Hydraulic control device for controlling a boom-swing frame combined motion in an excavator
A hydraulic control device includes first and second pumps, a swing control spool, a boom first-speed control spool, a boom second-speed control spool, a swing motor, a boom cylinder, a pilot control valve, and a confluence line for merging the hydraulic flow from the boom second-speed control spool with that from the boom first-speed control spool. Provided on the confluence line is a swing priority valve having an orifice for variably reducing the hydraulic flow supplied to the boom cylinder through the confluence line. A swing priority control line is provided to interconnect a pressure receiving part of the swing priority valve and a swing control pilot pressure signal line of the pilot control valve in such a manner that an aperture area of the variable orifice of the swing priority valve is reduced in proportion to the magnitude of a swing control pilot pressure of the pilot control valve.
1. A hydraulic control device for controlling a boom-swing frame combined motion in an excavator, comprising first and second fluid pumps (P 1 , P 2 ), a swing control spool ( 13 ) and a boom second-speed control spool ( 11 B) respectively provided on parallel lines ( 16 , 17 ) for receiving a hydraulic flow from the first pump (P 1 ) via the parallel lines ( 16 , 17 ), a boom first-speed control spool ( 11 A) for receiving a hydraulic flow from the second pump (P 2 ), a swing motor ( 1 ) actuated by the hydraulic flow supplied from the first pump (P 1 ) through the swing control spool ( 13 ), a boom cylinder ( 3 ) actuated by the hydraulic flows supplied from the first and second pumps (P 1 , P 2 ) through the boom second-speed control spool ( 11 B) and the boom first-speed control spool ( 11 A), a pilot control valve ( 24 ) for providing a pilot pressure to displace the swing control spool ( 13 ), the boom first-speed control spool ( 11 A) and the boom second-speed control spool ( 11 B), and a confluence line ( 25 ) for merging the hydraulic flow from the boom second-speed control spool ( 11 B) with that from the boom first-speed control spool ( 11 A), characterized by further comprising:
a swing priority valve ( 30 ) provided on the confluence line ( 25 ) and having a variable orifice ( 31 ) for variably reducing the hydraulic flow supplied to the boom cylinder ( 3 ) through the confluence line ( 25 ); and
a swing priority control line ( 27 ) interconnecting a pressure receiving part of the swing priority valve ( 30 ) and a swing control pilot pressure signal line of the pilot control valve ( 24 ) in such a manner that an aperture area of the variable orifice ( 31 ) of the swing priority valve ( 30 ) is reduced in proportion to the magnitude of a swing control pilot pressure of the pilot control valve ( 24 ).
2. The hydraulic control device as recited in claim 1 , wherein the variable orifice ( 31 ) of the swing priority valve ( 30 ) comprises a variable throttling section (X) for reducing the aperture area in proportion to the magnitude of a swing control pilot pressure in the swing priority control line ( 27 ) and a bleed-off section (Y) formed contiguous to the variable throttling section (X) for keeping the aperture area constant.
3. The hydraulic control device as recited in claim 1 , further comprising a selection switch ( 28 ) and a selection valve ( 29 ) provided on the swing priority control line ( 27 ) for selectively opening and shutting off the swing priority control line ( 27 ) in response to activation and deactivation of the selection switch ( 28 ).
4. The hydraulic control device as recited in claim 2 , further comprising a selection switch ( 28 ) and a selection valve ( 29 ) provided on the swing priority control line ( 27 ) for selectively opening and shutting off the swing priority control line ( 27 ) in response to activation and deactivation of the selection switch ( 28 ).