JP4879042B2 - Hydraulic control device for work vehicle - Google Patents

Description

  The present invention relates to a hydraulic control device that can be used for both a work vehicle that runs on a crawler and a work vehicle that runs on a wheel.

For example, a work vehicle such as a power shovel includes a travel system actuator and a work machine system actuator. Such work vehicles include those that can operate a work machine system actuator while traveling and those that do not require a work machine system actuator to operate during travel.
Specifically, in a crawler-type power shovel, pressure oil is supplied simultaneously to the traveling system actuator and the work machine system actuator so that the work machine system actuator can be operated while traveling. . On the other hand, since a wheel-type power shovel is premised on road running, there is no need to operate an actuator of a work implement system during running. Therefore, when supplying pressure oil to the traveling system actuator, the supply of pressure oil to the work machine system actuator may be stopped.

As a hydraulic control device for a work vehicle as described above, the invention disclosed in Patent Document 1 is conventionally known. In the hydraulic control device, a pair of circuit systems for controlling the actuators of the traveling system and the work machine system are provided in the valve body, and a pump is connected to each of these two circuit systems. Both circuit systems provided in the valve body are provided with a plurality of switching valves for controlling the actuators, and these switching valves are connected in tandem to the pump. Further, the switching valve located at the most upstream among the switching valves controls the actuator of the traveling system.
In this way, when the switching valve for controlling the actuator of the traveling system is positioned at the most upstream, and when the switching valve for traveling is switched, the working switching valve located downstream thereof is shut off from the pump, The travel system actuator can be operated with priority.

Note that the hydraulic control device shown in Patent Document 1 is based on the crawler specification, and the circuit configuration of the traveling system is different in the case of the wheel specification.
However, the configuration of the work implement system, that is, the configuration on the downstream side of the switching valve located in the uppermost stream in both circuit systems, is not particularly required to be different between the crawler specification and the wheel specification.
JP-A-6-017449

In the hydraulic control apparatus for work vehicles described above, the circuit configuration of the traveling system differs between the crawler specification and the wheel specification. Therefore, the hydraulic control device cannot be shared between the crawler specification and the wheel specification even though the circuit configuration of the work machine system is exactly the same.
In other words, at the manufacturing site, the hydraulic control device mounted on the wheel specification work vehicle and the hydraulic control device mounted on the crawler specification work vehicle must be stocked separately in order to fulfill orders. There is a problem that inventory management becomes complicated.

  An object of the present invention is to provide a hydraulic control device that can be used in common for work vehicles having the same work machine system circuit configuration even when the travel system circuit configuration is different.

  In this invention, the valve body is provided with a first circuit system connected to the first pump via the first pump passage and a second circuit system connected to the second pump via the second pump passage, In the first circuit system, the neutral flow path is kept open at the neutral position, the neutral flow path is kept in the throttled state or the closed state at the switching position other than the neutral position, and the supply port, tank port, A plurality of switching valves that open and close the actuator port, a first center bypass passage that connects each of the neutral flow paths in tandem, and the first center bypass passage that is located downstream of the switching valve that is positioned on the most upstream side, A first parallel passage connected to the supply port of all or any of the switching valves located downstream of the upstream switching valve, the uppermost switching valve having its neutral flow path and supply port While each is connected to the first pump passage, in the second circuit system, the neutral flow path is kept open when neutral, and the neutral flow path is set to a throttled state or closed state at a switching position other than the neutral position. A plurality of switching valves that open and close the supply port, tank port, and actuator port at the switching position, a second center bypass passage that connects these neutral flow paths in tandem, and a supply port of each switching valve. And a hydraulic control device for a work vehicle comprising a second parallel passage connected to the second pump via the second pump passage.

  On the premise of the above configuration, the first aspect of the present invention is that a connecting passage of the valve body for connecting a sub-body which is another valve section is provided with a branch passage communicating with the first pump passage. A first passage port, a second passage port that opens a branch passage that communicates with the first parallel passage, a third passage port that opens a branch passage that communicates with the second pump passage, and a second circuit It is characterized in that a neutral flow path in the most upstream switching valve of the system and a fourth passage opening formed by opening a branch passage communicating with the supply port are formed.

  According to a second aspect of the present invention, a crawler sub-body which is another valve section is fixed to the connecting surface of the valve body, and the first passage port and the second passage port are connected to the sub-body. A communication passage and a second communication passage connecting the third passage port and the fourth passage port are provided, and a selector valve is connected to both the communication passages. The first communication passage and the second communication passage are maintained in communication with each other at the position, and when switched from the predetermined switching position, the first passage port is communicated with the fourth passage port, and the third passage port Is characterized in that it is configured to communicate with the second passage port.

  According to a third aspect of the present invention, a wheel sub-body, which is another valve section, is fixed to the connecting surface of the valve body. The sub-body maintains a neutral flow path open when neutral, and other than the neutral position. A traveling switching valve that keeps the neutral flow path in a throttled or closed state at the switching position and opens and closes the supply port, the tank port, and the actuator port at the switching position, the supply port of the traveling switching valve, A first connection passage that communicates with one passage port; a second connection passage that communicates the third passage port with the fourth passage port via a neutral flow channel when the travel switching valve is neutral; and the second passage port It has a feature in that it includes a blocking portion that blocks the.

According to the first to third aspects of the invention, the valve body is provided with a circuit configuration that can be used in common between the crawler specification and the wheel specification, and a predetermined passage that communicates with different circuit components in both specifications is provided to other valves. The sub-body, which is a section, was opened on the connecting surface for connecting. In other words, because only the part that can be used in common between the crawler specification and the wheel specification is formed in the valve body, it is possible to use the valve body in common on both specification work vehicles, reducing stock on the work site. Inventory management can be facilitated.
In addition, since a predetermined passage communicating with different circuit components in both specifications is opened in the connecting surface of the valve body, it is easy to hydraulically simply fix the sub-body that configures different circuits according to the specifications to the surface. The function as a control device can be exhibited.

An embodiment of the present invention will be described with reference to FIGS. Incidentally, FIG. 1, by a valve body VB and the sub-body SB _1, constitute the hydraulic circuit of the crawler specification, FIG. 2, by a valve body VB and the sub-body SB _2, constitute a hydraulic circuit of the wheel specifications Yes.
A portion surrounded by a two-dot chain line in the figure corresponds to the valve body VB of the present invention, and the valve body VB constitutes the illustrated circuit.
That is, the valve body VB includes a first circuit system A configured on the left side in the figure and a second circuit system B configured on the right side in the figure. The first pump P ₁ and the second pump P ₂ are connected.

The first circuit system A, provided with a first pump passage 1 which communicates with the first pump P _1, are connected to switchable switching valve 2 to the first pump passage 1. When the switching valve 2 is in the neutral position, the neutral flow path 2a is kept open, and the first pump passage 1 and the neutral flow path 2a are communicated with each other. The switching valve 2 is provided with a supply port 2b, a tank port 2c, and actuator ports 2d ₁ and 2d _2, and the first pump passage 1 is connected to the supply port 2b.
The actuator ports 2d ₁ and 2d ₂ are connected to predetermined actuators described later. When the switching valve 2 is switched, the neutral flow path 2a is kept in the throttled state or the closed state, and the actuator is at the switching position. The ports 2d ₁ and 2d ₂ are connected to the supply port 2b or the tank port 2c.

In the first circuit system A, switching valves 3 to 6 having neutral flow paths 3a to 6a are provided so as to be switchable. And the neutral flow paths 2a-6a of each switching valve 2-6 are connected to the tandem by the 1st center bypass passage 7. FIG.
Similarly to the switching valve 2, each of the switching valves 3 to 6 keeps the neutral flow paths 3a to 6a in an open state when the switching valve 3 is in the neutral position, and allows the first center bypass passage 7 to communicate with the tank. Therefore, if all the switching valves 2 to 6 are in the neutral position, the first pump P ₁ communicates with the tank via the first pump passage 1 and the first center bypass passage 7.

On the other hand, each switching valve 3-6, the supply port 3B～6b, tank port 3C～6c, and the actuator port _{3d 1, 3d 2 ~6d 1,} 6d 2 forms a, each selector valve 3-6 When in the switching position, the neutral flow paths 3a to 6a are kept in a throttled state or a closed state, and the actuator ports 3d ₁ , 3d _{2 to} 6d ₁ and 6d ₂ communicate with the supply ports 3b to 6b or the tank ports 3c to 6c. Like to do.
In this embodiment, the switching valve 3 is a spare, and controls a predetermined actuator necessary for each work vehicle, the switching valve 4 controls the turning motor, and the switching valve 5 increases the boom. For speed, the switching valve 6 controls the arm cylinder.

  The first center bypass passage 7 is connected to the first parallel passage 8 downstream of the most upstream switching valve 2 and upstream of the switching valve 3. The first parallel passage 8 is connected to the supply ports 3 b to 6 b of the switching valves 3 to 6 located on the downstream side of the upstreammost switching valve 2. That is, the switching valves 3 to 6 are connected in parallel. In this embodiment, the switching valves 3 to 6 are connected in parallel. However, all the switching valves 3 to 6 are not necessarily connected in parallel, and any one of the switching valves 3 to 6 is connected. You may make it connect.

A branch passage 9 that branches the upstream side of the switching valve 2 is connected to the first pump passage 1. The branch passage 9 communicates with the first passage port po ₁ that opens to the connecting surface X of the valve body VB. A second passage port po ₂ is opened on the connecting surface X, and a branch passage 10 connected to the first parallel passage 8 is communicated with the second passage port po ₂ . Incidentally, articulating surface X of the valve body VB is a surface fixed by concatenating sub-body SB ₁ below is another valve section.

On the other hand, in the second circuit system B, a second pump passage 11 communicating with the second pump P ₂ is provided, and a second parallel passage 12 is connected to the second pump passage 11. The second parallel passage 12 is connected in parallel to supply ports 13b-16b formed in the switching valves 13-16.
Each of the switching valves 13 to 16 forms a neutral flow path 13a to 16a as well as the switching valves 2 to 6, and the tank ports 13c to 16c and the actuator ports 13d ₁ , 13d _{2 to} 16d ₁ , 16d _2. Is forming.
In this embodiment, the switching valve 13 controls a predetermined actuator, which will be described later, the switching valve 14 controls the bucket cylinder, the switching valve 15 controls the boom cylinder, and the switching valve 16 is for arm acceleration. It is used as

And in the 2nd circuit system B, the 2nd center bypass channel | path 17 which connects the neutral flow paths 13a-16a formed in each said switching valve 13-16 to a tandem is provided, and each switching valve 13-16 is neutral. When in position, the neutral flow paths 13a to 16a are maintained in an open state, and the second center bypass passage 17 is communicated with the tank.
In each switching valve 14 to 16, when it is in a neutral position, while maintaining the port in the closed state, the changeover valve 13, when it is in a neutral position, both actuator ports _13d 1, 13d ₂ And the tank port 13c are communicated with each other, and the supply port 13b is kept closed. And in the switching position of each switching valve 13-16, while the neutral flow paths 13a-16a maintain a throttled state or a closed state, various ports are connected.

Further, the second circuit system B is provided with a branch passage 18 communicating with the second pump passage 11, and this branch passage 18 is connected to the third passage port po ₃ opening in the connection surface X. Further, a fourth passage port po ₄ is opened on the connecting surface X, and a branch passage 19 is connected to the fourth passage port po _4, and the neutral passage 13a of the switching valve 13 is connected via the branch passage 19. However, it communicates with the fourth passage port po ₄ .
A check valve 20 is provided in the second parallel passage 12 that branches to the supply port 13b of the switching valve 13 (reference numeral 12a in the figure), and an introduction passage 21 connected to the branch passage 19 is provided. Provided. The check valve 20 allows only the flow from the second pump passage 11 side to the supply port 13b and the introduction passage 21 side.
Further, tank passages 22 and 23 are formed in the valve body VB. The tank passages 22 and 23 are connected to the tank at one end, and the other end is opened to the connection surface X of the valve body VB. 5 and ₆ are connected to passage ports po ₅ and ₆ .

In FIG. 1, a crawler sub-body SB ₁ is indicated by a one-dot chain line below the valve body VB. The sub-body SB ₁ is fixed to the connecting surface X of the valve body VB with a bolt, and constitutes the following circuit inside.
That is, the first communication passage 24 and the second communication passage 25 are formed in the subbody SB ₁ . Both the communication passages 24 and 25 are opened at opposite surfaces Y opposite to the connection surface X of the valve body VB. More specifically, when the sub body SB ₁ and the valve body VB are fixed, the first communication passage 24 has one end connected to the first passage port po ₁ and the other end connected to the second passage port po ₂ . I try to connect. The second communication passage 25 is configured such that one end is connected to the third passage port po ₃ and the other end is connected to the fourth passage port po ₄ when the sub body SB ₁ and the valve body VB are fixed.

A selector valve 26 is connected to both the communication passages 24 and 25. The selector valve 26 is normally in the illustrated normal position and maintains both the communication passages 24 and 25 in the communication state. However, during operation, the selector valve 26 is operated to operate the switching valves 3 to 6 and the switching valves 14 to 14. When any one of 16 is switched, the left side position in the figure is switched.
Thus, when the selector valve 26 is in the illustrated normal position, the first passage port po ₁ and the second passage port po ₂ communicate with each other through the first communication passage 24 and discharge from the first pump P _1. The pressure oil is introduced into the first parallel passage 8 via the first pump passage 1 → the branch passage 9 → the first communication passage 24 → the selector valve 26 → the branch passage 10. Further, the second communication passage 25, with the third passage opening po ₃ and the fourth passage hole po ₄ is communicated, the pressure oil discharged from the second pump _{P 2} is a second pump passage 11 → the branch passage 18 → It is led to the second center bypass passage 17 via the second communication passage 25 → the selector valve 26 → the branch passage 19.

On the other hand, when the selector valve 26 is switched to the left position, the first passage port po ₁ and the fourth passage port po ₄ communicate with each other, and the third passage port po ₃ and the second passage port po ₂ communicate with each other. Thus, pressure oil discharged from the first pump P _1, together led to the second center bypass passage 17 through the first pump passage 1 → first communication passage 24 → the selector valve 26 → the branch passage 19, second pump The pressure oil discharged from P ₂ is guided to the first parallel passage 8 through the second pump passage 11 → the second communication passage 25 → the selector valve 26 → the branch passage 10.

As described above, when the sub-body SB ₁ is fixed to the valve body VB and is configured as a crawler, the left travel hydraulic motor is connected to the switching valve 2 positioned at the uppermost stream of the first circuit system A, and A hydraulic motor for right travel is connected to the switching valve 13 located at the uppermost stream of the two-circuit system B. That is, in the case of the crawler specification, the switching valve that controls the actuator of the traveling system is positioned in the uppermost stream of both circuit systems A and B.
In such a state, when only the traveling actuator is operated, that is, when only traveling is performed, the operation lever (not shown) is operated to switch the switching valves 2 and 13 in either direction.

Then, pressure oil discharged from the first pump P ₁ is supplied to the left travel motor via the first pump passage 1 → switching valve 2 feed port 2b → actuator port 2d. Meanwhile, pressure oil discharged from the second pump P _2, the second pump passage 11 → via a second parallel passage 12, and the second pump passage 11 → the branch passage 18 → second communication passage 25 → the selector valve 26 → Supplied via the branch passage 19 → the introduction passage 21 from the supply port 13b of the switching valve 13 → the actuator port 13d to the hydraulic motor for right travel. Therefore, straight traveling of the vehicle is guaranteed.
Further, when one of the switching valves 3 to 6 and the switching valves 14 to 16 is switched to operate the actuator of the work machine system while the vehicle is running, the selector valve 26 is switched along with the switching operation of the switching valve. Switches to the left position in the figure.

When the selector valve 26 is switched to the left position as described above, the pressure oil discharged from the first pump P ₁ is supplied from the first pump passage 1 to the hydraulic motor for left travel through the switching valve 2. At the same time, the oil is supplied to the right traveling hydraulic motor through the first pump passage 1 → the branch passage 9 → the first communication passage 24 → the selector valve 26 → the branch passage 19 → the switching valve 13.
Also, pressure oil discharged from the second pump P _2, together with the guided to the switching valve 14 to 16 to control the actuators of the working machine system from the second pump passage 11, a second pump passage 11 → the branch passage 18 → second It is guided to the switching valves 3 to 6 through the communication passage 25 → the selector valve 26 → the branch passage 10 → the first parallel passage 8.

In other words, in the above state, the pressure oil discharged from the first pump P ₁ is supplied only to the traveling hydraulic motor, and the pressure oil discharged from the second pump P ₂ is supplied to the actuator of the work machine system. . Therefore, the traveling hydraulic motor and the work machine system actuator do not affect each other, and the straight traveling performance of the vehicle is not impaired according to the load condition of the work machine system actuator.
As described above, if the sub-body SB ₁ is fixed to the connecting surface X of the valve body VB, and a traveling hydraulic motor is connected to the switching valves 2 and 13 located at the uppermost stream of both circuit systems A and B, The said hydraulic control apparatus can be used for the work vehicle of a crawler specification.

On the other hand, in the case of using the hydraulic control system in the working vehicle wheel specification, as shown in FIG. 2, the articulating surface X of the valve body VB, it may be fixed to the sub-body SB ₂ for wheel.
The sub body SB ₂ incorporates a travel switching valve 27 so as to be switchable. The travel switching valve 27 keeps the neutral flow path 27a open when neutral, and keeps the neutral flow path 27a in the throttled state or closed state at a switching position other than the neutral position. The travel switching valve 27 is provided with actuator ports 27d ₁ and 27d ₂ connected to a supply port 27b, a tank port 27c, and a travel hydraulic motor, and both actuator ports 27d ₁ and 27d _{2 are in} a neutral position. And the tank port 27c are communicated with each other, and the supply port 27b is kept closed. On the other hand, when the travel switching valve 27 is switched, both actuator ports 27d ₁ and 27d ₂ are communicated with the supply port 27b or the tank port 27c.
The sub body SB ₂ is provided with a first connection passage 28 connected to the supply port 27 b of the travel switching valve 27. The first connection passage 28 is connected to a first passage port po ₁ formed in the connection surface X when the connection surface X of the valve body VB and the opposing surface Y of the sub body SB ₂ are fixed to face each other. . That is, the first connection passage 28 connects the first passage port po ₁ and the supply port 27 b of the travel switching valve 27.

Further, when the travel switching valve 27 is in a neutral position, a second connection passage 29 that connects the third passage port po ₃ and the fourth passage port po ₄ via the neutral flow passage 27 a is provided. To the supply port 27b. A tank passage 30 is connected to the tank port 27c of the travel switching valve 27, and the tank port 27c is formed in the connecting surface X of the valve body VB via the tank passage 30 through fifth and sixth passage ports. Pos ₅ and ₆ are communicated.
Furthermore, the opposing surface Y of the sub body SB ₂ is formed with a blocking portion 31 that blocks the second passage port po ₂ that opens to the connecting surface X of the valve body VB. In other words, the sub body SB ₂ is not provided with a passage corresponding to the branch passage 10 and the second passage port po ₂ .
In addition, although this interruption | blocking part 31 is trying to prevent the oil leak from the branch passage 10 by a seal | sticker etc., the structure in particular is not limited.

When the hydraulic control device is used for a wheel-spec work vehicle, the switching valve 2 is used for the second speed control of the traveling hydraulic motor. Specifically, in the case of the wheel specification, the passage following the actuator ports 2d ₁ and 2d ₂ of the switching valve 2 is blocked. Therefore, even if the switching valve 2 is switched, the actuator is not controlled by the pressure oil guided to the actuator ports 2d ₁ and 2d ₂ through the switching valve 2, and the switching valve 2 is not connected to the first pump passage 1. Only functions to shut off from the tank.
Further, in the case of the wheel specification, an outrigger is connected to the actuator ports 13 d ₁ and 13 d ₂ of the switching valve 13, and the outrigger is controlled by the switching valve 13.

As described above, the control targets of the switching valves 2 and 13 are different between the wheel specification and the crawler specification. That travel, when the crawler specification, both circuit system A, with respect to the switching valve 2, 13 located at the most upstream to control the running of B, and when the wheel specifications provided in the sub-body SB ₂ The switching valve 27 for control controls traveling. In the case of the crawler specification, a switching valve for controlling the traveling motor must be provided on each of the left and right sides, whereas in the case of the wheel specification, there is only one switching valve for controlling the traveling motor. This is due to the fact that the sub-body SB ₂ is provided with a switching valve for controlling traveling.
In the above embodiment, in the case of the wheel specification, the switching valves 2 and 13 located at the uppermost stream of both circuit systems A and B are used for the control of the second speed running and the outrigger, but other actuators are used. It may be used for controlling.

Thus, when a crawler specification work vehicle is driven, the travel switching valve 27 is switched to connect the supply port 27b to one of the actuator ports 27d ₁ and 27d _{2 and to} the other of the other ports. The port is communicated with the tank port 27c.
Then, the pressure oil discharged from the second pump P ₂ is used for traveling via the second pump passage 11 → the branch passage 18 → the second connection passage 29 → the supply port 27 _b → the actuator ports 27 d ₁ and 27 d ₂ . The vehicle is driven by the hydraulic motor.
In the work vehicle wheel specification for during running does not control the actuators of the working machine system, located in the changeover valve 2-6 neutral position, even when the first pressurized oil from the pump P ₁ is not ejected, the total amount thereof It is returned to the tank via the first center bypass passage 7.

When the switching valve 2 is switched from the above state to the second speed, the neutral flow path 2a is closed and the first pump passage 1 is shut off from the tank. Then, the pressure oil discharged from the first pump P ₁ is guided to the supply port 27 _{b of} the travel switching valve 27 through the branch passage 9 and the first connection passage 28 and discharged from both the pumps P ₁ and P _2. The pressurized oils merged and guided to a traveling hydraulic motor. Therefore, if the switching valve 2 is switched during traveling, the traveling motor can be controlled at the second speed.
In addition, what is necessary is just to determine suitably the actuator which each switching valve 2-6 and switching valves 13-16 control as needed, and is not restricted to the said embodiment. However, when used in a crawler specification work vehicle, the switching valves 2 and 13 need to control the left and right traveling hydraulic motors.

On the other hand, when operating the work machine system actuator, if the work machine system switching valves 3 to 6 and the switching valves 13 to 16 are controlled, the pressure oil discharged from both the pumps P ₁ and P _{2 is used} to generate a predetermined actuator. Can be activated.
As described above, in the hydraulic control apparatus according to the above-described embodiment, a portion requiring a different circuit configuration between the crawler specification work vehicle and the wheel specification work vehicle is not configured in the valve body VB. Then, a passage communicating with a portion having a different circuit configuration between them, in other words, a passage having a different oil action between the crawler specification and the wheel specification, is opened on a specific surface of the valve body VB, and a subbody is formed in this opening. Aisle can be connected.
Therefore, the hydraulic control device can be used for a work vehicle of any specification simply by fixing the sub-body whose circuit configuration has been changed to the valve body VB.

It is a figure which shows the state which comprised the circuit of the crawler specification. It is a figure which shows the state which comprised the circuit of the wheel specification.

Explanation of symbols

1 first pump passage 2-6 switching valve 2a~6a neutral flow passage 2b~6b supply port 2c~6c tank port _{2d 1, 2d 2 ~6d 1,} 6d 2 actuator port 7 first center bypass passage 8 first parallel passage 9,10 branch passage 11 second pump passage 12 second parallel passage 13 to 16 the switching valve 13a~16a neutral flow passage 13b~16b supply port 13c~16c tank port _{13d 1, 13d 2 ~16d 1,} 16d 2 actuator ports 17 Second center bypass passages 18, 19 Branch passage 24 First communication passage 25 Second communication passage 26 Selector valve 27 Traveling switching valve 27a Neutral flow passage 27b Supply port 27c Tank port 27d Actuator port 28 First connection passage 29 Second connection Passage 31 Blocking part A First circuit system B Second circuit system P ₁ 1st pump P ₂ 2nd pump SB _{1, 2} Subbody VB Valve body X Connecting surface po ₁ 1st passage port po ₂ 2nd passage port po ₃ 3rd passage port po ₄ 4th passage port

Claims (3)

  The valve body is provided with a first circuit system connected to the first pump via the first pump passage and a second circuit system connected to the second pump via the second pump passage, and the first circuit system In the neutral position, the neutral flow path is kept open, the neutral flow path is kept in the throttled state or closed state at the switching position other than the neutral position, and the supply port, tank port, and actuator port are opened and closed at the switching position. A plurality of switching valves, a first center bypass passage that connects each of the neutral flow paths in tandem, and the first center bypass passage on the downstream side of the switching valve that is positioned on the most upstream side. A first parallel passage connected to the supply port of all or any of the switching valves located on the downstream side, wherein the uppermost switching valve has its neutral flow path and supply port respectively While the second circuit system is connected to the first pump passage, the neutral flow path is kept open when neutral, and the neutral flow path is kept in a throttled state or closed state at a switching position other than the neutral position, In addition, a plurality of switching valves that open and close the supply port, tank port, and actuator port at the switching position, a second center bypass passage that connects these neutral flow paths to the tandem, and a supply port of each switching valve In the hydraulic control device for a work vehicle comprising a second parallel passage connected to the second pump via the second pump passage, the connection of the valve body for connecting the sub-body which is another valve section The surface has a first passage port formed by opening a branch passage communicating with the first pump passage, and a second passage formed by opening a branch passage communicating with the first parallel passage. An opening, a third passage opening that opens a branch passage that communicates with the second pump passage, and a branch passage that communicates with the neutral flow path and the supply port in the most upstream switching valve of the second circuit system. The hydraulic control apparatus for work vehicles which formed the 4th passage opening which becomes.   A crawler sub-body, which is another valve section, is fixed to the connecting surface of the valve body. The sub-body includes a first communication passage that connects the first passage port and the second passage port, and A second communication passage connecting the third passage port and the fourth passage port is provided, and a selector valve is connected to both the communication passages. The selector valve is connected to the first communication passage at a predetermined switching position. The second communication passage is maintained in the communication state, and when the predetermined switching position is switched, the first passage port is communicated with the fourth passage port, and the third passage port is used as the second passage port. The hydraulic control device for a work vehicle according to claim 1, wherein the hydraulic control device is configured to communicate with each other.   The connecting body of the valve body is fixed with a wheel sub-body that is another valve section. The sub-body keeps the neutral flow path open when neutral, and this neutral flow at a switching position other than the neutral position. A travel switching valve that opens and closes the supply port, the tank port, and the actuator port at the switching position, and that connects the first passage port with the supply port of the travel switching valve. A first connection passage, a second connection passage that communicates the third passage port and the fourth passage port via a neutral passage when the travel switching valve is neutral, and a blocking portion that blocks the second passage port The hydraulic control device for a work vehicle according to claim 1, further comprising:

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