Aircraft twin propeller turbine engine

Abstract

The invention relates to a twin-propeller turbine engine (101) for an aircraft, the turbine engine (101) having a main axis (X) and comprising:-a first propeller (S1),-a second propeller (S2),-a gas generator, the invention relates to a gas generator comprising a power transmission mechanism, a first shaft (104a) for rotating a first propeller (S1) about a main axis (X), and a second shaft (104b) for rotating a second propeller (S2) about the main axis (X), characterized in that the power transmission mechanism is a mechanical differential (160).

Description

TECHNICAL FIELD

[0001] The present application relates to the field of twin-screw turbomachines for aircraft. BACKGROUND

[0002] The prior art notably includes documents WO-A1-2010 / 092263, US-B2-11,492,979, FR-A1-2 987 416, FR-A1-3 008 462 and FR-A1-3 041 054.

[0003] An aircraft turbomachine generally comprises a propulsive screw called a fan, which is driven in rotation by a shaft of a gas generator to produce a thrust to propel the aircraft.

[0004] Turbomachines with twin screws, for example of the open-rotor type, are also known. The screws are driven by a shaft of a gas generator and can rotate co-rotatively or counter-rotatively, i.e. the screws can rotate around the same axis in the same direction or in opposite directions. The screws can be located upstream or downstream of the gas generator.

[0005] It is also known to use a power transmission mechanism, generally of the mechanical reduction gear type, in an aircraft turbomachine.

[0006] The role of a mechanical reduction gear is to change the speed and torque ratio between the input shaft and the output shaft of a mechanical system.

[0007] New-generation turbofan engines, in particular those with a high bypass ratio, comprise a mechanical reduction gear to drive the shaft of the fan. The usual aim of the reduction gear is to convert the rotational speed of the shaft of the power turbine, called high speed, into a slower rotational speed of the shaft driving the fan.

[0008] Such a reduction gear comprises a central pinion called sun gear, a ring gear and pinions called planet gears, which are engaged between the sun gear and the ring gear. The planet gears are held by a frame called planet carrier. The sun gear, the ring gear and the planet carrier are planetary because their axes of rotation coincide with the main axis or longitudinal axis X of the turbomachine. The planet gears each have a different axis of rotation and are uniformly distributed around the axis of the planets on the same operating diameter. These axes are parallel to the longitudinal axis X.

[0009] There are several reduction gear structures. In the prior art of twin-flow turbomachines, the reduction gear is planetary or epicyclic. In other similar applications, there are structures called differential structures or "complex" structures.

[0010] - in a planetary reduction gear, the planet carrier is stationary and the ring gear is the output shaft of the device rotating in the opposite direction to the sun gear.

[0011] - in epicyclic reduction gears, the ring gear is stationary and the planet carrier is the output shaft of the device, rotating in the same direction as the sun gear.

[0012] - on compound reduction gears, no element is attached to rotate. The ring gear rotates in the opposite direction to the sun gear and the planet carrier.

[0013] Reduction gears can be composed of one or more meshing stages. This meshing is achieved in different ways, for example by contact, friction or magnetic field.

[0014] In the present application, "stage" means a toothed portion configured to mesh with a complementary toothed portion. The toothed portions can be internal or external.

[0015] Planetary gears can comprise one or two meshing stages. Single-stage planetary gears comprise a toothed portion which can be straight, helical or herringbone, and the teeth of the toothed portion are located on the same diameter. This toothed portion cooperates with both the sun gear and the ring gear.

[0016] Double-stage planetary gears comprise two toothed portions located on different diameters. The first toothed portion cooperates with the sun gear and the second toothed portion cooperates with the ring gear.

[0017] Each toothed portion of a planetary gear can comprise a single series of teeth or two independent series of teeth, i.e. at an axial distance from each other. A planetary gear has been proposed whose meshing toothed portion with the sun gear comprises two series of teeth arranged on either side of the median plane of the planetary gear, and whose meshing toothed portion with the ring gear also comprises two series of teeth arranged on either side of this plane, the two toothed portions of each planetary gear having different diameters.

[0018] Reduction gears with meshing double stages have the advantage of having a higher reduction ratio than reduction gears with a single meshing stage of the same overall size. However, the disadvantage of this type of reduction gear is the moment generated in the planetary gears because of the difference in force applied to the stages of the planetary gears.

[0019] The present invention provides a power transmission mechanism solution which is particularly suitable for the rotational driving of the propeller screws of a turbomotor engine. SUMMARY

[0020] The present invention relates to a twin-screw turbomotor engine for an aircraft, said turbomotor engine having a main axis and comprising: - a first propeller, - a second propeller, - a gas generator comprising a power transmission mechanism, a first shaft which rotates the first propeller about the main axis, and a second shaft which rotates the second propeller about the main axis, characterized in that said power transmission mechanism is a mechanical differential, said mechanical differential comprising: - a sun gear centered on the main axis and coupled to the shaft of the gas generator, - a ring gear centered on the main axis and coupled to said first shaft, - a planet carrier centered on the main axis and coupled to said second shaft, and - planet gears carried by the planet carrier and meshing with the sun gear and the ring gear, each planet gear having an axis of rotation parallel to the main axis and comprising a first toothing meshing with the toothing on the sun gear and a second toothing meshing with the toothing of the ring gear, the first toothing of each planet gear comprising two series of teeth at an axial distance from each other and arranged on either side of a median plane of the planet gear, the median plane being perpendicular to the axis of the planet gear, the second toothing of each planet gear comprising two series of teeth at an axial distance from each other and arranged on either side of said median plane and the series of teeth of the first toothing.

[0021] Thus, the application uses a mechanical differential as power transmission mechanism, i.e. a mechanism in which all elements, including the sun gear, the ring gear and the planet carrier, are rotatably mobile. The particular feature of this differential is that its planet gears are double- stepped, making it have a very high reduction ratio.

[0022] In particular, the application is particularly compatible with: - a multi-step reduction gear; - straight toothing or herringbone toothing.

[0023] The turbine engine according to the application can comprise one or more of the following features, taken independently of each other or in combination with each other: - the diameter of the first toothing of each planet gear is greater than the diameter of the second toothing of the planet gear; - the toothing of the sun gear comprises two series of teeth at an axial distance from each other and meshing respectively with the two series of teeth of the first toothing of each planet gear; - the toothing of the ring gear comprises two series of teeth at an axial distance from each other and meshing respectively with the two series of teeth of the second toothing of each planet gear; - the ring gear has an upstream ring gear half and a downstream ring gear half, the ring gear halves being symmetrical and arranged on either side of the series of teeth of the first toothing of each planet gear; - the propeller counter-rotates; - the first toothing of each planet gear is of the straight type or of the herringbone type with the toothing of the sun gear; - the second toothing of each planet gear is herringbone with the toothing of the ring gear; - the planet gears are guided in rotation by fluid dynamic bearings comprising a cylindrical body passing through the planet gears, the body extending along the rotation axis of the planet gears and comprising at the longitudinal ends of the body an extension housed in an orifice forming a seat for the planet carrier; - the planet carrier comprises an integral cage in which the planet gears are housed; - the first shaft extends around the second shaft and is guided in rotation around the second shaft by at least one bearing; - the first shaft comprises a cylindrical section connected to the ring gear by a ring gear retainer comprising a cylindrical wall around at least a portion of the ring gear and a frustoconical section for connecting the first shaft to the cylindrical wall, the diameter of the cylindrical section of the first shaft being smaller than the diameter of the cylindrical wall of the ring gear retainer or even smaller than the outer diameter of the planet carrier; - the cylindrical section of the first shaft forms an integral piece with the frustoconical and cylindrical walls of the ring gear retainer; - the second shaft comprises a cylindrical section connected to the disc of the planet carrier and for example forming an integral piece with said disc or with the planet carrier; - each planet gear is guided in rotation by a fluid dynamic bearing comprising a cylindrical body passing through the planet gear, the body extending along the rotation axis of the planet gear and comprising at the longitudinal ends of the body an extension housed in an orifice forming a seat for the planet carrier; - the ring gear is the only ring gear in the differential; - the differential has no fixed ring gear. BRIEF DESCRIPTION OF DRAWINGS

[0024] Further features and advantages will become apparent from the following description of non-limiting embodiments of the application, with reference to the annexed drawings, in which: [ Figure 1 ] Figure 1 is a schematic axial section of a turbomachine, [ Figure 2 ] Figure 2 is a partial axial section of a mechanical reduction gear, [ Figure 3 ] Figure 3 is another partial axial section of a mechanical reduction gear and illustrates the prior art of the application, [ Figure 4 ] Figure 4 is a schematic axial cross-section and perspective view of a symmetrical meshing two-stage reduction gear and also illustrates the prior art of the application, [ Figure 5 ] Figure 5 is Figure 4 another schematic axial section of the reduction gear in [ Figure 6 ] Figure 6 is a very schematic partial view in axial cross-section of a mechanical differential according to the application, [ Figure 7 ] Figure 7 is a very schematic partial axial section view of a turbomachine according to the application, [ Figure 8 ] Figure 8 is a schematic perspective view of an axial cross section of a differential for a turbomachine according to one embodiment of the application, [ Figure 9 ] Figure 9 is a schematic axial section view of one of the planetary gears of the differential of Figure 8 .DETAILED DESCRIPTION

[0025] Figure 1 A turbomachine 1 is described, comprising a gas generator comprising in a conventional manner a fan S, a low-pressure compressor la, a high-pressure compressor lb, an annular combustion chamber lc, a high-pressure turbine Id, a low-pressure turbine le and an exhaust nozzle lh. The high-pressure compressor lb and the high-pressure turbine Id are connected by a high-pressure shaft 2 and form together a high-pressure (HP) body. The low-pressure compressor la and the low-pressure turbine le are connected by a low-pressure shaft 3 and form together a low-pressure (BP) body.

[0026] The fan S is driven by a fan shaft 4, which is driven by the BP shaft 3 through a reduction gear 6. This reduction gear 6 is generally of the planetary type or of the epicyclic type.

[0027] The following description relates to a reduction gear of the epicyclic type, in which the planet carrier and the sun gear are rotatably mobile, the ring gear of the reduction gear being fixed in the reference frame of the engine.

[0028] The reduction gear 6 is located in the upstream part of the turbomachine. The fixed structure (constituting the engine casing or stator 5) comprising here schematically an upstream part 5a and a downstream part 5b is arranged to form an enclosure E around the reduction gear 6. This enclosure E is closed upstream by a seal joint at the level of the bearing through which the fan shaft 4 passes, and downstream by a seal joint at the level of the passage of the BP shaft 3.

[0029] Figure 2 An epicyclic reduction gear 6 is shown. In input, the reduction gear 6 is connected to the BP shaft 3, for example by internal splines 7a. The BP shaft 3 thus drives a pinion called sun gear 7. Generally, the sun gear 7 (the axis of rotation of which coincides with the axis of rotation X of the turbomachine) drives a series of pinions called planetary gears 8, which are uniformly distributed around the axis of rotation X on the same diameter. This diameter is equal to twice the working center distance between the sun gear 7 and the planetary gears 8. The number of planetary gears 8 is generally limited between three and seven for this type of application.

[0030] The assembly of planetary gears 8 is held by a frame called planet carrier 10. Each planetary gear 8 rotates around its own axis Y and engages with the ring gear 9.

[0031] In the output: - In this epicyclic configuration, all planetary gears 8 drive the planet carrier 10 around the axis X of the turbomachine. The ring gear is attached to the engine casing or stator 5 via a ring gear holder 12 and the planet carrier 10 is attached to the fan shaft 4.

[0032] - In another epicyclic configuration, all planetary gears 8 are held by the planet carrier 10 which is attached to the engine casing or stator 5. Each planetary gear 8 drives a ring gear which is fitted to the fan shaft 4 through a ring gear holder 12.

[0033] - In another differential configuration, all planetary gears 8 are held by the planet carrier 10 which is connected to the first fan shaft 5. Each planetary gear 8 drives a ring gear 9 which is fixed to the fan shaft 4 via a ring gear holder 12.

[0034] Each planetary gear 8 is mounted freely rotating by means of bearings 11 of the rolling bearing or hydrodynamic bearing type for example. Each bearing 11 is mounted on one of the shafts 10b of the planet carrier 10 and all the shafts are positioned relative to each other with one or more structural frames 10a of the planet carrier 10. There are several shafts 10b and bearings 11, the number of which is equal to the number of planetary gears. The shafts 10b and the frames 10a can be divided into several parts for reasons of operation, mounting, manufacturing, inspection, repair or replacement.

[0035] For the same reasons mentioned above, the toothings of the planetary gears can be divided into several helices or teeth, each helix or tooth having a median plane P, P'. In our example, we describe in detail the operation of a reduction gear in which each planetary gear comprises two series of herringbone teeth cooperating with a ring gear divided into two ring gear halves: - The upstream ring gear half 9a is composed of a rim 9aa and of an attachment flange half 9ab. On the rim 9aa are the upstream helices which mesh with the helices of the toothings 8d of each planetary gear 8. The helices of the toothings 8d also mesh with the helices of the sun gear 7.

[0036] - The downstream ring gear half 9b is composed of a rim 9ba and of an attachment flange half 9bb. The downstream helices are located on the rim 9ba and mesh with the helices of the toothings 8d of each planetary gear 8. The helices of the toothings 8d also mesh with the helices of the sun gear 7.

[0037] If the spiral width varies between the sun gear 7, the planet gears 8 and the ring gear 9 due to the tooth overlap, they are all centered on the median plane P of the upstream tooth and on the other median plane P' of the downstream tooth.

[0038] Thus, Figure 2 The case of an engaged single reduction gear 6 is shown, i.e. the same toothings 8d of each planet gear 8 cooperate with both the sun gear 7 and the ring gear 9. Even if the toothings 8d comprise two series of teeth, these teeth have the same average diameter and form a single toothing called a herringbone toothings.

[0039] The attachment flange half 9ab of the upstream ring gear 9a and the attachment flange half 9bb of the downstream ring gear 9b form the attachment flange 9c of the ring gear. The ring gear 9 is attached to the ring gear holder by assembling the attachment flange 9c of the ring gear and the attachment flange 12a of the ring gear holder, for example by means of bolted fittings.

[0040] Figure 2 The arrows in the figure describe the oil transport in the reduction gear 6. The oil enters from the reduction gear 6 of the stator portion 5 into the turbine stator vanes 13 by different means which will not be specified in this view as they are specific to one or more types of structures. The turbine stator vanes 13 comprise injectors 13a and arms 13b. The function of the injectors 13a is to lubricate the toothings and the function of the arms 13b is to lubricate the bearings. The oil is fed towards the injectors 13a and exits by the end 13c to lubricate the toothings. The oil is also fed towards the arms 13b and circulates via the supply ports 13d of the bearings. Then, the oil circulates through the shaft into one or more buffer zones 10c and exits through the orifices 10d in order to lubricate the bearings of the planet gears.

[0041] Figure 3 Another example of a reduction gear structure 6 is shown, called double stage engagement, in which each planet gear 8 comprises two separate toothings 8d1, 8d2 configured to cooperate respectively with the ring gear 9 and the sun gear 7.

[0042] In this Figure 3 In this

[0043] The toothings 8d1 engaged with the ring gear 9 have an average diameter D2 and are located in the plane P. The toothings 8d2 engaged with the sun gear 7 have an average diameter D1 and are located in the other plane P'. The planes P, P' are parallel to each other and perpendicular to the axis X. The diameter D2 is smaller than the diameter D1. Finally, each toothings 8d1, 8d2 comprises a single spiral or a series of teeth.

[0044] As mentioned above, this "double stage" structure generates significant moments at the level of the planetary gear 8, in particular because this double stage has asymmetric toothing.

[0045] Figure 4 and Figure 5 A reduction gear 60 is shown, with a symmetric double toothing, which allows to solve the problems mentioned above.

[0046] This reduction gear 60 comprises: - a sun gear 70 having an axis of rotation X, - a ring gear 90 extending around the sun gear 70 and being configured such that it can not rotate around the axis X, and - planetary gears 80 meshing with the sun gear 70 and the ring gear 90 and being held by a planet carrier 100 configured to be rotatably mobile around the axis X.

[0047] A plane H is defined as perpendicular to the axis X and passing substantially through the middle of the reduction gear 60. Figure 5 .

[0048] The sun gear 70 comprises an inner spline 70a for coupling with the BP shaft 30 and an outer toothing 70b for meshing with the planetary gears 80. The toothing 70b has two series of adjacent herringbone teeth separated from each other by an annular groove 72 oriented radially outward. The toothing 70b is symmetrical with respect to the plane H, the teeth of the toothing 70b being located on both sides of the plane H passing through the groove 72.

[0049] The ring gear 90 is formed by two independent rings 90a, 90b and comprises a toothing 90d split into two series of herringbone teeth 90dl, 90d2 carried respectively by the two rings.

[0050] The rings 90a, 90b are arranged symmetrically with respect to the plane H, which thus extends between these rings. The rings are connected by annular connecting flasques 122 and attached to a ring gear holder 120. The flasques 122 are independent from each other, each having a generally S shape on an axial half-section, which provides a certain radial flexibility to the flasques by elastic deformation during operation.

[0051] Each ring 90a, 90b extends around the axis X and is attached by its outer periphery to a respective flasque 122. The inner periphery of the ring comprises one of these series of teeth 90dl, 90d2.

[0052] Like the ring gear 90, the ring gear holder 120 is symmetrical with respect to the plane H.

[0053] Each planetary gear 80 comprises a first toothed portion 82 having an average diameter D1 for engaging the sun gear 70, and a second toothed portion 84 having an average diameter D2 for engaging the ring gear 90, D2 being different from D1 and in particular smaller than D1. The average diameter is measured from the axis Y of each planetary gear 80, and each average diameter represents the average between the maximum and minimum diameters of the toothed portion of the planetary gear.

[0054] Each planetary gear 80 comprises a cylindrical sleeve 86 and an annular web 88 extending substantially radially outward from the middle of the sleeve 86. The toothed portion 84 is divided into two series of herringbone teeth 84d1, 84d2, one on each axial end of the sleeve 86. The toothed portion 82 comprises two series of herringbone teeth 82d1, 82d2, one at the outer periphery of the web 88 and separated from the other by an annular groove 89 opening radially outward with respect to the axis Y.

[0055] The toothed portion 82 is crossed in its middle by a plane H passing through the groove 89, so that the teeth 82d1, 82d2 are arranged on either side of the plane H. The teeth 84d1, 84d2 are also symmetrically arranged with respect to the plane H.

[0056] The outer periphery of the web 88 and the axial dimension of the toothed portion 82 are smaller than the axial distance between the rings 90a, 90b and between the bottles 122, so that each planetary gear 80 can rotate freely in the ring holder 120 and between the rings 90a, 90b and the bottles 122.

[0057] Each planetary gear 80 is guided in rotation by a hydrodynamic bearing 81 comprising a cylindrical body 81a passing through the planetary gear 80, in particular through the sleeve 86 of the planetary gear, and configured to form an oil film inside the planetary gear.

[0058] The body 81a of the bearing 81 extends along the axis Y and comprises at its longitudinal ends extensions 81b housed in orifices forming seats of the carrier 100.

[0059] The body 81a is generally tubular and comprises an internal oil circulation cavity in communication with a first oil supply duct supplying oil to the outer cylindrical surface of the body 81a, so as to form an oil film between this surface and the inner cylindrical surface of the planetary gear 80.

[0060] Figure 6 and Figure 7 The general principle of the application is illustrated. Figure 6The power transmission mechanism is shown, which is no longer a mechanical reduction gear but a mechanical differential 160. The mechanical differential 160 has a sun gear 70, a ring gear 90 and a planet carrier 100, all of which are rotatably movable.

[0061] Figure 6 The differential 160 itself is shown, and Figure 7 The turbomotor 101 comprising this differential 160 is shown.

[0062] The turbomotor 101 is similar to the turbomotor shown in Figure 1 , so the above description regarding Figure 1 applies to the turbomotor 1 in Figure 7 . Figure 7 The particularity of the turbomotor 101 shown is that it comprises two propeller screws S1, S2, coaxial, counter-rotating and mounted upstream of the gas generator.

[0063] Figure 6 The differential 160 of Figure 7 comprises: - a sun gear 70, the rotation axis of which is centered on the main axis X of the turbomotor 101, - a ring gear 90 extending around the sun gear 70 and the axis X, - planet gears 80 meshing with the sun gear 70 and the ring gear 90, and - a planet carrier 100 having a rotation axis coinciding with the axis X and carrying bearings 81 for guiding the planet gears 80 in rotation about an axis Y parallel to the axis X and distributed around this axis X.

[0064] The sun gear 70 is coupled to the shaft of the gas generator, in this case the low-pressure shaft 3.

[0065] The ring gear 90 is coupled to a first shaft 104a which drives in rotation a first of the two propeller screws S1.

[0066] The planet carrier 100 is coupled to a second shaft 104b which makes the second propeller screw S2 rotate.

[0067] In the example shown, the propeller S1 connected to the ring gear 90 is located downstream of the propeller S2 connected to the planet carrier 100. The shaft 104a extends around the shaft 104b and is guided in rotation with respect to this shaft 104b by at least one or more bearings 200. The shaft 104a is also guided in rotation by one or more bearings 202 carried by a support 204 fixed to a stator casing 206 of the turbine engine. This stator casing 206 extends around the differential 160 and is fixed to another support 208 which carries one or more bearings 210 for guiding the rotation of the low-pressure shaft 3.

[0068] The propellers S1, S2 rotate around the same axis which is the axis X of the turbine engine 101.

[0069] Each planet gear 80 has an axis of rotation Y which is parallel to the axis X and comprises a first toothing 82 meshing with the sun gear 70 and a second toothing 84 meshing with the ring gear 90.

[0070] The first toothing 82 of each planet gear 80 comprises two series of teeth 82d1, 82d2 axially spaced apart and arranged on either side of a median plane H of the planet gear 80. Figure 8 and Figure 9 ).

[0071] The second toothing 84 comprises two series of teeth 84d1, 84d2 axially distant from each other and arranged on either side of the median plane H and separated from each other by the first toothing 82. These series of teeth 84d1, 84d2 of the second toothing 84 are thus arranged on either side of the first toothing 82.

[0072] The median plane H is perpendicular to the axis Y of the planet gear 80 and can be a plane of symmetry of the planet gear 80.

[0073] The diameter D1 of the first toothing 82 of each planet gear 80 is greater than the diameter D2 of the second toothing 84 of the planet gear 80. Figure 8 and Figure 9 The planet gears 80 in Figure 4 and Figure 5 are similar to those in and

[0074] The above explanations are therefore applicable to these planet gears 80.

[0075] In the detailed description of a more particular embodiment of the application Figure 8 and Figure 9It can be seen that the toothing 70b of the sun gear 70 is formed by two series of teeth 70b1, 70b2 which are axially distant from each other and which mesh respectively with the two series of teeth 82d1, 82d2 of the first toothing 82 of each planetary gear 80.

[0076] The ring gear 90 comprises a toothing 90d formed by two series of teeth 90d1, 90d2 which are axially distant from each other and which mesh respectively with the two series of teeth 84d1, 84d2 of the second toothing 84 of each planetary gear 80.

[0077] The ring gear 90 is divided into two ring gear halves: - an upstream ring gear half 190a, composed of a rim 190aa and of an attachment flange half 190ab. On the rim 190aa there is the first series of teeth 90d1 of the toothing 90d which meshes with one of the series of teeth 84d1 of the second toothing 84 of each planetary gear 80; - a downstream ring gear half 190b, composed of a rim 190ba and of an attachment flange half 190bb. On the rim 190ba is the second series of teeth 90d2 of the toothing 90d which meshes with the other of the series of teeth 84d2 of the second toothing 84 of each planetary gear 80.

[0078] The two ring gear halves 190a, 190b are symmetrical with respect to the plane H and are located on either side of the series of teeth 82d1, 82d2 of the first toothing 82 of each planetary gear 80.

[0079] The flange halves 190ab, 190bb are attached together to form the flange of the ring gear 90 and are also attached to the flange of the ring gear holder 120 which is connected to the drive shaft 104a of the propeller S1.

[0080] In the example shown, the shaft 104a comprises a cylindrical section 104a1 which is connected to the ring gear 90 by the ring gear holder 120. The ring gear holder 120 comprises a cylindrical wall 120a which surrounds at least part of the ring gear 90, in particular the ring gear half 190a, and a frustoconical section 120b for connecting the first shaft 104a to the cylindrical wall 120a. In the example shown, the frustoconical wall 120b thus flares downstream.

[0081] The diameter D3 of the cylindrical section 104a1 is less than the diameter D4 of the cylindrical wall 120a, or even less than the outer diameter D5 of the planetary carrier 100, as is shown in the example.

[0082] The cylindrical section 104a1 of the first shaft 104a is preferably integral with the frustoconical and cylindrical walls 120a, 120b of the ring gear holder 120.

[0083] The shaft 104b comprises a cylindrical section 104b1 connected to the disc 100a of the planet carrier 100 and for example integral with this disc 100a or with the planet carrier 100. The diameter D6 of the section 104b1 is less than D3.

[0084] Alternatively, the ring gear 90 can also be formed in one piece.

[0085] The series of teeth 82d1, 82d2, 70b1, 70b2 of the toothings 82, 70b are V-shaped or straight. The series of teeth 84d1, 84d2, 90d1, 90d2 of the toothings 84, 90 are V-shaped.

[0086] The planet carrier 100 comprises a cage delimited by two discs 100a connected by a bridge 100b.

[0087] The cylindrical bodies 81a extend between the discs 100a and are attached to these discs. The cylindrical bodies 81a are distributed around the axis X and define an axis Y. These bodies 81a pass through the planetary gears 80 to guide the planetary gears.

[0088] The planetary gears 80 are centred and guided in rotation respectively by the sliding bearings on the cylindrical bodies 81a.

[0089] Each body 81a extends along the axis Y and comprises at its longitudinal end an extension 81b housed in an orifice of a seat formed in the planet carrier 100.

[0090] Each body 81a is generally tubular and comprises an internal oil circulation cavity in communication generally with an oil supply duct supplying oil to the outer cylindrical surface of the body 81a to form the sliding bearing.

[0091] The use of a symmetrical double planetary gear 80 limits the occurrence of torques on the bearings.

[0092] The cage formed by the discs 100a and the bridge 100b can also be formed in one piece, as shown in the example.

[0093] In a variant of the application not shown, the propeller can be located downstream of the turbine engine or at least in a position different from Figure 7 that shown.

[0094] The differential according to the application is adapted to provide a large reduction ratio, for example greater than 5. The differential has a small overall radial size, easy to integrate into a turbine engine. The turbine engine is preferably double-flow.

Claims

1. A twin-propeller turbine engine (101) for an aircraft, the turbine engine (101) having a main axis (X) and comprising: - First propeller (S1). - Second propeller (S2) - A gas generator, the gas generator including a power transmission mechanism, a first shaft (104a) for rotating the first propeller (S1) about the main axis (X), and a second shaft (104b) for rotating the second propeller (S2) about the main axis (X). The characteristic feature is that the power transmission mechanism is a mechanical differential (160), the mechanical differential comprising: - Sun gear (70), which is centered on the main axis (X) and connected to the shaft (3) of the gas generator. - Gear ring (90), the gear ring is centered on the main axis (X) and connected to the first shaft (104a). - Planet carrier (100), the planet carrier being centered on the main axis (X) and connected to the second axis (104b), and - Planetary gears (80), which are carried by the planet carrier (100) and mesh with the sun gear (70) and the ring gear (90), each planetary gear (80) having a rotation axis (Y) parallel to the main axis (X), and including a first tooth (82) meshing with the teeth of the sun gear (70) and a second tooth (84) meshing with the teeth of the ring gear (90), the first tooth (82) of each planetary gear (80) including two series of teeth (82d1, 82d2) spaced apart by an axial distance and arranged on both sides of the intermediate plane (H) of the planetary gear, the intermediate plane being perpendicular to the axis (Y) of the planetary gear (80), the second tooth (84) of each planetary gear (80) including two series of teeth (84d1, 84d2) spaced apart by an axial distance and arranged on both sides of the intermediate plane (H) and the series of teeth (82d1, 82d2) of the first tooth (82).

2. The turbine engine (101) according to the preceding claim, wherein, The diameter (D1) of the first tooth (82) of each planetary gear (80) is greater than the diameter of the second tooth (84) of the planetary gear (80).

3. The turbine engine (101) according to claim 1 or 2, wherein, The teeth (70b) of the sun gear (70) include two series of teeth (70b1, 70b2) that are axially spaced from each other and mesh with two series of teeth (82d1, 82d2) of the first teeth (82) of each planetary gear (80).

4. The turbine engine (101) according to any one of the preceding claims, wherein, The teeth (90d) of the gear ring (90) include two series of teeth (90d1, 90d2) that are axially spaced apart from each other and respectively mesh with two series of teeth (84d1, 84d2) of the second teeth (84) of each planetary gear (80).

5. The turbine engine (101) according to any one of the preceding claims, wherein, The gear ring (90) has an upstream gear ring half (190a) and a downstream gear ring half (190b), which are symmetrical and arranged on both sides of the series of teeth (82d1, 82d2) of the first tooth portion (82) of each planetary gear (80).

6. The turbine engine (101) according to any one of the preceding claims, wherein, The propellers (S1, S2) rotate in opposite directions.

7. The turbine engine (101) according to any one of the preceding claims, wherein, The first tooth (82) of each planetary gear (80) and the tooth (70b) of the sun gear (70) are of straight or herringbone type.

8. The turbine engine (101) according to any one of the preceding claims, wherein, The second tooth (84) of each planetary gear (80) and the tooth (90d) of the gear ring (90) are herringbone shaped.

9. The turbine engine (101) according to any one of the preceding claims, wherein, The planetary gear (80) is guided by the sliding bearing of the planet carrier (100).

10. The turbine engine (101) according to any one of the preceding claims, wherein, The planetary carrier (100) includes an integral cage in which the planetary gears (80) are housed.

11. The turbine engine (101) according to any one of the preceding claims, wherein, The first shaft (104a) extends about the second shaft (104b) and is guided by at least one bearing to rotate about the second shaft (104b).

12. The turbine engine (101) according to any one of the preceding claims, wherein, The first shaft (104a) includes a cylindrical section (104a1) connected to the gear ring (90) via a gear ring retainer (120). The gear ring retainer (120) includes a cylindrical wall (120a) surrounding at least a portion of the gear ring (90) and a truncated conical section (120b) for connecting the first shaft (104a) to the cylindrical wall (120a). The diameter (D3) of the cylindrical section (104a1) of the first shaft (104a) is smaller than the diameter (D4) of the cylindrical wall (120a) of the gear ring retainer (120), or even smaller than the outer diameter (D5) of the planet carrier (100).

13. The turbine engine (101) according to any one of the preceding claims, wherein, The cylindrical section (104a1) of the first shaft (104a) is integral with the truncated conical and cylindrical walls (120a, 120b) of the gear ring retainer (120).

14. The turbine engine (101) according to any one of the preceding claims, wherein, The second shaft (104b) includes a cylindrical section (104b1) that is connected to the disk (100a) of the planet carrier (100) and forms an integral part with, for example, the disk (100a) or the planet carrier (100).

15. The turbine engine (101) according to any one of the preceding claims, wherein, Each of the planetary gears (80) is guided to rotate by a hydrodynamic bearing (81) comprising a cylindrical body (81a) passing through the planetary gear (80), the body (81a) extending along the axis of rotation (Y) of the planetary gear and including an extension (81b) at the longitudinal end of the body, the extension being received in an aperture forming a seat portion in the planet carrier (100).

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