阅读说明：本技术 涡轮发动机的具有包括交联结构的辐板的小齿轮 (Pinion gear of turbine engine with web comprising cross-linked structure ) 是由 雷米·约瑟夫·兰奎廷 阿诺德·乔治斯·尼芬克尔 安托尼·拉赫泰特 于 2020-05-15 设计创作，主要内容包括：本发明涉及一种用于飞行器涡轮发动机齿轮系的小齿轮,所述小齿轮包括：-圆柱形主体(2),所述圆柱形主体沿轴线延伸,并且被配置为与容纳在所述圆柱形主体中的轴接合,-轮缘(4),所述轮缘与所述圆柱形主体同轴,-辐板(3),所述辐板由前壁(32)和后壁(33)轴向地限定并且从所述圆柱形主体径向地延伸到所述轮缘,所述前壁和后壁中的每一者都具有密度,所述小齿轮包括在所述前壁和所述后壁之间围绕所述圆柱形主体的交联结构(5),所述交联结构包括沿三维坐标系的三个轴线重复的晶胞,所述晶胞的密度严格地小于所述前壁和后壁中的每一者的密度。(The invention relates to a pinion for an aircraft turbine engine gear train, the pinion comprising: -a cylindrical body (2) extending along an axis and configured to engage with a shaft housed in said cylindrical body, -a rim (4) coaxial with said cylindrical body, -a web (3) axially defined by a front wall (32) and a rear wall (33) and extending radially from said cylindrical body to said rim, each of said front and rear walls having a density, said pinion comprising a cross-linking structure (5) around said cylindrical body between said front and rear walls, said cross-linking structure comprising a unit cell repeating along three axes of a three-dimensional coordinate system, said unit cell having a density strictly lower than the density of each of said front and rear walls.)

1. A pinion gear for an aircraft turbine gear train, the pinion gear comprising:

-a cylindrical body (2) extending along an axis (A) and configured to engage with a shaft housed in said cylindrical body,

-a rim (4) coaxial with the cylindrical body (2),

-a web (3) axially defined by a front wall (32) and a rear wall (33), each of which having a density, and radially extending from the cylindrical body (2) to the rim (4),

the pinion is characterized in that the web includes: a cross-linking structure (5) around the cylindrical body (2) between the front wall (32) and the rear wall (33), the cross-linking structure comprising a unit cell (M) repeated along three axes of a three-dimensional coordinate system, the density of the unit cell being strictly less than the density of each of the front and rear walls.

2. Pinion according to claim 1, wherein the cross-linking structure (5) extends radially to an interface (I) between the cross-linking structure and the rim (4).

3. Pinion according to claim 1 or 2, wherein the cross-linking structure (5) has axial symmetry around the axis (a) of the cylindrical body.

4. Pinion according to any of claims 1 to 3, wherein the front wall (32) and/or the rear wall (33) extend radially from the cylindrical body (2) to the rim (4).

5. Pinion according to any one of claims 1 to 4, wherein the rim (4) comprises a cantilever (41) extending axially beyond the front wall (32) or the rear wall (33), preferably the cantilever (41) has an average axial width (43) less than 80% of the average axial width (42) of the rim (4).

6. Pinion according to any one of claims 1 to 5, wherein the radial distance between the cross-linking structure (5) and the cylindrical body (2) at any axial position along the axis (A) is greater than a non-zero minimum radial clearance (8).

7. Pinion according to any one of claims 1 to 6, wherein the front and rear walls are materially continuous with the cylindrical body (2) and with the rim (4), the front and rear walls meeting the rim at the interface (I).

8. Pinion according to any of claims 1 to 7, wherein the unit cell (M) of the cross-linked structure (5) has a hexagonal diamond geometry.

9. Pinion according to any one of claims 1 to 8, wherein the material density of the unit cells (M) of the cross-linked structure (5) is less than or equal to 5%.

10. A reduction gearbox for a turbine, comprising a reduction gear train (18) configured to be rotationally coupled with a turbine shaft (15) of a turbine and with an output shaft (17) of the turbine, the reduction gear train comprising a pinion according to any one of claims 1 to 9.

11. An aircraft turbomachine, preferably a helicopter turbine engine (1), said turbomachine comprising at least one shaft and comprising a pinion according to any one of claims 1 to 9, said shaft being rotationally coupled with said pinion.

12. An aircraft comprising a turbine according to claim 11.

13. A method of manufacturing a pinion for an aircraft turbine gear train, the method comprising the sequential steps of:

-obtaining (E2) a cylindrical body of said pinion;

-obtaining (E3) a front wall of a web (3) of said pinions and obtaining a rim materially continuous with said front wall, said front wall having a density;

-positioning (E4) a cross-linking structure (5) against the front wall, the cross-linking structure being obtained by repeating a unit cell (M) along three axes of a three-dimensional coordinate system, the density of the unit cell being strictly less than the density of the front wall,

-obtaining (E5) a rear wall of said web of said pinion against said cross-linked structure, the material of said rear wall being chosen such that the density of said rear wall is strictly greater than the density of said cross-linked structure,

said cylindrical body, said front and rear walls of said web (3) and said rim (4) being obtained in a single piece by additive manufacturing, said web (3) thus obtained incorporating said cross-linked structure (5), the pinion obtained being according to any one of claims 1 to 9.

14. Manufacturing method according to claim 13, wherein the front wall and/or the rear wall of the web (3) is obtained by selective laser melting on a powder bed.

15. Manufacturing process according to claim 13 or 14, comprising a step (E1) of obtaining the crosslinked structure (5), said step comprising repeating the unit cell (M) along the three axes to obtain a deformable matrix, and further comprising deforming the deformable matrix, preferably by stretching, so as to give it a predetermined shape.

16. The manufacturing method according to any one of claims 13 to 15, wherein:

-during the positioning (E4) step, contact is achieved between the front wall and the cross-linking structure (5) at a first inclination angle with respect to a plane perpendicular to the axis (A) of the cylindrical body, preferably greater than 20 degrees,

-during the step of obtaining (E5) the rear wall, contact is achieved between the rear wall and the cross-linking structure (5) at a second inclination with respect to the plane, strictly less than the first inclination, the cross-linking structure (5) acting as a support for obtaining the rear wall.

Technical Field

The present invention is in the field of power transmissions with gear trains for aircraft turbines.

In particular, the invention relates to a pinion for a drive shaft of an aircraft turbine, to a reduction gearbox comprising a pinion of this type, to a turbine comprising a pinion of this type and to a manufacturing method for a pinion of this type.

Background

The mechanical power generated by the rotation of the movable parts of the turbine is usually transmitted to other parts of the aircraft through a gear transmission.

For example, a helicopter turbine engine comprises, in a known manner: a reduction gearbox enabling transmission between a shaft connected to the free turbine and the output shaft. The reduction gearbox includes a gear train and an accessory drive train. Based on the rotational movement of the free turbine, the reduction gear train transmits the reduced rotational movement to the main transmission gearbox for driving the rotor of the helicopter. The accessory drive train transmits the rotary motion to the different accessories necessary for the operation of the turbine engine: lubrication unit, fuel pump, and electric power supply unit …

The different mechanical force transmission chains in reduction gearboxes comprise a transmission with pinions which performs the transmission step at a predetermined reduction ratio.

Typically, the pinion gear includes a hub portion extending along an axis and teeth on a rim located around the hub portion, wherein the hub portion has a hollow cylindrical space for receiving the turbine shaft. In known pinions, the rim is connected to the hub by a simple web. A simple web may be considered a solid disc having a thickness less than the maximum thickness of the rim. The disc is perforated at the center of the hub to allow passage of a shaft that mates with the pinion.

In aeronautical applications, it is desirable to reduce the mass of the turbine components in order to limit the overall fuel consumption and to optimize the reliability of the components. The reduction in the quality of the turbomachine component (by removing material from a specific region) should not compromise its mechanical properties, but is adapted to optimize the performance of each region of the component according to the mechanical loads expected for that region.

In particular for the pinion of the transmission, care should be taken during operation of the turbine to preserve the deformation of the rim under load and the modal behaviour of the pinion. In the case where the rim of the pinion includes lateral cantilevers on either side of the web, these cantilevers may experience large vibrations and be damaged during operation.

Thus, the level of mechanical performance of the pinion of the turbine shaft may be increased.

Further, in order to reduce the quality of the pinion, it has been proposed to make the solid web of the pinion in an hollowed-out structure by making a plurality of through holes. However, making the web in an hollowed-out structure increases windage loss to degrade the performance of the pinion, and the mass that can be reduced thereby remains insufficient.

Disclosure of Invention

Therefore, there is a need for a pinion gear for a turbine shaft having less mass while having optimized mechanical properties in order to limit the on-board mass of the turbine. It is desirable to distribute the force over the web of the pinion gears so that the transmission containing the pinion gears avoids excessive localized mechanical stress during operation.

In particular, the deformation of the web and the rim under load must be limited. It is also desirable to limit vibration of the transverse faces of the web.

Furthermore, a method of manufacturing a turbine shaft pinion that can achieve a reduction in mass is sought. The sought method must be able to control precisely the mechanical structure of the pinion to optimize the mechanical properties of each region of the component according to the expected stress level.

In response to these needs, a first object of the present invention is a pinion for a gear train of a turbomachine, said pinion comprising:

-a cylindrical body extending along an axis and configured to engage with a shaft received in the cylindrical body,

-a rim coaxial with the cylindrical body,

-a web defined axially by a front wall and a rear wall and radially by said rim, each of said front and rear walls having a density,

the pinion is characterized in that the web includes: a cross-linking structure surrounding the cylindrical body between the front and rear walls, the cross-linking structure comprising a unit cell repeating along three axes of a three-dimensional coordinate system, the unit cell having a density that is strictly less (i.e., less than and not equal to) the density of each of the front and rear walls.

The pinion of the present invention further comprises a web whose internal volume is partially occupied by a cross-linked structure having a density less than the density of said front and rear walls axially defining said web. Thus, an improvement in mass is achieved and the on-board mass of the turbine including the pinion is reduced. It is to be noted that the mass reduction achieved thereby does not require the web to be formed as an openwork structure.

Furthermore, current techniques for manufacturing (e.g. lattice-type) structures, in particular additive manufacturing, provide the cross-linked structure with the mechanical properties necessary for the pinion to withstand the load. The rigidity provided to the web by the cross-linked structure makes it possible to consider reducing the thickness of the transverse faces of the web, or even reducing the thickness of the cantilevers of the rim.

The pinion of the present invention thus combines an improvement in mass with optimized mechanical performance.

Other additional and non-limiting features of the pinion of the invention, either alone or in any of their technically possible combinations, are as follows:

-the cross-linked structure extends radially to an interface between the cross-linked structure and the rim.

-the cross-linked structure has axial symmetry around the axis of the cylindrical body.

-the front wall and/or the rear wall extending radially from the cylindrical body to the rim.

-the rim comprises a cantilever arm extending axially beyond the front wall or the rear wall.

-the cantilever arms have an average axial width less than 80% of the average axial width of the rim, with the cantilever arms extending axially beyond the leading wall or the trailing wall.

-a radial distance between the cross-linking structure and the cylindrical body at any axial position along the axis is greater than a non-zero minimum radial gap.

-the front and rear walls are materially continuous with the cylindrical body and with the rim, the front and rear walls meeting the rim at the interface.

-the unit cells of the cross-linked structure have a hexagonal diamond geometry.

-the material density of the unit cells of the cross-linked structure is less than or equal to 5%.

A second object of the invention is a reduction gearbox for an aircraft turbine, comprising a reduction gear train configured to be rotationally coupled with a turbine shaft of the turbine and with an output shaft of the turbine, the reduction gear train comprising a pinion as described above.

A third object of the present invention is an aircraft turbomachine, preferably a helicopter turbine engine, comprising at least one shaft and comprising a pinion as described above, said shaft being rotationally coupled with said pinion. A fourth object of the invention is an aircraft comprising a turbomachine of this type.

A fifth object of the invention is a method for manufacturing a pinion for a gear train of an aircraft turbomachine, comprising the following successive steps:

-obtaining a cylindrical body of said pinion,

-obtaining a front wall of a web of said pinions and obtaining a rim materially continuous with said front wall, said front wall having a density,

-positioning a cross-linking structure against the front wall, the cross-linking structure being obtained by repeating a unit cell along three axes of a three-dimensional coordinate system, the density of the unit cell being strictly less than the density of the front wall,

-obtaining a rear wall of said web of said pinion against said cross-linked structure, such that the density of said rear wall is strictly greater (i.e. greater than and not equal) than the density of said cross-linked structure,

said cylindrical body, said front and rear walls of said web and said rim are obtained in a single piece by additive manufacturing, said web thus obtained incorporating said cross-linked structure.

The manufacturing method optionally and without limitation has the following features, alone or in combination:

-said front and rear walls of said web are obtained by selective laser melting on a powder bed.

-said method comprises a step of obtaining said cross-linked structure, said step comprising repeating said unit cell along said three axes to obtain a deformable matrix, and further comprising deforming said deformable matrix, preferably by stretching, so as to give said deformable matrix a predetermined shape.

-during the positioning step, contact is achieved between the front wall and the cross-linking structure at a first inclination with respect to a plane perpendicular to the axis of the cylindrical body, said first inclination being preferably greater than 20 degrees, and during the step of obtaining the rear wall, contact is achieved between the rear wall and the cross-linking structure at a second inclination with respect to said plane, said second inclination being strictly smaller than said first inclination, said cross-linking structure acting as a support for obtaining the rear wall.

Drawings

Other features, objects, and advantages of the invention will be apparent from the following description, which is intended to be illustrative only and not limiting, and the following description should be read with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a helicopter turbine engine;

FIG. 2a is a schematic illustration of an intermediate pinion of the turbine engine of FIG. 1, as viewed in longitudinal cross-section along an axis of a pinion hub, in accordance with an embodiment of the present invention;

FIG. 2b shows a side view of the pinion gear of FIG. 2a from the rear thereof;

FIG. 3 shows an example of a three-dimensional unit cell for a pinion internal cross-linking structure;

FIG. 4 illustrates steps of a manufacturing method for a pinion gear according to an embodiment of the present invention;

fig. 5a and 5b are graphs of stresses exerted on the model of the cross-linked structure before and after the front surface of the model of the cross-linked structure is stretched during the mechanical test, respectively.

Detailed Description

The following description relates to examples of pinions suitable for use in the gear train of a reduction gearbox of a helicopter turbine engine. It will be appreciated that the pinion of the present invention can be used with the same advantage for any gear to be fitted to a turbine shaft.

Throughout the following description, like elements shown on the drawings are referred to by the same reference numerals.

Turbine engine structure

Fig. 1 shows a helicopter turbine engine 10. The rotor (not shown) of the helicopter is driven by the free turbine 14 through a reduction gearbox, schematically indicated in fig. 1 with reference numeral 19. The turbine engine 10 includes a compressor 11, a combustor 12, a linked turbine 13, and a free turbine 14. The linked turbine 13 is coupled to the compressor 11 by a shaft 20. Free turbine 14 is attached to turbine shaft 15. In a known manner, the turbine converts the energy released by the exhaust gases into mechanical energy for the helicopter rotor.

The shaft 15 constitutes an input shaft of a reduction gear box 19. The reduction gearbox also has an output shaft 17. The mechanical transmission between the input shaft 15 and the output shaft 17 is provided by a reduction gear train 18 inside a reduction gear box 19. The reduction gear train transmits a reduced rotational movement, proportional to the speed N2 of the turbine engine, to the final drive gearbox through the shaft 17. The reduction gearbox also comprises an accessory drive gearbox (not shown in fig. 1) which transmits the rotary motion with a speed proportional to the speed N1 to the different accessories required for the operation of the turbine engine: lubrication components, fuel pump, power supply … ….

The reduction gear train 18 includes a drive pinion 1a, first and second intermediate pinions 1b, and an output pinion 1 c. In this example, the four pinions are helical gears.

The drive pinion 1a is coupled to the input shaft 15 and meshes with the first intermediate pinion 1 b. The second intermediate pinion 1b meshes with an output pinion 1c coupled to the output shaft 17. The reduction gear train achieves a predetermined reduction ratio. For example, during operation of turbine engine 10, the rotational speed of drive pinion 1a is 42014 revolutions per minute, and the rotational speed of output pinion 1c is 5610 revolutions per minute.

Pinion structure

Fig. 2a shows an example of a pinion 1 according to the invention in longitudinal section. The pinion 1 is suitable for use in a reduction gear train of a reduction gearbox of a turbine engine, for example, as a drive pinion, as an intermediate pinion or as an output pinion. The pinion comprises a hub 2 having a substantially cylindrical shape, configured to engage with a turbine shaft extending along an axis a. The hub 2 supports a web 3 and a rim 4 coaxial with the hub 2. By "coaxial" it is meant that the inner face of the rim 4 and the hub 2 are centred on the same axis a. The rim 4 comprises teeth 40 configured to mesh with other teeth of another gear. For example, if the pinion is the input pinion 1a, the teeth 40 are configured to mesh with the teeth of the intermediate pinion 1b arranged facing the teeth. Preferably, there is a continuity in material between the hub 2, web 3 and rim 4.

In the following, the radial direction is with respect to the axis a.

The hub 2 comprises a front portion and a rear portion. In fig. 2a, the front is on the left and the back is on the right.

The front part of the hub comprises an inner wall 20a and an outer wall 21a and the hub opens into the hollow space 6 of the pinion through a circular opening 24. The rear part of the hub comprises an inner wall 20b and an outer wall 21b and the hub opens into the same hollow space 6 through a circular opening 25. A portion of the inner wall 20a of the forward portion of the hub includes splines 22 for engaging with a complementary element of the outer wall (not shown) of a shaft received in the hub 2 to rotationally fix the pinion gear and the shaft.

The web 3 extends radially from the hub 2 to the rim 4. The web 3 is secured to the front of the hub by a front wall 32 having a front face 30. The web 3 is also secured to the rear of the hub by a rear wall 33 having a rear face 31. The web 3 is also fixed to the rim.

The web 3 is axially defined by a front wall 32 and a rear wall 33 and radially defined by the rim 4.

Fig. 2b shows a side view of the same pinion from the rear of the hub along a visual axis which coincides with the axis a of the hub 2. As shown in fig. 2b, the rear surface 31 of the web 3 of the pinion does not necessarily have a through hole (as does the front surface, which is not visible in this figure). In fact, the cross-linked structure included in the web is of lower quality than a solid web occupying the same space, and it is not necessary to make the web an open structure.

In the example of fig. 2a and 2b, the front wall 32 comprises an inner surface and an outer surface at a lower part of its radial extension. The two surfaces are parallel and each has an inclination of about 40 ° with respect to a plane perpendicular to axis a (vertical in the figure). The front portion of the hub 2 projects from the inner surface of the front wall 32 toward the interior of the pinion. Thus, the front wall 32 of the web funnels radially outward and axially rearward from the outer wall 21a of the hub front portion.

Likewise, the lower portion of the rear wall 33 is funneled extending radially outward and axially forward from the outer wall 21b of the hub rear portion.

The web 3 further comprises a cross-linking structure 5 surrounding the cylindrical body 2 between the front wall 32 and the rear wall 33. The cross-linked structure is formed in whole or in part (in this example, in whole) by a repetition of the same unit cell. The unit cell is repeated along three directions of space to form a cross-linked structure 5. The term "lattice" is often used to designate this type of cross-linked structure.

The density of the unit cells of the cross-linked structure is strictly less than the density of each of the front and rear walls. The mass of the cross-linked structures 5 is therefore smaller than the mass of the continuous material of the front and rear walls, wherein the volume occupied by the continuous material of the front and rear walls is the same as the volume occupied by the cross-linked structures in the web. Thus, the cross-linking structure 5 fills the space between the front wall 32 and the rear wall 33, while the overall mass of the pinion can be reduced.

The structure of the exemplary web 3 in fig. 2a is explained in detail below.

In the example of fig. 2a, the rim 4 has a forward cantilever 41. The cantilever 41 extends axially beyond the front wall 32 and projects from the front surface 30 of the web.

There are a number of configurations possible with respect to the location of the cantilevers of the rims relative to the webs.

In the present example, as shown in fig. 2a, the cantilever 41 extends forwardly by an average axial width 43 which is less than 80%, preferably less than 66%, of the average axial width 42 of the rim 4.

Alternatively, the pinion may comprise a web axially centred with respect to the rim. The pinion then has a rim comprising a rear cantilever of the same size range as the front cantilever. It is also possible to provide the front and rear cantilevers with different axial dimensions.

Alternatively, the pinion may have no front cantilever but only a rear cantilever.

If desired, the ratio of the cantilever of the rim 4 with respect to the thickness of the web can be further reduced with respect to the size of the cantilever 41 shown in figure 2a, without compromising the mechanical properties of the pinion. Such a reduction in the thickness ratio can be obtained by increasing the axial width of the crosslinked structure 5. Alternatively, the pinion may be free of cantilever.

Wheel disk

According to the invention, the pinion comprises a cross-linked structure 5 in the inner volume of the web 3.

By "crosslinked structure" is meant a mechanical structure obtained by multiple repetitions of a three-dimensional unit cell in space. In this example, the unit cell repeats along three dimensions of space that are orthogonal to each other. The cross-linked structure has a low density, and the volume occupied by the three-dimensional unit cell is mainly composed of empty space (empty space). The density of the cross-linked structures 5 is strictly less than the density of the front wall 32 and the density of the rear wall 33 of the web 3. For example, the density of the crosslinked structure 5 is more than ten times smaller than the densities of the walls 32 and 33.

The presence of the cross-linked structure 5, instead of and in place of the material volume that would fill the axial space between the two webs without the cross-linked structure, enables a very large mass improvement without sacrificing the mechanical properties of the pinion.

The presence of the cross-linked structure may reduce the mass of the pinion by more than 15%, or even up to 20%. In this example, for a pinion with a mass of 3.1 kilograms initially, a mass improvement of 600 grams can be achieved if the cross-linked structure is replaced with a solid web, and the mass of the pinion including the cross-linked structure is reduced to 2.5 kilograms.

The presence of the cross-linked structure 5 makes it possible in particular to reduce the thickness of the front wall 32 and of the rear wall 33 with respect to the case in which hollow spaces are used to occupy the volume of the cross-linked structure. As shown in fig. 2a, the maximum thickness of the front and rear walls is preferably less than 50% of the minimum thickness of the cross-linked structure along axis a, and, even more preferably, less than 25% of the minimum thickness of the cross-linked structure along axis a. This helps to reduce the overall mass of the pinion.

The reduction in thickness of the front wall 32 and the rear wall 33 does not compromise the mechanical properties of the web. The mechanical stiffness provided by the cross-link structure 5 may reduce the maximum resonance of the front and rear walls of the web 3 when the pinion is loaded.

Without a cross-linked structure, the rim 4 may be susceptible to excessive deformation under load. The rigidity provided by the crosslinked structure 5 can strongly reduce the deformation. The acceptable level of deformation of the rim under load depends on the type of tooth facing the rim. In this example, the deformation of the rim under load is required to be less than 50 microns.

The mechanical strength provided by the cross-linked structure 5 makes it possible to redistribute the mechanical stresses in the web and reduce the maximum stresses, which in turn prolongs the reliability and the lifetime of the pinion. It is sought that the maximum stress is less than the fatigue bearing capacity of the material from which the web front and rear walls are constructed.

In the present example, the cross-linked structure 5 has axial symmetry about the axis a of the hub 2, which facilitates the manufacture of the pinion.

In the present example, the cross-linked structure 5 advantageously extends in the radial direction to the rim 4. The outer radial part of the cross-linked structure 5 is in contact with the rim 4 at the interface I shown in dashed lines in fig. 2 a. Thus, the cross-linked structure supports the rim in the radial direction.

Alternatively, a radial space may be provided between the outer radial portion of the cross-linked structure and the inner side of the rim 4.

In the example of fig. 2a, the cross-linked structure 5 is not in radial contact with the front portion of the hub 2, nor with the rear portion of the hub 2. Along the axis a, the radial distance between the inner radial wall 50 of the cross-linking structure 5 and the hub 2 is greater than the non-zero minimum radial gap 8. Preferably, the minimum radial gap 8 is greater than or equal to 10%, preferably greater than or equal to 20%, of the total radial extension of the crosslinked structure.

One advantage of this configuration is that the overall mass of the pinion is reduced even more. A minimum radial clearance of the cross-linked structure of 20% of the radial extension achieves a satisfactory compromise between mass reduction and web stiffness retention. In contrast to the construction of the pinion, which is customary in turbines, the overall mass of the pinion is thereby reduced without the web of the pinion having to be hollowed out. Thus, additional losses due to wind resistance are avoided.

Crosslinked structure

Advantageously, the crosslinked structure 5 consists of at least 90% (preferably 100%) of three-dimensional unit cells M of hexagonal diamond type, which are repeated in space along three dimensions of space. Thus, the cross-linked structure includes a three-dimensional lattice formed by the repetition of hexagonal diamond unit cells.

Alternatively, the crosslinked structure may be formed in whole or in part by a repetition of a three-dimensional unit cell of a central cubic type.

The material of the cross-linked structure is typically a metallic material, such as steel. Alternatively, the crosslinked structure may be formed of a polymer.

The crosslinked structure can be obtained in particular by additive manufacturing, in particular by Selective Laser Melting (SLM). And a crosslinked structure is obtained by melting the metal powder. One advantage of the selective laser melting technique is its reliability and speed of execution.

In fig. 3, hexagonal diamond unit cell M is shown. Fig. 3 shows three perspective views of the unit cell M at three different viewing angles in the same three-dimensional coordinate system (X, Y, Z).

The material density of the hexagonal diamond unit cells is advantageously less than 10% to limit the total mass of the cross-linked structure and to allow the onboard mass of the turbine comprising the pinion to be greatly improved. However, the material density must be maintained sufficiently to ensure good mechanical strength of the crosslinked structure. In this example, the material density of the unit cell is 1/20, or 5%. In other words, the ratio of the volume occupied by the empty space to the total volume occupied by the crosslinked structure was 95%. However, the material density of the cross-linked structure may be adjusted so as to minimize the stress exerted on the cross-linked structure by the pinion gear when loaded.

It should be noted that although the cross-linked structure according to the examples shown in fig. 2a, 2b and 3 is entirely composed of repetitions of hexagonal diamond unit cells similar to those shown in fig. 3, a variety of three-dimensional unit cell geometries can be integrated into a single cross-linked structure. The cross-linked structure thus comprises a plurality of regions, each region consisting of a repetition of one three-dimensional unit cell.

Pinion manufacturing method

FIG. 4 illustrates steps of a method 100 of manufacturing a pinion gear according to an embodiment of the present invention. For example, the method 100 may result in a pinion of a turbine reduction gear train similar to the pinion shown in FIG. 2 a. In the following, the example of the pinion in fig. 2a will be used.

In an optional step E1, the cross-linked structure 5 is manufactured and given the desired shape for the front and rear walls of the pinion. Very advantageously, the crosslinked structure 5 is obtained by additive manufacturing. Additive manufacturing constitutes a fast and very flexible solution to obtain the cross-linked structure 5 at moderate cost. A wide variety of cross-linked structure geometries can be obtained by additive manufacturing in terms of the shape and material density of the mesh and the shape of the walls of the cross-linked structure.

The deformable matrix is manufactured, for example, by additive manufacturing, and then shaped to obtain the crosslinked structure 5. The initially obtained matrix may have the shape of a parallelepiped. In order to adapt the cross-linked structure to the desired shape of the pinion, it is appropriate to give the structure an overall cylindrical shape. Such a shape may be obtained by stretching and/or by cutting the substrate.

One advantage of forming the cylindrical shape by stretching is to avoid the open cells at the edges of the cross-linked structure. By "open cell" is meant a cell with one or more edges interrupting the pattern. In fact, open cells have less mechanical strength than non-open cells.

It is also suitable to perforate the central axis of the cross-linking structure 5 to enable positioning of the cross-linking structure around the hub.

Optionally and advantageously, the edge of the crosslink 5 is stretched before the front wall 32 is brought against the crosslink. It has been noted that the edges, in particular the corners, of the unstretched, crosslinked structure may be locally subjected to greater mechanical stress than other regions of the structure. This phenomenon is called the "KT effect". The applicant has observed that stretching the edge can locally reduce the maximum level of mechanical stress to which the edge is subjected.

By way of illustration, a three-dimensional diagram of the stress within the controlling crosslink structure 7 obtained by repeating the hexagonal diamond unit cell is shown in fig. 5a, which is subjected to a load on its lower and upper surfaces during mechanical testing.

Fig. 5b shows a three-dimensional view of the stress in the control structure 7 after stretching the front surface 70 of the control structure.

Prior to stretching, the maximum mechanical stress to which the control structure 7 was subjected during the test was 73432 pascals, and this maximum mechanical stress occurred on the front surface 70.

After the front surface 70 is stretched forward, the mechanical stress experienced by the front surface 70 is redistributed and reduced, as shown in fig. 5 b. The points of maximum stress no longer occur on the front surface 70 but rather at the rear of the structure. The stress on the front surface 70 is less than 31207 pascals.

Thus, by stretching the cross-linked structure 5 of the pinion, the maximum stress level to which the cross-linked structure is subjected under load can be reduced, and the life and reliability of the pinion can be increased. For example, the lower edge of the front surface (on the left side of fig. 2 a) of the crosslinked structure 5 is stretched forward to give the crosslinked structure 5a trapezoidal shape as seen in fig. 2 a.

Returning to fig. 4, the method 100 then comprises a step E2 of obtaining a cylindrical body of the pinion, in this example the cylindrical body of the hub 2. The hub is preferably made by additive manufacturing. Alternatively, the hub is manufactured by any method known to those skilled in the art.

At step E3, the front wall 32 is obtained, as well as the rim 4 fixed to the hub 2. The front wall 32 and the rim 4 are preferably obtained in a continuous manner with the front portion of the hub 2.

Advantageously, the parison forming the teeth 40 of the rim 4 can be manufactured by additive manufacturing during step E3 or subsequently during the method 100. Therefore, the subsequent step of forming the parison of the teeth by cutting can be omitted, which reduces the manufacturing cost of the pinion.

In step E4, the previously obtained cross-linked structure 5 is positioned against the front wall 32. In the present example, the cross-linking structure 5 is positioned in contact with the inner surface of the rim 4 (interface I in fig. 2 a).

The crosslinked structure 5 is previously obtained by repeating one (or possibly more) three-dimensional unit cells. The cross-linked structure is either fabricated during step E1, directly against the front wall 32, or prior to the method 100 being performed.

In step E5, the rear wall 33 of the web 3 against the cross-linked structure 5 is obtained. The rear wall 33 is preferably obtained by additive manufacturing, preferably by selective laser melting on a powder bed. The rear surface of the cross-linked structure 5 serves as a support for the manufacture of the rear wall 33, which may eliminate a separate mechanical part for forming the support.

Between steps E3 and E5, the stack of front wall 32, (subsequent) cross-linked structure 5 and (final) rear wall 33 is thus completed.

The respective densities of the front and rear walls of the web are strictly greater than the density of the cells of the cross-linked structure, or if applicable, the respective densities of the front and rear walls of the web are greater than the density of each of the cells used in the cross-linked structure.

At the end of the method 100, a pinion is obtained in which the cross-linked structure 5 is incorporated in the inner volume of the web 3.

The method 100 provides a simple and fast solution for the manufacture of pinions.

Very advantageously, the pinion can be produced entirely by additive manufacturing, for example by selective laser melting or SLM. The entire pinion is then manufactured as one integral piece. One advantage of selective laser melting is that the mechanical properties of different regions of the component can be optimized according to the expected mechanical stress of the pinion under load and the total mass of the component elements can be limited.

Advantageously, the hub 2, the web 3 and the rim 4 of the pinion are made of a metallic material, for example steel. Alternatively, these components may be composed wholly or partly of a thermoplastic polymer, such as polyetheretherketone, commonly known by the abbreviation PEEK.

Obtaining a pinion by additive manufacturing generally enables an optimized design of the components while maximizing the functional requirements, in particular in terms of modal behaviour and deformation of the pinion under load. Additive manufacturing enables optimization of the mechanical properties of each region of the component according to the expected stress level.

Optimization of pinion mechanical performance is coupled with improved quality. The mass of the cross-linked structure is less than the mass of a solid web occupying the same space because the density of the unit cells is less than the density of the front and rear walls defining the web in the axial direction. Thus, the on-board mass of the turbine including the pinion is reduced.

According to a preferred variant of the method, during the positioning of the cross-linked structure 5 against the front wall 32 by E4, contact is achieved between the front wall and the cross-linked structure at a first inclination with respect to a plane perpendicular to the axis a. The first angle of inclination is greater than 20 ° with respect to said plane. When E5 obtains the back wall 33, contact between the back wall and the cross-linked structure is achieved at a second angle of inclination less than the first angle of inclination.

For example, in fig. 2a, the two surfaces of the front wall 32 have an inclination of about 40 ° with respect to a plane orthogonal to the axis a (corresponding to the vertical in fig. 2 a). Both surfaces of the rear wall 33 have a very slight inclination of less than 5 ° with respect to said plane.

One advantage of this variant is that the crosslinked structure 5 acts as a support for the rear wall during the step E5 of obtaining the rear wall. The use of the cross-linked structure 5 as a support in this way is particularly advantageous when the front wall 32 and the rear wall 33 are obtained by additive manufacturing, in particular by selective laser melting on a powder bed.

Another advantage is that the cross-linked structure, which is thus used as a support for the walls making up the web 3, is integrated inside the web of the final pinion. The cross-linked structure thus has the dual advantages of acting as a support during manufacture and of being able to reduce the overall mass of the pinion after manufacture, while being able to maintain the best mechanical properties of the pinion.

It is noted that alternatively, the rear wall may have a greater inclination than the front wall with respect to a plane orthogonal to the axis. It is thus possible to manufacture the rear wall first and use the cross-linked structure as a support for obtaining the front wall.