Method for controlling a turbomachine valve

Abstract

The invention concerns a method for controlling a control valve (20) of a turbomachine operating at an engine speed at a cruise value (Vc) and oscillating around the cruise value (Vc) of same, the method being implemented by a calculation unit (40), and being characterised in that it comprises a step of determining a position control for the control valve (20), filtered of the oscillations of the engine speed around the cruise value (Vc).

Claims

1. A method implemented by a calculation unit, the method comprising: monitoring, by a monitoring valve that directs air flow from a flow path toward a casing disposed opposite blades in a turbine of a turbomachine, an air flow rate from the flow path; and receiving a value of an engine speed of the turbomachine at a cruise value, the value of the engine speed oscillating about the cruise value and determining, for the monitoring valve, a position command for the monitoring valve based on the engine speed; and controlling the monitoring valve based on the determined position command, wherein the position command is determined by: receiving data quantifying the engine speed of the turbomachine, determining a flow rate command from the data quantifying the engine speed, determining the position command from the flow rate command, and filtering, from the oscillations of the engine speed about the cruise value, the position command.

2. The method according to claim 1, wherein the filtering is carried out using a low-pass filter whose cutoff frequency is greater than a frequency associated with the thermal response time of the casing.

3. The method according to claim 2, wherein the low-pass filter is a first-order filter.

4. The method according to claim 2, wherein said monitoring valve is configured to supply air to an inside of the casing in order to modify an expansion of the casing.

5. The method according to claim 2, wherein the cutoff frequency is between 0.05 Hz and 0.15 Hz.

6. The method according to claim 2, comprising deactivating the filtering by: determining a gradient of the position command, comparing the gradient with a deactivation threshold, and deactivating the filter if the gradient is greater than the deactivation threshold.

7. The method according to claim 2, comprising activating the filtering by: determining a gradient of the position command, comparing the gradient with an activation threshold, activating the filter if the gradient is smaller than the activation threshold during at least one confirmation period.

8. The method according to claim 7, wherein the filtering is activated if the gradient is smaller than the activation threshold and if each of the engine speed, an altitude, and a Mach are at respective corresponding values.

9. The method according to claim 2, wherein filtering the position command comprises filtering the data quantifying the engine speed.

10. The method according to claim 1, wherein the filtering is carried out using a low-pass filter whose cutoff frequency is less than a frequency of the engine speed oscillations about the cruise value.

11. A system comprising: a monitoring valve; a filtration block; and a calculation unit that is configured to execute the following operations: monitoring, by the monitoring valve that directs air flow from a flow path toward a casing disposed opposite blades in a turbine of a turbomachine, an air flow rate from the flow path; and receiving a value of an engine speed of the turbomachine at a cruise value, the value of the engine speed oscillating about the cruise value and determining, for the monitoring valve, a position command for the monitoring valve based on the engine speed; and controlling the monitoring valve based on the determined position command, wherein the position command is determined by: receiving data quantifying the engine speed of the turbomachine, determining a flow rate command from the data quantifying the engine speed, determining the position command from the flow rate command, and filtering, by the filtering block from the oscillations of the engine speed about the cruise value, the position command.

12. A turbomachine comprising the system according to claim 11.

Description

PRESENTATION OF THE FIGURES

(1) Other characteristics, objects and advantages of the invention will become apparent from the following description which is purely illustrative and non-restrictive and which should be read with reference to the appended drawings, in which:

(2) FIG. 1a illustrates the overall architecture of a turbomachine,

(3) FIG. 1b illustrates the overall architecture of the elements for monitoring the flow rate taken from the secondary flow path and sent to the casing opposite the turbine blades according to the state of the art,

(4) FIG. 2 illustrates in steps a mode of implementation of the invention,

(5) FIG. 3 illustrates the architecture in block diagram of a method for activating or deactivating the filter, complementary to the mode of implementation of FIG. 2,

(6) FIGS. 4 and 5 illustrate in steps other modes of implementation of the invention.

DETAILED DESCRIPTION

(7) Several modes of implementation will now be described.

(8) First Mode of Implementation

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

(10) The advantage of such a filtering at the end of the method is that it is easily implementable on the software of the apparatuses in service and that it does not affect the integrity of the already existing code: its integration in an on board software is thus simplified.

(11) In a preferred mode, the filtering is carried out with a first-order low-pass filter having a unique cut-off frequency fc.

(12) 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.

(13) It is technically possible to put a second-order filter or higher but in order to limit the impact in terms of calculation time, preference will be given to the simplest filters.

(14) The determination of the cut-off frequency fc is an important condition for obtaining an effective filtering that does not slow down the control method in a redhibitory manner.

(15) The response time of the filter was chosen by a compromise between two constraints. Indeed, this response time must be high enough to remove a maximum of oscillations without slowing down the system in unacceptable proportions from a point of view of the thermal response of the casing. Indeed, a too low frequency would filter the nominal value of the command and the monitoring valve 20 would remain almost immobile.

(16) Engine tests allow defining the thermal response of the casing and obtaining a characteristic response time (and its associated frequency). Insofar as the thermal response of the casing is generally different at different points, the most restrictive case is chosen to delimit the minimum response time (that is to say the maximum frequency at which the cutoff frequency must remain lower). Insofar as a frequency fr associated with the most restrictive response time of the casing 16 (that is to say the lowest response time among the measurements made on the casing 16) is generally much smaller than the frequency fo of the oscillations, it can be ensured that the cutoff frequency fc is greater than the frequency fr associated with the response time of the casing 16 without introducing too much constraints on the frequency fc.

(17) These conditions on the cutoff frequency guarantee the performances of the system.

(18) The frequency fo of the micro-oscillations has also been 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.

(19) For example, depending on the frequency fo, a cut-off frequency fc of between 0.05 and 0.15 Hz, or even 0.08 and 0.12 Hz or more broadly between 0.01 and 0.20 Hz, is chosen. For the record, the frequency fo is of about 1 Hz, which is quite far from the previous upper limits to ensure efficient filtering. For cutoff frequencies fc in the latter interval, it is ensured to have response times lower than those of the casing 16.

(20) Nevertheless, the addition of the filter slows down a bit the system and should be preferably applied only in relevant flight phases. In this case, it is desired to apply this filtering only in cruise flight condition, that is to say when the engine speed is in steady state (speed at which the oscillations at the frequency fo are observed).

(21) A condition for the application of the filter is primarily related to the cruise speed. For this, three indicators are verified: The engine speed, The Mach (that is to say the ratio of the local speed in a fluid on the speed of sound in this same fluid), The altitude.

(22) Several values related to these indicators are predetermined to characterize a cruise phase. If the cruise phase is confirmed, then the filtering step can be activated.

(23) In addition, when the system requires a rapid reaction of the monitoring valve 20, it is desired that the command is not slowed down by a filter (for example an action of the pilot, during takeoff or landing or for example upon a sudden change of environment).

(24) Preferably, the method complementarily comprises a sub-method for deactivating the filter. FIG. 3 represents a block diagram indicating the different steps of this sub-method.

(25) 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 command resulting from step E3, is determined. It is therefore not the filtered command. For this, several cascade delay blocks can be used (the number of three is related to the internal logic of the calculation unit 40, for which the iteration rate is of 0.240 s, namely 0.720 s for the three iterations).

(26) In a step E52, this gradient is compared with a deactivation threshold value Sg. More precisely, in order to overcome the questions of signs, the absolute value of this gradient is compared with the deactivation threshold value Sg.

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

(28) By way of example, a threshold value is chosen which is comprised between 0.5 and 2.5% per second, that is to say, at one second intervals, the command varies between 0.5 and 2.5% from its original value. In the diagram, the threshold value is of 1% for 0.72 second, namely 1.4% per second. An interval of 1 and 2% per second may also be suitable.

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

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

(31) The reactivation (or activation) of the filtering step is also carried out under condition using another sub-method, also represented in FIG. 3.

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

(33) 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 is made more selectively, it is possible to set the threshold value Sg′ lower than the threshold value Sg. In FIG. 3, Sg=Sg′.

(34) In a step E63, the filtering step Ef is activated if the gradient remains smaller than the threshold Sg′ during a set confirmation period T. The confirmation period T is comprised between two and eight seconds (T=5 s in FIG. 3), or even 4 and 6 seconds.

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

(36) Step E63 is misrepresented in FIG. 3, since the drawn block outputs an activation condition, which is then preferably combined with the other activation conditions to effectively activate the filter.

(37) 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-set.

(38) Thus, it is ensured that the system is stable and that the engine is in cruise speed before reactivating the filtering step Ef and suppressing the oscillations.

(39) Second Mode of Implementation

(40) In a second mode of implementation represented in FIG. 4, the filtering step Ef is applied to the engine speed data resulting from step E1, so that a filtered position command is again obtained as output. The step of determining a flow rate command E2 is then carried out from the filtered data relating to the engine speed.

(41) Such filtering at the beginning of the method for calculating the position command allows avoiding the processing of data with noise.

(42) In such a mode of implementation, the filtering is preferably integrated in fact in step E2 of determining a flow rate command.

(43) Embodiments with activation and deactivation thresholds may also be implemented.

(44) Third Mode of Implementation

(45) It is also conceivable to apply the filtering step to the flow rate command resulting from step E2. The step of determining the position command E3 is then carried out from one filtered flow rate command data. This embodiment is illustrated in FIG. 5.

(46) Embodiments with activation and deactivation thresholds may also be implemented.