Abstract:
A system for supervising the speed of at least one engine of an aircraft includes three independent information sources determining first, second and third values for an aerodynamic parameter of the aircraft and precision information indicating the precision of these values. A control unit acts on the operation of the engine, and a sensor measures a fourth value for the parameter. An arithmetic unit selects a control value by using the first, second, third and fourth values of the aerodynamic parameter and the precision information and uses the control value to determine a control sequence for the control unit. An information transmission network, to which the three independent information sources and the arithmetic unit are connected, permits a transmission of information between the sources of information and the arithmetic unit.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system for supervising the speed of at least one engine of an aircraft, in particular of a transport plane. 
     BACKGROUND OF THE RELATED ART 
     Generally, with each engine of a transport plane is associated a supervising unit which comprises in particular:
         a means of regulation for acting on the speed of the engine, as a function of control orders received. This means of regulation is able to adjust the flow rate of fuel intended to supply the engine; and   a computation unit, for example an engine electronic regulator of the EEC (“Electronic Engine Control”) type, which determines the control orders for said means of regulation.       

     This computation unit uses in particular information relating to the conditions under which the aircraft is maneuvering, that is to say information relating to aerodynamic parameters such as the static and total temperatures and/or the static and total pressures, to determine these control orders. For safety reasons, said computation unit uses several different sources to obtain this information, namely generally:
         an engine sensor, which is able to measure on the engine the value of the relevant aerodynamic parameter; and   two airplane sources, for example of the ADIRU (“Air Data Inertial Reference Unit”) type, which also have access to values of this aerodynamic parameter and which are connected individually by specific links, for example of ARINC 429 type, to said computation unit.       

     The computation unit must therefore select, from the various values of the aerodynamic parameter that it receives, that one which it will use for its computations. 
     In certain situations, a poor selection is possible, which may have very damaging effects. Specifically, an erroneous item of information which is not representative of the actual flight conditions of the aircraft brings about an erroneous computation of the engine speed so that the engine may then be led to operate in a mode inappropriate for said flight conditions. It may then even stop, for example when the speed demanded is too low for the conditions encountered. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to remedy these drawbacks. It relates to a particularly reliable and cheap system for supervising the speed of at least one engine of an aircraft, making it possible to avoid erroneous selection of the value of an aerodynamic parameter used. 
     For this purpose, according to the invention, said supervising system of the type comprising:
         a first and a second information source determining first and second values of at least one predetermined aerodynamic parameter of the aircraft; and   at least one unit for supervising said engine, comprising:
           at least one means of regulation for acting on the speed of the engine as a function of control orders received;   at least one sensor which is able to measure a fourth value of said aerodynamic parameter, on said engine; and   a computation unit which is connected to said first and second information sources, to said means of regulation and to said sensor, which receives said first, second and fourth values of said aerodynamic parameter, which takes them into account so as to select a value of said aerodynamic parameter as control value, and which uses the control value thus selected at least to determine a control order which is transmitted to said means of regulation,   
               

     is noteworthy in that
         said system furthermore comprises:
           a third information source determining a third value of said predetermined parameter; and   an information transmission network, to which are linked said first, second and third information sources and said computation unit allowing transmission of information between said information sources and said computation unit;   
           said first, second and third information sources are independent of one another;   said first, second and third information sources respectively determine first, second and third correctness information indicating the correctness respectively of said first, second and third values of said aerodynamic parameter; and   said computation unit selects said control value by using said first, second, third and fourth values of the aerodynamic parameter, as well as said first, second and third correctness information.       

     Thus, the computation unit avails itself not only of a large number of values (first to fourth values) for making the selection and choosing the most accurate and most appropriate value for the relevant aerodynamic parameter, but also of valuable aid afforded by said correctness information, which allows it to make the best possible value selection, and especially to avoid any poor selection (in contradistinction to the aforesaid known solution), as will be seen in greater detail hereinbelow. Moreover, as the various information sources are independent of one another, any error of one of said sources cannot affect the other sources. 
     Consequently, the supervising system in accordance with the invention is particularly reliable. 
     Furthermore, by virtue of said information transmission network, it is not necessary to connect the new elements (in particular said third information source) individually to the other elements, which would require numerous bulky and expensive specific links, so that the new elements can communicate with the others. It is in fact sufficient to link them, simply and directly, to said information transmission network. 
     Advantageously, to select the control value, the computation unit gives priority to the first, second, third values of said information sources with respect to said fourth value of the sensor, it chooses said fourth value only in case of lack of agreement between all the values, and it uses said correctness information at least to resolve any ambiguities. 
     In a preferred embodiment, said computation unit uses as control value: 
     1/ if said fourth value of the sensor is not valid:
         A/ if said first, second and third values of said first, second and third information sources are valid and are in agreement, said first value of said first information source;   B/ otherwise:
           α) if two of said first, second and third values are valid and are in agreement and if the product of the two corresponding items of correctness information is equal to 1, a correctness item equaling 1 if the corresponding value is apparently correct and 0 otherwise, the lower value of said two values in agreement;   β) otherwise:   a) if one of said first, second and third values is valid and if the corresponding correctness item equals 1, this value which is valid;   b) otherwise, a predetermined value; and   
               

     2/ if said fourth value is valid:
         A/ if one of said first, second and third values is valid and is in agreement with one other of them, as well as with said fourth value, this value in agreement;   B/ otherwise:
           α) if two of said first, second and third values are valid and are in agreement and if the product of the two corresponding items of correctness information is equal to 1, the lower value of said two values in agreement;   β) otherwise:
               a) if one of said first, second and third values is valid, if it is in agreement with said fourth value and if its correctness item equals 1, this value which is valid;   b) otherwise, said fourth value of the sensor.   
               
               

     According to the invention:
         two values are in agreement when their difference is less than a predetermined threshold value; and   a value is valid when it lies between two predetermined limit values.       

     Furthermore, advantageously, said computation unit carries out a weighting upon a change of selection of value for the control value (for example when it uses as control value firstly said third value of the third information source, then said first value of the first information source) so as to avoid abrupt jumps of the control value selected and used in the subsequent processing. 
     Additionally, advantageously:
         said computation unit is disconnectable as regards the selection of the control value; and/or   said computation unit receives said fourth value on two different channels, and uses the two values thus received.       

     According to the invention, for supervising the speeds of the engines of an aircraft fitted with a plurality of engines, for example four engines, the supervising system in accordance with the invention comprises, for each engine whose speed it supervises, a specific supervising unit (such as aforesaid) comprising a means of regulation, a sensor and a computation unit. 
     Advantageously, each of said information sources receives from all the supervising units the fourth values measured by the sensor of each of said supervising units and determines its correctness item from these fourth values. 
     Consequently, in the case of an aircraft with n engines, each computation unit uses directly or indirectly n+3 values of the relevant aerodynamic parameter (namely said first, second and third values of said information sources, which are taken into account directly (as well as its fourth value), and the  n  fourth values of said  n  sensors, which are taken into account indirectly in the computation of the correctness information), this making it possible to raise the accuracy of selection and to increase safety. 
     In a preferred embodiment, to determine its correctness item, each information source:
         computes all the differences between, on the one hand, said fourth values and, on the other hand, its own value of said aerodynamic parameter;   compares the differences with a predetermined threshold value; and   deduces therefrom:
           if at least half of said differences are below said threshold value, that said correctness item equals 1;   otherwise, that it equals 0.   
               

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures of the appended drawing will elucidate the manner in which the invention may be embodied. In these figures, identical references designate similar elements. 
         FIG. 1  is the schematic diagram of a system in accordance with the invention. 
         FIG. 2  diagrammatically illustrates the various steps of a mode of selection implemented by a computation unit of a system in accordance with the invention. 
         FIGS. 3 to 8  diagrammatically show various computation elements allowing the implementation of various steps of the mode of selection illustrated in  FIG. 2 . 
         FIG. 9  diagrammatically shows a system in accordance with the invention, applied to an aircraft fitted with a plurality of engines. 
         FIG. 10  diagrammatically shows a source of information of a system in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The system  1  in accordance with the invention and represented diagrammatically in  FIG. 1  is intended to supervise the speed of at least one engine  2  of an aircraft, in particular of a transport plane. 
     Said system  1  is of the type comprising:
         a first and a second standard information source  3  and  4  of the aircraft, for example of ADIRU (“Air Data Inertial Reference Unit”) type, which are able to determine first and second values of at least one predetermined aerodynamic parameter of said aircraft, such as for example the static temperature, the total temperature, the static pressure or the total pressure; and   at least one unit  5  for supervising said engine  2 , comprising:
           at least one standard means of regulation  6  for acting on the speed of the engine  2 , as a function of control orders received. This means of regulation  6  is able to adjust the flow rate of fuel intended to supply the engine  2 ;   at least one sensor  7  which is able to measure a fourth value of said aerodynamic parameter, on said engine  2 ; and   a computation unit  8 , for example an engine electronic regulator of EEC (“Electronic Engine Control”) type, which determines the control orders for said means of regulation  6  and which can form part of a full authority digital electronic regulating system of the engine of FADEC (“Full Authority Digital Engine Control”) type. Said computation unit  8  is connected to said first and second information sources  3  and  4 , as specified hereinbelow, as well as to said means of regulation  6  and to said sensor  7 , respectively by way of links  10  and  11 . The computation unit  8  receives said first, second and fourth values of said aerodynamic parameter, and takes them into account to select a value of said aerodynamic parameter as control value. It uses the control value thus selected at least to determine a control order which is transmitted to said means of regulation  6 .   
               

     According to the invention, said supervising system  1  moreover comprises:
         a third information source  9  similar to said sources  3  and  4 , which determines a third value of said predetermined aerodynamic parameter; and   an information transmission network  12  to which are linked said information sources  3 ,  4 ,  9  and said computation unit  8 , as represented in  FIG. 1  in a general and diagrammatic manner by links L 1 , L 2 , L 3  and L 4 . Said network  12  allows transmission of information between said information sources  3 ,  4 ,  9  and said computation unit  8 .       

     Thus, these elements  3 ,  4 ,  8 ,  9  may communicate among themselves without it being necessary to connect them directly together by specific individual connections (of the ARINC 429 type for example), thereby making it possible to reduce the cost and the bulk of the system  1 . 
     Moreover, according to the invention:
         said first, second and third information sources  3 ,  4 ,  9  are independent of one another;   said first, second and third information sources  3 ,  4 ,  9  respectively determine first, second and third correctness information indicating the correctness respectively of said first, second and third values of said aerodynamic parameter, as specified hereinbelow; and   the computation unit  8  selects said control value by using said first, second, third and fourth values of the aerodynamic parameter, as well as said first, second and third correctness information.       

     Accordingly, according to the invention, said computation unit  8  gives priority to the values of said information sources  3 ,  4 ,  9  with respect to said fourth value of the sensor  7 . It chooses said fourth value only in case of lack of agreement between all the values received, and it uses said correctness information at least to resolve any ambiguities, as specified hereinbelow. 
     Thus, the computation unit  8  avails itself not only of a large number of values (first to fourth values) for making the selection and choosing the most accurate and most appropriate value for the relevant aerodynamic parameter, but also of valuable aid afforded by said correctness information, which allows it to make the best possible value selection, and especially to avoid any (poor) selection or an inappropriate value (caused for example by a malfunction of a sensor). 
     According to the invention, the computation unit  8  implements a particular mode (or law) of selection to select the control value on the basis of the various values received, mentioned previously. 
     In a preferred embodiment, said computation unit  8  implements the selection law whose schematic comprising steps E 1  to E 7  has been represented in  FIG. 2 . 
     The computation unit  8  firstly verifies in step E 1  whether the fourth value received from the sensor  7  is available and valid. If this is not the case (yes: O; no: N), it implements step E 2 , to verify whether said first, second and third values of said first, second and third information sources  3 ,  4  and  9  are valid and are in agreement. Within the context of the present invention:
         a value (or an information source from which it arises) is valid when this value lies between two predetermined limits. It is therefore invalid if it is outside said limits, and is so preferably for a predetermined duration, for example for five seconds; and   two values are in agreement when their difference is less than a predetermined threshold value.       

     This step E 2  can be implemented with the aid of the computation element C 2  represented diagrammatically in  FIG. 3 . This computation element C 2  comprises:
         a first logic AND gate  14 , whose inputs  14 . 1 ,  14 . 2  and  14 . 3  receive the information item regarding validity of said sources  3 ,  4  and  9 ; and   a second logic AND gate  15 , whose inputs  15 . 1 ,  15 . 2  and  15 . 3  respectively receive the information item regarding agreement between the sources  3  and  4 , the item regarding agreement between the sources  3  and  9 , and the result arising from the gate  14 , and the result of which is available at the output  15 . 4 .       

     If the result is positive (o), the solution S 1  of the selection concerns the selection of said first value arising from the source  3  as control value. 
     On the other hand, if the result is negative (N), the computation unit  8  implements step E 3  to verify whether two of said first, second and third values are valid and are in agreement and whether the product of the two corresponding items of correctness information is equal to 1, a correctness item equaling 1 if the corresponding value is apparently correct and 0 otherwise, as specified hereinbelow. This step E 3  may be implemented with the aid of the computation element C 3  represented in  FIG. 4 . This computation element C 3  comprises:
         a first logic AND gate  16 , whose inputs  16 . 1  and  16 . 2  receive the item regarding validity of two chosen sources. The computation element C 3  is implemented for all the pairs of sources possible, comprising two of said three sources  3 ,  4  and  9 ;   a second logic AND gate  17 , whose inputs  17 . 1  and  17 . 2  are informed if the correctness information are at 1 or otherwise; and   a third logic AND gate  18 , whose inputs  18 . 1 ,  18 . 2  and  18 . 3  respectively receive the information item regarding the agreement of the two relevant sources and the results arising from said gates  17  and  16 , and the result of which is available at the output  18 . 4 .       

     If the result at the output  18 . 4  is positive (o), the solution S 2  of the selection concerns the selection of the lower value of the two sources in agreement, as control value. 
     On the other hand, if the result is negative (N), the computation unit  8  implements step E 4  to verify whether one of said first, second and third values is valid and whether the corresponding correctness item equals 1 or otherwise. This step E 4  may be implemented with the aid of the computation element C 4  represented in  FIG. 5 . This computation element C 4  comprises a logic AND gate  19 , whose inputs  19 . 1  and  19 . 2  are informed, in respect of the relevant source, respectively if the (first, second or third) corresponding value is valid and if its correctness item is at 1 or otherwise, and the result of which is available at the output  19 . 3 . If the result at the output  19 . 3  is positive (o), the solution S 3  of the selection concerns the selection of this value which is valid, as control value, and, if the result is negative (N), the solution S 4  concerns the selection of a predetermined value (which is therefore selected by default). 
     Additionally, if the fourth value received from the sensor  7  is available and valid (step E 1 ), the computation unit  8  implements step E 5  to verify whether one of said first, second and third values of the sources  3 ,  4  and  9  is valid and is in agreement with one other of them, as well as with said fourth value. This step E 5  can be implemented with the aid of the computation element C 5  represented in  FIG. 6 . This computation element C 5  comprises a logic AND gate  20  of output  20 . 3 , and whose inputs  20 . 1  and  20 . 2  are connected respectively to logic OR gates  21  and  22 . The logic OR gate  21  is connected to a computation unit  23  by its inputs  21 . 1  and  21 . 2 . 
     This computation unit  23  comprises:
         a first logic AND gate  24 , whose inputs  24 . 1  and  24 . 2  respectively receive the information item if the value of the source  i  ( 3 ,  4  and  9 ) considered is in agreement with a first indication or value VA of said fourth value from the sensor  7 , and if this source  i  ( 3 ,  4  and  9 ) is valid. The fourth value measured by the sensor  7  is in fact sent on two different channels A and B according to two indications or values VA and VB; and   a second logic AND gate  25 , whose inputs  25 . 1  and  25 . 2  respectively receive the information item if the value of the source  i  ( 3 ,  4  and  9 ) considered is in agreement with the second indication or value VB of said fourth value (channel B), and if this source  i  ( 3 ,  4  and  9 ) is valid.       

     Furthermore, the logic OR gate  22  is connected by its inputs  22 . 1  and  22 . 2  respectively:
         to a first logic AND gate  26 , whose inputs  26 . 1 ,  26 . 2  and  26 . 3  respectively receive the information items if the source  i  and a source  j  (out of the sources  3 ,  4  and  9 ) are in agreement, if the source  i  is valid and if the source  j  is valid; and   to a second logic AND gate  27 , whose inputs  27 . 1 ,  27 . 2  and  27 . 3  respectively receive the information items if the source  i  is valid, if the third source  k  is valid and if said sources  i  and  k  are in agreement.       

     If the result of the processing implemented by the computation means C 5  is positive (o), the solution S 5  of the selection concerns the selection of the value (of said source  i ) which is in agreement, as control value. 
     On the other hand, if the result is negative (N), the computation unit  8  implements step E 6  to verify whether two of said first, second and third values are valid and in agreement (substep E 6 A) and if the product of the two corresponding items of correctness information is equal to 1 (substep E 6 B). This step E 6  may be implemented with the aid of the computation element C 6  represented in  FIG. 7 . This computation element C 6  comprises:
         a logic AND gate  28 , whose inputs  28 . 2  and  28 . 3  are informed if the correctness information items respectively of two sources  i  and  j  (out of the sources  3 ,  4  and  9 ) are at 1 or otherwise, whose input  28 . 1  is connected to a logic AND gate  29 , and whose output  28 . 4  provides the result; and   said logic AND gate  29 , whose input  29 . 1  is informed if the values of the sources  i  and  j  are in agreement, whose input  29 . 2  is informed if the source  i  is valid, and whose input  29 . 3  is informed if the source  j  is valid.       

     If the result of the processing implemented by the computation means C 6  is positive (o), the solution S 6  of the selection concerns the selection of the lower value of the two sources  i  and  j  in agreement, as control value. 
     On the other hand, if the result is negative (N) for substep E 6 A or for substep E 6 B, the computation unit  8  implements step E 7 , to verify whether one of said first, second and third values is valid and whether it is in agreement with said fourth value (substep E 7 A) and whether its correctness item equals 1 (substep E 7 B). This step E 7  can be implemented with the aid of the computation element C 7  represented in  FIG. 8 . This computation element C 7  comprises a logic AND gate  30 , of which an input  30 . 1  is connected to the computation unit  23  via the gate  21  (similar to that of  FIG. 6 ), whose input  30 . 2  is informed if the correctness item of the relevant source does indeed equal 1 or otherwise, and whose result is available at the output  30 . 3 . 
     If the result at the output  30 . 3  is positive (o), the solution S 7  of the selection concerns the selection of this value which is valid and in agreement with the fourth value, as control value and, if the result is negative (N), the solution S 8  concerns the selection of said fourth value. 
     Said computation elements C 2  to C 7  are built into said computation unit  8 . 
     Preferably, said computation unit  8  carries out a weighting upon a change of selection of value for the control value and, moreover, it is disconnectable as regards the selection of the control value. This is beneficial in particular on the ground for avoiding erroneous detections. 
     The supervising system  1  in accordance with the invention is most particularly appropriate for simultaneously supervising the speeds of all the engines  2 A,  2 B,  2 C,  2 D of a multi-engine aircraft, as represented in  FIG. 9 . To do this, the supervising system  1  comprises, in addition to the three information sources  3 ,  4  and  9  and the information transmission network  12 , a supervising unit  5 A,  5 B,  5 C,  5 D for each of said engines  2 A,  2 B,  2 C,  2 D, said supervising units  5 A,  5 B,  5 C,  5 D being similar to the supervising unit  5  of  FIG. 1  (the same elements having the same references, accompanied in  FIG. 9  by one of the letters A, B, C or D to differentiate between them, as a function of the engine  2 A,  2 B,  2 C or  2 D with which they are associated). 
     Each of said information sources  3 ,  4 ,  9  transmits to said network  12 , its (first, second or third) predetermined value of the aerodynamic parameter via a link  37 , and its correctness item via a link  31 . 
     Moreover, each supervising unit  5 A,  5 B,  5 C and  5 D receives:
         via a link  32 . 3 , the first value of the source  3 ;   via a link  32 . 4 , the second value of the source  4 ;   via a link  32 . 9 , the third value of the source  9 ;   via a link  33 . 3 , the first correctness item of the source  3 ;   via a link  33 . 4 , the second correctness item of the source  4 ; and   via a link  33 . 9 , the third correctness item of the source  9 .       

     Additionally, each of said supervising units  5 A,  5 B,  5 C and  5 D transmits the corresponding fourth value, by way of a link  34 , to the network  12 . These fourth values are then transmitted to the various sources  3 ,  4 ,  9  by way of links  35 A,  35 B,  35 C and  35 D. 
     By virtue of this information, each of said sources  3 ,  4 ,  9 , one of which is represented in  FIG. 10 , can determine its correctness item on the basis of the four values measured on the various engines  2 A,  2 B,  2 C and  2 D and from its own value received via a link  36 . According to the invention, to determine its correctness item, each information source  3 ,  4 ,  9 :
         computes all the differences between, on the one hand, said fourth values and, on the other hand, its own value of said aerodynamic parameter;   compares these differences with a predetermined threshold value; and   deduces therefrom:
           if at least half of said differences are below said threshold value, that said correctness item equals 1;   otherwise, that it equals 0.