JP2010138924A - Hydraulic system for working vehicle, and method of controlling the hydraulic system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic system for a working vehicle capable of improving fuel economy. <P>SOLUTION: In this hydraulic system, a flow joining/dividing selector valve is switched between a flow dividing state and a flow joining state. In the flow dividing state, operating fluid discharged from a first hydraulic pump is supplied to a high-pressure circuit including a hydraulic clutch, and operating fluid discharged from a second hydraulic pump is supplied to a low-pressure circuit. In the flow joining state, the operating fluid discharged from the first hydraulic pump and the operating fluid discharged from the second hydraulic pump are supplied to the high-pressure circuit. A filling completion detecting section detects completion of filling of the operating fluid in the hydraulic clutch. A control section controls the flow joining/dividing selector valve to the flow joining state from a start of supply of the operating fluid to the hydraulic clutch to completion of filling. The control section controls the flow joining/dividing selector valve to the flow dividing state after completion of filling is detected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hydraulic system for a work vehicle and a control method for the hydraulic system.

Conventionally, as shown in Patent Document 1 and Patent Document 2, a hydraulic system has been devised that can reduce power loss by switching between merging and splitting of two hydraulic pumps. This hydraulic system includes a small-capacity high-pressure pump, a high-capacity low-pressure pump, a clutch circuit, and a lubrication circuit. The clutch circuit supplies hydraulic oil for switching the transmission clutch. The lubrication circuit supplies hydraulic oil for lubricating the transmission. A priority valve is provided between the clutch circuit and the lubrication circuit. When the clutch is operated, the priority valve is operated, so that the hydraulic oil from the high-capacity low-pressure pump merges with the hydraulic oil from the small-capacity high-pressure pump and is supplied to the clutch circuit. When the clutch operation is completed, the priority valve is switched so that the hydraulic oil from the high-capacity low-pressure pump is supplied to the clutch circuit, and the hydraulic oil from the small-capacity high-pressure pump is supplied to the lubrication circuit.
Japanese Utility Model Publication No. 5-27423 JP 2007-177868 A

  When the hydraulic oil is supplied to the clutch, the supply of the hydraulic oil is started at a relatively large flow rate in order to complete the filling of the hydraulic oil into the clutch (hereinafter referred to as “fill”) at an early stage. Next, the flow rate of the hydraulic oil is reduced before the filling is completed, and the modulation is performed so that the clutch pressure is increased in a desired manner after the filling is completed. Then, when the clutch pressure reaches a predetermined set pressure, the clutch operation is completed.

  Here, in the above prior art, the hydraulic oil from the high-capacity low-pressure pump always joins the hydraulic oil from the small-capacity high-pressure pump to the clutch circuit from the start of supply of hydraulic oil to the clutch until the completion of the clutch operation. Have been supplied. Therefore, in the above conventional technique, the hydraulic oil from the high-capacity low-pressure pump and the hydraulic oil from the small-capacity high-pressure pump are merged and supplied to the clutch circuit until the clutch pressure reaches a predetermined set pressure. Accordingly, it is necessary to select a high-capacity low-pressure pump that can discharge a predetermined set pressure. It is true that a large flow rate of hydraulic oil is required from the start of the supply of hydraulic oil to the clutch until the completion of filling in order to complete the filling at an early stage. However, from the completion of filling to the completion of clutch operation, the hydraulic oil supplied to the clutch needs to have a sufficiently high pressure, but does not necessarily have to have a large flow rate. In the above prior art, since a large flow rate of hydraulic oil is always supplied from the start of supply of hydraulic oil to the clutch until the completion of clutch operation, wasteful supply of hydraulic oil occurs. For this reason, power loss occurs.

  An object of the present invention is to provide a hydraulic system for a work vehicle and a control method for the hydraulic system, which can reduce power loss and can use a low pressure pump as a high capacity low pressure pump.

  A hydraulic system for a work vehicle according to a first aspect of the present invention includes an engine, a first hydraulic pump and a second hydraulic pump, a high pressure circuit, a low pressure circuit, a combined / divergence switching valve, a fill completion detection unit, and a control unit. Prepare. The first hydraulic pump and the second hydraulic pump are driven by the engine and discharge hydraulic oil. The high pressure circuit is a hydraulic circuit including a hydraulic clutch. The low pressure circuit is a hydraulic circuit to which hydraulic oil having a lower pressure than that of the high pressure circuit is supplied. The merge / division switching valve is switched between a diversion state and a merge state. In the diversion state, the hydraulic oil discharged from the first hydraulic pump is supplied to the high pressure circuit, and the hydraulic oil discharged from the second hydraulic pump is supplied to the low pressure circuit. In the merged state, the hydraulic oil discharged from the first hydraulic pump and the hydraulic oil discharged from the second hydraulic pump are supplied to the high pressure circuit. The fill completion detection unit detects the completion of fill of hydraulic oil to the hydraulic clutch. The control unit brings the joining / separating switching valve into a joining state from the start of supplying hydraulic oil to the hydraulic clutch until the completion of filling is detected. Then, after the completion of the fill is detected, the control unit sets the combined / diverting switching valve to the diversion state.

  In this hydraulic system, the merging / separating switching valve is maintained in the merging state from the start of supplying hydraulic oil to the hydraulic clutch until the completion of filling is detected. As a result, a large flow rate of hydraulic oil discharged from the first hydraulic pump and the second hydraulic pump is supplied to the high-pressure circuit. When the completion of the fill is detected, the merge / division switching valve is switched to the diversion state. Thus, the hydraulic oil from the second hydraulic pump is supplied to the low pressure circuit, and the hydraulic oil from the first hydraulic pump is supplied to the high pressure circuit. For this reason, the flow volume of the hydraulic fluid supplied to the hydraulic clutch is suppressed, and wasteful supply of hydraulic fluid can be suppressed. As a result, the fuel consumption of the engine can be improved.

  A control method for a hydraulic system for a work vehicle according to a second aspect of the present invention includes an engine, a first hydraulic pump and a second hydraulic pump, a high pressure circuit, a low pressure circuit, a combined / divergence switching valve, and a fill completion detection unit. It is a control method of a hydraulic system. The first hydraulic pump and the second hydraulic pump are driven by the engine and discharge hydraulic oil. The high pressure circuit is a hydraulic circuit including a hydraulic clutch. The low pressure circuit is a hydraulic circuit to which hydraulic oil having a lower pressure than that of the high pressure circuit is supplied. The merge / division switching valve is switched between a diversion state and a merge state. In the diversion state, the hydraulic oil discharged from the first hydraulic pump is supplied to the high pressure circuit, and the hydraulic oil discharged from the second hydraulic pump is supplied to the low pressure circuit. In the merged state, the hydraulic oil discharged from the first hydraulic pump and the hydraulic oil discharged from the second hydraulic pump are supplied to the high pressure circuit. The fill completion detection unit detects the completion of fill of hydraulic oil to the hydraulic clutch. The control method of the hydraulic system includes a step of starting supply of hydraulic oil to the hydraulic clutch by setting the merging / separating switching valve to a merging state, and the merging / separating switching valve after the completion of filling is detected by the fill detecting unit. And setting the state.

  In this control method, the merging / separating switching valve is maintained in the merging state from the start of supplying hydraulic oil to the hydraulic clutch until the completion of filling is detected. As a result, a large flow rate of hydraulic oil discharged from the first hydraulic pump and the second hydraulic pump is supplied to the high-pressure circuit. When the completion of the fill is detected, the merge / division switching valve is switched to the diversion state. Thus, the hydraulic oil from the second hydraulic pump is supplied to the low pressure circuit, and the hydraulic oil from the first hydraulic pump is supplied to the high pressure circuit. For this reason, the flow volume of the hydraulic fluid supplied to the hydraulic clutch is suppressed, and wasteful supply of hydraulic fluid can be suppressed. As a result, the fuel consumption of the engine can be improved.

  The present invention can suppress wasteful supply of hydraulic oil to the hydraulic clutch, reduce power loss, and use a low-pressure high-capacity low-pressure pump.

[Configuration of hydraulic system]
A hydraulic system according to an embodiment of the present invention is shown in FIG. This hydraulic system is mounted on a work vehicle such as a bulldozer or a dump truck, for example, and includes an engine 2, a first hydraulic pump 3 and a second hydraulic pump 4, a clutch circuit 5, and a lubrication circuit 6. A shunt switching circuit 7, a relief valve 8, and a controller 9 are provided.

  The engine 2 is, for example, a diesel engine, and the output torque and the rotational speed are controlled by controlling the fuel injection amount from a fuel injection device (not shown). The rotational speed of the engine 2 is detected by the engine rotational speed sensor 12 and sent to the controller 9 as a detection signal.

  The first hydraulic pump 3 and the second hydraulic pump 4 are driven by the engine 2 to discharge hydraulic oil. The first hydraulic pump 3 and the second hydraulic pump 4 are fixed displacement hydraulic pumps that change the discharge amount of hydraulic oil in accordance with the rotational speed of the engine 2. The discharge capacity of the first hydraulic pump 3 is smaller than the discharge capacity of the second hydraulic pump 4. Also, the first hydraulic pump 3 can discharge higher pressure oil than the second hydraulic pump 4.

  The clutch circuit 5 is a circuit including the clutch 13 of a transmission (not shown). For example, a circuit disclosed in Japanese Patent Laid-Open No. 2001-343032 can be used. The clutch circuit 5 can control the hydraulic oil to a desired pressure and supply it to the clutch 13. The clutch circuit 5 can collect oil from the clutch 13 and discharge it to the tank 14. In this hydraulic system, a plurality of clutch circuits are provided corresponding to forward, reverse, and a plurality of speed stages, but only one clutch circuit 5 is shown in FIG. The clutch circuit 5 includes a clutch 13, a pressure control valve 15, and an electromagnetic control valve 16.

  The pressure control valve 15 is a device for controlling the hydraulic pressure (hereinafter referred to as “clutch pressure”) supplied to the clutch 13. The pressure control valve 15 is connected to the input flow path 11, the output flow path 17, and the drain flow path 18. The input channel 11 is connected to a first channel 19 described later. The output flow path 17 is connected to the clutch 13. The drain channel 18 is connected to the tank 14. The pressure control valve 15 adjusts the hydraulic pressure of the input flow path 11 according to the magnitude of the pilot pressure of the pilot flow path 21 connected to the electromagnetic proportional valve 16 described later, and guides it to the output flow path 17. That is, the pressure control valve 15 changes the clutch pressure according to the input pilot pressure. In the state where the pilot pressure is not supplied to the pressure control valve 15, the pressure control valve 15 connects the output flow path 17 and the drain flow path 18. As a result, the hydraulic oil is discharged from the clutch 13 and collected in the tank 14. A pilot flow path 21 is connected to the pilot port of the pressure control valve 15.

  The electromagnetic control valve 16 is a device for controlling the pilot pressure input to the pressure control valve 15. The electromagnetic control valve 16 is connected to the input flow path 11 via the throttle 34. The pilot flow path 21 described above is connected between the electromagnetic control valve 16 and the throttle 34. Further, the electromagnetic control valve 16 is connected to the tank 14 via the drain flow path 33. The electromagnetic control valve 16 can be switched between a connection state in which the input flow path 11 and the drain flow path 33 are connected and a blocking state in which the input flow path 11 and the drain flow path 33 are blocked. The electromagnetic control valve 16 is switched between a connected state and a disconnected state according to the magnitude of the command current input from the controller 9. Thereby, the electromagnetic control valve 16 can control the pilot pressure supplied to the pilot flow path 21 according to the command current.

  The clutch circuit 5 is provided with a pressure switch 22. The pressure switch 22 outputs a detection signal to the controller 9 when the clutch pressure reaches a predetermined set pressure. As the set pressure, a value corresponding to the pressure (fill pressure) at the completion of filling of the hydraulic oil to the clutch 13 is set. Therefore, the pressure switch 22 detects the completion of filling and outputs a detection signal to the controller 9.

  The lubrication circuit 6 includes a torque converter 23 and supplies hydraulic oil for driving the torque converter 23 to the torque converter 23.

  The merge / separation switching circuit 7 includes a merge / divergence switching valve 24 and an electromagnetic switching valve 25.

  The merge / division switching valve 24 is a valve that can be switched between a merge state and a diversion state. The merge / divergence switching valve 24 connects the first flow path 19 and the second flow path 26 in the merged state. The first flow path 19 is a flow path that connects the first hydraulic pump 3 and the input flow path 11 of the clutch circuit 5. The second flow path 26 is a flow path connected to the second hydraulic pump 4. Therefore, when the merging / separation switching valve 24 is in the merging state, the hydraulic oil discharged from the first hydraulic pump 3 and the hydraulic oil discharged from the second hydraulic pump 4 merge and are supplied to the clutch circuit 5. Is done. Further, the combined / divergence switching valve 24 connects the second flow path 26 and the third flow path 27 in the diversion state. The third flow path 27 is a flow path connected to the lubrication circuit 6 via the torque converter 23. For this reason, when the combined flow switching valve 24 is in the diversion state, the hydraulic oil discharged from the first hydraulic pump 3 flows to the first flow path 19 and the hydraulic oil discharged from the second hydraulic pump 4. Flows to the third flow path 27 via the second flow path 26. That is, the hydraulic oil discharged from the first hydraulic pump 3 is supplied to the clutch circuit 5, and the hydraulic oil discharged from the second hydraulic pump 4 is supplied to the lubrication circuit 6. The second flow path 26 is connected to the first flow path 19 via the check valve 31. The check valve 31 allows the flow of hydraulic oil from the second flow path 26 to the first flow path 19, but prevents the hydraulic oil from flowing from the first flow path 19 to the second flow path 26. It is configured. The merging / separating switching valve 24 is switched from the merging state to the diverting state when hydraulic oil is supplied via the pilot flow path 28 and the pilot pressure is applied. Further, the joining / dividing flow switching valve 24 is maintained in the joining state by the urging force of the spring when the pilot pressure is not applied. The pilot flow path 28 is connected to the pilot port of the merge / separation switching valve 24 and the electromagnetic switching valve 25. The pilot flow path 28 is connected to the first flow path 19 via the restriction 32.

  The electromagnetic switching valve 25 is connected to the drain channel 18 and the pilot channel 28. When the electromagnetic switching valve 25 is in the open state, the drain passage 18 and the pilot passage 28 are connected. In this case, the pilot flow path 28 is connected to the tank 14 via the drain flow path 18. For this reason, no hydraulic pressure is established in the pilot flow path 28, and no pilot pressure is applied to the combined flow switching valve 24. When the electromagnetic switching valve 25 is in the closed state, the pilot flow path 28 and the drain flow path 18 are blocked. In this case, a predetermined pilot pressure is generated in the pilot flow path 28, and the pilot pressure is applied to the joining / dividing flow switching valve 24.

  A pressure switch 29 is provided in the pilot flow path 28. The pressure switch 29 outputs a detection signal to the controller 9 when the pilot pressure reaches a predetermined set pressure. This set pressure corresponds to the pilot pressure when the combined / diverging switching valve 24 is switched to the divided state against the urging force of the spring. Therefore, the pressure switch 29 detects the switching state of the merge / separation switching valve 24 and outputs it to the controller 9 as a detection signal.

  The relief valve 8 is connected to the first flow path 19 and the third flow path 27. The relief valve 8 blocks between the first flow path 19 and the lubricating circuit 6 when the hydraulic oil flowing through the first flow path 19 is equal to or lower than a predetermined relief pressure. In addition, when the hydraulic fluid flowing through the first flow path 19 is higher than the relief pressure, the relief valve 8 opens between the first flow path 19 and the lubrication circuit 6 and the hydraulic fluid in the first flow path 19. To the lubrication circuit 6. Accordingly, the relief valve 8 plays a role of supplying hydraulic oil to the lubricating circuit 6 after compensating the pressure of the hydraulic oil flowing through the first flow path 19 to a predetermined high pressure. As a result, a relatively high pressure hydraulic oil is supplied to the clutch circuit 5, and a relatively low pressure hydraulic oil is supplied to the lubrication circuit 6.

  The controller 9 includes an arithmetic device such as a CPU and a storage device such as a RAM and a ROM. The controller 9 controls the electromagnetic control valve 16 and the electromagnetic switching valve 25 by sending a command current to the electromagnetic control valve 16 and the electromagnetic switching valve 25.

  The controller 9 can control the pilot pressure supplied to the pilot flow path 21 by controlling the electromagnetic control valve 16, and as a result, can control the pilot pressure supplied to the pressure control valve 15. . Thereby, the controller 9 can control the pressure control valve 15.

  Further, the controller 9 can control the pilot pressure supplied to the pilot flow path 28 by controlling the electromagnetic switching valve 25, and as a result, controls the pilot pressure supplied to the joining / dividing switch valve 24. be able to. Thereby, the controller 9 can control switching of the merge state and the diversion state of the merge / division switching valve 24.

[Control when switching the clutch 13]
Hereinafter, control at the time of switching of the clutch 13 executed by the controller 9 will be described with reference to FIGS. 2 and 3. FIG. 2 is a flowchart showing the control contents when the clutch 13 is switched. FIG. 3A is a timing chart showing changes in the command current to the electromagnetic control valve 16 when the clutch 13 is switched. FIG. 3B is a timing chart showing changes in the clutch pressure when the clutch 13 is switched. FIG. 3C is a timing chart showing the switching of the merge / separation switching valve 24 when the clutch 13 is switched.

First, in step S1, it is determined whether or not a shift command has been generated. The shift command is
This occurs when the controller 9 decides to switch the transmission speed according to the vehicle speed or the engine speed, or when the operator manually operates the shift operation member (not shown) to instruct a shift. When a shift command is generated, the process proceeds to step S2.

  In step S2, it is determined whether or not the merging / separation switching valve 24 is in the merging state. If the merge / separation switching valve 24 is in the merge state, the process proceeds to step S4. When the merge / division switching valve 24 is not in the merge state, that is, when it is in the diversion state, the process proceeds to step S3.

  In step S3, the merge / divergence switching valve 24 is switched to the merge state. Here, the electromagnetic switching valve 25 is switched to the open state by a command signal from the controller 9. Thereby, as shown in the time t1 of FIG.3 (c), the joining / dividing flow switching valve 24 is switched from a dividing state to a joining state.

  In step S4, a trigger command is output. Here, as shown at time t <b> 1 in FIG. 3A, a command current having a predetermined trigger command value I <b> 1 is output from the controller 9 to the electromagnetic control valve 16. This trigger command is maintained from time t1 to time t2. As a result, between time t1 and time t2, hydraulic oil having a relatively large flow rate is supplied to the clutch 13, and the clutch pressure slightly increases as shown in FIG. 3 (b). However, since the oil chamber of the clutch 13 is not yet filled at this time, the clutch pressure becomes lower than a clutch set pressure P3 described later.

  In step S5, the command current is reduced. Here, the command current is reduced to a predetermined set current value I2 at a time t2 when a predetermined time has elapsed from the start of trigger command output. Then, the command current is maintained at the set current value I2 until the completion of fill is detected in step S6. As a result, the flow rate of the hydraulic oil supplied to the clutch 13 is reduced, and the clutch pressure becomes smaller than from the time point t1 to the time point t2 as shown in FIG. 3B. .

  In step S6, it is determined whether or not fill completion is detected. Here, based on the detection signal of the hydraulic switch 22, it is determined whether or not the fill is completed. As shown at time t3 in FIG. 3B, when the clutch pressure reaches a predetermined fill pressure P2, a detection signal is output from the pressure switch 22, and the completion of fill is detected. If the completion of filling is detected, the process proceeds to step S7.

  In step S7, the combined / divergence switching valve 24 is switched to the divided state. Here, the electromagnetic switching valve 25 is switched to a closed state by a command signal from the controller 9. As a result, a predetermined pilot pressure is applied to the merge / divergence switching valve 24 via the pilot flow path 28, and the merge / divergence switching valve 24 changes from the merged state to the divided state as shown at time t3 in FIG. 3 (c). Can be switched.

  In step S8, modulation is started. Here, the pressure control valve 15 is controlled to increase in a predetermined manner until the clutch pressure reaches the predetermined clutch set pressure P3 from the fill pressure P2. Specifically, as shown from time t3 to time t4 in FIG. 3A, the command current is gradually increased from the set current value I2 to I3. At time t4, the clutch pressure reaches the clutch set pressure P3, and the switching of the clutch 13 is completed.

〔Characteristic〕
In this hydraulic system, when a shift command is generated, the hydraulic oil from the first hydraulic pump 3 and the hydraulic oil from the second hydraulic pump 4 are merged to supply a large amount of hydraulic oil to the clutch circuit 5. Is done. Thereby, the fill can be completed at an early stage, and the switching response of the clutch 13 can be improved. When the completion of filling is detected, the hydraulic oil from the first hydraulic pump 3 and the hydraulic oil from the second hydraulic pump 4 are diverted, and only the hydraulic oil from the first hydraulic pump 3 flows to the clutch circuit 5. Supplied. After completion of filling, the clutch 13 is in a state of being filled with hydraulic oil. Therefore, even if the flow rate of hydraulic oil decreases, there is little possibility that the response of switching the clutch 13 will decrease. For this reason, supply of useless hydraulic fluid can be suppressed compared with the conventional hydraulic system. As a result, the fuel efficiency of the engine can be improved.

  Further, in this hydraulic system, when the completion of filling is detected and the clutch pressure is gradually increased toward the clutch set pressure P3, the flow is divided, and the second flow path 26 connected to the second pump 4 is connected to the clutch. It is separated from the input flow path 11 of the circuit 5. For this reason, a lower pressure pump can be used as the second hydraulic pump 4.

[Other Embodiments]
(A) In the above-described embodiment, the transmission clutch for transmission is exemplified as the hydraulic clutch, but the present invention may be used for the lock-up clutch of the torque converter 23.

  (B) In the above embodiment, the lubrication circuit 6 is exemplified as the low pressure circuit, but another circuit to which hydraulic oil having a lower pressure than the clutch circuit 5 is supplied may be used.

  (C) In the above embodiment, a clutch operated type that controls the pressure control valve 15 by the pilot pressure of the pilot flow path 21 is exemplified as the clutch circuit. However, in Japanese Patent No. 2745128 and Utility Model Registration No. 2606138 You may apply to the circuit which controls a pressure clutch pressure directly by a proportional solenoid valve as shown.

  (D) In the above embodiment, the hydraulic switch 22 is exemplified as the fill completion detection unit of the clutch circuit, but other detection means such as a hydraulic sensor may be used. Further, a sensor that detects the input side rotational speed and the output side rotational speed of the clutch 13 may be used, and the completion of fill may be detected based on the ratio between the input side rotational speed and the output side rotational speed. Further, as shown in Japanese Patent Application Laid-Open No. 2003-83428 and Japanese Patent No. 2745128, the completion of fill may be detected by a flow rate detection valve.

  The present invention has an effect of improving fuel consumption and is useful as a hydraulic system for work vehicles.

The hydraulic circuit diagram which shows the structure of a hydraulic system. The flowchart which shows the control content in a hydraulic system. The timing chart which shows the change of the command current at the time of clutch switching, clutch pressure, and the state of a joint / divergence switching valve.

Explanation of symbols

2 Engine 3 First hydraulic pump 4 Second hydraulic pump 5 Clutch circuit (high pressure circuit)
6 Lubrication circuit (low pressure circuit)
9 Controller (control unit)
22 Hydraulic switch (fill completion detector)
24 Combined flow switching valve

Claims (2)

Engine,
A first hydraulic pump and a second hydraulic pump driven by the engine and discharging hydraulic oil;
A high-pressure circuit including a hydraulic clutch;
A low-pressure circuit to which hydraulic oil having a pressure lower than that of the high-pressure circuit is supplied;
A shunting state in which hydraulic oil discharged from the first hydraulic pump is supplied to the high-pressure circuit and hydraulic oil discharged from the second hydraulic pump is supplied to the low-pressure circuit, and from the first hydraulic pump A merging / separating switching valve that is switched to a merging state in which the discharged hydraulic oil and the hydraulic oil discharged from the second hydraulic pump are supplied to the high-pressure circuit;
A fill completion detection unit for detecting the completion of fill of hydraulic oil to the hydraulic clutch;
A control unit that sets the merging / separating switching valve to the merging state from the start of supplying hydraulic oil to the hydraulic clutch until the completion of filling is detected, and setting the merging / separating switching valve to the divergence state after the completion of filling is detected. When,
A working vehicle hydraulic system comprising: An engine, a first hydraulic pump and a second hydraulic pump driven by the engine and discharging hydraulic oil, a high-pressure circuit including a hydraulic clutch, and a low-pressure circuit to which hydraulic oil having a lower pressure than the high-pressure circuit is supplied; A shunting state in which hydraulic oil discharged from the first hydraulic pump is supplied to the high-pressure circuit and hydraulic oil discharged from the second hydraulic pump is supplied to the low-pressure circuit, and from the first hydraulic pump Detecting completion of filling of hydraulic oil to the hydraulic clutch, and a merging / separation switching valve for switching between the discharged hydraulic oil and the hydraulic oil discharged from the second hydraulic pump to a merging state supplied to the high pressure circuit And a fill completion detection unit for controlling the hydraulic system of the work vehicle, wherein the step of starting supply of hydraulic oil to the hydraulic clutch is performed by setting the merging / separating switching valve to a merging state. And
After the completion of the fill is detected by the fill detector, the step of setting the combined flow switching valve to a diverted state;
A control method for a hydraulic system of a work vehicle.

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