Hydraulic drive circuit

Abstract

In order to reduce manufacturing costs, the present invention is provided with: a bridge oil passage 30 that mutually communicates a first bridge port 23c and a second bridge port 23g; and a communication oil passage 31 that connects the bridge oil passage 30 and a center bridge port 23a. When a spool 22 is arranged at a first position, pump oil supply ports 23b, 23f and the center bridge port 23a are connected, the first bridge port 23c is cut off, and the second bridge port 23g and a second actuator port 23h are connected. When the spool 22 is arranged at a second position, the pump oil supply ports 23b, 23f and the center bridge port 23a are connected, the second bridge port 23g is cut off, and the first bridge port 23c and a first actuator port 23d are connected. A relief valve 33 is provided to the bridge oil passage 30.

Description

Hydraulic Drive Circuit

[0001] The present invention relates to a hydraulic drive circuit that controls the supply of oil from a hydraulic pump to a hydraulic device by operating a spool.

[0002] For example, in a hydraulic drive circuit that controls the supply of oil to a hydraulic cylinder, a first actuator port and a second actuator port are provided in a spool bore of a directional control valve, with the first actuator port connected to a bottom chamber of the hydraulic cylinder and the second actuator port connected to a rod chamber. When the spool moves from this state, the first actuator port and the second actuator port are selectively connected to a hydraulic pump, causing the hydraulic cylinder to reciprocate between an extended state and a retracted state. In this type of hydraulic drive circuit, a relief valve is provided in an oil passage that supplies oil from the spool to the hydraulic cylinder to prevent oil from being supplied to the hydraulic cylinder at a pressure above a set pressure (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2003-202003

[0004] The above-mentioned relief valve needs to function both when supplying oil to the bottom chamber and when supplying oil to the rod chamber. That is, in the above-mentioned hydraulic drive circuit, a relief valve is provided in each oil passage that supplies oil from the spool to the hydraulic cylinder, thereby preventing excessive hydraulic pressure from being applied to both the bottom chamber and the rod chamber. However, this conventional technology requires multiple relief valves, which inevitably increases manufacturing costs. This problem is not limited to hydraulic cylinders, but can also occur in other hydraulic equipment such as hydraulic motors.

[0005] SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a hydraulic drive circuit that can reduce manufacturing costs.

[0006] In order to achieve the above object, the hydraulic drive circuit according to the present invention is a hydraulic drive circuit that controls the supply of oil from a hydraulic pump to a hydraulic device by operating a spool of a directional control valve interposed between the hydraulic pump and the hydraulic device, and the directional control valve has a pump oil supply port connected to the hydraulic pump, a first actuator port and a second actuator port connected to the hydraulic device, a first bridge port, a second bridge port and a third bridge port, a bridge oil passage that connects the first bridge port and the second bridge port to each other, and a bridge oil passage that connects the bridge oil passage to the third bridge port. a communication oil passage is provided, and when the spool is positioned at a first position, the pump oil supply port and the third bridge port are connected, the first bridge port is blocked, and the second bridge port and the second actuator port are connected; and when the spool is positioned at a second position, the pump oil supply port and the third bridge port are connected, the second bridge port is blocked, and the first bridge port and the first actuator port are connected; and a relief valve is provided in either the bridge oil passage or the communication oil passage.

[0007] According to the present invention, whether oil is supplied from the first actuator port or the second actuator port, the oil passes through the communication oil passage and the bridge oil passage. Therefore, if only one relief valve is provided in the communication oil passage or the bridge oil passage, relief can be provided if the oil pressure exceeds a set pressure regardless of which of the two actuator ports oil is supplied from, making it possible to prevent excessive pressure from being applied to hydraulic equipment while keeping manufacturing costs down.

[0008] FIG. 1 is a circuit diagram of a hydraulic drive circuit according to a first embodiment of the present invention, in which a spool is disposed in a neutral position. FIG. 2 is a cross-sectional view showing the structure of the hydraulic drive circuit shown in FIG. 1. FIG. 3 is a circuit diagram of the hydraulic drive circuit shown in FIG. 1, in which a spool is disposed in a first position. FIG. 4 is a cross-sectional view showing the structure of the hydraulic drive circuit shown in FIG. 3. FIG. 5 is a circuit diagram of the hydraulic drive circuit shown in FIG. 1, in which a spool is disposed in a second position. FIG. 6 is a cross-sectional view showing the structure of the hydraulic drive circuit shown in FIG. 5. FIG. 7 is a circuit diagram of a hydraulic drive circuit according to a second embodiment of the present invention, in which a spool is disposed in a neutral position. FIG. 8 is a circuit diagram of the hydraulic drive circuit shown in FIG. 7, in which the spool is disposed in the first position. FIG. 9 is a circuit diagram of the hydraulic drive circuit shown in FIG. 7, in which the spool is disposed in the second position.

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a hydraulic drive circuit according to the present invention will now be described in detail with reference to the accompanying drawings.

[0010] 1 and 2 show a hydraulic drive circuit according to a first embodiment of the present invention. The hydraulic drive circuit illustrated here is for driving a hydraulic cylinder (hydraulic equipment) 10 with oil supplied from a hydraulic pump 1. The hydraulic pump 1 is a variable displacement type in which the displacement volume changes by changing the tilt angle of the swash plate or inclined axis. The hydraulic cylinder 10 is a double-acting type in which an actuating rod 12 reciprocates relative to a cylinder body 11 by selectively supplying oil to a rod chamber 11a and a bottom chamber 11b. This type of hydraulic cylinder 10 can be used, for example, as at least one of a boom hydraulic cylinder, an arm hydraulic cylinder, and a bucket hydraulic cylinder provided in a work machine.

[0011] A hydraulic valve device is provided between the hydraulic pump 1 and the hydraulic cylinder 10. The hydraulic valve device has a directional control valve 20 that selectively supplies oil from the hydraulic pump 1 to the rod chamber 11a and the bottom chamber 11b of the hydraulic cylinder 10, and is provided with a spool 22 in a valve body 21. The spool 22 is cylindrical and has a plurality of lands divided by annular grooves, and is disposed in a spool hole 23 of the valve body 21 in a state that allows it to move axially.

[0012] A central bridge port (third bridge port) 23a is provided in the spool hole 23 of the valve body 21 that houses the spool 22, at a location that is approximately in the center in the axial direction in Fig. 2. A first pump oil supply port 23b, a first bridge port 23c, a first actuator port 23d, and a first tank port 23e are provided in this order in the spool hole 23 on the left side of the central bridge port 23a in Fig. 2. A second pump oil supply port 23f, a second bridge port 23g, a second actuator port 23h, and a second tank port 23i are provided in this order in the spool hole 23 on the right side of the central bridge port 23a in Fig. 2.

[0013] When the spool 22 moves in the axial direction, the connection states between the first pump oil supply port 23b and the second pump oil supply port 23f and the central bridge port 23a, and the connection states between the first bridge port 23c and the second bridge port 23g and the first actuator port 23d and the second actuator port 23h are switched, respectively.

[0014] More specifically, when the spool 22 is in the neutral position, the central bridge port 23a is connected to the second tank port 23i, while the first pump oil supply port 23b, the second pump oil supply port 23f, the first bridge port 23c, the second bridge port 23g, the first actuator port 23d, and the second actuator port 23h are all blocked. When the spool 22 moves from the neutral position to the right in Figure 1, as shown in Figures 3 and 4, the central bridge port 23a and the first pump oil supply port 23b are connected, and the second bridge port 23g and the second actuator port 23h are connected, while the first actuator port 23d is connected to the first tank port 23e. The first bridge port 23c and the second tank port 23i remain blocked (first position of the spool 22). 1, as shown in Figures 5 and 6, the center bridge port 23a and the second pump oil supply port 23f are connected, the first bridge port 23c and the first actuator port 23d are connected, and the second actuator port 23h is connected to the second tank port 23i. The second bridge port 23g and the first tank port 23e remain blocked (second position of the spool 22).

[0015] A second pump oil supply port 23f of the spool hole 23 is connected to the hydraulic pump 1 through an oil supply passage 24. A main relief valve 24a is provided in the oil supply passage 24. A first actuator port 23d of the spool hole 23 is connected to the bottom chamber 11b of the hydraulic cylinder 10 through a bottom oil passage 25, and a second actuator port 23h is connected to the rod chamber 11a of the hydraulic cylinder 10 through a rod oil passage 26. Suction safety valves 25a, 26a are provided in the middle of the bottom oil passage 25 and the middle of the rod oil passage 26, respectively. The suction safety valves 25a, 26a connect the oil passages 25, 26 to the tank T only when the pressure in the respective oil passages 25, 26 exceeds a set value, and allow oil to pass from the tank T to the bottom oil passage 25 and the rod oil passage 26 when negative pressure is applied to the respective oil passages 25, 26. The first tank port 23e and the second tank port 23i of the spool hole 23 are connected to the tank T through drain oil passages 27, respectively.

[0016] The first pump oil supply port 23b and the second pump oil supply port 23f are connected to each other by a pump supply oil passage 28 provided in the valve body 21. The pump supply oil passage 28 extends from the first pump oil supply port 23b radially outward of the spool 22, then curves, and extends radially toward the spool 22, thereby connecting to the second pump oil supply port 23f.

[0017] The first bridge port 23c and the second bridge port 23g are connected to each other by a bridge oil passage 30 provided in the valve body 21. The bridge oil passage 30 extends from the first bridge port 23c radially outward of the spool 22, then curves to the right in FIG. 2 and extends along the axial direction of the spool 22. Its extended end further extends radially toward the spool 22 and connects to the second bridge port 23g. In the illustrated example, the pump supply oil passage 28 and the bridge oil passage 30 are positioned approximately 180° apart from each other around the spool 22. A communication oil passage 31 is provided between the bridge oil passage 30 and the central bridge port 23a. The communication oil passage 31 extends radially outward from the central bridge port 23a of the spool 22, so that its extending edge communicates with the middle portion of the bridge oil passage 30.

[0018] A pressure compensating valve 32 is provided in the communication oil passage 31, and a relief valve 33 is provided in the bridge oil passage 30. The pressure compensating valve 32 is configured to increase its opening when the pressure on the bridge oil passage 30 side is higher than the pressure on the central bridge port 23a side. The relief valve 33 opens to discharge oil into the tank T when the pressure in the bridge oil passage 30 exceeds a preset relief pressure (< the set pressure of the main relief valve 24a). In the first embodiment, an electromagnetic relief valve 33 is used, which can change the relief pressure in response to a given control signal.

[0019] The spool 22 has a neutral spring 40 at one end and pressure chambers 41a, 41b at both ends. The neutral spring 40 maintains the spool 22 in a neutral position and is housed inside a spring box 42. The pressure chambers 41a, 41b accommodate the ends of the spool 22 and are filled with oil. Although not shown in the figure, each pressure chamber 41a, 41b is individually connected to a pilot oil passage for applying pilot pressure output from an operating valve. When the pilot pressure output in response to operation of the operating valve is applied to the pressure chambers 41a, 41b through the pilot oil passage, the spool 22 can be moved axially against the spring force of the neutral spring 40. When the pilot pressure applied to the pressure chambers 41a, 41b is removed, the spring force of the neutral spring 40 returns the spool 22 to the neutral position.

[0020] In the hydraulic drive circuit configured as described above, when the spool 22 is positioned in the neutral position, the first pump oil supply port 23b, the second pump oil supply port 23f, the first bridge port 23c, the second bridge port 23g, the first actuator port 23d, and the second actuator port 23h are all blocked, as described above. Therefore, no oil flows through the rod chamber 11a and the bottom chamber 11b of the hydraulic cylinder 10, and the actuating rod 12 maintains its current position relative to the cylinder body 11.

[0021] 1 and 2 by operating the operating valve from this state, oil supplied to the oil feed passage 24 from the hydraulic pump 1 is supplied to the rod chamber 11a of the hydraulic cylinder 10 through the second pump oil feed port 23f, the central bridge port 23a, the connecting oil passage 31, the pressure compensation valve 32, the bridge oil passage 30, the second bridge port 23g, the second actuator port 23h, and the rod oil passage 26, as shown in Figures 3 and 4. At the same time, oil in the bottom chamber 11b is discharged to the tank T through the bottom oil passage 25, the first actuator port 23d, the first tank port 23e, and the drain oil passage 27. Therefore, the hydraulic cylinder 10 is in a state in which the operating rod 12 is retracted relative to the cylinder body 11.

[0022] Conversely, when the spool 22 is moved to the left in the figure by operating the operating valve, as shown in Figures 5 and 6, oil supplied from the hydraulic pump 1 to the oil feed passage 24 is supplied to the bottom chamber 11b of the hydraulic cylinder 10 through the second pump oil feed port 23f, the central bridge port 23a, the connecting oil passage 31, the pressure compensation valve 32, the bridge oil passage 30, the first bridge port 23c, the first actuator port 23d, and the bottom oil passage 25. At the same time, oil in the rod chamber 11a is discharged to the tank T through the rod oil passage 26, the second actuator port 23h, the second tank port 23i, and the drain oil passage 27. Therefore, the hydraulic cylinder 10 is in a state in which the operating rod 12 is advanced relative to the cylinder body 11.

[0023] During these operations, the hydraulic drive circuit causes oil to pass through the communication oil passage 31 and the bridge oil passage 30 whether oil is being supplied to the bottom chamber 11b or the rod chamber 11a of the hydraulic cylinder 10. Therefore, although only the bridge oil passage 30 is provided with the relief valve 33, it can relieve oil pressure when it exceeds a set pressure whether oil is being supplied to the bottom chamber 11b or the rod chamber 11a. This makes it possible to prevent excessive pressure from being applied to the hydraulic cylinder 10 while keeping manufacturing costs down.

[0024] In the first embodiment described above, the relief valve 33 is provided in the bridge oil passage 30, but the present invention is not limited to this. The relief valve 33 may be provided in the communication oil passage 31 in a portion between the pressure compensation valve 32 and the bridge oil passage 30.

[0025] (Embodiment 2) Figure 7 shows a hydraulic drive circuit according to Embodiment 2 of the present invention. The hydraulic drive circuit illustrated here is for driving a hydraulic cylinder (hydraulic equipment) 10 with oil supplied from a hydraulic pump 1, similar to Embodiment 1, and differs only in the configuration of the hydraulic valve device. Below, configurations that differ from Embodiment 1 will be described, and other common configurations will be assigned the same reference numerals.

[0026] In the hydraulic valve device of the second embodiment, a first pump oil supply port 53a and a second pump oil supply port 53b, a first actuator port 53c and a second actuator port 53d, a first bridge port 53e and a second bridge port 53f, and a first tank port 53g and a second tank port 53h are provided in a spool hole of a valve body that accommodates a spool 52 of a directional control valve 50. When the spool 52 moves in the axial direction, the connection states of the first pump oil supply port 53a and the second pump oil supply port 53b and the first bridge port 53e, the second bridge port 53f, the first actuator port 53c, and the second actuator port 53d are switched.

[0027] More specifically, when the spool 52 is positioned in the neutral position, the first pump oil supply port 53a, the second pump oil supply port 53b, the first bridge port 53e, the second bridge port 53f, the first actuator port 53c, and the second actuator port 53d are all blocked. When the spool 52 moves from the neutral position to the right in Fig. 7, as shown in Fig. 8, the first pump oil supply port 53a and the first bridge port 53e are connected, the second bridge port 53f and the second actuator port 53d are connected, and the first actuator port 53c is connected to the first tank port 53g. When the spool 52 moves from the neutral position to the left in Fig. 8, the second pump oil supply port 53b and the second bridge port 53f are connected, the first bridge port 53e and the first actuator port 53c are connected, and the second actuator port 53d is connected to the second tank port 53h.

[0028] The second pump oil supply port 53b of the spool hole is connected to the hydraulic pump 1 through an oil supply passage 54. A main relief valve 54a is provided in the oil supply passage 54. The first actuator port 53c of the spool hole is connected to the bottom chamber 11b of the hydraulic cylinder 10 through a bottom oil passage 55, and the second actuator port 53d is connected to the rod chamber 11a of the hydraulic cylinder 10 through a rod oil passage 56. Suction safety valves 55a and 56a are provided in the middle of the bottom oil passage 55 and the middle of the rod oil passage 56, respectively. The first tank port 53g and the second tank port 53h of the spool hole are connected to the tank T through a drain oil passage 57. The first pump oil supply port 53a and the second pump oil supply port 53b are connected to each other by a pump supply oil passage 58 provided in the valve body.

[0029] The first bridge port 53e and the second bridge port 53f are connected to each other by a bridge oil passage 60 provided in the valve body. A relief valve 61 is provided in this bridge oil passage 60. The relief valve 61 opens to discharge oil into the tank T when the pressure in the bridge oil passage 60 exceeds a preset relief pressure (<the set pressure of the main relief valve 54a). In the second embodiment as well, an electromagnetic relief valve 61 is used, which can change the relief pressure in response to a given control signal.

[0030] In the hydraulic drive circuit configured as described above, when the spool 52 is located in the neutral position, the first pump oil supply port 53a, the second pump oil supply port 53b, the first bridge port 53e, the second bridge port 53f, the first actuator port 53c, and the second actuator port 53d are all blocked, as described above. Therefore, no oil flows through the rod chamber 11a and the bottom chamber 11b of the hydraulic cylinder 10, and the actuating rod 12 maintains its current position relative to the cylinder body 11.

[0031] 7 by operating the operating valve from this state, oil supplied from the hydraulic pump 1 to the oil supply passage 54 is supplied to the rod chamber 11a of the hydraulic cylinder 10 through the first pump oil supply port 53a, the first bridge port 53e, the bridge oil passage 60, the second bridge port 53f, the second actuator port 53d, and the rod oil passage 56, as shown in FIG. 8. At the same time, oil in the bottom chamber 11b is discharged to the tank T through the bottom oil passage 55, the first actuator port 53c, the first tank port 53g, and the drain oil passage 57. Therefore, the hydraulic cylinder 10 is in a state in which the operating rod 12 is retracted relative to the cylinder body 11.

[0032] Conversely, when the spool 52 is moved to the left in Figure 7 by operating the operating valve, as shown in Figure 9, oil supplied from the hydraulic pump 1 to the oil feed passage 54 is supplied to the bottom chamber 11b of the hydraulic cylinder 10 through the second pump oil feed port 53b, the second bridge port 53f, the bridge oil passage 60, the first bridge port 53e, the first actuator port 53c, and the bottom oil passage 55. At the same time, oil in the rod chamber 11a is discharged to the tank T through the rod oil passage 56, the second actuator port 53d, the second tank port 53h, and the drain oil passage 57. Therefore, the hydraulic cylinder 10 is in a state in which the operating rod 12 is advanced relative to the cylinder body 11.

[0033] During these operations, the hydraulic drive circuit causes oil to pass through the bridge oil passage 60 whether oil is supplied to the bottom chamber 11b or the rod chamber 11a of the hydraulic cylinder 10. Therefore, although only the relief valve 61 is provided in the bridge oil passage 60, whether oil is supplied to the bottom chamber 11b or the rod chamber 11a, relief can be provided if the hydraulic pressure exceeds a set pressure, making it possible to prevent excessive pressure from being applied to the hydraulic cylinder 10 while keeping manufacturing costs down.

[0034] In the above-described embodiments, the hydraulic cylinder 10 is used as an example of the hydraulic equipment, but the present invention can also be applied to devices that control the supply of oil to other hydraulic equipment such as hydraulic motors. Also, although electromagnetic relief valves 33 and 61 are used as an example, the present invention is not limited to this.

[0035] REFERENCE SIGNS LIST 1 Hydraulic pump 10 Hydraulic cylinder 20, 50 Directional switching valve 22, 52 Spool 23a Central bridge port (third bridge port) 23b, 53a First pump oil supply port 23c, 53e First bridge port 23d, 53c First actuator port 23e, 53g First tank port 23f, 53b Second pump oil supply port 23g, 53f Second bridge port 23h, 53d Second actuator port 23i, 53h Second tank port 28, 58 Pump supply oil passage 30, 60 Bridge oil passage 31 Connecting oil passage 32 Pressure compensation valve 33, 61 Relief valve T Tank

Claims

1. A hydraulic drive circuit which controls the supply of oil from a hydraulic pump to hydraulic equipment by operating a spool of a directional control valve interposed between a hydraulic pump and the hydraulic equipment, wherein the directional control valve is provided with a pump oil supply port connected to the hydraulic pump, a first actuator port and a second actuator port connected to the hydraulic equipment, a first bridge port, a second bridge port and a third bridge port, a bridge oil passage connecting the first bridge port and the second bridge port to each other, and a communication oil passage connecting the bridge oil passage and the third bridge port, wherein when the spool is placed in a first position, the pump oil supply port and the third bridge port are connected, the first bridge port is blocked, and the second bridge port and the second actuator port are connected, and when the spool is placed in a second position, the pump oil supply port and the third bridge port are connected, the second bridge port is blocked, and the first bridge port and the first actuator port are connected, a relief valve provided in either one of the bridge oil passage and the communication oil passage.

2. A hydraulic drive circuit as claimed in claim 1, characterized in that a pressure compensation valve is provided in the communication oil passage for controlling the flow rate of oil supplied to the hydraulic equipment in accordance with the load pressure of the hydraulic equipment.

3. The hydraulic drive circuit according to claim 1, characterized in that the directional control valve is provided with the third bridge port in the axial center portion, the pump oil supply port, the first bridge port, the first actuator port, and a tank port connected to a tank are sequentially provided from the third bridge port toward one end, and the pump oil supply port, the second bridge port, the second actuator port, and a tank port connected to a tank are sequentially provided from the third bridge port toward the other end, and the pump oil supply port provided on the one end side of the third bridge port and the pump oil supply port provided on the other end side of the third bridge port are connected to each other by a pump communication oil passage.

4. A hydraulic drive circuit which controls the supply of oil from a hydraulic pump to hydraulic equipment by operating a spool of a directional control valve interposed between the hydraulic pump and the hydraulic equipment, wherein the directional control valve is provided with a pump oil supply port connected to the hydraulic pump, a first actuator port and a second actuator port connected to the hydraulic equipment, a first bridge port and a second bridge port, and a bridge oil passage which interconnects the first bridge port and the second bridge port, wherein when the spool is located in a first position, the pump oil supply port is connected to the first bridge port and the second bridge port is connected, and when the spool is located in a second position, the pump oil supply port is connected to the second bridge port and the first bridge port is connected, and a relief valve is provided in the bridge oil passage.

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