(57) In a swing type excavator a horizontal pin 31 as the coupling point between boom
14 and the swing post 13 is positioned rearwardly of a swing pin 30 as the swing center
of the swing post 13 away from the front attachment. With this arrangement, the so-called
ultra-small or undercarriage-width turn is realized without reducing both the side
ditch distance in a side ditch digging condition and the maximum digging depth in
a deep digging posture. Also, a swing post 13 is attached to an upper structure 11,
which is able to turn within a width of an undercarriage 10, at a position forwardly
and laterally of a cab 12. A front attachment 1, including a bucket 22, an arm 19,
an upper boom 17, a lower boom 14 and a cross link 15, is mounted to the swing post
13. The cross link 15 intersects a line connecting a coupling point between the upper
boom 17 and the lower boom 14 and a coupling point between the lower boom 14 and the
swing post 13, and changes an opening angle between the upper boom 17 and the lower
boom 14 depending on a vertical tilt angle of the lower boom 14. With this arrangement,
the upper structure including the front attachment can be turned within the undercarriage
width by a simple construction with no need of using a complex link mechanism, and
interference between the front attachment and the cab can be easily avoided when the
front attachment is swung.
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