Patent Publication Number: US-10760439-B2

Title: Method of testing the integrity of a fluid flow regulator system for a turbine engine

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to the field of detecting failures of mechanical elements in a fluid flow regulator system for a fluid-passing duct in a turbine engine. More precisely, the invention relates to a method of testing integrity in a fluid flow regulator system for a turbine engine. 
     A particular application of such a fluid flow regulator system, when the fluid is air bled from an air passage in the turbine engine, relates to managing the radial clearance between a rotor and a stator of a turbine in the turbine engine, e.g. between rotor blades and a stator ring surrounding the blades. This management is particularly important for controlling the performance of the turbine engine, in particular for controlling its efficiency and its maximum thrust. In order to control this radial clearance, it is known to make use of a circuit for cooling the stator by bleeding air from the flow passage for the secondary stream through a bypass turbine engine. Advantageously, the rate at which air is bled from the air stream is regulated and, by cooling the stator, it serves to control expansion of the stator, and thus to control its radial clearance relative to the rotor. 
     For a bypass turbine engine, a first known method consists in using a scoop to act passively to bleed off a portion of the air stream in the flow passage for the secondary stream, and then to regulate the flow rate of the air stream that has been bled off by means of a flow regulator valve inserted in the air bleed circuit. By way of example, one such solution is described in Document FR 2 614 073. The main drawback of that solution lies in the fact that installing an open scoop in the flow passage for the secondary stream gives rise to large head losses. 
     In order to mitigate that problem, and thereby improve the performance of the turbine engine, it is known to form a scoop in a services-passing arm that extends across the flow passage of the secondary stream, with the scoop then bleeding off an air stream actively from the flow passage for the secondary stream. Under such circumstances, the scoop is active in the sense that it is associated with a flap that is pivotable between an open position and a closed position, thereby enabling the flow rate of air that enters the scoop to be regulated as a function of the position of the flap. By way of example, one such solution is described in Document FR 3 025 843. 
     The movable flap of that scoop is commonly opened using an actuation force that results from moving a drive rod of an actuator. The actuation force is transmitted to the movable flap via a push-pull cable, thereby serving to control movement of the movable flap. The actuation rod is moved when the actuator is powered, the power supply to the actuator being controlled by an electronic computer. In the event of the computer detecting a problem, it can then cause the power supply to the actuator to be stopped, thereby stopping any opening of the movable flap of the scoop. 
     Furthermore, the scoop includes safety return means in the form of a spring serving, in the absence of any actuation force being transmitted by the cable to the movable flap, to bring the movable flap into its closed position, which position corresponds to a safe position for the movable flap of the scoop, commonly referred to as its “fail-safe” position. 
     For reasons of accessibility, in particular concerning temperature, the electronic computer uses closed loop regulation only for the movement of the drive rod of the electrical actuator. Such regulation is performed on the basis of measurements delivered by a position sensor that measures the successive positions of the drive rod of the actuator. The opening of the movable flap of the scoop is then correlated by the electronic computer as a function of the position of the drive rod of the actuator. 
     A major drawback involved in implementing such a solution then occurs whenever there is a break in the safety return spring or in the cable making the connection between the drive rod of the actuator and the movable flap. If it is the spring that breaks, it is no longer possible to ensure that the movable flap of the scoop will take up its fail-safe position in the event of a failure of the power supply to the actuator. If it is the cable that breaks, the actuator can no longer transmit its actuation force to the movable flap and thereby open it. 
     In the above-mentioned situations, the drive rod of the actuator nevertheless continues to be movable and its movement continues to be measurable by the position sensor. Since the physical states of the cable and of the safety spring are not supervised by the electronic computer, it can therefore not detect that the spring or the push-pull cable has broken, and consequently it will assume that the operation of the air flow regulator system is nominal, even when that is not so. 
     Such situations are therefore dormant. In addition, their impact cannot be observed in the short term on the engine itself. Specifically, it is then difficult to observe degraded performance or wear in mechanical parts. Consequently, breakage of the spring or of the push-pull cable can remain dormant during a large number of cycles and, in the longer term, can lead to irreversible degradation of the engine, e.g. excessive wear of abradable surfaces or a reduction in the lifetime of the casing of the low-pressure turbine. 
     An analysis of failure trees in order to identify the cause of such degradations cannot allow the presence of dormant contributors, particularly if such failures may occur at a potentially large rate. Specifically, the persistence of dormancy for the above-mentioned failures greatly limits the viability of air flow regulator systems that make use of scoops of that type. 
     OBJECT AND SUMMARY OF THE INVENTION 
     An object of the present invention is to remedy the above-mentioned drawbacks. More precisely, the present invention seeks to propose a solution that makes it possible in general manner to detect failures due to a broken push-pull cable or to an inability of the safety return means of a fluid flow regulator system that includes a fluid flow duct associated with a movable flap. 
     To this end, the invention provides a method of testing the integrity of a fluid flow regulator system for a turbine engine, the system comprising:
         a fluid-passing duct associated with a movable flap for shutting the duct and suitable for pivoting about an axis between a closed position and an open position;   an actuator having a movable drive element, said drive element being suitable for delivering a movement force between a first position corresponding to the closed position of the movable flap and a second position corresponding to the open position of the movable flap;   a push-pull cable interconnecting the drive element of the actuator and the movable flap, and suitable for transmitting a movement force to the movable flap; and   safety return means exerting a return force suitable for moving the movable flap towards the closed position in the absence of force being transmitted by the cable to the movable flap;       

     said method of testing the integrity of the system comprising in succession:
         a step of supplying power to the actuator in order to place the drive element in the second position;   a step of interrupting the supply of power to the actuator; and   a step of measuring the position of the drive element.       

     Advantageously, as a function of the result of the measurement step, it is possible to determine whether or not there is a problem of integrity in the air flow regulator system. Furthermore, the method is applicable to any system for regulating airflow in a turbine engine and presenting the above-described architecture. The performance of such a method can be executed in a predetermined number of cycles, making it possible to detect any potential dormant fault due to breakage of the safety spring or of the push-pull cable. Consequently, this makes it possible to take appropriate action, e.g. accommodating to any detected failures in order to prevent degradation of the turbine engine. This serves to lengthen the lifetime of the engine. 
     In an aspect, the method comprises:
         comparing the measured position of the drive element with said second position in order to identify a movement of the drive element; and   detecting an inability of the safety return means or breakage of the push-pull cable when the measured position of the drive element corresponds to said second position.       

     In another aspect, after deducing the inability of the safety return means or the breakage of the push-pull cable, the method comprises supplying power to the actuator in order to place the drive element in said first position. 
     In another aspect, the method comprises:
         comparing the measured position of the drive element with said second position; and   deducing integrity of the regulator system when the measured position differs from said second position.       

     In another aspect, after deducing integrity of the regulator system, the method comprises:
         comparing the measured position of the actuator element with said first position; and   when the position of the drive element differs from said first position:
           redefining the first position by allocating the measured position of the drive element to the first position; and   as a function of the redefined first position, reconfiguring a pre-stored control relationship relating to the movement of the drive element.   
               

     The invention also provides a fluid flow regulator system for a turbine engine, the system comprising:
         a fluid-passing duct associated with a movable flap for shutting the duct and suitable for pivoting about an axis between a closed position and an open position;   an actuator having a movable drive element, said drive element being suitable for delivering a movement force between a first position corresponding to the closed position of the movable flap and a second position corresponding to the open position of the movable flap;   an electronic computer suitable for:
           supplying power to the actuator so as to cause its drive element to be moved; and   estimating the movement of the drive element from measurements returned by at least one position sensor measuring the position of that element;   
           a push-pull cable interconnecting the drive element of the actuator and the movable flap and suitable for transmitting a movement force to the movable flap; and   safety return means exerting a return force suitable for moving the movable flap towards the closed position in the absence of force being transmitted by the cable to the movable flap;       

     the computer being configured to proceed with a test of the integrity of the system by causing the following in succession:
         power to be supplied to the actuator to place the drive element in the second position;   interrupting the power supply to the actuator; and   measuring the position of the drive element.       

     In an aspect of the system, the electronic computer is configured:
         to compare the measurement of the position of the drive element with said second position in order to identify a movement of the drive element; and   to detect an inability of the safety return means or a breakage of the push-pull cable when the measured position of the drive element corresponds to said second position.       

     In another aspect of the system, after deducing the inability of the safety return means or the breakage of the push-pull cable, the electronic computer is configured to supply power to the actuator so as to place the drive element in said first position. 
     In another aspect of the system, the electronic computer is configured:
         to compare the measured position of the drive element with said second position; and   to deduce the integrity of the regulator system when the measured position differs from said second position.       

     In another aspect of the system, the computer is configured;
         after deducing integrity of the regulator system, to compare the measured position of the actuator element with said first position; and   when the position of the drive element differs from said first position:
           to redefine the first position by allocating the measured position of the drive element to the first position; and   as a function of the redefined first position, to reconfigure a pre-stored control relationship relating to the movement of the drive element.   
               

     In another aspect, the regulator system comprises:
         an air bleed scoop constituting said fluid-passing duct; and   a mechanical spring constituting said safety return means and potentially suffering a break leading to its inability to produce said return force exerted on the movable flap.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention appear from the following description of particular implementations of the invention, given as non-limiting examples, and with reference to the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic longitudinal section view of a turbine engine including an embodiment of an air flow regulator system; 
         FIG. 2  is a perspective view of a services-passing arm associated with an embodiment of the air flow regulator system; 
         FIG. 3  is a view from above of the services-passing arm associated with an embodiment of the air flow regulator system, the system presenting a movable flap in the closed position for a nominal situation; 
         FIG. 4  is a view from above of the services-passing arm associated with an embodiment of an air flow regulator system, the system presenting a movable flap in the open position for a nominal situation; 
         FIG. 5  is a view from above of the services-passing arm associated with an embodiment of an air flow regulator system, the system presenting a first failure situation; 
         FIG. 6  is a view from above of the services-passing arm associated with an embodiment of an air flow regulator system, the system presenting a second failure situation; and 
         FIG. 7  is a flow chart showing the various steps of testing the integrity of the air flow regulator system in various implementations. 
     
    
    
     DETAILED DESCRIPTION OF IMPLEMENTATIONS 
     The terms “upstream” and “downstream” are used below relative to the flow direction of gas through the turbine engine. 
       FIG. 1  shows a bypass turbine engine comprising in conventional manner from upstream to downstream in succession: at least one fan  2 ; an engine portion comprising in succession at least one low-pressure compressor stage  3  and at least one high-pressure compressor stage  4 ; a combustion chamber  5 ; at least one high-pressure turbine stage  6  and at least one low-pressure turbine stage  7 ; together with an exhaust nozzle  8  for the primary stream F 1 , i.e. the gas flowing in the primary passage. 
     Rotors, rotating about the main axis A of the turbine engine and potentially coupled together by various transmission and gearing systems, correspond to these various elements. 
     The air stream driven by the fans is split into a portion F 1  entering the primary circuit that corresponds to the engine proper and a secondary stream portion F 2  that contributes most of the thrust delivered by the turbine engine. 
     The secondary stream F 2  passes around the engine portion via a secondary passage  9 . 
     In general, a turbine engine has at least one system for passing services such as air ducts, oil ducts, electric cables, so as to enable them to cross a passage, such as the flow passage  9  for the secondary stream F 2 , while minimizing disturbances to the flow. The services serve to connect first equipment situated radially inside the passage with second equipment situated radially outside the passage  9 , where the term “radially” should be understood relative to the main axis A of the turbine engine. 
     A services-passing system as shown in the secondary passage  9  in  FIG. 1  generally comprises an annular body having two coaxial annular shrouds, respectively an inner shroud  10  and an outer shroud  11 . These two shrouds are connected together by arms  12  that are substantially radial and tubular and that include internal passages for passing services. The system may be mounted downstream from an intermediate casing of the turbine engine, with the shrouds  10  and  11  providing continuity for the walls of the passage  9  where the services-passing system passes through. 
     Generally, the arms  12  of the services-passing system are streamlined and aligned in the flow direction of the main air stream F 2  in the passage  9  so as to limit disturbances to that stream and reduce head losses. Radial stator vanes may be installed upstream, e.g. guide vanes. Under such circumstances, the arms of the services-passing system extend downstream from those vanes in order to avoid disturbing the flow passing between the vanes. 
     In this example, one of the arms  12  of the services-passing system also includes an opening  13  for bleeding off air and situated in the proximity of its leading edge  14 . 
     The inside of the arm  12  also contains the inlet of a duct  15  that forms a scoop for bleeding air from the secondary stream F 2  and connected to the opening  13 . The duct  15  passes inside the arm  12  and passes through the shroud  11  so as to take cold air bled from the secondary stream F 2  and convey it to cooling devices. Preferably, but not necessarily, the air bled off by the duct  15  is used by means  16  for cooling an outer casing  17  of the low-pressure turbine  7  in order to regulate the clearance between the casing  17  and the rotor blades of the turbine  7 . The duct  15  then extends in an inter-passage space, also referred to as the “core zone”, that lies between the primary flow passage and the secondary flow passage  9  and that contains equipment forming part of the engine. 
     In an example shown in  FIG. 2 , the services-passing arm  12  includes a main portion  12   a  for passing services and presenting a shape that is streamlined in a longitudinal direction X that is substantially parallel to the flow of the secondary stream F 2  in the vicinity of the arm  12 . This main portion  12   a  crosses the flow passage  9  for the secondary stream F 2  and is of substantially constant shape between the two shrouds  10  and  11  in the direction in which the arm Z extends, which direction is substantially radial and perpendicular to the longitudinal direction X. 
     The opening  13  has a movable flap  18  for shutting the duct  15 , the flap being pivotable about an axis parallel to the radial direction Z at the corresponding upstream edge of the opening. The shape of the movable shutter flap  18  of the duct  15  corresponds to the surface of the plate that has been cut away so as to form the opening  13 . 
     Under such circumstances, the air bleed duct  15  has an inlet  15   a  that is connected to the downstream edge  13   b  of the opening  13  so as to form an air bleed scoop  19 . 
     The air bleed scoop  19  is thus associated with the movable flap  18 , which flap can pivot about its pivot axis between an open position and a closed position in order to regulate the flow of air entering into the scoop  19 . Depending on the degree of cooling that is desired, the air bled by the scoop  19  can then be distributed to various zones of the turbine engine  1 , e.g. around the casing of the low-pressure turbine  7 , by means of an air distributor manifold. 
     An embodiment of the mechanism for actuating the movable flap  18  is shown in  FIGS. 3 and 4 , which are views from above relative to the arm  12 . 
     In these figures, and also in the preceding figures, the movable flap  18  is actuated by a moving force from a movable drive rod  20  of an actuator  21  when the actuator is powered. More precisely, the drive rod  20  of the actuator  21  serves to deliver a movement force between a first position corresponding to the closed position of the movable flap  18  and a second position corresponding to the open position of the movable flap  18 . 
     By way of example, the actuator  21  may be an electric actuator, a pneumatic actuator, or indeed a hydraulic actuator. Nevertheless, a necessary condition for performing an integrity test as described in detail below is that the actuator  21  must present behavior that is astable when it is no longer powered. By “astable” behavior, it should be understood that the position of the drive rod of the actuator is determined solely by forces external to the actuator that act on the rod. 
     The movement of the drive rod  20  of the actuator  21  is controlled by an electronic computer  30 , referenced in  FIG. 2 , and configured:
         to control the supply of power to the actuator  21  (arrow  31 ) in such a manner as to control movement of its rod  20 . By way of example, if the actuator  21  is an electric actuator, the electronic computer  30  may cause an electric switch connecting the actuator  21  to an electrical power supply to open or to close; and   to estimate the movement of the drive rod  20  of the actuator  21  on the basis of measurements returned (arrow  32 ) by at least one position sensor  21 - 1  measuring the position of the rod  20 .       

     The movement force is transmitted from the drive rod  20  to the movable flap  18  by means of a push-pull cable  22  that connects together, directly or indirectly, the drive rod  20  of the actuator  21  and the movable flap  18 . The push-pull cable  22  may optionally be arranged in a sheath  23  providing it with guidance and protection. 
     In general manner, the movable flap  18  may be actuated by any suitable actuator  21  that possesses a movable drive element  20  connected to the push-pull cable  22  and that is suitable for transmitting its movement force to the movable flap  18 . The movement of the movable drive element  20  is not necessarily exclusively movement in translation. It is possible to envisage a movable drive element  20  that is in the form of a rotary arm. 
     Furthermore, the term “push-pull” cable is used broadly in the present description to cover any driving connection enabling both thrust and traction to be transmitted between the movable drive element  20  and the movable flap  18 . This therefore covers not only in conventional manner a cable that can slide by way of example in a guide and protection sheath, but equally well other driving connections such as in particular a linkage comprising hinged rods or an association of one or more rods and one or more cables. The actuator  21  and the electronic computer  30  may be positioned by way of example in a zone of space close to the fan  2 , such as a compartment in the nacelle around the fan  2 . Such a zone is particularly advantageous since it is a cool zone suitable for receiving electrical equipment. In the example shown, the sheath  23  of the cable  22  then passes from the nacelle of the fan  2  to the arm  12 . 
     It is possible for the actuator  21  to be located elsewhere, in some other space of the nacelle situated radially outside the secondary passage  9 , or indeed in the space between passages if the problem of ensuring that the actuator  21  is not subjected to excessive temperatures is overcome. 
     In the absence of force being transmitted by the cable  22  to the movable flap  18 , a safety spring  24  is configured to move the movable flap  18  towards its closed position so as to put the movable flap  18  into a safe position, commonly referred to as its “fail-safe” position. 
     Thus, in order to ensure that the movable flap  18  can occupy its safe position, the spring  24  is dimensioned so as to be capable of moving the movable flap  18  and also the elements to which the movable flap  18  is connected for moving it, in particular the cable  22  and the drive rod  20  of the actuator  21 . 
     The air bleed scoop  19 , the movable flap  18 , the safety spring  24 , the push-pull cable  22 , and the actuator  21  controlled by electronic computer  30  thus together form a system for regulating air flow in the turbine engine. 
       FIGS. 3 and 4  show situations relating to nominal operation of this air flow regulator system. As can be seen in the figures:
         in the closed position ( FIG. 3 ), the movable flap  18  shuts the opening  13  in the arm  12 , thus preventing any entry of the secondary stream F 2  into the air bleed scoop  19 . The air of the secondary stream F 2  then flows along the arm  12 , this air flow being represented by successive single-headed arrows. In nominal operation, as shown in this figure, the closed position of the movable flap  18  is guaranteed by the safety spring  24 , which is in an extended position. The actuator  21  is no longer powered and its drive rod  20  is retraced into the first position. Retraction of the drive rod  20  of the actuator  12  is indirectly the result of the return force exerted by the spring  24  on the movable flap  18 , this force being transmitted to the drive rod  20  via the push-pull cable  22 ;   in the open position ( FIG. 4 ), the movable flap  18  is held in abutment against a wall  12   c  of the arm away from the opening  13  in the arm  12 , which is then no longer shut, thus enabling a portion of the secondary stream F 2  to enter into the air bleed scoop  19 . Air from the secondary stream F 2  then flows in part into the scoop  19  and in part along the arm  12 , this air flow being represented by successive single-headed arrows. In nominal operation, as shown in this figure, the open position of the movable flap  18  is provided by the actuator  21  which is then powered, this power being represented by two single-headed arrows I. More precisely, the rod  20  of the actuator  21  is moved to its position extended towards the second position and the force that it exerts is transmitted via the push-pull cable  22  to the movable flap  18 . The safety spring  24  is then in its compressed position as a result of the force applied by the rod  20  on the movable flap  18 .       

     In the example shown in the figures, the movable flap  18  is actuated by a lever  25  arranged at the top of the arm  12  and outside the secondary passage, the lever  25  being capable of pivoting about the pivot axis of rotation of the movable flap  18 . The lever is also connected firstly to the cable  22  and secondly to the safety spring  24 , these both being arranged above the arm  12 . The respective interconnections between the drive rod  20  of the actuator  21  and the movable flap  18 , and between the movable flap  18  and the spring  24  are thus implemented in this example indirectly by means of the lever  25 . Nevertheless, it is also possible for direct interconnections to be made with the movable flap  18 , i.e. without necessarily using the lever  25 , these figures serving merely as illustrative example for the embodiments described below. 
       FIGS. 5 and 6  use the same numerical references as  FIGS. 3 and 4 , these figures showing the same elements in the same three-dimensional configuration as those described above. 
       FIG. 5  shows a first failure situation that can occur in the system for regulating the air flow in the turbine engine  1 . This first situation corresponds to a mechanical break in the push-pull cable  22 , thus preventing any movement force being transmitted from the drive rod  20  of the actuator  21  to the movable flap  18 . 
     In this example, the actuator  21  is powered, this power supply being represented by two single-headed arrows II so as to move its drive rod  20  towards the second position, i.e. towards the extended position needed by the rod  20  for opening the movable flap  18 . Nevertheless, the break in the cable  22  means the movement force can no longer be transmitted from the rod  20  of the actuator  21  in order to move the movable flap  18  towards its open position. Consequently, the safety spring  24  remains in or returns to its extended position, exerting a return force (single-headed arrow III) that holds the movable flap  18  in the closed position or that moves the movable flap  18  into that position (single-headed arrow IV), i.e. into the “fail-safe” position, as contrasted to the expected open position. 
     Furthermore, since the actuator  21  presents astable behavior when it is no longer powered, the position of the rod  20  is determined solely by forces external to the actuator  21  and acting on the rod  20 . As a result of the break in the cable  22 , the rod  20  of the actuator  21  is no longer subjected to force from the cable and therefore remains in its extended position. 
       FIG. 6  shows a second failure situation that can occur in the system for regulating air flow in the turbine engine  1 . This second situation corresponds to a mechanical break in the safety spring  24 . 
     In this example, the actuator  21  has previously been powered so as to move its drive rod  20  towards the second position, i.e. towards the extended position of the rod  20  in order to open the movable flap  18 . This time the movement of the rod  20  takes place in nominal manner so that the movable flap  18  is moved into its open position. Breakage of the spring  24  might occur equally well before or after the movement of the rod  20 . In other words, the mechanical break of the safety spring  24  could take place equally well while the movable flap  18  was still in its closed position. 
     Furthermore, in the situation when mechanical breakage of the push-pull cable  22  is combined with mechanical breakage of the safety spring  24 , the movable flap  18  would be subjected solely to the aerodynamic forces of the secondary stream F 2 , which would then push the flap towards its open position. The method of testing the integrity of the system applies equally well in this very unlikely situation of combined breaks, and makes it possible to detect the occurrence of the failure in the same manner as in the second failure situation shown in  FIG. 6 . 
     After the drive rod  20  has been moved to its second position, and in order to verify the integrity of the air flow regulator system, the actuator  21  is no longer powered. When the integrity of the air flow regulator system is good, the spring  24  pushes back the movable flap  18  to its closed (fail-safe) position and pushes back the rod  20  of the actuator  12  to its closed position, i.e. its retraced position. 
     However, breakage of the spring  24  prevents the return force from acting on the movable flap  18  and indirectly from acting on the rod  20  of the actuator  21 . 
     The movable flap  18  then remains in the open position, mainly as a result of the aerodynamic forces exerted on the flap by the secondary stream F 2 . Furthermore, since the actuator  21  is no longer powered, the position of the rod  20  is determined solely by the forces external to the actuator  21  that act on the rod  20 . Since the rod  20  is connected to the movable flap  18  via the push-pull cable  22 , it is thus the position of the movable flap  18  that controls the position of the rod. Since the movable flap  18  remains in the open position, the rod  20  of the actuator remains in the extended position. 
     The air stream entering into the turbine engine  1  is no longer regulated, nor is the movable flap  18  put into its safe position. 
     To detect the possible occurrence of the above-described faults, and consequently provide a response to such situations, the electronic computer  30  then causes a test to be executed for testing the integrity of the air flow regulator system, with the various steps of the method being shown in  FIG. 7 . 
     The integrity of the air flow regulator system is verified as follows. 
     Firstly, the electronic computer  30  powers the actuator  21  to cause it to move its drive rod  20  towards the second position (step ST 1 ), for the desired purpose of indirectly moving the movable flap  18  into the open position. For this step, any absence or presence of a failure in the mechanical drive system formed by the cable  22  and the spring  24  for moving the movable flap  18  has not yet been determined. Thus, although moving the rod  20  towards its second position is proposed to move the movable flap  18  into the open position, in practice such opening might or might not take place in the steps of the test as described below, it being possible that such a situation results from a mechanical break in the cable  22 . 
     Once the drive rod  20  has been moved into the second position, the electronic computer  30  switches off the power supply to the actuator  21  (step ST 2 ). By way of example, if the actuator  21  is an electric actuator, the electronic computer  30  may cause the electric switch connecting the actuator  21  to the electrical power supply of the aircraft to open. As a result of switching off the power supply, the drive rod  20  of the actuator  21  can no longer transmit movement force to the movable flap  18 . 
     Thereafter, the computer  30  causes the position of the rod  20  to be measured by at least one position sensor (step ST 3 ). The electronic computer  30  receives the measurement it requested and it compares it with the value for the second position. In this way, the electronic computer  30  determines that the drive rod  20  has indeed moved or has not moved at all relative to the second position (step ST 4 ), which second position is assumed to enable the movable flap  18  to open. 
     In a nominal situation, the electronic computer  30  determines that the rod  20  has moved relative to the second position, representing proper operation of the push-pull cable  22  and of the safety spring  24 . Specifically, assuming proper integrity for the cable  22  and the spring  24 , as set out above, turning off the power supply to the actuator  21  results in no movement force being transmitted from the rod  20  to the movable flap  18 . The spring  24  then exerts a return force on the movable flap  18 , with the return force then being transmitted indirectly to the drive rod  20  via the push-pull cable  22 . The rod  20  is thus observed to move. 
     Thus, as a result of detecting movement of the rod  20 , the electronic computer  30  deduces that the push-pull cable  22  and the safety spring  24  are operating properly (step ST 5 ). 
     On the contrary, if as a result of switching off the power supply to the actuator  21 , the computer  30  determines that there is no movement of the rod  20  relative to the second position, the computer then deduces inability (e.g. breakage) of the spring  24  or breakage of the cable  22  (step ST 6 ). 
     As a result of this diagnosis, the computer  30  then causes the actuator  21  to be powered so as to move its rod  20  towards the first position (step ST 7 ). 
     Advantageously, this movement of the rod  20  serves to accommodate any failure situation. Specifically, in the event of the cable  22  breaking, corresponding to the first failure situation in  FIG. 5 , the second position of the rod  20  does not enable the movable flap  18  to be controlled, so extending the rod in this way is unnecessary. Furthermore, the safety spring  24  then puts the movable flap  18  into the fail-safe position by moving the flap towards its closed position. In the event of the safety spring  24  breaking, corresponding to the second failure situation of  FIG. 6 , the safety spring  24  is no longer capable of putting the movable flap  18  into the fail-safe position. Consequently, moving the rod  20  towards the first position serves to cause the movable flap  18  to take up its safe position, by moving the flap towards its closed position by means of a traction force communicated to the movable flap  18  by the cable  22  from the actuator  21 . 
     Advantageously, the above-described test of the integrity of the air regulator system may be executed periodically, with that periodicity being selected as a function of the acceptable length of dormancy for a failure, which itself may be determined, by way of example, by analyzing a failure tree. 
     By way of example, such an integrity test may be performed on the ground before starting the turbine engine  1 , or indeed after stopping it. Performing this test during one of the above-mentioned stages in the life of the engine is particularly advantageous, since during those stages there is no particular need for the air flow regulator system. In particular, there is no flow of air entering into the scoop  19 , regardless of the position of the movable flap  18 . It is then possible to manipulate the movable flap  18  without any consequence for the engine. 
     It is also possible to perform this test at other times in the life cycle of the engine, so long as the consequences on the operation of the engine due to variations in the air flows while the movable flap  18  is being manipulated are deemed to be acceptable. 
     Furthermore, an optional implementation shown in dashed lines can be implemented after diagnosing proper operation of the cable  22  and of the spring  24  (step ST 5 ). 
     Commonly, the electronic computer  30  includes in memory a pre-stored control relationship for the drive rod  20  of the actuator  21 , this relationship modeling in particular the movement of the rod  20  between the first position and the second position. During aging of the mechanical elements of the air flow regulator system, e.g. the cable  22  and the spring  24 , variations in clearance may appear between those various elements, leading to the movement of the movable flap  18  being controlled less accurately. 
     In order to mitigate this drawback, in an implementation, after diagnosing proper operation of the cable  22  and of the spring  24  (step ST 5 ), the computer  30  compares the measured position of the rod  20  with the value of the first position, corresponding to the extended position of the rod  20  for moving the flap into its closed position. Thus, the electronic computer  30  determines a possible movement of the drive rod  20  possibly all the way to the first position. More precisely the electronic computer  30  determines a potential difference between the position of the rod  20  and the first position (step ST 8 ). If this difference is zero, then the test ends. 
     Conversely, when the position of the drive rod  20  differs from the first position, the electronic computer  30  then redefines the first position by allocating to the first position the measured position of the drive rod (step ST 9 ). 
     Finally, on the basis of the redefined first position, the electronic computer  30  reconfigures its control relationship for the movement of the rod  20  of the actuator  21  (step ST 10 ). Advantageously, this serves to refine the accuracy with which the movement of the flap  18  is controlled by the computer  30 . 
     If the consequences for the engine due to the variations in the air flow rate that result from manipulating the movable flap  18  are acceptable, and as a function of the accuracy required for the manipulation, this implementation can be performed at the beginning of the stage of flight of the aircraft. 
     Performing this test during this stage of life is particularly advantageous, since it then makes it possible when reconfiguring of the control relationship for the rod  20  of the actuator  21  to take account of the effects of thermal deformation acting on the dynamics of the air flow regulator system. 
     In order to enable the control relationship to be reconfigured accurately during this stage in the life of the engine, the actuator  21  may be made so as to filter the vibration associated with the stage of flight, thereby limiting unwanted movements of its actuator rod  20 . 
     The implementations described above are described for a particular example of a cooling system in a turbine engine. Nevertheless, these implementations are applicable to any air flow regulator system, and more generally to any system for regulating a flow of fluid (gas or liquid) in a turbine engine. For example, for regulating an airflow, it is possible to envisage applying the method to an air-oil heat exchanger (also known as an air-cooled oil cooler (ACOC)) fed with air coming from the secondary stream, to controlling the clearance that exists in a low- or high-pressure turbine, to a fan air valve (FAV) for the pre-cooler, or indeed to a ventilation scoop. 
     As mentioned above, the regulation may apply to a flow of fluid in general. When regulating a liquid flow, it is possible to envisage making provision to apply the integrity test to a regulator system comprising a valve in which the pivoting shutter member in the form of a movable flap, e.g. of the butterfly type, is controlled by an actuator via a push-pull cable connecting the drive rod of the actuator to the rotary shaft of the shutter member. By way of example, the fluid-passing duct associated with the valve may be connected to a heat exchanger in such a manner that regulating the flow of liquid serves to vary the heat exchange taking place within the heat exchanger between the liquid and some other fluid. The valve may have a failsafe position that is open or closed, obtained by means of a mechanical return spring or indeed by return means resulting from the pivot axis of the movable flap (butterfly) of the valve having an off-center position. 
     The movable flap (generally a disk) of a butterfly type valve conventionally presents a pivot axis that is centered, i.e. that extends along a diameter of the flap. It is known that an off-center axis serves to unbalance the pressure forces from the fluid that act on the flap on either side of the axis, thereby exerting a turning torque on the flap. This torque may be used to generate the return force for bringing the movable flap of the valve back into a failsafe position in the absence of any drive force being exerted on the flap, in particular in the event of a break in the push-pull cable that drives turning of the flap. 
     This provision makes it possible to omit a mechanical return spring while still obtaining the failsafe position. The safety return means provided by the off-center axis of the flap can nevertheless become dysfunctional, even in the absence of mechanical breakage. For example, the shaft of the flap may seize in an angular position that is different from the failsafe position in a manner capable of generating an opposing torque that is large enough to prevent the above-mentioned return force returning the flap into the failsafe position in the absence of force being transmitted by the cable to the flap. 
     Furthermore, the term “closed” position of the movable flap for shutting the fluid-passing duct  15  should be understood as a position in which the duct is at least partially closed by the flap.