FR3060525A1 - ELECTROMECHANICAL STEM ACTUATION SYSTEM FOR A TURBOMACHINE PROPELLER - Google Patents

Abstract

Pitch actuation system (22) for a turbine engine propeller (10), comprising an actuator (24) of which a movable part (26) is configured to be connected to the blades (14) of the propeller in order to move in rotation with respect to the axes (B) for setting the pitch of the blades, characterized in that the actuator is an electromechanical actuator, in that it comprises: - a transmission screw (26) movable in rotation and in translation along a longitudinal axis (A), a nut (28) through which said transmission screw passes and cooperating with this screw in order to move in translation along the axis (A) in order to modify the pitch of the blades the propeller and decoupling means ((80, 82, 83, 84, 87) between the rotation of the propeller and said nut, fixed in rotation, - first means (25) for controlling the pitch of the blades, which comprise at least one electric drive motor (40a, 40b) configured to drive the transmission screw in rotation and in translation, - Means for locking the rotation of the transmission screw configured to lock it in rotation when the first means for controlling the pitch of the blades operate and release it in rotation when second means (50) for feathering the blades operate.

Description

TECHNICAL AREA

The present invention relates to a pitch actuation system for a turbomachine propeller, such as a turboprop.

STATE OF THE ART

A turboprop comprises at least one propeller comprising a hub and blades carried by the hub and extending substantially radially outward relative to the hub and to the axis of rotation of the propeller.

The turboprop engine is generally equipped with a propeller pitch actuation system, also called the propeller blade angular timing system. The regulation of the propeller blade timing improves their efficiency by guaranteeing a propeller rotation speed for each flight phase.

Each blade is rotatable around an axis, generally radial, between a first emergency position called feathering in which it extends substantially parallel to the axis of rotation of the propeller, and a second position in which it is strongly inclined relative to this axis. It can take any position between these two extreme positions.

In the current technique, the actuation system used is a hydraulic system, which is relatively complex and has several drawbacks. This system includes an actuator, a movable part of which is connected to the propeller blades for their setting.

The actuation system must not only be able to perform the pitch control function but also the back-up function for feathering the blades. The pitch actuation system therefore includes an auxiliary system for the emergency function.

Failure related to hydraulic leakage, a common mode between the pitch control system and the auxiliary system, must be covered. In the absence of a pressure source, it is essential to add counterweights at the blades to ensure the feathering function.

The pitch actuation system must also provide protection functions in the event of overspeed, in the event of an engine stopped, in the event of failure of the FADEC computer (acronym for Full Authority Digital Engine Control), and to limit small steps in flight. A set of mechanical and hydraulic systems is therefore part of the pitch actuation system to perform these functions in the current technique.

The pitch control system is also subject to very stringent failure rate requirements, which involve redundancies and additional protection systems.

In conclusion, the technology and operating principle of a hydraulic propeller drive system are currently complex. A multitude of hydraulic components integrate these systems.

The present invention overcomes these drawbacks and provides a solution to all or part of the problems of the current technique set out below.

The first problem (problem A) concerns the severe FHA (acronym for Functional Hazard Assessment) requirements for pitch control, which imply robust architectures with redundancy.

The second problem (problem B) concerns the feathering function, which must be able to be ensured even after a failure of the pitch control means.

The third problem (problem C) concerns the risk of blocking the movable part of the actuator. In a hydraulic system, the rotation of a propeller blade is obtained by the translation of an eccentric at the foot of the blade. The axial locking of the hydraulic cylinder is considered as a failure.

Furthermore, in a hydraulic system, the rotation of the propeller is transmitted to the hydraulic actuator positioned in the rotary reference frame (piston and body without angular displacement). This cylinder is supplied by pipes via a hydraulic slide positioned in the fixed mark. In this hydraulic concept, the rotation of the propeller does not cause a propeller pitch shift. The fourth problem (problem D) concerns the management of this phenomenon.

Finally, the fifth problem (problem E) concerns the protection functions other than that covering the failure of the pitch control, which require additional mechanical and hydraulic devices in a hydraulic system of the prior art.

STATEMENT OF THE INVENTION

The invention proposes a pitch actuation system for a turbomachine propeller, comprising an actuator of which a movable part is configured to be connected to blades of the propeller in order to move them in rotation relative to the setting axes of not blades, characterized in that the actuator is an electromechanical actuator, and in that it comprises:

- a first mobile transmission screw in rotation and in translation along a longitudinal axis,

- a first nut traversed by said first transmission screw and cooperating with this screw in order to move in translation along the axis,

- Means which are configured so that a displacement in translation of the first nut causes a modification of the pitch of the propeller blades but that a displacement in rotation of the propeller does not entail a displacement in rotation of the nut ,

- first blade pitch control means, which comprise at least one electric motor for driving a first rotor around the axis, a second nut driven in rotation around the axis by said first rotor and a second transmission screw which is integral with the first transmission screw and which cooperates with the second rotating nut in order to move in rotation or in translation on the axis,

- second means for feathering the blades, which comprise at least one electric motor for driving a second rotor around the axis,

- connecting means configured so that a rotation of the second rotor causes a rotation of the first screw and of the second transmission screw without translation,

- Locking means configured to block a rotation of the second and of the first transmission screw when said at least one motor of the first blade pitch control means is operating, and to release the rotation of the second and of the first screw transmission when said at least one engine of the second feathering means is operating.

With this actuation system, an activation of the electric motors of the first means makes it possible to control the pitch of the propeller because it causes a translation of the first transmission screw, therefore of the first nut, because the rotation of the second transmission screw is locked in the second nut by the locking means. On the other hand, when the electric motor of the second means is activated, for example because the first means have failed, deactivation of the blocking means allows the transmission screws to rotate to put the first nut in translation in order to put the feathered propeller blades.

Advantageously, the system is not configured to activate the electric motors of the first and second rotor in parallel, which makes it possible to reduce the operating complexity of this configuration. The transmission screw is driven in translation only during pitch control with rotation blocked by the brake and in rotation only during feathering to cover the case of blockage of the second transmission screw with the second nut.

The hydraulic actuator of the prior art is thus replaced by an electromechanical actuator, the movable part of which comprises a transmission screw. The displacement in rotation of the blades is obtained by a translation of the nut on the first transmission screw, which is driven either by the first rotor in translation, or by the second rotor in rotation during a blocking of this screw in the second nut.

In a hydraulic system, the rotation of a propeller blade is obtained by the translation of an eccentric at the foot of the blade. The failure resulting from the axial blockage of the hydraulic cylinder (problem C), which generates this translation, is considered extremely unlikely. This low value of the failure rate seems to be consolidated by feedback. With the system according to the invention, the basic system includes a redundancy of the transmission screw:

- if the first transmission screw is blocked in the first nut, unlikely case because this first screw is not active during pitch control, pitch control and feathering can always be carried out by the first rotor, which drives the second transmission screw in translation, therefore the first transmission screw, by the rotation of the second nut;

- if the second transmission screw is blocked in the second nut more likely since this second screw is active during pitch control, feathering can always be carried out - by the second rotor, which drives the first transmission screw in pure rotation (the translation being blocked by the second nut); in fact, without activating the electric motor of the first means, the second nut is rotated by the second screw and the first transmission screw which was in passive mode switches to active mode.

Preferably, said blocking means are configured to block a rotation of the first transmission screw when said at least one motor of the second feathering means is stopped.

In this way, the first means can control the pitch of the blades by causing pure translation of the first transmission screw while keeping the second feathering means inactive.

Preferably, the system is configured to deactivate said blocking means are configured in the event of blockage of the second transmission screw in the second nut.

Oversizing the screw is a solution to the aforementioned problem C. However, the fatigue dimensioning of the screw does not cover all the aspects linked to the various failure cases (pollution, icing, etc.). The invention makes it possible to respond satisfactorily to this need by allowing the first transmission to be driven in rotation by the rotation of the second rotor in the event of the second transmission screw jamming in the second nut.

With regard to problem E, the proposed concept does not require any additional device unlike the hydraulic system, to cover the protection functions other than that covering the failure of the pitch control. In a hydraulic system, the case of a stopped engine or loss of engine power leads to a suppression of the hydraulic energy of the pump coupled to the engine, so an auxiliary system must be provided. In an electromechanical system, for these failure cases, the electrical energy is delivered by an independent source. The feathering function therefore remains active to cover these breakdowns, preferably via a protective box. In a hydraulic system, the case of overspeed is covered by a mechanical counterweight system. In the electromechanical system, preferably thanks to speed feedback, the motor control laws can act on the electric pitch control motors via the protective casing to ensure feathering.

Furthermore, the decoupling of the rotation of the propeller with the actuator makes it possible to maintain the pitch of the blades without turning the electric motors during the rotation of the propeller, which reduces energy consumption and minimizes the engine wear. Without this decoupling, the size of the rotating machines and the electronic unit would be penalized because it depends on the electrical power to be delivered.

In addition, the fact that the first and second control means have connection means acting directly on the first transmission screw makes it possible to maintain their stators and their rotors in a fixed casing, and therefore to reduce the complexity of the transmission of energy to the motors.

Advantageously, an electromagnetic brake linked to the second rotor forms said means for blocking the rotation of the first transmission screw.

Advantageously, said first means comprise two electric motors, preferably synchronous, for driving the same first rotor. The choice of technology and the strategy for sizing these electrical means makes it possible to minimize the short-circuiting torque and to achieve reasonable motor sizes. The electrical redundancy at the level of the electric motors makes it possible to comply with the FHA reliability requirements (problem A). To keep a simple architecture, it is proposed here to communalize the rotors of electric motors. This allows to keep only one transmission chain and to have a relatively compact system. The proposed concept offers this advantage.

The proposed system is preferably capable of ensuring the reliability required by electrical redundancy at the level of the electrical components, at the level of the control and at the level of the independent power supply circuits controlled by a computer. This system is then able to perform its pitch control function even in the event of a short circuit in the power supply.

This electromechanical concept may require no mechanical energy from the turbomachine. In the event of failure of the loss of engine power and of the engine stopped, it can therefore be ensured via a protective box by the nominal electromechanical system without any additional device. This electromechanical concept also makes it possible to cover the case of overspeed and the failure of the FADEC without additional device.

The system according to the invention may include one or more of the following characteristics, taken in isolation from one another or in combination with each other:

said first rotor is connected to the second transmission screw by a first reduction gear, for example planetary,

part of the connection means between the first transmission screw and the second rotor is connected to said second rotor by a second reduction gear, for example planetary,

- a planet carrier of the or each gearbox is guided in rotation by a pair of bearings with oblique and inverted contacts,

- said first means comprise at least two resolvers,

- the electric motor of said second means is an asynchronous motor; the choice of this type of electric motor for feathering makes it possible to reduce the control unit and to eliminate any resistive torque linked to a short circuit (problem B),

said electric motors include stators carried by a fixed casing, and

- The two electric motors of said first means are respectively connected to two separate electronic control units.

The present invention also relates to a turbomachine, such as a turboprop, comprising a propeller whose blades are of variable pitch and a system as described above, in which the first nut drives means which cooperate with eccentrics provided on support and rotation plates for the blades.

The present invention finally relates to a method for actuating the pitch of the blades of a turbomachine propeller, by means of a system as described above, comprising the steps consisting in:

- Modify the pitch of the blades by actuating at least one motor of the first pitch control means as well as the means of locking in rotation of the first transmission screw, so that a rotation of the second nut drives, by cooperating with the second transmission screw, an axial displacement of the first transmission screw and the first nut,

- feathering the blades by actuating at least one motor of the second feathering means, so that a rotation of the second shaft causes a rotation of the first transmission screw.

It will be noted that this step is normally only considered in the event of the second transmission screw being blocked in the second nut, therefore the translation of this screw is blocked.

DESCRIPTION OF THE FIGURES

The invention will be better understood and other details, characteristics and advantages of the invention will appear more clearly on reading the following description given by way of non-limiting example and with reference to the accompanying drawings in which:

- Figure 1 is a partial schematic half-view in axial section of a blade pitch actuation system according to the invention associated with a turbomachine propeller; and

- Figure 2 is a block diagram showing the general architecture of the actuation system and electrical control means of the system of Figure 1.

DETAILED DESCRIPTION

We first refer to Figure 1.

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A propeller 10 of a turbomachine, and in particular of a turboprop engine is generally not faired and comprises a movable hub 12 (arrow ΘΗ in FIG. 1) of axis A of rotation, the hub carrying blades 14 which extend substantially radially by relative to axis A. Each blade 14 is connected at its radially internal end to a substantially cylindrical plate 16 for supporting and guiding the blade in rotation with a view to its setting in rotation about an axis B, here substantially radial . The plate 16 of each blade 14 is mounted in a housing of the hub 12 and is centered and guided in this housing by bearings 18 extending around the axis B. The radially internal end of each blade comprises an eccentric 20. The latter is integrally connected to the plate 16 and an actuation system 22 can move it in rotation around the axis B. The displacement of the eccentrics 20 causes a rotation movement of the plates 16 and therefore of the blades 14 around the axes B. Each blade 14 can be wedged at a step or in a given position around its axis B, between two extreme positions, one of which, called feathering, corresponds to the case where the chord of the cross section of the blade extends substantially parallel to the axis A.

In the prior art, the actuation system was hydraulic, and had many disadvantages. Figure 1 shows an electromechanical actuation system.

The actuation system 22 of FIG. 1 comprises an electromechanical actuator 24 comprising a fixed casing 32 and a movable part which comprises a transmission screw 26 which is associated with a nut 28.

The transmission screw is movable in rotation around the axis A (arrow Θ) and in translation along this axis (arrow X).

The nut 28 is guided in translation relative to the hub 12 by means 87 of anti-rotation of the nut 28 on the transmission screw 26. These means 87 here comprise an axial finger carried by the casing 32 and engaged in a housing of complementary shape to the nut 28. The nut 28 is thus arranged to be movable in translation relative to the axis A in the same fixed reference.

The transmission screw 26 passes through the nut 28 and therefore includes a thread complementary to that of the nut. We understand that the rotation of the transmission screw 26 (arrow θ in Figure 1) causes a displacement in translation of the nut 28 along the axis A (arrow X ’). The transmission screw 26 advantageously has a reversibility function in the sense that it is capable of being subjected by the actuator to a torque so as to cooperate with the nut and move it, and also to be subjected by the 'nut to axial forces causing a rotation of the transmission screw. On this point, it differs from a worm which has an irreversibility function.

The transmission screw 26 is also capable of being subjected to axial forces by the actuator 24. It is understood in this case that an axial displacement (arrow X) of the transmission screw causes an axial displacement (arrow X ') of the nut 28, which will be of the same value if the transmission screw is also locked in rotation (Θ = 0).

The coupling with the eccentrics 20 of the blades 14, with a view to their displacement in rotation relative to the axis B, is effected by means of decoupling means described below.

The member 80 is movable in translation and in rotation with respect to the axis A. It comprises orifices for receiving the eccentrics 20 of the blades 14 and is thus made integral in rotation with the blades 14. It is therefore intended to turn with the propeller 10 around the axis A according to its rotation ΘΗ. Its translational movements along the axis A move the eccentrics and therefore the blades 14 around their axes B.

The member 80 comprises a cylindrical end engaged in a blind hole of a sleeve 81. The nut 28 and the sleeve 81 are surrounded by a movable ring 82. A first bearing 83 (here ball) angular contact is mounted between the nut 28 and the ring 82 and a second bearing 84 (ball) angular contact is mounted between the sleeve 81 and the ring 82. In a conventional manner, the inner ring of each bearing 83, 84 is integral in rotation, respectively, with the nut 28 or the sleeve 81, and its outer ring is integral in rotation with the ring 82.

The bearings 83, 84 with oblique contact make it possible to transmit the translation X ′ of the nut 28 to the member 80 and then to the eccentrics 20 subjected to the rotation of the propeller 10. The displacement of the eccentrics 20 in turn causes a rotation of the blades 14 with respect to the axis B. The displacement of the eccentrics depends on the balance between the external force and the force developed by the actuator 24 via the transmission screw 26.

On the other hand, the rotation ΘΗ of the propeller is decoupled from the movement of the nut 28 thanks to the angular contact bearing 84. The movement of the nut 28 can therefore be limited to translation.

In addition, maintaining the pitch of the propeller blades does not require the transmission screw 26 to be rotated, since its rotational movement is decoupled from that of the propeller by the mechanism described above.

Furthermore, an electric motor 85 is mounted between the nut 28 and the ring 82 and comprises a stator secured to the nut and a rotor secured to the ring. This motor 85 is associated with a sensor 86 which is also mounted between the nut 28 and the ring 82 and comprises a stator element secured to the nut and a rotor element secured to the ring. The sensor is of the Hall effect or inductive type to control the rotation of the outer ring.

The decoupling means further comprise a device allowing the stop to control the state of the two bearings 83, 84. This device consists of the elements of the motor 85 and of the sensor 86. When the engine stops, the motor 85 drives in rotation the outer ring of the two bearings 83, 84 by delivering sufficient torque to overcome the friction of these two bearings. The rotation of the outer ring is then controlled by the sensor 86. In the event of seizure or aging of only one of the two bearings, the degradation can be observed both by the value of the motor current and by the rotation of the outer ring. This device therefore eliminates any risk of dormant failure before flight. If one of the angular contact bearings jams, the other ensures decoupling and prevents breakage of the anti-rotation means.

This electromechanical concept, thanks to the decoupling of the rotation of the propeller and its control device, makes it possible to reduce the power of the actuator, the size of all the electrical components and the size of all the mechanical components by relieving the solicitations.

The actuation system 22 further comprises at least one sensor 46 of the LVDT type (acronym for English Linear Variable Differential Transformer). In the example shown, the transmission screw 26 comprises an internal axial bore in which is slidably engaged a ferromagnetic plunger 46a of LVDT carried by a rear cover 48 of the actuator 22, which is itself fixed to the fixed casing 32. Although this is not shown, the plunger 46a is surrounded by several windings carried by the transmission screw 26, including at least one primary winding supplied by an alternating current and two secondary windings. These windings are preferably redundant to increase the reliability of the system. The axial displacement of the plunger 46a inside the coils, channels the flow and generates voltages in the secondary windings whose amplitudes depend on the position thereof. The sensor 46 thus supplies a voltage proportional to the displacement of the plunger 46a.

Here, the movable part of the actuator further comprises a rod 70 centered on the longitudinal axis A, which sinks into the casing 32 and which comprises:

- at its end facing the propeller 10, the first transmission screw 26, intended to participate in the coupling device with the eccentrics 20,

a second screw 68 located on the body of the rod, intended to participate in a coupling device with first means 25 of pitch control described in the following,

- at its end opposite the propeller 10, a device 72 intended to participate in a coupling device with second means 50 for feathering.

The first means 25 for controlling the actuator 24 comprise first electrical means 36 for controlling the pitch of the blades which drive a rotor 30. The rotor 30 has an elongated shape of axis A and is here guided in the fixed casing 32 by at least one bearing 34. The bearing 34, here rolling and more specifically ball, is mounted at the axial end of the rotor 30, opposite the propeller (end left in the drawing).

In the example shown, these electrical means 36 comprise two resolvers 38a, 38b and two electric motors 40a, 40b, which are here synchronous machines. The resolvers 38a, 38b are arranged next to each other and have as their common axis, the axis A. The electric motors 40a, 40b are arranged next to each other and also have as their common axis , axis A. The resolvers 38a, 38b are here arranged between the bearing 34 and the electric motors 40a, 40b.

Each resolver 38a, 38b comprises a resolver rotor mounted on the common rotor 30, and a resolver stator secured to the casing 32. The rotors and resolver stators are generally composed of windings. In known manner, a resolver makes it possible to obtain an electrical value from a change of angle of a rotor. A resolver works like a transformer whose coupling varies with the mechanical angle of the rotor. When the rotor winding is energized with an AC voltage, an AC voltage is recovered on the stator winding. The redundancy linked to the use of two resolvers 38a, 38b instead of one, makes it possible to guarantee the reliability requirements mentioned above.

Each electric motor 40a, 40b is here of the synchronous machine type and comprises a rotor mounted on the common rotor 30, and a stator integral with the casing 32. The rotor can consist of permanent magnets or consist of a winding supplied with current continuous and a magnetic circuit (electromagnet). To produce current, an external force is used to turn the rotor: its magnetic field, by turning, induces an alternating electric current in the stator coils. The speed of this rotating field is called "synchronism speed". The synchronism speed is directly related to the frequency of the power supply. The motors here are powered by a three-phase current system.

The coupling of the second screw 68 with the first electrical means 36 is carried out in the manner described below.

As can be seen in the drawing, a nut 71 is driven by the common rotor 30 using a gear reducer 42, which is here a planetary or planetary gear reducer. This reduction gear 42 comprises a planetary shaft 42a integral in rotation with the common rotor 30, an outer crown 42b surrounding the planetary shaft and integral with the casing 32, satellites 42c meshing with the planetary shaft 42a and the crown 42b, and carried by a planet carrier 42d which here is integral in rotation with the transmission screw 26. In the example shown, the nut 71 and the satellite carriers 42d are formed in one piece.

The part comprising the planet carrier 42d and the nut 71 is centered and guided in the casing 32 by a pair of rolling bearings, here ball bearings. These bearings 44 are oblique contact. They are reversed and mounted one next to the other at the axial end of the actuator 24 located on the side of the propeller 10 (right end in the drawing).

The nut 71 is therefore fixed in translation and participates in the maintenance in the fixed casing 32 of the rotor 30 of the first electrical means 36.

The nut 71 is crossed by the second transmission screw 68. The nut 71 cooperates with the second transmission screw 68. Due to the fixed position of the nut on the axis A, a rotation Θ 'of the nut 71 around the axis A causes a displacement in translation of the second transmission screw 68 on the nut along the axis A. Thus, the assembly formed by the transmission screw 68 and the nut 71 is with three degrees of freedom: the transmission screw 68 has two degrees of freedom (in translation and in rotation with respect to the axis A - arrows X and respectivement respectively), and the nut 71 has only one degree of freedom (in rotation - arrow θ ') but no mode of operation, either pitch control or feathering, will simultaneously cause rotation and translation of the second transmission screw. This screw is driven either in pure rotation during feathering or in pure translation during pitch control.

In general, it is understood that a rotation Θ and a translation X of the second transmission screw 68 correspond respectively to a rotation Θ and to an equivalent axial displacement X of the first transmission screw 26 and of the device 72.

The turboprop is equipped with an auxiliary system 50 for feathering the blades 14, which is here electromechanical. The system 50 is integrated into the actuator 24 and includes an electric motor 52, which in the example is an asynchronous machine (so as not to generate resistive torque in the event of a short circuit).

The stator of the electric motor 52 of the feathering means 50 is fixed to the casing 32, between the rear cover 48 of the actuator 24 and the bearing 34 of the first electric means. The rotor of the electric motor 52 is mounted on a shaft 60 which is independent of the rotor 30 of the actuator 24.

The shaft 60 is guided in rotation around the axis A by means of a rolling bearing, here a ball, mounted between the shaft 60 and the casing 32.

The coupling of the device 72 with the second electrical means 52 is carried out in the manner described below.

The shaft 60 rotates a gear device 73 by means of a gear reducer 64, which here is also a planetary reducer.

This reduction gear 64 comprises a planetary shaft 64a integral in rotation with the shaft 60, an outer crown 64b surrounding the planetary shaft and integral with the casing 32, and satellites 64c meshing with the planetary shaft 64a and the crown 64b and carried by a planet carrier 64d which is here rotationally integral with the gear device 73. In the example shown, the nut 71 and the planet carrier 64d are formed in one piece.

The gear device 73 cooperates with the device 72 of the rod 70 so as to secure the rotational movement Θ of the rod 70 with that of the planet carrier 64d and to allow it to slide axially X of the rod 70 relative to the planet carrier 64d, which is fixed.

The gear device 72 can, for example, correspond to a carriage sliding on ball bearings along a rod, the device 73 then being a radial tab leaving the rod 70 and fixed to the carriage. The length of the carriage stroke then corresponds to the travel sought for the axial displacement of the assembly X of the first 26 and second 68 transmission screws.

Furthermore, the shaft 60 of the second electrical means 52 is coupled to an anti-rotation electromagnetic brake 74 which can be activated (in active mode the brake is supplied and the anti-rotation not activated, in non-active mode the brake is not powered and anti-rotation activated) when the asynchronous machine 52 is in operation. Here, the shaft 60 passes through the cover 48 of the casing 32, the electromagnetic brake 74 being outside.

In a variant, not shown, the asynchronous machine 52 is replaced by a synchronous machine with reluctant torque, the residual reluctant torque at standstill is arranged to block the rotational movements of the shaft 60 and therefore the rotation Θ of the screws transmissions 26, 68.

It is therefore understood, with respect to the operation of the first transmission screw 26 and the first nut 28 for modifying the pitch of the blades of the propeller 10, that:

the operation of the first electrical means 36 causes an axial displacement X of the transmission screw 26, by means of a rotation of the second nut 71, the second electrical means 52 being stopped and the transmission screws 26, 68 being locked in rotation by the electromagnetic brake 74;

It is therefore understood, with respect to the operation of the first transmission screw 26 and the first nut 28 for feathering that:

- the operation of the second electrical means 52 causes a rotation Θ of the transmission screw 26 by means of the gear devices 72, 73 when the second transmission screw 68 is blocked in the second nut 71.

We now refer to FIG. 2 which schematically represents the electrical diagram of the principle of the operation of the system of FIG. 1.

The elements described in the foregoing are designated by the same reference numerals in Figure 2.

FIG. 2 shows in particular the control means of the electrical machines of the system, namely, in the case where the redundancy applies to all these machines, two sensors 46 LVDT, two resolvers 38a, 38b, and two electric motors 40a, 40b .

The control means include in particular two segregated electronic control units 54a, 54b which are each connected to a resolver, a sensor and an electric motor, and which have the capacity to drive these machines independently.

The boxes 54a, 54b operate in "passive-active" mode. In nominal mode, the pitch is controlled by the electronic unit 54a for example, and the electronic unit 54b is in passive mode. In the event of a failure detected by a position error for example, the housing 54a is deactivated and the housing 54b is activated. The packages 54a, 54b have three local nested servo loops: a torque loop using phase current measurements, a speed loop using the resolver, and a linear position loop using the LVDT sensor. The boxes 54a, 54b receive the position setpoint respectively from computer boxes 56a, 56b and are associated with electrical networks 58a, 58b, to send a current command to the motors 40a, 40b.

Although this is not shown in FIG. 2, the control means also comprise an independent device for supplying power to the electric motor 52.

The architecture thus comprises two transmission chains, one 25 dedicated to controlling the pitch of the blades, the other 50 dedicated to feathering only when the second transmission screw 68 is blocked in the second nut 71. Each it has a transmission screw. These two transmission screws here have completely different operating modes. This asymmetrical combination has been designed so that if one of the two screws is blocked, the feathering function can always be activated.

In addition, when controlling the pitch or when feathering only one transmission screw is active, while the other is passive.

Indeed, during the pitch control, the electrical means 36 are activated to rotate the nut 71, while the electromagnetic brake 74 blocks any rotation of the assembly of the two transmission screws 26, 68. The rotation Θ 'of the nut 71 therefore causes an axial displacement X of the second transmission screw 68, transmitted to the first screw 26. The gear device 72, 73 leaves this displacement free. The axial displacement X of the first screw 28 in turn causes an axial displacement of the eccentrics 20, according to the operation of the decoupling mechanism described above.

When feathering is only functional when the second transmission screw 68 is blocked in the second nut 71, the electromagnetic brake is released and the electrical means 52 are activated.

They therefore drive in rotation θ the transmission screws 26, 68 by the cooperation of the gear devices 72, 73. In this case the electrical control means 36 are not controlled, the nut 71 blocked in translation also blocks in translation the second transmission screw 68. The nut 71 rotates with the transmission screw 68. The rotation of the screws 68, 26 then makes it possible to control the movement of the nut 28, locked itself in rotation by the anti-rotation device 87, which causes the axial displacement of the eccentrics 20. The pitch control, for its part, can also be ensured by this mechanism by activating the feathering means.

When the first screw 26 is locked in the nut 28, the pitch control can still be carried out normally, and feathering is then ensured by the pitch control means.

. When the second screw 68 is blocked in the nut 71, the magnetic device 74 rotates the blocked screw in its nut. This electromechanical concept has been studied in principle to cover all cases of breakdown.

This electromechanical concept for the pitch actuation system is very innovative because it offers the following advantages:

- simple and robust architecture with a minimum of electromechanical components while respecting the binding reliability criteria,

- operation with one active screw and the other passive,

- insertion of a propeller decoupling system,

- architecture whose mechanical components are relieved in fatigue,

- removal of the displacement of the housings of rotating machines

- elimination of dormant breakdowns by the insertion of a control device

- elimination of the case of breakdown linked to the hydraulic leak, case which required the addition of counterweight for feathering,

- removal of counterweights of the prior art, for feathering of the blades,

- in the event of one of the two transmission screws blocking, the translational control of the eccentric of the blades remains functional thanks to the rotation of the non-blocked transmission screw.

- the use of an electromechanical system for feathering allows the use of a simple control box with high reliability.

Claims (12)

1. System (22) of pitch actuation for a propeller (10) of a turbomachine, comprising an actuator (24) of which a movable part (26) is configured to be connected to blades (14) of the propeller in view to move them in rotation relative to the pitch pitch axes (B) of the blades, characterized in that the actuator is an electromechanical actuator, and in that it comprises: - a first transmission screw (26) movable in rotation and in translation along a longitudinal axis (A), - a first nut (28) traversed by said first transmission screw and cooperating with this screw in order to move in translation along the axis (A), - Means (80, 82, 83, 84, 87) which are configured so that a displacement in translation of the first nut (28) causes a modification of the pitch of the blades of the propeller but that a displacement in rotation of the the propeller (10) does not cause the nut (28) to move in rotation, - first means (25) of pitch control of the blades, which comprise at least one electric motor (40a, 40b) for driving a first rotor (30) around the axis (A), a second nut ( 71) driven in rotation about the axis (A) by said first rotor and a second transmission screw (68) which is integral with the first transmission screw (26) and which cooperates with the second rotating nut (71) in order to move in rotation or in translation on the axis (A), - second means (50) for feathering the blades, which comprise at least one electric motor (52) for driving a second rotor (60) around the axis (A), - connecting means (72,73) configured so that a rotation of the second rotor (60) causes rotation of the first screw (26) and the second transmission screw (68), without translation, - blocking means (74) configured to block a rotation of the second screw (68) and of the first transmission screw (26) when said at least one motor (40a, 40b) of the first means (25) for controlling no blades work, and to release the rotation of the second and of the first transmission screw when said at least one motor (52) of the second feathering means (50) operates. 2. System (22) according to claim 1, in which said blocking means (74) are configured to block a rotation of the first transmission screw (26) when said at least one motor (52) of the second means (50) feathering is stopped. 3. System (22) according to one of the preceding claims, configured to deactivate said locking means (74) in the event of the second transmission screw (68) blocking in the second nut (71). 4. System (22) according to one of the preceding claims, in which an electromagnetic brake (74) forms said locking means. 5. System (22) according to one of the preceding claims, wherein said first means comprise two electric motors (40a, 40b), preferably synchronous, for driving the same first rotor (30). 6. System (22) according to one of the preceding claims, wherein said first rotor (30) is connected to the second nut (71) by a first reducer (42), for example planetary. 7. System (22) according to one of the preceding claims, in which a part (73) of the connection means between the first transmission screw (26) and the second rotor (60) is connected to said second rotor (60) by a second reducer (64), for example planetary. 8. System (22) according to claim 6 or 7, in which a satellite carrier (42d, 64d) of the or each reducer (42, 64) is guided in rotation by a pair of bearings (44, 66) with oblique contacts and reversed. 9. Turbomachine, such as a turboprop, comprising a propeller 5 (10) whose blades (14) are of variable pitch and a system (22) according to one of the preceding claims, in which the first nut (28) drives means (80) which cooperate with eccentrics (20) provided on plates (16) for supporting and rotating the blades. 10. Method for actuating the pitch of the blades of a propeller 10 turbomachine, by means of a system (22) according to one of claims 1 to 8, comprising the steps of: - Modify the pitch of the blades by actuating at least one motor (40a, 40b) of the first means (25) for controlling the pitch as well as the means (74) for locking in rotation of the first screw (26) of 15 transmission, so that a rotation of the second nut (71) causes, by cooperating with the second transmission screw (68), an axial displacement of the first transmission screw (26), - feather the blades by actuating at least one motor (52) of the second feathering means (50), so that a 20 rotation of the second shaft (60) causes rotation of the first transmission screw (26). χν-22