FR3060524A1 - ELECTROMECHANICAL STEM ACTUATION SYSTEM FOR A TURBOMACHINE PROPELLER - Google Patents

Abstract

A pitch actuating system (22) for a turbomachine propeller (10), comprising an actuator (24) having a movable portion (26) configured to be connected to propeller blades (14) for moving in rotation with respect to the pitch pitch axes (B) of the blades, comprising: - a transmission screw (26) movable in rotation and in translation along a longitudinal axis (A), a main nut (28) traversed by said transmission screw and cooperating with this screw in order to move in translation along the axis (A) in order to modify the pitch of the blades of the propeller and the decoupling means ((80, 82, 83 , 84, 87) between the rotation of the helix and said nut, fixed in rotation, - first pitch control means (25) for the blades, which comprise at least one drive electric motor (40a, 40b), configured to drive a member (62) in translation along the axis (A), - second blade feathering means (50), comprising at least one electric motor (52) for driving a second rotor (60) about the axis (A), configured to rotate the second rotor (60) to rotate the first screw (26) and to transmit the translation of the member (62).

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 provide the pitch control function but also the feathering feathering function of the blades. The pitch actuation system therefore includes an auxiliary system for the emergency function.

Failure related to hydraulic leakage, 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 provides 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 comprising:

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

- a main nut traversed by said main 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 main nut causes a modification of the pitch of the blades of the propeller but that a displacement in rotation of the propeller does not entail a displacement in rotation of the 'main nut,

first means for controlling the pitch of the blades, which comprise at least one first electric motor for driving a first rotor around the axis, and a transmission device, for example screw / nut, comprising a first member, for example a screw, driven in rotation by said first rotor and a second member, for example a nut, cooperating with said first member to have a translational movement along the axis,

- second feathering means, which comprise at least one second electric motor for driving a second rotor around the axis, the main transmission screw being rotated by said second rotor, and in that the second blade feathering means are configured to transmit the translation of the second member of the transmission device of the first blade pitch control means to the main transmission screw and to block the rotation of the main screw when said at least one second electric motor is not activated.

During feathering, the translation of the main screw driven in rotation by the second electric motor is blocked translation by the reluctant torque of the first electric motor. The main transmission screw is therefore active during feathering and the transmission device for the first pitch control is inactive.

During pitch control, this translational movement of the main transmission screw is transmitted to the main nut because this transmission screw is blocked in rotation by the second feathering means which are inactive. The main transmission screw is therefore inactive during the pitch control and the transmission device of the first pitch control active.

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 locking 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 transmission screw is blocked in the nut, unlikely case because this first screw is not active during the pitch control, the pitch control and feathering can always be carried out by the first rotor of the means of pitch control, rotor which moves in translation the second member of its transmission device, the latter transmitting an overall translation to the second means therefore to the coupling means with the propeller; in fact, the electric motor of the second feathering means must not be activated to block the rotation of the transmission screw since the latter is blocked by the anti-rotation of the nut.

- If the device for transmitting the first pitch control means in translation is blocked, the pitch control and feathering can still be carried out by the second rotor, which drives the first transmission screw in pure rotation; in fact, by activating the second electrical means, the nut is driven in translation by the rotation of this transmission screw, due to the blocking in translation of the second member of the transmission device.

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 cases of failure (pollution, icing, etc.). The invention makes it possible to respond satisfactorily to this need.

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, therefore 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 case. 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 housing 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.

Preferably, at least one electric motor of the second feathering means for the blades is arranged to present a resistive reluctant torque capable of blocking the main screw for rotation.

In this way, the first means can control the pitch of the blades by causing a pure translation of the transmission screw, while keeping the second feathering means inactive. Therefore in pitch control operation a single screw is active that of the transmission device of the first control means and not the transmission screw on the propeller side with its nut which is passive.

In addition, this arrangement makes it possible to mount the first pitch control means in a fixed casing. They are therefore not in motion when they are active. In particular, this improves the reliability of the mounting of these means which are commonly used during the operation of the turboprop. But especially in pitch control operation, the assembly constituting the first pitch control means which integrates the larger electric motors does not move in translation but only the assembly which integrates the smaller electric motor.

Preferably, said at least one electric motor of the first pitch control means comprises a stator carried by a first fixed casing, and said at least one electric motor of the second blade feathering means comprises a stator carried by a second casing which is mounted sliding in translation only, along the axis in the first casing.

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.

FHA reliability also imposes another requirement: no simple failure can lead to uncontrolled operation, therefore a loss of control.

To cover this requirement, all blocking cases must be analyzed with their impact.

- The case of the blocking of the transmission screw and the case of the blocking of the transmission device have already been analyzed

- The cases of bearing blockages must also be analyzed. If the bearings located in the sun gear or the angular contact bearing of the second feathering means become blocked, the first pitch control means nevertheless remain functional and the feathering can also be controlled by these first pitch control means .

If the bearings located in the sun gear or the angular contact bearing of the first pitch control means become blocked, the second feathering means nevertheless remain functional. The second feathering means are functional only if the transmission device is locked in anti-rotation, except the rotation of the first member of the transmission device is indeed blocked during the locking of the planetary bearings or the locking of the angular contact bearing. .

If the radial force recovery bearing on the side of the first pitch control means is blocked, the electric motor of the second feathering means can be supplied, but the functionality will not be acquired because the planet carrier is not not locked in rotation. It would be necessary to supply the synchronous machines of the first pitch control means to generate an anti-rotation torque in order to be able to guarantee feathering.

According to a first embodiment, the second member of the device for transmitting the first blade pitch control means is connected to the second rotor of the second feathering means through an angular contact bearing.

This additional angular contact bearing positioned between the first control means and the second control means makes it possible to obtain a rotational movement of the second rotor without being blocked by the second member of the transmission control device which is blocked by an anti-rotation.

According to a second embodiment, the second member of the device for transmitting the first blade pitch control means is mounted on the second casing.

The second casing is sliding along the axis as indicated above and therefore only moves in translation like the second transmission member. Advantageously, this casing includes an anti-rotation.

In the first embodiment, if the angular contact bearing blocks, the second feathering means no longer ensure their functionality, the rotation of the second rotor being blocked by the anti-rotation of the second member of the transmission device . On the other hand, the first means of step control remain functional.

In the second embodiment, this angular contact bearing has been eliminated. Therefore, if the transmission device becomes blocked, the second feathering means remain functional.

It will be noted that even after activation of the electric motor of the second feathering means, the feathering functionality is not acquired because the first member of the transmission device should be locked in rotation. It would therefore be necessary to power the synchronous machines to generate an anti-rotation torque. The proposed solution therefore comprises two operating cases which simultaneously require a supply of synchronous machines and asynchronous machines.

This electromechanical concept may not require any mechanical energy from the turbomachine. The cases of failure of the loss of engine power and of the engine stopped can therefore be ensured via a protective housing by the nominal electromechanical system without any additional device. This electromechanical concept also covers the case of overspeed and the failure of the FADEC without additional device.

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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 first member of the device for transmitting the first means by a first reduction gear, for example planetary,

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

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

said first means comprise at least two resolvers, 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 main nut drives means which cooperate with eccentrics provided on support plates and blades rotation.

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 a motor of the first pitch control means, so that a rotation of the first shaft causes an axial displacement of the main transmission screw,

- feather the blades by actuating a motor of the second feathering means so that a rotation of the second shaft causes a rotation of the main transmission screw.

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 n

following description given by way of nonlimiting example and with reference to the appended drawings in which:

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

- Figure 2 is a partial schematic half-view in axial section of a second embodiment of a pitch actuation system of the blades according to the invention associated with a turbomachine propeller; and

- Figure 3 is a block diagram showing the general architecture of the actuation system and electrical control means of the system of Figure 1 or 2.

DETAILED DESCRIPTION

We first refer to Figure 1.

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 movement of the eccentrics 20 causes the plates 16 and therefore the blades 14 to rotate in rotation around the axes B. Each blade 14 can be wedged at one 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 according to the invention.

The actuation system 22 of FIG. 1 comprises an electromechanical actuator 24 comprising a fixed casing 32a and a casing 32b, movable in translation along the axis A but locked in rotation around this axis A by means 88 of anti rotation. These means 88 can be slides on the fixed casing 32a.

The actuation system 22 further comprises 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 movable casing 32b and engaged in a housing of complementary shape to the nut 28. The nut 28 is thus also 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. It is understood 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 to move it, and also to be subjected by the nut to axial forces causing the transmission screw to rotate. On this point, it differs from a worm which has an irreversibility function.

The transmission screw is also able to be 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 rotational movement relative to the axis B, is carried out by means of decoupling 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 rolling bearing 83 (here ball) with angular contact is mounted between the nut 28 and the ring 82 and a second rolling bearing 84 (ball) with angular contact is mounted between the sleeve 81 and the ring 82. Conventionally, 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 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 also 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 includes an internal axial bore in which a ferromagnetic LVDT plunger 46a is slidably engaged carried by a rear cover of the actuator 22, which is itself fixed to the fixed casing 32a . 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.

The actuator 24 comprises 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 32a by at least one bearing. The bearing, here rolling and more specifically ball, is mounted at the axial end of the electromechanical actuator 24, opposite the propeller (left end in the drawing).

In the example shown, the first 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 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 32a. 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 functions 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 secured to the casing 32a. The rotor can consist of permanent magnets or consist of a coil supplied with direct current 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.

As can be seen in the drawing, the common rotor 30 drives a second transmission screw 68 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 32a, satellites 42c meshing with the planetary shaft 42a and the crown 42b and carried by a door -satellites 42d which here is integral in rotation with the transmission screw 68. In the example shown, the transmission screw 68 and the planet carrier 42d are formed in one piece.

The part comprising the planet carrier 42d and the transmission screw 68 is centered and guided in the casing 32a 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 between the reducer 42 and the screw 68.

The transmission screw 68 is therefore able to be driven in rotation about the axis A thanks to a torque supplied by the first electrical means 36 but it is blocked in translation by the bearings 44 which take up the axial forces on the fixed casing 32a .

The second transmission screw 68 passes through a second nut 62 and therefore includes a thread complementary to that of the nut. Anti-rotation means 89 prevent the second nut 62 from rotating about the axis A relative to the fixed casing 32a.

It is understood that the rotation of the transmission screw 68 (arrow θ ’in Figure 1) causes a displacement in translation of the nut 62 along the axis A (arrow X). The transmission screw 68 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 to move it, and also to be subjected by the nut to axial forces causing the transmission screw to rotate. On this point, like the first transmission screw 26, it differs from a worm which has an irreversibility function.

In a variant not shown, it may be the second nut 62 which is driven by the shaft 30 and the second transmission screw 68 which is fixed to the mobile casing.

The turboprop is equipped with an auxiliary system 50 for feathering the blades 14, which in this case is electromechanical. The system 50 is integrated into the actuator 22 and includes an electric motor 52, which is preferably an asynchronous machine (so as not to generate resistive torque) ·

The stator of the electric motor 52 of the feathering means 50 is fixed to the mobile casing 32b, between the nut 62 and the first transmission screw 26. The rotor of the electric motor 52 is mounted on a shaft 60.

The shaft 60 is guided in rotation about the axis A by means of a rolling bearing 61, here a ball, mounted between the shaft 60 and the movable casing 32b.

The shaft 60 is independent of the shaft 30 of the first electrical means 36. On the other hand, the shaft 30 is here connected to the second nut 62 by a pair of bearings 90 with bearings, here ball bearings. These bearings 90 are oblique contact. They are reversed and mounted one next to the other between the nut 62 and the rolling bearing 61. The shaft 60 is therefore locked in translation relative to the nut 62. Thus, in particular through of the bearing 61, it is the entire feathering system 50, including the mobile casing 32b, which follows the translational movement of the nut 62.

In an alternative embodiment described in FIG. 2, there are no coupling bearings between the shaft 60 and the nut 62. The shaft 60 remains confined in the movable casing 32b. The second nut 62 is integral with the movable casing 32b, for example mounted on a cover of the said casing on the side opposite the propeller. The movable housing 32b moves with the second nut 62 and drives the entire feathering system 50.

The shaft 60 rotates the first transmission screw 26 via 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 32b, and satellites 64c meshing with the planetary shaft 64a and the crown 64b and carried by a satellite carrier 64d which is here integral in rotation with the first transmission screw 26. In the example shown, the transmission screw 26 and the planet carrier 64d are formed in one piece.

The part comprising the planet carrier 64d and the first screw 26 is centered and guided in the casing 32b by a pair of bearings 66 with bearings, here ball bearings. These bearings 66 are oblique contact. They are reversed and mounted one next to the other between the reduction gear 64 and the transmission screw 26. The first transmission screw 26 is therefore blocked in translation relative to the movable casing 32b by the bearings 66 which take up the forces axial on the housing 32b.

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 the displacement of the second nut 62 and of the movable casing 32b;

- the operation of the second electrical means 52 causes a rotation Θ of the transmission screw 26 via the reduction gear 64.

Reference is now made to FIG. 3 which schematically represents the electrical schematic diagram of the operation of the system of FIG. 1 or of FIG. 2.

The elements described in the foregoing are designated by the same reference numerals in Figures 1 and 2.

FIG. 3 shows in particular the means for controlling the electrical machines of the system, namely, in the case where the redundancy applies to all these machines, two LVDT sensors 46, 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. Each has a transmission screw. Only one chain is active and the other passive.

Indeed, during the pitch control, the electrical means 36 are activated to rotate the screw 68. The rotation Θ ’of the screw 68 therefore causes an axial displacement X of the second nut 62 and. of the mobile casing 32b. Advantageously, the electric motor 52 of the second means is arranged to present a residual reluctant torque making it possible to counter a rotation of the first transmission screw 26 under the effect of an axial force from the first nut 28 imposed by the blades of the propeller . The first transmission screw 26 is therefore passive, fixed in rotation in this case. Its axial displacement X in turn causes an axial displacement of the eccentrics 20, according to the operation of the decoupling mechanism described above.

To control the displacement of the eccentrics 20 by the second electrical means 52 with a view to feathering the blades by the sole rotation of the first transmission screw26, the second transmission screw 68 must be prevented from being driven in rotation θ 'by the reaction of the second nut 62, subjected to external forces which are transmitted to it by the transmission chain of the feathering means. When feathering the first electrical means 36 must therefore be actuated to create a torque resistant to the rotation of the second transmission screw 68.

If the transmission screw 68 of the pitch control chain is blocked in the nut 62 (problem B), the feathering chain can ensure its function and control the pitch of the blades by the rotation of the first screw 26 because the second transmission screw 68 does not allow the nut 62 to move.

If the oblique bearings 66 in the feathering chain are blocked, the first electrical means 36 can be used to modify the pitch so as to effect feathering. Indeed, in this case, the rotation of the first transmission screw 26 is blocked.

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,

- elimination of the case of breakdown related to hydraulic leakage, case which required the addition of counterweight for feathering,

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

- operation of an active screw and the other passive one which relieves in fatigue all the mechanical components,

- absence of activation of an additional electrical device when switching from one transmission chain to another,

- no single fault generates uncontrolled operation.

Claims (12)

1. Pitch actuation system (22) 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 with respect to the pitch pitch axes (B) of the blades, characterized in that the actuator is an electromechanical actuator comprising: - a main transmission screw (26) movable in rotation and in translation along a longitudinal axis (A), - a main nut (28) through which said main transmission screw and cooperating with this screw in order to move in translation along the axis (A), - Means (80, 82, 83, 84) which are configured so that a displacement in translation of the main 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 main 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), and a device for transmission (62, 68), for example screw / nut, comprising a first member (68), for example a screw, driven in rotation by said first rotor and a second member (62), for example a nut, cooperating with said first member to have a translational movement along the axis (A), - second feathering means (50), which comprise at least one electric motor (52) for driving a second rotor (60) around the axis (A), the main transmission screw (26) being rotated by said second rotor, and in that the second means (50) for feathering the blades are configured to transmit to the main transmission screw (26) the translation of the second member of the device (62, 68) for transmitting the first means (25) for controlling the pitch of the blades and for blocking the rotation of the main transmission screw (26) when said at least one second electric motor (52) is not activated. 2. System (22) according to claim 1, in which at least one electric motor of the second means (52) for feathering the blades is arranged to present a resistive reluctant torque capable of blocking the main transmission screw (26). rotation. 3. System (22) according to one of the preceding claims, in which said at least one electric motor (40a, 40b) of the first pitch control means (25) comprises a stator carried by a first fixed casing (32a), and said at least one electric motor (52) of the second means (50) for feathering the blades comprises a stator carried by a second casing (32b) which is mounted to slide in translation only along the axis (A ) in the first casing (32a). 4. System (22) according to the preceding claim, in which the second member (62) of the device for transmitting the first means (25) of pitch control of the blades is connected to the second rotor (60) of the second means (50) of feathering through an angular contact bearing (90). 5. System (22 ') according to claim 3, in which the second member (62') of the device (62 ', 68') for transmitting the first means (25) of pitch control of the blades is mounted on the second casing (32b). 6. System (22) according to one of the preceding claims, in which said first pitch control means (25) comprise two electric motors (40a, 40b), preferably synchronous, for driving the same first rotor ( 30). 7. System (22) according to one of the preceding claims, in which said first rotor (30) is connected to the first member (68) of the device for transmitting the first means (25) by a first reduction gear (42), for example planetary. 8. System (22) according to one of the preceding claims, in which the main transmission screw (26) is connected to the second rotor (60) 5 by a second reducer (64), for example planetary. 9. A turbomachine, such as a turboprop, comprising a propeller (10) whose blades (14) are of variable pitch and a system (22 ') according to one of the preceding claims, in which the main nut (28) drives means (50) which cooperate with eccentrics (20) 10 provided on plates (16) for supporting and rotating the blades. 10. Method for actuating the pitch of the blades of a turbomachine propeller, by means of a system (22 ’) according to one of claims 1 to 8, comprising the steps consisting in: - modify the pitch of the blades by actuating a motor (40a, 40b) First 15 means (25) of pitch control, so that a rotation of the first shaft (30) causes an axial displacement of the main transmission screw (26), - feathering the blades by actuating a motor (52) of the second feathering means (50), so that a 20 rotation of the second shaft (60) causes rotation of the main transmission screw (26). < 1/2