초록 ▼

For enabling a boom to be smoothly raised during the triple combined operation of boom-up, arm-crowd and bucket-crowd in a hydraulic circuit system for a hydraulic excavator, in a first valve group of a hydraulic valve apparatus (12), a variable throttle valve (70) is installed in a feeder passage (

For enabling a boom to be smoothly raised during the triple combined operation of boom-up, arm-crowd and bucket-crowd in a hydraulic circuit system for a hydraulic excavator, in a first valve group of a hydraulic valve apparatus (12), a variable throttle valve (70) is installed in a feeder passage (32) of a bucket directional control valve (21) downstream of a load check valve (32a), and a secondary pressure C as a boom-up operation command is introduced through a line (71) to a pilot control sector (70a) of the variable throttle valve (70) which sector operates in the throttling direction, so that when the secondary pressure C is 0 or small, the variable throttle valve (70) is fully opened and, as the secondary pressure C increases, an opening area of the variable throttle valve (70) is reduced to restrict the flow rate of a hydraulic fluid supplied through the bucket directional control valve (21).

대표청구항 ▼

A hydraulic circuit system mounted on a hydraulic excavator having at least three kinds of working elements of a boom (300), an arm (301) and a bucket (302), and comprising a plurality of actuators including a boom cylinder (50) for driving said boom, an arm cylinder (52) for driving said arm and a

A hydraulic circuit system mounted on a hydraulic excavator having at least three kinds of working elements of a boom (300), an arm (301) and a bucket (302), and comprising a plurality of actuators including a boom cylinder (50) for driving said boom, an arm cylinder (52) for driving said arm and a bucket cylinder (54) for driving said bucket, said hydraulic circuit system further comprising at least two first and second hydraulic pumps (10, 11), and a hydraulic valve apparatus (12) for supplying hydraulic fluids from said first and second hydraulic pumps to at least said boom cylinder, said arm cylinder and said bucket cylinder therethrough, said hydraulic valve apparatus comprising a first boom directional control valve (22) for controlling a flow of the hydraulic fluid supplied from the first hydraulic pump (10) to said boom cylinder (50), a bucket directional control valve (21) for controlling a flow of the hydraulic fluid supplied from said first hydraulic pump to said bucket cylinder (54), a second boom directional control valve (26) for controlling a flow of the hydraulic fluid supplied from said second hydraulic pump to said boom cylinder (50), and an arm directional control valve (25) for controlling a flow of the hydraulic fluid supplied from said second hydraulic pump to said arm cylinder (52), said first boom directional control valve (22) and said bucket directional control valve (21) having feeder passages (33, 32) connected to said first hydraulic pump so that the hydraulic fluid from said first hydraulic pump is supplied in parallel to said first boom directional control valve and said bucket directional control valve, said second boom directional control valve (26) and said arm directional control valve (25) having feeder passages (37, 36a) connected to said second hydraulic pump so that the hydraulic fluid from said second hydraulic pump is supplied in parallel to said second boom directional control valve and said arm directional control valve, wherein said hydraulic circuit system for the hydraulic excavator further comprises: boom-up detecting means (71) for detecting the boom-up operation of moving said boom (300) upwardly, and auxiliary flow control means (70; 90) disposed in the feeder passage (32) of said bucket directional control valve (21) for restricting the flow rate of the hydraulic fluid supplied through said bucket directional control valve when the boom-up operation is detected by said boom-up detecting means.