PROPULSION SYSTEM OF AN AIRCRAFT, AIRCRAFT AND HELICOPTER COMPRISING SUCH A PROPULSION SYSTEM AND METHOD FOR CONTROLLING A PROPULSION SYSTEM

Abstract

The system (100) comprises a control system (124) designed to: - in response to receiving a quick start instruction, accelerate a first output shaft (116A) disengaged from a first turbine engine (102A); - during acceleration, not implement a limitation of the acceleration instruction of the first output shaft (116A); - calculate and monitor an estimate of a time before engagement; - when the estimate of the time before engagement falls below a predefined threshold, reduce the acceleration of the first output shaft (116A); then - before engagement, implement the limitation of the acceleration instruction of the first output shaft (116A). Figure for abstract: 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 a propulsion system of an aircraft, an aircraft and a helicopter comprising such a propulsion system and a method of controlling a propulsion system. Technological background

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

[0003] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, 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 and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work covers new generations of aircraft engines, the lightening of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as essential complements to technological progress, aeronautical biofuels.

[0006] For example, we know from the state of the art a propulsion system for a aircraft 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 load mechanics; - a freewheel clutch system between the first and second output shafts and the main output shaft; - a control system designed to: • controlling the first turbine engine while the first output shaft is engaged to the main output shaft, by implementing a limitation of the acceleration setpoint of the first output shaft to an acceleration limit; • control the first turbine engine so that the first output shaft is disengaged and the second turbine engine so that the second output shaft is engaged; • in response to receiving a quick start command, accelerate the first disengaged output shaft.

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

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

[0009] In the patent application published under number US 2020 / 0508148 A1, it is proposed to apply a speed setpoint for the first output shaft, this setpoint 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) setpoint is limited to a limit allowing clutch engagement. However, the response of the first output shaft to the ramp depends on the conditions internal and / or external to the turbine engine, so that it is not possible to predict whether the speed of the output shaft will increase slowly or quickly in response to the ramp.Thus, 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 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, causing a shock when re-engaging.

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

[0011] The invention is the result of technological research aimed at significantly improving the performance of aircraft and, in this sense, contributes to reducing the environmental impact of aircraft. For this purpose, the invention relates to an aircraft propulsion system 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; an overrunning clutch system between the first and second output shafts and the main output shaft; a control system designed to: controlling the first turbine engine while the first output shaft is engaged to the main output shaft, by implementing a limitation of the acceleration setpoint of the first output shaft to an acceleration limit; controlling the first turbine engine so that the first output shaft is disengaged and the second turbine engine so that the second output shaft is engaged; in response to receiving a quick start command, accelerating the first disengaged output shaft;

[0012] characterized in that the control system is designed, during acceleration in response to receipt of the rapid start instruction, 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 before engagement falls below a predefined threshold, reduce the acceleration of the first output shaft; then before 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 fast start phase, which allows for a faster increase in speed. This last point involves braking the first output shaft strongly before the clutch and then reactivating the limitation of the acceleration setpoint, acceleration control so that the clutch is carried out in good conditions.

[0014] Furthermore, the use of the estimation of the time before engagement to begin to reduce the acceleration, makes it possible to ensure that the speed of the first output shaft will reach that of the main output shaft while limiting the risk of shock and in a short time, substantially independently of the internal or external conditions of the turbo-engine.

[0015] The invention may further comprise one or more of the following optional features, in 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 makes it possible to control the acceleration reduction, which is not possible by immediately applying the acceleration limit.

[0017] Also optionally, the acceleration limit is a function of a rotational speed of the first output shaft.

[0018] Also optionally, to accelerate the first disengaged output shaft, the control system is designed to set a fuel flow setpoint for the first turbine 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 derive the flow setpoint therefrom, this avoids the control chain's reaction time and thus allows acceleration to be implemented more quickly in response to receiving the quick start setpoint.

[0019] Also optionally, the propulsion system further comprises 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] Also optionally, to reduce the acceleration of the first output shaft, the control system is designed to set a fuel flow setpoint for the first turbine engine to a predefined value, for example a minimum possible value.

[0021] Also optionally, 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] There is also provided a helicopter comprising a propulsion system according to the invention and, as mechanical load, a main rotor.

[0024] There is also provided a method for controlling a propulsion system of an aircraft comprising: a first turbine engine having a first output shaft; a second turbine 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: - controlling the first turboshaft engine while the first output shaft is engaged to the main output shaft, by implementing a limitation of the acceleration setpoint of the first output shaft to an acceleration limit; - controlling the first turbine engine so that the first output shaft is disengaged and the second turbine engine so that the second output shaft is engaged; - in response to receiving a quick start instruction, accelerate the first disengaged output shaft; 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 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 engagement falls below a predefined threshold, reduce the acceleration of the first output shaft; then - before clutch engagement, implement the limitation of the acceleration setpoint of the first output shaft.

[0025] There is also provided a computer program downloadable from a communication network and / or recorded on a computer-readable medium, characterized in that it comprises instructions for executing the steps of a method 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 with reference to the appended drawings in which: - [Fig.l] is a simplified view of a propulsion system according to the invention, - [Fig.2] is a block diagram of a control method of the system of propulsion of the [Fig.l], - [Fig.3] groups together timing diagrams of physical quantities of the propulsion system of [Fig.l], - [Fig.4] is a chronogram of the evolution of a flow rate and a value minimum flow rate of a first turbine engine of the propulsion system of [Fig.l], and - [Fig.5] is a functional diagram of a control system of the system propulsion of [Fig.l]. Detailed description of the invention

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

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

[0029] The propulsion system 100 further comprises 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 in rotation.

[0030] The propulsion system 100 further comprises 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 turbine engine 102A, 102B, an associated starter 122A, 122B. Each starter 122A, 122B comprises, for example, an electrical machine designed to rotate the gas generator 104A, 104B of the associated turbine engine 102A, 102B.

[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 comprises in particular, for each turbine 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 turbine engine 102A, 102B.

[0034] The control system 124 further comprises, for each turbine engine 102A, 102B, an acceleration limitation module 128A, 128B, designed to limit the acceleration setpoint of n2A'*, n2B'* to an acceleration limit LA, LB which varies for example in particular as a function of the speed n2A, n2B. Generally, this acceleration limit LA, LB remains less than 6% of the nominal speed per second (with the nominal speed expressed in revolutions per second). For example, the acceleration limit La, Lb is between 4% and 6% of the nominal speed per second, depending on the operating point of the turbine engine 102A, 102B.

[0035] With reference to [Fig.2], [Fig.3] and [Fig.4], an example 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 turbine engine 102A while its output shaft 116A is engaged to the main output shaft 118. During this step 202, the control device 124 uses the control chain 126A and the acceleration limitation module 128A to implement the limitation of the acceleration setpoint from n2'A* to the acceleration limit LA. The limitation of the acceleration setpoint makes it possible, when the output shaft 116A is engaged, to ensure that the acceleration of the main rotor during start-up or following a drop in speed, for example due to a high power demand, is not too high. 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 turn 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 turbine engine 102A is in a standby mode, called turning mode, in which the combustion chamber 110A is off and the gas generator 104A is driven by the starter 122A (command C equal to one in [Fig. 3]), at a speed sufficiently low so that the speed n2A of the output shaft 116A is zero (0% of the nominal 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 gas generator 104A.

[0038] During a step 206, the control system 124 receives a request for rapid starting of the output shaft 116A, i.e. a request for 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 quick start request, the control system 124 controls the turbine engine 102A and / or the starter 122A to accelerate the output shaft 116A. During this step, the control system 124 inhibits the acceleration limitation 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 which are always applied. Furthermore, 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.Still for example, the control system 124 controls the starter 122A to accelerate the output shaft 116A.

[0040] In parallel with the step 208 of accelerating the output shaft 116A, the control system 124 calculates over time, during a step 210, an estimate T of a time before clutch engagement, that is to say the time that the rotation speed n2A of the output shaft 116A will take 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 controls the turboshaft engine 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 change over time, as illustrated in [Fig. 4], depending on the operating point of the first turbine engine 102A. By remaining above or at this minimum value DA*min, the first turbine 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], we are within the maximum deceleration capacity of the first 102A turboshaft engine.

[0044] Still for example, the control system 124 deactivates the starter 122A (command C at 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 fallen 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 a step 220, the output shaft 116A reaches the speed nr of the main output shaft 118, and engages with the latter. Since the acceleration limitation module 128A is at this time activated, the engagement takes place at an acceleration lower than 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 a RAM memory, 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 and accessible via the network interface through a communication network) or even a removable medium (such as a USB key, 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 disk reader).A computer program 508 containing instructions for the processing unit 502 is recorded 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 executes its instructions. The computer program comprises in particular instructions for executing the steps of the method 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 in the form of hardware modules, that is to say in the form of an electronic circuit, for example micro-wired, not involving a computer program.

[0050] In conclusion, it will also be noted that the invention is not limited to the embodiments described above. It will indeed appear 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 which is made above, the terms used must not be interpreted as limiting the invention to the embodiments set out in the present description, but must be interpreted to include all equivalents whose prediction is within the reach of those 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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