Mobile lift crane with variable position counterweight

A method of operating a mobile lift crane, the lift crane comprising a carbody having moveable ground engaging members;

• a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members;
• a boom pivotally mounted on a front portion of the rotating bed, with a hoist line extending therefrom;
• a mast mounted at its first end on the rotating bed;
• at least one hydraulic cylinder;
• and a moveable counterweight unit;
• the method comprising:
• a) performing a pick, move and set operation with a load wherein the moveable counterweight is moved toward and away from the front portion of the rotating bed by extending and retracting the hydraulic cylinder during the pick, move and set operation to help counterbalance the load, but wherein the counterweight is never supported by the ground other than indirectly by the moveable ground engaging members on the carbody during the pick, move and set operation.

A mobile lift crane comprising:

• a) a carbody having moveable ground engaging members;
• b) a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members;
• c) a boom pivotally mounted on a front portion of the rotating bed, and boom hoist rigging connected to the boom and used to control the angle between the boom and the rotating bed;
• d) a mast mounted at its first end on the rotating bed;
• e) a backhitch connected between the mast and a rear portion of the rotating bed;
• f) a moveable counterweight unit;
• g) at least one hydraulic cylinder;
• and
• h) at least one arm pivotally connected at a first end to the rotating bed and pivotally connected at a second end to the hydraulic cylinder, the arm and hydraulic cylinder being 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 over a range of positions that relate to the range of extension of the hydraulic cylinder.

A mobile lift crane comprising:

• a) a carbody having moveable ground engaging members;
• b) a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members about an axis of rotation;
• c) a boom pivotally mounted on a front portion of the rotating bed;
• d) a mast mounted at its first end on the rotating bed at a fixed angle compared to the plane of rotation of the rotating bed;
• e) a moveable counterweight unit suspended from a tension member connected adjacent a second end of the mast;
• and
• f)a counterweight movement structure connected between the rotating bed and the counterweight unit such that the counterweight unit may be moved to and held at a first position in front of the top of the mast and moved to and held at a second position rearward of the top of the mast;
• g) wherein the top of the mast is defined as the furthest back position on the mast from which any line or tension member supported from the mast is suspended, and if no line or tension member is supported from the mast, then the top of the mast is the position to which any backhitch is attached;
• and wherein the position of the counterweight unit is defined as the center of gravity of the combination of all counterweight elements and any holding tray to which the counterweights are attached, or otherwise move in conjunction with, with all counterweight units on a crane that are tied together so as to always move simultaneously being treated as a single counterweight for purposes of determining the center of gravity.