GB2588596A

GB2588596A - Control system for aircraft

Info

Publication number: GB2588596A
Application number: GB1915217.2A
Authority: GB
Inventors: Bidmead Ashley; Becher Florian
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-10-21
Filing date: 2019-10-21
Publication date: 2021-05-05
Also published as: GB201915217D0

Abstract

A control system 100 for an aircraft 1 having a hydraulic system 200 comprises a controller 110 that is configured to determine whether one or more predetermined criteria have been met during a flight of the aircraft 1. A determination that the one or more criteria have been met is indicative that a change, or rate of change, in temperature of a component of the hydraulic system 200 is within a predetermined range and permit control of one or more characteristics of the hydraulic system 200 on the basis of the determination. The one or more characteristics may comprise fluid pressure 233 in a hydraulic accumulator 230 or may comprise the pre-charge gas pressure 232 in the accumulator.

Description

CO ROI, SYSTEM FOR AIRCRAFT

TECHNIC-FIELD

[00011 The present invention relates to control systems for aircraft comprising hydraulic systems, and to methods of controlling hydraulic systems ofaircraft.

BACKGROUND

100021 Hydraulic systems on aircraft, such as hydraulic braking systems, typically comprise at least one hydraulic accumulator. The hydraulic accumulator absorbs, releases and stores energy in the hydraulic system. The hydraulic accumulator may store and release energy for operating certain components of the hydraulic system, such as brake actuators of a hydraulic braking system, or door actuators of a landing gear bay door, for example.

[0003] Genera]ly, an amount of hydraulic fluid in at least a pait of the hydraulic y stem may reduce over time, for instance due to small leaks, or as hydraulic fluid is transferred between different parts of the hydraulic system. For example, hydraulic fluid may be transferred from an auxiliary, or emergency, line of the hydraulic system to a main line of the hydraulic system. The fluid may then be prevented from returning to the auxiliary hue, for instance by a non-return valve, thereby leading to a reduced amount of fluid in the auxiliary line of the hydraulic system.

[0004] Conventionally, the amount of fluid in the hydraulic system, or an amount of energy stored in the hydraulic accumulator, may be determined by detecting a pressure of the fluid in the hydraulic system. Fluid may be added to the hydraulic system, such as to the hydraulic accumulator, if the amount of hydraulic fluid drops below a threshold value. Adding fluid to the hydraulic system or components thereof may be referred to as refilling the hydraulic system or components thereof If a rate of reduction of hydraulic fluid in the system is high, this may indicate a thult in the hydraulic system. There is a need for a system for reliably determining an amount of fluid in the hydraulic system or an amount of energy stored in the hydraulic accumulator.

SUMMARY

[0005] A first aspect of the present invention provides a control system for an airc the aircraft comprising a hydraulic system, the control system comprising a controller that is configured to: determine whether one or more predetermined criteria have been met during a flight of the aircraft, wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of a component of the hydraulic system is within a predetermined range; and permit control of one or more characteristics of the hydraulic system on the basis of the determination.

[0006] Optionally, tile controller is configured to receive at least one signal comprising information representative of at least one characteristic of the aircraft, and the controller is configured to determine thether the one or more criteria have been met on the basis of the at least one signal.

[0007] Optionally, the at least one characteristic of the aircraft comprises a status relating to the: flight of the aircraft comprising any one or more of: an elapsed duration of the flight; an elapsed duration of a phase of the flight; an estimated time to landing; and a location of the aircraft.

[0008] Optionally, the at least one characteristic of the aircraft comprises a status of the aircraft, the status comprising any one of more of: an ambient temperature internal or external to the aircraft; an ambient pressure internal or external to the aircraft; a temperature of a hydraulic fluid in the hydraulic system; an airspeed an altitude; and a configuration of the aircraft.

[0009] Optionally, the component of the hydraulic system comprises at least one hydraulic accumulator, and a determination that the one or more criteria have been met is indicative that a change or rate of change of ure of gas in the hydraulic accumulator is within the predetermined range.

[0010] Optionally, the change or rate of change in temperature being within the predetermined range is indicative that a gas temperature of gas in the hydraulic accumulator has substantially equilibrated.

[0011] 0 onally, the controller is configured to control a pressure in the component of the hydraulic system on the basis of the determination.

[0012] Optionally, he controller is configured to detenriine whethera pressure in the component of the hydraulic system is at or below a predefined threshold, and cause initiation of a procedure to refill the hydraulic system, on the basis of the detemination that the pressure in the component of the hydraulic system is at or below the predefined threshold.

[0013] Optionally, the controller is configured to determine whether a change or rate of change of pressure in the component of the hydraulic system is at or above a predefined threshold, and cause initiation of a pmcedure to refill the hydraulic system, on the basis of the determination that the change or rate of change of pressure in the component of the hydraulic system is at or above the predefined threshold.

[0014] Opttonally" the control systen is configured to carry out the procedure to refill the hydraulic system.

10015] Optionally, the hydraulic s stem is a iraulic braking system o. e aircraft.

[0016] A second aspect of the present invention provides a method of controlling a hydraulic system of an aircraft, the method comprising: receiving at least one signal during a flight of the aircraft; determining whether one or more predetermined criteria have been met" on the basis of the at least one signal, wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of a component of the hydraulic system is within a predetermined range; and initiating control of one or more characteristics of the hydraulic system on the basis of the determination.

[0017] 0 tic nally" the method of controlling the hydraulic system of the aircraft is a method of operating a controller of a. control system ofthe aircraft to control the hydraulic system of the aircraft, and the method comprises the controller performing the recited actions.

[0018] Optionally, the at least one signal comprises information representative of at least one characteristic of the aircraft.

[0019] Optionally, the at least one characteristic of the aircraft comprises a status relating to the flight of the aircraft comprising any one or more of: an elapsed duration of the flight; an elapsed duration of a phase of the flight; an estimated time to landing; and a location of the aircraft.

[0020] Optionally, the at least one characteristic of the aircraft comprises a status of the aircraft comprising any one of more of an ambient temperature internal or external to the aircraft; an ambient pressure internal or external -to the aircraft; a temperature of a hydraulic fluid in the hydraulic system; an airspeed; an altitude; and a configuration of the aircraft.

[0021] Optionally, the component of the hydraulic system comprises at least one hydraulic accumulator, and a determination that the one or more criteria have been met is indicative that a change or rate of change of temperature of gas in the hydraulic accumulator is within the predetenuined range.

[0022] Optionally, the change or rate of change in temperature being within the predetermined range is indicative that a gas temperature of gas in the hydraulic accumulator has substantially equilibrated.

[0023] Optionally,the method comprises controlling a pressure in the component of the hydraulic system on the basis of the determination.

[0024] Optionally. the method comprises determining whether a pressure in the component of the hydraulic system is at or below a predefined threshold and causing refilling of the component of the hydraulic system after determining that the pressure in the hydraulic system is at or below the predefined threshold.

[0025] Optionally, the method comprises detemining whether a change or rate of range of pressure in the component ofthe hydraulic system is at or above a. predefined threshold, and causing refilling of the hydraulic system, on the basis of the determination that the change or rate of change of pressure in the component of the hydraulic system is at or above the predefined threshold.

[0026] Optionally, the at least one characteristic of the aircraft comprises a status of the flight of the aircraft, and the method comprises: determining a refill rate threshold on the basis of the status of the flight; monitoring a rate of refills of the hydraulic system during the flight of the aircraft; determining whether the rate of refills exceeds the refill rate threshold; and causing at least one action to be taken on determination that the rate of refills exceeds the refill rate threshold.

[0027] Optionally, the at least one action to be taken comprises any one or more of causing a warning device to issue a warning; recording data indicative ofthe rate of refills; and recording data indicative of the rate of refills exceeding the refill rate threshold.

[0028] Optionally, the warning may be issued to flight crew in a cockpit.

[0029] A third aspect of the present invention provides a non-transitory computer-readable storage medium storing instructions that, if executed by a controller of a control system of an aircraft, cause the controller to carry out the method according to the second aspect of the present invention.

[0030] A fourth aspect of the present invention provides an aircraft system for an aircraft, the aircraft system comprising: a hydraulic system comprising a hydraulic system controller that is configured to receive an instruction, and to control a pressure of hydraulic fluid in a component of the hydraulic system on the basis of the instruction; and an aircraft control system comprising a control system controller that is configured to: receive at least one signal during flight of the aircraft; determine whether one or more criteria have been met, on the basis ofthe at least one signal, wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of the component of the hydraulic system is within a predetermined ramie; and send the instruction to the hydraulic system controller, on the basis of the determination.

[0031] Optionally, the component of the hydraulic system comprises a hydraulic accumulator, and the hydraulic system controller is configured to control the pressure of the hydraulic fluid in the hydraulic accumulator to control an amount of hydraulic fluid in the hydraulic accumulator, and/or to control an amount of energy stored in the hydraulic accumulator.

[0032] Optionally, a determination that the one or more criteria have been met is indicative change or rate of change of temperature of gas in the hydraulic accumulator is within the predetermined range.

[0033] Optionally, the change or rate of change of temperature being within the predetermined range is indicative that the temperature of the gas in the hydraulic accumulator has substantially equilibrated, [0034] Optionally, the at least one characteristic of the aircraft comprises a status relating to the flight of the aircraft comprising any one or more of: an elapsed duration of the flight; an elapsed duration of a phase of the flight; an estimated time to landing; and a location oldie aircraft.

[0035] Optionally, the at least one characteristic of the aircraft comprises a status of the aircraft, the status comprising any one of more of: an ambient temperature internal or external to the aircraft; an ambient pressure internal or external to the aircraft; a temperature of a hydraulic fluid in the hydraulic system; an airspeed; an altitude; and a configuration of the aircraft.

[0036] Optionally, the aircraft system comprises a sensor system configured to sense at least one characteristic of the aircraft and to send the at least one signal to the controller, wherein the signal comprises information representative of at least one aircraft characteristic.

[0037] Optionally, the al is received from a remo so,a, outside the aircraft [0038] Optionally, the hydraulic system controller is configured, on receipt of the at least one instruction; to: interrogate a parameter of the component of the hydraulic system; determine that the parameter has reached a predefined threshold; and cause refilling of the component of the hydraulic system on the basis of the determination that the parameter has reached the predefined threshold.

[0039] Optionally, the parameter is a. pressure or a change or rate of change in pressure.

[00401 Optionally, the hydraulic system is ic braking system of the aircraft.

[0041] A fifth aspect of the present invention provides an aircraft system comprising a hydraulic system, a hydraulic system controller, and an aircraft system controller, the hydraulic system controller configured to: cause interrogation of one or more characteristics of the hydraulic system; determine when the one or more characteristics reach a predefined threshold; and cause refilling of the hydraulic system with hydraulic fluid on the basis of the determination. The controller is configured to: determine whether one or more criteria have been met during a flight., wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of a component of the hydraulic system is within a. predetermined range; and inhibit operation of the hydraulic system controller to cause the refilling until the comrolle determines that the one or more criteria have been met during the flight.

[0042] A sixth aspect of the present invention provides an aircraft comprising the control system according to the first aspect or the aircraft system according to the fourth or fifth aspects of the present invention, or comprising the non-transitory computer-readable storage medium according to the third aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[00431 Embodiments of the invention will now be described, by way of exa only, with reference to the accompanying: drawings, in which: [00441 Figure 1 shows a schematic view of an example of an aircraftsystem: [00451 Figure 2 shows a schematic view of an example he accumulator of the aircraft system of Figure I; [00461 Figure 3 is a flow diagram showing an example of a method of a g characteristic of the hydraulic accumulator of Figure 2; [00471 Figure 4 shows a schematic diagram of an example of a riontransitory compu readable storage medium; and [00481 Figure 5 is a schematic front vicw of an example of an aircraft.

DETAILED DESCRIPTION

[00491 Aircraft and aircraft systems are typically exposed to a range of temperatures, particularly but not exclusively during a flight of the aircraft. Such exposure may cause a variation in a gas temperature of gas in the hydraulic accumulator, which may affect a pressure of hydraulic fluid in the hydraulic system This presents challenges in accurately/ determining and reliably controlling characteristics of the hydraulic system, such as an amount of fluid in the hydraulic system, or an energy stored in a hydraulic accumulator of the hydraulic system. Examples described herein are concerned with providing improved systems and methods that address those issues.

[0050] Figure 1 shows a schematic view of an aircraft system 10 according to an example. Broadly-speaking, the aircraft system 10 comprises a control system 100, a sensor system 300 that is communicatively connected to a control system controller 110 of the control system 100, a hydraulic system 200 comprising a hydraulic system controller 210 that is communicatively connected to the control system controller 110, a warning device 410 and a cockpit flight control 420 located in a cockpit 400 of the aircraft, and a storage 600. In some examples herein, the control system controller 110 may be referred to as an aircraft system controller 110, [0051] The control system controller 110 n ake any suitable form. The control system controller 110 may comprise a processor, such as a microprocessor. Broadly speaking, the control system controller 110 is configured to determine whether one or more predetermined criteria have been met during a flight of the aircraft, wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of a. component of the hydraulic system 200 is within a predetermined range. The control system controller 110 is further configured to permit control of one or more characteristics of the hydraulic system 200 on the basis of the determination.

[0052] The hydraulic system 200 is a hydraulic braking system for braking the yyheels of at least one landing gear of the aircraft. In other examples, the hydraulic system 200 may be any other hydraulic system of the aircraft, such as a hydraulic system for extending or trading a landing gear of the aircraft, a hydraulic system for opening or closing a. landing gear bay door of the aircraft, or a hydraulic system for operating control surfaces of the aircraft. The hydraulic system 200 comprises hydraulic fluid, a hydraulic accumulator 220 and at least one or a combination of a valve 240; an actuator 250; a pump 260; a reservoir 270; and a filter 280. The hydraulic system 200 may comprise any other components typically found in a hydraulic system of an aircraft. In some examples, components of the hydraulic system 200, such a valve 240 or an actuator 25accurnu0, arc operated electro-mechanically. Power may be supplied to the hydraulic system 200 from a power supply (not shown), such as an engine-driven power supply, or an energy storage device, such as a battery.

100531 The sensor system 300 in this example corn sensor arrangements 310 and 320. In other examples, one or both of the sensor arrangements 310 and 320 may be omitted. Each oldie sensor arrangements 310 and 320, and thus the sensor system 300 as a whole, is configured -to sense at least one characteristic of the aircraft. In some examples, the controller 100 is configured to receive the at least one signal comprising information representative of the at least one characteristic of the aircraft. In some examples, the sensor system 300 is configured to send the at least one signal to the controller 100.

[00541 More specifically, in this example, the sensor system 300 comprises at least one flight status sensor 310 that is configured to sense a status of the flight of the aircraft. The at least one flight status sensor 310 may he configured to sense any one or more of a geographical location of the aircraft; an elapsed duration of the flight; an elapsed duration of a phase of the flight, such as an elapsed duration of a cruise phase of the flight: an estimated time to landing; and a flight heading, fin example. Therefore, the at least one flight status sensor 310 may comprise a timer, a data logger, a satellite 'based radio navigation system (such as the Global Positioning System, or "UPS), a RADAR system, or the like, [0055l The sensor arrangement 320 comprises at least one aircraft status sensor 320 that is configured to sense a status of the aircraft. The at least one aircraft status sensor 320 may be configured to sense any one or more of an ambient temperature intemal or external to the aircraft; an ambient pressure internal or external to the aircraft; a temperature of hydraulic fluid in the hydraulic system 200; a pressure of hydraulic fluid in the hydraulic system 200 an airspeed; an altitude; and a configuration of the aircraft, for exainple. Therefore, the at least one aircraft status sensor 320 may comprise any suitable temperature sensor, pressure sensor, airspeed sensor, altitude sensor, or the like. For example, the at least one aircraft status sensor may comprise a thermometer, a thermistot, a thermocouple, a Pilot tube, a pressure altimeter, a some altimeter, a radio altimeter, a RADAR altimeter, a satellite-based radio navigation system, a data logger, or the like.

100561 The configuration of the aircraft may comprise a status or a position of a component of the aircraft. Therefore, the at least one aircraft status sensor 320 may comprise any sensor suitable for sensing a configuration of a flap, aileron, spoiler, landing gear, autopilot, or the like. Alternatively, or in addition, the at least one aircraft status sensor may be configured to detect a configuration signal issued by a cockpit flight control 420 located in the cockpit 400 of the aircraft, the configuration signal indicative of a desired or achieved configuration of a component oldie aircraft.

[00571 Given the teaching of the present disclosure" the skilled person will be able to identifi, other relevant aircraft characteristic sensors, the outputs of which are suitable for use with the present disclosure. It will be understood that, in some examples, the at least one signal may be received by a receiver (not shown) of the aircraft system 10 front a location remote from the aircraft, and the receiver may be configured to send the at least one signal to the controller 100. For example, the at least one signal may lac received front an air traffic control system, a satellite system, another aircraft, or any other air-, space-or ground-based system. In this way, the aircraft may require fewer sensors andlor reduced processing power. Moreover, receiving the at least one signal from a ground-based system, for instance, near to an airport may provide an accurate determination of aircraft characteristics, such as a location of the aircraft, or a proximity of the aircraft to a runway. The ground-based system may' be a nautical system.

[00581 The warning device 410 is a device that is configured to emit a warning to flight crew in the cockpit 400. The warning may be an audible warning such as a beep, ring or buzz, and/or a visual wanting such as a flashing light or illuminated indicia, and/or a. tactile warning such as a vibration The purpose of the warning device 410 will be described below. In some other examples, the warning device 410 is omitted. Ii

[00591 The cockpit flight control 420 is a control that s operable by a member of the flight crew to send a signal to the controller TOO, or to any other controller of the aircraft. It may, for example, comprise a lever, a button, a different type of user-movable device, touchpad, a touchsereen, a gesture-operable device, a voice-operable device, or any combination thereof In some other examples, the cockpit flight control 420 is omitted.

[0060] Figure 2 shows a schematic diagram of the hydraulic accumulator 230. The hydraulic accumulator 230 is a scaled hydraulic accumulator 230 comprising a steel body 231. The body 231 may be made of any other suitable material, such as a -ferrous material or non-ferrous material, in other examples. The hydraulic accumulator 230 comprises a piston 234 (although the piston 234 could be replaced by a bladder, diaphragm or other fluid separating device), with hydraulic -fluid 233 on one side of the piston 234 and compressed gas 232 on the other side of the piston 234. The hydraulic accumulator 230 comprises a connector 235 for fluid connection of the one side of the piston 234 with a fluid line of the hydraulic system 200, The pressure sensor 221 is connected to the connector 235.

[0061] In the present example, the hydraulic accumulator 230 is pre-charged with a volume of gas 232 and sealed so that the gas cannot leak from the hydraulic accumulator 230. The hydraulic accumulator 230 may be sealed by welding at least a part of the body 231 of the hydraulic accumulator 230. In the present example, except for the connector 235, there are no connections or Nits to the interior of the hydraulic accumulator 230. For instance, there are no ports for refilling or replacing the gas 232 in the hydraulic accumulator 230, or for detecting certain characteristics of the hydraulic accumulator 230 such as a temperature of the gas 232 or a. position of the piston 2.34. In this way, a risk of compromising the integrity of the hydraulic accumulator may be reduced. In this way, the present invention avoids the need for an intrusive sensor, such as a linear variable differential transformer (LEATT), for sensing a position of the piston 234, for example. An intrusive sensor would wine an opening to be provided in the body 231 for the sensor to pass through. The hydraulic fluid 233 and/or the gas 232 may escape through such an opening. Additionally, an intrusive sensor may comprise a portion external to the accumulator which may be caught or damaged, for example during a maintenance procedure. By avoiding the need for an intrusive sensor, a risk of compromising the integrity of the hydraulic accumulator 210 may be reduced.

100621 Returning now to Figure 1, the hydraulic system 200 further comprises a hydraulic sensor system 220 for sensing one or more characteristics of the hydraulic system 200. In some examples, the one or more characteristics comprises a fluid pressure of the hydraulic fluid 233 and/or the gas 232 in the hydraulic accumulator 230. In other examples, the one OT more characteristics comprises a fluid temperature of the hydraulic fluid 233 in the hydraulic accumulator 230, or a body temperature of the body 231 of the hydraulic accumulator 230. The hydraulic sensor system 220 of the present example comprises a pressure sensor 211 configured to sense the fluid pressure of fluid in the hydraulic system 200. The fluid pressure may be a fluid pressure of the hydraulic fluid 233 in the hydraulic accumulator 230. In some examples, the hydraulic sensor system 220 comprises a temperature sensor 222 for sensing the body temperature of the body 231 of the hydraulic accumulator 230. The sensor system 220 may be configured to send a signal comprising information representative of the one or more characteristics of the hydraulic system 200 to the hydraulic system controller 210.

[0063] The hydrauhc system controller 210 of the present example is configured to control the one or more characteristics of hydraulic fluid in the hydraulic system 200. In some examples, the one or more characteristics comprise the fluid pressure of hydraulic fluid 233 or gas 232 in the hydraulic accumulator 230, and the hydraulic system controller 0 is configured to control the fluid pressure of the hydraulic fluid 233 or gas 232. This may be to control a level of hydraulic fluid in the hydraulic system 200 in general or in the hydraulic accumulator 230 specifically. In some examples, the controlling the pressure of hydraulic fluid 233 in the hydraulic accumulator 230 may be to control an amount of energy stored in the hydraulic accumulator 230.

10064] in the present example, the hydraulic system controller 21.0 is configured to cause interrogation of the one or more characteristics of the hydraulic system, such as the fluid pressure of fluid in the hydraulic system 200, an amount of fluid in the hydraulic system, and/or an energy stored in a hydraulic accumulator of the hydraulic system. The controller 210 is further configured to determine yhen the one or more characteristics reach a predefined threshold. If the hydraulic system controller 210 determines, for instance, that the fluid pressure is belmix the predefined threshold, the hydraulic system controller 210 may cause initiation of a procedure to refill hydraulic fluid in the hydraulic system 200, such as the hydraulic fluid 233 in the hydraulic accumulator 230. In other words, the hydraulic system controller may cause refilling of a component of the hydraulic s:Stellil 200 after determining that the pressure in the hydraulic system 200 is at or below the predefined threshold. In some examples, the controller may cause refillirw, of the component of the hydraulic system 200 after determining that a change or rate of change of pressure in the hydraulic system 200 is at or above a predefined threshold. In some examples, a change or rate of change in pressure is a reduction or rate of reduction in pressure.

[0065] In some examples, the hydraulic system controller 210 may cause refilling of hydraulic fluid in the hydraulic accumulator 230 by causing operation of the pump 260 to pump fluid from the reservoir 270 into the hydraulic accumulator 230, optionally via the filter 280. In other examples, on a positive determination that the fluid pressure is below the predetemnned threshold value, the hydraulic system controller 210 may cause operation of the valve 230 to re-direct fluid from a main fluid line of the hydraulic system 200 into an auxiliary fluid line of the hydraulic system 200 to which the hydraulic accumulator 230 is fluidically coupled.

100661 Tt will be understood that the hydraulic controller 210 may cause refilling of the hydraulic system 200 and/or components of the hydraulic system 200, such as the hydraulic accumulator 230, by any other appropriate mechanism. TT will also be understood that, in sonic examples, the refilling the hydraulic system 200 or components thereof comprises adding fluid to an already partially full component. In some examples, fluid is added to the hydraulic system 200 or components thereof until an amount of fluid therein reaches a predefined upper threshold. The upper threshold may be lower than a capacity of the hydraulic system 200 or components thereof [0067] The hydraulic system controller 210 may further be configured to receive an instruction from the control system controller 110. In some examples, the hydraulic system controller 210 is configured to control the pressure of the hydraulic fluid in the hydraulic system on the basis of the instruction. In some examples, operation of the hydraulic system controller 210 to refill the hydraulic system is inhibited until the hydraulic system controller 210 receives the instruction from the control system controller 110. In other words, the control system controller 110 is configured to permit control of the one or more characteristics of the hydraulic system [0068] As noted above, the control system controller 110 is configured to permit the control of the one or more characteristics on the basis of a determination that one or more criteria have been met during a flight of the aircraft. The determination that the one or more criteria, have been net is indicative that a change or rate of change in temperature of a component of the hydraulic system is within a predetermined range In the present example, the component of the hydraulic system 200 is the accumulator 230, and the change or rate of change in temperature is a. change or rate of change in temperature of the gas 232 in the hydraulic accumulator 230, The change or rate of change in temperature being within the predetermined range may be indicative that the gas temperature of the gas 232 in the accumulator has substantially equilibrated. That is, in sonic examples, a determination that the one or more criteria have been met during a flight is indicative that the gas temperature of the gas 232 in the hydraulic accumulator 230 is substantially constant or is fluctuating to only a small degree, such as less than 10%, less than 5%, less than 2% or less than 1%.

100691 As discussed above, a gas pressure of the, gas 232, and -therefore a pressure of the hydraulic fluid 233 in the hydraulic accumulator 230 may be sensitive to changes in a gas temperature of the gas 232. For example, as an aircraft climbs in altitude, an ambient temperature may drop, leading to a reduction in the gas temperature of the gas 232. The gas temperature of a perfect gas is directly proportional to the pressure of the gas, in tIje relationship JV= WE Here, P is the gas pressure, V is a volume of the gas. R is a gas constant, and T is the gas temperature. 'The gas 232 in the hydraulic accumulator 230 may be considered a perfect gas. Therefore_ a reduction in. the gas temperature of the gas 232 as the aircraft climbs in altitude may result in a reduction in the gas pressure of the gas 232, and therefore also a reduction in the pressure of the hydraulic fluid 233, [0070] Such a reduction in pressure of the gas pressure of the gas 232 and the pressure of the hydraulic fluid 233 may cause the hydraulic system controller 210 to prematurely deteniiine that the pressure has dropped below the predefined pressure threshold. In other words, the hydraulic system may erroneously determine that an amount of fluid in the hydraulic accumulator 230 has reduced, The hydraulic system controller 210 may then cause a refilling of the hydraulic system 200 or components thereof on the basis of the determination, even when such a refill is not required.

[0071] The control system controller 110 may be configured to inhibit the operation of the hydraulic control system to cause the refilling until the control system controller 110 determines that the one or more criteria have been met during a flight. That is, the control system controller 110 may be configured to permit control of the one or more characteristics of the hydraulic system, such as pressure, only when it is determined that the one or more criteria have been met during the flight_ This may be by sending an instruction to the hydraulic system controller:, as described above.

[0072] The control system controller 110 may be configured to determine whether the one or more criteria, have been met on the basis of at least one signal received by the control system controller 110 from the sensor system 300, for exampl-. The at least one signal _day comprise information representative of the at least one characteristic of the aircraft. In some examples, the least one characteristic of the aircraft is a status relating to the flight of the aircraft, for instance as sensed by the flight status sensor 210 described above. In this way, one criterion may be that the aircraft has been in a phase of the flight, such as a cruise phase, for a [predefined period of time, such as for 2 hours. The aircraft being in a cruise phase of the flight for the predefined period of time may be indicative that a gas temperature of the gas 232 hi the hydraulic accumulator 230 should have stabilised, and that a reduction in pressure detected by the hydraulic system controller 210 is indicative of a reduction in the amount of hydraulic fluid 233 in the hydraulic accumulator, as described above. In other examples, the one or more criteria may be any other criteria relating to a flight of the aircraft, such as an aircraft being a predefined period of time away from landing, such as one hour away from landing, or the like.

[0073] in some examples, the at least one characteristic of the aircraft is a status of the aircraft, for instance as sensed by the aircraft status sensor 220. hi this way, one criterion might be that a change or rate of change of ambient temperature in proximity to the hydraulic system 200 or components thereof' is within a predetermined range. This may indicate, for example, that the ambient temperature is relatively constant, and that the gas temperature of the gas 232 in the hydraulic accumulator 230 is unlikely to vary significantly. In other examples, the one or more criteria may be any other criteria relating to a status of the aircraft, such as the aircraft being above a predefined altitude for a given period of time, such as for 30 minutes, or the like.

[0074] In some exam ' s, the aircraft controller 100 is configured to cause the warning device 410 to issue a \yarning, when the aircraft controller 100 determines that the one or more predetermined criteria have been met during the flight of the aircraft. The warning can alert the flight crew to the initiation of control of the one or more characteristics of the hydraulic system. This may, for example, enable them to take sonic action in response to the initiation. In some examples, the warning may prompt flight crew to approve the initiation. For example, the flight crew may use the cockpit flight control 420 to send an approval signal to the control system controller 110, the approval signal indicative of an approval to cause the initiation of the control of one or more characteristics of the hydraulic system 200. The initiation may be prevented until such approval is given In other examples, no such warning(s) may be given.

[0075] in some examples, the hydraulic system 200 or components thereof may be refilled multiple times per flight, particularly if a duration or a distance of the flight is high. In some examples, the hydraulic system controller 210 is configured to determine a refill rate threshold on the basis of a status of the flight. In some examples, the hydraulic system controller monitors a rate of refills of the hydraulic system during the flight and determines whether the rate of refills exceeds the refill rate threshold. In some examples, the rate of refills is determined as a. number of refills during a flight, and the refill rate threshold is a threshold number of refills during the flight. The refill rate threshold may be determined based on a time nail landing of the aircraft, or a projected journey time, for example. In this way. a refill rate threshold may be larger for a longer flight. In some examples, the refill rate threshold is determined before the flight. In other examples, the refill rate threshold is determined during the flight, such as periodically during the flight, for instance to account for a diverted flight.

[0076] Tn some examples, the hydraulic system controller 210 is configured to cause at least one action to be taken on determination that the rate of refills exceeds the refill rate threshold. In some examples, the at least one action to be taken comprises any one or more of causing a warning device to issue a warning; recording data indicative of the rate of refills; and recording data indicative of the rate of refills exceeding the refill rate threshold. For example, the causing a warning device to issue a warning may comprise causing the warning device 410 to issue a warning, as described above. In some examples, recording data comprises storing data in the storage 600. The storage 600 may be any suitable computer-readable storage medium. In the present example, the data is stored in the storage 600 by the control system controller 110_ In other examples, the data is stored by the hydraulic system controller 210, [007 Figure 3 is a flow diagram showing an example of a method 800 of controlling a hydraulic system of all aircraft. In some examples, the method 800 is performed by a controller of a control system of the aircraft, such as the control system controller 110, so that the method is a method of operating a controller of a control system of the aircraft, such as the control system controller 110, to control the hydraulic system of the aircraft. The method 800 comprises: receiving 810 at least one signal during a flight oldie aircraft; determining 820 whether one or more predetermined criteria have been met, on the basis of the at least one signal, wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of a component of the hydraulic system is within a predetermined range; and initiating 830 control of one or more characteristics of the hydraulic system on the basis of the determination.

[0078] in some examples, the at least one signal comprises information representative of at least one characteristic of the aircraft, such as a status relating to the flight of the aircraft, or a status of the aircraft., as described above with reference to Figure 1. In some examples, the signal is received from sensors on the aircraft. In other examples, the signal is received from a location remote from the aircraft, such as air traffic control.

[0079] in some examples, the component of the hydraulic system comprises at least one hydraulic accumulator, such as hydraulic accumulator 230, and a determination that the one or more criteria have been met is indicative that a change or rate of change of temperature of gas in the hydraulic accumulator is within the predetermined range. In some examples, the initiating 830 control of the one m more characteristics comprises initiating.e Ling the control of a pressure or an amount of hydraulic fluid in the hydraulic accumulator.

[0080] In some examples, the method compr ses causing. a warning device to issue a warning, when the determining 820 results in a conclusion that the one or more predetermined criteria have been met h.: some examples, the causing 835 the warning device to issue the warning occurs before the initiating 830 control of the one or more characteristics of the hydraulic system. In other examples, the causing 835 the warning device to issue the warning occurs on or after the initiating 830 control of the one or more characteristics of the hydraulic system.

[0081] In some examples, the method comprises controlling the one or more characteristics of the hydraulic system by determining 840 whether a pressure in the component of the hydraulic system is at or below a. predefined threshold, or whether a change or rate of change of pressure in the hydraulic system is at or above a predefined threshold. In some examples, the method comprises controlling the one or more characteristics of the hydraulic system by causing 845 refilling of the component of the hydraulic system after determining 840 that the pressure in the hydraulic system is at or below the predefined threshold, or that the change or rate of change of pressure in the hydraulic accumulator is at or above the predefined threshold, as described above with reference to Figure 1.

[0082] in some examples, the at least one characteristic of the aircraft comprises a. status of the flight of the aircraft, and the method comprises: determining 850 a refill rate threshold on the basis of the status of the flight; monitoring 8.55 a rate of refills of the hydraulic system during the flight of the aircraft; determining 860 whether the rate of refills exceeds the refill rate threshold; and causing 865 at least one action to be taken on determination that the rate of refills exceeds the refill rate threshold. in some examples, the rate of refills is determined as a number of refills during a flight, and the refill rate threshold is a threshold number of refills during the flight, as described above with reference to Figure 1. In some examples, the causing 865 the at least one action to be taken comprises any one or more of causing a warning device to issue a warning; recording data indicative of the rate of refills; and recording data indicative ofthe rate of refills exceeding the refill rate threshold, as described above with reference to Figure I. [0083] Figure 4 shows a schematic diagram of a ion-transitory computer-readable storage medium 900 according to an example. The non-transitory computer-readable storage medium 900 stores instructions 930 that, if executed by a processor 920 of a controller 910 of an aircraft, cause the processor 920 to perfbrm one of the methods described herein. In some examples, the controller 910 is the control system controller 110 described above with reference to Figure 1 or a. variant thereof described herein. The instructions 930 comprise: receiving 810 at least one signal during a flight of the aircraft, determining 820 whether one or more predetermined criteria have been met, on. the basis of the at least one signal, wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of a component of the hydraulic system is within a predetermined range; and initiating 830 control of one or more characteristics of the hydraulic system on the basis of the determination. The instructions 930 may comprise instructions to perform any of the methods 800 described above with reference to Figure 2.

[0084] Figure 5 is a schematic front view of an aircraft i.. The aircraft 1 comprises an aircraft system 10 as discussed herein, such as the aircraft system 10 discussed herein with reference to Figure 1 or any variant thereof discussed herein. The aircraft 1 also comprises a hydraulic system 200 as discussed herein, such as the hydraulic system 200 discussed herein with reference to Figure 1 or any variant thereof discussed herein. The aircraft 1 also comprises the non-transitory computer-readable storage medium 900 discussed herein with reference to Fiume 4.

[0085] Examples of the uniion address the of reliably controlling one or more characteristics °fa hydraulic system 200 o f an aircraft 1, such as a pressure or volume of fluid in a hydraulic accumulator 230 of the hydraulic system 200, in the presence of varying temperatures to which the aircraft is exposed during flight. For example, inhibiting the control of the one or more characteristics until a temperature of the gas 232 in the hydraulic accumulator 230 has stabilised, as described above in some examples, may ensure that an amount of fluid in the hydraulic system 200 is accurately determined and controlled. This may, -for instance, reduce a number of times the hydraulic system 200 is refilled during a flight, as described above in some examples.

100861 lt is to be noted that the tem herein is to be interpreted to mean "and/or", unless expressly stated otherwise 100871 Although the invention has been escribed above with reference to particular examples, it will be appreciated that various changes or modification may be made without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS: A control system for an aircraft" the aircraft comprising hydraulic system the control system comprising a controller that is configured to: determine whether one or more predetermined criteria have been met during a flight of the aircraft, wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of a component of the hydraulic system is within a predetermined range; and permit control of one OT more characteristics of the hydraulic system on the basis of the determination.
2. The control system according to claim 1, wherein the controller is configured to receive at least one signal comprising information representative of at least one characteristic of the aircraft, and wherein the controller is configured to determine whether the one or more criteria have been met on the basis of the at least one signal The control system according to claim 1, wherein the at least one characteristic of the aircraft comprises a status relating to the flight of the aircraft, the status comprising any one or more of an elapsed duration of the flight; an elapsed duration of a phase of the flight; an estimated time to landing; and a location of the aircraft.4. The control system according to any one of claurts 1 to 3, wherein the at least one characteristic of the aircraft comprises a status of the aircraft, the status of the aircraft comprising any one of more of an ambient temperature internal or external to the aircraft; an ambient pressure internal or external to the aircraft; a temperature of a hydraulic fluid in the hydraulic system; an airspeed:, an altitude:, and a configuration of the aircraft.5. The control system according to any one of the preceding claims, wherein the component of the hydraulic system comprises at least one hydraulic accumulator, and wherein a determination that the one or more criteria have been met is indicative that a change or rate of change of temperature of gas in the hydraulic accumulator is within the predetermined range.6. The control system according to any one of the preceding claims, wherein the controller is configured to control a pressure in the component of the hydraulic system on the basis oldie determination.7. The control system according to claim 6; wherein the controller is configured to: determine whetner a pressure in the component of the hvdi-aulic system is at or below a predefined threshold; and cause initiation of a procedure to refill the hydraulic system on the basis of the determination that, the pressure in the component of the hydraulic system is at or below the predefined threshold.8 A method of controlling a hydraulic system of an aircraft, the method comp "i receiving at least one signal during a flight of the aircraft; determining whether one or more predetermined criteria have been met, on the basis of the at least one signal, wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of a component of the hydraulic system is within a predetermined range; and initiating control of one or more characteristics of the hydraulic system on basis ofthe determination.9. The method according to claim 8, when..in the at least one signal comprises information representative of at least one characterisLic of the aircraft.10. The method according to either claim 8 or claim 9, wherein component of the hydraulic system comprises at least one hydraulic accumulator, and wherein a determination that the one or more criteria have been met is indicative that a change or rate of change of temperature of gas in the hydraulic accumulator is within the predetermined range.11, The method according to any one of claims 8 to 10, further comprising determining whether a pressure in the component of the hydraulic system is at or below a predefined threshold, and causing refilling of the component of the hydraulic system after determining that the pressure in the hydraulic system is at or below the predefined threshold, 12. The method according to claim 11, wherein the at least one characteristic of the aircraft comprises a status of the flight of the aircraft, and the method comprises: determining a refill rate threshold on the basis ofthe status of the flight; monitoring a rate of refills ofthe hydraulic system during the of the determining whether the rate of refills e weeds the refill rate threshold; and causing at least one action to be taken on determination that the rate of refills exceeds the refill rate threshold.13. A non-transitory computer-readable storage medium stormn tructions that, if executed by a controller of a control system of an aircraft, cause the controller to carry out the method according to any one of claims 8 to 12.14. An aircraft system for an aircraft, the aircraft system comprising: a hydraulic system comprising a hydraulic system controller that is configured to receive an instruction, and to control a pressure of hydraulic fluid in a compommt of the hydraulic system on the basis ofthe instruction, and an aircraft control system comprising a control system controller that is configured to: receive at least one signal during flight of the aircraft; determine whether one or more criteria have been met, on the basis of the at least one signal, wherein a determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of the component of the hydraulic system is within a predetermined range; and send the instruction to the hydraulic system controller, on the basis of the determination.15. The aircraft system according to claim 14, comprising a sensor system configured to sense at least one characteristic of the aircraft and to send the at least one signal to the controller, 'herein the signal comprises information representative of at least one aircraft characteristic.16. The aircraft systemaccording to claim 14 or claim 5, wherein the hydraulic, system controller is configured, on receipt of the at least one instruction, to: interrogate a parameter of the component of the hydraulic system; determine that the parameter has reached a predefined threshold; and cause refilling of the component of the hydraulic system on the basis of the dcterrnmation that the parameter has reached the predefined threshold.17. An aircraft system comprising a hydraulic system, a hydraulic system controller, and an aircraft system controller, the hydraulic system controller configured to: cause interrogation of one or more characteristics of the hydraulic system.: determine when the one or more characteristics reach a predefined threshold; and cause refilling of the hydraulic system with hydraulic fluid on the basis of the detenninat ion; the controller configured to: determine whether one or more criteria have been met during a flight, wherein a. determination that the one or more criteria have been met is indicative that a change or rate of change in temperature of a component of the hydraulic system is within a predetermined range; and inhibit operation of the hydraulic system controller to cause the refilling until the controller determines that the one or more criteria have been met during the flight.18. An aircraft comprising the control system according to any one of claims 1 to 7 or the aircraft system according to any one of claims 14 to 17, or the non-transitory computer-readable storage medium according to claim 13