from the cross beam to the rear side of the vehicle body. According to Patent Literature 3, it is possible to improve the strength and rigidity of the subframe by the connecting member.

[0015] However, in the subframe of Patent Literature 3, there is a large space between the cross beam on the front side of the vehicle and the connecting member on the rear side of the vehicle. Thus, with respect to various directions of the load input from other vehicle body members, which are assembled to the subframe, and the mounting portion mounted to the vehicle body, the rigidity cannot be sufficiently improved.

[0016] The present application has been achieved in order to solve the above problem, and an object thereof is to provide a subframe structure of an automobile, which has high rigidity with respect to various directions of the load input from other vehicle body members, which are assembled to the subframe, and a mounting portion mounted to the vehicle body, in addition to the load input from the suspension arm.

[0017] Means for solving the problem

[0018] The subframe structure of the automobile according to the present application is provided with: a pair of left and right side members extending in the vehicle front-rear direction, suspension arm connecting portions provided at both positions in the vehicle front-rear direction; and a cross member extending in the vehicle width direction, both end portions of which are connected to the left and right side members, wherein the cross member is provided with: a hollow substantially rectangular cross section hollow member provided on a straight line connecting the suspension arm connecting portions on the vehicle front side, having a substantially rectangular cross section; and a plate-shaped member formed in a plate shape from a metal plate, provided on the vehicle rear side compared to the substantially rectangular cross section hollow member, and connected to the left and right side members with the rear end of the side edge portion in the vehicle width direction positioned on the vehicle rear side compared to the suspension arm connecting portion on the vehicle rear side, the plate-shaped member having a rib portion curved in a convex shape toward the vehicle front side from a position on the vehicle rear side compared to the suspension arm connecting portion on the vehicle rear side toward the center in the vehicle width direction, the rib portion formed in a manner that the rib width gradually increases from the center of the curvature toward both ends.

[0019] The plate-shaped member can be curved in a convex shape toward the vehicle front side from both ends in the vehicle width direction toward the center, and the rib portion can be formed along the rear edge portion.

[0020] A hollow bent protruding portion can be provided at the front end portion of each side member, the bent protruding portion protruding toward the vehicle front side compared to the substantially rectangular cross section hollow member and bent in a crank shape by being inclined toward the vehicle outer side in the vehicle width direction.

[0021] An opening portion can be formed at a side surface portion on the vehicle outer side at an inclined position of the bent protruding portion inclined toward the vehicle outer side in the vehicle width direction.

[0022] A hollow cross section closing vertical wall portion can be provided at an inner surface side of a valley portion on the vehicle inner side of the bent protruding portion, the hollow cross section closing vertical wall portion closing a part or all of the hollow cross section by connecting an upper surface and a lower surface.

[0023] The cross member can be formed from a steel sheet having a tensile strength of 590 MPa or more.

[0024] Effects of the invention

[0025] The subframe structure of the automobile according to the present application can improve rigidity against various loads input from other vehicle body components and mounting portions mounted to the vehicle body in addition to the load input from the suspension arm when the vehicle is running.

[0026] Furthermore, in the subframe structure of the automobile of the present invention, a bent protrusion is provided in the longitudinal beam. This bent protrusion protrudes forward of the vehicle from the crossbeam and bends obliquely outward in the vehicle width direction into a crank shape. Thus, during the initial, transitional elastic deformation phase of a frontal collision until the longitudinal beam undergoes plastic deformation, the bent protrusion undergoes crushing, bellows-shaped plastic deformation, thereby absorbing collision energy. Moreover, in the subframe structure of the automobile of the present invention, as long as the length of the bent protrusion in the vehicle's longitudinal direction is set to the level required for absorbing collision energy in the initial stage of a collision, it can also be applied to electric vehicles and the like, where the front end of the vehicle is becoming increasingly shorter. Attached Figure Description

[0027] Figure 1 This is a top view illustrating the structure of the subframe of the automobile according to Embodiment 1 of the present invention.

[0028] Figure 2 This is a diagram showing the input load mode in the subframe structure, which is the object of rigidity investigation in the process of completing the present invention.

[0029] Figure 3 This is a cross-sectional view showing a specific example of a plate-shaped member of a crossbeam in the subframe structure of an automobile according to Embodiment 1 of the present invention.

[0030] Figure 4 This is a top view showing an example of adding a reinforcing rib formed on a plate-like member to the subframe structure of an automobile according to Embodiment 1 of the present invention.

[0031] Figure 5 This is a top view showing another specific example of the suspension arm connection portion provided in the longitudinal beam of the subframe structure of the automobile according to Embodiment 1 of the present invention.

[0032] Figure 6 This is a top view showing the subframe structure of the automobile according to Embodiment 2 of the present invention.

[0033] Figure 7 The figures illustrate the bent protrusion in the subframe structure of the automobile according to Embodiment 2 of the present invention ((a) is a top view, (b) is a side view).

[0034] Figure 8is a graph showing a deformation behavior of the bent protrusion portion calculated by front collision analysis of a vehicle equipped with the subframe structure of the automobile of Embodiment 2 of the present application (Fig. 1: (a) at the start of collision, (b) rigid wall intrusion amount 4 mm, (c) intrusion amount 20 mm).

[0035] Figure 9 is a graph showing a deformation behavior of the bent protrusion portion calculated by front collision analysis of a vehicle equipped with the subframe structure of the automobile of Embodiment 2 of the present application (Fig. 2: (d) rigid wall intrusion amount 40 mm, (e) intrusion amount 80 mm).

[0036] Figure 10 is a graph showing a hollow cross-section closed longitudinal wall portion provided inside the bent protrusion portion provided at the front end portion of the longitudinal beam in the subframe structure of the automobile of the present application.

[0037] Figure 11 is a graph showing an example of an attached member provided inside the bent protrusion portion as a hollow cross-section closed longitudinal wall portion in the subframe structure of the automobile of the present application.

[0038] Figure 12 is a graph showing an example of a reinforcing member provided at the front end portion of the longitudinal beam as a part of the bent protrusion portion in the subframe structure of the automobile of the present application.

[0039] Figure 13 is a graph showing the subframe structure as a rigid body investigated in Example 1 ((a) Invention Example 1, (b) Comparative Example).

[0040] Figure 14 is an enlarged view of the bent protrusion portion provided at the front end portion of the longitudinal beam in the subframe structure as a collision performance investigation object in the example ((a) only a hollow bent protrusion portion is provided, (b) an attached member is provided inside the bent protrusion portion, (c) a reinforcing member is joined to the front end portion of the longitudinal beam having a longitudinal wall formed at the front end).

[0041] Figure 15 is a graph showing load-displacement curves calculated by collision analysis of a vehicle equipped with the subframe structures of Invention Examples 2 to 4 in Example 2. DETAILED DESCRIPTION

[0042] [History of the Invention]

[0043] The present inventors have conducted intensive research on a subframe structure for improving rigidity when an automobile is running.

[0044] In this research, the present inventors have found that Figure 2The subframe structure 1 having the left and right longitudinal members 10 and the cross member 20 as shown is the object. And, the rigidity of the subframe structure 1 is evaluated with respect to an input load mode (a) of the input load to the suspension arm connecting portions 11, 13 Figure 2 and an input load mode (b) of the input load to the mounting portion, i.e., the front end portion 10a of the longitudinal member 10, mounted to the vehicle body Figure 2

[0045] As shown in (a) (i) to (iii) of Figure 2 , the input load mode to the suspension arm connecting portions 11, 13 is three modes of the direction of the load input to the suspension arm 101 being different. Figure 2 (a) (i) is a mode of the load being input in the right direction in the vehicle width direction, Figure 2 (a) (ii) is a mode of the load being input in the rear direction in the vehicle front-rear direction, Figure 2 (a) (iii) is a mode of the load being input in the upper direction in the vehicle up-down direction.

[0046] Further, as shown in (b) (i) to (iii) of Figure 2 , the input load mode to the mounting portion (the front end portion 10a of the longitudinal member 10) mounted to the vehicle body is three modes of the size and the direction of the load input to the front end portion 10a of the left and right longitudinal members 10 being different, respectively. Figure 2 (b) (i) is an input load mode (torsion) of the load being input in the vehicle up direction and the vehicle down direction being reversed, Figure 2 (b) (ii) is an input load mode (transverse bending) of the load being input in one direction in the vehicle width direction, Figure 2 (b) (iii) is an input load mode (folding deformation) of the load being input in the vehicle up direction being different in size.

[0047] The rigidity of the subframe structure 1 with respect to these input load modes was investigated, and as a result, the following (1) to (3) were found to be effective in order to effectively improve the rigidity of the subframe structure 1.

[0048] (1) As the cross member 20 linking the left and right longitudinal members 10, a substantially rectangular cross section hollow member having a substantially rectangular cross section with a high geometrical moment of inertia is provided on a straight line linking the left and right suspension arm connecting portions 11 on the vehicle front side to each other.

[0049] ​(2) Further, as the cross member 20, a plate-shaped member is provided at a position on the vehicle rear side of the substantially rectangular cross-section hollow member, and the side portion in the vehicle width direction is connected to a position on the vehicle rear side of the suspension arm connecting portion of the longitudinal member 10.

[0050] (3) As the plate-shaped member, a rib portion which is curved convexly toward the vehicle front side in plan view is provided, and the rib width is gradually increased toward both ends in the vehicle width direction.

[0051] Further, it was ascertained that by having the above (1) to (3), the input load modes (b) (i) torsion, (iii) folding deformation) which cause the subframe structure 1 as a whole to bend out-of-plane, and the input load modes (b) (ii) lateral bending) which cause the subframe structure 1 as a whole to bend in-plane are particularly effective. Figure 2 Figure 2

[0052] The present application was completed based on such a study, and the structure thereof will be described below.

[0053] [Embodiment 1]

[0054] As shown in Figure 1 , the subframe structure 1 of the present embodiment 1 has a longitudinal member 10 and a cross member 20. Further, a suspension arm 101 and a mounting portion 103 which is mounted to a vehicle body are provided in the subframe structure 1. Hereinafter, each component of the subframe structure 1 will be described. In the drawings of the present application, "front and rear" indicates the vehicle front and rear direction, "left and right" indicates the vehicle width direction (the left and right direction toward the traveling direction of the vehicle), and "up and down" indicates the vehicle up and down direction.

[0055] <Longitudinal Member>

[0056] As shown in Figure 1 , the longitudinal member 10 extends in the vehicle front and rear direction, and is a pair of longitudinal members provided with suspension arm connecting portions 11, 13 at both places in the vehicle front and rear direction.

[0057] <Cross Member>

[0058] As shown in Figure 1 , the cross member 20 extends in the vehicle width direction, and both end portions 20a are connected to the longitudinal members 10 on the left and right, and has a substantially rectangular cross-section hollow member 21 and a plate-shaped member 23. Figure 3 (a) indicates a cross-sectional view of the A-A section of the cross member 20. Figure 1

[0059] (Substantially Rectangular Cross-Section Hollow Member)

[0060] As shown in Figure 1 ​​​As shown, a hollow member 21 with a generally rectangular cross-section is arranged on a straight line connecting the suspension arm connecting portions 11 on the front side of the left and right longitudinal beams 10 to each other. It is a hollow member with a generally rectangular cross-section in a section orthogonal to the vehicle width direction. Moreover, both ends 21a are connected to the longitudinal beams 10.

[0061] (Plate-shaped component)

[0062] like Figure 1 As shown, the plate-shaped member 23 is formed from a metal plate and is disposed at a position relative to the rear of the vehicle, which is larger than the hollow member 21 with a roughly rectangular cross-section. Furthermore, the plate-shaped member 23 is connected to the left and right longitudinal beams 10 such that the rear end 23a1 of the side portion 23a in the vehicle width direction is located at a position relative to the rear of the vehicle, which is closer to the rear of the vehicle than the suspension arm connection portion 13.

[0063] Furthermore, the plate-shaped member 23 has a rib 25 that curves convexly toward the center in the vehicle width direction from a position near the rear of the suspension arm connection 13. The rib 25 is formed such that its width gradually increases from the center of the curve toward both ends 25a. The rib width is defined as the width of the rib 25 in a cross-section orthogonal to the direction of curvature.

[0064] Effects and Functions

[0065] The subframe structure 1 of this embodiment 1 has the following effects. The approximately rectangular cross-section hollow member 21 is arranged on the straight line connecting the left and right suspension arm connecting portions 11 on the front side of the vehicle, and is therefore located near the front end 10a of the longitudinal beam 10, which is connected to the vehicle body on the front side and is subjected to load input. Thus, it not only provides load input modes for the suspension arm connecting portions 11 and 13 (… Figure 2 (a)(i) to (iii)), for the input load mode of inputting load to the front end 10a of the longitudinal beam 10 ( Figure 2 (b)(i) to (iii)) also improve the rigidity.

[0066] Furthermore, the plate-shaped member 23 is positioned on the rear side of the roughly rectangular cross-section hollow member 21, and its side portion 23a in the vehicle width direction is connected to the left and right longitudinal beams 10 with its rear end 23a1 located on the rear side of the suspension arm connection portion 13. Thus, a structure can be formed in which the left and right longitudinal beams 10 rear of the roughly rectangular cross-section hollow member 21 are integrated with the plate-shaped member 23, improving the performance for... Figure 2 The rigidity of various input load modes shown in (a) and (b).

[0067] Further, the plate-shaped member 23 has a rib portion 25 that is curved convexly toward the vehicle front side and in which the rib width gradually increases from the center of the curve toward both ends. Thereby, it is possible to improve the rigidity against Figure 2 the lateral bending input load mode shown in (b) (ii) of the input load mode, Figure 2 the folding deformation input load mode shown in (b) (iii) of the input load mode.

[0068] Thus, in the subframe structure 1 of the automobile of Embodiment 1, it is possible to improve the rigidity against various input load modes. Further, in the subframe structure 1 of the automobile of Embodiment 1, by improving the rigidity against various input load modes to suppress deformation, it is also possible to expect improvement in the collision strength, the single input strength (deformation strength against one load input), and the fatigue strength. Further, by reducing the plate thickness of each vehicle body member in a manner that offsets the amount of improvement in rigidity, it is also possible to achieve weight reduction while maintaining the structure equivalent to the conventional subframe structure. As for the improvement in rigidity of the subframe structure of Embodiment 1, verification is performed in Embodiment 1 described later.

[0069] In the subframe structure 1 of Embodiment 1, the substantially rectangular cross-section hollow member 21 is preferably arranged in a manner that links the suspension arm link portions 11 on the left and right vehicle front sides. Thereby, it is possible to effectively improve the rigidity against input loads from the suspension arm link portions 11.

[0070] Further, the substantially rectangular cross-section hollow member 21 is preferably arranged such that the corner portion 21c (see (a) of Figure 3 ) on the vehicle front side in the substantially rectangular cross-section is located at a position further toward the vehicle front side than the suspension arm link portion 11. Thereby, it is possible to effectively utilize the space obtained by the electrification of the automobile.

[0071] In the subframe structure 1 shown in Figure 1 , the rear edge portion 23b of the plate-shaped member 23 in the vehicle front-rear direction is curved convexly toward the vehicle front side from both ends in the vehicle width direction toward the center, and the rib portion 25 is formed along the curve of the rear edge portion 23b. Thereby, it is possible to improve the rigidity of the subframe structure 1, and it is possible to achieve weight reduction, and thus is preferable.

[0072] In the present application, as long as the rib portion formed in the plate-shaped member is such that the rib width gradually increases from the center of the curve toward both ends, the shape such as the rib width, the rib height, etc. is not particularly limited. However, in order to improve the rigidity against the lateral bending input load mode and the folding deformation input load mode of the input load mode in which a load is input to the front end portion of the side member, it is preferable that the rib width at both ends of the curve be about 4 to 5 times the rib width at the center of the curve, and the rib width at both ends of the curve be about 90 to 120 mm. Further, the rib height is preferably about 10 to 30 mm.

[0073] In addition, in the sub frame structure of the present application, the plate-shaped member 23 can be formed of one sheet metal, and in particular, as shown in Figure 3 the lower portion 21d of the substantially rectangular cross-section hollow member 21 can be formed by bulge forming of one sheet metal. Thus, weight reduction and productivity improvement due to reduction in the number of components can be achieved.

[0074] As shown in (b) of Figure 3 the plate-shaped member 23 can also be formed with the recess 27 by deep drawing. By forming the recess 27 in this way, components such as the steering gear can be arranged in the recess 27, the rigidity of the sub frame structure 1 can be improved, and the limited space inside the vehicle can be effectively utilized.

[0075] Further, regarding the plate-shaped member 23, as exemplified in Figure 4 by additionally forming the reinforcing rib portion 29, the rigidity of the sub frame structure 1 can also be easily further improved.

[0076] In the sub frame structure 1 shown in Figure 1 an opening portion is provided on the side of the vehicle width direction outer side of the longitudinal beam 10, and the suspension arm 101 is inserted into the opening portion to be connected to the suspension arm connecting portions 11, 13. In such a sub frame structure 1, the rigidity and fatigue strength against input loads from the suspension arm 101 are high, but since the longitudinal beam 10 cannot be provided as a closed cross-section structure, it can be difficult to ensure the collision strength from the front of the vehicle.

[0077] Therefore, as exemplified in Figure 5 the present application can also be a sub frame structure 1A in which the flange portion 15 is used as a suspension arm connecting portion for the longitudinal beam 10 and the suspension arm 101. In such a sub frame structure 1A, the rigidity against input load modes from the suspension arm connecting portions (the flange portion 15, the suspension arm connecting portion 17) can also be improved, and further the collision strength from the front of the vehicle can be improved.

[0078] [Embodiment 2]

[0079] The sub frame structure 1 of the foregoing Embodiment 1 improves the rigidity against various input load modes during vehicle travel. However, the sub frame structure of the present Embodiment 2 can improve not only the rigidity but also the collision performance from the front surface of the vehicle.

[0080] As shown as an example in Figure 6 the sub frame structure 3 of the present Embodiment 2 is provided with a longitudinal beam 30 and a cross beam 20. The cross beam 20 is provided with a substantially rectangular cross-section hollow member 21 and a plate-shaped member 23, and the plate-shaped member 23 is connected to the suspension arm connecting portion 17 of the longitudinal beam 30. Figure 1), extends in the vehicle width direction, and both end portions are connected to the left and right longitudinal beams 30, and has a substantially rectangular cross-section hollow member 21 and a plate-shaped member 23.

[0081] As shown in Figure 6 , the longitudinal beam 30 is a pair of longitudinal beams extending in the vehicle front-rear direction and provided with suspension arm connecting portions 31, 33 at two places in the vehicle front-rear direction. Also, a hollow bent protruding portion 35 is provided at the front end portion 30a of each longitudinal beam 30, the bent protruding portion 35 protruding to the vehicle front side beyond the substantially rectangular cross-section hollow member 21 and being bent obliquely to the vehicle width direction outer side in a crank shape.

[0082] The valley portion 35a on the vehicle inner side of the bent protruding portion 35 is a site that becomes the start of crushing (plastic deformation) of the bent protruding portion 35 in the vehicle front-rear direction when receiving a collision load from the vehicle front side at the time of a front collision. Therefore, in the bent protruding portion 35 of the subframe structure 3, collision energy can be absorbed at the initial stage of a collision before plastic deformation of the longitudinal beam 10. In this embodiment 2, by the substantially rectangular cross-section hollow member 21 and the plate-shaped member 23, the rigidity of the subframe structure 3 on the rear side of the bent protruding portion 35 in the vehicle front-rear direction against a front collision can be improved. Therefore, when receiving a collision load from the vehicle front side at the time of a front collision, the bent protruding portion 35 receives a reaction force from the subframe structure 3, and can effectively crush (buckling deformation).

[0083] Also, the bent protruding portion 35 can be set to a length in the vehicle front-rear direction to the extent necessary to absorb collision energy at the initial stage of a collision. Therefore, the subframe structure 3 can also be favorably applied to an electric vehicle in which a shortening of the vehicle front end portion is progressing.

[0084] As shown in Figure 7 , the bent protruding portion 35 preferably has an opening portion 35b2 formed in a side surface portion 35b1 of an oblique portion 35b oblique to the vehicle width direction outer side. In this regard, a vehicle having the subframe structure 3 shown in Figure 6 , a front collision with a wall was analyzed, and the results of the analysis of the deformation behavior of the bent protruding portion 35 crushing when receiving a collision load from the vehicle front side are described.

[0085] As shown in Figure 7 , the side surface portion 35b1 having the opening portion 35b2 is opposite to the valley portion 35a that becomes the start of crushing (crushing) in the vehicle front-rear direction when receiving a collision load from the vehicle front side. Figure 8(a) of FIG. 1. Thus, when a collision load is received from the front of the vehicle, first, buckling starts at the valley portion 35a of the buckling protrusion 35 as a start point of crushing Figure 8 (b) of FIG. 1. Also, when the wall intrudes as the collision proceeds, the opening portion 35b2 provided at the side surface portion 35bl on the vehicle outer side opposite to the valley portion 35a is crushed in the vehicle front-rear direction to be deformed in a manner of expanding toward the vehicle up-down direction Figure 8 (b) to (c) of FIG. 1.

[0086] The buckling starting at the valley portion 35a is promoted by the deformation of the opening portion 35b2, as shown in Figure 9 (d) and (e) of FIG. 1. As the intrusion amount of the wall progresses to 40 mm to 80 mm, plastic deformation in which the upper surface 35c and the lower surface 35d of the buckling protrusion 35 are crushed (buckling deformation) into a corrugated shape is generated. In this way, by forming the opening portion 35b2 at the side surface portion on the vehicle outer side of the buckling protrusion 35, the corrugated crushing at the initial stage of the collision is promoted, and the collision energy absorption amount is increased.

[0087] The buckling protrusion 35 is preferably inclined at an angle (θ) of 10° to 45° with respect to the vehicle front-rear direction at the inclined portion 35b in order to stably generate crushing (buckling deformation) starting at the valley portion 35a Figure 7 (θ) shown in (a) of FIG. 1. Figure 7 (θ = 30°) in (a) of FIG. 1.

[0088] If the inclined angle is less than 10°, the position at which crushing is generated in the buckling protrusion 35 varies, and it can be difficult to generate stable crushing. Also, when the inclined angle is greater than 45°, the component of force in the vehicle front-rear direction of the collision load input to the front end of the buckling protrusion 35 becomes small, and the collision energy absorption amount generated by crushing in the vehicle front-rear direction of the buckling protrusion 35 becomes small, and thus it is not preferable.

[0089] The higher the load at the initial stage of the collision at which crushing (buckling deformation) starts (buckling strength), the greater the collision energy absorption amount based on crushing of the buckling protrusion 35 can be. Also, in order to increase the buckling strength of the buckling protrusion 35, it is effective to suppress cross-section collapsing of the hollow buckling protrusion 35 accompanying deformation of the opening portion 35b2.

[0090] Thus, as Figure 10As shown, a hollow cross-section closed longitudinal wall portion 37 is preferably provided on the inner surface side of the valley portion 35a on the vehicle interior side in the bent protruding portion 35, the hollow cross-section closed longitudinal wall portion 37 connecting the upper surface and the lower surface and closing all or a part of the hollow cross-section. Thereby, the buckling resistance of the bent protruding portion 35 can be improved, and the collision energy absorption amount can be increased.

[0091] As a specific example of the bent protruding portion 35 provided with the hollow cross-section closed longitudinal wall portion 37, the structure shown in (a) of FIG. 10 can be cited. Figure 11 and Figure 12 of FIG. 10.

[0092] Figure 11 is a bent protruding portion 35 in which the attaching member 37A is provided on the inner surface side of the valley portion 35a as the hollow cross-section closed longitudinal wall portion. On the other hand, Figure 12 (a) of FIG. 10 is a structure in which the wall surface of the front end portion of the substantially hollow member 30A is bent to form the hollow cross-section closed longitudinal wall portion 37B (b) of FIG. 10), and the reinforcing member 39 (c) of FIG. 10, which corresponds to the front end portion of the bent protruding portion 35, is joined. Figure 12 Figure 12

[0093] The hollow cross-section closed longitudinal wall portion 37 preferably closes more than 1 / 3 (33%) of the hollow cross-section of the bent protruding portion 35. This is because, if less than 1 / 3, the effect of suppressing the collapse of the cross-section of the bent protruding portion 35 in conjunction with the deformation of the opening portion 35b2 of the side surface portion 35b1 formed on the vehicle exterior side of the bent protruding portion 35 is small, and the buckling resistance cannot be sufficiently improved.

[0094] In addition, the bent protruding portion 35 is preferably formed in a shape in which the front end on the vehicle front side is closed. Thereby, at the time of a frontal collision of the vehicle, the deformation of the front end of the bent protruding portion 35 can be suppressed, and the reduction in buckling resistance can be prevented. In order to form a shape in which the opening end portion is closed, for example, a plate-shaped member can be joined to the front end of the bent protruding portion 35.

[0095] In the sub frame structure 3 of the present embodiment 2, as described above, the bent protruding portion absorbs the collision energy by collapsing at the early stage of the collision in which the collision load is input from the vehicle front side. Therefore, at the late stage of the deformation in which the collapse of the bent protruding portion ends, there is a tendency for the collision load input to the vehicle to become excessively high, and thus the occupant injury value sometimes increases due to the increase in collision load. From this viewpoint, in the sub frame structure of the present application, in order to reduce the load at the late stage of the deformation to absorb the collision energy, for example, a deformation induction bead or the like is preferably provided on the rear side of the suspension arm connecting portion on the vehicle rear side in the longitudinal beam.

[0096] ​​In the subframe structure of the automobile of the present invention, it is preferable that the longitudinal beams are made of steel plates with a tensile strength of 590 MPa or higher, regardless of whether there are bent protrusions. This not only improves the impact strength from the front of the vehicle, but also improves the deformation strength and fatigue strength. On the other hand, the material of the crossbeams is not particularly limited, and can be appropriately selected according to the required impact strength and deformation strength.

[0097] [Example 1]

[0098] Since an investigation was conducted into the effects of the subframe structure of the automobile used to verify the present invention, this will be explained below.

[0099] In Example 1, for Figure 13 The rigidity of the subframe structure of the car shown was investigated. Figure 13 (a) is the subframe structure 41 of Invention Example 1. Figure 13 (b) is the subframe structure 43 of the comparative example.

[0100] The subframe structure 41 of Example 1 and the subframe structure 1 described in Embodiment 1 ( Figure 1 Similarly, it has a pair of left and right longitudinal beams 50 and a crossbeam 60 extending along the width direction of the vehicle and connected to the longitudinal beams at both ends. Furthermore, the crossbeam 60 has a hollow member 61 with a generally rectangular cross section and a plate-like member 63.

[0101] like Figure 13 As shown in (a), the hollow member 61 with a roughly rectangular cross section is arranged in a straight line to connect the suspension arm connecting parts 51 on the front side of the left and right longitudinal beams 50 to each other.

[0102] The plate-shaped member 63 is disposed on the rear side of the hollow member 61, which is larger than a roughly rectangular cross-section, and has a rib 65 formed by a rear side portion 63b that curves convexly toward the center from both ends toward the front side of the vehicle in the width direction of the vehicle. Furthermore, the rib 65 is formed such that the width of the rib gradually increases toward its two ends 65a.

[0103] like Figure 13 As shown in (b), the comparative example subframe structure 43 includes left and right longitudinal beams 50 and crossbeams 70. In the comparative example subframe structure 43, the longitudinal beams 50 are the same as in Invention Example 1. In contrast, as... Figure 13 As shown in (b), the crossbeam 70 has a first crossbeam 71, a second crossbeam 73, and a third crossbeam 75. The first crossbeam 71 is a plate-like member configured to connect the suspension arm connection 51 on the front side of the vehicle. In contrast, the second crossbeam 73 and the third crossbeam 75 are hollow members with a generally rectangular cross section, configured to be separate from each other in the longitudinal direction of the vehicle.

[0104] The sub-frame structure 41 of the invention example 1 removes the four parts (the parts indicated by the arrows in (b) of Figure 13 of the comparative example sub-frame structure 43, and a substantially rectangular cross-section hollow member 61 and a plate-shaped member 63 are provided as the cross member 60. In addition, the plate-shaped member 63 is a member obtained by extending the first cross member 71 of the comparative example toward the vehicle rear side.

[0105] Also, in the sub-frame structure 41 of the invention example 1, the plate thickness of the substantially rectangular cross-section hollow member 61 is 2.4 mm, the plate thickness of the plate-shaped member 63 is 2.1 mm, and the plate thicknesses of the other members (the longitudinal members 50, etc.) are the same as those of the comparative example. The longitudinal members 50 of the sub-frame structure 41 of the invention example 1 and the sub-frame structure 43 of the comparative example are composed of a steel sheet of a tensile strength of 590 MPa grade.

[0106] In the embodiment 1, the rigidity of the sub-frame structure 41 of the invention example 1 and the sub-frame structure 43 of the comparative example was evaluated for each of the input load modes shown in FIG. 2. Figure 2

[0107] Also, according to the rigidity calculated for the invention example 1 and the comparative example, respectively, the rigidity improvement rate of the sub-frame structure 41 of the invention example 1 was calculated. The rigidity improvement rate is the rigidity improvement rate of the invention example 1 when the rigidity of the comparative example is taken as a reference, and is calculated by the following formula.

[0108] Rigidity improvement rate [%] = (rigidity of the invention example 1 - rigidity of the comparative example) / (rigidity of the comparative example) x 100

[0109] Table 1 shows the results of the rigidity improvement rate of the sub-frame structure of the invention example 1 with respect to the comparative example.

[0110] [Table 1]

[0111]

[0112] As shown in Table 1, in the sub-frame structure 41 of the invention example 1, the result is that the rigidity is improved in all of the input load modes shown in (a), (b) of Figure 2 Particularly, in the input load modes (b) (i) to (iii) of Figure 2 of the comparative example, the rigidity improvement rate increases by 30%, and a significant improvement in rigidity can be confirmed.

[0113] [Embodiment 2]

[0114] In the embodiment 2, a collision analysis was performed in which the vehicle having the sub-frame structure 41 shown in (a) of Figure 13 of the comparative example, which was the object in the embodiment 1, was taken as the analysis object, and the crash performance was investigated.

[0115] ​The subframe structure 41 has a pair of left and right side members 50 and a cross member 60 having a substantially rectangular cross-section hollow member 61 and a plate-shaped member 63. Each side member 50 is provided with a hollow bent protruding portion 55 that protrudes toward the vehicle front side beyond the substantially rectangular cross-section hollow member 61 and is obliquely bent into a crank shape toward the vehicle width direction outer side (see Figure 13 (a) of FIG. 1). Also, on each bent protruding portion 55, an opening portion (not shown) is formed on the side surface portion on the vehicle width direction outer side of the oblique portion oblique to the vehicle front-rear direction toward the vehicle width direction outer side.

[0116] In Example 2, as shown in Figure 14 , the crash performance in the case where a hollow cross-section closed longitudinal wall portion is provided inside the hollow bent protruding portion 55 to improve the buckling resistance was investigated. Figure 14 The bent protruding portion 55 shown in (a) of FIG. 1 is not provided with a hollow cross-section closed longitudinal wall portion (Invention Example 2). Figure 14 The bent protruding portion 55A shown in (b) of FIG. 1 is provided with an attached member 57A on the inner surface side of the valley portion 55a on the vehicle inner side in the bent of the crank shape, which connects the upper surface 55c and the lower surface 55d and closes a portion of the hollow cross-section (43%>33% of the hollow cross-section of the bent protruding portion 55A) (see Invention Example 3, Figure 11 ). Figure 14 The bent protruding portion 55B shown in (c) of FIG. 1 is a substantially hollow member in which the inside (the entire hollow cross-section of the bent protruding portion 55B) is closed by a hollow cross-section closed longitudinal wall portion 57B formed by bending a portion of the front end portion, and a reinforcing member 59 corresponding to the front end portion of the bent protruding portion 55B is joined thereto (see Invention Example 4, Figure 12 ).

[0117] In Example 2, as a vehicle having the subframe structure 41 of Invention Examples 2 to 4 as the analysis target, the rigid wall was made to intrude from the vehicle front side, and the fastening portion on the vehicle rear side (the rear end of the side member 30 in the vehicle front-rear direction) was completely fixed to perform the crash analysis. Figure 6

[0118] Figure 15 The load-displacement curve at the initial stage of the crash, which was obtained by the crash analysis of the vehicle having the subframe structure 41 of Invention Examples 2 to 4, respectively, is shown. The load is set as the reaction force with respect to the rigid wall that intrudes from the vehicle front side, and the displacement is set as the amount of intrusion of the rigid wall into the vehicle body in the vehicle front-rear direction.

[0119] As shown in Figure 15 , the load increases in conjunction with the increase in the displacement due to the collision of the rigid wall, that is, the intrusion of the rigid wall, and gradually decreases after reaching the peak value. ​

[0120] If the invention examples 2 to 4 are compared, no large difference is found in the increase in load immediately after the collision, but in the invention examples 3 and 4 in which the bending protrusion 55 is provided with the attached member 57A or the hollow cross-section closed longitudinal wall portion 57B, the peak value of the load is increased by 14%, 12%, respectively (invention example 2: 243 kN, invention example 3: 278 kN, invention example 4: 273 kN).

[0121] According to the above results, it is known that by providing the hollow cross-section closed longitudinal wall portion (attached member 57A, hollow cross-section closed longitudinal wall portion 57B) inside the valley portion 55a which is the starting point of the crushing in the bending protrusion 55, the buckling resistance of the bending protrusion 55 can be increased. Also, in the invention examples 3 and 4, in the stage of the initial stage of the collision from the start of the collision to 40 ms, the load shows a higher value than that of the invention example 2, so it is suggested that the collision energy absorption amount is increased.

[0122] [Industrial applicability]

[0123] According to the present application, a subframe structure of an automobile having high rigidity with respect to loads input from a suspension arm and various kinds of loads input from other vehicle body members and mounting portions mounted to the vehicle body can be provided.

[0124] Explanation of reference numerals

[0125] 1 Subframe structure

[0126] 1A Subframe structure

[0127] 3 Subframe structure

[0128] 10 Longitudinal beam

[0129] 10a Front end portion

[0130] 11 Suspension arm connecting portion

[0131] 13 Suspension arm connecting portion

[0132] 15 Flange portion

[0133] 17 Suspension arm connecting portion

[0134] 20 Cross beam

[0135] 20a End portion

[0136] 21 Substantially rectangular cross-section hollow member

[0137] 21a End portion

[0138] 21b Corner portion

[0139] 21c Corner portion

[0140] 21d lower portion

[0141] 23 plate-shaped member

[0142] 23a side edge portion

[0143] 23al rear end

[0144] 23b rear edge portion

[0145] 25 rib portion

[0146] 25a both ends

[0147] 27 recess

[0148] 29 reinforcing rib portion

[0149] 30 longitudinal beam

[0150] 31 suspension arm connecting portion

[0151] 33 suspension arm connecting portion

[0152] 35 bent protruding portion

[0153] 35a valley portion

[0154] 35b inclined portion

[0155] 35bl side surface portion

[0156] 35b2 opening portion

[0157] 35c upper surface

[0158] 35d lower surface

[0159] 37 hollow cross-section closed longitudinal wall portion

[0160] 37A attached member

[0161] 37B hollow cross-section closed longitudinal wall portion

[0162] 39 reinforcing member

[0163] 41 subframe structure

[0164] 43 subframe structure

[0165] 50 longitudinal beam

[0166] 50a front end portion

[0167] 51 suspension arm connecting portion

[0168] 53 suspension arm connecting portion

[0169] 55, 55A, 55B bent protruding portion

[0170] 55a valley portion

[0171] 55b inclined portion

[0172] 55b1 side portion

[0173] 55b2 opening portion

[0174] 55c upper surface

[0175] 55d lower surface

[0176] 57A attaching member

[0177] 57B hollow cross-section closed longitudinal wall portion

[0178] 59 reinforcing member

[0179] 60 cross member

[0180] 61 substantially rectangular cross-section hollow member

[0181] 63 plate-like member

[0182] 63a side edge portion

[0183] 63a1 rear end

[0184] 63b rear edge portion

[0185] 65 rib portion

[0186] 70 cross member

[0187] 71 first cross member

[0188] 73 second cross member

[0189] 75 third cross member

[0190] 101 suspension arm

[0191] 103 mounting portion

Claims

1. A subframe structure of an automobile, comprising: a pair of left and right side members extending in a vehicle front-rear direction, suspension arm connecting portions being provided at both of the vehicle front-rear directions; and a cross member extending in a vehicle width direction, both end portions of which are connected to the left and right side members, wherein the cross member comprises: a substantially rectangular hollow member provided on a straight line connecting the suspension arm connecting portions on the vehicle front side, the substantially rectangular hollow member having a substantially rectangular cross section; and a plate-shaped member formed of a metal plate, the plate-shaped member being provided on the vehicle rear side compared to the substantially rectangular hollow member, and the plate-shaped member being connected to the left and right side members with a side edge portion of the plate-shaped member on the vehicle rear side compared to the suspension arm connecting portion on the vehicle rear side, the side edge portion being curved convexly toward the vehicle front side from a position on the vehicle rear side compared to the suspension arm connecting portion on the vehicle rear side toward a center in the vehicle width direction, the side edge portion being curved convexly toward the vehicle front side from both ends in the vehicle width direction toward the center in the vehicle width direction.

2. The subframe structure of an automobile according to claim 1, wherein the plate-shaped member is curved convexly toward the vehicle front side from both ends in the vehicle width direction toward the center in the vehicle width direction, the rib portion being formed along the side edge portion.

3. The subframe structure of an automobile according to claim 1 or 2, wherein a hollow bent protrusion is provided at a front end portion of each of the side members, the bent protrusion being protruded toward the vehicle front side compared to the substantially rectangular hollow member, and being bent into a crank shape by being inclined toward the vehicle outer side in the vehicle width direction.

4. The subframe structure of an automobile according to claim 3, wherein an opening portion is formed in a side surface portion on the vehicle outer side of an inclined portion of the bent protrusion, the inclined portion being inclined toward the vehicle outer side in the vehicle width direction.

5. The subframe structure of an automobile according to claim 3 or 4, wherein a hollow cross section closing longitudinal wall portion is provided on an inner surface side of a valley portion on the vehicle inner side of the bent protrusion, the longitudinal wall portion closing a part or all of a hollow cross section by connecting an upper surface and a lower surface.

6. The subframe structure of an automobile according to any one of claims 1 to 5, wherein the cross member is formed of a steel sheet having a tensile strength of 590 MPa or more. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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