JPH0643260Y2 - Hydraulic equipment for construction machinery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a hydraulic system for a construction machine.

[Conventional technology]

As a hydraulic device of this type, for example, a hydraulic circuit for civil engineering / construction machinery described in JP-A-58-65828 is known. As shown in FIG. 3, this device connects working machine switching valves 102 and 103 and a first traveling switching valve 104 to a first pump 101 through a parallel passage 105. The second pump 106 has a work machine switching valve 107, 108, 1
09 is connected by the parallel passage 110, and the second traveling switching valve 111 is connected in tandem downstream thereof, and the input port of the second traveling switching valve 111 and the upstream parallel passage 110 are connected via the throttle 112. Connecting. Further, the input port of the second traveling switching valve 111 is connected to the first traveling switching valve 1 via the merging switching valve 113.
It is connected to the entrance port of 04. Then, the boom cylinder 118 connected to the work machine switching valve 103 includes the first pump 101.
Since there is a case where the discharge oil of 10 is insufficient, it is connected to the working machine switching valve 108 of another circuit system by the supply pipelines 119 and 120 so that the second pump 106 can also supply oil.

When the work implement actuator is not operated while the vehicle is traveling, the merging switching valve 113 is switched to the off position. As a result, the oil discharged from the first pump 101 is supplied to the traveling motor 115 via the parallel passage 105 and the travel switching valve 104, and the oil delivered from the second pump 106 passes through the center bypass passage 114 and the travel switching valve 111. Since the vehicle is supplied to the traveling motors 116, the vehicle travels straight by the traveling motors 115 and 116 driven by their own pumps.

To operate, for example, the arm cylinder 117 while the vehicle is traveling, the working machine switching valve 109 is switched to the functional position and the merging switching valve 113 is switched on. If the merging switching valve 113 is off, the amount of oil supplied to the second travel motor 116 is reduced by the amount of oil supplied to the arm cylinder 117, and the vehicle will bend due to the difference in the amount of oil supplied to the travel motors 115 and 116. . Yotsutte
By turning on the merging switching valve 113, the inlet ports of the traveling switching valves 111 and 104 are communicated, and both traveling motors 115,
It is trying to equalize the amount of refueling of 116.

Even when the boom cylinder 118 is operated while the vehicle is traveling, the working machine switching valves 103 and 108 are switched to the functional positions and the merging switching valve 113 is switched on. As a result, the total amount of oil discharged from the first pump 101 and the second pump 106 is changed to the boom cylinder.
The remaining discharge oil after subtracting the oil supply to 118 and the traveling motor 115
It will be sorted to 116 and the vehicle will go straight.

[Problems to be Solved by the Invention] By the way, in this conventional device, the boom cylinder 118 has a first
2 to supply the discharge oil of the pump 101 and the second pump 106
In addition to the working machine switching valve 103 connected to the boom cylinder 118 through the book supply / discharge line, a second working machine switching valve 108 connected to the second pump 106 and the working machine switching valve 103 connected thereto Since the two supply / drain pipes 119 and 120 are required, the hydraulic system becomes large in size and the cost is increased.

It is an object of the present invention to provide a hydraulic system for a construction machine that solves the above-mentioned problems.

[Means for Solving the Problems]

In order to achieve this object, in the present invention, two sets of circuit systems are provided, and each circuit system is provided with an upstream switching valve connected to a pump and a plurality of working machines connected in parallel passages. Construction in which the switching valve and the switching valve are connected in tandem via the center bypass passage, and the actuator is controlled by the merging switching valve connected with the traveling switching valve of both circuit systems, the parallel passage and the pump, and the switching valve of the actuator. In the hydraulic circuit of the machine, in the first circuit system, the first pump is connected to the first traveling switching valve and the merging switching valve, and
The parallel passage is connected to the merging switching valve via a throttle, and the second
In the circuit system, the second pump is connected to the parallel passage through the throttle, the upstream of the throttle and the upstream of the second traveling switching valve are connected to the confluence switching valve, and the work of the center bypass passage of each circuit system is performed. A throttle is provided downstream of the machine switching valve group,
The merging switching valve, when taking the non-merging position, connects the second pump of the second circuit system and the second traveling switching valve, and at the same time
When the first travel switching valve and the parallel passage communicating with the first pump of the circuit system are cut off from each other and the merging position is taken, both travel switching valves are communicated with each other and the communication passage is in the merging switching valve And a parallel passage connected to the second pump and the throttle of the second circuit system and a parallel passage connected to the throttle of the first circuit system via the throttle.

In the above configuration, a means for switching the working machine switching valve and the traveling switching valve with pilot command pressures, a means for switching a predetermined working machine (boom cylinder) switching valve and a confluence switching valve with the same pilot command pressure, and a vehicle Means may be provided for switching the merging switching valve by a function position switching signal of the working machine switching valve during traveling.

[Action]

(A) When the working machine (except the boom cylinder 47) is operated when the vehicle is stopped: The merging switching valve 13 is set to the non-merging position b, and the working machine switching valve (predetermined working machine switching valve) is set to the functional position. Then, the discharge oil is supplied from the pump of the circuit system to which it belongs to the working machine through the traveling switching valve, the parallel passage, and the working machine switching valve.

(B) When the working machine (boom cylinder 47) is operated by the oil discharged from both pumps when the vehicle is stopped, the merging switching valve 13 is set to the merging position a, and the working machine switching valve 9
Is set to the functional position, the discharge oil of the pump 1 communicating with the two switching valves 5 and 11 for traveling travels to the working machine switching valve group of the center bypass passage 61 of the circuit system 6 which does not have the working machine switching valve 9. Another pump 7 is held at the proper pressure by the downstream throttle 80.
And the discharge oil of the above are merged in the parallel passage 8 and supplied to the working machine through the working machine switching valve 9.

(C) When traveling the vehicle With the merging switching valve 13 at the non-merging position b, there are two traveling switching valves.
When 5, 11 are set to the functional positions, the discharge oil is supplied from the pump of the circuit system to which the traveling switching valve belongs to the traveling motor through the traveling switching valve.

(D) When operating the working machine (excluding the boom cylinder 47) while the vehicle is traveling When the merging switching valve 13 is set to the merging position a and the working machine switching valve is set to the functional position, both traveling switching valves 5, The discharge oil of one pump 1 communicating with 11 is supplied to both traveling motors 39 and 41,
The discharge oil of the other pump 7 is guided to the working machine through the throttle, the parallel passage, and the working machine switching valve, and the surplus oil is combined with the discharging oil of the one pump 1 through the throttle 20 of the merging switching valve 13. The shunt is split to the drive motors 39 and 41.

(E) When the working machine (boom cylinder 47) is operated with a part of the oil discharged from both pumps while the vehicle is running When the merging switching valve 13 is set to the merging position a and the working machine switching valve is set to the functional position, The discharge oil of the other pump 7 of the same circuit system as the working machine switching valve is guided to the working machine switching valve via the throttle 14 and the parallel passage 15, and the discharge oil of one pump 1 is supplied to both sides by the merging switching valve 13. Although divided into the traveling switching valves 5 and 11, some of the discharge oil merges with the discharge oil of the other pump 7 through the throttle 20 of the merge switching valve 13 and is guided to the working machine switching valve.

(F) When the merging switching valve 13 is switched to the merging position a, the discharge passage of the other pump 7 is connected to the parallel passages 8 and 2 through the throttles 15 and 18, and the one pump 1 and the two traveling rams are used. Since it is connected to the switching valves 5 and 11 via the throttle 20 of the merging switching valve 13, for example, when operating one of the working machines while the vehicle is traveling, even if the load of the working machine is a light load, the other pump 7 is operated.
The pressure of the discharge oil of is kept high (appropriately) by the throttles 14 and 18 connecting to the parallel passages 8 and 2, and a part of the discharge oil of the pump 1 on one side connected to the switching valves 5 and 11 for both traveling works. Since it can be prevented from flowing out to the machine side, the operation of the working machine and the operation of the vehicle can be surely performed.

(G) With the configuration in which the working machine switching valve and the traveling switching valve are controlled by the pilot command pressure, the working machine operation and the vehicle traveling can be obtained by the pilot command pressure. In the configuration in which the merging switching valve is switched to the merging position by the function position switching signal of the working machine switching valve while the vehicle is traveling, a combined operation of the vehicle and the working machine is obtained.
Further, in the configuration in which the switching valve and the merging switching valve of the working machine that needs the discharged oil of both pumps are switched by one pilot command pressure, the discharged oil of both pumps can be guided to the working machine regardless of the stop of the traveling of the vehicle. Therefore, the combined operation of the vehicle and the working machine can be obtained while the vehicle is traveling.

〔Example〕

An embodiment of the present invention will be described with reference to the drawings. In FIG. 1, a first pump 1 includes a swing motor switching valve 3 and an arm cylinder switching valve 4 connected by a parallel passage 2 and these working machine switching valves 3 and 4 via a center bypass passage. It is connected to the pressure port of the first traveling switching valve 5 of the first circuit system 6 which is composed of the uppermost first traveling switching valve 5 connected in tandem. The second pump 7 is connected in tandem to the boom cylinder switching valve 9, the bucket cylinder switching valve 10 and the working machine switching valves 9 and 10 connected through the parallel passage 8 through the center bypass passage. It is connected to the pressure port of the second traveling switching valve 11 of the second circuit system 12 constituted by the second upstream switching valve 11 and the like via the confluence switching valve 13, and the second circuit system 12 is connected in parallel. Squeeze to passage 8
It is connected by a passage 15 with 14 interposed. The merging switching valve 13 is the first
The passage 16 connects the pump 1 and the first travel switching valve 5 to each other.
The connection is made via 17 and at the same time, it is connected to the parallel passage 2 of the first circuit system 6 by a passage 19 having a throttle 18.

In the illustrated state in which the merging switching valve 13 is in the non-merging position, the second pump 7 and the second traveling switching valve 11 are communicated with each other, the passages 17 and 19 are blocked, and the merging switching valve 13 switches to the first merging position. The pump 1, the first travel switching valve 5 and the second travel switching valve 11 are communicated with each other, and the communication portion thereof is connected to the second pump 7 and the passage 19 via the throttle 20 and another communication portion.

In addition, a relief valve 81 and other appropriate known means for controlling the flow of fluid such as the throttle 80 are arranged in parallel in the center bypass passage 61 downstream of the working machine switching valve group.

Now, when only the arm cylinder switching valve 4 is switched to the functional position, for example, the position a in the illustrated state in which the vehicle and the working machine are stopped, the discharge oil of the first pump 1 is transferred to the traveling switching valve 5 and the parallel passage 2. It is guided to the rod chamber 23 of the arm cylinder 22 through the check valves 71, 72, the arm cylinder switching valve 4, and the passage 46, and the head chamber 24 passes through the passage 25, the arm cylinder switching valve 4, the return passages 26, 27, and the tank. Since it is opened to 28, the arm cylinder 22 is shortened.

Similarly, when only the swing motor switching valve 3 is switched to the functional position, for example, the position a, the discharge oil of the first pump 1 causes the travel switching valve 5, the check valves 71 and 73 in the parallel passage 2, and the swing motor switching valve 3 to flow. Through the turning motor 29,
The oil discharged from the tank returns to the tank 28 through the passage 30, the swing motor switching valve 3, and the return passages 31 and 27, and the swing motor 29 is started.

Further, if only the bucket cylinder switching valve 10 is switched to the functional position, for example, the position a, the discharge oil of the second pump 7 joins the switching valve 13, the second traveling switching valve 11, and the check valves 74 and 75 of the parallel passage 8. The oil discharged from the rod chamber 34 is guided to the head chamber 33 of the bucket cylinder 32 through the bucket cylinder switching valve 10 and the passage 35, the bucket cylinder switching valve 10, and the return passage 3
After returning to the tank 28 via 6,37, the bucket cylinder 32 extends.

Next, in the state shown in the figure, if only the traveling switching valves 5 and 11 are switched to the functional position a, the oil discharged from the first pump 1 passes through the traveling switching valve 5 and the passage 38 to the right traveling motor 39 and the second pump. The discharge oil of 7 is led to the left traveling motor 41 through the merging switching valve 13, the second traveling switching valve 11 and the passage 40, and the return oil from the traveling motors 39 and 41 is passages 42 and 43 and the traveling switching valve 5 , 11, return corridor 44,45
After returning to the tank 28 from the return passages 27 and 37, the vehicle starts traveling by the left and right traveling motors.

To drive the arm cylinder 22 while the vehicle is traveling, the arm cylinder switching valve 4 is switched to the functional position, for example, the position b, and the merging switching valve 13 is switched to the merging position a. As a result, the oil discharged from the first pump 1 is diverted to the first travel switching valve 5 and the second travel switching valve 11, and the oil discharged from the second pump 7 is directed to the throttle 20 and the passage 19 side at the merging switching valve 13. To shunt,
The oil discharged from the first pump 1 merges with the oil discharged from the throttle 20 and is branched to the travel motors 39 and 41 via the switching valves 5 and 11 for traveling, while the oil discharged into the passage 19 is throttled in parallel with the throttle 18. Passage 2
Since it is guided to the head chamber 24 of the arm cylinder 22 via the check valve 72, the arm cylinder switching valve 4, and the passage 25, the arm work can be performed while the vehicle is traveling (combined operation).

Similarly, in order to operate the swing motor 29 (or the bucket cylinder 32) while the vehicle is traveling, the swing motor switching valve 3 (or the bucket cylinder switching valve 10) is switched to the functional position, and the merging switching valve 13 is moved to the merging position. Switch to a. As a result, a part of the oil discharged from the second pump 7 is reduced by the throttle 18 (or the throttle 1
4), it flows into the swing motor 29 (or bucket cylinder 32) through the working machine switching valve, and the remaining discharge oil of the second pump 7 passes through the throttle 20 of the merging switching valve 13 and is discharged by the first pump 1. It merges with the oil and travel motor 3 via travel switching valves 5 and 11
Since the flow is divided into 9,41, combined operation by the vehicle and the turning motor 29 (or the bucket cylinder 32) can be obtained.

By the way, since the boom cylinder 47 requires a large amount of hydraulic oil, the discharge oil is supplied from both pumps 1 and 7 regardless of whether the vehicle is running or stopped.

That is, when the boom cylinder 47 is operated while the vehicle is stopped, the boom cylinder switching valve 9 is switched to the functional position, for example, the position a, and the merging switching valve 13 is switched to the merging position a. As a result, the oil discharged from the first pump 1 is held at a proper pressure by the throttle downstream of the arm cylinder switching valve 4 in the center bypass passage of the first circuit system 6, and the merging switching valve 13, the second traveling switching valve 11, When flowing to the boom cylinder 47 through the check valves 74 and 76 of the parallel passage 8 and the boom cylinder switching valve 9, the throttle 14 or 20 from the second pump 7 or the throttles 14 and 2
The return oil from the rod chamber 50 of the boom cylinder 47 returns to the tank 28 via the return passages 48, 37 from the boom cylinder switching valve 9 together with the discharged oil that has passed through 0 and flows into the head chamber 49. When operating the boom cylinder 47 while the vehicle is traveling,
The boom cylinder switching valve 9 is switched to the functional position and the merging switching valve 13 is switched to the merging position a. This makes the first
A part of the discharge oil of the pump 1 and the second pump 7 flows into the travel motors 39, 41 via the travel switching valves 5, 11, while the remaining discharge oil is the throttle 14, the check valve 76 of the parallel passage 8, the boom. It flows into the boom cylinder 45 via the cylinder switching valve 9.

In the above-described embodiment, the traveling switching valves 5 and 11, the working machine switching valves 3 and 4,
Although both 9, 10 and the merging switching valve 13 were manually operated, another embodiment in which this is a pilot operated system will be described with reference to FIG. In the figure, a first pump 1 includes a swing motor switching valve 3 ', an arm cylinder switching valve 4', and a working machine switching valves 3 ', 4'connected by a parallel passage 2.
Uppermost first directional switching valve 5'connected to the tandem
And the like are connected to the inlet port of the first traveling switching valve 5'of the first circuit system 6. The second pump 7 includes a boom cylinder switching valve 9 ′ and a bucket cylinder switching valve 10 ′ connected by a parallel passage 8 and a topmost stream type tandem connected to these working machine switching valves 9 ′, 10. It is connected to the inlet port of the second traveling switching valve 11 'of the second circuit system 12 composed of the second traveling switching valve 11' and the like via the confluence switching valve 13 ', and the second circuit system 12 is connected in parallel. The passage 8 is connected to the passage 8 via a passage 15. The merging switching valve 13 'is provided in a passage 16 which connects the first pump 1 and the first traveling switching valve 5'.
The connection is made via 17 and at the same time, it is connected to the parallel passage 2 of the first circuit system 6 by a passage 19 having a throttle 18.

The first traveling switching valve 5'and the second traveling switching valve 11 'are provided with auxiliary valves 51, 52 for connecting the pilot passage 59 in the functional position, and working machine switching valves 3', 4 ', 9', 10 are provided. ′ Is an auxiliary valve 53, 54,5 which cuts off the pilot passage 59 in the functional position.
Provide 5,56. And the pilot pump 57 is an auxiliary valve
52, 51, 53, 54, 55, 56 are sequentially connected to a pilot passage 59 which is connected to the tank 58. The pilot passage 59 connects the passage between the auxiliary valves 51 and 53 to the pilot port of the merging switching valve 13 'via the pilot passage 60, and also connects it to the center bypass passage 61 downstream of the arm cylinder switching valve 4'. It is connected to a pilot port of the mounted pilot opening / closing valve 62 via a pilot passage 63.

The boom cylinder switching valve 9'is connected to the remote control valve 66 via the pilot passages 64 and 65, the pilot passages 64 and 65 are connected to the shuttle valve 67, and the secondary port of the shuttle valve 67 is from the shuttle valve 67. Is connected to the pilot passage 59 between the auxiliary valves 53 and 54 via a check valve 68 that allows only the fluid flow of the above. The work machine switching valves 10 ', 11', 5 ', 3', 4'other than the boom cylinder switching valve 9 'are controlled by dedicated remote control valves (not shown).

In this embodiment, when the traveling switching valves 5'and 11 'are in the neutral position and the vehicle is in a stopped state, the pilot passage 59 has the auxiliary valves 52 and 51.
Since it is cut off and the pilot passage 60 communicates with the tank 58, the merging switching valve 13 ′ is biased by the spring 69 to the non-merging position b.
Take In this state, when one of the working machine switching valves 3 ', 4'10' is switched to the functional position, it is the swing motor switching valve 3 ', and the discharge oil of the first pump 1 is the first traveling switching valve. 5 ', check valves 71, 73 of the parallel passage 2, switching valve 3'
And is guided to the swing motor 29 via the arm cylinder switching valve 4 ', the discharge oil of the first pump 1 is discharged from the first pump 1', the check valves 71, 72 of the parallel passage 2 and the switching valve 4 '.
And is guided to the arm cylinder 22 via the flow path, and in the bucket cylinder switching valve 10 ', the oil discharged from the second pump 7 is combined with the merging switching valve 1'.
3 ', the second traveling switching valve 11', the check valves 74 and 75 of the parallel passage 8, and the switching valve 10 'are introduced to the bucket cylinder 32. Further, the oil discharged from the working machine is returned to the tank 28 through the working machine switching valve and the return passage, so that the working machine is started.

If only the drive switching valves 5 ', 11' are switched to the functional position in order to drive the vehicle, the auxiliary passages 52, 51 allow the pilot passage 5
Since 9 is connected and the pilot pump 57 communicates with the tank 58, the merging switching valve 13 'takes the non-merging position b by the spring 69 and disconnects the communication between the traveling switching valves 5'and 11'. Therefore, the discharge oil of the first pump 1 passes through the first traveling switching valve 5'to the right traveling motor 39, and the discharge oil of the second pump 7 passes through the merging switching valve 13 'and the second traveling switching valve 11'. After that, the return oil is guided to the left travel motor 41, the return oil from the travel motors 39, 41 returns to the tank 28, and the vehicle travels straight by the left and right travel motors.

When any one of the working machine switching valves 3 ', 4', 10 'is switched to the functional position while the vehicle is traveling, the pilot passage 59 is blocked or cut off by the auxiliary valve of the switched working machine switching valve in any case. It On the other hand, the auxiliary valves 51, 52 of the traveling switching valves 5 ', 10' communicate with the pilot passage 59 upstream of the auxiliary valve 53. Therefore, the merging switching valve 13 'is switched to the merging position a by the pilot pressure from the pilot pump 57, and like the embodiment of FIG. 1, a part of the oil discharged from the second pump 7 is guided to the working machine. , The remaining discharge oil merges with the discharge oil of the first pump 1 through the throttle 20, travels through the travel switching valves 5 ', 11', and the travel motor 39,
Since it is divided into 41, a combined operation of the vehicle and work equipment can be obtained.

To operate the boom cylinder 47 while the vehicle is traveling, the boom cylinder switching valve 9'is switched to the functional position. As a result, the auxiliary valve 55 cuts off the pilot passage 59, so that the merging switching valve 13 'is switched to the merging position a by the pilot pressure of the pilot pump 57, which has been cut off from the communication with the tank 28. As in the example, part of the oil discharged from the first pump 1 is diverted to the traveling motors 39 and 41 through the traveling switching valves 5'and 11 ',
The remaining discharge oil passes through the throttle 20 of the merging switching valve 13 ', and the second
It merges with the oil discharged from the pump 7, and flows into the boom cylinder 47 via the throttle 14, the check valve 76 in the parallel passage 8 and the boom cylinder switching valve 9 '. To operate the boom cylinder 47 with the vehicle stopped, the boom cylinder switching valve 9'is switched to the functional position by the remote control valve 66. Accordingly, the pilot pressure of the remote control valve 66 is provided in the shuttle valve 67 and the check valve in the pilot passage between the auxiliary valve 55 that is in the off position and the auxiliary valve 51 of the traveling switching valve 5 ′ that is in the off position when the vehicle is stopped. The pilot pressure is introduced via 68, and this pilot pressure acts on the merging switching valve 13 'via the pilot passage 60 to switch the merging switching valve 13' to the merging position a. As a result, the discharge oil of the second pump 7 flowing into the parallel passage 8 from the passage 15 having the throttle 14 interposed, the merging switching valve 13 ', and the second traveling switching valve 1
The discharge oil of the first pump 1 flowing into the parallel passage 8 via 1'is merged and passed through the switching valve 9'and the boom cylinder 47.
The return oil flows back to the tank 28 through the switching valve 9'and the return passages 48 and 37.

In the embodiment shown in FIG. 2, since the switching operation of the merging switching valve 13 for performing the combined operation or the operation of only the boom cylinder is automatically performed by the operation of the actuator switching valve, the operation is simplified.

[Effect of device]

Since the present invention is configured as described above, it has the following effects.

Regardless of whether the vehicle is running or stopped, the supply of discharge oil from both pumps to the boom cylinders can be obtained by operating one boom cylinder switching valve and one merging switching valve. Since it is not necessary to increase the number or to increase the supply pipe line to the boom cylinder, the hydraulic device can be simple and compact and can be manufactured at low cost.

Further, when the merging switching valve is switched to the merging position, the discharge pressure of the other pump connected to both parallel passages through the throttle is maintained high even when the load of the working machine is light,
Since it is possible to prevent a part of the oil discharged from one of the pumps connected to both traveling switching valves from flowing out to the working machine side, both the working machine and vehicle traveling operations can be reliably performed.

In the hydraulic system according to the second aspect, since the switching operation of the merging switching valve is unnecessary, the operation is simple and the work efficiency is improved, and the operation error can be eliminated.

[Brief description of drawings]

1 and 2 are hydraulic circuit diagrams of an embodiment of the present invention, and FIG. 3 is a hydraulic circuit diagram of a conventional device. 1 …… First pump, 2,8 …… Parallel passage, 3,4,9,10,
3 ', 4', 9 ', 10' ... Switching valve for working machine, 5,5 '... First
Traveling switching valve, 6 ... First circuit system, 7 ... Second pump, 11,11 '... Second traveling switching valve, 12 ... Second circuit system, 13,13' ... Joining switching valve , 14,18,20 …… Aperture, 61…
… Center bypass passage, 80… Throttle.

Claims (3)

[Scope of utility model registration request] 1. A center bypass passage is provided with two sets of circuit systems, and each circuit system comprises a most upstream travel switching valve connected to a pump and a plurality of working machine switching valves connected in parallel passages. In the hydraulic circuit of the construction machine, which is connected to the tandem through the control circuit to control the actuator by the merging switching valve connecting the traveling switching valve of both circuit systems, the parallel passage and the pump, and the switching valve of the actuator, 1
In the circuit system (6), the first pump (1) is connected to the first traveling switching valve (5) and the merging switching valve (13), and the parallel passage (2) is connected via the throttle (18). In the second circuit system (12), the second pump (7) is connected to the parallel passage (8) via the throttle (14), and the upstream side of the throttle (14) and for the second traveling. The upstream of the switching valve (11) is connected to the merging switching valve (13), and further, a throttle (80) is provided downstream of the working machine switching valve group in the center bypass passage (61) of each circuit system to switch the merging switching. When the valve (13) is in the non-merging position (b), it connects the second pump (7) of the second circuit system (12) and the second travel switching valve (11), and
First communicating with the first pump (1) of the first circuit system (6)
When the traveling switching valve (5) and the parallel passage (2) are cut off from each other and the merging position (a) is taken, both traveling switching valves (11) and (5) are communicated with each other and the communication passage is formed. Is connected to the second pump (7) and the throttle (14) of the second circuit system (12) via the throttle (20) in the merging switching valve (13) and the parallel passage (8) and the first circuit system (6). A hydraulic system for a construction machine, which is configured to be connected to a parallel passage (2) connected to the throttle (18). 2. A work machine switching valve (3), (4), (9),
(10) and means for switching the traveling switching valves (5), (11) by pilot command pressure, and means for switching the predetermined working machine switching valve (9) and the confluence switching valve (13) with the same pilot command pressure 2. The hydraulic system for a construction machine according to claim 1, further comprising means for switching the merging switching valve (13) by a function position switching signal of the working machine switching valve while the vehicle is traveling. 3. The hydraulic system for a construction machine according to claim 2, wherein the predetermined working machine switching valve (9) is a boom cylinder switching valve.