Propeller pitch change mechanism having an actuator for biasing the propeller counterweights

The field of the present invention is that of aeronautical turbomachines and more particularly that of turboshaft engines with non-ducted propellers, called open-rotor or high-speed propeller, and that of devices for controlling the orientation of the blades of these propellers.

Aeronautical engine technology is evolving rapidly and one of the avenues explored to improve the specific consumption of civil aircraft engines is currently the development of open-rotor engines. Such engines, such as that described in the applicant's patent application FR2941493, comprise a conventional turbine engine gas generator, one or more turbine stages of which drive a non-ducted fan extending outside the engine. For reasons of the level of thrust to be reached and reduction of the noise generated by the blades, the engine generally comprises two non-ducted contra-rotating propellers, that is to say which turn in opposite directions, and which are located downstream. engine to keep them as far as possible from the passenger cabin. The general configuration of an open-rotor motor is given in figure 1. As in the case of conventional turboprop engines, the blades of the propellers of open-rotors are variable-pitched, that is to say that the pitch of these propellers can be modified during the flight to change the thrust of the engine and optimize the efficiency of the engine. the propeller as a function of the speed of the aircraft. Multiple devices have been devised to vary the pitch of the blades, which generally include a rotation of the vane around its main axis by means of bevel gears, located under the root of the vane, which cooperate with bevel gears of a control system.

One of the constraints of propeller blade pitch control systems is having to bring them to the so-called feathered position in the event of failure of this system. The feathered position consists of rotating the propeller until its chord aligns appreciably in the bed of the wind, thus minimizing the drag it generates and, consequently, the yaw imbalance produced on the lane. 'plane. The feathered position should correspond to an equilibrium position automatically taken by the propeller when the timing control system no longer transmits torque. For this, weights forming a counterweight are generally attached to the bevel gears of the control system and placed overhang with respect to them. In normal operation they are held in position by the control system. In the event of failure of this system, the action of the centrifugal force due to the rotation of the propeller drives them towards a rest position which corresponds to the flag position of the blade.

In normal use, during phases of flight, the timing of a propeller changes between two extreme limits corresponding to a low pitch position at low forward speed, of the order of 30 ° with respect to the plane of rotation of the propellers. , and a large pitch position at high speed, which is of the order of 65 ° with respect to this same plane of rotation of the propellers.

The flag position corresponds to a setting greater than that of the large pitch, and equal to approximately 90 °. The settings under these normal conditions of use are, by convention, said to be positive.

After landing, the aircraft should be slowed down in order to reduce its rolling distance and thus allow it to use runways of reduced length. For this, the engines are placed in a so-called reverse position, which tends to direct their thrust towards the upstream side of the engine. On an open rotor engine, as is already the case on turboprop engines, the reverse is obtained by giving the propellers a negative pitch, that is to say by positioning the leading edge of their blades in the rear sector. relative to the plane of rotation of the propeller. This position is obtained by continuing the rotation of the propeller, around its longitudinal axis, beyond the small pitch, until crossing the zero pitch position, that is to say the one where the blades are in the plane. propeller rotation, and increasing the pitch to a determined negative setting.

Commonly, the blade root bevel gear results in a reduction ratio of 2 between the counterweight pitch angle and the blade pitch angle. Consequently, a 90 ° rotation of the propeller between the flag position and that of zero pitch corresponds to a rotation of the weights of 180 °, which causes them to pass from the upper vertical position, and therefore stable, of the flag to a lower vertical position, unstable, located opposite it.

One of the problems to be solved on these engines, whether they are open rotor or turboprop engines, is to ensure that the weights do not remain in this unstable position when the pilot controls the passage in reverse, and that we be sure that the propeller blades are in the negative setting position when the pilot restarts power after landing. Failing this, the throttle will result in a runaway of the engine if the propellers remain in zero setting, with the risk of overspeed and therefore of rupture of the blades, or even by traction exerted by the propellers if the timing has remained in. the zone of the positive settings, even though the pilot is waiting for a braking action by them.

It is therefore important to ensure that the propellers pass the zero setting position during a reverse shift maneuver, i.e. that the weights do not remain in the unstable position located between the positive settings and the settings. negative.

The object of the present invention is to remedy these drawbacks by proposing a device for controlling the pitch of a propeller which guarantees the passage of the zero setting position by the weights in the event of a request for reverse passage.

To this end, the subject of the invention is a device for controlling the passage into the reverse mode of a turbine engine with propellers, by an action on a control axis for the setting of said propellers, said device comprising at least one weight mounted on the door. - false on said control axis and arranged so as to drive said propellers towards their flag position under the action of the centrifugal force generated by the rotation of the turbomachine, the device also comprising an actuator capable of rotating said control shaft to change the propeller timing from a traction mode to a reverse mode, by passing through a zero-pitch setting position in which the weight is in a position of unstable equilibrium with respect to the action of centrifugal force, characterized in that it comprises an actuating means exerting a torque on said control axis when the weight is in said unstable equilibrium position, so as to prevent it from remaining in this position.

The torque exerted by the actuating means makes it possible, on the one hand, to guarantee that the propellers will not remain in a zero-pitch position, and, on the other hand, that they will not return to traction mode, the one or the other configuration presenting a danger if the pilot puts the throttle in thinking that his engine is reversed.

Advantageously, said actuating means exerts a torque on said axis both when switching from traction mode to reverse mode and when returning from reverse mode to traction mode. This guarantees the effective passage of the propellers in the desired configuration, whether in reverse or in traction.

Preferably, the actuator does not exert torque on said control shaft when the weights are in the unstable equilibrium position. This configuration eliminates possible interference between the torques applied to the control shaft by the reverse passage device and by the actuator. It simplifies the development of the reverse passage device.

In a preferred embodiment, said actuating means exerts its torque on said control axis by means of a crank pin mounted to rotate freely by one of its ends on said weight.

Advantageously, said actuating means is held at one of its ends by an axis of rotation offset parallel to the control axis and is biased in rotation around this axis, in the direction of the crankpin, by means forming a return torque.

Preferably, the crank pin carries at its free end a transfer means capable of cooperating with said actuating means so as to transfer the torque supplied by said actuating means to the control shaft.

In a particular embodiment, said actuating means is a pawl and the transfer means is a rod shaped to slide on said pawl during the reverse passage.

More preferably, said pawl comprises at its free end a retaining means capable of limiting the sliding of said rod on the pawl during the reverse passage, so as to provide a bearing for said crankpin.

In a preferred embodiment, said rod is in abutment against said retaining means before it reaches its unstable equilibrium position by said weight. Advantageously, during the passage of said weight in its unstable equilibrium position, the rod is in abutment against said retaining means and the crankpin is oriented so as to push the weight beyond said unstable position.

In a particular embodiment, the control device comprises two actuating means as described above, a first means exerting a torque on the crankpin for the passage from the position of use to the reverse position and the second means exerting a torque on said crankpin for the return to the position of use. The invention also relates to a propeller for a turbomachine comprising a blade root fitted with a device for controlling the passage into the reverse mode such as described above, or also to a turbomachine comprising at least one such propeller.

The invention will be better understood, and other aims, details, characteristics and advantages thereof will emerge more clearly during the detailed explanatory description which follows, of an embodiment of the invention given by way of illustration. A purely illustrative and non-limiting example, with reference to the accompanying schematic drawings.

On these drawings:

- Figure 1 is a schematic sectional view of a high speed propeller turbine engine;

FIG. 2 is a perspective view of a device for controlling the pitch of the blades of the turbine engine of FIG. 1, according to one embodiment of the invention;

- Figure 3 is a detail view showing the actuator of the control device of Figure 2;

- Figure 4 is a front view of the device of Figure 2, the propeller setting corresponding to the cruising position;

FIG. 5 is a front view of the device of FIG. 2, the propeller setting corresponding to the position of the small pitch, the engine being at idle speed on the ground;

- Figures 6 to 8 are successive front views of the device of Figure 2, the propeller setting progressively changing from the position of the small pitch of idling on the ground to that of the small reverse pitch, and

- Figure 9 is a front view of the device of Figure 2, the propeller setting being in its final position, corresponding to the small reverse pitch.

Referring to Figure 1, we see a fast propeller turbine engine 1, comprising, on the one hand, a conventional gas generator consisting among others of a compressor 2, a combustion chamber 3 and a turbine 4 which drives the compressor 2, and, on the other hand, a free turbine 5 located downstream of the linked turbine 4, which drives the two series of blades of the counter-rotating propellers 6. The propellers are positioned outside the casing 7 of the gas generator and their blades are held by a blade root 8 movable in rotation about a radial axis relative to the turbomachine 1, which passes through the center of the root. blade and which constitutes the main axis of the blade. The rotation of the blade is ensured by an actuator, in the form of a rod 9, which acts on a pair of bevel gears, one of which is fixed on the blade, surrounding the root of the blade 8. As indicated previously, the size of these bevel gears gives rise to a reduction ratio of 2, so that the propeller describes the path between its flag position and its zero-pitch position when the associated weights perform a rotation of 180 °. A regulation system 10 controls, via the rods 9, the angular position of the blades of each of the propellers 6 and ensures their synchronized rotation.

FIG. 2 shows a protective enclosure 11 of the device for controlling the timing of the blades according to the invention, which surrounds the blade root 8 and which is fixed to the retaining ring 12 of the blades. This rotating ring secures the blades to the motor shaft and drives them in rotation to generate the thrust. The enclosure 11 has essentially the shape of a cylinder which surrounds the blade root 8 and which comprises a lateral window from which a control pin 13 exits, carrying bevel gears which mesh with the blade root gears for ensure the control of the blade setting. On this axis are fixed, cantilevered, weights 14 having the shape of two angular sectors centered on the axis, which are placed side by side and fixed on a disc 15 fitted on the support axis 13. These two sectors are positioned angularly so as to exert, under the action of centrifugal force, a torque tending to cause a rotation of the axis 13 and, consequently, a rotation of the blades of the propeller 6 towards their position of flag.

Referring now to FIG. 3, the device for controlling the timing of the blades 6 can be seen. The rod 9 is fixed, at its outer end, on the weights 14 by means of a journal 16 which passes through the two weights, extending parallel to the axis 13 and being offset laterally with respect to it. The connection between the outer end of the rod 9 and the journal 16 is a connection free to rotate around the journal, so that the rod 9 can rotate the weights 14 by its longitudinal displacement, acting as a connecting rod would.

Each of the weights 14 also carries an axis on which is mounted a crankpin 17 having the shape of a metal tongue capable of rotating in a plane perpendicular to the control axis 13. The axis of rotation of the crankpins is positioned on the bisector. angular sectors constituting the weights 14, on the outer side of the weights to give the crankpins 17 the largest possible lever arm. The two crank pins 17 move around their common axis, remaining parallel to one another, their free ends being connected by a connecting rod 18 extending in the direction of the control axis 13.

At the same time, the retaining ring 12 carries, on each side of the root of the propeller blade 6, two latches 19, that is to say two parts in the form of tabs fixed to the ring 12 by one of their ends, by means of an axis 20 around which they can rotate. There is a first pawl 19a which acts during the reverse passage and a second latch 19b which acts when it returns to normal operation. Torsion springs (not shown), carried by these pawl pins 20, provide a return of the pawls in the direction of the weights 14 and the median plane of the retaining ring 12. The pawl pins 20 are positioned on the retaining ring 12, on either side of the root of the blade, at points spaced laterally with respect to the control pin 13, so that the pawls face each other. and come, by their free end, into abutment against the weights 14, when there is no interference between them and the crankpins 17. The latches 19 each have a flat tongue-like shape extending in a plane parallel to the control axis 13, from the axes 20 to a free end 21 which has a hook shape. The latter's function is to serve as a stop for the connecting rod 18 when it slides on said pawl. The hook has the shape of a double hook which straightens, at first, in the direction of the weights 14 to serve as a stop as indicated above and then which, in a second step, folds back in the opposite direction to serve as an entry ramp to said connecting rod 18. The latter can thus return to be integrated into the latch 19 after having exited therefrom, in order to slide on it in the rest of its movement as will be explained below.

While the rod 9 serves as an actuator for controlling the rotation of the weights 14, and, as a result of the pinions carried by the control shaft 13, the assembly consisting of the latches 19 and the crankpins 17 serves as an additional actuator for the rotation of these weights by transmitting to them, under certain operating conditions, the torque provided by the return springs mounted on the latch pins 20.

While FIG. 4 shows the relative position of all the elements participating in the control of the setting of the propellers 6, in cruising operation, FIGS. 5 to 9 detail the evolution of this positioning during a reverse passage from idle. ground (figure 5) to the reverse position (figure 9). These figures also appear, at the top right, the orientation of the propeller with respect to the zero setting and the value of the setting β thereof.

In FIG. 4, illustrating cruising operation, the weights 14 are in a half-up position, in a position of equilibrium imposed by the position of the rod 9, a balance being established between the centrifugal force exerted by the rotation of the ring 12, which tends to drive the weights upwards, and the traction imposed by the rod 9 which opposes this rotation. This position of the weights corresponds to an angular position of the axis 13 giving the propeller the setting β requested by the regulation system 10, which is between the low pitch position and the high pitch position. Note that in this position the crankpin 17 is not in contact with the first pawl 19a, its connecting rod 18 being free to position itself against the two weights 14 and to follow any required rotations, by the regulation system 10 , to these weights and to the control pin 13. The two pawls 19 are biased towards the control shaft 13 by their torsional return spring and come into a standby position where they are each in abutment against a spoiler 22 carried by the retaining ring 12.

In FIG. 5, the propeller is in a position corresponding to that of idling on the ground, during landing, and which corresponds to that of low pitch. The setting β has decreased compared to its value in cruising and the weights 14 have moved towards the bottom of the figure, that is to say in the direction of zero setting. In this position, the crankpin 17 has moved closer to the pawl 19a and its connecting rod 18 has come into contact with the latter. No force is currently exerted by the latch on the connecting rod, the latter still resting against the spoiler 22.

In FIG. 6 the propeller is in an intermediate position in the rotation to pass in reverse, in response to a traction exerted by the regulation system 10 on the rod 9. The weights 14 have passed the position of small pitch, the wedging always being positive. Compared to FIG. 5, the connecting rod 18 has slipped on the latch 19a, which remains resting on the spoiler 22, and it has come into contact against the rim formed by the hook 21a thereof.

In Figure 7, the propeller is in an even more advanced position towards zero timing, while still remaining with positive timing. The crankpin 17, the free end of which is blocked by the hook 21a, has rotated which now causes it to be oriented substantially perpendicular to the first pawl 19a. This rotation could only take place by a pushing action of the crank pin on the latch 19a which moves away from the spoiler 22. The torsional return spring located on the axis of the pawl is then compressed and its return force produces, in return, a thrust of the pawl on the crankpin 17 and, ultimately on the weights 14.

In FIG. 8 the propeller is in the zero setting position, the position of the weights corresponding to their unstable position in rotation around the control axis 13, under the action of centrifugal force. The free end of the crankpin 17 and the connecting rod 18 are still retained by the hook 21a. In this situation the rod 9 is pulled to the maximum and its orientation is such that it points in the direction of the control axis 13; it then no longer has any rotational drive action of the weights 14 and does not allow them to pass the low point to reach the negative wedges. On the other hand, the geometric configuration given to the crankpin-pawl assembly is such that the force exerted by the pawl does not pass through the control axis 13 and pushes the weights beyond their current position. The weights 14 cannot then remain in this unstable position, which is the aim sought by the invention.

In FIG. 9 the propeller is in the reverse position. The devices participating in the control of its setting are in a position symmetrical to that which they have at idle on the ground, in normal use. The weights 14 are in a mid-high position, in equilibrium between a centrifugal force which tends to bring them towards the flag by the negative wedges, and a traction of the rod 9 which fixes their position so that the reverse wedging corresponds to that which gives the engine the best thrust backwards. The crankpin 17 was driven by the weights 14 and escaped the hook 21a of the first pawl 19a; it slipped under the second latch 19b, associated with the negative wedges, using the ramp of the hook 21b thereof. As in FIG. 5, the connecting rod 18 is bent against the weights 14 under the action of the second latch and its return spring and the second latch 19b bears against the corresponding spoiler 22.

The operation of the control device according to the invention will now be described by detailing the change in the timing of the propellers of a fast propeller engine by going from the cruising position to that of reverse, at the end of the landing of the aircraft. .

In normal operation, when cruising in flight or on approach before landing, the setting of the propellers 6 is between the position of the small pitch and that of the high pitch, in a configuration described in FIG. 4. The weights 14 are retained. by the rod 9 which prevents them from coming into the flag position under the action of the centrifugal force exerted on them. The crankpins 17 are free to rotate around the journal 16 of the weights and the connecting rod 18 does not interfere with the first pawl 19a. The setting of the propellers is normally carried out by an action of the rod 9 on the weights, without the device for assisting the reverse passage intervening.

After the aircraft has landed, the pilot reduces throttle and brings the engine to ground idle speed, which results in sending the propeller setting to the small pitch position shown in FIG. 5. The control system regulation 10 has, for this, pulled on the rod 9 and rotates the weights 14 to a position corresponding to a setting of about 30 °. In this position, the crankpins 17 have come to the low position, where the connecting rod 18 comes, by construction, into contact with the first pawl 19a. This contact between the connecting rod 18 and the first pawl is established substantially in the middle of the latter, without pressure still being established between the two parts.

The pilot then initiates the reverse passage by asking the regulation system to pull on the rod 9 to bring it to its position as retracted as possible with respect to the weights 14. These then rotate in the direction of their position. corresponding to zero setting, dragging in their wake the crankpins 17 and the connecting rod 18. This slides, first of all, along the first pawl 19a until it becomes wedged against the hook 21a (position illustrated in FIG. 6). Beyond this position, the rotation of the weights 14 continuing, they drive the crankpins 17 which gradually push the pawl 19a away from the weights, and compressing the torsional return spring located on its axis of rotation 20 (cf. figure 7).

Due to the continued action of the rod 9, the weights arrive in a position of symmetry with respect to the median plane of the retaining ring 12, which corresponds to their position of unstable equilibrium (see figure 8 ). In this position, the rod 9 is pulled to the maximum by the regulation system 10 and is found to point in the direction of the control axis 13; it therefore no longer has any effect on the rotation of the weights 14 and cannot extend it by additional traction. On the other hand, when the weights are in this unstable equilibrium position, the crankpins 17 receive a thrust from the first pawl 19a, which comes from the reaction torque of its torsion spring. This thrust is, for its part, not oriented towards the control axis 13 but it points to the side of the negative wedges. The weights are thus led to continue their rotation and to escape this position of unstable equilibrium, which thus responds to the technical problem which the invention proposes to solve.

From there, the centrifugal force which is exerted on the weights 14 naturally causes them in a continuation of the rotation which increases the pitch of the propellers, in the direction of the negative settings. The rod 9 is left free so as to allow this movement to occur up to a preprogrammed angular position. This rotation also causes the connecting rod 18 to come out of the hook 21a of the first latch, and the latter comes to meet the hook 21b of the second latch 19b. The ramp shape given at the end of the hook allows this rod 18 to slide on it and to be integrated between the second latch 19b and the weights 14, thus putting in place the elements to ensure the passage of the weights through. from their unstable equilibrium point when returning to normal regulation. The system comes to a standstill in a position where the rod 9 blocks any subsequent movement and compensates for the action of this centrifugal force (see FIG. 9). The position retained is chosen by the designer of the device to give the propeller timing the value which gives the best rear traction, taking into account the speed given to the engine in the reverse situation. As shown in FIG. 9, without this value being imperative, the reverse setting corresponds in negative to that of the ground idle speed (-30 °).

The return to the normal use position is effected in a similar fashion, the passage through the unstable equilibrium point being made by a thrust generated by the second latch 19b, which acts in the same way as the first one. latch 19a during the reverse passage, this time resting on the hook 21b of the second latch 19b.