Aircraft propulsion system, aircraft and helicopter incorporating such a propulsion system, and method for controlling a propulsion system

Abstract

The system (100) includes a control system (124) designed to: - in response to a received rapid start command, accelerate a first output shaft (116A) disengaged from a first turboshaft engine (102A); - during acceleration, not implement any limitation on the acceleration command of the first output shaft (116A); - calculate and monitor an estimate of the time to clutch engagement; - when the estimated time to clutch engagement falls below a predefined threshold, reduce the acceleration of the first output shaft (116A); then - before clutch engagement, implement the limitation on the acceleration command of the first output shaft (116A). Figure for the abbreviation: Fig. 1

Description

Title of the invention: PROPULSION SYSTEM OF AN AIRCRAFT, AIRCRAFT AND HELICOPTER COMPRISING SUCH A PROPULSION SYSTEM AND METHOD FOR CONTROLLING A PROPULSION SYSTEM Technical field of the invention

[0001] The present invention relates to an aircraft propulsion system, an aircraft and a helicopter comprising such a propulsion system and a method for controlling a propulsion system. Technological background

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those currently in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain less energy-intensive and more environmentally friendly aeronautical components and products, whose integration and use in civil aviation have moderate environmental impacts, with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

[0006] For example, a propulsion system of a aircraft comprising: - a first turboshaft engine having a first output shaft; - a second turboshaft engine with a second output shaft; - a main output shaft designed to be connected to a load mechanics; - a freewheel clutch system between the first and second output shafts and the main output shaft; - a control system designed to: • control the first turboshaft engine while the first output shaft is engaged with the main output shaft, by implementing a limitation of the acceleration setpoint of the first output shaft to an acceleration limit; • control the first turboshaft engine so that the first output shaft is disengaged and the second turboshaft engine so that the second output shaft is engaged; • In response to a received rapid start instruction, accelerate the first disengaged output shaft.

[0007] The first turboshaft engine is in particular disengaged from the main output shaft in order to idle, or even to stop (so-called "standby" engine in English) while the second turboshaft engine provides all the power, thus optimizing efficiency.

[0008] In response to the demand for rapid start-up, the re-engagement of the first output shaft must be as rapid as possible while ensuring that there is no damage to the freewheel clutch system.

[0009] In patent application published under number US 2020 / 0508148 A1, it is proposed to apply a speed command to the first output shaft, this command being in the form of a ramp up to the clutch speed. When the speed of the first output shaft reaches a predefined threshold, the acceleration (or, equivalently, torque) command is limited to a limit enabling clutch engagement. However, the response of the first output shaft to the ramp depends on the internal and / or external conditions of the turboshaft engine, such that it is not possible to predict whether the output shaft speed will increase slowly or rapidly in response to the ramp.Therefore, by applying the acceleration setpoint limit when the speed of the first output shaft reaches the predefined threshold, the acceleration limit may be applied too early (when the speed of the first output shaft increases slowly) or too late (when the speed of the first output shaft increases rapidly). When the acceleration limit is applied too early, the speed of the first output shaft will take a long time to reach that of the second shaft. main output shaft. When the acceleration limit is applied too late, the speed of the first output shaft will reach that of the main output shaft too quickly, resulting in a shock during re-engagement.

[0010] The invention therefore aims to solve at least some of the aforementioned problems and constraints. Summary of the invention

[0011] The invention is the result of technological research aimed at significantly improving aircraft performance and, in this respect, contributes to reducing the environmental impact of aircraft. To this end, the invention relates to an aircraft propulsion system comprising: a first turboshaft engine having a first output shaft; a second turboshaft engine with a second output shaft; a main output shaft designed to be connected to a mechanical load; a freewheel clutch system between the first and second output shafts and the main output shaft; a control system designed for: command the first turboshaft engine while the first output shaft is engaged with the main output shaft, by implementing a limitation of the acceleration setpoint of the first output shaft to an acceleration limit; control the first turboshaft engine so that the first output shaft is disengaged and the second turboshaft engine so that the second output shaft is engaged; in response to a received instruction to start quickly, accelerate the first disengaged output shaft;

[0012] characterized in that the control system is designed, during acceleration in response to receiving the rapid start command, not to implement limiting the acceleration setpoint of the first output shaft such that the acceleration of the first output shaft exceeds the acceleration limit, and in that the control system is further designed to: calculate and monitor an estimate of a time before clutch engagement; When the estimated time to clutch engagement falls below a predefined threshold, reduce the acceleration of the first output shaft; then Before engaging the clutch, implement the limitation of the acceleration setpoint of the first output shaft.

[0013] Thus, thanks to the invention, the limitation of the acceleration setpoint is no longer Applied at the beginning of the rapid start-up phase, this allows for a faster acceleration. This last point involves strongly braking the first output shaft before the clutch and then reactivating the acceleration setpoint limitation, thus controlling the acceleration so that the clutch engages properly.

[0014] Furthermore, the use of the time before clutching estimation to begin reducing acceleration makes it possible to ensure that the speed of the first output shaft will reach that of the main output shaft by limiting the risk of shock and in a short time, substantially independent of the internal or external conditions of the turbomotor.

[0015] The invention may further include one or more of the following optional features, according to any technically possible combination.

[0016] Optionally, during the reduction of the acceleration of the first output shaft, this acceleration is monitored, and the limitation of the acceleration setpoint of the first output shaft is implemented when the acceleration of the first output shaft falls below the acceleration limit. This allows control of the acceleration decrease, which is not possible by immediately applying the acceleration limit.

[0017] Optionally also, the acceleration limit is a function of a rotation speed of the first output shaft.

[0018] Optionally, to accelerate the first disengaged output shaft, the control system is designed to set a fuel flow setpoint for the first turboshaft engine to a predefined value, for example, a maximum possible value. By setting the flow setpoint rather than providing a speed setpoint and allowing a control chain to deduce the flow setpoint, it is possible to avoid the reaction time of the control chain and thus implement the acceleration more quickly in response to receiving the rapid start setpoint.

[0019] Optionally also, the propulsion system further includes a starter coupled to the first gas generator and, to accelerate the first disengaged output shaft, the control system is designed to activate the starter.

[0020] Optionally also, to reduce the acceleration of the first output shaft, the control system is designed to set a fuel flow setpoint for the first turboshaft engine to a predefined value, for example a minimum possible value.

[0021] Optionally also, to reduce the acceleration of the first output shaft, the control system is designed to disable the starter.

[0022] An aircraft comprising a propulsion system according to the invention is also proposed.

[0023] A helicopter is also proposed comprising a propulsion system according to the invention and, as a mechanical load, a main rotor.

[0024] A method for controlling an aircraft propulsion system is also proposed, comprising: a first turboshaft engine having a first output shaft; a second turboshaft engine having a second output shaft; a main output shaft designed to be connected to a mechanical load; and a freewheel clutch system between the first and second output shafts and the main output shaft, the method comprising the steps of: - control the first turboshaft engine while the first output shaft is engaged with the main output shaft, by implementing a limitation of the acceleration setpoint of the first output shaft to an acceleration limit; - to control the first turboshaft engine so that the first output shaft is disengaged and the second turboshaft engine so that the second output shaft is engaged; - in response to a received instruction to start quickly, accelerate the first disengaged output shaft; characterized in that, during acceleration in response to receiving the fast start command, the limitation of the acceleration command of the first output shaft is not implemented, so that the acceleration of the first output shaft exceeds the acceleration limit, and in that it further comprises: - calculate and monitor an estimate of a time before clutch engagement; - when the estimated time before clutch engagement falls below a predefined threshold, reduce the acceleration of the first output shaft; then - before clutching, implement the limitation of the acceleration setpoint of the first output shaft.

[0025] Also proposed is a computer program downloadable from a communication network and / or recorded on a computer-readable medium, characterized in that it includes instructions for the execution of the steps of a process according to the invention, when said program is executed on a computer. Brief description of the figures

[0026] The invention will be better understood with the aid of the following description, given solely by way of example and made with reference to the accompanying drawings in which: - [Fig. 1] is a simplified view of a propulsion system according to the invention, - [Fig. 2] is a block diagram of a system control method propulsion of the [Fig.1], - [Fig.3] groups together chronograms of physical quantities of the propulsion system of [Fig.1], - Figure 4 is a chronogram showing the evolution of a flow rate and a value minimum flow rate of a first turboshaft engine of the propulsion system of the [Fig. 1], and - Figure 5 is a functional diagram of a system control system propulsion of the [Fig.l]. Detailed description of the invention

[0027] With reference to [Fig. 1], a propulsion system 100 according to the invention for an aircraft will now be described. The aircraft is, for example, a helicopter.

[0028] The propulsion system 100 comprises, firstly, first and second turboshaft engines 102A, 102B. Each turboshaft engine 102A, 102B comprises a gas generator 104A, 104B and a free turbine 106A, 106B supplied by the gas generator 104A, 104B. The gas generator 104A, 104B comprises an air compressor 108A, 108B and a combustion chamber 110A, 110B connected to each other. In the combustion chamber 110A, 110B, fuel is intended to be burned with air compressed by the air compressor 108A, 108B to deliver gases providing kinetic energy. Each gas generator 104A, 104B further comprises a turbine 112A, 112B for the partial expansion of these gases, connected to the air compressor 108A, 108B by a drive shaft 114A, 114B, in order to rotate the air compressor 108A, 108B. The gases are also designed to rotate the free turbine 106A, 106B.Each turboshaft engine 102A, 102B further comprises an output shaft 116A, 116B connected to the free turbine 106A, 106B in order to be driven in rotation by the latter, at a speed denoted n2A, respectively n2B. Each speed n2A, n2B is generally expressed as a percentage of a fixed rated speed.

[0029] The propulsion system 100 further includes a main output shaft 118 designed to be connected to a mechanical load (not shown), for example a main rotor of the helicopter, and to rotate at a speed denoted nr to drive this mechanical load into rotation.

[0030] The propulsion system 100 further includes a freewheel clutch system 120 between the output shafts 116A, 116B of the turboshaft engines 102A, 102B and the main output shaft 118.

[0031] The propulsion system 100 further comprises, for each turboshaft engine 102A, 102B, an associated starter 122A, 122B. Each starter 122A, 122B comprises, for example, an electric machine designed to drive the gas generator 104A, 104B of the associated turboshaft engine 102A, 102B in rotation.

[0032] The propulsion system 100 further comprises a control system 124 for the turboshaft engines 102A, 102B and the starters 122A, 122B.

[0033] The control system 124 includes, in particular, for each turboshaft engine 102A, 102B, a control chain 126A, 126B designed to determine an acceleration setpoint n2'A*, n2'B* of the output shaft 116A, 116B from a speed setpoint n2A*, n2B* of the output shaft 116A, 116B and to determine a fuel flow setpoint DA*, DB* from the acceleration setpoint n2'A*, n2'B*. The control system 124 is thus designed to apply this fuel flow setpoint DA*, DB* to the turboshaft engine 102A, 102B.

[0034] The control system 124 further includes, for each turboshaft engine 102A, 102B, an acceleration limiting module 128A, 128B, designed to limit the acceleration setpoint of n2A'*, n2B'* to an acceleration limit LA, LB which varies, for example, according to the speed n2A, n2B. Generally, this acceleration limit LA, LB remains below 6% of the rated speed per second (with the rated speed expressed in revolutions per second). For example, the acceleration limit LA, LB is between 4% and 6% of the rated speed per second, depending on the operating point of the turboshaft engine 102A, 102B.

[0035] With reference to [Fig.2], [Fig.3] and [Fig.4], an example of a method 200 for controlling the propulsion system 100, implemented by the control device 124, will now be described.

[0036] During a step 202, the control system 124 controls the turboshaft engine 102A while its output shaft 116A is engaged with the main output shaft 118. During this step 202, the control device 124 uses the control chain 126A and the acceleration limiting module 128A to limit the acceleration setpoint of n2'A* to the acceleration limit LA. Limiting the acceleration setpoint ensures that, when the output shaft 116A is engaged, the acceleration of the main rotor during startup or following a drop in speed, for example due to a high power demand, is not excessive. This limitation makes it possible, in the case of a helicopter, to avoid yaw jerks, that is to say a tendency of the helicopter to rotate on itself resulting from a different consideration of the acceleration between the main rotor and the tail rotor of the helicopter.

[0037] During a step 204, the control system 124 rotates the output shaft 116A at a speed lower than that of the main output shaft 118 so that it is disengaged from the main output shaft 118. For example, the turboshaft engine 102A is in a standby, or turning, mode in which the combustion chamber 110A is shut down and the gas generator 104A is driven by the starter 122A (control C equal to one in [Fig. 3]), at a speed low enough that the speed n2A of the output shaft 116A is zero (0% of the rated speed of the output shaft 116A). For example, the gas generator 104A is driven by the starter 122A at a speed between 5 and 20% of a nominal speed of the 104A gas generator.

[0038] During a step 206, the control system 124 receives a request for a rapid start of the output shaft 116A, i.e. a request for a rapid re-engagement of the output shaft 116A. This therefore means that the speed n2A of the output shaft 116A must reach that of the main output shaft 118 as quickly as possible.

[0039] During a step 208, in response to receiving the request for a rapid start, the control system 124 commands the turboshaft engine 102A and / or the starter 122A to accelerate the output shaft 116A. During this step, the control system 124 inhibits the acceleration limiting module 128A so as not to implement the limitation of the acceleration setpoint n2'A* to the limit LA. For example, the control system 124 is designed to apply no limitation to the acceleration setpoint n2'A*. Alternatively, one or more other limitations of the acceleration setpoint n2'A* than the limit LA could be applied, for example, very high safety limits that are always applied. In addition, the control system 124 accelerates the output shaft 116A. For this purpose, the control system 124 sets, for example, the flow rate setpoint DA to a very high predefined value, for example the maximum value.For example, control system 124 commands starter 122A to accelerate output shaft 116A.

[0040] In parallel with step 208, which accelerates the output shaft 116A, the control system 124 calculates, over time, during step 210, an estimate T of the time to engagement, that is, the time it will take for the rotational speed n2A of the output shaft 116A to reach the speed nr of the main output shaft 118. The calculation of this estimate uses, for example, an acceleration n2'A of the output shaft 116A. For example, the control system 124 uses the following formula: T = (nr - n2A) / n2'A. During step 210, the control system 124 further monitors this estimate T to detect when it falls below a predefined threshold.

[0041] During a step 212, the control system 124 detects that the estimate T has fallen below the predefined threshold.

[0042] During a step 214, in response to the detection that the estimate T has fallen below the predefined threshold, the control system 124 commands the turbomotor 124 and / or the starter 122A to reduce the acceleration of the output shaft 116A.

[0043] For example, the control system 124 sets the flow rate setpoint DA* to a low value, for example a minimum value DA*min which can vary over time, as illustrated in [Fig. 4], depending on the operating point of the first turboshaft engine 102A. By remaining above or at this minimum value DA*min, the first turboshaft engine 102A is ensured not to shut down. When the flow rate setpoint Da* is equal to the minimum value DA*min as illustrated in [Fig. 4], the system is operating at the optimal operating point. in the maximum deceleration capacity of the first 102A turboshaft engine.

[0044] Again, for example, the control system 124 deactivates the starter 122A (control C set to zero in [Fig. 3]). During step 214, the control system 124 further monitors the acceleration n2'A to detect when it falls below the acceleration limit LA.

[0045] During a step 216, the control system 124 detects that the acceleration n2'A has passed below the acceleration limit LA.

[0046] During a step 218, in response to the detection that the acceleration n2'A has fallen below the acceleration limit LA, the control system 124 activates the acceleration limitation module 128A to implement the limitation of the acceleration setpoint n2'A*.

[0047] During step 220, the output shaft 116A reaches the speed nr of the main output shaft 118 and engages with it. As the acceleration limiting module 128A is activated at this time, the engagement occurs at an acceleration below the limit LA.

[0048] With reference to [Fig. 5], the control system 124 is, for example, a computer system comprising a data processing unit 502 (such as a microprocessor) and a main memory 504 (such as RAM, from the English "Random Access Memory") accessible by the processing unit 502. The computer system further comprises, for example, a network interface and / or a computer-readable medium, such as, for example, a local medium (such as a local hard disk 506) or a remote medium (such as a remote hard disk accessible via the network interface through a communication network) or a removable medium (such as a USB flash drive, from the English "Universal Serial Bus", or a CD, from the English "Compact Disc" or a DVD, from the English "Digital Versatile Disc") readable by means of an appropriate reader of the computer system (such as a USB port or a CD and / or DVD disc drive).A computer program 508 containing instructions for the processing unit 502 is stored on the medium 506 and / or downloadable via the network interface. This computer program 508 is, for example, intended to be loaded into the main memory 504, so that the processing unit 502 can execute its instructions. The computer program includes, in particular, instructions for executing the steps of process 200 when said program is executed by the processing unit 502 of the computer system.

[0049] Alternatively, all or part of these modules could be implemented as hardware modules, i.e. in the form of an electronic circuit, for example micro-wired, not involving a computer program.

[0050] In conclusion, it should also be noted that the invention is not limited to the embodiments described above. It will indeed be apparent to those skilled in the art that various Modifications may be made to the embodiments described above, in light of the teaching which has just been disclosed to him.

[0051] In the detailed presentation of the invention given above, the terms used shall not be interpreted as limiting the invention to the embodiments set forth in this description, but shall be interpreted as including all equivalents which can be foreseen by a person skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

Claims

Claims

1. Aircraft propulsion system (100) comprising: - a first turboshaft engine (102A) having a first output shaft (116A); - a second turboshaft engine (102B) having a second output shaft (116B); - a main output shaft (118) adapted to be connected to a mechanical load; - a freewheel clutch system (120) between the first and second output shafts (116A, 116B) and the main output shaft (118); - a control system (124) designed to: • controlling (202) the first turboshaft engine (102A) while the first output shaft (116A) is engaged to the main output shaft (118), by implementing a limitation of the acceleration setpoint of the first output shaft (116A) to an acceleration limit (LA); • control (204) the first turbine engine (102A) so that the first output shaft (116A) is disengaged and the second turbine engine (102B) so that the second output shaft (116B) is engaged; • in response to receiving (206) a quick start instruction, accelerating (208) the first disengaged output shaft (116A); characterized in that the control system (124) is configured, during acceleration (208) in response to receiving the quick start command, not to implement the limitation of the acceleration command of the first output shaft (116A) so that the acceleration of the first output shaft (116A) exceeds the acceleration limit, and in that the control system (124) is further configured to: - calculate and monitor (210) an estimate of a time before engagement; - when the estimated time before engagement falls below a predefined threshold, reduce the acceleration of the first output shaft (116A); then - before clutch engagement, implement (218) the limitation of the acceleration setpoint of the first output shaft (116A).

2. Propulsion system (100) according to claim 1, wherein, during the reduction of the acceleration of the first output shaft (116A), this acceleration is monitored and wherein the limitation of the acceleration setpoint of the first output shaft (116A) is implemented when the acceleration of the first output shaft (116A) falls below the acceleration limit (LA).

3. A propulsion system (100) according to claim 1 or 2, wherein the acceleration limit (LA) is a function of a rotational speed (n2A) of the first output shaft (116A).

4. Propulsion system (100) according to any one of claims 1 to 3, wherein, to accelerate (208) the disengaged first output shaft (116A), the control system (124) is designed to set a fuel flow rate (DA) for the first turbine engine (102A) to a predefined value, for example a maximum possible value.

5. A propulsion system (100) according to any one of claims 1 to 4, further comprising a starter (122A) coupled to the first gas generator (104A) and wherein, to accelerate (208) the disengaged first output shaft (116A), the control system (124) is adapted to activate the starter (122A).

6. A propulsion system (100) according to any one of claims 1 to 5, wherein, to reduce the acceleration (212) of the first output shaft (116A), the control system (124) is adapted to set a fuel flow rate setpoint (DA) for the first turbine engine (102A) to a predefined value, for example a minimum possible value.

7. A propulsion system (100) according to any one of claims 1 to 6, wherein, to reduce the acceleration (212) of the first output shaft (116A), the control system (124) is adapted to deactivate the starter (122A).

8. A helicopter comprising a propulsion system according to any one of claims 1 to 7 and, as mechanical load, a main rotor.

9. Method (200) of controlling a propulsion system of an aircraft comprising: a first turbine engine (102A) having a first output shaft (116A); a second turbine engine (102B) having a second output shaft (116B); a main output shaft (118) adapted to be connected to a mechanical load; and a freewheel clutch system between the first and second output shafts (116A, 116B) and the main output shaft (118), the method comprising: - controlling (202) the first turboshaft engine (102A) while the first output shaft (116A) is engaged to the main output shaft (118), by implementing a limitation of the acceleration setpoint of the first output shaft (116A) to an acceleration limit (LA); - controlling (204) the first turbine engine (102A) so that the first output shaft (116A) is disengaged and the second turbine engine (102B) so that the second output shaft (116B) is engaged; - in response to receiving (206) a quick start instruction, accelerating (208) the first disengaged output shaft (116A); characterized in that, during acceleration in response to receipt of the quick start command, the limitation of the acceleration command of the first output shaft (116A) is not implemented so that the acceleration of the first output shaft (116A) exceeds the acceleration limit, and in that it further comprises: - calculate and monitor (210) an estimate of a time before engagement; - when the estimate of the time before engagement falls below a predefined threshold, reduce (214) the acceleration of the first output shaft (116A); then - before clutching, implement (218) the limitation of the acceleration setpoint of the first output shaft (116A).

10. Computer program (508) downloadable from a communications network and / or recorded on a computer-readable medium, characterized in that it comprises instructions for the execution of the steps of a method (200) according to claim 9, when said program is executed on a computer.

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