Mechanical speed reducer for an aircraft turbine

Abstract

A mechanical reducer (6) for a turbine engine of an aircraft, comprising a sun gear (7), a ring gear (9) formed by two half ring gears (9a, 9b), planetary gears (8) arranged between the sun gear and the ring gear, and at least one shaft (4, 30) rotationally fixed to the ring gear, characterized in that the mechanical reducer further comprises an annular covering part (20) which extends around the ring gear and is independently fixed to each of the half ring gears by means of flanges and / or splines (26a, 26b, 26c).

Description

Technical Field

[0001] The present invention relates to a mechanical speed reducer for a turbine, and more particularly to a mechanical speed reducer for a turbine of an aircraft. Background Art

[0002] The background art particularly includes the documents US-A1-2008 / 098716, US-A1-6,223,616, US-A-4,433,674, WO-A1-2015 / 019025, WO-A1-2010 / 092263, FR-A1-2 987 416 and FR-A1-3 041 054.

[0003] The function of a mechanical speed reducer is to change the speed ratio and torque between the input shaft and the output shaft of a mechanism.

[0004] New generation double-flow turbines, especially those with a high dilution rate, include a mechanical speed reducer to drive the shaft of the fan. Generally, the purpose of the speed reducer is to convert the so-called fast rotation speed of the shaft of the power turbine into a slower rotation speed for driving the shaft of the fan.

[0005] Such a speed reducer includes a central pinion called the sun gear, a ring gear, and pinions called planet gears, which are meshed between the sun gear and the ring gear. The planet gears are held by a frame called the planet carrier. The sun gear, the ring gear, and the planet carrier are planetary gears because the rotation axes of the sun gear, the ring gear, and the planet carrier coincide with the longitudinal axis X of the turbine. Each of the planet gears has a different rotation axis, which is evenly distributed on the same operating diameter around the axis of the planet gear. These axes are parallel to the longitudinal axis X.

[0006] There are various speed reducer architectures. In the prior art of double-flow turbines, the speed reducer is planetary or epicyclic. In other similar applications, there are so-called differential architectures or "compound" architectures.

[0007] In a planetary speed reducer, the planet carrier is fixed and the ring gear constitutes the output shaft of the device that rotates in a direction opposite to that of the sun gear.

[0008] In an epicyclic speed reducer, the ring gear is fixed and the planet carrier constitutes the output shaft of the device that rotates in the same direction as the sun gear.

[0009] In a compound speed reducer, no element is rotationally fixed. The ring gear rotates in a direction opposite to that of the sun gear and the planet carrier.

[0010] The speed reducer can be composed of one or more meshing stages. This meshing is achieved in different ways, such as by contact, friction, or magnetic fields.

[0011] There are various types of contact meshing, such as spur gear meshing or herringbone gear meshing.

[0012] In the case of herringbone gear meshing, the gear ring is usually formed by two coaxial half gear rings. Each half gear ring includes the teeth of the gear on its inner circumference and a fastening flange on its outer circumference. The fastening flange is particularly used for attachment to the shaft when the gear ring rotates. The teeth are carried by an annular edge which is connected to the flange by a frustoconical web.

[0013] The disadvantage of this technique is its size. In particular, the radial dimension of the components and the method of fastening the half gear rings have a significant impact on the radial dimension of the entire speed reducer.

[0014] The present invention proposes a simple, effective and economical improvement to this technique. Summary of the Invention

[0015] The present invention relates to a mechanical speed reducer for a turbine, in particular for a turbine of an aircraft. The mechanical speed reducer includes:

[0016] - A central sun gear having a rotational axis X,

[0017] - A gear ring that extends around the axis X and the sun gear and includes herringbone teeth. The gear ring is formed by two coaxial half gear rings that are spaced apart from each other by an annular space and each include the teeth of the gear. The gear ring is capable of rotating around the axis X,

[0018] - A planetary gear that is disposed between the sun gear and the gear ring and is supported by a planet carrier that is fixed and cannot rotate around the axis X,

[0019] - At least one shaft that is rotationally fixed to the gear ring,

[0020] - An annular covering member that extends around the space and at least a portion of the gear ring. The member is independently fixed to each of the half gear rings by a flange and / or a spline,

[0021] Characterized in that the gear ring is rotationally fixed to two shafts that extend on each side of the speed reducer respectively.

[0022] Therefore, the present invention proposes a new technique for assembling and fixing the half gear rings. Thus, it is possible to remove the webs of the prior art that have large dimensions in the radial direction. Each half gear ring is made to be rotationally fixed to the covering member by fastening means that are independent of the fastening means for fastening the member to the other half gear ring. These fastening means have flanges and / or splines.

[0023] The gear ring is rotatably fixed to two separate shafts by means of an intermediate covering member, which enables this connection to be ensured in a simple manner and with reduced space requirements.

[0024] The gear ring of the speed reducer can be rotatably fixed to the fan shaft and the turbine shaft of the turbine. The speed reducer according to the invention can be integrated into a turbine, for example, having contra-rotating turbines.

[0025] The speed reducer according to the invention can comprise one or more of the following features, taken independently of each other or in combination with each other:

[0026] - The covering member extends between the two shafts, or covers a part of the two shafts, or is integrally formed with one of the shafts;

[0027] - The covering member comprises a first spline for coupling to one of the half gear rings and a second spline for coupling to the other half gear ring, the half gear rings being axially clamped against each other and against an element of the covering member by means of nuts screwed into or onto the covering member;

[0028] - One of the half gear rings is integrally formed with one of the shafts, and the other half gear ring is integrally formed with the other shaft;

[0029] - The covering member is integrally formed with one of the shafts and further comprises a third spline for coupling to the other shaft;

[0030] - The gear ring does not have a fastening flange;

[0031] - The covering member comprises a cylindrical wall which is connected at each of its axial ends to a radial flange, the first radial flange of the radial flanges of the covering member being fixed to the radial flange of one of the half gear rings, and the second radial flange of the radial flanges of the covering member being fixed to the radial flange of the other half gear ring;

[0032] - The flange of one of the half gear rings is clamped between the flange of the covering member and the radial flange of one of the shafts, and the flange of the other half gear ring is clamped between the flange of the covering member and the radial flange of the other shaft;

[0033] - Each half gear ring comprises an annular edge which has a substantially parallelepiped shape in an axial cross-section, the edge comprising teeth at its inner circumference and an outer cylindrical surface at its outer circumference, the covering member surrounding this surface with minimal or no clearance;

[0034] - The part has a radial thickness that varies, in particular increases, from one axial end to the opposite axial end; this makes it possible, in particular, to optimize the stiffness of the part as a function of the forces applied to the teeth of the semi-ring gear during operation, so as to avoid misalignment of the teeth of the semi-ring gear relative to the complementary teeth of the planetary gear.

[0035] The invention also relates to a turbine, in particular a turbine for an aircraft, which turbine comprises a speed reducer as described above. Description of the Drawings

[0036] During the reading of the following detailed description, other features and advantages of the invention will become apparent. To understand these other features and advantages of the invention, reference will be made to the drawings, in which:

[0037] Figure 1 is a schematic axial sectional view of a turbine using the invention,

[0038] Figure 2 is a partial schematic axial sectional view of the mechanical speed reducer,

[0039] Figure 3 is a schematic axial sectional and perspective view of a part of a mechanical speed reducer according to a first embodiment of the invention,

[0040] Figure 4 is a schematic axial sectional and perspective view of a part of a mechanical speed reducer according to a second embodiment of the invention, and

[0041] Figure 5 is a schematic axial sectional and perspective view of a part of a mechanical speed reducer according to a third embodiment of the invention. Detailed Description of the Embodiments

[0042] Figure 1 The turbine 1 is described, which generally comprises a fan S, a low-pressure compressor 1a, a high-pressure compressor 1b, an annular combustion chamber 1c, a high-pressure turbine 1d, a low-pressure turbine 1e and an exhaust nozzle 1h. The high-pressure compressor 1b and the high-pressure turbine 1d are connected by a high-pressure shaft 2 and form a high-pressure (HP) body with this high-pressure shaft. The low-pressure compressor 1a and the low-pressure turbine 1e are connected by a low-pressure shaft 3 and form a low-pressure body (LP) with this low-pressure shaft.

[0043] The fan S is driven by a fan shaft 4 which is connected to the LP shaft 3 by means of a speed reducer 6. This speed reducer is generally a planetary or epicyclic speed reducer.

[0044] The following description and the invention more particularly relate to a planetary speed reducer.

[0045] The reducer 6 is positioned in the upstream or downstream part of the turbine relative to the general direction of the gas within the turbine. A fixed structure is arranged to form a casing E around the reducer 6, which fixed structure schematically includes here an upstream part 5a and a downstream part 5b of the engine casing or stator 5. Here, the casing E is sealed upstream at the bearing height to allow the fan shaft 4 to pass through, and is sealed downstream at the height of the passage of the LP shaft 3.

[0046] Figure 2 A part of the reducer 6 is shown. On the input side, the reducer 6 is connected, for example via a spline 7a, to the LP shaft 3. Thus, the LP shaft 3 drives a planetary gear known as the sun gear 7. Conventionally, the sun gear 7 (whose axis of rotation is the same as the axis X of the turbine) drives a series of pinions (known as planet gears 8), which are evenly distributed around the axis of rotation X at the same diameter. This diameter is equal to twice the operating center distance between the sun gear 7 and the planet gears 8. For this type of application, the number of planet gears 8 is typically limited between three and eight.

[0047] All the planet gears 8 are held by a frame known as the planet carrier 10. Each planet gear 8 rotates about its own axis Y and meshes with the ring gear 9.

[0048] At the output of the reducer, in this planetary configuration, all the planet gears 8 are held by the planet carrier 10 fixed to the engine casing or stator 5. Each planet gear drives the ring gear, which is connected to the fan shaft 4 via the ring gear carrier 12.

[0049] Each planet gear 8 is mounted for free rotation by means of a bearing 11 (such as a rolling bearing or a hydrostatic bearing). 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 by means of one or more structural frames 10a of the planet carrier 10. The number of shafts and bearings is equal to the number of planet gears. For reasons of operation, installation, manufacture, testing, repair or spare parts, the shafts 10b and the frames 10a can be divided into multiple parts.

[0050] For the same reasons as above, the toothing of the reducer can be a herringbone toothing and is formed by two coaxial annular rows of teeth, the teeth of the first row having a helix angle opposite to that of the second row.

[0051] The ring gear 9 includes a herringbone toothing and is formed by two half-ring gears:

[0052] Upstream half ring gear 9a, which includes an edge 9aa and a fastening flange 9ab, and the edge 9aa and the fastening flange 9ab are connected to each other by a frustoconical web 13a. The edge 9aa includes teeth of the front helix or the tooth portion of the reducer at its inner circumference. The front helix meshes with the front helix of the planetary gear 8, and the front helix of the planetary gear meshes with the front helix of the sun gear 7. The web 13a extends radially outward at the outer circumference of the edge 9aa. The flange 9ab extends in a plane perpendicular to the axis X.

[0053] Downstream half ring gear 9b, which includes an edge 9ba and a fastening flange 9bb, and the edge 9ba and the fastening flange 9bb are connected to each other by a frustoconical web 13b. The edge 9ba includes the rear teeth of the helix or the tooth portion of the reducer at its inner circumference. The downstream helix meshes with the downstream helix of the planetary gear 8, and the downstream helix of the planetary gear meshes with the downstream helix of the sun gear 7. The web 13b extends radially outward at the outer circumference of the edge 9ba. The flange 9bb extends in a plane perpendicular to the axis X.

[0054] The fastening flange 9ab of the front ring gear 9a and the fastening flange 9bb of the rear ring gear 9b form the fastening flange 9c of the ring gear. The flange 9c extends perpendicular to the annular space 14, which is located between the half ring gears 9a, 9b or more precisely between the edges 9aa, 9ba. For example, the ring gear 9 is fixed to the ring gear carrier 12 by assembling the fastening flange 9c of the ring gear and the fastening flange 12a of the ring gear carrier using bolts.

[0055] Figure 2 The arrow in shows the oil flow for lubricating the various components and gears of the reducer in the reducer 6.

[0056] Figure 2 The technology of has the disadvantages related to the large size of its ring gear 9, especially the large radial dimension.

[0057] The present invention proposes to modify the assembly method of the ring gear so as to be able to remove the above-mentioned web in particular.

[0058] Figures 3 to 5 An alternative embodiment is shown, in which the elements described above are denoted by the same reference numerals.

[0059] These variants have at least one common point related to the use of the annular covering member 20 to ensure the assembly of the ring gear 9, especially its half ring gears 9a, 9b. The member 20 extends around the space between the ring gears or between the edges 14 and at least a part of the ring gear 9, and is independently fixed to each of the half ring gears 9a, 9b by flanges and / or splines.

[0060] In Figure 3 the embodiment, the half gear rings 9a, 9b do not have flanges. Each edge 9aa, 9ba includes teeth on its inner circumference and splines 22a, 22b on its outer circumference. In particular, these splines can be in the involute of a circle centered on the head. Additionally, each edge 9aa, 9ba can include cylindrical front edges 24a, 24b.

[0061] The covering member 20 has a generally cylindrical shape and extends around the half gear rings 9a, 9b. The upstream end of the covering member 20 is connected to the fan shaft 4. As in the example shown, the member 20 and the shaft 4 can be formed as a single part. The shaft 4 extends upstream from the speed reducer 6 and is thus located on the upstream side of the speed reducer.

[0062] The member 20 includes splines 26a for coupling to the splines 22a and splines 26b for coupling to the splines 22b on its inner circumference. The splines 26a, 26b can extend in a combined or aligned manner with each other.

[0063] Upstream of the splines 26a, 26b, the member 20 includes a radially inner annular edge 28 that forms an axial support for the upstream edge 24a of the upstream half gear ring 9a. The upstream edge 24b of the downstream half gear ring 9b abuts against the downstream annular face of the upstream half gear ring 9a.

[0064] Downstream of the splines 26a, 26b, the member 20 includes splines 26c for coupling to complementary splines 30a of another shaft 30 of the turbine. The shaft 30 extends downstream from the speed reducer 6 and is thus located on the downstream side of the speed reducer. As a non - limiting example, if the turbine is the turbine of the type described above and is shown in Figure 1 then the shaft 30 will be connected to the low - pressure body.

[0065] Alternatively, in the case where the speed reducer of the turbine is located on the downstream side of the turbine, the shaft 4 can be connected to the turbine rotor, and the shaft 30 can be connected to the fan disk.

[0066] Here, the splines 30a are located on the upstream cylindrical portion 30b of the shaft 30, and the upstream end of this upstream cylindrical portion abuts against the downstream annular face of the rear half gear ring 9b. This portion 30b includes a downstream radial face 30c downstream of the splines 30a, which can be defined by the outer annular edge 32 of this portion 30b.

[0067] Downstream of the splines 26a, 26b, 26c, the component 20 further includes an internal thread for screwing on the nut 34, which is axially supported on the face 30d. Thus, it can be understood that in the example shown, the half-tooth rings 9a, 9b and the part 30b of the shaft 30 are axially clamped against each other and clamped against the edge 28 by screwing and clamping the nut 34.

[0068] In the case where the shaft 30 is not present, the nut 34 can be screwed on and directly supported on the downstream face of the rear half-tooth ring 9b.

[0069] Figure 3 A relatively small radial clearance is shown between the component 20 and the edges 9ab, 9bb of the half-tooth rings 9a, 9b. It can also be seen that the stiffness of the component can be adapted to avoid misalignment of the teeth during operation. In the example shown, the radial thickness of the component 20 varies, in particular increasing from its upstream end to its downstream end in order to reinforce this downstream end.

[0070] In Figure 4 the embodiment shown, the half-tooth rings 9a, 9b do not have flanges. Each edge 9aa, 9ba includes tooth parts on its inner circumference and straight splines 22a, 22b on its outer circumference. Additionally, each edge 9aa, 9ba may include upstream cylindrical edges 24a, 24b.

[0071] The covering component 20 has a generally cylindrical shape and extends around the half-tooth rings 9a, 9b.

[0072] In the example shown, the upstream half-tooth ring 9a is particularly connected to the shaft 4 through its edge 24a and may form a single piece with the shaft 4. The shaft 4 extends upstream from the reducer 6 and is thus located on the upstream side of the reducer.

[0073] The downstream half-tooth ring 9b is connected to the shaft 30 and may form a single piece with the shaft 30. The shaft 30 extends downstream from the reducer 6 and is thus located on the downstream side of the reducer.

[0074] If the turbine includes an intermediate turbine (located between the high-pressure turbine and the low-pressure turbine), the shaft 30 may be connected to the rotor of this intermediate turbine. The component 20 includes splines 26a for coupling to the spline 22a and splines 26b for coupling to the spline 22b on its inner circumference. The splines 26a, 26b may extend in a combined or straight-line manner with respect to each other.

[0075] Upstream of the splines 26a, 26b, the component 20 includes a radially inner annular edge 28, which forms an axial support abutment against the upstream edge 24a of the upstream half-tooth ring 9a. The upstream edge 24b of the rear half-tooth ring 9b is supported on the downstream annular face of the upstream half-tooth ring 9a.

[0076] The part 30b of the shaft 30 includes a downstream radial face 30c which may be defined by the outer annular edge 32 of the part 30b.

[0077] Downstream of the splines 26a, 26b, 26c, the component 20 includes an internal thread for screwing on a nut 34 which is axially supported on the face 30d. Thus, it can be understood that the half-toothed rings 9a, 9b are axially clamped against each other and against the edge 28 by screwing on and clamping the nut 34.

[0078] Figure 4 A relatively small radial clearance is also shown between the component 20 and the edges 9ab, 9bb of the half-toothed rings 9a, 9b. It can also be seen that the stiffness of the component can be adapted to avoid misalignment of the teeth during operation. In the example shown, the radial thickness of the component 20 varies, in particular increasing from its front end to its rear end in order to reinforce the rear end.

[0079] In Figure 5 the embodiment shown, the half-toothed rings 9a, 9b are equipped with radial flanges 9ab, 9bb and do not have webs for connecting to the edges 9aa, 9ba of the half-toothed rings. Each edge 9aa, 9ba includes tooth flanks on its inner circumference and radial flanges 9ab, 9bb on its outer circumference.

[0080] The covering component 20 includes a cylindrical wall 20a which is connected to radial flanges 20b, 20c at each of its axial ends. The component 20 does not have coupling splines here.

[0081] The wall 20a extends between the flanges 9ab, 9bb of the toothed ring and directly around the edges 9aa, 9ba, preferably without a gap or with a very small gap in the radial direction. The upstream flange 20b of the component 20 abuts axially against the flange 9ab of the upstream half-toothed ring 9a. The downstream flange 20c of the component 20 presses axially against the flange 9bb of the downstream half-toothed ring 9b.

[0082] The shaft 4 extends upstream from the speed reducer 6 and is thus located on the upstream side of the speed reducer. The shaft 4 includes a radial flange 4a for attachment to the flanges 9ab, 20b. The flanges 4a, 9ab, 20b include through-holes for a screw / nut or similar fastening means (not shown) to pass through.

[0083] The shaft 30 extends downstream from the speed reducer 6 and is thus located on the downstream side of the speed reducer. The shaft 30 includes a radial flange 30d for attachment to the flanges 9bb, 20c. The flanges 30d, 9bb, 20c include through-holes for a screw / nut or similar fastening means (not shown) to pass through.

[0084] As described above, the speed reducer 6 according to the invention can be integrated into a turbine having a counter-rotating turbine.

[0085] In particular, the invention makes it possible to obtain the smallest possible radial dimensions while complying with the following constraints:

[0086] - The assembly of the half-rings must be such that it is possible to transmit the torque from the planet gears to the shaft,

[0087] - The assembly must keep the half-rings in place relative to each other (radially and angularly positioned), and

[0088] - The assembly must maintain the engagement of the teeth of the ring gears.

Claims

1. A mechanical speed reducer (6) for a turbine, comprising: - a central sun gear (7) having a rotational axis X, - a ring gear (9) that extends around the axis X and the sun gear (7) and includes a herringbone tooth portion, the ring gear being formed by two coaxial first half-ring gears (9a) and second half-ring gears (9b), the first half-ring gear and the second half-ring gear being spaced apart from each other by an annular space (14) and each including teeth of the tooth portion, the ring gear being rotatable around the axis X, - planet gears (8) that are disposed between the sun gear (7) and the ring gear (9) and are supported by a planet carrier (10), the planet carrier being fixed and non-rotatable around the axis X, - two shafts that are rotationally fixed to the ring gear (9), - an annular covering member (20) that extends around the annular space (14) and at least a portion of the ring gear (9), the covering member (20) being fixed to each of the first half-ring gear (9a) and the second half-ring gear (9b) by a first radial flange (20b) and a second radial flange (20c), and / or the covering member (20) being fixed to each of the first half-ring gear (9a) and the second half-ring gear (9b) by a first spline (26a), a second spline (26b), and a third spline (26c), characterized in that the ring gear (9) is rotationally fixed to the two shafts that extend on each side of the mechanical speed reducer respectively.

2. The mechanical speed reducer (6) according to claim 1, wherein, the covering member (20): - extends between the two shafts, or - covers a portion of the two shafts, or - is integrally formed with one of the two shafts.

3. The mechanical speed reducer (6) according to claim 1 or 2, wherein, the covering member (20) includes a first spline (26a) for coupling to the first half-ring gear (9a) and a second spline (26b) for coupling to the second half-ring gear (9b), the first half-ring gear and the second half-ring gear being axially clamped against each other and axially abutting against an abutting portion (28) of the covering member by a nut (34) screwed into or onto the covering member.

4. The mechanical speed reducer (6) according to claim 3, wherein, the first half-ring gear (9a) is integrally formed with a first shaft (4) of the two shafts, and the second half-ring gear (9b) is integrally formed with a second shaft (30) of the two shafts.

5. The mechanical speed reducer (6) according to claim 3, wherein, the covering member (20) is integrally formed with a first shaft (4) of the two shafts and further includes a third spline (26c) for coupling to a second shaft (30) of the two shafts.

6. The mechanical speed reducer (6) according to claim 3, wherein, the ring gear (9) does not have fastening flanges.

7. The mechanical speed reducer (6) according to claim 1 or 2, wherein, the covering member (20) includes a cylindrical wall (20a) which is connected to the first radial flange (20b) and the second radial flange (20c) at each of its axial ends, the first radial flange (20b) of the covering member is fixed to the radial flange (9ab) of the first half-ring gear (9a), and the second radial flange (20c) of the covering member is fixed to the radial flange (9bb) of the second half-ring gear (9b).

8. The mechanical speed reducer (6) according to claim 7, wherein, the radial flange (9ab) of the first half-ring gear is clamped between the first radial flange (20b) of the covering member (20) and the radial flange (4a) of the first shaft (4) of the two shafts, and the radial flange (9bb) of the second half-ring gear (9b) is clamped between the second radial flange (20c) of the covering member and the radial flange (30d) of the second shaft (30) of the two shafts.

9. The mechanical speed reducer (6) according to claim 1, wherein, the turbine is a turbine for an aircraft.

10. A turbine comprising the mechanical speed reducer (6) according to any one of claims 1 to 9.

11. The turbine according to claim 10, wherein, the turbine is an aircraft turbine.

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