HYDRAULIC DRIVE OF MACHINERY

摘要

To rapidly stop a upperstructure even though a relief pressure is lowered due to an abnormality in a hydraulic device included in a swing motor driving circuit while it is intended to stop the upperstructure when a predetermined delay time has passed since a swing operation tool is brought back to a neutral position. According to the present invention, configuration is made so that there are provided: a first choke 34 for controlling a parking brake 29 to apply a braking force to a swing motor 16 when a predetermined delay time T has passed since a swing operation tool 15 is brought back to a neutral position in a state where the swing operation tool 15 is connected to a pilot pump 12; and an on-off valve 36 and a second choke 37 for controlling the parking brake 29 to apply a braking force to the swing motor 16 when a delay time t shorter than the predetermined delay time T has passed since the swing operation tool 15 is brought back to the neutral position and the swing operation tool 15 is disconnected from the pilot pump 12.