HYDRAULIC DRIVE DEVICE FOR CONSTRUCTION MACHINERY

摘要

To cope with a variety of flow rate balance required of two actuators flexibly in combined operations driving two actuators of high maximum demanded flow rates at the same time while suppressing the wasteful energy consumption caused by the throttle pressure loss in a pressure compensating valve, the arrangement is such that when the demanded flow rate of a boom cylinder 3a is lower than a prescribed flow rate, the boom cylinder 3a is driven only by hydraulic fluid delivered from a single flow type main pump 202 and when the demanded flow rate of the boom cylinder 3a is higher than the prescribed flow rate, the hydraulic fluid delivered from the single flow type main pump 202 and hydraulic fluid delivered from a first delivery port 102a of a split flow type main pump 102 are merged together and the boom cylinder 3a is driven by the merged fluids. Further, when the demanded flow rate of an arm cylinder 3b is lower than a prescribed flow rate, the arm cylinder 3b is driven only by hydraulic fluid delivered from a second delivery port 102b of the split flow type main pump 102 and when the demanded flow rate of the arm cylinder 3b is higher than the prescribed flow rate, hydraulic fluid delivered from the first delivery port 102a and hydraulic fluid delivered from the second delivery port 102b are merged together and the arm cylinder 3b is driven by the merged fluids.