Patent Description:
The present invention relates to valves and, in particular, to systems and methods for monitoring a health of a landing gear servo valve.

Aircraft typically include a braking system operatively coupled to the wheels of the aircraft and configured to slow the wheels, and the aircraft, during, for example, landing or a rejected takeoff. Brake systems typically employ a series of friction disks located about an axle. The friction disks may be compressed together to stop the aircraft. The compression of the friction disks may be controlled by one or more hydraulic actuator(s). Hydraulic fluid is typically provided to the hydraulic actuators via flexible hosing or tubing that is connected to a hydraulic fluid source located proximate the aircraft fuselage or wing. A servo valve controls the flow of the hydraulic fluid to and from the brake actuators. Wear of the servo valve can lead to performance degradation and/or improper function of the brake system. Monitoring servo valves is disclosed in <CIT>.

A system for monitoring an electrohydraulic servo valve is provided as defined by claim <NUM>.

In a preferred embodiment, the operations may further comprise commanding, by the brake control unit, a display to output an alert in response to at least one of determining, by the brake control unit, the pressure in the conduit is greater than the upper pressure threshold; or determining, by the brake control unit, the pressure in the conduit is less than the lower pressure threshold.

In a preferred embodiment, the operations may further comprise determining, by the brake control unit, a first difference between the pressure in the conduit and the upper pressure threshold; determining by the brake control unit, a second difference between the pressure in the conduit and the lower pressure threshold; and comparing, by the brake control unit, each of the first difference and the second different to a difference threshold.

In a preferred embodiment, the operations may further comprise commanding, by the brake control unit, a display to output a warning alert, in response to at least one of the first difference or the second difference being less than the difference threshold.

In a preferred embodiment, determining, by the brake control unit, the upper pressure threshold based on the current of the pressure signal may comprise determining, by the brake control unit, an expected pressure of the conduit based on the current of the pressure signal; and adding, by the brake control unit, a first value to the expected pressure.

In a preferred embodiment, determining, by the brake control unit, the upper pressure threshold based on the current of the pressure signal may comprise locating, by the brake control unit, a point on an upper threshold line corresponding the current of the pressure signal. The upper threshold line may be a linear line having a constant slope.

A method for monitoring an electrohydraulic servo valve of an aircraft landing gear is also provided as defined by claim <NUM>.

In a preferred embodiment, the method may further comprise commanding, by the brake control unit, a display to output an alert in response to at least one of determining, by the brake control unit, the pressure in the conduit is greater than the upper pressure threshold; or determining, by the brake control unit, the pressure in the conduit is less than the lower pressure threshold.

In a preferred embodiment, comparing, by the brake control unit, the pressure in the conduit to the upper pressure threshold and to the lower pressure threshold may comprise determining, by the brake control unit, a first difference between the pressure in the conduit and the upper pressure threshold; determining by the brake control unit, a second difference between the pressure in the conduit and the lower pressure threshold; and comparing, by the brake control unit, each of the first difference and the second different to a difference threshold.

In a preferred embodiment, the method may further comprise commanding, by the brake control unit, the display to output a warning alert, in response to at least one of the first difference or the second difference being less than the difference threshold.

In a preferred embodiment, determining, by the brake control unit, the lower pressure threshold based on the current of the pressure signal may comprise locating, by the brake control unit, a point on a lower threshold line corresponding the current of the pressure signal. The lower threshold line may be parallel to the upper threshold line.

A landing gear is also disclosed herein. In accordance with various embodiments, the landing gear comprises a brake assembly including a brake stack and an actuator configured to apply pressure to the brake stack, an electrohydraulic servo valve configured to control a flow of fluid to the brake assembly, a conduit fluidly connecting a control port of the electrohydraulic servo valve and an inlet of the actuator, a valve monitoring sensor configured to measure at least one of a pressure or a fluid flow rate in the conduit, and a brake control unit in communication with the electrohydraulic servo valve and the valve monitoring sensor. The brake control unit may be configured to output a pressure signal to the electrohydraulic servo valve and to receive a sensor signal from the valve monitoring sensor. The brake control unit is configured to determine a health of the electrohydraulic servo valve based on the sensor signal and the pressure signal.

According to the invention, the brake control unit determines the health of the electrohydraulic servo valve by determining an upper pressure threshold and a lower pressure threshold based on a current of the pressure signal, determining the pressure in the conduit based on the sensor signal, and comparing the pressure in the conduit to the upper pressure threshold and the lower pressure threshold.

In a preferred embodiment, the brake control unit may be configured to determine a first difference between the pressure in the conduit and the upper pressure threshold and a second difference between the pressure in the conduit and the lower pressure threshold.

In a preferred embodiment, the brake control unit may be configured to command a display to output a first alert in response to determining at least one of the pressure in the conduit is greater than the upper pressure threshold or the pressure in the conduit is less than the lower pressure threshold.

In a preferred embodiment, the brake control unit may be configured to command the display to output a second alert, different from the first alert, in response to determining at least one of the pressure in the conduit is less than or equal to the upper pressure threshold and the first difference is less than a difference threshold, or the pressure in the conduit is greater than or equal to the lower pressure threshold and the second difference is less than the difference threshold.

The subject matter of the present invention is defined in the appended claims, while exemplary embodiments are contained in this description and figures, wherein like numerals denote like elements.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the exemplary embodiments of the invention, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made within the scope of the claims. Thus, the detailed description herein is presented for purposes of illustration only and not limitation. The steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented, and are limited only by the claims.

Cross-hatching may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials. Throughout the present invention, like reference numbers denote like elements. Accordingly, elements with like element numbering may be shown in the figures but may not necessarily be repeated for the sake of brevity.

With reference to <FIG>, an aircraft <NUM> including a fuselage <NUM> and wings <NUM> is illustrated, in accordance with various embodiments. Aircraft <NUM> includes landing gear such as left landing gear <NUM>, right landing gear <NUM>, and nose landing gear <NUM>. Left landing gear <NUM>, right landing gear <NUM>, and nose landing gear <NUM> may generally support aircraft <NUM> when aircraft <NUM> is not flying, allowing aircraft <NUM> to taxi, take off, and land without damage. Left landing gear <NUM> may include left outboard (LOB) wheel 13A and left inboard (LIB) wheel 13B coupled by an axle <NUM>. Right landing gear <NUM> may include right outboard (ROB) wheel 15A and right inboard (RIB) wheel 15B coupled by an axle <NUM>. Nose landing gear <NUM> may include left nose wheel 17A and right nose wheel 17B coupled by an axle <NUM>. The nose wheels may differ from the left and right landing gear wheels in that the nose wheels may not include a brake.

Aircraft <NUM> may comprise a brake control unit (BCU) <NUM> and cockpit controls <NUM>. In various embodiments, the BCU <NUM> may be located in the fuselage of the aircraft. Left landing gear <NUM> and right landing gear <NUM> may be in communication with BCU <NUM> and may receive commands from BCU <NUM>. For example, BCU <NUM> may send brake commands to left landing gear <NUM> and right landing gear <NUM> based on signals received from cockpit controls <NUM> (e.g., from a pilot or autobrake system), from sources external to the aircraft (e.g., from a ground controller), or from onboard sensors.

With reference to <FIG>, a brake system <NUM> is shown, in accordance with various embodiments. In various embodiments, brake system <NUM> may be configured to control braking of left landing gear <NUM> and right landing gear <NUM>. Brake system <NUM> may include a LOB brake assembly <NUM> coupled to LOB wheel 13A, a LIB brake assembly <NUM> coupled to LIB wheel 13B, a ROB brake assembly <NUM> coupled to ROB wheel 15A, and a RIB brake assembly <NUM> coupled to RIB wheel 15B. While <FIG> illustrates brake system <NUM> comprising two landing gears (i.e., left landing gear <NUM> and right landing gear <NUM>) with four total wheels, it is further contemplated and understood that the systems and methods described herein may apply to brake systems comprising any number of landing gears and/or number of wheels per landing gear.

Brake assemblies <NUM>, <NUM>, <NUM>, <NUM> are configured to apply and release braking force on their respective wheels. Brake assemblies <NUM>, <NUM>, <NUM>, <NUM> may each comprise an actuator (e.g., a piston assembly) configured to apply pressure to a brake stack of the brake assembly. In this regard, LOB brake assembly <NUM> includes a LOB actuator <NUM> and a LOB brake stack <NUM>, LIB brake assembly <NUM> includes a LIB actuator <NUM> and a LIB brake stack <NUM>, ROB brake assembly <NUM> includes a ROB actuator <NUM> and a ROB brake stack <NUM>, and RIB brake assembly <NUM> includes a RIB actuator <NUM> and a RIB brake stack <NUM>. Each of the brake actuators <NUM>, <NUM>, <NUM>, <NUM> is configured to apply pressure to its respective brake stack, thereby decreasing a rotational speed of the wheel coupled to the brake and/or preventing rotation of the wheel.

In accordance with various embodiments, BCU <NUM> controls the pressure applied by brake actuators <NUM>, <NUM>, <NUM>, <NUM> via an electrohydraulic servo valve (EHSV) fluidly coupled to each of the brake actuators. In this regard, a LOB EHSV <NUM> is operably coupled to BCU <NUM> and LOB actuator <NUM>, a LIB EHSV <NUM> is operably coupled to BCU <NUM> and LIB actuator <NUM>, a ROB EHSV <NUM> is operably coupled to BCU <NUM> and ROB actuator <NUM>, and a RIB EHSV <NUM> is operably coupled to BCU <NUM> and RIB actuator <NUM>.

BCU <NUM> may include a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or some other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. A tangible, non-transitory computer-readable storage medium <NUM> may be in communication with BCU <NUM>. The storage medium <NUM> may comprise any tangible, non-transitory computer-readable storage medium known in the art. The storage medium <NUM> has instructions stored thereon that, in response to execution by BCU <NUM>, cause BCU <NUM> to perform operations related to monitoring a health of EHSVs <NUM>, <NUM>, <NUM>, <NUM>.

The term "non-transitory" is to be understood to remove only propagating transitory signals per se from the claim scope and does not relinquish rights to all standard computer-readable media that are not only propagating transitory signals per se.

In accordance with various embodiments, LOB EHSV <NUM> receives LOB pressure signals <NUM> from BCU <NUM> and provides fluid <NUM> to LOB actuator <NUM>. LOB EHSV <NUM> may be fluidly connected to and may receive fluid <NUM> from a fluid source <NUM>. LOB EHSV <NUM> modulates the flow rate and/or pressure of the fluid <NUM> provided to LOB actuator <NUM> based on the LOB pressure signal <NUM> received from BCU <NUM>. In various embodiments, the pressure of the fluid <NUM> in the conduit (or fluid path) <NUM> connecting an outlet of LOB EHSV <NUM> and an inlet of LOB actuator <NUM> is proportional to the current of the LOB pressure signal <NUM> sent by BCU <NUM>. Thus, the pressure applied by LOB actuator <NUM> to LOB brake stack <NUM> may be proportional to the current of LOB pressure signal <NUM>. For example, BCU <NUM> may increase or decrease a pressure applied to LOB brake stack <NUM> by increasing or decreasing, respectively, the current of LOB pressure signal <NUM>.

In accordance with various embodiments, a LOB valve monitoring sensor <NUM> may be coupled to conduit <NUM>. LOB valve monitoring sensor <NUM> is configured to measure a pressure and/or flow rate of the fluid <NUM> in conduit <NUM>. In this regard, LOB valve monitoring sensor <NUM> is located between the outlet of LOB EHSV <NUM> and the inlet of LOB actuator <NUM>. LOB valve monitoring sensor <NUM> outputs a sensor signal <NUM> corresponding to the pressure and/or fluid flow rate in conduit <NUM> to BCU <NUM>. Stated differently, BCU <NUM> receives sensor signal <NUM> from LOB valve monitoring sensor <NUM> and determines a pressure and/or a flow rate in conduit <NUM> based on the sensor signal <NUM>. As described in further detail below, BCU <NUM> is configured to monitor a health of LOB EHSV <NUM> using sensor signal <NUM>.

In accordance with various embodiments, LIB EHSV <NUM> receives LIB pressure signals <NUM> from BCU <NUM> and provides fluid <NUM> to LIB actuator <NUM>. LOB EHSV <NUM> may be fluidly connected to and may receive fluid <NUM> from fluid source <NUM>. While <FIG> shows LOB EHSV <NUM> and LIB EHSV <NUM> both receiving fluid from fluid source <NUM>, in various embodiments, LOB EHSV <NUM> and LIB EHSV <NUM> may each have their own dedicated fluid source. In accordance with various embodiments, LIB EHSV <NUM> modulates the flow rate and/or pressure of the fluid <NUM> provided to LIB actuator <NUM> based on a LIB pressure signal <NUM> received from BCU <NUM>. In various embodiments, the pressure of the fluid <NUM> in the conduit (or flow path) <NUM> connecting an outlet of LIB EHSV <NUM> and an inlet of LIB actuator <NUM> is proportional to the current of the LIB pressure signal <NUM> sent by BCU <NUM>. Thus, the pressure applied by LIB actuator <NUM> to LIB brake stack <NUM> may be proportional to the current of LIB pressure signal <NUM>. For example, BCU <NUM> may increase or decrease a pressure applied to LIB brake stack <NUM> by increasing or decreasing, respectively, the current of LIB pressure signal <NUM>.

In accordance with various embodiments, a LIB valve monitoring sensor <NUM> may be coupled to conduit <NUM>. LIB valve monitoring sensor <NUM> is configured to measure a pressure and/or flow rate of the fluid <NUM> in conduit <NUM>. In this regard, LIB valve monitoring sensor <NUM> is located between the outlet of LIB EHSV <NUM> and the inlet of LIB actuator <NUM>. LIB valve monitoring sensor <NUM> outputs a sensor signal <NUM> to BCU <NUM>. Sensor signal <NUM> corresponds to (i.e., is indicative of) the pressure and/or fluid flow rate in conduit <NUM>. Stated differently, BCU <NUM> receives sensor signal <NUM> from LIB valve monitoring sensor <NUM> and determines a pressure and/or a flow rate in conduit <NUM> based on the sensor signal <NUM>. As described in further detail below, BCU <NUM> is configured to monitor a health of LIB EHSV <NUM> based on sensor signal <NUM>.

In accordance with various embodiments, ROB EHSV <NUM> receives ROB pressure signals <NUM> from BCU <NUM> and provides a fluid <NUM> to ROB actuator <NUM>. ROB EHSV <NUM> may be fluidly connected to and may receive fluid <NUM> from a fluid source <NUM>. ROB EHSV <NUM> modulates the flow rate and/or pressure of the fluid <NUM> provided to ROB actuator <NUM> based on the ROB pressure signal <NUM> received from BCU <NUM>. In various embodiments, the pressure and/or flow rate of the fluid <NUM> in a conduit <NUM> (or flow path) connecting ROB EHSV <NUM> and ROB actuator <NUM> is proportional to the current of the ROB pressure signal <NUM> sent by BCU <NUM>. Thus, the pressure applied by ROB actuator <NUM> to ROB brake stack <NUM> may be proportional to the current of ROB pressure signal <NUM>. For example, BCU <NUM> may increase or decrease a pressure applied to ROB brake stack <NUM> by increasing or decreasing, respectively, the current of ROB pressure signal <NUM>.

In accordance with various embodiments, a ROB valve monitoring sensor <NUM> may be coupled to conduit <NUM>. In this regard, ROB valve monitoring sensor <NUM> is located between the outlet of ROB EHSV <NUM> and the inlet of ROB actuator <NUM>. ROB valve monitoring sensor <NUM> is configured to measure a pressure and/or flow rate of the fluid <NUM> in conduit <NUM>. ROB valve monitoring sensor <NUM> outputs a sensor signal <NUM> to BCU <NUM> corresponding to the pressure and/or fluid flow rate in conduit <NUM>. Stated differently, BCU <NUM> receives sensor signal <NUM> from ROB valve monitoring sensor <NUM> and determines a pressure and/or a flow rate in conduit <NUM> based on the sensor signal <NUM>. As described in further detail below, BCU <NUM> is configured to monitor a health of ROB EHSV <NUM> using sensor signal <NUM>.

In accordance with various embodiments, RIB EHSV <NUM> receives RIB pressure signals <NUM> from BCU <NUM> and provides fluid <NUM> to RIB actuator <NUM>. RIB EHSV <NUM> may be fluidly connected to and may receive fluid <NUM> from fluid source <NUM>. While <FIG> shows ROB EHSV <NUM> and RIB EHSV <NUM> both receiving fluid <NUM> from fluid source <NUM>, in various embodiments, ROB EHSV <NUM> and RIB EHSV <NUM> may each have their own dedicated fluid source. In various embodiments, LOB EHSV <NUM>, LIB EHSV <NUM>, ROB EHSV <NUM>, and RIB EHSV <NUM> may be fluidly connected to the same fluid source.

RIB EHSV <NUM> is configured to modulate the flow rate and/or pressure of the fluid <NUM> provided to RIB actuator <NUM> based on the RIB pressure signal <NUM> received from BCU <NUM>. In various embodiments, the pressure and/or flow rate of the fluid <NUM> in the conduit (or flow path) <NUM> connecting RIB EHSV <NUM> and RIB actuator <NUM> is proportional to the current of the RIB pressure signal <NUM> sent by BCU <NUM>. Thus, the pressure applied by RIB actuator <NUM> to RIB brake stack <NUM> may be proportional to the current of RIB pressure signal <NUM>. For example, BCU <NUM> may increase or decrease a pressure applied to RIB brake stack <NUM> by increasing or decreasing, respectively, the current of RIB pressure signal <NUM>.

In accordance with various embodiments, a RIB valve monitoring sensor <NUM> may be coupled to conduit <NUM>. In this regard, RIB valve monitoring sensor <NUM> is located between the outlet of RIB EHSV <NUM> and the inlet of RIB actuator <NUM>. RIB valve monitoring sensor <NUM> is configured to measure a pressure and/or flow rate of the fluid <NUM> in conduit <NUM>. RIB valve monitoring sensor <NUM> outputs a sensor signal <NUM> to BCU <NUM> corresponding to the pressure and/or fluid flow rate in conduit <NUM>. Stated differently, BCU <NUM> receives sensor signal <NUM> from RIB valve monitoring sensor <NUM> and determines a pressure and/or a flow rate in conduit <NUM> based on the sensor signal <NUM>. As described in further detail below, BCU <NUM> is configured to monitor a health of RIB EHSV <NUM> using sensor signal <NUM>.

With reference to <FIG>, additional details of RIB EHSV <NUM> are illustrated. While <FIG>, <FIG>, and <FIG> illustrate components of RIB EHSV <NUM>, it should be understood that LOB EHSV <NUM>, LIB EHSV <NUM>, and ROB EHSV <NUM> include the elements and functionalities as described herein with respect to RIB EHSV <NUM>. In accordance with various embodiments, RIB EHSV <NUM> includes a torque motor <NUM>. Torque motor <NUM> includes an armature <NUM> and a coil <NUM>.

RIB EHSV <NUM> further includes a spool <NUM> and a sleeve <NUM>. Sleeve <NUM> is configured to surround an outer circumferential surface <NUM> of spool <NUM>. A diameter of spool <NUM> may be varied along outer circumferential surface <NUM>. Outer circumferential surface <NUM> and sleeve <NUM> may define various flow paths about spool <NUM>. In this regard, sleeve <NUM> contacts portions of outer circumferential surface <NUM>, thereby forming a sealing interface with the contacted portions of outer circumferential surface <NUM>, and sleeve <NUM> is spaced apart from other portions of outer circumferential surface <NUM>, thereby forming flow paths between the outer circumferential surface <NUM> of spool <NUM> and an inner circumferential surface <NUM> of sleeve <NUM>. In various embodiments, one or more fluid path may also be formed through an interior of spool <NUM>.

Spool <NUM> is configured to translate relative to and within sleeve <NUM>. In this regard, spool <NUM> may translate axially along axis A. Sleeve <NUM> may be located about axis A. A flapper <NUM> is attached to armature <NUM>. In response to receiving current in a first, or positive, direction (e.g., in response to a first pressure signal <NUM> (<FIG>)), coil <NUM> generates a first magnetic field. The first magnetic field is configured to translate armature <NUM> in a first direction, thereby driving flapper <NUM> toward and/or into contact with a first nozzle <NUM> (as shown in <FIG>). In response to receiving current in a second, or negative, direction (e.g., in response to a second pressure signal <NUM> (<FIG>)), coil <NUM> generates a second magnetic field in the opposite direction of the first magnetic field. The second magnetic field is configured to translate armature <NUM> in a second direction, thereby driving flapper <NUM> toward and/or into contact with a second nozzle <NUM> (as shown in <FIG>).

With reference to <FIG>, translation of flapper <NUM> into contact with first nozzle <NUM> increases the fluid pressure in within a first pressure stage <NUM> of RIB EHSV <NUM>. First pressure stage <NUM> may be defined, at least partially, by a first end <NUM> of spool <NUM>. The increase in fluid pressure in first pressure stage <NUM> increases a pressure exerted on first end <NUM> of spool <NUM> and thereby forces spool <NUM> to translate in a first axial direction D1. With reference to <FIG>, translation of flapper <NUM> into contact with second nozzle <NUM> increases the fluid pressure in within a second pressure stage <NUM> of RIB EHSV <NUM>. Second pressure stage <NUM> may be defined, at least partially, by a second end <NUM> of spool <NUM>. The increase in fluid pressure in second pressure stage <NUM> increases the pressure exerted on second end <NUM> of spool <NUM> and thereby forces spool <NUM> to translate in a second axial direction D2. Thus, the axial direction of translation of spool <NUM> may be controlled by applying current in either the first direction (e.g., positive current) or in the second direction (e.g., negative current) to coil <NUM>.

RIB EHSV <NUM> includes a supply port <NUM>. With combined reference to <FIG> and <FIG>, fluid <NUM> (<FIG>) from fluid source <NUM> (<FIG>) may be received at supply port <NUM>. Stated differently, the fluid <NUM> from fluid source <NUM> flows into RIB EHSV <NUM> via supply port <NUM>. In various embodiments, a filter assembly <NUM> may be fluidly coupled to supply port <NUM> such that fluid flows into filter assembly <NUM> upon entering RIB EHSV <NUM> via supply port <NUM>. Filter assembly <NUM> may define multiple orifices and flow paths configured to fluidly connect supply port <NUM> to various components of RIB EHSV <NUM>.

RIB EHSV <NUM> also includes a control port <NUM>. Conduit <NUM> (<FIG>) may be fluidly connected to control port <NUM> (e.g., control port <NUM> may form an outlet of RIB EHSV <NUM>). Fluid <NUM> (<FIG>) may flow between conduit <NUM> (<FIG>) and RIB EHSV <NUM> via control port <NUM>.

In <FIG>, spool <NUM> is illustrated in a first, or closed, position. In the first position, supply port <NUM> may be fluidly sealed from control port <NUM>. Stated differently, in the first position, spool <NUM> may block fluid from supply port <NUM> from reaching control port <NUM>. In <FIG>, spool <NUM> is illustrated in a second, or open, position. In the second position, supply port <NUM> is fluidly connected to control port <NUM>. Stated differently, in the second position, spool <NUM> and sleeve <NUM> may define a fluid path that allows the fluid from supply port <NUM> to reach control port <NUM>.

In various embodiments, the second position may represent a fully open, or <NUM>% open, position and the first position may represent a closed, or <NUM>% open, position. The position of spool <NUM> between the fully open position and the closed position (i.e., the <NUM>% open position and <NUM>% open position) may be controlled by the amount of current supplied to coil <NUM>. For example, spool <NUM> may be located between the fully open and close position (e.g., at a <NUM>% open position, a <NUM>% open position, a <NUM>% open position, etc.) and the current applied to coil <NUM> may control the position of spool <NUM>. The pressure in conduit <NUM> (<FIG>) may be proportional to the position of spool <NUM> and increasing the open percentage increases the pressure and/or flow rate of fluid <NUM> (<FIG>) in conduit <NUM> (<FIG>). Thus, the pressure and/or flow rate of fluid <NUM> (<FIG>) is also proportional to the current applied to coil <NUM> (e.g., an increase in the current, increases the pressure and flow rate in conduit <NUM>).

With reference <FIG>, a graphical representation <NUM> of normalized servo valve pressure versus normalized current is illustrated. With combined reference to <FIG>, <FIG>, and <FIG>, normalized current, which is located along the x-axis, is representative of the current supplied to coil <NUM>. In this regard, the current values on the x-axis are determined based on the current of the pressure signal output by BCU <NUM> (e.g., the current of pressure signal <NUM>, <NUM>, <NUM> or <NUM>). Normalized servo valve pressure, which is located along the y-axis, is representative of the pressure in conduit <NUM>. In this regard, servo valve pressure values are determined from the sensor signals output by the valve monitoring sensor (e.g., by valve monitoring sensor <NUM>, <NUM>, <NUM> or <NUM>). Line <NUM> in graph <NUM> illustrates the static gain of a healthy EHSV. As shown in graph <NUM>, in a healthy EHSV, line <NUM> is generally linear and/or has a constant, linear slope when the normalized pressure is greater than <NUM>% and less than <NUM>% (e.g., between approximately <NUM>% and <NUM>% normalized current). Thus, in a healthy EHSV, the change pressure in conduit <NUM> is proportional to the current supplied to coil <NUM>. In accordance with various embodiments, an expected pressure may be determined from line <NUM>. In this regard, the points along line <NUM> represent the expected pressure values relative to the current provided to coil <NUM>.

Line <NUM> in graph <NUM> represents an upper pressure threshold. Line <NUM> represents a lower pressure threshold. The upper pressure threshold <NUM> and the lower pressure threshold <NUM> may a have a slope that is equal to the static gain (e.g., line <NUM>) of a healthy EHSV between normalized pressures greater than <NUM>% and less than <NUM>%. In this regard, the slope of upper pressure threshold line <NUM> between approximately <NUM>% normalized current and approximately <NUM>% normalized current may be linear and/or constant and/or parallel to line <NUM>. Similarly, the slope of lower pressure threshold line <NUM> between approximately <NUM>% normalized current and approximately <NUM>% normalized current may be linear and/or constant and/or parallel to line <NUM>.

The translation of spool <NUM> relative to sleeve <NUM> can cause spool <NUM> and/or sleeve <NUM> to wear. Wear of the spool <NUM> and/or of the sleeve <NUM> may create clearance(s) between the inner circumferential surface <NUM> of the sleeve <NUM> and the outer circumferential surface <NUM> of the spool <NUM>. The clearance(s) may allow fluid to leak between the spool <NUM> and the sleeve <NUM> and this fluid leakage tends to result in the static gain characteristics of the servo valve no longer being linear. For example, not to be bound by theory, it is believed that leakage flow is proportional to the cube of diametrical clearance and inversely proportional to length of clearance. With increase in wear at spool-sleeve interface, diametric clearance increases as a cubical function resulting in loss of the linearity of static gain characteristics of the EHSV. Similarly, debris may also find its way into the EHSV and/or cause fluid flow blockage, which can result in the loss of the linearity of static gain characteristics of the EHSV.

For example, with reference to <FIG>, line <NUM> and line <NUM> in graph <NUM> illustrate the static gain of unhealthy EHSVs. For example, EHSV having a worn spool, a worn sleeve and/or blockage from debris. The slope of line <NUM>, which is nonlinear, indicates an EHSV is experiencing a fault condition and/or is exhibiting wear. Further, at approximately <NUM>% normalized current, line <NUM> crosses upper pressure threshold <NUM>. The steeper than expected slope of line <NUM> indicates that the pressure in conduit <NUM> is greater than expected based on the current being provided to the EHSV coil. Similarly, the slope of line <NUM>, which is nonlinear, also indicates an EHSV that experiencing a fault condition and/or is exhibiting wear. Further, at approximately <NUM>% normalized current, line <NUM> crosses lower pressure threshold <NUM>. The flatter than expected slope of line <NUM> indicates that the pressure in conduit <NUM> is less than expected based on the current being provided to the EHSV coil.

With reference to <FIG>, a system <NUM> for monitoring the health of an EHSV is illustrated. In various embodiments, system <NUM> may be installed in aircraft <NUM> (<FIG>). Elements of system <NUM> with like numbering to <FIG> are intending to be the same and may not necessarily be repeated for the sake of brevity. While system <NUM> is shown as monitoring the health of RIB EHSV, it is contemplated and understood that similar systems may be employed to monitor the health of the other EHSVs. System <NUM> includes BCU <NUM>. BCU is configured to receive a brake command <NUM>. Brake command <NUM> may be sent from cockpit controls <NUM> in <FIG> (e.g., from a pilot or autobrake system of aircraft <NUM>), from sources external to the aircraft <NUM> (e.g., from a ground controller), or from onboard sensors.

BCU <NUM> is configured to determine a current for pressure signal <NUM> based on brake command <NUM>. BCU <NUM> sends pressure signal <NUM> to EHSV <NUM> (e.g., to coil <NUM> <FIG>). Pressure signal <NUM> causes translation of spool <NUM> (<FIG>) and thereby changes (e.g., increases) the flow rate of fluid <NUM> through conduit <NUM> and/or the fluid pressure in conduit <NUM>. As used here, the "flow rate" of a fluid refers to the volume of fluid flowing through an area relative to a duration of time (e.g. cubic feet or cubic meters per second). The change in flow rate and/or fluid pressure in conduit <NUM> changes the pressure applied by actuator <NUM> to brake stack <NUM>.

BCU <NUM> may further receive a brake pressure signal <NUM> from a brake pressure sensor <NUM>. Brake pressure sensor <NUM> is configured to measure a pressure applied to brake stack <NUM> by actuator <NUM>. The brake pressure signal <NUM> corresponds to the measured pressure. In this regard, BCU <NUM> may determine the pressure applied to brake stack <NUM> based on brake pressure signal <NUM>. BCU <NUM> may compare the pressure applied to an expected brake stack pressure <NUM>. BCU <NUM> may determine the expected brake stack pressure based on the brake command. If the pressure applied to brake stack <NUM> is different from the expected brake stack pressure, BCU <NUM> may adjust the current of pressure signal <NUM>. BCU <NUM> may continue to adjust the current of pressure signal <NUM>, until the pressure applied to brake stack <NUM> is equal, or approximately equal, to the expected brake stack pressure.

System <NUM> includes valve monitoring sensor <NUM>. Valve monitoring sensor <NUM> is coupled to conduit <NUM> and is configured to measure at least one of the flow rate or the pressure in conduit <NUM>. Valve monitoring sensor <NUM> outputs sensor signal <NUM> corresponding the pressure and/or flow rate measured by valve monitoring sensor <NUM>. BCU receives sensor signal <NUM> and determines a pressure in conduit <NUM> based on sensor signal <NUM>. If sensor signal <NUM> corresponds to a flow rate, BCU <NUM> may determine the pressure that corresponds to the flow rate.

In accordance with various embodiments, BCU <NUM> also determines the health of EHSV <NUM> based on the pressure in conduit <NUM>. In this regard, BCU <NUM> may compare the pressure in conduit <NUM> to an upper pressure threshold and a lower pressure threshold. BCU <NUM> may determine the upper pressure threshold and the lower pressure threshold based on the current of the pressure signal <NUM> sent to EHSV <NUM>. In this regard, BCU <NUM> may access a look up table stored in storage medium <NUM> (or any other memory accessible to BCU <NUM>). The upper pressure threshold values in the lookup table may correspond to points along an upper threshold line similar to line <NUM> in <FIG>. The lower pressure threshold values in the lookup table may correspond to points along a lower threshold line similar to line <NUM> in <FIG>.

In various embodiments, BCU <NUM> may determine the upper pressure threshold and the lower pressure threshold by determining an expected pressure based on the current of pressure signal <NUM> and adding or subtracting a set value to or from the expected pressure to calculate the upper and lower pressure thresholds, respectively. The expected pressure is proportional to the current such that a slope of the expected static gain is linear.

BCU <NUM> compares the pressure in conduit <NUM> to the upper and lower pressure threshold. System <NUM> includes a display <NUM>. BCU <NUM> may send display commands <NUM> to display <NUM>. Display <NUM> may be configured to convey a health status of EHSV <NUM> to aircraft crew, ground crew, and/or maintenance personnel. Display <NUM> may be configured to output various status alerts based on the display command <NUM> received from BCU <NUM>. The status alert output by display <NUM> may be images, symbols, text messages, audio messages, illuminated lights, or any other alert capable of conveying information about the health of EHSV <NUM> to aircraft crew, ground crew, and/or maintenance personnel.

For example, BCU <NUM> may output a first display command <NUM> configured to cause display <NUM> to output an immediate maintenance needed (or first) alert in response to BCU <NUM> determining the pressure in conduit <NUM> is greater than the upper pressure threshold or less than the lower pressure threshold. The immediate maintenance needed alert is configured to convey to aircraft crew, ground crew, and/or maintenance personnel that maintenance and/or replacement of one or more components of EHSV <NUM> is needed immediately. BCU <NUM> may output a second display command <NUM> configured to cause display <NUM> to output a warning (or second) alert in response to BCU <NUM> determining the pressure in conduit <NUM> is less than the upper pressure threshold and that the difference between the pressure in conduit <NUM> and the upper pressure threshold is less than a threshold difference (e.g., in response to the determining the pressure in conduit <NUM> is approaching the upper pressure threshold). BCU <NUM> may similarly output the second display command <NUM> configured to cause display <NUM> to output the warning alert in response to BCU <NUM> determining the pressure in conduit <NUM> is greater than the lower pressure threshold and the difference between the pressure in conduit <NUM> and the lower pressure threshold is less than the threshold difference (e.g., in response to determining the pressure in conduit <NUM> is approaching the lower pressure threshold). The warning alert may be configured to convey to aircraft crew, ground crew, and/or maintenance personnel that maintenance of EHSV <NUM> should be scheduled. Alerting that maintenance should be scheduled tends to allow aircraft operators to better plan the aircraft's availability and/or reduces occurrences of unexpected and/or immediate maintenance operations.

With reference to <FIG>, a method <NUM> for monitoring an electrohydraulic servo valve of an aircraft landing gear is shown. With combined reference to <FIG> and <FIG>, in accordance with various embodiments, method <NUM> may be carried out by system <NUM>. For example, one or more of the steps of method <NUM> may be performed by BCU <NUM>. In various embodiments, method <NUM> may comprise receiving a brake command (step <NUM>). Step <NUM> may include BCU <NUM> receiving brake command <NUM> from, for example, cockpit controls <NUM> (<FIG>). Method <NUM> further includes BCU <NUM> outputting pressure signal <NUM> to the EHSV <NUM> based on the brake command <NUM> (step <NUM>) and BCU <NUM> receiving sensor signal <NUM> from valve monitoring sensor <NUM> (step <NUM>) with valve monitoring sensor <NUM> being configured to measure at least one of the pressure or the fluid flow in conduit <NUM>, which is fluidly coupled to control port <NUM> of EHSV <NUM>. Method <NUM> may further include BCU <NUM> determining the health of the EHSV <NUM> based on the sensor signal <NUM> (step <NUM>).

With reference to <FIG>, in various embodiments, step <NUM> may include BCU <NUM> determining an upper pressure threshold and a lower pressure threshold based on the current of pressure signal <NUM> (step 408A). In various embodiments, BCU <NUM> may determine the upper pressure threshold by determining an expected pressure of the conduit <NUM> based on the current of the pressure signal and then adding a first value to the expected pressure. BCU <NUM> may determine the lower pressure threshold by determining the expected pressure of the conduit <NUM> based on the current of the pressure signal <NUM> and then subtracting a second value from the expected pressure. The second value may be equal to or different from the first value.

In various embodiments, BCU <NUM> may determine the upper pressure threshold by locating a point on an upper threshold line (e.g., line <NUM> in FIG. 5A) corresponding the current of the pressure signal <NUM>, where the upper pressure threshold line <NUM> is a linear line and has a constant slope. BCU <NUM> may determine the lower pressure threshold by locating a point on a lower threshold line (e.g., line <NUM> in FIG. A) corresponding the current of the pressure signal <NUM>. The lower pressure threshold line <NUM> is parallel to the upper pressure threshold line <NUM>.

In various embodiments, step <NUM> may further include BCU <NUM> determining the pressure in the conduit <NUM> based on the sensor signal <NUM> (step 408B) and BCU <NUM> comparing the pressure in the conduit <NUM> to the upper pressure threshold and to the lower pressure threshold (step 408C).

In various embodiments, method <NUM> may further comprise BCU <NUM> commanding display <NUM> to output an alert in response to BC determining that the pressure in the conduit <NUM> is greater than the upper pressure threshold or that the pressure in the conduit is less than the lower pressure threshold (step 410A).

With reference to <FIG>, in various embodiments, step 408C may include BCU <NUM> determining a first difference between the pressure in the conduit <NUM> and the upper pressure threshold and a second difference between the pressure in the conduit <NUM> and the lower pressure threshold (step 408C-<NUM>). BCU <NUM> may then compare each of the first difference and second difference to a difference threshold (step 408C-<NUM>). In various embodiments, the first difference and the second difference may be compared to the same difference threshold. In various embodiments, a first difference threshold used for the first difference may be different from a second difference threshold used for the second difference.

In various embodiments, method <NUM> may further include BCU <NUM> commanding display <NUM> to output a warning alert, in response to at least one of the first difference or the second difference being less than the difference threshold (step 410B).

Benefits and other advantages have been described herein with regard to specific embodiments. However, the benefits, advantages, and any elements that may cause any benefit or advantage to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the invention. The scope of the invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more.

Claim 1:
A system for monitoring an electrohydraulic servo valve (<NUM>), comprising:
a brake control unit (<NUM>);
a valve monitoring sensor (<NUM>) configured to measure at least one of a pressure or a fluid flow rate in a conduit (<NUM>) fluidly connected to a control port of the electrohydraulic servo valve; and
a tangible, non-transitory memory (<NUM>) configured to communicate with the brake control unit, the tangible, non-transitory memory having instructions stored thereon that, in response to execution by the brake control unit, cause the brake control unit to perform operations comprising:
receiving, by the brake control unit (<NUM>), a brake command;
outputting, by the brake control unit, a pressure signal to the electrohydraulic servo valve (<NUM>) based on the brake command;
receiving, by the brake control unit, a sensor signal from the valve monitoring sensor (<NUM>); characterised by
determining, by the brake control unit, an upper pressure threshold based on a current of the pressure signal;
determining, by the brake control unit, a lower pressure threshold based on the current of the pressure signal;
determining, by the brake control unit, the pressure in the conduit based on the sensor signal; and
comparing, by the brake control unit, the pressure in the conduit to the upper pressure threshold and the lower pressure threshold; and
determining, by the brake control unit, a health of the electrohydraulic servo valve based on the comparison of the pressure in the conduit to the upper pressure threshold and the lower pressure threshold.