Hydraulic circuit of construction machinery

A hydraulic circuit for a construction machine, said hydraulic circuit having an engine, 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 pressure oil fed 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

• one of said actuators, which is driven by pressure oil fed from said third hydraulic pump, is a specific actuator to which a larger load pressure is applied during driving thereof than those applied to remaining ones of said actuators, which are driven by said first and second hydraulic pumps, respectively,
• 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 quantities of states associated with respective torque consumptions by said first, second and third hydraulic pumps,
• said capacity control means for said first and second hydraulic pumps controls disulacements of said first and second hydraulic pumps on a basis of said quantities of states detected by said first, second and third state quantity detection means,
• said capacity control means for said third hydraulic pump controls a disulacement of said third hydraulic pump on a basis of said quantity of state 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 of 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 deliyery 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,
• wherein limiting means for applying a predetermined limit to a delivery pressure signal from said third hydraulic pump is arranged on said third guide line, wherein said limiting means is a reducing valve for limiting said delivery pressure signal to a pressure not higher than a predetermined setting pressure, and
• wherein said predetermined setting pressure for said limiting means is a delivery pressure from said third hydraulic pump when no control is performed on a delivery rate of said third hydraulic pump.

A hydraulic circuit for a construction machine, said hydraulic circuit having an engine, 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 pressure oil fed 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

• one of said actuators, which is driven by pressure oil fed from said third hydraulic pump, is a specific actuator to which a larger load pressure is applied during driving thereof than those applied to remaining ones of said actuators, which are driven by said first and second hydraulic pumps, respectively,
• 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 quantities of states associated with respective torque consumptions by said first, second and third 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 quantities of states 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 quantity of state 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 of 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,
• wherein limiting means for applying a predetermined limit to a delivery pressure signal from said third hydraulic pump is arranged on said third guide line,
• wherein said limiting means is a reducing valve for limiting said delivery pressure signal to a pressure not higher than a predetermined setting pressure, and
• wherein said predetermined setting pressure for said limiting means is a pressure corresponding to a value equal to a maximum input torque allotted to said third hydraulic pump.

A hydraulic circuit for a construction machine, said hydraulic circuit having an engine, 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 pressure oil fed 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

• one of said actuators, which is driven by pressure oil fed from said third hydraulic pump, is a specific actuator to which a larger load pressure is applied during driving thereof than those applied to remaining ones of said actuators, which are driven by said first and second hydraulic pumps, respectively,
• 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 quantities of states associated with respective torque consumptions by said first, second and third 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 quantities of states 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 quantity of state 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 of 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,
• wherein limiting means for applying a predetermined limit to a delivery pressure signal from said third hydraulic pump is arranged on said third guide line, wherein said limiting means is a reducing valve for limiting said delivery pressure signal to a pressure not higher than a predetermined setting pressure, and
• wherein said predetermined setting pressure for said limiting means is a pressure corresponding to a value slightly smaller than a maximum input torque allotted to said third hydraulic pump.