EP3545175B1 - Method for controlling a turbomachine valve - Google Patents

Description

GENERAL TECHNICAL FIELD

The invention relates to turbomachines and methods or devices for controlling valves controlling an air flow, and in particular LPTACC valves (“ low pressure turbine active clearance command ” in English according to the terminology used in aeronautics for active control. low pressure turbine clearances), that is to say the valves which aim to control the clearance between a turbine blade and a casing disposed radially around it. By injecting air into the crankcase, it can be cooled and its thermal expansion controlled, which causes a reduction in its size and therefore a reduction in play.

The expansion of elements depends on several parameters, including materials, assemblies, speed of rotation, temperature, etc. The LPTACC valve therefore makes it possible to influence the temperature of the crankcase.

The game is modulated according to the phases of flight, engine speed, altitude ...

STATE OF THE ART

A turbomachine 10 with double flow for aeronautical propulsion is shown in figure 1a . It comprises a fan 11 delivering an air flow, a central part of which is injected into a primary stream VP comprising a compressor 12 which supplies a turbine 14 driving the fan. The turbine 14 comprises a plurality of radially extending vanes 140 and is housed radially inside a casing 16.

The peripheral part of the air flow coming from the blower circulates in a secondary vein VS. This peripheral part of the air flow is ejected towards the atmosphere to provide the major part of the thrust of the turbomachine 10.

In order to control the clearance between the blades 140 of the turbine 14 and the casing 16, a control valve 20, which is preferably of the LPTACC type, is provided. The figure 1b schematically illustrates the architecture of the environment of this valve 20 and of its active control.

This control valve 20 makes it possible to continuously control an air flow coming from the secondary stream, from a sample 18, and to direct it towards the casing 16 arranged opposite the blades 140 of the turbine 14. The sampling 18 communicates with a supply duct 22 which brings the air flow to the control valve 20. A reject duct 24 then brings this air from the control valve 20 to the housing 16.

A calculation unit 40 receives in particular as input the value of the engine speed and calculates a flow control which is converted into a position control. This position command is sent to an actuator 30 which controls the valve 20. Position sensors (not shown) allow feedback to the calculation unit 40.

On the figure 1b , it is a hydraulic actuator 30 which controls a hydraulic servo valve 20. The link 41 between the calculation unit 40 and the actuator 30 is electrical. The connection 31 between the actuator 30 and the valve 20 is hydraulic. The return link 21 between the control valve 20 and the computing unit 40 is electrical.

The main aim of the active control is to reduce the clearance at the top of the blade 140 of the turbine 14 in order to optimize the specific consumption, that is to say the quantity of fuel necessary to produce a thrust of one Newton for one hour.

One of the objectives of the control is to define an optimal air flow for the active control, making it possible to limit as much as possible the clearance at the top of the blades 140 while minimizing the quantity of air taken from the fan, because the air flowing in this way does not directly contribute to the thrust provided by the turbomachine 10. This objective is mainly aimed at during the cruising phases (“ cruise ” in English, ie the steady state).

The service life of these control valves is often lower than that expected by the manufacturers. Solutions have been to strengthen the valves, using more resistant materials, but the problem is only partially resolved.

The reference patent application is also known WO2007 / 086893 presenting a system for controlling the blade tip play in turbomachines.

PRESENTATION OF THE INVENTION

As indicated in the introduction, the invention relates to the control valves 20 of a turbomachine 10 and the associated methods. The elements and their references indicated in the introduction will be reused for the description below.

• Une étape E1 de réception des données quantifiant le régime moteur de la turbomachine,
• Une étape E2 de détermination d'une commande en débit à partir notamment des données quantifiant le régime moteur,
• Une étape E3 de détermination d'une commande en position à partir de la commande en débit.

The methods for controlling the control valve 20 generally comprise the following steps implemented by the computing unit 40:

• A step E1 of receiving data quantifying the engine speed of the turbomachine,
• A step E2 of determining a flow control based in particular on data quantifying the engine speed,
• A step E3 of determining a position control from the flow control.

The position control is intended to allow the control of the valve 20, in particular via an actuator 30 if the latter is not integrated into the valve 20.

Other data is involved for the position control, in particular the constants of the transfer function of the actuator 30. These known data do not directly relate to the invention and will not be detailed further.

Other steps then take place, such as a step of piloting by the actuator of the valve, the actuator receiving as input the command in position of step E3. These steps do not concern the calculation unit 40 directly.

On existing equipment, it was observed that the service life of the control valves was shorter than expected. As indicated in the introduction, corrective actions relating to the quality of the materials were launched but could only temporarily and partially alleviate the problem.

During more in-depth studies, the Applicant has noticed that the control valve 20 oscillates around its equilibrium position. The amplitude of these oscillations is small compared to the value of the command, but the frequency is high compared to the thermal response of the housing 16.

These oscillations can represent up to two-thirds of the total stroke of the valve 20 during a flight and therefore lead to premature wear of the valve 20.

However, the Applicant has also noticed that the oscillations are not due to the air flow which could generate disturbances but are due to step E2 of determining the flow control. Now, step E3 of determining the control in position of the valve directly follows step E2.

It has thus been found that the flow control supplied by the computing unit 40 is very sensitive to the oscillations of the engine speed which varies by a few percent when it is in cruising mode. We now define a cruising value Vc around which the engine speed oscillates at a frequency fo and an amplitude Ao (Ao being low compared to Vc, typically less than 5% of Vc). The frequency fo is about 1 Hz (variable depending on the turbomachines).

Since, in the cruising phase, the position control of the valve 20 is substantially proportional to the engine speed, this oscillation of the speed results in an oscillation of the position control.

The engine speed can in particular be obtained by sensors measuring the speed of rotation of the shaft of the low-pressure turbine.

By way of illustration, the change in flow rate induced by these oscillations of the position control is approximately 5%. Due to its magnitude and frequency, such a change has no physical utility since the thermal response time of the housing 16 is slower.

The invention therefore proposes a control method comprising a step of determining for the control valve 20 a control in the filtered position of the oscillations of the engine speed around the cruising value Vc.

In particular, the filtering uses a low-pass filter whose cutoff frequency is greater than a frequency associated with the thermal response time of the casing, in order to ensure that the filtering does not disturb the function of the valve.

Indeed, the oscillation of the valve being due to an oscillation of the control in position, a suitable filtering makes it possible to eliminate the noise of the signal and to optimize the management of the valve. The cumulative stroke of the valve can thus be divided by three on a flight, which increases its service life.

The filtering is performed using a low pass filter, a cutoff frequency fc of which is lower than the frequency of the oscillations fo, in order to attenuate them. More generally, the cutoff frequency fc is chosen to attenuate the oscillations throughout the cruising phase.

The filtering provided in the process makes it possible to limit the influence of the oscillations on the control in position and thus to improve the service life of the valve 20.

In view of the architecture of the steps carried out in the calculation unit, the filtering can be carried out on different signals but ultimately produces a similar result, namely that the position control is filtered from the oscillations of the engine speed.

The invention applies advantageously to LPTACC valves (that is to say intended to supply the casing with air to modify its expansion), but also to any type of valve including the computer unit which controls it in Input of engine speed data and therefore applies to valves whose position oscillates in response to engine speed oscillations. These valves control the flow of fluid, in particular air.

• l'étape de détermination comprend les sous-étapes suivantes :
  • (E1) réception des données quantifiant le régime moteur de la turbomachine,
  • (E2) détermination d'une commande en débit à partir des données quantifiant le régime moteur,
  • (E3) détermination d'une commande en position à partir de la commande en débit, ladite commande en position étant destinée à la vanne de contrôle,
  • (Ef) filtrage de la commande en position issue de l'étape de détermination de la commande en position (E3),
  dans lequel le filtrage est effectué à l'aide d'un filtre passe-bas dont une fréquence de coupure fc est inférieure à une fréquence (fo) des oscillations du régime moteur autour de la valeur de croisière Vc,
• le filtre est un filtre passe-bas du premier ordre,
• la vanne de contrôle est destinée à alimenter en air un carter pour modifier sa dilatation et dans lequel la fréquence de coupure fc est supérieure à une fréquence fr associée au temps de réponse thermique du carter,
• la fréquence de coupure fc est comprise entre 0,05Hz et 0,15Hz,
• le procédé comprend un sous-procédé de désactivation de l'étape de filtrage Ef mis en œuvre par l'unité de calcul, ledit sous-procédé comprenant les étapes suivantes :
  • (E51) détermination du gradient de la commande en position issue de l'étape de détermination d'une commande en position (E3),
  • (E52) comparaison de ce gradient à un seuil de désactivation Sg,
  • (E53) désactivation du filtre si le gradient est supérieur audit seuil Sg,
• le procédé comprend un sous-procédé d'activation de l'étape de filtrage Ef mis en œuvre par l'unité de calcul, ledit sous-procédé comprenant les étapes suivantes :
  • (E61) détermination du gradient de la commande en position issue de l'étape de détermination d'une commande en position (E3),
  • (E62) comparaison de ce gradient à un seuil d'activation Sg',
  • (E63) activation du filtre si le gradient est inférieur audit seuil Sg' pendant au moins une durée de confirmation,
• préférablement l'étape d'activation du filtre (E63) se fait si l'altitude, le régime moteur et le Mach vérifient, en outre, chacun une certaine valeur,
• l'étape de détermination comprend les sous-étapes suivantes :
  • (E1) réception des données quantifiant le régime moteur de la turbomachine,
  • (Ef) filtrage sur données des données quantifiant le régime moteur issue de l'étape précédente,
  • (E2, E3) détermination d'une commande en position destinée à la vanne de contrôle,
  dans lequel le filtrage est effectué à l'aide d'un filtre passe-bas dont une fréquence de coupure (fc) est inférieure à une fréquence (fo) des oscillations du régime moteur autour de la valeur de croisière (Vc).

Finally, the invention can have the following characteristics, taken alone or in combination:

• the determination step comprises the following sub-steps:
  • (E1) reception of data quantifying the engine speed of the turbomachine,
  • (E2) determination of a flow control from data quantifying the engine speed,
  • (E3) determining a position command from the flow rate command, said position command being intended for the control valve,
  • (Ef) filtering of the command in position resulting from the step of determining the command in position (E3),
  in which the filtering is carried out using a low-pass filter whose cut-off frequency fc is less than a frequency (fo) of the oscillations of the engine speed around the cruising value Vc,
• the filter is a first order low pass filter,
• the control valve is intended to supply a casing with air to modify its expansion and in which the cut-off frequency fc is greater than a frequency fr associated with the thermal response time of the casing,
• the cut-off frequency fc is between 0.05Hz and 0.15Hz,
• the method comprises a sub-method for deactivating the filtering step Ef implemented by the computing unit, said sub-method comprising the following steps:
  • (E51) determination of the gradient of the command in position resulting from the step of determining a command in position (E3),
  • (E52) comparison of this gradient with a deactivation threshold Sg,
  • (E53) deactivation of the filter if the gradient is greater than said threshold Sg,
• the method comprises a sub-method for activating the filtering step Ef implemented by the computing unit, said sub-method comprising the following steps:
  • (E61) determination of the gradient of the command in position resulting from the step of determining a command in position (E3),
  • (E62) comparison of this gradient with an activation threshold Sg ',
  • (E63) activation of the filter if the gradient is less than said threshold Sg 'for at least one confirmation period,
• preferably the step of activating the filter (E63) is carried out if the altitude, the engine speed and the Mach each further verify a certain value,
• the determination step comprises the following sub-steps:
  • (E1) reception of data quantifying the engine speed of the turbomachine,
  • (Ef) data filtering of the data quantifying the engine speed from the previous step,
  • (E2, E3) determination of a command in position intended for the control valve,
  in which the filtering is carried out using a low-pass filter of which a cut-off frequency (fc) is less than a frequency (fo) of the oscillations of the engine speed around the cruising value (Vc).

The invention also proposes a system for controlling a control valve of a turbomachine operating at engine speed at a cruising value Vc, said control valve being intended to supply air to a casing in order to modify its expansion, said system comprising a control valve and a calculation unit configured to implement the method as described above.

The calculation unit comprises a data reception interface, a processor capable of processing data, a memory (for storing data) and a data output interface. In particular, the computing unit comprises a filtration unit (typically the processor which executes operations), which performs the filtering operation.

The invention also proposes a turbomachine comprising a system as described above.

PRESENTATION OF FIGURES

• La figure la illustre l'architecture globale d'une turbomachine,
• La figure 1b illustre l'architecture globale des éléments de contrôle du débit prélevé sur la veine secondaire et envoyé vers le carter en regard des aubes de turbines selon l'état de la technique,
• La figure 2 illustre par étapes un mode de mise en œuvre de l'invention,
• La figure 3 illustre l'architecture en schéma-bloc d'un procédé d'activation ou de désactivation du filtre, complémentaire du mode de mise en œuvre de la figure 2,
• Les figures 4 et 5 illustrent par étapes d'autres modes de mise en œuvre de l'invention.

Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which should be read in conjunction with the accompanying drawings, in which:

• Figure la illustrates the overall architecture of a turbomachine,
• The figure 1b illustrates the overall architecture of the flow control elements taken from the secondary stream and sent to the casing facing the turbine blades according to the state of the art,
• The figure 2 illustrates in stages one mode of implementation of the invention,
• The figure 3 illustrates the block diagram architecture of a process for activating or deactivating the filter, complementary to the mode of implementation of the figure 2 ,
• The figures 4 and 5 illustrate in stages other embodiments of the invention.

DETAILED DESCRIPTION

Several modes of implementation will now be described.

First mode of implementation

In a first mode of implementation presented in figure 2 , the filtering step Ef is applied to the command in position resulting from step E3, so that a command in filtered position is obtained at the output.

The advantage of such filtering at the end of the process is that it is easily implemented on the software of the devices in service and that it does not call into question the integrity of the already existing code: its integration into an on-board software is thus simplified.

In a preferred mode, the filtering is carried out with a first order low pass filter, having a single cutoff frequency fc.

The choice of the type of filter is based on the fact that the frequencies to be suppressed are much higher than the nominal behavior of the logic.

It is technically feasible to put a filter of order two or higher, but to limit the impact in terms of computation time, the simplest filters will be preferred.

Determining the cutoff frequency fc is an important condition for obtaining effective filtering that does not cripple the control process.

The response time of the filter was chosen by a compromise between two constraints. Indeed, this response time must be high enough to eliminate a maximum of oscillations without slowing down the system to unacceptable proportions from the point of view of the thermal response of the casing. In fact, too low a frequency would filter the nominal value of the control and the control valve 20 would remain virtually stationary.

Motor tests are used to define the thermal response of the crankcase and obtain a characteristic response time (and its associated frequency). Since the thermal response of the crankcase is generally different at different points, the most restrictive case is chosen to delimit the minimum response time (i.e. the maximum frequency at which the cut-off frequency must remain below ). Insofar as a frequency fr associated with the most restrictive response time of the housing 16 (that is to say the weakest response time among the measurements taken on the housing 16) is generally significantly lower than the frequency fo oscillations, it is possible to ensure that the cut-off frequency fc is greater than the frequency fr associated with the response time of the housing 16 without this introducing excessively strong stresses on the frequency fc.

These conditions on the cutoff frequency guarantee the performance of the system.

The frequency fo of the micro-oscillations was also estimated, which made it possible to determine a lower limit of the response time, and therefore an upper limit for the cut-off frequency fc.

For example, depending on the frequency fo, we choose a cutoff frequency fc between 0.05 and 0.15 Hz, or even 0.08 and 0.12 Hz or more broadly between 0.01 and 0.20Hz . As a reminder, the frequency fo is around 1 Hz, which is far enough from the previous upper bounds to ensure effective filtering. For cut-off frequencies fc in the latter interval, it is ensured to have response times lower than those of the housing 16.

However, the addition of the filter slows down the system somewhat and it should preferably only be applied in relevant flight phases. In this case, it is only desirable to apply this filtering in cruising flight conditions, that is to say when the engine speed is in steady state (speed at which the oscillations are observed at the frequency fo).

• Le régime moteur,
• Le Mach (c'est-à-dire le rapport de la vitesse locale dans un fluide sur la vitesse du son dans ce même fluide),
• L'altitude.

A condition of filter application is firstly related to cruising speed. For this, we check three indicators:

• The engine speed,
• The Mach (i.e. the ratio of the local speed in a fluid to the speed of sound in this same fluid),
• The altitude.

Several values linked to these indicators are predetermined to characterize a cruising phase. If the cruise phase is confirmed, then the filtering step can be activated.

In addition, when the system requests a rapid reaction from the control valve 20, it is desired that the control is not slowed down by a filter (for example an action of the pilot, during take-off or landing or for example a sudden change environment).

Preferably, the method additionally comprises a sub-method for deactivating the filter. The figure 3 represents a block diagram indicating the different steps of this sub-process.

In a step E51, the gradient between two instants (that is to say the variation between two values at two instants of a digital signal) of the position control resulting from step E3 is determined. It is therefore not the filtered order. For this, several cascade delay blocks can be used (the number of three is linked to the internal logic of the calculation unit 40, for which the iteration rate is 0.240s, or 0.720s for the three iterations ).

In a step E52, this gradient is compared with a deactivation threshold value Sg. More precisely, to get rid of questions of signs, the absolute value of this gradient is compared with the deactivation threshold value Sg.

Finally, in a step E53, the filtering step Ef is deactivated if the gradient is greater than or equal to said threshold Sg.

By way of example, we choose a threshold value which is between 0.5 and 2.5% per second, that is to say that at one second interval, the command varies between 0.5 and 2.5% of its original value. In the diagram, the threshold value is 1% for 0.72 seconds, or 1.4% per second. An interval of 1 and 2% per second may also be suitable.

A gradient greater than the threshold Sg means that it is not a micro-oscillation which is detected, but a relevant change for the system which can have an impact on the housing 16.

Thus, as soon as the valve is used more, the filtering stops and the system recovers its classic operation. In this deactivation sub-process, the value analyzed is the control gradient and not the physical measurement given by the sensors: the solution would take filtering into account (since the control in position has been filtered) and would be too slow.

The reactivation (or activation) of the filtering step is also done under condition using another sub-process, also represented in figure 3 .

In steps E61, E62 similar to steps E51 and E52 respectively, the gradient is compared with an activation threshold value Sg ′.

The activation threshold value Sg 'may or may not be identical to the deactivation threshold value Sg. If it is desired that the activation of the filter be done more selectively, the threshold value Sg 'can be set lower than the threshold value Sg. In figure 3 , we have Sg = Sg '.

In a step E63, the filtering step Ef is activated if the gradient remains below the threshold Sg ′ for a fixed confirmation period T. The confirmation time T is between two and eight seconds (T = 5s on the figure 3 ), or even 4 and 6 seconds.

The additional conditions of the cruising phase (Mach, altitude and engine speed) are also analyzed here.

Step E63 is improperly represented on the figure 3 , since the drawn block outputs an activation condition, which is then preferably combined with the other activation conditions to effectively activate the filter.

If the three additional conditions are met (engine speed at a certain value, Mach at a certain value and altitude at a certain value), then the filter can be re-engaged.

Thus, it is ensured that the system is stable and that the engine is at cruising speed before reactivating the filtering step Ef and eliminating the oscillations.

Second mode of implementation

In a second mode of implementation presented in figure 4 , the filtering step Ef is applied to the engine speed data from step E1, so that a command in the filtered position is again obtained at the output. The step of determining a flow rate control E2 is then carried out on the basis of the filtered data relating to the engine speed.

Such filtering at the start of the method for calculating the position command makes it possible to avoid processing data with noise.

In such an implementation mode, the filtering is preferably integrated in fact in the step E2 of determining a flow control.

Embodiments with activation and deactivation thresholds can also be implemented.

Third mode of implementation

It is also conceivable to apply the filtering step to the flow control resulting from step E2. The step of determining the command in position E3 is then carried out on the basis of filtered flow control data. This embodiment is illustrated in figure 5 .

Embodiments with activation and deactivation thresholds can also be implemented.

Claims (12)

1. A method for controlling a valve (20) for monitoring a turbomachine, said valve being intended to monitor the clearance between a turbine blade and a casing by injection of air on the casing, the turbomachine operating in engine speed at a cruise value (Vc) and oscillating about its cruise value (Vc),
   the method being implemented by a calculation unit (40), and
   being characterized in that it comprises a step of determining, for the monitoring valve (20), a position command, filtered from the oscillations of the engine speed about the cruise value (Vc).
2. The method according to claim 1, wherein the filtering is carried out using a low-pass filter whose cutoff frequency (fc) is greater than a frequency (fr) associated with the thermal response time of the casing (16).
3. The method according to claim 1 or 2, wherein the determination step comprises the following sub-steps:

   - (E1) receiving data quantifying the engine speed of the turbomachine,

   - (E2) determining a flow rate command from the data quantifying the engine speed,

   - (E3) determining a position command from the flow rate command, said position command being intended for the monitoring valve,

   - (Ef) Filtering the position command resulting from the step of determining the position command (E3).
4. The method according to claim 2 or 3, wherein the low-pass filter is a first-order filter.
5. The method according to any one of claims 2 to 4, wherein said monitoring valve (20) is intended to supply air to the inside of a casing (16) in order to modify its expansion.
6. The method according to any one of claims 2 to 5, wherein the cutoff frequency (fc) is comprised between 0.05Hz and 0.15Hz.
7. The method according to any one of claims 2 to 6 comprising a sub-method for deactivating the command filtering step (Ef), implemented by the calculation unit (40), said sub-method comprising the following steps:

   - (E51) determining the gradient of the position command resulting from the step of determining a position command (E3),

   - (E52) comparing this gradient with a deactivation threshold (Sg),

   - (E53) deactivating the filter if the gradient is greater than said threshold (Sg).
8. The method according to any one of claims 2 to 7, comprising a sub-method for activating the filtering step (Ef) implemented by the calculation unit (40), said sub-method comprising the following steps:

   - (E61) determining the gradient of the position command resulting from the step of determining a position command (E3),

   - (E62) comparing this gradient with an activation threshold (Sg'),

   - (E63) activating the filter if the gradient is smaller than said threshold (Sg') during at least one confirmation period (T), and preferably if the altitude, the engine speed and the Mach also each verify a certain value.
9. The method according to claim 2, wherein the determination step comprises the following sub-steps:

   - (E1) receiving data quantifying the engine speed of the turbomachine,

   - (Ef) data-filtering the data quantifying the engine speed resulting from the preceding step,

   - (E2, E3) determining a position command intended for the monitoring valve (20).
10. The method according to any one of claims 1 to 9, wherein the filtering is carried out using a low-pass filter whose cutoff frequency (fc) is less than a frequency (fo) of the engine speed oscillations about the cruise value (Vc).
11. A system for controlling a valve (20) for monitoring a turbomachine operating in engine speed at a cruise value (Vc), said monitoring valve (20) being intended to supply air to a casing (16) in order to modify its expansion, said system comprising a monitoring valve and a calculation unit (40), comprising a filtration block filtering engine speed oscillations about the cruise value (Vc), the calculation unit (40) being configured to implement the method according to any one of claims 1 to 10, the filtration block implementing the filtering step.
12. A turbomachine comprising a system according to claim 11.

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