Propulsion unit with a pair of propellers for an aircraft

Abstract

The present invention relates to a propulsion unit comprising a pair of contra-rotating coaxial propellers, that are referred to as upstream (2) and downstream (3), the downstream propeller, forming a rotating reference frame, being mounted for rotation about a central member forming a stationary reference frame, and being provided with a device for changing the pitch of the blades, characterized in that the downstream propeller is supported by bearings arranged externally on the cylindrical central support, an upstream bearing (40) of which is arranged downstream of a device for changing the pitch of the blades of the upstream propeller, and in that said device for changing the pitch of the downstream propeller comprises a linear actuator (23) in the stationary reference frame with an element (235) that is able to move axially along the axis of the downstream propeller, the upstream bearing comprising an inner ring that is rigidly connected to the linear actuator and an outer ring that is rigidly connected to a rotating casing (20) of the downstream propeller, and a movement-transmission mechanism (24) connecting said movable element of the linear actuator to the blades, comprising a load-transfer bearing arranged to transmit the axial forces from the linear actuator to the rotating reference frame of the downstream propeller.

Claims

1. A propulsion unit for an aircraft comprising a pair of contra-rotating coaxial propellers that are referred to as upstream and downstream relative to the flow of air passing through it, the downstream propeller, forming a rotating reference frame, being mounted for rotation about a cylindrical central support forming a stationary reference frame, and being provided with a device for changing the pitch of the vanes, wherein the downstream propeller is supported by bearings arranged externally on the cylindrical central support, an upstream bearing of which is arranged downstream of a device for changing the pitch of the blades of the upstream propeller, and in that said device for changing the pitch of the downstream propeller comprises: a. a linear actuator in the stationary reference frame with an element that is able to move axially along the axis of the downstream propeller, the upstream bearing comprising an inner ring that is rigidly connected to the linear actuator and an outer ring that is rigidly connected to a rotating casing of the downstream propeller, and b. a movement-transmission mechanism connecting said movable element of the linear actuator to the blades, comprising a load-transfer bearing arranged to transmit the axial forces from the linear actuator to the rotating reference frame of the downstream propeller, wherein the load transfer bearing of the movement-transmission mechanism comprises a non-rotating cylindrical collar that is rigidly connected to the axially movable element of the linear actuator, and a rotating collar mounted on the non-rotating collar by means of bearings.

2. The propulsion unit according to claim 1, wherein the device for changing the pitch of the upstream propeller comprises a linear actuator arranged entirely upstream of the upstream bearing of the downstream propeller and separate from the linear actuator of the downstream propeller.

3. The propulsion unit according to claim 1, characterised in that the non-rotating cylindrical collar is connected to the linear actuator by an anti-rotation means.

4. The propulsion unit according to claim 1, wherein the upstream bearing is upstream of the blades.

5. The propulsion unit according to claim 1, further comprising a downstream bearing, situated downstream of the blades.

6. The propulsion unit according to claim 1 further comprising a downstream bearing situated downstream close to the upstream bearing and upstream of the blades.

7. The propulsion unit according to claim 1, wherein the bearings of the movement transmission device are lubricated by oil supplied by telescopic pipes.

8. A turboshaft engine, comprising a gas generator and a propulsion unit according to claim 1 downstream of the gas generator.

9. A propulsion unit for an aircraft comprising a pair of contra-rotating coaxial propellers that are referred to as upstream and downstream relative to the flow of air passing through it, the downstream propeller, forming a rotating reference frame, being mounted for rotation about a cylindrical central support forming a stationary reference frame, and being provided with a device for changing the pitch of the vanes, wherein the downstream propeller is supported by bearings arranged externally on the cylindrical central support, an upstream bearing of which is arranged downstream of a device for changing the pitch of the blades of the upstream propeller, and in that said device for changing the pitch of the downstream propeller comprises: a. a linear actuator in the stationary reference frame with an element that is able to move axially along the axis of the downstream propeller, the upstream bearing comprising an inner ring that is rigidly connected to the linear actuator and an outer ring that is rigidly connected to a rotating casing of the downstream propeller, and a movement-transmission mechanism connecting said movable element of the linear actuator to the blades, comprising a load-transfer bearing arranged to transmit the axial forces from the linear actuator to the rotating reference frame of the downstream propeller, wherein the load transfer bearing of the movement-transmission mechanism comprises a non-rotating cylindrical collar that is rigidly connected to the axially movable element of the linear actuator, and a rotating collar mounted on the non-rotating collar by means of bearings, wherein the device for changing the pitch of the upstream propeller comprises a linear actuator arranged entirely upstream of the upstream bearing of the downstream propeller and separate from the linear actuator of the downstream propeller, and wherein the upstream bearing is upstream of the blades.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood, and other aims, details, features and advantages thereof will become more apparent from the following detailed explanatory description of an embodiment of the invention given by way of purely illustrative and non-limiting example, with reference to the accompanying schematic drawings.

(2) In these drawings:

(3) FIG. 1 is a schematic cross-sectional of a fast-propeller turboshaft engine;

(4) FIG. 2 is an axial section of a pitch-change system according to the invention for the variable setting of the blades of the downstream rotor of a propulsion unit with a pair of propellers; it comprises an actuator shown in two positions;

(5) FIG. 3 is a perspective view of the pitch-change system in FIG. 2.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

(6) With reference to FIG. 2 and FIG. 3, the schematic view of a pitch-change system for the blades of the downstream rotor in a pair of propellers of an engine as described with FIG. 1 can be seen.

(7) To the left in FIG. 2, the references 19 and 20 denote the rotating casings of the upstream 19 and downstream 20 rotors of the pair of propellers. These two propellers are contra-rotating and are driven by the turbine 11, not shown, situated upstream with respect to FIG. 2.

(8) The pitch-change device of the invention is situated inside the downstream rotating casing 20. This downstream rotating casing 20 comprises a plurality of elements 201 and 202 which are bolted to one another and support the pivots 30 of the blades 3A of the downstream rotor, which extend radially in a transverse plane relative to the axis of the engine. The rotating casing 20 is supported itself by an inter-shaft bearing 191; it projects. The pivots 30 are mounted so as to rotate in bearings and the setting thereof is controlled by levers 31 that extend radially relative to the pivot axis of the pivots 30. The angular position of the pivots 30 is provided by the pitch-change device which is described below.

(9) This device comprises a linear actuator 23 in a stationary reference frame and a mechanism 24 for transmitting movement to the blades.

(10) The linear actuator is situated in line with a sleeve 60 for routing the ground equipment, only the downstream end of which can be seen. This sleeve is housed inside the rotary shafts driving the rotors while being fixed relative to these shafts. It constitutes a stationary reference frame. FR 1450440 in the name of the present applicant describes a connection device which is housed inside the shafts of the rotors of the pair of propellers, allowing blind assembly.

(11) The actuator comprises a hollow cylindrical member 231 in line with a bell housing 234 which is mounted on a plate 233 which is bolted at the end of the sleeve 60. The cylindrical element comprises a transverse disc 231d.

(12) The actuator also comprises a cylindrical element 235 that is able to move axially relative to the radial disc 231d. The cylindrical element 235 forms, with the element 231 and the disc 231d thereof, two actuator chambers C1 and C2. These two chambers are respectively in fluidic communication with two pipes 240. These two ducts are fixed to the plate 233 and are supplied with actuating fluid by the sleeve 60. FIG. 2 shows the actuator in two extreme positions. The top part of the figure shows the actuator with the chamber C1 extended and the chamber C2 in reduced volume. The bottom part of the figure shows, conversely, the chamber C2 extended and the chamber C1 in reduced volume. This corresponds to two extreme positions of the movable element 235. In the top part of the figure, the movable element 235 is in the extreme position towards the left with respect to the figure and in the bottom part of the figure the movable element of the actuator is in the extreme position towards the right with respect to the figure. By acting on the supply of actuating fluid to the pipes 240, it is thus possible to move the movable element in translation as required.

(13) The movable element 235 is connected to a mechanism 24 for transmitting movement to the pivots 30 of the blades 3A.

(14) This mechanism 24 comprises a collar 241 that is rigidly connected to the movable element 235 and coaxial therewith. The collar 241 is bolted here, by means of a radial flange 241a, to the downstream face of the movable element 235. The collar 241 is also in sliding abutment on a radial leg 237 that is rigidly connected to the cylindrical body 231.

(15) Anti-rotation axial rods 247 extend along the fixed body of the actuator. These rods pass through the radial flanges 241a for fixing the collar. Rollers, which are not visible in FIG. 2, provide the axial sliding of the collar 241 along these anti-rotation rods and prevent any rotation movement of the rod about the axis of the engine.

(16) The transmission mechanism 24 comprises a rotating collar 243 that is coaxial with and connected to the non-rotating collar 241 by means of bearings 245. Here the bearings are double. The two collars 241 and 243 form the cage of a ball bearing. The rotating collar can rotate about the collar 241, while being immobilised axially relative to said collar.

(17) The rotating collar 243 is connected by links 249 to the levers 31 actuating the pivots 30 of the rotor blades.

(18) The downstream propeller is supported by bearings arranged externally on the cylindrical central support. A first bearing 40, preferably of the ball-bearing type, provides the radial and axial holding of the actuator relative to the rotating casing of the downstream propeller. This bearing is situated upstream relative to the propeller blades. The upstream bearing 40 comprises an inner ring that is rigidly connected to the linear actuator 23 (optionally rigidly connected to the piston 235), and an outer ring that is rigidly connected to a rotating casing 20 of the downstream propeller. A second bearing 41 is situated downstream relative to the rotor blades. The function thereof is substantially that of providing radial holding of the end of the actuator relative to the rotating casing 20.

(19) In a variant shown in broken lines, the second bearing 41 is arranged upstream of the blades while being downstream of the first bearing. Finally, the lubrication of the bearings of the mechanism 24 is provided, according to the embodiment shown, by telescopic pipes 50 connected at one end to a supply from the sleeve and at the other end to the bearing cage 245.

(20) The functioning of this device is deduced from the above description. When a chamber C1 or C2 is supplied with actuating fluid by the pipes 234 from the control box, not shown, and the sleeve through the plate 233, the movable element 235 moves for example in FIG. 2 from the position shown in the top half of the figure to the position corresponding to the bottom half of the figure. The movement-transmission mechanism moves axially. The rotating external collar 243 is then rotated by the rotating casing 20. This axial movement sets the pivots into rotation about their respective axes because of the connection by the levers and links. By virtue of this arrangement the force loop remains confined to the inside of the rotating casing, the reaction to the forces produced by the actuator passing through the first bearing in order to close the loop.

(21) In summary, the downstream system is based on the following principles:

(22) The actuator is situated in the stationary reference framethat is to say the movements thereof are translations. The actuator is not set into rotation with the rotor.

(23) The actuator is positioned in the downstream rotor by means of bearings. The force path of the downstream system and in particular the reaction of the actuator does not pass through the fixed parts of the engine.

(24) The mechanical, electrical and hydraulic interface is unique with the fixed part of the engine placed at the rear of the system in the fixed part.

(25) The movement is transmitted via a load transfer bearing for transmitting the setting forces and passing from the stationary reference frame to the rotating reference frame.

(26) The absorption of the torque created by the bearing is applied to the actuator via an anti-rotation device in the fixed part.

(27) The positioning of the downstream system by means of two bearings; a ball bearing absorbing the axial and radial loads of the system and a roller bearing absorbing the radial loads.

(28) The lubrication of the downstream chamber with the oil residues used for the lubrication of the bearings of the system.