JP5918516B2 - Hydraulic circuit for construction machinery - Google Patents

Description

  The present invention relates to a hydraulic circuit of a construction machine having three system circuits.

  An example of this type of hydraulic circuit is described in Patent Document 1. According to the hydraulic circuit described in Patent Document 1 (for example, FIG. 1), when the boom is operated alone, pressure oil is supplied from the first pump (22) and the third pump (24) to the boom cylinder (10). The pressure oil supplied from the second pump (23) is returned to the tank without being used.

JP 2010-190330 A

  In this case, the difference between the load of the first pump (22) and the load of the second pump (23) becomes large, resulting in the result that the efficient discharge amount range of the second pump (23) is not used. On the other hand, in a construction machine having a boom, generally, improvement in workability can be expected by increasing the boom raising speed.

  The present invention has been made in view of the above circumstances, and its object is to provide pressure oil to the three system circuits respectively when the boom raising operation is performed among the boom operations. To provide a hydraulic circuit of a construction machine that can efficiently use a pump and consequently increase a boom raising speed.

Means and effects for solving the problems

  In order to achieve the above object, the present invention provides a first unload passage connected to a first pump, and a boom direction switching valve connected to the first unload passage for supplying and discharging pressure oil to a boom actuator. And a second unload passage connected to the second pump, and an arm direction switching valve connected to the second unload passage for supplying and discharging pressure oil to the arm actuator. A second system circuit, a third unload passage connected to the third pump, a turning direction switching valve connected to the third unload passage and supplying and discharging pressure oil to the turning actuator; In a hydraulic circuit of a construction machine having a third system circuit, the boom actuator is operated from the first pump, the second pump, and the third pump when a boom raising operation is performed. Characterized in that the pressure oil is supplied to the motor, to provide a hydraulic circuit for a construction machine.

  According to this configuration, it is possible to reduce the load difference among the first pump, the second pump, and the third pump, and as a result, the first pump, the second pump, and the third pump are all efficient. Can be used well. Further, since the boom is raised by the pressure oil from the three pumps, the boom raising speed is also increased.

  In the present invention, when both the boom raising operation and the turning operation are performed, pressure oil is supplied from the first pump, the second pump, and the third pump to the boom actuator. preferable.

  According to this configuration, the boom raising speed can be significantly increased compared to the turning speed.

  Further, in the present invention, a second direction switching valve for a boom that is provided in the second system circuit, is connected to the second unload passage, and supplies / discharges pressure oil to / from the boom actuator, and the direction switching valve for turning A merging valve that is connected to a merging passage that branches from the third unloading passage on the upstream side, and that connects the third pump to the first system circuit. As a result, the merging passage is connected to the boom direction switching valve, and the third unload passage on the downstream side of the turning direction switching valve becomes a first merging position for connecting to the tank, and the boom is raised. When both the operation and the turning operation are performed, the merging valve is in the first merging position, and the boom door is moved from the first pump and the third pump through the boom direction switching valve. With pressure oil is supplied to the Chueta, pressure oil to the boom actuator from the second pump via the second directional control valve for the boom is preferably supplied.

  According to this configuration, when the boom raising operation is performed, pressure oil is supplied from the first pump, the second pump, and the third pump to the boom actuator on the condition that the turning operation is performed. That is, when the turning operation is performed, more pressure oil is supplied to the boom actuator, and the boom raising speed is increased.

  Furthermore, in the present invention, there is provided an arm second direction switching valve provided in the first system circuit, connected to the first unload passage, and configured to supply / discharge pressure oil to / from the arm actuator. When both the lowering operations are performed, pressure oil is supplied from the second pump to the arm actuator via the arm direction switching valve, and the boom direction switching valve is supplied from the first pump. It is preferable that pressure oil is supplied to the boom actuator through the first pump, and pressure oil is supplied from the first pump to the arm actuator through the second arm direction switching valve.

  According to this configuration, when only the arm operation and the boom lowering operation are performed simultaneously by supplying the pressure oil from the first pump also to the arm actuator, the first pump and the second pump according to the respective operation amounts. The flow rate of the two pumps can be distributed, and energy loss can be reduced.

It is a circuit diagram showing a hydraulic circuit concerning one embodiment of the present invention. It is the A section enlarged view of FIG. It is the B section enlarged view of FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. An embodiment as a hydraulic circuit of a hydraulic excavator is shown below. Although not shown, the excavator includes a traveling device, a swinging body, a boom attached to the turning body, an arm attached to the tip of the boom, a bucket attached to the tip of the arm, and the like.

  As shown in the circuit diagram of FIG. 1, the hydraulic excavator includes a split pump 51 with a regulator 52 that controls the discharge flow rate of pressure oil, a third pump 53, a pilot pump 54, tanks 55 and 59, and a bucket hydraulic cylinder 56. , A boom hydraulic cylinder 57, an arm hydraulic cylinder 58, a dozer hydraulic cylinder 60, a turning actuator 61, a boom swing hydraulic cylinder 62, a traveling hydraulic motor (not shown), and the like are provided as accessory devices. The hydraulic circuit 1 is assembled to the hydraulic cylinders (56 to 58, 60, 62), actuators such as a traveling hydraulic motor, and pumps (51, 53, 54). The pumps (51, 53, 54) are driven by the engine.

  The split pump 51 is a variable-capacity one-cylinder two-port discharge pump, and discharges the same amount of pressure oil from the two discharge ports 51a and 51b. The split pump 51 corresponds to a combination of the first pump and the second pump in the present invention. The discharge port 51a side corresponds to the first pump, and the discharge port 51b side corresponds to the second pump. Two pumps for discharging one cylinder and one port may be prepared and used as the first pump and the second pump, respectively.

(Configuration of hydraulic circuit)
As illustrated in FIGS. 1 to 3, the hydraulic circuit 1 includes first to third system circuits. The first system circuit is a system in which pressure oil is supplied from the discharge port 51 a of the split pump 51. The second system circuit is a system in which pressure oil is supplied from the discharge port 51 b of the split pump 51. The third system circuit is a system to which pressure oil is supplied from the third pump 53.

(First system circuit)
The first system circuit includes a first unload passage 12 connected to one discharge port 51a of the split pump 51, four direction switching valves 4w to 4z connected in series to the first unload passage 12, and direction switching. And a first auxiliary unloading valve 7 disposed on the downstream side of the direction switching valve 4z located on the most downstream side of the valves 4w to 4z. The first unload passage 12 communicates with the tank 55. The direction switching valves 4w to 4z are center bypass type and hydraulic pilot type direction switching valves. Further, center bypass type sub-valves 17w to 17z are provided integrally with the direction switching valves 4w to 4z, respectively.

  Here, the direction switching valve 4w is a traveling direction switching valve that supplies and discharges pressure oil to and from the traveling hydraulic motor, and the direction switching valve 4x is a boom direction that supplies and discharges pressure oil to the boom hydraulic cylinder 57. The direction switching valve 4 y is a bucket direction switching valve for supplying and discharging pressure oil to and from the bucket hydraulic cylinder 56, and the direction switching valve 4 z is an arm for supplying and discharging pressure oil to the arm hydraulic cylinder 58. This is a second directional switching valve.

(Second system circuit)
The second system circuit includes a second unload passage 13 connected to the other outlet 51 b of the split pump 51, three direction switching valves 5 w to 5 y connected in series to the second unload passage 13, and direction switching. And a second auxiliary unloading valve 8 disposed on the downstream side of the direction switching valve 5y located on the most downstream side among the valves 5w to 5y. The second unload passage 13 communicates with the tank 55. The direction switching valves 5w to 5y are center bypass type and hydraulic pilot type direction switching valves. Further, center bypass type sub-valves 18w to 18y are provided integrally with the direction switching valves 5w to 5y, respectively.

  Here, the direction switching valve 5w is a traveling direction switching valve that supplies and discharges pressure oil to and from the traveling hydraulic motor, and the direction switching valve 5x supplies pressure oil to the cylinder chamber 57a of the boom hydraulic cylinder 57. The second direction switching valve for the boom, the direction switching valve 5y is an arm direction switching valve that supplies and discharges pressure oil to and from the arm hydraulic cylinder 58.

  The boom is raised by supplying pressure oil to the cylinder chamber 57a of the boom hydraulic cylinder 57 (boom raising), and the boom is lowered by supplying pressure oil to the cylinder chamber 57b of the boom hydraulic cylinder 57 ( Boom down).

(3rd system circuit)
The third system circuit includes a third unload passage 29 connected to the third pump 53, and three direction switching valves 6 w to 6 y connected in series to the third unload passage 29. The third unload passage 29 communicates with the tank 55 via a junction valve 9 described later. The direction switching valves 6w to 6y are center bypass type and hydraulic pilot type direction switching valves.

  Here, the direction switching valve 6w is a turning direction switching valve for supplying and discharging pressure oil to the turning actuator 61, and the direction switching valve 6x is a direction switching for dozer for supplying and discharging pressure oil to the dozer hydraulic cylinder 60. The direction switching valve 6 y is a boom swing direction switching valve that supplies and discharges pressure oil to and from the boom swing hydraulic cylinder 62.

  On the other hand, a pilot passage 20 that branches to the first pilot passage 24, the second pilot passage 25, and the third pilot passage 26 on the downstream side is connected to a pilot pump 54. The first pilot passage 24, the second pilot passage 25, and the third pilot passage 26 are all in communication with the tank 55. The four sub valves 17w to 17z of the first system are connected in series to the first pilot passage 24, and the three sub valves 18w to 18y of the second system are connected to the second pilot passage 25 in series. The sub-valves 17w to 18y are in the communication position when the corresponding direction switching valves 4w to 5y are in the neutral position (when not operated), and when the direction switching valves 4w to 5y are in the switching position (when operated). It is formed so as to be a blocking position (the same applies to the sub-valves 18w to 18y).

  The two sub valves 17x and 17y of the first system and the sub valve 18y of the second system are connected in series to the third pilot passage 26. The first system sub-valve 17w and the second system sub-valve 18w are each independently connected to the third pilot passage 26. Further, apart from these, the third pilot passage 26 is connected to one chamber 93 of the junction valve 9 described later. A third pilot line throttle 34 is provided on the upstream side of one chamber 93 of the merging valve 9 and on the upstream side of each sub valve (17w to 17x, 18w, 18y).

[Joint valve]
Here, a merging valve 9 is arranged on the downstream side of the direction switching valve 6y located on the most downstream side among the direction switching valves 6w to 6y. The junction valve 9 is a three-position valve for supplying the pressure oil from the third pump 53 to the first system circuit and the second system circuit.

  The merging passage 11 is branched from the third unload passage 29 on the upstream side of the turning direction switching valve 6 w, and the merging passage 11 is connected to the merging valve 9. A third unload passage 29 on the downstream side of the direction switching valve 6 y is also connected to the merging valve 9.

  The junction valve 9 and the first system circuit are connected by a first system integrated flow passage 33, and the joint valve 9 and the second system circuit are connected by a second system integrated flow passage 35. The first system integrated flow passage 33 is connected to the boom direction switching valve 4x, the bucket direction switching valve 4y, and the arm second direction switching valve 4z. The second system integrated flow passage 35 is connected to the boom second direction switching valve 5x.

  The merging valve 9 is connected to the non-merging position 9a connecting the third unload passage 29 on the downstream side of the direction switching valve 6y to the tank 55, the merging passage 11 to the first system circuit, and the direction switching valve 6y. The first union passage 9b connecting the downstream third unload passage 29 to the tank 55, the third unload passage 29 and the joining passage 11 downstream of the direction switching valve 6y are connected to the first system circuit and the second system. A second joining position 9c connected to the circuit.

  A pilot pressure downstream of the third pilot line throttle 34 is input to one chamber 93 of the merging valve 9, and a boom raising pilot pressure is input to the chamber 92 formed on the same side as the chamber 93. Yes. A spring 91 (biasing means) is disposed in the other chamber of the merging valve 9. The pressure of the third unload passage 29 on the downstream side of the direction switching valve 6y is input to the other chamber of the merging valve 9 when the merging valve 9 is at the non-merging position 9a and the first merging position 9b. Yes.

  When the pilot pressure for raising the boom is input to one chamber 92 of the merging valve 9, the merging valve 9 becomes the first merging position 9b. Further, any one of the sub valves 17x, 17y, and 18y is in a blocking position in conjunction with the direction switching valves 4x, 4y, and 5y, the sub valve 17w is in a blocking position in conjunction with the direction switching valve 4w, and the direction switching valve 5w. When the sub valve 18w is in the shut-off position in conjunction with the pilot pressure, the pilot pressure from the pilot pump 54 is introduced into one chamber 93, and the merging valve 9 becomes the second merging position 9c.

  A constriction 94 is provided in the passage between the joining passage 11 and the first system integrated passage 33 when the joining valve 9 is in the first joining position 9b, and for joining when the joining valve 9 is in the second joining position 9c. A throttle 95 is provided in the passage between the passage 11 and the first system integrated flow passage 33.

[Auxiliary unloading valve]
The first auxiliary unloading valve 7 receives the first negative control pressure, which is the hydraulic pressure downstream of the direction switching valve 4z, and the pilot pressure from the first pilot passage 24, and all the direction switching valves 4w of the first system. ˜4z is a valve configured to output the pilot pump pressure to the first unload valve 2 and the low pressure selection valve 10 instead of the first negative control pressure (second auxiliary unload). The same applies to the valve 8).

[Low pressure selection valve]
The low pressure selection valve 10 includes an output pressure of the first auxiliary unloading valve (first negative control pressure or pilot pressure from the first pilot passage 24) and an output pressure of the second auxiliary unloading valve (second negative control pressure (direction switching valve). A valve configured to output the lower hydraulic pressure of the hydraulic pressure downstream of 5y) or the pilot pressure from the second pilot passage 25) to the regulator 52 and the first unload valve 2 as the third negative control pressure. is there.

[Unload valve]
The first unload valve 2 is configured to discharge oil from the split pump 51 to the tank 59 in accordance with the output pressure of the first auxiliary unload valve 7 and the third negative control pressure from the low pressure selection valve 10. (The same applies to the second unloading valve 3).

(Hydraulic excavator operation)
(Boom raising + turning operation)
First, the operation when the boom raising operation and the turning operation are performed simultaneously will be described. In the following description, the operation when the boom raising operation is performed prior to the turning operation will be described. However, the turning operation may be performed prior to the boom raising operation, or the boom raising operation and the turning may be performed. The operation may be started at the same time.

  By the boom raising operation, pilot pressure is introduced into the pilot chamber 4xa of the boom direction switching valve 4x, pilot pressure is introduced into the pilot chamber 5xa of the boom second direction switching valve 5x, and the pilot chamber of the junction valve 9 The pilot pressure is also introduced into 92.

  Thus, pressure oil is supplied from the discharge port 51a (first pump) of the split pump 51 to the cylinder chamber 57a of the boom hydraulic cylinder 57 via the boom direction switching valve 4x, and the discharge port 51b of the split pump 51. Pressure oil is supplied from the (second pump) to the cylinder chamber 57a of the boom hydraulic cylinder 57 via the boom second direction switching valve 5x.

  At this time, the merging valve 9 is switched from the non-merging position 9a to the first merging position 9b. Since the turning operation has not been performed yet, the discharge oil of the third pump 53 flows out from the third unload passage 29 on the downstream side of the turning direction switching valve 6w to the tank 55 via the junction valve 9. Therefore, the pressure in the joining passage 11 branched from the third unload passage 29 does not increase, and no oil flows into the first system integrated passage 33.

  When the turning operation is performed with a slight delay, and the pilot pressure is introduced into the pilot chamber 6wa of the turning direction switching valve 6w, the turning direction switching valve 6w operates (switches), whereby the turning direction switching valve 6w. The pressure in the third unload passage 29 on the upstream side increases, and oil flows into the joining passage 11. As a result, oil flows from the third pump 53 to the first system integrated flow passage 33, and pressure oil is supplied to the cylinder chamber 57a of the boom hydraulic cylinder 57 via the boom direction switching valve 4x. As a result, pressure oil is supplied to the cylinder chamber 57a of the boom hydraulic cylinder 57 from any of the discharge port 51a, the discharge port 51b, and the third pump 53 of the split pump 51.

[effect]
During the boom raising operation, pressure oil is supplied to the boom hydraulic cylinder 57 from any of the discharge port 51a, the discharge port 51b, and the third pump of the split pump 51, so that the discharge port 51a (first pump) of the split pump 51 is supplied. ), The difference in load between the discharge port 51b (second pump) and the third pump can be reduced. As a result, the first pump, the second pump, and the third pump can be used efficiently. can do.

  In particular, in the case of the split pump 51, since the oil discharge amount from the two discharge ports 51a and 51b is the same, the excess flow returning to the tank 55 without being used from the second system discharge port 51b (second pump) is reduced. By being able to be made, an energy loss can be reduced.

  Moreover, since the boom is raised by the pressure oil from the three pumps, the boom raising speed is remarkably increased. For example, in a hydraulic excavator, unlike the excavation work, the boom raising operation only lifts the earth and sand in the bucket, so that a large load is not applied. In addition, in the pre-operation for loading and unloading the earth and sand in the bucket, the bucket moves above the ground, so that the boom driving with good visibility for the worker is required. In such pre-operations, workability is improved by dramatically increasing the boom raising speed. Furthermore, the fuel efficiency of the engine is improved by shortening the work time per operation from excavation to sediment discharge.

  Further, as in the example described above, when the boom raising operation and the turning operation are performed simultaneously, the boom raising speed is remarkably increased compared to the turning speed. This is because the turning actuator 61 is supplied with pressure oil from one pump, but the boom hydraulic cylinder 57 is supplied with pressure oil from three pumps. More specifically, for example, in a sediment load operation on a truck, the bucket can be raised from the ground level to the truck bed height while the turning body turns about 45 degrees at maximum acceleration and deceleration.

  Here, when the boom raising operation is performed, the pressure oil is supplied from the three pumps to the boom hydraulic cylinder 57 on the condition that the turning operation is performed. That is, when the turning operation is performed, more pressure oil is supplied to the boom hydraulic cylinder 57, and the boom raising speed is increased.

(Arm operation + boom lowering)
Next, an operation when the arm operation and the boom lowering operation are performed simultaneously (simultaneously operated) will be described.

  When the arm operation and the boom lowering operation are performed simultaneously, the pilot pressure is introduced into, for example, the pilot chamber 5ya of the arm direction switching valve 5y, and the pilot pressure is introduced into the pilot chamber 4xb of the boom direction switching valve 4x. Pilot pressure is introduced into the pilot chamber 4za of the arm second direction switching valve 4z.

  Thus, pressure oil is supplied from the discharge port 51b (second pump) of the split pump 51 to the arm hydraulic cylinder 58 via the arm direction switching valve 5y, and the discharge port 51a (first pump) of the split pump 51. ) To the cylinder chamber 57b of the boom hydraulic cylinder 57 via the boom direction switching valve 4x, and the arm second direction switching valve 4z from the discharge port 51a (first pump) of the split pump 51. The pressure oil is supplied to the arm hydraulic cylinder 58 through the via.

[effect]
When the pressure oil from the first pump is not supplied only to the boom hydraulic cylinder 57 but also supplied to the arm hydraulic cylinder 58, only the arm operation and the boom lowering operation are simultaneously operated (first system) Of the actuators connected to the circuit and the second system circuit (when only the arm and the boom are operated) can distribute the flow rates of the first pump and the second pump according to the respective operation amounts, resulting in energy loss. Can be reduced. As a result, the fuel efficiency of the engine is improved. In particular, the split pump 51 is advantageous because it can be used while reducing the difference between the load of the first pump and the load of the second pump.

  Further, for example, in any of excavation, sediment loading / unloading, and leveling work, the amount of boom operation relative to the amount of arm operation is very small. (Conventionally, pressure oil was supplied from the second pump and the third pump 53 to the arm hydraulic cylinder 58). According to the hydraulic circuit 1 of the present embodiment, when the arm operation and the boom lowering operation are performed simultaneously, the surplus portion of the first pump is supplied to the arm hydraulic cylinder 58, thereby reducing the load on the third pump 53. be able to. As a result, a large amount of engine output can be distributed to the split pump 51 (first pump and second pump).

  For example, even when only the arm operation is performed, since the pressure oil is supplied from the first pump and the second pump to the arm hydraulic cylinder 58, the difference between the load of the first pump and the load of the second pump is reduced. be able to.

(Modification)
A modification of the hydraulic circuit 1 described above will be described. When the merging valve 9 is at the first merging position 9b, it is also preferable to provide a throttle in a passage (valve inner passage) between the third unload passage 29 and the tank 55 on the downstream side of the direction switching valves 6w to 6y. . With this restriction, when the boom raising operation is performed and the junction valve 9 is switched to the first junction position 9b, the pressure oil from the third pump 53 is supplied to the boom direction switching valve even when the turning operation is not performed. 4x and the boom second direction switching valve 5x can be supplied to the boom hydraulic cylinder 57. That is, the pressure oil from the third pump 53 can be sent from the two valves, the boom direction switching valve 4x and the boom second direction switching valve 5x, and pressure loss can be reduced.

1: Hydraulic circuit 2: First unloading valve 3: Second unloading valve 4x: Boom direction switching valve 5y: Arm direction switching valve 6w: Turning direction switching valve 9: Junction valve 10: Low pressure selection valve 12: First unload passage 13: Second unload passage 29: Third unload passage 51: Split pump (first pump and second pump)
52: Regulator 53: Third pump 54: Pilot pump 55, 59: Tank 56: Bucket hydraulic cylinder (bucket actuator)
57: Hydraulic cylinder for boom (actuator for boom)
58: Hydraulic cylinder for arm (actuator for arm)
61: Actuator for turning

Claims (3)

A first unload passage connected to the first pump;
A boom direction switching valve connected to the first unload passage and supplying and discharging pressure oil to and from the boom actuator;
A first system circuit comprising:
A second unload passage connected to the second pump;
An arm direction switching valve connected to the second unload passage and supplying and discharging pressure oil to and from the arm actuator;
A second system circuit having
A third unload passage connected to the third pump;
A turning direction switching valve connected to the third unload passage and supplying and discharging pressure oil to the turning actuator;
A third system circuit having
In the hydraulic circuit of a construction machine comprising
A second direction switching valve for a boom provided in the second system circuit, connected to the second unload passage, and supplying and discharging pressure oil to and from the boom actuator;
A merging valve connected to a merging passage branched from the third unloading passage on the upstream side of the turning direction switching valve, and connecting the third pump to the first system circuit;
Have
When the boom raising operation is performed, the merging valve connects the merging passage to the boom direction switching valve and connects the third unloading passage downstream of the turning direction switching valve to the tank. To become the first merge position
When both the boom raising operation and the turning operation are performed, the merging valve is in the first merging position, and the boom directional valve is connected to the boom from the first pump and the third pump via the boom direction switching valve. Pressure oil is supplied to the actuator, and pressure oil is supplied from the second pump to the boom actuator via the boom second direction switching valve.
Construction is characterized in that pressure oil is supplied from the first pump, the second pump, and the third pump to the boom actuator when both the boom raising operation and the turning operation are performed. The hydraulic circuit of the machine. A first unload passage connected to the first pump;
A boom direction switching valve connected to the first unload passage and supplying and discharging pressure oil to and from the boom actuator;
A first system circuit comprising:
A second unload passage connected to the second pump;
An arm direction switching valve connected to the second unload passage and supplying and discharging pressure oil to and from the arm actuator;
A second system circuit having
A third unload passage connected to the third pump;
A turning direction switching valve connected to the third unload passage and supplying and discharging pressure oil to the turning actuator;
A third system circuit having
In the hydraulic circuit of a construction machine comprising
A second direction switching valve for a boom provided in the second system circuit, connected to the second unload passage, and supplying and discharging pressure oil to and from the boom actuator;
A merging valve connected to a merging passage branched from the third unloading passage on the upstream side of the turning direction switching valve, and connecting the third pump to the first system circuit;
Have
When the boom raising operation is performed, the merging valve connects the merging passage to the boom direction switching valve and connects the third unloading passage downstream of the turning direction switching valve to the tank. To become the first merge position
When the merging valve is switched to the first merging position, pressure oil from the third pump can be supplied from the boom direction switching valve and the boom second direction switching valve to the boom actuator. It is further equipped with an aperture,
A hydraulic circuit for a construction machine, wherein pressure oil is supplied from the first pump, the second pump, and the third pump to the boom actuator when a boom raising operation is performed. In the hydraulic circuit of the construction machine according to claim 1 or 2 ,
An arm second direction switching valve provided in the first system circuit, connected to the first unload passage, for supplying and discharging pressure oil to and from the arm actuator;
When both the arm operation and the boom lowering operation are performed, pressure oil is supplied from the second pump to the arm actuator via the arm direction switching valve, and the boom is supplied from the first pump. Pressure oil is supplied to the boom actuator via a direction switching valve, and pressure oil is supplied from the first pump to the arm actuator via the arm second direction switching valve. And hydraulic circuit of construction machinery.

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