Patent ID: 6810993
Filing Date: 2004-11-02
Classification: B66F

Abstract:
An aerial lift apparatus comprising:a support unit; a lower boom and an upper boom, said lower boom being pivotally connected by a lower pivot unit to said support unit and extending outwardly therefrom, said upper boom being pivotally connected to the outer end of said lower boom by an upper pivot unit and adapted to be angularly oriented from a collapsed position adjacent to the lower boom and in an extended position raised with respect to said lower boom for locating the outer end of said upper boom in a raised position relative to said lower boom; a lower boom hydraulic control unit connected to said support unit and to said lower boom for raising and lowering of the lower boom about its pivot axis; an upper boom compensating hydraulic unit including an upper boom direct positioning unit for presetting of the angular orientation of the upper boom relative to the lower boom, said upper boom compensating hydraulic unit further including a compensating hydraulic unit interconnected between said lower boom and said upper boom, wherein said upper boom compensating hydraulic unit including a single cylinder having a first open end and a second closed end with a piston and rod unit mounted within and extending from a first end of said cylinder and defining a positioning chamber at the rod end and further defining a compensating chamber at a base end formed by said second closed end of said cylinder, said upper boom compensating hydraulic unit including a flow circuit having a hydraulic fluid supply input and output, said flow circuit including control valve assemblies connected to said positioning chamber and to said compensating chamber of said upper boom compensating hydraulic unit and to said lower boom hydraulic unit to provide a selected interrelated movement of said upper boom relative to said lower boom in accordance with the movement of said lower boom about said pivot connection to said support unit, with said control valve assembly including a first valve unit connected to the rod end and a second valve unit connected to the base end of said upper boom compensating single cylinder, said first and second valve units being interconnected into circuits with first and second valve units connected to the boom cylinder and said lower boom fluid supply for providing said positioning of the lower boom with automated and direct repositioning compensation of the upper boom, with each of said valve units including a gated holding valve in combination with a bypass check valve to selectively provide for interrelated fluid control to and from said compensating cylinder and to and from said lower boom cylinder.