Patent Description:
<CIT> discloses a method of monitoring engine health. The method may include the step of monitoring a vibration of a gearbox using a vibration sensor to detect a primary amplitude at a primary mesh frequency and a sideband amplitude at a sideband frequency. The method may further include calculating a ratio of the primary amplitude to the sideband amplitude, and evaluating a health of the gearbox based on the ratio of the primary amplitude to the sideband amplitude.

<CIT> discloses a system for monitoring an acoustic signal in a gas turbine engine. The system includes a gas turbine engine component that emits the acoustic signal. A microphone senses the acoustic signal and creates a microphone signal indicative of one or more characteristics of the acoustic signal. A controller receives the microphone signal and is configured to analyze the microphone signal to identify a gearbox event peak. If the gearbox event peak is present, the controller quantifies an amplitude of the gearbox event peak. The controller compares the amplitude of the gearbox event peak to a threshold to determine whether the gas turbine engine component needs maintenance.

Power gearboxes are e.g. in the context of aircraft engines gearboxes which transmit a large torque required for propulsion. This differentiates power gearboxes from e.g. accessory gearboxes. In many cases, epicyclic gearboxes are used as power gearboxes. Power gearboxes, in particular epicyclic gearboxes are often subject to high mechanical loads or have to operate for a long time without maintenance. One typical application of power gearboxes are epicyclic gearboxes is a geared turbofan aircraft engine in which the epicyclic gearbox lowers the rotational speed of the fan shaft which is driven by the turbine section of the geared turbofan engine.

Therefore, is important to find ways to monitor power gearboxes for mechanical failures.

This issue is addressed by a method for detecting a functional failure with the features of claim <NUM>.

First operational data in the gas turbine engine is measured using at least two operational parameters dependent on the power generation and / or power consumption of the gas turbine engine and / or the epicyclic gearbox.

The operational parameter depend e.g. on way the engine power is controlled by the combined effect of at least two parameters.

The power transmitted across the power gearbox is given by torque x speed determined at input and output shaft.

For example control of engine power for a geared turbofan engine comprising a fan shaft and a two-spool core engine is achieved by regulating fuel flow (throttle) and stator variable positions to regulate the air flow intake - primarily at an intermediate compressor - and variable inlet guide vanes and / or variable stator vane angles, as they change the compressor flow capacity. On geared turbofan control action can take part on two vanes at the same time.

As will be explained below, changes in parameters related to the power characteristics transmitted across the gearbox are indicators for some of the planetary gear train component failures, in particular planet bearings.

Then analyzed operational data is obtained, the analyzed operational data comprising time data, angular data of a rotation, frequency data and / or magnitude data and phase data from the measured operational data. This means that data can e.g. be filtered and transformed into different domains in a signal processing unit.

The analyzed operational data then compared with stored baseline operational data to determine deviation data from the baseline nominal operational data. The baseline operational data represents nominal behavior of the system (e.g. without a planet bearing failure), so that the comparison yields deviations from that nominal behavior. Any trend described hereby in the general method is related and comparable under equivalent operative conditions, such engine power, torque, speed, altitude, external pressure and temperature, propeller pitch, cross wind etc..

Time dependent trend data from the deviation data is determined. Trend data has to be understood in a broad sense, as e.g. all occurring changes in the time dependent data and / or a drift in the engine performance can be considered as a trend. The changes can be detected between different parameters (e.g. a set of parameters) in an engine controller, e.g. to obtain a given engine power at the certain flight conditions, of changes in the fuel flow and / or changes in the compressor variable vanes or flow inlets, due to failure in the mechanical torque load path (e.g. planets bearing).

The engine power control can have two or more active parameters that are necessary to be control the engine performance. Besides active parameters, temprature, pressure, and altitude are parameters that are considered in the engine power regulation setting. Embodiments described herein have the capability of recognising variations in the engine power settings that, if related with specific trend and phase changes of the characteristic vibration frequencies, allow an early detection of the mechanical failure, e.g. a bearing failure.

When a change happens in the torque load path of the gear train, the control system will automatically compensates it injecting or reducing energy and therefore changing torque shared by the planet gears and bearings.

Then a signal and / or a protocol is generated for controlling the epicyclic gearbox and / or the gas turbine engine based on the time dependent trend data, in particular if a predetermined condition or threshold is exceeded. This allows that the failure has an operational consequence to prevent e.g. more damage to the engine and actuate a safety protocol.

In one embodiment, at least one measured operational parameter and / or at least one baseline operational parameter is.

These parameters are all related to the power consumption. If a failure occurs in the epicyclic gearbox, one of those parameters and hence the power consumption will be affected. For example an increase in the oil temperature of the scavenged oil in a gearbox could be an indication of a mechanical failure which increased friction within the gearbox.

Regarding the vibrations, frequencies of e.g. up to <NUM> would provide essential discriminating information to detect a planet bearing failure in <NUM>% of the cases, Gear mesh frequencies mesh and its multiples, GFM (<NUM> and more) is an indicator of a gearbox transmission failure that can sometime generate an ancillary trend in parallel to the main planet bearing failure indicators at much lower frequencies.

In a further embodiment, the time data obtained from the measured operational data is subjected to windowing in a signal processing unit.

The deviation data can e.g. comprise a change in magnitude of an amplitude and / or a change in the phase of a signal in the frequency domain. Time dependent deviation data can e.g. comprises data on.

Load measures are not always available in flight situations. The method and system discussed here has have capability to identify from vibration and performance as a combined analysis a combination parameters that represent dynamic loads indicators of an future failure in planet bearings e.g. a gearbox output and input unbalance rotating vector (magnitude and phase) or journal oil film rotating vectors. Torque oscillations can be obtained by fuel oscillation data and tangential vibration.

In a further embodiment, the trend data is checked if a condition or threshold is exceeded for at least.

In one embodiment the threshold is adapted for range of operation points by the use of á priori knowledge, in particular that known magnitudes of harmonics which are not related to a failure are considered in filtering out relevant harmonics for the failure. Not all magnitudes are relevant for detecting the failure, so the filtering makes sure that relevant data is generated and processed.

Another embodiment comprises a signal and / or the protocol used for indicating a functional failure of a bearing, in particular a ball bearing or a journal bearing in the epicyclic gearbox, the ring gear, planet carrier, the sun gear and / or the planet gears. These components are in the power train of the gas turbine engine, so that a failure affects the power output. Further, is possible that the signal and / or the protocol is used for generating a lifetime prediction and / or a maintenance schedule for the epicyclic gearbox and / or the gas turbine engine.

The signal and / or protocol can e.g. be triggered when the measured operational data comprises at least one significant deviation from the baseline, e.g. involving one or more vibrational frequencies characteristic of the planet bearing failure, in particular shaft x number of failing bearing and harmonics.

The measured operational data is obtained in one embodiment from at least one power sensor, fuel flow sensor, torque sensor, rotational speed sensor, speed sensor, vibration sensor, temperature sensor and / or pressure sensor. Again, those quantities are related to the power consumption of the gas turbine engine and the epicyclic gearbox. The vibration sensor can e.g. be an acceleration sensor, an acoustic sensor and / or a strain gauge.

At least one sensor can be positioned at a static part of the epicyclic gearbox, in particular at housing of the epicyclic gearbox, a ring gear of the epicyclic gearbox and / or the ring gear mount of the epicyclic gearbox.

It should be noted that the epicyclic gearbox could comprise planetary gears in a star arrangement or in a planetary arrangement. This means that the ring gear, the carrier or the sun gear can static, i.e. fixed.

The issue is also addressed by a system with the features of claim <NUM> and a gas turbine engine with the features of claim <NUM>.

Each fan blade may be defined as having a radial span extending from a root (or hub) at a radially inner gas-washed location, or <NUM>% span position, to a tip at a <NUM>% span position. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip may be less than (or on the order of) any of: <NUM>, <NUM>, <NUM><NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). These ratios may commonly be referred to as the hub-to-tip ratio. The radius at the hub and the radius at the tip may both be measured at the leading edge (or axially forwardmost) part of the blade. The hub-to-tip ratio refers, of course, to the gas-washed portion of the fan blade, i.e. the portion radially outside any platform.

The radius of the fan may be measured between the engine centreline and the tip of a fan blade at its leading edge. The fan diameter (which may simply be twice the radius of the fan) may be greater than (or on the order of) any of: <NUM> (around <NUM> inches), <NUM>, <NUM> (around <NUM> inches), <NUM> (around <NUM> inches), <NUM> (around <NUM> inches), <NUM> (around <NUM> inches), <NUM>, <NUM> (around <NUM> inches), <NUM> (around <NUM> inches), <NUM> (around <NUM> inches), <NUM>, <NUM> (around <NUM> inches), <NUM> (around <NUM> inches), <NUM> (around <NUM> inches) cm or <NUM> (around <NUM> inches). The fan diameter may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds).

The rotational speed of the fan may vary in use. Generally, the rotational speed is lower for fans with a higher diameter. Purely by way of non-limitative example, the rotational speed of the fan at cruise conditions may be less than <NUM> rpm, for example less than <NUM> rpm. Purely by way of further non-limitative example, the rotational speed of the fan at cruise conditions for an engine having a fan diameter in the range of from <NUM> to <NUM> (for example <NUM> to <NUM>) may be in the range of from <NUM> rpm to <NUM> rpm, for example in the range of from <NUM> rpm to <NUM> rpm, for example in the range of from <NUM> rpm to <NUM> rpm. Purely by way of further non-limitative example, the rotational speed of the fan at cruise conditions for an engine having a fan diameter in the range of from <NUM> to <NUM> may be in the range of from <NUM> rpm to <NUM> rpm, for example in the range of from <NUM> rpm to <NUM> rpm, for example in the range of from <NUM> rpm to <NUM> rpm.

In use of the gas turbine engine, the fan (with associated fan blades) rotates about a rotational axis. This rotation results in the tip of the fan blade moving with a velocity Utip. The work done by the fan blades <NUM> on the flow results in an enthalpy rise dH of the flow. A fan tip loading may be defined as dH/Utip<NUM>, where dH is the enthalpy rise (for example the <NUM>-D average enthalpy rise) across the fan and Utip is the (translational) velocity of the fan tip, for example at the leading edge of the tip (which may be defined as fan tip radius at leading edge multiplied by angular speed). The fan tip loading at cruise conditions may be greater than (or on the order of) any of: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> (all units in this paragraph being Jkg-<NUM>K-<NUM>/(ms-<NUM>)<NUM>). The fan tip loading may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds).

Gas turbine engines in accordance with the present disclosure may have any desired bypass ratio, where the bypass ratio is defined as the ratio of the mass flow rate of the flow through the bypass duct to the mass flow rate of the flow through the core at cruise conditions. In some arrangements the bypass ratio may be greater than (or on the order of) any of the following: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. The bypass ratio may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The bypass duct may be substantially annular. The bypass duct may be radially outside the core engine. The radially outer surface of the bypass duct may be defined by a nacelle and/or a fan case.

The overall pressure ratio of a gas turbine engine as described and/or claimed herein may be defined as the ratio of the stagnation pressure upstream of the fan to the stagnation pressure at the exit of the highest pressure compressor (before entry into the combustor). By way of non-limitative example, the overall pressure ratio of a gas turbine engine as described and/or claimed herein at cruise may be greater than (or on the order of) any of the following: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The overall pressure ratio may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds).

Specific thrust of an engine may be defined as the net thrust of the engine divided by the total mass flow through the engine. At cruise conditions, the specific thrust of an engine described and/or claimed herein may be less than (or on the order of) any of the following: <NUM> Nkg-<NUM>s, <NUM> Nkg-<NUM>s, <NUM> Nkg-<NUM>s, <NUM> Nkg-<NUM>s, <NUM> Nkg-<NUM>s, <NUM> Nkg-<NUM>s or <NUM> Nkg-<NUM>s. The specific thrust may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). Such engines may be particularly efficient in comparison with conventional gas turbine engines.

A gas turbine engine as described and/or claimed herein may have any desired maximum thrust. Purely by way of non-limitative example, a gas turbine as described and/or claimed herein may be capable of producing a maximum thrust of at least (or on the order of) any of the following: 160kN, 170kN, 180kN, 190kN, 200kN, 250kN, 300kN, 350kN, 400kN, 450kN, 500kN, or 550kN. The maximum thrust may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The thrust referred to above may be the maximum net thrust at standard atmospheric conditions at sea level plus <NUM> deg C (ambient pressure <NUM>. 3kPa, temperature <NUM> deg C), with the engine static.

In use, the temperature of the flow at the entry to the high pressure turbine may be particularly high. This temperature, which may be referred to as TET, may be measured at the exit to the combustor, for example immediately upstream of the first turbine vane, which itself may be referred to as a nozzle guide vane. At cruise, the TET may be at least (or on the order of) any of the following: <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. The TET at cruise may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The maximum TET in use of the engine may be, for example, at least (or on the order of) any of the following: <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. The maximum TET may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The maximum TET may occur, for example, at a high thrust condition, for example at a maximum take-off (MTO) condition.

A fan blade and/or aerofoil portion of a fan blade described and/or claimed herein may be manufactured from any suitable material or combination of materials. For example at least a part of the fan blade and/or aerofoil may be manufactured at least in part from a composite, for example a metal matrix composite and/or an organic matrix composite, such as carbon fibre. By way of further example at least a part of the fan blade and/or aerofoil may be manufactured at least in part from a metal, such as a titanium based metal or an aluminium based material (such as an aluminium-lithium alloy) or a steel based material. The fan blade may comprise at least two regions manufactured using different materials. For example, the fan blade may have a protective leading edge, which may be manufactured using a material that is better able to resist impact (for example from birds, ice or other material) than the rest of the blade. Such a leading edge may, for example, be manufactured using titanium or a titanium-based alloy. Thus, purely by way of example, the fan blade may have a carbon-fibre or aluminium based body (such as an aluminium lithium alloy) with a titanium leading edge.

A fan as described and/or claimed herein may comprise a central portion, from which the fan blades may extend, for example in a radial direction. The fan blades may be attached to the central portion in any desired manner. For example, each fan blade may comprise a fixture which may engage a corresponding slot in the hub (or disc). Purely by way of example, such a fixture may be in the form of a dovetail that may slot into and/or engage a corresponding slot in the hub/disc in order to fix the fan blade to the hub/disc. By way of further example, the fan blades maybe formed integrally with a central portion. Such an arrangement may be referred to as a blisk or a bling. Any suitable method may be used to manufacture such a blisk or bling. For example, at least a part of the fan blades may be machined from a block and/or at least part of the fan blades may be attached to the hub/disc by welding, such as linear friction welding.

The gas turbine engines described and/or claimed herein may or may not be provided with a variable area nozzle (VAN). Such a variable area nozzle may allow the exit area of the bypass duct to be varied in use. The general principles of the present disclosure may apply to engines with or without a VAN.

The fan of a gas turbine as described and/or claimed herein may have any desired number of fan blades, for example <NUM>, <NUM>, <NUM>, or <NUM> fan blades.

As used herein, cruise conditions may mean cruise conditions of an aircraft to which the gas turbine engine is attached. Such cruise conditions may be conventionally defined as the conditions at mid-cruise, for example the conditions experienced by the aircraft and/or engine at the midpoint (in terms of time and/or distance) between top of climb and start of decent.

Purely by way of example, the forward speed at the cruise condition may be any point in the range of from Mach <NUM> to <NUM>, for example <NUM> to <NUM>, for example <NUM> to <NUM>, for example <NUM> to <NUM>, for example <NUM> to <NUM>, for example <NUM> to <NUM>, for example on the order of Mach <NUM>, on the order of Mach <NUM> or in the range of from <NUM> to <NUM>. Any single speed within these ranges may be the cruise condition. For some aircraft, the cruise conditions may be outside these ranges, for example below Mach <NUM> or above Mach <NUM>.

Purely by way of example, the cruise conditions may correspond to standard atmospheric conditions at an altitude that is in the range of from <NUM> to <NUM>, for example in the range of from <NUM> to <NUM>, for example in the range of from <NUM> to <NUM> (around <NUM> ft), for example in the range of from <NUM> to <NUM>, for example in the range of from <NUM> to <NUM>, for example in the range of from <NUM> (around <NUM> ft) to <NUM>, for example in the range of from <NUM> to <NUM>, for example in the range of from <NUM> to <NUM>, for example on the order of <NUM>. The cruise conditions may correspond to standard atmospheric conditions at any given altitude in these ranges.

Purely by way of example, the cruise conditions may correspond to: a forward Mach number of <NUM>; a pressure of <NUM> Pa; and a temperature of -<NUM> deg C.

As used anywhere herein, "cruise" or "cruise conditions" may mean the aerodynamic design point. Such an aerodynamic design point (or ADP) may correspond to the conditions (comprising, for example, one or more of the Mach Number, environmental conditions and thrust requirement) for which the fan is designed to operate. This may mean, for example, the conditions at which the fan (or gas turbine engine) is designed to have optimum efficiency.

In use, a gas turbine engine described and/or claimed herein may operate at the cruise conditions defined elsewhere herein. Such cruise conditions may be determined by the cruise conditions (for example the mid-cruise conditions) of an aircraft to which at least one (for example <NUM> or <NUM>) gas turbine engine may be mounted in order to provide propulsive thrust.

The planet carrier <NUM> constrains the planet gears <NUM> to process around the sun gear <NUM> in synchronicity whilst enabling each planet gear <NUM> to rotate about its own axis.

Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in <FIG> has a split flow nozzle <NUM>, <NUM> meaning that the flow through the bypass duct <NUM> has its own nozzle that is separate to and radially outside the core engine nozzle <NUM>. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct <NUM> and the flow through the core <NUM> are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine <NUM> may not comprise a gearbox <NUM>.

From the above it is clear that the gearbox <NUM> is subjected to considerable mechanical loads while having long maintenance intervals. In the following embodiments of a method and a system for detecting mechanical failures are described in connection with an epicyclic gearbox <NUM> in a planetary arrangement, i.e. with a fixed ring gear mount <NUM> and a rotatable planet carrier <NUM>. The embodiments are also applicable for epicyclic gearboxes in a star arrangement, i.e. with a fixed planet carrier and a rotatable ring gear mount.

Even if the embodiments are described with an epicyclic gearbox <NUM> in the context of an aircraft gas turbine engine <NUM>, the embodiments described herein are generally applicable to epicyclic gearboxes <NUM>.

In <FIG>, the side-sectional view of an epicyclic gearbox <NUM> in a planetary arrangement, also shows possible locations for sensors 110a, 110b, 110b. The sun gear <NUM> is driven by the shaft <NUM>. As described above, the ring gears <NUM> are mounted statically on the ring gear mount <NUM>. The planet gears <NUM> are moving rotatably between the sun gear <NUM> and the ring gear <NUM> transmitting the input torque from the shaft <NUM> to the planet carrier <NUM> which in turn drives the output shaft <NUM> (fan shaft, carrier shaft) of the epicyclic gearbox <NUM>.

In the following, embodiments of methods and systems for the detection of functional failures in an epicyclic gearbox are described in more detail. Input data for those embodiments is in part gathered by sensors <NUM>. <FIG> shows three sensors 110a, 110b, 110c that are placed on static parts of the epicyclic gearbox <NUM>, here the ring gear mount <NUM> and the ring gear <NUM>.

In alternative embodiments, less than three or more than three sensors <NUM> can be used. The static part on which the sensors <NUM> are located can be elsewhere, e.g. further away from the epicyclic gearbox <NUM>, depending on the operational parameter measured by the sensor <NUM>. The sensors <NUM> do not have to be placed in proximity together, as suggested by <FIG>. Depending on the operational parameter measured, the sensors <NUM> can be placed apart from each other.

In the embodiment shown in <FIG>, the three sensors 110a, 110b, 110c are all vibrational sensors using e.g. an accelerometer to detect vibrations (in radial, axial and / or tangential direction) relatively close to the epicyclic gearbox <NUM>. Alternatively, at least one of the sensors <NUM> could be an acoustic sensor detecting solid body sound from the epicyclic gearbox <NUM>, a strain gauge or a pressure sensor detecting the air pressure in the space surrounding the epicyclic gearbox <NUM>. Other possibilities are described below.

In <FIG>, a schematic overview of a method for detecting functional (operational, mechanical) failures in an epicyclic gearbox <NUM> is given.

In epicyclic gearboxes <NUM> an incipient failure or malfunctioning e.g. in the pinion bearings of the planetary gears <NUM> can be detected from the early stages by monitoring deviations from nominal conditions in the engine power over time in comparison to a nominal baseline obtained throughout the flight envelope conditions.

The power transmitted across the planetary gear train can be expressed by <MAT> or <MAT> being the two different equations for the amount of epicyclic gearbox power loss and fixed-gear assembly elastic deformation. The assembly elastic deformation being inversely proportional to the torsional stiffness of the static ring gear mount <NUM> and the engine frame.

In flight, the malfunctioning of e.g. one or more of the bearings of the planet gears <NUM> generates bearing loads outside the nominal design envelope, in particular the torque tangential distribution on the epicyclic gearbox <NUM> shafts (i.e. input and output shafts <NUM>, <NUM>) is altered, and a consequent change (deviation) in the power transmitted across the epicyclic gearbox <NUM> takes place.

The above-mentioned change in the torque tangential distribution is mathematically related to the modification of the load sharing factor.

The tangential torque deviation, or redistribution (i.e. among the planet gears), due to one or more planet bearing malfunctioning generates dynamic loads that are detected with engine sensors <NUM> such as torque meters (AC), vibration sensors and / or speed encoders as a spectral component at the frequency:.

together with a combination their harmonics and subharmonics. The frequencies and harmonics can be obtained from measured operational data <NUM> using e.g. a Fast Fourier Transformation. This allows an analysis of amplitudes and / phase properties of the frequency data.

The focus is here on the tangential direction, as loads in tangential direction are those directly controlled by the engine power controller (i.e. the speed controller acts in tangential direction). However, radial and / or axial loads can be subjected to major deviation too, depending on the gearbox <NUM> stiffness, inertia ratios and typology of teeth and bearings.

The magnitude of the tangential, radial and axial dynamic load generated by a pinion bearing malfunctioning depends on the epicyclic gearbox <NUM> stiffness to inertia ratio, the pinion bearing design, gear typology and the entity of the incipit failure. The dynamic load magnitudes are also known to be variable versus the engine power across the flight envelope due to change in stiffness and whole engine critical speeds. Therefore, changes in magnitude allow an assessment of the physical relationships mentioned.

The phase of the dynamic loads generated by a torque deviation remains almost constant versus engine speed, when measured on a period equal to a epicyclic gearbox <NUM> shaft revolution, being the torque tangential redistribution due to a bearing failure almost independent from the response to unbalance, which phase is instead strongly variable with engine speed (inversion at resonances). Phase analysis is used here in order to distinguish the power deviation indicators from rotor dynamic loads (unbalance, misalignments etc.).

Considering this, embodiments are able to distinguish if a rotating load is coming from a bearing failure or anomaly or form some dynamic response of the rotors. The latter are considered and accounted in the vibration limits and are not considered here. For instance in a fixed ring gear planetary gearbox, a single planet bearing failure would generate a load tracked at the frequency of the <NUM>/Rev carrier (i.e. <NUM> per revolution of the planet carrier <NUM>); the <NUM>/Rev carrier is also the frequency at which the carrier unbalance would excite the system resonances. Therefore the present system recognizes if a rotor response is due to a bearing failure or to a critical speed. This can be achieved by the mean of phase analysis, but is not limited to this method.

In the following, an embodiment using these relationships for the detection of operational failures in an epicyclic gearbox <NUM> will be described.

In a first step, operational data <NUM> is measured in the gas turbine engine <NUM>. The measured operational data <NUM> comprises at least two operational parameters dependent on the power generation and / or power consumption of the gas turbine engine <NUM> and / or the epicyclic gearbox <NUM>. The operational parameters measured can e.g. be:.

Data (and temporal variations in that data) related to at least one of those parameters gives an indication about the functional state of the gas turbine engine <NUM> and / or the epicyclic gearbox <NUM>.

They parameters mentioned are indicators of the engine power level and consequently they correspond to the parameters in the active control loops of the engine controller (FADEC). If e.g. planet bearing is failing, being it located in the torque (power) load path, the control system will see a change the system characteristics and therefore will be in need to compensate with a different setting regulation (e.g. fuel flow and variable stator geometry). Embodiments recognizes this variation from the engine standard conditions (baseline) at that speed, power, altitude, temperature etc. that otherwise could even accelerate the bearing failure. In parallel to the variation in the control system parameters, the presented method looks for dynamic load indicators (e.g. rotating load at <NUM>/Rev carrier).

In a next step, a signal processing unit <NUM> (see <FIG>) in a computational device process the measured operational data <NUM> to obtain analyzed operational data <NUM> comprising time data, angular data of a rotation, frequency data and / or phase data from the measured operational data <NUM>. Details about the analyzing are given in context with <FIG>.

In a subsequent step, the analyzed operational data <NUM> is compared with stored baseline operational data <NUM> representing nominal operation conditions of the gas turbine engine <NUM> and / or the epicyclic gearbox <NUM>. The baseline operational data <NUM> comprises analyzed data in similar way to enable the determination of deviation data <NUM> from the baseline operational data <NUM>. This comparison allows a detection of deviations from the nominal operating conditions, i.e. in absolute terms.

Next, time dependent trend data <NUM> is determined from the deviation data <NUM>. This means that not only absolute deviations are detected but changes in the deviations over time, i.e. time dependent trends. One example of trend is the occurrence of a peak under a failure of a part in frequency domain data.

When comparing the baseline <NUM> to the actual vibration analysis algorithms <NUM>, some variables can be monitored. This results in some logical if-then comparisons.

Based on that time dependent trend data <NUM>, a signal and / or a protocol <NUM> for controlling the epicyclic gearbox <NUM> and / or the gas turbine engine <NUM> is generated. Such signal and / or protocol <NUM> could e.g. be a command to shut down the gas turbine engine <NUM>, to separate the output shaft <NUM> from the propulsive fan <NUM> or to reduce the rotational speed of the sun shaft <NUM>.

In connection with <FIG> an embodiment is described in more detail.

Starting point is the measured operational data <NUM>. <FIG> gives a number of possibilities, which necessarily do not have to be used in total.

The rotational speeds N1 (speed of output shaft <NUM> of epicyclic gearbox <NUM>), N2 (speed of input shaft <NUM> of epicyclic gearbox) with N1 < N2 can be e.g. measured by an engine speed encoder and / or a torquemeter. N3 is the speed of the high pressure/high velocity rotor shafts. N3 it is directly regulated by the fuel intake and is mainly determining the maximal temperature in the engine. It is a good indicator of power.

A change in the speed, in and in particular a trend in the change can give an indication that there is an operational failure in an epicyclic gearbox <NUM>, in particular in an aircraft gas turbine engine <NUM>.

Another set of information can be obtained through vibration sensors <NUM>, which detect vibrations in up to three-directions X,Y,Z in the epicyclic gearbox <NUM> and or the WES (Whole Engine Systems).

A further set of information is related to the power received and / or transmitted by the epicyclic gearbox <NUM>. As discussed above, changes in power data can be indicative of failure of a part in an epicyclic gearbox <NUM>. Fuel consumption data and / or data related to vane positions or movements in the gas turbine engine <NUM> allow a direct assessment of the power data. It is also possible to use calculated power data directly or to calculate the power loss over the epicyclic gearbox <NUM>, i.e. the difference between power input and power output.

All this data is input for a signal processing unit <NUM>, in which measured operational data <NUM> is transformed into analyzed operational data <NUM>. In the embodiment shown, a Fast-Fourier Transformation (FFT) is used to find individual frequencies in the measured operational data <NUM>. The time-dependent data can be analyzed using time domain analysis. From the FFT phase information is derived which then can be analyzed further.

In signal analysis, order tracking is to detect and follow (track) the causes of vibration over time or speed. In this, frequencies are harmonics or subharmonics of the shaft rotational frequency: e.g. <NUM>/Rev of the shaft, <NUM>/Rev of the shaft, <NUM> of the shaft etc..

Many of the engine orders are indicators of rotors unbalance (<NUM> × shaft), rotor misalignment (<NUM> × shaft), electrical motor drive problems (n × number of poles), blade passing frequency (number of rotor blades × shaft), planet passing frequency, planet bearing failure indicators etc. Engine order can be defined as e.g. sun shaft frequency divided by carrier shaft frequency.

All or a subset of the operational parameter information is used to detect changes (deviations from nominal) in the torque of the epicyclic gearbox <NUM> by comparing the analyzed operational data <NUM> with baseline operational data <NUM> which has been gathered before. The baseline operational data <NUM> is indicative of nominal operation conditions, in particular an operation without functional failures in the epicyclic gearbox <NUM>. The baseline operational data <NUM> essentially comprises the same parameter set as the measured operational data <NUM>, e.g. data obtained by engine speed encoders, torquemeters, vibration sensors and / or power control parameters. The baseline operational data <NUM> is stored also as time domain data, angular domain data and / or frequency domain data, so it can be compared with respective analyzed operational data <NUM>.

By comparing the two datasets, deviation data <NUM> is determined showing deviations from the baseline, i.e. the nominal operation conditions.

The deviation data <NUM> is subjected to a trend analysis, i.e. it is checked if over time certain characteristics of the data changes. As an example, three trend analyses 105a, 105b, 105c are performed here in parallel.

In the first trend analysis 105a it is checked of there is any temporal trend in the radial, axial and / or tangential vibrational data. A determined trend could trigger a generation of a signal and / or protocol <NUM> if e.g. a predetermined growth rate threshold is exceeded. The threshold is valid for a range of operation points in order to take into account resonances of the drive train. The threshold could be adapted for the whole range of operation points by the use of á priori knowledge. This means that known magnitudes of harmonics which not related to a bearing failure can be considered to filter out the relevant harmonics for the bearing failure.

This would indicate a deviation of the torque. If the determined trend is below the threshold, no signal and / or protocol <NUM> is generated.

A second trend analysis 105b is performed checking if the radial, axial and / or tangential dynamic load trend exceeds a predetermined growth rate, again being indicative of a deviation of the torque. If the threshold is exceeded, a signal and / or protocol <NUM> is automatically generated. If not, no signal and / or protocol <NUM> is generated.

A third trend analysis 105c is performed checking if there are speed fluctuations exceeding predetermined thresholds, this also being indicative of a deviation of torque. If the threshold is exceeded, a signal and / or protocol <NUM> is automatically generated. If not, no signal and / or protocol <NUM> is generated.

In other alternatives, other operational parameters are checked for trends exceeding some thresholds. It is possible that less or more than three trend analyses 105a, 105b, 105c are performed. Furthermore, it is possible to use classification algorithms to identify trends in the data. The occurrence of a peak in frequency domain data might e.g. be found with a pattern recognition algorithm.

The signal and / or protocol <NUM> generated as a result of the trend analysis <NUM> can have different effects.

One possible effect is the use as a control signal to effect the operation of the gas turbine engine <NUM> by e.g. reducing the rotation of shafts or shutting the engine off if a damage is detected through the trend analysis <NUM>.

Alternatively or in addition the operational data can be automatically stored.

As there is data available for confirmed functional failures, a damage such as a bearing damage can the identified through a look-up table.

The data could also be used in a life expectation algorithm and / or in the automatic scheduling of maintenance.

In <FIG> an embodiment for the signal processing for the obtaining of analyzed operational data <NUM> is shown.

Starting point is the measured operational data <NUM>, such as e.g. vibrational data obtained from vibrational sensors <NUM> (see <FIG>) mounted to static parts of the epicyclic gearbox <NUM>, the ring gear <NUM> or ring gear mount <NUM>.

This data is subjected to signal conditioning and anti-alias filtering in step <NUM> and subsequently to an Analog-Digital conversion step <NUM>.

The digital data is then transmitted to a signal processing unit <NUM> which can e.g. be part of an engine monitoring unit (EMU) of an aircraft gas turbine engine <NUM>.

From the continuous time domain data (i.e. step <NUM>) a time frame (window function) is determined which is used <NUM> in the signal processing unit <NUM>. The windowed data is then further processed by applying a filter (e.g. low pass filter, bandpass filter) <NUM> on the time domain data. The cut-off frequency of the filter depends on the engine order <NUM> (see above) which is calculated using speed information, i.e. speed of shafts and / or speed of planets. After the filtering, features such as RMS (root mean square), skewness, crest factor and / or kurtosis can be determined <NUM> from time domain data.

Parallel to the processing of time domain data, frequency domain data is generated <NUM> by a FFT. From that analysis, features, such as harmonics can be extracted <NUM>.

The output of steps <NUM>, <NUM>, i.e. analyzed operational data <NUM> (time and frequency domain) is further subjected to a classification of the functional failure (e.g. a bearing failure) by analyzing thresholds as discussed in connection with <FIG>. It is also possible to use classification algorithms, such as Bayes classification.

<FIG> show the nominal behavior (<FIG>) and the behavior under failure of a journal bearing in an epicyclic gearbox <NUM> in frequency domain data. The amplitude data has been scaled into a range of <NUM> to <NUM> in <FIG>. The frequency data on the x-axis has been normalized to <NUM>.

<FIG> show data obtained by using three radial vibration sensors <NUM> distributed around the ring gear of the epicyclic gearbox <NUM>.

<FIG> shows the nominal behavior with three prominent peaks at frequencies just under <NUM> and at around <NUM>. Under failure condition, <FIG> shows an additional peak at a frequency of <NUM> which was detected by one of the sensors <NUM>, indicative of a failure in the journal bearing. In principle, this result would also be applicable to other kinds of planet bearings, e.g. roller bearings.

<FIG> show data obtained by using three vibration sensors <NUM> distributed around a different part of the epicyclic gearbox <NUM>. The sensors measured radial vibrations.

<FIG> shows the nominal behavior with four prominent peaks at frequencies just under <NUM>, and at around <NUM>, at around <NUM> and at around <NUM>. Under failure condition, there are additional peaks at frequencies <NUM>, <NUM> and a number of frequencies around <NUM> in Figure 8d indicative of a failure of the journal bearing.

The emergence of the peaks in <FIG> is indicative of the failure of a part, which is a time dependent trend as discussed in connection with <FIG>. The trend data <NUM> would comprises the information about the newly emerging peak due to the failure of the part.

<FIG> shows operational data for the experiment depicted in <FIG>). The rotation of a shaft of the epicyclic gearbox <NUM> (speed values normalized to <NUM>) is shown in the upper part, the carrier torque (values scaled into the range -<NUM> to <NUM>), i.e. the torque on the output side of the epicyclic gearbox <NUM> in planetary arrangement, is shown in the lower part. The x-axis is time units.

At t ≈ <NUM> the failure in the journal bearing shown in <FIG> occurs and a control signal <NUM> to shut down the gas turbine engine <NUM> (see <FIG>) is generated automatically based on the trend analysis described above. About <NUM> time units later the engine shut-off can be seen as the shaft speed linearly decreases and the carrier torque drops rapidly.

In <FIG> time domain data (corresponding to the time axis in <FIG>, with time units from <NUM> to <NUM>) for RMS is shown in normalized ranges. The figures show radial acceleration data at the diaphragm on the output side of the epicyclic gearbox <NUM>. At time unit <NUM>, the failure occurs, corresponding to t ≈ <NUM> in <FIG>.

Claim 1:
Method for detecting a functional failure in a power gearbox, in particular an epicyclic gearbox (<NUM>) in an aircraft gas turbine engine (<NUM>) comprising
a) measuring operational data (<NUM>) in the gas turbine engine (<NUM>) of at least two operational parameters dependent on the power generation and / or power consumption of the gas turbine engine (<NUM>) and / or the power gearbox (<NUM>),
b) obtaining analyzed operational data (<NUM>) comprising time data, angular data of a rotation, frequency data and / or phase data from the measured operational data (<NUM>),
c) using the analyzed operational data (<NUM>) in a comparison with stored baseline operational data (<NUM>) to determine deviation data (<NUM>) from the baseline operational data (<NUM>),
d) determining at least two time dependent trend data analyses (<NUM>) from the deviation data (<NUM>), and
e) generating a signal and / or a protocol (<NUM>) for controlling the epicyclic power gearbox (<NUM>) and / or the gas turbine engine (<NUM>) based on the at least two time dependent trend data analyses (<NUM>), in particular if a predetermined condition or threshold is exceeded.