Mobile Lift Crane with Variable Position Counterweight

Abstract

A mobile lift crane includes a carbody; a rotating bed; a boom; a moveable counterweight unit; at least one linear actuation device; and at least one arm pivotally connected at a first end to the rotating bed and at a second end to the linear actuation device. The arm and linear actuation device are connected between the rotating bed and the counterweight unit such that extension and retraction of the linear actuation device changes the position of the counterweight unit compared to the rotating bed. In one method of operation, the counterweight unit is never supported by the ground during crane pick, move and set operations other than indirectly by the ground engaging members on the carbody.

1 . A mobile 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;   a mast mounted at a first end on the rotating bed;   a moveable counterweight unit suspended from a tension member connected adjacent a second end of the mast;   at least one linear actuation device connected between the rotating bed and the moveable counterweight unit such that the moveable counterweight unit is configured to move toward a front portion of the rotating bed to a first position and configured to move away from the front portion of the rotating bed to a second position;   wherein a top of the mast is defined as a furthest back position on the mast from which any line or tension member supported from the mast is suspended; and   wherein a position of the moveable counterweight unit is defined as a center of gravity of a combination of at least one counterweight element and any holding tray to which the at least one counterweight element is attached, wherein the at least one counterweight element and any holding tray being treated as a single counterweight for purposes of determining the center of gravity.   
     
     
         2 . The mobile lift crane of  claim 1 , further comprising at least one arm pivotally connected at a first end to the rotating bed and pivotally connected at a second end to the at least one linear actuation device, the arm and the at least one linear actuation device being connected between the rotating bed and the moveable counterweight unit such that extension and retraction of the linear actuation device changes the position of the counterweight unit compared to the rotating bed. 
     
     
         3 . The mobile lift crane of  claim 2 , wherein the at least one arm comprises a pivot frame and at least one rear arm, the pivot frame connected between the rotating bed and the at least one linear actuation device, and the rear arm connected between the pivot frame and the counterweight unit. 
     
     
         4 . The mobile lift crane of  claim 1 , wherein the at least one linear actuation device comprises at least one hydraulic cylinder. 
     
     
         5 . The mobile lift crane of  claim 4 , wherein the counterweight movement structure further comprises at least one pivot arm. 
     
     
         6 . The mobile lift crane of  claim 1 , wherein the at least one linear actuation device is pivotally connected to the rotating bed. 
     
     
         7 . The mobile lift crane of  claim 1 , wherein the at least one linear actuation device comprises a rack and pinion assembly. 
     
     
         8 . The mobile lift crane of  claim 1 , wherein the moveable counterweight unit is configured to be moved to a far forward position in which the moveable counterweight unit is positioned forward of a rear most portion of a rear ground engaging member of the moveable ground engaging members. 
     
     
         9 . The mobile lift crane of  claim 1 , wherein the first position is in front of the top of the mast and the second position is rearward of the top of the mast. 
     
     
         10 . The mobile lift crane of  claim 1 , further comprising a backhitch. 
     
     
         11 . A mobile 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;   a first linear actuation device;   a moveable counterweight unit;   wherein the first linear actuation device is operable to move the moveable counterweight unit toward and away from a front portion of the rotating bed during a pick, move, and set operation by extending and retracting the first linear actuation device;   wherein the crane is configured such that the moveable counterweight unit is never supported by the ground other than indirectly by the moveable ground engaging members on the carbody throughout all pick, move, and set operations; and   wherein the moveable counterweight unit is operable to be moved a greater horizontal distance toward and away from the front portion of the rotating bed than a distance of a stroke of the first linear actuation device that causes the moveable counterweight unit to move.   
     
     
         12 . The mobile lift crane of  claim 11 , further comprising a second linear actuation device comprising a hydraulic cylinder; wherein the first linear actuation device comprises a hydraulic cylinder; and wherein the counterweight unit is operable to be moved the greater distance toward and away from the front portion of the rotating bed than the distance of the stroke of the first linear actuation device that causes the counterweight unit to move due to the movement of the second linear actuation device. 
     
     
         13 . The mobile lift crane of  claim 11 , wherein the counterweight unit is operable to be moved, during the pick, move, and set operation, to at least a first position in front of a rearmost portion of the rotating bed and a second position behind the rearmost portion of the rotating bed, wherein the rearmost portion of the rotating bed is configured not to move relative to the front portion of the rotating bed during the pick, move, and set operation. 
     
     
         14 . The mobile lift crane of  claim 11 , further comprising a mast mounted at a first end on the rotating bed. 
     
     
         15 . The mobile lift crane of  claim 14 , further comprising a tension member connected adjacent a second end of the mast that suspends the moveable counterweight unit. 
     
     
         16 . The mobile lift crane of  claim 11 , wherein the first linear actuation device comprises a rack and pinion assembly. 
     
     
         17 . 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; and a moveable counterweight unit; the method comprising:
 positioning the moveable counterweight unit at a first position toward a front portion of the rotating bed when a load is not on the hoist line;   positioning the moveable counterweight at a second position away from the front portion of the rotating bed the hoist line is supporting the load;   wherein the moveable counterweight unit is never supported by the ground during a pick, move, and set operation other than indirectly by the moveable ground engaging members on the carbody;   wherein a top of the mast is defined as a furthest back position on the mast from which any line or tension member supported from the mast is suspended; and   wherein a position of the moveable counterweight unit is defined as a center of gravity of a combination of at least one counterweight element and any holding tray to which the at least one counterweight element is attached, wherein the at least one counterweight element and any holding tray being treated as a single counterweight for purposes of determining the center of gravity.   
     
     
         18 . The method of  claim 17 , further comprising extending and retracting a hydraulic cylinder to move the moveable counterweight unit. 
     
     
         19 . The method of  claim 17 , further comprising extending and retracting a rack and pinion assembly to move the moveable counterweight unit. 
     
     
         20 . The method of  claim 17 , wherein the first position is in front of the top of the mast and the second position is rearward of the top of the mast.