FASTENING STRUCTURE FOR VEHICULE
FIG3 is a bottom view of the mount portion in FIG2
FIG3 is a bottom view (to the positive direction along the U axis) of FIG2. In FIG3, the upper member 40 and the weld bead 46 are omitted. As shown in FIG3, the collar 50 is inserted in the insertion hole 42a formed in the lower member 42. The outer diameter of the flange 54 that extends around the cylindrical portion 52 of the collar 50 is larger than the diameter of the insertion hole 42a. The flange 54 is disposed to be partially overlapped with the lower member 42. The outer circumference of the flange 54 and the lower member 42 are secured together by arc welding such that the weld bead 62 lies between them. As shown in FIG3, the weld bead 62 is formed partially along the circumference of the flange 54. Specifically, welding is applied at two portions in angle ranges θa and θb (radians) about the cylindrical axis. The length L2 of the weld bead 62 can be approximately obtained by the following Equation (2): L2=θa+θb×D/2 where D is the outer diameter of the flange 54. In the embodiment shown in FIG3, welding is applied so that the welding strength on the flange 54 side is higher than the welding strength on the cylindrical portion 52 side. In general, the welding strength increases with increasing cross sectional area of the welded portion. In the arc welding according to the present embodiment, because the cross sectional area of the welded portion is proportional to the welded length, the welded length L1 represented by Equation (1) and the welded length L2 represented by Equation (2) are set to satisfy the following relationship: L1<L2 On the flange 54 side, the lengths of the two weld beads 62 are set to be substantially equal to each other (θa = θb), and the two weld beads 62 are positioned to be substantially point symmetrical about the cylindrical axis. In this way, welding is applied to enhance isotropy of the weld bead 62 to ensure high strength against external force from different directions. Welding of the flange 54 at two or more portions that satisfy the relationship defined in Inequality (3) (better with a higher isotropy) can achieve a sufficiently high welding strength on the flange 54 side. Although it is also possible to apply the welding along the entire circumference of the flange 54, time and cost required for the welding process will be increased in that case. Thus, partial welding as shown in FIG3 that can ensure a required strength is advantageous.
bottom view
42
lower member
52
cylindrical portion
50
collar collars
54
flange
62
weld bead weld beads
['1. A fastening structure for a vehicle using a collar (50, 70) as a reinforcing member to fasten a closed section member (12), the fastening structure comprising: two insertion holes (40a, 42a) respectively formed in opposing first and second walls (40, 42) of the closed section member; and the collar (50, 70) comprising a cylindrical portion inserted through the two insertion holes, wherein the cylindrical portion (52, 72) of the collar (50, 70) and the first wall (40) are welded together, the collar (50, 70) comprises a flange (54, 74) that extends on an outer circumferential side of the cylindrical portion (52, 72) and is disposed on an outer surface side of the second wall (42), and the flange (54, 74) and the second wall (42) are welded together, and the welding is applied such that a welded area on the second wall (42) is larger than a welded area on the first wall (40).']