The present invention relates to the field of systems for actuating turbomachine elements by means of jacks. The invention relates more particularly to the monitoring of such actuation systems.

STATE OF THE ART

A turbomachine conventionally comprises modules having moving elements such as nozzles or blades. These elements must be able to move on command and their movement is controlled by means of one or more actuators. These mobile elements form the kinematics of the module considered and are conventionally actuated by jacks. For reasons of safety and redundancy, two position measurements are carried out as standard on the cylinder(s) by means of a system indicating a position feedback.

For cost reasons, it is not possible to provide each jack with such a position feedback system. Thus, if there is a number greater than two jacks, only two jacks, called master jacks, are conventionally provided with such position feedback.

Such position feedback is in fact a measured position of the jacks in response to a position instruction applied to the jacks. Indeed, the cylinder position makes it possible to know the degree of movement of the kinematics of the module, for example the position of the nozzle or the degree of pivoting of a blade.

In known manner, the two cylinders must have the same position feedback in response to the same instruction. If there is a difference between the measured positions of the two cylinders, there is a problem of "measurement difference between cylinders" which is due to wear of the actuation system which can cause breakdowns. Multiple cases of repeated “measurement deviations between actuators” maintenance messages have been observed on actuation systems with significant cumulative operating times. These “measurement differences between cylinders” are linked to significant wear of the kinematics of the actuation system which generates a position shift between the two cylinders equipped with position feedback but which are not necessarily characteristic of a failure.

This resurgence of breakdowns (real or not) leads to repairs under the wing (repair directly on the aircraft without having to remove the actuation system) and in the workshop. These repairs are very costly in terms of personnel and time (fault finding, exchange of cylinders).

To avoid these maintenance operations and extend the service life under the wing before removal, there is a need to improve the detection of measurement deviations between cylinders, failing which this may lead to an increase in the number of measurement deviations observed between jacks as the actuation systems age. This increase in deviation messages reduces engine availability and increases the cost associated with maintenance operations.

There is therefore a need to improve the detection of “measurement difference between cylinders” by taking account of the specificity due to normal wear of the actuation system.

DISCLOSURE OF THE INVENTION

An object of the invention is to provide a surveillance system which does not have the drawbacks of the prior art.

As such, it is proposed, according to a first aspect, a method for monitoring a system for actuating a moving element, in particular a moving element of a turbomachine such as a nozzle or a blade, said system of actuation comprising a control device configured to deliver a position setpoint to a first jack and a second jack, each jack being configured to deliver a position feedback measurement in response to said position setpoint, the method being implemented in a monitoring system and comprising,

- A first monitoring mode according to which deviations between the position feedback measurements of the two cylinders are detected;

- A second monitoring mode according to which differences between the position feedback measurements of the two cylinders are not detected;

process in which the second mode is selected when at least one of the two position feedback measurements is in a transient phase.

The invention is advantageously completed by the following characteristics, taken alone or in any of their technically possible combination

the method comprises detection (T 1 , T2) of the transient phase of a position feedback measurement (12, 22) consisting in comparing (E3) a gradient of a measurement voltage with a threshold.

the measurement voltage is in transient phase if the gradient of the measurement voltage is greater than said threshold.

the detection of the transient phase comprises a step of confirmation of the transient phase consisting in detecting a transient phase of said measurement voltage for a predetermined duration, called the confirmation duration.

the predetermined duration is between 60 and 100 ms, typically 80 ms.

According to a second aspect, the invention relates to a system for monitoring an actuation system for a mobile element, in particular a mobile element of a turbomachine such as a nozzle or a blade, said actuation system comprising a control device configured to deliver a position setpoint to a first jack and a second jack, each jack being configured to deliver a position feedback measurement in response to said position setpoint, said monitoring system being configured to implement a method according to the first aspect of the invention.

According to a third aspect, the invention relates to an element of a turbine engine configured to be actuated by an actuation system monitored by means of a monitoring system according to the second aspect of the invention.

The advantages of the invention are multiple.

The detection of position feedback measurement differences between each cylinder makes it possible to detect the electrical drifts of the components of the position feedback acquisition chain.

In the case of kinematics controlled by two master actuators each equipped with a position feedback, the differences seen between the two actuators can be of electrical but also mechanical origin. Consequently, the transient phenomena of clearance or wear take-up introduce non-robustness in the deviation monitoring, deviations being wrongly detected.

DESCRIPTION OF FIGURES

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and which must be read in conjunction with the appended drawings in which:

- Figure 1 illustrates an implementation environment of the invention.

- Figure 2 is a flowchart of steps of a method according to one embodiment of the invention.

- Figure 3 illustrates problems solved by the invention.

- Figure 4 illustrates visible and invisible transients discriminated by the invention;

- Figure 5 is a flow chart of sub-steps of a method according to one embodiment of the invention.

In all the figures, similar elements bear identical references.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a system 10 for actuating an element of a turbine engine such as a nozzle or a blade which comprises a control device 1 configured to deliver a position setpoint CONS to a first cylinder 11 and to a second jack 21. The

first jack 11 and second jack 21 are notably so-called “master” jacks of an actuation system: they are each provided with a position feedback module 12, 22. The other jacks, if any , are not equipped with such a module.

The position setpoint CONS is converted into a setpoint voltage to control the jack 11, 21. Following the application of the position setpoint CONS to each jack, each jack 11, 21 moves in accordance with said setpoint CONS. In order to check that the cylinder

11, 21 has moved from the position setpoint, each cylinder 11, 21 is, as mentioned above; equipped with a position feedback module 12, 22 which measures the actual movement of the jack 11, 21 (hereafter position feedback measurement 12, 22). In the present case, position feedback measurement 12, 22 means a measured voltage proportional to the effective movement of the jack 11, 21. Those skilled in the art will also understand that another type of signal corresponding to the position feedback of the jack may be considered.

In order to verify the correct operation of the actuation system, the position feedback measurements 12, 22 from the position feedback modules are communicated to a monitoring system 20 which makes it possible in particular to evaluate the deviations of position feedback measurements

12, 22 of each actuator 11, 21. As such, the monitoring system 20 comprises a processing unit such as a processor to implement a monitoring method described below, in relation to Figure 2.

The monitoring system 20 takes as input each position feedback measurement 12, 22 from the position feedback modules.

Based on the position feedback measurements 12, 22, detection of a transient phase (steps T1, T2 respectively) of the position feedback measurement 12, 22 of each cylinder 11, 21 is implemented.

Such detection T1, T2 makes it possible to assess whether the position feedback measurement 12, 22 relating to each jack 11, 21 is in a transient phase, that is to say not stabilized and therefore unreliable, or whether it is in a stabilized phase considered reliable

Indeed, the Applicant has observed that the differences in position feedback measurements between cylinders 11, 21 increased when these measurements were in a transient phase. The phase during which the kinematics is in motion is called transient phase.

Figure 3 illustrates that the differences between measurements between the jacks 11, 21 increased during transient phases. In these figures we have represented:

- the variation of the position feedback measurement of the first actuator 11 (curve Mes1)

- the variation of the position feedback measurement of the second cylinder 21 (curve Mes2)

- the variation of the difference between the two measurements (curve |Mes2 - Mes1 |)

- A first detection threshold S0 and a second detection threshold S1.

Thus, it was found that even by increasing the detection threshold from S0 to S1 the difference between the two measurements was always above the threshold S1 for a significant period of time.

so that it was difficult to set a threshold and a duration of observation of the deviation (in order to ensure that the deviation was well above the threshold) which would allow both to have reliable monitoring (impacted by the definition of a high detection threshold) and which would not detect false failures.

Consequently, given this finding, the Applicant proposes not to monitor the position feedback measurement deviation during these transient phases since the monitoring in this case is not robust, i.e. it is unreliable.

Thus, depending on whether the position feedback measurements have a transient character or not, the monitoring method implemented by the monitoring system comprises two monitoring modes which can be selected (step SEL) accordingly. This defines: a first monitoring mode M1 during which deviations between the position feedback measurements of the two actuators 11, 21 are detected;

a second monitoring mode M2 ​​during which differences between the position feedback measurements of the two cylinders 11, 21 are not detected.

The second monitoring mode M2 ​​is selected (step SEL) as soon as at least one of the two position feedback measurements 12, 22 is in transient phase.

Thus, when one of the two position feedback measurements is in a transitional phase, select the first mode or the second monitoring mode.

When the first mode M1 is selected, the position feedback measurement deviation 12, 22 makes it possible to generate, if necessary, an alert relating to an abnormal measurement deviation which will trigger maintenance (ALE step). As such, a trigger threshold is fixed and depends on the parameters of the actuated system and its actuation system.

To compensate for the variability of the transient phases due to the aging of the engine, and/or to the mode of operation, and/or to the flight envelope, and/or to the types of maneuvers

(slow or fast accelerations/decelerations), and to have a fine management of the detection of the transient phase at the level of the jacks 11, 21, the detection of the transient phase is made by means of a monitoring of a gradient of each measurements of positions 12, 22 and not at the level of a transient phase of the engine itself (change in speed/temperature/overall pressure of the engine and not just of the module considered). Indeed, there are certain transitory phases visible at the level of the jacks 11, 21 and not at the level of the motor as shown in FIG. 4. Thus, advantageously, the transient nature of each position feedback measurement 12, 22 is evaluated considering the gradient of each measurement. Of course, other possibilities for obtaining the transitional nature of the measures could be implemented.

The detection of the transient character (steps T1, T2) comprises the following steps described in relation to FIG. 5.

The gradient of the position feedback measurement, for a given actuator 11, 21, is obtained as follows (step E1):

gradient, = measure, - measure M ,

with i and i-1 the instant of taking the measurement. Thus the gradient calculated at time i is the difference between two consecutive measurements.

The detection of the transient phase is therefore developed on the position feedback measurement 12, 22 (image of the actual position of the jacks 11, 21) rather than on the setpoint of

CONS positioning of the cylinders 11, 21. Indeed, the CONS setpoint is not

representative at any time of the actual behavior of the actuators 11, 21, in particular at the end of the transient phase where the setpoint CONS is stabilized but where the actuators 11, 21 complete their movement. This has the disadvantage of having a position feedback measurement 12, 22 electrically noisy and having variations due to the forces applied to the jacks 11, 21. The gradient produced on such a measurement is therefore all the more noisy, thus imposing to perform transient phase detection on a filtered 12, 22 position feedback measurement.

The gradient calculated at time i is then filtered as follows (step E2):

Filtered_gradienti = filtered_gradient-i + CTE. (gradient, - gradient_filteredi-i).

The filtering takes into account two values ​​of the gradient calculated consecutively.

The constant CTE of the filter is fixed taking into account the following elements:

- a significant time constant makes it possible to filter the majority of the electrical and mechanical disturbances but significantly delays the detection of the gradient and greatly attenuates levels of transient phase(s) variations;

- a low time constant makes it possible to quickly detect a transient phase but favors false detections of transient phase(s) as soon as they reach levels close to the threshold (which can be quite low depending on the dynamics of the kinematics at points where the hydromechanical power is low).

The value of the filtered gradient at time i is then compared with a threshold (step E3). In particular, to indicate a transient nature of the position return measurement 12, 22 of the jack 11, 21 considered, this value of the filtered gradient at instant i must be greater than a predetermined threshold.

In order not to deactivate monitoring too soon, this transient character must be confirmed, during a confirmation step (step E4).

To do this, the filtered gradient must be greater than a certain threshold for a duration fixed in advance, called the confirmation duration. Such a duration is typically between 60 and 100 ms, preferably 80 ms. The confirmation duration must be long enough to provide robustness without being too high so as not to cause too much delay in deactivating deviation monitoring. As such, the confirmation duration will be a function of the duration of the shortest transient phase existing on the kinematics. The confirmation time is therefore fixed empirically.

If the transient nature of the position feedback measurement of the cylinder 11, 21 considered is confirmed, monitoring of the measurement difference between cylinders 11, 21 is deactivated.

A monitoring mode selection is implemented, the second monitoring mode

monitoring M2 is selected. If this is not the case, the first monitoring mode M1 is selected.

Confirmation time is advantageous for two reasons:

- the filtering of the gradient introduces a delay in the detection of the transient character and an attenuation of the amplitude of the value, which leads to providing a lowering of the detection threshold with respect to detection on non-filtered values.

- lowering the detection threshold can lead to untimely detection of transient phases and thus deactivate monitoring when this is not justified.

The invention described above advantageously presents a self-supporting transient phase detection with respect to the cylinders 11, 21 of the module considered: it depends only on parameters intrinsic to the cylinders 11, 21, not basing itself on the engine state (regime steady state, transient state, etc.), nor on the setpoint CONS applied to the jacks 11, 21. Consequently, the monitoring system 20 is made independent of any mode of failure (starting from an electrical drift measurement) and of any engine-to-engine variability. Furthermore, the present invention proposes means of overcoming the defects linked to the use of raw measurements by introducing a filtering of the position feedback measurements 12, 22 and a confirmation of the start and end of the transient phase. Finally,

CLAIMS

1. Method for monitoring an actuation system (10) of a moving element, in particular a moving element of a turbomachine such as a nozzle or a blade, said actuation system (10) comprising a device for control (1) configured to deliver a position setpoint (CONS) to a first jack (11) and a second jack (21), each jack (11, 21) being configured to deliver a position feedback measurement (12, 22) in response to said position instruction (CONS), the method being implemented in a monitoring system (20) and comprising,

- a first monitoring mode (M1) according to which differences between the position feedback measurements (12, 22) of the two cylinders (11, 21) are detected;

- A second monitoring mode (M2) according to which differences between the position feedback measurements (12, 22) of the two cylinders (11, 21) are not detected;

process in which the second mode (M2) is selected as soon as at least one of the two position feedback measurements (12, 22) is in a transient phase.

2. Method according to claim 1, comprising detection (T1, T2) of the transient phase of a position feedback measurement (12, 22) consisting in comparing (E3) a gradient of a measurement voltage with a threshold.

3. Method according to the preceding claim, in which the measurement voltage is in transient phase if the gradient of the measurement voltage is greater than said threshold.

4. Method according to one of claims 2 to 3, in which the detection of the transient phase comprises a step of confirming the transient phase consisting in detecting a transient phase of said measurement voltage for a predetermined duration, called the confirmation duration. .

5. Method according to the preceding claim, in which the predetermined duration is between 60 and 100 ms, typically 80 ms.

6. Monitoring system (20) of an actuation system (10) of a moving element, in particular a moving element of a turbomachine such as a nozzle or a blade, said actuation system (10) comprising a control device (1) configured to deliver a position instruction (CONS) to a first jack (11) and a second jack (12), each jack (11, 12) being configured (12, 22) to deliver a measurement return position in response to said position instruction, said monitoring system being configured to implement a method according to one of claims 1 to 5.

7. Element of a turbine engine configured to be actuated by an actuation system monitored by means of a monitoring system (20) according to the preceding claim.