HYDRAULIC SYSTEM FOR CONSTRUCTION MACHINERY

摘要

Provided is a hydraulic system for a construction machinery capable of suppressing irregularity in the operation of the front structure not intended by the operator. The hydraulic system comprises: a regeneration motor 55 adapted to be driven by return fluid from a bottom port of a boom cylinder; a regeneration electric motor 54 adapted to convert rotary power of the regeneration motor into electric energy; return fluid control valves adapted to control the flow of the return fluid according to pilot pressure that is led from the pilot hydraulic pressure source 45 in conjunction with an operation on a boom control lever; solenoid valves for return fluid control valve adapted to control the pilot pressures for driving the return fluid control valves; and a malfunction prevention device adapted to be activated by pressure fluctuation caused by malfunction of a solenoid valve for return fluid control valve, for example, and interrupts the delivery of the pilot secondary pressure from the solenoid valve for return fluid control valve to the corresponding return fluid control valve.