Turbine fan assembly including roller bearings and double-row ball bearings with angular contact

Abstract

The invention relates to an aircraft propulsion assembly comprising a fan shaft (12) connected to a turbine shaft (100) via a speed reducer (14). The fan shaft (12) is guided by a first bearing (15) and a second bearing (16), the first bearing comprising cylindrical rollers and the second bearing comprising two rows of balls in oblique contact.

Description

Technical Field

[0001] The present invention relates to the field of guiding and axial retention of fan shafts of aircraft turbomachines.

[0002] Without being limiting, the invention more particularly relates to the field of turbojet engines comprising a speed reducer between the fan shaft and the turbine shaft. Background Art

[0003] Some twin-spool turbojets include a speed reducer between the fan shaft and the low-pressure turbine shaft. This speed reducer results in axial decoupling of these shafts, meaning that an axial force applied to one of these shafts does not itself induce axial stresses in the other shaft.

[0004] The axial forces exerted on the fan shaft can be reversed depending on the flight phase of the aircraft. During the cruise phase, the fan shaft is subjected to axial forces tending to drive it upstream of the turbojet engine, while during the deceleration phase or during the autorotation phase, the shaft is subjected to axial forces tending to drive it downstream of the turbojet engine.

[0005] In a reducer architecture, the axial retention of the fan is usually ensured by one or more guide bearings of the fan shaft.

[0006] In particular, there are turbojets in which the fan shaft is guided in rotation by a bearing comprising two rows of tapered rollers. Such a bearing enables the fan to be held axially, each row of rollers forming an axial stop in the respective direction together with a corresponding inner and outer ring.

[0007] This bearing preload directly affects the axial and radial movement of the fan blades, and therefore the radial clearance that should be provided between these blades and the fan housing. Conversely, this radial clearance should also allow the fan housing to expand when heated. Therefore, the thermal expansion of the fan housing requires a reduction in the bearing preload to achieve a relatively flexible preload. This leads to a reduction in aerodynamic performance and a shortened reducer service life.

[0008] Furthermore, the above-described construction is complex to implement, in particular with regard to the provision of a bearing having double rows of tapered rollers. Summary of the Invention

[0009] The object of the present invention is to provide a fan assembly capable of overcoming these drawbacks, in order to improve the aerodynamic performance of the turbomachine and, where appropriate, to increase the service life of the reducer.

[0010] Another object of the present invention is to provide a fan assembly that is simpler to implement than a construction comprising a bearing having double rows of tapered rollers.

[0011] To this end, the object of the present invention is to provide a fan assembly for an aircraft turbine, comprising a fan shaft and a first bearing and a second bearing, the first bearing and the second bearing being configured to guide the fan shaft in rotation about a central axis, the assembly being characterized in that the first bearing has cylindrical rollers and the second bearing has a double row of balls in oblique contact.

[0012] The first bearing with cylindrical rollers makes it possible to absorb the radial forces of the fan and the radial stresses caused by thermal expansion of the bearing support and the housing of the fan. Among other advantages, the radial volume of such a bearing is relatively limited.

[0013] The second double-row ball bearing with oblique contact makes it possible to accommodate the axial forces of the fan shaft as well as the radial forces in both directions.

[0014] Such a fan assembly enables a relatively large preload of the second bearing and thus increases the stiffness of the second bearing to reduce the amplitude of the axial and radial movements of the fan shaft.

[0015] The invention thus makes it possible to reduce the radial clearance between the blades and the casing of the fan, thereby improving the aerodynamic performance of the turbine.

[0016] When such a fan assembly is installed in a turbine including a reducer between the fan shaft and the turbine shaft, the rigid preload of the second bearing also makes it possible to reduce the radial and axial clearances in the gears of the reducer, which makes it possible to protect the teeth of the gears and increase the service life of the reducer.

[0017] Due to the reduction in axial and radial movement of the fan shaft, it is further possible to use a reducer with herringbone teeth, thereby reducing the corresponding vibration.

[0018] More specifically, regarding the structure of the second bearing, preferably, the second bearing includes a first row of balls and a second row of balls, and an inner ring and an outer ring, the inner ring and the outer ring each include a first seat ring (piste) and a second seat ring, the first seat ring of the inner ring and the outer ring accommodates the first row of balls, and the second seat ring of the inner ring and the outer ring accommodates the second row of balls.

[0019] In one embodiment, one of the inner ring and the outer ring of the second bearing may include a first ring half forming a first raceway of the ring and a second ring half forming a second raceway of the ring.

[0020] Preferably, the first ring half and the second ring half may together form an inner ring of the second bearing.

[0021] Providing one of the rings of the second bearing in the form of two ring halves facilitates mounting and dismounting of this bearing.

[0022] Preferably, the other of the inner ring and the outer ring of the second bearing may comprise distinct portions forming the first race and the second race of the ring. For example, the inner ring of the second bearing may comprise said first and second ring halves, and the outer ring of the bearing may be made integrally.

[0023] In one embodiment, the first row of balls may have a different diameter than the second row of balls.

[0024] The difference in diameter between the first and second rows of balls enables the dimensions of the first and second rows of balls to be designed according to the respective forces to which they are actually subjected during operation of the turbine.

[0025] In particular, the axial force applied to the fan shaft from downstream to upstream along the central axis during the cruising phase is higher than the axial force applied from upstream to downstream along the central axis during the idling or automatic rotation phase.

[0026] Therefore, in the case of an X-mounting of the second bearing, the diameter of the upstream row of balls can be larger than the diameter of the downstream row of balls, because in this case the upstream row of balls is loaded during the cruising phase, and vice versa in the case of an O-mounting (see the description below on X-mounting or O-mounting).

[0027] Preferably, the difference in diameter between the first and second rows of balls is such that the ratio of the diameter of one row of balls to the diameter of the other row of balls is higher than 1.5.

[0028] According to a first variant, the mounting of the second bearing may be performed in an X-shaped manner, ie the first and second races of the outer ring of the second bearing may be located axially between the first and second races of the inner ring of the second bearing.

[0029] In other words, in the case of the X-shaped arrangement, the two rows of balls establish axially outward contact with the corresponding races of the outer ring and axially inward contact with the corresponding races of the inner ring.

[0030] According to a second variant, the mounting of the second bearing may be performed in an O-shaped manner, ie the first and second races of the outer ring of the second bearing may be located axially between the first and second races of the inner ring of the second bearing.

[0031] In other words, in the case of an O-mount, the two rows of balls establish axially outward contact with the corresponding races of the inner ring and axially inward contact with the corresponding races of the outer ring.

[0032] Compared to an X-mount, this O-mount increases the stability of the bearing and, in particular, the angular rigidity of the fixed support portion supporting the outer ring. In cases where this fixed support portion also supports the outer ring of the first roller bearing, the rigidity imparted by this O-mount makes it possible, where appropriate, to reduce the loads on the flexible cage of the first bearing and to restrain this flexible cage.

[0033] The fan assembly according to the invention may comprise a fixed support portion configured to support an outer ring of a second bearing, the support portion and the outer ring of the second bearing each comprising a connecting element forming a respective bearing surface, the connecting element being configured such that:

[0034] - a force exerted on the fan shaft according to a first direction along said central axis tends to press the bearing surfaces of said connection elements against each other,

[0035] A force exerted on the fan shaft according to a second direction along the central axis tends to move the bearing surfaces of the connection element away from each other.

[0036] Preferably, the bearing surface may be perpendicular to said centre axis, such that the bearing surface formed by the connecting element of the fixed support is axially opposite the bearing surface formed by the outer ring of the second bearing.

[0037] In order to hold the bearing surfaces against each other, in particular when a force is applied to the fan shaft according to the second direction, the fan assembly may include fastening means (e.g. bolts) configured to secure the support portion and the outer ring of the second bearing together via connecting elements of the support portion and the outer ring.

[0038] In particular, the above configuration makes it possible to apply no load to the fastening device at cruising speed.

[0039] In one embodiment, the fan shaft may include: a first support portion, the first support portion carries the inner ring of the first bearing; a second support portion, the second support portion carries the inner ring of the second bearing; a first frustoconical connecting portion, the first frustoconical connecting portion connects the first support portion and the second support portion together; and a second frustoconical connecting portion, the second frustoconical connecting portion is intended to connect the reducer of the turbine and the second support portion together, the radial thickness of the second support portion being greater than the radial thickness of the first frustoconical connecting portion and the second frustoconical connecting portion.

[0040] In other words, it is possible to provide additional thickness of the fan shaft at the second bearing, which makes it possible to limit creep phenomena of the shaft in the event of overheating and to avoid embrittlement of the fan assembly and other parts of the shaft.

[0041] Another object of the invention is to provide an aircraft turbomachine comprising a fan assembly as defined above.

[0042] In one embodiment, the turbine may include a turbine shaft and a speed reducer between the turbine shaft and the fan shaft, the speed reducer being configured to reduce a rotational speed.

[0043] Preferably, the first bearing having cylindrical rollers may be axially aligned with a blade of a fan assembly of the turbomachine.

[0044] The second bearing having double-row balls in oblique contact may be arranged axially between the first bearing having cylindrical rollers and the speed reducer.

[0045] Another object of the invention is to provide a propulsion unit comprising such a turbine, or more generally a fan assembly as defined above, and an aircraft comprising such a propulsion unit.

[0046] Finally, the invention also relates to a method for mounting and dismounting a fan assembly as defined above.

[0047] Other advantages and characteristics of the invention will appear on reading the following detailed non-limiting description. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The following detailed description refers to the accompanying drawings, in which:

[0049] [ Figure 1 ] is a schematic diagram of an axial section of an aircraft propulsion unit comprising a twin-shaft, twin-ducted turbojet engine according to the present invention;

[0050] [ Figure 2 ] is a schematic diagram of an aircraft propulsion unit architecture according to the present invention;

[0051] [ Figure 3 ] is a partial schematic diagram of an axial cross section of a fan assembly according to the present invention, the fan assembly including a double-row ball bearing with oblique contact according to the first embodiment;

[0052] [ Figure 4 ]yes Figure 3 A partial schematic diagram of an axial cross section of a double-row ball bearing with oblique contact;

[0053] [ Figure 5 ] is a partial schematic diagram of an axial cross-section of a double-row ball bearing with oblique contact according to a second embodiment for a fan assembly according to the present invention. DETAILED DESCRIPTION

[0054] exist Figure 1In FIG, an aircraft propulsion unit 1 is shown comprising a turbine 2, which is streamlined by a nacelle 3. In this example, the turbine 2 is a twin-shaft, twin-duct turbojet engine known in the aviation industry.

[0055] In the following, the terms "upstream" and "downstream" are defined relative to the main direction D1 of the gas flow through the propulsion unit 1 when the propulsion unit is propelled.

[0056] The turbojet engine 2 has a longitudinal central axis A1 around which the different components of the turbojet engine extend, in this case from upstream to downstream of the turbojet engine 2: the fan (the blades 4 of which are located at Figure 1 ), a low-pressure compressor 5, a high-pressure compressor 6, a combustion chamber 7, a high-pressure turbine 8, and a low-pressure turbine 9. The compressors 5 and 6, the combustion chamber 7, and the turbines 8 and 9 form a gas generator.

[0057] The turbojet 2 is a twin-shaft turbojet, which means that the low-pressure compressor 5 and the low-pressure turbine 9 comprise rotors carried by a low-pressure shaft, while the high-pressure compressor 6 and the high-pressure turbine 8 comprise rotors carried by a low-pressure shaft. These high-pressure and low-pressure shafts are intended to rotate about an axis A1 at different speeds.

[0058] Typically, during operation of such a turbojet engine 2, an air flow 10 passes through the propulsion unit 1 through an air inlet upstream of the nacelle 3, passes through the fan blades 4, and is then divided into a central main flow 10A and a secondary flow 10B. The main flow 10A flows through a primary duct 11A, which circulates the gases passing through the compressors 5 and 6, the combustion chamber 7, and the turbines 8 and 9. The secondary flow 10B, in turn, flows through a secondary duct 11B, which surrounds the gas generator and is radially delimited to the outside by the nacelle 3.

[0059] Figure 2 The architecture of a turbojet engine 2 is schematically shown, comprising a fan assembly 13 according to the invention, a low-pressure shaft 100 and a speed reducer 14 .

[0060] The fan assembly 13 comprises at least a portion of a fan, which comprises a fan shaft 12 and means 16 for guiding the shaft 12 .

[0061] In a manner known per se, the reducer 14 is an epicyclic reducer comprising a ring gear 141 , an internal sun gear 142 and planetary gears 143 .

[0062] In this example, the ring gear 141 is fixed to the fan shaft 12 and the internal sun gear 142 is fixed to the low-pressure shaft 100. The planetary gears 143 are guided in rotation by a planet carrier (not shown) fixed to the inlet casing 110 of the turbojet engine 2.

[0063] Therefore, the speed reducer 14 connects the fan shaft 12 to the low-pressure shaft 100 to reduce the rotational speed of the fan shaft 12 relative to the rotational speed of the low-pressure shaft 100 , which makes it possible to improve the propulsion efficiency of the turbojet engine 2 .

[0064] exist Figure 3 The fan assembly 13 according to the present invention is shown in more detail in FIG.

[0065] Reference Figure 3 The guidance of the fan shaft 12 in rotation about the longitudinal center axis A1 of the turbojet engine 2 is ensured by two bearings 15 and 16 .

[0066] The first bearing 15 (or upstream bearing) is a roller bearing 17 .

[0067] In this example, the rollers 17 of the upstream bearing 15 are cylindrical.

[0068] The upstream bearing 15 comprises a radially inner ring 18 mounted, for example by press-fitting, on a first support portion 19 of the fan shaft 12 so as to be fixed to this shaft 12 in rotation about the axis A1 .

[0069] The upstream bearing 15 comprises a radially outer ring 20 connected to a branch 21 of the stationary casing of the turbojet 2 by means of a flexible cage 22 having a radial damping function. In this example, the stationary casing corresponds to Figure 2 The inlet housing 110 is provided in the housing.

[0070] The implementation of such a flexible retainer 22 is well known in the prior art, and the structure and operation of the flexible retainer will not be further described in this specification.

[0071] Furthermore, the connection between the outer ring 20 of the upstream bearing 15 and the housing 110 may be made by any other connection means, for example by a direct connection.

[0072] The second bearing 16 (or downstream bearing) is a double-row ball bearing with oblique contact.

[0073] Reference Figure 4 , Figure 4 Shown Figure 3 The downstream bearing 16 comprises a radially inner ring 23 and a radially outer ring 24 .

[0074] The inner ring 23 is mounted on a second support portion 25 of the fan shaft 12, for example by press-fitting, so as to be fixed to this shaft 12 for rotation about the axis A1. In this example, the inner ring 23 is retained in its axial position by a nut 26 which is screwed onto the shaft 12 upstream of the inner ring 23 and which exerts pressure on the shaft against a shoulder 27 of the fan shaft 12. In an embodiment not shown, a washer may be arranged between the inner ring 23 and the shoulder 27 (see further below).

[0075] In turn, the outer ring 24 is connected to the support 28 , for example by press-fitting, and is fastened to the support 28 by screw-nut type fastening means 29 , thereby ensuring axial and rotational retention of the outer ring 24 relative to the support 28 .

[0076] Reference Figure 3 In this example, the support portion 28 of the outer ring 24 of the downstream bearing 16 and the branch portion 21 of the casing 110 are connected to each other by fastening means 35 (for example screws) to form together a part of the fixed casing 110 of the turbojet engine 2, the branch portion of the casing being connected to the outer ring 20 of the upstream bearing 15.

[0077] exist Figure 4 In the example of , the inner ring 23 of the downstream bearing 16 is made in one piece and the outer ring 24 comprises two parts 32 and 33 forming an upstream outer ring element (or upstream outer ring half) and a downstream outer ring element (or downstream outer ring half), respectively.

[0078] The upstream outer ring element 32 forms an integral part of the outer ring 24 , in particular it connects the outer ring 24 to the support 28 and in this example carries the downstream outer ring element 33 .

[0079] To this end, the upstream outer ring element 32 comprises a housing for receiving the downstream outer ring element 33 (see Figure 4 ).

[0080] The upstream outer ring element 32 and the downstream outer ring element 33 are maintained in axial position relative to each other by a threaded element 34 which is screwed onto the upstream outer ring element 32 to clamp the downstream outer ring element 33 between the threaded element 34 and a shoulder of the upstream outer ring element 32 .

[0081] The downstream bearing 16 comprises a first row of balls 40 (or downstream row of balls) and a second row of balls 41 (or upstream row of balls). These two rows of balls 40 and 41 are fitted in the corresponding races of the rings 23 and 24 so as to establish oblique contact with these races.

[0082] More specifically, in Figure 4In the configuration of , the downstream row of balls 40 bears against a race 42 formed by the inner ring 23 and a race 43 formed by the downstream outer ring element 33. Furthermore, the upstream row of balls 41 bears against a race 44 formed by the inner ring 23 and a race 45 formed by the upstream outer ring element 32.

[0083] Races 42 and 43 are referred to as "downstream races" or "first races" because they engage the downstream row of balls 40 or the first row of balls. Similarly, races 44 and 45 are referred to as "upstream races" or "second races" because they engage the upstream row of balls 41 or the second row of balls.

[0084] The downstream races 42 and 43 and the upstream races 44 and 45 are configured so that Figure 4 In the configuration, the downstream race and the upstream race apply axial prestressing force on the downstream row of balls 40 and the upstream row of balls 41 respectively to prevent relative axial movement of the inner ring 23 and the outer ring 24 in the first direction and the second direction respectively.

[0085] This axial prestress or preload is obtained by fastening the upstream outer ring element 32 and the downstream outer ring element 33 against each other using threaded elements 34 .

[0086] Of course, the bearing 16 includes cages 46 and 47 configured to retain the downstream row of balls 40 and the upstream row of balls 41 , respectively, which are circumferentially spaced apart from each other to distribute forces circumferentially and enable the bearing 16 to function properly.

[0087] Figure 4 The bearing 16 corresponds to an X-shaped mounting of the elements of the bearing, the downstream race 42 and the upstream race 44 of the inner ring 23 being located axially between the downstream race 43 and the upstream race 45 of the outer ring 24 .

[0088] exist Figure 4 In the embodiment, the upstream row of balls 41 has a larger diameter, which is approximately twice the diameter of the downstream row of balls 40 .

[0089] In fact, in this case, the upstream row of balls 41 is loaded during the cruise phase, during which the fan shaft 12 is driven from downstream to upstream. Therefore, in principle, the upstream row of balls is loaded more than the downstream row of balls 40.

[0090] However, this difference in ball size presupposes a corresponding difference in the radial coordinates of the respective raceways of the inner ring 23 and the outer ring 24. Figure 4In the example of FIG, this condition is met by dividing the outer ring 24 into two elements 32 and 33, the downstream outer ring element 33 being configured to displace the race 43 formed by this element radially inwards relative to the radial coordinates of the race 45 formed by the upstream outer ring element 32.

[0091] Figure 5 Another embodiment of the downstream bearing 16 is shown, in which the balls of each row have the same size, which makes it possible in particular to simplify the bearing.

[0092] In the following, through Figure 5 Bearings and Figure 4 The difference between bearings is described Figure 5 Bearing 16.

[0093] Figure 5 The inner ring 23 of the bearing 16 includes two ring halves 30 and 31 having substantially the same axial dimensions relative to one another, each forming a substantially symmetrical annular axial portion of the inner ring 23. The upstream inner ring half 30 and the downstream inner ring half 31 form, respectively, an upstream race 44 and a downstream race 42 of the inner ring 23. The upstream inner ring half 30 and the downstream inner ring half 31 are configured to be axially opposed to one another so that tightening of the nut 26 causes the upstream inner ring half 30 to press against the downstream inner ring half 31 and causes the downstream inner ring half to press against a shim 80 that is interposed between the downstream inner ring half 31 and the shoulder 27 of the fan shaft 12 (a description of such shim 80 will be further provided below).

[0094] Figure 5 The outer ring 24 of the bearing 16 is made integrally and forms a downstream race 43 for receiving the downstream row of balls 40 and an upstream race 45 for receiving the upstream row of balls 41 .

[0095] Figure 5 The bearing 16 corresponds to an O-mounting, the downstream race 43 and the upstream race 45 of the outer ring 24 being axially located between the downstream race 42 and the upstream race 44 of the inner ring 23 .

[0096] The rigidity imparted by the O-ring mounting of the downstream bearing 16 enables the upstream bearing 15 to be freed, potentially enabling the fan assembly 13 to be installed without the flexible cage 22 .

[0097] Without limitation, the inner ring 23 and the outer ring 24 of the downstream bearing 16 may be made of a metal material, such as M50 steel for the inner ring 23 and M50NIL or 32CDV13 steel for the outer structural ring 24. The upstream row of balls 41 and the downstream row of balls 40 may be made of M50 steel or ceramic.

[0098] exist Figure 4 and Figure 5 In each of the embodiments, the support portion 28 is configured to support the outer ring 24 of the bearing 16 via corresponding connecting elements of these components.

[0099] More specifically, the support 28 comprises a connecting element 49 comprising a portion of the support and forming a bearing surface substantially perpendicular to the axis A1 .

[0100] The outer ring 24 also comprises a connecting element 50 projecting radially outwards relative to the rest of the outer ring 24 , forming a bearing surface substantially perpendicular to the axis A1 and axially opposite the bearing surface of the connecting element 49 of the support 28 .

[0101] This configuration of the connecting elements 49 and 50 of the support portion 28 and the outer ring 24 results, on the one hand, in the bearing surfaces of these connecting elements 49 and 50 being pressed against each other when a force is exerted on the fan shaft 12 along the central axis A1 in the direction from downstream to upstream. On the other hand, this results in these bearing surfaces moving away from each other when a force is exerted on the fan shaft 12 along the central axis A1 in the opposite direction from upstream to downstream.

[0102] This configuration enables the support 28 to absorb the thrust of the fan shaft 12 when it is driven upstream of the turbojet engine 2 , in particular in the cruise phase, without loading the fastening means 29 .

[0103] In addition, regarding Figure 3 The geometry of the fan shaft 12 can be seen in FIG. 1 , which comprises, from upstream to downstream, in particular:

[0104] a section 48 carrying a disc comprising the blades 4 of the fan, the connection between this section 48 and the disc preferably being a spline connection,

[0105] said first supporting portion 19 carrying the inner ring 18 of the upstream bearing 15 , the diameter of which is close to the diameter of the segment 48 and which is axially adjacent to this segment 48 ,

[0106] a first frustoconical coupling portion 51 connecting the first support portion 19 and the second support portion 25 together, such that the diameter of the second support portion 25 is greater than the diameter of the first support portion 19 , this first frustoconical coupling portion 51 delimiting the lubricating housing E1 of the downstream bearing 16 ,

[0107] - said second supporting portion 25 , which carries the inner ring 23 of the downstream bearing 16 ,

[0108] A second frustoconical coupling portion 52 connecting the second support portion 25 and the reducer 14 together, such that the diameter of the portion of the shaft 12 cooperating with the reducer 14 is greater than the diameter of the second support portion 25 .

[0109] These different parts of the fan shaft 12 are generally connected to each other via the axial ends of these different parts, except for the second support part 25 , which is connected to the first frustoconical coupling part 51 by forming a portion with radially additional thickness at the axial center area of ​​the support part 25 .

[0110] The second supporting portion 25 thus comprises a free upstream axial end which also delimits the lubricating enclosure E1 .

[0111] exist Figure 3 In the example shown in FIG. 5 , the sprayer 60 is configured to introduce lubricating oil into the housing E1 .

[0112] Under the action of centrifugal force, the oil present in the housing E1 enters the downstream bearing 16 through the holes 61-64 and the grooves 65 arranged in the second support portion 25 and the inner ring 23 of the downstream bearing 16 (see Figure 4 ). The oil is discharged from the bearing 16 through the drain hole 66.

[0113] A method for installing and removing the downstream bearing 16 is given below as an example.

[0114] Figure 4 The installation of the bearing 16 may preferably include the following steps in sequence:

[0115] - Positioning the inner ring 23 on the second support portion 25 of the fan shaft 12, optionally inserting a spacer between the inner ring 23 and the shoulder 27 to position the fan shaft 12 axially relative to the stationary housing 110 (spacer in Figure 4 not shown);

[0116] - Provide a downstream row of balls 40 and an upstream row of balls 41 and corresponding cages 46 and 47;

[0117] - Positioning the downstream outer ring element 33;

[0118] - Arranging the upstream outer ring element 32 on the downstream outer ring element 33 by interlocking;

[0119] - screwing the threaded element 34 to clamp the upstream outer ring element 32 and the downstream outer ring element 33 to each other, this step making it possible to apply a preload to the bearing 16;

[0120] - Positioning and fastening the support 28 on the outer ring 24;

[0121] The nut 26 is tightened to axially block the inner ring 23 .

[0122] Figure 5 The installation of the bearing 16 may preferably include the following steps in sequence:

[0123] - placing the downstream inner ring half 31 on the second support portion 25 of the fan shaft 12 , optionally inserting a spacer 80 between the downstream inner ring half 31 and the shoulder 27 , in order to axially position the fan shaft 12 relative to the stationary housing 110 ;

[0124] - Provide a downstream row of balls 40 and corresponding cages 46;

[0125] - placing the outer ring 24 on the support 28;

[0126] - Provide an upstream row of balls 41 and corresponding cages 47;

[0127] - providing an upstream inner ring half 30 on the second support portion 25 of the fan shaft 12;

[0128] - Screwing the nut 26 to fasten the upstream inner ring half 30 and the downstream inner ring half 31 to each other, this step making it possible to preload the bearing 16 and axially block the inner ring 23 .

[0129] exist Figure 4 and Figure 5 In each of the embodiments, disassembly of the bearing 16 may include corresponding steps performed in reverse order.

[0130] Removal of the inner ring 23 relative to the fan shaft 12 may be performed using a jaw puller that engages the grooves 70 of the inner ring 23 .

[0131] Reference Figure 2 According to the foregoing description, the preload of the bearing 16 makes it possible to limit the axial clearance of the ring gear 141 of the speed reducer 14, which is fixed to the fan shaft 12 and guided in rotation by the bearing 16. This results in a reduction in misalignment in the speed reducer 14, in particular, a reduction in misalignment between the ring gear 141 and the planetary gears 143, which makes it possible to extend the service life of the speed reducer 14.

[0132] The embodiments described above are by no means restrictive, and the present invention encompasses any fan assembly 13 whose fan shaft 12 is guided by a first roller bearing 15 and a second double-row ball bearing 16 in oblique contact. For example, the present invention is also applicable to a turbine without a speed reducer 14 between the fan shaft 12 and the gas generator, where the turbine architecture may result in a reversal of the axial force on the fan shaft during turbine operation.

Claims

1. A fan assembly (13) for an aircraft turbomachine (2), comprising a fan shaft (12) and a first bearing (15) and a second bearing (16), the first bearing and the second bearing being configured to guide the fan shaft (12) in rotation about a central axis (A1), the fan assembly being characterized in that the first bearing (15) has cylindrical rollers (17) and the second bearing (16) has double rows of balls (40, 41) in oblique contact. in, The second bearing (16) includes a first row of balls (40) and a second row of balls (41), and an inner ring (23) and an outer ring (24), the inner ring and the outer ring each including a first race (42, 43) and a second race (44, 45), the first races (42, 43) of the inner ring (23) and the outer ring (24) receiving the first row of balls (40), and the second races (44, 45) of the inner ring (23) and the outer ring (24) receiving the second row of balls (41), The fan shaft (12) comprises: a first support portion (19) carrying an inner ring (18) of the first bearing (15); a second support portion (25) carrying an inner ring (23) of the second bearing (16); a first frustoconical coupling portion (51) connecting the first support portion (19) and the second support portion (25); and a second frustoconical coupling portion (52) intended to connect the reducer (14) of the aircraft turbine (2) and the second support portion (25), the radial thickness of the second support portion (25) being greater than the radial thickness of the first frustoconical coupling portion (51) and the second frustoconical coupling portion (52).

2. A fan assembly (13) for an aircraft turbomachine (2) according to claim 1, wherein: One of the inner ring (23) and the outer ring (24) of the second bearing (16) comprises a first ring half (31) and a second ring half (30), the first ring half forming a first race of the ring and the second ring half forming a second race of the ring.

3. A fan assembly (13) for an aircraft turbine (2) according to claim 1, wherein: The first row of balls (40) has a different diameter than the second row of balls (41).

4. A fan assembly (13) for an aircraft turbomachine (2) according to claim 1, wherein: The first race and the second race of the outer ring (24) of the second bearing (16) are axially located between the first race and the second race of the inner ring (23) of the second bearing (16).

5. The fan assembly (13) for an aircraft turbine (2) according to claim 1, comprising a fixed support (28) configured to support an outer ring (24) of the second bearing (16), the fixed support (28) and the outer ring (24) of the second bearing (16) each comprising a connecting element (50) forming a respective bearing surface, the connecting element (50) being configured such that: - a force exerted on the fan shaft (12) according to a first direction along the central axis (A1) tends to press the bearing surfaces of the connecting element (50) against each other, - A force exerted on the fan shaft (12) according to a second direction along the central axis (A1) tends to move the bearing surfaces of the connecting element (50) away from each other.

6. A fan assembly (13) for an aircraft turbomachine (2) according to claim 3, wherein: The ratio of the diameter of the balls of one of the rows of balls to the diameter of the balls of the other row is higher than 1.

5.

7. An aircraft turbomachine (2) comprising a fan assembly (13) for an aircraft turbomachine (2) according to claim 1.

8. Aircraft turbomachine (2) according to claim 7, comprising a turbine shaft and a speed reducer (14) between the turbine shaft and the fan shaft (12), the speed reducer being configured to reduce the rotational speed.

9. A propulsion unit (1) for an aircraft, the propulsion unit (1) comprising an aircraft turbine (2) according to claim 7.

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