Patent Description:
Aircraft hydraulic systems are used to move flight control surfaces, landing gears, thrust reversers, and the like. Hydraulic systems are also used to control the aircraft in flight. Hydraulic pumps provide a source of hydraulic power for the hydraulic system through powered compression of an incompressible hydraulic fluid. Hydraulic pumps can convert mechanical energy power from various power sources present on the aircraft, such as aircraft engines, electric motors, ram air turbines, and pneumatic systems.

Hydraulic pumps are conventionally operated until failure. Failed pumps may cause service disruptions because a scheduled flight may be delayed, canceled, or diverted in order to perform the unscheduled maintenance of replacing the failed pump. Beyond service disruptions, some failure modes can damage components of the aircraft, increasing the expense and time required to correct the failure. Known fault monitoring for hydraulic pumps is limited to detection of pump or system overheat conditions based on a monitored temperature exceeding a high temperature overheat threshold. The overheat threshold may be set at a very high value due to variability of the system and environmental factors (such as ambient temperature) to limit false positive detections of overheat conditions. Pumps may degrade well prior to reaching the overheat condition. A degraded pump may have issues, such as lower flow rates, no flow on start-up, may operate intermittently, may fail to produce pressure, and/or the like. The high overheat thresholds do not allow for early detection of pump issues.

<CIT> states, in accordance with its abstract: "In one or more embodiments, a system for predicting health of a hydraulic pump comprising a reservoir tank temperature sensor to measure a temperature of a reservoir tank. The system further comprises a hydraulic pump temperature sensor to measure a temperature of the hydraulic pump. Also, the system comprises a differential pressure sensor to measure a differential pressure across a filter associated with the hydraulic pump. Further, the system comprises a processor(s) to determine a differential temperature by subtracting the temperature of the reservoir tank from the temperature of the hydraulic pump, to compare the differential temperature to a differential temperature threshold, to compare the differential pressure to a differential pressure threshold, and to generate an alert signal indicating failure of the hydraulic pump, when the processor(s) determines that the differential temperature exceeds the differential temperature threshold and the differential pressure exceeds the differential pressure threshold.

<CIT> states, in accordance with its abstract: "An EHA system (<NUM>) for lifting/lowering landing gear is provided with: a hydraulic circuit (<NUM>) comprising a hydraulic actuator (hydraulic cylinder <NUM>) for lifting/lowering landing gear of an aircraft, at least one electric hydraulic pump (<NUM>), and a hydraulic path; pressure sensors (<NUM>, <NUM>); a temperature sensor (<NUM>); and a control unit (controller <NUM>) which outputs a control signal for operating the electric hydraulic pump during lifting/lowering of the landing gear. The hydraulic circuit includes a pressure boosting element; meanwhile, when the electric hydraulic pump is operating, the control unit performs health monitoring with respect to the performance of the electric hydraulic pump on the basis of the pressure and temperature of hydraulic oil and the rotation speed of the electric hydraulic pump.

<CIT> states, in accordance with its abstract: "A method of health monitoring of a hydraulic actuator includes sensing a first hydraulic fluid pressure at a first chamber of a hydraulic cylinder, the first chamber defined by a piston disposed in the cylinder and a first cylinder wall. The method further includes sensing a second hydraulic fluid pressure at a second chamber of the hydraulic cylinder, the second chamber defined by the piston and a second cylinder wall opposite the first cylinder wall. The pressures are summed to derive a pressure sum leakage estimate. An actual piston position in the hydraulic cylinder is determined and compared to an intended piston position to determine a positional error of the piston. A command-response error leakage estimate is derived from the positional error. The pressure sum leakage estimate and the command-response error leakage estimate are fused to determine an internal hydraulic fluid leakage in the hydraulic cylinder.

<CIT> states, in accordance with its abstract: "The invention relates to a method (<NUM>) of determining the health status of a hydraulic circuit arrangement comprising at least one hydraulic fluid working machine (<NUM>, <NUM>). The health status is determined (<NUM>) using at least in part an actual temperature information (<NUM>) of the hydraulic circuit arrangement (<NUM>) that is compared to an expected temperature information (<NUM>) of the hydraulic circuit arrangement (<NUM>).

A need exists for a diagnostic system and methods to provide early detection of degraded hydraulic pumps prior to pump failure, which would enable scheduled maintenance to address a degraded, though still operable, pump to avoid aircraft service disruptions and pump failures.

With those needs in mind, the present disclosure provides an aircraft comprising: a diagnostic system comprising: a hydraulic system onboard the aircraft, the hydraulic system comprising a pump configured to pump hydraulic fluid from a reservoir to a hydraulic load on the aircraft; a first temperature sensor configured to measure a first temperature of the hydraulic fluid upstream of an inlet of the pump; a second temperature sensor configured to measure a second temperature of the hydraulic fluid within a cooling flow stream downstream of an outlet of the pump; and a controller including one or more processors and configured to: determine a value of a temperature rise of the hydraulic fluid across the pump as a difference between the first temperature and the second temperature; obtain an expected range for the temperature rise of the hydraulic fluid across the pump based on a speed of the pump; and in response to the value of the temperature rise being outside of the expected range, generate a maintenance message for communication to one or more devices that are off-board the aircraft, wherein the maintenance message indicates that the pump is operating in a degraded state.

The present disclosure also provides a method comprising: determining a value of a temperature rise of hydraulic fluid across a pump of a hydraulic system onboard an aircraft, the temperature rise determined between a first temperature of the hydraulic fluid measured upstream of an inlet of the pump and a second temperature of the hydraulic fluid measured within a cooling flow stream downstream of an outlet of the pump; obtaining an expected range for the temperature rise of the hydraulic fluid across the pump based on a speed of the pump; and in response to the value of the temperature rise being outside of the expected range, generating a maintenance message for communication to one or more devices that are off-board the aircraft, wherein the maintenance message indicates that the pump is operating in a degraded state.

These and other features and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like numerals represent like parts throughout the drawings, wherein:.

Examples of the present disclosure provide a diagnostic system that provides early detection of degraded hydraulic pumps. The early detection refers to detecting a degraded pump before a temperature associated with the pump exceeds a high temperature overheat threshold or another condition indicating pump failure is detected. The system and method described herein may detect a degraded hydraulic pump while the pump is operational, prior to failing. For example, a degraded pump may have reduced performance characteristics relative to a healthy pump, such as providing a lower flow rate, lower pressure, fluctuating flow rate and/or pressure, intermittent issues, and/or the like. A degraded pump is still operational, as the performance characteristics are sufficient to satisfy a baseline functional criteria. Pumps that fail to satisfy the baseline functional criteria are referred to as failed pumps, and are not operational. Failed pumps may trigger a fault or failure mode, such as when a temperature rise across the pump exceeds a high temperature overheat threshold or the pump fails to produce output flow. The early detection of degraded pumps provided by the system and method allows for scheduling maintenance to address (e.g., repair or replace) degraded pumps at a convenient time to avoid aircraft service disruptions. For example, a degraded pump may be replaced during a normal scheduled maintenance event for the aircraft, before the pump fails. Furthermore, the diagnostic system and method described herein may use devices present on the aircraft and introduce new aircraft failure modes, without requiring additional devices that would increase cost and add weight.

<FIG> is a perspective illustration of an aircraft <NUM>. The aircraft <NUM> may include a fuselage <NUM> extending from a nose <NUM> to an empennage <NUM>. The empennage <NUM> (or tail) may include movable tail surfaces, such as a rudder <NUM> and elevators <NUM>, for directional control of the aircraft <NUM>. The aircraft <NUM> includes a pair of wings <NUM> extending from the fuselage <NUM>. The wings <NUM> may include movable wing surfaces <NUM>, such as ailerons, flaps, and/or spoilers. One or more propulsion systems <NUM> propel the aircraft <NUM>. The propulsion systems <NUM> are supported by the wings <NUM> of the aircraft <NUM>, but may be mounted to the fuselage <NUM> or empennage <NUM> in other types of aircraft. Each propulsion system <NUM> includes a rotor assembly <NUM> with rotors that spin to direct air and a nacelle <NUM>. The nacelle <NUM> is an outer casing or housing that holds and surrounds the rotor assembly <NUM>. The rotor assembly <NUM> may be a portion of a gas turbine engine, which burns a fuel, such as gasoline or kerosene, to generate thrust for propelling the aircraft <NUM>. In some alternative examples, the rotor assemblies <NUM> of some of all of the propulsion systems <NUM> may be driven by electrically-powered motors, rather than by the combustion of fuel within a gas turbine engine. For example, the motors of such propulsion systems <NUM> may be electrically-powered by an onboard electrical energy storage device (e.g., a battery system) and/or an onboard electrical energy generation system.

The aircraft <NUM> may include a hydraulic system that uses hydraulic fluid to control movement and positioning of mechanical aircraft components necessary for safe, controlled flight of the aircraft. The hydraulics may produce steering, braking, thrust reverser control, and/or the like for on-board or on-ground control of the aircraft. For example, flight control surfaces (e.g., rudder <NUM>, elevators <NUM>, movable wing surfaces <NUM>) for steering the aircraft, landing gears, thrust reversers, and/or the like may be controlled via the flow of hydraulic fluid. The hydraulic system may be controlled based on control signals generated by a user input device that controls movement and operations of the aircraft. The user input device may be operated by a pilot or co-pilot. Optionally, the hydraulic system may be controlled by control signals generated by an automated system, such as an autopilot system or autonomous flight system.

The diagnostic system and method described herein is directed to monitoring the condition (or health) of pumps of aircraft hydraulic systems. The entire diagnostic system may be disposed onboard the aircraft <NUM>. Alternatively, a first portion of the diagnostic system may be onboard the aircraft <NUM>, and a second portion of the diagnostic system may be off-board the aircraft <NUM>. The diagnostic system and method of the examples described herein may be implemented to monitor hydraulic pumps on existing aircraft and new aircraft. The system and method may be used with various types of aircraft that have hydraulic systems. Example types may include passenger aircraft, military aircraft, cargo aircraft, drones, or the like.

<FIG> is a schematic illustration of a hydraulic pump <NUM>. The hydraulic pump <NUM> may be monitored by the diagnostic system and method described in the examples herein. The hydraulic pump <NUM> includes an inlet <NUM> and two outlets <NUM>, <NUM>. The two outlets are referred to as a discharge outlet <NUM> and a case drain outlet <NUM>. In operation, the hydraulic pump <NUM> receives a low pressure stream of hydraulic fluid via the inlet <NUM>. The hydraulic fluid may be received from a reservoir. The hydraulic pump <NUM> compresses the hydraulic fluid. The work performed on the hydraulic fluid generates heat due at least in part to internal leakage and friction in the hydraulic pump <NUM>. Fluid flow and heat exit the pump through the outlets <NUM>, <NUM>. For example, a high pressure flow stream of the hydraulic fluid may be delivered from the discharge outlet <NUM>. The high pressure flow stream may be directed to a hydraulic load on the aircraft. A second stream of hydraulic fluid may exit the hydraulic pump <NUM> through the case drain outlet <NUM>. The second stream is referred to herein as a cooling flow stream. The hydraulic fluid in the cooling flow stream is discrete from the hydraulic fluid in the high pressure flow stream and may have a lower pressure than the high pressure flow stream. The hydraulic fluid that enters the hydraulic pump <NUM> through the inlet <NUM> gets distributed between the cooling flow stream and the high pressure flow stream. The cooling flow stream may be used to cool additional system components, electric motors, gearboxes, or electronics, before being directed back to the reservoir.

The amount of waste heat rejected into the high pressure flow stream may vary relative to the waste heat rejected into the cooling flow stream depending on flight conditions of the aircraft. For example, at a cruise state, when the aircraft is flying at relatively steady altitude and speed and there is little if any flight control activity requiring hydraulic fluid, most of the waste heat generated by the pump is rejected into the cooling flow stream that is emitted through the case drain outlet <NUM>.

<FIG> is a graph <NUM> reflecting heat rejection of a pump relative to a flow rate of high pressure flow stream through the discharge outlet <NUM>. A first line <NUM> represents heat rejection through the case drain outlet <NUM> into the cooling flow stream (also referred to herein as case drain stream), and a second line <NUM> represents heat rejection through the discharge outlet <NUM> into the high pressure flow stream (also referred to herein as discharge stream). The data in the graph <NUM> may be based on various factors including the type of pump, the inlet fluid temperature, and the speed (e.g., RPM) of the pump. The graph <NUM> shows an inverse relationship between the heat rejection into the discharge stream <NUM> and the case drain stream <NUM>. At low discharge flow rates, most of the waste heat is rejected into the case drain stream <NUM>. For example, approximately all (e.g., at least <NUM>%, at least <NUM>%, or the like) of the waste heat is rejected into the case drain stream <NUM> when the discharge flow rate is less than <NUM> gallon per minute (GPM: <NUM> GPM = <NUM>/s). As the flow rate of the discharge stream <NUM> increases, the amount of heat rejection into the discharge stream <NUM> increases, and the amount of heat rejection into the case drain stream <NUM> proportionately decreases. For example, at a discharge flow rate of about <NUM> GPM (<NUM>/s) in the graph <NUM>, the heat rejection into the two streams <NUM>, <NUM> is approximately equal. More waste heat is rejected into the discharge stream <NUM> than the case drain stream <NUM> at discharge flow rates above <NUM> GPM (<NUM>/s). Although the data in <FIG> may be specific to a particular type of pump at a specific fluid inlet temperature and pump speed, the inverse trend shown in the graph <NUM> may be common to other pump types, fluid inlet temperatures, pump speeds, and/or the like.

In one or more examples, the temperature of the cooling flow stream is measured to determine a temperature rise across the hydraulic pump <NUM>. Relevant temperature measurements for pump monitoring may occur at low hydraulic activity conditions of a flight. A low hydraulic activity condition may represent a condition in which there is little or no pilot control inputs that require hydraulic system activity. This may be when the aircraft is operating at a cruise state, flying with relatively constant altitude, speed, and direction. An elliptical indicator <NUM> in <FIG> highlights the case drain stream <NUM> at the low hydraulic activity condition. As indicated in the graph <NUM>, most of the waste heat (e.g., at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, or the like of total waste heat) generated by the pump is rejected to the case drain stream <NUM> when in the low hydraulic activity condition. The system and method described herein may measure the temperature of the case drain (or cooling flow) stream while the aircraft is in the low hydraulic activity condition. Because it is assumed based on the inverse trend shown in <FIG> that little or no heat is rejected into the discharge stream <NUM> at this condition, the temperature of the case drain stream can be used to determine total heat generated by the pump.

In one or more examples, only the temperature of the case drain stream <NUM> is monitored while the aircraft is in the low hydraulic activity condition. The temperature of the high pressure discharge stream <NUM> may not be measured, so there is no need for a temperature sensor along the high pressure flow stream downstream of the pump. Furthermore, temperatures of the case drain stream <NUM> when the aircraft is not in the low hydraulic activity condition may not be used to monitor the condition or health of the pump. The diagnostic system and method may monitor the health of the pump only in certain flight conditions, such as the low hydraulic activity condition. In other examples, there may be a second flight condition of the aircraft in which it is determined that the pump is rejecting waste heat to both the discharge stream <NUM> and the case drain stream <NUM> at a determined proportion. In that case, the temperature of the case drain stream <NUM> can be measured while the aircraft is in the second flight condition and used, with the known proportional allocation, to determine the total heat generated by the pump. For example, if the second flight condition is associated with equal or approximately equal heat rejection to both streams <NUM>, <NUM>, then the diagnostic system may use that proportional allocation with the measured temperature of the case drain stream <NUM> to determine the total heat generated by the pump.

In some examples, the diagnostic system may avoid the use of flow meters to directly measure hydraulic flow into and/or from the hydraulic pump <NUM>. The diagnostic system may avoid the cost and weight of adding such devices. The diagnostic system described herein may indirectly estimate hydraulic flow and/or proportional allocation of waste heat based on particular flight conditions, pump speeds, and/or the like. For example, by determining that the aircraft is in a cruise state or another low hydraulic activity state highlighted by the indicator <NUM> in <FIG>, the diagnostic system can assume that a substantial majority of the waste heat is rejected to the case drain stream <NUM> without measuring the temperature of the discharge stream <NUM>. In some alternative examples, the diagnostic system may measure the flow rate of the discharge stream <NUM> and/or the case drain stream <NUM> using a flow meter, and use the measured flow rate with the graph <NUM> to determine the waste heat rejection into the streams <NUM>, <NUM>, or at least the proportional allocation of heat between the two streams <NUM>, <NUM>.

<FIG> is a block diagram showing a hydraulic system <NUM> and a diagnostic system <NUM> that monitors the health or condition of one or more hydraulic pumps <NUM> of the hydraulic system <NUM> according to an example. The diagnostic system <NUM> is designed to provide early detection of hydraulic pumps <NUM> that are degraded, prior to those hydraulic pumps <NUM> actually failing (e.g., triggering a fault, exceeding an overheat threshold temperature, or the like). The hydraulic system <NUM> is disposed onboard an aircraft, such as the aircraft <NUM> in <FIG>.

The hydraulic system <NUM> includes a reservoir <NUM> that contains hydraulic fluid, one or more hydraulic pumps <NUM>, a pressure filter module <NUM>, a hydraulic load <NUM>, a case drain filter module <NUM>, and various conduits, valves, and the like for providing closed flow paths for conveying the hydraulic fluid between the components. The hydraulic pump(s) <NUM> deliver hydraulic fluid from the reservoir <NUM> to the hydraulic load <NUM>. The hydraulic load <NUM> may include or represent mechanical devices that are actuated and moved to control movement of the aircraft. The hydraulic load <NUM> may include rudders, elevators, ailerons, spoilers, flaperons, thrust reversers, landing gears, and/or the like. The hydraulic system <NUM> includes a first pump 200A and a second pump 200B in some examples including the illustrated example. The pressure filter module <NUM> and the case drain filter module <NUM> may include various devices for conditioning and/or regulating the hydraulic fluid. For example, the filter modules <NUM>, <NUM> may each include one or more sensors, relief valves, check valves, ground hook-ups, heat exchangers, and/or the like. The first pump 200A may be a primary pump, and the second pump 200B may be a secondary pump. Each of the pumps 200A, 200B may have a respective inlet <NUM>, discharge outlet <NUM>, and case drain outlet <NUM> as described in <FIG>. The hydraulic system may have only one hydraulic pump <NUM> or at least three hydraulic pumps <NUM> in other examples.

Each pump 200A, 200B is powered by a respective driver component <NUM>. The driver component <NUM> powers the pump to compress the hydraulic fluid. The driver components <NUM> may include a fuel combustion engine, an electric motor, a ram air turbine, or the like. In some examples including the illustrated example, the first pump 200A is powered by a fuel combustion engine <NUM> which represents the respective driver component <NUM>, and the second pump 200B is powered by an electric motor <NUM> which represents the respective driver component <NUM>.

The inlet <NUM> of each pump 200A, 200B is fluidly connected to the reservoir <NUM> via conduits. When operating, the pumps 200A, 200B draw hydraulic fluid from the reservoir <NUM> into the pumps 200A, 200B through the inlets <NUM>. Each pump 200A, 200B compresses the hydraulic fluid and emit the hydraulic fluid as a high pressure flow stream from the discharge outlet <NUM> and cooling flow stream from the case drain outlet <NUM>. The two streams are separate and discrete, and are delivered to different locations. Hydraulic fluid that is at the reservoir <NUM> and in the incoming flow stream between the reservoir <NUM> and the inlet <NUM> is referred to herein as upstream of a respective pump. Hydraulic fluid in the high pressure flow stream and the cooling flow stream is referred to as downstream of the respective pump. In the illustrated configuration, the high pressure flow streams (e.g., discharge streams) from the pumps 200A, 200B are delivered to the pressure filter module <NUM>. The lower pressure cooling flow streams (e.g., case drain streams) from the pumps 200A, 200B are delivered to the case drain filter module <NUM>. The case drain filter module <NUM> may include one or more heat exchangers for permitting the hydraulic fluid in the cooling flow stream to disperse heat from one or more aircraft components before returning to the reservoir <NUM>. The pressure filter module <NUM> may condition and/or regulate the hydraulic fluid in the high pressure flow stream before the high pressure flow stream is delivered to the hydraulic load <NUM> to perform work. The work may involve moving a flight control surface, such as a rudder, elevator, aileron, flaperon, and/or the like, extending or retracting landing gears, extending or retracting thrust reversers, and/or the like. The hydraulic fluid of the high pressure flow stream may return to the reservoir <NUM> after the hydraulic load <NUM>. Optionally, the hydraulic system <NUM> may include a return filter module downstream of the case drain filter module <NUM> and the hydraulic load <NUM>. The return filter module may condition and/or regulate the hydraulic fluid that is recycled back to the reservoir <NUM>.

The diagnostic system <NUM> includes a controller <NUM> and multiple temperature sensors <NUM>, and may include a communication device <NUM>. The controller <NUM> is operably connected to the other components via wired and/or wireless communication links to permit the transmission of information in the form of signals. The controller <NUM> is configured to receive sensor signals generated by the temperature sensors <NUM>. The sensor signals represent a measured temperature of the hydraulic fluid in the hydraulic system <NUM> at a location of the respective sensor <NUM>. The controller <NUM> generates control signals that may be transmitted to the communication device <NUM> and/or other components to control operation of the communication device <NUM> and/or the other components. The diagnostic system <NUM> may have additional components that are not shown in <FIG>, such as a user input/output device. In some alternative examples, the diagnostic system <NUM> may lack one or more of the components shown in <FIG>.

The temperature sensors <NUM> may be integrated into the hydraulic system <NUM> and are disposed at multiple spaced-apart locations in the hydraulic system <NUM>. A first temperature sensor 316A is disposed upstream of both pumps 200A, 200B. The first temperature sensor 316A measures a first temperature of the hydraulic fluid measured upstream of the pump inlets <NUM>. The first temperature sensor 316A may be disposed at the reservoir <NUM> or along the conduit pathway that extends from the reservoir <NUM> towards the pumps 200A, 200B. The first temperature may represent a temperature of the hydraulic fluid in the reservoir <NUM>. The first temperature is referred to herein as an upstream temperature. Each pump 200A, 200B has an associated temperature sensor <NUM> that is located downstream of the case drain outlet <NUM> of the respective pump 200A, 200B and measures a second temperature of the hydraulic fluid within the cooling flow stream. The second temperature is referred to herein as a downstream temperature. For example, a second temperature sensor 316B is located downstream of the first pump 200A. The second sensor 316B may be coupled to the first pump 200A at the case drain outlet <NUM> or disposed along the conduit pathway that extends from the case drain outlet <NUM> of the first pump 200A to the case drain filter module <NUM>. A third temperature sensor 316C may be located downstream of the second pump 200B. The third temperature sensor 316C may be coupled to the second pump 200B at the case drain outlet <NUM> or disposed along the conduit pathway that extends from the case drain outlet <NUM> of the second pump 200B to the case drain filter module <NUM>. The temperature sensors <NUM> may be thermocouples, resistance temperature detectors (RTDs), thermistors, or semiconductor based integrated circuits (IC).

The controller <NUM> determines a temperature rise of the hydraulic fluid across a hydraulic pump <NUM> as a difference between the first, upstream temperature and the second, downstream temperature. The controller <NUM> receives sensor signals generated by the temperature sensors 316A-C, for instance via wired or wireless communication pathways. The controller <NUM> determines a value of the temperature rise across the first pump 200A as the difference between the downstream temperature measured by the second temperature sensor 316B and the upstream temperature measured by the first temperature sensor 316A. The controller <NUM> determines a value of the temperature rise across the second pump 200B as the difference between the downstream temperature measured by the third temperature sensor 316C and the upstream temperature measured by the first temperature sensor 316A.

The controller <NUM> represents hardware circuitry that includes one or more processors <NUM> (e.g., one or more microprocessors, integrated circuits, microcontrollers, field-programmable gate arrays, etc.). The controller <NUM> includes and/or is connected with a tangible and non-transitory, computer-readable memory storage device (e.g., data storage medium or device), referred to herein as memory <NUM>. The memory <NUM> may store programmed instructions (e.g., software) that are executed by the one or more processors <NUM> to perform diagnostic health monitoring and maintenance scheduling operations described herein. The programmed instructions may include one or more algorithms stored in the memory <NUM> and utilized by the one or more processors <NUM>. References herein to the controller <NUM> may refer to the one or more processors <NUM>. The memory <NUM> may store databases of information utilized by the one or more processors <NUM> to determine whether a pump is operating in a degraded state and/or has failed. In some examples, the memory <NUM> stores one or more look-up tables <NUM> that list expected ranges of temperature rises across pumps for each of multiple different conditions, such as different speed ranges of the pumps and/or different ambient temperatures of the surrounding environment. The memory <NUM> may store additional information, such as various application program interfaces (APIs) that link to cloud hosting services, via the communication device <NUM>, for accessing information from remote storage devices, such as servers.

The communication device <NUM> represents hardware circuitry that can wirelessly communicate electrical signals. For example, the communication device <NUM> can represent transceiving circuitry, one or more antennas, and the like. The transceiving circuitry may include a transceiver or a separate transmitter and receiver. The electrical signals can form data packets that in the aggregate represent messages. In some examples, the communication device <NUM> may wirelessly communicate electrical signals as radio frequency (RF) signals. In other examples, the communication device <NUM> may be a modem, router, or the like, that is connected to a network (e.g., the Internet). The communication device <NUM> may communicate messages that are generated by the controller of the diagnostic system. The messages sent by the communication device <NUM> may include maintenance messages and restriction messages, as described herein. The messages may be communicated remotely to devices that are off-board the aircraft. The communication device <NUM> may receive messages from off-board the aircraft, and forward the received messages to the controller <NUM> for analysis.

<FIG> is a flow chart <NUM> of a method of monitoring a condition of a hydraulic pump according to an example. The method may be performed, at least in part, by the controller <NUM> of the diagnostic system <NUM> shown in <FIG>. The method optionally may include at least one additional step than shown, at least one fewer step than shown, and/or at least one different step than shown in <FIG>. The method may be performed to concurrently monitor multiple different pumps in a hydraulic system. For example, the method may be used to monitor both pumps 200A, 200B shown in <FIG>.

At step <NUM>, a value of a temperature rise of hydraulic fluid across a pump is determined. The controller <NUM> may determine the temperature rise of the hydraulic fluid across the first pump 200A by subtracting the upstream temperature measured by the first temperature sensor 316A from the downstream temperature measured by the second temperature sensor 316B. In some examples, if the upstream temperature is <NUM>°F (<NUM>), and the downstream temperature measured by the sensor 316B is <NUM>°F (<NUM>), the controller <NUM> determines the value of the temperature rise across the first pump 200A to be <NUM>°F (<NUM>). The method is described herein with reference to the first pump 200A, but the same steps can be applied to monitor the second pump 200B. For example, the value of the temperature rise across the second pump 200B can be determined by subtracting the upstream temperature measured by the first temperature sensor 316A from the downstream temperature measured by the third temperature sensor 316C, which is associated with the second pump 200B.

At step <NUM>, an expected range for the temperature rise across the hydraulic pump <NUM> is obtained. The expected range represents a range that is expected to encompass the value of the temperature rise across the hydraulic pump <NUM> based on the type of pump and operating conditions, if the hydraulic pump <NUM> has a healthy (non-degraded) state. The expected range may be obtained based on the operating conditions experienced by the hydraulic pump <NUM>. For example, different operating conditions affect the amount of waste heat rejected by the hydraulic pump <NUM> into the hydraulic fluid. The operating conditions include a speed of the hydraulic pump <NUM>. In some examples, the controller may determine the speed of the hydraulic pump <NUM> indirectly based on a measured rotational speed of the driver component <NUM> that powers the hydraulic pump <NUM>. For example, the controller may obtain a speed of the engine <NUM>, and then determine the speed of the first pump 200A based on a known ratio (e.g., gear ratio) between the engine <NUM> and the hydraulic pump 200A. If the engine <NUM> is operating at <NUM> rpm and the ratio of engine speed to pump speed is <NUM>:<NUM>, then the controller <NUM> may determine the pump speed to be <NUM> rpm. For other pumps, the pump speed may be determined based on the rotational speeds of the respective driver component, such as a motor speed, turbine speed, or other known indication of pump speed at the aircraft level. Alternatively, a sensor may be disposed on the hydraulic pump <NUM> to enable direct measurement of the pump speed.

In some examples, the controller <NUM> may obtain the expected range for the temperature rise by accessing the look-up table <NUM> stored in the memory storage device <NUM>. <FIG> is a table <NUM> providing multiple expected ranges <NUM> for the temperature rise across a pump for different corresponding pump speeds <NUM>. The table <NUM> may be one of the one or more look-up tables <NUM> stored in the memory <NUM>. The table <NUM> lists a respective upper limit <NUM> of the expected range <NUM> and a respective lower limit <NUM> of the expected range <NUM> for each of multiple different ranges <NUM> of the speed <NUM> of the pump. For example, if the pump speed is determined to be <NUM> rpm, then the expected range <NUM> of the temperature rise across the pump is from <NUM>°F to <NUM>°F (<NUM> to <NUM>). This range means that the waste heat rejected by the hydraulic pump <NUM> into the cooling flow stream is expected to raise the temperature of the hydraulic fluid by <NUM>°F to <NUM>°F (<NUM> to <NUM>).

Another operating condition that may affect the amount of waste heat rejected by the hydraulic pump <NUM> into the hydraulic fluid is the ambient temperature of the environment surrounding the aircraft, and more specifically the temperature at the reservoir <NUM> of the hydraulic system <NUM>. For example, the viscosity of the hydraulic fluid changes based on the ambient temperature. The viscosity affects how the fluid flows through the pump and the amount of heat absorbed by the fluid. The table <NUM> in <FIG> is designed for reservoir temperatures that are from <NUM>°F to <NUM>°F (-<NUM> to <NUM>). Another factor is the size and type of the pump, as different types and sizes of pumps may generate different amounts of waste heat.

Another operating condition that may affect the heat rejection by the hydraulic pump <NUM> is flight condition. For example, as shown in the heat rejection graph in <FIG>, the hydraulic pump <NUM> may reject heat through both the discharge outlet <NUM> and the case drain outlet <NUM> at different proportions for different flight conditions. Based on these different proportions, the amount of heat rejected into the cooling flow stream can differ between two different flight conditions, even if the total heat generated by the pump is constant. The table <NUM> in <FIG> may be specific to a particular flight condition. In some examples, the table <NUM> is designed for a low hydraulic activity state of the aircraft, such as while the aircraft is at cruise.

In some examples, the flight condition may be used as a triggering event to actively begin monitoring the temperature rise across the pump. For example, the method may include as an initial step, detecting a flight condition of the aircraft. One or more flight conditions may be detected based on the presence or absence of control signals received from a user input device that controls the movement of the aircraft. For example, the low hydraulic activity state (e.g., cruise state) can be detected in response to an absence of pilot control signals received from the user input device for at least a threshold period of time. If the hydraulic system has not received any pilot input control signals for over the threshold period of time (e.g., two minutes or the like), while other aircraft sensor data indicates that the aircraft is in flight at a relatively constant speed and elevation, then the controller <NUM> may detect that the aircraft is in the cruise state.

In some examples, the expected range of the temperature rise is based on little or no hydraulic activity conditions, so detecting that the aircraft is in the cruise state serves as a prerequisite before determining the value of the temperature rise at step <NUM>. Stated more generically, the expected range of the temperature rise may be based on a particular flight condition, and the controller <NUM> may not begin monitoring the temperature rise across the hydraulic pump <NUM> until detecting that the aircraft is indeed in that particular flight condition. The value of the temperature rise is determined while the aircraft is in the flight condition on which the expected range is based. In at least some cruise state examples, the controller <NUM> may not determine the value of the temperature rise across the hydraulic pump <NUM> until the controller <NUM> detects that the aircraft is in the cruise state. Furthermore, the controller <NUM> may only monitor the temperature rise across the hydraulic pump <NUM> while the aircraft is in the cruise state, such that the controller <NUM> does not continue to monitor the temperature rise once the flight condition switches from the cruise state.

In some examples, the table <NUM> in <FIG> may be one of multiple different tables <NUM> stored in the memory <NUM>. The controller <NUM> may select which table to access and use to obtain the expected range based on the operating conditions. The operation conditions used to select the table may include the ambient temperature (e.g., the reservoir temperature), the type and size of the pump, the flight condition, and/or the like. The table <NUM> in <FIG> is specific to the cruise state and reservoir temperatures that are from <NUM>°F to <NUM>°F (-<NUM> to <NUM>). A second table may be for reservoir temperatures that are from <NUM>°F to <NUM>°F (<NUM> to <NUM>). A third table and a fourth table may be similar to the first and second tables, but correspond to a different type and/or size of pump than the first and second tables. The values of the upper limits and lower limits of the expected ranges may vary slightly among the different tables.

The upper and lower limits <NUM>, <NUM> in the look-up table <NUM> may be derived through calculation, modeling, or observing through experimentation. In some examples, the controller <NUM> may calculate the upper and lower limits <NUM>, <NUM> for the expected ranges <NUM>. The calculation may involve obtaining a volumetric flow rate of the hydraulic fluid based on the speed of the pump. Once the speed of the hydraulic pump <NUM> is determined, then the controller <NUM> may derive the volumetric flow rate of the cooling flow stream based on the pump speed and pump specifications (e.g., type and size). The flow rate may be a function of the pump speed, and may be specified by the pump manufacturer. For example, at <NUM> rpm, the flow rate of the cooling flow stream may be <NUM> GPM (<NUM>/s) within a designated margin. The controller <NUM> may then calculate a mass flow rate of the hydraulic fluid based on the volumetric flow rate and a density property of the hydraulic fluid. For example, the volumetric flow rate of the cooling flow stream may be multiplied by a density or specific gravity of the hydraulic fluid to determine the mass flow rate. If the volumetric flow rate is <NUM> GPM (<NUM>/s) and the density is <NUM> lbs/gal (<NUM>/m<NUM>), then the mass flow rate is calculated as <NUM> lbs/min (<NUM>/s). The controller <NUM> may then calculate both the upper limit of the expected range for the temperature rise and the lower limit of the expected range for the temperature rise based, at least in part, on the mass flow rate. For example, the controller <NUM> may plug the mass flow rate into thermal equations. The upper limit of the expected range may be calculated by dividing a maximum heat input for a given reservoir temperature range (in BTU/min) by a product of the specific heat of the hydraulic fluid and the mass flow rate (in lbs/min). The lower limit may be calculated by dividing a minimum heat input for a given reservoir temperature range (in BTU/min) by the product of the specific heat of the hydraulic fluid and the mass flow rate (in lbs/min). The maximum and minimum heat inputs may be determined from recorded heat rejection curves for different types and sizes of pumps at the given reservoir temperature range. In some examples, the controller <NUM> may generate the tables <NUM> stored in the memory <NUM> based on a series of these calculations.

In some alternative examples, rather than generate look-up tables and then access the look-up tables, the controller <NUM> may calculate the upper and lower limits of the expected range of the temperature rise on demand based on operating conditions that are monitored and stored data about the type and size of the pump.

Returning back to the flow chart <NUM> in <FIG>, once the expected range is obtained, the controller <NUM> may compare the value of the temperature rise that is determined in step <NUM> to the expected range. At step <NUM>, the controller <NUM> determines whether the value of the temperature rise (which represents the actual, measured temperature increase) of the hydraulic fluid is within the expected range. For example, if the value is <NUM>°F (<NUM>) and the expected range is determined to be <NUM>°F to <NUM>°F (<NUM> to <NUM>), then the value is determined to be within the expected range. The controller <NUM> may consider the ends of a range to qualify as being within the range. The value being within the expected range indicates that the hydraulic pump <NUM> is operating as expected. The pump may be classified as healthy (e.g., non-degraded). In this scenario, the flow of the method proceeds to step <NUM>. At step <NUM>, the controller <NUM> may wait for an interval time period before returning to step <NUM> to determine an updated value of the temperature rise across the pump. The interval time period may be on the order of seconds or minutes, such as <NUM> seconds, <NUM> minute, <NUM> minutes, <NUM> minutes, <NUM> minutes, or the like. The interval time period may be set by an operator or a default setting.

If, on the other hand, the expected range is determined at step <NUM> to be <NUM>°F to <NUM>°F (<NUM> to <NUM>), then the value of <NUM>°F (<NUM>) is determined to be outside of the expected range at step <NUM>. The value being outside of the expected range indicates that the hydraulic pump <NUM> is not operating as expected. The hydraulic pump <NUM> may be classified as degraded or in a degraded state. Flow of the method may proceed to step <NUM>, and the controller <NUM> may generate a maintenance message which indicates that the hydraulic pump <NUM> is operating in a degraded state. The maintenance message may identify the particular hydraulic pump <NUM> that is on the degraded state and may request scheduling or modifying a pre-scheduled maintenance appointment for the aircraft to address the degraded pump. The controller <NUM> may generate the maintenance message to be communicated by the communication device <NUM> to one or more devices that are off-board the aircraft. For example, the communication device <NUM> may transmit the maintenance message to a maintenance facility, to a personal device of a mechanic or other employee tasked with aircraft maintenance, to a server for cloud-based management of maintenance tickets, and/or the like. Optionally, the maintenance message may not be communicated to the pilot of the aircraft. For example, the maintenance message may be communicated to maintenance personnel, rather than pilots or other control personnel.

In some examples, the maintenance message may state that "pump A" has a higher than expected temperature rise. Optionally, the maintenance message may suggest a timeline for scheduling maintenance to repair or replace the pump. For example, the maintenance message may suggest scheduling a service appointment within <NUM> months. Optionally, the maintenance message may suggest operating conditions based on the degraded pump. For example, the maintenance message may state that continued operation of the aircraft is permissible without concern about the degraded pump as long as the ambient temperature is below <NUM>°F (<NUM>). Optionally, the controller may tier the content of the maintenance message based on how far the measured value of the temperature rise is outside of the expected range. A larger discrepancy between the measured value and the expected range may indicate a greater severity of degradation of the pump. A pump with a greater severity of degradation may fail before a pump that has less severe degradation. In some examples, the maintenance message may suggest scheduling maintenance in a shorter timeframe for more severe degradation. For example, the controller <NUM> may suggest maintenance within one month if the measured value of the temperature rise is over <NUM>°F (<NUM>) outside of the expected range, and may suggest maintenance within <NUM> months if the measured value is less than <NUM>°F (<NUM>) outside of the expected range.

The method in <FIG> may also be used to monitor for fault or failures of the pumps. For example, the controller <NUM> may compare the measured value of the temperature rise across the hydraulic pump <NUM> to a designated overheat threshold. The upper limit <NUM> of the expected range <NUM> is below the designated overheat threshold. For example, the designated overheat threshold may be a <NUM>°F (<NUM>) temperature rise. Alternatively, the designated overheat threshold may be a set temperature value to which the case drain temperature measurement is compared. In response to the value of the temperature rise (or the case drain temperature measurement) exceeding the designated overheat threshold, the controller <NUM> may determine that the hydraulic pump <NUM> is in a failed or fault state. The controller <NUM> may generate a restriction message that is more restrictive than the maintenance message. For example, the restriction message may be communicated to the pilot as well as to devices of an entity that operates the aircraft and devices of an entity that controls a flight network (e.g., FAA). The restriction message may prohibit subsequent flights of the aircraft until maintenance is performed on the aircraft to address the failed hydraulic pump <NUM>.

In some examples, the controller <NUM> may perform trend analysis on the temperature data over time. For example, after determining the value of the temperature rise of the hydraulic fluid across the pump, the controller may determine multiple updated values of the temperature rise of the hydraulic fluid across the pump over an extended time period. The extended time period may extend over days, weeks, months, or years. The controller <NUM> may record the value and the updated values of the temperature rise in a database, such as in the memory <NUM> or in an off-board data storage device. The controller <NUM> may analyze the data over time to predict a remaining operational life of the pump based on a variation in the value and the updated values over the extended time period.

<FIG> is a graph <NUM> depicting hydraulic fluid temperature rise values across a given pump over an extended time period according to an example. The horizontal axis depicts months of operational life of the pump. The trend line <NUM> is defined by hundreds or thousands of data points representing the measured temperature rise across the pump (e.g., as determined at step <NUM> in the method). The trend line <NUM> is relatively constant for the first five months and then begins to increase. The controller <NUM> may compare newer data points to older data points to determine a variation in the temperature rise over time. For example, the controller <NUM> may calculate a variation between the initial or baseline temperature rise within the first month of operation and the temperature rise values within the latest month of operation. The controller <NUM> may determine a slope of the trend line <NUM>. The controller <NUM> may detect step changes and analyze the step changes, such as the magnitude and frequency of step changes.

The controller <NUM> may predict a remaining operational life of the pump based on the variation in the temperature rise values plotted in the trend line <NUM>. For example, the controller <NUM> may extrapolate the trend line <NUM> to predict a time at which a future value of the temperature rise will exceed a designated overheat threshold <NUM> for the pump. In <FIG>, the trend line <NUM> ends at month <NUM>. The controller <NUM> may use the slope of the trend line <NUM> to predict a future segment <NUM> of the trend line <NUM>. The controller <NUM> may determine, based on an intersection between the future segment <NUM> and the overheat threshold <NUM>, a time in the future at which the future value of the temperature rise will exceed the overheat threshold for the pump. In <FIG>, the future segment <NUM> intersects the overheat threshold <NUM> at about <NUM> months. The controller <NUM> may generate a maintenance message that states that the pump has an estimated two months of operational life remaining before failure. The estimated time before failure may be included as part of the maintenance message generated at step <NUM> of the method.

While various spatial and direction terms such as top, bottom, lower, mid, lateral, horizontal, vertical, front and the like can be used to describe examples of the present disclosure, it is understood that such terms are merely used with respect to the orientations shown in the drawings.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described examples (and/or features thereof) can be used in combination with each other, as long as the result is within scope of the appended claims.

In addition, many modifications can be made to adapt a particular situation or material to the teachings of the various examples of the disclosure without departing from the scope of the claims. While the dimensions and types of materials described herein are intended to define the parameters of the various examples of the disclosure, the examples are by no means limiting. Many other examples will be apparent to those of skill in the art upon reviewing the above description. The scope of the disclosure should, therefore, be determined with reference to the appended claims. In the appended claims and the detailed description herein, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein. " Moreover, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

Claim 1:
An aircraft (<NUM>) comprising:
a diagnostic system (<NUM>) comprising:
a hydraulic system (<NUM>) onboard the aircraft (<NUM>), the hydraulic system (<NUM>) comprising a pump (<NUM>) configured to pump hydraulic fluid from a reservoir (<NUM>) to a hydraulic load (<NUM>) on the aircraft (<NUM>);
a first temperature sensor (316A) configured to measure a first temperature of the hydraulic fluid upstream of an inlet (<NUM>) of the pump (<NUM>);
a second temperature sensor (316B) configured to measure a second temperature of the hydraulic fluid within a cooling flow stream downstream of an outlet (<NUM>) of the pump (<NUM>); and
a controller (<NUM>) including one or more processors (<NUM>) and configured to:
determine a value of a temperature rise of the hydraulic fluid across the pump (<NUM>) as a difference between the first temperature and the second temperature;
obtain an expected range (<NUM>) for the temperature rise of the hydraulic fluid across the pump (<NUM>) based on a speed (<NUM>) of the pump (<NUM>); and
in response to the value of the temperature rise being outside of the expected range (<NUM>), generate a maintenance message for communication to one or more devices that are off-board the aircraft (<NUM>), wherein the maintenance message indicates that the pump (<NUM>) is operating in a degraded state.