Electrically insulating turbomachine seal

Abstract

This presentation concerns a gas turbine engine comprising: - a casing, - a turbine section, - a stator and a rotor, - an electrical machine, and - a seal to ensure fluid sealing between the rotor and stator components. The seal comprises a gasket formed from an electrically insulating material and arranged to prevent the propagation of an electric current between the rotor and stator components through the seal. The insulating material comprises boron nitride. Figure for the abstract: Fig. 3

Description

Title of the invention: Electrically insulating turbomachine seal Technical field

[0001] This disclosure relates to the field of turbomachines. More specifically, it relates to sealing devices, in particular sealing devices for turbomachine bearings. STATE OF THE ART

[0002] Certain parts of a turbomachine are subject to the circulation of leakage electric currents or induced electric currents which can be emitted by electrical machines, or by the passage of high intensity currents, present in the turbomachine.

[0003] The circulation of these electric currents can lead to damage or generate wear in parts of the turbomachine, such as parts in relative motion with respect to other parts of the turbomachine. These parts can be, for example, bearings or seals.

[0004] It is therefore necessary to electrically insulate these parts in order to avoid their degradation, harming their performance or creating resistant forces, which harm the efficiency of the turbomachine. GENERAL STATEMENT

[0005] An aim of the present disclosure is to increase the service life of seals of an aircraft turbomachine.

[0006] To this end, according to one aspect of the present disclosure, a gas turbine engine is provided comprising: a casing, a turbine section and a stator part mounted fixedly relative to the casing and a rotor part adapted to be driven in rotation relative to the stator part, by means of the turbine section. The engine further comprises an electric machine and a seal. The electric machine comprises an electric machine stator and an electric machine rotor, adapted to be driven in rotation relative to the electric machine stator, the electric machine rotor being mechanically coupled to the rotor part and the stator of the electric machine being mounted fixedly relative to the casing.The seal provides a fluid seal between the rotor part and the stator part, the seal comprising a seal part formed from an electrically insulating material and arranged to prevent propagation of an electric current between the rotor part and the stator part through the seal, the insulating material comprising boron nitride.

[0007] Such an engine comprises a seal comprising a seal part capable to electrically isolate the rotor part from the stator part.

[0008] The presence of the boron nitride sealing part makes it possible to prevent the propagation of electric currents through the seal, and thus to preserve the seal from damage caused by the propagation of these electric currents.

[0009] In addition, boron nitride has been found to have fluid sealing and electrical insulation performance that improves the operation of the seal.

[0010] The life span and reliability of the engine is therefore improved.

[0011] Advantageously, but optionally, the disclosed engine comprises at least one of the following characteristics, taken alone or in any combination:

[0012] - the seal piece is attached to one of the stator piece and the rotor piece, and is arranged facing each other of the stator part and the rotor part;

[0013] - the insulating material is crystalline boron nitride with hexagonal crystal structure h-BN;

[0014] - the insulating material consists of a matrix and boron nitride fillers crystalline with hexagonal crystal structure, dispersed in the matrix;

[0015] - the matrix of the insulating material is made of amorphous boron nitride or a polymer non-conductive;

[0016] - the seal is a segmented radial seal comprising a crown outer annular, and wherein the seal part comprises a plurality of segments positioned radially internally relative to the outer annular crown, the segments being arranged successively and circumferentially end to end to form a ring;

[0017] - the seal is a floating ring seal comprising a device for retainer surrounding the seal part and comprising an annular retaining groove, and wherein the seal part comprises a ring positioned in the retaining groove of the retainer, the retaining groove allowing radial movement of the ring while preventing axial movement of the ring;

[0018] - the seal is a radial face seal comprising a fixed ring and a pin, and wherein the joint part comprises a contact ring arranged radially internally relative to the fixed ring, and being locked in rotation relative to the fixed ring by the pin;

[0019] - the seal is a brush seal comprising a retaining ring annular having a recess, and wherein the seal part comprises an annular brush housed in the recess of the retaining ring;

[0020] - the engine comprises an enclosure suitable for containing lubricating fluid, the stator part being a wall of the enclosure, and the enclosure comprising an opening at through which the rotor part extends, the seal being arranged between the enclosure wall and the rotor part to limit leakage of lubricating fluid through the opening;

[0021] - the motor includes an additional seal positioned around the rotor part, in contact with the seal and between the seal and the enclosure, the additional seal comprising a helical groove adapted to push the lubricating fluid from the seal into the enclosure;

[0022] - the additional seal is: - either ceramic, - either in a composite material comprising a hexagonal boron nitride filler and an amorphous boron nitride or polymer matrix, - either placed in a layer of electrical insulation;

[0023] - the electric machine is a motor and / or an electric generator.

[0024] According to another aspect, there is provided an aircraft comprising an airframe and a gas turbine engine as previously described and wherein the gas turbine engine is attached to the airframe. DESCRIPTION OF FIGURES

[0025] Other characteristics, aims and advantages will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0026] [Fig.l] illustrates an aircraft schematically;

[0027] [Fig.2] illustrates a schematic sectional view of an aircraft propulsion unit;

[0028] [Fig. 3] illustrates a partial and schematic sectional view of a propulsion assembly comprising an electric machine according to an embodiment of the present invention;

[0029] [Fig.4] illustrates a path of an electric current passing through a seal, according to an embodiment of the present invention;

[0030] Figures [Fig.5a], [Fig.5b], [Fig.5c] and [Fig.5d] schematically illustrate different types of seal, according to an embodiment of the present invention.

[0031] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION Aircraft

[0032] An aircraft is a device configured to rise and move in the air, and may, for example, be an airplane, civil or military, or even a helicopter. The aircraft 100, as illustrated in [Fig.l] comprises an airframe and a propulsion unit 1. The aircraft 100 is for example an airplane. In this case, the airframe comprises a fuselage, a wing comprising two wings, empennages, flight control surfaces and landing gear. In the example illustrated in [Fig.l], the aircraft 100 comprises two propulsion units 1, each propulsion unit 1 being fixed on a respective wing of the airframe. Propulsion unit

[0033] The propulsion unit 1, as illustrated by [Fig. 2] comprises a gas turbine engine 2 (or turbomachine) and a nacelle 3, and has a main direction extending along a longitudinal axis XX. The propulsion unit 1 is configured to be fixed to the airframe of the aircraft 100, for example under its wings, in the case of an airplane, and this by means of a pylon (or mast). The propulsion unit 1 can also be mounted on the wing of the airplane or at the rear of its fuselage, or even be integrated into its fuselage.

[0034] The engine 2 may be a twin-spool, twin-flow, direct-drive ducted turbojet engine, as described below, but may also have a different number of spools and / or flows, and / or be another type of turbojet engine, such as a geared turbojet engine or a turboprop engine, with or without afterburner, ducted or unducted.

[0035] Unless otherwise specified, the terms “upstream” and “downstream” are used with reference to the overall direction of airflow through the propulsion unit 1 in operation. Similarly, an axial direction corresponds to the direction of the longitudinal axis XX and a radial direction is a direction perpendicular to the longitudinal axis XX and intersecting the longitudinal axis XX. Furthermore, an axial plane is a plane containing the longitudinal axis XX and a radial plane is a plane perpendicular to the longitudinal axis XX. A circumference is understood to be a circle belonging to a radial plane and whose center belongs to the longitudinal axis XX. A tangential or circumferential direction is a direction tangent to a circumference: it is perpendicular to the longitudinal axis XX but does not pass through the longitudinal axis XX.Finally, the adjectives "inner" (or "internal") and "outer" (or "external") are used with reference to a radial direction so that the inner part of an element is, in a radial direction, closer to the longitudinal axis XX than the outer part of the same element.

[0036] The engine 2 comprises, from upstream to downstream, a fan 20, a compressor section 22, comprising a low pressure compressor 220 and a high pressure compressor 222, a combustion chamber 24 and a turbine section 26, comprising a high pressure turbine 262 and a low pressure turbine 260.

[0037] The fan 20 comprises a fan rotor 201. The fan rotor 201 comprises fan blades and an engine nose cone. The fan rotor 201 is driven in rotation by a low pressure shaft 280, and, if necessary, via a reducer.

[0038] The compressor section 22 comprises a succession of stages each comprising a wheel of moving blades 221 rotating in front of a wheel of fixed blades 223. The turbine section 26 also comprises a succession of stages each comprising a wheel of fixed blades 263 behind which a wheel of moving blades 261 rotates.

[0039] The fan 20, the rotor part of the low-pressure compressor 220, and the rotor part of the low-pressure turbine 260 are connected to each other by the low-pressure shaft 280 extending along the longitudinal axis XX, thus forming a low-pressure body 200. The rotor part of the high-pressure compressor 222 and the rotor part of the high-pressure turbine 262 are connected to each other by a high-pressure shaft 282 extending along the longitudinal axis XX, thus forming a high-pressure body 202. The low-pressure shaft 280 is generally housed, over a section of its length, in the high-pressure shaft 282 and is coaxial with the high-pressure shaft 282. The low-pressure body 200 and the high-pressure body 202 form the rotor parts of the engine 2 called rotor. More specifically, the low pressure shaft 280 and the high pressure shaft 282 can be referred to as the rotor part of the engine 2.

[0040] The fixed blade wheel 223 of the compressor section 22 and the fixed blade wheel 263 of the turbine section 26 thus form stator parts of the engine 2 called stator or stator part.

[0041] The compressor section 22, the combustion chamber 24 and the turbine section 26 are surrounded by a motor casing 23, to which the stator parts of the low-pressure compressor 220, the high-pressure compressor 222, the high-pressure turbine 262 and the low-pressure turbine 260 are connected, while the fan 20 is surrounded by a fan casing 25. The motor casing 23 and the fan casing 25 are connected to each other by profiled arms 27 forming rectifiers (or OGV for "Outlet Guide Vanes" in English terminology) distributed circumferentially all around the longitudinal axis XX. Hereinafter, any part of the engine 2 mounted fixedly relative to the motor casing 23 and / or to the fan casing 25 will be called a stator.

[0042] The longitudinal axis XX defines the axis of rotation for the fan 20, the rotor parts 221 of the compressor section 22 and the rotor parts 261 of the turbine section 26, in other words for the low pressure body 200 and the high pressure body 202 which are each capable of being driven in rotation about the longitudinal axis XX relative to the engine casing 23 and the fan casing 25.

[0043] Advantageously and as illustrated by [Fig. 3], the motor 2 comprises one or more bearings 283 supporting the low pressure shaft 280 in rotation around the longitudinal axis XX relative to the stator and one or more bearings 283 supporting the shaft high pressure 282 rotating around the longitudinal axis XX relative to the stator. Each bearing 283 may comprise a rolling bearing. Each bearing 283 is arranged in an enclosure 284 configured to ensure its lubrication. The enclosure 284 provided around each bearing 283 preferably contains a mixture of air and lubricating fluid. The lubricating fluid is adapted to ensure the lubrication of the bearing 283 but also the cooling of the bearing 283. Each enclosure 284 comprises a wall 2841 fixedly mounted on the motor casing 23. The wall 2841 of each enclosure 284 delimits a cavity containing the bearing 283 and has an opening 2842 through which the shaft 280, 282 extends.

[0044] Furthermore, the engine 2 may comprise one or more electrical machines 29 connected to the high-pressure body 202 and / or to the low-pressure body 200. With regard to the low-pressure body 200, power may be taken, through a power take-off on the low-pressure shaft 280, downstream of the low-pressure turbine 260. The electrical machine 29 may operate as an electrical generator, which transforms the mechanical energy received from the low-pressure shaft 280 into electrical energy. The electrical energy generated by the electrical machine 29 may be stored in an electrical storage means. The electrical machine 29 may also operate as an electric motor, which transforms the previously stored electrical energy into mechanical energy to assist the rotation of the low-pressure shaft 280. The electrical machine 29 connected to the low-pressure body 200 comprises a stator 291 and a rotor 292.The rotor 292 is capable of being driven in rotation relative to the stator 291, and is mechanically coupled to the low pressure shaft 280.

[0045] In the same way, power can be taken from the high-pressure body 202, for example through a power take-off on the high-pressure shaft 282, upstream of the high-pressure compressor 222. The power is extracted by a high-pressure power extraction shaft, extending radially relative to the high-pressure shaft 282. The power is taken through a gear comprising a first pinion fixedly mounted on the high-pressure shaft 282 and a second pinion fixedly mounted on the extraction shaft, the second pinion meshing with the first pinion. The high-pressure power extraction shaft opens onto a reduction gear. As previously, the reduction gear is connected to an electrical machine 29 which can operate as an electrical generator, which transforms the received mechanical energy into electrical energy.The electrical machine 29 connected to the high pressure body 202 is distinct and different from the electrical machine 29 connected to the low pressure body 200. The electrical machine 29 connected to the high pressure body 202 comprises a stator 291 and a rotor 292. The rotor 292 is capable of being driven in rotation relative to the stator 291, and is mechanically coupled to the high pressure shaft 282.

[0046] Each electrical machine 29 may comprise an electrical generator and / or a electric motor or preferably be an electric motor / generator assembly. Thus, the power taken from one or both shafts 280, 282, whether or not stored, is intended to be reinjected into one or the other or both shafts 280, 282, by the electric machine 29 operating as an electric motor.

[0047] The electrical storage means may be of the lithium-ion battery, super capacity or fuel cell type.

[0048] The engine 2 may also comprise at least one accessory box, called AGB (for “Accessory gear box” in English terminology), for example housed in a cavity provided within the nacelle 3. The accessory box comprises a set of rotating elements, such as gears, making it possible to drive a plurality of shafts in rotation around their own axis, accessories being mounted on these shafts to derive useful mechanical power from their rotation. The gear assembly is itself driven using a power take-off shaft (or RDS for “Radial Drive Shaft” in English terminology) connecting, possibly via a transfer case, the accessory case to at least one of the high pressure body 202 and the low pressure body 200, typically by being meshed with at least one of the high pressure shaft 282 and the low pressure shaft 280.In this regard, the power take-off shaft may extend inside a longitudinal cavity provided within one of the arms 27. In this way, mechanical power may be taken from at least one of the high pressure shaft 282 and the low pressure shaft 280 to be delivered to at least one of the accessories via the accessory housing.

[0049] The combustion chamber 24 comprises a fuel injection rail and a plurality of ignition injectors. The injection rail and / or the ignition injectors constitute fuel-consuming members of the engine 2.

[0050] Advantageously, the engine 2 may also comprise defrosting means located on upstream parts of the engine 2 and more particularly on the fan 20. The defrosting means are powered by electrical cables traversed by high currents. These electrical cables are configured to connect the defrosting means to an electrical machine 29 of which a stator 291, for example a magnet, is fixed to the engine casing 23 and of which a rotor 292, for example another magnet, is fixed to the fan rotor 201.

[0051] The nacelle 3 extends radially outside the engine 2, all around the longitudinal axis XX, so as to surround both the fan casing 25 and the engine casing 23, and to define, with a downstream part of the engine casing 23, a downstream part of a secondary vein B, the upstream part of the secondary vein B being defined by the fan casing 25 and an upstream part of the engine casing 23. The upstream part of the nacelle 3 further defines an air inlet 31 through which the fan 20 sucks in the air flow circulating through the propulsion unit 1. The nacelle 3 is integral with the fan casing 25 and attached and fixed to the aircraft 100 by means of the mast.

[0052] In operation, the fan 20 draws in an air flow, a portion of which, circulating within a primary vein A passing through the engine casing 23 from one side to the other, is successively compressed within the compressor section 22, ignited within the combustion chamber 24 by combustion of fuel, and expanded within the turbine section 26 before being ejected from the engine 2. Another portion of the air flow circulates within the secondary vein B which takes an elongated annular shape surrounding the engine casing 23, the air drawn in by the fan 20 being straightened by the straighteners 27 and then ejected from the propulsion unit 1. In this way, the propulsion unit 1 generates thrust. This thrust can, for example, be used for the benefit of the aircraft 100 on which the propulsion unit 1 is attached and fixed.

[0053] Sealing gasket

[0054] As explained previously, each bearing 283 supporting the low pressure shaft 280 or the high pressure shaft 282 is included in an enclosure 284 containing lubricating fluid ensuring the lubrication and cooling of the bearing 283. The lubricating fluid included in the enclosures 284 is a two-phase mixture consisting essentially of air and lubricant, injected into the enclosure 284 in the form of jets, drops, droplets and mist.

[0055] Each enclosure 284 is itself included in a second enclosure 285 called the air enclosure. The air enclosure 285 must remain free of lubricating fluid because any rise of lubricating fluid in certain compartments of the engine 2 would be detrimental to proper operation of the engine 2. Any migration of lubricating fluid outside the enclosure 284 must therefore be avoided. The air enclosures 285 essentially serve as pressurized barriers such that the pressure differences ensure that the leakage air flows between the enclosures 284 and the air enclosures 285 always take place from the air enclosure 285 towards the enclosure 284, thus preventing the lubricating fluid from escaping from the enclosure 284.

[0056] The engine 2 preferably comprises a seal 4 configured to ensure the sealing of the enclosures 284 comprising the lubrication fluid of the bearings 283. The seal 4 makes it possible to contain the lubrication fluid in the enclosure 284 and thus prevent the passage of the lubrication fluid from the enclosure 284 to the respective air enclosure 285.

[0057] Each seal 4 is preferably positioned around the low pressure shaft 280 or the high pressure shaft 282, between the wall 2841 of the enclosure 284 and the shaft 280, 282, upstream or downstream of the respective enclosure 284 and between the enclosure 284 and the air enclosure 285, to limit a leak of lubricating fluid through the opening 2842. Optionally, a seal 4 can further be positioned around the low pressure shaft 280 or the high pressure shaft 282, between a wall 2851 of the air enclosure 285 and the shaft 280, 282, upstream or downstream of the respective air enclosure 285. The seal 4 is advantageously fixed to the enclosure 284 and / or to the air enclosure 285. The seal 4 is therefore used between two parts in relative movement with respect to each other, the shaft 280, 282, and the motor casing 23, the enclosure 284 and the air enclosure 285 being mounted fixed with respect to the motor casing 23.

[0058] The seal 4 is an annular fluid seal. The seal 4 preferably comprises an annular seal part 41 extending all around the shaft 280, 282 and is positioned directly opposite the shaft 280, 282. The seal part 41 comprises an electrically insulating material capable of preventing propagation of an electric current between the shaft 280, 282, around which the seal 4 is positioned and the motor housing 23, through the seal 4. The insulating material comprises boron nitride. Boron nitride (BN) has friction properties similar to those of graphite (hC).

[0059] According to one embodiment, the insulating material forming the electrically insulating joint part 41 is crystalline boron nitride with a hexagonal crystalline structure.

[0060] According to another embodiment, the insulating material forming the electrically insulating joint part 41 consists of a matrix and fillers of crystalline boron nitride with hexagonal crystalline structure (h-BN), dispersed in the matrix. Preferably, the matrix of the insulating material is made of amorphous boron nitride or a non-conductive polymer such as for example polytetrafluoroethylene (PTFE), polyimide, polyetheretherketone (PEEK) or even phenoplast.

[0061] Thus, such a seal 4 comprising a boron nitride seal part 41 has a low coefficient of friction, good wear resistance, good dynamic sealing, with low permeability, a good service life and good electrical insulation. The presence of such a seal 4 makes it possible to avoid the addition of an insulating intermediate part between the seal 5 and the motor casing 23 and / or the shaft 280, 282.

[0062] The seal 4 thus makes it possible to prevent the passage of an electric current between the motor casing 23 and the shaft 280, 282, through the seal 4. The electric current can be created by the electric machine 29 and induce losses of electric power and premature wear of the parts of the motor 2 if it circulates through the seal 4, as illustrated by [Fig. 4]. [Fig. 4] in fact illustrates an embodiment in which the rotor 292 of the electric machine 29 is driven by the low pressure shaft and generates an induced electric current between the casing 23 and the low pressure shaft 282. The seal 4 comprising a seal part 41 makes it possible to block the passage of this current.

[0063] Advantageously, the motor 2 can comprise, for each seal 4, an additional seal 40, annular, positioned around the shaft 280, 282, in contact with the seal 4 as illustrated by [Fig.4]. The additional seal 40 is positioned between the seal 4 and the enclosure 284. According to a possible embodiment, the additional seal 40 is a de-oiling spiral. The de-oiling spiral comprises a helical groove suitable for repelling the lubricating fluid from the seal 4. Indeed, the lubricating fluid from the enclosure 284 being driven in rotational movement by its contact with the shaft 280, 282, the helical groove, by its helical orientation opposite to the direction of rotation of the shaft 280, 282, opposes a barrier to the approach of the lubricating fluid to the seal 4. The additional seal 40 is advantageously: either made of ceramic, or of a composite material comprising a hexagonal boron nitride filler and an amorphous boron nitride or polymer matrix, or placed in a layer of electrical insulation.

[0064] The seal 4 may be of different types. By way of non-limiting examples, the seal 4 may be a segmented radial seal, a floating ring seal, a radial face seal or a brush seal.

[0065] Segmented radial seal

[0066] According to one embodiment, the seal 4 is a segmented radial seal 5. The segmented radial seal 5, as illustrated by [Fig.5a], comprises an annular body 51 comprising an external crown 511 and an annular flange 512, assembled to each other by pins or pins engaged in radial orifices of the external crown 511 and of the flange 512.

[0067] The segmented radial seal 5 also comprises a plurality of segments 52 which are arranged radially internal to the crown 511, successively and circumferentially end to end to form a ring. The seal part 41 described previously comprises the segments 52 of the segmented radial seal 5. The segments 52 are thus made of boron nitride so as to allow the seal 5 to have good dynamic sealing, with low permeability, a good service life, very good resistance to high temperatures and good electrical insulation without requiring the addition of an insulating intermediate part between the seal 5 and the motor casing 23 or the shaft 280, 282.

[0068] Each segment 52 may comprise two radial tabs 521 at its circumferential ends. Each tab 521 comprises a mounting groove for a first elastic annular element 53, which element surrounds all the carbon segments 52 in order to hold them in the annular body 51.

[0069] The crown 511 may comprise an annular rim 5111 and also radial fingers 5112 regularly spaced circumferentially and which are opposite the rim 5111. The flange 512 is positioned in the extension of the rim 5111 and may be fixed to the rim 5111 via pins. The radial fingers 5112 separate, in the axial direction, the segments 52 of the enclosure 284. These fingers 5112 ensure with the rim 5111 of the crown 511 and the flange 512 an axial locking of the segments 52. The flange 512 and the rim 5111 form a radial wall of the body 51.

[0070] The first elastic annular element 53 may comprise a helical spring. The segmented radial seal 5 may advantageously comprise a plurality of second elastic elements 54 arranged to exert an axial force on the segments 52 tending to press the segments 52 against the fingers 5112. These second elastic elements 54 are mounted in axial housings of the segments 52 and are elastically prestressed between the radial wall of the body 511 and the bottom of the housings of the segments 52. The second elastic elements 54 may be helical springs.

[0071] Floating ring seal

[0072] According to one embodiment, the seal 4 is a floating ring seal 6. The floating ring seal 6, as illustrated in [Fig.5b], comprises an annular holding device 61 and an annular ring 62 positioned in the holding device 61 in a radially internal manner.

[0073] The holding device 61 is fixedly mounted on the engine casing 23. The holding device 61 has a holding groove 611 in which the ring 62 is received. The holding groove 611 is annular. The holding groove 611 is positioned radially internally. The walls of the holding groove 611 have a surface roughness of between 0.2 and 0.4 μm in order to allow the ring 62 to move in rotation relative to the holding device 61. The holding groove 611 makes it possible to guide the rotational movement about the longitudinal axis XX of the ring 62 in the groove 611. The annular holding groove 611 allows radial movement of the ring 62 while preventing axial movement of the ring 62.

[0074] The ring 62 advantageously has an axial thickness of between 10 and 15 mm. The ring 62 is slidably mounted around the axis of the shaft 280, 282. The seal part 41 described previously comprises the ring 62. The ring 62 is made of boron nitride so as to allow the seal 6 to have good dynamic sealing, with low permeability, a good service life, very good resistance to high temperatures and good electrical insulation without requiring the addition of an intermediate insulating part between the seal 6 and the motor casing 23 or the shaft 280, 282.

[0075] Radial face seal

[0076] According to one embodiment, the seal 4 is a radial face seal 7 (or “facial ring” according to English terminology). The radial face seal 7, as illustrated in [Fig.5c], comprises an annular fixed ring 71 and an annular contact ring 72. The fixed ring 71 is fixedly mounted on the engine casing 23. The fixed ring 71 comprises a crown 710 and a branch 711. The branch 711 extends radially inward from the crown 710.

[0077] The contact ring 72 is positioned radially internal to the crown 710 of the fixed ring 71. The contact ring 72 comprises an internal face 721 facing the shaft 280, 282 and a radial face 722 in contact with the branch 711 of the fixed ring 71, the branch 711 separating the radial face 722 of the contact ring 72 from the wall of the enclosure 284. The internal face 721 and the radial face 722 are configured to ensure the sealing of the radial face seal 7. The seal part 41 comprises the contact ring 72. The contact ring 72 is made of boron nitride so as to allow the seal 7 to have good dynamic sealing, with low permeability, a good service life, very good resistance to high temperatures and good electrical insulation without requiring the addition of a intermediate insulating part between the seal 7 and the motor housing 23 or the shaft 280, 282.

[0078] Preferably, the radial face seal 7 comprises an anti-rotation pin 73 positioned in a radial direction between the fixed ring 71 and the contact ring 72 so as to prevent the contact ring 72 from rotating relative to the fixed ring 71.

[0079] Brush seal

[0080] According to one embodiment, the seal 4 is a brush seal 8. The brush seal 8, as illustrated in [Fig.5d], comprises an annular retaining ring 81 comprising an annular recess 811 and an annular brush 82 housed in the recess 811. The recess 811 is positioned radially internally. Advantageously, the brush seal 82 further comprises an annular toric core 83.

[0081] The brush 82 preferably comprises an annular sleeve 821 surrounding the toric core 83 and bristles 822 extending from the sleeve 821, in a radial direction towards the shaft 280, 282. The free ends of the bristles 822 are directed towards the shaft 280, 282. The seal part 41 described previously comprises the brush 82. The brush 82, and more particularly the bristles 822, are made of boron nitride, or of a material consisting of a matrix and charges of crystalline boron nitride with a hexagonal crystalline structure (h-BN), dispersed in the matrix, so as to allow the seal 8 to have good dynamic sealing, with low permeability, a good service life, very good resistance to high temperatures and good electrical insulation without requiring the addition of an intermediate insulating part between the seal 8 and the motor casing 23 or tree 280, 282.

Claims

Claims

1. Gas turbine engine (2) comprising: - a casing (23,25), - a turbine section (26), - a stator part (223,263) fixedly mounted relative to the casing (23,25) and a rotor part (280,282) suitable for being driven in rotation relative to the stator part (223,263), by means of the turbine section (26), - an electric machine (29) comprising an electric machine stator (291) and an electric machine rotor (292), suitable for being driven in rotation relative to the electric machine stator (291), the electric machine rotor (292) being mechanically coupled to the rotor part (280,282) and the stator of the electric machine (291) being fixedly mounted relative to the casing (23,25), - a seal (4) for ensuring a fluid seal between the part rotor (280,282) and stator part (223,263),the seal (4) comprising a seal part (41) formed of an electrically insulating material and arranged to prevent propagation of an electric current between the rotor part (280,282) and the stator part (223,263) through the seal (4), the insulating material comprising boron nitride (BN).,

2. A gas turbine engine (2) according to claim 1, wherein the seal piece (41) is fixed to one of the stator piece (223,263) and the rotor piece (280,282), and is disposed facing the other of the stator piece (223,263) and the rotor piece (280,282).

3. A gas turbine engine (2) according to any one of claims 1 to 2, wherein the insulating material is crystalline boron nitride with a hexagonal crystal structure h-BN.

4. A gas turbine engine (2) according to any one of claims 1 to 2, wherein the insulating material consists of a matrix and crystalline boron nitride fillers with a hexagonal crystal structure, dispersed in the matrix.

5. A gas turbine engine (2) according to claim 4, wherein the matrix of the insulating material is amorphous boron nitride or a non-conductive polymer.

6. A gas turbine engine (2) according to any one of claims 1 to 5, wherein the seal (4) is a segmented radial seal (5) comprising an outer annular crown (511), and wherein the joint part (41) comprises a plurality of segments (52) positioned radially internally relative to the outer annular crown (511), the segments (52) being arranged successively and circumferentially end to end to form a ring.

7. A gas turbine engine (2) according to any one of claims 1 to 5, wherein the seal (4) is a floating ring seal (6) comprising a retaining device (61) surrounding the seal part (41) and comprising an annular retaining groove (611), and wherein the seal part (41) comprises a ring (62) positioned in the retaining groove of the retaining device (61), the retaining groove (611) allowing radial movement of the ring (62) while preventing axial movement of the ring (62).

8. A gas turbine engine (2) according to any one of claims 1 to 5, wherein the seal (4) is a radial face seal (7) comprising a fixed ring (71) and a pin (73), and wherein the seal part (41) comprises a contact ring (72) arranged radially internally relative to the fixed ring (71), and being locked in rotation relative to the fixed ring (71) by the pin (73).

9. A gas turbine engine (2) according to any one of claims 1 to 5, wherein the seal (4) is a brush seal (8) comprising an annular retaining ring (81) having a recess (811), and wherein the seal part (41) comprises an annular brush (82) housed in the recess (811) of the retaining ring (81).

10. A gas turbine engine (2) according to any one of claims 1 to 9, comprising an enclosure (284) adapted to contain lubricating fluid, the stator part (223,263) being a wall of the enclosure (2841), and the enclosure (284) comprising an opening (2842) through which the rotor part (280,282) extends, the seal (4) being arranged between the wall of the enclosure (2841) and the rotor part (280,282) to limit leakage of lubricating fluid through the opening (2842).

11. A gas turbine engine (2) according to any one of claims 1 to 10, comprising an additional seal (40) positioned around the rotor part (280,282), in contact with the seal (4) and between the seal (4) and the enclosure (284), the additional seal (40) comprising a helical groove (401) suitable for repelling the fluid from lubrication of the seal (4) in the enclosure (284).

12. Gas turbine engine (2) according to claim 11, in which the additional seal (40) is: - either ceramic, - or a composite material comprising a hexagonal boron nitride filler and an amorphous boron nitride or polymer matrix, - or placed in a layer of electrical insulation.

13. A gas turbine engine (2) according to any one of claims 1 to 12, wherein the electrical machine (29) is an electric motor and / or generator.

14. An aircraft (100) comprising an airframe and a gas turbine engine (2) according to any one of claims 1 to 13, wherein the gas turbine engine (2) is attached to the airframe.

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