HYDRAULIC SYSTEM FOR A CONSTRUCTION MACHINE

摘要

Disclosed is a hydraulic system for a construction machine, which makes it possible to adjust the geometric position of a working device comprising a boom and an arm by means of a single manipulation lever, thereby enabling a leveling/flattening process to be conveniently performed. The hydraulic system includes: a working mode selection switch for selecting a leveling/flattening process; a boom driving switch valve for controlling the driving of a boom cylinder in response to a control signal from a first manipulation lever; an arm driving switch valve for controlling the driving of an arm cylinder in response to a control signal from a second manipulation lever; a shuttle valve including input parts that connect to both an electronic proportional control valve and to the first manipulation lever, respectively, and an output part connecting to the boom driving switch valve; and an electronic controller. When a manipulation signal according to a selection of the leveling/flattening process is inputted from the working mode selection switch to the electronic controller, the electronic controller detects and calculates a secondary signal pressure generated according to the manipulation of the second manipulation lever so as to control a discharge flow rate of a second hydraulic pump on the basis of a calculated value of the secondary signal pressure, and uses a secondary signal pressure generated by the electronic proportional control valve on the basis of the calculated value to switch on the boom driving switch valve by means of the shuttle valve, thereby controlling a discharge flow rate of a first hydraulic pump.