Patent ID: 7407038

Claim:
A lifting framework for an industrial truck, comprising: a guide mast; at least one extendible mast, the extendible mast being guided on the guide mast by rollers such that the extendible mast is movable in a vertical direction between a bottom end position and a top end position; and means for bracing the extendible mast with the guide mast, this bracing means taking effect, at least when the extendible mast is located in the top end position, so as to prevent the extendible mast from inclining in a lateral direction of the lifting framework relative to the guide mast, wherein the lifting framework includes a vertical mast, a first extendible mast guided on the vertical mast, and a second extendible mast guided on the first extendible mast, wherein the framework includes a lifting-drive device configured such that, in a first instance, the first extendible mast, together with the second extendible mast, is raised relative to the vertical mast and, thereafter, the second extendible mast is raised relative to the first extendible mast, wherein the lifting-drive device includes a hydraulic telescopic cylinder located at each side of the lifting framework, the telescopic cylinders comprising a cylinder tube, a first piston moveable in the cylinder tube, and a second piston moveable in the first piston, wherein the first piston of the telescopic cylinder directly raises the first extendible mast relative to the vertical mast, and the second piston of the telescopic cylinder directly raises the second extendible mast relative to the first extendible mast, wherein the cylinder tube of the telescopic cylinder is connected to the vertical mast, the first piston of the telescopic cylinder is connected to the first extendible mast, and the second piston of the telescopic cylinder is connected to the second extendible mast, and wherein a stop is located in each cylinder tube and is configured to engage the first piston, and wherein pressure in the cylinder tube pushes on a bottom surface of the first piston to move the first piston until the first piston engages the stop, at which time fluid pressure on a bottom surface of the second piston moves the second piston in the first piston.