HYDRAULIC DRIVING DEVICE OF CONSTRUCTION MACHINE

摘要

PROBLEM TO BE SOLVED: To provide a hydraulic driving device of a construction machine which can automatically switch an operation characteristic of a boom direction selector valve by detecting a condition where a hydraulic cylinder for a boom requires a driving pressure when the boom is operated downward. SOLUTION: The hydraulic driving device is provided with a control device 42 which controls an electromagnetic selector valve 40 so that a limit position of boom lowering side stroke of a directional control valve 31 for the boom is set in intermediate position L1 by selecting a pilot oil passage 38b having a pressure reducing valve 39 if a rod-side pressure of the hydraulic cylinder 20 for the boom detected by a pressure sensor 41 is less than a threshold value and so that the limit position of boom lowering side stroke of the directional control valve 31 for the boom is set in maximum position L2 by selecting the pilot oil passage 38a if the rod-side pressure of the hydraulic cylinder 20 for the boom detected by the pressure sensor 41 is threshold value or more. COPYRIGHT: (C)2011,JPO&INPIT