EP3759320A1

EP3759320A1 - Method and control unit for controlling the play of a high-pressure turbine

Info

Publication number: EP3759320A1
Application number: EP19715143.4A
Authority: EP
Inventors: Patrice Fraisse; Tangi Rumon Brusq; Jean-Loïc Hervé LECORDIX
Original assignee: Safran Aircraft Engines SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 2018-02-28
Filing date: 2019-02-26
Publication date: 2021-01-06
Also published as: FR3078362B1; US20210003028A1; CN111788368B; WO2019166734A1; CN111788368A; FR3078362A1; US11639668B2

Abstract

Method for controlling a play between apexes of vanes of a high-pressure turbine of a gas turbine aircraft engine and a turbine shroud, comprising the control of a valve which supplies an air flow to the turbine shroud, this method further comprising the following steps: - detection (301) of a transitory acceleration phase of the engine; - receiving (302) a data item which represents the temperature of the gas being discharged from the combustion chamber of the engine; - an instruction (304) to open the valve in order to supply the air flow to the turbine shroud or to increase the flow rate of the air flow supplied if the transitory acceleration phase is detected and if the temperature of the gas being discharged from the combustion chamber is greater than a first temperature threshold (TI) corresponding to a degraded play which is characteristic of an ageing engine, this threshold being less than a limit operating temperature of the engine.

Description

METHOD AND CONTROL UNIT FOR CONTROLLING THE PLAY OF A HIGH PRESSURE TURBINE Background of the Invention

The present invention relates to the general field of turbomachines for aeronautical gas turbine engines. It aims more precisely the control of the game between, on the one hand, the tips of moving blades of a turbine rotor and, on the other hand, a turbine ring of an outer casing surrounding the blades.

The clearance between the top of the blades of a turbine and the ring around them is dependent on the differences in dimensional variations between the rotating parts (disk and blades forming the turbine rotor) and the fixed parts (external casing of which the turbine ring that he understands). These dimensional variations are at the same time of thermal origin (related to the variations of temperature of the blades, the disc and the crankcase) and of mechanical origin (in particular related to the effect of the centrifugal force exerted on the turbine rotor ).

To increase the performance of a turbine, it is desirable to minimize the game as much as possible. On the other hand, during an increase in engine speed, for example during the transition from a ground idling speed to a take-off speed in an aircraft engine turbomachine, the centrifugal force acting on the turbine rotor tends to bring the blade tips closer to the turbine ring before the turbine ring has had time to expand under the effect of the temperature increase related to the increase in speed. There is therefore a risk of contact at this operating point called pinch point.

It is known to use an active steering system to control the blade tip clearance of a turbomachine turbine. A system of this type generally operates by directing on the outer surface of the turbine ring air taken for example at a compressor and / or the fan of the turbomachine. Fresh air sent to the outer surface of the turbine ring has the effect of cooling the latter and thus limiting its thermal expansion. The game is therefore minimized. Conversely, warm air promotes thermal expansion of the turbine ring, which increases the clearance and allows for example to avoid contact at the aforementioned pinch point.

Such active control is controlled by a control unit, for example by the full authority control system (or FADEC) of the turbomachine. Typically, the control unit acts on a regulating position valve to control the flow rate and / or the temperature of the air directed on the turbine ring, according to a set point and a game estimate. of real blade tips.

The turbomachine also has an operating limit temperature. The operating limit temperature of the engine is defined with respect to a limit temperature of the combustion gases determined downstream of its combustion chamber, for example deduced from at least one measurement carried out within the high-pressure or low-pressure turbine. engine pressure. This temperature is commonly referred to as "Red Line EGT". The Red Line EGT is identified by the manufacturer in ground tests ("Block Tests") and communicated by the manufacturer. In other words, the Red Line EGT is the maximum value declared by the manufacturer, which is certified according to the life cycle of the engine (eg new or refurbished engine). Once this limit is reached the engine is deposited for maintenance in order to restore a positive EGT margin. By EGT margin is meant here the difference the EGT-certified Red Line EGT and a flue gas temperature determined downstream of the combustion chamber of the engine.

The temperature of the combustion gases downstream of the combustion chamber of the engine is generally maximum during a rapid acceleration phase, taking into account the thermal response of the engine. Typically, about 60 seconds after an acceleration phase, the clearance between the rotor blades of the high pressure turbine and the ring around them increases. The increase in this game results in an increase in the temperature of the combustion gases. Measured downstream of the combustion chamber, by way of example at the output of the high-pressure turbine, are temperatures of the order of 20 to 30K higher compared to a temperature of the engine under steady state conditions, the stabilized speed being obtained after a given period of time following the acceleration phase of the engine. The difference in temperature between the maximum temperature of the combustion gases determined during an acceleration phase of the turbomachine and the temperature of its stabilized speed determined following this acceleration phase is commonly referred to as the "Overshoot".

In practice, the older the engine, the higher the temperature of the combustion gases increases. The maximum temperature of the combustion gases thus tends to approach the operating limit temperature of the engine (Red Line EGT) as it ages. This degradation in temperature is generally justified, at least in part, by a degradation of the high pressure turbine resulting in an increase in its clearance.

In this context, given the aging of the engine, it would be interesting to keep a positive EGT margin for as long as possible in order to push the deposit into engine maintenance.

During an acceleration phase, optimizing the clearance between the rotor blades of the high pressure turbine and the ring around them can reduce the Overshoot, and therefore the maximum temperature of the combustion gases. However, such optimization may present a risk of premature wear of the high pressure turbine. By way of example, an excessive reduction of the Overshoot linked to a prolonged reduction in the clearance of the high-pressure turbine for a new engine, hot, or already having an undervalued clearance of its high-pressure turbine, can lead to a point nip between the blades and the ring of the high pressure turbine. Thus, the limitation of an Overshoot during a phase / a transient state of the engine may present a risk of permanent degradation of the vanes of the high pressure turbine, thus imparting the overall performance of the engine and its fuel consumption.

It would therefore be desirable to minimize G Overshoot in the temperature of the high pressure turbine during a variation of the engine speed, while avoiding the possible risk of degradation of the vanes of the high pressure turbine.

Object and summary of the invention The present invention aims to overcome the aforementioned drawbacks.

For this purpose, the invention proposes a method of controlling a clearance between, on the one hand, blade tips of a rotor of a high-pressure turbine of a gas turbine engine engine and on the other hand, a turbine ring of a casing surrounding said blades of the high pressure turbine, the method comprising controlling a valve delivering a flow of air directed towards said turbine ring, this method being characterized in what it includes the following steps:

a detection of a transient motor acceleration phase from at least one representative parameter of the motor;

a reception of a data representative of the temperature of the gases at the outlet of the combustion chamber of the engine;

an opening command of the valve, for delivering said air flow to the turbine ring or for increasing the flow rate of said delivered air flow, if the transient phase of acceleration is detected and if the temperature of the gases at the outlet of the combustion chamber of the engine is greater than a first temperature threshold corresponding to a deteriorated play characteristic of an aged engine, the first temperature threshold being lower than an engine operating limit temperature.

Advantageously, the above method makes it possible to adapt the control of the game during an acceleration phase of the engine, while taking into account the residual margin existing between the engine operating limit temperature and the combustion gas temperature. output from the combustion chamber of the engine. As explained above, as the engine ages, the maximum temperature of the combustion gases of the engine increases, and tends to approach the engine operating limit temperature (Red Line EGT). In other words, the EGT margin tends to decrease as the engine ages. Taking into account the difference between the operating limit of the engine and the temperature of the combustion gases of the engine, via the first temperature threshold, therefore takes into account the aging of the engine. Thus, the play setpoint of the high pressure turbine is adapted according to the aging of the engine. Subsequently, the adaptation of this game set itself influences the temperature variation of the combustion gases at the outlet of the chamber combustion engine, allowing to reduce Overshoot. The play of the high pressure turbine and Overshoot are therefore regulated in a closed loop and adaptively according to the aging of the engine. This process is applicable throughout the life cycle of the engine. Typically an aged engine has in its high pressure turbine a larger game compared to a new engine. Depending on the aging of the engine, the method described above then makes it possible to minimize the play of its high-pressure turbine, via a control of the valve, without the risk of damaging the vanes of the turbine. The performance of the turbomachine is therefore optimized throughout its life cycle. It therefore extends the engine for the shelf life of a positive EGT margin, which increases the life of the engine and push its deposit maintenance.

Preferably, in this process a larger valve opening percentage is controlled if the temperature of the combustion gases temporarily exceeds the first temperature threshold.

In an exemplary embodiment of this method, said at least one representative parameter of the engine is the engine speed and the detection of a transient motor acceleration phase comprises a continuous determination of the engine speed and a determination of a variation of the engine speed. engine speed for a predetermined time interval, the transient acceleration phase of the motor being detected during said predetermined time interval if the variation of the engine speed is greater than or equal to a variation threshold characterizing a transient phase of acceleration of the engine.

In an exemplary embodiment, said at least one representative parameter of the engine is chosen from: the speed of a low-pressure turbine of the engine, the speed of the high-pressure turbine, the angular position of a throttle control lever of the engine. plane and the data representative of the temperature of the gases at the outlet of the combustion chamber of the engine.

In an exemplary embodiment of this method, the valve is an on-off type valve configured to switch between an open state or a closed state, the method further comprising, following the opening of the valve, a control closing the valve when the temperature of the gases leaving the combustion chamber of the engine is lower than a second temperature threshold, the second temperature threshold being lower than the first temperature threshold.

In another embodiment of this method, the valve is a controlled position valve, the method comprising a progressive opening control of the valve according to a predefined control law taking into account a difference between the temperature of the gases. at the outlet of the combustion chamber of the engine and the first temperature threshold.

In an exemplary embodiment of this method, the data representative of the temperature of the gases at the outlet of the combustion chamber is a temperature measurement made at the high pressure turbine.

According to another aspect, the invention also proposes a control unit for controlling a clearance between, on the one hand, blade tips of a rotor of a high-pressure turbine of a combustion engine. gas turbine aircraft and, secondly, a turbine ring of a housing surrounding said blades of the high pressure turbine, the control unit comprising valve control means, the valve being configured to deliver a flow of air towards said ring of the turbine, the control unit being characterized in that it comprises:

detection means configured to detect a transient motor acceleration phase from at least one representative parameter of the motor;

receiving means configured to receive a data representative of the temperature of the gases at the outlet of the combustion chamber of the engine;

the control means being configured to control an opening of the valve to deliver said flow of air to the turbine ring, or to control an increase in flow rate of said delivered air flow, if the transient phase of acceleration is detected and if the temperature of the gases leaving the combustion chamber of the engine is greater than a first temperature threshold corresponding to a deteriorated play characteristic of an aged engine, the first temperature threshold being below an operating limit temperature. of the motor.

Preferably, the control means are further configured to control a greater percentage of opening of the valve if the temperature of the combustion gases temporarily exceeds the first temperature threshold.

Advantageously, in order to judge the state of aging of the motor, the control unit counts a number of tripping of the additional opening command of the valve.

In an exemplary embodiment, in this control unit, said at least one representative parameter of the motor is the speed of the motor and the detection means are configured for:

- continuously determine the engine speed;

- determining a variation of the engine speed for a predetermined time interval;

- Detecting the transient acceleration phase of the motor during said predetermined time interval if the variation of the engine speed is greater than or equal to a variation threshold characterizing a transient motor acceleration phase.

In an exemplary embodiment, in this control unit, the valve is an all-or-nothing type valve configured to switch between an open state or a closed state, the control means being configured to control, following the opening of the valve, closing the valve when the temperature of the gases at the outlet of the combustion chamber of the engine is less than a second temperature threshold, the second temperature threshold being lower than the first temperature threshold.

In another exemplary embodiment, in this control unit, the valve is a controlled position valve, the control means being configured to control a progressive opening of the valve according to a predefined control law taking into account a deviation between the temperature of the gases leaving the combustion chamber of the engine and the first temperature threshold.

The invention also proposes, in another aspect, a gas turbine engine comprising the control unit summarized above and at least one valve for acting on a flow of air directed towards the turbine ring. and wherein the valve is controlled by the control means.

Brief description of the drawings Other characteristics and advantages of the invention will emerge from the following description of particular embodiments of the invention, given by way of non-limiting examples, with reference to the appended drawings, in which:

- Figure 1 is a schematic view in longitudinal section of a portion of a gas turbine engine engine according to one embodiment of the invention;

- Figure 2 is an enlarged view of the engine of Figure 1 showing in particular the high pressure turbine thereof;

- Figure 3 is a block diagram of a control module of a valve for controlling the blade tip set in the motor of Figure 1 according to a first embodiment;

- Figure 4 is a block diagram of a control module of a valve for controlling the blade tip set in the engine of Figure 1 according to a second embodiment.

Detailed description of embodiments

FIG. 1 schematically represents a turbojet engine 10 of the double-flow, double-body type to which the invention applies in particular. Of course, the invention is not limited to this particular type of gas turbine engine.

In a well known manner, the turbojet engine 10 of longitudinal axis XX comprises in particular a fan 12 which delivers a flow of air into a primary flow stream 14 and into a secondary flow stream 16 coaxial with the vein primary flow. From upstream to downstream in the direction of flow of the gaseous flow therethrough, the primary flow flow channel 14 comprises a low-pressure compressor 18, a high-pressure compressor 20, a combustion chamber 22, a high-pressure turbine 24 and a low pressure turbine 26.

As more specifically shown in FIG. 2, the high-pressure turbine 24 of the turbojet engine comprises a rotor formed of a disc 28 on which a plurality of movable vanes 30 arranged in the flow vein of the primary flow 14 are mounted. The rotor is surrounded by a turbine casing 32 comprising a turbine ring 34 carried by a outer casing of turbine 36 by means of fixing struts 37.

The turbine ring 34 may be formed of a plurality of adjacent sectors or segments. On the inner side, it is provided with a layer 34a of abradable material and surrounds the vanes 30 of the rotor, making with the apices 30a thereof a clearance 38.

According to the invention, there is provided a system for controlling the clearance 38 by modifying, in a controlled manner, the internal diameter of the outer casing of turbine 36. For this purpose, a control unit 50 controls the flow and / or the temperature of the air directed towards the outer turbine casing 36. The control unit 50 is for example the full authority control system (or FADEC) of the turbojet engine 10.

In the example shown, a control box 40 is arranged around the outer turbine casing 36. This housing receives fresh air by means of an air duct 42 opening at its upstream end in the duct. flow of the primary flow at one of the stages of the high pressure compressor 20 (for example by means of a scoop known per se and not shown in the figures). The fresh air circulating in the air duct is discharged on the outer casing of turbine 36 (for example by means of a multi-perforation of the walls of the control unit 40) causing a cooling thereof and therefore a decrease in its internal diameter.

As shown in FIG. 1, a valve 44 is disposed in the air duct 42. This valve 44 is controlled by the control unit 50.

In a first exemplary embodiment, the valve 44 may be an all-or-nothing valve able to switch between an open state or a closed state. The use of such a valve is advantageous, especially in terms of cost, bulk, reliability and power required for control.

It will be understood that by controlling the valve 44 to play on the one hand on the opening frequency and on the other hand on the opening / closing duty cycle of the valve, it is possible to obtain a variation of the average flow rate air directed towards the crankcase. Different all-or-nothing type valve architectures are well known to those skilled in the art and will not be described here. Preferably, one will choose a valve to electrical control that would remain in the closed position in the absence of power supply (thus, it is ensured that the valve remains closed in the event of a control fault).

In a second exemplary embodiment, the valve 44 may be a valve with a controlled position. The position of the valve 44 can be between 0%, corresponding to a closed valve, and 100%, corresponding to an open valve. When the valve 44 is open (100% position), the fresh air is supplied to the outer turbine casing 36, which has the effect of a thermal contraction of the latter and therefore a reduction of the clearance 38. On the contrary, when the valve 44 is closed (position 0%), the fresh air is not brought to the outer casing turbine 36 which is heated by the primary flow. This has the effect either of a thermal expansion of the casing 1 and an increase of the clearance 38, or at least a controlled limitation (or a stop) of the expansion of the casing 1 and a control of the clearance 38. In the intermediate positions, the outer casing turbine 36 contracts or expands and the clearance 38 increases or decreases, to a lesser extent. As will be seen later, the control of the clearance 38 is used so as to preserve a positive EGT margin, thus making it possible to extend the life of the turbojet engine 10.

Of course, the invention is not limited to these two examples. Thus, another example may consist of taking air at two different stages of the compressor and controlling valves 44 to modulate the flow of each of these samples to adjust the temperature of the mixture to be directed on the outer casing of the turbine 36.

The control of the valve 44 is now described by the control unit 50.

According to the invention, the control unit 50 comprises:

detection means 51 configured to detect a transient acceleration phase of the turbojet engine 10 over a predetermined time interval;

- Reception means 52 configured to receive at least one data representative of the temperature of the combustion gases from the combustion chamber 22 of the turbojet engine 10;

control means 53 configured to control the valve 44.

The detection means 51, the reception means 52 and the control means 53 together form a control module of the valve 44 integrated in the control unit 50. This control module corresponds for example to a computer program executed by the control unit 50, to an electronic circuit of the control unit 50 (for example of the type programmable logic circuit) or a combination of an electronic circuit and a computer program.

Here is meant by transient phase of acceleration of the turbojet engine 10, a regime transition linked to an acceleration phase of the turbojet engine 10 occurring between two stabilized speeds thereof. The transient acceleration phase that is to be detected by means of the detection means 51 may, for example, correspond to a transition between the ground idling speed and the stabilized flight regime, that is, ie the acceleration phase between these two regimes. In another example, the transient phase of acceleration can correspond to the acceleration phase between any intermediate regime (ex: mid gas) and the flight regime.

The possible detection of a transient phase of acceleration of the turbojet engine 10 can be made from one or more parameters representative of the turbojet engine 10.

A representative parameter of the turbojet engine 10 is, for example, its rotational speed. The detection of a transient acceleration phase of the turbojet engine 10 is then performed from a continuous determination of its speed. The detection of the speed variation of the turbojet engine 10 by the detection means 51 then makes it possible to identify a transient acceleration phase of the turbojet engine 10 over a predefined period, for example chosen between 1 second and 5 minutes. During this predetermined time interval, the detection means 51 can identify a transient phase of acceleration by observing the variations of speed of the turbojet engine 10. These variations are then compared to a reference characterizing a variation in the speed of the turbojet engine 10. Thus, if during the predetermined interval the variation of the rotational speed of the turbojet engine 10 is greater than or equal to a variation threshold characterizing a transient acceleration phase of the turbojet engine 10, the detection means 51 detect a transient phase of acceleration.

In other examples, the determination of the speed of the turbojet engine 10, as well as the detection of a transient phase turbojet engine acceleration can be performed from any representative parameter (s) of the engine.

By way of example, the determination of the rotational speed of the turbojet engine 10 as well as the detection of a transient phase of acceleration thereof can be carried out from one or more of the following parameters: the speed of the turbine high pressure 24, the speed of the low-pressure turbine 26, the angular position of the throttle control lever of the aircraft, a measured or calculated temperature of the combustion gases at the outlet of the combustion chamber 22.

In parallel, the receiving means 52 receive at least one data representative of the temperature of the combustion gases at the outlet of the combustion chamber 22 of the turbojet engine 10. The representative data of the combustion gases is, by way of example, a temperature measurement. performed somewhere between the outlet of the combustion chamber 22 of the turbojet and the nozzle of the aircraft, for example at any point of the high-pressure turbine 24 or the low-pressure turbine 26. The receiving means 52 then obtain known, directly from the representative data or indirectly by calculation from it, the temperature of the combustion gases. By way of example, the data representative of the temperature of the gases at the outlet of the combustion chamber 22 is a temperature measurement made at the high-pressure turbine 24, that is to say, produced in or out of the the latter, allowing the receiving means 52 to access the temperature of the gases at the outlet of the combustion chamber 22.

The configuration of the control means 53 is a function of the type of valve 44 implemented as will be described in FIGS. 3 and 4. These figures respectively illustrate the method of piloting the valve 44, respectively of the all-or-nothing type, and in a regulated position.

Steps 301, 401 and 302, 402 are similar in these figures. These steps correspond to a detection step 301, 401 of the speed variation of the turbojet engine 10 by the detection means 51, and to a reception step 302, 402 of at least one data item representative of the temperature of the gases leaving the engine. combustion chamber 22 of the engine by the receiving means 52. It is understood that the order of the steps illustrated in these figures is given for illustrative purposes, these steps being able in a non-illustrated example to be carried out in parallel.

The control unit 50 is configured to identify from the detection means 51 and the reception means 52 the possible occurrence of a situation for which:

a transient phase of acceleration of the turbojet engine 10 is detected, and

the temperature of the combustion gases at the outlet of the combustion chamber (22) of the engine (10) is greater than a first temperature threshold T1.

The first temperature threshold T1 is previously chosen to be lower than the EGT Red Line which characterizes the operating limit temperature of the turbojet engine 10, so as to maintain an EGT margin (difference between the Red Line EGT and the gas temperature of the engine). combustion) positive if the temperature of the combustion gases of the turbojet engine 10 reaches the temperature threshold T1. The temperature threshold T1 is, by way of example, defined to be 1 to 10 ° C. lower than the Red Line EGT. This temperature threshold T1 thus constitutes a protection threshold for the Red Line EGT, the achievement of this threshold in parallel with a detection of a transient phase of acceleration of the turbojet engine 10 thus reflecting an Overshoot situation for an aged engine or with degraded performance.

Moreover, the temperature threshold T1 is chosen with respect to the state of health of the turbojet engine 10, the temperature value T1 being supposed to be reached by the combustion gases only for an aged engine, for example having a clearance 38 degraded. Indeed, as explained above, the older an engine, the higher the temperature of its combustion gases increases and tends to approach the Red Line EGT. Conversely, a new turbojet or outgoing maintenance does not present a risk of seeing the temperature of the gas at the outlet of its combustion chamber to approach the temperature T1, let alone the Red Line EGT. The identification by the control unit 50 of a situation for which a transient phase of acceleration of the turbojet engine 10 is detected and for which the temperature of the combustion gases is higher than the temperature threshold T1 can not occur only for an aged engine and / or with degraded performance.

After each step 301, 302, 401, 402 the control unit 50 attempts to detect (steps 303, 403) the possible occurrence of the aforementioned situation. The step 303 may be, for example, carried out by the control means 53 or by other dedicated detection means.

If the occurrence of such a situation is not identified, the control unit 50 deduces the non-occurrence of an Overshoot in temperature of the combustion gases at the outlet of the combustion chamber 22 which could bring it closer to the Red Line EGT. Steps 301, 302, 401, 402 are then performed again.

Conversely, if the aforementioned situation is detected, the control unit 50 deduces a situation of Overshoot temperature flue gas potentially at risk of approaching the Red Line EGT. The control unit 50 then seeks to minimize Overshoot by optimizing the clearance 38 of the high pressure turbine 24. In fact, in the absence of optimization of the game 38, an Overshoot situation for an aged or degraded engine could reduce its EGT margin and therefore its life before being placed in maintenance. The optimization of the game 38 then aims to maintain a positive margin EGT as long as possible.

When the valve 44 is of all-or-nothing type (Figure 3) the control means 53 are then configured to control an opening (step 304) of the valve 44 so as to deliver a flow of air to the ring of turbine 34 and thus reduce the clearance 38 of the high-pressure turbine 24. The reduction of the clearance 38 optimizes the performance of the high-pressure turbine 24, resulting in a decrease in the temperature of the combustion gases at the outlet of the combustion chamber 22. The temperature of the combustion gases is then periodically compared (step 305) with a second temperature threshold T2 chosen as equal to or lower than the first temperature threshold T1 to avoid the effects of bagotement. As long as the temperature of the combustion gases remains higher than the second temperature threshold T2, the valve 44 is kept open. When the temperature of the combustion gases is detected as lower than the second temperature threshold T2, the control means 53 control (step 306) the closure of the valve 44. When the valve 44 is in a controlled position, the control means 53 are configured to control (step 404) the percentage of opening of the valve 44 as a function of the difference between the current temperature of the combustion gases and the first threshold of In other words, the opening of the valve 44 is carried out progressively according to a prerecorded control law in the control means 53, this law taking into account the difference between the temperature of the gases. the combustion means at the outlet of the combustion chamber 22 and the first temperature threshold T1. The control means 53 are, by way of example, configured to control a greater percentage of opening of the valve 44 (resulting from an overconsign). , and therefore an increase in the flow of air delivered to the turbine ring 34, if the temperature of the combustion gases temporarily exceeds the first temperature threshold T1. Thus, the clearance 38 of the high-pressure turbine 24 is not yet optimized, resulting in a reduction of the combustion gases and therefore the Overshoot. In other words, when the temperature threshold T1 is reached, a clearance overkill inducing an additional valve opening (up to 200%) with respect to an open valve position (at 100%) is triggered.

Thus, the control of a valve 44 of all-or-nothing type or controlled position as described above allows to maintain a positive EGT margin by decreasing the temperature of the combustion gases.

The embodiments described above have the following advantages. The control of the clearance 38 of the high-pressure turbine 24 during an acceleration phase of the engine 10 takes into account the residual margin existing between the Red Line EGT and the temperature of the combustion gases at the outlet of the combustion chamber 22. This margin is made possible by comparing the temperature of the combustion gases with the first temperature threshold T1, chosen with respect to the Red Line EGT as the protection threshold.

As explained in the introductory part, as the high-pressure turbine 24 ages, the maximum temperature of the combustion gases tends to progressively approach the Red Line EGT. Taking into account the difference between the Red Line EGT and the temperature of the combustion gases, via the temperature Tl, therefore allows to take into account the aging of the engine of the turbojet engine 10. The crossing of the temperature T1 by the combustion gases notably reflects an aging or a degradation of the performance of the turbojet engine 10 requiring a reduction of its Overshoot in order to limit any risk of approaching the engine. Red Line EGT.

The setpoint of the clearance 38 of the high-pressure turbine 24 is then adjusted by the control means 53 as a function of the aging of the engine. The adaptation of this game set itself influences the variation of the temperature of the combustion gases of the combustion chamber 22 and reduces the Overshoot temperature of the turbojet engine 10.

Likewise, the number of triggering the over-setpoint giving rise to a greater percentage of opening of the valve can be counted and stored in the control unit in order to be operated later in maintenance to judge the state engine aging.

The clearance 38 of the high-pressure turbine 24 as well as the Overshoot are thus regulated in a closed loop and adaptively according to the aging of the engine and this throughout the life cycle of the turbojet engine 10. Typically the high pressure turbine 24 an aged engine has a larger clearance 38 compared to a new engine. The method described above thus makes it possible to minimize the clearance 38 of the high-pressure turbine 24 as a function of the aging of the turbojet engine 10, via a control of the valve 44, without the risk of damaging the vanes of the turbine. The performance of the turbojet engine 10 is optimized throughout its life cycle. The EGT margin is maintained in particular for as long as possible, extending the life of the turbojet engine 10 before a possible maintenance deposit.

Claims

1. A method of controlling a clearance (38) between, on the one hand, vertices (30a) of blades (30) of a rotor of a high-pressure turbine (24) of an engine (10) of a gas turbine aircraft and, secondly, a turbine ring (34) of a housing (32) surrounding said vanes (30) of the high pressure turbine (24), the method comprising the control of a valve (44) delivering a flow of air directed towards said turbine ring (34), said method being characterized in that it comprises the following steps:

a detection (301, 401) of a transient acceleration phase of the motor (10) from at least one representative parameter of the motor (10);

a reception (302, 402) of data representative of the temperature of the gases leaving the combustion chamber (22) of the engine (10);

a command (304, 404) for opening the valve (44), for delivering said air flow to the turbine ring (34) or for increasing the flow rate of said delivered air flow, if the transitional phase of acceleration is detected and if the temperature of the gases at the outlet of the combustion chamber (22) of the engine (10) is greater than a first temperature threshold (T1) corresponding to a deteriorated play characteristic of an aged engine, the first temperature threshold (T1) being lower than an operating limit temperature of the engine (10).

2. The driving method according to claim 1, wherein a greater percentage of opening of the valve (44) is controlled if the temperature of the combustion gases temporarily exceeds the first temperature threshold T1.

3. Control method according to claim 1, wherein said at least one representative parameter of the engine (10) is the engine speed (10) and wherein the detection (301, 401) of a transient phase of acceleration of the motor (10) comprises a continuous determination of the speed of the motor (10) and a determination of a variation of the speed of the motor (10) for a predetermined time interval, the transient phase of acceleration of the motor (10) being detected during said interval of predetermined time if the variation of the engine speed (10) is greater than or equal to a variation threshold characterizing a transient phase of acceleration of the engine (10).

4. Control method according to any one of claims 1 to 3, wherein said at least one parameter representative of the engine is selected from: the speed of a low-pressure turbine engine (10), the speed of the high turbine pressure, the angular position of a throttle control lever of the aircraft and the data representative of the temperature of the gases at the outlet of the combustion chamber (22) of the engine (10).

The driving method according to any one of claims 1 to 4, wherein the valve (44) is an all-or-nothing type valve configured to switch between an open state or a closed state, the method further comprising , following the opening (304) of the valve (44), a control (306) closing the valve (44) when the temperature of the gases at the outlet of the combustion chamber (22) of the engine (10) is less than a second temperature threshold (T2), the second temperature threshold (T2) being lower than the first temperature threshold (T1).

6. A method according to any one of claims 1 to 4, wherein the valve (44) is a controlled position valve, the method comprising a control (404) of progressive opening of the valve (44) as a function of a predefined control law taking into account a difference between the temperature of the gases at the outlet of the combustion chamber (22) of the engine (10) and the first temperature threshold (T1).

7. Method according to any one of claims 1 to 6, wherein the data representative of the temperature of the gases at the outlet of the combustion chamber (22) is a temperature measurement made at the high-pressure turbine (24). .

8. Control unit (50) for controlling a game (38) between, on the one hand, vertices (30a) of blades (30) of a rotor of a high turbine pressure (24) of a gas turbine engine engine (10) and, secondly, a turbine ring (34) of a housing (32) surrounding said blades (30) of the high pressure turbine (24), the control unit (50) comprising control means (53) for a valve (44), the valve (44) being configured to deliver a flow of air to said turbine ring (34). ), the control unit (50) being characterized in that it comprises:

detection means (51) configured to detect a transient acceleration phase of the motor (10) from at least one representative parameter of the motor (10);

- receiving means (52) configured to receive a data representative of the temperature of the gases at the outlet of the combustion chamber (22) of the engine (10);

the control means (53) being configured to control an opening of the valve (44) to deliver said flow of air to the turbine ring (34), or to control an increase in flow rate of said delivered airflow , if the transient phase of acceleration is detected and if the temperature of the gases at the outlet of the combustion chamber (22) of the engine (10) is greater than a first temperature threshold (T1) corresponding to a characteristic gradient play of an aged engine, the first temperature threshold (T1) being lower than an operating limit temperature of the engine (10).

A control unit according to claim 8, wherein the control means (53) is further configured to control a greater percentage of valve opening (44) if the temperature of the combustion gases temporarily exceeds the first threshold temperature Tl.

10. Control unit according to claim 9, wherein, to judge the aging state of the motor, the control unit counts a trigger number of the additional opening control of the valve (44).

The control unit according to claim 8, wherein said at least one representative parameter of the motor (10) is the speed of the motor (10) and wherein the detection means (51) is configured to:

- continuously determine the engine speed (10);

- determining a variation of the engine speed (10) for a predetermined time interval;

- detecting the transient acceleration phase of the motor (10) during said predetermined time interval if the variation of the engine speed (10) is greater than or equal to a variation threshold characterizing a transient motor acceleration phase (10) .

A control unit according to any one of claims 8 to 11, wherein the valve (44) is an all-or-nothing type valve configured to switch between an open state or a closed state, the control means ( 53) being configured to control, following the opening of the valve (44), a closing of the valve (44) when the temperature of the gases at the outlet of the combustion chamber (22) of the engine (10) is less than a second temperature threshold (T2), the second temperature threshold (T2) being lower than the first temperature threshold.

Control unit according to any one of claims 8 to 11, wherein the valve (44) is a regulating valve, the control means (53) being configured to control a progressive opening of the valve (44). according to a predefined control law taking into account a difference between the temperature of the gases at the outlet of the combustion chamber (22) of the engine (10) and the first temperature threshold (Tl).

A gas turbine engine engine (10) comprising a control unit (50) according to any one of claims 8 to 13 and at least one valve (44) for acting on a flow of air directed towards the turbine ring (34) and wherein the valve (44) is controlled by the control means (53).