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A service valve circuit of a hydraulic excavator connected beforehand for use in controlling a special attachment in addition to a prescribed actuator control valve. The service valve circuit comprises a confluence valve 17 for performing electromagnetic proportional flow rate control, disposed in a

A service valve circuit of a hydraulic excavator connected beforehand for use in controlling a special attachment in addition to a prescribed actuator control valve. The service valve circuit comprises a confluence valve 17 for performing electromagnetic proportional flow rate control, disposed in a confluence circuit 16 in communication with the section between inflow circuits 3F and 3R of two variable pumps 2F and 2R, an electrical switch 21 for switching the confluence valve 17 on or off according to a required flow rate and a volume 22 for adjusting the quantity of flow after passing through a confluence valve 17 in a range of flow for a maximum of one to two pumps. Since the requirement of confluence with respect to a required quantity of flow for a special attachment e and the quantity of confluence are set in advance, there will be no excess or shortage of the quantity of confluence. Therefore, the adjustment of flow rate using the number of rotations of an engine is not required and the action will not be slowed down even if switched from a special attachment control to a pivoting or traveling control.

대표청구항 ▼

Apparatus comprising a first variable capacity type hydraulic pump having an output, a second variable capacity type hydraulic pump having an output, a first group of control valves with each of the control valves in said first group being connected to a respective one of a first plurality of hydrau

Apparatus comprising a first variable capacity type hydraulic pump having an output, a second variable capacity type hydraulic pump having an output, a first group of control valves with each of the control valves in said first group being connected to a respective one of a first plurality of hydraulic actuators, a second group of control valves with each of the control valves in said second group being connected to a respective one of a second plurality of hydraulic actuators, a first hydraulic supply line connected between the outlet of said first variable capacity type hydraulic pump and said first group of control valves to supply hydraulic fluid to the first plurality of hydraulic actuators connected to the first group of control valves, a second hydraulic supply line connected between the outlet of said second variable capacity type hydraulic pump and said second group of control valves to supply hydraulic fluid to the second plurality of hydraulic actuators connected to the second group of control valves, and a confluence circuit connected to said first hydraulic supply line and to said second hydraulic supply line, said confluence circuit having an electromagnetically actuated confluence valve positioned therein for performing proportional flow rate control in the confluence circuit when confluence is desired; wherein said confluence valve comprises an electromagnetically actuated piloting valve and a proportional flow rate control valve; said proportional flow rate control valve having first and second control inputs and first and second flow ports, said first flow port of said proportional flow control valve being connected to said first hydraulic supply line, said second flow port of said proportional flow control valve being connected to said second hydraulic supply line; said piloting valve having a first position, in which it provides fluid communication between said first hydraulic supply line and said first control input of said proportional flow control valve, and a second position in which the fluid communication between said first hydraulic supply line and said first control input of said proportional flow control valve is interrupted; said second control input of said proportional flow control valve being connected to said second flow port of said proportional flow control valve.