Abstract:
A method for detecting the opening of a thrust reverser for a jet engine of an aircraft is disclosed. According to the method, an operating parameter of the turbojet ( 1 ) is determined being responsive to the opening of a mobile element ( 2   a,    2   b ) of the thrust reverser and reacting to such an opening by a sudden variation of the value thereof, the parameter is measured continuously and the mobile element ( 2   a,    2   b ) is considered as being opened when the sudden variation is detected.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to French Patent Application 0902691, filed Jun. 4, 2009, the contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a method enabling to detect the opening of at least one mobile element of a thrust reverser in an aircraft turbojet, such as a pivoting door, as well as an electronic system controlling the turbojet and implementing such a method, and an aircraft comprising such an electronic system. 
     BACKGROUND OF THE INVENTION 
     In aircrafts, the FADEC (&lt;&lt;Full Authority Digital Engine Control&gt;&gt;) electronic system controls the engine speed of the turbojet and fills the protection, diagnosis and maintenance aid function of the engine. Such an electronic system allows, more specifically, to determine the maximum operating speed of the engine for which the airplane remains controllable with at least one pivoting door of the thrust reverser being opened. Indeed, the opening of an reverser pivoting door impacts the controllability of the aircraft, the thrust of the engine being suddenly decreased. 
     Different devices for detecting the closure and the latching of pivoting doors in a thrust reverser generally using electric contactors are already known. 
     The FADEC electronic system connected to such detection devices receives signals indicating the closure and the latching of pivoting doors in the thrust reverser. When it no longer receives such signals, the pivoting door is in the opening position and the FADEC electronic system modifies the operating speed of the engine. 
     Adapting the engine speed by the FADEC electronic system should only be implemented when it is indispensable for maintaining the controllability of the aircraft, this means that the opening of the pivoting door of the thrust reverser should be proved. 
     In particular, should an untimely, that it to say, not requested by the pilot, opening be detected, it would then be advantageous to be able to validate the detection of the current devices. 
     Furthermore, in cases of breakdowns or malfunctions of such detection devices, it would be useful to obtain auxiliary information relating to the closure and the opening states of the thrust reverser. 
     SUMMARY OF THE INVENTION 
     The present invention aims at meeting such requirements, and relates to a method being adapted for detecting the opening of at least one mobile element of a thrust reverser in an aircraft turbojet, and that could be applied to validating information emitted by the detection devices. 
     To this end, the method according to this invention is remarkable in that:
         an operating parameter of the turbojet is determined, responsive to the opening of said mobile element and reacting to the latter by a sudden variation of the value thereof;   said operating parameter is measured continuously, and said mobile element is considered as being opened when said sudden variation is detected.       

     When the method is applied to a turbojet comprising a usual detection system indicating, continuously, by means of an electric signal, the closure and the latching of at least one mobile element of the reverser, it comprises validating the detection of the opening of said mobile element when, in addition to the lack of reception of the electric signal indicating the closure and the latching of the reverser, said sudden variation of the operating parameter is detected. 
     In a first embodiment of the method, the operating parameter of the engine is the real rotation speed of the blowing unit, and the opening of the mobile element of the reverser is detected as soon as the increase of the value of real rotation speed with respect to the value of the requested rotation speed exceeds a determined threshold. 
     In a second embodiment of the method, the operating parameter of the engine is the time variation of the static pressure at the outlet of the high pressure compressor, and the opening of the mobile element of the reverser is detected as soon as the value of the time variation of the static pressure exceeds a determined threshold. 
     Naturally, it results from the foregoing that the present invention further relates to a FADEC type electronic system controlling the turbojet, wherein the above mentioned method and an aircraft comprising such a FADEC type electronic system are implemented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures of the appended drawing will better explain how this invention could be implemented. In these figures like reference numerals relate to like components. 
         FIG. 1  schematically shows, in a side view, a double flow turbojet fastened by means of a pole on an aircraft wing. 
         FIG. 2  schematically illustrates, in an exploded perspective view, the double flow turbojet of  FIG. 1 . 
         FIG. 3  is a diagram illustrating the rotation speed NI of the blowing unit of the double flow turbojet as a function of time. 
         FIG. 4  is a diagram illustrating the static pressure Ps at the outlet of the high pressure compressor as a function of time. 
         FIG. 5  illustrates a preferred application of the method according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The double flow turbojet  1  shown on  FIGS. 1 and 2  comprises a thrust reverser  2  with pivoting doors  2   a  and  2   b.    
     The double flow turbojet  1  is fastened by means of a pole  3  to an aircraft wing  4 . It comprises a cradle  5  having an upstream part  7  and a downstream part  11 . The upstream part  7  has a side hood  8  wherein there are housed a blowing unit  9  and a FADEC electronic system  10 , steering the engine speed of the double flow turbojet  1  by emitted Se and received Sr signals. The downstream part  11  is provided with the thrust reverser  2  with pivoting doors  2   a  and  2   b.    
     The interior of the cradle  5  of the double flow turbojet  1  described on  FIG. 2  comprises the blowing unit  9 , a central generator  12  emitting, through the outlet port thereof  13 , a hot flow f, and the diversion channel  6  surrounding the central generator  12  and through which a cold flow F is circulated, coming from the blowing unit  9 . The central generator  12  comprises, as known, a low pressure compressor  14   a , a high pressure compressor  14   b , a low pressure turbine  15   a , a high pressure turbine  15   b  and a combustion chamber  16 . 
     The pivoting door  2   a  is shown in a folded position wherein it is part of the fairing of the turbojet  1  while the other pivoting door  2   b  is shown in an extended position. 
     In order to ensure the doors  2   a  and  2   b  are closed, the electronic system  10  receives from known detection devices, such as electric contactors, signals indicating that the pivoting doors  2   a  and  2   b  are closed and latched. 
     If the opening of at least one pivoting door  2   b  of the thrust reverser  2  occurs in flight or upon a take off, and if the latter is not generated by a request from the pilot, but it is triggered as a result of a malfunction of the known closure and latching means of the reverser  2 , the engine speed is not decreased by the electronic system  10  at the time where the event occurs. The engine speed corresponds to the flight conditions of the aircraft established by the electronic system  10  before the opening of the pivoting door  2   b.    
     The first embodiment of the method according to this invention allows the opening of the pivoting door  2   b  to be detected for a quite high air flow rate circulating across the turbojet  1  before the opening, corresponding to an average to high velocity of the aircraft. 
     After the opening of the pivoting door  2   b , the air flow rate circulating across the blowing unit  9  suddenly drops and, thus the aerodynamic load of the blowing unit  9  suddenly drops. The real velocity N 1   r  of the blowing unit  9  then accelerates as a result of the decrease of the stress exerted by the air flow on the blowing unit  9 . An increase of the real velocity N 1   r  of the blowing unit  9  is thus experimentally observed with respect to the velocity N 2   c  requested by the electronic system  10 . As illustrated on the diagram on  FIG. 3 , such increase is characterized by a peak between the times t 0  and t 2  respectively corresponding to the opening and the closure of the pivoting door  2   b.    
     Thus, in this first embodiment, the method according to this invention comprises measuring continuously the value of the real velocity N 1   r , comparing the value of the real velocity N 1   r  to the value of the velocity N 1   c  requested by the electronic system  10  and detecting the opening of the pivoting door  2   b  of the reverser  2  if the comparison between the real velocity N 1   r  and the requested velocity N 1   c  exceeds a predetermined threshold. For example, on  FIG. 3 , the threshold is exceeded for N 1   s  at time t 1 . The threshold corresponds to given conditions of velocity, temperature and pressure. 
     The second embodiment of the method according to this invention allows the opening of the pivoting door  2   b  of the thrust reverser  2  to be detected for a low air flow rate, circulating across the double flow turbojet  1  before the opening. In such a case, the air flow circulating across the central generator  12  emitting a hot flow could be inverted and a pumping phenomenon of the low pressure compressor is observed. 
     The pumping phenomenon at the low pressure compressor  14   a  is propagated to the high pressure compressor  14   b.    
     In the case of the stall of the high pressure compressor  14   b , the variation of the real velocity N 1   r  with respect to the requested velocity N 1   e  is not satisfactory for making up a valid detection of the opening of the pivoting door  2   b  in the thrust reverser  2  by the electronic system  10 . On the other hand, the static pressure Ps at the outlet of the high pressure compressor  14   b  suddenly oscillates, as illustrated on  FIG. 4  between the times t′ 0  and t′ 1  respectively corresponding to the opening and to the closure of the pivoting door  2   b . Such an oscillation is sufficiently different from the variations of the static pressure Ps observed for the nominal engine operating speeds for making up a valid detection of the opening of the pivoting door  2   b  in the thrust reverser  2 . 
     Thus, in this second embodiment, the method according to this invention comprises measuring continuously the variation as a function of the time of the static pressure PS, comparing the value of the variation to a predetermined threshold selected as being characteristic of the stall, and detecting the opening of the pivoting door  2   b  of the thrust reverser  2  as soon as the value of the variation of the static pressure exceeds the threshold. The threshold corresponds to given conditions of velocity, temperature and pressure. 
     The static pressure could be replaced by other operating parameters of the turbojet  1  such as the temperature at the outlet of the high pressure compressor or the velocity N 2  of the high pressure stage. 
     Advantageously, in a preferred application of the method according to this invention and illustrated on  FIG. 5 , the detection of the opening of the pivoting door  2   b  is only validated by a validation device  17  located in the electronic system  10  when both following conditions are simultaneously met:
         the electric signal S 1  sent by a known detection device  18  comprising electric contactors and indicating the closure and the latching of the reverser  2  is not longer received by the validation device  17 ; and   a sudden variation of the operating parameter Ni or Ps of the double flow turbojet  1  has been detected by sensors  19  and has been transmitted in the form of a signal S 2  to the validation device  17 .       

     The validation device  17  delivers at the outlet a validation signal S 3  for the detection of the opening of said pivoting door  2   b  when it only receives the signal S 2 . 
     The method does not require adding any new device, as it uses the on-board existing systems such as the FADEC electronic system and the sensors for measuring operation magnitudes of the double flow turbojet, including, for example, pressure, velocity, temperature. 
     Although on figures, there are only shown pivoting door reversers, it is obvious that the present invention could be implemented by reversers of any other type, and including sliding door reversers.