FR3116562A1 - Method for monitoring the quality of oil contained in an oil circuit of an aircraft engine, associated monitoring device - Google Patents

Abstract

Method for monitoring the quality of oil contained in an oil circuit of an aircraft engine, associated monitoring device The invention relates to a method for monitoring the quality of the oil contained in an oil circuit of an aircraft engine. Said method comprises a set of steps implemented for at least one time interval of at least one flight of said aircraft and during which said engine is in operation, said set of steps comprising steps of:- determining (E10) of a duration of said time interval, - obtaining (E20) of at least one oil temperature value, - determination (E30) of an oxidation constant of said oil as a function of the temperature value obtained, - determination (E40) of a level of antioxidants present in the oil at the end of said at least one time interval, as a function of said duration, of said oxidation constant as well as of a level of antioxidants present in oil at the beginning of said time interval. Figure for abstract: Fig. 4

Description

Method for monitoring the quality of oil contained in an oil circuit of an aircraft engine, associated monitoring device

The present invention belongs to the general field of monitoring the operation of an aircraft engine. It relates more particularly to a method for monitoring the quality of the oil contained in an oil circuit of an aircraft engine. It also relates to a monitoring device configured to implement such a monitoring method. The invention finds a particularly advantageous application, although in no way limiting, in the case of an aircraft comprising engines of the turbomachine type.

An aircraft engine comprises many elements requiring, during operation of the aircraft, to be dynamically lubricated using an oil system, such as for example bearings, pistons, gears, etc., in order to reduce possible friction between them. In order to ensure such lubrication, said oil system comprises, in a conventional manner, an oil circuit forming a closed circuit comprising one or more pumps configured to set the oil in motion within pipes of said oil circuit .

In addition to being configured to allow oil circulation, the oil system also has the function, via said oil circulation and the physico-chemical characteristics thereof, of regulating the temperature of elements of the engine set in motion during the operation of the aircraft, such as bearings. This thermal regulation is for example implemented at the level of heat exchangers of the oil-fuel type.

The lubrication and thermal regulation thus ensured by the oil are vital for the proper functioning of the engine. However, for the oil to fully play its role with regard to these two aspects, it is important that its quality is sufficient.

By "quality of the oil", it refers to the level of antioxidants present in the oil. In other words, said antioxidant level forms an indicator of the quality of the oil. Such antioxidants are additives conventionally added to oil to slow its degradation over time.

Indeed, when the engine of the aircraft is in operation, in particular at high temperatures, as well as in the presence of oxygen, the oil contained in the oil circuit is highly stressed, which has an impact on its oxidation stability. However, an increase in the oxidation of the oil can lead to a change in its viscosity. Deposits can thus form and corrosion appear, ultimately leading to failure of the oil system and therefore of the engine.

The antioxidants added to the oil therefore make it possible to slow down its degradation (ie its oxidation). However, such antioxidants are also subject to degradation. Indeed, and when no oil is added to the oil circuit, the level of antioxidants present in the oil decreases following a chemical reaction whose kinetics are all the greater as the temperature of oil is high. More particularly, at a fixed temperature T, these kinetics follow an exponential decay law over time according to the following formula:
C(t) = C_0 x exp[-k(T) xt],
Or :
- C is representative of the level of antioxidants present in the oil when no oil is added to the oil circuit,
- C_0 is a constant representative of an initial level of antioxidants present in the oil (ie the level of antioxidants in t=0),
- t is representative of the time that elapses from an initial instant at which the concentration of antioxidants present in the oil is equal to C_0, and
- k is a parameter which, at a fixed temperature T of the oil, is also called the “oxidation constant”. This parameter k is a parameter intrinsic to the oil used, typically estimated during characterization tests of the oil in question, and is therefore representative of the speed of the exponential decrease.

In known manner, the coefficient k is an increasing function of said temperature. Consequently, the higher the oil temperature, the faster the decrease in the level of antioxidants when no oil is added to the oil circuit.

Of course, the determination of the temporal evolution of the level of antioxidants present in the oil is not reduced to the use of the previous formula. Indeed, it is also necessary to take into account the consumption of oil specific to the engine, and which implies that new oil is regularly added to the oil circuit in order to compensate for the losses linked to this consumption (possibly, any the oil contained in the oil circuit can be renewed). Insofar as the rate of antioxidants present in the new oil is higher than in the oil already present in the oil circuit (and which has therefore already been able to experience oxidation), it is understood that the addition of new oil makes it possible to compensate at least in part for the reduction in the level of antioxidants. It therefore emerges from these aspects that the more an engine consumes oil, the more it is necessary to regularly add new oil to its oil circuit, which then contributes, for an average volume of oil in the circuit of oil, with an average rate of antioxidants which stabilizes over time at a high level. Conversely, the less oil an engine consumes, the less it is necessary to regularly add new oil to its oil circuit, which then contributes, for said average volume, to an average rate of antioxidants which stabilizes over time at a low level.

These aspects are illustrated by the which is a graph representing the temporal evolution of the level of antioxidants present in the oil according to several cases. The abscissa axis (respectively the ordinate) of this graph indicates the time t in hours (respectively indicates the level of antioxidants C(t) in percent).

This graph shows three curves respectively associated with three distinct cases: a first case associated with an engine with high oil consumption (curve A1), a second case associated with an engine with low oil consumption (curve A2), and a third fictitious case associated with an engine that does not consume oil (curve A3). Note that curves A1 and A2 each have a “sawtooth” profile. The fact that, for a curve A1 or A2, the level of antioxidant rises in a substantially periodic manner is linked to the addition of new oil (we therefore note that the frequency of these additions of new oil is greater in the first case). On the other hand, insofar as the engine associated with the third case does not consume oil, no oil is added (i.e. the profile of the curve A3 is smooth according to a decreasing exponential, as mentioned above) .

As can be seen, the level of antioxidants stabilizes around 77% in the first case. Regarding the second case, the average level of antioxidants stabilizes at around 53%. Finally, for the third case, the level of antioxidants converges as expected towards zero.

Also, it emerges from the above that the temporal evolution of the level of antioxidants present in the oil, in other words the quality of the oil, depends on two competing factors, namely the temperature of the oil as well as the engine oil consumption.

Such a finding is important insofar as the dimensioning of the oil system depends in particular on the quality of the oil. However, to date, when one seeks to ensure that all the engines in a fleet have sufficient oil quality, the sizing of their respective oil systems is generally carried out by considering the constraints at worst, i.e. taking as a reference the engine of the fleet having the most extreme operation (low oil consumption and limit of the highest oil temperature, the average level of antioxidant required being therefore more important). The quality of the oil can therefore be seen as an oil system sizing constraint in that it implies the implementation of design margins that are far too large with regard to the differences in operation between engines.

Moreover, to this sizing constraint is also added the fact that the monitoring of the quality of the oil is carried out today by means of oil samples in the oil circuit, these samples subsequently the subject of laboratory analyzes to assess the level of antioxidants they contain. By way of example, such analyzes can implement high performance liquid chromatography techniques or even gas phase chromatography. In any case, these samplings and these analyzes are tedious and costly to implement, which compromises the possibility of carrying out effective and regular monitoring of the oil quality, in particular in an operational context.

The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above, by proposing a solution which makes it possible to monitor in an efficient and regular manner, as well as at lower cost, the quality oil contained in an oil circuit of an aircraft engine. Thanks to such monitoring, the solution proposed by the invention also makes it possible to relax said dimensioning constraint of the oil system, in particular for engines intended to operate under conditions which are not extreme. In other words, the oil system of such engines can be sized to accept a lower oil quality than that required for an engine with extreme operation.

To this end, and according to a first aspect, the invention relates to a method for monitoring the quality of the oil contained in an oil circuit of an aircraft engine. Said method comprises a set of steps implemented for at least one time interval of at least one flight of said aircraft and during which said engine is in operation, said set of steps comprising steps of:
- determination of a duration of said time interval,
- obtaining at least one oil temperature value,
- determination of an oxidation constant of said oil as a function of said at least one temperature value obtained,
- determination of a level of antioxidants present in the oil at the end of said at least one time interval, as a function of said duration, of said oxidation constant as well as of a level of antioxidants present in the oil at the beginning of said time interval.

The monitoring method proposed by the invention therefore makes it possible to monitor over time the level of antioxidants present in the oil contained in the oil circuit. More particularly, the monitoring method offers the possibility of determining one or more values of said antioxidant level, if for example one or more time intervals are considered for said at least one flight. This or these antioxidant level values can, for example, be recorded in order to be analyzed very quickly afterwards, without the need for expensive and time-consuming laboratory tests.

For each time interval considered, the monitoring method according to the invention proposes not only to determine the duration of this interval, but also to obtain at least one oil temperature value associated with this time interval (i.e. at least one value temperature to which the oil is or was brought during said time interval). Therefore, from a temperature value thus obtained, it is possible to determine an oxidation constant attached to the time interval considered, to finally deduce the level of antioxidants sought on the basis of the analytical formulation mentioned previously.

The monitoring thus established of the level of antioxidants is therefore particularly simple to implement, and offers the possibility of effectively and regularly monitoring the evolution of said level of antioxidants, and therefore ultimately of the quality of the oil contained. in the oil circuit. In other words, the method according to the invention offers the possibility of carrying out active monitoring of the quality of the oil contained in the oil circuit.

What is more, the temperature value(s) can be acquired by means of acquisition means of a type known per se conventionally fitted to each engine of the aircraft. The invention therefore does not require the deployment of instrumentation other than that which conventionally equips an aircraft engine, which has the advantage of limiting the implementation costs.

It is also understood that offering active oil quality monitoring also provides an opportunity for an airline to recoup the oil cost of operating an aircraft engine. Indeed, by having a precise idea of the quality of the oil, the said airline can decide in an informed manner whether a partial or total renewal of the oil contained in the oil circuit of an engine should be considered.

Furthermore, the monitoring method according to the invention is also remarkable in that it makes it possible to relax the dimensioning constraint of the oil system, in particular for engines intended to operate under conditions which are not extreme. Indeed, the fact of being able to monitor actively (and therefore regularly) the level of antioxidants favors the detection of a possible anomaly as to the value of said level of antioxidants, and therefore advantageously makes it possible to consider the design of engines able to operate with a lower level of antioxidants than in the state of the art. However, authorizing the reduction of said antioxidant level amounts to authorizing a reduction in the quality of the oil, or even, in an equivalent manner, to authorizing an engine to operate with an oil brought to a higher temperature than in the state of the art, which therefore amounts to relaxing the dimensioning constraint of the oil system.

In particular modes of implementation, the monitoring method may also include one or more of the following characteristics, taken in isolation or in all technically possible combinations.

In particular modes of implementation, said set of steps further comprises steps of:
- comparison of the level of antioxidants determined for said at least one time interval with a given threshold value,
and, if said antioxidant level is below said threshold value,
- detection of an anomaly in the quality of the oil contained in the oil circuit.

Such arrangements make it possible to effectively detect an anomaly as to the quality of the oil contained in the oil circuit.

In particular modes of implementation, said set of steps further comprises a step of issuing an alert if an anomaly in the quality of the oil is detected.

The fact of issuing an alert in the event of an anomaly makes it possible to obtain information without delay as to the existence of an anomaly in the quality of the oil.

In particular modes of implementation, said method further comprises, at the end of said at least one flight and if an anomaly in the quality of the oil has been detected, steps of:
- renewal of all or part of the oil contained in the oil circuit, by adding a volume of oil in said oil circuit, the added oil being associated with a given antioxidant rate called "rate new ",
- obtaining a volume of oil remaining in said oil circuit before the addition of oil, the remaining oil being associated with a rate of antioxidants called "old rate" determined for the last time interval considered before said oil renewal,
- determination of the volume of oil added,
- calculation of a quantity equal to the sum of the old and new rates respectively weighted by said remaining and added volumes of oil, said quantity corresponding to a rate of antioxidants present in the oil contained in the oil circuit at the from the oil change.

This embodiment is particularly advantageous in that it makes it possible to avoid damage to the engine via a total or partial renewal of the oil contained in the oil circuit. This is all the more advantageous with regard to an engine intended to operate under extreme conditions insofar as it is the engine whose asymptotic evolution of the level of antioxidants is the lowest, and therefore the closest a threshold below which an anomaly can be detected. Consequently, by closely monitoring the evolution of the level of antioxidants, in particular for an engine intended to operate in extreme conditions, a maintenance operation aimed at a partial or total renewal of the oil can be envisaged in order to replace the oil degraded by new oil and thus leave with an oil with a high antioxidant rate.

In particular modes of implementation, said method further comprises, at the end of said at least one flight and if no anomaly has been detected, steps of:
- detection of a possible addition of a volume of oil in the oil circuit, the added volume of oil being associated with a given rate of antioxidants called "new rate",
and, if a step of adding said volume of oil to the oil circuit has been implemented such that the addition of said volume of oil is detected,
- obtaining a volume of oil remaining in said oil circuit before the addition of oil, the remaining oil being associated with a rate of antioxidants called "old rate" determined for the last time interval considered before the adding oil,
- determination of the volume of oil added,
- calculation of a quantity equal to the sum of the old and new rates respectively weighted by said remaining and added volumes of oil, said quantity corresponding to a rate of antioxidants present in the oil contained in the oil circuit at the after adding oil.

In particular modes of implementation, the steps of said set of steps are iterated recurrently during said at least one time interval.

In this way, regular monitoring of the quality of the oil is carried out during a flight.

In particular modes of implementation, a single time interval is considered during said at least one flight, said time interval comprising an initial instant and a final instant corresponding respectively to the instants at which the aircraft begins a taxiing phase before takeoff and completes another taxiing phase after landing.

In particular modes of implementation, a plurality of flights of the aircraft is considered, the steps of the method being iterated for each of said flights.

According to a second aspect, the invention relates to a computer program comprising instructions for the implementation of a monitoring method according to the invention, with the exception of said step of renewing as well as of said step of adding , when said computer program is executed by a computer.

This program may use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in partially compiled form, or in any other desirable form.

According to a third aspect, the invention relates to a computer-readable information or recording medium on which a computer program according to the invention is recorded.

The information or recording medium can be any entity or device capable of storing the program. For example, the medium may include a storage medium, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or even a magnetic recording medium, for example a floppy disk or a disk. hard.

On the other hand, the information or recording medium can be a transmissible medium such as an electrical or optical signal, which can be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can in particular be downloaded from an Internet-type network.

Alternatively, the information or recording medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

According to a fourth aspect, the invention relates to a device for monitoring the quality of the oil contained in an oil circuit of an aircraft engine. Said device comprises:
- a first determination module configured to determine, for at least one time interval of at least one flight of said aircraft and during which said engine is in operation, the duration of said time interval,
- an obtaining module configured to obtain at least one oil temperature measurement for said at least one time interval,
- a second determination module configured to determine an oxidation constant of said oil as a function of the temperature obtained,
- a third determination module configured to determine a rate of antioxidants present in the oil at the end of said at least one time interval, as a function of said duration, of said oxidation constant as well as of a rate of antioxidants present in the oil at the beginning of said time interval.

In particular embodiments, said device further comprises:
- a comparison module configured to compare the level of antioxidants determined for said at least one time interval with a given threshold value,
- a detection module configured to detect an anomaly in the quality of the oil contained in the oil circuit if said level of antioxidants is lower than said threshold value.

According to a fifth aspect, the invention relates to a system for monitoring the quality of oil contained in the oil circuit of the engine of the aircraft, said monitoring system comprises:
- acquisition means configured to acquire at least one temperature measurement of the oil contained in the oil circuit,
- A monitoring device according to the invention.

According to a sixth aspect, the invention relates to an aircraft comprising a monitoring system according to the invention.

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof which is devoid of any limiting character. In the figures:
there is a graph representing the evolution over time of the level of antioxidants present in the oil contained in the oil circuit of an aircraft engine, according to the type of engine considered, and in accordance with the state of the art ;
there schematically represents, in its environment, a particular embodiment of a monitoring system according to the invention, said monitoring system being configured to monitor the quality of oil contained in the oil circuit of an aircraft engine ;
there schematically represents an example of hardware architecture of a monitoring device according to the invention belonging to the monitoring system of the ;
there represents, in the form of a flowchart, a first particular mode of implementation of a monitoring method according to the invention by the device for monitoring the ;
there represents, in the form of a flowchart, a second particular mode of implementation of a monitoring method according to the invention by the device for monitoring the ;
there represents, in the form of a flowchart, a third particular mode of implementation of a monitoring method according to the invention by the device for monitoring the .

The present invention finds its place in the field of monitoring the operation of an aircraft engine, for an aircraft (not shown in the figures) comprising one or more engines, for example two identical engines.

Conventionally, each engine of the aircraft is equipped with an oil system comprising an oil circuit, the aircraft therefore comprising as many engines as there are oil circuits. The oil circuit of each engine forms a closed circuit comprising one or more pumps configured to set the oil in motion within the pipes of said oil circuit, so as to ensure a lubrication function. The oil circuit of each engine also includes a tank, in which the oil is stored when the engine it equips is not in operation, and in which the oil is pumped for circulation in the pipes. .

The oil circuit of an engine of the aircraft is furthermore in contact, at the level of a plurality of interfaces, such as for example seals, walls, equipment, etc., with a fuel circuit of said engine, so as to provide a thermal regulation function by heat exchange between said oil and fuel circuits.

The remainder of the description relates more specifically, but in no way limiting, to an aircraft of the airplane type, for example a civil airplane capable of transporting passengers, equipped with a plurality of identical engines of the turboshaft type. By way of example, said engines are turbojets.

Nothing excludes however, following other examples not detailed here, considering other types of turbine engines, such as for example a turboprop, but also, and more generally, engines which are not turbine engines, such as example of piston engines. The invention is indeed applicable to any type of engine for which it is desired to monitor the quality of the oil contained in the oil circuit of said engine, as described in detail later. There is also nothing to exclude considering an aircraft of another type, such as a helicopter.

Furthermore, no limitation is attached to the number of engines fitted to the aircraft. There is also nothing to prevent the aircraft from having, in addition to one or more identical engines, one or more engines which, considered individually, differ from all the other engines.

The remainder of the description attempts to describe the invention (oil quality monitoring) in relation to a single engine of the aircraft, to which reference will henceforth be made in a defined manner using the expressions "the engine/ engine” of the aircraft. It is however important to note that the following description can be generalized in an obvious way to the case where the aircraft is equipped with a plurality of engines, the monitoring in question can therefore be implemented for each of the engines of said plurality.

There schematically represents, in its environment, a particular embodiment of a monitoring system 10 according to the invention.

Said monitoring system 10 is configured to monitor the quality of oil contained in the oil circuit of the aircraft engine, and, for this purpose, comprises acquisition means 11 configured to acquire:
- at least one temperature measurement of the oil contained in the oil circuit
- at least one measurement of the volume of oil present in the oil circuit.

Conventionally, said acquisition means 11 comprise an acquisition chain comprising at least one sensor dedicated to volume measurements, such as for example a level probe, and at least one sensor dedicated to temperature measurements, such as for example a temperature sensor. Said acquisition chain may also include other elements, such as for example an acquisition card, electronic means of amplification and/or filtering, an analog-digital converter, etc., these aspects not being more detailed here because outside the scope of the present invention.

In general, the person skilled in the art knows how to carry out and acquire volume and temperature measurements, and will therefore know, in particular, how to choose suitable sensors for each of the quantities considered (volume, temperature), for example in the catalogs products offered by specialized manufacturers. He will also know how to position these sensors.

The measurements acquired by the acquisition means 11 are carried out at different measurement instants. More particularly, the temperature measurements are taken during operation of the engine of the aircraft. Volume measurements, on the other hand, do not require the aircraft engine to be running.

“Aircraft engine operation” refers herein to the fact that the aircraft engine has started. Such a configuration naturally covers the taxiing phases before and after landing (phases also called "taxi" in Anglo-Saxon literature), the take-off phase, the cruising phase, the landing phase, but also the phases during which the aircraft has not yet left its parking lot before take-off or has already reached its parking lot after landing, its engines nevertheless being in operation.

It should be noted that no limitation is attached to the measurement instants at which the volume and temperature measurements are made. In particular, nothing excludes that the instants of measurement associated with the measurements of volume are at least partly, even all, different from the instants of measurement associated with the measurements of temperature. Of course, and in a known manner, obtaining the value of a quantity (volume of oil or temperature) at a time when no measurement of this quantity has been carried out remains possible, for example by using techniques interpolation between measurements.

The monitoring system 10 also comprises a monitoring device 12 configured to carry out, in particular from the measurements acquired by the acquisition means 11, processing operations making it possible to monitor (i.e. to carry out monitoring of) the quality of the oil contained in the engine oil circuit, by implementing a monitoring method according to the invention.

In the present embodiment, the monitoring device 12 is integrated into a calculation unit fitted to the aircraft and also known by the name of FADEC (acronym of the English expression “Full Authority Digital Engine Control”). Said FADEC unit is, in a manner known per se, configured to optimally control and regulate the operation of the engine. However, and unlike a FADEC unit of the state of the art, the FADEC unit described here also makes it possible, because the monitoring device 12 is integrated therein, to monitor the quality of the oil contained in the oil circuit.

The choice according to which the monitoring device 12 is integrated into the FADEC unit of the aircraft only constitutes, however, a variant implementation of the invention. Thus, nothing excludes having, for example, a processing device 12 external (i.e. not electronically integrated) to the FADEC unit.

There schematically represents an example of hardware architecture of the monitoring device 12 according to the invention belonging to the monitoring system 10 of the .

As illustrated by the , the monitoring device 12 has the hardware architecture of a computer. Thus, the monitoring device 12 comprises, in particular, a processor 1, a random access memory 2, a read only memory 3 and a non-volatile memory 4. It also comprises means of communication 5.

The read only memory 3 of the monitoring device 12 constitutes a recording medium in accordance with the invention, readable by the processor 1 and on which is recorded a computer program PROG in accordance with the invention, comprising instructions for the execution of steps of the monitoring method according to the invention. The program PROG defines functional modules of the monitoring device 12, which rely on or control the hardware elements 1 to 5 of the monitoring device 12 mentioned above, and which include in particular:
- a first determination module MOD_DET_1 configured to determine, for at least one time interval INT_i (i "both an integer index) of at least one flight of said aircraft and during which said engine is in operation, the duration D_i of said time interval INT_i,
- a module for obtaining MOD_OBT configured to obtain at least one value T_i_j (j being an integer index) of the temperature of the oil (contained in the oil circuit) for said at least interval INT_i,
- a second determination module MOD_DET_2 configured to determine an oxidation constant k_i of said oil as a function of said at least one temperature value T_i_j obtained,
- a third determination module MOD_DET_3 configured to determine a level of antioxidants C_i present in the oil at the end of said at least one time interval INT_i, as a function of said duration D_i, of said oxidation constant k_i as well as d a level of antioxidants C_0_i present in the oil at the beginning of said time interval INT_i.

In addition, in the present example, said functional modules also include:
- a comparison module MOD_COMP configured to compare the level of antioxidants C_i determined for said at least one time interval INT_i with a given threshold value S_i,
- a detection module MOD_DETECT configured to detect an anomaly in the quality of the oil contained in the oil circuit if said level of antioxidants C_i is lower than said threshold value S_i,
- an alert module MOD_ALERT configured to issue an alert if an oil quality anomaly is detected.

The communication means 5 are configured to allow the monitoring device 12 to communicate, in particular, with the acquisition means 11, so as to be able to directly obtain one or more volume and/or temperature measurements acquired by the latter. To this end, the means of communication 5 are based on a communication interface, wired or wireless, capable of implementing any known protocol (Ethernet, Wifi ®, Bluetooth ®, 3G, 4G, 5G, etc.) adapted to an exchange of data between the monitoring device 12 and the acquisition means 11. It is noted that, in this embodiment, the communication means 5 incorporate said obtaining module MOD_OBT. Of course, the acquisition means 11 are themselves provided with communication means adapted to the transmission of one or more volume and/or temperature measurements.

There is also nothing to exclude the monitoring device 12 from obtaining, via its MOD_OBT obtaining module, one or more volume and/or temperature measurements after these have been acquired and stored in storage means external to the monitoring device 12, such as for example a dedicated database.

In general, no limitation is attached to the way in which the monitoring device 12 can obtain one or more volume and/or temperature measurements.

As mentioned above, the determinations of the oxidation constant k_i and of the level of antioxidants C_i, respectively by the second determination module MOD_DET_2 and the third determination module MOD_DET_3, are carried out for at least an interval INT_i of at least one flight of the aircraft. Consequently, there can be no renewal of all or part of the oil in the oil circuit during said at least time interval INT_i, so that the level of antioxidants C_i can be determined in accordance with the formula described above . Thus, for said at least one interval INT_i, we have:
C_i = C_0_i x exp[-k_i x D_i].

According to a particular exemplary embodiment, a plurality of consecutive time intervals INT_1, ..., INT_N (N being an integer strictly greater than 1) is considered for said at least flight. These intervals INT_1, …, INT_N can have respective durations D_1, …, D_N which are identical or else at least partly distinct. For example, each time interval corresponds to a given flight phase of the aircraft (taxi phases, take-off phase, cruise phase, landing phase, etc.) or else to a combination of several of these flight phases (or even the entire flight).

Alternatively, a single time interval INT_1 is considered for said at least one flight. In a manner similar to what was mentioned above in the context of a plurality of time intervals, said single time interval INT_1 can correspond to a given flight phase of the aircraft (taxi phases, take-off phase, cruise, landing phase, etc.) or a combination of several of these flight phases (or even the entire flight).

In general, no limitation is attached to the number of time intervals INT_i that can be considered for a single flight, nor even to the way in which these intervals are distributed over time during a flight. Nor is there any limitation attached to the number of flights that can be considered within the framework of the invention.

It is also understood that the level of antioxidants C_0_i present in the oil at the beginning of a time interval INT_i can depend on several factors, including in particular the number of time intervals which are considered during a flight and the fact that all or part of the oil contained in the oil circuit is renewed.

To illustrate this, two flights of the aircraft can be considered by way of example, namely a first flight and a second flight. It is also considered that two time intervals INT_1 and INT_2 partition the duration of the first flight. We then have, for said first flight, that the level of antioxidants C_0_2 is equal to the level of antioxidants C_1 determined at the end of the interval INT_1 insofar as the two intervals INT_1 and INT_2 are consecutive (ie the initial instant of INT_2 corresponds to the final instant of INT_1). The level of C_2 antioxidants determined at the end of the INT_2 interval in the context of said first flight can:
- correspond to the level of antioxidants present in the oil at the beginning of a first interval considered for the second flight, if no oil renewal takes place between said first and second flights, or else
- be used to determine the level of antioxidants present in the oil at the beginning of a first interval considered for the second flight, depending on whether all or part of the oil is renewed between said first and second flights, and as explained in detail later in the context of the description of the monitoring method according to the invention.

The rest of the description aims to describe particular modes of implementation of the monitoring method according to the invention. Also, for the rest of the description, and for the sole purpose of simplifying it, we now place ourselves in the configuration according to which a single flight of the aircraft is considered, but also according to which a single time interval INT_1 is considered during said flight. It is also considered purely by way of illustration that said time interval INT_1 comprises an initial instant and a final instant corresponding respectively to the instants at which the aircraft begins a taxiing phase before takeoff (beginning of the taxi-out phase) and ends a another taxiing phase after landing (end of the taxi-out phase).

There represents, in the form of a flowchart, a first particular mode of implementation of the monitoring method according to the invention by the monitoring device 12 of the .

As illustrated by the , the monitoring method comprises, for said time interval INT_1, a set of steps. Said set of steps notably comprises a step E10 of determining a duration D_1 of said time interval INT_1. Said step E10 is implemented by the first determination module MOD_DET_1 equipping the monitoring device 12.

Said duration D_1 is determined in a conventional manner, by subtracting from the final instant of the interval INT_1 the initial instant of said interval INT_1. To this end, the FADEC calculation unit is configured to record in memory means which equip it with said initial and final instants during the flight of the aircraft, so that they are then accessible for the implementation of step E10.

Said set of steps also includes a step E20 of obtaining at least one oil temperature value T_1_j (for said one time interval INT_1). Said step E20 is implemented by the MOD_OBT obtaining module fitted to the monitoring device 12.

By way of non-limiting example, several values T_1_1, …, T_1_M (M being an integer strictly greater than 1) are obtained for said time interval INT_1, these values T_1_1, …, T_1_M corresponding to measurements acquired by the means of acquisition 11 during time interval INT_1. Thus, in this example, step E20 consists of obtaining said measurements acquired by monitoring device 12 via data transmission between acquisition means 11 and said monitoring device 12.

Nothing, of course, excludes only a temperature value T_1_1 from being obtained for said time interval INT_1, this value T_1_1 therefore corresponding to a measurement acquired during the time interval INT_1. Thus, the obtaining that is the subject of step E20 concerns only the transmission of this single temperature measurement.

Said set of steps also includes a step E30 of determining an oxidation constant k_1 of the oil as a function of said at least one temperature value T_1_j obtained. Said step E30 is implemented by the second determination module MOD_DET_2 equipping the monitoring device 12.

For example, when only one temperature value T_1_1 is obtained for the time interval INT_1 following the implementation of step E20, said oxidation constant k_1 is determined from this single temperature value T_1_1. The determination of the oxidation constant k_1 is carried out in a manner known per se, for example by consulting a table of values (abacus) stored in the memory means of the monitoring device 12 (example: the non-volatile memory 4 ), or even by executing code instructions contained in the program PROG and dedicated to the calculation of said oxidation constant k_1.

According to another example of implementation, when a plurality of values T_1_1, ..., T_1_M are obtained for the interval INT_1 following the implementation of step E20, step E30 comprises first of all a calculation of an average of the values T_1_1, …, T_1_M, the oxidation constant k_1 then being determined from the average thus calculated.

The choice according to which an average is calculated when a plurality of values T_1_1, ..., T_1_M are acquired only constitutes one implementation variant of the invention. Thus, other variants are possible, such as for example: calculation of an average of only part of the values T_1_1, …, T_1_M acquired (the said average can also be weighted), selection of a value from among the values T_1_1 , …, T_1_M, etc. Ultimately, what matters above all is to determine a single temperature value from said plurality of values T_1_1, …, T_1_M, so that the oxidation constant k_1 can be determined from said single temperature value ( k_1 which can be seen as a real function with only one variable).

It is important to note that, when a plurality of measurements are acquired during the interval INT_1, nothing excludes said single value from being determined from said plurality of measurements acquired during the implementation of step E20 for obtaining and not during the implementation of step E30 for determining the constant k_1. In other words, and within the meaning of the present invention, the term “obtaining” in relation to step E20 can just as well refer, as described above, to a transmission of temperature measurements between the means acquisition 11 and the monitoring device 12, but also to obtaining as such said single temperature value.

Of course, still other examples of implementation can be envisaged when a plurality of values T_1_1, …, T_1_M are obtained for said interval INT_1, such as for example a determination of oxidation constants k_1_1, …, k_1_M for each of these values T_1_1, …, T_1_M, the oxidation constant k_1 therefore being determined as being equal to a weighted average of all or part of said constants k_1_1, …, k_1_M, or else equal to any one of said constants k_1_1, …, k_1_M, etc.

In said first mode of implementation, said set of steps also includes a step E40 of determining a level of antioxidants C_1 present in the oil at the end of said at least one time interval INT_1, as a function of said duration D_1, said oxidation constant k_1 as well as a level of antioxidants C_0_1 present in the oil at the beginning of said time interval. Said step E40 is implemented by the third determination module MOD_DET_3 equipping the monitoring device 12.

As already detailed above, the determination of said level of antioxidants C_1 is carried out according to the following formula:
C_1= C_0_i x exp[-k_1(T_i) x D_1]

As illustrated by the , said set of steps further comprises a step E50 of comparing the level of antioxidants C_1 determined for a time interval INT_1 with a given threshold value S_1. Said step E50 is implemented by the comparison module MOD_COMP equipping the monitoring device 12.

Said threshold value S_1 corresponds to a limit value below which it is considered that the level of antioxidants C_1 present in the oil contained in the engine circuit is too low, therefore implying an oil quality deemed to be unsatisfactory.

No limitation is attached to said threshold value S_1, the person skilled in the art being able to set it insofar as he knows the design and dimensioning constraints which are associated with the engine of the aircraft. Thus, and according to a more specific example of implementation, said threshold value S_1 is set by taking into account a margin with respect to a level of antioxidants considered unsatisfactory because presenting a risk for maintaining the integrity of the engine .

Said comparison step E50 therefore makes it possible to test whether the level of antioxidants C_1 is lower or higher than the threshold value S_1. Depending on the result of this comparison, the monitoring method may include one or more additional steps.

Thus, in said first mode of implementation, and if the level of antioxidants C_1 is lower than the threshold value S_1, said set of steps includes a step E60 of detecting an anomaly in the quality of the oil contained in the oil circuit. Said step E60 is implemented by the detection module MOD_DETECT equipping the monitoring device 12.

As mentioned above, the detection of an oil quality anomaly here corresponds to the result of a comparison between numerical quantities (quantities C_1 and S_1). In other words, at this stage of the monitoring method, the information according to which the quality of the oil is possibly not sufficient corresponds to digital information, typically encoded in the form of bits, which is for example recorded by means of storage of the monitoring device 12 to be analyzed in real time or in deferred time.

Also, in said first mode of implementation, said set of steps further comprises a step E70 of issuing an alert if an anomaly in the quality of the oil is detected. Said step E70 is implemented by the alert module MOD_ALERT equipping the monitoring device 12.

Said alert corresponds for example to a sound signal, a light signal, etc., this signal being able to be transmitted to an operator on the ground in charge of the maintenance of the aircraft, or even also to the cockpit of the aircraft in order to alert the flight crew.

It is noted that if no anomaly is detected, then, of course, no alert is emitted ( step E75 on the ).

The monitoring method has so far been described considering that said set of steps included the comparison step E50 as well as the said steps of detection E60 and of emission or not of an alert E70/E75 if necessary. It should however be noted that these steps E50, E60 and E70/E75 are not essential to the invention insofar as the fact of implementing only the steps E10, E20, 30 and E40 for said set of steps allows already to monitor effectively (and possibly on a regular basis if several flights and/or several intervals are considered), as well as at a lower cost, the quality of the oil contained in the oil circuit of an engine of aircraft. Indeed, access to the level of antioxidants C_1 determined following the implementation of step E40 already offers the possibility of carrying out engine monitoring, this level C_1 being able for example to be stored in order to be analyzed later on the flight . Consequently, the fact that the monitoring device 12 is equipped with the MOD_COMP comparison, MOD_DETECT detection and MOD_ALERT alert modules is also not essential to the invention.

Moreover, if the steps E10 to E70/E75 are executed for the time interval INT_1, they are not necessarily executed during the flight of the aircraft. Thus, nothing excludes all or part of the steps E10 to E70/E75 from being executed once the flight of the aircraft has ended, the various data necessary for the steps executed once the flight has ended having been stored and therefore being accessible.

The rest of the description aims to detail other particular modes of implementation of the monitoring method according to the invention.

There represents, in the form of a flowchart, a second particular mode of implementation of the monitoring method according to the invention by the monitoring device 12 of the .

Said second mode of implementation repeats steps E10 to E70/E75 of the first mode of implementation (step E70/E75 being optional in said second mode).

According to said second mode of implementation, and as illustrated by the , the monitoring method also comprises, at the end of the flight and if an anomaly in the quality of the oil has been detected, a step E80 of renewing all or part of the oil contained in the oil circuit. Said renewal is carried out by adding a volume of oil to said oil circuit, the added oil being associated with a given level of antioxidants called “new level”.

Renewing all or part of the oil obviously results from the fact that an anomaly in the quality of the oil has been detected. The level of this anomaly (i.e. in the present case, the difference between the level of antioxidants C_1 and the threshold S_1) determines whether all the oil or only part of it must be renewed.

According to said second mode of implementation, the monitoring method also comprises a step E90 of obtaining a volume of oil remaining in said oil circuit before the addition of oil, the remaining oil being associated with a so-called “old rate” level of antioxidants determined for the last time interval considered before said oil renewal. In the present mode, said last time interval corresponds to the interval INT_1 insofar as only the latter is considered during the flight. Consequently, said old level corresponds to the level of antioxidants C_1 previously determined.

Said step E90 is implemented by a dedicated module (not shown in the figures) of the monitoring device 12. For example, a measurement of the volume of oil present in the oil circuit before the addition of oil is acquired by a suitable sensor belonging to the acquisition means 11, then transmitted to the monitoring device 12.

According to another example, said remaining volume of oil is calculated, in a manner known per se, from the volume of oil contained in the oil circuit at the start of the flight of the aircraft as well as from the value of the consumption engine oil and flight time.

According to said second mode of implementation, the monitoring method also includes a step E100 of determining the volume of oil added. Said step E100 is implemented, in a manner known per se, by a dedicated module (not shown in the figures) of the monitoring device 12.

For example, a measurement of the volume of oil present in the oil circuit after renewal is acquired by a suitable sensor belonging to the acquisition means 11, then transmitted to the monitoring device 12 which can therefore determine the volume of oil added from said remaining volume of oil and from said volume of oil present in the oil circuit after renewal.

Finally, the monitoring method also comprises, in said second mode of implementation, a step E110 of calculating a quantity Q1 equal to the sum of the old and new rates respectively weighted by said remaining and added volumes of oil, said quantity Q1 corresponding to a level of antioxidants present in the oil contained in the oil circuit after the oil renewal. Said step E110 is implemented by a dedicated module (not shown in the figures) of the monitoring device 12.

It should be noted that in the event that another flight is envisaged at the end of the implementation of the monitoring method according to this second mode, said quantity Q1 would therefore constitute the level of antioxidants present in the oil at the beginning of the first interval that would be considered for this other flight. It would be the same with regard to the volume of oil present in the oil circuit at the end of the renewal.

There represents, in the form of a flowchart, a third particular mode of implementation of the monitoring method according to the invention by the monitoring device 12 of the .

Said third mode of implementation repeats steps E10 to E110 of the first and second modes of implementation.

According to said third mode of implementation, and as illustrated by the , the monitoring method also comprises, at the end of the flight and if no anomaly has been detected, a step E130 of detecting a possible addition of a volume of oil in the oil circuit, the volume of added oil being associated with a given level of antioxidants called “new level”.

Said step E130 is implemented by a dedicated module (not shown in the figures) of the monitoring device 12. For example, and in a manner similar to what was described above with reference to the , a measurement of the volume of oil present in the oil circuit at the end of a given time period (ie the time required to carry out a possible additional oil) is acquired by a suitable sensor belonging to the acquisition means 11 , then transmitted to the monitoring device 12. This volume measurement is then compared with another measurement of the volume of oil remaining in the oil circuit, the obtaining of which is described below.

For the remainder of the description of said third mode of implementation, it is assumed that a volume of oil is added to the oil circuit at the end of the flight and before step E130 of detection. More particularly, and as illustrated by the , the monitoring method here comprises a step E120 of adding a volume of oil, so that the result of the detection step E130 is positive. It is understood of course that such a step E120 of adding a volume of oil is optional, and that if no oil is added (not shown in the ), the result of the detection step E130 is this time negative.

According to said third mode of implementation, the monitoring method also includes a step E140 obtaining a volume of oil remaining in said oil circuit before adding oil, the remaining oil being associated with a rate of antioxidants called “old rate” determined for the last time interval considered before the addition of oil, as well as a step E150 for determining the volume of oil added. Said steps E140 and E150 are respectively implemented in a manner similar to the implementations of steps E90 and E100 described above.

Finally, the monitoring method also comprises, in said third mode of implementation, a step E160 of calculating a quantity Q2 equal to the sum of the old and new rates respectively weighted by said remaining and added volumes of oil, said quantity Q2 corresponding to a level of antioxidants present in the oil contained in the oil circuit after the addition of oil. Said step E160 is implemented in a manner similar to the implementation of step E110 described above.

Furthermore, it should be noted that in the event that another flight is envisaged at the end of the implementation of the monitoring method according to this third mode, said quantity Q2 would therefore constitute the level of antioxidants present in the oil at the beginning of the first interval that would be considered for this other flight. Of course, if no oil volume addition was detected, the antioxidant level to be taken into account for said other flight would correspond to said old antioxidant level.

We also note that the third mode of implementation of the has been written above as being combined with the first and second embodiments of FIGS. 4 and 5 respectively. However, nothing excludes considering, according to yet another mode of implementation, a combination of steps E120 to E160 with only steps E10 to E70/E75 (step E70/E75 being optional in said third mode), in other words without the second mode of implementation being envisaged.

The monitoring method according to the invention has been described so far by considering a single flight of the aircraft. Said method nevertheless remains applicable in the case where a plurality of flights is considered, in which case the steps of the method, and this regardless of the mode of implementation envisaged, are iterated for each of said flights. It should be noted that the antioxidant level threshold value considered for one flight may be different for another flight.

The monitoring method was further described considering that the steps of said set of steps were implemented only once during said interval INT_1. However, nothing excludes considering that said steps of the set of steps are iterated in a recurring manner, for example according to a given time step, during said interval INT_1. It should be noted that such an implementation option is equivalent to the fact of considering a plurality of time slots for the same flight, said steps of the set of steps then being executed only once for each of the time slots of said plurality of time intervals.

Claims (14)

Method for monitoring the quality of the oil contained in an oil circuit of an aircraft engine, said method comprising a set of steps implemented for at least one time interval of at least one flight of said aircraft and during which said engine is in operation, said set of steps comprising steps of:
- determination (E10) of a duration of said time interval,
- obtaining (E20) of at least one oil temperature value,
- determination (E30) of an oxidation constant of said oil as a function of said at least one temperature value obtained,
- determination (E40) of a level of antioxidants present in the oil at the end of said at least one time interval, as a function of said duration, of said oxidation constant as well as of a level of antioxidants present in oil at the beginning of said time interval. A method according to claim 1, wherein said set of steps further includes steps of:
- comparison (E50) of the level of antioxidants determined for said at least one time interval with a given threshold value,
and, if said antioxidant level is below said threshold value,
- detection (E60) of an anomaly in the quality of the oil contained in the oil circuit. A method according to claim 2, wherein said set of steps further includes a step of issuing (E70) an alert if an oil quality abnormality is detected. Method according to any one of claims 2 and 3, said method further comprising, at the end of said at least one flight and if an anomaly in the quality of the oil has been detected, steps of:
- renewal (E80) of all or part of the oil contained in the oil circuit, by adding a volume of oil to said oil circuit, the added oil being associated with a given level of antioxidants called “new rate”,
- obtaining (E90) a volume of oil remaining in said oil circuit before the addition of oil, the remaining oil being associated with a rate of antioxidants called "old rate" determined for the last time interval considered before said oil change,
- determination (E100) of the volume of oil added,
- calculation (E110) of a quantity equal to the sum of the old and new rates respectively weighted by said remaining and added volumes of oil, said quantity corresponding to a rate of antioxidants present in the oil contained in the circuit of oil after the oil change. Method according to any one of claims 2 to 4, said method further comprising, at the end of said at least one flight and if no anomaly has been detected, steps of:
- detection (E130) of a possible addition of a volume of oil in the oil circuit, the volume of oil added being associated with a given level of antioxidants called "new level",
and, if a step of adding (E120) said volume of oil to the oil circuit has been implemented such that the addition of said volume of oil is detected,
- obtaining (E140) a volume of oil remaining in said oil circuit before the addition of oil, the remaining oil being associated with a rate of antioxidants called "old rate" determined for the last time interval considered before adding oil,
- determination (E150) of the volume of oil added,
- calculation (E160) of a quantity equal to the sum of the old and new rates respectively weighted by said remaining and added volumes of oil, said quantity corresponding to a rate of antioxidants present in the oil contained in the circuit of oil after adding oil. A method according to any of claims 1 to 5, wherein during said at least one time interval the steps of said set of steps are iterated recursively. Method according to any one of Claims 1 to 6, in which a single time interval is considered during said at least one flight, said time interval comprising an initial instant and a final instant corresponding respectively to the instants at which the aircraft begins a taxiing phase before takeoff and completes another taxiing phase after landing. Method according to any one of Claims 1 to 7, in which a plurality of flights of the aircraft are considered, the steps of the method being iterated for each of said flights. Computer program comprising instructions for implementing a monitoring method according to any one of Claims 1 to 8, with the exception of the renewal step according to Claim 4 as well as the step d addition according to claim 5, when said computer program is executed by a computer. A computer-readable recording medium on which a computer program according to claim 9 is recorded. Device (12) for monitoring the quality of the oil contained in an oil circuit of an aircraft engine, said device comprising:
- a first determination module (MOD_DET_1) configured to determine, for at least one time interval of at least one flight of said aircraft and during which said engine is in operation, the duration of said time interval,
- an obtaining module (MOD_OBT) configured to obtain at least one oil temperature measurement for said at least one time interval,
- a second determination module (MOD_DET_2) configured to determine an oxidation constant of said oil as a function of the temperature obtained,
- a third determination module (MOD_DET_3) configured to determine a level of antioxidants present in the oil at the end of said at least one time interval, as a function of said duration, of said oxidation constant as well as of a level of antioxidants present in the oil at the beginning of said time interval. A monitoring device (12) according to claim 11, said device further comprising:
- a comparison module (MOD_COMP) configured to compare the level of antioxidants determined for said at least one time interval with a given threshold value,
- a detection module (MOD_DETECT) configured to detect an anomaly in the quality of the oil contained in the oil circuit if said level of antioxidants is lower than said threshold value. System (10) for monitoring the quality of oil contained in the oil circuit of the aircraft engine, said monitoring system comprises:
- acquisition means (11) configured to acquire at least one temperature measurement of the oil contained in the oil circuit,
- a monitoring device (12) according to any one of claims 11 to 12. Aircraft comprising a monitoring system (10) according to claim 13.