STARTING PROCEDURE FOR AN AIRCRAFT ENGINE

Abstract

An aspect of the invention relates to a start-up method (100) for an aircraft engine (1), wherein the engine (1) is connected to a lubrication circuit (6) comprising, in particular, an oil pump system (7), the lubrication circuit (6) being constructed and arranged to circulate oil in the engine (1), and wherein an operating mode of the engine (1) comprises a stop mode and a standby mode, the start-up method (100) being characterised in that it comprises, during a start-up phase, the steps of: - measuring (101) an oil temperature, the measuring step (101) being carried out by a temperature detection device; - as a function of the temperature measured compared with a threshold temperature, and as a function of the operating mode of the engine, selecting (102) an oil flow profile for start-up to be applied in the engine, the step of selecting (102) being carried out by a computer; - applying (103) the oil flow profile for start-up selected by means of the oil pump system, the oil pump system being controlled by the computer.

Description

DESCRIPTION TITLE: METHOD FOR STARTING AN AIRCRAFT ENGINE TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the starting of an aircraft engine, such as a gas turbine for a turboshaft engine or turbogenerator. The invention's field of application is more particularly that of light aircraft, especially helicopters. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] An aircraft engine is usually coupled to an electric starter. To start the engine, the starter receives electrical power, for example from a battery bank or auxiliary power unit. The starter operates as an electric motor and drives the engine to rotate.

[0003] It is known that the viscosity of an engine's lubricating oil increases as the temperature drops. Thus, in extremely cold conditions, for example below -40°C, the oil has a high viscosity, resulting in high engine starting torque. Tests have shown that a major portion of the total resisting torque is generated by the oil pump. Indeed, it must circulate and pressurize extremely viscous oil, which induces significant losses, potentially representing up to 80% of the resisting torque provided by the gas turbine itself and its associated equipment.

[0004] The starter motor can be sized to provide torque corresponding to the engine's starting torque in extremely cold conditions. However, this torque is significantly higher than the starting torque at warmer temperatures. Therefore, starting in very cold weather necessitates oversizing the starter motor and its power electronics, resulting in significant weight and size. Furthermore, the battery bank must be capable of supplying the high power required for starting.

[0005] A method for starting an aircraft engine is known from document FR-B1-2960592, which consists of preheating the oil before starting the engine using a starter motor. More specifically, if the measured temperature is below a Once a temperature threshold is reached, for example -15°C, icing conditions are indicated by a warning light on the instrument panel. This signals to the pilot that engine oil preheating is required. The pilot can then issue a preheating command, which engages the starter motor to rotate the engine at a low speed. For example, the engine is rotated at a speed between 8% and 12% of its windmill speed. This controls the torque required from the starter motor. Due to heat losses from the starter motor, the oil temperature gradually increases. Heat losses from the engine housing bearings and, to a lesser extent, from the gearbox, also contribute to the oil temperature increase. Consequently, the engine's resistive torque gradually decreases.This stage during which the engine is driven at low speed therefore constitutes an oil preheating stage, which can last for example between 8 and 10 minutes.

[0006] Even though the oil pressure is reduced due to the low engine speed, it is still present, resulting in significant losses and necessitating the use of an oversized starter. Furthermore, this setup only optimizes starting in cold weather.

[0007] Furthermore, such a solution for preheating the oil to reduce its viscosity, and therefore mechanical losses, is not suitable for helicopters. Indeed, during certain specific operations, for example a mountain rescue in sub-zero temperatures, the pilot does not have the necessary time to preheat the oil before starting the engine. SUMMARY OF THE INVENTION

[0008] The invention provides a technical solution to the technical problems mentioned above by allowing an aircraft engine to be started under optimal conditions regardless of the oil temperature and also allows an aircraft to be equipped with a non-oversized starter.

[0009] In this context, one aspect of the invention relates, in its broadest sense, to a method for starting an aircraft engine in which said engine is coupled to a lubrication circuit comprising, in particular, an oil pump system, said lubrication circuit being constructed and arranged to circulate oil in said engine, and in which a mode of operation the engine includes a stop mode and a standby mode, said starting process being characterized in that it comprises, during a starting phase, the steps of: measuring an oil temperature, said measurement step being carried out by a temperature detection device; depending on said measured temperature, compared to a threshold temperature, and depending on the operating mode of said engine, selecting a starting oil flow profile to be applied in said engine, said selection step being carried out by a computer; applying said selected starting oil flow profile by means of said oil pump system, said oil pump system being controlled by said computer.

[0010] Thanks to the aircraft engine starting method according to this aspect of the invention, it is possible, during startup, to select an oil flow profile based on the oil temperature. For example, if the oil temperature is low, it is possible to select a zero oil flow rate for a short period in order to eliminate losses caused by the oil being displaced by the oil pump system. A short period is defined as a period shorter than the nominal starting time (for the temperature considered) and which does not degrade overall mechanical reliability. A short period could, for example, be less than 10 seconds.

[0011] These features eliminate the need to equip aircraft, and particularly helicopters, with an oversized starter. Conversely, when the oil temperature is high, a high oil flow rate can be selected to maximize lubrication, for example, of the oil bearings during the starting phase. In addition to the features mentioned in the preceding paragraph, the aircraft engine starting method according to this aspect of the invention may have one or more of the following complementary features, considered individually or in all technically feasible combinations.

[0012] According to one aspect of the invention, each oil flow profile comprises a first phase and a second phase, said second phase corresponding to a predetermined oil pressure at the engine inlet, applied when the engine speed reaches a threshold speed value.

[0013] According to one aspect of the invention, if the measured oil temperature is below the threshold temperature and if the engine operating mode is the stop mode, the oil flow profile comprises: a first phase during which the oil pressure at the engine inlet is zero until the engine speed reaches a threshold speed; a second phase during which the oil pressure at the engine inlet is equal to a limit oil pressure value.

[0014] According to one aspect of the invention, if the measured oil temperature is above the threshold temperature, and if the engine operating mode is standby mode, the oil flow profile comprises: a first phase during which the oil pressure at the engine inlet is equal to a limit oil pressure value until the engine speed reaches a threshold speed; a second phase during which the oil pressure at the engine inlet is equal to a threshold oil pressure value, said threshold oil pressure value being lower than said limit oil pressure value.

[0015] According to one aspect of the invention, if the oil temperature is above the threshold temperature and if the engine operating mode is the stop mode, the oil flow profile comprises: a first phase during which the oil pressure at the engine inlet is increasing until the engine speed reaches a threshold speed; a second phase during which the oil pressure at the engine inlet is equal to a limit oil pressure value.

[0016] Another aspect of the invention relates to an aircraft comprising: an engine whose operating mode includes a stop mode and a standby mode; and a temperature detection device constructed and arranged to measure an oil temperature; said aircraft implementing the above method and comprising: a computer constructed and arranged to, as a function of said measured temperature, select a starting oil flow profile to be applied in said engine; a lubrication circuit comprising in particular an oil pump system, said oil pump system being constructed and arranged to apply said selected starting oil flow profile.

[0017] According to one aspect of the invention, the oil pump system includes a variable displacement oil pump.

[0018] According to one aspect of the invention, the oil pump system comprises an oil pump and an electro-valve, said electro-valve being located downstream of said oil pump and being constructed and arranged to redirect all or part of the oil flow from said oil pump into a reservoir.

[0019] According to one aspect of the invention, the oil pump system comprises an oil pump and a mechanical decoupling device constructed and arranged to activate or deactivate the rotation of the oil pump.

[0020] According to one aspect of the invention, the oil pump system comprises an oil pump assisted in rotation by a rotating electrical machine.

[0021] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0022] The figures are presented for illustrative purposes only and are in no way limiting to the invention.

[0023] [Fig. 1] schematically illustrates a method for starting an aircraft engine according to one aspect of the invention.

[0024] [Fig. 2] schematically illustrates a first example of an oil flow profile according to one aspect of the invention.

[0025] [Fig. 3] schematically illustrates a second example of an oil flow profile according to one aspect of the invention.

[0026] [Fig. 4] schematically illustrates a third example of an oil flow profile according to one aspect of the invention.

[0027] [Fig. 5] schematically illustrates an aircraft engine according to a first aspect of the invention.

[0028] [Fig. 6] schematically illustrates an aircraft engine according to a second aspect of the invention.

[0029] [Fig. 7] schematically illustrates an aircraft engine according to a third aspect of the invention.

[0030] [Fig. 8] schematically illustrates an aircraft engine according to a fourth aspect of the invention.

[0031] [Fig. 9] is a flowchart illustrating the selection of the oil flow profile as a function of the oil temperature and the engine operating mode. DETAILED DESCRIPTION

[0032] Unless otherwise specified, the same element appearing on different figures has a unique reference.

[0033] Figure 1 illustrates a method for starting an aircraft engine according to one aspect of the invention. The engine, or turboshaft engine, is coupled to a lubrication circuit including an oil pump system, the lubrication circuit being constructed and arranged to circulate oil in the engine.

[0034] When the aircraft is on the ground and the engine is stopped or in standby, the starting procedure 100 includes a step 101 of measuring an oil temperature, the measurement step 101 being carried out by a temperature sensing device, for example a temperature sensor.

[0035] Based on the temperature measured in step 101, the starting procedure 100 includes a step 102 for selecting a starting oil flow profile to be applied to the engine. This selection step 102 is performed by a control unit. The selection step 102 is based on both the measured oil temperature and the engine's operating mode. The selection based on the measured oil temperature is made by comparison with a threshold temperature. The engine's operating mode can be either standby or shutdown.

[0036] For example, when the aircraft is on the ground, the engine is off and the temperature sensor detects an oil temperature below a predetermined temperature threshold, for example -15°C, a starting oil flow profile corresponding to extreme cold conditions is selected.

[0037] Figure 2 illustrates an example of an oil flow profile P1 suitable for extreme cold conditions. "Extreme cold" refers to conditions where the engine oil temperature is below the threshold temperature, which is determined by the engine's operating mode. This P1 profile is selected in step 102 of the oil flow profile selection process if the measured oil temperature is below the threshold temperature and the engine is in stop mode. The P1 oil flow profile can be selected when the oil temperature is below -15°C.

[0038] In Figure 2, as in Figures 3 and 4, the ordinate axis illustrates the oil pressure and the abscissa axis represents the engine speed.

[0039] In this case, the oil flow profile P1 includes a first phase Ph1 during which the oil pressure at the engine inlet is zero until the engine speed reaches a threshold speed N. Considering a nominal speed set at 100%, the threshold speed N can for example be equal to 10 - 50% of the nominal speed.

[0040] Following the first phase Ph1, the oil flow profile P1 includes a second phase Ph2 during which the oil pressure at the engine inlet is equal to a limit pressure value Plim. This limit pressure Plim can be, for example, on the order of 5 bar.

[0041] In order to obtain zero oil pressure at the engine inlet, it is possible to control different types of oil pump systems.

[0042] The starting procedure 100 includes for this purpose a step 103 of applying the selected starting oil flow profile by means of the oil pump system, the oil pump system being controlled by the computer.

[0043] According to one aspect of the invention, the selected starting oil flow profile is applied by means of an oil pump system comprising a variable displacement oil pump. Such a variable displacement oil pump allows the flow rate at the outlet of the oil pump system to be adjusted, or even eliminated, by movement via a controlled actuator, thereby reducing the eccentricity of the rotor. the pump in relation to the pump stator. Such technology is known as a vane pump.

[0044] Thus, it is possible to apply a zero oil flow in the lubrication circuit and consequently eliminate the significant losses generated by viscous oil, which can represent up to 80% of the resisting torque provided by the engine itself and its equipment.

[0045] According to another aspect of the invention, the selected starting oil flow profile is applied by means of an oil pump system comprising an oil pump, a solenoid valve, and a reservoir. The solenoid valve is located downstream of the oil pump and is constructed and arranged to redirect all or part of the oil flow from the oil pump outlet into the reservoir without pressurizing the oil.

[0046] According to another aspect of the invention, the selected starting oil flow profile is applied by means of an oil pump system comprising an oil pump and a mechanical decoupling device constructed and arranged to activate or deactivate the rotation of the oil pump. This mechanical decoupling means may be, for example, a dog clutch or a clutch enabling or preventing the rotation of the oil pump.

[0047] Figure 3 illustrates an example of an oil flow profile P2 suitable for high temperatures and engine standby mode. "High temperatures" refers to oil temperatures exceeding the threshold temperature resulting from the engine's operating mode. Profile P2 is selected in step 102 of the oil flow profile selection process if the measured oil temperature is above the threshold temperature and the engine is in standby mode.

[0048] Engine standby mode is characterized by a low engine speed. High oil pressure allows operation for extended periods in speed ranges considered "critical" from a vibration perspective (generally between 10 and 30% of the turboshaft engine's nominal speed). During this operating phase, 11. It is possible to adapt the profile for other functions such as prioritizing pressure for damping vibration modes.

[0049] The oil damping devices equipping the turboshaft engines require a minimum oil pressure. Thanks to this invention, in order to optimize vibration behavior during a standby mode, a pressure higher than nominal is used. Once this standby mode is over, it is possible to supply these damping devices with a lower pressure.

[0050] This type of P2 oil flow profile is also suitable for positive displacement pumps, for which the oil flow is dictated by the engine speed.

[0051] In this case, the oil flow profile P2 selected during step 102 includes a first phase Ph1 during which the oil flow pressure is equal to a limit oil pressure value Plim until the engine speed reaches a threshold speed N. During this phase, the oil supply to the damping systems can be optimized.

[0052] Following the first phase Ph1, the oil flow profile P2 includes a second phase Ph2 during which the oil pressure reaches a threshold oil pressure value Ps. This threshold oil pressure value Ps is lower than the limit oil pressure value Plim. This threshold pressure Ps can be, for example, on the order of 3 bar.

[0053] In other words, this P2 oil flow profile is selected when the engine is in standby mode and not completely shut down. The turbocharger is in standby mode, for example, in one of the following two cases: The combustion chamber is shut off and the turbocharger is driven at low speed: the oil pump then operates on a given operating point, characterized by the pressure plateau of phase Ph1 of profile P2; The combustion chamber is lit and the turbocharger has a low-positioned speed, which can be autonomous or electrically assisted: the oil pump then operates on a given operating point, characterized by the pressure plateau of phase Ph1 of profile P2.

[0054] In both cases, if a restart of the turbocharger, initially in its standby mode, is required, the oil pump operating point will move along the pressure plateau of phase Ph1 to the threshold speed N and then position itself on the pressure plateau of phase Ph2, which is a plateau of Regulated and determined pressure. During phase Ph1, the supply to the damping components is adequate and the cooling of the so-called critical hot zones is improved because, in standby mode, the chamber may be switched on or very recently switched off (thermal transient present). At the end of the start-up, that is, when the engine speed N exceeds a threshold speed, the oil pressure drops to a sufficient pressure plateau Ps.

[0055] In other words, this P2 oil flow profile allows, for example, the active supply of oil to certain critical engine components from the very beginning of the start-up phase to ensure optimal operation. Furthermore, in a second phase of the engine's standby mode, it allows the oil requirements to be adjusted.

[0056] The selected P2 oil flow profile is then applied in step 103 using the oil pump system.

[0057] Just like the P1 oil flow profile, the P2 oil flow profile can be applied using the oil pump system with a variable displacement oil pump.

[0058] Similarly, the selected P2 starting oil flow profile can be applied using an oil pump system comprising an oil pump, a solenoid valve, and a reservoir. The solenoid valve is located downstream of the oil pump and is designed and arranged to redirect all or part of the oil flow from the pump outlet into the reservoir while controlling the target engine inlet pressure from zero to a predetermined value.

[0059] In a different implementation, the selected P2 starting oil flow profile can be applied using an oil pump system comprising an oil pump and a rotating electric machine designed and arranged to assist the oil pump's rotation. This auxiliary electric machine is fully controllable by the ECU in terms of torque and speed as required.

[0060] Figure 4 illustrates an example of a P3 oil flow profile that maintains optimal engine performance without requiring an oversized starter. The P3 oil flow profile is selected in step 102 of the oil flow profile selection procedure if the measured oil temperature is above the threshold temperature and if the engine operating mode is stop mode.

[0061] In this case, the oil flow profile P3 includes a first phase Ph1 during which the oil pressure increases until the engine speed reaches a threshold speed N.

[0062] At the end of the first phase Ph1, the oil flow profile P3 includes a second phase Ph2 during which the oil pressure at the engine inlet is equal to a limit oil pressure value Plim.

[0063] The selected P3 oil flow profile is then applied in step 103 using the oil pump system.

[0064] Just like the P1 oil flow profile, the P3 oil flow profile can be applied using the oil pump system comprising: a variable displacement oil pump, or an oil pump, a solenoid valve and a reservoir.

[0065] In addition, the P3 oil flow profile can be applied by means of the oil pump system comprising an oil pump and a rotating electric machine constructed and arranged to assist the oil pump in rotation.

[0066] Figure 9 is a flowchart illustrating step 102 of selecting the oil flow profile P1, P2, P3 as a function of: the oil temperature relative to the threshold temperature, and the engine operating mode.

[0067] If the oil temperature is below the threshold temperature, the engine is in shutdown mode and profile P1 is selected. If the oil temperature is above the threshold temperature, the selected oil flow profile will be either oil flow profile P2 or oil flow profile P3. Oil flow profile P2 is selected if the engine is in standby mode. Profile P3 is selected if the engine is in shutdown mode.

[0068] Figure 5 illustrates an aircraft conforming to a first aspect of the invention. Aircraft 1 comprises a turboshaft engine 2 mechanically coupled to an electric starter 3. Aircraft 1 comprises: a temperature sensing device 4 constructed and arranged to measure an oil temperature; a computer 5 constructed and arranged to, as a function of the measured temperature, select a starting oil flow profile to be applied in the engine 2; a lubrication circuit 6 comprising in particular an oil pump system 7, the oil pump system 7 being constructed and arranged to apply the selected starting oil flow profile.

[0069] In the example illustrated in Figure 5, the oil pump system 7 includes a variable displacement oil pump 8 mechanically driven by the turbomotor 2 via an accessory box not shown.

[0070] In the example illustrated in Figure 6, the oil pump system 7 includes an oil pump 8 which is mechanically driven by the turbomotor 2 via an accessory box not shown, a solenoid valve 9 and a reservoir 10. The solenoid valve 9 is located downstream of the oil pump 8 and is constructed and arranged to redirect all or part of the oil flow from the oil pump 8 into the reservoir 10.

[0071] In the example illustrated in Figure 7, the oil pump system 7 includes an oil pump 8 which is mechanically driven by the turbomotor 2 via an accessory gearbox not shown, and a mechanical decoupling device 11. The oil pump 8 is associated with the mechanical decoupling device 11 which is constructed and arranged to activate or deactivate the rotation of the oil pump 8.

[0072] In the example illustrated in Figure 8, the oil pump system 7 comprises an oil pump 8 and a rotating electric machine 12. The oil pump 8 is therefore assisted in rotation by the rotating electric machine 12.

[0073] Of course, the aspects of the invention presented above are not limiting. It is evident, for example, that a person skilled in the art can propose different oil flow profiles and different oil pump systems constructed and arranged to apply different oil flow profiles.

Claims

DEMANDS

1. A method for starting (100) an aircraft engine (1) wherein said engine (1) is coupled to a lubrication circuit (6) including an oil pump system (7), said lubrication circuit (6) being constructed and arranged to circulate oil in said engine (1), and wherein an operating mode of the engine (1) includes a shutdown mode and a standby mode, said starting method (100) being characterized in that it comprises, during a starting phase, the steps of: - measure (101) an oil temperature, said measurement step (101) being carried out by a temperature detection device (4); - depending on said measured temperature, compared to a threshold temperature, and depending on the operating mode of said engine, select (102) a starting oil flow profile (P1, P2, P3) to be applied in said engine (1), said selection step (102) being carried out by a computer (5); - apply (103) said start-up oil flow profile (P1, P2, P3) selected by means of said oil pump system (7), said oil pump system (7) being controlled by said computer (5).

2. Method of starting (100) an aircraft engine (1) according to claim 1, characterized in that each oil flow profile (P1, P2, P3) comprises a first phase (Ph1) and a second phase (Ph2), said second phase (Ph2) corresponding to a predetermined oil pressure at the engine inlet, applied when the engine speed reaches a threshold speed value (N).

3. A method for starting (100) an aircraft engine (1) according to claim 1 or 2, characterized in that if the measured oil temperature is below the threshold temperature and if the operating mode of the engine (1) is the shutdown mode, the oil flow profile (P1) comprises: - a first phase (Ph1) during which the oil pressure at the inlet of the engine (2) is zero until the engine speed (2) reaches a threshold speed (N); - a second phase (Ph2) during which the oil pressure at the engine inlet (2) is equal to a limit oil pressure value (Plim).

4. A method for starting (100) an aircraft engine (1) according to claim 1 or 2, characterized in that if the measured oil temperature is above the threshold temperature and if the operating mode of the engine (1) is standby mode, the oil flow profile (P2) comprises: - a first phase (Ph1) during which the oil pressure at the inlet of the engine (2) is equal to a limit oil pressure value (Plim) until the engine speed (2) reaches a threshold speed (N); - a second phase (Ph2) during which the oil pressure at the inlet of the engine (2) is equal to a threshold oil pressure value (Ps), said threshold oil pressure value (Ps) being less than said limit oil pressure value (Plim).

5. A method for starting (100) an aircraft engine (2) according to claim 1 or 2, characterized in that if the measured oil temperature is above the threshold temperature and if the operating mode of the engine (1) is the shutdown mode, the oil flow profile (P3) comprises: - a first phase (Ph1) during which the oil pressure at the inlet of the engine (2) is increasing until the engine speed (2) reaches a threshold speed (N); - a second phase (Ph2) during which the oil pressure at the engine inlet (2) is equal to a limit oil pressure value (Plim).

6. Aircraft (1) comprising an engine (2) whose operating mode includes a shutdown mode and a standby mode and a temperature sensing device (4) constructed and arranged to measure an oil temperature, said aircraft (1) being characterized in that it implements the method according to any one of claims 1 to 5 and that it comprises: - a computer (5) constructed and arranged to, as a function of said measured temperature, select a starting oil flow profile (P1, P2, P3) to be applied in said engine (2); - a lubrication circuit (6) including in particular an oil pump system (7), said oil pump system (7) being constructed and arranged to apply said selected starting oil flow profile (P1, P2, P3).

7. Aircraft (1) according to the preceding claim characterized in that the oil pump system (7) comprises an oil pump (8) with variable displacement.

8. Aircraft (1) according to claim 6 characterized in that the oil pump system (7) comprises an oil pump (8) and an electro-valve (9), said electro-valve (9) being located downstream of said oil pump (8) and being constructed and arranged to redirect all or part of the oil flow out of said oil pump (8) into a reservoir (10).

9. Aircraft (1) according to claim 6, characterized in that the oil pump system (7) comprises an oil pump (8) and a mechanical decoupling device (11) constructed and arranged to activate or deactivate the rotation of the oil pump (8).

10. Aircraft according to claim 6, characterized in that the oil pump system (7) comprises an oil pump (8) whose rotation is assisted by a rotating electrical machine (12).