| 摘要 |
A mobile lift crane (10) comprises a carbody (12) having movable ground engaging members (14, 16). A rotating bed (20) is rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members. A boom (22) is pivotally mounted on a front portion of the rotating bed. A mast (28) is mounted at its first end on the rotating bed. A backhitch (30) is connected between the mast and a rear portion of the rotating bed. The crane (10) further comprises a movable counterweight unit, at least one hydraulic cylinder, and at least one arm pivotally connected at a first end to the rotating bed and at a second end to the hydraulic cylinder. The arm and hydraulic cylinder are connected between the rotating bed and the counterweight unit such that extension and retraction of the hydraulic cylinder changes the position of the counterweight unit compared to the rotating bed.
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