Patent ID: 9618019
Date: 2017-04-11
CPC Classifications: B60T,E02F,F15B

Claim:
1. A hydraulic control apparatus for a construction machine, comprising: a pilot pump configured to provide a pilot hydraulic pressure; a swing motor configured to swingably rotate an upper swing structure; a swing motor brake coupled to the swing motor to brake the swing motor at a normal condition and configured to be released to rotate the swing motor when the pilot hydraulic pressure is supplied thereto; a brake control valve installed between the pilot pump and the swing motor brake and configured to control a direction of the pilot hydraulic pressure to allow for the braking and release of the swing motor brake; a controller configured to receive a command signal for driving the swing motor and apply the received command signal to the brake control valve; a relief valve installed between the brake control valve and the pilot pump and, if a hydraulic pressure that exceeds a predetermined relief pressure is generated between the brake control valve and the pilot pump, configured to allow the hydraulic pressure to be returned to a hydraulic tank; and a drain control valve installed in parallel with the brake control valve and configured to be opened or closed so that the pilot hydraulic pressure is selectively returned to the hydraulic tank depending on a state of the brake control valve, wherein if the brake control valve is shifted to rotate the swing motor, the drain control valve is closed, while if the brake control valve is shifted to brake the swing motor, the drain control valve is opened so that the hydraulic pressure is drained to the hydraulic tank without passing through the relief valve.