Aircraft propulsion system with turbine engine coupled to an electric generator the power of which is limited as a function of engine speed

Abstract

This aircraft propulsion system (12) comprises a turbine engine (20), a control system (24), a member (72) for determining a current engine speed (Rc) of the spool of the turbine engine (20), and a rotary machine (22) coupled to the transmission shaft of the turbine engine (20) to generate electrical power by the take-off of mechanical power from the transmission shaft. The control system (24) is configured to limit a current electrical power (Pc) generated by the rotary machine (22), at least when the engine spool is in an accelerating spool-up phase, to a maximum authorized power (Pmax) that is dependent on the current engine speed (Rc) prior to acceleration. The propulsion system further comprises a device (74) for determining the current electrical power (Pc) generated by the rotary machine (22), the control system (24) being configured to establish an engine speed which is above an idling speed (Rr) dependent on the current electrical power.

Description

[0001] DESCRIPTION

[0002] TITLE: Aircraft propulsion system with turboshaft engine coupled to an electric generator with power restricted according to engine speed

[0003] 5 FIELD OF THE INVENTION

[0004] The present invention relates to an aircraft propulsion system, of the type 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

[0005] 10 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.

[0006] The present invention also relates to a method for controlling a system of

[0007] 15 propulsion for aircraft of the aforementioned type.

[0008] TECHNOLOGICAL BACKGROUND

[0009] Propulsion systems of the aforementioned type are known, for example from EP 3 845 750 A1 and US 7,514,810 B2.

[0010] On these known systems, the engine idle speed, i.e. the speed of

[0011] 20 rotation 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.

[0012] It is also known that the propulsion systems equipping aircraft must,

[0013] 25 for safety reasons, be able in all circumstances to restore 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 turboshaft engine at idle must be able to reach a substantial percentage of its full throttle engine speed, that is to say its engine speed when the turboshaft engine produces

[0014] 30 its full throttle thrust, in said critical time. It is therefore appropriate to dimension the engine idle speed so as to be able to achieve this objective when the engine body is accelerated to its maximum capacity. It is also known that the maximum acceleration rate that can be supported by the engine body of a turboshaft engine depends on the resistive torque applied to said engine body. Indeed, the acceleration rate of the engine body of a turboshaft engine is a function of the difference between the temperature at the outlet of the combustion chamber during the acceleration phase and the

[0015] 5 combustion chamber outlet temperature when the turboshaft 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 combustion chamber outlet temperature, for a given engine speed, is capped: the higher the combustion chamber outlet temperature, the greater the outlet flow rate of the

[0016] 10 compressor is low, to the point that, beyond a threshold temperature, the output 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 greater the difference between the temperature

[0017] 15 threshold and the temperature in steady state, and therefore the maximum acceleration rate, is low.

[0018] 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.

[0019] 20 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, the engine idle speed being the same regardless of the electrical power generated by the rotating machine, any other value of the rate

[0020] 25 maximum permissible acceleration would lead to compressor stall when the electrical power generated by the rotating machine is close to its maximum.

[0021] 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 maximum, the

[0022] 30 propulsion system manages to restore most of its maximum thrust within the critical time.

[0023] However, these known systems are not entirely satisfactory. Indeed, with the improvement of the thrust produced by aircraft propulsion systems and the reduction of their drag, the ratio of drag to thrust at the engine speed

[0024] 35 engine idle speed is decreasing. However, it is necessary for this ratio to remain high enough 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 brake wear.

[0025] STATEMENT OF THE INVENTION

[0026] 5 An objective of the invention is to reduce the idle thrust of an aircraft propulsion system.

[0027] 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 body

[0028] 10 engine is in the acceleration phase, at a maximum authorized power depending on the current engine speed before acceleration, and in which 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.

[0029] 15 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 system

[0030] 20 control being configured to accelerate the engine body when said future need is greater than the maximum authorized 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

[0031] 25 in which the engine body, accelerating to the limit of stalling 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;

[0032] 30 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 limit power for which the engine body, accelerating to the stall limit

[0033] 5 from the current engine speed while the rotating machine is generating said acceleration limit 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 maximum authorized power is less than or equal to a limit power of

[0034] 10 overheating 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 limit power

[0035] 15 acceleration and overheating limit power; the control system is configured to limit the electrical power generated by the rotating machine when the engine body is not in the acceleration phase; the propulsion system comprises an electric motor coupled to the shaft of

[0036] 20 transmission; and the turboshaft engine is a turbojet.

[0037] 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 turboshaft engine with a combustion chamber and an engine body, the engine body

[0038] 25 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

[0039] 30 comprising the following successive steps: determination of a current electrical power generated by the rotating machine, definition of an idle speed depending on the current electrical power, and establishment of the engine speed above the idle speed,

[0040] 35 determination of a current engine speed of the engine body, definition of a maximum authorized power as a function of the current engine speed, and acceleration of the engine body, the current electrical power generated by the rotating machine being limited to the maximum authorized power.

[0041] 5 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 control method also comprises the following steps:

[0042] O deduction of a future need of the aircraft in generated electrical power

[0043] 10 by the rotating machine,

[0044] O modification of the idle speed to meet said future need, o comparison of the new idle speed with the current engine speed, and

[0045] O if the new idle speed is higher than the current engine speed, acceleration of the engine body;

[0046] 15 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

[0047] 20 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 the idle speed includes the following sub-steps: o calculation of an acceleration limit speed for which the engine body,

[0048] 25 accelerating to the limit of stall from said acceleration limit speed while the rotating machine is generating 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

[0049] 30 o assignment to the idle speed of a value greater than or equal to that of the acceleration limit speed; the definition of the idle speed includes the following sub-steps: o calculation of an overheating limit speed for which, when the engine body is rotating at said overheating limit speed while the machine

[0050] 35 rotating generates the current electrical power, the temperature of the gases at the outlet of the turboshaft engine is equal to a predetermined maximum temperature, and

[0051] O allocation to the idle speed of a value greater than or equal to that of the overheating limit speed;

[0052] 5 the definition of the 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 control method also includes a step of accelerating the engine body from the current engine speed while the rotating machine

[0053] 10 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 turbine engine produces a substantial percentage of full throttle thrust; the definition of the maximum authorized power includes the sub-steps

[0054] 15 following:

[0055] O calculation of an acceleration limit power for which the engine body, accelerating to the stall limit from the current engine speed while the rotating machine generates said acceleration limit power, reaches without stalling, in a given time less than or

[0056] 20 equal to 10 seconds, a target speed at which the turboshaft engine produces a substantial percentage of full throttle thrust, and

[0057] O 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 sub-steps

[0058] 25 following:

[0059] O calculation of a superheating limit power for which, when the engine body is running at current speed while the rotating machine is generating said superheating limit power, the temperature of the gases at the outlet of the turbine engine is equal to a maximum temperature

[0060] 30 predetermined, and

[0061] O 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 the minimum of the values ​​of the power

[0062] 35 acceleration limit and 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 step comprises injecting mechanical power onto the shaft

[0063] 5 transmission by an electric motor coupled to the transmission shaft.

[0064] BRIEF DESCRIPTION OF THE FIGURES

[0065] 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 appended drawings, in which:

[0066] 10 Figure 1 is a top view of an aircraft comprising two propulsion systems according to an exemplary embodiment of the invention, Figure 2 is a block diagram of one of the propulsion systems of the aircraft of Figure 1, Figure 3 is a simplified longitudinal sectional view of a turbine engine of the

[0067] 15 propulsion system of Figure 2, Figure 4 is a diagram illustrating a method implemented by a control system of the propulsion system of Figure 2, Figure 5 is a graph giving the relationship between an engine idle speed and a current electrical power of the propulsion system of the

[0068] 20 Figure 2, Figure 6 is a first graph showing the characteristic curves of a compressor of the turboshaft engine of Figure 3 in different scenarios, Figure 7 is a first graph showing the evolution over time of the engine speed of the turboshaft engine of Figure 3 in different scenarios,

[0069] 25 Figure 8 is a first graph giving the relationship between the engine speed and the outlet temperature of the turbine engine of Figure 3 in different scenarios, Figure 9 is a graph giving the relationship between a current engine speed and a maximum authorized power of the propulsion system of the

[0070] 30 Figure 2, Figure 10 is a second graph giving the evolution over time of the engine speed of the turboshaft engine of Figure 3 in different scenarios, Figure 11 is a second graph showing the characteristic curves of a compressor of the turboshaft engine of Figure 3 in

[0071] 35 different scenarios, and Figure 12 is a second graph giving the relationship between engine speed and turbine outlet temperature from Figure 3 in different scenarios.

[0072] DETAILED DESCRIPTION OF AN EMBODIMENT

[0073] 5 The aircraft 10 shown in Figure 1 includes propulsion systems 12 for propelling it.

[0074] 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

[0075] 10 (not shown), the propulsion systems 12 are arranged along the fuselage 14, for example near the empennage 16. As a further variant (also not shown), the aircraft 10 comprises a single propulsion system 12 or at least three propulsion systems 12.

[0076] The aircraft 10 also includes an electrical network (not shown).

[0077] 15 One of the propulsion systems 12 is shown in Figure 2.

[0078] 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.

[0079] 20 28.

[0080] 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.

[0081] With reference to Figure 3, the turbine engine 20 conventionally comprises a

[0082] 25 engine casing 30, an internal vein 32 for circulating an air flow through the engine casing 30, a combustion chamber 34 housed in the vein 32, an engine body 36 and a gas exhaust nozzle 38.

[0083] 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.

[0084] 30 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 exiting

[0085] 35 of the combustion chamber 34. 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.

[0086] 5 The transmission shaft 44 is guided in rotation relative to the engine casing 30 by means of bearings (not shown).

[0087] 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.

[0088] 10 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.

[0089] 15 The low pressure body 50 comprises a low pressure compressor 52, a low pressure turbine 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.

[0090] The low pressure compressor 52 is arranged upstream of the high pressure compressor

[0091] 20 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.

[0092] The low pressure shaft 56 is guided in rotation relative to the engine casing 30 by means of bearings (not shown).

[0093] The low pressure shaft 56 is coaxial with the high pressure shaft 44. It therefore also has

[0094] 25 for axis of rotation the longitudinal axis X. In particular, the low pressure shaft 56 extends inside the high pressure shaft 44.

[0095] 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 is thus distinguished

[0096] 30 A (hot), consisting of the portion of the air flow entrained in the internal circulation vein 32, and a secondary air flow B (cold), consisting of the portion of the air flow entrained in the external circulation vein 62.

[0097] 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

[0098] 35 B (cold) on the flow rate of the primary flow A (hot). 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.

[0099] Here, the blower 60 is arranged upstream of the internal circulation vein 32 and

[0100] 5 also drives the airflow into the latter.

[0101] The external circulation vein 62 is here defined between the engine casing 30 and a fan casing 67 surrounding the fan 60.

[0102] 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

[0103] 10 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.

[0104] 15 blower 68.

[0105] The fan shaft 68 is guided in rotation relative to the engine casing 30 by means of bearings (not shown).

[0106] The 20 turboshaft engine is typically a turbojet.

[0107] As seen in Figure 3, the rotating machine 22 is coupled to the high shaft

[0108] 20 pressure 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.

[0109] Advantageously, the rotating machine 22 is able to be decoupled from the high pressure shaft 44.

[0110] 25 Still with reference to Figure 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 X axis. This motor 28 is capable of converting electrical power into mechanical power and injecting the latter onto the high pressure shaft 44.

[0111] Advantageously, the electric motor 28 is suitable for being decoupled from the shaft

[0112] 30 high pressure 44.

[0113] Returning to Figure 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.

[0114] 35 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 Pi, P2 to the turbine engine 20 and / or to the electric motor 28 to establish the engine speed at a target speed.

[0115] The current R regime c is for example determined by the engine control module

[0116] 5 72 based on the control parameters Pi, 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 R c is communicated to the engine control module 72 by a sensor (not shown) of the turbine engine 20 (closed loop operation).

[0117] The engine control module 72 is in particular configured to communicate with the

[0118] 10 turbo engine 20 at least one control parameter Pi adapted to stabilize the engine speed above an idle speed R rprovided by the management system 78. It is also configured to receive a thrust instruction C p of the aircraft 10 and to communicate to the turbine engine 20 and / or to the electric motor 28 at least one control parameter Pi, P2 adapted to accelerate the engine body 36 at an acceleration rate depending

[0119] 15 of the thrust instruction C p and the current engine speed R c The acceleration rate is capped at a maximum acceleration rate T max provided by the management system 78.

[0120] The thrust instruction C p is less than or equal to a full throttle thrust setpoint. 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

[0121] 20 thrust called “full throttle” 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 R gaz on the Figures. When the thrust instruction C p is equal to the full throttle thrust setpoint, this is therefore interpreted by the engine control module 72 as a setpoint

[0122] 25 acceleration of the engine body 36 at said full throttle speed.

[0123] A first control parameter Pi, communicated to the turboshaft 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.

[0124] 30 The engine control module 72 is still configured to communicate the current engine speed R cto the 76 clamping system.

[0125] 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

[0126] 35 current electric power P c generated by the rotating machine 22 and an auxiliary electrical power P a 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 instruction C1, C2 adapted to adjust the current electrical power P c and the auxiliary electrical power P a .

[0127] The current and auxiliary electrical powers P c , P a are for example determined

[0128] 5 by the control module 74 on the basis of the instructions C1, 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 P c , P a are communicated to the control module 74 by sensors (not shown) at the level of the rotating machine 22, of the or each auxiliary source 26

[0129] 10 and / or the transmission member 29 (closed loop operation).

[0130] A first instruction C1, 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 connection switch of the source

[0131] 15 auxiliary 26 to the distribution member 29.

[0132] Typically, the control module 74 is configured to receive information 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 C1, C2 adapted so that the sum of the current and auxiliary electrical powers P c , P a

[0133] 20 satisfies the needs reflected by the information.

[0134] In particular, the control module 74 is configured to limit the current electrical power P c , at least during certain phases, at a maximum authorized electrical power P max provided by the clamping system 76, and to control the auxiliary source(s) 26 so that the latter(s) complete(s) the needs of

[0135] 25 the aircraft 10 in electrical power. In other words, the control module 74 is configured to control the rotating machine 22 so that the current electrical power P c generated by the latter is equal to the power P max or, if these are lower, to the current needs reflected by the information, and to control the auxiliary source(s) 26 so that the latter(s) provide(s), when the needs

[0136] 30 currents reflected by the information are greater than the power P max , an auxiliary electrical power P a equal to the difference between said current needs and the power P max .

[0137] The control module 74 is configured to apply this limitation of the current electrical power P c especially when the motor body 36 is in phase

[0138] 35 acceleration. Preferably, the control module 74 is configured to apply this limitation of the current electrical power P c at any time, including when the engine body 36 is not in the acceleration phase.

[0139] Advantageously, the control module 74 is also configured to communicate the current electrical power P c to the management system 78.

[0140] 5 The restriction system 76 is configured to receive from the engine control module 72 information representative of the current engine speed R c and to deduce from the latter the maximum authorized power P max . The bridling system 76 is also configured to communicate this maximum authorized power P max to command module 74.

[0141] 10 In particular, the limiting system 76 is configured to determine the maximum authorized power P maxso that the following two constraints are respected: the engine body 36, accelerating from the current engine speed R c while the rotating machine 22 generates the maximum authorized power P max , reached without dropping out in a given time t, (Figure 7) less than or equal to

[0142] 15 10 seconds, for example between 7.5 and 8.5 seconds, a target speed R cible (Figure 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 turbine engine 20, for example at the outlet of the low pressure turbine 54, remains below a maximum temperature

[0143] 20 T° max (Figure 8) predetermined when the motor body 36 rotates at the current speed R c while the rotating machine 22 generates the maximum authorized power P max .

[0144] For this purpose, the limiting system 76 is configured to determine the maximum authorized power P max so that it is less than or equal to:

[0145] 25 an acceleration limit power for which the engine body 36, accelerating to the stall limit from the current engine speed R c while the rotating machine 22 generates said acceleration limit power, reaches said target speed R without stalling cible in the said allotted time t i , and to

[0146] 30 an overheating limit power for which, when the motor body 36 is running at the current speed R c 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 said predetermined maximum temperature T° max. In particular, the limiting system 76 is configured to determine the maximum authorized power P maxso that it is equal to the minimum of the acceleration limit power and the superheat limit power.

[0147] For this purpose, the clamping system 76 is for example configured to calculate, from

[0148] 5 of turboshaft parameters 20 and current engine speed R c , the acceleration power limit and the overheating power limit, and then to determine the maximum permitted power P max depending on the said power limits. Alternatively, a maximum authorized power P max respecting these constraints and depending on the flight conditions was determined upstream for each possible engine speed, and the restriction system 76 is

[0149] 10 configured with a function associating with each possible engine speed, depending on the flight conditions, the maximum authorized power P max corresponding.

[0150] The management system 78 is configured to receive from the control module 74 information representative of the current electrical power P c and to deduce from the latter the idle speed R r and the maximum acceleration rate T max . The management system

[0151] 15 78 is also configured to communicate said idle speed R r and maximum acceleration rate T max to the engine control module 72.

[0152] In particular, the management system 78 is configured to define the maximum acceleration rate T max below a limit acceleration rate beyond which the compressor 40 stalls when the current electrical power P c is generated.

[0153] 20 The management system 78 is further configured to define the idle speed R rso that the following two constraints are respected: the engine body 36, accelerating from idle speed R r at the maximum acceleration rate T max while the rotating machine 22 generates the current electrical power P c , reaches the target speed R without dropping out cible

[0154] 25 in the allotted time t,, 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 maximum temperature T o max predetermined when the engine body 36 is running at idle speed R r while the rotating machine 22 generates the current electrical power

[0155] 30 Pc.

[0156] For this purpose, the management system 78 is configured to determine the idle speed R rso that it is greater than or equal to: an acceleration limit speed for which the engine body 36, accelerating to the limit of stalling from said acceleration limit speed during

[0157] 35 that the rotating machine 22 generates the current electrical power P c , achieved without dropping said target regime R cible in said allotted time t,, and at an overheating limit speed for which, when the motor body 36 rotates at said overheating limit speed while the rotating machine 22

[0158] 5 generates the current electric power P c , the temperature of the gases at the outlet of the turboshaft engine 20 is equal to the maximum temperature T° max predetermined.

[0159] In particular, the management system 78 is configured to determine the idle speed R r so that it is equal to the maximum of the acceleration limit speed and the overheating limit speed.

[0160] 10 For this purpose, the management system 78 is for example configured to calculate, from parameters of the turbine engine 20 and the current electrical power P c , the acceleration limit speed and the overheating limit speed, and then to determine the idle speed R r depending on the said limit speeds. Alternatively, an idle speed R r respecting these constraints and depending on the flight conditions was determined in advance for each

[0161] 15 possible generated electrical power, and the management system 78 is configured with a function associating with each possible generated electrical power, depending on the flight conditions, the idle speed R r corresponding.

[0162] It is easily understood that, when the engine speed is established at idle speed R r , the current electric power P c constitutes the maximum authorized power P max .

[0163] 20 The management system 78 is also configured to receive from the aircraft 10 information k representative of a future need of the aircraft 10 in electrical power and to deduce from this information k the future need of the aircraft 10 in electrical power. The management system 78 is also configured to modify the idle speed R r to meet this future need and to communicate the idle speed R r so modified

[0164] 25 to engine control module 72.

[0165] In particular, the management system 78 is configured to only modify the idle speed R r based on information k only when the future need is greater than the current electrical power P c (it being understood that the management system 78 is also configured to modify the idle speed R r , up or down, depending on the

[0166] 30 current electric power P c ). The management system 78 is configured so that, in such a case, the idle speed R r is increased so that the following two constraints are met: the engine body 36, accelerating from idle speed R r at the maximum acceleration rate T max while the rotating machine 22 generates a

[0167] 35 electrical power equal to the future need, reaches the target regime R without dropping out cible in the allotted time t,, 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 maximum temperature T° max predetermined when the engine body 36 is running at idle speed R r while the rotating machine 22 generates an equal electrical power

[0168] 5 for future needs.

[0169] For this purpose, the management system 78 is configured to modify the idle speed R r so that it is greater than or equal to: a future acceleration limit regime for which the engine body 36, accelerating to the limit of stalling from said future limit regime

[0170] 10 of acceleration while the rotating machine 22 generates an electrical power equal to the future need, reached without stalling said target speed R cible in said allotted time t,, and at a future overheating limit speed for which, when the motor body 36 rotates at said future overheating limit speed while the machine

[0171] 15 rotating 22 generates an electrical power equal to the future need, the temperature of the gases at the outlet of the turboshaft engine 20 is equal to the maximum temperature T° max predetermined.

[0172] In particular, the management system 78 is configured to modify the idle speed R rso that it is equal to the maximum of the future acceleration limit regime and the

[0173] 20 future overheating limit regime.

[0174] For this purpose, the management system 78 is for example configured to calculate, from parameters of the turboshaft engine 20 and the future requirement, the future acceleration limit speed and the future overheating limit speed, and to then modify the idle speed R r depending on the said future limit regimes. Alternatively, an idle regime R r respecting these

[0175] 25 constraints and function of the flight conditions was determined upstream for each possible generated electrical power, and the management system 78 is configured with a function associating with each possible generated electrical power the idle speed R r corresponding depending on the flight conditions.

[0176] It is easily understood that when the future need is greater than the power

[0177] 30 maximum authorized P max , the idle speed R r thus modified is brought to a value higher than that of the current regime R c This mechanically causes the engine body 36 to accelerate, since the engine control module 72 is configured to set the engine speed above the idle speed R r .

[0178] The control system 24, including in particular the engine control module 72, the

[0179] 35 control module 74, the bridling 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

[0180] 5 propulsion system 12.

[0181] A control method 100 implemented by the propulsion system 12 will now be described, with reference to Figure 4.

[0182] This method 100 comprises a first step 110 of determining the current electrical power P c . During this step 110, the control module 74 determines the

[0183] 10 current electric power P cgenerated by the rotating machine 22, for example on the basis of the instructions C1, C2 which 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 level of the rotating machine 22 or the transmission member 29 (closed loop operation).

[0184] 15 This step 110 is followed by a step 120 of defining the idle speed R r . During this step, the management system 78 defines the idle speed R r depending on the current electrical power P c .

[0185] 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 speed

[0186] 20 overheating limit, and a third sub-step 126 of assigning a value to the idle speed R r. During the first sub-step 122, the management system 78 calculates the acceleration limit speed as a function of the current electrical power P c . During the second sub-step 124, the management system 78 calculates the overheating limit regime as a function of the current electrical power P c . Finally, during the third sub-

[0187] 25 step 126, the management system 78 assigns to the idle speed R r 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 R r , during this sub-step 126, a value equal to the maximum of the acceleration limit speed and the overheating limit speed.

[0188] 30 As a variant (not shown), step 120 comprises the single sub-step 126 of assigning a value to the idle speed R r. In this variant, the management system 78 assigns to the idle speed R r , during this sub-step 126, a value determined by a function configured in the management system 78, said function associating with the current electrical power P c , for a given flight condition, the idle speed R r

[0189] 35 corresponding. An example of such a function is given in Figure 5. As seen in Figure 5, the engine idle speed R r increases with the current electric power P c : the first engine idle speed R r1 associated with a first current power P c i is less than the second engine idle speed R r2 associated with a second current power P C2 greater than the first current power

[0190] 5 P c1 This is easily explained, as detailed below with reference to Figures 6 to 8.

[0191] Figure 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. Represented therein are: the pumping line Lp of the high pressure compressor 40; as well known

[0192] 10 of the person 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 the person skilled in the art, this is a line beyond which the risks of stalling of the high pressure compressor 40 do not allow compliance

[0193] 15 aeronautical safety requirements; Lf operating lines Pc1 and Lf Pc2 of the high pressure compressor 40 when the electrical power generated by the rotating machine 22 is equal, respectively, to the first current power P c1and to the second current power P C2 ; as well known to those skilled in the art, these lines

[0194] 20 operating Lf pc1 and Lf Pc2 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 P999c1 and to the second current power P C2 ;

[0195] 25 the isoregime lines Li Rr1 , Li Rr2 and Li Rgaz from high pressure compressor 40 to first engine idle speed R r1 , at the second engine idle speed Rr2 and at full throttle speed R gaz ; as well known to those skilled in the art, these isoregime lines Li Rr1 , Li Rr2 and LiR gaz define the flow rate - compression ratio couples achievable by the high pressure compressor 40 when the

[0196] 30 engine body 36 rotates, respectively, at the first engine idle speed R r1 , at the second engine idle speed R r2 and at full throttle R gaz ; and the acceleration transient curves Ta 1-1-1 , Your 1-1-2 and your 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: o from the first engine idle speed R r1 , at a first acceleration rate T1 while the electrical power generated by the rotating machine 22 is equal to the first current power P c i,

[0197] O from the first engine idle speed R r1 , at the first rate

[0198] 5 acceleration T1 while the electrical power generated by the rotating machine 22 is equal to the second current power P C2 , And

[0199] O from the second engine idle speed Rr2 , at a second acceleration rate T2 lower than the first acceleration rate T1 while

[0200] 10 the electrical power generated by the rotating machine 22 is equal to the second current power P C2 .

[0201] Figure 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 C a1-1 of the engine body 36 when this

[0202] 15 last is accelerated from the first engine idle speed R r1 at the first acceleration rate T1, a second acceleration curve C a1-2 of the engine body 36 when the latter is accelerated from the first engine idle speed R r1 at the second acceleration rate T2, and

[0203] 20 a third acceleration curve C a2-2of the engine body 36 when the latter is accelerated from the second engine idle speed R r2 at the second acceleration rate T2.

[0204] As seen in Figure 6, the Tai-1-1 transient acceleration curve partly runs along the margin line Lm. This means that the high pressure compressor 40 is at the

[0205] 25 limit of stalling during the acceleration phase at the first acceleration rate Ti. The first acceleration rate T1 therefore constitutes the maximum acceleration rate T max for the first current power P c i. As illustrated by the acceleration curve C a1-1 in Figure 7, this acceleration rate T1 allows the engine body 36 to be accelerated from the first engine idle speed R r1 so as to reach the target regime R cible in time

[0206] 30 allocated t,.

[0207] If we wanted to accelerate the engine body 36 at this same first acceleration rate T1 from the same first engine speed R r1 when the electrical power generated by the rotating machine 22 is equal to the second current power P C2 , the compression ratio of the high pressure compressor 40 would follow the transient acceleration curve

[0208] 35 Ta 1-1-2 . However, as visible in Figure 6, this transient acceleration curve Ta 1-1-2 crosses the margin line Lm. Accelerate 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 P C2 therefore involves excessive risks of stalling of the high pressure compressor 40, so that this first acceleration rate Ti is unacceptable. To accelerate the engine body 36 when the electrical power generated by

[0209] 5 the rotating machine 22 is equal to the second current power P C2 , 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 Ta 2-2-2 in Figure 6.

[0210] 10 However, as illustrated by the acceleration curve Ca 1-2 in Figure 7, accelerate the engine body 36 to the second acceleration rate T2 from the first engine idle speed R r1 does not allow the target regime R to be reached cible in the allotted time t i . To achieve this objective, it is therefore necessary to raise the engine idle speed R r at the second engine idle speed R r2 , as illustrated by curve Ca 2-2 of the Figure

[0211] 15 7.

[0212] The second engine idle speed R r2 must therefore be higher than the first engine idle speed R r1 to allow the engine body 36 to reach the target speed R cible in the allotted time t i , without stalling, when the electrical power generated by the rotating machine 22 is equal to the second current power P C2 .

[0213] 20 The second engine idle speed R r2 must also be higher than the first engine idle speed R r1 to prevent the temperature of the exhaust gases at the outlet of the turboshaft engine 20 from exceeding the maximum temperature T° max , as understood from reading Figure 8.

[0214] Figure 8 is in fact a graph giving the relationship between the engine speed of the

[0215] 25 engine body 36 and the temperature at the outlet of the turboshaft engine 20 in different scenarios. Represented there: a first temperature curve T Pc1 from the output of the turbine engine 20 when the electrical power generated by the rotating machine 22 is equal to the first current power P c i, and

[0216] 30 a second temperature curve T Pc2 of the output of the turbine engine 20 when the electrical power generated by the rotating machine 22 is equal to the second current power P C2 .

[0217] As seen in Figure 8, the first and second temperature curves T Pc1 , TRC2 each have a U-shaped profile, the idle speed variation range R r itself

[0218] 35 located in the region of the graph where these curves are decreasing. In addition, the first idle speed R r1is such that when the engine body 36 rotates at said idle speed R r1 while the electrical power generated by the rotating machine 22 is equal to the first current power P c i, the temperature at the outlet of the turboshaft engine 20 is equal to the maximum temperature T o max . Finally, the second temperature curve T Pc2 is logically located above the first temperature curve T Pc1 , to the extent that

[0219] 5 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 R r1 when the electrical power generated by the rotating machine 22 is equal to the second current power P C2 , the temperature at the outlet of the turboshaft engine 20 would be at a value T° sup

[0220] 10 higher than the maximum temperature T o max To avoid this, a second engine idle speed R is chosen. r2 higher, this second engine idle speed R r2 being constituted by the lowest engine speed for which the temperature at the outlet of the turboshaft engine 20 is less than or equal to the maximum temperature T max when the electrical power generated by the rotating machine 22 is equal to the second current power

[0221] 15 Pc2.

[0222] Returning to Figure 4, step 120 is followed by a step 130 of establishing the engine speed above the idle speed R r . During this step 130, the engine control module 72 sends at least one control parameter Pi, P2 to the turbine engine 20 and, optionally, to the electric motor 28 so that the engine speed of the body

[0223] 20 engine 36 is established at a current engine speed Rc greater than or equal to idle speed R r . For example, during this step 130, the engine speed is set at engine idle speed R r This is typically the case when the aircraft 10 requests minimal propulsion from the propulsion system 12, such as when parking on the runway or during descent.

[0224] 25 The control method 100 also comprises a step 140 of determining the current engine speed R c . During this step 140, the engine control module 72 determines the current engine speed R c on the basis of the control parameter(s) Pi, P2 which 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

[0225] 30 shown) of the turboshaft engine 20 (closed loop operation).

[0226] Step 140 is followed by a step 150 of defining the maximum authorized power P max . During this step, the bridling system 76 defines the maximum authorized power P max depending on the current engine speed R c .

[0227] In the example shown, step 150 comprises a first sub-step 152 of

[0228] 35 calculation of the acceleration limit power, a second sub-step 154 ​​of calculation of the overheating limit power, and a third sub-step 156 of allocation of a value to the maximum authorized power P max . During the first sub-step 152, the limiting system 76 calculates the acceleration limit power as a function of the current engine speed R c . During the second sub-step 154, the limiting system 76 calculates the overheating limit power as a function of the current engine speed R c . Finally, during

[0229] 5 the third sub-step 156, the limiting system 76 attributes to the maximum authorized power P max a value less than or equal to those of the acceleration limit power and the overheating limit power. Typically, the limiting system 76 assigns to the maximum authorized power P max , during this sub-step 156, a value equal to the minimum of the values ​​of the acceleration limit power and the limit power of

[0230] 10 overheating.

[0231] Alternatively (not shown), step 150 comprises the single sub-step 156 of assigning a value to the maximum authorized power P max . In this variant, the bridling system 76 assigns the maximum authorized power P max , during this sub-step 156, a value determined by a function parameterized in the system of

[0232] 15 bridle 76, said function associating with the current engine speed R c, for a given flight condition, the maximum authorized power P max corresponding. An example of such a function is given in Figure 9.

[0233] As seen in this Figure, the maximum authorized power P max increases with the current engine speed R c : the first maximum authorized power P max1 associated

[0234] 20 to a first current regime R c1 is less than the second maximum authorized power P max2 associated with a second current regime R c2 higher than the first current regime R c1 This is easily explained, as detailed below with reference to Figures 10 to 12.

[0235] Figure 10 is a graph showing the evolution over time of the engine speed of the engine body 36 in different scenarios. It shows:

[0236] 25 a first acceleration curve Ca' 1-1of the engine body 36 when the latter is accelerated from the first current engine speed R c1 at a first acceleration rate Ti, a second acceleration curve Ca' 1-2 of the engine body 36 when the latter is accelerated from the first current engine speed R c1 to a

[0237] 30 second acceleration rate T2 lower than the first acceleration rate T1, and a third acceleration curve Ca'2-2 of the motor body 36 when the latter is accelerated from the second current motor speed R c2 at the second acceleration rate T2.

[0238] 35 As illustrated by the third acceleration curve Ca' 2-2 , the second acceleration rate T2 is sufficient to allow the engine body 36 to reach the target speed R ciblein the allotted time t, when it is accelerated from the second current speed RC2. On the other hand, as illustrated by the second acceleration curve Ca'1-2, this second acceleration rate T2 is insufficient to allow the motor body 36 to reach the target speed R cible in the given time t, when it is accelerated from the first regime

[0239] 5 current R c1 . As illustrated by the first acceleration curve Ca'1-1, in order for the motor body 36 to reach the target speed R cible in the given time t, when it is accelerated from the first current regime R c1 , it must be accelerated at the first acceleration rate Ti.

[0240] Figure 11 is a throughput vs. compression ratio graph showing the curves

[0241] 10 characteristics of the high pressure compressor 40 of the turboshaft engine 20 in different scenarios. Represented are: the pumping line Lp of the high pressure compressor 40; the margin line Lm of the high pressure compressor 40; the operating lines Lfp max1 and Lf pmax2 of the high pressure compressor

[0242] 15 40 when the electrical power generated by the rotating machine 22 is equal, respectively, to the first maximum authorized power P max1 and to the second maximum authorized power P max2 ; the isoregime lines Li Rc1 , Li Rc2 and LiR gaz from the high pressure compressor 40 to the first current engine speed R c1 , at the second current engine speed R c2

[0243] 20 and at full throttle R gaz; and the acceleration transient curves Ta'1-1-1, Ta'1-1-2 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:

[0244] O from the first current engine speed R c1 , at the first rate

[0245] 25 acceleration T1 while the electrical power generated by the rotating machine 22 is equal to the first maximum authorized power P max1 ,

[0246] O from the first current engine speed R c1 , at the first acceleration rate T1 while the electrical power generated by the

[0247] 30 rotating machine 22 is equal to the second maximum authorized power P max2 , and o from the second current engine speed R C 2, at the second acceleration rate T2 while the electrical power generated by the rotating machine 22 is equal to the second maximum power

[0248] 35 authorized P max2 . As illustrated by the acceleration transient curve Ta'2-2-2, when the motor body 36 is accelerated at the second acceleration rate T2 from the second current regime R C 2 while the electrical power generated by the rotating machine 22 is equal to the second maximum authorized power P max2 , the compression ratio of the compressor

[0249] 5 high pressure 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'1-1-2, if we wish to accelerate the motor body 36 at the first acceleration rate T1 from the first current speed R c1 while the electrical power generated by the rotating machine 22 is always equal to the second maximum power

[0250] 10 authorized P max2, the compression ratio of the high pressure compressor 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 P max2 when the first acceleration rate T1 is applied. To be able to apply this first acceleration rate T1 and thus allow the motor body 36 to reach the

[0251] 15 target diet R cible in the given time t, when it is accelerated from the first current regime R c1 while the electrical power generated by the rotating machine 22 is equal to the maximum authorized power P max , it is necessary to lower this maximum authorized power P max to a P value max1 lower, as illustrated by the acceleration transient curve Ta' 1-1-1.

[0252] 20 The first maximum authorized power P max1must therefore be less than the second maximum authorized power P max2 to allow the engine body 36 to reach the target speed R cible in the allotted time t, without stalling when the motor body 36 rotates at the first current motor speed R c1 .

[0253] Another reason why the first maximum permitted power P max1 East

[0254] 25 less than the second maximum authorized power P max2 is illustrated by Figure 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. It shows: a first temperature curve T Pmax1 from the outlet of the turboshaft engine 20

[0255] 30 when the electrical power generated by the rotating machine 22 is equal to the first maximum authorized power P max1 , and a second temperature curve Tpmax2 of the output of the turbine engine 20 when the electrical power generated by the rotating machine 22 is equal to the second maximum authorized power P max2 .

[0256] 35 As seen in Figure 12, the first and second temperature curves Tp max1 , Tp max2 each have a U-shaped profile, the range of variation of the current engine speed R c located in the region of the graph where these curves are decreasing. In addition, the second current engine speed R c2 is such that when the engine body 36 rotates at said second current engine speed R c2 while the electrical power generated by the rotating machine 22 is equal to the second maximum authorized power P max2 , there

[0257] 5 temperature at the outlet of the turboshaft engine 20 is equal to the maximum temperature T° max . Finally, the second temperature curve Tp max2is logically located above the first temperature curve Tp max1 , 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

[0258] 10 generate the second maximum authorized power P max2 when the engine body 36 rotates at the first current engine speed R c1 , the temperature at the outlet of the turboshaft engine 20 would be at a value T° sup higher than the maximum temperature T o max . To avoid this, the maximum permitted power P max when the engine body 36 rotates at the first current engine speed R c1 is set to a value P max2 lower, said value being constituted by

[0259] 15 the greatest electrical power generated for which the temperature at the outlet of the turbine engine 20 is less than or equal to the maximum temperature T o max when the engine body 36 rotates at the first current engine speed R c1 .

[0260] It is easy to see that the curves in Figures 5 and 9 overlap. The curve giving the maximum authorized power P max depending on the current regime R c is therefore the

[0261] 20 reciprocal of the curve giving the idle speed R r depending on the current power P c . This means that when the engine speed is established at idle speed R r , in other words when the idle speed R r constitutes the current engine speed R c , as in the example detailed here, then the current electric power P c constitutes the maximum authorized power P max .

[0262] 25 Step 150 is followed by a step 160 of limiting the electrical power generated to the maximum authorized power P max . During this step 150, the control module 74 limits the electrical power generated by the rotating machine 22 to the maximum authorized power P max . In particular, the control module 74 controls the rotating machine 22 so that the current electrical power P c generated by the latter

[0263] 30 is equal to the power P max or, if these are lower, to the current electrical power requirements of the aircraft 10 reflected by the information le. The control module 74 applies this limitation while the engine body 36 is running at the current engine speed R c and during any subsequent acceleration phase, until the engine speed stabilizes at a new value.

[0264] 35 The control method 100 also 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 P max . If the generated electrical power varies, the control method 100 returns to step 110. Otherwise, the control method 100 continues.

[0265] According to a first variant of continuation of the piloting method 100, the step making

[0266] 5 following step 170 is a step 180 of increasing the thrust setpoint C p . During this step 180, the engine control module 72 receives a thrust instruction C from the aircraft 10. p increased. This step 180 is followed by a step 182 of acceleration of the motor body 36 which will be detailed later.

[0267] According to a second variant of continuation of the piloting method 100, the step making

[0268] 10 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 k representative of a future need of the aircraft 10 in electrical power and deduces from this information k the future need of the aircraft 10 in electrical power.

[0269] Step 190 is followed by a step 192 of comparing said future need with the

[0270] 15 current electric power P c . During this step 192, the management system 78 compares the future need reflected by the information k to the current electrical power P c . If this future need is less than or equal to the current electrical power P c , the method returns to step 160. Otherwise, if the future need is greater than the current electrical power P c, step 192 is followed by a step 194 of modification of the idle speed R r so that he

[0271] 20 meets the future need.

[0272] During step 194, the management system 78 modifies the idle speed R r based on the future need reflected by the information f . For this purpose, the management system 78 calculates, for example, a future acceleration limit speed and a future overheating limit speed based on said future need, and assigns to the idle speed R r a new one

[0273] 25 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 R r a new value determined by the function associating with the current electrical power P c idle speed R rcorresponding parameterized in the management system 78 (Figure 5). Then the system

[0274] 30 management 78 communicates this new value to the engine control module 72.

[0275] Step 194 is followed by step 196 of comparing the new value of the idle speed R r at current engine speed R c . During this step 196, the engine control module 72 compares the new value of the idle speed R r received from the management system 78 at current engine speed R c . If this new value is less than or equal to the

[0276] 35 current engine speed R c , the method 100 returns to step 130. Otherwise, if the new value is greater than the current engine speed R c , step 196 is followed by step 182 of accelerating the motor body 36.

[0277] 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 body

[0278] 5 engine 36 then accelerates from the current engine speed R c , while the rotating machine 22 generates an electrical power less than or equal to the maximum authorized power P max , until reaching a new current regime R c .

[0279] In the case where step 182 follows step 196, the new current regime R c is made up of a new engine idle speed R r .

[0280] 10 In the case where step 182 follows step 180 and where the thrust instruction C p increased is constituted by a full throttle thrust instruction, acceleration is done at the maximum acceleration rate T max . The current engine speed R c 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 P max , the motor body 36 then reaches without

[0281] 15 get the target diet R cible in the allotted time t,.

[0282] It should be noted that the maximum authorized power P max is a function of the current regime R c 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 P max remains constant at a value depending on the current regime R c before acceleration.

[0283] 20 The control method 100 then returns to step 130.

[0284] 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

[0285] 25 mechanical energy on the high pressure shaft 44 and contributes to the acceleration of the motor body 36. This makes it possible to increase the maximum acceleration rate T max for a given generated electrical power. Therefore, the engine idle speed R r associated with a current power P c data can be lowered and the maximum electrical power P max associated with a current engine speed R c can be increased.

[0286] 30 Thanks to the embodiment described above, the engine idle speed R rcan be modulated according to the electrical power actually generated by the rotating machine 22. It is therefore possible to lower the engine idle speed R r 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

[0287] 35 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 engine idle speed at a value high enough so that the descent gradient of the aircraft 10 is not too low. Thus, it is not necessary to carry out descent maneuvers to break the aircraft's lift or increase its drag, which saves fuel. Similarly, on the ground, reducing the engine idle speed R r helps reduce wear and tear

[0288] 5 aircraft brakes 10.

Claims

CLAIMS 1. 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 5 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 (R c ) of the motor body (36) and a rotating machine (22) coupled to the transmission shaft (44) for the 10 generation of 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 (P c) generated by the rotating machine (22), at least when the motor body (36) is in the acceleration phase, at maximum power 15 authorized (P max ) function of the current engine speed (R c ) before acceleration, and in which the propulsion system (12) comprises a device (74) for determining the current electrical power (P c ) generated by the rotating machine (22), the control system (24) being configured to establish the engine speed above an idle speed (R r ) function of electrical power 20 current (P c ).

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 power 25 authorized (P max ).

3. Propulsion system (12) according to any one of claims 1 and 2, wherein, when the engine speed is set at idle speed (R r ), the current electric power (P c ) constitutes the maximum authorized power (P max ).

4. Propulsion system (12) according to any one of claims 1 to 3, in 30 which the idle speed (R r ) is greater than or equal to an acceleration limit speed for which the engine body (36), accelerating to the limit of stalling from said acceleration limit speed while the machine rotating (22) generates the current electrical power (P c ), reaches without stalling, in a given time (t,) less than or equal to 10 seconds, a target speed (R cible ) at which the turbine engine (20) produces a substantial percentage of full throttle thrust. 5 5. Propulsion system (12) according to any one of claims 1 to 4, in which the idle speed (R r ) is greater than or equal to an overheating limit speed for which, when the motor body (36) rotates at said overheating limit speed while the rotating machine (22) generates the current electrical power (P c ), the temperature of the gases at the outlet of the turboshaft engine (20) is equal to a 10 maximum temperature (T max ) predetermined.

6. Propulsion system (12) according to claims 4 and 5, wherein the idle speed (R r ) is equal to the maximum of the acceleration limit speed and the overheating limit speed.

7. Propulsion system (12) according to any one of claims 1 to 6, in 15 which the maximum authorized power (P max) is less than or equal to an acceleration power limit for which the engine body (36), accelerating to the stall limit from the current engine speed (R c ) while the rotating machine (22) generates said acceleration limit power (P max ), reaches without stalling, in a given time (t,) less than or equal to 10 seconds, a target speed 20 (R cible ) at which the turbine engine (20) produces a substantial percentage of full throttle thrust.

8. Propulsion system (12) according to any one of claims 1 to 7, in which the maximum authorized power (P max ) is less than or equal to an overheating limit power for which, when the motor body (36) rotates 25 at current rate (R c ) while the rotating machine (22) generates said superheat limit power, the temperature of the gases at the outlet of the turboshaft engine (20) is equal to a maximum temperature (Tmax ) predetermined.

9. Propulsion system (12) according to claims 7 and 8, wherein the maximum authorized power (P max ) is equal to the minimum of the limiting power 30 acceleration and overheating limit power.

10. Propulsion system (12) according to any one of claims 1 to 9, 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.

11. Method (100) for controlling a propulsion system (12) for an aircraft, the propulsion system (12) comprising a turbine engine (20) with a combustion chamber 5 combustion (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 10 transmission (44) for generating electrical power by taking mechanical power from 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), 15 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 (R c) of the engine body (36), definition (150) of a maximum authorized power (P max ) depending on the regime 20 current motor (R c ), and acceleration (180) of the motor body (36), the current electric power (P c ) generated by the rotating machine (22) being limited to the maximum authorized power (P max ).

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