Apparatus for lifting a heavy load with respect to the bed of a truck

An apparatus adapted for attachment to a truck, the truck having a frame, front and rear ends, and right and left sides, and the apparatus being adapted for attachment to the frame near the truck's rear end for the purpose of lifting a heavy load with respect to the frame, comprising:

• a. a generally planar base adapted for attachment to the frame of a truck in the vicinity of the truck's rear end;
• b. a platform positioned above and connected to the base with a pair of four-bar linkages, and one of said pair of linkages being associated with the right and left sides of the truck, respectively, and each of said linkages including at least one set of rotatable and approximately parallel legs, and said platform having a first, low position at which it is in close proximity to the base, and said platform having a second, high position at which it is appreciably higher than the base;
• c. a double-acting hydraulic cylinder having a barrel and an extensible rod, and the hydraulic cylinder having two ends and a longitudinal axis between said two ends, and the hydraulic cylinder being functionally anchored at one of its ends to the base and connected at its other end to the platform, and the platform being connected to the base in such a way that extension of the rod will cause the platform to be raised with respect to the base, and the cylinder and its associated rod being sufficiently long that the platform will both rise and translate rearwardly with respect to the base when the platform is in its low position and the cylinder is pressurized;
• d. means for selectively pressurizing the hydraulic cylinder to cause extension and retraction of the rod;
• and
• e. a bell crank assembly interjected between the barrel end of the hydraulic cylinder and the base, such that forces generated when the hydraulic cylinder is pressurized will be passed through the bell crank assembly to the base, and the bell crank assembly having a bell crank with two diverging arms, and a first one of said two arms being effective to apply a lifting force to the platform when the platform is near its first, low position and the cylinder is pressurized, and the other arm being effective to apply a lifting force to the platform when the cylinder is pressurized and the platform is substantially removed from the first, low position, and the platform being in load-supporting contact with the first arm of the bell crank only when the platform is near its first, low position.