Hydraulic control device and construction machinery including same
A hydraulic control device includes: a hydraulic pump connected in parallel to steering and boom cylinders; a steering control valve that controls the direction of operating oil flowing through the steering cylinders; a boom control valve that connects the hydraulic pump to a tank when the valve is at a neutral position and controls the direction of the oil flowing through the boom cylinders when the valve is at an offset position; a meter-in pressure compensator that increases flow rate of the oil flowing through a variable restrictor of the steering control valve in accordance with pressure in front of and behind the restrictor; and a bleed-off pressure compensator that decreases flow rate of the oil flowing through the boom control valve in accordance with the increase in pressure of the oil flowing through the steering cylinders to maintain the predetermined pressure of the oil in the steering control circuit.
1. A hydraulic control device comprising:
a steering device;
a plurality of work machine actuators;
a hydraulic pump connected to the steering device and the plurality of work machine actuators so as to supply operating oil to the steering device and the work machine actuators in parallel;
a steering control valve configured to cause a spool thereof to move to control a direction of the operating oil flowing to the steering device;
a plurality of actuator control valves provided so as to correspond to the respective work machine actuators, each of the actuator control valves being configured to connect the hydraulic pump to a tank when the actuator control valve is located at a neutral position and control the direction of the operating oil flowing through the corresponding work machine actuator when the actuator control valve is located at an offset position;
a meter-in pressure compensator including a first pilot port and a second pilot port and provided upstream of a steering control circuit including the steering control valve, to control a flow of the operating oil, supplied to the steering control valve, to maintain differential pressure between pressure of the operating oil at an upstream side of the steering control valve and pressure of the operating oil at a downstream side of the steering control valve at constant pressure regardless of an opening degree of the spool of the steering control valve, the pressure of the operating oil at the downstream side of the steering control valve being input as first pilot pressure to the first pilot port and corresponding to load pressure of the steering device, the pressure of the operating oil at the upstream side of the steering control valve being input as second pilot pressure to the second pilot port against the first pilot pressure; and
a bleed-off pressure compensator including a third pilot port and a fourth pilot port and provided upstream of a work machine control circuit including the plurality of actuator control valves, to control the flow of the operating oil supplied to the actuator control valves, the pressure of the operating oil at the downstream side of the steering control valve being input as third pilot pressure to the third pilot port and corresponding to the load pressure of the steering device, ejection pressure of the hydraulic pump being input as fourth pilot pressure to the fourth pilot of port against the third pilot pressure, wherein:
the meter-in pressure compensator and the bleed-off pressure compensator are connected to the hydraulic pump in parallel with each other,
when the steering device is operated, the load pressure of the steering device during the operation is input to the first pilot port of the meter-in pressure compensator to act against the pressure of the operating oil at the upstream side of the steering control valve, and the meter-in pressure compensator therefore operates to open a passage through which the hydraulic pump and the steering control valve communicate with each other, while adjusting an opening degree of the passage, through which the hydraulic pump and the steering control valve communicate with each other, in accordance with differential pressure between the load pressure input to the first pilot port and the pressure of the operating oil at the upstream side of the steering control valve which pressure is input to the second pilot port, and
when the steering device is operated, the load pressure of the steering device during the operation is input to the third pilot port of the bleed-off pressure compensator to act against the ejection pressure of the hydraulic pump, and the bleed-off pressure compensator therefore operates to close a passage through which the hydraulic pump and the actuator control valve communicate with each other, while adjusting an opening degree of the passage, through which the hydraulic pump and the actuator control valve communicate with each other, in accordance with differential pressure between the load pressure input to the third pilot port and the ejection pressure input to the fourth pilot port.
2. The hydraulic control device according to claim 1 , wherein the bleed-off pressure compensator operates so as to:
decrease the flow rate of the operating oil, supplied to the actuator control valve, in accordance with an increase in the pressure of the operating oil supplied to the steering device; and
cause the pressure of the operating oil, ejected from the hydraulic pump, to become pressure higher than the pressure of the operating oil necessary to drive the steering device.
3. The hydraulic control device according to claim 2 , further comprising a restrictor interposed between the actuator control valve and the tank, wherein
the hydraulic pump is a variable displacement pump configured to adjust an ejection flow rate thereof in accordance with the pressure of the operating oil flowing between the actuator control valve and the restrictor.
4. The hydraulic control device according to claim 3 , wherein the meter-in pressure compensator utilizes the operating oil at the upstream side of the steering control valve and the operating oil at the downstream side of the steering control valve as two different pilot oil acting against each other,
the hydraulic control device further comprising
a steering relief valve configured to discharge the pilot oil, which is the operating oil at the downstream side, to the tank when the pressure of the pilot oil, which is the operating oil at the downstream side, becomes predetermined pressure.
5. A construction machinery comprising the hydraulic control device according to claim 4 .
6. A construction machinery comprising the hydraulic control device according to claim 3 .
7. The hydraulic control device according to claim 2 , wherein the meter-in pressure compensator utilizes the operating oil at the upstream side of the steering control valve and the operating oil at the downstream side of the steering control valve as two different pilot oil acting against each other,
the hydraulic control device further comprising
a steering relief valve configured to discharge the pilot oil, which is the operating oil at the downstream side, to the tank when the pressure of the pilot oil, which is the operating oil at the downstream side, becomes predetermined pressure.
8. A construction machinery comprising the hydraulic control device according to claim 7 .
9. A construction machinery comprising the hydraulic control device according to claim 2 .
10. The hydraulic control device according to claim 1 , further comprising a restrictor interposed between the actuator control valve and the tank, wherein
the hydraulic pump is a variable displacement pump configured to adjust an ejection flow rate thereof in accordance with the pressure of the operating oil flowing between the actuator control valve and the restrictor.
11. The hydraulic control device according to claim 10 , wherein the meter-in pressure compensator utilizes the operating oil at the upstream side of the steering control valve and the operating oil at the downstream side of the steering control valve as two different pilot oil acting against each other,
the hydraulic control device further comprising
a steering relief valve configured to discharge the pilot oil, which is the operating oil at the downstream side, to the tank when the pressure of the pilot oil, which is the operating oil at the downstream side, becomes predetermined pressure.
12. A construction machinery comprising the hydraulic control device according to claim 11 .
13. A construction machinery comprising the hydraulic control device according to claim 10 .
14. The hydraulic control device according to claim 1 , wherein the meter-in pressure compensator utilizes the operating oil at the upstream side of the steering control valve and the operating oil at the downstream side of the steering control valve as two different pilot oil acting against each other,
the hydraulic control device further comprising
a steering relief valve configured to discharge the pilot oil, which is the operating oil at the downstream side, to the tank when the pressure of the pilot oil, which is the operating oil at the downstream side, becomes predetermined pressure.
15. A construction machinery comprising the hydraulic control device according to claim 14 .
16. A construction machinery comprising the hydraulic control device according to claim 1 .