Mechanical gearbox for aircraft turbomachines

Abstract

The present application relates to a mechanical gearbox (160) for an aircraft turbomachine (1), in particular an aircraft turbomachine, comprising: a sun gear (70) having an axis of rotation; a ring gear (90) surrounding the sun gear (70); planet gears (80) meshing with the sun gear (70) and the ring gear (90), each planet gear (80) having a first toothing portion meshing with the sun gear (84) and a second toothing portion meshing with the ring gear (84), the first toothing portion (82) comprising a series of upstream teeth (82d1) and a series of downstream teeth (82d2) located on either side of a plane (H) perpendicular to the axis of rotation (X) of the sun gear (70), the second toothing portion (84) comprising a series of upstream teeth (84d1) and a series of downstream teeth (84d2) located on either side of the plane (H) and separated from each other by the first toothing portion (82), the teeth being parallel to each other and parallel to the axis of rotation of the planet gears (80).

Description

Technical Field

[0001] This invention relates to the field of mechanical gearboxes for turbines, and particularly to mechanical gearboxes for aircraft turbines. Background Technology

[0002] Prior art includes, in particular, documents WO-A1-2010 / 092263, FR-A1-2987416, FR-A1-3008462, FR-A1-3008463, FR-A1-3041054, EP-A1-3726031 and US-A-3307433.

[0003] The function of a mechanical gearbox is to change the speed ratio and torque ratio between the input and output shafts of a mechanical system.

[0004] New-generation multi-flow turbines, especially those with high bypass ratios, include mechanical gearboxes to drive the shaft of the propeller (e.g., a fan). Typically, the purpose of the gearbox is to convert the so-called rapid rotational speed of the power turbine shaft into a slower rotational speed for the drive shaft of the fan.

[0005] This gearbox comprises a central gear called the sun gear, a ring gear, and gears called planetary gears, which mesh between the sun gear and the ring gear. The planetary gears are held in place by a frame called the planet carrier. The sun gear, ring gear, and planet carrier form a planetary assembly because their axes of rotation coincide with the longitudinal axis X of the turbine. The planetary gears have different axes of rotation, and these axes are evenly distributed along the same running diameter around the axis of the planet. These axes are parallel to the longitudinal axis X.

[0006] There are various gearbox architectures. In existing multi-flow turbines, the gearbox is planetary or epicyclic. In other similar applications, there are so-called differential or "composite" architectures.

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

[0008] In a planetary gearbox, the ring gear is fixed, and the planet carrier is the output shaft of the device, which rotates in the same direction as the sun gear.

[0009] In a compound gearbox, no component is stationary during rotation. The ring gear rotates in the opposite direction to the sun gear and planet carrier.

[0010] A gearbox may include one or more meshing stages. This meshing is achieved in different ways, such as by contact, friction, or by a magnetic field. Contact meshing has several types, such as spur gear meshing, helical gear meshing, or herringbone gear meshing.

[0011] The increased reduction ratios in the target engine's architecture led to the use of a so-called "two-stage" gearbox. In fact, for reduction ratios exceeding 6 or 7, the so-called "single-stage" technology loses its purpose because it is no longer compact enough; thus, a so-called "two-stage" gearbox must be used.

[0012] In single-stage technology, the same toothed portion of the planetary gear mates with both the sun gear and the ring gear. In two-stage technology, the toothed portions of the planetary gear that mate with the sun gear and those that mate with the ring gear are different. Generally, the toothed portions of the planetary gear that mate with the sun gear and the ring gear respectively have different average diameters.

[0013] The main problem with two-stage gearboxes (each stage or gear joint consists of a single set of teeth) is that these gearboxes are asymmetrical about a plane perpendicular to the axis X. As a result, the power entering from the downstream side on the inside and exiting from the upstream side on the outside generates a significant torque at the planetary gears (the terms "upstream" and "downstream" refer to the overall gas flow in a turbine).

[0014] One solution to this problem is to arrange the two gear joints symmetrically about a plane perpendicular to the X-axis (each stage or gear joint includes two sets of teeth). These two gear joints are herringbone-shaped, meaning they each include a series of upstream teeth axially separated from a series of downstream teeth. The upstream teeth are substantially parallel to each other and inclined relative to the X-axis. The downstream teeth are also substantially parallel to each other and inclined relative to the X-axis and relative to the upstream teeth, such that the upstream and downstream teeth form multiple herringbone patterns around the planetary gear. In the herringbone gear joints, the helix angles of the two sets of teeth have the same value (and opposite inclinations), thus causing these sets of teeth to generate opposite axial forces with the same value.

[0015] The upstream and downstream teeth of the gear engagement portion, which mate with the sun gear, are separated from each other by an annular groove. In this technology, the upstream and downstream teeth of the gear engagement portion are symmetrical about the aforementioned plane, meaning that imaginary lines passing through the vertices of the upstream and downstream teeth and extending along these vertices intersect at points located in the plane of symmetry. This also means that an imaginary line passing through the vertex of one of the corresponding upstream and downstream teeth passes through the vertex of one of the downstream and upstream teeth respectively.

[0016] This design has drawbacks in the manufacturing process of planetary gears, particularly during the grinding of the teeth at the meshing joint between the planetary gear and the sun gear. This is because the grinding wheel moves parallel to the teeth and over and / or between the teeth along their entire axial length. When grinding the upstream teeth (or vice versa), to prevent damage from contact between the grinding wheel and the downstream or upstream teeth respectively, the axial groove size between the teeth needs to be excessively large to allow for the end of the stroke and removal of the grinding wheel. This excessive axial size leads to an increase in the axial size of the planetary gear, which in turn increases the axial size of the gearbox, which is detrimental.

[0017] Another drawback of this symmetrical herringbone tooth joint technology is that axial positioning is fixed by each tooth in the tooth series pair, the function of which is:

[0018] - This can introduce potential overstressing into the gearbox, necessitating an increase in its size, ultimately resulting in a larger and heavier gearbox; this has significant implications, especially when the number of planetary gears is greater than three, because the load distribution among the planetary gears is naturally uneven, so an overstressing factor associated with this phenomenon needs to be considered.

[0019] - Alternatively, the sun gear can be forced to be axially free, since the axial position of the first stage is free at this point, and the planetary gear can axially align itself with the position of the meshing teeth of the ring gear, the position of which is itself fixed by the position of the ring gear; this is usually achieved by using a spline that can slide axially to connect the sun gear to its drive shaft; such a connection is at risk of wear and may also introduce damping on the shaft driving the sun gear, which has a negative impact on the dynamic performance of the gearbox and engine.

[0020] This invention provides an improvement to the technology, offering a solution to at least some of the aforementioned drawbacks in a simple, effective, and economical manner. Summary of the Invention

[0021] This invention relates to a mechanical gearbox for a turbine, particularly an aircraft turbine, the gearbox comprising:

[0022] - A sun gear, which has an axis of rotation.

[0023] - A ring gear extending around the sun gear

[0024] - Planetary gears, which mesh with the sun gear and the ring gear and are held by a planet carrier, each planetary gear having an axis of rotation, and each planetary gear including a first toothed portion having an average diameter D1 for meshing with the sun gear, and a second toothed portion having an average diameter D2 different from the average diameter D1 for meshing with the ring gear.

[0025] The first toothed portion includes a series of upstream teeth and a series of downstream teeth, the upstream teeth and downstream teeth being located on either side of a plane perpendicular to the rotation axis of the sun gear and substantially passing through the middle of the planetary gear.

[0026] The second toothed portion includes a series of upstream teeth and a series of downstream teeth, the upstream teeth and downstream teeth being located on opposite sides of the plane and separated from each other by the first toothed portion.

[0027] The feature is that the upstream and downstream teeth of the second toothed portion are parallel to each other and parallel to the rotation axis of the planetary gear.

[0028] The parallelism of the upstream and downstream teeth of the second toothed joint means that these teeth are straight rather than herringbone, which is different from the prior art.

[0029] Using spur gears instead of herringbone gears is advantageous for addressing the axial overpressure issue of planetary gears mentioned above. In fact, using spur gears means that the axial position of the planetary gears is not fixed by the second gear engagement, thus limiting overpressure because spur gears allow axial slippage. Therefore, the planetary gears can be axially aligned with only the sun gear. This allows the axial position of the sun gear to be fixed, which avoids the need for rotating splines to connect the sun gear to its drive shaft, as these splines can wear and limit the gearbox's lifespan.

[0030] The gearbox according to this application may include one or more of the features described below, which may be independent of each other or in combination with each other:

[0031] The upstream and downstream teeth of the first tooth joint and / or the upstream and downstream teeth of the second tooth joint are arranged at an angle around the rotation axis of the planetary gear, thus exhibiting a symmetry fault about the plane. Therefore, contrary to the prior art, the teeth of the first tooth joint are asymmetrical about the midplane of the planetary gear perpendicular to the rotation axis of the sun gear. This symmetry fault is useful for the tooth correction steps described above. In fact, through this symmetry fault, the risk of interaction between the grinding tool and the teeth is limited. When the grinding tool moves on or between the first series (upstream or downstream) teeth, the grinding tool reaches the interdental slot and finds itself in front of the interdental space but not in front of the second series (downstream or upstream) teeth. Thus, the axial dimension of the interdental slot from which the grinding tool is disengaged can be reduced accordingly, thereby reducing the axial dimension of the planetary gear and, consequently, the axial dimension of the gearbox.

[0032] - The first toothed portion may be herringbone type, but alternatively, it may be straight type; in this application, the herringbone toothed portion refers to a toothed portion comprising two series of teeth oriented in different directions; the first series of teeth is inclined relative to an axis (around which the first series of teeth extends), and the second series of teeth is inclined relative to the axis in a different manner than the first series of teeth; thus, the two series of teeth are inclined relative to each other to form a herringbone shape; the helix angles of the two series of teeth have the same value and opposite inclination directions;

[0033] The upstream and downstream teeth of the first tooth joint each include a vertex ridge and two side wing surfaces. The upstream and downstream teeth of the first tooth joint are positioned at an angle about the rotation axis of the planetary gear, such that the vertex ridge of each of the upstream teeth is located on an imaginary line passing through one of the side wing surfaces of one of the downstream teeth.

[0034] - The upstream teeth of the first gear joint are arranged with a pitch between them, and the downstream teeth of the first gear joint are arranged with the same pitch between them. The upstream teeth of the first gear joint are offset relative to the downstream teeth of the first gear joint at an angle of half the pitch about the axis of rotation of the planetary gear. This offset provides sufficient space for the grinding wheel because at the end of the grinding process, the grinding wheel is positioned relative to the space between two of the opposing teeth, thus allowing the tooth series to be closer together without any risk of interference with the grinding wheel. Therefore, several millimeters can be saved in the axial dimension of the planetary gear and the gearbox.

[0035] -The upstream and downstream teeth of the first toothed joint are spaced apart from each other by an annular groove located in the plane;

[0036] - The upstream and downstream teeth of the first toothed joint are parallel to each other and parallel to the rotation axis of the planetary gear, and meet at the level of the plane.

[0037] - The ring gear includes a toothed portion having a series of upstream teeth and downstream teeth, the upstream teeth and downstream teeth of the toothed portion of the ring gear being located on both sides of the plane and separated from each other by the second toothed portion, the upstream teeth and downstream teeth of the ring gear being parallel to each other and parallel to the rotation axis of the sun gear;

[0038] - The sun gear includes a toothed portion (preferably having herringbone teeth), the toothed portion of the sun gear including a series of upstream teeth and downstream teeth, the upstream teeth and downstream teeth being located on both sides of the plane respectively;

[0039] - The toothed portion of the sun gear is integrated with the shaft that drives the sun gear;

[0040] The toothed portion of the sun gear is mounted and fixed to a shaft for driving the sun gear, the drive shaft including an external spline that engages with the complementary internal spline of the sun gear.

[0041] - An annular nut is threaded onto the free end of the shaft and axially presses against the sun gear to axially fix the sun gear to the shaft; thus, the nut locks the sun gear's degree of freedom relative to the shaft;

[0042] - The ring gear is configured to be fixed and not rotate about the axis, and the planet carrier is configured to be movably rotated about the axis;

[0043] The ring gear is configured to rotate movably about the axis, and the planet carrier is configured to be fixed and not rotate about the axis.

[0044] The present invention also relates to a turbine, particularly an aircraft turbine, the turbine comprising the mechanical gearbox described above. Attached Figure Description

[0045] The present invention will now be described with reference to the accompanying drawings, wherein:

[0046] Figure 1 This is a schematic axial cross-sectional view of a turbine according to the present invention;

[0047] Figure 2 This is a partial axial cross-sectional view of a single-stage mechanical gearbox, and illustrates the prior art of the present invention;

[0048] Figure 3This is a partial axial cross-sectional view of a dual-stage mechanical gearbox, and illustrates prior art prior to this invention;

[0049] Figure 4 for Figure 3 Another schematic cross-sectional view of the gearbox;

[0050] Figure 5 A partial axial cross-section and perspective view of a dual-stage mechanical gearbox are shown, and embodiments of the invention are illustrated.

[0051] Figure 6 A purely schematic view of one of the teeth in the gear mesh of a planetary gear in a gearbox;

[0052] Figure 7 for Figure 6 A magnified view of a portion showing an example of the sun gear mounted on its drive shaft, and

[0053] Figure 8 A schematic perspective view of a portion of the first tooth contact of a planetary gear in a gearbox according to the present invention. Detailed Implementation

[0054] Figure 1 A turbine 1 is shown, which typically includes 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 together form a high-pressure (HP) body. The low-pressure compressor 1b and the low-pressure turbine 1d are connected by a low-pressure shaft 3 and together form a low-pressure (LP) body.

[0055] Fan S is driven by fan shaft 4, which is driven by LP shaft 3 via gearbox 6. Gearbox 6 is typically planetary or epicyclic.

[0056] The following description relates to a planetary gearbox, in which the planet carrier and sun gear are rotatably movable, and the gearbox's ring gear is fixed in the engine's frame of reference.

[0057] Gearbox 6 is located in the upstream portion of the turbine. Here, schematically, a fixed structure comprising an upstream portion 5a and a downstream portion 5b (forming the engine housing or stator 5) is arranged to form a housing E surrounding gearbox 6. This housing E is sealed upstream at the bearing level through which the fan shaft 4 passes, and downstream at the passage level of the LP shaft 3.

[0058] Figure 2 The planetary gearbox 6 is shown. On the input side, the gearbox 6 is connected to the LP shaft 3, for example, via an internal spline 7a. Therefore, the LP shaft 3 drives a center gear called the sun gear 7. Conventionally, the axis of rotation of the sun gear 7 coincides with the axis X of the turbine, and the sun gear drives a series of gears called planetary gears 8, which are evenly distributed around the axis X on the same diameter. This diameter is equal to twice the operating center distance between the sun gear 7 and the planetary gears 8. For this type of application, the number of planetary gears 8 is typically limited to between three and seven.

[0059] The set of planetary gears 8 is held by a frame called planet carrier 10. Each planetary gear 8 rotates about its own axis Y and meshes with a ring gear 9.

[0060] The output will be as follows:

[0061] In this planetary configuration, the set of planetary gears 8 causes the planet carrier 10 to rotate about the turbine axis X. The ring gear is attached to the engine housing or stator 5 via the ring gear carrier 12, and the planet carrier 10 is attached to the fan shaft 4.

[0062] - In another planetary configuration, the set of planetary gears 8 is held by a planet carrier 10 attached to the engine housing or stator 5. Each planetary gear is driven by an annular gear fixed to the fan shaft 4 via an annular gear carrier 12.

[0063] - In another different configuration, the set of planetary gears 8 is held by a planet carrier 10 connected to the first fan shaft 5. Each planetary gear is driven by an annular gear fixed to the annular gear of the second counter-rotating fan shaft 4 via an annular gear carrier 12.

[0064] Each planetary gear 8 is rotatably mounted by means of a bearing 11 (e.g., a bearing or hydrodynamic bearing). Each bearing 11 is mounted on one of the shafts 10b of the planet carrier 10, and all shafts are positioned relative to each other by one or more structural frames 10a of the planet carrier 10. The number of shafts 10b and the number of bearings 11 are equal to the number of planetary gears. The shafts 10b and frames 10a may be divided into multiple parts for reasons of operation, assembly, manufacturing, inspection, maintenance, or replacement.

[0065] For the same reasons as described above, the toothed portion of a planetary gear can be divided into multiple helices or teeth, each helix or tooth having an intermediate plane P, P'. The example details the operation of the gearbox, wherein each planetary gear includes two series of herringbone teeth that mesh with a ring gear (which is divided into two ring gear halves):

[0066] - The upstream ring gear half 9a consists of a rim 9aa and a fastening flange half 9ab. On the rim 9aa is a front helix that meshes with the helical engagement of the toothed portion 8d of each planetary gear 8. The helix of the toothed portion 8d also meshes with the helix of the sun gear 7.

[0067] The downstream ring gear half 9b includes a rim 9ba and a fastening flange half 9bb. On the rim 9ba is a rear helix that meshes with the helical engagement of the toothed portion 8d of each planetary gear 8. The helix of the toothed portion 8d also meshes with the helix of the sun gear 7.

[0068] Although the helical width varies between the sun gear 7, planet gear 8 and ring gear 9 due to tooth overlap, these helical widths are centered on the intermediate plane P for the upstream tooth and on another intermediate plane P for the downstream tooth.

[0069] therefore, Figure 2 The example shown is a single-stage gearbox, where the same toothed portion 8d of each planetary gear 8 meshes with both the sun gear 7 and the ring gear 9. Even though the toothed portion 8d comprises two sets of teeth, these teeth have the same average diameter and form a single toothed portion known as a herringbone tooth profile.

[0070] The fastening flange half 9ab of the upstream gear ring 9a and the fastening flange half 9bb of the downstream gear ring 9b form the fastening flange 9c of the ring gear. For example, the ring gear 9 is fixed to the ring gear carrier by assembling the fastening flange 9c of the ring gear and the fastening flange 12a of the ring gear carrier together using a bolt assembly.

[0071] Figure 2 The arrows in the diagram depict oil delivery within gearbox 6. Oil enters gearbox 6 from stator section 5 into turbine stator 13 via various pathways, which will not be specifically specified in this view as they pertain to one or more architecture types. Turbine stator 13 includes injectors 13a and arms 13b. Injectors 13a lubricate the gear teeth, while arms 13b lubricate the bearings. Oil is supplied to injectors 13a and exits through end 13c to lubricate the gear teeth. Oil is also supplied to arms 13b and flows through the bearing supply inlet 13d. The oil then flows through the shaft into one or more buffers 10c and subsequently exits through orifice 10d to lubricate the planetary gear bearings.

[0072] Figure 3 and Figure 4 Another example of a gearbox architecture known as a dual-stage gearbox is shown, which includes:

[0073] - Sun gear 70, the sun gear having a rotation axis X

[0074] - Ring gear 90, the ring gear extending about the sun gear and configured to be fixed and not rotate about axis X, and

[0075] - Planetary gear 80, which meshes with sun gear 70 and ring gear 90 and is held by planet carrier 100, which causes movable rotation about axis X.

[0076] Plane H is defined as a mid-plane perpendicular to axis X and passing substantially through the middle of gearbox 60. Figure 4 ).

[0077] The sun gear 70 includes an internal spline 70a for connection with the LP shaft 30 and an external toothed portion 70b for meshing with the planetary gear 80. The toothed portion 70b has two sets of adjacent herringbone teeth, separated from each other by radially outwardly oriented annular grooves 72. The toothed portion 70b is symmetrical about a plane H, with the teeth located on either side of the plane H passing through the grooves 72.

[0078] The ring gear 90 is formed by two independent rings 90a and 90b and includes a toothed portion which is divided into two series of herringbone teeth 90d1 and 90d2 supported by the two rings respectively.

[0079] Rings 90a and 90b are arranged symmetrically about plane H, which thus extends between the rings. The rings are connected and secured to the annular gear carrier 120 by annular connecting covers 122. The covers 122 are independent of each other, and each cover has an axial half-section of approximately S-shape, which provides a certain degree of radial flexibility to the cover 122 through elastic deformation during operation.

[0080] Each ring 90a, 90b extends around axis X and is secured to the corresponding cover 122 via the outer periphery of the ring. The inner periphery of the ring includes one of teeth 90d1, 90d2.

[0081] The ring gear carrier 120 has a generally annular shape around axis X, and more particularly a double-conical shape. Therefore, the ring gear carrier includes a first upstream (left side in the figure) section, which includes an upstream end with a smaller diameter and a downstream end with a larger diameter, the downstream end with the larger diameter connecting to the upstream end with the larger diameter of another downstream (right side in the figure) section. The ends with the larger diameters of the sections are thus interconnected, and the ends with the smaller diameters of the sections form the axial ends of the ring gear carrier.

[0082] The upstream end of the ring gear carrier 120 extends around the planet carrier 100 or a shaft connected to the planet carrier, and is centered on the planet carrier or shaft and rotatably guided by means of at least one bearing 124. Similarly, the downstream end of the ring gear carrier 120 extends around the planet carrier 100 or a shaft connected to the planet carrier, and is centered on the planet carrier or shaft and rotatably guided by means of at least one additional bearing 126.

[0083] Similar to the case of the ring gear 90, the ring gear carrier 120 is symmetrical about the plane H, which intersects the ring gear carrier at the middle and thus passes through the end of the aforementioned section with a larger diameter.

[0084] Each planetary gear 80 includes a first toothed portion 82 for meshing with a sun gear 70 and a second toothed portion 84 for meshing with a ring gear 90. The first toothed portion has an average diameter D1, and the second toothed portion has an average diameter D2, which is different from and, in particular, smaller than the average diameter D1. The average diameter is measured from the axis Y of each planetary gear and represents the average between the maximum and minimum diameters of the toothed portion of that planetary gear.

[0085] Each planetary gear 80 includes a cylindrical body 86 and an annular web 88 extending substantially radially outward from the center of the body 86. A gear engagement 84 is divided into two sets of herringbone teeth 84d1, 84d2 located at corresponding axial ends of the body 86. A gear engagement 82 includes two series of herringbone teeth 82d1, 82d2 located at the outer periphery of the web 88 and separated from each other by an annular groove 89 that opens radially outward relative to the axis Y.

[0086] The toothed portion 82 is passed through by the plane H through the groove 89 in its middle, so the teeth 82d1 and 82d2 are arranged on both sides of the plane H. The teeth 84d1 and 84d2 are also arranged symmetrically about the plane H.

[0087] The outer periphery of the toothed portion 82 and the web 88 has an axial dimension smaller than the axial distance between rings 90a and 90b and between cover 122, so that each planetary gear 80 can rotate freely in the ring gear carrier 120 and between rings 90a and 90b and between cover 122.

[0088] This architecture has some drawbacks, which are addressed by improvements made to the gearbox 160 according to the invention, as illustrated in the embodiment shown below. Figure 5 middle.

[0089] The above text about Figure 3 and Figure 4 The described elements are in Figure 5 The same reference numerals are used to indicate them. Therefore, the above text regarding... Figure 3 and 4 The description applies to Figure 5 An embodiment may be adopted, provided that it does not contradict or be replaced by the following content.

[0090] The first improvement to the gearbox 160 involves teeth 82d1 and 82d2 of the first toothed portion 82. The first toothed portion 82 is herringbone shaped, which is consistent with... Figure 3 and Figure 4 The gearbox is the same as 60. However, with Figure 3 and Figure 4 Unlike the gearbox 60, the teeth 82d1 and 82d2 of the gear engagement 82 are asymmetrical about the plane H. Conversely, in the gearbox 160 according to the invention, the upstream tooth 82d1 is offset at an angle relative to the downstream tooth 82d2 about the axis Y, as shown below. Figure 8 As shown.

[0091] Figure 6 This is a purely schematic illustration of the teeth 82d1, 82d2 of the toothed joint 82. Each tooth 82d1, 82d2 includes a vertex 82s with a generally straight ridge. Each tooth 82d1, 82d2 also includes two side surfaces 82f extending from the vertex 82s or the vertex ridge into the inter-tooth space 82e. As schematically shown, the cross-section of each tooth 82d1, 82d2 is generally triangular or trapezoidal.

[0092] The upstream teeth 82d1 and downstream teeth 82d2 of the first toothed portion 82 are arranged at an angle around the axis Y, such that the vertex ridge 82s of each upstream tooth 82d1 lies on an imaginary line L passing through one of the side wing surfaces 82f of the downstream tooth 82d2 (see [reference]). Figure 8 ).

[0093] The upstream teeth 82d1 are arranged with a pitch P between them. The downstream teeth 82d2 are arranged with the same pitch P between them. Preferably, the upstream teeth 82d1 are offset relative to the downstream teeth 82d2 at an angle of half the pitch about the axis of rotation Y of the planetary gear 80.

[0094] This offset allows sufficient space for the grinding wheel, which is positioned relative to the space or gap 82e between two adjacent teeth at the end of the grinding process. Therefore, by reducing the axial dimension of the groove 89 located between the tooth series, the tooth series 82d1, 82d2 can be brought closer together without the risk of interference with the grinding wheel. This saves several millimeters in the axial dimension of the planetary gear 80 and the gearbox 160.

[0095] Another improvement to the gearbox 160 involves the second toothed portion 84, which is no longer herringbone but a straight toothed portion (see...). Figure 5The toothed portion 84 includes an upstream tooth 84d1 and a downstream tooth 84d2 that are parallel to each other and parallel to the axis of rotation Y of the planetary gear 80. Therefore, unlike the first toothed portion 82, the second toothed portion 84 is symmetrical about the aforementioned plane H (a plane that passes through the groove 89 and is perpendicular to the axis X).

[0096] Using a straight toothed joint 84 instead of a herringbone joint is advantageous for resolving the aforementioned problem of axial overpressure on the planetary gear 80. Since the straight toothed joint 84 allows the planetary gear to slide axially relative to the ring gear 90, using the straight toothed joint 84 prevents the axial position of the planetary gear 80 from locking due to the joint 84, thus limiting the occurrence of overpressure.

[0097] Therefore, planetary gear 80 can be aligned axially only with sun gear 70, and thus the axial position of sun gear can be ensured.

[0098] like Figure 7 As shown, the sun gear 70 includes a toothed portion 70b with herringbone teeth, which is complementary to the toothed portion 82 of the planetary gear 80 for meshing. Therefore, the toothed portion 70b includes upstream and downstream teeth located on opposite sides of plane H and spaced apart from each other by slots 72. Due to the complementarity of the toothed portion 70b with the toothed portion 82 of the planetary gear, the series of toothed portions 70b also exhibits a symmetrical defect (offset) about plane H.

[0099] The sun gear 70 and its toothed portion 70b can be integral with the LP shaft 30. In the variant shown here, the sun gear 70 is mounted and fixed to the LP shaft 30.

[0100] In this variant, the LP shaft 30 includes an external spline that engages with the complementary internal spline 70a of the sun gear 70, and an annular nut 94 is threaded onto the free end of the LP shaft 30 and axially pressed against the sun gear to axially secure it to the shaft. The sun gear 70 includes, for example, an inner annular edge 96, which is axially clamped between the nut 94 and an annular shoulder (not shown) of the LP shaft 30. Thus, the nut 94 locks the degree of freedom of the sun gear 70 relative to the LP shaft 30.

[0101] The ring gear 90 of gearbox 160 is similar to that of gearbox 60, except that the teeth 90d1 and 90d2 of its toothed portion 90 are straight teeth and are therefore parallel to each other and parallel to the axis X.

[0102] The improvements mentioned above can be used independently or in combination.

[0103] Other improvements are also possible.

[0104] The teeth 84d1 and 84d2 of the gear joint 84 can be offset from each other at an angle around the axis Y of each planetary gear 80. This offset can be used alone or in combination with the offset of the teeth 82d1 and 82d2 of the gear joint 82.

[0105] In another, unshown, alternative to the gearbox according to the invention, the toothed portion 82 of each planetary gear 80 may also be spur gear. Therefore, it should be understood that the toothed portion 70B of the sun gear will also be spur gear. The toothed portion 84 of each planetary gear 80 may be spur gear, as described above, or may have herringbone teeth. In this configuration, the teeth 82d1, 82d2 of the spur geared portion 82 may be spaced apart from each other by the groove 89, or they may meet at the level of plane H.

[0106] The gearbox 160 of the present invention is particularly compatible with the following situations:

[0107] - "Plane" applications with a rotating planetary carrier and a fixed ring gear;

[0108] - "Planetary" applications with rotating ring gears and fixed planetary carriers;

[0109] - Differential applications with rotating ring gears and planetary carriers;

[0110] - Rolling bearings and hydrodynamic bearings;

[0111] - Integrated or multi-part planetary carrier.

Claims

1. A mechanical gearbox (160) for a turbine (1), the gearbox comprising: - Sun gear (70), which has a rotation axis (X). - A ring gear (90) extending around the sun gear (70). - Planetary gears (80), which mesh with the sun gear (70) and the ring gear (90) and are held by a planet carrier (100), each of the planetary gears (80) having an axis of rotation (Y), and each planetary gear including a first toothed portion (82) having an average diameter D1 for meshing with the sun gear (70), and a second toothed portion (84) having an average diameter D2 different from the average diameter D1 for meshing with the ring gear (90). The first toothed portion (82) includes a series of upstream teeth (82d1) ​​and a series of downstream teeth (82d2), the upstream and downstream teeth being located on both sides of a plane (H) perpendicular to the rotation axis (X) of the sun gear (70) and substantially passing through the middle of the planetary gear (80). The second toothed portion (84) includes a series of upstream teeth (84d1) and a series of downstream teeth (84d2), the upstream teeth and downstream teeth being located on both sides of the plane (H) and separated from each other by the first toothed portion (82). The second toothed portion (84) is characterized in that the upstream tooth (84d1) and the downstream tooth (84d2) are parallel to each other and parallel to the rotation axis (Y) of the planetary gear (80).

2. The mechanical gearbox (160) according to claim 1, wherein, The upstream teeth (82d1) ​​and downstream teeth (82d2) of the first toothed portion (82) and / or the upstream teeth (84d1) and downstream teeth (84d2) of the second toothed portion (84) are arranged at an angle around the rotation axis (Y) of the planetary gear (80), thereby presenting a symmetrical defect about the plane (H).

3. The mechanical gearbox (160) according to claim 1 or 2, wherein, The first toothed part (82) has a herringbone tooth shape.

4. The mechanical gearbox (160) according to claim 2, wherein, The first toothed portion (82) is herringbone toothed, and the upstream tooth (82d1) ​​and downstream tooth (82d2) of the first toothed portion (82) each include a vertex ridge and two side wing surfaces. The upstream tooth (82d1) ​​and downstream tooth (82d2) of the first toothed portion (82) are angularly positioned about the rotation axis (Y) of the planetary gear (80) such that the vertex ridge of each of the upstream teeth (82d1) ​​is located on an imaginary line passing through one of the side wing surfaces of one of the downstream teeth (82d2).

5. The mechanical gearbox (160) according to claim 4, wherein, The upstream teeth (82d1) ​​of the first toothed portion (82) are arranged to have a pitch (P) between them, and the downstream teeth (82d2) of the first toothed portion (82) are arranged to have the same pitch (P) between them. The upstream teeth (82d1) ​​of the first toothed portion (82) are offset relative to the downstream teeth (82d2) of the first toothed portion (82) at an angle of half the pitch about the axis of rotation (Y) of the planetary gear (80).

6. The mechanical gearbox (160) according to claim 1 or 2, wherein, The upstream tooth (82d1) ​​and downstream tooth (82d2) of the first toothed portion (82) are spaced apart from each other by an annular groove located in the plane (H).

7. The mechanical gearbox (160) according to claim 1 or 2, wherein, The upstream tooth (82d1) ​​and downstream tooth (82d2) of the first toothed portion (82) are parallel to each other and parallel to the rotation axis (Y) of the planetary gear (80), and meet at the level of the plane (H).

8. The mechanical gearbox (160) according to claim 1 or 2, wherein, The ring gear (90) includes a toothed portion having a series of upstream and downstream teeth (90d1, 90d2), the upstream and downstream teeth of the ring gear being located on both sides of the plane (H) and separated from each other by the second toothed portion (84), the upstream and downstream teeth (90d1, 90d2) of the ring gear (90) being parallel to each other and parallel to the rotation axis (X) of the sun gear (70).

9. The mechanical gearbox (160) according to claim 1 or 2, wherein, The sun gear (70) includes a toothed portion (70b) having a series of upstream and downstream teeth, the upstream and downstream teeth of the toothed portion of the sun gear being located on opposite sides of the plane (H).

10. The mechanical gearbox (160) according to claim 9, wherein, The toothed portion of the sun gear (70) is integrated with the shaft (30) used to drive the sun gear.

11. The mechanical gearbox (160) according to claim 9, wherein, The toothed portion of the sun gear (70) is mounted and fixed to a shaft (30) for driving the sun gear, the shaft (30) including an external spline that engages with the complementary internal spline (70a) of the sun gear (70).

12. The mechanical gearbox (160) according to claim 11, wherein, An annular nut (94) is threaded onto the free end of the shaft (30) and axially pressed against the sun gear (70) to axially fix the sun gear onto the shaft (30).

13. The mechanical gearbox (160) according to claim 1 or 2, wherein, The ring gear (90) is configured to be fixed and not rotate about the axis, and the planet carrier (100) is configured to be movably rotated about the axis (X).

14. The mechanical gearbox (160) according to claim 1 or 2, wherein, The ring gear (90) is configured to rotate movably about the axis, and the planet carrier (100) is configured to be fixed and not rotate about the axis (X).

15. The mechanical gearbox (60) according to claim 1, wherein, The turbine in question is the turbine of the aircraft.

16. A turbine (1) comprising a mechanical gearbox (160) according to any one of claims 1-15.

17. The turbine (1) according to claim 16, wherein, The turbine in question is the turbine of the aircraft.

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