Method for starting an aircraft engine

Abstract

Aspects of the invention relate to a starting method (100) for an aircraft engine (1), in which the engine (1) is connected to a lubrication circuit (6) comprising in particular an oil pump system (7), the lubrication circuit (6) being configured and arranged to circulate oil in the engine (1), and in which the operating modes of the engine (1) comprise a stop mode and a standby mode, the starting method (100) being characterized in that, during a starting phase, it comprises the following steps: - measuring (101) the oil temperature, the step (101) of measuring being performed by a temperature detection device; - selecting (102), as a function of the measured temperature compared to a threshold temperature and as a function of the operating mode of the engine, a starting oil flow profile to be applied in the engine, the step (102) of selecting being performed by a computer; - applying the selected starting oil flow profile by means of the oil pump system (103), the oil pump system being controlled by the computer.

Description

Technical Field

[0001] This invention relates to the starting of aircraft engines, such as the starting of gas turbines for turboshaft engines or turbogenerators. The invention is particularly applicable to light aircraft, especially helicopters. Background Technology

[0002] Aircraft engines are typically connected to an electric starter. To start the engine, electricity is supplied to the starter from, for example, a ground power unit or auxiliary power unit. The starter operates as an electric motor and rotatably drives the engine.

[0003] It is known that the viscosity of engine lubricating oil increases as temperature decreases. Therefore, under extremely cold conditions, such as temperatures below -40°C, the oil exhibits high viscosity, resulting in high engine starting torque. Tests have shown that the oil pump generates a major portion of the absolute level of resistance torque. This is because the oil pump must deliver and pressurize extremely viscous oil, leading to significant losses, which can reach up to 80% of the load torque provided by the gas turbine itself and its components.

[0004] The size of the starter motor can be determined to provide the torque corresponding to the engine starting torque under extremely cold conditions. However, at higher temperatures, this torque is significantly higher than the starting torque. Therefore, starting under extremely cold conditions means that the starter motor and its power electronics must be excessively large, resulting in significant mass and space requirements. Furthermore, the ground power unit must be able to provide the high power required for starting.

[0005] A method for starting an aircraft engine is known from FR-B1-2960592, which includes preheating the oil via a starter motor before starting the engine. Specifically, if the measured temperature is below a certain temperature threshold, such as -15°C, an icing condition is signaled by illuminating a warning light on the instrument panel. This indicates to the pilot that the engine oil needs to be preheated. The pilot can then generate a preheating command to control the starter motor to rotatably drive the engine at a low speed. For example, the engine is driven at a speed between 8% and 12% of its windmill speed. Therefore, the torque required by the starter motor is controlled. Due to heat losses in the starter motor, the oil temperature gradually increases. Heat losses in the bearings of the motor housing and, to a lesser extent, in the gearbox also contribute to the increase in oil temperature. Therefore, the resistance torque of the motor gradually decreases. This step of driving the motor at a low speed during this period is therefore a preheating step for the oil, which can last, for example, between 8 and 10 minutes.

[0006] Even though the oil pressure decreases due to low engine speed, it still exists, causing significant losses and requiring an excessively large starter motor. Furthermore, this implementation is optimized only for starting in cold weather.

[0007] Furthermore, this method of preheating the oil to reduce its viscosity and thus reduce mechanical loss is unsuitable for helicopters. In fact, during certain interventions, such as rescue operations in the mountains at sub-zero temperatures, the pilot does not have the necessary time to preheat the oil before starting the engine. Summary of the Invention

[0008] This invention provides a technical solution to the above-mentioned technical problems by allowing aircraft engines to start under optimal conditions, regardless of oil temperature, and further allows aircraft to be equipped with starters that are not too large.

[0009] In this context, one aspect of the invention, therefore of the widest acceptance, relates to a method for starting an aircraft engine, wherein the engine is coupled to a lubrication circuit, the lubrication circuit particularly including an oil pump system, the lubrication circuit being constructed and arranged to circulate oil in the engine, and wherein the engine operating modes include a stop mode and a standby mode, the starting method being characterized in that, during the starting phase, the starting method includes the following steps:

[0010] -Measure the oil temperature, the measurement steps are performed by a temperature detection device;

[0011] -Based on the measured temperature compared with the threshold temperature, and according to the engine's operating mode, a starting oil flow curve to be applied in the engine is selected, and the selection step is performed by a calculator;

[0012] - The oil pump system is controlled by the calculator by applying the selected start-up oil flow curve to the oil pump system.

[0013] The method for starting an aircraft engine according to this aspect of the invention allows for the selection of an oil flow profile based on oil temperature during startup. For example, if the oil temperature is low, a zero oil flow rate can be selected for a short time period to eliminate losses caused by oil discharged by the oil pump system. The short time period is defined as a period shorter than the nominal startup time (for the temperature in question) and without reducing overall mechanical reliability. The short time period can, for example, be less than 10 seconds.

[0014] These features allow for the avoidance of equipping aircraft (especially helicopters) with oversized starters. On the other hand, when the oil temperature is high, a high oil flow rate can be selected to provide maximum lubrication to, for example, oil bearings during the start-up phase. In addition to the features just discussed in the preceding paragraphs, the method for starting an aircraft engine according to this aspect of the invention may have one or more of the following features, individually or in any technically possible combination.

[0015] According to one aspect of the invention, each oil flow curve includes a first stage and a second stage, the second stage corresponding to a predetermined oil pressure applied at the engine inlet when the engine speed reaches a threshold speed value.

[0016] According to one aspect of the invention, if the measured oil temperature is below a threshold temperature, and if the engine operating mode is a stop mode, the oil flow profile includes:

[0017] -In the first stage, during which the oil pressure at the engine inlet is zero until the engine speed reaches the threshold speed;

[0018] - Second stage, during which the oil pressure at the engine inlet is equal to the limit oil pressure value.

[0019] According to one aspect of the invention, if the measured oil temperature is higher than a threshold temperature, and if the engine operating mode is standby mode, the oil flow curve includes:

[0020] -In the first stage, during which the oil pressure at the engine inlet is equal to the limit oil pressure value until the engine speed reaches the threshold speed;

[0021] - Second stage, during which the oil pressure at the engine inlet is equal to a threshold oil pressure value, which is lower than the limit oil pressure value.

[0022] According to one aspect of the invention, if the oil temperature is above a threshold temperature and if the engine operating mode is a stop mode, the oil flow rate profile includes:

[0023] -In the first stage, during which the oil pressure at the engine inlet increases until the engine speed reaches the threshold speed;

[0024] - Second stage, during which the oil pressure at the engine inlet is equal to the limit oil pressure value.

[0025] Another aspect of the present invention relates to an aircraft comprising:

[0026] - An engine with operating modes including a stop mode and a standby mode; and

[0027] -A temperature detection device, which is constructed and arranged to measure the oil temperature;

[0028] The aircraft implements the above method and includes:

[0029] - A calculator configured and arranged to select a starting oil flow profile to be applied to the engine based on the measured temperature;

[0030] - A lubrication circuit, the lubrication circuit including an oil pump system configured and arranged to apply the selected starting oil flow rate profile.

[0031] In one aspect of the invention, the oil pump system includes a variable reciprocating oil pump.

[0032] According to one aspect of the invention, an oil pump system includes an oil pump and an electric valve located downstream of the oil pump and configured and arranged to redirect all or a portion of the oil flow from the oil pump back to an oil tank.

[0033] In one aspect of the invention, the oil pump system includes an oil pump and a mechanical disconnection device configured and arranged to start or stop the rotation of the oil pump.

[0034] In one aspect of the invention, the oil pump system includes an oil pump rotatably driven by a rotary electric motor.

[0035] The invention and its various applications will be better understood by reading the following description and by examining the accompanying drawings. Attached Figure Description

[0036] The accompanying drawings are described for the purpose of indicating rather than limiting the invention.

[0037] Figure 1 A method for starting an aircraft engine according to one aspect of the invention is illustrated schematically.

[0038] Figure 2 A first embodiment of an oil flow rate curve according to one aspect of the invention is illustrated schematically.

[0039] Figure 3 A second embodiment of an oil flow curve according to one aspect of the invention is illustrated schematically.

[0040] Figure 4 A third embodiment of an oil flow curve according to one aspect of the invention is illustrated schematically.

[0041] Figure 5 An aircraft engine according to a first aspect of the invention is schematically shown.

[0042] Figure 6 An aircraft engine according to a second aspect of the invention is schematically shown.

[0043] Figure 7 An aircraft engine according to a third aspect of the invention is schematically shown.

[0044] Figure 8 An aircraft engine according to the fourth aspect of the invention is schematically shown.

[0045] Figure 9 It is a flowchart showing the selection of the oil flow curve based on oil temperature and engine operating mode. Detailed Implementation

[0046] Unless otherwise stated, the same elements appearing in different figures have a single figure reference numeral.

[0047] Figure 1 A method 100 for starting an aircraft engine according to an aspect of the present invention is shown. The engine or turboshaft engine is coupled to a lubrication circuit including an oil pump system, the lubrication circuit being configured and arranged to circulate oil through the engine.

[0048] When the aircraft is on the ground and the engine is stopped or in standby mode, the starting method 100 includes a step 101 of measuring the oil temperature, which is performed by a temperature detection device (e.g., a temperature sensor).

[0049] Based on the temperature measured in step 101, the starting method 100 includes a step 102 of selecting a starting oil flow profile to be applied in the engine, performed by a calculator. The selection step 102 is performed on one hand based on the measured oil temperature, and on the other hand based on the engine operating mode. The selection is made based on the measured oil temperature by comparing it with a threshold temperature. The engine operating mode can be a standby mode or a stopped mode.

[0050] For example, when the aircraft is on the ground, the engine stops and the temperature sensor detects an oil temperature below a certain threshold, such as -15°C, and a starting oil flow curve corresponding to extreme cold conditions is selected.

[0051] Figure 2 An example of an oil flow rate curve P1 suitable for extreme cold conditions is shown. "Extreme cold conditions" are defined as conditions where the engine oil temperature is below a threshold temperature, which is a result of the engine's operating mode. If the measured oil temperature is below the threshold temperature, and if the engine is in a stopped mode, curve P1 is selected in step 102 of selecting the oil flow rate curve. Oil flow rate curve P1 can be selected when the oil temperature is below -15°C.

[0052] exist Figure 2 In, such as in Figure 3 and Figure 4 In the diagram, the y-axis represents the oil pressure, and the x-axis represents the engine speed.

[0053] In this scenario, the oil flow curve P1 includes a first stage, Ph1, during which the oil pressure at the engine inlet is zero until the engine speed reaches a threshold speed N. Considering 100% of the nominal speed, the threshold speed N can, for example, be equal to 10%–50% of the nominal speed.

[0054] At the end of the first stage, Ph1, the oil flow curve P1 includes a second stage, Ph2, during which the oil pressure at the engine inlet equals the ultimate pressure value, Plim. This ultimate pressure, Plim, can be, for example, approximately 5 bar.

[0055] To achieve zero oil pressure at the engine inlet, it is possible to control different types of oil pump systems.

[0056] For this purpose, the starting method 100 includes step 103 of applying a selected starting oil flow curve by means of an oil pump system, with the oil pump system controlled by a calculator.

[0057] According to one aspect of the invention, an oil pump system, comprising a variable reciprocating oil pump, is used by means of a selected starting oil flow rate profile. This variable reciprocating oil pump allows the output flow rate of the oil pump system to be adjusted or even canceled by a controlled actuator via displacement, thereby reducing the eccentricity of the pump rotor relative to the pump stator. This technique is known as a vane pump.

[0058] Therefore, it is possible to apply zero oil flow in the lubrication circuit and thus eliminate significant losses caused by viscous oil, which can represent up to 80% of the resisting torque provided by the engine itself and its equipment.

[0059] According to another aspect of the invention, a selected starting oil flow rate profile is applied by means of an oil pump system including an oil pump, an electric valve, and an oil tank. The electric valve is located downstream of the oil pump and is configured and arranged to redirect all or part of the oil flow from the oil pump back to the oil tank without pressurizing the oil.

[0060] According to another aspect of the invention, by means of an oil pump system including an oil pump and a mechanical disengagement device, the mechanical disengagement device is constructed and arranged for starting or stopping the rotation of the oil pump by applying a selected starting oil flow rate profile. Such a mechanical disengagement device can be, for example, a clutch or a clutch for starting or stopping the rotation of the oil pump.

[0061] Figure 3An example of an oil flow curve P2 suitable for both high-temperature and standby operation of the engine is shown. High temperature is defined as oil temperature exceeding a threshold temperature caused by the engine operating mode. If the measured oil temperature is above the threshold temperature and the engine operating mode is standby mode, curve P2 is selected in step 102 of selecting the oil flow curve.

[0062] Engine standby mode is characterized by low engine speed. High oil pressure allows for prolonged cyclic operation within the so-called critical vibration speed range (typically between 10% and 30% of the engine's rated speed). During this operating phase, the pressure profile can be adapted for other functions, such as pressures favorable for damping vibration modes.

[0063] Oil damping devices mounted on the axis of a turboshaft engine require a minimum level of oil pressure. Due to this invention, a pressure higher than nominal is preferred to optimize vibration behavior during engine idle operation. Once this operation phase ends, lower pressures can be applied to these damping devices.

[0064] This type of P2 oil flow curve also applies to reciprocating pumps, where the oil flow rate is determined by the engine speed.

[0065] In this case, the oil flow curve P2 selected in step 102 includes a first stage Ph1, during which the oil flow pressure is equal to the limit oil pressure value Plim until the engine speed reaches the threshold speed N. During this stage, the oil supply to the damping system can be optimized.

[0066] Following the first stage, Ph1, the oil flow curve P2 includes a second stage, Ph2, in which the oil pressure equals the threshold oil pressure value Ps. The threshold oil pressure value Ps is lower than the ultimate oil pressure value Plim. This threshold pressure Ps can be, for example, approximately 3 bar.

[0067] In other words, when the engine is in standby mode and not completely stopped, select oil flow curve P2. Turboshaft engines are in standby mode, for example, in one of the following two situations:

[0068] - The combustion chamber is closed and the turboshaft engine is driven at low speed: then the oil pump operates at a given operating point, characterized by the pressure plateau segment of stage Ph1 of curve P2.

[0069] - The combustion chamber is ignited, and the turboshaft engine has a low-speed position, which can be autonomous or electrically assisted: then, the oil pump operates at a given operating point, characterized by the pressure plateau segment of stage Ph1 of curve P2.

[0070] In both cases, if the turboshaft engine is required to restart initially in its standby mode, the oil pump's operating point will move along the pressure plateau of stage Ph1 until the threshold speed N, then position itself on the pressure plateau of stage Ph2, which is a regulated and defined pressure plateau. During stage Ph1, power supply to the damping element is sufficient, and cooling of the so-called critical hot zone is improved because, in standby mode, the chamber can be opened or recently closed (a thermal transient exists). At the end of the start-up, i.e., when the speed N becomes above the threshold speed, the oil pressure passes through a sufficient pressure plateau Ps.

[0071] In other words, the oil flow curve P2 makes it possible, for example, to actively supply oil to certain critical engine components from the start-up phase to ensure optimal operation. It also allows for adjustment of oil demand during the second phase of engine idle mode.

[0072] Then, using the oil pump system, the selected oil flow rate curve P2 is applied in step 103.

[0073] Similar to oil flow curve P1, oil flow curve P2 can be applied using an oil pump system with a variable reciprocating oil pump.

[0074] Similarly, a selected starting oil flow curve P2 can be applied using an oil pump system, which includes an oil pump, an electric valve, and an oil tank. The electric valve is located downstream of the oil pump and is configured and arranged to redirect all or part of the oil flow from the oil pump to the oil tank while controlling the target engine inlet pressure level from zero to a predetermined value.

[0075] In different implementations, a selected starting oil flow curve P2 can be applied using an oil pump system, which includes an oil pump and a rotary electric motor constructed and arranged to assist the rotation of the oil pump. The torque and speed of this auxiliary electric motor are fully controllable by a calculator as needed.

[0076] Figure 4 An embodiment of oil flow profile P3 is shown to maintain optimal engine performance without requiring an excessively large starter motor. Oil flow profile P3 is selected in oil flow profile selection step 102 if the measured oil temperature is above a threshold temperature and if the engine operating mode is off.

[0077] In this case, the oil flow curve P3 includes a first stage Ph1, in which the oil pressure increases until the engine speed reaches the threshold speed N.

[0078] After the first stage Ph1, the oil flow curve P3 includes the second stage Ph2, in which the oil pressure at the engine inlet is equal to the limit oil pressure value Plim.

[0079] Then, using the oil pump system, the selected oil flow rate curve P3 is applied in step 103.

[0080] Similar to oil flow curve P1, oil flow curve P3 can be applied using an oil pump system, which includes:

[0081] - Variable reciprocating oil pump, or

[0082] - Oil pump, electric valve and oil tank.

[0083] Furthermore, an oil flow curve P3 can be applied using an oil pump system, which includes an oil pump and a rotary electric machine configured and arranged to rotatably assist the oil pump.

[0084] Figure 9 This is a flowchart illustrating step 102 of selecting oil flow curves P1, P2, and P3 based on the following:

[0085] - Oil temperature related to threshold temperature, and

[0086] - Engine operating mode.

[0087] If the oil temperature is below the threshold temperature, the engine is in stop mode and characteristic curve P1 is selected. If the oil temperature is above the threshold temperature, the selected oil flow curve will be either oil flow curve P2 or oil flow curve P3. If the engine is in standby mode, oil flow curve P2 is selected. If the engine is in stop mode, P3 is selected.

[0088] Figure 5 An aircraft according to a first aspect of the present invention is shown. The aircraft 1 includes a turboshaft engine 2 mechanically coupled to an electric starter 3. The aircraft 1 includes:

[0089] - Temperature detection device 4, which is constructed and arranged for measuring oil temperature;

[0090] -Calculator 5, which is constructed and arranged to select the initial oil flow characteristic curve in the engine 2 to be applied based on the measured temperature;

[0091] - Lubrication circuit 6, which includes oil pump system 7, which is constructed and arranged to apply a selected starting oil flow rate profile.

[0092] exist Figure 5In the illustrated embodiment, the oil pump system 7 includes a variable reciprocating oil pump 8, which is mechanically driven by the turboshaft engine 2 via an auxiliary gearbox (not shown).

[0093] exist Figure 6 In the illustrated embodiment, the oil pump system 7 includes an oil pump 8, an electric valve 9, and an oil tank 10. The oil pump is mechanically driven by a turboshaft engine 2 via an auxiliary gearbox (not shown). The electric valve 9 is located downstream of the oil pump 8 and is configured and arranged to redirect all or part of the oil flow from the oil pump 8 into the oil tank 10.

[0094] exist Figure 7 In the illustrated embodiment, the oil pump system 7 includes an oil pump 8 and a mechanical disconnect device 11, the oil pump being mechanically driven by a turbine shaft engine 2 via an auxiliary gearbox (not shown). The oil pump 8 is associated with the mechanical disconnect device 11, which is configured and arranged to start or stop the rotation of the oil pump 8.

[0095] exist Figure 8 In the illustrated embodiment, the oil pump system 7 includes an oil pump 8 and a rotary electric machine 12. Therefore, the oil pump 8 is rotatably assisted by the rotary electric machine 12.

[0096] Of course, the aspects of the invention described above are not limiting. For example, it will be apparent to those skilled in the art that different oil flow rates, and different oil pump systems constructed and arranged to apply different oil flow rates, can be provided.

Claims

1. A method for starting an (100) aircraft engine, wherein, The engine is connected to a lubrication circuit (6), the lubrication circuit including an oil pump system (7), the lubrication circuit (6) being constructed and arranged to circulate oil, which is delivered to an oil supply line to supply oil damping devices to the engine, and wherein the engine operating modes include a stop mode and a standby mode characterized by low engine speed, the method for starting (100) is characterized in that, during the starting phase, the method includes the following steps: - Measure the oil temperature (101), the measurement step (101) is performed by the temperature detection device (4); - Based on the measured temperature compared with the threshold temperature and based on the engine's operating mode, select (102) the initial oil flow curve (P1, P2, P3) to be applied in the engine from multiple initial oil flow curves, and the selection step (102) is performed by the calculator (5). The application (103) uses the initial oil flow curve (P1, P2, P3) selected by the oil pump system (7), and the calculator (5) controls the oil pump system (7), and - In response to the measured oil temperature being higher than the threshold temperature and the engine operating mode being in standby mode, oil is circulated at a pressure higher than the nominal value in the oil damping device; and in response to the engine standby mode ending, oil is supplied to the oil damping device at a pressure lower than the pressure higher than the nominal value.

2. The method (100) for starting an aircraft engine according to claim 1, characterized in that, Each oil flow curve (P1, P2, P3) includes a first stage (Ph1) and a second stage (Ph2), the second stage (Ph2) corresponding to the predetermined oil pressure applied at the engine inlet when the engine speed reaches a threshold speed value (N).

3. The method for starting an (100) aircraft engine according to claim 1 or 2, characterized in that, If the measured oil temperature is below the threshold temperature, and if the engine is operating in a stopped mode, the oil flow curve (P1) includes: - First stage (Ph1), during which the oil pressure at the inlet of the engine (2) is zero until the speed of the engine (2) reaches the threshold speed (N). - Second stage (Ph2), during which the oil pressure at the engine (2) inlet is equal to the limit oil pressure value (Plim).

4. The method for starting an (100) aircraft engine according to claim 1 or 2, characterized in that, If the measured oil temperature is above the threshold temperature, and if the engine is operating in standby mode, the oil flow curve (P2) includes: - First stage (Ph1), during the first stage, the oil pressure at the inlet of the engine (2) is equal to the limit oil pressure value (Plim) until the speed of the engine (2) reaches the threshold speed (N). - Second stage (Ph2), during which the oil pressure at the engine (2) inlet is equal to the threshold oil pressure value (Ps), which is lower than the limit oil pressure value (Plim).

5. The method for starting an (100) aircraft engine according to claim 1 or 2, characterized in that, If the measured oil temperature is above the threshold temperature, and if the engine is operating in a stopped mode, the oil flow curve (P3) includes: - First stage (Ph1), during which the oil pressure at the inlet of the engine (2) increases until the speed of the engine (2) reaches the threshold speed (N). - Second stage (Ph2), during which the oil pressure at the engine (2) inlet is equal to the limit oil pressure value (Plim).

6. An aircraft (1) comprising an engine (2) and a temperature detection device (4), wherein the engine operates in a stop mode and a standby mode, and the temperature detection device is configured and arranged to measure oil temperature, the aircraft (1) being characterized in that it implements the method according to any one of claims 1 to 5, and is characterized in that, The aircraft includes: - Calculator (5), which is configured and arranged to select the initial oil flow curve (P1, P2, P3) to be applied in the engine (2) based on the measured temperature. - Lubrication circuit (6), the lubrication circuit including oil pump system (7), the oil pump system (7) being constructed and arranged to apply a selected initial oil flow curve (P1, P2, P3).

7. The aircraft (1) according to claim 6, characterized in that, The oil pump system (7) includes a variable reciprocating oil pump (8).

8. The aircraft (1) according to claim 6, characterized in that, The oil pump system (7) includes an oil pump (8) and an electric valve (9) located downstream of the oil pump (8) and configured and arranged to redirect all or part of the oil flow from the oil pump (8) back to the oil tank (10).

9. The aircraft (1) according to claim 6, characterized in that, The oil pump system (7) includes an oil pump (8) and a mechanical disconnect device (11) which is configured and arranged to enable or disable the rotation of the oil pump (8).

10. The aircraft according to claim 6, characterized in that, The oil pump system (7) includes an oil pump (8) that is rotatably assisted by a rotary electric motor (12).

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