FR3072749A1 - EPICYCLOIDAL GEAR TRAIN - Google Patents

Abstract

An annular support piece (80) for supporting an outer sun gear (38) in an epicyclic gear train, comprising a first radial annular flange (66) formed at a first axial end and a second radial annular flange ( 68) formed at a second axial end, the first annular flange (66) and the second annular flange (68) being connected to each other by an annular connecting wall (78). According to the invention, the annular connecting wall (78) comprises a connecting portion to the second flange (68) which forms an annular bulge (76) surrounding the second annular flange (68).

Description

EPICYCLOIDAL GEAR TRAIN

FIELD [001] The present invention relates to an epicyclic gear train as well as a support part of an outer or planetary outer ring of such an epicyclic gear train.

BACKGROUND Conventionally, a planetary gear train comprises planet gears engaged with an outer ring gear and a central gear. The planet gears are carried by a planet carrier and mounted to rotate freely on pivots. Such a planetary gear train can be used in particular for the transmission of power from a drive shaft such as the shaft of a low pressure compressor, connected to the central pinion to a fan wheel connected to the planet carrier. In such a configuration, the outer ring gear is fixed in rotation and the central pinion and the planet carrier are driven and driven, respectively. This arrangement is commonly called a planetary gear reducer since the speed of rotation of the planet carrier is less than the speed of rotation of the central pinion. With such an arrangement, it is for example possible, in a turbomachine, to drive the fan wheel connected to the planet carrier by means of the pressure compressor shaft.

The outer ring is commonly fixed to a stator of the low pressure compressor by means of an annular support piece. This structural part is commonly called the crown holder because it actually carries the outer crown. It comprises a first upstream annular flange for fixing to said stator of the low pressure compressor and a second downstream annular flange for fixing to the external crown.

The crown holder performs several functions:

- transmit the torque from the external crown to the stator of the low pressure compressor,

- center the crown around the axis of the turbomachine,

- maintain the quality of the meshes due to the different mechanical stresses which is obtained by:

o compensating for relative displacements / misalignments between the axis of the planet carrier and the axis of the first annular flange of the crown holder, o limiting misalignments under the effect of the meshing forces.

- maintain the link between the crown and the stator of the low-pressure compressor in the event of objects being ingested, and

- ensure the evacuation of oil.

Thus, it is understood that the crown carrier must both provide a structuring function to transmit the torque to the stator of the low pressure compressor but must at the same time be flexible enough to take up any misalignment of the teeth and centering, which is difficult to achieve.

SUMMARY OF THE INVENTION The present invention firstly relates to an annular piece for supporting an external sun gear in a planetary gear train, comprising a first annular radial flange formed at a first axial end and a second flange radial annular formed at a second axial end, the first annular flange and the second annular flange being connected to one another by an annular connecting wall, characterized in that the annular connecting wall comprises a junction portion with the second flange which forms an annular bulge surrounding the second annular flange.

According to the invention, the integration of such a junction portion having the form of an annular bulge makes it possible to restore flexibility at the second end of the annular support piece. When the annular support piece is fixed to an external sun gear of a planetary gear train, the misalignments between the axes of the planet carrier and the first flange are consecutive due to the meshing forces, which ensures good power transmission to a fan wheel which would be connected to the planet carrier. The annular bulge here has a hairpin shape, that is to say having a bent portion. The integration of an annular bulge makes it possible to limit the overloads to the meshing due to the deformation of an internal sun gear to which the annular part is connected.

In one embodiment, each bulge extends radially inward and comprises a substantially cylindrical bottom or having in section a substantially circular shape.

The invention also relates to a gear train of a gas turbomachine for aircraft, comprising an outer ring and planet gears engaged with the central pinion and with the outer ring and each mounted free in rotation on a door -satellites, the outer ring comprising at least one radial annular flange fixed to the second radial annular flange of an annular part as described above.

It also relates to a gas turbomachine for an aircraft comprising such a gear train, the central pinion of which surrounds and is rotatably integral with a shaft of the compressor of the turbomachine, the first annular radial flange of the annular support part. being attached to a compressor stator.

According to another characteristic, the junction portion can extend in axial projection relative to the second radial annular flange.

Preferably, the annular connecting wall may comprise at least one annular bulge extending radially inwards, preferably two bulges. The use of two bulges of different shape allows better recovery of the different misalignments.

The invention will be better understood and other details, characteristics and advantages of the invention will appear on reading the following description given by way of nonlimiting example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a schematic perspective view of a turbomachine according to the known technique;

Figure 2 is a schematic sectional view of a planetary gear train for use in a turbomachine according to Figure 1;

Figure 3 is a schematic sectional view of the upstream part of a double-flow turbomachine of a known type and comprising a gear train as in Figure 2;

Figure 4 is a schematic perspective view of the connection of an outer ring to a stator via an annular support piece according to the invention;

Figure 5 is a schematic perspective view of an annular support piece according to the invention, seen from its second end or downstream end;

Figure 6 is a schematic perspective view of an annular support piece according to the invention, seen from its first end or upstream end;

Figure 7 is another partial schematic perspective view of the annular support piece according to the invention;

Figures 8 to 10 are schematic views of three different embodiments of an annular support piece according to the invention.

DETAILED DESCRIPTION [014] First of all, reference is made to FIG. 1 which represents a schematic view of a turbomachine 10 according to the known technique comprising from upstream to downstream a fan wheel 12 whose rotation induces an acceleration of air in an annular secondary air stream 14 (air flow B) successively surrounding an annular primary air stream 16 (air flow A) flowing in a low pressure compressor 18, a high pressure compressor 20, a annular combustion chamber 22, a high pressure turbine 24 and a low pressure turbine 26. Conventionally, the low pressure turbine 26 rotates the rotor 30 of the low pressure compressor which is connected to the blower wheel 12. However, to limit the speed of rotation of the fan wheel 12 relative to the speed of rotation of the rotor 30 of the low pressure compressor 18, it is known to mount a planetary gear train 32 radially to the within the low pressure compressor 18, the epicyclic gear train 32 then being qualified reducer because of its function of rotational speed reduction.

Such a gear train 32 comprises planet gears 34 engaged with an internal sun gear 36 or central pinion and with an external sun gear 38 or outer ring, the internal sun gear 36 and external 38 being coaxial with the axis X of the turbomachine. Each satellite pinion 34 is mounted to rotate freely around a pivot 40 and the pivots 40 are integral with a planet carrier 42. In an epicyclic reduction gear, the central pinion 36 is integral in rotation with the shaft 30 of the low compressor pressure 18 which forms an inlet to a gear train, the planet carrier 42 secured to the blower wheel 12 forms an outlet for reducing the speed of the epicyclic gear train and the outer sun gear 38 is made integral with a casing 44 of the turbomachine externally defining an annular enclosure 46 in which the gear train is mounted.

[016] Figure 3 shows a sectional view of a reducer 32 integrated in the annular enclosure 46 formed radially inside the low pressure compressor. As is clearly visible in this figure, the satellite carriers 42 is connected to the fan wheel 12 by means of a connecting shaft 48 guided in rotation by a bearing 50 of upstream roller bearing and a bearing 52 of bearing to downstream balls. The upstream 50 and downstream 52 bearings are carried by two annular walls 54, 56 comprising at their radially external ends radial annular flanges 58, 60 fixed one on the other. The radial annular flange 60 of the annular wall 56 supporting the downstream bearing 52 extends radially outside the radial annular flange 58 of the annular wall 54 supporting the upstream bearing 50 and is fixed to a structural element 62 integral with the casing 44 or with an intermediate casing of the turbomachine. FIG. 3 also represents an annular piece 64 of support for the outer sun gear, also called crown carrier, which comprises a first annular radial flange 66 formed at the upstream end and fixed to the annular radial flange 60 of the annular support wall 56 of the downstream bearing 52 and a second annular radial flange 68 formed at the downstream end and fixed to the outer sun gear 38.

As can be seen in this figure, the crown holder 64 comprises an annular wall 70 of connection connecting the first annular flange 66 upstream to the second annular flange 68 downstream. The upstream radial annular flange 66 extends radially outward while the downstream radial annular flange 68 extends radially inward, relative to the annular connecting wall 70. This annular connecting wall 70 comprises two bulges annulars 72, 74 or annular protrusions extending radially inwards and axially spaced from one another. These bulges 72, 74 correspond to a deformation of the connecting wall.

As indicated above, these protuberances 72, 74 which can still be qualified as axial undulations make it possible to give a certain radial flexibility and ensure a flexible mounting to the reducer. Such a degree of freedom prevents it from being clamped on the structure and from undergoing significant stresses during vibration or displacement by expansion of the various components of the turbojet engine.

[019] However, this type of mounting proves to be insufficient to limit the misalignments between the planet carrier 42 and the first flange 66 due to the meshing forces. Considering all the satellite meshes - internal planetary - external planetary, the external planetary conforms like a flower.

To this end, the invention proposes, as shown in Figures 4 to 6, to form a protrusion 76 or annular bulge is formed at an axial end portion of the annular connecting wall 78 of the crown carrier 80, this annular projection or bulge 76 making the junction with the downstream radial annular flange 68 or second annular radial flange of the crown holder 80 and surrounding the downstream annular flange 68.

[021] This annular bulge 76 extends in axial projection relative to the second annular radial flange 68, more particularly projecting downstream in the assembly shown in the figures. The annular bulge 76 of junction has a hairpin shape or an annular elbow having a radius of curvature of the order of 5 mm.

[022] The outer sun gear 38 includes a first ring 38a and a second ring 38b meshing together with the satellites. The first ring 38a or upstream ring externally carries a radial annular flange 38c. Similarly, the second ring 38b or downstream ring externally carries a radial annular flange 38d. The radial annular flange 38d of the downstream ring 38b is centered on an annular flange 38e, here cylindrical, formed at the base of the radial annular flange 38c of the upstream ring 38a. These two radial annular flanges 38c, 38d are fixed to each other by bolts 82 also serving for fixing the downstream radial annular flange 68 of the annular piece 80 of support or annular crown holder.

[023] As is clearly visible in FIG. 4, the crown holder 80 also includes two annular bulges 82, 84 extending radially inwards and can also be considered as forming annular grooves. The upstream annular bulge 82 is connected to the annular bulge immediately downstream by a portion of cylindrical wall 86. Likewise, another portion of cylindrical wall 88 connects the bulge 76 as a pin to the annular bulge 84 immediately upstream. These portions 86, 88 of cylindrical walls are provided with holes 90 for the passage of lubricating oil. The annular bulge 82 of the annular connecting wall located near the upstream annular flange 66 of the crown carrier 80 has a depth greater than the depth of the downstream annular bulge 84. It is also observed that the axial dimension of the upstream annular bulge 82 is less than the axial dimension of the downstream annular bulge 84.

Figures 8, 9 and 10 show variants of the invention, each figure comprising a left part representing a half-view in section of a crown holder 92, 94, 96 and a right part representing the holder crown 92, 94, 96 in perspective from its upstream end.

In the embodiment of Figure 8, the crown holder 92 only comprises an annular bulge 76 in a pin and the connecting wall is devoid of annular bulge extending radially inward. In the embodiment of FIG. 9, the crown holder 94 comprises an annular pin bulge 76 and the connecting wall 94a comprises an annular bulge 94b extending radially inwards. In the embodiment of FIG. 10, the crown holder 96 comprises a pin-shaped annular bulge 76 and the connecting wall 96a comprises two annular bulges 96b extending radially inwards. The annular bulges 96b extending radially inwards can have a curved bottom having for example a radius of curvature, for example constant.

Claims (6)

1. Annular piece (80) for supporting an external sun gear (38) in a planetary gear train (32), comprising a first radial annular flange (66) formed at a first axial end and a second radial annular flange ( 68) formed at a second axial end, the first annular flange (66) and the second annular flange (68) being connected to one another by an annular connecting wall (78), characterized in that the wall annular connection (78) includes a junction portion to the second flange (68) which forms an annular bulge (76) surrounding the second annular flange (68). 2. Annular part according to claim 1, characterized in that the junction portion (76) extends in axial projection relative to the second radial annular flange (68). 3. Annular part according to claim 1 or 2, characterized in that the annular connecting wall (78) comprises at least one annular bulge (82, 84) extending radially inwards, preferably two bulges. 4. Annular part according to claim 3, characterized in that each bulge (82, 84) extending radially inwards comprises a substantially cylindrical bottom or having in section a substantially circular shape. 5. Gear train of a gas turbomachine for aircraft, comprising an outer ring (38) and planet gears (34) engaged with the central pinion (36) and with the outer ring (38) and each mounted free in rotation on a planet carrier (42), the outer ring (38) comprising at least one radial annular flange (38c, 38d) fixed to the second radial annular flange (68) of an annular part (80) according to the any one of claims 1 to 4. 6. Gas turbomachine for aircraft comprising a gear train according to claim 5, the central pinion (36) of which surrounds and is rotatably connected to a shaft (30) of the compressor of the turbomachine, the first annular radial flange (66 ) of the annular support part (80) being fixed to a stator of the compressor.