HYDRAULIC DRIVE UNIT FOR CIVIL ENGINEERING AND CONSTRUCTION MACHINERY

摘要

A hydraulic drive unit provided with a hydraulic pump (11, 11 A), a plurality of actuators (4-6) driven by a pressure oil supplied from the hydraulic pump, which include an arm cylinder (5) and a boom cylinder (4), a plurality of flow rate control valves (12, 14, 16) adapted to control the flows of the pressure oil supplied to these actuators, which include an arm direction control valve (14) and a boom direction control valve (12), and a plurality of divided flow compensating valves (13, 15, 17; 13A, 15A, 17A) adapted to control the pressure differences across these flow rate control valves and having driving means (13d, 15d, 17d; 13e, 13f, 15e, 15f, 17e, 17F) for setting target levels of pressure differences across the corresponding flow rate control valves. It is characterized in that it has a first means (21) for detecting an arm crowding action made by driving the arm cylinder (5), and second means (24,30,31;24,30A,31) for controlling the driving means (15d, 15f) for the corresponding divided flow compensating valves (15; 15A) so that the target level of pressure difference across at least the flow rate control vale (14) related to the arm cylinder decrease when an arm crowding action is detected.