Hydraulic system and method for controlling hydraulic system

Abstract

A hydraulic system 100 comprises: a high hydraulic pressure source 11 that supplies hydraulic pressure to a high-pressure operation part 102; a low hydraulic pressure source 12 that supplies hydraulic pressure to a low-pressure operation part 103; and a pressure reduction valve 20 that reduces the hydraulic pressure supplied to the low-pressure operation part 103. The hydraulic system 100 performs at least one of: reducing the hydraulic pressure from the high hydraulic pressure source 11 by using the pressure reduction valve 20 and supplying the reduced hydraulic pressure to the low-pressure operation part 103 when the low hydraulic pressure source 12 is abnormal; and raising the hydraulic pressure from the low hydraulic pressure source 12 and supplying the raised hydraulic pressure to the high-pressure operation part 102 when the high hydraulic pressure source 11 is abnormal.

Description

Hydraulic System and Control Method of Hydraulic System

[0001] This invention relates to a hydraulic system and a control method of a hydraulic system.

[0002] Conventionally, a hydraulic system is known (for example, see Patent Document 1).

[0003] Patent Document 1 describes an electro-hydraulic actuator system for raising and lowering the landing gear of an aircraft. The electro-hydraulic actuator system described in Patent Document 1 includes a plurality of hydraulic supply sources provided in parallel with each other on a hydraulic circuit. The plurality of hydraulic supply sources sequentially supply hydraulic oil to a plurality of hydraulic actuators that operate by sequentially receiving the supply of hydraulic oil when the landing gear of the aircraft is retracted and deployed. In the electro-hydraulic actuator system described in Patent Document 1, since the plurality of hydraulic supply sources are provided in parallel, the hydraulic supply sources are redundant.

[0004] Japanese Patent Application Laid-Open No. 2014-132189

[0005] Here, although not described in Patent Document 1, there are cases where hydraulic pressure is supplied to a plurality of hydraulic systems that operate with different operating hydraulic pressures. In that case, when the hydraulic pressure source is made redundant by arranging a plurality of hydraulic supply sources as in the electro-hydraulic actuator system described in Patent Document 1, for each of the plurality of hydraulic systems with different operating hydraulic pressures, a plurality of hydraulic supply sources are arranged for redundancy. Therefore, due to the arrangement of a plurality of hydraulic supply sources for redundancy for each of the plurality of hydraulic systems with different operating hydraulic pressures, the weight of the entire system for supplying hydraulic pressure increases and the number of components increases. Therefore, even when supplying hydraulic pressure from a redundant hydraulic supply source (hydraulic pressure source) to a plurality of hydraulic systems (operating parts) that operate with different operating hydraulic pressures, it is desired to suppress an increase in weight and an increase in the number of components.

[0006] This invention was made to solve the above-mentioned problems, and one objective of this invention is to provide a hydraulic system and a control method for a hydraulic system that can suppress an increase in weight and the number of parts even when hydraulic pressure is supplied from a redundant hydraulic source to multiple operating parts that operate by different operating hydraulic pressures.

[0007] To achieve the above objective, the hydraulic system according to the first aspect of this invention comprises a high-pressure source that supplies hydraulic pressure to a high-pressure operating part that operates with a relatively high operating hydraulic pressure, a low-pressure source that is arranged separately from the high-pressure source and supplies hydraulic pressure to a low-pressure operating part that operates with a relatively low operating hydraulic pressure, and a pressure reducing valve that reduces the hydraulic pressure supplied to the low-pressure operating part, and at least one of the following is performed: when the low-pressure source malfunctions, the hydraulic pressure from the high-pressure source is reduced by the pressure reducing valve and supplied to the low-pressure operating part, and when the high-pressure source malfunctions, the hydraulic pressure from the low-pressure source is increased and supplied to the high-pressure operating part.

[0008] The hydraulic system according to the first aspect of this invention, as described above, performs at least one of the following: when the low hydraulic source malfunctions, it reduces the hydraulic pressure from the high hydraulic source using a pressure reducing valve and supplies it to the low-pressure operating unit; and when the high hydraulic source malfunctions, it increases the hydraulic pressure from the low hydraulic source and supplies it to the high-pressure operating unit. As a result, when either the high hydraulic source or the low hydraulic source malfunctions, hydraulic pressure can be supplied from the other, thus reducing the number of hydraulic sources that need to be deployed compared to the case where both the high and low hydraulic sources are individually redundant. Therefore, the increase in the weight of the hydraulic system can be suppressed by the amount by which the number of hydraulic sources is reduced, and the increase in the number of parts of the hydraulic system can also be suppressed. As a result, even when supplying hydraulic pressure from redundant hydraulic sources to multiple operating units that operate with different operating hydraulic pressures, the increase in weight and the increase in the number of parts can be suppressed.

[0009] In the hydraulic system according to the first aspect described above, preferably, the low-pressure source includes a hydraulic pump that discharges hydraulic fluid to supply hydraulic pressure and a motor that serves as the drive source for the hydraulic pump. With this configuration, hydraulic pressure can be supplied by operating the hydraulic pump with the drive of the motor, and the hydraulic pressure supplied from the low-pressure source can be easily controlled by controlling the operation of the motor. Furthermore, in the event of a malfunction of the high-pressure source, if the hydraulic pressure from the low-pressure source is increased and supplied to the high-pressure operating section, the low-pressure source includes a hydraulic pump and a motor, so the hydraulic pressure from the low-pressure source can be easily increased by controlling the operation of the motor. Therefore, even in the event of a malfunction of the high-pressure source, operating hydraulic pressure can be easily supplied to the high-pressure operating section.

[0010] In the hydraulic system according to the first aspect described above, preferably, the high-pressure source supplies a relatively high operating hydraulic pressure to the high-pressure operating section while simultaneously supplying a relatively low operating hydraulic pressure to the low-pressure operating section via a pressure reducing valve when the low-pressure source malfunctions, and the low-pressure source supplies a relatively high operating hydraulic pressure to the high-pressure operating section by increasing the pressure it supplies while simultaneously supplying a relatively low operating hydraulic pressure to the low-pressure operating section via a pressure reducing valve when the high-pressure source malfunctions. With this configuration, when the low-pressure source malfunctions, the reduced operating hydraulic pressure is supplied from the high-pressure source, and when the high-pressure source malfunctions, the increased operating hydraulic pressure is supplied from the low-pressure source, thus enabling redundancy in which the high-pressure source and the low-pressure source back each other up. Therefore, it is possible to suppress the cessation of the supply of operating hydraulic pressure in the event of a malfunction in either the high-pressure source or the low-pressure source, thereby further improving the stability of the operation of the hydraulic system compared to a configuration where only one of the high-pressure source or the low-pressure source backs up the other. Furthermore, because the high-pressure and low-pressure sources are redundant and back each other up, the number of hydraulic sources that need to be deployed can be reduced compared to when either the high-pressure or low-pressure source is redundant individually. As a result, the increase in weight and the number of parts can be further suppressed.

[0011] In this case, preferably, the system further includes a high-pressure gauge for detecting the output pressure of a high-pressure source, a low-pressure gauge for detecting the output pressure of a low-pressure source, and a control unit for controlling the operation of the high-pressure and low-pressure sources. The control unit determines an abnormality in the high-pressure source based on the detection result from the high-pressure gauge and determines an abnormality in the low-pressure source based on the detection result from the low-pressure gauge. When an abnormality occurs in the low-pressure source, the control unit stops the operation of the low-pressure source and reduces the hydraulic pressure from the high-pressure source using a pressure reducing valve before supplying it to the low-pressure operating unit. When an abnormality occurs in the high-pressure source, the control unit stops the operation of the high-pressure source and increases the hydraulic pressure from the low-pressure source before supplying it to the high-pressure operating unit. With this configuration, the control unit can automatically determine abnormalities in the high-pressure and low-pressure sources based on the detection results from the high-pressure and low-pressure gauges, and can also automatically control the supply of operating hydraulic pressure in the event of an abnormality. Therefore, even if an abnormality occurs in either the high-pressure or low-pressure source, operating hydraulic pressure can be easily supplied to multiple operating units that operate with different operating hydraulic pressures.

[0012] In the hydraulic system according to the first aspect described above, preferably, a high-pressure hydraulic source is located on the aircraft and supplies hydraulic pressure to a high-pressure operating part located on the aircraft, and a low-pressure hydraulic source is located on the aircraft separately from the high-pressure hydraulic source and supplies hydraulic pressure to a low-pressure operating part located on the aircraft. With this configuration, when at least one of the high-pressure hydraulic source and the low-pressure hydraulic source located on the aircraft malfunctions, hydraulic pressure can be supplied from the other, thus suppressing an increase in weight and the number of parts compared to the case where both the high-pressure hydraulic source and the low-pressure hydraulic source are individually redundant on the aircraft. Therefore, since the increase in weight and the number of parts of the hydraulic system located on the aircraft can be suppressed, the increase in the weight of the aircraft due to the weight of the hydraulic system can be effectively suppressed, and the complexity of the aircraft's configuration due to the number of parts of the hydraulic system can be effectively suppressed.

[0013] In this case, preferably, the high-pressure hydraulic source supplies hydraulic pressure to the high-pressure operating parts that operate the landing gear in the aircraft, and the low-pressure hydraulic source supplies hydraulic pressure to the low-pressure operating parts that operate the control surfaces in the aircraft. With this configuration, even if the operating hydraulic pressures for operating the landing gear and the control surfaces are different, hydraulic pressure can be supplied from the other when at least one of the high-pressure and low-pressure hydraulic sources installed in the aircraft malfunctions. This effectively suppresses the increase in weight and the number of parts compared to when both the high-pressure and low-pressure hydraulic sources are individually redundant in the aircraft.

[0014] In the hydraulic system according to the first aspect described above, preferably, a backup oil passage connects a high-pressure oil passage that supplies hydraulic fluid from a high-pressure source to a high-pressure operating section and a low-pressure oil passage that supplies hydraulic fluid from a low-pressure source to a low-pressure operating section, wherein the backup oil passage is connected upstream of a pressure reducing valve located in the low-pressure oil passage, and a flow control valve is provided to switch between blocking and opening the flow of hydraulic fluid in the backup oil passage by opening and closing, wherein when either the high-pressure source or the low-pressure source malfunctions, the flow control valve opens, thereby opening the flow of hydraulic fluid in the backup oil passage. With this configuration, when the low-pressure source malfunctions, appropriate operating hydraulic pressure can be supplied to the high-pressure operating section from the high-pressure source via the high-pressure oil passage, and appropriate operating hydraulic pressure can be supplied to the low-pressure operating section via the backup oil passage where the flow control valve is located and the pressure reducing valve located in the low-pressure oil passage. Furthermore, even if the high-pressure oil source malfunctions and the oil pressure is increased from the low-pressure oil source, the appropriate operating oil pressure can be supplied to the low-pressure operating section via the low-pressure oil passage where the pressure reducing valve is located, and the appropriate operating oil pressure can be supplied to the high-pressure operating section via the backup oil passage. Therefore, by connecting the high-pressure oil passage and the upstream of the pressure reducing valve in the low-pressure oil passage with the backup oil passage, and opening the flow control valve located in the backup oil passage when either of the oil sources malfunctions, it is possible to easily prevent the supply of operating oil pressure from being stopped in the event of a malfunction in either the low-pressure oil source or the high-pressure oil source.

[0015] In the hydraulic system according to the first aspect described above, preferably, a high-pressure side backup oil passage connects a high-pressure side oil passage that supplies hydraulic fluid from a high-pressure source to a high-pressure operating part and a low-pressure side oil passage that supplies hydraulic fluid from a low-pressure source to a low-pressure operating part; a low-pressure side backup oil passage that is arranged separately from the high-pressure side backup oil passage and connects the high-pressure side oil passage and the low-pressure side oil passage; a high-pressure side flow control valve that switches between shutting off and opening the flow of hydraulic fluid in the high-pressure side backup oil passage by opening and closing; and a low-pressure side flow control valve that switches between shutting off and opening the flow of hydraulic fluid in the low-pressure side backup oil passage by opening and closing, wherein when there is an abnormality in the low-pressure source, the high-pressure side flow control valve opens, thereby opening the flow of hydraulic fluid in the high-pressure side backup oil passage, and when there is an abnormality in the high-pressure source, the low-pressure side flow control valve opens, thereby opening the flow of hydraulic fluid in the low-pressure side backup oil passage. With this configuration, in the event of a malfunction in the low-pressure oil source, the high-pressure side flow control valve opens, opening the flow of hydraulic fluid in the high-pressure side backup oil passage, and allowing appropriate operating hydraulic pressure to be supplied to the low-pressure operating section via the pressure reducing valve. Also, in the event of a malfunction in the high-pressure oil source, the low-pressure side flow control valve opens, opening the flow of hydraulic fluid in the low-pressure side backup oil passage, so that appropriate operating hydraulic pressure can be supplied to the high-pressure operating section via the low-pressure side backup oil passage when the hydraulic pressure from the low-pressure oil source is increased. Furthermore, by arranging the high-pressure side backup oil passage and the low-pressure side backup oil passage separately, the risk of, for example, simultaneous loss of both the high-pressure side backup oil passage and the low-pressure side backup oil passage can be reduced. In addition, each of the high-pressure side flow control valve and the low-pressure side flow control valve can be designed to suit the hydraulic pressure of the hydraulic fluid flowing through them.

[0016] In this case, preferably, the high-pressure side backup oil passage is connected to the low-pressure side oil passage upstream of the pressure reducing valve located in the low-pressure side oil passage, and the high-pressure side flow control valve is an electromagnetic shut-off valve, and includes a control unit that controls the opening and closing of the high-pressure side flow control valve. With this configuration, by controlling the opening and closing of the high-pressure side flow control valve with the control unit, it is possible to control whether or not to supply hydraulic pressure from the high-pressure source to the low-pressure operating unit via the high-pressure side backup oil passage.

[0017] In a hydraulic system comprising the high-pressure side backup oil passage and the low-pressure side backup oil passage described above, preferably, the high-pressure side backup oil passage is connected to the low-pressure side oil passage upstream of the pressure reducing valve located in the low-pressure side oil passage, and the high-pressure side flow control valve is a passive shut-off valve that opens and closes in accordance with the oil pressure from the low-pressure oil source. When the low-pressure oil source is functioning normally, it closes when oil pressure of a predetermined value or higher is supplied from the low-pressure oil source, thereby blocking the flow of hydraulic fluid in the high-pressure side backup oil passage. When the low-pressure oil source is abnormal, it opens when oil pressure of a predetermined value or higher is not supplied from the low-pressure oil source, thereby opening the flow of hydraulic fluid in the high-pressure side backup oil passage. With this configuration, by arranging a passive shut-off valve as the high-pressure side flow control valve, the opening and closing of the shut-off valve can be automatically switched depending on whether the oil pressure from the low-pressure oil source is normal or not. Therefore, it is possible to easily switch between the normal operation and the abnormal operation of the low-pressure oil source without providing a configuration to control the opening and closing of the shut-off valve.

[0018] In a hydraulic system comprising the high-pressure side backup oil passage and the low-pressure side backup oil passage described above, preferably, the pressure reducing valve includes a low-pressure side pressure reducing valve located in the low-pressure side oil passage and a high-pressure side pressure reducing valve located in the high-pressure side backup oil passage. The low-pressure side pressure reducing valve reduces the hydraulic pressure supplied from the low-pressure source to the low-pressure operating unit, the high-pressure side pressure reducing valve reduces the hydraulic pressure supplied from the high-pressure source to the low-pressure operating unit, and the high-pressure side backup oil passage is connected to the low-pressure side oil passage downstream of the low-pressure side pressure reducing valve. With this configuration, the hydraulic pressure supplied from the high-pressure source to the low-pressure operating unit via the high-pressure side backup oil passage can be reduced by the high-pressure side pressure reducing valve, and the hydraulic pressure supplied from the low-pressure source to the low-pressure operating unit via the low-pressure side oil passage can be reduced by the low-pressure side pressure reducing valve. Furthermore, since pressure reducing valves can be located in both the low-pressure side oil passage and the high-pressure side backup oil passage, the pressure reducing valves can be made redundant. Moreover, for example, if the low-pressure side pressure reducing valve fails and hydraulic pressure cannot be supplied from the low-pressure source to the low-pressure operating unit, hydraulic pressure can be supplied from the high-pressure source to the low-pressure operating unit via the high-pressure side backup oil passage.

[0019] In this case, preferably, the high-pressure side flow control valve is a high-pressure side pressure reducing valve, which reduces the hydraulic pressure supplied to a pressure lower than the pressure reduced by the low-pressure side pressure reducing valve. With this configuration, since the high-pressure side pressure reducing valve reduces the hydraulic pressure supplied to a pressure lower than the pressure reduced by the low-pressure side pressure reducing valve, under normal conditions of the low-pressure oil source, the hydraulic pressure output from the low-pressure side pressure reducing valve in the low-pressure oil passage can be made greater than the hydraulic pressure output from the high-pressure side pressure reducing valve in the high-pressure side backup oil passage. Therefore, under normal conditions of the low-pressure oil source, hydraulic pressure can be preferentially supplied to the low-pressure operating part from the low-pressure oil source via the low-pressure side pressure reducing valve. As a result, energy waste of the high-pressure oil source can be suppressed under normal conditions of the low-pressure oil source. In addition, since the high-pressure side pressure reducing valve functions as a high-pressure side flow control valve, the complexity of the device configuration can be suppressed compared to the case where a high-pressure side flow control valve is arranged separately from the high-pressure side pressure reducing valve.

[0020] In a hydraulic system comprising the high-pressure side backup oil passage and the low-pressure side backup oil passage described above, preferably, the low-pressure side flow control valve is an electromagnetic shut-off valve and includes a control unit that controls the opening and closing of the low-pressure side flow control valve. With this configuration, the control unit can control the shut-off and opening of the low-pressure side flow control valve, thereby controlling whether or not to supply hydraulic pressure from the low-pressure source to the high-pressure operating unit.

[0021] In a hydraulic system comprising the high-pressure side backup oil passage and the low-pressure side backup oil passage described above, preferably, the low-pressure side flow control valve is a passive shut-off valve that opens and closes in response to the oil pressure from the low-pressure source. It closes when the oil pressure supplied from the low-pressure source is lower than a predetermined pressure to shut off the flow of hydraulic fluid in the low-pressure side backup oil passage, and opens when the oil pressure supplied from the low-pressure source is higher than a predetermined pressure to open the flow of hydraulic fluid in the low-pressure side backup oil passage. With this configuration, the flow of hydraulic fluid is switched between shutting off and opening by comparing the oil pressure supplied from the low-pressure source with a predetermined pressure, and by adjusting the oil pressure supplied from the low-pressure source, it is possible to control whether or not to supply oil pressure from the low-pressure source to the high-pressure operating part.

[0022] In a hydraulic system equipped with the high-pressure side backup oil passage and the low-pressure side backup oil passage described above, preferably, the low-pressure side flow control valve is a high-pressure shut-off check valve when the high-pressure oil source is functioning normally, and shuts off the flow of hydraulic fluid in the low-pressure side backup oil passage by suppressing the flow of hydraulic fluid from the high-pressure side oil passage side more than the high-pressure shut-off check valve. With this configuration, when the high-pressure oil source is functioning normally, the flow of hydraulic fluid in the low-pressure side backup oil passage can be shut off by suppressing the flow of hydraulic fluid from the high-pressure side oil passage side more than the high-pressure shut-off check valve. For example, when the high-pressure oil source and the low-pressure oil source are functioning normally, it is easy to suppress the supply of hydraulic fluid from the high-pressure oil source to the low-pressure operating part side via the low-pressure side backup oil passage, and the supply of hydraulic fluid from the low-pressure oil source to the high-pressure operating part side. Furthermore, when the high-pressure oil source malfunctions, the pressure in the low-pressure side oil passage becomes greater than the pressure in the high-pressure side oil passage, so the high-pressure shut-off check valve opens automatically, making it easy to switch the flow of hydraulic fluid in the low-pressure side backup oil passage.

[0023] In the hydraulic system according to the first aspect described above, preferably, a bypass valve is further provided that switches between supplying hydraulic pressure to the low-pressure operating section via a pressure reducing valve and supplying hydraulic pressure to the low-pressure operating section via a bypass oil passage that bypasses the pressure reducing valve. The bypass valve switches to supplying hydraulic pressure to the low-pressure operating section via the bypass oil passage when the pressure upstream of the pressure reducing valve is below a predetermined pressure. With this configuration, for example, when supplying relatively low operating hydraulic pressure from a low-pressure source to the low-pressure operating section, it is possible to prevent the pressure reducing valve from becoming a resistive element.

[0024] In a hydraulic system equipped with the above-mentioned backup oil passage and flow control valve, preferably, a bypass oil passage is provided that bypasses the pressure reducing valve and connects the upstream and downstream sides of the pressure reducing valve, and the flow control valve has a bypass function that opens the bypass oil passage when blocking the flow of hydraulic fluid and closes the bypass oil passage when opening the flow of hydraulic fluid. With this configuration, there is no need to provide a separate bypass valve from the flow control valve, which contributes to suppressing an increase in weight and the number of parts, and prevents the pressure reducing valve from becoming a resistive element when, for example, a relatively low operating hydraulic pressure is supplied from a low hydraulic pressure source to a low-pressure operating part.

[0025] In the hydraulic system according to the first aspect described above, preferably, the pressure reducing valve is configured to reduce the supplied hydraulic pressure by allowing hydraulic fluid to flow from the upstream to the downstream side when the downstream pressure is less than a predetermined pressure, and by blocking the flow of hydraulic fluid from the upstream to the downstream side when the downstream pressure exceeds a predetermined pressure. However, if the pressure reducing valve is configured to reduce the hydraulic pressure by distributing the hydraulic fluid to another flow path, the energy efficiency decreases by the amount of hydraulic pressure that is distributed. Taking this into consideration, in the present invention, the reduction in energy efficiency can be suppressed by configuring the pressure reducing valve to allow hydraulic fluid to flow from the upstream to the downstream side when the downstream pressure is less than a predetermined pressure, and by blocking the flow of hydraulic fluid from the upstream to the downstream side when the downstream pressure exceeds a predetermined pressure.

[0026] In the hydraulic system according to the first aspect described above, preferably, the system further comprises a high-pressure actuator that operates with a relatively high operating hydraulic pressure in the high-pressure operating section, and a low-pressure actuator that operates with a relatively low operating hydraulic pressure in the low-pressure operating section. With this configuration, since the hydraulic system includes a high-pressure actuator and a low-pressure actuator to which hydraulic pressure is supplied from a high-pressure source and a low-pressure source, the operation of each of the high-pressure source and the low-pressure source can be set to supply a more appropriate operating hydraulic pressure compared to when hydraulic pressure is supplied to an external actuator.

[0027] Furthermore, in order to achieve the above objective, a control method for a hydraulic system according to the second aspect of this invention comprises the steps of: supplying hydraulic pressure from a high-pressure source to a high-pressure operating part that operates with a relatively high operating hydraulic pressure, and supplying hydraulic pressure from a low-pressure source, which is arranged separately from the high-pressure source, to a low-pressure operating part that operates with a relatively low operating hydraulic pressure; and, in the event of a malfunction of the low-pressure source, supplying hydraulic pressure from the high-pressure source to the low-pressure operating part after reducing the pressure of the hydraulic pressure supplied to the low-pressure operating part using a pressure reducing valve; and, in the event of a malfunction of the high-pressure source, supplying hydraulic pressure from the low-pressure source to the high-pressure operating part after increasing its pressure.

[0028] The hydraulic system control method according to the second aspect of this invention, as described above, involves at least one of the following: when a low hydraulic source malfunctions, hydraulic pressure from a high hydraulic source is reduced by a pressure reducing valve that reduces the hydraulic pressure supplied to the low-pressure operating unit and supplied to the low-pressure operating unit; and when a high hydraulic source malfunctions, hydraulic pressure from a low hydraulic source is increased and supplied to the high-pressure operating unit. As a result, when at least one of the high hydraulic source and the low hydraulic source malfunctions, hydraulic pressure can be supplied from the other, thus reducing the number of hydraulic sources that need to be deployed compared to the case where both the high hydraulic source and the low hydraulic source are individually redundant. Therefore, the increase in the weight of the hydraulic system can be suppressed by the amount by which the number of hydraulic sources is reduced, and the increase in the number of parts of the hydraulic system can also be suppressed. As a result, it is possible to provide a hydraulic system control method that can suppress the increase in weight and the increase in the number of parts even when supplying hydraulic pressure from redundant hydraulic sources to multiple operating units that operate with different operating hydraulic pressures.

[0029] According to the present invention, as described above, even when hydraulic pressure is supplied from redundant hydraulic sources to multiple operating parts that operate with different operating hydraulic pressures, it is possible to suppress increases in weight and the number of parts.

[0030] This is a schematic diagram illustrating the configuration of an aircraft equipped with a hydraulic system according to the first embodiment of the present invention. This is a block diagram illustrating the configuration of a hydraulic system according to the first embodiment. This is a schematic diagram illustrating the operation of a pressure reducing valve. This is a diagram illustrating the operation of the hydraulic system according to the first embodiment in the event of an abnormality in the low-pressure side hydraulic source. This is a diagram illustrating the operation of the hydraulic system according to the first embodiment in the event of an abnormality in the high-pressure side hydraulic source. This is a flowchart illustrating the control method of the hydraulic system according to the first embodiment of the present invention. This is a block diagram illustrating the configuration of a hydraulic system according to the second embodiment of the present invention. This is a diagram illustrating the operation of the hydraulic system according to the second embodiment in the event of an abnormality in the low-pressure side hydraulic source. This is a diagram illustrating the operation of the hydraulic system according to the second embodiment in the event of an abnormality in the high-pressure side hydraulic source. This is a block diagram illustrating the configuration of a hydraulic system according to the third embodiment of the present invention. This is a diagram illustrating the normal operation of the hydraulic source in the hydraulic system according to the third embodiment. This is a diagram illustrating the operation of the hydraulic system according to the third embodiment in the event of an abnormality in the low-pressure side hydraulic source. This is a diagram illustrating the operation of the hydraulic system according to the third embodiment in the event of an abnormality in the high-pressure side hydraulic source. This is a block diagram illustrating the configuration of a hydraulic system according to the fourth embodiment of the present invention. This is a block diagram illustrating the configuration of a hydraulic system according to the first modified example of the present invention. This is a block diagram illustrating the configuration of a hydraulic system according to the second modified example of the present invention. This is a block diagram showing the configuration of a hydraulic system according to the third modification of the present invention. This is a block diagram showing the configuration of a hydraulic system according to the fourth modification of the present invention. This is a block diagram showing the configuration of a hydraulic system according to the fifth modification of the present invention. This is a block diagram showing the configuration of a hydraulic system according to the sixth modification of the present invention. This is a block diagram showing the configuration of a hydraulic system according to the seventh modification of the present invention. This is a block diagram showing the configuration of a hydraulic system according to the eighth modification of the present invention. This is a block diagram showing the configuration of a hydraulic system according to the ninth modification of the present invention. This is a block diagram showing the configuration of a hydraulic system according to the tenth modification of the present invention. This is a block diagram showing the configuration of a hydraulic system according to the eleventh modification of the present invention.

[0031] Embodiments of the present invention will be described below with reference to the drawings.

[0032] [First Embodiment] The configuration of the hydraulic system 100 according to the first embodiment of the present invention will be described with reference to Figures 1 to 5.

[0033] As shown in Figure 1, the hydraulic system 100 is mounted on the aircraft 101. The hydraulic system 100 includes a landing gear system 102 and a flight control system 103 (hereinafter referred to as FCS 103). The hydraulic system 100 supplies hydraulic pressure to the landing gear system 102 and the FCS 103, which are separately located on the aircraft 101. The landing gear system 102 and the FCS 103 switch their operation based on input operations received by an operating unit 104 located in the cockpit of the aircraft 101. Here, in the aircraft 101, the landing gear system 102 and the FCS 103 are designed to operate with different operating hydraulic pressures. For example, the landing gear system 102 operates with sufficient performance using a relatively high operating hydraulic pressure of 4000 psi to 5000 psi. The FCS 103 operates with sufficient performance using a relatively low operating hydraulic pressure of 2000 psi to 3000 psi. The leg lifting system 102 and FCS 103 are examples of the "high-pressure operating unit" and "low-pressure operating unit" as defined in the claims, respectively.

[0034] The landing gear retraction system 102 operates the landing gear 102a that supports the aircraft 101 on the ground. The landing gear 102a comprises wheels and struts to which the wheels are attached, and is configured as the main landing gear and nose gear of the aircraft 101. The landing gear retraction system 102 includes hydraulically operated actuators 102b and 102c. Actuator 102b includes a door actuator that opens and closes the door of the bay that houses the landing gear 102a. Actuator 102c includes a gear actuator that raises and lowers the landing gear 102a. The landing gear retraction system 102 retracts and deploys the landing gear 102a inside and outside the aircraft 101 by operating actuators 102b and 102c. For example, in the landing gear retraction system 102, actuator 102b, which is a door actuator that opens and closes the door, is operated by a relatively high operating hydraulic pressure of 5000 psi or less. The actuator 102c, which is a geared actuator for raising and lowering the leg portion 102a, operates by being supplied with a relatively high operating hydraulic pressure of 5000 psi or less in the leg lifting system 102. Actuators 102b and 102c are examples of "high-pressure actuators" as defined in the claims.

[0035] The FCS 103 operates the control surfaces 103a in the aircraft 101 to control the flight of the aircraft 101. The control surfaces 103a operate to control the attitude of the aircraft 101 during flight or to increase or decrease lift. The control surfaces 103a include, for example, ailerons, elevators, rudder, and flaps. The FCS 103 is equipped with a hydraulically operated actuator 103b. The actuator 103b changes the orientation of the control surfaces 103a. The actuator 103b is operated by a relatively low operating hydraulic pressure of 3000 psi or less supplied to the FCS 103. The actuators 102b and 102c of the landing gear system 102 and the actuator 103b of the FCS 103 are, for example, hydraulic cylinders operated by the supplied hydraulic pressure. Note that actuator 103b is an example of a "low-pressure actuator" in the claims.

[0036] In each of the leg lifting and lowering systems 102 and FCS 103, a directional control valve (not shown) is provided to control the operation of actuators 102b and 102c and actuator 103b. In each of actuators 102b, 102c, and 103b, the directional control valve switches between connecting either the input or output oil passage to the hydraulic chambers on one side and the other side of the hydraulic cylinder's operating direction, or leaving neither oil passage connected, thereby controlling the extension, retraction, and stopping of the hydraulic cylinder. The drive of the directional control valve is controlled by a control unit located in each of the leg lifting and lowering systems 102 and FCS 103.

[0037] (Configuration of the hydraulic system) As shown in Figure 2, the hydraulic system 100 of the first embodiment includes a hydraulic power source 11, a hydraulic power source 12, and a pressure reducing valve 20. The hydraulic power source 11 is an example of a "high hydraulic power source" in the claims. The hydraulic power source 12 is an example of a "low hydraulic power source" in the claims.

[0038] Hydraulic source 11 supplies hydraulic pressure to the landing gear system 102. Hydraulic source 12 supplies hydraulic pressure to the FCS 103. Hydraulic sources 11 and 12 are located separately from each other in the aircraft 101. Hydraulic sources 11 and 12 have a common structure. Hydraulic source 11 includes a hydraulic pump 11a and a motor 11b. Hydraulic source 12 includes a hydraulic pump 12a and a motor 12b. Hydraulic pumps 11a and 12a discharge hydraulic fluid to supply hydraulic pressure to the landing gear system 102 and the FCS 103, respectively. Motors 11b and 12b are the driving sources for hydraulic pumps 11a and 12a, respectively.

[0039] Each of the hydraulic pumps 11a and 12a is a gear pump that discharges hydraulic fluid by rotating gears driven by, for example, motors 11b and 12b. Motors 11b and 12b are servo motors whose rotational speed is controlled by, for example, a control unit 60, which will be described later. That is, the hydraulic pressure output from each of the hydraulic sources 11 and 12 is controlled by the control unit 60. Each of the motors 11b and 12b has an encoder that detects rotation. Motors 11b and 12b are rotated by electricity from a generator provided in the auxiliary power unit of the aircraft 101, for example. In other words, the hydraulic system 100 of the first embodiment supplies hydraulic pressure by driving the electric pumps, hydraulic pumps 11a and 12a, with the electric motors 11b and 12b. In other words, the hydraulic system 100 constitutes an electro-hydraulic actuator system (EHA system).

[0040] The hydraulic system 100 includes oil passages 41, 42, and 43 through which hydraulic fluid from hydraulic sources 11 and 12 flows. Oil passage 41 carries hydraulic fluid from hydraulic source 11 to the leg lifting system 102. Oil passage 42 connects oil passages 41 and 43 to each other. Oil passage 43 carries hydraulic fluid from hydraulic source 12 to the FCS 103. Oil passage 42 is connected to the upstream side of oil passage 43, above the pressure reducing valve 20 located in oil passage 43. That is, hydraulic source 11 supplies hydraulic pressure to oil passage 41 for supplying hydraulic pressure to the leg lifting system 102 and to oil passage 42 for supplying hydraulic pressure to the FCS 103. Hydraulic source 12 supplies hydraulic pressure to oil passage 42 for supplying hydraulic pressure to the leg lifting system 102 and to oil passage 43 for supplying hydraulic pressure to the FCS 103. In other words, the hydraulic fluid output from the hydraulic power source 11 is branched into an oil passage 41 leading to the leg lifting system 102 and an oil passage 42 leading to the FCS 103. The hydraulic fluid output from the hydraulic power source 12 is branched into an oil passage 42 leading to the leg lifting system 102 and an oil passage 43 leading to the FCS 103. Oil passage 42 merges with oil passage 41 from the hydraulic power source 11. Oil passage 42 also merges with oil passage 43 from the hydraulic power source 12. Oil passages 41, 42, and 43 are examples of the "high-pressure oil passage," "backup oil passage," and "low-pressure oil passage" as defined in the claims.

[0041] In the first embodiment, the hydraulic power sources 11 and 12 are configured to receive hydraulic fluid discharged from the actuator 103b of the FCS 103, the actuator 102b of the leg lifting system 102, and the actuator 102c of the leg lifting system 102 via a return path 90. Specifically, the hydraulic fluid supplied from the hydraulic power sources 11 and 12 to the FCS 103 and the leg lifting system 102 is returned to the reservoir 91 via the return path 90. The reservoir 91 is a tank for storing hydraulic fluid. The reservoir 91 is connected to the respective suction ports of the hydraulic pump 11a of the hydraulic power source 11 and the hydraulic pump 12a of the hydraulic power source 12. The hydraulic power sources 11 and 12 supply hydraulic pressure to the FCS 103 and the leg lifting system 102 by outputting the hydraulic fluid supplied from the reservoir 91 toward the FCS 103 and the leg lifting system 102. Therefore, in the hydraulic system 100 in the first embodiment, a hydraulic circuit, which is a circulating circuit, is formed. In the return path 90, the oil passage from the FCS 103 and the oil passage from the leg lifting system 102 are connected to the reservoir 91 in a merged state. In addition, in the return path 90, a check valve 92 is located on the leg lifting system 102 side and a check valve 93 is located on the FCS 103 side. Check valves 92 and 93 suppress the backflow of hydraulic fluid to the leg lifting system 102 and FCS 103, respectively, in the return path 90. Therefore, it is possible to prevent actuators 102b, 102c, and 103b from moving backward due to the backflow of hydraulic fluid through the return path 90.

[0042] The pressure reducing valve 20 reduces the hydraulic pressure supplied to the FCS 103 from the hydraulic power sources 11 and 12. In the hydraulic system 100, the pressure reducing valve 20 is located downstream of the point where the oil passage 42 merges in the oil passage 43 leading from the hydraulic power source 12 to the FCS 103. The pressure reducing valve 20 reduces the hydraulic pressure supplied from the hydraulic power sources 11 and 12 to 3000 psi or less, which is a relatively low operating hydraulic pressure required to operate the FCS 103. In the first embodiment, the pressure reducing valve 20 is configured to reduce the supplied hydraulic pressure by allowing hydraulic fluid to flow from the upstream side to the downstream side when the downstream pressure is less than a predetermined pressure, and by blocking the flow of hydraulic fluid from the upstream side to the downstream side when the downstream pressure exceeds the predetermined pressure. Alternatively, the pressure reducing valve 20 may be configured to reduce the supplied hydraulic pressure by blocking the flow of hydraulic fluid from the upstream side to the downstream side when the downstream pressure is above a predetermined pressure, for example, when the downstream pressure reaches a predetermined pressure. For example, due to valve hysteresis, the pressure at which the pressure reducing valve 20 closes and the pressure at which the valve opens may differ. Taking such cases into consideration, the criteria for shutting off the flow of hydraulic fluid by the pressure reducing valve 20 may be set as when the pressure exceeds a predetermined pressure or falls below a predetermined pressure, or as being above or below a predetermined pressure.

[0043] Specifically, as shown in FIG. 3, the pressure reducing valve 20 has a spool 20a and a spring 20b. In the pressure reducing valve 20, the spool 20a, which is a valve body, moves by the hydraulic pressure on the downstream side while resisting the elastic force of the spring 20b, thereby switching the flow and interruption of the hydraulic oil from the upstream to the downstream. For example, the pressure reducing valve 20 is configured to reduce the pressure supplied up to 3000 psi as a predetermined pressure. As shown in the left diagram of FIG. 3, when the upstream side is 5000 psi and the downstream side is 1000 psi, which is less than 3000 psi, the spool 20a moves to a position where it allows the hydraulic oil to flow due to the elastic force of the spring 20b. On the other hand, as shown in the right diagram of FIG. 3, when the hydraulic pressure on the downstream side reaches 3000 psi, the spool 20a moves to a position where it blocks the hydraulic oil while resisting the elastic force of the spring 20b due to the hydraulic pressure on the downstream side. In addition, when the hydraulic pressure on the downstream side becomes less than 3000 psi again from the state where the hydraulic oil is blocked, the spool 20a moves to a position where it allows the hydraulic oil to flow again due to the elastic force of the spring 20b. In this way, the pressure reducing valve 20 is configured to reduce the hydraulic pressure from the upstream by blocking the flow of the hydraulic oil so that the hydraulic pressure on the downstream side does not exceed a predetermined pressure of 3000 psi.

[0044] Also, as shown in FIG. 2, the hydraulic system 100 includes a check valve 31 and a check valve 32 that are separately arranged from each other. The check valve 31 is arranged on the upstream side of the confluence position (branch position) with the oil passage 42 in the oil passage 41 from the hydraulic source 11 toward the leg lifting and lowering system 102. The check valve 32 is arranged on the upstream side of the pressure reducing valve 20 in the oil passage 43 from the hydraulic source 12 toward the FCS 103, and is arranged on the upstream side of the confluence position (branch position) with the oil passage 42.

[0045] The check valve 31 suppresses the backflow of hydraulic fluid to the hydraulic source 11. The check valve 32 suppresses the backflow of hydraulic fluid to the hydraulic source 12. The check valves 31 and 32 allow hydraulic fluid to flow from the upstream side where the hydraulic sources 11 and 12 are located towards the downstream side where the leg lifting system 102 and FCS 103 are located, and block the flow of hydraulic fluid in the opposite direction, from the downstream side to the upstream side. Specifically, the check valves 31 and 32 allow hydraulic fluid to flow from upstream to downstream when the hydraulic pressure on the upstream side is higher than the hydraulic pressure on the downstream side, and block the flow of hydraulic fluid that would otherwise flow from downstream to upstream when the hydraulic pressure on the downstream side is higher than the hydraulic pressure on the upstream side. In other words, the check valves 31 and 32 block the flow of hydraulic fluid that would otherwise flow from the leg lifting system 102 side and the FCS 103 side towards the hydraulic source 11 side and the hydraulic source 12 side.

[0046] The hydraulic system 100 also includes pressure gauges 51 and 52, and a control unit 60. Pressure gauge 51 detects the output pressure of the hydraulic power source 11. Pressure gauge 52 detects the output pressure of the hydraulic power source 12. Each of pressure gauges 51 and 52 outputs a detection result indicating the detected output pressure to the control unit 60. Pressure gauge 51 is connected on the output side of the hydraulic power source 11 upstream of the check valve 31 in the portion before it branches into oil passages 41 and 42. Pressure gauge 52 is connected on the output side of the hydraulic power source 12 upstream of the check valve 32 in the portion before it branches into oil passages 42 and 43. Pressure gauges 51 and 52 are examples of the "high-pressure side pressure gauge" and "low-pressure side pressure gauge" in the claims, respectively.

[0047] The control unit 60 controls the operation of the hydraulic power sources 11 and 12. The control unit 60 is composed of a computer equipped with a processor such as a CPU (Central Processing Unit) and an FPGA (Field-Programmable Gate Array), and a storage device such as volatile or non-volatile memory. The control unit 60 may also include, for example, a personal computer or a circuit. In the first embodiment, the control unit 60 controls the operation of the hydraulic power sources 11 and 12 by hydraulic feedback control using the output pressure detected by the pressure gauges 51 and 52. In this embodiment, the control unit 60 automatically controls the operation of the hydraulic power sources 11 and 12 by hydraulic feedback control. The control unit 60 controls the operation of the hydraulic power source 11 by controlling the rotation of the motor 11b by hydraulic feedback control using the output pressure detection result from the pressure gauge 51. The control unit 60 controls the operation of the hydraulic power source 12 by controlling the rotation of the motor 12b through hydraulic feedback control using the output pressure detection result from the pressure gauge 52. In hydraulic feedback control, the control unit 60 controls the rotation of the motors 11b and 12b so that the output pressure detected by the pressure gauges 51 and 52 follows a set command value, for example, by P control, PI control, or PID control. The control unit 60 controls the electrical signals supplied from the motor driver to the motors 11b and 12b by controlling the gate signal output to the motor driver having an inverter circuit. The control unit 60 also controls the operation of the shut-off valve 80, which will be described later.

[0048] In the first embodiment, the hydraulic system 100 includes a shut-off valve 80. The shut-off valve 80 is disposed in the oil passage 42. The shut-off valve 80 blocks the flow of the hydraulic fluid between the high-pressure side where the hydraulic source 11 is disposed and the low-pressure side where the hydraulic source 12 is disposed in the oil passage 42. The opening and closing of the shut-off valve 80 are controlled by the control unit 60. The shut-off valve 80 switches between blocking and releasing the flow of the hydraulic fluid in the oil passage 42 by opening and closing. The shut-off valve 80 is, for example, a direct-acting electromagnetic shut-off valve. The shut-off valve 80 blocks the flow of the hydraulic fluid in the oil passage 42 by closing when the hydraulic sources 11 and 12 are normal. Then, the shut-off valve 80 releases the flow of the hydraulic fluid in the oil passage 42 by opening when the hydraulic source 11 or the hydraulic source 12 is abnormal. Note that the shut-off valve 80 is an example of the "flow control valve" in the claims.

[0049] (Operation when the hydraulic sources are normal) When both the hydraulic source 11 and the hydraulic source 12 are normal, control in the normal operation is performed. In the control in the normal operation, the hydraulic pressure from the hydraulic source 11 is supplied to the leg lifting and lowering system 102, and the hydraulic pressure from the hydraulic source 12 is supplied to the FCS 103. Also, in the control in the normal operation, the control unit 60 blocks the oil passage 42 by the shut-off valve 80. In the first embodiment, when the hydraulic source 12 is normal, the hydraulic source 11 supplies hydraulic pressure only to the leg lifting and lowering system 102 without supplying hydraulic pressure to the FCS 103 via the pressure reducing valve 20 for the FCS 103. When the hydraulic source 11 is normal, the hydraulic source 12 supplies hydraulic pressure only to the FCS 103 without supplying hydraulic pressure to the leg lifting and lowering system 102.

[0050] When the hydraulic system 100 supplies operating hydraulic pressure to both the leg lifting system 102 and the FCS 103, the control unit 60 controls the hydraulic source 11 to output a relatively high operating hydraulic pressure target of 5000 psi, and controls the hydraulic source 12 to output a relatively low operating hydraulic pressure target of 3000 psi. As a result, the hydraulic pressure on the upstream side of the check valve 31 becomes greater than that on the downstream side, so 5000 psi of hydraulic pressure from the hydraulic source 11 is supplied to the oil passage 41 and then to the leg lifting system 102. Also, because the hydraulic pressure on the upstream side of the check valve 32 becomes greater than that on the downstream side, 3000 psi of hydraulic pressure from the hydraulic source 12 is supplied to the oil passage 43 and then to the FCS 103 via the pressure reducing valve 20. When the hydraulic power sources 11 and 12 are outputting operating hydraulic pressure normally, the control unit 60 closes the shut-off valve 80, thereby blocking the flow of hydraulic fluid in the oil passage 42. As a result, the hydraulic pressure supplied from the hydraulic power source 11 is not supplied to the FCS 103 side via the oil passage 42, but is supplied to the leg lifting system 102 via the oil passage 41. Similarly, when the hydraulic power sources 11 and 12 are outputting operating hydraulic pressure normally, the hydraulic pressure supplied from the hydraulic power source 12 is not supplied to the leg lifting system 102 side via the oil passage 42, but is supplied to the FCS 103 via the oil passage 43.

[0051] (Backup operation in case of hydraulic power source malfunction) As shown in Figures 4 and 5, in the hydraulic system 100, the high-pressure hydraulic power source 11 and the low-pressure hydraulic power source 12 are configured such that one of them acts as a backup hydraulic power source for the other. In the first embodiment, when either the hydraulic power source 11 or the hydraulic power source 12 malfunctions, the shut-off valve 80 opens, thereby opening the flow of hydraulic fluid in the oil passage 42. If a malfunction occurs in the low-pressure hydraulic power source 12, the high-pressure hydraulic power source 11 supplies operating hydraulic pressure to both the leg lifting system 102 and the FCS 103. Also, if a malfunction occurs in the high-pressure hydraulic power source 11, the low-pressure hydraulic power source 12 supplies operating hydraulic pressure to both the leg lifting system 102 and the FCS 103. In the hydraulic system 100, the hydraulic power sources are redundant because the high-pressure hydraulic power source 11 and the low-pressure hydraulic power source 12 back each other up.

[0052] In the first embodiment, the control unit 60 is configured to determine abnormalities in the hydraulic power sources 11 and 12, and to switch the operation of the hydraulic power sources 11 and 12 if an abnormality is determined. The control unit 60 is also configured to switch the opening and closing of the shut-off valve 80 when an abnormality is determined in the hydraulic power sources 11 and 12. For example, the control unit 60 determines that the hydraulic power source 11 is normal if the output pressure of the hydraulic power source 11 detected by the pressure gauge 51 is greater than a predetermined high-pressure side determination threshold. Similarly, the control unit 60 determines that the hydraulic power source 12 is normal if the output pressure of the hydraulic power source 12 detected by the pressure gauge 52 is greater than a predetermined low-pressure side determination threshold. In the first embodiment, the control unit 60 determines that there is an abnormality in the hydraulic power source 11 based on the detection result from the pressure gauge 51, and determines that there is an abnormality in the hydraulic power source 12 based on the detection result from the pressure gauge 52. The control unit 60 determines that there is an abnormality in the hydraulic power source 11 if the output pressure of the hydraulic power source 11 detected by the pressure gauge 51 falls below a predetermined high-pressure side determination threshold. The control unit 60 determines that the hydraulic power source 12 is abnormal when the output pressure of the hydraulic power source 12 detected by the pressure gauge 52 falls below a predetermined low-pressure threshold. The high-pressure threshold and the low-pressure threshold are set, for example, as numerical values ​​obtained by multiplying the command value in hydraulic feedback control by a predetermined ratio. Alternatively, the high-pressure threshold and the low-pressure threshold may be set as fixed values ​​in advance.

[0053] As shown in Figure 4, in the first embodiment, when the low-pressure hydraulic source 12 malfunctions, the hydraulic pressure from the high-pressure hydraulic source 11 is reduced by the pressure reducing valve 20 and supplied to the FCS 103. The control unit 60 controls the operation of the hydraulic source 12 to stop when the hydraulic source 12 malfunctions, and to reduce the hydraulic pressure from the hydraulic source 11 by the pressure reducing valve 20 and supply it to the FCS 103. Specifically, when a malfunction occurs in the hydraulic source 12, hydraulic pressure is no longer supplied in the oil passage 43 from the hydraulic source 12. Therefore, the supply of hydraulic pressure is lost in the region 72a including the upstream side of the check valve 32 of the oil passage 43. On the other hand, when the low-pressure hydraulic source 12 malfunctions, the control unit 60 controls the shut-off valve 80 to open and continues to supply hydraulic pressure from the hydraulic source 11. Therefore, the hydraulic pressure supplied from the hydraulic power source 11 provides a relatively high hydraulic pressure of 5000 psi or less to the entire oil passage 41, the entire oil passage 42, and the region 71a including the portion of the oil passage 43 downstream of the check valve 32 and upstream of the pressure reducing valve 20. As a result, even in the event of a malfunction of the hydraulic power source 12, a relatively high operating hydraulic pressure of 5000 psi or less is supplied to the leg lifting system 102 from the hydraulic power source 11. However, in the event of a malfunction of the hydraulic power source 12, the supply of hydraulic pressure from the hydraulic power source 12 is lost, and therefore the supply of hydraulic pressure in the region 72a upstream of the check valve 32 of the oil passage 43 is lost. As a result, the hydraulic pressure supplied from the hydraulic power source 11 tries to flow upstream of the check valve 32. However, the check valve 32 blocks the flow of hydraulic fluid from downstream to upstream.

[0054] Furthermore, the pressure reducing valve 20 reduces the pressure of the oil passage 43 downstream of the pressure reducing valve 20 to 3000 psi or less. Therefore, in the event of a malfunction of the hydraulic power source 12, the region 73a including the area downstream of the pressure reducing valve 20 in the oil passage 43 is supplied with a relatively low hydraulic pressure of 3000 psi or less from the hydraulic power source 11, just as in normal conditions. As a result, the hydraulic pressure from the hydraulic power source 11 is supplied to the FCS 103 via the pressure reducing valve 20. In this way, in the first embodiment, when a malfunction of the hydraulic power source 12 occurs, the hydraulic power source 11 supplies a relatively high operating hydraulic pressure of 5000 psi or less to the leg lifting system 102, while simultaneously supplying a relatively low operating hydraulic pressure of 3000 psi or less to the FCS 103 via the pressure reducing valve 20.

[0055] Furthermore, as shown in Figure 5, in the first embodiment, when there is an abnormality in the high-pressure hydraulic source 11, the hydraulic pressure from the hydraulic source 12 is increased and supplied to the leg lifting system 102. The control unit 60 controls the operation of the hydraulic source 11 to stop when there is an abnormality in the hydraulic source 11, and to increase the hydraulic pressure from the hydraulic source 12 and supply it to the leg lifting system 102. Specifically, when an abnormality in the hydraulic source 11 is detected, the control unit 60 controls the operation of the hydraulic source 12 to output a hydraulic pressure of 5000 psi, which is a relatively high operating hydraulic pressure target, by changing the command value of the hydraulic feedback control to the hydraulic source 12, and also controls the shut-off valve 80 to open. When an abnormality occurs in the hydraulic source 11, hydraulic pressure is not supplied to the oil passage 41 from the hydraulic source 11, so the supply of hydraulic pressure is lost in the region 71b including the area upstream of the check valve 31 of the oil passage 41. On the other hand, since the shut-off valve 80 is open and a relatively high hydraulic pressure of 5000 psi or less is supplied from the hydraulic power source 12, a relatively high hydraulic pressure of 5000 psi or less is supplied to the region 72b, which includes the area upstream of the pressure reducing valve 20 in the oil passage 43, the entire oil passage 42, and the area downstream of the check valve 31 in the oil passage 41. As a result, even in the event of a malfunction in the hydraulic power source 11, a relatively high operating hydraulic pressure of 5000 psi or less is supplied to the leg lifting system 102 from the hydraulic power source 12. However, in the event of a malfunction in the hydraulic power source 11, the supply of hydraulic pressure from the hydraulic power source 11 is lost, and therefore the supply of hydraulic pressure in the region 71b upstream of the check valve 31 in the oil passage 41 is lost. As a result, the hydraulic pressure supplied from the hydraulic power source 12 tries to flow upstream of the check valve 31. However, the check valve 31 blocks the flow of hydraulic fluid that tries to flow from downstream to upstream.

[0056] Furthermore, the pressure reducing valve 20 reduces the oil passage 43 downstream of the pressure reducing valve 20 from a relatively high oil pressure of 5000 psi or less to 3000 psi or less. Therefore, a relatively low oil pressure of 3000 psi or less, similar to that under normal conditions, is supplied to the region 73a of the oil passage 43, including the downstream side of the pressure reducing valve 20. As a result, the oil pressure from the oil pressure source 12 is supplied to the FCS 103 via the pressure reducing valve 20. In this way, in the first embodiment, when the oil pressure source 11 malfunctions, the oil pressure source 12 supplies a relatively high operating oil pressure of 5000 psi or less to the leg lifting system 102 by increasing the pressure of the supplied oil pressure, while simultaneously supplying a relatively low operating oil pressure of 3000 psi or less to the FCS 103 via the pressure reducing valve 20.

[0057] (Control Method for Hydraulic System) Next, with reference to Figure 6, the control method for the hydraulic system 100 in the aircraft 101 will be described. The control processes of steps S1 to S8 in the control method for the hydraulic system 100 are performed by the control unit 60. The control unit 60 performs the control processes of steps S1 to S8 at predetermined control cycles, for example.

[0058] First, in step S1, hydraulic pressure is supplied from hydraulic power sources 11 and 12. The control unit 60 supplies hydraulic pressure from hydraulic power source 11 to the leg lifting system 102 and from hydraulic power source 12 to the FCS 103. Note that in step S1, the shut-off valve 80 is in a shut-off state.

[0059] Next, in step S2, the output pressures of the hydraulic power sources 11 and 12 are acquired. The control unit 60 acquires the output pressure of the hydraulic power source 11 based on the detection result of the pressure gauge 51. Similarly, the control unit 60 acquires the output pressure of the hydraulic power source 12 based on the detection result of the pressure gauge 52.

[0060] Next, in step S3, abnormalities in the high-pressure side hydraulic source 11 and the low-pressure side hydraulic source 12 are determined. Specifically, based on the output pressure of the hydraulic source 11 obtained in step S2, it is determined whether or not the output pressure is below a predetermined high-pressure side determination threshold to determine whether or not there is an abnormality in the hydraulic source 11. Similarly, based on the output pressure of the hydraulic source 12 obtained in step S2, it is determined whether or not the output pressure is below a predetermined low-pressure side determination threshold to determine whether or not there is an abnormality in the hydraulic source 12. If the high-pressure side hydraulic source 11 is determined to be abnormal and the low-pressure side hydraulic source 12 is determined to be normal, the process proceeds to step S4. If the high-pressure side hydraulic source 11 is determined to be normal and the low-pressure side hydraulic source 12 is determined to be abnormal, the process proceeds to step S6. If both the high-pressure side hydraulic source 11 and the low-pressure side hydraulic source 12 are determined to be abnormal, the process proceeds to step S8. If both the high-pressure hydraulic power source 11 and the low-pressure hydraulic power source 12 are determined to be functioning normally, the control process is terminated with the shut-off valve 80 closed and hydraulic pressure continuing to be supplied by the hydraulic power sources 11 and 12.

[0061] In step S4, when the high-pressure hydraulic source 11 malfunctions, the operation of the high-pressure hydraulic source 11 is stopped, and the hydraulic pressure from the low-pressure hydraulic source 12 is increased. The control unit 60 stops the operation of the hydraulic source 11 when the hydraulic source 11 malfunctions, and increases the hydraulic pressure output by the hydraulic source 12 by controlling the operation of the motor 12b.

[0062] Next, in step S5, the shut-off valve 80 is opened. When the hydraulic power source 11 malfunctions, the control unit 60 opens the shut-off valve 80, thereby opening the flow of hydraulic fluid in the oil passage 42. As a result, the hydraulic pressure from the hydraulic power source 12, which was pressurized in step S4, is supplied to the leg lifting system 102 via the oil passage 42. In steps S4 and S5, when the hydraulic power source 11 malfunctions, the control unit 60 pressurizes the hydraulic pressure output by the hydraulic power source 12 and opens the shut-off valve 80, thereby supplying the hydraulic pressure from the hydraulic power source 12 to the leg lifting system 102 and also to the FCS 103 via the pressure reducing valve 20.

[0063] In step S6, if there is an abnormality in the low-pressure hydraulic power source 12, the operation of the hydraulic power source 12 is stopped.

[0064] Next, in step S7, the shut-off valve 80 is opened in the same manner as in step S5. When the hydraulic power source 12 malfunctions, the control unit 60 opens the shut-off valve 80 in the same manner as in step S5, thereby opening the flow of hydraulic fluid in the oil passage 42. In steps S6 and S7, when the hydraulic power source 12 malfunctions, the control unit 60 opens the shut-off valve 80, thereby supplying hydraulic pressure from the hydraulic power source 11 to the leg lifting system 102 and also to the FCS 103 via the pressure reducing valve 20.

[0065] In step S8, if both the high-pressure hydraulic power source 11 and the low-pressure hydraulic power source 12 are malfunctioning, the operation of hydraulic power source 11 is stopped and the operation of hydraulic power source 12 is stopped. The control unit 60 stops the operation of hydraulic power sources 11 and 12 while keeping the shut-off valve 80 closed in the event of a malfunction in both hydraulic power sources 11 and 12. Then the control process is terminated.

[0066] (Effects of the First Embodiment) In the first embodiment, the following effects can be obtained.

[0067] In the first embodiment, as described above, the hydraulic system 100 performs at least one of the following: when the hydraulic source 12 (low hydraulic source) malfunctions, it reduces the hydraulic pressure from the hydraulic source 11 (high hydraulic source) using the pressure reducing valve 20 and supplies it to the FCS 103 (low-pressure operating unit); and when the hydraulic source 11 malfunctions, it increases the hydraulic pressure from the hydraulic source 12 and supplies it to the leg lifting system 102 (high-pressure operating unit). This allows hydraulic pressure to be supplied from the other when either the hydraulic source 11 or the hydraulic source 12 malfunctions, thus reducing the number of hydraulic sources that need to be deployed compared to the case where both the hydraulic source 11 and the hydraulic source 12 are individually redundant. As a result, the weight of the hydraulic system 100 can be suppressed by the amount by which the number of hydraulic sources is reduced, and the number of parts in the hydraulic system 100 can also be suppressed. Consequently, even when supplying hydraulic pressure from redundant hydraulic sources to multiple operating units (leg lifting system 102 and FCS 103) that operate with different operating hydraulic pressures, the increase in weight and the increase in the number of parts can be suppressed.

[0068] Furthermore, since the hydraulic power source 11 (high-pressure source) that supplies hydraulic pressure to the leg lifting system 102 (high-pressure operating section), which operates with a relatively high operating hydraulic pressure, and the hydraulic power source 12 (low-pressure source) that supplies hydraulic pressure to the FCS 103 (low-pressure operating section), which operates with a relatively low operating hydraulic pressure, are arranged separately, the output specifications of the hydraulic power source 11 can be appropriately set to correspond to the leg lifting system 102, and the output specifications of the hydraulic power source 12 can be appropriately set to correspond to the FCS 103. As a result, it is possible to arrange hydraulic power sources (hydraulic power source 11 and hydraulic power source 12) with appropriately set output specifications for each of the multiple operating sections (leg lifting system 102 and FCS 103) that operate with different operating hydraulic pressures, thus suppressing wasted output from the hydraulic power sources.

[0069] Furthermore, in the first embodiment, as described above, the hydraulic power source 12 (low hydraulic power source) includes a hydraulic pump 12a that discharges hydraulic fluid to supply hydraulic pressure and a motor 12b that serves as the drive source for the hydraulic pump 12a. As a result, hydraulic pressure can be supplied by operating the hydraulic pump 12a by driving the motor 12b, and the hydraulic pressure supplied from the hydraulic power source 12 can be easily controlled by controlling the operation of the motor 12b. Also, in the event of a malfunction of the hydraulic power source 11 (high hydraulic power source), when the hydraulic pressure from the hydraulic power source 12 is increased and supplied to the leg lifting system 102 (high-pressure operating section), since the hydraulic power source 12 includes the hydraulic pump 12a and the motor 12b, the hydraulic pressure from the hydraulic power source 12 can be easily increased by controlling the operation of the motor 12b. Therefore, even in the event of a malfunction of the hydraulic power source 11, operating hydraulic pressure can be easily supplied to the leg lifting system 102.

[0070] Furthermore, in the first embodiment, as described above, when the hydraulic source 12 (high hydraulic source) malfunctions, the hydraulic source 11 (high hydraulic source) supplies a relatively high operating hydraulic pressure to the leg lifting system 102 (high-pressure operating section) while simultaneously supplying a relatively low operating hydraulic pressure to the FCS 103 (low-pressure operating section) via the pressure reducing valve 20. When the hydraulic source 11 malfunctions, the hydraulic source 12 supplies a relatively high operating hydraulic pressure to the leg lifting system 102 by increasing the pressure of the supplied hydraulic pressure while simultaneously supplying a relatively low operating hydraulic pressure to the FCS 103 via the pressure reducing valve 20. As a result, when the hydraulic source 12 malfunctions, reduced operating hydraulic pressure is supplied from the hydraulic source 11, and when the hydraulic source 11 malfunctions, increased operating hydraulic pressure is supplied from the hydraulic source 12, thus enabling redundancy in which the hydraulic source 11 and the hydraulic source 12 back up each other. Therefore, since the supply of operating hydraulic pressure can be prevented from being stopped in the event of a malfunction in either hydraulic source 11 or hydraulic source 12, the operational stability of the hydraulic system 100 can be further improved compared to a configuration where only one of the hydraulic sources 11 or 12 acts as a backup for the other. In addition, since hydraulic sources 11 and 12 are redundant to back up each other, the number of hydraulic sources to be deployed can be reduced compared to a configuration where either hydraulic source 11 or hydraulic source 12 is individually redundant. As a result, the increase in weight and the number of parts can be further suppressed.

[0071] Furthermore, in the first embodiment, as described above, the hydraulic system 100 includes a pressure gauge 51 (high-pressure side pressure gauge) that detects the output pressure of the hydraulic source 11 (high-pressure source), a pressure gauge 52 (low-pressure side pressure gauge) that detects the output pressure of the hydraulic source 12 (low-pressure source), and a control unit 60 that controls the operation of the hydraulic source 11 and the hydraulic source 12. The control unit 60 determines an abnormality in the hydraulic source 11 based on the detection result from the pressure gauge 51, and determines an abnormality in the hydraulic source 12 based on the detection result from the pressure gauge 52. In addition, when an abnormality occurs in the hydraulic source 12, the control unit 60 stops the operation of the hydraulic source 12 and reduces the hydraulic pressure from the hydraulic source 11 using the pressure reducing valve 20 and supplies it to the FCS 103 (low-pressure operating unit). In addition, when an abnormality occurs in the hydraulic source 11, the control unit 60 stops the operation of the hydraulic source 11 and increases the hydraulic pressure from the hydraulic source 12 and supplies it to the leg lifting system 102 (high-pressure operating unit). As a result, the control unit 60 can automatically determine abnormalities in the hydraulic power sources 11 and 12 based on the detection results from the pressure gauges 51 and 52, and can also automatically control the supply of operating hydraulic pressure in the event of an abnormality. Therefore, even if an abnormality occurs in either the hydraulic power source 11 or 12, operating hydraulic pressure can be easily supplied to multiple operating parts (leg lifting system 102 and FCS 103) that operate with different operating hydraulic pressures.

[0072] Furthermore, in the first embodiment, as described above, the hydraulic source 11 (high hydraulic source) is located on the aircraft 101 and supplies hydraulic pressure to the landing gear lifting system 102 (high-pressure operating section) located on the aircraft 101. The hydraulic source 12 (low hydraulic source) is located on the aircraft 101 separately from the hydraulic source 11 and supplies hydraulic pressure to the FCS 103 (low-pressure operating section) located on the aircraft 101. This allows hydraulic pressure to be supplied from the other when at least one of the hydraulic sources 11 and 12 located on the aircraft 101 malfunctions, thus suppressing an increase in weight and the number of parts compared to the case where both the hydraulic source 11 and 12 are individually redundant on the aircraft 101. Therefore, since the increase in weight and the number of parts of the hydraulic system 100 located on the aircraft 101 can be suppressed, an increase in the weight of the aircraft 101 due to the weight of the hydraulic system 100 can be effectively suppressed, and the complexity of the aircraft 101's configuration due to the number of parts of the hydraulic system 100 can be effectively suppressed.

[0073] Furthermore, in the first embodiment, as described above, the hydraulic source 11 (high hydraulic source) supplies hydraulic pressure to the landing gear lifting system 102 (high-pressure operating part) that operates the landing gear 102a in the aircraft 101. The hydraulic source 12 (low hydraulic source) supplies hydraulic pressure to the FCS 103 (low-pressure operating part) that operates the control surface 103a in the aircraft 101. As a result, even when the operating hydraulic pressures differ between operating the landing gear 102a and operating the control surface 103a in the aircraft 101, hydraulic pressure can be supplied from the other when at least one of the hydraulic sources 11 and 12 located in the aircraft 101 malfunctions. Therefore, compared to the case where both the hydraulic source 11 and the hydraulic source 12 are individually redundant in the aircraft 101, an increase in weight and an increase in the number of parts can be effectively suppressed.

[0074] Furthermore, in the first embodiment, as described above, the hydraulic system 100 connects an oil passage 41 (high-pressure oil passage) that supplies hydraulic fluid from the hydraulic source 11 (high-pressure source) to the leg lifting system 102 (high-pressure operating section), and an oil passage 43 (low-pressure oil passage) that supplies hydraulic fluid from the hydraulic source 12 (low-pressure source) to the FCS 103 (low-pressure operating section), and also includes an oil passage 42 (backup oil passage) connected upstream of the pressure reducing valve 20 located in the oil passage 43. The hydraulic system 100 also includes a shut-off valve 80 (flow control valve) that switches between shutting off and opening the flow of hydraulic fluid in the oil passage 42 by opening and closing. In the event of an abnormality in either the hydraulic source 11 or the hydraulic source 12, the shut-off valve 80 opens, thereby opening the flow of hydraulic fluid in the oil passage 42. As a result, in the event of a malfunction in the hydraulic power source 12, appropriate operating hydraulic pressure can be supplied from the hydraulic power source 11 to the leg lifting system 102 via the oil passage 41, and appropriate operating hydraulic pressure can be supplied to the FCS 103 via the pressure reducing valves 20 located in the oil passages 42 and 43, where the shut-off valve 80 is located. Furthermore, even if the hydraulic pressure from the hydraulic power source 12 is increased in the event of a malfunction in the hydraulic power source 11, appropriate operating hydraulic pressure can be supplied to the FCS 103 via the oil passage 43 where the pressure reducing valve 20 is located, and appropriate operating hydraulic pressure can be supplied to the leg lifting system 102 via the oil passage 42. Therefore, by connecting the upstream of the pressure reducing valve 20 in the oil passages 41 and 43 with the oil passage 42, and opening the shut-off valve 80 located in the oil passage 42 in the event of a malfunction in either the hydraulic power source 11 or the hydraulic power source 12, it is possible to easily prevent the supply of operating hydraulic pressure from being stopped in the event of a malfunction in both the hydraulic power source 12 and the hydraulic power source 11.

[0075] Furthermore, in the first embodiment, as described above, the pressure reducing valve 20 is configured to reduce the supplied hydraulic pressure by circulating hydraulic fluid from the upstream side to the downstream side when the downstream pressure is less than a predetermined pressure, and by blocking the circulation of hydraulic fluid from the upstream side to the downstream side when the downstream pressure exceeds a predetermined pressure. However, if the pressure reducing valve 20 is configured to reduce the hydraulic pressure by distributing the hydraulic fluid to another flow path, the energy efficiency will decrease by the amount of hydraulic pressure that is distributed. Taking this into consideration, in the first embodiment, the pressure reducing valve 20 is configured to reduce the supplied hydraulic pressure by circulating hydraulic fluid from the upstream side to the downstream side when the downstream pressure is less than a predetermined pressure, and by blocking the circulation of hydraulic fluid from the upstream side to the downstream side when the downstream pressure exceeds a predetermined pressure, thereby suppressing the decrease in energy efficiency.

[0076] Furthermore, in the first embodiment, as described above, the hydraulic system 100 includes an actuator 102c (high-pressure actuator) that operates with a relatively high operating hydraulic pressure in the leg lifting system 102 (high-pressure operating section), and an actuator 103b (low-pressure actuator) that operates with a relatively low operating hydraulic pressure in the FCS 103 (low-pressure operating section). As a result, since the hydraulic system 100 includes actuators 102c and 103b that are supplied with hydraulic pressure from the hydraulic source 11 (high-pressure source) and hydraulic source 12 (low-pressure source), the operation of each of the hydraulic sources 11 and 12 can be set to supply a more appropriate operating hydraulic pressure compared to when hydraulic pressure is supplied to an external actuator.

[0077] [Second Embodiment] Next, the configuration of the hydraulic system 200 according to the second embodiment will be described with reference to Figures 7 to 9. In the second embodiment, unlike the first embodiment in which an oil passage 42 was arranged as a common backup oil passage, the oil passage 242 as a low-pressure side backup oil passage and the oil passage 243 as a high-pressure side backup oil passage are arranged separately from each other. Components similar to those in the first embodiment are denoted by the same reference numerals and their description is omitted.

[0078] As shown in Figure 7, in the second embodiment, the hydraulic system 200 includes a hydraulic power source 11 and a hydraulic power source 12, similar to the hydraulic system 100 of the first embodiment. Similar to the first embodiment, the output of the hydraulic power source 11 and the hydraulic power source 12 is controlled by hydraulic feedback control using the output pressure detected by pressure gauges 51 and 52, respectively.

[0079] In the second embodiment, the hydraulic system 200 includes an oil passage 241 that supplies hydraulic fluid from the hydraulic source 11 to the leg lifting system 102, and an oil passage 244 that supplies hydraulic fluid from the hydraulic source 12 to the FCS 103. The hydraulic system 200 also includes an oil passage 242 that connects oil passages 241 and 244 to each other, and an oil passage 243 that is separately arranged from oil passage 242 and connects oil passages 241 and 244 to each other. The hydraulic pressure from the hydraulic source 11 is supplied by branching into an oil passage 241 that supplies hydraulic pressure from the hydraulic source 11 to the leg lifting system 102, and an oil passage 243 that supplies hydraulic pressure from the hydraulic source 11 to the FCS 103. The hydraulic pressure from the hydraulic source 12 is supplied by branching into an oil passage 242 that supplies hydraulic pressure from the hydraulic source 12 to the leg lifting system 102, and an oil passage 244 that supplies hydraulic pressure from the hydraulic source 12 to the FCS 103. Oil passage 242 from hydraulic power source 12 merges with oil passage 241 from hydraulic power source 11. Also, oil passage 243 from hydraulic power source 11 merges with oil passage 244 from hydraulic power source 12. Oil passages 241 and 244 are examples of the "high-pressure oil passage" and "low-pressure oil passage" as defined in the claims, respectively. Oil passage 242 is an example of the "backup oil passage" and "low-pressure backup oil passage" as defined in the claims. Oil passage 243 is an example of the "backup oil passage" and "high-pressure backup oil passage" as defined in the claims.

[0080] Furthermore, the hydraulic system 200 is equipped with a pressure reducing valve 220 that reduces the hydraulic pressure supplied to the FCS 103. The configuration of the pressure reducing valve 220 is the same as that of the pressure reducing valve 20 in the first embodiment. The pressure reducing valve 220 reduces the supplied hydraulic pressure to 3000 psi or less, which is a relatively low operating hydraulic pressure required to operate the FCS 103. In addition, the pressure reducing valve 220 is located downstream of the point where the oil passage 243 merges in the oil passage 244. That is, the oil passage 243 is connected to the oil passage 244 upstream of the pressure reducing valve 220 located in the oil passage 244. In the second embodiment, the pressure reducing valve 220 is configured to reduce the hydraulic pressure supplied from the high-pressure hydraulic source 11 and the hydraulic pressure supplied from the low-pressure hydraulic source 12 in common, similar to the pressure reducing valve 20 in the first embodiment.

[0081] Furthermore, the hydraulic system 200 includes check valves 231, 232, and 233, which are arranged separately from each other. Check valve 231 suppresses the backflow of hydraulic fluid to the hydraulic source 11. Check valves 232 and 233 suppress the backflow of hydraulic fluid to the hydraulic source 12. Check valves 231 and 233, like check valves 31 and 32 in the first embodiment, allow hydraulic fluid to flow from the upstream side where the hydraulic sources 11 and 12 are located towards the downstream side where the leg lifting system 102 and FCS 103 are located, and block the flow of hydraulic fluid in the opposite direction, from the downstream side to the upstream side. Check valve 231 is located in the oil passage 241 leading from the hydraulic source 11 to the leg lifting system 102. Check valve 232 is located in the oil passage 242 leading from the hydraulic source 12 to the leg lifting system 102. The check valve 232 suppresses the flow of hydraulic fluid from the oil passage 241 side of the check valve 232. The check valve 233 is located upstream of the point where the oil passage 243 merges in the oil passage 244 leading from the hydraulic power source 11 to the FCS 103. The check valve 232 is an example of a "flow control valve," a "low-pressure side flow control valve," and a "high-pressure shutoff check valve" as defined in the claims.

[0082] Furthermore, the hydraulic system 200, like the hydraulic system 100 of the first embodiment, includes a pressure gauge 51, a pressure gauge 52, and a control unit 60. Similar to the first embodiment, the control unit 60 controls the operation of the hydraulic power sources 11 and 12 by hydraulic feedback control using the output pressure detection results from the pressure gauges 51 and 52. Also, similar to the first embodiment, the control unit 60 is configured to determine abnormalities in the hydraulic power sources 11 and 12, and to switch the operation of the hydraulic power sources 11 and 12 if an abnormality is detected.

[0083] In the second embodiment, the hydraulic system 200 is equipped with a shut-off valve 280. The shut-off valve 280 is located in the oil passage 243. Similar to the shut-off valve 80 in the first embodiment, the shut-off valve 280 shuts off the flow of hydraulic fluid between the high-pressure side where the hydraulic power source 11 is located and the low-pressure side where the hydraulic power source 12 is located in the oil passage 243. In the second embodiment, the shut-off valve 280 is a passive shut-off valve that opens and closes in response to the hydraulic pressure from the hydraulic power source 12. When the hydraulic power source 12 is functioning normally, the shut-off valve 280 closes when the hydraulic power source 12 supplies hydraulic pressure above a predetermined value, thereby shutting off the flow of hydraulic fluid in the oil passage 243. When the hydraulic power source 12 malfunctions, the shut-off valve 280 opens when the hydraulic power source 12 does not supply hydraulic pressure above a predetermined value, thereby opening up the flow of hydraulic fluid in the oil passage 243. Specifically, the shut-off valve 280 is a pilot-operated shut-off valve whose valve body is operated by the hydraulic pressure upstream of the check valve 232 in the oil passage 242, which is supplied with hydraulic pressure from the hydraulic power source 12. In other words, the shut-off valve 280 opens and closes automatically by passive operation in response to the hydraulic pressure in the oil passage 242, without performing any active operation such as a control signal from the control unit 60. The shut-off valve 280 shuts off the flow of hydraulic fluid in the oil passage 243 when the hydraulic pressure upstream of the check valve 232 in the oil passage 242 is equal to or greater than a predetermined opening / closing hydraulic pressure set as a predetermined value. The shut-off valve 280 then opens the flow of hydraulic fluid in the oil passage 243 when the hydraulic pressure upstream of the check valve 232 in the oil passage 242 falls below a predetermined opening / closing hydraulic pressure set as a predetermined value. The predetermined opening / closing hydraulic pressure is set, for example, to a predetermined value that is sufficiently lower than the pressure at which the FCS 103 can operate. In the second embodiment, the check valve 232 switches between shutting off and opening the flow of hydraulic fluid in the oil passage 242 by opening and closing. The shut-off valve 280 switches between shutting off and opening the flow of hydraulic fluid in the oil passage 243 by opening and closing. The shut-off valve 280 is an example of the "flow control valve" and "high-pressure side flow control valve" in the claims.

[0084] (Operation of the hydraulic power source under normal conditions) In the hydraulic system 200 of the second embodiment, similar to the hydraulic system 100 of the first embodiment, when both the hydraulic power source 11 and the hydraulic power source 12 are functioning normally, hydraulic pressure from the hydraulic power source 11 is supplied to the leg lifting system 102, and hydraulic pressure from the hydraulic power source 12 is supplied to the FCS 103. When both the hydraulic power source 11 and the hydraulic power source 12 are functioning normally, the hydraulic power source 11 supplies a relatively high hydraulic pressure of 5000 psi or less to the oil passage 241, and the hydraulic power source 12 supplies a relatively low hydraulic pressure of 3000 psi or less to the oil passage 244. In the oil passage 241, the hydraulic pressure on the upstream side of the check valve 231 is greater than that on the downstream side, so a relatively high operating hydraulic pressure from the hydraulic power source 11 is supplied to the leg lifting system 102. Furthermore, in the oil passage 244, the hydraulic pressure on the upstream side of the check valve 233 is greater than that on the downstream side, so the relatively low operating hydraulic pressure from the hydraulic power source 12 is supplied to the FCS 103 via the pressure reducing valve 220.

[0085] Furthermore, when both the hydraulic power source 11 and the hydraulic power source 12 are functioning normally, a relatively high hydraulic pressure is supplied from the hydraulic power source 11 to the downstream side of the check valve 232 in the oil passage 242, while a relatively low hydraulic pressure is supplied from the hydraulic power source 12 to the upstream side. As a result, the flow of hydraulic fluid in the check valve 232 is blocked, suppressing the supply of hydraulic pressure from the hydraulic power source 11 to the FCS 103, and also suppressing the supply of hydraulic pressure from the hydraulic power source 12 to the leg lifting system 102. In addition, in the oil passage 243, as described above, since the hydraulic power source 12 is functioning normally, the flow of hydraulic fluid is blocked in the shut-off valve 280, thereby suppressing the supply of hydraulic pressure from the hydraulic power source 11 to the FCS 103. Therefore, in the hydraulic system 200, as in the hydraulic system 100 of the first embodiment, when both the hydraulic power source 11 and the hydraulic power source 12 are functioning normally, hydraulic pressure is not supplied from the hydraulic power source 11 to the FCS 103, and hydraulic pressure is not supplied from the hydraulic power source 12 to the leg lifting system 102.

[0086] (Backup operation in case of hydraulic power source malfunction) As shown in Figures 8 and 9, in the hydraulic system 200, similar to the hydraulic system 100, the high-pressure hydraulic power source 11 and the low-pressure hydraulic power source 12 are configured such that one serves as a backup hydraulic power source for the other. In the second embodiment, when the hydraulic power source 12 malfunctions, the shut-off valve 280 opens, opening the flow of hydraulic fluid in the oil passage 243, and when the hydraulic power source 11 malfunctions, the check valve 232 opens, opening the flow of hydraulic fluid in the oil passage 242.

[0087] As shown in Figure 8, in the hydraulic system 200 as well, in the event of an abnormality in the hydraulic power source 12, the control unit 60 stops the operation of the hydraulic power source 12 and reduces the hydraulic pressure from the hydraulic power source 11 using the pressure reducing valve 220 before supplying it to the FCS 103. Specifically, if an abnormality occurs in the hydraulic power source 12, hydraulic pressure will no longer be supplied to the oil passages 242 and 244 branched from the hydraulic power source 12, resulting in a loss of hydraulic pressure in the region 272a including the upstream side of the check valve 232 in the oil passage 242 and the upstream side of the check valve 233 in the oil passage 244. As a result, the shut-off valve 280 opens, and hydraulic pressure from the hydraulic power source 11 is supplied via the oil passage 243 to the downstream side of the check valve 233 in the oil passage 244. Therefore, the hydraulic pressure supplied from the hydraulic power source 11 provides a relatively high hydraulic pressure of 5000 psi or less to the region 271a, which includes the entire oil passage 241, the downstream side of the check valve 232 in the oil passage 242, the entire oil passage 243, and the portion of the oil passage 244 downstream of the check valve 233 and upstream of the pressure reducing valve 220. As a result, even in the event of a malfunction in the hydraulic power source 12, a relatively high operating hydraulic pressure of 5000 psi or less is supplied from the hydraulic power source 11 to the leg lifting system 102.

[0088] Furthermore, since a relatively high hydraulic pressure of 5000 psi or less is supplied from the hydraulic power source 11 to the upstream side of the pressure reducing valve 220, a reduced hydraulic pressure of 3000 psi or less is supplied to the region 273a of the oil passage 244 downstream of the pressure reducing valve 220. As a result, even in the hydraulic system 200, operating hydraulic pressure from the hydraulic power source 11 is supplied to the FCS 103 when the hydraulic power source 12 malfunctions. In this way, in the second embodiment as well, when the hydraulic power source 12 malfunctions, the hydraulic power source 11 supplies a relatively high operating hydraulic pressure of 5000 psi or less to the leg lifting system 102, while simultaneously supplying a relatively low operating hydraulic pressure of 3000 psi or less to the FCS 103 via the pressure reducing valve 220.

[0089] Furthermore, as shown in Figure 9, in the hydraulic system 200, in the event of an abnormality in the hydraulic source 11, the control unit 60 stops the operation of the hydraulic source 11 and increases the hydraulic pressure from the hydraulic source 12 to supply to the leg lifting system 102. Specifically, when an abnormality in the hydraulic source 11 is detected, the control unit 60 controls the hydraulic source 12 to output an operating hydraulic pressure of 5000 psi, which is a relatively high target operating hydraulic pressure. If an abnormality occurs in the hydraulic source 11, hydraulic pressure will not be supplied to the oil passages 241 and 243 branched from the hydraulic source 11, resulting in a loss of hydraulic pressure supply in the region 271b, which includes the area upstream of the check valve 231 in the oil passage 241 and the area on the side of the shut-off valve 280 in the oil passage 243. Note that since the hydraulic source 12 is functioning normally and a relatively high hydraulic pressure of 5000 psi or less is supplied from the hydraulic source 12, the shut-off valve 280 is shutting off the oil passage 243. Furthermore, because a relatively high hydraulic pressure of 5000 psi or less is supplied from the hydraulic power source 12, a relatively high hydraulic pressure of 5000 psi or less is supplied to the region 272b, which includes the area upstream of the pressure reducing valve 220 in the oil passage 244, the area on the side of the shut-off valve 280 in the oil passage 243, the entire oil passage 242, and the area downstream of the check valve 231 in the oil passage 241. As a result, even in the event of a malfunction in the hydraulic power source 11, operating hydraulic pressure from the hydraulic power source 12 is supplied to the leg lifting system 102.

[0090] Furthermore, similar to the case of a malfunction in the hydraulic power source 12, a relatively high hydraulic pressure of 5000 psi or less is supplied from the hydraulic power source 12 to the upstream side of the pressure reducing valve 220, so that a reduced hydraulic pressure of 3000 psi or less is supplied to the region 273a of the oil passage 244 downstream of the pressure reducing valve 220. As a result, even in the case of a malfunction in the hydraulic power source 11, the operating hydraulic pressure from the hydraulic power source 12 is supplied to the FCS 103. In this way, in the second embodiment as well, when a malfunction occurs in the hydraulic power source 11, the hydraulic power source 12 supplies a relatively high operating hydraulic pressure of 5000 psi or less to the leg lifting system 102 by increasing the pressure of the supplied hydraulic pressure, while simultaneously supplying a relatively low operating hydraulic pressure of 3000 psi or less to the FCS 103 via the pressure reducing valve 220. In the second embodiment, a passive shut-off valve 280 is provided in the oil passage 243 and a check valve 232 is provided in the oil passage 242. Therefore, backup operation in the event of an abnormality in the hydraulic power sources 11 and 12 is performed without the control unit 60 controlling the opening and closing of the flow in the oil passages 242 and 243. The other configurations of the second embodiment are the same as those of the first embodiment.

[0091] (Effects of the Second Embodiment) In the second embodiment, as described above, the hydraulic system 200 includes an oil passage 243 (high-pressure backup oil passage) that connects an oil passage 241 (high-pressure side oil passage) that supplies hydraulic fluid from a hydraulic source 11 (high-pressure source) to a leg lifting system 102 (high-pressure operating section) and an oil passage 244 (low-pressure side oil passage) that supplies hydraulic fluid from a hydraulic source 12 (low-pressure source) to an FCS 103 (low-pressure operating section). The hydraulic system 200 also includes an oil passage 242 (low-pressure side backup oil passage) which is arranged separately from the oil passage 243 and connects the oil passages 241 and 244. The hydraulic system 200 also includes a shut-off valve 280 (high-pressure side flow control valve) that switches between shutting off and opening the flow of hydraulic fluid in the oil passage 243 by opening and closing. Furthermore, the hydraulic system 200 is equipped with a check valve 232 (low-pressure side flow control valve) that switches between shutting off and opening the flow of hydraulic fluid in the oil passage 242 by opening and closing. In the hydraulic system 200, when the hydraulic power source 12 malfunctions, the shut-off valve 280 opens, opening the flow of hydraulic fluid in the oil passage 243, and when the hydraulic power source 11 malfunctions, the check valve 232 opens, opening the flow of hydraulic fluid in the oil passage 242. As a result, when the hydraulic power source 12 malfunctions, the shut-off valve 280 opens, opening the flow of hydraulic fluid in the oil passage 243, and appropriate operating hydraulic pressure can be supplied to the FCS 103 (low-pressure operating part) via the pressure reducing valve 220. Also, when the hydraulic power source 11 malfunctions, the check valve 232 opens, opening the flow of hydraulic fluid in the oil passage 242, so that appropriate operating hydraulic pressure can be supplied to the leg lifting system 102 via the oil passage 242 when the hydraulic pressure from the hydraulic power source 12 is increased. Furthermore, by arranging the oil passages 243 and 242 separately, the risk of simultaneous loss of both oil passages 243 and 242 can be reduced. In addition, the shut-off valve 280 and the check valve 232 can each be designed to suit the hydraulic pressure of the hydraulic fluid being supplied.

[0092] Furthermore, in the second embodiment, as described above, the oil passage 243 (high-pressure side backup oil passage) is connected to the oil passage 244 (low-pressure side oil passage) upstream of the pressure reducing valve 220 located in the oil passage 244. The hydraulic system 200 includes a passive shut-off valve 280 (low-pressure side flow control valve) that opens and closes in response to the hydraulic pressure from the hydraulic power source 12 (low-pressure source). When the hydraulic power source 12 is functioning normally, the shut-off valve 280 closes when the hydraulic power source 12 supplies hydraulic pressure above a predetermined value, thereby blocking the flow of hydraulic fluid in the oil passage 243. When the hydraulic power source 12 is malfunctioning, the shut-off valve 280 opens when the hydraulic power source 12 does not supply hydraulic pressure above a predetermined value, thereby opening the flow of hydraulic fluid in the oil passage 243. As a result, by providing a passive shut-off valve 280, the opening and closing of the shut-off valve 280 can be automatically switched depending on whether the hydraulic pressure from the hydraulic power source 12 is normal or not. Therefore, it is possible to easily switch between the normal operation and the abnormal operation of the hydraulic power source 12 without providing a configuration to control the opening and closing of the shut-off valve 280.

[0093] Furthermore, in the second embodiment, as described above, the check valve 232 (low-pressure side flow control valve, high-pressure shut-off check valve) shuts off the flow of hydraulic fluid in the oil passage 242 (low-pressure side backup oil passage) by suppressing the flow of hydraulic fluid from the oil passage 241 (high-pressure side oil passage) side of the check valve 232 when the hydraulic power source 11 (high-pressure hydraulic power source) is functioning normally. As a result, when the hydraulic power source 11 is functioning normally, the flow of hydraulic fluid in the oil passage 242 can be shut off by suppressing the flow of hydraulic fluid from the high-pressure side oil passage side of the high-pressure shut-off check valve. For example, when the hydraulic power source 11 and hydraulic power source 12 are functioning normally, it is easy to suppress the supply of hydraulic pressure from the hydraulic power source 11 to the FCS 103 (low-pressure operating part) side via the oil passage 242 (low-pressure side backup oil passage) and the supply of hydraulic pressure from the hydraulic power source 12 to the leg lifting system 102 (high-pressure operating part). Furthermore, in the event of a malfunction in the hydraulic power source 11, the pressure in the oil passage 244 (low-pressure oil passage) becomes greater than the pressure in the oil passage 241, causing the check valve 232 to open automatically, thereby easily switching the flow of hydraulic fluid in the oil passage 242. Other effects of the second embodiment are the same as those of the first embodiment.

[0094] [Third Embodiment] Next, the configuration of the hydraulic system 300 according to the third embodiment will be described with reference to Figures 10 to 13. Unlike the first embodiment, which had one pressure reducing valve 20, the third embodiment is equipped with a pressure reducing valve 321 that reduces the hydraulic pressure from the hydraulic source 11 and a pressure reducing valve 322 that reduces the hydraulic pressure from the hydraulic source 12. Components similar to those in the first embodiment are denoted by the same reference numerals and their descriptions are omitted.

[0095] (Configuration of the hydraulic system) As shown in Figure 10, the hydraulic system 300 of the third embodiment includes a hydraulic source 11, a hydraulic source 12, a pressure reducing valve 321, and a pressure reducing valve 322. The pressure reducing valve 321 is an example of the "pressure reducing valve," "high-pressure side pressure reducing valve," "flow control valve," and "high-pressure side flow control valve" in the claims. The pressure reducing valve 322 is an example of the "pressure reducing valve" and "low-pressure side pressure reducing valve" in the claims.

[0096] The hydraulic system 300 includes oil passages 341, 342, 343, and 344 through which hydraulic fluid from the hydraulic power sources 11 and 12 flows. Oil passage 341 carries hydraulic fluid from the hydraulic power source 11 to the leg lifting system 102. Oil passage 344 carries hydraulic fluid from the hydraulic power source 12 to the FCS 103. Oil passage 342 connects oil passages 341 and 344 to each other. Oil passage 343 is located separately from oil passage 342 and connects oil passages 341 and 344 to each other. Oil passage 342 is installed upstream of the pressure reducing valve 322 located in oil passage 344. Oil passage 343 is installed downstream of the pressure reducing valve 322 located in oil passage 344. In other words, the hydraulic power source 11 supplies hydraulic pressure by branching into an oil passage 341 for supplying hydraulic pressure to the leg lifting system 102 and an oil passage 343 for supplying hydraulic pressure to the FCS 103. The hydraulic power source 12 supplies hydraulic pressure by branching into an oil passage 342 for supplying hydraulic pressure to the leg lifting system 102 and an oil passage 344 for supplying hydraulic pressure to the FCS 103. In other words, the hydraulic fluid output from the hydraulic power source 11 is branched and flows into an oil passage 341 toward the leg lifting system 102 and an oil passage 343 toward the FCS 103. The hydraulic fluid output from the hydraulic power source 12 is branched and flows into an oil passage 342 toward the leg lifting system 102 and an oil passage 344 toward the FCS 103. The oil passage 342 from the hydraulic power source 12 merges with the oil passage 341 from the hydraulic power source 11. Also, the oil passage 343 from the hydraulic power source 11 merges with the oil passage 344 from the hydraulic power source 12. Oil passages 341 and 344 are examples of the "high-pressure oil passage" and "low-pressure oil passage" as defined in the claims, respectively. Oil passage 342 is an example of the "backup oil passage" and "low-pressure backup oil passage" as defined in the claims. Oil passage 343 is an example of the "backup oil passage" and "high-pressure backup oil passage" as defined in the claims.

[0097] Pressure reducing valves 321 and 322 reduce the hydraulic pressure supplied to the FCS 103, similar to the pressure reducing valve 20 in the first embodiment. Pressure reducing valves 321 and 322 are located separately from each other. Pressure reducing valve 321 reduces the hydraulic pressure supplied from the hydraulic source 11 to the FCS 103. Pressure reducing valve 322 reduces the hydraulic pressure supplied from the hydraulic source 12 to the FCS 103. In the hydraulic system 300, pressure reducing valve 321 is located in the oil passage 343 leading from the hydraulic source 11 to the FCS 103. Pressure reducing valve 322 is located in the oil passage 344 leading from the hydraulic source 12 to the FCS 103. Pressure reducing valve 322 reduces the hydraulic pressure supplied from the hydraulic source 12 to 3000 psi or less, which is a relatively low operating hydraulic pressure for operating the FCS 103. In the third embodiment, pressure reducing valve 321 reduces the hydraulic pressure supplied to a pressure lower than the pressure reduced by pressure reducing valve 322. Specifically, the pressure reducing valve 321 reduces the hydraulic pressure supplied from the hydraulic power source 11 to 2500 psi or less, which is a relatively low operating hydraulic pressure required to operate the FCS 103. Note that the pressure reducing valves 321 and 322 have common configurations except that they have different predetermined pressure settings.

[0098] Furthermore, as shown in Figure 10, the hydraulic system 300 includes check valves 331, 332, 333, and 334, which are arranged separately from each other. Check valve 331 is located in the oil passage 341 leading from the hydraulic power source 11 to the leg lifting system 102. Check valve 332 is located in the oil passage 342 leading from the hydraulic power source 12 to the leg lifting system 102. Check valve 333 is located downstream of the pressure reducing valve 321 in the oil passage 343 leading from the hydraulic power source 11 to the FCS 103. Check valve 334 is located downstream of the pressure reducing valve 322 in the oil passage 344 leading from the hydraulic power source 12 to the FCS 103. Check valves 331 and 332 are located upstream of the point where oil passages 341 and 342 merge. Pressure reducing valves 321 and 322, and check valves 333 and 334 are positioned upstream of the point where oil passages 343 and 344 merge. Note that check valve 332 is an example of a "flow control valve," a "low-pressure flow control valve," and a "high-pressure shutoff check valve" within the scope of the claims.

[0099] Check valves 331 and 333 suppress the backflow of hydraulic fluid to the hydraulic source 11. Check valves 332 and 334 suppress the backflow of hydraulic fluid to the hydraulic source 12. Check valves 331, 332, 333, and 334 allow hydraulic fluid to flow from the upstream side where the hydraulic sources 11 and 12 are located towards the downstream side where the leg lifting system 102 and FCS 103 are located, and block the flow of hydraulic fluid in the opposite direction, from the downstream side to the upstream side. Specifically, check valves 331, 332, 333, and 334 allow hydraulic fluid to flow from upstream to downstream when the hydraulic pressure on the upstream side is higher than the hydraulic pressure on the downstream side, and block the flow of hydraulic fluid that would otherwise flow from downstream to upstream when the hydraulic pressure on the downstream side is higher than the hydraulic pressure on the upstream side. Specifically, check valves 331 and 332 block the flow of hydraulic fluid attempting to move from the leg lifting system 102 side to the hydraulic power source 11 side and the hydraulic power source 12 side, respectively. Check valves 333 and 334 block the flow of hydraulic fluid attempting to move from the FCS 103 side to the hydraulic power source 11 side and the hydraulic power source 12 side, respectively.

[0100] (Operation of hydraulic power sources under normal conditions) As shown in Figure 11, when both hydraulic power sources 11 and 12 are functioning normally, control is performed under normal operating conditions. Under normal operating conditions, hydraulic pressure from hydraulic power source 11 is supplied to the leg lifting system 102, and hydraulic pressure from hydraulic power source 12 is supplied to the FCS 103. In the third embodiment, when hydraulic power source 12 is functioning normally, hydraulic power source 11 preferentially supplies hydraulic pressure to the leg lifting system 102 and does not supply hydraulic pressure to the FCS 103 unless the hydraulic pressure consumption in the FCS 103 increases and the supplied operating hydraulic pressure drops so much that the check valve 333 or pressure reducing valve 321 opens. When hydraulic power source 11 is functioning normally, hydraulic power source 12 preferentially supplies hydraulic pressure to the FCS 103 and does not supply hydraulic pressure to the leg lifting system 102 unless the hydraulic pressure consumption in the leg lifting system 102 increases and the supplied operating hydraulic pressure drops so much that the check valve 332 opens.

[0101] When the hydraulic system 300 supplies operating hydraulic pressure to both the leg lifting system 102 and the FCS 103, the control unit 60 controls the hydraulic source 11 to output a relatively high operating hydraulic pressure target of 5000 psi, and controls the hydraulic source 12 to output a relatively low operating hydraulic pressure target of 3000 psi. As a result, the hydraulic pressure supplied from the hydraulic source 11 supplies a relatively high hydraulic pressure of 5000 psi or less to the region 371, which includes the entire oil passage 341, the area downstream of the check valve 332 in the oil passage 342, and the area upstream of the pressure reducing valve 321 in the oil passage 343. In addition, the hydraulic pressure supplied from the hydraulic source 12 supplies a relatively low hydraulic pressure of 3000 psi or less to the region 372, which includes the area upstream of the check valve 332 in the oil passage 342 and the area upstream of the pressure reducing valve 322 in the oil passage 344. When the hydraulic power sources 11 and 12 are functioning normally, the hydraulic pressure in the oil passage 342 is relatively low (3000 psi or less) upstream of the check valve 332, and relatively high (5000 psi or less) downstream of the check valve 332. As a result, the check valve 332 blocks the flow of hydraulic fluid in the oil passage 342, suppressing the supply of relatively high hydraulic pressure (5000 psi or less) from the hydraulic power source 11 to the FCS 103, and also suppressing the supply of hydraulic pressure from the hydraulic power source 12 to the leg lifting system 102.

[0102] Furthermore, the oil pressure downstream of the pressure reducing valve 322 in the oil passage 344 is relatively low, at 3000 psi or less. Note that under normal conditions of the oil pressure source 12, a relatively low oil pressure of 3000 psi or less is supplied upstream of the pressure reducing valve 322, so the pressure reducing valve 322 does not actively reduce pressure. As a result, a relatively low oil pressure of 3000 psi or less, equivalent to the oil pressure in region 372, is supplied to region 373, which includes the area downstream of the pressure reducing valve 322 in the oil passage 344 and the area downstream of the check valve 333 in the oil passage 343. Then, because a relatively high oil pressure of 5000 psi or less is supplied from the oil pressure source 11 upstream of the pressure reducing valve 321, a reduced oil pressure of 2500 psi or less is supplied to the area downstream of the pressure reducing valve 321 in the oil passage 343. As a result, in the oil passage 343, a relatively low hydraulic pressure of 2500 psi or less is supplied to the region 374 downstream of the pressure reducing valve 321 and upstream of the check valve 333. Therefore, when the hydraulic power sources 11 and 12 are functioning normally, the hydraulic pressure in the oil passage 343 becomes relatively low, below 3000 psi downstream of the check valve 333, and even lower, below 2500 psi upstream. Consequently, the check valve 333 blocks the flow of hydraulic fluid downstream of the pressure reducing valve 321 in the oil passage 343. This also blocks the flow of hydraulic fluid in the oil passage 343. Therefore, when the hydraulic power sources 11 and 12 are outputting operating hydraulic pressure normally, the hydraulic pressure supplied from the hydraulic power source 11 is not supplied to the FCS 103 side via the oil passages 342 and 343, but is supplied to the leg lifting system 102 via the oil passage 341. Similarly, when the hydraulic power sources 11 and 12 are outputting operating hydraulic pressure normally, the hydraulic pressure supplied from the hydraulic power source 12 is not supplied to the leg lifting system 102 side via the oil passages 342 and 343, but is supplied to the FCS 103 via the oil passage 344.

[0103] (Backup operation in case of hydraulic power source malfunction) As shown in Figures 12 and 13, in the hydraulic system 300, similar to the hydraulic system 100 of the first embodiment, the high-pressure side hydraulic power source 11 and the low-pressure side hydraulic power source 12 are configured such that one serves as a backup hydraulic power source for the other. In the third embodiment, the opening and closing of the check valve 332 is switched depending on whether the hydraulic power source 11 is malfunctioning, thereby switching between shutting off and opening the flow of hydraulic fluid in the oil passage 342. Then, the opening and closing of the pressure reducing valve 321 is switched depending on whether the hydraulic power source 12 is malfunctioning, thereby switching between shutting off and opening the flow of hydraulic fluid in the oil passage 343. That is, in the third embodiment, the pressure reducing valve 321 functions as a high-pressure side flow control valve that shuts off the flow of hydraulic fluid in the oil passage 343 when the hydraulic power source 12 is normal and opens the flow of hydraulic fluid in the oil passage 343 when the hydraulic power source 12 is malfunctioning, and also functions as a high-pressure side pressure reducing valve that reduces the hydraulic pressure supplied from the hydraulic power source 11 to the FCS 103 in the oil passage 343.

[0104] As shown in Figure 12, in the third embodiment, when the low-pressure hydraulic source 12 malfunctions, hydraulic pressure from the high-pressure hydraulic source 11 is reduced by the pressure reducing valve 321 and supplied to the FCS 103. The control unit 60 stops the operation of the hydraulic source 12 when it malfunctions. Specifically, when a malfunction occurs in the hydraulic source 12, hydraulic pressure is no longer supplied to the oil passages 342 and 344 branched from the hydraulic source 12. Therefore, the supply of hydraulic pressure is lost in the region 372a including the upstream side of the check valve 332 in the oil passage 342 and the upstream side of the check valve 334 in the oil passage 344. On the other hand, the control unit 60 continues to supply hydraulic pressure from the hydraulic source 11. Therefore, as in normal operation, the hydraulic pressure supplied from the hydraulic power source 11 provides a relatively high hydraulic pressure of 5000 psi or less to the entire oil passage 341, the area downstream of the check valve 332 in the oil passage 342, and the area upstream of the pressure reducing valve 321 in the oil passage 343, as well as to normal operation. As a result, even in the event of a malfunction in the hydraulic power source 12, a relatively high operating hydraulic pressure of 5000 psi or less is supplied from the hydraulic power source 11 to the leg lifting system 102.

[0105] Furthermore, as in normal operation, the pressure reducing valve 321 reduces the pressure in the oil passage 343 downstream of the pressure reducing valve 321 to 2500 psi or less. When the hydraulic power source 12 malfunctions, the supply of hydraulic pressure from the hydraulic power source 12 is lost, and therefore the supply of hydraulic pressure downstream of the check valve 333 is lost. Consequently, at the check valve 333, the hydraulic pressure upstream of 2500 psi or less becomes greater than that downstream, so the flow of hydraulic fluid from upstream to downstream is opened at the check valve 333. As a result, hydraulic pressure from the hydraulic power source 11 is supplied to the FCS 103 via the pressure reducing valve 321 and the check valve 333. In oil passage 344, the hydraulic pressure upstream of the check valve 334 is lost. Therefore, the hydraulic pressure supplied from the hydraulic power source 11 tries to flow upstream of the check valve 334. However, the check valve 334 blocks the flow of hydraulic fluid trying to flow from downstream to upstream. Therefore, in the event of a malfunction in the hydraulic power source 12, a hydraulic pressure of 2500 psi or less is supplied to the region 374a, which includes the area downstream of the pressure reducing valve 321 in the oil passage 343 and the area downstream of the check valve 334 in the oil passage 344, by the hydraulic pressure from the hydraulic power source 11. In this way, in the third embodiment, when a malfunction occurs in the hydraulic power source 12, the hydraulic power source 11 supplies a relatively high operating hydraulic pressure of 5000 psi or less to the leg lifting system 102, while simultaneously supplying a relatively low operating hydraulic pressure of 2500 psi or less to the FCS 103 via the pressure reducing valve 321.

[0106] Furthermore, as shown in Figure 13, in the third embodiment, similar to the first embodiment, when there is an abnormality in the high-pressure hydraulic source 11, the hydraulic pressure from the hydraulic source 12 is increased and supplied to the leg lifting system 102. The control unit 60 controls the operation of the hydraulic source 11 to stop when there is an abnormality in the hydraulic source 11, and to increase the hydraulic pressure from the hydraulic source 12 and supply it to the leg lifting system 102. If an abnormality occurs in the hydraulic source 11, hydraulic pressure will not be supplied to the oil passages 341 and 343 branched from the hydraulic source 11, so the supply of hydraulic pressure will be lost in the region 371a including the area upstream of the check valve 331 in the oil passage 341 and the area upstream of the check valve 333 in the oil passage 343. On the other hand, because a relatively high hydraulic pressure of 5000 psi or less is supplied from the hydraulic power source 12, a relatively high hydraulic pressure of 5000 psi or less is supplied to the region 372b, which includes the area upstream of the pressure reducing valve 322 in the oil passage 344, the entire oil passage 342, and the area downstream of the check valve 331 in the oil passage 341. As a result, even in the event of a malfunction in the hydraulic power source 11, operating hydraulic pressure from the hydraulic power source 12 is supplied to the leg lifting system 102.

[0107] Furthermore, the pressure reducing valve 322 reduces the oil pressure in the oil passage 344 downstream of the pressure reducing valve 322 from a relatively high oil pressure of 5000 psi or less to 3000 psi or less. As a result, oil pressure from the oil pressure source 12 is supplied to the FCS 103 via the pressure reducing valve 322. In addition, in the oil passage 343, the supply of oil pressure from the oil pressure source 11 is lost upstream of the check valve 333. Therefore, the oil pressure supplied from the oil pressure source 12 tries to flow upstream of the check valve 333. However, the check valve 333 blocks the flow of hydraulic fluid that tries to flow from downstream to upstream. Consequently, a relatively low oil pressure of 3000 psi or less, similar to that under normal conditions, is supplied to the region 373, which includes the area downstream of the check valve 333 in the oil passage 343 and the area downstream of the pressure reducing valve 322 in the oil passage 344. In this way, in the third embodiment as in the first embodiment, when the hydraulic power source 11 malfunctions, the hydraulic power source 12 increases the hydraulic pressure it supplies to supply, thereby supplying a relatively high operating hydraulic pressure of 5000 psi or less to the leg lifting system 102, while simultaneously supplying a relatively low operating hydraulic pressure of 3000 psi or less to the FCS 103 via the pressure reducing valve 322.

[0108] In the third embodiment, the hydraulic system 300 is configured to be reduced to 2500 psi or less by the pressure reducing valve 321 and to 3000 psi or less by the pressure reducing valve 322, as described above. Here, when the hydraulic power sources 11 and 12 are operating normally, if the hydraulic power consumption on the FCS 103 side temporarily increases, it is thought that the hydraulic power downstream of the check valve 333 in the oil passage 343 may fall below 2500 psi. In that case, hydraulic power from the hydraulic power source 11 is temporarily supplied to the FCS 103 via the pressure reducing valve 321, thereby assisting the hydraulic power supply from the hydraulic power source 12. This allows the output capacity of the hydraulic power source 12 to be reduced to account for the assistance of the hydraulic power source 11, thus enabling miniaturization of the hydraulic power source 12. Alternatively, by increasing the output capacity of the hydraulic power source 11 to account for the assistance of the hydraulic power source 12, the operating speed of the leg lifting system 102 may be improved when no assistance operation is being performed. In the third embodiment, the check valve 333 is used to shut off the oil passage 343 when the hydraulic power source 11 is functioning normally and to prevent backflow when the hydraulic power source 11 is malfunctioning. However, since the functions of shutting off the oil passage 343 when the hydraulic power source 11 is functioning normally and preventing backflow when the hydraulic power source 11 is malfunctioning can be achieved by a pressure reducing valve 321 instead of the check valve 333, the check valve 333 may not be placed in the oil passage 343. The other configurations of the third embodiment are the same as those of the first embodiment described above.

[0109] (Effects of the Third Embodiment) In the third embodiment, as described above, the hydraulic system 300 includes a pressure reducing valve 322 (low-pressure side pressure reducing valve) located in the oil passage 344 (low-pressure side oil passage) and a pressure reducing valve 321 (high-pressure side pressure reducing valve) located in the oil passage 343 (high-pressure side backup oil passage). The pressure reducing valve 321 reduces the hydraulic pressure supplied from the hydraulic power source 11 (high-pressure source) to the FCS 103 (low-pressure operating unit). The pressure reducing valve 322 reduces the hydraulic pressure supplied from the hydraulic power source 12 (low-pressure source) to the FCS 103. The oil passage 343 is connected to the oil passage 344 downstream of the pressure reducing valve 322. As a result, the hydraulic pressure supplied from the hydraulic power source 11 to the FCS 103 via the oil passage 343 can be reduced by the pressure reducing valve 321, and the hydraulic pressure supplied from the hydraulic power source 12 to the FCS 103 via the oil passage 344 can be reduced by the pressure reducing valve 322. Furthermore, since pressure reducing valves can be placed in oil passages 344 and 343, the pressure reducing valves can be made redundant. In addition, for example, if the pressure reducing valve 322 fails and hydraulic pressure cannot be supplied from the hydraulic power source 12 to the FCS 103, hydraulic pressure can be supplied from the hydraulic power source 11 to the FCS 103 via oil passage 343.

[0110] Furthermore, in the third embodiment, as described above, the pressure reducing valve 321 (high-pressure side flow control valve, high-pressure side pressure reducing valve) reduces the hydraulic pressure supplied to a pressure lower than the pressure reduced by the pressure reducing valve 322 (low-pressure side pressure reducing valve). As a result, the pressure reducing valve 321 reduces the hydraulic pressure supplied to a pressure lower than the pressure reduced by the pressure reducing valve 322, so that when the hydraulic power source 12 (low-pressure source) is functioning normally, the hydraulic pressure output from the pressure reducing valve 322 in the oil passage 344 (low-pressure side oil passage) can be made greater than the hydraulic pressure output from the pressure reducing valve 321 in the oil passage 343 (high-pressure side backup oil passage). Therefore, when the hydraulic power source 12 is functioning normally, the hydraulic pressure supplied to the FCS 103 (low-pressure operating unit) can be preferentially supplied from the hydraulic power source 12 via the pressure reducing valve 322. As a result, when the hydraulic power source 12 is functioning normally, the waste of energy in the hydraulic power source 11 (high-pressure source) can be suppressed. Furthermore, since the pressure reducing valve 321 functions as a high-pressure side flow control valve, the complexity of the device configuration can be suppressed compared to the case where a high-pressure side flow control valve is arranged separately from the pressure reducing valve 321. Other effects of the third embodiment are the same as those of the first embodiment.

[0111] [Fourth Embodiment] Next, the configuration of the hydraulic system 400 according to the fourth embodiment will be described with reference to Figure 14. In the fourth embodiment, hydraulic pressure is bypassed to the oil passage 444 that bypasses the pressure reducing valve 20. Components similar to those in the first embodiment are denoted by the same reference numerals and their descriptions are omitted.

[0112] As shown in Figure 14, in the fourth embodiment, the hydraulic system 400 includes a shut-off valve 481. The shut-off valve 481 switches between supplying hydraulic pressure to the FCS 103 via the pressure reducing valve 20 and supplying hydraulic pressure to the FCS 103 via an oil passage 444 that bypasses the pressure reducing valve 20. The shut-off valve 481 switches to supplying hydraulic pressure to the FCS 103 via the oil passage 444 when the pressure upstream of the pressure reducing valve 20 is below a predetermined pressure. The shut-off valve 481 allows hydraulic fluid to flow when the upstream hydraulic pressure is below a predetermined bypass threshold, and shuts off the flow of hydraulic fluid when the upstream hydraulic pressure is above the predetermined bypass threshold. The predetermined bypass threshold is set, for example, to 3000 psi or less, which is the upper limit of the relatively low operating hydraulic pressure required to operate the FCS 103. The shut-off valve 481 may also be configured to allow hydraulic fluid to flow when the pressure is above the bypass threshold, including the case of the bypass threshold. The shut-off valve 481 is located in the oil passage 444. The oil passage 444 connects the lower-pressure side of the shut-off valve 80 of the oil passage 42 to the downstream side of the pressure reducing valve 20 of the oil passage 43. In other words, the oil passage 444 bypasses the pressure reducing valve 20 by connecting the upstream and downstream sides of the pressure reducing valve 20 to each other. The oil passage 444 may also connect the space between the check valve 32 and the pressure reducing valve 20 of the oil passage 43 to the downstream side of the pressure reducing valve 20 of the oil passage 43 to each other. The shut-off valve 481 is an example of a "bypass valve" in the claims. The oil passage 444 is also an example of a "bypass oil passage" in the claims.

[0113] In the hydraulic system 400, when the hydraulic power source 12 is functioning normally, the control unit 60 shuts off the oil passage 42 with the shut-off valve 80, similar to the first embodiment. As a result, a relatively low hydraulic pressure of 3000 psi or less is supplied from the hydraulic power source 12 to the upstream side of the pressure reducing valve 20 in the oil passage 43 and to the low-pressure side of the shut-off valve 80 in the oil passage 42. Therefore, when the hydraulic power source 12 is functioning normally, a relatively low hydraulic pressure of 3000 psi or less is supplied from the hydraulic power source 12 to the upstream side of the shut-off valve 481 in the oil passage 444. When the FCS 103 operates and hydraulic pressure is consumed, the hydraulic pressure on the upstream side of the shut-off valve 481 in the oil passage 444 drops further, causing the shut-off valve 481 to open the flow of hydraulic fluid. Consequently, when the hydraulic power source 12 is functioning normally, the hydraulic fluid from the hydraulic power source 12 bypasses the pressure reducing valve 20 and is supplied to the FCS 103 through the oil passage 444.

[0114] On the other hand, if the hydraulic power source 12 is abnormal, the control unit 60 opens the shut-off valve 80, similar to the first embodiment, thereby opening the flow of hydraulic fluid in the oil passage 42. As a result, a relatively high hydraulic pressure of 5000 psi or less from the hydraulic power source 11 is supplied to the entire oil passage 42, and a relatively high hydraulic pressure of 5000 psi or less is supplied to the upstream side of the shut-off valve 481 of the oil passage 444 connected to the oil passage 42. In this case, the shut-off valve 481 blocks the flow of hydraulic fluid because the hydraulic pressure on the upstream side becomes greater than a predetermined bypass threshold. Therefore, if the hydraulic power source 12 is abnormal, the hydraulic fluid from the hydraulic power source 11 does not pass through the oil passage 444, but is depressurized by the pressure reducing valve 20 in the oil passage 43 and supplied to the FCS 103.

[0115] Therefore, in the fourth embodiment, when the upstream hydraulic pressure is a relatively low operating hydraulic pressure required to operate the FCS 103, the shut-off valve 481 opens the flow of hydraulic fluid, thereby supplying hydraulic pressure to the FCS 103 via the oil passage 444 that bypasses the pressure reducing valve 20. On the other hand, when the upstream hydraulic pressure is a relatively high operating hydraulic pressure required to operate the leg lifting system 102, the shut-off valve 481 blocks the flow of hydraulic fluid, thereby supplying hydraulic pressure to the FCS 103 via the pressure reducing valve 20. In the event of an abnormality in the hydraulic power source 12, if the hydraulic power source 11 is outputting a relatively low operating hydraulic pressure of 3000 psi or less, the shut-off valve 481 is opened in the same way as when the hydraulic power source 12 is functioning normally, so that hydraulic pressure is supplied to the FCS 103 via the oil passage 444 that bypasses the pressure reducing valve 20. Furthermore, in the fourth embodiment, the shut-off valve 481 may be a solenoid valve that opens and closes under the control of the control unit 60, similar to the shut-off valve 80. The other configurations of the fourth embodiment are the same as those of the first embodiment described above.

[0116] (Effects of the Fourth Embodiment) In the fourth embodiment, as described above, the hydraulic system 400 is equipped with a shut-off valve 481 (bypass valve) that switches between supplying hydraulic pressure to the FCS 103 (low-pressure operating section) via the pressure reducing valve 20 and supplying hydraulic pressure to the FCS 103 via an oil passage 444 (bypass oil passage) that bypasses the pressure reducing valve 20. The shut-off valve 481 switches to supplying hydraulic pressure to the FCS 103 via the oil passage 444 when the pressure upstream of the pressure reducing valve 20 is below a predetermined pressure. This prevents the pressure reducing valve 20 from becoming a resistive element when, for example, a relatively low operating hydraulic pressure is supplied to the FCS 103 from a hydraulic power source 12 (low hydraulic power source). For example, when a relatively low operating hydraulic pressure is supplied to the upstream side of the pressure reducing valve 20, such as when the hydraulic power source 12 (low hydraulic power source) is functioning normally, the shut-off valve 481 can be switched to supply hydraulic pressure to the FCS 103 via the oil passage 444, thereby supplying hydraulic pressure to the FCS 103 without going through the pressure reducing valve 20. As a result, the pressure reducing valve 20 can be prevented from acting as a resistance to the flow of hydraulic fluid, and the wasted hydraulic pressure supplied in the pressure reducing valve 20 can be prevented. As a result, a decrease in energy efficiency can be prevented. The other effects of the fourth embodiment are the same as those of the first embodiment.

[0117] (Modifications) It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims rather than the description of the embodiments above, and further includes all modifications (modifications) within the meaning and scope equivalent to the claims.

[0118] (First Modification) For example, in the first embodiment described above, an example was shown in which a shut-off valve 80 (flow control valve), which is a direct-acting electromagnetic shut-off valve, is placed in the oil passage 42 (backup oil passage), but the present invention is not limited thereto. In the present invention, as in the hydraulic system 500 according to the first modification shown in Figure 15, a shut-off valve 581, which is a pilot-operated electromagnetic shut-off valve, may be provided as a flow control valve. In the hydraulic system 500 according to the first modification, instead of the shut-off valve 80 of the hydraulic system 100 in the first embodiment, a shut-off valve 581 is placed in the oil passage 42, which is a backup oil passage. In the hydraulic system 500, a shuttle valve 582 is provided that selectively supplies the higher of the hydraulic pressure supplied from the hydraulic power source 11 (high hydraulic power source) and the hydraulic power source 12 (low hydraulic power source) to the shut-off valve 581. The shut-off valve 581 includes an electromagnetic valve 581a that switches between supplying and shutting off the hydraulic pressure supplied from the shuttle valve 582 under the control of the control unit 60, and a shut-off valve 581b that performs opening and closing operations using the hydraulic pressure supplied from the shuttle valve 582 as a drive source. In other words, the shut-off valve 581 is configured to switch between shutting off and opening the flow of hydraulic fluid in the oil passage 42 under the control of the control unit 60, and operates using hydraulic pressure supplied from either the hydraulic power source 11 or the hydraulic power source 12 as the driving source for the switching operation. As a result, in the hydraulic system 500 of the first modified example, since hydraulic pressure from the hydraulic power source 11 and the hydraulic power source 12 is used as the driving source for the switching operation, the solenoid valve in the shut-off valve 581 can be made smaller compared to the case in which a direct-acting solenoid shut-off valve is used.

[0119] (Second Modification) In addition, the first to fourth embodiments described above show an example in which hydraulic pressure is supplied to two operating parts, the leg lifting system 102 (high-pressure operating part) and the FCS 103 (low-pressure operating part), which operate with different operating hydraulic pressures, but the present invention is not limited thereto. In the present invention, as shown in the second modification hydraulic system 600 in Figure 16, hydraulic pressure may be supplied to three different operating parts, the high-pressure operating part 602, the first low-pressure operating part 603a, and the second low-pressure operating part 603b. The second modification hydraulic system 600 shown in Figure 16 comprises a hydraulic source 611 which is a high-pressure hydraulic source, and hydraulic sources 612a and 612b which are low-pressure hydraulic sources. The hydraulic source 611 supplies hydraulic pressure to the high-pressure operating part 602. The hydraulic source 612a supplies hydraulic pressure to the first low-pressure operating part 603a. The hydraulic source 612b supplies hydraulic pressure to the second low-pressure operating part 603b. Furthermore, the hydraulic system 600 according to the second modification includes pressure reducing valves 621a (high-pressure side pressure reducing valve, flow control valve, high-pressure side flow control valve) and 622a (low-pressure side pressure reducing valve) for reducing the hydraulic pressure supplied to the first low-pressure operating unit 603a, and pressure reducing valves 621b (high-pressure side pressure reducing valve, flow control valve, high-pressure side flow control valve) and 622b (low-pressure side pressure reducing valve) for reducing the hydraulic pressure supplied to the second low-pressure operating unit 603b. The hydraulic system 600 according to the second modification also includes check valves 631, 632 (high-pressure shut-off check valve, flow control valve, low-pressure side flow control valve), 633 (high-pressure shut-off check valve, flow control valve, low-pressure side flow control valve), 634, 635, 636, 637, 638, and 639.

[0120] As shown in Figure 16, in the hydraulic system 600 according to the second modification, for example, a relatively high operating hydraulic pressure of 5000 psi or less is output from the hydraulic source 611, and a relatively low operating hydraulic pressure of 3000 psi or less is output from the hydraulic sources 612a and 612b. Pressure reducing valves 621a and 621b reduce the supplied hydraulic pressure to 2500 psi or less, similar to the pressure reducing valve 321 in the third embodiment. Pressure reducing valves 622a and 622b reduce the supplied hydraulic pressure to 3000 psi or less, similar to the pressure reducing valve 322 in the third embodiment. Each of the check valves 631, 632, 633, 634, 635, 636, 637, 638, and 639 suppresses the flow of hydraulic fluid from the downstream side where the high-pressure operating section 602, the first low-pressure operating section 603a, and the second low-pressure operating section 603b are located, to the upstream side where the hydraulic power sources 611, 612a, and 612b are located.

[0121] In the hydraulic system 600 according to the second modified example, when all of the hydraulic power sources 611, 612a, and 612b are functioning normally, the flow of hydraulic fluid is blocked in the check valves 632, 633, 635, and 638. Furthermore, as in the third embodiment, the hydraulic pressure output by the pressure reducing valves 621a and 621b is less than that of the pressure reducing valves 622a and 622b, so the flow of hydraulic fluid in the pressure reducing valves 621a and 621b is also blocked. Therefore, when all three hydraulic sources 611, 612a, and 612b are functioning normally, they preferentially supply hydraulic pressure to the high-pressure operating section 602, the first low-pressure operating section 603a, and the second low-pressure operating section 603b, respectively. They do not supply hydraulic pressure to other operating sections unless the hydraulic pressure consumption in other operating sections increases to such an extent that the supplied operating hydraulic pressure drops so drastically that a check valve or pressure reducing valve opens.

[0122] In the second modified hydraulic system 600, the three hydraulic sources 611, 612a, and 612b are configured to back each other up. For example, in the event of a malfunction in hydraulic source 611, at least one of hydraulic sources 612a and 612b switches to outputting a relatively high hydraulic pressure of 5000 psi or less. In this case, the check valve 631 is shut off, and at least one of check valves 632 and 633 allows hydraulic fluid to flow from upstream to downstream, thereby supplying operating hydraulic pressure to the high-pressure operating unit 602. Alternatively, both hydraulic sources 612a and 612b may be controlled to output a relatively high operating hydraulic pressure, or the lower-priority hydraulic source of 612a and 612b may be used to output a relatively high operating hydraulic pressure, so as not to increase the load on the higher-priority source. Furthermore, in the event of a malfunction in the hydraulic power source 612a, hydraulic pressure from the hydraulic power source 611 is supplied to the first low-pressure operating unit 603a via the check valve 634 and the pressure reducing valve 621a. In the event of a malfunction in the hydraulic power source 612b, hydraulic pressure from the hydraulic power source 611 is supplied to the second low-pressure operating unit 603b via the check valve 637 and the pressure reducing valve 621b. In either case, the check valve 635 or the check valve 638 prevents the hydraulic fluid from flowing back into the normal hydraulic power source 612a or hydraulic power source 612b.

[0123] Furthermore, if two of the hydraulic power sources 611, 612a, and 612b are determined to be abnormal, hydraulic pressure will be supplied to the high-pressure operating unit 602, the first low-pressure operating unit 603a, and the second low-pressure operating unit 603b from the remaining hydraulic power source 611, 612a, and 612b that are not determined to be abnormal. In that case as well, check valves 631, 632, 633, 634, 635, 636, 637, 638, and 639 appropriately suppress the backflow of hydraulic fluid to the hydraulic source among the hydraulic sources 611, 612a, and 612b that is determined to be abnormal, while pressure reducing valves 621a, 621b, 622a, and 622b are used to supply appropriate operating hydraulic pressure to each of the high-pressure operating section 602, the first low-pressure operating section 603a, and the second low-pressure operating section 603b.

[0124] Furthermore, while Figure 16 shows an example in which a relatively low operating hydraulic pressure of 3000 psi or less is output from both the hydraulic source 612a and the hydraulic source 612b in the hydraulic system 600 according to the second modified example, the present invention is not limited to this. In the present invention, hydraulic pressure may be supplied to two or more types of low-pressure operating parts that operate with different operating hydraulic pressures by having multiple low-pressure hydraulic sources output different operating hydraulic pressures from each other. That is, in the present invention, hydraulic pressure may be supplied to three or more types of operating parts that operate with different operating hydraulic pressures. For example, in the hydraulic system 600 according to the second modified example shown in Figure 16, when the first low-pressure operating part 603a operates by being supplied with a relatively low operating hydraulic pressure of 2000 psi or more and 3000 psi or less, and the second low-pressure operating part 603b operates by being supplied with an even relatively lower operating hydraulic pressure of 500 psi or more and 1000 psi or less, the hydraulic source 612a and the hydraulic source 612b output operating hydraulic pressures of 3000 psi or less and 1000 psi or less, respectively. In this case, pressure reducing valves 621a and 622a reduce the supplied hydraulic pressure to 2500 psi or less and 3000 psi or less, respectively, in accordance with the operating hydraulic pressure of the first low-pressure operating unit 603a, similar to the second modified example in Figure 16. Then, pressure reducing valves 621b and 622b reduce the supplied hydraulic pressure to 800 psi or less and 1000 psi or less, respectively, in accordance with the operating hydraulic pressure of the second low-pressure operating unit 603b. With this configuration, an appropriate operating hydraulic pressure is supplied to each of the three or more operating units that operate with different operating hydraulic pressures, and even when three or more types of hydraulic pressures are output from high-pressure and low-pressure sources, the hydraulic sources are configured to back up each other. Note that even when supplying hydraulic pressure to three operating units, a shut-off valve may be arranged as in the first or second embodiment, or a bypass valve may be arranged as in the fourth embodiment.

[0125] (Third Modification) In addition, as shown in the hydraulic system 700 according to the third modification shown in Figure 17, the check valves 632, 633, 634, and 637 in the hydraulic system 600 according to the second modification shown in Figure 16 may be replaced with electromagnetic shut-off valves 732 (flow control valve, low-pressure side flow control valve), shut-off valve 733 (flow control valve, low-pressure side flow control valve), shut-off valve 734, and shut-off valve 737, respectively, whose opening and closing can be controlled. Shut-off valves 732 and 733 are examples of "low-pressure side flow control valves" in the claims. The control unit 60 controls the opening and closing of shut-off valves 732, 733, 734, and 737. By replacing check valves 632 and 633 with shut-off valves 732 and 733, respectively, it becomes possible to operate the low-pressure hydraulic sources 612a and 612b while stopping the operation of the high-pressure hydraulic source 611. In other words, the control unit 60 can control the shut-off and opening of the low-pressure side flow control valves, shut-off valves 732 and 733, and thus control whether or not to supply hydraulic pressure from the hydraulic source 12 (low-pressure hydraulic source) to the leg lifting system 102 (high-pressure operating unit). By closing the shut-off valves 732 and 733 while the operation of the hydraulic source 611 is stopped, the flow of hydraulic pressure from the hydraulic sources 612a and 612b to the high-pressure operating unit 602 is suppressed. Furthermore, if either the hydraulic power source 612a or the hydraulic power source 612b is determined to be abnormal while the hydraulic power source 611 is stopped, the other can supply operating hydraulic pressure to both the first low-pressure operating unit 603a and the second low-pressure operating unit 603b.

[0126] Furthermore, if either hydraulic source 612a or hydraulic source 612b is determined to be abnormal while hydraulic source 611 is operating, the check valves 634 and 637 can be replaced with shut-off valves 734 and 737, respectively, so that hydraulic pressure can be supplied by the hydraulic source 612a or hydraulic source 612b that is not experiencing an abnormality, instead of hydraulic source 611. In addition, check valves 635 and 638 may be replaced with shut-off valves. In that case, if an oil leak abnormality occurs in the first low-pressure operating section 603a or the second low-pressure operating section 603b, the hydraulic source corresponding to the abnormal low-pressure operating section can be stopped, and all shut-off valves located in the oil passage that supplies backup operating hydraulic pressure to the abnormal low-pressure operating section can be closed. This prevents the operation of the hydraulic sources corresponding to low-pressure and high-pressure operating sections other than the abnormal low-pressure operating section from being stopped, allowing these operating sections to continue operating while preventing hydraulic fluid from leaking from the abnormal low-pressure operating section. Furthermore, when an electromagnetic shut-off valve is used as the low-pressure side flow control valve, it may be configured to supply hydraulic pressure to two operating parts, as in the third embodiment. Also, when the high-pressure side flow control valve is a pilot-operated shut-off valve, as in the second embodiment, the low-pressure side flow control valve may be an electromagnetic shut-off valve. In addition, both the high-pressure side flow control valve and the low-pressure side flow control valve may be electromagnetic shut-off valves.

[0127] (Fourth Modification) In the third embodiment described above, an example was shown in which a pressure reducing valve 321 (high-pressure side pressure reducing valve) that reduces the hydraulic pressure supplied from the hydraulic source 11 (high-pressure source) to the FCS 103 (low-pressure operating unit) and a pressure reducing valve 322 (low-pressure side pressure reducing valve) that reduces the hydraulic pressure supplied from the hydraulic source 12 (low-pressure source) to the FCS 103 are arranged, but the present invention is not limited thereto. In the present invention, as shown in the hydraulic system 800 according to the fourth modification shown in Figure 18, a pressure boosting pump 814 may be arranged in the oil passage 342 (low-pressure side backup oil passage) for supplying hydraulic pressure from the hydraulic source 12, which is a low-pressure source, to the leg lifting system 102 (high-pressure operating unit), without arranging a low-pressure side pressure reducing valve. In the hydraulic system 800, in the event of an abnormality in the hydraulic source 11, which is a high-pressure source, the operation of the hydraulic source 12 itself is not switched, and the hydraulic pressure from the hydraulic source 12 is increased in pressure by the pressure boosting pump 814 and supplied to the leg lifting system 102. In other words, in the present invention, a pressure boosting unit that increases the hydraulic pressure from a low hydraulic pressure source in the event of an abnormality in the high hydraulic pressure source may be arranged separately from the low hydraulic pressure source.

[0128] (Fifth Modification) In the fourth embodiment described above, an example was shown in which a shut-off valve 80 (flow control valve) is placed in the oil passage 42 (backup oil passage) and a shut-off valve 481 (bypass valve) is placed in the oil passage 444 (bypass oil passage), but the present invention is not limited thereto. In the present invention, as shown in the fifth modification hydraulic system 900 in Figure 19, a shut-off valve 980 that serves as both a flow control valve and a bypass valve may be placed in the oil passage 42, which is a backup oil passage. The shut-off valve 980 has a bypass function that opens the oil passage 944 (bypass oil passage) when shutting off the flow of hydraulic fluid and shuts off the oil passage 944 when opening the flow of hydraulic fluid. The oil passage 944 bypasses the pressure reducing valve 20 and connects the upstream and downstream sides of the pressure reducing valve 20 to each other. The shut-off valve 980 switches between a state in which the high-pressure side and low-pressure side of the oil passage 42 are connected, and a state in which the low-pressure side of the oil passage 42 is connected to the bypass oil passage 944, under the control of the control unit 60. The shut-off valve 980 is a solenoid valve that switches the flow path under the control of the control unit 60. For example, when the hydraulic power source 11 (high hydraulic power source) and hydraulic power source 12 (low hydraulic power source) are functioning normally, the control unit 60 uses the shut-off valve 980 to shut off the flow between the low-pressure side and high-pressure side of the oil passage 42, and connects the low-pressure side of the oil passage 42 to the oil passage 944, which bypasses the pressure reducing valve 20. The oil passage 944 connects the shut-off valve 980 to the oil passage 43 downstream of the pressure reducing valve 20. As a result, when the hydraulic power source 12 is functioning normally, the hydraulic pressure from the hydraulic power source 12 is supplied to the FCS 103 (low-pressure operating unit) by bypassing the pressure reducing valve 20. On the other hand, in the event of a malfunction in the hydraulic power source 12 or hydraulic power source 11, the control unit 60 uses the shut-off valve 980 to shut off the flow between the low-pressure side of the oil passage 42 and the oil passage 944 that bypasses the pressure reducing valve 20, while also connecting the low-pressure side and the high-pressure side of the oil passage 42. As a result, in the event of a malfunction in the hydraulic power source 12, a relatively high hydraulic pressure from the hydraulic power source 11 (high-pressure source) is supplied to the FCS 103 via the pressure reducing valve 20, and in the event of a malfunction in the hydraulic power source 11, a boosted relatively high hydraulic pressure from the hydraulic power source 12 (low-pressure source) is supplied to the FCS 103 via the pressure reducing valve 20. By arranging the shut-off valve 980, which serves as both a flow control valve and a bypass valve, in the oil passage 42, the complexity of the device configuration can be suppressed compared to the case where the bypass valve is arranged separately from the flow control valve.Furthermore, since there is no need to provide a separate bypass valve in addition to the flow control valve, it contributes to suppressing an increase in weight and the number of parts, and prevents the pressure reducing valve 20 from becoming a resistive element when, for example, a relatively low operating hydraulic pressure is supplied from the hydraulic power source 12 (low hydraulic power source) to the FCS 103 (low-pressure operating part).

[0129] (Sixth Modification) In addition, as shown in Figure 20, the hydraulic system 1000 according to the sixth modification may have the same configuration as the hydraulic system 200 of the second embodiment, but with a shut-off valve 481 as a bypass valve, as in the fourth embodiment. In the hydraulic system 1000 of the sixth modification, a passive shut-off valve 280 is arranged in the oil passage 243, which is a bypass oil passage, similar to the hydraulic system 200 of the second embodiment. In the hydraulic system 1000 of the sixth modification, a shut-off valve 481 is arranged in the oil passage 1045, which is a bypass oil passage that bypasses the pressure reducing valve 220, as in the fourth embodiment. The oil passage 1045 connects the low-pressure side of the oil passage 243, which is a backup oil passage, and the downstream side of the pressure reducing valve 220 in the oil passage 244. As a result, even when a passive shut-off valve 280 is placed in the oil passage 243, as in the hydraulic system 200 of the second embodiment, the shut-off valve 481 can switch between supplying hydraulic pressure to the FCS 103 (low-pressure operating section) via the pressure reducing valve 220 and supplying hydraulic pressure to the FCS 103 via the oil passage 1045 that bypasses the pressure reducing valve 220, similar to the fourth embodiment.

[0130] (Seventh Modification) In addition, as shown in Figure 21, the hydraulic system 1100 according to the seventh modification may have the same configuration as the hydraulic system 300 of the third embodiment, but with a shut-off valve 481 as a bypass valve, as in the fourth embodiment. In the hydraulic system 1100 of the seventh modification, a pressure reducing valve 321, which is a high-pressure side pressure reducing valve, and a pressure reducing valve 322, which is a low-pressure side pressure reducing valve, are arranged separately, similar to the hydraulic system 300 of the third embodiment. In the hydraulic system 1100 of the seventh modification, the shut-off valve 481 is arranged in an oil passage 1145, which is a bypass oil passage that bypasses the pressure reducing valve 322, which is the low-pressure side pressure reducing valve. The oil passage 1145 connects the upstream and downstream sides of the pressure reducing valve 322 in the oil passage 344. As a result, even when the hydraulic system 300 of the third embodiment is equipped with a pressure reducing valve 321 as a high-pressure side pressure reducing valve and a pressure reducing valve 322 as a low-pressure side pressure reducing valve, the shut-off valve 481 can switch between supplying hydraulic pressure to the FCS 103 (low-pressure operating section) via the pressure reducing valve 322 and supplying hydraulic pressure to the FCS 103 via the oil passage 1145 that bypasses the pressure reducing valve 322, similar to the fourth embodiment.

[0131] (Eighth Modification) In the second embodiment described above, an example was shown in which a pilot-operated shut-off valve 280 (high-pressure side flow control valve) is arranged in the oil passage 243 (high-pressure side backup oil passage), but the present invention is not limited thereto. In the present invention, as shown in the eighth modification hydraulic system 1200 in Figure 22, an electromagnetic shut-off valve 1280 may be arranged as the high-pressure side flow control valve. In the hydraulic system 1200, the control unit 60 controls the opening and closing of the shut-off valve 1280. When an abnormality is detected in the hydraulic source 12 (low hydraulic source), the control unit 60 controls the opening of the shut-off valve 1280 to open the flow of hydraulic fluid in the oil passage 243. When an abnormality is detected in the hydraulic source 11 (high hydraulic source), or when both the hydraulic source 11 and the hydraulic source 12 are functioning normally, the control unit 60 controls the closing of the shut-off valve 1280 to shut off the flow of hydraulic fluid in the oil passage 243. With this configuration, the control unit 60 controls the opening and closing of the shut-off valve 1280, thereby controlling whether or not to supply hydraulic pressure from the hydraulic power source 11 (high-pressure source) to the FCS 103 (low-pressure operating unit) via the oil passage 243.

[0132] (9th Modification) In the second embodiment described above, an example was shown in which a check valve 232 (low-pressure side flow control valve) is placed in the oil passage 242 (low-pressure side backup oil passage), but the present invention is not limited thereto. In the present invention, as shown in the 9th modification hydraulic system 1300 in Figure 23, a passive shut-off valve 1381 may be placed in the oil passage 242 (low-pressure side backup oil passage) as a low-pressure side flow control valve. The shut-off valve 1381 opens and closes in accordance with the hydraulic pressure from the hydraulic source 12 (low-pressure source). The shut-off valve 1381 closes when the hydraulic pressure supplied from the hydraulic source 12 is lower than a predetermined pressure to block the flow of hydraulic fluid in the oil passage 242, and opens when the hydraulic pressure supplied from the hydraulic source 12 is higher than a predetermined pressure to open the flow of hydraulic fluid in the oil passage 242. The predetermined pressure is, for example, a relatively high hydraulic pressure required to operate the leg lifting system 102 (high-pressure operating part). The shut-off valve 1381 is configured to open when the hydraulic pressure supplied from the hydraulic source 12 increases in the event of an abnormality in the hydraulic source 11 (high-pressure source), due to the pilot pressure on the upstream side. That is, the predetermined pressure here is greater than the predetermined value (predetermined opening / closing hydraulic pressure) for opening and closing the shut-off valve 280 located in the oil passage 243 (high-pressure side backup oil passage) of the second embodiment. While the shut-off valve 280 in the oil passage 243 opens and closes depending on whether or not a relatively low hydraulic pressure is supplied to operate the FCS 103 (low-pressure operating part), the shut-off valve 1381 in the oil passage 242 opens and closes depending on whether or not a relatively low hydraulic pressure is supplied to operate the leg lifting system 102 (high-pressure operating part). As a result, by adjusting the hydraulic pressure supplied from the hydraulic source 12, it is possible to control whether or not hydraulic pressure is supplied from the hydraulic source 12 to the leg lifting system 102 (high-pressure operating part) in order to switch between shutting off and opening the flow of hydraulic fluid by comparing the hydraulic pressure supplied from the hydraulic source 12 with a predetermined pressure.

[0133] (Tenth Modification) In the second embodiment described above, an example was shown in which a passive shut-off valve 280 that opens and closes in accordance with the hydraulic pressure from the hydraulic source 12 (low hydraulic source) is provided, but the present invention is not limited thereto. In the present invention, as shown in the tenth modification hydraulic system 1400 in Figure 24, a passive shut-off valve 1480 that opens and closes in accordance with the hydraulic pressure from the hydraulic source 11 (high hydraulic source) and the hydraulic pressure from the hydraulic source 12 may be provided as a low-pressure side flow control valve. The direction of spring biasing of the shut-off valve 1480 is opposite to that of the shut-off valve 280 in the second embodiment. The shut-off valve 1480 is configured so that a preload is applied in the closing direction when the hydraulic system 1400 is started due to the biasing of the spring. The opening and closing of the shut-off valve 1480 is controlled by applying different pilot pressures to both sides. That is, when the hydraulic source 12 is functioning normally, the shut-off valve 1480 closes due to the hydraulic pressure from the hydraulic source 12 and the biasing force of the spring, thereby blocking the flow of hydraulic fluid in the oil passage 243. Furthermore, the shut-off valve 1480 opens due to hydraulic pressure from the hydraulic power source 11 when the hydraulic power source 12 malfunctions, thereby opening the flow of hydraulic fluid in the oil passage 243. As a result, the shut-off valve 1480 is closed by the biasing force of the spring before the hydraulic system 1400 is started, so when both the hydraulic power source 11 and the hydraulic power source 12 are operating at startup, it is possible to suppress the supply of pressure from the hydraulic power source 11 to the FCS 103 (low-pressure operating section).

[0134] (11th Modification) In the first embodiment described above, an example was shown in which the pressure reducing valve 20 is placed in the oil passage 43 (low-pressure oil passage) downstream of the confluence point of the oil passage 42 (backup oil passage) to supply hydraulic pressure from the hydraulic source 11 (high-pressure oil source) and hydraulic pressure from the hydraulic source 12 (high-pressure oil source) to the FCS 103 via a common pressure reducing valve 20. However, the present invention is not limited thereto. In the present invention, as shown in the hydraulic system 1500 according to the 11th modification shown in Figure 25, a pressure reducing valve 1521 is placed in the oil passage 1542, which is a backup oil passage, as a high-pressure side pressure reducing valve, and a pressure reducing valve 1522 is placed in the oil passage 43, which is a low-pressure oil passage, upstream of the confluence point of the oil passage 1542, as a low-pressure side pressure reducing valve, thereby making the pressure reducing valves redundant. In the hydraulic system 1500 according to the 11th modification, the oil passage 1542, which is a backup oil passage, is connected downstream of the pressure reducing valve 1522 in the oil passage 43 (low-pressure oil passage). Pressure reducing valves 1521 and 1522 are configured to reduce the supplied hydraulic pressure to a common hydraulic pressure level. In addition, even when there is an oil passage 242 which is a low-pressure backup oil passage and an oil passage 243 which is a high-pressure backup oil passage, as in the second embodiment, redundancy may be achieved by placing a pressure reducing valve in each of the low-pressure backup oil passage and the high-pressure backup oil passage. When the hydraulic pressure from the hydraulic power source 12 and the hydraulic pressure from the hydraulic power source 11 are supplied to the FCS 103 via common pressure reducing valves 20 and 220, as in the first and second embodiments, or when the hydraulic pressure supplied to the FCS 103 is reduced to a common hydraulic pressure level by pressure reducing valves 1521 and 1522, as in the 11th modified example, it is possible to suppress differences in the hydraulic pressure supplied to the FCS 103, both when the hydraulic power source 12 is functioning normally and when it is malfunctioning. As a result, it is possible to suppress differences in the operation of the FCS 103 caused by differences in the supplied hydraulic pressure, both when the hydraulic power source 12 is functioning normally and when it is malfunctioning.

[0135] (Other Modifications) In the first to fourth embodiments described above, when the hydraulic power source 12 (low hydraulic power source) malfunctions, hydraulic pressure from the hydraulic power source 11 (high hydraulic power source) is reduced by the pressure reducing valves 20, 220, and 321 and supplied to the FCS 103 (low-pressure operating unit), and when the hydraulic power source 11 (high hydraulic power source) malfunctions, hydraulic pressure from the hydraulic power source 12 (low hydraulic power source) is increased and supplied to the leg lifting system 102 (high-pressure operating unit). However, the present invention is not limited to these. In the present invention, when the low hydraulic power source malfunctions, hydraulic pressure from the high hydraulic power source may not be supplied to the low-pressure operating unit. Also, when the high hydraulic power source malfunctions, hydraulic pressure from the low hydraulic power source may not be supplied to the high-pressure operating unit. That is, only one of the high hydraulic power source or the low hydraulic power source may be configured to operate as a backup for the other.

[0136] Furthermore, while the first to fourth embodiments described above show examples in which the hydraulic power sources 11 (high hydraulic power source) and 12 (low hydraulic power source) include gear pumps 11a and 12a and motors 11b and 12b, the present invention is not limited thereto. In the present invention, at least one of the high hydraulic power source and the low hydraulic power source may include a hydraulic pump other than a gear pump, such as a vane pump or a piston pump. Also, at least one of the high hydraulic power source and the low hydraulic power source does not have to include a motor. For example, at least one of the high hydraulic power source and the low hydraulic power source may not be electric, but may be driven by the main engine of an aircraft or an auxiliary power unit. Also, when at least one of the high hydraulic power source and the low hydraulic power source is an electric hydraulic power source including a motor, power may be supplied to the motor from a generator provided in addition to the auxiliary power unit, or power may be supplied to the motor from an energy storage device such as a battery. Furthermore, the high hydraulic power source and the low hydraulic power source do not have to have a common structure with each other.

[0137] Furthermore, while the first to fourth embodiments described above show examples in which the control unit 60 controls the operation of the hydraulic power source 11 (high hydraulic power source) and the hydraulic power source 12 (low hydraulic power source) by performing hydraulic feedback control, the present invention is not limited thereto. In the present invention, at least one of the high hydraulic power source and the low hydraulic power source may be operated without performing hydraulic feedback control. For example, the operation of the high hydraulic power source and the low hydraulic power source may be controlled based on a command value without using the output pressure detection result. Alternatively, the operation of the high hydraulic power source and the low hydraulic power source may be controlled manually. In this case, for example, the output pressure detected by the high-pressure gauge and the low-pressure gauge is displayed on a display unit located in the aircraft cockpit. Then, after the pilot operating the aircraft checks the display unit, the control unit adjusts the operation of the high hydraulic power source and the low hydraulic power source based on the input operation of the control unit. That is, by manually controlling the operation of the high hydraulic power source and the low hydraulic power source, the pilot's will can be introduced into the feedback control, increasing the opportunity to reflect human will in the hydraulic system.

[0138] Furthermore, in the first to fourth embodiments described above, an example was shown in which an abnormality in the hydraulic source 11 (high hydraulic source) is determined based on the detection result of the pressure gauge 51 (high pressure side pressure gauge), and an abnormality in the hydraulic source 12 (low hydraulic source) is determined based on the detection result of the pressure gauge 52 (low pressure side pressure gauge). However, the present invention is not limited thereto. In the present invention, abnormalities in the high hydraulic source and low hydraulic source may be determined by detecting an abnormality in the motor based on the current supplied to the motor, the voltage, or the rotation of the motor. Alternatively, abnormalities in the high hydraulic source and low hydraulic source may be determined by detecting an abnormality in temperature.

[0139] Furthermore, while the first to fourth embodiments described above show an example in which the operation of the hydraulic power source 11 (high hydraulic power source) and the operation of the hydraulic power source 12 (low hydraulic power source) are controlled by a common control unit 60, the present invention is not limited thereto. In the present invention, the operation of the high hydraulic power source and the operation of the low hydraulic power source may be controlled by control devices that are arranged separately from each other. That is, the control unit that controls the operation of the high hydraulic power source and the low hydraulic power source may include a high-pressure side control unit that controls the operation of the high hydraulic power source and a low-pressure side control unit that controls the operation of the low hydraulic power source. In that case, for example, the high-pressure side control unit and the low-pressure side control unit may communicate with each other to control the operation of the high hydraulic power source and the low hydraulic power source in the event of an abnormality. In addition, each of the high-pressure side control unit and the low-pressure side control unit may also acquire the output pressure of a hydraulic power source that is not under control under normal conditions from a pressure gauge, and use the acquired output pressure to detect an abnormality in the hydraulic power source that is not under control under normal conditions when the high hydraulic power source or the low hydraulic power source is abnormal.

[0140] Furthermore, while the first to fourth embodiments described above show examples in which hydraulic pressure is supplied to the FCS 103 (low-pressure operating unit) that operates the control surface 103a in the aircraft 101 and the landing gear lifting system 102 (high-pressure operating unit) that operates the landing gear 102a in the aircraft 101, the present invention is not limited thereto. In the present invention, hydraulic pressure may be supplied to an operating unit located in a vehicle or ship instead of an aircraft. Also, hydraulic pressure may be supplied to a stationary operating unit located in a factory or the like. Furthermore, hydraulic pressure may be supplied to a steering system or a braking system in an aircraft. In that case, the steering system and the braking system may be low-pressure operating units or high-pressure operating units. Also, the FCS that operates the control surface may be a high-pressure operating unit, and the landing gear lifting system that operates the landing gear may be a low-pressure operating unit. Also, in the FCS that operates the control surface, some operating units such as hydraulic actuators may be high-pressure operating units, and other operating units such as hydraulic actuators may be low-pressure operating units. Similarly, in a leg lifting system that operates the legs, some hydraulic actuators and other operating parts may be high-pressure operating parts, while other hydraulic actuators and other operating parts may be low-pressure operating parts. In other words, a single device or system may have both low-pressure and high-pressure operating parts. For example, in a leg lifting system, a low-pressure operating part that operates the front leg and a high-pressure operating part that operates the main leg may be arranged, and different operating hydraulic pressures may be supplied to each other for the leg lifting system.

[0141] Furthermore, in the third embodiment described above, an example was shown in which the pressure reducing valve 321 (high-pressure side pressure reducing valve) is configured to reduce hydraulic pressure supplied to a pressure lower than the pressure reduced by the pressure reducing valve 322 (low-pressure side pressure reducing valve), but the present invention is not limited to this. In the present invention, the high-pressure side pressure reducing valve and the low-pressure side pressure reducing valve may be configured to reduce the pressure to the same magnitude.

[0142] Furthermore, in the first embodiment described above, an example was shown in which the shut-off valve 80 (flow control valve) located in the oil passage 42 (backup oil passage) is an electromagnetic shut-off valve that opens and closes under the control of the control unit 60, and in the second embodiment described above, an example was shown in which the shut-off valve 280 (high-pressure side flow control valve) located in the oil passage 243 (high-pressure side backup oil passage) is a passive type that opens and closes when hydraulic pressure is supplied from the hydraulic power source 12 (low-pressure hydraulic power source), but the present invention is not limited thereto. In the present invention, any of the flow control valve, low-pressure side flow control valve, or high-pressure side flow control valve may be an electromagnetic or passive type shut-off valve. In addition, a shut-off valve that opens and closes by manual operation may be provided as the flow control valve, low-pressure side flow control valve, or high-pressure side flow control valve. Furthermore, in the high-pressure side oil passage and the low-pressure side oil passage, a shut-off valve may be provided that opens when the backup oil passage is shut off and closes when the backup oil passage is open.

[0143] Furthermore, while the first and fourth embodiments show examples in which check valves 31 and 32 are provided, the second embodiment shows examples in which check valves 231, 232, and 233 are provided, and the third embodiment shows examples in which check valves 331, 332, 333, and 334 are provided, the present invention is not limited thereto. In the present invention, shut-off valves that block the flow of hydraulic fluid, such as solenoid valves, may be provided instead of check valves. For example, in the third embodiment, by replacing check valve 332 with a shut-off valve, the operation of the hydraulic power source 11 (high-pressure hydraulic power source) may be stopped during the period when the operation of the leg lifting system 102 (high-pressure operating part) is stopped, thereby stopping the supply of hydraulic fluid from the hydraulic power source 11. Also, during the period when the operation of the FCS 103 (low-pressure operating part) is stopped, the operation of the hydraulic power source 12 may be stopped, thereby stopping the supply of hydraulic fluid from the hydraulic power source 12.

[0144] In the aircraft 101, the FCS 103 (low-pressure operating section) operates continuously, while the landing gear retraction system 102 (high-pressure operating section) operates intermittently. For example, during the operation of the aircraft 101, such as during flight, the FCS 103 is always operating. On the other hand, the landing gear retraction system 102 operates only temporarily during takeoff and landing. Taking this into consideration, the control unit may be configured to acquire the operating status of the landing gear retraction system 102 and the FCS 103, and to switch the operation of the hydraulic power sources 11 and 12, and the opening and closing operation of the shut-off valve which is placed in place of the check valve, according to the operating status of the landing gear retraction system 102 and the FCS 103. That is, the control unit may be configured to change the hydraulic pressure output from the high-pressure and low-pressure hydraulic power sources, as well as change the flow of the oil passages, according to the operating status of the high-pressure and low-pressure operating sections. The operating status referred to here indicates whether or not the high-pressure and low-pressure operating sections are operating, or the operating status in which the operating hydraulic pressure required by the high-pressure and low-pressure operating sections is changed. Furthermore, the control unit may be configured to stop the operation of the low hydraulic power source if an abnormality is detected in the low hydraulic power source during a period when the operation of the high-pressure operating unit is stopped, and to control the operation of the high hydraulic power source to output a relatively low operating hydraulic pressure because the operating hydraulic pressure required for the entire hydraulic system is relatively low.

[0145] Furthermore, signals indicating the operating status of the low-pressure and high-pressure operating units may be acquired based on signals from the control unit 104. Alternatively, signals indicating the operating status may be acquired from either the high-pressure or low-pressure operating unit. For example, by acquiring timing information indicating the timing of operation of the door actuator and the gear actuator from the landing gear system as the operating status, the output from the high-pressure hydraulic power source may be controlled to switch according to the timing of door opening and closing and landing gear raising and lowering in the landing gear system. Signals from the landing gear system as the low-pressure operating unit include, for example, a landing gear uplock signal indicating that the landing gear is locked in the retracted position, and a door uplock signal indicating that the hangar door is locked in the closed position. Additionally, signals indicating the operating status may be acquired from a higher-level control device located on a different aircraft from the high-pressure and low-pressure operating units. Furthermore, the operation of the high-pressure and low-pressure hydraulic power sources may be switched to switch the output to three or more values ​​according to the operating status of the high-pressure and low-pressure operating units. Furthermore, regardless of the operating state of the high-pressure and low-pressure operating parts, a constant hydraulic pressure may be output from the high-pressure and low-pressure sources. The low-pressure operating part may operate intermittently, or the high-pressure operating part may operate continuously. Both the high-pressure and low-pressure operating parts may operate intermittently or continuously. In the case where both the high-pressure and low-pressure operating parts operate intermittently, for example, the timing of the high-pressure and low-pressure operating parts may overlap, or they may operate at different times.

[0146] Furthermore, in the first to fourth embodiments described above, examples were shown in which hydraulic pressure is not supplied from the hydraulic pressure source 11 (high hydraulic pressure source) to the FCS 103 (low-pressure operating unit) when the hydraulic pressure source 12 (low hydraulic pressure source) is functioning normally, and in which hydraulic pressure is not supplied from the hydraulic pressure source 12 to the leg lifting system 102 (high-pressure operating unit) when the hydraulic pressure source 11 is functioning normally. However, the present invention is not limited to these examples. In the present invention, hydraulic pressure may be supplied from the high hydraulic pressure source to the low-pressure operating unit when the low hydraulic pressure source is functioning normally, and hydraulic pressure may be supplied from the low hydraulic pressure source to the high-pressure operating unit when the high hydraulic pressure source is functioning normally.

[0147] Furthermore, in the first to fourth embodiments described above, examples were shown in which the pressure reducing valves 20, 220, 321, and 322 are configured to reduce the supplied hydraulic pressure by blocking the flow of hydraulic fluid from the upstream side to the downstream side, but the present invention is not limited thereto. In the present invention, the pressure reducing valve may be configured to reduce the supplied hydraulic pressure by distributing hydraulic fluid from the upstream side.

[0148] Furthermore, while the first to fourth embodiments described above show examples in which hydraulic pressure is supplied to actuators 102b, 102c (high-pressure actuator), and 103b (low-pressure actuator), which are hydraulic cylinders, the present invention is not limited thereto. In the present invention, hydraulic pressure may be supplied to a hydraulic motor. Also, as pressure reducing valves, for example, servo valves and priority valves can be considered.

[0149] Furthermore, while the first to fourth embodiments described above show examples in which the hydraulic systems 100 and 200 include actuators 102b and 102c (high-pressure actuators) and actuator 103b (low-pressure actuator), the present invention is not limited thereto. In the present invention, the hydraulic system may supply hydraulic pressure to external actuators. That is, the hydraulic system may be an electric hydraulic power pack that does not include actuators.

[0150] Furthermore, in the first and fourth embodiments described above, examples were shown in which the oil passage 42 (backup oil passage) connects the oil passage 41 (high-pressure oil passage) and the oil passage 43 (low-pressure oil passage) to each other, and in the second and third embodiments, examples were shown in which the oil passages 242 and 342 (low-pressure backup oil passages) and the oil passages 243 and 343 (high-pressure backup oil passages) each separately connect the oil passages 241 and 341 (high-pressure oil passages) and the oil passages 244 and 344 (low-pressure oil passages) to each other, but the present invention is not limited thereto. In the present invention, the backup oil passages, high-pressure backup oil passages, and low-pressure backup oil passages may not connect oil passages to each other, but rather connect the high-pressure oil source and the low-pressure oil source to the high-pressure operating unit and the low-pressure operating unit. For example, the high-pressure backup oil passage may be configured to connect the discharge port of the high-pressure source pump to the low-pressure operating unit, or the low-pressure backup oil passage may be configured to connect the discharge port of the low-pressure source pump to the high-pressure operating unit. That is, the backup oil passages, the high-pressure backup oil passage, and the low-pressure backup oil passage may be configured to connect each other indirectly, not only by directly connecting the oil passages to each other, but also by connecting the high-pressure source and the low-pressure source to the high-pressure operating unit and the low-pressure operating unit.

[0151] Furthermore, in the cases where a high-pressure side backup oil passage and a low-pressure side backup oil passage are provided, as in the second and third embodiments described above, and a high-pressure side flow control valve and a low-pressure side flow control valve are provided, the configurations of the high-pressure side flow control valve and the low-pressure side flow control valve can vary. For example, both the high-pressure side flow control valve and the low-pressure side flow control valve may be electromagnetic shut-off valves. Alternatively, the high-pressure side flow control valve may be an electromagnetic shut-off valve and the low-pressure side flow control valve may be a check valve. Also, the high-pressure side flow control valve may be a passive shut-off valve or a pressure reducing valve and the low-pressure side flow control valve may be a sequence valve.

[0152] [Embodiments] The exemplary embodiments described above will be understood by those skilled in the art to be specific examples of the following embodiments.

[0153] (Item 1) A hydraulic system comprising: a high-pressure source that supplies hydraulic pressure to a high-pressure operating part that operates with a relatively high operating hydraulic pressure; a low-pressure source that is disposed separately from the high-pressure source and supplies hydraulic pressure to a low-pressure operating part that operates with a relatively low operating hydraulic pressure; and a pressure reducing valve that reduces the hydraulic pressure supplied to the low-pressure operating part, wherein in the event of a malfunction of the low-pressure source, the hydraulic pressure from the high-pressure source is reduced by the pressure reducing valve and supplied to the low-pressure operating part, and in the event of a malfunction of the high-pressure source, the hydraulic pressure from the low-pressure source is increased and supplied to the high-pressure operating part.

[0154] (Item 2) The hydraulic system according to Item 1, wherein the high-pressure source supplies a relatively high operating hydraulic pressure to the high-pressure operating section while simultaneously supplying a relatively low operating hydraulic pressure to the low-pressure operating section via the pressure reducing valve when the low-pressure source is in an abnormal state, and the low-pressure source supplies a relatively high operating hydraulic pressure to the high-pressure operating section by increasing the pressure of the supplied hydraulic pressure while simultaneously supplying a relatively low operating hydraulic pressure to the low-pressure operating section via the pressure reducing valve when the high-pressure source is in an abnormal state.

[0155] (Item 3) The hydraulic system according to Item 2, wherein the pressure reducing valve includes a high-pressure side pressure reducing valve that reduces the hydraulic pressure supplied from the high-pressure source to the low-pressure operating unit, and a low-pressure side pressure reducing valve that reduces the hydraulic pressure supplied from the low-pressure source to the low-pressure operating unit, the high-pressure source supplies hydraulic pressure by branching into a high-pressure side oil passage for supplying hydraulic pressure to the high-pressure operating unit and a high-pressure side backup oil passage in which the high-pressure side pressure reducing valve is located and for supplying hydraulic pressure to the low-pressure operating unit, and the low-pressure source supplies hydraulic pressure by branching into a low-pressure side oil passage in which the low-pressure side pressure reducing valve is located and for supplying hydraulic pressure to the low-pressure operating unit and a low-pressure side backup oil passage for supplying hydraulic pressure to the high-pressure operating unit.

[0156] This allows for the supply of appropriate operating hydraulic pressure to the high-pressure operating section via the high-pressure oil passage from the high-pressure source in the event of a low-pressure source malfunction, and also allows for the supply of appropriate operating hydraulic pressure to the low-pressure operating section via the high-pressure backup oil passage where the high-pressure pressure reducing valve is located. Furthermore, even if the hydraulic pressure from the low-pressure source is increased in the event of a high-pressure source malfunction, appropriate operating hydraulic pressure can be supplied to the low-pressure operating section via the low-pressure oil passage where the low-pressure pressure reducing valve is located, and also allows for the supply of appropriate operating hydraulic pressure to the high-pressure operating section via the low-pressure backup oil passage. Therefore, by branching the hydraulic pressure from the high-pressure source into the high-pressure oil passage and the high-pressure backup oil passage where the high-pressure pressure reducing valve is located, and by branching the hydraulic pressure from the low-pressure source into the low-pressure oil passage where the low-pressure pressure reducing valve is located and the low-pressure backup oil passage, it is possible to easily prevent the supply of operating hydraulic pressure from being interrupted in the event of a low-pressure source malfunction or a high-pressure source malfunction.

[0157] (Item 4) The hydraulic system according to Item 1, further comprising a shut-off valve in a backup oil passage for supplying hydraulic pressure from the high-pressure source to the low-pressure operating section, which shuts off the flow of hydraulic fluid when the low-pressure source is functioning normally.

[0158] As a result, when the low-pressure oil source is functioning normally, the shut-off valve can shut off the backup oil passage, preventing the supply of hydraulic pressure from the high-pressure oil source to the low-pressure operating section, thereby suppressing energy waste in the high-pressure oil source. Furthermore, when the low-pressure oil source malfunctions, opening the flow of the shut-off valve allows for easy supply of hydraulic pressure from the high-pressure oil source to the low-pressure operating section via the backup oil passage. Consequently, by switching the opening and closing of the shut-off valve located in the backup oil passage, the decrease in energy efficiency of the high-pressure oil source when the low-pressure oil source is functioning normally can be suppressed, and operating hydraulic pressure can be easily supplied to the low-pressure operating section when the low-pressure oil source malfunctions. In addition, by placing a shut-off valve in the backup oil passage, hydraulic pressure from both the low-pressure oil source and the high-pressure oil source can be supplied to the low-pressure operating section via a common pressure reducing valve. Therefore, in both normal and abnormal conditions of the low-pressure oil source, hydraulic pressure can be supplied to the low-pressure operating section via a common pressure reducing valve, thus suppressing differences in the hydraulic pressure supplied to the low-pressure operating section. As a result, differences in the operation of the low-pressure operating section caused by differences in supplied hydraulic pressure can be suppressed in both normal and abnormal conditions of the low-pressure oil source.

[0159] (Item 5) The hydraulic system according to Item 1, wherein the high-pressure source supplies hydraulic pressure to the high-pressure operating section without supplying hydraulic pressure to the low-pressure operating section via the pressure reducing valve when the low-pressure source is functioning normally, and the low-pressure source supplies hydraulic pressure to the low-pressure operating section without supplying hydraulic pressure to the high-pressure operating section when the high-pressure source is functioning normally.

[0160] As a result, when the low-pressure source is functioning normally, hydraulic pressure is not supplied from the high-pressure source to the low-pressure operating part, and when the high-pressure source is functioning normally, hydraulic pressure is not supplied from the low-pressure source to the high-pressure operating part. Therefore, during periods when both the high-pressure and low-pressure sources are operating normally, energy waste in both sources can be suppressed. Consequently, the decrease in energy efficiency during normal operation can be further suppressed.

[0161] (Item 6) The hydraulic system according to Item 5, further comprising a high-pressure shut-off check valve that prevents hydraulic pressure from the high-pressure source from being supplied to the low-pressure operating section when the low-pressure source is functioning normally.

[0162] This makes it easy to prevent hydraulic pressure from being supplied from the high-pressure source to the low-pressure operating part when the low-pressure source is functioning normally, by installing a high-pressure shut-off check valve. Therefore, it is easy to prevent a decrease in energy efficiency in the high-pressure source when the low-pressure source is functioning normally.

[0163] (Item 7) The hydraulic system according to Item 1, comprising: a high-pressure side backup oil passage for supplying hydraulic pressure from the high-pressure source to the low-pressure operating unit; and a low-pressure side backup oil passage, which is disposed separately from the high-pressure side backup oil passage, for supplying hydraulic pressure from the low-pressure source to the high-pressure operating unit, wherein in the event of a malfunction of the low-pressure source, the hydraulic pressure from the high-pressure source is reduced by the pressure reducing valve via the high-pressure side backup oil passage and supplied to the low-pressure operating unit; and in the event of a malfunction of the high-pressure source, the hydraulic pressure from the low-pressure source is increased via the low-pressure side backup oil passage and supplied to the high-pressure operating unit, at least one of these.

[0164] This allows for redundancy of the backup oil passages, thereby reducing the risk of, for example, the simultaneous loss of both the high-pressure and low-pressure backup oil passages. Furthermore, in the hydraulic system described in item 7, if the high-pressure backup oil passage is equipped with a high-pressure flow control valve and the low-pressure backup oil passage is equipped with a low-pressure flow control valve, then, for example, the high-pressure and low-pressure flow control valves can be configured to suit the pressure of the hydraulic fluid flowing through each backup oil passage.

[0165] 11, 611 Hydraulic source (high hydraulic source) 12, 612a, 612b Hydraulic source (low hydraulic source) 20, 220, 1521, 1522 Pressure reducing valve 41, 241, 341 Oil passage (high pressure side oil passage) 42, 1542 Oil passage (backup oil passage) 43, 244, 344 Oil passage (low pressure side oil passage) 51 Pressure gauge (high pressure side pressure gauge) 52 Pressure gauge (low pressure side pressure gauge) 60 Control unit 80, 581, 980 Shut-off valve (flow control valve) 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500 Hydraulic system 101 Aircraft 102 102a. Landing gear lifting system (high-pressure operating part) 102a. Landing gear 102b, 102c. Actuator (high-pressure actuator) 103. Flight control system (low-pressure operating part) 103a. Control surface 103b. Actuator (low-pressure actuator) 232, 332, 632, 633. Check valves (high-pressure shut-off check valve, flow control valve, low-pressure side flow control valve) 242, 342. Oil passages (backup oil passage, low-pressure side backup oil passage) 243, 343. Oil passages (backup oil passage, high-pressure side backup oil passage) 280, 1280, 1480. Shut-off valves (flow control valve, high-pressure side flow control valve) 321, 621a, 621b. Pressure reducing valves (high-pressure side pressure reducing valve, flow control valve, high-pressure side flow control valve) 322, 622a, 622b. Pressure reducing valve (low-pressure side pressure reducing valve) 444, 944, 1045, 1145 Oil passages (bypass oil passages) 481, 980 Shut-off valves (bypass valves) 602 High-pressure operating section 603a First low-pressure operating section (low-pressure operating section) 603b Second low-pressure operating section (low-pressure operating section) 732, 733, 1381 Shut-off valves (flow control valves, low-pressure side flow control valves) 980 Shut-off valves (flow control valves, bypass valves)

Claims

1. A hydraulic system comprising: a high-pressure source that supplies hydraulic pressure to a high-pressure operating part that operates with a relatively high operating hydraulic pressure; a low-pressure source that is disposed separately from the high-pressure source and supplies hydraulic pressure to a low-pressure operating part that operates with a relatively low operating hydraulic pressure; and a pressure reducing valve that reduces the hydraulic pressure supplied to the low-pressure operating part, wherein, in the event of a malfunction of the low-pressure source, the hydraulic pressure from the high-pressure source is reduced by the pressure reducing valve and supplied to the low-pressure operating part, and in the event of a malfunction of the high-pressure source, the hydraulic pressure from the low-pressure source is increased and supplied to the high-pressure operating part.

2. The hydraulic system according to claim 1, wherein the low hydraulic power source includes a hydraulic pump that discharges hydraulic fluid to supply hydraulic pressure and a motor that serves as a drive source for the hydraulic pump.

3. The hydraulic system according to claim 1 or 2, wherein the high-pressure hydraulic source supplies a relatively high operating hydraulic pressure to the high-pressure operating section while simultaneously supplying a relatively low operating hydraulic pressure to the low-pressure operating section via the pressure reducing valve when the low-pressure hydraulic source is in an abnormal state, and the low-pressure hydraulic source supplies a relatively high operating hydraulic pressure to the high-pressure operating section by increasing the pressure of the supplied hydraulic pressure while simultaneously supplying a relatively low operating hydraulic pressure to the low-pressure operating section via the pressure reducing valve.

4. The hydraulic system according to claim 3, further comprising: a high-pressure gauge for detecting the output pressure of the high-pressure source; a low-pressure gauge for detecting the output pressure of the low-pressure source; and a control unit for controlling the operation of the high-pressure source and the low-pressure source, wherein the control unit determines an abnormality in the high-pressure source based on the detection result of the high-pressure gauge, and determines an abnormality in the low-pressure source based on the detection result of the low-pressure gauge; in the event of an abnormality in the low-pressure source, stops the operation of the low-pressure source and reduces the hydraulic pressure from the high-pressure source by the pressure reducing valve and supplies it to the low-pressure operating unit; and in the event of an abnormality in the high-pressure source, stops the operation of the high-pressure source and increases the hydraulic pressure from the low-pressure source and supplies it to the high-pressure operating unit.

5. The hydraulic system according to claim 1 or 2, wherein the high-pressure hydraulic source is located in the aircraft and supplies hydraulic pressure to the high-pressure operating unit located in the aircraft, and the low-pressure hydraulic source is located separately from the high-pressure hydraulic source in the aircraft and supplies hydraulic pressure to the low-pressure operating unit located in the aircraft.

6. The hydraulic system according to claim 5, wherein the high-pressure hydraulic source supplies hydraulic pressure to the high-pressure operating section that operates the landing gear in the aircraft, and the low-pressure hydraulic source supplies hydraulic pressure to the low-pressure operating section that operates the control surfaces in the aircraft.

7. A hydraulic system according to claim 1 or 2, comprising: a high-pressure oil passage for supplying hydraulic fluid from the high-pressure source to the high-pressure operating section; and a backup oil passage connecting the high-pressure oil passage for supplying hydraulic fluid from the low-pressure source to the low-pressure operating section, wherein the backup oil passage is connected upstream of the pressure reducing valve located in the low-pressure oil passage; and a flow control valve that switches between blocking and opening the flow of hydraulic fluid in the backup oil passage by opening and closing, wherein in the event of an abnormality in either the high-pressure source or the low-pressure source, the flow control valve opens to open the flow of hydraulic fluid in the backup oil passage.

8. A hydraulic system according to claim 1 or 2, comprising: a high-pressure side oil passage for supplying hydraulic fluid from the high-pressure source to the high-pressure operating section; a low-pressure side oil passage for supplying hydraulic fluid from the low-pressure source to the low-pressure operating section, and a high-pressure side backup oil passage connecting these two passages; a low-pressure side backup oil passage, separately arranged from the high-pressure side backup oil passage, for connecting the high-pressure side oil passage and the low-pressure side oil passage; a high-pressure side flow control valve for switching between shutting off and opening the flow of hydraulic fluid in the high-pressure side backup oil passage by opening and closing; and a low-pressure side flow control valve for switching between shutting off and opening the flow of hydraulic fluid in the low-pressure side backup oil passage by opening and closing, wherein when the low-pressure source malfunctions, the high-pressure side flow control valve opens, thereby opening the flow of hydraulic fluid in the high-pressure side backup oil passage; and when the high-pressure source malfunctions, the low-pressure side flow control valve opens, thereby opening the flow of hydraulic fluid in the low-pressure side backup oil passage.

9. The hydraulic system according to claim 8, wherein the high-pressure side backup oil passage is connected to the low-pressure side oil passage upstream of the pressure reducing valve located in the low-pressure side oil passage, the high-pressure side flow control valve is an electromagnetic shut-off valve, and the system includes a control unit that controls the opening and closing of the high-pressure side flow control valve.

10. The hydraulic system according to claim 8, wherein the high-pressure side backup oil passage is connected to the low-pressure side oil passage upstream of the pressure reducing valve located in the low-pressure side oil passage, and the high-pressure side flow control valve is a passive shut-off valve that opens and closes in accordance with the oil pressure from the low-pressure source, and when the low-pressure source is functioning normally, it closes when an oil pressure of a predetermined value or higher is supplied from the low-pressure source, thereby shutting off the flow of hydraulic fluid in the high-pressure side backup oil passage, and when the low-pressure source is abnormal, it opens when an oil pressure of a predetermined value or higher is not supplied from the low-pressure source, thereby opening the flow of hydraulic fluid in the high-pressure side backup oil passage.

11. The hydraulic system according to claim 8, wherein the pressure reducing valve includes a low-pressure side pressure reducing valve disposed in the low-pressure side oil passage and a high-pressure side pressure reducing valve disposed in the high-pressure side backup oil passage, the low-pressure side pressure reducing valve reduces the hydraulic pressure supplied from the low-pressure source to the low-pressure operating unit, the high-pressure side pressure reducing valve reduces the hydraulic pressure supplied from the high-pressure source to the low-pressure operating unit, and the high-pressure side backup oil passage is connected to the low-pressure side oil passage downstream of the low-pressure side pressure reducing valve.

12. The hydraulic system according to claim 11, wherein the high-pressure side flow control valve is the high-pressure side pressure reducing valve, and reduces the hydraulic pressure supplied to a pressure lower than the pressure reduced by the low-pressure side pressure reducing valve.

13. The hydraulic system according to claim 8, wherein the low-pressure side flow control valve is an electromagnetic shut-off valve and comprises a control unit that controls the opening and closing of the low-pressure side flow control valve.

14. The hydraulic system according to claim 8, wherein the low-pressure side flow control valve is a passive shut-off valve that opens and closes in accordance with the hydraulic pressure from the low-pressure source, and closes when the hydraulic pressure supplied from the low-pressure source is lower than a predetermined pressure to shut off the flow of hydraulic fluid in the low-pressure side backup oil passage, and opens when the hydraulic pressure supplied from the low-pressure source is higher than a predetermined pressure to open the flow of hydraulic fluid in the low-pressure side backup oil passage.

15. The hydraulic system according to claim 8, wherein the low-pressure side flow control valve is a high-pressure shut-off check valve, and in the normal operation of the high-pressure hydraulic source, it shuts off the flow of hydraulic fluid in the low-pressure side backup oil passage by suppressing the flow of hydraulic fluid from the high-pressure side oil passage side more than the high-pressure shut-off check valve.

16. The hydraulic system according to claim 1 or 2, further comprising a bypass valve that switches between supplying hydraulic pressure to the low-pressure operating section via the pressure reducing valve and supplying hydraulic pressure to the low-pressure operating section via a bypass oil passage that bypasses the pressure reducing valve, wherein the bypass valve switches to supplying hydraulic pressure to the low-pressure operating section via the bypass oil passage when the pressure upstream of the pressure reducing valve is below a predetermined pressure.

17. The hydraulic system according to claim 7, comprising a bypass oil passage that bypasses the pressure reducing valve and connects the upstream and downstream sides of the pressure reducing valve, wherein the flow control valve has a bypass function that opens the bypass oil passage when blocking the flow of hydraulic fluid and closes the bypass oil passage when opening the flow of hydraulic fluid.

18. The hydraulic system according to claim 1 or 2, wherein the pressure reducing valve is configured to reduce the supplied hydraulic pressure by allowing hydraulic fluid to flow from the upstream side to the downstream side when the downstream pressure is less than a predetermined pressure, and by blocking the flow of hydraulic fluid from the upstream side to the downstream side when the downstream pressure exceeds a predetermined pressure.

19. The hydraulic system according to claim 1 or 2, further comprising: a high-pressure actuator that operates with a relatively high operating hydraulic pressure in the high-pressure operating section; and a low-pressure actuator that operates with a relatively low operating hydraulic pressure in the low-pressure operating section.

20. A method for controlling a hydraulic system, comprising the steps of: supplying hydraulic pressure from a high-pressure source to a high-pressure operating section that operates with a relatively high operating hydraulic pressure; and supplying hydraulic pressure from a low-pressure source, which is separately arranged from the high-pressure source, to a low-pressure operating section that operates with a relatively low operating hydraulic pressure; and, in the event of an abnormality in the low-pressure source, supplying hydraulic pressure from the high-pressure source to the low-pressure operating section after reducing the pressure using a pressure reducing valve that reduces the pressure supplied to the low-pressure operating section; and, in the event of an abnormality in the high-pressure source, supplying hydraulic pressure from the low-pressure source to the high-pressure operating section after increasing its pressure.

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