Hydraulic control circuit for fan-blade pitch adjustment with a deactivatable pump

Abstract

The invention relates to a hydraulic control circuit (11) for an orienting actuator (14) for orienting fan blades of a turbojet engine, the circuit (11) comprising an oil reservoir (17) and an axial piston pump (18) comprising a tiltable plate (23), as well as a control chamber (24) and a compensation chamber (27) for increasing the tilt of the plate (23) when the pressure inside these chambers increases, the pump (18) being supplied by the reservoir (17) and having its outlet configured so as to be able to be connected by a supply line (19) to one of the chambers (12, 13) of the orienting actuator (14), the other chamber of the orienting actuator (14) being connected to the reservoir (17), this control circuit comprising a valve (42) controlled by a computer (FADEC), which valve (42) allows the outlet of the pump (18) to be connected to the reservoir (17) in order to deactivate this pump (18).

Description

[0001] DESCRIPTION

[0002] TITLE of the invention: Hydraulic control circuit for fan blade adjustment with a switchable pump

[0003] TECHNICAL FIELD

[0004] The invention relates to an aircraft engine comprising variable pitch blades allowing control and / or reversal of the thrust generated by this engine.

[0005] PREVIOUS STATE OF THE ART

[0006] In a turbojet aircraft engine, air is admitted at the inlet to pass through a propulsion propeller before splitting into a central primary flow and a secondary flow surrounding the primary flow.

[0007] The primary flow then passes through compression stages before reaching a combustion chamber, after which it is expanded through high-pressure and low-pressure turbines before being discharged downstream. The secondary flow, on the other hand, is propelled directly downstream by the propeller into a channel externally delimited by the engine's fairing.

[0008] Such an engine comprises a low-pressure body through which the propulsion propeller is coupled to the low-pressure turbine, and a high-pressure body through which the high-pressure compressor is coupled to the high-pressure turbine, these two bodies being coaxial and independent in rotation.

[0009] The propeller of such an engine can be of the variable pitch type, which means that the orientation of its blades around their span axes, which extend radially with respect to the axis of rotation of the engine, can be changed in flight, such a propeller can also be implemented in an unfaired turboprop engine or an "open rotor" engine with a double contra-rotating propeller.

[0010] This type of propeller allows the angle of the blades to be adjusted to the flight conditions in order to optimize engine performance, but also to rotate the blades significantly (by about 30°) to reverse the thrust during landing.

[0011] The timing angle is controlled by a hydraulic circuit comprising a pump driven in rotation by the high-pressure body of the engine via a transmission gearbox, such an arrangement being described in document FR3131274A1. In normal operation, it is therefore the rotation of the engine resulting from the combustion of the fuel that drives the pump.

[0012] In the event of engine failure, it is the airflow passing through the engine which causes the propeller and the low-pressure body to rotate, this situation being usually referred to as windmilling.

[0013] This situation is detrimental because the pump, which is then driven by the high-pressure body, exerts a resisting torque on it, tending to brake the propeller, which constitutes an obstacle to restarting the engine.

[0014] Similarly, during a normal engine start-up phase, the resisting torque exerted by the pump requires an unnecessarily increased power to be injected into the engine to start it.

[0015] The aim of the invention is to provide a solution to overcome these drawbacks.

[0016] DESCRIPTION OF THE INVENTION

[0017] To this end, the invention relates to a hydraulic control circuit for a double-acting slewing cylinder for orienting the fan blades of a turbojet engine, comprising an oil reservoir supplying an axial piston pump having an outlet connected to a supply line, a distributor valve for connecting one of the chambers of the slewing cylinder to the supply line and the other chamber of the slewing cylinder to the reservoir or vice versa, the axial piston pump being a variable displacement pump comprising a tilting swashplate as well as a control chamber and a compensation chamber for controlling the tilt of the swashplate, the control and compensation chambers both being capable of being pressurized with a pressure corresponding to the pump outlet pressure, and being arranged to increase the tilt of the swashplate when the pressurization of these chambers increases,This control circuit includes a deactivation valve controlled by a turbojet computer; this deactivation valve allows the fuel line to be connected to the tank in order to deactivate the axial piston pump.

[0018] This solution limits the power of the pitch drive pump by deactivating it through a reduction or even elimination of the pressure increase it generates at its outlet. This ensures that the pump does not create a resisting torque on the motor shaft (high-pressure body) in the event of motor shutdown (windmilling), thus facilitating motor starting, restarting, or reigniting.

[0019] The invention also relates to a circuit thus defined, in which the deactivation valve is a solenoid valve equipped with a return spring to be normally closed, and which opens in the absence of power supply to its solenoid.

[0020] The invention also relates to a circuit thus defined, comprising a volumetric pump interposed between the reservoir and the axial piston pump.

[0021] The invention also relates to a circuit thus defined, comprising a recirculation line connecting the outlet of the volumetric pump to the reservoir via a recirculation valve.

[0022] The invention also relates to a circuit defined as follows, in which the computer is configured to deactivate the pump in the event of detection of an engine stoppage.

[0023] The invention also relates to a circuit defined as follows, in which the computer is configured to deactivate the pump during engine start-up on the ground and / or engine restart or reignition in flight.

[0024] The invention also relates to a circuit thus defined, in which the compensation chamber of the axial piston pump is supplied by the outlet of this pump, in which the two chambers of the slewing cylinder are connected to the distributing valve, in which the distributing valve can occupy a position in which it connects one of the chambers to the supply line and the other chamber to the reservoir, or another position in which it connects one of the chambers to the reservoir and the other chamber to the supply line.

[0025] The invention also relates to a circuit thus defined, further comprising a selection valve connected to the two chambers of the slewing cylinder and to the control chamber by a control line, for pressurizing the pump's control chamber with the higher pressure of the two chambers of the slewing cylinder. The invention also relates to a circuit thus defined, comprising a spring tending to tilt the platform.

[0026] The invention also relates to a turbojet engine comprising a circuit according to claim 1 and variable pitch fan blades which are controlled by this circuit.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The [Fig. 1] is a longitudinal cross-sectional view of a turbofan engine;

[0029] Figure 2 is a schematic view of the control circuit according to the invention in nominal operation;

[0030] Fig. 3 is a schematic view of the control circuit according to the invention in a windmilling situation;

[0031] Figure 4 is a schematic view of the control circuit according to a variant of the invention in nominal operation;

[0032] Figure 5 is a schematic view of the control circuit according to a variant of the invention in a windmilling situation.

[0033] DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0034] In an aircraft engine such as engine 1 in Figure 1, air is admitted into an inlet 2 to pass through the blades 3 of a propeller, also called a fan, before splitting into a central primary flow and a secondary flow surrounding the primary flow. These two flows circulate in the engine along its longitudinal direction AX, from the upstream AM to the downstream AV of this engine when it generates propulsive thrust.

[0035] After passing through the propeller, the primary flow is admitted into an air intake 4 located downstream of the propeller, then passes through low- and high-pressure compressors 5 and 6 before reaching a combustion chamber 7. This primary flow is then expanded in high- and low-pressure turbines 8 and 9 before being discharged downstream. The secondary flow, on the other hand, is propelled directly downstream by the propeller.

[0036] Such an engine comprises a low-pressure body through which the propeller is coupled to the low-pressure turbine 9, and a high-pressure body through which the high-pressure compressor 6 is coupled to the high-pressure turbine 8, these two bodies being coaxial and independent in rotation.

[0037] The engine in Figure 1 is an engine with a variable pitch propeller: the pitch of the blades of this propeller, that is to say their angle of pitch, is thus adjusted according to the flight conditions, by being controlled by a hydraulic circuit 11 shown in Figure 2.

[0038] This hydraulic circuit 11 pressurizes a first upstream chamber 12 or a second downstream chamber 13 of a double-acting slewing cylinder 14, which acts on the longitudinal position of a central shaft of an engine. This allows the propeller blades to be maintained at a predetermined pitch angle by holding this shaft in a given position, and the pitch angle to be changed by moving this shaft.

[0039] This cylinder 14 is carried by the central shaft which is rotating, being supplied by the control circuit which is carried by fixed elements of the motor, via a rotating bearing identified by 16.

[0040] In general, this circuit 11 includes an oil reservoir 17 supplying a pump 18 whose outlet is connected to a high-pressure supply line 19, and a low-pressure return line 21 opening into the reservoir 17.

[0041] Pump 18 is arranged to increase its flow rate in the event of an increase in pressure at its outlet, so as to be able to adjust to the aerodynamic forces exerted on the propeller blades, to counteract them in order to modify their pitch angle.

[0042] As can be seen in Figure 2, this pump 18 comprises an axial piston pump body 22 driven by a drive shaft mechanically linked to the low-pressure body of the motor, and a tilting plate 23 whose orientation conditions the stroke of each piston to adjust the displacement of the pump, i.e. its volumetric flow rate per revolution.

[0043] The tilt of the platform 23 is controlled by a control chamber 24 of a control cylinder 26, and by a compensation chamber T1 of a compensation cylinder 28. The control cylinder 26 incorporates in its chamber 24 a return spring 29, tending to deploy it, its rod bearing against the platform 23. Similarly, the compensation cylinder 28 has a rod bearing against the platform 23. The compensation chamber T1 is pressurized by an oil outlet from the pump 22. The control chamber 24 is also pressurized, via a control line 31, with a pressure corresponding to the outlet pressure of the pump, but it has a larger cross-section than that of the compensation cylinder, in order to exert a higher torque on the platform 23.

[0044] At startup, spring 29 pushes the rod of cylinder 26 to tilt the plate so that the pump generates an initial flow. During operation, if the pressure in the control chamber decreases, the plate returns to its upright position, thus reducing the flow.

[0045] Thus, if the pressure increases at the pump outlet, it also increases in chambers 24 and Tl, which increases the inclination of the plate to increase the flow rate: the inclination of the plate 23 is all the more important as the supply pressure of chambers 24 and Tl is high.

[0046] More generally, pump 18 is a positive displacement pump self-regulating via cylinders 26 and 28, which control the tilt of its swashplate 23. When there is a demand for flow at the pump outlet, the pressure drops in chamber T1, and through the action of spring 29 and cylinders 26 and 28, the tilt of swashplate 23 increases to increase the displacement. The flow rate at the outlet of pump 18 then increases, which allows the pressure at the pump outlet to be maintained constant.

[0047] Additionally, a recirculation line 32 connects the supply line 19 to the reservoir 17 and is equipped with a recirculation valve 33 to reduce the pressure in the line 19 as soon as it exceeds the maximum permissible pressure for the circuit. This line 32, along with its recirculation valve, can be integrated into the pump 18.

[0048] In the example shown in the figures, chambers 24 and T1 are part of two separate cylinders, but they could also constitute the two chambers of a single double-acting cylinder. In the case of Figures 2 and 3, pump 18 is supplied directly from reservoir 17. However, a positive displacement pump 34 can be interposed between reservoir 17 and pump 18, as shown in Figures 4 and 5, thus ensuring a minimum pressure at the inlet of pump 18. Another recirculation line 36, equipped with a further recirculation valve 37, then connects the outlet of the positive displacement pump 34 to reservoir 17, to reduce the pressure at its outlet as soon as it exceeds a threshold value. This other recirculation line 36, with its recirculation valve, can also be integrated into the positive displacement pump 34.

[0049] Additionally, another recirculation line 38, equipped with another recirculation valve 39, connects the control line 31 to the reservoir 17 to depressurize it when its pressure is above a threshold value.

[0050] In the examples in the figures, the recirculation lines 32, 36 and 38 are connected to a general recirculation line 41 opening into the reservoir 17, and the recirculation valves are, for example, ball valves.

[0051] The pump 18 is driven by the rotating shaft of the engine, preferably its high-pressure body, so that in normal operation, it is the combustion of the fuel driving the engine that also drives this pump 18. In practice, the shaft of the pump is mechanically connected to a transmission box not shown, usually designated by the acronym AGB (Accessory Gear Box), and which is mechanically connected to the high-pressure body by means of a radial transmission shaft.

[0052] If the engine stops while the aircraft is in flight, the airflow through the engine drives the propeller, including both the low-pressure and high-pressure sections. Under these conditions, the rotational speed of the low-pressure section decreases, and the speed of the high-pressure section decreases more rapidly.

[0053] In the event of an in-flight engine restart—that is, without the assistance of a starter motor if the high-pressure (HP) speed induced by the autorotation of the low-pressure (LP) cylinder is already within the desired ignition range—or in the event of a restart with the assistance of a starter motor to bring the HP speed into the desired ignition range, a substantial resistive torque on the HP cylinder can hinder the necessary increase in HP cylinder speed before and / or after ignition. This could compromise the success of the in-flight restart. The pump's drive by this high-pressure cylinder generates a resistive torque on the propeller that negatively impacts engine restarting, and the invention aims to limit this resistive torque to facilitate engine restarting in flight. Similarly, in the event of an engine start when the aircraft is on the ground, limiting the resistive torque generated by the pump on the high-pressure cylinder facilitates this start.

[0054] The idea behind the invention is to connect the output of the pump 18 to the low pressure part of the control circuit 11 in the event of motor failure, so as to deactivate this pump by reducing the pressure increase it generates at its output, so that it does not generate a resisting torque on the shaft ensuring its rotational drive.

[0055] According to the invention, the outlet of the pump 18 is connected to the oil reservoir 17 by a deactivation valve 42 which is controlled by an engine computer, identified by FADEC in figures 2 to 5.

[0056] This deactivation valve 42 is equipped with a spring 43 that tends to keep it open, and it is a solenoid valve, meaning it is electrically controlled. Thus, when the FADEC control unit injects a control current to power the solenoid of the valve 42, it holds it closed against the spring 43, and this valve 42 opens as soon as its solenoid is no longer powered by the FADEC control unit.

[0057] In normal operation, the deactivation valve 42 is closed, so as not to disturb the pressure in the high pressure line 19 (i.e. at the outlet of the pump 18) to allow normal operation of the control circuit 11, which corresponds to the situation in Figure 2.

[0058] In the event of engine failure, the deactivation valve 42 is controlled by the FADEC computer to open, which has the effect of lowering the pressure in the high-pressure line 19 and therefore at the outlet of the pump 18.

[0059] Due in particular to leaks existing at the bearing 16, the pressure drops throughout the circuit 11, since it is no longer pressurized by the pump 18, which corresponds to the situation in Figure 3. As a result, the control chamber 24 and the compensation chamber T1 are depressurized, so that the pump 18 generates a very small increase in pressure at its outlet.

[0060] The invention thus makes it possible to deactivate the pump 18 in the event of a motor stoppage, so that it generates a very small pressure increase at its outlet, so that its drive by the motor shaft (high pressure body) does not generate a resisting torque, in order not to slow down the rotation of the propeller.

[0061] The invention also makes it possible to temporarily disable the pump 18 during the engine start-up phase on the ground, to reduce the power that must be injected into it in order to start it, and similarly it makes it possible to disable the pump 18 during an engine restart.

[0062] The FADEC computer, which is the main computer managing the turbojet, is thus advantageously configured to stop the electrical supply to valve 42 in the event of engine shutdown and during its start-up phases.

[0063] The invention is also adapted to the case where a volumetric pump 34 is interposed between the reservoir 17 and the pump 18, as in figures 4 and 5. In this case, in normal operation, the deactivation valve 42 is closed, which corresponds to the situation in figure 4.

[0064] When the engine is stopped, the opening of the deactivation valve 42 allows the pump 18 to be deactivated, which causes the pressure in the entire circuit to drop, as shown in Figure 5. The inlet of the pump 18 connected to the outlet of the volumetric pump 34 then admits a flow of oil which is minimal or even zero, which tends to increase the pressure between the outlet of the pump 34 and the pump 18, so that the recirculation valve 39 opens to recirculate the oil to the reservoir 17.

[0065] In practice, the recirculation valve 39 opens at a relatively low pressure, slightly higher than the low supply pressure of the pump 18. Thus, if the engine stops, the rotation of the positive displacement pump 34 is not impeded, but since the torque required to turn it is low, this results in very little braking of the impeller. Furthermore, the flow rate that can be injected by the pump 34 into the inlet of the pump 18 tends to cause the latter to rotate, because it then has an inlet pressure higher than its outlet pressure. Consequently, the pump 18 rotates, generating a driving torque, that is, tending to rotate the low-pressure body instead of braking it.

[0066] The hydraulic circuit 11 is arranged to control the pitch angle of the blades, in order to increase it, reduce it, or maintain it at its current value, by means of a three-position distributor valve.

[0067] The supply lines 19 and return lines 21 are connected to the cylinder 14 via the three-position distributing valve 44, comprising a central neutral position corresponding to the one it occupies in Figure 4, as well as a step increase position and a step reduction position.

[0068] This distributing valve 44, which is here a spool valve, is connected to the upstream chamber 12 by an upstream pipe 46, and it is connected to the downstream chamber 13 by a downstream pipe 47.

[0069] In the neutral position of Figure 2, the pipes 19 and 21 are isolated from the chambers 12 and 13, which are at pressures of intermediate value between high pressure and low pressure, the blades 3 of the propeller therefore having their orientation angle fixed at a fixed value.

[0070] When the distributing valve 44 is placed in its pitch increase position, it is offset downwards relative to its position in Figure 2. It then connects the upstream chamber 12 with the high-pressure supply line 19, and the downstream chamber 13 with the low-pressure return line 21. This moves the rod of the cylinder 14 to the right in Figure 2, to increase the pitch angle of the blades 3.

[0071] When the diverter valve 44 is in its pitch reduction position, it is offset upwards relative to its position in Figure 2. It then connects the upstream chamber 12 with the return line 21, and the downstream chamber 13 with the high-pressure line 19. This moves the rod of the cylinder 14 to the left in Figure 2 to decrease the pitch angle of the blades 3. Additionally, the circuit 11 includes a selector valve 48 connected to the upstream line 46, the downstream line 47, and the control line 31 supplying the control chamber 24. This selector valve 48, which is a shuttle valve, continuously connects the control line 31 to the line with the higher pressure between the upstream line 46 and the downstream line 47.

[0072] Thanks to the selection valve 48 and the control line 31, the pressure in the downstream chamber 13 automatically adjusts to the force exerted by the blades on the rod of the cylinder 14.

[0073] An increase in the force exerted by the blades on the rod of the cylinder 14 tends to retract it, which increases the pressure in the downstream chamber 13. This increase is passed on to the control chamber 24, which is connected to this downstream chamber 13 by the selection valve 48. This causes an increase in the inclination of the plate 23, to increase the flow of the pump 18, which makes it possible to increase the pressure in the chamber 13 to counteract the increase in the force exerted by the blades.

[0074] Similarly, a decrease in the force exerted by the blades on the cylinder 14 tends to deploy it, which leads to a decrease in pressure in chamber 13. This decrease is passed on by the control chamber, which leads to a reduction in the inclination of the platform, and therefore a decrease in the flow rate of the pump resulting in a reduction of pressure in chamber 13.

[0075] As can be seen in the figures, the control line 31 is connected to the selector valve 48 by a restriction 49, and similarly it is also connected to the lines 46 and 47 by two other restrictions 51 and 52. These restrictions make it possible to smooth out pressure peaks or irregularities in the circuit, so as to avoid unnecessarily jerky control behavior.

[0076] Generally, the blades can be configured in a propulsion orientation, where the engine generates thrust directed downstream (AV), and in a thrust reversal orientation, where it generates thrust directed upstream (AM). This latter orientation is intended for use only when the aircraft is on the ground for deceleration. Several malfunctions can, however, lead to a pitch drift in flight towards the thrust reversal position. This can be due to a failure of the pitch control system, i.e., a computer controlling the hydraulic circuit, or a failure of the hydraulic circuit itself.

[0077] In this context, circuit 11 includes a protection system 53 ensuring that the blades 3 cannot accidentally reach a thrust reversal orientation while the aircraft is in flight.

[0078] This protection system comprises a first protection valve 54 and a second protection valve 56 in the form of a pair of distributor drawers rigidly joined to each other.

[0079] This system is equipped with a return spring 57, a hydraulic activation inlet 58 located on the side of the spring 57, and a hydraulic deactivation inlet 59 located on the opposite side of the spring 57.

[0080] When the activation inlet 58 is depressurized and the deactivation inlet 59 is pressurized, the pair of spools is pushed by the deactivation inlet against the spring 57, to place the valves 54 and 56 in the deactivated position, as in Figures 2 and 4. In this deactivated position, the valve 54 is simply traversed by the oil from the upstream line 46, and the valve 56 is simply traversed by the oil from the downstream line 47.

[0081] When the activation inlet 58 is pressurized and the deactivation inlet 59 is depressurized, the spools are pushed to place the two valves in the activated position as shown in Figures 3 and 5. In this activated position, the valve 54 directly connects the upstream chamber 12 with the high-pressure line 19, while isolating this chamber 12 from the distributing valve 44, and the valve 56 directly connects the downstream chamber 13 with the low-pressure line 21, while isolating this chamber 13 from the distributing valve 44.

[0082] As will be understood, when the protection valves 54 and 56 are deactivated, the position of the cylinder 14, and therefore the angle of the blades 3, is governed by the distributing valve 44, which allows the angle of these blades 3 to be increased or decreased. Conversely, when these two protection valves 54 and 56 are activated, the upstream chamber 12 is pressurized and the downstream chamber 13 is depressurized, which moves the rod of the cylinder 14 to the right in the figures to bring the pitch angle of the blades 3 back to a propulsion orientation.

Claims

DEMANDS 1. Hydraulic control circuit (11) of a double-acting slewing cylinder (14) for orienting the fan blades of a turbojet engine, comprising an oil reservoir (17) supplying an axial piston pump (18) having an outlet connected to a supply line (19), a diverter valve (44) for connecting one of the chambers (12, 13) of the slewing cylinder (14) to the supply line (19) and the other chamber of the slewing cylinder (14) to the reservoir (17) or vice versa, the axial piston pump (18) being a variable displacement pump comprising a tilting swashplate (23) as well as a control chamber (24) and a compensation chamber (27) for controlling the tilt of the swashplate (23), the control chambers (24) and compensation chamber (27) both being capable of being pressurized with a pressure corresponding to pump outlet pressure (18),and being arranged to increase the inclination of the platform (23) when the pressurization of these chambers increases, this control circuit (11) comprising a deactivation valve (42) controlled by a turbojet computer (FADEC), this deactivation valve (42) allowing the supply line (19) to be connected to the tank (17) in order to deactivate the axial piston pump (18).

2. Circuit according to claim 1, wherein the deactivation valve (42) is a solenoid valve equipped with a return spring (43) to be normally closed, and which opens in the absence of power supply to its solenoid.

3. Circuit according to claim 1, comprising a volumetric pump (34) interposed between the reservoir (17) and the axial piston pump (18).

4. Circuit according to claim 3, comprising a recirculation line (38) connecting the outlet of the volumetric pump (34) to the reservoir (17) via a recirculation valve (39).

5. Circuit according to claim 1, wherein the computer (FADEC) is configured to deactivate the pump (18) in the event of detection of an engine stop.

6. Circuit according to claim 1, wherein the computer (FADEC) is configured to deactivate the pump (18) during engine start-up on the ground and / or engine restart or re-ignition in flight.

7. Circuit according to any one of the preceding claims, wherein the compensation chamber (27) of the axial piston pump (18) is supplied by the outlet of this pump (18), wherein the two chambers (12, 13) of the slewing cylinder (14) are connected to the distributing valve (44), wherein the distributing valve (44) can occupy a position in which it connects one of the chambers (12) to the supply line (19) and the other chamber (13) to the reservoir (17), or another position in which it connects one of the chambers (12) to the reservoir (17) and the other chamber (13) to the supply line (19).

8. Circuit (11) according to claim 7, further comprising a selection valve (48) connected to the two chambers (12, 13) of the slewing cylinder (14) and to the control chamber (24) by a control line (31), to pressurize the control chamber (24) of the pump (18) with the higher pressure of the two chambers (12, 13) of the slewing cylinder.

9. Circuit according to claim 1, comprising a spring (29) tending to tilt the plate (23).

10. Turbojet comprising a circuit according to claim 1 and variable pitch fan blades which are controlled by this circuit.

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