HYDRAULIC DRIVING SYSTEM IN CONSTRUCTION MACHINE.

摘要

A hydraulic driving system in a construction machine comprising: a group of changeover valves (52) including a plurality of center bypass type directional changeover valves (9-13) for controlling pressure oil supplied from a hydraulic pump (2) to a plurality of hydraulic actuators (44-48); a center bypass line (2a) for serially connecting center bypasses of a plurality of directional changeover valves to a low pressure circuit (29); a plurality of bleedoff variable throttle valves (56) respectively provided on the center bypass of the plurality of directional changeover valves, for decreasing the opening area in accordance with an increase in the control inputs of the associated directional changeover valves; a pressure compensation valve (20) provided on the center bypass line; and first and second pressure difference detecting lines (22, 24) connected to the center bypass line, for transmitting the pressure differences to the pressure compensation valve. One (22) of the first and second pressure difference detecting lines (22, 24) is connected to the center bypass line (2a) at a position between the bleedoff variable throttle means (56) of at least one specific valve (9) and the bleedoff variable throttle means (56) of the other directional changeover valve (10) adjoining the aforesaid directional changeover valve (9), and the other (24) of the first and second pressure difference detecting lines (22, 24) is connected to the center bypass line (2a) at a position of detecting the pressure difference across the bleedoff throttle means of at least the other directional changeover valves, whereby load compensation function is given to the directional changeover valves (10-13) of the actuators (45-48) requiring load compensation characteristics and pressure control function is given to the directional changeover valve (9) of the actuator (44) requiring pressure control characteristics.