| 摘要 |
PROBLEM TO BE SOLVED: To provide a structure where increase in weight can be suppressed while joint strength is secured even when using light alloy material for an upper frame, a side frame and a bracket, in a back frame having a structure formed by joining the upper frame and the side frame via the bracket.SOLUTION: A back frame 10 is formed into a portal shape by joining an upper end part of a first frame 20 extending in a longitudinal direction, and a tip end part of a second frame 30 extending in a longitudinal direction and also extending while curving in a horizontal direction from mid-course via a belt guide bracket 40. The first frame 20 has a closed cross-sectional shape part 27. The second frame 30 also has a closed cross-sectional shape part 37. A first engagement part 42 of the belt guide bracket 40 is inserted into the closed cross-sectional shape part 27 of the first frame 20 to be fixed, and a second engagement part 43 of the belt guide bracket 40 is inserted into the closed cross-sectional shape part 37 of the second frame 30 to be fixed. |
