Dual hydraulic, parallelogram arm wheelchair lift

Abstract

An improved dual hydraulic, parallelogram arm wheel chair lift assembly for use in commercial vehicles, such as vans or buses. The lift assembly includes a platform connected at one end to a pair of parallelogram linkages, each of which is provided with a power-up, gravity-down hydraulic cylinder for pulling the parallelogram linkages and platform from a lowered loading position to an immediate transfer position, and thence to a folded, generally upright stored position. The pulling action of the hydraulic cylinders with hydraulic fluid working on the rod side reduces side loading on the piston head and wear on pivot pins of the parallelogram linkages. The hydraulic cylinders are self-bleeding of air during gravity down operation to reduce spongy and jerky operation. The lift assembly has an improved base member employing an additional base support plate to form a box structure to increase strength and reduce moment-induced bending of the mounting plate. Tie downs are also provided to the side supports to assist in reducing sway movement of the side supports. An improved, highly precise microswitch trigger assembly mounted independent of arm pivot pins and large bearing surface fixed arm pivot pins are disclosed. The hydraulic cylinders are mounted base down and act at right angles to the conventional mounting scheme, with full extension at lower load position and fully closed (retracted) at the upper stowed position.