CONSTRUCTION MACHINE BOOM CONTROL HYDRAULIC DRIVE Russian patent published in 2000 - IPC

FIELD: construction engineering. SUBSTANCE: boom control hydraulic drive has pump, hydraulic cylinder, tank, pressure and drain main lines, safety valve, four-position seven-line spool with U-shaped channel provided with built-in normally open valve with throttle at side of rod space of hydraulic cylinder controlled by line connected with rod space of hydraulic cylinder. In neutral position, spool connects pump pressure line through overflow channel with tank, in second position, rod space of hydraulic cylinder is connected with piston space through U- shaped channel in spool connected also through controlled throttle with drain. Normally open valve with throttle set at side of rod space of hydraulic cylinder is built into U-shaped channel, valve being controlled by line connected with rod space of hydraulic cylinder. Pump pressure line is connected with drain, spool is locked in this position owing to hydraulic stop, and in third position, pump is connected with rod space of hydraulic cylinder, and piston space is connected with drain, while is fourth position pump is connected with piston space of hydraulic, and rod space is connected with drain. Constant pressure can be delivered to hydraulic stop piston from side opposite to spool. Working edge of valve can serve as throttle. In third position of spool, valve inlet and its control line can be connected with pump pressure line. EFFECT: possibility of relieving hydraulic drive from load separating free and forced lowering motions of boom, eliminating settlement. 4 cl, 2 dwg