Protecting circuit for controlling orientation of propeller blade of aircraft engine

Abstract

The invention relates to a hydraulic control circuit (17) of a steering actuator (21) having first and second chambers (18, 19) for orienting blades of an aircraft engine thruster propeller, the circuit (17) comprising: a high-pressure line (23) and a low-pressure line (24); a first protective valve (33) which can be in a deactivated position or an activated position to arrange the first chamber (18) in communication with the high-pressure line (23); a second protective valve (34), which can be in a deactivated position or an activated position to arrange the second chamber (19) in communication with the low pressure line (24), each protective valve (33, 34) comprising a hydraulic activated inlet (37, 41) and a hydraulic deactivated inlet (38, 42), which can be pressurized to activate or deactivate these valves (33, 34). The circuit comprises an electromagnetic protection valve (31) which controls an amplifying valve (32) connected to the inlet of the protection valve (33, 34) in order to activate the protection valve when the electromagnetic protection valve (31) is activated.

Description

Technical Field

[0001] The invention relates to an aircraft engine comprising variable pitch blades for controlling and / or reversing the thrust generated by the engine and has the object of providing protection against unintended thrust reversal when the aircraft is in flight in the event of a control system failure. Background Art

[0002] In an aircraft engine of the turbojet type, air is introduced into an inlet duct to pass through a propeller comprising a series of rotating blades and then divided into a central main flow and a secondary flow surrounding the main flow.

[0003] The main flow is then compressed in the compression stage before reaching the combustion chamber, after which it is expanded by means of the high-pressure turbine and the low-pressure turbine before being discharged to the rear. The secondary flow, for its part, is propelled directly downstream by the propeller propeller into a duct externally delimited by the engine cowling.

[0004] This engine comprises a low-pressure shaft, via which the propeller propeller is coupled to a low-pressure turbine, and a high-pressure shaft, via which the high-pressure compressor is coupled to the high-pressure turbine, the two shafts being coaxial and rotationally independent.

[0005] Thrust reversal of such an engine can be ensured by providing variable pitch propeller blades, that is to say the orientation of the variable pitch propeller blades about a span axis of the variable pitch propeller blades can be changed in flight, the span axis extending radially with respect to the rotation axis of the engine.

[0006] In this case, the blades can be in a thrust orientation so that the engine produces thrust directed in a direction downstream of the engine, and the blades can be in an orientation known as thrust reversal, in which the engine produces thrust directed in a direction upstream of the engine, which thrust is intended to be used only when the aircraft is on the ground to slow the aircraft.

[0007] In practice, the thrust-reverse orientation is often referred to as coarse pitch, while the thrust-reverse orientation is often referred to as fine pitch.

[0008] The transition from a thrust-to-reverse orientation is typically accomplished by rotating the blades through approximately 90°, with directional control typically provided by a hydraulic circuit.

[0009] However, a number of faults may result in a drift of the flight pitch towards the thrust reverse position. This may be a fault in the pitch control component (ie the computer controlling the hydraulic circuit) or a fault in the hydraulic circuit itself.

[0010] In this context, protection systems integrated into the hydraulic circuit ensure that the blades cannot change to a thrust-reversing orientation when the aircraft is, for example, in cruising flight, such protections being described in patent documents FR2981684A1, FR2978953A1, FR2985284A1 and FR3014153A1.

[0011] Thus, when it is detected that the blades are in or approaching a thrust reversal orientation when the engine is in the flight configuration, the protection device is actuated to act on the hydraulic circuit so that the blades return to the thrust orientation.

[0012] Typically, this type of protection device may be implemented in non-ducted turboprop engines or open rotor engines with counter-rotating twin propellers, or in ducted engines such as turbojets with variable pitch fan blades.

[0013] In practice, the reaction time of the existing protection devices is approximately one second between the moment they are controlled and the moment the blade effectively starts to return to the propulsion orientation.

[0014] The object of the present invention is to provide a solution which improves the reactivity of such a protection device. Summary of the invention

[0015] To this end, the object of the invention is a hydraulic control circuit for actuating a double-acting steering actuator for orienting the blades of a propeller of an aircraft engine, the double-acting actuator comprising a first chamber and a second chamber, the circuit comprising:

[0016] - High-pressure pipelines and low-pressure pipelines;

[0017] a distribution valve for connecting the first chamber to the high-pressure line and the second chamber to the low-pressure line, or for connecting the first chamber to the low-pressure line and the second chamber to the high-pressure line, or for isolating the two chambers from the high-pressure line and the low-pressure line;

[0018] a first protection valve which can be placed in a deactivated position or in an activated position, wherein the first protection valve places the first chamber in communication with the high-pressure line;

[0019] a second protection valve which can be placed in a deactivated position or in an activated position, wherein the second protection valve places the second chamber in communication with the low-pressure line;

[0020] Features:

[0021] - the protection valves include a start hydraulic inlet and a stop hydraulic inlet, which can be connected to a high pressure line or a low pressure line to place the protection valves in a stop position or a start position;

[0022] an amplification valve capable of being in a deactivated position or in an activated position, wherein the amplification valve connects a high-pressure line to each activation inlet and a low-pressure line to each deactivated inlet, in order to activate the protection valves;

[0023] - the amplification valve comprises a hydraulic control inlet for placing the hydraulic control inlet in an activated position when the control inlet is connected to the low-pressure line, and for placing the hydraulic control inlet in a deactivated position when the control inlet (46) is connected to the high-pressure line;

[0024] and a protection solenoid valve which can be in a deactivated position or an activated position, wherein the protection solenoid valve connects the control inlet of the amplification valve to the low-pressure pipeline so that the amplification valve is activated.

[0025] With this solution, the amplification valve makes it possible to hydraulically control the protection valve so that the protection valve changes position rapidly under the effect of the pressurization of the activation inlet of the protection valve.

[0026] The invention also relates to a circuit defined thereby, in which the first protection valve and the second protection valve are mechanically coupled and share a common activation hydraulic inlet and a common deactivation hydraulic inlet.

[0027] The invention also relates to a circuit defined thereby, wherein the first protection valve and the second protection valve each comprise a sliding valve, and wherein the two sliding valves are connected to one another via a rod.

[0028] The invention also relates to a circuit defined thereby, in which each protection valve is equipped with a return spring tending to return the protection valve continuously to its actuated position.

[0029] The invention also relates to a circuit defined thereby, in which the amplification valve is equipped with a return spring tending to continuously return the amplification valve to its start position.

[0030] The invention also relates to a circuit defined thereby, wherein the protection valve separates the first chamber and the second chamber from the distribution valve during activation.

[0031] The invention also relates to an aircraft engine comprising a circuit thus defined. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] [ Figure 1 ] is a longitudinal cross-sectional view of a double-ducted turbojet engine;

[0033] [ Figure 2 ] is a view along the span axis of a propeller blade of a propeller having a propulsive orientation;

[0034] [ Figure 3 ] is a view along the span axis of a pusher propeller blade having thrust reverse orientation;

[0035] [ Figure 4 ] is a schematic diagram of a control loop according to the present invention in nominal operation;

[0036] [ Figure 5 ] is a schematic diagram of a control loop according to the present invention when the protection system of the control loop is started. DETAILED DESCRIPTION

[0037] In such Figure 1 In an aircraft engine of an engine marked by 1, air is introduced into an intake duct 2 located upstream AM to pass through blades 3 of a propeller, which is also called a fan and includes a series of rotating blades, and then is divided into a central main flow and a secondary flow surrounding the main flow. When the engine generates propulsive thrust, these two flows circulate in the engine from the upstream AM to the downstream AV of the engine along the longitudinal direction AX of the engine.

[0038] The main flow is introduced into the air inlet 4, located downstream of the propeller and extending around the longitudinal axis AX, and is then compressed in the low-pressure compressor 5 and the high-pressure compressor 6 before reaching the combustion chamber 7. This main flow is then expanded by the high-pressure turbine 8 and the low-pressure turbine 9 before being discharged downstream. The secondary flow, for its part, is propelled directly downstream by the propeller into the duct externally delimited by the nacelle 11 carrying the entire engine.

[0039] This twin-shaft engine comprises a low-pressure shaft, by means of which the propeller propeller is connected to the low-pressure turbine 9, and a high-pressure shaft, by means of which the high-pressure compressor 6 is connected to the high-pressure turbine 8, the two shafts being coaxial and rotationally independent. These shafts are surrounded by a set of casings 12 extending along the longitudinal axis around which the casings surround.

[0040] exist Figure 3 , a variable pitch thruster propeller blade 3 comprises a pressure face and a suction face extending between a leading edge 14 and a trailing edge 16. The blade 3 extends along a so-called span axis EV radial to the axis AX from a root, by which the blade is rigidly fixed to a rotor element (not shown), to a tip corresponding to the free end of the blade, the tip being opposite the inner surface of the nacelle 11.

[0041] The pitch angle of the blade is the angle between the chord axis AC, which passes through the leading edge 14 and the trailing edge 16 and extends in a plane perpendicular to the axis EV, and the plane of the propeller, which is perpendicular to the axis AX. In the following, when such a pitch angle has a positive value, it corresponds to a downstream thrust, i.e. a thrust direction, of the air flow in which the rotating blade is immersed. Negative values ​​correspond to a thrust upstream of the air flow.

[0042] exist Figure 3 In , the blades 3 are in a propulsive orientation corresponding, for example, to the so-called cruising speed: the chord axis AC is inclined at a positive pitch angle CC relative to the plane PS.

[0043] In the corresponding Figure 3 In the configuration of the propulsive orientation, the pitch angle of the blades 13 is positive so that it propels the air flow from upstream AM to downstream AV by being driven to rotate in the direction marked by R in the figure. The direction of rotation R corresponds to the clockwise direction when the propeller is viewed from the front along the axis AX, i.e. from upstream AM of this axis.

[0044] The blades are of variable pitch type: their orientation about the axis EV can be adjusted according to the operating conditions of the engine. Figure 3 In the case of , the orientation of the blades 13 corresponds to a propulsive operation of the engine, that is to say in which the flow F through the engine is propulsive from upstream AM to downstream AV.

[0045] In the thrust reversal phase, for example when the aircraft is landing and the engines are operated to brake the aircraft, the propeller blades are controlled to change the orientation of the propeller blades. The propeller blades are then pivoted about the span axis of the propeller blades to change from the direction corresponding to Figure 3 The propulsion orientation changes to correspond to Figure 4 The thrust for the situation shown is directed in the opposite direction.

[0046] exist Figure 2 and Figure 3 In the example of , the blade is pivoted in the forward direction to change from the propulsion orientation to the thrust reverse orientation so that the leading edge of the blade is downstream of the trailing edge of the blade in the thrust reverse orientation. As the blade changes from one orientation to the other, the blade passes through a transition position referred to as 0°, in which the chord axis of the blade passes through the plane PS of the propeller. It is important that the blade remain in this transition position for a short period of time, as this may result in an engine overspeed.

[0047] A different configuration may also be provided in which the blades are rotated in the opposite direction to change from the propulsive orientation to the thrust reverse orientation, and then the trailing edge of the blade is maintained upstream of the leading edge of the blade when the blade is in the thrust reverse orientation. As the blades pass from one orientation to the other, the blades pass through a so-called mark position in which the chord axis of the blade is parallel to the axis AX.

[0048] exist Figure 4 In the embodiment of the invention, the hydraulic circuit 17 ensures the pressurization of the first upstream chamber 18 or the second downstream chamber 19 acting on the double-acting steering actuator 21 in the longitudinal position of the central shaft of the engine. This makes it possible to keep the blades of the propeller at a predetermined pitch angle by keeping the shaft in a given position and to vary the pitch angle of these blades by moving the shaft.

[0049] This actuator 21 is carried by a central shaft that rotates while being powered by a control circuit carried by the fixed element of the motor thanks to a hydraulic transmission bearing 22 surrounding the central shaft, which bearing is the seat of the hydraulic leakage.

[0050] This circuit 17 comprises a high-pressure supply line 23 supplied by a pump not shown and a low-pressure return line 24 leading to a reservoir not shown.

[0051] The supply line 23 and the return line 24 are connected to the actuator 21 via a three-position distribution valve 26, which includes a Figure 4 The center neutral position corresponding to the center neutral position in which the propeller is located, as well as the pitch increase position and the pitch reduction position.

[0052] A distribution valve 26 , here a sliding valve, is connected to the upstream chamber 18 via an upstream line 27 and a bearing 22 , and is connected to the downstream chamber 19 via a downstream line 28 and a bearing 22 .

[0053] exist Figure 4 In the neutral position, the lines 23 and 24 are separated from the chambers 18 and 19, which are at a pressure of an intermediate value between the high pressure and the low pressure, so that the blades 3 of the propeller have an orientation angle of the blades fixed at a fixed value.

[0054] When the distribution valve 26, which is a sliding valve in this case, is arranged in the pitch increase position of the distribution valve, that is, when the distribution valve is in the pitch increase position relative to the distribution valve, Figure 4 When the position in the middle is shifted to the right, the distribution valve arranges the upstream chamber 18 to communicate with the high-pressure supply line 23 and arranges the downstream chamber 19 to communicate with the low-pressure return line 24. This has the effect of making the rod of the actuator 21 Figure 4 The effect of moving the blade 2 to the right is to increase the pitch angle CC of blade 3 to arrange the blade in a propulsive orientation.

[0055] When the distribution valve 26 is in the Figure 5 When the pitch reduction position of the distribution valve is shown, that is, when the distribution valve is in the position relative to the distribution valve Figure 4 When the position in the middle is shifted to the left, the distribution valve arranges the upstream chamber 18 to communicate with the return line 24 and arranges the downstream chamber 19 to communicate with the high-pressure line 23. This has the effect of making the rod of the actuator 21 Figure 4 The effect of the leftward movement is to reduce the pitch angle CC of blade 3 to arrange blade 3 in a thrust-reversing orientation.

[0056] The circuit 17 integrates a protection system 29 which ensures that the blades 3 do not accidentally reach a thrust-reversal orientation while the aircraft is in flight.

[0057] The protection system includes a protection solenoid valve 31 , an amplification valve 32 , a first protection valve 33 and a second protection valve 34 .

[0058] The protection valve 33 is here a two-position sliding valve which is equipped with a return spring 36 and has an activation hydraulic inlet 37 on one side of the spring 36 and a deactivation hydraulic inlet 38 on the side opposite to the spring 36 .

[0059] When the activation inlet 37 is depressurized and the deactivation inlet 38 is pressurized, the slider is pushed by the deactivation inlet against the spring 36 to place the valve 33 in the deactivation position, such as Figure 3 When the activation inlet 37 is pressurized and the deactivation inlet 38 is depressurized, the slider is pushed by pressurizing the activation inlet to arrange the valve in the activation position, as shown in FIG. Figure 4 shown.

[0060] In the corresponding Figure 3 In the deactivated position, the oil in the upstream pipeline 27 simply passes through the valve 33. In the activated position, as Figure 3 As shown, the valve 33 places the upstream chamber 18 in direct communication with the high pressure line 23 , while isolating the chamber 18 from the distribution valve 26 .

[0061] The protection valve 34 is a two-position sliding valve which is equipped with a return spring 39 and has an activation hydraulic inlet 41 on one side of the spring 39 and a deactivation hydraulic inlet 42 on the side opposite to the spring 39 .

[0062] When the activation inlet 41 is depressurized and the deactivation inlet 42 is pressurized, the slider is pushed by the deactivation inlet against the spring 39 to place the valve 34 in the deactivation position, as shown in FIG. Figure 3 When the activation inlet 41 is pressurized and the deactivation inlet 42 is depressurized, the slider is pushed by the activation inlet 41 to place the valve in the activation position, as shown in FIG. Figure 4 shown.

[0063] In the corresponding Figure 3 In the deactivated position, the oil in the downstream pipeline 28 simply passes through the valve 34. When the valve is in the activated position of the valve, such as Figure 3 As shown, the valve places the downstream chamber 19 in direct communication with the low-pressure line 24 , while isolating this chamber 19 from the distribution valve 26 .

[0064] As will be understood, when the two protection valves 33 and 34 are deactivated, the position of the actuator 21 and therefore the angle of the vanes 3 are controlled by the distribution valve 26 , which makes it possible to increase or decrease the angle of these vanes 3 .

[0065] Conversely, when both 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 actuator 21 to the right in the figure to return the pitch angle of the blade 3 to the propulsive orientation.

[0066] like Figure 4 As shown, the activation inlet and the deactivation inlet of the two valves 33 and 34 are supplied by the amplification valve 32, which is a two-position sliding valve here. The sliding valve comprises a return spring 43, a passive hydraulic inlet 44 located on one side of the spring 43, and a hydraulic control inlet 46 located on the side opposite to the spring 43. The passive inlet 44 is continuously subjected to low pressure because it is permanently connected to the low pressure line 24.

[0067] In the corresponding Figure 4 In nominal operation, the control inlet 46 of the valve 32 is pressurized, so that the slider of the valve 32 is pushed against the spring 43 by pressurizing the control inlet 46 to arrange the valve in the deactivation position. In this position, the valve 32 connects the deactivation inlets 38 and 42 of the protection valves 33 and 34 to the high-pressure line 23 to pressurize the deactivation inlets, and the valve connects the activation inlets 37 and 41 of the protection valves to the low-pressure line 24 to depressurize the activation inlets, so that both valves 33 and 34 are in the deactivation position of the valves. Therefore, the pitch angle of the blade 3 is controlled by controlling the distribution valve 26.

[0068] In the corresponding Figure 5 In the protection operation, the control inlet 46 is depressurized, such as in Figure 5 In the case of the valve 32 being pushed by the spring 43, the slider of the valve 32 is arranged in the start 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 the deactivation inlets, and the valve connects the activation inlets 37 and 41 of the protection valves to the high-pressure line 23 to pressurize the activation inlets, which arranges the valves 33 and 34 in the valve start position. 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, the pitch angle of the blade 3 automatically returns to the propulsion orientation.

[0069] Alternatively, the spring 43 can be omitted by providing different sections for the hydraulic chambers connected to the inlets 44 and 46, respectively. If the cross section of the chamber connected to the passive inlet 44 is larger than the cross section of the chamber connected to the control inlet 46, and these inlets 44 and 46 are subjected to the same pressure, the thrust of the first chamber is greater than the thrust of the second chamber. The resulting thrust then moves the slide of the valve 32 to the valve's actuation position.

[0070] According to another alternative, a high-stiffness spring is provided to omit the passive inlet 44 of the valve 32 and, therefore, also the line portion 48 connecting the passive inlet 44 to the low-pressure line 24. When the control inlet 46 is depressurized, i.e., when the pressure at the inlet 46 is less than a predetermined threshold, the stiffness of the spring is sufficient to generate a force greater than the hydraulic thrust generated by the control inlet. In this way, the force of the spring counteracts the hydraulic thrust in the opposite direction to move the slider of the valve 32 to the start position of the valve. When the inlet 46 is pressurized by the high-pressure line 23, the stiffness of the spring is selected to generate a force less than the hydraulic thrust generated by the inlet 46. In this case, in nominal operation, when the protection solenoid valve 31 is closed, the pressurization of the inlet 46 keeps the amplification valve 32 in the deactivated position of the amplification valve, and then the spring 43 is compressed by the opposite hydraulic pressure.

[0071] The amplification valve 32 is controlled by the protection solenoid valve 31, which can be in the start position, that is, Figure 5 As shown in FIG. 1 , the protection solenoid valve 31 is opened, wherein the protection solenoid valve 31 depressurizes the control inlet 46 of the amplification valve 32 by connecting the control inlet 46 to the low-pressure pipeline 24. In nominal operation, the protection solenoid valve 31 is in the deactivated position, that is, Figure 4 4. As shown closed, this ensures that the inlet 46 of the amplification valve 32 is pressurized so that the valve 32 is in the deactivated position.

[0072] like Figure 5 It can be seen that the high-pressure line 23 is equipped with a diaphragm 49 which prevents the line 23 from being short-circuited with the line 24 when the line 23 and the line 24 are connected to each other during activation of the solenoid valve 31 .

[0073] This protection solenoid valve 31 is electrically controlled by the engine computer (usually the Full Authority Digital Engine Control (FADEC)) to be deactivated in nominal operation and activated when the system detects that the blades 3 are in thrust reversal orientation when the aircraft is in flight. As will be understood, this solenoid valve 31 is, for example, a slide valve equipped with a solenoid that makes it possible to move the slide from one position to another depending on whether the solenoid is energized or not.

[0074] The protection solenoid valve 31 is equipped with a return spring 47, which tends to continuously return the protection solenoid valve to the deactivated position of the protection solenoid valve, and the change of the protection solenoid valve 31 to the activated position of the protection solenoid valve is obtained by supplying power to the protection solenoid valve so that the protection solenoid valve moves against the spring 47 to the activated position of the protection solenoid valve.

[0075] As mentioned above, the protection valves 33 and 34 are equipped with return springs 36 and 39 which tend to return the protection valve continuously to its activated position: it is the pressurization of the deactivation inlets 38 and 42 of the protection valves that ensures that these valves are deactivated in nominal operation.

[0076] In the event of a hydraulic circuit failure, the activation inlets 37, 41 and inlet 46 and the deactivation inlets 38, 42 of the amplification valve 32 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 amplification valve 32 move these valves to activate them, which has the effect of returning the blades of the propeller to the propulsion orientation in the event of a hydraulic circuit failure.

[0077] In other words, due to the return springs, if the pressures at the two inlets of one or the other of the protection valves 33 , 34 are the same, the protection valve is returned by these springs to its actuated position.

[0078] In addition, Figure 4 and Figure 5 In the example of , valves 33 and 34 are distinct and independent. However, valves 33 and 34 can be mechanically connected to each other, for example by means of a rod that rigidly fixes the sliding valves of the valves to each other, to be controlled by the same activation inlet and the same deactivation inlet shared by the two valves.

[0079] Typically, if a drift in the orientation of the blades toward a thrust-reversing orientation of the blades is detected, the computer electrically controls the protection solenoid valve to activate the protection solenoid valve.

[0080] This actuation has the effect of actuating the amplification valve to depressurize the deactivation inlets of both protection valves and to pressurize the activation inlets of both protection valves, thereby causing very rapid actuation of the protection valves to return the blades to their advance orientation.

[0081] In practice, the implementation of the amplification valve makes it possible to obtain a reaction time of approximately one tenth of a second, whereas in a system without the amplification valve, in which the protection valve is a solenoid valve, the activation time is approximately one second.

[0082] The circuit structure according to the present invention makes it possible to provide an amplifying valve with a small size, the amplifying valve with a small size includes a small-sized distributor so that a small flow rate is sufficient to change the position of the amplifying valve, and the amplifying valve with a small size has a short stroke so that the amplifying valve can have a smaller mass and size than other valves in the circuit.

[0083] In the example of the attached figures, the invention is implemented on a turbojet engine equipped with variable pitch fan blades, but it can be implemented in an engine of the unshrouded turboprop type or in an engine of the “open rotor” type with counter-rotating twin propellers.

Claims

1. A hydraulic control circuit (17) for actuating a double-acting (21) steering actuator (21) for orienting the blades (3) of a propeller of an aircraft engine, the double-acting actuator (21) comprising a first chamber and a second chamber (18, 19), the circuit (17) comprising: - a high pressure pipeline (23) and a low pressure pipeline (24); a distribution 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 for connecting the first chamber to the low-pressure line and the second chamber to the high-pressure line, or for isolating the two chambers (18, 19) from the high-pressure line and the low-pressure line; a first protection valve (33) which can be placed in a deactivated position or an activated position, wherein the first protection valve places the first chamber (18) in communication with the high-pressure line (23); a second protection valve (34) which can be placed in a deactivated position or in an activated position, wherein the second protection valve places the second chamber (19) in communication with the low-pressure line (24); - the protection valves (33, 34) comprise a starting hydraulic inlet (37, 41) and a deactivation hydraulic inlet (38, 42), which can be connected to the high-pressure line (23) or the low-pressure line (24) to place the protection valves in a deactivation position or an starting position; an amplifying valve (32) which can be in a deactivated position or an activated position, wherein the amplifying valve connects the high-pressure line (23) to each activation inlet (37, 41) and connects the low-pressure line (24) to each deactivated inlet (38, 42) so as to activate the protection valves (33, 34); the amplification valve (32) comprising a hydraulic control inlet (46) for placing the hydraulic control inlet in an activated position when the control inlet (46) is connected to the low-pressure line (24), and for placing the hydraulic control inlet in a deactivated position when the control inlet (46) is connected to the high-pressure line (23); - and a protection solenoid valve (31) which can be in a deactivated position or an activated position, wherein the protection solenoid valve connects the control inlet (46) of the amplifying valve (32) to the low-pressure pipeline (24) so ​​that the amplifying valve is activated.

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

3. The circuit according to claim 2, wherein: The first protection valve and the second protection valve (33, 34) each include a sliding valve, and wherein the two sliding valves are connected to each other via a rod.

4. A circuit according to any one of the preceding claims, wherein: Each protection valve (33, 34) is equipped with a return spring (36, 39) which tends to continuously return the protection valve to its actuated position.

5. A circuit according to any one of the preceding claims, wherein: The amplifying valve (32) is equipped with a return spring (43) which tends to continuously return the amplifying valve to its starting position.

6. A circuit according to any one of the preceding claims, wherein: The protection valves (33, 34) isolate the first chamber (18) and the second chamber (19) from the distribution valve (26) when activated.

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

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