Method for stopping an engine in overspeed, and associated system and rotorcraft

Abstract

A method for stopping an engine of a rotorcraft in overspeed, the rotorcraft comprising at least one engine, the engine comprising a gas generator and a power assembly, the power assembly comprising at least one power turbine rotated by gases originating from the gas generator, the power assembly comprising at least one power shaft rotationally secured to the power turbine, the power assembly rotating about a longitudinal axis at a speed referred to as the “speed of rotation”. The method comprises steps consisting in measuring a current value of the speed of rotation, determining a time derivative of the current value of the speed of rotation, referred to as the “current derivative $\left(\frac{dN2i}{dt}\right)”,$
and automatically stopping the engine when the current derivative $\left(\frac{dN2i}{dt}\right)$
changes sign.

Claims

1. A method for stopping an engine of a rotorcraft in overspeed, the rotorcraft comprising at least one engine, the engine comprising a gas generator and a power assembly, the power assembly comprising at least one power turbine rotated by gases originating from the gas generator, the power assembly comprising at least one power shaft rotationally secured to the power turbine, the power assembly rotating about a longitudinal axis at a speed of rotation (N2); wherein, during a flight, the method comprises: measuring a current value (N2i) of the speed of rotation reached by the power assembly during a predetermined time period (T); determining a current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ by determining a time derivative of the current value of the speed of rotation; and automatically stopping the engine when the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ changes sign over the predetermined time period (T) from a strictly negative value to a strictly positive value.

2. The method according to claim 1 wherein the stopping step is implemented when the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ is less than or equal to a first predetermined threshold value (S1) during a first intermediate time period (T1) and the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ is then greater than or equal to a second predetermined threshold value (S2) during a second intermediate time period (T2).

3. The method according to claim 2 wherein the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ being expressed as a percentage of the current value N2i per second (% N2i.Math.s.sup.−1), the first predetermined threshold value S1 is between −50% N2i.Math.s.sup.−1 and −100% N2i.Math.s.sup.−1.

4. The method according to claim 2 wherein the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ is expressed as a percentage of the current value (N2i) per second (% N2i.Math.s.sup.−1), the second predetermined threshold value (S2) is between +50% N2i.Math.s.sup.−1 and +200% N2i.Math.s.sup.−1.

5. The method according to claim 2 wherein the first intermediate time period (T1) is less than 1 second.

6. The method according to claim 2 wherein the second intermediate time period (T2) is less than 1 second.

7. The method according to claim 1 wherein the gas generator comprises a rotating assembly that rotates about the longitudinal axis at a speed of rotation (N1) of the rotating assembly, the method comprises a step comprising measuring a current value (N1i) of the speed of rotation (N1) reached by the gas generator.

8. The method according to claim 7 wherein the stopping step is conditioned by a current value (N1i) of the speed of rotation (N1) greater than a third predetermined threshold value (S3).

9. The method according to claim 1 wherein the method includes a step comprising measuring a current value (Tqi) of an engine torque (Tq) transmitted to the at least one power shaft.

10. The method according to claim 9 wherein the stopping step is conditioned by a current value (Tqi) of the engine torque (Tq) greater than a fourth predetermined threshold value (S4).

11. The method according to claim 1 wherein the method comprises a step of processing the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right),$ the processing step enabling filtering the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ and/or calculating an average value of the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right).$

12. An overspeed safety system for an engine of a rotorcraft, the engine comprising a gas generator and a power assembly, the power assembly comprising at least one power turbine rotated by gases originating from the gas generator, the power assembly comprising at least one power shaft rotationally secured to the power turbine, the power assembly rotating about a longitudinal axis at a speed of rotation (N2), the overspeed safety system comprising: a speed sensor for measuring a current value (N2i) of the speed of rotation (N2) reached by the power assembly during a predetermined time period T; a shut-down system for stopping operation of the engine; and a processing unit connected to both the speed sensor and the shutdown system, wherein the processing unit is configured to implement a method comprising: measuring a current value (N2i) of the speed of rotation reached by the power assembly during a predetermined time period (T); determining a current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ by determining a time derivative of the current value of the speed of rotation; and automatically stopping the engine when the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ changes sign over the predetermined time period (T) from a strictly negative value to a strictly positive value.

13. A rotorcraft comprising at least one engine and an overspeed safety system for the at least one engine wherein the safety system is according to claim 12.

14. The method according to claim 2 wherein the first intermediate time period (T1) is between 100 milliseconds and 800 milliseconds.

15. The method according to claim 2 wherein the second intermediate time period (T2) is between 100 milliseconds and 800 milliseconds.

16. A method for stopping an engine of a rotorcraft in overspeed, the rotorcraft comprising at least one engine, the engine comprising a gas generator and a power assembly, the power assembly comprising at least one power turbine rotated by gases originating from the gas generator, the power assembly comprising at least one power shaft rotationally secured to the power turbine, the power assembly rotating about a longitudinal axis at a speed of rotation (N2); wherein, during a flight, the method consisting of: measuring a current value (N2i) of the speed of rotation reached by the power assembly during a predetermined time period (T); determining a current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ by determining a time derivative of the current value of the speed of rotation; and automatically stopping the engine when the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ changes sign over the predetermined time period (T) from a strictly negative value to a strictly positive value.

17. The method according to claim 16 wherein the stopping step is implemented when the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ is less than or equal to a first predetermined threshold value (S1) during a first intermediate time period (T1) and the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ is then greater than or equal to a second predetermined threshold value (S2) during a second intermediate time period (T2).

18. The method according to claim 17 wherein the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ being expressed as a percentage of the current value N2i per second (% N2i.Math.s.sup.−1), the first predetermined threshold value S1 is between −50% N2i.Math.s.sup.−1 and −100% N2i.Math.s.sup.−1.

19. The method according to claim 17 wherein the current derivative $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$ is expressed as a percentage of the current value (N2i) per second (% N2i.Math.s.sup.−1), the second predetermined threshold value (S2) is between +50% N2i.Math.s.sup.−1 and +200% N2i.Math.s.sup.−1.

20. The method according to claim 16 wherein the first intermediate time period (T1) is less than 1 second and the second intermediate time period (T2) is less than 1 second.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure and its advantages appear in greater detail from the following description of examples given by way of illustration with reference to the accompanying figures, in which:

(2) FIG. 1 is a side view of a rotorcraft according to the disclosure;

(3) FIG. 2 is a schematic diagram showing an overspeed safety system according to the disclosure;

(4) FIG. 3 is a diagram showing the variations of a current derivative

(5) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
as a function of time, according to the disclosure;

(6) FIG. 4 is a first logic diagram showing a first variant of the method for stopping a rotorcraft engine in overspeed, according to the disclosure;

(7) FIG. 5 is a second logic diagram showing a second variant of the method for stopping a rotorcraft engine in overspeed, according to the disclosure;

(8) FIG. 6 is a third logic diagram showing a third variant of the method for stopping a rotorcraft engine in overspeed, according to the disclosure; and

(9) FIG. 7 is a fourth logic diagram showing a fourth variant of the method for stopping a rotorcraft engine in overspeed, according to the disclosure.

DETAILED DESCRIPTION

(10) Elements present in more than one of the figures are given the same references in each of them.

(11) As mentioned above, the disclosure relates to a method for stopping a rotorcraft engine, to an overspeed safety system and to a rotorcraft thus equipped.

(12) As shown in FIG. 1, such a rotorcraft 1 comprises at least one engine 10 rotating at least one rotor 2 contributing at least to the lift of the rotorcraft 1 in the air. In addition, the engine(s) 10 are connected to a power transmission system 3.

(13) Such an engine 10 may conventionally be a turboshaft engine and comprise a gas generator 11 and a power assembly 19.

(14) As shown in FIG. 2, the power assembly 19 comprises at least one power turbine 15 rotated by gases originating from the gas generator 11 and at least one power shaft 16 rotationally secured to the power turbine 15.

(15) A rotating assembly 13 of the gas generator 11 may in particular comprise a compressor and an expansion turbine having a degree of rotational mobility about a longitudinal axis AX and rotating on themselves at a speed referred to as the “speed of rotation N1” relative to a casing of the gas generator 11.

(16) Similarly, the power assembly 19 may also have a degree of rotational mobility about a longitudinal axis AX relative to a chassis and rotate on itself at a speed referred to as the “speed of rotation N2”.

(17) In addition, the rotorcraft 1 may be equipped with an overspeed safety system 20. This overspeed safety system 20 comprises a speed sensor 30 for measuring a current value N2i of the speed of rotation N2 reached by the power assembly 19 during a predetermined time period T.

(18) Such a speed sensor 30 may comprise, for example, an electromagnetic sensor positioned opposite a phonic wheel rotationally secured to the power shaft 16.

(19) Such a phonic wheel may comprise teeth arranged at a peripheral zone, these teeth being distributed circumferentially at regular intervals. As the teeth of the phonic wheel pass in front of the speed sensor 30, they may in particular modify a magnetic field and generate an alternating current in a coil of the speed sensor 30, the frequency of which is proportional to the speed of rotation of the power shaft 16.

(20) The overspeed safety system 20 also comprises a shut-down system 25 for stopping operation of the engine 10 when detection conditions are fulfilled.

(21) Such a shut-down system 25 may include a fuel metering valve that delivers fuel to the gas generator 11.

(22) This shut-down system 25 may also include at least one pump that delivers fuel to the gas generator 11.

(23) The overspeed safety system 20 also comprises a processing unit 21 connected by wired or wireless means both to the speed sensor 30 and to the shut-down system 25.

(24) This processing unit 21 may, for example, comprise at least one processor and at least one memory, at least one integrated circuit, at least one programmable system, or at least one logic circuit, these examples not limiting the scope given to the expression “processing unit”. The term “processor” may refer equally to a central processing unit or CPU, a graphics processing unit or GPU, a digital signal processor or DSP, a microcontroller, etc.

(25) The processing unit 21 makes it possible to calculate a derivative of the current value N2i of the speed of rotation N2 referred to as the “current derivative”

(26) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
during a predetermined time period T.

(27) As shown in FIG. 3, the current derived values

(28) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
can vary as a function of time and, for example, oscillate around a zero value.

(29) The processing unit 21 then compares the current derivative

(30) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
with first and second predetermined threshold values S1 and S2. Such first and second predetermined threshold values S1 and S2 can be defined in different ways and, in particular, by computer simulations, by flight tests and/or by trials. The first and second predetermined threshold values S1 and S2 and the first and second intermediate time periods T1 and T2 are also specific to each rotorcraft and, for the same rotorcraft, can vary as a function of different parameters linked, for example, to the type of mission of the rotorcraft and/or its mass.

(31) Furthermore, these first and second predetermined threshold values S1 and S2 and first and second intermediate time periods T1 and T2 may be constant values stored in a memory on board the rotorcraft.

(32) Alternatively, the first and second predetermined threshold values S1 and S2 and the first and second intermediate time periods T1 and T2 can also be determined during flight and vary over time according to predetermined calculation laws stored in a memory on board the rotorcraft.

(33) The shut-down system 25 controls the stopping of the engine(s) 10 when the current derivative

(34) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
changes sign over the predetermined time period T from a strictly negative value to a strictly positive value.

(35) In practice, the shut-down system 25 can stop the engine(s) 10 when the current derivative

(36) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
is less than or equal to a first predetermined threshold value S1 during a first intermediate time period T1, and the current derivative

(37) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
is then greater than or equal to a second predetermined threshold value S2 during a second intermediate time period T2.

(38) For example, the first predetermined threshold value S1 is between −50% N2i.Math.s.sup.−1 and −100% N2i.Math.s.sup.−1 and the second predetermined threshold value S2 is between +50% N2i.Math.s.sup.−1 and +200% N2i.Math.s.sup.−1.

(39) The first intermediate time period T1 and the second intermediate time period T2 are respectively less than 1 second and are preferably between 100 milliseconds and 800 milliseconds. Added together, the first intermediate time period T1 and the second intermediate time period T2 are equal to the predetermined time period T.

(40) As shown in FIGS. 4 to 7, the disclosure also relates to a method for stopping an engine 10 of a rotorcraft 1 in overspeed.

(41) Thus, as shown in FIG. 4, a first variant of the method for stopping an engine 10 of a rotorcraft 1 in overspeed comprises a measurement step 42 for measuring the current value N2i of the speed of rotation N2 reached by the power assembly 19 during the predetermined time period T.

(42) The method 40 then includes a determination step 43 for determining the current derivative

(43) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right).$

(44) Finally, the method 40 implements a stopping step 45 for automatically stopping the engine 10 when the current derivative

(45) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
changes sign over the predetermined time period T from a strictly negative value to a strictly positive value.

(46) According to a second variant of the method 50 shown in FIG. 5, the stopping of the engine 10 may be conditioned by at least one other parameter. Thus, the method 50 may comprise a step of measuring a current value N1i of the speed of rotation N1 reached by the gas generator 11.

(47) The method 50 then implements a measurement step 52 for measuring the current value N2i of the speed of rotation N2 reached by the power assembly 19 during the predetermined time period T, a step 53 for determining the current derivative

(48) 0$\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
and a stopping step 55 for automatically stopping the engine 10.

(49) According to this second variant of the method 50, the stopping step 55 makes it possible to automatically stop the engine when the current value N1i of the speed of rotation N1 is greater than a third predetermined threshold value S3, and the current derivative

(50) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
then changes sign over the predetermined time period T from a strictly negative value to a strictly positive value.

(51) According to a third variant of the method 60 shown in FIG. 6, a measurement step 61 may alternatively be implemented to measure a current value Tqi of an engine torque Tq transmitted to the power shaft 16.

(52) As in the two preceding variants, the method 60 then implements a measurement step 62 for measuring the current value N2i of the speed of rotation N2 reached by the power assembly 19 during the predetermined time period T, a step 63 for determining the current derivative

(53) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
and a stopping step 65 for automatically stopping the engine 10.

(54) According to this third variant of the method 60, the stopping step 65 then makes it possible to automatically stop the engine 10 when the current value Tqi of the engine torque Tq is greater than a fourth predetermined threshold value S4, and the current derivative

(55) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
then changes sign over the predetermined time period T by passing from a strictly negative value to a strictly positive value.

(56) According to a fourth variant of the method 70 shown in FIG. 7, the method implements a measurement step 72 for measuring the current value N2i of the speed of rotation N2 reached by the power assembly 19 during the predetermined time period T, a step 73 for determining the current derivative

(57) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right),$
a step 74 for processing this current derivative

(58) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
in order to filter the current derivative

(59) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
and/or calculate an average value of the current derivative

(60) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right),$
and a stopping step 75 for automatically stopping the engine 10.

(61) This stopping step 75 makes it possible to automatically stop the engine 10 when the filtered and/or averaged current derivative

(62) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
changes sign over the predetermined time period T from a strictly negative value to a strictly positive value.

(63) Naturally, in addition to a change of sign, the filtered and/or averaged current derivative

(64) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
can be used to stop the engine(s) 10 when this filtered and/or averaged current derivative

(65) 0$\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
is less than or equal to the first predetermined threshold value S1 during a first intermediate time period T1, and this filtered and/or averaged current derivative

(66) $\left(\frac{\mathrm{dN}2i}{\mathrm{dt}}\right)$
is then greater than or equal to a second predetermined threshold value S2 during a second intermediate time period T2.

(67) Naturally, the present disclosure is subject to numerous variations as regards its implementation. Although several implementations are described above, it should readily be understood that an exhaustive identification of all possible embodiments is not conceivable. It is naturally possible to replace any of the means described with equivalent means without going beyond the ambit of the present disclosure.