In general, a hydraulic control valve is used to control hydraulic fluid that is supplied from hydraulic pumps to actuators that drive working devices, such as a boom and an arm, of a construction machine, such as an excavator. Particularly, in driving working devices, such as the boom and the arm, the driving speed of the working devices can be increased by making the hydraulic fluid supplied from a plurality of hydraulic pumps in a confluent state.
A hydraulic control valve for a construction machine in the related art, as shown in FIGS. 1 and 2, includes a first boom block 1 forming a supply path therein to supply hydraulic fluid of a first hydraulic pump P1 to a boom cylinder 6; a second boom block 2 making close contact with the first boom block 1 to be vertically symmetric to the first boom block 1 and forming a supply path therein to supply hydraulic fluid of a second hydraulic pump P2 to the boom cylinder 6; a first boom spool 3 installed in the supply path 16 of the first hydraulic pump P1 to be shifted to control a start, stop, and direction change of the boom cylinder 6; a second boom spool 4 installed in the supply path 31 of the second hydraulic pump P2 to be shifted to make the hydraulic fluid of the second hydraulic pump P2 join the hydraulic fluid of the first hydraulic pump P1 to increase the driving speed of the boom cylinder 6; and poppets 9 elastically supported by springs 8, respectively, to open and close the supply path 16 of the first hydraulic pump P1 and the supply path 31 of the second hydraulic pump P2.
In the drawing, the reference numerals “12” and “15” denote guides on which springs 13 are seated, which are oppositely fixed to end portions of the first boom spool 3 and the second boom spool 4, and “14” denotes stoppers arranged between the guides 12 and 15 of the first boom spool 3 and the second boom spool 4, respectively, to limit strokes of the first boom spool 3 and the second boom spool 4.
Hereinafter, the operation of the hydraulic control valve as constructed above will be described.
(A) The operation of the hydraulic control valve during a boom-up operation will be described.
As shown in FIG. 1, if pilot signal pressure (pressure that exceeds the predetermined set pressure of a spring 13) for a boom-up operation is supplied to a pilot b port 28 of the cover 10 to lift up the boom, the first boom spool 3 that is slidingly coupled in the first boom block 1 is shifted to the left side.
At this time, the high-pressure hydraulic fluid in the supply path 16 of the first hydraulic pump P1 pushes the poppet 9 that is elastically supported by the spring 8 upward to be supplied to the bridge path 17, and is supplied to the cylinder path 19 through a notch 18 of the first boom spool 3 that is shifted to the left side.
At the same time, as the pilot signal pressure (pressure that exceeds the predetermined set pressure of the spring 13) for the boom-up operation is supplied to a pilot b′ port 29 of the cover 10, the second boom spool 4 that is slidingly coupled in the second boom block 2 is shifted to the left side.
At this time, the high-pressure hydraulic fluid in the supply path 31 of the second hydraulic pump P2 pushes the poppet p that is elastically supported by the spring 8 downward to be supplied to the bridge path 32, and is supplied to the cylinder path 34 through a notch 33 of the second boom spool 4 that is shifted to the left side.
The hydraulic fluid supplied to the cylinder path 34 joins the hydraulic fluid in the cylinder path 19 on the side of the first boom block 1, and then is supplied to a large chamber of the boom cylinder 6 through an actuator B port 20 and a boom large chamber path 21. Through this, the boom is lifted up.
At this time, leakage of the high-pressure hydraulic fluid is prevented by an O-ring 36 provided on a mutual close-contact surface of the first and second boom blocks 1 and 2.
On the other hand, the hydraulic fluid that returns from a small chamber of the boom cylinder 6 passes through the boom small chamber path 22, the actuator A port 23, and the cylinder path 24 in order, and returns to the tank path 26 through the notch 25 of the first boom spool 3 that is shifted to the left side. Accordingly, the boom is lifted up.
At this time, since the amount of hydraulic fluid that returns from the small chamber of the boom cylinder 6 is equal to or less than a half of the hydraulic fluid of the large chamber, the hydraulic fluid returns to the hydraulic tank only through the first boom spool 3. At this time, in the second boom spool 4 that is shifted to the left side, the notch that communicates with the tank path 37 is not formed, and the hydraulic fluid does not return to the hydraulic tank through the second boom spool 4.
At this time, if the pressure that exceeds the predetermined set pressure is applied to the boom cylinder 6, relief valves 5, which are installed on the actuator A port 23 and the actuator B port 20, make the hydraulic fluid having the excessive pressure return to the hydraulic tank to maintain the predetermined set pressure, and thus the boom cylinder 6 can be protected.
(B) The operation of the hydraulic control valve during a boom-down operation will be described.
As shown in FIG. 1, if pilot signal pressure for a boom-down operation is supplied to a pilot a port 27 and a′ port 30, the first boom spool 3 that is slidingly coupled in the first boom block 1 and the second boom spool 4 that is slidingly coupled in the second boom block 2 are shifted to the right side.
At this time, the high-pressure hydraulic fluid in the supply path 16 of the first hydraulic pump P1 pushes the poppet 9 that is elastically supported by the spring 8 upward to be supplied to the bridge path 17, and is supplied to the cylinder path 24 through the notch 38 of the first boom spool 3 that is shifted to the right side.
Further, the high-pressure hydraulic fluid in the supply path 31 of the second hydraulic pump P2 pushes the poppet 9 that is elastically supported by the spring 8 downward to be supplied to the bridge path 32. By contrast, in the second boom spool 4 that is shifted to the right side, the notch that communicates with the bridge path 32 is not formed, and thus the high-pressure hydraulic fluid in the supply path 31 of the second hydraulic pump P2 is not supplied to the cylinder path 39 through the second boom spool 4.
Accordingly, only the hydraulic fluid on the side of the first hydraulic pump P1 is supplied to the small chamber of the boom cylinder 6 through the actuator A port 23 and the boom small chamber path 22.
On the other hand, the hydraulic fluid, which returns from the large chamber of the boom cylinder 6 passes through the boom large chamber path 21, the actuator B port 20, and the cylinder path 19 in order, and then dispersedly returns to the tank path 42 and the tank path 43 through the notch 40 formed on the first boom spool 3 that is shifted to the right side and the notch 41 formed on the second boom spool 4. Accordingly, the boom can lower.
FIG. 2 is a hydraulic circuit diagram of a hydraulic control valve for a construction machine in the related art.
(A) The boom-up operation will be described with reference to the hydraulic circuit.
If the pilot signal pressure for the boom-up operation is supplied to a b port of the first boom block 1, the first boom spool 3 that is coupled to the first boom block 1 is shifted to the right side. At this time, the high-pressure hydraulic fluid in the supply path 16 of the first hydraulic pump P1 pushes a check valve 55, and is supplied to paths 56 and 57 through the internal path of the first boom spool 3 that is shifted to the right side.
At the same time, if the pilot signal pressure for the boom-up operation is supplied to a b′ port of the second boom block 2, the second boom spool 4 of the second boom block 2 is shifted to the right side. At this time, the high-pressure hydraulic fluid in the supply path 31 of the second hydraulic pump P2 pushes a check valve 62, and is supplied to a path 63 through the internal path of the second boom spool 4 that is shifted to the right side. Through this, the hydraulic fluid that is supplied to the path 63 joins the hydraulic fluid on the side of the first hydraulic pump P1 in the path 57 and is supplied to the large chamber of the boom cylinder 6.
At this time, the hydraulic fluid that returns from the small chamber of the boom cylinder passes through the path 59, and then is supplied to the tank path 60 through the internal path of the first boom spool 3 that is shifted to the right side.
(B) The boom-down operation will be described with reference to the hydraulic circuit.
If the pilot signal pressure for the boom-down operation is supplied to a port of the first boom block 1 and an a′ port of the second boom block 2 to let the boom can lower, the first boom spool 3 of the first boom block 1 and the second boom spool 4 of the second boom block 2 are shifted to the left side, respectively. At this time, the high-pressure hydraulic fluid in the supply path 16 of the first hydraulic pump P1 pushes the check valve 55, and is supplied to a path 59 through the internal path of the first boom spool 3 that is shifted to the left side. Through this, the hydraulic fluid is supplied to the small chamber of the boom cylinder 6.
At this time, the hydraulic fluid that returns from the larger chamber of the boom cylinder 6 is supplied to the paths 57 and 56, and is supplied to the tank path 60 through the internal path of the first boom spool 3 that is shifted to the left side.
At the same time, the hydraulic fluid that returns from the large chamber of the boom cylinder 6 is supplied to the path 63 that is branched to the path 57, and is supplied to the tank path 64 through the internal path of the second boom spool 4 that is shifted to the left side. Through this, the boom can lower.
As described above, the hydraulic control valve in the related art includes the first boom block 1 and the second boom block 2 for the boom-up or boom-down operation, the first boom spool 3 and the second boom spool 4 that are slidingly coupled to the first boom block and the second boom block 2, and the poppets 9 that are elastically supported by the springs 8 to open and close the supply path 16 of the first hydraulic pump P1 and the supply path 31 of the second hydraulic pump P2. Since such construction is applied to a first arm spool and a second arm spool in the same manner, the hydraulic control value becomes large-sized.
Further, in the case of mounting the hydraulic control valve onto the construction machine, the large-sized hydraulic control valve causes inconvenience during piping and layout of the hydraulic control valve which increases the manufacturing cost.