(57) A pin inserting/withdrawing mechanism (18) which is provided between left and right
first brackets (12), (13) is constituted by a hydraulic cylinder (19) disposed in
such a manner as to be spaced apart from left and right connecting pins (16), (17)
so as to be capable of extending and contracting in the same direction as the axis
of the left and right connecting pins (16), (17); a floating link (20) disposed in
a floating state between the left and right first brackets (12), (13); a left link
(21) for connecting the left connecting pin (16) and the hydraulic cylinder (19) by
means of the floating link (20); and a right link (24) for connecting the right connecting
pin (17) and the hydraulic cylinder (19) by means of the floating link (20). In consequence,
the left and right connecting pins (16), (17) respectively connected to one end sides
(21A), (24A) of these left and right links (21), (24) move in the left-right direction
in correspondence with the extension and contraction of the hydraulic cylinder (19).
As a result, the left and right connecting pins (16), (17) can be smoothly inserted
into or withdrawn from the left and right first brackets (12), (13) and the left and
right second brackets (14), (15).
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