Patent ID: 7076947
Filing Date: 2006-07-18
Classification: E02F,F04B,F15B

Abstract:
1. A hydraulic circuit having an engine, a pilot hydraulic pump, a first hydraulic pump of a variable displacement type, second hydraulic pump of the variable displacement type and third hydraulic pump, all of which are drivable by said engine, capacity control means for controlling displacements of said first hydraulic pump and second hydraulic pump, plural actuators drivable by hydraulic pressures from said first, second and third hydraulic pumps, and plural directional control valves for controlling flows of pressure oil to be fed to said actuators, wherein said third hydraulic pump is a hydraulic pump of the variable displacement type, said hydraulic circuit is provided with capacity control means for said third hydraulic pump to control a displacement of said third hydraulic pump and also with first, second and third state quantity detection means for detecting delivery pressures from said first, second and third hydraulic pumps as quantities of states of the respective hydraulic pumps, said capacity control means for said first and second hydraulic pumps controls displacements of said first and second hydraulic pumps on a basis of said delivery pressures detected by said first, second and third state quantity detection means, said capacity control means for said third hydraulic pump controls a displacement of said third hydraulic pump on a basis of said delivery pressures detected by said third state quantity detection means, said first state quantity detection means comprises a first guide line for guiding a delivery pressure from said first hydraulic pump to said capacity control means for said first and second hydraulic pumps, said second state quantity detection means comprises a second guide line for guiding a delivery pressure from said second hydraulic pump to said capacity control means for said first and second hydraulic pumps, said third state quantity detection means comprises a third guide line for guiding a delivery pressure from said third hydraulic pump to said capacity control means for said first and second hydraulic pumps and a fourth guide line for guiding the delivery pressure from said third hydraulic pump to said capacity control means for said third hydraulic pump, said capacity control means for said first and second hydraulic pumps and said capacity control means for said third hydraulic pump control input torques to said first, second and third hydraulic pumps on a basis of said delivery pressures from the respective hydraulic pumps as detected in said first, second, third and fourth guide lines such that a sum of said input torques to said first, second and third hydraulic pumps does not exceed an output force power of said engine a first proportional solenoid valve arranged on a line, through which said capacity control means for said first and second hydraulic pumps are connected with the pilot hydraulic pump to control a delivery pressure from said pilot hydraulic pump, a second proportional solenoid valve arranged on a line, through which said capacity control means for said third hydraulic pump is connected with the pilot hydraulic pump to control the delivery pressure from said pilot hydraulic pump, a controller receiving signals from said first, second and third state quantity detection means to compute and output drive signals to said first and second proportional solenoid valves; said capacity control means for said first and second hydraulic pumps is operated by a pilot pressure reduced by said first proportional solenoid valve, and said capacity control means for said third hydraulic pump is operated by a pilot pressure reduced by said second proportional solenoid valve, wherein said construction machine is further provided with a fourth state quantity detection means for detecting a quantity of state associated with operation of said construction machine, and based on a signal from said fourth state quantity detection means, said controller computes and outputs a drive signal to said first and second proportional solenoid valve; and wherein said construction machine is a hydraulic excavator provided with front members comprising a boom, an arm and an attachment, and said fourth state quantity detection means is attitude detection means for detecting attitudes of said front members.