Stiffening member for epicyclical gear system housing assembly

A planet gear housing assembly is disclosed in an epicyclical gear system of a gas turbine engine having an engine casing. The planet gear housing assembly comprises an aft planet carrier assembly, a forward planet carrier assembly, and a plurality of planet gears. An aft flange of the aft planet carrier assembly is coupled to the engine casing to define a first torsional stiffness. A forward flange of the forward planet carrier assembly is coupled to the aft flange to define a second torsional stiffness. The second torsional stiffness may be between 60% and 80% of the first torsional stiffness. The planet gear housing assembly may further comprise a stiffening member positioned between the forward planet carrier assembly and the aft planet carrier assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to concurrently filed and co-pending U.S. patent application Ser. No. 16/592,492 entitled “EPICYCLICAL GEAR SYSTEM HOUSING ASSEMBLY,” U.S. patent application Ser. No. 16/592,494 entitled “BEARING SPRING FOR EPICYCLICAL GEAR SYSTEM HOUSING ASSEMBLY,” and U.S. patent application Ser. No. 16/592,499 entitled “STATIC CURVIC JOINT FOR EPICYCLICAL GEAR SYSTEM HOUSING ASSEMBLY,” the entirety of each of which are herein incorporated by reference.

BACKGROUND

Epicyclical gear systems may be used in rotating machinery to transfer energy from one component, such as a rotatable shaft, to another. By altering certain variables such as the number, size, and teeth of the gears, an epicyclical gear system may be designed to transfer energy between components at a desired ratio and often convert a high-speed, low-torque input to a lower-speed, higher-torque output.

Epicyclical gear systems may be suitable for a wide range of applications, including the transfer of energy from a turbine shaft to a fan rotor in a geared turbofan engine. However, in such dynamic applications the epicyclical gear system must be designed to allow some degree of relative movement between parts of the system to avoid excessive wear and, in extreme conditions, system failure.

SUMMARY

According to some aspects of the present disclosure, a planet gear housing assembly is disclosed for an epicyclical gear system of a gas turbine engine having an engine casing. The planet gear housing assembly comprises an aft planet carrier assembly, a forward planet carrier assembly, and a plurality of planet gears. The aft planet carrier assembly comprises an aft flange defining a central aperture and a plurality of gear shaft pockets positioned about the circumference and radially outward of the central aperture. Each pocket has a cylindrical wall, and the aft flange is coupled to the engine casing to define an aft torsional stiffness. The forward planet carrier assembly comprises a forward flange defining a central aperture and a plurality of gear shaft pockets positioned about the circumference and radially outward of the central aperture. Each pocket has a cylindrical wall, and the forward flange is coupled to the aft planet carrier assembly to define a forward torsional stiffness. The plurality of planet gears each comprise a cylindrical shaft having a forward end portion disposed in a gear shaft pocket of the forward planet carrier assembly coaxially with the cylindrical wall of the pocket, an aft end portion disposed within a gear shaft pocket of the aft planet carrier assembly coaxially with the cylindrical wall of the pocket, and one or more gears carried by the shaft between the forward and aft end portions. The forward torsional stiffness is between 60% and 80% of the aft torsional stiffness.

In some embodiments the forward torsional stiffness is between 65% and 75% of the aft torsional stiffness. In some embodiments the aft planet carrier assembly further comprises an annular mounting flange extending from the aft flange, the annular mounting flange positioned forward of and coaxial with the central aperture, the mounting flange forming a forward facing mounting surface. In some embodiments the forward planet carrier assembly further comprises an annular mounting flange extending from the forward flange, the annular mounting flange positioned aft of and coaxial with the central aperture, the mounting flange forming an aft facing mounting surface. In some embodiments the mounting surfaces are positioned relative to each other to thereby couple the aft planet carrier assembly and the forward planet carrier assembly.

In some embodiments the shaft and gears form a compound star gear in an epicyclical gear system. In some embodiments the forward planet carrier assembly further comprises a stiffening member positioned between the aft planet carrier assembly and the forward flange, the stiffening member comprising: an annular body defining a central aperture; and a plurality of radial flanges extending radially outward from the annular body, each of the plurality of radial flanges partly defining a gear-facing surface. In some embodiments the stiffening member abuts both the forward flange and the aft planet carrier assembly.

According to further aspects of the present disclosure, a planet gear housing assembly in an epicyclical gear assembly comprises an aft planet carrier assembly, a forward planet carrier assembly, a plurality of planet gears, and a stiffening member. The aft planet carrier assembly comprises an aft flange defining a central aperture and a plurality of gear shaft pockets positioned about the circumference and radially outward of the central aperture, each pocket having a cylindrical wall. The forward planet carrier assembly comprises a forward flange defining a central aperture and a plurality of gear shaft pockets positioned about the circumference and radially outward of the central aperture, each pocket having a cylindrical wall. The plurality of planet gears each comprise a cylindrical shaft having a forward end portion disposed in a gear shaft pocket of the forward planet carrier assembly coaxially with the cylindrical wall of the pocket, an aft end portion disposed within a gear shaft pocket of the aft planet carrier assembly coaxially with the cylindrical wall of the pocket, and one or more gears carried by the shaft between the forward and aft end portions. The stiffening member is positioned between the aft planet carrier assembly and the forward planet carrier assembly. The stiffening member comprises an annular body defining a central aperture and a plurality of radial flanges extending radially outward from the annular body, each of the plurality of radial flanges partly defining a gear-facing surface.

In some embodiments the aft planet carrier assembly is coupled to the forward planet carrier assembly. In some embodiments the aft planet carrier assembly further comprises an annular mounting flange extending from the aft flange, the annular mounting flange positioned forward of and coaxial with the central aperture, the mounting flange forming a forward facing mounting surface. In some embodiments the forward planet carrier assembly further comprises an annular mounting flange extending from the forward flange, the annular mounting flange positioned aft of and coaxial with the central aperture, the mounting flange forming an aft facing mounting surface. In some embodiments the mounting surfaces are positioned relative to each other to thereby couple the aft planet carrier assembly and the forward planet carrier assembly.

In some embodiments the shaft and gears form a compound star gear in an epicyclical gear system. In some embodiments the epicyclical gear assembly is a portion of a gas turbine engine having an engine casing, and wherein the aft flange is coupled to the engine casing to define an aft torsional stiffness and the forward flange is coupled to the aft planet carrier assembly to define a forward torsional stiffness, and wherein the forward torsional stiffness is between 50% and 90% of the aft torsional stiffness. In some embodiments the forward torsional stiffness is between 60% and 80% of the aft torsional stiffness. In some embodiments the forward torsional stiffness is between 65% and 75% of the aft torsional stiffness. In some embodiments the stiffening member comprises seven gear-facing surfaces. In some embodiments the aft flange comprises a radially outer mounting surface for mounting the planet gear housing assembly to the engine casing.

According to still further aspects of the present disclosure, a gas turbine engine for an aircraft comprises an engine core, a fan, and a gearbox. The engine core comprises a turbine, a compressor, and a core shaft connecting the turbine to the compressor. The fan is located upstream of the engine core and comprises a plurality of fan blades. The gearbox receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft. The gearbox has a planet gear housing assembly comprising an aft planet carrier assembly, a forward planet carrier assembly, a plurality of planet gears, and a stiffening member. The aft planet carrier assembly comprises an aft flange defining a central aperture and a plurality of gear shaft pockets positioned about the circumference and radially outward of the central aperture, each pocket having a cylindrical wall. The forward planet carrier assembly comprises a forward flange defining a central aperture and a plurality of gear shaft pockets positioned about the circumference and radially outward of the central aperture, each pocket having a cylindrical wall. The plurality of planet gears each comprise a cylindrical shaft having a forward end portion disposed in a gear shaft pocket of the forward planet carrier assembly coaxially with the cylindrical wall of the pocket, an aft end portion disposed within a gear shaft pocket of the aft planet carrier assembly coaxially with the cylindrical wall of the pocket, and one or more gears carried by the shaft between the forward and aft end portions. The stiffening member is positioned between and abutting the aft planet carrier assembly and the forward planet carrier assembly. The stiffening member comprises an annular body defining a central aperture and a plurality of radial flanges extending radially outward from the annular body, each of the plurality of radial flanges partly defining a gear-facing surface.

In some embodiments each of the plurality of planet gears comprise a sun gear engaging gear and a ring gear engaging gear carried by the shaft between the forward and aft end portions. In some embodiments the shaft and gears form a compound star gear in an epicyclical gear system. In some embodiments the gearbox further comprises a roller element bearing disposed over at least a portion of one or both of the forward end portion and the aft end portion of the gear shaft. In some embodiments the aft planet carrier assembly defines an aft torsional stiffness and the forward planet carrier assembly defines a forward torsional stiffness, and wherein the forward torsional stiffness is between 65% and 75% of the aft torsional stiffness.

The present application discloses illustrative (i.e., example) embodiments. The claimed inventions are not limited to the illustrative embodiments. Therefore, many implementations of the claims will be different than the illustrative embodiments. Various modifications can be made to the claimed inventions without departing from the spirit and scope of the disclosure. The claims are intended to cover implementations with such modifications.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to a number of illustrative embodiments in the drawings and specific language will be used to describe the same.

The gearbox may be a reduction gearbox (in that the output to the fan is a lower rotational rate than the input from the core shaft). Any type of gearbox may be used. For example, the gearbox may be a “planetary” or “star” gearbox, as described in more detail elsewhere herein. The gearbox may have any desired reduction ratio (defined as the rotational speed of the input shaft divided by the rotational speed of the output shaft), for example greater than 2.5, for example in the range of from 3 to 4.2, or 3.2 to 3.8, for example on the order of or at least 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1 or 4.2. The gear ratio may be, for example, between any two of the values in the previous sentence. Purely by way of example, the gearbox may be a “star” gearbox having a ratio in the range of from 3.1 or 3.2 to 3.8. In some arrangements, the gear ratio may be outside these ranges.

The radius of the fan may be measured between the engine centreline and the tip of a fan blade at its leading edge. The fan diameter (which may simply be twice the radius of the fan) may be greater than (or on the order of) any of: 220 cm, 230 cm, 240 cm, 250 cm (around 100 inches), 260 cm, 270 cm (around 105 inches), 280 cm (around 110 inches), 290 cm (around 115 inches), 300 cm (around 120 inches), 310 cm, 320 cm (around 125 inches), 330 cm (around 130 inches), 340 cm (around 135 inches), 350 cm, 360 cm (around 140 inches), 370 cm (around 145 inches), 380 (around 150 inches) cm, 390 cm (around 155 inches), 400 cm, 410 cm (around 160 inches) or 420 cm (around 165 inches). The fan diameter may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 240 cm to 280 cm or 330 cm to 380 cm.

The overall pressure ratio of a gas turbine engine as described and/or claimed herein may be defined as the ratio of the stagnation pressure upstream of the fan to the stagnation pressure at the exit of the highest pressure compressor (before entry into the combustor). By way of non-limitative example, the overall pressure ratio of a gas turbine engine as described and/or claimed herein at cruise may be greater than (or on the order of) any of the following: 35, 40, 45, 50, 55, 60, 65, 70, 75. The overall pressure ratio may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 50 to 70.

Specific thrust of an engine may be defined as the net thrust of the engine divided by the total mass flow through the engine. At cruise conditions, the specific thrust of an engine described and/or claimed herein may be less than (or on the order of) any of the following: 110 Nkg−1s, 105 Nkg−1s, 100 Nkg−1s, 95 Nkg−1s, 90 Nkg−1s, 85 Nkg−1s or 80 Nkg−1s. The specific thrust may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 80 Nkg−1s to 100 Nkg−1 s, or 85 Nkg−1 s to 95 Nkg−1 s. Such engines may be particularly efficient in comparison with conventional gas turbine engines.

A gas turbine engine as described and/or claimed herein may have any desired maximum thrust. Purely by way of non-limitative example, a gas turbine as described and/or claimed herein may be capable of producing a maximum thrust of at least (or on the order of) any of the following: 160 kN, 170 kN, 180 kN, 190 kN, 200 kN, 250 kN, 300 kN, 350 kN, 400 kN, 450 kN, 500 kN, or 550 kN. The maximum thrust may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). Purely by way of example, a gas turbine as described and/or claimed herein may be capable of producing a maximum thrust in the range of from 330 kN to 420 kN, for example 350 kN to 400 kN. The thrust referred to above may be the maximum net thrust at standard atmospheric conditions at sea level plus 15 degrees C. (ambient pressure 101.3 kPa, temperature 30 degrees C.), with the engine static.

In use, the temperature of the flow at the entry to the high pressure turbine may be particularly high. This temperature, which may be referred to as TET, may be measured at the exit to the combustor, for example immediately upstream of the first turbine vane, which itself may be referred to as a nozzle guide vane. At cruise, the TET may be at least (or on the order of) any of the following: 1400K, 1450K, 1500K, 1550K, 1600K or 1650K. The TET at cruise may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds). The maximum TET in use of the engine may be, for example, at least (or on the order of) any of the following: 1700K, 1750K, 1800K, 1850K, 1900K, 1950K or 2000K. The maximum TET may be in an inclusive range bounded by any two of the values in the previous sentence (i.e. the values may form upper or lower bounds), for example in the range of from 1800K to 1950K. The maximum TET may occur, for example, at a high thrust condition, for example at a maximum take-off (MTO) condition.

The fan of a gas turbine as described and/or claimed herein may have any desired number of fan blades, for example 14, 16, 18, 20, 22, 24 or 26 fan blades.

As used herein, cruise conditions have the conventional meaning and would be readily understood by the skilled person. Thus, for a given gas turbine engine for an aircraft, the skilled person would immediately recognise cruise conditions to mean the operating point of the engine at mid-cruise of a given mission (which may be referred to in the industry as the “economic mission”) of an aircraft to which the gas turbine engine is designed to be attached. In this regard, mid-cruise is the point in an aircraft flight cycle at which 50% of the total fuel that is burned between top of climb and start of descent has been burned (which may be approximated by the midpoint—in terms of time and/or distance—between top of climb and start of descent. Cruise conditions thus define an operating point of the gas turbine engine that provides a thrust that would ensure steady state operation (i.e. maintaining a constant altitude and constant Mach Number) at mid-cruise of an aircraft to which it is designed to be attached, taking into account the number of engines provided to that aircraft. For example where an engine is designed to be attached to an aircraft that has two engines of the same type, at cruise conditions the engine provides half of the total thrust that would be required for steady state operation of that aircraft at mid-cruise.

In other words, for a given gas turbine engine for an aircraft, cruise conditions are defined as the operating point of the engine that provides a specified thrust (required to provide—in combination with any other engines on the aircraft—steady state operation of the aircraft to which it is designed to be attached at a given mid-cruise Mach Number) at the mid-cruise atmospheric conditions (defined by the International Standard Atmosphere according to ISO 2533 at the mid-cruise altitude). For any given gas turbine engine for an aircraft, the mid-cruise thrust, atmospheric conditions and Mach Number are known, and thus the operating point of the engine at cruise conditions is clearly defined.

Purely by way of example, the cruise conditions may correspond to an operating point of the engine that provides a known required thrust level (for example a value in the range of from 30 kN to 35 kN) at a forward Mach number of 0.8 and standard atmospheric conditions (according to the International Standard Atmosphere) at an altitude of 38000 ft (11582 m). Purely by way of further example, the cruise conditions may correspond to an operating point of the engine that provides a known required thrust level (for example a value in the range of from 50 kN to 65 kN) at a forward Mach number of 0.85 and standard atmospheric conditions (according to the International Standard Atmosphere) at an altitude of 35000 ft (10668 m).

According to an aspect, there is provided an aircraft comprising a gas turbine engine as described and/or claimed herein. The aircraft according to this aspect is the aircraft for which the gas turbine engine has been designed to be attached. Accordingly, the cruise conditions according to this aspect correspond to the mid-cruise of the aircraft, as defined elsewhere herein.

According to an aspect, there is provided a method of operating a gas turbine engine as described and/or claimed herein. The operation may be at the cruise conditions as defined elsewhere herein (for example in terms of the thrust, atmospheric conditions and Mach Number).

According to an aspect, there is provided a method of operating an aircraft comprising a gas turbine engine as described and/or claimed herein. The operation according to this aspect may include (or may be) operation at the mid-cruise of the aircraft, as defined elsewhere herein.

FIG. 4provides a schematic view of an epicyclical gear system100in accordance with some embodiments of the present disclosure. The epicyclical gear system100may be a compound star gear system. A sun gear101is coupled to and driven by a first rotatable shaft103. The sun gear101is engaged with one or more planet gears105, such that rotation of the sun gear101causes rotation of the one or more planet gears105. The planet gears105may be star gears, such that the planet gears105rotate about an axis that is fixed relative to the axis of rotation of the sun gear101.

Each of the one or more planet gears105are engaged with a ring gear107. The ring gear107is coupled via a ring gear hub108to a second rotatable shaft109. Rotation of the first rotatable shaft103thus drives rotation of the second rotatable shaft109via rotation of the sun gear101, one or more planet gears105, and ring gear107. In some embodiments, the first rotatable shaft103may be a turbine shaft (i.e. high or low speed spool) of a turbine engine, and the second rotatable shaft109may be a fan shaft or fan rotor.

FIG. 5provides a detailed and schematic view of a housing assembly111of an epicyclical gear system100in accordance with some embodiments of the present disclosure. Each of the one or more planet gears105may comprise a cylindrical gear shaft123, a sun gear engaging gear125, and a ring gear engaging gear127. The sun gear engaging gear125and ring gear engaging gear127may be carried by the cylindrical gear shaft123. Each of the one or more planet gears105is carried by the housing assembly111. The planet gears105may be a compound star gear of the epicyclical gear system100.

The housing assembly111may comprise a forward housing member113and an aft housing member115. In some embodiments, the housing assembly111further comprises an intermediate housing member114. One or more of the housing members113,114,115may be joined together. The forward housing member113and aft housing member115each define a plurality of gear shaft pockets116having a cylindrical wall120. The intermediate housing member114may define a plurality of bores118.

A cylindrical gear shaft123of a planet gear105may have a forward end portion141disposed within one of the plurality of gear shaft pockets116formed by the forward housing member113. The cylindrical gear shaft123of the same planet gear105may have an aft end portion142disposed within one of the plurality of gear shaft pockets116formed by the aft housing member115. The cylindrical gear shaft123may be disposed within each gear shaft pocket116coaxially with the cylindrical wall120of the gear shaft pocket116. The cylindrical gear shaft123may extend through the bore118defined by the intermediate housing member114. The sun gear engaging gear125and ring gear engaging gear127of planet gear105may be carried by the gear shaft123between the forward end portion141and the aft end portion142.

The housing assembly111may further comprise a bearing assembly117. The housing assembly111may comprise a forward bearing assembly and an aft bearing assembly. The bearing assembly117may comprise a bearing. For example, a forward bearing119may be disposed over at least a portion of the forward end portion141of the gear shaft123and an aft bearing121may be disposed over at least a portion of the aft end portion142of the gear shaft123. Each of the bearings119,121may rotatably carry the planet gear105. Each of the bearings119,121may be a roller element bearing.

During operation of the epicyclical gear system100the constituent pieces of the system100as described above and including additional carrier assemblies, housings, and bearings, may move relative to one another. Even small changes in the relative positioning of one component to another can have significant impacts on performance of the system100. For example, misalignment of enmeshed gear teeth and/or bearings can cause uneven gear and/or bearing loading, and degradation or damage to gear teeth. For example, misalignment of enmeshed gear teeth and/or bearings can cause uneven gear and/or bearing loading, degradation or damage to gear teeth, and reduction of bearing lives and bearing stability.

Of particular concern is the fore-to-aft alignment of the gear shaft123of each planet gear105. Since each planet gear105is carried by the gear shaft123partly disposed within gear shaft pockets116of a forward housing member113and an aft housing member115, relative movement or changes in relative positioning between the forward housing member113and aft housing member115can cause misalignment of the planet gear105. Similarly, relative movement or changes in relative positioning between the intermediate housing member114and either or both of the forward housing member113and aft housing member115can cause misalignment of the planet gear105.

This misalignment may in turn lead to uneven load sharing among the planet gears105, gear degradation, and shortened useful life of the planet gears105and/or the planet bearings119,121. Factors that may contribute to planet gear misalignment include unaligned forces between the forward bearing119and aft bearing121, manufacturing inaccuracies for the positions of the gear shaft pockets116and bore118, ability to reassembly the forward and aft housings in the same position that they were machined, gear tolerance, and inflexibility and/or relative stiffness between each of the housing members113,114,115.

The present disclosure is therefore directed to systems and methods for improving and maintaining planet gear alignment in an epicyclical gear system. More specifically, the present disclosure is directed to a planet gear housing assembly for an epicyclical gear system having a forward planet carrier assembly, an aft planet carrier assembly, a stiffening member positioned between the forward and aft planet carrier assemblies, and a plurality of planet gears each carried by the forward and aft planet carrier assemblies. The stiffening member may achieve a desired stiffness ratio between the forward and aft planet carrier assemblies.

As shown inFIGS. 4-8, a planet gear housing assembly111may comprise an aft planet carrier assembly131, a forward planet carrier assembly161, a stiffening member171, and a plurality of planet gears105each carried by the aft planet carrier assembly131and forward carrier planet assembly.FIG. 6is an isometric view of a forward planet carrier assembly, a stiffening member, and an aft carrier housing assembly of a planet gear housing assembly in accordance with some embodiments of the present disclosure.FIG. 7is a partial cross sectional view of a stiffening member coupled between a forward planet carrier assembly and an aft planet carrier assembly of a planet gear housing assembly in accordance with some embodiments.FIGS. 8A and 8Bprovide isometric views of a stiffening member in accordance with some embodiments.

An aft planet carrier assembly131may comprise one or both of the intermediate housing member114and the aft housing member115. The aft planet carrier assembly131may comprise an aft flange136. The aft flange136may be the intermediate housing member114, the aft housing member115, or another flange member. The aft flange136may comprise more than one flange, as shown inFIG. 6with a first aft flange136A and a second aft flange136B. The aft flange136may define a central aperture132and a plurality of gear shaft pockets137positioned about the circumference of and radially outward of the central aperture132. Each of the gear shaft pockets116may have a cylindrical wall138. In some embodiments the aft flange136may further comprise a radially outer mounting surface139for coupling the aft planet carrier assembly131to an engine casing.

The aft planet carrier assembly131may further comprise an annular mounting flange133. The annular mounting flange133may be positioned forward of and coaxial with the central aperture132. The annular mounting flange133may extend substantially perpendicularly from the aft flange136. The annular mounting flange133may form a forward facing mounting surface134that may comprise a curvic structure.

A forward planet carrier assembly161may comprise a forward flange162and an annular mounting flange143. The forward planet carrier assembly161may be the forward housing member113. The forward flange162may define a central aperture144and a plurality of gear shaft pockets145positioned about the circumference and radially outward of the central aperture144. Each gear shaft pocket145may have a cylindrical wall146. The annular mounting flange143may be positioned aft of and coaxial with the central aperture144. The annular mounting flange143may form an aft facing mounting surface147that may comprise a curvic structure. The annular mounting flange143may extend substantially perpendicularly from the forward flange162.

A plurality of planet gears105may be carried by the forward planet carrier assembly161and the aft planet carrier assembly131. Each of the planet gears105may comprise a cylindrical shaft123having a forward end portion141disposed in a gear shaft pocket145of the forward flange162. The forward end portion141may be disposed in the gear shaft pocket145coaxial with the cylindrical wall146defining gear shaft pocket145. The cylindrical shaft may have an aft end portion142disposed within a gear shaft pocket137of the aft flange136, and may be disposed in the gear shaft pocket137coaxial with the cylindrical wall138.

Each planet gear105may further comprise one or more gears carried by the cylindrical shaft123between the forward end portion141and the aft end portion142. The gears may be, for example, a sun gear engaging portion125of the planet gear105and/or a ring gear engaging portion127of the planet gear105.

The planet gear housing assembly111and/or the forward planet carrier assembly161may further comprise a stiffening member171. The stiffening member171may comprise an annular body172defining a central aperture173. The stiffening member171may further comprise a plurality of radial flanges174extending radially outward from the annular body172. Each of the radial flanges174may at least partly define a gear-facing surface175. In some embodiments the stiffening member171comprises seven radial flanges174and defines seven gear-facing surfaces175.

The stiffening member171may be positioned between the aft planet carrier assembly131and the forward planet carrier assembly161. In some embodiments the stiffening member171may abut one or both of the forward flange162and the aft flange136. In some embodiments the stiffening member171is coupled to one or both of the forward flange162and the aft flange136by a plurality of bolts, pins, or other fasteners176.

When the epicyclical gear system100is fully assembled, a respective planet gear105may be carried by the forward flange162and the aft flange136, and may have a gear portion such as the ring gear engaging portion127positioned proximate the gear-facing surface175of the stiffening member171. The stiffening member171may be coupled between the forward flange162and the aft flange136to improve torsional stiffness of the forward planet carrier assembly161with reference to the aft planet carrier assembly131.

The epicyclical gear system100may be an epicyclical gear system of a gas turbine engine. The gas turbine engine may comprise an engine casing177, a portion of which is illustrated in cross section atFIG. 7. The aft flange136may be coupled to the engine casing177to define an aft torsional stiffness. The forward flange162may be coupled to the aft flange136to define a forward torsional stiffness. The forward flange162may be coupled to the aft flange136, for example, with the forward facing mounting surface134of the mounting flange133positioned relative to the aft facing mounting surface147of the mounting flange143. The forward flange162may be coupled to the aft flange136by a static curvic joint.

In some embodiments the forward torsional stiffness may be between 60% and 80% of the aft torsional stiffness. The aft torsional stiffness may be greater due to the mounting of the aft flange136to the aft casing177at a greater radius than the forward flange162is mounted to the aft flange136. More broadly, the forward torsional stiffness may be between 50% and 90% of the aft torsional stiffness. In other embodiments the forward torsional stiffness may be between 65% and 75% of the aft torsional stiffness.

FIG. 9is a flow diagram of a method900of reducing relative movement between static components of an epicyclical gear system in accordance with some embodiments of the present disclosure. Method900starts at Block901. The steps of method900, presented at Blocks901through919, may be performed in the order presented inFIG. 9or in another order. One or more steps of the method900may not be performed.

At Block903a static forward planet carrier assembly161and a static aft planet carrier assembly131may be provided. The forward planet carrier assembly161may comprise a forward flange162defining a central aperture144and a plurality of gear shaft pockets145positioned about the circumference of the central aperture144. The forward planet carrier assembly161may further comprise an annular mounting flange143extending from said forward flange162, said annular mounting flange143positioned aft of and coaxial with said central aperture144. The mounting flange143may form an aft facing mounting surface147.

The aft planet carrier assembly131may comprise an aft flange136defining a central aperture132and a plurality of gear shaft pockets137positioned about the circumference and radially outward of said central aperture132. The aft planet carrier assembly131may further comprise an annular mounting flange133extending from said aft flange136, said annular mounting flange133positioned forward of and coaxial with said central aperture132. The mounting flange133may form a forward facing mounting surface134.

At Block905a stiffening member171may be positioned between said aft planet carrier assembly131and said forward planet carrier assembly161. The stiffening member171may comprise an annular body172defining a central aperture173and a plurality of radial flanges174extending radially outward from said annular body172. Each of said plurality of radial flanges174may partly define a gear-facing surface175.

At Block907a bearing119,121may be positioned at least partly in a gear shaft pocket145,137of the forward planet carrier assembly161and/or the aft planet carrier assembly131.

At Block909a planet gear105of a plurality of planet gears105may be positioned in each of the plurality of axially aligned gear shaft pocket pairs formed between the pocket145,137of the forward planet carrier assembly161and/or the aft planet carrier assembly131. Each planet gear105may comprise a cylindrical shaft123having a forward end portion141disposed in a gear shaft pocket145of said forward planet carrier assembly161coaxially with the cylindrical wall146of said pocket145, an aft end portion142disposed within a gear shaft pocket137of said aft planet carrier assembly131coaxially with the cylindrical wall138of said pocket137. The planet gear105may further comprise one or more gears125,127carried by said shaft123between said forward and aft end portions141,142.

At Block911, a portion of a cylindrical shaft123of a planet gear105may be carried with said bearing119,121.

At Block913the method may further comprise positioning a mounting surface134of the aft planet carrier assembly131relative to a mounting surface147of the forward planet carrier assembly161.

At Block915the forward planet carrier assembly161may be coupled to the aft planet carrier assembly131.

At Block917the cylindrical shaft123of each planet gear105may be rotated. The rotation may be driven by a sun gear101of a compound star gear assembly100.

The presently disclosed systems and methods provide numerous advantages over prior art systems. By providing a stiffening member positioned between and joining a forward and aft planet carrier assembly, the disclosed planet gear housing assembly reduces fore-to-aft misalignment of planet gear shafts caused by relative movement between the forward and aft planet carrier assemblies. The aft planet carrier assembly may be rigidly mounted to the engine casing at the outer diameter of the aft flange. Since the forward flange may be mounted to the aft flange at an inner diameter, the forward-to-aft coupling of flanges may be inherently less stiff and therefore allow increased torsional deflection for an equal bearing reaction load.

By coupling the aft planet carrier assembly and forward planet carrier assembly with a stiffening member between them, the forward planet carrier assembly may be held to the aft planet carrier assembly with less relative movement between the two than in a standard coupling. While typical epicyclical gear systems may have a forward torsional stiffness of 25-40% of the aft torsional stiffness, the disclosed stiffening member provides for an increase to a forward torsional stiffness of 60-80% of the aft torsional stiffness. Less relative movement is advantageous during assembly as well as operation of the epicyclical gear system.

The present disclosure may be used in combination with the disclosure of one or more of the related applications listed above. In particular, the present disclosure may be used in combination with “Static Curvic Joint for an Epicyclical Gear System Housing Assembly.” A static curvic joint assures bore-to-bore alignment during machining and assembly but may decrease the forward torsional stiffness. The stiffening member described herein may counter this decrease in forward torsional stiffness, such that the combination of a static curvic joint and stiffening member in an epicyclical gear system is advantageous. The combination may assure bore-to-bore alignment during manufacture, machining, assembly, and operation.

Although examples are illustrated and described herein, embodiments are nevertheless not limited to the details shown, since various modifications and structural changes may be made therein by those of ordinary skill within the scope and range of equivalents of the claims.