Vehicle subframe

Abstract

To provide a vehicular subframe capable of ensuring required strength while appropriately establishing rigidity.SOLUTION: In a lower member 30, middle parts 62 and 72 between exterior parts 60, 70 and interior parts 65, 75 include exterior curve bottom parts 63, 73 and interior curve bottom parts 64, 74, and adjacently-arranged closed sections SE1 and SE2 in which a first closed section SE1 of a first cross member 10 and a second closed section SE2 of a lower member 30 are separated by a wall part 12 of a first cross member 10 defining a first closed section SE1 are constituted by adjacently arranging vertically in an adjacent mode is provided to meet at least a part of the exterior curve bottom parts 63, 73 and the interior curve bottom parts 64, 74.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vehicle subframe, and more particularly to a vehicle subframe that supports a suspension arm or the like and is mounted on a vehicle such as an automobile. [Background technology]

[0002] In recent years, in vehicles such as automobiles, there has been a demand for improved ride quality in addition to improved driving performance, so subframes installed in such vehicles are now required to not only ensure strength but also to have appropriate rigidity.

[0003] Therefore, for such subframes, there is a need to provide a configuration that allows for greater freedom in setting the support rigidity of the suspension members while maintaining productivity and that can avoid local concentrations of stress.

[0004] Under these circumstances, Patent Document 1, regarding the rear body structure of an automobile, aims to improve the lightness and rigidity of the rear subframe while ensuring arm length and to improve rear-end collision safety. The patent document discloses a rear subframe 21 in which rear portions 26 of left and right side member portions 22, 22 are attached to left and right rear side frames 7, 7, and front portions 25 of the left and right side member portions 22, 22 are attached to a portion of a vehicle body cross member 10 that is suspended between the left and right rear side frames 7, 7, which is more inward than the rear side frame 7, and in which a bracket 31 constituting a support portion 29 of a front lower arm 33 has a front panel 34 and a rear panel 35, each of which has an L-shaped cross section and is substantially triangular in front view, and side panels 36 that close outer openings of the front panel 34 and the rear panel 35, thereby presenting a closed cross-sectional structure and being joined to the side member portions 22 and the cross member portions 23, which are made of pipe material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-95393 Summary of the Invention [Problem to be solved by the invention]

[0006] However, according to the inventor's investigations, in the configuration of Patent Document 1, a cutout is provided at the inner end of bracket 31, where stress is likely to increase due to input loads from the lower arm, etc., when the vehicle is in motion, to open up the closed cross section of bracket 31, and the front panel 34 and rear panel 35 have a simple triangular shape with an area that decreases linearly toward the inside. Therefore, there is a natural limit to increasing the degree of freedom in setting the support rigidity of the suspension member while appropriately reducing stress concentration. In this regard, it is believed that there is room for improvement in terms of setting appropriate rigidity while ensuring the necessary strength and balancing strength and rigidity.

[0007] The present invention was made after taking into account the above considerations, and aims to provide a subframe for a vehicle that can ensure the required strength while appropriately setting the rigidity by realizing a configuration that increases the freedom in setting the rigidity, thereby optimizing the strength and rigidity while balancing them. [Means for solving the problem]

[0008] In order to achieve the above object, a subframe for a vehicle according to a first aspect of the present invention comprises: a cylindrical first cross member extending in the width direction of the vehicle;a second cross member facing the first cross member in the front-to-rear direction of the vehicle and extending in the width direction; a pair of side members facing each other in the width direction, each extending in the front-to-rear direction and joined to the first cross member and the second cross member; and a lower member extending in the width direction below the first cross member in the up-down direction of the vehicle and joined to the first cross member, wherein the lower member has, in order from outside to inside in the width direction, an outer portion provided with a lower support portion that supports a suspension member of the vehicle, a middle portion connected to the outer portion, and an inner portion connected to the middle portion, The cross member has an outer curved bottom portion that follows a locus that curves upward without descending from the bottom portion of the outer portion as it moves inward, and an inner curved bottom portion that is connected to the bottom portion of the inner portion and follows a locus that curves downward without ascending from the bottom portion of the inner portion as it moves outward, wherein the first cross member presents a first closed cross section in a cross section cut on a plane defined by the front-rear direction and the up-down direction, and the lower member presents a second closed cross section in a cross section cut on the plane, and the first closed cross section and the second closed cross section are adjacent to each other but separated by a wall portion of the first cross member that defines the first closed cross section, and juxtaposed closed cross sections that are juxtaposed in the up-down direction are provided corresponding to at least a part of the outer curved bottom portion and the inner curved bottom portion in the intermediate portion. Each of the pair of side members has a pair of side walls opposing each other in the width direction, an upper wall connecting upper ends of the pair of side walls in the up-down direction, and a bottom wall opposing the upper wall at the lower side and connecting lower ends of the pair of side walls in the up-down direction, and the upper wall has, at a front portion in the front-rear direction, a recessed portion where the upper wall is recessed toward the lower side at a middle portion in the width direction, and and a pair of convex portions protruding relatively upward from the recessed portion of the top wall, wherein a front end of the recessed portion of the top wall is joined to the first cross member, and the bottom wall has, in the front portion thereof, a recessed portion formed by recessing the bottom wall toward the upper side at a middle portion in the width direction of the bottom wall, and a pair of convex portions protruding relatively downward from the recessed portion at both end portions in the width direction of the bottom wall, wherein the front end of the recessed portion of the bottom wall is joined to the first cross member. It has the following configuration.

[0009] In addition to the first aspect, the present invention has a second aspect in which the juxtaposed closed cross section is necessarily provided corresponding to at least a part of the inner curved bottom portion.

[0010] In addition to either the first or second aspect, the present invention has a third aspect in which the juxtaposed closed cross section is continuous in the width direction across the inner curved bottom portion and one or both of the outer curved bottom portion and the bottom portion of the inner portion.

[0011] In addition to any of the first to third aspects, the present invention has a fourth aspect in which an upper support member is provided that faces the lower member above in the vertical direction across the first cross member and has an upper support portion that supports a suspension member of the vehicle, and is joined to the first cross member, and the upper support member is joined to an inclined surface portion that is formed by recessing and inclining a portion of the cylindrical wall of the first cross member. [Effects of the Invention]

[0013] According to the configuration of the first aspect of the present invention, the lower member has, in order from the outside to the inside in the width direction, an outer portion provided with a lower support portion that supports a suspension member of the vehicle, an intermediate portion connected to the outer portion, and an inner portion connected to the intermediate portion, and the intermediate portion has an outer curved bottom portion that connects to the bottom of the outer portion and follows a locus that curves upward without descending from the bottom of the outer portion as it goes inward, and an inner curved bottom portion that connects to the bottom of the inner portion and follows a locus that curves downward without ascending from the bottom of the inner portion as it goes outward, and the first cross member is The cross section cut at the plane presents a first closed cross section, and the lower member presents a second closed cross section when cut at the plane, and the first closed cross section and the second closed cross section are adjacent and separated by the wall portion of the first cross member that defines the first closed cross section, and the juxtaposed closed cross sections arranged in the vertical direction are provided in correspondence with at least a portion of the outer curved bottom and inner curved bottom in the middle portion.This configuration allows the necessary strength of the vehicle subframe to be ensured while increasing the freedom to set the support rigidity of the suspension member, and allows the strength and rigidity to be optimized while balancing them, making it possible to set the desired rigidity and ensure the required strength. According to a configuration of a first aspect of the present invention, each of the pair of side members has a pair of side walls facing each other in the width direction, an upper wall connecting upper ends of the pair of side walls in the up-down direction, and a bottom wall facing below the upper wall and connecting lower ends of the pair of side walls in the up-down direction, and the upper wall has, at a front portion in the front-rear direction, a recessed portion recessed downward at a middle portion in the width direction of the upper wall, and protruding upward relatively to the recessed portion at both ends in the width direction of the upper wall. The upper wall has a pair of convex portions formed by recessing the recessed portion, and the front end of the recessed portion is joined to the first cross member.The bottom wall has, in its front portion, a recessed portion where the bottom wall is recessed upward at a middle portion in the width direction, and a pair of convex portions where the bottom wall is protruded downward relative to the recessed portion at both ends in the width direction.By joining the front end of the recessed portion to the first cross member, the bottom wall can improve the coverage of the paint on the pair of side members while ensuring the weld length and increasing the weld strength.

[0014] Furthermore, according to the configuration of the second aspect of the present invention, the juxtaposed closed cross section is always provided corresponding to at least a part of the inner curved bottom portion, so that the support rigidity of the suspension member can be appropriately set while ensuring the required strength of the vehicle subframe with the juxtaposed longitudinal cross section having the smallest range in the width direction.

[0015] Furthermore, according to the configuration of the third aspect of the present invention, the juxtaposed closed cross section is provided continuously in the width direction across the inner curved bottom portion and one or both of the outer curved bottom portion and the bottom portion of the inner portion, thereby reducing stress concentration in the vehicle subframe, eliminating localized weak portions, and further increasing the strength thereof.

[0016] In addition, according to the configuration of the fourth aspect of the present invention, an upper support member is provided which faces the lower member above in the vertical direction across the first cross member and has an upper support portion which supports the vehicle's suspension members, and is joined to the first cross member.The upper support member is joined to an inclined surface portion which is formed by recessing and inclining a portion of the cylindrical wall of the first cross member, so that the upper support member can be joined to each other while being securely abutted against the inclined surface portion, thereby suppressing the occurrence of peeling and failure at the joint. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a perspective view of a subframe for a vehicle according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the vehicle subframe according to the embodiment. [Figure 3] FIG. 2 is a bottom view of the vehicle subframe according to the embodiment. [Figure 4] FIG. 2 is a front view of the vehicle subframe according to the embodiment. [Figure 5] FIG. 2 is a right side view of the vehicle subframe according to the embodiment. [Figure 6] FIG. 6(a) is a front view of the front portion of the right side frame of the vehicle subframe in this embodiment, and FIG. 6(b) is a DD cross-sectional view of FIG. 6(a). [Figure 7] 5 is a cross-sectional view taken along the line AA in FIG. 4. [Figure 8] 5 is a cross-sectional view of FIG. 4 taken along line B-B. [Figure 9] 5 is a cross-sectional view taken along CC in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a vehicle subframe according to an embodiment of the present invention will be described in detail with reference to Figs. 1 to 9 as appropriate. In the drawings, the x-axis, y-axis, and z-axis form a three-axis Cartesian coordinate system. The positive direction of the x-axis is the leftward direction of the vehicle body, the positive direction of the y-axis is the forward direction of the vehicle body, and the positive direction of the z-axis is the upward direction of the vehicle body. The direction of the x-axis may be referred to as the width direction, the direction of the y-axis may be referred to as the front-rear direction, and the direction of the z-axis may be referred to as the up-down direction. The x-y plane may be referred to as the horizontal plane.

[0020] FIG. 1 is a perspective view of a vehicle subframe according to this embodiment, FIG. 2 is a plan view of the vehicle subframe according to this embodiment, FIG. 3 is a bottom view of the vehicle subframe according to this embodiment, FIG. 4 is a front view of the vehicle subframe according to this embodiment, and FIG. 5 is a right side view of the vehicle subframe according to this embodiment. FIG. 6(a) is a front view of a front portion of a right side frame of the vehicle subframe according to this embodiment, and FIG. 6(b) is a DD cross-sectional view of FIG. 6(a). Also, FIGS. 7 to 9 are AA cross-sectional views, BB cross-sectional views, and CC cross-sectional views of FIG. 1, respectively. For ease of explanation, in FIGS. 5 to 6(b), some of the components on the left side of the vehicle subframe are indicated by reference numerals in parentheses together with the reference numerals of the components on the right side as necessary, and in FIGS. 7 to 9, some of the components on the right side of the vehicle subframe are indicated by reference numerals in parentheses together with the reference numerals of the components on the left side as necessary.

[0021] 1 to 9, a subframe 1 in this embodiment, none of which is shown, is mounted on a vehicle body such as a rear side frame of a vehicle such as an automobile and supports a suspension arm. Typically, such subframe 1 has a shape that is basically symmetrical (plane symmetrical) with respect to a plane that is parallel to the yz plane and passes through the center of the vehicle body in the width direction.

[0022] Specifically, the subframe 1 has as its main structural elements a front cross member 10 formed of a tubular member extending in the width direction and having a lattice shape in a plan view, a rear cross member 100 facing the rear of the front cross member 10 and extending in the width direction, and a left side member 120 and a right side member 220 facing each other in the width direction, extending in the fore-and-aft direction, and joined to the front cross member 10 and the rear cross member 100, respectively. Each of these structural elements is typically welded together by arc welding or the like. The front-to-rear arrangement of the subframe 1 may be reversed depending on the type of vehicle to which it is applied, etc.

[0023] The front cross member 10 is typically made of a cylindrical steel pipe, and a portion of the cylindrical peripheral wall 12 is formed by hydroforming or the like to be partially recessed from its original shape and flattened, thereby providing flat portions such as an inclined flat portion 14 inclined with respect to the xz plane and a flat portion 16 parallel to the xz plane. Note that the front cross member 10 may also have a flat portion parallel to the xy plane, where the top or bottom of the peripheral wall 12 is partially flattened. Note that the front cross member 10 may also be composed of multiple members each obtained by press-forming a flat plate member such as a steel plate.

[0024] Specifically, the front cross member 10 has a main body portion 20 extending in the width direction and having a curved shape that is convex toward the rear in a plan view, a left extension portion 22 extending in the left front direction at the left end of the main body portion 20 in the width direction while curving at a curvature greater than that of the main body portion 20, and a right extension portion 26 extending in the right front direction at the right end of the main body portion 20 in the width direction while curving at a curvature greater than that of the main body portion 20. The left end of the left extension portion 22 forms a left cutout portion 24 cut out in a substantially arc-shaped manner, and a collar member 310 is welded to the left cutout portion 24 by arc welding or the like. Similarly, the right end of the right extension portion 26 forms a right cutout portion 28 cut out in a substantially arc-shaped manner, and a collar member 310 is welded to the right cutout portion 28 by arc welding or the like.

[0025] In the front cross member 10, the main body portion 20, the left extension portion 22, and the right extension portion 26 have open ends at the left cutout portion 24 and the right cutout portion 28, which open the insides of the main body portion 20, the left extension portion 22, and the right extension portion 26 to the outside, but in a longitudinal cross section cut along a plane parallel to the yz plane, they form a closed cross section SE1.

[0026] In the front cross member 10, the curvature of each of the left extension portion 22 and the right extension portion 26 is set to be larger than the curvature of the main body portion 20 in order to increase the layout space in front of the main body portion 20 while ensuring the rigidity of the main body portion 20 in the width direction, and to position the left end portion of the left extension portion 22 and the right end portion of the right extension portion 26 further forward, thereby positioning the collar members 310 and 310, which are welded to correspond to the left cutout portion 24 and the right cutout portion 28 and each serve as a front body mounting portion, further forward and away from the rear body mounting portion, thereby increasing the span between the front and rear body mounting portions.

[0027] In the front cross member 10, assuming that the collar members 310 and 310 to which the required capacity of subframe mounting members (not shown) are attached can be welded with the required welding strength corresponding to the left cutout portion 24 and the right cutout portion 28, and that the required strength and rigidity of the left extension portion 22 and the right extension portion 26 can be ensured, the vertical length of the left extension portion 22 and the right extension portion 26 is set shorter than the vertical length of the main body portion 20, and the left extension portion 22 and the right extension portion 26 are flattened, in order to increase the layout freedom of the left extension portion 22 and the right extension portion 26 in the vertical direction.

[0028] The front cross member 10 also has a lower member 30 that extends in the width direction below the front cross member 10 and is joined to the front cross member 10. Note that the lower member 30 may be joined by straddling the left side member 120 and the right side member 220 only at the portions thereof that are offset rearward from the front cross member 10 at both ends in the width direction.

[0029] The lower member 30 typically includes a first member 40 and a second member 50 each obtained by press-forming a flat plate member such as a steel plate, and each having a substantially L-shaped longitudinal cross section cut along a plane parallel to the yz plane. Note that the lower member 30 may be formed using a single plate member instead of the two plate members, the first member 40 and the second member 50, as necessary.

[0030] The first member 40 is a vertical wall that closes the front side of the lower member 30, and has a front vertical wall 42 that stands upright in the vertical direction and extends in the width direction, and a front bottom wall 44 that bends rearward at the lower end of the front vertical wall 42 parallel to the horizontal plane and extends in the width direction while protruding rearward from the lower end. A left front through-hole 46 is formed in the left end of the front vertical wall 42, and a right front through-hole 48 is formed in the right end of the front vertical wall 42, and nut members 320 and 320 are welded to the left front through-hole 46 and the right front through-hole 48, respectively, so as to stand forward from the front surface of the front vertical wall 42.

[0031] The second member 50 has a basic configuration similar to that of the first member 40, with the front and rear reversed, and includes a rear vertical wall 52 that is a vertical wall that closes the rear side of the lower member 30 and that stands upright in the vertical direction while extending in the width direction, and a rear bottom wall 54 that bends forward at the lower end of the rear vertical wall 52 parallel to the horizontal plane and extends in the width direction while protruding forward from the lower end. A left rear through-hole 56 is formed in the left end of the rear vertical wall 52, and a right rear through-hole 58 is formed in the right end of the rear vertical wall 52, and the left rear through-hole 56 and the right rear through-hole 58 face the left front through-hole 46 and the right front through-hole 48 on their rear sides.

[0032] In detail, the lower member 30 has, in order from the left outer side to the inside, a nut member 320 arranged on the left front lower support portion that supports a vehicle suspension arm such as a lower arm, a left outer part 60 provided with a left front through hole 46 and a left rear through hole 56, a left intermediate part 62 connected to the left outer part 60 on its right side, and a left inner part 65 connected to the left intermediate part 62 on its right side, closer to the center in the width direction. The left intermediate portion 62 has a left outer curved bottom portion 63 that is connected to the left outer bottom portion 61, which is the front bottom wall 44 and rear bottom wall 54 of the left outer portion 60, and has a curved shape that extends inward from the left outer bottom portion 61 without descending, and that exhibits a curved trajectory that rises while the inclination of the tangent (angle with respect to the horizontal plane) increases as it goes inward, and that exhibits a convex curved shape toward the diagonally lower right side; and a left inner curved bottom portion 64 that is connected to the left inner bottom portion 66, which is the front bottom wall 44 and rear bottom wall 54 of the left inner portion 65, and that exhibits a curved shape that extends outward from the left inner bottom portion 66 without ascending, and that exhibits a curved trajectory that descends while the inclination of the tangent (angle with respect to the horizontal plane) increases as it goes outward, and that exhibits a convex curved shape toward the diagonally upper left side. By providing the left outer curved bottom portion 63 and the left inner curved bottom portion 64, changing their curvatures (radii of curvature RO, RI) during design makes it possible to change the rigidity against an input load applied from the suspension arm, mainly in the width direction. This allows for a high degree of freedom in setting the desired support rigidity for the suspension arm, in other words, the shapes of the left outer curved bottom portion 63 and the left inner curved bottom portion 64 for providing that support rigidity, provided that the required strength of the lower member 30 and ultimately the subframe 1 is ensured. Note that, provided that the required strength and desired rigidity can be ensured, a non-curved, flat bottom portion may be interposed between the left outer curved bottom portion 63 and the left inner curved bottom portion 64. Furthermore, the curvatures (radii of curvature RO, RI) of the left outer curved bottom portion 63 and the left inner curved bottom portion 64 are not limited to being a single curvature (radii of curvature RO, RI), but may also be a composite curvature consisting of multiple curvatures (radii of curvature RO, RO'... RI, RI'...) as necessary.

[0033] The configuration related to the right outer portion 70, right intermediate portion 72 and right inner portion 75, which are arranged in order from the right outer side to the inside of the lower member 30, is bilaterally symmetrical with respect to the configuration related to the left outer portion 60, left intermediate portion 62 and left inner portion 65, with respect to a plane parallel to the yz plane and passing through the center of the vehicle width direction, so detailed explanations will be omitted. However, the right outer portion 70, right outer bottom portion 71, right intermediate portion 72, right outer curved bottom portion 73, right inner curved bottom portion 74, right inner portion 75 and right inner bottom portion 76 are provided in correspondence with the left outer portion 60, left outer bottom portion 61, left intermediate portion 62, left outer curved bottom portion 63, left inner curved bottom portion 64, left inner portion 65 and left inner bottom portion 66. Furthermore, provided that the required strength and desired rigidity can be ensured, the lower member 30 may be divided into left and right halves in the central region of the subframe 1 in the width direction or in its adjacent regions, typically the left inner portion 65, the right inner portion 75, and the portions therebetween in the width direction, rather than being continuous in the width direction, provided that the required strength and desired rigidity can be ensured.

[0034] In the lower member 30, the upper end of the front vertical wall 42 is welded by arc welding or the like to the outer surface of the front flat portion 16 of the front cross member 10 while its inner surface is abutting against the outer surface of the front flat portion 16 of the front cross member 10 at the left inner portion 65, the right inner portion 75, the portion between them in the width direction, the left intermediate portion 62, and the right intermediate portion 72, thereby joining and integrating the first member 40 with the front cross member 10, and the upper end of the rear vertical wall 52 is welded by arc welding or the like to the outer surface of the rear flat portion 16 of the front cross member 10 while its inner surface is abutting against the outer surface of the rear flat portion 16 of the front cross member 10, thereby joining and integrating the second member 50 with the front cross member 10. As a result, even under conditions in which the input load to the lower member 30 and the input load to the left support member 80 or the right support member 90 are aligned in the same direction in the width direction, causing large shear stress in the welded portion between the front cross member 10 and the lower member 30, it is possible to suppress the occurrence of peeling and fracture in the welded portion and ensure the required weld strength. In addition, the first member 40 and the second member 50 are joined and integrated as the lower member 30 by welding, for example, by arc welding along the boundary between the rear end of the front bottom wall 44 and the front end of the rear vertical wall 52, which is defined by overlapping them, over the entire width direction. In the left outer portion 60 and the right outer portion 70, a flange portion is provided at the upper end of the front vertical wall 42, bending forward parallel to the horizontal plane, and a flange portion is provided at the upper end of the rear vertical wall 52, bending rearward parallel to the horizontal plane. The upper surfaces of these flange portions are welded to the outer surface of the bottom flat portion 18 of the front cross member 10 by arc welding or the like while abutting against the outer surface of the bottom flat portion 18. Similar to the flat portion 16, the bottom flat portion 18 is a flat portion parallel to the xy plane that is formed by hydroforming or the like to partially recess the bottom of the peripheral wall 12 of the front cross member 10. The welds in the left outer portion 60 and the right outer portion 70 are sufficient to serve a supplementary purpose, with shorter weld lengths and longitudinal spans than the welds in the left inner portion 65, the right inner portion 75, the portions therebetween in the width direction, and the left intermediate portion 62 and the right intermediate portion 72.

[0035] That is, in the front cross member 10 and the lower member 30, the ends of these abutting components are welded and joined together to form an integrated unit, so that the peripheral wall 12 of the front cross member 10 and the front vertical wall 42, front bottom wall 44, rear vertical wall 52, and rear bottom wall 54 of the lower member 30 cooperate to form a closed cross section SE2 in a vertical section taken along a plane parallel to the yz plane. The closed cross section SE2 is defined by welding the upper ends of the front vertical wall 42 and the rear vertical wall 52 to the outer surface of the flat surface 16 of the front cross member 10 at least in the left intermediate portion 62 and the right intermediate portion 72, with their inner surfaces abutting against the outer surface of the flat surface 16, making it possible to increase the length in the fore-and-aft direction and ensure a large cross-sectional area. Here, the closed cross section SE2 is adjacent to the lower side of the closed cross section SE1 of the front cross member 10 via the peripheral wall 12 thereof, and the closed cross sections SE1 and SE2 form a cross section formed of two layers stacked adjacently arranged side by side in the vertical direction. From the viewpoint of increasing the strength of the subframe 1 in cooperation with the closed cross section SE1 and enhancing the support rigidity of the suspension arm, the closed cross section SE2, i.e., the juxtaposed closed cross sections SE1 and SE2, are preferably located in at least a portion of both the left intermediate section 62 and the right intermediate section 72, where stress tends to concentrate due to input loads applied from the suspension arm, etc. Furthermore, because the portions of the left intermediate section 62 and the right intermediate section 72 where stress is most likely to concentrate are near the left inner section 65 and the right inner section 75, the closed cross section SE2, i.e., the juxtaposed closed cross sections SE1 and SE2, are more preferably located in a position corresponding to at least a portion of both the left inner curved bottom section 64 and the right inner curved bottom section 74. Furthermore, from the viewpoint of further alleviating stress concentration due to input loads applied from the suspension arms, etc., it is more preferable that the closed cross section SE2, i.e., the closed cross sections SE1 and SE2 arranged side by side, be arranged continuously in the width direction across the left inner curved bottom portion 64 and the right inner curved bottom portion 74 and the corresponding left inner bottom portion 66 and the right inner bottom portion 76.Similarly, from the viewpoint of further reducing stress concentration due to input loads applied from the suspension arms, etc., it is more preferable that the closed cross section SE2, i.e., the juxtaposed closed cross sections SE1 and SE2, be arranged continuously in the width direction across the left inner curved bottom portion 64 and the right inner curved bottom portion 74 and the corresponding left outer curved bottom portion 63 and right outer curved bottom portion 73. In other words, in principle, it is not possible to arrange holes such as drain holes or paint drain holes in the portion of the lower member 30 where the closed cross section SE2 is arranged in this manner, but depending on the specifications of the subframe 1, etc., if the degree of stress concentration between the left outer curved bottom portion 63 and the right outer curved bottom portion 73, the left inner bottom portion 66 and the right inner bottom portion 76, and the left inner bottom portion 66 and the right inner bottom portion 76 in the width direction is low, it is possible to provide holes therein, provided that the required strength and rigidity can be ensured. Similarly, if there is sufficient strength in the left outer portion 60 and the right outer portion 70, it is also possible to provide holes or openings in the left outer bottom portion 61 and the right outer portion 70. Furthermore, the size of the closed cross section SE2, particularly its vertical length, increases from the inner portion closer to the center toward the left and right outer portions, particularly in the left intermediate portion 62 and right intermediate portion 72, in conjunction with the positioning of the left lower support portion and right lower support portion that support the suspension arm.

[0036] The front cross member 10 also has a left support member 80 and a right support member 90 that extend widthwise on both ends of its upper side width and are each joined to the front cross member 10. Note that the left support member 80 and the right support member 90 may be joined so that the portions of their widthwise ends that extend beyond the front cross member 10 straddle the left side member 120 and the right side member 220.

[0037] The left support member 80 typically has a generally hat-shaped vertical cross section that is open downward and is obtained by press-forming a flat plate member such as a steel plate, and includes a front vertical wall 82 having a left front through-hole 88 penetrating its left end in the front-to-rear direction, a rear vertical wall 84 that penetrates its left end in the front-to-rear direction and has a left rear through-hole 89 that penetrates its left end in the front-to-rear direction and faces the left front through-hole 88 of the front vertical wall 82 on the rear side thereof, and faces the left front through-hole 88 of the front vertical wall 82, and an upper wall 86 that connects the front vertical wall 82 and the rear vertical wall 84. A nut member 320 is welded to the left front through-hole 88.

[0038] The left support member 80 also includes a front flange 83 extending forward from the lower end of its front vertical wall 82, and a rear flange 85 extending rearward from the lower end of its rear vertical wall 84, and the respective ends of the front flange 83 and the rear flange 85 are welded to the outer surfaces of the inclined flat surface portion 14 of the front cross member 10 and the upper wall 136 of the left upper member 130 of the left side member 120, typically by arc welding, while their inner surfaces are in contact with these surfaces. As a result, even under conditions in which an input load to the lower member 30 and an input load to the left support member 80 or the right support member 90 are aligned in the same direction in the width direction, causing large shear stresses at the welds between the front cross member 10 and the left support member 80, it is possible to suppress the occurrence of peeling fracture at the welds and ensure the required weld strength.

[0039] The abutting ends of the front cross member 10 and the left support member 80 are welded together and joined together, so that the peripheral wall 12 of the front cross member 10 and the front vertical wall 82, rear vertical wall 84, and upper wall 86 of the left support member 80 cooperate to form a closed cross section SE3 in a vertical cross section taken along a plane parallel to the yz plane. From the perspective of increasing the strength of the subframe 1 and enhancing the support rigidity of the suspension arm, it is preferable that this closed cross section SE3 have a portion that faces the closed cross section SE2 of the lower member 30 in the up-down direction, with the closed cross section SE1 of the front cross member 10 in between.

[0040] The configuration related to the right support member 90 is bilaterally symmetrical to the configuration related to the left support member 80, and therefore a detailed description thereof will be omitted, but in correspondence with the front vertical wall 82, front flange 83, rear vertical wall 84, rear flange 85, upper wall 86, left front through hole 88, left rear through hole 89 and planar cross section SE3, a front vertical wall 92, a front flange 93, a rear vertical wall 94, a rear flange 95, an upper wall 96, a right front through hole 98, a right rear through hole 99 and a planar cross section SE3 are provided.

[0041] The rear cross member 100 typically has a generally hat-shaped vertical cross section that is open downward and is obtained by press-forming a flat plate member such as a steel plate, and has a left front through-hole 103 and a right front through-hole 104 that pass through the left and right ends of its front vertical wall 102 in the front-to-rear direction, and a left rear through-hole 107 and a right rear through-hole 108 that pass through the left and right ends of its rear vertical wall 106 in the front-to-rear direction and are located rearward of and opposite the left front through-hole 103 and right front through-hole 104 of the front vertical wall 102, and the front vertical wall 102 and the rear vertical wall 106 are connected via an upper wall 112. Although not shown, guide members may be attached to the left front through-hole 103, the right front through-hole 104, the left rear through-hole 107, and the right rear through-hole 108 to guide a suspension arm such as a lower arm.

[0042] The rear cross member 100 has a left widened portion 116 and a right widened portion 118 whose lengths in the front-to-rear direction gradually increase from a main body portion 114, which is the center portion in the width direction, toward the left and right outer sides. The left end of the left widened portion 116 and the right end of the right widened portion 118 are each cut out as notches and are joined to the left side member 120 and the right side member 220 by welding, typically by arc welding or the like. However, the front end of the left end of the left widened portion 116 and the front end of the right end of the right widened portion 118 are offset forward by a greater offset length than the respective rear ends, and are located in positions closer to the front end faces of recessed portions 136a, 236a and 156a, 256a of the left side member 120 and the right side member 220, which will be described later. This allows the rear cross member 100 to have a longer welding length to the left side member 120 and the right side member 220, and allows it to be joined to the front cross member 10 and lower member 30, which have greater strength and rigidity.

[0043] Left side member 120 is typically obtained by press-forming flat plate members such as steel plates, and has upper-left member 130 and lower-left member 150 that are generally U-shaped in vertical cross section and face each other in the vertical direction, and has a curved shape that convexly curves to the right in plan view. Note that left side member 120 may also be made of a pipe member such as a steel pipe.

[0044] The upper-left member 130 has an outer wall 132 and an inner wall 134 that extend in the front-to-rear direction and face each other in the width direction, and an upper wall 136 that connects the outer wall 132 and the inner wall 134. At a front portion 142 of the upper wall 136, a middle portion in the width direction of the upper wall 136 (the central portion in the width direction and portions on the left and right thereof) has a recessed portion 136a recessed downward, and at a rear end portion of the upper wall 136, a rear notch 148 is cut out in a substantially arc shape. At the front portion 142, both ends in the width direction of the recessed portion 136a form upper convex portions 144 and 144 that protrude upward relatively from the recessed portion 136a.

[0045] The lower-left member 150 has a basic configuration similar to that of the upper-left member 130, turned upside down, and includes an outer wall 152 and an inner wall 154 that face each other in the width direction and extend in the front-to-rear direction, as well as a bottom wall 156 that connects the outer wall 152 and the inner wall 154. A front portion 162 of the bottom wall 156 has a recessed portion 156a that is recessed upward at the middle portion in the width direction of the bottom wall 156, and a rear cutout portion 168 that is cut out in a substantially arc shape at the rear end of the bottom wall 156. At the front portion 162, both ends in the width direction of the recessed portion 156a form lower convex portions 164 and 164 that protrude downward relatively from the recessed portion 156a.

[0046] The upper-left member 130 and the lower-left member 150 are joined and integrated by welding the corresponding outer wall 132 and inner wall 134, and the corresponding outer wall 152 and inner wall 154, typically by arc welding or the like, to form the left side member 120 having a closed cross-sectional shape. Note that the upper-left member 130 and the lower-left member 150 may have different plate thicknesses.

[0047] In the front portions 142 and 162 of the upper-left member 130 and the lower-left member 150, the front ends of the recesses 136a and 156a and the front ends of the outer wall 152 and the inner wall 154 are welded to the outer surface, mainly the rear side, of the peripheral wall 12 of the front cross member 10 while abutting against that outer surface, so that the front cross member 10 and the left side member 120 are joined together as a single unit. Here, the front ends of the upper convex portion 144 and the lower convex portion 164 are separated from the outer surface of the peripheral wall 12 of the front cross member 10 with a gap therebetween without abutting against the outer surface, so that the internal space of the left side member 120 communicates with the outside through these gaps. This ensures a long contact length between the front ends of each of the recesses 136a and 156a and the front ends of each of the outer wall 152 and inner wall 154 and the outer surface, mainly the rear side, of the peripheral wall 12 of the front cross member 10, thereby ensuring a long welding length for the front cross member 10 and the left side member 120.In addition, paint can penetrate through the gap between the front ends of each of the upper convex portion 144 and the lower convex portion 164 and the outer surface of the peripheral wall 12 of the front cross member 10, ensuring good paint coverage on the left side member 120.

[0048] In the rear cutouts 148 and 168 located opposite each other in the vertical direction at the rear ends of the upper-left member 130 and the lower-left member 150, collar members 310 are disposed with their vertical ends protruding from the top wall 136 and the bottom wall 156, respectively, and are typically fixed thereto by arc welding or the like.

[0049] The configuration related to right side member 220 is bilaterally symmetrical with respect to the configuration related to left side member 120 with respect to a plane parallel to the yz plane and passing through a center line running in the front-to-rear direction through the center in the width direction of the vehicle body, and therefore a detailed description thereof will be omitted. However, the configuration related to left upper member 130, outer wall 132, inner wall 134, upper wall 136, recessed portion 136a, front portion 142, upper convex portion 144, left extending portion 146, rear notch portion 148, left lower member 150, outer wall 152, inner Corresponding to wall 154, bottom wall 156, recessed portion 156a, front portion 162, lower convex portion 164, left extending portion 166 and rear cutout portion 168, there are provided upper right upper member 230, outer wall 232, inner wall 234, upper wall 236, recessed portion 236a, front portion 242, upper convex portion 244, right extending portion 246, rear cutout portion 248, lower right member 250, outer wall 252, inner wall 254, bottom wall 256, recessed portion 256a, front portion 262, lower convex portion 264, right extending portion 266 and rear cutout portion 268.

[0050] In the above-described configuration, the subframe 1 includes a first opening, a second opening, a third opening, a fourth opening, a fifth opening, and a sixth opening, which are portions where the interiors of the components constituting the subframe 1 open to the outside. Specifically, the first opening is a portion where the interiors of the lower member 30 open to the outside between the left front through-hole 48 and the left rear through-hole 56. The second opening is a portion where the interiors of the lower member 30 open to the outside between the right front through-hole 48 and the right rear through-hole 58. The third opening is a portion where the interiors of the rear cross member 100 open to the outside between the left front through-hole 103 and the left rear through-hole 107. The fourth opening is a portion where the interiors of the rear cross member 100 open to the outside between the right front through-hole 104 and the right rear through-hole 99. The fifth opening is a portion where the interiors of the left support member 80 open to the outside between the left front through-hole 88 and the left rear through-hole 89. The sixth opening is a portion between the right front through-hole 98 and the right rear through-hole 99 of the right support member 90, the interior of which opens to the outside.

[0051] Here, the first opening, second opening, third opening, fourth opening, fifth opening, and sixth opening are respectively set to correspond to the first support portion S1 on the lower left front, the second support portion S2 on the lower right front, the third support portion S3 on the lower left rear, the fourth support portion S4 on the lower right rear, the fifth support portion S5 on the upper left front, and the sixth support portion S6 on the upper right front.

[0052] More specifically, at the first support portion S1 arranged corresponding to the first opening, the right pivot of the suspension arm (not shown) is fastened and attached using fastening members such as fastening bolts via the left front through-hole 46, the left rear through-hole 56 and the nut member 320 provided in the lower member 30.

[0053] At the second support portion S2 arranged corresponding to the second opening, the left pivot of the suspension arm (not shown) is fastened and attached using fastening members such as fastening bolts via the right front through-hole 48, right rear through-hole 58 and nut member 320 provided in the lower member 30.

[0054] At the third support portion S3, which is positioned corresponding to the third opening, the right pivot of the suspension arm, not shown, is fastened and attached using fastening members such as fastening bolts via the left front through hole 103 and left rear through hole 107 provided in the rear cross member 100 and a guide member, not shown.

[0055] At the fourth support portion S4, which is positioned corresponding to the fourth opening, the left pivot of the suspension arm, not shown, is fastened and attached using fastening members such as fastening bolts via a right front through hole 104 and a right rear through hole 108 provided in the rear cross member 100 and a guide member, not shown.

[0056] At the fifth support portion S5, which is positioned corresponding to the fifth opening, the right pivot of the suspension arm (not shown) is fastened and attached using fastening members such as fastening bolts via the left front through-hole 88, the left rear through-hole 89, and the nut member 320 provided in the left support member 80.

[0057] At the sixth support portion S6 arranged corresponding to the sixth opening, the left pivot of the suspension arm (not shown) is fastened and attached using fastening members such as fastening bolts via a right front through-hole 98, a right rear through-hole 99, and a nut member 320 provided in the right support member 90.

[0058] The left and right pivots are suspension pivots located inwardly in the width direction of the corresponding left and right pivots (not shown), and define the longitudinal and widthwise positions of the left and right rear wheels (not shown) and apply a relatively large external force to the subframe, mainly in the width direction. A typical configuration of the left and right pivots is an insulator bushing member having a rubber portion bonded to a collar member through which a fastening member is inserted, and having a small spring constant in the front-to-rear direction and a large spring constant in the width direction. The spring reaction force of a suspension spring (not shown) may be applied to a given pair of the left and right pivots described above.

[0059] Additionally, the subframe 1 is also provided with a first mounting portion A1 on the left front, a second mounting portion A2 on the left rear, a third mounting portion A3 on the right front, and a fourth mounting portion A4 on the right rear.

[0060] More specifically, the first mounting portion A1 is disposed in correspondence with the collar member 310 of the left cutout portion 24 in the left extension portion 22 of the front cross member 10. At this first mounting portion A1, the left extension portion 22 is fastened to the left rear side frame by fastening members such as fastening bolts (not shown) via a subframe mount member (not shown) attached to the collar member 310, and is attached to the vehicle body side.

[0061] The second mounting portion A2 is disposed in correspondence with the collar member 310 of the right cutout portion 28 in the right extension portion 26 of the front cross member 10. At this second mounting portion A2, the right extension portion 26 is fastened to the right rear side frame by fastening members such as fastening bolts (not shown) via a subframe mount member (not shown) attached to the collar member 310, and is mounted to the vehicle body side.

[0062] The third mounting portion A3 is disposed in correspondence with the collar members 310 of the rear cutout portions 148 and 168 in the left extending portions 146 and 166 of the left side member 120. In the third mounting portion A3, the left extending portions 146 and 166 are fastened to the left rear side frame by fastening members such as fastening bolts (not shown) via subframe mount members (not shown) attached to the collar member 310, and are thereby attached to the vehicle body side.

[0063] The fourth mounting portion A4 is disposed in correspondence with the collar members 310 of the rear cutout portions 248 and 268 in the right extending portions 246 and 266 of the right side member 220. At the fourth mounting portion A4, the right extending portions 246 and 266 are fastened to the left rear side frame by fastening members such as fastening bolts (not shown) via subframe mount members (not shown) attached to the collar member 310, and are thereby attached to the vehicle body side.

[0064] A typical configuration of such a subframe mounting member is an insulator bushing member having a rubber portion bonded to a collar member through which the fastening member is inserted, and having a small spring constant in the vertical direction and a large spring constant in the width direction.

[0065] In the configuration of this embodiment described above, the lower member 30 has, in order from the outside to the inside in the width direction, outer portions 60 and 70 provided with lower support portions that support suspension members of the vehicle, intermediate portions 62 and 72 connected to the outer portions 60 and 70, and inner portions 65 and 75 connected to the intermediate portions 62 and 72, and the intermediate portions 62 and 72 have outer curved bottom portions 63 and 73 connected to the bottom portions 61 and 71 of the outer portions 60 and 70 and following a locus that curves upward without descending from the bottom portions 61 and 71 of the outer portions 60 and 70 as they move inward, and inner curved bottom portions 64 and 74 connected to the bottom portions 66 and 76 of the inner portions 65 and 75 and following a locus that curves downward without ascending from the bottom portions 66 and 76 of the inner portions 65 and 75 as they move outward, and the first cross member The cross member 10 has a first closed cross section SE1 when cut along a plane defined by the longitudinal and vertical directions, and the lower member 30 has a second closed cross section SE2 when cut along said plane, and the first closed cross section SE1 and the second closed cross section SE2 are adjacent to each other but separated by the wall portion 12 of the first cross member 10 that defines the first closed cross section SE1, and the juxtaposed closed cross sections SE1 and SE2 that are juxtaposed in the vertical direction are arranged corresponding to at least a portion of the outer curved bottom portions 63 and 73 and the inner curved bottom portions 64 and 74 in the intermediate portions 62 and 72.This configuration allows the necessary strength of the vehicle subframe 1 to be ensured while increasing the freedom to set the support rigidity of its suspension members, and allows the strength and rigidity to be balanced and optimized, making it possible to set the desired rigidity and ensure the required strength.

[0066] Furthermore, in the configuration of this embodiment, the juxtaposed closed cross sections SE1 and SE2 are always provided corresponding to at least a portion of the inner curved bottom portions 64 and 74, and therefore it is possible to appropriately set the support rigidity of the suspension members while ensuring the required strength of the vehicle subframe 1 with a juxtaposed longitudinal cross section having the smallest range in the width direction.

[0067] Furthermore, in the configuration of this embodiment, the juxtaposed closed cross sections SE1 and SE2 are provided continuously in the width direction across the inner curved bottom portions 64 and 74 and one or both of the outer curved bottom portions 63 and 73 and the bottom portions 66 and 76 of the inner portions 65 and 75, thereby reducing stress concentration in the vehicle subframe 1, eliminating local weak portions, and further increasing its strength.

[0068] In addition, in the configuration of this embodiment, upper support members 80 and 90, which face the lower member 30 above in the vertical direction across the first cross member 10 and have upper support portions that support the vehicle's suspension members, are provided in a manner joined to the first cross member 10, and the upper support members 80 and 90 are joined to the inclined surface portion 14, which is formed by recessing and inclining a portion of the cylindrical wall 12 of the first cross member 10, so that the upper support members 80 and 90 can be joined to each other while being securely abutted against the inclined surface portion 14, thereby suppressing the occurrence of peeling and failure at the joint.

[0069] In the configuration of this embodiment, the pair of side members 120 and 220 each have a pair of side walls 132 and 134, 232 and 234 facing each other in the width direction, upper walls 136 and 236 connecting upper ends of the pair of side walls 132 and 134, 232 and 234 in the up-down direction, and bottom walls 156 and 256 facing below the upper walls 136 and 236 and connecting lower ends of the pair of side walls 132 and 134, 232 and 234 in the up-down direction. The upper walls 136 and 236 have, at front portions 142 and 242 in the front-rear direction, recessed portions 136a and 236a recessed downward at an intermediate portion in the width direction of the upper walls 136 and 236, and recessed portions 136a and 236a recessed upward at both ends in the width direction of the upper walls 136 and 236 relative to the recessed portions 136a and 236a. The top walls 136 and 236 have a pair of convex portions 144 and 244 that protrude relatively, and in the top walls 136 and 236, the front ends of the recessed portions 136a and 236a are joined to the first cross member 10, and the bottom walls 156 and 256 have, in their front portions 162 and 262, recessed portions 156a and 256a that are recessed upward at the middle portion of the bottom walls 156 and 256 in the width direction, and a pair of convex portions 164 and 264 that protrude downward relatively from the recessed portions 156a and 256a at both ends of the bottom walls 156 and 256 in the width direction, and in the bottom walls 156 and 256, the front ends of the recessed portions 156a and 256a are joined to the first cross member 10, thereby improving the coverage of the paint on the pair of side members 120 and 220 while ensuring the weld length and increasing the weld strength.

[0070] In this embodiment, the various nut members, collar members, and guide members are typically made of metal such as steel.

[0071] In addition, in this embodiment, the suspension arm may be one other than that exemplified in this embodiment, as long as it has the same function.

[0072] In addition, in this embodiment, the subframe 1 may be mounted to the vehicle body in a so-called rigid manner, rather than in a so-called floating manner.

[0073] Furthermore, the present invention is not limited to the above-described embodiments in terms of the type, shape, arrangement, number, etc. of the components, and it goes without saying that these components can be appropriately modified within the scope of the gist of the invention, such as by appropriately replacing the components with components that have equivalent effects. [Industrial Applicability]

[0074] As described above, the present invention makes it possible to provide a vehicle subframe that can ensure the required strength while balancing and optimizing its strength and rigidity by realizing a configuration that increases the freedom in setting the rigidity, thereby appropriately setting the rigidity.Therefore, due to its versatile and universal nature, it is expected to be widely applicable to the field of subframes for vehicles and other moving bodies. [Explanation of symbols]

[0075] 1...Subframe 10...Front cross member 12...Circumference wall 14…Slanted plane part 16...Plane part 18…Bottom plane part 20...Main body 22...Left extension 24...Left cutout 26...Right extension part 28...Right cutout 30...Lower member 40...First member 42...Front vertical wall 44...Front bottom wall 46...Left front through hole 48...Right front through hole 50...Second member 52…Rear vertical wall 54...Rear bottom wall 56...Left rear through hole 58...Right rear through hole 60...Left outer part 61…Left outer bottom 62...left center 63…Left outer curved bottom 64…Left inner curved bottom 65...left inner part 66…Left inner bottom 70…Right outer part 71…Right outer bottom 72...Right middle 73...Right outer curved bottom 74...Right inner curved bottom 75...Right inner part 76...Right inner bottom 80...Left support member 82...Front vertical wall 83...Front flange 84…Rear vertical wall 85...Rear flange 86...Upper wall 88…Left front through hole 89…Left rear through hole 90...Right support member 92...Front vertical wall 93...Front flange 94…Rear vertical wall 95...Rear flange 96...Upper wall 98...Right front through hole 99…Right rear through hole 100...Rear cross member 102...Front vertical wall 103...Left front through hole 104...Right front through hole 106…Rear vertical wall 107...Left rear through hole 108…Right rear through hole 112...Upper wall 114...Main body 116...Left widening section 118...Right widening section 120...Left side member 130...Upper left member 132...Exterior wall 134…Inner wall 136...Upper wall 136a... Depression 142...front part 144...Upper convex part 146...Left extension 148...Rear cutout 150...Lower left member 152...Exterior wall 154…Inner wall 156...Bottom wall 156a... Depression 162…front part 164...Lower convex part 166...Left extension 168...Rear cutout 220...Right side member 230...Upper right member 232...Exterior wall 234…Inner wall 236...Upper wall 236a...depression 242...front part 244...Upper convex part 246...Right extension part 248...Rear cutout 250...Lower right member 252...Exterior wall 254…Inner wall 256...Bottom wall 256a... Depression 262...Front part 264...Lower convex part 266...Right extension part 268...Rear cutout 310...Colored parts 320...Nut member A1...First mounting part A2...Second mounting part A3...Third mounting section A4...4th mounting part S1...first support part S2…Second support part S3…Third support part S4...4th support part S5...5th support part S6…6th support part SE1, SE2, SE3…Closed section

Claims

1. a cylindrical first cross member extending in a width direction of the vehicle; a second cross member facing the first cross member in the front-rear direction of the vehicle and extending in the width direction; a pair of side members that face each other in the width direction, extend in the front-rear direction, and are joined to the first cross member and the second cross member, respectively; a lower member extending in the width direction below the first cross member in the up-down direction of the vehicle and joined to the first cross member; A vehicle subframe comprising: the lower member has, in order from the outside to the inside in the width direction, an outer portion provided with a lower support portion that supports a suspension member of the vehicle, an intermediate portion connected to the outer portion, and an inner portion connected to the intermediate portion, the intermediate portion has an outer curved bottom portion that is connected to the bottom of the outer portion and that curves upward without descending from the bottom of the outer portion as it moves inward, and an inner curved bottom portion that is connected to the bottom of the inner portion and that curves downward without ascending from the bottom of the inner portion as it moves outward, the first cross member presents a first closed cross section when cut along a plane defined by the longitudinal direction and the vertical direction, the lower member has a second closed cross section when cut along the plane; The first closed cross section and the second closed cross section are adjacent to each other and separated by a wall portion of the first cross member that defines the first closed cross section, and juxtaposed closed cross sections are provided in the up-down direction corresponding to at least a part of the outer curved bottom portion and the inner curved bottom portion in the intermediate portion, Each of the pair of side members has a pair of side walls opposing each other in the width direction, an upper wall connecting upper ends of the pair of side walls in the up-down direction, and a bottom wall opposing the upper wall on the lower side and connecting lower ends of the pair of side walls in the up-down direction, The upper wall has, at a front portion thereof in the front-rear direction, a recessed portion formed by recessing the upper wall toward the lower side at a middle portion in the width direction, and a pair of convex portions formed by protruding the upper wall toward the upper side relative to the recessed portion at both ends in the width direction, and In the upper wall, a front end portion of the recessed portion is joined to the first cross member, The bottom wall has, in the front portion thereof, a recessed portion formed by recessing the bottom wall toward the upper side at a middle portion in the width direction, and a pair of convex portions formed by protruding the bottom wall toward the lower side relative to the recessed portion at both end portions in the width direction, A vehicle subframe, wherein a front end of the recessed portion of the bottom wall is joined to the first cross member.

2. The vehicle subframe according to claim 1 , wherein the juxtaposed closed cross section is necessarily provided corresponding to at least a part of the inner curved bottom portion.

3. 3. The vehicle subframe according to claim 1, wherein the juxtaposed closed cross section is provided continuously in the width direction across the inner curved bottom portion and one or both of the outer curved bottom portion and the bottom portion of the inner portion.

4. 4. The subframe for a vehicle according to claim 1, wherein an upper support member is joined to the first cross member, facing the lower member above in the vertical direction across the first cross member and having an upper support portion that supports a suspension member of the vehicle, and the upper support member is joined to an inclined surface portion formed by recessing and inclining a portion of a cylindrical wall of the first cross member.

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