Turbine engine with a pair of contrarotating propellers placed upstream of the gas generator

Abstract

Engine comprising a propeller unit with a pair of contrarotating propellers (31, 32), a gas generator (5) supplying a power turbine (53), the pair of propellers being rotationally driven by the shaft (53A) of the power turbine via a speed reduction gearbox, the axis of rotation (XX) of the pair of propellers not being coaxial with that (YY) of the power turbine, the speed reduction gearbox comprising a differential gearset (7) and a first stage (6) comprising a simple gearset connecting the turbine shaft (53A) and the differential gearset (7), the engine air intake comprising an air intake duct (11), the air intake duct (11) being in the shape of a lobe adjacent to the assembly formed by the simple gearset and the differential gearset (7).

Claims

1. An engine comprising: a propeller unit with a pair of contrarotating propellers; a power turbine; a power turbine shaft coupled to the power turbine; a gas generator configured to supply exhaust gases to the power turbine, a speed reduction gearbox comprising a differential gearset and a simple gearset, the speed reduction gearbox coupled to the pair of contrarotating propellers and the power turbine shaft such that the power turbine is configured to drive the pair of contrarotating propellers through the speed reduction gearbox, wherein the simple gearset is coupled to the power turbine shaft and the differential gearset; and an air intake comprising an air intake duct, the air intake duct having a shape of a lobe, the air intake duct being positioned adjacent to the speed reduction gearbox; wherein an axis of rotation of the pair of contrarotating propellers is not coaxial with an axis of rotation of the power turbine, wherein the simple gearset comprises a first toothed wheel, the first toothed wheel being integral with the power turbine shaft, said first toothed wheel in meshing engagement with a second toothed wheel of the simple gearset, said second toothed wheel being mounted coaxially with the axis of rotation of the pair of contrarotating propellers.

2. The engine according to claim 1, wherein the simple gearset and the differential gearset are located to one side of the air intake duct.

3. The engine according to claim 1, wherein the simple gearset and the differential gearset are located between the pair of contrarotating propellers and the gas generator.

4. The engine according to claim 1, wherein an angle defined between the axis of rotation of the power turbine and a straight line connecting an apex of a compressor of the gas generator to an inner elbow of the air intake duct is between 20 and 60.

5. The engine according to claim 1, wherein the second toothed wheel of the simple gearset is coupled to a sun gear of the differential gearset.

6. The engine according to claim 1, wherein at least one of the differential gearset or the simple gearset comprises duplicated toothed wheels.

7. The engine according to claim 6, wherein the simple gearset comprises two toothed wheels in parallel meshing engagement with a toothed wheel connected to a sun gear of the differential gearset.

8. The engine according to claim 1, wherein the differential gearset comprises a sun gear, a planet carrier and a ring, the planet carrier being connected to an upstream propeller of the pair of contrarotating propellers and the ring being connected to a downstream propeller of the pair of contrarotating propellers.

9. The engine according to claim 1, in wherein the differential gearset comprises a sun gear, a planet carrier and a ring, the planet carrier being connected to a downstream propeller of the pair of contrarotating propellers and the ring being connected to an upstream propeller of the pair of contrarotating propellers.

10. The engine according to claim 1, wherein the engine further comprises a fixed structure with a sleeve, a first shaft member being supported via bearings inside the sleeve, said first shaft member connecting a ring of the differential gearset to a first propeller of the pair of contrarotating propellers.

11. The engine according to claim 10, wherein the engine further comprises a second shaft member supported via bearings inside the first shaft member, the second shaft member connecting a planet carrier of the differential gearset to a second propeller of the pair of contrarotating propellers.

12. The engine according to claim 10, wherein the engine further comprises an additional shaft member supported via bearings on the fixed structure, said additional shaft member connecting the second toothed wheel of the simple gearset to a sun gear of the differential gearset.

13. The engine according to claim 8, further comprising a sleeve containing services, the sleeve being housed within an innermost shaft member of a plurality of shaft members.

14. The engine according to claim 1, wherein the sleeve is a fixed sleeve.

Description

DESCRIPTION OF THE FIGURES

(1) It will be easier to understand the invention, and the other aims, details, features and advantages thereof will become clearer on reading the following detailed, explanatory description of an embodiment of the invention given by way of purely illustrative, non-restrictive example, with reference to the accompanying diagrammatic drawings.

(2) In these drawings:

(3) FIG. 1 shows diagrammatically, in axial section, an example of an engine according to the invention;

(4) FIG. 2 shows in greater detail the structural members of the embodiment of an engine according to the invention;

(5) FIG. 3 shows the details of FIG. 2 relating to the propeller unit;

(6) FIG. 4 shows a variant embodiment of the invention;

(7) FIG. 5 shows, in a perspective view, an example of a reduction gear with double toothed wheels;

(8) FIG. 6 shows another example of a reduction gear;

(9) FIG. 7 shows the engine, in perspective, with the positioning of the air intake duct relative to the offset axes.

DETAILED DESCRIPTION

(10) With reference to FIG. 1, the engine 1 is shown mounted on an aircraft A in the rear portion of the fuselage. It is attached to the latter at two planes of suspension, an upstream plane P1 and a downstream plane P2. It comprises, from upstream to downstream, a propeller unit 3 formed of two contra-rotating propellers, 31 and 32, rotating about an axis XX known as a propeller unit axis. Downstream, a gas generator 5 is formed of a gas turbine engine with a compression assembly, a combustion chamber and a turbine assembly. The gases from the gas generator 5 are ejected into the atmosphere via an exhaust nozzle 12 at the rear of the engine. The shafts of the generator 5 are coaxial and mounted so as to rotate about an axis YY, called the gas generator axis. The axes XX and YY are offset from one another. In relation to position on the aircraft, in FIG. 1, the axis XX is positioned above the axis YY; this means that the distance from the ground to the propeller unit can be increased and an engine can be positioned lower on the aircraft or positioned on an aircraft that needs a lot of ground clearance.

(11) The offset also allows the engine to be mounted on the aircraft so as to bring the gas generator closer to the fuselage, to limit the overhang of the engine while placing the propellers further away. In this case the axes will instead be at the same height but offset horizontally or else offset in terms of height and horizontally. FIG. 7 shows diagrammatically the engine of the invention with its two axes XX and YY and the air intake duct, the axis of which is coplanar with the first two. The bidirectional arrow F illustrates how the relative position of the axes can be varied relative to each other on the aircraft by pivoting them relative to each other.

(12) Part of the power provided by the gas generator 5 is transmitted by a shaft 53a to the propeller unit. The shaft 53a extends upstream and drives the rotors 31 and 32 of the propeller unit through a speed reducer comprising a differential reduction gear 7 and a first stage 6 with a simple gearset. The gearset is said to be simple since the axes of rotation of the toothed wheels are fixed.

(13) According to this embodiment, the first stage 6, with a simple gearset, comprises a toothed wheel 61 integral with the shaft 53A, meshing with a toothed wheel 63, mounted so as to rotate about the axis XX of the propeller unit. The offset between the axes XX and YY corresponds to the distance between the axes of the two wheels 61 and 63. Depending on the respective radii of the two wheels, this first stage 6 leads to a reduction or increase in rotational speed between the inlet and outlet wheels. The gearset is said to be simple since the axes are fixed, unlike the differential.

(14) The wheel 63 drives the wheels of the differential reduction gear 7. This differential comprises a sun gear 71, a ring 73 and, between the two, the planet gears 72 mounted on the planet carrier 72P. The three members 71, 73 and 72P of the differential and the axis XX are coaxial.

(15) The shafts 31A and 32A of the propeller unit rotors are coaxial with the axis XX and are integral respectively with the planet carrier 72P and the ring 73 of the differential reduction gear.

(16) The outlet wheel 63 of the first reduction stage, via its shaft, drives the shaft of the sun gear 71.

(17) The blade pitch of each of the propellers is controlled by an actuator shown diagrammatically as 31V and 32V respectively. For example, the pitch is changed by driving the blades about their axis with a crank. Patent FR 3001 264 filed by the applicant describes an embodiment of a pitch change control.

(18) The gas generator 5 is housed in a nacelle 10 comprising an air intake duct 11 for supplying the gas generator with air. This air intake duct is adjacent to the reduction gears 6 and 7 with, here, an intake plane 11a perpendicular to the axis XX, and it is arranged so as to direct the air in a direction parallel to XX and then divert it towards the intake of the generator 5. The curvature of the air intake duct makes it possible to incorporate a trap 13 for particulates and foreign objects that might damage the engine.

(19) The simple gearset 6 and the differential gearset 7 are located radially on the same side of the air intake duct 11, above the air intake duct 11. In this way, the axis of the air delivery duct at the intake of the duct 11 is located below the axis YY of the gas generator, which is itself located below the axis XX of the propeller unit.

(20) The deflection of the air stream entering the engine is given by the angle between the axis YY and the straight line D connecting the apex of the gas generator compressor to the inner elbow of the air intake duct. This angle is chosen, according to aerodynamic considerations, to be between 20 and 60 to avoid flow distortion at the compressor intake and penetration of foreign bodies into the engine. This angle is determined according to the compressor, the geometry of the engine and aircraft, etc. The axial dimension of the channel 14 is thus determined from the centre-to-centre distance and this angle. It is therefore desirable to reduce this centre-to-centre distance.

(21) As indicated above, there is now only the radius of the intake wheel to be bypassed, and no longer the radius of the differential ring. Preferably, the radius of the intake wheel is at least twice as small as that of the differential ring. It should be noted that the ring normally has a larger inner toothing and therefore overall dimensions than the outer toothing of the intake wheel of the simple gear unit. It is also necessary to add the oil scavenging device, though this has equivalent overall dimensions in both cases.

(22) It should be noted that the height offset of the axes allows the air duct 11 to be incorporated with a more favourable opening height in terms of pressure drop relative to the annular openings, since the boundary layer in the air intake occupies a relatively small portion thereof compared with fresh air. The width of the duct 11 extends over a portion of a circle, for example 90.

(23) Furthermore, advantageously, the upstream lip 11b of the air intake duct, on the nacelle side, is separated from the latter so as to prevent or, at least, reduce intake of the boundary layer air formed by the flow along the rotating nacelle.

(24) Advantageously too, a device for scavenging the lubrication oil of the reduction gear units is housed in the lower portion of the reduction gear, close to the air intake duct. This scavenge oil is at a sufficient temperature to form a means of de-icing the air duct.

(25) This engine operates as follows. The air is guided by the duct 11 towards the gas generator 5, which supplies appropriate power to drive the power turbine 53. The gases leaving the turbine are ejected through the exhaust nozzle 12.

(26) The shaft 53a rotates the wheels of the first stage 6, the rotational speed of the wheel at the outlet, relative to that of the shaft 53a, being determined by the reduction or increase ratio defined with the characteristics of the engine.

(27) The outlet wheel of the first stage drives the planet gear of the differential 7, which rotates the planet carrier and the planet wheels supported by the latter. These planet wheels drive the ring in inverse rotation relative to that of the planet gear.

(28) The design of such an engine permits further improvements when developed in several steps. This development comprises: an aeroacoustic optimisation step in which the absolute value of the torque ratio of the upstream propeller is set at between 0.8 and 1.5 or 2 of the propeller speed. The torque ratio sets the reduction ratio of the differential; a step of optimising the turbine in which an ideal turbine speed is set depending on the turbine engine parameters, i.e. power, shape of air stream and maximum speed. The overall reduction ratio between the turbine and the propellers is deduced from this. In this way the reduction ratio of the reduction gear is set; a step of optimising the mass of the reduction gear assembly and the size of offset between the axes XX and YY, in which the torque ratio is varied by +1-10%, to determine a lower mass point.

(29) Referring to FIGS. 2 and 3, these show an embodiment of the engine in greater detail.

(30) The gas generator 5 is formed of a gas turbine engine with a compression assembly, a combustion chamber 54 and a turbine assembly. The generator is here formed of three rotors 51, 52, 53. The two rotors 51 and 52 comprise respectively a compressor 51C, 52C and a turbine 51T, 52T, connected by a shaft 51A and 52A. The shafts of the generator 5 are coaxial and mounted so as to rotate about the axis YY. The combustion chamber 54 is positioned between the compressor 52C, a high-pressure compressor, and the turbine 52T, a high-pressure turbine. Downstream of the turbine 51T, which is a low-pressure turbine, a power turbine 53 is mounted on the shaft 53A coaxial with the shafts 51A and 52A.

(31) The combustion chamber 54 is positioned between the compressor 52C, a high-pressure compressor, and the turbine 52T, a high-pressure turbine. Downstream of the turbine 51T, which is a low-pressure turbine, a power turbine 53 is mounted on the shaft 53a coaxial with the shafts 51a and 52a.

(32) According to this embodiment, the first stage 6, with a simple gearset, comprises a toothed wheel 61 integral with the shaft 53a, meshing with a toothed wheel 63, mounted so as to rotate about the axis XX of the propeller unit. The offset between the axes XX and YY corresponds to the distance between the axes of the two wheels 61 and 63. Depending on the respective radii of the two wheels, this first stage 6 leads to a reduction or increase in rotational speed between the intake and outlet wheels. The gearset is said to be simple since the axes are fixed, unlike the differential.

(33) The wheel 63 drives the wheels of the differential reduction gear 7. This differential comprises a sun gear 71, a ring 73 and, between the two, the planet gears 72 mounted on the planet carrier 72P. The three members 71, 73 and 72P of the differential and the axis XX are coaxial.

(34) The shafts 31A and 32A of the propeller unit rotors are coaxial with the axis XX and are integral respectively with the planet carrier 72P and the ring 73 of the differential reduction gear.

(35) The outlet wheel 63 of the first reduction stage drives, via its shaft, the shaft of the sun gear 71.

(36) The turbine rotates the wheels of the first reduction stage 6. The rotational speed of the wheel at the outlet relative to that of the shaft 53A is determined by the reduction or increase ratio defined with the characteristics of the engine.

(37) The outlet wheel of the first stage drives the planet gear, which rotates the planet carrier and the planet wheels supported by the latter. These planet wheels drive the ring in inverse rotation relative to that of the planet gear. During flight and on the ground, the blade pitches are adjusted by actuators. The blade pitch of each of the propellers is controlled by an actuator shown diagrammatically as 31V and 32V respectively. For example, the pitch is changed by driving the blades about their axis with a crank. Patent FR 3001 264 filed by the applicant describes an embodiment of a pitch change control.

(38) The diagram in FIG. 2 makes it easier to understand the operation of the engine; FIG. 3 uses the same engine members relating to the propeller unit portion and shows how these are integrated into the structure.

(39) The fixed structure 20 comprises a set of casing members forming bearing supports. In this way, the casing comprises a sleeve 21 extending upstream. This sleeve 21 is coaxial with the shafts 32A and 31A of the two propellers. It supports, via bearings 22, the shaft 32A of the downstream propeller connected to the ring 73 of the differential reduction gear. This shaft 32A is integral at its other end with the propeller hub 32. It should be noted that the sleeve 21 supports the blade pitch control actuator 32V of the downstream propeller 32. To transmit a translation movement of the control member of the fixed actuator 32V, a ring 32v1 is mounted with bearings on the actuator control member. This ring is connected to the connecting rods securing the pivot 32p of the blades.

(40) The shaft 31A connected to the upstream propeller 31 is supported by the shaft 32A via inter-shaft bearings 321. Downstream, the shaft 31A is attached to the planet carrier 72p.

(41) The shaft 63A connecting the toothed wheel of the first stage 6 to the sun gear 71 is supported by a fixed casing member via bearings 24.

(42) A fixed sleeve 25 is housed within the shafts 63A and 31A. It connects the upstream propeller blade pitch control actuator 31V to a zone located downstream of the reduction gears. The function of this sleeve is to act as a guide for the fluid and electrical services for the actuator 31V, for instance. This actuator is fixed and, like the actuator 32V, it transmits movement to the pivots 31P of the upstream propeller blades via a rotary ring.

(43) According to another embodiment the upstream actuator can rotate about the axis XX. An appropriate seal is then provided between the actuator and the sleeve.

(44) FIG. 4 shows a variant embodiment where the attachment of the shafts of the two propellers has been modified. The shaft 32A is arranged so as to be driven by the planet carrier 72P and to drive the downstream propeller in turn. The shaft 31A is arranged so as to be driven by the ring 73 of the differential reduction gear and to drive the upstream propeller 31.

(45) FIG. 5 shows an exemplary embodiment of the first stage with a simple gearset, allowing transmission of a high power density owing to distribution of the effort applied to the toothings over a larger surface area. In this example, the shaft of the turbine 53A is integral with two coaxial toothed wheels 61, which mesh simultaneously with two coaxial toothed wheels 63. These two wheels 63 are secured to two coaxial wheels 71 forming the planet gear of the differential 7. Similarly, the planet gears 72 are duplicated axially, as is the ring 73.

(46) This arrangement has the advantage of distributing the torque transmitted between the two duplicated wheels, which limits the load on the toothings without hampering the reduction gear in the lengthwise direction.

(47) FIG. 6 shows a variant embodiment of the reduction gear aimed at the same objective. In this figure the ring of the differential has not been represented. The toothed wheel 61 integral with the shaft 53A can be seen. Here it drives two wheels 62 in parallel. These two wheels are placed in the same transverse plane relative to the shaft 53A and engage with the wheel 63. This wheel is coaxial with the planet wheel of the differential which, as in the previous example, has been duplicated. Similarly, the two wheels of the planet gears drive the planet wheels themselves, duplicated axially like the ring, not represented. This solution allows the axial dimensions of the reduction gear to be reduced without affecting the ability to transmit high torques. The length of the engine, particularly its cantilevered portion, is reduced by the same amount.

(48) A mechanism for equalising torque between the two wheels is, where appropriate, added to this gearset to avoid premature wear on one of the effort paths.