Aircraft propulsion system with a turboshaft engine coupled to an electric generator with power limited according to engine speed

Abstract

This aircraft propulsion system (12) comprises a turboshaft engine (20), a control system (24), a device (72) for determining the current engine speed (Rc) of the turboshaft engine (20), and a rotating machine (22) coupled to the turboshaft engine's (20) drive shaft for generating electrical power by drawing mechanical power from the drive shaft. The control system (24) is configured to limit the current electrical power (Pc) generated by the rotating machine (22), at least when the engine is accelerating, to a maximum permissible power (Pmax) that is a function of the current engine speed (Rc) before acceleration. Figure for the abbreviation: Fig. 2

Description

Title of the invention: Aircraft propulsion system with turbo-engine coupled to an electric generator with power restricted according to the engine speed FIELD OF THE INVENTION

[0001] The present invention relates to an aircraft propulsion system, of the type comprising a turbine engine with a combustion chamber and an engine body, the engine body comprising a turbine downstream of the combustion chamber, a compressor upstream of the combustion chamber and a transmission shaft for driving the compressor by the turbine, the propulsion system also comprising a control system, a member for determining a current engine speed of the engine body and a rotating machine coupled to the transmission shaft for generating electrical power by taking mechanical power from the transmission shaft.

[0002] The present invention also relates to a method for controlling a propulsion system for an aircraft of the aforementioned type. TECHNOLOGICAL BACKGROUND

[0003] Propulsion systems of the aforementioned type are known, for example from EP 3 845 750 A1 and US 7,514,810 B2.

[0004] In these known systems, the engine idle speed, that is to say the rotation speed of the engine body when the aircraft does not need propulsion, is most often unique and does not depend on the electrical power generated by the rotating machine. The engine idle speed is therefore the same regardless of the electrical power generated by the rotating machine.

[0005] It is also known that the propulsion systems equipping aircraft must, for safety reasons, be capable in all circumstances of restoring the greater part, typically more than 90%, of their full throttle thrust in a very short critical time, typically equal to 8 seconds. This implies in particular that the engine body of a turbine engine at idle must be able to reach a substantial percentage of its full throttle engine speed, that is to say of its engine speed when the turbine engine produces its full throttle thrust, in said critical time. It is therefore appropriate to dimension the engine idle speed so as to be able to meet this objective when the engine body is accelerated to its maximum capacity.

[0006] It is also known that the maximum acceleration rate that can be supported by the engine body of a turbine engine depends on the resistive torque applied to said engine body. Indeed, the acceleration rate of the engine body of a turbine engine is a function of the difference between the temperature at the combustion chamber outlet during the acceleration phase and the temperature at the combustion chamber outlet when the turbo-engine is in steady state: the greater the temperature difference, the greater the acceleration rate. However, this difference cannot be increased at will because the temperature at the combustion chamber outlet, for a given engine speed, is capped: the higher the temperature at the combustion chamber outlet, the lower the compressor outlet flow, to the point that, beyond a threshold temperature, the outlet flow is insufficient and the compressor stalls. The maximum acceleration rate is therefore a function of the difference between this threshold temperature and the temperature in steady state.However, for a given engine speed, the greater the resistive torque applied, the higher the temperature in steady state, and therefore the lower the difference between the threshold temperature and the temperature in steady state, and therefore the maximum acceleration rate.

[0007] It is therefore easy to understand that, in propulsion systems of the aforementioned type, the maximum acceleration rate that can be supported by the motor body decreases as the electrical power generated by the rotating machine increases.

[0008] Thus, in known propulsion systems, the maximum acceleration rate permitted at engine idle speed is at most equal to the maximum acceleration rate that can be supported by the engine body when the electrical power generated by the rotating machine is at its maximum. Indeed, since the engine idle speed is the same regardless of the electrical power generated by the rotating machine, any other value of the maximum acceleration rate permitted would lead to a stall of the compressor when the electrical power generated by the rotating machine is close to its maximum.

[0009] In known propulsion systems, the engine speed at idle is therefore fixed at a value such that, by applying the maximum acceleration rate that can be supported by the engine body when the electrical power generated by the rotating machine is at its maximum, the propulsion system manages to restore most of its maximum thrust within the critical time.

[0010] However, these known systems are not entirely satisfactory. Indeed, with the improvement in the thrust produced by aircraft propulsion systems and the reduction in their drag, the ratio of drag to thrust at engine idle speed is decreasing. However, it is necessary for this ratio to remain sufficiently high so that, at flight idle, the descent slope is sufficiently steep. Otherwise, means must be used to reduce the aircraft's lift or increase its drag, which consumes fuel. Similarly, at ground idle, excessively high idle thrust leads to accelerated wear of the brakes. Statement of the invention

[0011] An objective of the invention is to reduce the idle thrust of an aircraft propulsion system.

[0012] To this end, the invention relates, according to a first aspect, to a propulsion system of the aforementioned type, in which the control system is configured to limit a current electrical power generated by the rotating machine, at least when the motor body is in the acceleration phase, to a maximum authorized power depending on the current engine speed before acceleration.

[0013] According to particular embodiments of the invention, the propulsion system also has one or more of the following characteristics, taken in isolation or in any possible technical combination(s): - the propulsion system comprises a system for deducing a future need of the aircraft for electrical power generated by the rotating machine, the control system being configured to accelerate the engine body when said future need is greater than the maximum authorized power; - the propulsion system comprises a device for determining the current electrical power generated by the rotating machine, the control system being configured to establish the engine speed above an idle speed depending on the current electrical power; - when the engine speed is set at idle speed, the current electrical power constitutes the maximum authorized power; - the idle speed is greater than or equal to an acceleration limit speed for which the engine body, accelerating to the limit of stall from said acceleration limit speed while the rotating machine generates the current electrical power, reaches without stalling, in a given time less than or equal to 10 seconds, a target speed at which the turbine engine produces a substantial percentage of full throttle thrust; - the idle speed is greater than or equal to an overheating limit speed for which, when the engine body is rotating at said overheating limit speed while the rotating machine is generating the current electrical power, the temperature of the gases at the outlet of the turbine engine is equal to a predetermined maximum temperature; - the idle speed is equal to the maximum of the acceleration limit speed and the overheating limit speed; - the maximum authorized power is less than or equal to an acceleration power limit for which the engine body, accelerating to the limit of stalling from the current engine speed while the rotating machine generates said acceleration power limit, reaches without stalling, in a given time less than or equal to 10 seconds, a target speed at which the tur- bomoteur produces a substantial percentage of full throttle thrust; - the maximum authorized power is less than or equal to an overheating limit power for which, when the engine body is running at current speed while the rotating machine is generating said overheating limit power, the temperature of the gases at the outlet of the turbine engine is equal to a predetermined maximum temperature; - the maximum authorized power is equal to the minimum of the acceleration limit power and the overheating limit power; - the control system is configured to limit the electrical power generated by the rotating machine when the motor body is not in the acceleration phase; - the propulsion system comprises an electric motor coupled to the drive shaft; and - the turboshaft engine is a turbojet.

[0014] The invention also relates, according to a second aspect, to a method for controlling a propulsion system for an aircraft, the propulsion system comprising a turbine engine with a combustion chamber and a motor body, the motor body comprising a turbine downstream of the combustion chamber, a compressor upstream of the combustion chamber and a transmission shaft for driving the compressor by the turbine, the propulsion system also comprising a rotating machine coupled to the transmission shaft for generating electrical power by taking mechanical power from the transmission shaft, the control method comprising the following successive steps: - determining a current engine speed of the motor body, - defining a maximum authorized power as a function of the current engine speed, and - acceleration of the motor body, a current electrical power generated by the rotating machine being limited to the maximum authorized power.

[0015] According to particular embodiments of the invention, the control method also has one or more of the following characteristics, taken in isolation or according to any possible technical combination(s): - the piloting process also includes the following steps: • determination of the current electrical power generated by the rotating machine, • definition of an idle speed depending on the current electrical power, and • establishing the engine speed above the idle speed; - the piloting process also includes the following steps: • deduction of a future need of the aircraft in electrical power generated by the rotating machine, • modification of the idle speed to meet said future need, • comparison of the new idle speed to the current engine speed, and • if the new idle speed is higher than the current engine speed, acceleration of the engine body; during the engine speed establishment step, the engine speed is established at idle speed, the current electrical power then constituting the maximum authorized power; the control method also comprises a step of accelerating the engine body from said idle speed while the rotating machine generates the current electrical power, the engine body reaching without stalling, in a given time less than or equal to 10 seconds, a target speed at which the turbine engine produces a substantial percentage of full throttle thrust; The definition of idle speed includes the following sub-steps: • calculation of an acceleration limit speed for which the engine body, accelerating to the stall limit from said acceleration limit speed while the rotating machine generates the current electrical power, reaches without stalling, in a given time less than or equal to 10 seconds, a target speed at which the turboshaft engine produces a substantial percentage of full throttle thrust, and • allocation to the idle speed of a value greater than or equal to that of the acceleration limit speed; The definition of idle speed includes the following sub-steps: • calculation of a limit overheating speed for which, when the engine body is rotating at said limit overheating speed while the rotating machine is generating the current electrical power, the temperature of the gases at the outlet of the turbine engine is equal to a predetermined maximum temperature, and • allocation to the idle speed of a value greater than or equal to that of the overheating limit speed; the definition of idle speed includes assigning to the idle speed a value equal to the maximum of the acceleration limit speed and the overheating limit speed; - the piloting method also comprises a step of accelerating the engine body from the current engine speed while the rotating machine generates the maximum authorized power, the engine body reaching without stalling, in a given time less than or equal to 10 seconds, a target speed at which the turboshaft engine produces a substantial percentage of full throttle thrust; - the definition of the maximum authorized power includes the following sub-steps: • calculation of an acceleration power limit for which the engine body, accelerating to the stall limit from the current engine speed while the rotating machine generates said acceleration power limit, reaches without stalling, in a given time less than or equal to 10 seconds, a target speed at which the turboshaft engine produces a substantial percentage of full throttle thrust, and • allocation to the maximum power of a value less than or equal to that of the acceleration limit power; - the definition of the maximum authorized power includes the following sub-steps: • calculation of a superheating limit power for which, when the engine body is running at the current speed while the rotating machine generates said superheating limit power, the temperature of the gases at the outlet of the turbine engine is equal to a predetermined maximum temperature, and • allocation to the maximum power of a value less than or equal to that of the overheating limit power; - the definition of the maximum authorized power includes the allocation to the maximum power of a value equal to, at least, the values ​​of the acceleration limit power and the overheating limit power; - the method also comprises, before the step of accelerating the motor body, a step of limiting the electrical power generated by the rotating machine while the motor body is rotating at the current engine speed; and - the acceleration stage includes the injection of mechanical power onto the drive shaft by an electric motor coupled to the drive shaft. BRIEF DESCRIPTION OF THE FIGURES

[0016] Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and made with reference to the attached drawings, in which: - [Fig.l] is a top view of an aircraft comprising two propulsion systems according to an exemplary embodiment of the invention, - [Fig.2] is a block diagram of one of the propulsion systems of the aircraft of [Fig.l], - [Fig.3] is a simplified longitudinal sectional view of a turbine engine of the propulsion system of [Fig.2], - [Fig.4] is a diagram illustrating a process implemented by a control system of the propulsion system of [Fig.2], - [Fig.5] is a graph giving the relationship between an engine idle speed and a current electrical power of the propulsion system of [Fig.2], - [Fig.6] is a first graph showing the characteristic curves of a compressor of the turboshaft engine of [Fig.3] in different scenarios, - [Fig.7] is a first graph showing the evolution over time of the engine speed of the turboshaft engine in [Fig.3] in different scenarios, - [Fig.8] is a first graph giving the relationship between the engine speed and the outlet temperature of the turboshaft engine of [Fig.3] in different scenarios, - [Fig.9] is a graph showing the relationship between a current engine speed and a maximum authorized power of the propulsion system of [Fig.2], - [Fig. 10] is a second graph showing the evolution over time of the engine speed of the turboshaft engine in [Fig. 3] in different scenarios, - [Fig. 11] is a second graph showing the characteristic curves of a compressor of the turboshaft engine of [Fig.3] in different scenarios, and - [Fig. 12] is a second graph giving the relationship between engine speed and turbine engine outlet temperature from [Fig.3] in different scenarios. DETAILED DESCRIPTION OF AN EMBODIMENT

[0017] The aircraft 10 shown in [Fig.l] comprises propulsion systems 12 for propelling it.

[0018] In the example shown, the aircraft 10 is an airplane. This comprises, in a conventional manner, a fuselage 14, a tailplane 16 and two wings 18. The propulsion systems 12 are here two in number and are each housed under a respective wing 18. As a variant (not shown), the propulsion systems 12 are arranged along the fuselage 14, for example near the tailplane 16. As a further variant (also not shown), the aircraft 10 comprises a single propulsion system 12 or at least three propulsion systems 12.

[0019] The aircraft 10 also includes an electrical network (not shown).

[0020] One of the propulsion systems 12 is shown in [Fig.2].

[0021] This propulsion system 12 comprises a turbine engine 20, a rotating machine 22 for generating electricity, and a control system 24. In the example shown, the propulsion system 12 also comprises at least one auxiliary source of electrical power 26, for example a battery or a fuel cell, and an electric motor 28.

[0022] The propulsion system 12 also comprises a transmission member 29 for transmitting to the electrical network of the aircraft 10 the electricity produced by the rotating machine 22 or supplied by the or each auxiliary power source 26.

[0023] With reference to [Fig. 3], the turboshaft engine 20 comprises, in a conventional manner, an engine casing 30, an internal flow path 32 for circulating an air flow through the engine casing 30, a combustion chamber 34 housed in the flow path 32, an engine body 36 and a gas exhaust nozzle 38.

[0024] In the following, the terms “upstream” and “downstream” are understood to refer to a direction of flow of an air flow through the vein 32.

[0025] The engine body 36 comprises a compressor 40, a turbine 42 and a transmission shaft 44 coupling the turbine 42 to the compressor 40 for driving the compressor 40 by the turbine 42. The compressor 40 is arranged upstream of the combustion chamber 34 and supplies the combustion chamber 34 with compressed air. The turbine 42 is arranged downstream of the combustion chamber 34 and receives the exhaust gases leaving the combustion chamber 34.

[0026] The transmission shaft 44 has a longitudinal axis X as its axis of rotation. The longitudinal axis X is typically an axis of angular symmetry of the turbine engine 20, that is to say that there is at least one angle for which the turbine engine 20 is invariant by rotation around the longitudinal axis X.

[0027] The transmission shaft 44 is guided in rotation relative to the engine casing 30 by means of bearings (not shown).

[0028] The engine body 36 is capable of rotating around the X axis at a rotational speed called the engine speed. This engine speed is in particular a function of the temperature of the gases leaving the combustion chamber 34.

[0029] In the example shown, the turboshaft engine 20 is a multi-spool turboshaft engine, in particular a double-spool engine, comprising a low-pressure spool 50 in addition to the engine spool 36. The engine spool 36 then constitutes a high-pressure spool, the compressor 40 being a high-pressure compressor, the turbine 42 being a high-pressure turbine and the transmission shaft 44 being a high-pressure shaft.

[0030] The low pressure body 50 comprises a low pressure compressor 52, a turbine low pressure 54 and a low pressure shaft 56 coupling the low pressure turbine 54 to the low pressure compressor 52 for driving the low pressure compressor 52 by the low pressure turbine 54.

[0031] The low pressure compressor 52 is arranged upstream of the high pressure compressor 40 and supplies the latter with compressed air. The low pressure turbine 54 is arranged downstream of the high pressure turbine 42 and receives the exhaust gases leaving the latter.

[0032] The low pressure shaft 56 is guided in rotation relative to the engine casing 30 by means of bearings (not shown).

[0033] The low pressure shaft 56 is coaxial with the high pressure shaft 44. It therefore also has the longitudinal axis X as its axis of rotation. In particular, the low pressure shaft 56 extends inside the high pressure shaft 44.

[0034] In the example shown, the turboshaft engine 20 is also a dual-flow turboshaft engine comprising a fan 60 for driving the air flow in an external circulation vein 62 surrounding the engine casing 30. A primary air flow A (hot) is thus distinguished, consisting of the portion of the air flow driven in the internal circulation vein 32, and a secondary air flow B (cold), consisting of the portion of the air flow driven in the external circulation vein 62.

[0035] The turboshaft engine 20 advantageously has a high bypass ratio, the bypass ratio being defined as the ratio of the flow rate of the secondary flow B (cold) to the flow rate of the primary flow A (hot).

[0036] The blower 60 comprises a blower disc 64 provided with blower blades 66 at its periphery which, when rotated, drive the air flow into the external circulation vein 62.

[0037] Here, the blower 60 is arranged upstream of the internal circulation vein 32 and also drives the air flow in the latter.

[0038] The external circulation vein 62 is here defined between the engine casing 30 and a fan casing 67 surrounding the fan 60.

[0039] The fan 60 is driven in rotation by the low-pressure turbine 54, via the low-pressure shaft 56. In the example shown, this drive is indirect, in order to allow the fan 60 to rotate at a speed lower than that of the low-pressure turbine 54. For this purpose, the turbine engine 20 here comprises a fan shaft 68 on which the fan disc 64 is fixedly mounted and a reduction gear 70 coupling the fan shaft 68 to the low-pressure shaft 56. The fan 60 is thus driven in rotation by the low-pressure shaft 56 via the reduction gear 70 and the fan shaft 68.

[0040] The fan shaft 68 is guided in rotation relative to the engine casing 30 by means of bearings (not shown).

[0041] The turboshaft engine 20 is typically a turbojet.

[0042] As visible in [Fig. 3], the rotating machine 22 is coupled to the high pressure shaft 44 so as to be driven in rotation by said high pressure shaft 44. It is capable of generating electrical power by drawing mechanical power from said high pressure shaft 44.

[0043] Advantageously, the rotating machine 22 is capable of being decoupled from the high pressure shaft 44.

[0044] Still with reference to [Fig. 3], the electric motor 28 is coupled to the high pressure shaft 44 so as to drive said high pressure shaft 44 in rotation around the axis X. This motor 28 is capable of converting electrical power into mechanical power and injecting the latter onto the high pressure shaft 44.

[0045] Advantageously, the electric motor 28 is capable of being decoupled from the high pressure shaft 44.

[0046] Returning to [Fig. 2], the control system 24 comprises an engine control module 72 and an electrical source control module 74. It also comprises a power draw restriction system 76 and an engine idle management system 78.

[0047] The engine control module 72 is configured to control the engine speed of the engine body 36. For this purpose, the engine control module 72 is configured to determine a current speed Rc of the engine body 36 and to communicate at least one control parameter Pb P2 to the turbine engine 20 and / or to the electric motor 28 to establish the engine speed at a target speed.

[0048] The current speed Rc is for example determined by the engine control module 72 on the basis of the control parameters PH P2 communicated by the engine control module 72 to the turbine engine 20 and / or to the electric motor 28 (open loop operation). Alternatively, the current speed Rc is communicated to the engine control module 72 by a sensor (not shown) of the turbine engine 20 (closed loop operation).

[0049] The engine control module 72 is in particular configured to communicate to the turbine engine 20 at least one control parameter Pi adapted to stabilize the engine speed above an idle speed Rr provided by the management system 78. It is also configured to receive a thrust setpoint Cp from the aircraft 10 and to communicate to the turbine engine 20 and / or to the electric motor 28 at least one control parameter Pb P2 adapted to accelerate the engine body 36 at an acceleration rate depending on the thrust setpoint Cp and the current engine speed Rc. The acceleration rate is capped at a maximum acceleration rate Tmax provided by the management system 78.

[0050] The thrust setpoint Cp is less than or equal to a full thrust setpoint gas. This full throttle thrust setpoint is, in a known manner, intended to induce the fan 60 to move at a predetermined speed so as to obtain a so-called “full throttle” thrust depending on the flight conditions. This predetermined speed of the fan 60 corresponds to a speed that we will call “full throttle” of the engine body 36, which is thus itself a function of the flight conditions. This full throttle speed is noted Rgas in the Figures. When the thrust setpoint Cp is equal to the full throttle thrust setpoint, this is therefore interpreted by the engine control module 72 as an acceleration setpoint of the engine body 36 at said full throttle speed.

[0051] A first control parameter Pb communicated to the turbine engine 20 is, for example, a fuel dosage instruction to be injected into the combustion chamber 34. A second control parameter P2, communicated to the electric motor 28, is, for example, a torque instruction.

[0052] The engine control module 72 is further configured to communicate the current engine speed Rc to the restriction system 76.

[0053] The control module 74 is configured to control the electrical power supplied to the electrical network of the aircraft 10 by the rotating machine 22 and the or each auxiliary source 26. For this purpose, the control module 74 is configured to determine a current electrical power Pc generated by the rotating machine 22 and an auxiliary electrical power Pa supplied by the auxiliary source(s) 26 and to communicate to the rotating machine 22 and / or to the or each auxiliary source 26 at least one setpoint Ci, C2 adapted to adjust the current electrical power Pc and the auxiliary electrical power Pa.

[0054] The current and auxiliary electrical powers Pc, Pa are for example determined by the control module 74 on the basis of the setpoints Ci, C2 communicated by the control module 74 to the rotating machine 22 and to the or each auxiliary source 26 (open loop operation). Alternatively, the current and auxiliary electrical powers Pc, Pa are communicated to the control module 74 by sensors (not shown) at the rotating machine 22, the or each auxiliary source 26 and / or the transmission member 29 (closed loop operation).

[0055] A first instruction Ch communicated to the rotating machine 22 is, for example, an instruction to inject an excitation current into a winding of the rotating machine 22. A second instruction C2, communicated to an auxiliary source 26, is, for example, an instruction to close a switch connecting the auxiliary source 26 to the distribution member 29.

[0056] Typically, the control module 74 is configured to receive information Ic on the current electrical power requirements of the aircraft 10 and to communicate to the rotating machine 22 and / or to the or each auxiliary source 26 at least one instruction Ci, C2 adapted so that the sum of the current and auxiliary electrical powers Pc, Pa satisfies the needs reflected by the information Ic.

[0057] In particular, the control module 74 is configured to limit the current electrical power Pc, at least during certain phases, to a maximum authorized electrical power Pmax provided by the restraint system 76, and to control the auxiliary source(s) 26 so that the latter supplement(s) the electrical power needs of the aircraft 10. In other words, the control module 74 is configured to control the rotating machine 22 so that the current electrical power Pc generated by the latter is equal to the power Pmax or, if these are lower, to the current needs reflected by the information Ic, and to control the auxiliary source(s) 26 so that the latter provide(s), when the current needs reflected by the information Ic are greater than the power Pmax, an auxiliary electrical power Pa equal to the difference between said current needs and the power Pmax.

[0058] The control module 74 is configured to apply this limitation of the current electrical power Pc in particular when the motor body 36 is in the acceleration phase. Preferably, the control module 74 is configured to apply this limitation of the current electrical power Pc at any time, including when the motor body 36 is not in the acceleration phase.

[0059] Advantageously, the control module 74 is also configured to communicate the current electrical power Pc to the management system 78.

[0060] The limiting system 76 is configured to receive from the engine control module 72 information representative of the current engine speed Rc and to deduce from the latter the maximum authorized power Pmax. The limiting system 76 is also configured to communicate this maximum authorized power Pmax to the control module 74.

[0061] In particular, the limiting system 76 is configured to determine the maximum authorized power Pmax so that the following two constraints are respected: - the engine body 36, accelerating from the current engine speed Rc while the rotating machine 22 generates the maximum authorized power Pmax, reaches without stalling in a given time h ([Fig.7]) less than or equal to 10 seconds, for example between 7.5 and 8.5 seconds, a target speed RciMe ([Fig.7]) at which the turbine engine 20 produces a substantial percentage, typically between 89 and 91%, of the full throttle thrust, and - the temperature at the outlet of the turboshaft engine 20, for example at the outlet of the low pressure turbine 54, remains below a predetermined maximum temperature T°max ([Fig.8]) when the engine body 36 is running at the current speed Rc while the rotating machine 22 generates the maximum authorized power px max*

[0062] For this purpose, the limiting system 76 is configured to determine the maximum authorized power Pmax so that it is less than or equal to: - an acceleration limit power for which the engine body 36, accelerating to the stall limit from the current engine speed Rc while the rotating machine 22 generates said acceleration limit power, reaches said target speed RciMe without stalling within said allotted time h, and - an overheating limit power for which, when the engine body 36 is running at the current speed Rc while the rotating machine 22 generates said overheating limit power, the temperature of the gases at the outlet of the turbo-engine 20 is equal to said predetermined maximum temperature T°max.

[0063] In particular, the limiting system 76 is configured to determine the maximum authorized power Pmax so that it is equal to the minimum of the acceleration limit power and the overheating limit power.

[0064] For this purpose, the limiting system 76 is for example configured to calculate, from parameters of the turboshaft engine 20 and the current engine speed Rc, the acceleration limit power and the overheating limit power, and to then determine the maximum authorized power Pmax as a function of said limit powers. As a variant, a maximum authorized power Pmax respecting these constraints and depending on the flight conditions has been determined upstream for each possible engine speed, and the limiting system 76 is parameterized with a function associating with each possible engine speed, as a function of the flight conditions, the corresponding maximum authorized power P max.

[0065] The management system 78 is configured to receive from the control module 74 information representative of the current electrical power Pc and to deduce from the latter the idle speed Rr and the maximum acceleration rate Tmax. The management system 78 is also configured to communicate said idle speed Rr and maximum acceleration rate Tmax to the engine control module 72.

[0066] In particular, the management system 78 is configured to define the maximum acceleration rate Tmax below a limit acceleration rate beyond which the compressor 40 stalls when the current electrical power Pc is generated.

[0067] The management system 78 is further configured to define the idle speed R r so that the following two constraints are respected: - the engine body 36, accelerating from the idle speed Rr to the maximum acceleration rate Tmax while the rotating machine 22 generates the current electrical power Pc, reaches the target speed Rcibie without stalling in the allotted time tj, and - the temperature at the outlet of the turboshaft engine 20, for example at the outlet of the low pressure turbine 54, remains below the predetermined maximum temperature T°max when the engine body 36 is running at idle speed Rr while the rotating machine 22 generates the current electrical power Pc.

[0068] For this purpose, the management system 78 is configured to determine the idle speed Rr so that it is greater than or equal to: - an acceleration limit speed for which the motor body 36, accelerating to the stall limit from said acceleration limit speed while the rotating machine 22 generates the current electrical power Pc, reaches said target speed RciMe without stalling in said allotted time h, and - a limit overheating regime for which, when the engine body 36 is rotating at said limit overheating regime while the rotating machine 22 generates the current electrical power Pc, the temperature of the gases at the outlet of the turbine engine 20 is equal to the predetermined maximum temperature T°max.

[0069] In particular, the management system 78 is configured to determine the idle speed Rr so that it is equal to the maximum of the acceleration limit speed and the overheating limit speed.

[0070] For this purpose, the management system 78 is for example configured to calculate, from parameters of the turboshaft engine 20 and the current electrical power Pc, the acceleration limit speed and the overheating limit speed, and to then determine the idle speed Rr as a function of said limit speeds. As a variant, an idle speed Rr respecting these constraints and depending on the flight conditions has been determined upstream for each possible generated electrical power, and the management system 78 is parameterized with a function associating with each possible generated electrical power, as a function of the flight conditions, the corresponding idle speed Rr.

[0071] It is easily understood that, when the engine speed is established at idle speed Rr, the current electrical power Pc constitutes the maximum authorized power Pmax.

[0072] The management system 78 is further configured to receive from the aircraft 10 information If representative of a future need of the aircraft 10 for electrical power and to deduce from this information If the future need of the aircraft 10 for electrical power. The management system 78 is also configured to modify the idle speed Rr so that it meets this future need and to communicate the idle speed Rr thus modified to the engine control module 72.

[0073] In particular, the management system 78 is configured to modify the idle speed Rr on the basis of the information If only when the future need is greater than the current electrical power Pc (it being understood that the management system 78 is also configured to modify the idle speed Rr, upwards or downwards, in function of the current electrical power Pc). The management system 78 is configured so that, in such a case, the idle speed Rr is increased so that the following two constraints are respected: - the engine body 36, accelerating from the idle speed Rr to the maximum acceleration rate Tmax while the rotating machine 22 generates electrical power equal to the future requirement, reaches the target speed Rcibie without stalling within the allotted time h, and - the temperature at the outlet of the turboshaft engine 20, for example at the outlet of the low pressure turbine 54, remains below the predetermined maximum temperature T°max when the engine body 36 is running at idle speed Rr while the rotating machine 22 generates electrical power equal to the future requirement.

[0074] For this purpose, the management system 78 is configured to modify the idle speed Rr so that it is greater than or equal to: - a future acceleration limit speed for which the motor body 36, accelerating to the stall limit from said future acceleration limit speed while the rotating machine 22 generates electrical power equal to the future requirement, reaches said target speed Rcibie without stalling in said allotted time h, and - a future overheating limit regime for which, when the engine body 36 is rotating at said future overheating limit regime while the rotating machine 22 generates electrical power equal to the future requirement, the temperature of the gases at the outlet of the turbine engine 20 is equal to the predetermined maximum temperature T°max.

[0075] In particular, the management system 78 is configured to modify the idle speed Rr so that it is equal to the maximum of the future acceleration limit speed and the future overheating limit speed.

[0076] For this purpose, the management system 78 is for example configured to calculate, from parameters of the turbine engine 20 and the future requirement, the future acceleration limit speed and the future overheating limit speed, and to then modify the idle speed Rr as a function of said future limit speeds. As a variant, an idle speed Rr respecting these constraints and depending on the flight conditions has been determined upstream for each possible generated electrical power, and the management system 78 is parameterized with a function associating with each possible generated electrical power the corresponding idle speed Rr as a function of the flight conditions.

[0077] It is easy to understand that, when the future requirement is greater than the maximum authorized power Pmax, the idle speed Rr thus modified is brought to a value greater than that of the current speed Rc. This mechanically leads to an access leration of the engine body 36, since the engine control module 72 is configured to establish the engine speed above the idle speed Rr.

[0078] The control system 24, including in particular the engine control module 72, the control module 74, the restriction system 76 and the management system 78, is typically implemented in the form of a computer program stored in a memory of a processing system (not shown) of the propulsion system 12 and capable of being executed by a processor (not shown) associated with said memory. Alternatively, the control system 24 is implemented at least partially in the form of a programmable logic component, or in the form of a dedicated integrated circuit, included in the propulsion system 12.

[0079] A piloting method 100 implemented by the propulsion system 12 will now be described, with reference to [Fig.4].

[0080] This method 100 comprises a first step 110 of determining the current electrical power Pc. During this step 110, the control module 74 determines the current electrical power Pc generated by the rotating machine 22, for example on the basis of the setpoints Ci, C2 that it communicates to the rotating machine 22 or on the basis of information communicated to the control module 74 by a sensor (not shown) at the rotating machine 22 or the transmission member 29 (closed loop operation).

[0081] This step 110 is followed by a step 120 of defining the idle speed Rr. During this step, the management system 78 defines the idle speed Rr as a function of the current electrical power Pc.

[0082] In the example shown, step 120 comprises a first sub-step 122 of calculating the acceleration limit speed, a second sub-step 124 of calculating the overheating limit speed, and a third sub-step 126 of assigning a value to the idle speed Rr. During the first sub-step 122, the management system 78 calculates the acceleration limit speed as a function of the current electrical power Pc. During the second sub-step 124, the management system 78 calculates the overheating limit speed as a function of the current electrical power Pc. Finally, during the third sub-step 126, the management system 78 assigns to the idle speed Rr a value greater than or equal to those of the acceleration limit speed and the overheating limit speed.Typically, the management system 78 assigns to the idle speed Rr, during this sub-step 126, a value equal to the maximum of the acceleration limit speed and the overheating limit speed.

[0083] As a variant (not shown), step 120 comprises the single sub-step 126 of assigning a value to the idle speed Rr. In this variant, the management system 78 assigns to the idle speed Rr, during this sub-step 126, a value determined by a function configured in the management system 78, said function associating the current electrical power Pc, for a given flight condition, with the corresponding idle speed Rr. An example of such a function is given in [Fig.5].

[0084] As visible in [Fig.5], the engine idle speed Rr increases with the current electrical power Pc: the first engine idle speed RH associated with a first current power Pc[ is lower than the second engine idle speed Rr2 associated with a second current power Pc2 greater than the first current power Pci. This is easily explained, as detailed below with reference to Figures 6 to 8.

[0085] [Fig.6] is a flow rate / compression ratio graph showing the characteristic curves of the high pressure compressor 40 of the turboshaft engine 20 in different scenarios. The following are represented: - the pumping line Lp of the high pressure compressor 40; as well known to those skilled in the art, this is a line beyond which the high pressure compressor 40 stalls; - the margin line Lm of the high pressure compressor 40; as well known to those skilled in the art, this is a line beyond which the risks of stalling of the high pressure compressor 40 do not allow aeronautical safety requirements to be met; - the operating lines LfPci and LfPc2 of the high-pressure compressor 40 when the electrical power generated by the rotating machine 22 is equal, respectively, to the first current power Pci and to the second current power Pc2; as well known to those skilled in the art, these operating lines LfPci and LfPc2 define the flow rate - compression ratio pairs for which the high-pressure compressor 40 has stable operation when the electrical power generated by the rotating machine 22 is equal, respectively, to the first current power Pc[ and to the second current power Pc2; - the isoregim lines Li^i, Li^ and LiRgaz of the high-pressure compressor 40 at the first engine idle speed RH, at the second engine idle speed Rr2 and at the full throttle speed Rgaz; as well known to those skilled in the art, these isoregim lines Li^i, LiRr2 and LiRgaz define the flow rate - compression ratio pairs achievable by the high-pressure compressor 40 when the engine body 36 rotates, respectively, at the first engine idle speed Rri, at the second engine idle speed Rr2 and at the full throttle speed Rgaz; and - the acceleration transient curves TaPM, TaPP2 and Ta2.2.2 representing the variation of the compression ratio as a function of the flow rate when the engine body 36 is respectively accelerated: • from the first engine idle speed R|H to a first acceleration rate Ti while the electrical power generated by the rotating machine 22 is equal to the first current power Pc[, • from the first engine idle speed Rr[, to the first acceleration rate Ti while the electrical power generated by the rotating machine 22 is equal to the second current power Pc2, and • from the second engine idle speed Rr2, at a second acceleration rate T2 lower than the first acceleration rate Ti while the electrical power generated by the rotating machine 22 is equal to the second current power Pc2.

[0086] [Fig.7] is a graph showing the evolution over time of the engine speed of the engine body 36 in different scenarios. It shows: - a first acceleration curve CaM of the engine body 36 when the latter is accelerated from the first engine idle speed R,i to the first acceleration rate Th - a second acceleration curve Cai_2 of the engine body 36 when the latter is accelerated from the first engine idle speed R,i to the second acceleration rate T2, and - a third acceleration curve Ca2 2 of the engine body 36 when the latter is accelerated from the second engine idle speed Rr2 to the second acceleration rate T2.

[0087] As visible in [Fig.6], the transient acceleration curve Tai_M partly runs along the margin line Lm. This means that the high pressure compressor 40 is at the limit of stalling during the acceleration phase at the first acceleration rate Th. The first acceleration rate Ti therefore constitutes the maximum acceleration rate Tmax for the first current power Pci. As illustrated by the acceleration curve CaM in [Fig.7], this acceleration rate Ti makes it possible to accelerate the engine body 36 from the first engine idle speed RH so as to reach the target speed R cibie in the given time L

[0088] If one wanted to accelerate the motor body 36 at this same first acceleration rate Ti from the same first engine speed RH when the electrical power generated by the rotating machine 22 is equal to the second current power Pc2, the compression ratio of the high-pressure compressor 40 would follow the transient acceleration curve TaM_2. However, as visible in [Fig.6], this transient acceleration curve TaM_2 crosses the margin line Lm. Accelerating the motor body 36 at the first acceleration rate Ti when the electrical power generated by the rotating machine 22 is equal to the second current power Pc2 therefore involves risks excessive stalling of the high pressure compressor 40, so that this first acceleration rate Ti is unacceptable. To accelerate the motor body 36 when the electrical power generated by the rotating machine 22 is equal to the second current power Pc2, it is therefore appropriate to use a lower acceleration rate for which the transient acceleration curve at least partly runs along the margin line Lm without ever crossing it: this lower acceleration rate is constituted by the second acceleration rate T2, as illustrated by the transient acceleration curve Ta2 2 2 in [Fig.6].

[0089] However, as illustrated by the acceleration curve CaP2 in [Fig.7], accelerating the engine body 36 to the second acceleration rate T2 from the first engine idle speed Rri does not allow the target speed RciMe to be reached within the allotted time L. To achieve this objective, it is therefore necessary to raise the engine idle speed Rr to the second engine idle speed Rr2, as illustrated by the curve Ca2 2 in [Fig.7].

[0090] The second engine idle speed Rr2 must therefore be greater than the first engine idle speed Rr[ to allow the engine body 36 to reach the target speed R Cibie in the allotted time h, without stalling, when the electrical power generated by the rotating machine 22 is equal to the second current power Pc2.

[0091] The second engine idle speed Rr2 must also be higher than the first engine idle speed Rr[ to prevent the temperature of the exhaust gases at the outlet of the turboshaft engine 20 from exceeding the maximum temperature T°max, as can be understood from reading [Fig.8].

[0092] [Fig.8] is in fact a graph giving the relationship between the engine speed of the engine body 36 and the outlet temperature of the turbine engine 20 in different scenarios. The following are represented: - a first temperature curve TPci of the outlet of the turboshaft engine 20 when the electrical power generated by the rotating machine 22 is equal to the first current power Pci, and - a second temperature curve TPc2 of the outlet of the turboshaft engine 20 when the electrical power generated by the rotating machine 22 is equal to the second current power Pc2.

[0093] As visible in [Fig. 8], the first and second temperature curves TPci, TPc2 each have a U-shaped profile, the range of variation of the idle speed Rr being in the region of the graph where these curves are decreasing. In addition, the first idle speed Rr[ is such that when the engine body 36 rotates at said idle speed Rr[ while the electrical power generated by the rotating machine 22 is equal to the first current power Pci, the temperature at the outlet of the turbine engine 20 is equal to the maximum temperature T°max. Finally, the second temperature curve T Pc2 is logically located above the first temperature curve TPcb insofar as the supply of mechanical energy to the rotating machine 22 requires, at equal engine speed, burning more oxidant in the combustion chamber 34. This implies that if the engine body 36 could rotate at the first idle speed Rri when the electrical power generated by the rotating machine 22 is equal to the second current power Pc2, the outlet temperature of the turbine engine 20 would be at a value T°sup higher than the maximum temperature T°max. To avoid this, a second higher engine idle speed Rr2 is chosen, this second engine idle speed Rr2 being constituted by the lowest engine speed for which the outlet temperature of the turbine engine 20 is less than or equal to the maximum temperature Tmax when the electrical power generated by the rotating machine 22 is equal to the second current power Pc2.

[0094] Returning to [Fig. 4], step 120 is followed by a step 130 of establishing the engine speed above the idle speed Rr. During this step 130, the engine control module 72 sends at least one control parameter Pb P2 to the turbine engine 20 and, optionally, to the electric motor 28 so that the engine speed of the engine body 36 is established at a current engine speed Rc greater than or equal to the idle speed Rr. For example, during this step 130, the engine speed is established at the engine idle speed Rr. This is typically the case when the aircraft 10 requests minimal propulsion from the propulsion system 12, such as for example when parking on the runway or during the descent phase.

[0095] The control method 100 also comprises a step 140 of determining the current engine speed Rc. During this step 140, the engine control module 72 determines the current engine speed Rc on the basis of the control parameter(s) Pb P2 that it communicates to the turbine engine 20 and / or to the electric motor 28 (open loop operation), or on the basis of information communicated by a sensor (not shown) of the turbine engine 20 (closed loop operation).

[0096] Step 140 is followed by a step 150 of defining the maximum authorized power Pmax. During this step, the limiting system 76 defines the maximum authorized power Pmax as a function of the current engine speed Rc.

[0097] In the example shown, step 150 comprises a first sub-step 152 of calculating the acceleration limit power, a second sub-step 154 ​​of calculating the overheating limit power, and a third sub-step 156 of assigning a value to the maximum authorized power Pmax. During the first sub-step 152, the limiting system 76 calculates the acceleration limit power as a function of the current engine speed Rc. During the second sub-step 154, the limiting system 76 calculates the overheating limit power as a function of the current engine speed Rc. Finally, during the third sub-step 156, the limiting system 76 assigns to the maximum authorized power Pmax a value less than or equal to those of the acceleration limit power and the superheat limit power. Typically, the limiting system 76 assigns to the maximum authorized power Pmax, during this sub-step 156, a value equal to the minimum of the values ​​of the acceleration limit power and the superheat limit power.

[0098] As a variant (not shown), step 150 comprises the single sub-step 156 of assigning a value to the maximum authorized power Pmax. In this variant, the limiting system 76 assigns to the maximum authorized power Pmax, during this sub-step 156, a value determined by a function parameterized in the limiting system 76, said function associating with the current engine speed Rc, for a given flight condition, the corresponding maximum authorized power Pmax. An example of such a function is given in [Fig.9].

[0099] As visible in this Figure, the maximum authorized power Pmax increases with the current engine speed Rc: the first maximum authorized power Pmaxi associated with a first current speed Rci is lower than the second maximum authorized power Pmax2 associated with a second current speed Rc2 higher than the first current speed Rci. This is easily explained, as detailed below with reference to Figures 10 to 12.

[0100] [Fig. 10] is a graph showing the evolution over time of the engine speed of the engine body 36 in different scenarios. It shows: - a first acceleration curve Ca'M of the engine body 36 when the latter is accelerated from the first current engine speed Rc[ to a first acceleration rate Th - a second acceleration curve Ca'b2 of the motor body 36 when the latter is accelerated from the first current engine speed Rc[ to a second acceleration rate T2 lower than the first acceleration rate TH and - a third acceleration curve Ca'2 2 of the motor body 36 when the latter is accelerated from the second current engine speed Rc2 to the second acceleration rate T2.

[0101] As illustrated by the third acceleration curve Ca'2_2, the second acceleration rate T2 is sufficient to allow the motor body 36 to reach the target speed Rcibie in the allotted time h when it is accelerated from the second current speed Rc2. On the other hand, as illustrated by the second acceleration curve Ca'i.2, this second acceleration rate T2 is insufficient to allow the motor body 36 to reach the target speed Rcibie in the allotted time f when it is accelerated from the first current speed Rci. As illustrated by the first acceleration curve Ca' ii, in order for the motor body 36 to be able to reach the target speed Rcibie in the allotted time h when it is accelerated from the first current speed Rci, it must be accelerated to the first acceleration rate Tb

[0102] [Fig. 11] is a flow rate / compression ratio graph showing the characteristic curves of the high pressure compressor 40 of the turboshaft engine 20 in different scenarios. Represented therein are: - the pumping line Lp of the high pressure compressor 40; - the margin line Lm of the high pressure compressor 40; - the operating lines LfPmaxi and LfPmax2 of the high pressure compressor 40 when the electrical power generated by the rotating machine 22 is equal, respectively, to the first maximum authorized power Pmaxi and to the second maximum authorized power Pmax2; - the isoregime lines LiRci, LiRc2 and LiRgaz of the high pressure compressor 40 at the first current engine speed Rl H at the second current engine speed Rc2 and at the full throttle speed Rgaz; and - the acceleration transient curves Ta' Pm, Ta' PP2 and Ta'2.2.2 representing the variation of the compression ratio as a function of the flow rate when the engine body 36 is respectively accelerated: • from the first current engine speed Rci, at the first acceleration rate Ti while the electrical power generated by the rotating machine 22 is equal to the first maximum authorized power Pmaxi, • from the first current engine speed Rc[, at the first acceleration rate Ti while the electrical power generated by the rotating machine 22 is equal to the second maximum authorized power Pmax2, and • from the second current engine speed Rc2, at the second acceleration rate T2 while the electrical power generated by the rotating machine 22 is equal to the second maximum authorized power Pmax2.

[0103] As illustrated by the acceleration transient curve Ta'2.2.2, when the motor body 36 is accelerated to the second acceleration rate T2 from the second current speed Rc2 while the electrical power generated by the rotating machine 22 is equal to the second maximum authorized power Pmax2, the compression ratio of the high-pressure compressor 40 remains below the margin line Lm: the compressor 40 therefore presents no risk of stalling. On the other hand, as illustrated by the acceleration transient curve Ta'PP2, if it is desired to accelerate the motor body 36 to the first acceleration rate Ti from the first current speed Rci while the electrical power generated by the rotating machine 22 is still equal to the second maximum authorized power Pmax2, the compression ratio of the compressor high pressure 40 crosses the margin line Lm: this implies excessive risks of stalling of the high pressure compressor 40, so that it is unacceptable to maintain the maximum authorized power at the value Pmax2 when the first acceleration rate Ti is applied. To be able to apply this first acceleration rate T i and thus allow the motor body 36 to reach the target speed RciMe in the allotted time h when it is accelerated from the first current speed Rc[ while the electrical power generated by the rotating machine 22 is equal to the maximum authorized power Pmax, it is necessary to lower this maximum authorized power Pmax to a lower value Pmaxi, as illustrated by the acceleration transient curve Ta'm i

[0104] The first maximum authorized power Pmaxi must therefore be less than the second maximum authorized power Pmax2 to allow the motor body 36 to reach the target speed RciWe in the allotted time f without stalling when the motor body 36 is running at the first current engine speed Rci.

[0105] Another reason why the first maximum authorized power Pmaxi is lower than the second maximum authorized power Pmax2 is illustrated by [Fig. 12]. This Figure is a graph giving the relationship between the engine speed of the engine body 36 and the outlet temperature of the turbine engine 20 in different scenarios. The following are represented: - a first temperature curve TPmaxi of the outlet of the turboshaft engine 20 when the electrical power generated by the rotating machine 22 is equal to the first maximum authorized power Pmaxi, and - a second temperature curve TPmax2 of the outlet of the turboshaft engine 20 when the electrical power generated by the rotating machine 22 is equal to the second maximum authorized power Pmax2.

[0106] As visible in [Fig. 12], the first and second temperature curves TP maxl, TPmax2 each have a U-shaped profile, the range of variation of the current engine speed Rc being in the region of the graph where these curves are decreasing. In addition, the second current engine speed Rc2 is such that when the engine body 36 rotates at said second current engine speed Rc2 while the electrical power generated by the rotating machine 22 is equal to the second maximum authorized power Pmax2, the temperature at the outlet of the turbine engine 20 is equal to the maximum temperature T°max. Finally, the second temperature curve TPmax2 is logically located above the first temperature curve TPmaxi, insofar as the supply of mechanical energy to the rotating machine 22 requires, at equal engine speed, burning more oxidant in the combustion chamber 34.This implies that if the rotating machine 22 could generate the second maximum authorized power Pmax2 when the engine body 36 rotates at the first engine speed. current Rcb the temperature at the outlet of the turbine engine 20 would be at a value T° sup higher than the maximum temperature T°max. To avoid this, the maximum authorized power Pmax when the engine body 36 is running at the first current engine speed Rci is set at a lower value Pmax2, said value being constituted by the greatest electrical power generated for which the temperature at the outlet of the turbine engine 20 is lower than or equal to the maximum temperature T°max when the engine body 36 is running at the first current engine speed Rci.

[0107] It is easy to see that the curves in Figures 5 and 9 overlap. The curve giving the maximum authorized power Pmax as a function of the current speed Rc is therefore the reciprocal of the curve giving the idle speed Rr as a function of the current power Pc. This means that when the engine speed is established at the idle speed Rr, in other words when the idle speed Rr constitutes the current engine speed Rc, as in the example detailed here, then the current electrical power Pc constitutes the maximum authorized power Pmax.

[0108] Step 150 is followed by a step 160 of limiting the electrical power generated to the maximum authorized power Pmax. During this step 150, the control module 74 limits the electrical power generated by the rotating machine 22 to the maximum authorized power Pmax. In particular, the control module 74 controls the rotating machine 22 so that the current electrical power Pc generated by the latter is equal to the power Pmax or, if these are lower, to the current electrical power requirements of the aircraft 10 reflected by the information Ic. The control module 74 applies this limitation while the engine body 36 is running at the current engine speed Rc and during any subsequent acceleration phase, until the engine speed stabilizes at a new value.

[0109] The control method 100 further comprises, following step 160, a step 170 of controlling the variations in the electrical power generated by the rotating machine 22. These power variations are capped at the maximum authorized power Pmax. If the generated electrical power varies, the control method 100 returns to step 110. Otherwise, the control method 100 continues.

[0110] According to a first variant of continuation of the piloting method 100, the step following step 170 is a step 180 of increasing the thrust setpoint Cp. During this step 180, the engine control module 72 receives from the aircraft 10 an increased thrust setpoint Cp. This step 180 is followed by a step 182 of accelerating the engine body 36 which will be detailed below.

[0111] According to a second variant of continuation of the piloting method 100, the step following step 170 is a step 190 of deducing a future need of the aircraft 10. During this step 190, the management system 78 receives from the aircraft 10 information If representative of a future need of the aircraft 10 in electrical power and deduced from this information If the future need of the aircraft 10 in electrical power.

[0112] Step 190 is followed by a step 192 of comparing said future need with the current electrical power Pc. During this step 192, the management system 78 compares the future need reflected by the information If with the current electrical power Pc. If this future need is less than or equal to the current electrical power Pc, the method returns to step 160. Otherwise, if the future need is greater than the current electrical power Pc, step 192 is followed by a step 194 of modifying the idle speed Rr so that it meets the future need.

[0113] During step 194, the management system 78 modifies the idle speed Rr according to the future need reflected by the information If. For this purpose, the management system 78 calculates for example a future acceleration limit speed and a future overheating limit speed according to said future need, and assigns to the idle speed Rr a new value greater than or equal to those of the future acceleration limit speed and the future overheating limit speed, typically equal to the maximum of the two future limit speeds. Alternatively, the management system 78 assigns to the idle speed Rr a new value determined by the function associating with the current electrical power Pc the corresponding idle speed Rr configured in the management system 78 ([Fig.5]). Then the management system 78 communicates this new value to the engine control module 72.

[0114] Step 194 is followed by a step 196 of comparing the new value of the idle speed Rr with the current engine speed Rc. During this step 196, the engine control module 72 compares the new value of the idle speed Rr received from the management system 78 with the current engine speed Rc. If this new value is less than or equal to the current engine speed Rc, the method 100 returns to step 130. Otherwise, if the new value is greater than the current engine speed Rc, step 196 is followed by step 182 of accelerating the engine body 36.

[0115] During step 182, the engine control module 72 sends to the turbine engine 20 at least one control parameter Pi adapted so that the engine body 36 accelerates. The engine body 36 then accelerates from the current engine speed Rc, while the rotating machine 22 generates an electrical power less than or equal to the maximum authorized power Pmax, until reaching a new current speed Rc.

[0116] In the case where step 182 follows step 196, the new current speed Rc is constituted by a new engine idle speed Rr.

[0117] In the case where step 182 follows step 180 and where the increased thrust setpoint Cp is constituted by a full throttle thrust setpoint, the acceleration is carried out at the maximum acceleration rate Tmax. The current engine speed Rc being greater than or equal to the idle speed Rr and the electrical power generated by the rotating machine 22 being capped at the maximum authorized power Pmax, the engine body 36 reaches then without dropping the target diet RciMe within the allotted time t;.

[0118] It will be noted that the maximum authorized power Pmax is a function of the current regime Rc before the start of step 180 and is not updated during step 182, that is to say that, during the entire acceleration phase 182, the maximum authorized power Pmax remains constant at a value depending on the current regime Rc before acceleration.

[0119] The control method 100 then returns to step 130.

[0120] Optionally, step 182 includes a sub-step 184 of power injection by the electric motor 28. During this step 184, the engine control module 72 sends to the electric motor 28 at least one control parameter P2 adapted to increase the torque of the electric motor 28. Thus the electric motor 28 injects mechanical energy onto the high pressure shaft 44 and contributes to the acceleration of the engine body 36. This makes it possible to increase the maximum acceleration rate Tmax for a given generated electrical power. As a result, the engine idle speed Rr associated with a given current power Pc can be lowered and the maximum electrical power Pmax associated with a current engine speed Rc can be increased.

[0121] Thanks to the exemplary embodiment described above, the engine idle speed Rr can be modulated as a function of the electrical power actually generated by the rotating machine 22. It is therefore possible to lower the engine idle speed Rr below the minimum engine speed necessary to support the maximum electrical power that can be generated by the rotating machine 22. The thrust of the propulsion system 12 at idle can therefore be reduced. This makes it possible to maintain the ratio of the drag of the aircraft 10 to the thrust of the propulsion system 12 at the engine idle speed at a sufficiently high value so that the descent gradient of the aircraft 10 is not too low. Thus, it is not necessary to perform descent maneuvers to break the lift of the aircraft or increase its drag, which makes it possible to save fuel.Similarly, on the ground, reducing the engine idle speed Rr helps reduce wear on the aircraft brakes 10.

Claims

Claims

1. A propulsion system (12) for an aircraft, comprising a turbine engine (20) with a combustion chamber (34) and a motor body (36), the motor body (36) comprising a turbine (42) downstream of the combustion chamber (34), a compressor (40) upstream of the combustion chamber (34) and a transmission shaft (44) for driving the compressor (40) by the turbine (42), the propulsion system (12) also comprising a control system (24), a member (72) for determining a current engine speed (Rc) of the motor body (36) and a rotating machine (22) coupled to the transmission shaft (44) for generating electrical power by taking mechanical power from the transmission shaft (44), in which the control system (24) is configured to limit a current electrical power (Pc) generated by the rotating machine (22), at least when the motor body (36) is in phase acceleration,at a maximum authorized power (Pmax) depending on the current engine speed (Rc) before acceleration, and in which the propulsion system (12) comprises a device (74) for determining the current electrical power (Pc) generated by the rotating machine (22), the control system (24) being configured to establish the engine speed above an idle speed (Rr) depending on the current electrical power (Pc).,

2. Propulsion system (12) according to claim 1, comprising a system (78) for deducing a future need of the aircraft for electrical power generated by the rotating machine (22), the piloting system (24) being configured to accelerate the engine body (36) when said future need is greater than the maximum authorized power (Pmax).

3. Propulsion system (12) according to any one of claims 1 and 2, wherein, when the engine speed is set at idle speed (Rr), the current electrical power (Pc) constitutes the maximum authorized power (Pmax).

4. A propulsion system (12) according to any one of claims 1 to 3, wherein the idle speed (Rr) is greater than or equal to an acceleration limit speed for which the motor body (36), accelerating to the stall limit from said acceleration limit speed while the rotating machine (22) generates the current electrical power (Pc), reaches without stalling, in a given time (h) less than or equal to 10 seconds, a target speed (Rcibie) at which the turboshaft engine (20) produces a substantial percentage of full throttle thrust.

5. Propulsion system (12) according to any one of claims 1 to 4, in which the idle speed (Rr) is greater than or equal to an overheating limit speed for which, when the engine body (36) is rotating at said overheating limit speed while the rotating machine (22) generates the current electrical power (Pc), the temperature of the gases at the outlet of the turbine engine (20) is equal to a predetermined maximum temperature (Tmax).

6. Propulsion system (12) according to any one of claims 1 to 5, in which the maximum authorized power (Pmax) is less than or equal to an acceleration limit power for which the engine body (36), accelerating to the limit of stall from the current engine speed (Rc) while the rotating machine (22) generates said acceleration limit power (Pmax), reaches without stalling, in a given time (f) less than or equal to 10 seconds, a target speed (Rcibie) at which the turbine engine (20) produces a substantial percentage of full throttle thrust.

7. Propulsion system (12) according to any one of claims 1 to 6, in which the maximum authorized power (Pmax) is less than or equal to an overheating limit power for which, when the engine body (36) is rotating at the current speed (Rc) while the rotating machine (22) generates said overheating limit power, the temperature of the gases at the outlet of the turbine engine (20) is equal to a predetermined maximum temperature (Tmax).

8. Propulsion system (12) according to any one of claims 1 to 7, wherein the control system (24) is configured to limit the electrical power generated by the rotating machine (22) when the motor body (36) is not in the acceleration phase.

9. Method (100) for controlling a propulsion system (12) for an aircraft, the propulsion system (12) comprising a turbine engine (20) with a combustion chamber (34) and a motor body (36), the motor body (36) comprising a turbine (42) downstream of the combustion chamber (34), a compressor (40) upstream of the combustion chamber (34) and a transmission shaft (44) for driving the compressor (40) by the turbine (42), the propulsion system (12) also comprising a rotating machine (22) coupled to the transmission shaft (44) for generating electrical power by taking mechanical power on the transmission shaft (44), the control method (100) comprising the following successive steps: - determination (110) of a current electrical power (Pc) generated by the rotating machine (22), - definition (120) of an idle speed (Rr) as a function of the current electrical power (Pc), - establishment (130) of the engine speed above the idle speed (Rr), - determination (140) of a current engine speed (Rc) of the engine body (36), - definition (150) of a maximum authorized power (Pmax) as a function of the current engine speed (Rc), and - acceleration (180) of the motor body (36), the current electrical power (Pc) generated by the rotating machine (22) being limited to the maximum authorized power (Pmax).

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