Hydraulic circuit for construction machine

1. A hydraulic circuit for a construction machine, the hydraulic circuit being connected to a first pump, a second pump, a tank, and a plurality of actuators, the hydraulic circuit comprising:

a first unload passage connected to the first pump;

a second unload passage connected to the second pump;

a tank passage connected to the first unload passage, the second unload passage, and the tank;

a plurality of directional control valves connected to the plurality of actuators, respectively, and configured to feed an oil from the first pump or the second pump to the plurality of actuators and discharge to the tank the oil discharged from the plurality of actuators;

a negative control pressure sensing unit configured to output, as a negative control pressure, lower one of a pressure sensed at a first pressure sensing point in a most downstream portion of the first unload passage and a pressure sensed at a second pressure sensing point in a most downstream portion of the second unload passage;

a regulator configured to control discharge rates of the first pump and the second pump in association with each other in accordance with the negative control pressure output from the negative control pressure sensing unit;

a recycling passage connected to a recycling actuator included in the plurality of actuators; and

a sensing pressure rising passage connected to the recycling actuator,

wherein the plurality of directional control valves include a recycling directional control valve configured to feed discharge oil from the second pump to the recycling actuator,

the recycling passage is configured to perform pressure oil recycling, in which the recycling passage feeds recycling discharge oil discharged from the recycling actuator, to the actuator actuated with feeding of the discharge oil from the second pump, and

the sensing pressure rising passage is configured to feed a part of the recycling discharge oil to the first unload passage upstream of the first pressure sensing point or the second unload passage upstream of the second pressure sensing point when the pressure oil recycling is performed.

2. The hydraulic circuit for a construction machine according to claim 1 , wherein the sensing pressure rising passage includes a first sensing pressure rising passage configured to feed a part of the recycling discharge oil to the first unload passage upstream of the first pressure sensing point when the pressure oil recycling is performed.

3. The hydraulic circuit for a construction machine according to claim 2 , wherein the sensing pressure rising passage includes a second sensing pressure rising passage configured to feed a part of the recycling discharge oil to the second unload passage upstream of the second pressure sensing point when the pressure oil recycling is performed.

4. The hydraulic circuit for a construction machine according to claim 2 , wherein the first sensing pressure rising passage is disposed inside the recycling directional control valve.

5. The hydraulic circuit for a construction machine according to claim 2 , wherein the plurality of directional control valves include:

an arm-related directional control valve serving as the recycling directional control valve; and

a boom-related directional control valve disposed downstream of the arm-related directional control valve,

wherein the boom-related directional control valve has:

a boom-lowering position selected for lowering a boom, the boom-lowering position causing the first unload passage to be unblocked, and

a boom-raising position selected for raising the boom, the boom-raising position causing the first unload passage to be blocked or throttled.

6. The hydraulic circuit for a construction machine according to claim 1 , wherein the recycling directional control valve is a boom-related directional control valve or an arm-related directional control valve.

7. The hydraulic circuit for a construction machine according to claim 1 , wherein the sensing pressure rising passage is configured to feed a part of the recycling discharge oil to the second unload passage upstream of the second pressure sensing point when the pressure oil recycling is performed.