Hydraulic lifting unit for a lifting appliance

摘要

The invention relates to a hydraulic lifting unit for a lifting appliance, comprising a lifting piston, adjustably guided in a lifting cylinder and lifting or lowering a vertically adjustable chassis of the lifting appliance, and a pump piston mounted in a pump cylinder and adjustable by means of an actuating member. The pump piston draws in hydraulic medium from a reservoir during the suction stroke and feeds the hydraulic medium to the lifting cylinder during the subsequent working stroke. Provided in the lifting cylinder is a reversing member which, after a predetermined limit pressure is exceeded, causes the hydraulic medium to act on an additional cross-section of the lifting piston. A substantial reduction in the overall height of the lifting appliance is achieved according to the invention owing to the fact that the lifting piston is provided with an end recess towards the reversing member, which recess separates at the lifting piston an outer first end face and an inner, stepped, second end face, and that the reversing member is arranged in the bottom end area of the lifting cylinder in front of the first end face of the lifting cylinder, and the hydraulic medium, below the limit pressure, is fed only to the first end face or only to the second end face and, after the limit pressure is exceeded, to both the first end face and the second end face of the lifting piston.