Automobile subframe structure

Abstract

To provide a sub-frame structure of an automobile capable of enhancing vertical bending rigidity and torsional rigidity of a cross member with respect to a side member.SOLUTION: In a sub-frame structure of an automobile, each of open ends 20a of a cross member 20 has a polygonal closed cross section, and is connected to outer surfaces of side cross members 24, 26. Above and / or below the vicinity of connection portions (20a, 22a), a protrusion 20c extending longitudinally and protruding upward is formed at one corner of the polygonal closed cross-section of the cross member 20. The protrusion 20c includes an extension portion 20d extending longitudinally outwardly beyond other portions of the open end 20a. Above and / or below each of the side cross members 24, 26, the extension portion 20d is connected to an outer surface of each of the side cross members 24, 26.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a sub-frame structure of an automobile, and more particularly to a sub-frame structure of an automobile configured in a grid shape by a pair of side members extending in the longitudinal direction of the vehicle and front and rear cross members extending in the vehicle width direction so as to connect the pair of side members to each other.

Background Art

[0002] Conventionally, as a multi-link suspension device, there is known one including five I-links, wherein the body-side end portions of the respective links are connected to a sub-frame attached to the vehicle body, and the wheel-side end portions of the respective links are connected to a wheel support that supports the wheels. As such a sub-frame of a multi-link suspension, there is known one in which a frame is configured in a grid shape by a pair of side members and front and rear cross members. In such a sub-frame, a structure is known in which the front and rear cross members are abutted against and joined to the inner side surfaces in the vehicle width direction of the side members (for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a grid-shaped sub-frame, the pair of side members and the front and rear cross members are each a closed cross-section body formed of a plate-like member, and a structure in which the left and right open end portions of the cross member extending in the vehicle width direction are abutted against and joined to the inner side surfaces in the vehicle width direction of the side members is common.

[0005] However, in the case of a lattice-shaped subframe, when the vehicle travels on the road surface, loads such as vertical forces (bumps) and lateral forces applied from the wheels become the main factors, and bending forces and torsional forces are applied to the entire subframe. Therefore, in order to improve handling stability and prevent vibrations, it is necessary to increase the rigidity against such forces.

[0006] Therefore, the present invention has been made to solve the above-described problems, and an object thereof is to provide an automobile subframe structure capable of improving the vertical bending rigidity and torsional rigidity of a cross member with respect to a side member.

Means for Solving the Problems

[0007] In order to solve the above-described problems, the present invention provides a subframe structure for an automobile configured in a lattice shape by a pair of side members extending in the vehicle longitudinal direction on both left and right sides in the vehicle width direction, and a front cross member and a rear cross member extending in the vehicle width direction so as to connect the pair of side members to each other. The cross member constituting the front cross member and / or the rear cross member is formed of a plate-shaped member and has a polygonal closed cross section at at least both left and right end portions thereof. The open end portions of both left and right end portions having these polygonal closed cross sections are respectively joined to the outer surfaces of the pair of side members. Upper side In the vicinity of the joint portion of the cross member to the side member, a protruding portion is formed at one corner portion of the polygonal closed cross section of the cross member, which extends in the longitudinal direction of the cross member and Upper protrudes. Further, these protruding portions have extension portions that extend outward in the longitudinal direction more than the other portions of the open end portions, and these extension portions are joined to the outer surfaces of the side members Upper side at the On the outer surface of the side member, two opposing plate-like members constituting the pivot shaft support of the suspension arm are welded at positions facing the joint of the cross member to the side member. An extension of the cross member is welded at a position facing one of the two plate-like members. On the upper surface of the side member, the welded portions at the front and rear parts of the extension extend toward the linearly extending welded base edge of one of the plate-like members. side members. This is the gist of the present invention.

[0008] According to the present invention configured as described above, the cross member has increased strength (rigidity) against bending in the vertical direction due to the protruding portions protruding above and / or below it, and the strength (rigidity) of the protruding portions themselves against bending in the vertical direction is also increased. Since the extension portions of the protruding portions with increased strength are joined to the outer surface of the side member above and / or below the side member, the bending rigidity and torsional rigidity of the joint portion of the cross member to the side member can be improved. Therefore, the bending rigidity and torsional rigidity of the cross member in the vertical direction with respect to the side member can be improved.

[0009] Further, in the present invention, preferably, both the left and right end portions of the cross member have curved portions that conform to the shape of the outer surface of the side member before and after the extension portions of the protruding portions, and these front and rear curved portions are welded to the outer surface of the side member. According to the present invention configured as described above, while extending the cross member above and below the side member by the extension portions of the protruding portions with increased strength, by welding the front and rear curved portions that conform to the shape of the outer surface of the side member to the outer surface of the side member, the joining strength of the cross member to the side member can be increased. Thereby, the bending rigidity and torsional rigidity of the cross member in the vertical direction with respect to the side member can be more effectively improved.

Advantages of the Invention

[0010] According to the subframe structure of the automobile of the present invention, the bending rigidity and torsional rigidity of the cross member in the vertical direction with respect to the side member can be improved.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Mode for Carrying Out the Invention

[0012] Hereinafter, with reference to the accompanying drawings, the subframe structure of an automobile according to an embodiment of the present invention will be described.

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, with reference to FIGS. 1 to 3, the overall configuration of the subframe structure of an automobile according to an embodiment of the present invention will be described. FIGS. 1 to 3 show an embodiment in which a rear wheel suspension device 1 (hereinafter simply referred to as a rear suspension) according to an embodiment of the present invention is applied to the rear wheels on both the left and right sides of the automobile. FIG. 1 is a perspective view of a rear suspension assembly of an automobile to which the subframe structure of the automobile according to an embodiment of the present invention is applied. FIG. 2 is a top view of the rear suspension assembly shown in FIG. 1. FIG. 3 is a rear view of the rear suspension assembly shown in FIG. 1. Although not shown, the automobile (vehicle) of the present embodiment is a rear-wheel drive vehicle in which an engine is mounted in an engine room at the front of the vehicle body, a differential is disposed at the rear of the vehicle body, and the rear wheels 2 are driven by an axle (not shown). As shown in FIGS. 1 to 3, the rear suspension assembly of the rear wheel suspension device 1 includes a subframe 3 to which a pair of left and right rear suspensions are connected.

[0014] First, the schematic configuration of the rear suspension device 1 will be described. The rear suspension device 1 of this embodiment is a multi-link type in which the wheel support 10 of the rear wheel 2 is connected to the vehicle body by five independent I-links 4 to 8 so as to be strokeable. The rear suspension device 1 includes a front upper link (upper arm) 4 and a rear leading link (leading arm) 5 that virtually constitute an upper arm, a front trailing link (trailing arm) 6 and a rear lower link (lower arm) 7 that virtually constitute a lower arm, and a toe control link (toe control arm) 8 that regulates the rotational displacement of the rear wheel 2 around the virtual kingpin axis IK (see FIG. 5). The upper arm 4, the leading arm 5, the trailing arm 6, and the lower arm 7 swing up and down around the connection parts (44, 52, 60, 68) on the vehicle body side, respectively, so that the wheel support 10 and the rear wheel 2 stroke up and down along a predetermined locus.

[0015] Further, a shock absorber 16 including a coil spring 12 and a damper 14 is provided to apply a predetermined biasing force and damping force while allowing such a stroke of the rear wheel 2. The shock absorber 16 has a vertically long cylindrical shape in which the coil spring 12 and the damper 14 are arranged substantially coaxially, and its upper end is attached to the vehicle body. The lower end of the shock absorber 16 is pivotally attached to the lower arm 7. In addition, a stabilizer bar 18 extending to connect the left and right lower arms 7 is rotatably attached to the suspension device 1.

[0016] Next, the schematic configuration of the sub-frame 3 according to this embodiment will be described. The sub-frame 3 is mainly formed by combining four steel plate frames into a rectangular frame shape / grid shape in a plan view, and includes a front cross member (front cross member) 20 and a rear cross member (rear cross member) 22 extending in the vehicle width direction, and a pair of side cross members (side members) 24, 26 extending in the vehicle longitudinal direction on both left and right sides of the vehicle body so as to connect the ends on both left and right sides thereof.

[0017] First, the front cross member 20 of the present embodiment is configured as a hollow body with a closed cross-section formed by joining upper and lower plate-like members 120 and 220 to each other. When viewed from above the vehicle, it extends linearly in the vehicle width direction, and at both left and right end portions / open end portions 20a in the vehicle width direction, it is coupled to respective front end side portions of the left and right side cross members 24 and 26. As shown in FIGS. 1 and 2, the front cross member 20 is formed in an arch shape that curves as a whole such that the central portion in its longitudinal direction is positioned above the left and right end portions when viewed in the vehicle front-rear direction.

[0018] Also, as shown in FIG. 2, when viewed from above the vehicle, the central portion in the longitudinal direction of the front cross member 20 extends linearly, and extends such that the front-rear length expands from the central portion toward both left and right end portions 20a. More specifically, when viewed from above, the front edge of the front cross member 20 extends linearly in the vehicle width direction, and the central portion of the rear edge extends linearly in the vehicle width direction while the left and right side portions of the rear edge are curved so as to be positioned rearward of the central portion and extend in the vehicle width direction. Portions 20b where the front-rear length expands on both left and right sides include the open end portions 20a of the closed cross-section. As shown in FIGS. 1 and 2, each open end portion 20a is coupled (welded) to respective front end side portions of the side members 24 and 26.

[0019] Also, on both left and right end sides of the front cross member 20, mounting seats (pivot shaft support portions) 28 for the upper arm 4 and mounting seats (pivot shaft support portions) 30 for the trailing arm 6 are provided respectively at positions close to the coupling portions 20a with the side cross members 24 and 26, and on the upper side and lower side of the side cross members 24 and 26 (see FIGS. 4 to 6). The body side ends of the upper arms 4 are respectively connected to the mounting seats 28 on both left and right sides, and the body side ends of the trailing arms 6 are respectively connected to the mounting seats 30 on both left and right sides.

[0020] Next, the rear cross member 22 of the present embodiment includes a rear cross member main body 21 that forms part of the truss-shaped sub-frame 3, and left and right lower portions (vertical portions) 23 of the rear cross member that mainly serve to support the lower arms. When viewed from above the vehicle, at the left and right both ends / open ends 22a in the vehicle width direction, they are respectively joined to the front end side portions of the left and right side cross members 24 and 26. The rear cross member main body 21 is configured as a hollow body with a closed cross-section formed by joining front and rear plate-like members 121 and 221 to each other. When viewed from above the vehicle, the central portion in its longitudinal direction is formed substantially linearly, and on both the left and right sides in the vehicle width direction, enlarged portions 22b with an increasing longitudinal length towards both ends are formed. The open ends 22a of these enlarged portions 22b are respectively joined (by welding) to the rear end side portions of the side cross members 24 and 26. In the present embodiment, with such a configuration, the rigidity of the rear cross member 22 itself and the sub-frame 3 is ensured. Also, as shown in FIG. 3, when viewed from the rear of the vehicle, the rear cross member main body 21 is formed in an arch shape that curves as a whole such that the central portion in its longitudinal direction is positioned below the left and right both ends.

[0021] Further, the lower portion 23 of the rear cross member is configured as a hollow body with a closed cross-section formed by joining three front and rear plate-like members 123, 124, and 223 (see FIG. 5) to each other. The lower portion 23 of the rear cross member is joined (by welding) to the lower part of the rear cross member main body 21 at positions inside and in the vicinity of the side cross members 24 and 26 in the vehicle width direction, and extends to the outer side in the vehicle width direction of the side cross members 24 and 26, and is joined (by welding) to the lower surface and the outer surface of the side cross members 24 and 26.

[0022] On both the left and right ends of the rear cross member 22, mounting seats (pivot shaft support parts) 32 of the leading arm 5 and mounting seats (pivot shaft support parts) 34 of the lower arm 7 are provided above and below the side cross members 24 and 26, respectively (see FIGS. 4 and 5). The body-side ends of the leading arms 5 are connected to the mounting seats 32 on both the left and right sides, and the body-side ends of the lower arms 7 are connected to the mounting seats 34 on both the left and right sides, respectively. In the present embodiment, the lower end of the lower part 23 of the rear cross member is formed as the mounting seat 34 of the lower arm 7, and the upper end of the lower part 23 of the rear cross member is formed as a part of the mounting seat 32 of the leading arm 5 (see FIGS. 4 and 5).

[0023] Further, on the rear surface 23b of the lower part 23 of the rear cross member, mounting seats (pivot shaft support parts) 36 of the toe control arms 8 are provided at positions inward in the vehicle width direction of the side cross members 24 and 26 when viewed from above and at positions diagonally downward of the side cross members 24 and 26 when viewed from behind. The body-side ends of the toe control arms 8 are connected to the mounting seats 36 on both the left and right sides, respectively.

[0024] Next, each of the left and right side cross members 24 and 26 is curved such that the central portion in its longitudinal direction is located inward in the vehicle width direction compared to the front and rear end portions when viewed from above the vehicle, and extends obliquely downward toward the front of the vehicle from the rear end portion to the front end portion in a side view (see FIG. 5). The above-described mounting seats 28 and 30 are provided on the front side portions of these side cross members 24 and 26, and the above-described mounting seats 32 and 34 are provided on the rear side portions thereof.

[0025] In addition, the side cross members 24 and 26 are provided with elastic mounts 38 and 40 for elastically supporting the entire subframe 3 on the vehicle body. These elastic mounts 38 and 40 are provided at a total of four locations at the front and rear ends of each side cross member 24 and 26. Each elastic mount 38 and 40 has a cylindrical shape with an axis in the vertical direction and is attached to a recess formed in each side cross member 24 and 26. In each side cross member 24 and 26, each elastic mount 38 and 40 is arranged such that a straight line connecting the elastic mount 38 at the front end and the elastic mount 40 at the rear end is substantially parallel to the center line CL (shown only in FIG. 2) in the longitudinal direction of the vehicle body when viewed from above the vehicle.

[0026] A predetermined gap called "suguri" is formed in each elastic mount 38 and 40, and each elastic mount 38 and 40 is formed such that its hardness (characteristic indicated by the magnitude of the load (N) that causes a predetermined amount of deflection (mm)) is different in the front-rear direction and the left-right direction with respect to its axis. Each elastic mount 38 and 40 is attached to the side cross members 24 and 26 such that the hardness in the vehicle width direction is greater than the hardness in the longitudinal direction of the vehicle.

[0027] Next, with reference to FIGS. 4 to 6, the arrangement configuration of each arm 4 to 8 and the arm support configuration of the subframe 3 of the rear suspension device 1 on the left side of the vehicle will be described. FIG. 4 is a top view of the rear suspension on the left side of the vehicle according to the present embodiment, FIG. 5 is a left side view of the rear suspension in FIG. 4, and FIG. 6 is a front view of the rear suspension in FIG. 4. Since the rear suspension device 1 on the right side of the vehicle has the same configuration as the rear suspension 1 on the left side of the vehicle, the description thereof will be omitted below.

[0028] First, as shown in FIGS. 4 to 6, for the upper arm 4, the end on the vehicle body side is connected to the pivot shaft support portion 28 of the side cross member 24 (26) via an elastic bush (a bush made of rubber, hereinafter referred to as "bush") 42. The upper arm 4 is inclined rearward so that, when viewed from above the vehicle, it is gradually positioned rearward as it extends outward in the vehicle width direction from the connection portion 44 on the vehicle body side. At the connection portion 46 on the wheel side, the end on the wheel side of the upper arm 4 is connected to the wheel support 10 via a bush 48.

[0029] The pivot shaft support portion 28 of the upper arm 4 is composed of two opposing plate-like members whose bases are welded to the side cross members 24 and 26. By these plate-like members, the pivot portion on the vehicle body side of the upper arm 4 is pivotally supported (see FIGS. 4 to 6).

[0030] Next, for the leading arm 5, the end on the vehicle body side is connected to the above-mentioned pivot shaft support portion 32 via a bush 50. The leading arm 5 is inclined forward so that, when viewed from above the vehicle, it is gradually positioned forward as it extends outward in the vehicle width direction from the connection portion 52 on the vehicle body side. At the connection portion 54 on the wheel side, the end on the wheel side of the leading arm 5 is connected to the wheel support 10 via a bush 56.

[0031] The pivot shaft support portion 32 of the leading arm 5 is composed of two opposing plate-like members. In this embodiment, one of them is the upper end portion of the lower part 23 of the rear cross member described above, and the other is a plate-like member whose base is welded to the side cross members 24 and 26 (see FIGS. 4 and 5).

[0032] In this way, the two upper arms 4 and 5 are arranged so as to approach each other toward the outer side of the vehicle body when viewed from above the vehicle. In this embodiment, spherical joints are adopted for the bushes 42 and 50 on the vehicle body side and the bushes 48 and 56 on the wheel side.

[0033] Next, the trailing arm 6 has its body-side end connected to the pivot shaft support portion 30 described above via a bush 58. The trailing arm 6 extends while being tilted rearward such that, when viewed from above the vehicle, it is positioned gradually rearward from the body-side connection portion 60 toward the outside in the vehicle width direction. At the wheel-side connection portion 62, the wheel-side end of the trailing arm 6 is connected to the wheel support 10 via a bush 64.

[0034] The pivot shaft support portion 30 of the trailing arm 6 is an arm support bracket 30 having a U-shaped cross section formed by welding two opposing L-shaped side members to each other, and the pivot portion on the body side of the trailing arm 6 is pivotally supported by the opposing side faces (see FIGS. 5 and 6).

[0035] Next, the lower arm 7 has its body-side end connected to the pivot shaft support portion 34 described above via a bush 66. The lower arm 7 extends while being tilted forward such that, when viewed from above the vehicle, it is positioned gradually forward from the body-side connection portion 68 toward the outside in the vehicle width direction. At the wheel-side connection portion 70, the wheel-side end of the trailing arm 6 is connected to the wheel support 10 via a bush 72.

[0036] The pivot shaft support portion 34 of the lower arm 7 is the lower end portion of the above-described rear cross member lower portion 23, and the pivot portion on the body side of the lower arm 7 is pivotally supported by the plate-like members 123 and 223 in front of and behind the lower end portion (see FIG. 5).

[0037] In this way, the two lower arms 6 and 7 are arranged so as to approach each other toward the outside in the vehicle width direction when viewed from above the vehicle. Mainly due to this arrangement, when a braking force from the road surface G (see FIG. 3) acts on the rear wheel 2 during braking or the like, toe-in is geometrically applied to the rear wheel 2 as the vehicle is displaced rearward (longitudinal force compliance steer). Also, when a lateral force is applied to the rear wheel 2 during turning, mainly due to the deflection of the bushes 56 and 64 of the lower arms 6 and 7, the rear wheel 2 changes in the direction of toe-in (lateral force compliance steer). In the present embodiment, spherical joints are adopted for the bushes 58, 66 on the vehicle body side and the bushes 64, 72 on the wheel side.

[0038] Next, one end of the toe control arm 8 on the vehicle body side is connected to the pivot shaft support portion 36 described above via a bush 74. The toe control arm 8 extends forward with a forward tilt so that it is gradually positioned forward as it goes outward in the vehicle width direction from the connection portion 76 on the vehicle body side when viewed from above the vehicle. At the connection portion 78 on the wheel side, the wheel side end of the trailing arm 6 is connected to the wheel support 10 via a bush 80. In the present embodiment, spherical joints are adopted for the bush 74 on the vehicle body side and the bush 80 on the wheel side.

[0039] The pivot shaft support portion 36 of the toe control arm 8 has a U-shaped cross-section arm support bracket 37 integrally formed by press molding. The pivot shaft support portion 36 is composed of a shaft support portion of this arm support bracket 37 and a shaft support portion on the side of the lower portion 23 of the rear cross member formed at a position facing in the front-rear direction. The pivot portion of the control arm 8 on the vehicle body side is pivotally supported by such two opposing shaft support portions (see FIGS. 3 and 5).

[0040] Here, in the rear suspension, a virtual kingpin axis IK (see FIG. 5) is formed that connects the intersection of the virtual extension line of the upper arm 4 and the virtual extension line of the leading arm 5 and the intersection of the virtual extension line of the trailing arm 6 and the virtual extension line of the lower arm 7 vertically. This virtual kingpin axis is the instantaneous rotation center of the rear wheel 2 during turning in the steering direction (toe direction).

[0041] Next, the configuration of the wheel support 10 and the mounting configuration of each arm will be described with reference to FIGS. 4 to 6. First, as shown in FIGS. 4 to 6, a hub 82 is attached to the central portion of the wheel support 10, and an opening 84 through which an axle (not shown) passes is formed. Further, on the wheel support 10, a front vertical wall portion 86 that protrudes inward in the vehicle width direction is formed in a portion on the vehicle front side of the opening 84, and the upper arm 4, the leading arm 5, and the trailing arm 6 are connected to the front vertical wall portion 86. As shown in FIG. 6, a reinforcing rib 86a is formed on the outer edge of the front vertical wall portion 86. Also, on the wheel support 10, a lower vertical wall portion 88 that protrudes inward in the vehicle width direction is formed in a lower portion of the opening 84, and the lower arm 7 is connected to the lower vertical wall portion 88. Furthermore, on the wheel support 10, a rear vertical wall portion 90 that protrudes inward in the vehicle width direction is formed in a portion on the vehicle rear side of the opening 84, and the toe control arm 8 is connected to the rear vertical wall portion 90.

[0042] Next, with reference to FIGS. 7 to 10, the coupling structure of the front cross member 20 to the side cross members 24 and 26 of the front cross member will be described. FIG. 7 is a perspective view seen obliquely from the front showing the structure of the front cross member on the left side of the vehicle of the subframe of the automobile according to the present embodiment and the coupling structure to the side cross member. FIG. 8 is a perspective view seen obliquely from the rear of the vehicle showing the structure of the same portion as in FIG. 7. FIG. 9 is a perspective view seen obliquely from below at the rear of the vehicle showing the structure of the front cross member on the left side of the vehicle of the subframe of the automobile according to the present embodiment and the coupling structure to the side cross member. FIG. 10 is a perspective view seen obliquely from below at the rear of the vehicle showing the structure of the same portion as in FIG. 9. First, as shown in FIGS. 7 to 10, the front cross member 20 is a hollow body with a closed cross-section formed by welding a plate-like member (upper member) 120 on the upper side and a plate-like member (lower member) 220 on the lower side to each other. The enlarged portion (portion near the left and right ends 20a) 20b of the front-rear length including the left and right open ends 20a has a polygonal closed cross-section having approximately four corners (see FIGS. 13 and 16). These left and right open ends (openings that are open in the vehicle width direction on the left and right sides) 20a are respectively coupled to the outer surfaces of the side cross members 24 (26). Also, a part of each of the left and right open ends 20a is coupled so as to abut against the inner surfaces of the side cross members 24 (26).

[0043] Next, as shown in FIGS. 7 and 8, in the vicinity portions 20b of both left and right end portions 20a, at the corner portions of the trailing edge portions, there are formed projecting portions 20c that extend along the trailing edge portions (along the longitudinal direction of the front cross member 20) and project upward. In the present embodiment, these projecting portions 20c are formed on the upper member 120. This projecting portion 20c further has an extension portion 20d that extends outward in the longitudinal direction of the front cross member 20 more than the other portions of the open end portion 20a. That is, the projecting portion 20c has an extension portion 20d that extends outward in the vehicle width direction more than the other portions of the open end portion 20a with respect to the position of the inner surface of the side cross member 24 (26) when viewed from above.

[0044] In the present embodiment, such an extension portion 20d is joined to the upper surface of the side cross member 24 (26). The joining of this extension portion 20d is configured such that the front and rear portions 20e of the extension portion 20d are welded to the outer surface of the side cross member 24 (26) along the welding line W indicated by the reference symbol W in the figures, as shown in FIGS. 7 and 8. More specifically, the front and rear portions 20e of the extension portion 20d are portions formed in a curved shape along the shape of the outer surface of the side cross member 24 (26) at the open end portion 20a in the upper member 120, and these front and rear curved portions 20e are welded to the upper surface of the side cross member 24 (26). Also, on the outer surface of the side cross member 24 (26), on the position facing the extension portion 20d, one side plate member of the pivot shaft support portion 28 of the upper arm 4 is welded (see the welding line W).

[0045] As a modification, such a projecting portion 20c and extension portion 20d may be formed on the lower member 220 and joined to the outer surface of the side cross member 24 (26), that is, the lower surface of the side cross member 24 (26) in this case, in the same manner as the upper member 120. Also, in this case, the projecting portion (20c) in the lower member 220 is preferably made to project downward.

[0046] Next, as shown in FIGS. 7, 9, and 10, a bulging portion 20f that bulges downward is formed in the vicinity of the corner of the front edge and the lower edge of the open end portion 20a of the front cross member 20. In this bulging portion 20f, a substantially L-shaped notch portion 20g is formed along the outer shape of the arm support bracket 30 of the trailing arm 6 (see FIG. 16). Here, the arm support bracket 30 of the trailing arm 6 is an arm support bracket 30 having a U-shaped cross section formed by welding two opposing L-shaped side members to each other, and has side portions 30a, 30b facing in the front-rear direction and a rear portion 30c on the inner side in the vehicle width direction. Such an arm support bracket 30 has its base portion 30d joined (welded) to the side cross members 24 and 26, and the pivot portion on the vehicle body side of the trailing arm 6 is pivotally supported by the two opposing side portions (see FIGS. 7, 9, and 10).

[0047] In the present embodiment, as shown in FIGS. 9 and 10, the notch portion 20g of the bulging portion 20f is welded to one of the two opposing side portions 30a of the arm support bracket 30 (see welding line W), and as shown in FIGS. 7 and 9, it is also welded to the rear portion 30c of the bracket 30 (see welding line W). Further, in the present embodiment, as shown in FIG. 7, the notch portion 20g is welded to one of the two L-shaped cross-section members constituting the arm support bracket 30 (see welding line W).

[0048] Thus, in the present embodiment, a part of the open end portion 20a of the front cross member 20 forms the bulging portion 20f and the notch portion 20g in the lower member 220, and is attached and welded so as to surround one side portion 30a and the rear portion 30c of the bracket 30. Note that the notch portion 20g may be formed as a U-shaped opening so as to surround both side surfaces 30a, 30b and the rear portion 30c of the bracket 30, and the opening may be abutted and welded.

[0049] Next, as shown in FIGS. 9 and 10, on the open end portion 20a of the lower member 220, an outer edge portion 20h is formed on the rear side portion of the bulging portion 20f described above in a shape that follows the shape of the outer surface of the side cross member 24(26). This outer edge portion 20h is welded to the lower surface of the side cross member 24(26) along the welding line W indicated by the symbol W in the figure.

[0050] Here, the base portion 30d of the U-shaped arm support bracket 30 that extends in a U-shape is welded to the lower surface of the side cross member 24(26) (see the welding line W). In the present embodiment, by forming the bulging portion 20f that bulges downward and the notch portion 20g in the lower member 220, as shown in FIGS. 9 and 10, it is welded to the side surface portion 30a of the bracket 30 at a position spaced downward from the base portion 30d of the arm support bracket 30. As a result, particularly as shown in FIG. 10, a space S is formed between the base portion 30d, the downward bulging portion 20f, and the lower surface portion of the side cross member 24(26), thereby enhancing the arm support rigidity by the arm support bracket 30. That is, the space S mainly formed by the bulging portion 20f is formed because the outer edge portion 20h supports the bracket 30 from the side via the bulging portion 20f on its front side. In particular, the strength against the bending force applied to the vicinity of the base portion 30d of the arm support bracket 30 is improved, and accordingly, the bending rigidity of the bracket 30 is improved, and the pivot position of the trailing arm 6 does not shift.

[0051] As a modification, such a bulging portion 20f may be formed on the upper member 120 and welded to the arm pivot shaft support portion (for example, the pivot shaft support portion 28 of the upper arm 4) in the same manner as the lower member 220. Also, in this case, the bulging portion (20f) in the upper member 120 is preferably bulged upward. Also, as a modification, such a bulging portion 20f and notch portion 20g may be welded to the support portion of an arm other than the trailing arm 6 (for example, the upper arm 4 or the leading arm 5) as described above. Further, as a modification, the structure of such a front cross member 20 may be applied to a rear cross member.

[0052] Next, as shown in FIGS. 11 to 13, the upper member 120 of the front cross member 20 is formed by press-molding a plate-shaped steel plate member, has the both end portions 20a and the front and rear enlarged portions 20b described above, and the upper member 120 is formed with the protruding portion 20c, the extending portion 20d, and the front and rear curved portions 20e described above.

[0053] Next, as shown in FIGS. 14 to 16, the lower member 220 of the front cross member 20 is formed by press-molding a plate-shaped steel plate member, has the both end portions 20a described above, and the lower member 220 is formed with the bulging portion 20f, the notch portion 20g, and the outer edge portion 20h described above.

[0054] Next, the operation and effects of the present embodiment and the modification will be described. According to the present embodiment and its modification, the cross members constituting the front cross member 20 and / or the rear cross member 22 are formed of plate members, and have polygonal closed cross-sections at at least the left and right both end portions 20a (22a). The open end portions 20a (22a) of the left and right both end portions having these polygonal closed cross-sections are respectively joined to the outer surfaces of a pair of side cross members 24 and 26. In the upper side and / or lower side in the vicinity of the joining portions (20a, 22a) to the side cross members 24 and 26 in the cross members 20 and 22, a protruding portion 20c that extends in the longitudinal direction and protrudes upward and / or downward is formed at one corner of the polygonal closed cross-section of the cross members 20 and 22. Further, these protruding portions 20c have extending portions 20d that extend outward in the longitudinal direction more than the other portions of the open end portions 20a (22a), and these extending portions 20d are joined to the outer surfaces of the side cross members 24 and 26 above and / or below the side cross members 24 and 26.

[0055] According to the present embodiment and the modified example configured as described above, the cross members 20 and 22 have increased strength (rigidity) against bending in the vertical direction due to the protruding portions 20c protruding above and / or below them. Also, the strength (rigidity) of the protruding portions 20c themselves against bending in the vertical direction is increased. Since the extension portions 20d of the protruding portions 20c with increased strength are joined to the outer surfaces of the side cross members 24 and 26 above and / or below the side cross members 24 and 26, the bending rigidity and torsional rigidity of the joints of the cross members 20 and 22 to the side cross members 24 and 26 can be improved.

[0056] Further, in the present embodiment and the modified example, both left and right end portions 20a (22a) of the cross member 20 (22) have curved portions 20e that match the shape of the outer surfaces of the side cross members 24 and 26 before and after the extension portion 20d of the protruding portion 20c, and since these front and rear curved portions 20e are welded to the outer surfaces of the side cross members 24 and 26, the joining strength of the cross member 20 (22) to the side cross members 24 and 26 can be increased.

Explanation of Reference Numerals

[0057] 1 Suspension device of an automobile / Rear suspension assembly 2 Rear wheel 3 Subframe 4 Upper arm 5 Leading arm 6 Trailing arm 7 Lower arm 8 Toe control arm (control arm) 10 Wheel support 16 Shock absorber 18 Stabilizer bar (stabilizer link) 20 Front cross member 20a Both end portions / Left and right open end portions 20b Enlarged portion 20c Protruding portion 20d Extension portion 20e Front and rear curved portions 20f Bulge 20g Notch 20h Outer edge 21 Rear cross member body 23 Lower part of rear cross member 22 Rear cross member 22a Both ends / Left and right open ends / 24, 26 Side cross members (side members) 30 Support bracket (pivot shaft support) of trailing arm 6 30a, 30b Side faces of arm support bracket 30c Rear face of arm support bracket 30d Base of arm support bracket 120, 220 Upper and lower plate-like members of front cross member 20 123, 124, 223 Front and rear plate-like members of rear cross member IK Virtual kingpin axis S Space W Welding line (welding seam)

Claims

1. A sub-frame structure of an automobile configured in a grid-like shape by a pair of side members extending in the vehicle front-rear direction on both left and right sides in the vehicle width direction, and a front cross member and a rear cross member extending in the vehicle width direction so as to connect the pair of side members to each other, The cross members constituting the front cross member and / or the rear cross member are formed of plate-like members, and have polygonal closed cross-sections at at least both left and right end portions thereof, and the open end portions of both left and right end portions having these polygonal closed cross-sections are respectively joined to the outer surfaces of the pair of side members, Above the vicinity of the joint portion of the cross member to the side member, at one corner of the polygonal closed cross-section of the cross member, a protruding portion is formed that extends in the longitudinal direction of the cross member and protrudes upward. Further, these protruding portions have extension portions that extend outward in the longitudinal direction from the other portions of the open end portions, and these extension portions are joined to the outer surface of the side member above the side member, On the outer surface of the side member, at a position facing the joint portion of the cross member to the side member, two opposing plate-like members constituting the pivot shaft support portion of the suspension arm are welded. At a position facing one of the two plate-like members, the extension portion of the cross member is welded. On the upper surface of the side member, the welded portions of the front and rear portions of the extension portion extend toward the linearly extending welded base edge portion of the one plate-like member. A sub-frame structure of an automobile, characterized by this.

2. The left and right end portions of the cross member have curved portions that coincide with the shape of the outer surface of the side member before and after the extension portion of the protruding portion, and these front and rear curved portions are welded to the outer surface of the side member. The sub-frame structure of an automobile according to Claim 1.

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