JP2018066286A - Hydraulic system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a swash plate type pump motor to operate as a pump even when high-pressure working fluid is not accumulated in an accumulator.SOLUTION: A hydraulic system 20 includes: a swash plate type pump motor 33 operable in accordance with an inclination angle of a swash plate 33A; an accumulator 25; and a pressure reduction valve 43 capable of reducing a pressure of working fluid between the swash plate type pump motor 33 and the accumulator 25 to a predetermined control pressure. The hydraulic system further includes: a swash plate adjustment section 34 capable of adjusting an inclination angle of the swash plate by supplying and/or discharging the working fluid; and a control valve unit 30 that receives supply of the working fluid having the predetermined control pressure from the pressure reduction valve 43 and controls the supply and/or discharge of the working fluid to the swash plate adjustment section 34. In the swash plate type pump motor 33, the swash plate 33A is maintained at the inclination angle enabling the swash plate type pump motor 33 to operate as a pump while a driving source of a vehicle is stopped.SELECTED DRAWING: Figure 2

Description

  The present invention uses a swash plate pump / motor connected to a drive shaft capable of transmitting power to / from drive wheels, and operates the swash plate pump / motor as a pump during braking of the vehicle. The present invention relates to a hydraulic system for accumulating hydraulic oil in an accumulator, supplying hydraulic oil from the accumulator to a swash plate type pump / motor when the vehicle is started, etc., and operating the swash plate type pump / motor as a motor.

  Conventionally, in a hydraulic system including a swash plate type pump motor connected to a drive shaft connected to a drive wheel, a pump connected coaxially to the drive shaft is used, and hydraulic fluid output from this pump is used. Thus, the inclination angle of the swash plate of the swash plate type pump / motor is adjusted to change the operation mode of the swash plate type pump / motor and the discharge amount of hydraulic oil.

  For example, a technique is known in which the inclination angle of a swash plate of a swash plate type pump motor is variably controlled based on the hydraulic pressure from a pilot hydraulic source connected to a drive shaft (for example, Patent Document 1).

JP-A-6-1213

  For example, according to the technique of Patent Document 1 described above, the pilot hydraulic power source is always rotated by the drive shaft to supply hydraulic oil even when there is no need to variably control the inclination angle of the swash plate. As described above, since the pilot hydraulic pressure source is always rotated by the drive shaft, energy loss is generated and fuel consumption is deteriorated.

  On the other hand, for example, it is considered that energy loss can be reduced by adjusting the inclination angle of the swash plate using the hydraulic oil accumulated in the accumulator. In this case, since the pressure of the hydraulic oil accumulated in the accumulator becomes high, it cannot be supplied to the control valve for adjusting the swash plate as it is. Therefore, it is necessary to supply high pressure hydraulic oil to the control valve after the pressure is reduced by the pressure reducing valve.

  In such a configuration, high-pressure hydraulic fluid is accumulated in the accumulator, for example, when the hydraulic fluid in the accumulator is used up or when the hydraulic fluid is discharged from the accumulator for fail-safe during parking. If not, hydraulic oil with sufficient pressure cannot be supplied to the control valve. Therefore, the inclination angle of the swash plate cannot be adjusted, and the swash plate pump / motor should be operated as a pump. I can't.

  Accordingly, an object of the present invention is to provide a technique capable of operating a swash plate type pump / motor as a pump even when high-pressure hydraulic oil is not accumulated in an accumulator.

  In order to achieve the above object, a hydraulic system according to an aspect of the present invention includes a drive shaft capable of transmitting power to and from a drive wheel of a vehicle, and a swash plate, and the inclination of the swash plate Swash plate pump / motor that can be operated according to the angle, and hydraulic oil supplied from the swash plate pump / motor can be stored under pressure, and the stored hydraulic fluid is supplied to the swash plate pump / motor. In a hydraulic system having a possible accumulator and a pressure reducing valve capable of reducing the hydraulic oil between the swash plate type pump motor and the accumulator to a predetermined control pressure, the swash plate is supplied by supplying and / or discharging the hydraulic oil. A swash plate adjustment unit capable of adjusting the inclination angle of the swash plate, and a control valve that receives supply of hydraulic oil at a predetermined control pressure from the pressure reducing valve and controls supply and / or discharge of hydraulic oil to the swash plate adjustment unit, Equipped with a swash plate pump motor , In a state in which stops driving source of the vehicle, the swash plate is maintained at an inclination angle operable swash plate pump motor as a pump.

  In the hydraulic system, the swash plate adjustment unit may be configured to stop the swash plate at an inclination angle at which the swash plate type pump motor can operate as a pump when not affected by hydraulic fluid.

  Further, in the hydraulic system, when the vehicle drive source is stopped, the swash plate adjustment unit stops the swash plate at an inclination angle at which the swash plate type pump / motor can operate as a pump so that the state can be maintained. You may make it further provide the stop state control means to control to.

  In the hydraulic system, the state specifying means for specifying that the swash plate pump / motor is not operated as a pump or a motor based on the state of the vehicle, and the state not being operated as a pump or a motor by the state specifying means If it is determined that the swash plate has an inclination angle that does not operate the swash plate type pump / motor as a pump or a motor, an operation control means for controlling the control valve may be further provided.

  According to the present invention, the swash plate type pump / motor can be operated as a pump even when high-pressure hydraulic oil is not accumulated in the accumulator.

1 is a schematic overall configuration diagram of a vehicle equipped with a hydraulic system according to an embodiment of the present invention. It is a detailed block diagram of the hydraulic system which concerns on one Embodiment of this invention. It is a flowchart of the free operation control process which concerns on one Embodiment of this invention. It is a block diagram of the hydraulic system which concerns on the 1st modification of this invention. It is a flowchart of the inclination angle control process at the time of a stop which concerns on the 1st modification of this invention.

  Hereinafter, based on an accompanying drawing, the hydraulic system concerning one embodiment of the present invention is explained. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  FIG. 1 is a schematic overall configuration diagram of a vehicle equipped with a hydraulic system according to an embodiment of the present invention.

  An output shaft of the engine 10 as an example of a drive source is connected to an input shaft (input shaft) (not shown) of the transmission 12 via a clutch 11. An output shaft (not shown) of the transmission 12 is connected to drive wheels (left and right rear wheels) 16L and 16R via a propeller shaft 13, a differential 14 and a drive shaft 15, respectively.

  The clutch 11 connects and disconnects a power transmission path between the output shaft of the engine 10 and the input shaft of the transmission 12.

  The transmission 12 is, for example, an automatically controlled manual transmission (AMT).

  An input / output mechanism (PTO: Power take-off) 17 is coupled to one shaft inside the transmission 12 (for example, a counter shaft arranged in parallel with the input shaft) so as to be able to transmit power. For example, the input / output shaft 17A of the input / output mechanism unit 17 is connected to one shaft of the transmission 12 via a plurality of gears. Therefore, power can be transmitted from the shaft of the transmission 12 to the input / output shaft 17A, and power can be transmitted from the input / output shaft 17A to the shaft of the transmission 12.

  The input / output shaft 17A collects the energy of the driving force of the drive wheels 16L and 16R during braking of the vehicle 1, and uses the energy of the swash plate pump / motor described later of the hydraulic system 20 that can be used when starting or accelerating. 33 drive shafts.

  The hydraulic system 20 includes a swash plate pump / motor unit 21, a valve unit 22, a low pressure tank 24, an accumulator 25, pipes 71, 72, 76, 77 and the like, an electronic control unit (hereinafter referred to as ECU) 60. With.

  FIG. 2 is a detailed configuration diagram of a hydraulic system according to an embodiment of the present invention.

  The low-pressure tank 24 is a tank that stores low-pressure hydraulic oil. The low pressure tank 24 is connected to an air vent pipe 78 for discharging the air in the low pressure tank 24, a pipe 71 connected to the swash plate type pump / motor unit 21, and a pipe 76 connected to the valve unit 22. ing. The pipe 71 and the pipe 76 are provided with coolers 27 and 28 for cooling the hydraulic oil passing therethrough.

  The accumulator 25 can store energy (accumulate pressure) due to the pressure of the supplied hydraulic oil, and can supply hydraulic oil (discharge of energy) by the stored energy. The accumulator 25 includes a hydraulic oil storage unit 25A that stores hydraulic oil, and a gas storage unit 25B in which a gas (for example, nitrogen gas) is sealed. In the accumulator 25, when high-pressure hydraulic oil is supplied to the hydraulic oil storage unit 25A, the gas in the gas storage unit 25B is compressed accordingly to accumulate energy, while the gas in the gas storage unit 25B is expanded. The energy is released by supplying the hydraulic oil in the hydraulic oil storage section 25A to the outside. A pipe 74 is connected to the accumulator 25.

  The swash plate type pump / motor unit 21 has an input / output shaft 17A as a drive shaft, a swash plate type pump / motor 33 having a swash plate 33A, a swash plate adjustment unit 34 for adjusting the inclination angle of the swash plate 33A, and a swash plate adjustment. And a control valve unit 30 for controlling the supply of hydraulic oil for controlling the section 34.

  The swash plate type pump motor 33 is, for example, a swash plate type axial piston pump motor, and one port is connected to a pipe 71 communicating with the low pressure side (low pressure tank 24 side), and the other port is connected to the high pressure side. A pipe 72 communicating with (for example, the accumulator 25 side) is connected. The swash plate type pump motor 33 supplies hydraulic oil from the pipe 71 to the pipe 72 side using the driving force of the input / output shaft 17A according to the inclination angle (specifically, the direction of the inclination) of the swash plate 33A. An operation as a pump or an operation as a motor for applying a driving force to the input / output shaft 17A by the energy of hydraulic oil supplied from the accumulator 25 via the pipe 72 can be performed. Further, the swash plate type pump motor 33 can change the driving force related to each operation according to the inclination angle (specifically, the magnitude of the inclination angle) of the swash plate 33A.

  The swash plate adjustment unit 34 includes a cylinder 35 that houses the piston 36. The cylinder 35 is partitioned into two hydraulic chambers 37 and 38 by a piston 36. A rod 39 connected to the swash plate 33A is fixed to the piston 36. With such a configuration, the inclination angle of the swash plate 33 </ b> A can be adjusted via the rod 39 by adjusting the amount of hydraulic oil in the hydraulic chambers 37 and 38 and moving the piston 36. In this embodiment, the swash plate adjusting unit 34 is in a non-controlled state (the hydraulic oil of the control pressure is not supplied to the hydraulic chamber 37 and the hydraulic chamber 38, and the piston 36 is not moved due to the influence of the hydraulic oil. The position of the piston 36 in the state) is set so that the inclination angle of the swash plate 33A becomes an inclination angle that enables the swash plate type pump motor 33 to operate as a pump. Therefore, when the control by the control valve unit 30 is not performed, the swash plate type pump motor 33 is operable as a pump.

  The control valve unit 30 includes a first control valve 31 and a second control valve 32. The first control valve 31 can be switched between a pipe 82 communicating with the hydraulic chamber 37 and a pipe 77 connected to the pressure reducing valve 43 or a pipe 84 communicating with a predetermined hydraulic oil discharge destination. ing. When the pipe 82 and the pipe 84 are communicated by the first control valve 31, the hydraulic oil in the pressure chamber 37 is discharged to the hydraulic oil discharge destination via the pipe 82 and the pipe 84. On the other hand, when the pipe 82 and the pipe 77 are communicated with each other by the first control valve 31, the hydraulic oil supplied from the pipe 77 is supplied to the pressure chamber 37 via the pipe 82.

  The second control valve 32 can switch between a pipe 83 communicating with the hydraulic chamber 38 and a pipe 77 connected to the pressure reducing valve 43 or a pipe 85 communicating with a predetermined hydraulic oil discharge destination. ing. When the pipe 83 and the pipe 85 are communicated by the second control valve 32, the hydraulic oil in the pressure chamber 38 is discharged to the hydraulic oil discharge destination via the pipe 83 and the pipe 85. On the other hand, when the pipe 83 and the pipe 77 are communicated by the second control valve 32, the hydraulic oil supplied from the pipe 77 is supplied to the pressure chamber 38 through the pipe 83. The first control valve 31 and the second control valve 32 are controlled in accordance with a control signal from the ECU 60.

  The valve unit 22 includes a three-way valve 40, a valve 41, a relief valve 42, and a pressure reducing valve 43.

  The three-way valve 40 includes any one of a pipe 72 communicating with the swash plate type pump / motor unit 21, a pipe 75 communicating with the pipe 76 communicating with the low pressure tank 24, and a pipe 74 communicating with the accumulator 25. The piping can be selectively communicated. During normal use, the three-way valve 40 is set so that the pipe 72 and the pipe 74 communicate with each other. The valve 41 can open and close between the pipe 75 and the pipe 76. For example, the valve 41 is opened when the hydraulic oil accumulated in the accumulator 25 is simply discharged to the low-pressure tank 24. The relief valve 42 discharges the hydraulic oil to the low pressure side when the pressure of the hydraulic oil inside the three-way valve 40 or the piping 75 becomes high. The pressure reducing valve 43 is arranged between a pipe 73 branched from the pipe 72 and a pipe 77 connected to the swash plate type pump / motor unit 21, and the high pressure hydraulic oil on the pipe 73 side is subjected to a predetermined control pressure (control). Pressure) and supplied to the pipe 77 side.

  In the hydraulic system 20, the pipes 71 and 76 are low-pressure pipes, the pipes 72, 73, 74, and 75 are high-pressure pipes, and the pipe 77 is for control pressure (pressure between high pressure and low pressure). ) Piping. The hydraulic system 20 also includes a pressure sensor 44 that measures the pressure of hydraulic oil on the high pressure side of the swash plate type pump motor 33 (in this example, the pressure of the pipe 74).

  The ECU 60 performs various controls in the hydraulic system 20 and includes a known CPU, ROM, RAM, input port, output port, and the like.

  The ECU 60 includes a state specifying unit 61 as an example of a state specifying unit and an operation control unit 62 as an example of an operation control unit as some functional elements. Each of these functional elements will be described as being included in the ECU 60 which is an integral hardware, but any one of them can be provided in separate hardware.

  Whether the state specifying unit 61 is in a state in which the swash plate type pump / motor 33 is operated by a motor or in a state in which a pump is operated in accordance with the state of the vehicle 1 (for example, a change in accelerator opening, a brake pedal being turned on, etc.) Then, it is specified whether the motor or the pump is not operated, that is, the state where the free operation is performed, and the specified state is notified to the operation control unit 62. In the present embodiment, the state specifying unit 61 specifies that the swash plate type pump / motor 33 is in a state of operating the motor when the accelerator opening is equal to or larger than a predetermined value, and when the brake pedal is on, It is specified that the swash plate type pump / motor 33 is in a state of operating the pump, and otherwise, it is specified that the swash plate type pump / motor 33 is in a state of operating freely.

  When the operation control unit 62 receives a notification from the state specifying unit 61 that the swash plate 33A is in a free operation state, the swash plate 33A performs a free operation by the swash plate 33A (in this embodiment, an input angle). The control valve unit 30 is controlled to have an inclination angle perpendicular to the output shaft 17A (this inclination angle is 0 degree). In addition, in order to control the tilt angle to be 0 degree, the control amount by the control valve unit 30 to make the tilt angle become 0 degree from a predetermined tilt angle (for example, the tilt angle at the time of no control) in advance. Further, it may be stored in a memory (not shown) of the ECU 60 and controlled so that the inclination angle of the swash plate 33A becomes 0 degrees based on the control amount. In addition, when the operation control unit 62 receives a notification from the state specifying unit 61 that the pump operation is in progress, the swash plate adjustment unit 34 controls the swash plate 33A to have an inclination angle for performing the pump operation. The valve unit 30 is controlled. In addition, when the operation control unit 62 receives a notification from the state specifying unit 61 that the motor is in a state of being operated, the swash plate adjustment unit 34 controls the swash plate 33A to have an inclination angle for performing the motor operation. The valve unit 30 is controlled.

  Next, a processing operation in the hydraulic system 20 according to an embodiment will be described.

  FIG. 3 is a flowchart of the free operation control process according to the embodiment of the present invention.

  The free operation control process is executed, for example, when the vehicle is powered on (key switch of the ignition switch is turned on) and after a certain amount of hydraulic oil is accumulated in the accumulator 25.

  Based on the state of the vehicle 1, the state specifying unit 61 specifies whether or not the swash plate type pump / motor 33 is not operated as a motor or a pump, that is, is in a state of performing a free operation (step S <b> 11), and performs a free operation. If it is not in a state (step S11: NO), the process proceeds to step S11. When the free operation is not performed, the swash plate 33A is adjusted by another process so that the swash plate pump / motor 33 operates as a motor or operates as a pump.

  On the other hand, when it is in a state where the free operation is performed (step S11: YES), the state specifying unit 61 notifies the operation control unit 62 to that effect, and the operation control unit 62 that has received the notification controls the control valve unit 30. Is controlled so that the swash plate 33A is adjusted to an inclination angle (0 degree) at which the swash plate pump motor 33 performs a free operation (step S12), and then the process proceeds to step S11. . Thereby, in the non-control state, the swash plate type pump motor 33 that will perform the pump operation can be appropriately operated free of charge.

  As described above, according to the hydraulic system 20 according to the present embodiment, the swash plate adjustment unit 34 is not affected by the hydraulic oil, and in the uncontrolled state, the swash plate 33A uses the swash plate pump / motor 33 as a pump. The swash plate is configured to be stopped at an operable inclination angle, and the swash plate is maintained at an inclination angle at which the swash plate type pump motor 33 can be operated as a pump in a state where the driving source of the vehicle is stopped. Therefore, even if hydraulic oil is not accumulated in the accumulator 25 and hydraulic oil having a control pressure for adjusting the inclination angle of the swash plate 33A cannot be supplied, the swash plate type pump motor 33 is used as a pump. The hydraulic oil can be accumulated in the accumulator 25.

  Further, according to the hydraulic system 20 according to the present embodiment, the state specifying unit 61 specifies that the swash plate type pump / motor 33 is not operated as a pump or a motor, and in this case, the operation control unit 62 is Since the swash plate 33A is controlled to have an inclination angle that does not operate the swash plate type pump / motor 33 as a pump or a motor, the swash plate type pump / motor 33 can be appropriately operated to be free.

  Next, a hydraulic system according to a first modification of the present invention will be described.

  FIG. 4 is a configuration diagram of a hydraulic system according to a first modification of the present invention.

  The hydraulic system 20 according to the first modification is different from the hydraulic system 20 according to the above-described embodiment in that the position of the piston 36 in the uncontrolled state of the swash plate adjusting unit 34 is made different, and the ECU 60 has the state specifying unit 61 and the operation control. Instead of the unit 62, an adjustment control unit 63 and a stop state control unit 64 are provided, and on-off valves 86 and 87 are further provided.

  The swash plate control unit 34 in the first modification is in an uncontrolled state (the hydraulic oil of the control pressure is not supplied to the hydraulic chamber 37 and the hydraulic chamber 38, and the piston 36 is not moved due to the influence of the hydraulic oil. The position of the piston 36 in the state) is set so that the inclination angle of the swash plate 33A does not operate the swash plate type pump / motor 33 as a pump and does not operate as a motor, that is, an inclination angle that allows free operation. ing. Therefore, in a state where control by the control valve unit 30 is not performed, the swash plate type pump motor 33 is in a state of performing a free operation.

  The opening / closing valve 86 is provided at a position between the first control valve 31 and the hydraulic chamber 37 of the pipe 82, and the state of the hydraulic oil in the hydraulic chamber 37 can be maintained by closing the opening / closing valve 86. It is like that. The opening / closing valve 87 is provided at a position between the second control valve 32 and the hydraulic chamber 38 of the pipe 83. By closing the opening / closing valve 87, the state of the hydraulic oil in the hydraulic chamber 38 is changed. It can be maintained. Opening / closing of the opening / closing valve 86 and the opening / closing valve 87 is controlled by the ECU 60.

  The ECU 60 includes an adjustment control unit 63 and a stop state control unit 64 as an example of a stop state control unit as some functional elements. Each of these functional elements will be described as being included in the ECU 60 which is an integral hardware, but any one of them can be provided in separate hardware.

  The adjustment control unit 63 outputs a control request for controlling the swash plate type pump / motor 33 in accordance with the state of the vehicle 1 (for example, change in accelerator opening degree, brake pedal on, etc.). Specifically, the adjustment control unit 63 controls the control valve unit 30 (the first control valve 31 and the second control valve 31) to set the swash plate 33A to a target inclination angle by the swash plate adjustment unit 34 according to the state of the vehicle 1. The control content (supply and / or discharge of hydraulic oil) for the control valve 32) is determined, and a control signal corresponding to the control content is output to the swash plate pump / motor unit 21.

  The stop state control unit 64 operates the swash plate 33A as a pump using the swash plate 33A as a pump by the swash plate adjusting unit 34 when the drive source of the vehicle 1 is stopped (when the power of the vehicle 1 is turned off). Stop at the possible tilt angle and maintain that state. In the present embodiment, for example, the stop state control unit 64 closes the open / close valves 86 and 87 to stop the swash plate 33A at an inclination angle at which the swash plate type pump motor 33 can operate as a pump, Maintained.

  FIG. 5 is a flowchart of the stop inclination angle control process according to the first modification of the present invention.

  The stop angle control process at the time of stop is executed, for example, when the vehicle is powered on (the key switch of the ignition switch is turned on).

  The stop state control unit 64 determines whether or not there has been a request for turning off the power of the vehicle 1, that is, an operation of turning off the key switch of the ignition switch (step S21). As a result, when there is no request to turn off the power (step S21: NO), the stop state control unit 64 advances the process to step S21.

  On the other hand, when there is a request to turn off the power (step S21: YES), the stop state control unit 64 causes the swash plate adjusting unit 34 to tilt the swash plate 33A so that the swash plate type pump / motor 33 can operate as a pump. The swash plate 33A is maintained at a tilt angle at which the swash plate type pump motor 33 can operate as a pump by stopping at the corner and closing the open / close valves 86 and 87 (step S22). Next, the stop state control unit 64 executes a process of turning off the power, that is, a process of stopping the supply of power to unnecessary portions (step S23), and ends the stop angle control process.

  According to the hydraulic system 20 according to the first modification, when the drive source of the vehicle 1 is stopped (when the power of the vehicle 1 is turned off), the swash plate 33A can operate the swash plate type pump motor 33 as a pump. Since the vehicle is stopped at the inclination angle and maintained in this state, when the drive source is operated next time (when the vehicle 1 is powered on), hydraulic oil having sufficient pressure is accumulated in the accumulator 25. Even when the inclination angle of the swash plate 33A cannot be adjusted by the hydraulic oil decompressed by the pressure reducing valve 43, the hydraulic oil is accumulated in the accumulator 25 by operating the swash plate pump motor 33 as a pump. Can do. Therefore, after that, the swash plate 33A can be adjusted to a desired inclination angle, and the swash plate pump motor 33 can be operated as a motor.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, in the first modified example, the open / close valves 86 and 87 are provided. However, the present invention is not limited to this. For example, the first control valve 82 and the second control valve 83 are provided in the hydraulic chambers 37 and 38. As long as the state of the hydraulic oil can be maintained, the open / close valves 86 and 87 may not be provided. For example, the open / close valve is provided in the pipe 77 to operate the hydraulic chambers 37 and 38. The oil state may be maintained. In short, it is only necessary to be able to maintain the state of the hydraulic oil in the hydraulic chambers 37 and 38 when the drive source is stopped.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Engine 11 Clutch 12 Transmission 13 Propeller shaft 14 Differential device 15 Drive shaft 16L, 16R Drive wheel 17 Input / output mechanism 17A Input / output shaft 20 Hydraulic system 21 Swash plate type pump / motor unit 22 Valve unit 24 Low pressure tank 25 Accumulator 30 Control valve unit 31 First control valve 32 Second control valve 33 Swash plate type pump motor 33A Swash plate 34 Swash plate adjustment part 43 Pressure reducing valve 44 Pressure sensor 60 ECU
61 State identification unit 62 Operation control unit 63 Adjustment control unit 64 Stop state control unit

Claims (4)

A swash plate type pump motor having a drive shaft capable of transmitting power to and from a drive wheel of a vehicle and a swash plate and operable in accordance with an inclination angle of the swash plate, and the swash plate type pump An accumulator capable of accumulating the hydraulic oil supplied from a motor in a pressurized state, and capable of supplying the accumulated hydraulic oil to the swash plate type pump motor; and the swash plate type pump motor and the accumulator; A hydraulic valve having a pressure reducing valve capable of reducing the hydraulic fluid between to a predetermined control pressure,
A swash plate adjustment section capable of adjusting the inclination angle of the swash plate by supplying and / or discharging hydraulic oil;
A control valve that receives supply of hydraulic oil at a predetermined control pressure from the pressure reducing valve and controls supply and / or discharge of the hydraulic oil to the swash plate adjustment unit,
The swash plate type pump motor is a hydraulic system in which the swash plate is maintained at an inclination angle capable of operating with the swash plate type pump motor as a pump in a state where a driving source of a vehicle is stopped. The swash plate adjusting section is configured to stop the swash plate at an inclination angle at which the swash plate type pump motor can operate as a pump when not affected by the hydraulic oil. Hydraulic system. When stopping the drive source of the vehicle, the swash plate is controlled by the swash plate adjusting section so that the swash plate stops at the tilt angle at which the swash plate type pump / motor can operate as a pump, and the state can be maintained. The hydraulic system according to claim 1, further comprising stop state control means for performing the stop state control. Based on the state of the vehicle, state specifying means for specifying that the swash plate type pump / motor is not operated as a pump or a motor;
When the state specifying means specifies that the swash plate is not operated as a pump or motor, the control valve is controlled so that the swash plate has an inclination angle that does not operate the swash plate type pump motor as a pump or motor. The hydraulic system according to claim 1, further comprising an operation control unit that performs the operation control.

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