Regulation system for controlling the vibratory behavior and/or the twisting stability of a drivetrain, a rotorcraft fitted with such a regulation system, and an associated regulation method

Abstract

A regulation system for controlling the vibratory behavior in twisting and/or the twisting stability of a drivetrain of a rotorcraft, the regulation system comprising two regulation loops that are interleaved one in the other, the two regulation loops being arranged in cascade relative to each other to regulate firstly a first speed of rotation NG of a gas generator of at least one turboshaft engine driving said drivetrain in rotation, and secondly a second speed of rotation NTL of a free turbine of the engine(s).

Claims

1. A regulation system for controlling vibratory behavior in twisting and/or twisting stability of a drivetrain of a rotorcraft, the regulation system comprising two regulation loops that are interleaved one another, the regulation loops being arranged in cascade relative to each other to regulate firstly a first speed of rotation NG of a gas generator of at least one turboshaft engine driving the drivetrain in rotation, and secondly a second speed of rotation NTL of a free turbine of the turboshaft engines(s), the regulation system comprising at least: a fuel metering member controlled by a control device, the control device responding to a fuel flow rate setpoint (Set) to generate a metering command (Met) for fuel that is to be injected into the turboshaft engine(s); first measurement means for measuring a first measured speed of rotation (NG.sub.measured) of the gas generator of the turboshaft engine(s); a first comparator for generating a first difference (.sub.NG) of a first regulation loop, the first difference (.sub.NG) being generated by comparing a first setpoint (NG.sub.set) for the first speed of rotation with the first measured speed of rotation (NG.sub.measured) a first corrector for correcting the first difference (.sub.NG) and for generating the fuel flow rate setpoint (Set); second measurement means for measuring a second measured speed of rotation (NTL.sub.measured) of the free turbine of the engine(s); a filter for filtering the second measured speed of rotation (NTL.sub.measured) and for generating a filtered signal (NTL.sub.filtered); a second comparator for generating a second difference (.sub.NTL) of a second regulation loop, the second difference (.sub.NTL) being generated by comparing a second setpoint (NTL.sub.set) for the second speed of rotation with the filtered signal (NTL.sub.filtered); and a second corrector for correcting the second difference (.sub.NTL) and for generating the first setpoint (NG.sub.set) for the first speed of rotation; wherein the filter is of adaptive type, the regulation system including computation means for determining filter coefficients of the filter, the filter coefficients being variable and associated with the filter in recursive manner by the computation means for controlling the vibratory behavior in twisting and/or the twisting stability of the drivetrain of the rotorcraft, wherein the filter is a band-stop type filter in order to stop a frequency band including a frequency of a first resonant mode in twisting of the drivetrain, and wherein the filter is a second order filter, the filter being defined by a transfer function of the following form: $\frac{\mathrm{NTLfiltered}}{\mathrm{NTLmeasured}}=\frac{\left(1+\frac{2Z1p}{W1p}p+\frac{1}{W1p^2}{p}^2\right)}{\left(1+\frac{2Z2p}{W2p}p+\frac{1}{W2p^2}{p}^2\right)}$ where NTL.sub.measured is the second speed of rotation measured by the second measurement means, NTL.sub.filtered is the filtered signal generated by the filter from the second speed of rotation NTL.sub.measured, W1p, W2p, Z1p, and Z2p correspond to the filter coefficients.

2. The system according to claim 1, wherein the regulation system includes a first memory for storing at least two distinct sets of predetermined values for the filter coefficients (W1p, W2p, Z1p, Z2p), the computation means determining a first set (E1) for application to the filter when the second measured speed of rotation (NTL.sub.measured) lies in a first range [a,b[, a second set (E2) for applying to the filter when the second measured speed of rotation (NTL.sub.measured) lies in a second range [b,c[, and an n.sup.th set (En) for applying to the filter when the second measured speed of rotation (NTL.sub.measured) lies in an n.sup.th range [x1,x].

3. The system according to claim 1, wherein the system includes an accelerometer for measuring vibration to which the rotorcraft is subjected, a measurement member for measuring frequency of rotation (f.sub.rot) of a main rotor of the rotorcraft, and a second memory for storing at least one threshold value for a vibration amplitude, the computation means acting, when the measured amplitude of the vibration is greater than the threshold value(s) for a predetermined duration, in order to modify the filter coefficients so that the frequency band stopped by the filter (F2) includes the frequency of rotation (f.sub.rot) of the main rotor.

4. The system according to claim 1, wherein the second corrector implements a transfer function including fixed gains regardless of the value of the second measured speed of rotation (NTL.sub.measured).

5. A rotorcraft fitted with a regulation system for controlling vibratory behavior in twisting and/or twisting stability of a drivetrain of the rotorcraft, the regulation system having two regulation loops interleaved one another, the two regulation loops being arranged in cascade relative to each other, in order to regulate firstly a first speed of rotation NG of a gas generator of at least one turboshaft engine driving the drivetrain in rotation, and secondly a second speed of rotation NTL of a free turbine of the turboshaft engine(s), wherein the regulation system is according to claim 1.

6. A regulation method for controlling vibratory behavior in twisting and/or twisting stability of a drivetrain of a rotorcraft, the regulation method implementing two regulation loops that are interleaved one another, the regulation loops being arranged in cascade relative to each other to regulate firstly a first speed of rotation NG of a gas generator of at least one turboshaft engine driving the drivetrain in rotation, and secondly a second speed of rotation NTL of a free turbine of the turboshaft engine(s), the regulation method comprising at least: a fuel metering member controlled by a control device, the control device, responding to a fuel flow rate setpoint (Set) to generate a metering command (Met) for fuel that is to be injected into the turboshaft engine(s); a first measurement means for measuring, a first measured speed of rotation (NG.sub.measured) of the gas generator of the engine(s); a first comparison step for generating a first difference (.sub.NG) of a first regulation loop, the first difference (.sub.NG) being generated by comparing a first setpoint (NG.sub.set) for the first speed of rotation with the first measured speed of rotation (NG.sub.measured) a first correction step for correcting the first difference (.sub.NG) and for generating the fuel flow rate setpoint (Set); a second measurement means for measuring a second measured speed of rotation (NTL.sub.measured) of the free turbine of the turboshaft engine(s); a filtering step for filtering the second measured speed of rotation (NTL.sub.measured) and for generating a filtered signal (NTL.sub.filtered); a second comparison step for generating a second difference (.sub.NTL) of a second regulation loop, the second difference (.sub.NTL) being generated by comparing a second setpoint (NTL.sub.set) for the second speed of rotation with the filtered signal (NTL.sub.filtered); and a second correction step for correcting the second difference (.sub.NTL) and for generating the first setpoint (NG.sub.set) for the first speed of rotation; wherein the filtering step is performed by a filter of adaptive type, the regulation method including at least one calculation step for determining filter coefficients of the filter, the filter coefficients being variable and associated with the filter in recursive manner during the calculation step(s) to control the vibratory behavior in twisting and/or the twisting stability of the drivetrain of the rotorcraft, wherein the filtering step stops a frequency hand including the frequency of a first resonant mode in twisting of the drivetrain, and wherein the filtering step is performed by a second order filter, the filter being defined by a transfer function of the following form: $\frac{\mathrm{NTLfiltered}}{\mathrm{NTLmeasured}}=\frac{\left(1+\frac{2Z1p}{W1p}p+\frac{1}{W1p^2}{p}^2\right)}{\left(1+\frac{2Z2p}{W2p}p+\frac{1}{W2p^2}{p}^2\right)}$ where NTL.sub.measured is the second speed of rotation measured by the second measurement means, NTL.sub.filtered is the filtered signal generated by the filter from the second speed of rotation NTL.sub.measured, and W1p, W2p, Z1p, and Z2p correspond to the filter coefficients.

7. The method according to claim 6, wherein the regulation method includes a first storage step for storing at least two distinct sets of predetermined values for the filter coefficients (W1p, W2p, Z1p, Z2p), the calculation step(s) determining a first set (E1) for application to the filter when the second measured speed of rotation (NTL.sub.measured) lies in a first range [a,b[, a second set (E2) for applying to the filter when the second measured speed of rotation (NTL.sub.measured) lies in a second range [b,c[, and an n.sup.th set (En) for applying to the filter when the second measured speed of rotation (NTL.sub.measured) lies in an n.sup.th range [x1, x].

8. The method according to claim 6, wherein the regulation method includes a third measurement step for measuring vibration to which the rotorcraft is subjected, a fourth measurement step for measuring frequency of rotation (f.sub.rot) of a main rotor of the rotorcraft, and a second storage step for storing at least one threshold value for a vibration amplitude, the calculation step(s) acting, when the measured amplitude of the vibration is greater than the threshold value (s) for a predetermined duration, in order to modify the filter coefficients so that the frequency band stopped by the filter includes the frequency of rotation (f.sub.rot) of the main rotor.

9. A regulation system for controlling vibratory behavior in twisting and/or twisting stability of a drivetrain of a rotorcraft, the regulation system comprising two regulation loops in cascade relative to each other to regulate firstly a first speed of rotation NO of a gas generator of an engine driving the drivetrain in rotation, and a second speed of rotation NTL of a free turbine of the engine, the regulation system comprising: a fuel metering device controllable by a control device, the control device respondable to a fuel flow rate setpoint (Set) to generate a metering command (Met) for fuel to be injected into the engine; a first measurement device for measuring a first measured speed of rotation (NG.sub.measured) of the gas generator of the engine; a first comparator device for generating a first difference (.sub.NG) of a first regulation loop, the first difference (.sub.NG) being generated by comparing a first setpoint (NG.sub.set) for the first speed of rotation with the first measured speed of rotation (NG.sub.measured) a first correction device for correcting the first difference (.sub.NG) and for generating, the fuel flow rate setpoint (Set); a second measurement device for measuring a second measured speed of rotation (NTL.sub.measured) of the free turbine of the engine; a filter for filtering the second measured speed of rotation (NTL.sub.measured) and for generating a filtered signal (NTL.sub.filtered); a second comparator device for generating a second difference (.sub.NTL) of a second regulation loop, the second difference (.sub.NTL) being generated by comparing a second setpoint (NTL.sub.set) for the second speed of rotation with the filtered signal (NTL.sub.filtered); and a second correction device for correcting the second difference (.sub.NTL) and for generating the first setpoint (NG.sub.set) for the first speed of rotation; wherein the filter is an adaptive type, the regulation system including a computation device means for determining filter coefficients of the filter, the filter coefficients being variable and associated with the filter in recursive manner by the computation device for controlling the vibratory behavior in twisting and/or the twisting stability of the drivetrain of the rotorcraft, wherein the filter is a band-stop type filter in order to stop a frequency band including a frequency of a first resonant mode in twisting of the drivetrain, and wherein the filter is a second order filter, the filter being defined by a transfer function of the following form: $\frac{\mathrm{NTLfiltered}}{\mathrm{NTLmeasured}}=\frac{\left(1+\frac{2Z1p}{W1p}p+\frac{1}{W1p^2}{p}^2\right)}{\left(1+\frac{2Z2p}{W2p}p+\frac{1}{W2p^2}{p}^2\right)}$ Where NTL.sub.measured is the second speed of rotation measured by the second measurement means, NTL.sub.filtered is the filtered signal generated by the filter from the second speed of rotation NTL.sub.measured, and W1p, W2p, Z1p, and Z2p correspond to the filter coefficients.

10. The system according to claim 9, wherein the regulation system includes a first memory for storing at least two distinct sets of predetermined values for the filter coefficients (W1p, W2p, Z1p, Z2p), the computation device determining a first set (E1) for application to the filter when the second measured speed of rotation (NTL.sub.measured) lies in a first range [a,b[, a second set (E2) for applying to the filter when the second measured speed of rotation (NTL.sub.measured) lies in a second range [b, c[, and an n.sup.th set (En) for applying to the filter when the second measured speed of rotation (NTL.sub.measured) lies in an n.sup.th range [x1,x].

11. The system according to claim 9, wherein the system includes an accelerometer for measuring vibration to which the rotorcraft is subjected, a measurement device for measuring frequency of rotation (f.sub.rot) of a main rotor of the rotorcraft, and a second memory for storing a threshold value for a vibration amplitude, the computation device acting, when the measured amplitude of the vibration is greater than the threshold value for a predetermined duration, in order to modify the filter coefficients so that the frequency band stopped by the filter includes the frequency of rotation (f.sub.rot) of the main rotor.

12. The system according to claim 9, wherein the second correction device implements a transfer function including fixed gains regardless of the value of the second measured speed of rotation (NTL.sub.measured).

13. A rotorcraft fitted with the regulation system according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 is a block diagram showing a regulation system in accordance with the invention;

(3) FIG. 2 is a block diagram showing a first example of a regulation system in accordance with the invention;

(4) FIG. 3 is a block diagram showing a second example of a regulation system in accordance with the invention;

(5) FIG. 4 is a side view of a helicopter fitted with a regulation system in accordance with the invention;

(6) FIG. 5 is a flow chart showing a regulation method in accordance with the invention;

(7) FIG. 6 is a flow chart showing a first variant of a regulation method in accordance with the invention; and

(8) FIG. 7 is a flow chart showing a second variant of the regulation method in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

(9) Elements present in several distinct figures may be given the same references in each of them.

(10) As mentioned above, the invention thus relates to a regulation system for controlling the stability in twisting of a drivetrain of a rotorcraft.

(11) As shown in FIG. 1, such a regulation system 1, 11 has two regulation loops 4 and 5 interleaved one in the other, these two regulation loops 4 and 5 being arranged in cascade relative to each other, by using first measurement means 9 and second measurement means 19 respectively for measuring a first speed of rotation NG.sub.measured of a gas generator of a turboshaft engine 6 and a second speed of rotation NTL.sub.measured of a free turbine of the engine 6.

(12) The regulation system 1, 11 also has a fuel metering member 7 for injecting fuel into the engine 6. Such a fuel metering member 7 is thus controlled by a control device 8 suitable for generating a metering command Met as a function of a fuel flow rate setpoint Set.

(13) A first comparator Comp1 serves to compare a first setpoint NG.sub.set for the first speed of rotation with the first speed of rotation NG.sub.measured from the first measurement means 9. The first comparator Comp1 then generates a first difference .sub.NG specific to the first regulation loop 4 and a first corrector Corr1 uses this first difference .sub.NG to generate the fuel flow rate setpoint Set.

(14) In the second regulation loop 5, a filter F1, F2 serves to filter the second speed of rotation NTL.sub.measured as transmitted by the second measurement means 19 and thus generates a filtered signal NTL.sub.filtered. Such a filter F1, F2 may for example be a filter of the band-stop type, thus making it possible to eliminate a frequency band that includes a first resonant mode in twisting of the drivetrain of the rotorcraft.

(15) A second comparator Comp2 then serves to compare a second setpoint NTL.sub.set for the second speed of rotation with the filtered signal NTL.sub.filtered. On the basis of this comparison, the second comparator Comp2 thus generates a second difference .sub.NTL for the second regulation loop 5.

(16) Finally, this second difference .sub.NTL is corrected by a second corrector Corr2 in order to generate the first setpoint NG.sub.set.

(17) The filter F1, F2 is remarkable in that it is of adaptive type, with the filter coefficients of the filter F1, F2 being variable over time so as to at least guarantee stability in twisting of the drivetrain of the rotorcraft in which the speed of rotation NR of the main rotor is variable, in particular in order to respond to constraints concerning sound level in the environment and/or in order to limit blade tip speed at high speeds of advance of the rotorcraft.

(18) In addition, the regulation system 1, 11 has computation means 2, 12 acting recursively to determine the filter coefficients for applying to the filter F1, F2. Such computation means 2, 12 are thus suitable for acting in real time, e.g. while the rotorcraft is in flight, to modify the filter coefficients of the filter F1, F2.

(19) In practice, the filter F1, F2 may be a second order filter, thus making it possible to obtain optimized performance by presenting a transfer function of the form:

(20) $\frac{\mathrm{NTLfiltered}}{\mathrm{NTLmeasured}}=\frac{\left(1+\frac{2Z1p}{W1p}p+\frac{1}{W1p^2}{p}^2\right)}{\left(1+\frac{2Z2p}{W2p}p+\frac{1}{W2p^2}{p}^2\right)}$
where NTL.sub.measured is the second speed of rotation as measured by the second measurement means, NTL.sub.filtered is the filtered signal generated from the second speed of rotation NTL.sub.measured, and W1p, W2p, Z1p, and Z2p correspond to the filter coefficients.

(21) Furthermore, there are various ways of setting the computation means 2, 12 in order to determine the filter coefficients F1, F2.

(22) Thus, in a first embodiment of the regulation system 1 as shown in FIG. 2, the regulation system 1 may include a first memory 21. Under such circumstances, the computation means 2 may be connected to the first memory 21 for storing various sets E1, E2, . . . , En of predetermined values for the filter coefficients W1p, W2p, Z1p, and Z2p.

(23) The computation means 2 can then give the filter F1 a set of predetermined values for the filter coefficients as a function of the value of the second measured speed of rotation NTL.sub.measured. For example, the computation means 2 may monitor the current value of the second measured speed of rotation NTL.sub.measured and select a first set E1 when the second measured speed of rotation NTL.sub.measured lies in a first range [a,b[, a second set E2 when the second measured speed of rotation NTL.sub.measured lies within a second range [b,c[, and an n.sup.th set En when the second measured speed of rotation NTL.sub.measured lies in an n.sup.th range [x1,x].

(24) In a second embodiment of the regulation system 11 as shown in FIG. 3, the regulation system 11 may include an accelerometer 22 for measuring the vibration to which the rotorcraft is subjected. The regulation system 11 then also has a measurement member 23 for measuring the frequency of rotation f.sub.rot of a main rotor 24 of the rotorcraft 13, as shown in FIG. 4.

(25) In addition, the regulation system 11 also has a second memory 25 for storing at least one threshold value for an amplitude of vibration to which the rotorcraft 13 is subjected.

(26) The accelerometer 22, the measurement member 23, and the second memory 25 are then connected to the computation means 12 that act when the measured amplitude of the vibration is greater than the threshold value for a predetermined duration to modify the filter coefficients so that the frequency band stopped by the filter F2 includes the frequency of rotation f.sub.rot of the main rotor 24 of the rotorcraft 13.

(27) As shown in FIG. 4, the invention also relates to a rotorcraft 3, 13 having a regulation system 1, 11 as described above with reference to FIGS. 1 to 3. Such a regulation system 1, 11 thus makes it possible to control the vibratory behavior in twisting and/or the twisting stability of the drivetrain 10 of the rotorcraft 3, 13 at the outlet from the turboshaft engine 6. Such a drivetrain 10 generally comprises a main power transmission gearbox (MGB) and power transmission shafts serving to transmit rotary motion from the engine 6 to a main rotor 24.

(28) As shown in FIGS. 5 to 7, the invention also relates to a regulation method 30, 40 for controlling the vibratory behavior in twisting and/or the twisting stability of the drivetrain 10 of the rotorcraft 3, 13.

(29) As shown in FIG. 5, such a regulation method 30, 40 thus includes a step 37 of metering fuel under the control of the control device 8. Such a control device 8 acts on the basis of a fuel flow rate setpoint Set to generate a fuel metering command Met for metering the fuel that is to be injected into the engine(s) 6.

(30) The regulation method 30, 40 also has a first measurement step 39 for measuring a first speed of rotation NG.sub.measured of a gas generator of the engine(s) 6 of the rotorcraft 3, 13.

(31) The regulation method 30, 40 then performs a first comparison step 31 in order to generate a first difference .sub.NG of the first regulation loop 4. As mentioned above, the first difference .sub.NG is then generated by comparing a first setpoint NG.sub.set for the first speed of rotation with the first measured speed of rotation NG.sub.measured.

(32) The regulation method 30, 40 then includes a first correction step 32 for correcting the first difference .sub.NG and generating the fuel flow rate setpoint Set.

(33) A second measurement step 49 serves to measure a second speed of rotation NTL.sub.measured of a free turbine of the engine(s) 6. Thereafter, a filtering step 33 filters the second measured speed of rotation NTL.sub.measured and generates a filtered signal NTL.sub.filtered. Such a filtering step 33 is performed by a filter F1, F2 of adaptive type, which may be a second order filter of the band-stop type, for example.

(34) The regulation method 30, 40 also has a second comparison step 34 for generating a second difference .sub.NTL of the second regulation loop 5. This second difference .sub.NTL is obtained by comparing a second setpoint NTL.sub.set for the second speed of rotation with the filtered signal NTL.sub.filtered.

(35) Furthermore, a second correction step 35 serves to correct the second difference .sub.NTL and to generate the first setpoint NG.sub.set.

(36) Such a regulation method 30, 40 finally includes at least one calculation step 36, 46 in order to determine the filter coefficients of the filter F1, F2. Specifically, these filter coefficients are variable and they are given to the filter F1, F2 in recursive manner during the calculation step 36, 46. The filter coefficients are then selected so as to act constantly to control the vibratory behavior in twisting and/or the twisting stability of the drivetrain 10 of the rotorcraft 3, 13.

(37) Naturally, such a calculation step 36, 46 may be performed in various ways.

(38) As shown in FIG. 6, in a first variant of the invention, the regulation method 30 may also include a first storage step 38 for storing at least two distinct sets E1, E2, . . . , En of predetermined values for the filter coefficients W1p, W2p, Z1p, and Z2p.

(39) Under such circumstances, the calculation step 36 then serves to apply a first set E1 to the filter F1 when the second measured speed of rotation NTL.sub.measured lies in a first range [a,b[, a second set E2 to the filter F1 when the second measured speed of rotation NTL.sub.measured lies in a second range [b,c[, and an n.sup.th set En to the filter F1 when the second measured speed of rotation NTL.sub.measured lies in an n.sup.th range [x1,x].

(40) In a second variant of the invention, as shown in FIG. 7, the regulation method 40 may alternatively include a third measurement step 41 for measuring the vibration to which the rotorcraft 13 is subjected, a fourth measurement step 42 serving to measure the frequency of rotation f.sub.rot of the main rotor 24 of the rotorcraft 13, and a second storage step 43 for storing at least one threshold value for a vibration amplitude.

(41) In this second variant of the invention, the calculation step 46 serves, when the measured amplitude of the vibration is greater than the threshold value for a predetermined duration, to modify the filter coefficients so that the frequency band stopped by the filter F2 includes the frequency of rotation f.sub.rot of the main rotor 24.

(42) Naturally, the present invention may be subjected to numerous variations as to its implementation. Although several embodiments are described, it will readily be understood that it is not conceivable to identify exhaustively all possible embodiments. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the invention.