HYDRAULIC DRIVE SYSTEM

摘要

A hydraulic drive system comprises a flow control valve (21) having variable restrictors (19-22) to control a flow rate of the hydraulic fluid, a pressure compensating valve (17) for holding constant a differential pressure across the variable restrictor (19, 20), and a recovery circuit (40) having a recovery line (42) with a check valve (43) allowing only a flow of the hydraulic fluid toward the supply line (23). Through the recovery circuit (40) hydraulic fluid returns to the supply line (23) at a portion between the pressure compensating valve (17) and the variable restrictor (19, 20) upon controlling by the variable restrictor (21, 22). A third variable restrictor (41) disposed in the return line (26) controls a recovery pressure of the hydraulic fluid returned to the supply line (23) and is arranged to change its restriction amount dependent upon an input amount of the flow rate control valve (11).