Method for monitoring planetary gear trains by measuring the value of traveling mechanical waves

Abstract

The present invention discloses a method for monitoring a planetary gear train of an aircraft, the method comprising the following steps: acquiring a first value (5(ti)) of a signal formed by a traveling mechanical wave generated in the planetary gear train at a predetermined sampling frequency; measuring the value of the rotation speed of at least one toothed wheel of the gear train at multiple consecutive moments (Vmes_r(tj)); calculating the value of the rotation speed of a contact point between two toothed wheels of the planetary gear train (Vc(tj)); determining a second value of a signal formed by a traveling mechanical wave generated in the planetary gear train, sampling the second value according to the phase of the contact point and forming secondary mechanical wave data; and using the secondary mechanical wave data to detect abnormalities related to the operation of the planetary gear train.

Description

Technical Field

[0001] The invention relates to the field of monitoring mechanical transmissions in aircraft. Background Art

[0002] Various systems and methods are known from the prior art for monitoring mechanical transmissions in aircraft.

[0003] In patent application EP3217170, it is taught to monitor such a mechanical transmission device by means of an acoustic sensor. The acoustic sensor measures the acoustic signal generated by the mechanical vibration in the mechanical transmission device. Abnormalities in the operation of the mechanical transmission device will cause characteristic peaks to appear in the spectrum of the measured acoustic signal.

[0004] The object of the present invention is to provide an improved method for monitoring a mechanical transmission in an aircraft, which method is particularly suitable for monitoring a planetary gear train. Summary of the invention

[0005] This object is achieved by a method for monitoring a planetary gear train of an aircraft, wherein the planetary gear train comprises two coaxially mounted first toothed wheels and at least one second toothed wheel meshing with the first toothed wheels, the method comprising the following steps:

[0006] - acquiring, at a predetermined sampling frequency, a first value of a signal formed by a traveling mechanical wave generated in a planetary gear train, said first value forming main mechanical wave data;

[0007] - measuring values ​​of the rotation speed of at least one of the two first toothed wheels and the at least one second toothed wheel at a plurality of consecutive moments, said values ​​measured forming the main rotation data;

[0008] - calculating, from the primary rotation data, a value of the rotation speed of the contact point between a first toothed wheel and a second toothed wheel of the planetary gear train, said calculated value forming the secondary rotation data;

[0009] - determining, from the primary mechanical wave data and the secondary rotation data, a second value of the signal formed by the traveling mechanical wave generated in the planetary gear train, the second value corresponding to a regular sampling as a function of the phase of the contact point and forming the secondary mechanical wave data; and

[0010] -Use secondary mechanical wave data to detect anomalies related to the operation of the planetary gear train.

[0011] The two coaxially mounted first toothed wheels are respectively referred to as the ring gear and the sun gear, wherein the sun gear is surrounded by the ring gear. The at least one second toothed wheel is referred to as a planet gear.

[0012] The main mechanical wave data corresponds to the sampling of the signal formed by the traveling mechanical wave generated in the planetary gear train as a function of time. The signal is related to the vibration in the elastic medium. The signal can be an acoustic signal or a vibration signal that can be measured by an accelerometer. The time interval between two consecutive sampling moments is constant.

[0013] The main rotation data are measured at different moments, in parallel with the acquisition of the main mechanical wave data. The main rotation data refer to the measured values ​​of the corresponding rotation speed of at least one toothed wheel of the planetary gear train. For example, the rotation speed or the engine speed is expressed in revolutions per unit time. For example, the rotation speed is measured using an optical sensor, which detects the passage of a predetermined reference point on the toothed wheel.

[0014] The secondary rotation data are calculated values ​​of the rotation speed of the contact point between two toothed wheels in a planetary gear train. The rotation speed of the contact point forms the so-called virtual speed. The contact point is the contact point between the planet gear and the ring gear, or the contact point between the planet gear and the sun gear. Any of these contact points can be considered. The values ​​of the rotation speed of the contact point are determined for a plurality of moments, preferably corresponding to the measurement moments of the primary rotation data.

[0015] The calculated value of the rotational speed of the contact point is then used to simulate a resampling of the signal formed by the traveling mechanical wave generated in the planetary gear train. The resampling is a time constant as a function of the phase of the contact point. In other words, there is a constant phase difference between the two resampled points, where the phase is related to the contact point and the phase is obtained by the rotational speed of the contact point. This new sampling of the traveling mechanical wave signal generated in the planetary gear train forms the secondary mechanical wave data.

[0016] These secondary mechanical wave data are then used to detect anomalies in the operation of the planetary gear train. To this end, a model can be used that associates anomalies with predefined features that depend on a function of the secondary mechanical wave data. The model can be determined by experiment or simulation.

[0017] The invention thus provides a method for monitoring a planetary gear train of an aircraft, the method being based on a clever resampling of the signal formed by the travelling mechanical waves generated in the planetary gear train.

[0018] When the mechanical transmission is a simple gear with only two toothed wheels, it may be advantageous to resample in phase the signal formed by the traveling mechanical wave generated in the mechanical transmission. In the case of a planetary gear train, the complex arrangement of the toothed wheels leads the skilled person to avoid such resampling. The basic idea of ​​the invention is to keep the resampling in phase, but not with reference to one toothed wheel of the planetary gear train, but with reference to the contact point between two of these toothed wheels. The inventors have been able to show that this idea makes it possible to obtain resampled data making it possible to effectively locate mechanical anomalies of a planetary gear train.

[0019] Advantageously, the rotational speed of the point of contact between the first and second toothed wheels of the planetary gear train is a linear combination of the respective rotational speeds of said first and second toothed wheels.

[0020] At least one of the respective rotational speeds may be based on the main rotational data The number of teeth of at least two of the two first toothed wheels and the at least one second toothed wheel is calculated.

[0021] According to an advantageous embodiment, the secondary mechanical wave data is used To detect anomalies related to the operation of the planetary gear train including:

[0022] - Calculate and analyze data, including calculating secondary mechanical wave data The Fourier transform of , wherein the Fourier transform transforms the phase function into an order function; and

[0023] - Using said analysis data to detect anomalies associated with the operation of the planetary gear train.

[0024] The analysis data associated with the at least one integer order may then be used to detect anomalies associated with the operation of the planetary gear train.

[0025] Calculation of analytical data may include calculation of secondary mechanical wave data The power spectral density of .

[0026] Alternatively, calculating the analysis data may include calculating secondary mechanical wave data The average power spectral density.

[0027] Further alternatively, computing and analyzing the data may include computing and collecting secondary mechanical wave data Spectrum plot of multiple values ​​of the average power spectral density.

[0028] The signal formed by the traveling mechanical wave generated in the planetary gear train may be an acoustic signal acquired using an acoustic wave sensor. The acoustic wave sensor is advantageously arranged at a position spaced apart from the planetary gear train.

[0029] Alternatively, the signal formed by the traveling mechanical wave generated in the planetary gear train is a vibration signal acquired using an accelerometer.

[0030] The monitoring method may also include: when using the secondary mechanical wave data A step of performing maintenance on the planetary gear train when an abnormality related to the operation of the planetary gear train is detected.

[0031] Finally, the monitoring method may further include a preliminary step of determining health indicators, the preliminary step including the following sub-steps:

[0032] - For multiple flights, obtain primary mechanical wave data and primary rotation data, and determine corresponding secondary rotation data and secondary mechanical wave data;

[0033] - for each flight of the plurality of flights, computing the analysis data, said computing comprising computing a Fourier transform of the secondary mechanical wave data; and

[0034] - Correlate the analysis data with information about anomalies or lack of anomalies in the operation of the planetary gear train. The invention also relates to a monitoring system for monitoring a planetary gear train of an aircraft, the system comprising:

[0035] a planetary gear train comprising two coaxially mounted first toothed wheels and at least one second toothed wheel meshing with the two first toothed wheels;

[0036] at least one mechanical wave sensor arranged to acquire, at a predetermined sampling frequency, a first value of a signal formed by a traveling mechanical wave generated in the planetary gear train, said first value forming the main mechanical wave data (S(t i ));

[0037] at least one rotational speed sensor, the at least one rotational speed sensor being arranged to acquire values ​​of the rotational speed of at least one of the two first toothed wheels and the at least one second toothed wheel at a plurality of consecutive moments, the values ​​measured forming the primary rotational data (V mes_r (t j ));as well as

[0038] - a processor configured to receive the main mechanical wave data (S(t i )) and the main rotation data (V mes_r (t j)) as input to calculate the rotational speed of a contact point between a first toothed wheel and a second toothed wheel of a planetary gear train to determine a second value of the signal formed by a traveling mechanical wave generated in the planetary gear train, and output a piece of information (D) related to whether there is an abnormality in the operation of the planetary gear train, the second value being sampled as a function of the phase of the contact point.

[0039] The mechanical wave sensor is typically an acoustic sensor, arranged at a location spaced apart from the planetary gear train. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The invention will be better understood by reading the description of exemplary embodiments given purely by way of illustrative and non-limiting examples, with reference to the accompanying drawings, in which:

[0041] - Figure 1 and Figure 2 A planetary gear train is schematically shown in perspective and front view respectively;

[0042] - Figure 3 Schematically shows a method for monitoring Figure 1 Method of planetary gear train;

[0043] - FIG. 4A to FIG. 4E Resampling according to the present invention is shown;

[0044] - Figure 5A and Figure 5B They are shown respectively by Figure 1 The signal formed by the traveling mechanical wave generated in the planetary gear train as a function of time and the corresponding power spectral density;

[0045] - Fig. 6A and Figure 6B They are shown respectively with Figure 5A The same signal and the corresponding power spectral density in time as a function of the phase of the contact point in the planetary gear train;

[0046] - Figure 7 and Figure 8 shows detailed views of spectra obtained using the method according to the invention, centered on the 1st and 2nd orders respectively;

[0047] - Fig. 9 schematically illustrates a system according to the invention; and

[0048] - Fig.10 A turbomachine of an aircraft receiving a planetary gear train as monitored in the present invention is schematically shown. DETAILED DESCRIPTION

[0049] Figure 1 An example of a planetary gear train 100 to which the present invention can be applied is shown in a perspective view. Here, the planetary gear train 100 includes:

[0050] - a ring gear 110 , which is mounted integrally with a downstream propeller of a turboshaft engine (not shown);

[0051] - a sun gear 120 mounted integrally with a shaft connected to a power turbine (not shown); and

[0052] - Three planetary gears 130 , which are integrally mounted with the upstream propeller of a turboshaft engine (not shown) via a three-branch connection 131 .

[0053] The ring gear 110 and the sun gear 120 are coaxially mounted, wherein the ring gear 110 is arranged around the sun gear 120. The ring gear and the sun gear form two first toothed wheels.

[0054] The three planetary gears 130 are evenly distributed around the sun gear 120, and each planetary gear is arranged between the ring gear 110 and the sun gear 130. The three planetary gears together form three second toothed wheels, each of which meshes with the ring gear 110 and the sun gear 130. Each of the three branches of the connecting member 131 is attached to the rotation axis of one of the planetary gears 130.

[0055] Figure 2 The planetary gear train 100 is schematically shown in a front view. The rotation direction of each element of the planetary gear train 100 is indicated by an arrow. The respective rotation directions of the ring gear 110 and the sun gear 120 are opposite to each other. Each of the three planetary gears 130 can rotate around itself and / or around the sun gear 120. The rotation of the planetary gears 130 around the sun gear 120 is Figure 2 The rotation direction of the planetary gear 130 around the sun gear 120 corresponds to the rotation direction of the sun gear 120 around itself.

[0056] Figure 2 The two contact points P in the planetary gear train 100 are also shown. C1 , P C2 .P C1 It is the contact point between one of the planetary gears 130 and the ring gear 110. C2 is a contact point between one of the planetary gears 130 and the sun gear 120. Each of the three planetary gears has two contact points, which are contact points where each planetary gear contacts the ring gear 110 and the sun gear 120, respectively.

[0057] Figure 3 A method according to the invention for monitoring a running planetary gear train 100 is schematically shown.

[0058] In a first step 301, a series of values ​​S(t) of a signal S(t) formed by a traveling mechanical wave generated in the planetary gear train 100 is acquired. i ). The traveling mechanical waves are in particular elastic waves. The traveling mechanical waves are generated in particular by the collision of the teeth of the planetary gears with the teeth of the ring gear and the teeth of the sun gear. The characteristics of these collisions depend in particular on the manufacturing errors and elastic deformations of the teeth. The signal S(t) is preferably an acoustic signal related to the waves radiated by the planetary gear train and is acquired using an acoustic wave sensor (e.g. a microphone) or a sound pressure sensor. Since acoustic signals can propagate through any solid, liquid or gaseous medium, the acoustic wave sensor can be freely arranged, directly on the planetary gear train or away from the planetary gear train. Alternatively, the signal S(t) is a vibration signal related to the waves conducted in an elastic solid medium and is acquired using a sensor (e.g. an accelerometer). In this case, the accelerometer should be arranged in direct physical contact with the planetary gear train or in direct physical contact with an intermediate solid medium, which itself is in direct physical contact with the planetary gear train. At a sampling frequency f ech To obtain the value S(t i ). In other words, with different values ​​of S(t i ) The associated acquisition time t i Separated by a fixed time interval. The obtained value S(t i ) forms data known as main mechanical wave data.

[0059] In a second step 302, carried out in parallel with step 301, a series of values ​​V of one or more rotational speeds r of the respective ring gear, the sun gear and at least one of the toothed wheels of the three planetary gears is acquired. mes_r (t j ). In other words, a series of values ​​of the respective speeds r of the ring gear, the sun gear and at least one of the toothed wheels of the three planetary gears of the planetary gear train are obtained. The value of the rotation speed V mes_r (t j ) is the angular velocity, for example expressed in revolutions per minute. Here, each rotational speed refers to the rotational speed of the toothed wheel itself. In the case of the planetary gear 130, this rotational speed only relates to the rotation of the planetary gear 130 itself, without taking into account a possible rotation of the planetary gear around the sun gear 120. Preferably, it is assumed that all three planetary gears have the same rotational speed. A tachometer-type sensor is used to obtain the value V mes_r (t j), a sensor of the tachometer type comprises, for example, an optical sensor capable of locating the passage of a predetermined reference point on the toothed wheel, or a sensor capable of measuring the duration of the passage of the toothed wheel (a short duration corresponds to a rapid passage of the teeth and therefore to a high rotational speed). Where applicable, the rotational speed of the toothed wheel is measured at the propeller or turbine integrally mounted therewith. Different values ​​V mes_r (t j ) and a series of acquisition times t j These values ​​V mes_r (t j ) forms data called main rotation data.

[0060] In a third step 303, the primary rotation data are used to calculate a value V of the theoretical rotation speed of the contact point in the planetary gear train 100 c (t j ). This rotation speed is also referred to as a “virtual speed”. The contact point refers to any one of a contact point between one of the planetary gears 130 and the ring gear 110 and a contact point between one of the planetary gears 130 and the sun gear 120 . Figure 2 Two such contact points P are shown. C1 and P C2 .

[0061] The rotational speed of the contact point is the rotational speed considered in the reference coordinate system attached to the vehicle receiving the planetary gear train. The rotational speed of all the contact points of the planetary gear train 100 is the same, therefore any one of these contact points can be considered equally.

[0062] The rotation speed of the contact point between the two toothed wheels of a planetary gear train is a linear combination of the rotation speeds of the two toothed wheels respectively. It also depends on the respective number of teeth of the two toothed wheels.

[0063] Therefore, V is calculated using the values ​​of the respective rotational speeds of the two toothed wheels in contact in the planetary gear train. c (t j). These used values ​​may belong to the main rotation data acquired in step 302. Alternatively, at least some of the values ​​used may be obtained by calculation from the main rotation data and the number of teeth of the toothed wheels in the planetary gear train. In fact, in a planetary gear train, the ratio of the rotation speeds of the two toothed wheels in contact is a function of the ratio of the corresponding numbers of teeth of the wheels. In any case, the method according to the present invention is preferably suitable for collecting rotation speed values ​​associated with each of the three types of toothed wheels (ring gear 110, sun gear 120, planetary gears 130) of the planetary gear train. These values ​​may all be acquired in step 302. Alternatively, some of these values ​​are not acquired in step 302, but are determined by calculation using the relationship between the respective rotation speeds and the number of teeth of the two toothed wheels in contact in the planetary gear train described above.

[0064] Preferably, for each time t defined above j Calculated value V c (t j ). Therefore, the calculated value V c (t j ) together form data known as secondary rotation data.

[0065] In the fourth step 304, the main mechanical wave data S(t i ) and secondary rotation data V c (t j ) is used to simulate the sampling of the signal S formed by the traveling mechanical wave generated in the planetary gear train 100 at a constant phase interval. The phase is the phase of the contact point of the rotation speed that has been determined in step 303. FIG. 4A to FIG. 4E This step is described in detail. This step preferably includes obtaining the value S(t i At the end of step 304, a series of values ​​of the signal S formed by the traveling mechanical wave generated in the planetary gear train 100 are obtained. in, refers to the phase of the contact point considered in step 303. These values This forms data called secondary mechanical wave data.

[0066] Finally, in step 305, the secondary mechanical wave data are used to detect possible anomalies in the operation of the planetary gear train. Information about the presence or absence of anomalies in the operation of the planetary gear train and, if applicable, about the nature of the detected anomalies together form the so-called diagnostic information D.

[0067] The anomaly may be related to a functional failure of the planetary gear train, damage to a component of the planetary gear train, operation outside nominal use conditions (e.g., cold start, or lubrication failure in the toothed wheels), or any other cause that may change the traveling mechanical wave generated by the collision of the teeth of the toothed wheels in contact in the planetary gear train 100. In particular, lubrication failure of the planetary gears, torque increase on the planetary gears, lack of heat dissipation, misalignment between the respective rotation axes of at least two toothed wheels, etc. may be detected. Sudden damage or gradual wear of the planetary gear train may be detected.

[0068] Abnormal detection uses secondary mechanical wave data, and the secondary wave mechanical data is preferably transformed to facilitate analysis. These transformed data are called analysis data. The transformation is particularly intended to eliminate the influence of noise and environment. The transformation preferably includes the application of Fourier transform. Fourier transform is applied to secondary mechanical wave data, or to a function obtained by interpolating the secondary mechanical wave data. Here, Fourier transform transforms the function of phase into an order function. For example, the power spectral density or average power spectral density or a spectrogram of the average power spectral density of the secondary mechanical wave data or the function obtained by interpolating the secondary mechanical wave data is calculated.

[0069] Detecting possible anomalies in the operation of a planetary gear train can use models that characterize normal or abnormal operation of the planetary gear train and locate deviations or similarities related to these models. These models are called health indicators.

[0070] The health indicator can be determined by numerical simulation or using experimental measurements performed on a planetary gear train associated with known characteristics and operating conditions. The method according to the invention may comprise preliminary steps for determining such a health indicator, these preliminary steps comprising:

[0071] - for a plurality of flights of at least one aircraft, and where applicable a plurality of flight phases per flight, acquiring primary mechanical wave data and primary rotation data, and determining corresponding secondary rotation data and secondary mechanical wave data;

[0072] - for each flight of the plurality of flights, and, where applicable, for each flight phase of the plurality of flight phases of each flight, calculating analysis data using the corresponding secondary mechanical wave data; and

[0073] - Correlating said analysis data with information about the presence or absence of an anomaly related to the functioning of the planetary gear train and, where applicable, with information about the exact nature of said anomaly.

[0074] The flight phases include in particular one or more of a take-off phase, a climbing phase, a cruising phase, a descending phase, a landing phase and a taxiing phase. The analysis data corresponds to the secondary mechanical wave data transformed as described above.

[0075] The health indicator not only detects abnormal operation of the planetary gear train, but also identifies the anomaly when it is detected. Planetary gear train wear can also be located at an early stage, before excessive defects occur. Early detection of planetary gear train wear provides great flexibility in planning maintenance operations. Therefore, the schedule of maintenance operations can be optimized to minimize the total downtime of the aircraft receiving the planetary gear train.

[0076] In any case, the method may include a maintenance step (not shown) performed on the planetary gear train 100 in response to detecting an anomaly in step 305 .

[0077] FIG. 4A to FIG. 4E The in-phase synchronous resampling step 304 is shown in detail.

[0078] Figure 4A shows the rotational velocity V of the considered contact point c (t) as a function of time t. The x-axis is time in seconds. The y-axis is rotational speed (or rpm) in revolutions per minute. Curve V c (t) is obtained by rotating the secondary data V c (t j Here, the curve corresponds to the acceleration phase.

[0079] Figure 4B shows the phase of the contact point under consideration As a function of time t. The x-axis is time in seconds. The y-axis is phase in revolutions. Function is through the function V c (t) is obtained by integrating over time. Therefore, the phase corresponds to the accumulated number of revolutions made by the considered contact point.

[0080] Figure 4C Corresponds to Figure 4B , where the point P of regular in-phase sampling has been identified n . Each point P n Located in Representative The curve of the phase and the value of time t ech_k . Different points P n is associated with regularly spaced phase values. In other words, n The difference between the associated phases is a constant, which is called the in-phase sampling interval. Here, the in-phase sampling interval is 1 revolution per minute.

[0081] Figure 4D The signal S formed by the traveling mechanical wave generated in the planetary gear train is shown as a function of time t. The x-axis is time in seconds. Here, the y-axis is the sound pressure in Pa. The curve S(t) is obtained by analyzing the main mechanical wave data S(t i ) is interpolated. Figure 4D In the figure, the sampling point R is also shown. n . Sampling point R n is the value t on the curve S(t) at the previously determined time t ech_k Therefore, these values ​​t ech_k Corresponding to regular in-phase sampling. Each sampling point R n and the value S( tech_k ) and the value t at time t ech_k Associated.

[0082] like Figure 4C As shown, the value of each time t ech_k The value of the phase with the contact point under consideration Therefore, each value S(t) of the signal S(t) ech_k ) can be connected to the phase value Among them, the value The sequence of S(t) corresponds to regular in-phase sampling. ech_k ) can be expressed as These values ​​form secondary mechanical wave data according to the invention, associated with regular sampling as a function of the phase of the contact point considered.

[0083] exist Figure 4E In the figure, the x-axis is the phase in revolutions, and the y-axis is the sound pressure in Pa. n Each of the values A value in and the corresponding phase value By comparing different points T n Interpolate and get the representative function The curve of the function The signal S formed by the traveling mechanical wave generated in the planetary gear train is represented as the phase of the contact point under consideration. function.

[0084] Switching from regular sampling as a function of time to regular sampling as a function of phase makes it possible to eliminate the influence of the time-varying rotation speed of the toothed wheels of the planetary gear. A clever idea behind the invention is to choose the phase of the contact points of the planetary gear instead of the phase of one of the toothed wheels of the planetary gear. The inventors have shown that this choice enables a more relevant localization of anomalies related to the operation of the planetary gear.

[0085] As mentioned above, the detection of anomalies related to the operation of the planetary gear train is advantageously performed on so-called analysis data corresponding to the secondary mechanical wave data transformed so as to facilitate their analysis.

[0086] The transformation preferably comprises applying a function comprising a Fourier transform calculation. Here, the Fourier transform transforms the phase of the contact point under consideration into a function The transformation is a function of a variable called the "order".

[0087] The function may be a power spectral density. The power spectral density is a function representing the order distribution of the power of the Fourier transform (the square of the modulus of the Fourier transform). For a digital signal x of N samples n , the indicator of the power spectral density is a vector with N points, and the k-th element is defined by:

[0088]

[0089] Among them, D X is the power spectral density of signal x, and X(k) is the k-th element of the discrete Fourier transform of signal x.

[0090] Advantageously, the transformation of the secondary mechanical wave data to form the analysis data may comprise interpolation of said secondary mechanical wave data. A function comprising a Fourier transform calculation is then applied to the result of said interpolation.

[0091] Figure 5A , Figure 5B and Fig. 6A , Figure 6B The benefit of regular resampling as a function of the phase at the contact point and then transferring to the order domain is shown.

[0092] Figure 5A The signal S formed by the traveling mechanical wave generated in the planetary gear train is shown as a function of time t. The x-axis is time in seconds. Here, the y-axis is the sound pressure in Pa. Figure 5B Shows Figure 5A The power spectral density of the signal as a function of frequency, with frequency in Hz.

[0093] Fig. 6AThe signal S formed by the traveling mechanical wave generated in the planetary gear train is shown as the phase of the contact point under consideration. The x-axis is the phase in revolutions, and the y-axis is the sound pressure in Pa. Figure 6B Shows Fig. 6A The power spectral density of the signal in as a function of the order (the inverse of the phase).

[0094] Fig. 6A The signal in corresponds to the resampled signal where the effect of the time-varying rotational speed in the planetary gear train is eliminated. By transferring this signal to the order domain, the majority of components centered around the 1st order can be easily identified (see Figure 6B peak amplitude).

[0095] By resampling according to the phase of the contact point and then transferring to the order domain, the signal component caused by the planetary gear train and the signal component caused by the noise and environment around the planetary gear train can be easily distinguished.

[0096] The values ​​of the power spectral density corresponding to integer orders, particularly to order 1, are most relevant to determining the presence or absence of an anomaly associated with the operation of the planetary gear train, and identifying the nature of the anomaly when applicable. Other order values ​​may be used, preferably in symmetrical positions on either side of the integer order.

[0097] The use of power spectral density calculations to obtain analytical data has been described in detail above.

[0098] According to an advantageous alternative, the average power spectral density (of the secondary mechanical wave data or of a function obtained by interpolating the secondary mechanical wave data) is calculated instead. The average power spectral density of a signal is obtained by multiplying the signal by an apodisation window, calculating the power spectral density of the result of the multiplication, and then repeating these steps after offsetting the apodisation window by 50% of its length, and so on, until a series of power spectral densities are obtained, which are then averaged (Welch's method). The apodisation window is a function that takes the value of zero everywhere except in a narrow band with a peak shape. For example, the apodisation window is defined by a Hamming function. This technique eliminates some noise and orders that are not dominant.

[0099] A spectrogram can also be used to collect multiple power spectral densities (average or non-average) calculated over consecutive time intervals. The time intervals considered overlap each other. The time intervals each correspond to the phase intervals of the contact points considered. On the spectrogram, the power spectral density associated with a given phase interval corresponds to a vertical line. The vertical line is aligned with the phase value corresponding to the center value of the phase interval. One advantage of analyzing secondary mechanical wave data in the form of such a spectrogram is that the analysis is performed on a compilation of many measurement results, thereby eliminating noise and marginal effects.

[0100] On the spectrogram, different significant lines can be distinguished, each corresponding to a high value of the power spectral density that remains constant over time. Of these significant lines, only those associated with constant values ​​of the order are related to the planetary gear train. Thus, it is possible to distinguish significant lines related to the planetary gear train from those related to the surroundings. This distinction is particularly useful when the main mechanical wave data are acoustic data, since the acoustic radiation associated with the collision of the toothed wheel actually makes only a small contribution to the total noise emitted at the housing housing the planetary gear train.

[0101] Therefore, lines or spectrogram lines associated with constant values ​​of the order are used to determine the presence or absence of anomalies related to the operation of the planetary gear train and, where applicable, to identify the nature of the anomaly. These lines form the acoustic signature of the planetary gear train. In particular, spectrogram lines associated with integer values ​​of the order, in particular a value of one, are used. The presence or absence of one or more of these lines forms a health indicator for the planetary gear train, characterizing the presence or absence of an anomaly in the operation of the planetary gear train and, where applicable, the characteristics of the specific nature of the anomaly.

[0102] Figure 7 A detailed view of such a spectrogram centered around order 1 is shown. The x-axis is the phase in revolutions. The y-axis is the order. The hue scale is the amplitude of the power spectral density, on a logarithmic scale. One of the power spectral densities forming the spectrogram has been indicated on the right, here corresponding to the vertical line A-A' on the spectrogram. Figure 7 In , the area that has been framed with a dotted line includes a horizontal line aligned with the 1st order. This line represents the maximum power spectral density that exists at the 1st order and for a long period of time.

[0103] Figure 8 A detailed view of the same spectrogram centered on order 2 is shown. One of the power spectral densities forming the spectrogram has been indicated on the right, here corresponding to the vertical line BB' on the spectrogram. It is observed that the vertical line indicates the maximum power spectral density present at order 2 and for a long period of time (see the boxed area).

[0104] By comparison Figure 7 and Figure 8, a reversal of the dominance of the 1st and 2nd order is observed (the disappearance of the line at the 1st order coincides with the appearance of the line at the 2nd order), which reflects an event on the planetary gear train. This event may be related to a sudden degradation of the planetary gear train, or simply to a change in the conditions of use, for example a change in the torque applied to the planetary gear train. It is therefore advantageous to combine the analytical data calculated in the method according to the invention with other measurement and monitoring operations carried out simultaneously in the aircraft (detection of impacts of flying objects, measurement of the quality of the oil that lubricates the toothed wheels of the planetary gear train, detection of torque variations, measurement of upstream and downstream temperatures, speeds, position in the flight domain, etc.).

[0105] Fig. 9 Schematically shows a method for implementing the reference Figure 3 A system 10 of the method described. The system 10 includes:

[0106] - Planetary gear train 100, see Figure 1 and Figure 2 As described, the planetary gear train may be a component of a turboprop engine or a reduction gear motor;

[0107] at least one mechanical wave sensor 11 (e.g. an accelerometer) or more preferably an acoustic wave sensor (e.g. a microphone), arranged to acquire a signal representative of a traveling mechanical wave generated in the planetary gear train 100 by the collision of the teeth of the toothed wheel (primary mechanical wave data);

[0108] at least one rotation speed sensor 12 for acquiring rotation speed measurements (primary rotation data) relating to at least one toothed wheel of the planetary gear train 100 ; and

[0109] - a processor 13, the processor being configured to receive as input the main mechanical wave data acquired by the mechanical wave sensor 11 and the main rotation data acquired by the rotation speed sensor 12, so as to implement Figure 3 Steps 303, 304 and 305 of the method shown are performed and output diagnostic information D relating to the presence or absence of an anomaly in the operation of the planetary gear train and, where applicable, the nature of the anomaly.

[0110] The mechanical wave sensor 11 is preferably located inside a housing to protect the housing from dust or sand and the mechanical wave sensor is close to the planetary gear train. It is particularly advantageous to use an acoustic wave sensor as the mechanical wave sensor 11. In fact, data related to each toothed wheel constituting the planetary gear train can be acquired in a single signal. In addition, the acoustic wave sensor can be arranged away from the planetary gear train without direct physical contact with the planetary gear train. The acoustic wave sensor can even be located at an airport to measure acoustic signals emitted by an aircraft approaching or taking off. The planetary gear train is then monitored based on the noise emitted by the planetary gear train during operation.

[0111] Fig.10 Schematically, a turbomachine of an aircraft receiving a planetary gear train 100 is shown. The planetary gear train is connected to an upstream propeller 20, a downstream propeller 30 and a turboshaft engine 40. The upstream propeller and the downstream propeller are counter-rotating (they rotate in opposite directions) and non-spinning (they are located outside a spinner 50 receiving the planetary gear train 100 and the turboshaft engine 40). The upstream propeller and the downstream propeller are of large size, each having a diameter greater than 1.5 meters, for example two meters.

[0112] The invention is particularly applicable in the field of high-power turbojets for aircraft, which have an engine power of about 40% and support an energy of up to 30 MW / h. The invention is particularly applicable to the monitoring of planetary gear train power transmissions for transmitting power from a power turbine to upstream and downstream propellers rotating in opposite directions.

[0113] The invention is based on a comparison between an expected model of the noise or vibrations emitted by a planetary gear train and analytical data obtained through measurements and mathematical processing.

[0114] Alerts can be implemented to notify maintenance operators of abnormal conditions related to the operation of the planetary gear train. Maintenance advisory services can also be implemented for aircraft operators.

[0115] Advantageously, the analysis data obtained using the secondary mechanical wave data according to the invention can be combined with auxiliary data from sensors of the accelerometer type.

[0116] In the examples detailed above, an example of a planetary gear train with three planetary gears has been shown. The invention is not limited to this example and can be implemented to monitor various planetary gear trains, with any number of planetary gears, used as a reducer motor or as a propeller, or even multiple planetary gear trains arranged in series.

Claims

1. A method for monitoring a planetary gear train (100) of an aircraft, wherein: The planetary gear train (100) comprises two coaxially mounted first toothed wheels (110, 120) and at least one second toothed wheel (130), wherein the at least one second toothed wheel meshes with the two first toothed wheels, and the method comprises the following steps: - acquiring a first value (S(t) of a signal formed by a traveling mechanical wave generated in the planetary gear train (100) at a predetermined sampling frequency i )), the first value forms the main mechanical wave data; - measuring at a plurality of consecutive moments the value (V) of the rotational speed of at least one of the two first toothed wheels (110, 120) and the at least one second toothed wheel (130); mes_r (t j )), the measured values ​​form primary rotation data; - According to the main rotation data (V mes_r (t j )), calculate the value (V) of the rotation speed of the contact point between one of the first toothed wheels (110, 120) and one of the second toothed wheels (130) of the planetary gear train (100) c (t j )), the calculated values ​​form secondary rotation data; - According to the main mechanical wave data (S(t i )) and the secondary rotation data (V c (t j )), determining a second value of the signal formed by a traveling mechanical wave generated in the planetary gear train (100) The second values ​​correspond to regular sampling as a function of the phase of the contact point and form secondary mechanical wave data; and -Using the secondary mechanical wave data To detect abnormalities related to the operation of the planetary gear train (100).

2. The method according to claim 1, wherein: The rotational speed of the contact point between one of the first toothed wheels (110, 120) and one of the second toothed wheels (130) of the planetary gear train (100) is a linear combination of the respective rotational speeds of the first toothed wheel and the second toothed wheel.

3. The method according to claim 2, wherein: At least one of the respective rotational speeds is based on the main rotational data (V mes_r (t j )) and the respective numbers of teeth of at least two of the two first toothed wheels (110, 120) and the at least one second toothed wheel (130) are calculated.

4. The method according to claim 1, wherein: Using the secondary mechanical wave data To detect anomalies related to the operation of the planetary gear train (100) includes: - Calculate and analyze data, including calculating the secondary mechanical wave data wherein the Fourier transform transforms the phase function into an order function; and - Using the analysis data to detect anomalies associated with the operation of the planetary gear train (100).

5. The method according to claim 4, wherein: Anomalies associated with the operation of the planetary gear train (100) are detected using analytical data associated with at least one integer order.

6. The method according to claim 4 or 5, wherein: Calculating the analysis data includes calculating the secondary mechanical wave data The power spectral density of .

7. The method according to claim 4, wherein: Calculating the analysis data includes calculating the secondary mechanical wave data The average power spectral density.

8. The method according to claim 4, wherein: Calculating the analysis data includes calculating and collecting the secondary mechanical wave data Spectrum plot of multiple values ​​of the average power spectral density.

9. The method according to claim 1, wherein: The signal formed by the traveling mechanical wave generated in the planetary gear train (100) is an acoustic signal acquired using an acoustic wave sensor.

10. The method according to claim 9, wherein: The acoustic wave sensor is arranged to be spaced apart from the planetary gear train (100).

11. The method according to claim 1, wherein: A signal formed by a traveling mechanical wave generated in the planetary gear train (100) is a vibration signal acquired using an accelerometer.

12. The method according to claim 1, wherein: The method further comprises: when using the secondary mechanical wave data When an abnormality related to the operation of the planetary gear train (100) is detected, the planetary gear train (100) is maintained.

13. The method according to claim 1, wherein: The method further comprises a preliminary step of determining a health indicator, the preliminary step comprising the following steps: - for a plurality of flights, obtaining the primary mechanical wave data and the primary rotation data, and determining the corresponding secondary rotation data and the secondary mechanical wave data; - for each flight of the plurality of flights, calculating analysis data, said calculating comprising calculating a Fourier transform of said secondary mechanical wave data; and - correlating the analysis data with information on anomalies or the absence of anomalies in the operation of the planetary gear train (100).

14. A monitoring system (10) for monitoring a planetary gear train (100) of an aircraft, the system comprising: a planetary gear train (100) comprising two coaxially mounted first toothed wheels (110, 120) and at least one second toothed wheel (130) meshing with the two first toothed wheels; - at least one mechanical wave sensor (11), at least one of the mechanical wave sensors being arranged to acquire, at a predetermined sampling frequency, a first value of a signal formed by a traveling mechanical wave generated in the planetary gear train (100), the first value forming a primary mechanical wave data (S(t i )); at least one rotation speed sensor (12), at least one of said rotation speed sensors being arranged to acquire values ​​of the rotation speed of at least one of said two first toothed wheels and said at least one second toothed wheel at a plurality of consecutive moments, said acquired values ​​forming primary rotation data (V mes_r (t j ));as well as - a processor (13), the processor being configured to receive the main mechanical wave data (S(t i )) and the main rotation data (V mes_r (t j )) as input to calculate the value (V) of the rotation speed of the contact point between one of the first toothed wheels (110, 120) and one of the second toothed wheels (130) of the planetary gear train (100) c (t j )), the value of the rotation speed forms secondary rotation data, thereby determining a second value of the signal formed by the traveling mechanical wave generated in the planetary gear train (100) based on the primary mechanical wave data and the secondary rotation data And outputting a piece of information (D) related to the presence or absence of abnormality in the operation of the planetary gear train (100), the second value being sampled as a function of the phase of the contact point.

15. The monitoring system (10) for monitoring a planetary gear train (100) of an aircraft according to claim 14, characterized in that: The mechanical wave sensor (11) is an acoustic sensor, and the acoustic sensor is arranged to be spaced apart from the planetary gear train (100).

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