Closed liquid system

Abstract

A closed liquid system (1) comprises: a positive displacement pump (7) that is connected to objects (21 to 26) via a supply path (41) and supplies liquid to the objects; a reservoir (6) that is connected to the objects via a return path (42) and pressurizes liquid stored therein; and a booster device (8) that is located in a second supply path (43) connecting the positive displacement pump and the reservoir, and has a non-positive displacement pump that boosts the pressure of the pressurized liquid from the reservoir and sends the boosted liquid to the positive displacement pump.

Description

Closed liquid system

[0001] The technology disclosed herein relates to a closed liquid system.

[0002] Patent Document 1 describes a conventional EHA (Electro Hydraulic Actuator) system. The EHA system is an example of a closed liquid system. The EHA system of Patent Document 1 is mounted on an aircraft. The EHA system raises and lowers the landing gear. The EHA system includes a hydraulic actuator and an electro-hydraulic pump. The hydraulic actuator is attached to the landing gear of the aircraft and raises and lowers the landing gear. The electro-hydraulic pump is connected to the hydraulic actuator via a supply line and supplies hydraulic oil to the hydraulic actuator. The EHA system further includes a reservoir. The reservoir is a tank for absorbing the change in volume within the hydraulic actuator as the hydraulic actuator expands and contracts. The reservoir is connected to the electro-hydraulic pump via a supply line and to the hydraulic actuator via a return line.

[0003] Japanese Patent No. 7228747

[0004] In the conventional EHA system, the pressure of the hydraulic oil supplied to the electro-hydraulic pump was increased by the reservoir. This is to suppress the occurrence of cavitation in the suction part of the electro-hydraulic pump. The reservoir is required to have (1) a function of increasing the pressure of the hydraulic oil supplied to the electro-hydraulic pump even when the amount of hydraulic oil stored in the reservoir decreases, and (2) a function of withstanding high pressure within the reservoir. To satisfy these required functions, the reservoir of the conventional EHA system was large.

[0005] In particular, the EHA system mounted on an aircraft, for example, due to the large amount of hydraulic oil supplied to the actuator accompanying the raising and lowering of the landing gear, and / or the large temperature change between when the aircraft is on the ground and during flight, the amount of hydraulic oil stored in the reservoir changes greatly. To satisfy the above-described required functions even when the storage amount of the hydraulic oil changes greatly, the size of the reservoir mounted on an aircraft tends to be larger. On the other hand, weight reduction is strongly required for the system mounted on an aircraft.

[0006] Furthermore, the need to enlarge reservoirs is not limited to systems mounted on aircraft or EHA systems. It is a technical challenge that can arise in any closed liquid system that supplies liquid to an object.

[0007] The technology disclosed herein reduces the size of reservoirs in closed liquid systems.

[0008] The technology disclosed herein relates to a closed liquid system. The closed liquid system comprises: a positive displacement pump connected to an object via a supply path and supplying liquid to the object; a reservoir connected to the object via a return path, which pressurizes the stored liquid; and a pressurizing device located in a second supply path connecting the positive displacement pump and the reservoir, which has a non-positive displacement pump that pressurizes the pressurized liquid from the reservoir and sends it to the positive displacement pump.

[0009] The closed liquid system includes a booster device. The booster device is located in a second supply path connecting the positive displacement pump and the reservoir. The booster device boosts the pressurized liquid from the reservoir and sends it to the positive displacement pump. The boosting of the liquid by the booster device suppresses the occurrence of cavitation at the suction section of the positive displacement pump. The booster device has a non-positive displacement pump. Compared to a positive displacement pump, a non-positive displacement pump is less prone to cavitation even at low pressures at the suction section. Because cavitation is less likely to occur in the booster device and the booster device pressurizes the liquid, the pressurizing capacity of the reservoir can be reduced compared to conventional systems. In other words, the pressure of the liquid pressurized by the reservoir can be set lower than conventional systems. Also, because the pressure can be reduced, the pressure resistance performance required of the reservoir can be reduced. By being able to set the liquid pressure lower and reducing the pressure resistance performance, the reservoir of the closed liquid system can be made smaller.

[0010] The closed liquid system is a bypass path that bypasses the boosting device and connects the reservoir to the positive displacement pump, and may further include an openable and closable bypass path.

[0011] For example, if the booster device malfunctions or the booster device operates inefficiently, the closed fluid system can supply fluid from the reservoir to the positive displacement pump through an open bypass. A decrease in the booster device's operating efficiency can occur, for example, if the fluid is hydraulic fluid and its viscosity increases at extremely low temperatures. Bypasses improve the reliability of the closed fluid system and are advantageous for its stable operation.

[0012] The bypass may be opened or closed depending on the state of the closed liquid system.

[0013] Because the bypass path is opened and closed depending on the state of the closed liquid system, the closed liquid system can continue stable operation by switching between using and not using the bypass path. In addition, the closed liquid system can ensure a fail-safe function by using the bypass path when necessary.

[0014] The bypass path may be opened and closed according to the difference between the discharge pressure of the booster device and the pressure of the reservoir. In other words, the "closed liquid system state" may be the difference between the discharge pressure of the booster device and the pressure of the reservoir.

[0015] The closed liquid system may further include a check valve located in the bypass path and preventing backflow from the second supply path to the reservoir.

[0016] The check valve prevents the liquid pressurized by the booster device from flowing back into the reservoir through the bypass.

[0017] The closed liquid system may further include a switching valve that opens the bypass passage and closes the second supply passage when the difference between the discharge pressure of the booster device and the pressure of the reservoir exceeds a predetermined value, and closes the bypass passage and opens the second supply passage when the difference between the discharge pressure of the booster device and the pressure of the reservoir falls below the predetermined value.

[0018] The switching valve ensures that the reservoir pressure is sufficiently high when the difference between the discharge pressure of the booster device and the reservoir pressure exceeds a predetermined value, i.e., when [reservoir pressure] - [discharge pressure of booster device] ≥ predetermined value. Even if liquid is supplied directly from the reservoir to the positive displacement pump, cavitation at the suction section of the positive displacement pump is suppressed. Furthermore, if only the positive displacement pump boosts the liquid pressure and the booster device is omitted, the efficiency of the entire closed liquid system is increased.

[0019] When [reservoir pressure] - [pressure booster device discharge pressure] < a predetermined value, the pressure booster device pressurizes the liquid and sends it to the positive displacement pump. As mentioned above, the occurrence of cavitation at the suction section of the positive displacement pump is suppressed.

[0020] The bypass passage may be opened and closed in accordance with the pressure of the reservoir. In other words, the "state of a closed liquid system" may be the pressure of the reservoir.

[0021] For example, if the reservoir pressure is above a predetermined value, the bypass path may be opened and the second supply path closed, and if the reservoir pressure falls below the predetermined value, the bypass path may be closed and the second supply path opened. If the reservoir pressure is sufficiently high, liquid is supplied directly from the reservoir to the positive displacement pump. If the reservoir pressure is relatively low, a booster device boosts the liquid and sends it to the positive displacement pump.

[0022] The degree of opening of the bypass passage may change depending on the state of the closed liquid system.

[0023] The bypass opening can be set to an intermediate opening between fully open and fully closed, in addition to fully open and fully closed. This is advantageous for the stable operation of a closed fluid system.

[0024] The positive displacement pump, the reservoir, the boosting device, the supply path, the return path, and the second supply path may constitute a closed circulation circuit isolated from the outside.

[0025] A closed liquid system, by forming a closed circulation circuit, is unaffected by the pressure of the surrounding environment. In a closed circulation circuit, the reservoir and booster device increase the pressure of the liquid supplied to the positive displacement pump, thereby suppressing cavitation in the pump. Furthermore, as will be discussed later, a closed liquid system including a closed circulation circuit is effective as a closed liquid system installed in an aircraft.

[0026] The reservoir may have a storage chamber and a pressure accumulation chamber, and the liquid in the storage chamber may be pressurized by the pressure of the gas filled in the pressure accumulation chamber.

[0027] In a reservoir that pressurizes the liquid in the storage chamber using the gas pressure in the accumulator chamber, setting the liquid pressure low allows for a lower pressurizing capacity of the reservoir, which is advantageous for miniaturizing the reservoir and simplifying its structure. This miniaturization also leads to a reduction in weight.

[0028] The boosting device may have one or more of the non-positive displacement pumps.

[0029] Positive displacement pumps are advantageous for increasing the pressure of the liquid supplied to the object, but cavitation is prone to occur at the suction. Non-positive displacement pumps are less prone to cavitation at the suction. Non-positive displacement pumps are less prone to cavitation even when low-pressure liquid is supplied from the reservoir. Because non-positive displacement pumps increase the pressure of low-pressure liquid before supplying it to positive displacement pumps, the occurrence of cavitation at the suction of the positive displacement pump is suppressed.

[0030] The boosting device may include at least one of a centrifugal pump and an inducer.

[0031] Centrifugal pumps are less prone to cavitation at the suction. Inducers are also less prone to cavitation at the suction. Centrifugal pumps or inducers are effective as pressurizing devices in closed liquid systems.

[0032] The boosting device may include the centrifugal pump and an inducer provided at the suction section of the centrifugal pump.

[0033] The inducer further suppresses cavitation in the suction section of the centrifugal pump. This makes it possible to further reduce the pressurization capacity in the reservoir. A booster device having an inducer and a centrifugal pump allows for miniaturization and simplification of the reservoir's structure.

[0034] The pressure boosting device may include a centrifugal pump and a diffuser provided at the discharge section of the centrifugal pump.

[0035] A diffuser increases the pressure of the liquid discharged from a centrifugal pump. When the centrifugal pump alone lacks sufficient pressurizing capacity, a diffuser can supplement the centrifugal pump's capacity and suppress cavitation at the suction section of a positive displacement pump. Because the diffuser increases the pressure, it becomes possible to reduce the pressurizing capacity of the reservoir.

[0036] The pressure boosting device may include a centrifugal pump, an inducer provided at the suction section of the centrifugal pump, and a diffuser provided at the discharge section of the centrifugal pump.

[0037] As mentioned earlier, the inducer suppresses cavitation in the booster device. Additionally, the diffuser can increase the pressure of the liquid supplied to the positive displacement pump, allowing for a reduction in the reservoir's pressurization capacity. A booster device incorporating an inducer, centrifugal pump, and diffuser enables miniaturization and simplification of the reservoir's structure.

[0038] The enclosed liquid system may further include a prime mover connected to both the positive displacement pump and the booster device, and driving the pump and the booster device, respectively.

[0039] By having a single prime mover drive both the positive displacement pump and the booster device, the structure of the closed liquid system is simplified.

[0040] The closed liquid system may be mounted on an aircraft.

[0041] In a closed liquid system mounted on an aircraft, due to the large temperature change between when the aircraft is on the ground and during flight, the volume change of the liquid stored in the reservoir is large. Reservoirs mounted on aircraft generally tend to be large in order to pressurize the liquid to the required pressure while allowing for a large volume change. In contrast, in the above-described closed liquid system, the reservoir can be downsized by interposing a pressure boosting device. A closed liquid system equipped with a small and lightweight reservoir is effective as a system to be mounted on an aircraft.

[0042] The object includes at least one of an actuator for flight control of the aircraft and an actuator for takeoff and landing, and the positive displacement pump may supply hydraulic oil for operating the actuator to the actuator.

[0043] Among the actuators of an aircraft, especially the actuator for takeoff and landing has a large operating stroke, so the amount of hydraulic oil supplied to the actuator is large. Since the amount of hydraulic oil stored in the reservoir varies greatly, conventional reservoirs have been larger. Since the above-described closed liquid system includes a small reservoir as described above, the closed liquid system is effective as a system to be mounted on an aircraft.

[0044] The closed liquid system can reduce the size of the reservoir.

[0045] Figure 1 shows an aircraft-mounted hydraulic system as a closed liquid system. Figure 2 shows various configurations of a booster device. Figure 3 shows the change in hydraulic fluid pressure from the reservoir to the pump. Figure 4 shows a part of the liquid system according to a modification, with the upper figure showing the hydraulic fluid supply state through the booster device and the lower figure showing the hydraulic fluid supply state through the bypass. Figure 5 shows the operation of a switching valve according to a modification. Figure 6 shows a part of the liquid system according to a modification, with the upper figure showing the hydraulic fluid supply state through the booster device and the lower figure showing the hydraulic fluid supply state through the bypass. Figure 7 shows a part of the liquid system according to a modification, with the upper figure showing the hydraulic fluid supply state through the booster device and the lower figure showing the hydraulic fluid supply state through the bypass.

[0046] The following describes embodiments of a closed liquid system with reference to the drawings. The closed liquid system described herein is illustrative.

[0047] (Overall configuration of the closed-loop fluid system) Figure 1 shows the overall configuration of the closed-loop fluid system 1. The closed-loop fluid system 1 is installed on an aircraft. The closed-loop fluid system 1 supplies hydraulic fluid to the hydraulic equipment installed on the aircraft. The closed-loop fluid system 1 is the aircraft's hydraulic system. The closed-loop fluid system 1 comprises a hydraulic circuit 10 including a plurality of hydraulic devices.

[0048] The hydraulic equipment includes, as an example, the following hydraulic actuators 21 - 26. That is, as shown in FIG. 1, the elevator actuator 21, the elevator actuator 22, the ladder actuator 23, the flap actuator 24, the slat actuator 25, and the landing gear actuator 26 are included in the hydraulic equipment. The landing gear actuator 26 includes at least one of, for example, a gear actuator, a door actuator, and a downlock release actuator. The gear actuator is an actuator that raises and lowers the landing gear strut. The door actuator is an actuator that opens and closes the door of the storage compartment for storing the landing gear. The downlock release actuator is an actuator that releases the downlock mechanism that fixes the landing gear strut in the lowered state.

[0049] These hydraulic actuators 21 - 26 are an example of an object to which the closed liquid system 1 supplies hydraulic oil. The hydraulic oil is an example of a liquid. The closed liquid system 1 may supply hydraulic oil to a part of the hydraulic actuators 21 - 26. The closed liquid system 1 may supply hydraulic oil to a hydraulic equipment different from the hydraulic actuators 21 - 26.

[0050] The hydraulic actuators 21 - 26 are, for example, telescopic actuators having a cylinder and a piston. The elevator actuator 21, the elevator actuator 22, and the ladder actuator 23 are primary flight control actuators that operate during cruise flight and takeoff / landing of an aircraft. The primary flight control actuator has a relatively short stroke and operates at any time for a long time during the flight of the aircraft. The pressure required for the operation of the primary flight control actuator is relatively high. Also, the flow rate of the hydraulic oil required for the operation of the primary flight control actuator is relatively low.

[0051] The flap actuator 24 and the slat actuator 25 are secondary flight control actuators. The flap actuator 24 and the slat actuator 25 are also included in the flight control actuators. The flap actuator 24 and the slat actuator 25 have a moderate stroke and operate temporarily during aircraft takeoff and landing. The pressure required for the operation of the secondary flight control actuators is moderate. The hydraulic fluid flow rate required for the operation of the secondary flight control actuators is also moderate. Hereinafter, the aileron actuator 21, elevator actuator 22, rudder actuator 23, flap actuator 24, and slat actuator 25 may be collectively referred to as flight control actuators 21-25.

[0052] The landing gear actuator 26 is an example of a takeoff and landing actuator that operates during aircraft takeoff and landing. The landing gear actuator 26 has a relatively long stroke and operates temporarily during aircraft takeoff and landing. The pressure required for the operation of the landing gear actuator 26 is relatively high. Also, the flow rate of the hydraulic fluid required for the operation of the landing gear actuator 26 is relatively high.

[0053] The aileron actuator 21, elevator actuator 22, rudder actuator 23, flap actuator 24, slat actuator 25, and landing gear actuator 26 are each connected to the hydraulic circuit 10 via valves 211, 221, 231, 241, 251, and 261. Valves 211, 221, 231, 241, 251, and 261 switch the supply and discharge of hydraulic fluid to the actuators and adjust the amount of fluid supplied and discharged.

[0054] The enclosed fluid system 1 includes a main pump 7. The main pump 7 is a positive displacement pump. More specifically, the main pump 7 is an internal gear pump. The internal gear pump enables the hydraulic fluid pressure to be raised to the high pressure required by each hydraulic actuator 21-26. Note that the positive displacement pump is not limited to an internal gear pump.

[0055] The discharge port 71 of the main pump 7 is connected to the supply passage 41. The supply passage 41 is connected to each of the hydraulic actuators 21-26. Each of the hydraulic actuators 21-26 is in parallel with the main pump 7. The main pump 7 supplies hydraulic fluid individually to each of the aileron actuator 21, elevator actuator 22, rudder actuator 23, flap actuator 24, slat actuator 25, and landing gear actuator 26 via the supply passage 41.

[0056] The enclosed fluid system 1 includes a reservoir 6. The reservoir 6 is connected to a return path 42. The return path 42 connects each hydraulic actuator 21-26 to the reservoir 6. The reservoir 6 stores hydraulic fluid. The reservoir 6 is a tank for absorbing the volume fluctuations within each hydraulic actuator 21-26 as they extend and retract. The reservoir 6 also absorbs volume changes of the hydraulic fluid due to temperature changes between when the aircraft is on the ground and when it is in flight.

[0057] The reservoir 6 has a storage chamber 61 and a pressure accumulator chamber 62. The storage chamber 61 and the pressure accumulator chamber 62 are separated. The storage chamber 61 stores hydraulic fluid. The storage chamber 61 is connected to a return passage 42 and also to a second supply passage 43, which will be described later. Hydraulic fluid returns from each hydraulic actuator 21-26 to the storage chamber 61 through the return passage 42, and hydraulic fluid is supplied from the storage chamber 61 to the main pump 7 through the second supply passage 43. The pressure accumulator chamber 62 is filled with a gas, such as nitrogen. The pressure accumulator chamber 62 pressurizes the hydraulic fluid stored in the storage chamber 61 with the pressure of the gas it is filled with. The volume of the pressure accumulator chamber 62 changes according to the amount of hydraulic fluid stored in the storage chamber 61 (see the dotted arrow in Figure 1). The reservoir 6 has a structure that maintains the pressure of the hydraulic fluid at or above a predetermined pressure, regardless of the amount of hydraulic fluid stored in the storage chamber 61.

[0058] The reservoir 6 and the suction port 72 of the main pump 7 are connected to each other by a second supply passage 43. The main pump 7 receives hydraulic fluid from the reservoir 6.

[0059] A booster device 8 is installed in the second supply channel 43. The booster device 8 has the function of pressurizing the hydraulic fluid from the reservoir 6 and supplying it to the main pump 7. By pressurizing the hydraulic fluid, the booster device 8 suppresses the occurrence of cavitation at the suction section of the main pump 7, as will be described later. The configuration of the booster device 8 will be described later.

[0060] The hydraulic circuit 10, comprising the main pump 7, supply line 41, hydraulic actuators 21-26, return line 42, reservoir 6, second supply line 43, and booster device 8, constitutes a closed circulating circuit isolated from the outside. The closed fluid system 1 installed on the aircraft is unaffected by the pressure of the surrounding environment, whether the aircraft is on the ground or in flight. The hydraulic fluid returns to the reservoir 6 from the reservoir 6 through the second supply line 43, booster device 8, main pump 7, supply line 41, hydraulic actuators 21-26, and return line 42, as shown by the solid arrows in Figure 1.

[0061] The enclosed liquid system 1 includes a prime mover. The prime mover may be, for example, an electric motor 5. The electric motor 5 may be, for example, a servo motor. The prime mover may also be an engine. The electric motor 5 is connected to the main pump 7 and the booster device 8, respectively. The electric motor 5 drives both the main pump 7 and the booster device 8. In the configuration example of Figure 1, the electric motor 5, the main pump 7, and the booster device 8 are connected in series. The connection of the electric motor 5, the main pump 7, and the booster device 8 is not limited to the example in Figure 1. The enclosed liquid system 1 may also include a prime mover for the main pump 7 and a prime mover for the booster device 8.

[0062] A controller 3 is electrically connected to the electric motor 5. A pressure sensor 31 is also electrically connected to the controller 3. Note that the pressure sensor 31 is not an essential element of the closed fluid system 1 disclosed herein. The pressure sensor 31 is connected to a supply line 41. The pressure sensor 31 outputs a measurement signal to the controller 3 that corresponds to the pressure of the hydraulic fluid in the supply line 41.

[0063] Controller 3 outputs a control signal to the electric motor 5 so that the pressure of the hydraulic fluid in the supply line 41 reaches the target pressure, in accordance with the measurement signal from the pressure sensor 31 and the target pressure. Controller 3 may acquire the target pressure from a higher-level controller connected to Controller 3 at any time. Controller 3 may store the value of the target pressure internally, for example. Upon receiving the supply of hydraulic fluid from the main pump 7, the flight control actuators 21-25, the landing gear retraction actuators 26, or the flight control actuators 21-25 and the landing gear retraction actuators 26 operate.

[0064] The sensors in the closed liquid system 1 are not limited to the pressure sensor 31. Furthermore, the closed liquid system 1 may include multiple main pumps 7 and electric motors 5 for redundancy. The boosting device 8 may be multiple for redundancy, or there may be one for multiple main pumps 7.

[0065] (Various Configurations of the Booster Device) Figure 2 shows various configuration examples of the booster device 8. The booster device 81 in the first configuration example includes a centrifugal pump 86 as a non-positive displacement pump. The centrifugal pump 86 has an impeller and a housing that houses the impeller, and the impeller rotates with an electric motor 5, thereby imparting energy to the hydraulic fluid drawn into the housing and discharging the pressurized hydraulic fluid from the housing. The centrifugal pump 86 has the characteristic of being less prone to cavitation compared to the main pump 7, which is a positive displacement pump. On the other hand, the centrifugal pump 86 has a lower hydraulic fluid pressurization capacity than the main pump 7, which is a positive displacement pump.

[0066] The booster device 82 in the second configuration example includes an inducer 87 instead of a centrifugal pump 86. The inducer 87 is an example of a non-positive displacement pump having one or more rotors. The inducer 87 has the characteristic of being less prone to cavitation compared to the main pump 7, which is a positive displacement pump. Because the inducer 87 is less prone to cavitation than the centrifugal pump 86, it is advantageous in suppressing cavitation at the suction section of the booster device 85. Although the inducer 87 has a low pressurizing capacity for the hydraulic fluid, it increases the pressure of the hydraulic fluid supplied to the main pump 7, thereby suppressing cavitation at the suction section of the main pump 7.

[0067] The third configuration example of the booster device 83 includes a centrifugal pump 86 and an inducer 87. The inducer 87 is located at the suction portion of the centrifugal pump 86. The inducer 87 has the function of drawing hydraulic fluid into the centrifugal pump 86. The inducer 87 suppresses the generation of cavitation in the centrifugal pump 86. It also suppresses the generation of cavitation in the inducer 87. The booster device 82, which includes the centrifugal pump 86 and the inducer 87, allows low-pressure hydraulic fluid to be supplied to the booster device 82, thus making it possible to further reduce the pressurization capacity of the reservoir 6, which will be described later.

[0068] The fourth configuration example of the boosting device 84 includes a centrifugal pump 86 and a diffuser 88. The diffuser 88 is located at the discharge section of the centrifugal pump 86 and has the function of further increasing the pressure of the hydraulic fluid supplied to the main pump 7 by converting the dynamic pressure of the hydraulic fluid discharged from the centrifugal pump 86 into static pressure. When the boosting capacity of the centrifugal pump 86 alone is insufficient, the diffuser 88 can supplement the boosting capacity of the centrifugal pump 86. Because the diffuser 88 increases the pressure, it becomes possible to reduce the pressurizing capacity of the reservoir 6. Reducing the pressurizing capacity of the reservoir 6 is advantageous for miniaturizing the reservoir 6.

[0069] The booster device 85 of the fifth configuration example includes a centrifugal pump 86, an inducer 87, and a diffuser 88. The inducer 87 is located at the suction portion of the centrifugal pump 86, and the diffuser 88 is located at the discharge portion of the centrifugal pump 86. In the booster device 84 of the fifth configuration example, the inducer 87 located at the suction portion of the booster device 85 suppresses the generation of cavitation in the booster device 85. The diffuser 88 can supplement the boosting of the centrifugal pump 86 and increase the pressure of the liquid supplied to the main pump 7.

[0070] The boosting device 8 may also include other pumps as non-positive displacement pumps, such as axial flow pumps or mixed flow pumps.

[0071] As mentioned above, the boosting device 8 boosts the pressure of the hydraulic fluid from the reservoir 6 before supplying it to the main pump 7. The main pump 7 is a positive displacement pump and is relatively prone to cavitation. The boosting device 8 increases the pressure of the hydraulic fluid supplied to the main pump 7, thereby suppressing the occurrence of cavitation at the suction section of the main pump 7.

[0072] Figure 3 shows an example of the change in hydraulic fluid pressure from the reservoir 6 to the main pump 7 in the hydraulic circuit 10 of a closed liquid system 1. The vertical axis of Figure 3 represents pressure, and the horizontal axis of Figure 3 represents the positions of devices 6, 8, and 7 in the hydraulic circuit 10. The hydraulic fluid flows from left to right on the horizontal axis. As the hydraulic fluid flows from the reservoir 6 to the boosting device 8 through the second supply passage 43, the hydraulic fluid pressure decreases due to pressure loss.

[0073] In Figure 3, Ps represents an example of the pressure at which cavitation may occur in the suction section of the main pump 7. When the pressure at the suction section of the main pump 7 falls below Ps, cavitation may occur in the main pump 7. Since the main pump 7 is a positive displacement pump and is relatively prone to cavitation, Ps is relatively high.

[0074] If the closed liquid system 1 does not have a booster device 8, in order to raise the hydraulic fluid pressure at the suction of the main pump 7 to Ps or higher, the hydraulic fluid pressure in the reservoir 6 must be raised to Pr', as shown by the dashed line in Figure 3. If the pressurizing capacity of the reservoir 6 is increased, the reservoir 6 will have to be made larger.

[0075] In contrast, in a closed liquid system 1 equipped with a boosting device 8, the pressure of the hydraulic fluid in the reservoir 6 can be set to Pr (Pr < Pr').

[0076] First, as the hydraulic fluid flows from the reservoir 6 to the booster device 8 through the second supply passage 43, the pressure of the hydraulic fluid decreases due to pressure loss. Pb in Figure 3 illustrates the pressure at which cavitation may occur at the suction section of the booster device 8. If the pressure at the suction section of the booster device 8 falls below Pb, cavitation may occur in the booster device 8. The booster device 8 has a non-positive displacement pump and is less prone to cavitation than the main pump 7, so Pb < Ps. Pb is determined by the configuration of the booster device 8. If the suction section of the booster device 8 is an inducer 87, cavitation is even less likely to occur in the booster device 8, so Pb will be even lower. When Pb is low, the pressure at the suction section of the booster device 8 can be maintained above Pb even if the pressurizing capacity of the reservoir 6 is reduced.

[0077] The booster device 8 increases the pressure of the hydraulic fluid. The pressure of the hydraulic fluid is increased by the booster device 8 to a pressure exceeding Ps. At the suction section of the main pump 7, the pressure of the hydraulic fluid is maintained at a pressure exceeding Ps. If the pressure of the hydraulic fluid in the reservoir 6 is Pr, the occurrence of cavitation at the suction section of the main pump 7 is suppressed.

[0078] The main pump 7 increases the pressure of the hydraulic fluid to, for example, Pd (>Ps) and supplies the hydraulic fluid to each hydraulic actuator 21-26.

[0079] In the example shown in Figure 3, the pressure at the suction section of the boost device 8 is greater than or equal to Pb, but the pressure at the suction section of the boost device 8 may be lower than Pb. In other words, cavitation may occur in the boost device 8.

[0080] (Modification 1) Figure 4 shows a part of a closed liquid system 100 according to a modification. The closed liquid system 100 includes an openable and closable bypass passage 44.

[0081] The bypass line 44 bypasses the boost device 8 and connects the reservoir 6 and the main pump 7. The first end of the bypass line 44 is branched and connected to the second supply line 43 between the reservoir 6 and the boost device 8. The second end of the bypass line 44 is connected to the switching valve 90.

[0082] The switching valve 90 has a first port 91, a second port 92, and a discharge port 93. The first port 91 opens at the first end of the cylindrical casing of the switching valve 90, and the second port 92 opens at the second end of the cylindrical casing, opposite to the first end. The discharge port 93 opens on the side of the cylindrical casing.

[0083] The second supply path 43, connected to the discharge side of the boost device 8, is connected to the first port 91. The second end of the bypass path 44 is connected to the second port 92. The discharge port 93 is connected to the suction port 72 of the main pump 7.

[0084] The switching valve 90 is a shuttle valve in which the valve body 94 moves back and forth. The valve body 94 divides the inside of a cylindrical casing into a first end side and a second end side, and is biased from the second end side towards the first end side by a mechanical spring 95.

[0085] The switching valve 90 switches according to the difference between the discharge pressure of the booster device 8 and the pressure of the reservoir 6. The upper diagram of Figure 4 shows a state where the rotational speed of the electric motor 5 is high. When the rotational speed of the electric motor 5 is high, the rotational speed of the main pump 7 also increases, resulting in a high flow rate in the closed liquid system 1. This creates a situation where cavitation is likely to occur at the suction part of the main pump 7. As shown in Figure 1, the electric motor 5 drives both the main pump 7 and the booster device 8. When the rotational speed of the electric motor 5 is high, the rotational speed of the booster device 8 is also high, and therefore the discharge pressure of the booster device 8 increases. In the switching valve 90, the pressure on the first port 91 side becomes higher than the pressure on the second port 92 side, and the valve body 94 is pushed toward the second end side. This corresponds to the case where [reservoir pressure] - [discharge pressure of booster device] < predetermined value.

[0086] The switching valve 90 connects the first port 91 and the discharge port 93, and closes the second port 92. In other words, the bypass passage 44 is effectively closed. Since the hydraulic fluid pressurized by the pressurizing device 8 is supplied to the main pump 7, the occurrence of cavitation at the suction section of the main pump 7 is suppressed. The switching valve 90 also functions as a check valve to prevent backflow from the second supply passage 43 to the bypass passage 44.

[0087] The lower diagram in Figure 4 shows the state when the rotational speed of the electric motor 5 is low. When the rotational speed of the electric motor 5 is low, the rotational speed of the main pump 7 is also low, and the flow rate of the closed liquid system 1 is low. This makes it less likely for cavitation to occur at the suction section of the main pump 7. When the rotational speed of the electric motor 5 is low, the rotational speed of the booster device 8 is also low, so the discharge pressure of the booster device 8 is also relatively low.

[0088] When the pressure in reservoir 6 is high, the sum of the pressure on the second port 92 side and the pressure corresponding to the force of the spring 95 in the switching valve 90 becomes higher than the pressure on the first port 91 side, causing the valve body 94 to be pushed toward the first end. This corresponds to the case where [reservoir pressure] - [discharge pressure of booster device] ≥ a predetermined value.

[0089] The switching valve 90 connects the second port 92 and the discharge port 93, and closes the first port 91. In other words, the second supply passage 43 is effectively closed. Since relatively high-pressure hydraulic fluid is supplied from the reservoir 6 to the main pump 7, the occurrence of cavitation at the suction section of the main pump 7 is suppressed. Only the main pump 7 pressurizes the liquid, and the supply of hydraulic fluid by the pressurizing device 8 is omitted, thus increasing the efficiency of the entire closed liquid system 1. In this case, the non-positive displacement pump of the pressurizing device 8 continues to rotate without discharging hydraulic fluid.

[0090] Furthermore, the lower diagram in Figure 4 is not limited to cases where the rotational speed of the electric motor 5 is low, but also corresponds to cases where the booster device 8 does not function due to some malfunction and the discharge pressure of the booster device 8 is low, or, for example, in an extremely low temperature environment, the viscosity of the hydraulic fluid becomes significantly higher and the efficiency of the booster device 8 is poor. In these cases as well, the discharge pressure of the booster device 8 becomes low, and hydraulic fluid is supplied from the reservoir 6 to the main pump 7, bypassing the booster device 8. The supply of hydraulic fluid to the main pump 7 can be continued stably. The closed liquid system 100 has a fail-safe function.

[0091] The switching valve 90 has a mechanical structure and automatically opens and closes the bypass passage 44 according to the difference between the discharge pressure of the booster device 8 and the pressure of the reservoir 6. This ensures high reliability of the closed liquid system 100.

[0092] (Modification 2) Figure 5 shows a modified version of the switching valve. The switching valve 900 may be able to change the opening degree of the second supply passage 43 and the opening degree of the bypass passage 44.

[0093] The casing of the switching valve 900 has a first port 901, a second port 902, and a discharge port 903, as well as a third port 904 and a fifth port 905. The first port 901 is connected to the discharge side of the boosting device 8. The second port 902 is connected to the bypass path 44. The discharge port 903 is connected to the suction port 72 of the main pump 7. The first port 901, the second port 902, and the discharge port 903 each open side by side on the side of the casing.

[0094] The third port 904 opens at the first end of the casing. Like the first port 901, the third port 904 is connected to the discharge side of the boost device 8. The fourth port 905 opens at the second end of the casing. The second end is the opposite end from the first end. Like the second port 902, the fourth port 905 is connected to the bypass path 44.

[0095] The valve body 940 divides the inside of the cylindrical casing into a first end side and a second end side, and is biased from the second end side towards the first end side by a mechanical spring 950.

[0096] The upper diagram in Figure 5 shows the state where the electric motor 5 is rotating at a high speed. The upper diagram in Figure 5 corresponds to the upper diagram in Figure 4. When the rotation speed of the electric motor 5 is high, as described above, the discharge pressure of the boost device 8 increases, and the valve body 940 is pushed toward the second end. The switching valve 900 connects the first port 901 and the discharge port 903, and closes the second port 902. In other words, the bypass passage 44 is effectively closed.

[0097] The lower diagram in Figure 5 shows the state where the rotational speed of the electric motor 5 is low. The lower diagram in Figure 5 corresponds to the lower diagram in Figure 4. When the discharge pressure of the boosting device 8 is low, as described above, the valve body 940 is pushed toward the first end by the pressure of the reservoir 6. The switching valve 900 connects the second port 902 and the discharge port 903, and closes the first port 901. In other words, the second supply passage 43 is substantially closed.

[0098] The middle diagram in Figure 5 shows the intermediate state. The valve body 940 receives pressure from the third port 904 and the fourth port 905, respectively, and sets the opening of the first port 901 to an intermediate position, as well as the opening of the second port 902 to an intermediate position. Both the hydraulic fluid pressurized by the booster device 8 and the hydraulic fluid bypassed by the booster device 8 are sent to the main pump 7 (see solid arrow). The position of the valve body 940 is determined according to the difference between the discharge pressure of the booster device 8 and the pressure of the reservoir 6. By providing an intermediate state, the closed fluid system can achieve stable operation by reducing the transient response of the valve body 940 position.

[0099] Furthermore, since the switching valve 900 has a mechanical structure, it automatically changes the opening degree of the bypass passage 44 according to the difference between the discharge pressure of the boosting device 8 and the pressure of the reservoir 6. This ensures high reliability of the closed liquid system 100.

[0100] (Modification 3) Figure 6 shows a part of the closed liquid system 101 according to modification. The closed liquid system 101 opens and closes the bypass passage 44 in accordance with the pressure of the reservoir 6.

[0101] The switching valve 910 differs from the switching valve 90 in Figure 4. The first port 91 and the second port 92 of the switching valve 910 each open to the side of the switching valve 910. The first port 91 is connected to the discharge side of the boost device 8. The second port 92 is connected to the bypass path 44.

[0102] The first end of the switching valve 910 has an opening. A mechanical spring 95 is housed in a chamber 97 that is in communication with the atmosphere through the opening. The spring 95 biases the valve body 94 toward the second end.

[0103] The fourth port 96 opens at the second end of the casing. Like the second port 92, the fourth port 96 is connected to the bypass path 44.

[0104] The upper diagram in Figure 6 shows the state where the pressure in reservoir 6 is low (i.e., the gauge pressure is low). Because the pressure in reservoir 6 is low, if hydraulic fluid were supplied directly from reservoir 6 to the main pump 7, cavitation would easily occur at the suction section of the main pump 7. The switching valve 910 automatically switches so that the boosting device 8 boosts the hydraulic fluid. In other words, the valve body 94 is pushed by the spring 95 and changes position, closing the second port 92. The bypass passage 44 is effectively closed.

[0105] Furthermore, the valve body 94 connects the first port 91 and the discharge port 93. Since the hydraulic fluid pressurized by the pressurizing device 8 is supplied to the main pump 7 through the switching valve 910, the occurrence of cavitation in the suction section of the main pump 7 is suppressed. The switching valve 910 also functions as a check valve to prevent backflow from the second supply passage 43 to the bypass passage 44.

[0106] The lower diagram in Figure 6 shows the state where the pressure in reservoir 6 is high. When the pressure in reservoir 6 is high, cavitation is less likely to occur at the suction section of main pump 7, even if hydraulic fluid is supplied directly from reservoir 6 to main pump 7. By omitting the supply of hydraulic fluid by the pressure boosting device 8, the overall efficiency of the closed liquid system 100 is improved.

[0107] When the pressure in reservoir 6 is high, the pressure on the fourth port 96 side of the switching valve 910 becomes relatively higher, and the valve body 94 is pushed toward the first end.

[0108] The switching valve 910 connects the second port 92 and the discharge port 93, and closes the first port 91. In other words, the second supply passage 43 is effectively closed. Relatively high-pressure hydraulic fluid from the reservoir 6 is supplied to the main pump 7 through the switching valve 910. Cavitation at the suction section of the main pump 7 is suppressed. Since only the main pump 7 pressurizes the liquid and supply by the pressurizing device 8 is omitted, the efficiency of the entire closed liquid system 100 is increased. In this case, the non-positive displacement pump of the pressurizing device 8 continues to rotate without discharging hydraulic fluid.

[0109] Furthermore, since the housing chamber 97 containing the spring 95 is in communication with the atmosphere, the spring 95 can extend even after it has been compressed, as shown in the lower diagram of Figure 6.

[0110] Furthermore, the switching valve 910 has a mechanical structure and automatically opens and closes the bypass passage 44 in accordance with the pressure of the reservoir 6. This ensures high reliability of the closed liquid system 101.

[0111] (Modification 4) Figure 7 shows a part of the closed liquid system 102 according to modification. Compared with the liquid system 101 in Figure 6, the liquid system 102 aims to stabilize the switching of operations.

[0112] The switching valve 910 does not have a second port 92. Similar to the switching valve 910 in Figure 6, the switching valve 910 has a first port 91, a discharge port 93, and a fourth port 96. The switching valve 910 also has a valve body 94, a mechanical spring 95, and a containment chamber 97 that communicates with the atmosphere.

[0113] The bypass path 44 branches off and connects to the fourth port 96, as well as to the suction port 72 of the main pump 7. A check valve 98 is located in the middle of the bypass path 44. The check valve 98 prevents backflow from the second supply path 43 to the reservoir 6.

[0114] The upper diagram of Figure 7 shows the state where the pressure in the reservoir 6 is low. The valve body 94 moves when pushed by the spring 95, connecting the first port 91 and the discharge port 93. The hydraulic fluid, pressurized by the pressurizing device 8, is supplied to the main pump 7 through the switching valve 910, thereby suppressing the occurrence of cavitation in the suction section of the main pump 7. At this time, the check valve 98 of the bypass passage 44 prevents backflow from the second supply passage 43 to the bypass passage 44.

[0115] The lower diagram in Figure 7 shows the state when the pressure in reservoir 6 is high. When the pressure in reservoir 6 is high, the pressure on the fourth port 96 side of the switching valve 910 becomes relatively higher, and the valve body 94 is pushed toward the first end side. The switching valve 910 closes the first port 91 and the discharge port 93.

[0116] The relatively high-pressure hydraulic fluid from the reservoir 6 is supplied to the main pump 7 through the bypass passage 44. This suppresses the occurrence of cavitation at the suction section of the main pump 7.

[0117] In the closed liquid system 102, the hydraulic fluid supplied to the main pump 7 via the bypass passage 44 does not pass through the switching valve 910, thus suppressing chattering of the switching valve 910 associated with the switching operation of the closed liquid system 102.

[0118] (Other variations) Note that the switching valves 90, 900, and 910 are not limited to valves that have a mechanical structure and switch automatically in response to the pressure of the reservoir 6, or the pressure of the reservoir 6 and the discharge pressure of the boosting device 8. The switching valve may also be a control valve that is switched and controlled by the controller 3.

[0119] The reservoir 6 is not limited to a structure that pressurizes the hydraulic fluid in the storage chamber 61 with a gas-filled accumulator chamber 62. The reservoir may also have a structure that pressurizes the hydraulic fluid in the storage chamber 61 using, for example, a mechanical spring. Even a reservoir using a spring can be made smaller than a conventional reservoir in the closed liquid system 1 disclosed herein.

[0120] The closed liquid system 1 disclosed herein is not limited to an EHA system mounted on an aircraft. The closed liquid system 1 may be applied to a closed liquid system mounted on an aircraft that supplies coolant to an object. Furthermore, the closed liquid system 1 is not limited to a system mounted on an aircraft. The closed liquid system 1 may be applied to a closed liquid system in, for example, an industrial machine. Moreover, the closed liquid system 1 is not limited to a hydraulic system, but may be a hydraulic system.

[0121] 1 Closed liquid system 10 Hydraulic circuit (circulation circuit) 21 Aileron actuator (object) 22 Elevator actuator (object) 23 Rudder actuator (object) 24 Flap actuator (object) 25 Slat actuator (object) 26 Landing gear actuator (object) 41 Supply line 42 Return line 43 Second supply line 44 Bypass line 5 Electric motor (prime mover) 6 Reservoir 61 Storage chamber 62 Accumulator chamber 7 Main pump (positive displacement pump) 8 Booster device 81 Booster device 82 Booster device 83 Booster device 84 Booster device 85 Booster device 86 Centrifugal pump (non-positive displacement pump) 87 Inducer (non-positive displacement pump) 88 Diffuser 90 Switching valve 900 Switching valve 910 Switching valve 98 Check valve

Claims

1. A closed liquid system comprising: a positive displacement pump connected to an object via a supply path and supplying liquid to the object; a reservoir connected to the object via a return path, which pressurizes the stored liquid; and a pressurizing device located in a second supply path connecting the positive displacement pump and the reservoir, and having a non-positive displacement pump that pressurizes the pressurized liquid from the reservoir and sends it to the positive displacement pump.

2. The closed liquid system according to claim 1, further comprising a bypass path that bypasses the boosting device and connects the reservoir to the positive displacement pump, the bypass path being openable and closable.

3. A closed liquid system according to claim 2, wherein the bypass is opened and closed according to the state of the closed liquid system.

4. A closed liquid system according to claim 3, wherein the bypass path is opened and closed in accordance with the difference between the discharge pressure of the booster device and the pressure of the reservoir.

5. The closed liquid system according to claim 4, further comprising a check valve located in the bypass passage and preventing backflow from the second supply passage to the reservoir.

6. A closed liquid system according to claim 4, further comprising a switching valve that opens the bypass passage and closes the second supply passage when the difference between the discharge pressure of the booster device and the pressure of the reservoir exceeds a predetermined value, and closes the bypass passage and opens the second supply passage when the difference between the discharge pressure of the booster device and the pressure of the reservoir falls below the predetermined value.

7. A closed liquid system according to claim 3, wherein the bypass is opened and closed in accordance with the pressure of the reservoir.

8. A closed liquid system according to claim 2, wherein the opening of the bypass passage changes according to the state of the closed liquid system.

9. A closed liquid system according to any one of claims 1 to 8, wherein the positive displacement pump, the reservoir, the boosting device, the supply path, the return path, and the second supply path constitute a closed circulation circuit isolated from the outside.

10. A closed liquid system according to any one of claims 1 to 9, wherein the reservoir has a storage chamber and a pressure accumulation chamber, and pressurizes the liquid in the storage chamber by the pressure of a gas filled in the pressure accumulation chamber.

11. A closed liquid system according to any one of claims 1 to 10, wherein the boosting device comprises one or more non-positive displacement pumps.

12. The closed liquid system according to claim 11, wherein the boosting device comprises at least one of a centrifugal pump and an inducer.

13. The closed liquid system according to claim 12, wherein the boosting device comprises the centrifugal pump and the inducer provided at the suction portion of the centrifugal pump.

14. A closed liquid system according to any one of claims 1 to 10, wherein the boosting device comprises a centrifugal pump and a diffuser provided at the discharge portion of the centrifugal pump.

15. A closed liquid system according to any one of claims 1 to 10, wherein the boosting device comprises a centrifugal pump, an inducer provided at the suction portion of the centrifugal pump, and a diffuser provided at the discharge portion of the centrifugal pump.

16. A closed liquid system according to any one of claims 1 to 15, further comprising a prime mover connected to both the positive displacement pump and the booster device, and for driving each of the positive displacement pump and the booster device.

17. A closed liquid system according to any one of claims 1 to 16, wherein the closed liquid system is mounted on an aircraft.

18. The enclosed liquid system according to claim 17, wherein the object includes at least one of the aircraft's flight control actuator and takeoff and landing actuator, and the positive displacement pump supplies hydraulic fluid to the actuator to power the actuator.

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