PROTECTION FOR THE CONTROL UNIT FOR THE ALIGNMENT OF PROPELLER BLADES OF AN AIRCRAFT ENGINE

Description

TECHNICAL FIELD

[0001] The invention relates to an aircraft engine comprising variable pitch blades allowing control and / or reversal of the thrust generated by this engine, and it has as its object a protection to prevent, in the event of failure of the control system, an accidental reversal of thrust when the aircraft is in flight. PREVIOUS STATE OF THE ART

[0002] In a turbojet-type aircraft engine, air is admitted into an inlet sleeve to pass through a propulsion propeller consisting of a series of rotating blades before splitting into a central primary flow and a secondary flow surrounding the primary flow.

[0003] The primary flow is then compressed in 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 propulsion propeller into a channel externally defined by an engine fairing.

[0004] 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.

[0005] The reversal of thrust of such an engine can be ensured by providing propeller blades with variable pitch, that is to say whose orientation around their span axis, which extends radially with respect to the axis of rotation of the engine, can be modified in flight.

[0006] In this case, the blades can occupy a propulsion orientation so that the engine generates thrust directed towards its downstream direction, and a so-called thrust reversal orientation, in which it generates thrust directed towards its upstream direction, the latter being intended to be used only when the aircraft is on the ground to decelerate the aircraft.

[0007] In practice, propulsion directions are commonly referred to as large steps, and thrust reversal directions are commonly referred to as small steps.

[0008] The transition from propulsion orientation to thrust reversal orientation is typically achieved by a rotation of the blades of approximately 90°, with orientation control generally provided by a hydraulic circuit.

[0009] However, several failures can lead to a drift in flight of the pitch control unit towards the thrust reversal position. This can be a failure of the pitch control unit, i.e., a computer controlling the hydraulic circuit, or a failure of the hydraulic circuit itself.

[0010] In this context, a protection system integrated into the hydraulic circuit ensures that the blades cannot switch to the thrust reversal orientation when the aircraft is, for example, in cruise flight, such protections being described in patent documents FR2981684A1, FR2978953A1, FR2985284A1, FR30104153A1, and EP1178223.

[0011] Thus, when it is detected that the blades are or are approaching a thrust reversal orientation while the engine is in flight configuration, the protection is activated to act on the hydraulic circuit so that it returns them to a propulsion orientation.

[0012] In general, this type of protection can be implemented in an unfaired turboprop engine or an "open rotor" engine with a double counter-rotating propeller, or in a faired engine such as a turbojet with variable pitch fan blades.

[0013] In practice, it appears that the reaction time of existing protections is on the order of a second, between the moment they are ordered and the moment the blades actually begin to be brought back towards a propulsion orientation.

[0014] The aim of the invention is to provide a solution to improve the responsiveness of such protection. DESCRIPTION OF THE INVENTION

[0015] To this end, the invention relates to a hydraulic control circuit for actuation of a double-acting slewing cylinder for orienting the blades of an aircraft engine propulsion propeller, this double-acting cylinder comprising a first and a second chamber, this circuit comprising: a high-pressure line and a low-pressure line; a diverter valve to connect the first chamber to the high-pressure line and the second chamber to the low-pressure line or vice versa, or to isolate the two chambers from the high-pressure and low-pressure lines; a first protective valve that can occupy a deactivated position or an activated position in which it connects the first chamber with the high-pressure line; a second protective valve that can occupy a deactivated position or an activated position in which it connects the second chamber with the low-pressure line; characterized in that : These protective valves include a hydraulic activation inlet and a hydraulic deactivation inlet which can be connected to the high-pressure line or the low-pressure line to place them in the deactivation or activation position; an amplification valve which can occupy a deactivated position or an activation position in which it connects the high-pressure line to each activation inlet and the low-pressure line to each deactivation inlet to activate the protective valves; the amplification valve having a hydraulic pilot inlet to place it in the activation position when this pilot inlet is connected to the low-pressure line, and to place it in the deactivated position when this pilot inlet (46) is connected to the high-pressure line;and a protective solenoid valve that can occupy a deactivation position or an activation position in which it connects the pilot input of the boost valve to the low-pressure line in order to activate it.

[0016] With this solution, the amplification valve allows the protection valves to be controlled hydraulically so that they quickly change position under the effect of the pressurization of their activation inlets.

[0017] The invention also relates to a circuit defined as follows, in which the first and second protective valves are mechanically coupled and share the same hydraulic activation inlet and the same hydraulic deactivation inlet. The invention also relates to a circuit defined as follows, in which the first and second protective valves each comprise a spool valve, and in which these two spool valves are connected to each other by a stem.

[0018] The invention also relates to a circuit defined as follows, in which each protective valve is equipped with a return spring that continually tends to return it to its activation position.

[0019] The invention also relates to a circuit defined as follows, in which the amplification valve is equipped with a return spring that continually tends to bring it back to its activation position.

[0020] The invention also relates to a circuit defined as follows, in which the protection valves isolate the first chamber and the second chamber of the distributing valve when they are activated.

[0021] The invention also relates to an aircraft engine comprising a circuit defined as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] There [ Fig. 1 ] is a longitudinal cross-sectional view of a turbofan engine; The [ Fig. 2] is a view along the span axis of a propeller blade having a propulsion orientation; The [ Fig. 3 ] is a view along the span axis of a pusher propeller blade having a thrust reversal orientation; The [ Fig. 4 ] is a schematic view of the control circuit according to the invention in nominal operation; The [ Fig. 5 ] is a schematic view of the control circuit according to the invention when its protection system is activated. DETAILED DESCRIPTION OF SPECIFIC IMPLEMENTATION METHODS

[0023] In an aircraft engine such as the engine marked with 1 on the figure 1Air is admitted through an inlet 2 located upstream AM to pass through the blades 3 of a propulsion propeller, also called a fan, which has a series of rotating blades 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 upstream AM to downstream AV of the engine when it generates propulsion thrust.

[0024] The primary airflow is admitted into an air intake 4 located downstream of the propeller and extending around the longitudinal axis AX, where it is then compressed in low-pressure compressors 5 and high-pressure compressors 6 before entering a combustion chamber 7. This primary airflow is then expanded through a high-pressure turbine 8 and a low-pressure turbine 9 before being discharged downstream. The secondary airflow, on the other hand, is propelled directly downstream by the propeller into a channel externally delimited by a nacelle 11 supporting the entire engine assembly.

[0025] Such a twin-spool engine comprises a low-pressure spool through which the propulsion propeller is coupled to the low-pressure turbine 9, and a high-pressure spool through which the high-pressure compressor 6 is coupled to the high-pressure turbine 8, these two spools being coaxial and independent in rotation. These spools are surrounded by a series of casings 12 arranged along the longitudinal axis they enclose.

[0026] On the figure 3 , a variable pitch propeller blade 3 has an intrados face and an extrados face extending between a leading edge 14 and a trailing edge 16. This blade 3 extends along a so-called radial span axis EV relative to the axis AX, from a base by which it is rigidly attached to a rotor element not shown, to a top corresponding to its free end which is opposite the inner face of the nacelle 11.

[0027] The blade pitch angle is the angle between the chord axis Ac, which passes through the leading edge 14 and the trailing edge 16 extending in a plane normal to the EV axis, and the propeller plane PS, which is normal to the AX axis. In the following, a positive pitch angle indicates a downstream propulsion of the airflow surrounding the rotating blade, i.e., a propulsion direction. A negative pitch angle indicates an upstream propulsion of the airflow.

[0028] On the figure 3 , blade 3 occupies a propulsion orientation, corresponding for example to a so-called cruising regime: the chord axis Ac is inclined at a positive pitch angle Cc relative to the plane PS.

[0029] In the configuration corresponding to a propulsion orientation of the figure 3The pitch angle of blade 13 is positive, so that when rotated in the direction marked by R in the figures, it propels the airflow from upstream AM to downstream AV. The direction of rotation R corresponds to clockwise when viewed along the AX axis, from the front, i.e., from its upstream AM.

[0030] This blade is of the variable pitch type: its orientation around the EV axis is adjustable according to the engine's operating conditions. In the situation of the figure 3 , the orientation of blade 13 corresponds to an engine operation in propulsion, that is to say in which the flow F passing through the engine is propelled upstream AM towards downstream AV.

[0031] During thrust reversal, for example when the aircraft is landing and the engine is used to brake, the propeller blades are controlled to change their orientation. They then pivot around their span axes to switch from the propulsion orientation corresponding to the figure 3 , to the thrust reversal orientation corresponding to the situation represented on the figure 4 .

[0032] For example figures 2 And 3The blade pivots in the forward direction to switch from the propulsion orientation to the thrust reversal orientation, so that its leading edge is located downstream of its trailing edge in the thrust reversal orientation. During the transition from one orientation to the other, the blade passes through a transitional position known as 0°, in which its chord axis passes through the PS plane of the propeller. It is important that the blade remains in this transitional position only briefly, as it can cause engine overspeed.

[0033] It is also possible to use a different configuration, in which the blade rotates in the opposite direction to switch from the propulsion orientation to the thrust reversal orientation, its trailing edge remaining ahead of its leading edge when in the thrust reversal orientation. During the transition from one orientation to the other, the blade passes through a position known as feathered, in which its chord axis is parallel to the AX axis.

[0034] On the figure 4 A hydraulic circuit 17 pressurizes a first chamber 18 upstream or a second chamber 19 downstream of a double-acting slewing cylinder 21 acting on the longitudinal position of a central shaft of an engine. This makes it possible to maintain the propeller blades at a predetermined pitch angle by holding this shaft in a given position and to change the pitch angle by moving this shaft.

[0035] This cylinder 21 is carried by the central shaft which is rotating, being supplied by the control circuit which is carried by fixed elements of the motor, thanks to a hydraulic transfer bearing 22 surrounding the central shaft, this bearing being able to be the site of hydraulic leaks.

[0036] This circuit 17 includes a high-pressure supply line 23 supplied by a pump not shown, and a low-pressure return line 24 emptying into a reservoir not shown.

[0037] The supply lines 23 and return lines 24 are connected to the cylinder 21 via a three-position diverter valve 26, including a central neutral position corresponding to the one it occupies in the figure 4 , as well as a step increase position and a step decrease position.

[0038] This distributing valve 26, which is here a spool distributor, is connected to the upstream chamber 18 by an upstream pipe 27 and by the bearing 22, and it is connected to the downstream chamber 19 by a downstream pipe 28 and by the bearing 22.

[0039] In the neutral position of the figure 4 , pipes 23 and 24 are isolated from chambers 18 and 19, which are at pressures of intermediate value between high pressure and low pressure, the blades 3 of the propeller therefore having their angle of orientation fixed at a fixed value.

[0040] When the distributing valve 26, which is here a spool valve, is placed in its increased step position, that is to say offset to the right relative to its position of the figure 4The distributing valve connects the upstream chamber 18 with the high-pressure supply line 23, and the downstream chamber 19 with the low-pressure return line 24. This has the effect of moving the rod of the cylinder 21 to the right on the figure 4 , to increase the angle Cc of the blade pitch 3 in order to place them in a propulsion orientation.

[0041] When the distributing valve 26 is in its reduced pitch position as on the figure 5 that is to say, shifted to the left relative to its position in the figure 4 It connects the upstream chamber 18 with the return line 24, and the downstream chamber 19 with the high-pressure line 23. This has the effect of moving the rod of the cylinder 21 to the left on the figure 4 to decrease the angle Cc of the blade pitch 3 in order to place them in a thrust reversal orientation.

[0042] Circuit 17 incorporates a protection system ensuring that the blades 3 cannot accidentally reach a thrust reversal orientation while the aircraft is in flight.

[0043] This protection system includes a protective solenoid valve 31, an amplification valve 32, as well as a first protective valve 33 and a second protective valve 34.

[0044] The protection valve 33 is here a two-position spool valve equipped with a return spring 36, and having an activation hydraulic inlet 37 located on the side of the spring 36, and a deactivation hydraulic inlet 38 located on the opposite side of the spring 36.

[0045] When the activation inlet 37 is depressurized and the deactivation inlet 38 is pressurized, the spool is pushed by the deactivation inlet against the spring 36, to place the valve 33 in the deactivated position, as on the figure 3When the activation inlet 37 is pressurized and the deactivation inlet 38 is depressurized, the spool is pushed by the pressurization of the activation inlet to place the valve in the activated position as shown in the diagram. figure 4 .

[0046] In the deactivated position corresponding to the figure 3 , valve 33 is simply traversed by the oil from the upstream line 27. In the activated position, as in the figure 3 , valve 33 directly connects the upstream chamber 18 with the high-pressure pipe 23, while isolating this chamber 18 from the distributing valve 26.

[0047] The protection valve 34 is here a two-position spool valve equipped with a return spring 39, and having an activation hydraulic inlet 41 located on the side of the spring 39, and a deactivation hydraulic inlet 42 located on the opposite side of the spring 39.

[0048] When the activation inlet 41 is depressurized and the deactivation inlet 42 is pressurized, the spool is pushed by the deactivation inlet against the spring 39, to place the valve 34 in the deactivated position, as in the figure 3 When the activation inlet 41 is pressurized and the deactivation inlet 42 is depressurized, the spool is pushed by the activation inlet 41 to place the valve in the activated position, as on the figure 4 .

[0049] In the deactivated position corresponding to the figure 4 , valve 34 is simply traversed by the oil from the downstream line 28. When it is in its activated position, as in the figure 5It directly connects the downstream chamber 19 with the low-pressure pipe 24, while isolating this chamber 19 from the distributing valve 26. As will be understood, when the two protection valves 33 and 34 are deactivated, the position of the cylinder 21, and therefore the angle of the blades 3, is governed by the distributing valve 26, which allows the angle of these blades 3 to be increased or decreased.

[0050] Conversely, when the two protection valves 33 and 34 are activated, the upstream chamber 18 is pressurized and the downstream chamber 19 is depressurized, which moves the rod of the cylinder 21 to the right in the figures to bring the pitch angle of the blades 3 back to a propulsion orientation.

[0051] As seen on the figure 4The activation and deactivation inlets of the two valves 33 and 34 are supplied by the amplification valve 32, which is a two-position spool valve. This spool valve includes a return spring 43, a passive hydraulic inlet 44 located on the side of the spring 43, and a pilot hydraulic inlet 46 located on the opposite side of the spring 43. The passive inlet 44 is continuously subjected to low pressure because it is permanently connected to the low-pressure line 24.

[0052] In nominal operation corresponding to the figure 4The pilot inlet 46 of valve 32 is pressurized, so that the spool of this valve 32 is pushed against the spring 43 by the pressurization of the pilot inlet 46 to place it in the inactive position. In this position, valve 32 connects the deactivation inlets 38 and 42 of the protective valves 33 and 34 to the high-pressure line 23 to pressurize them, and it connects their activation inlets 37 and 41 to the low-pressure line 24 to depressurize them, so that valves 33 and 34 are both in their deactivated positions. The pitch angle of the blades 3 is then thus controlled by the piloting of the diverter valve 26.

[0053] In protection mode corresponding to the figure 5The pilot inlet 46 is depressurized, and the valve spool 32 is pushed by the spring 43 to place it in the activation position. In this position, the valve 32 connects the deactivation inlets 38 and 42 of the protection valves 33 and 34 to the low-pressure line 24 to depressurize them, and it connects their activation inlets 37 and 41 to the high-pressure line 23 to pressurize them, which places the valves 33 and 34 in their activation positions. The pitch angle of the blades 3 is then automatically returned to a propulsion orientation, due to the pressurization of the upstream chamber 18 and the depressurization of the downstream chamber 19 caused by the activation of the protection valves 33 and 34. Alternatively, it is possible to do without the spring 43 by providing different sections for the hydraulic chambers connected respectively to the inlets 44 and 46.If the cross-sectional area of ​​the chamber connected to the passive inlet 44 is larger than that of the chamber connected to the pilot inlet 46, and if these inlets 44 and 46 are subjected to the same pressure, the thrust in the first chamber is greater than that in the second. The resulting thrust then moves the spool of the valve 32 to its activation position. Alternatively, a high-stiffness spring is used, eliminating the passive inlet 44 of the valve 32 and therefore also the section of pipe 48 connecting this passive inlet 44 to the low-pressure pipe 24. The spring stiffness is then sufficient to generate a force greater than the hydraulic thrust produced by the pilot inlet 46 when it is depressurized, that is, when the pressure at this inlet 46 is below a predetermined threshold.In this way, the spring forces counteract the opposing hydraulic thrust to move the valve spool 32 to its activation position. The spring stiffness is then chosen to generate a force less than the hydraulic thrust produced by the inlet 46 when it is pressurized by the high-pressure line 23. In this case, during nominal operation when the protective solenoid valve 31 is closed, the pressurization of the inlet 46 keeps the boost valve 32 in its inactivation position, the spring 43 then being compressed by the opposing hydraulic pressure.

[0054] The amplification valve 32 is controlled by the protective solenoid valve 31, which can occupy an activated position, i.e., open as in the figure 5, in which it depressurizes the pilot inlet 46 of the valve 32 by connecting this inlet to the low-pressure line 24. In nominal operation, the protective solenoid valve 31 occupies an inactivated, i.e., closed, position, as on the figure 4 , which ensures that the inlet 46 of the amplification valve 32 is pressurized so that this valve 32 is in the inactivation position.

[0055] As seen on the figure 5 , the high pressure line 23 is equipped with a diaphragm 49 which prevents short-circuiting of the line 23 with the line 24 when they are connected to each other during the activation of the solenoid valve 31.

[0056] This protective solenoid valve 31 is electrically controlled by an engine control unit, usually designated by the acronym FADEC ( Full Authority Digital Engine Control") so as to be deactivated during nominal operation, and to be activated when the system detects that the blades 3 are in a thrust reversal orientation while the aircraft is in flight. As will be understood, this solenoid valve 31 is, for example, a spool valve equipped with a solenoid that moves this spool from one position to another depending on whether the solenoid is electrically powered or not. The protective solenoid valve 31 is equipped with a return spring 47 that continuously tends to return it to its deactivated position, and its movement to its activated position is achieved by electrically energizing it to move it towards its activated position against the spring 47.

[0057] As mentioned above, the protection valves 33 and 34 are equipped with return springs 36 and 39 which continually tend to bring them back to their active positions: it is the pressurization of their deactivation inlets 38 and 42 which ensures that these valves are inactive in nominal operation.

[0058] In the event of a hydraulic circuit failure, the activation inlets 37, 41 and the inlet 46 of the boost valve 32, as well as the deactivation inlets 38, 42, are depressurized. In this case, the return springs 36 and 39 of the protection valves 33 and 34, and the return spring 43 of the boost valve 32, move these valves to activate them, which has the effect of returning the propeller blades to a propulsion orientation in the event of a hydraulic circuit malfunction.

[0059] In other words, thanks to the return springs, if the pressures are identical at the two inlets of either of the protection valves 33, 34, they are returned by these springs to their activation positions.

[0060] Furthermore, in the example of figures 4 And 5 Valves 33 and 34 are separate and independent. However, they can be mechanically linked to each other, for example by means of a rod rigidly joining their spools together, so as to be controlled by the same activation input and the same deactivation input common to both valves.

[0061] In general, if a drift in the orientation of the blades towards their thrust reversal orientation is detected, the computer electrically commands the protection solenoid valve to activate it.

[0062] This activation has the effect of activating the amplification valve so that it depressurizes the deactivation inlets of the two protection valves and pressurizes their activation inlets, which results in a very rapid activation of the protection valves to return the blades to their propulsion orientation.

[0063] In practice, the implementation of the amplification valve makes it possible to obtain a reaction time on the order of a tenth of a second, whereas in a system without an amplification valve, in which the protection valves are solenoid valves, the activation time is on the order of a second.

[0064] The circuit architecture according to the invention makes it possible to provide an amplification valve with a small dimension comprising a small distributor so that a small flow rate is sufficient to change its position, and having a small stroke, so that this amplification valve can have a mass and size much lower than those of the other valves in the circuit.

[0065] In the example shown in the figures, the invention is implemented on a turbojet equipped with variable pitch fan blades, but it can be implemented in an unfaired turboprop engine or an open rotor engine with a double counter-rotating propeller.

Claims

1. Hydraulic control circuit (17) for actuating a double-acting (21) steering actuator (21) for orienting the blades (3) of an aircraft engine pusher propeller, this double-acting actuator (21) comprising a first and a second chamber (18, 19), this circuit (17) comprising: - a high-pressure line (23) and a low-pressure line (24); - a distributing valve (26) for connecting the first chamber (18) to the high-pressure line (23) and the second chamber (19) to the low-pressure line (24) or vice versa, or for isolating the two chambers (18, 19) from the high-pressure and low-pressure lines; - a first protection valve (33) being able to assume a deactivated position or an activation position wherein it places the first chamber (18) in communication with the high-pressure line (23); - a second protection valve (34) being able to assume a deactivated position or an activation position wherein it places the second chamber (19) in communication with the low-pressure line (24); characterized in that : - these protection valves (33, 34) include an activation hydraulic inlet (37, 41) and a deactivation hydraulic inlet (38, 42) that can be connected to the high-pressure line (23) or to the low-pressure line (24) to place them in the deactivation or activation position; and in that it comprises : - an amplification valve (32) being able to assume a deactivated position or an activation position wherein it connects the high-pressure line (23) to each activation inlet (37, 41) and the low-pressure line (24) to each deactivation inlet (38, 42) to activate the protection valves (33, 34); and in that : - the amplification valve (32) including a hydraulic control inlet (46) for placing it in the activation position when this control inlet (46) is connected to the low-pressure line (24) and for placing it in the deactivated position when this control inlet (46) is connected to the high-pressure line (23); - and a protection solenoid valve (31) being able to assume a deactivation position or an activation position wherein it connects the control inlet (46) of the amplification valve (32) to the low-pressure line (24) in order to activate it.

2. Circuit according to claim 1, wherein the first and the second protection valve (33, 34) are mechanically coupled and share the same activation hydraulic inlet and the same deactivation hydraulic inlet.

3. Circuit according to claim 2, wherein the first and the second protection valve (33, 34) each include a slide valve, and wherein these two slide valves are connected to one another by a rod.

4. Circuit according to claim 1, wherein each protection valve (33, 34) is equipped with a return spring (36, 39) tending continuously to return it towards the activation position thereof.

5. Circuit according to claim 1, wherein the amplification valve (32) is equipped with a return spring (43) tending continuously to return it to the activation position thereof.

6. Circuit according to claim 1, wherein the protection valves (33, 34) isolate the first chamber (18) and the second chamber (19) from the distributing valve (26) when they are activated.

7. Aircraft engine including a circuit according to one of the preceding claims.