Idle speed maintenance control method and device

Abstract

The present invention relates to a method for controlling a turbine engine, comprising: - detecting the speed of an engine shaft of the turbine engine below an idle speed; - detecting the saturation of the fuel setpoint; - selecting a combined fuel and torque control loop from at least one single-variable engine control loop; - determining, in a combined manner, a value representative of a fuel setpoint and a value representative of a torque setpoint such that the torque setpoint compensates for the saturation of the fuel setpoint so as to allow a stabilised turbine engine speed to be maintained.

Description

[0001]Description Title of the invention: device and method for controlling idle speed maintenance Technical field The invention relates to the field of blocker-unscrewer type engines and more particularly to the control of such an engine for its maintenance at idle speed. Prior art Ensuring the correct operation of the engine, particularly when the engine is fitted to an aircraft, is a constant concern for manufacturers. Several parameters linked to the engine environment are taken into account during design and controlled during operation so as to apply the correct instructions to the engine to ensure correct operation during all phases, and particularly during all phases of flight when the engine is on board an aircraft. Furthermore, the design of a turbomachine requires taking into account a sufficient margin against the so-called surge phenomenon.This phenomenon, which results from an excessive impact of the air flow on the blades of one of the compressors, results in significant and rapid fluctuations in the pressure downstream of the compressor concerned and can lead to a flameout of the combustion chamber. It also generates significant jolts on the compressor blades and can thus lead to mechanical damage. It is therefore particularly important to avoid its occurrence. Among the parameters to be taken into account when designing a turbomachine, the correction of the fuel stop according to the air bleed, when it is underestimated, can lead to an insufficient pumping margin of the engine's high-pressure compressor, leading to a fuel setpoint below the stabilized operating line, causing the engine to run out of steam. Solutions exist to overcome this drawback, in particular by adding a wastegate.This relief valve is controlled to open below a high-pressure compressor speed threshold and thus allows pumping margin to be regained at the high-pressure compressor. However, such a solution based on a pumping valve has the disadvantage of having to size the pumping valve to take into account changes in demand and therefore generates a cost in terms of mass and size. In addition to maintaining the high-pressure regime to avoid unscrewing, there is also a need to maintain the low-pressure regime in an aircraft.Presentation of the invention The invention makes it possible to overcome at least one of the drawbacks of the prior art and proposes for this purpose a method for controlling a turbomachine comprising: - the detection of a speed of a drive shaft of the turbomachine below an idle speed; - the detection of a saturation of the fuel setpoint; - the selection of a combined fuel and torque control loop from at least one single-variable engine control loop and, - the determination, in a combined manner, of a value representative of a fuel setpoint and a value representative of a torque setpoint such that said torque setpoint compensates for the saturation of said fuel setpoint to allow a stabilized speed of said turbomachine to be maintained.According to certain embodiments, said turbomachine having a high pressure body, said speed is the speed of said high pressure body and said determined torque setpoint allows maintenance of the stabilized speed at idle of said turbomachine to avoid unscrewing of said engine. According to certain embodiments, said turbomachine having a low pressure body, said speed is the speed of said low pressure body and said determined torque setpoint allows maintenance of the stabilized speed at idle of said engine. According to certain embodiments, the determination of values ​​representative of a fuel setpoint and a torque setpoint comprises, in said combined control loop, the calculation of a fuel increment and a torque setpoint increment relative to a previous instant.According to certain embodiments, the combined torque and fuel setpoints for a current instant are determined from - sequencing parameters, - a value representative of the engine shaft speed at the current instant and at the previous instant - an idle setpoint value, - torque and fuel setpoint values ​​calculated at a previous instant According to certain embodiments, the method comprises in said combined control loop - determining a variation (∆^^, ∆^^)^of the engine shaft speed between the current instant and the previous instant, - determining a difference (^^^, ^^^)^between said idle setpoint value and the value representative of the engine shaft speed at the current instant, - determining a difference. ^ ∆^^ ^ , ∆^^^ ^ )^between the fuel and torque increment at the output of said control loop and an increment calculated from the difference between two previous determined setpoint values, -the determination of a state vector representative of the engine shaft speed at the following instant ^∆^^ ^^^ , ∆^^ ^^^ )^and a difference between said idle setpoint value and the engine shaft speed at the following instant (^^^ ^^^ , ^^^ ^^^ )^according to: Δ^^^^ [MATH. 1] ^ ^^^^^^ ^ 0 ^^^^ ^ ^^^^^ ^ = ^ − ^ ^ ^ ^ ^^^ ^ + ^ ^ ^0 ^ ^ ^ Δ^^^^^^ ^ + ^ 0 ^^ ∆^^ ^ for the low pressure motor shaft or ^ 0 ^^^^ ^ Δ^^^^ ^ 0 ^ for the high pressure motor shaft A, B and I being determined constants, ∆^^ ^ being the difference between the low pressure regime setpoint at time k and at time k-1, ∆^^ ^being the difference between the high pressure speed setpoint at time k and at time k- 1, - the determination of a gain matrix K, - obtaining the fuel increment and the torque setpoint increment relative to a previous time being obtained according to the following formula: for the high pressure motor shaft and for the low pressure engine shaft. According to certain embodiments, the method comprises an integration of the torque and fuel increment obtained at the output of the control loop according to the following formulas: [MATH. 5] ^^ ^ = ∆^^ ^ +^^^ ^"^ and [MATH. 6] ^^^ ^ = ∆^^^ ^ +^^^^ ^"^The present invention also relates to a computer program comprising instructions for implementing a control method according to the present invention when said computer program is executed by a computer. The present invention also relates to a computer-readable recording medium on which a computer program according to the present invention is recorded.The present invention also relates to a control device, in a turbomachine, comprising one or more processors configured to - detect a speed of a drive shaft of the turbomachine below an idle speed and - detect a saturation of the fuel setpoint, and following said detections, - select a combined fuel and torque control loop from among at least one mono-variable engine control loop - determine, in a combined manner, a value representative of a fuel setpoint and a value representative of a torque setpoint such that said torque setpoint compensates for the saturation of said fuel setpoint to allow a stabilized speed of said turbomachine to be maintained. Brief description of the drawings [Fig. 1] Figure 1 is a schematic representation of a turbomachine according to embodiments of the present invention. [Fig.2] Figure 2 is a schematic representation of a control device according to embodiments of the present invention. [Fig. 3] Figure 3 is a schematic representation of an anti-unscrewing loop. Description of the Embodiments As illustrated in Figure 1, an aircraft engine assembly 100 according to one embodiment may comprise a turbomachine 200, a first electric motor 300 and a second electric motor 400, and a control unit 500. The turbomachine 200 may comprise a low pressure shaft 210 and a high pressure shaft 220. The low pressure shaft 210 and the high pressure shaft 220 may be arranged coaxially, as illustrated.The turbomachine 200 may also comprise a low-pressure compressor 230, a high-pressure compressor 240, a combustion chamber 250, a high-pressure turbine 260, a low-pressure turbine 270, and an exhaust nozzle 275, arranged successively in the direction of flow in an annular vein of working fluid, so that air admitted upstream of the low-pressure compressor 230 is successively compressed in the low-pressure compressor 230 and in the high-pressure compressor 240, to then generate in the combustion chamber 250 hot combustion gases by combustion of a fuel injected into this combustion chamber 250. These combustion gases can then be successively expanded in the high-pressure turbine 260 and in the low-pressure turbine 270, so as to actuate them in rotation, before escaping through the nozzle 275.The high-pressure shaft 220 may be mechanically coupled to the high-pressure turbine 260 and the high-pressure compressor 240, such that the high-pressure turbine 260 can rotate the high-pressure shaft 220 and the high-pressure compressor 240, while the low-pressure shaft 210 may be mechanically coupled to the low-pressure turbine 270 and the low-pressure compressor 230, such that the low-pressure turbine 270 can rotate the low-pressure shaft 210 and the low-pressure compressor 230. As in the illustrated embodiment, the turbomachine 200 may be a bypass turbojet engine also comprising a fan 280, which may also be mechanically coupled to the low-pressure shaft 230, such that it can also be rotated by the low-pressure turbine 270 through the low-pressure shaft 210.As illustrated, the turbomachine 200 could also comprise a reduction gear 290 interposed between the low-pressure shaft 210 and the fan 280, so that the fan 280 can be driven with a lower rotational speed than the low-pressure shaft 210. However, a fan with direct drive by the low-pressure shaft 210 is also conceivable. Furthermore, other architectures of the turbomachine 200, without a fan, are also conceivable. Thus, the turbomachine 200 could alternatively be a turboprop, with at least one propulsive propeller mechanically coupled to the low-pressure shaft 210 through the reduction gear 290, or a turboshaft engine, with at least one lift rotor mechanically coupled to the low-pressure shaft 210 through the reduction gear 290.It is also conceivable, in particular for a turboshaft or a turboprop, that the turbomachine 200 comprises only a single compressor, mechanically coupled to the high-pressure shaft 210. The first electrical machine 300 may be, as illustrated, configured as a motor-generator to selectively transform electrical energy into mechanical work in motor mode and mechanical work into electrical energy in generator mode. This first electrical machine 300 may be mechanically coupled to the low-pressure shaft 210 to actuate, in motor mode, the low-pressure shaft 210, and to be actuated, in generator mode, by the low-pressure shaft 210. However, it is also conceivable, within the scope of the present invention, that it is configured only as an electrical generator, capable only of transforming mechanical work into electrical energy.Similarly, the second electrical machine 400 may also be, as illustrated, configured as a motor-generator to selectively transform electrical energy into mechanical work in motor mode and mechanical work into electrical energy in generator mode. This motor may be mechanically coupled to the high-pressure shaft 220 to actuate, in motor mode, the high-pressure shaft 220, and to be actuated, in generator mode, by the high-pressure shaft 220. However, it is also conceivable, within the scope of the present invention, that it is configured only as an electrical generator, capable only of transforming mechanical work into electrical energy. The control unit 500 may be an electronic control unit, possibly a full authority digital engine control unit (FADEC).It may in particular take the form of an electronic processor capable of implementing the instructions of a computer program to control the operation of the engine assembly 200. This control unit 500 obtains signals representing operating parameters of the turbomachine 200. This control unit 500 may be connected to the turbomachine 200 to control in particular the supply of fuel to the combustion chamber 250, by providing it with a fuel flow setpoint WF_CMD, as well as to the engine 400 to provide it with a torque setpoint TRQ_CMD to control the injection and / or extraction of mechanical work from the high-pressure shaft 220.The control unit 500 can also be connected to a manual control, such as for example a throttle lever 80, and / or to a flight computer 90, in order to receive an operating instruction from the engine assembly 200, which can for example take the form of a thrust, power, or rotation speed instruction for the low pressure shaft 210 and / or the high pressure shaft 220.The control unit 500 may furthermore be connected to temperature sensors 276 and 277, arranged, respectively, directly downstream and upstream of the low-pressure turbine 270, to receive temperatures of the combustion gases at the outlet of the low-pressure turbine 270 and at the outlet of the high-pressure turbine 260, to one or more pressure sensors (not shown), arranged in the combustion chamber 250 to sense a static pressure at the inlet of the combustion chamber 250 and transmit it to the control unit 500, and to one or more flow sensors (not shown), arranged in a circuit for supplying fuel to the combustion chamber 250. Figure 2 is a schematic representation of a control device 500 according to embodiments of the present invention. As explained previously, the device 500 may be included in a FADEC type control device.The given schematic view can be implemented in the form of software or hardware modules. The control device 500 can comprise a module 520 responsible for obtaining the instructions and limitations specific to the turbomachine 200. In particular, it can be responsible for obtaining parameters of temperature, pressure and engine speed at each instant or at several instants. These parameters are obtained for example by data from the sensors which can be present in the device 100 and more precisely in connection with the operation of the turbomachine 200. These parameters are provided to a module 530 which detects that the engine speed is too low, it can for example be a detection of unscrewing of the turbomachine 200. The detection of unscrewing is done when the engine speed NH of the high pressure shaft is lower than a determined threshold value, for example but not limited to 14950 rpm (revolutions per minute).The module 530 provides an indicator signal to a loop selection module 550 to indicate that a run-out condition of the turbomachine is detected. The detection of a speed hold can be done for any other speed value that it is desired to maintain or below which it is not desirable for the engine to run and can also apply to the low pressure shaft. The control device 500 also comprises a speed hold loop or regulation loop 510 which will be described in more detail with reference to FIG. 3. The speed hold loop 510 provides as output a fuel setpoint as well as a torque setpoint, calculated at the same time interval or simultaneously, or in a combined manner. It makes it possible to maintain an engine speed of the high pressure shaft or a maintenance of the engine speed of the low pressure shaft.In certain embodiments, two holding loops may exist, one for the high pressure shaft 220 and the other for the low pressure shaft 210. The control device 500 also comprises one or more single variable 540 motor loops 540-1 to 540-n which are responsible for delivering fuel and torque commands, these setpoints being calculated individually.These monovariable loops may include engine parameters such as: - A temperature input T2, - A speed input NL of the turbomachine 200, - A speed input NH of the turbomachine 200, - A setpoint speed input NLCONS defined by the position of the control lever that can be manipulated by the pilot of the aircraft, - A setpoint speed input NHCONS defined by the position of the control lever that can be manipulated by the pilot of the aircraft, - A fuel flow setpoint output WF transmitted to the turbomachine 200, - A torque setpoint output WTRQ transmitted to the turbomachine 200, - Protection setpoints at shutdown: minimum HP speed and / or minimum LP speed, - Protection setpoints at low overspeed: maximum HP speed, - Chamber burst protection: maximum PS3 pressure, - Maintenance of the desired air bleed level: minimum PS3 pressure.At least two of these mono-variable loops deliver a fuel setpoint for one and an engine torque setpoint for the other. The loop selection module 550 selects one of the engine loops 540-i, i being a variable between 1 and n, of the module 540 or the speed maintenance loop 510. The selection of the speed maintenance loop is made following the detection of a certain number of parameters: - a deceleration indicator at the value 0, i.e. no deceleration detected and, - the non-detection of events such as extinction, pumping, rotating separation. Other additional and optional parameters can participate individually or cumulatively in the selection of the speed maintenance loop.Examples include: - detecting a speed of the high pressure body of said engine below an idle speed and - detecting a speed of the low pressure body of said engine below an idle speed, - detecting a saturation of the fuel setpoint. The detection of a saturation of the fuel setpoint is done by measuring the difference between: - The CsP stop (richness in the combustion chamber) which is a function of the speed P reduced by the inlet temperature of the HP compressor (T25) and the total pressure at the inlet of said engine (PT2) - The measured CsP which is calculated from the pressure at the inlet of the combustion chamber (PS3), fuel and the inlet temperature of the HP compressor (T25). According to certain embodiments, the selection of the speed maintenance loop could integrate a hysteresis so as to be robust with respect to oscillations.The fuel correction quantity (or increment) ∆WF from the selected loop is supplied to an integration module 560. The integration module 560 determines the fuel flow setpoint WF by integrating the fuel correction quantity ∆WF. The torque correction quantity (or increment) ∆TRQ from the selected loop is also supplied to the integration module 560. The integration module 560 determines the torque flow setpoint TRQ by integrating the torque correction quantity ∆TRQ. The quantities obtained at the output of the module 560 are obtained as follows for an instant k: [MATH. 7] ^^. ^ =^∆^^ ^ +^^^ ^"^ and [MATH. 8] ^^^ ^ =^∆^^^ ^ +^^^^ ^"^The fuel setpoints WF and torque TRQ at the output of the integration module 560 are transmitted to a stop management module 570. The stop management module 570 limits the value of the fuel flow setpoint WF determined by the integration module 560. In a known manner, the stop management module 570 implements a stop, called a C / P stop known to those skilled in the art and not presented in more detail. Preferably, the stop management module 570 determines the stops as a function of the static pressure in the combustion chamber PS3 and the NH regime (high pressure body regime) or the NL regime (low pressure). The stop management module 570 also limits the value of the torque flow setpoint TRQHP determined by the integration module 560. In a known manner, the stop management module 570 implements a stop, called a C / P stop, known to those skilled in the art and not presented in more detail.Preferably, the stop management module 570 determines the stops as a function of the static pressure in the combustion chamber PS3 and the NH speed (high pressure body speed) or the NL speed (low pressure). The stop management module 570 therefore provides the final fuel and torque TRQ setpoints WF as output to the turbomachine. Figure 3 shows a schematic view of the anti-unscrewing loop 510. The anti-unscrewing loop 510 makes it possible to calculate the correct dosage of fuel and torque to be supplied to the turbomachine when unscrewing of the turbomachine is detected. The two quantities, fuel and torque, influence each other and thus a multi-variable anti-unscrewing loop makes it possible to deliver a torque and fuel setpoint making it possible to keep the engine at idle while avoiding unscrewing.Loop 510 is a multivariable loop in the sense that it allows a correction at the same time, or simultaneously, or in a combined manner, to determine a fuel setpoint and a torque setpoint allowing a speed to be maintained at idle. Loop 510 is of the state feedback type with integration of the servo control error of the high pressure NH or low pressure NL speed (class 1 system) to simultaneously calculate the fuel increment setpoint Δ^^^^ and the torque setpoint Δ^^^^^ which allow the high pressure body speed to be maintained at idle or the fuel increment setpoint Δ^^^^ and the torque setpoint Δ^^^^^ which allow the low pressure body speed to be maintained at idle. Loop 510 receives sequencing parameters as input.The sequencing parameters may include parameters relating to flight altitude, pressure (in the different parts of the engine), engine temperature (in the different parts of the engine). It also receives information relating to, or values ​​representative of, the high pressure NH or low pressure NL engine speed at the current instant and information or idle setpoint value as well as the torque and fuel setpoints calculated at the previous calculation step at the output of the module 500. The loop 510 includes a first differentiator 514 which calculates the difference between the engine speed at the current instant k+1 and at the previous instant k, ∆^^ for the high pressure shaft or ∆^^ for the low pressure shaft. The values ​​representative of the previous instant may for example be recorded by the holding loop 510.It also includes a first subtractor 515 which calculates a value ^^^^ for the high pressure shaft or a value ^^^^for the low pressure shaft. This value corresponds to a difference between an engine speed setpoint and an engine speed measurement. In other words, each measurement is associated with a setpoint, the measurement and the setpoint both being in temporal coincidence. The regulation tries to make each measurement closer to the setpoint. The setpoint, which can be an idle setpoint, makes it possible to guarantee the constraints of: - not exceeding the overheating limit at T5 (temperature at the outlet of the low pressure turbine), - maintaining a sufficient pumping margin, - maintaining a sufficient combustion chamber extinction margin, - minimum thrust to be provided.It also includes a second differentiator 517 which calculates the difference between the final setpoint for each of the quantities ^^^^ and ^^^^^ for the high pressure shaft or ^^^^ and ^^^^^ for the low pressure shaft at the output of the module 500 at the previous instant k and at the still previous instant k-1. It also includes a second subtractor 516 which calculates a difference between the value ∆^^ at the output of the second differentiator 517 and the value ∆^^ calculated by the loop 510 at the previous instant as well as a difference between the value ∆^^^ at the output of the second differentiator 517 and the value ∆^^^ calculated by the loop 510 at the previous instant. It is noted here that ∆^^ corresponds either to the value ∆^^^^^ or to the value ∆^^^^^ depending on whether the high pressure or low pressure regime is maintained. Loop 510 also includes a state vector calculation module 512. State vector calculation module 512 receives as input the outputs of modules 514, 515 and 516.According to a first embodiment, the module 512 determines the value ∆NH for the high pressure shaft, at the current time #, noted. ∆NHk respectively ∆NL for the low pressure shaft, at the current time #, noted ∆NL k . This determination is based on a particular modeling of the turbomachine by a linear system also called LTI for “linear time invariant”. This equation represents a synthesis model which makes it possible to link the fuel setpoint / torque setpoint to the engine speed. In this equation, “A” represents a time constant characteristic of the response time of the turbomachine and is therefore linked to it. The term “B” is a static gain establishing a link between a setpoint increment and a speed increment obtained by this setpoint increment once the speed has stabilized. According to a second embodiment, to cancel the dynamic error, also called “lag”, i.e. a delay between a linear variation of the setpoint and the corresponding variation of the engine speed, an augmented synthesis model can be used. This augmented synthesis model determines the values ​​∆NH and ENH at the current time # noted ∆NH k and ENHk for the high pressure shaft and ∆^^ and ^^^ at the current time #, noted ∆^^ ^ and ^^^ ^ for the low pressure shaft The values ​​noted ∆NH k and ENH k are obtained by the following equation: ^ ^^^^ = ^ ^ 0 ^ ^^^^"^ ^ + ^^ Δ^^^^ ^ ^ ^"^ ^ ^ 0 ^ ^ k and k are by: ^ ^^^^ ^ ^ ^ 0 ^^^^"^ ^ ^ ^ Δ^^^^ ^"^ 0 In these equations, according to a particular embodiment, the constant “I” takes the value “1”. The loop 510 also comprises a gain interpolation module 511. The module 511 comprises a matrix K for each point of the operating domain. These interpolation matrices comprise coefficients k i , jwhich represent the state of the turbomachine as a function of the sequencing parameters. Thus, as a function of the sequencing parameters which represent the state of the turbomachine in the operating domain, each coefficient ki,j is interpolated linearly. Determining the gain matrix K amounts to performing “multi-variable computer synthesis”. This synthesis is of the linear quadratic (LQ) state feedback type and consists of minimizing a criterion 'J' or a quantity 'J' in which the weighting matrices Q, R and S appear. These are set at the start of the calculation as a function of the desired behavior of the engine, and in particular as a function of the desired absence of drag.More precisely, it is the choice of the weighting matrices Q, R and S which makes it possible to obtain different settings of the corrector and the desired motor behavior, for example the elimination of dragging, i.e. the minimization of the transfer between the setpoint and the servo error in the sense of standard 2 by constraining the dynamics of the error. For the high pressure shaft:. ^ For the low pressure shaft: ^ Δ^^^^^^ ^ The minimization of the criterion J by the Lagrangian allows us to work with an analytical expression of the gain matrix K in the form: [MATH. 14] ! = ^^ + ^ / ^^) "^ ^^ / ^^ + *) In this analytical expression, the matrices R, B, A and S are known, only the matrix P is discrete Riccati: [MATH. 15] ^0 / ^^0 − ^ − ^^0 / ^ + *)1^2 / ^^2 "^+ ^3 ^^2 / ^^0 + * / ) + ^ = 0 With: ^ 0 = ^ ^ 0 And = This last equation makes it possible to determine P and consequently the gain matrix K. It should be noted that the gain matrix K actually depends on the engine operating point. More precisely, the gain matrix K is determined from the terms A and B which themselves depend on the engine operating point. This is taken into account in practice by predetermining a set of reference matrices and, depending on the measurement of the engine operating point, calculating the gain matrix by interpolation between two reference matrices. The set of reference matrices is previously determined before implementing the method. Each reference matrix is ​​associated with an operating point of the turbomachine, called the reference point.A reference matrix is ​​associated with an equation for the evolution of a tracking vector of an angular speed command formed from a variation in angular speed at an instant, a speed difference at the command at the instant and an integral of the difference. The operating point can in particular be deduced from an internal measurement of the engine such as for example a measurement of the speed of the motor shaft or a measurement of the pressure at the inlet of the combustion chamber, and from a measurement external to the engine such as for example the external pressure. The operating point can therefore be associated with a vector of several measurements. The measured operating point (or rather the "operating point" vector) makes it possible to determine the gain matrix K to be used at this point by linear interpolation between reference matrices associated with reference vectors which frame the "operating point" vector.The anti-lock loop also includes a matrix multiplication module 513 to determine fuel and electric torque setpoint values ​​at the current time. Knowing the gain matrix K allows, during the control process, to simultaneously determine the variation in fuel flow ∆WF and the variation in electric torque ∆TRQ as a function of ∆^ and the quantity ^^ using the following equation:. [MATH. 18] ^ Δ^^^^^^ ^ = −! ^ ^^^ ^ ^ ^ And for the low pressure shaft ^ Δ^^^^^ ^ = −! ^^^ The electric torque and ∆TRQ obtained by the module 513 are transmitted to the loop selection module 550. As mentioned previously, these torque and fuel setpoints can be declined either for the high pressure shaft 220, or for the low pressure shaft 210, or for both.

Claims

Claims

1. Method for controlling a turbomachine characterized in that it comprises - the detection of a speed of a drive shaft of the turbomachine below an idle speed; - the detection of a saturation of the fuel setpoint; - the selection of a combined fuel and torque control loop from at least one mono-variable engine control loop and, - the determination, in a combined manner, of a value representative of a fuel setpoint and a value representative of a torque setpoint such that said torque setpoint compensates for the saturation of said fuel setpoint to allow a stabilized speed of said turbomachine to be maintained.

2. Method according to claim 1, characterized in that said turbomachine having a high pressure body, said speed is the speed of said high pressure body and said determined torque setpoint allows maintenance of the stabilized speed at idle of said turbomachine to avoid unscrewing of said engine.

3. Method according to claim 1 characterized in that said turbomachine having a low pressure body, said speed is the speed of said low pressure body and said determined torque setpoint allows maintenance of the stabilized speed at idle of said engine.

4. Method according to one of the preceding claims characterized in that the determination of values ​​representative of a fuel setpoint and a torque setpoint comprises, in said combined control loop, the calculation of a fuel increment and a torque setpoint increment relative to a previous instant.

5. Method according to claim 4 characterized in that it determines said combined torque and fuel setpoints for a current instant from - sequencing parameters, - a value representative of the engine shaft speed at the current instant and at the previous instant, - an idle setpoint value and, - the torque and fuel setpoint values ​​calculated at a previous instant.

6. Method according to claims 2, 3 and 5 characterized in that it comprises in said combined control loop: - the determination of a variation (∆^^, ∆^^)^of the engine shaft speed between the current instant and the previous instant, - the determination of a difference (^^^, ^^^)^between said idle setpoint value and the value representative of the engine shaft speed at the current instant, - the determination of a difference ^∆^^. ^ , ∆^^^ ^ )^between the fuel increment and torque at the output of said control loop and an increment calculated from the difference between two previous setpoint values ​​determined, - the determination of a state vector representative of the speed of the motor shaft at the following instant ^∆^^ ^^^ , ∆^^ ^^^ )^and a difference between said idle setpoint value and the engine shaft speed at the following instant (^^^ ^^^ , ^^^ ^^^ )^according to: ^ Δ^^^^ ^ ^^^^^^ ^ ^ 0 ^^^^ ^ ^^ ^ 0^ A, B and I being determined constants, ^^^ ^ being the difference between the low pressure torque setpoint at time k and at time k-1, ^^^ ^being the difference between the high pressure torque setpoint at time k and at time k-1, - determining a gain matrix K, - obtaining the fuel increment and the torque setpoint increment relative to a previous time being obtained according to the following formula: ^ Δ^^^^^ ^ Δ ^^^^^^ ^ = −! ^ ^^ ^ ^^ ^ ^^ for high pressure motor shaft and ^ low pressure motor.

7. Method according to one of claims 4 to 6, characterized in that it comprises an integration of the torque and fuel increment obtained at the output of the regulation loop according to the following formula ^^ ^ =^∆^^ ^ +^^^ ^"^ ^and ^^^ ^ =^∆^^^ ^ +^^^^ ^"^.

8. Computer program comprising instructions for implementing a control method according to any one of claims 1 to 7, when said computer program is executed by a computer.

9. Computer-readable recording medium on which a computer program according to claim 8 is recorded.

10. Control device, in a turbomachine, comprising one or more processors configured to - detect a speed of a drive shaft of the turbomachine below an idle speed and - detect a saturation of the fuel setpoint, - select a combined fuel and torque control loop from at least one mono-variable engine control loop - determine, in a combined manner, a value representative of a fuel setpoint and a value representative of a torque setpoint such that said torque setpoint compensates for the saturation of said fuel setpoint to allow a stabilized speed of said turbomachine to be maintained.

11. Aircraft comprising a control device according to claim 10.

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