Patent ID: 7356991

Claim:
A hydraulic control device of an excavator comprising a first hydraulic pump ( 1 ), a second hydraulic pump ( 2 ), a swing control valve ( 6 ) in fluid communication with the first hydraulic pump ( 1 ) for controlling hydraulic flow from the first hydraulic pump ( 1 ) to a swing motor ( 14 ), a boom high-speed control valve ( 7 ) disposed at downstream of the swing control valve ( 6 ) and in fluid communication with the first hydraulic pump ( 1 ) via a pressured fluid supply line ( 8 ) for controlling hydraulic flow from the first hydraulic pump ( 1 ) to boom cylinders ( 15 ), and a boom low-speed control valve ( 11 ) for controlling hydraulic flow from the second hydraulic pump ( 2 ) to the boom cylinders ( 15 ), further comprising: a working-on-slope detecting means ( 27 ) for detecting a tilt angle of the excavator and outputting a working-on-slope signal if the tilt angle detected is greater than a predetermined value; and a swing priority valve ( 20 ) provided on the pressured fluid supply line ( 8 ) for the boom high-speed control valve ( 7 ) and throttling the hydraulic flow rate supplied to the boom high-speed control valve ( 7 ) from the first hydraulic pump ( 1 ), thereby relatively increasing the hydraulic flow rate to the swing control valve ( 6 ), in case of the working-on-slope signal being provided from the working-on-slope detecting means ( 27 ) and at the same time a swing control pilot pressure (SW 1 ,SW 2 ) for shifting the swing control valve ( 6 ) being provided thereto.