MX2008004549A - Mobile lift crane with variable position counterweight. - Google Patents

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 is never supported by the ground during crane pick, move and set operations other than indirectly by the ground engaging members on the carbody. The linear actuation device can include at least one rack and pinion assembly or hydraulic cylinder. In another embodiment, the crane comprises a counterweight movement structure including a rack and pinion assembly having a housing and a rack, the rack having a rectangular cross section with first an d second sides opposite one another and third and fourth sides opposite one another, and having teeth on the first side and second sides, and at least first and third pinion gears engaged with the teeth on the first side of the rack and second and fourth pinion gears engaged with the teeth on the second side of the rack, and wherein each pinion gear is driven by a separate hydraulic motor, and wherein the motor driving the first pinion gear is mounted on the housing adjacent an opposite side of the rack from the motor driving the third pinion gear, and wherein the motor driving the second pinion gear is mounted on the housing adjacent an opposite side of the rack from the motor driving the fourth pinion gear. In another embodiment the crane includes a counterweight support structure attached to the counterweight unit. The counterweight support structure includes at least two ground engaging members that can provide support to the counterweight in the event of a sudden release of the l oad. The support structure comprises a telescoping structure connected to and between the ground engaging members such that the distance between the ground engaging members can be adjusted between a first and second position.